jrenhep009 0..2 jrenhep.com editorial welcome to the journal of renal and hepatic disorders jeffrey halldorson department of surgery, division of transplantation, university of california medical center, san diego, ca, usa received: 20 december 2016; accepted after revision: 31 december 2016; published: 03 february 2017. author for correspondence: jeffrey halldorson, department of surgery, division of transplantation, university of california medical center, san diego, ca, usa. email: jhalldorson@ucsd.edu how to cite: jeffrey halldorson. welcome to the journal of renal and hepatic disorders. j ren hepat disord 2017;1(1):1–2. doi: http://dx.doi.org/10.15586/jrenhep.2017.9 copyright: halldorson j license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 welcome to the inaugural issue of the journal of renal and hepatic disorders. the aim of the journal is to promote the study and dissemination of research involving both renal and hepatic organ systems and their impact on the whole organism in both healthy and diseased states. in addition, the focus of the journal will provide a unique forum in which the interdependence and interactions between the liver and kidney will be of particular interest. although there seems to be a proliferation of open journals in the medical arena, our editorial board feels that the study of the interdependence of organ systems is underrepresented. those of us in the field of transplantation have an intuitive understanding of the interrelationship between organ systems, given our exposure to patients with dual organ failure. when a single organ system fails, the impact is felt throughout several systems in a cascade of effects that may or may not be reversible once the primary organ failure has been reversed. a common and well-known example of this interaction is the hepatorenal syndrome in end-stage cirrhosis of the liver in which the vasogenic effects of liver disease initially result in acute kidney injury but may progress to irreversible ischemic renal failure if the vasogenic influence of liver failure is not reversed quickly enough (1–3). the increasing importance of this phenomenon is evidenced by the proliferation of simultaneous liver/kidney transplantation over the last decade (4, 5). although the pathogenesis and reversal of the hepatorenal syndrome is an excellent example of the area of focus for the journal, the aims of the journal are wider in scope than endstage disease and transplantation alone. as the kidney and liver are two of the most metabolically influential organs in the body, the potential for the study of physiological and/or pathophysiologic interactions is unlimited. a pubmed search using the title keywords “kidney” and “liver” for the year 2015 returned 250 titles widely ranging from exercise physiology to the impact of hepatitis b and c in renal transplant recipients (6, 7). other sampled articles involved markers of co-toxicities, and micro-rna profiles involving both organ systems were described due to acetaminophen overdose (8). the emerging pathophysiology of fatty liver disease is a growing topic (9). the interdependence of homeostatic mechanisms originating from the combined effects of the liver and kidney in maintaining nitrogen balance is exemplified in the recent articles with novel transporter mutations (10, 11). furthermore, the impact of inherited disorders such as polycystic disease or nitrogen metabolism may be a fruitful area for further discovery (12). the editorial board of the journal of renal and hepatic disorders aims to promote the greater understanding and dissemination of original works in all areas involving the interplay of these two organ systems, both in the basic scientific and clinical realms. toward this aim, original articles, comprehensive reviews, case reports, short communications, and letters to the editor on any aspects of kidneys and liver are suitable for submission. all submitted manuscripts will codon publications journal of renal and hepatic disorders 2017; 1(1): 1–2 mailto:jhalldorson@ucsd.edu http://dx.doi.org/10.15586/jrenhep.2017.9 http://creativecommons.org/licenses/by/4.0 undergo a rigorous peer review and will be published in an open access manner for the widest potential dissemination. our goal is to achieve widespread indexing and continued growth and to increase the prestige of the journal in the scientific community. we look forward to a rewarding and scientifically productive relationship with our community and contributors. conflict of interest jh is one of the editors-in-chief of the journal. the author declares no conflicts of interest with respect to research, authorship, and/or publication of this article. references 1. kanubhai sutariya v, tank a, ramanlal modi p. combined liver-kidney transplantation for hepatorenal syndrome. int j organ transplant med. 2015;6(3):131–3. 2. rognant n. acute kidney injury in patients with chronic liver disease. world j hepatol. 2015;7(7):993–1000. http://dx.doi. org/10.4254/wjh.v7.i7.993 3. jindal a, bhadoria as, maiwall r, sarin sk. evaluation of acute kidney injury and its response to terlipressin in patients with acute-on-chronic liver failure. liver int. 2016;36(1): 59–67. http://dx.doi.org/10.1111/liv.12895 4. sung rs, wiseman ac. simultaneous liver-kidney transplant: too many or just enough? adv chronic kidney dis. 2015;22 (5):399–403. http://dx.doi.org/10.1053/j.ackd.2015.06.005 5. brennan tv, lunsford ke, vagefi pa, bostrom a, ma m, feng s. renal outcomes of simultaneous liver-kidney transplantation compared to liver transplant alone for candidates with renal dysfunction. clin transplant. 2015;29(1):34–43. http://dx. doi.org/10.1111/ctr.12479 6. mosconi g, roi gs, totti v, zancanaro m, tacconi a, todeschini p, et al. renal function in kidney and liver transplant recipients after a 130-km road cycling race. transplant direct. 2015;1(9):e36. http:// dx.doi.org/10.1097/txd.0000000000000546 7. pipili c, cholongitas e. pharmaceutical management of hepatitis b and c in liver and kidney transplant recipients. world j gastrointest pharmacol ther. 2015;6(4):105–10. http://dx.doi. org/10.4292/wjgpt.v6.i4.105 8. vliegenthart ad, shaffer jm, clarke ji, peeters le, caporali a, bateman dn, et al. comprehensive microrna profiling in acetaminophen toxicity identifies novel circulating biomarkers for human liver and kidney injury. sci rep. 2015;5:15501. http:// dx.doi.org/10.1038/srep15501 9. musso g, cassader m, cohney s, pinach s, saba f, gambino r. emerging liver-kidney interactions in nonalcoholic fatty liver disease. trends mol med. 2015;21(10):645–62. http://dx.doi. org/10.1016/j.molmed.2015.08.005 10. chan k, busque sm, sailer m, stoeger c, broer s, daniel h, et al. loss of function mutation of the slc38a3 glutamine transporter reveals its critical role for amino acid metabolism in the liver, brain, and kidney. pflugers arch. 2016;468(2):213–27. http://dx. doi.org/10.1007/s00424-015-1742-0 11. hack v, gross a, kinscherf r, bockstette m, fiers w, berke g, et al.abnormal glutathione and sulfate levels after interleukin 6 treatment and in tumor-induced cachexia. faseb j. 1996;10 (10):1219–26. 12. gevers tj, hol jc, monshouwer r, dekker hm, wetzels jf, drenth jp. effect of lanreotide on polycystic liver and kidneys in autosomal dominant polycystic kidney disease: an observational trial. liver int. 2015;35(5):1607–14. http://dx.doi.org/10. 1111/liv.12726 halldorson j codon publications journal of renal and hepatic disorders 2017; 1(1): 1–2 2 http://dx.doi.org/10.4254/wjh.v7.i7.993 http://dx.doi.org/10.4254/wjh.v7.i7.993 http://dx.doi.org/10.1111/liv.12895 http://dx.doi.org/10.1053/j.ackd.2015.06.005 http://dx.doi.org/10.1111/ctr.12479 http://dx.doi.org/10.1111/ctr.12479 http://dx.doi.org/10.1097/txd.0000000000000546 http://dx.doi.org/10.1097/txd.0000000000000546 http://dx.doi.org/10.4292/wjgpt.v6.i4.105 http://dx.doi.org/10.4292/wjgpt.v6.i4.105 http://dx.doi.org/10.1038/srep15501 http://dx.doi.org/10.1038/srep15501 http://dx.doi.org/10.1016/j.molmed.2015.08.005 http://dx.doi.org/10.1016/j.molmed.2015.08.005 http://dx.doi.org/10.1007/s00424-015-1742-0 http://dx.doi.org/10.1007/s00424-015-1742-0 http://dx.doi.org/10.1111/liv.12726 http://dx.doi.org/10.1111/liv.12726 pdf jrenhep_104.indd journal of renal and hepatic disorders 2021;6(1): 7–9 7 journal of renal and hepatic disorders case series gabapentin toxicity and role of dialysis; case series and literature review muzamil latief1, mohd iqbal bhat2, mohd latief wani1, obeid shafi 3, l. naresh goud4, farhat abbas5, mohsin wani6 1nephrology division, government medical college, srinagar, india; 2nephrology division, ascoms hospital, jammu, india; 3flushing hospital medical center, new york, ny, usa; 4nova college of pharmaceutical education and research, hyderabad, india; 5pathology division, gmc, srinagar, india; 6government medical college, srinagar, india abstract gabapentin is frequently used as an analgesic in patients with chronic kidney disease (ckd). it is excreted exclusively through kidney, and therefore impairment in kidney function could lead to gabapentin accumulation and hence toxicity. we present our experience of 3 cases with gabapentin toxicity who were managed according to the severity of symptoms. case 1: a 32-year-old male was found lying unconscious after consuming around 12,000 mg of gabapentin and had respiratory depression, rhabdomyolysis, and acute kidney injury (aki). patient was managed with supportive care and hemodialysis (hd). case 2: a 64-year-old male ckd stage 5 (5d) patient with diabetic neuropathy was started on gabapentin 300 mg daily by his primary care physician 1 week back. patient started to feel sleepy and developed altered sensorium and myoclonus. discontinuation of gabapentin and a session of hd led to dramatic improvement in patient’s status. case 3: a 70-year-old female diabetic patient with ckd stage 3 and had diabetic neuropathy. her neuropathic symptoms had improved with gabapentin 300 mg twice daily, but lately patient was feeling sleepy during the day and was confused. discontinuation of the drug led to improvement in symptoms. gabapentin is a relatively safe medication, but in certain clinical scenarios, particularly in impaired renal functions, can lead to severe complications. moreover, it per se can rarely lead to rhabdomyolysis and aki. clinical suspicion and timely decontamination are needed, and sometimes dialytic therapy may be needed. keywords: dialysis; gabapentin; myoclonus received: 23 may 2021; accepted after revision: 1 september 2021; published: 14 december 2021 author for correspondence: farhat abbas, pathology division, government medical college, srinagar, 190010 kashmir, india. email: farahabbas.m@gmail.com how to cite: latief m et al. gabapentin toxicity and role of dialysis; case series and literature review. j ren hepat disord. 2021 6(1):7–9. doi: https://doi.org/10.15586/jrenhep.v6i1.104 copyright: latief m, et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/ licenses/by/4.0 p u b l i c a t i o n s codon introduction gabapentin is frequently used as an analgesic in patients with chronic kidney disease (ckd). gabapentin has a favorable pharmacokinetic profi le (1). this drug has been often used in elderly patients who have multiple comorbidities, including ckd (2). gabapentin is excreted exclusively via kidney, and therefore impairment in kidney function could lead to gabapentin accumulation and hence toxicity. most of the published literature on gabapentin toxicity in ckd are case studies (3,4). gabapentin is eliminated unmetabolized latief m et al. journal of renal and hepatic disorders 2021;6(1): 7–9 8 through urine at a rate that is proportional to creatinine clearance. in patients with impaired renal function, gabapentin half-life can be prolonged up to 132 h. this prolonged half-life increases the risk of toxicity. in cases reported with gabapentin toxicity, patients had varying manifestations including tremors, altered mental status, and respiratory depression requiring intubation (5). rhabdomyolysis is a very rare adverse effect of gabapentin and has been reported in a case study (6). we report three patients with gabapentin toxicity, which highlight the need of early suspicion and timely intervention. case series case 1 a 32-year-old male, driver by occupation, was found in unconscious state with four empty strips of gabapentin (10 tablets in each strip of gabapentin 300 mg) lying bedside. the patient was rushed to hospital and on presentation had a bp of 110/70, was not responding to deep painful stimuli, and had passed urine and stools in bed. the patient had features of respiratory distress. the patient underwent endotracheal intubation and lavage. his labs revealed respiratory acidosis with normal counts and x-ray of the chest. after taking a sample for gabapentin levels, the patient underwent a hemodialysis (hd) session via femoral catheter, and post dialysis session he had dramatic improvement in sensorium and respiratory parameters and was extubated in next 12 h. over next 3 days, creatinine peaked at 2.1 mg/dl. serum creatine phosphokinase (cpk) was 1756 u/l, and lactate dehydrogenase (ldh) was 1140 u/l. serum gabapentin level was 57 mcg/ml, and he received another session of hd next day. the patient was continued on supportive care and discharged on day 5 after psychiatric consultation. on follow up at 2 weeks, he is doing well, and renal functions have normalized so have muscle enzymes, and he is continuing follow up with the psychiatrist. case 2 a 64-year-old male ckd stage 5 (5d) patient with diabetic neuropathy was started on gabapentin 300 mg daily by his primary care physician 1 week back. the patient started to feel sleepy and subsequently developed altered sensorium and myoclonic jerks. the patient reported to our hospital, and his hemodynamic parameters were normal including biochemical parameters (such as sodium 136 meq/l, potassium 4.7 meq/l, and calcium 9.9 mg/dl) and blood sugar (112 mg/ dl). suspecting gabapentin toxicity, serum sample was sent for testing. the patient was given a session of hd for 4 h, and post dialysis he had dramatic improvement. serum gabapentin level was 27 mcg/ml. the patient and caregivers were counselled regarding the toxicity risk of this medication. case 3 a 70-year-old female diabetic patient with ckd stage 3 and diabetic neuropathy was our third patient. her neuropathic symptoms had improved with gabapentin 300 mg twice daily, but lately the patient was feeling sleepy during the day and was confused. her serum electrolytes and ecg were normal, and blood sugars were reasonably controlled. suspecting gabapentin toxicity, it was stopped, and the patient had marked improvement. she was put on nortriptyline for neuropathic pain and is doing well on follow up. discussion in a study which included two cases of myoclonus associated with gabapentin toxicity in the setting of renal disease, the patients settled with hd and peritoneal dialysis (pd). the first patient after discontinuation of gabapentin and two sessions of hd had marked improvement and was discharged with normal renal function, a blood urea nitrogen (bun) level of 20 mg/dl and creatinine (cr) level of 1.1 mg/dl, and myoclonus had disappeared. in the same study, the second patient was a 55-year-old man with end-stage kidney disease on pd. the patient’s pd treatment was modified from four to six pd exchanges daily. the treatment modification along with discontinuation of gabapentin led to disappearance of myoclonus, and mental status improved within 4 days (7). in patients with renal impairment, the development of myoclonus and neurotoxicity may require withdrawal of gabapentin. evidence suggests that serum gabapentin concentrations greater than 15 μg/ml are associated with symptomatic toxicity. in patients who have normal kidney function, gabapentin is rapidly cleared based on its short half-life, therefore toxicity is rare. but in patients with kidney function impairment, the threshold for gabapentin toxicity is low. patients with severe symptomatic toxicity should be considered for dialysis. both intermittent and continuous forms of renal replacement therapy have been effectively utilized to treat gabapentin-induced neurotoxicity and myoclonus. neurological sequelae following administration of the drug to patients with renal failure, varying from subtle changes in mental status to drowsiness and coma, have been reported in the literature. however, serious cardiovascular and neurological sequelae seen with ingestion of other anticonvulsants such as carbamazepine and phenytoin are not seen with gabapentin, particularly in patients who have normal kidney functions (4). gabapentin also finds its use in generalized uremic pruritus in patients on dialysis who fail to respond to antihistamines and/or topical emollients (8). the molecular weight of gabapentin is 171.24, which is close to the molecular weight of glucose (mw: 180). the low molecular weight, low protein binding, and low volume of distribution make gabapentin amenable to removal using gabapentin toxicity and role of dialysis journal of renal and hepatic disorders 2021;6(1): 7–9 9 3. miller a, price g. gabapentin toxicity in renal failure: the importance of dose adjustment. pain med. 2009;10:190–2. http://dx.doi.org/10.1111/j.1526-4637.2008.00492.x 4. hung t-y, seow v-k, chong c-f, wang t-l, chen c-c. gabapentin toxicity: an important cause of altered consciousness in patients with uraemia. emerg med j. 2008;25:178–9. http://dx.doi.org/10.1136/emj.2007.053470 5. jones h, aguila e, farber hw. gabapentin toxicity requiring intubation in a patient receiving long-term hemodialysis. ann intern med. 2002;137(1):74. http://dx.doi. org/10.7326/0003-4819-137-1-200207020-00029 6. qiu x, tackett e, khitan z. a case of gabapentin overdose induced rhabdomyolysis requiring renal replacement therapy. clin case rep. 2019;7:1596–9. http://dx.doi.org/10.1002/ ccr3.2302 7. kaufman kr, parikh a, chan l, bridgeman m, shah m. myoclonus in renal failure: two cases of gabapentin toxicity. epilepsy behav case rep. 2014;2:8–10. http://dx.doi. org/10.1016/j.ebcr.2013.12.002 8. lau t, leung s, lau w. gabapentin for uremic pruritus in hemodialysis patients: a qualitative systematic review. can j kidney health dis. 2016;3:14. http://dx.doi.org/10.1186/ s40697-016-0107-8 9. goldfrank lr, flomenbaum nf, lewin na, weisman rs, howland ma, hoffman rs. goldfrank’s toxicologic emergencies. 6th ed. stamford (ct): appleton & lange; 1998. 694–5 p. 10. fernandez mc, walter fg, petersen lr, walkotte sm. gabapentin, valproic acid, and ethanol intoxication: elevated blood levels with mild clinical effects. j toxicol clin toxicol. 1996;34(4):437–9. http://dx.doi.org/10.3109/15563659609013815 11. verma a, st clair ew, radtke ra. a case of sustained massive gabapentin overdose without serious side effects. therap drug monit. 1999;21:615–17. http://dx.doi. org/10.1097/00007691-199912000-00006 12. fernandez mc, walter fg, kloster jc, do sm, brady la, villarin a, et al. hemodialysis and hemoperfusion for treatment of valproic acid and gabapentin poisoning. vet human toxicol. 1996;38:438–43. 13. ibrahim h, oman z, schuelke m, edwards jc. treatment of gabapentin toxicity with peritoneal dialysis: assessment of gabapentin clearance. am j kidney dis. 2017;70(6):878–80. http:// dx.doi.org/10.1053/j.ajkd.2017.05.010 dialysis modalities (5). while the therapeutic and toxic ranges of plasma serum gabapentin levels have not been definitively established, it is suggested that serum level of 2–15 mcg/ml (2–15 mg/l) is therapeutic (9,10). patients with toxicity symptoms need monitoring until their symptoms resolve  (11). early gastric lavage, if the ingestion occurred within 1 h of presentation to a health care facility, and activated charcoal help in decontamination. further measures that have been used include extracorporeal membrane oxygenation, plasmapheresis, and dialysis, in addition to the usual supportive care. there is no specific antidote for the drug. hd may be needed, particularly in patients with impaired renal function. in a series describing gabapentin overdose, symptomatic toxicity effects resolve within 24 h (12). pd also helps in removal of gabapentin. intensive pd can be used to treat gabapentin toxicity, provided the patient is stable; however, in case of emergency, hd will provide much more rapid removal of gabapentin. to avoid toxicity, it would be prudent to monitor gabapentin concentrations in dialysis patients, particularly after changes to dialysis prescription have been inducted (13). conclusion gabapentin is a relatively safe medication, but in certain clinical scenarios, particularly in impaired renal functions, can lead to severe complications. moreover, it per se can rarely lead to rhabdomyolysis and acute kidney injury. references 1. bassilios n, launay-vacher v, khoury n, rondeau e, deray g, sraer jd. gabapentin neurotoxicity in a chronic haemodialysis patient. nephrol dial transplant. 2001;16:2112–13. http://dx. doi.org/10.1093/ndt/16.10.2112 2. dogukan a, aygen b, berilgen ms, dag s, bektas s, gunal ai. gabapentin-induced coma in a patient with renal failure. hemodial int. 2006;10:168–9. http://dx.doi. org/10.1111/j.1542-4758.2006.00089.x jrenhep008 2..4 jrenhep.com editorial alcoholic hepatitis and liver transplantation gianni testino1, silvia leone2 1alcohologic regional center-ligurian region, irccs azienda ospedaliera universitaria san martino-ist, genova, italy; 2school in toxicology and clinical pharmacology, university of genova, genova, italy received: 09 december 2016; accepted after revision: 29 december 2016; published: 03 february 2017. author for correspondence: gianni testino, alcohologic regional center-ligurian region, irccs azienda ospedaliera universitaria san martino-ist, genova, italy. email: gianni.testino@hsanmartino.it how to cite: testino g et al. alcoholic hepatitis and liver transplantation. j ren hepat disord 2017;1(1):3–4. doi: http://dx.doi.org/10.15586/jrenhep.2017.8 copyright: testino g and leone s license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 some authors affirm that early liver transplant (lt) provides excellent short-term survival in patients with severe alcoholic hepatitis (sah) (1–4) and similar rates of alcohol relapse compared to patients with 6 months of abstinence. we agree with the choice of not excluding patients who manifest their decompensation with bleeding and infections (common complications of sah) and patients with psychiatric comorbidities. data from the literature have stated for a long time that the approach to patients with alcoholic liver disease (ald) should be changed with no ethical or technical preconceptions. the reasons in favor of this change are as follows: 1) ald is common: it is responsible for 80% of deaths from liver disease and 50% of deaths from cirrhosis (5). 2) it is the second cause of lt, and with the arrival of direct-acting antiviral drugs, it will become the primary cause. 3) relapse post-lt varies from 11% to 50%, but a loss of graft occurs in less than 17% of cases and death in less than 5% of cases (6). 4) mathurin et al. (1) have brought an innovation to lt indication: 26 patients were listed for lt (average age 47.4 years), who had not responded to steroidal therapy (average time 13 days). six-month survival was 77% (compared with 23% in a nonrandomized case-matched control group). it is important to also remember the experience of singal et al. (7). they first compared the survival of post-lt patients with alcoholic hepatitis (11 cases, days waiting for lt 67 ± 86) and of patients with alcoholic cirrhosis (35 cases, days waiting for lt 145 ± 340). the 5-year graft and patient survival of alcoholic hepatitis were 75% and 73% (p=0.97), and for alcoholic cirrhosis it was 80% and 78% (p=0.90), respectively. we have experience of seven nonresponder patients (median age 49 years), with clinical evidence of sah and type 1 hepatorenal syndrome, receiving a transjugular intrahepatic portosystemic shunt and then being successfully transplanted. sah was histologically diagnosed in the removed liver. no patients had an alcoholic relapse post-lt (8). we think that lt indication without the 6-month rule should also be extended to patients with progressive end-stage liver disease (esld) who come to the transplant team for the first time and who do not improve after a 3-month abstinence period. in 2014, an italian position statement (6) suggested proposals to ensure the right balance between ethics and clinical success (9–12). the proposals in relation to the complex population of ald patients are as follows: 1) patients with sah can be placed on an lt list if it is their first episode, if there is no response to medical therapy with steroids, and if family and environmental supports are available. codon publications journal of renal and hepatic disorders 2017; 1(1): 3–4 mailto:gianni.testino@hsanmartino.it http://dx.doi.org/10.15586/jrenhep.2017.8 http://creativecommons.org/licenses/by/4.0 2) patients with progressive esld (a model esld score [meld score] equal to or greater than 19) may be placed on the list if after 3 months of abstinence there is no clinical regression. 3) patients with a meld of <19 and who have been treated at an alcohol rehabilitation center for some time must ensure 6 months of abstention. from these proposals, it becomes clear that the “6-month” rule should not be considered as dogmatic. however, for the optimal management of these patients, a change of hepatology services is needed. patients, in fact, are affected by a double pathology: alcohol dependence and ald. patients should be seen in a nonjudgmental environment made up of professionals with appropriate psycho-relational skills. this provides a closer adherence to the path of care and greater motivation for abstention from alcohol, both preand post-lt. collaboration with self-help groups (shgs) is necessary, particularly during the post-lt period, to ensure abstention. however, in a multidisciplinary team, the presence of an addiction specialist and a hepatologist with well-defined alcohological experience is needed. addolorato et al. (13) suggested how the presence of an addiction unit could be useful. this allows the addition of patients onto an lt list independently of the 6-month abstention period with a reduction in deaths caused by a wait that is sometimes too long in relation to their serious medical conditions. therefore, even though ald is a self-inflicted pathology, in a society that promotes the consumption of alcohol in relation to success, sport, and well-being, we have a duty to ensure patient care. a new way of working in managing patients with alcohol dependence and liver pathology is needed. during the post-lt phase in particular, the patient must be surrounded by a network of protection where health practitioners and families cooperate closely with the indispensable actions of shgs. this allows the avoidance of alcoholic relapse in a high percentage of cases and, therefore, indirectly the preservation of the graft. in addition, during the post-lt period, adequate treatment of metabolic syndrome (ms) and close oncological surveillance are necessary. cardiovascular complications and tumors are the most frequent causes of death in transplant patients with ald. one year post-lt, 90% of cases develop at least one factor of ms (obesity, hypertension, dyslipidemia, or hyperglycemia); on the contrary, alcohol-related oncological risk decreases by about 10% per year (14). ethanol, in fact, has been placed in group 1 by the international agency for research on cancer (iarc)—world health organization (15). in conclusion, according to lee et al. (4), it is necessary to validate models that can help us predict eventual alcoholic relapse post-lt, and it is even more important to review hepato-alcohological activity in transplant teams. conflict of interest the authors declare no conflicts of interest with respect to research, authorship, and/or publication of this article. references 1. mathurin p, moreno c, samuel d, dumortier j, salleron j, durand f, et al. early liver transplantation for severe alcoholic hepatitis. n engl j med. 2011;365:1790–800. http://dx.doi.org/ 10.1056/nejmoa1105703 2. immordino g, gelli m, ferrante r, ferrari c, piaggio f, ghinolfi d, et al. alcohol abstinence and orthotopic liver transplantation in alcoholic liver cirrhosis. transplant proc. 2009;41: 1253–5. http://dx.doi.org/10.1016/j.transproceed.2009.03.092 3. testino g, borro p. alcoholic hepatitis and liver transplantation: is an abstinence of six months necessary? hepato-gastroenterology 2012;59:1–2. 4. lee bp, chen ph, haugen c, hernaez r, gurakar a, philosophe b, et al. three-year results of a pilot program in early transplantation for severe alcoholic hepatitis. ann surg. 2017;265:20–9. http://dx.doi.org/10.1097/sla.0000000000001831 5. prado v, caballería j, vargas v, bataller r, altamirano j. alcoholic hepatitis: how far are we and where are we going? ann hepatol. 2016;15:463–73. 6. testino g, burra p, bonino f, piani f, sumberaz a, peressutti r, et al. acute alcoholic hepatitis, end stage alcoholic liver disease and liver transplantation. world j gastroenterol. 2014;20:14642–51. http://dx.doi.org/10.3748/wjg.v20.i40.14642 7. singal ak, bashar h, anand bs, jampana sc, singal v, kuo yf, et al.outcomes after liver transplantation for alcoholic hepatitis are similar to alcoholic cirrhosis: exploratory analysis from the unos database. hepatology 2012;55:1398–405. http://dx. doi.org/10.1002/hep.25544 8. testino g, sumberaz a, borro p. comment to “liver transplantation for patients with alcoholic liver disease: an open question.” dig liver dis. 2013;45:80–1. http://dx.doi.org/10.1016/ j.dld.2012.06.003 9. testino g, leone s. liver transplantation and alcoholic liver disease: a point of view. austin transplant sci.2016;1:1002–3. 10. testino g, leone s. alcoholic liver disease and orthotopic liver transplantation. j dig dis hepatol. 2016;2016(3). 11. leon m, varon j, surani s. when a liver transplant recipient goes back to alcohol abuse: should we be more selective? world j gastroenterol. 2016;22:4789–93. http://dx.doi.org/10. 3748/wjg.v22.i20.4789 12. zambrano a. why alcoholics ought to compete equally for liver transplants. bioethics. 2016;30:689–97. http://dx.doi.org/10.1111/ bioe.12274 13. addolorato g, mirijello a, leggio l, ferrulli a, d'angelo c, vassallo g, et al. liver transplantation in alcoholic patients: impact of an alcohol addiction unit within a liver transplant center. alcohol clin exp res.2013;37:1601–8. http://dx.doi.org/10.1111/acer.12117 14. heckley ga, jarl j, asamoah bo, g-gerdtham u. how the risk of liver cancer changes after alcohol cessation: a review and meta-analysis of the current literature. bmc cancer. 2011;11: 446. http://dx.doi.org/10.1186/1471-2407-11-446 15. iarc. a review of human carcinogens. iarc monographs on the evaluation of carcinogenic risks to humans, vol. 100. lyon, france: international agency for research on cancer; 2011. p. 2011. http://monographs.iarc.fr/eng/monographs/ pdfs/index.php. testino g and leone s codon publications journal of renal and hepatic disorders 2017; 1(1): 3–4 4 http://dx.doi.org/10.1056/nejmoa1105703 http://dx.doi.org/10.1056/nejmoa1105703 http://dx.doi.org/10.1016/j.transproceed.2009.03.092 http://dx.doi.org/10.1097/sla.0000000000001831 http://dx.doi.org/10.3748/wjg.v20.i40.14642 http://dx.doi.org/10.1002/hep.25544 http://dx.doi.org/10.1002/hep.25544 http://dx.doi.org/10.1016/j.dld.2012.06.003 http://dx.doi.org/10.1016/j.dld.2012.06.003 http://dx.doi.org/10.3748/wjg.v22.i20.4789 http://dx.doi.org/10.3748/wjg.v22.i20.4789 http://dx.doi.org/10.1111/bioe.12274 http://dx.doi.org/10.1111/bioe.12274 http://dx.doi.org/10.1111/acer.12117 http://dx.doi.org/10.1186/1471-2407-11-446 http://monographs.iarc.fr/eng/monographs/pdfs/index.php http://monographs.iarc.fr/eng/monographs/pdfs/index.php journal of renal and hepatic disorders 2018; 2(2): 6–9 6 review article potassium profiling in hemodialysis nikhil agrawal1, sahil agrawal2, nishita tripathi3, mark segal4 1division of nephrology, beth israel deaconess medical center, boston, ma, usa; 2cardiology, st luke’s hospital, allentown, pa, usa; 3medicine, kempegowda institute of medical sciences, bangalore, karnataka, india; 4nephrology, university of florida, gainesville, fl, usa abstract cardiac dysrhythmia and sudden death account for a large proportion of cardiac mortality in dialysis patients. risk factors for sudden death that are specific to dialysis patients include fluid and electrolyte imbalances during hemodialysis, particularly those of potassium. the risk of arrhythmia may be related to changes in serum k+ concentration during dialysis, and thus close attention should be paid to the dialysate k+ concentration and the serum–dialysate concentration gradient. potassium profiling is a technique where the dialysate k+ concentration is gradually reduced to keep the gradient between blood and dialysate at a non-fluctuating low level. we provide a review of studies that compare constant potassium concentration in dialysate to gradual reduction in dialysate potassium concentration. these studies illustrate that adequate and more gradual potassium removal can be achieved with potassium profiling techniques, while having lower cardiac irritability. keywords: arrhythmia; dialysate potassium; potassium profiling; potassium removal; sudden cardiac death received: 30 may 2018; accepted after revision: 19 july 2018; published: 07 august 2018 author for correspondence: nikhil agrawal, division of nephrology, beth israel deaconess medical center, 185 pilgrim road, boston, ma 02215, usa. email: nagrawa2@bidmc.harvard.edu how to cite: agrawal n et al. potassium profiling in hemodialysis. j ren hepat disord. 2018;2(2):6–9 doi: http://dx.doi.org/10.15586/jrenhep.2018.34 copyright: agrawal n et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction mortality and morbidity in end stage renal disease (esrd) patients on hemodialysis (hd) remains high, and higher than non-dialysis patients with similar co-morbidity burden (1). cardiac dysrhythmia and sudden death account for a large proportion of cardiac mortality in these patients, amounting to 26.9% of total deaths (1). risk factors for sudden death that are specific to dialysis patients include fluid and electrolyte imbalances during hd, particularly those of potassium(k+) (2). most of the evidence linking the risk of arrhythmia to dialysis is derived from electrocardiogram (ekg) markers such as ventricular repolarization indices which include qt duration (qtc), qt dispersion (qtd), pca-t (principal component analysis of t wave), and e1-t (first eigenvalue of t wave) (3–11). these indices are known to reflect increased risk of arrhythmia (11, 12) and one of the factors which has been shown to change these indices is the change in serum potassium, stemming from the critical role of the k+ ion in myocardial repolarization (6, 13–15). both hypokalemia and hyperkalemia have been shown to have associations with higher mortality in hd patients (16). due to lack of renal function to handle potassium excretion, esrd patients undergo potassium removal during dialysis. in hd, this is achieved by diffusion of potassium from a higher concentration in serum to lower concentration codonpublications.comjrenhep.com mailto:nagrawa2@bidmc.harvard.edu http://dx.doi.org/10.15586/jrenhep.2018.34 http://creativecommons.org/licenses/by/4.0 potassium profiling in hemodialysis journal of renal and hepatic disorders 2018; 2(2): 6–9 7 in dialysate, and is thus directly proportional to the concentration gradient between blood and dialysate. hyperkalemia is associated with higher mortality in dialysis patients (16) and high potassium concentration in dialysate might impair potassium removal. but at the same time, multiple studies have associated low dialysate potassium with higher risk of sudden cardiac death. it was noted in a study with the dialysate k+ concentration of 0 and 1 meq/l (17), and with dialysate k+ of less than 3 (18). further, another study showed less arrhythmia when the k+ bath was 3.5 versus 2 (19). this may be related to rapid changes in serum potassium during dialysis, and the challenge is to balance adequate potassium removal with risk of arrhythmia while doing it. potassium profiling is a technique where the dialysate k+ concentration is gradually reduced to limit the gradient between blood and dialysate constant and low. it has the potential advantage of reducing rapid changes in serum potassium level during dialysis (and thus reducing cardiac irritability), while also allowing for adequate potassium removal. here we provide a review of the randomized control trials that have compared potassium profiling of dialysate to a fixed dialysate potassium concentration. methods we searched the pubmed database using search terms “potassium profiling,” “potassium profiling in hemodialysis,” “potassium hemodialysis,” and “dialysate potassium.” we included only the randomized control trials done in the past 25 years. the first study in our literature review to employ this technique was published in 1990 by ebel et al. (20). using a computerized program, they removed k+ slowly at a rate of 15%/hour and showed that incidence of arrhythmia was reduced from 60 to 25% (20). since then, multiple randomized control trials have looked at potassium profiling. although they have used different profiling techniques, all these studies have looked at effects of potassium profiling on cardiac stability using electrocardiographic markers and also ability to effectively remove potassium during dialysis. results a brief overview of these studies is provided in table 1 (21–26). all studies included in our review used a cross over design to compare constant potassium concentration in dialysate to gradual reduction in dialysate potassium concentration. the number of subjects was small, ranging from 10 to 36 patients. inclusion and exclusion criteria were variable; some studies excluded patients with significant cardiovascular disease (3, 4), while others included only those who were considered high risk for arrhythmias (1, 6, 7). although none of these studies looked exclusively at hyperkalemic patients, the average serum k+ concentration in these studies was normal or slightly high (up to 6 meq/l) and two studies excluded patients with hypokalemia (2, 6). the dialysate potassium in control patients was mostly 2 meq/l. the potassium profiling techniques used in study  population varied in different studies and are listed in table 1. a limitation of these studies is that arrhythmic risk using indirect ekg and holter markers was assessed rather than actual arrhythmia events. this relates to the rather small number of study subjects and therefore the low overall incidence of arrhythmia. in the absence of a unanimous ekg marker for predicting arrhythmia with changes in k+, indirect measures of cardiac excitability and ventricular repolarization including premature ventricular contractions (pvcs), changes in qtc/qtd/pca-t/e1-t were used as surrogate markers of arrhythmic risk. lower cardiac irritability with potassium profiling was shown in all studies. the effects were generally more pronounced in patients who are at higher risk of arrhythmia or who are dialysis sensitive. comparison of potassium removal with standard versus potassium profiled dialysate techniques was done by measuring post-hd or pre-hd (prior to next session) serum potassium concentrations. there was no significant difference in these levels between the two techniques. further, the training and technical requirements to implement this technique in a hd unit did not increase the work load of the nephrologist or the nurses, nor did it increase the technical complexity (27). conclusion there are no standard practices for dialysate potassium concentrations and no recommendation has been provided in the nkf-kdoqi (national kidney foundation–kidney disease outcomes quality initiative) cardiovascular disease guideline. in a large international cohort of hd patients, dialysate potassium concentration varied among clinical practices and countries and ranged anywhere from 1 meq/l to 3 meq/l (28). there are no large studies showing a difference in clinically significant arrhythmic events when gradually removing potassium in dialysis patients via potassium profiling of dialysate. however, there are multiple small studies suggesting a lower risk of arrhythmia with potassium profiling by using indirect markers of cardiac excitability and ventricular repolarization. also, these studies suggest that an adequate amount of potassium could be removed without having a high gradient, at no extra financial cost. in our opinion, it would thus make sense to consider potassium profiling of dialysate in hd patients to reduce cardiac irritability, especially in patients who are at higher risk. nikhil agrawal et al. journal of renal and hepatic disorders 2018; 2(2): 6–9 8 conflict of interest the authors declare no potential conflicts of interest with respect to research, authorship, and/or publication of this article. 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hemodialysis. saudi j kidney dis transpl. 2010;21(3):460–5. 6. floccari f, aloisi e, nostro l, caccamo c, crisafulli a, barillà a, et al. qtc interval and qtc dispersion during haemodiafiltration. nephrology. 2004;9(6):335–40. https://doi. org/10.1111/j.1440-1797.2004.00333.x table 1. randomized controlled trials on potassium profiling. study no. no. of patients/type of study control dialysate batha k conc in meq/l study dialysate bathb k conc in meq/l measurement of outcomes difference in potassium removal result redaelli (21) 36, rct, crossover <3 mean 2.3 serum k-1.5,b reduce to k-2.5 pvc no change in pre-hd serum k level reduced pvc significantly santoro (22) 10, rct, crossover 2 serum k-1, reduce to k-1.5 pvc, qtd, pca-t, e1-t no change in post-hd serum k levels lesser pvc in pro-arrhythmic patients, lesser qt-prolongation severi (23) 10, rct, crossover 2 serum k-0.5, reduce to k-1.5 qtd, qrs duration, st depression, pca-t, e1-t no change in post-hd serum k levels lesser variation in pca-t, e1-t santoro (24) 12, rct, crossover 2 serum k-3.24, reduce to k-1-1.3 qtc, qtd, pvcs no change in post-hd k levels lesser change in qtc, reduce high grade pvcs santoro (25) 15, rct, crossover 2 serum k-1, reduce to k-1.5 ectopic beats no change in post-hd k levels less ectopic beats significantly in pro-arrhythmic patients buemi (26) 24, rct, crossover 2 serum k-1, reduce to k-2 rbc remp,c qtc, qtd no change in post-hd serum k levels lesser change in qtc, qtd, remp muñoz (27) 30, rct, crossover 2.5 serum k-0.5, reduce to k-1.5 pvc no change in post-hd k levels lesser pvcs, lesser qt-prolongation acontrol bath = dialysate potassium fixed during the entire dialysis session (not profiled). bstudy bath = potassium profiled bath. in this case, dialysate k concentration kd = serum k – 1.5 meq/l. cred blood cell electrical membrane potential at rest (rbc remp). premature ventricular contraction (pvc), qt duration (qtc), qt dispersion (qtd), principal component analysis of t wave 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cardiac arrhythmias in patients at risk: a pilot study. hemodial int. 2008;12(1):108–13. https://doi.org/10.1111/j.1542-4758.2008.00250.x 28. karaboyas a, zee j, brunelli sm, usvyat la, weiner de, maddux fw, et al. dialysate potassium, serum potassium, mortality, and arrhythmia events in hemodialysis: results from the dialysis outcomes and practice patterns study (dopps). am j kidney dis. 2017; 69(2);266–77. https://doi.org/10.1053/j. ajkd.2016.09.015 https://doi.org/10.1136/pmj.78.919.273 https://doi.org/10.1016/0022-0736(92)90032-u https://doi.org/10.1016/0022-0736(92)90032-u https://doi.org/10.1111/j.1440-1797.2005.00362.x https://doi.org/10.1053/ajkd.2002.32005 https://doi.org/10.1053/ajkd.2002.32005 https://doi.org/10.1159/000045387 https://doi.org/10.1177/000331970005100607 https://doi.org/10.2215/cjn.04451206 https://doi.org/10.1046/j.1523-1755.2001.00806.x https://doi.org/10.1046/j.1523-1755.2001.00806.x https://doi.org/10.2215/cjn.08850811 https://doi.org/10.2215/cjn.08850811 https://doi.org/10.1038/ki.1980.93 https://doi.org/10.1038/ki.1980.93 https://doi.org/10.1093/ndt/5.suppl_1.165 https://doi.org/10.1038/ki.1996.356 https://doi.org/10.1159/000085691 https://doi.org/10.1159/000073440 https://doi.org/10.1159/000060222 https://doi.org/10.1093/ndt/gfh770 https://doi.org/10.1111/j.1542-4758.2008.00250.x https://doi.org/10.1053/j.ajkd.2016.09.015 https://doi.org/10.1053/j.ajkd.2016.09.015 jrenhep020 25..28 jrenhep.com codonpublications.com case report renal recovery following orthotopic liver transplant after prolonged kidney injury: perspectives on diagnosing hepatorenal syndrome and determining which patients should undergo simultaneous liver– kidney transplantation mary elizabeth card 1 , gilbert moeckel 2 , jeffrey m. turner 3 1department of internal medicine, yale school of medicine, new haven, ct, usa; 2department of pathology, yale school of medicine, new haven, ct, usa; 3yale-new haven hospital, department of internal medicine, new haven, ct, usa abstract we present a case of an individual with cirrhosis and renal failure. this case is notable because the patient was found to have hepatorenal syndrome (hrs) superimposed on immunoglobulin a (iga) nephropathy. after 8 months of dialysis, the patient had significant renal recovery following orthotopic liver transplant (olt). cases such as this are not likely to be rare, as case series have shown that iga deposits are a common occurrence in patients with cirrhosis, including those who have hrs. while current diagnostic criteria for hrs emphasize the importance of excluding glomerular lesions, we argue that this approach should be reconsidered. more specifically, we feel that the diagnostic approach to hrs should be more inclusive of cases in which patients have simultaneous hrs and glomerular injury. in addition, our case highlights the challenges in determining which patients will benefit most from simultaneous liver–kidney transplants over olts alone. keywords: hepatorenal syndrome; liver cirrhosis; organ allocation; simultaneous liver–kidney transplantation; treatment outcome received: 01 june 2017; accepted after revision: 21 june 2017; published: 20 july 2017. author for correspondence: jeffrey m. turner, boardman 114, 330 cedar street, new haven, ct 06520, usa. email: jeffrey.turner@yale.edu how to cite: card me et al. renal recovery following orthotopic liver transplant after prolonged kidney injury: perspectives on diagnosing hepatorenal syndrome and determining which patients should undergo simultaneous liver kidney transplantation. j ren hepat disord 2017; 1(2):25–28. doi: http://dx.doi.org/10.15586/jrenhep.2017.20 copyright: card me et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction kidney injury in the setting of cirrhosis is a common phenomenon. a number of different renal pathologies are commonly associated with liver disease, including immunoglobulin a (iga) nephropathy, cryoglobulinemia, membranous nephropathy, membranoproliferative glomerulonephritis, and hepatorenal syndrome (hrs) (1–3). for treating kidney disease, a number of treatment options exist, which vary based on the cause of the kidney injury. orthotopic liver transplant (olt) has been well described as a definitive treatment in some cases of hrs (4). our understanding of why some patients with hrs recover renal function after olt and why others do not is limited; however, some data suggest that duration of kidney injury prior to transplant is an important factor (5). duration of injury is a plausible factor, as it is well appreciated that the common final pathway for all kidney injury, irrespective of initial etiology, is diffuse, irreversible fibrosis (6). journal of renal and hepatic disorders 2017; 1(2): 25–28 mailto:jeffrey.turner@yale.edu http://dx.doi.org/10.15586/jrenhep.2017.20 http://creativecommons.org/licenses/by/4.0 therefore, it is reasonable to speculate that during prolonged courses of hrs, the injury transforms from a functional change in renal function to an irreversible injury on the pathway to fibrosis. however, it is unclear what specific factors dictate the timing of this transformation in hrs. therefore, significant challenges exist regarding the prediction of whether a given individual will actually recover renal function after olt or not, as there is likely to be significant heterogeneity with respect to the time it takes to develop irreversible kidney injury among subjects with hrs. under the current organ procurement and transplantation network (optn) policy, adult candidates seeking simultaneous liver–kidney transplantation (slk) must meet one of the following medical eligibility criteria: (i) presence of chronic kidney disease (ckd) defined as a glomerular filtration rate (gfr) <60 ml/min for ≥90 days and either on dialysis as an end-stage renal disease (esrd) patient or a creatinine clearance (crcl) or estimated glomerular filtration rate (egfr) of ≤30 ml/min at the time of kidney transplant listing, (ii) sustained acute kidney injury (aki) defined as a crcl or egfr ≤25 ml/min or dialysis dependence lasting for at least 6 weeks, or (iii) one of several metabolic diseases (7). the appropriateness of these criteria has been under debate since it was adopted in 2016 (8, 9). in this article, we report a case of a patient with esrd in the setting of liver cirrhosis from alpha-1 antitrypsin deficiency (a1atd) who recovered renal function following olt. our case is notable as the subject had prolonged kidney injury, requiring hemodialysis (hd) for 8 months, but still regained significant renal function. our case is important to report in the literature because it adds perspective to the challenges of diagnosing hrs as well as determining eligibility for slk in patients with cirrhosis and ckd. case report a 56-year-old male with decompensated cirrhosis secondary to a1atd type zz/30 presented with aki. the patient’s renal dysfunction was first noted on surveillance lab work, which revealed an elevated serum creatinine of 1.9 mg/dl (from a baseline of 1.0 mg/dl). his creatinine initially improved after discontinuation of diuretics and transition to large volume paracenteses (lvps) for volume control. however, about 1 month later his serum creatinine rose to 3.4 mg/dl, prompting a hospital admission for expedited evaluation of his subacute kidney injury. despite having developed aki in the setting of decompensated cirrhosis, the diagnosis of hrs as the etiology of his aki was only transiently entertained. on admission, his urine electrolytes were consistent with pre-renal aki and the renal function failed to improve after a trial of intravascular volume expansion challenge, both of which can be suggestive of hrs. furthermore, he had no known recent exposure to nephrotoxins and no evidence of shock or hemodynamic compromise; renal ultrasound was unremarkable. however, his urinalysis was significant for 3+ proteinuria (spot urine protein:creatinine = 1400 mg/gcr), and urine microscopy revealed an active urine sediment, including dysmorphic red blood cells with both granular and red blood cells casts. this suggestion of intrinsic renal disease challenged the diagnosis of hrs, which is currently a diagnosis of exclusion. a renal biopsy was performed, and the light microscopy slides showed diffuse acute tubular injury, mesangial proliferation, and focal interstitial infiltrate with lymphocytes. immunofluorescence studies revealed 3+ iga and c3 deposition in the mesangium and 1+ positivity for igm in capillary loops. igg was negative. electron microscopy showed increased mesangial matrix deposits. based on these biopsy findings, the patient was diagnosed with iga nephropathy, for which he was treated with lisinopril, fish oil, and prednisone. the patient’s renal dysfunction progressed to end-stage renal failure in coming weeks and hemodialysis was initiated. he was subsequently listed for slk on the advice of his clinicians. his model for end-stage liver disease (meld) score was 34. after awaiting dual organ offers for several months, the patient decided to change his listing status to oltalone. the motivation behind this was that his anticipated waiting time for an olt alone would be much shorter than an slk. three days after unlistinghimselffordualorgantransplant,thepatientunderwent olt. following olt, the patient’s average pre-hemodialysis serum creatinine improved from 7.1 mg/dl to 1.5 mg/dl. a measured crcl was found to be 39 ml/min. hemodialysis was subsequently discontinued. two years post-olt, his renal recovery has persisted. he has remained off of hd, and his creatinine has stabilized at 1.4–1.7 mg/dl (egfr 40–50 ml/min). given his degree of renal recovery following olt, the patient was retrospectively diagnosedwithhrsdespitethe presence of structural renal injury. discussion our case is noteworthy for a few reasons. first, it highlights the challenge of diagnosing hrs despite the existence of established diagnostic criteria, and it serves as a reminder to clinicians to consider this diagnosis in cirrhotic patients with renal dysfunction despite evidence of glomerular disease in the urine or on kidney biopsy. second, it demonstrates the difficulty of deciding whether a cirrhotic patient with ckd should be eligible for an slk, even in those with prolonged esrd. furthermore, it suggests that under the current optn/united network for organ sharing (unos) medical eligibility criteria established for kidney allocation to slk candidates, a significant proportion of patients are likely to receive a kidney graft that they do not need. hrs is understood to be a functional injury to the kidneys involving maladaptive hemodynamic changes that include increases in nitric oxide-mediated splanchnic arterial dilatation and the compensatory upregulation of the renin–angiotensin– aldosterone system and sympathetic nervous system leading to renal vasoconstriction (10, 11). the current paradigm by which we diagnose hrs emphasizes it as a diagnosis of journal of renal and hepatic disorders 2017; 1(2): 25–28 26 card me et al. exclusion. the international ascites club (iac) hrs diagnostic criteria infer that the probability of a patient having hrs increases with the exclusion of shock, nephrotoxin exposure, and glomerular injury (based on the presence of significant proteinuria [>500 mg/24 hours] or hematuria [>50 rbc/hpf]). this is a challenging proposition because there is no pathophysiologic reason that hrs could not be present concurrently with ischemic/nephrotoxic acute tubular injury or glomerular injury. a more appropriate approach to emphasize may be to ponder whether hrs is the sole cause of kidney injury or whether it is superimposed on another etiology. given that patients with cirrhosis are severely ill, they are undoubtedly at high risk of many types of renal insults. low mean arterial pressures, gastric varices, and impaired coagulation function make ischemic injury common. frequent exposure to infections, antibiotics, contrast dye, and proton pump inhibitors makes nephrotoxic injury common. in addition, it has been well documented since the 1940s that the majority of cirrhotic patients have biopsy-proven glomerular abnormalities, many of which contain iga deposits, as was the case with our patient (12–23). thus, the likelihood of having iga deposits in a patient with cirrhosis and simultaneous hrs is not likely to be rare. the subject we report on had aki and met five out of the six criteria for the diagnosis of hrs based on the 2015 ica diagnostic guidelines. however, hrs was excluded as a diagnosis because his aki was associated with the presence of an active urine sediment and a biopsy that confirmed iga mesangial deposits. it was not until our patient had been on hd for 8 months and then had dramatic renal recovery immediately following olt that the diagnosis of superimposed hrs was confirmed. this case therefore highlights the challenges associated with diagnosing hrs in patients with simultaneous glomerular disease. given the relative scarcity of organs available for transplant, it is imperative that cirrhotic patients with reversible kidney injury are accurately distinguished from those who have irreversible kidney injury in order to ensure just allocation of resources. incorrectly diagnosing cirrhotic patients with irreversible renal failure leads to needlessly listing these patients for slk. on an individual level, this translates to increased time on the transplant waitlist and its associated stress, anxiety, and relative negative quality of life (24–26). on a societal level, this means that fewer kidneys are available to esrd patients, who face a 6% annual mortality on the kidney transplant waitlist (27). although our patient met eligibility for slk based on the current criteria, his renal outcome was excellent after olt alone. therefore, this case underscores the challenges in rightly allocating kidneys for transplantation in patients with cirrhosis and kidney disease. data show that those with mild ckd are not likely to benefit from slk (7, 28). in terms of those with severe kidney disease or those requiring dialysis prior to transplant, data show a small survival benefit of about 5% at 1 year in those undergoing slk versus olt alone (29). however, the benefit of slk may be especially difficult to determine in patients with hrs. data from a single center showed that 33% of patients with hrs undergoing slk had significant recovery of their native renal function post-transplant (30). many of the kidneys being used for slk have a low kidney donor profile index (kdpi) score (<35%). this has raised concerns among some members of the transplant community that organs with an expected long-term survival are preferentially being given to older recipients awaiting slk over younger recipients awaiting an olt alone (8, 9). conclusion this case highlights the challenges associated with diagnosing hrs in patients with simultaneous glomerular disease. we feel it warrants a change in how we think about and discuss hrs. clinical reasoning surrounding the diagnostic approach to hrs should be more inclusive of cases in which patients have hrs simultaneous to glomerular injury. clinicians should be wary of excluding the diagnosis solely based on the presence of an active urine sediment. in addition, it should cause us to rethink if there is any role for performing a kidney biopsy in these patients. it is well appreciated that the bleeding and infection risk of performing a kidney biopsy is high in this population, but it should also be well appreciated that finding glomerular injury or other structural changes on biopsy will not by itself exclude hrs. this further re-enforces the fact that the risks associated with kidney biopsy in patients with cirrhosis far outweigh any 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http://dx.doi.org/10.1016/j.transproceed.2012.07.046 http://dx.doi.org/10.1002/lt.23899 http://dx.doi.org/10.1111/j.1600-6143.2006.01526.x http://dx.doi.org/10.1097/tp.0b013e318168476d http://dx.doi.org/10.1097/tp.0b013e318168476d https://dx.doi.org/10.1016/j.transproceed.2006.12.006 https://dx.doi.org/10.1016/j.transproceed.2006.12.006 journal of renal and hepatic disorders 2018; 2(2): 1–5 case report monitoring the effects of tenofovir disoproxil fumarate to tenofovir alafenamide switch for tubulotoxicity in highly treatmentexperienced or in very sick individuals infected with hiv nicole lioufas1, alan street2, paul champion de crespigny1, stephen g. holt1,3 1department of nephrology, the royal melbourne hospital, parkville, australia; 2victorian infectious diseases service, the royal melbourne hospital, parkville, australia; 3school of medicine, the university of melbourne, parkville, australia abstract tenofovir disoproxil fumarate (tdf) is a common antiretroviral utilised in the treatment of human immunodeficiency virus (hiv) and hepatitis b infections. it is associated with the development of tubulotoxicity and tubulopathies, and is not recommended in the treatment of patients with baseline chronic kidney disease. until now, guidelines have suggested frequent monitoring of serum biochemistry to detect the development of such complications. in recent trials, a new prodrug formulation of tenofovir alafenamide (taf) has been shown to exhibit less tubular toxicity than its counterpart due to a lower serum concentration of its metabolites. in this article, we share our experience with two patients who developed tubulotoxicity following the commencement of tdf-based regimens in hiv, and its improvement following its change to taf, and review the available literature regarding tenofovir-based nephrotoxicity. keywords: anti-retroviral; hiv; tenofovir alafenamide; tenofovir disoproxil fumarate; tubulotoxicity received: 27 april 2018; accepted after revision: 11 june 2018; published: 29 june 2018 author for correspondence: nicole lioufas, department of nephrology, royal melbourne hospital, parkville, australia. email: nicole.lioufas2@wh.org.au how to cite: lioufas n et al. monitoring the effects of tenofovir disoproxil fumarate to tenofovir alafenamide switch for tubulotoxicity in highly treatment-experienced or in very sick individuals infected with hiv. j ren hepat disord. 2018;2(2):1–5. doi: http://dx.doi.org/10.15586/jrenhep.2018.33 copyright: lioufas n et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction combined anti-retroviral treatment (cart) regimens for human immunodeficiency virus (hiv) and hepatitis b virus (hbv) infection are often formulated for patients with normal renal function, and finding suitable regimes for patients whose renal function has deteriorated can be challenging. tenofovir disoproxil fumarate (tdf), a nucleotide reverse transcriptase inhibitor (nrti), has been extensively used as a ‘backbone’ for such treatment, with more than 50% of patients on a tdf-based regimen. tdf is a prodrug, being converted intracellularly to tenofovir diphosphate, a structural analogue of deoxyadenosine triphosphate which suppresses viral replication by inhibiting viral reverse transcriptase (1). however, tdf has been associated with the development of a progressive, predominantly proximal, tubulopathy with renal impairment in a small number of patients (2). frequent renal function testing has been advocated to detect this complication (3), and proximal tubulopathy may be detected by looking for evidence of metabolic acidosis, hypophosphatemia, hyperphosphaturia, hypokalaemia, codonpublications.comjrenhep.com mailto:nicole.lioufas2@wh.org.au http://dx.doi.org/10.15586/jrenhep.2018.33 http://creativecommons.org/licenses/by/4.0 n. lioufas et al. journal of renal and hepatic disorders 2018; 2(2): 1–5 2 hyperuricaemia, tubular proteinuria, aminoaciduria and glycosuria. urinary tubular markers are expensive and difficult to monitor; therefore, tubular proteinuria may be inferred by the ratio of urinary albumin (conveniently measured by urine albumin to creatinine ratio (uacr) on a spot sample) compared with urinary total protein (measured with urine protein to creatinine ratio [upcr]) (4). thus, uacr/upcr is a simple way to monitor tubular dysfunction in patients with hiv, with a urine albumin to protein ratio (uapr) of ~0.4 or less suggesting tubular proteinuria (5). however, for patients with creatinine clearance <50 ml/min, tdf is not recommended by prescribing guidelines, and if used should be dose reduced. however, finding a suitable regimen to switch to in such patients may be tricky due to the side effects of alternative medications or preexisting antiretroviral resistance. tenofovir alafenamide (taf), another prodrug of tenofovir, which is preferentially concentrated in lymphoid tissue, offers an improved renal safety profile and may offer a simple switch in patients with renal issues, where alternatives may be less desirable. we report the cases of two complex patients in whom tdf-based therapy was associated with significant side effects, who showed clear benefit by a switch from tdf to taf. case 1 a 62-year-old man diagnosed with hiv-1 infection in 1985 was referred in 2013 for assessment of renal impairment and proteinuria. he was highly treatment experienced and previous genotypic testing had demonstrated acquired hiv resistance to all nrtis except for intermediate resistance to emtricitabine, to all non-nucleoside rtis, to all protease inhibitors except low level resistance to darunavir, and likely non response to the entry inhibitor maraviroc. nevertheless, his treatment regimen of tdf, emtricitabine, ritonavir-boosted darunavir and raltegravir kept his hiv viral load undetectable and cd4 count within the reference range (480 cells/µl [reference range 400–1500]). other comorbidities included previous hodgkin’s lymphoma diagnosed and treated in 2007 with adriamycin, bleomycin, vincristine and dacarbazine from which he achieved a complete response, with no obvious immediately or long-term toxicities noted. he had type-2 diabetes mellitus for 8 years treated with oral hypoglycaemic agents, cirrhosis due to non-alcoholic steatohepatitis, hyperlipidaemia on a statin, paroxysmal atrial flutter and treated hypertension. he had no family history of renal disease, did not consume alcohol and had given up smoking more than 10 years ago. his creatinine had been stable at ~110 µmol/l (mdrd ~58 egfr ml/min/1.73 m2) for the last 3 years, but at presentation his urinary protein level had begun to creep up with a urine protein–creatinine ratio of 110 mg/mmol and an albumin– creatinine ratio of 40 mg/mmol. at clinic visits prior to this, his blood pressure had been well controlled (<140/80 mmhg). most electrolytes were within reference ranges, but serum bicarbonate 21 mmol/l (25–35 mmol/l), corrected calcium 2.39 mmol/l (2.1–2.6 mmol/l), magnesium 0.84 mmol/l (0.7–1.1) and phosphate 0.32–0.80 mmol/l (0.80–1.5). at this time, he was also noted to be glycosuric on dipstick with normal plasma glucose. ultrasound showed normal renal sized kidneys and his autoantibodies were negative. there was no change in urinary protein leak in response to the addition of an angiotensin-converting enzyme inhibitor. given this patient’s previous treatment exposure, resistance mutations and comorbidities, the options for alternative treatments were extremely limited. initially, a trial of dose reduction of the tdf component of his therapy was attempted, reducing 300 mg daily to 300 mg second daily dosing. however, there was no significant improvement in figure 1. this graph illustrates the reduction in proteinuria (upcr), initially without much change in albuminuria (uacr) after starting taf. this increases uapr above 0.4 for the first time since the patient developed proteinuria. the significance of uapr with low total urine protein is unknown and is not shown when upcr < 30 mg/mmol shaded (as per ref [5]). tdf to taf switch for tubulotoxicity journal of renal and hepatic disorders 2018; 2(2): 1–5 3 renal parameters including those of glomerular filtration rate (gfr), proteinuria, serum bicarbonate, or phosphate levels, but his hiv viral load remained suppressed on a lower dose regimen. a switch from tdf to taf 10 mg daily was performed, and he remained on emtricitabine 200 mg daily. on a tafbased regimen, there were significant improvements within a month (mean ± standard deviation) in upcr 72 ± 26 to 56 ± 17 mg/mmol (p < 0.05), uapr 0.3 ± 0.06 to 0.39 ± 0.07, (p < 0.001), serum albumin 42 ± 3 to 44 ± 4 (p < 0.05), serum phosphate (0.69 ± 0.16 to 0.87 ± 0.13 mmol/l (p < 0.001) and serum urate (0.21 ± 0.01 to 0.26 ± 0.03; p < 0.02) (figure 1). serum creatinine (112 ± 8 to 115 ± 10, p = ns), uacr (23 ± 10 to 23 ± 10, p = ns) and egfr (58 ± 5 to 55 ± 5, p = ns) remained unchanged and viral load stayed undetectable with good cd4 counts. case 2 a 45-year-old man with a history of amphetamine use was admitted with exertional dyspnoea, 15 kg weight loss and intermittent fever, but no cough or orthopnoea. chest x-ray showed bilateral pulmonary infiltrates and follow-up computed tomography of the chest showed bilateral central ground glass changes with associated interstitial septal thickening and abruptly demarcated upper lobe emphysema. an hiv test was positive, hiv viral load was 982, 444 copies/ml and cd4 count was 20 cells/µl. pneumocystis jiroveci pneumonia (pjp) was confirmed at bronchoscopy in addition to myocbacterium avium complex (mac). he was treated with high-dose trimethoprim/ sulphamethoxazole, prednisolone, ethambutol, clarithromycin and rifampicin. at admission, his creatinine was 75 µmol/l, and no proteinuria was noted upon urine dipstick. his admission was further complicated by staphylococcal pneumonia, and cytomegalovirus encephalitis treated with valganciclovir. his creatinine peaked at 130 µmol/l, which then normalised to 70 µmol/l as he recovered from his acute infection. two weeks after admission he was started on tdf/emtricitabine. within 1 week, his serum phosphate fell to a nadir of 0.31 mmol/l and he required significant phosphate replacement, up to 100 mmol/day, in addition to diet (recommended dietary intake 32 mmol/day) for 2 weeks, with inability to wean. fractional excretion of phosphate was 42% (normal < 20%). additionally, he had a protein–creatinine ratio of 179 mg/ mmol, and an urine acr of 9.29 mg/mmol (uapr of 0.05). he was switched to taf/emtricitabine and improvement was noted with his electrolytes within 1 week, with a rapid wean of his phosphate replacement until stabilisation of serum phosphate at 1.2 mmol/l within 1 week (figure 2). one month following his change to taf, his creatinine remained within the normal range and his levels of proteinuria fell to within the normal range by 3 months (pcr 28 mg/mmol) and by 1 year (pcr 18, acr 1.1 mg/mmol). phosphate levels have remained within the normal range on no replacement. discussion an estimated 36.7 million people were living with hiv in 2016 (6) and the increasing prevalence is mainly related to the longer life expectancy due to cart (7). thus, an older prevalent population is emerging with many years of well-suppressed hiv who are developing more issues related to chronic disease such as cardiovascular disease, diabetes  and  chronic kidney figure 2. serum phosphate levels rise and oral phosphate replacement requirements fall significantly and acutely on change from tdf to taf. n. lioufas et al. journal of renal and hepatic disorders 2018; 2(2): 1–5 4 disease (ckd). the  complex interplay between chronic viral infection, cart and natural ageing contributes to increased chronic morbidity in this population (8). patients living with hiv have higher rates of ckd than the general population, in developed countries, and whilst specific hiv-related glomerular disorders (e.g. hiv-associated nephropathy or immune complex kidney disease) contribute to renal disease burden, this is becoming an increasingly rare contributor to the causes of kidney dysfunction (9). tubulointerstitial disorders and tubulopathies are estimated to cause approximately 15% of renal disease in retrospective renal biopsy series (10–12). in a retrospective cohort single-centre study, 222 renal biopsies from hiv-positive patients were analysed for aetiology of renal impairment. one-third of biopsies were thought to show tubulopathy, of which ~80% were thought to be drug related and tdf was the main culprit. a further half of the biopsies showed acute or chronic interstitial nephritis, and tdf was implicated in approximately one quarter of these (12). it should be noted that interstitial nephritis in this biopsy series was also associated with opportunistic infections such as mac or tuberculosis. current recommendations for tdf-related nephrotoxicity are vague, given the absence of strong evidence. in 2014, the infectious diseases society of america (idsa) guidelines recommended that all patients should be screened regularly for blood pressure, ckd and electrolyte parameters at diagnosis and at the commencement of tdf-based therapy (13). in the more recent australian consensus statement, it was recommended that both the urinary albumin and urinary protein should be measured separately to detect the possible development of tubular proteinuria (3). furthermore, idsa recommends that regimens containing tdf should not be commenced if the patient has a gfr < 60 ml/min, and to change antiretroviral therapy from tdfcontaining regimens if there is a >25% decline in gfr or development of tubular dysfunction (13). similar recommendations have been made by the european association for the study of the liver (14). the pharmacokinetics of taf make this an ideal replacement for tdf as similar intracellular levels in target cells allow much lower levels of plasma tenofovir, and hopefully lower incidence of nephrotoxicity. randomised studies of tafversus tdf-based regimes in patients with creatinine clearance >50 ml/min showed non-inferior efficacy in viral suppression and a smaller increase in creatinine and lower increases in urinary protein at 48 weeks (15). one single-arm open-label study switching patients with renal dysfunction (estimated creatinine clearance 30–60 ml/min) from tdf to taf-based regimes showed improvement in proteinuria (16). a more recent randomised control trial of tdf to taf in 1443 hiv-1 patients revealed non-inferiority in terms of viral suppression at 96 weeks, with improvement in gfr and bone mineral density (17). similar evidence in the treatment of hepatitis b has emerged with again non-inferiority and improved renal outcomes in phase 3 trials (18, 19). in these cases, we observed a change in tubular proteinuria following the change from tdf to taf. case 1 was noted at referral to have a creatinine of approximately 110 µmol/l, which did not improve significantly following his change in drug regimen. this patient had other risk factors for preexisting renovascular ckd, which would likely account for no change in creatinine despite change to taf. the improvement in electrolyte parameters and tubular proteinuria in both patients suggests that there is a degree of reversibility, which is likely to be more significant if the earlier change in therapy from tdf to taf is made. the world health organization guidelines regarding antiretroviral therapy mention caution with regard to ckd and suggest that taf may be helpful in this patient group; however, the guidelines have not routinely recommended the drug due to lack of safety data in pregnant women (20, 21). taf has been more recently approved in the usa, europe (22) and recently in australia as part of fixed-dose formulations in combination with emtricitabine alone or with addition of a third antiretroviral agent. in summary, we show here that it appears safe and efficacious to switch treatment-experienced and inexperienced patients with tubulopathy and renal impairment to a tafbased regimen. the efficacy of such a switch can be assured by following biochemical markers suggestive of tubular damage like proteinuria, uapr and the degree of phosphaturia. conflict of interest stephen g. holt has received research funding and/or honoraria from amgen, astra zenica, baxter, gilead and sanofi. the other authors declare no potential conflicts of interest with respect to research, authorship and/or publication of this article. references 1. fernandez-fernandez b, montoya-ferrer a, sanz ab, sanchez-nino md, izquierdo mc, ppveda j, et al. tenofovir nephrotoxicity: 2011 update. aids res treat. 