Fibroblast Growth Factor 19 and 7α-Hydroxy-4-Cholesten-3-one in the Diagnosis of Patients With Possible Bile Acid Diarrhea

Advances in the Comprehensive Management of Postoperative Crohn's Disease

Patients with postoperative Crohn's disease are difficult to manage because of their risk of experiencing a more severe course, multiple symptom confounders, and poor sensitivity of symptomatic remission to rule out intestinal inflammation. In this group, data are lacking on biologic therapeutic efficacy, and recommendations are lacking for those with multiple medication failures. Novel noninvasive testing can simultaneously exclude alternate causes of symptoms (serum C4, fecal fat, small intestinal bowel overgrowth breath testing) and assess intestinal inflammation (fecal calprotectin, endoscopic healing index). In addition, endoscopy-based disease activity assessment and management are required. Endoscopy should be performed within 6 months of surgery, and aggressive disease activity monitoring can be considered with colonoscopy every 1-2 years subsequently to ensure late recurrence is detected. Patients with multiple resections should be screened for short bowel syndrome. Predictive biomarkers are needed to guide medication selection in this high-risk population. Postoperative prophylactic biologic therapy is prudent for patients with preoperative biologic failure. However, there are no high-quality data to guide which agent should be selected. Selecting biologics with an alternative mechanism of action in those who had failed a biologic with adequate drug concentrations and selection of different agents in those with previous intolerance are reasonable. Significantly more study is required to assess the efficacy of therapies in this setting.

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.

Fecal microbiome and bile acid metabolome in adult short bowel syndrome

Loss of functional small bowel surface area causes short bowel syndrome (SBS), intestinal failure, and parenteral nutrition (PN) dependence. The gut adaptive response following resection may be difficult to predict, and it may take up to 2 yr to determine which patients will wean from PN. Here, we examined features of gut microbiota and bile acid (BA) metabolism in determining adaptation and ability to wean from PN. Stool and sera were collected from healthy controls and from patients with SBS (n = 52) with ileostomy, jejunostomy, ileocolonic, and jejunocolonic anastomoses fed with PN plus enteral nutrition or who were exclusively enterally fed. We undertook 16S rRNA gene sequencing, BA profiling, and 7α-hydroxy-4-cholesten-3-one (C4) quantitation with LC-MS/MS and serum amino acid analyses. Patients with SBS exhibited altered gut microbiota with reduced gut microbial diversity compared with healthy controls. We observed differences in the microbiomes of patients with SBS with ileostomy versus jejunostomy, jejunocolonic versus ileocolonic anastomoses, and PN dependence compared with those who weaned from PN. Stool and serum BA composition and C4 concentrations were also altered in patients with SBS, reflecting adaptive changes in enterohepatic BA cycling. Stools from patients who were weaned from PN were enriched in secondary BAs including deoxycholic acid and lithocholic aicd. Shifts in gut microbiota and BA metabolites may generate a favorable luminal environment in select patients with SBS, promoting the ability to wean from PN. Proadaptive microbial species and select BA may provide novel targets for patient-specific therapies for SBS.NEW & NOTEWORTHY Loss of intestinal surface area causes short bowel syndrome, intestinal failure, and parenteral nutrition dependence. We analyzed the gut microbiota and bile acid metabolome of a large cohort of short bowel syndrome adult patients with different postsurgical anatomies. We report a novel analysis of the microbiome of patients with ileostomy and jejunostomy. Enrichment of specific microbial and bile acid species may be associated with the ability to wean from parenteral nutrition.

Bile acid-farnesoid X receptor-fibroblast growth factor 19 axis in patients with short bowel syndrome: The randomized, glepaglutide phase 2 trial

BACKGROUND

The gut-liver axis and enterohepatic circulation have gained increasing attention lately. Patients with short bowel syndrome (SBS) are, in fact, human knock-out models that may assist in the understanding of bile acid synthesis and regulation. We evaluated effect of glepaglutide (a long-acting glucagon-like peptide-2 analog) on bile acid synthesis (the enterohepatic circulation of bile acids and liver biochemistry in patients with SBS).

METHOD

In a single-center, double-blinded, dose-finding, crossover phase 2 trial, 18 patients with SBS were randomly assigned to 2 of 3 treatment arms (0.1, 1, and 10 mg) with daily subcutaneous injections of glepaglutide for 3 weeks. The washout period between the 2 treatment periods was 4-8 weeks. Measurements were performed at baseline and at the end of each treatment period and included postprandial plasma samples for fibroblast growth factor 19 (FGF19), 7α-hydroxy-4-cholesten-3-one (C4), total excretion of fecal bile acids, gene expression of farnesoid X receptor (FXR) in intestinal mucosal biopsies, total plasma bile acids, and liver biochemistry.

RESULTS

Compared with baseline, the median (interquartile range) postprandial response (area under the curve 0-2h) of FGF19 increased by 150 h × ng/L (41, 195; P = 0.001) and C4 decreased by 82 h × µg/L (-169, -28; p = 0.010) in the 10-mg dose. FXR gene expression did not change in any of the groups. Alkaline phosphatase significantly decreased.

CONCLUSION

Glepaglutide may stimulate the bile acid/FXR/FGF19 axis, leading to increased plasma concentrations of FGF19. Thereby, glepaglutide may ameliorate the accelerated de novo bile acid synthesis and play a role in the prevention and/or treatment of intestinal failure-associated liver disease.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

INTRODUCTION

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

METHODS

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

RESULTS

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

DISCUSSION

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

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.

Ten Reasons to Think About Bile Acids in Managing Inflammatory Bowel Disease

There are ten good reasons why it is important to think about abnormalities in bile acid control in inflammatory bowel disease. Before reviewing these reasons, it is relevant to review essential elements in the enterohepatic circulation, synthesis and actions of bile acids.

