Pharmacogenetics of the effects of colesevelam on colonic transit in irritable bowel syndrome with diarrhea

β-Klotho as novel therapeutic target in Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD): A narrative review

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) represents the most frequent cause of hepatic disorder, and its progressive form defined as Metabolic Dysfunction-Associated Steatohepatitis (MASH) contributes to the development of fibrosis/cirrhosis and hepatocellular carcinoma (HCC). Today effective therapeutic strategies addressing MASH-related comorbidities, inflammation, and fibrosis are needed. The fibroblast growth factor (FGF) 19 and 21 and their fibroblast growth factor receptor/β-Klotho (KLB) complexes have recently emerged as promising druggable targets for MASLD. However, less is known regarding the causative association between KLB activity and advanced stages of liver disease. In the present narrative review, we aimed to provide an up-to-date picture of the role of the KLB co-receptor in MASLD development and progression. We performed a detailed analysis of recently published preclinical and clinical data to decipher the molecular mechanisms underlying KLB function and to correlate the presence of inherited or acquired KLB aberrancies with the predisposition towards MASLD. Moreover, we described ongoing clinical trials evaluating the therapeutic approaches targeting FGF19-21/FGFR/KLB in patients with MASLD and discussed the challenges related to their use. We furtherly described that KLB exhibits protective effects against metabolic disorders by acting in an FGF-dependent and independent manner thus triggering the hypothesis that KLB soluble forms may play a critical role in preserving liver health. Therefore, targeting KLB may provide promising strategies for treating MASLD, as supported by experimental evidence and ongoing clinical trials.

Evidence-Based Clinical Guidelines for Chronic Diarrhea 2023

The Japan Gastroenterological Association (JGA) published the first version of clinical guidelines for chronic diarrhea 2023. These guidelines describe the definition, classification, diagnostic criteria, diagnostic testing methods, epidemiology, pathophysiology, and treatment of chronic diarrhea, and provide flowcharts for the diagnosis and treatment of chronic diarrhea based on the latest evidence. Treatment for chronic diarrhea begins by distinguishing secondary chronic constipation with a clear etiology, such as drug-induced diarrhea, food-induced diarrhea, systemic disease-associated diarrhea, infection-associated diarrhea, organic disease-associated diarrhea, and bile acid diarrhea. The first line of treatment for chronic diarrhea in the narrow sense, defined in these guidelines as functional diarrhea in routine medical care, is lifestyle modification and dietary therapy. The first medicines to be considered for oral treatment are probiotics for regulating the gut microbiome and anti-diarrheals. Other medications, such as 5HT3 receptor antagonists, anticholinergics, Kampo medicine, psychotherapy, antibiotics, bulking agents, adrenergic agonists, and somatostatin analogs, lack sufficient evidence for their use, highlighting a challenge for future research. This Clinical Guidelines for Chronic Diarrhea 2023, which provides the best clinical strategies for treating chronic diarrhea in Japan, will also be useful for medical treatment worldwide.

Pharmacogenetics in IBS: update and impact of GWAS studies in drug targets and metabolism

INTRODUCTION

Medications are frequently prescribed for patients with irritable bowel syndrome (IBS) or disorders of gut brain interaction. The level of drug metabolism and modifications in drug targets determine medication efficacy to modify motor or sensory function as well as patient response outcomes.

AREAS COVERED

The literature search included PubMed searches with the terms: pharmacokinetics, pharmacogenomics, epigenetics, clinical trials, irritable bowel syndrome, disorders of gut brain interaction, and genome-wide association studies. The main topics covered in relation to irritable bowel syndrome were precision medicine, pharmacogenomics related to drug metabolism, pharmacogenomics related to mechanistic targets, and epigenetics.

EXPERT OPINION

Pharmacogenomics impacting drug metabolism [CYP 2D6 (cytochrome P450 2D6) or 2C19 (cytochrome P450 2C19)] is the most practical approach to precision medicine in the treatment of IBS. Although there are proof of concept studies that have documented the importance of genetic modification of transmitters or receptors in altering responses to medications in IBS, these principles have rarely been applied in patient response outcomes. Genome-wide association (GWAS) studies have now documented the association of symptoms with genetic variation but not the evaluation of treatment responses. Considerably more research, particularly focused on patient response outcomes and epigenetics, is essential to impact this field in clinical medicine.

