Development of a Systematic Approach to Identify Metabolites for Herbal Homologs Based on Liquid Chromatography Hybrid Ion Trap Time-of-Flight Mass Spectrometry: Gender-Related Difference in Metabolism of Schisandra Lignans in Rats

Metabolic research for herbal medicine (HM) is a formidable task, which is still in its infancy due to complicated components in HM, complex metabolic pathways, and lack of authentic standards. The present work contributes to the development of a powerful technical platform to rapidly identify and classify metabolites of herbal components based on a liquid chromatography hybrid ion trap time-of-flight mass spectrometry. Taking Schisandra lignans extract as an example, the metabolic studies were completed both in vitro and in vivo. In the in vitro study, metabolites for five representative Schisandra lignans were identified and structurally characterized. The major metabolic pathways were summed as demethylation, hydroxylation, and demethylation and hydroxylation. In the in vivo study, 44 metabolites were detected in rat urine. These metabolites were identified and classified rapidly according to the metabolic rules obtained in the in vitro studies, and hydroxylation was confirmed as the primacy metabolic pathway for lignans in rat urine. In addition, "relative cumulative excretion" (RCE) for the metabolites in female and male rats were calculated according to their relative intensities in the urine samples collected at 0 to 12, 12 to 24, and 24 to 36 h. As a result, great gender-related difference on RCE was observed. For most metabolites, RCE in female rats was significantly lower than that in male rats. In conclusion, the presently developed methodology and approach on metabolic research for Schisandra lignans will find its wide use in metabolic studies for herbal medicines.