Interaction of Ethanol with Enflurane Metabolism and Toxicity: Role of P450IIE1

Administration of enflurane (EF), a widely‐used anesthetic agent, sooetimes results in occult liver injury. As hepatic cytochromes P450 oxidize EF to a reactive intermediate, we assessed whether one such microsomal enzyme, ethanol‐inducible P450IIE1, plays an obligatory role in EF metabolic activation and hepatotoxicity. Liver microsomes from rats fed ethanol (36% of total calories for 14 days) oxidized 1 mm EF (measured by its defluorination) at rates nearly 10‐fold greater than those from control rats, reflecting the markedly enhanced content of immunoreactive microsomal P450IIE1 in the former animals. P450IIE1 involvement in hepatic EF oxidation was further suggested by the pronounced inhibition of microsomal defluorination noted with P450IIE1 antibodies and with ethanol, a specific substrate for this enzyme. EF administration to rats treated chronically with ethanol caused significant elevations in plasma levels of aspartate and alanine aminotransferases and glutamate dehydrogenase, indicative of hepatic injury, whereas concurrent treatment of naive rats with EF and ethanol failed to produce the same effect. Our results imply that ethanol‐inducible P450IIE1 is the primary catalyst of hepatic EF bioactivation and that the increased bioactivation occurring in vivo secondary to chronic ethanol consumption is attendant with an increased incidence of EF hepatotoxicity.