Most patients with disorders of gut-brain interaction receive pharmacotherapy with major or moderate drug-gene interactions

BACKGROUND

How variations predicted by pharmacogenomic testing to alter drug metabolism and therapeutic response affect outcomes for patients with disorders of gut- brain interaction is unclear.

AIMS

To assess the prevalence of pharmacogenomics-predicted drug-gene interactions and symptom outcomes for patients with disorders of gut-brain interaction.

METHODS

Patients who were treated in our clinical practice for functional dyspepsia/bowel disorder underwent pharmacogenomic testing. The change in symptoms from baseline to 6 months was compared for patients with variations in CYP2D6 and CYP2C19, which metabolize neuromodulators, and SLC6A4, which encodes the sodium- dependent serotonin transporter.

RESULTS

At baseline, 79 of 94 participants (84%) had at least one predicted major drug- gene interaction, and all 94 (100%) had at least one predicted moderate interaction. For the 44 participants who completed a survey of their symptoms at 6 months, the mean (SD) irritable bowel syndrome-symptom severity score decreased from 284 (71) at baseline to 231 (95) at 6 months (p < 0.001). Among patients taking selective serotonin reuptake inhibitors, the decrease in symptom severity (p = 0.03) and pain (p = 0.002) scores from baseline to 6 months was greater for patients with a homozygous SLC6A4 long/long genotype (n = 30) (ie, increased serotonin transporter activity) than for patients with homozygous short/short or heterozygous long/short genotypes (n = 64). Symptom outcomes were not affected by CYP2D6 or CYP2C19 variations.

CONCLUSIONS

The homozygous SLC6A4 long/long genotype confers better symptom resolution for patients with disorders of gut-brain interaction who take selective serotonin reuptake inhibitors than do the homozygous short/short or heterozygous long/short genotypes.

Interplay between gut microbiota and bile acids in diarrhoea-predominant irritable bowel syndrome: a review

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disease that disturbs the physiology and psychology of patients and increases the burden on families, the healthcare system, society, and economic development, affecting more and more people around the world. Despite the multiple factors that account for IBS remaining incompletely studied, emerging evidence demonstrated the abnormal changes in gut microbiota and bile acids (BAs) metabolism closely associated with IBS. Moreover, microbiota drives significant modifications for BAs, consisting of deconjugation, 7α-dehydroxylation, oxidation, epimerization, desulfation, esterification, and so on, while BAs, in turn, affect the microbiota directly or indirectly. In light of the complex connection among gut microbiota, BAs, and IBS, it is urgent to review the latest research progress in this field. In this review, we described the disorders of intestinal microecology and BAs profiles in IBS-D and also highlighted the cross-talk between gut microbiota and BAs in the context of IBS-D. Integrating these, we suggest that new therapeutic strategies targeting the microbiota-BAs axis for IBS-D, even for other related diseases caused by bacteria-bile acid dysbiosis should be expected.

Effects of Colesevelam on Bowel Symptoms, Biomarkers, and Colonic Mucosal Gene Expression in Patients With Bile Acid Diarrhea in a Randomized Trial

BACKGROUND & AIMS

Approximately one-third of patients with IBS-diarrhea (IBS-D) have increased bile acid (BA) synthesis or excretion. An open-label study showed benefits of colesevelam on bowel functions, consistent with luminal BA sequestration by colesevelam. We compared the effects of colesevelam vs placebo on symptoms and gene expression patterns in the sigmoid colon mucosa in patients with BA diarrhea associated with IBS-D.

