Bile acids: short and long term effects in the intestine

Gut proinflammatory bacteria is associated with abnormal functional connectivity of hippocampus in unmedicated patients with major depressive disorder

Accumulating evidence has revealed the gut bacteria dysbiosis and brain hippocampal functional and structural alterations in major depressive disorder (MDD). However, the potential relationship between the gut microbiota and hippocampal function alterations in patients with MDD is still very limited. Data of resting-state functional magnetic resonance imaging were acquired from 44 unmedicated MDD patients and 42 demographically matched healthy controls (HCs). Severn pairs of hippocampus subregions (the bilateral cornu ammonis [CA1-CA3], dentate gyrus (DG), entorhinal cortex, hippocampal-amygdaloid transition area, and subiculum) were selected as the seeds in the functional connectivity (FC) analysis. Additionally, fecal samples of participants were collected and 16S rDNA amplicon sequencing was used to identify the altered relative abundance of gut microbiota. Then, association analysis was conducted to investigate the potential relationships between the abnormal hippocampal subregions FC and microbiome features. Also, the altered hippocampal subregion FC values and gut microbiota levels were used as features separately or together in the support vector machine models distinguishing the MDD patients and HCs. Compared with HCs, patients with MDD exhibited increased FC between the left hippocampus (CA2, CA3 and DG) and right hippocampus (CA2 and CA3), and decreased FC between the right hippocampal CA3 and bilateral posterior cingulate cortex. In addition, we found that the level of proinflammatory bacteria (i.e., Enterobacteriaceae) was significantly increased, whereas the level of short-chain fatty acids producing-bacteria (i.e., Prevotellaceae, Agathobacter and Clostridium) were significantly decreased in MDD patients. Furthermore, FC values of the left hippocampal CA3- right hippocampus (CA2 and CA3) was positively correlated with the relative abundance of Enterobacteriaceae in patients with MDD. Moreover, altered hippocampal FC patterns and gut microbiota level were considered in combination, the best discrimination was obtained (AUC = 0.92). These findings may provide insights into the potential role of gut microbiota in the underlying neuropathology of MDD patients.

Considering traditional Chinese medicine as adjunct therapy in the management of chronic constipation by regulating intestinal flora

Chronic constipation is one of the most common gastrointestinal disorders worldwide. Due to changes in diet, lifestyle, and the aging population, the incidence of chronic constipation has increased year by year. It has had an impact on daily life and poses a considerable economic burden. Nowadays, many patients with chronic constipation try to seek help from complementary and alternative therapies, and traditional Chinese medicine (TCM) is often their choice. The intestinal flora play an important role in the pathogenesis of constipation by affecting the body's metabolism, secretion, and immunity. Regulating the intestinal flora and optimizing its composition might become an important prevention and treatment for chronic constipation. TCM has unique advantages in regulating the imbalance of intestinal flora, and its curative effect is precise. Therefore, we reviewed the relationship between intestinal flora and chronic constipation as well as advances in research on TCM as adjunct therapy in the management of chronic constipation by regulating intestinal flora. Some single Chinese herbs and their active ingredients (e.g., Rheum palmatum, Radix Astragalus, and Cistanche deserticola), some traditional herbal formulations (e.g., Jichuan decoction, Zengye decoction, and Zhizhu decoction) and some Chinese patent medicines (e.g., Maren pills and Shouhui Tongbian capsules) that are commonly used to treat chronic constipation by regulating intestinal flora are highlighted and summarized. Moreover, some external forms of TCM, and especially acupuncture, have also been found to improve intestinal movement and alleviate constipation symptoms by regulating intestinal flora. We hope this review can contribute to an understanding of TCM as an adjunct therapy for chronic constipation and that it can provide useful information for the development of more effective constipation therapies.

The alteration of mucosal bile acid profile is associated with nerve growth factor expression in mast cells and bowel symptoms in diarrhea-predominant irritable bowel syndrome

Mucosal bile acid (BA) profile is still unestablished in diarrhea-predominant irritable bowel syndrome (IBS-D). The aim of this study was to explore colonic mucosal BAs and their associations with mucosal mast cell (MMC)-derived nerve growth factor (NGF) and bowel symptoms in IBS-D. Colonic mucosal biopsies from 36 IBS-D patients and 35 healthy controls (HCs) were obtained for targeted BA profiling. MMC count and the expression of NGF and tight junction proteins (TJPs) were examined. We found that colonic mucosal BA profile was altered in the IBS-D cohort. The proportion of primary BAs was significantly higher and that of secondary BAs was lower in IBS-D patients. According to the 90th percentile of total mucosal BA content of HCs, IBS-D patients were divided into BA-H (n = 7, 19.4%) and BA-L (n = 29, 80.6%) subgroups. BA-H patients showed significantly higher total mucosal BA content compared to BA-L subgroup and HCs. The mucosal content of 11 BA metabolites significantly increased in BA-H subgroup, e.g. cholic acid (CA) and taurocholic acid (TCA). Moreover, BA-H patients displayed significantly elevated MMC count and NGF expression, with decreased expression of TJPs (claudin-1, junctional adhesion molecule-A and zonula occludens-1). Correlation analyses revealed that mucosal TCA content positively correlated with MMC count, MMC-derived NGF levels, and abdominal pain while negatively correlated with TJP expression. In conclusion, IBS-D patients showed an altered BA profile in the colonic mucosa. Approximately 20% of them exhibit elevated mucosal BA content, which may be associated with MMC-derived NGF signaling and bowel symptoms.

Gut Metabolites Acting on the Gut-Brain Axis: Regulating the Functional State of Microglia

The gut-brain axis is a communication channel that mediates a complex interplay of intestinal flora with the neural, endocrine, and immune systems, linking gut and brain functions. Gut metabolites, a group of small molecules produced or consumed by biochemical processes in the gut, are involved in central nervous system regulation via the highly interconnected gut-brain axis affecting microglia indirectly by influencing the structure of the gut-brain axis or directly affecting microglia function and activity. Accordingly, pathological changes in the central nervous system are connected with changes in intestinal metabolite levels as well as altered microglia function and activity, which may contribute to the pathological process of each neuroinflammatory condition. Here, we discuss the mechanisms by which gut metabolites, for instance, the bile acids, short-chain fatty acids, and tryptophan metabolites, regulate the structure of each component of the gut-brain axis, and explore the important roles of gut metabolites in the central nervous system from the perspective of microglia. At the same time, we highlight the roles of gut metabolites affecting microglia in the pathogenesis of neurodegenerative diseases and neurodevelopmental disorders. Understanding the relationship between microglia, gut microbiota, neuroinflammation, and neurodevelopmental disorders will help us identify new strategies for treating neuropsychiatric disorders.

Dietary Bile Acid Supplementation Could Regulate the Glucose, Lipid Metabolism, and Microbiota of Common Carp (Cyprinus carpio L.) Fed with a High-Lipid Diet

This study sought to examine the role of bile acids in the regulation of glucose and lipid metabolism, intestinal flora, and growth in high-fat diet-fed common carp (Cyprinus carpio L.). Fish (6.34 ± 0.07 g) were fed for 56 days with three different diets, the control diet (CO, 5.4% lipid), high-fat diet (HF, 11% lipid), and high-fat diet with 60 mg/kg bile acids (BAs, 11% lipid). The results showed that high-fat diets resulted in poor growth performance and increased triglyceride (TG) in serum and the liver. The addition of bile acids significantly alleviated the adverse effects of a high-fat diet. The mRNA expression results indicated that bile acids may improve lipid metabolism through the enhancement of the peroxisome proliferator-activated receptor (PPARa). The expression of gluconeogenesis-related phosphoenolpyruvate carboxykinase (PEPCK) mRNA was inhibited, while fibroblast growth factor 19 (FGF19) was significantly higher. Bile acids reshaped the intestinal microflora community, with the level of Bacteroidetes increasing. The correlation analysis indicated that Patescibacteria, Dependentiae, Myxococcota, and Planctomycetota in the gut are associated with genes involved in glucose and lipid metabolism. These results indicated that bile acids could ameliorate the negative effects of high-fat diets on common carp.

Apple juice relieves loperamide-induced constipation in rats by downregulating the intestinal apical sodium-dependent bile acid transporter ASBT

Apples are known to exhibit various beneficial effects on human health. In the present study, we investigated the effect of continuous intake of apple juice (AJ) on constipation status. A single dose of loperamide in rats as the constipation model markedly decreased the weight and number of fecal pellets compared to saline-administered rats as a control. After the administration of AJ twice a day for seven days, recovery of defecation close to that of the control was observed in loperamide-treated rats. In addition, the total bile acid content in the feces increased from day 4 after the administration of AJ. Among hepatic and intestinal transporters and enzymes that regulate bile acids, the mRNA expression of the apical sodium-dependent bile acid transporter (Asbt, slc10a2) was decreased by AJ in rats. Furthermore, the Asbt-mediated bile acid transport activity in the rat ileum decreased after AJ administration. Moreover, in human colonic cancer-derived Caco-2 cells, AJ exposure for 24 and 48 h decreased the expressions of ASBT mRNA and protein, and the uptake activity of taurocholic acid in both 7- and 21-d cultures. Several components of AJ, such as procyanidins, decreased the expression of ASBT in Caco-2 cells. In conclusion, ASBT downregulation is a possible mechanism responsible for the constipation-relieving effect of apples, and procyanidins may play a role in downregulating ASBT, which leads to the beneficial effects of apples against constipation. Although it is generally agreed that the common dietary compositions play a role in constipation relief, the novel specific mechanism of apples found in this study would facilitate understanding food functions.

