Isolation and identification of phase I metabolites of resibufogenin in rats

Abstract

1. Resibufogenin (1), a major bufadienolide of Chinese medicine Chan Su, had a wide range of pharmacological activities. In present work, the metabolism of 1 in male Sprague-Dawley rats was investigated by identifying the metabolites of resibufogenin excreted in rat bile.

2. Following an oral dose of 60 mg/kg resibufagenin, nine metabolites were isolated from bile of rats, and their structures were identified as 3-keto- resibufogenin (2), 3-epi-resibufogenin (3), 5β-hydroxy-3-epi-resibufogenin (4), 1α, 5β-dihydroxy-3-epi-resibufogenin (5), 3α, 5β, 14α, 15β-tetrahydroxyl-bufa- 20, 22-dienolide (6), 3α, 14α, 15β-trihydroxy-bufa-20, 22-dienolide (7), 3-epi- 5β-hydroxy-bufalin (8), 12α, 16β-dihydroxy-3-epi-resibufogenin (9), and 5β, 16β-dihydroxy-3-epi-resibufogenin (10), respectively, on the basis of widely spectroscopic methods including 2D-NMR technology. It is first time to describe the metabolites of 1 in vivo, and metabolites 5–7 and 9–10 are novel.

3. On the basis of these identified metabolites, a possible metabolism pathway for 1 in rats has been proposed. This is the first systematic study on the phase I metabolites of resibufogenin.

Keywords::

• Resibufogenin
• bufadienolide
• metabolites
• hydroxylation

Acknowledgments

We thank National Natural Science Foundation of China (30701088, 81274047 and 81202589), Education Department of Liaoning Province (LS2010059) and Program for Liaoning Excellent Talents in University (LJQ2011095) for financial support.