Interplay between gut microbiota and bile acids in diarrhoea-predominant irritable bowel syndrome: a review.

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disease that disturbs the physiology and psychology of patients and increases the burden on families, the healthcare system, society, and economic development, affecting more and more people around the world. Despite the multiple factors that account for IBS remaining incompletely studied, emerging evidence demonstrated the abnormal changes in gut microbiota and bile acids (BAs) metabolism closely associated with IBS. Moreover, microbiota drives significant modifications for BAs, consisting of deconjugation, 7α-dehydroxylation, oxidation, epimerization, desulfation, esterification, and so on, while BAs, in turn, affect the microbiota directly or indirectly. In light of the complex connection among gut microbiota, BAs, and IBS, it is urgent to review the latest research progress in this field. In this review, we described the disorders of intestinal microecology and BAs profiles in IBS-D and also highlighted the cross-talk between gut microbiota and BAs in the context of IBS-D. Integrating these, we suggest that new therapeutic strategies targeting the microbiota-BAs axis for IBS-D, even for other related diseases caused by bacteria-bile acid dysbiosis should be expected.

Involvement of mucosal flora and enterochromaffin cells of the caecum and descending colon in diarrhoea-predominant irritable bowel syndrome.

BACKGROUND: Accumulating evidence supports the pivotal role of intestinal flora in irritable bowel syndrome (IBS). Serotonin synthesis by enterochromaffin (EC) cells is influenced by the gut microbiota and has been reported to have an interaction with IBS. The comparison between the microbiota of the caecal and colonic mucosa in IBS has rarely been studied. The aim of this study was to investigate the relationship between the gut microbiota, EC cells in caecum and descending colon, and diarrhoea-predominant IBS (IBS-D) symptoms. RESULTS: A total of 22 IBS-D patients and 22 healthy controls (HCs) were enrolled in our study. Hamilton anxiety (HAM-A) and Hamilton depression (HAM-D) grades increased significantly in IBS-D patients. In addition, the frequency of defecation in IBS-D patients was higher than that in HCs. Among the preponderant bacterial genera, the relative abundance of the Ruminococcus_torques_ group increased in IBS-D patients in caecum samples while Raoultella and Fusobacterium were less abundant. In the descending colon, the abundance of the Ruminococcus_torques_group and Dorea increased in IBS-D patients and Fusobacterium decreased. No difference was observed between the descending colon and caecum in regards to the mucosal-associated microbiota. The number of EC cells in the caecum of IBS-D patients was higher than in HCs and the expression of TPH1 was higher in IBS-D patients both in the caecum and in the descending colon both at the mRNA and protein level. Correlation analysis showed that the Ruminococcus_torques_group was positively associated with HAM-A, HAM-D, EC cell number, IBS-SSS, degree of abdominal pain, frequency of abdominal pain and frequency of defecation. The abundance of Dorea was positively associated with EC cell number, IBS-SSS, HAM-A, HAM-D and frequency of abdominal pain. CONCLUSIONS: EC cell numbers increased in IBS-D patients and the expression of TPH1 was higher than in HCs. The Ruminococcus torques group and Dorea furthermore seem like promising targets for future research into the treatment of IBS-D patients.

Impact of symptom severity in patients with diarrhoea-predominant irritable bowel syndrome (IBS-D): results from two separate surveys of HCPs and patients with IBS-D.

BACKGROUND: Management of diarrhoea-predominant irritable bowel syndrome (IBS-D) is generally based on patient-reported symptoms; however, limited information on symptom severity exists. The objective of the study was to assess the impact of IBS-D severity on patient burden and patient and healthcare professional attitudes towards IBS. METHODS: We conducted two web-based surveys of healthcare professionals and patients from Australia, Canada and Europe. We analysed patient characteristics and attitudes by IBS-D severity, which was assessed retrospectively using a composite of four variables: worst abdominal pain, IBS symptom frequency, Bristol Stool Form Scale and quality of life. RESULTS: Of 679 healthcare professional respondents, one-third routinely classified patients by severity. The patient survey was completed by 513 patients with mild (26%), moderate (33%) and severe (41%) IBS-D, classified using the composite scale. Age, sex and treatment satisfaction did not change with severity; however, 19% of patients classified with severe IBS-D agreed with the statement: 'When my IBS is bad, I wish I was dead' versus 4 and 7% of patients with mild and moderate IBS-D, respectively (p < 0.05). Significantly more patients classified with severe IBS-D reported medication use versus mild IBS-D. CONCLUSION: Compared with milder symptoms, severe IBS-D was associated with increased medication use and a negative perspective of IBS-D. This highlights the need for a validated severity scale to inform treatment decisions.

