title: Secretory phospholipase A2 and lipoprotein lipase enhance 15-lipoxygenase-induced enzymic and nonenzymic lipid peroxidation in low-density lipoproteins.
abstract: The oxidation of low-density lipoprotein (LDL) is thought to contribute to atherogenesis. 15-Lipoxygenase (15LO) induces LDL oxidation, and phospholipase A2 enhances this process [Sparrow, C. P. , Parthasarathy, S., and Steinberg, D. (1988) J. LipidRes. 29, 745-753]. As the underlying mechanism of the enhancing effect has not been investigated previously, we here show that in the presence of soybean 15LO (SLO) or human 15LO (rhLO), the addition of lipoprotein lipase, porcine pancreatic, or human type IIa secretory phospholipase A2 (sPLA2) greatly enhanced the accumulation of hydro(pero)xides of all major classes of LDL's lipids. Hydroperoxides of free fatty acids accumulated exclusively as enzymic products with kinetics reflecting both the formation of free fatty acids and the initial 'build-up' of alpha-tocopheroxyl radical. In contrast, hydroperoxides of cholesteryl esters and phosphatidylcholine accumulated linearly over comparatively longer periods of time and, in the case of rhLO, well beyond inactivation of the oxygenase. With SLO, formation of oxidized esterified lipids occurred nonenzymically, independent of the presence of lipase and despite the oxygenase remaining active until the end of the incubation. Enhancement of rhLO-induced LDL lipid peroxidation by sPLA2 was eliminated by a neutralizing anti-sPLA2 antibody, indicating that lipolytic activity was required for this effect. LDL depleted of alpha-tocopherol was resistant to oxidation by 15LO alone, whereas lipase overcame this resistance, demonstrating that lipases enhance 15LO-induced enzymic and nonenzymic peroxidation of LDL lipids. This is likely due to provision of free fatty acid substrate, resulting in an enhanced rate of free radical formation which itself causes nonenzymic peroxidation of esterified lipids. As lipases and 15LO are present in atherosclerotic lesions, our findings could be of pathophysiological significance.
authors.affiliation: Biochemistry Group, The Heart Research Institute, Sydney, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Neuzil
authors.forename: J M
authors.initials: JM
authors.lastname: Upston
authors.forename: P K
authors.initials: PK
authors.lastname: Witting
authors.forename: K F
authors.initials: KF
authors.lastname: Scott
authors.forename: R
authors.initials: R
authors.lastname: Stocker
mesh_terms: D000818:Animals; D001093:Arachidonate 15-Lipoxygenase / Q000378:metabolism*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002788:Cholesterol Esters / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D005609:Free Radicals / Q000378:metabolism; D006801:Humans; D006893:Hydroxyeicosatetraenoic Acids / Q000378:metabolism; D008041:Linoleic Acids / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism* / Q000494:pharmacology; D054467:Phospholipases A2; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity; D013552:Swine; D014810:Vitamin E / Q000378:metabolism
chemical_list: D002788:Cholesterol Esters; D005230:Fatty Acids, Nonesterified; D005609:Free Radicals; D006893:Hydroxyeicosatetraenoic Acids; D008041:Linoleic Acids; D008077:Lipoproteins, LDL; D011994:Recombinant Proteins; C066323:tocopheroxy radical; D014810:Vitamin E; C024348:13-hydroxy-9,11-octadecadienoic acid; C025984:15-hydroxy-5,8,11,13-eicosatetraenoic acid; D001093:Arachidonate 15-Lipoxygenase; D010741:Phospholipases A; D008071:Lipoprotein Lipase; D054467:Phospholipases A2