The response of patients with bile acid diarrhoea to the farnesoid X receptor agonist obeticholic acid

Making the Diagnosis of Bile Acid Diarrhea

Bile acid diarrhea is a frequent, treatable cause of functional diarrhea but is difficult to diagnose when the nuclear medicine seleno-taurohomocholic acid test is unavailable. An alternative approach is testing blood for the bile acid precursor, 7α-OH-4-cholesten-3-one, which is raised with increased bile acid synthesis. A recent article has defined measurements that have high negative and positive predictive values, further exploring how they can be improved by incorporating measures such as age, stool number, fibroblast growth factor 19, or plasma sulfated bile acids. Other articles have looked at the percentage of fecal primary bile acids. Together, they promise better use of diagnostic biomarkers for this condition.

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.

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.

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

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

Lactobacillus casei YRL577 ameliorates markers of non-alcoholic fatty liver and alters expression of genes within the intestinal bile acid pathway

Non-alcoholic fatty liver disease (NAFLD) has become the main cause of end-stage liver disease. Probiotics have the potential effect of alleviating NAFLD. The aim of this study was to explore functional probiotics and their underlying mechanisms. The bile salt hydrolase (BSH) activity in thirty-four strains was determined in vitro. Then, C57BL/6 mice were used to explore the effects of probiotics on NAFLD. Body weight and food intake were measured, and serum lipid concentrations, oxidative stress and proinflammatory cytokines levels were determined using commercial kits. The expressions of intestinal bile acid pathway genes were evaluated via real-time PCR. The results showed that Lactobacillus casei YRL577 and L. paracasei X11 had higher BSH activity. L. casei YRL577 significantly reduced liver weight and liver index and could regulate the levels of lipid metabolism, oxidative stress and proinflammatory cytokines as compared with L. paracasei X11. Furthermore, the results indicated that L. casei YRL577 up-regulated the mRNA levels of farnesoid X receptor and fibroblast growth factor 15, whereas down-regulated the mRNA level of apical Na-dependent bile acid transporter. These findings suggested that L. casei YRL577 modified genes in the intestinal bile acid pathway which might contribute to the alleviation of NAFLD.

Bariatric Surgery and Its Complications in Inflammatory Bowel Disease Patients

Recent data have suggested that bariatric procedures, especially laparoscopic sleeve gastrectomy (SG), are safe and effective weight loss measures in patients with inflammatory bowel disease (IBD). But most of the studies have looked at short-term outcomes, and there is a general lack of awareness of underlying disease processes and baseline comorbidities in IBD patients undergoing bariatric procedures. Postbariatric issues in IBD patients including diarrhea from dumping syndrome, choleretic diarrhea, a high prevalence of small intestinal bacterial overgrowth, gastroesophageal reflux disease, Barrett's esophagus, stomal ulcerations, stenosis, and renal and gallstones can complicate the natural history of IBD. This could lead to unnecessary hospitalizations, change of medical therapy, and poor surgical and quality of life outcomes. In this review, we will discuss major complications after common bariatric procedures (SG, Roux-en-Y gastric bypass, and gastric banding) and suggest possible management strategies.

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.

Irritable Bowel Syndrome: News from an Old Disorder

Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder, which can affect all members of a society, regardless of age, sex, race or socioeconomic status. Because of its high prevalence and chronic nature, it represents a significant economic burden. In fact, these patients have a relevant impairment of their quality of life, which limits their work productivity and daily social activities, especially when it is associated with other disorders, such as anxiety and depression. The diagnosis of IBS relies on symptom-based diagnostic criteria with normal results on a limited number of complementary tests that rule out other possible diagnoses. The aetiology of this condition is incompletely established. However, evidence suggests that it is a multifactorial disorder with several different mechanisms that have been implicated as responsible for the symptoms. Since the treatment strategy is usually based on predominant symptoms and their severity, it is important to recognise the underlying mechanisms in order to successfully relief the visceral pain and altered bowel habits. The aim of this non-systematic review of the literature was to explore the pathophysiology and treatment options of IBS, highlighting the most recent evidence, from the new Rome IV criteria to the new drug armamentarium.

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.

Bile acid receptors FXR and TGR5 signaling in fatty liver diseases and therapy

Bile acid synthesis is the most significant pathway for catabolism of cholesterol and for maintenance of whole body cholesterol homeostasis. Bile acids are physiological detergents that absorb, distribute, metabolize, and excrete nutrients, drugs, and xenobiotics. Bile acids also are signal molecules and metabolic integrators that activate nuclear farnesoid X receptor (FXR) and membrane Takeda G protein-coupled receptor 5 (TGR5; i.e., G protein-coupled bile acid receptor 1) to regulate glucose, lipid, and energy metabolism. The gut-to-liver axis plays a critical role in the transformation of primary bile acids to secondary bile acids, in the regulation of bile acid synthesis to maintain composition within the bile acid pool, and in the regulation of metabolic homeostasis to prevent hyperglycemia, dyslipidemia, obesity, and diabetes. High-fat and high-calorie diets, dysbiosis, alcohol, drugs, and disruption of sleep and circadian rhythms cause metabolic diseases, including alcoholic and nonalcoholic fatty liver diseases, obesity, diabetes, and cardiovascular disease. Bile acid-based drugs that target bile acid receptors are being developed for the treatment of metabolic diseases of the liver.

