Cvetković, V. et al.  Toxicity of dimethyl sulfoxide against Drosophila… BIOLOGICA NYSSANA 6 (2)  December 2015: 91-95 Cvetković, V. et al.  Toxicity of dimethyl sulfoxide against Drosophila… 91 Original Article Received: 11 July 2015 Revised: 17 August 2015 Accepted: 01 October 2015 Toxicity of dimethyl sulfoxide against Drosophila melanogaster Vladimir J. Cvetković1*, Tatjana Lj. Mitrović1, Boris Jovanović2, Slaviša S. Stamenković1, Miljana Todorović1, Miljana Đorđević3, Niko Radulović3 1University of Niš, Faculty of Sciences and Mathematics, Department of Biology and Ecology, Višegradska 33, 18000 Niš, Serbia 2Chair for Fisheries Biology and Fish Diseases, Ludwig Maximilian University of Munich, Kaulbachstrasse 37, 80539, Munich, Germany 3University of Niš, Faculty of Sciences and Mathematics, Department of Chemistry, Višegradska 33, 18000 Niš, Serbia * E-mail: biovlada@yahoo.com Abstract: Cvetković, V.J., Mitrović, T.Lj., Jovanović, B., Stamenković, S.S., Todorović, M., Đorđević, M., Radulović, N.: Toxicity of dimethyl sulfoxide against Drosophila melanogaster. Biologica Nyssana, 6 (2), December 2015: 91-95. Dimethyl sulfoxide (DMSO) is commonly used as a solvent for organic compounds but its toxic properties can affect both in vitro and in vivo studies. Thus, evaluation of DMSO toxicity must be performed on the model organism before its application as a solvent in the target studies. Present study aimed to determine the lethal concentration required to kill 50% of the population in a given period of time (LC50), no observed effect concentration (NOEC), and lowest observed effect concentration (LOEC) values for DMSO on Drosophila melanogaster which is frequently used as a model for toxicity studies. Twelve different concentrations of DMSO were tested on three-day old D. melanogaster larvae for 12 days. At the end of the life cycle, number of live hatched adults and un-hatched pupae were counted. Based on probit analysis 12 days LOEC was 0.04% v/v, 12 days NOEC was ˂ 0.04% v/v and 12 days LC50 was 0.42% v/v. The results indicate that DMSO may be more toxic to D. melanogaster than it was initially considered. Key words: Drosophila melanogaster, NOEC, LOEC, LC50, DMSO, toxicity Apstrakt: Cvetković, V.J., Mitrović, T.Lj., Jovanović, B., Stamenković, S.S., Todorović, M., Đorđević, M., Radulović, N.: Toksičnost dimetil sulfoksida na modelu Drosophila melanogaster. Biologica Nyssana, 6 (2), December 2015: 91-95. Dimetil sulfoksid (DMSO) se često koristi kao organski rastvarač ali njegova toksičnost može da utiče na ishode in vitro i in vivo istraživanja. Zato se procena toksičnosti DMSO-a mora ispitati na model organizmu pre njegove primene kao rastvarača u željenom istraživanju. Ovo istraživanje ima za cilj da se za DMSO ustanovi letalna koncentracija koja ubija 50% populacije u posmatranom vremenskom periodu (Lethal concentration 50 - LC50), koncentracija koja ne uzrokuje detektabilne promene (No observed effect concentration - NOEC) i koncentracija koja uzrokuje najmanje detektabilne promene (Lowest observed effect concentration - LOEC) na modelu Drosophila melanogaster koji se veoma često koristi u toksikološkim 6 (2) • December 2015: 91-95 BIOLOGICA NYSSANA 6 (2)  December 2015: 91-95 Cvetković, V. et al.  Toxicity of dimethyl sulfoxide against Drosophila… 92 istraživanjima. Larve D. melanogaster stare tri dana tretirane su sa dvanaest različitih koncentracija DMSO-a u periodu od 12 dana. Na kraju životnog ciklusa, prebrojani su adulti koji su se izlegli i lutke iz kojih se adulti nisu izlegli. Prema probit analizi, za 12 dana tretmana LOEC je 0.04% v/v, NOEC je ˂ 0.04% v/v i LC50 je 0.42% v/v. Rezultati ukazuju da je DMSO toksičniji za D. melanogaster nego što se prvobitno smatralo. Key words: Drosophila melanogaster, NOEC, LOEC, LC50, DMSO, toksičnost Introduction DMSO originates from 19th century as a by-product in the process of paper production from a wood pulp (C a p r i o t t i & C a p r i o t t i , 2012; H o r i t a & W e b e r , 1964). Since then, colorless liquid DMSO is characterized as a good aprotic solvent which can easily dissolve various non-polar and polar molecules (C a p r i o t t i & C a p r i o t t i , 2012; H o r i t a & W e b e r , 1964). The concern regarding the toxicity of solvents is always a topical issue in toxicology studies. Thus, the pre-testing of solvents on certain model organism, which is planned to be used in further toxicology