Study on pre-treatment of melatonin against radiation-induced oxidative stress in mice

Antioxidants are part of the primary cellular defense against radiation-generated free radicals. Reports on low-level chronic administration of melatonin with its antiradiation influence are scanty. Although compelling logic suggests that melatonin may be effective for a variety of disorders, the mode and optimal dose of melatonin are still not clear. Most studies have used doses of supraphysiological blood levels. Present investigation reported that pre-treatment with the lower concentration of melatonin (0.1mg/kg b.w./day) for 15 consecutive days affords potential protective effect against radiation-induced oxidative stress and mortality in mice. Radiation-induced augmentation in the levels of lipid peroxidation, glutathione disulphide (GSSG) and acid phosphatase was significantly ameliorated by melatonin pre-treatment. Radiation-induced depletion in the level of reduced glutathione (GSH), as well as glutathione peroxidase (GSH-Px) and alkaline phosphatase activities, was inhibited significantly by melatonin administration. Regression analysis of survival data yielded LD(50/30) as 7.16 and 11Gy for control (irradiation alone) and experimental (melatonin-treated irradiated) mice, respectively, and produced a dose reduction factor (DRF), 1.53. Radiation-induced deficit in the body and organ weight also got inhibited significantly in the melatonin pre-treated mice. The findings support property of melatonin as a free radical scavenger and singlet oxygen quencher and indicate the antioxidative properties of melatonin against the gamma radiation.