Structural characterization of a polysaccharide isolated from Allium macrostemon Bunge bulbus and its mechanism in ameliorating DSS-induced ulcerative colitis in mice.

A polysaccharide (AMP) was isolated and purified from the bulbus of Allium macrostemon Bunge (AMB) and structurally characterized. AMP, with the weight-average molecular weight of 9.007 kDa, is a branched polysaccharide with a main chain composed of →1)-β-D-Fruf-(2→ and →1,6)-β-D-Fruf-(2→ linkages, with short side chains formed by β-D-Fruf-(2 → 6)-β-D-Fruf-(2→. AMP administration effectively mitigated DSS-induced ulcerative colitis (UC) in mice by reinforcing the integrity of the intestinal barrier, balancing gut microbiota, replenishing short-chain fatty acids (SCFAs) levels, and restoring normal metabolic activity in the colon. AMP treatment decreased the harmful bacterial, including Bacteroides, Escherichia-Shigella, Parabacteroides, and the Clostridia vadinBB60 cluster, while increasing beneficial SCFAs-producing such as Ruminococcus and the Christensenellaceae R-7 group. Fecal microbiota transplantation experiments further demonstrated that AMP exerted its anti-colitis effect through a microbiota-dependent manner. In addition, in vitro fermentation experiment showed that AMP can be translated to SCFAs by gut microbiota. Meanwhile, AMP regulated metabolic pathways such as the glycerophospholipid, arachidonic acid, and linoleic acid metabolism in colon tissue. The acute toxicity test showed AMP possesses a wide safety margin. Collectively, our data highlight AMP as a promising functional food component for the prevention of UC, and provide a scientific basis for developing AMP-derived bioactive products.