Effects of melatonin on the Nrf2-ARE signaling pathway after spinal cord injury

Abstract

Objective To observe the effects of melatonin (MT) on the expression of heme oxygenase-1 (HO-1), phosphorylated adenine dinucleotide quinone oxidoreductase-1 (NQO-1) and nuclear factor erythroid-2-related factor 2 (Nrf2), so as to explore the mechanism of MT′s action in the Nrf2-ARE signaling pathway. Methods A total of 72 Sprague-Dawley rats were randomly divided into a control group, an injury group and a melatonin group, each of 24. T11-T12 acute SCI was induced in the injury and melatonin groups using the modified Allen′s method. Ten minutes after the injury, equal amounts of absolute ethyl alcohol and melatonin were intraperitoneally injected into the rats in the injury and melatonin groups. For the control group, the vertebral plate was cut to expose the T11-T12 spinal cord without any injury of the nerves. Six rats from each group were randomly selected for sacrifice at 6, 12 and 24 hours after the operation, and T11-T12 spinal cord specimens were collected. The spinal cord injury and inflammatory response were observed using haematoxylin eosin staining. The expression of HO-1, NQO-1 and Nrf2 was examined using immunofluorescence, while the expression of HO-1, NQO-1 and Nrf2 protein and mRNA were detected using RT-PCRs. Results The neuronal cells in the spinal cords of the control rats were of normal shape, without edema, necrosis or obvious hemorrhagic foci. Hemorrhagic foci, significantly more inflammatory cells and some spinal cord neurons with edema and necrosis were observed in the injury group. However, significantly fewer hemorrhagic spots and cells with edema were found in the melatonin group compared with the injury group. The average expression of HO-1, NQO-1 and Nrf2 protein and mRNA was significantly higher in the melatonin group than in the other two groups. The levels in the injury group were also significantly higher than in the control group 12 and 24 hours after the experiments. Immunofluorescence showed that the greatest number of cells with HO-1, NQO-1 and Nrf2 was found in the melatonin group, followed by the injury group and then the control group, with significant differences among all 3 groups. Conclusion Melatonin can promote the expression of HO-1, NQO-1 and Nrf2 in rats with acute spinal cord injury, which might be related with its activating the Nrf2-ARE signaling pathway. Key words: Spinal cord injury; Melatonin; Nrf2-ARE signaling pathway