The cumulative effects of hypoxia and hyperglycemia on cardiac oxidative stress
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Hyperglycaemia-induced oxidative stress plays an important role in cardiomyocyte cell death leading to cardiac dysfunction. Autophagy is an intracellular bulk degradation process and can be induced by stressors such as nutrient depletion and acute ischemia, to promote cell survival. Oxidative stress is an important regulator of autophagy in various pathophysiological conditions such as ischemia/reperfusion injury and hypoxia. The role of autophagy in the oxidative stress tolerance of cardiac cells exposed to simultaneous hyperglycemia and hypoxia has not been studied. The aim of the present study is to determine the role of autophagy in cardiac cells in response to combined hyperglycemia and hypoxia. H9c2 rat cardiac cell lines were grown in DMEM supplemented with standard (5.6 mM), moderately high (25 mM) and high (33 mM) glucose concentrations. The cells were then exposed to hypoxia condition (1% oxygen, O2) for 24h and 48h using the hypoxia chamber. Cell viability and oxidative stress was measured by the 2,5- diphenyl-2H-tetrazolium bromide (MTT) and 2'7'-dichlorofluorescein (DCF) assays respectively. Apoptosis and autophagy was assessed via Caspatag 3/7 In Situ assay and western blotting. Results obtained demonstrated that high glucose andhypoxia additively reduced H9c2 cell viability. Simultaneous high glucose and hypoxia-induced oxidative stress suppresses autophagy and promotes cell death by apoptosis. A biphasic induction of ROS production, caspase 3/7 activity and PAMPK protein expression, in simultaneous high glucose and hypoxia conditions, calls for further research.