Inhibition of erythropoietin activity by cyanate.
OBJECTIVE
Increased urea concentration is a measure of advanced renal failure and the adequacy of renal replacement therapy in end-stage renal disease (ESRD). Altered biologic activity due to changes in protein structure occurs when cyanate, formed spontaneously from urea, reacts with proteins. Carbamylation results in impaired erythropoietin (EPO) activity when high concentrations of cyanate react with EPO. In this study, the activity of carbamylated EPO (C-EPO), formed at a cyanate concentration which may occur in vivo, was studied in Sprague-Dawley rats.


METHODS
The extent of carbamylation, causing loss of free amino groups, was monitored using trinitrobenzenesulfonic acid. Erythrocyte, hemoglobin, hematocrit and leukocyte levels were measured after either EPO, incubated EPO, C-EPO, physiologic saline or cyanate (1.5 microM; 0.2 ml) were injected subcutaneous twice weekly for 3 weeks in rats.


RESULTS
In vitro carbamylation of EPO was time- and concentration-dependent. C-EPO concentration increased as the duration of exposure to cyanate increased from 6 to 72 h, or as cyanate concentration increased from 15 nM to 1.5 microM. Injections of EPO caused significant increases in vivo in all erythropoietic measures. In contrast, injections of C-EPO, physiologic saline or 1.5 microM cyanate caused no change from baseline.


CONCLUSIONS
These results demonstrated diminished biologic activity in healthy rats by C-EPO formed in vitro at cyanate concentrations that may be found in vivo. C-EPO and high urea-derived cyanate levels may contribute to suboptimal erythropoietic responses to EPO therapy for chronic renal failure and ESRD, and may provide another measurement indicating inadequate dialysis.
Park
Kyung-Dae
KD
Dong San Kidney Institute, Keimyung University School of Medicine, Taegu, South Korea.
Mun
Kyo-Cheol
KC
Chang
Eun-Ju
EJ
Park
Sung-Bae
SB
Kim
Hyun-Chul
HC
D000818:Animals; D003485:Cyanates / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004920:Erythropoiesis / Q000187:drug effects* / Q000502:physiology; D004921:Erythropoietin / Q000096:biosynthesis*; D007279:Injections, Subcutaneous; D008297:Male; D023421:Models, Animal; D011336:Probability; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D012680:Sensitivity and Specificity
D003485:Cyanates; D004921:Erythropoietin