Effects of Rifampin on the Glutathione Depletion and Cytochrome c Reduction by Acetaminophen Reactive Metabolites in an In Vitro P450 Enzyme System

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The present study examined whether rifampin attenuated glutathione(GSH)depletion by acetaminophen reactive metabolites generated in the in vitro P450 enzyme system prepared from mouse liver and the possible mechanism involved in this effect.The results showed that GSH concentration was decreased concentration−dependently by acetaminophen in the in vitro P450 enzyme system.Rifampin significantly attenuated acetaminophen−mediated GSH depletion in a concentration−dependent manner.The concentration−response curve for GSH depletion of acetaminophen was shifted to the right in a parallel fashion in the presence of rifampin at the concentration of 3.2×10^-5 M, which appeared to result from the competitive binding of rifampin to acetaminophen metabolites.Cytochrome c was markedly reduced by acetaminophen metabolites in this enzyme system, and GSH concentration−dependently increased the cytochrome c reduction by acetaminophen metabolites.These findings suggested that cytochrome c was reduced by the GSH conjugate of acetaminophen metabolites rather than by acetaminophen−derived superoxide anion(O₂^·-)and other unbound free radicals.Rifampin was shown to possess an effect similar to that of GSH.It is concluded that the decrease in GSH depletion by rifampin is most likely attributable to the binding of rifampin to the acetaminophen toxic species, and the increase in cytochrome c reduction by rifampin is attributable to the conjugate formed between rifampin and acetaminophen metabolites.