Toshihiko Osawa

Acrolein Is a Product of Lipid Peroxidation Reaction FORMATION OF FREE ACROLEIN AND ITS CONJUGATE WITH LYSINE RESIDUES IN OXIDIZED LOW DENSITY LIPOPROTEINS

Lipoprotein peroxidation, especially the modification of apolipoprotein B-100, has been implicated to play an important role in the pathogenesis of atherosclerosis. However, there have been few detailed insights into the chemical mechanism of derivatization of apolipoproteins during oxidation. In the present study, we provide evidence that the formation of the toxic pollutant acrolein (CH2=CH–CHO) and its conjugate with lysine residues is involved in the oxidative modification of human low density lipoprotein (LDL). Upon incubation with LDL, acrolein preferentially reacted with lysine residues. To determine the structure of acrolein-lysine adduct in protein, the reaction of acrolein with a lysine derivative was carried out. EmployingN α-acetyllysine, we detected a single product, which was identified to be a novel acrolein-lysine adduct,N α-acetyl-N ε-(3-formyl-3,4-dehydropiperidino)lysine. The acid hydrolysis of the adduct led to the derivative that was detectable with amino acid analysis. It was revealed that, uponin vitro incubation of LDL with acrolein, the lysine residues that had disappeared were partially recovered byN ε-(3-formyl-3,4-dehydropiperidino)lysine. In addition, we found that the same derivative was detected in the oxidatively modified LDL with Cu2+ and that the adduct formation was correlated with LDL peroxidation assessed by the consumption of α-tocopherol and cholesteryl ester and the concomitant formation of cholesteryl ester hydroperoxide. Enzyme-linked immunosorbent assay that measures free acrolein revealed that a considerable amount of acrolein was released from the Cu2+-oxidized LDL. Furthermore, metal-catalyzed oxidation of arachidonate was associated with the formation of acrolein, indicating that polyunsaturated fatty acids including arachidonate represent potential sources of acrolein generated during the peroxidation of LDL. These results indicate that acrolein is not just a pollutant but also a lipid peroxidation product that could be ubiquitously generated in biological systems.