MICHAEL ADDITION-TYPE 4-HYDROXY-2-NONENAL ADDUCTS IN MODIFIED LOW-DENSITY LIPOPROTEINS - MARKERS FOR ATHEROSCLEROSIS

It has been proposed that plasma low-density lipoprotein (LDL) undergoes oxidative modification before it can give rise to foam cells in atherosclerosis. Oxidation of LDL generates a variety of reactive aldehyde products including 4-hydroxy-2-nonenal (HNE), which may covalently attach to the LDL apolipoproteins. We here present direct evidence that HNE derivatization of LDL forms Michael addition-type adducts of HNE with histidine and lysine residues of apolipoprotein B-100 (apo B) and also demonstrate the utility of an antibody specific to the HNE adducts generated in the LDL treated with HNE or oxidatively modified by CU2+ Or cultured endothelial cells. HNE adducts present in the LDL that had been treated with HNE were attested to be Michael addition-type adducts on the basis of the fact that incubation of LDL with 1 mM HNE (2 h, 37 degrees C) resulted primarily in the formation of Michael addition-type HNE-histidine (39.9 mol/mol of LDL) and HNE-lysine (19.3 mol/mol of LDL) adducts. An enzyme-linked immunosorbent assay (ELISA) and an SDS-polyacrylamide gel electrophoresis (SDS-PAGE)/immunoblot analysis of HNE-modified LDL demonstrated that these HNE adducts were detectable with the HNE-specific antibody affinity-purified with the Michael adduct (HNE-histidine) as a ligand. The following lines of evidence indicated the presence of Michael addition-type HNE adducts in the oxidatively modified LDL in vitro: (i) Amino acid analysis of LDL that had been treated with CU2+ (24 h, 37 degrees C) demonstrated the presence of a Michael addition-type HNE-histidine adduct (7-9 mol/mol of LDL). (ii) Competitive ELISA demonstrated the inhibition of antibody binding to HNE-modified LDL by the addition of Cu2+ oxidized LDL. (iii) SDS-PAGE/immunoblot analysis of the Cu2+-oxidized LDL demonstrated the appearance of HNE adducts, which were abolished by the addition of a HNE-modified histidyl peptide. Furthermore, HNE adducts were detected in the LDL that had been treated with cultured bovine aortic endothelial cells (24 h, 37 degrees C), Taken together, this evidence suggests that the Michael addition-type HNE adducts may be reliable markers for atherosclerosis.