Nitric Oxide Regulation of Superoxide and Peroxynitrite-dependent Lipid Peroxidation

Abstract

Superoxide (O:), nitric oxide ('NO), and their reaction product peroxynitrite (ONOO-) have all been shown to independently exert toxic target molecule reactions. Because these reactive species are often generated in excess during diverse inflammatory and other pathologic circumstances, we assessed the influence of 'NO on membrane lipid peroxidation induced by O;, H,O,, and 'OH derived from xanthine oxidase (XO) and by ONOO-. Experimental conditions in lipid oxidation systems were adjusted to yield different rates of delivery of 'NO, relative to rates of 0; and HaOz generation, by infusion of either 'NO or via 'NO released from S-nitroso-Nacetylpenicillamine or S-nitrosoglutathione. Peroxidation of phosphatidylcholine liposomes was assessed by formation of thiobarbituric acid-reactive products and by liquid chromatography-mass spectrometry. Liposomes exposed to XO-derived reactive species in the presence of 'NO exhibited both stimulation and inhibition of lipid peroxidation, depending on the ratio of the rates of reactive oxygen species production and 'NO introduction into reaction systems. Nitric oxide alone did not induce lipid peroxidation. Linolenic acid emulsions peroxidized by XO-derived reactive species showed similar dose-dependent regulation of lipid peroxidation by 'NO. Mass spectral analysis of oxidation products showed formation of nitrito-, nitro-, nitrosoperoxo-, andor nitrated lipid oxidation adducts, demonstrating that 'NO serves as a potent terminator of radical chain propagation reactions. Electron spin resonance (ESR) analysis of incubation mixtures provided no evidence for formation of paramagnetic iron-lipid-nitric oxide complexes in reaction systems. Peroxynitrite-dependent lipid peroxidation, which predominantly occurs by metal-independent mechanisms, was also inhibited by 'NO. Peroxynitrite-mediated benzoate hydroxylation was partially inhibited by 'NO, inferring reaction between 'NO and ONOOH. It is concluded that 'NO can both stimulate O;/H,O,/'OH-induced lipid oxidation and