Functional, Diagnostic and Therapeutic Aspects of Bile

Bile is a unique body fluid synthesized in our liver. Enterohepatic circulation preserves bile in our body through its efficient synthesis, transport, absorption, and reuptake. Bile is the main excretory route for bile salts, bilirubin, and potentially harmful exogenous lipophilic substances. The primary way of eliminating cholesterol is bile. Although bile has many organic and inorganic contents, bile acid is the most physiologically active component. Bile acids have a multitude of critical physiologic functions in our body. These include emulsification of dietary fat, absorption of fat and fat-soluble vitamins, maintaining glucose, lipid, and energy homeostasis, sustenance of intestinal epithelial integrity and epithelial cell proliferation, reducing inflammation in the intestine, and prevention of enteric infection due to its antimicrobial properties. But bile acids can be harmful in certain altered conditions like cholecystectomy, terminal ileal disease or resection, cholestasis, duodenogastric bile reflux, duodenogastroesophageal bile reflux, and bile acid diarrhea. Bile acids can have malignant potentials as well. There are also important diagnostic and therapeutic roles of bile acid and bile acid modulation.

Role of gut microbiota-derived signals in the regulation of gastrointestinal motility

The gastrointestinal (GI) tract harbors trillions of commensal microbes, called the gut microbiota, which plays a significant role in the regulation of GI physiology, particularly GI motility. The GI tract expresses an array of receptors, such as toll-like receptors (TLRs), G-protein coupled receptors, aryl hydrocarbon receptor (AhR), and ligand-gated ion channels, that sense different gut microbiota-derived bioactive substances. Specifically, microbial cell wall components and metabolites, including lipopeptides, peptidoglycan, lipopolysaccharides (LPS), bile acids (BAs), short-chain fatty acids (SCFAs), and tryptophan metabolites, mediate the effect of gut microbiota on GI motility through their close interactions with the enteroendocrine system, enteric nervous system, intestinal smooth muscle, and immune system. In turn, GI motility affects the colonization within the gut microbiota. However, the mechanisms by which gut microbiota interacts with GI motility remain to be elucidated. Deciphering the underlying mechanisms is greatly important for the prevention or treatment of GI dysmotility, which is a complication associated with many GI diseases, such as irritable bowel syndrome (IBS) and constipation. In this perspective, we overview the current knowledge on the role of gut microbiota and its metabolites in the regulation of GI motility, highlighting the potential mechanisms, in an attempt to provide valuable clues for the development of gut microbiota-dependent therapy to improve GI motility.

Gut Microbiome-Linked Metabolites in the Pathobiology of Major Depression With or Without Anxiety—A Role for Bile Acids

Background

The gut microbiome may play a role in the pathogenesis of neuropsychiatric diseases including major depressive disorder (MDD). Bile acids (BAs) are steroid acids that are synthesized in the liver from cholesterol and further processed by gut-bacterial enzymes, thus requiring both human and gut microbiome enzymatic processes in their metabolism. BAs participate in a range of important host functions such as lipid transport and metabolism, cellular signaling and regulation of energy homeostasis. BAs have recently been implicated in the pathophysiology of Alzheimer's and several other neuropsychiatric diseases, but the biochemical underpinnings of these gut microbiome-linked metabolites in the pathophysiology of depression and anxiety remains largely unknown.

Method

Using targeted metabolomics, we profiled primary and secondary BAs in the baseline serum samples of 208 untreated outpatients with MDD. We assessed the relationship of BA concentrations and the severity of depressive and anxiety symptoms as defined by the 17-item Hamilton Depression Rating Scale (HRSD₁₇) and the 14-item Hamilton Anxiety Rating Scale (HRSA-Total), respectively. We also evaluated whether the baseline metabolic profile of BA informs about treatment outcomes.

Results

The concentration of the primary BA chenodeoxycholic acid (CDCA) was significantly lower at baseline in both severely depressed (log₂ fold difference (LFD) = −0.48; p = 0.021) and highly anxious (LFD = −0.43; p = 0.021) participants compared to participants with less severe symptoms. The gut bacteria-derived secondary BAs produced from CDCA such as lithocholic acid (LCA) and several of its metabolites, and their ratios to primary BAs, were significantly higher in the more anxious participants (LFD's range = [0.23, 1.36]; p's range = [6.85E-6, 1.86E-2]). The interaction analysis of HRSD₁₇ and HRSA-Total suggested that the BA concentration differences were more strongly correlated to the symptoms of anxiety than depression. Significant differences in baseline CDCA (LFD = −0.87, p = 0.0009), isoLCA (LFD = −1.08, p = 0.016) and several BA ratios (LFD's range [0.46, 1.66], p's range [0.0003, 0.049]) differentiated treatment failures from remitters.

Conclusion

In patients with MDD, BA profiles representing changes in gut microbiome compositions are associated with higher levels of anxiety and increased probability of first-line treatment failure. If confirmed, these findings suggest the possibility of developing gut microbiome-directed therapies for MDD characterized by gut dysbiosis.

Mechanism of Bile Acid-Induced Programmed Cell Death and Drug Discovery against Cancer: A Review

Bile acids are major signaling molecules that play a significant role as emulsifiers in the digestion and absorption of dietary lipids. Bile acids are amphiphilic molecules produced by the reaction of enzymes with cholesterol as a substrate, and they are the primary metabolites of cholesterol in the body. Bile acids were initially considered as tumor promoters, but many studies have deemed them to be tumor suppressors. The tumor-suppressive effect of bile acids is associated with programmed cell death. Moreover, based on this fact, several synthetic bile acid derivatives have also been used to induce programmed cell death in several types of human cancers. This review comprehensively summarizes the literature related to bile acid-induced programmed cell death, such as apoptosis, autophagy, and necroptosis, and the status of drug development using synthetic bile acid derivatives against human cancers. We hope that this review will provide a reference for the future research and development of drugs against cancer.

Intestinal FXR Activation via Transgenic Chimera or Chemical Agonism Prevents Colitis-Associated and Genetically-Induced Colon Cancer

Simple Summary

Disruption of Bile Acids (BA) regulation with increased BA concentration and modulation or their detergent pro-inflammatory activity has been linked to colorectal cancer (CRC). Farnesoid X Receptor (FXR) is the master regulator of BA homeostasis; FXR is a nuclear receptor that transcriptionally modulates their synthesis, transport and metabolism. In this study, we demonstrated that intestinal FXR activation prevented both inflammation- and genetically-driven colorectal tumorigenesis by modulating BA pool size and composition. This could open new avenues for the therapeutic management of intestinal inflammation and tumorigenesis.

Abstract

The Farnesoid X Receptor (FXR) is the master regulator of Bile Acids (BA) homeostasis orchestrating their synthesis, transport and metabolism. Disruption of BA regulation has been linked to gut-liver axis diseases such as colorectal cancer (CRC). In this study, firstly we examined the role of constitutive activation of intestinal FXR in CRC; then we pre-clinically investigated the therapeutic potential of a diet enriched with a synthetic FXR agonist in two models of CRC (chemically-induced and genetic models). We demonstrated that mice with intestinal constitutive FXR activation are protected from AOM/DSS-induced CRC with a significant reduction of tumor number compared to controls. Furthermore, we evaluated the role of chemical FXR agonism in a DSS model of colitis in wild type (WT) and FXR^null mice. WT mice administered with the FXR activating diet showed less morphological alterations and decreased inflammatory infiltrates compared to controls. The FXR activating diet also protected WT mice from AOM/DSS-induced CRC by reducing tumors’ number and size. Finally, we proved that the FXR activating diet prevented spontaneous CRC in APC^Min/+ mice via an FXR-dependent modulation of BA homeostasis. Our results demonstrate that intestinal FXR activation prevented both inflammation- and genetically-driven colorectal tumorigenesis by modulating BA pool size and composition. This could open new avenues for the therapeutic management of intestinal inflammation and tumorigenesis.

