The dietary fibre rhamnogalacturonan improves intestinal epithelial barrier function in a microbiota‐independent manner

• Published in: British journal of pharmacology 2022-01, Vol.179 (2), p.337-352
• Main Authors: Baggio, Cristiane H., Shang, Judie, Gordon, Marilyn H., Stephens, Matthew, Weid, Pierre Yves, Nascimento, Adamara M., Román, Yony, Cipriani, Thales R., MacNaughton, Wallace K.
• Format: Article
• Language: English
• Subjects: Caco-2 Cells; Cell lines; colonoid monolayer; Cytokines; Dextran; Dietary fiber; Dietary Fiber - pharmacology; Electrical resistivity; epithelial barrier; Epithelial cells; Epithelial Cells - metabolism; Fatty acids; Fermented food; Fluorescein isothiocyanate; Humans; Inflammatory bowel diseases; Intestinal microflora; Intestinal Mucosa - metabolism; intestinal permeability; Intestine; Isoforms; Microbiota; Mucosa; Organoids; Permeability; polysaccharide; Polysaccharides; Protein kinase C; Rhamnogalacturonan; Rhamnogalacturonans - pharmacology; Signal transduction; Tight Junctions - metabolism; TLR4; TLR4 protein; Toll-Like Receptor 4 - metabolism; Toll-like receptors
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/bph.15739

Background and Purpose Dietary fibre comprises a complex group of polysaccharides that are indigestible but are fermented by gut microbiota, promoting beneficial effects to the intestinal mucosa indirectly through the production of short chain fatty acids. We found that a polysaccharide, rhamnogalacturonan (RGal), from the plant Acmella oleracea, has direct effects on intestinal epithelial barrier function. Our objective was to determine the mechanism whereby RGal enhances epithelial barrier function. Experimental Approach Monolayers of colonic epithelial cell lines (Caco‐2, T84) and of human primary cells from organoids were mounted in Ussing chambers to assess barrier function. The cellular mechanism of RGal effects on barrier function was determined using inhibitors of TLR‐4 and PKC isoforms. Key Results Apically applied RGal (1000 μg ml−1) significantly enhanced barrier function as shown by increased transepithelial electrical resistance (TER) and reduced fluorescein isothiocyanate (FITC)‐dextran flux in Caco‐2, T84 and human primary cell monolayers, and accelerated tight junction reassembly in Caco‐2 cells in a calcium switch assay. RGal also reversed the barrier‐damaging effects of inflammatory cytokines on FITC‐dextran flux and preserved the tight junction distribution of occludin. RGal activated TLR4 in TLR4‐expressing HEK reporter cells, an effect that was inhibited by the TLR4 inhibitor, C34. The effect of RGal was also dependent on PKC, specifically the isoforms PKCδ and PKCζ. Conclusion and Implications RGal enhances intestinal epithelial barrier function through activation of TLR4 and PKC signalling pathways. Elucidation of RGal mechanisms of action could lead to new, dietary approaches to enhance mucosal healing in inflammatory bowel diseases.