A practical strategy for the characterization of ponicidin metabolites in vivo and in vitro by UHPLC-Q-TOF-MS based on nontargeted SWATH data acquisition.

Ponicidin is an active natural ent-kaurane diterpenoid ingredient originating from many Isondon herbs and is expected to become a new anticancer agent. In this study, a practical strategy was developed for the identification of ponicidin metabolites in vivo and in vitro utilizing ultra-high-performance liquid chromatography coupled with hybrid triple quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS). The analytical strategy was as follows: potential ponicidin metabolites were detected by a novel on-line data acquisition approach, i.e., sequential window acquisition of all theoretical fragment-ion spectra (SWATH™). Compared to the traditional information-dependent acquisition (IDA) method, SWATH™ significantly improved the hit rate of low-level or trace metabolites because it could obtain all MS/MS spectra. Moreover, many data post-processing methods were used to deduce the metabolites structures. As a result, a total of 20 metabolites were characterized in vivo and in vitro. The results showed that ponicidin could undergo general metabolic reactions, such as oxidation, reduction, hydrolysis, methylation and glucuronidation. Furthermore, there was an obvious difference in the ponicidin metabolites among four species in vitro. This is the first time that the SWATH™ data acquisition mode has been used to characterize ponicidin metabolites in trace amounts or in a biological matrix. These results not only provided a better understanding of the safety and efficacy of ponicidin but also showed a valuable methodology for the identification of other ent-kaurane diterpenoid metabolites.