METHODS

We performed a double-blind, parallel-group study of 30 adults with IBS-D and evidence of increased BA synthesis or fecal excretion, from December 2017 through December 2018 at a single center. Patients were randomly assigned (1:1) to groups given colesevelam (3 tablets, 625 mg each) or matching placebo, orally twice daily for 4 weeks. Stool diaries documented bowel functions for 8 days before and 28 days during colesevelam or placebo. Stool and fasting serum samples were collected for analyses of fecal BAs and serum levels of C4 and FGF19. We measured colonic transit by scintigraphy, mucosal permeability by in vivo excretion of saccharide probes, and mRNA levels in rectosigmoid biopsies. All measurements were made at baseline and on the last days of treatment. The primary endpoints were change in total fecal BA concentration and stool consistency.

RESULTS

Compared with placebo, colesevelam was associated with significant changes in sequestered fecal total BA excretion (P < .001) and serum levels of C4 and FGF19 (both P < .001), and with a mean increase in fecal level of deoxycholic acid (10%; P = .07) compared to placebo. Colesevelam decreased colon mucosal expression of NR1H4 and P2RY4 and increased expression of GPBAR1, compared with baseline. Stool frequency and consistency, colonic transit, and permeability did not differ significantly between groups. Colesevelam was well tolerated.

CONCLUSIONS

In a randomized trial, we found that colesevelam increases delivery of total and secondary BAs to stool, hepatic BA synthesis, and colonic mucosal expression of genes that regulate BA, farnesoid X, and GPBAR1 receptors. Larger studies are needed to determine the effects on clinical responses. ClinicalTrials.gov no: NCT03270085.

Implications of Pharmacogenomics to the Management of IBS

The objectives are to review the role of pharmacogenomics in drug metabolism of medications typically used in patients with irritable bowel syndrome (IBS) focusing predominantly on cytochrome P450 metabolism. Other aims are to provide examples of genetic variation of receptors or intermediary pathways that are targets for IBS drugs and to critically appraise the situations where precision medicine is impacting health in IBS. Pharmacogenomics impacts both pharmacokinetics and pharmacodynamics. Although large clinical trials have not incorporated testing for genetic variations that could impact the efficacy of medications in IBS, there are therapeutic advantages to inclusion of pharmacogenomics testing for individual patients, as has been demonstrated particularly in the treatment with central neuromodulators in psychiatry practice. Clinical practice in IBS is moving in the same direction with the aid of commercially available tests focused on drug metabolism. Specific mechanisms leading to pathophysiology of IBS are still poorly characterized, relative to diseases such as cancer and inflammatory bowel disease, and, therefore, pharmacogenomics related to drug pharmacodynamics is still in its infancy and requires extensive future research. With increased attention to pharmacogenomics affecting drug metabolism, it is anticipated that pharmacogenomics will impact care of IBS.

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.

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.

Pharmacogenetics and the treatment of functional gastrointestinal disorders

The diagnosis and management of functional gastrointestinal disorders (FGIDs) remain very challenging. In the era of precision medicine, it is important to individualize the treatment of these conditions by providing targeted and effective therapies while minimizing the risk of medication side effects. By using genetic information that predicts and affects the responses to specific medications, it is anticipated that the science of pharmacogenetics in FGIDs will advance the practice of precision medicine. The pathophysiology of FGIDs is complex, involving the interaction between predisposing genetic and environmental factors. Studies have shown that genetic polymorphisms may contribute to the variable responses to specific medications among individuals with FGIDs. Genetic variations in the CYP450 system can affect the metabolism and, hence, the pharmacokinetics of drugs used to treat FGIDs. Polymorphisms in the genes controlling proteins that are involved in the direct action of medications targeting the serotonergic, cannabinoid, adrenergic and bile acid pathways can affect the pharmacologic effects of the medications. In this review, we summarize the published literature on the pharmacogenetics of FGIDs and address the potential clinical utility and future challenges in this field. Since it was the dominant topic in the majority of the articles relevant to FGIDs, our review will focus on irritable bowel syndrome.

