Mechanisms of H2O2-induced oxidative stress in endothelial cells

Hydrogen peroxide, produced by inflammatory and vascular cells, induces oxidative stress that may contribute to endothelial dysfunction. In smooth muscle cells, H2O2 induces production of O2− by activating NADPH oxidase. However, the mechanisms whereby H2O2 induces oxidative stress in endothelial cells are poorly understood. We examined the effects of H2O2 on O2− levels on porcine aortic endothelial cells (PAEC). Treatment with 60 μmol/L H2O2 markedly increased intracellular O2− levels (determined by conversion of dihydroethidium to hydroxyethidium) and produced cytotoxicity (determined by propidium iodide staining) in PAEC. Overexpression of human manganese superoxide dismutase in PAEC reduced O2− levels and attenuated cytotoxicity resulting from treatment with H2O2. L-NAME, an inhibitor of nitric oxide synthase (NOS), and apocynin, an inhibitor of NADPH oxidase, reduced O2− levels in PAEC treated with H2O2, suggesting that both NOS and NADPH oxidase contribute to H2O2-induced O2− in PAEC. Inhibition of NADPH oxidase using apocynin and NOS rescue with L-sepiapterin together reduced O2− levels in PAEC treated with H2O2 to control levels. This suggests interaction-distinct NOS and NADPH oxidase pathways to superoxide. We conclude that H2O2 produces oxidative stress in endothelial cells by increasing intracellular O2− levels through NOS and NADPH oxidase. These findings suggest a complex interaction between H2O2 and oxidant-generating enzymes that may contribute to endothelial dysfunction.