Resistance to LDL oxidative modifications of an N-terminal apolipoprotein B epitope.

The immunoreactivity of human apolipoprotein B (apo B) towards 5 monoclonal antibodies was studied by enzyme immunoassay in native and in vitro oxidized low density lipoproteins (LDL). LDL oxidative modifications were obtained by incubation with either copper ions or an association of lipoxygenase and phospholipase A2. The monoclonal antibodies used in the inhibition analysis were directed to epitopes located in the amino-terminal region (1D1), in the middle part (2D8, L7, 4G3) and in the carboxy-terminal region (L3) of the apo B molecule. The results demonstrated that the immuno-reactivity of 1D1 epitope was little affected by LDL oxidation with copper ions or lipoxygenase plus phospholipase A2, whereas the immunoreactivity of the other epitopes were markedly decreased by these LDL modifications. Immunoreactivity changes were more important in L3 and L7 epitopes than in 2D8 and 4G3 epitopes. Since it is known that L3 and L7 epitopes are located in apo B domains rich in lipid-associated peptides whereas 1D1 is in a domain poor in such peptides, these results suggest a relationship between the lipid environment of an apo B epitope and its susceptibility to alteration by LDL oxidation.