Measurement of receptor-independent metabolism of low-density lipoprotein. An application of glycosylated low-density lipoprotein.
Incubation of human low-density lipoprotein (LDL) with glucose results in a nonenzymatic formation of a Schiff base between the monosaccharide and lysyl residues of apolipoprotein B. Increasing the percentage of lysyl residues of apolipoprotein B modified by glycosylation decreases the fractional catabolic rate of the glycosylated LDL, and decreases the metabolism of the glycosylated LDL by human skin fibroblasts. The glycosylated LDL, containing 20-40% of total lysyl residues of apoprotein B modified, was metabolized at a slow rate by both human skin fibroblasts and mouse peritoneal macrophages. These results led to the suggestion that glycosylated LDL is primarily catabolized via a receptor-independent process. Assuming LDL catabolism occurs via receptor-dependent and receptor-independent processes, the ratio of (fractional catabolic rate of glycosylated LDL)/(fractional catabolic rate of native LDL) should be an estimate of the percentage of LDL catabolism via the receptor-independent process. From the fractional catabolic rates of glucose-LDL (20-40% of lysyl residues modified) and galactose-LDL (30-60% of lysyl residues modified) 41% and 30% respectively, of LDL catabolism occurred by a receptor-independent process.
D000818:Animals; D005347:Fibroblasts / Q000378:metabolism; D017127:Glycation End Products, Advanced; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism; D008297:Male; D008657:Metabolic Clearance Rate; D051379:Mice; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011973:Receptors, LDL; D000093844:Glycated Proteins
D017127:Glycation End Products, Advanced; D008077:Lipoproteins, LDL; D011956:Receptors, Cell Surface; D011973:Receptors, LDL; C031797:glycated lipoproteins, LDL; D000093844:Glycated Proteins