Monoclonal antibody-based immunoassay for evaluation of lipoprotein oxidation

Numerous reports indicate that the oxidation of low-density lipoprotein (LDL) can significantly change its metabolic and physiological properties. Most methods for evaluation of LDL oxidation require isolation of lipoprotein, making the procedure laborious and increasing the probability of artifactual modification of LDL. In this paper we describe an immunochemical approach which can be used to measure the oxidation of isolated LDL and apoprotein B in unfractionated serum and to evaluate the effects of antioxidants on these processes. The procedure is based on differential recognition by monoclonal antibodies of native and oxidized lipoproteins. The results obtained with our assay indicate a strong correlation between the changes of apo B epitope expression during oxidation and the formation of conjugated dienes, changes in lipoprotein electrophoretic mobility, and interaction with fibroblast and macrophage receptors. The sensitivity of apo B to oxidation varies greatly among serum samples obtained from individual donors. These differences do not correlate with the differences in sensitivity to oxidation of LDL isolated from the blood samples of the same donors. It is also shown that apo B oxidation in serum can be progressively inhibited in the presence of increasing amounts of various antioxidants.