Performance characteristics of serum C4 and FGF19 measurements to exclude the diagnosis of bile acid diarrhoea in IBS-diarrhoea and functional diarrhoea

High throughput bioanalysis of serum 7a-hydroxy-4-cholesten-3-one (C4) using LC-MS/MS: Devising an end-to-end single vial solution for a sample limited application

Crohn's disease (CD) is characterized by chronic ileal/ileocolonic inflammation, and in some cases, can result in bile acid malabsorption (BAM) and subsequent bile acid diarrhea (BAD). Although BAD is common in CD, diagnosis is difficult. In patients with CD who had ileal resection (IR), elevated serum 7a-hydroxy-4-cholesten-3-one (C4), a cholesterol-derived stable intermediate in bile acid synthesis, is associated with diarrhea attributable to BAM and therefore, may have diagnostic utility. The previously existing validated methodology to measure C4 in human serum required 100 μL with an analytical range of 0.5-100 ng/mL, making it incompatible with the clinical trial sample set we had available for analysis due to limited serum volume and an extended assay range requirement (up-to 1 μg/mL). We present here a simplified, end-to-end single vial approach performed in a 96-well format for clinical sample C4 analysis for application in sample limited settings.

Involvement of bile acid in diarrhoea and therapeutic effect of colestimide in hereditary ATTR amyloidosis

BACKGROUND

Diarrhoea is one of the most serious complications in hereditary ATTR (ATTRv) amyloidosis. However, its precise pathomechanism remains unknown. The present study investigated the involvement of bile acid in diarrhoea along with the therapeutic effect of colestimide, a bile acid sequestrant, in ATTRv amyloidosis.

METHODS

We prospectively enrolled 19 ATTRv amyloidosis patients (9 with refractory diarrhoea and 10 without diarrhoea) and 20 healthy individuals for measurements of serum 7a-hydroxy-4-cholesten-3-one (C4) levels. The patients with diarrhoea were then treated with oral colestimide (1.5 g twice daily) for 28 days. The frequency of diarrhoea and C4 level were evaluated before and after colestimide treatment.

RESULTS

Mean serum C4 level was significantly higher in ATTRv patients with diarrhoea (62.3 ng/mL) than in ATTRv patients without diarrhoea (24.0 ng/mL, p = 0.03). Colestimide treatment significantly decreased mean diarrhoea frequency (pre-treatment period: 9.1 times/week, colestimide treatment period, 6.6 times/week, p = 0.04) and increased mean C4 level (before treatment: 66.2 ng/mL, after treatment: 187.1 ng/mL, p = 0.02).

CONCLUSIONS

Bile acid status was significantly associated with diarrhoea in ATTRv amyloidosis. Colestimide and other bile acid sequestrants may reduce diarrhoea frequency in afflicted patients.

Bile acid diarrhea in patients with chronic diarrhea. Current appraisal and recommendations for clinical practice

Bile Acid Diarrhea (BAD) is a common cause of chronic diarrhea, often accompanied by urgency, occasional fecal incontinence, abdominal pain, and fatigue. A nationwide survey has shown limited awareness of BAD within the Italian medical community, prompting a panel of experts to develop a Position Paper that outlines the most practical and cost-saving diagnostic investigations and treatments for this frequently overlooked condition. The document provides an overview of the epidemiology, pathophysiology, clinical manifestations, and classification of the different types of Bile Acid Diarrhea (BAD). A key focus is the diagnostic approach to identifying and managing the many undiagnosed BAD patients in both primary care and specialized medical settings. Finally, the paper addresses the optimal therapeutic strategies for BAD, including traditional bile acid sequestrants and newer, promising treatments.

Analysis of C4 Concentrations to Predict Impact of Patient-Reported Diarrhea Associated With the Ileal Bile Acid Transporter Inhibitor Linerixibat

Linerixibat, an ileal bile acid transporter (IBAT) inhibitor, is being evaluated for the treatment of pruritus in primary biliary cholangitis (PBC). Diarrhea is commonly reported with this drug class as IBAT inhibition redirects bile acids (BA) to the colon. Serum 7-alpha-hydroxy-4-cholesten-3-one (C4) measurement is a validated method to identify BA diarrhea. To inform dose selection, we characterized the relationship between linerixibat dose, C4 levels, and patient-reported bother on the gastrointestinal symptom rating scale (GSRS) diarrhea question. A kinetic-pharmacodynamic model was developed using data from five Phase 1/2 trials, to describe the effect of linerixibat dose (1-180 mg) and regimen (once/twice daily) on C4 concentrations over time. GSRS data from patients with PBC and pruritus in the Phase 2b GLIMMER study (NCT02966834) were used to develop a proportional odds model to predict the probability of a score of 1-7 (no-very severe discomfort) to the question "Have you been bothered by diarrhea during the past week?" in relation to linerixibat dose. The two models were linked to describe the linerixibat dose-C4-diarrhea bother relationship. Models were validated using graphical and numerical assessment and visual predictive checks. Linerixibat caused dose-dependent increases in C4 until saturation (~180 mg total daily dose). Increased C4 concentrations trended with increased GSRS diarrhea scores. Simulations demonstrated increases in moderate-to-very severe (≥ 4) diarrhea scores with increasing linerixibat dose. Increases in patient-reported diarrhea scores were linerixibat dose-dependent. Selecting an optimal dose that maximizes linerixibat's ability to improve pruritus while minimizing patient-reported diarrhea bother is important to support treatment adherence.

Development and validation of a novel 7α-hydroxy-4-cholesten-3-one (C4) liquid chromatography tandem mass spectrometry method and its utility to assess pre-analytical stability

OBJECTIVES

7α-Hydroxy-4-cholesten-3-one (C4) is the common intermediary of both primary bile acids. C4 is recommended by the British Society of Gastroenterology for the investigation of bile acid diarrhoea (BAD) in patients with chronic diarrhoea. This project aimed to develop and validate an assay to quantitate C4 in serum and assess the stability of C4 in unseparated blood.

METHODS

Accuracy was underpinned by calibrating to quantitative nuclear magnetic resonance analysis. C4 was analysed in a 96-well plate format with a deuterated C4 internal standard and liquid-liquid extraction. Validation followed the 2018 Food and Drug Administration guidelines. To assess C4 stability, healthy volunteers (n=12) donated 8 fasted samples each. Samples were incubated at 20 °C for up to 72 h and retrieved, centrifuged, aliquoted and frozen for storage at different time points prior to C4 analysis.

RESULTS

The C4 method demonstrated excellent analytical performance and passed all validation criteria. The method was found to be accurate, precise, free from matrix effects and interference. After 72 h of delayed sample separation, C4 concentration gradually declined by up to 14 % from baseline. However, the change was not significant for up to 12 h.

CONCLUSIONS

We present a robust method of analysing serum C4, offering a convenient alternative to 75SeHCAT for BAD investigation. C4 was found to decline in unseparated blood over time; however, after 12 h the mean change was <5 % from baseline. Our results suggest C4 is suitable for collection from both primary and secondary care prior to gastroenterology referral.

Advances in the pathophysiology, diagnosis and management of chronic diarrhoea from bile acid malabsorption: a systematic review

Bile acid malabsorption (BAM) is an important disorder of digestive pathophysiology as it generates chronic diarrhoea. This condition originates from intricate pathways involving bile acid synthesis and metabolism in the liver and gut, the composition of gut microbiota, enterohepatic circulation and key receptors as farnesoid X receptor (FXR), fibroblast growth factor receptor 4 (FGFR4), and the G-protein bile acid receptor-1 (GPBAR-1). Although symptoms can resemble those related to disorders of gut brain interaction, accurate diagnosis of BAM may greatly benefit the patient. The empiric diagnosis of BAM is primarily based on the clinical response to bile acid sequestrants. Specific tests including the 48-hour fecal bile acid test, serum levels of 7α-hydroxy-4-cholesten-3-one (C4) and fibroblast growth factor 19 (FGF19), and the 75Selenium HomotauroCholic Acid Test (SeHCAT) are not widely available. Nevertheless, lack of diagnostic standardization of BAM may account for poor recognition and delayed management. Beyond bile acid sequestrants, therapeutic approaches include the use of FXR agonists, FGF19 analogues, glucagon-like peptide-1 (GLP-1) receptor agonists, and microbiota modulation. These novel agents can best make their foray into the therapeutic armamentarium if BAM does not remain a diagnosis of exclusion. Ignoring BAM as a specific condition may continue to contribute to increased healthcare costs and reduced quality of life. Here, we aim to provide a comprehensive review of the pathophysiology, diagnosis, and management of BAM.