2011;2011:354908. 2. gupta sk, anderson am, ebrahimi r, fralich t, graham h, scharen-guivel v, et al. fanconi syndrome accompanied 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http://dx.doi.org/10.1159/000112851 http://dx.doi.org/10.1038/ki.2008.604 http://dx.doi.org/10.1038/ki.2008.604 http://dx.doi.org/10.2215/cjn.10051012 http://dx.doi.org/10.2215/cjn.10051012 http://dx.doi.org/10.1093/cid/ciu730 http://dx.doi.org/10.1016/j.jhep.2012.02.010 http://dx.doi.org/10.1016/j.jhep.2012.02.010 http://dx.doi.org/10.1016/s0140-6736(15)60616-x http://dx.doi.org/10.1097/qai.0000000000000908 http://dx.doi.org/10.1016/s1473-3099(15)00348-5 http://dx.doi.org/10.1016/s2468-1253(16)30024-3 http://dx.doi.org/10.1080/17512433.2017.1323633 http://dx.doi.org/10.1080/17512433.2017.1323633 http://dx.doi.org/10.1016/j.bcp.2016.04.015 jrenhep002 5..10 jrenhep.com original article outcomes of albumin use in the treatment of acute hepatorenal disorders: a single center experience krishna pothugunta1, santhi voora1, holly kramer1–3, anil k. bidani1,3, kavitha vellanki1,3 1division of nephrology and hypertension, department of medicine, loyola university chicago, maywood, il, usa; 2department of public health sciences, loyola university chicago, maywood, il, usa; 3hines veterans affair medical center, hines, il, usa abstract intravenous albumin is recommended for hepatorenal disorders (hrd), but individuals who do not recover renal function may be at a high risk for pulmonary edema. we reviewed outcomes by the amount of albumin infused in 93 patients not receiving dialysis at admission but being treated with intravenous albumin for acute hrd at our institution. absence of renal recovery was defined as no decrease in serum creatinine and requirement of dialysis during hospitalization, and partial renal recovery was defined as a decrease in serum creatinine but not to prehospitalization levels. associations of clinical factors including total albumin infused, presence of renal recovery, and oliguria with the development of pulmonary edema during hospitalization were determined using logistic regression. of the 93 patients, 20 patients had complete renal recovery, 17 patients had partial renal recovery, and 56 patients showed no renal recovery. most patients received 300–600 g of albumin. overall, 47.3% of patients developed pulmonary edema (n=44), but the risk was 75% in patients with oliguria on presentation and no renal recovery versus 17% in those with no oliguria and complete renal recovery (p<0.001). in the logistic regression model, oliguria (3.32; 95% confidence interval [ci]: 1.12, 9.81) and no renal recovery (3.38; 95% ci: 1.24, 9.16) were each associated with higher odds of pulmonary edema after adjustment for covariates. no association was noted between total albumin infused and pulmonary edema. in summary, absence of renal recovery and oliguria in patients with hrd receiving intravenous albumin is associated with a higher risk of pulmonary edema. keywords: acute renal failure; albumin; cirrhosis; hepatorenal syndrome; pulmonary edema received: 26 october 2016; accepted after revision: 08 december 2016; published: 03 february 2017. author for correspondence: holly kramer, department of medicine, loyola university medical center, 2160 s. first avenue, maywood, il 60153, usa. email: hkramer@lumc.edu how to cite: pothugunta k et al. outcomes of albumin use in the treatment of acute hepatorenal disorders: a single center experience. j ren hepat disord 2017;1(1):5–10. doi: http://dx.doi.org/10.15586/jrenhep.2017.2 copyright: pothugunta k et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction intravenous albumin plus midodrine and octreotide are recommended for the treatment of type i hepatorenal syndrome (hrs) (1). in clinical practice, albumin use is not just limited to type i hrs and is used in the setting of any acute renal failure (arf) with underlying cirrhosis (hepatorenal disorders, or hrd) for volume expansion. in 1996, the international club of ascites proposed a definition and diagnostic criteria for hrs (2), which was later revised in 2007 with albumin replacing normal saline for volume replacement (3). the recommended dose of albumin for volume resuscitation is 1 g/kg of body weight per day with up to a maximum of 100 g/day; however, the evidence for this threshold is not supported by clinical trials. volume resuscitation with albumin codon publications journal of renal and hepatic disorders 2017; 1(1): 5–10 mailto:hkramer@lumc.edu http://dx.doi.org/10.15586/jrenhep.2017.2 http://creativecommons.org/licenses/by/4.0 infusions in cirrhosis is expected to increase total body volume and circulatory function with resultant improvement in renal function (4). it is also thought to reduce the formation of ascites and edema by increasing the microvascular oncotic pressure, but the pathophysiological basis and evidence supporting this remains controversial (5, 6). the distribution of infused albumin between intravascular and extravascular compartments depends on the transcapillary membrane permeability, which is dependent on multiple factors, including intravascular volume status, and comorbid conditions such as hypertension, diabetes, heart failure, and infections (7, 8). studies involving human volunteers have shown that rapid increases in plasma volume that occur immediately with albumin infusions are not seen with repeated infusions despite increasing serum albumin levels (9). most importantly, response to albumin infusions varies across individuals with cirrhosis, and intravascular volume does not consistently rise in all cirrhotic patients (10, 11). earlier studies have reported cases of increasing pleural effusions, development of pulmonary edema, and heart failure and rupture of esophageal varices with albumin infusions in cirrhotic patients (12). however, recent guidelines (1, 13) poorly address the potential side effects of continued albumin infusions in cirrhotic patients with compromised renal function, where volume status is difficult to determine. we retrospectively reviewed the incidence of new onset pulmonary edema as well as patient outcomes in cirrhotic patients who received albumin infusions as part of the treatment for acute hrd at our university medical center. we hypothesized that oliguria is associated with a significantly increased risk of pulmonary edema in patients with hrd receiving intravenous albumin. materials and methods study population we conducted a retrospective chart review of all cirrhotic patients who were admitted to our institution between 2011 and 2013 with arf and received albumin as part of management of acute hrd. diagnostic codes (icd-9) for cirrhosis (571, 571.2, 571.5, and 571.6), hrs (572.4), and arf (584 and 584.9) were used to identify patients for the study. all identified charts were then manually reviewed to confirm the diagnosis of cirrhosis and arf and that albumin was given as part of management of acute hrd (verified by physician documentation in chart). a total of 115 cirrhotic patients who were admitted between january 2011 and december 2013 were identified. after excluding patients who had an abnormal chest x-ray (cxr), were intubated or were dialysis dependent at admission, or were transferred to another hospital for care, a total of 93 patients were included in the final analysis. all 93 patients had clinically attributed hrd as the etiology of arf, with no evidence of urinary tract obstruction or primary glomerular disease by clinical criteria. the study was approved by the institutional review board of loyola university chicago’s health sciences campus. information collected from the electronic medical record included age, sex, cause of liver disease, model for end-stage liver disease (meld) score, serum creatinine at admission and at 72 hours after admission, urine output (uop) during the first 24 hours of hospitalization, urine electrolytes before and after treatment, dialysis start date, presence of pulmonary edema on cxr, total amount of albumin administered during the hospital stay and prior to the development of pulmonary edema, and need for endotracheal intubation. albumin infusions contained 4% albumin at initial presentation and 25% albumin at subsequent infusions. the dose varied from 100 ml twice daily to 100 ml thrice daily based on physician discretion. incidence of renal recovery was defined as complete renal recovery (serum creatinine decreasing to prehospitalization baseline values), partial renal recovery (serum creatinine decreasing but not back to prehospitalization baseline values), and absence of renal recovery (no decrease in serum creatinine and requirement of dialysis during hospitalization). pulmonary edema was defined as the presence of bilateral infiltrates on cxr in the absence of clinically suspected acute respiratory distress syndrome. statistical analyses characteristics of the study population by pulmonary edema status were compared using fisher’s exact test to compare categorical variables, and unpaired t-tests were used to compare continuous variables with a normal distribution. nonparametric variables were compared using the wilcoxon rank-sum test. the percentage of patients with pulmonary edema was plotted by the presence of complete or partial renal recovery and by oliguria status at admission. to determine significant differences across categories of renal recovery and oliguria status, a chi-square test for linear trend was used. logistic regression models were fitted to examine the association of pulmonary edema with total albumin infused and renal recovery status while simultaneously adjusting for age, peak serum creatinine, meld score, and oliguria on presentation. these covariates were chosen based on a backward selection logistic regression model which included age, meld score, initial serum albumin and creatinine, peak serum albumin and creatinine, total albumin infused, diuretic use during the first 24 hours of admission, oliguria during the first 24 hours after admission, and renal recovery status (no, partial, and complete). p<0.05 was considered statistically significant. analyses were completed using stata/ic 13.1 (statacorp lp, college station, tx, usa). results a total of 93 patients had clinically attributed hrs as the etiology of arf (hrd). the mean age of the patients was 57.9 years with a mean meld score of 29 (range: 145–58), pothugunta k et al. codon publications journal of renal and hepatic disorders 2017; 1(1): 5–10 6 mean serum albumin of 2.37 (range: 0.5–3.6), and mean serum creatinine of 2.35 mg/dl (range: 0.77–12.8 mg/dl) on presentation. oliguria (defined as less than 500 ml of uop in the first 24 hours after admission) was present in 29% of the patients. renal recovery status was complete and partial in 20 and 17 patients, respectively, while 56 patients had no renal recovery. the amount of albumin infused ranged from 300 to 600 g of albumin in 52 patients while four patients received more than 1000 g of albumin during the hospital course. peak serum albumin achieved during hospitalization ranged from 2.1 to 9.4 g/dl with a mean of 3.7 g/dl, and 35 of 93 patients had a peak serum albumin of 4.0 g/dl or higher. the baseline characteristics by renal recovery status are shown in table 1. the presence or absence of oliguria, age, and development of pulmonary edema differed significantly by renal recovery status while the presenting meld score, serum creatinine, or the etiology of liver disease did not. of the 20 patients with complete renal recovery, 7 patients died by the end of the study period, 10 were alive, and 3 received an orthotropic liver transplant (olt). in the partial renal recovery group (n=17), a total of 12 patients died, four received organ transplant (2 olt and 2 simultaneous liver– kidney transplants), and one patient remained alive without dialysis at the end of the study period. of the 56 patients that had no renal recovery, 12 died without receiving dialysis, one patient received a simultaneous liver–kidney transplant and the remaining 43 required dialysis. of the 43 patients that required dialysis, 23 died, 4 received olt, 5 received a simultaneous liver–kidney transplant, and the rest remained alive on dialysis at the end of the study period. the risk of new onset pulmonary edema during the hospitalization was 47% (n=44). the baseline characteristics by the development of pulmonary edema are shown in table 2. both oliguria on presentation (15.1% vs. 43.4%, p=0.002) and the presence of partial or complete renal recovery (52.7% vs. 23.7%, p=0.002) differed significantly by the development of pulmonary edema. when stratified by renal outcomes and oliguria, there was a statistically significant linear trend in the incidence of pulmonary edema (figure 1) by renal recovery and oliguria status (p<0.001), with the highest risk noted in those with oliguria and no renal recovery (60.7%). a total of 29 patients required mechanical table 1. baseline characteristics of patients with hepatorenal disorders receiving intravenous albumin (n=93) characteristic total (n=93) complete renal recovery (n=20) partial renal recovery (n=17) no renal recovery (n=56) age (years) 57.9 (10.1) 54.8 (10.5) 63.5 (9.7) 57.3 (9.6)* % male 52.2 50 47 55 +meld score 29.0 (14.9, 58.0) 27.7 (20.4, 35.9) 32.5 (26.7–33.1) 29.4 (24.7, 39.7) liver disease etiology alcoholic 52.7 50.5 70.0 48.2 hcv 15.1 15.1 0 19.6 % nash 21.5 15.1 18.0 24.7 other 10.8 19.3 12.0 7.5 initial serum cr (mg/dl) (mean with sd) 2.90 (1.77) 3.49 (2.01) 3.73 (2.73) 2.44 (1.03) peak creatinine (mg/dl) (mean with sd) 4.74 (2.01) 4.14 (2.06) 5.45 (2.28) 4.72 (1.88) oliguria 29.0% 25% 29.4% 30.4%** albumin baseline (g/dl) (mean with sd) 2.37 (0.61) 2.39 (0.51) 2.49 (0.60) 2.36 (0.65) peak albumin (g/dl) (mean with sd) 3.74 (0.94) 3.42 (0.57) 3.81 (0.99) 3.83 (1.02) +total albumin infused (g) 325 (200, 550) 350 (218.8, 531.25) 275 (170, 537.5) 325 (200, 687.5) % pulmonary edema 47.3 20.4 37.6 60.2** meld, model for end-stage liver disease; hcv, hepatitis c virus; nash, non-alcoholic steatohepatitis; sd, standard deviation. +values shown as median (interquartile range); **p<0.001 for oliguria and pulmonary edema; *p=0.02 for age. albumin for hepatorenal syndrome codon publications journal of renal and hepatic disorders 2017; 1(1): 5–10 7 intubation during the hospital course of which 12 patients had no recovery of renal function. on univariate analysis, the presenting meld score, serum creatinine, oliguria, and renal recovery status showed significant associations with the development of pulmonary edema (table 3). after adjustment for age, and meld score, both oliguria (3.32; 95% confidence interval [ci]: 1.12, 9.81) and no renal recovery (3.38; 95% ci: 1.24, 9.16) were significantly associated with higher odds of developing pulmonary edema. discussion our study examined the incidence of new onset pulmonary edema with albumin infusions in patients with hrd. while traditionally hrs is subdivided into two types (14), type i and type ii, based on rapidity of deterioration of renal function, a recent consensus conference has proposed hrd as a term to describe concurrent renal dysfunction in the setting of advanced cirrhosis (13). we chose to use the term acute hrd for our study as albumin infusions are not just limited table 2. comparison of baseline characteristics of patients with hepatorenal disorders receiving intravenous albumin by the development of pulmonary edema (n=93) characteristic no pulmonary edema (n=49) pulmonary edema (n=44) p age 61.1 (10.2) 59.6 (10.6) 0.7 % male 30.5 54.3% 0.4 meld score 27.8 (15.6–58.0) 32.6 (14.9–51.4) 0.2 initial serum cr (mg/dl) 2.44 (1.03–12.84) 2.22 (0.77–5.93) 0.3 peak creatinine (mg/dl) 4.25 (1.77–12.84) 4.98 (2.64–10.18) 0.6 % oliguria 15.1 43.4 0.002 initial albumin (g/dl) 2.30 (1.2–3.6) 2.35 (0.5–3.5) 0.6 peak albumin (g/dl) 3.7 (2.1–4.51) 3.65 (2.1–9.4) 0.4 % partial or complete renal recovery 52.7 23.7 0.002 % paracentesis 70.2 56.5 0.1 meld, model for end-stage liver disease. 80% 70% 60% 50% 40% 17% p<0.001 for trend cr + no pr + no nr + no nr + o p u lm o n a ry e d e m a 25% 53% 75% 30% 20% 10% 0% figure 1. risk of new onset pulmonary edema stratified by renal recovery status and oliguria in 93 patients with hepatorenal disorders receiving intravenous albumin. cr, complete recovery; no, nonoliguric; nr, no recovery; o, oliguric; pr, partial recovery. pothugunta k et al. codon publications journal of renal and hepatic disorders 2017; 1(1): 5–10 8 to type i hrs in clinical practice. liver transplantation is the treatment of choice for hrd but pharmacological treatment with albumin infusions for volume replacement is also widely recommended (1, 13–19). volume overload with continued albumin infusions is of particular concern in cirrhotic patients. although the guidelines from the international club of ascites acknowledge the risk of pulmonary edema, the risk is considered to be low (3). we noted a high risk of pulmonary edema among adults with acute hrd receiving intravenous albumin, and this risk was the highest in patients with oliguria and absence of renal recovery. the presenting meld score or serum albumin was not associated with a risk of pulmonary edema. hence, we postulate that new onset pulmonary edema was from volume overload in the setting of continued albumin infusions. the graded increase in the incidence of pulmonary edema when stratified by the presence of oliguria or renal response to treatment further supports our conclusion. in our study, the amount of albumin infused was not associated with renal recovery status or the development of pulmonary edema. this could be related to the variable response to albumin infusions based on intravascular volume status on presentation. almost all patients in our study did not have invasive monitoring of hemodynamic parameters which is the case in routine clinical practice. also, there was a wide variation in the total amount of albumin given per day with the total amount of albumin infused varying between 150 and 1100 g, with one patient having a peak serum albumin as high as 9.4 g/dl on multiple readings during the hospital course. a lag period between albumin infusions and cxr findings and/or symptoms of pulmonary edema could be a major confounder when trying to determine a correlation between the amount of albumin infused and the development of pulmonary edema. the limitations of our study include the observational design and the small sample size. hemodynamic monitoring was not performed in patients, and we do not have information on the baseline volume status of the patients with acute hrd. patients were not weighed daily and so we do not have information on change in their weight from admission to the development of pulmonary edema. oliguria on presentation was determined by physician documentation in the chart and verified from the outputs documented in the chart on admission. however, documentation of total fluid intake versus uop may not have been accurately recorded. pulmonary edema was defined by new cxr findings. the dose and duration of intravenous albumin was determined by the treating physician. due to the small number of cases of pulmonary edema, we could not control for a large number of potential confounders, and residual confounding is possible. conclusion in our retrospective study, the risk of new onset pulmonary edema was high in oliguric patients whose renal function did not improve with intravenous albumin. caution should be exercised while giving continued albumin infusions to patients with oliguria, and close monitoring of volume status should be mandated to avoid the risk of pulmonary edema. table 3. univariate and multivariable adjusted associations between clinical factors and pulmonary edema among adults with hepatorenal disorders univariate odds ratio (95% ci) multivariate odds ratio (95% ci) age 0.97 (0.94, 1.02) 0.99 (0.94, 1.03) meld score 1.05 (0.99, 1.10) 1.04 (0.98, 1.09) initial serum albumin 0.77 (0.39, 1.51) — peak serum albumin 1.05 (0.68, 1.63) — total albumin infused 1.00 (0.99, 1.01) — use of diuretics at admission 1.39 (0.58, 3.30) — oliguria 5.00 (1.85, 13.53) 3.32 (1.12, 9.81) initial serum creatinine 0.95 (0.75, 1.21) — peak serum creatinine 1.45 (1.12, 1.87) 1.14 (0.83–1.54) no renal recovery 5.18 (2.05, 13.08) 3.38 (1.24–9.16) meld, model for end-stage liver disease; ci, confidence interval. variables in the multivariate analysis were selected by backward selection with all variables in univariate analysis fitted in the model. albumin for hepatorenal syndrome codon publications journal of renal and hepatic disorders 2017; 1(1): 5–10 9 acknowledgments there was no funding for this research. data were presented as poster at the american society of nephrology meeting, november 2014, philadelphia, pa (dr. pothugunta). conflict of interest the authors declare no conflicts of interest with respect to 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http://dx.doi.org/10.1186/cc11188 http://dx.doi.org/10.1186/cc11188 http://dx.doi.org/10.1056/nejmra0809139 http://dx.doi.org/10.1056/nejmra0809139 http://dx.doi.org/10.1056/nejm199908053410603 http://dx.doi.org/10.1056/nejm199908053410603 http://dx.doi.org/10.1002/hep.510290629 http://dx.doi.org/10.1002/hep.20262 http://dx.doi.org/10.1002/hep.20262 http://dx.doi.org/10.1007/s10620-006-9312-0 http://dx.doi.org/10.1007/s10620-006-9312-0 http://dx.doi.org/10.1097/mcg.0b013e318188947c http://dx.doi.org/10.1097/mcg.0b013e318188947c jrenhep012 copy 55..61 jrenhep.com codonpublications.com review article an update on hepatorenal syndrome samuel chan 1,2 , kenneth au 2,3 , ross francis 1 , david w. mudge 1 , david w. johnson 1 , tony rahman 3 1department of nephrology, princess alexandra hospital, brisbane, queensland, australia; 2centre for health services research, university of queensland, brisbane, queensland, australia; 3department of gastroenterology and hepatology, the prince charles hospital, chermside, queensland, australia abstract hepatorenal syndrome (hrs) is one of the many potential causes of acute kidney injury (aki) in patients with decompensated liver disease. hrs is associated with poor prognosis and represents the end-stage of a sequence of reductions in renal perfusion induced by progressively severe hepatic injury. the pathophysiology of hrs is complex with multiple mechanisms interacting simultaneously, although hrs is primarily characterised by renal vasoconstriction. a recently revised diagnostic criteria and management algorithm for aki has been developed for patients with cirrhosis, allowing physicians to commence treatment promptly. vasopressor therapy and other general management, such as antibiotic prophylaxis, need to be initiated whilst patients are assessed for eligibility for transplantation. liver transplantation remains the treatment of choice for hrs but is limited by organ shortage. other management options, such as transjugular intrahepatic portosystemic shunt, renal replacement therapy and molecular absorbent recirculating system, may provide short-term benefit for patients not responding to medical therapy whilst awaiting transplantation. clinicians need to be aware of the pathophysiology and management principles of hrs to provide quality care for patients with multi-organ failure. keywords: acute kidney injury; hepatorenal syndrome; molecular absorbent recirculating system; renal replacement therapy; transjugular intrahepatic portosystemic shunt received: 17 february 2017; accepted after revision: 01 march 2017; published: 22 march 2017. author for correspondence: samuel chan, department of nephrology, princess alexandra hospital, 199 ipswich road, woolloongabba, brisbane, queensland, australia. email: samuel.chan@uqconnect.edu.au how to cite: chan s et al. an update on hepatorenal syndrome. j ren hepat disord 2017;1(1):55–61. doi: http://dx.doi.org/10.15586/jrenhep.2017.12 copyright: chan s et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction renal failure is common amongst patients with decompensated cirrhosis and is associated with a poor prognosis, with life expectancy ranging from weeks to months. hepatorenal syndrome (hrs) is a functional form of acute kidney injury (aki) characterised by renal vasoconstriction. studies attempting to develop renal biomarkers to differentiate aetiologies of aki have shown promise, but such endeavour remains in its infancy. there are different approaches to the management of hrs, although liver transplantation still shows the highest survival rates amongst patients with both hepatic and renal failure (1). this review article will provide an update on the pathophysiology, diagnostic criteria and treatment options, including prophylaxis, in patients with hrs. journal of renal and hepatic disorders 2017; 1(1): 55–61 mailto:samuel.chan@uqconnect.edu.au http://dx.doi.org/10.15586/jrenhep.2017.12 http://creativecommons.org/licenses/by/4.0 epidemiology the incidence and the prevalence of hrs in patients with advanced liver disease are approximately 7.6% and 13%, respectively (2). hrs occurs predominantly in portal hypertension associated with cirrhosis, but it has been described in severe alcoholic hepatitis and fulminant hepatic failure (3). hrs may occur either spontaneously or may be precipitated by an acute insult, including spontaneous bacterial peritonitis (sbp), non-steroidal anti-inflammatory drugs (nsaids) or upper gastrointestinal bleeding. pathophysiology there are a plethora of simultaneous mechanisms underlying the pathophysiology of hrs, including arterial vasodilatory effects, systemic inflammation, bacterial translocation and hepatorenal reflex (4) (figure 1). these mechanisms appear to be mostly functional, as normalisation of kidney function may be achieved either by pharmacotherapy or by liver transplantation. the arterial vasodilation theory arterial vasodilation appears to be the most plausible explanation for circulatory dysfunction that occurs in patients with cirrhosis and ascites (3). this involves two major mechanisms as follows: firstly, systemic circulatory disturbances and, secondly, activation of neurohumoral systems. splanchnic vasodilatation, resulting from portal hypertension secondary to cirrhosis, leads to decreased systemic vascular resistance and subsequent reduction in effective blood volume, which is clinically mediated by an increased production of nitric oxide (no), carbon monoxide and/or endogenous cannabinoids (3). in the early stages, the effective arterial blood volume and arterial pressure are maintained by increased cardiac output resulting in a hyperdynamic circulation. in later stages, the progressive splanchnic vasodilatation results in a decrease in effective arterial blood volume that can no longer be compensated by cardiac output. moreover, the subsequent decrease in cardiac output may be due to cirrhotic cardiomyopathy, thereby contributing to further arterial underfilling and worsening of renal function (4). in order to maintain arterial pressure, systemic vasoconstrictor systems, such as the renin-angiotensin-aldosterone system (raas), the sympathetic nervous system (sns) and the non-osmotic hypersecretion of arginine vasopressin (avp), are activated leading to increased plasma renin activity and increased plasma norepinephrine levels. however, the activation of neurohumoral systems has harmful impacts on kidneys. development of renal sodium and solute-free water retention leads to ascites and oedema, and hypervolemic hyponatremia, respectively. this results in significant renal vasoconstriction, which leads to a decrease in glomerular filtration rate and subsequently hrs (5). renal factors prostaglandins (pgs), specifically pgi2 and pge2, induce renal vasodilation, thereby providing renal protective effects by compensating for the vasoconstrictor systems of raas, activation of neurohumoral system (raas, sns, avp) renal vasoconstriction hrs-aki hyponatremia and ascites sodium and water retention neurally mediated reflex activation of chemoreceptors, baroreceptors and osmoreceptors in the liver ↓ renal blood flow ↓ effective arterial blood volume splanchnic/systemic arterial dilatation portal hypertension cirrhosis bacterial translocation inflammatory cytokines (tnf, endotoxins) compensatory ↑ cardiac output figure 1. proposed mechanisms for pathophysiology of hepatorenal syndrome. avp, arginine vasopressin; raas, renin-angiotensin-aldosterone system; sns, sympathetic nervous system; tnf, tumour necrosis factor. chan s et al. journal of renal and hepatic disorders 2017; 1(1): 55–61 56 sns and avp. the levels of renal pgs are increased in patients with cirrhosis and ascites (6). nsaids are a common cause of kidney failure in patients with cirrhosis (6), illustrating the probable important role of pg production for maintaining renal function in patients with cirrhosis. cytokines and vasoactive mediators systemic inflammation plays a role in the pathophysiology of hrs. bacterial translocation has been implicated in the haemodynamic derangement of cirrhotic patients, thereby leading to hrs (4). in the clinical setting, increased levels of pro-inflammatory cytokines, such as tumour necrosis factor α (tnfα), interleukin-6 (il-6) and no, in the splanchnic area lead to reduced systemic vascular resistance and increased cardiac output (7). hepatorenal reflex the existence of sensor(s) in the hepatic circulation, which play a role in regulating extracellular fluid volume, is pathologically stimulated by hepatic haemodynamic irregularities. this may contribute to volume overload and ascites by activating renal sympathetic nerves to promote salt and water retention (8). diagnostic criteria aki is a frequent complication in patients with advanced liver disease, with several potential causes. recent consensus guidelines have been published by the international club of ascites (ica) updating the recommended threshold for diagnosing aki in patients with cirrhosis (table 1), which now align with the kidney disease improving global outcomes (kdigo) aki classification (2). hrs is a diagnosis of exclusion and should be suspected in patients presenting with new renal impairment in the setting of cirrhosis with ascites. criteria for the diagnosis of hrs were first published by the ica in 1996 with subsequent revisions (2, 9), and the current recommended criteria are listed in table 2. a vital step in evaluating patients with potential hrs is to exclude other possible causes of aki. hrs has traditionally been subdivided into type 1 or type 2 disease based on the rate of onset of aki and prognosis. type 1 hrs is characterised by a rapid (less than 2 weeks) onset of aki, often precipitated by other events, in particular sbp. type 1 hrs is usually associated with a poor prognosis. type 2 hrs typically presents with a more insidious onset of renal impairment over several weeks in patients with cirrhosis and refractory ascites. currently, there are no clinical criteria to reliably distinguish between hrs and other causes of aki. this has prompted researchers to search for biomarkers, such as urinary neutrophil gelatinase-associated lipocalin (ngal), with the potential to aid the differential diagnosis and management of aki occurring in cirrhotic patients (4). however, these biomarkers are yet to be validated in large randomised control trials and therefore cannot be routinely recommended in clinical practice yet. table 1. ica-aki new definitions for the diagnosis of aki in patients with cirrhosis subject definition baseline scr a value of scr obtained in the previous 3 months, when available, can be used as baseline scr. in patients with more than one value within the previous 3 months, the value closest to the admission time to the hospital should be used. in patients without a previous scr value, the scr on admission should be used as baseline. definition of aki • increase in scr ≥0.3 mg/dl (≥26.5 μmol/l) within 48 h; or • a percentage increase in scr ≥50% from baseline that is known, or presumed, to have occurred within the previous 7 days. staging of aki • stage 1: increase in scr ≥0.3 mg/dl (26.5 μmol/l) or an increase in scr ≥1.5-fold to 2-fold from baseline. • stage 2: increase in scr >2-fold to 3-fold from baseline. • stage 3: increase of scr >3-fold from baseline or scr ≥4.0 mg/dl (353.6 μmol/l) with an acute increase ≥0.3 mg/dl (26.5 μmol/l) or initiation of renal replacement therapy. reproduced with permission from angeli et al. (2). aki, acute kidney injury; ica, international club of ascites; scr, serum creatinine. an update on hepatorenal syndrome journal of renal and hepatic disorders 2017; 1(1): 55–61 57 prognosis prognosis is poor when patients with cirrhosis develop renal impairment, and hrs is associated with the worst mortality rate amongst the different causes of aki in the setting of cirrhosis (10). a study in 2005 showed the median survival times for type 1 hrs and type 2 hrs to be 1 month and 6 months, respectively (11). further prognostic studies with the newly revised hrs diagnostic criteria will be required. management the ica has proposed a new algorithm for managing aki based on the ica-aki criteria, which potentially allows patients to receive earlier treatment for aki-hrs (figure 2) (2). due to scarce supply of organs for transplantation, medical treatments are often initiated first. prevention of hrs in patients with sbp, a meta-analysis of four randomised trials demonstrated that treatment with antibiotics and albumin was associated with a significant reduction in renal impairment (8% vs. 31%) and mortality (16% vs. 35%) compared with controls (12). furthermore, another randomised controlled trial reported that primary prophylaxis with norfloxacin reduced the incidence of sbp, delayed the development of hrs and improved survival in patients with cirrhosis, ascites and either advanced liver failure or impaired renal function (13). the phosphodiesterase inhibitor, pentoxifylline, which has anti-inflammatory properties through inhibition of leukotriene and tnfα synthesis, was included in management for prevention of hrs. however, a recent randomised study demonstrated that pentoxifylline is not statistically equivalent to the efficacy of prednisolone in patients with severe alcoholic hepatitis (14). vasoconstrictor therapy medical treatment for patients with suspected hrs usually consists of vasopressor and albumin infusion, with the aims of improving splanchnic arterial circulation and plasma volume expansion, respectively. several vasopressor therapies have been trialled in hrs, including terlipressin, norepinephrine and midodrine plus octreotide. terlipressin is not licensed for use in the united states nor is it on the pharmaceutical beneficial scheme (pbs) in australia, whilst midodrine is only available through special assess scheme (sas). a pooled analysis of 501 patients in 21 studies showed that an increase in mean arterial pressure of at least 5 mmhg correlated with improvement in renal function regardless of which vasopressor was used (15). a systematic review and meta-analysis of randomised controlled trials of norepinephrine versus terlipressin in patients with type 1 hrs found no significant difference in reversal of hrs, mortality at 30 days or recurrence of hrs (16). furthermore, a recent study indicated that the efficacy of a midodrine plus octreotide regimen might not be as significant as previous studies suggested (17). in 2015, a randomised controlled trial of 49 patients comparing terlipressin with octreotide/midodrine illustrated a significantly higher rate of improvement in renal function with terlipressin (≥50% serum creatinine decrease, 70.4% vs. 28.6%, p = 0.01), although there was no significant difference in survival between the two groups (18). terlipressin is a bridging option, despite its high cost, to liver transplantation in patients who are transplant candidates as it may improve both renal function and short-term survival for patients awaiting a liver transplant. further clinical trials will be required to assess the indication, efficacy and duration of different vasopressors under the new ica-aki criteria and management algorithm. table 2. diagnostic criteria of hrs type of aki in patients with cirrhosis hrs – aki • diagnosis of cirrhosis and ascites • diagnosis of aki according to ica-aki criteria • no response after two consecutive days of diuretic withdrawal and plasma volume expansion with albumin 1 g per kg of body weight • absence of shock • no current or recent use of nephrotoxic drugs (nsaids, aminoglycosides, iodinated contrast media, etc.) • no macroscopic signs of structural kidney injury*, defined as: ○ absence of proteinuria (>500 mg/day) ○ absence of microhaematuria (>50 rbcs per high power field) ○ normal findings on renal ultrasonography reproduced with permission from angeli et al. (2). aki, acute kidney injury; hrs, hepatorenal syndrome; ica, international club of ascites; nsaids, non-steroidal anti-inflammatory drugs; rbcs, red blood cells. *patients who fulfil these criteria may still have structural damage such as tubular damage. chan s et al. journal of renal and hepatic disorders 2017; 1(1): 55–61 58 transjugular intrahepatic portosystemic shunt although limited studies have suggested that transjugular intrahepatic portosystemic shunt (tips) may lead to improvement of renal function in a well-selected group of patients (19), poor prognosis has been associated with patients with advanced liver disease undergoing tips procedure (20). tips aims to reduce portal pressure by inserting an intrahepatic stent, which shunts portal blood into the systemic circulation, and in theory may benefit some patients with hrs. however, many patients with hrs are ineligible for tips due to contraindications including severe hyperbilirubinaemia or childpugh class c (e.g., bilirubin >5 mg/dl, child-pugh score >11). moreover, the risks associated with tips, namely hepatic encephalopathy, liver failure, cardiac failure and renal injury due to contrast, also need to considered (21). extracorporeal support systems renal replacement therapy (rrt) has been shown to improve short-term survival in patients with aki and may provide a bridge to liver transplantation for patients with hrs who are unresponsive to vasopressors and ineligible for tips (22). however, in the absence of an acute reversible component to the aki or a plan for liver transplantation, initiation and/or continuation of rrt should be evaluated carefully, as these patients have a poor prognosis and are unlikely to recover with rrt alone (22). molecular absorbent recirculating system (mars) removes albumin-bound and water-soluble substances, including no and tnf, which are involved in pathogenesis of hrs. mars has been shown to improve neurological function and coagulation parameters although a randomised trial of 189 patients reported no beneficial effect on survival of mars therapy in patients with acute or chronic liver failure (23). liver transplantation the definitive treatment for type 1 hrs is liver transplantation, as this will reverse both portal hypertension and liver failure, the two main factors leading to systemic circulatory disturbances in hrs. a case-control study suggested that patients with hrs treated with vasopressin before transplantation had similar outcomes compared with patients transplanted with normal renal function (24). however, other studies have demonstrated that vasopressors, regardless of the agent used, had no significant impact on survival (1, 25). simultaneous liver–kidney transplantation is not necessary for patients with isolated hrs and should only be considered in selected patients at high risk for non-recovery of renal function, such as patients with heavy proteinuria and other evidence of advanced primary renal disease. conclusion hrs remains an important and life-threatening complication for patients with advanced liver disease. recent advances in the understanding of the pathophysiology of hrs have identified potential targets for novel diagnostic progressionstableresolution close follow up further treatment of aki decided on a caseby-case basis specific treatment for other aki phenotypes vasoconstrictors and albumin no no yes yes response withdrawal of diuretics (if not withdrawn already) and voulme expansion with albumin (1g/kg) for 2 days satge 2 and 3 aki#satge 1 aki# close monitoring remove risk factors (withdrawal of nephrotoxic drugs, vasodilators and nsaids; decrease/withdrawal of diuretics, treatment of infections* when diagnosed), plasma volume expansion in case of hypovolaemia meet criteria for hrs figure 2. proposed algorithm for the management of acute kidney injury in patients with cirrhosis and ascites. *treatment of spontaneous bacterial peritonitis should include albumin infusion according to current guidelines. #initial aki stage is defined as aki stage at the time of first fulfilment of the aki criteria. aki, acute kidney injury; hrs, hepatorenal syndrome; nsaids, non-steroidal anti-inflammatory drugs. reproduced with permission from angeli et al. (2). an update on hepatorenal syndrome journal of renal and hepatic disorders 2017; 1(1): 55–61 59 and therapeutic approaches. hrs is now recognised as hrs–aki and the diagnostic criteria have recently been revised. whilst liver transplantation in appropriate patients is the only definitive treatment for hrs, vasopressors and albumin remain the key supportive medical therapy for hrs-aki. novel biomarkers may play a future significant role in helping clinicians to identify the aetiology of aki in patients with cirrhosis. conflict of interest david johnson has previously received consultancy fees, research grants, speaker’s honoraria and travel sponsorships from baxter healthcare and fresenius medical care. he has also received consultancy fees from astra zeneca and travel sponsorship from amgen. all other authors declare no conflicts of interest with respect to research, authorship or publication of this article. references 1. boyer td, sanyal aj, garcia-tsao g, regenstein f, rossaro l, appenrodt b, et al. impact of liver transplantation on the survival of patients treated for hepatorenal syndrome type 1. liver transpl. 2011;17(11):1328–32. http://dx.doi.org/10.1002/ lt.22395 2. angeli p, ginès p, wong f, bernardi m, boyer td, gerbes a, et al. diagnosis and management of acute kidney injury in patients with cirrhosis: revised consensus recommendations of the international club of ascites. j hepatol. 2015;62(4): 968–74. http://dx.doi.org/10.1016/j.jhep.2014.12.029 3. garcia-tsao g, parikh cr, viola a. acute kidney injury in cirrhosis. hepatology. 2008;48(6):2064–77. http://dx.doi.org/ 10.1002/hep.22605 4. wong f. the evolving concept of acute kidney injury in patients with cirrhosis. nat rev gastroenterol hepatol. 2015;12(12): 711–19. http://dx.doi.org/10.1038/nrgastro.2015.174 5. chayanupatkul m, liangpunsakul s. cirrhotic cardiomyopathy: review of pathophysiology and treatment. hepatol int. 2014; 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1(1): 55–61 61 http://dx.doi.org/10.1186/cc11188 http://dx.doi.org/10.1186/cc11188 http://dx.doi.org/10.1002/hep.26185 http://dx.doi.org/10.1002/hep.26185 http://dx.doi.org/10.1016/j.jhep.2003.09.019 http://dx.doi.org/10.1016/j.jhep.2003.09.019 http://dx.doi.org/10.1002/lt.24049 jrenhep003 29..34 jrenhep.com case report plasmapheresis in the management of acute pancreatitis due to severe hypertriglyceridemia—reporting new cases andreia campos, josefina santos, cristina freitas, ana castro, sofia santos, joão pedro pimentel, antónio cabrita nephrology department, centro hospitalar do porto, porto, portugal abstract acute pancreatitis is a potentially life-threatening disease. if the diagnosis and the treatment are not prompt, it can rapidly evolve to a medical emergency. severe hypertriglyceridemia, defined as above 1000 mg/dl, is the third most common cause of acute pancreatitis. conventional management includes fat dietary restriction and pharmacological treatment; however, these measures take time to be effective. plasmapheresis seems to be an alternative and safe adjunctive therapy because it allows the rapid reduction of the trigger agent in circulation. its use, especially in severe cases, has been increasingly reported. the authors report three cases of severe hypertriglyceridemia-induced pancreatitis in which early plasmapheresis was successfully used with other supportive clinical management. keywords: acute pancreatitis; plasmapheresis; severe hypertriglyceridemia received: 24 november 2016; accepted after revision: 21 december 2016; published: 03 february 2017. author for correspondence: andreia campos, serviço de nefrologia (nephrology department), centro hospitalar do porto, largo do prof. abel salazar, 4099-001 porto, portugal. email: andcriscampos@hotmail.com how to cite: campos a et al. plasmapheresis in the management of acute pancreatitis due to severe hypertriglyceridemia—reporting new cases. j ren hepat disord 2017;1(1):29–34. doi: http://dx.doi.org/10.15586/jrenhep.2017.3 copyright: campos a et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction acute pancreatitis (ap) is a potentially life-threatening disease. without prompt diagnosis and treatment, it can rapidly evolve to a medical emergency, leading into pancreatic necrosis and ultimately to death (1, 2). serum hypertriglyceridemia (htg) is the third most frequent cause of ap after gallstones and alcohol, with a reported incidence of 1%–10% (3). serum triglyceride levels >1000 mg/dl, also known as severe hypertriglyceridemia (shtg), are usually needed to trigger ap (4–6). conventional management of shtg includes fat dietary restriction and pharmacological treatment; however, the slow action of antihyperlipidemic therapy poses a problem when the situation requires a rapid reduction of the offending agent in circulation (2). plasmapheresis (pf) seems to be an alternative and safe therapy for these kinds of cases because it allows the rapid reduction of triglycerides (tg) in just a few hours (7, 8). its use, especially in high-risk patients admitted in intensive care units, has been increasingly reported. unfortunately, there are no controlled or randomized studies to prove its benefit in mortality reduction. most of the data are based on single case reports. that is why the american society for apheresis (asfa) recommendation for this indication is only grade 2c (9). pf does not interfere in tg production, and therefore, it should always be considered as an adjunctive therapy to medical treatment. codon publications journal of renal and hepatic disorders 2017; 1(1): 29–34 mailto:andcriscampos@hotmail.com http://dx.doi.org/10.15586/jrenhep.2017.3 http://creativecommons.org/licenses/by/4.0 in our hospital, pf is a technique performed by nephrologists, regardless of whether the indication is nephrologic or not. due to the importance of describing all new cases, the authors report three cases of shtg-induced ap in which early pf was used with other supportive clinical management. case reports the patients were admitted to the emergency department with an ap; the etiology factor identified was shtg. all of them had an unfavorable course under medical management in the first 24–48 h. there was no previous available lipid profile, history of treatment with cholesterol or tg-lowering drugs, or history of gallstones or relevant family history. pf was done according to tg levels. a temporary central venous catheter was placed with no complications. a double membrane filtration device and 5% albumin as the replacement fluid were used. the volume treated was correspondent to one plasma volume and the duration of the session was according to the replacement. nonfractioned heparin was used for anticoagulation. there were no pf-related complications. at discharge, the patients were medicated with lower lipid drugs. at follow-up, as an outpatient, all of them were asymptomatic and their tg and pancreatic enzyme levels were within the normal range. to clarify, data in table 1 refer to variables at admission. in figure 1, it is represented as the effect of pf on serum tg. case 1 this is a case of a 43-year-old male with type 2 diabetes diagnosed 6 years before, with poor metabolic control, dyslipidemia, and obesity (body mass index (bmi): 30.6 kg/m2). he had no history of gallstones or alcohol intake. he was admitted with an epigastric abdominal pain with dorsal irradiation, nausea, and vomiting that begun 24 h before. on examination, he had no fever, pulse rate was 124/min, and blood pressure was 100/60 mm hg. he was prostrate and with signs of dehydration. the abdomen was diffusely table 1. initial laboratory data of patients prior to the plasmapheresis treatment laboratory findings case 1 case 2 case 3 reference values hemoglobin (g/dl) 16 17 16.6 13–18 hematocrit (%) 40 38 42 40–52 platelets/mm3 287,000 151,000 201,000 150–440 total leucocyte count/μl 17670 14290 5850 3800–10600 crp (mg/dl) 327.65 56.5 337 <5.0 amylase (u/l) 663 1033 70 <3.0 lipase (u/l) 2686 750 2485 13–60 triglycerides (mg/dl) 1229 5565 1348 <200 total cholesterol (mg/dl) 630 750 350 <200 ast/alt (mg/dl) 50/26 109/72 67/91 4–50/4–33 total bilirubin/direct bilirubin (mg/dl) 0.7/0.1 0.9/0.2 1.0/0.1 0.1–1.1; 0.1–0.3 sodium (mmol/l) 122 128 135 135–145 calcium (mg/dl) 9.0 8.7 8.8 8.8–10.2 glucose (mg/dl) 575 >400 180 60–100 lactate desidrogenase (u/l) 474 370 259 135–225 creatinine (mg/dl) 1.96 0.71 1.7 0.67–1.17 urea (mg/dl) 65 28 29 15–45 bicarbonate (mmol/l) 12 16 17 22–26 lactates 5.0 2 2.6 hba1c (%) 11.6 12 11 <7.0 ast, aspartate transaminase/alt, alanine transaminase; crp, c-reactive protein. codon publications journal of renal and hepatic disorders 2017; 1(1): 29–34 30 campos a et al. painful. he was oliguric. there were no other abnormalities. laboratory tests showed leukocytosis and neutrophilia, an elevated c-reactive protein (crp), a diabetic ketoacidosis, hyperlactacidemia; pancreatic alpha-amylase 663 mg/dl, lipase 2686 mg/dl; and tg 1229 (table 1). abdominal computed tomography (ct) showed a gallbladder without cholecystitis or lithiasis, pancreas with necrosis (~90%), and a necro-hemorrhagic collection in the tail. delayed renal excretion of iodinated contrast was observed. microbiological cultures were negative. the patient started on a fasting regimen, and treatment began with endovenous fluids and insulin. the initial response was unfavorable, with sustained hemo‐ dynamic instability, respiratory distress, and oliguria. he was admitted to the intensive care unit with acute physiology and chronic health evaluation ii (apache ii) score 14 with need of hemodynamic and respiratory support. tg and lipase increased in the first 24 h and renal function worsened (creatinine 4.96 mg/dl). he was submitted to an urgent pf on day 2 of admission. the tg decreased to <1000 mg/dl and 248 mg/dl after the first and second sessions of pf, respectively; the pancreatic enzymes normalized. the patient showed significant clinical improvement with resolution of multiorgan dysfunction, namely, renal dysfunction. he was started on oral fat-free diet and fenofibrate on day 4 and discharged from the intensive care unit to the surgery department on day 10. a ct follow-up at 72 h showed a regression of pancreas necrosis and of hemorrhagic collection, with no signs of infection. a revaluation ct scan was done 2 weeks after showing a complete recovery of pancreatic necrosis. fortunately, he did not present any late complications of this severe pancreatitis, including acute fluid collections, pancreatic necrosis pseudocysts, abscesses, ascitis and pancreatic fistulas, splenic vein thrombosis, or false aneurysms. on follow-up after 2 months, his tg levels were found normal. case 2 this is a case of a 42-year-old man with type 2 diabetes, hypertension, obesity (bmi 41.5 kg/m2), and a past history of dyslipidemia. he had a schizophrenia and the therapeutic compliance was very poor. he was admitted with a diffuse abdominal pain. on physical examination at admission, he had no fever and was hemodynamically stable. the abdominal examination showed tenderness in the right upper quadrant, with no other abnormalities. respiratory, cardiovascular, and neurologic examinations were unremarkable. laboratory studies at admission showed leukocytosis with neutrophilia, an elevated crp, and a severe hypertriglyceridemia (tg 5565 mg/dl). other relevant laboratory results at admission and in posterior workup are presented in table 1. the abdominal ct showed an acute nonlithiasic edematous pancreatitis. the patient was admitted to the intermediate care unit with apache ii score 10, and started on a fasting regimen, insulin perfusion, and fluids. in the context of severe pancreatitis and vigorous fluid therapy, he developed signs of heart failure in the first 48 h, requiring oxygen and diuretic therapy. transthoracic echocardiography did not show any abnormalities. the abdominal pain and the pancreatic markers worsened. in the absence of response to medical therapy during the first 48 h, he started on pf treatment. he needed two consecutive sessions. the procedure was complicated by the clotting of the filters due to the high plasma viscosity requiring high doses of unfractionated heparin. after the first session, his tg levels were 826 mg/dl. one additional pf session was performed in the subsequent day (figure 1). a complete clinical and analytical recovery was seen on the patient. case 3 a 38-year-old male with uncontrolled type 2 diabetes and a known history of high alcohol consumption (>200 g/day) was admitted to the emergency room with an epigastric pain and nausea. on examination, he was hemodynamically stable. respiratory and cardiovascular examinations were normal. he presented with abdominal pain and distention. laboratory tests at admission are shown in table 1. the abdominal ct showed aspects of ap without dilation of the bile ducts or gallstones. the blood was highly lipemic and on ultracentrifuge showed tg 1348 mg/dl. the patient was admitted to the intermediate care unit, with apache ii score 8. he was initially managed with fasting, glucose control, and enteral fibrate. despite the medical management, 24 h after admission, there was a lack of improvement; the renal function worsened with serum creatinine/urea (2.5/85 mg/dl). therefore, we started pf. he underwent two sessions in consecutive days with clinical, analytical, and imagological improvements. the patient was discharged 7 days after admission with oral atorvastatin, fenofibrate, and insulin. discussion and conclusions ap could be a medical emergency associated with higher morbidity and mortality. due to potential associated tg (admission) pf 1 pf 2 case 1 1229 760 248 case 2 5565 826 557 case 3 1348 410 0 1000 2000 3000 4000 5000 6000 t g ( m g /d l) figure 1. effect of plasmapheresis on serum triglycerides (tg). pf1: tg after first plasmapheresis treatment; pf2: tg after second plasmapheresis treatment. plasmapheresis in severe hypertriglyceridemia codon publications journal of renal and hepatic disorders 2017; 1(1): 29–34 31 complications, such as sepsis, pancreatic necrosis, abscess formation and renal insufficiency, or multiorgan dysfunction, ap is considered a potential life-threatening illness with a mortality rate of up to 7%–0% (2, 8). the diagnostic criteria of ap require two of the following three features: characteristic abdominal pain; serum amylase or lipase more than three times the normal upper limit; findings of ap on ct scan (10, 11). our patients presented with all of these criteria. however, in the setting of shtg, amylase and lipase serum levels may be normal or only mildly raised obscuring the correct diagnosis. it was important to exclude other diagnoses for abdominal pain, such as cholecystitis, appendicitis, peptic ulcer disease, and splenic or hepatic infarction, and other causes for ap, namely, the presence of gallstones which was not uncommon in patients with very high bmi, such as ours. however, we cannot completely exclude this etiology. for excluding that, it would be advisable to make a magnetic resonance cholangiopancreatography (mrcp) to study the bile and pancreatic ducts and to exclude the presence of small stones. although none of the patients had a mrcp to exclude lithiasis, the abdominal ct did not show lithiasis evidence and there was no analytical evidence of cholestasis. the suggestive history of higher alcohol consumption in one of our patients and the presence of shtg in all of them appeared to be the cause of ap. normal tg metabolism maintains safe levels lower than 150 mg/dl (12, 13). excessive ingestion, excessive synthesis, or ineffective tg clearance leads to htg. therefore, the causes of htg may be categorized into primary disorders (genetically based) such as lipoprotein lipase (lpl) and apolipoprotein c-ii deficiency, which are usually present in childhood as chylomicronemia syndromes, and secondary disorders such as obesity, untreated diabetes mellitus, alcoholism, pregnancy, drugs associated (estrogens, glucocorticoids, and thiazide diuretics) or lithiasis. abnormalities of insulin responsiveness are present in some of these cases (3, 14). the association of shtg and ap was first postulated by speck in 1865 (15). shtg is reported to account for up to 10% of all ap episodes (16). it is generally believed that tg levels of >1000 mg/dl are a greater risk factor for ap (3). this threshold is arbitrary and the level above which ap might occur is actually unknown (4). the exact pathophysiology still remains unclear. several mechanisms have been proposed, including the genetic predisposition. the sheer size of tg can impede pancreatic blood flow and produce local acinar ischemia. the disturbance of the acinar structure liberates pancreatic lipase; this enzyme degrades chylomicrons and there is a production of pro-inflammatory free fatty acids. this pro-inflammatory state plays a major role in the systemic responses to ap and can accelerate pancreatic damage, producing local tissue necrosis (12, 13). to remember, our patients have some risk factors to htg—those with type 2 diabetes, obesity, and hypothyroidism have reduced lpl activity, although the mechanism for this is unclear; therefore, the tg clearance is reduced. acute alcohol consumption has been shown to increase plasma tg through two mechanisms: acute inhibition of lpl and increased hepatic synthesis of very-low-density lipoprotein (vldl). the aim of the treatment is to reduce endogenous and exogenous sources of tg and promote their clearance. exogenous sources can be reduced by low-fat diets and fasting; endogenous sources can be reduced by lipid-lowering medications and limited alcohol intake; clearance can be promoted by insulin and heparin. insulin activates lpl and heparin stimulates the release of endothelial lpl into the circulation, leading to an acceleration of chylomicron degradation. lifestyles such as dietary changes, avoidance of alcohol, weight reduction, exercise, and control of concomitant endocrinopathy are imperative measures in the management of shtg. all of these measures take time, and in patients with shtg with hemodynamic instability or lack of response to medical treatment, such as the cases reported here, there is an urgent need of lowering the tg levels in order to prevent a multi‐ organ failure. pf consists in an extracorporeal separation of blood components resulting in a filtered plasma product, and it has some clinical applications. in the setting of shtg, the goal is to remove the tg component of the blood. but pf is a nonselective removal process; so it could remove also circulating pro-inflammatory molecule stopping the underlying inflammatory cascade. its use for lowering tg levels was first reported in 1978 by betteridge et al. (14). nowadays, experience with pf in acute hypertriglycerideinduced pancreatitis is limited to case reports and case series, and there are no consensus guidelines on optimal therapy. although rare, htg is the cause of ap in pregnancy in 50% of cases and, in these cases, there is a greater consensus regarding its use because the use of fibrates is not recommended. ewald et al. (15) showed that a single session of pf can lower tg by 70%. similarly, yeh (16) reported that a single cycle of pf lowered tg by 65% and a second cycle by 80%. however, these authors did not find any association between the number of sessions and survival rates (4, 17, 18). in the cases reported here, one or two sessions were sufficient. ramirez et al. (17) described 11 patients submitted to pf— in eight patients, a single plasma exchange was sufficient to reduce tg <1000 mg/dl. only three patients died, all with the worst severity indexes and who experienced most delay before the procedure (19). the clinical practice guidelines recommend daily pf for 1–3 days depending on the patient course and tg level (15, 20). the goal is to achieve tg concentrations lower than 500–1000 mg/dl. heparin use as anticoagulant for the procedure may have advantages considering its ability to release lpl, enhancing tg reduction (19). data suggest that pf should be performed as early as possible in order to achieve best results (21). our patients underwent pf in the first 48 h after admission—they showed not only a rapid reduction of tg but also a clinical improvement. the asfa (6) conducted a literature review to evaluate the rationale use of pf in hypertriglyceridemic pancreatitis. this review is consistent with the findings of chen and campos a et al. codon publications journal of renal and hepatic disorders 2017; 1(1): 29–34 32 gubensek (19) and reported the absence of randomized controlled trials about the effectiveness of the technique (9, 22). however, there has been an increasing number of successful cases described. it is also unclear whether pf increases hospital stay and/or mortality (22–24). risks associated with pf are low but they exist. the risk of infection may be better weighed; pf does not selectively remove lipoproteins and tg; coagulation factors and immunoglobulins are also removed. selective whole blood lipoprotein aphaeresis is feasible in some centers without the undesired consequences of pf, but it causes only a moderate reduction in tg levels (18). bleeding and catheter-associated complications may occur. when 5% albumin is used, there is a progressive loss of coagulation factors. thus, the patient’s bleeding risk increases, especially as the initial treatment requires intensive anticoagulation to avoid system clotting. hypersensitivity reactions to fresh frozen plasma if used as a replacement fluid have been reported (16). there is no data recommending one replacement fluid over another. most studies have used 5% albumin, while some have used fresh frozen plasma which contains lpl; this could enhance tg removal (25, 26). we have to consider that pf is an expensive technique that is not available in all centers. protocols should be created for standardized clinical practice. we suggest that in ap due to shtg, pf should be performed concomitantly with medical therapy in the first 48 h after admission of patients with one or more of the following severity criteria: ranson score on admission or in the first 48 h greater than or equal to 3; apache ii score greater than 8, at any time; presence of one or more organ failures; and presence of one or more local complications. we suggest the use of 5% albumin replacement solution or fresh frozen plasma if there are hemorrhagic complications, coagulation abnormalities, or severe thrombocytopenia. pf should be performed until tg is less than 500 mg/dl. in conclusion, pf seems to be a relatively safe technique that should be considered as a complementary treatment to medical therapeutic in severe cases of acute hypertriglyceridemic pancreatitis, preferably in the early stages of the disease. a strictly pharmacologic treatment may be necessary for the prevention of shtg that leads to ap, but lifestyle changes are also imperative. ideally, multicenter prospective studies should be conducted in order to provide a sufficient sample size in which the patients could be randomized to receive either conventional treatment or pf. however, it poses a big problem to the clinicians—to give or not to give a treatment that quickly removes the aggression trigger which may affect the patient recovery and even survival. it would be important to establish some guidelines for pf use, namely, the number of cycles that are necessary and the timing in which the process should be initiated. maybe in the future, the process will be selective with using membrane-coated antibodies at low costs. although rare, the complications of pf may contribute to morbidity or even mortality, especially in the hemodynamically compromised patients. we do not know whether there is an improvement in mortality. however, we should consider this technique if it is available in severe cases wherein the medical therapy is not fast enough to prevent the inflammatory cascade leading to multiorgan dysfunction. therefore, it is important to report all of similar cases to ascertain the efficacy, timing, and cost–benefit ratio of pf in the setting of ap due to shtg. maybe in the future, it can be used as a first-line therapy in selected cases as a bridge to medical treatment. conflicts of interest the authors declare no conflicts of interest with respect to research, authorship, and/or publication of this article. references 1. cappell m. acute 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catanzaro, italy; 4cnr – institute of clinical physiology, reggio calabria, italy abstract tenofovir, a third generation oral nucleos(t)ide analogue, currently represents one of the first-line drugs recommended for treating chronic hepatitis b virus (hbv) infection. after oral administration, tenofovir is mostly excreted in the urine by glomerular filtration and proximal tubular secretion. hence, an impaired kidney function may lead to an increased renal exposure to the drug in patients with coexistent renal damage. this could further worsen kidney disease through different mechanisms of nephrotoxicity such as mitochondrial dna depletion and tubular cytotoxicity. despite several studies performed so far to assess tenofovir-related renal toxicity, data in hbv patients are not yet conclusive. screening of risk factors for kidney disease