Polysaccharides from Er Chen Decoction: gastrointestinal fate, gut microbiota modulation and metabolomics

Er Chen Decoction (ECD), a classical formula for phlegm-related disorders, contains polysaccharides (PECD) as an important bioactive fraction. This study systematically assessed their gastrointestinal absorption, digestive stability, fecal fermentation, and correlations with gut microbiota and metabolic changes.

In vivo gastrointestinal absorption of PECD were evaluated using fluorescence tracing of fluorescein isothiocyanate (FITC)-labeled polysaccharides. The stability of PECD during simulated oral, gastric, and intestinal digestion was assessed by determining total/reducing sugar contents, molecular weight distribution, monosaccharide composition, and Fourier transform infrared spectra. Subsequently, in vitro fecal fermentation of PECD was evaluated by pH, short-chain fatty acids (SCFAs), 16S rRNA gene sequencing, and untargeted metabolomics.

No appreciable systemic absorption of FITC-labeled PECD was detected following gastrointestinal administration. During simulated digestion, the total sugar and reducing sugar contents, molecular weight distribution, monosaccharide composition, and infrared spectral profiles of PECD showed no significant changes, suggesting that its major polysaccharides were largely resistant to upper gastrointestinal digestion. During in vitro fecal fermentation, PECD was progressively utilized by the gut microbiota, accompanied by a reduction in pH and an increase in SCFAs concentrations. PECD supplementation was also associated with shifts in microbial community composition by enriching genera such as Bifidobacterium and Mitsuokella, while depleting others including Klebsiella and Bilophila. Untargeted metabolomic analysis revealed alterations in metabolites related to phenylalanine metabolism, caffeine metabolism, and arginine biosynthesis, suggesting their potential involvement in microbial response to PECD.

PECD exhibited limited absorption, resistance to upper gastrointestinal digestion, susceptibility to fecal microbial fermentation, which altered microbial composition, SCFAs, and metabolic profiles, supporting its further study as a candidate bioactive polysaccharide.