Cordyceps cicadae polysaccharides ameliorate ulcerative colitis by modulating the gut microbiota and regulating the bile acid/FXR/NF-κB signaling pathway.

BACKGROUND: Ulcerative colitis (UC) is a chronic, relapsing inflammatory bowel disease, closely linked to dysbiosis of the intestinal microbiota and abnormal bile acid homeostasis. Polysaccharides derived from Paecilomyces cicadae (CCP) exhibit immunomodulatory and anti-inflammatory effects. However, their therapeutic potential and underlying mechanisms in UC remain poorly elucidated.

PURPOSE: This research seeks to evaluate the therapeutic efficacy of CCP in the treatment of UC and utilizing the "microbiota-bile acid metabolism-immunity" axis, elucidates the mechanisms by which CCP enhances intestinal barrier integrity and ameliorates inflammation via modulation of the gut microbiota-mediated farnesoid X receptor (FXR)/NF-κB signaling pathway.

METHODS: The physicochemical properties of CCP were characterized by FTIR spectroscopy, HPLC, and SEM analyses. A dextran sulfate sodium (DSS)-induced colitis mouse model was used to evaluate the ameliorative effects of CCP. Gut microbial alterations were profiled by 16S rDNA sequencing, while targeted metabolomics enabled comprehensive quantification of bile acid profiles in serum and fecal samples. Fecal microbiota transplantation (FMT) was conducted to validate the microbiota-mediated actions of CCP. Downstream molecular mechanisms were examined using Western blotting and immunofluorescence assays to assess modulation along the microbiota-bile acid axis.

RESULTS: CCP is primarily composed of glucose, mannose, and galactose, exhibiting a characteristic polysaccharide structure with a uniform molecular weight distribution. Treatment with CCP significantly ameliorated DSS-induced colitis in mice, as evidenced by reduced weight loss, preserved colon length, and decreased histopathological damage. 16S rDNA analysis demonstrated CCP-driven restoration of intestinal microbial diversity and a marked increase in Clostridium Kas107-2 (cluster XIVa). Metabolomics revealed normalization of bile acid metabolism, with elevated synthesis of secondary bile acids (deoxycholic acid, lithocholic acid, 12-keto LCA) and reduced levels of primary bile acids (α/β-MCA). Mechanistically, CCP activated FXR signaling, suppressed IκBα phosphorylation, downregulated NF-κB signaling, and reduced production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6). Enhanced expression of tight junction proteins (ZO-1, Occludin, Claudin-1) indicated improved epithelial barrier function. Notably, FMT from CCP-treated donors replicated these protective effects, confirming colitis attenuation, bile acid restoration, and inhibition of FXR/NF-κB signaling.

CONCLUSIONS: CCP ameliorate experimental UC by promoting the proliferation of Clostridium cluster XIVa, modulating bile acid metabolism to facilitate secondary bile acid biosynthesis, activating FXR pathways, and suppressing NF-κB-driven inflammatory responses, thereby reinforcing intestinal epithelial barrier integrity.