Effects of resveratrol on changes in trimethylamine-N-oxide and circulating cardiovascular factors following exercise training among older adults

PURPOSE

Trimethylamine-N-oxide (TMAO) is a gut-derived metabolite associated with cardiovascular disease (CVD). In preclinical and observational studies, resveratrol and exercise training have been suggested as potential strategies to reduce the systemic levels of TMAO. However, evidence from experimental studies in humans remains unknown. This project examined the dose-dependent effects of a combined resveratrol intervention with exercise training on circulating TMAO and other related metabolite signatures in older adults with high CVD risk.

METHODS

Forty-one older adults [mean (±SD) age of 72.1 (6.8) years] participated in a 12-week supervised center-based, multi-component exercise training intervention [2×/week; 80 min/session] and were randomized to one of two resveratrol dosages [Low: 500 vs. High:1000 mg/day] or a cellulose-based placebo. Serum/plasma were collected at baseline and post-intervention and evaluated for TMAO and associated analytes.

RESULTS

After the 12-week intervention, TMAO concentration increased over time, regardless of treatment [mean (±SD) Placebo: 11262 (±3970); Low:13252 (±1193); High: 12661(±3359) AUC; p = 0.04]. Each resveratrol dose produced different changes in metabolite signatures. Low dose resveratrol upregulated metabolites associated with bile acids biosynthesis (i.e., glycochenodeoxycholic acid, glycoursodeoxycholic acid, and glycocholic acid). High dose resveratrol modulated metabolites enriched for glycolysis, and pyruvate, propanoate, β-alanine, and tryptophan metabolism. Different communities tightly correlated to TMAO and resveratrol metabolites were associated with the lipid and vascular inflammatory clinical markers [|r| > 0.4, p < 0.05].

CONCLUSION

These findings suggest a distinct dose-dependent adaptation response to resveratrol supplementation on circulating metabolite signatures but not on TMAO among high-risk CVD older adults when combined with an exercise training intervention.

[Bile Acid Diarrhea]

Diarrhea is a very common gastrointestinal symptom, and the presence of higher concentrations of bile acid in the colon leads to bile acid diarrhea (BAD). In BAD patients, a portion of bile from the small intestine that is normally controlled by enterohepatic circulation is present at a high concentration in the lumen of the large intestine, resulting in increased motility and secretion of the large intestine. The prevalence of BAD is estimated to be 1-2% of the general population, and it comprises one-third of the instances of diarrhea-predominant irritable bowel syndrome. The clinical symptoms of BAD include chronic diarrhea, increased frequency of defecation, urgency to defecate, fecal incontinence, and cramping abdominal pain. The pathophysiology of BAD has not yet been fully elucidated. However, recent studies have reported increased intestinal permeability, shortened intestinal transit time, and changes in the intestinal microbial community to be the possible causes of BAD. Although fecal and serum bile acid tests are widely used for diagnosis, new test methods that are non-invasive, inexpensive, and have high sensitivity and specificity are needed at various institutions to facilitate the diagnosis. The selenium homo-tauro-cholic acid (SeHCAT) test is the gold standard for BAD diagnosis and severity assessment. The validation of several other serum markers, such as 7-hydroxy-4-cholesten-3-one (serum 7αC4) and the fibroblast growth factor 19 (FGF19) for use in clinical practice is ongoing. Although bile acid sequestrants are the mainstay of treatment, the development of drugs that are more effective and have better compliance is required. Farnesoid X receptor (FXR) agonists are showing promising results.

Total alditols from Cistanche deserticola attenuate functional constipation by regulating bile acid metabolism

HEADINGS ETHNOPHARMACOLOGICAL RELEVANCE

Functional constipation (FC), characterized by chronic constipation, significantly impacts physiological function and induces psychological stress in patients. However, current clinical treatment options for FC are currently limited. Cistanche deserticola, a traditional Chinese medicine that promotes intestinal moisture and bowel relaxation, contains cistanche total alditol extract (CTAE) as its primary active extract. However, the production of CTAE, its overall efficacy, and potential mechanisms for treating FC have yet to been investigated.

AIM OF THE STUDY

This study aimed to reveal the overall efficacy and potential mechanism of action of CTAE in rats with FC using a combination of stable preparation, pharmacodynamics, non-targeted metabolomics, bile acid metabolomics, and western blotting.

MATERIALS AND METHODS

Fourteen batches of CTAE underwent quality testing. A rat model of FC was developed using diphenoxylate tablets. The comprehensive pharmacodynamic effects of CTAE on FC were evaluated using fecal characteristics (wet weight, dry weight, and water content), intestinal transmission (colonic EMG amplitude, colonic EMG frequency, propulsion length, and propulsion rate), serum and colon biochemical indicators, distribution of interstitial cells of Cajal (ICC), and pathological examination. Non-targeted metabolomics was performed to assess the changes in endogenous metabolite profiles induced by CTAE. Bile acid metabolomics and western blotting analyses were employed to validate the potential mechanisms of action of CTAE.

RESULTS

CTAE, with a total content of betaine, mannitol, D-fructose, glucose, and sucrose of (75.67 ± 3.73) %, significantly enhanced intestinal transit, regulated neurotransmitters, increased the expression of c-kit in ICC, and alleviated intestinal inflammation in rats with FC. Non-targeted metabolomics revealed that CTAE significantly alleviated FC-induced metabolic disorders, mainly the biosynthesis of primary bile acids. Targeted metabolomic analysis confirmed that CTAE regulated FC-induced bile acid disorders. Western-blotting results confirmed that CTAE increased the expression of CYP8B1, FGF15, TGR5, and FXR, thereby modulating bile acid synthesis and enterohepatic circulation.

CONCLUSION

CTAE demonstrates significant therapeutic effects on FC, primarily through the regulation of bile acid synthesis and enterohepatic circulation. These findings provide a promising foundation for the development and clinical application of novel CATE-based drugs.

Population Dose-Response-Time Analysis of Itch Reduction and Patient-Reported Tolerability Supports Phase III Dose Selection for Linerixibat

Increase in serum bile acids (BAs) in patients with primary biliary cholangitis (PBC) may play a causal role in cholestatic pruritus (itch). Linerixibat is a selective small molecule inhibitor of the ileal bile acid transporter, which blocks re-absorption of BAs in the gastrointestinal tract thereby lowering BAs in the systemic circulation and reducing itch. One consequence is excess BAs in the colon, leading to diarrhea and abdominal pain. GLIMMER (NCT02966834) was a placebo-controlled phase IIb dose-ranging trial of linerixibat once (q.d.) or twice daily (b.i.d.) in adults with moderate to severe pruritus and PBC. To determine the optimal dose for maximum itch reduction while minimizing diarrhea, a kinetic-pharmacodynamic (k-PD) model was developed using data from GLIMMER. The PD end point modeled was worst daily itch, derived from itch score reported by patients b.i.d. A proportional odds model was developed post hoc to indicate the probability of diarrhea occurrence, a patient-reported outcome (GI-5) recorded weekly. The final k-PD model successfully described the effects of linerixibat and placebo on itch. Model simulations were consistent with the observed dose-dependent increase in the average number of itch responders (patients with a ≥ 2-point improvement in itch). This was paralleled by a dose-dependent increase in the probability of higher diarrhea frequency scores. The b.i.d. dosing regimens led to a modest increase in the number of itch responders as compared with q.d. dosing. This quantitative framework highlights the trade-off between benefit and tolerability and supported the selection of 40 mg b.i.d. in the phase III GLISTEN trial (NCT04950127).