Recent advances in the diagnosis of irritable bowel syndrome

The symptom-based diagnosis of irritable bowel syndrome (IBS) has not been established in everyday clinical practice, and the diagnosis of this disorder remains one of exclusion. It has been demonstrated that the densities of duodenal chromogranin A, rectal peptide YY and somatostatin cells are good biomarkers for the diagnosis of sporadic IBS, and low-grade mucosal inflammation is a promising biomarker for the diagnosis of postinfectious IBS. Genetic markers are not useful as biomarkers for IBS since the potential risk genes have yet to be validated, and the intestinal microbiota cannot be used because of the lack of an association between a specific bacterial species and IBS. Furthermore, gastrointestinal dysmotility and visceral hypersensitivity tests produce results that are too nonconsistent and noncharacteristic to be used in the diagnosis of IBS. A combination of symptom-based assessment, exclusion of overlapping gastrointestinal diseases and positive biomarkers appears to be the best way to diagnose IBS.

Irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disease with a high population prevalence. The disorder can be debilitating in some patients, whereas others may have mild or moderate symptoms. The most important single risk factors are female sex, younger age and preceding gastrointestinal infections. Clinical symptoms of IBS include abdominal pain or discomfort, stool irregularities and bloating, as well as other somatic, visceral and psychiatric comorbidities. Currently, the diagnosis of IBS is based on symptoms and the exclusion of other organic diseases, and therapy includes drug treatment of the predominant symptoms, nutrition and psychotherapy. Although the underlying pathogenesis is far from understood, aetiological factors include increased epithelial hyperpermeability, dysbiosis, inflammation, visceral hypersensitivity, epigenetics and genetics, and altered brain-gut interactions. IBS considerably affects quality of life and imposes a profound burden on patients, physicians and the health-care system. The past decade has seen remarkable progress in our understanding of functional bowel disorders such as IBS that will be summarized in this Primer.

Pharmacological, Pharmacokinetic, and Pharmacogenomic Aspects of Functional Gastrointestinal Disorders

This article reviews medications commonly used for the treatment of patients with functional gastrointestinal disorders. Specifically, we review the animal models that have been validated for the study of drug effects on sensation and motility; the preclinical pharmacology, pharmacokinetics, and toxicology usually required for introduction of new drugs; the biomarkers that are validated for studies of sensation and motility endpoints with experimental medications in humans; the pharmacogenomics applied to these medications and their relevance to the FGIDs; and the pharmacology of agents that are applied or have potential for the treatment of FGIDs, including psychopharmacologic drugs.

Lessons learned--resolving the enigma of genetic factors in IBS

IBS is the most prevalent functional gastrointestinal disorder and phenotypically characterized by chronic abdominal discomfort, pain and altered defecation patterns. The pathophysiology of IBS is multifactorial, albeit with a substantial genetic component. To date, studies using various methodologies, ranging from family and twin studies to candidate gene approaches and genome-wide association studies, have identified several genetic variants in the context of IBS. Yet, despite enlarged sample sizes, increased statistical power and meta-analyses in the past 7 years, positive associations are still scarce and/or have not been reproduced. In addition, epigenetic and pharmacogenetic approaches remain in their infancy. A major hurdle is the lack of large homogenized case-control cohorts recruited according to standardized and harmonized criteria. The COST Action BM1106 GENIEUR (GENes in Irritable Bowel Syndrome Research Network EURope) has been established to address these obstacles. In this Review, the (epi)genetic working group of GENIEUR reports on the current state-of-the-art in the field, highlights fundamental flaws and pitfalls in current IBS (epi)genetic research and provides a vision on how to address and improve (epi)genetic approaches in this complex disorder in the future.

Review article: biomarkers and personalised therapy in functional lower gastrointestinal disorders

BACKGROUND

Treatment of IBS and functional lower gastrointestinal disorders is still based predominantly on symptoms; biomarkers that reflect the mechanism or pathophysiology have been identified. Given the diverse mechanisms that result in the same clinical phenotype of IBS, it is hypothesised that identification of biomarkers may lead to individualisation of medical therapy.

AIM

To review the biomarkers that have been appraised in IBS.

METHODS

A single author reviewed the published literature on biomarkers appraised in IBS.

