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 dysf unction. These complications are more common in preterm neonates and in tho se who receive total parenteral nutrition. Elevated levels of reactive oxyg en species (eg, hydrogen peroxide) have been reported in these "at-risk" pa tients and may be the mediators of liver impairment via their effect on oxi dative energy metabolism. The aim of this study was to test the hypothesis that elevated levels of hydrogen peroxide (H2O2) impair neonatal liver oxid ative energy metabolism. Methods: An in vitro model to test this hypothesis was developed in hepatoc ytes isolated from neonatal (11-day to 15-day) rats. The cells, respiring o n palmitate (0.5 mmol/L in 2% bovine serum albumin), were exposed to H2O2. Oxygen consumption was measured polarographically. In experiment A, H2O2 wa s 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 o f inhibitors of mitochondrial respiration to define the site of action of H 2O2 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 cons umption at 1.5 and 2 mmol/L. In experiment B, in the presence of inhibitors of mitochondrial respiration, myxothiazol (inhibitor of substrate oxidatio n), and oligomycin (inhibitor of adenosine triphosphate (ATP) synthase), no further inhibition by H2O2 occurred, indicating that the effect of H2O2 wa s intramitochondrial and affecting the synthesis of ATP. In experiment C, m icroscopic alterations of mitochondria were noticed exclusively in hepatocy tes incubated with 2 mmol/L H2O2 Conclusions: Results of this study demonstrate that H2O2 impairs neonatal l iver oxidative metabolism. H2O2 probably directly inhibits ATP synthase. Th e authors hypothesize that H2O2 may play a role in the biochemical pathogen esis of liver dysfunction associated with sepsis. Identification of the pre cise target site of H2O2 may be valuable in directing therapy in septic neo nates. J Pediatr Surg 34:1107-1111. Copyright (C) 1999 by W.B. Saunders Com pany.