Immunochemical detection of a novel lysine adduct using an antibody to linoleic acid hydroperoxide-modified protein

We have previously prepared the polyclonal antibody to the 13-hydroperoxyoctadecadienoic acid-modified protein (13Ab) (Kato et al. 1997. J Lipid Res. 38: 1334-1346), however, the epitopes have not yet been structurally identified. In this study, we identified a novel amide-type adduct as one of the major epitopes of 13Ab and characterized the endogenous formation. Upon incubation of the lysine derivative with peroxidized linoleic acid, the formation of N-epsilon-(azelayl)lysine (AZL) was confirmed using liquid chromatography-mass spectrometry. The chemically synthesized azelayl protein was significantly recognized by 13Ab. The peroxidation products of different polyunsaturated fatty acids also generated several analogous carboxyalkylamide-type adducts to AZL by the reaction with the lysine derivative, whereas 13Ab specifically recognized AZL, suggesting that the AZL moiety may be one of the major epitopes of 13Ab. The immunoreactive materials of 13Ab were immunohistochemically detected in atherosclerotic lesions from hypercholesterolemic rabbits. More strikingly, the immunoreactivity was significantly enhanced when the sections were treated with alkali or phospholipase A(2) for hydrolyzing the ester bonds prior to the staining. El These results suggest that the lipid hydroperoxide-derived carboxylic adducts, such as AZL, and their esters linked with phospholipids may be generated in vivo and involved in the pathogenesis of atherosclerosis associated with oxidative stress.