Secondary Bile Acids and Tumorigenesis in Colorectal Cancer

Colorectal cancer (CRC) is one of the most common and deadly cancers in the world and is a typical inflammatory tumor. In recent years, the incidence of CRC has been increasing year by year. There is evidence that the intake of high-fat diet and overweight are associated with the incidence of CRC, among which bile acids play a key role in the pathogenesis of the disease. Studies on the relationship between bile acid metabolism and the occurrence of CRC have gradually become a hot topic, improving the understanding of metabolic factors in the etiology of colorectal cancer. Meanwhile, intestinal flora also plays an important role in the occurrence and development of CRC In this review, the classification of bile acids and their role in promoting the occurrence of CRC are discussed, and we highlights how a high-fat diet affects bile acid metabolism and destroys the integrity of the intestinal barrier and the effects of gut bacteria.

Ileal Bile Acid Transporter Inhibition Reduces Post-Transplant Diarrhea and Growth Failure in FIC1 Disease—A Case Report

Familial intrahepatic cholestasis 1 (FIC1) disease is a genetic disorder characterized by hepatic and gastrointestinal disease due to ATP8B1 deficiency, often requiring liver transplantation (LT). Extrahepatic symptoms, such as diarrhea, malabsorption, and failure to thrive, do not improve and instead may be aggravated after LT. We describe a patient with FIC1 disease who underwent LT at 2 years, 8 months of age. After LT, the child developed severe refractory diarrhea and failed to thrive. The response to bile acid resins was unsatisfactory, and the parents declined our recommendation for partial external biliary diversion (PEBD). Quality of life was extremely impaired, especially due to severe diarrhea, making school attendance impossible. Attempting to reduce the total bile acids, we initiated off-label use of the ileal bile acid transporter (IBAT) inhibitor Elobixibat (Goofice^™), later converted to Odevixibat (Bylvay^™). After six months of treatment, the patient showed less stool output, increased weight and height, and improved physical energy levels. The child could now pursue higher undergraduate education. In our patient with FIC1 disease, the use of IBAT inhibitors was effective in treating chronic diarrhea and failure to thrive. This approach is novel; further investigations are needed to clarify the exact mode of action in this condition.

Exposure to the mycotoxin deoxynivalenol reduces the transport of conjugated bile acids by intestinal Caco-2 cells

Conjugated bile acids are synthesized in liver and subsequently secreted into the intestinal lumen from which they are actively reabsorbed and transported back to liver. The efficient enterohepatic circulation of conjugated bile acids is important to maintain homeostasis. The mycotoxin deoxynivalenol (DON) is a fungal secondary metabolite that contaminates cereal food. Upon human exposure, it can cause intestinal dysfunction. We explored the effects of DON exposure on the intestinal absorption of conjugated bile acids and the expression of bile acid transporters using an in vitro model based on Caco-2 cell layers grown in transwells. Our study shows that the transport rate of taurocholic acid (TCA) is decreased after 48-h pre-exposure of the Caco-2 cells to 2 µM DON, which is a realistic intestinal DON concentration. Exposure to DON downregulates expression of the genes coding for the apical sodium-dependent bile acid transporter (ASBT), the ileal bile acid-binding protein (IBABP) and the organic solute transporter α (OSTα), and it counteracts the agonist activity of Farnesoid X receptor (FXR) agonist GW4064 on these genes. In addition, the transport of ten taurine or glycine-conjugated bile acids in a physiological relevant mixture by the intestinal Caco-2 cell layers was decreased after pre-exposure of the cells to DON, pointing at a potential for DON-mediated accumulation of the conjugated bile acids at the intestinal luminal side. Together the results reveal that DON inhibits intestinal bile acid reabsorption by reducing the expression of bile acid transporters thereby affecting bile acid intestinal kinetics, leading to bile acid malabsorption in the intestine. Our study provides new insights into the hazards of DON exposure.

The roles of microbial products in the development of colorectal cancer: a review

A large number of microbes exist in the gut and they have the ability to process and utilize ingested food. It has been reported that their products are involved in colorectal cancer development. The molecular mechanisms which underlie the relationship between gut microbial products and CRC are still not fully understood. The role of some microbial products in CRC is particularly controversial. Elucidating the effects of gut microbiota products on CRC and their possible mechanisms is vital for CRC prevention and treatment. In this review, recent studies are examined in order to describe the contribution metabolites and toxicants which are produced by gut microbes make to CRC, primarily focusing on the involved molecular mechanisms.Abbreviations: CRC: colorectal cancer; SCFAs: short chain fatty acids; HDAC: histone deacetylase; TCA cycle: tricarboxylic acid cycle; CoA: cytosolic acyl coenzyme A; SCAD: short chain acyl CoA dehydrogenase; HDAC: histone deacetylase; MiR-92a: microRNA-92a; KLF4: kruppel-like factor; PTEN: phosphatase and tensin homolog; PI3K: phosphoinositide 3-kinase; PIP2: phosphatidylinositol 4, 5-biphosphate; PIP3: phosphatidylinositol-3,4,5-triphosphate; Akt1: protein kinase B subtype α; ERK1/2: extracellular signal-regulated kinases 1/2; EMT: epithelial-to-mesenchymal transition; NEDD9: neural precursor cell expressed developmentally down-regulated9; CAS: Crk-associated substrate; JNK: c-Jun N-terminal kinase; PRMT1: protein arginine methyltransferase 1; UDCA: ursodeoxycholic acid; BA: bile acids; CA: cholic acid; CDCA: chenodeoxycholic acid; DCA: deoxycholic acid; LCA: lithocholic acid; CSCs: cancer stem cells; MHC: major histocompatibility; NF-κB: NF-kappaB; GPR: G protein-coupled receptors; ROS: reactive oxygen species; RNS: reactive nitrogen substances; BER: base excision repair; DNA: deoxyribonucleic acid; EGFR: epidermal growth factor receptor; MAPK: mitogen activated protein kinase; ERKs: extracellular signal regulated kinases; AKT: protein kinase B; PA: phosphatidic acid; TMAO: trimethylamine n-oxide; TMA: trimethylamine; FMO3: flavin-containing monooxygenase 3; H₂S: Hydrogen sulfide; SRB: sulfate-reducing bacteria; IBDs: inflammatory bowel diseases; NSAID: non-steroidal anti-inflammatory drugs; BFT: fragile bacteroides toxin; ETBF: enterotoxigenic fragile bacteroides; E-cadherin: extracellular domain of intercellular adhesive protein; CEC: colonic epithelial cells; SMOX: spermine oxidase; SMO: smoothened; Stat3: signal transducer and activator of transcription 3; Th17: T helper cell 17; IL17: interleukin 17; AA: amino acid; TCF: transcription factor; CDT: cytolethal distending toxin; PD-L1: programmed cell death 1 ligand 1.

Chronic Refractory Constipation in Children: Think Beyond Stools

Chronic refractory constipation (CRC) is defined as children who are unable to pass stools in spite of being on maximum laxative therapy and require daily rectal stimulation in the form of enemas or suppositories to pass stools for >3 months. Children are often referred for treatment of refractory constipation that may result from uncontrolled underlying disease or ineffective treatment. Constipated children can be managed by a variety of medical therapeutic options that yield satisfying results in most cases. However, a subset of constipated children fails to benefit from conventional treatments. On treatment failure or on suspicion of organic disease the patient should be referred for further evaluation. Treatment options for treatment-resistant patients are presented. Pharmalogical and non-pharmalogical treatment modalities are reviewed and an algorithm for refractory constipation in children are presented.

Altered profiles of fecal bile acids correlate with gut microbiota and inflammatory responses in patients with ulcerative colitis

BACKGROUND

Gut microbiota and its metabolites may be involved in the pathogenesis of inflammatory bowel disease. Several clinical studies have recently shown that patients with ulcerative colitis (UC) have altered profiles of fecal bile acids (BAs). It was observed that BA receptors Takeda G-protein-coupled receptor 5 (TGR5) and vitamin D receptor (VDR) participate in intestinal inflammatory responses by regulating NF-ĸB signaling. We hypothesized that altered profiles of fecal BAs might be correlated with gut microbiota and inflammatory responses in patients with UC.

AIM

To investigate the changes in fecal BAs and analyze the relationship of BAs with gut microbiota and inflammation in patients with UC.

METHODS

The present study used 16S rDNA sequencing technology to detect the differences in the intestinal flora between UC patients and healthy controls (HCs). Fecal BAs were measured by targeted metabolomics approaches. Mucosal TGR5 and VDR expression was analyzed using immunohistochemistry, and serum inflammatory cytokine levels were detected by ELISA.

