Evidence for binding of in vitro glycated low-density lipoproteins by fructosyllysine-specific sites on macrophages and U937 monocyte-like cells

Summary

Early development of arteriosclerosis is a main late complication of diabetes mellitus. Although its uptake by LDL receptors is impaired, glycated LDL is thought to play a role in foam cell formation from macrophages. In the present study we show binding of glycated LDL (8-9 mol iructosyllysine/mol apo B) to macrophages and to the monocyte-like cell line U937. The binding involves fructosyllysine-specific binding sites, as well as LDL and scavenger receptors. Fructosyllysine and glycated albumin were competitors for binding of ¹²⁵I-labelled glycated LDL by macrophages and U937 cells. Scatchard analysis of binding data using a two ligands binding model snowed a linear plot with K_a = 2.6 X 10⁷ M⁻¹ for U937 cells, which lack scavenger receptors. On U937 cells only the 200 kDa fructosyllysine-specific receptor protein and the 165 kDa LDL receptor were involved in binding glycated LDL as evidenced by ligand blotting. U937 cell uptake and degradation of glycated LDL was mediated by fructosyllysine-specific and LDL receptors. Binding of glycated LDL by macrophages via fructosyllysine-specific sites could be demonstrated in only 6 from 35 rats investigated, indicating that the receptor is not expressed in each individual. Whether the fructosyllysine-specific receptor mediated pathway is relevant for uptake and degradation of glycated LDL in vivo is yet to be determined.

Abbreviations: AGE, advanced glycation end products; DETAPAC, diethylene-triaminepentaacetic acid; FL, fructosyllysine; MDA, malonyldialdehyde; LDL, low-density lipoprotein; SDS-PAGE, sodium dodecylsulfate-polyacrylamide gel electrophoresis; PBS, phosphate buffered saline; TBS, Tris buffered saline, TBARS, thiobarbituric acid-reactive substances.

Key words

Glycated low-density lipoproteins (LDL) - receptor - fructosyllysine - macrophage - monocyte-like cell