β-1,3-glucans from Euglena Gracilis protects against ulcerative colitis via modulating the gut barrier, T-cell immunity and gut microbiota.

Ulcerative colitis (UC) is characterized by impaired gut barrier, dysregulated immune responses and pronounced gut dysbiosis. Euglena gracilis (EG), rich in β-1,3-glucan (EGP), exhibits immunomodulatory properties, yet its effects on colitis and EGP's role as a core bioactive component are unclear. The aim of this study was to investigate the protective effects of EGP against UC by targeting gut barrier, T-cell immunity and gut microbiota. Results indicated that EG and EGP effectively improved the body weight, colon growth and reduced disease activity index of the DSS-induced mice. Both treatments also significantly suppressed the level of TNF-α and IL-6, restored gut barrier by upregulating ZO-1 and balanced Th17/Treg cells ratio. Microbiota analysis revealed EG and EGP reshaped gut microbiota composition, with an increase in beneficial strains, particularly within the Bacteroidota phylum. Metabolomics linked these changes to enhanced amino acid metabolism. Bacteroides fragilis, a Bacteroidota member, displayed similar anti-colitis bioactivity. In vitro fermentation with fecal samples from UC patients confirmed EGP's role in reshaping gut microbiota, increasing beneficial families such as Clostridiaceae and Lactobacillaceae, while enhancing tryptophan metabolism with anti-inflammatory indoles. These findings identify EGP as the core active component of EG, highlighting its potential in UC prevention through microbiota modulation, gut barrier support and immune regulation.