SYNTHESIS OF GUANIDINOSUCCINATE FROM ARGININOSUCCINATE AND REACTIVE OXYGEN IN-VITRO

Synthesis of guanidinosuccinic acid (GSA), a uremic toxin, has been su ggested to relate to the urea concentration and urea synthetic rate. A mong the urea cycle enzymes, inhibition of argininosuccinate (ASA) lya se by urea has been reported. Argininosuccinate which contains a GSA s tructure is a candidate of a GSA precursor. We found that another urem ic toxin, methylguanidine, is formed from creatinine with reactive oxy gen species. Therefore, we investigated in vitro whether GSA is formed from ASA with reactive oxygen species. GSA was measured by HPLC by a post-column-labeling method using 9,10-phenathrequinone. When 1 mmol/l ASA was reacted with the hydroxyl radical-generating system for 5 min at pH 7.4, 9 mu mol/l GSA was formed. Dimethylsulfoxide, a hydroxyl r adical scavenger, markedly inhibited GSA synthesis. The superoxide rad ical generated by xanthine and xanthine oxidase reaction also formed 1 mu mol/l GSA from 1 mmol/l ASA and the GSA formation was inhibited by superoxide dismutase or catalase almost completely. Addition of FeCl2 to the xanthine/xanthine oxidase reaction further increased GSA synth esis. These results indicate that GSA is formed from ASA by reaction w ith the hydroxyl radical and the superoxide radical.