Background and objective: Inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis, is a chronic inflammatory disorder characterized by aberrant immune responses and compromised barrier function in the gastrointestinal tract. IBD is associated with altered gut microbiota and their metabolites in the colon. Butyrate, a gut microbial metabolite, plays a crucial role in regulating immune function, epithelial barrier function, and intestinal homeostasis. In this review, we aim to present an overview of butyrate synthesis and metabolism and the mechanism of action of butyrate in maintaining intestinal homeostasis and to discuss the therapeutic implications of butyrate in IBD. Methods: We searched the literature up to March 2023 through PubMed, Web of Science, and other sources using search terms such as butyrate, inflammation, IBD, Crohn’s disease, and ulcerative colitis. Clinical studies in patients and preclinical studies in rodent models of IBD were included in the summary of the therapeutic implications of butyrate. Results: Research in the last two decades has shown the beneficial effects of butyrate on gut immune function and epithelial barrier function. Most of the preclinical and clinical studies have shown the positive effect of butyrate oral supplements in reducing inflammation and maintaining remission in colitis animal models and IBD patients. However, butyrate enema showed mixed effects. Butyrogenic diets, including germinated barley foodstuff and oat bran, are found to increase fecal butyrate concentrations and reduce the disease activity index in both animal models and IBD patients. Conclusions: The current literature suggests that butyrate is a potential add-on therapy to reduce inflammation and maintain IBD remission. Further clinical studies are needed to determine if butyrate administration alone is an effective therapeutic treatment for IBD.
Background and Aims
Exclusive enteral nutrition (EEN) with a liquid diet is the only established dietary treatment for Crohn’s’ disease (CD). However, the mechanism of action of EEN in CD is unclear. T helper 17 (Th17) immune response plays a critical role in CD. We hypothesized that EEN alleviates Th17 response by eliminating mechanical stress–induced expression of Th17-polarizing cytokines.
Methods
A rat model of Crohn’s-like colitis was established by intracolonic instillation of TNBS (65 mg/kg in 250 µL of 40% ethanol). Control rats were treated with saline. We characterized immunophenotypes and molecular changes of the colon in control and colitis rats with and without EEN treatment. Th17 differentiation was determined using coculture assays.
Results
TNBS instillation induced transmural inflammation with stenosis in the inflammation site and a marked increase of Th17-polarizing cytokines interleukin (IL)-6 and osteopontin and the Th17 cell population in the mechanically distended preinflammation site (P-site). EEN treatment eliminated mechanical distention and the increase of IL-6, osteopontin, and Th17 response in the P-site. IL-6 and osteopontin expression was found mainly in the muscularis externa. Mechanical stretch of colonic smooth muscle cells in vitro induced a robust increase of IL-6 and osteopontin. When naïve T cells were cultured with conditioned media from the P-site tissue or stretched cells, Th17 differentiation was significantly increased. Inhibition of IL-6, but not deletion of osteopontin, blocked the increase of Th17 differentiation.
Conclusions
Mechanical stress induces Th17-polarizing cytokines in the colon. EEN attenuates Th17 immune response by eliminating mechanical stress–induced IL-6 in Crohn’s-like colitis.
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