Protopanaxatriol metabolites identified by LC-MS/MS after oral administration in mice.

Objective: 20(S)-Protopanaxatriol (Ppt), a well-known end metabolite of protopanaxatriol-type saponins, has recently been reported to have the same bioactivity as its prototype. Whether or not Ppt could be further metabolized into other compounds in vivo is still unknown. The present study is aimed to determine the structures of Ppt metabolites in mice. Materials: The metabolites were produced by intragastric gavage of Ppt in mice. The homogenate of small intestine was used for analysis after solid phase extraction. Methods: The metabolic profile of Ppt was investigated by using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), which were also used to identify the structures of metabolites. Accurate mass measurement using LC-time of flight MS was applied to determine the element composition of metabolites and thus to confirm their proposed structures. Results: One Phase I and three Phase II metabolites were detected at 1 h, 5 h, and 10 h after administration of Ppt, which were the same at the three time points. The Phase I metabolic changes observed included dehydrogenation and hydroxylation of the steroid-like structure, as well as formation of an ester bond at C-20 of the side chain. The Phase II metabolites involved conjugation to aminoethyl-sulfonic acid after hydrolysis of the ester bond. A possible biotransformation pathway was proposed. Conclusions: Ppt yielded four metabolites in vivo, and 1 h was enough to complete the biotransformation process of Ppt.