Upsala J Med Sci 84: 215-227
Hepatic Triglyceride and Lipoprotein Lipase Activities
of Post-heparin Plasma in Normals
and Hypertriglyceridemics
Jonas Boberg*, Merike Boberg, Richard Gross, John D. Turner,
Jan Augustin** and W. Virgil Brown
Department of Medicine, School of Medicine, University of California, San Diego,
La Jolla, California, U S A
ABSTRACT
Post-heparin plasma hepatic triglyceride lipase (H-TGL) and lipoprotein li-
pase (LPL) activities were 8-34 and 3.5-21 (range) pmol/ml/hr respectively in
males with normal serum lipid concentrations. In females the corresponding
values were 4-25 and 4-16 pmol/ml/hr. No significant differences were observed
between ages or between the two sexes.
Male patients with hypertriglyceridaemia had similar activities of H-TGL
but significantly lower values for LPL activities than the control males.
Significant linear correlations were found between serum triglyceride con-
centrations and LPL activities both for males (coefficient of correlation =
r = -0.64) and for females (r = -0.62).
INTRODUCTION
Several studies (1-3) have demonstrated that the serum triglyceride (S-TG)
concentrations in man during fasting conditions to a great part are determined
by the removal process of TG rich S-lipoproteins - very low density lipopro-
teins (VLDL) and chylomicrons - from the blood stream. This removal process is
thought to be mediated essentially by lipoprotein lipase (4). In man the act&
vity of this enzyme has been demonstrated in adipose (5-6) and muscle tissue
(7). Although the most common way to determine this enzyme activity in man has
been in post-heparin plasma (4). However, recently post-heparin lipolytic act&
vity (PHLA) has been shown to contain at least two triglyceride lipase activi-
Preliminary report given at the American Heart Association 47th Scientific
Sessions, November 18-2 1 , 1974.
*Visiting postdoctoral NIH research fellow and also supported by the Swedish
Medical Research Council (60F-4187 and 19R-4187).
Present address: Department of Geriatrics, University of Uppsala, Box 12042,
S-750 12 Uppsala, Sweden
**Visiting postdoctoral research fellow supported by the "Deutsche Forschungs-
gemeinschaft", Westgermany (An 4511).
215
ties*. One probably originating from liver and the other from extrahepatic
tissues (8). A method for isolation from post-heparin plasma, these two trigly-
ceride lipase activities and for quantitative determination of the two enzyme
activities separately has previously been described (9). This method includes
affinity chromatography where the enzymes are partly purified to avoid inter-
ference from serum lipoproteins and apo-lipoproteins. The present report de-
monstrates a clinical application of this method in which human subjects with
normal serum lipid concentrations and male patients with hypertriglyceridaemia
have been investigated.
METHODS
Subjects and experimental procedure
The subjects were 42 males between 20 and 81 years and 38 females between
12 and 78 years of age. In both these groups all subjects had normal S-TG
< 2 . 4 8 mmol/l ( 2 2 0 mg/100 ml) and cholesterol <7.8 mmol/l (300 mg/100 ml) con-
centrations. The subjects were recruited either from the laboratory personel
or from volunteers in the community. The latter subjects participated in a
pilot study done prior to a health screening survey. All were free living and
apparently healthy. They had normal fasting blood sugar and urine analyses.
None were on prescription except for digoxin medications. The male patients
with hypertriglyceridaemia were those referred to the Lipid Research Clinic or
the metabolic unit at the Veterans Administration Hospital, San Diego. No pa-
tients with diabetes mellitus, hypothyroidism, liver or renal disease were in-
cluded in the study.
The procedure was performed in the morning after over-night fast. Firstly
the subjects were weighed and a short medical history was recorded. A scalp
vein needle was introduced into an anticubital vein and a venous blood sample
of 15 ml was taken into EDTA glas tubes. Immediately thereafter 6 0 IU per kg
body weight of heparin (Riker laboratories, 5000 IU/ml) was injected intra-
venously through the scalp vein needle followed by about 10 ml of saline wash.
Fifteen minutes after the heparin injection the post-heparin sample was with-
drawn (30 ml of blood). All blood samples were kept on ice for 1 to 2 hours be-
fore centrifugation.
Analytical methods
Blood samples were centrifuged at 5000 g x min and the blood plasma was re-
covered into capped vial8. The preheparin samples were kept for 1 to 36 hours
at 4OC before serum lipid and lipoprotein analyses were done. Post-heparin plae
ma samples were frozen in 6 ml aliquots at -7OOC for not more than one month
*In this paper these two lipase activities are called hepatic triglyceride li-
pase (H-TGL) activity and lipoprotein lipase (LPL) activity.
216
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before determination of H-TGL and LPL activities were done. Serum
lipids and lipoproteins were determined according to the stan'dar-
dized methods routinely used at the Lipid Research Clinic Labora-
tory (10).