RESULTS

The current literature suggests that these biomarkers are insufficiently sensitive or specific to differentiate IBS from health or from other diseases causing similar symptoms, such as coeliac disease or inflammatory bowel disease. Most of the proposed biomarkers are not actionable, that is, they do not lead to an efficacious therapy based on the biological inference of the biomarker itself. However, among proposed biomarkers in IBS, some are actionable, as they specifically reflect a quantitative difference in a mediator of dysfunction or result in a quantifiable disturbance of function that can be specifically treated. Such biomarkers may potentially identify relevant subgroups that respond to specific therapy. The most promising actionable biomarkers are measurement of colonic transit (leading to treatments that reverse the abnormal transit) and measurements of bile acid diarrhoea to identify responders to bile acid sequestrants.

CONCLUSIONS

Therefore, although biomarkers are not ready for prime time as diagnostic tests in IBS, some biomarkers could identify subgroups of patients with IBS for inclusion in clinical trials that target specific dysfunctions. Such an approach may enhance treatment efficacy, and may ultimately help reduce costs in drug development and in the management of patients in clinical practice.

Pharmacogenetics in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic disease characterized by complex interactions between genetic predisposition and the environment. Current treatments for IBS are characterized by a highly variable response. Gene variations may result from insertions or deletions, gene rearrangements, splice variants or copy number variants, or, more commonly, from substitutions in the DNA of one (single nucleotide polymorphism [SNPs]) or more than one nucleotide. The objective of this editorial is to review the potential importance of pharmacogenetics in the treatment of IBS based on current evidence.

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.

Increased colonic bile acid exposure: a relevant factor for symptoms and treatment in IBS

OBJECTIVE

Bile acids may play a role in the pathogenesis of IBS. We investigated the potential effects of bile acids entering the colon and its role in the symptom pattern in IBS.

DESIGN

We measured 75Se-labelled homocholic acid-taurine (75SeHCAT) retention, and serum levels of 7α-hydroxy-4-cholesten-3-one (C4) and fibroblast growth factor (FGF) 19 in patients with IBS (n=141) and control subjects (75SeHCAT n=29; C4 and FGF19 n=435). In patients with IBS stool frequency and form, as well as GI symptom severity were registered, and in a proportion of patients colonic transit time and rectal sensitivity were measured (n=66). An 8-week open-label treatment with colestipol was offered to patients with 75SeHCAT <20%, and the effect of treatment was evaluated with IBS severity scoring system and adequate relief of IBS symptoms.

RESULTS

Compared with controls, patients with IBS had lower 75SeHCAT values (p=0.005), higher C4c levels (C4 corrected for cholesterol) (p<0.001), but similar FGF19 levels. Abnormal 75SeHCAT retention (<10%) was seen in 18% of patients, whereas 23% had elevated C4c levels. Patients with IBS with 75SeHCAT retention <10% had more frequent stools, accelerated colonic transit time, rectal hyposensitivity, a higher body mass index, higher C4c and lower FGF19 levels. Colestipol treatment improved IBS symptoms (IBS severity scoring system 220±109 vs. 277±106; p<0.01), and 15/27 patients fulfilled criteria for treatment response (adequate relief ≥50% of weeks 5-8).

CONCLUSIONS

Increased colonic bile acid exposure influences bowel habit and colonic transit time in patients with IBS. A high response rate to open label treatment with colestipol supports this, but placebo-controlled studies are warranted.

Colesevelam for the treatment of bile acid malabsorption-associated diarrhea in patients with Crohn's disease: a randomized, double-blind, placebo-controlled study

BACKGROUND AND AIMS

Bile acid malabsorption (BAM)-associated diarrhea is an important clinical issue in patients with Crohn's disease (CD). We analyzed the efficacy and safety of the bile acid sequestrant colesevelam for treatment of BAM-associated diarrhea in CD patients in a randomized, double-blind, placebo-controlled study.

METHODS

The primary endpoint was the proportion of patients with >30% reduction of liquid stools/day from baseline to termination visit at week 4. Secondary endpoints were reduction of the number of liquid stools/day, improvement of stool consistency and quality of life.

