SUPEROXIDE AND PEROXYNITRITE IN ATHEROSCLEROSIS

The role of reactive oxygen species in the vascular pathology associat ed with atherosclerosis was examined by testing the hypothesis that im paired vascular reactivity results from the reaction of nitric oxide ( .NO) with superoxide (O2-), yielding the oxidant peroxynitrite (ONOO-) . Contractility studies were performed on femoral arteries from rabbit s fed a cholesterol-supplemented diet. Cholesterol feeding shifted the EC50 for acetylcholine (ACh)-induced relaxation and impaired the maxi mal response to ACh. We used pH-sensitive liposomes to deliver CuZn su peroxide dismutase (SOD; superoxide:superoxide oxidoreductase, EC 1.15 .1.1) to critical sites of .NO reaction with O2-. Intravenously inject ed liposomes (3000 units of SOD per ml) augmented ACh-induced relaxati on in the cholesterol-fed group to a greater extent than in controls. Quantitative immunocytochemistry demonstrated enhanced distribution of SOD in both endothelial and vascular smooth muscle cells as well as i n the extracellular matrix. SOD activity in vessel homogenates of lipo some-treated rabbits was also increased. Incubation of beta very low d ensity lipoprotein with ONOO- resulted in the rapid formation of conju gated dienes and thiobarbituric acid-reactive substances. Our results suggest that the reaction of O2- with .NO is involved in the developme nt of atherosclerotic disease by yielding a potent mediator of lipopro tein oxidation, as well as by limiting .NO stimulation of vascular smo oth muscle guanylate cyclase activity.