A Physiology-Based Model of Bile Acid Distribution and Metabolism Under Healthy and Pathologic Conditions in Human Beings

BACKGROUND & AIMS

Disturbances of the enterohepatic circulation of bile acids (BAs) are seen in a number of clinically important conditions, including metabolic disorders, hepatic impairment, diarrhea, and gallstone disease. To facilitate the exploration of underlying pathogenic mechanisms, we developed a mathematical model built on quantitative physiological observations across different organs.

METHODS

The model consists of a set of kinetic equations describing the syntheses of cholic, chenodeoxycholic, and deoxycholic acids, as well as time-related changes of their respective free and conjugated forms in the systemic circulation, the hepatoportal region, and the gastrointestinal tract. The core structure of the model was adapted from previous modeling research and updated based on recent mechanistic insights, including farnesoid X receptor-mediated autoregulation of BA synthesis and selective transport mechanisms. The model was calibrated against existing data on BA distribution and feedback regulation.

RESULTS

According to model-based predictions, changes in intestinal motility, BA absorption, and biotransformation rates affected BA composition and distribution differently, as follows: (1) inhibition of transintestinal BA flux (eg, in patients with BA malabsorption) or acceleration of intestinal motility, followed by farnesoid X receptor down-regulation, was associated with colonic BA accumulation; (2) in contrast, modulation of the colonic absorption process was predicted to not affect the BA pool significantly; and (3) activation of ileal deconjugation (eg, in patents with small intestinal bacterial overgrowth) was associated with an increase in the BA pool, owing to higher ileal permeability of unconjugated BA species.

CONCLUSIONS

This model will be useful in further studying how BA enterohepatic circulation modulation may be exploited for therapeutic benefits.

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.

Serum Concentrations of 7α-hydroxy-4-cholesten-3-one Are Associated With Bile Acid Diarrhea in Patients With Crohn's Disease

BACKGROUND & AIMS

Patients with Crohn's disease (CD) often have bile acid diarrhea (BAD), due to bile acid malabsorption following ileal resection (IR). Bile acid malabsorption increases production of 7α-hydroxy-4-cholesten-3-one (C4), a bile acid precursor. We investigated relationships between serum concentrations of C4 and BAD in patients with CD.

METHODS

We collected demographic data, serum samples, and information on the presence of diarrhea (>3 liquid bowel movements/day), as well as clinical, endoscopic, and histologic scores from 26 patients with CD and IR, 21 patients with CD without IR, and 37 patients with ulcerative colitis (UC). We compared serum concentrations of C4 and fibroblast growth factor 19 (FGF19) between groups. We performed area under the receiver operating characteristic curve (AUROC) analysis to identify the optimal cutoff C4 concentrations for the diagnosis of diarrhea attributable to bile acid malabsorption (BAD), defined as diarrhea and a serum concentration of FGF19 <60 pg/mL.

RESULTS

Patients with UC had a median serum C4 concentration of 11.8 ng/mL, whereas patients with CD and IR with ileitis (documented endoscopically) had a median concentration of 100.0 ng/mL (P compared to UC < .0001) and patients with CD and IR without ileitis had a median concentration of 51.6 ng/mL (P compared to UC < .001). Patients with CD without IR did not have a significantly higher median concentration of C4 than patients with UC (P = .71), regardless of ileitis (P = .34). When endoscopic findings were confirmed histologically, similar results were found to analyses using endoscopic findings alone. A higher proportion of patients with active UC had diarrhea (72.0% vs 0 patients with inactive UC; P < .001), but their median concentrations of C4 did not differ significantly from that of patients with inactive UC (12.1 ng/mL vs 9.7 ng/mL; P = .3). A cutoff concentration of C4 of 48.3 ng/mL or greater identified patients with diarrhea attributable to bile acid malabsorption with 90.9% sensitivity, 84.4% specificity, and an AUROC 0.94. A significantly higher proportion of patients with concentrations of C4 above this cutoff had BAD (50.0%) than below this cutoff (1.8%) (P < .001). When we analyzed only patients with diarrhea, a C4 cutoff of 48.3 ng/mL identified those with low FGF19 concentrations (<60 pg/mL) with 91% sensitivity and 95.5% specificity (AUROC, 0.99). Above this cutoff, 83.3% of patients had a serum concentration of FGF19 <60 pg/mL compared to 4.5% below this threshold (P < .0001). C4 concentrations correlated with the number of daily bowel movements (r = 0.41; P = .004) and correlated inversely with FGF19 concentrations (r = -0.72; P<.0001).

