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Characterization of Metabolic Pathways and Absorption of Sea Cucumber Saponins, Holothurin A and Echinoside A, in Vitro and in Vivo.

Sea cucumber saponins (SCSs) exhibit a wide spectrum of bioactivities, but their metabolic characteristics are not well elucidated. In this study, the metabolism of holothurin A (HA) and echinoside A (EA), 2 major saponins in sea cucumber, by gut microflora were investigated. First, we conducted an in vitro study, where in the SCSs were incubated with intestinal microflora and the metabolites were detected by high pressure liquid chromatography-high resolution mass spectrometry. We also conducted an in vivo study on rats, where in the intestinal contents, serum, urine, and feces were collected and evaluated after oral administration of SCSs. In the in vitro study, we identified 6 deglycosylated metabolites of HA and EA, assigned M1-M6. In the in vivo study, we found all the deglycosylated metabolites in the intestinal contents after oral administration, and both the metabolites and their prototype components could be absorbed. Four metabolites were identified in the serum, 6 in the urine, and 4 in the feces. The saponins with different structures showed different absorption characteristics in rats. According to our results, deglycosylation is the main intestinal microflora-mediated metabolic pathway for SCSs, and both the SCSs and deglycosylated metabolites can be absorbed by intestine. This study improves the understanding of the metabolism of HA and EA by gut flora, which will be useful for further analysis of the bioactivity mechanism of SCSs.