A4 <i>SACCHAROMYCES BOULARDII</i> CNCM I-745 ENHANCES DUODENAL MICROBIOTA-MEDIATED TRYPTOPHAN METABOLISM IMPROVING GLUTEN IMMUNOPATHOLOGY

Abstract Background 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. Aims We tested whether Saccharomyces boulardii CNCM I-745 (Sbou) influences indole production and AhR activation through stimulation of microbial enzymatic activity. Methods 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 Sbou or water during the study. Additional immunized mice treated or not with Sbou, received daily gavage with AhR antagonist CH-223191 (10 mg/kg) or vehicle. Small intestinal pathology was analysed 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 supplemented with 10 g/L Gelatin or Casein as additional protein sources with and without 1x106Sbou CFUs. Free tryptophan and AhR activation were assayed using a commercial kit and a transfected reporter cell line, respectively. Resulting microbiota was assessed by 16S rRNA gene sequencing and PICRUSt-predicted functions. Results Sbou increased Cyp1a1 levels, mucosal tryptophan and AhR activation in gluten immunized mice. This was paralleled by improved V/C ratios and lower IELs vs no probiotic, which was inhibited by AhR antagonist. In immunized mice treated with Sbou microbiota analysis revealed higher expression of genes involved in protein digestion and lower tryptophan 2,3-dioxygenase, a tryptophan degrader. Mouse duodenal microbiota cultures treated with Sbou had higher proteolytic activity but lower tryptophan 2,3-dioxygenase, paralleled by higher tryptophan vs cultures with no probiotic. In duodenal microbiota cultures from CeD patients Sbou increased tryptophan vs no probiotic. Conclusions S. boulardii CNCM I-745 reduced gluten immunopathology in immunized NOD/DQ8 mice through activation of the AhR pathway. In vitro experiments suggest Sbou synergises 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. boulardii CNCM I-745 in celiac disease and should encourage clinical testing in this population. Funding Agencies CIHRBiocodex, France