RESULTS

Thirty-two UC patients and twenty-three HCs were enrolled in this study. It was found that the diversity of gut microbiota in UC patients was reduced compared with that in HCs. Firmicutes, Clostridium IV, Butyricicoccus, Clostridium XlVa, Faecalibacterium, and Roseburia were significantly decreased in patients with UC (P = 3.75E-05, P = 8.28E-07, P = 0.0002, P = 0.003, P = 0.0003, and P = 0.0004, respectively). Proteobacteria, Escherichia, Enterococcus, Klebsiella, and Streptococcus were significantly enriched in the UC group (P = 2.99E-09, P = 3.63E-05, P = 8.59E-05, P = 0.003, and P = 0.016, respectively). The concentrations of fecal secondary BAs, such as lithocholic acid, deoxycholic acid, glycodeoxycholic acid, glycolithocholic acid, and taurolithocholate, in UC patients were significantly lower than those in HCs (P = 8.1E-08, P = 1.2E-07, P = 3.5E-04, P = 1.9E-03, and P = 1.8E-02, respectively) and were positively correlated with Butyricicoccus, Roseburia, Clostridium IV, Faecalibacterium, and Clostridium XlVb (P < 0.01). The concentrations of primary BAs, such as taurocholic acid, cholic acid, taurochenodeoxycholate, and glycochenodeoxycholate, in UC patients were significantly higher than those in HCs (P = 5.3E-03, P = 4E-02, P = 0.042, and P = 0.045, respectively) and were positively related to Enterococcus, Klebsiella, Streptococcus, Lactobacillus, and pro-inflammatory cytokines (P < 0.01). The expression of TGR5 was significantly elevated in UC patients (0.019 ± 0.013 vs 0.006 ± 0.003, P = 0.0003). VDR expression in colonic mucosal specimens was significantly decreased in UC patients (0.011 ± 0.007 vs 0.016 ± 0.004, P = 0.033).

CONCLUSION

Fecal BA profiles are closely related to the gut microbiota and serum inflammatory cytokines. Dysregulation of the gut microbiota and altered constitution of fecal BAs may participate in regulating inflammatory responses via the BA receptors TGR5 and VDR.

Chronic Jet Lag Exacerbates Jejunal and Colonic Microenvironment in Mice

Background

Evidence suggests that circadian rhythm disorder is associated with a variety of gastrointestinal diseases, and the circadian rhythm plays a key role in maintaining the homeostasis of intestinal flora. The underlying mechanisms are still not completely identified. This study was aimed to explore whether jet lag-caused circadian disruption influences gut microbiome and its metabolites.

Methods

Mice were synchronized with 12-h light/dark cycles (control group) or subjected to daily 8-h advance of the light/dark cycle for every 3 days (jet-lagged group). Four months later, fecal samples and jejunal contents were collected and analyzed by 16S rRNA gene sequencing. In addition, fecal samples were subjected to metabolome analysis with ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS).

Results

The results of 16s rRNA sequencing showed that chronic jet lag led to decreased microbial abundance, richness, and diversity in both feces and jejunal contents. ANOSIM analysis revealed significant difference between control and jet-lagged groups. As the colonic microbiome, the abundance of Bacteroidetes phylum was significantly decreased and that of Actinobacteria phylum was increased in jet-lagged mice. Jet lag increased the ratio of Firmicutes to Bacteroidetes, an indicator for the imbalance of gut microbiota. Metabolome analysis of fecal samples showed that the levels of tryptophan and its derivatives were decreased in jet-lagged mice. In addition, fecal levels of secondary bile acids changed under jet lag conditions. Correlation analysis identified associations between tryptophan (and its derivatives) levels and colonic microbiota.

Conclusions

This study presents a comprehensive landscape of gut microbiota and its metabolites in mice subjected to chronic jet lag. The results suggest that circadian disruption may lead to changes in fecal and jejunal microbiota and fecal metabolites. Moreover, our results demonstrate a novel interplay between the gut microbiome and metabolome.

Identification of colorectal neoplasia by using serum bile acid profile

BACKGROUND

Colonoscopy is the gold standard for detecting earlier stages of CRC, although screening of patients is difficult because of invasiveness, low compliance and procedural health risks. Therefore, the need for new screening methods for CRC is rising. Previous studies have demonstrated the diagnostic ability of serum BAs; however, the results have been inconsistent. In this study, we conducted a comprehensive analysis of serum BAs from patients with CRC and verified their diagnostic ability to detect CRC.

METHODS

A total of 56 CRC patients (n = 14 each of stages I-IV), 59 patients with colonic adenoma and 60 healthy controls were included. Age and sex were matched for each group. Serum BA compositions were measured by LC-MS/MS and serum concentration of 30 types of BAs were analysed by discriminant analysis with multidimensional scaling method.

RESULTS

Free CA, 3epi-DCA&CDCA, 3-dehydro CA, GCA and TCA were extracted as principal component (PC) 1 and free 3-dehydroDCA as PC 2 by canonical discriminant function coefficients. The verification of discriminability using cross-validation method revealed that the correct classification rate was 66.3% for original data and 52.6% for cross-validation data.

CONCLUSIONS

A combined analysis using comprehensive serum BA concentration can be an efficient method for screening CRC.

Role of the Intestinal Microbiome, Intestinal Barrier and Psychobiotics in Depression

The intestinal microbiota plays an important role in the pathophysiology of depression. As determined, the microbiota influences the shaping and modulation of the functioning of the gut-brain axis. The intestinal microbiota has a significant impact on processes related to neurotransmitter synthesis, the myelination of neurons in the prefrontal cortex, and is also involved in the development of the amygdala and hippocampus. Intestinal bacteria are also a source of vitamins, the deficiency of which is believed to be related to the response to antidepressant therapy and may lead to exacerbation of depressive symptoms. Additionally, it is known that, in periods of excessive activation of stress reactions, the immune system also plays an important role, negatively affecting the tightness of the intestinal barrier and intestinal microflora. In this review, we have summarized the role of the gut microbiota, its metabolites, and diet in susceptibility to depression. We also describe abnormalities in the functioning of the intestinal barrier caused by increased activity of the immune system in response to stressors. Moreover, the presented study discusses the role of psychobiotics in the prevention and treatment of depression through their influence on the intestinal barrier, immune processes, and functioning of the nervous system.

Deoxycholic Acid-Induced Gut Dysbiosis Disrupts Bile Acid Enterohepatic Circulation and Promotes Intestinal Inflammation

BACKGROUND

A Western diet is a risk factor for the development of inflammatory bowel disease (IBD). High levels of fecal deoxycholic acid (DCA) in response to a Western diet contribute to bowel inflammatory injury. However, the mechanism of DCA in the natural course of IBD development remains unanswered.

AIMS

The aim of this study is to investigate the effect of DCA on the induction of gut dysbiosis and its roles in the development of intestinal inflammation.

METHODS

Wild-type C57BL/6J mice were fed an AIN-93G diet, either supplemented with or without 0.2% DCA, and killed at 24 weeks. Distal ileum and colon tissues were assessed by histopathological analysis. Hepatic and ileal gene expression was examined by qPCR, and the gut microbiota was analyzed by high-throughput 16S rRNA gene sequencing. HPLC-MS was used for fecal bile acid quantification.

RESULTS

Mice fed the DCA-supplemented diet developed focal areas of ileal and colonic inflammation, accompanied by alteration of the composition of the intestinal microbiota and accumulation of fecal bile acids. DCA-induced dysbiosis decreased the deconjugation of bile acids, and this regulation was associated with the repressed expression of target genes in the enterohepatic farnesoid X receptor-fibroblast growth factor (FXR-FGF15) axis, leading to upregulation of hepatic de novo bile acid synthesis.

CONCLUSIONS

These results suggest that DCA-induced gut dysbiosis may act as a key etiologic factor in intestinal inflammation, associated with bile acid metabolic disturbance and downregulation of the FXR-FGF15 axis.

Aberrant Gut-To-Brain Signaling in Irritable Bowel Syndrome - The Role of Bile Acids

Functional bowel disorders such as irritable bowel syndrome (IBS) are common, multifactorial and have a major impact on the quality of life of individuals diagnosed with the condition. Heterogeneity in symptom manifestation, which includes changes in bowel habit and visceral pain sensitivity, are an indication of the complexity of the underlying pathophysiology. It is accepted that dysfunctional gut-brain communication, which incorporates efferent and afferent branches of the peripheral nervous system, circulating endocrine hormones and local paracrine and neurocrine factors, such as host and microbially-derived signaling molecules, underpins symptom manifestation. This review will focus on the potential role of hepatic bile acids in modulating gut-to-brain signaling in IBS patients. Bile acids are amphipathic molecules synthesized in the liver, which facilitate digestion and absorption of dietary lipids. They are also important bioactive signaling molecules however, binding to bile acid receptors which are expressed on many different cell types. Bile acids have potent anti-microbial actions and thereby shape intestinal bacterial profiles. In turn, bacteria with bile salt hydrolase activity initiate the critical first step in transforming primary bile acids into secondary bile acids. Individuals with IBS are reported to have altered microbial profiles and modified bile acid pools. We have assessed the evidence to support a role for bile acids in the pathophysiology underlying the manifestation of IBS symptoms.

Synthetic G protein-coupled bile acid receptor agonists and bile acids act via basolateral receptors in ileal and colonic mucosa

BACKGROUND

The G protein-coupled bile acid (BA) receptor, GPBA (previously named TGR5), mediates BA gastrointestinal (GI) activities. Our aim was to elucidate the mucosal and motility responses to selective GPBA agonists compared with conjugated BA (eg, taurodeoxycholate, TDCA) in mouse and human colon.

