Nicotinamide adenine dinucleotide phosphate (reduced form) oxidase is important for LPS-induced endothelial cell activation.

Activation of the endothelium plays an important role in the innate immune response. This process is associated with an increase in the production of superoxide (O2-) by nicotinamide adenine dinucleotide phosphate (reduced form; NADPH) oxidase. Our objective was to determine if O2- from NADPH oxidase contributes to activation of human umbilical vein endothelial cells by LPS as it does for TNF-alpha. We used the adhesion molecule intracellular adhesion molecule 1 and cytokine IL-8 as indicators of human umbilical vein endothelial cell activation and measured O2- production with chemiluminescence. LPS increased baseline and NADPH-stimulated O2- production. The increase was reduced by tiron, a protein kinase C inhibitor (bisindolylmaleimide I hydrochloride), the flavin inhibitor (diphenylene iodonium), and by a short interfering RNA against the p22phox component of NADPH oxidase. Inhibition of NADPH oxidase with the short interfering RNA reduced the induction by LPS of intracellular adhesion molecule 1 mRNA, protein, and IL-8 release (by enzyme-linked immunosorbent assay). The production of O2- by NADPH oxidase contributes to intracellular signaling by LPS in endothelial cells as it does for TNF-alpha and helps turn on the innate immune response in these cells.