Microbial transformation of three bufadienolides by Penicillium aurantigriseum and its application for metabolite identification in rat

Eighteen strains of filamentous fungi (from nine genera) were screened for their capabilities to transform three major bufadienolides, cinobufagin (1), bufalin (2) and resibufogenin (3), from the traditional Chinese medicine Chan Su. Penicillium aurantigriseum AS 3.4512 was found to be the most potent strain to transform these compounds into in vivo metabolites in rat. Ten transformation products were obtained with high yield and identified using chromatographic and spectral means. Among them, six products were found to be same with the in vitro metabolites transformed by rat liver microsome. Three compounds were the major in vivo metabolites of 1, 2 and 3, respectively. Compound 3a was a firstly reported metabolite of 3 in vivo. All of these suggested the bioconversion of 1, 2 and 3 by P. aurantigriseum were very similar with the metabolism of them in vivo, and these transformed products could be used as the reference standards to investigate the mammalian metabolism of bufadienolides.