Tests that now deserve to be more widely adopted in IBD clinical practice

Inflammatory bowel diseases are chronic relapsing immune-mediated diseases of the intestinal tract with multifaceted manifestations and treatment related morbidity. Faecal and blood tests, radiological, endoscopic and histologic investigations are now widely used for managing both ulcerative colitis and Crohn's disease. Over the years, a number of new investigations have been proposed but not widely adopted yet. Patients with Crohn's disease may have multiple causes of diarrhoea, not always attributable to disease exacerbation, but sometimes linked to bile acid malabsorption; we have a reliable serum test, C4, that allows us to recognize and treat this cause of diarrhoea efficaciously and not empirically, but it is not available or used widely. There is genetic inter-individual variability in drug responses, in terms of both efficacy and toxicity, leading to high rates of therapeutic failure. Patients treated with thiopurine or, more rarely, 5-aminosalicylic acid may suffer from unpredictable and serious adverse events, some of these with pathogenesis related to genetic variants: myelosuppression, acute pancreatitis and nephrotoxicity. The identification of pre-treatment genetic tests can optimize therapeutic choice and avoid adverse events. With regard to biological drugs, patients can experience primary non-response or loss of response due to induction of immune responses to the drugs affecting drug efficacy and determining hypersensitivity reactions. We have specifically reviewed a number of investigations, whose use is currently limited, and highlighted four tests that deserve to be more widely incorporated in clinical practice as these could improve medical decision-making and patient outcomes.

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 malabsorption in patients with chronic diarrhea and Crohn's disease

INTRODUCTION AND AIM

Crohn's disease (CD) is a form of inflammatory bowel disease and is mainly characterized by diarrhea and abdominal pain. The aim of our study was to analyze the usefulness of performing a 75SeHCAT scan in CD patients with chronic diarrhea and suspected bile acid malabsorption (BAM). In addition, we aimed to determine whether there was a relationship with the clinical features of the disease and a previous bowel resection.

PATIENTS AND METHODS

this was an observational cross-sectional study of 39 patients with a diagnosis of CD and chronic diarrhea. All cases underwent a 75SeHCAT scan for BAM diagnosis, after discarding disease activity.

RESULTS

the study cohort included 19 females and 20 males. The median age was 44 years and the majority of patients were A2 L1 B1 according to the Montreal classification; 84.6% of patients had undergone a previous bowel resection. BAM was present in 97.4% of patients (100% and 83.3% of patients with and without previous surgery, respectively), which was severe in 92.1% of cases. Treatment with bile acid sequestrants was initiated and a favorable response was obtained in 72.2% of patients. The relationship between BAM degree (moderate or severe), bowel surgery and the response to bile acid sequestrant treatment was also analyzed but not statistically significant.

CONCLUSION

BAM is a frequent cause of diarrhea in CD patients in endoscopic or radiological remission. This condition was present in all patients with a history of a bowel resection. A response to bile acid sequestrants treatment was observed in 73% of patients.

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.

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.

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.

Chemical synthesis of 7α-hydroxycholest-4-en-3-one, a biomarker for irritable bowel syndrome and bile acid malabsorption

7α-Hydroxy-cholest-4-en-3-one is a biomarker for bile acid loss, irritable bowel syndrome, and other diseases associated with defective bile acid biosynthesis. Furthermore, 7α-hydroxy-cholest-4-en-3-one is the physiological substrate for cytochrome P450 8B1 (P450 8B1 or CYP8B1), the oxysterol 12α-hydroxylase enzyme implicated in obesity and cardiovascular health. We report the chemical synthesis of this physiologically important oxysterol beginning with cholesterol. The key feature of this synthesis involves a regioselective C3-allylic oxidation of a 3-desoxy-Δ⁴-7α-formate steroid precursor to form 7α-formyloxy-cholest-4-en-3-one, which was saponified to yield 7α-hydroxy-cholest-4-en-3-one.

AGA Technical Review on the Evaluation of Functional Diarrhea and Diarrhea-Predominant Irritable Bowel Syndrome in Adults (IBS-D)

BACKGROUND & AIMS

The evaluation of patients with chronic watery diarrhea represents a diagnostic challenge for clinicians because organic causes, including inflammatory bowel disease, microscopic colitis, and chronic infection, must be differentiated from functional diarrhea and diarrhea-predominant irritable bowel syndrome. The purpose of this review is to summarize the available evidence on the usefulness of diagnostic tests in such patients.

METHODS

We searched MEDLINE and EMBASE via OVID, from 1978 until April 2017. We included diagnostic test accuracy studies reporting on the use of fecal and blood tests for the evaluation of adult patients with functional diarrhea, including irritable bowel syndrome. We assessed the risk of bias of included studies using a modified version of the Quality Assessment of Diagnostic Accuracy Studies II, and the certainty in the evidence using the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach. We calculated pooled sensitivity and specificity, and the proportion of patients with true and false positive and negative results. We evaluated the following tests: erythrocyte sedimentation rate, C-reactive protein, fecal lactoferrin, fecal calprotectin, serologic tests for celiac disease, tests for bile acid diarrhea, the commercially available version of anti-cytolethal distending toxin B and anti-vinculin antibodies, and tests for Giardia infection. We did not evaluate breath tests for small intestinal bacterial overgrowth, as they are not part of a standard diarrhea workup.