Tong-Xie-Yao-Fang improves intestinal permeability in diarrhoea-predominant irritable bowel syndrome rats by inhibiting the NF-κB and notch signalling pathways.

BACKGROUND: Tong-Xie-Yao-Fang (TXYF) has been shown to be effective in diarrhoea-predominant irritable bowel syndrome (IBS-D) patients. However, the underlying mechanism remains to be clarified. The aim of this study was to investigate the efficacy and related mechanisms of TXYF in an IBS-D rat model. METHODS: The IBS-D rat model was established with 4% acetic acid and evaluated by haematoxylin-eosin (HE) staining. Then, IBS-D rats were divided into control, TXYF and rifaximin groups and treated intragastrically with normal saline, TXYF and rifaximin, respectively, for 14 days. The following indicators were measured before and after treatment: defecation frequency, faecal water content (FWC) and colorectal distension (CRD). Histopathological changes in the distal colon were observed after treatment. The expression of OCLN and ZO1 in the distal colon of IBS-D rats reflected the intestinal mucosal permeability, as measured by qRT-PCR, western blot, and enzyme-linked immunosorbent assays (ELISAs). The NF-κB and Notch signalling pathways and inflammation-related factors were investigated. RESULTS: After treatment with TXYF, the defecation frequency, FWC and CRD were significantly lower than those in the model group (P < 0.05). HE staining showed that colonic epithelial cells (CECs) in the IBS-D rats displayed significant oedema, impaired intestinal mucosal integrity and an increased influx of inflammatory cells. A significant reduction in granulocyte and CEC oedema was observed after the administration of TXYF and rifaximin compared to that of the model group and blank group (P < 0.05). TXYF significantly upregulated the expression of OCLN and ZO-1 and downregulated inflammation-related factors (IL-6, IL-1ß, and TNF-α and the chemokine KC) in IBS-D rats compared to those in the model group rats (P < 0.05). In terms of the NF-κB and Notch signalling pathways, the expression of NICD, p-ERK, Hes-1 and p-P65 decreased significantly in the TXYF and rifaximin groups, while the expression of ATOH1 increased significantly compared to that in the model group (P < 0.05). CONCLUSION: TXYF can effectively improve intestinal permeability and enhance intestinal mucosal barrier function, which may be related to inhibition of the inflammatory cascade and the NF-κB and Notch signalling pathways.

Noninvasive biomarkers of gut barrier function identify two subtypes of patients suffering from diarrhoea predominant-IBS: a case-control study.

BACKGROUND: Alterations of the small-intestinal permeability (s-IP) might play an essential role in both diarrhoea-predominant IBS (D-IBS) and celiac disease (CD) patients. Our aims were to analyse in D-IBS patients the symptom profile along with the levels of urinary sucrose (Su), lactulose (La), mannitol (Ma), and circulating biomarkers (zonulin, intestinal fatty acid binding protein - I-FABP, and diamine oxidase - DAO) of the gastrointestinal (GI) barrier function. The pro-inflammatory interleukins 6 and 8 (IL-6 and IL-8), the plasma values of lipopolysaccharide (LPS), and Toll-like receptor 4 (TLR-4) were also investigated. Besides, these biomarkers were compared with those in CD and healthy controls (HC). Finally, comparisons were performed between D-IBS patients with [D-IBS(+)] and without [D-IBS(-)] increased s-IP according to normal or altered La/Ma ratio. METHODS: The study included 39 D-IBS patients, 32 CD patients, and 20 HC. GI permeability was assayed by high-performance liquid chromatography determination in the urine of Su and La/Ma ratio. ELISA kits assayed circulating concentrations of zonulin, I-FABP, DAO, IL-6, IL-8, LPS, and TLR-4. The Mann-Whitney or the Kruskal-Wallis with Dunn's post-test was used to assess differences among the groups. RESULTS: As for the La/Ma ratio, %Su, and I-FABP levels, D-IBS patients were significantly different from CD, but not HC. IL-6 levels were significantly higher in CD than HC, whereas IL-8 levels were significantly higher in both D-IBS and CD patients than HC. By opposite, LPS, and TLR-4 concentrations did not differ significantly among the groups. When D-IBS patients were categorised according to normal or altered s-IP, D-IBS(+) patients had %La, %Su, I-FABP, and DAO levels significantly higher than D-IBS(-) ones. The inflammatory parameters and markers of bacterial translocation (namely, IL-6 and LPS) were significantly higher in D-IBS(+) patients than D-IBS(-) ones. CONCLUSIONS: The present study suggests that two distinct D-IBS subtypes could be identified. The investigation of possible s-IP alterations (i.e., considering the La/Ma ratio) might be useful to assess better and categorise this heterogeneous D-IBS population. TRIAL REGISTRATION: NCT01574209 . Registered March 2012. First recruitment started in April 2012.

