Oxidation of Apolipoprotein B-100 in Circulating LDL Is Related to LDL Residence Time

Abstract

Abstract —5-Hydroxy-2-aminovaleric acid (HAVA) has been suggested to be a specific marker of oxidation of apolipoprotein (apo) B-100 proline (Pro) and arginine (Arg) side-chain residues in low density lipoprotein (LDL) in vitro. Here we describe the application of sensitive mass spectrometric techniques to the characterization of Pro/Arg-modified apoB-100 in LDL 1 (S f 7 to 12) and LDL 2 (S f 0 to 7) in vivo. We studied 7 subjects with familial defective apoB-100 (FDB) and 8 normolipidemic controls. In FDB subjects, the presence of a mutant apoB-100 (FDB 3500Q ) in LDL markedly reduced its affinity for the LDL receptor, leading to increased residence times (RTs) of LDL 1 (65±21 versus 32±12 hours, P <0.005) and LDL 2 (230±40 versus 53±7 hours, P <0.001) when compared with controls, as determined by stable-isotope turnover studies. LDL 1 HAVA content was not different between the groups (FDB, 0.004±0.001 mol/mol apoB-100 versus controls, 0.003±0.001 mol/mol apoB-100, P =0.200). LDL 2 HAVA content was higher in FDB subjects (0.374±0.088 versus 0.013±0.002 mol/mol apoB-100, P <0.001). In both groups, LDL 2 HAVA was positively associated with LDL 2 RT (FDB, r =0.893, P =0.003; controls, r =0.976, P =0.000) and negatively correlated with LDL 2 α-tocopherol content (FDB, r =−0.929, P =0.003; controls, r =−0.903, P =0.002). No significant correlations could be found between LDL 1 HAVA, LDL 1 RT, and α-tocopherol, respectively. The low LDL 1 HAVA content observed in both FDB and control groups was thought to be due to the relatively lower RT as well as the higher α-tocopherol content of these lipoproteins. In contrast, LDL 2 seemed to be strongly prone to direct oxidation of apoB-100 in vivo. The longer these particles linger in the circulation, the more apoB-100 Pro/Arg residues become modified.