before starting therapy and a careful monitoring of serum creatinine, glomerular filtration rate, serum phosphate and urine analysis during treatment are advocated to adjust the dose or stop treatment if needed. new biomarkers of tubular injury, such as neutrophil gelatinase associated lipocalin, could become helpful in the future for the timely identification and risk stratification of renal damage induced by tenofovir. keywords: antiretroviral therapy; hepatitis b; ngal; nucleos(t)ide analogue; tenofovir received: 10 february 2017; accepted after revision: 03 march 2017; published: 23 march 2017. author for correspondence: davide bolignano, cnr – institute of clinical physiology, c/o euroline, via vallone petrara 55–57, 89124 reggio calabria, italy. email: davide.bolignano@gmail.com how to cite: coppolino g et al. renal concerns in the treatment of chronic hepatitis b with tenofovir. j ren hepat disord 2017;1(1):50–54. doi: http://dx.doi.org/10.15586/jrenhep.2017.11 copyright: coppolino g et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/ licenses/by/4.0 introduction chronic hepatitis b virus (hbv) infection is a relevant public health problem all over the world, with different prevalence between low-income and high-income countries. the virus responsible for the disease is a hepatotropic virus belonging to the hepadnaviridae family (1). vaccination is recommended by the world health organization in all newborns and in unvaccinated subjects, particularly in high-risk individuals including haemodialysis patients, recipients of organ transplantation or blood transfusion, partners of patients with hbv infection and people who travel to endemic areas (2). nevertheless, hbv infection is still widespread. because patients affected are at high risk of morbidity and mortality, primarily related to the development and progression of liver cirrhosis and cancer, identifying the most effective therapeutic options is mandatory (3). the drugs currently recommended as first-line therapy of chronic hbv infection are interferon (ifn) or third-generation oral nucleos(t)ide analogues, such as tenofovir and entecavir (etv). according to current guidelines, the use of lamivudine (lam), telbivudine and adefovir (adv) as first-line drugs is not recommended because of their limited efficacy, their side journal of renal and hepatic disorders 2017; 1(1): 50–54 mailto:davide.bolignano@gmail.com http://dx.doi.org/10.15586/jrenhep.2017.11 http://creativecommons.org/licenses/by/4.0 http://creativecommons.org/licenses/by/4.0 effects and the higher rates of drug resistance. ifn is indicated in young patients with mild-to-moderate liver disease, but it cannot be prescribed in patients with non-compensated liver disorder, autoimmune disease, psychosis, depression and during pregnancy. also, ifn should not be prescribed in renal transplant recipients because of the increased risk of rejection, although this drug has the advantage of limited treatment duration with the hypothetic absence of drug resistance. long-term treatment with nucleos(t)ide analogues is necessary for patients not achieving sustained virological response or for those needing extended therapy (4). tenofovir: pharmacokinetics and mechanisms of action tenofovir disoproxil fumarate (tdf) is a nucleotide reverse transcriptase inhibitor acting as a structural analogue of the usual substrate for viral rna–directed dna polymerase used against the human immunodeficiency (hiv) and hepatitis b (hbv) viruses. tenofovir has been used worldwide since 2001 as part of a highly active antiretroviral therapy (haart) against hiv infection. since 2008, it has been indicated for the treatment of adults with chronic hbv infection or hiv/hbv co-infection. it is administered orally as the prodrug tdf or tenofovir alafenamide (5, 6). following oral administration, tdf is essentially completely absorbed in the gastrointestinal tract and peak plasma concentrations are reached within 0.25–1.5 h. the prodrug moiety of tdf is efficiently cleaved and minimal intact prodrug is observed in systemic circulation. major sites of tissue uptake include the liver, kidney and bowel. half-life of tdf is approximately 17 h. the kidney eliminates tdf with minimal metabolic transformation. after an oral dose, 70%–80% is excreted in the urine unchanged. although side effects are mostly represented by bone mineral diseases, gastrointestinal disorders and acute pancreatitis, concerns have been raised also about potential renal damage. in fact, specific renal metabolism leads tdf to be eliminated through urine by glomerular filtration (80%) and proximal tubular secretion (20%) (7). renal clearance abnormalities may affect tdf pharmacokinetics and systemic concentration, and the consequent increased renal exposure to this drug in patients with different degrees of coexistent kidney damage could result in a further decline of renal function (8). mechanisms of tenofovir-induced renal toxicity tdf nephrotoxicity may be explained by various mechanisms including mitochondrial dna depletion, tubular cytotoxicity and intra-individual differences in tdf clearance because of polymorphisms in genes encoding for drug transporters (9, 10). tdf acts primarily by disturbing the mitochondrial function through the inhibition of dna polymerase-gamma responsible fordnareplicationandbydepletingdifferentenzymesinvolved in the electron transport chain function and oxidative phosphorylation. in vitro experimental studies demonstrated the potential of tdf to induce mitochondrial dysfunction but with a lower toxicity as compared to other nucleoside reverse transcriptase inhibitors (10). after absorption, tdf is phosphorylated in two sites and it is filtered unmodified through the glomerulus, beingforlittleparttakenfromthebloodbytheproximal tubular cells (11). as a consequence of phosphorylation, the drug is activated and becomes a structural analogue of the usual substrateofviralrna–directeddnapolymerase.thedrughas theabilitytohaltviraldnasynthesisbyinhibitingtheactivityof host alfaand beta-dna polymerases and mitochondrial dna gamma-polymerase. this mechanism is useful to stop viral replication but is also at the basis of tdf-induced mitochondriopathies, in particular, in the kidney proximal tubule. in the basolateral membrane of the proximal tubular epithelial cells, provided with numerous mitochondria, tdf is implicated in active cellular uptake by the organic anion transporters hoat1 and hoat3. in the apical membrane, tdf takes part in the process of active uptake mediated by multidrug resistance proteins mrp-2 and mrp-4 (12). hoat-1 and hoat-3 are responsible for carrying 20%–30% drug into the proximal tubule cells for its elimination by urine. secretion into the urinary space is mediated also by mrp-2 and mrp-4 on the apical membrane (13). tdf affinity for hoat-1 and hoat-3 is at the basis of tdf nephrotoxicity. moreover, interaction with mrp-2 and mrp-4 may induce mitochondrial dna depletion and dysfunction, with renal accumulation of the drug (14, 15). tdf may cause different kinds of renal damage, including proximal tubular dysfunction such as fanconi syndrome, hyperphosphaturia and normal phosphataemia in patients with preserved or decreased renal function, acute interstitial nephritis, acute tubular necrosis and acute kidney injury. renal biopsies in patients treated with tdf usually show normal glomeruli and necrotic or apoptotic tubular epithelial cells (12, 16). rats treated with 300 mg/kg of tdf for 28 days showed increased tubular hyaline droplets positive for α2-microglobulin; electron microscopy revealed condensed, fibrillar electron-dense material in the proximal convoluted tubule epithelial cells (17). tenofovir and renal function in clinical trials renal toxicity due to tdf is clearly described in the literature (11, 18, 19), but many studies were designed to demonstrate the long-term safety and efficacy of tdf in chronic hbv patients with normal or impaired renal function (20). a decline of estimated glomerular filtration rate (egfr) was observed in patients with mild-to-moderate renal disease before therapy and in patients with normal renal function (13–15). in hiv-infected patients, tdf leads to a significant decline in creatinine clearance (crcl) compared with nontdf-containing regimens which is reversible partially or completely after drug discontinuation (8, 21). clinical trials seem to suggest that tdf does not interfere with renal safety in hbv population and dose adjustment according to basal gfr does not influence viral response to therapy, preventing renal concerns with tenofovir therapy journal of renal and hepatic disorders 2017; 1(1): 50–54 51 renal side effects (22). a similar safety profile has been described in subjects with normal gfr and in those with mild renal impairment at baseline. fixed thresholds for renal tdf toxicity included an increase of 0.5 mg/dl serum creatinine (scr) from baseline (23). in a randomised clinical trial (24), patients did not experience renal failure or progressive deterioration in renal function, although the majority (80%) had mild renal impairment. furthermore, scr levels remained stable within each crcl category over the course of the study and the mean crcl values remained relatively stable over time. in spite of these findings, the severity and the risk of tdf-associated nephrotoxicity in patients with chronic hepatitis b without pre-existing renal disease or facilitating factors for renal involvement are still not well defined (25–27). moreover, a cockroft–gault estimated crcl ≥70 ml/min is an entry criterion for most clinical trials now available, limiting the experience in patients with established renal damage (23). in preliminary data of naïve patients treated with tdf or etv, the risk of renal function worsening was similar in both groups; older age and impaired renal function before starting therapy were predictors of renal damage during treatment (28). combined antiviral therapy (tdf plus etv) was not associated with increased risk of renal damage when compared with etv monotherapy. in a recent study, the increase of scr values (≥0.3 mg/dl) had similar frequency in patients receiving combined therapy or monotherapy at week 96. elevation of scr levels above 0.5 mg/dl was more frequent in patients in monotherapy, but in any case, antiviral drug dose reduction was necessary (29). renal safety profile of the new prodrug tenofovir alafenamide fumarate (taf) seemed to be different from tdf. taf showed no in vitro interaction with hoat receptors, whichareinvolvedinrenaltdfnephrotoxicity(30,31).aphase 2studywasperformedinhivpatientstocomparethesafetyprofile of taf with that of tdf. patients treated with taf had a similar virological response, a smaller reduction of crcl and lower proteinuria than patients treated with tdf after 48 weeks of therapy. taf effective dosage was lower than tdf (10 mg vs. 300 mg) (32). tenofovir in kidney transplantation and haemodialysis patients tdf is even less studied and used in kidney transplant recipients, probably because of its potential nephrotoxic effect. after liver transplantation, additional nephrotoxicity should also be considered because of the concomitant use of calcineurin inhibitors (24). recently, a study was performed using tdf in solid organ recipients, including three kidney transplant recipients. patients were partial responders to previous therapies with other nucleos(t)ide agents. renal parameters were stable after 12 months of therapy, and nearly half of the patients were hbv dna negative at month 12 (33). in a retrospective community-based cohort study by gish et al. (23), scr increased by 0.2 mg/dl from basal levels in 18.8% non-transplant patients receiving tdf; a similar incidence (20.9%) of scr increase was reported in patients treated withetv.inthisstudy,transplantationandpre-existingreduced renal function were the only factors independently associated with scr increase. long-term studies performed with lam showed reduced mortality rates and improved patient survival in kidney transplant recipients with hbv infection. also, in patients undergoing haemodialysis, long-term use of tdf has been poorly studied. sparse evidenceindicatesthat high-fluxhaemodialysis is able to remove tdf efficaciously. according to this finding, it is now being recommended to treat hbv patients on haemodialysis with 300 mg tdf once a week after the 12th hour of dialysis (34). dose adjustment of tdf and early diagnosis of tdf-related renal damage the american association for the study of liver diseases (aasld) guidelines recommend to measure egfr, phosphaturia, urine protein/creatinine ratio, glycosuria and tubular proteinuria in patients with hiv infection every 6 months during tdf therapy. they recommend to reduce tdf dosage if egfr is below 60 ml/min and to stop tdf treatment if egfr, phosphaturia, urine protein/creatinine ratio and glycosuria change significantly (35). in patients with chronic hbv infection, scr, egfr (with cockcroft–gault formula) and phosphataemia should be measured before and every 6 months during tdf exposure. particular attention has to be given in patients at higher risk for kidney disease and in haemodialysis patients. in patients at risk for renal disease, renal parameters must be measured every month during the first 3 months of therapy, then every 3 months until the end of the first year and every 6 months thereafter. patients developing egfr <60 ml/min and/or serum phosphorus <2 mg/dl during therapy have to be monitored more closely. tdf dosage adjustment is required in patients with gfr <50 ml/ min (2). lampertico et al. suggested making dose reduction also in patients with egfr <60 ml/min [estimated using modification of diet in renal disease (mdrd) study equation] and/or low levels of serum phosphorus. in their study cohort, the estimated cumulative probability of dose reduction for renal adverse events was 11% for naïve patients and 24% in patients previously treated with adv at month 48 (36, 37). many studies were performed to compare the available equations to calculate egfr in hbv patients. indeed, establishing what is the better formula is already a challenging question for practical nephrology. in the general population, the mdrd study equation is usually more accurate than the cockroft–gault equation; however, in some cases, both formulas showed similar results. in particular, the cockroft–gault equation is less accurate than the mdrd equation in older and obese patients, whereas the mdrd study equation should not be applied to children, during pregnancy, to patients aged >85 years or those belonging to some racial or ethnic subgroups, coppolino g et al. journal of renal and hepatic disorders 2017; 1(1): 50–54 52 such as hispanic people. mdrd formula is also less accurate in patients affected by diabetes mellitus type 1 without micro albuminuria and in kidney transplants donors (because its accuracy decreases for egfr >60 ml/min). the kidney disease improving global outcomes (kdigo) 2013 guidelines recommend to use the new chronic kidney disease epidemiology collaboration (ckd-epi) formula, which is more accurate than mdrd for egfr values >60 ml/min and generally improves performances of mdrd equation. yet, the cockroft–gault equation is still largely used for drug adjustment recommendations, because kidney function was estimated by this formula in the majority of pharmacokinetics studies (38, 39). new markers of tubular dysfunction, such as neutrophil gelatinase-associated lipocalin (ngal), may be used to evaluate kidney damage during tdf therapy (40–42). in the past, various studies have been published demonstrating the usefulness of ngal as an early biomarker of tubular damage in hiv-infected patients treated with tdf (43–46). conversely, the body of evidence in hbv patients, at present, is equivocal. in a randomised clinical trial, hiv patients treated with tdf showed an increase in ngal values when compared with those treated with abacavir (44); however, more recent studies did not show significant differences in plasma and urinary ngal after tdf treatment (45, 46). conclusion despite a large body of evidence has accrued on the safety profile of tdf therapy in hiv-infected patients, clinical guidance in the chronic hepatitis b population requires further insights, in particular, with respect to renal toxicity and bone mineral disease incidence. screening of risk factors for renal disease before starting tdf therapy and a careful monitoring of scr, egfr, serum phosphate and urine analysis during treatment are important mainstays for guiding 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http://dx.doi.org/10.1097/qai.0b013e31828175c9 http://dx.doi.org/10.1097/qai.0b013e31828175c9 jrenhep015 1..9 jrenhep.com codonpublications.com original article vitamin d levels are associated with liver disease severity in patients with cirrhosis megan a. rech 1,2,3 , natasha von roenn 4 , ramon durazo-arvizu 5 , scott j. cotler 3,4 , holly kramer 3,5,6 1department of emergency medicine, loyola university chicago, maywood, il, usa; 2department of pharmacy, loyola university chicago, maywood, il, usa; 3department of medicine, loyola university chicago, maywood, il, usa; 4division of hepatology, loyola university chicago, maywood, il, usa; 5department of public health sciences, loyola university chicago, maywood, il, usa; 6division of nephrology and hypertension, loyola university chicago, maywood, il, usa abstract vitamin d deficiency is common in advanced liver disease but its clinical significance remains controversial. the aim of this study was to examine the correlation of 25-hydryoxyvitamin d levels with liver disease severity and calcium levels in adults with cirrhosis. this cross-sectional study included 180 adults with cirrhosis enrolled in a clinical cohort study at a single university hospital. the mean age was 58.8 (±9.2) years, and cirrhosis was attributed to alcohol use in 27.2%, hepatitis c in 35.0%, non-alcoholic steatohepatitis in 27.2%, and both alcohol and hepatitis c in 10.6%. the median model for end-stage liver disease-sodium (meld-na) score was 12.0 (interquartile range 9.0–16.0), and mean serum albumin levels were 3.4 (±0.7) gm/dl. median serum 25-hydroxyvitamin d levels were 28.0 (interquartile range 20–38) ng/ml, with 16 patients (8.9%) having levels <12 ng/ml and 43 (23.9%) with 25(oh)d levels <20 ng/ml. no correlation was noted between levels of 25-hydroxyvitamin d and albumincorrected calcium in the total group and in groups stratified by vitamin d supplementation. in contrast, both serum albumin (r = 0.32; p < 0.001) and meld-na scores were significantly correlated with 25-hydroxyvitamin d levels (r = –0.29; p < 0.001). correlations between 25-hydroxyvitamin d levels and serum albumin (r = −0.39; p < 0.001) and meld-na scores did not change substantially after excluding 67 patients receiving vitamin d supplementation (r = −0.33; p = 0.009). in conclusion, total 25-hydroxyvitamin d levels correlate inversely with liver disease severity in adults with cirrhosis. keywords: cirrhosis; liver disease; serum calcium; vitamin d; vitamin d deficiency received: 07 april 2017; accepted after revision: 03 may 2017; published: 26 may 2017. author for correspondence: megan a. rech, emergency medicine clinical pharmacist, loyola university medical center, 2160 s 1st ave, maywood, il 60153, usa. email: mrech@lumc.edu how to cite: rech ma et al. vitamin d levels are associated with liver disease severity in patients with cirrhosis. j ren hepat disord 2017;1(2):1–9. doi: http://dx.doi.org/10.15586/jrenhep.2017.15 copyright: rech ma et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction vitamin d impacts bone mineralization and calcium homeostasis by increasing intestinal calcium absorption (1, 2). without vitamin d, only 10% to 15% of dietary calcium and less than 60% of dietary phosphate is absorbed (3). the liver plays an important role in vitamin d metabolism. vitamins d2 and d3 derived from food and supplements, and vitamin d3 obtained via sunlight exposure, undergo hydroxylation in journal of renal and hepatic disorders 2017; 1(2): 1–9 mailto:mrech@lumc.edu http://dx.doi.org/10.15586/jrenhep.2017.15 http://creativecommons.org/licenses/by/4.0 the liver forming 25-hydroxyvitamin d [25(oh)d], which is then hydroxylated mainly in the kidneys to 1,25 dihydroxyvitamin d [1,25(oh)2d], the biologically active form of vitamin d. the liver also produces bile acids, which are necessary for optimal gastrointestinal absorption of vitamin d obtained from foods or supplements (4). vitamin d metabolites undergo enterohepatic circulation, and in the setting of liver dysfunction, impaired excretion of vitamin d metabolites may inhibit production or activation of 25(oh)d (5). several previous studies showed a high prevalence of low 25(oh)d levels among adults with cirrhosis (6–9), and low 25(oh)d levels have been hypothesized to play a role in the progression of several liver diseases (10–14). however, it is possible that low 25(oh)d levels simply reflect liver disease severity because hepatocytes produce vitamin d binding globulin (vdbg), the major vehicle for vitamin d transport. over 90% of 25(oh)d circulates bound to vdbg and albumin, while the rest circulates unbound or free (15). total 25(oh)d levels measured in clinical practice mainly reflect 25(oh)d bound to vdbg and albumin (16). thus, 25(oh)d levels as currently measured in clinical practice may be low in patients with hepatic synthetic dysfunction due to low serum levels of vdbg and albumin (9, 17). in the current study, we evaluated data from a cohort of adults with cirrhosis receiving care at a single academic institution. the aim of the study was to evaluate the association of 25(oh)d levels with liver disease severity measures and albumin-corrected serum calcium levels in patients with cirrhosis. liver disease severity was assessed with serum albumin levels (18) and the modeling end-stage liver disease-sodium score (meld-na) (19). the original meld score predicted prognosis in patients with cirrhosis based on kidney function and dialysis requirements, serum bilirubin, and the international normalized ratio (inr). in recognition of the independent association between serum sodium and transplant waitlist mortality for patients with cirrhosis (19–23), the organ procurement and transplantation network began incorporating the meld-na score for prioritizing transplants based on liver disease severity in 2016 (24). this study also examined the proportion of 25(oh)d variance attributed to the meld-na score, serum albumin levels, and demographic variables and the use of vitamin d supplements. we hypothesized that 25(oh)d levels are inversely correlated with measures of liver disease severity but not albumin-corrected calcium levels in patients with advanced liver disease. we further hypothesized that liver disease severity accounts for a substantial proportion of the variance in 25(oh)d levels in adults with cirrhosis. methods study population this cross-sectional study included patients with cirrhosis receiving hepatology care at loyola university medical center, a large, urban academic medical institution. patients with cirrhosis were enrolled in a cohort study designed to examine the determinants of liver disease progression during a routine clinic visit from august 29, 2013 to january 28, 2015 and clinical, biochemical, and radiological tests were performed. the study was approved by the loyola university chicago institutional review board, and all patients provided written informed consent. diagnosis of cirrhosis was based on clinical and radiological examination or liver histology. overall, a total of 456 adults with cirrhosis enrolled in the main cohort study. we excluded 68 participants with cirrhosis from hepatitis b infection, hemochromatosis, wilson’s disease, or autoimmune hepatitis, due to the low number of participants with each of these disorders. among the 388 patient participants with alcohol (etoh)-related, table 1. demographics of the patient participants (n = 180) age (years) 58.8 ± 9.2 male (%) 53.3 race (%) white african american asian pacific islander unknown 76.7 8.3 1.1 0.5 13.3 cirrhosis etiology (%) alcohol hcv nash both alcohol and hcv 27.2 35.0 27.2 10.6 bmi (kg/m2) 31.8 ± 7.6 calcium (mg/dl) 9.1 ± 0.6 corrected calciuma (mg/dl) 9.5 ± 0.5 albumin (g/dl) 3.4 ± 0.7 international normalized ratio 1.3 ± 0.3 creatinine (mg/dl) 1.1 ± 0.8 sodium (meq/l) 137.7 ± 3.5 total bilirubinb (mg/dl) 1.2 (0.7–2.1) meld-na scoreb 12.0 (9.0–16.0) vitamin db (ng/ml) 28.0 (20.0–38.0) vitamin d supplementation (%) 37.2 calcium supplementation (%) 22.8 data shown as frequency (%) or mean ± standard deviation; acorrected calcium = measured total calcium in mg/dl + [0.8 × (4 – albumin in g/dl)]; bdata shown as median (interquartile range); bmi = body mass index, hcv = hepatitis c virus, nash = non-alcohol steatohepatitis, meld-na = modeling end-stage liver disease-sodium score (19). rech ma et al. journal of renal and hepatic disorders 2017; 1(2): 1–9 2 hepatitis c virus (hcv), or non-alcohol steatohepatitis (nash)-related cirrhosis, we excluded 184 with missing data on 25(oh)d levels and 24 with missing serum calcium and albumin levels measured at the time when vitamin d was measured. this left a total of 180 patient participants included in the analyses. disease etiology, demographics information on demographics was obtained using standardized questionnaires, while the primary etiology of liver disease and presence of co-morbidities were obtained from the electronic medical record. diabetes was defined as a physician diagnosis of diabetes and/or use of glucose-lowering medications. at the clinic visit, weight was measured without shoes to the nearest 0.1 kg using a standard balance, and height was measured using a stadiometer without shoes. body mass index (bmi) was defined as weight in kilograms divided by the height in meters squared. information on medication use and vitamin d supplementation, including ergocalciferol or cholecalciferol, and calcium supplementation was obtained from the medication list in the electronic medical record at the time of enrollment. laboratory parameters non-fasting blood specimens were collected during a clinic visit and were sent immediately to the loyola laboratory for measurement of routine clinical measurements. serum 25(oh)d was measured using the chemiluminescent immunoassay. serum albumin, creatinine, and total bilirubin were measured using a colorimetric method, and calcium table 2. characteristics of patient participants by serum 25-hydroxyvitamin d [25(oh)d] groups 25(oh)d groups <12 ng/ml 12–19.9 ng/ml 20–29.9 ng/ml ≥30 ng/ml overall p-value n 16 27 58 79 age 55.6 ± 10.2 56.8 ± 9.1 58.7 ± 8.6 60.2 ± 9.3 0.2 male (%) 53.6 66.7 52.7 58.5 0.4 bmi (kg/m2) 30.4±6.5 32.3±8.5 32.2 ± 6.6 31.6 ± 8.2 0.9 25(oh)d (ng/ml)a 10.0 (7.0–11.0) 17.0 (15.0–19.0)* 25.0 (22.0–27.0)* 39 (32.3–47.0)* <0.001 meld-naa 20.0 (17.0–28.0) 14.0 (9.5–16.5)* 12.0 (9.0–15.0)* 10.5 (8.0–15.0)* <0.001 calcium (mg/dl) 8.5±0.5 9.0±0.4 9.0 ± 0.6 9.2 ± 0.6 0.003 corrected calciumb (mg/dl) 9.4±0.1 9.6±0.1* 9.5 ± 0.1* 9.6 ± 0.1* 0.7 albumin (g/dl) 2.86±0.2 3.20±0.1* 3.29 ± 0.1* 3.60 ± 0.1* <0.001 international normalized ratio 1.6±0.6 1.3±0.3* 1.2 ± 0.3)* 1.2 ± 0.2* <0.001 total bilirubin (mg/dl) 2.4 (1.0–3.6) 1.7 (1.0–2.9)* 1.2 (0.7–2.1)* 1.0 (0.7–2.1)* <0.001 sodium (meq/l) 133.9±5.4 137.8±3.9* 138.1 ± 3.0* 138.2 ± 2.6* <0.001 cirrhosis etiology (%) hcv etoh etoh and hcv nash 18.8 43.8 18.8 18.8 25.9 37.0 11.2 25.9 42.6 24.6 3.3 29.5 34.6 22.2* 13.6 29.6 0.6 0.05 0.2 0.2 vitamin d supplementation (%) 31.3 25.9 34.5 44.3 0.3 calcium supplementation (%) 25.0 14.8 20.7 26.6 0.6 data shown as frequency (%) or mean ± standard deviation; adata shown as median (interquartile range); bmi = body mass index, hcv = hepatitis c virus, meld-na = modeling end-stage liver disease score (19), nash = non-alcohol steatohepatitis; bcorrected calcium = measured total calcium in mg/dl + [0.8 × (4 – albumin in g/dl)]; *p < 0.01 compared to group with 25(oh)d <12 ng/ml. vitamin d and cirrhosis journal of renal and hepatic disorders 2017; 1(2): 1–9 3 was measured using indirect ion selective electrodes. blood reference range values were as follows: serum calcium (8.5–10.5 mg/dl), serum 25(oh)d (20–80 ng/ml), and serum albumin (3.6–5.0 g/dl). the following equation was used to calculate corrected calcium levels: corrected ca (mg/dl) = measured total calcium in mg/dl + [0.8 × (4 – albumin in g/dl)]. serum sodium was measured using an ion-specific electrode. the meld-na score was calculated as a measure of liver disease severity using the serum creatinine, total bilirubin, inr, and serum sodium measured during the clinic visit when 25(oh)d was also measured (19). statistical analyses we used stata/ic 13.1 (statacorp lp, college station, tx, usa) to perform all statistical analyses. normality for variables was examined using the shapiro–wilk test. patients were categorized based on their 25(oh)d levels (25), and then summary statistics for key baseline characteristics were compared by vitamin d categories. mean and median values are shown for variables with and without normal distributions, respectively, and frequencies were reported for categorical variables. continuous variables were compared using anova, and categorical variables were compared using the fishers exact test. to compare variables without a normal distribution across groups, the variable was log transformed and then compared using anova. if the overall f-test was statistically significant, then each vitamin d category was compared to the lowest category using an unpaired t-test. the level of statistical significance was set as p < 0.01 to account for multiple comparisons (3 vitamin d categories compared to the lowest category). scatterplots of serum levels of corrected calcium, albumin, and meld-na scores by 25(oh)d levels were examined. spearman rank correlation coefficients were calculated to quantify the correlation between corrected calcium and albumin levels and meld-na scores in the total group and after stratifying by vitamin d and calcium supplementation. locally weighted regression smooth scatterplot (loess) lines were fitted to characterize the association between 25(oh)d and liver disease severity measures (meld-na and serum albumin levels) and serum calcium levels, and all associations were found to be linear. linear regression models were then used to examine the adjusted association of serum albumin and meld-na scores with total 25(oh)d levels. the models adjusted for age, sex, race (white vs. non-white), bmi, liver disease etiology (etoh vs. other causes), and vitamin d supplementation use (yes/no). these covariates figure 1. scatterplot of corrected serum calcium levels by 25-hydroxyvitamin d [25(oh)d] levels in the total group of patient participants with cirrhosis (n = 180). rech ma et al. journal of renal and hepatic disorders 2017; 1(2): 1–9 4 were selected because they may influence vitamin d levels (2, 6). due to the strong correlation between meld-na scores and serum albumin levels (r = −0.58; p < 0.001), separate models were created to examine meld-na and serum albumin levels as explanatory variables. results demographic data for the selected cohort are displayed in table 1. most of the patient participants were white (76.7%), and male (53.3%) and the mean age was 58.8 ± 9.2 years. cirrhosis etiology was etoh in 27.2%, hcv in 35.0%, nash in 27.2%, and both etoh and hcv in 10.6%. the median meld-na score was 12.0 (interquartile range 9.0–16.0) and mean serum albumin level was 3.4 ± 0.7 gm/dl. overall, 37.2% and 22.8% were taking vitamin d and calcium supplements, respectively, and 26.0% were taking both. the dose of vitamin d and type of vitamin d varied. a total of 18 patients were taking ergocalciferol 50,000 international units (iu) weekly, and 28 patients were taking cholecalciferol with doses ranging from 400 to 2000 iu daily. twenty-one patients were taking over the counter vitamin d3 supplements with doses ranging from 400 to 1200 iu daily. among the patients taking calcium supplements, the median supplemental calcium intake was 1000 iu (interquartile range 615–1200 iu). figure 2. scatterplot of relationship of serum 25-hydroxyvitamin d [25(oh)d] and serum-corrected calcium in patients receiving both vitamin d and calcium supplementation (n = 37) (top) and in patients not receiving vitamin d or calcium supplementation (n = 109) (bottom). vitamin d and cirrhosis journal of renal and hepatic disorders 2017; 1(2): 1–9 5 the median serum 25(oh)d level was 28.0 ng/ml (interquartile range 20–38 ng/ml), and 16 patients (8.9%) had 25(oh)d levels <12 ng/ml and 43 (23.9%) had 25(oh)d levels <20 ng/ml. table 2 shows the characteristics of the participants by 25(oh)d groups. overall, serum calcium and albumin levels generally increased and meld-na scores decreased across increasing 25(oh)d groups. in contrast, corrected serum calcium levels did not differ significantly across 25(oh)d groups. vitamin d supplementation was similar across the 25(oh)d groups. no correlation was noted between albumin-corrected calcium and 25(oh)d levels in the total group (figure 1) or in groups stratified by vitamin d and calcium supplementation use (figure 2). in contrast, both serum albumin (r = 0.32; p < 0.001) and meld-na scores (r = –0.29; p < 0.001) were significantly correlated with 25(oh)d levels (figure 3). after excluding 67 patients receiving vitamin d supplementation, correlations between 25(oh)d and serum albumin (r = 0.39; p < 0.001) and meld-na scores (r = −0.33; p = 0.009) did not change substantially. the results of the linear regression models are shown in table 3. serum albumin and meld-na scores alone accounted for 9% and 17% of the variance in log-transformed 25(oh)d levels, respectively. serum albumin levels combined with all covariates and meld-na scores combined with all covariates accounted for 12.6% and 23.1% of the variance of log-transformed 25(oh)d figure 3. scatterplots of 25-hydroxyvitamin d [25(oh)d] levels by serum albumin levels (top) and by meld-na scores (bottom) in patients with cirrhosis (n = 180). rech ma et al. journal of renal and hepatic disorders 2017; 1(2): 1–9 6 levels, respectively. in the linear regression models, only serum albumin and meld-na scores were significantly associated with log-transformed 25(oh)d levels. discussion in this single center study, we show that low vitamin d levels are common in patients with cirrhosis, as demonstrated in previous studies (6, 7, 9, 26–28). however, the prevalence of low vitamin levels, defined as 25(oh)d levels <20 ng/ml, was less than many previous studies (7, 26–28), which may be due to higher use of vitamin d supplementation and lower disease severity in our patient population. one study of 202 pre-liver transplant patients reported that 25(oh)d levels were less than 20 ng/ml among 84% of patients prior to liver transplantation, with 13% having undetectable concentrations (9). our study also confirms the findings of several previous studies that demonstrated an inverse correlation between 25(oh)d levels and measures of liver disease severity (6, 9, 26, 29–31), such as the child pugh score and meld score, and a positive correlation with serum albumin concentrations. another important finding of the present study was that low 25(oh)d levels were not associated with serum calcium levels in patients with cirrhosis. in fact, no patient had an albumin-corrected serum calcium value <8.5 mg/dl. while the relationship between cirrhosis and vitamin d deficiency is well-described (6, 28), it remains uncertain how vitamin d deficiency impacts calcium homeostasis in patients with cirrhosis. one study of 158 pre-transplant patients with end-stage liver disease examined the serum levels of calcium and intact parathyroid hormone levels (ipth) across the spectrum of 25(oh)d levels. this study found no differences in mean serum ipth and corrected calcium levels among these patients (32). the lack of a correlation between calcium, ipth, and total 25(oh)d levels may be due to the fact that total 25(oh)d includes a large fraction of 25(oh)d that is tightly bound to vdbg, and relatively small amounts of 25(oh)d bound loosely to albumin and 25(oh)d circulating freely or unbound. it has been hypothesized that the 25(oh)d circulating tightly bound to vdbg is not as clinically important as the vitamin d circulating free or loosely bound to albumin, known as bioavailable vitamin d (16, 33). the existence of compensatory mechanisms for vitamin d homeostasis in advanced liver disease was suggested by findings from a small study, which showed significantly lower total 25(oh)d levels among 24 patients with cirrhosis compared to 107 healthy controls while measured free 25(oh)d levels were higher among the adults with cirrhosis (33). a study of liver transplant recipients, most of who were vitamin d deficient pre-transplant, found that total and free 25(oh)d along with vdbg increased after transplantation (9). while vitamin d has been hypothesized to modulate inflammation and fibrosis in liver disease (26, 34), it is not clear whether lower vitamin d levels in patients with cirrhosis are a cause or an effect of liver disease progression. the possibility that low vitamin d levels contribute to liver disease progression is intriguing, although the available data have not established a clear causal association. it is also possible that low total vitamin d levels simply reflect the severity of liver disease. as liver disease worsens, hepatic production of vdbg decreases and total measured 25(oh)d levels are consequently lower. indeed, our study table 3. results of linear regression models with log transformed 25(oh)d levels as dependent variable model with meld-na +r2 model with albumin +r2 beta (se) p-value 0.23 beta (se) p-value 0.13 albumin – 0.23 (0.23) <0.001 meld −0.04 (0.01) <0.001 – age 0.01 (0.004) 0.07 0.01 (0.005) 0.8 sex −0.04 (0.08) 0.7 −0.05 (0.08) 0.5 white race vs. non-white race 0.13 (0.10) 0.2 0.07 (0.09) 0.4 bmi (kg/m2) −0.01 (0.01) 0.2 0.0001 (0.006) 0.9 liver disease due to alcohol vs. other 0.02 (0.1) 0.8 −0.03 (0.09) 0.8 vitamin d supplementation 0.14 (0.08) 0.1 0.10 (0.08) 0.2 meld-na = modeling end-stage liver disease score(19); se = standard error; r2 indicates the amount of variance in log transformed 25(oh)d levels explained by the model; beta represents the change in log transformed 25(oh)d levels with every unit increase in the predictor variable after adjustment for all variables in the linear regression model. vitamin d and cirrhosis journal of renal and hepatic disorders 2017; 1(2): 1–9 7 showed a significant and inverse correlation between 25(oh) d levels and meld-na scores. these findings are supported by previous studies, which also showed significant and inverse correlations between 25(oh)d levels and liver disease measures (26, 28). this study includes a large number of adults with cirrhosis, and the 25(oh)d and serum calcium levels were evaluated as part of a routine clinical examination. the study is limited by lack of information on levels of 1,25-dihydroxyvitamin d levels, the active form of vitamin d, and vdbg. we also did not have information on other markers of vitamin d homeostasis such as ipth levels. serum calcium levels may be affected by several factors other than vitamin d, including serum ipth levels and dietary calcium intake. while we did have information on calcium supplement use, information on dietary calcium intake was not collected. in addition, we did not have measures of patient compliance with the vitamin d and calcium supplements. conclusion this study shows that total 25(oh)d levels correlate inversely with liver disease severity in adults with cirrhosis, while no correlation exists between 25(oh)d levels and albumin-corrected serum calcium levels. the findings from this study along with other previous studies support the existence of compensatory mechanisms for maintaining calcium homeostasis in patients with advanced liver diseases. future studies should examine changes in measures of vitamin d and vitamin d homeostasis with vitamin d supplementation in patients with cirrhosis. such information may help elucidate whether vitamin d 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department, university of peloponnese, sparta, greece abstract the aim of this study was to assess the quality of life (qol) in end-stage renal disease (esrd) patients undergoing hemodialysis and to examine the clinical and demographic attributes associated with it.this is a multicenter, cross-sectional study, conducted in 2018, in which 367 patients with esrd undergoing hemodialysis were recruited. data were collected through a two-part anonymous, self-completed questionnaire. the first part contained questions regarding demographic, social, and clinical information, and the greek version of missoula–vitas quality of life index-15 (mvqol-15) scale was used to assess qol. descriptive and inferential statistical methods were applied. all reported p-values were two-tailed, and the statistical significance level was set at 0.05. of the study participants, 62.1% were male, with a mean age of 61.80 ±15.11. of the participants, 67.3% were living in urban areas and 59.1% were married. the majority of the hemodialysis (hd) patients evaluated possessively all the domains of mvqol except the wellbeing domain. qol was found to be influenced, among others, by age (0.001), occupation (0.002), education (0.003), and additional health problems (<0.001). the role of patient characteristics in qol is an area of interest, and early and proper intervention is important to enhance qol. keywords: clinical factors; demographic factors; end-stage renal disease; hemodialysis; quality of life received: 11 january 2020; accepted after revision: 16 march 2020; published: 07 may 2020. author for correspondence: evangelos c. fradelos, nursing department, university of peloponnese, sparta, greece. email: efradelos@med.uoa.gr how to cite: evangelos c. fradelos. the effect of clinical and demographic factors on quality of life in end-stage renal disease. a multicenter cross-sectional study. j ren hepat disord. 2020;4(1):1–9. doi: http://dx.doi.org/10.15586/jrenhep.2020.58 copyright: evangelos c. fradelos license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/ licenses/by/4.0 introduction the number of patients with chronic kidney disease (ckd) is increasing dramatically. it is estimated that more than 1.4 million people worldwide are undergoing a renal replacement procedure with an annual increase of 8%. hemodialysis is the most widely used method of kidney replacement, and it was first used in 1945 for the treatment of acute renal failure (1). patients on dialysis visit dialysis centers thrice a week for 3–4 h per session, which can affect both their professional and personal lives (2). every patient with ckd requires a personalized treatment plan to ensure their survival and a satisfactory standard of living. the view of qol is subjective, with expectations, experiences, behaviors, values and philosophies. hemodialysis patients account for 88%, and the remaining 12% undergo other forms of renal replacement therapy. they visit the nearest artificial kidney unit, morning or afternoon. changes are needed both at the professional level as well as with regard to eating and entertainment habits. as the kidney function decreases, patients needs are increasing and changing (3). nowadays, there is a growing interest in the concept of quality of life (qol). many researchers, especially in social p u b l i c a t i o n s codon journal of renal and hepatic disorders mailto:efradelos@med.uoa.gr http://dx.doi.org/10.15586/jrenhep.2020.58 http://creativecommons.org/licenses/by/4.0 http://creativecommons.org/licenses/by/4.0 evangelos c. fradelos journal of renal and hepatic disorders 2020; 4(1): 1–9 2 and biomedical sciences, are trying to measure and determine the qol, reaching the point of seeking safe conclusions through various indicators. these indicators can be used by economists and policymakers to design interventions concerning the economy, environment, social and health policy (4). evaluating qol is particularly important, especially in cases where treatment does not deliver the expected results that will contribute to achieving increased patient life expectancy. therefore, a functional definition of qol can be a situation in which human life is characterized as a good on the basis of two components: (a) the patient’s ability to perform activities that require physical, mental and social well-being and (b) to satisfy the individual with regard to his or her functionality and disease control (5). in addition, qol can be defined as the functional outcome of the disease and treatment that accompanies it from the perspective of the patients themselves (6). assessment of qol in patients with ckd undergoing hemodialysis is an important aspect of patient care as many patients face chronic health issues (7). the impact of ckd at the physical and psychosocial levels can significantly affect the qol of the patients and their satisfaction with their daily lives. the disease directly affects the profession and career of those affected, thereby having a negative impact not only on the income required to combat the disease, whether it be peritoneal dialysis or hemodialysis, but also on their social status (8). research data support the fact that individual differences can be associated with qol and the well-being of patients undergoing hemodialysis. women tend to report reduced qol as opposed to men. poorer qol is often associated with increased age in patients with end-stage renal disease (esrd) (9). in addition, individuals with a lower socio-economic status report lower qol and poorer psychological well-being. on the contrary, higher economic and educational levels are associated with higher health-related qol. similarly, marital status can be associated with qol as married individuals seem to be related to better physical health and well-being (9, 10). additional factors that have been found to affect qol in esrd, for example, are educational level and how patients respond to the environment in which they are living. it is also important to change one’s habits as therapeutic intervention (e.g., dialysis) will force the individual to come to terms with a number of limitations. moreover, comorbidities, psychological distress and the various restrictions on daily routine have been associated with poorer qol (9–11). although various researches addressing qol in hemodialysis patients have been published, there are no multicenter researches addressing the effect of clinical and demographic characteristics in greece. thus, the aim of the present study was to evaluate qol of hemodialysis patients in greece and to examine the effect of clinical and demographic characteristics on qol of hemodialysis patients. material and methods study design and sample a multicenter, cross-sectional study in five public dialysis units and one private dialysis unit, covering six major regions of greece, was conducted in 2018. a total of 367 patients with esrd undergoing hemodialysis thrice a week were recruited. this accounts for approximately 3.5% of the patients undergoing hemodialysis in greece. the inclusion criteria were the following: (a) age above 18 years, (b) undergoing hd three times/week for at least 6 months, (c) native language—greek, (d) ability to read and sign the consent form, (e) time-space oriented, and (f) not currently undergoing transplant procedures. patients with mental or cognitive disorders were excluded from the study. ethical consideration for the study was approved by the ethics committees of the six hd units, and permission to conduct the study was also granted by the greek data protection authority (protocol number: γν/εξ/4670-3/04-08-2016). in addition, informed consent was obtained from all participants, who were ensured of the voluntary nature of their participation, the confidentiality involved, their anonymity, and their right to withdraw at any time during the study. instruments data were collected through an anonymous, self-completed questionnaire that consisted of two parts: (1) the first part contained questions regarding demographics (age, gender), social attributes (marital status), and clinical information such as duration of dialysis and comorbidities. additional information about religiosity was assessed using two questions in a four-point likert scale (i) how religious are you (ii) how close to god are you . current activity level was assessed using a fourpoint likert scale, where 1 corresponded to no symptoms and fully active and 4 corresponded to the extent of symptom burden and inability to get out of bed.” (2) the greek version of missoula–vitas quality of life index-15 (mvqol-15) scale was used to assess qol. it is a 15item, self-reported, five-point likert scale (“strongly agree” to “strongly disagree”) , which was designed to gather information regarding patients’ qol, especially in advanced and chronic diseases. it was developed as a brief measure that can assess subjective qol of patients that can be quickly interpreted by health professionals in order to assist them in identifying and addressing patients’ concerns that affect qol. it is divided into five domains, namely, symptoms, functionality, interpersonal relationships, well-being, and transcendence. it has a general question about the overall qol. it was created by byock and merriman, and translated and validated in greek by theophilou et al. (12). statistical analyses empirical data of the study were processed with spss v. 22.0 for windows (spss, inc., chicago, il, usa). descriptive and inferential statistical methods were applied. mean, standard quality of life in hemodialysis journal of renal and hepatic disorders 2020; 4(1): 1–9 3 deviation, and relative (%) frequencies were calculated. in addition, to investigate the effect of patient characteristics on qol, student’s t-test and one-way analysis of variance were used for the association between categorical and continuous variables, and pearson’s correlation coefficient for the correlation between continuous variables. all reported p-values were two-tailed, and the statistical significance level was set at 0.05. results of the total participants, 62.1% were male, with a mean age 61.80 ±15.11; 67.3% were living in urban areas; 59.1% were married; 61% were retired; and the majority of the patients were christian orthodox (95.9%). while 52.6% reported additional health problems, the mean duration on dialysis was 5.69 years. self-reported religiosity was 2.56±1.08 and connection with god was 2.54±1.11. finally, the reported activity level was 2.46±1.09. regarding the reported qol, the mean value of mvqoli-15 (17.22, sd = 3.85) that is larger than the 15 value that corresponds to the median point of the response mea surement scale (theoretical index range), indicating that the majority of patients had satisfactory total qol values. the majority of the hd patients evaluated positively for the different dimensions of mvqoli-15, with the exception of well-being, which had mean and median values with a negative sign, that is, a negative evaluation. more specifically, global qol score was 3.41 ± 0.93; symptoms domains, 4.39 ± 9.95; functionality, 6.59 ± 10.56; interpersonal, 12.24  ± 12.97; well-being, -6.70 ± 13.38; transcendence, 5.67 ± 14.78; and finally total qol, 17.22 ± 3.85. in tables 1 and 2 are reporting the association between qol domain and patient’s characteristic (bivariate analysis). bivariate analysis revealed that the domain global qol was negatively associated with age (p < 0.001), area of residence (p = 0.009), marital status (p = 0.001), number of children (p = 0.003), cohabitate (p = 0.019), educational level (p < 0.001), occupation (p < 0.001), additional health problems (p < 0.001), and current activity level (p < 0.001). symptoms domain was associated with marital status (p = 0.003), educational level (p = 0.032), (p < 0.001), connection to god (p = 0.017), additional health problems (p < 0.001), and current activity level (p < 0.001). functionality domain was only associated with area of residence (p = 0.001) and current activity level (p = 0.001). the domain interpersonal relationships was found to be associated with marital status (p < 0.001), cohabitate (p < 0.001), religiosity (p = 0.009), connection to god (p = 0.002), additional health problems (p < 0.001), and current activity level (p < 0.001). patients’ well-being was associated only with current activity level (p  < 0.001). transcendence domain was found to be associated with gender (p = 0.016), age (p < 0.001), area of residence (p = 0.049), marital status (p = 0.002), educational level (p < 0.001), additional health problems (p < 0.001), and current activity level (p < 0.001). finally, total qol domain was associated with age (p = 0.001), area of residence (p = 0.001), marital status (p = 0.002), cohabitate (p = 0.006), educational level (p = 0.003), connection to god (p = 0.005), additional health problems (p < 0.001), and current activity level (p < 0.001). discussion the aim of the present study was to assess qol of esrd patients undergoing hemodialysis. according to our results, patients reported satisfactory level of qol in most of the domains that were assessed except for the well-being domain. most of the demographic, social and clinical factors appear to have an influence on qol both as a total and individual domains. among the socio-demographic factors, age, female gender, non-urban residence, lack of companionship and low educational attainment are associated with lower qol. concerning clinical features, comorbidity and high level of activity due to symptoms are associated with lower qol, consistent with findings in the international literature (13–15). in the present study, there was no relationship between sex and qol, which contradicts existing research in international literature that claims women to report poorer qol (16–18). those findings could be attributed to the fact that women perform multiple roles and have lower levels of support. while the demands of day-to-day life and the complexity of the roles that women are called to embody today may be almost the same in all societies, the greek society is characterized by an extended family type, which is a rich source of social support that can be a source of encouragement to face the challenges of life. it is widely accepted that age is an important factor that is either positively or negatively related to patients’ qol. patients who participated in the study and were older had a poorer qol. specifically, according to the results of the present study, age was negatively correlated with almost all dimensions of qol. this may be because older people have more psychological and social problems. in addition, qol is related not only to the course of the disease over time but also to the expected decline in aging (13–15). in terms of marital status, it has been found that married patients have a better qol than single people. it is well known that a family environment is a source of support. however, marital status has been the focus of several studies. on the one hand, there is a belief that family is a social support network (19), while, on the other hand, researchers argue that family obligations increase family anxiety, resulting in negative qol (13). moreover, in this study, the level of education was found to be positively related to most of the dimensions of qol. specifically, secondary and tertiary graduates had higher levels of both overall qol, as well as the transcendence and symptoms of mvqoli-15. this finding strengthens existing studies that show qol is positively correlated with patients’ educational level (14, 20). in a study conducted in turkey in 2009, formal education graduates were found to have higher evangelos c. fradelos journal of renal and hepatic disorders 2020; 4(1): 1–9 4 table 1. association of qol and patient’s characteristics (n = 367) characteristic global quality of life symptoms functionality interpersonal relationships gender male 3.48 ± 0.89 4.52 ± 9.26 6.10 ± 11.16 12.44 ± 12.87 female 3.31 ± 0.99 4.17 ± 11.01 7.40 ± 9.48 11.91 ± 13.16 t 1.689 0.326 1.140 0.376 p 0.092 0.745 0.255 0.707 age r −0.202 −0.097 −0.004 −0.039 p <0.001 0.064 0.935 0.459 place of residence urban area 3.50 ± 0.92 4.85 ± 10.47 7.91 ± 10.90 12.93 ± 13.61 non-urban area 3.23 ± 0.94 3.45 ± 8.75 3.88 ± 9.29 10.82 ± 11.45 t 2.615 1.263 3.487 1.558 p 0.009 0.208 0.001 0.120 marital status married 3.55 ± 0.91 5.68 ± 9.67 6.01 ± 11.69 14.35 ± 12.30 unmarried 3.21 ± 0.92 2.53 ± 10.08 7.43 ± 8.62 9.18 ± 13.33 t 3.489 3.016 1.342 3.772 p 0.001 0.003 0.180 <0.001 children yes 3.39 ± 0.98 4.26 ± 10.79 6.58 ± 11.10 12.97 ± 12.93 no 3.47 ± 0.80 4.70 ± 7.60 6.63 ± 9.18 10.48 ± 12.93 t 0.837 0.449 0.045 1.682 p 0.404 0.654 0.964 0.093 number of children r −0.156 −0.046 0.032 0.074 p 0.003 0.379 0.543 0.157 living alone? yes 3.21 ± 1.04 3.01 ± 10.52 7.71 ± 8.24 7.26 ± 14.19 no 3.48 ± 0.89 4.81 ± 9.74 6.25 ± 11.16 13.77 ± 12.19 t 2.347 1.471 1.315 3.842 p 0.019 0.142 0.190 <0.001 educational status primary education (1) 3.14 ± 0.94 2.92 ± 11.65 5.68 ± 10.17 10.86 ± 13.50 high school (2) 3.59 ± 0.86 4.79 ± 8.89 6.91 ± 10.19 12.83 ± 12.29 university (3) 3.59 ± 0.94 6.71 ± 7.57 7.86 ± 12.22 13.89 ± 13.29 (continued) quality of life in hemodialysis journal of renal and hepatic disorders 2020; 4(1): 1–9 5 table 1. (continued) characteristic global quality of life symptoms functionality interpersonal relationships f 10.929 3.463 1.063 1.494 p <0.001 0.032 0.346 0.226 post hoc test least significant difference (lsd) (1)<(2) p < 0.001 (1)<(2) p = 0.100 (1)<(3) p = 0.001 (1)<(3) p = 0.012 occupation working 3.83 ± 0.74 7.36 ± 6.46 7.64 ± 9.42 13.90 ± 11.54 not working 3.32 ± 0.95 3.69 ± 10.49 6.34 ± 10.81 11.85 ± 13.27 t 4.913 3.731 0.926 1.299 p <0.001 <0.001 0.355 0.197 religion christian orthodox 3.41 ± 0.93 4.37 ± 9.99 6.70 ± 10.58 12.22 ± 12.97 not christian orthodox 3.47 ± 0.99 4.87 ± 9.19 4.00 ± 10.10 12.73 ± 13.24 t 0.223 0.189 0.971 0.150 p 0.824 0.850 0.332 0.881 how religious are you? r 0.078 0.073 0.046 0.136 p 0.138 0.160 0.381 0.009 how close to god are you? r 0.085 0.124 0.031 0.160 p 0.105 0.017 0.556 0.002 duration of dialysis r 0.005 0.042 −0.077 −0.097 p 0.921 0.424 0.141 0.063 additional health problems yes 3.20 ± 0.99 2.45 ± 10.58 6.23 ± 10.22 10.02 ± 13.10 no 3.66 ± 0.80 6.54 ± 8.73 6.99 ± 10.94 14.70 ± 12.39 t 4.905 4.053 0.694 3.516 p <0.001 <0.001 0.488 <0.001 current activity level r 0.241 0.320 0.167 0.215 p <0.001 <0.001 0.001 <0.001 data are presented as mean ± sd; bold indicates significant p values. evangelos c. fradelos journal of renal and hepatic disorders 2020; 4(1): 1–9 6 table 2. association of qol and patient’s characteristics (n = 367) characteristics well-being transcendence total qol gender male −6.43 ± 13.07 7.18 ± 13.58 17.38 ± 3.70 female −7.14 ± 13.91 3.19 ± 16.31 16.95 ± 4.09 t 0.492 2.415 1.031 p 0.623 0.016 0.303 age r −0.097 −0.270 −0.177 p 0.063 <0.001 0.001 place of residence urban area −5.97 ± 14.12 6.64 ± 15.88 17.64 ± 4.07 non-urban area −8.21 ± 11.63 3.68 ± 12.03 16.36 ± 3.21 t 1.505 1.978 3.256 p 0.133 0.049 0.001 marital status married −6.33 ± 13.75 7.65 ± 15.10 17.74 ± 3.87 unmarried −7.25 ± 12.86 2.81 ± 13.87 16.47 ± 3.72 t 0.647 3.122 3.134 p 0.518 0.002 0.002 children yes −6.80 ± 13.69 5.32 ± 15.66 17.23 ± 4.03 no −6.46 ± 12.66 6.52 ± 12.45 17.19 ± 3.41 t 0.222 0.779 0.102 p 0.825 0.437 0.919 number of children r −0.016 −0.049 −0.003 p 0.763 0.349 0.961 living alone? yes −8.86 ± 13.23 3.02 ± 13.82 16.21 ± 3.77 no −6.04 ± 13.38 6.48 ± 14.99 17.53 ± 3.83 t 1.713 1.905 2.791 p 0.087 0.058 0.006 educational status primary education (1) −6.74 ± 12.69 1.44 ± 14.97 16.42 ± 4.06 high school (2) −7.15 ± 14.34 8.44 ± 14.50 17.58 ± 3.62 university (3) −5.48 ± 12.50 8.32 ± 12.85 18.13 ± 3.66 (continued) quality of life in hemodialysis journal of renal and hepatic disorders 2020; 4(1): 1–9 7 table 2 . (continued) characteristics well-being transcendence total qol f 0.354 10.205 5.751 p 0.702 <0.001 0.003 post hoc test (lsd) (1)<(2) p < 0.001 (1)<(2) p = 0.008 (1)<(3) p = 0.002 (1)<(3) p = 0.003 occupation working −4.09 ± 13.23 10.10 ± 11.49 18.49 ± 3.33 not working −7.32 ± 13.36 4.63 ± 15.29 16.92 ± 3.91 t 1.825 3.348 3.109 p 0.069 0.001 0.002 religion christian orthodox −6.76 ± 13.42 5.47 ± 14.89 17.20 ± 3.88 not christian orthodox −5.47 ± 12.88 10.33 ± 11.34 17.65 ± 3.21 t 0.365 1.248 0.439 p 0.715 0.213 0.661 how religious are you? r 0.014 0.001 0.082 p 0.794 0.994 0.116 how close to god are you? r 0.060 0.084 0.148 p 0.251 0.108 0.005 duration of dialysis r 0.005 0.033 −0.029 p 0.929 0.532 0.582 additional health problems yes −7.12 ± 13.82 3.13 ± 15.53 16.47 ± 3.89 no −6.24 ± 12.89 8.49 ± 13.40 18.05 ± 3.64 t 0.627 3.548 3.997 p 0.531 <0.001 <0.001 current activity level r 0.182 0.406 0.420 p <0.001 <0.001 <0.001 data are presented as mean ± sd; bold indicates significant p values. evangelos c. fradelos journal of renal and hepatic disorders 2020; 4(1): 1–9 8 scores, both in overall qol and in the dimension of fitness and symptoms (20). in addition, according to the results of a recent study (21), educational level was positively correlated with psychosocial dimensions of qol, which is confirmed by the present results, as the spiritual dimension of qol was found to be influenced by the educational background of the participants. this may be due to the fact that those with a good educational background can more easily understand the nature of the disease and avoid aggravating factors and consequently have better qol levels. however, this relationship between educational level and qol is controversial as studies reject it (22). according to the results of the present study, another factor that influences several dimensions is the place of residence. in particular, urban dwellers appear to have higher levels of qol in terms of overall spirituality and functionality, compared to non-urban dwellers. this is another finding that is controversial in international literature, as there are studies that reinforce such claims (23) and others that refute them (24). one possible explanation for such controversial results is the disparities in healthcare systems across countries. one factor that seems to have a positive effect on qol in our results is the existence of work. a study by parvan, lakdizaji, roshangar, & mostofi (25), which included 245 hemodialysis patients, found that those who reported being unemployed had lower levels of qol than those who had a job. similar to the study of tel (20), the same findings were found, concluding that appropriate occupational status is an important factor that is effective in improving the treatment of patients undergoing dialysis (20). regarding clinical factors that appear to be related to qol in ckd, the duration of dialysis has a negative effect on interpersonal relationships, which is in agreement with several studies on social life in ckd (26). it is widely accepted that ckd, and especially dialysis, has a negative impact on social lives, whether it be the marital, parental, or professional roles. in addition, the problematic self-image these patients usually have, coupled with dietary restrictions on food and drink, leads to reduced participation in family and social events. additional health problems also had a negative impact on overall qol, and on the dimensions of symptoms and transcendence, as in the present study, the proportion reporting comorbidity with ckd was 52.6%. this high rate of comorbidity is confirmed in other studies (27). high comorbidity has been found to affect qol (28) adversely. in a prospective study conducted in china involving 179 end-stage renal patients, patients with comorbid conditions were found to have lower levels of qol (29). also, a cross-sectional study in saudi arabia, which included 205 patients undergoing dialysis, found that the presence of comorbid conditions had a negative impact on qol. peripheral vascular disease was associated with poorer levels of qol (27). finally, the burden of symptomatic functionality appears to affect all dimensions of qol adversely. patients with ckd experience a number of symptoms that vary in intensity and affect the ph and potentially their functionality. according to researchers, symptom burden in combination with other clinical variables are key factors that lead to low qol in ckd (30). the intensity and the number of symptoms have been found to negatively affect several dimensions of qol, thus indicating the importance of effective symptom management in ckd (29). conclusions the results of this study add to our knowledge on the qol and associated factors of patients with ckd, as existing data from greece are limited. the overall score for the mvqol index was above the median, which means that patients were reporting satisfactory qol. in general, the role of patient 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2019; 3(1): 33–39 33 review article cholemic nephropathy: hyperbilirubinemia and its impact on renal function jonathan s. chávez-iñiguez1,2, alejandra meza-ríos3, arturo santos-garcia3, guillermo garcía-garcía1,2, juan armendariz-borunda3,4 1servicio de nefrología, hospital civil de guadalajara fray antonio alcalde, guadalajara, jalisco, méxico; 2centro universitario de ciencias de la salud cucs, universidad de guadalajara, guadalajara, jalisco, méxico; 3tecnologico de monterrey, campus guadalajara, mexico; 4 instituto de biología molecular en medicina y terapia génica, cucs, universidad de guadalajara, jalisco, méxico abstract cholemic nephropathy represents a spectrum of renal injury, from proximal tubulopathy to intrarenal bile cast formation, found in patients with severe liver dysfunction. it is caused by hyperbilirubinemia, usually in jaundiced patients. acute kidney injury is one of the most important complications in patients with end-stage liver disease. the relationship between liver disease and renal impairment, especially the effect of hyperbilirubinemia on renal tissue and renal function, has not been fully elucidated. these considerations deem necessary for nephrologists, when performing a clinical evaluation of patients with liver diseases, for the implementation of an integrated medical approach. this review focuses on the current knowledge on cholemic nephropathy with emphasis on the role of hyperbilirubinemia on renal impairment. the treatment strategies and outcome are also discussed. keywords: cholemic nephropathy; extracorporeal albumin dialysis; hyperbilirubinemia; molecular adsorbent recirculating system; ursodeoxycholic acid received: 09 january 2019; accepted after revision: 20 february 2019; published: 18 march 2019 author for correspondence: juan armendariz-borunda, instituto de biología molecular y terapia génica, cucs, universidad de guadalajara, mexico. email: armdbo@gmail.com how to cite: chávez-iñiguez js et al. cholemic nephropathy: hyperbilirubinemia and its impact on renal function. j ren hepat disord. 