Determination of the metabolic profile of gentianine after oral administration to rats by high performance liquid chromatography/electrospray ionization-trap mass spectrometry

• The metabolic fate of gentianine in rats was investigated for the first time.
• Four new metabolites of gentianine in rat plasma were identified.
• Gentianine together with its metabolites in plasma were quantified.
• The metabolic pathway of gentianine in rats was proposed.

We investigated the metabolic fate of gentianine after oral administration to Wistar rats for the first time. Liquid chromatography/ion trap mass spectrometry detected four metabolites secogentianoxide, gentiandiol, gentianepoxide and gentianoxide in rat plasma together with the original compound gentianine. The structures of the metabolites were identified by comparing the retention times, as well as MS (mass) and MS/MS (tandem mass) spectra with those of authentic compounds, which were synthesized from gentianine or isolated from the urine. Three of the metabolites, secogentianoxide, gentianepoxide and gentianoxide, are novel compounds. The major in vivo metabolic processes associated with gentianine include N-oxide, epoxidation, dihydroxylation of double bond and hydrolysis of lactone. Gentianine together with the metabolites in plasma were quantified using gentianone as the internal standard. The mean Cmax of G0, G1, G2 and G3 are 425.76, 287.56, 188.45 and 85.05 ng/mL, respectively. The mean Tmax of G0, G1, G2 and G3 are 1.16, 3.87, 6.23 and 4.28 h, respectively. The mean T1/2 of G0, G1, G2 and G3 are 5.23, 12.34, 7.78 and 5.64 h, respectively. A comprehensive metabolic pathway was proposed. The new metabolites may shed light on clinical efficacy of gentianine.