Quigley, Eamonn M M

AbstractBackgroundThere is compelling evidence that microbe‐host interactions in the intestinal tract underlie many human disorders, including disorders of gut‐brain interactions (previously termed functional bowel disorders), such as irritable bowel syndrome (IBS). Small intestinal bacterial overgrowth (SIBO) has been recognized for over a century in patients with predisposing conditions causing intestinal stasis, such as surgical alteration of the small bowel or chronic diseases, including scleroderma and is associated with diarrhea and signs of malabsorption. Over 20 years ago, it was hypothesized that increased numbers of small intestine bacteria might also account for symptoms in the absence of malabsorption in IBS and related disorders. This SIBO‐IBS hypothesis stimulated significant research and helped focus the profession's attention on the importance of microbe‐host interactions as a potential pathophysiological mechanism in IBS.PurposeHowever, after two decades, this hypothesis remains unproven. Moreover, it has led to serious unintended consequences, namely the widespread use of unreliable and unvalidated breath tests as a diagnostic test for SIBO and a resultant injudicious use of antibiotics. In this review, we examine why the SIBO hypothesis remains unproven and, given the unintended consequences, discuss why it is time to reject this hypothesis and its reliance on breath testing. We also examine recent IBS studies of bacterial communities in the GI tract, their composition and functions, and their interactions with the host. While these studies provide important insights to guide future research, they highlight the need for further mechanistic studies of microbe‐host interactions in IBS patients before we can understand their possible role in diagnosis and treatment of patient with IBS and related disorders.

Summary Background MRx1234 is a live biotherapeutic product that contains a strain of Blautia hydrogenotrophica. It is in development for the treatment of irritable bowel syndrome (IBS). Aims To assess the efficacy and safety of MRx1234 in patients with IBS with predominant constipation (IBS‐C) or diarrhoea (IBS‐D) Methods We conducted a multicentre, randomised, double‐blind, placebo‐controlled, phase 2 trial. Patients aged 18–70 years in two parallel cohorts (IBS‐C; IBS‐D) were randomised (1:1) to MRx1234 or placebo for 8 weeks. The primary efficacy endpoint was overall responder rate—a composite of improved bowel habit (IBS‐C: stool frequency; IBS‐D: stool consistency) and abdominal pain intensity—for ≥50% of the treatment period in each cohort. Statistical testing was at a one‐sided 0.10 significance level. Results Of 366 randomised patients (164 IBS‐C; 202 IBS‐D), 365 received any study medication (177 MRx1234, 188 placebo). Numerically, although not statistically significantly different, more patients who received MRx1234 than placebo were overall responders in the IBS‐C (25.0% vs. 17.1%) and IBS‐D (23.4% vs. 17.8%) cohorts. Similar results were observed in the additional combined cohort analysis (24.1% vs. 17.5%; p = 0.063). For the components of the primary endpoint, significantly more patients on MRx1234 than placebo reported improvement in bowel habit in the IBS‐C, IBS‐D and combined cohorts, while improvements in abdominal pain were observed in each cohort. The safety profile of MRx1234 was similar to placebo. Conclusions MRx1234 has the potential to become a novel, safe treatment option for patients with IBS‐C or IBS‐D, and for those who have mixed symptoms or transition between subtypes. ClinicalTrials.gov #NCT03721107.

AbstractIrritable bowel syndrome (IBS) is a gut‐brain disorder in which symptoms are shaped by serotonin acting centrally and peripherally. The serotonin transporter gene SLC6A4 has been implicated in IBS pathophysiology, but the underlying genetic mechanisms remain unclear. We sequenced the alternative P2 promoter driving intestinal SLC6A4 expression and identified single nucleotide polymorphisms (SNPs) that were associated with IBS in a discovery sample. Identified SNPs built different haplotypes, and the tagging SNP rs2020938 seems to associate with constipation‐predominant IBS (IBS‐C) in females. rs2020938 validation was performed in 1978 additional IBS patients and 6,038 controls from eight countries. Meta‐analysis on data from 2,175 IBS patients and 6,128 controls confirmed the association with female IBS‐C. Expression analyses revealed that the P2 promoter drives SLC6A4 expression primarily in the small intestine. Gene reporter assays showed a functional impact of SNPs in the P2 region. In silico analysis of the polymorphic promoter indicated differential expression regulation. Further follow‐up revealed that the major allele of the tagging SNP rs2020938 correlates with differential SLC6A4 expression in the jejunum and with stool consistency, indicating functional relevance. Our data consolidate rs2020938 as a functional SNP associated with IBS‐C risk in females, underlining the relevance of SLC6A4 in IBS pathogenesis.

Linked ContentThis article is linked to Ford et al and Sun et al papers. To view these articles, visit https://doi.org/10.1111/apt.15001 and https://doi.org/10.1111/apt.15230.

Summary Background Irritable bowel syndrome ( IBS ) is a chronic functional bowel disorder. Disturbances in the gastrointestinal microbiome may be involved in its aetiology. Aim To perform a systematic review and meta‐analysis to examine the efficacy of prebiotics, probiotics, synbiotics and antibiotics in IBS . Methods MEDLINE , EMBASE , and the Cochrane Controlled Trials Register were searched (up to July 2017). Randomised controlled trials ( RCT s) recruiting adults with IBS , comparing prebiotics, probiotics, synbiotics or antibiotics with placebo or no therapy were eligible. Dichotomous symptom data were pooled to obtain a relative risk ( RR ) of remaining symptomatic after therapy, with a 95% confidence interval ( CI ). Continuous data were pooled using a standardised mean difference with a 95% CI . Results The search identified 4017 citations. Data for prebiotics and synbiotics were sparse. Fifty‐three RCT s of probiotics, involving 5545 patients, were eligible. Particular combinations of probiotics, or specific species and strains, appeared to have beneficial effects on global IBS symptoms and abdominal pain, but it was not possible to draw definitive conclusions about their efficacy. There were five trials of similar design that used rifaximin in non‐constipated IBS patients, which was more effective than placebo ( RR of symptoms persisting = 0.84; 95% CI 0.79‐0.90). Adverse events were no more common with probiotics or antibiotics. Conclusions Which particular combination, species or strains of probiotics are effective for IBS remains, for the most part, unclear. Rifaximin has modest efficacy in improving symptoms in non‐constipated IBS .