Modulation of Intestinal Epithelial Barrier Function by Rhamnogalacturonan
Authors: Baggio Cristiane Hatsuko , Lopes Fernando , Nascimento Adamara , Cipriani Thales , McKay Derek , MacNaughton Wallace 
Published: November 2023

Background

The Inflammatory Bowel Diseases (IBD) are chronic inflammatory disorders of the gastrointestinal tract and are associated with changes in intestinal epithelial barrier function. However, despite several effective therapeutic options, many patients become refractory to the treatment and adverse effects have been reported. For this reason, the development of new drugs targeting the epithelial barrier function is essential. Recently, polysaccharides isolated from plants and fungi have emerged as an important class of natural products with immunomodulatory, anti‐inflammatory and wound healing activity. Previous studies showed that rhamnogalacturonan (RGal), a polysaccharide isolated from Acmella oleracea, protected mice against colitis induced by dextran sulfate sodium (DSS). However, the exact mechanism of action of RGal are not fully clarified. We hypothesized that RGal modulates the intestinal epithelial barrier function and assessed the signaling pathways involved in RGal effect.

Methods

Human colonic epithelial Caco‐2 cells were seeded on Snapwells, grown for 6 days, and mounted in Ussing chambers to measure the epithelial barrier function [transepithelial electrical resistance (TER) and FITC‐dextran permeability]. Cells were apically treated with RGal (10–1000 μg/ml) after 30 min of FITC‐dextran addition. In a calcium‐switch assay, the epithelial monolayers were temporarily exposed to zero calcium conditions (calcium‐free buffer containing the calcium chelator, EGTA) to disassemble tight junctions. RGal (10–1000 μg/ml) was added during calcium‐free conditions. The FITC‐dextran permeability was also evaluated in Caco‐2 cells stimulated with IFNg plus TNF‐a (25 ng/ml, basolateral) and treated with RGal (1000 μg/ml, apical) every 24 h for 48 h. To evaluate the signaling pathways, the cells were pre‐treated with selective inhibitors of MEK1/2, p38 or PI3K 30 minutes before RGal addition.

Results

Apical addition of RGal at concentration of 1000 μg/ml significantly increased TER in 185% and caused a 64% reduction in FITC‐dextran flux compared to control group. In addition, RGal also was able to accelerate the tight junction reassembly in 155% during a reversible barrier disruption induced by calcium depletion. When the barrier disruption was caused by cytokines, RGal (1000 μg/ml) significantly reduced the FITC‐dextran flux by 33 and 24% at 30 and 60 min, respectively. However, the signaling pathway inhibitors did not reverse the RGal effect on TER suggesting that MAPkinase and PI3K pathways were not involved.

Conclusions

These findings demonstrated that RGal increases intestinal epithelial barrier function which appears to be due to effects on tight junction assembly. Further experiments will be carried out to determine the tight junction proteins and signaling pathways are involved in the RGal effect. Elucidation of RGal mechanisms of action could lead to new approaches to the treatment of IBD.

Support or Funding Information

Dr. Baggio is supported by an Eyes High postdoctoral fellowship from the University of Calgary. Her research project is funded by a grant from Crohn's and Colitis Canada.