potassium-cyanate and Kidney-Failure--Chronic

Chronic renal failure (CRF) patients have an increased plasma level of urea, which can be a source of cyanate. This compound can cause protein carbamoylation thereby changing biological activity of proteins. Therefore, in renal failure patients, cyanate can disturb metabolism and functioning of the liver. This work presents studies demonstrating that the treatment of rats with cyanate alone causes the following changes in the liver: (1) inhibition of rhodanese (TST), cystathionase (CST) and 3-mercaptopyruvate sulfotransferase (MPST) activities, (2) decrease in sulfane sulfur level (S*), (3) lowering of nonprotein sulfhydryl groups (NPSH) group level, and (4) enhancement of prooxidant processes (rise in reactive oxygen species (ROS) and malondialdehyde (MDA) level). This indicates that cyanate inhibits anaerobic cysteine metabolism and shows prooxidant action in the liver. Out of the above-mentioned changes, lipoate administered with cyanate jointly was able to correct MDA, ROS and NPSH levels, and TST activity. It had no significant effect on MPST and CST activities. It indicates that lipoate can prevent prooxidant cyanate action and cyanate-induced TST inhibition. These observations can be promising for CRF patients since lipoate can play a dual role in these patients as an efficient antioxidant defense and a protection against cyanate and cyanide toxicity.

Topics: Animals; Antioxidants; Cyanates; Cysteine; Hydrogen Sulfide; Kidney Failure, Chronic; Lipid Peroxidation; Liver; Male; Molecular Targeted Therapy; Oxidants; Oxidative Stress; Poisons; Rats; Rats, Wistar; Reactive Oxygen Species; Sulfhydryl Compounds; Thioctic Acid; Thiosulfate Sulfurtransferase; Uremia

During advanced renal failure, and particularly in patients with end-stage renal disease, proteins are carbamylated as a result of a reaction with cyanate. If the carbamylation of proteins adversely alters their biologic activities and structures, then urea must be viewed as an uremic toxin, rather than a surrogate. Therefore, we studied in this paper the role of cyanate as a hemolytic factor of erythrocytes to explain anemia observed in patients with high blood urea levels due to inadequate dialysis. Cyanate was added to make the final concentration 150, 300 and 600 nmol to each test tube containing the final concentration of 140 x 10(6) with human erythrocytes per mL of phosphate buffered saline solution. And they were incubated at 37 degrees C for 24, 48 and 72 hours. The extent of hemolysis and carbamylation was monitored. The levels of hemolysis and carbamylated erythrocytes increased as the time of exposure to cyanate increased from 24 hours to 72 hours. Furthermore, those increased as cyanate concentration in the incubation media rose from 150 nmol to 600 nmol. Cyanate can induce hemolysis by carbamylation of erythrocytes. Urea, through cyanate, may contribute to hemolysis. If one extrapolates these results to patients with end-stage renal disease, it may help explain one of the reasons for the anemia in patients with high levels of BUN due to inadequate dialysis.

Topics: Anemia, Hemolytic; Blood Urea Nitrogen; Cyanates; Erythrocytes; Hemolysis; Humans; Kidney Failure, Chronic

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

The effect of in vitro carbamylation of serum protein with potassium cyanate on protein binding of penbutolol, a basic agent exclusively bound to alpha 1 acid glycoprotein (AAG), was investigated. Carbamylation of serum resulted in a weak increase on free fraction of penbutolol (4.45 +/- 0.54% before carbamylation vs 5.66 +/- 0.40% after; p < 0.025). Parallelly, potassium cyanate added to pure AAG and incubated for 90 min induced carbamylation of this protein (38 mumoles of 14C cyanate incorporated per gram of protein). A study in serum from patients with chronic renal disease (pre and postdialysis) showed no changes in protein binding of penbutolol, although AAG levels were significantly higher. However, Scatchard [1949] plot for penbutolol binding to serum from renal patients (both pre and postdialysis) showed a decrease in affinity constant (nKa = 11.13 x 10(5) M-1 in healthy volunteers, vs 5.56 x 10(5) M-1 in patients before dialysis and 4.57 x 10(5) M-1 after dialysis). We concluded that carbamylation of serum AAG in uremic patients could explain, in part, the absence of changes in protein binding of any basic drugs in this pathological condition. It appears that a decreased affinity constant could balance the effect of increased AAG levels.

Topics: Adult; Aged; Blood Proteins; Cyanates; Female; Humans; Kidney Failure, Chronic; Male; Middle Aged; Orosomucoid; Penbutolol

Topics: Cyanates; Humans; Kidney Failure, Chronic; Kinetics; Protein Binding; Reference Values; Serum Albumin; Warfarin