Lipoxygenase-induced lipid oxidation contributes to plasma lipoprotein oxidation and may be an underlying pathogenic mechanism of atherogenesis. Since inactivation of the vasorelaxant actions of nitric oxide plays a critical role in the impaired function of atherosclerotic vessels and because nitric oxide reacts rapidly with other radical species, we assessed the influence of nitric oxide on lipoxygenase-catalyzed oxidation of linoleic and linolenic acid, 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (PC) liposomes, hypercholesterolemic rabbit -very-low-density lipoprotein, and human low-density lipoprotein. Soybean lipoxygenase (SLO)-induced lipid oxidation was assessed by accumulation of conjugated dienes, formation of lipid hydroperoxides, oxygen consumption, and liquid chromatography-mass spectrometry. Different rates of delivery of nitric oxide to lipid oxidation systems were accomplished either by infusion of nitric oxide gas equilibrated with anaerobic buffer or nitric oxide released from S-nitrosoglutathione. Nitric oxide alone did not induce lipid peroxidation, while exposure to SLO yielded significant oxidation of fatty acids, PC liposomes, or lipoproteins in a metal ion-independent mechanism. Low concentrations of nitric oxide, which did not significantly inhibit the activity of the iron-containing lipoxygenase, induced potent inhibition of lipid peroxidation in a dose-dependent manner. We conclude that nitric oxide can play a potent oxidant-protective role in the vessel wall by inhibiting lipoxygenase-dependent lipid and lipoprotein oxidation. This occurs via termination of lipid radical chain propagation reactions catalyzed by alkoxyl (LO ) and LOO intermediates of lipid peroxidation rather than by inhibition of lipoxygenase-catalyzed initiation reactions.
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