Melatonin limits paclitaxel-induced mitochondrial dysfunction in vitro and protects against paclitaxel-induced neuropathic pain in the rat

Chemotherapy-induced neuropathic pain is a debilitating and common side effect of cancer treatment. Mitochondrial dysfunction associated with oxidative stress in peripheral nerves has been implicated in the underlying mechanism. We investigated the potential of melatonin, a potent antioxidant that preferentially acts within mitochondria, to reduce mitochondrial damage and neuropathic pain resulting from the chemotherapeutic drug paclitaxel. In vitro, paclitaxel caused a 50% reduction of mitochondrial membrane potential and metabolic rate, independent of concentration (20-100µM). Mitochondrial volume was increased dose-dependently by paclitaxel (200% increase at 100µM). These effects were prevented by co-treatment with 1µM melatonin. Paclitaxel cytotoxicity against cancer cells was not affected by co-exposure to 1µM melatonin of either the breast cancer cell line MCF-7, or the ovarian carcinoma cell line A2780. In a rat model of paclitaxel-induced painful peripheral neuropathy, pre-treatment with oral melatonin (5/10/50mg/kg), given as a daily bolus dose, was protective, dose-dependently limiting development of mechanical hypersensitivity (19/43/47% difference from paclitaxel control, respectively). Melatonin (10mg/kg/day) was similarly effective when administered continuously in drinking water (39% difference). Melatonin also reduced paclitaxel-induced elevated 8-isoprostane F2 levels in peripheral nerves (by 22% in sciatic; 41% in saphenous) and limited paclitaxel-induced reduction of C fibre activity-dependent slowing (by 64%). Notably melatonin limited the development of mechanical hypersensitivity in both male and female animals (by 50/41%, respectively) and an additive effect was found when melatonin was given with the current treatment, duloxetine (75/62% difference, respectively). Melatonin is therefore a potential treatment to limit the development of painful neuropathy resulting from chemotherapy treatment.