Adsorption of low-density lipoprotein, its oxidation, and subsequent binding of specific recombinant antibodies: An in situ ellipsometric study

BackgroundLow-density lipoprotein (LDL) particles accumulate in the arterial wall and become oxidized during atherogenesis, leading to the formation of atherosclerotic plaques. The major protein of the LDL particle, apolipoprotein B-100 (apoB-100), becomes fragmented during oxidation and a target for the immune system.MethodsIn this study we used in situ ellipsometry to monitor the adsorption of LDL to solid silica surfaces and the effects of oxidation on the structure of the adsorbed LDL layer. We additionally investigated the binding kinetics of two recombinant human antibodies with different specificities recognizing epitopes of apoB-100 in surface-bound native and CuCl2-oxidized LDL (oxLDL). The latter process was studied by adsorbing LDL and then adding the antibody and CuCl2 while continuously monitoring adsorbed amount and the thickness of the film. The molar ratios between the antibodies and surface-bound LDL and oxLDL were calculated from these data.ResultsOur results indicate that oxidation of surface-bound LDL induces swelling of the layer, accompanied by a slight desorption. We further found that both antibodies were able to recognize LDL and oxLDL in its adsorbed orientation. Quantitative information was obtained on the number of available binding sites on surface-bound LDL and oxLDL for these two antibodies.General significanceUsing ellipsometry for real-time monitoring of adsorption, in situ oxidation of LDL and binding of specific recombinant antibodies to surface-bound LDL, will open up possibilities to map different conformations and orientations of LDL in the adsorbed state.

Research highlights
► In situ ellipsometry allows quantification of molar ratios between antibody and oxLDL.
► LDL binding takes place at the solid/liquid interface in a concentration-dependent way.
► OxLDL specific antibodies recognize oxLDL in its adsorbed orientation.
► Two oxLDL specific antibodies recognize diverse number of epitopes on adsorbed oxLDL.