Bile Acids In Colon Research Articles

The role of the colonic microbiota and bile acids in colorectal cancer.

Colorectal cancer (CRC) is the third most common cancer and the second most common cause of cancer-related deaths. Of the various established risk factors for this aggressive condition, diet is a notable modifiable risk factor. This review aims to summarize the mounting evidence to suggest the role of diet, the microbiota and their cross-talk in modulating an individual's risk of developing CRC. Specifically, the metabolism of bile acids and its symbiosis with the microbiota has gained weight given its basis on a high meat, high fat, and low fibre diet that is present in populations with the highest risk of CRC. Bacteria modify bile acids that escape enterohepatic circulation to increase the diversity of the human bile acid pool. The production of microbial bile acids contributes to this as well. Epidemiological studies have shown that changing the diet results in different levels and composition of bile acids, which has in turn modified the risk of CRC at a population level. Evidence to identify underlying mechanisms have tied into the microbiota-led digestions of various foods into fatty acids that feedback into bile acid physiology as well as modulation of endogenous receptors for bile acids. There is adequate evidence to support the role of microbiota in in the metabolism of bile acids, and how this relates to colorectal cancer. Further work is necessary to identify specific bacteriome involved and their underlying mechanistic pathways.

Folate deficiency enhances the in vitro genotoxicity of bile acids in human colon and liver cells.

Obese subjects have a high baseline of genotoxic stress, but the underlying mechanism is poorly understood. Given that obesity is associated with high bile acids (BA) and low folate, we aimed to determine the interactive effect of folate deficient or supplementation to the genotoxicity and cytotoxicity of BA in human colon and liver cells. NCM460 and L-02 cells were cultured in folate-deficient (22.6 nM) and replete (2260 nM) Roswell Park Memorial Institute (RPMI)-1640 medium with or without 50 μM deoxycholic acid (DCA) or lithocholic acid (LCA) for 7 days. Moreover, these cells were cultured in folate supplemented (5.65, 11.3 and 22.6 μM) and standard (2.26 μM) medium with 200 μM DCA or LCA for 7 days. Genotoxicity and cytotoxicity were measured using the cytokinesis-block micronucleus cytome assay. Our results showed that under folate-replete condition, 50 μM DCA or LCA significantly increased the rate of micronuclei (MN) in NCM460 and L-02 cells. Significantly, the MN-inducing effect of 50 μM DCA or LCA was further enhanced by folate deficiency. Interestingly, folate supplementation exerted a dose-dependent manner to significantly decrease the rates of MN, nucleoplasmic bridges, nuclear buds, apoptosis, and necrosis induced by 200 μM DCA or LCA in NCM460 and L-02 cells. In conclusion, the genotoxicity of moderate BA (50 μM) was exacerbated by folate deficiency and folate supplementation could efficiently protect cells against the genotoxicity and cytotoxicity of high BA (200 μM).

Bile Acid Diarrhea in Adults and Adolescents.

Bile acids are central to enterohepatic signaling pathways activated through natural receptors, farnesoid X receptor [FXR mediates synthesis of fibroblast growth factor-19 (FGF-19)], and G protein-coupled bile acid receptor 1 (GPBAR1, also known as TGR5). Although bile acid diarrhea (BAD) is more commonly encountered in ileal resection or disease, there is evidence documenting "idiopathic" BAD in about 20% of adolescents and 30% of adults presenting with chronic, non-bloody diarrhea often attributed to irritable bowel syndrome. Mechanism(s) leading to increased hepatic synthesis and colonic bile acid levels in "idiopathic" BAD include reduced synthesis of FGF-19 by the ileal mucosa, or genetic variation in hepatocyte proteins klotho β and FGF receptor 4 (FGFR4) that mediate negative feedback of bile acid synthesis. The objective of this review is to summarize the diagnosis of BAD in adults and adolescents. In addition to 75 SeHCAT retention for diagnosis of BAD, studies have validated fasting serum 7αC4 and FGF-19, respectively, by-product and inhibitor of hepatic bile acid synthesis, as well as fecal bile acid measurements. These assays are widely available through reference laboratories, and they are being simplified (eg, measurement of primary fecal bile acids in a random stool sample). BAD has also been identified as a co-factor contributing to persistent diarrhea in other diseases in remission including inflammatory bowel disease, microscopic colitis, celiac disease, and neuroendocrine tumors. In summary, advances in diagnosis of BAD provide opportunities for generalists and pediatric and adult gastroenterologists to provide targeted treatment for BAD presenting as chronic non-bloody diarrhea.

