Vascular superoxide production is increased in animal models of atherosclerosis, diabetes and hypertension, and reduces nitric oxide (NO) bioactivity. However, the functional importance of superoxide production in human atherosclerosis is poorly characterised. We aimed to determine the relationships between NAD(P)H oxidase activity and NO-mediated endothelial dysfunction in human blood vessels, and investigate the influence of clinical risk factor profile. Methods: We used human saphenous vein (HSV) and internal mammary artery (IMA) segments from patients undergoing coronary bypass surgery, to study: (1) Basal and NAD(P)H-stimulated superoxide production, using lucigenin-enhanced chemiluminescence. (2) NO-dependent vasorelaxations, as a bioassay of NO production. (3) Immunochemistry to show endothelial cells and eNOS protein. Results: Superoxide production by NAD(P)H oxidase was observed in all HSV (n=110) and IMA (n=25). NO-mediated vasorelaxations varied from 0 to 61% between patients, was not caused by lack of endothelial cells or eNOS, but was correlated in HSV and IMA (p < 0.05), indicating that endothelial dysfunction is a systemic phenomenon. NAD(P)H oxidase activity was also highly variable, and correlated with reduced NO-mediated vasorelaxations (n=91, R=-0.48, p < 0.001). Both of these parameters were related to the number of major risk factors present (smoking, hypercholesterolemia, hypertension, diabetes; R=0.5; p < 0.01). Conclusions: Increased NAD(P)H oxidase activity in human blood vessels is associated with systemic endothelial dysfunction and increased clinical risk factor profile in human atherosclerosis.


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