Characterizing Factors Associated With Differences in FGF19 Blood Levels and Synthesis in Patients With Primary Bile Acid Diarrhea

[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.

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.

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.

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.

Comparison of biochemical, microbial and mucosal mRNA expression in bile acid diarrhoea and irritable bowel syndrome with diarrhoea

OBJECTIVE

There are altered mucosal functions in irritable bowel syndrome with diarrhoea (IBS-D); ~30% of patients with IBS-D have abnormal bile acid (BA) metabolism (ABAM) and diarrhoea (summarised as BAD).

AIM

To compare biochemical parameters, gastrointestinal and colonic transit, rectal sensation and pathobiological mechanisms in IBS-D without ABAM and in BAD (serum 7C4>52 ng/mL).

DESIGN

In patients with Rome III criteria of IBS-D, we compared biochemical features, colonic transit, rectal sensation, deep genotype of five BA-related genes, ileal and colonic mucosal mRNA (differential expression (DE) analysis) and stool dysbiosis (including functional analysis of microbiome). Results in BAD were compared with IBS-D without ABAM.

RESULTS

Compared with 161 patients with IBS-D without ABAM, 44 patients with BAD had significantly faster colonic transit, lower microbial alpha diversity, different compositional profile (beta diversity) and higher Firmicutes to Bacteroidetes ratio with evidence of decreased expression of bile acid thiol ligase (involved in transformation of primary to secondary BAs) and decreased sulfatases. In BAD (compared with IBS-D without ABAM), terminal ileal biopsies showed downregulation of SLC44A5 (a BA transporter), and ascending colon biopsies showed upregulation in barrier-weakening genes (CLDN2), serine protease inhibitors, immune activation, cellular differentiation and a cellular transporter (FABP6; BA binding). No DE of genes was documented in descending colon biopsies. The two groups had similar rectal sensation.

CONCLUSION

Though sharing clinical symptoms with IBS-D, BAD is associated with biological differences and mechanisms that have potential to enhance diagnosis and treatment targeting barrier dysfunction, inflammatory and microbial changes.

Recent advances on FXR-targeting therapeutics

The bile acid receptor FXR has emerged as a bona fide drug target for chronic cholestatic and metabolic liver diseases, ahead of all non-alcoholic fatty liver disease (NAFLD). FXR is highly expressed in the liver and intestine and activation at both sites differentially contributes to its desired metabolic effects. Unrestricted FXR activation, however, also comes along with undesired effects such as a pro-atherogenic lipid profile, pruritus and hepatocellular toxicity under certain conditions. Several pre-clinical studies have confirmed the potency of FXR activation for cholestatic and metabolic liver diseases, but overall it remains still open whether selective activation of intestinal FXR is advantageous over pan-FXR activation and whether restricted or modulated FXR activation can limit some of the side effects. Even more, FXR antagonist also bear the potential as intestinal-selective drugs in NAFLD models. In this review we will discuss the molecular prerequisites for FXR activation, pan-FXR activation and intestinal FXR in/activation from a therapeutic point of view, different steroidal and non-steroidal FXR agonists, ways to restrict FXR activation and finally what we have learned from pre-clinical models and clinical trials with different FXR therapeutics.

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.

Physiological and pathophysiological role of endocrine fibroblast growth factors

The endocrine subfamily of fibroblast growth factors (FGF) includes three factors: FGF19, FGF21, FGF23. They act on distal tissues through FGF receptors (FGFRs). The FGFR activation requires two cofactors: α- and β-Klotho, which are structurally related single-pass transmembrane proteins. The endocrine FGFs regulate various metabolic processes involved in the regulation of glucose and lipid metabolism as well as bile acid circulation, vitamin D modulation, and phosphate homeostasis. The FGF-FGFR dysregulation is widely implicated in the pathogenesis of various disorders. Significant alterations in plasma FGF concentration are associated with the most prevalent chronic diseases, including dyslipidemia, type 2 diabetes, cardiovascular diseases, obesity, non-alcoholic fatty liver disease, diseases of the biliary tract, chronic kidney disease, inflammatory bowel disease, osteomalacia, various malignancies, and depression. Therefore, the endocrine FGFs may serve as disease predictors or biomarkers, as well as potential therapeutic targets. Currently, numerous analogues and inhibitors of endocrine FGFs are under development for treatment of various disorders, and recently, a human monoclonal antibody against FGF23 has been approved for treatment of X-linked hypophosphatemia. The aim of this review is to summarize the current data on physiological and pathophysiological actions of the endocrine FGF subfamily and recent research concerning the therapeutic potential of the endocrine FGF pathways.