CONCLUSION

We observed significantly increased serum concentrations of C4 in patients with CD with IR, compared to patients with UC. A cutoff concentration of C4 above 48.3 ng/mL identifies patients with diarrhea likely attributable to bile acid malabsorption (BAD) with an AUROC value of 0.94. Increased serum levels of bile acid precursors identify patients with diarrhea and a low serum concentration of FGF19, and concentrations of C4 correlate with daily liquid bowel movements and correlate inversely with FGF19 concentrations. C4 may be a biomarker to identify patients with diarrhea attributable to bile acid malabsorption.

What's in the pipeline for lower functional gastrointestinal disorders in the next 5 years?

The overall objectives of this review are to summarize actionable biomarkers for organic etiology of lower functional gastrointestinal disorders (FGIDs) that lead to individualized treatment for their FGIDs and to assess the pipeline for novel approaches to the management of constipation, diarrhea, and chronic abdominal pain in lower FGIDs. The new approaches to therapy include ion exchangers/transporters for functional constipation (sodium-glucose cotransporter 1, Na+/H+ exchanger 3, and solute carrier family 26 member 3 inhibitors), bile acid modulators for constipation such as ileal bile acid transporter inhibitors and fibroblast growth factor 19 analog for functional constipation, and bile acid sequestrants or farnesoid X receptor agonists for functional diarrhea. Treatment for chronic abdominal pain remains an unmet need in patients with lower FGIDs, and promising novel approaches include delayed-release linaclotide, nonclassical opioid visceral analgesics, and selective cannabinoid receptor agonists. The role of probiotics, fecal microbial transplantation, and possible future microbiome therapies is discussed.

Diagnosis and management of bile acid diarrhoea: a survey of UK expert opinion and practice

OBJECTIVE

Bile acid diarrhoea (BAD), which includes bile acid malabsorption, causes a variety of digestive symptoms. Diagnostic rates and management vary considerably. We conducted a survey of current practice to review expert opinion and provide guidance on diagnosis and management.

DESIGN/METHOD

An online survey was conducted of clinical members of the UK Bile Acid Related Diarrhoea Network, who had all published research on BAD (n=21). Most were National Health Service consultants who had diagnosed over 50 patients with the condition.

RESULTS

The preferred terminology was to use BAD, with primary and secondary to classify causes. A wide range of presenting symptoms and associated conditions were recognised. SeHCAT (tauroselcholic acid) was the preferred diagnostic test, and 50% of respondents thought general practitioners should have access to this. Patients who met the Rome IV diagnostic criteria for functional diarrhoea, irritable bowel syndrome (IBS) with predominant diarrhoea or postcholecystectomy diarrhoea were usually investigated by SeHCAT, which was used sometimes in other types of IBS. Treatment with a bile acid sequestrant was offered to patients with low SeHCAT values, with expected response rates >70% in the most severe. Colestyramine was the usual sequestrant, starting between 2 g and 8 g daily; colesevelam was an alternative. In patients who had an incomplete response, increasing the dose, changing to an alternative sequestrant, use of loperamide and a low fat diet were suggested. Recommendations for follow-up and to improve the overall patient experience were made.

CONCLUSION

This expert survey indicates current best practice in the diagnosis and management of BAD.

Associations of chronic diarrhoea with non-alcoholic fatty liver disease and obesity-related disorders among US adults

Mechanisms explaining observed associations between diarrhoea and obesity or increased body mass index (BMI) are unclear.

Obeticholic acid ameliorates dyslipidemia but not glucose tolerance in mouse model of gestational diabetes

Metabolism alters markedly with advancing gestation, characterized by progressive insulin resistance, dyslipidemia, and raised serum bile acids. The nuclear receptor farnesoid X receptor (FXR) has an integral role in bile acid homeostasis and modulates glucose and lipid metabolism. FXR is known to be functionally suppressed in pregnancy. The FXR agonist, obeticholic acid (OCA), improves insulin sensitivity in patients with type 2 diabetes with nonalcoholic fatty liver disease. We therefore hypothesized that OCA treatment during pregnancy could improve disease severity in a mouse model of gestational diabetes mellitus (GDM). C57BL/6J mice were fed a high-fat diet (HFD; 60% kcal from fat) for 4 wk before and throughout pregnancy to induce GDM. The impact of the diet supplemented with 0.03% OCA throughout pregnancy was studied. Pregnant HFD-fed mice displayed insulin resistance and dyslipidemia. OCA significantly reduced plasma cholesterol concentrations in nonpregnant and pregnant HFD-fed mice (by 22.4%, P < 0.05 and 36.4%, P < 0.001, respectively) and reduced the impact of pregnancy on insulin resistance but did not change glucose tolerance. In nonpregnant HFD-fed mice, OCA ameliorated weight gain, reduced mRNA expression of inflammatory markers in white adipose tissue, and reduced plasma glucagon-like peptide 1 concentrations (by 62.7%, P < 0.01). However, these effects were not evident in pregnant mice. OCA administration can normalize plasma cholesterol levels in a mouse model of GDM. However, the absence of several of the effects of OCA in pregnant mice indicates that the agonistic action of OCA is not sufficient to overcome many metabolic consequences of the pregnancy-associated reduction in FXR activity.

