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 in mitochondrial membrane potential and metabolic rate, independent of concentration (20‐100 μmol/L). Mitochondrial volume was increased dose‐dependently by paclitaxel (200% increase at 100 μmol/L). These effects were prevented by co‐treatment with 1 μmol/L melatonin. Paclitaxel cytotoxicity against cancer cells was not affected by co‐exposure to 1 μmol/L 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, pretreatment with oral melatonin (5/10/50 mg/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 (10 mg/kg/day) was similarly effective when administered continuously in drinking water (39% difference). Melatonin also reduced paclitaxel‐induced elevated 8‐isoprostane F(2)α levels in peripheral nerves (by 22% in sciatic; 41% in saphenous) and limited paclitaxel‐induced reduction in 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.