title: Lipoperoxides in LDL incubated with fibroblasts that overexpress 15-lipoxygenase.
abstract: Oxidative modification of LDL plays an important role in early atherogenesis but the mechanisms, nonenzymatic and/or enzymatic, by which LDL is oxidized in vivo remain to be established. Several lines of evidence suggest that cellular 15-lipoxygenase (arachidonate 15-oxidoreductase, EC.1.13.11.13) (15-LO) may contribute to oxidative modification of LDL, including recent studies demonstrating that murine fibroblasts overexpressing 15-LO have an enhanced capacity to oxidize LDL in the medium. The present studies were undertaken to better understand the mechanisms by which cells expressing 15-LO bring about oxidative modification of LDL. LDL incubated 1-2 h with the 15-LO-enriched cells showed a much higher lipoperoxide (LOOH) content than did LDL incubated with control cells. By far the largest absolute increase occurred in cholesteryl ester hydroperoxide (CE-OOH), a much lesser increase in free fatty acid hydroperoxides (FFA-OOH), and only a very small increase in phospholipid hydroperoxides (PL-OOH). Addition of EDTA to the medium abolished these increases in LDL lipid hydroperoxides. Enrichment of LDL with probucol or vitamin E also prevented CE-OOH accumulation. Incubation of LDL with linoleic acid hydroperoxide in the absence of cells also caused a significant increase in CE-OOH and this was markedly inhibited by EDTA. These findings provide further evidence for the potential of 15-LO to participate in LDL oxidation by way of a mechanism involving introduction of LOOH into the LDL particle followed by metal-catalyzed propagation.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla 92093-0682, USA.
authors.forename: M
authors.initials: M
authors.lastname: Ezaki
authors.forename: J L
authors.initials: JL
authors.lastname: Witztum
authors.forename: D
authors.initials: D
authors.lastname: Steinberg
mesh_terms: D000818:Animals; D001093:Arachidonate 15-Lipoxygenase / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003300:Copper / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D005347:Fibroblasts / Q000201:enzymology*; D015870:Gene Expression; D018014:Gene Transfer Techniques; D006801:Humans; D007700:Kinetics; D015227:Lipid Peroxidation; D008054:Lipid Peroxides / Q000032:analysis*; D008077:Lipoproteins, LDL / Q000032:analysis* / Q000378:metabolism; D008163:Luminescent Measurements; D051379:Mice; D011994:Recombinant Proteins
chemical_list: D008054:Lipid Peroxides; D008077:Lipoproteins, LDL; D011994:Recombinant Proteins; D003300:Copper; D004492:Edetic Acid; D001093:Arachidonate 15-Lipoxygenase