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.

SLC10A2 deficiency-induced congenital chronic bile acid diarrhea and stunting

Background

Diarrhea is a common occurrence in children below the age of 5 years. In chronic cases, it induces malnutrition that severely stunts growth. Bile acid diarrhea (BAD), caused by malabsorption of bile acid (BA), is a rare form of chronic diarrhea seldom observed in pediatric patients. Here, we present a clinical report on a novel case of chronic BAD, with severe stunting in an infant, induced by a homozygous mutation of SLC10A2.

Methods

We performed DNA extraction, whole‐exome sequencing analysis, and mutation analysis of SLC10A2 to obtain genetic data on the patient. We subsequently analyzed the patient's clinical and genetic data.

Results

The patient's clinical manifestations were chronic diarrhea with increased BAs in the feces and extreme stunting, which was diagnosed as BAD. A homozygous mutation of SLC10A2 at the c.313T>C (rs201206937) site was detected.

Conclusion

Our report reveals the youngest case illustrating the characteristics of BAD induced by genetic variant at 313T>C, and the second case entailing a clear association between a SLC10A2 genetic mutation and the onset of BAD. Our findings expand the mutant spectrum of the SLC10A2 gene and contribute to the refinement of the genotype–phenotype mapping of severe stunting induced by pediatric BAD. Moreover, they highlight the value of molecular genetic screening for diagnosing BAD in young patients.

Differential mRNA Expression in Ileal Mucosal Biopsies of Patients With Diarrhea- or Constipation-Predominant Irritable Bowel Syndrome

INTRODUCTION

Previous studies in patients with irritable bowel syndrome (IBS) showed immune activation, secretion, and barrier dysfunction in duodenal, jejunal, or colorectal mucosa. This study aimed to measure ileal mucosal expression of genes and proteins associated with mucosal functions.

METHODS

We measured by reverse transcription polymerase chain reaction messenger RNA (mRNA) expression of 78 genes (reflecting tight junction proteins, chemokines, innate immunity, ion channels, and transmitters) and 5 proteins (barrier, bile acid receptor, and ion exchanger) in terminal ileal mucosa from 11 patients with IBS-diarrhea (IBS-D), 17 patients with IBS-constipation (IBS-C), and 14 healthy controls. Fold changes in mRNA were calculated using 2(-Δ, ΔCT) formula. Group differences were measured using analysis of variance. Protein ratios relative to healthy controls were based on Western blot analysis. Nominal P values (P < 0.05) are reported.

RESULTS

In ileal mucosal biopsies, significant differences of mRNA expression in IBS-D relative to IBS-C were upregulation of barrier proteins (TJP1, FN1, CLDN1, and CLDN12), repair function (TFF1), and cellular functions. In ileal mucosal biopsies, mRNA expression in IBS-C relative to healthy controls was reduced GPBAR1 receptor, myosin light chain kinase (MYLK in barrier function), and innate immunity (TLR3), but increased mRNA expression of cadherin cell adhesion mechanisms (CTNNB1) and transport genes SLC9A1 (Na-H exchanger [NHE1]) and INADL (indirect effect on ion transport).

DISCUSSION

These data support a role of ileal mucosal dysfunction in IBS, including barrier dysfunction in IBS-D and alterations in absorption/secretion mechanisms in IBS-C.

Bile acids and their receptors in metabolic disorders

Bile acids are a large family of atypical steroids which exert their functions by binding to a family of ubiquitous cell membrane and nuclear receptors. There are two main bile acid activated receptors, FXR and GPBAR1, that are exclusively activated by bile acids, while other receptors CAR, LXRs, PXR, RORγT, S1PR2and VDR are activated by bile acids in addition to other more selective endogenous ligands. In the intestine, activation of FXR and GPBAR1 promotes the release of FGF15/19 and GLP1 which integrate their signaling with direct effects exerted by theother receptors in target tissues. This network is tuned in a time ordered manner by circadian rhythm and is critical for the regulation of metabolic process including autophagy, fast-to-feed transition, lipid and glucose metabolism, energy balance and immune responses. In the last decade FXR ligands have entered clinical trials but development of systemic FXR agonists has been proven challenging because their side effects including increased levels of cholesterol and Low Density Lipoproteins cholesterol (LDL-c) and reduced High-Density Lipoprotein cholesterol (HDL-c). In addition, pruritus has emerged as a common, dose related, side effect of FXR ligands. Intestinal-restricted FXR and GPBAR1 agonists and dual FXR/GPBAR1 agonists have been developed. Here we review the last decade in bile acids physiology and pharmacology.