2019;3(1):33–39. doi: http://dx.doi.org/10.15586/jrenhep.2019.52 copyright: chávez-iñiguez js et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/ licenses/by/4.0 introduction cholemic nephropathy (cn) is the clinical manifestation of hyperbilirubinemia that encompasses acute kidney injury (aki) with characteristic histological changes in the distal segment of the nephron and intraluminal casts in jaundiced patients (1). since the pioneer studies of hecher and schroeder, it has been known that impairment of kidney function is a common event in the clinical course of cirrhosis, and it is associated with poor prognosis (2, 3). an important non-vasomotor mechanism of aki in cirrhosis is the nephrotoxicity of bilirubin and bile acids (4). nephrologists are frequently asked to evaluate patients with liver disease associated kidney disease, and the spectrum can include both acute and chronic kidney diseases. kidney disorders occur in up to 25% of patients with liver disease (5). an understanding of the kidney–liver interaction is essential for the implementation of an integrated medical approach. herein we present our current understanding of cn, the effect of p u b l i c a t i o n s codon journal of renal and hepatic disorders mailto:armdbo@gmail.com http://dx.doi.org/10.15586/jrenhep.2019.52 http://creativecommons.org/licenses/by/4.0 http://creativecommons.org/licenses/by/4.0 chávez-iñiguez js et al. journal of renal and hepatic disorders 2019; 3(1): 33–39 34 hyperbilirubinemia on renal dysfunction, and the treatment strategies, although mostly experimental, for the management of cn. hyperbilirubinemia bilirubin is a metabolite of ferroprotoporphyrin ix (heme), a potentially toxic metabolite, for which the body has developed detoxification and disposition mechanisms. eighty percent of bilirubin comes from the breakdown of the hemoglobin of senescent red blood cells in the reticuloendothelial system and other erythroid cells destroyed in the bone marrow. the remaining 20% originates from the turnover of heme-containing proteins from other tissues like liver and muscles, and sources such as myoglobin, cytochromes, catalase, peroxidase, and tryptophan pyrrolase. kupffer cells in the liver take up the heme where the enzyme heme oxygenase acts on them liberating the chelated iron; this reaction leads the formation of the green pigment, biliverdin. biliverdin is acted on by a nicotinamide adenine dinucleotide phosphate (nadph)-dependent enzyme, biliverdin reductase, releasing an orange–yellow pigment known as bilirubin. bilirubin is insoluble in aqueous solution and is carried in circulation bound to albumin and transported throughout the body (6). hyperbilirubinemia can be the result of disorders that lead to excessive bilirubin production (hemolysis), or a decrease in bilirubin clearance (hepatic or intestinal), or a combination of the two (7). hyperbilirubinemia in adult patients can be the result of many benign or life-threatening disorders. the causes could be prehepatic, intrahepatic, or posthepatic. prehepatic causes include hemolysis and hematoma resorption, leading to an increase in unconjugated bilirubin levels. intrahepatic disorders can generate either unconjugated or conjugated hyperbilirubinemia. causes of conjugated hyperbilirubinemia include (i) hepatocellular diseases like viral infections, chronic alcohol consumption, and autoimmune disorders; (ii) drug toxicity; (iii) pregnancy; (iv) parenteral nutrition; (v) sarcoidosis; (vi) dubin–johnson syndrome; (vii) rotor´s syndrome; (viii) primary biliary cirrhosis; and (ix) primary sclerosing cholangitis. posthepatic or extrahepatic disorders that elevate conjugated bilirubin can be either intrinsic or extrinsic to the ductal system—intrinsic factors include gallstones, surgical strictures, infections, intrahepatic malignancy, and cholangiocarcinoma, while extrinsic factors include extrahepatic malignancy and pancreatitis (8). patients with high levels of unconjugated bilirubin are at risk of developing bilirubin encephalopathy (kernicterus). the adverse effects of bilirubin could be the result of inhibition of dna synthesis, uncoupling oxidative phosphorylation, and inhibition of adenosine triphosphatase (atpase) activity of brain mitochondria. furthermore, bilirubin-mediated inhibition of some enzyme systems, rna and protein synthesis in the brain and liver, and modification of carbohydrate metabolism in the brain contribute to its toxicity. the abnormal accumulation of bilirubin in plasma and tissues lead to a yellow discoloration of tissues known as icterus or jaundice (9). aki in cirrhosis patients in the context of hyperbilirubinemia aki that occurs in patients with cirrhosis due to severe hypoperfusion and impairment in the systemic arterial circulation has been known as hepatorenal syndrome (hrs) (10). in addition, impairment of kidney function can be the result of a variety of other causes, particularly volume depletion, bacterial infections, nephrotoxic agents, chronic kidney disease, intratubular deposition of bilirubin, or a combination thereof (11–14). bilirubin can cause adverse effects on kidney cells. a study using cortical slices of kidney showed that bilirubin was internalized by renal epithelial cells via the organic anion transport system, leading to the inhibition of adenosine triphosphate (atp) production, induction of mitochondrial structural defects, alteration of membrane permeability, and modification of electrolyte content and cell volume (4). the clinical picture to distinguish cn from hrs is that, in hrs, the following alterations are usually present: altered hemodynamic function characterized by peripheral vasodilation and renal vasoconstriction, and tubular dysfunction with increased water and sodium reabsorption. in contrast, the above pathophysiological mechanisms are absent or rarely present in cn. previous studies on cirrhosis in which impairment of kidney function was diagnosed with criteria other than aki underscore the importance of kidney function in determining prognosis in cirrhosis (15, 16). one of the problems is the stratification of aki by urinary thresholds; these patients may have an increased urine output because of diuretic treatment. thus, urine collection is often inaccurate in clinical practice and the use of kinetic changes in serum creatinine (scr) has now become the key for aki diagnosis in cirrhosis. however, it should be noted that the use of scr in patients with cirrhosis is affected by decreased formation of creatinine from creatine in muscles secondary to muscle wasting, increased renal tubular secretion of creatinine, increased volume distribution that could dilute scr, and interference of elevated serum bilirubin with assays of scr (17, 18). because of the negatively charged reactant, bilirubin interferes with creatinine/picrate reaction (18). watkins et al. were the first to report the considerable negative interference on the part of bilirubin; they found, comparing the automatic clinical analyzer (aca) and end point technicon sma 6/60 method to measure scr, that the aca kinetic method gave considerably lower results with samples that were highly jaundiced (19). as a consequence, measurement of scr in patients with cirrhosis overestimates glomerular filtration rate (gfr) or kidney function. also, in patients with cirrhosis, scr is an unreliable tool in assessing kidney function owing to the low production rate of creatine (the precursor of creatinine) by the liver with reduced muscle mass (5). cystatin c has been cholemic nephropathy journal of renal and hepatic disorders 2019; 3(1): 33–39 35 proposed as an alternative marker to assess kidney function, but using cystatin c–based formulas to assess kidney function in cirrhotic patients also has yielded mixed results (20). aki is a common and serious complication in patients with liver disease; among the etiologies, those related to hyperbilirubinemia have been less explored (15) and therefore our knowledge is scarce. it has been overlooked in recent medical literature despite its frequency (21). in addition, the lack of kidney biopsy in patients with liver dysfunction makes it difficult to establish the association between liver and kidney disorders (4). aki in patients with hepatic diseases or cirrhosis is now defined according to the proposal of the kidney disease improving global outcome (kdigo) criteria, as an increase in scr of >0.3 mg/dl (22). aki affects almost 50% of hospitalized patients with cirrhosis and is associated with poor prognosis with mortality rates reaching as high as 90% (23). in 2012, the international club of ascites (ica) organized a consensus in order to reach a new definition of aki in patients with cirrhosis (table 1). in the new ica criteria for the diagnosis of aki, the use of urine output as one of the criteria has been removed as it does not apply to patients with cirrhosis. further, two other changes to the kdigo criteria were adopted: (i) an scr within the last 3 months before admission is considered a baseline value for the diagnosis of aki when a value within the previous 7 days is not available and (ii) the calculation of the baseline scr by the reverse application of the modification of diet in renal disease (mdrd) formula using an arbitrarily defined normal value of gfr of 75 ml/min/1.73 m2 was not included (17). the main differences between these new criteria and the conventional criteria in patients with cirrhosis are the following: (i) an absolute increase in scr is considered; (ii) the threshold of scr > 1.5 mg/dl (133 μmol/l) is abandoned; and (iii), a staging system of aki based on a change in scr over a slightly longer time frame, arbitrarily set at 1 week, to enable assessment of progression as well as regression of stage (modified from akin staging) (table 1). even a minor increment in scr in patients with cirrhosis is strongly associated with mortality. fagundes et al. demonstrated that, in cirrhotic patients, the occurrence of aki and its stage were associated with 3-month survival. while there was no statistically significant difference in survival rate between stages 2 and 3, when stage 1 patients were categorized into two groups according to the level of scr used in the classical definition of kidney impairment (1.5 mg/dl), those with scr less than 1.5 mg/dl, had a better survival (24). in another study, aki was attributed to hyperbilirubinemia based on the following rationale: (i) alternative diagnoses were actively ruled out; (ii) the onset of aki coincided with the onset of severe hyperbilirubinemia; (iii) renal pathology showed large bile tubular casts and a marked tubular necrosis; and (iv) scr dramatically decreased when bilirubin levels improved (25). diagnosis of cholemic nephropathy cn represents a spectrum of renal injury, from proximal tubulopathy to intrarenal bile cast formation, found in patients with severe liver dysfunction. cn and its numerous synonyms (i.e., icteric nephrosis, jaundice-related nephropathy, bile cast nephropathy, bile acid nephropathy) (1) have been reported in many liver diseases (table 2). essentially, cncan be suspected in any disorders that increases the bilirubin levels. there is a strong interaction between the bile salts and the kidney. elevated plasma concentrations of bile salts and bilirubin, conjugated or not, putatively mediate nephrotoxicity. however, it seems that a total serum bilirubin less than 15.1 mg/dl is not enough to trigger aki (26). sitprija et al. showed that in obstructive jaundice (oj) due table 1. definition of aki in patients with cirrhosis stage criteria 1 increase in scr ≥ 0.3 mg/dl (26.5 μmol/l) or an increase in scr ≥ 1.5-fold to 2-fold from baseline 2 increase in scr > 2-fold to 3-fold from baseline 3 increase of scr > 3-fold from baseline or scr ≥ 4.0 mg/dl (353.6 μmol/l), with an acute increase ≥ 0.3 mg/dl (26.5 μmol/l) or initiation of renal replacement therapy scr, serum creatinine. table 2. disorders reported in cholemic nephropathy condition disorder liver failure subacute liver failure, autoimmune hepatitis, alcoholic steatohepatitis, cirrhosis hepatic obstruction cholangiocarcinoma, gallstones in the bile duct, obstructive cholestasis, cholangiocellular carcinoma systemic diseases hodgkin’s lymphoma, infectious mononucleosis, falciparum malaria drug-induced anabolic steroids, antibiotics, flucloxacillin chávez-iñiguez js et al. journal of renal and hepatic disorders 2019; 3(1): 33–39 36 to cholangiocarcinoma, patients with bilirubin level >26 mg/dl, presented with severe renal dysfunction (26). van slambrouck et al. proposed that renal abnormalities that accompany hyperbilirubinemia be named bile cast nephropathy as the appropriate pathological term (21). mohapatra et al presented microscopy findings of centrifuged urine that characteristically showed bile-stained casts, leucocytes, and renal epithelial cells containing granular or crystalline bilirubin (27). there may be some clues in the urinalysis of patients with cn, but these findings are nonspecific and lacks sensitivity and specificity for diagnosis. to the best of our knowledge, the biomarkers used for aki have not been explored in the setting of cn. cn diagnosis relies mostly on kidney biopsy. it may otherwise be overlooked in these patient populations because of the obvious concern of complication related to the procedure, which carries almost a 12% risk of significant bleeding (5). whether a transjugular approach may represent a suitable and safe alternative to significantly reduce such risks in this difficult-to-manage group of patients needs to be explored (1). cholemic nephropathy with dysfunctional tubular manifestation since 1930, it has been observed that patients with oj are prone to kidney damage as a result of urinary excretion of bilirubin and bile salts. bilirubin accumulation in tubular cells directly damages the mitochondria, decreasing atpase activity. it also alters the hemodynamic response to angiotensin ii and catecholamines, together with increased natriuresis and reduced renal flow (28). when the bilirubin levels reach >20 mg/dl, exceeding the binding capacity of albumin to bilirubin, it accumulates in mitochondria and renal tubules, resulting in tubular dysfunction and acute tubular necrosis in conjunction with intratubular bilirubin cast (28). martinez et  al. demonstrated that in patients with oj, an increase in lipid peroxidation products, higher levels of total bilirubin, and the depletion activity of superoxide dismutase in blood were all related to renal dysfunction. patients with oj showed a marked increase in plasma levels of oxidative stress markers; higher levels in blood were predictors of renal dysfunction in oj patients (29). the hypothetical mechanisms implicated in renal impairments largely come from experimental studies. in a murine model, fickert et al. ligated the common bile duct and, 3 days later, observed renal tubular epithelial lesions; at 7 days, there was dilation and partial, but progressive, occlusion of the distal and collecting tubules, followed by overexpression of proinflammatory cytokines, progressive interstitial nephritis, and tubulointerstitial fibrosis. this model reinforces the hypothesis that the accumulation and consequent excessive urinary excretion of potentially toxic bile acids are the main causes of injury (30). odell et al. in homozygous icteric rats, noted accumulation of bilirubin in the renal papilla (31). however, there are few studies that have documented the effects on kidney function of hyperbilirubinemia in humans. increased serum levels of bile acids or bilirubin can impair proximal tubular function (proximal tubulopathy), which resolves as the serum levels normalize (21). as proof of tubular dysfunctions by bilirubins, bairaktari et al. demonstrated in 35 patients with oj that uricosuria and phosphaturia, imitating fanconi syndrome, were present (32). they performed a noninvasive study of the renal tubular function, by evaluating the excretion pattern of low-molecular weight endogenous metabolites. on admission, patients with oj had significantly lower serum uric acid and phosphate levels and higher bile acid concentrations compared with 40 ageand sex-matched controls. serum uric acid levels presented a negative correlation with total and direct bilirubin as well as fractional excretion of uric acid. these patients were more prone to developing proximal tubular dysfunction such as glucosuria, phosphaturia, and increased excretion of alpha (1)-microglobulin, decreased levels of citrate and hippurate, and increased levels of 3-hydroxybutyrate and acetate. in 12 patients, partial or complete remission of jaundice was followed by an improvement of the proximal renal tubular damage, which can be interpreted as transitory tubular renal dysfunction caused by bilirubin (32). increased urinary sodium excretion and decreased free and negative water clearances were observed in patients with total serum bilirubin >27.0 mg/dl. these were further exacerbated in the presence of f hypoalbuminemia. these findings suggest that bilirubin inhibits sodium chloride reabsorption in the thick ascending limb of henle’s loop and alters anti-diuretic hormone (adh) function in the collecting tubules, resulting in increased hydraulic conductivity and decreased free water clearance (26) cholemic nephropathy and histologic lesions of the renal tubules the vast majority of histologic lesions in cn have been reported in the tubular segment of the nephron (figure 1). holmes studied 68 autopsies of oj patients and observed swelling of the tubular epithelium, pigmented casts, hypertrophy, and hyperplasia of the parietal layer of bowman’s capsule in 50 (73.5%) cases (33). van slambprouck et al. carried out a clinicopathological study in 44 jaundice patients and identified that biliary pigments cause obstructive and inflammatory renal damage, identical to myeloma or myoglobin nephropathy (21). this study described the presence of tubular bile casts across the renal tubules, and the casts significantly correlated with higher total and direct bilirubin levels in serum, and a trend toward higher scr, aspartate transaminase (ast), and alanine transaminase (alt) levels. most interestingly, bile casts were predominantly present in jaundice patients with cirrhosis, especially in those related to alcohol (21). krones et al. have described the typical appearance of kidneys macroscopically and microscopically (1). cholemic nephropathy journal of renal and hepatic disorders 2019; 3(1): 33–39 37 macroscopically, kidneys looked yellow or green due to the high concentration of bilirubin. histologically, normal glomeruli are found with dilated tubules, obstructed by intraluminal casts. with hall (or fouchet) histochemical stain, these casts appear as green to yellow casts, and with periodic-acid schiff (pas) staining, they appear as red to dark red-colored casts. in masson trichrome staining using aniline green, bile casts show a green color. in addition to bile casts, kidney histology may show variable degrees of acute tubular injury as in tubular acute necrosis and intense inflammatory reaction. treatment and outcome the lack of specific therapeutic options remains an important limitation for the clinical management of cn (34). as the liver injury resolves and renal function recovers, the bilestained casts in the urine decrease in frequency until they disappear altogether (35, 36). the treatment is primarily supportive; renal replacement therapy has no role in directly treating cn but may be instituted for other indications. the total bilirubin is also a strong predictor of mortality in patients with cirrhosis and kidney failure. in a retrospective univariate analysis, high bilirubin values >3.6 mg/dl were associated with 30-day mortality (or 7.20, 1.55-33.56 ci) (37). in a prospective study, nazar et al. assessed the predictive factors of response to treatment with terlipressin and albumin in patients with type 1 hrs. one of the independent predictive factors of response to therapy was baseline serum bilirubin levels, and the cutoff level of serum bilirubin that best predicted response to treatment was 10 mg/dl (area under the curve (auc)  0.77; p < 0.0001; sensitivity, 89%; specificity, 61%). response rates in patients with serum bilirubin <10 mg/dl or ≥10 mg/dl were 67 and 13%, respectively (p = 0.001) (38). ursodeoxycholic acid (udca) is thought to reduce bile toxicity by increasing the hydrophilicity index of biliary bile acids, exerting an anti-apoptotic effect, and initiating possible  anti-inflammatory action related to its glucocorticoid receptor agonist activity (39); however, the effect of udca in cn has not been clinically proven yet. in addition, norursodeoxycholic acid (norudca) has antilipotoxic, antiproliferative, antifibrotic as well as anti-inflammatory effects, potentially helping improve bile duct injury (40). krones et al. explored the therapeutic efficacy and mechanisms of (norucda) in cn in a murine model. in cbdl mice fed with norudca, they found that norudca significantly lowered the serum urea and ungal levels, resulting in less severe cn as demonstrated by normal urine cytology and significantly reduced tubulointerstitial nephritis and renal fibrosis as compared to controls. potentially, norudca may represent an option for the treatment of cn (41). other treatments aiming to reduce bilirubin levels in patients with cn, such as farsenoid x receptors, peroxisome proliferator-activated receptor α, pregnane x receptor, and glucocorticoid receptor, might be used in future studies (40). removing bilirubin from the circulation makes sense and has been previously tried by means of extracorporeal treatment. sens et al. reported the case of a 37-year-old male figure 1. interactions between hyperbilirubinemia and kidney. macroscopically, the kidney may look brownish or greenish. in renal tubular cells, hyperbilirubinemia affects mitochondrial function, causes phosphaturia, uricosuria, and glycosuria. hyperbilirubinemia also changes the tubular architecture with necrosis and apoptosis, modulates the tonicity of the afferent and efferent arteriole, and, through the formation of casts, it generates obstruction and tubulointerstitial inflammation. chávez-iñiguez js et al. journal of renal and hepatic disorders 2019; 3(1): 33–39 38 who presented with a sudden alteration of his clinical status in the context of the onset of jaundice and pruritus. laboratory findings showed hyperbilirubinemia (344 mmol/l), mostly conjugated (260 mmol/l), and aki. in order to decrease the hyperbilirubinemia and limit its nephrotoxicity, the patient received nine extracorporeal albumin dialysis (ecad) sessions: one with molecular adsorbent recirculating system (mars) and eight with single-pass albumin dialysis (spad). the first four sessions reduced the bilirubin level from 480 to 172 mmol/l, and the scr from 444 to 248 mmol/l without requiring hemodialysis. the aim of ecad was to reduce endogenous albumin-bound toxins accumulated during liver failure. the two methods used in this case report, namely the mars and spad techniques, proved their feasibility and efficacy to reduce bilirubin levels in plasma to a similar extent (25). conclusion cn is renal dysfunction due to hyperbilirubinemia, appearing when bilirubin is greater than 20 mg/dl. although it occurs frequently, it is underdiagnosed. it is obstructive and cytotoxic. the mechanisms of injury, although not precisely known, appears to involve inflammation. there is no established therapeutic approach for its management. it seems plausible to explore the use of antioxidants that limit the 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http://dx.doi.org/10.1001/archinte.1937.00180060081008� http://dx.doi.org/10.1001/archinte.1937.00180060081008� http://dx.doi.org/10.1097/00000441-194003000-00001� http://dx.doi.org/10.1097/00000441-194003000-00001� http://dx.doi.org/10.1002/hep.23283� http://dx.doi.org/10.1002/hep.23283� http://dx.doi.org/10.1111/liv.13306� http://dx.doi.org/10.1111/liv.13306� http://dx.doi.org/10.1053/j.gastro.2011.09.051� http://dx.doi.org/10.1016/j.jhep.2017.02.019� journal of renal and hepatic disorders 2019; 3(1): 15–22 review article the role of stearoyl-coenzyme a desaturase 1 in liver development, function, and pathogenesis fatemeh mohammadzadeh1, vahid hosseini2, alireza alihemmati3, maghsod shaaker1, gholamali mosayyebi4, masoud darabi1, amir mehdizadeh5 1emergency medicine research center team, department of emergency medicine, tabriz university of medical sciences, tabriz, iran; 2 department of biochemistry and clinical laboratories, faculty of medicine, tabriz university of medical sciences, tabriz, iran; 3 department of anatomical sciences, faculty of medicine, tabriz university of medical sciences, tabriz, iran; 4liver and gastrointestinal research center, tabriz university of medical sciences, tabriz, iran; 5endocrine research center, tabriz university of medical sciences, tabriz, iran abstract stearoyl-coenzyme a desaturase 1 (scd1) is a microsomal enzyme that controls fatty acid metabolism and is highly expressed in hepatocytes. scd1 may play a key role in liver development and hepatic lipid homeostasis through promoting monounsaturated protein acylation and converting lipotoxic saturated fatty acids into monounsaturated fatty acids. imbalanced activity of scd1 has been implicated in fatty liver induction, inflammation and stress. in this review, the role of scd1 in hepatic development, function and pathogenesis is discussed. additionally, emerging novel therapeutic agents targeting scd1 for the treatment of liver disorders are presented. keywords: hepatic lipogenesis; hydroxy pyridine; mk-8245; stearoyl-coenzyme a desaturase 1; scd1 received: 20 december 2018; accepted after revision: 15 january 2019; published: 06 february 2019 authors for correspondence: masoud darabi, emergency medicine research center team, department of emergency medicine, tabriz university of medical sciences, tabriz, iran. email: darabim@tbzmed.ac.ir; amir mehdizadeh, endocrine research center, tabriz university of medical sciences, tabriz, iran. email: mehdizadeha@tbzmed.ac.ir how to cite: mohammadzadeh f et al. the role of stearoyl-coenzyme a  desaturase 1 in liver development, function and pathogenesis. j ren hepat disord. 2019;3(1):15–22. doi: http://dx.doi.org/10.15586/jrenhep.2019.49 copyright: mohammadzadeh f et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction stearoyl-coenzyme a desaturase 1 (scd1) was discovered in 1988 when ntambi and colleagues identified an mrna transcript whose expression was highly induced during adipogenic differentiation (1). scd1 is an iron-containing lipidregulating enzyme that is highly expressed in the liver and is the main enzyme responsible for de novo synthesis of monounsaturated fatty acids (mufas). palmitoyl-coa and stearoyl-coa are the main substrates of this enzyme, converting them into palmitoleoyl-coa and oleoyl-coa, respectively (2). scd1 is coded by its gene on the long arm of chromosome 24, in the sub-band 3 of region 24 (3). promoter activity region is located within the initial 609 bp upstream of transcription initiation site which constitutes a ccaat-box identified as p u b l i c a t i o n s codon journal of renal and hepatic disorders mailto:darabim@tbzmed.ac.ir mailto:mehdizadeha@tbzmed.ac.ir http://dx.doi.org/10.15586/jrenhep.2019.49 http://creativecommons.org/licenses/by/4.0 mohammadzadeh f et al. journal of renal and hepatic disorders 2019; 3(1): 15–22 16 a cis-element binding site. sterol regulatory element-binding transcription factor 1 (srebp-1c), liver x receptor (lxr), peroxisome proliferator-activated receptor alpha (ppar-α) and ccaat/enhancer-binding protein alpha (c/ebp-α) are among the most important transcription factors that bind to scd1 promoter and control its gene expression (4). the pseudogene of scd1, containing two premature stop codons downstream of the original start codon, is located on the short arm of chromosome 24 in the sub-band 32 of region 11 (5). scd1 protein is a microsomal enzyme containing four transmembrane domains in which both the n-terminus and c-terminus are located in the cytoplasm (figure 1). eight histidine residues on the single cytoplasmic loop and cterminus are conserved and important for desaturase catalytic activity (6). purified scd1 protein migrates as a 37 kda band by sds gel electrophoresis (7, 8). as fatty acids are important components of phospholipids, triglycerides and esterified cholesterol, changes in scd1 expression and activity can affect membrane stability, lipid metabolism and the amount of adipose tissue; consequent changes may be associated with obesity, fatty liver, cancers, diabetes and atherosclerosis (9). this review provides an overview of the role of scd1 on various aspects of liver pathophysiology such as development, hepatic lipogenesis and inflammation. it also summarizes the role of novel small molecules targeting scd1 as potential agents for the treatment of various liver disorders. scd1 activity contributes to liver development through protein acylation the wnt family of proteins are signaling molecules that orchestrate numerous homeostatic events from embryonic development to adult tissue function (10). their malfunction causes various hepatic abnormalities. the products of scd1 can regulate wnt trafficking and function through mufa acylation or lipidation (figure 2). monounsaturated fatty acyl moieties render wnts hydrophobic and insoluble in aqueous environment (11). during the embryonic stage, the inner layer, endoderm, is partitioned into three regions termed as foregut, midgut, and hindgut, with the foregut containing liver precursors. the liver and biliary tracts develop from the foregut at the 4th week of gestation (12). the intermediate germ layer, mesoderm, produces wnt which contributes to the development of hindgut in the posterior endoderm. in the anterior endoderm, however, suppression of wnt signaling retains foregut fate and allows subsequent development of the liver (13, 14). overall, wnt signaling is tightly regulated during embryo development, which is particularly important at the initial stages of liver development. absence of wnt signaling activity will result in impaired hepatic development. this is supported by the elevated expression of wnt downstream core transcription factors during the terminal differentiation of hepatocytes (15). scd1 shows a determinant role in the in vitro differentiation process of human-induced pluripotent stem cells toward hepatic lineage. inhibition of scd1 by a selective inhibitor in early stages of in vitro induced differentiation has resulted figure 1. stearoyl-coenzyme a desaturase 1 (scd1) is an iron-containing transmembrane enzyme. scd1 protein is exclusively localized on the er membrane with both the nand c-terminal domains stretched into the cytosol. it has four transmembrane helices (purple cylindrical shapes). the eight histidines (hexagonal shapes) on the single cytoplasmic loop and c-terminus are highly conserved, particularly regions surrounding the  di-iron center. the cytosolic domain provides a structural frame for the regioselectivity and stereospecificity of the desaturation reaction (6). figure 2. stearoyl-coenzyme a desaturase 1 (scd1) contributes to liver development and regeneration by modulating wnt activity. microsomal scd1 produces monounsaturated fatty acids that can be attached to wnts. this process, termed acylation, enables wnt secretion and activation. wnt acylation is also a prerequisite for the formation of concentration and activity gradients of wnts. the wnt gradients mediate zonal development of liver and regeneration. stearoyl-coenzyme a desaturase 1 and liver journal of renal and hepatic disorders 2019; 3(1): 15–22 17 in decreased hepatic markers. in the rescue experiments with the combination of the scd1 inhibitor and its main product oleate, the effect of inhibitor was strongly reversed (16). our ongoing in vivo work is to identify the role of scd1 in the early stages of liver organogenesis and development, especially its role in the formation of a complete liver before birth. apart from hepatocyte differentiation, wnt signaling pathway plays a central role in liver zonation (17). hepatocytes adjacent to portal vein are named periportal hepatocytes (zone 1) and involved in glyconeogenesis and β-oxidation, whereas those near the central vein are called pericentral hepatocytes (zone 3) and play a distinct role in drug metabolism and glycolysis. hepatocytes in zone 2 exhibit an intermediary role having both periportal and pericentral functions. in a recent study, a high β-catenin-dependent wnt signaling activity was observed in zone 3 (17–19). these findings collectively highlight the importance of the scd1produced mufas in mediating liver development through wnt regulation. recent studies using animal models of partial hepatectomy have also implicated the direct involvement of wnt signaling pathway in liver regeneration. the expression and nuclear translocation of β-catenin significantly increase within minutes of hepatectomy and promote hepatocyte proliferation rate (20). in acetaminophen-induced liver injury, wnt/βcatenin not only induces the expression of enzymes involved in drug metabolism such as cytochrome p450 2e1 and cytochrome p450 1a2 but also helps liver regeneration (21, 22). in line with this finding, scd1 gene expression was increased 3.5-fold in regenerating liver following major liver resection (23). after tissue damage, the residual cells start the repair process (24), and the proliferating cells accumulate several categories of lipids including triglycerides, fatty acids (both saturated and unsaturated), and cholesterol esters (25). these lipids are thought to undergo oxidation and provide the required energy for cell proliferation. in addition, they are the main components of newly synthetized membranes. besides, these lipids can contribute to various signal transduction cascades related to cell proliferation and differentiation such as wnt and hedgehog signaling pathways (26). it is hypothesized that mufas produced by scd1 not only provide metabolic energy source and structural components, but also promote protein acylation–mediated signaling, which are essential for liver regeneration. scd1 prevents lipotoxicity and controls hepatic lipogenesis palmitic acid and stearic acid are the major de novo synthesized lipotoxic saturated fatty acids (sfas) in the liver. scd1 mediates the addition of a double bond to the saturated carbon chain. on one hand, scd1 activity attenuates sfas lipotoxic effects through their conversion into the mufas palmitoleic acid and oleic acid (27). on the other hand, scd1 generates unsaturated fatty acids serving as rate-limiting substrates for lipogenesis (28). thus, an improper increase in its activity may cause hepatic lipid accumulation. despite oleate being the major dietary mufa, scd1 expression is highly regulated in response to developmental, dietary, environmental, and hormonal factors. de novo synthesized mufas are the preferred substrates for neutral hepatic lipid synthesis including triglycerides and cholesterol ester. scd1 inhibition protects against high-fat high-carbohydrate diet, leptin-deficiency-induced obesity, and hepatic steatosis (29). leptin-deficient mice exhibit scd1 overexpression causing palmitoleate and oleate accumulation in liver as fat droplets. recent studies on high-carbohydrate-fed rats have revealed that deficiency in scd1 decreased lipid synthesis, elevated fatty acid oxidation and thermogenesis, and insulin susceptibility in different tissues, especially in the liver (30). sampath et al. (31) showed that stearate-rich diet causes scd1 induction and hepatic lipid accumulation in wild-type mice but not in scd1-/mice. however, in scd1-/mice, stearate does not induce genes involved in lipogenesis. additionally, sterol regulatory element-binding protein-1c (srebp-1c) and peroxisome proliferator-activated receptor coactivator-1 (pgc-1) transcription factors, which are necessary mediators for pro-lipogenic activities of saturated fatty acids (sfas), were downregulated in scd1-/mice. instead, fatty acid oxidation genes such as carnitine palmitoyltransferase-1 (cpt-1) were induced, resulting in hepatic glycogen depletion. lui et  al. (32), in a study on zinc finger transcription factor knockout mouse model, showed a significant decrease in scd1 expression and triglyceride accumulation compared to controls. binding of this transcription factor to scd1 promoter in hepatocytes was also reported in this study, indicating its critical role in the activation of scd1 expression. the role of scd1 in gut microbiota-dependent hepatic lipogenesis has been studied by singh et al. (28). they reported that mice with deficient toll-like receptor-5, which is expressed in gut epithelial cells and plays an important role in microbiota homeostasis, exhibit a microbiota-dependent metabolic syndrome with elevated hepatic lipogenesis, scd1 expression and activity, and hepatic neutral lipids accumulation with a high oleate and palmitoleate content. furthermore, the expression level of scd1 and fatty acid synthase along with endoplasmic reticulum (er) stress markers was downregulated in response to the inhibition of poly adp-ribose polymerase (parp), which is overexpressed in long-term high-fat high-sucrose diet in mice, indicating the parp-scd1 interaction as a major mechanism in the induction of non-alcoholic fatty liver disease (33). the role of scd1 in an alcoholic fatty liver disease model was studied by louinis et al. (34). in that study, mice fed with a low-mufa diet containing 5% ethanol for 10 days and a single ethanol gavage (5 g/kg) developed severe hepatic injury. liver-specific scd1-knock-out (scd1-lko) mice were resistant to such hepatic injury. mohammadzadeh f et al. journal of renal and hepatic disorders 2019; 3(1): 15–22 18 in a recent cross-sectional clinical study, it has been shown that the serum scd1 activity index is significantly related to the risk of non-alcoholic fatty liver disease in patients with primary dyslipidemia (35). of course, while interpreting these data, it should be noted that the index of serum scd1 activity is not solely determined by the liver. in this field, the ntambi laboratory has recently shown that hepatic triglyceride accumulation in mice may be induced by increased hepatic trafficking of mufas originating from non-liver tissues (36). the latter finding further supports the hypothesis that fine-tuning of hepatic scd1 activity is critical in variable metabolic states. scd1 modulates hepatic inflammation and oxidative stress current evidence indicates the regulatory role of fatty acids in cellular inflammation. scd1 plays an important role in maintaining the balance between sfas and mufas. toxic accumulation of sfas that are reflected as mufas/sfas imbalance leads to activation of oxidative stress imbalance in hepatocytes (37, 38). sfas mediate cellular inflammatory response through binding to toll-like receptor-4, cd14, and myeloid differentiation protein-2, causing increased production of bacterial lipopolysaccharides, oxidized phospholipids, and oxidized low-density lipoproteins through intestinal microbiota modification (39). these findings support the hypothesis that scd1 activity may be protective against sfainduced oxidative stress and hepatic inflammation. lu et al. (40) reported that ikk2 (an activator of nfκb) activation can induce hepatic scd1 overexpression and triglyceride accumulation in mouse. however, such activation decreased the expression of oxidative stress and prevented hepatic inflammation and fibrosis. paradoxically, there is evidence that increased scd1 activity may contribute to inflammation and oxidative stress. in the high-carbohydrate or high-sucrose, very-low-fat diet, oleate supplementation leads to decreased hepatic injury and oxidative stress in mice with liver-specific scd1-lko (41). a high-fructose diet in female c57bl/6j mice also induced oxidative stress characterized by hepatic scd1 overexpression and elevation of inducible nitric oxide synthase levels (42). ochi et al. (43) also showed the association of scd1 with the development of non-alcoholic steatohepatitis (nash) under induced stress condition. indeed, a knockout c57bl/6 mice model with a low expression and activity of scd1 showed lower hepatic lipid accumulation and steatosis following tunicamycin-induced er stress than the wild-type mice with er stress. overall, as illustrated in figure 3, balanced activity of scd1 is important for stabilizing the ratio of unsaturated to saturated fatty acids. an increase in this ratio can lead to lipid accumulation and a decrease in this ratio is associated with lipotoxicity. a rise in both lipid accumulation and lipotoxicity may lead to hepatic inflammation and oxidative stress. scd-1 as a potential therapeutic target the aforementioned studies highlight the significant role of scd1 activity in hepatic pathophysiology. therapeutic strategies targeting scd1 may have applications in managing liver disorders. several studies have examined small molecule inhibitors in this regard. the following sections review recent advances in small molecule scd1 inhibitors and their potential therapeutic application in hepatic disorders (table 1). mk-8245 scd1 enzyme is expressed in many cell types of the body. therefore, potential scd1 inhibitors for the treatment of liver diseases will have a lot of side effects although they might be highly selective toward scd1. for example, scd1 knockout rodent models and scd1 inhibitor–treated rats develop severe skin and eye abnormalities (44, 45). therefore, liver-specific targeting of scd1 may be an effective strategy for the treatment of liver-related disorders. one such inhibitor is mk-8245 (46). it has a transporting element that specifically interacts with heptocytes via the liver-specific organic anion transporting polypeptides. administration of mk-8245 to mice fed with a high-fat diet did not reduce food intake. despite this, a reduction in liver steatosis and a decrease in liver triglyceride levels were observed. mk-8245 also exhibited anti-diabetic and anti-dyslipidemic properties. administration of mk-8245 to individuals with type 2 diabetes mellitus in a phase ii clinical trial showed no serious adverse events (47). mk-8245 may also be an option for anti-hepatitis c virus (hcv) therapy as evaluated using recombinant hcv culture systems (48). the potential therapeutic effects of this compound on liver diseases are yet to be clinically examined. figure 3. stearoyl-coenzyme a desaturase 1 (scd1) activity is associated with normal liver function. the schematic balance represents that the equilibrium between saturated fatty acids (sfas) and monounsaturated fatty acids (mufas) is important in the physiological state. the loss of this equilibrium is due to overactivity and underactivity of scd1 in hepatic lipid accumulation and  lipotoxicity, respectively. stearoyl-coenzyme a desaturase 1 and liver journal of renal and hepatic disorders 2019; 3(1): 15–22 19 hydroxy pyridone another compound that was used for targeted liver scd1 inhibition is 4-hydroxy pyridine (49). according to the pharmacokinetic analysis, this scd1 inhibitor had a significantly higher concentration in liver than in plasma and eyelid. it showed a good potency in reducing the mouse liver ratio of palmitoleate to palmitate as a biomarker for scd1 activity (49). pyridazine derivative a piperazine-based scd-1 inhibitor, n-(2-hydroxy-2phenylethyl)-6-[4-(2 methylbenzoyl)piperidin-1-yl]pyridazine-3-carboxamide, has been shown to produce beneficial effects in experimental modes of nash (50, 51). when administered orally for 8 weeks, once daily, triglyceride accumulation in the liver was reduced by 80% from the fourth week. it also attenuated the increase of aspartate aminotransferase and alanine transaminase by 86% and 78%, respectively. hepatic steatosis, hepatocellular degeneration, and inflammatory cell infiltration were also ameliorated after the treatment (50). thiazole analogs current evidence shows that host cell lipid homeostasis plays a critical role in the pathogenesis of hcv by facilitating the formation of viral membrane-associated replication complex. since inhibiting lipogenesis has a negative effect on virus proliferation, inhibiting the lipid synthesis enzyme scd1 is a potential strategy for hcv treatment (52, 53). lyn et al. (54) showed that the thiazole compound mf-152 can repress hcv infection in human hepatoma cells by modifying membrane functions which are required for hcv replication. cell imaging studies showed that the inability of viral rnas to interact with modified membranes exposes them to degradation by endogenous nucleases. this process ultimately prevents the formation of hcv viral complexes and arrests hcv replication. thiazole-4-acetic acid derivative another potent liver-selective scd1 inhibitor, compound 48 (a thiazole-4-acetic acid derivative), has recently been discovered through high-throughput screening efforts following an ex vivo assay approach on mice liver and eyelids (55). administration of compound 48 to mice fed a highfat diet for 43 days improved glucose tolerance and decreased body weight without adverse effects on skin or eyes. furthermore, compound 48 significantly attenuated hepatic triglyceride accumulation in rats fed a high-sucrose, verylow-fat diet (55). these findings suggest that compound 48 may have clinical benefits in the treatment of diabetes, hepatic steatosis, and obesity through targeting scd1 activity in liver. conclusion scd1, one of the predominantly expressed enzymes in the liver, is a major factor in fatty acid metabolism. it plays a regulatory role in posttranslational protein modifications via protein acylation. wnts play an important role in hepatic differentiation, zonation, and regeneration. the wnts pathway, at least in part, is regulated by scd1mediated palmitoleoylation and oleoylation. in addition, scd1 is crucial for sfa detoxification and mufa production. sfas overproduction induces hepatic inflammation and oxidative stress, and scd1 attenuates these effects via monounsaturation of sfas. meanwhile, de novo produced mufas promote and participate in cellular lipogenesis and their overproduction can lead to hepatic lipid accumulation. targeting scd1 as a novel therapeutic approach may be beneficial in liver disorders. in this regard, several studies have tested small molecule inhibitors of scd1 table 1. stearoyl-coenzyme a desaturase 1 small molecule inhibitors with potential applications for hepatic diseases. compound liver-selective therapeutic application current evidence reference mk-8245 + diabetes, dyslipidemia, hcv preclinical/animal/ phase ii clinical trial (46, 48) hydroxy pyridone + dyslipidemiain vivo (49) n-(2-hydroxy-2-phenylethyl)-6-[4(2-methylbenzoyl)piperidin-1-yl] pyridazine-3-carboxamide reduction in triglyceride accumulation in nash in vivo (50, 51) thiazole analogs hcv infection in vitro (54) thiazol-4-acetic acid derivatives + diabetes, hepatic steatosis and obesity in vivo (55) hcv, hepatitis c virus; nash, nonalcoholic steatohepatitis; oatp, organic-anion-transporting polypeptide. mohammadzadeh f et al. journal of renal and hepatic disorders 2019; 3(1): 15–22 20 in vitro and in vivo, which opens a promising point of view in the treatment of liver metabolic diseases. acknowledgments 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inhibition blocks formation of hepatitis c virus-induced specialized membranes. sci rep. 2014 apr;4:4549. https://doi.org/10.1038/srep04549 55. iida t, ubukata m, mitani i, nakagawa y, maeda k, imai h, et  al. discovery of potent liver-selective stearoyl-coa desaturase-1 (scd1) inhibitors, thiazole-4-acetic acid derivatives, for the treatment of diabetes, hepatic steatosis, and obesity. eur j med chem. 2018 oct;158:832–52. https://doi.org/10.1016/j. ejmech. 2018.09.003 https://doi.org/10.1248/bpb.b12-00702 https://doi.org/10.1039/b924668c https://doi.org/10.1039/b924668c https://doi.org/10.1016/j.tem.2011.03.004 https://doi.org/10.1016/j.tem.2011.03.004 https://doi.org/10.1038/srep04549 https://doi.org/10.1016/j.ejmech.2018.09.003 https://doi.org/10.1016/j.ejmech.2018.09.003 journal of renal and hepatic disorders 2019; 3(1): 40–46 40 review article wasting away with cirrhosis: a review of hepatic sarcopenia ernesto robalino gonzaga1, austin andrew2, freeman jan george2 1department of internal medicine, university of central florida college of medicine, orlando, fl, usa 2hepatology unit, university hospitals of derby and burton on trent, derby, united kingdom abstract the complications of decompensated cirrhosis are well documented and include variceal bleeding, fluid retention, and hepatic encephalopathy. a less well recognized complication of cirrhosis is muscle wasting or sarcopenia. it is now recognized to have a significant impact on patient survival, especially in patients who are awaiting liver transplantation. an understanding of the pathophysiology of muscle protein homeostasis has led to several proposed mechanisms of sarcopenia and the potential to reverse muscle loss. this review discusses the potential mechanisms of sarcopenia and highlights the possible future means of reversing sarcopenia. keywords: sarcopenia; cirrhosis; wasting; end-stage liver disease; muscle received: 14 june 2019; accepted after revision: 30 july 2019; published: 09 september 2019 author for correspondence: freeman jan george, hepatology unit, university hospitals of derby and burton on trent, derby, de22 3ne, united kingdom. email: j.freeman115@btinternet.com how to cite: gonzaga er et al. wasting away with cirrhosis: a review of hepatic sarcopenia. j ren hepat disord. 2019;3(1):40–46. doi: http://dx.doi.org/10.15586/jrenhep.2019.56 copyright: gonzaga er et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/ licenses/by/4.0 introduction malnutrition is a common finding in end-stage liver disease (esld) (1), leading to a loss of muscle mass and an increase in frailty. the causes of malnutrition include inadequate dietary intake, anorexia, malabsorption, low salt and protein diets offered, and the complications of esld such as encephalopathy and ascites. esld patients with malnutrition have longer hospital stays, increased hepatic complications, and in-hospital mortality (2). loss of muscle mass, sarcopenia, is not synonymous with malnutrition although they often overlap. sarcopenia is a common complication of cirrhosis and is frequently overlooked. it is defined as a reduction in the skeletal muscle mass and strength. it is often not addressed as  a prognostic factor in esld or in patients assessed for liver transplantation. the mechanisms behind the cause of sarcopenia are not fully understood, but it is a complication that adversely affects esld patient’s survival and quality of life. the prevalence of sarcopenia is higher than any other complications of esld. the mean prevalence is 48% compared to esophageal varices (10–15%), refractory ascites (−10%), or hepatocellular cancer (3, 4). there appears to be some gender and ethnicity factors in the development of sarcopenia, with it being more prevalent in western societies (5). the prevalence of sarcopenia in cirrhosis is higher than any other gastrointestinal disorder, being only 21% in patients with inflammatory bowel disease (4). the aim of this review is to assess the current state of knowledge of the mechanisms of muscle wasting in liver disease, diagnostic issues, and potential therapies. p u b l i c a t i o n s codon journal of renal and hepatic disorders mailto:j.freeman115@btinternet.com http://dx.doi.org/10.15586/jrenhep.2019.56 http://creativecommons.org/licenses/by/4.0 http://creativecommons.org/licenses/by/4.0 hepatic sarcopenia journal of renal and hepatic disorders 2019; 3(1): 40–46 41 body composition and muscle physiology in order to assess the loss of muscle mass, it is important to have an understanding of relative body composition and muscle physiology in a healthy individual. the assessment of body composition and of somatic protein stores relies on measuring the different body compartments, that is, water, fat, bone, muscle, and visceral organs. body composition techniques aid in the diagnosis of protein depletion. protein levels are usually preserved at the expense of fat utilization as an energy source. the amount of body fat compared to muscle volume varies according to the cirrhotic stage. in compensated cirrhotics, there is a high amount of body fat. while in decompensated cirrhotics there is a much lower amount of body fat, implying lipolysis occurring in the latter stages of cirrhosis is an alternative energy source (6). the utilization of fat thus spares muscle in the early stages of cirrhosis but as it becomes depleted glycogenesis in the muscle leads to a rapid muscle breakdown leading to sarcopenia. the assessment of body composition ranges from simple anthropometric tests such as skin thickness to more complex measures such as bioelectrical impedance. measuring such composition is essential when evaluating malnutrition and sarcopenia in liver patients. the homeostasis of muscle bulk is tightly regulated requiring a balance between muscle protein synthesis and muscle proteolysis. muscle protein synthesis and muscle satellite cell recruitment are important factors in maintaining muscle bulk. the major pathway regulating protein synthesis is the exercise activation of mammalian target of rapamycin (mtor). recent evidence suggests that exercise increases intracellular calcium levels triggering both mtor and mitogen-activated protein kinase (mapk) to stimulate muscle protein formation (7). other suggested stimuli of muscle protein production include insulin-like growth factor (igf-1), insulin, leucine, testosterone (8), and interleukin (1). muscle replacement requires the activation and recruitment of muscle satellite cells, the adult stem cell of skeletal muscle located between the sarcolemma and basal lamina within the muscle tissue. when activated they proliferate to expand the population of myoblasts and differentiate into myotubes capable of fusing together to form new myofibers. muscle protein synthesis and satellite cell recruitment are negatively controlled by the cytokine myostatin. myostatin belongs to the transforming growth factor beta family. acting in a paracrine fashion, its action is via a linkage with activin(s), which is a type 2 transmembrane receptor leading to a serine threonine kinase phosphorylation of smad2/3 that in turn transcriptionally regulates target genes responsible for muscle protein synthesis. to maintain muscle homeostasis, myostatin levels are regulated by follistatin, a widely expressed glycoprotein acting as an extracellular ligand trap to regulate the availability of myostatin and activins. its actions are to increase/activate satellite cell recruitment and inhibit smad2/3, thereby negating the action of myostatin. in experimental models, follistatin infusions increase muscle protein synthesis leading to muscle hypertrophy (9). muscle breakdown or proteolysis is driven by two pathways: ubiquitin–proteasome pathway (upp) and the autophagy system. upp is the major proteolysis pathway. muscle protein is conjugated with ubiquitin, then degraded by 26s proteasome and removed. upp can be induced by inactivity, injury, and inflammation driven by tumor necrosis factor (tnf), whereas it can be inhibited by protein kinase b. autophagy contributes to cell homeostasis removing misfolded proteins and damaged organelles by the formation of autophagasome, which in turn delivers its contents to lysosomes for degradation. a factor in controlling autophagy rate is mtor. rapamycin has been demonstrated to stimulate autophagy by inhibiting mtor. thus myostatin, which inhibits mtor, probably increases muscle proteolysis as a consequence of autophagy stimulation. an ongoing trial of leucine-enriched essential amino acid mixture seeks to demonstrate a reduction in autophagia and thus improve hepatic sarcopenia as leucine is a direct stimulant of mtor (clinical trials identifier nct03208868). potential mechanisms of sarcopenia dysregulated muscle proteostasis in esld may result from a number of factors including cirrhosis being a metabolic starvation disorder, hormonal dysfunction (i.e., reduced testosterone), defective ureagenesis, alterations in branched chain amino acids, and a chronic inflammatory response to endotoxemia leading to elevated levels of tnf. this leads to an imbalance between muscle protein synthesis and proteolysis being disrupted in favor of proteolysis. as one may expect, there is marked interplay between the various potential mechanisms of sarcopenia. a considerable amount of research has concentrated on defective ureagenesis leading to elevated levels of ammonia or hyperammonemia. ammonia is derived from purine, amino acid, and gut bacteria metabolism. in the face of a reduction of the number of effective hepatocytes, which are metabolically distressed, as a consequence of cirrhosis and portal hypertension leading to portocaval shunting, ammonia levels are raised in cirrhosis to cytotoxic levels. as the cirrhotic liver is unable to metabolize ammonia, skeletal muscle uptake of ammonia increases where it is converted to glutamine via a glutamate pathway. within the skeletal muscle, excess ammonia induces transregulation of myostatin by a nf-kappa-mediated mechanism (10). myostatin is a primary inhibitor of protein synthesis and increases autophagy leading to accelerated sarcopenia. it  is well established that myostatin levels are increased in cirrhosis (11). gonzaga er et al. journal of renal and hepatic disorders 2019; 3(1): 40–46 42 the resultant detoxification of ammonia within the mitochondria leads to high levels of glutamine in the circulation. this is utilized by other peripheral tissues generating another source of ammonia thus maintaining the need for skeletal muscle to continually metabolize it. the biochemical step to  convert ammonia to glutamate requires the tricarboxylic acid cycle intermediary alpha-ketoglutarate. the constant demand for it eventually leads to its depletion resulting in mitochondrial dysfunction and consequently decreased protein synthesis. in addition, the mitochondria become increasingly leaky generating reactive oxidative species further inducing autophagy and proteolysis (12, 13). hyperammonemia, and the resultant intracellular amino acid deficiency, further stresses the cell resulting in a reduction of mrna translation and protein synthesis, which occurs via a eukaryotic initiation factor (eif2) alpha kinase, general control nondepressed two (gcn2) pathway (12–15). due to cirrhosis being a state of accelerated starvation, and with the reduction in available branched chain amino acids (bcca) because of their role in anaplerosis, it has also been suggested that muscle synthesis is restricted as amino acids are diverted to other cells for the synthesis of other critical amino acids such as albumin (16). reduced cellular amino acid concentrations also activate increased skeletal muscle autophagy in cirrhosis (17). hormonal disarray may also play a role in sarcopenia. both testosterone and growth hormone are known to inhibit myostatin expression and signaling (18, 19). in cirrhosis, both are reduced and therefore may contribute to decreased muscle protein synthesis (20, 21). in addition to being a starvation disorder, cirrhosis is also a state of chronic endotoxemia leading to increased circulating levels of tnf. tnf has been shown to impair muscle synthesis, activate autophagy, and inhibit hormones such as growth hormone and igf-1 (22–24). diagnosis of sarcopenia in cirrhosis a full dietary survey should be undertaken to address any concomitant malnutrition. bioelectrical impedance analysis, dual energy x-ray absorptiometry (dexa), and air displacement plethismography reflect indirect measures of muscle mass (25). ct and mri are now the recommended investigations offering both sensitive and specific measure of adiposity and muscle mass. measurement of peripheral muscle mass is not acceptable due to changes in muscle bulk associated with activity. evaluation of psoas and paraspinal muscles using ct at the level of the third lumbar vertebra (l3) is a more reproducible means of sequentially following muscle bulk. the definition of sarcopenia in patients with cirrhosis lacks a consensus regarding adequate cut-off values. most studies defining sarcopenia use the l3 skeletal mass index cut-off values suggested by prado (l3 smi: ≤ 38.5 cm2/m2 for women and ≤ 52.4 cm2/m2 for men) (26). however, both ct and mri have limited access in routine practice (27). recently, the use of the combination of body mass index and thigh muscle thickness measured by ultrasound has been shown to be almost as good as ct in assessing cirrhotic sarcopenia and may offer a cheaper more accessible means of diagnosing sarcopenia (28). potential treatments of sarcopenia there are no definitive therapies to reverse cirrhotic sarcopenia. attempts at improving muscle mass by means of nutritional support, increasing exercise, and correcting hormonal disarray have proved disappointing although reducing ammonia levels and myostatin levels are promising in some studies. general nutritional support the caloric and protein intake in esld is usually reduced due to alterations in taste, anorexia, salt restriction, and impaired gut motility leading to a relative malabsorptive state (29). this lack of intake accelerates the state of metabolic starvation in patients. several studies of enteral and parenteral feeding have not shown any improvement in muscle mass, nutritional status, nitrogen retention, or survival (30). only a single study of high energy–high protein supplementation was able to demonstrate significant nitrogen retention. the utilization of a multidisciplinary nutrition support team and patient education appears to benefit quality of life and improve survival (31). the timing of nutritional support appears to be important. evidence suggests that a late evening snack and an early morning protein supplement are the most likely to stabilize muscle homeostasis (32). the amounts of caloric and protein intake are well documented in the european association for study of the liver (easl) clinical practice guidelines on nutrition in chronic liver disease (33). exercise exercise stimulates muscle protein synthesis through the activation of mtor but whether this pathway in cirrhosis is inhibited by hyperammonemia and elevated myostatin is unknown. there is evidence that hyperammonemia alters muscle function by altering contractile function and increasing muscle fatigue in patients with esld (34). exercise generates muscle ammonia, which may negate any potential muscle protein synthesis (35). despite these theoretical considerations, a combination of moderate intensity resistance and endurance exercise may benefit sarcopenia in esld (36). a recent study has suggested that a combination of bcaa supplementation and walking exercise improved muscle volume and hand grip strength which if confirmed could be easily implemented (37). hepatic sarcopenia journal of renal and hepatic disorders 2019; 3(1): 40–46 43 branched chain amino acid supplementation in esld, it is well established that there is a decrease in bcaa and an increase in aromatic amino acids (aaa) which may contribute to hepatic encephalopathy (he) (38, 39). the role of bcaa therapy in he is not established with some trials showing no benefit, while a recent cochrane review favors benefit (40–42). a further study of bcaa supplementation in he suggests that minimal he can be prevented and interestingly muscle mass can be recovered (43). bcaa may be of benefit by acting as a substrate for anaplerosis in the alpha-ketoglutamate, glutamine–glutamate pathway in muscle, and thereby remove ammonia. a further potential mechanism of bcaa therapy maybe to act as an inhibitor of the amino acid deficiency sensor gcn2 and reverse eif2 phosphorylation leading to an increase in muscle synthesis (44). the specific use of leucine-rich amino acid supplementation stimulates mtor activation leading to higher rate of protein synthesis via messenger rnas (mrna) (45–47). if mtor signaling is impaired, autophagy is increased in cirrhosis, and it has been shown that this can be reversed by an enriched leucine bcaa supplementation. in addition, the study suggested the reversal of the gnc2/ eif2 pathway (48). anabolic hormones testosterone, growth hormone, and insulin-like growth factor-1 (igf-1) are known to influence muscle protein synthesis by activating mtor and suppressing myostatin (49). these anabolic hormones are reduced in cirrhosis (50) but studies have not shown any definitive benefit in cirrhotic sarcopenia. in a rat model of cirrhosis, igf-1 treatment has been shown a decrease in myostatin and improved nitrogen retention (51, 52). recently, nutmeg extract has been demonstrated to increase skeletal muscle mass in the elderly acting via the igf-1, protein kinase b(akt), and mtor pathway inhibiting autophagy (53). whether this could be applied to esld patients with sarcopenia begs further clinical studies. testosterone trials in reversing sarcopenia have been inconclusive, although one small study demonstrated improved hand grip (54). a further study of men with cirrhosis was able to show an increase in bone mass and muscle mass, and a reduction in the fat mass (55). ammonia lowering therapy reducing ammonia levels may potentially reverse sarcopenia. however, sarcopenia continues to be a problem following liver transplantation which should correct the metabolic changes of esld (56) it has been suggested that the use of post-transplant immunosuppressant drugs, such as cyclosporine a and mtor inhibitors, may be responsible for the ongoing sarcopenia (3, 57). in a recent animal model of portal hypertension, the use of rifaximin and l-orthenine l-aspartate (lola) for 4 weeks was seen to restore muscle proteostasis and reverse sarcopenia. the treatment was seen to downregulate the ammonia-induced myostatin production, reverse autophagy, and partially reverse gcn2/eif2 pathway activity. as lowering of ammonia is an established therapy for hepatic encephalopathy, long-term clinical studies of such therapy are now indicated (12). myostatin inhibition myostatin inhibitors have the potential to promote muscle protein synthesis although no human data are available. recently, antibodies to myostatin and its precursor pro myostatin have been shown in rats and non-human primates to inhibit myostatin activity and induce muscle anabolic activity. similar results in non-human primates have been found with domagrozumab therapy (58, 59). the use of recombinant follistatin-288 has been shown to promote growth of skeletal muscle (9). prognosis of sarcopenia the overall rate of mortality in cirrhotic patients is 12.5 in every 100,000 patients (60). with the onset of sarcopenia, there is a threefold increase in mortality compared to cirrhotic patients without sarcopenia (61). sarcopenia is an independent prognostic indicator for patients awaiting liver transplantation with estimated survival rates at 1, 2, and 3 years being 63%, 51%, and 51%, respectively, compared to nonsarcopenic patients with survival rates of 79%, 74%, and 70% over a similar period (62). a number of studies have identified sarcopenia to be a prognostic factor in the increased mortality of patients awaiting liver transplantation. in a study of 232 consecutive transplant recipients, sarcopenia increased the length of hospital stay, intensive care unit (icu) stay, and 12-month mortality; 6% of the sarcopenic patients did not survive the 12-month period (63). a meta-analysis comparing patients with sarcopenia and non-sarcopenia demonstrated an increased mortality by 3.25% for patients with esld and sarcopenia. the sarcopenia patients also had an increased complication rate in post-transplant infections, sepsis, and mechanical ventilation periods compared to non-sarcopenia patients who were less likely to experience these complications. the analysis highlights that due to sarcopenia’s significant influence on mortality and complications, it is an important prognostic factor, independent of the current model of end-stage liver disease (meld) and child-turcotte-pugh (ctp) scores used (4). a large retrospective study of sarcopenia-related esld (64) found that paraspinal muscles index (psmi) seems to be the most reliable diagnostic aid in predicting transplant outcomes. its use not only predicts death but also estimates associated complications for patients on the transplant gonzaga er et al. journal of renal and hepatic disorders 2019; 3(1): 40–46 44 waiting list. this study supports kalafateli et al.’s paper, and in that it calculates the improved outcomes of patients per unit of improved muscle mass. the traditional meld score does not incorporate sarcopenia as a factor of assessment. the evidence above and many other existing studies support that sarcopenia is, in itself, a prognostic indicator of survival for esld patients. a  more recent modified version, known as the meldsarcopenia score, has been proposed, offering a better prognostic value for patients awaiting or undergoing liver transplant. therefore, consideration and management of skeletal muscle may improve transplantation outcomes. conclusion sarcopenia is a common and significant complication of cirrhosis. it is a prevalent and important issue to address in patient’s awaiting liver transplant, as sarcopenia greatly increases mortality. there have been multiple hypotheses proposed regarding the mechanism(s) underlying sarcopenia in order to determine an effective treatment. this includes defective ureagenesis with ammonia elevation, alterations in bcaa, and chronic inflammatory response with the presence of elevated tnf leading to increased proteolysis. based on these hypotheses, interventions have been attempted with some promising results, including nutrition support, exercise focused on resistance and endurance, and bcaa supplementation. targeting ammonia 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clinical laboratories, faculty of medicine, tabriz university of medical sciences, tabriz, iran abstract a large number of patients are affected by liver dysfunction worldwide. liver transplantation is the only efficient treatment in a variety of enduring liver disorders including inherent and end-stage liver diseases. the generation of human functional hepatocytes in high quantities for liver cell therapy is an important goal for ongoing therapies in regenerative medicine. reprogrammed cells are considered as a promising and unlimited source of hepatocytes, mainly because of their expected lack of immunogenicity and minimized ethical concerns in clinical applications. despite gained advances in the reprogramming of somatic cells to functional hepatocytes in vitro, production of primary adult hepatocytes that can proliferate in vivo still remains inaccessible. as part of efforts toward translation of cell reprogramming science into clinical practice, more careful cell selection strategies should be integrated into improvement of dedifferentiation and redifferentiation protocols, especially in precision medicine where gene correction is needed. furthermore, advances in cellular reprogramming highlight the need for developing and evaluating novel standards addressing clinical research interests in this field. keywords: cell therapy; gene editing; liver transplantation; regenerative medicine; stem cells received: 09 december 2016; accepted after revision: 05 january 2017; published: 03 february 2017. author for correspondence: masoud darabi, stem cell research center, tabriz university of medical sciences, tabriz 51666-15556, iran. email: darabim@tbzmed.ac.ir how to cite: mehdizadeh a et al. reprogrammed cell‐based therapy for liver disease: from lab to clinic. j ren hepat disord 2017;1(1):20–28. doi: http://dx.doi.org/10.15586/jrenhep.2017.6 copyright: mehdizadeh a and darabi m license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction a large number of patients are affected by liver dysfunction worldwide. liver transplantation is the only efficient treatment in a variety of enduring liver disorders including inherent and end-stage liver diseases. however, there is a high shortage of liver organ donors causing almost 40% of patients with high rate of mortality receiving no organ transplantation. therefore, new strategies supporting liver transplantation are in high demand. familial hypercholesterolemia, crigler–najjar syndrome type i, glycogen storage disease type 1a, urea cycle defects and congenital deficiency of coagulation factor vii, hepatitis, cirrhosis, and liver cancer are the main liver diseases having clinical indications for cell therapy (1). there are several cell sources for human liver cell therapy, including primary hepatocytes (1), tumor cell lines (2), immortalized hepatocyte lines from normal human hepatocytes (3), liver stem cells (4), hepatocyte-like cells from bone-marrowderived stem cells (5), hepatocyte-like cells from fetal annex codon publications journal of renal and hepatic disorders 2017; 1(1): 20–28 mailto:darabim@tbzmed.ac.ir http://dx.doi.org/10.15586/jrenhep.2017.6 http://creativecommons.org/licenses/by/4.0 (6) and embryo (4), or reprogrammed somatic cells (7). among them, reprogrammed cells are considered as a promising and unlimited source of hepatocytes (figure 1), mainly because of their expected lack of immunogenicity and minimized ethical concerns in clinical applications (1). these cells can be obtained by redifferentiation of any accessible somatic cells including skin, mucosa, and urine cells. in the first stage, mature somatic cells (e.g., fibroblasts) are dedifferentiated to the pluripotent stages. besides their full pluripotency potential, these dedifferentiated cells are able to self-renew in vitro, which means they can potentially produce sufficient source for cell-based therapies. during the second stage, pluripotent cell reservoirs are induced to differentiate into functional hepatocytes. in the case of genetic deficiency, dedifferentiated cells undergo gene-editing strategies before redifferentiation. somatic cell dedifferentiation the concept of somatic cell dedifferentiation into pluripotent stem cells, which are capable to form the three germinal layers and to differentiate into other cell types, provides a promising approach for regenerative medicine. this dedifferentiation technique enables us to obtain donoror patient-specific pluripotent stem cells (8). in the following section, current methods for dedifferentiation of somatic cells are briefly reviewed. somatic cell nuclear transfer into oocyte the principles of this method involve in vitro removal of oocyte nucleus followed by its replacement with donor somatic nucleus. then, cell division is stimulated by chemicals or electricity up to blastocyst stage. at this stage, cellular mass is isolated and cultured. the resulting embryonic stem (es) cells are immunologically very identical to donor cells, and no immunosuppressant is required after transplantation to prevent their rejection. however, mitochondrial dna from maternal oocytes could be potentially immunogenic (9). major limitations of this method for clinical application are ethical concerns related to germ cell manipulation, chromosomal disorders in derived stem cells, low efficiency of transfer technique, and insufficient supply of human oocytes (8). somatic cell fusion with embryonic stem cell an advanced method of cell fusion was developed by cowan et al. (10) which reprogrammed human normal diploid fibroblasts into es cells. in this method, human embryonic cells were fused with human fibroblasts, resulting in hybrid cells with stable tetraploid dna. characteristics of these cells were similar to human es cells. however, before clinical application, a set of technical limitations should be resolved. the most important challenge is to abolish es-like cells after cell fusion. somatic cell dedifferentiation using cell extracts different cell extracts can alter gene expression profile in somatic cells (11). data obtained from experiments on 293t cells, an embryonic kidney cell line, have revealed that extracts of es cells or embryonic carcinoma cells can induce es cell phenotype and expression of pluripotency genes. expression of somatic gene markers such as lamin a es cell extracts 2 1 3 4 somatic cell differentiation somatic cell somatic cell somatic cell nuclear transfer unfertilized oocyte pluripotent stem cell mesoderm specific differentiation liver, kidney, lung, pancreas, stomach, intestine, bladder, germ cells heart, muscle, blood, blood vessel, connective tissue brain spinal cord, neurons, skin, hair, teeth, eyes, ears, nose oct4, sox2, klf-4 and c-myc gene transduction endodermendoderm eun clea ntio n cell fusio n figure 1. approaches for creating reprogrammed cells from somatic cells. 