Melatonin decreases oxidative stress in Drosophila melanogaster exposed to manganese

In a previous study we found that manganese induces a prooxidant effect on Drosophila melanogaster. In the present study the effect of melatonin (MEL; 0.43 mM) in oxidative stress markers of D. melanogaster after manganese (Mn; 30 mM) intoxication was determined after 6 days of treatment. Three groups were used: 1. Mn (exposed to Mn); 2. Control (maintained in standard medium); 3. MEL 6 d (treated with MEL). In four additional groups, the effect of MEL treatment for 40 days after the intoxication was determined: a. Mn-Control (exposed to Mn and no additional treatment for 40 days); b. Mn-MEL (exposed to Mn and treated with MEL for 40 days); c. Control 40 d (maintained in standard medium for 40 days); d. MEL 40 d (treated with MEL for 40 days). After 6 days, an increase in the concentrations of H2O2, NO•, MDA, protein carbonyl and 8-OHdG, and the activities of SOD, CAT, NOS and GSH-Px was observed in Mn intoxicated flies. A decrease of GSH was also detected. At 40 days, in the Mn-Control group, the increase in the concentrations of H2O2, protein carbonyl and 8-OHdG and in the activities of GSH-Px, CAT and SOD was maintained. In contrast, the concentration of GSH and MDA was decreased. Similarly the concentrations of H2O2, NO•, GSH and the activities of SOD, CAT, GSH-Px and NOS were decreased in the Mn-MEL group compared to the MnControl. In conclusion, the prolonged treatment with MEL mitigated the oxidative stress in D. melanogaster after exposure to Mn. Melatonin reduces manganese-induced oxidative stress 231 Vol. 59(3): 230 241, 2018 INTRODUCTION Melatonin (MEL) is a hormone that has been shown to protect against oxidative stress due to its ability to scavenge free radicals and induce protective mechanisms through the stimulation of antioxidant enzymes (1-4). Manganese (Mn) is a “transition metal” which is a co-factor of a number of enzymes such as hydrolases, kinases, decarboxylases and transferases (5). Although Mn has low toxicity, it may cause intoxication in humans, when they are exposed to high concentrations of this metal or to low doses for long periods of time (6). The major mechanism for induction of toxicity by Mn is unknown. However, oxidative stress has been suggested to play a key role in the neurotoxicity caused by the metal (7-9). The greatest risk of intoxication occurs in mining workers in the steel industry and those working in the manufacture of electrodes and dry cells