Effects of rifampin on the glutathione depletion and cytochrome c reduction by acetaminophen reactive metabolites in an in vitro P450 enzyme system

The present study examined whether rifampin attenuated glutathione (GSH) de pletion by acetaminophen reactive metabolites generated in the in vitro P45 0 enzyme system prepared from mouse liver and the possible mechanism involv ed in this effect. The results showed that GSH concentration was decreased concentration-dependently by acetaminophen in the in vitro P450 enzyme syst em. Rifampin significantly attenuated acetaminophen-mediated GSH depletion in a concentration-dependent manner. The concentration-response curve for G SH depletion of acetaminophen was shifted to the right in a parallel fashio n in the presence of rifampin at the concentration of 3.2 x 10(-5) M, which appeared to result from the competitive binding of rifampin to acetaminoph en metabolites. Cytochrome c was markedly reduced by acetaminophen metaboli tes in this enzyme system, and GSH concentration-dependently increased the cytochrome c reduction by acetaminophen metabolites. These findings suggest ed that cytochrome c was reduced by the GSH conjugate of acetaminophen meta bolites rather than by acetaminophen-derived superoxide anion (O-2(.-)) and other un bound free radicals. Rifampin was shown to possess an effect simi lar to that of GSH. It is concluded that the decrease in GSH depletion by r ifampin is most Likely attributable to the binding of rifampin to the aceta minophen toxic species, and the increase in cytochrome c reduction by rifam pin is attributable to the conjugate formed between rifampin and acetaminop hen metabolites.