RESULTS

Thirty-eight studies proved eligible to evaluate 1 or more of these tests. Erythrocyte sedimentation rate and C-reactive protein were similar at discriminating organic from functional disease, with sensitivity and specificity, respectively, of 0.54-0.78 and 0.46-0.95 for erythrocyte sedimentation rate and 0.73 and 0.78 for C-reactive protein. Among fecal tests, fecal calprotectin in a range of 50-60 μg/g (pooled sensitivity 0.81; 95% confidence interval [CI], 0.75-0.86; pooled specificity 0.87; 95% CI, 0.78-0.92) and fecal lactoferrin in a range of 4.0-7.25 μg/g (pooled sensitivity 0.79; 95% CI, 0.73-0.84; pooled specificity 0.93; 95%CI 0.63-0.99) presented the lowest proportion of false-negative results (low certainty in the evidence). Among tests for celiac disease, IgA tissue transglutaminase presented the best diagnostic test accuracy (sensitivity range, 0.79-0.99; specificity range, 0.90-0.99) with moderate certainty in the evidence. Among tests for bile acid diarrhea, the ⁷⁵selenium homotaurocholic acid test performed better than serum fibroblast growth factor 19 and 7α-hydroxy-4-cholesten-3-one, but is not available in the United States. There was insufficient evidence to recommend serologic tests for irritable bowel syndrome at this time. There are several good diagnostic tests for Giardia infection.

CONCLUSIONS

Moderate to low certainty in the evidence indicates that available fecal and blood tests may play a role in the diagnostic workup of adult patients with functional diarrhea. At the moment, no tests are available to reliably rule in irritable bowel syndrome.

75Se-Homocholic acid taurine scintigraphy (75SeHCAT®), a standard benchmark test in bile acid malabsorption?

Chronic diarrhoea due to bile acid malabsorption (BAM) is an underdiagnosed pathology. Different diagnostic tools are available. However, there is currently no consensus on which of these would be the benchmark test or gold standard. This review evaluates the possibility of using ⁷⁵Se-taurocholic acid (⁷⁵SeHCAT^®) scintigraphy as a benchmark diagnostic test and its perspective for the future. A literature review was conducted in Pubmed and OVID obtaining a total of 57 papers, 26 of which were finally used after being selected under the concepts of gold standard, diagnostic accuracy and other biomarkers. We evaluated the advantages and disadvantages of the different diagnostic tools: ¹⁴C-glycocholate, measurement of bile acids in faeces, C4 in serum, FGF19 in serum, cholestyramine, and ⁷⁵Se-tauroselcolic acid scintigraphy. We consider that the ⁷⁵SeHCAT^® scan is the most recommended diagnostic test in Europe for diagnosing BAM as it presents the highest values of sensitivity and specificity. It has a significant cost-benefit ratio, making it the test with the highest degree of recommendation. However, it is still not possible to use it in a recognised way as a gold standard due to the lack of studies that provide conclusive data that allow consensus. In the meantime, the combined use of cholestyramine testing in all patients we want to evaluate, regardless of the scintigraphy result, could be encouraged as a benchmark standard.

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.

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.

A 19F magnetic resonance imaging-based diagnostic test for bile acid diarrhea

In up to 50% of people diagnosed with a common ailment, diarrhea-predominant irritable bowel syndrome, diarrhea results from excess spillage of bile acids into the colon-data emerging over the past decade identified deficient release of a gut hormone, fibroblast growth factor 19 (FGF19), and a consequent lack of feedback suppression of bile acid synthesis as the most common cause. ⁷⁵Selenium homotaurocholic acid (SeHCAT) testing, considered the most sensitive and specific means of identifying individuals with bile acid diarrhea, is unavailable in many countries, including the United States. Other than SeHCAT, tests to diagnose bile acid diarrhea are cumbersome, non-specific, or insufficiently validated; clinicians commonly rely on a therapeutic trial of bile acid binders. Here, we review bile acid synthesis and transport, the pathogenesis of bile acid diarrhea, the reasons clinicians frequently overlook this disorder, including the limitations of currently available tests, and our efforts to develop a novel ¹⁹F magnetic resonance imaging (MRI)-based diagnostic approach. We created ¹⁹F-labeled bile acid analogues whose in vitro and in vivo transport mimics that of naturally occurring bile acids. Using dual ¹H/¹⁹F MRI of the gallbladders of live mice fed ¹⁹F-labeled bile acid analogues, we were able to differentiate wild-type mice from strains deficient in intestinal expression of a key bile acid transporter, the apical sodium-dependent bile acid transporter (ASBT), or FGF15, the mouse homologue of FGF19. In addition to reviewing our development of ¹⁹F-labeled bile acid analogue-MRI to diagnose bile acid diarrhea, we discuss challenges to its clinical implementation. A major limitation is the paucity of clinical MRI facilities equipped with the appropriate coil and software needed to detect ¹⁹F signals.

Attenuated Accumulation of Novel Fluorine (19F)-Labeled Bile Acid Analogues in Gallbladders of Fibroblast Growth Factor-15 (FGF15)-Deficient Mice

Our work has focused on defining the utility of fluorine (¹⁹F)-labeled bile acid analogues and magnetic resonance imaging (MRI) to identify altered bile acid transport in vivo. In the current study, we explored the ability of this approach to differentiate fibroblast growth factor-15 (FGF15)-deficient from wild-type (WT) mice, a potential diagnostic test for bile acid diarrhea, a commonly misdiagnosed disorder. FGF15 is the murine homologue of human FGF19, an intestinal hormone whose deficiency is an underappreciated cause of bile acid diarrhea. In a pilot and three subsequent pharmacokinetic studies, we treated mice with two ¹⁹F-labeled bile acid analogues, CA-lys-TFA and CA-sar-TFMA. After oral dosing, we quantified ¹⁹F-labeled bile acid analogue levels in the gallbladder, liver, small and large intestine, and plasma using liquid chromatography mass spectrometry (LC-MS/MS). Both ¹⁹F bile acid analogues concentrated in the gallbladders of FGF15-deficient and WT mice, attaining peak concentrations at approximately 8.5 h after oral dosing. However, analogue levels in gallbladders of FGF15-deficient mice were several-fold less compared to those in WT mice. Live-animal ¹⁹F MRI provided agreement with our LC-MS/MS-based measures; we detected robust CA-lys-TFA ¹⁹F signals in gallbladders of WT mice but no signals in FGF15-deficient mice. Our finding that ¹⁹F MRI differentiates FGF15-deficient from WT mice provides additional proof-of-concept for the development of ¹⁹F bile acid analogues and ¹⁹F MRI as a clinical test to diagnose bile acid diarrhea due to FGF19 deficiency and other disorders.

