Oxidation of apolipoprotein B-100 in circulating LDL is related to LDL residence time - In vivo insights from stable-isotope studies

5-Hydroxy-2-aminovaleric acid (HAVA) has been suggested to be a specific ma rker of oxidation of apolipoprotein (apo) B-100 proline (Pro) and arginine (Arg) side-chain residues in low density lipoprotein (LDL) in vitro. Here w e describe the application of sensitive mass spectrometric techniques to th e characterization of Pro/Arg-modified apoB-100 in LDL1 (S-f 7 to 12) and L DL2 (S-f 0 to 7) in vivo. We studied 7 subjects with familial defective apo B-100 (FDB) and 8 normolipidemic controls. In FDB subjects, the presence of a mutant apoB-100 (FDB3500Q) in LDL markedly reduced its affinity for the LDL receptor, leading to increased residence times (RTs) of LDL1 (65+/-21 v ersus 32+/-12 hours, P<0.005) and LDL2 (230+/-40 versus 53+/-7 hours, P<0.0 01) when compared with controls, as determined by stable-isotope turnover s tudies. LDL1 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). LDL2 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, LDL2 HAVA was po sitively associated with LDL2 RT (FDB, r=0.893, P=0.003; controls, r=0.976, P=0.000) and negatively correlated with LDL2 <alpha>-tocopherol content (F DB, r=-0.929, P=0.003; controls, r=-0.903, P=0.002). No significant correla tions could be found between LDL1 HAVA, LDL1 RT, and alpha -tocopherol, res pectively. The low LDL1 HAVA content observed in both FDB and control group s was thought to be due to the relatively lower RT as well as the higher al pha -tocopherol content of these lipoproteins. In contrast, LDL2 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 be come modified.