Bile Acid Diarrhea: From Molecular Mechanisms to Clinical Diagnosis and Treatment in the Era of Precision Medicine

Bile acid diarrhea (BAD) is a multifaceted intestinal disorder involving intricate molecular mechanisms, including farnesoid X receptor (FXR), fibroblast growth factor receptor 4 (FGFR4), and Takeda G protein-coupled receptor 5 (TGR5). Current diagnostic methods encompass bile acid sequestrants (BAS), 48-h fecal bile acid tests, serum 7α-hydroxy-4-cholesten-3-one (C4), fibroblast growth factor 19 (FGF19) testing, and 75Selenium HomotauroCholic acid test (75SeHCAT). Treatment primarily involves BAS and FXR agonists. However, due to the limited sensitivity and specificity of current diagnostic methods, as well as suboptimal treatment efficacy and the presence of side effects, there is an urgent need to establish new diagnostic and treatment methods. While prior literature has summarized various diagnostic and treatment methods and the pathogenesis of BAD, no previous work has linked the two. This review offers a molecular perspective on the clinical diagnosis and treatment of BAD, with a focus on FXR, FGFR4, and TGR5, emphasizing the potential for identifying additional molecular mechanisms as treatment targets and bridging the gap between diagnostic and treatment methods and molecular mechanisms for a novel approach to the clinical management of BAD.

Editorial: Bile acid diarrhoea - simplified clinico-biochemical diagnosis

This article is linked to Borup et al paper. To view this article, visit https://doi.org/10.1111/apt.17739

Recent developments in diagnosing bile acid diarrhea

INTRODUCTION

Bile acid diarrhea (BAD) commonly causes chronic diarrhea. Symptoms may be mistaken for disorders of gut brain interaction. Due to the lack of widely available diagnostic tests and poor recognition of BAD, there is a delay in diagnosis leading to increased healthcare system burden and decreased patient quality of life.

AREAS COVERED

A thorough review of the literature was conducted using PubMed for articles on the biological functions of bile acids, pathophysiology and management of BAD, but focusing on diagnostic testing including 75SeHCAT retention, 7αC4, FGF-19, fecal bile acids, and single stool tests. This narrative review discusses available modalities focusing on noninvasive stool and serum testing that are more widely available and show good sensitivity and specificity for diagnosis of BAD. 75SeHCAT retention is not available in many countries. Alternative diagnostic tests include total and primary fecal bile acid (BA) excretion in 48-hour collection or a single stool sample, serum7αC4 >46 or 52.5 ng/mL, and combination of single stool and serum 7αC4 ±watery stools (Bristol Stool Form Scale 6-7).

EXPERT OPINION

Given the ease of serum and single stool sample acquisition and diagnostic advances, clinical practice should embrace positive diagnosis, rather than BAS therapeutic trial. BAD needs to be considered in diverse gastrointestinal diseases.

Serum lipidome unravels a diagnostic potential in bile acid diarrhoea

OBJECTIVE

Bile acid diarrhoea (BAD) is debilitating yet treatable, but it remains underdiagnosed due to challenging diagnostics. We developed a blood test-based method to guide BAD diagnosis.

DESIGN

We included serum from 50 treatment-naive patients with BAD diagnosed by gold standard 75selenium homotaurocholic acid test, 56 feature-matched controls and 37 patients with non-alcoholic fatty liver disease (NAFLD). Metabolomes were generated using mass spectrometry covering 1295 metabolites and compared between groups. Machine learning was used to develop a BAD Diagnostic Score (BDS).

RESULTS

Metabolomes of patients with BAD significantly differed from controls and NAFLD. We detected 70 metabolites with a discriminatory performance in the discovery set with an area under receiver-operating curve metric above 0.80. Logistic regression modelling using concentrations of decanoylcarnitine, cholesterol ester (22:5), eicosatrienoic acid, L-alpha-lysophosphatidylinositol (18:0) and phosphatidylethanolamine (O-16:0/18:1) distinguished BAD from controls with a sensitivity of 0.78 (95% CI 0.64 to 0.89) and a specificity of 0.93 (95% CI 0.83 to 0.98). The model was independent of covariates (age, sex, body mass index) and distinguished BAD from NAFLD irrespective of fibrosis stage. BDS outperformed other blood test-based tests (7-alpha-hydroxy-4-cholesten-3-one and fibroblast growth factor 19) currently under development.

CONCLUSIONS

BDS derived from serum metabolites in a single-blood sample showed robust identification of patients with BAD with superior specificity and sensitivity compared with current blood test-based diagnostics.

New Developments in Bile Acid Diarrhea

Bile acid diarrhea (BAD) is characterized by increased frequency of bowel movements, looser stool consistency, urgency, and need for proximity to toilet facilities owing to the severity of the diarrhea, when compared with or relative to irritable bowel syndrome with diarrhea. Consequently, BAD leads to decreased quality of life. The condition is often misdiagnosed as irritable bowel syndrome with diarrhea or functional diarrhea. Patients with BAD have accelerated colonic transit, increased intestinal or colonic mucosal permeability, and altered stool microbiome composition associated with reduced dehydroxylation of primary to secondary bile acids. The established diagnostic test, selenium-75 homocholic acid taurine retention, is not available in the United States. Therefore, 48-hour fecal bile acid excretion has been the gold standard for diagnosis. With recent validation of combined measurement of primary bile acids in a single, random stool in addition to fasting serum 7α-hydroxy-4-cholesten-3-one, a practical point-of-care diagnostic test will soon be available. Randomized controlled trials have documented superiority of colesevelam to placebo and, in a separate study, superiority of the glucagon-like peptide 1 agonist liraglutide compared with colesevelam. Novel experimental approaches for BAD include farnesoid X receptor agonists and fibroblast growth factor 19 analogs. This article updates information on the pathophysiology, mechanisms, manifestations, diagnosis, and treatment of BAD.

The regulatory effects of fucoidan and laminarin on functional dyspepsia mice induced by loperamide

Gastrointestinal dysmotility is a common cause of functional dyspepsia. As two kinds of polysaccharides derived from brown algae, fucoidan and laminarin possess many physiological properties; however, their relative abilities in regulating gastrointestinal motility have not been illustrated yet. In this study, we aimed to investigate the regulatory effect of fucoidan and laminarin on functional dyspepsia mice induced by loperamide. Mice with gastrointestinal dysmotility were treated with fucoidan (100 and 200 mg per kg bw) and laminarin (50 and 100 mg per kg bw). As a result, fucoidan and laminarin reversed the dysfunction mainly through regulating gastrointestinal hormones (motilin and ghrelin), the cholinergic pathway, the total bile acid level, c-kit protein expression, and gastric smooth muscle contraction-related gene expression (ANO1 and RYR3). Moreover, fucoidan and laminarin intervention modulated the gut microbiota profile including the altered richness of Muribaculaceae, Lachnospiraceae, and Streptococcus. The results indicated that fucoidan and laminarin may restore the rhythm of the migrating motor complex and regulate gut microecology. In conclusion, we provided evidence to support that fucoidan and laminarin might have potential abilities to regulate gastrointestinal motility.

Bile acid diarrhea - as bad as it gets?

PURPOSE OF REVIEW

Bile acid diarrhea (BAD) is a common but under-recognized gastrointestinal condition that manifests with increased stool frequency and urgency, and a looser stool consistency. The aim of this review is to present recent advances in the pathophysiology, mechanisms, manifestations, diagnosis, and treatment of BAD.

RECENT FINDINGS

Patients with BAD have evidence of accelerated colonic transit, increased gut mucosal permeability, altered stool microbiome composition, and decreased quality of life. Single, random stool measurements of bile acids, alone or in combination with fasting serum 7-alpha-hydroxy-4-cholesten-3-one, have shown good sensitivity and specificity for the diagnosis of BAD. Novel therapeutic approaches include farnesoid X receptor agonists and glucagon-like peptide 1 agonists.

