In Vitro and in Vivo Studies of the Metabolic Activation of 8-Epidiosbulbin E Acetate

Furanoid 8-epidiosbulbin E acetate (EEA) is a major constituent of herbal medicine Dioscorea bulbifera L. (DB), a traditional Chinese medicine herb. Our preliminary studies demonstrated that administration of EEA caused acute hepatotoxicity in mice, and the observed toxicity required cytochromes P450-mediated metabolism. Metabolic activation studies of EEA were performed in vitro and in vivo. Microsomal incubations of EEA supplemented with N-acetyl lysine (NAL) and glutathione (GSH) generated six metabolites (M1-M6). M1-M4 were characterized as pyrrole derivatives, and M5 and M6 were pyrrolinones. M2-M6 were detected in bile and/or urine of rats given EEA. Dimethyldioxirane-mediated oxidation of EEA in the presence of NAL and GSH produced M1-M6, all of which were generated in microsomal incubations. The structures of M3 and M6 were confirmed by H-1 and C-13 NMR. These findings provide evidence for the metabolic activation of EEA to the corresponding cis-enedial intermediate both in vitro and in vivo. Ketoconazole inhibited the microsomal production of the cis-enedial, and P450 3A4 was found to be the primary enzyme involved in the bioactivation of EEA.