RESULTS

26 patients were analyzed in the intention-to-treat (ITT) analysis. The primary endpoint was reached by 10 patients (69.7%) in the colesevelam group compared to 3 patients (27.3%) in the placebo group (risk difference RD=.394, 95%CI:[-0.012; 0.706]; P=.0566). In the per-protocol analysis (n=22), the risk difference was statistically significant (RD=.470, 95%CI:[0.018; 0.788], P(H0: RD=0)=0.0364; 95% CI:[1.3;54.7]). Regarding secondary endpoints, in the ITT population colesevelam-treated patients had a significant reduction of liquid stools/day at week 4 (median 5.0 to 2.0; P=0.01), while patients treated with placebo had no significant reduction (median 4.0 to 3.0; P=0.42). Significantly more patients in the colesevelam group had improvement of stool consistency of at least one level in the Bristol stool chart, as compared to the placebo group (P=0.003).

CONCLUSIONS

We found significant differences in favor for colesevelam treatment compared to placebo treatment for CD patients with BAM regarding the reduction of the number of liquid stools/day and stool consistency. ClinicalTrials.gov number: NCT01203254.

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.

Irritable bowel syndrome-diarrhea: characterization of genotype by exome sequencing, and phenotypes of bile acid synthesis and colonic transit

The study objectives were: to mine the complete exome to identify putative rare single nucleotide variants (SNVs) associated with irritable bowel syndrome (IBS)-diarrhea (IBS-D) phenotype, to assess genes that regulate bile acids in IBS-D, and to explore univariate associations of SNVs with symptom phenotype and quantitative traits in an independent IBS cohort. Using principal components analysis, we identified two groups of IBS-D (n = 16) with increased fecal bile acids: rapid colonic transit or high bile acids synthesis. DNA was sequenced in depth, analyzing SNVs in bile acid genes (ASBT, FXR, OSTα/β, FGF19, FGFR4, KLB, SHP, CYP7A1, LRH-1, and FABP6). Exome findings were compared with those of 50 similar ethnicity controls. We assessed univariate associations of each SNV with quantitative traits and a principal components analysis and associations between SNVs in KLB and FGFR4 and symptom phenotype in 405 IBS, 228 controls and colonic transit in 70 IBS-D, 71 IBS-constipation. Mining the complete exome did not reveal significant associations with IBS-D over controls. There were 54 SNVs in 10 of 11 bile acid-regulating genes, with no SNVs in FGF19; 15 nonsynonymous SNVs were identified in similar proportions of IBS-D and controls. Variations in KLB (rs1015450, downstream) and FGFR4 [rs434434 (intronic), rs1966265, and rs351855 (nonsynonymous)] were associated with colonic transit (rs1966265; P = 0.043), fecal bile acids (rs1015450; P = 0.064), and principal components analysis groups (all 3 FGFR4 SNVs; P < 0.05). In the 633-person cohort, FGFR4 rs434434 was associated with symptom phenotype (P = 0.027) and rs1966265 with 24-h colonic transit (P = 0.066). Thus exome sequencing identified additional variants in KLB and FGFR4 associated with bile acids or colonic transit in IBS-D.

Advances in understanding of bile acid diarrhea

Bile acids (BA) are actively reabsorbed in the terminal ileum by the apical Na(+)-dependent bile salt transporter. This review addresses the epidemiology, pathophysiology, diagnosis and treatment of BA diarrhea (BAD). BAD is typically caused by ileal resection or disease; 25-33% of patients with chronic functional diarrhea or irritable bowel syndrome-diarrhea (IBS-D) have BAD, possibly from deficiency in the ileal hormone, FGF-19, which normally provides feedback inhibition of BA synthesis. Diagnosis of BAD is typically based on reduced BA retention of radiolabeled BA ((75)SeHCAT), increased BA synthesis (serum C4) or increased fecal BA loss. In clinical practice, diagnosis is often based on response to BA sequestrants (e.g., cholestyramine or colesevelam). Diagnostic tests for BA malabsorption (BAM) need to be used more extensively in clinical practice. In the future, farnesoid X receptor agonists that stimulate ileal production of FGF-19 may be alternative treatments of BAD.