SUMMARY

Recent research has led to a better understanding of the pathophysiology and mechanisms of BAD, which might pave the way towards more targeted treatment strategies for BAD. Newer, more affordable, and easier diagnostic methods facilitate the diagnosis of BAD.

Irritable bowel syndrome: treatment based on pathophysiology and biomarkers

OBJECTIVE

To appraise the evidence that pathophysiological mechanisms and individualised treatment directed at those mechanisms provide an alternative approach to the treatment of patients with irritable bowel syndrome (IBS).

DESIGN

A PubMED-based literature review of mechanisms and treatment of IBS was conducted independently by the two authors, and any differences of perspective or interpretation of the literature were resolved following discussion.

RESULTS

The availability of several noninvasive clinical tests can appraise the mechanisms responsible for symptom generation in IBS, including rectal evacuation disorders, abnormal transit, visceral hypersensitivity or hypervigilance, bile acid diarrhoea, sugar intolerances, barrier dysfunction, the microbiome, immune activation and chemicals released by the latter mechanism. The basic molecular mechanisms contributing to these pathophysiologies are increasingly recognised, offering opportunities to intervene with medications directed specifically to food components, receptors and potentially the microbiome. Although the evidence supporting interventions for each mechanism is not at the same level of proof, the current state-of-the-art provides the opportunity to advance the practice from treatment based on symptoms to individualisation of treatment guided by pathophysiology and clinically identified biomarkers.

CONCLUSION

These advances augur well for the implementation of evidence-based individualised treatment for patients with IBS based on actionable biomarkers or psychological disturbances.

Current and Future Therapeutic Options for Irritable Bowel Syndrome with Diarrhea and Functional Diarrhea

Irritable bowel syndrome with diarrhea and functional diarrhea are disorders of gut-brain interaction presenting with chronic diarrhea; they have significant impact on quality of life. The two conditions may exist as a continuum and their treatment may overlap. Response to first-line therapy with antispasmodics and anti-diarrheal agents is variable, leaving several patients with suboptimal symptom control and need for alternative therapeutic options. Our aim was to discuss current pharmacologic options and explore alternative therapeutic approaches and future perspectives for symptom management in irritable bowel syndrome with diarrhea and functional diarrhea. We conducted a search of PubMed, Cochrane, clinicaltrial.gov, major meeting abstracts for publications on current, alternative, and emerging drugs for irritable bowel syndrome with diarrhea and functional diarrhea. Currently approved therapeutic options for patients with first-line refractory irritable bowel syndrome with diarrhea and functional diarrhea include serotonin-3 receptor antagonists, eluxadoline and rifaximin. Despite their proven efficacy, cost and availability worldwide impact their utilization. One-third of patients with disorders of gut-brain interaction with diarrhea have bile acid diarrhea and may benefit from drugs targeting bile acid synthesis and excretion. Further understanding of underlying pathophysiology of irritable bowel syndrome with diarrhea and functional diarrhea related to bile acid metabolism, gastrointestinal transit, and microbiome has led to evaluation of novel therapeutic approaches, including fecal microbiota transplantation and enterobacterial "crapsules". These opportunities to treat disorders of gut-brain interaction with diarrhea should be followed with formal studies utilizing large samples of well-characterized patients at baseline and validated response outcomes as endpoints for regulatory approval.

Safety and Efficacy of Eluxadoline in Patients with Irritable Bowel Syndrome-Diarrhea With or Without Bile Acid Diarrhea: Open-Label Study

BACKGROUND

Eluxadoline, a peripherally acting, mixed µ- and κ-opioid receptor (OR) agonist and δ-OR antagonist, is approved for treatment of adults with irritable bowel syndrome-diarrhea (IBS-D). About a third of IBS-D patients has bile acid diarrhea (BAD); opioids may stimulate TGR5 (bile acid) receptors.

AIM

To evaluate eluxadoline's efficacy on altered bowel functions and safety in IBS-D patients with or without BAD.

METHODS

In a single-center, phase 4, parallel-group, open-label study, patients with IBS-D (cohort 1) and patients with BAD were treated with eluxadoline, 100 mg tablets BID, with food for 4 weeks. Patients recorded bowel functions by electronic daily diary. BAD was based on fasting serum 7αC4 (> 52.5 ng/mL) or concurrent criteria of increased total or primary fecal BAs excreted in 48 h. We assessed efficacy on treatment compared to baseline in the two cohorts. Primary outcome measures were changes from baseline in average stool consistency Bristol Stool Form Scale (BSFS) score (range 1-7) and safety.

RESULTS

Mean changes from baseline in cohorts 1 and 2 (data presented in this order) were similar for: BSFS score averaged over 4 weeks' treatment (- 1.25 and - 1.09); daily bowel movement frequency (- 1.48 and - 0.79); daily urgent bowel movements (- 0.52 and - 0.80); IBS-QoL (5.9 and 13.6); serum 7αC4 (- 5.59 and - 8.78 ng/mL). There were no deaths, serious treatment-emergent adverse events, or discontinuations due to adverse events during the study.

CONCLUSION

Eluxadoline is similarly efficacious in the treatment of IBS-D and BAD, and it appears to be safe and efficacious as documented in large clinical trials.

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.

Bile Acid-Related Regulation of Mucosal Inflammation and Intestinal Motility: From Pathogenesis to Therapeutic Application in IBD and Microscopic Colitis

Inflammatory bowel diseases (IBD) and microscopic colitis are chronic immune-mediated inflammatory disorders that affect the gastroenterological tract and arise from a complex interaction between the host’s genetic risk factors, environmental factors, and gut microbiota dysbiosis. The precise mechanistic pathways interlinking the intestinal mucosa homeostasis, the immunological tolerance, and the gut microbiota are still crucial topics for research. We decided to deeply analyze the role of bile acids in these complex interactions and their metabolism in the modulation of gut microbiota, and thus intestinal mucosa inflammation. Recent metabolomics studies revealed a significant defect in bile acid metabolism in IBD patients, with an increase in primary bile acids and a reduction in secondary bile acids. In this review, we explore the evidence linking bile acid metabolites with the immunological pathways involved in IBD pathogenesis, including apoptosis and inflammasome activation. Furthermore, we summarize the principal etiopathogenetic mechanisms of different types of bile acid-induced diarrhea (BAD) and its main novel diagnostic approaches. Finally, we discuss the role of bile acid in current and possible future state-of-the-art therapeutic strategies for both IBD and BAD.

Pathophysiology and Clinical Management of Bile Acid Diarrhea

Bile acid malabsorption (BAM) represents a common cause of chronic diarrhea whose prevalence is under-investigated. We reviewed the evidence available regarding the pathophysiology and clinical management of bile acid diarrhea (BAD). BAD results from dysregulation of the enterohepatic recirculation of bile acids. It has been estimated that 25–33% of patients with functional diarrhea and irritable bowel syndrome with diarrhea have BAM. Currently, the selenium homotaurocholic acid test is the gold standard for BAD diagnosis and severity assessment. However, it is an expensive method and not widely available. The validation of the utility in the clinical practice of several other serum markers, such as 7α-hydroxy-4-cholesten-3-one (C4) and the fibroblast growth factor 19 (FGF19) is ongoing. The first-line treatment of patients with BAD is bile acid sequestrants. Patients that are refractory to first-line therapy should undergo further diagnostics to confirm the diagnosis and to treat the underlying cause of BAD. An early and correct diagnosis of BAD would improve patient’s quality of life, avoiding additional diagnostic tests that burden health care systems. Considering the limited availability and tolerability of specific medications for BAD treatment, future research is awaited to identify other therapeutic approaches, such as gut microbiota modulating therapies.

