The mechanism of apolipoprotein B-100 thiol depletion during oxidative modification of low-density lipoprotein.
Oxidation of low-density lipoprotein (LDL) is recognized to be a key step in atherogenesis. Previous studies show that LDL contains low-molecular-weight antioxidants such as vitamin E, beta-carotene, and ubiquinol, which can retard oxidative modification. In this report, we have evaluated the antioxidant potential of apolipoprotein B-100 (apo-B) thiols during LDL oxidation. Both apo-B thiols and vitamin E were depleted concomitantly during the lag phase of Cu(2+)-mediated LDL oxidation. The rate of thiol depletion was significantly inhibited by the lipophilic spin trap N-tert-butyl-alpha-phenylnitrone (PBN) but not by the water-soluble spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN). Blocking apo-B thiols with sulfhydryl modifying agents increased the oxidizability of LDL. As with Cu2+, peroxynitrite also caused depletion of apo-B thiols, and again thiol depletion was inhibited by PBN but not by POBN. A PBN/lipid-derived radical adduct was observed by the electron spin resonance technique during oxidation of LDL with peroxynitrite. We conclude that apo-B thiol depletion is mediated by lipid peroxidation, prior to the onset of the propagation phase of LDL oxidation. The implications of apo-B thiols an intrinsic antioxidants of LDL are discussed.
Ferguson
E
E
Biophysics Research Institute, Medical College of Wisconsin, Milwaukee 53226, USA.
Singh
R J
RJ
Hogg
N
N
Kalyanaraman
B
B
D000975:Antioxidants / Q000494:pharmacology*; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B / Q000737:chemistry*; D003300:Copper / Q000494:pharmacology; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D015227:Lipid Peroxidation / Q000187:drug effects*; D008077:Lipoproteins, LDL / Q000737:chemistry*; D009566:Nitrates / Q000494:pharmacology; D009589:Nitrogen Oxides / Q000494:pharmacology; D010084:Oxidation-Reduction; D011725:Pyridines; D013113:Spin Labels; D013438:Sulfhydryl Compounds / Q000737:chemistry* / Q000494:pharmacology; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D014810:Vitamin E / Q000494:pharmacology
D000975:Antioxidants; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B; D003497:Cyclic N-Oxides; D008077:Lipoproteins, LDL; D009566:Nitrates; D009589:Nitrogen Oxides; D011725:Pyridines; D013113:Spin Labels; D013438:Sulfhydryl Compounds; D013439:Sulfhydryl Reagents; C043438:alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone; C099252:oxidized low density lipoprotein; D014810:Vitamin E; C039642:peroxynitric acid; C029217:phenyl-N-tert-butylnitrone; D003300:Copper