Biotransformation and metabolic profile of Xian-Ling-Gu-Bao capsule, a traditional Chinese medicine prescription, with rat intestinal microflora by ultra-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry analysis

Xian-Ling-Gu-Bao capsule (XLGB), a well-known traditional Chinese medicine prescription, has been used for the prevention and treatment of osteoporosis. The safety and efficacy of XLGB have been confirmed based on the principle of evidence-based medicine. XLGB is usually administered orally, after which its multiple components are brought into contact with intestinal microflora in the alimentary tract and biotransformed. However, investigations on the comprehensive metabolic profile of XLGB are absent. In this study, 12 representative compounds bearing different typical structures (including iridoid glycosides, prenylated flavonol glycosides, prenylated flavonoids, triterpenoid saponins, steroidal saponins, coumarins and monoterpene phenols) were selected and then investigated for their biotransformation in rat intestinal microflora. In addition, the metabolic profile of XLGB in rat intestinal microflora was investigated by ultra-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry. As a result, a total of 87 biotransformation components were identified from incubated solutions of 12 representative compounds and XLGB, which underwent 16 metabolic reactions (including deglycosylation, glycosylation, dehydrogenation, hydrogenation, oxidation, epoxidation, hydroxylation, dehydration, hydration, hydrolysis, methylation, isomerization, cyclization, pyrolysis reaction, amino acid conjugation and nucleophilic addition reaction with NH3). This demonstrated that the deglycosylation reaction by cleavage of the sugar moieties is the main metabolic pathway of a variety of glycosides, including prenylated flavonol glycosides, coumarin glycosides, iridoid glycosides and saponins. In addition, compared with the biotransformation of 12 representative compounds, a different biotransformed fate was observed in the XLGB incubated samples of rat intestinal microflora. It is worth noting that the amino acid conjugation was first discovered in the metabolism of prenylated flavonol glycosides in rat intestinal microflora.