Melatonin mitigates arsenic and fluoride-induced cardiotoxicity in chickens by maintaining mitochondrial homeostasis

Co-exposure to geogenic arsenic and fluoride is widely recognized in numerous countries and has been shown to induce severe cardiac injury in both humans and animals. Our previous studies have demonstrated that mitochondria are primary targets of arsenic and fluoride toxicity, as evidenced by alterations in ultrastructure, mitochondrial membrane potential, respiratory chain function, etc. Therefore, targeting mitochondrial homeostasis to develop pharmacological interventions for mitigating arsenic and fluoride-induced cardiotoxicity holds significant promise. Melatonin has emerged as a potent antioxidant and free radical scavenger. In this study, we reveal the substantial therapeutic potential of melatonin in mitigating arsenic and fluoride-induced cardiac injury in chicken models. A total of 72 one-day-old male Hy-Line Brown broilers were randomly allocated into eight groups: Control Group (basal diet), Arsenic Group (36 mg/kg As₂O₃ in diet), Fluoride Group (400 mg/kg NaF in diet), Arsenic + Fluoride Group (36 mg/kg As₂O₃ and 400 mg/kg NaF in diet), Melatonin Group (2.5 mg/kg melatonin in diet), Arsenic + Melatonin Group (36 mg/kg As₂O₃ and 2.5 mg/kg melatonin in diet), Fluoride + Melatonin Group (400 mg/kg NaF and 2.5 mg/kg melatonin in diet), and Arsenic + Fluoride + Melatonin Group (36 mg/kg As₂O₃, 400 mg/kg NaF, and 2.5 mg/kg melatonin in diet). Following a 23-week intervention with arsenic, fluoride, or their combination, the chickens exhibited significant cardiac damage and myocardial fibrosis. This was evidenced by elevated serum levels of lactate dehydrogenase (LDH), aspartic transaminase (AST), and troponin I (cTn-I), as well as marked changes observed in histopathological examinations. Dietary supplementation with melatonin significantly mitigated these cardiac damages induced by arsenic and fluoride. Mechanistically, we identified that melatonin exerted cardioprotective effects by reducing oxidative stress and apoptosis, and by restoring mitochondrial homeostasis through attenuating pathological mitochondrial fission, enhancing mitochondrial fusion, and promoting mitochondrial biogenesis. Collectively, our findings highlight melatonin as a potent cardioprotective agent against arsenic and fluoride-induced heart injury in chickens.