Resumo

Introduction and Objectives: Melatonin prevents neuronal death in a large number of neurodegeneration models. It is synthesized by the pineal gland and it is known as a powerful antioxidant. Acting on membrane receptors (MT1 and MT2) melatonin can induce the expression of the antioxidant enzymes superoxide dismutase and glutathione peroxidase preventing the oxidative stress. The cocaine base heating during crack smoking produces methylecgonidine, also called methyl ester anhydroecgonine (AEME). AEME is a potent inducer of cell death. Micrurus lemniscatus is a snake from the Elapidae family. The predominant clinical manifestations of Elapid snake bite are related to the neurotoxic and myotoxic actions of the venom, causing blockade of the peripheral nervous transmission. The phospholipase A2 neurotoxins isolated from the venom of Micrurus lemniscatus induced neuronal death in primary culture of embryonic hippocampal neurons. In this work we investigated the protective effect of melatonin against the actions of the Micrurus lemniscatus phospholipase neurotoxins (Mlx-8, Mlx-9, Mlx-11 e Mlx-12) and the AEME, studying the cell viability of hippocampal neurons. Methods: Wistar rats with 18-19 days of embryonic life were used. The pregnant rats were anesthetized with pentobarbital and cesarean section was performed to remove the embryos. The hippocampus were identified and dissected. Hippocampal neurons were isolated by tripsin digestion and maintained in culture for 7 days in Neurobasal medium supplemented with B27. The cells were incubated for 24 h with different concentrations of AEME (0.1, 1 and 10mM), Mlx-8 (10 ng/mL), Mlx-9 (100 and 1000 ng/mL), Mlx-11 (10, 100 and 1000 ng/mL) and Mlx-12 (10, 100 and 1000 ng/mL) and melatonin (10-7 and 10-9 M). The MTT test was used for evaluation of cell viability. Results: There was a significant reduction in cell viability when the cells were treated with AEME, Mlx-8, Mlx-9, Mlx-11 and Mlx-12, in all the concentrations used. Melatonin (10-9M) reversed the induction of neuronal death by AEME (0.1 and 1mM) and by the neurotoxins Mlx-8 (10 ng/mL) and Mlx-12 (100 and 1000 ng/mL), but not by Mlx-9 and Mlx-11. Melatonin at the concentration of 10-7M did not present any protective effect on the cells treated with AEME, Mlx-8, Mlx-9 and Mlx-11. On the other hand, neuroprotection was observed when the treatment also involved 100 and 1000 ng/mL of the toxin Mlx-12. Conclusion: Melatonin acts as a neuroprotective agent against the cell death induced by AEME and some phospholipase neurotoxins of Micrurus snake venom and this effect is more evident at the physiological concentration of 10-9M. Supported by: CNPq-PIBIC, INCTTOX