Structural characteristics of oligosaccharides obtained from Undaria pinnatifida polysaccharides and their alleviation of colitis by modulating macrophage polarization and gut microbiota

Undaria pinnatifida oligosaccharides (UPO) are recognized for their multifaceted bioactive properties. Nevertheless, further investigation is required to establish the protective effects of UPO in mitigating UC. In this study, the structural characteristics of UPO were elucidated as 1,4-linked α-L-fucopyranose units with minor 1,2-linked β- d -galactopyranose units through NMR spectroscopy. UPO treatment improved the structural integrity of the intestinal barrier in DSS-induced colitis mice. Additionally, UPO administration induced the polarization of macrophages towards the anti-inflammatory M2 phenotype, evidenced by the downregulation of M1 macrophage marker (CD68) and upregulation of M2 macrophage marker (CD163). UPO treatment, significant alterations in the composition and diversity of bacterial and fungal microbiota were observed compared to colitis mice. UPO boosted the concentrations of short-chain fatty acids in fecal samples. These findings indicate that UPO could alleviate DSS-induced colitis in mice, potentially offering insights into its application as a novel therapeutic option for colitis treatment.