1: somatic cell nuclear transfer into oocyte; 2, adding embryonic stem cell (es) extract to somatic cells; 3: somatic and es cell fusion; and 4: transduction of pluripotency genes. generated reprogrammed cells from each strategy can create three germ layers known as ectoderm, endoderm, and mesoderm. induced redifferentiation of these reprogrammed cells can provide functional calls and tissues. liver cell therapy using reprogrammed cells codon publications journal of renal and hepatic disorders 2017; 1(1): 20–28 21 was reduced after this manipulation. besides, these cells gained the ability to differentiate into mesoderm and ectoderm lineages (12). bru et al. (13) also reported the elevation in expression of pluripotency genes including oct3/4, sox2, klf-4, and c-myc after exposure of mouse es cell extracts to 293t cells for 48 h. however, these cells are generally limited in pluripotency potential. somatic cell reprogramming using pluripotency-related genes in 2006, the discovery of somatic cell reprogramming to induced pluripotent stem cells (ipscs) led to a revolution in regenerative medicine (14). ipscs are basically patient-specific pluripotent cells that are produced by inserting four genes, including oct4, sox2, kfl4, and c-myc, necessary for fibroblasts to evolve es-like properties. recent studies have indicated that only the presence of oct4 gene may be sufficient to induce pluripotency in adult cells (15). in vitro, ipscs have efficiently been used for liver tissue construction (15). takebe et al. (16) showed that co-culture of human ipscsderived hepatic endoderm cells with human umbilical vein endothelial cells and human mesenchymal stem cells leads to the formation of liver buds (lbs) in 3d culture condition. furthermore, ipscs–lbs injection to mouse resulted in dynamic vascularization. therefore, these cells can potentially be applied in vast areas including disease modeling, tissue engineering, and drug discovery (17, 18). cellular redifferentiation to functional liver cells the generation of human functional hepatocytes in high quantities for liver cell therapy is an important goal for ongoing therapies in regenerative medicine. here, we introduce main practical strategies for redifferentiation of pluripotent cells to liver cells. precision medicine: crispr/cas9 genome editing to date, therapies based on human es cells are associated with controversial issues related to ethical concerns in using human embryos and potential risk of immune-mediated tissue rejection. utilization of patient’s cells in order to avoid ethical concerns and rejection complications is possible by cellular reprogramming, particularly ipscs technology (19). based on the present protocols, fibroblasts with skin biopsy origin can be returned to pluripotent stage and serve as a renewable and autologous cellular source (20). however, the original mutation that causes disease will be present in patient-derived pluripotent stem cells. precise correction of mutation is possible by gene-editing technique, “clustered regularly interspersed short palindromic repeats (crispr)/cas9 system,” which evolutionarily serves as an immune system in bacteria and archaea against virus and plasmid invasion (figure 2). the specificity of this technique mainly depends on a guide rna (grna) that can be readily reprogrammed to loci of target gene (21). editing mutations in ipscs derived from patients with retinitis pigmentosa was recently used double stranded viral dna inactivation of viral dna cas/crrna complex cas iii cas iii targeting viral dna (degradation) creation a novel spacer transcription processed crrnas cas iicas ii cas cas figure 2. schematic presentation of clustered regularly interspersed short palindromic repeats (crispr/cas9) system. it is basically a bacterial adaptive immune system. when an exogenous viral or bacteriophage genome is inserted into a bacterium, cas protein, which acts as a nuclease, detects the exogenous unmethylated genome by attachment to a 3–5 nucleotide sequence. then, cas protein cuts the target sequence and inserts the fragment just before 3–5 nucleotide sequence into host genome. after transcription, crispr rnas (crrnas) are produced which are complementary to the exogenous genome. crrnas can recognize the exogenous genome if a viral reinfection occurs. mehdizadeh a and darabi m codon publications journal of renal and hepatic disorders 2017; 1(1): 20–28 22 through crispr/cas9 approach (19), which opens a promising era in regenerative medicine and genome engineering. cytokines and growth factors hepatic regeneration is a complicated process regulated by growth factors, cytokines, transcription factors, hormones, micrornas, metabolic pathways, and products of oxidative stress (22). the use of a specific pool of cytokines in a serumfree medium is a prerequisite for liver organogenesis step in differentiation process (23). for example, high doses of activin a are widely used for endodermal induction in human pluripotent stem cells (24, 25). some protocols have added low doses of serum for promoting essential effects of activin a in the development of endodermal induction (26, 27). furthermore, fibroblast growth factor (fgf) and wnt signaling, which play important roles in normal liver development, are also effective in endodermal induction programs (28, 29). researchers have also combined bone morphogenetic protein and fgfs to promote endodermal induction specificity (26, 30). hepatocyte growth factor is also widely used in hepatic differentiation of pluripotent stem cell, mainly because of its ability in developing hepatoblast proliferation, migration, and survival through c-met as tyrosine kinase part (31). combination of fgf10 and retinoic acid with simultaneous inhibition of activin a is also another effective hepatic endodermal maturation protocol (32). in addition, oncostatin, which is a member of interleukin-6 family, in combination with glucocorticoids, can induce hepatocyte maturation (33, 34). genetic and epigenetic manipulation genetic manipulation for the purpose of overexpression of specific genes involved in hepatic induction is another approach in regenerative medicine. transducing some transcription factors such as sox17, gata, and hepatic nuclear factor 4α elevates ipsc hepatic induction at specific time intervals in culture media (35, 36). furthermore, epigenetic interferences have also been used to improve hepatic differentiation protocols (32). for instance, sodium butyrate, a specific inhibitor of histone deacetylase, is frequently used to differentiate pluripotent stem cells into different cell lineages including hepatocytes in higher concentrations and longer time intervals (37–39). chemicals (small molecules) recent studies have proposed novel growth-factor-free protocols for the differentiation of pluripotent stem cells (40). siller et al. (40) introduced a three-phasic protocol including 1) inhibition of glycogen synthase kinase 3 by chir99021 for definitive endoderm induction, 2) hepatic specification through dimethyl sulfoxide treatment, and 3) using dexamethasone and dihexa, a hepatocyte growth factor receptor agonist, to differentiate pluripotent stem cells into hepatocyte-like cells. zhu et al. (41) also used a cocktail of small molecules for incompletely reprogrammed human fibroblast cells to hepatocytes. in addition, shan. et al. (42) identified 12,480 small molecules in a liver platform, and they classified them into two large groups: functional proliferation hits and functional hits, which were able to promote the differentiation of ipscs and the maturation of resulted hepatocyte-like cells. improved directed redifferentiation using small molecules can improve results on a cost-benefit basis in large-scale applications. transplantation of redifferentiated cells in liver therapy the liver cell therapy procedure involves direct injection of prepared isolated cells into portal vein or spleen (43) or transplantation of in vitro developed tissue clusters (44). special anatomic location of liver provides different ways for cell transplantation, including percutaneous and intravascular delivery through both portal vein and hepatic artery (45). however, studies on rat model suggest that hepatic sinusoidal delivery is the most effective approach for cell transplantation (46). transplantation of hepatocytes under a low flow hepatic artery condition, accompanied with cellular attachment factors and extracellular matrix components, is another highthroughput strategy (47). ideally, self-regenerating capacity of transplanted liver cells is critical for cell therapy in patients with liver failure. guo et al. (48) conditioned mice by administration of retrosin, a cell cycle inhibitor, for arresting proliferation of native hepatocyte. after elimination of drug effects, a fresh 2 million β-galactosidase-labeled cell suspension was injected into the spleen pole. donor cell proliferation was assessed after injection of three doses of ccl4, 0.5 ml/kg. an average 20% repopulation of liver cells was recorded. more recently, post-surgery infusion of adult-derived human liver stem cells improved liver regeneration in a mouse model with 70% hepatectomy (49). overall, the application of stem cell technology in treatment of liver diseases is promising at present (50). several gene-editing clinical trials have just been approved and will be started in 2017, promoting reprogrammed cell-based therapy (51, 52). clinical examples inherent liver diseases a major indication for liver transplantation is inherent metabolic liver diseases in children (53). ipsc technology provides a unique method for designing patientand disease-specific therapies (54). yusa et al. (55) showed that a combination of ipscs and a transposon-based vector technology results in biallelic correction of a point mutation in α1-antitrypsin gene which is responsible for α1-antitrypsin deficiency. additionally, genetic correction of ipscs in patients with wilson’s disease using a lenti-viral vector could reverse the functional liver cell therapy using reprogrammed cells codon publications journal of renal and hepatic disorders 2017; 1(1): 20–28 23 genetic defect of wilson’s disease gene in vitro (56). in principle, genetic correction of patient-derived cells is plausible in inherent liver diseases with known mutations (figure 3) (57). liver failure acute liver failure (alf) and acute-on-chronic liver failure are two main indications for cell transplantation. ipscs that are originated from these diseases can provide an unlimited cellular source (54). in vivo studies by isobe et al. (58) showed that liver cells differentiated from ipscs can save rodent from lethal drug-induced alf. indeed, transplanted cells exhibited proliferative and liver functional properties (59). liver cirrhosis because of inevitable hepatocellular damage and fibrosis of hepatic tissue in cirrhosis, therapies should mostly rely on replacement of damaged cells and fibrosis correction (54). different studies have reported that ipsc-derived hepatocytes promote hepatic regeneration, decrease fibrosis, and stabilize chronic liver disease in mice model (59–61). despite these advances, ipsc-derived hepatocytes can temporarily support liver function and are hardly able to regenerate the original structure of the liver and to eliminate collagen deposition (62). thus, other strategies are needed to help liver structure regeneration in cirrhosis through reprogramming of fibrogenic cells or transplantation of liver tissue construct (62). liver cancer it has been reported that downregulation of cyclin-dependent kinase inhibitor 1, an important cell cycle mediator, in pluripotent stem cells generated from patients with hepatocellular carcinoma can promote differentiation into normal human hepatoma-like cells (63). furthermore, it was shown that inhibition of aldo-ketoreductase 1 member b10 promotes retinoic acid-induced differentiation. however, efficacy and patient specificity of the first-mentioned method seem to be higher, as it avoids the toxic effects of combination therapy (63). lei et al. (64) also introduced a protocol for generating cytotoxic t lymphocytes from ipscs as an unlimited cellular source in breast cancer therapy. in future, this strategy can be used as a novel method for liver cancer. clinical limitations using viral vectors for transducing oct4, sox2, klf4, and cmyc is an exciting method for generating human ipscs. despite high efficacy of this procedure, there remain some critical limitations for the application of ipscs in clinics (65). applications of retroviral-generated ipscs are limited because of the 1) integration of retroviral dna into host genome with variable copy numbers which interfere with promoter elements, polyadenylation signals, and coding sequences, affecting transcription potency (20), and 2) loss of pluripotency potential because of low expression of exogenous patient with inherent liver disease mutation correction using crispr/cas9 technology healthy ipscsdiseased ipscspatient derived skin fibroblasts differentiated healthy cells cell transplantation (functional, efficient, safe) figure 3. clinical application of clustered regularly interspersed short palindromic repeats (crispr/cas9). skin fibroblasts from patient source can be dedifferentiated to pluripotent stem cells containing the disease causing mutation. this mutation can be corrected by crispr/cas9 technology resulting in healthy stem cells which can be redifferentiated to patient-specific healthy cells for transplantation. mehdizadeh a and darabi m codon publications journal of renal and hepatic disorders 2017; 1(1): 20–28 24 oct4, sox2, klf4, and c-myc from viral constructs (66). another critical concern is the exogenous genes itself; overexpression of oct4, sox2, klf4, and c-myc increases the chance of tumorigenesis (66, 67). overexpression of oct4 induces epithelial cell dysplasia (68). sox2 overexpression is also associated with serrated adenoma and mucinous colon carcinoma (69). klf4 and c-myc are also associated with breast cancer and some other human carcinomas (70). tumor progression is also observed in murine chimeras after injection of retroviral-generated ipscs to blastocysts which has been attributed to c-myc overexpression (71, 72). despite gained advances in the differentiation of pluripotent stem cells into functional hepatocytes in vitro, production of primary adult hepatocytes that can proliferate in vivo still remains inaccessible (73, 74). the reason for this problem is that expansion and proliferation of transplanted cells need a tense sustain of hepatic cell mass (75). furthermore, besides pluripotent stem cells-related problems, cell delivery complications are another important limiting factor of liver cell therapy. direct injection of cells to liver parenchyma may increase the risk of cell entry to hepatic vein outflow and pulmonary vein, causing embolic complications (76). injection of cells to hepatic or splenic artery, theoretically, also seems to be achievable. however, these methods may increase the risk of tissue necrosis due to embolic occlusion of vessels. in high blood flow condition, engrafted cells may be destroyed because of incoming mechanical forces (47). furthermore, in portal hypertension and chronic liver diseases, the transplanted cell may be translocated to lungs through portosystemic collaterals or channels causing cardiovascular problems (figure 4) (45,77). therefore, there is an urgent need for clinical trial designing for the application of successful cell delivery methods to liver sinusoids. obviously, standards of professional practice play an important role in the clinical setting. there is no international standard for reprogrammed liver cell therapy, as cell therapy in general has been limited to heterologous primary cells with resource scarcity and little satisfactory outcome. the major obstacle in hepatocyte transplantation is poor engraftment results, encouraging researchers to suggest new strategies. prominent among these are modifying metabolic status in the recipients of liver cell therapy (78) and cotransplantation of mesenchymal stem cells (79) because of their significant effects on liver regeneration and repair. conclusion the restoration of hepatic function by patient-specific cell transplantation remains a promising strategy for liver therapy. reprogramming strategy exploits preexisting somatic cells to produce other mature cell types or progenitors. the cornerstone of this strategy is to keep the cellular genome stability during dedifferentiation and efficient redifferentiation. patient-derived hepatic cells can be transplanted directly in the form of isolated cells or as in vitro-generated liver tissue constructs. animal model data suggest that liver tissue constructs may offer better regeneration and improved survival, but teratoma formation and rejection by immune system are observed in both strategies. these occur primarily due to the presence of residual undifferentiated cells in hepatocytes derived from human ipscs. as a part of efforts toward translation of cell reprogramming science into clinical practice, more careful cell selection strategies should be integrated into improvement of dedifferentiation and redifferentiation protocols, especially in precision medicine where gene correction is needed. furthermore, advances in cellular reprogramming highlight the need for developing and evaluating novel standards addressing clinical research interests in this field. acknowledgments the research was financially supported by grants from the stem cell research center at tabriz university of medical sciences and iranian council for development of stem cell sciences and technologies. the authors would like to thank the liver and gastrointestinal diseases research center at intraportal infusion catheter through umbilical vein (in newborn) hickman line in inferior messenteric vein figure 4. liver cell transplantation routs. the portal circulation can pass directly infused cells to the liver tissue. the routine ways to directly access the portal circulation are percutaneous intraportal infusion, umbilical catheterization, and insertion of hickman line in inferior mesenteric vein. the main concerns for transplantation of reprogrammed cells include using fresh or cryopreserved hepatocytes with cell viability of more than 60%, a minimum of 109 cell/infusion, and portal pressure monitoring (77). liver cell therapy using reprogrammed cells codon publications journal of renal and hepatic disorders 2017; 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2(2): 10–19 review article imaging of renal angiomyolipomatosis federico greco, carlo augusto mallio, vincenzo cirimele, pasquale d’alessio, bruno beomonte zobel, rosario francesco grasso unit of diagnostic imaging, università campus bio-medico di roma, rome, italy abstract angiomyolipoma is a type of benign renal tumor. it is sporadic and isolated in 80% of cases. the remaining 20% is associated with tuberous sclerosis complex or pulmonary lymphangioleiomyomatosis. generally, angiomyolipomas manifest themselves as angiomyolipomatosis, in which the angiomyolipomas are larger, bilateral, and widespread. understanding whether angiomyolipomas are present in the context of angiomyolipomatosis is of considerable importance because it might be associated with malignant lesions. this article provides an overview of the radiological features of renal angiomyolipomatosis under different imaging techniques such as ultrasound, computed tomography, and magnetic resonance. keywords: angiomyolipoma; lymphangioleiomyomatosis; pecoma; renal angiomyolipomatosis; tuberous sclerosis received: 05 september 2018; accepted after revision: 21 october 2018; published: 14 november 2018 author for correspondence: federico greco, unit of diagnostic imaging, università campus bio-medico di roma, via alvaro del portillo, 21, 00128, rome, italy. email: federico.greco@unicampus.it how to cite: greco f, mallio ca, cirimele v, d’alessio p, beomonte zobel b, grasso rf. imaging of renal angiomyolipomatosis. j ren hepat disord. 2018;2(2):10–19. doi: http://dx.doi.org/10.15586/jrenhep.2018.37 copyright: greco f et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction angiomyolipoma (aml) is a type of benign renal tumor, with an estimated prevalence of 0.3–3% of all renal tumors and a greater female predilection (1, 2). it is characteristically a solid “triphasic” tumor composed of dysmorphic blood vessels, smooth muscle components, and mature adipose tissue which may be present in varying amounts (3). aml was once considered a hamartoma and, most recently, a choristoma; it is now considered a part of perivascular epithelioid cell tumors (pecoma) (4–6). pecoma are mesenchymal neoplasms formed by nests and sheets of epithelioid and spindle cells that show immunoreactivity for both smooth muscle and melanocytic markers (7). the pecomas now include aml, pulmonary clear cell “sugar” tumor and lymphangioleiomyomatosis (lam), primary extrapulmonary sugar tumor, clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres, abdominopelvic sarcoma of perivascular epithelioid cells, and other neoplasms with similar characteristics (8). renal angiomyolipomatosis is a common manifestation in patients with tuberous sclerosis (ts) and lam, where amls are larger, multiple, almost always bilateral, and have a greater predisposition to bleeding. aml is sporadic and isolated in 80% of cases, while the remaining 20% is associated with tuberous sclerosis complex (tsc) or pulmonary lam (9, 10). radiologically, the sporadic aml is predominantly classified into classic (common) and fat-poor aml (uncommon). fat-poor aml is further classified into three subtypes: hyperattenuating aml (approximately 4.5% of all amls), isoattenuating aml (rare), and aml with epithelial cyst codonpublications.comjrenhep.com mailto:federico.greco@unicampus.it http://dx.doi.org/10.15586/jrenhep.2018.37 renal angiomyolipomatosis journal of renal and hepatic disorders 2018; 2(2): 10–19 11 figure 1. ct axial scan of the abdomen during venous phase of a 45-year-old woman with ts showing the presence of renal angiomyolipomatosis (a and b) and caliectasia at the level of the left upper calyceal group (a). furthermore, a cystic lesion with solid peripheral tissue indissociable from the left inferior renal pole is evident (b). at the follow-up ct scan performed approximately 6 months later, the cystic lesion showed an increase of the solid component. consequently, the patient underwent left nephrectomy and tumorectomy. histological examination revealed the diagnosis of dedifferentiated liposarcoma. (rare). another type of sporadic aml is epithelioid aml (rare). syndromic aml is subdivided into aml in tsc and aml in lam (11).the majority (>80%) of amls are detected incidentally during imaging. most patients are asymptomatic when aml is diagnosed (10). the most common presentation is spontaneous retroperitoneal hemorrhage, although this happens in less than 15% of cases (10). other clinical presentations are anemia, hematuria, palpable mass, flank pain, urinary tract infection, or renal failure (12, 13). as most classic amls do not increase in size and remain asymptomatic, the management is conservative. however, some grow gradually, showing a growth rate of 5% or 0.19 cm per year (14, 15). oesterling et al. (16) proposed an algorithm for the management of aml based on tumor size and symptoms. for small aml (≤ 4 cm), follow-up with ultrasound (us) imaging is recommended every 12 months; for small aml in symptomatic patients, arterial embolization or partial nephrectomy can be chosen although observation is often favored in clinical practice. treatment is recommended for symptomatic patients with large tumors, especially if the aml has bled. in asymptomatic patients with large aml, follow-up with computed tomography (ct) or us is recommended (16). other options introduced for aml treatment are transarterial ethanol and percutaneous ablation using cryoablation or radiofrequency (17–19). in this article, we describe the radiological features of renal angiomyolipomatosis. a pubmed search was performed by a radiologist for the term “angiomyolipomatosis.” the research showed 20 articles published in a period from 1969 to 2013. a total of 10 articles were excluded: four in german, three in french, one in russian, and two did not describe the radiological features of renal angiomyolipomatosis. the remaining 10 articles in english, italian, and spanish languages describing radiological features of renal angiomyolipomatosis were selected. angiomyolipomatosis in tuberous sclerosis complex tuberous sclerosis is largely the result of loss-of-function mutations of tsc1 (9q34) or tsc2 (16p13.3) genes. in addition to conditions such as mental retardation and seizures, tsc is associated with amls, lam, pulmonary multifocal micronodular hyperplasia, subependymal giant cell tumors, cutaneous angiofibromas, and cardiac rabdomyomas (20). amls occur in 55–75% of patients with ts; amls in ts typically develop at a young age and are frequently multiple, almost always bilateral and larger in size, presenting as angiomyolipomatosis (figure 1) (11, 21). patients with tsc are more likely to show multiple, bilateral, and larger amls than amls in sporadic cases (22, 23). most of the amls in tsc manifest as the classic type, while fat-poor amls are found in over one-third of these patients. fat-poor amls in tsc tend to be larger than those of the sporadic form (24). as renal cell carcinoma may occur in patients with tsc, renal masses without visible characteristic adipose tissue may require a percutaneous biopsy or closer follow-up (15). patients with tsc have also shown the presence of epithelioid aml and aml with epithelial cysts; tsc patients are more likely to show these two variants of aml compared to amls found sporadically (25, 26). epithelioid aml shows variable biological behavior including malignancy; in fact, during adulthood, it can infiltrate adjacent tissue or metastasize to the lungs, liver, peritoneum, or bone (27, 28). as patients with tsc risk premature loss of nephrons due to increasing numbers and dimensions of cysts and amls, selective arterial embolization, percutaneous ablation, or partial nephrectomy are preferred conservative therapies for the treatment of these lesions (29). moreover, these patients present a high risk of spontaneous hemorrhage; aml >4 cm and aml aneurysms >0.5 cm are risk factors for aml greco f et al. journal of renal and hepatic disorders 2018; 2(2): 10–19 12 hemorrhage (30, 31). approximately 43% of patients with tsc may have recurrent aml bleeding, which is not usually seen in sporadic amls (32, 33). indeed, angiomyolipomatosis is often associated with multiple spontaneous bleeding events. the mtor inhibitor sirolimus allows the prevention of tumor growth and recurrence of bleeding in patients with tsc by inhibiting the activation of the mtor pathway (34). transcatheter embolization is an effective treatment for controlling bleeding in the acute context and can be performed in combination with surgery (17). angiomyolipomatosis in lymphangioleiomyomatosis renal angiomyolipomatosis can be detected in patients with lam, a rare disease characterized by destructive cystic changes in the lungs. sporadic lam manifests itself in one in 400,000 adult females; it may also happen in tsc, occurring in 30–40% of adult females and rarely in males and children (11, 35). in addition to renal amls, lam presents other disorders including lymphangioleiomyomas, abdominal lymphadenopathy, and chylous ascites, and an increase in the frequency of meningioma (11, 35–38). as well as sporadic amls, the guidelines for lam patients with amls recommend us examination per year for small amls (<4 cm), while larger amls and amls with aneurysms of 5 mm or greater diameter should be checked twice a year with us examination. the treatments of choice for a bleeding aml are renal arterial embolization and partial nephrectomy. furthermore, the mtor inhibitor sirolimus reduces the volume of aml (34, 35, 39). imaging features of angiomyolipomatosis several studies have described the radiological features of angiomyolipomatosis; for this review, we analyzed the radiological features described in several clinical cases. imaging features of the cases of renal angiomyolipomatosis described in the literature are listed in table 1 (40–49). renal angiomyolipomatosis generally occurs with multiple and diffuse amls, bilaterally localized. often the masses extend almost entirely covering the abdomen, displacing the table 1. imaging features of cases of renal angiomyolipomatosis references imaging method imaging features segal et al. (40) angiography hypervascular renal enlargement deformed calyces ahuja et al. (41) radiography thick mass of soft tissue with many thin cloud-like calcification figures excretory urogram marked congestion and stenosis of the left ureteral outlet left kidney well delimited right calico-pielic cavities deformed right kidney not well defined angiography prominent vascular tortuosity with aneurysmal dilatation at lower pole of the left kidney altered vascular architecture with peripheral ectasies and microaneurysm of the right kidney; furthermore, the lower pole showed a region with a roundish morphology, highly vascularized, surrounded by wide arteries and a number of blood pools delayed passage time kalra et al. (42) ultrasound dimensional increase of the kidneys multiple bilateral echogenic masses contrast enhancement computed tomography numerous irregular hypodense areas of adipose tissue density numerous isodense to hyperdense areas varying from soft tissue density to blood density poor excretion of contrast medium (continued ) renal angiomyolipomatosis journal of renal and hepatic disorders 2018; 2(2): 10–19 13 table 1. (continued ) references imaging method imaging features granata et al. (43) ultrasound and color-power-doppler (first patient) dimensional increase of the kidneys hyperechogenic parenchyma no evidence of cortico-medullary differentiation absence of localized hypervascularization areas four renal cysts hypoechoic area in the right upper pole contrast enhancement magnetic resonance imaging (first patient) coarse localized mass at the right upper pole of difficult interpretation. the differential diagnosis was with fat-poor aml, epithelioid aml, and renal cell carcinoma; biopsy examination showed a diagnosis of fat-poor aml ultrasound (second patient) dimensional increase of the kidneys irregular profiles of the kidneys structural subversion of the renal parenchyma with numerous and coarse nodules that alter to cysts magnetic resonance imaging (second patient) numerous bilateral amls liu et al. (44) unenhanced computed tomography huge bilateral masses consisting primarily of adipose tissue ponce díaz-reixa et al. (45) ultrasound and contrast enhancement computed tomography (first patient) bilateral amls ultrasound (second patient) nodule of the right kidney isoecogenous compared to perirenal adipose tissue contrast enhancement computed tomography (second patient) mass at the right kidney, with heterogeneous appearance and adipose areas in the context, highly suggestive of aml histological and immunohistochemical examination confirmed the diagnosis of aml computed tomography (third patient) mass at the right kidney, compatible with aml histological examination of the tumor demonstrated aml with epithelioid areas with infiltration of two lymph nodes that showed the same histological diagnosis er et al. (46) unenhanced computed tomography bilateral, renal masses (massive in the right kidney), with the density of adipose tissue incedayi et al. (47) ultrasound multiple bilateral hyperechogenic renal masses unenhanced computed tomography massive renal masses fluid accumulation and high-density areas at the right kidney, developed following the previous hemorrhage stallone et al. (48) ultrasound multiple renal hyperechogenic lesions contrast enhancement computed tomography multiple renal lesions, describing a framework compatible with angiomyolipomatosis. histological analysis confirmed the diagnosis of angiomyolipomatosis vergnani et al. (49) unenhanced computed tomography widespread angiomyolipomatosis in the context of which fat components and soft-tissue tumor components were evident; hematomas were also present aml, angiomyolipoma. greco f et al. journal of renal and hepatic disorders 2018; 2(2): 10–19 14 intestine. signs of previous bleeding may be present. renal cysts could also be detected. in amls with a predominantly fatty component, the adipose tissue localized within these lesions assumes fundamental importance in the diagnosis. on us examination, it appears hyperechoic compared to renal cortex. in ct examination, it appears as hypodense area of adipose tissue density, mixed, or with soft-tissue attenuation due to vascular or smooth muscle components, hemorrhage or fibrosis (2). bosniak described the angiographic features of aml. the author observed three patterns in particular: aneurysmal and tortuous vessels, berry-like aneurysms, and slow-flowing vessels with contrast medium retention (50). on magnetic resonance imaging (mri), it appears isointense compared with fat on t1-weighted images; moreover, with the use of in-phase and opposed-phase imaging, amls with predominant adipose component show the characteristic india ink artifact that appears at the interface between the lesion and the normal renal parenchyma on opposed-phase t1-weighted images. in t2-weighted images, however, the intensity can be variable, depending on the amount of adipose tissue present in the lesion, resulting homogeneously high in amls with a higher adipose component (figure 2) (51–54). the diagnosis is more difficult if there is the presence of fat-poor aml, epithelial aml, and aml with epithelial cysts, as we must discriminate these lesions from malignant lesions, such as renal cell carcinoma or the same epithelioid aml with malignant biological behavior, being able to be present in renal angiomyolipomatosis. for example, it is difficult to differentiate fat-poor aml from other solid tumors, especially renal cell carcinoma. in this case, double-echo gradient-echo chemical-shift mri could be used in which the values of the signal intensity are measured on the renal lesion and on the spleen in on-phase and opposed-phase t1weighted gradient-echo mri (54). the presence of small calcifications within the lesion, which can be easily detected with ct, is considered to be suggestive of renal cell carcinoma (55). furthermore, central necrosis is indicative of renal cell carcinoma, this being frequently present in medium-to-large clear cell renal cell carcinoma and very rare in aml. in fat-poor aml, the low amounts of adipose tissue can be detected on opposed-phase and in-phase imaging. it also appears homogeneously hypointense on t2-weighted images (53). finally, even contrast enhancement us can be used in the differential diagnosis between malignant and benign renal lesions (56). in a retrospective study, lu et al. found a slow figure 2. mri axial scan of the abdomen shows two amls of the left kidney. (a) opposed-phase shows the characteristic  india ink artifact of the amls. (b) amls appear hyperintense on t2-weighted images and (c) hypointense on t2-weighted images with fat suppression. (d) t1-weighted image with fat suppression shows contrast enhancement of the amls. renal angiomyolipomatosis journal of renal and hepatic disorders 2018; 2(2): 10–19 15 figure 3. unenhanced ct axial scan of the abdomen (a and c) and ct of the abdomen during arterious phase (b and d) of a 53-year-old woman showing the presence of classic amls, recognizable by the adipose component of the lesion. centripetal enhancement in the cortical phase and a homogeneous enhancement in the peak phase in fat-poor renal aml (57). radiologic diagnosis of renal angiomyolipoma jinzaki et al. proposed an aml classification in which clinical features, radiologic features, and pathologic features coexist. this section focuses on the radiologic characteristics indicated in the aml classification of jinzaki et al. (11). classic angiomyolipoma classic aml is a subtype of triphasic aml. the typical characteristic of classic aml is the presence of abundant adipose tissue (11). this aml almost always appears markedly hyperechoic compared to the renal parenchyma. in addition, 21–33% of amls smaller than 3 cm show acoustic shadowing (58, 59). the fat present in aml can be identified on unenhanced ct with a region of interest (roi) showing an attenuation less than −10 hu (figure 3) (50, 60, 61). the ct features of classic aml vary due to variable amounts of the three components present in the lesion (11). furthermore, intralesional hemorrhage may be present, especially in tumors larger than 4 cm (62). mri can be used to diagnose aml also by detecting fat cells; india ink artifact visible with a loss of signal at the boundary between the mass and the renal parenchyma is indicative of aml (52). differential diagnosis of classic aml is with renal cell carcinoma, wilms tumor, and retroperitoneal liposarcoma and teratoma (11). fat-poor angiomyolipoma fat-poor amls are those triphasic amls that contain too little fat to be identified with unenhanced ct (4, 63). there are three subtypes of fat-poor aml; their subdivision is based on the number of fat cells and their distribution within the lesion; they are hyperattenuating and isoattenuating amls, and aml with epithelial cysts (64). hyperattenuating angiomyolipoma hyperattenuating aml makes up about 4–5% of all amls (65). this subtype of fat-poor aml is generally small, with an average of 3 cm of diameter, and accounts for only 4% (3–10% range) of fat cells (65–67). as there is an abundant amount of smooth muscle component, they present characteristics similar to those of smooth muscle: they appear greco f et al. journal of renal and hepatic disorders 2018; 2(2): 10–19 16 hyperattenuating compared to renal parenchyma on unenhanced ct (usually greater than 45 hu); t1-hypointense and t2-hypointense on mri; no signal loss on fat-suppressed pulse sequences, and chemical shift suppression; and isoechoic on us, with one study suggesting could be hyperechoic (65–67). differential diagnosis of hyperattenuating aml is with renal cell carcinoma (typically the papillary renal cell carcinoma), metastases, oncocytoma, lymphoma, metanephric adenoma, and leiomyoma (63, 68). isoattenuating angiomyolipoma isoattenuating amls possess ct attenuations similar to those of the renal parenchyma on unenhanced ct. this type of aml does not possess regions of adipose tissue attenuation at unenhanced ct. in particular, fat cells are dispersed between smooth muscle and vessel components, too few to be detected with imaging but in sufficient quantities to reduce the overall attenuation compared to hyperattenuating aml (69). on mri, this subtype of fat-poor aml appears typically t2-hypointense. this feature is given by its smooth muscle component (70). furthermore, jinzaki et al. claim that isoattenuating aml characteristics on all mri pulse sequences are not well known because it is a rare lesion; this lesion may or may not show signal loss on fatsuppressed pulse sequences; the loss of signal depends both on the quantity and the distribution of fat cells within the lesion (11). it also shows chemical shift suppression (54, 70). jinzaki et al. also state that, based on their experience, isoattenuating aml appears slightly hyperechoic on us (11). differential diagnosis of isoattenuating aml is with renal cell carcinoma (11). angiomyolipoma with epithelial cysts aml with epithelial cysts is a very rare variant of the fatpoor aml which contains epithelial-lined cysts. these amls have very few or no fat cells (71). this subtype of aml is benign and more common in female (69, 71–74). aml with epithelial cysts contains smooth muscle component, which represents the predominant component, and epithelial cysts and subepithelial stroma, which are typical of this subtype of fat-poor aml (69, 72). the imaging features of aml with epithelial cyst are not fully understood. a case was described in which the lesion presented a small cyst, and a non-cystic part that enhanced homogeneously. this lesion appeared hyperattenuating on unenhanced ct and, on mri, t2-hypointense for the smooth muscle component (71). another case described a multilocular cystic mass with the cystic component separated from that smooth muscle (73). differential diagnosis is with multilocular cystic renal cell carcinoma, multilocular cyst, cystic nephroma, and a mixed epithelial and stromal tumor (73, 75). epithelioid angiomyolipoma epithelioid aml is a subtype of extremely rare potentially malignant aml (3, 25). male and female are equally affected and the average age is 38 years (3). approximately one-third has local extension or metastasis at diagnosis (76). epithelioid aml contains numerous atypical epithelioid muscle cells; in most of these lesions there are few or no fat cells (25, 77, 78). this aml subtype typically appears as large masses (≥5 cm in size) with intralesional hemorrhage and necrosis; it can also be detected as spontaneous perirenal hematoma (79–85). these lesions may show small foci of adipose tissue on ct or mri; moreover, epithelioid aml appears hyperattenuating on unenhanced ct (typically greater than 45 hu) and t2-hypointense (due to epithelioid muscle component) (83, 84). furthermore, this aml subtype may appear as solid masses that enhance homogeneously or heterogeneously or as multilocular cystic masses (84). differential diagnosis of epithelioid aml is with renal cell carcinoma and cystic renal cell carcinoma (25, 77, 84). new radiologic classification of renal angiomyolipoma song et al. classified renal aml into fat-rich, fat-poor, and fat-invisible aml based on the amount of fat detected by ct or mri (86). fat-rich aml was identified by attenuation value less than or equal to −10 hu obtained by placing a roi in the most hypodense area of the lesion (61). when the most hypodense area showed attenuation value greater than −10 hu, the chemical shift imaging was evaluated. tumor-to-spleen ratio and signal intensity index were calculated using the values obtained by placing the roi in the most hypointense area on opposed-phase images. fat-poor aml was detected when the tumor-to-spleen ratio was <0.71 or when the signal intensity index value was >16.5%. fat-invisible aml was detected when the tumor-to-spleen ratio was ≥0.71 and when the signal intensity index value was ≤16.5% (86). both fat-poor aml and fat-invisible aml exhibit attenuation values greater than –10 hu on unenhanced ct. song et al. showed that the attenuation value of fat-invisible aml detected in the roi located in the most hypodense area of the lesion was greater than that of the fat-poor aml (86). conclusion renal angiomyolipomatosis is a common manifestation in patients with ts and lam. amls are larger, multiple, almost always bilateral, and have a greater predisposition to bleeding, which is the reason why follow-up must be performed in these patients. furthermore, specific subtypes of aml, such as poor-fat aml, are difficult to distinguish from malignant lesions. for this reason, further imaging examinations must be performed to obtain further information on the nature of the lesions. renal angiomyolipomatosis journal of renal and hepatic disorders 2018; 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krishnan 1, debbie trinder 2,3,4, anita c. g. chua 2,3,4, aron chakera 1, grant a. ramm 5,6, john k. olynyk 2,3,7,8,9,10 1department of nephrology, sir charles gairdner hospital, perth, western australia, australia; 2school of medicine and pharmacology, university of western australia, perth, western australia, australia; 3fiona stanley hospital, murdoch, western australia, australia; 4harry perkins institute of medical research, murdoch, western australia, australia; 5qimr berghofer medical research institute, brisbane, queensland, australia; 6faculty of medicine and biomedical sciences, the university of queensland, brisbane, queensland, australia; 7department of gastroenterology, fiona stanley hospital, perth, western australia, australia; 8faculty of health sciences, edith cowan university, joondalup, western australia, australia; 9school of biomedical sciences, curtin university, bentley, western australia, australia; 10school of veterinary and life sciences, murdoch university, murdoch, western australia, australia abstract our understanding of the pathophysiology of the anaemia of chronic kidney disease (ckd) has improved considerably in the last decade with the discovery of the iron regulatory peptide hepcidin. reduced clearance of hepcidin and the presence of a chronic inflammatory state contribute to elevated hepcidin levels in kidney disease. the recent discovery of the various factors and signalling pathways regulating hepcidin has opened up an exciting avenue for research into the development of newer agents that could treat anaemia of ckd. this review highlights our current understanding of iron metabolism in health, the regulators of hepcidin, issues associated with the current available therapies for the treatment of anaemia in ckd and potential novel therapies that could be available in the near future targeting the various factors that regulate hepcidin. keywords: anaemia; chronic kidney disease; iron metabolism; hepcidin; inflammation; erythropoietin-stimulating agents received: 28 november 2016; accepted after revision: 02 january 2017; published: 03 february 2017. author for correspondence: john k. olynyk, fiona stanley hospital, 11, robin warren drive, murdoch, western australia, australia 6150, postal address: locked bag 100, palmyra dc, wa 6961. email: john.olynyk@health.wa.gov.au how to cite: krishnan ar et al. anaemia of chronic kidney disease: what we know now. j ren hepat disord 2017;1(1):11–19. doi: http://dx.doi.org/10.15586/jrenhep.2017.5 copyright: krishnan ar et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction anaemia of chronic kidney disease (ckd) is widely prevalent in patients with renal impairment and is associated with significant morbidity and mortality (1, 2). deficient erythropoietin (epo) production and reduced bioavailability of iron ultimately lead to absolute or functional iron deficiency anaemia. hepcidin, an iron regulatory protein produced in the liver by hepatocytes, plays an important role in iron metabolism by regulating iron absorption from the duodenum and iron release from macrophages by interacting with, and inactivating, ferroportin—the iron transport protein (3). hepcidin is regulated by a number of factors including iron status, inflammation, erythropoiesis and hypoxia, which are often affected by kidney disease. iron metabolism iron is an essential trace element required for a number of catabolic and metabolic processes within the body. as there are no effective means of excreting iron, the regulation of dietary iron absorption from the duodenum plays an codon publications journal of renal and hepatic disorders 2017; 1(1): 11–19 http://dx.doi.org/10.15586/jrenhep.2017.5 http://creativecommons.org/licenses/by/4.0 important role in iron homeostasis. in healthy individuals, approximately 1–2 mg of iron is absorbed from the diet per day to maintain iron balance. once absorbed, the iron is bound by the plasma protein transferrin and is transported to the tissues where most of the iron is taken up by the bone marrow for incorporation into haemoglobin for erythropoiesis and to a lesser degree by the muscle for the synthesis of myoglobin and respiratory enzymes. excess iron is stored primarily in the liver. macrophages degrade erythrocytederived haemoglobin and release the iron back into the plasma so that it can be re-utilised for erythropoiesis in the bone marrow. if the availability of iron for erythropoiesis is insufficient, anaemia will develop. too much iron can result in iron overload. common causes include genetic diseases such as hereditary haemochromatosis and acquired causes such as from transfusional overload and repeated parenteral iron infusions. iron excess is detrimental to health as this generates free radicals causing oxidative stress and tissue damage primarily in the liver, heart and pancreas (4–8). hepcidin and its regulators iron metabolism is tightly regulated by the hormone hepcidin which is highly expressed by hepatocytes and at lower levels in other tissues including the kidneys (9). hepcidin, a 25amino acid cysteine-rich peptide, is a negative regulator of iron absorption by the intestine and iron release from macrophages and hepatic stores. it is secreted into the circulation and binds to the iron exporter ferroportin, expressed on the surface of enterocytes, macrophages and hepatocytes, causing ferroportin internalisation and degradation. this limits the absorption and release of iron and increases retention in the liver and macrophages (6, 10). in addition to regulating iron metabolism, hepcidin may also contribute indirectly to host defence mechanisms by reducing body iron concentrations, as iron is needed for bacterial growth and low levels of iron are thought to be bacteriostatic. in murine models and cultured macrophages, hepcidin has been found to modulate lipopolysaccharide-induced transcription, suggesting it might have a role in modulating acute inflammatory responses to bacterial infections (11, 12). the two main positive regulators of hepcidin are iron status and inflammation with higher levels limiting the availability of iron for erythropoiesis and other iron-dependent processes. similarly, erythropoiesis and hypoxia downregulate hepcidin expression, resulting in increased bioavailability of iron (figure 1). these factors regulate hepcidin levels via pathways listed in table 1, and some of these pathways could be potential targets for novel therapies to treat anaemia of ckd. regulation of hepcidin iron status tissue iron stores and circulating transferrin-bound iron exert distinct signals that regulate hepcidin expression in hepatocytes. hepcidin gene transcription is stimulated by the dual effect of liver iron stores and the concentration of plasma holotransferrin (iron-saturated transferrin), conveyed through iron-regulated production of bone morphogenetic proteins (bmp) acting on bmp receptors and the associated mothers against decapentaplegic-related protein (smad) pathway (13). intracellular iron stores interact with hepcidin via the bmp6 pathway activating smad and increasing hepcidin levels. circulating transferrin-bound iron exerts its effects via the haemochromatosis protein (hfe)/transferrin receptor 2 (tfr2) pathway (14, 15). mutations of these receptors are associated with hereditary haemochromatosis resulting in iron overload via dysregulated hepcidin expression (16, 17). inflammation hepcidin levels are increased by states of inflammation, and this is thought to have evolved as a host defence mechanism. interleukin-6, acting through the jak2/stat3 pathway and, to a lesser extent, interferon γ, and interleukin-1 are the primary inflammatory inducers of hepcidin expression (18, 19). recently, a new inflammatory signalling pathway was identified, stimulating hepcidin production via activin b, bmp receptors and smad (20). hypoxia this is a potent inhibitor of hepcidin production, even in the absence of anaemia, and thus increases iron availability (18). hypoxia-inducible factors (hifs) are transcription factors that regulate expression of genes in response to hypoxia including genes required for iron metabolism and erythropoiesis. epo synthesis is regulated in the liver and kidney via hif-2α. hif activity is controlled by prolyl-4-hydroxylase domains (phd), which act as oxygen sensors. at normal oxygen concentrations, phd enzymes hydroxylate the hif-α subunit resulting in its rapid degradation. at lower concentrations of oxygen, hif–ph activity is reduced, and there is accumulation of hif-α, leading to increased levels of epo and its receptor, and decreased hepcidin levels, ultimately increasing iron availability and erythropoiesis (21–24). similar effects were seen during hypoxia at high altitude. in a study of healthy volunteers who were exposed to high altitude levels (3400–5400 m above sea level), hypoxia induced a marked suppression of hepcidin, which appeared to result from the combined action of hypoxia-induced increased erythropoiesis and iron depletion (25). erythropoiesis increased erythropoiesis appears to suppress hepcidin levels, allowing for higher iron bioavailability to meet increased demands for red blood cell production in such states. erythroferrone (erfe), a relatively new hormone identified in 2014, was found to regulate iron metabolism by decreasing hepcidin levels during periods of stress erythropoiesis (26). this protein krishnan ar et al. codon publications journal of renal and hepatic disorders 2017; 1(1): 11–19 12 is thought to be the long-sought erythroid factor that inhibits hepcidin during increased erythropoietic activity and may contribute to the pathogenesis of iron-loading anaemias. kautz et al. showed in animal models that bleeding or administration of epo leads to release of erfe from erythroblasts, which acts directly on hepatocytes to suppress hepcidin (26). in ineffective erythropoiesis, erfe secreted by the massively increased numbers of erythroid precursors may overwhelm the iron storage signal and shut off hepcidin production (26, 27). erythropoietin-stimulating agents (esas) are widely used to treat anaemia of ckd. esas significantly suppress levels of serum hepcidin and ferritin, resulting in effective erythropoiesis liver iron iron iron iron iron intestine iron macrophage erythropoiesis hypoxia erfe erfe epo kidney bone marrow normal iron homeostasis positive regulations inflammation iron negative regulators erythropoiesis hypoxia chronic kidney disease positive regulators inflammation iron therapy erythropoietin deficiency negative regulators iron deficiency anaemia hypoxia erythropoietin therapy iron inflammation hepcidin hepcidin ferroportin ferroportin ferroportin figure 1. schematic representation of the role of hepcidin in iron metabolism in health and in chronic kidney disease (ckd). both iron and erythropoietin (epo) are required for the production of red blood cells in the bone marrow. hepcidin regulates iron absorption from the intestine, macrophage iron recycling from senescent red blood cells and iron release from the liver via ferroportin, the iron transport protein. hepcidin causes degradation of ferroportin leading to cellular iron retention and decreased absorption of ingested iron. several factors including iron and inflammation act directly on the liver to up-regulate hepcidin production. erythropoiesis and hypoxia negatively regulate hepcidin production indirectly, by increasing epo production by the kidneys. this stimulates synthesis of erythroferrone (erfe) by the bone marrow, which in turn controls liver hepcidin production. in ckd, anaemia occurs due to reduced epo production from the kidneys and from reduced iron absorption and availability, the latter resulting from elevated levels of hepcidin. in ckd, hepcidin levels are raised due to the combination of increased inflammation, decreased epo levels and reduced renal clearance. epo therapy decreases hepcidin levels leading to iron mobilisation from body stores during erythropoiesis. table 1. regulation of hepcidin regulators signalling pathway iron status bmp6/smad and hfe/tfr2 inflammation (interleukin-6) jak2/stat3, activin b hypoxia hifs and epo erythropoiesis epo and erfe bmp6: bone morphogenic protein 6; smad: mothers against decapentaplegic-related protein; hfe/tfr2: haemochromatosis iron protein/ transferrin receptor 2; jak: janus kinase; stat3: signal transducer and activation of transcription 3; hifs: hypoxia-inducible factors; epo: erythropoietin; erfe: erythroferrone. anaemia of chronic kidney disease codon publications journal of renal and hepatic disorders 2017; 1(1): 11–19 13 and release of stored iron (28, 29). honda et al. examined the association between erfe and biomarkers of iron metabolism in haemodialysis patients and found that levels of erfe were inversely correlatedwith levelsof hepcidin and ferritin and positively correlated with soluble transferrin receptor. they also showed that the use of esas increased the levels of erfe that regulated hepcidin and led to iron mobilisation from body stores during erythropoiesis (30). additional studies of this pathway and its potential effects in ckd are warranted. anaemia of ckd anaemia is a common feature of ckd, which increases in prevalence as the severity of ckd progresses. anaemia in patients with renal failure is associated with poor quality of life and high morbidity rates as evidenced by increased hospitalisations and incidence of cardiovascular disease incorporating left ventricular hypertrophy, heart failure and higher rates of mortality from adverse cardiac events (31, 32). anaemia of ckd is typically normochromic and normocytic and is thought to result from two main mechanisms— deficient production of epo by the kidney and reduced iron absorption and availability. in ckd, iron deficiency can be classified into absolute iron deficiency (marked by low iron stores and circulating iron concentrations) and functional iron deficiency (marked by low circulating iron in the setting of normal iron stores), with both forms leading to ironrestricted erythropoiesis that leads to anaemia of ckd as well as esa hyporesponsiveness (33). the reduced absorption and bioavailability of iron is thought to result from excessive production of hepcidin (34, 35), partly contributed by reduced renal clearance (36–38) and partly in response to elevated interleukin-6 or other proinflammatory cytokines produced in ckd (6, 39, 40). ckd is associated with a chronic inflammatory state, in particular, elevated interleukin-6 plasma levels, which are a major mediator of the acute-phase response. in in ckd patients, higher levels of interleukin-6 may be related to loss of kidney function, uraemia and its sequelae (such as fluid overload and susceptibility to infections) and possibly dialysis related factors. (41). excess levels of hepcidin contribute to impaired dietary iron absorption and iron release from body stores (37, 42, 43). reduced iron availability occurs due to retention of iron in macrophages and hepatocytes, thus elevating iron stores but reducing serum iron and transferrin saturation levels (functional iron deficiency), causing anaemia even in the presence of adequate iron reserves, in contrast to true iron deficiency. additional mechanisms have been suggested to contribute to the pathogenesis of anaemia of ckd, including shortened red blood cell lifespan, nutritional deficiencies (folate and b12) due to anorexia, loss via dialysis and increased iron losses (due to uraemia-related platelet dysfunction causing subclinical blood loss, frequent phlebotomy and trapping of blood in dialysis circuits) (44, 45). more recently, there has been an interest in vitamin d and its associations with anaemia. initially, this was attributed to the anti-inflammatory and pro-erythropoietic effects of vitamin d (46). data now suggest that vitamin d may actually modulate iron homeostasis via hepcidin, with a study showing that 1,25-dihydroxycholecalciferol directly inhibits hepcidin expression by binding to a vitamin d response element in the gene coding for hepcidin (47). current management of anaemia of ckd intravenous iron therapy and esas are the cornerstones of current therapy for anaemia related to ckd; however, they are not without their side effects. issues with iron therapy with regard to iron administration during episodes of acute infection or inflammation which results in elevated serum ferritin levels, opinions suggest that iron therapy should be withheld under such circumstances, citing a concern that iron may further help in the proliferation of microorganisms. iron loading has been shown to be associated with worse outcomes in infectious diseases such as malaria, tuberculosis and hiv (48–50). however, surprisingly, the recent intravenous iron or placebo for anaemia in the intensive care unit (ironman) clinical trial demonstrated no adverse effects of ironadministration in acutely unwell intensive care patients but there were significant improvements in haemoglobin levels (51). moreover, there are concerns related to iron therapyinduced iron overload, with a study by barany et al. suggesting that haemodialysis patients with very high ferritin levels have a mean liver iron concentration similar to that of patients with untreated idiopathic haemochromatosis (52). iron deposition has been associated with the pathogenesis of several other disorders such as diabetes mellitus, neurodegenerative diseases and atherosclerosis (53–55). iron could be a potential link between oxidative stress and cardiovascular disease (56, 57). iron has been found in advanced human atherosclerotic plaques (58), and free iron may play a role in plaque destabilisation post intra-plaque haemorrhage (59), although, despite pathogenic hypotheses, hard evidence linking iron, oxidative stress and cardiovascular disease is limited (60). also, the long-term effects of high-dose iron therapy remain unclear. large prospective randomised controlled trials in the ckd population are long overdue to assess the efficacy of recurrent iron infusions with regard to long-term safety, mortality and morbidity. in the absence of clear target values for serum ferritin and transferrin, clinicians continue to make a case-by-case decision on the best treatment option for their patients. advent of esas the treatment of anaemia of ckd was revolutionised in the 1980s with the development of recombinant esas, which has reduced the need for blood transfusions (which in turn krishnan ar et al. codon publications journal of renal and hepatic disorders 2017; 1(1): 11–19 14 reduces the chances of acquiring blood-borne infection and avoids sensitisation in potential renal transplant candidates) (61, 62) and improves exercise tolerance, quality of life symptoms and left ventricular hypertrophy (63, 64). risk profile of esas the target haemoglobin level in the treatment of ckd has been debated for some time, and a number of clinical trials have sought to assess whether full correction of anaemia to normal levels confers benefits; however, results have been disappointing. in 2006, two large randomised control trials in ckd showed that complete correction of anaemia had no effect (65) or conferred a greater risk for attaining the primary composite cardiovascular endpoint (66). the trial to reduce cardiovascular events with aranesp therapy (treat)-diabetic patients showed no survival benefit in patients when a haemoglobin target of 13 g/l was set and a secondary analysis suggested higher risk for stroke, death resulting from cancer in patients with a history of malignancies, and venous and arterial thromboembolic events (67, 68). another limitation of esas is that they also necessitate regular injections, either subcutaneous for patients with ckd and on peritoneal dialysis or via the intravenous route for patients on haemodialysis. supra-physiologic effects of esas, especially at high doses, have off-target effects on other cell types expressing epo receptors including endothelial cells. this results in adverse effects such as hypertension (69), intimal hyperplasia especially in the setting of inflammation (70) and promotion of tumour growth (71). other drawbacks include the development of esa hyporesponsiveness (which can occur in 10%–20% of patients with end-stage kidney disease). patients needing greater doses are those with concomitant infectious, inflammatory or malignant conditions resulting in relative esa resistance, which may contribute to increased mortality (72). given the high costs and potential disadvantages of esas, further elucidation of the molecular mechanisms of anaemia in ckd and the development of better targeted therapies have become a priority. the hunt for new therapies pentoxifylline given that inflammation contributes to elevated hepcidin levels and may contribute to esa hyporesponsiveness, it was thought that pentoxifylline might partially correct proinflammatory cytokines levels in ckd, resulting in improved iron utilisation and erythropoiesis. the drug has been shown to have anti-inflammatory properties (anti-apoptosis, antioxidant, anti-tnf-α and anti-ifn-γ) (73–75). in the handling erythopoietin resistance with oxpentifylline (hero) trial, which was a double-blind, randomised, placebo-controlled trial, johnson et al. studied the effects of pentoxifylline on esa hyporesponsive anaemia in 53 patients with ckd stage 4 or 5 (including dialysis) (76). although pentoxifylline did not significantly modify esa hyporesponsiveness as measured by the erythropoiesis resistance index, it did safely increase mean haemoglobin concentration significantly, relative to the control group. a smaller sub-study of the hero trial examined the effect of pentoxifylline on serum hepcidin level but found no significant difference in patients who received the drug as compared to those on placebo (77). a small uncontrolled pilot study that looked at the effect of this drug on inflammation showed that pentoxifylline reduced levels of interleukin-6 and improved haemoglobin levels in non-inflammatory moderate to severe ckd (78). a systematic review and meta-analysis of 11 studies did not demonstrate conclusive effects of pentoxifylline on haematocrit and esa dosing (79). whether this drug may provide any benefits remains to be seen in larger randomised trials. hif–ph inhibitors the role of hypoxia in hepcidin regulation has been briefly explained above. small-molecule inhibitors of the phd enzymes mimic the response to a cellular reduction in oxygen levels, increase hif levels and thereby increase epo production, thus promoting erythropoiesis. these drugs are in various phases of clinical development for the treatment of renal anaemia. one such agent roxadustat, an oral hif–ph inhibitor, was trialled in 60 incident dialysis patients in a phase 2 clinical trial and was shown to increase haemoglobin levels by ≥2.0 g/l within 7 weeks, regardless of baseline iron repletion status, c-reactive protein levels, iron regimen or dialysis modality. it was also found to reduce serum hepcidin levels. roxadustat by inhibiting hif–phs results in increased levels of hif and stimulates erythropoiesis (80). more recently, pergola et al. studied the effect of vadadustat as compared to placebo in 210 non-dialysis-dependent ckd patients (stages 3–5) in a 20-week multi-centre phase 2b study (81). they showed that 55% of the candidates who received vadadustat achieved the primary end point (percentage of participants who during the last 2 weeks of the treatment achieved or maintained a mean haemoglobin level of >11 g/dl or an increase in haemoglobin level of ≥1.2 g/dl over the pre-dose average) as compared to 10% of the placebotreated candidates, and the drug raised and maintained haemoglobin in a predictable manner with no significant side effects as compared to placebo. they noted significant increases in both reticulocyte and total iron-binding capacity and significant decreases in both serum hepcidin and ferritin levels. similar small preclinical and clinical studies have demonstrated some pleiotropic effects of this class of drug (molidustat corrected anaemia in rat studies and also helped normalise blood pressure; daprodustat was shown to improve cholesterol levels) (82, 83). advantages of this new class of drug include oral administration, low immunogenicity, anaemia of chronic kidney disease codon publications journal of renal and hepatic disorders 2017; 1(1): 11–19 15 product stability and possibly lower costs as well as potential cardiovascular benefits (84). safety concerns of targeting the hif pathway include the potential for raised vascular endothelial growth factor (vegf) production, which is a hif-related angiogenic growth factor known to be associated with vasculopathies and progression of tumour growth (85), and the potential for development of pulmonary and systemic hypertension, given the role of hif in regulation of vascular tone (86, 87). results of phase 3 trials that continue to monitor for these side effects are awaited. hepcidin antagonists several agents that can antagonise hepcidin are under development, including neutralising hepcidin peptide by antihepcidin antibodies or by engineered hepcidin binders such as anticalins (engineered human proteins that can bind specific target molecules). cooke et al. demonstrated an increase in haemoglobin by 1.5 g/dl within 1 week of injection of an anti-hepcidin antibody in humanised murine models where endogenous mouse hepcidin was replaced by human hepcidin and inflammation was induced using heat-killed brucella abortus (88). the most effective method was the combination of esa and anti-hepcidin antibody, which increased haemoglobin by >3 g/dl after 1 week compared with inflamed mice injected with a control antibody. the improvement in haemoglobin resulted from increased serum iron levels and better haemoglobinisation of erythroid precursors, without affecting inflammatory responses in these mice. pieris pharmaceuticals are conducting a phase 1b placebo-controlled study using a hepcidin-antagonist in patients on dialysis, after demonstrating that the drug was shown to reduce hepcidin levels and increase serum iron and transferrin saturation in 48 healthy male subjects in a single ascending dose study with no significant adverse effects (89). vitamin d recent studies have shown that vitamin d concentrations are inversely associated with hepcidin levels and positively associated with haemoglobin and iron concentrations (36, 90, 91). zughaier et al. demonstrated in vitro that vitamin d is associated with reduced production of pro-hepcidin cytokines such as il-6 and interleukin-1β. in their in vivo pilot study of 38 patients with early stage (2/3) ckd who received high doses of oral vitamin d3 as compared to placebo, the percent change from baseline to 3 months in serum 25-hydroxy cholecalciferol concentrations was inversely associated with the percent change in serum hepcidin levels (92). these findings are relevant as a large majority of patients with ckd are vitamin d deficient, and correction of vitamin d levels, as an adjunct therapy, is attractive, given the inexpensive cost, easy availability, favourable safety profile and potential to reduce dependence on other more expensive therapies. future considerations although there is uncertainty surrounding optimal laboratory investigations and haemoglobin targets, our understanding of the mechanisms causing anaemia in ckd has improved over the years. new markers of anaemia are being investigated, and a number of new agents are in evaluation, awaiting completion of phase 2/3 clinical trials. these novel treatments may not only be safer and cheaper but could also reduce our dependence on iron and esas 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transduction. this includes remodelling of the extracellular matrix, release of membrane-bound cytokines and receptor ectodomains, as well as the initiation of intracellular signalling cues. members of the adamalysin protease subfamily, in particular the adam (a disintegrin and metalloprotease) and adamts (the adam containing thrombospondin motif) families, are involved in these processes. this review presents an overview of how adam and adamts proteins are involved in liver physiology and pathophysiology. keywords: adam; adamts; metzincin superfamily; thrombotic thrombocytopenia purpura; von willebrand factor received: 10 december 2018; accepted after revision: 17 january 2019; published: 07 february 2019 author for correspondence: dirk schmidt-arras, christian-albrechts-university kiel, institute of biochemistry, kiel, germany. email:  darras@biochem.uni-kiel.de how to cite: bolik j. et al. adam and adamts proteases in hepatic disorders. j ren hepat disord. 