Human serum albumin minimally modified by methylglyoxal binds to human mononuclear leukocytes via the RAGE receptor and is displaced by Nε-carboxymethyl-lysine and hydroimidazolone AGE epitopes

Abstract

Proteins modified by advanced glycation endproducts (AGEs) may activate functional responses in cells by binding to one or more cell surface AGE receptors. We investigated the binding of human serum albumin (HSA) minimally modified by methylglyoxal (MGmin–HSA) to peripheral human mononuclear leukocytes (HMLs) in vitro. MGmin–HSA bound to HMLs specifically with a dissociation constant KD of 265±4 nM and a mean receptor number of 6.5±0.9×105 receptors per cell. Antibodies to the receptor for advanced glycation endproducts (RAGE) inhibited the specific binding of MGmin–HSA to HMLs but antibodies to 80K-H, galectin-3 and control antibodies did not. This suggests that MGmin–HSA binds to HMLs via the RAGE receptor. Human serum albumin minimally modified by glucose-derived AGEs and Nε-carboxymethyl-lysine, and a synthetic hydroimidazolone, 2-ethylamino-5-hydro-5-methylimidazolon-4-one (EtMG-H1), displaced MGmin–HSA from specific binding sites. This suggests that both hydroimidazolone- and CML-like AGE epitopes influenced the binding of AGE-modified proteins to the RAGE receptor.