(W1030-06-40) Gastrointestinal Digestion and Fermentation of Astragalus membranaceus Polysaccharides

Purpose: Previous studies reported that gut microbiota was involved in the hypoglycemic effect of Astragalus membranaceus polysaccharides (AMP) ^[1]. Although the regulation potential of AMP on disordered gut microbiota community of diabetic mice has been identified ^[2], few literatures investigated the metabolic process of AMP in the gastrointestinal tract of diabetic condition. The current project aimed to illustrate such process of AMP via monitoring its chemical alteration during the simulated digestion and fermentation process in the gastrointestinal tract.

Methods: AMP was prepared and subject to an in-vitro digestion and fermentation system to simulate its alteration in gastrointestinal tract. First, AMP was digested by simulated gastric fluid and intestinal fluid sequentially followed by monitoring its changes in total sugar level and reducing sugar level during the whole digestion process. Then the digested AMP sample was lyophilized and fermented with fecal slurry from db/db mice in the anerobic environment at 37℃ for 48h followed by monitoring the chemical alteration of AMP in terms of its total sugar level, monosaccharide composition and molecular weight distribution analysis. In addition, the changes in gut microbiota composition during fermentation process was analyzed by 16s-rRNA sequencing method. Furthermore, the impact of AMP on three short chain fatty acids (acetic acid, propanoic acid and butyric acid) level during fermentation process was monitored by GC-MS.

Results: The total sugar level of AMP remained unchanged during the whole digestion process (Figure 1A). The reducing sugar level of AMP also exhibited no significant alteration during gastric digestion while it was increased significantly during simulated small intestinal digestion (Figure 1B). During the fermentation process with fecal slurry from db/db mice, it was found that the total sugar level of AMP was significantly decreased with only 11.3%±1.1% remained after 48h fermentation (Figure 2A). Monosaccharide composition analysis indicated that our prepared AMP was comprised of mannose, rhamnose, galacturonic acid, galactose, glucose and arabinose. All these monosaccharides except mannose could be utilized significantly by gut microbiota (Figure 2B). Molecular weight distribution analyses showed that the macromolecular peak of AMP (about 550 KDa) was absent after 48 h fermentation, suggesting that the sugar chain of AMP might be broken during such process. Further 16s-rRNA analyses revealed that gut microbiota composition could also be regulated by AMP. Short chain fatty acids analyses (Figure 2C) showed that all the three short chain fatty acids in AMP fermentation fluid were increased significantly (p < 0.001), suggesting that AMP might be utilized by gut microbiota and lead to increased formation of short chain fatty acids.

Conclusion: Although AMP has no obvious alteration after gastric digestion, it was significantly utilized by gut microbiota with increased formation of short chain fatty acids in the intestinal fermentation process.

References: 1. Liu, Y. M., Liu, W., Li, J., Tang, S., Wang, M. J. & Gao, X. D. (2019). A polysaccharide extracted from Astragalus membranaceus residue improves cognitive dysfunction by altering gut microbiota in diabetic mice 205(1), 500–512. https://doi.org/10.1016/j.carbpol.2018.10.041
2. Song, Q., Cheng, S. W., Li, D., Cheng, H., Lai, Y. S., Han, Q., Wu, H. Y., Shaw, P. C., & Zuo, Z. (2022). Gut microbiota mediated hypoglycemic effect of Astragalus membranaceus polysaccharides in db/db mice. Frontiers in Pharmacology, 13. 1043527. https://doi.org/10.3389/fphar.2022.1043527

Acknowledgements:Li Dak Sum Yip Yio Chin R & D Center for Chinese Medicine at The Chinese University of Hong Kong.

Alterations of total sugar content (A) and reducing sugar content (B) of AMP during the digestion process

Alterations of total sugar level (A), monosaccharide composition (B) and short chain fatty acids level (C) of AMP fermentation fluid