Glutamine and glutathione counteract the inhibitory effects of mediators of sepsis in neonatal hepatocytes

Background/Purpose: Surgical neonates are at risk of sepsis-associated live r dysfunction. Hydrogen peroxide (H2O2) and nitric oxide (NO) are important mediators of sepsis, which impair neonatal hepatic metabolism. Glutamine h as been shown to have beneficial effects on hepatocyte metabolism during ne onatal sepsis. However, the molecular basis of these effects are unknown. T he aim of this study was to test the hypotheses that (1) glutamine and its dipeptides counteract the inhibitory effect of septic mediators on neonatal hepatocyte oxygen consumption and (2) the effects of glutamine are specifi c and not shared by other amino acids. In addition, we wished to determine the metabolic pathways and mediators involved in the action of glutamine. Methods: Hepatocytes were isolated from suckling rats, and O-2 consumption measured polarographically. Study A: the ability of 10 mmol/L glutamine to reverse the inhibitory effects of 1.5 mmol/L H2O2 and 300 mu mol/L S-Nitros o-N-acetylpenicillamine (SNAP; a nitric oxide donor) on O-2 consumption was examined. Study B: the ability of other amino acids and dipeptides of glut amine to reverse the effects of H2O2 was examined. Study C: various concent rations of glutamine were tested for their ability to reverse the H2O2 inhi bition of O-2 consumption. Study D: the mechanism of action of glutamine wa s examined by incubating hepatocytes with either an inhibitor of entry into the Krebs cycle or an inhibitor of glutathione synthesis. Study E: the abi lity of glutathione to reverse the inhibitory effects of H2O2 was examined. Results: Study A: glutamine reversed the inhibition of hepatocyte O-2 consu mption exerted by either H2O2 or NO. Study B: glutamine dipeptides reversed the inhibition of hepatocyte O-2 consumption by H2O2, but other amino acid s did not. Study C: the counteracting effect of glutamine was proportional to the dose administered. Study D: blocking entry of glutamine into the Kre bs cycle did not abolish the effects of glutamine, but blocking glutathione synthesis completely abolished the effect of glutamine. Study E: exogenous glutathione reversed the inhibitory effect of H2O2 on hepatocyte O-2 consu mption. Conclusions: This study found that glutamine and its dipeptides are unique in reversing the effects of septic mediators on neonatal rat liver oxidativ e metabolism. The effectiveness of glutamine appears to be mediated via glu tathione synthesis. Addition of glutamine, glutamine dipeptides, or glutath ione to total parenteral nutrition (TPN) may be beneficial in preventing li ver damage in neonatal sepsis. Copyright (C) 2001 by W.B. Saunders Company.