H2O2-induced endothelial NO production contributes to vascular cell apoptosis and increased permeability in rat venules

Zhou X, Yuan D, Wang M, He P. H2O2-induced endothelial NO production contributes to vascular cell apoptosis and increased permeability in rat venules. Am J Physiol Heart Circ Physiol 304: H82-H93, 2013. First published October 19, 2012; doi:10.1152/ajpheart.00300.2012.-Although elevated levels of H2O2 have been implicated to play important roles in the pathogenesis of various cardiovascular diseases, the underlying mechanisms remain unclear. This study aims to examine the effect of H2O2 on endothelial nitric oxide (NO) production in intact venules, and elucidate the role and mechanisms of NO in H2O2-induced increases in microvessel permeability. Experiments were conducted on individually perfused rat mesenteric venules. Microvessel permeability was determined by measuring hydraulic conductivity (Lp), and endothelial [Ca2+](i) was measured on fura-2-loaded vessels. Perfusion of H2O2 (10 mu M) caused a delayed and progressively increased endothelial [Ca2+](i) and Lp, a pattern different from inflammatory mediator-induced immediate and transient response. Under the same experimental conditions, measuring endothelial NO via DAF-2 and the spatial detection of cell apoptosis by fluorescent markers revealed that H2O2 induced two phases of NO production followed by caspase activation, intracellular Ca2+ accumulation, and vascular cell apoptosis. The initial NO production was correlated with increased endothelial NO synthase (eNOS) Ser(1177) phosphorylation in the absence of elevated endothelial [Ca2+](i), whereas the second phase of NO depended on increased [Ca2+](i) and was associated with Thr(495) dephosphorylation without increased Ser(1177) phosphorylation. Inhibition of NOS prevented H2O2-induced caspase activation, cell apoptosis, and increases in endothelial [Ca2+](i) and Lp. Our results indicate that H2O2 at micromolar concentration is able to induce a large magnitude of NO in intact venules, causing caspase activation-mediated endothelial Ca2+ accumulation, cell apoptosis, and increases in permeability. The mechanisms revealed from intact microvessels may contribute to the pathogenesis of oxidant-related cardiovascular diseases.