studies, is an imperative. One of the widest and frequently used model organisms in toxicity and genotoxicity studies is fruit fly, Drosophila melanogaster (S t a m e n k o v i ć - R a d a k et al., 2008; P a t e n k o v i ć et al., 2009; V a l e s et al., 2013). Drosophila is a remarkable model for in vivo assays in toxicology because of high number of progeny and its short lifespan. In addition, culturing and maintaining of Drosophila is more economical compared to other model organisms. It was demonstrated that administration of the test substances through the feeding medium is simple (N a z i r et al., 2003; S t a m e n k o v i ć - R a d a k et al., 2008) making toxicology assays on Drosophila even easier. The adverse effects of DMSO in Drosophila were noticed in the 1980's (M a s s i e et al., 1985; B r o d b e r g et al., 1987) when the authors recommended that DMSO must be used carefully as a solvent. Therefore, present study aimed to determine the lethal concentration required to kill 50% of the population in a given period of time (LC50), no observed effect concentration (NOEC), and lowest observed effect concentration (LOEC) values for DMSO on a three-day-old D. melanogaster larvae of the wild-type strain. Material and methods Test organism In this experiment the D. melanogaster Oregon-RC (wild-type flies, stock no. 5) ("Bloomington Drosophila Stock Center", Indiana University, USA) were used. Flies were cultivated on a standard feeding medium for Drosophila (9% sugar, 10% corn meal, 2% agar, 2% yeast) with addition of fungicide 2.50 mg mL-1 methyl 4-hydroxybenzoate (Nipagin®, Alfa Aesar GmbH & Co KG, Germany) diluted in 95% EtOH (ethanol). The flies were cultivated in a standard cultivating 200 ml vials on 25 oC, 60% humidity, with 12 h/12 h day-night cycle. Adults were allowed to lay eggs during the eight hour period, after that they were removed from the vials. After three days larvae which were 72±4 h old, have been removed from the cultivating medium, washed with distilled water and used in further procedure. Test substance and treatment schedule Twelve concentrations of DMSO (Carl Roth, Germany) were tested in duplicates and each experimental group consisted of 30 three-day-old larvae. Therefore, final concentrations of DMSO in 3ml of standard feeding medium were: 0.16%, 0.32%, 0.48%, 0.64%, 0.80%, 0.97%, 1.13%, 1.29%, 1.45%, 1.61%, 2.42% and 3.23% v/v. Negative, water control, was also included. At the end of incubation time, which lasted up to 12 days, numbers of live hatched units (adults) and un-hatched units (at pupal stadium) were counted. Statistical analysis Mean values were calculated and used for further analysis. Risk Assessment software tool (RA V1.0; Pensacola, Florida, USA) and probit analysis were utilized in order to calculate values for LC50, LOEC, and NOEC. Also, the confidence intervals (95%) were calculated. Results and discussion The toxic effects of DMSO, particularly antimicrobial and virucidal properties, were noticed in the 1960's. DMSO was shown to inhibit bacterial and fungal growth at concentration of 30-50% and at concentration of 80% inactivated infectivity of some RNA and DNA viruses (B a s c h & G a d e b u s c h , 1968; C h a n & G a d e b u s c h , 1968; W a g n e r et al., 2002). Even nowadays, the adverse properties of DMSO, which is used as a solvent in toxicology studies of aquatic model organisms, was noticed (M á c h o v á et al., 2009). M á c h o v á et al. (2009) tried to establish general value for the non-toxic concentration of DMSO as a solvent that could be applied across different conditions in aquatic model organism such as fish. But they found that effect of BIOLOGICA NYSSANA 6 (2)  December 2015: 91-95 Cvetković, V. et al.  Toxicity of dimethyl sulfoxide against Drosophila… 93 DMSO on fish model depends on fish age, species, type of test and indicators observed so they concluded that general value for the non-toxic concentration of DMSO can't be found and every experiment should include solvent control (M á c h o v á et al., 2009). It implies that DMSO must be pre-tested on certain model organism if it is planned to be used in experiment as solvent. The Fig. 1a represents survival plot of D. melanogaster units exposed to different concentration of DMSO which unambiguously shows that number of hatched flies decreased in dose- depended manner. Fig. 1b represents probability of D. melanogaster units