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).

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.

Bile acid diarrhoea: pathophysiology, diagnosis and management

The actual incidence of bile acid diarrhoea (BAD) is unknown, however, there is increasing evidence that it is misdiagnosed in up to 30% with diarrhoea-predominant patients with irritable bowel syndrome. Besides this, it may also occur following cholecystectomy, infectious diarrhoea and pelvic chemoradiotherapy. BAD may result from either hepatic overproduction of bile acids or their malabsorption in the terminal ileum. It can result in symptoms such as bowel frequency, urgency, nocturnal defecation, excessive flatulence, abdominal pain and incontinence of stool. Bile acid synthesis is regulated by negative feedback loops related to the enterohepatic circulation, which are dependent on the farnesoid X receptor and fibroblast growth factor 19. Interruption of these feedback loops is thought to cause bile acid overproduction leading to BAD. This process may occur idiopathically or following a specific trigger such as cholecystectomy. There may also be an interplay with the gut microbiota, which has been reported to be significantly different in patients with severe BAD. Patients with suspected BAD are investigated in various ways including radionucleotide imaging such as SeHCAT scans (though this is not available worldwide) and blood tests. However, other methods such as bile acid measurement in stool (either spot test or 48 hours samples) and urine tests have been explored. Importantly, delay in diagnosis and treatment of BAD greatly affects patient's quality of life and may double the overall cost of diagnosis.

Randomised clinical trial: significant biochemical and colonic transit effects of the farnesoid X receptor agonist tropifexor in patients with primary bile acid diarrhoea

BACKGROUND

In primary bile acid diarrhoea, feedback by farnesoid X receptor (FXR) and fibroblast growth hormone 19 (FGF19) on hepatic bile acid production is impaired.

AIMS

To evaluate the safety, mechanisms and efficacy of negative feedback by FXR activation with tropifexor, a non-bile acid FXR agonist, in patients with primary bile acid diarrhoea.

METHODS

In this double-blind, multicentre, randomised, cross-over study, patients received tropifexor 60 µg or placebo once daily for 14 days in each of two treatment periods. Primary objectives included tropifexor safety and tolerability, and on stool frequency and form. Other assessments included pharmacokinetic and pharmacodynamic measures, biochemical markers and gastrointestinal transit.

RESULTS

Twenty patients (tropifexor 60 µg/placebo [N = 10]; placebo/tropifexor 60 µg [N = 10]) were enrolled. Adverse event rates were lower with tropifexor vs placebo (52.9% vs 73.7%). No patient had pruritus during tropifexor intake. There were no significant differences in stool frequency, stool form or loperamide use between treatments. Tropifexor increased FGF19 and decreased 7α-hydroxy-4-cholesten-3-one (C4) levels for up to 8 h. Plasma tropifexor concentrations peaked at 5 hours post-dose on days 1 and 12. At day 12, tropifexor caused reduction in peak total bile acid concentration (33%, P = 0.032) and exposure (36%, P = 0.005). Moreover, tropifexor showed a significant increase in ascending colon half-emptying time (P = 0.036).

CONCLUSIONS

Tropifexor 60 µg once daily had acceptable safety and tolerability. Changes in FGF19 and C4 showed effective target engagement; however, higher doses may be required to observe stool frequency changes. Slowing of ascending colon emptying suggests therapeutic potential of tropifexor in patients with primary bile acid diarrhoea. ClinicalTrials.gov number: NCT02713243.

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

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

Chronic diarrhea, bile acids, and Clostridia

Excessive fecal bile acid (BA) loss causes symptoms in a large proportion of people diagnosed with irritable bowel syndrome with diarrhea, a common functional bowel disorder. This BA diarrhea (BAD) results from increased hepatic synthesis of BAs, with impaired negative feedback regulation by the ileal hormone fibroblast growth factor 19 (FGF19). In this issue of the JCI, Zhao et al. investigated BA metabolism, including fecal BAs, serum BAs, and FGF19, in patients and controls. They identified associations between fecal bacterial BA metabolism and specific microbiota, especially Clostridium scindens. These findings have been tested in a mouse model using microbiota transplants and antibiotic treatment. This group of organisms has potential as a biomarker for BAD and to be a target for therapy.

