Endothelial NADH/NADPH-dependent enzymatic sources of superoxide production: relationship to endothelial dysfunction.

There is growing evidence that endothelial dysfunction, which is often defined as the decreased endothelial-derived nitric oxide (NO) bioavailability, is a crucial factor leading to vascular disease states such as hypertension, diabetes, atherosclerosis, heart failure and cigarette smoking. This is due to the fact that the lack of NO in endothelium-dependent vascular disorders contributes to impaired vascular relaxation, platelet aggregation, increased vascular smooth muscle proliferation, and enhanced leukocyte adhesion to the endothelium. During the last several years, it has become clear that reduction of NO bioavailability in the endothelium-impaired function disorders is associated with an increase in endothelial production of superoxide (O2̇̄). Because O2̇̄ rapidly scavenges NO within the endothelium, a reduction of bioactive NO might occur despite an increased NO generation. Among many enzymatic systems that are capable of producing O2̇̄, NAD(P)H oxidase and uncoupled endothelial NO synthase (eNOS) apparently are the main sources of O2̇̄ in the endothelial cells. It seems that O2̇̄ generated by NAD(P)H oxidase may trigger eNOS uncoupling and contribute to the endothelial balance between NO and O2̇̄. That is maintained at diverse levels.