Gallbladder Dyskinesia Is Associated With an Impaired Postprandial Fibroblast Growth Factor 19 Response in Critically Ill Patients

Critical illness is associated with a disturbed regulation of gastrointestinal hormones resulting in functional and metabolic anomalies. Fibroblast growth factor 19 (FGF19) is an ileum-derived metabolic hormone induced by bile salts upon gallbladder emptying after enteral nutrient stimulation. Our aim was to study the nutrient-stimulated FGF19 response in 24 patients admitted to the intensive care unit (ICU) compared with 12 healthy controls. All subjects received intraduodenal high-lipid nutrient infusion for 120 minutes. Blood was collected every 30 minutes until 1 hour after infusion, and gallbladder emptying was studied by ultrasound. Serum levels of bile salts and FGF19 were assessed. ICU patients had significantly higher fasting bile salt serum levels compared with controls, whereas FGF19 serum levels were similar. In both groups, nutrient infusion elicited substantial bile salt elevations (P < 0.001), peaking at 90 minutes, albeit with a significantly lower peak in the ICU patients (P = 0.029). In controls, FGF19 was significantly elevated relative to baseline from 120 minutes onward (P < 0.001). In ICU patients, the FGF19 response was blunted, as reflected by significantly lower FGF19 elevations at 120, 150, and 180 minutes (P < 0.05) and significantly lower area under the curve (AUC) values compared with controls (P < 0.001). Gallbladder dysmotility was associated with the impaired FGF19 response in critical illness. The gallbladder ejection fraction correlated positively with FGF19 AUC values (ρ = +0.34, P = 0.045). In 10 of 24 ICU patients, gallbladder emptying was disturbed. These patients had significantly lower FGF19 AUC values (P < 0.001). Gallbladder emptying and the FGF19 response were respectively disturbed or absent in patients receiving norepinephrine. Conclusion: The nutrient-stimulated FGF19 response is impaired in ICU patients, which is mechanistically linked to gallbladder dysmotility in critical illness. This may contribute to disturbed liver metabolism in these patients and has potential as a nutritional biomarker.

Semisynthetic bile acids: a new therapeutic option for metabolic syndrome

Bile acids are endogenous emulsifiers synthesized from cholesterol having a peculiar amphiphilic structure. Appreciation of their beneficial effects on human health, recognized since ancient times, has expanded enormously since the discovery of their role as signaling molecules. Activation of farnesoid X receptor (FXR) and Takeda G-protein receptor-5 (TGR5) signaling pathways by bile acids, regulating glucose, lipid and energy metabolism, have become attractive avenue for metabolic syndrome treatment. Therefore, extensive effort has been directed into the research and synthesis of bile acid derivatives with improved pharmacokinetic properties and high potency and selectivity for these receptors. Minor modifications in the structure of bile acids and their derivatives may result in fine-tuning modulation of their biological functions, and most importantly, in an evasion of undesired effect. A great number of semisynthetic bile acid analogues have been designed and put in preclinical and clinical settings. Obeticholic acid (INT-747) has achieved the biggest clinical success so far being in use for the treatment of primary biliary cholangitis. This review summarizes and critically evaluates the key chemical modifications of bile acids resulting in development of novel semisynthetic derivatives as well as the current status of their preclinical and clinical evaluation in the treatment of metabolic syndrome, an aspect that is so far lacking in the scientific literature. Taking into account the balance between therapeutic benefits and potential adverse effects associated with specific structure and mechanism of action, recommendations for future studies are proposed.

Increased fecal primary bile acids in multiple myeloma with engraftment syndrome diarrhea after stem cell transplant

Autologous stem cell transplant (ASCT) for multiple myeloma (MM) is associated with diarrhea during the peri-transplant period. We aimed to appraise mechanisms of peri-ASCT diarrhea in a prospective, longitudinal study of patients with MM. We compared by repeated measures (RM)-ANOVA daily bowel movements (BMs) and consistency [7-point Bristol Stool Form Scale (BSFS)], fecal calprotectin (intestinal inflammation), ¹³C-mannitol excretion in urine 0-2 h (small intestinal permeability), fasting serum C4 (bile acid synthesis) and total and primary bile acid in stool samples during baseline, peri-transplant period (Days 5-7 after stem cell infusion), and after hematological recovery post-ASCT. The 12 (5F, 7M) patients' median age was 61 y (IQR 54.8-63.3). All participants reported increased BMs (increase of 2 and 1 per day with and without engraftment syndrome, respectively). There were no significant increases in serum C4, total fecal bile acids, or intestinal permeability. Relative to patients without engraftment syndrome, four participants with engraftment syndrome had looser stool consistency (mean 2.6 points higher BSFS compared to without engraftment syndrome), increased primary fecal bile acids relative to baseline (>33 µmol/L vs. 6 µmol/L without engraftment syndrome), and increased fecal calprotectin compared to baseline (313 μg/mL vs. 35.6 μg/mL without engraftment syndrome; p = 0.06). Engraftment syndrome post-ASCT is associated with increased fecal primary bile acids.

Bile Acid Receptors and Gastrointestinal Functions

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

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.