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.

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.

Personalized medicine in functional gastrointestinal disorders: Understanding pathogenesis to increase diagnostic and treatment efficacy

There is overwhelming evidence that functional gastrointestinal disorders (FGIDs) are associated with specific mechanisms that constitute important targets for personalized treatment. There are specific mechanisms in patients presenting with functional upper gastrointestinal symptoms (UGI Sx). Among patients with UGI Sx, approximately equal proportions (25%) of patients have delayed gastric emptying (GE), reduced gastric accommodation (GA), both impaired GE and GA, or neither, presumably due to increased gastric or duodenal sensitivity. Treatments targeted to the underlying pathophysiology utilize prokinetics, gastric relaxants, or central neuromodulators. Similarly, specific mechanisms in patients presenting with functional lower gastrointestinal symptoms, especially with diarrhea or constipation, are recognized, including at least 30% of patients with functional constipation pelvic floor dyssynergia and 5% has colonic inertia (with neural or interstitial cells of Cajal loss in myenteric plexus); 25% of patients with diarrhea-predominant irritable bowel syndrome (IBSD) has evidence of bile acid diarrhea; and, depending on ethnicity, a varying proportion of patients has disaccharidase deficiency, and less often sucrose-isomaltase deficiency. Among patients with predominant pain or bloating, the role of fermentable oligosaccharides, disaccharides, monosaccharides and polyols should be considered. Personalization is applied through pharmacogenomics related to drug pharmacokinetics, specifically the role of CYP2D6, 2C19 and 3A4 in the use of drugs for treatment of patients with FGIDs. Single mutations or multiple genetic variants are relatively rare, with limited impact to date on the understanding or treatment of FGIDs. The role of mucosal gene expression in FGIDs, particularly in IBS-D, is the subject of ongoing research. In summary, the time for personalization of FGIDs, based on deep phenotyping, is here; pharmacogenomics is relevant in the use of central neuromodulators. There is still unclear impact of the role of genetics in the management of FGIDs.

Non-alcoholic fatty liver disease is associated with dysregulated bile acid synthesis and diarrhea: A prospective observational study

Background

Non-alcoholic fatty liver disease (NAFLD) may be associated with changes in bile acid (BA) metabolism. Hepatic BA production, measured by serum levels of the precursor 7α-hydroxy-4-cholesten-3-one (C4), is regulated by the farnesoid-X-receptor (FXR)-dependent ileal hormone fibroblast growth factor 19 (FGF19). Low FGF19 and high C4 are features of chronic BA diarrhea. Obeticholic acid, an FXR agonist, stimulates FGF19 and has shown therapeutic potential in both BA diarrhea and in NAFLD. We hypothesized there are associations of FGF19, C4 and BA diarrhea with NAFLD.

Methods and findings

127 patients with known NAFLD were recruited prospectively. Clinical features, including metformin use, markers of NAFLD severity and BA synthesis were analyzed. The overall incidence of chronic diarrhea was 25%, with features of BA diarrhea in 12%. FGF19 negatively correlated with C4 (r_s = -0.43, p = 0.001) and with alanine aminotransferase (r_s = -0.22, p = 0.03), but not with either NAFLD fibrosis or Fibroscan scores. High C4 was associated with a higher NAFLD fibrosis score (p < 0.05), and with diarrhea (p = 0.001). The median NAFLD fibrosis score was higher in those with diarrhea (p = 0.002). Metformin use, in 44% overall, was particularly associated with diarrhea (in 36% vs 17%, p = 0.02), and a lower median FGF19 (74 vs 105 pg/mL, p < 0.05).

Conclusions

Increased hepatic BA production and diarrhea, but not low FGF19, were associated with increased NAFLD fibrosis score, indicating dysregulation of the FXR-FGF19 axis and suggesting hepatic FGF19 resistance. Metformin use was an important factor in a subgroup, lowering FGF19, and resulting in bile acid diarrhea.

Guts and Gall: Bile Acids in Regulation of Intestinal Epithelial Function in Health and Disease

Epithelial cells line the entire surface of the gastrointestinal tract and its accessory organs where they primarily function in transporting digestive enzymes, nutrients, electrolytes, and fluid to and from the luminal contents. At the same time, epithelial cells are responsible for forming a physical and biochemical barrier that prevents the entry into the body of harmful agents, such as bacteria and their toxins. Dysregulation of epithelial transport and barrier function is associated with the pathogenesis of a number of conditions throughout the intestine, such as inflammatory bowel disease, chronic diarrhea, pancreatitis, reflux esophagitis, and cancer. Driven by discovery of specific receptors on intestinal epithelial cells, new insights into mechanisms that control their synthesis and enterohepatic circulation, and a growing appreciation of their roles as bioactive bacterial metabolites, bile acids are currently receiving a great deal of interest as critical regulators of epithelial function in health and disease. This review aims to summarize recent advances in this field and to highlight how bile acids are now emerging as exciting new targets for disease intervention.