METHODS

Ion transport responses to GPBA agonists or BAs were measured in mucosal preparations with intact submucous innervation, from C57Bl/6, PYY-/-, or GPBA-/- mice and compared with GPBA signaling in human colon. We also investigated the mechanisms underlying GPBA agonism in mucosae and on natural fecal pellet propulsion.

KEY RESULTS

GPBA agonist Merck V stimulated basolateral responses involving peptide YY (PYY), cholinergic, and 5-HT mechanisms in colonic mucosa. The PYY-mediated GPBA signal was glucose-sensitive. Luminal TDCA crossed the epithelial lining via the apical sodium-dependent BA transporter (ASBT) and its inhibitor, GSK2330672 significantly reduced luminal, but not basolateral TDCA activity. Merck V also slowed natural fecal pellet progression in wild-type and PYY-/- colons but not in GPBA-/- colon, while TDCA increased motility in wild-type colon. The antimotile GPBA effect was reversed by blockade of glucagon-like peptide 1 (GLP-1) receptors or nitric oxide synthase, indicating involvement of GLP-1 and nitric oxide.

CONCLUSIONS & INFERENCES

We conclude that several different targets within the lamina propria express GPBA, including L cells (that release PYY and GLP-1), enterochromaffin cells and neurons (that release 5-HT), and other enteric neurons. Furthermore, luminal-conjugated BAs require transport across the epithelium via ASBT in order to activate basolateral GPBA.

Gut Microbiota-Bile Acid Crosstalk in Diarrhea-Irritable Bowel Syndrome

The occurrence of diarrhea-predominant irritable bowel syndrome (IBS-D) is the result of multiple factors, and its pathogenesis has not yet been clarified. Emerging evidence indicates abnormal changes in gut microbiota and bile acid (BA) metabolism have a close relationship with IBS-D. Gut microbiota is involved in the secondary BA production via deconjugation, 7α-dehydroxylation, oxidation, epimerization, desulfation, and esterification reactions respectively. Changes in the composition and quantity of gut microbiota have an important impact on the metabolism of BAs, which can lead to the occurrence of gastrointestinal diseases. BAs, synthesized in the hepatocytes, play an important role in maintaining the homeostasis of gut microbiota and the balance of glucose and lipid metabolism. In consideration of the complex biological functional connections among gut microbiota, BAs, and IBS-D, it is urgent to review the latest research progress in this field. In this review, we summarized the alterations of gut microbiota in IBS-D and discussed the mechanistic connections between gut microbiota and BA metabolism in IBS-D, which may be involved in activating two important bile acid receptors, G-protein coupled bile acid receptor 1 (TGR5) and farnesoid X receptor (FXR). We also highlight the strategies of prevention and treatment of IBS-D via regulating gut microbiota-bile acid axis, including probiotics, fecal microbiota transplantation (FMT), cholestyramine, and the cutting-edge technology about bacteria genetic engineering.

[The inhibitors of the apical sodium-dependent bile acid transporter (ASBT) as promising drugs]

Inhibition of the apical sodium-dependent bile acid transporter (ASBT, also known as IBAT - ileal bile acid transporter, SLC10A2) leads to disruption of the enterohepatic circulation of bile acids and their excretion with fecal masses. This is accompanied by cholesterol utilization for synthesis of new bile acids. ASBT inhibitors are promising drugs for the treatment of such diseases as non-alcoholic fatty liver disease, non-alcoholic steatohepatitis, type 2 diabetes mellitus, necrotic enterocolitis, chronic constipation, atherosclerosis. To date the most known chemically synthesized inhibitors are: A3309, SHP626, A4250, 264W94, GSK2330672, SC-435. All of them are at different stages of clinical trials, which confirm the high efficacy and good tolerance of these inhibitors. Current trends in this field also include directed chemical synthesis of ASBT inhibitors, as well as their search among substances of plant origin.

Soil metabolome correlates with bacterial diversity and co-occurrence patterns in root-associated soils on the Tibetan Plateau

Metabolites in root-zone soils mediate microbe-to-microbe interactions and govern the overall microbial community. However, how chemicals relate to diversity and co-occurrence patterns of bacterial communities in root-associated soils is still poorly understood. Here, we studied the relationships of soil metabolome with bacterial community diversity and co-occurrence patterns in root-associated soils across different land types on the Tibetan Plateau. The soil metabolome mainly encompassed a range of organic acids, and sugars and sugar derivatives, which were widely negatively correlated with bacterial alpha-diversity. Compared to the investigated environmental variables, metabolites accounted more for the variations in the Shannon diversity and bacterial community compositions. Compared to sugars, organic acids accounted more for bacterial community compositions at high taxonomic ranks, while reversed at genus and species levels. The relative abundances of some bacterial genera and metabolites were closely linked to soil types and plant genotypes. The differential compounds were significantly correlated with the distinctive bacterial taxa across land types and plant genotypes. Keystone species in co-occurrence network, such as Bradyrhizobium, Bryobacter, and Microvirga were significantly correlated with sugars and organic acids. Structural equation modeling revealed that sugar metabolism can play a crucial role in altering the bacterial community diversity. This study provides new insights into the ecological mechanism that maintains bacterial community in the root-associated soils on the Tibetan Plateau.

Molecular Physiology of Bile Acid Signaling in Health, Disease, and Aging

Over the past two decades, bile acids (BAs) have become established as important signaling molecules that enable fine-tuned inter-tissue communication from the liver, their site of production, over the intestine, where they are modified by the gut microbiota, to virtually any organ, where they exert their pleiotropic physiological effects. The chemical variety of BAs, to a large extent determined by the gut microbiome, also allows for a complex fine-tuning of adaptive responses in our body. This review provides an overview of the mechanisms by which BA receptors coordinate several aspects of physiology and highlights new therapeutic strategies for diseases underlying pathological BA signaling.

A Clostridia-rich microbiota enhances bile acid excretion in diarrhea-predominant irritable bowel syndrome

An excess of fecal bile acids (BAs) is thought to be one of the mechanisms for diarrhea-predominant irritable bowel syndrome (IBS-D). However, the factors causing excessive BA excretion remain incompletely studied. Given the importance of gut microbiota in BA metabolism, we hypothesized that gut dysbiosis might contribute to excessive BA excretion in IBS-D. By performing BA-related metabolic and metagenomic analyses in 290 IBS-D patients and 89 healthy volunteers, we found that 24.5% of IBS-D patients exhibited excessive excretion of total BAs and alteration of BA-transforming bacteria in feces. Notably, the increase in Clostridia bacteria (e.g., C. scindens) was positively associated with the levels of fecal BAs and serum 7α-hydroxy-4-cholesten-3-one (C4), but negatively correlated with serum fibroblast growth factor 19 (FGF19) concentration. Furthermore, colonization with Clostridia-rich IBS-D fecal microbiota or C. scindens individually enhanced serum C4 and hepatic conjugated BAs but reduced ileal FGF19 expression in mice. Inhibition of Clostridium species with vancomycin yielded opposite results. Clostridia-derived BAs suppressed the intestinal FGF19 expression in vitro and in vivo. In conclusion, this study demonstrates that the Clostridia-rich microbiota contributes to excessive BA excretion in IBS-D patients, which provides a mechanistic hypothesis with testable clinical implications.

MAIT cell activation in adolescents is impacted by bile acid concentrations and body weight

Bile acids (BAs) are produced by liver hepatocytes and were recently shown to exert functions additional to their well-known role in lipid digestion. As yet it is not known whether the mucosal-associated invariant T (MAIT) cells, which represent 10-15% of the hepatic T cell population, are affected by BAs. The focus of the present investigation was on the association of BA serum concentration with MAIT cell function and inflammatory parameters as well as on the relationship of these parameters to body weight. Blood samples from 41 normal weight and 41 overweight children of the Lifestyle Immune System Allergy (LISA) study were analyzed with respect to MAIT cell surface and activation markers [CD107a, CD137, CD69, interferon (IFN)-γ, tumor necrosis factor (TNF)-α] after Escherichia coli stimulation, mRNA expression of promyelocytic leukemia zinc finger protein (PLZF) and major histocompatibility complex class I-related gene protein (MR1), the inflammatory markers C-reactive protein (CRP), interleukin (IL)-8 and macrophage inflammatory protein (MIP)-1α as well as the concentrations of 13 conjugated and unconjugated BAs. Higher body weight was associated with reduced MAIT cell activation and expression of natural killer cell marker (NKp80) and chemokine receptor (CXCR3). BA concentrations were positively associated with the inflammatory parameters CRP, IL-8 and MIP-1α, but were negatively associated with the number of activated MAIT cells and the MAIT cell transcription factor PLZF. These relationships were exclusively found with conjugated BAs. BA-mediated inhibition of MAIT cell activation was confirmed in vitro. Thus, conjugated BAs have the capacity to modulate the balance between pro- and anti-inflammatory immune responses.

