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Advanced Glycation End Products Promote Pro-Atherogenic Changes in Cholesterol Transport: A Possible Mechanism for Cardiovascular Risk in Diabetes

Iryna Voloshyna, Jose Gamez-Godoy, Michael J. Littlefield1, Joshua De Leon, Mariano Castro-Magana and Allison B. Reiss

Hyperglycemia is the major cause of diabetic vascular complications. Advanced glycation end products (AGEs) accumulate under hyperglycemic conditions and contribute to atherosclerosis. ATP binding cassette transporters (ABC) A1, ABCG1, and cholesterol 27-hydroxylase are reverse cholesterol transport proteins (RCT) that facilitate cholesterol removal from macrophages and constitute a first line of defense against atherosclerosis. ABCA1 and ABCG1 are known to be suppressed by AGEs. Here we investigate the effects of AGEs on the expression of RCT proteins and scavenger receptors in THP-1 human macrophages and peripheral blood mononuclear cells (HPBMC). Adherent THP-1 macrophages and HPBMC were incubated in the presence or absence of 50 μg/ml carboxymethyl lysine-human serum albumin over a time course. Following incubation, RNA and protein were isolated and subjected to quantitative real-time PCR with specific primers for the 27-hydroxylase, ABCA1, ABCG1, CD36, lectin-like oxidized low density lipoprotein receptor (LOX) 1, scavenger receptor (SR)A1 and chemokine CXC ligand 16 (CXCL16). PCR results were confirmed by Western blot. Expression of ABCA1 and ABCG1 were diminished in the presence of AGEs in both cell lines. For the first time, we demonstrate that AGEs decrease message and protein level for 27-hydroxylase (by 54.5 ± 2.9% and 48.7 ± 9.23%, respectively). In our study uptake of AGE products in THP-1 macrophages and HPBMC occurs mainly through the CD36 and CXCL16 receptors, leading to increased oxidized LDL uptake upon lipid overload and transformation of macrophages into foam cells. Expression of SRA1 and LOX- 1 were not affected by introduction of AGEs. Therefore, we conclude that AGEs may contribute to accelerated atherosclerosis in diabetes through effects on both forward and reverse cholesterol movement. AGEs promote lipid overload through enhancing expression of proteins that facilitate lipid uptake (CD36 and CXCL16) and through suppressing RCT proteins 27-hydroxylase, ABCA1 and ABCG1. Our present study provides a novel atheromapromoting effect of AGEs on lipid handling.