Current and future pharmacological treatments for diarrhea-predominant irritable bowel syndrome

INTRODUCTION

Diarrhea-predominant irritable bowel syndrome (IBS-D) affects about one-third of patients with IBS, which is observed in about 12% of people across five continents. The ultimate goal in this field is to identify the underlying cause of symptoms in order to individualize education of the patient, and to provide optimal treatment of this highly prevalent condition.

AREAS COVERED

This review addresses the pharmacological treatments for IBS-D under three categories: drugs for IBS-D (i.e., the 5-HT3 antagonist, alosetron); drugs approved for other indications that are used in IBS-D (e.g., opioid agonists; other 5-HT3 antagonists; serotonergic psychoactive agents; bile acid binders; 5-ASA compounds; probiotics and non-absorbable antibiotics); as well as development of drugs that are likely to impact the management of IBS-D in the future (e.g., drug absorbents; TPH1 inhibitors; mast cell stabilizers; centrally acting benzodiazepines). The final section addresses key findings: regulatory roadblocks; weaknesses in the current research in this field so far and opportunities to address unmet needs including restoration of normal intestinal barrier function or permeability, and suppression within the intestines of local immune activation that is thought to trigger abnormal motor, sensory and secretory functions in IBS-D.

EXPERT OPINION

While symptomatic treatment of diarrhea is effective, there is a need for new treatments for the IBS-D complex. Greater understanding of the mechanisms in IBS-D has led to promising approaches to develop more efficacious therapies.

FGFR4 genetic polymorphisms determine the chemotherapy response of Chinese patients with non-small cell lung cancer

AIM

To investigate the relationship of fibroblast growth factor receptor 4 (FGFR4) gene polymorphisms with the response of Chinese patients with non-small cell lung cancer (NSCLC) to chemotherapy.

METHODS

A total of 629 patients with Stage III (A+B) or IV NSCLC, as well as 729 age- and gender-matched healthy controls were recruited. All the patients received platinum-based chemotherapy, and the therapeutic effects were evaluated. Three polymorphisms in the FGFR4 gene (rs351855G/A, rs145302848C/G, and rs147603016G/A) were genotyped, and the association between the 3 polymorphisms and the chemotherapy effect was analyzed using SPSS software, version 16.0.

RESULTS

The genotype frequencies of rs145302848C/G and rs147603016G/A were not significantly different between NSCLC patients and healthy controls on one hand, and between the responders and non-responders to the chemotherapy on the other hand. The distribution of AA genotype and A-allele of rs351855G/A was significantly lower in NSCLC patients than in healthy controls. Using patients with the GG genotype as a reference, the AA carrier had a significantly reduced risk for the development of NSCLC after normalizing to age, sex and smoking habits. In NSCLC patients, this genotype occurred more frequently in the responders to the chemotherapy than in non-responders. The chance of being a responder was significantly increased with the AA genotype as compared to G genotype. The AA genotype of rs351855G/A had a better prognosis compared with GA and GG genotype carriers: the overall survival of patients with the AA genotype of rs351855G/A was significantly longer than those with the GG+GA genotype (21.1 vs 16.5 months).

CONCLUSION

The rs351855G/A polymorphisms of FGFR4 gene can be used to predict the occurrence, chemotherapy response and prognosis of NSCLC.

Increased bile acid biosynthesis is associated with irritable bowel syndrome with diarrhea

BACKGROUND & AIMS

Variations in genes that regulate bile acid (BA) synthesis are associated with colonic transit in patients with irritable bowel syndrome (IBS). We investigated features of BA synthesis and excretion and genetic features of patients with different types of IBS.

METHODS

In 26 healthy volunteers, 26 patients with IBS and constipation (IBS-C), and 26 with IBS and diarrhea (IBS-D), we measured serum levels of 7α-hydroxy-4-cholesten-3-one (C4; a surrogate for BA synthesis) and fibroblast growth factor (FGF) 19 (an ileal hormone that downregulates BA synthesis). For stool samples, we measured concentration of BA, weight, and amount of fat when participants were given high-fat diets. Spearman correlations were used to explore relationships among factors. We analyzed 1 polymorphism in Klotho-β (KLB) and 3 in fibroblast growth factor receptor-4 (FGFR4) for all members of each group using analysis of covariance.

