Expression of phagocyte NADPH oxidase components in human endothelial cells

Low-level generation of reactive oxygen species (ROS) by endothelial cells in response to a variety of stimuli has been observed; however, the enzyme system responsible is unknown. Using a variety of techniques, we examined for components of the phagocyte superoxide-generating NADPH oxidase to elucidate whether this enzyme could be a source of endothelial-derived ROS. Superoxide generation on addition of 100 mu M NAD(P)H to human umbilical vein endothelial cell (HUVEC) sonicates (using lucigenin-enhanced chemiluminescence) was partially inhibited on addition of the flavoenzyme inhibitor diphenyliodonium (IDP). Reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated expression of gp91(phox), p22(phox), p67(phox), and p47(phox) four independent HUVEC isolates. Expression of p22(phox) was also confirmed by Northern blotting. RT-PCR for tumor necrosis factor-alpha was negative, indicating an absence of mononuclear cell contamination (a potential source of NADPH oxidase). Immunoperoxidase staining, using anti-p47(phox) (JW-1)- and anti-p67(phox) (JW-2)-specific antibodies, showed protein expression of these cytosolic components. However, heme spectroscopy failed to indicate the presence of the low-potential cytochrome b558. These data indicate that cultured human endothelial cells express both mRNA and protein for cytosolic components of the phagocyte superoxide-generating NADPH oxidase. However, because the cytochrome b558 heme could not be conclusively demonstrated, a contribution of the phagocyte NADPH oxidase to endothelial oxidant generation may be unlikely.