Isolation of H-TGL and LPL activities from postheparin plasma
were done with affinity chromatography on sepharose covalently
linked with heparin ( 1 1 ) according to a method previously descri-
bed in detail ( 9 ) . Aliquots of the enzyme fractions recovered
from the chromatography were incubated with a labelled triglyce-
ride emulsion (8). Labelled free fatty acids released during in-
cubation for 30 minutes were measured ( 1 2 ) . Lipase activity was
expressed as umoles fatty acids released per ml of post-heparin
plasma per hour of incubation. During the whole investigation a
frozen control post-heparin plasma sample was run to check for
the interday variations of the procedures. Statistical analyses
were done according to Snedecor (13).
RESULTS
Postheparin triglyceride lipase activity in normal subjects.
Results obtained in normal subjects, males and females, are
presented in tables 1 and 2 respectively.
The females were not obese and the average S-TG concentration
was 0.88 mmol/l with no significant trend o f either increase o r
decrease with age. S- cholesterol concentration (both total and
in beta-lipoproteins) showed the increase with age which has been
demonstrated several times before. Mean value of the whole group
was 5 . 3 ? 0 . 2 mmol/l for total and 3.2+0.2 mmol/l for beta-lipopro-
tein cholesterol concentration.
H-TGL activities of the younger females ( ( 3 0 years) were on
the average higher than for the groups of older people. However
this difference was not significant. No significant change with
age was demonstrated for LPL activity. Mean values of H-TGL and
LPL activities for normal females were 1 3 . 5 and 7.7 umoles/ml/hr
respectively.
The normal male subjects were slightly heavier than the fe-
males. Similar concentrations of S-TG and total and beta-choleste-
rol were found for males and females. Alfa-lipoprotein choleste-
rol concentrations were slightly lower in the males compared to
the females. H-TGL and LPL activities did not change with age in
the normal males. The mean values were 19.6 and 6.6 umol/ml/hr
218
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Fig.1. Relationship
between post-heparin
1 ipop ro t e in 1 ip as e
( L P L ) activity and ser-
um triglyceride (TG)
concentration in heal-
thy females with "nor-
mal" serum lipid values.
Correlation analysis of
logarithmic values of
both parameters resul-
ted in r=-0.62, p<O.OOl.
Fig. 2. Relationship
between post-heparin
lipoprotein lipase (LPL)
activity and serum tri-
glyceride (TG) concentra-
tion in healthy males
with "normal" serum lipid
values. Correlation ana-
lysis of logarthmic val-
ues of both parameters
resulted in r=-0.64,
p<o .oo 1 .
220
respectively. These values for H-TGL activity are significantly
higher for the males than for the females, while no significant
difference of LPL activity was found between the sexes.
Postheparin triglyceride lipase activities in patients with
hypertriglyceridemia
Only male patients with hypertriglyceridemia were investi-
gated. Results for a comparison between normal and hypertriglyce-
ridemicmales are summarized in table 3 . Naturally serum TG and
cholesterol concentrations were higher in the hypertriglycerid-
emics compared to the controls. Furthermore the hypertriglycerid-
emics were heavier and had significantly lower alfa-lipoprotein
cholesterol concentrations. H-TGL activity was on the average
significantly higher in the patients with elevated S-TG concentra-
tions than the controls, showing mean values of 2 2 . 8 compared to
1 9 . 6 umol/ml/hr for the controls. LPL activities on the other
hand were significantly (p < O . O O l > lower in the patients with
hypertriglyceridemia compared t o the controls. The mean values
were 4 . 7 for hypertriglyceridemics compared to 6 . 6 umol/ml/hr for
the male controls.
Relationship between S-TG concentrations and H-TGL and LPL
activities
No significant correlations were found between H-TGL activity
and concentrations o f any serum lipid or lipoprotein fraction.
Between S-TG concentrations and LPL activities significant
correlations were found for both female and male normotriglycerid-
emics (figures 1 and 2 ) . The correlation coefficients were r =
- 0 . 6 2 and r = - 0 . 6 4 . A s shown in figure 3 about one third of the
male patients with hypertriglyceridemia fell outside the range
of LPL activity for the controls. However, for the rest of the
patients there were overlap of the data.
A s demonstrated in figure 4 no significant correlations
occurred between the two post-heparin triglyceride lipase acti-
vities. The two enzyme activities seem to vary quite independent-
lyinboth the female and male controls and also in the patients
with high S-TG concentrations.
221
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0
W
I-
-
a
0
c 0 . 0
0
z
a
3
W
cn
4 0
a
i
k 20
>
c
-
V
4
I
0
NORMAL MALES
0 HYPERlIPOPROTffN€MfC
MALES
10 c : O O
0 0
O %
O w "oo
o o t O 0 O 0 8" 0"
0
0
0
0. s=
I t
a
Fig. 3. Relationship bet-
ween post-heparin lipopro-
tein lipase (LPL) activity
and serum triglyceride (TG)
concentration in normotri-
glyceridemic and hypertri-
glyceridemic males. Further
data of the former group
see under figure 2.
