Oral administration of low‐molecular‐weight heparin ameliorates colitis by enhancing the gut mucus barrier via microbial tryptophan metabolites

BACKGROUND AND PURPOSE: Previous studies have reported that oral low-molecular-weight heparin (LMWH) ameliorated colitis by undefined mechanisms in ulcerative colitis (UC) patients. Our study explored the mechanisms of LMWH on colitis from the perspective of gut microbiota and its metabolites. EXPERIMENTAL APPROACH: Dextran sulfate sodium (DSS; 2.5%) was used to induce colitis in mouse model, and LMWH was administered by either oral gavage, intracolonic delivery or subcutaneous injection to compare their therapeutic effects. Pseudo-germ-free mice was established by using antibiotic cocktail, and faecal microbial transplantation (FMT) was performed to verify the role of microbiota in LMWH actions. Alcian blue staining, fluorescence in situ hybridization of EUB338 and immunohistochemical staining were performed to evaluate the integrity of gut mucus barrier. Amplicon sequencing, transcriptome sequencing and untargeted metabolome studies were used to explore LMWH mechanisms. The ameliorating effect of indole-3-propionic acid (IPA) was verified in vitro and in vivo. KEY RESULTS: Oral, but not subcutaneous, administration of LMWH alleviated colitis and enhanced the gut mucus barrier. Pseudo-germ-free mice and FMT assays confirmed that therapeutic effects of oral LMWH were dependent on gut microbiota. Oral LMWH increased Firmicutes abundance and decreased Escherichia/Shigella abundance, subsequently increasing microbial tryptophan metabolites, especially IPA. The protective effects of oral LMWH were reproduced by IPA supplementation, with mucus barrier enhancing through regulating the Wnt/β-catenin pathway. CONCLUSION AND IMPLICATIONS: The results provide new insights into the signalling mechanisms associated with the therapeutic potential of LMWH in colitis, and highlight the application of IPA for UC treatment.