The role of bile acids and their TGR5 receptor in irritable bowel syndrome and diarrhoea

This commentary looks at recent findings relating to bile acids in patients with irritable bowel syndrome with diarrhoea (IBS-D). Bile acid diarrhoea is recognised to be a frequent, treatable cause of chronic diarrhoea, with a clinical picture which overlaps IBS-D. In the study - by Wei and colleagues, a large proportion of IBS-D patients were shown to have increased faecal bile acids, and an increase in primary bile acids, reflecting changes in bacterial metabolism. Expression of the colonic membrane bile acid receptor, TGR5, was associated with faecal bile acids and the severity of symptoms.

Deoxycholic Acid Modulates Cell-Junction Gene Expression and Increases Intestinal Barrier Dysfunction in Caco-2 Cell Monolayers

ObjectivesDiet-related obesity is associated with an increased risk of developing intestinal hyperpermeability. High dietary fat intake causes an increase in colonic bile acids (BAs), particularly deoxycholic acid (DCA, secondary BA), which may disrupt the intestinal epithelial barrier. To determine the potential role of bile acids in barrier dysfunction, we hypothesize that DCA modulates the gene expression in multiple cell junction pathways and increases intestinal permeability. MethodsWith a Caco-2 cell intestinal barrier model, we used cell proliferation, PCR array, biochemical, western blotting and immunofluorescent assays to examine the impact of DCA on the integrity of intestinal barrier and gene expression. ResultsHuman intestinal Caco-2 cells were grown in monolayers and challenged with DCA at physiological concentrations (sub mM levels). DCA increased transcellular and paracellular permeability (>30%) via transepithelial electrical resistance and phenol red flux measurements. Similarly, DCA increased intracellular reactive oxidative species production (>1-fold) and accompanied a modification of cellular p38 and ERK1/2 signaling pathways. Further characterization of underlying genes related to epithelial barrier with PCR array analysis identified that 23 genes (in tight junction, focal adhesion, gap junction and adhere junction pathways) were decreased at least 40% in (0.25 mM) DCA-treated Caco-2 cells when compared to untreated cells. Finally, we demonstrated that DCA decreased the protein levels of occludin gene at both cellular tight junction and nucleus in epithelial cells. ConclusionsCollectively, our data suggest that at physiological concentrations, DCA alters the gene expression of multiple pathways related to cell junctions and increases permeability in a Caco-2 intestinal barrier model. These molecular events may represent the underlying mechanistic pathways that are responsible for DCA-induced transcellular and paracellular permeation. Funding SourcesThis work was supported by U.S. Department of Agriculture, Agricultural Research Service, research project 3062-51,000-056–00D.

The Bile Acids Specifically Modulate Colonic MUC2 and Tight Junction Protein Expression in the Human Colon Cancer Cell Line

Abstract Objectives Alterations to mucin secretion and epithelial tight junctions can compromise the ability of the epithelium to act as a barrier for the host to prevent pathogenic attack. Bile acids are synthesized in hepatocytes and released into the intestine, further modified by gut bacteria. Although many studies have investigated the changes of intestinal bile acids in the pathogenesis of various immune disorders, there are few reports about its function in preventing or interventing the dysfunction of the intestinal barrier. In this study, we sought to investigate the effects of the colonic bile acids on MUC2 and tight junction protein expression, which are crucial to colonic barrier. Methods Regulation of MUC2 and tight junction protein expression was assayed in the human colon cancer LS174T and T84 cells. The cells were treated with deoxycholic acid (DCA), lithocholic acid (LCA), 3-oxo-DCA, 3-oxo-LCA, isoDCA and isoLCA (100 μM or 200 μM), respectively. Proliferation of the cells was investigated with the MTT assay. mRNA expression of MUC2, ZO-1, occludin, claudin1 were measured by RT-PCR. Nuclear bile acid receptor FXR and TGR5, toll-like receptors and TLR adaptor MyD88, and genes (CDX2, AGR2, MyD88) related to mucin synthesis and secretion were also measured. Results In comparison with the untreated control, DCA, 3-oxo-DCA, isoDCA and isoLCA (100 μM) significantly upregulated the ZO-1, occludin and bile acid receptor FXR gene expression in the T84 cell. LCA, 3-oxo-LCA and isoLCA upregulated MUC2 expression at 200 μM, but showed no significant effect at 100 μM. DCA only significantly upregulated MUC2 expression at 200 μM, but isoDCA upregulated MUC2 expression independent of concentration in the LS174T cell. The expression of CDX2, AGR2, MyD88 was consistent with MUC2. Conclusions Bile acids at various concentrations specifically modulate MUC2 and tight junction protein expression, and thereby alter the colonic barrier function. This regulatory effect of bile acids could be mediated by activating bile acid receptors FXR. Funding Sources This work was financially supported by Ministry of Science and Technology of China (10000 Talent Project).

