Impaired biological activity of erythropoietin by cyanate carbamylation.
OBJECTIVE
During advanced renal failure, particularly in patients with end-stage renal disease (ESRD), proteins are carbamylated as a result of a reaction with cyanate. Some or all of the cyanate is derived from urea. If the carbamylation of proteins adversely alters their biologic activities, then urea must be viewed as an uremic toxin, rather than a surrogate. Therefore, we studied the effect of cyanate carbamylation on the erythropoietic activity of erythropoietin (EPO) in a rodent model.


METHODS
EPO was carbamylated by incubation with cyanate at 37 degrees C. The extent of carbamylation was monitored using trinitrobenzenesulfonic acid. In Sprague-Dawley rats the erythrocyte count, hemoglobin concentration, and hematocrit were measured after the twice-weekly subcutaneous injection of either EPO or carbamylated EPO for 3 weeks. Two additional control groups received physiologic saline or 0.2 ml of 1 M cyanate.


RESULTS
The level of carbamylated EPO was increased as the time of exposure to cyanate increased from 1 to 6 h, and as the cyanate concentration increased from 8 to 2,000 mM. EPO injections caused significantly large increases in all erythropoietic measures. Physiologic saline or 1 M cyanate-injected controls and the carbamylated EPO-injected animals demonstrated no change from baseline in erythropoietic parameters.


CONCLUSIONS
These results support that EPO exposed to high levels of cyanate in vitro demonstrates diminished biologic activity in healthy Sprague-Dawley rats. This effect may be manifested by the carbamylation of EPO by the cyanate. Should this occur in ESRD patients, it may contribute to the suboptimal erythropoietic response to EPO therapy associated with high urea levels, especially related to inadequate dialysis. Targeting dialysis doses specifically to urea concentrations may be more important than previously considered.
Mun
K C
KC
Department of Biochemistry, Keimyung University School of Medicine, Taegu, South Korea. mun@dsmc.or.kr
Golper
T A
TA
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002219:Carbamates / Q000097:blood* / Q000378:metabolism; D003485:Cyanates / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D004906:Erythrocyte Count / Q000187:drug effects; D004921:Erythropoietin / Q000037:antagonists & inhibitors / Q000097:blood / Q000378:metabolism*; D006400:Hematocrit; D006454:Hemoglobins / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012965:Sodium Chloride / Q000008:administration & dosage / Q000494:pharmacology; D013997:Time Factors
D002219:Carbamates; D003485:Cyanates; D006454:Hemoglobins; D004921:Erythropoietin; D012965:Sodium Chloride