Identification of ginkgolide B metabolites in urine and rat liver cytochrome P450 enzymes responsible for their formation in vitro

Aim: To identify metabolites of ginkgolide B in rat urine, the predominant metabolism of ginkgolide B and the major cytochrome (CYP) P450 enzymes responsible for the metabolism of ginkgolide B in rat liver microsomes. Methods: A liquid chromatography quadrupole mass spectrometer and liquid chromatography ion-trap-time-of-fight mass spectrometer with electrospray ionization in negative-ion mode were used for the structure elucidation of metabolites in rat urine and liver microsome incubation. Various selective CYP450 inhibitors were applied to investigate their effects on the metabolism of ginkgolide B and the formation of the major metabolite in rat liver microsomes. Results: Three metabolites were identified in rat urine. One hydroxyl metabolite of ginkgolide B were identified in rat liver microsomes, and quinidine uncompetitively inhibited the formation of the metabolite; its inhibitor constant (K-i) value for the inhibition of hydroxyl metabolite was estimated to be 8 mu mol/L, while alpha-naphthoflavone, ketoconazole, sulfaphenazole, and diethyldithiocarbamate had no inhibitory effects. Conclusion: Ginkgolide B was metabolized to its hydroxyl metabolite in rats, and CYP2D6 was the major rat CYP isoform responsible for the ginkgolide B metabolism in rat liver microsomes.