CARBAMYLATION-INDUCED ALTERATIONS IN LOW-DENSITY-LIPOPROTEIN METABOLISM

Low-density lipoprotein was derived from carbamyl (carbamyl-LDL) by incubating LDL in potassium cyanate (KCNO). The proportion of free amino groups in the carbamyl-LDL was negatively correlated (r = -0.95) with the time of incubation in potassium cyanate (ranged from 5 to 360 min). The carbamylation did not change the chemical composition or the flotation characteristics of the LDL particles. However, the electrophoretic mobility of carbamyl-LDL was distinctly increased with the extent of carbamylation. The carbamyl-LDL had substantially decreased binding to the LDL apoB/E receptors of the bovine adrenocortical membranes when compared to the control-LDL. The reduced binding was already observed when only 9% of the free amino groups were derived from carbamyl. A minor carbamylation of LDL (less than 20% of the free amino groups) decreased the in vivo clearance of LDL from rabbit plasma. However, when more than 20% of the free amino groups were derived the carbamyl-LDL had accelerated clearance compared to the control-LDL. LDL isolated from uremic patients was cleared in rabbits at a slower rate than LDL isolated from a control subject. Providing that carbamylation of LDL could also occur in vivo resulting in similar alterations of the LDL binding to the LDL B/E receptors, as observed in the present study, the uremia-related accelerated atherosclerosis could have one additional mechanistic explanation.