High-density lipoprotein impedes glycation of low-density lipoprotein

Glycation of low-density lipoprotein (LDL) increases its atherogenicity, but whether high-density lipoprotein (HDL) can protect LDL against glycation is not known. LDL and HDL were isolated from 32 volunteers with serum HDL cholesterol concentrations ranging from 0.76 to 2.01 (mean = 1.36) mmol/L. Glycation of LDL was induced by incubation with 0-80 mmol/L glucose for 7 days at 37°C under nitrogen in the presence of and absence of human HDL. Glycation of LDL apolipoprotein B (apoB) doubled at glucose 50 and 80 mmol/L (both p < 0.001), and this increase was ameliorated by HDL. In the absence of glucose, 0.11 (0.01) [mean (standard error, SE)] mg apoB/mg LDL protein was glycated increasing to 0.22 (0.02) mg/mg at glucose 80 mmol/L in the absence of HDL, but remaining at 0.13 (0.01) mg/mg when autologous HDL was present. Heterologous HDL from a further study of 12 healthy participants was similarly effective in impeding LDL apoB glycation. HDL impeded not only glycation but also the lipid peroxidation, free amino group consumption and increased electrophoretic mobility of LDL which accompanied glycation. HDL from participants with higher serum paraoxonase1 (PON1) was more effective in impeding glycation and the related processes. In conclusion, HDL can impede the glucose-induced glycoxidation of LDL. PON1 may be important for this function of HDL.