Fibroblast Growth Factor 15/19: From Basic Functions to Therapeutic Perspectives

Discovered 20 years ago, fibroblast growth factor (FGF)19, and its mouse ortholog FGF15, were the first members of a new subfamily of FGFs able to act as hormones. During fetal life, FGF15/19 is involved in organogenesis, affecting the development of the ear, eye, heart, and brain. At adulthood, FGF15/19 is mainly produced by the ileum, acting on the liver to repress hepatic bile acid synthesis and promote postprandial nutrient partitioning. In rodents, pharmacologic doses of FGF19 induce the same antiobesity and antidiabetic actions as FGF21, with these metabolic effects being partly mediated by the brain. However, activation of hepatocyte proliferation by FGF19 has long been a challenge to its therapeutic use. Recently, genetic reengineering of the molecule has resolved this issue. Despite a global overlap in expression pattern and function, murine FGF15 and human FGF19 exhibit several differences in terms of regulation, molecular structure, signaling, and biological properties. As most of the knowledge originates from the use of FGF19 in murine models, differences between mice and humans in the biology of FGF15/19 have to be considered for a successful translation from bench to bedside. This review summarizes the basic knowledge concerning FGF15/19 in mice and humans, with a special focus on regulation of production, morphogenic properties, hepatocyte growth, bile acid homeostasis, as well as actions on glucose, lipid, and energy homeostasis. Moreover, implications and therapeutic perspectives concerning FGF19 in human diseases (including obesity, type 2 diabetes, hepatic steatosis, biliary disorders, and cancer) are also discussed.

Elobixibat for the treatment of constipation

INTRODUCTION

Chronic idiopathic constipation (CC) is highly prevalent worldwide. A subset of patients with CC have reduced fecal (and by inference, intra-colonic) bile acids (BA). Elobixibat, a locally-acting ileal bile acid transporter (IBAT) inhibitor, leads to increased BA delivery to the colon and represents a new class of treatment for CC. BAs accelerate colonic transit and increase colonic secretion. Therefore, IBAT inhibitors have potential to treat patients with CC. Areas covered: Rationale for IBAT inhibitor in therapeutics, and preclinical and clinical pharmacology of elobixibat: In vitro, elobixibat is a highly potent, selective IBAT inhibitor. In humans, elobixibat accelerated colonic transit. In phase 2A, 2B and 3 studies in CC, elobixibat was efficacious, well tolerated and safe. An open-label, phase 3 trial (52 weeks) confirmed the safety of elobixibat. Elobixibat reduces LDL cholesterol, increases serum GLP-1, and has potential in metabolic syndrome. Expert commentary: Uniquely among current treatments of CC, elobixibat stimulates both motor and secretory functions in the colon. These dual effects suggest that, when approved, elobixibat may be a first-line choice for constipation associated with colonic BA deficiency and a second-line treatment for all patients with CC and constipation-predominant irritable bowel syndrome. Further studies are required to confirm efficacy for relief of CC. Once approved, elobixibat will likely become a second-line choice for treatment of CC.

Obeticholic acid for severe bile acid diarrhea with intestinal failure: A case report and review of the literature

Bile acid diarrhea results from excessive amounts of bile acids entering the colon due to hepatic overexcretion of bile acids or bile acid malabsorption in the terminal ileum. The main therapies include bile acid sequestrants, such as colestyramine and colesevelam, which may be given in combination with the opioid receptor agonist loperamide. Some patients are refractory to conventional treatments. We report the use of the farnesoid X receptor agonist obeticholic acid in a patient with refractory bile acid diarrhea and subsequent intestinal failure. A 32-year-old woman with quiescent colonic Crohn’s disease and a normal terminal ileum had been diagnosed with severe bile acid malabsorption and complained of watery diarrhea and fatigue. The diarrhea resulted in hypokalemia and sodium depletion that made her dependent on twice weekly intravenous fluid and electrolyte infusions. Conventional therapies with colestyramine, colesevelam, and loperamide had no effect. Second-line antisecretory therapies with pantoprazole, liraglutide, and octreotide also failed. Third-line treatment with obeticholic acid reduced the number of stools from an average of 13 to an average of 7 per 24 h and improved the patient’s quality of life. The fluid and electrolyte balances normalized. The effect was sustained during follow-up for 6 mo with treatment at a daily dosage of 25 mg. The diarrhea worsened shortly after cessation of obeticholic acid. This case report supports the initial report that obeticholic acid may reduce bile acid production and improve symptoms in patients with bile acid diarrhea.