Bile acid homeostasis in gastrointestinal and metabolic complications of cystic fibrosis

With the improved treatment of the pulmonary complications of cystic fibrosis (CF), gastrointestinal problems have become more important in the morbidity in CF. A hallmark of the gastrointestinal phenotype of CF, apart from pancreatic insufficiency, is a disruption of bile acid homeostasis. Bile acid homeostasis is important for many gastrointestinal processes including fat absorption, inflammation, microbial composition, as well as regulation of whole body energy metabolism. This review describes the impairment of bile acid homeostasis in CF, its possible consequences for gastrointestinal and metabolic complications and its potential as a target for therapy.

Bile acids and FXR in functional gastrointestinal disorders

Functional gastrointestinal disorders (FGIDs), such as irritable bowel syndrome (IBS) and chronic constipation (CC), are commonly diagnosed conditions in clinical practice which create a substantial global burden. Since the farnesoid X receptor (FXR) and bile acids (BAs) are responsible for maintaining homeostasis in the GI tract, any disturbances in the expression of FXR or the composition of BAs may contribute to the development of the GI symptoms. Alterations in the mechanism of action of FXR directly affect the BAs pool and account for increased intestinal permeability and changes in abundance and diversity of gut microbiota leading to intestinal dysmotility. Current review focuses on the correlation between the FXR, BAs and the composition of gut microbiota and its influence on the occurrence of GI symptoms in FGIDs.

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.

Diet1, bile acid diarrhea, and FGF15/19: mouse model and human genetic variants

Diet1 modulates intestinal production of the hormone, fibroblast growth factor (FGF)15, which signals in liver to regulate bile acid synthesis. C57BL/6ByJ mice with a spontaneous Diet1-null mutation are resistant to hypercholesterolemia compared with wild-type C57BL/6J mice through enhanced cholesterol conversion to bile acids. To further characterize the role of Diet1 in metabolism, we generated Diet1^-/- mice on the C57BL/6J genetic background. C57BL/6J Diet1^-/- mice had elevated bile acid levels, reduced Fgf15 expression, and increased gastrointestinal motility and intestinal luminal water content, which are symptoms of bile acid diarrhea (BAD) in humans. Natural genetic variation in Diet1 mRNA expression levels across 76 inbred mouse strains correlated positively with Ffg15 mRNA and negatively with serum bile acid levels. This led us to investigate the role of DIET1 genetic variation in primary BAD patients. We identified a DIET1 coding variant (rs12256835) that had skewed prevalence between BAD cases and controls. This variant causes an H1721Q amino acid substitution that increases the levels of FGF19 protein secreted from cultured cells. We propose that genetic variation in DIET1 may be a determinant of FGF19 secretion levels, and may affect bile acid metabolism in both physiological and pathological conditions.

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.

A UHPLC-MS/MS method for the quantification of 7α-hydroxy-4-cholesten-3-one to assist in diagnosis of bile acid malabsorption

Bile acids malabsorption (BAM) is encountered in numerous gastrointestinal pathologies and is a good example of a treatable cause of watery diarrhea after ileal resection. The gold standard for diagnosing BAM is the selenium homocholic acid taurine test (SeHCAT), an expensive and complex analysis. An alternative method is the quantification of 7α-hydroxy-4-cholesten-3-one (C4). Here, we present a simple, ultra high-performance liquid chromatography-tandem mass spectrometry method to measure C4 in human serum. To avoid time consuming sample preparation (e.g., derivatization, solid phase extraction), we used absorption chemistry-based extraction plates. This method demonstrates a lower limit of quantification of 5 ng/mL and is linear over a concentration range from 5 to 300 ng/mL (R2 = 0.9977). Inaccuracy and imprecision were less than 15%. The validated method is currently used for routine measurement of C4 from serum in patients to confirm BAM diagnosis.

Hepatic deletion of X-box binding protein 1 impairs bile acid metabolism in mice

The unfolded protein response (UPR) is an adaptive response to endoplasmic reticulum stress and the inositol-requiring enzyme 1α/X-box binding protein 1 (IRE1α/XBP1) pathway of the UPR is important in lipid metabolism. However, its role in bile acid metabolism remains unknown. We demonstrate that liver-specific Xbp1 knockout (LS-Xbp1^-/-) mice had a 45% reduction in total bile acid pool. LS-Xbp1^-/- mice had lower serum 7α-hydroxy-4-cholesten-3-one (C4) levels compared with Xbp1^fl/fl mice, indicating reduced cholesterol 7α-hydroxylase (CYP7A1) synthetic activity. This occurred without reductions of hepatic CYP7A1 protein expression. Feeding LS-Xbp1^-/- mice cholestyramine increased hepatic CYP7A1 protein expression to levels 2-fold and 8-fold greater than cholestyramine-fed and chow-fed Xbp1^fl/fl mice, respectively. However, serum C4 levels remained unchanged and were lower than both groups of Xbp1^fl/fl mice. In contrast, although feeding LS-Xbp1^-/- mice cholesterol did not increase CYP7A1 expression, serum C4 levels increased significantly up to levels similar to chow-fed Xbp1^fl/fl mice and the total bile acid pool normalized. In conclusion, loss of hepatic XBP1 decreased the bile acid pool and CYP7A1 synthetic activity. Cholesterol feeding, but not induction of CYP7A1 with cholestyramine, increased CYP7A1 synthetic activity and corrected the genotype-specific total bile acid pools. These data demonstrate a novel role of IRE1α/XBP1 regulating bile acid metabolism.