A single faecal bile acid stool test demonstrates potential efficacy in replacing SeHCAT testing for bile acid diarrhoea in selected patients

This study examines the validity of measuring faecal bile acids (FBA) in a single stool sample as a diagnostic tool for bile acid diarrhoea (BAD) by direct comparison to the ⁷⁵selenium-homotaurocholic acid (SeHCAT) scan. A prospective observational study was undertaken. Patients with chronic diarrhoea (> 6 weeks) being investigated for potential BAD with SeHCAT scan provided stool samples for measurement of FBA, using an enzyme-linked immunosorbent assay. Patients were characterised into four groups: SeHCAT negative control group, post-cholecystectomy, idiopathic BAD and post-operative terminal ileal resected Crohn's disease. Stool samples were collected at baseline and 8-weeks post treatment to determine whether FBA measurement could be used to monitor therapeutic response. 113 patients had a stool sample to directly compare with their SeHCAT result. FBA concentrations (μmol/g) and interquartile ranges in patients in the control group (2.8; 1.6-4.2), BAD (3.6; 1.9-7.2) and post-cholecystectomy cohort 3.8 (2.3-6.8) were similar, but all were significantly lower (p < 0.001) compared to the Crohn's disease cohort (11.8; 10.1-16.2). FBA concentrations in patients with SeHCAT retention of < 15% (4.95; 2.6-10.5) and < 5% (9.9; 4.8-15.4) were significantly higher than those with a SeHCAT retention > 15% (2.6; 1.6-4.2); (p < 0.001 and p < 0.0001, respectively). The sensitivity and specificity using FBA cut-off of 1.6 μmol/g (using ≤ 15% SeHCAT retention as diagnostic of BAD) were 90% and 25% respectively. A single random stool sample may have potential use in diagnosing severe BAD or BAD in Crohn's patients. Larger studies are now needed to confirm the potential efficacy of this test to accurately diagnose BAD in the absence of SeHCAT testing.

Bile acid-gut microbiota crosstalk in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common disorder of gut-brain interaction with an increasing prevalence, and its precise aetiology remains unclear. Gut microbiota dysbiosis has been found to be associated with IBS pathogenesis. In addition, a high incidence of bile acid diarrhoea and disturbed bile acid metabolism has been observed in IBS patients. The abundant microorganisms inhabited in human gut have essential functions in bile acid biotransformation, and can immensely affect the size and constitution of bile acid pool. Meanwhile, the alterations of bile acid profile can inversely interfere with the gut microbiota. This review discussed the role of intricate correlations between bile acids and gut microbiota in IBS pathogenesis and delineated the possible molecular mechanisms, mainly the signalling induced by farnesoid X receptor and transmembrane G protein-coupled receptor 5. Besides, some biomarkers for identifying bile acid diarrhoea in IBS population were listed, assisting the diagnosis and classification of IBS. Moreover, it also assessed some therapeutic strategies for IBS that regulate the bile acid-gut microbiota axis, such as dietary modulation, probiotics/prebiotics, faecal microbiota transplantation, and antibiotics. Collectively, this article illustrated the relationship between bile acids and gut microbiota in IBS pathophysiology and might offer some novel therapeutic options for IBS.

Bile Acid Diarrhea in Adults and Adolescents

BACKGROUND

Bile acids are central to enterohepatic signaling pathways activated through natural receptors, farnesoid X receptor [FXR mediates synthesis of fibroblast growth factor-19 (FGF-19)], and G protein-coupled bile acid receptor 1 (GPBAR1, also known as TGR5). Although bile acid diarrhea (BAD) is more commonly encountered in ileal resection or disease, there is evidence documenting "idiopathic" BAD in about 20% of adolescents and 30% of adults presenting with chronic, non-bloody diarrhea often attributed to irritable bowel syndrome. Mechanism(s) leading to increased hepatic synthesis and colonic bile acid levels in "idiopathic" BAD include reduced synthesis of FGF-19 by the ileal mucosa, or genetic variation in hepatocyte proteins klotho β and FGF receptor 4 (FGFR4) that mediate negative feedback of bile acid synthesis.

PURPOSE

The objective of this review is to summarize the diagnosis of BAD in adults and adolescents. In addition to ⁷⁵ SeHCAT retention for diagnosis of BAD, studies have validated fasting serum 7αC4 and FGF-19, respectively, by-product and inhibitor of hepatic bile acid synthesis, as well as fecal bile acid measurements. These assays are widely available through reference laboratories, and they are being simplified (eg, measurement of primary fecal bile acids in a random stool sample). BAD has also been identified as a co-factor contributing to persistent diarrhea in other diseases in remission including inflammatory bowel disease, microscopic colitis, celiac disease, and neuroendocrine tumors. In summary, advances in diagnosis of BAD provide opportunities for generalists and pediatric and adult gastroenterologists to provide targeted treatment for BAD presenting as chronic non-bloody diarrhea.

Downregulation of Serum and Distal Ileum Fibroblast Growth Factor19 in Bile Acid Diarrhoea Patients

BACKGROUND

Bile acid diarrhoea or BAD is a common but little recognised cause of chronic diarrhoea. Few of these patients in China have been diagnosed due to a lack of diagnostic options.

AIMS

To clarify the diagnostic value of serum fibroblast growth factor19 (FGF19) in BAD patients.

METHODS

We reported on 60 chronic diarrhoea patients and 80 healthy volunteers (HV). Based on the 90th percentile levels of serum 7a-hydroxy-4-cholesten-3-one (C4) of HV, these patients were divided into BAD group (C4 ≥ 90th) and non-bile acid diarrhoea group (NBAD, C4 < 90th). Serum FGF19 in the two clinical groups and HV group were compared, as was distal ileum FGF19 in clinical groups. The diagnostic value of serum FGF19 for BAD was evaluated.

RESULTS

The 90th percentile of serum C4 in HV group was 65.87 ng/ml. Serum FGF19 concentrations in BAD group (Median 69.28 pg/ml; n = 23) were significantly lower than those in HV (Median 122.18 pg/ml; n = 80) and NBAD (Median 129.57 pg/ml; n = 29) groups. FGF19 mRNA of the distal ileum in BAD group, was lower than that in NBAD group, P = 0.002. The rate of FGF19 protein low expression of distal ileum in BAD and NBAD group were 78.3% and 48.3%, P = 0.027. Using an ROC curve, statistical analysis yielded a threshold FGF19 concentration of 117.3 pg/ml (AUC, 0.906; 91.3% sensitivity, 79.3% specificity) for a clinical diagnosis of BAD.

CONCLUSIONS

Serum and distal ileum expression of FGF19 significantly decreased in BAD patients. The suggested clinical ranges for serum FGF19 < 117.3 pg/ml has high sensitivity and specificity for BAD patients with a normal structural and histological ileum.

Review article: Diagnosis and investigation of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common disorder of gut-brain interaction. It is defined by the Rome criteria as the presence of abdominal pain, related to defaecation, associated with a change in stool form and/or frequency. The approach to diagnosis and investigation of suspected IBS varies between clinicians and, due in part to the uncertainty that can surround the diagnosis, many still consider it to be a diagnosis of exclusion. However, exhaustive investigation is both unnecessary and costly, and may also be counterproductive. Instead, physicians should aim to make a positive diagnosis, based on their clinical assessment of symptoms, and limit their use of investigations. The yield of routine blood tests in suspected IBS is low overall, but normal inflammatory markers may be reassuring. All patients should have serological testing for coeliac disease, irrespective of their predominant stool form. Routine testing of stool microbiology or faecal elastase is unnecessary; however, all patients with diarrhoea aged <45 should have a faecal calprotectin or a similar marker measured which, if positive, should lead to colonoscopy to exclude possible inflammatory bowel disease. Colonoscopy should also be undertaken in any patient reporting alarm symptoms suggestive of colorectal cancer, and in those whose presentation raises suspicion for microscopic colitis. Testing for bile acid diarrhoea should be considered for patients with IBS with diarrhoea where available. Hydrogen breath tests for lactose malabsorption or small intestinal bacterial overgrowth have no role in the routine assessment of suspected IBS. Adopting a standardised approach to the diagnosis and investigation of IBS will help to promote high-quality and high-value care for patients overall.

