Beneficial effect of tetrahydrobiopterin on the survival of rats exposed to hepatic ischemia-reperfusion injury

Introduction. The protective role of nitric oxide (NO) against hepatic ischemia-reperfusion (I/R) injury remains controversial. In this study we investigated the effect of tetrahydrobiopterin (BH4) on the survival of rats exposed to an hepatic I/R injury. Methods. The rats were subjected to 100 minutes of 70% hepatic ischemia 30 minutes after administration of BH4 or saline. A specific inducible NO synthase (iNOS) blocker, 1400W, was used to evaluate endogenous iNOS. NOS protein measured the histological appearance of the liver by Western blotting, and survival was evaluated after reperfusion. Results. The 1-week survival rate was 60% among the BH4 group and 10% for the saline group. The serum ALT and bilirubin values in the BH4 group were significantly lower than the saline group. Histological examination of the liver revealed only a small necrotic area in the BH4 group as opposed to massive necrosis and cell infiltration in the saline group. Injection of 1400W significantly decreased the prolongation of survival produced by BH4. Conclusions. BH4 significantly improved the survival rate, the histological findings, and the liver function, thereby reducing liver failure. Western blotting showed a higher level of iNOS protein in the BH4 group than the saline group, 1400W suppressed this effect of BH4. Taken together, these observations suggest that NO derived from reactions driven by BH4-induced iNOS exerts a protective effect against reperfusion injury.