Involvement of Cytochrome P-450 in n-Butyl Nitrite-Induced Hepatocyte Cytotoxicity

      Addition of n-butyl nitrite to isolated rat hepatocytes caused an immediate glutathione depletion followed by an inhibition of mitochondrial respiration, inhi- bition of glycolysis and ATP depletion. At cytotoxic butyl nitrite concentrations, lipid  peroxidation  occurred  before  the  plasma  membrane  was  disrupted. Cytochrome P-450 inhibitors inhibited peroxynitrite formation and prevented butyl nitrite-induced mitochondrial respiration inhibition, ATP depletion, lipid peroxidation and plasma membrane disruption. However, glutathione depletion, S-nitroso-glutathione (GSNO) formation, or the inhibition of glycolysis was not affected by cytochrome P-450 inhibitors. Glutathione-depleted hepatocytes were resistant to butyl nitrite which suggests that cytotoxicity and peroxynitrite forma- tion results from GSNO formation. Peroxynitrite formation was also inhibited by reactive oxygen scavengers. These findings suggest that cytochrome P-450 iso- forms (particularly CYP2E1) act as a source of superoxide anion radicals in the formation of cytotoxic peroxynitrite from nitric oxide.