Autoimmune response to advanced glycosylation end-products of human LDL

Abstract

Advanced glycosylation end-products (AGEs) are believed to play a significant role in the development of vascular complications in diabetic patients. One such product, AGE-LDL, has been shown to be immunogenic. In this report, we describe the isolation and characterization of human AGE-LDL antibodies from the sera of seven patients with Type 1 diabetes by affinity chomatography using an immobilized AGE-LDL preparation that contained primarily the AGE Nε(carboxymethyl)lysine (CML, 14.6 mmol/mol lysine), and smaller amounts of Nε(carboxyethyl)lysine (CEL, 2.7 mmol/ mol lysine). The isolated antibodies were predominantly IgG of subclasses 1 and 3, and considered proinflammatory because of their ability to promote FcγR-mediated phagocytosis and to activate complement. We determined dissociation constants (Kd) for the purified antibodies. The average Kd values (4.76 ± 2.52 × 10-9 mol/l) indicated that AGE-LDL antibodies are of higher avidity than oxidized LDL antibodies measured previously (Kd = 1.53 ± 07 × 10 -8 ml/l), but of lower avidity than rabbit polyclonal LDL antibodies (Kd = 9.34 × 10-11). Analysis of the apolipoprotein B-rich lipoproteins isolated with polyethylene glycol-precipitated antigen-antibody complexes from the same patients showed the presence of both CML and CEL, thus confirming that these two modifications are recognized by human autoantibodies. A comparative study of the reactivity of purified AGE-LDL antibodies with CML-LDL and CML-serum albumin showed no cross-reactivity.