Review article: fungal alterations in inflammatory bowel diseases

BACKGROUND

Emerging data suggest that alterations in gut fungi may be associated with the pathogenesis of inflammatory bowel disease (IBD). In healthy individuals, gut commensal fungi act synergistically with other members of the microbiota to maintain homeostasis but their role in IBD is less clear.

AIM

To review the role of gut fungi and their trans-kingdom interactions with bacteria in IBD METHODS: A literature search was conducted on Ovid and Pubmed to select relevant animal and human studies that have reported fungi and IBD.

RESULTS

There is an increased total fungal load particularly of Candida and Malassezia species in the faeces and mucosa of Crohn's disease patients, and a lower fungal diversity in the faeces of ulcerative colitis patients. Caspase recruitment domain-containing protein (CARD)-9 polymorphism in Crohn's disease patients favours Malassezia colonisation that worsens gut inflammation. Diet high in carbohydrates increased the total abundance of Candida species, whereas protein-rich diet had the opposite effect. Anti-fungal therapies are mostly used to treat Candida albicans or Histoplasma capsulatum infections in IBD, whereas pilot studies of supplementing fungal probiotics Saccharomycopsis fibuligera, Saccharomyces boulardii and Saccharomyces cerevisiae CNCM I-3856 strain showed therapeutic effects in IBD.

CONCLUSIONS

Gut fungi are altered in patients with Crohn's disease and ulcerative colitis. Modulation of the fungal microbiota can be considered as a therapeutic approach for IBD. Future research should focus on understanding how the fungal microbiota interacts with other components of the gut microbiota in association with the pathogenesis and development of IBD.

The Role of Bacteria and Its Derived Metabolites in Chronic Pain and Depression: Recent Findings and Research Progress

BACKGROUND

Chronic pain is frequently comorbid with depression in clinical practice. Recently, alterations in gut microbiota and metabolites derived therefrom have been found to potentially contribute to abnormal behaviors and cognitive dysfunction via the "microbiota-gut-brain" axis.

METHODS

PubMed was searched and we selected relevant studies before October 1, 2019. The search keyword string included "pain OR chronic pain" AND "gut microbiota OR metabolites"; "depression OR depressive disorder" AND "gut microbiota OR metabolites". We also searched the reference lists of key articles manually.

RESULTS

This review systematically summarized the recent evidence of gut microbiota and metabolites in chronic pain and depression in animal and human studies. The results showed the pathogenesis and therapeutics of chronic pain and depression might be partially due to gut microbiota dysbiosis. Importantly, bacteria-derived metabolites, including short-chain fatty acids, tryptophan-derived metabolites, and secondary bile acids, offer new insights into the potential linkage between key triggers in gut microbiota and potential mechanisms of depression.

CONCLUSION

Studying gut microbiota and its metabolites has contributed to the understanding of comorbidity of chronic pain and depression. Consequently, modulating dietary structures or supplementation of specific bacteria may be an available strategy for treating chronic pain and depression.

Protection of the Ovine Fetal Gut against Ureaplasma-Induced Chorioamnionitis: A Potential Role for Plant Sterols

Chorioamnionitis, clinically most frequently associated with Ureaplasma, is linked to intestinal inflammation and subsequent gut injury. No treatment is available to prevent chorioamnionitis-driven adverse intestinal outcomes. Evidence is increasing that plant sterols possess immune-modulatory properties. Therefore, we investigated the potential therapeutic effects of plant sterols in lambs intra-amniotically (IA) exposed to Ureaplasma. Fetal lambs were IA exposed to Ureaplasma parvum (U. parvum, UP) for six days from 127 d-133 d of gestational age (GA). The plant sterols β-sitosterol and campesterol, dissolved with β-cyclodextrin (carrier), were given IA every two days from 122 d-131 d GA. Fetal circulatory cytokine levels, gut inflammation, intestinal injury, enterocyte maturation, and mucosal phospholipid and bile acid profiles were measured at 133 d GA (term 150 d). IA plant sterol administration blocked a fetal inflammatory response syndrome. Plant sterols reduced intestinal accumulation of proinflammatory phospholipids and tended to prevent mucosal myeloperoxidase-positive (MPO) cell influx, indicating an inhibition of gut inflammation. IA administration of plant sterols and carrier diminished intestinal mucosal damage, stimulated maturation of the immature epithelium, and partially prevented U. parvum-driven reduction of mucosal bile acids. In conclusion, we show that β-sitosterol and campesterol administration protected the fetus against adverse gut outcomes following UP-driven chorioamnionitis by preventing intestinal and systemic inflammation.

Farnesoid X receptor represses matrix metalloproteinase 7 expression, revealing this regulatory axis as a promising therapeutic target in colon cancer

The farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily of bile acid-activated transcription factors and an important regulator of cell proliferation, apoptosis, and Wnt signaling. Down-regulated expression of FXR plays an important role in some malignancies such as colon cancer, and in rodent models of intestinal neoplasia, FXR knockout increases the size and number of colon tumors. These previous observations implicate FXR as a tumor suppressor, but the underlying molecular mechanisms are unclear. Employing complementary experimental approaches and using human colon cancer specimens, human and murine colon cancer cell lines, and FXR transgenic mice, here we identified an additional, potentially important role for FXR. We observed an inverse relationship between the expression of FXR and matrix metalloproteinase-7 (MMP7), a collagenase and signaling molecule consistently associated with colon cancer progression. We noted that FXR gene ablation increases MMP7 expression. Consistent with this finding, FXR overexpression and a dominant-negative FXR mutation reduced and augmented, respectively, MMP7 expression. Of note, MMP7 was the only MMP gene family member whose expression was down-regulated after FXR activation. FXR-mediated regulation of MMP7 transcription did not require heterodimerization with the retinoid X receptor (RXR), indicating that FXR represses MMP7 expression independently of RXR. Last, we uncovered that FXR suppresses MMP7 transcription by binding to a negative FXR-responsive element in the 5' MMP7 promoter, an event that inhibited colon cancer cell proliferation and invasion. These findings identify the FXR-MMP7 axis as a potential therapeutic target for managing colon cancer.

Secondary Bile Acids and Short Chain Fatty Acids in the Colon: A Focus on Colonic Microbiome, Cell Proliferation, Inflammation, and Cancer

Secondary bile acids (BAs) and short chain fatty acids (SCFAs), two major types of bacterial metabolites in the colon, cause opposing effects on colonic inflammation at chronically high physiological levels. Primary BAs play critical roles in cholesterol metabolism, lipid digestion, and host–microbe interaction. Although BAs are reabsorbed via enterohepatic circulation, primary BAs serve as substrates for bacterial biotransformation to secondary BAs in the colon. High-fat diets increase secondary BAs, such as deoxycholic acid (DCA) and lithocholic acid (LCA), which are risk factors for colonic inflammation and cancer. In contrast, increased dietary fiber intake is associated with anti-inflammatory and anticancer effects. These effects may be due to the increased production of the SCFAs acetate, propionate, and butyrate during dietary fiber fermentation in the colon. Elucidation of the molecular events by which secondary BAs and SCFAs regulate colonic cell proliferation and inflammation will lead to a better understanding of the anticancer potential of dietary fiber in the context of high-fat diet-related colon cancer. This article reviews the current knowledge concerning the effects of secondary BAs and SCFAs on the proliferation of colon epithelial cells, inflammation, cancer, and the associated microbiome.

Bile Acid Receptors and Gastrointestinal Functions

Bile acids modulate several gastrointestinal functions including electrolyte secretion and absorption, gastric emptying, and small intestinal and colonic motility. High concentrations of bile acids lead to diarrhea and are implicated in the development of esophageal, gastric and colonic cancer. Alterations in bile acid homeostasis are also implicated in the pathophysiology of irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). Our understanding of the mechanisms underlying these effects of bile acids on gut functions has been greatly enhanced by the discovery of bile acid receptors, including the nuclear receptors: farnesoid X receptor (FXR), vitamin D receptor (VDR), pregnane X receptor (PXR), and constitutive androstane receptor (CAR); and the G protein-coupled receptors: Takeda G protein-coupled receptor (TGR5), sphingosine-1-phosphate receptor 2 (S1PR2), and muscarinic acetylcholine receptor M3 (M3R).. For example, various studies provided evidence demonstrating the anti-inflammatory effects FXR and TGR5 activation in models of intestinal inflammation. In addition, TGR5 activation in enteric neurons was recently shown to increase colonic motility, which may lead to bile acid-induced diarrhea. Interestingly, TGR5 induces the secretion of glucagon-like peptide-1 (GLP-1) from L-cells to enhance insulin secretion and modulate glucose metabolism. Because of the importance of these receptors, agonists of TGR5 and intestine-specific FXR agonists are currently being tested as an option for the treatment of diabetes mellitus and primary bile acid diarrhea, respectively. This review summarizes current knowledge of the functional roles of bile acid receptors in the gastrointestinal tract.

