tert.-Butyl hydroperoxide metabolism and stimulation of the pentose phosphate pathway in isolated rat hepatocytes

Abstract

The metabolism of tert.-butyl hydroperoxide (TBHP) by the glutathione peroxidase/reductase system in isolated hepatocytes results in the rapid depletion of reduced glutathione and NADPH. The regeneration of NADPH can occur through the pentose phosphate pathway, but only when the pathway is stimulated, for example, by NADP+ and possibly oxidized glutathione, both of which can be elevated in hepatocytes exposed to TBHP. TBHP is a cytotoxicant and the role of NADPH and the pentose phosphate pathway in protecting hepatocytes from TBHP-induced injury is unknown. Isolated rat hepatocytes exposed to TBHP (0.5 mM) for 30 min metabolized more [1-14C]glucose to 14CO2 than control (638.2 +/- 96.2 vs 306.9 +/- 69.5 dpm/10(6) cells) whereas 14CO2 evolution from [6-14C]glucose was unchanged, indicating that TBHP increases the activity of the pentose phosphate pathway and not glycolysis. TBHP (0.25 mM) metabolism also resulted in a rapid oxidation of hepatocyte NADPH from 2.85 +/- 0.32 to 0.55 +/- 0.24 nmol/10(6) cells which rapidly returned to 3.58 +/- 0.27 nmol NADPH/10(6) cells. Inhibition of the pentose phosphate pathway with 6-aminonicotinamide (70 mg/kg; 5 hr prior to hepatocyte isolation) inhibited TBHP-stimulated 14CO2 evolution from [1-14C]glucose and decreased the rate of NADP+ reduction. Hepatocytes isolated from 6-aminonicotinamide-treated animals were more susceptible to TBHP-induced cell injury than were control hepatocytes. These data demonstrate the following: The metabolism of TBHP by isolated hepatocytes stimulated the activity of the pentose phosphate pathway; and inhibition of the pentose phosphate pathway with 6-aminonicotinamide potentiated the toxicity of TBHP to isolated rat hepatocytes. These results suggest that the regeneration of NADPH by the pentose phosphate pathway may play a significant role in protecting hepatocytes from TBHP-induced damage.