Oxidative stress and endothelial activation.

The vascular endothelial surface is a major target of oxidative stress, but we are only now beginning to understand the molecular sources and physiologic consequences of such oxidative activity. Along with exogenous oxidants, provided by professional phagocytes or circulating enzymes, vascular cells generate oxidants in response to cytokine and growth factor stimulation, and these endogenous oxidants participate in vascular cell signal transduction. Endothelial cells express at least four of the five principal subunits of an NADPH oxidase, and we review evidence that such an oxidase is tightly regulated in both activity and in subcellular targeting. Both of these features are likely to contribute to the signal specificity of unstable oxidants.