Markers of Bile Acid Metabolism in Pediatric Diarrhea Predominant Irritable Bowel Syndrome and Healthy Controls

OBJECTIVES

Excessive fecal bile acids in adults have been associated with diarrhea-predominant irritable bowel syndrome (IBS-D), but their role in pediatric IBS-D is unknown. Serum markers including 7α-hydroxy-4-cholesten-3-one (C4) and fibroblast growth factor-19 (FGF-19) were validated in adults to detect bile acid diarrhea (BAD) compared to 48-hour fecal bile acid collection (48FBA). Our aims were to assess fasting serum C4 and FGF-19 and 48FBA in a pediatric population, to compare measurements in IBS-D patients and healthy controls (HC), and to determine the prevalence of BAD among children with IBS-D.

METHODS

Using a cross-sectional design, 26 patients with IBS-D and 56 HC were recruited in two pediatric tertiary care centers. Fasting serum C4 and FGF-19 and 48FBA were obtained. Participants completed a 7-day bowel diary coinciding with stool collection. Associations were analyzed using Spearman correlations.

RESULTS

Mean age was 14.7 ± 2.5 years (42.3% female) in IBS-D and 12.6 ± 2.4 years (39.3% female) in HC. There was a significant correlation of C4 with 48FBA (r = 0.48, P < 0.05) and an inverse association with FGF-19 (r = -0.43, P < 0.05). No significant differences were noted in C4 (P = 0.32), FGF-19 (P = 0.1), or 48FBA (P = 0.5) between IBS-D and HC groups; however, 20% of IBS-D patients had elevated C4 and 28% had low FGF-19 values.Fecal primary BA was significantly correlated with stool frequency (r = 0.45, P < 0.002).

CONCLUSIONS

Correlations of C4 with 48FBA and FGF-19 are confirmed in a pediatric population. Twenty percent of pediatric patients with IBS-D had abnormal fasting serum C4. This serum test could be applied to identify BAD in pediatric IBS-D.

Serum 7-alfa-hydroxy-4-cholesten-3-one and fibroblast growth factor-19 as biomarkers diagnosing bile acid malabsorption in microscopic colitis and inflammatory bowel disease

BACKGROUND

Bile acid malabsorption is common in microscopic colitis, irritable bowel syndrome with diarrhea, and inflammatory bowel disease. We investigated the diagnostic accuracy of 7-alfa-hydroxy-4-cholesten-3-one and compared it with fibroblast growth factor-19 as biomarkers for bile acid malabsorption.

METHODS

We enrolled consecutively 109 chronic diarrhea patients with standard laboratory tests, fecal calprotectin, and endoscopy separated into six groups: n = 30 with active inflammatory bowel disease, n = 21 with inflammatory bowel disease in remission reporting >3 bowel movements per day, n = 21 with inflammatory bowel disease after surgery, n = 23 with irritable bowel syndrome with diarrhea, n = 14 with microscopic colitis and 11 healthy subjects (controls). We defined bile acid malabsorption as >3 bowel movements and lower fibroblast growth factor-19 (<60 pg/ml).

RESULTS

Median levels of 7-alfa-hydroxy-4-cholesten-3-one in inflammatory bowel disease active were 53.1 ng/ml, inflammatory bowel disease remission were 52.2 ng/ml, inflammatory bowel disease after surgery were 85.7 ng/ml, irritable bowel syndrome with diarrhea were 7.5 ng/ml, microscopic colitis were 69.3 ng/ml, and healthy controls were 3.7 ng/ml. We estimate a 7-alfa-hydroxy-4-cholesten-3-one cutoff of 48.9 ng/ml with 82.6% sensitivity and 84.3% specificity for detecting bile acid malabsorption. Both 7-alfa-hydroxy-4-cholesten-3-one >48.9 ng/ml and fibroblast growth factor-19 (<60 pg/ml) were found in 52% of the patients, compared with those 8% of patients below this 7-alfa-hydroxy-4-cholesten-3-one cutoff (P < 0.001). Serum 7-alfa-hydroxy-4-cholesten-3-one correlated with the number of bowel movements/day (r = -0.709; P < 0.001) and correlated inversely with fibroblast growth factor-19 (r = -0.741; P < 0.001).

CONCLUSIONS

Serum 7-alfa-hydroxy-4-cholesten-3-one above 48.9 ng/ml and fibroblast growth factor-19 below 60 pg/ml identify patients with diarrhea likely attributable to bile acid malabsorption with high diagnostic accuracy and they can be used as screening biomarkers for bile acid malabsorption in microscopic colitis and inflammatory bowel disease.

Biochemical Diagnosis of Bile Acid Diarrhea: Prospective Comparison With the 75Seleno-Taurohomocholic Acid Test

INTRODUCTION

The diagnosis of bile acid diarrhea is often missed because the availability of the seleno-taurohomocholic acid (SeHCAT) test is limited. We aimed to compare the biomarkers 7α-hydroxy-4-cholesten-3-one (C4) and fibroblast growth factor 19 (FGF19) with the SeHCAT test.

METHODS

Patients with chronic diarrhea without intestinal resection referred for SeHCAT were prospectively recruited for this diagnostic accuracy study. Blood was sampled at fasting and after a stimulation meal with chenodeoxycholic acid. SeHCAT retention ≤10% defined bile acid diarrhea and >10% defined miscellaneous diarrhea. Receiver operating characteristics (ROC) were analyzed with SeHCAT as the gold standard. www.clinicaltrials.gov (NCT03059537).

RESULTS

Patients with bile acid diarrhea (n = 26) had mean C4 of 30 ng/mL (95% confidence interval: 19-46) vs 8 (7-11; P < 0.001) in the miscellaneous diarrhea group (n = 45). Area under the ROC curve (ROCAUC) for C4 was 0.83 (0.72-0.93). C4 < 15 ng/mL had 85% (74%-96%) negative predictive value; C4 > 48 ng/mL had 82% (59%-100%) positive predictive value. Twenty patients had C4 values 15-48 ng/mL, of whom 11/20 had SeHCAT ≤10%. Median fasting FGF19 was 72 pg/mL (interquartile range: 53-146) vs 119 (84-240) (P = 0.004); ROCAUC was 0.71 (0.58-0.83). Stimulated FGF19 responses did not differ (P = 0.54).

DISCUSSION

We identified C4 thresholds with clinically useful predictive values for the diagnosis of and screening for bile acid diarrhea in patients with chronic watery diarrhea. Further validation of the cutoff values with the placebo-controlled effect of sequestrant therapy is warranted (see Visual Abstract, Supplementary Digital Content 2, http://links.lww.com/AJG/B603).

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.

Bile acid diarrhoea: Current and potential methods of diagnosis

Chronic diarrhoea is common and mostly due to diarrhoea predominant irritable bowel syndrome. Diarrhoea predominant irritable bowel syndrome affects about 11% of the population; however, up to a third of these patients actually have bile acid diarrhoea. There are, therefore, more than one million sufferers of bile acid diarrhoea in the UK. Bile acid diarrhoea is caused by small bowel malabsorption of bile acids and the increased bile acids in the large intestine cause diarrhoea. Once diagnosed, the treatment of bile acid diarrhoea is simple and effective. Bile acid diarrhoea , however, is often not diagnosed because of a lack of easily available and reliable diagnostic methods. In the United Kingdom, the radiolabelled 23-seleno-25-homotaurocholic acid test is the gold-standard method of diagnosis. 23-seleno-25-homotaurocholic acid test, however, is expensive, inconvenient to the patient, involves radiation exposure and has limited availability. As such, a laboratory biomarker is desirable. This review briefly discusses the pathophysiology and management of bile acid diarrhoea and critically evaluates methods for its diagnosis, including serum 7α-hydroxy-4-cholesten-3-one, faecal bile acid measurement, serum fibroblast growth factor 19, urine-2-propanol, and the ¹⁴C-glycocholate breath and stool test.