Faecal bile acids and colonic bile acid membrane receptor correlate with symptom severity of diarrhoea-predominant irritable bowel syndrome: A pilot study

AimsTo compare both the faecal bile acids (BAs) and the levels of two bile acid receptors, Takeda G protein-coupled receptor 5 (TGR5) and vitamin D receptor (VDR), in the colonic mucosa between patients with irritable bowel syndrome with predominant diarrhea (IBS-D) and healthy controls, and explore the correlations among clinical characteristics, bile acid receptors expression, and BAs. MethodsThe severity of abdominal pain and diarrhoea was assessed in IBS-D patients using validated questionnaires, faecal BAs were measured by ultraperformance liquid chromatography coupled to tandem mass spectrometry, and rectosigmoid biopsies were taken for the analyses of TGR5 and VDR expression using immunohistochemistry. ResultsThe level of TGR5 immunoreactivity in rectosigmoid mucosal biopsies was significantly higher in IBS-D patients than in controls, while the VDR immunoreactivity displayed no significant difference between patients and controls. The patients with more severe or more frequent abdominal pain had significantly higher TGR5 level. Faecal primary BAs were significantly increased in IBS-D patients and were positively correlated with the severity of diarrhoea. The level of TGR5 was positively associated with primary BAs and negatively associated with secondary BAs among all participants providing both mucosal and stool samples. ConclusionsColonic mucosal TGR5 protein expression and faecal bile acids were correlated with the symptom severity of IBS-D patients.

A nonbile acid farnesoid X receptor agonist tropifexor potently inhibits cholestatic liver injury and fibrosis by modulating the gut-liver axis.

Tropifexor (TXR) is a novel nonbile acid that acts as an agonist of farnesoid X receptor (FXR). TXR is currently in Phase 2 trials for the treatment of non-alcoholic steatohepatitis (NASH). Herein, we report the impact of TXR on in a piglet model in which cholestatic liver damage and fibrosis where induced by bile duct ligation (BDL). The piglets received BDL and TXR for 2wk. Hepatic, portal and colonic bile acid and amino acid profiles and gut microbiome were analysed. Portal fibroblast growth factor (FGF) 19 levels were measured using an enzyme-linked immunosorbent assay (ELISA). We first showed that bile acid metabolism and signalling are dysfunctional in patients with biliary atresia. Next, we observed that TXR potently suppresses BDL-induced liver injury, fibrosis and ductular reaction in piglets. Within the ileum, TXR enhances FGF19 expression and subsequently increases portal FGF19 levels. In the liver, TXR promotes the expression of small heterodimer partner (SHP) and inhibits cholesterol 7α-hydroxylase (CYP7A1). Additionally, TXR increases the abundance of bile acid-biotransforming bacteria in the distal ileum and alters the composition of amino acids in the colon. Lastly, TXR ameliorates intestinal barrier injury in piglets subjected to BDL. TXR potently ameliorated cholestatic liver injury and fibrosis by modulating the gut-liver axis in piglets. It supports the clinical evaluation of TXR as a therapeutic strategy for cholestatic liver diseases, such as biliary atresia.

Adequacy of calcium and vitamin D reduces inflammation, β-catenin signaling, and dysbiotic Parasutterela bacteria in the colon of C57BL/6 mice fed a western-style diet

