A7 AN INULIN-TYPE FRUCTAN ENRICHED EXCLUSIVE ENTERAL NUTRITION FORMULA MODULATES THE GUT MICROBIOME AND PROMOTES EXPANSION OF ANTI-INFLAMMATORY T CELL SUBSETS TO SUPPRESS COLITIS

Abstract Background Exclusive enteral nutrition (EEN), a nutritionally complete fiber-free enteral formula, is the gold standard therapy for newly diagnosed children with Crohn’s disease (CD) but this therapy is not routinely used in pediatric ulcerative colitis patients due to lower efficacy in this subgroup. EEN therapy leads to high remission rates, however it also leads to a dysbiotic gut microbiota profile and disease relapse occurs in 60–80% of CD patients within 12 months of EEN discontinuation. Little is known about the mechanisms underlying the actions of EEN. Notably, previous studies have demonstrated that prebiotics, such as inulin-type fructans (IN), can beneficially modulate the gut microbiome, increase butyrate production and reduce inflammation by leading to anti-inflammatory T cell (i.e. FOXP3+IL10+ CD4+) expansion. To date, the effects of an IN enriched EEN (EEN IN) have not been studied. Aims To examine the effects of EEN vs EEN IN on colitis development, the gut microbiome and CD4+ T cell subsets using an adoptive T cell transfer model of colitis. Methods Mice were split into four groups: 1) Control – normal chow + PBS (n=13; negative control), 2) Chow – normal chow + naive T cell transfer (n=13; positive control), 3) EEN – Ensure Plus® + naive T cell transfer (n=13) and 4) EEN IN – Ensure Plus® with 3% IN + naive T cell transfer (n=13). Naïve T cells (or PBS) were transferred into TCR-b deficient mice and each group was started on their subsequent diets. The naïve T cells will expand into anti- or pro-inflammatory T cells subsets to either cause or suppress colitis in a gut microbiome dependent manner. Body weight and disease activity were monitored for 5-weeks. At the end of the experiment, spleen weights and colon lengths were recorded. Spleen and mesenteric/colonic lymph nodes (MLN) were collected for T cell subset analysis using flow cytometry. Gut microbiota differences were assessed using ddPCR. Short-chain fatty acid levels were analyzed using gas chromatography. The histopathology of the distal colon was scored. Results Mice fed EEN IN showed a reduction in colonic shortening (p<0.001) and histology scores (p=0.0088) compared to EEN mice, and reduced disease activity (p=0.0046) compared to Chow mice. Moreover, EEN IN mice showed a higher expansion of FOXP3+IL10+ CD4+ T cells in the MLN (p=0.0424) and spleen (p=0.0088). EEN IN also led to higher butyrate, Bifidobacterium and Bacteroides concentrations compared to EEN (p=0.0113, p=0.0063, p=0.0224; respectively) and Chow (p=0.0252, p=0.0042, p=0.0416; respectively). Conclusions EEN IN lead to superior outcomes compared to EEN and Chow. These results provide evidence to support undertaking a clinical trial utilizing EEN IN in pediatric inflammatory bowel disease patients. Funding Agencies Michael Smith Foundation for Health Research

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