Glycated phosphatidylethanolamine promotes macrophage uptake of low density lipoprotein and accumulation of cholesteryl esters and triacylglycerols.

Non-enzymatic glycation of low density lipoprotein (LDL) has been suggested to be responsible for the increase in susceptibility to atherogenesis of diabetic individuals. Although the association of lipid glycation with this process has been investigated, the effect of specific lipid glycation products on LDL metabolism has not been addressed. This study reports that glucosylated phosphatidylethanolamine (Glc-PtdEtn), the major LDL lipid glycation product, promotes LDL uptake and cholesteryl ester (CE) and triacylglycerol (TG) accumulation by THP-1 macrophages. Incubation of THP-1 macrophages at a concentration of 100 micrograms/ml protein LDL specifically enriched (10 nmol/mg LDL protein) with synthetically prepared Glc-PtdEtn resulted in a significant increase in CE and TG accumulation when compared with LDL enriched in non-glucosylated PtdEtn. After a 24-h incubation with LDL containing Glc-PtdEtn, the macrophages contained 2-fold higher CE (10.11 +/- 1.54 micrograms/mg cell protein) and TG (285.32 +/- 4.38 micrograms/mg cell protein) compared with LDL specifically enriched in non-glucosylated PtdEtn (CE, 3.97 +/- 0.95, p < 0.01 and TG, 185.57 +/- 3.58 micrograms/mg cell protein, p < 0.01). The corresponding values obtained with LDL containing glycated protein and lipid were similar to those of LDL containing Glc-PtdEtn (CE, 11.9 +/- 1.35 and TG, 280.78 +/- 3.98 micrograms/mg cell protein). The accumulation of both neutral lipids was further significantly increased by incubating the macrophages with Glc-PtdEtn LDL exposed to copper oxidation. By utilizing the fluorescent probe, 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorate (DiI), a 1.6-fold increase was seen in Glc-PtdEtn + LDL uptake when compared with control LDL. Competition studies revealed that acetylated LDL is not a good competitor for DiI Glc-PtdEtn LDL (5-6% inhibition), whereas glycated LDL gave an 80% inhibition, and LDL + Glc-PtdEtn gave 93% inhibition of uptake by macrophages. These results indicate that glucosylation of PtdEtn in LDL accounts for the entire effect of LDL glycation on macrophage uptake and CE and TG accumulation and, therefore, the increased atherogenic potential of LDL in hyperglycemia.