Increased NADH-oxidase-mediated superoxide production in the early stages of atherosclerosis - Evidence for involvement of the renin-angiotensin system

Background-Angiotensin II activates NAD(P)H-dependent oxidases via AT(1)-re ceptor 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 ass ociated with increased NAD(P)H-dependent vascular O-2(-) production and whe ther AT(1)-receptor blockade may inhibit this oxidase and in parallel impro ve 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 b y Northern analysis, and AT(1)-receptor density was measured by radioligand binding assays. Hypercholesterolemia was associated with impaired endothel ium-dependent vasodilation and increased O-2.(-) production in intact vesse ls. In vessel homogenates, we found a significant activation of NADH-driven O-2.(-) production in both models of hyperlipidemia. Treatment of choleste rol-fed animals with the AT(1)-receptor antagonist Bay 10-6734 improved end othelial 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, receptor mRNA was upre gulated to 166+/-11%, accompanied by a comparable increase in AT(1)-recepto r density. Conclusions-Hypercholesterolemia is associated with AT(1)-receptor upregula tion, 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 anta gonist suggests a crucial role of angiotensin II-mediated O-2.(-) productio n in the early stage of atherosclerosis.