Comparative Effect of ACE Inhibition and Angiotensin II Type 1 Receptor Antagonism on Bioavailability of Nitric Oxide in Patients With Coronary Artery Disease: Role of Superoxide Dismutase

Abstract

Background —Flow-dependent, endothelium-mediated vasodilation (FDD) and activity of extracellular superoxide dismutase (EC-SOD), the major antioxidative enzyme of the arterial wall, are severely impaired in patients with coronary artery disease (CAD). We hypothesized that both ACE inhibitor (ACEI) and angiotensin II type 1 receptor antagonist (AT 1 -A) increase bioavailability of nitric oxide (NO) by reducing oxidative stress in the vessel wall, possibly by increasing EC-SOD activity. Methods and Results —Thirty-five patients with CAD were randomized to 4 weeks of ACEI (ramipril 10 mg/d) or AT 1 -A (losartan 100 mg/d). FDD of the radial artery was determined by high-resolution ultrasound before and after intra-arterial N -monomethyl- l -arginine (L-NMMA) to inhibit NO synthase and before and after intra-arterial vitamin C to determine the portion of FDD inhibited by oxygen free radicals. EC-SOD activity was determined after release from endothelium by heparin bolus injection. FDD was improved after ramipril and losartan (each group P <0.01), and in particular, the portion of FDD mediated by NO, ie, inhibited by L-NMMA, was increased by >75% (each group P <0.01). Vitamin C improved FDD initially, an effect that was lost after ramipril or losartan. After therapy, EC-SOD activity was increased by >200% in both groups (ACEI, 14.4±1.1 versus 3.8±0.9 and AT 1 -A, 13.5±1.0 versus 3.9±0.9 U · mL −1 · min −1 ; each P <0.01). Conclusions —Four weeks of therapy with ramipril or losartan improves endothelial function to similar extents in patients with CAD by increasing the bioavailability of NO. Our results suggest that beneficial long-term effects of interference with the renin-angiotensin system may be related to reduction of oxidative stress within the arterial wall, mediated in part by increased EC-SOD activity.