Nonsteroidal FXR Ligands: Current Status and Clinical Applications

FXR agonists have demonstrated very promising clinical results in the treatment of liver disorders such as primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC), and nonalcoholic steatohepatitis (NASH). NASH, in particular, is one of the last uncharted white territories in the pharma landscape, and there is a huge medical need and a large potential pharmaceutical market for a NASH pharmacotherapy. Clinical efficacy superior to most other treatment options was shown by FXR agonists such as obeticholic acid (OCA) as they improved various metabolic features including liver steatosis as well as liver inflammation and fibrosis. But OCA's clinical success comes with some major liabilities such as pruritus, high-density lipoprotein cholesterol (HDL_c) lowering, low-density lipoprotein cholesterol (LDL_c) increase, and a potential for drug-induced liver toxicity. Some of these effects can be attributed to on-target effects exerted by FXR, but with others it is not clear whether it is FXR- or OCA-related. Therefore a quest for novel, proprietary FXR agonists is ongoing with the aim to increase FXR potency and selectivity over other proteins and to overcome at least some of the OCA-associated clinical side effects through an improved pharmacology. In this chapter we will discuss the historical and ongoing efforts in the identification and development of nonsteroidal, which largely means non-bile acid-type, FXR agonists for clinical use.

Pharmacological Applications of Bile Acids and Their Derivatives in the Treatment of Metabolic Syndrome

Apart from well-known functions of bile acids in digestion and solubilization of lipophilic nutrients and drugs in the small intestine, the emerging evidence from the past two decades identified the role of bile acids as signaling, endocrine molecules that regulate the glucose, lipid, and energy metabolism through complex and intertwined pathways that are largely mediated by activation of nuclear receptor farnesoid X receptor (FXR) and cell surface G protein-coupled receptor 1, TGR5 (also known as GPBAR1). Interactions of bile acids with the gut microbiota that result in the altered composition of circulating and intestinal bile acids pool, gut microbiota composition and modified signaling pathways, are further extending the complexity of biological functions of these steroid derivatives. Thus, bile acids signaling pathways have become attractive targets for the treatment of various metabolic diseases and metabolic syndrome opening the new potential avenue in their treatment. In addition, there is a significant effort to unveil some specific properties of bile acids relevant to their intrinsic potency and selectivity for particular receptors and to design novel modulators of these receptors with improved pharmacokinetic and pharmacodynamic profiles. This resulted in synthesis of few semi-synthetic bile acids derivatives such as 6α-ethyl-chenodeoxycholic acid (obeticholic acid, OCA), norursodeoxycholic acid (norUDCA), and 12-monoketocholic acid (12-MKC) that are proven to have positive effect in metabolic and hepato-biliary disorders. This review presents an overview of the current knowledge related to bile acids implications in glucose, lipid and energy metabolism, as well as a potential application of bile acids in metabolic syndrome treatment with future perspectives.

Pros and Cons of the SeHCAT Test in Bile Acid Diarrhea: A More Appropriate Use of an Old Nuclear Medicine Technique

Bile acid malabsorption (BAM) causing chronic diarrhea may be due to organic as well as functional disorders, and some of them were included under the general label of diarrheic-type irritable bowel syndrome (IBS-D). The 75-selenium homocholic acid taurine (SeHCAT) test is a nuclear medicine investigation considered to be the gold standard for the diagnosis of bile acid malabsorption (BAM). Many studies demonstrate that it could be effective in the clinical workout of chronic diarrhea due to different conditions. The SeHCAT test provides a quantitative assessment to estimate the severity of BAM and the possible response to therapy with bile acid sequestrants (BASs). However, there is no general agreement regarding its cutoff value and the test is not widely available. The aim of this review is to discuss the advantages and disadvantages of the SeHCAT test in clinical practice.

New treatments and therapeutic targets for IBS and other functional bowel disorders

Functional bowel disorders (FBDs) are a spectrum of disorders characterized by combinations of symptoms attributable to the lower gastrointestinal tract. Most current first-line therapies for IBS and other FBDs target the predominant symptom and mainly affect one symptom in the symptom complex. Additional broadly effective treatment alternatives targeting the entire symptom complex are needed. New drugs for FBDs (such as lubiprostone, linaclotide, plecanatide, prucalopride, eluxadoline and rifaximin) target key mechanisms in the pathophysiology of these disorders and improve both the abnormal bowel habit and other key symptoms, such as abdominal pain and bloating. The current development of new treatment alternatives is focusing on different aspects of the complex pathophysiology of IBS and other FBDs: gut microenvironment (via diet and modulation of gut microbiota), enterohepatic circulation of bile acids, gastrointestinal secretion, motility and sensation, gut-brain interactions, gut barrier function and the immune system within the gastrointestinal tract. Studies also suggest that personalized treatment of IBS and other FBDs is possible using various diagnostic markers.

IVACAFTOR restores FGF19 regulated bile acid homeostasis in cystic fibrosis patients with an S1251N or a G551D gating mutation

OBJECTIVE

Disruption of the enterohepatic circulation of bile acids (BAs) is part of the gastrointestinal phenotype of cystic fibrosis (CF). Ivacaftor (VX-770), a cystic fibrosis transmembrane conductance regulator (CFTR) potentiator, improves pulmonary function in CF patients with class III gating mutations. We studied the effect of ivacaftor on the enterohepatic circulation by assessing markers of BA homeostasis and their changes in CF patients.

