Surface Plasmon Resonance Measurement of the Binding of Low-Density Lipoprotein at a Heparin Surface

Abstract

Low-density lipoprotein (LDL) adsorption to heparin-like surface is of wide clinical interest since such a mechanism might be responsible for cholesterol accumulation in the arterial wall. By modifying the surface plasmon resonance sensor surface with heparin and albumin (BSA) LDL adsorption to this surface was investigated and characterized. Heparin was seen to be a potentially useful ligand for LDL detection and analysis in a clinical context. It was found that N-acetylheparin had a lower affinity for LDL than heparin and that the binding strength of LDL to N-acetylheparin was reduced. Assuming a random distribution of heparin on the surface, it was calculated from the data obtained that a maximum of 4.0 × 109 heparin or 4.8 × 109N-acetylheparin “rods” can be found on a millimeter square and that one LDL molecule (380 nm2) covers on average only 1.5 heparin molecules or 1.8 N-acetylheparin molecules, yet maximum LDL binding cannot be increased beyond a surface coverage of 7.5 or 5.8% for heparin and N-acetyl heparin, respectively. This could lead to the suggestion that the glycosaminoglycan–LDL atheroclerosis mechanism would involve only 1–2 heparin molecules in “binding” each LDL, but 20–30 molecules are required to attract it to the surface in the first place.