RESULTS

The concentration of BA in stool was associated with group (for a comparison of 3 groups; P = .057); it was higher in patients with IBS-D than IBS-C (P = .017). The serum level of C4 was higher in patients with IBS-D than IBS-C (P = .02) or healthy volunteers (P = .01); 38% of patients with IBS-D had increased serum levels of C4, compared with healthy volunteers. Serum level of C4 correlated with stool concentration of BA (rs = 0.606; P < .001), serum FGF19 (rs = -0.324; P = .007), and stool weight (rs = 0.366; P = .003). Stool concentration of BA correlated with weight (rs = 0.737; P < .001) and level of fat (rs = 0.528; P < .001). Body mass index correlated with serum level of C4 (rs = 0.423, P < .001) and stool concentration of BA (rs = 0.507, P < .001), and was higher in patients with IBS-D compared with other groups (overall P = .036). FGFR4 rs1966265 was associated with stool level of BA (P = .032).

CONCLUSIONS

Patients with IBS-D have greater body mass index and synthesize and excrete higher levels of BA than individuals with IBS-C or healthy volunteers. Serum levels of C4 might be used to identify patients with IBS-D who have BA malabsorption; studies are needed to determine if some patients have a genetic predisposition to this disorder.

Irritable bowel syndrome: methods, mechanisms, and pathophysiology. Genetic epidemiology and pharmacogenetics in irritable bowel syndrome

The objectives of this review are twofold. Our first objective is to evaluate the evidence supporting a role for genetics in irritable bowel syndrome (IBS). Specific examples of the associations of genetic variation and symptoms, syndromes, and intermediate phenotypes, including neurotransmitter (serotonergic, α(2)-adrenergic, and cannabinoid) mechanisms, inflammatory pathways (IL-10, TNFα, GNβ3, and susceptibility loci involved in Crohn's disease), and bile acid metabolism, are explored. The second objective is to review pharmacogenetics in IBS, with the focus on cytochrome P-450 metabolism of drugs used in IBS, modulation of motor and sensory responses to serotonergic agents based on the 5-hydroxytryptamine (5-HT) transporter-linked polymorphic region (5-HTTLPR) and 5-HT(3) genetic variants, responses to a nonselective cannabinoid agonist (dronabinol) based on cannabinoid receptor (CNR1) and fatty acid amide hydrolase (FAAH) variation, and responses to a bile acid (sodium chenodeoxycholate) and bile acid binding (colesevelam) based on klothoβ (KLB) and fibroblast growth factor receptor 4 (FGFR4) variation. Overall, there is limited evidence of a genetic association with IBS; the most frequently studied association is with 5-HTTLPR, and the most replicated association is with TNF superfamily member 15. Most of the pharmacogenetic associations are reported with intermediate phenotypes in relatively small trials, and confirmation in large clinical trials using validated clinical end points is still required. No published genome-wide association studies in functional gastrointestinal or motility disorders have been published.

The role of pharmacogenetics in nonmalignant gastrointestinal diseases

Genetic variation influences the absorption and efflux of drugs in the intestine, the metabolism of drugs in the liver and the effects of these drugs on their target proteins. Indeed, variations in genes whose products have a role in the pathophysiology of nonmalignant gastrointestinal diseases, such as IBD, have been shown to affect the response of patients to therapy. This Review provides an overview of pharmacogenetics in the management of nonmalignant gastrointestinal diseases on the basis of data from clinical trials. Genetic variants that have the greatest effect on the management of patients with IBD involve the metabolism of thiopurines. Variation in drug metabolism by cytochrome P450 enzymes also requires attention so as to avoid drug interactions in patients receiving tricyclic antidepressants and PPIs. Few genotyping tests are currently used in the clinical management of patients with nonmalignant gastrointestinal diseases, owing to a lack of data from clinical trials showing their effectiveness in predicting nonresponse or adverse outcomes. However, pharmacogenetics could have a beneficial role in enabling pharmacotherapy for nonmalignant gastrointestinal diseases to be targeted to the individual patient.