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Guts and Gall: Bile Acids in Regulation of Intestinal Epithelial Function in Health and Disease.
Hegyi, P, Maléth, J, Walters, JR, Hofmann, AF, Keely, SJ
Physiological reviews. 2018;98(4):1983-2023
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Plain language summary
Bile acids are bioactive bacterial metabolites which recent research shows may be helpful in protecting the epithelial cells which line the entire surface of the gastrointestinal tract. Many conditions such as inflammatory bowel disease, chronic diarrhoea, pancreatitis, reflux esophagitis, and cancer are influenced by the integrity of the intestinal lining and/or disruption of epithelial transport; the movement of digestive enzymes, nutrients, electrolytes, and fluids. Bile acids are now being further studied as a new target for therapies to help these conditions. Typically, bile acids help with the digestion of fats. These acids are created in the liver and stored in the gall bladder and transported throughout the small and large intestines where they support the cells in the intestinal lining. This is the same lining which acts as a barrier to external pathogens and toxins. All the conditions above appear to show alterations in bile acid activity indicating a role for therapeutic targeting of bile acids in intestinal disease. This may include dietary manipulation, probiotics and fecal transfers to support bile acid production and function.
Abstract
Epithelial cells line the entire surface of the gastrointestinal tract and its accessory organs where they primarily function in transporting digestive enzymes, nutrients, electrolytes, and fluid to and from the luminal contents. At the same time, epithelial cells are responsible for forming a physical and biochemical barrier that prevents the entry into the body of harmful agents, such as bacteria and their toxins. Dysregulation of epithelial transport and barrier function is associated with the pathogenesis of a number of conditions throughout the intestine, such as inflammatory bowel disease, chronic diarrhea, pancreatitis, reflux esophagitis, and cancer. Driven by discovery of specific receptors on intestinal epithelial cells, new insights into mechanisms that control their synthesis and enterohepatic circulation, and a growing appreciation of their roles as bioactive bacterial metabolites, bile acids are currently receiving a great deal of interest as critical regulators of epithelial function in health and disease. This review aims to summarize recent advances in this field and to highlight how bile acids are now emerging as exciting new targets for disease intervention.
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Interplay of host genetics and gut microbiota underlying the onset and clinical presentation of inflammatory bowel disease.
Imhann, F, Vich Vila, A, Bonder, MJ, Fu, J, Gevers, D, Visschedijk, MC, Spekhorst, LM, Alberts, R, Franke, L, van Dullemen, HM, et al
Gut. 2018;67(1):108-119
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Patients with inflammatory bowel disease (IBD) present with a variety of clinical characteristics, making prevention, diagnosis and therapy very complex. Based on recent studies, it is hypothesised that the heterogeneity among patients with IBD is likely due to individual differences in the interaction between the host genome and gut microbiota. The aim of this case-control study was to analyse the gut microbiota, host genetics and clinical characteristics of 313 patients with IBD compared with 582 healthy controls. This extensive analysis has identified the gut microbiota as the key mediator in the development of IBD through new associations at the genetic and clinical level. Based on these findings, the authors conclude that a better understanding of gene-microbiota interactions can lead to new therapeutics and improved prevention strategies.
Abstract
OBJECTIVE Patients with IBD display substantial heterogeneity in clinical characteristics. We hypothesise that individual differences in the complex interaction of the host genome and the gut microbiota can explain the onset and the heterogeneous presentation of IBD. Therefore, we performed a case-control analysis of the gut microbiota, the host genome and the clinical phenotypes of IBD. DESIGN Stool samples, peripheral blood and extensive phenotype data were collected from 313 patients with IBD and 582 truly healthy controls, selected from a population cohort. The gut microbiota composition was assessed by tag-sequencing the 16S rRNA gene. All participants were genotyped. We composed genetic risk scores from 11 functional genetic variants proven to be associated with IBD in genes that are directly involved in the bacterial handling in the gut: NOD2, CARD9, ATG16L1, IRGM and FUT2. RESULTS Strikingly, we observed significant alterations of the gut microbiota of healthy individuals with a high genetic risk for IBD: the IBD genetic risk score was significantly associated with a decrease in the genus Roseburia in healthy controls (false discovery rate 0.017). Moreover, disease location was a major determinant of the gut microbiota: the gut microbiota of patients with colonic Crohn's disease (CD) is different from that of patients with ileal CD, with a decrease in alpha diversity associated to ileal disease (p=3.28×10-13). CONCLUSIONS We show for the first time that genetic risk variants associated with IBD influence the gut microbiota in healthy individuals. Roseburia spp are acetate-to-butyrate converters, and a decrease has already been observed in patients with IBD.