1β-Hydroxydeoxycholic Acid as an Endogenous Biomarker in Human Plasma for Assessment of CYP3A Clinical Drug-Drug Interaction Potential

4β-Hydroxycholesterol (4β-HC) in plasma has been used as a biomarker to assess CYP3A drug-drug interaction (DDI) potential during drug development. However, due to the long half-life and narrow dynamic range of 4β-HC, its use has been limited to the identification of CYP3A inducers, but not CYP3A inhibitors. The formation of 1β-hydroxydeoxycholic acid (1β-OH DCA) from deoxycholic acid (DCA) is mediated by CYP3A, thus 1β-OH DCA can potentially serve as an alternative to 4β-HC for assessment of CYP3A DDI potential. To study this feasibility, we developed a sensitive LC-MS/MS method for the simultaneous quantitation of 1β-OH DCA and its glycine and taurine conjugates in human plasma with the LLOQ of 50 pg/mL, which enabled the quantitation of basal levels and further reduction. The method was applied to a DDI study to assess how 1β-OH DCA and its glycine and taurine conjugates would respond to CYP3A induction or inhibition. Rifampin induction resulted in an increase of 1β-OH DCA and its conjugates in plasma, with 6.8-, 7.8-, 8.3-, 10.3-fold increases of AUC