OXIDATION OF LOW-DENSITY LIPOPROTEINS PRODUCES LEVUGLANDIN-PROTEIN ADDUCTS

Free-radical oxidation of human low-density lipoprotein (LDL) produces levuglandin (LG)protein adducts that were detected with an enzyme-lin ked immunosorbent assay using LGE(2)-KLH antibodies which recognize LG E(2)-derived pyrroles. The level of immunoreactivity increases with ti me of oxidation and reaches a maximum by 8 h. The yield of pyrrole var ies nonlinearly with the level of LG adduction to LDL. At low LG:LDL r atios, such as those detected in oxidized LDL, the reaction of primary amino groups with LGE(2) produces mostly non-pyrrole adducts that are not immunoreactive. Concommitant phospholipolysis must occur if the g eneration of immunoreactive epitopes in LDL involves oxidation of arac hidonyl phospholipids. Thus, since a protein adduct prepared from synt hetic LGE(2)-2-lysophosphatidylcholine ester showed, at most, only 0.5 % cross-reactivity with the LGE(2)-KLH antibodies, the epitopes detect ed in oxidized LDL are almost certainly not protein adducts of LG-phos pholipid esters. As expected, hydrolysis of the carboxylic ester in th e protein adduct of LGE(2)-2-lysophosphatidylcholine ester by treatmen t with phospholipase A:! produced a fully immunoreactive LGE(2)-protei n adduct.