Glycation of low‐density lipoprotein results in the time‐dependent accumulation of cholesteryl esters and apolipoprotein B‐100 protein in primary human monocyte‐derived macrophages

Abstract

Nonenzymatic covalent binding (glycation) of reactive aldehydes (from glucose or metabolic processes) to low-density lipoproteins has been previously shown to result in lipid accumulation in a murine macrophage cell line. The formation of such lipid-laden cells is a hallmark of atherosclerosis. In this study, we characterize lipid accumulation in primary human monocyte-derived macrophages, which are cells of immediate relevance to human atherosclerosis, on exposure to low-density lipoprotein glycated using methylglyoxal or glycolaldehyde. The time course of cellular uptake of low-density lipoprotein-derived lipids and protein has been characterized, together with the subsequent turnover of the modified apolipoprotein B-100 (apoB) protein. Cholesterol and cholesteryl ester accumulation occurs within 24 h of exposure to glycated low-density lipoprotein, and increases in a time-dependent manner. Higher cellular cholesteryl ester levels were detected with glycolaldehyde-modified low-density lipoprotein than with methylglyoxal-modified low-density lipoprotein. Uptake was significantly decreased by fucoidin (an inhibitor of scavenger receptor SR-A) and a mAb to CD36. Human monocyte-derived macrophages endocytosed and degraded significantly more (125)I-labeled apoB from glycolaldehyde-modified than from methylglyoxal-modified, or control, low-density lipoprotein. Differences in the endocytic and degradation rates resulted in net intracellular accumulation of modified apoB from glycolaldehyde-modified low-density lipoprotein. Accumulation of lipid therefore parallels increased endocytosis and, to a lesser extent, degradation of apoB in human macrophages exposed to glycolaldehyde-modified low-density lipoprotein. This accumulation of cholesteryl esters and modified protein from glycated low-density lipoprotein may contribute to cellular dysfunction and the increased atherosclerosis observed in people with diabetes, and other pathologies linked to exposure to reactive carbonyls.