75SeHCAT scan in bile acid malabsorption in chronic diarrhoea

Chronic diarrhoea is a common entity in daily clinical practice and it leads to a loss in these patients quality of life. It may be the main symptom of multiple ethiologies including bile acid malabsorption (BAM) which has a comparable prevalence to celiac disease. The BAM results from imbalances in the homeostasis of bile acids in the enterohepatic circulation. It can be a consequence of ileal disease or ileal dysfunction (BAM type i), it can be considered idiopathic or primary (BAM type ii) or associated with other gastrointestinal entities (BAM type iii). Among the different diagnostic methods available, ⁷⁵SeHCAT study is the primary current method due to its sensitivity, specificity, safety and low cost. The main disadvantage is that it's not available in all countries, so other diagnostic methods have appeared, such as serum measurement of FGF19 and C4, however they are significantly more complex and costly. The first-line treatment of bile acid diarrhoea is bile acid sequestrant, such as cholestyramine, which can be difficult to administer due to its poor tolerability and gastrointestinal side effects. These are less prominent with newer agents such as colesevelam. In summary, the BAM is a common entity underdiagnosed and undertreated, so it is essential to establish a diagnosis algorithm of chronic diarrhoea in which the ⁷⁵SeHCAT study would be first or second line in the differential diagnosis of these patients.

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

OBJECTIVES

Chronic diarrhea caused by primary bile acid diarrhea (PBAD) is a common condition. We have previously shown PBAD is associated with low fasting serum levels of the ileal hormone, fibroblast growth factor 19 (FGF19). FGF19 is a negative regulator of hepatic bile acid synthesis and is stimulated by farnesoid X receptor agonists, which produce symptomatic improvement in PBAD. We aimed to assess possible causes for low serum FGF19 in patients with PBAD.

METHODS

Patients with PBAD, defined by reduced (75)Se-labelled homocholic acid taurine (SeHCAT) retention, and idiopathic diarrhea controls had measurements of fasting lipids and fasting/post-prandial FGF19 serum profiles. Specific functional variants in candidate genes were investigated in exploratory studies. In further groups, basal and bile acid-stimulated transcript expression was determined in ileal biopsies and explant cultures by quantitative PCR.

RESULTS

FGF19 profiles in PBAD patients included low fasting and meal-stimulated responses, which were both strongly correlated with SeHCAT. A subgroup of 30% of PBAD patients had fasting hypertriglyceridemia and higher FGF19. No clear significant differences were found for any genetic variant but there were borderline associations with FGFR4 and KLB. SeHCAT retention significantly correlated with the basal ileal transcript expression of FGF19 (rs=0.59, P=0.03) and apical sodium-dependent bile acid transporter (ASBT) (rs=0.49, P=0.04), and also with the degree of stimulation by chenodeoxycholic acid at 6 h for transcripts of FGF19 (median 184-fold, rs=0.50, P=0.02) and ileal bile acid binding protein (IBABP) (median 2.2-fold, rs=0.47, P=0.04). Median stimulation of FGF19 was lower in patients with SeHCAT retention <10% (P=0.01).

CONCLUSIONS

These studies demonstrate a complex, multifactorial etiology of PBAD, including impairments in ileal FGF19 expression and responsiveness.

Bile Acid diarrhea: prevalence, pathogenesis, and therapy

Bile acid diarrhea (BAD) is usually seen in patients with ileal Crohn’s disease or ileal resection. However, 25% to 50% of patients with functional diarrhea or diarrhea-predominant irritable bowel syndrome (IBS-D) also have evidence of BAD. It is estimated that 1% of the population may have BAD. The causes of BAD include a deficiency in fibroblast growth factor 19 (FGF-19), a hormone produced in enterocytes that regulates hepatic bile acid (BA) synthesis. Other potential causes include genetic variations that affect the proteins involved in BA enterohepatic circulation and synthesis or in the TGR5 receptor that mediates the actions of BA in colonic secretion and motility. BAs enhance mucosal permeability, induce water and electrolyte secretion, and accelerate colonic transit partly by stimulating propulsive high-amplitude colonic contractions. There is an increased proportion of primary BAs in the stool of patients with IBS-D, and some changes in the fecal microbiome have been described. There are several methods of diagnosing BAD, such as ⁷⁵selenium homotaurocholic acid test retention, serum C4, FGF-19, and fecal BA measurement; presently, therapeutic trials with BA sequestrants are most commonly used for diagnosis. Management involves the use of BA sequestrants including cholestyramine, colestipol, and colesevelam. FXR agonists such as obeticholic acid constitute a promising new approach to treating BAD.

Diagnosis of bile acid diarrhoea by fasting and postprandial measurements of fibroblast growth factor 19

BACKGROUND

A deficiency in the ileal hormone fibroblast growth factor 19 (FGF19) has been described in patients with bile acid diarrhoea (BAD), but fasting FGF19 levels have insufficient diagnostic power. We assess whether single postprandial sampling of FGF19 has greater discriminative value than fasting FGF19 for detection of BAD and we evaluate the reproducibility of fasting FGF19.

MATERIALS AND METHODS

Twenty-six patients consecutively referred to Se homocholic acid retention test (SeHCAT) were included. Serum FGF19 was measured after an overnight fast and again 1 h postprandially and again in the fasting state 1 week later.

RESULTS

Nine of 26 patients had SeHCAT less than 10% and fasting FGF19 was lower [median 62 pg/ml, interquartile range (IQR): 47-67] than in the 17 diarrhoea controls with SeHCAT at least 10% (median 103 pg/ml, IQR: 77-135, P=0.006). Postprandial FGF19 in BAD patients (61 pg/ml, IQR: 48-69) was similar to fasting values (P=0.59) and increased insignificantly in diarrhoea controls (137 pg/ml, IQR: 88-182; P=0.25). The difference in postprandial FGF19 between patients with BAD and diarrhoea controls was highly significant (P<0.001).

