Chronic arsenic (As) exposure, mainly as a result of drinking contaminated water, is associated with cardiovascular diseases. Mitochondrial dysfunction, oxidative stress, inflammation, apoptosis, and autophagy have been suggested as the molecular etiology of As cardiotoxicity. Melatonin (Mel) is a powerful antioxidant. Mel improves diabetic cardiomyopathy, cardiac remodeling, and heart failure. Following pre-treatment with Mel (10, 20, or 30 mg/kg/day i.p.), rats were orally gavaged with As (15 mg/kg/day) for 28 days. Electrocardio- graphic findings showed that Mel decreased the As-mediated QT interval pro- longation. The effects of As on cardiac levels of glutathione (GSH) and malondialdehyde (MDA) were reversed by Mel pretreatment. Mel also modu- lated the Sirt1 and Nrf2 expressions promoted by As. Mel down-regulated autophagy markers such as Beclin-1 expression and the LC3-II/I ratio. More- over, the cardiac expression of cleaved-caspase-3 and Bax/Bcl-2 ratio was decreased by Mel pretreatment. Reduced expression of miR-34a and miR-144 by As were reversed by Mel. The histopathological changes of cardiac injury associated with As exposure was moderated by Mel. Mel may improve As- induced cardiac dysfunction through anti-oxidative, anti-apoptotic, and anti- autophagic mechanisms.

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