potassium-cyanate and homocitrulline

Previous studies have shown that the increase of carbamylated LDL (cLDL), a product of nonenzymatic modification of LDL in human serum by urea-derived cyanate, may cause cardiovascular complications in patients with chronic renal insufficiency. This study examined the inhibitory effect of ascorbic acid, alpha-tocopherol and lycopene on LDL carbamylation in an in vitro model system.. After isolation of LDL from plasma using an ultracentrifuge technique, cyanate was added to it and then LDL carbamylation was measured in both the absence and presence of ascorbic acid, alpha-tocopherol and/or lycopene by the colorimetric method at 530 nm.. The findings indicated that these vitamins inhibit LDL carbamylation and the most effective vitamin of the three is lycopene. Moreover, the effect of lycopene on this process increased in the presence of ascorbic acid and alpha-tocopherol.. This study indicated that ascorbic acid, alpha-tocopherol and lycopene with antioxidant activity can probably inhibit LDL carbamylation and therefore may have a role in ameliorating atherosclerotic risk of patients with kidney failure. However in vitro and in vivo investigations are required to confirm the exact effects of these vitamins on patients suffering from uremic disorders.

Topics: Adult; alpha-Tocopherol; Ascorbic Acid; Atherosclerosis; Carotenoids; Citrulline; Cyanates; Electrophoresis, Agar Gel; Humans; Lipoproteins, LDL; Lycopene; Male; Protein Processing, Post-Translational; Uremia; Vitamins; Young Adult

Carbamoylated proteins have been located by using a site-specific polyclonal antihomocitrulline antibody and a fluorescent secondary antibody in leukocytes from patients with end-stage renal disease who were undergoing maintenance continuous ambulatory peritoneal dialysis. A covalent reaction with urea-derived cyanate and the epsilon-amino group of lysine forms homocitrulline residues in carbamoylated proteins. Isocyanic acid, the reactive form of cyanate, is spontaneously formed from urea in aqueous solution at physiologic pH and temperature. In washed, fixed monolayers of cells, an intracellular fluorescent antigen-antibody complex was located throughout the cytoplasm of polymorphonuclear neutrophils (PMNs) and monocytes from 11 patients with blood urea nitrogen (BUN) levels ranging from 32 to 102 mg/dl who were undergoing dialysis for 2 to 135 months. A punctate fluorescence present in the cell surface proteins of living cells demonstrated that lysine residues in the external domain of proteins were carbamoylated, forming homocitrulline. In contrast, we found a perinuclear fluorescence in PMNs in normal subjects with no history of renal insufficiency and BUN levels of 6 to 19 mg/dl. This suggests that homocitrulline is located in carbamoylated proteins within the perinuclear membrane, a structural organelle continuous with the endoplasmic reticulum. It appears that continuous exposure to urea-derived cyanate in low levels results in increasing carbamoylation of stable proteins over the PMN's lifetime. When normal PMNs were exposed to 120 mmol/L cyanate ion in vitro for 10 to 30 minutes, the ability of PMNs to release microbicidal superoxide was strongly inhibited. Thus protein carbamoylation may provide a regulatory mechanism. The altered function of PMNs in renal disease may be due in part to the posttranslational modification of proteins by urea-derived cyanate.

Topics: Adult; Aged; Blood Proteins; Blood Urea Nitrogen; Citrulline; Cyanates; Female; Fluorescein-5-isothiocyanate; Fluorescent Antibody Technique; Fluorescent Dyes; Humans; Kidney Failure, Chronic; Leukocytes; Male; Middle Aged; Neutrophils; Peritoneal Dialysis; Superoxides; Urea