Neonatal oxidative liver metabolism: effects of hydrogen peroxide, a putative mediator of septic damage

BACKGROUND/PURPOSE: Surgical neonates are at risk for sepsis and liver dysfunction. These complications are more common in preterm neonates and in those who receive total parenteral nutrition. Elevated levels of reactive oxygen species (eg, hydrogen peroxide) have been reported in these "at-risk" patients and may be the mediators of liver impairment via their effect on oxidative energy metabolism. The aim of this study was to test the hypothesis that elevated levels of hydrogen peroxide (H2O2) impair neonatal liver oxidative energy metabolism. METHODS: An in vitro model to test this hypothesis was developed in hepatocytes isolated from neonatal (11-day to 15-day) rats. The cells, respiring on palmitate (0.5 mmol/L in 2% bovine serum albumin), were exposed to H2O2. Oxygen consumption was measured polarographically. In experiment A, H2O2 was added to the cell preparation at different concentrations (0.5 mmol/L, 1 mmol/L, 1.5 mmol/L, 2 mmol/L) to assess the effect on oxygen consumption. In experiment B, H2O2 (2 mmol/L) was added to hepatocytes in the presence of inhibitors of mitochondrial respiration to define the site of action of H2O2. In experiment C, electron microscopy was performed on hepatocytes after incubation with 1 mmol/L and 2 mmol/L of H2O2. RESULTS: In experiment A, H2O2 significantly reduced hepatocyte oxygen consumption at 1.5 and 2 mmol/L. In experiment B, in the presence of inhibitors of mitochondrial respiration, myxothiazol (inhibitor of substrate oxidation), and oligomycin (inhibitor of adenosine triphosphate (ATP) synthase), no further inhibition by H2O2 occurred, indicating that the effect of H2O2 was intramitochondrial and affecting the synthesis of ATP. In experiment C, microscopic alterations of mitochondria were noticed exclusively in hepatocytes incubated with 2 mmol/L H2O2. CONCLUSIONS: Results of this study demonstrate that H2O2 impairs neonatal liver oxidative metabolism. H2O2 probably directly inhibits ATP synthase. The authors hypothesize that H2O2 may play a role in the biochemical pathogenesis of liver dysfunction associated with sepsis. Identification of the precise target site of H2O2 may be valuable in directing therapy in septic neonates.