MALONDIALDEHYDE ADDUCTS TO, AND FRAGMENTATION OF, APOLIPOPROTEIN-B FROM HUMAN PLASMA

Many recent in vitro experiments support the hypothesis that oxidative ly modified low density lipoproteins (LDLs) could participate in ather ogenesis. Oxidation of LDLs, especially derivatization by aldehydes or iginating from peroxidation of fatty acids and fragmentation of apolip oprotein (apo) B-100 which is their major apolipoprotein, probably occ urs extra-vascularly and the presence of oxidized LDLs in the circulat ion is not well documented. Using electophoresis and immunodetection t echniques, we studied the structure of apo B and the presence of adduc ts of malondialdehyde (MDA) to this protein in LDLs from plasma of a l imited population of five healthy subjects and nine patients with seve re atherosclerosis. In the patient-derived LDLs, apo B appeared extens ively fragmented, much more so than in those from the healthy subjects , although LDLs were isolated in all cases in the presence of antioxid ants, protease inhibitors and antibiotics. Additionally, in all health y subjects, we found a minor fragment of apo B-100, apo B-74, whereas the complementary peptide, apo B-26, was not detected; thus the presen ce of this minor form cannot be related to cleavage of apo B-100, eith er by proteolysis or by oxidation. We also present evidence that MDA a dducts are present in circulating apo B and most of its fragments not only in atheromatous patients, but also in healthy subjects. Our resul ts are consistent with the existence of oxidized LDLs in the human cir culation. However, the role of non-oxidative phenomena in the structur al modifications affecting apo B which are reported here cannot be exc luded.