The Role of Bile Acids in Chronic Diarrhea

Bile acids (BAs) are the central signals in enterohepatic communication, and they also integrate microbiota-derived signals into enterohepatic signaling. The tissue distribution and signaling pathways activated by BAs through natural receptors, farsenoid X receptor and G protein-coupled BA receptor 1 (GPBAR1, also known as Takeda G-coupled receptor 5), have led to a greater understanding of the mechanisms and potential therapeutic agents. BA diarrhea is most commonly encountered in ileal resection or disease, in idiopathic disorders (with presentation similar to functional diarrhea or irritable bowel syndrome with diarrhea), and in association with malabsorption such as chronic pancreatitis or celiac disease. Diagnosis of BA diarrhea is based on Se-homocholic acid taurine retention, 48-hour fecal BA excretion, or serum 7αC4; the latter being a marker of hepatic BA synthesis. BA diarrhea tends to be associated with higher body mass index, increased stool weight and stool fat, and acceleration of colonic transit. Biochemical markers of increased BA synthesis or excretion are available through reference laboratories. Current treatment of BA diarrhea is based on BA sequestrants, and, in the future, it is anticipated that farsenoid X receptor agonists may also be effective. The optimal conditions for an empiric trial with BA sequestrants as a diagnostic test are still unclear. However, such therapeutic trials are widely used in clinical practice. Some national guidelines recommend definitive diagnosis of BA diarrhea over empirical trial.

Increasing Evidence That Irritable Bowel Syndrome and Functional Gastrointestinal Disorders Have a Microbial Pathogenesis

The human gastrointestinal tract harbors most of the microbial cells inhabiting the body, collectively known as the microbiota. These microbes have several implications for the maintenance of structural integrity of the gastrointestinal mucosal barrier, immunomodulation, metabolism of nutrients, and protection against pathogens. Dysfunctions in these mechanisms are linked to a range of conditions in the gastrointestinal tract, including functional gastrointestinal disorders, ranging from irritable bowel syndrome, to functional constipation and functional diarrhea. Irritable bowel syndrome is characterized by chronic abdominal pain with changes in bowel habit in the absence of morphological changes. Despite the high prevalence of irritable bowel syndrome in the global population, the mechanisms responsible for this condition are poorly understood. Although alterations in the gastrointestinal microbiota, low-grade inflammation and immune activation have been implicated in the pathophysiology of functional gastrointestinal disorders, there is inconsistency between studies and a lack of consensus on what the exact role of the microbiota is, and how changes to it relate to these conditions. The complex interplay between host factors, such as microbial dysbiosis, immune activation, impaired epithelial barrier function and motility, and environmental factors, including diet, will be considered in this narrative review of the pathophysiology of functional gastrointestinal disorders.

Fecal Bile Acid Testing in Assessing Patients With Chronic Unexplained Diarrhea: Implications for Healthcare Utilization

INTRODUCTION

Bile acid (BA) diarrhea is the cause in ∼26% of chronic unexplained (nonbloody) diarrhea (CUD) based on SeHCAT testing. To assess fecal BA excretion and healthcare utilization in patients with CUD.

METHODS

In a retrospective review of 1,071 consecutive patients with CUD who completed 48-hour fecal BA testing, we analyzed the symptoms, diagnostic tests performed, and final diagnoses.

RESULTS

After 135 patients were excluded because of mucosal diseases, increased BA excretion was identified in 476 (51%) of the 936 patients with CUD: 29% with selective increase in primary BA and 22% with increased total BA excretion (35% with normal primary BA excretion). There were no differences in demographics, clinical symptoms, or history of cholecystectomy in patients with elevated total or selective primary fecal BA excretion compared with patients with normal excretion. Before the 48-hour fecal BA excretion test was performed, patients completed on average 1.2 transaxial imaging, 2.6 endoscopic procedures, and 1.6 miscellaneous tests/person. Less than 10% of these tests identified the etiology of CUD. Total fecal BAs >3,033 µmol/48 hour or primary BAs >25% had a 93% negative predictive value to exclude mucosal disease. Among patients with increased fecal BA excretion, >70% reported diarrhea improved with BA sequestrant compared with 26% with normal fecal BA excretion. Patients with selective elevation in primary fecal BAs were 3.1 times (95% confidence interval, 1.5-6.63) more likely to respond to BA sequestrant therapy compared with those with elevated total fecal BAs.

DISCUSSION

Increased fecal BA excretion is frequent (51%) in patients with CUD. Early 48-hour fecal BA evaluation has the potential to decrease healthcare utilization in CUD.

Bile Acid Diarrhea and NAFLD: Shared Pathways for Distinct Phenotypes

Irritable bowel syndrome with diarrhea (IBS-D) and NAFLD are both common conditions that may be influenced by shared pathways of altered bile acid (BA) signaling and homeostatic regulation. Pathophysiological links between IBS-D and altered BA metabolism include altered signaling through the ileal enterokine and fibroblast growth factor 19 (FGF19) as well as increased circulating levels of 7α-hydroxy-4-cholesten-3-one, a metabolic intermediate that denotes increased hepatic BA production from cholesterol. Defective production or release of FGF19 is associated with increased BA production and BA diarrhea in some IBS-D patients. FGF19 functions as a negative regulator of hepatic cholesterol 7α-hydroxylase; therefore, reduced serum FGF19 effectively de-represses hepatic BA production in a subset of IBS-D patients, causing BA diarrhea. In addition, FGF19 modulates hepatic metabolic homeostatic response signaling by means of the fibroblast growth factor receptor 4/klotho beta receptor to activate cascades involved in hepatic lipogenesis, fatty acid oxidation, and insulin sensitivity. Emerging evidence of low circulating FGF19 levels in subsets of patients with pediatric and adult NAFLD demonstrates altered enterohepatic BA homeostasis in NAFLD. Conclusion: Here we outline how understanding of shared pathways of aberrant BA homeostatic signaling may guide targeted therapies in some patients with IBS-D and subsets of patients with NAFLD.

Regulation of bile acid metabolism-related signaling pathways by gut microbiota in diseases

Over the past decade, there has been increasing attention on the interaction between microbiota and bile acid metabolism. Bile acids are not only involved in the metabolism of nutrients, but are also important in signal transduction for the regulation of host physiological activities. Microbial-regulated bile acid metabolism has been proven to affect many diseases, but there have not been many studies of disease regulation by microbial receptor signaling pathways. This review considers findings of recent research on the core roles of farnesoid X receptor (FXR), G protein-coupled bile acid receptor (TGR5), and vitamin D receptor (VDR) signaling pathways in microbial-host interactions in health and disease. Studying the relationship between these pathways can help us understand the pathogenesis of human diseases, and lead to new solutions for their treatments.

Similarities in Clinical and Psychosocial Characteristics of Functional Diarrhea and Irritable Bowel Syndrome With Diarrhea

BACKGROUND & AIMS

There have been few published studies of clinical and psychological characteristics of patients with functional diarrhea (FDr). We studied the clinical and psychological characteristics of patients with FDr presenting to a tertiary care clinic, and compared symptom profiles of FDr with those of IBS-diarrhea (IBS-D).

METHODS

Consecutive patients with a diagnosis of FDr (n = 48) or IBS-D (n = 49), per Rome IV criteria, completed a detailed symptom survey from October 2017 through July 2018. Abdominal pain and diarrhea severity were assessed using patient-reported outcomes measurement information system (PROMIS) questionnaires. Patients with anxiety, depression, or sleep disturbances were identified based on PROMIS T-score of 60 or more. Mean and proportions were compared using the Student t test and chi-square analyses, respectively.

RESULTS

A significantly lower proportion of patients with FDr reported abdominal pain (77.1%) than patients with IBS-D (100%, P < .001). The proportion of patients reporting abdominal bloating and level of severity did not differ significantly between groups. Proportions of bowel movements with diarrhea did not differ significantly between groups (P = .54), but the mean diarrhea PROMIS T-score was significantly higher among patients with IBS-D (P = .03). This difference resulted from the significantly higher levels of fecal urgency-related distress reported by patients with IBS-D (P = .007). Proportions of patients with anxiety, depression, or sleep disturbance, and their severities, did not differ significantly between groups.

CONCLUSIONS

In an analysis of about 100 patients with FDr or IBS-D, we found overlap in gastrointestinal and psychosomatic symptoms. These 2 entities appear to be a continuum.