Adoption of an obesogenic diet low in calcium and vitamin D (CaD) leads to increased obesity, colonic inflammation, and cancer. However, the underlying mechanisms remain to be elucidated. We tested the hypothesis that CaD supplementation (from inadequacy to adequacy) may reduce colonic inflammation, oncogenic signaling, and dysbiosis in the colon of C57BL/6 mice fed a Western diet. Male C57/BL6 mice (4-weeks old) were assigned to 3 dietary groups for 36 weeks: (1) AIN76A as a control diet (AIN); (2) a defined rodent “new Western diet” (NWD); or (3) NWD with CaD supplementation (NWD/CaD). Compared to the AIN, mice receiving the NWD or NWD/CaD exhibited more than 0.2-fold increase in the levels of plasma leptin, tumor necrosis factor α (TNF-α) and body weight. The levels of plasma interleukin 6 (IL-6), inflammatory cell infiltration, and β-catenin/Ki67 protein (oncogenic signaling) were increased more than 0.8-fold in the NWD (but not NWD/CaD) group compared to the AIN group. Consistent with the inflammatory phenotype, colonic secondary bile acid (inflammatory bacterial metabolite) levels increased more than 0.4-fold in the NWD group compared to the NWD/CaD and AIN groups. Furthermore, the abundance of colonic Proteobacteria (e.g., Parasutterela), considered signatures of dysbiosis, was increased more than four-fold; and the α diversity of colonic bacterial species, indicative of health, was decreased by 30% in the NWD group compared to the AIN and NWD/CaD groups. Collectively, CaD adequacy reduces colonic inflammation, β-catenin oncogenic signaling, secondary bile acids, and bacterial dysbiosis in mice fed with a Western diet.

Baitouweng Tang ameliorates DSS-induced ulcerative colitis through the regulation of the gut microbiota and bile acids via pathways involving FXR and TGR5

In China, Baitouweng Tang (BTWT) is a commonly prescribed remedy for the treatment of ulcerative colitis (UC). Herein, the present study aims to assess the anti-colitis activity of BTWT and its underlying mechanisms in UC BALB/c mice. Induction of UC in BALB/c mice was carried out by adding 3.5% DSS in the drinking water of underlined mice. After UC induction, the mice were administrated with BTWT for 7 days. Clinical symptoms were assessed, followed by analyzing the bile acids (BAs) in serum, liver, colon, bile, and feces of UC mice through UPLC-MS/MS. The modified 16S rDNA high-throughput sequencing was carried out to examine the gut microbiota of feces. BTWT significantly improved the clinical symptoms such as and histological injury and colon shortening in UC induced mice. Furthermore, BTWT remarkably ameliorated colonic inflammatory response. After BTWT treatment, the increased concentrations of UDCA, HDCA, αMCA, βMCA, CA, and GLCA in UC were decreased, and the levels of some BAs, especially CA, αMCA, and βMCA were normalized. Moreover, the relative species abundance and gut microbiota diversity in the BTWT-exposed groups were found to be considerably elevated than those in the DSS-treated group. BTWT increased the relative abundance of Firmicutes, Proteobacteria, Actinobacteria, Tenericutes, and TM7, which were statistically lower in the fecal microbiota of UC mice. The relative abundance of Bacteroidetes was found to be elevated in the DSS group and normalized after BTWT treatment. BTWT increased the expression of FXR and TGR5 in the liver. BTWT administration improved DSS-induced mice signs by increasing the TGR5 and FXR expression levels. This result was achieved by the regulation of the BAs and gut microbiota.

The pathophysiology of bile acid diarrhoea: differences in the colonic microbiome, metabolome and bile acids

Bile acid diarrhoea (BAD) is a common disorder resulting from increased loss of bile acids (BAs), overlapping irritable bowel syndrome with diarrhoea (IBS-D). The gut microbiota metabolises primary BAs to secondary BAs, with differing impacts on metabolism and homeostasis. The aim of this study was to profile the microbiome, metabolic products and bile acids in BAD. Patients with BAD diagnosed by SeHCAT testing, were compared with other IBS-D patients, and healthy controls. Faecal 16S ribosomal RNA gene analysis was undertaken. Faecal short chain fatty acid (SCFA) and urinary volatile organic compounds (VOCs) were measured. BAs were quantified in serum and faeces. Faecal bacterial diversity was significantly reduced in patients with BAD. Several taxa were enriched compared to IBS-D. SCFA amounts differed in BAD, controls and IBS-D, with significantly more propionate in BAD. Separation of VOC profiles was evident, but the greatest discrimination was between IBS-D and controls. Unconjugated and primary BA in serum and faeces were significantly higher in BAD. The faecal percentage primary BA was inversely related to SeHCAT. BAD produces dysbiosis, with metabolite differences, including VOC, SCFA and primary BAs when compared to IBS-D. These findings provide new mechanistic insights into the pathophysiology of BAD.