METHODS

In CF patients with an S1251N mutation (N = 16; age 9-35 years S125N study/NTR4873) or a G551D mutation (N = 101; age 10-24 years; GOAL study/ NCT01521338) we analyzed plasma fibroblast growth factor 19 (FGF19) and 7α-hydroxy-4-cholesten-3-one (C4) levels, surrogate markers for intestinal BA absorption and hepatic synthesis, respectively, before and after treatment with ivacaftor.

RESULTS

At baseline, median FGF19 was lower (52% and 53%, P < .001) and median C4 higher (350% and 364%, P < .001), respectively, for the S1251 N and G551D mutation patient groups compared to healthy controls. Treatment with ivacaftor significantly increased FGF19 and reduced C4 levels towards normalization in both cohorts but this did not correlate with CFTR function in other organs, as measured by sweat chloride levels or pulmonary function.

CONCLUSIONS

We demonstrate that patients with CFTR gating mutations display interruption of the enterohepatic circulation of BAs reflected by lower FGF19 and elevated C4 levels. Treatment with ivacaftor partially restored this disruption of BA homeostasis. The improvement did not correlate with established outcome measures of CF, suggesting involvement of modulating factors of CFTR correction in different organs.

Ileal Bile Acid Transporter Inhibition for the Treatment of Chronic Constipation, Cholestatic Pruritus, and NASH

Bile acids are synthesized from cholesterol in the liver, excreted with bile into the duodenum, almost completely taken up again in the distal ileum and finally returned to the liver with portal blood in a process termed enterohepatic circulation. Bile acid synthesis, excretion, and reuptake are tightly regulated. The apical sodium-dependent bile acid transporter [ASBT; also known as ileal bile acid transporter (IBAT) and SLC10A2] is pivotal for the almost complete reabsorption of conjugated bile acids in the ileum. Dysfunctional IBAT may be the cause of bile acid diarrhea. Pharmacological IBAT inhibition results in an increased bile acid load in the colon and subsequently a lower bile acid pool, which is associated with improved liver histology in animal models of cholestatic liver disease and non-alcoholic steatohepatitis (NASH). In humans, IBAT inhibitors have been tested in clinical trials with widely different indications: in patients with idiopathic chronic constipation, an increased number of bowel movements was observed. In adult and pediatric cholestatic liver diseases with pruritus, various IBAT inhibitors showed potential to improve itching. Adverse events of IBAT inhibitors, based on their mode of action, are abdominal pain and diarrhea which might patients to withdraw from study medications. So far, no data are available of a study of IBAT inhibitors in patients with NASH. In this review we summarize the preclinical and most recent clinical studies with various IBAT inhibitors and discuss the difficulties that should be addressed in future studies.

In Silico Analysis Identifies Intestinal Transit as a Key Determinant of Systemic Bile Acid Metabolism

Bile acids fulfill a variety of metabolic functions including regulation of glucose and lipid metabolism. Since changes of bile acid metabolism accompany obesity, Type 2 Diabetes Mellitus and bariatric surgery, there is great interest in their role in metabolic health. Here, we developed a mathematical model of systemic bile acid metabolism, and subsequently performed in silico analyses to gain quantitative insight into the factors determining plasma bile acid measurements. Intestinal transit was found to have a surprisingly central role in plasma bile acid appearance, as was evidenced by both the necessity of detailed intestinal transit functions for a physiological description of bile acid metabolism as well as the importance of the intestinal transit parameters in determining plasma measurements. The central role of intestinal transit is further highlighted by the dependency of the early phase of the dynamic response of plasma bile acids after a meal to intestinal propulsion.

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.

Chronic diarrhoea following surgery for colon cancer-frequency, causes and treatment options

PURPOSE

The growing population of survivors after colon cancer warrants increased attention to the long-term outcome of surgical treatment. The change in bowel anatomy after resection disrupts normal gastrointestinal function and may cause symptoms. Thus, many patients surviving colon cancer have to cope with bowel dysfunction for the rest of their lives. We here aim to provide an overview of the literature on this topic.

METHODS

We review long-term functional outcomes of surgical treatment for colon cancer, the underlying pathology, and treatment options.

RESULTS

Common symptoms include constipation, urge for defecation and diarrhoea. Causes of diarrhoea after colon cancer surgery are sparsely studied, but they probably include bile acid malabsorption, small intestinal bacterial overgrowth and disruption of the ileal brake. Specific diagnosis should be made to allow individual treatment based on the underlying pathology. Studies on treatment of functional problems after surgery for colon cancer are extremely few, but some lessons can be drawn from the treatment of other patient groups having undergone colon surgery.

CONCLUSION

Diarrhoea is likely a common long-term complication after colon cancer surgery. Attention to this complication and a specific diagnosis will aid the targeted treatment of patients suffering from this complication.

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.