Evaluation of chronic diarrhea and irritable bowel syndrome with diarrhea in adults in the era of precision medicine

Chronic diarrhea is a common clinical problem, affecting roughly 5% of the population in any given year. Evaluation and management of these patients can be difficult due to the extensive differential diagnosis of this symptom. Many patients with chronic diarrhea have structural problems, such as inflammatory bowel disease or celiac disease, that can be readily identified. Others do not, and often are given a diagnosis of irritable bowel syndrome with diarrhea (IBS-D). When based on generally accepted clinical criteria, a diagnosis of IBS-D identifies a group of patients who are unlikely to have disorders producing anatomical changes in the gut. It is less clear that a diagnosis of IBS-D identifies a specific pathophysiology or leads to better management of symptoms. Disorders such as small intestinal bacterial overgrowth, bile acid malabsorption, food intolerance, and motility disorders may account for symptoms in patients with IBS-D. More effective tests are being developed to identify the clinical problems underlying IBS-D and may lead to more specific diagnoses that may improve the results of therapy. Application of the principles of precision medicine (identifying a specific mechanism for disease and applying treatments that work on that mechanism) should lead to more expeditious diagnosis and treatment for patients with chronic diarrhea including IBS-D, but currently is limited by the availability of sufficiently sensitive and specific tests for underlying mechanisms that can predict response to treatment.

Intestinal Involvement in Systemic Sclerosis: A Clinical Review

Systemic sclerosis (SSc) is a chronic systemic disease characterized by microvasculopathy, autoantibodies, and extensive fibrosis. Intestinal involvement is frequent in SSc and represents a significant cause of morbidity. The pathogenesis of intestinal involvement includes vascular damage, nerve dysfunction, smooth muscle atrophy, and fibrosis, causing hypomotility, which leads to small intestinal bacterial overgrowth (SIBO), malabsorption, malnutrition, diarrhea, pseudo-obstruction, constipation, pneumatosis intestinalis, and fecal incontinence. Manifestations are often troublesome and reduce quality of life and life expectancy. Assessment of intestinal involvement includes screening for small intestine hypomotility, malnutrition, SIBO, and anorectal dysfunction. Current management of intestinal manifestations is largely inadequate. Patients with diarrhea are managed with low-fat diet, medium-chain triglycerides, avoidance of lactulose and fructose, and control of bacterial overgrowth with antibiotics for SIBO. In diarrhea/malabsorption, bile acid sequestrant and pancreatic enzyme supplementation may help, and nutritional support is needed. General measures are applied for constipation, and intestine rest plus antibiotics for pseudo-obstruction. Fecal incontinence is managed with measures for associated SIBO, or constipation, and with behavioral therapies. Pneumatosis intestinalis is usually an incidental finding that does not require any specific treatment. Immunomoduation should be considered early in intestinal involvement. Multidisciplinary approach of intestinal manifestations in SSc by gastroenterologists and rheumatologists is required for optimum management.

Update on Bile Acid Malabsorption: Finally Ready for Prime Time?

PURPOSE OF REVIEW

To provide an update on the prevalence, pathophysiology, disease associations, and treatment options for bile acid malabsorption (BAM).

RECENT FINDINGS

•Molecular mechanisms-BAs prevent water reabsorption and increase water secretion by intracellular mediators, increasing aquaporin channels and intracellular permeability. •Inflammatory bowel disease-new molecular mechanisms of BAM are identified in patients without ileal disease, including changes in expression of ileal BA transporter and nuclear receptors involved in BA homeostasis. •Microscopic colitis-BAM is one of the mechanisms leading to microscopic colitis. •Diagnostic testing-new diagnostic tests have been launched in the USA (serum C4 and fecal 48-h BA excretion); stimulated FGF19 has higher detection of BAM compared to fasting sample alone. •Treatment-investigational FXR agonists may provide a daily, oral option for treatment of BAM instead of BA sequestrants. There is a greater appreciation of the biological role of bile acids across multiple fields of medicine, including gastrointestinal indications.

