Radioprotective effect of melatonin in reducing oxidative stress in rat lenses

Abstract

Objective: Ocular morbidity is widely observed when radiotherapy includes the orbit. Oxidative stress generated by irradiation is responsible for this complication. In different studies, it has been shown that melatonin has antioxidative properties and a radioprotective role. The aim of this study was to evaluate the antioxidant role of melatonin against radiation-induced oxidative injury in rats' lenses after total cranial irradiation.

Materials and methods: Thirty-six adult female Sprague-Dawley rats were divided into six groups. Group I was the control group, group II only received total cranial gamma irradiation of 5 Gy, group III was exposed as the second group but at the dose of 8 Gy, group IV received 30 mg/kg melatonin 30 minutes prior to radiation plus total cranial irradiation of 5 Gy plus 5 mg/kg melatonin daily through intraperitoneal injection for ten days after irradiation, group V was treated similar to the fourth group, i.e. received irradiation plus melatonin, but at the dose of 8 Gy, and group VI only received melatonin (30 mg/kg on the first day and 5 mg/kg on the following days). Ten days after irradiation, all rats were sacrificed and their eyes were enucleated to measure the biochemical parameters i.e. malondialdehyde (MDA) and glutathione (GSH).

Results: The levels of MDA in rat lenses increased and the levels of glutathione in lenses decreased after gamma ray irradiation but these parameters were still within normal limits in rats that received melatonin.

Conclusion: It could be concluded that melatonin is useful in preventing radiation-induced oxidative injury due to its antioxidative and free radical scavenging properties.

Keywords: Cataract; Free Radicals; Melatonin; Radiation; Radioprotector.

Fig 1

The effect of melatonin on the level of MDA in rats after total cranial gamma irradiation. Data represent mean standard error of mean. (n=6 animals per group). *p<0.05 (compared to control group), **p<0.002 (compared to the control group), ***p<0.001 (compared to the radiated groups).

Fig 2

The effect of melatonin on GSH levels in rats after total cranial gamma irradiation. Data represent mean standard error of mean. (n=6 animals per group). *p<0.05 (compared to control group), **p<0.001 (compared to control group), ***p<0.05 (compared to radiated groups). Although significant differences were seen between irradiated and melatonin-treated groups in GSH concentration, we could not observe the biological effect of this antioxidant agent and concluded that these changes were not of clinical importance.