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

AIMS: To 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. METHODS: The 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. RESULTS: The 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. CONCLUSIONS: Colonic mucosal TGR5 protein expression and faecal bile acids were correlated with the symptom severity of IBS-D patients.

The mechanisms of action of WeiChang'An Pill (WCAP) treat diarrhoea-predominant irritable bowel syndrome (IBS-D) using network pharmacology approach and in vivo studies.

ETHNOPHARMACOLOGICAL RELEVANCE: WeiChang'An Pill (WCAP) is used in Traditional Chinese Medicine (TCM) to clinically treat diarrhoea-predominant irritable bowel syndrome (IBS-D); however, the underlying pharmacological mechanisms are unclear to date. AIM OF THE STUDY: To explore the mechanism underlying the therapeutic action of WCAP in IBS-D using a network pharmacology approach and in vivo experiments. MATERIALS AND METHODS: The active compounds of WCAP were selected from the TCM Systems Pharmacology Database and TCM Integrated Database, and the potential targets were identified using the Swiss Target Prediction and Similarity Ensemble Approach (SEA) databases. The targets related to IBS-D were mined from the Therapeutic Target Database (TTD), National Center for Biotechnology Information Search database (NCBI), DrugBank database, and DisGeNET database. The intersecting protein-protein interactions (PPIs) of the drug-disease crossover genes were analysed, and the central PPI network was constructed using the String database, version 11.0, and Cytoscape version 3.7.2. Following Gene Ontology and Kyoto Encyclopaedia of Genes and Genomes pathway analyses, the gene-pathway network was constructed for identifying the key target genes and pathways. Based on the results and existing evidence, it was selected the cyclic adenosine monophosphate (cAMP) signalling pathway for further validation using in vivo experiments. RESULTS: A total of 872 targets were identified from the 77 active compounds in WCAP, which shared 78 targets that were predicted to be related to IBS-D. Twenty-one core targets were identified from the PPI network, which was constructed from the common targets. The results of enrichment analysis revealed that HRT2B, ADRA1A, ADRA1D, and CHRM2 could be the key targets of WCAP in IBS-D, and 11 signalling pathways, including the neuroactive ligand-receptor interaction, calcium signalling, and cAMP signalling pathways, were identified as crucial for the therapeutic activity of WCAP in IBS-D. We also identified the possibility of several interactions and crosstalk between the different pathways. Subsequent molecular biology experiments revealed that the expression levels of cAMP, phospho-(Ser/Thr) protein kinase A substrates (p-PKA), 5-hydroxytryptamine, and proteins in the cAMP signalling pathway, including G protein-coupled receptor (GPCR), adenylyl cyclase 5 (AC5), and cAMP-response element binding protein (CREB), were significantly upregulated in rat models of IBS-D following treatment with WCAP (P < 0.05). However, a reverse trend was observed in the expression of nuclear factor kappa-B (NF-κB) (P < 0.05), which could be attributed to the low-grade inflammation that occurs in IBS-D. CONCLUSION: We demonstrated that WCAP may alleviate the symptoms of diarrhoea and visceral sensitivity in IBS-D by regulating the cAMP signalling pathway.

Efficacy and safety of Gelsectan for diarrhoea-predominant irritable bowel syndrome: A randomised, crossover clinical trial.

Background: Irritable bowel syndrome (IBS) is highly prevalent and presents a clinical challenge. Gelsectan is a medical device containing xyloglucan (XG), pea protein and tannins (PPT) from grape seed extract, and xylo-oligosaccharides (XOS), which act together to protect and reinforce the intestinal barrier. Objective: The objective of this study is to evaluate the efficacy and safety of XG + PPT + XOS in patients with diarrhoea-predominant IBS (IBS-D). Methods: In this double-blind study, 60 patients were randomly assigned to receive XG + PPT + XOS or placebo for 28 days, then crossed over to the alternative treatment. Patients were followed for 60 days. Results: At Day 28, a significantly higher proportion of patients starting treatment with XG + PPT + XOS than placebo (87 vs 0%; p = 0.0019) presented normal stools (Bristol Stool Form Scale type 3-4). At Day 56, a significantly higher proportion of patients who crossed over to XG + PPT + XOS than placebo (93% vs 23%; p = 0.0001) presented normal stools. In the group allocated to receive XG + PPT + XOS after placebo, benefits of XG + PPT + XOS were maintained during follow-up. Subjective assessments of abdominal pain, bloating, quality of life and general health indicated significant improvement with XG + PPT + XOS over placebo. There were no related adverse events. Conclusion: XG + PPT + XOS effectively controlled diarrhoea and alleviated clinical symptoms in patients with IBS-D, and was well tolerated.