2019;3(1):23–32 doi: http://dx.doi.org/10.15586/jrenhep.2019.47 copyright: bolik j. et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction the liver harbours different cell types, including hepatocytes, cholangiocytes, resident macrophages called kupffer cells (kcs), sinusoidal endothelial cells (secs) and hepatic stellate cells (hscs). hepatocytes, the liver parenchymal cells, make up the vast majority of cells and fulfil multiple vital body functions such as protein synthesis and storage; detoxification; synthesis of cholesterol, phospholipids and bile salts; and secretion of bile. bile is then stored in the gallbladder and drained through bile ducts formed by cholangiocytes to aid in the digestion and absorption of dietary fats and fat-soluble vitamins in the duodenum. the liver sinusoids are lined with kcs and secs, while hscs represent perisinusoidal cells found in the space of disse, an area between liver secs and hepatocytes. in homeostatic conditions, hscs store fat and fat-soluble vitamins in the liver, in particular vitamin a (retinol, retinoic acid). upon acute liver damage, hepatocytes restore the lost liver mass by proliferation and hypertrophy (1). however, under chronic toxic, viral or carcinogenic insult, the proliferation of hepatocytes is inhibited, and they often become senescent. under these circumstances, hepatic progenitor cells (hpcs) are activated and observed to proliferate in a variety of chronic liver diseases, including alcoholic liver disease, non-alcoholic fatty liver disease, steatohepatitis and in the iron overload disorder, haemochromatosis. hpcs are small, stem-cell-like cells with unclear origin and have the capacity to differentiate into hepatocytes or cholangiocytes, depending on the underlying injury stimulus (2). damage signals from cellular compartments lead to the transdifferentiation of hscs to proliferative and fibrogenic myofibroblasts. these “activated” hscs respond by depositing collagen, resulting in the formation of scar tissue, which may progress to liver cirrhosis in severe cases. numerous studies have reported a close temporal and spatial organisation of kcs, hpcs and hscs, which display an intimate interplay and orchestrate liver regeneration versus disease progression through cytokine and chemokine cross-talk (2–6). these complex signalling networks require precise regulations not only at the cellular level but also at the molecular level. members of the metzincin journal of renal and hepatic disorders 2019; 3(1): 23–32 p u b l i c a t i o n s codon journal of renal and hepatic disorders mailto:darras@biochem.uni-kiel.de http://dx.doi.org/10.15586/jrenhep.2019.47 http://creativecommons.org/licenses/by/4.0 bolik j. et al. journal of renal and hepatic disorders 2019; 3(1): 23–32 24 protease family have been shown to be involved in different aspects of chronic liver disease and tumour formation. the metzincin superfamily the superfamily of zinc proteases or metzincins is characterised by the presence of a protease domain containing an invariant hexxhxxgxxh zinc-binding motif (7, 8). it is subdivided into four subfamilies: matrixins, adamalysins, astacins and bacterial serralysins. the svmps (snake venom metalloproteinases), the adams (a disintegrin and metalloproteinases) and adamts (adams containing thrombospondin motifs) form the adamalysin subfamily (9). the catalytic domains of metzincins share a similar overall structure with the catalytic cleft positioned between an n-terminal subdomain (nsd) and a c-terminal subdomain (csd) (8). the nsd is anchored by a five-stranded β sheet, followed by a central α helix which contains the hexxh motif supplying two of the histidines involved in zn2+-coordination and the glutamate residue that participates in catalysis (figure  1). c-terminal to the α-helix, a conserved methionine turn is packed against the zinc-binding site (8, 10). both adam and adamts protein structures are thought to exist as “open” or “closed” structures representing another layer of regulation. currently, this has been shown for the members adam17 and adamts4 and 5, respectively (11, 12). in the case of the closed adamts4 conformation, movement of the s2’ loop towards the catalytic centre precludes substrate binding and leads to the release of an additional ca2+ ion (11). the adam family in mammals, adams are expressed in a wide range of tissues. given their numerous substrates, they have diverse functions in development, physiology and pathology (9). the human genome encodes for 22 functional adam proteins, of which 10 are considered proteolytically inactive (13). adams without protease activity are thought to facilitate protein folding and protein–protein interactions. the domain structure of adam proteases comprises an n-terminal inhibitory pro-domain, a catalytic metalloprotease domain, a disintegrin domain with a cysteine-rich region, an epidermal growth factor (egf)-like domain, a transmembrane domain and a cytoplasmic tail (figure 1a). adam proteases are synthesised as catalytically inactive transmembrane proteins of about 750 amino-acid length into the endoplasmic reticulum. the n-terminal pro-domain is thought to have chaperone and inhibitory functions as it interferes with the zn2+-ion in the catalytic centre. within the golgi apparatus, adams undergo further complex glycosylation and are subjected to proteolytic cleavage by the furin protease, thereby liberating the n-terminal pro-domain. however, for adam8 and adam28, autocatalytic pro-domain cleavage was demonstrated (14, 15). recently it has been shown that the recombinant pro-domain of adam17 can be harnessed as a specific inhibitor in vitro and in vivo (16). the catalytic domain is conserved among the adam family members and contains the zinc-binding motif (hexghxxgxxhd) (figure 1 a and b) (17). the adjacent disintegrin and cysteine-rich domains are suggested to be involved in autoregulation as they fold back and limit access to the catalytic site in the unliganded state (10, 18). the disintegrin domain may also participate in cell–cell adhesion processes and has been shown for adam10 to play a role in substrate recognition in concert with the cysteine-rich domain (9, 19). the cytoplasmic tails of transmembrane adams contain phosphorylation sites for several kinases, denoting a role in regulation of protease activity and downstream signalling (9). adam-mediated shedding can either be constitutive or activated by g-protein-coupled receptors; ser/thr-kinase activity, including protein kinase c (pkc), erk and p38; and increased intracellular ca2+(9, 20, 21). adam proteases play a major role in proteolytic ectodomain cleavage, a process termed “shedding” (figure 2). functionally diverse proteins have been shown to be subjected to ectodomain shedding with differential physiological consequences. shedding of receptor molecules such as transforming growth factor (tgf) β receptor abrogates its signalling. importantly, the soluble ectodomain has the capacity to work as a scavenger and binds the corresponding cytokine (22). the receptor for interleukin 6 (il-6) is an exception because the il-6/soluble il-6r (sil-6r) complex figure 1. general structure of adam and adamts proteases. (a) general domain structure of adam proteases. (b) x-ray structure (6be6.pdb) of adam10, including catalytic, disintegrin and cysteine-rich domains. the catalytic zinc is highlighted in grey and the zinc-binding motif in pale green. (c) general domain structure of adamts proteases. (d) x-ray structure of adamts1 (2v4b.pdb), including catalytic and disintegrin domain. the catalytic zinc is highlighted in grey and the zinc-binding motif in pale green. adam and adamts in the liver journal of renal and hepatic disorders 2019; 3(1): 23–32 25 figure 2. signal activities of adam and adamts proteinases in the liver. (a) adam protease activity, adam17 in particular, can be regulated by protein phosphorylation. active adam proteases are involved in the release of receptor ectodomains, thereby blunting receptor signalling in most of the cases, the release of membrane-bound cytokines and the initiation of intracellular signalling by regulated intramembrane proteolysis (rip). (b) selected proteolytic events of the indicated adam proteinases in different cell types of the liver. (c) selected proteolytic and non-proteolytic events of the indicated adamts proteinases in different hepatic cell types. bec, biliary epithelial cells; ec, endothelial cell; gp130, glycoprotein 130; hsc, hepatic stellate cells; hc, hepatocyte; icd, intracellular domain; il-6r, interleukin 6 receptor; kc, kupffer cell; lap-tgfβ, latency-associated peptide-transforming growth factor β; mica, mhc class i polypeptide-related sequence a; sil-6r, soluble il-6r; vwf – von willebrand factor. induces signalling via gp130 on target cells. this process has been termed “il-6 trans-signalling.” (23, 24) membrane-bound cytokines and growth factors are also liberated from the membrane by ectodomain shedding ( figure  2). the most prominent example is the family of egf ligands, comprising heparin-binding egf (hb-egf), tgfα, epiregulin and neuregulin, which are shed by adam17, and known to play key roles in tumour growth (25). the most prominent substrate of adam10 is the notch receptor, which has been implicated in developmental processes, stem cell growth and differentiation (26). in addition, there is evidence that adams are able to degrade extracellular matrix (ecm) components: adam10 cleaves type iv collagen; adam13 and adam9 degrade fibronectin (27). adam9 adam9 processes a wide range of substrate molecules, including amyloid precursor protein (app), collagen xvii and hb-egf, and has been linked to cell proliferation, adhesion and migration (28). transcriptomic analysis of fibrotic liver tissue revealed that expression of adam9 correlated with the activation of hscs, as assessed by quantitation of alpha-smooth muscle actin (αsma), independent of the underlying disease aetiology. northern blots analysis demonstrated that adam9 expression was localised to hscs (figure 2b) and that expression of adam9 significantly increased in activated compared to quiescent hscs (table 1) (29). these data suggest that adam9 is important for ecm remodelling during hepatic fibrosis progression and may bolik j. et al. journal of renal and hepatic disorders 2019; 3(1): 23–32 26 table 1. overview of known adam and adamts proteinase activities in the liver and their association with hepatic diseases. the adam family family member associated disease substrate(s) cell type reference adam9 fibrotic liver disease ecm components activated hscs (29, 30) hcc mic-a hepatocytes (32) liver metastasis laminin, binding to integrin α 6 β 4 , α 2 β 1 activated hscs (33) adam10 liver homeostasis pot. indep. of catalytic activity hepatocytes, hpcs (37) liver fibrosis cx3cl1 activated hscs (38, 39) murine cholestasis c-met hepatocytes (41) hcc mic-a hepatocytes (39) liver metastasis l1cam tumour cells (43) c-met hscs (44, 45) adam12 cirrhotic liver pot. ecm remodelling activated hscs (47) hcc pot. ecm remodelling activated hscs (48) adam17 liver damage cx3cl1 activated hscs (38) hcc notch activated hscs (53) pot. egfr ligands hepatocytes (50, 51) pot. il-6r kupffer cells (56) the adamts family family member associated disease substrate(s) cell type reference adamts1 fibrotic liver disease binding to lap-tgfβ hscs (59) adamts2 murine liver fibrosis pro-collagen hscs (62) adamts13 sah vwf endothelium (71) ali, alf (72) fibrotic liver disease (74–78) adam, a disintegrin and metalloprotease; adamts; the adams containing thrombospondin motif; ecm, extracellular matrix; hcc, hepatocellular carcinoma; mic-a, major histocompatibility class i-related chain a; hsc, hepatic stellate cell; hpc, hepatic progenitor cell; l1cam, l1 cell adhesion molecule; il-6r, interleukin 6 receptor; egfr, epidermal growth factor receptor; lap-tgfβ, latency-associated peptide-transforming growth factor β; sah, severe alcoholic hepatitis; ali, acute liver injury; alf, acute liver failure; vwf, von willebrand factor. thereby contribute to the establishment of an environment conducive to hepatocellular carcinoma (hcc). indeed, various studies have reported adam9 overexpression in hcc (30–32), and high expression levels of adam9 have been linked to tumour aggressiveness (30). beside its effect on hscs, adam9 was found to promote ectodomain shedding of major histocompatibility class i-related chain a (figure 2b). consequently, hcc cells with sirnamediated suppression of adam9 were more susceptible to natural killer cell-mediated cytolysis. interestingly, sorafenib-treatment reduced adam9 expression, and enhanced major histocompatibility class i-related chain a protein levels and anti-tumour response of natural killer cells (32). an alternatively spliced adam9 variant (adam9-s), secreted by activated hscs and stromal liver myofibroblasts, has been shown to promote tumour metastasis to the liver (table 1). through its disintegrin domain, adam9-s directly binds to α 6 β 4 and α 2 β 1 integrins on colon carcinoma cells and is able to cleave laminin, thereby promoting tumour cell invasion (33). adam and adamts in the liver journal of renal and hepatic disorders 2019; 3(1): 23–32 27 adam10 in most tissues investigated, adam10 is the major protease that initiates notch signalling. in the liver, biliary tree formation (34, 35) and differentiation of hpcs into cholangiocytes (4) are dependent on notch signalling (figure 2a). this is also reflected by the finding that patients with alagille syndrome who suffer from biliary paucity and subsequent cholestasis display mutations in the notch ligand jagged-1 (36). we recently investigated the role of adam10 under physiological conditions by generating liver-specific adam10-deficient mice. surprisingly, we observed that adam10 was dispensable for notch2 activation in vitro in an hpc line, and for biliary tree formation in vivo (37), further suggesting that during development, notch signalling in hepatoblasts does not rely on adam10. however, we observed that hepatic loss of adam10 leads to the down-regulation of biliary transporters, resulting in spontaneous hepatocyte necrosis (table 1). furthermore, loss of adam10 resulted in an accumulation of hpcs that might at least, in part, be the consequence of enhanced signalling through the hepatocyte growth factor receptor c-met (37). overexpression of adam10 has been reported in chronic liver disease associated with liver fibrosis (38) and in hcc (39, 40) (table 1). in hscs, adam10 is involved in the release of the soluble chemokine, cx3cl1, thereby facilitating recruitment of inflammatory cells (38). furthermore, c-met ectodomain release by adam10 from hscs correlated with hepatic injury in the murine 3,5-diethoxycarbonyl-1,4-dihydrocollidine (ddc) cholestasis model (41). soluble c-met has previously been identified as a decoy receptor and might therefore restrict the proliferative response after liver damage (42). sirna-mediated suppression of adam10 in the human liver cancer cell line, hepg2, decreased cellular proliferation, the ability to grow in semi-solid medium and its tumorigenic potential in xenografts (39, 40). adam10 might also be involved in anti-tumour immunity as it has been demonstrated that major histocompatibility class i-related chain a is a substrate for adam10 in hepg2 cells ( figure  2b, table  1), where its surface localisation was enhanced in the absence of adam10 (39). inhibition of adam10 might therefore represent an attractive avenue to increase the anti-tumour immune response. in addition to its role in fibrotic liver disease and hcc, adam10 seems to have a role in the establishment of liver metastasis. the neuronal cell adhesion receptor l1-cam, which is expressed on colon cancer cells, is proteolytically processed by adam10, generating a l1-cam intracellular domain (icd). an increased l1-cam icd formation through enhanced adam10 activity resulted in enhanced liver metastasis (table 1) (43). furthermore, tumour cell-secreted tissue inhibitor of metalloproteinase (timp) 1 was shown to inhibit adam10-mediated c-met processing (figure 2b) and thereby c-met signalling in liver metastasis. suppression of timp-1 lowered the metastatic potential of tumour cells, while circulating timp-1 levels correlated with an increased risk for liver metastasis formation (44, 45). very recently, the same group demonstrated that timp-1 secreted from pancreatic premalignant lesions activates hscs in the liver via binding to the tetraspanin cd63, thereby preparing a hepatic premetastatic niche (46). adam12 due to alternative splicing, adam12 can be expressed as a long (adam12l) or as a short (adam12s) form. the latter is soluble due to its lack of transmembrane and cytoplasmic domains (47). both adam12 isoforms were found to be up-regulated upon tgfβ stimulation in activated hscs but not in hepatocytes. furthermore, expression of adam12 was increased in cirrhotic livers and liver cancer and localised to cells of the tumour stroma, presumably hscs (table 1) (30, 48). adam12 was also detectable in circulation and correlated with overall survival (48). interestingly, in another study, overall patient survival and adam12 expression correlated with the expression of the tetraspanin tspan8 (49), which is often up-regulated in hcc (50). down-regulation of tspan8 in hcc lines reduced adam12l expression and tumourigenicity in a mouse xenograft model (49). however, more in-depth analysis is needed to identify definite substrates of adam12 and decipher its potential role in tumour stroma dynamics and ecm remodelling. adam17 reports using in vitro experiments demonstrated that adam17 mediates the release of egfr ligands in hepatocytes upon exposure to tumour necrosis factor (tnf) α (51) or tgfβ (52), suggesting that adam17 on hepatocytes might be involved in liver regeneration (table 1). furthermore, release of cx3cl1 from hscs was also shown to be mediated by adam17, correlating with enhanced inflammatory cell infiltration upon liver damage (38). however, a clear in vivo evidence for a role of adam17 in liver regeneration is still lacking. overexpression of adam17 has been reported in human hcc and diethylnitrosamine (den)-induced murine hcc model (53). in tumour cells, adam17 is essential for notch signalling (figure 2b), resulting in the maintenance of a cancer stem cell phenotype (54) with enhanced migratory abilities through activation of integrin β1 (53, 55). interestingly, it was shown that formation of hepatic metastases is enhanced by the release of soluble notch ligands from endothelial cells, which in turn activates notch on colorectal cancer cells. in vitro experiments using small molecule inhibitors suggested that proteolytic release of notch ligands might be mediated by adam17 (56). however, the question whether adam17 is also important for notch signalling under physiological conditions, in particular in the liver, remains unanswered. adam17 is a major protease for the membrane-bound il-6r, leading to the release of soluble il-6r (figure 2b). bolik j. et al. journal of renal and hepatic disorders 2019; 3(1): 23–32 28 in contrast to many other soluble receptors, sil-6r is able to bind il-6 and induce signalling through the signal-transducing subunit, gp130 (24). this process is called il-6 trans-signalling. we recently demonstrated that il-6 trans-signalling is critically involved in hcc tumour initiation and tumour angiogenesis (56). taken together, liver tumourigenesis appears to depend on adam17 proteolysis. however, more detailed in vivo analyses are needed to clarify if adam17 can be harnessed as a potential target in hcc therapy. the adamts family unlike adam family proteins, members of the adamts protease family contain neither transmembrane nor cytoplasmic domains and are synthesised as extracellular proteins. instead, all family members contain at least one thrombospondin (tsp) type-1 repeat (tsr) that comprises approximately 50 amino-acids and is similar to the type-1 repeats in tsp-1 and tsp-2 (57). the human adamts family contains 19 members that can be clustered into eight different evolutionary clades, depending on their domain organisation and known functions. the aggrecanase and proteoglycanase clades contain members (adamts1, 4, 5, 8, 15, 9, 20) that are involved in the processing of hyaluronan-binding chondroitin sulphate proteoglycan extracellular proteins, including versican and aggrecan. another clade encloses pro-collagen n-propeptidases (adamts2, 3, 14) that confer maturation of triple helical collagen fibrils (57). the overall domain organisation of adamts proteins can be structured into a metalloproteinase domain and an ancillary domain (figure 1c). the metalloproteinase domain consists of a pro-domain, the catalytic metalloprotease domain and a disintegrin-like module. the catalytic domain of adamts members contain a hexxhxbg(n/s)bxhd consensus motif, with b as a large non-polar residue and three histidines that coordinate the zn2+ metal ion (figure 1c and d) (8, 57, 58). to date, no adamts protein has been identified to associate with integrins. in contrast, crystal structure data suggest that the disintegrin-like domain is an integral part of the catalytic core of adamts proteins (11, 59). the composition of the ancillary domain varies between the different adamts members; however, all have at least one tsr motif in common (figure 1c). adamts proteins display multiple functions during tissue development and homeostasis, and their dysregulation has been associated with various diseases. during development, members of the aggrecanase and proteoglycanase clade process the ecm component versican ensuring enough structural support on the one hand, while allowing dynamic remodelling on the other hand (57). adamts1 and adamts2 the aggrecanase/proteoglycanase group member adamts1 is involved in the processing of ecm components (60). expression of adamts1 positively correlated with progression of hepatic fibrosis to cirrhosis. adamts1 was localised to hscs. interestingly, adamts1 expression is elevated in activated hscs and is associated with latency-associated peptide (lap)-tgfβ, resulting in tgfβ activation (figure 2c, table 1). consequently, a ktfr sequence-containing peptide derived from adamts1 was sufficient to reduce collagen deposition in the murine carbon tetrachloride cirrhosis model (61). adamts2 cleaves the pro-peptides of type i and type ii pro-collagens prior to fibril formation. its prominent role in collagen maturation has been further emphasised by the discovery of adamts2 mutations in ehlers-danlos syndrome type viic (62), which is characterised by extreme skin fragility and joint laxity, among other symptoms. the impact of adamts2 on liver biology has been previously shown in experimental liver disease using carbon tetrachloride (table 1). while the initial parenchymal damage was similar, hsc activation and collagen deposition were significantly reduced in adamts2-/mice compared to appropriate controls (figure 2c, table 1) (63). adamts13 adamts13 is the sole member of the von willebrand factor (vwf)-cleaving protease (vwfcp) clade. the vwf is a pro-thrombogenic glycoprotein, produced constitutively as ultra-large, multimeric protein by endothelial cells (64). after endothelial injury, vwf binds on one side to sub-endothelial collagen and on the other side to platelet glycoproteins, gpib/ix/v, leading to platelet tethering at the injury site. under fluid shear stress, vwf gets proteolytically processed. thus, adamts13 generates smaller, non-functional vwf fragments (figure 2c) (65). loss of adamts13 catalytic activity, either by recessive mutations (66) or by inhibitory auto-antibodies (67), leads to the accumulation of ultra-large vwf and the formation of platelet-rich microthrombi in the micro-vasculature causing a life-threatening rare disorder called thrombotic thrombocytopenia purpura (68, 69). low levels of adamts13 are also found in patients with sepsis-induced disseminated intravascular coagulation and are associated with increased mortality (70). adamts13 expression is predominantly found in the liver but also to some extent in skeletal muscles, placenta and the lung (71). it is therefore not surprising that patients with severe alcoholic hepatitis (sah) display reduced plasma activity of adamts13 and reduced vwf proteolysis (table  1). in sah patients with multiorgan failure, adamts13 levels were markedly reduced, resulting in increased platelet clumping and subsequent multiorgan failure (72). similarly, patients with acute liver injury and acute liver failure displayed an imbalance between vwf and adamts13 (table 1), and low adamts13 levels were associated with higher grades of encephalopathy and lower survival rates potentially linked to microthrombus formation (73). adam and adamts in the liver journal of renal and hepatic disorders 2019; 3(1): 23–32 29 a more detailed analysis localised adamts13 expression to αsma-positive hscs in a patient with hepatitis c-related chronic hepatitis, suggesting a role in fibrotic liver disease (74). accordingly, adamts13 expression levels were increased not only in activated rat hscs in vitro but also in hscs in vivo in carbon tetrachloride-injured rats (75). patients with liver cirrhosis displayed increasing levels of vwf with increasing severity according to child-pugh classification, while collagen-binding activity of vwf was decreased in these patients, partially correlating with increased adamts13 activity (76). however, two other studies detected decreased adamts13 levels in cirrhotic livers, linking adamts13 levels to an increased platelet thrombi formation (77, 78). a very recent study demonstrated that while adamts13 did not correlate with the child-pugh score in cirrhotic patients, low levels of adamts13 were associated with portal vein thrombosis (79). in contrast, in patients with non-alcoholic fatty liver disease, the increased risk in thrombosis was not linked to aberrant adamts13 levels or hyperactive haemostasis (80). conclusion as summarised above, selected members of adam and adamts proteinase families display altered expression in different liver pathologies, and a mechanistical role in the pathology has been shown for some members. however, we are still far from fully understanding the complex nature of adam and adamts proteinases and their impact on liver physiology and pathology. substrate analysis on a proteomics level will help to unveil how adam and adamts proteinases regulate liver biology. further studies will also show if adam and adamts expression and activity can be harnessed for diagnostic or therapeutic purposes. adamts13 activity is already routinely assessed for the diagnosis of thrombotic thrombocytopenia purpura. extended studies will determine the utility and benefit of adamts13 activity measurement in the clinical management of acute and chronic liver disease. albeit overexpression of some adam proteases has been shown in liver pathologies, more extended human studies, and experimental in vivo studies using targeted deletion, in particular hepatic cell types of the liver, are warranted to better understand the role of adam proteases in liver pathologies and targeted diagnosis and therapeutics. there have been numerous research activities in the past to develop small molecule inhibitors for adam17 to treat chronic inflammatory diseases such as rheumatoid arthritis. however, the first chemical entities displayed musculoskeletal and hepatic toxicities and therefore did not proceed beyond phase i/ii clinical trials (81). a recently developed dual-specific adam10/17 inhibitor, incb7839 (25), is a promising candidate that is currently in a clinical trial phase i/ii study (nct02142451) for the treatment of diffuse large b-cell non-hodgkin lymphoma. in addition, very recently, the recombinant pro-domain of adam17 has been developed as a specific adam17 inhibitor in vitro and in vivo and might represent a novel strategy to specifically inhibit adam and adamts proteinases (16). in summary, the world of adam and adamts proteinases remains a rich but largely underexplored sea of therapeutic opportunities. conflict of interest the authors report no conflict of interest with respect to research, authorship and/or publication of this article. acknowledgement this work was supported by the deutsche forschungsgemeinschaft (dfg), bonn [grant number sfb841; liver inflammation: infection, immune regulation and consequences, to d.s.-a.] and the australian technology network/ deutscher akademischer austauschdienst [atn-daad ppp to d.s.-a. and j.t.-p.] references 1. gilgenkrantz h, collin de l’hortet a. understanding liver regeneration: from mechanisms to regenerative medicine. am j pathol. 2018;188:1316–27. https://doi.org/10.1016/j.ajpath. 2018.03.008 2. köhn-gaone j, gogoi-tiwari j, ramm ga, olynyk jk, tirnitz-parker jee. the role of liver progenitor cells during liver regeneration, fibrogenesis, and carcinogenesis. am j physiol. 2016;310:g143–54. 3. ruddell rg, knight b, tirnitz-parker jee, akhurst b, summerville l, subramaniam vn, et al. 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renal disease. liver transplantation may be regarded as a substitute for an injured liver or as supplying a tissue that may replace a mutant protein. two groups of diseases should be distinguished. in the first group, the kidney tissue may be severely damaged while the liver tissue is almost normal. in this group, renal transplantation is recommended according to the degree of renal damage and liver transplantation is essential as a genetic therapy for correcting the metabolic disorder. in the second group, the liver parenchymal damage is severe. in this group, liver transplantation is essential to avoid liver failure. lta may also avoid the progression of the renal disease; otherwise a clkt is needed. in this review, we describe monogenic metabolic diseases involving the kidney that may have beneficial effects from lta or clkt. we also highlight the limitations of such procedures and the choice of alternative medical conservative treatments. keywords: atypical hemolytic uremic syndrome; glycogen storage disease; monogenic metabolic diseases; organic acidurias; primary hyperoxaluria received: 23 may 2017; accepted after revision: 26 june 2017; published: 19 july 2017. author for correspondence: maurizio salvadori, renal unit careggi university hospital, viale pieraccini, 18, 50139, florence, italy. email: maurizio.salvadori1@gmail.com how to cite: salvadori m and tsalouchos a. liver transplantation for monogenic metabolic diseases involving the kidney. j ren hepat disord 2017;1(2):29–40. doi: http://dx.doi.org/10.15586/jrenhep.2017.18 copyright: salvadori m and tsalouchos a. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction monogenic metabolic diseases involving the kidney are relatively rare and primarily found in children. in these diseases, genes encoding enzymes that allow the regulation of complex metabolic pathways, or circulating proteins mainly produced by the liver, are involved. in some diseases, the liver itself is affected along with other organs. conversely, in some cases, the liver is free from significant parenchymal damage, but other organs, for example, the kidneys, may be severely injured. tables 1 and 2 give a summary of these monogenic metabolic diseases (1, 2). in addition to the diseases shown in the tables, other monogenic metabolic diseases do exist with possible involvement of the kidneys and the liver. alagille syndrome, wilson’s disease, and hemochromatosis are a few examples. for this review, the diseases listed in tables 1 and 2 were selected because they are more frequent with severe renal involvement and may be cured either by liver transplantation alone (lta) or by combined liver–kidney transplantation (clkt). for some diseases, an enzyme replacement therapy (ert) is a possible option; however, ert is journal of renal and hepatic disorders 2017; 1(2): 29–40 mailto:maurizio.salvadori1@gmail.com http://dx.doi.org/10.15586/jrenhep.2017.18 http://creativecommons.org/licenses/by/4.0 not always available and is extremely expensive (3). a different approach could be gene therapy but its application encounters technical difficulties and to date is not a real option (4). when an alternative medical and conservative therapy is not available, organ transplantation may represent the only alternative therapy. whether lta or liver after kidney, or clkt is the preferred strategy depends on kidney function or the availability of organs. due to the fact that these diseases are rare, epidemiological data come from national or international registries. according to the european liver transplant registry (eltr), between 1968 and 2010, orthotopic liver transplantation (olt) for monogenic metabolic diseases was performed in 5.4% of adults, and in 17.3% of pediatric population (1). in the latter group, the predominant disorder was alpha 1 antitrypsin deficiency (aatd)(16%),followedbytyrosinemia(7%),primaryhyperoxaluria (ph1) (7%), and glycogen storage disease (gsd) (4%). according to the united network for organ sharing (unos) data (5), from 1996 to 2006, ph1 was the most predominant disorder (20.8%) with few patients transplanted because of atypical hemolytic uremic syndrome (ahus) (0.8%) or aatd (0.8%). in these data, a large number of liver transplantation is reportedwithout clarifyingtheoriginal disease(33.6%).areview performed in 2013 (6), which included only clkt in children, showed that ph1 prevailed with 72%, followed by ahus (1%), organic acidurias (1%), and aatd (0.5%). finally, according to the japanese multicenter registry for living donor liver transplantation (ldlt) for pediatric patients with metabolic disorders, the first cause of ldlt is methylmalonic aciduria (10.3%), followed by gsd (7.7%), tyrosinemia (6.7%), and ph1 (4.6%) (7). these registries report discordant data. the causes may be multifactorial: geographic and ethnic disparities, and ldlt data versus olt versus clkt data. additionally, an important role may have been exerted by various considerations given to alternative treatments and different periods for collecting the data. finally, the lack of olt or clkt for ahus in registries such as the unos and eltr, even during periods when eculizumab was not available, means a different therapeutic approach to the disease. the efforts of the organ procurement and transplantation network (optn) to realize guidelines for clkt document the aforementioned concerns (8). at the meeting held in 2012 at the university of south california (8), the authors highlighted several previous consensus and tried to develop recommendations for the selection of candidates for clkt (9, 10), but these recommendations have not yet become optn policy. in a recent review, bacchetta et al. (11) pointed out that the experience of clkt is limited and that some issues such as the respective place of a combined versus sequential liver kidney transplantation or the role of alternative therapies remain unanswered. according to the authors, the following key points should be highlighted: • clkt has encouraging results, provided that highly trained multidisciplinary teams are involved. • the first issue is the safety of the procedure, principally in smaller children or in severely sick patients. • specific managements after clkt or lta are needed to avoid the recurrence of diseases such as ph1 and ahus. • the timing of clkt, whether to perform a combined or sequential transplantation. in this review, we describe monogenic metabolic diseases involving the kidney that may have beneficial effects from lta or clkt. we also highlight the limitations of such procedures and the choice of alternative medical conservative treatments. a literature search was performed in web of science, pubmed, embase, scopus, and directory of open access journals (doaj). the search was performed using the following key words: kidney–liver transplantation monogenic diseases, hyperoxaluria, ahus, organic acidurias, gsd, tyrosinemia, and alpha-1-antitrypsin deficiency (aatd). metabolic monogenic diseases affecting mainly the kidney primary hyperoxaluria the autosomal recessive inherited primary hyperoxaluria types i, ii, and iii are caused by defects in glyoxylate metabolism that lead to the endogenous overproduction of oxalate (12). ph1 is the most severe form of the disease and is present in approximately 80% of patients included in the two international registries (13, 14). it is an autosomal recessive liver disease caused by deficiency or loss of activity of peroxisomal alanine glyoxylate aminotransferase (agxt) (table 3). this results in an overproduction of oxalate and glycolate (15, 16), with oxalate deposition in several organs and tissues including the kidney. ph2 is caused by deficiencies of the glyoxylate reductase/hydroxypyruvate reductase (grhpr) enzyme. grhpr is ubiquitous, but its expression is higher in the liver (17). the clinical expression is less severe although patients may be affected by severe urolithiasis with end-stage renal disease (esrd) (18). ph3 has only recently been described (19). table 1. monogenic metabolic diseases caused by the liver that affect the kidney or both liver and kidney diseases affecting the kidney primary hyperoxaluria types i and ii atypical hemolytic uremic syndrome methylmalonic acidosis transthyretin amyloidosis diseases affecting kidney and liver glycogen storage disease tyrosinemia type i α-1-antitrypsin deficiency journal of renal and hepatic disorders 2017; 1(2): 29–40 30 salvadori m and tsalouchos a it is caused by loss of function of the mitochondrial 4-hydroxy2-oxoglutarate aldolase (hoga) enzyme. ph3 does not appear to progress to esrd (20). table 3 reports the incidence percentage of ph according to hoppe et al. (21). it should be highlighted that the percentage of ph2 and ph3 may be slightly higher. indeed, ph2 may be undiagnosed because of the less severe clinical course. the conservative treatment of ph1 has several limitations. patients should intake high quantities of fluids (22). in addition to fluid intake, patients are recommended to take alkaline citrate or orthophosphate to increase urinary ph and urinary citrate excretion (23). in one-third of the patients, supraphysiological dosages of pyridoxine may reduce the oxalate excretion (23). it has been documented that patients with a homozygous c.508g>a mutation of the agxt gene experience a better response from pyridoxine therapy (24). oxalate-degrading bacteria usually colonize the intestinal tract. oxalobacter-driven activation of the intestinal transporter results in an increased oxalate elimination with feces, and a decrease of plasma oxalate (25). peritoneal dialysis and hemodialysis are relatively ineffective in removing oxalate (26). table 2. diseases involving the kidney amenable to lta or clkt as surgical therapy disorder, type, and acronym gene symbol inheritance mechanism of disease deficient enzyme liver features clinical features primary hyperoxaluria type i agxt ar calcium oxalate accumulation in tissues alanine-glyoxylate-aminotransferase normal liver nephrolithiasis; renal failure atypical hemolytic uremic syndrome (ahus1) cfh ar, ad thrombotic microangiopathy, complement activation complement factor h normal liver acute renal failure; hypertension methylmalonic acidemia (mma) mut ar disorder of methylmalonate and cobalamin leading to methylmalonyl-coa accumulation methylmalonyl coa mutase normal liver toxic encephalopathy; acidosis; renal failure ttr familial amyloid polyneuropathy ttr1-fap ttr ad deposit of insoluble protein fibrils in the extracellular matrix transthyretin normal liver polyneuropathy; cardiomyopathy; renal failure glycogen storage disease type ia g6pase ar abnormal accumulation of glycogen in the tissues glucose-6phosphatase glycogen in the liver; adenomas hcc hepatomegly; nephromegaly; growth retardation tyrosinemia type i fah ar lack of tyrosine degradation fumarylacetoacetate hydrolase (fah) liver failure; hcc secondary renal tubular dysfunction α-1 antitrypsin deficiency (aatd) pi ar lack of inhibitory action against neutrophil elastase protease inhibitor cirrhosis hcc emphysema; glomerulonephritis aatd, α-1antitrypsin deficiency; ad, autosomal dominant; agxt, alanine-glyoxylate aminotransferase; ar, autosomal recessive; cfh, complement factor h; g6pase, glucose-6-phosphatase; fah, fumaryl-acetoacetate hydroxylase; mma, methylmalonic academia; mut, methylmalonyl-coa mutase; pi, protease inhibitor; ttr, transthyretin; ttr1-fap, transthyretin-type familial acidosis polyneuropathy. liver or combined liver-kidney transplantation journal of renal and hepatic disorders 2017; 1(2): 29–40 31 the best transplantation strategy for a patient affected by ph1 has been a matter of discussion. preemptive lta is the best strategy for patients before the occurrence of esrd, and to prevent systemic oxalosis (27). lta is the best strategy for patients with glomerular filtration rate (gfr) higher than 40 ml/min/1.73 m2 (28). clkt is the preferred option when gfr is below 40 ml/min/1.73 m2 (29). the transplant outcome is optimal in clkt according to the international primary hyperoxaluria registry (30) and the recently published french experience (31), which concludes that clkt for ph1 provides better kidney graft survival, less rejection rate, and is not associated with an increased short-time mortality risk. medical treatment is effective in ph2; in patients with esrd, kidney transplantation alone is the treatment of choice, as the defective enzyme is not liver-specific (17). reports of clkt for ph2 do exist (32); however, kidney transplantation followed by appropriate measures to decrease oxalate levels is the method of choice (33). atypical hemolytic uremic syndrome ahus is a rare disease often associated with mutations in genes encoding complement regulatory proteins, causing secondary disorders of complement regulation. cfh mutations (gene encoding factor h) are the most common, but mutations in genes encoding complement factor i (cfi), c3, complement factor b (cfb), and thrombomodulin (thbd) have also been recognized (34). the mortality rate is high (35) and many patients progress to esrd. kidney transplantation is a therapeutic measure, but disease recurrence in the transplanted kidney frequently occurs (36) as the liver does not produce the normal protein. conservative treatment with plasma exchange and plasma infusion reduces mortality rate (35) but is unable to cure the disease or prevent recurrences after kidney transplantation. several studies documented the efficacy of eculizumab, a human monoclonal antibody directed against the complement protein c5 (37). the best option is still a matter of debate. a comparison between kidney transplantation alone with chronic eculizumab and clkt is given in table 4 (38). it should be highlighted that certain gene mutations are associated with altered response to eculizumab. for example, mutations in diacylglycerol kinase epsilon (dgke) gene are associated with complementindependent forms of ahus and are resistant to eculizumab (39). also, genetic variants in c5 confer resistance to eculizumab (40). table 3. different types of primary hyperoxaluria type gene/gene product/locus ph cases (%) definition mode of inheritance ph 1 agxt/agt/2q37.3 70–80 uox >1 mmol/1.73 m 2 per day/elevated urinary oxalate to creatinine ratios ar ph ii grhpr/grhpr/ 9q11 ~10 uox >1 mmol/1.73 m 2 per day/elevated urinary oxalate to creatinine ratios ar ph iii hoga1/ hoga1/ 10q24.2 ~10 uox >1 mmol/1.73 m 2 per day/elevated urinary oxalate to creatinine ratios ar agxt, alanine-glyoxylate aminotransferase; ar, autosomal recessive; grhpr, glyoxylate and hydroxypyruvate reductase; hoga 1, 4-hydroxy-2-oxoglutarate aldolase 1. table 4. comparison of transplant approaches in ahus kidney transplantation alone with chronic eculizumab liver–kidney transplant lower short-term risk long-term outcomes yet to emerge long-term dependence to prevent ahus more “immunosuppressive” increased infection risk? lower rejection risk? iv infusion every 2 weeks limited availability worldwide very high financial cost higher short-term mortality long-term outcomes stable ahus recurrence unlikely less immunosuppressive lower rejection risk better lifestyle-no infusions lower monetary cost more widely available limited organ (liver) resource salvadori m and tsalouchos a journal of renal and hepatic disorders 2017; 1(2): 29–40 32 in 2009, a consensus study group identified the guidelines for clkt and lta (41). with the adoption of such measures, the mortality rate decreased, and 16 out of 20 patients (80%) could be safely cured with clkt (42). in a 2016 international consensus statement by experts from europe, canada, turkey, and the united states, prophylactic eculizumab is the recommended treatment after kidney transplantation alone. the consensus group recognized that lta or clkt is the only therapeutic measure to definitively cure ahus in patients with mutations of complement factors synthesized in the liver (43). they also recommended that clkt should be discussed with the family and patients, with emphasis on risks and benefits of the alternative treatments. organic acidurias organic acidurias are inborn errors of organic acid metabolism, characterized by the excretion of nonamino organic acids in the urine. the two commonest forms are methylmalonic acidemia (mma) and propionic acidemia. only mma is of interest to kidney because of the nephrotoxicity of methylmalonate to renal tubular epithelial cells (44). mma is a rare autosomal recessive disorder caused by complete or partial deficiency of methylmalonil-coa mutase or by defects in the synthesis of its cofactor adenosylcobalamin (45). if the acute metabolic crises are not corrected by maintenance therapy, esrd may occur. in such conditions, a clkt may be indicated (46). otherwise, lta can be performed (47). conservative management to correct acute metabolic crisis relies on protein restriction (low-protein and high-caloric diet with overnight continuous feeding), amino acids supplementation, carnitine, and cobalamin (44). although dietary management has been the major component of mma therapy for a long time, patients are at risk for renal, cardiac, ophthalmological, and neurological complications (47). due to poor prognosis, lta has been attempted and clkt is indicated when esrd occurs. in addition to the aforementioned series, and the one from kasahara et al. (45) who reported 13 children who received lta and 5 who received clkt, numerous patients with mma have undergone either lta or clkt (48–55). the most recent report is the one by niemi et al. (56) who reported six mma patients with lta and eight mma patients with clkt. the results of this study are excellent with a 3-year patient survival of 100% and liver survival of 93%. the same study reports a unos 5-year survival of 88%, with a 99% survival for children older than 2 years. however, the effectiveness of lt in patients with mma caused by methylmalonyl-coa mutase deficiency is questionable because in such patients the de novo synthesis of propionyl-coa within the central nervous system leads to brain methylmalonate accumulation that is not affected by transplantation (53). transthyretin-type familial amyloidosis polyneuropathy transthyretin-type familial amyloidosis polyneuropathy (ttrfap) is a rare adult onset progressive disorder characterized by extracellular amyloid fibril formation with polymerized ttr accumulation. the disorder is inherited as an autosomal trait, and about 100 different mutations or deletions in the ttr gene are known (57). clinical manifestations are represented by progressive polyneuropathy and in the final stages patients die from esrd or, most frequently, from heart failure. a number of drugs, for example, diflunisal (58) and benzoxazoles (59), stabilize ttr or inhibit fibril formation. the most promising drug is tafamidis (60). as the liver produces most of the amyloidogenetic ttr, lta has been tried to stop the variant of ttr. the results of lta for ttr-fap are good as reported by the data of single institutions (61) or by the transplant registry (62). the worse outcomes are related to cardiac amyloidosis (63), and in a few cases combined heart–liver transplantation has been attempted (64, 65). metabolic monogenic diseases affecting both kidney and liver glycogen storage disease gsds are inherited disorders that affect glycogen metabolism and cause abnormal accumulation of glycogen both in quantity and in quality (66). in general, liver and muscles are the two major tissues abundant in glycogen and thus the most seriously affected in gsds. to date, 23 types (or subtypes) of gsds have been identified. in all 23 types, gene mutations have been detected. this has been the result of a gene-by-gene sequencing technique in combination with the detection of biochemical and clinical hallmarks (67). gsds are classified depending on the organ affected and the enzyme deficiency involved. to date, seven gsds affect mainly the liver, nine gsds affect mainly the muscles, and three gsds the heart. a simplified and useful classification is shown in table 5 (68), where, in addition to gsds affecting liver and/or muscles, gsds also affecting the kidney are shown. the latter are described in detail as may be treated by lta or clkt according to the clinical conditions. gsd type i (gsdi) is an autosomal recessive inborn error of carbohydrate metabolism caused by defects in the glucose6-phospate transporter (g6pt)/glucose-6-phosphatase (g6pase) complex (69, 70). deficient activity of g6pase causes gsdia (71), and deficient activity of g6pt causes gsdib (72). the human g6pase gene was cloned by lei et al. (71). these authors identified mutations causing gsdia. the human g6pt gene, which causes gsdib, has also been cloned. approximately, 80% of people with gsdi have type ia and 20% have type ib. gsd type 1a is characterized by hypoglycemia, hepatomegaly, nephromegaly, hyperlipidemia, hyperuricemia, and growth retardation (73). renal findings may be diverse. focal segmental glomerulosclerosis caused by hyperfiltration has been frequently found; amyloidosis, fanconi-like syndrome, renal stones, and nephrocalcinosis may be found as well (66). interstitial fibrosis may develop and some patients may progress to esrd (74, 75). almost 70% of patients affected by gsdi liver or combined liver-kidney transplantation journal of renal and hepatic disorders 2017; 1(2): 29–40 33 develop hepatic adenomas with the potential of transforming into hepatocellular carcinoma (hcc) (76, 77). gsdiii results from a defect in glycogen debranching enzyme activity that leads to the accumulation of an abnormal form of glycogen in affected tissues. in the united states, more than 80% of patients with gsdiii have both liver and muscle involvement (78). renal function is often normal, but cases of acute renal failure (79) are reported even if the pathogenesis is not clear. full guidelines on the gsdi diagnosis and management have been published by the american table 5. different types of glycogen storage diseases and main clinical findings number name enzyme defect glycogen structure clinical manifestations 1 glucose-6-phosphatase deficiency (von gierke’s disease) glucose-6phosphatase normal enlarged liver and kidneys; failure to thrive; hepatic adenomas; focal segmental glomerulosclerosis and interstitial fibrosis; amyloidosis; fanconi-like syndrome renal stones/ nephrocalcinosis 2 infantile acid maltase deficiency (pompe’s disease) acid maltase normal cardiorespiratory death 3 late infantile and adult acid maltase deficiency acid maltase abnormal short outer chains hip weakness; slow motor development 4 debrancher deficiency (cori’s disease) amylo-1, 6-glucosidase abnormal short outer chains, increased branch points hepatomegaly; renal tubular acidosis 5 brancher deficiency amylo-1,4→1, 6-transglucosidase abnormal cirrhosis; growth failure; muscle wasting 6 myophosphorylase deficiency (mcardle’s disease) muscle phosphorylase normal atrophy in older patients; myoglobinuria 7 hepatophosphorylase deficiency muscle phosphorylase normal hepatomegaly; cirrhosis 8 phosphorylase kinase deficiency phosphorylase kinase normal marked hepatomegaly; cirrhosis 9 phosphoglucomutase deficiency phosphoglucomutase normal weakness; regression in motor development 10 phosphohexose isomerase deficiency phosphohexose isomerase normal myopathy 11 phosphofructokinase deficiency phosphofructokinase normal atrophy in older patients; myoglobinuria 12 glycogen synthetase deficiency glycogen synthetase normal mental retardation; seizures salvadori m and tsalouchos a journal of renal and hepatic disorders 2017; 1(2): 29–40 34 college of medical genetics and genomics (80). the differential diagnosis among the different types of gsd is essential. laboratory testing and genetics are essential. the principal findings are the following: • blood/plasma hypoglycemia, lactic acidosis, hypercholesterolemia, hypertriglyceridemia, and hyperuricemia are consistent with gsdi. • neutropenia suggests gsd ib. • diagnosis should be confirmed by full gene sequencing of the gspc and slc37a4 genes. • if liver biopsy is performed, histology typically shows fat and glycogen in hepatocytes without fibrosis. • diagnostic studies should be performed to follow renal manifestations, including: ∘ renal ultrasound to assess kidney size, nephrolithiasis, and nephrocalcinosis ∘ urinalysis for hematuria and proteinuria ∘ measurement of blood urea nitrogen and serum creatinine with calculation of estimated gfr (egfr) medical and nutritional treatment • maintaining blood glucose levels > 70 mg/dl is important to achieve a good metabolic control. • avoid fasting for more than 5 h. • access via ng or g tube placement is recommended for emergencies in infants. • multivitamins, calcium, and vitamin d are necessary because of the restricted nature of the diet. for the kidney • consider initiating an ace inhibitor or arb with the evidence of hyperfiltration. • initiate an ace inhibitor or arb for persistent microalbuminuria. • initiate citrate supplementation for hypocitraturia. • consider a thiazide diuretic for hypercalciuria. • maintain normal blood pressure for age. liver transplantation is indicated in case of liver failure and to avoid the transforming of adenomas into hcc. isolated liver transplantation has been performed in gsdi patients with multiple unresectable adenomas, poor metabolic control, and progressive liver failure (81, 82). indications for pediatric liver transplantation in gsdi children are multiple liver adenomas, growth failure, and poor metabolic control (83). a 15-year follow-up after liver transplantation with an optimal outcome has been reported (84). the japanese registry (7) reports ldlt for 15 patients with a 10-year graft and patient survival of 67%. however, the group included 70% of patients with gsd type iv. in a recent review, boers et al. (85) identified 58 patients with gsdia who underwent a liver transplantation between 1982 and 2012. the authors conclude that there arestill many complications relatedto the liver transplant procedure (18/58) as well as complications related to immune suppressive therapy. taking into account of these complications, the authors highlight the relevance of new therapies such as hepatocyte and liver stem cell transplantation. there have been reports of clkts that have been successfully performed in gsdia patients (83, 86–90). the physicians involved in liver–kidney transplantation recommend that clkt should be considered for patients with esrd secondary to gsdia. tyrosinemia type i tyrosinemia type i (tt1) is an autosomal recessive metabolic disorder characterized by the deficiency of the enzyme fumarylacetoacetate hydrolase (fah) involved in the final step of the catabolism of tyrosine and phenylalanine (91). mutations occur in the gene fah located on chromosome 15. the incidence of tt1 is around 1:100,000, but is higher in areas where specific programs for diagnosing have been carried out (92, 93). the deficient enzyme causes the accumulation of toxic metabolites such as fumarylacetoacetate and malelylacetoacetate. these metabolites induce apoptosis of both hepatocytes and kidney tubular cells. the toxic metabolites may affect hepatocyte dna, increasing the risk of hcc. the acute form of tyrosinemia i is characterized by acute renal failure and its incidence is higher up to the fourth month of life. the chronic form is characterized by chronic liver disease, cardiomyopathy, fanconi-like tubular dysfunction, rickets, and renal failure (94). a conservative treatment of the disease is available with 2(2-nitro-trifluoromethylbenzoyl)-1, 3 cycloexemedione (ntbc) (95), which blocks the formation of toxic metabolites. with ntbc and a phenylalanineand tyrosine-restricted diet, an improvement in kidney and liver function is achieved (96–98). after the introduction in therapy of ntbc, the need for lta dropped from 35% to 12% (93). to date, the indications for lta are as follows: • patients failing with the first-line medications • onset of acute renal failure • hcc • poor quality of life according to some group, a nodular liver is also an indication for lta, due to the high risk of hcc (99). clkt was indicated in the pre-ntbc era, but is no longer indicated. the highest number of lta for tyrosinemia i are those reported by arnon et al. (100), who analyzed the unos database, and herzog et al. (101), who reported 27 lta followed by stabilization or improvement of the renal function. the 1-year graft survival is higher than 88%, and only in selected cases ntbc treatment is needed after lta. liver or combined liver-kidney transplantation journal of renal and hepatic disorders 2017; 1(2): 29–40 35 alpha1-antitrypsin deficiency the most common genetic cause of liver disease in children is aatd (102), an autosomal recessive disorder caused by mutations in the serpina 1 gene (103). aat protects tissues from proteases such as neutrophil elastase. the phenotype pimm (protease inhibitor mm) is present in 95% of the population. several mutations have been described, the most common related to alleles being piz and pis that result in reduced circulating levels of aat. liver disease develops in children with pizz mutation. lung disease occurs mainly in pizz and pisz phenotypes, and is related to low plasma levels, causing lack of anti-inflammatory activity of aat in the alveoli (104). glomerular diseases, mainly mesangiocapillary glomerulonephritis, develop in some children with aatd and may progress to esrd (105). the pathologic features usually involve the liver, lung, and kidneys. the study by davis et al. (106) evaluated renal specimens from 34 patients affected by aatd. glomerular lesions were found in 79%, including mesangial proliferative glomerulonephritis, mesangiocapillary glomerulonephritis, and focal segmental glomerulonephritis. pim and piz were found in the subendothelial region of glomerular basement membrane and this fact suggested a possible role for these proteins in the pathogenesis of these lesions. several approaches to medical treatment of aatd are possible (107). deficient aat can be replaced using recombinant aat. this replacement therapy (usually by inhalation) may slow the progression of lung disease, but not liver or kidney disease. the same limitations occur with gene therapy and stem cell therapy (108). the indication for lta in aatd is either end-stage liver disease (esld) or hcc. lta not only cures the esld but also prevents the development of lung disease, as the recipient develops the pi phenotype of the donor. hughes et al. (109) reported a single-center largest series of lta with a 5-year patient survival of 76.5%. concerning the effect of lta on the kidney, grewal et al. (105) did not document the reversal of membranoproliferative glomerulonephritis. by contrast, the reversibility of the glomerulonephritis was documented by elzouki (110) after lta. the success of clkt in the case of esrd has been repeatedly documented (86, 111). the latter authors recommend native kidney biopsy and gfr measurement in all patients with aatd referred for lta. conclusion these monogenic metabolic diseases affecting either kidney or liver account for 10 out of 1000 births, and represent a frequent cause of mortality, mainly in the pediatric population. effective medical conservative treatments are rarely available with the exception of ahus and tt1. the introduction of the eculizumab changed the therapeutic prospective of ahus principally after renal transplantation. the introduction of ntbc for tt1 dropped the indication for lta from 35% to 12%. for other diseases, organ transplantation remains the standard of care treatment. whether to adopt lta or clkt continues to be a matter of debate. in ph1, clkt should be the treatment of choice in the case of esrd. lta may represent the preferred option if renal function is still over 40 ml/min/1.73 m2. reversal of renal damage after lta has been observed. lta offers a curative approach in patients with primary hepatic parenchymal damage and also in liverbased genetic disorders with prevalent extra-hepatic lesions. when the genetic defect is ubiquitous and the liver is one among several targets for systemic injury, the results of liver transplantation may be quite poor. the identification of the genetic defect allows for a better understanding of the disease and an improvement of treatment after transplantation. ert could represent a viable option, but ert is extremely expensive and not available everywhere. gene therapy has recently shown great promise as an effective treatment for a number of metabolic diseases caused by genetic defects in both animal models and human clinical trials. most of the current 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http://dx.doi.org/10.1089/hum.2011.053 http://dx.doi.org/10.1089/hum.2011.053 journal of renal and hepatic disorders 2019; 3(1): 1–14 review article hepatitis c virus infection and renal disorders maurizio salvadori1, aris tsalouchos2 1renal unit, careggi university hospital, florence, italy; 2division of nephrology and dialysis unit, saints cosmas and damian hospital, pescia, italy abstract hepatitis c virus (hcv) infection is frequently associated with extrahepatic disorders, among which renal diseases are frequent. this article highlights the most frequent hcv-associated renal disorders, the impact of hcv infection on chronic renal disease and renal transplantation, and the role of current direct-acting antiviral therapies. hcv is associated with membranoproliferative glomerulonephritis, acceleration of end-stage renal diseases in patients with glomerulopathies, and a higher risk of death in patients affected by chronic kidney disease. before the introduction of direct-acting antiviral drugs as treatment modality, renal transplantation was a challenging clinical problem because the drugs available until 2011 obtained a poor sustained virologic response, had several side effects, and caused acute rejection when used after transplantation. the knowledge of the viral structure and its replication allowed the discovery of new classes of direct-acting antiviral drugs that revolutionized this scenario. these new drugs are comparatively more effective and safer. accumulating evidence suggests that it is possible to cure hcv-related glomerulonephritis, and obtain a sustained virologic response in patients with renal failure, or on dialysis, before commencing transplantation. finally, it became possible to transplant hcv-positive kidneys into hcv-positive or hcv-negative recipients. keywords: direct antiviral agents; extrahepatic disorders; hepatitis c virus; membranoproliferative glomerulonephritis; mixed cryoglobulinemia received: 12 november 2018; accepted after revision: 20 december 2018; published: 16 january 2019 author for correspondence: maurizio salvadori, renal unit, careggi university hospital, viale pieraccini, florence, italy. email: maurizio.salvadori1@gmail.com how to cite: salvadori m, tsalouchos a. hepatitis c virus infection and renal disorders. j ren hepat disord. 2019;3(1):1–14. doi: http://dx.doi.org/10.15586/jrenhep.2019.43 copyright: salvadori m, tsalouchos a. