Simultaneous determination of resibufogenin and its eight metabolites in rat plasma by LC-MS/MS for metabolic profiles and pharmacokinetic study

Background: Resibufogenin is one of the main active compounds of Venenum Bufonis and exhibits diverse pharmacological activities. It is brought into focus for its potency in heart failure and cancer therapy. Purpose: The purpose of this study was to establish a convenient and effective method which was used to simultaneously determine the resibufogenin and its metabolites in rat plasma for further understanding the metabolic profiles of resibufogenin in vivo and pharmacokinetic study by LC-MS/MS. Methods: The analytes were separated on a BEH C18 column with a mobile phase of water containing 0.05% formic acid and acetonitrile under gradient elution at a flow rate of 0.4 ml/min. Resibufogenin and its eight metabolites were quantified in positive electrospray ionization and MRM mode with transitions of m/z 385.5 -> 349.2 for resibufogenin; m/z 513.7 -> 145.3 for IS (internal standard); m/z 401.23 -> 365.21, m/z 417.23 -> 285.21 and m/z 385.24 -> 349.21 for three main metabolites (hydroxylated-resibufogenin; dihydroxylated-resibufogenin and 3-epi-resibufogenin, respectively). Results: This method was successfully validated with a good linearity over the concentration ranges of 1-200 ng/ml for resibufogenin and the correlation coefficients was more than 0.990. The lower limit of quantification was 1 ng/ml and the precision and accuracy values were less than 15%. The method was applied to study the metabolic profiles of resibufogenin in rat plasma after oral administration of 20 mg/kg. The results indicated that the metabolic reactions of resibufogenin were mainly hydroxylation, dihydroxylation, dehydrogenation and isomerization. Totally eleven metabolites were identified, among which eight were successfully quantified. Conclusion: The results could provide further research foundation for the mechanisms study of activity and toxicity in vivo and facilitate the appropriate clinical application of resibufogenin.