title: Protein hydroperoxides are a major product of low density lipoprotein oxidation during copper, peroxyl radical and macrophage-mediated oxidation.
abstract: Damage to apoB100 on low density lipoprotein (LDL) has usually been described in terms of lipid aldehyde derivatisation or fragmentation. Using a modified FOX assay, protein hydroperoxides were found to form at relatively high concentrations on apoB100 during copper, 2,2'-azobis(amidinopropane) dihydrochloride (AAPH) generated peroxyl radical and cell-mediated LDL oxidation. Protein hydroperoxide formation was tightly coupled to lipid oxidation during both copper and AAPH-mediated oxidation. The protein hydroperoxide formation was inhibited by lipid soluble alpha-tocopherol and the water soluble antioxidant, 7,8-dihydroneopterin. Kinetic analysis of the inhibition strongly suggests protein hydroperoxides are formed by a lipid-derived radical generated in the lipid phase of the LDL particle during both copper and AAPH mediated oxidation. Macrophage-like THP-1 cells were found to generate significant protein hydroperoxides during cell-mediated LDL oxidation, suggesting protein hydroperoxides may form in vivo within atherosclerotic plaques. In contrast to protein hydroperoxide formation, the oxidation of tyrosine to protein bound 3,4-dihydroxyphenylalanine (PB-DOPA) or dityrosine was found to be a relatively minor reaction. Dityrosine formation was only observed on LDL in the presence of both copper and hydrogen peroxide. The PB-DOPA formation appeared to be independent of lipid peroxidation during copper oxidation but tightly associated during AAPH-mediated LDL oxidation.
authors.affiliation: Free Radical Biochemistry Laboratory, Department of Zoology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. s.gieseg@zool.canterbury.ac.nz
authors.forename: Steven P
authors.initials: SP
authors.lastname: Gieseg
authors.forename: Joseph
authors.initials: J
authors.lastname: Pearson
authors.forename: Carole A
authors.initials: CA
authors.lastname: Firth
mesh_terms: D000328:Adult; D000578:Amidines / Q000378:metabolism; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B / Q000378:metabolism; D002478:Cells, Cultured; D003300:Copper / Q000378:metabolism*; D005260:Female; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D015227:Lipid Peroxidation; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010545:Peroxides / Q000378:metabolism*
chemical_list: D000578:Amidines; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B; D008077:Lipoproteins, LDL; D010545:Peroxides; C049375:perhydroxyl radical; C046728:2,2'-azobis(2-amidinopropane); D003300:Copper; D006861:Hydrogen Peroxide