Abstract

Recent studies have shown that cytochrome P450 2E1 (CYP2E1) is a major catalyst of formation of trifluoroacetylated proteins, which have been implicated as target antigens in the mechanism of halothane hepatitis. In the present investigation, trifluoroacetylated CYP2E1 was detected immunochemically in livers of rats treated with halothane. Furthermore, high levels of autoantibodies that recognized purified rat CYP2E1 but not purified rat CYP3A were detected by enzyme-linked immunosorbent assay in 14 of 20 (70%) sera from patients with halothane hepatitis. Only very low levels of such antibodies were detected in sera from healthy controls, from patients anesthetized with halothane without developing hepatitis, or from patients with other liver diseases. The intracellular distribution of CF3CO-adducts was studied in highly differentiated FGC4 rat hepatoma cell cultures. High levels of adducts were found after 22-hr culture in the presence of halothane, and their generation was dependent on the expression of CYP2E1. Adducts were predominantly located in the endoplasmic reticulum but also, to a minor extent, on the cell surface, as detected by immunofluorescence. A very similar distribution was found for CYP2E1 in FGC4 cells, and immunoprecipitation experiments performed in cultures of FGC4-related Fao hepatoma cells suggest that surface immunoreactivity originates from a small fraction of intact CYP2E1 apoprotein. Human CYP2E1, expressed in V79 cells after cDNA transfection, was also detected to a minor extent in the plasma membrane, whereas no immunofluorescence was evident in parental V79 cells. It is suggested that immune responses to cell surface CYP2E1 could be involved in the pathogenesis of halothane hepatitis.