Long-term effect of medical treatment of diarrhoea in 377 patients with SeHCAT scan diagnosed bile acid malabsorption from 2003 to 2016; a retrospective study

BACKGROUND

Excessive amounts of bile acids entering the colon due to bile acid malabsorption cause chronic bile acid diarrhoea. Diagnosis is possible by measuring the retention fraction of orally ingested ⁷⁵ Selenium homotaurocholic acid (SeHCAT). The knowledge of long-term effects of medical treatment is sparse.

AIM

To describe diarrhoea, adherence to treatment, treatment effects and quality of life in a large, well-defined cohort of patients with bile acid diarrhoea.

METHODS

A retrospective survey was performed among 594 patients with bile acid malabsorption verified by SeHCAT scans at our unit between 2003 and 2016. Questionnaires about medical history, diarrhoea, use of medication, and quality of life scores were mailed to all patients.

RESULTS

Among 594 patients 377 (69%) responded. Among respondents, 121 (32%) had bile acid diarrhoea due to ileal disease or resection (type 1), 198 (52%) idiopathic bile acid diarrhoea (type 2) and 58 (16%) bile acid diarrhoea due to other non-ileal disease, mainly cholecystectomy (type 3). At follow-up, half of the patients, 184 (50%), reported improvement of diarrhoea. However, 273 patients (74%) still reported diarrhoea and 234 (62%) regularly used anti-diarrhoeal medication. In spite of treatment, 235 (64%) considered reduced quality of life by diarrhoea and 184 (50%) reported that diarrhoea was unaltered or worse than before established diagnosis.

CONCLUSION

Many patients with bile acid diarrhoea continue to have bothersome diarrhoea in spite of correct diagnosis and treatment.

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.

Advancements in drug development for diarrhea-predominant irritable bowel syndrome

INTRODUCTION

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a common disorder characterized by a complex pathophysiology hampering optimal targeted drug development. Recent advances in our understanding of key underlying mechanisms prompted novel therapeutics including novel pharmacological approaches.

AREAS COVERED

This review summarizes the latest advancements in the pipeline of IBS-D drugs focusing on new pharmacological targets, efficacy and safety of medicinal products considering the recent harmonization of regulatory requirements by the FDA and the EMA.

EXPERT OPINION

The new 5-HT₃ receptor antagonist ramosetron appears a promising therapeutic approach devoid of significant adverse events, although it is presently unavailable in Western countries, most likely because of the precautionary approach taken by regulatory agencies with this drug class. New pharmacological concepts on full agonists/antagonists, mixed-receptor activity and novel drug targets may streamline the present drug pipeline along with the adherence on new regulatory guidelines on outcome measures. Eluxadoline can be taken as an example of this paradigm shift. It has now been granted marketing authorization for IBS-D on both sides of the Atlantic, but it is still considered as a second-line agent by the NICE. There is still much work to be done to fully cover clinical needs of patients with IBS-D.

Bile acid signaling and bariatric surgery

The rapid worldwide rise in obesity rates over the past few decades imposes an urgent need to develop effective strategies for treating obesity and associated metabolic complications. Bariatric surgical procedures, such as Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), currently provide the most effective treatment for obesity and type 2 diabetes (T2D), as well as for non-alcoholic steatohepatitis (NASH). However, the underlying mechanisms of the beneficial effects of bariatric surgery remain elusive. Recent studies have identified bile acids as potential signaling molecules involved in the beneficial effects of bariatric surgery. This review focuses on the most recent studies on the roles of bile acids and bile acid receptors Farnesoid X receptor (FXR) and G protein-coupled bile acid receptor 5 (TGR5) in bariatric surgery. We also discuss the possibility of modulating bile acid signaling as a pharmacological therapeutic approach to treating obesity and its associated metabolic complications.

Existing and emerging therapies for managing constipation and diarrhea

Functional bowel disorders (i.e., constipation and diarrhea) are characterized by abdominal pain, bloating, distention, and/or bowel habit abnormalities in the absence of obvious anatomic or physiologic abnormalities on routine diagnostic tests. These symptoms are attributable to gastrointestinal sensorimotor dysfunctions resulting from peripheral and/or central mechanisms. Available drugs target the underlying bowel disturbance (i.e., constipation, diarrhea, or both), supplemented when necessary by management of pain. Osmotic and stimulant laxatives, secretagogues, and serotonin 5-HT4 receptor agonists are approved for treating constipation. Loperamide, anticholinergic agents, rifaximin, bile-acid binding agents, eluxadoline, and clonidine are used to treat diarrhea. Several exciting new compounds, some of which have been evaluated in humans, are currently under development.

Modulating bile acid pathways and TGR5 receptors for treating liver and GI diseases

Bile acids are central signals in enterohepatic communication and also integrate microbiota-derived signals into this signaling axis. Discovery of the tissue distribution and signaling pathways activated by the natural receptors for bile acids, farnesoid X receptor and G protein-coupled bile acid receptor 1 (GPBAR1) also known as TGR5, and bile acid transporters has led to the development of therapeutic agents that target these molecules. Obeticholic acid, a selective FXR agonist, and NGM282, a non-mitogenic FGF-19 analog, are two of the agents in this pipeline. Obeticholic acid has been approved by regulatory agencies for use in patients with primary biliary cholangitis.

