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

Abstract

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.

Higher dietary fibre intake is associated with lower risk of inflammatory bowel disease: prospective cohort study

“…Dietary fibre from fruit and vegetable sources tends to be mainly composed of soluble fibres which were reported to improve intestinal epithelial barrier function. 24 Fermentable fibres are soluble fibres without viscosity that are metabolised by anaerobic bacteria and produce SCFA. 3 This is an important anti-inflammatory metabolite that inhibits NFκβ and reduces the transcription of pro-inflammatory mediators.…”

“…Several mechanisms may explain the protective role of specified sources of dietary fibre intake in IBD prevention. Dietary fibre from fruit and vegetable sources tends to be mainly composed of soluble fibres which were reported to improve intestinal epithelial barrier function 24 . Fermentable fibres are soluble fibres without viscosity that are metabolised by anaerobic bacteria and produce SCFA 3 .…”

Xylobiose treatment strengthens intestinal barrier function by regulating claudin 2 and heat shock protein 27 expression in human Caco‐2 cells

“…Therefore, the sensory mechanism must be located at the apical membrane of intestinal epithelial cells. Previous studies have shown that other NDSs, such as pectin and rhamnogalacturonan, stimulate TLRs to exert biological effects, including anti‐inflammatory and barrier effects in intestinal epithelial cells 12,13 . Further studies are required to elucidate the sensory mechanisms of xylobiose.…”

“…10 The physiological functions of nondigestible saccharides (NDSs), including xylobiose and XOS, are often exerted through the production of short-chain fatty acids by gut microbiota, 11 and recent studies have demonstrated that NDSs directly interact with the intestinal epithelium to regulate cellular functions. For example, rhamnogalacturonan has been reported to enhance intestinal epithelial barrier function by stimulating toll-like receptor (TLR)-4, 12 and pectin directly interacts with TLR2-TLR1 receptors to reduce intestinal inflammation in mice. 13 However, the direct effects of xylobiose on intestinal epithelial cells, specifically with regard to intestinal barrier function, are unknown.…”

Structure and function of non-digestible carbohydrates in the gut microbiome

“…This research emphasises the potential of knowledge still to be gathered on the function of oligomer structures derived from RG-I molecules. Baggio et al (2022) reported that RG-l enhances intestinal epithelial barrier function in a microbiota-independent manner through activation of TLR4 and PKC signalling pathways. The authors suggested that RG-I may be implemented in dietary approaches to enhance mucosal healing in inflammatory bowel diseases).…”