# A14 SACCHAROMYCES BOULARDII CNCM I-745 SYNERGIZES WITH THE SMALL INTESTINAL MICROBIOTA TO BOOST AHR SIGNALING IN CELIAC DISEASE

## TL;DR

This study shows that the probiotic Saccharomyces boulardii CNCM I-745 helps reduce intestinal damage in celiac disease by boosting a key receptor pathway linked to gut health.

## Contribution

The study identifies a specific mechanism by which a probiotic synergizes with gut microbiota to enhance AhR signaling in celiac disease.

## Key findings

- S. boulardii CNCM I-745 increased AhR activation and reduced intestinal inflammation in gluten-sensitized mice.
- The probiotic improved tryptophan metabolism and indole production in both mouse and human microbiota cultures.
- Combining S. boulardii with L. reuteri further enhanced AhR activation in celiac patient microbiota.

## Abstract

Impaired microbial indole production and decreased activation of the aryl hydrocarbon receptor (AhR) pathway has been reported in active coeliac disease (CeD). However, whether and how this can be targeted by specific microbial therapies is unknown.

We tested whether Saccharomyces boulardii CNCM I-745 (S. bou) influences indole production and AhR activation through stimulation of microbial enzymatic activity.

Transgenic NOD/DQ8 mice were immunized with partially digested gliadin and cholera toxin weekly for 3 weeks followed by gluten challenges (10 mg; alternate days/ 3 weeks). Non-sensitized mice were used as controls. Mice were treated daily with 3 g/kg of S. bou or water during the study. Additional immunized mice treated or not with S. bou, received daily gavage with AhR antagonist CH-223191 (10 mg/kg) or vehicle. Small intestinal pathology was analyzed by villus to crypt (V/C) ratios and CD3+ intraepithelial lymphocyte (IEL) counts. Expression levels of the AhR-activated gene Cyp1a1 were determined by RT-qPCR. Small intestinal microbiota of NOD/DQ8 mice and CeD patients were cultured in BHI media with and without 1x106  S. bou CFUs or 1x108  Lactobacillus reuteri (L. reuteri) CFUs. Free tryptophan levels, AhR activation, and total protein degradation were assayed using a commercial kit, a transfected reporter cell line, and an enzymatic assay respectively. Resulting microbiota was assessed by 16S rRNA gene sequencing and PICRUSt-predicted functions.

S. bou increased Cyp1a1 levels, protein degradation, mucosal tryptophan and AhR activation in gluten immunized mice, paralleled by improved V/C ratios and lower IELS vs no probiotic, which was inhibited by AhR antagonist. In immunized mice treated with S. bou, microbiota analysis revealed lower PICRUSt-predicted tryptophan 2,3-dioxygenase genes, a tryptophan degrader. Mouse duodenal microbiota cultures treated with S. bou had higher total protein degradation, higher tryptophan levels and AhR activation vs cultured with no probiotic. In duodenal microbiota cultures from CeD patients the combination of S. bou and L. reuteri increased AhR activation vs cultures without S. bou.

S. bou CNCM I-745 reduced gluten immunopathology in immunized NOD/DQ8 mice through activation of the AhR pathway. In vitro experiments suggest S. bou synergizes with the microbiota to increase free tryptophan from protein sources and inhibit tryptophan degradation, leading to higher indole production and AhR activation. The results identify a specific mechanistic pathway by S. bou CNCM I-745 in celiac disease and should encourage clinical testing in this population.

CIHRBiocodex, France