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction hepatitis c virus (hcv) infection is a relevant health issue  with 150–170 million people chronically infected worldwide (1). these patients are at high risk of developing liver complications such as cirrhosis and liver cancer. a large proportion of patients with hcv infection are also affected by extrahepatic complications (2–5), as summarized in table  1. some of these clinical conditions are common, while  others are anecdotal or infrequently reported (2–5). this article provides an overview of renal disorders associated with hcv infection, their main characteristics, and therapy, with emphasis on direct-acting antiviral (daa) therapies. hcv epidemiology in patients affected by renal diseases the prevalence of hcv infection in the general population is estimated to be approximately 3% (6). in dialysis patients, the prevalence is higher, and the dialysis outcomes and p u b l i c a t i o n s codon journal of renal and hepatic disorders mailto:maurizio.salvadori1@gmail.com http://dx.doi.org/10.15586/jrenhep.2019.43 http://creativecommons.org/licenses/by/4.0 salvadori m and tsalouchos a journal of renal and hepatic disorders 2019; 3(1): 1–14 2 practice patterns study (dopps) reported prevalence rates ranging from 2.6% to 22.9% (7). excluding dialysis patients, hcv prevalence is higher in patients with kidney diseases with respect to general population. hcv may cause chronic kidney disease (ckd) via specific forms of glomerulonephritis (gn), primarily membranoproliferative gn (mpgn) which is associated with mixed cryoglobulinemia (mc). in such cases, mc represents hcv/anti-hcv immune complex in association with rheumatoid factor (rf) and complement (8). epidemiological studies conducted in the united states (nhanes ii) and taiwan, where hcv infection is endemic, have documented the interaction and relationship between hcv infection and ckd (9, 10). the expression by renal parenchyma of cd81 and srb1 receptor facilitates the binding of hcv to the renal cell surface and its endocytosis (11). consequently, hcv-rna and the related proteins have been found in the mesangial, tubular, epithelial, and endothelial cells of the kidney (12, 13). hcv-associated renal injury may also be facilitated by the presence of toll-like receptors (tlrs) on renal cells. tlrs are able to recognize molecules associated with microbial pathogens and, once activated, may induce an immunological response (14). the increased expression of tlr3 on renal cells, observed in renal biopsy samples, may justify a link between tlr3 and hcv-related glomerular diseases. hcv and ckd hcv infection is frequently associated with ckd stages 4 and 5. blood transfusions and nosocomial transmission in dialysis patients are the causes of the higher prevalence of hcv infection in these patients when compared with the general population. in patients on dialysis, the nosocomial transmission also seems to occur independently of blood transfusions (15–17). in one study, of the 1423 hemodialysis patients who never received previous blood transfusions, 18% had hepatitis c antibodies (15). in addition to a higher frequency, epidemiological studies have demonstrated that hcv infection is an independent risk factor not only for the development of ckd, but also for the rapid progression of ckd (erchives study) (18). another study (19) confirmed that hcv-positive patients have a 40% higher chance of developing renal failure compared to hcv-negative patients. these findings were further confirmed by a systematic review and meta-analysis (20). in addition to being a risk factor for renal failure, hcv infection is also a risk factor for mortality in patients with end-stage renal disease (esrd). a meta-analysis of 14 observational studies confirmed that hcv-ab-positive serological status is an independent and significant risk factor for death in patients on dialysis (21). similarly, a prospective observational study of 16,720 hemodialysis patients found that hcv positivity is associated with an increased risk of mortality (rr 1.17) (22). the risk evaluation of viral load elevation and associated liver disease/cancer (reveal) hcv study is a large prospective community-based cohort study in taiwan that provides an excellent opportunity to investigate the natural history of hcv infection and associated diseases (23). recently, a study by lai et al. (24) demonstrated that chronic hcv infection is an independent risk factor for the development of esrd in patients with genotype 1. patients with low and high hcv-rna levels had, respectively, 2.6and 4.3-fold increased risk of developing esrd compared with patients who were not infected with hcv (figure 1). in a further study, lai et al. demonstrated that, in addition to viral load, genotype 2 is a strong predictor of ckd (25). the mechanism by which hcv infection increases the risk of morbidity and mortality in patients with ckd is not clear. about 50% of the deaths are related to cardiovascular diseases, and an association between malnutrition-inflammation syndrome (mia syndrome) and poor table 1. the major extrahepatic manifestations in patients with hepatitis c virus infection immune-related extrahepatic manifestations mixed cryoglobulinemia cryoglobulinemic vasculitis b-cell nhl sicca syndrome arthralgia/myalgia autoantibody production (cryoglobulins, rheumatoid factor, anticardiolipin, etc.) polyarteritis nodosa monoclonal gammopathies immune thrombocytopenia inflammatory-related extrahepatic manifestations type 2 diabetes mellitus insulin resistance glomerulonephritis renal insufficiency fatigue cognitive impairment depression impaired quality of life polyarthritis/fibromyalgia cardiovascular disorders (i.e. stroke and ischemic heart disease) nhl, non hodgkin lymphoma. hepatitis c virus and renal disorders journal of renal and hepatic disorders 2019; 3(1): 1–14 3 outcomes has been suggested (26). other studies have highlighted that hcv has an atherogenic role, which could aggravate metabolic syndrome (27). hcv-associated renal diseases hcv-related renal damage comprises several clinicopathological aspects that include glomerular and/or interstitial lesions (28–30) as summarized in table 2. mpgn is the typical and most frequent pathologic entity. kidney involvement may be the result of two different processes: the immune-mediated tissue damage or hcv-mediated direct injury. in addition, environmental or host factors, genetic background, decompensated cirrhosis, and diabetes may contribute to renal damage in the setting of hcv infection. the hcv lymphotropism represents the main pathogenetic mechanism of hcv-related clinical manifestations. the hcv antigen is responsible for both t-lymphocyte and b-lymphocyte activation, leading to the production of autoantibodies and immune complexes involved in the pathogenesis of hcv-related nephropathy (31). in addition, the virus per se may directly induce tissue damage by infecting the endothelial, tubular, and epithelial cells, and infiltrating leukocytes. a high prevalence of occult hcv infection in patients with primary and secondary glomerular nephropathies (32, 33) and the presence of hcv antigen in kidney tissue of patients with various glomerulopathies (34) support the hypothesis of direct injury mediated by hcv. mixed cryoglobulins and mpgn among the hcv-related extrahepatic manifestations, cryoglobulinemic vasculitis represents a severe condition often complicated by renal involvement (30). according to the type of immunoglobulins (igs) involved, cryoglobulins (cgs) have been classified into type i, type ii, and type iii (35). type i cg is frequently seen in monoclonal gammopathies like multiple  myeloma or waldenstrom’s macroglobulinemia. types ii and iii cgs are a mix of both polyclonal igg and monoclonal igm with rf activity. type ii cg is mainly found secondary to infections such as hcv, hepatitis b virus (hbv), and human immunodeficiency virus. type iii cg is frequently associated with connective tissue diseases and rarely found in hcv-related mpgn. mixed cryoglobulins (mcs) are the typical consequence of hcv infection and are often associated with mpgn. types ii and iii mcs are generally present. a polyclonal igg binds to another immunoglobulin, which acts as an antiglobulin and as an anti-igg rf. hcv is known to be the cause of 80% of mcs. the pathophysiological mechanism of hcv-related gn probably involves e2-cd81 interaction. the e2 protein of hcv interacts with the cd81 that is the cellular receptor for hcv and is required for the infection of hepatocytes  (36). type i mpgn is the most frequent gn associated with chronic 0 1 2 3 4 5 6 7 0 4 8 12 16 c u m u la � ve in ci d en ce years of follow-up no hcv infec�on low hcv rna level high hcv rna level figure 1. cumulative risk of end-stage renal disease in patients affected by genotype 1 (24). table 2. histopathological features of hepatitis c virus-related renal involvement renal disease pattern histologic features frequency diffuse or focal mpgn mesangial cells proliferation plus deposits of immune complexes typically found mesangial proliferative gn diffuse mild mesangial matrix expansion and mesangial cells proliferation occasionally found tubulointerstitial nephritis interstitial fibrosis with negative immunofluorescence rare membranous gn subepithelial deposits of immune complexes occasionally found iga nephropathy mesangial iga deposits rare focal segmental glomerulosclerosis sclerosed glomeruli and tubular atrophy, negative immunofluorescence rare immunotactoid glomerulopathy and fibrillary gn extracellular deposits of microfibrils; igg and c3 immunofluorescence rare mpgn, membranoproliferative gn; gn, glomerulonephritis. salvadori m and tsalouchos a journal of renal and hepatic disorders 2019; 3(1): 1–14 4 hcv infection. the pathogenesis of mpgn is due to glomerular deposition of immune complexes often containing mcs; however, glomerular deposition of immune complexes in hcv-mpgn may be observed even in the absence of mcs (37). the immune complex deposits in the mesangium and subendothelium activate the complement system and mononuclear cells, which alter glomerular permeability and cause subsequent cell damage through the release of proteases and oxidants (38). overall, the prevalence of mpgn is higher in hcv patients with mcs. hcv-rna has been observed in 80% of patients with cryoglobulinemia-associated mpgn, but only in 25% of mpgn patients without cryoglobulinemia (38). mpgn may be associated with hcv infection independently of circulating mcs. in such cases, the immunecomplexes containing hcv are responsible for the gn. viral nonstructural protein 3 (ns3) may be present in the deposits with a linear or granular pattern along the capillary walls and the mesangium (33). membranous nephropathy several cases of membranous nephropathy (mn) have been described in hcv-infected patients (39, 40). the findings are similar to those observed in the classic idiopathic mn due to phospholipase a2 receptor (pla2r). complement level in the serum is normal and both cgs and rf are absent. yamabe et al. (40) found that 8% of mn patients were hcvpositive compared to less than 1% of patients with different forms of gn with the exclusion of mpgn. other glomerulonephritis diffuse proliferative gn with paramesangial dense igm and c3 deposits may be occasionally observed in hcv-positive patients (41). the association of iga nephropathy with hcv infection has been reported (42–44). some of these reports describe a successful treatment with interferon alpha (ifnα). several studies have highlighted the association between hcv and focal segmental glomerulosclerosis (fsgs) (45, 46). shah et al. (46) reported that treatment with pegylated ifnα resulted in a sustained virologic response (svr), with a clinical remission lasting more than 5 years. six cases of fibrillary immunotactoid glomerulopathies associated with hcv infection have been described (47–49). the best described are six cases by markowitz et al. (47). they describe four cases of fibrillary gn and two cases of immunotactoid glomerulopathy associated with hcv infection. the renal biopsy showed a membranoproliferative pattern, but electron microscopy revealed fibrils of 16–28 nm diameter in fibrillary gn and 35–45 nm in immunotactoid glomerulopathy. both fibrillary gn and immunotactoid glomerulopathy are similar to cryoglobulinemic gn, suggesting a common pathogenetic mechanism of organized glomerular deposits. in a review article, johnson et al. (50) observed that patients affected by mpgn in association with hcv infection often have tubulointerstitial inflammation and scarring. more recently, in another study (51), tubulointerstitial changes were frequently observed in hcv-infected patients, and the viral antigens and hcv-rna were detected in the tubulointerstitium of these patients. kidney transplantation and hcv infection the pre-transplant prevalence of hcv infection has been reported to be as high as 40% (52). in recent reports, the prevalence is lower due to the prophylactic measures adopted in ckd patients but still ranges from 3% to 80% (53). the survival of hcv-positive rna-positive kidney transplant recipients is poor, but higher with respect to hcv-positive rna-positive patients who remain on dialysis (54–56); however, the survival rates in ckd and renal transplant patients have markedly improved after the introduction of the daa therapies. the most frequently reported hcv-related adverse events after kidney transplantation are acute and chronic graft dysfunction, infections, posttransplant diabetes mellitus (ptdm), posttransplant lymphoproliferative disease, and gn (57). cosio et al. (58) documented a high risk of acute transplant glomerulopathy and acute vascular rejection in hcv-positive recipients. an increased risk of chronic transplant glomerulopathy was documented in a meta-analysis of eight clinical trials (59) and in another large single-center study (60). a higher incidence of infections in hcv transplanted patients is debated, but a spanish study with 1302 kidney transplant patients documented a higher incidence of bacteremia and upper urinary infections (61). hcv infection is an independent risk factor for ptdm (62, 63). virus-induced pancreatic β-cell dysfunction has been proposed as the pathogenetic mechanism (64). an increase in posttransplant lymphoproliferative disorders has been described in hcv patients transplanted with kidney or other organs (65). both recurrent and de novo gn have been observed in hcv renal transplant patients. hcvassociated mpgn and mn recur after transplantation (66). the recurrence is more frequent after the second year and the incidence rate ranges from 20% to 30% for mpgn and from 3%  to 7% for mn (67), similar to native kidney disease. hcv is also a risk factor for development of de novo gn. one study reported an incidence rate as high as 63% for de novo gn (68). similar findings were reported by others (69). de novo fsgs has also been reported in hcv renal transplant patients and a direct pathogenesis by hcv on podocyte has been suggested in such patients (11). treatment the introduction of daa drugs has remarkably ameliorated virus-mediated pathological changes in renal transplant patients. relevant effects of these drugs are discussed in this section. hepatitis c virus and renal disorders journal of renal and hepatic disorders 2019; 3(1): 1–14 5 history of hcv therapy hcv is an enveloped virus with single stranded rna and a genome composed of structural and nonstructural proteins (figure 2) (6). seven genotypes have been identified and divided into subtypes and strains (70). the genotypes are differentially distributed worldwide and the efficacy of daa drugs may vary according to the hcv genotype. in the past, interferon-based regimen constituted the standard of care treatment. the first drug used was the recombinant alpha interferon (ifnα) in combination with ribavirin. initially, ifnα was used as monotherapy, but the efficacy in terms of svr was poor, the treatment was expensive, and several side effects were reported. in addition, when used in transplant patients, it could generate severe acute rejection (71). on the other hand, when used in combination with ribavirin, the treatment leads to dose-dependent hemolytic anemia (72). fabrizi et al. (73) performed a meta-analysis and concluded that the efficacy and safety of ifn-based therapies are unsatisfactory with low efficacy and high rate of side effects, particularly when used in transplant patients. this treatment was the standard of care until 1998. later, the introduction of pegylated-ifnα increased the svr and it became the standard of care until 2011. the knowledge of the mechanism of action of hcv and the viral proteins involved in its replication allowed for the development of specific drugs for direct antiviral (daa) treatment. the first generation of daa was represented by boceprevir and telaprevir, which inhibit the ns3/4a protease activity. however, these drugs frequently induced viral resistance and therefore are combined with pegifn and ribavirin. there are four classes of daa agents based on their mechanisms of action (table 3). c e1 e2 p7 ns2 ns3 ns4a ns4b ns5a ns5b 5’ntr 3’ntr direct ac�ng an�virals ns3/4a inhibitors protease inhibitors simeprevir paritaprevir grazoprevir ns5a inhibitors daclatasvir ledipasvir ombitasvir elbasvir velpatasvir ns5b inhibitors sofosbuvir dasabuvir structural proteins nonstructural proteins figure 2. the hepatitis c virus genome and target sites of action of the direct-acting antiviral agents (6). table 3. the four classes of direct-acting antiviral agents the four classes of daas mechanism of action drugs (targeted genotypes in brackets) ns3/4a pis block a viral enzyme (protease) that enables the hcv to survive and replicates in the host cells simeprevir (1, 4) paritaprevir (1, 4) grazoprevir (1, 3, 4) nucleoside and nucleotide ns5b polymerase inhibitors target the hcv to stop replicating itself in the liver sofosbuvir (1-4) ns5a inhibitors block a virus protein, ns5a, that hcv needs to replicate ombitasvirb (1, 4) pibrentasvir (1-6) daclatasvir (3) elbasvir (1, 4) ledipasvir (1) ombitasvir (1) velpatasvir (1-6) non-nucleoside ns5b polymerase inhibitors stop hcv from reproducing by inserting themselves into the virus so that other pieces of hcv cannot attach to it dasabuvir (1) daas, direct-acting antivirals; hcv, hepatitis c virus. salvadori m and tsalouchos a journal of renal and hepatic disorders 2019; 3(1): 1–14 6 the first class includes the protease inhibitors (pis) acting on ns3/4a. these drugs block a viral enzyme (protease) that enables the hcv to survive and replicate in host cells. the best-known drugs of this class are simeprevir and paritaprevir acting on genotypes 1 and 4, and grazoprevir acting on genotypes 1, 3, and 4. these drugs are usually used in combination to achieve a stable svr (74). the second class comprises nucleoside and nucleotide ns5b polymerase inhibitors that inhibit intrahepatic replication. the main drug belonging to this class is sofosbuvir. sofosbuvir acts against genotypes 1–4 and was recently approved for use in combination with other daas. in particular, sofosbuvir has been studied in the hcv-target study (75). as an increased rate of adverse events was observed in patients with renal failure, the current guidelines of the american association for the study of liver disease (aasld) recommend that sofosbuvir should be used only in patients with an estimated glomerular filtration rate (egfr) higher than 30 ml/min (74). the third class includes the ns5a inhibitors that block the virus protein ns5a, which is required for replication and various stages of infection. several drugs belong to this class, which include ombitasvir (acting against genotypes 1 and 4), pibrentasvir (a pangenotype drug), daclatasvir (acting on genotype 3), elbasvir (acting on genotypes 1 and 4), ledipasvir (acting on genotype 1), and velpatasvir (a pan-genotype drug). a combination of ombitasvir/paritaprevir-ritonavir and dasabuvir is often used and represents the 3d regimen, marketed as viekira pak. this combination has been studied in the ruby-i trial in ckd patients (76) obtaining a svr without side effects. the fourth class of drugs includes dasabuvir, a non-nucleoside ns5b polymerase inhibitor that stops hcv from reproducing by inserting itself into the virus so that other pieces of the hcv cannot attach to it. all the currently recommended regimens include at least two agents of different classes. the most common combination is a ns5a inhibitor with a polymerase inhibitor or a protease inhibitor. for resistant populations, the addition of ribavirin is recommended (77). treatment of hcv-related cryoglobulinemic gn in the days of interferon therapy, peg-ifn or ribavirin (rbv) in combination with rituximab (rtx) was found to be more effective than peg-ifn or rbv alone in the treatment of hcv-associated mc (78, 79). although the discovery of new daas has revolutionized the therapeutic approach, data on their efficacy in patients with hcv-associated cryoglobulinemic vasculitis and gn are disappointing, probably due to the inability of the drugs to suppress the immune-mediated process (80). rtx, in combination with daa drugs, seems to have some impact on hcv-related cryoglobulinemic vasculitis. however, with the new generation of daas, the percentage of patients needing to receive concomitant immunosuppression is decreasing. forty-three percent of patients treated with first-generation protease inhibitors required rtx or steroids, compared to 17% of patients treated with sofosbuvir (79, 81). in more recent studies on sofosbuvir-based therapy, only 4.5% of patients required rtx (82, 83). in severe forms of cryovasculitis, it is necessary to use immunosuppression as a rescue therapy during treatment with daas (84), and complete remission of mc in response to combination therapy with daa and rtx has been reported (85). all these findings have been incorporated in the recently published kdigo guidelines (86). accordingly, the recommendation is that patients with hcv-related glomerular disease should be initially treated with daa. for those patients who have flares or rapidly progressive kidney failure, in addition to daa, immunosuppression should be used with or without plasma exchange. in the case of lack of response to daa therapy, rtx treatment is recommended. hcv treatment in patients with ckd hcv infection is associated with a higher incidence of decreased egfr, increased risk of ckd progression, and mortality. in a meta-analysis that included 890,560 patients, seropositive patients against hcv had a 70% increased risk of reduced egfr (87) and in the reveal study, hcvpositive patients had a lower egfr and an increased risk of esrd (47, 88). these data were confirmed by another study performed on us veterans (89). in this study, hcv positivity was associated with a deterioration of kidney function and the development of esrd. also, the nhanes iii study confirmed a significantly higher microalbuminuria in hcvpositive patients (90). in addition to specific renal diseases, cardiovascular disease and diabetes mellitus account for the rapid evolution of ckd in hcv patients (31). the discovery of daa agents represented a relevant step in the evolution of hcv treatment by allowing to treat ckd patients independently of the existence of an hcv-related specific nephropathy. the aim of hcv treatment is to reach a stable svr over time as documented by hcv serology and nucleic acid testing (nat), 3 months after the end of treatment (91). most of the daa studies in the general population included patients with normal renal function and randomized controlled trials (rcts) for ckd included patients with stages 4 and 5. as patients with ckd stages 1–3 are not considered a priority (87), data for these patients derive from post-marketing or real-world studies (92). in the trio network, the combination of elbasvir and grazoprevir (ebr/ gzr) obtained a stable svr, and about 50% were ckd stages 1–3 patients (93). the same combination was equally effective in a different study (94). the hcv target database (73) did not find any difference in svr rates comparing different ckd stages. this study as well as a study by sise  et  al. (95) analyzed a sofosbuvir-based regimen. in this study, a sofosbuvir-based regimen reached a stable svr independently of the ckd stage. to date, the use of sofosbuvir is hepatitis c virus and renal disorders journal of renal and hepatic disorders 2019; 3(1): 1–14 7 only recommended for patients with an egfr >30/ml/min, and investigations on the use of sofosbuvir in patients with esrd are underway. based on pharmacokinetic studies, sofosbuvir may accumulate in esrd patients reaching an area under the curve (auc) increase of 171%. reports on safety of sofosbuvir in patients with esrd are still sparse, and the available data are based on few studies with limited number of patients (96–98). the use of daas in patients with ckd stages 4 and 5 (< 30/ml/min) is confirmed by several studies and rcts. in the c-surfer study (99), a combination of grazoprevir and elbasvir achieved a stable svr in esrd patients affected by hcv genotype 1. this combination therapy was approved by the fda in 2016. a retrospective analysis of this combination therapy confirmed its safety and efficacy (100). this is currently the recommended treatment for esrd patients affected by genotype 1 or 4 (table 4) (6). in august 2017, the fda approved the pan-genotypic combination of glecaprevir (ns3/4 protease inhibitor) and pibrentasvir (ns5a inhibitor). the expedition-4 rct investigated this combination (101). the combination therapy administered to esrd patients affected by genotypes 1–6 resulted in a stable svr in 98% of patients, with few adverse events. the results of expedition-4 are encouraging but need confirmatory studies because of the small numbers of patients affected by genotypes 5 and 6. even though daa therapy is expensive, recent studies documented that grazoprevir/elbasvir is cost-effective in the united states (102) and france (103). the recently published kdigo guidelines (104) are in line with these studies and recommend a combination of grazoprevir/elbasvir for hcv patients with ckd stages 4 and 5 (table 5) (104). a relevant question is: “how and when a dialysis patient should be treated?” this is discussed by davis et al. (105). rna-positive patients with an active infection should undergo a complete evaluation of liver disease. if they are affected by a severe decompensate cirrhosis, they should be listed for a combined liver–kidney transplant; otherwise, they can remain on dialysis and get treated for hcv. if the liver evaluation shows only a mild activity with mild fibrosis, then the patients are transplant candidates, and there are two options. first, patients who are transplant candidates and have living donors should be treated immediately for hcv infection and transplanted if found negative. second,  patients who do not have living donors could be listed for hcvpositive cadaver donor if the transplant center accepts this activity or should wait for a cadaver donor and treat hcv while on dialysis and waiting (figure 3). however, dialysis patients who are not transplant candidates should also table 4. recommended direct-acting therapies by egfr and viral genotype (aasld/idsa) (6) kidney function viral genotype recommended daas rating of recommendation egfr >30 ml/min per 1.73 m2 1, 3 daclatasvir (60 mg) 1, a 1, 4 daily fixed-dose combination of elbasvir (50 mg)/ grazoprevir (100 mg) 1–6 daily fixed-dose combination of glecaprevir (300 mg)/ pibrentasvir (120 mg) 1, 4, 5, 6 daily fixed-dose combination of ledipasvir (90 mg)/ sofosbuvir (400 mg) 1–6 daily fixed-dose combination of sofosbuvir (400 mg)/ velpatasvir (100 mg) 1 simeprevir (150 mg) 1–6 daily fixed-dose combination of sofosbuvir (400 mg)/ velpatasvir (100 mg)/voxilaprevir (100 mg) 1–4 sofosbuvir (400 mg) egfr< 30 ml/min per 1.73 m2 1, 4 daily fixed-dose combination of elbasvir (50 mg)/ grazoprevir (100 mg) 1, b 1–6 daily fixed-dose combination of glecaprevir (300 mg)/ pibrentasvir (120 mg) 1, b aasld/idsa, american association for the study of liver disease/ infectious diseases society of america; daa, direct-acting antiviral; egfr, estimated glomerular filtration rate. salvadori m and tsalouchos a journal of renal and hepatic disorders 2019; 3(1): 1–14 8 receive treatment for hcv infection. we have already highlighted that hcv dialysis patients are affected by multiple hepatic and extrahepatic adverse events. early data suggest a benefit with the new daas. the treatment cost does not justify withdrawing treatment for these patients, even if they are not transplant candidates (106). hcv treatment in transplant candidates before or after transplantation the optimal timing to treat kidney transplant candidates is a matter of debate. on one hand, treatment before transplantation decreases early posttransplant complications related to hcv infection. on the other hand, postponing treatment opens the possibility of transplanting a kidney from an hcv-positive donor, which means there is a shorter waiting time. whether or not to treat hcv dialysis patients before transplantation is a concern that should be based on several considerations, such as the extent of liver damage, availability of living donors, and extrahepatic manifestations of hcv. patients with early cirrhosis without portal hypertension are considered for kidney-alone transplantation and the decision to treat with daas prior to transplantation also relies on other factors such as the availability of a living donor (107). in this scenario, it is better to treat before transplant if the transplant itself is not imminent. based on several studies, it could be said that the delay of transplantation should be individualized according to specific conditions (108, 109). extrahepatic manifestations of hcv include mixed cryoglobulinemic syndrome (mcs) and lymphoproliferative disorders. patients table 5. recommended direct-acting antiviral (daa) treatment regimens for patients with chronic kidney disease g4-g5 and kidney transplant recipients by hepatitis c virus genotype (104) kidney function hcv genotype recommended regimen strength of evidence alternate regimen strength of evidence ckd g4–g5 (gfr <30 ml/min per 1.73 m2 ) including kidney transplant 1a grazoprevir/elbasvir 1b ritonavir boosted paritaprevir, ombitasvir and dasabuvir 2d glecaprevir/pibrentasvir 1b daclatasvir/asunaprevir 2c 1b grazoprevir/elbasvir 1b ritonavir boosted paritaprevir, ombitasvir and dasabuvir 2d glecaprevir/pibrentasvir 1b daclatasvir/asunaprevir 2c 2, 3 glecaprevir/pibrentasvir 1b 4 grazoprevir/elbasvir 2d glecaprevir/pibrentasvir 1b 5, 6 glecaprevir/pibrentasvir 2d ktr (gfr> 30 ml/ min per 1.73 m2 1a sofosbuvir with ledipasvir, daclatasvir, or simeprevir 1b sofosbuvir/ribavirin 2d glecaprevir/pibrentasvir 1c 1b sofosbuvir with ledipasvir, daclatasvir, or simeprevir 1b glecaprevir/pibrentasvir 1c 2, 3, 5, 6 glecaprevir/pibrentasvir 1d sofosbuvir/daclatasvir/ ribavirin 2d 4 sofosbuvir with ledipasvir, daclatasvir, or simeprevir 1d glecaprevir/pibrentasvir 1d ktr, kiney transplant; ckd, chronic kidney disease; hcv, hepatitis c virus. hepatitis c virus and renal disorders journal of renal and hepatic disorders 2019; 3(1): 1–14 9 with active hcv-associated mcs should undergo treatment before transplantation in order to avoid further complications (107). a regression of lymphoproliferative disorders related to hcv has been documented in 75% of patients (110). these patients too should be treated before transplantation. the advent of daas made it possible to transplant hcvpositive kidneys into hcv-positive recipients. before the advent of daas, a large study documented the long-term survival of patients transplanted with hcv-positive kidney (111). in the era of daa therapy, several studies have documented that transplantation of an hcv-positive kidney into an hcvpositive recipient, and treatment with daa post-transplant, had excellent outcomes, with stable svr rates (112, 113). in addition, daas have allowed the transplantation of hcvinfected kidneys into hcv-uninfected recipients. in addition to individual reports, two main studies examined this strategy. in the thinker trial, patients were enrolled and treated a few days after transplantation with elbasvir and grazoprevir. recipients became positive after transplantation, but an svr was obtained in all the patients at 3 months (114). in the expander-1 trial, eight patients were transplanted in the same way. daa therapy obtained an svr in 3 months (115). colombo et al. (116) performed a phase 2 rct to evaluate the safety and efficacy of the combination of ledipasvir and sofosbuvir in 114 renal transplant patients with hcv genotype 1 or 4. svr was obtained in all the patients with an excellent renal outcome. saxena et al. (117) reported the efficacy of daa therapy in 443 patients who received either kidney transplant or liver transplant, or combined liver– kidney transplant. the majority of patients were treated with sofosbuvir/ledipasvir with or without rbv. daa therapy was effective and safe in both kidney and liver transplantation. reau et al. (118) in the magellan 2 study investigated the safety and efficacy of glecaprevir and pibrentasvir in liver or kidney transplant patients. svr was achieved in 99% of patients, with a 100% kidney and graft survival. the 2017 aasld (119) published the guidelines for kidney transplant patients, and the kdigo guidelines recall what has been described above on the management of hcv-infected patients before and after kidney transplantation (table 5) (120). one important concern with the new daas in kidney transplant patients is the drug interactions with the immunosuppressive agents. cyclosporine, tacrolimus, and sirolimus are metabolized in the liver by the cytochrome 450. as a result, for most daas, a substrate competition may occur, influencing their elimination. a careful dosage of daas and immunosuppressive agents is therefore recommended (120). hcv rna test no active infection: screen every 6 months active infection mild activity/ mild fibrosis stage liver disease with fibroscan severe fibrosis/ cirrhosis decompensated cirrhosis? high risk of progressive liver disease ? transplant candidate? living donor option? rna negative yes list for combined liver–kidney transplant no yes treat hcv on dialysis no no treat hcv on dialysis yes yes treat hcv on dialysis or after transplant no list for hcv+ kidney and treat hcv after transplant figure 3. algorithm for hepatitis c virus antibody positive dialysis patients to determine timing of treatment (105). salvadori m and tsalouchos a journal of renal and hepatic disorders 2019; 3(1): 1–14 10 conclusion hcv infection is characterized by several extrahepatic disorders, among which renal disorders are frequent and relevant. some of the hcv-related renal disorders include cryoglobulinemic gn, especially mpgn, higher incidence of progression to esrd, and ckd-related mortality rate. the introduction of daas has revolutionized the management of hcv-mediated renal disorders. cryoglobulinemic gn may be controlled using immunosuppressants in addition to daas. patients at various stages of ckd may be treated for hcv to slow down the progression towards esrd. renal transplantation may be performed in hcv patients by treating them with daas before or soon after transplantation. finally, hcv-positive kidneys may be given to hcv-positive or hcv-negative recipients by following specific guidelines. conflict of interest the authors declare no potential conflicts of interest with respect to research, authorship and/or publication of this article. references 1. cacoub p, comarmond c, domont f, savey l, desbois ac, saadoun d. extrahepatic manifestations of chronic hepatitis c virus infection. ther adv infect dis. 2016;3(1):3–14. https://doi. org/10.1177/2049936115585942 2. cacoub p, poynard t, ghillani p, charlotte f, olivi m, piette jc, et al. extrahepatic manifestations of chronic hepatitis c. multivirc group. multidepartment virus c. arthritis rheum. 1999;42(10):2204–12. 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kidney int suppl. 2018;8(3):130–6. https://doi.org/ 10.1016/s2157-1716(18)30010-8 https://doi.org/10.1097/tp.0000000000000847 https://doi.org/10.1111/j.1365-2036.2005.02395.x https://doi.org/10.1111/j.1365-2036.2005.02395.x https://doi.org/10.1111/j.1600-6143.2010.03280.x https://doi.org/10.1097/tp.0000000000001336 https://doi.org/10.1111/tri.12954 https://doi.org/10.7326/m17-2871 https://doi.org/10.7326/m16-1205 https://doi.org/10.7326/m16-1205 https://doi.org/10.1002/hep.29258 https://doi.org/10.1002/hep.30046 https://doi.org/10.1002/hep.30046 https://doi.org/10.1093/cid/ciy585 https://doi.org/10.1016/s2157-1716(18)30010-8 jrenhep017 10..24 jrenhep.com codonpublications.com review article concepts in diabetic nephropathy: from pathophysiology to treatment mustafa kinaan 1 , hanford yau 1,2,3 , suzanne quinn martinez 1,2 , pran kar 1,4 1university of central florida college of medicine, orlando, fl, usa; 2division of endocrinology, orlando va medical center, orlando, fl, usa; 3university of california, san francisco – school of medicine, san francisco, ca, usa; 4division of nephrology, orlando va medical center, orlando, fl, usa abstract since the 1930s when kimmelstiel and wilson first described the classic nodular glomerulosclerosis lesions in diabetic kidneys, nephropathy has been recognized as a major and common complication of diabetes. nearly 40% of diabetics around the world have microalbuminuria, a marker of progression to chronic kidney disease (ckd). diabetic kidney disease (dkd) is also considered a leading cause of ckd worldwide. given the significant morbidity, mortality, and health-care burden, several clinical and scientific societies continue to seek a better understanding of this disease. screening for microalbuminuria and controlling hyperglycemia remain the pillars for the prevention of diabetic nephropathy. however, evidence from multiple studies suggests that controlling dkd is more challenging. some studies suggest that there is variability in the incidence of renal complications among patients despite comparable hyperglycemic control. therefore, there has been great interest in studying the inherent, renal protective role of the different antihyperglycemic agents. this review will shed light on the pathophysiology, screening, and diagnosis of dkd. it will also discuss the treatment and prevention of diabetic nephropathy, with a specific focus on comparing the mechanisms, safety profiles, and efficacy of the different antihyperglycemic medications. keywords: chronic kidney disease; diabetes; diabetic complications; diabetic nephropathy; microalbuminuria received: 21 may 2017; accepted after revision: 07 june 2017; published: 30 june 2017. author for correspondence: mustafa kinaan, university of central florida, college of medicine, internal medicine resident (pgy-3), 6850 lake nona blvd, orlando, fl 32827, usa. email: mustafa.kinaan@ucf.edu how to cite: kinaan m et al. concepts in diabetic nephropathy: from pathophysiology to treatment. j ren hepat disord 2017;1(2):10–24. doi: http://dx.doi.org/10.15586/jrenhep.2017.17 copyright: kinaan m et al. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction diabetes and chronic kidney disease (ckd) are worldwide public health problems that affect millions of people. a study speculates that the global prevalence of diabetes mellitus would grow from 2.8% in 2000 to nearly 4.4% in 2030, equivalent to nearly 366 million people. the greatest increases in prevalence are anticipated to occur in the middle east, subsaharan africa, and india (1). another global epidemiologic study estimated that 382 million people had diabetes in 2013, a number that is expected to rise to 592 million by 2035 (2). this pattern is even more pronounced in the united states with anticipated 165% increase in the prevalence of diabetes between 2000 and 2050 (3). diabetes is a leading cause of ckd worldwide. nearly 43% of diabetics in the united states have microalbuminuria, a marker of progression to ckd. according to data from national health and nutrition examination survey (nhanes), diabetic kidney disease (dkd) accounts for 39% of prevalent kidney failure (4). with the increasing prevalence of ckd, the costs of management are becoming a public health issue. in 2013, more than journal of renal and hepatic disorders 2017; 1(2): 10–24 mailto:mustafa.kinaan@ucf.edu http://dx.doi.org/10.15586/jrenhep.2017.17 http://creativecommons.org/licenses/by/4.0 30 billion dollars from medicare expenditure were spent on management of end-stage renal disease (esrd), 14 billion of which were due to dkd (4). given these factors, clinical societies continue to offer strategies to diagnose and manage dkd to improve outcomes. pathophysiology diabetes leads to progressive structural alterations of the kidneys including extracellular matrix (ecm) accumulation in the mesangium, glomerular basement membrane, and tubulointerstitial tissue. the pathophysiology of diabetic nephropathy is complex and multifactorial. poor glycemic control was previously considered the sole driving factor that drives diabetic nephropathy. however, some studies demonstrated variability in the development of renal complications despite comparable hyperglycemic control. for example, the diabetes control and complications trial (dcct) showed that nearly 30% of type i diabetics and 25%–40% of type ii diabetics develop nephropathy despite intensive glycemic control (5). variations between ethnic groups also point to the significant role of genetic background. relatives of african americans on renal replacement therapy secondary to diabetic nephropathy are at fivefold risk of developing esrd (6). additionally, the incidence of esrd per capita in african americans, hispanics, and native americans is significantly higher than the white population (7). the incidence of proteinuria among pima indians has also been increasing over the past 36 years. however, the incidence of progression to esrd declined after 1990, possibly due to improved control of risk factors (8). a multicenter study in 10 asian countries on type ii diabetic patients of different ethnic groups showed nearly 40% prevalence rate of microalbuminuria, a worrisome marker for developing esrd (9). familial aggregation further supports the role of genetics in development of esrd. a large population-based study showed that nearly 23% of incident dialysis patients had relatives with esrd, with greater prevalence in african americans compared to european americans (10). individuals with family history of esrd were also more likely to have diabetes and obesity (11). ages, rage, and oxidative stress advanced glycosylation end products (ages) are the result of nonenzymatic interaction of sugars like glucose with amino acid groups of proteins, lipoproteins, and nucleic acids. alteration of these cellular components leads to the formation of various reactive intermediate products like α-dicarbonyls or oxoaldehydes. these intermediate products react with intracellular and extracellular proteins to form irreversibly covalent products, known as ages. circulating ages have been implicated in the pathophysiology of diabetic nephropathy through mechanisms that are either receptor-dependent or receptor-independent. ages modify basement membrane proteins, cross-link ecm components, and increase expression of type iv collagen. these changes lead to structural alterations of the surface charge, membrane permeability, proteolytic digestion, and membrane stability. these changes disrupt intercellular interaction, and hence cause impairment of tissue function and maintenance (12). as for the receptor-dependent mechanisms, ages interact with a wide array of receptors on various cell types such as macrophages, monocytes, endothelial cells, podocytes, tubular epithelial cells, and smooth muscle cells. examples of these receptors are the macrophage scavenger receptor type i and ii, age-r1, age-r2, age-r3, receptor for age (rage), and cd36. rage is a multi-ligand receptor that mediates intracellular and extracellular signaling pathways leading to immune response initiation. this receptor exists in full-length, surface-bound form or as a soluble, truncated form known as soluble rage (srage). it is hypothesized that srage competes with full-length rage over ligand binding. the off-balance between the syntheses of these two forms is one of the age-induced nephropathy mechanisms (13). rage activation by ages leads to activation of several signal transduction pathways that lead to the generation of reactive oxygen species (ros) and activation of transcription factors, such as nf-kappab. consequently, nf-kappab leads to the release of cytokines and growth factors, including transforming growth factor-β1 (tgf-β1), interleukin-1β and interleukin-6, insulin-like growth factor-1, tumor necrosis factor (tnf-α), and platelet-derived growth factor. these proinflammatory growth factors play a key role in the development of diabetic complications (14). for example, tgf-β1 leads to the overexpression of mrna of glucose transporter 1 (glut-1) in mesangial cells, eventually leading to increased glucose uptake by cells and accelerated metabolic abnormalities (15). human studies support the proposed age-driven mechanism of diabetic nephropathy. a study in type i diabetic patients showed that significantly elevated levels of fluorescent non-carboxymethyllysine ages correlate with the deterioration of renal function (16). similarly, levels of ages concentrations were increased in type ii diabetic patients with nephropathy (17). as for other age receptors, age-r1 and age-r3 are considered clearance receptors. age-r1 expression is suppressed in diabetic human beings and mice, suggesting possible protective role against ages. whereas, age-r3 is involved in age turnover, tissue integrity, and macrophage endocytosis. these are important compensatory mechanisms that counteract age-induced injury. age-r2, like rage, is involved in fibroblast growth factor signaling and the inflammatory response propagation (14). metabolic reactions result in the formation of active byproducts and free radicals known as ros and reactive nitrogen species. inadequate removal of these active molecules leads to detrimental effects on the cellular level, a process known as oxidative stress. examples of these radicals are superoxide, peroxyl, hydroxyl, and hydroperoxyl molecules. superoxide (o2 −) is a common radical implicated in diabetic complications. diabetic nephropathy: from pathophysiology to treatment journal of renal and hepatic disorders 2017; 1(2): 10–24 11 it is produced by mitochondrial electron transport chain, oxidative phosphorylation, nad(p)h oxidase, cytochrome p-450, nitric oxide synthase, and other enzymatic processes (14). normally, superoxide radicals are eliminated by mitochondrial and cytosolic antioxidant defense mechanisms. impaired clearance, as in diabetes, leads to the oxidation of membrane lipids, dna, proteins, and carbohydrates. these alterations lead to impaired structure and function of several cellular components. there is evidence that diabetic complications arise from interplay between pathways of ages and oxidative stress. a study showed that diabetic glomerular lesions might undergo autoxidation by ros and could be converted to reactive carbonyl compounds, a subgroup of ages (18). sodium glucose cotransporter (sgl-2) a new target for pharmacotherapy of diabetic nephropathy is sodium–glucose cotransporter-2 (sglt-2), a major determinant of glucose reabsorption in kidneys. hyperglycemia and hyperinsulinemia in early diabetes may lead to increased expression of sglt-2, and hence, glucose reabsorption. this in turn is believed to lead to worsening of hypertension and maintain hyperglycemia (19). with emergence of sglt-2 inhibitors, studies started to examine the possible protective role of these medications on the kidneys. increasing tubuloglomerular feedback, weight loss, lowering blood pressure by osmotic diuresis, and decreasing inflammation through activation of ace2 and angiotensin 1-7/1-9 upregulation are all possible mechanisms of renal protection by sglt-2 inhibition (20, 21). glucagon-like peptide-1 glucagon-like peptide-1 (glp-1) is an incretin hormone that stimulates insulin secretion from β-islet cells. in addition to its antihyperglycemic function, glp-1 has antioxidative protective role in various tissues. glp-1 receptor (glp-1r) is expressed in pancreas, brain, gut, heart, lung, and kidneys. activation of this receptor leads to the stimulation of adenylate cyclase which in turn increases the production of cyclic adenosine monophosphate (camp). increased levels of camp lead to the activation of protein kinase a or guanine nucleotide exchange factor ii (epac2). this pathway mediates insulin secretion and inhibits renal nad(p)h oxidase, a major source of oxidative stress. a study showed that treatment with glp-1r agonist reduced albuminuria and mesangial expansion, and reduced expression of glomerular superoxide. these findings highlight the protective role of glp-1 pathway and its potential as a target for pharmacotherapy (22). screening and diagnosis historically, the term “diabetic nephropathy” has been used loosely to describe the pathologic effect of diabetes on renal function. however, there are key definitions and stages of this process to assist with diagnosis and management. dkd is the finding of proteinuria in a person with diabetes, regardless of the presence of pathologic changes or a decreased glomerular filtration rate (gfr). diabetic glomerulopathy on the other hand, is a term reserved for biopsy-proven renal disease caused by diabetes. measuring serum albumin on spot urine tests is the first step in screening and diagnosis of diabetic nephropathy as recommended by most professional medical societies concerned with diabetes and kidney disease (23). albuminuria over the years, the threshold for detection of albuminuria has changed with the introduction of more sensitive assays. albuminuria is reported as albumin excretion rate (aer), albumin-to-creatinine ratio (acr), or urinary albumin concentration (uac). estimation of aer is obtained from timed collections (expressed in µg/min) or 24-h collection (expressed in mg/24 h). urine spot test on the other hand provides information about acr (expressed in mg/g creatinine) and uac (mg/l). patients with acr between 30 and 300 mg/g creatinine on spot urine test (aer 20–200 µg/min or 30–300 mg/24 h) are considered to have microalbuminuria. greater degrees of albumin excretion are referred to as macroalbuminuria. variations in acr with gender are expected, given lower urine creatinine levels in females, which make diagnostic thresholds higher in females compared with males. sensitivity and specificity of acr is between 92% and 94%, whereas sensitivity and specificity of uac is between 89% and 90%, at discriminator value of 15 mg/l. although acr performs better than uac statistically, gender variations and cost make uac a feasible and accurate option (24). other studies suggest that using 17 mg/l of uac as cutoff for detecting microalbuminuria yields 100% sensitivity and 80% specificity when 24-h urine collection was used as reference (25). although patients with microalbuminuria have stable kidney function, they are at risk of progressing to macroalbuminuria and kidney failure (26). physicians must be cognizant of the variability in urine albumin excretion. levels can vary with exercise, time of day, fever, infection, heart disease, degree of hyperglycemia at time of collection, pregnancy, hypertension, and other physiologic processes (27). therefore, at least two specimens within 3 to 6 months should be obtained to confirm staging. twenty-four-hour and timed collections are cumbersome and prone to collection errors. glomerular filtration rate gfr should be measured routinely when screening for diabetic nephropathy. data from nhanes iii (third national health and nutrition examination survey) showed that nearly 30% of type 2 diabetic patients had worsening gfr despite absence of albuminuria and retinopathy (28). this might suggest that albuminuria may not truly reflect kinaan m et al. journal of renal and hepatic disorders 2017; 1(2): 10–24 12 underlying dkd and raises the question of the inevitability of the disease progression (29). american diabetes association, national kidney foundation, and other medical societies support annual screening for microalbuminuria, but they recognize the need for further studies to outline benefits of this approach. there is still lack of strong evidence about benefit of screening on major outcomes like esrd, cardiovascular risk, morbidity, and mortality. gfr can be measured by clearance of endogenous creatinine, insulin clearance, 51cr-edta, 125i-iothalamate, or iohexol techniques. equations for estimation of gfr are commonly used in clinical practice. national kidney foundation recommends using the modified diet in renal disease (mdrd) equation, which is more accurate than the cockroft–gault equation (30). retinopathy concomitant presence of retinopathy has been considered a helpful finding in screening for diabetic nephropathy. however, careful interpretation of the presence or lack of retinopathy must be done. type i diabetics with nephropathy almost always have signs of other microvascular complications like retinopathy or neuropathy (31). this correlation is not as clear with type ii diabetes. for example, in type ii diabetic patients with macroalbuminuria, the positive predictive value (ppv) of retinopathy for diabetic glomerulopathy ranges between 67% and 100%. however, the negative predictive value (npv) is lower, ranging between 20% and 84%. on the contrary, type ii diabetic patients with microalbuminuria had npv close to 100% and ppv as low as 45%. hence, the presence of retinopathy is strongly suggestive of dkd in type ii diabetics with macroalbuminuria, whereas its absence is highly indicative of non-dkd pathology in type ii diabetics with microalbuminuria (32). given shared determinants like poor glycemic control, hypertension, and hyperlipidemia between diabetic retinopathy and nephropathy, retinopathy should be considered a marker of microvascular involvement rather than a risk factor or diagnostic finding for dkd. atypical features presence of albuminuria and reduced gfr in patients in the absence of other identifiable causes of kidney disease are enough for establishing diagnosis of dkd. because diabetes is a highly prevalent problem, coincidence with other nondiabetic pathologies is somehow frequent. therefore, atypical features such as refractory hypertension, presence of urine sediments, nephrotic syndrome, rapid disease progression despite proper glycemic control, and renin–angiotensin system blockade should prompt further evaluation for nondiabetic kidney disease. workup for concomitant nondiabetic kidney disease should be tailored based on the patient’s medical history and risk factors. kidney biopsy can be very valuable in evaluating the underlying disease, but bleeding complications should be considered. diabetes causes several pathologic changes to the mesangium, tubules, and vasculature in the kidneys. these changes can be classified into four progressive groups according to the renal pathology society classification. class i is characterized by isolated glomerular basement membrane thickening and mild, nonspecific changes in the mesangium. mesangial expansion without diffuse glomerulosclerosis or nodular sclerosis (kimmelstiel– wilson lesions) is seen in class ii diabetic nephropathy. nodular sclerosis is noted in class ii, whereas more severe mesangial matrix changes are noted in class iii. global glomerulosclerosis involving more than 50% of glomeruli is the hallmark of class iv diabetic nephropathy (33). glycemic control: glycemic goals and measurements standard versus intensive control diabetic complications including nephropathy are mainly driven by hyperglycemia-induced vascular injury. therefore, glycemic control is in the center of management of dkd which may slowly progress to esrd. major medical societies like the national kidney foundation and the american diabetes association recommend intensive glucose control to goal hemoglobin a1c (hba1c) levels <7%. the dcct study closely examined the effect of intensive glycemic control compared with conventional treatment on the development of diabetic complications in 1441 subjects with type i diabetes. intensive treatment led to about 2% more reduction in hba1c in comparison to conventional treatment. after 6.5 years of intensive treatment, the incidence of microalbuminuria was reduced by nearly 34% in primary prevention group (patients with no retinopathy or albuminuria at baseline) and by 43% in secondary prevention group (patients with retinopathy and with or without albuminuria but normal gfr at baseline) (5). in 1993, the epidemiology of diabetes interventions and complications (edic) observational study examined 1349 of the original subjects from the dcct study. persistent benefits of intensive glycemic control on albuminuria were noted at 7–8 years after dcct study closeout (34). the dcct/edic research group further confirmed the persistence of these results after median follow-up period of 22 years (35). these results affirmed that intensive glycemic control should be pursued early in type i diabetic while keeping patient’s safety in mind and avoiding hypoglycemia. similar association between poor glycemic control and development of albuminuria is noted with type ii diabetes. the kumamoto study was designed similar to dcct, with 110 japanese subjects with type ii diabetes. mean hba1c was 7.1% in intensive glycemic control group compared to 9.4% in conventional treatment group. during 6 years, only 7.7% of subjects in the primary prevention group receiving intensive treatment developed albuminuria compared to 28% in the conventional treatment group. however, subjects of this trial were relatively young with normal body mass diabetic nephropathy: from pathophysiology to treatment journal of renal and hepatic disorders 2017; 1(2): 10–24 13 index, features that are not necessarily typical or generalizable to type ii diabetes population (36). in 1998, a larger trial that examined glycemic control effect on nephropathy was the united kingdom prospective diabetes study (ukpds) that examined 3867 newly-diagnosed type ii diabetics. this study randomized patients to conventional treatment with diet only versus intensive treatment, which was defined by goal fasting glucose of 108 mg/dl. diet, metformin, sulfonylurea, insulin, or a combination of agents, were used to achieve intensive control. over 10 years, mean hba1c in intensive group was 7.0% compared to7.9% in the conventional group, with no significant differences in hba1c among agents in the intensive group. relative risk reduction for the development of microalbuminuria after the duration of the study was 24%. no differences in risk reduction were noted between agents in the intensive group (37). effect of intensive glycemic control on diabetic complications in a population of 153 veterans was examined by veterans affairs cooperative study of diabetes mellitus (vacsdm). after 2 years, the incidence of microalbuminuria in the intensive treatment group (mean hba1c of 7.1%) was 17% compared to 35% in the conventional treatment group (mean hba1c of 9.2%). veterans who had microalbuminuria at baseline, and received intensive treatment, had retardation of the progression of albuminuria, but still had deterioration of creatinine clearance at 2 years nonetheless (38). the veterans affairs diabetes trail (vadt) was a large study with mean followup of 5.6 years that examined the effects of intensive glycemic control on vascular complications, mainly cardiovascular events. the study included nearly 1791 veterans with suboptimal diabetes type ii control. although the study showed no significant improvement in cardiovascular events, death, neuropathy, or retinopathy with intensive control (mean hba1c 6.9%) compared to the conventional treatment group (mean hba1c 8.4%), there was modest improvement in the progression of albuminuria. however, this improvement in albuminuria did not translate into prevention of creatinine and gfr worsening (39). lack of benefit of intensive control in vadt and vacsdm might be secondary to shorter follow-up duration (possible delayed effect of glycemic control) or longer duration of diabetes in the included veterans compared with the newly-diagnosed subjects in ukpds. in the action in diabetes and vascular disease: preterax and diamicron mr controlled evaluation (advance) trial, approximately 11,000 patients were randomized to intensive therapy (mean hba1c 6.5%) compared with standardcontrol group (mean hba1c 7.3%) and were followed up for median of 5 years. there was no significant improvement in retinopathy or macrovascular outcomes; however, intensive control was associated with 21% relative risk reduction in new or worsening nephropathy (defined as macroalbuminuria, doubling of creatinine, the need for renal replacement therapy, or death secondary to renal disease) (40). a followup study of the advance trial participants showed persistence of these results with no improvement in retinopathy or macrovascular outcomes but reduction in the progression to esrd after median total follow-up of 9.9 years (41). in the action to control cardiovascular risk in diabetes (accord) trial, 10,250 patients with type ii diabetes were assigned to intensive (median hba1c 6.4%) versus standard glycemic control (median hba1c 7.5%) and followed up for median 3.7 years. because of higher cardiovascular deaths in the intensive treatment group, patients were switched to standard treatment and microvascular outcomes were followed for the remaining duration of the study (5 years). there was 29% reduction in developing macroalbuminuria at transition and study end with the intensive treatment. there was 19% reduction in development of microalbuminuria at time of transition only with the intensive treatment (42). worsening or lack of improvement in the cardiovascular outcomes from the accord and advance trials despite the improvement of nephropathy markers raises concerns about glycemic control. intensive glucose control should be pursued in low-risk groups to avoid harm from hypoglycemia. as gfr deteriorates, patients become more prone to hypoglycemia, secondary to factors such as prolonged action of insulin, deficiency of gluconeogenic precursors, and malnutrition. hence, caution with glycemic control is warranted especially in advanced kidney disease. limitations of glycemia measurements intensive treatment is not the only area of uncertainty in management of dkd. the reliability of several glycemic measurement tests has been questioned. hba1c estimates time-averaged exposure to glucose for a red blood cell with 120-day life cycle. however, as kidney function deteriorates, the life cycle of red blood cells becomes much shorter, resulting in falsely lower hba1c readings (43). other comorbidities noted in dkd like acid–base disturbances, anemia, and erythropoietin deficiency may further lower hba1c (43). although imprecise, hba1c should still be performed to assist with therapy decisions while being cognizant of its limitations. serum fructosamine, a test reflecting glycemic levels over 2–3 weeks period, is a possible alternative to hba1c. it also reflects levels of total glycated serum proteins (43). therefore, it might be falsely decreased in dkd secondary to hypoalbuminemia. serum concentration of 1,5-anhydroglucitol, a monosaccharide that is present in nearly all foods, can be utilized to assess glycemic control. renal reabsorption of this sugar is dependent on glucose concentration and will be lost in the urine when blood glucose level is higher than 180 mg/dl (43). since many diabetics usually have higher levels of hyperglycemia, the utility of this test is very limited. in particular, it is not recommended in advanced kidney disease. glycated albumin is a new marker that reflects average glucose levels over 2–3 weeks. unlike hba1c, this test is not affected by low gfr or anemia. however, there is lack of data regarding clinical outcomes and correlation of levels with diabetic kinaan m et al. journal of renal and hepatic disorders 2017; 1(2): 10–24 14 complications. given the limitations of the aforementioned tests, self-monitoring of blood glucose remains the most valuable tool to guide treatment (43). glycemic control: antihyperglycemic agents like all diabetic complications, hyperglycemia is the major contributing factor to vascular injury and renal disease. therefore, antihyperglycemic agents are expected to exhibit their renal protective properties by controlling glucose levels. however, there is variability in incidence of renal complications with different antihyperglycemic agents despite comparable glycemic control. this observation led to interest in the inherent renal protective role of these agents that is independent of their antihyperglycemic effect (figure 1). our current understanding of these mechanisms is discussed in detail in the following sections. metformin metformin, a drug that was first used in 1958, is widely prescribed for its hypoglycemic and pleiotropic effects (e.g., endothelium protection, polycystic ovarian syndrome, hepatic steatosis, and obesity) (44). although it is considered the first line of treatment of diabetes, there is controversy about its safety in patients with kidney disease. for many years, the fear of developing lactic acidosis in patients with elevated creatinine deterred a lot of physicians from prescribing the medication. previous u.s food and drug administration (fda) guideline advised against using metformin in men with serum creatinine greater than or equal to 1.5 mg/dl and in women with serum creatinine greater than or equal to 1.4mg/dl. several proposed mechanisms link metformin to lactate accumulation (45). several mechanisms were proposed for metformin-associated lactic acidosis including inhibition of lactate conversion through gluconeogenesis in the liver, increased production by glycolysis augmentation, and activation of anaerobic metabolism of glucose in the intestine (46). these mechanisms do not lead to significant accumulation of lactate at usual metformin therapeutic doses because of the conversion of lactate back to glucose in the liver via the cori cycle (46). nevertheless, high levels of metformin reduce lactate clearance by the liver, which might ultimately lead to metformin-induced lactic acidosis. on the contrary, several studies questioned whether lactic acidosis in diabetic patients can solely be attributed to metformin use (46). diabetic patients are predisposed to hyperlactemia with lactate levels being double than those in healthy individuals. ketoacidosis, heart failure, impaired circulation, liver dysfunction, and physical exercise are all factors contributing to elevated lactate regardless of metformin use (46). although reported in literature, the risk of metformin-induced lactic acidosis is low and not strongly supported by epidemiologic evidence. a cochrane analysis of pooled data from 347 studies examined approximately 70,000 patient-years of metformin use. the study revealed no increased risk of fatal or nonfatal lactic acidosis compared to other antihyperglycemic treatments (47). given mounting evidence against the significance of “pure” metformin-induced lactic acidosis, the fda announced early in 2016 that metformin can be used safely in patients with stable mild-to-moderate renal impairment. metformin use is still contraindicated in patients with gfr < 30 ml/min/1.73m2, but no dosage adjustments are needed figure 1. the different antihyperglycemic agents exhibit their renal protective properties through hyperglycemia-dependent and independent mechanisms. this figure attempts to map out our understanding of some of these mechanisms. diabetic nephropathy: from pathophysiology to treatment journal of renal and hepatic disorders 2017; 1(2): 10–24 15 for gfr > 45 ml/min/1.73m2. initiation of metformin is not recommended or 50% dosage reduction is advised for gfr between 30 and 45 ml/min/1.73m2. frequent monitoring of renal functions is encouraged and discontinuation of treatment is necessary in the presence of concurrent conditions that further increase the risk of lactate accumulation (e.g., sepsis, acute kidney injury, shock, use of radiographic contrast, or myocardial infarction). second-generation sulfonylureas sulfonylureas are medications that bind to atp-sensitive k+ (katp) channels on the membranes of pancreatic beta cells (48). this leads to trapping of potassium intracellularly, causing cell depolarization and opening of voltage-gated calcium channels (48). the influx of intracellular calcium causes increased secretion of insulin. first-generation sulfonylureas (e.g., chlorpropamide, tolbutamide, acetohexamide) are not commonly used, given the risk of hypoglycemia owing to their long duration of action, risk of hyponatremia, and possible increased cardiovascular risk. second-generation sulfonylureas (e.g., glipizide, glyburide, glimepiride) are more commonly used for diabetes control (49). glyburide is almost entirely metabolized by the liver, with elimination of active metabolites in the urine (49). impaired renal function may lead to higher levels of active metabolites and increased risk of hypoglycemia. therefore, its use in ckd is not recommended. interestingly, although metabolized by the liver, glyburide levels were lower than expected in patients with ckd while metabolites remained elevated. this was attributed to possible decreased protein binding leading to rapid metabolism and elimination of parent drug (49). rapid metabolism of glyburide might contribute to risk of hypoglycemia in ckd. glipizide on the other hand is metabolized by the liver into inactive metabolites whose clearance is not affected by renal impairment. hence, dose adjustments for glipizide are not necessary. nonetheless, cautious use of sulfonylureas is necessary, given their inherent hypoglycemic effect (43). thiazolidinediones thiazolidinediones (tzds) (e.g., rosiglitazone, pioglitazone) are medications that act through the activation of peroxisome proliferator–activated receptors, a group of nuclear receptors (50). this process leads to the activation of an intranuclear pathway that leads to increased transcription of specific genes, and consequently, increased storage of fatty acids in the adipose tissue and increased cellular utilization of glucose and carbohydrates. eventually, these changes result in lower circulating fatty acids and glucose, and improved insulin sensitivity (50). like sulfonylureas, tzds are metabolized by the liver and no dosage adjustments are needed. relatively small studies evaluated whether tzds were more efficacious than metformin, sulfonylureas, or diet in decreasing albuminuria in type ii diabetics. in a 52-week cardiac safety study, rosiglitazone was associated with a decrease in microalbuminuria compared to glyburide (51). similar outcomes were noted when comparing troglitazone with metformin. it is not clear if tzds truly have a renal protective role or if these changes were because of better control of glycemia and hypertension in the involved subjects. however, side effects such as hypertension, fluid retention, increased fracture risk in women, bladder cancer, and anemia make its use in ckd unfavorable (43, 49). alpha-glucosidase inhibitors acarbose and miglitol are saccharides that bind to key enzymes in the small intestine that are required for carbohydrate absorption (48). competitive inhibition of these enzymes leads to reduced glucose absorption from food which leads to improved serum glucose levels. high frequency of gastrointestinal side effects, like flatulence, and modest hba1c-lowering effect (0.5%–1.0%) limit the use of those medications. there is no need for dose adjustments in mild or moderate ckd, but they should be avoided when gfr is less than 30 ml/min/1.73m2 due to increased plasma levels. there is lack of clinical data comparing alpha-glucosidase inhibitors (agis) to other antidiabetic agents in context of renal outcomes (49, 52). dipeptidyl peptidase-4 inhibitors dipeptidyl peptidase-4 (dpp-4) inhibitors or gliptins (e.g., sitagliptin, saxagliptin, and linagliptin) are relatively new hypoglycemic medications that were first approved by the fda for diabetes treatment in 2006. these medications inhibit dipeptidyl peptidase whose function is to inactivate incretins, glp-1, and gastric inhibitory polypeptide (53). subsequently, elevated levels of incretins lead to stimulation of insulin release and inhibition of glucagon release. these changes lead to lowering of blood glucose. with the exception of linagliptin, these medications require dosing adjustments in renal impairment. given lower risk of hypoglycemia, dpp-4 inhibitors are potentially useful in ckd patients, a population more prone to hypoglycemia (49). the effect of dpp-4 inhibitors on inflammation and microvascular complications was examined by several experimental studies. dpp-4 (also known as cd26) is expressed in the epithelial cells, renal tubules, endothelial cells, and as well as leukocytes. it can bind adenosine deaminase, the deficiency of which can lead to impaired cellular and humoral immunity (54). therefore, dpp-4 has been considered a possible culprit of renal injury and interest in its inhibition became a focus of many studies. however, the results were conflicting. tofovic et al. (55) showed that sitagliptin enhanced renovascular response to angiotensin ii in hypertensive rats, an effect that may cause a decline in renal function. in contrast, a study by mega et al. (56) found that chronic