Streptococcus macedonicus strains isolated from traditional fermented milks: resistance to gastrointestinal environment and adhesion ability

In this study, Streptococcus macedonicus (S. macedonicus) strains were identified from Algerian traditional fermented milks (Lben and Rayeb). Important prerequisites of probiotic interest such as acidity, bile salts tolerance, and adhesion ability to epithelial cells were investigated. A combination of phenotypic (ability to grow on Bile Esculin Azide medium, BEA; on high salt content medium NaCl 6.5%; on alkaline medium pH 9.6) and genotypic approaches (16S rRNA, ITS genes sequencing and MLST technique) allowed to identify four genetically distinct strains of S. macedonicus. These four strains and two references, Streptococcus thermophilus LMD-9 and Lactobacillus rhamnosus GG (LGG), were tested for their capacity to survive at low pH values, and at different concentrations of an equimolar bile salts mixture (BSM). Two different cell lines, Caco-2 TC7 and HT29-MTX, were used for the adhesion study. The results show that S. macedonicus strains selected constitute a distinct genetic entity from the Greek strain S. macedonicus ACA-DC-198. They were able to survive up to pH 3 and could tolerate high concentrations of bile salts (10 mM), unlike LMD-9 and LGG strains. Our strains also display in vitro adhesion similar to the LGG strain on Caco-2 TC7 and higher adhesion than the LMD-9 strain to Caco-2 TC7 and HT29-MTX cell models. This first characterization allows considering S. macedonicus as a potential candidate for possible probiotic effects that need to be investigated.

Bile acids induce visceral hypersensitivity via mucosal mast cell-to-nociceptor signaling that involves the farnesoid X receptor/nerve growth factor/transient receptor potential vanilloid 1 axis

Increased colonic bile acid (BA) exposure, frequent in diarrhea-predominant irritable bowel syndrome (IBS-D), can affect gut function. Nerve growth factor (NGF) is implicated in the development of visceral hypersensitivity (VH). In this study, we tested the hypothesis that BAs cause VH via mucosal mast cell (MMC)-to-nociceptor signaling, which involves the farnesoid X receptor (FXR)/NGF/transient receptor potential vanilloid (TRPV)1 axis. BAs were intracolonically administered to rats for 15 d. Visceral sensitivity to colorectal distention and colonic NGF expression were examined. BAs caused VH, an effect that involved MMC-derived NGF and was accompanied by enhanced TRPV1 expression in the dorsal root ganglia. Anti-NGF treatment and TRPV1 antagonism inhibited BA-induced VH. BAs induced NGF mRNA and protein expression and release in cultured mast cells. Colonic supernatants from patients with IBS-D with elevated colonic BA content transcriptionally induced NGF expression. In FXR^-/- mice, visceral sensitivity and colonic NGF expression were unaltered after BA treatment. Pharmacological antagonism and FXR silencing suppressed BA-induced NGF expression and release in mast cells. Mitogen-activated protein kinase kinase (MKK) 3/6/p38 MAPK/NF-κB signaling was mechanistically responsible for FXR-mediated NGF expression and secretion. The findings show an MMC-dependent and FXR-mediated pronociceptive effect of BAs and identify the BA/FXR/NGF/TRPV1 axis as a key player in MMC-to-neuron communication during pain processing in IBS.-Li, W.-T., Luo, Q.-Q., Wang, B., Chen, X., Yan, X.-J., Qiu, H.-Y., Chen, S.-L. Bile acids induce visceral hypersensitivity via mucosal mast cell-to-nociceptor signaling that involves the farnesoid X receptor/nerve growth factor/transient receptor potential vanilloid 1 axis.

Deoxycholic acid activates epidermal growth factor receptor and promotes intestinal carcinogenesis by ADAM17-dependent ligand release

High fat diet is implicated in the elevated deoxycholic acid (DCA) in the intestine and correlated with increased colon cancer risk. However, the potential mechanisms of intestinal carcinogenesis by DCA remain unclarified. Here, we investigated the carcinogenic effects and mechanisms of DCA using the intestinal tumour cells and Apc^min/+ mice model. We found that DCA could activate epidermal growth factor receptor (EGFR) and promote the release of EGFR ligand amphiregulin (AREG), but not HB‐EGF or TGF‐α in intestinal tumour cells. Moreover, ADAM‐17 was required in DCA‐induced promotion of shedding of AREG and activation of EGFR/Akt signalling pathway. DCA significantly increased the multiplicity of intestinal tumours and accelerated adenoma‐carcinoma sequence in Apc^min/+ mice. ADAM‐17/EGFR signalling axis was also activated in intestinal tumours of DCA‐treated Apc^min/+ mice, whereas no significant change occurred in tumour adjacent tissues after DCA exposure. Conclusively, DCA activated EGFR and promoted intestinal carcinogenesis by ADAM17‐dependent ligand release.

The Yin and Yang of bile acid action on tight junctions in a model colonic epithelium

Gastrointestinal epithelial barrier loss due to tight junction (TJ) dysfunction and bile acid‐induced diarrhea are common in patients with inflammatory diseases. Although excess colonic bile acids are known to alter mucosal permeability, few studies have compared the effects of specific bile acids on TJ function. We report that the primary bile acid, chenodeoxycholic acid (CDCA), and its 7α‐dehydroxylated derivative, lithocholic acid (LCA) have opposite effects on epithelial integrity in human colonic T84 cells. CDCA decreased transepithelial barrier resistance (pore) and increased paracellular 10 kDa dextran permeability (leak), effects that were enhanced by proinflammatory cytokines (PiC [ng/mL]: TNFα[10] + IL‐1ß[10] + IFNγ[30]). CDCA reversed the cation selectivity of the monolayer and decreased intercellular adhesion. In contrast, LCA alone did not alter any of these parameters, but attenuated the effects of CDCA ± PiC on paracellular permeability. CDCA, but not PiC, decreased occludin and not claudin‐2 protein expression; CDCA also decreased occludin localization. LCA ± CDCA had no effects on occludin or claudin expression/localization. While PiC and CDCA increased IL‐8 production, LCA reduced both basal and PiC ± CDCA‐induced IL‐8 production. TNFα + IL1ß increased IFNγ, which was enhanced by CDCA and attenuated by LCA. CDCA±PiC increased production of reactive oxygen species (ROS) that was attenuated by LCA. Finally, scavenging ROS attenuated CDCA's leak, but not pore actions, and LCA enhanced this effect. Thus, in T84 cells, CDCA plays a role in the inflammatory response causing barrier dysfunction, while LCA restores barrier integrity. Understanding the interplay of LCA, CDCA, and PiC could lead to innovative therapeutic strategies for inflammatory and diarrheal diseases.

Therapeutic modulation of the bile acid pool by Cyp8b1 knockdown protects against nonalcoholic fatty liver disease in mice

Bile acids (BAs) are surfactant molecules that regulate the intestinal absorption of lipids. Thus, the modulation of BAs represents a potential therapy for nonalcoholic fatty liver disease (NAFLD), which is characterized by hepatic accumulation of fat and is a major cause of liver disease worldwide. Cyp8b1 is a critical modulator of the hydrophobicity index of the BA pool. As a therapeutic proof of concept, we aimed to determine the impact of Cyp8b1 inhibition in vivo on BA pool composition and as protection against NAFLD. Inhibition of Cyp8b1 expression in mice led to a remodeling of the BA pool, which altered its signaling properties and decreased intestinal fat absorption. In a model of cholesterol-induced NAFLD, Cyp8b1 knockdown significantly decreased steatosis and hepatic lipid content, which has been associated with an increase in fecal lipid and BA excretion. Moreover, inhibition of Cyp8b1 not only decreased hepatic lipid accumulation, but also resulted in the clearance of previously accumulated hepatic cholesterol, which led to a regression in hepatic steatosis. Taken together, our data demonstrate that Cyp8b1 inhibition is a viable therapeutic target of crucial interest for metabolic diseases, such as NAFLD.-Chevre, R., Trigueros-Motos, L., Castaño, D., Chua, T., Corlianò, M., Patankar, J. V., Sng, L., Sim, L., Juin, T. L., Carissimo, G., Ng, L. F. P., Yi, C. N. J., Eliathamby, C. C., Groen, A. K., Hayden, M. R., Singaraja, R. R. Therapeutic modulation of the bile acid pool by Cyp8b1 knockdown protects against nonalcoholic fatty liver disease in mice.

Bile Acids and Cancer: Direct and Environmental-Dependent Effects

Bile acids (BAs) regulate the absorption of fat-soluble vitamins, cholesterol and lipids but have also a key role as singalling molecules and in the modulation of epithelial cell proliferation, gene expression and metabolism. These homeostatic pathways, when disrupted, are able to promote local inflammation, systemic metabolic disorders and, ultimately, cancer. The effect of hydrophobic BAs, in particular, can be linked with cancer in several digestive (mainly oesophagus, stomach, liver, pancreas, biliary tract, colon) and extra-digestive organs (i.e. prostate, breast) through a complex series of mechanisms including direct oxidative stress with DNA damage, apoptosis, epigenetic factors regulating gene expression, reduced/increased expression of nuclear receptors (mainly farnesoid X receptor, FXR) and altered composition of gut microbiota, also acting as a common interface between environmental factors (including diet, lifestyle, exposure to toxics) and the molecular events promoting cancerogenesis. Primary prevention strategies (i.e. changes in dietary habits and lifestyle, reduced exposure to environmental toxics) mainly able to modulate gut microbiota and the epigenome, and the therapeutic use of hydrophilic BAs to counterbalance the negative effects of the more hydrophobic BAs might be, in the near future, part of useful tools for cancer prevention and management.