mortality exposed to DMSO which was calculated by Risk Assessment software tool. 12 days LC50 value is 0.42% v/v (Tab. 1) and total number of adults hatched from pupal stadium drastically decreased from 0.32% v/v where almost every unit developed into adult to 0.97% v/v where none of the adults hatched. In addition, pupal mortality (un-hatched units) increased drastically in this concentration range, respectively (Fig 2). Concentration of DMSO in substrate, from 0.97% v/v up to the 3.23%, v/v caused increase of larval mortality (Fig. 2). Concentrations above 0.32% v/v decreased hatchability of adults. These observations are in accordance with similar study (N a z i r et al., 2003). In genotoxicity and toxicity studies larvae, or adults, of D. melanogaster, as a model organisms, are widely used (N a z i r et al., 2003; A d a m s k i et al., 2009; C a s t a ñ e d a - P a r t i d a et al., 2011; M i y a z a w a et al., 1998; 2000; G r a f et al., 1984). There are many references on DMSO toxicity, but only a few papers are on DMSO toxicity in Drosophila. For instance, G r a f et al. (1984) used DMSO in final concentration of 2% in feeding medium for Drosophila in somatic mutation and recombination test (G r a f et al., 1984). But recent research by N a z i r et al. (2003) showed that DMSO should be used very cautiously as solvent because it could results with false conclusions in the screening Fig 1. Survival plot of D. melanogaster units (a) and probability of the units mortality exposed to DMSO with 95% confidence intervals (b). Table 1. Probit analysis: LOEC, NOEC and LC50 values with confidence intervals after 12 days of exposure. % of population response Concentration in % (v/v) Lower limit 95% Upper limit 95% LOEC 12 days 0.01% 0.04555 0.00780 0.09803 0.10% 0.06642 0.01461 0.12884 1.00% 0.10502 0.03122 0.18004 5.00% 0.15806 0.06122 0.24374 10.00% 0.19656 0.08741 0.28734 20.00% 0.25598 0.13387 0.35252 30.00% 0.30967 0.18096 0.41093 40.00% 0.36435 0.23254 0.47149 LC50 12 days 50.00% 0.42404 0.29133 0.54068 BIOLOGICA NYSSANA 6 (2)  December 2015: 91-95 Cvetković, V. et al.  Toxicity of dimethyl sulfoxide against Drosophila… 94 Fig 2. Percentage of hatched (alive adults), un-hatched (non-survived units at pupal stadium) and non-survived units at larval stage (larval mortality) influenced with different concentration of DMSO (showed in % v/v) in feeding media and in water (negative) control. of test substances because of its toxicity to D. melanogaster (N a z i r et al., 2003). Our results confirmed observation that DMSO is toxic and can impact normal larval development in concentration greater than 0.04% v/v (LOEC value) in feeding medium. The present study was performed with twelve concentrations which provided better resolution of obtained results than in the study by N a z i r et al. (2003) where six concentrations were tested. Also, we treated three-day-old larvae of the wild-type strain of D. melanogaster which differs from the study by N a z i r et al. (2003) whose treatment started at the egg stadium of the transgenic strain of D. melanogaster and lasted for 10-14 days. Finally, probit analysis was performed as a common analysis in toxicology, in order to determine NOEC, LOEC and LC50. N a z i r et al. (2003) considered DMSO at 0.3% v/v as NOAEL (No Observed Adverse Effect Level) value which can be used as dietary concentration in toxicity studies with D. melanogaster. However, according to present research 12 days LOEC is 0.04% v/v so the absolutely safe dietary concentration of DMSO in feeding medium for D. melanogaster larvae of wild- type strain, should be less than 0.04% v/v. One of the reasons for higher toxicity (and lower value of LOEC) observed in the present study compared to the N a z i r et al. (2003) may be the lower sensitivity of D. melanogaster eggs to DMSO since the eggs do not actively feed on the exposure media thus the cumulative toxicity during same exposure time period is lower. Therefore, a more realistic scenario would be to start the exposure during the larval stage, as it was performed in the present study. Conclusion The probit analysis showed that 12 days LOEC was 0.04% v/v, NOEC was ˂ 0.04% v/v and LC50 was 0.42% v/v. Pupal mortality reached maximum at 0.97% v/v of DMSO in substrate while concentration greater than 0.32% v/v reduced hatchability of adults at the end of lifespan. 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