The oxidative modification of low density lipoprotein by nonenzymatically glycated peptide-Fe complex

Glycated polylysine, a model of glycated peptide, produces Fe(3+)-chelated compound, which could be converted to an active form in a nonenzymatic process. The exposure of human low density lipoprotein (LDL) to the active glycated polylysine-iron complex caused lipid peroxidation significantly higher than LDL exposed to Fe3+, accompanied by formation of fluorescence compound in apoprotein B (Ex.max. 360 nm, Em.max. 435 nm). Highly modified LDL, which can be judged by an obvious increase of fluorescence compound, could be easily endocytized by rat peritoneal macrophages. alpha-Tocopherol or probucol possessed powerful inhibitory action against active glycated polylysine-iron complex-induced lipid peroxidation of LDL. Each of intrinsic proteins tested, such as apotransferrin, ceruloplasmin and albumin, at the concentration of normal levels of human blood or at the lower levels, also exhibited inhibitory action on the lipid peroxidation of LDL.