We previously proposed that hyperglycemia-induced mitochondrial reactive oxygen species (mtROS) generation is a key event in the development of diabetic complications. Interestingly, some common aspects exist between hyperglycemia and hypoxia-induced phenomena. Thus, hyperglycemia may induce cellular hypoxia, and this phenomenon may also be involved in the pathogenesis of diabetic complications. In endothelial cells (ECs), cellular hypoxia increased after incubation with high glucose (HG). A similar phenomenon was observed in glomeruli of diabetic mice. HG-induced cellular hypoxia was suppressed by mitochondria blockades or manganese superoxide dismutase (MnSOD) overexpression, which is a specific SOD for mtROS. Overexpression of MnSOD also increased the expression of aquaporin-1 (AQP1), a water and oxygen channel. AQP1 overexpression in ECs suppressed hyperglycemia-induced cellular hypoxia, endothelin-1 and fibronectin overproduction, and apoptosis. Therefore, hyperglycemia-induced cellular hypoxia and mtROS generation may promote hyperglycemic damage in a coordinated manner.

Aims/IntroductionOverproduction of reactive oxygen species (ROS) in endothelial cells (ECs) plays a pivotal role in endothelial dysfunction. Mitochondrial ROS (mtROS) is one of the key players in the pathogenesis of diabetic vascular complications. Hypoglycemia is linked to increased ROS production and vascular events; however, the underlying mechanisms remain unclear. In the present study, we aimed to determine whether and how low glucose (LG) mediates mtROS generation in ECs, and to examine the impact of LG‐induced mtROS on endothelial dysfunction.Materials and MethodsMetabolomic profiling, cellular oxygen consumption rate, mtROS, endothelial nitric oxide synthase phosphorylation, and the expression of vascular cell adhesion molecule‐1 or intercellular adhesion molecule‐1 were evaluated in bovine aortic ECs.ResultsWe found that LG increased mtROS generation in ECs; which was suppressed by overexpression of manganese superoxide dismutase. Comprehensive metabolic analysis using capillary electrophoresis‐mass spectrometry and oxygen consumption rate assessment showed that the pathway from fatty acid to acetyl‐CoA through fatty acid oxidation was upregulated in ECs under LG conditions. In addition, etomoxir, a specific inhibitor of the free fatty acid transporter, decreased LG‐induced mtROS production. These results suggested that LG increased mtROS generation through activation of fatty acid oxidation. We further revealed that LG inhibited endothelial nitric oxide synthase phosphorylation, and increased the expression of vascular cell adhesion molecule‐1 and intercellular adhesion molecule‐1. These effects were suppressed either by overexpression of manganese superoxide dismutase or by treatment with etomoxir.ConclusionsThe activation of fatty acid oxidation followed by mtROS production could be one of the causes for endothelial dysfunction during hypoglycemia.

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