The benefit of elobixibat in chronic constipation is associated with faecal deoxycholic acid but not effects of altered microbiota

Elobixibat, a novel inhibitor of apical sodium-dependent bile acid transporter for treating chronic constipation, increases colonic bile acid concentrations, stimulating bowel function. However, it is not clear which bile acids are altered, or whether altered gut microbiota are associated with functional effects that may alter bowel function. To investigate the effects of elobixibat on changes in the faecal concentrations of total and individual bile acids and in faecal microbiota. This was a prospective, single-centre study. After baseline period, patients received 10mg daily of elobixibat for 2weeks. We evaluated the effects on bowel function, changes in faecal bile acid concentrations and composition of gut bacteria, before and after elobixibat administration. In the 30 patients analysed, the frequency of pre- and post-treatment bowel movements per fortnight was 7 and 10 (P<0.001), respectively. The pre-treatment faecal bile acid concentration increased significantly from 10.9 to 15.0µg/g stool post-treatment (P=0.030), with a significant increase in faecal deoxycholic acid (pre-treatment 3.94µg/g stool to post-treatment 5.02µg/g stool, P=0.036) and in glycine-conjugated deoxycholic and chenodeoxycholic acids. Shannon index was significantly decreased, but there were no significant changes at the genus and phylum levels. Short term treatment with elobixibat increased the concentrations of total bile acids and deoxycholic acid and decreased the diversity of faecal microbiota. The biological effects of elobixibat are associated with its effects on secretory bile acids, rather than the structural changes of an altered faecal microbiota.

Increasing the Hindgut Carbohydrate/Protein Ratio by Cecal Infusion of Corn Starch or Casein Hydrolysate Drives Gut Microbiota-Related Bile Acid Metabolism To Stimulate Colonic Barrier Function.

ABSTRACTDietary high protein and low carbohydrate levels compromise colonic microbiota and bile acid metabolism, which underlies a detrimental gut environment. However, it remains unclear if the diet-induced changes in colonic health are due to a change in hindgut nutrient availability and what key intermediates link the microbe-epithelium dialogue. To specifically alter the hindgut nutrient substrate availability, here we used a cecally cannulated pig model to infuse corn starch and casein hydrolysate directly into the cecum to generate a stepwise change of carbohydrate/nitrogenous compound (C/N) ratio. Pigs were cecally infused daily with either saline (Control), corn starch (Starch), or casein hydrolysate (Casein) (n = 8 per group), respectively, for 19 days. After infusion, C/N ratios in colonic digesta were 16.33, 12.56, and 8.54 for the starch, control, and casein groups, respectively (P < 0.05). Relative to the control group, casein infusion showed greater abundance of the bacteria (Eubacterium) capable of bile acid 7α-dehydroxylation (baiJ), higher levels of expression of bacterial genes encoding the baiJ enzyme, and higher levels of secondary bile acid (deoxycholic acid [DCA] and lithocholic acid [LCA]), while the starch infusion showed the opposite effect. Correspondingly, casein infusion downregulated expression of genes encoding tight junction proteins (ZO-1 and OCLD) and upregulated expression of genes encoding epidermal growth factor receptor (EGFR). The ratio of C/N was linearly related with the concentrations of DCA and LCA and gene expression levels of ZO-1, occludin, and EGFR. Caco-2 cell experiments further showed that DCA and LCA downregulated expression of genes involved in barrier function (ZO-1 and OCLD) and upregulated the gene expression of EGFR and Src. Inhibition of EGFR and Src could abolish DCA- and LCA-induced downregulation of ZO-1, indicating that DCA and LCA impair gut barrier function via enhancing the EGFR-Src pathway. These results suggest that the ratio of C/N in the large intestine is an important determinant of microbial metabolism and gut barrier function in the colon. The findings provide evidence that microbe-related secondary bile acid metabolism may mediate the interplay between microbes and gut barrier function.IMPORTANCE High-fiber or high-protein diets could alter gut microbiota and health in the large intestine, but factors involved in the effects remain unclear. The present study for the first time demonstrates that the starch- and casein-induced C/N ratio in the hindgut is an important factor. Using the cannulated pig model, we found that the distinct C/N ratio induced by cecal infusion of corn starch or casein hydrolysate was linearly correlated with microbial metabolites (secondary bile acids) and tight junction proteins (ZO-1 and OCLD). Cell culture study further demonstrates that the gut microbial metabolites (DCA and LCA) could impair the intestinal barrier function via the EGFR-Src pathway. These suggest that DCA and LCA were key metabolites mediating microbe-epithelium dialogue when the hindgut C/N ratios were altered by cecal infusion of corn starch or casein hydrolysate. These findings provide new insight into the impact of C/N ratio in the large intestine on colonic health and provide a new framework for therapeutic strategy in gut health through targeted manipulation of hindgut microbiota by increasing the carbohydrate level in the large intestine.

