Increased NADH-Oxidase–Mediated Superoxide Production in the Early Stages of Atherosclerosis: Evidence for Involvement of the Renin-Angiotensin System

Abstract

Background —Angiotensin II activates NAD(P)H-dependent oxidases via AT 1 -receptor stimulation, the most important vascular source of superoxide (O 2 · − ). The AT 1 receptor is upregulated in vitro by low-density lipoprotein. The present study was designed to test whether hypercholesterolemia is associated with increased NAD(P)H-dependent vascular O 2 · − production and whether AT 1 -receptor blockade may inhibit this oxidase and in parallel improve endothelial dysfunction. Methods and Results —Vascular responses were determined by isometric tension studies, and relative rates of vascular O 2 · − production were determined by use of chemiluminescence with lucigenin, a cypridina luciferin analogue, and electron spin resonance studies. AT 1 -receptor mRNA was quantified by Northern analysis, and AT 1 -receptor density was measured by radioligand binding assays. Hypercholesterolemia was associated with impaired endothelium-dependent vasodilation and increased O 2 · − production in intact vessels. In vessel homogenates, we found a significant activation of NADH-driven O 2 · − production in both models of hyperlipidemia. Treatment of cholesterol-fed animals with the AT 1 -receptor antagonist Bay 10-6734 improved endothelial dysfunction, normalized vascular O 2 · − and NADH-oxidase activity, decreased macrophage infiltration, and reduced early plaque formation. In the setting of hypercholesterolemia, the aortic AT 1 receptor mRNA was upregulated to 166±11%, accompanied by a comparable increase in AT 1 -receptor density. Conclusions —Hypercholesterolemia is associated with AT 1 -receptor upregulation, endothelial dysfunction, and increased NADH-dependent vascular O 2 · − production. The improvement of endothelial dysfunction, inhibition of the oxidase, and reduction of early plaque formation by an AT 1 -receptor antagonist suggests a crucial role of angiotensin II–mediated O 2 · − production in the early stage of atherosclerosis.