Glycation and oxidation of human low density lipoproteins reduces heparin binding and modifies charge

Abstract

The effects of glycation and oxidation of human low density lipoproteins (LDL) on heparin binding were studied and compared with modifications in the charge of the particles. Glycation of LDL at a molar ratio of 4mol glucose mol^-1 apoB, decreases affinity for heparin, as shown by heparin-agarose affinity chromatography since salt molarity needed for elution decreases from 550mmol1^-1 for control LDL (c-LDL) to 350mmol1^-1 for glycated LDL (glc-LDL). Oxidized LDL (oxi-LDL) shows marked heterogeneity, most of the fractions having decreased affinity. Heparin-agarose affinity chromatography of LDL preparations shows the presence of a small (5-7%), low-affinity fraction in euglycaemic human plasma LDL (c-LDL). Its elution volume coincides with both glc-LDL and a fraction of oxi-LDL, suggesting it may contain glycated and oxidized molecules present in plasma. DEAE-Trisacryl anion exchange chromatography elution profiles of c-LDL preparations shows the presence of a more electronegative fraction accounting for about 10% of total protein. This fraction elutes with 260mmoll^-1 NaCl instead of 130mmoll^-1 for the main fraction, it roughly coincides with elution volumes of main peaks of glc-LDL and oxi-LDL. Results indicate that glycated particles may be present in this fraction. Our data demonstrate then that glycation, and to a lesser degree, oxidation of LDL reduce affinity to heparin. From an analytical approach, modified LDL can be separated from the bulk of native LDL both by DEAE and heparin-agarose chromatographies. As high affinity heparin-binding sites have been proposed as putative participants in apoB-receptor recognition, our results suggest that glycation may indeed alter some of the residues involved.

Key Words:

• DEAE-Trisacryl
• diabetes
• glycosaminoglycans
• modified LDL