Glycation impairs high-density lipoprotein function

Abstract

Aims/hypothesis. To examine the effects of incubation of high-density lipoprotein (HDL) under hyperglycaemic conditions on several functions of HDL in vitro. Methods. Human HDL (5 mg protein) was incubated for 1 week at 37°C in the presence or absence of 25 mmol/l glucose. Additional samples of human HDL were incubated in butylated hydroxytoluene to control for oxidation. Results. High-density lipoprotein incubated for 1 week in 25 mmol/l glucose had significant increases in the glycation product, fructoselysine and in the advanced glycation end product, Nε-(carboxymethyl)lysine. High-density lipoprotein apolipoprotein AI and AII concentrations were not altered but glycated HDL had a 65% reduction in paraoxonase enzymatic activity. Glycated HDL did not inhibit monocyte adhesion to human aortic endothelial cells in response to oxidised low-density lipoprotein in vitro (43 ± 4 monocytes bound vs 21 ± 2 monocytes for control HDL, p < 0.0001). Hepatic lipase- mediated non-esterified fatty acid release from HDL lipids was enhanced in glycated HDL compared with control HDL (25 ± 1 vs 16 ± 1 nmol non- esterified fatty acid hydrolysed/min, respectively, p < 0.0001). Direct glycation of purified paraoxonase protein by incubation in 25 mmol/l glucose caused a 40% reduction in enzymatic activity. This glycated paraoxonase did not inhibit monocyte adhesion to human aortic endothelial cells in vitro (68 ±3 monocytes vs 49 ± 2 monocytes bound for control paraoxonase, respectively, p < 0.001). We also measured a 40% reduction in paraoxonase activity in patients with Type II (non-insulin-dependent) diabetes mellitus and documented coronary artery disease compared with nondiabetic subjects, p < 0.0001. Conclusions/interpretation. Alterations in function of HDL caused by exposure to hyperglycaemic conditions could contribute to the accelerated atherosclerosis observed in Type II diabetes.