Inhibitory effect of melatonin on products of lipid peroxidation resulting from chronic ethanol administration.

Despite decades of research, the role of free radicals in alcohol-induced organ injury is still a matter of debate. The present work was designed to investigate the potential protective effect of melatonin, a reported radical scavenger and antioxidant, on free radical toxicity induced by chronic ethanol administration. The major end-point of oxidative damage measured in this report was lipid peroxidation. Four groups of male Sprague-Dawley rats were used. The first group served as untreated controls and received a daily injection of alcoholic (<1% ethanol) saline. The second group of rats received daily at 18:00 a single subcutaneous injection of melatonin (10 mg/kg). Group 3 rats received only ethanol (3 g/kg) for 30 consecutive days; the ethanol was given at 18:30. The final group of rats was given both melatonin and ethanol with melatonin preceding ethanol by 30 min. Products of lipid peroxidation [malondialdehyde (MDA) and 4-hydroxyalkenals (4-HDA)] were measured in the brain, heart, liver, lung and testes. At the conclusion of the study, MDA + 4-HDA levels were significantly increased in brains, hearts, lungs and testes, but not livers, of alcohol-treated compared with control rats. The percentage increases in lipid peroxidation products were 21.8%, 28.8%, 35.9% and 45.3% for brain, heart, lung and testes, respectively. In animals given melatonin 30 min before ethanol, the increases in MDA + 4-HDA levels were significantly reduced in all organs investigated, with levels not different from those in control rats. Based on these findings, it is speculated that melatonin's direct and indirect antioxidative actions inhibited alcohol-induced lipid peroxidation. These results suggest a new strategy for the treatment of alcohol-related diseases using melatonin as an antioxidant to reduce the damage inflicted by aggressive radical species.