The Effect of Deoxycholic Acid on Secretion and Motility in the Rat and Guinea Pig Large Intestine

Background/Aims

Bile acid is an important luminal factor that affects gastrointestinal motility and secretion. We investigated the effect of bile acid on secretion in the proximal and distal rat colon and coordination of bowel movements in the guinea pig colon.

Methods

The short-circuit current from the mucosal strip of the proximal and distal rat colon was compared under control conditions after induction of secretion with deoxycholic acid (DCA) as well as after inhibition of secretion with indomethacin, 1,2-bis (o-aminophenoxy) ethane-N,N,N′,N′-tetra-acetic acid (an intracellular calcium chelator; BAPTA), and tetrodotoxin (TTX) using an Ussing chamber. Colonic pressure patterns were also evaluated in the extracted guinea pig colon during resting, DCA stimulation, and inhibition by TTX using a newly developed pressure-sensing artificial stool.

Results

The secretory response in the distal colon was proportionate to the concentration of DCA. Also, indomethacin, BAPTA, and TTX inhibited chloride secretion in response to DCA significantly (P < 0.05). However, these changes were not detected in the proximal colon. When we evaluated motility, we found that DCA induced an increase in luminal pressure at the proximal, middle, and distal sensors of an artificial stool simultaneously during the non-peristaltic period (P < 0.05). In contrast, during peristalsis, DCA induced an increase in luminal pressure at the proximal sensor and a decrease in pressure at the middle and distal sensors of the artificial stool (P < 0.05).

Conclusions

DCA induced a clear segmental difference in electrogenic secretion. Also, DCA induced a more powerful peristaltic contraction only during the peristaltic period.

Positive Glucose Breath Tests in Patients with Hysterectomy, Gastrectomy, and Cholecystectomy

Background/Aims

This study aimed to investigate the prevalence and characteristics of small intestinal bacterial overgrowth (SIBO) in patients undergoing abdominal surgeries, such as gastrectomy, cholecystectomy, and hysterectomy.

Methods

One hundred seventy-one patients with surgery (50 hysterectomy, 14 gastrectomy, and 107 cholecystectomy), 665 patients with functional gastrointestinal disease (FGID) and 30 healthy controls undergoing a hydrogen (H₂)-methane (CH₄) glucose breath test (GBT) were reviewed.

Results

GBT positivity (+) was significantly different among the surgical patients (43.9%), FGID patients (31.9%), and controls (13.3%) (p<0.01). With respect to the patients, 65 (38.0%), four (2.3%), and six (3.5%) surgical patients and 150 (22.6%), 30 (4.5%), and 32 (4.8%) FGID patients were in the GBT (H₂)+, (CH₄)+ and (mixed)+ groups, respectively (p<0.01). The gastrectomy group had a significantly increased preference in GBT+ (71.4% vs 42.0% or 41.1%, respectively) and GBT (H₂)+ (64.3% vs 32.0% or 37.4%, respectively) compared with the hysterectomy or cholecystectomy groups (p<0.01). During GBT, the total H₂ was significantly increased in the gastrectomy group compared with the other groups.

Conclusions

SIBO producing H₂ is common in abdominal surgical patients. Different features for GBT+ may be a result of the types of abdominal surgery.

Fungal microbiota dysbiosis in IBD

OBJECTIVE

The bacterial intestinal microbiota plays major roles in human physiology and IBDs. Although some data suggest a role of the fungal microbiota in IBD pathogenesis, the available data are scarce. The aim of our study was to characterise the faecal fungal microbiota in patients with IBD.

DESIGN

Bacterial and fungal composition of the faecal microbiota of 235 patients with IBD and 38 healthy subjects (HS) was determined using 16S and ITS2 sequencing, respectively. The obtained sequences were analysed using the Qiime pipeline to assess composition and diversity. Bacterial and fungal taxa associated with clinical parameters were identified using multivariate association with linear models. Correlation between bacterial and fungal microbiota was investigated using Spearman's test and distance correlation.

RESULTS

We observed that fungal microbiota is skewed in IBD, with an increased Basidiomycota/Ascomycota ratio, a decreased proportion of Saccharomyces cerevisiae and an increased proportion of Candida albicans compared with HS. We also identified disease-specific alterations in diversity, indicating that a Crohn's disease-specific gut environment may favour fungi at the expense of bacteria. The concomitant analysis of bacterial and fungal microbiota showed a dense and homogenous correlation network in HS but a dramatically unbalanced network in IBD, suggesting the existence of disease-specific inter-kingdom alterations.

CONCLUSIONS

Besides bacterial dysbiosis, our study identifies a distinct fungal microbiota dysbiosis in IBD characterised by alterations in biodiversity and composition. Moreover, we unravel here disease-specific inter-kingdom network alterations in IBD, suggesting that, beyond bacteria, fungi might also play a role in IBD pathogenesis.

Reduction of epithelial secretion in male rat distal colonic mucosa by bile acid receptor TGR5 agonist, INT-777: role of submucosal neurons

BACKGROUND

Recent evidence from rat neuron-free mucosa study suggests that the membrane bile acid receptor TGR5 decreases colonic secretion under basal and stimulated conditions. As submucosal neurons are key players in secretory processes and highly express TGR5, we investigated their role in TGR5 agonist-induced inhibition of secretion and the pathways recruited.

METHODS

TGR5 expression and localization were assessed in rat proximal (pC) and distal (dC) colon by qPCR and immunohistochemistry with double labeling for cholinergic neurons in whole-mount preparations. The influence of a selective (INT-777) or weak (ursodeoxycholic acid, UDCA) TGR5 agonist on colonic secretion was assessed in Ussing chambers, in dC preparation removing seromuscular ± submucosal tissues, in the presence of different inhibitors of secretion pathways.

KEY RESULTS

TGR5 mRNA is expressed in full thickness dC and pC and immunoreactivity is located in colonocytes and pChAT-positive neurons. Addition of INT-777, and less potently UDCA, decreased colonic secretion in seromuscular stripped dC by -58.17± 2.6%. INT-777 effect on basal secretion was reduced in neuron-free and TTX-treated mucosal-submucosal preparations. Atropine, hexamethonium, indomethacin, and L-NAME all reduced significantly INT-777's inhibitory effect while the 5-HT₄ antagonist, RS-39604, and lidocaine abolished it. INT-777 inhibited stimulated colonic secretion induced by nicotine, but not cisapride, carbachol or PGE2.

CONCLUSIONS & INFERENCES

TGR5 activation inhibits basal and stimulated distal colonic secretion in rats by acting directly on epithelial cells and also inhibiting submucosal neurons. This could represent a counter-regulatory mechanism, at the submucosal level, of the known prosecretory effect of bile acids in the colon.

Dose-response effect of berberine on bile acid profile and gut microbiota in mice

Background

Berberine (BBR) is a traditional antimicrobial herbal medicine. Recently, BBR has gained popularity as a supplement to lower blood lipids, cholesterol and glucose. Bile acids (BAs) are known to regulate blood levels of triglycerides, cholesterol, glucose and energy homeostasis, and gut flora play an important role in BA metabolism. However, whether BBR alters BAs metabolism or dose-response effect of BBR on gut flora is unknown.

Methods

In this study, the effects of various doses of BBR on the concentrations of BAs in liver and serum of male C57BL/6 mice were determined by UPLC-MS/MS, and the expression of BA-related genes, as well as the amount of 32 of the most abundant gut bacterial species in the terminal ileum and large intestine of male C57BL/6 mice were quantified by RT-PCR and Quantigene 2.0 Reagent System, respectively.

Results

Unconjugated BAs and total BAs were significantly altered by BBR in serum but not in liver. Increased primary BAs (βMCA, TβMCA and TUDCA) and decreased secondary BAs (DCA, LCA and the T-conjugates) were observed in livers and serum of mice fed BBR. The expression of BA-synthetic enzymes (Cyp7a1 and 8b1) and uptake transporter (Ntcp) increased 39-400 % in liver of mice fed the higher doses of BBR, whereas nuclear receptors and efflux transporters were not markedly altered. In addition, Bacteroides were enriched in the terminal ileum and large bowel of mice treated with BBR.

Conclusion

The present study indicated that various doses of BBR have effects on BA metabolism and related genes as well as intestinal flora, which provides insight into many pathways of BBR effects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1367-7) contains supplementary material, which is available to authorized users.