Supplementation of Calcium and Vitamin D Reduces Colonic Inflammation and Beta-Catenin Signaling in C57BL/6 Mice Fed a Western Diet

Abstract Objectives Adoption of a Western diet, low in calcium and vitamin D (CaD), is a global problem leading to increased obesity, colonic inflammation and neoplasia. However, the mechanisms underlying this relationship remains to be elucidated. We tested the hypothesis that CaD supplementation may reduce colonic inflammation, oncogenic signaling and dysbiosis in the colon of C57BL/6 mice fed a Western diet. Methods Male C57/BL6 mice (4-week old) were assigned to 3 dietary groups (n = 20/group) for 36 weeks: (1) AIN76A as a control diet (AIN); (2) a defined rodent “new Western diet” (NWD); or (3) NWD with CaD supplementation (NWD/CaD). We used biochemical, mass spectrometry, histological and multi-omics approaches to determine the interplay between CaD supplementation, colonic inflammation and microbiome composition. Results Mice receiving the NWD or NWD/CaD exhibited &amp;gt;0.2- fold increase in the concentrations of plasma leptin, tumor necrosis factor α (TNF-α) and body weight when compared with those on the AIN diet. However, the concentrations of plasma interleukin 6 (IL6), inflammatory cell infiltration and b-catenin/Ki67 protein (oncogenic signaling) were increased &amp;gt;0.8 - fold in the NWD (but not NWD/CaD) group when compared with the AIN group. Consistent with the inflammatory phenotype: (1) colonic secondary bile acid (an inflammatory bacterial metabolite) concentrations increased &amp;gt;0.4 - fold in the NWD group when compared with the NWD/CaD and AIN groups; (2) in contrast, α diversity of colonic bacterial species, a healthy gut microbiome marker, was decreased by 30% in the NWD group when compared with the AIN and NWD/CaD groups. Conclusions This study demonstrates that, in a mouse model, CaD supplementation reduces colonic inflammation, oncogenic signaling and bacterial dysbiosis in the context of Western diet consumption. Funding Sources This work was supported by U.S. Department of Agriculture, Agricultural Research Service, research project 3062–51,000-056–00D.

Western diet-induced increase in colonic bile acids compromises epithelial barrier in nonalcoholic steatohepatitis.

There is compelling evidence implicating intestinal permeability in the pathogenesis of nonalcoholic steatohepatitis (NASH), but the underlying mechanisms remain poorly understood. Here we examined the role of bile acids (BA) in western diet (WD)-induced loss of colonic epithelial barrier (CEB) function in mice with a genetic impairment in intestinal epithelial barrier function, junctional adhesion molecule A knockout mice, F11r-/- . WD-fed knockout mice developed severe NASH, which was associated with increased BA concentration in the cecum and loss of CEB function. Analysis of cecal BA composition revealed selective increases in primary unconjugated BAs in the WD-fed mice, which correlated with increased abundance of microbial taxa linked to BA metabolism. In vitro permeability assays revealed that chenodeoxycholic acid (CDCA), which was elevated in the cecum of WD-fed mice, increased paracellular permeability, while the BA-binding resin sevelamer hydrochloride protected against CDCA-induced loss of barrier function. Sequestration of intestinal BAs by in vivo delivery of sevelamer to WD-fed knockout mice attenuated colonic mucosal inflammation and improved CEB. Sevelamer also reduced hepatic inflammation and fibrosis, and improved metabolic derangements associated with NASH. Collectively, these findings highlight a hitherto unappreciated role for BAs in WD-induced impairment of the intestinal epithelial barrier in NASH.

A Pilot Integrative Analysis of Colonic Gene Expression, Gut Microbiota, and Immune Infiltration in Primary Sclerosing Cholangitis-Inflammatory Bowel Disease: Association of Disease With Bile Acid Pathways.