LPL A C T I V I T Y , p m o l l m l l h r
Fig. 4 . Relationship between lipoprotein lipase (LPL) activity and hepatic
triglyceride lipase (H-TGL) activity.
223
DISCUSSION
The present study reports on a clinical application of a method which
quantitatively determines two different TG lipase activities in post-heparin
plasma. The main advantage with the method used ( 9 ) compared to other methods
described (14-16) is that no interference with plasma components like apo-
lipoproteins or whole lipoproteins can occur. Two other methods have been
described to estimate H-TGL and LPL activities in human post-heparin plasma
( 1 4 - 1 6 ) . One of them using an antibody against H-TGL activity which is aimed
to completely abolish the contribution of this enzyme to whole TG lipase acti-
vity in post-heparin plasma ( 1 5 , 1 6 ) . The other method is based on the sugges-
tion that H-TGL activity is not inhibited while LPL activity is completely
inhibited by protamin-sulphate ( 1 4 ) . In both these methods whole post-heparin
plasma from the investigated patient is present during the assay, which means
presence of the patient’s own apoproteins an lipoproteins which might serve
as sustrate for the enzymes competing with the exogenous substrate added to
the assay. There might also be inhibitors present in the whole post-heparin
plasma ( 1 7 ) . Thus the present method seems to have one advantage compared to
previously described methods in quantitating H-TGL and LPL in human post-hepa-
rin plasma. However, the importance of this aspect is not fully evaluated
since the in vitro addition of serum lipoproteins did not change the estimated
activities of either H-TGL or LPL in the two methods described earlier (14,151.
The application of this method in normal males and females and in male
patients with hypertriglyceridemia demonstrated no relationship at all between
the two post-heparin TG activities H-TGL and LPL. This observation is an addi-
tional piece of evidence indicating that these two enzyme activities really
are two different enzymes. This has recently been demonstrated in a study
where the two enzyme proteins have been purified and characterized ( 1 8 ) . H-
TGL activity was higher in normal males compared to females, and also higher
in normal males compared to male patients with hypertriglyceridemia. None of
the patients or subjects were missing the H-TGL activity and we have found no
evidence for a relationship between this enzyme activity and any physiological
or pathophysiological condition. Others have reported, however, that this
enzyme activity might be low in patients with hypothyroidism ( 1 4 ) .
LPL activities in normal males and females occurred within the same ranges
and there was no age dependence demonstrable. The range of activity presented
here is slightly higher than described by Krauss et a1 ( 1 4 ) , who used the me-
thod dependent on complete protamine-sulphate inhibition of LPL activity. The
latter authors also found an age dependent LPL activity in females. A decrease
of LPL activity with age in both males and females was demonstrated by Hut-
tunen et a1 ( 1 9 ) who used the selective innnunochemical method ( 1 5 ) . These
224
authors also demonstrated higher absolute values than presented in this study
for both H-TGL and LPL activities ( 1 9 ) . The reason for this difference is not
known but might be explained either by differences in substrate preparation or
differences in the recovery of the enzyme isolation procedures. The isolation
procedure used in the present paper probably gives a lower yield than the im-
munochemical method.
There were significant correlations between LPL activities and S-TG concen-
trations both for normal females and normal males. This is in agreement with
two earlier studies ( 1 9 , 2 0 1 where different but still rather specific methods
have been used to quantitate LPL activities. Earlier it has been shown that
there is no correlation between endogenous S-TG production ("turnover") and
S- TG concentration in males with hypertriglyceridemia ( 3 ) . This finding may
indicate that the level of S-TG concentration in normals generally are deter-
mined by the rates of clearance of S-TG (or by the fractional removal rate)
evidence for which has been gained earlier with other methods ( 3 , 4 ) . Since the
enzyme LPL most probably plays an important role in the removal process of the
S-TG the significant correlations found in this study between LPL activities
and S-TG concentrations fit well with previous studies on serum TG turnover.
Earlier studies on post-heparin LPL (20) and tissue LPL activities ( 2 1 )
have reported significantly lower values in patients with hypertriglyceridemia.
However, the range of values measured for the LPL activities in these patients
overlaps that from analyses of subjects with normal serum TG concentrations.
Overlapping of activities in these two groups occurred also in this report,
however, this was slightly less pronounced. LPL activities were significantly
lower in patients with hypertriglyceridemia. In about one third of the patients
the low LPL activities might be the cause of the hypertriglyceridemia while in
the rest of the patients contribution of other factors must be added to explain
the cause of the hypertriglyceridemia.
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Accepted January 20, 1 9 7 9
Address for reprints:
Jonas Boberg, M.D.
Department of Geriatrics
University of Uppsala
p.0.Box 12042
S-750 12 Uppsala 12
Sweden
6-792856 227