CONCLUSION

The difference in serum FGF19 between groups of patients with BAD and diarrhoea controls is amplified postprandially. Within each group, the difference between fasting and postprandial FGF19 was not statistically significant. Further investigations are warranted on stimulated FGF19 response to elucidate its role in BAD.

Quantifying bile acid malabsorption helps predict response and tailor sequestrant therapy

Although recognised as a cause of chronic diarrhoea for over forty years, diagnostic tests and treatments for bile acid malabsorption (BAM) remain controversial. Recent National Institute for Health and Care Excellence (NICE) guidelines highlighted the lack of evidence in the field, and called for further research. This retrospective study explores the BAM subtype and severity, the use and response to bile acid sequestrants (BAS) and the prevalence of abnormal colonic histology. 264 selenium-75-labelled homocholic acid conjugated taurine (SeHCAT)-tested patient records were reviewed and the severity and subtype of BAM, presence of colonic histopathology and response to BAS were recorded. 53% of patients tested had BAM, with type-2 BAM in 45% of patients with presumed irritable bowel syndrome. Colonic histological abnormalities were similar overall between patients with (29%) or without (23%) BAM (p = 0.46) and between BAM subtypes, with no significant presence of inflammatory changes. 63% of patients with BAM had a successful BAS response which showed a trend to decreased response with reduced severity. Colestyramine was unsuccessful in 44% (38/87) and 45% of these (17/38) were related to medication intolerance, despite a positive SeHCAT. 47% (7/15) of colestyramine failures had a successful colesevelam response. No patient reported colesevelam intolerance. Quantifying severity of BAM appears to be useful in predicting BAS response. Colesevelam was better tolerated than colestyramine and showed some efficacy in colestyramine failures. Colestyramine failure should not be used to exclude BAM. Colonic histology is of no relevance.

Diarrhea in Crohn’s disease: investigating the role of the ileal hormone fibroblast growth factor 19

BACKGROUND

Bile acids [BA] are usually reabsorbed by the terminal ileum, but this process is frequently abnormal in Crohn’s disease [CD]. BA malabsorption occurs, and excess colonic BA cause secretory diarrhea. Furthermore, the hormone fibroblast growth factor 19 [FGF19] is synthesized in the ileum in response to BA absorption and regulates BA synthesis. We hypothesized that reduced serum FGF19 levels will be associated with diarrheal symptoms and disease activity in both ileal resected[IR-CD] and non-resected CD [NR-CD] patients.

METHODS

Fasting serum FGF19 levels were measured in 58 patients [23 IR-CD patients and 35NR-CD patients]. Disease activity was assessed using the Harvey Bradshaw Index and C-reactive protein [CRP]. Stool frequency, Bristol Stool Form Scale and length of previous ileal resection were recorded. FGF19 levels were also compared with healthy and diarrhea control patients.

RESULTS

FGF19 levels were inversely correlated with ileal resection length in IR-CD patients[r = -0.54, p = 0.02]. In NR-CD patients, median FGF19 levels were significantly lower in patients with active disease compared with inactive disease [103 vs. 158 pg/ml, p = 0.04] and in those with symptoms of diarrhea compared with those without [86 vs. 145 pg/ml, p = 0.035]. FGF19 levels were inversely correlated with stool frequency, Bristol stool form and CRP in NR-CD patients with ileal disease.

CONCLUSIONS

Reduced FGF19 levels are associated with ileal resection, diarrhea and disease activity. FGF19 may have utility as a biomarker for functioning ileum in CD. This study supports a potential role of FGF19 in guiding treatments for diarrhea in Crohn’s disease.

Bile acid malabsorption in inflammatory bowel disease

Bile acid malabsorption (BAM) is a common but an underestimated and often neglected sign of inflammatory bowel diseases (IBDs), especially those affecting the distal ileum. Clinically relevant BAM is most often present in patients with Crohn's ileitis and particularly in ileal-resected Crohn's disease patients. However, deterioration of bile acid (BA) metabolism occurs also in patients with IBD without ileal disease or in those in clinical remission, and the role of BAM in these patients is not well appreciated by clinicians. In a majority of cases, BAM in IBD is caused by impaired conjugated BA reabsorption, mediated by apical sodium/BA cotransporting polypeptide, localized at the luminal surface of the ileal enterocytes. As a consequence, numerous pathological sequelae may occur, including the malfunction of lipid digestion with clinical steatorrhea, impaired intestinal motility, and/or significant changes in the intestinal microflora environment. In this review, a detailed description of the pathophysiological mechanisms of BAM-related diarrhea is presented. Although BAM is present in a significant number of patients with Crohn's disease, its laboratory assessment is not routinely included in diagnostic workups, partially because of costs, logistical reasons, or the unavailability of the more sophisticated laboratory equipment needed. Simultaneously, novel findings related to the effects of the BA signaling pathways on immune functions (mediated through TGR5, cell membrane G protein-coupled BA receptor 1, nuclear farnesoid X receptor, nuclear pregnane X receptor, or nuclear vitamin D receptor) are discussed along with intestinal metabolism in its relationship to the pathogenesis of IBD.

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

BACKGROUND

Bile acid diarrhoea is a common cause of chronic diarrhoea, occurring as a primary condition or secondary to ileal disease or resection. Many patients have reduced levels of the ileal hormone fibroblast growth factor 19 (FGF19), an inhibitory regulator of hepatic bile acid synthesis, secreted in response to farnesoid X receptor (FXR) activation.

AIM

To investigate whether obeticholic acid, a potent FXR agonist, could increase FGF19 in patients with bile acid diarrhoea, and produce clinical benefits.

METHODS

After a 2 week run-in when bile acid sequestrants were discontinued, patients with previously diagnosed primary bile acid diarrhoea (n = 10), secondary bile acid diarrhoea (n = 10) or idiopathic chronic diarrhoea (n = 8), received oral obeticholic acid 25 mg daily for 2 weeks. Serum FGF19, total bile acids and 7α-OH-4-cholesten-3-one (C4) were measured, symptoms recorded and a diarrhoea index calculated.

