NITRIC-OXIDE REGULATION OF SUPEROXIDE AND PEROXYNITRITE-DEPENDENT LIPID-PEROXIDATION - FORMATION OF NOVEL NITROGEN-CONTAINING OXIDIZED LIPID DERIVATIVES

Superoxide (O-2(radical-anion)), nitric oxide ((NO)-N-.), and their re action product peroxynitrite (ONOO-) have all been shown to independen tly exert toxic target molecule reactions. Because these reactive spec ies are often generated in excess during diverse inflammatory and othe r pathologic circumstances, we assessed the influence of (NO)-N-. on m embrane lipid peroxidation induced by O-2(radical-anion), H2O2, and (O H)-O-. derived from xanthine oxidase (XO) and by ONOO-. Experimental c onditions in lipid oxidation systems were adjusted to yield different rates of delivery of (NO)-N-., relative to rates of O-2(radical-anion) and H2O2 generation, by infusion of either (NO)-N-. or via (NO)-N-. r eleased from S-nitroso-N-acetylpenicillamine or S-nitrosoglutathione. Peroxidation of phosphatidylcholine liposomes was assessed by formatio n of thiobarbituric acid-reactive products and by liquid chromatograph y-mass spectrometry. Liposomes exposed to XO derived reactive species in the presence of (NO)-N-. exhibited both stimulation and inhibition of lipid peroxidation, depending on the ratio of the rates of reactive oxygen species production and (NO)-N-. introduction into reaction sys tems. Nitric oxide alone did not induce lipid peroxidation. Linolenic acid emulsions peroxidized by XO-derived reactive species showed simil ar dose-dependent regulation of lipid peroxidation by (NO)-N-.. Mass s pectral analysis of oxidation products showed formation of nitrito-, n itro-, nitrosoperoxo-, and/or nitrated lipid oxidation adducts, demons trating that (NO)-N-. serves as a potent terminator of radical chain p ropagation reactions. Electron spin resonance (ESR) analysis of incuba tion mixtures provided no evidence for formation of paramagnetic iron- lipid-nitric oxide complexes in reaction systems. Peroxynitrite-depend ent lipid peroxidation, which predominantly occurs by metal-independen t mechanisms, was also inhibited by (NO)-N-.. Peroxynitrite-mediated b enzoate hydroxylation was partially inhibited by (NO)-N-., inferring r eaction between (NO)-N-. and ONOOH. It is concluded that (NO)-N-. can both stimulate O-2(radical-anion)/H2O2/(OH)-O-.-induced lipid oxidatio n and mediate oxidant-protective reactions in membranes at higher rate s of (NO)-N-. production, with the prooxidant versus antioxidant outco me critically dependent on relative concentrations of individual react ive species. Prooxidant reactions of (NO)-N-. will occur after O-2(rad ical-anion) reaction with (NO)-N-. to yield potent secondary oxidants such as ONOO- and the antioxidant effects of (NO)-N-. a consequence of direct reaction with alkoxyl and peroxyl radical intermediates during lipid peroxidation, thus terminating lipid radical chain propagation reactions.