BackgroundAlthough a majority of patients with PSC have colitis [PSC-IBD; primary sclerosing cholangitis-inflammatory bowel disease], this is phenotypically different from ulcerative colitis [UC]. We sought to define further the pathophysiological differences between PSC-IBD and UC, by applying a comparative and integrative approach to colonic gene expression, gut microbiota and immune infiltration data.MethodsColonic biopsies were collected from patients with PSC-IBD [n = 10], UC [n = 10], and healthy controls [HC; n = 10]. Shotgun RNA-sequencing for differentially expressed colonic mucosal genes [DEGs], 16S rRNA analysis for microbial profiling, and immunophenotyping were performed followed by multi-omic integration.ResultsThe colonic transcriptome differed significantly between groups [p = 0.01]. Colonic transcriptomes from HC were different from both UC [1343 DEGs] and PSC-IBD [4312 DEGs]. Of these genes, only 939 had shared differential gene expression in both UC and PSC-IBD compared with HC. Imputed pathways were predominantly associated with upregulation of immune response and microbial defense in both disease cohorts compared with HC. There were 1692 DEGs between PSC-IBD and UC. Bile acid signalling pathways were upregulated in PSC-IBD compared with UC [p = 0.02]. Microbiota profiles were different between the three groups [p = 0.01]; with inferred function in PSC-IBD also being consistent with dysregulation of bile acid metabolism. Th17 cells and IL17-producing CD4 cells were increased in both PSC-IBD and UC when compared with HC [p < 0.05]. Multi-omic integration revealed networks involved in bile acid homeostasis and cancer regulation in PSC-IBD.ConclusionsColonic transcriptomic and microbiota analysis in PSC-IBD point toward dysregulation of colonic bile acid homeostasis compared with UC. This highlights important mechanisms and suggests the possibility of novel approaches in treating PSC-IBD.

Advanced liver steatosis accompanies an increase in hepatic inflammation, colonic, secondary bile acids and Lactobacillaceae/Lachnospiraceae bacteria in C57BL/6 mice fed a high-fat diet

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in Western countries, and the gut-liver axis is implicated in liver disease pathogenesis. We hypothesize that advanced liver steatosis accompanies an increase in hepatic inflammation, colonic secondary bile acids (BAs) and secondary BA-producing bacteria in mice fed a high-fat (HF) diet model of obesity. Four-week old male C57BL/6 mice were fed an HF (45% energy) or a low-fat (LF) (10% energy) diet for 21 weeks. At the end of the study, body weight and body fat percentage in the HF group were 0.23- and 0.41-fold greater than those in the LF group, respectively. Similarly, the HF group exhibited an increase in hepatic lipid droplets, inflammatory cell infiltration, inducible nitric oxide synthase, and hepatocellular ballooning (but without hepatic Mallory bodies) which are key histological features of advanced hepatic steatosis. Furthermore, RNA sequencing, qPCR and immunohistological methods found that nicotinamide n-methyltransferase and selenoprotein P, two inflammation-related hepatic genes, were upregulated in the HF group. Consistent with the hepatic inflammation, the levels of proinflammatory plasma-cytokines (TNF-α and IL6), colonic secondary BAs (LCA, DCA) and secondary BA producing bacteria (e.g., lactobacillaceae/Lachnospiraceae) were at least 0.5-fold greater in the HF group compared with the LF group. Taken together, the data demonstrate that advanced liver-steatosis is concurrent with an elevated level of hepatic inflammation, colonic secondary bile acids and their associated bacteria in mice fed an HF diet. These data suggest a potential gut-liver crosstalk at the stage of advanced liver-steatosis.

The Pathophysiology of Bile Acid Diarrhoea: Differences in the Colonic Microbiome, Metabolome and Bile Acids

Background: Bile acid diarrhoea (BAD) is common, often unrecognised, or thought to be irritable bowel syndrome with diarrhoea (IBS-D). It results from increased loss of bile acids (BAs) into the colon but mechanisms are unclear. The gut microbiota plays key roles in the metabolism of primary BAs to form secondary BAs, which have differing impacts on intestinal metabolism and homeostasis. The aim of this study was to profile the gut microbiome in BAD and to investigate the differences in bacterial metabolic products and specific bile acids. Methods: Patients with BAD diagnosed by SeHCAT testing, were compared with other IBS-D patients, and healthy controls. Faecal 16S ribosomal RNA gene analysis was undertaken. Faecal short chain fatty acid (SCFA) and urinary fermentation metabolite profiles (volatile organic compounds; VOCs) were measured. BAs were quantified in serum and faeces. Findings: Faecal bacterial diversity was significantly reduced in patients with BAD, but several taxa were enriched compared to IBS-D. SCFA amounts differed in BAD, controls and IBS-D, with significantly more propionate in BAD. Separation of VOC profiles was evident between all groups with the greatest discrimination between IBS-D and controls. Unconjugated and primary BA in serum and faeces were significantly higher in BAD. The proportion of faecal primary BA was inversely related to SeHCAT values. Interpretation: BAD results in dysbiosis, with differences in metabolites including VOC, SCFA and higher concentrations of primary BAs when compared to IBS-D. These findings provide new mechanistic insights into the pathophysiology of BAD. Funding Statement: Funding was from UHCW Trust’s charity as well as the Midlands Gastroenterology Society and Bardhan Research and Education Trust (BRET). Declaration of Interests: JW has been a consultant for, and reports institutional grant funding from GE Healthcare, and Prometheus diagnostics. RA has delivered educational talks for GE Healthcare. No disclosures are made by all authors Ethics Approval Statement: Scientific and ethical approval was acquired from the local Research and Development Office as well as Warwickshire Ethical committee ref: 09/H1211/38. Written informed consent was obtained from all participants in the study.

