Mediation of L-arginine-induced retardation of hypercholesterolemic atherosclerosis in rabbits by antioxidant mechanisms

Abstract

Smooth muscle cell proliferation is a characteristic feature of atherosclerosis. Reactive oxygen species are suggested to play a role in smooth muscle cell proliferation. Nitric oxide (NO) is known to inhibit smooth muscle cell proliferation. But it is not known if NO can retard the development of hypercholesterolemic atherosclerosis. We hypothesized that L-arginine, the precursor of NO, may retard the development of hypercholesterolemic atherosclerosis through antioxidant mechanisms. We, therefore, investigated the effects of L-arginine on the high cholesterol diet-induced changes in the development of atherosclerosis in the female rabbit aorta. The indices studied included blood lipids, aortic tissue malondialdehyde (MDA), a measure of lipid peroxidation, aortic tissue chemiluminescence (CL), a measure of antioxidant reserve and activity of antioxidant enzymes [superoxide dismutase (SOD), catalase and glutathione peroxidase (GSH-Px)]. Animals were assigned to one of 3 groups: group I, regular rabbit diet; group II, 1% cholesterol added, group III, 1% cholesterol + L-arginine (2.5%) added. Blood samples were collected before and after 4 weeks and 10 weeks on the respective diets. The aorta was removed at the end of 10 weeks for assessment of atherosclerotic plaques and biochemical changes. There was an increase in the total serum cholesterol in groups II and III. Aortic MDA, CL, catalase, and GSH-Px increased in groups II as compared to group I and decreased in group III as compared to group II. Ninety-five percent of the intimal surface of aorta was covered with atherosclerotic plaques in group II but only 60% was covered in group III. This 35% inhibition of hypercholesterolemic atherosclerosis by L-arginine was associated with increase in the antioxidative reserve (as measured by aortic tissue chemiluminescence) without change in serum cholesterol levels. These results suggest that hypercholesterolemic atherosclerosis in rabbits is associated with oxidative stress, and that L-arginine may retard the development of hypercholesterolemic atherosclerosis through antioxidant mechanisms.