Effect of Cyanate on the Carbamylation and Biological Activity of Superoxide Dismutase

Seo, Sang Hyuck; Mun, Kyo Cheol; Park, Sung Bae; Kim, Hyun Chul

Abstract

The patients with end stage renal disease show several complications such as artherosclerosis, anemia and increased susceptibility to infection by damage due to oxygen free radicals. Superoxide dismutase(SOD) is directly linked to the fate of the highly reactive oxygen metabolites. If there is an alteration in the activity of SOD, this alteration may contribute to the complications by reactive oxygen species in patients with end stage renal disease. In this experiment, SOD activity and the effect of cyanate on the activity of SOD was studied to understand the mechanism of several complications mediated by oxygen free radicals in patients with end stage renal disease. SOD activity in the plasma and erythrocytes from patients with end stage renal disease was significantly lower than those from healthy controls. It is known that underproduction of SOD leads to excess production of superoxide and reduced iron favoring hydroxyl radical formation. The results in this experiment suggest that there is an overproduction of superoxide anion in patients with end stage renal disease. The overproduction of superoxide anion may contribute the patients with end stage renal disease susceptible to oxidant damages. To evaluate if cyanate could carbamylate SOD, SOD was incubated with cyanate. The level of carbamylated SOD increased as the time of exposure to cyanate increased from 0 hour to 72 hours. Furthermore, the degree of carbamylation of SOD increased as cyanate concentration in the incubation media rose from 20mM to 1M. There appears to be a maximum degree of carbamylation at a concentration of 1,000mM cyanate. To test the hypothesis that in vitro carbamylation of SOD alters its biological activity, SOD activity was measured after incubation with cyanate. The activity of carbamylated SOD decreased as the time of exposure to cyanate increased from 0 hour to 72 hours. Furthermore, the activity of carbamylated SOD decreased as cyanate concentration in the incubation media rose from 20mM to 1M and when albumin was added to the reaction mixture, the loss of SOD activity was prevented. These results are consistent with the hypothesis that SOD is also carbamylated and lost biological activity in end stage renal disease patients by cyanate, and that the degree of carbamylation depends on both the concentration of cyanate and the length of exposure. Also, these suggest that albumin may prevent carbamylation of SOD at least in vitro condition.