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.

Farnesoid X Receptor Expression in Microscopic Colitis: A Potential Role in Disease Etiopathogenesis

Introduction

Microscopic colitis (MC) is a chronic inflammatory bowel disease with unclear etiology. Bile acid (BA) malabsorption has been described in MC patients. Farnesoid X receptor (FXR) is the main BA receptor; FXR-mediated mechanisms prevent the noxious effects of BA accumulation, preserving the integrity of the intestinal epithelial barrier and preventing intestinal inflammation.

Aim

Our aim was to describe the expression of FXR in patients with MC.

Methods

Archival formalin-fixed paraffin-embedded samples from the terminal ileum, right and left colon were obtained from patients with MC and matched controls. Immunohistochemistry was performed and nuclear FXR expression scored in a semi-quantitative way.

Results

169 formalin-fixed paraffin-embedded samples from 35 patients with MC and 31 controls were retrieved. There was a significant reduction of FXR expression in patients with MC versus controls both in the right colon (moderate-strong FXR expression: 21.1 vs. 64.3%; p = 0.003) and left colon (moderate-strong FXR expression: 8.3 vs. 38.7%; p = 0.027). No significant differences in FXR expression were observed in the ileum of patients with MC (moderate-strong FXR expression: 76.9 vs. 90.9%; p = 0.5). We found no difference in FXR expression between the two types of MC. No association between the degree of lymphocyte infiltration or the thickness of collagen band and FXR expression was found.

Conclusions

Patients with MC present a significantly lower expression of FXR in the colon. This could render colonic epithelial cells more susceptible to the deleterious effects of BA, contributing to disease pathogenesis and symptoms in MC.

Incidence and predictive factors for positive 75SeHCAT test: improving the diagnosis of bile acid diarrhoea

AIMS

To determine the value of ⁷⁵SeHCAT retention in determining bile acid diarrhoea (BAD), treatment response and predictors of a positive result.

METHODS

Retrospective casenote review of consecutive patients undergoing ⁷⁵SeHCAT from 2008 to 2014, including gender, age, history, clinical, and laboratory parameters. This included diseases associated with Type 1 BAD (ileal resection, Crohn's disease) and Type 3 BAD. Chi-squared test and logistic regression determined factors predictive of BAD. Subjective response to treatment with bile acid sequestrants (BAS) was analysed with respect to the ⁷⁵SeHCAT result.

RESULTS

Of 387 patients, 154 (39.7%) were male and average age was 50 years. Ninety-five patients (24.5%) were investigated for Type 1 BAD, 86 (22.2%) for Type 3, and 206 patients (53.2%) for Type 2 or idiopathic BAD. There was a large increase in the number performed with time but no difference in percentage positive tests. One hundred and seventy-nine patients (46.2%) had BAD. Positive result was commonest in possible Type 1 and they had most severe BAD. Ninety-nine patients had severe BAD (<5% ⁷⁵SeHCAT retention), 47 moderate BAD (5% to <10% retention), and 33 mild BAD (10% to <15% retention). Predictors of a positive ⁷⁵SeHCAT were right hemicolectomy (OR 4.88), cholecystectomy (OR 2.44), and Crohn's (OR 1.86). A positive ⁷⁵SeHCAT predicted a good or partial response to BAS of 66.7% (mild), 78.6% (moderate), or 75.9% (severe BAD).

CONCLUSION

⁷⁵SeHCAT test use increased in 2008-2014, with high positive results throughout. Ileal resection, Crohn's, and cholecystectomy independently predict BAD. ⁷⁵SeHCAT predicted response to BAS.

Farnesoid X receptor agonist GW4064 ameliorates lipopolysaccharide-induced ileocolitis through TLR4/MyD88 pathway related mitochondrial dysfunction in mice

Inflammatory bowel disease (IBD) is a complex and relapsing inflammatory condition of the gastro intestinal tract characterized by diarrhoea and abdominal pain. Farnesoid X receptor (FXR) plays an important role in enteroprotection and mucosal injury by regulating inflammatory responses and barrier function in the intestinal tract. Here we show the mechanisms of FXR agonist, GW4064, inhibits mucosal injury in ileum caused by lipopolysaccharides (LPS). Ileum injury was induced by intraperitoneal injection of LPS in Wild-type (WT) and FXR knockout (KO) mice. GW4064 alleviates LPS-mediated tight junction dysfunction as well as macrophage infiltration in WT mice, but not in FXR KO mice. Interesting, GW4064 suppresses NACHT, LRR and PYD domains-containing protein 3 (NALP3) inflammasome mediates tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6 and IL-1β, as well as mitochondrial respiratory complexes mRNA expression in WT and FXR KO mice treated with LPS. This results demonstrated that central roles of FXR in coordinating regulation of both inflammation and mitochondrial dysfunction. We propose that GW4064 is promising therapeutic agent for treatment of ileocolitis.

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.