Canadian Association of Gastroenterology Clinical Practice Guideline on the Management of Bile Acid Diarrhea

BACKGROUND & AIMS

Chronic diarrhea affects about 5% of the population overall. Altered bile acid metabolism is a common but frequently undiagnosed cause.

METHODS

We performed a systematic search of publication databases for studies of assessment and management of bile acid diarrhea (BAD). The certainty (quality) of evidence and strength of recommendations were rated according to the Grading of Recommendation Assessment, Development and Evaluation approach. Patient population, intervention, comparator, and outcome questions were developed through an iterative process and were voted on by a group of specialists.

RESULTS

The certainty of evidence was generally rated as very low. Therefore, 16 of 17 recommendations are conditional. In patients with chronic diarrhea, consideration of risk factors (terminal ileal resection, cholecystectomy, or abdominal radiotherapy), but not additional symptoms, was recommended for identification of patients with possible BAD. The group suggested testing using ⁷⁵selenium homocholic acid taurine (where available) or 7α-hydroxy-4-cholesten-3-one, including patients with irritable bowel syndrome with diarrhea, functional diarrhea, and Crohn's disease without inflammation. Testing was suggested over empiric bile acid sequestrant therapy (BAST). Once remediable causes are managed, the group suggested cholestyramine as initial therapy, with alternate BAST when tolerability is an issue. The group suggested against BAST for patients with extensive ileal Crohn's disease or resection and suggested alternative antidiarrheal agents if BAST is not tolerated. Maintenance BAST should be given at the lowest effective dose, with a trial of intermittent, on-demand administration, concurrent medication review, and reinvestigation for patients whose symptoms persist despite BAST.

CONCLUSIONS

Based on a systematic review, BAD should be considered for patients with chronic diarrhea. For patients with positive results from tests for BAD, a trial of BAST, initially with cholestyramine, is suggested.

Intestinal Absorption of Bile Acids in Health and Disease

The intestinal reclamation of bile acids is crucial for the maintenance of their enterohepatic circulation. The majority of bile acids are actively absorbed via specific transport proteins that are highly expressed in the distal ileum. The uptake of bile acids by intestinal epithelial cells modulates the activation of cytosolic and membrane receptors such as the farnesoid X receptor (FXR) and G protein-coupled bile acid receptor 1 (GPBAR1), which has a profound effect on hepatic synthesis of bile acids as well as glucose and lipid metabolism. Extensive research has focused on delineating the processes of bile acid absorption and determining the contribution of dysregulated ileal signaling in the development of intestinal and hepatic disorders. For example, a decrease in the levels of the bile acid-induced ileal hormone FGF15/19 is implicated in bile acid-induced diarrhea (BAD). Conversely, the increase in bile acid absorption with subsequent overload of bile acids could be involved in the pathophysiology of liver and metabolic disorders such as fatty liver diseases and type 2 diabetes mellitus. This review article will attempt to provide a comprehensive overview of the mechanisms involved in the intestinal handling of bile acids, the pathological implications of disrupted intestinal bile acid homeostasis, and the potential therapeutic targets for the treatment of bile acid-related disorders. Published 2020. Compr Physiol 10:21-56, 2020.

Canadian Association of Gastroenterology Clinical Practice Guideline on the Management of Bile Acid Diarrhea

Background and Aims

Chronic diarrhea affects about 5% of the population overall. Altered bile acid metabolism is a common but frequently undiagnosed cause.

Methods

We performed a systematic search of publication databases for studies of assessment and management of bile acid diarrhea (BAD). The certainty (quality) of evidence and strength of recommendations were rated according to the Grading of Recommendation Assessment, Development and Evaluation approach. Patient population, intervention, comparator and outcome questions were developed through an iterative process and were voted on by a group of specialists.

Results

The certainty of evidence was generally rated as very low. Therefore, 16 of 17 recommendations are conditional. In patients with chronic diarrhea, consideration of risk factors (terminal ileal resection, cholecystectomy or abdominal radiotherapy), but not additional symptoms, was recommended for identification of patients with possible BAD. The group suggested testing using ⁷⁵selenium homocholic acid taurine (where available) or 7α-hydroxy-4-cholesten-3-one, including patients with irritable bowel syndrome with diarrhea, functional diarrhea and Crohn's disease without inflammation. Testing was suggested over empiric bile acid sequestrant therapy (BAST). Once remediable causes are managed, the group suggested cholestyramine as initial therapy, with alternate BAST when tolerability is an issue. The group suggested against BAST for patients with extensive ileal Crohn's disease or resection and suggested alternative antidiarrheal agents if BAST is not tolerated. Maintenance BAST should be given at the lowest effective dose, with a trial of intermittent, on-demand administration, concurrent medication review and reinvestigation for patients whose symptoms persist despite BAST.

Conclusions

Based on a systematic review, BAD should be considered for patients with chronic diarrhea. For patients with positive results from tests for BAD, a trial of BAST, initially with cholestyramine, is suggested.

Methods for diagnosing bile acid malabsorption: a systematic review

BACKGROUND

Bile acid malabsorption (BAM) and bile acid-related diarrhea represent an under-recognized cause of chronic diarrhea mainly because of limited guidance on appropriate diagnostic and laboratory tests. We aimed to perform a systematic review of the literature in order to identify and compare the diagnostic accuracy of different diagnostic methods for patients with BAM, despite a proven gold standard test is still lacking.

METHODS

A PubMed literature review and a manual search were carried out. Relevant full papers, evaluating the diagnostic accuracy of different methods for BAM, were assessed. Available data were analyzed to estimate the sensitivity and specificity of each published test.

RESULTS

Overall, more than one test was considered in published papers on BAM. The search strategy retrieved 574 articles; of these, only 16 were full papers (with a total of 2.332 patients) included in the final review. Specifically, n = 8 studies used ⁷⁵Selenium-homotaurocholic-acid-test (⁷⁵SeHCAT) with a < 10% retention threshold; n = 8 studies evaluated fasting serum 7-α-hydroxy-4-cholesten-3-one (C4); n = 3 studies involved total fecal bile acid (BA) excretion over 48 h; n = 4 studies assessed fibroblast growth factor 19 (FGF19). ⁷⁵SeHCAT showed an average sensitivity and specificity of 87.32 and 93.2%, respectively, followed by serum C4 (85.2 and 71.1%) and total fecal BA (66.6 and 79.3%). Fasting serum FGF19 had the lowest sensitivity and specificity (63.8 and 72.3%). All the extracted data were associated with substantial heterogeneity.

CONCLUSIONS

Our systematic review indicates that ⁷⁵SeHCAT has the highest diagnostic accuracy for BAM, followed by serum C4 assay. The diagnostic yield of fecal BA and FGF19 assays is still under investigation. Our review reinforces the need for novel biomarkers aimed to an objective detection of BAM and therefore improving the management of this condition.

Chronic diarrhoea in adults: what not to miss

PURPOSE OF REVIEW

Chronic diarrhoea remains a diagnostic challenge, with numerous causes and few effective symptomatic treatments. This review focuses on new methods for diagnosis of common disorders and alerts readers to rarer causes through a systematic approach to the underlying mechanisms.

RECENT FINDINGS

New strategies are emerging to stratify the need for endoscopic investigation. Faecal immunochemical testing, combined with standard blood tests, shows promise in excluding colorectal cancers, adenoma and inflammatory bowel disease, challenging the current use of faecal calprotectin. Serum analysis for markers of bile acid synthesis has been refined, potentially streamlining diagnostic pathways of bile acid malabsorption for those who are unable to access nuclear medicine scans, but the positive predictive value of faecal elastase in low prevalence populations has been questioned. Novel markers such as volatile organic compounds and stool DNA analyses continue to develop.

SUMMARY

A systematic approach to investigation of chronic diarrhoea will ensure all relevant causes are considered and minimize the chance of a missed diagnosis. Combination of clinical features with noninvasive testing supports a judicious approach to endoscopic investigations but further innovation will be needed to resolve the diagnostic challenge that diarrhoea poses.