Role of reactive oxygen and argininosuccinate in guanidinosuccinate synthesis in isolated rat hepatocytes

The synthesis of guanidinosuccinic acid (GSA) increases in uremics, and GSA is implicated as a uremic toxin. The GSA synthesis increases roughly in proportion to the serum urea level that increases in patients with renal failure. Urea is a specific inhibitor of argininosuccinase, the fourth urea cycle enzyme, and might lead to the increase of argininosuccinate (ASA). We found that GSA is formed from ASA by reactive oxygen species in vitro. In this paper, we investigated GSA synthesis from ASA in isolated rat hepatocytes and the effect of reactive oxygen species on this synthesis. When isolated rat hepatocytes were incubated with 5 mmol/l ASA, GSA was formed linearly with time up to 6 h (16 nmol/g wet liver/6 h). GSA was formed depending on the ASA concentration up to 10 mmol/l. Dimethylsulfoxide, a hydroxyl radical scavenger, inhibited GSA synthesis by 65%. GSA was actively formed when the hepatocytes were incubated with 32 mmol/l urea. The GSA formation in the presence of urea was also inhibited by dimethylsulfoxide, although the inhibition was less marked. FeCl2, that increases the hydroxyl radical generation, increased GSA synthesis. These results indicate that GSA is formed from ASA in isolated hepatocytes. The results also suggest that reactive oxygen species are important for GSA synthesis in the cells.