Novel associations of bile acid diarrhoea with fatty liver disease and gallstones: a cohort retrospective analysis

Background

Bile acid diarrhoea (BAD) is a common cause of chronic diarrhoea with a population prevalence of primary BAD around 1%. Previous studies have identified associations with low levels of the ileal hormone fibroblast growth factor 19 (FGF19), obesity and hypertriglyceridaemia. The aim of this study was to identify further associations of BAD.

Methods

A cohort of patients with chronic diarrhoea who underwent ⁷⁵selenohomocholic acid taurate (SeHCAT) testing for BAD was further analysed retrospectively. Additional clinical details available from the electronic patient record, including imaging, colonoscopy, chemistry and histopathology reports were used to calculate the prevalence of fatty liver disease, gallstones, colonic neoplasia and microscopic colitis, which was compared for BAD, the primary BAD subset and control patients with diarrhoea.

Findings

Of 578 patients, 303 (52%) had BAD, defined as a SeHCAT 7d retention value <15%, with 179 (31%) having primary BAD. 425 had an alanine aminotransferase (ALT) recorded, 184 had liver imaging and 176 had both. Overall, SeHCAT values were negatively associated with ALT (r_s=−0.19, p<0.0001). Patients with BAD had an OR of 3.1 for an ALT >31 ng/mL with imaging showing fatty liver (p<0.001); similar figures occurred in the primary BAD group. FGF19 was not significantly related to fatty liver but low levels were predictive of ALT >40 IU/L. In 176 subjects with gallbladder imaging, 27% had gallstones, 7% had a prior cholecystectomy and 34% either of these. The median SeHCAT values were lower in those with gallstones (3.8%, p<0.0001), or gallstones/cholecystectomy (7.2%, p<0.001), compared with normal gallbladder imaging (14%). Overall, BAD had an OR of 2.0 for gallstones/cholecystectomy (p<0.05). BAD was not significantly associated with colonic adenoma/carcinoma or with microscopic colitis.

Interpretation

The diagnosis of BAD is associated with fatty liver disease and with gallstones. The reasons for these associations require further investigation into potential metabolic causes.

Chenodeoxycholic acid stimulated fibroblast growth factor 19 response - a potential biochemical test for bile acid diarrhoea

BACKGROUND

Bile acid diarrhoea is underdiagnosed and better diagnostic tests are needed. Fasting serum fibroblast growth factor-19 (FGF19) has insufficient diagnostic value, but this may be improved by stimulation.

AIM

To explore if an impaired FGF19 response identifies primary bile acid diarrhoea.

METHODS

Eight patients with primary bile acid diarrhoea and eight healthy volunteers ingested (i) a meal plus 1250 mg chenodeoxycholic acid (CDCA), (ii) 1250 mg CDCA or (iii) the meal. Blood was sampled at fasting and repeatedly after stimulation. We analysed FGF19 by enzyme-linked immunosorbent assay and bile acids including 7α-hydroxy-4-cholesten-3-one by liquid chromatography-tandem mass spectrometry.

RESULTS

Stimulation with the meal plus CDCA increased median FGF19 in healthy volunteers from fasting 62 pg/mL [interquartile range (IQR): 41-138] to 99 pg/mL (IQR: 67-147; P = 0.012) after 90 min and peaked after 150 min at 313 pg/mL (IQR: 54-512). This response was impaired in primary bile acid diarrhoea patients [fasting 56 pg/mL (IQR: 42-79); 90 min: 48 pg/mL [IQR: 37-63); 150 min: 57 pg/mL (48-198)]. Receiver operating characteristics (ROC_AUC ) for fasting FGF19 was 0.55 (P = 0.75) and at 90 min 0.84 (P = 0.02). The difference in FGF19 from fasting to 90 min after the meal plus CDCA separated the groups (ROC_AUC 1.0; P = 0.001). 7α-hydroxy-4-cholesten-3-one was elevated in primary bile acid diarrhoea (P = 0.038) and not significantly affected by stimulation.

CONCLUSIONS

The FGF19 response following chenodeoxycholic acid plus meal is impaired in primary bile acid diarrhoea. This may provide a biochemical diagnostic test.

Bile acid disease: the emerging epidemic

PURPOSE OF REVIEW

Our objective was to review advances in bile acids in health and disease published in the last 2 years. Bile acid diarrhea (BAD) is recognized as a common cause of chronic diarrhea, and its recognition has been facilitated by development of new screening tests.

