Metabolite identification of gut microflora-cassia seed interactions using UPLC-QTOF/MS

Cassia seed is the dried ripe seed of Cassia obtusifolia L. or Cassia tora L., which is widely used as a food or traditional Chinese medicine. The aim of the present study was to detect the components and metabolites in the culture of human or rat intestinal microflora suspension with the water decoction of cassia seed in vitro, using an ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry system equipped with a negative ion scan mode. Initially, ellagic acid was identified in the cassia seed decoction. Subsequently, six different metabolites, including urolithin (uro)-A, uro-B, uro-D, uro-M6, uro-M7 and uro-B-glucuronide (glur), were detected after co-culture of the cassia seed decoction with intestinal microflora, but not in the cassia seed decoction alone. Uro-M6, uro-M7, uro-A and uro-B were common metabolites in the culture of human or rat intestinal microflora suspension with the water decoction of cassia seed. However, uro-D was only detected in the culture of rat intestinal microflora suspension with the water decoction of cassia seed, and uro-B-glur was only detected in the culture of human intestinal microflora with the water decoction of cassia seed. The uro and intermediate metabolites were produced by ellagic acid in the cassia seed decoction under the action of the intestinal microflora. The production of metabolites might be related to the abundance and diversity of the intestinal microflora in humans and rats. The present study provided rationale for further pharmacological and clinical studies on the mechanisms of action of cassia seeds.