A sensitive LC-MS/MS method for simultaneous quantification of geniposide and its active metabolite genipin in rat plasma and its application to a pharmacokinetic study.

Genipin (GP), an active metabolite of geniposide (GE), exhibits more potent pharmacological effects than its parent compound. In this paper, a sensitive LC-MS/MS method was developed and fully validated for the simultaneous determination of GE and GP in rat plasma. We found that GP degraded rapidly in rat plasma at room temperature as a result of irreversible binding with the endogenous nucleophiles in plasma. GP was stable when the sample's pH was ≤4.0. The degradation of GP in rat plasma was well prevented by immediate addition of 5% glacial acetic acid to the freshly collected plasma. The detection was performed on a tandem mass spectrometer coupled with electrospray ionization source in negative mode. Quantification was conducted by multiple reaction monitoring of the transitions [M + CH3 COO]- m/z 447.3 → 225.3 for GE and [M - H]- m/z 225.2 → 123.1 for GP. The method exhibited high sensitivity (LLOQ 1 ng/mL for GE and 0.2 ng/mL for GP) by selecting the acetate adduct ions as the precursor ions for GE. The robust developed method was successfully applied to a pharmacokinetic study in rats after oral administration of GE.