Increased small intestinal permeability and RNA expression profiles of mucosa from terminal ileum in patients with diarrhoea-predominant irritable bowel syndrome.

BACKGROUND: Altered intestinal permeability in diarrhoea-predominant irritable bowel syndrome (IBS-D) has been reported in some studies. AIMS: The study aimed to investigate the altered intestinal permeability and its associated clinical characteristics and RNA expression profiles in IBS-D. METHODS: We stratified IBS-D patients into two groups according to the P95 value of the permeability in controls. The clinical characteristics of the two groups were evaluated, and two biopsy cases from each of the two groups were selected for the RNA-seq analysis. RESULTS: IBS-D patients had a significant increase in the small intestinal permeability compared with controls [0.0245 (0.0229) median (interquartile range)] versus 0.0156 (0.0098), P=0.010), but no significant difference was found in the colonic permeability [23.286 (10.470) versus 21.650 (6.650), P=0.574]. The IBS-D patients with increased small intestinal permeability had worse psychological effects (P=0.027) and quality of life (P=0.044). Analysis of RNA-seq data revealed 185 genes differentially expressed, many of which were related to mucosal inflammation and immunity. CONCLUSIONS: Small intestinal permeability, but not colonic permeability, is increased in IBS-D patients. IBS-D patients with increased small intestinal permeability tend to be more severely impaired in terms of psychological effects and quality of life, and analysis of RNA-seq data reveals that increased small intestinal permeability is related to mucosal inflammation and immunity.

Diarrhoea-predominant irritable bowel syndrome distinguishable by 16S rRNA gene phylotype quantification.

AIM: To study whether selected bacterial 16S ribosomal RNA (rRNA) gene phylotypes are capable of distinguishing irritable bowel syndrome (IBS). METHODS: The faecal microbiota of twenty volunteers with IBS, subdivided into eight diarrhoea-predominant (IBS-D), eight constipation-predominant (IBS-C) and four mixed symptom-subtype (IBS-M) IBS patients, and fifteen control subjects, were analysed at three time-points with a set of fourteen quantitative real-time polymerase chain reaction assays. All assays targeted 16S rRNA gene phylotypes putatively associated with IBS, based on 16S rRNA gene library sequence analysis. The target phylotypes were affiliated with Actinobacteria, Bacteroidetes and Firmicutes. Eight of the target phylotypes had less than 95% similarity to cultured bacterial species according to their 16S rRNA gene sequence. The data analyses were made with repeated-measures ANCOVA-type modelling of the data and principle component analysis (PCA) with linear mixed-effects models applied to the principal component scores. RESULTS: Bacterial phylotypes Clostridium cocleatum 88%, Clostridium thermosuccinogenes 85%, Coprobacillus catenaformis 91%, Ruminococcus bromii-like, Ruminococcus torques 91%, and R. torques 93% were detected from all samples analysed. A multivariate analysis of the relative quantities of all 14 bacterial 16S rRNA gene phylotypes suggested that the intestinal microbiota of the IBS-D patients differed from other sample groups. The PCA on the first principal component (PC1), explaining 30.36% of the observed variation in the IBS-D patient group, was significantly altered from all other sample groups (IBS-D vs control, P = 0.01; IBS-D vs IBS-M, P = 0.00; IBS-D vs IBS-C, P = 0.05). Significant differences were also observed in the levels of distinct phylotypes using relative values in proportion to the total amount of bacteria. A phylotype with 85% similarity to C. thermosuccinogenes was quantified in significantly different quantities among the IBS-D and control subjects (-4.08 +/- 0.90 vs -3.33 +/- 1.16, P = 0.04) and IBS-D and IBS-M subjects (-4.08 +/- 0.90 vs -3.08 +/- 1.38, P = 0.05). Furthermore, a phylotype with 94% similarity to R. torques was more prevalent in IBS-D patients' intestinal microbiota than in that of control subjects (-2.43 +/- 1.49 vs -4.02 +/- 1.63, P = 0.01). A phylotype with 93% similarity to R. torques was associated with control samples when compared with IBS-M (-2.41 +/- 0.53 vs -2.92 +/- 0.56, P = 0.00). Additionally, a R. bromii-like phylotype was associated with IBS-C patients in comparison to control subjects (-1.61 +/- 1.83 vs -3.69 +/- 2.42, P = 0.01). All of the above mentioned phylotype specific alterations were independent of the effect of time. CONCLUSION: Significant phylotype level alterations in the intestinal microbiotas of IBS patients were observed, further emphasizing the possible contribution of the gastrointestinal microbiota in IBS.