FGF21 acts as a negative regulator of bile acid synthesis

Fibroblast growth factor 21 (FGF21) is a potent regulator of glucose and lipid homeostasis in vivo; its most closely related subfamily member, FGF19, is known to be a critical negative regulator of bile acid synthesis. To delineate whether FGF21 also plays a functional role in bile acid metabolism, we evaluated the effects of short- and long-term exposure to native FGF21 and long-acting FGF21 analogs on hepatic signal transduction, gene expression and enterohepatic bile acid levels in primary hepatocytes and in rodent and monkey models. FGF21 acutely induced ERK phosphorylation and inhibited Cyp7A1 mRNA expression in primary hepatocytes and in different rodent models, although less potently than recombinant human FGF19. Long-term administration of FGF21 in mice fed a standard chow diet resulted in a 50-60% decrease in bile acid levels in the liver and small intestines and consequently a 60% reduction of bile acid pool size. In parallel, colonic and fecal bile acid was decreased, whereas fecal cholesterol and fatty acid excretions were elevated. The long-acting FGF21 analog showed superiority to recombinant human FGF21 and FGF19 in decreasing bile acid levels with long duration of effect action in mice. Long-term administration of the long-acting FGF21 analogs in obese cynomolgus monkeys suppressed plasma total bile acid and 7α-hydroxy-4-cholesten-3-one levels, a biomarker for bile acid synthesis. Collectively, these data reveal a previously unidentified role of FGF21 in bile acid metabolism as a negative regulator of bile acid synthesis.

Deoxycholic acid activates colonic afferent nerves via 5-HT3 receptor-dependent and -independent mechanisms.

Increased bile acids in the colon can evoke increased epithelial secretion resulting in diarrhea, but little is known about whether colonic bile acids contribute to abdominal pain. This study aimed to investigate the mechanisms underlying activation of colonic extrinsic afferent nerves and their neuronal cell bodies by a major secondary bile acid, deoxycholic acid (DCA). All experiments were performed on male C57BL/6 mice. Afferent sensitivity was evaluated using in vitro extracellular recordings from mesenteric nerves in the proximal colon (innervated by vagal and spinal afferents) and distal colon (spinal afferents only). Neuronal excitability of cultured dorsal root ganglion (DRG) and nodose ganglion (NG) neurons was examined with perforated patch clamp. Colonic 5-HT release was assessed using ELISA, and 5-HT immunoreactive enterochromaffin (EC) cells were quantified. Intraluminal DCA increased afferent nerve firing rate concentration dependently in both proximal and distal colon. This DCA-elicited increase was significantly inhibited by a 5-HT3 antagonist in the proximal colon but not in the distal colon, which may be in part due to lower 5-HT immunoreactive EC cell density and lower 5-HT levels in the distal colon following DCA stimulation. DCA increased the excitability of DRG neurons, whereas it decreased the excitability of NG neurons. DCA potentiated mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. Together, this study suggests that DCA can excite colonic afferents via direct and indirect mechanisms but the predominant mechanism may differ between vagal and spinal afferents. Furthermore, DCA increased mechanosensitivity of high-threshold spinal afferents and may be a mechanism of visceral hypersensitivity.NEW & NOTEWORTHY Deoxycholic acid (DCA) directly excites spinal afferents and, to a lesser extent, indirectly via mucosal 5-HT release. DCA potentiates mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. DCA increases vagal afferent firing in proximal colon via 5-HT release but directly inhibits the excitability of their cell bodies.