20(S)-Protopanaxadiol (PPD), a dammarane-type triterpenoid sapogenin, acts as the pharmacophore of ginsenosides which are considered as the principal bioactive components in Chinese ginseng. To fully understand the mechanism of action of PPD, it is important to study its metabolic profiles in vivo.
Plasma, urine, fece and bile were collected after administration of PPD formulated in 0.5% aqueous Tween-80 to rats (150 mg/kg). Samples were analyzed by using a sensitive and reliable method based on ultra-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UPLC/Q-TOF-MS/MS) in both positive and negative ion mode. The chemical structures of metabolites were elucidated by comparing the retention time, accurate molecular mass, and fragmentation patterns of analytes with those of PPD.
In total 29 metabolites, including 10 new metabolites (M20–M29), were tentatively identified and characterized. Among them, two metabolites (M3 and M4) were unambiguously identified by matching their retention times and fragmentation patterns with their standards. Principal metabolites, namely, 20, 24-oxide metabolites (M3 and M4), 26/27-carboxylic acid derivatives (M22 and M23) and a glucuronidated product (M28), were found in the rat plasma.
The results showed that phase I metabolites are monooxygenation, dioxygenation and oxidative dehydrogenation metabolites, and phase II metabolic pathways were demonstrated to be cysteine conjugation and glucuronidation. The newly identified metabolites are useful to understand the mechanism of elimination of PPD and, in turn, its effectiveness and toxicity.