RESULTS

In primary bile acid diarrhoea, obeticholic acid increased median fasting FGF19 (133-237 pg/mL, P = 0.007) and significantly reduced fasting C4 and bile acid responses. Improvements occurred in median stool frequency (-24% after 2 weeks treatment, P = 0.03), stool form (-14%, P = 0.05) and diarrhoea index (-34%, P = 0.005). In the secondary bile acid diarrhoea group, significant clinical improvements were found predominantly in patients with shorter ileal resections. Symptoms of abdominal pain and urgency improved. FGF19 and bile acids changed in the control group, without significant clinical improvement. Total and LDL-cholesterol increased and triglycerides decreased. Obeticholic acid treatment was well tolerated.

CONCLUSIONS

This proof-of-concept study indicates that obeticholic acid stimulates FGF19, reduces bile acid synthesis and produces clinical benefits in bile acid diarrhoea. FXR agonists have therapeutic potential in chronic diarrhoea. EudraCT 2011-003777-28; Clinical Trials: NCT01585025.

Diet1 is a regulator of fibroblast growth factor 15/19-dependent bile acid synthesis

BACKGROUND

A fascinating aspect of bile acid homeostasis is the coordination between bile acid uptake in intestine and hepatic bile acid synthesis. In response to bile acid uptake in enterocytes, farnesoid X receptor is activated and induces transcription of fibroblast growth factor (FGF)15 in mice, or FGF19 in humans. FGF15/19 is secreted into the enterohepatic circulation, and through activation of hepatic receptors, leads to repression of Cyp7a1, a rate-limiting enzyme for bile acid synthesis. Using a genetic approach, we identified a novel protein, Diet1, as a control point for FGF15/19 production.

KEY MESSAGES

Mice with a Diet1-null mutation have reduced FGF15 secretion, causing impaired feedback repression of hepatic bile acid synthesis, and increased fecal bile acid excretion. As a result, Diet1-deficient mice constitutively convert cholesterol to bile acids and are resistant to diet-induced hypercholesterolemia and atherosclerosis. Diet1 affects FGF15/19 production at the posttranscriptional level, and the proteins appear to have overlapping subcellular localization in enterocytes. Diet1 appears to be a control point for the production of FGF15/19 in enterocytes, and thus a regulator of bile acid and lipid homeostasis. Studies to evaluate the role of common and rare DIET1 genetic variants in human health and disease are warranted.

CONCLUSIONS

Further elucidation of the Diet1-FGF15/19 interaction will provide new insights into the intricate regulatory mechanisms underlying bile acid metabolism.

Upregulation of hepatic bile acid synthesis via fibroblast growth factor 19 is defective in gallstone disease but functional in overweight individuals

BACKGROUND

Fibroblast growth factor 19 (FGF19) is an enteric hormone regulating bile acid de novo synthesis by sensing ileal bile acid flux. However, the role of FGF19 in cholelithiasis has not yet been elucidated and therefore is investigated in the present study.

METHODS

Total mRNA and protein were isolated from ileal biopsies and used for tissue expression analysis. FGF19, 7α-hydroxycholesterol (7α-OH-Chol), 27-hydroxycholesterol (27-OH-Chol), and different bile acids were determined in the blood samples.

RESULTS

FGF19 serum levels did not differ between gallstone carriers and controls but were significantly decreased in the overweight individuals (-32%, p = 0.0002), irrespective of gallstone status (normalweight to overweight controls -29%, p = 0.0017; normalweight to overweight gallstone carriers -44%, p = 0.0338), and correlated inversely with bodyweight (p < 0.0001, ρ = -0.3317). Compared to non-overweight controls, apical sodium-dependent bile acid transporter expression was significantly diminished in the non-overweight gallstone carriers (-42%, P mRNA = 0.0393; -52%, p protein = 0.0169) as well as in the overweight controls (-24%, P mRNA = 0.0148; -43%, p protein = 0.0017). FGF19 expression varied widely and was similar in all groups. A significant negative correlation was noted between 7α-OH-Chol, 27-OH-Chol, and FGF19 serum levels (p < 0.01; ρ7α-OH-Chol = -0.2155; ρ27-OH-Chol = -0.2144) in obesity.

CONCLUSION

Upregulation of hepatic bile acid synthesis via FGF 19 is defective in gallstone disease but functional in overweight individuals.

The role of bile acids in functional GI disorders

BACKGROUND

Bile acids are increasingly implicated in the pathogenesis of functional GI disorders. New mechanisms have recently been described in the irritable bowel syndrome, chronic diarrhea and chronic idiopathic constipation. Identification of bile acid signaling through farnesoid X receptor (FXR), transmembrane G-coupled receptor 5 (TGR5) and fibroblast growth factor 19 (FGF19) has led to the development of new, directly acting therapeutic agents. Despite these advances primary bile acid diarrhea remains under-recognized partly because of the lack of a widely available diagnostic test.

PURPOSE

In this review we will summarize the effects of bile acids on bowel function throughout the gastrointestinal tract and their roles in the pathogenesis of functional diseases. We will review established diagnostic tests and therapies for functional heartburn, dyspepsia and bile acid diarrhea. There will be a particular emphasis on recent trial data for emerging therapies such as Elobixibat and Obeticholic acid and novel diagnostic tests for bile acid diarrhea such as 7α-Hydroxy-4-cholesten-3-one (C4) and FGF19. Finally we will discuss future directions for research in this rapidly evolving field, such as bacterial bile acid modification and identification of genetic anomalies associated with functional disorders.

