Apolipoprotein B carbonyl formation is enhanced by lipid peroxidation during copper-mediated oxidation of human low-density lipoproteins.
To determine whether lipid peroxidation is required for apolipoprotein B (apoB) carbonyl formation of human low-density lipoproteins (LDL) during copper-mediated oxidation, we investigated oxidation of native and probucol-preloaded LDL by measuring thiobarbituric acid-reactive substances (TBARS) and apoB carbonyls. Probucol was used because it is known to inhibit lipid peroxidation, but not protein modification. During copper-mediated oxidation, apoB carbonyls formed in a time-dependent manner; high copper concentrations (> or = 30 microM) resulted in saturation of apoB carbonyl content. ApoB carbonyl formation and lipid peroxidation were linearly related during incubation of LDL with copper for 3 h. During Cu(2+)-mediated LDL oxidation of probucol-LDL, TBARS production was very low, nonetheless apoB carbonyls increased significantly, and vitamin E was depleted. Bovine serum albumin (fatty acid free; BSA) oxidation in the presence of trace amounts of LDL, linoleic acid, or tert-butyl hydroperoxide was used to further understand the role of lipid peroxidation in apoB carbonyl formation. Protein carbonyl formation during BSA incubation with copper (either Cu+ or Cu2+) was trivial; however, further addition of linoleic acid (1:1, m/m), trace amounts of LDL (10 micrograms/ml), or tert-butyl hydroperoxide (1:1, m/m) markedly increased protein carbonyl formation. These results demonstrate that lipid peroxidation enhances copper-mediated carbonyl formation and suggest that copper ions react with LDL lipid hydroperoxides producing the necessary reactive species.
Yan
L J
LJ
Department of Molecular and Cell Biology, University of California at Berkeley 94720-3200, USA.
Lodge
J K
JK
Traber
M G
MG
Packer
L
L
D000818:Animals; D000924:Anticholesteremic Agents / Q000737:chemistry; D001055:Apolipoproteins B / Q000737:chemistry*; D002417:Cattle; D003300:Copper / Q000737:chemistry*; D005609:Free Radicals; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D008077:Lipoproteins, LDL / Q000737:chemistry*; D010084:Oxidation-Reduction; D011341:Probucol / Q000737:chemistry; D012710:Serum Albumin, Bovine / Q000737:chemistry
D000924:Anticholesteremic Agents; D001055:Apolipoproteins B; D005609:Free Radicals; D008077:Lipoproteins, LDL; D012710:Serum Albumin, Bovine; D003300:Copper; D006861:Hydrogen Peroxide; D011341:Probucol