Leukocytes utilize myeloperoxidase-generated nitrating intermediates as physiological catalysts for the generation of biologically active oxidized lipids and sterols in serum

The initiation of lipid peroxidation and the concomitant formation of biolo gically active oxidized lipids and sterols is believed to play a central ro le in the pathogenesis of inflammatory and vascular disorders. Here we expl ore the role of neutrophil- and myeloperoxidase (MPO)-generated nitrating i ntermediates as a physiological catalyst for the initiation of lipid peroxi dation and the formation of biologically active oxidized lipids and sterols . Activation of human neutrophils in media containing physiologically relev ant levels of nitrite (NO2-), a major end product of nitric oxide (nitrogen monoxide, NO) metabolism, generated an oxidant capable of initiating perox idation of lipids. Formation of hydroxy-and hydroperoxyoctadecadienoic acid s [H(P)ODEs], hydroxy- and hydroperoxyeicosatetraenoic acids [H(P)ETEs]. F- 2-isoprostanes, and a variety of oxysterols was confirmed using on-line rev erse phase HPLC tandem mass spectrometry (LC/MS/MS). Lipid oxidation by neu trophils required cell activation and NO2-, occurred in the presence of met al chelators and superoxide dismutase, and was inhibited by catalase, heme poisons, and free radical scavengers. LC/MS/MS studies demonstrated formati on of additional biologically active lipid and sterol oxidation products kn own to be enriched in vascular lesions, such as 1-hexadecanoyl-2-oxovalaryl -sn-glycero-3 which induces upregulation of endothelial cell adhesion and c hemoattractant proteins, and 5-cholesten-3 beta-ol 7 beta-hydroperoxide, a potent cytotoxic oxysterol. In contrast to the oxidant formed during free m etal ion-catalyzed reactions, the oxidant formed during MPO-catalyzed oxida tion of NO2- readily promoted lipid peroxidation in the presence of serum c onstituents. Collectively, these results suggest that phagocytes may employ MPO-generated reactive nitrogen intermediates as a physiological pathway f or initiating lipid peroxidation and forming biologically active lipid and sterol oxidation products in vivo.