RECENT FINDINGS

Primary BAD can account for 30% of cases of chronic diarrhea. The mechanisms leading to BAD include inadequate feedback regulation by fibroblast growth factor 19 (FGF-19) from ileal enterocytes, abnormalities in synthesis or degradation of proteins involved in FGF-19 regulation in hepatocytes and variations as a function of the bile acid receptor, TGR5 (GPBAR1). SeHCAT is the most widely used test for diagnosis of BAD. There has been significant validation of fasting serum FGF-19 and 7 α-hydroxy-cholesten-3-one (C4), a surrogate measure of bile acid synthesis. Bile acid sequestrants are the primary treatments for BAD; the farnesoid X-receptor-FGF-19 pathway provides alternative therapeutic targets for BAD. Bile acid-stimulated intestinal mechanisms contribute to the beneficial effects of bariatric surgery on obesity, glycemic control and the treatment of recurrent Clostridium difficile infection.

SUMMARY

Renewed interest in the role of bile acids is leading to novel management of diverse diseases besides BAD.

Oxysterols: From cholesterol metabolites to key mediators

Oxysterols are cholesterol metabolites that can be produced through enzymatic or radical processes. They constitute a large family of lipids (i.e. the oxysterome) involved in a plethora of physiological processes. They can act through GPCR (e.g. EBI2, SMO, CXCR2), nuclear receptors (LXR, ROR, ERα) and through transporters or regulatory proteins. Their physiological effects encompass cholesterol, lipid and glucose homeostasis. Additionally, they were shown to be involved in other processes such as immune regulatory functions and brain homeostasis. First studied as precursors of bile acids, they quickly emerged as interesting lipid mediators. Their levels are greatly altered in several pathologies and some oxysterols (e.g. 4β-hydroxycholesterol or 7α-hydroxycholestenone) are used as biomarkers of specific pathologies. In this review, we discuss the complex metabolism and molecular targets (including binding properties) of these bioactive lipids in human and mice. We also discuss the genetic mouse models currently available to interrogate their effects in pathophysiological settings. We also summarize the levels of oxysterols reported in two key organs in oxysterol metabolism (liver and brain), plasma and cerebrospinal fluid. Finally, we consider future opportunities and directions in the oxysterol field in order to gain a better insight and understanding of the complex oxysterol system.

The Farnesoid X Receptor: Good for BAD

Diarrhea is a feature of several chronic intestinal disorders that are associated with increased delivery of bile acids into the colon. Although the prevalence of bile acid diarrhea is high, affecting approximately 1% of the adult population, current therapies often are unsatisfactory. By virtue of its capacity to inhibit colonic epithelial fluid secretion and to down-regulate hepatic bile acid synthesis through induction of the ileal fibroblast growth factor 19 release, the nuclear bile acid receptor, farnesoid X receptor, represents a promising target for the development of new therapeutic approaches. Here, we review our current understanding of the pathophysiology of bile acid diarrhea and the current evidence supporting a role for farnesoid X receptor agonists in treatment of the disease.

Mechanisms of triglyceride metabolism in patients with bile acid diarrhea

Bile acids (BAs) are essential for the absorption of lipids. BA synthesis is inhibited through intestinal farnesoid X receptor (FXR) activity. BA sequestration is known to influence BA metabolism and control serum lipid concentrations. Animal data has demonstrated a regulatory role for the FXR in triglyceride metabolism. FXR inhibits hepatic lipogenesis by inhibiting the expression of sterol regulatory element binding protein 1c via small heterodimer primer activity. Conversely, FXR promotes free fatty acids oxidation by inducing the expression of peroxisome proliferator-activated receptor α. FXR can reduce the expression of microsomal triglyceride transfer protein, which regulates the assembly of very low-density lipoproteins (VLDL). FXR activation in turn promotes the clearance of circulating triglycerides by inducing apolipoprotein C-II, very low-density lipoproteins receptor (VLDL-R) and the expression of Syndecan-1 together with the repression of apolipoprotein C-III, which increases lipoprotein lipase activity. There is currently minimal clinical data on triglyceride metabolism in patients with bile acid diarrhoea (BAD). Emerging data suggests that a third of patients with BAD have hypertriglyceridemia. Further research is required to establish the risk of hypertriglyceridaemia in patients with BAD and elicit the mechanisms behind this, allowing for targeted treatment.