Bile acid diarrhoea and FGF19: new views on diagnosis, pathogenesis and therapy

Chronic diarrhoea induced by bile acids is common and the underlying mechanisms are linked to homeostatic regulation of hepatic bile acid synthesis by fibroblast growth factor 19 (FGF19). Increasing evidence, including that from several large case series using SeHCAT (selenium homocholic acid taurine) tests for diagnosis, indicates that bile acid diarrhoea (BAD) accounts for a sizeable proportion of patients who would otherwise be diagnosed with IBS. Studies of other approaches for diagnosis of BAD have shown increased bile acid synthesis, increased faecal levels of primary bile acids, dysbiosis and different urinary volatile organic compounds when compared with healthy controls or with other diseases. The role of the ileal hormone FGF19 in BAD has been strengthened: a prospective clinical study has confirmed low FGF19 levels in BAD, and so a test to measure these levels could be developed for diagnosis. In animal models, FGF19 depletion by antibodies produces severe diarrhoea. Bile acids affect colonic function through farnesoid X receptor (FXR) and TGR5 receptors. As well as these effects in the colon, FXR-dependent stimulation of ileal FGF19 production could be a logical mechanism to provide therapeutic benefit in BAD. Further studies of FGF19 in humans hold promise in providing novel treatments for this cause of chronic diarrhoea.

Systematic review: the management of chronic diarrhoea due to bile acid malabsorption

BACKGROUND

Bile acid malabsorption (BAM) is a common, yet under-recognised, cause of chronic diarrhoea, with limited guidance available on the appropriate management of patients with BAM.

AIM

To summarise the evidence supporting different treatments available for patients with bile acid malabsorption, noting their impact on clinical outcomes, tolerability and associated side effects.

METHODS

A literature search was conducted through PubMed, the Cochrane Database of Systematic Reviews and Scopus. Relevant articles studied patients who had been diagnosed with BAM and were clinically assessed before and after therapy.

RESULTS

A total of 30 relevant publications (1241 adult patients) were identified, which investigated the clinical response to drugs, including colestyramine, colestipol, colesevelam, aluminium hydroxide and obeticholic acid. The most commonly used diagnostic test of bile acid malabsorption was the SeHCAT test (24 studies). Colestyramine treatment was by far the most studied of these agents, and was successful in 70% of 801 patients (range: 63-100%).

CONCLUSIONS

Colestyramine and colestipol are generally effective treatments of gastrointestinal symptoms from BAM, but may be poorly tolerated and reduce the bioavailability of co-administered agents. Alternative therapies (including colesevelam and aluminium hydroxide) as well as dietary intervention may also have a role, and the promising results of the first proof-of-concept study of obeticholic acid suggest that its novel approach may have an exciting future in the treatment of this condition. Future trials should employ accurate diagnostic testing and be conducted over longer periods so that the long-term benefits and tolerability of these different approaches can be evaluated.

Diacylglycerol acyltransferase 1 inhibition with AZD7687 alters lipid handling and hormone secretion in the gut with intolerable side effects: a randomized clinical trial

AIM

Inhibition of diacylglycerol acyltransferase 1 (DGAT1) is a potential treatment modality for patients with type 2 diabetes mellitus and obesity, based on preclinical data suggesting it is associated with insulin sensitization and weight loss. This randomized, placebo-controlled, phase 1 study in 62 overweight or obese men explored the effects and tolerability of AZD7687, a reversible and selective DGAT1 inhibitor.

METHODS

Multiple doses of AZD7687 (1, 2.5, 5, 10 and 20 mg/day, n = 6 or n = 12 for each) or placebo (n = 20) were administered for 1 week. Postprandial serum triacylglycerol (TAG) was measured for 8 h after a standardized 45% fat meal. Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) were measured and a paracetamol challenge was performed to assess gastric emptying.

RESULTS

Dose-dependent reductions in postprandial serum TAG were demonstrated with AZD7687 doses ≥5 mg compared with placebo (p < 0.01). Significant (p < 0.001) increases in plasma GLP-1 and PYY levels were seen at these doses, but no clear effect on gastric emptying was demonstrated at the end of treatment. With AZD7687 doses >5 mg/day, gastrointestinal (GI) side effects increased; 11/18 of these participants discontinued treatment owing to diarrhoea.

CONCLUSIONS

Altered lipid handling and hormone secretion in the gut were demonstrated during 1-week treatment with the DGAT1 inhibitor AZD7687. However, the apparent lack of therapeutic window owing to GI side effects of AZD7687, particularly diarrhoea, makes the utility of DGAT1 inhibition as a novel treatment for diabetes and obesity questionable.

Regulation of bile acid homeostasis by the intestinal Diet1-FGF15/19 axis

PURPOSE OF REVIEW

Hepatic bile acid synthesis is controlled, in part, by a complex enterohepatic feedback regulatory mechanism. In this review, we focus on the role of the intestinal FGF15/19 hormone in modulating bile acid levels, and additional metabolic effects on glucose metabolism, nonalcoholic liver disease (NAFLD), and liver regeneration. We also highlight the newly identified intestinal protein, Diet1, which is a modulator of FGF15/19 levels.

RECENT FINDINGS

Low FGF19 levels are associated with bile acid diarrhea and NAFLD. In contrast, high FGF19 levels are associated with diabetes remission following Roux-en-Y gastric bypass surgery, suggesting new therapeutic approaches against type 2 diabetes. The effect of FGF15/19 on liver plasticity is a double-edged sword: whereas elevated FGF15/19 levels improve survival of mice after partial hepatectomy, FGF19 mitogenic activity is associated with liver carcinoma. Finally, a recent study has identified Diet1, an intestinal factor that influences FGF15/19 levels in mouse intestine and human enterocytes. Diet1 represents the first factor shown to influence FGF15/19 levels at a post-transcriptional level.

SUMMARY

The biological effects of FGF15/19 make it an attractive target for treating metabolic dysregulation underlying conditions such as fatty liver and type 2 diabetes. Further elucidation of the role of Diet1 in FGF15/19 secretion may provide a control point for the pharmacological modulation of FGF15/19 levels.