low-dose sitagliptin in diabetic rats led to improvement of glomerular, tubulointerstitial, and vascular lesions. a japanese study of 36 type ii diabetic patients with inadequate control despite diet, exercise, and medical kinaan m et al. journal of renal and hepatic disorders 2017; 1(2): 10–24 16 management showed that treatment with sitagliptin led to lowering of postprandial glucose, hba1c, glycated albumin, blood pressure, and acr after 6 months of sitagliptin. however, it is not clear if these findings were independent of improved glycemic control (57). a pooled analysis of four studies with 217 subjects with type ii diabetes and albuminuria despite raas blockade (acr of 30–3000 mg/g creatinine) examined the effect of linagliptin on renal outcomes. this study concluded that the use of linagliptin in addition to stable raas inhibitors led to significant albuminuria reduction, independent of changes in glucose level or blood pressure (58). however, none of these studies were designed to specifically evaluate the effect of linagliptin on microalbuminuria. the efficacy, safety & modification of albuminuria in type 2 diabetes subjects with renal disease with linagliptin (marlina–t2d™) trial is a recent multicenter, multinational, randomized, double-blind, placebo-controlled trial that specifically evaluated the effects of linagliptin on glycemic control and renal function compared to placebo in total 350 patients. in 2016, the trial concluded and linagliptin was found to significantly reduce hba1c by 0.6% over 24 weeks. however, no significant changes in albuminuria were noted compared to placebo group (59, 60). interestingly, in the saxagliptin assessment of vascular outcomes recorded in patients with diabetes mellitus (savor) trial, patients receiving saxagliptin had better renal outcomes at the end of trial compared to placebo group. approximately 13% of saxagliptin group had worse acr compared to 15.9% of those in placebo group. also, more people in saxagliptin group had improvement in acr ratio compared to placebo group, 10.7% and 8.7%, respectively. although the difference in hba1c was relatively small, it is unclear whether this desirable effect is secondary to glycemic control or inherent property of saxagliptin (61). the data from savor-thrombolysis in myocardial infarction (savor-timi 53) trial did report improvement in acr that is not accounted for by changes in hba1c (62). glp-1r agonists glp-1 is an incretin and neuropeptide that is secreted in the intestine and hypothalamus in response to the presence of nutrients. it has potent antihyperglycemic effects such as enhancement of glucose-dependent insulin secretion, proliferation of β-cells, and inhibition of β-cell apoptosis. it also slows gastric emptying, increases satiety, and results in body weight loss (63). glp-1r agonists also have antioxidative and pleiotropic properties (64). liraglutide has been shown to inhibit nadph oxidase, nf-κb, and tnfα-induced oxidative stress pathways in endothelial cells (65). in an experimental study, fujita et al. (23) showed that glp-1 receptors are present in glomerular capillary wall, but not tubules, in mice. their study also showed that glp-1r-deficient mice had higher urinary albumin levels, increased oxidative stress markers, and more advanced mesangial expansion than mice in the control group despite comparable hyperglycemia levels. on the contrary, liraglutide treatment in nephropathyprone mice showed reduced albuminuria, mesangial expansion, and superoxide levels. these findings are suggestive of direct protective role against oxidative stress (22). another experimental study in streptozotocin-induced diabetic rats showed inhibition of oxidative stress and normalization of urinary albumin with liraglutide treatment (66). clinically, liraglutide has been shown to reduce albuminuria. the scale diabetes randomized trial showed nearly 18% reduction in acr in patients receiving 3.0 mg/day dosing of liraglutide for 56 weeks compared to placebo (67). the liraglutide effect and action in diabetes: evaluation of cardiovascular outcome results (leader) trial examined the effect of liraglutide treatment and safety in more than 9000 patients. this trial demonstrated better renal outcomes in liraglutide treatment group compared to placebo, defined as composite outcome of reduction in incident macroalbuminuria, doubling of the serum creatinine level, and egfr ≤ 45 ml/min/1.73m2, need for continuous renal replacement therapy, or death from renal disease (68). exenatide is a synthetic version of the salivary hormone exendin-4, which was first identified in gila monster in 1992. exendin-4 has similar properties to human glp-1. similarly, exenatide has been shown to have renoprotective potential. in a randomized controlled trial, exenatide was shown to significantly reduce urinary tgf-β1, type iv collagen excretion, and 24-h urinary albumin after 16 weeks compared to glimepiride (69). in terms of safety, there are some concerns about the use of glp-1r agonists in moderate and severe ckd. there are few case reports about acute renal injury with exenatide use. however, these patients had other possible contributory factors like gastrointestinal fluid loss and concomitant use of diuretics and angiotensin-converting enzyme (ace) inhibitors (70, 71). the consensus among most medical societies such as the american college of endocrinology/american association of clinical endocrinologists, the national kidney foundation, the canadian diabetes association, and the european association for the study of diabetes is that no dosing adjustments are necessary with mild impairment, cautious use is needed in moderate kidney, and avoidance is necessary with severe ckd (49). although there is lack of a large clinical study to assess the safety of glp-1 receptor agonists in ckd, the emerging evidence (67–69) for their possible renal protective role might change their future use. insulin assessing inherent role of insulin in prevention of diabetic nephropathy is difficult. there are no head-to-head comparative studies to evaluate for inherent, renoprotective role of insulin compared to other hypoglycemic agents. improved renal outcomes with insulin are likely driven by better glycemic control. the metabolism of insulin in kidney disease is another important focus which affects dosage requirements (49). diabetic nephropathy: from pathophysiology to treatment journal of renal and hepatic disorders 2017; 1(2): 10–24 17 nearly 60% of renal insulin clearance occurs by glomerular filtrations and 40% by peritubular vessels. once filtrated, it undergoes extensive reabsorption by the proximal tubule. as the renal function deteriorates, renal insulin clearance declines as well due to reduced renal blood flow (72). patients with renal failure also have worsening insulin sensitivity, the mechanism of which is not yet clear. endogenous insulin secretion also worsens with renal impairment (72). metabolic acidosis and excess parathyroid hormone have been implicated as possible causes of suppressed insulin production from pancreatic β cells (72). subsequently, these changes in metabolism of insulin reflect on daily requirements. in early kidney disease, insulin resistance leads to worsening of hyperglycemia and escalation of treatment might be necessary. however, impaired renal insulin clearance in advanced kidney disease can lead to higher serum insulin concentration, which in turn can cause hypoglycemia. this may warrant lowering of insulin doses or even cessation of insulin therapy (73). sodium-coupled glucose transporter type 2 (sglt2) inhibitors sglt2 inhibitors (e.g., canagliflozin, dapagliflozin, and empagliflozin) are new medications that inhibit filtered glucose reabsorption in the renal proximal tubule. this results in significant glycosuria which subsequently leads to low blood glucose levels, weight loss, lower lipid and uric acid levels, decreased oxidative stress, and sodium loss (74). reduced proximal tubular sodium reabsorption leads to increased sodium delivery to the macula densa, which activates tubuloglomerular feedback which in turn causes afferent vasomodulation and decreased hyperfiltration. these effects can be theoretically beneficial in preserving renal function (75). the increased glycosuria puts patients at increased incidence of dehydration, and genitourinary tract infections, especially candida infection. experimental studies also suggest that sglt2 inhibitors induce glucagon secretion from alpha cells, which is counter regulatory mechanism to the medication-induced hypoglycemia. this increase in glucagon secretion could mean that drops in serum glucose levels are less than anticipated with the degree of urinary glucose loss. another important consideration with the use of sglt2 inhibitors is that although they improve glycemic control, the increased glycosuria results in worsening of the typical diabetes symptoms such as polyuria, polydipsia, and genitourinary infections (76). recent clinical trials have shown possible protective role of sglt2 inhibitor against macrovascular and microvascular complications, nephropathy included. in 2015, the empa-reg outcome trial concluded that empagliflozin was associated with better cardiovascular and mortality outcomes compared with placebo (77). the trial also examined renal outcomes that were defined as progression to macroalbuminuria, doubling of serum creatinine level, egfr ≤ 45ml/min/1.73m2, initiation of renal replacement therapy, or death from renal disease. approximately 12.7% of the 4124 patients in empagliflozin group had composite incident or worsening of nephropathy, compared with 18.8% of 2061 patients in placebo group. this corresponds to a significant 39% relative risk reduction. of note, there was no difference between the two groups in rates of incident albuminuria in patients with normal albumin levels at baseline. some of the limitations of this study are that it was conducted in patients with high cardiovascular risk. generalization of results to diabetic patients with lower cardiovascular risk or to african–american patients might not reflect the same outcomes (75). although results of this study are encouraging, more comparative trials with other hypoglycemic agents are needed to shed light on effectiveness of sglt2 inhibitors. in terms of safety, sglt2 inhibitors can safely be used in mild kidney disease, but are contraindicated in severe and esrd (49). dosing adjustments and caution are recommended when using these medications in moderate kidney disease. safety aside, these medications are also not ideal with advanced renal disease because they lose their efficacy, given their tubular-based mechanism of action (49). studies examining cardiovascular outcomes of other sglt2 inhibitors like canagliflozin (canagliflozin cardiovascular assessment study [canvas]; clinicaltrials.gov number: nct01032629) and dapagliflozin (declare–timi58, clinicaltrials.gov number: nct01730534) are still ongoing. renal and safety outcomes from those studies will provide more information about the role of sglt2 inhibitors in dkd. hypertension management along with increasing albuminuria and decreasing gfr, worsening of hypertension is part of the natural process of dkd. it is one of the most common comorbidities in diabetic nephropathy, with prevalence of approximately 65% in patients with macroalbuminuria and insulin-dependent diabetics (78). even in the absence of albuminuria, the prevalence of hypertension is high at 58% in type ii diabetics. these numbers increase with progression of albuminuria and ckd and approach 90% (79). based on most recent joint national committee (jnc) 8 and kdigo (kidney disease: improving global outcomes) practice guideline, the goal blood pressure in patients with diabetes should be below 140/90 mmhg to reduce cardiovascular mortality and progression to ckd. this recommendation is based on trials that were designed to examine cardiovascular events and not ckd specifically. also, the trials that supported the goal bp of less than 140/90 mmhg in preventing ckd were in non-dkd patients and included african americans predominantly. therefore, the relevance of this recommendation was questioned by experts, and many physicians continue to aim for goal blood pressure of 130/80 mmhg in diabetics with moderate or severe albuminuria (80). the consensus is that more studies are needed to identify blood pressure targets in management of dkd. kinaan m et al. journal of renal and hepatic disorders 2017; 1(2): 10–24 18 as for the choice of antihypertensive medications, ace inhibitors and angiotensin receptor blockers (arbs) have been shown by several studies to decrease urine albumin excretion and delay progression of kidney disease in diabetes type i and ii. the irbesartan in diabetic nephropathy trial (idnt) was a randomized controlled trial that evaluated the effect of irbesartan on progression of dkd. approximately 1700 patients were randomized to irbesartan, amlodipine, or placebo groups. although rates of esrd and death were not significantly different between the groups, irbesartan led to significant slowing of rate of creatinine doubling (81). another landmark study is the reduction in endpoints in niddm with the angiotensin antagonist losartan (renaal), which randomized 1513 patients with type ii diabetes to losartan and placebo groups. the study showed that losartan was associated with reduction of doubling of creatinine but had no effect on death (82). unlike idnt, there was reduction in occurrence of esrd with losartan treatment. the irbesartan in microalbuminuria (irma) showed significant reduction in rates of progression from microalbuminuria to macroalbuminuria with 300 mg irbesartan compared to placebo, further supporting the protective role of arbs (83). as for primary prevention of albuminuria, the bergamo nephrologic diabetes complications trial (benedict) compared trandolapril, verapamil, combination therapy, and placebo. the study concluded that trandolapril monotherapy and combination therapy were associated with lower incidence of microalbuminuria compared to verapamil alone and placebo (79). this suggests that treatment with ace inhibitors could delay onset of microalbuminuria in type ii diabetics. the randomized olmesartan and diabetes microalbuminuria protection (roadmap) study showed similar findings to benedict (84). the diabetics exposed to telmisartan and enalapril (detail) trial demonstrated non-inferiority of arbs to ace inhibitors in preventing gfr decline in type ii diabetics. given the protective role of these medications individually, several studies were interested in assessing combination therapy of arbs and ace inhibitors (85). the candesartan and lisinopril microalbuminuria (calm ii) study showed that combination therapy was not different from maximization of initial monotherapy in terms of blood pressure control and albuminuria after 1 year (86). the ongoing telmisartan alone and in combination with ramipril global endpoint trial (ontarget) showed higher rates of hyperkalemia, decline in gfr, and incidence of acute kidney failure requiring dialysis with combination therapy (87). the va nephron-d study examined the rates of acute kidney injury with combined losartan and lisinopril therapy in nearly 1400 veterans. higher rates of acute renal injury were noted with combination therapy than monotherapy (88). based on these results, combination of ace inhibitors and arbs should not be offered to patients, given lack of strong evidence that shows benefit and potential harm. direct renin inhibitors like aliskiren can lower blood pressure and albuminuria in diabetic patients. a study showed that combination therapy with aliskiren and irbesartan achieved lower rates of albuminuria than monotherapy or placebo despite comparable blood pressure control (79). however, the aliskiren trial in type 2 diabetes using cardiorenal endpoints (altitude) trial showed increased risk of adverse events and no preservation of renal function. the trial included 8561 diabetic patients with either preexisting cardiac or renal condition. patients were randomized to 300 mg/day of aliskiren or placebo. all patients were receiving an ace inhibitor or arb at baseline as well. after 32 months, 18.3% of patients in aliskiren group reached primary endpoint of cardiovascular event, death from renal or cardiac cause, doubling of creatinine, or onset of esrd, compared to only 17.1% in placebo group. adverse effects like hyperkalemia were significantly higher in aliskiren group (13.2% vs. 10.2%). based on these results, the trial was stopped early (89). nondihydropyridine calcium channel blockers, diltiazem and verapamil, appear to have antiproteinuric effects. a small study of 30 type 2 diabetes patients showed that addition of verapamil to lisinopril led to much greater reductions in rates of albuminuria (90). although promising, there is still no strong evidence about the role of nondihydropyridine calcium channel blockers in management of dkd. dihydropyridine calcium channel blockers have an even more obscure role in dkd, with studies showing variable effects ranging from worsening proteinuria to no effect to improved albuminuria. another area of interest in hypertension management in dkd is the role of mineralocorticoid receptor antagonists. in some patients on ace inhibitors and arbs, plasma aldosterone levels increase to pretreatment level which may lead to detrimental changes in the kidneys like worsening of albuminuria and hypertension. this phenomenon is referred to as “aldosterone escape.” using mineralocorticoid receptor antagonists like spironolactone as an add-on therapy to ace inhibitor or arb has been shown to reduce albuminuria in several small, randomized controlled trials. however, increased risk of hyperkalemia raises concerns about combining ace inhibitors/arbs with mineralocorticoid receptor antagonists (79). bardoxolone methyl was an experimental antioxidant medication that was shown to have benefits in animal models with kidney injury. there was interest in the possible protective role of this medication in dkd. in the bardoxolone methyl treatment: renal function in ckd/type 2 diabetes (beam) trial, nearly 220 patients with type 2 diabetes and low gfr were randomized to bardoxolone methyl treatment or placebo. gfr improved in patients receiving bardoxolone methyl treatment, an effect that was not observed in placebo group (91). however, the bardoxolone methyl evaluation in patients with chronic kidney disease and type 2 diabetes mellitus (beacon) trial showed that bardoxolone methyl diabetic nephropathy: from pathophysiology to treatment journal of renal and hepatic disorders 2017; 1(2): 10–24 19 not only did not improve esrd or cardiovascular death outcomes but also increased the rate of cardiovascular events (a composite of cardiovascular death, heart failure hospitalization, nonfatal stroke, and nonfatal myocardial infarction). bardoxolone methyl was also associated with higher blood pressure and albuminuria in the beacon trial (92). despite the continuous interest in finding newer antihypertensive medications that could slow the progression of dkd, ace inhibitors and arbs remain the most important tools in our arsenal at this time in controlling blood pressure and albuminuria in diabetic nephropathy. hyperlipidemia management hyperlipidemia is common in patients with diabetes, a condition that is exacerbated with impaired renal function. elevated cholesterol not only promotes atherosclerosis but also accelerates glomerulosclerosis in ckd. the clinical impact of this process on diabetic nephropathy is not clear. a study in type i diabetics showed that total cholesterol concentration above 220 mg/dl and diastolic pressure above 85 mmhg were the strongest predictors for progressive renal disease (93). statins remain the most frequently used lipid-lowering medications in managing hyperlipidemia in diabetic patients. according to the 2013 acc/aha guidelines for assessment of cardiovascular risk and management of atherosclerotic cardiovascular disease, diabetic patients would benefit from lipid-lowering medications. different intensities of statins are used in diabetics based on the 10-year atherosclerotic cardiovascular disease (ascvd) risk estimate. patients with dkd have comparable magnitude of low-density lipoprotein cholesterol reduction with statin therapy to those with normal kidney function. cardiovascular events and mortality in patients with ckd are reduced with lipid-lowering treatment, statins or statin/ezetimibe, compared to placebo (94). although statin therapy improves cardiovascular outcomes, it has no beneficial effect on the progression of preexisting kidney disease (95). kdigo guidelines recommend initiating statin therapy in patients with nondialysis-dependent ckd; however, clinical trials showed no benefits in prevention of cardiovascular death in patients on dialysis. although there is no strong evidence to support initiating statin therapy in dialysis patients, it is clinically sound to continue statin therapy in patients with ckd who progress to esrd. a large meta-analysis also showed that statins have a reasonable safety profile in ckd with no significant adverse events (94). fenofibrates have been shown to slow down progression of albuminuria in type ii diabetics. possible mechanisms for their renoprotective role are suppression of inflammation, decreased production of type 1 collagen in mesangial cells, and increased activity of perioxisome proliferator–activated receptor– alpha (96–98). conclusion dkd remains the leading cause of ckd despite considerable progress in our understanding of its pathophysiology and risk factors. the focus remains on early screening and prevention of microalbuminuria through the adoption of multiple interventions and strategies targeting control of hyperglycemia, hypertension, and 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http://dx.doi.org/10.1038/sj.ki.5000209 http://dx.doi.org/10.1210/jc.2005-1615 http://dx.doi.org/10.1210/jc.2005-1615 jrenhep010 34..49 jrenhep.com codonpublications.com review article novel therapeutic strategies targeting molecular pathways of cystogenesis in autosomal polycystic kidney disease maurizio salvadori 1 , aris tsalouchos 2 1renal unit, careggi university hospital, viale pieraccini, florence, italy; 2division of nephrology, azienda ospedaliera careggi, largo alessandro brambilla, florence, italy abstract autosomal dominant polycystic kidney disease (adpkd) is the most common inherited kidney disease that results from mutations in pkd1 or pkd2. the disease is characterized by the progressive development of fluid-filled cysts derived from renal tubular epithelial cells that destroy the architecture of the renal parenchyma and lead to kidney failure. until recently, the causes and the molecular pathways that lead to cystogenesis remained obscure. in the last decade, enormous progress has been made in understanding the pathogenesis of adpkd and the development of new therapies. the purpose of this review is to update on the promising therapies that are being developed and tested based on knowledge of recent advances in molecular and cellular targets involved in cystogenesis. keywords: adult autosomal polycystic kidney disease; cystogenesis; mtor signaling; somatostatin analogues; vasopressin 2 receptors received: 31 january 2017; accepted after revision: 16 february 2017; published: 15 march 2017. author for correspondence: maurizio salvadori, renal unit, careggi university hospital, viale pieraccini, 18, 50139, florence, italy. email: maurizio.salvadori1@gmail.com how to cite: salvadori m et al. novel therapeutic strategies targeting molecular pathways of cystogenesis in autosomal polycystic kidney disease. j ren hepat disord 2017;1(1):35–49. doi: http://dx.doi.org/10.15586/jrenhep.2017.10 copyright: salvadori m and tsalouchos a. license: this open access article is licensed under creative commons attribution 4.0 international (cc by 4.0). http://creativecommons.org/licenses/by/4.0 introduction autosomal dominant polycystic kidney disease (adpkd) affects 1:400-1:1.000 live births, or 12.5 million people worldwide, and is the most common monogenic inherited form of kidney disease across all ethnic types. adpkd is characterized by cyst formation and enlargement in the kidney and other organs. it accounts for 5% to 10% of end-stage renal disease (esrd) cases, making it the fourth leading global cause for kidney failure with clinically significant impairment of renal function. esrd usually occurs by late middle age and requires renal replacement therapy in approximately 50% of patients by 70 years of age (1–2). in85% of cases,adpkdoccursasa result ofgermlinemutation in polycystin 1 gene (pkd1) localized within chromosome 16 [16p13.3], while in 15% of cases, it is due to germline mutation in polycystin 2 gene (pkd2) localized within chromosome 4 [4q21-q23] (3). although some authors have supposed that there is a third pkd gene, convincing evidence to support the existence of this gene is lacking. polycystin-1 (pc1) and polycystin-2 (pc2) interact with eachother throughtheir c-terminal cytoplasmic domains and are known to form a complex that functions as a transient receptor potential channel involved in the regulation of intracellular calcium homeostasis (4,5). on average, patients with mutations in pkd1 develop esrd at younger ages compared with patients (aged 54.3 vs. 74 years) with pkd2 mutations (6). journal of renal and hepatic disorders 2017; 1(1): 35–49 mailto:maurizio.salvadori1@gmail.com http://dx.doi.org/10.15586/jrenhep.2017.10 http://creativecommons.org/licenses/by/4.0 according to a widely accepted view, cystogenesis follows a two-hit model. adpkd is recessive at the cellular level and cysts develop clonally from a tubular cell only once the cell has acquired a second somatic mutation to inactivate the remaining normal allele (7). a somatic “second-hit” mutation, loss of heterozygosity, or haploinsufficiency may account for the mosaic nature of cyst formation, while in the mature organ, broad and fast cyst formation requires a third hit such as kidney injury (8–10). recent evidences suggest that a complete loss of function is not required for cystogenesis; rather, functional pc1 or pc2 must be reduced to a certain threshold level (1). although the exact mechanisms of cystogenesis remain to be elucidated, the pathological processes that facilitate cyst enlargement are probably the result of two specific abnormalities: (1) increased fluid secretion into the cyst lumen and (2) inappropriately increased cell division by the epithelium lining the cyst (11). the major signaling pathways implicated in these phenotypic changes include: the intracellular deregulation of calcium homeostasis, camp accumulation and activation of protein kinase a (pka), activation of mitogen-activated protein and mammalian target of rapamycin (mtor) kinases, canonical wnt signaling, and other intracellular signaling mechanisms (12–14). until recently, treatment of adpkd was aimed at the management of secondary conditions, particularly hypertension, to limit morbidity and mortality, after which the disease becomes symptomatic. the recent developments arising from a better mechanistic understanding of the molecular pathways involved in cyst growth have allowed for targeting the disease pathogenesis, rather than the disease complications. in this context, novel therapies with strong molecular rationales have entered into clinical trials as potentially modifying adpkd. a significant factor propelling these trials is the now accepted total kidney volume (tkv) imaging technology by magnetic resonance imaging (mri). according to the findings of the consortium of radiologic imaging studies of pkd (crisp), tkv correlates well with dimensions of cysts within the kidneys and with egfr. the rate of renal growth is a good predictor of renal functional decline, and thus it can be used as a surrogate marker of disease progression in clinical trials, along with measured glomerular filtration rate (gfr) or serum creatinine change as principal meaningful end points (15,16). the current review focuses on these novel therapeutic approaches that interfere with the molecular pathways of cystogenesis (figure 1). drugs targeting camp-dependent cystic expansion role of camp in cystogenesis in adpkd, disruption of intracellular ca2+ homeostasis due to mutations in the pkd genes leads to low intracellular calcium and consequently increased levels of intracellular camp. normally, the levels of camp are controlled by a balanced activity of membrane-bound (under the control of g protein–coupled receptors (gpcrs] and extracellular ligands) and soluble isoforms of adenylate cyclase (ac), which catalyzes the formation of camp from atp, and phosphodiesterases (pdes), which degrades camp to amp. decreased intracellular calcium inhibits the activity of pdes and activates acs, thus producing a net increase in camp concentration (12). camp exerts its effects via pka which phosphorylates a number of metabolic enzymes and promotes transepithelial fluid secretion, which involves chloride secretion through the cystic fibrosis transmembrane conductance regulator (cftr). chloride secretion drives sodium into the cystic cavity through paracellular mechanisms; this causes movement of water through aquaporins and cyst’s expansion (17,18). in addition, despite the evidence suggesting that camp is antimitogenic in normal cells, in adpkd camp promotes cyst enlargement by stimulating epithelial cell proliferation through the activation of the b-raf/mek/erk pathway (19–22). camp/pka signaling is also involved in cell proliferation by activating mtor (via erk-mediated phosphorylation of tuberin) (23,24) and wnt–β-catenin signaling (via phosphorylation of gsk3b and β-catenin) (25,26). in addition, camp upregulates the paired box gene 2 (pax2) (27) and signal transducer and activator of transcription 3 (stat3) (28–30). vasopressin 2 receptor antagonists normally, vasopressin (avp) is secreted into the circulation by the posterior pituitary gland, in response to an increase in serum osmolality or a decrease in effective circulating volume. in the kidney, avp binds to the v2 vasopressin receptor in the basolateral membranes of collecting duct cells in the last portion of the nephron. the v2 receptor is a typical member of the large superfamily of gpcrs. thus, occupancy of this receptor results in mediated activation of ac and the formation of camp with a subsequent activation of pka, which promotes the fusion of cytoplasmic vesicles containing aquaporin-2 water-channel proteins with the apical membrane. as a result, this normally water-tight membrane becomes water-permeable. driven by the osmotic gradient of sodium, water is then transcellularly reabsorbed, entering the cells through aquaporin-2 in the apical membrane and leaving the cells for the interstitium through aquaporin-3 and aquaporin-4, which reside in the basolateral membrane (31). in patients with adpkd, there is a pathologically hyperactive avp/v2 receptor system. the altered regulation of avp serum levels in adpkd have been reanalyzed in a number of recent studies. serum concentrations of vasopressin correlate positively with both serum osmolality as well with total kidney size and correlates negatively with gfr in adpkd patients (32–35). there are two major reasons for the deregulation of the neurohypophysis–kidney axis in adpkd. first, changes in kidney architecture cause salvadori m and tsalouchos a journal of renal and hepatic disorders 2017; 1(1): 35–49 36 a urinary concentration deficit with subsequently elevated plasma osmolalities. second, an altered central release of vasopressin might exist. indeed, ahrabi et al. (36) observed a syndrome of inappropriate antidiuretic hormone secretion-like phenotype in pkd1 haploinsufficient rodents. these rodents were able to reabsorb abnormally high amounts of water supporting the idea of a nontubular basis of the urinary concentration deficit. in addition, ho et al. (37) by investigating the osmoregulation parameters in adult and pediatric adpkd patients with intact gfr in comparison with nonaffected controls, showed a significant defect both in the release of vasopressin in response to plasma figure 1. illustration of the key mechanisms of adpkd pathogenesis and targets of potential treatments. polycystin-1 and polycystin-2 expressed in different subcellular locations and regulate (1) proliferation, (2) fluid secretion, (3) ciliary function, (4) cell–cell adhesion, and (5) cell–matrix interaction of renal epithelial cells. dysfunction of polycystin-1 or polycystin-2 results in aberrant signaling pathways, including: (a) activation of camp, (b) decreased intracellular calcium concentrations, and (c) activation of mtor. the targets of candidate drugs are depicted as gray circles. abbreviations: cftr, cystic fibrosis transmembrane regulator; er, endoplasmic reticulum; erk, extracellular signal-regulated kinase; glccer, glucosylceramide; hdac, histone deacetylase; il-6r, interleukin-6 receptor; mek, mitogen-activated protein kinase; mtor, the mammalian target of rapamycin; pc, polycystin; pde, phosphodiesterase; pka, protein kinase a; sr, somatostatin receptor; tsc, tuberous sclerosis; v2r, vasopressin v2 receptor. adpkd treatment journal of renal and hepatic disorders 2017; 1(1): 35–49 37 osmolality (central component) and in the v2r-mediated response (nephrogenic component) in adpkd patients. because of the aforementioned central role of camp in cystogenesis and the pathologically hyperactive avp/v2 receptor system in adpkd patients, the block of the effect of avp on v2r is particularly appealing as avp is the major hormone responsible for camp generation in isolated collecting ducts (38). nagao et al. (39) documented the importance of circulating avp in the natural progression of the disease by suppression of avp with high water intake in pck rats. the authors observed that an increased water intake, for 10 weeks, reduced renal cell proliferation, cystic area, and kidney weight, and improved renal function. in preclinical trials, a nonpeptide vasopressin antagonist mozavaptan (opc-31260), administered in murine cystic models orthologous to human disease, including the pkd2ws25/− mouse (adpkd), pck rat (arpkd), and pcy mouse (nephronophthisis type 3), reduced renal camp and inhibited disease progression measured by the reduction in kidney volume, the cystic area, the number of mitotic and apoptotic cells, and the blood urea nitrogen (bun) (40–42). however, initiation of mozavaptan in pkd1-deletion mouse model later in the disease progression did not reduce cyst formation, suggesting that early initiation of v2 receptor antagonism is most effective to decrease disease progression (43). additional studies were conducted to examine the effects of tolvaptan (opc-4106), a more potent and highly selective human v2r antagonist, in comparison with mozavaptan (44). tolvaptan showed similar results on renal camp and pkd progression in pck rat model using the lowest dose, which caused only modest aquaresis compared with the higher dose regimens. there was also a corresponding reduction in the renal activity of the b-raf/mek/erk pathway (45). subsequently, reif et al. (46), in an in vitro study, examined the effect of tolvaptan on intracellular camp, erk activity, cell proliferation, and transcellular chloride anion secretion using human adpkd cyst epithelial cells. tolvaptan caused inhibition of camp avp–induced production, erk signaling avp–induced, cell proliferation, and chloride anion secretion. these effects significantly contributed to a decrease in in vitro cyst growth. wang et al. (47) confirmed that the effect of these drugs in reducing disease progression and cyst development was due to the inhibition of avp effects by selectively knocking out avp in the pck rat. in the absence of avp, the pck rat had reduced renal camp accumulation, erk activity, cell proliferation, and fibrosis, and was essentially free of renal cysts, whereas administration of the v2r agonist 1-deamino-8d-arginine vasopressin fully rescues the cystic phenotype, providing clear evidence for the roles of avp and camp on cystic disease progression. the large, randomized, double-blind, placebo-controlled, multinational, phase iii tempo 3:4 trial (48) confirmed the aforementioned experimental studies. this trial enrolled 1445 patients aged 18–50 years with adpkd, rapidly progressive kidney growth (tkv ≥ 750 ml), as measured by mri and ckd stages 1–3. tolvaptan reduced the rate of tkv growth (primary endpoint) by 49% and the rate of estimated gfr (egfr) loss on treatment (secondary endpoint) by 26% per year during the median observation period of 3 years. the effect on tkv appeared greater during the first year of treatment than during the second or third years. in addition, the beneficial effects on renal function observed in all patient subgroups were greater in patients aged ≥35 years and in patients with hypertension or a tkv of ≥1500 ml. an early and reversible small reduction in gfr at the start of tolvaptan therapy, observed also in previous short-term trials (49–51), was likely caused by alterations in tubuloglomerular feedback and/or renal hemodynamics. another important secondary endpoint was the reduction in kidney pain occurring early and throughout treatment. the results of tempo 3:4 trial suggested that tolvaptan had no effect compared with placebo on albuminuria. conversely, a post hoc exploratory analysis documented that tolvaptan decreased albuminuria compared with placebo, also independently of blood pressure. in addition, the treatment efficacy of tolvaptan on changes in tkv and egfr was more readily detected in patients with higher albuminuria (52). the drug was assumed in a split dose regimen of 45 mg in the morning and 15 mg in the afternoon, uptitrated to 90/30 mg when tolerated. split dose regimen was preferred based on the findings of phase ii studies (tempo 2:4 and 156-05-002) in patients with adpkd that documented that a split dose regimen was more effective than a single dose in achieving sustained vasopressin suppression, as evidenced by a 24-h urine osmolality (53,54). based on the results of the tempo 3:4 trial, tolvaptan has been approved to delay the progression of adpkd in patients with a rapid increase in tkv in japan, canada, european union, united kingdom, and south korea. however, eligibility criteria for the prescription vary between countries (table 1). the european renal association-european dialysis and transplant association (era-edta) (55) and the renal association working group on tolvaptan in adpkd (56) have issued more detailed guidance on this topic. although the results of the tempo trial are highly encouraging, tolvaptan cannot be considered as an option for all patients. tolvaptan has significant adverse effects, including aquaretic effects (polyuria, nocturia, polydipsia) and elevation of aminotransferase enzyme concentrations with the potential for acute liver failure (48,57,58). appropriate patient selection is critical to optimize long-term benefits while minimizing adverse effects and hepatotoxic risk factors. studies to further assess the efficacy and tolerability of tolvaptan in patients with adpkd are ongoing or just completed. tempo 4:4 is a 2-year, open-label extension of tempo 3:4, completed in march 2016. this study aimed to evaluate the long-term efficacy and safety of tolvaptan in patients with adpkd; the findings are waiting to be salvadori m and tsalouchos a journal of renal and hepatic disorders 2017; 1(1): 35–49 38 published soon. in addition, the long-term safety of titrated tolvaptan in patients with adpkd is currently being assessed in a phase iii open-label trial (nct02251275) (59), while the ongoing phase iiib reprise trial aims to extend the understanding of the efficacy and safety of tolvaptan in patients with late stage 2 to early stage 4 ckd (60). somatostatin analogues somatostatin (sst) is an endogenous hormone secreted by the pancreatic islet δ-cells and by extra-islet neuroendocrine cells of the gastrointestinal tract, hypothalamus, and thyroid. sst has anti-secretory and anti-proliferative effects mediated by the interaction with five subtypes of gpcrs (sstr1-5) (61). sst receptors are expressed by renal tubular epithelial cells and by cholangiocytes. in particular, sstr1 and sstr2 are expressed in the ascending limb of henle’s loop, the distal tubule and collecting duct, while sstr3, sstr4 and sstr5 are expressed in the proximal tubule (62–65). it has been shown that sst selectively inhibits camp synthesis in the epithelial cells of the distal tubules and collecting ducts both in vitro and in vivo (66,67) and exerts similar effects to cholangiocytes (68). as plasma half-life of the native sst is very short (1–3 min), the synthetic analogues octreotide, lanreotide, and pasireotide were developed as stable alternatives for use in clinical practice. these analogues of sst differ in their stability and affinity with the sst receptors. in particular, octreotide and lanreotide have a half-life of 2 hours and present a high affinity for sstr2 and sstr3 and moderate affinity for sst5. instead, pasireotide has high affinity for all the receptors of sst, except sstr4, and its plasma half-life is about 12 hours (69). currently, formulations of octreotide and lanreotide with long acting release (lar), which allow their administration every 28 days intramuscularly or intradermally, have been introduced into clinical practice. ruggenenti et al. (70) have evaluated for the first time the effectiveness of octreotide-lar by performing a randomized, cross-over, placebo-controlled trial in 14 adpkd patients, which demonstrated the potential efficacy in slowing the growth of tkv and the relative safety of the treatment. a post hoc analysis of the same study showed that the volume of the liver cysts decreased significantly with octreotide-lar (71). following this initial experience, a number of preclinical studies have confirmed the effectiveness of treatment with sst analogues in inhibiting the growth of renal and hepatic cysts. bogert et al. (72) developed a zebrafish model that allows for the testing of the possible efficacy of drugs in inhibiting hepatorenal cystogenesis. table 1. eligibility criteria for the approved use of tolvaptan according to country or region country chronic kidney disease stage disease activity regulatory body approval date guidance (if any) japan 1–4 tkv > 750 ml δtkv > 5% per annum pharmaceuticals and medical devices agency march 2014 canada not specified not specified health canada february 2015 europe 1–3 evidence of rapid disease progression european medicines agency may 2015 european renal associationeuropean dialysis and transplant association england, wales, and northern ireland 2–3 evidence of rapid disease progression national institute for health and clinical excellence (nice) october 2015 renal association south korea 1–3 evidence of rapid disease progression ministry of food and drug safety/ health insurance review and assessment service december 2015 scotland 1–3 evidence of rapid disease progression scottish medicines consortium january 2016 renal association tkv, total kidney volume. adpkd treatment journal of renal and hepatic disorders 2017; 1(1): 35–49 39 in this experimental model, the exposure of zebrafish embryos to pasireotide significantly reduced the area of the cysts. a recent study also assessed the efficacy of pasireotide and tolvaptan, in a murine model of adpkd (73). treatment with pasireotide or tolvaptan alone, significantly reduced the growth of cysts, and the effect was even more marked by combining the two drugs. in another randomized study, van keimpema et al. (74) compared the effects of 6 months of treatment with lanreotide or placebo in 54 patients with polycystic liver disease (pld), including 32 with adpkd and the remaining with isolated polycystic liver disease (pcld). the average volume of the liver decreased in patients treated with lanreotide while it increased in the placebo group. moreover, in patients with adpkd, tkv was reduced after treatment with lanreotide while it increased in the placebo group. in a subsequent open-label extension study (75), patients who participated in the initial trial were re-enrolled to complete a treatment period of 12 months with lanreotide. liver volume decreased after 12 months of treatment with lanreotide, with the greatest effect seen during the first 6 months. in the 25 patients with adpkd, tkv remained stable at the end of 12 months. furthermore, in 15 patients with adpkd, a ct of the kidneys was repeated 6 months after the treatment with evidence of increased tkv during this period. in another 12 months of study, 42 patients with pld, including 34 with adpkd, were randomized to receive treatment with octreotide-lar or placebo (76). the total volume of the liver was reduced in the treatment arm with octreotide-lar but increased in the placebo group. in patients with adpkd, the tkv remained unchanged in the octreotide-lar group but increased in the placebo group. in addition, renal function had a slower reduction in patients treated with octreotide-lar, although the difference did not reach statistical significance. this study also had an open-label extension for 12 months (77). in the group initially randomized to octreotide-lar, the reduction of liver volume remained evident until the end of the second year of treatment, although the effect was not significant during the second year. instead, in the originally randomized placebo group who continued with octreotide-lar, the total volume of the liver decreased significantly after 1 year of treatment with the drug. in the cohort of patients with adpkd initially randomized to octreotide-lar, the inhibition of kidney growth observed during the first year was not observed in the second year of study, while in those originally randomized to placebo, tkv remained unchanged after 1 year of treatment with octreotide-lar. more recently, in the aladin multicenter study conducted in italy, 79 patients with adpkd and egfr > 40 ml/min/1.73 m2 were randomized to a 3-year treatment with octreotide-lar or placebo (78). after the first year, the average increase in tkv was significantly lower in patients treated with octreotide-lar compared with those receiving placebo. in the third year, the average increase in tkv in the treatment arm was lower than the placebo group without reaching statistical significance. during the entire study period, the annual reduction in gfr was lower in octreotide-lar group than in the placebo group, although the difference did not reach statistical significance. however, a further analysis documented that while the reduction of gfr after 1 year was comparable in the two groups, the chronic loss of renal function between the first and third year was significantly slower in the treatment arm compared with placebo group, with a difference of about 50%. a more recent open-label clinical study evaluated the efficacy of 6 months of treatment with lanreotide in 43 patients with symptomatic pld and adpkd (estimated gfr > 30 ml/min/ 1.73 m2) (79). compared with baseline, the median liver volume as well as that of the kidney decreased significantly. in addition, renal function remained stable until the end of the study. a recent meta-analysis confirmed the efficacy of sst analogues in reducing the progressive increase of tkv, on average with a reduction of 9% compared with the growth observed in patients treated with placebo or conventional therapies. however, treatment with sst analogues did not demonstrate significant effects on the egfr (80). based on these studies, in august 2015, european medicines agency (ema) attributed to lanreotide the orphan drug designation for the treatment of adpkd. in the studies mentioned above, treatment with sst analogues was generally well tolerated with no particular problems, diarrhea being the most common adverse event. however, recently, the authors of a randomized, controlled clinical trial assessing the efficacy of lanreotide to halt disease progression in patients with later stage adpkd (nct0 1616927) documented an increased risk for hepatic cyst infection during lanreotide treatment, especially in adpkd patients with a history of hepatic cyst infection. a literature review also suggested an increased risk for hepatic cyst infection during the use of somatostatin analogues (81). additional clinical trials of sst analogues for adpkd and/or pld are currently ongoing [nct01616927: study of lanreotide to treat polycystic kidney disease (dipak1); nct01377246: somatostatin in patients with autosomal dominant polycystic kidney disease and moderate to severe renal insufficiency (aladin 2); nct02127437: lanreotide in polycystic kidney disease study (lips); nct01670110: pasireotide lar in severe polycystic liver disease (som230)]. drugs targeting mtor signaling pathway role of mtor signaling pathway in cystogenesis serine/threonine-protein kinase mtor is an enzyme that plays a critical role in proliferation and cell growth (82). the first suggestion of a prominent role of mtor pathway in the pathogenesis of adpkd comes from studies in patients with severe infantile-onset of adpkd due to a large deletion of chromosome 16 involving pkd1 gene [16p13.3] and the adjacent tuberous sclerosis 2 (tsc2) gene [16p13.3] (83). mutations in tsc1 [9q34.13] or tsc2 are the causes of salvadori m and tsalouchos a journal of renal and hepatic disorders 2017; 1(1): 35–49 40 tuberous sclerosis complex, an autosomal-dominant, neurocutaneous, multisystem disorder characterized by the formation of benign hamartomas in various organs including kidneys that are also involved with bilateral cysts formation (84). tsc1 and tsc2 encode, respectively, for hamartin and tuberin. these two proteins together with tbc1 domain family member 7 (tbc1d7) form the tsc protein complex that acts as a critical negative regulator of mtor complex 1 (mtorc1) (85). pc1 also has an important function in the regulation of the mtor pathway, as c-terminal cytoplasmic tail of pc1 interacts with tuberin. in adpkd, this interaction is impaired and the mtor pathway is inappropriately activated in cyst-lining epithelial cells of human adpkd patients and mouse models (86). based on these data, mtor inhibitors have been suggested as possible therapeutic agents for adpkd. mtor inhibitors sirolimus, a macrocyclic lactone produced by fermentation of streptomyces hygroscopicus, exerts potent antiproliferative and antifibrotic effects by inhibiting the mtor pathway. sirolimus and its derivative everolimus, used in maintenance immunosuppression in patients undergoing kidney transplantation, have been proposed as potential new drugs to slow the growth of cysts and the progression of adpkd in esrd. the effects of treatment with mtor inhibitors have been assessed in different experimental models of adpkd (87–90). an early study showed that in han:sprd rats, the administration of sirolimus for 5 weeks significantly reduced the proliferation of tubular cells, inhibited cystogenesis and the growth of the kidney, and preserved renal function (91). more recently, prolonged treatment with sirolimus, in the same experimental model, has been observed to normalize the volume of the kidney, renal function, and blood pressure (92). these experimental studies have provided the rationale for the design of several prospective clinical trials aimed to verify the effectiveness of treatment with mtor inhibitors in adpkd patients. a first published randomized double-blind study, compared the effects of 2 years of treatment with everolimus (5 mg/day) or placebo in 433 patients with adpkd and gfr > 30 ml/min/1.73 m2 (93). during the first year of study, the increase of tkv was significantly lower in the treatment arm with everolimus compared with placebo. this effect was not confirmed at the end of the second year. in addition, the initial effectiveness of everolimus in slowing down tkv did not translate into an improvement in renal function. an important bias of this study could be the high proportion of patients who discontinued the study in the everolimus group due to poor tolerability to treatment with the mtor inhibitor. indeed, the urinary protein excretion was significantly increased, and the overall incidence of adverse events was higher in the everolimus group; hyperlipidemia, leukopenia, thrombocytopenia, acne, stomatitis, and peripheral edema were the most relevant events. the suisse study compared the effects of treatment for 18 months with sirolimus (2 mg/day) or conventional therapy in 100 patients with adpkd and gfr ≥ 70 ml/min/ 1.73 m2 (94). the median increase in tkv was comparable between the two groups as well as the egfr throughout the entire study period. in this study, proteinuria was also significantly higher in patients treated with sirolimus than in the control group. the randomized trial sirena compared the effects of treatment with sirolimus or with conventional therapy alone for 6 months in 21 patients with adpkd and gfr ≥ 40 ml/min/1.73 m2 (95). the treatment with sirolimus was associated with a minor increase of the tkv compared with conventional therapy, although the difference did not reach statistical significance. even in this trial, appreciable variations of gfr were not observed, and as in the above described studies, the same adverse events (proteinuria, hyper‐ lipidemia, thrombocytopenia, stomatitis) were presented. in a subsequent open-label study (rapyd), 55 patients with adpkd and mild to moderate renal impairment were randomized to 24 months of treatment with ramipril (control group), ramipril in combination with high doses of sirolimus (target blood levels: 6–8 ng/ml), or ramipril in combination with low-dose sirolimus (target blood levels: 2–4 ng/ml) (96). compared with baseline, total cyst volume decreased significantly in both treatment arms with sirolimus, while it increased in the control group. similarly, egfr remained relatively stable in both treatment groups with sirolimus but worsened in the control group. however, at the end of 2 years of treatment, the urinary excretion of proteins and the incidence of hyperlipidemia were significantly higher in patients treated with high doses of sirolimus compared with the control group. in a more recent study, 30 patients with adpkd and measured gfr ≥ 25 ml/min/1.73 m2 were randomized to receive for 12 months low-dose sirolimus (target blood levels 2–5 ng/ml), standard doses of sirolimus (target blood levels >5–8 ng/ml), or conventional therapy (97). tkv did not change significantly in the two treatment groups with sirolimus as in the group assigned to conventional therapy. in addition, the renal function improved (gfr measured by plasma clearance of iothalamate) with low-dose sirolimus, but not with the standard dose of the drug. various hypotheses have been formulated to explain the discrepancies between the results obtained in experimental studies and in clinical trials. it is possible that the dose of sirolimus or everolimus used in clinical trials is not sufficient to inhibit mtor enzyme activity in renal tubular cells or that the treatment was started in a too advanced stage of the disease to obtain an improvement of the renal function (86,87,98). in conclusion, the available clinical studies discourage the use of mtor inhibitors to slow the progression of renal disease in patients with adpkd. currently there are two ongoing trials that test mtors in adpkd: pulsed oral sirolimus in autosomal dominant polycystic kidney disease (rap) [nct02055079] and the efficacy of everolimus in reducing total native kidney volume in polycystic adpkd treatment journal of renal and hepatic disorders 2017; 1(1): 35–49 41 kidney disease transplanted recipients (everkyste) [nct02134899]. other therapeutic targets in preclinical studies and early clinical trials tyrosine kinase inhibitors c-src and bcr-abl are two cytoplasmatic tyrosine kinases (tks) involved in the development of malignancies (99). yamaguchi et al. (100) documented that in renal epithelia, the switch of camp from an anti-mitogen to a mitogenic stimulus not only correlates with decreased intracellular calcium levels but is also associated with an increased activity of src. furthermore, sweeney et al. (21) evaluated bosutinib (ski-606), a src/abl tyrosine kinase inhibitor, in the bpk and pck rodent models of adpkd. bosutinib was found to suppress kidney cyst formation by inhibiting epidermal growth factor receptor (egfr) activation and downregulating b-raf/erk signaling. in addition, bosutinib was effective in inhibiting epithelial cell proliferation and reducing extracellular matrix adhesion in an in vitro study on mouse inner medullary collecting duct cells and human adpkd cyst-lining epithelial cells. in the same study, the authors also highlighted the ability of bosutinib to delay renal cystic phenotype of pkd1 orthologous adpkd heterozygous mice in vivo (101). based on these evidences, a phase ii, multicenter, randomized, double-blind, placebo-controlled clinical trial with bosutinib [nct01233869] has been conducted and completed, and we currently are expecting publication of the study results. tesevatinib, a new tyrosine kinase inhibitor, is being currently evaluated in two ongoing trials [nct02616055 and nct01559363]. stimulation of polycystin-2-mediated ca 2+ release triptolide, a natural active component derived from the traditional chinese medicine, tripterygium wilfordii, was found to restore cytosolic ca2+ release in pkd1−/− murine kidney epithelial cells, by acting as a pc2 agonist. through this mechanism, triptolide has been effective in arresting cellular proliferation and attenuating overall cyst formation in this murine model (102,103). in a recent pilot study, triptolide was effective in decreasing proteinuria in adpkd patients but there were no effects on tkv and renal function (104). a clinical trial conducted in china has been terminated due to a high rate of drop-outs [nct00801268], and another trial is under way [nct02115659]. raf kinase inhibitors sorafenib is a nonselective raf inhibitor that decreases erk activity and inhibits the proliferation of various human cancer cell lines. in an experimental model, sorafenib reduced the basal activity of erk, inhibited camp-dependent activation of b-raf and mek/erk signaling, and caused a concentrationdependent inhibition of cell proliferation induced by camp and egf. in addition, sorafenib completely blocked in vitro cyst growth of human adpkd cystic cells (105). conversely, in a pc2 defective mice model, sorafenib inhibited b-raf but paradoxically activated raf-1, resulting in an increased erk1/2 phosphorylation, cell proliferation, and cyst growth in vivo. this effect has been interrupted in the same study by co-administration of sorafenib and octreotide with consequent simultaneous blocking of the camp/pka pathway (106). a different raf inhibitor (plx5568) has been evaluated in the han:sprd rat model (107). in this study, cyst enlargement attenuated without an improvement in kidney function. furthermore, the authors reported increased renal and liver fibrosis. cdk inhibitors the central role of cyclin-dependent kinases (cdks) in the regulation of cell proliferation is well defined. pc1 directly regulates cell cycle by inhibiting cdk2 activity through upregulation of p21, inducing cell cycle arrest in g0/g1 phase and controlling terminal differentiation of tubular epithelial cells (108). pc2 by binding with id2 protein (inhibitor of dna binding 2 protein) prevents its translocation to the nucleus, thus blocking cell cycle progression. in adpkd, tran‐ slocation of id2 is connected with downregulation of p21, leading to intensification of cdk2 activity and cell cycle progression (109). a preclinical study with the ckd inhibitor r-roscovitine in juvenile cystic kidney and congenital polycystic kidney mouse models of pkd, effectively attenuated cystogenesis by inhibiting cell cycle progression, proliferation, and apoptosis (110). in addition, a more potent second-generation analogue of roscovitine (s-cr8) showed effective inhibition of both renal and hepatic cystogenesis in an orthologous mouse model of adpkd with inactivated pkd1 gene (111). hdacs inhibitors histone deacetylases (hdacs) are part of a vast family of enzymes that regulate specific cellular processes through deacetylation of histones or nonhistone transcription factors, leading to transcriptional repression. altered expression of hdcas causes abnormal transcription of key genes controlling principal cellular functions such as cell proliferation, cell-cycle regulation, and apoptosis (112). to discover potential drug candidates in the therapy of adpkd, a pan-hdac inhibitor called trichostatin a (tsa) has been evaluated in a pkd2 zebrafish model showing the ability to suppress pronephric cyst formation (113). the same results have been obtained after administration of valproic acid (vpa), a class i hdac inhibitor (113), and confirmed in pkd1 and pkd2 mouse models (113–115). sirt1 (sirtuin 1) is a member of a mammalian family of proteins, the sirtuins, originally identified as a family of nicotinamide adenine dinucleotide– dependent (nad-dependent) class iii histone deacylases (116). zhou et al. (117) showed that sirt1 expression was upregulated through c-myc oncoprotein and could be induced salvadori m and tsalouchos a journal of renal and hepatic disorders 2017; 1(1): 35–49 42 by tnf-α, which is present in cyst fluid during cyst development. double conditional knockouts of pkd1 and sirt1 demonstrated delayed renal cyst formation. increased sirt1 expression in mutant renal epithelial cells regulated cystic epithelial cell proliferation through deacetylation and phosphorylation of rb and regulated cystic epithelial cell death through deacetylation of p53. furthermore, treatment with the pan-sirtuin inhibitor nicotinamide (nam) or a sirt1-specific inhibitor (ex-527) delayed cyst growth. an uncontrolled, open-label, pilot and feasibility study of niacinamide in polycystic kidney disease (niac-pkd1) [nct02140814] has just been completed, and we are currently awaiting publication of the results. in addition, another trial, the pilot study of niacinamide in polycystic kidney disease (niac-pkd2) [nct02558595], is currently recruiting participants. cftr and kca3.1 channel inhibitors the cftr gene, identified in the q21-31 region of chromosome 7 encodes a camp/pka-regulated cl− channel (118). cftr is an atp-binding cassette (abc) transporter composed of two transmembrane domains (tmds) and two nucleotide-binding domains (nbds), separated by a larger regulatory domain (rd) containing multiple phosphorylation sites. prior to channel opening, the rd is phosphorylated at multiple sites by pka (119). cftr mrna is expressed in all nephron segments and its protein is involved with chloride secretion in the distal tubule, and the principal cells of the cortical and medullary collecting ducts. several studies showed that cftr does not only transport cl− but also secretes atp and controls other conductances such as na+ (enac) and k+ (romk2) channels (120). as aforementioned, the elevation of intracellular camp in adpkd activates the camp/ pka pathway and leads to a consequent accumulation of fluid within cysts by cftr-mediated transepithelial ion transport (17,18). furthermore, individuals afflicted by both cftr and pkd mutations showed to have attenuated polycystic kidney disease phenotype than those with adpkd alone (121–123). based on these data, each of the three chemical classes of cftr inhibitors has been tested in pkd models: (1) thiazolidinones, (2) glycine and malonic acid hydrazides, and (3) pyrimido-pyrrolo-quinoxalinediones (ppqs). the best thiazolidinone, tetrazolo-cftrinh-172, and the best glycine hydrazide, ph-glyh-101, were found to inhibit cyst formation and enlargement in mdck (madin–darby canine kidney) cyst models and in pkd1 mice (124). in addition, the ppq-class cftr inhibitors ppq-102 and bpo-27 showed greater potency than the thiazolidinones and glycine hydrazides in embryonic kidney explant pkd models (125,126). the channels for potassium, kca3.1, located on the basolateral membrane of cells lining the cysts, have also an important role in the cl− and fluid secretion as mediate k+ efflux and maintain a negative intracellular membrane potential which indirectly enhances apical cl− secretion by the cftr. for confirmation, a specific kca3.1 channel inhibitor, tram-34, showed to inhibit cl− secretion and cyst formation by mdck cells (127). in conclusion, apart from experimental studies, currently there are no clinical trials to confirm the use of cftr e/or kca3.1 inhibitors in clinical practice. activation of ampk signaling pathway amp-activated protein kinase (ampk) is an extremely preserved metabolic sensor of intracellular adenosine nucleotide levels that is activated when even modest decreases in atp production result in relative increases in amp or adp, allowing for adaptive changes in growth, differentiation, and metabolism under conditions of low energy. the most well-described mechanism by which ampk regulates cell growth is via suppression of the mtorc1 pathway, by direct phosphorylation of the tumor suppressor tsc2 and raptor (regulatory associated protein of mtor) (128,129). in addition, ampk phosphorylates and directly inhibits cftr in the kidney (130,131). thus, targeting the activation of ampk signaling pathway in adpkd could be useful to arrest two major mechanisms of cystogenesis. metformin, a drug widely used clinically for diabetes mellitus is known to stimulate ampk (132,133). recently, takiar et al. (134) showed, in pkd1 mice model, that metformin inhibited renal cystogenesis and caused a significant decrease in the cystic index by activating ampk and suppressing mtor and cftr. currently, the tame trial [nct02656017] is recruiting participants to see if metformin is safe and well tolerated compared with placebo in adult adpkd patients with beginning stages of chronic kidney disease. the investigators will also measure the effect of metformin on progression of kidney disease as reflected in the kidney size and the kidney function, along with its effect on kidney pain and quality of life. agonists of ppar-γ agonists of peroxisome proliferator–activated receptor gamma (ppar-γ) are synthetic ligands, used in clinical practice as agents that increase insulin sensitivity in the treatment of diabetes mellitus type ii. in addition, they have been shown to have anti-cystogenic properties in pkd animal models (135–138). pioglitazone has been shown to inhibit the growth of renal and hepatic cysts in pck rats, by inhibiting the cftr-mediated ionic current and the secretion of fluid (135). in another study, pioglitazone also reduced cellular proliferation, highlighted by a reduction in the number of cells positive for ki67 (a proliferation marker) in the dilated tubules and in cysts from treated rats. the fact that it also reduced the number of positive cells for ki67 in noncystic tubular cells suggest that pioglitazone can inhibit the earliest events of cystic formation (136). inhibition of renal cell proliferation was mediated by the reduction of two of the crucial intracellular pathways in pkd: the signals mek/ erk and akt/mtor. the inhibitory effect on proliferation adpkd treatment journal of renal and hepatic disorders 2017; 1(1): 35–49 43 was similar in the liver with a reduced rate of the same proliferation markers. another powerful agonist of pparγ, rosiglitazone has been used to treat han:sprd rats. rosiglitazone delayed the onset of renal failure but was associated with cardiac enlargement due to excessive renal sodium reabsorption (138). based on these preclinical data, the use of low dose pioglitazone to treat autosomal dominant polycystic kidney disease (piopkd) trial [nct02697617] is currently recruiting participants to determine whether pioglitazone is a safe and effective treatment of adpkd when treated in its early stages. other drugs have been evaluated in preclinical studies without further investigation through clinical trials. in a seminal study, natoli et al. (139) showed that the glucosylceramide inhibitor, genz-123346, was able to block cell cycle progression and proliferation through inhibition of the akt-mtor pathway in mouse models for adpkd and nephronophthisis. subsequently, the same authors showed that a mutation in the synthase gene of ganglioside gm3 led to a milder cystic phenotype (140). these data suggest that sphingolipids are not only components of cell membranes but also play signaling roles in adpkd cystogenesis. some authors hypothesized that activation of purinergic receptors by atp modulates fluid secretion, cell proliferation, apoptosis and ciliary function in adpkd (141,142). chang et al. (143) showed that the blockade of the purinergic receptor p2x7 by a selective inhibitor reduced cyst formation in a pkd2 zebrafish model, suggesting that p2x7 antagonists could have therapeutic role in adpkd. another pathway that could be implicated in the pathogenetic process of cystogenesis is the janus kinase/signal transducer and activator of transcription (jak/stat) pathway. jak/stat indeed plays a relevant role in kidney development and mediates tubular cell proliferation after ischemic injury (28,30). indeed, pyrimethamine, a stat3 inhibitor, has been effective in inhibiting cyst growth in pkd1 mice model (30). subsequently, a stat3 specific inhibitor (s3i201) confirmed these beneficial effects (30). curcumin (diferuloylmethane) a component of the golden spice turmeric (curcuma longa) can modulate multiple cell signaling pathways (mtor, wnt, stat3) altered in adpkd and showed to reduce cystogenesis and postpone renal failure in pkd1 mice model (29). conclusion and future directions multiple signaling pathways are involved in cyst formation and progression, and studies of these signaling pathways have led to potential treatments for adpkd. in this review, we covered the successes that the scientific society obtained in recent years in understanding the pathogenesis of adpkd, and presented novel therapeutic strategies targeting molecular pathways of cystogenesis. v2r antagonists and sst analogues have been shown to safely slow kidney growth and protect renal function in patients with adpkd and represent the most well-characterized and promising candidate therapies to date. according to the results of the tempo3/4 study and registration by ema, tolvaptan seems to be the first-choice drug. unfortunately, some medical interventions successful in experimental models failed in clinical practice, and others still need to be evaluated in clinical trials. it is possible that monotherapy may not be sufficient and that targeting multiple molecular pathways will be 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