Altered levels of fecal chromogranins and secretogranins in IBS: relevance for pathophysiology and symptoms?

Metabolic biomarkers in irritable bowel syndrome diagnosis

Irritable bowel syndrome (IBS) is a chronic gastrointestinal (GI) disorder characterized by altered bowel habits and abdominal discomfort during defecation. It significantly impacts life quality and work productivity for those affected. Global data suggests a slightly higher prevalence in females than in males. Today, unambiguous diagnosis of IBS remains challenging due to the absence of a specific biochemical, histopathological, or radiological test. Current diagnosis relies heavily on thorough symptom evaluation. Efforts by the Rome committees have established standardized diagnostic criteria (Rome I-IV), improving consistency and clinical applicability. Recent studies in this framework, seem to have successfully employed metabolomics techniques to identify distinct metabolite profiles in breath and stool samples of IBS patients, differentiating them from healthy controls and those with other functional GI disorders, such as inflammatory bowel disease (IBD). Building on this success, researchers are investigating the presence of similar metabolites in easily accessible biofluids such as urine, potentially offering a less invasive diagnostic approach. Accordingly, this review focuses on key metabolites specifically detected in IBS patients' biological specimens, with a focus on urinary metabolites, using various methods, particularly mass spectrometry (MS)-based techniques, including gas chromatography-MS (GC-MS), liquid chromatography-tandem MS (LC-MS/MS), and capillary electrophoresis-MS (CE-MS) metabolomics assays. These findings may make provision for a new set of non-invasive biomarkers for IBS diagnosis and management.

Associations between various markers of intestinal barrier and immune function after a high-intensity exercise challenge

Strenuous exercise can result in disruption of intestinal barrier function and occurrence of gastrointestinal symptoms. The aim of this exploratory study was to elucidate systemic effects of increased intestinal permeability after high-intensity exercise. Forty-one endurance-trained subjects performed a 60-min treadmill run at 80% VO2max. Small intestinal permeability was measured as urinary excretion ratio of lactulose/rhamnose (L/R). Blood, saliva and feces were analyzed for gut barrier and immune-related biomarkers. The exercise challenge increased several markers of intestinal barrier disruption, immune function and oxidative stress. We found a negative correlation between L/R ratio and uric acid (r = -0.480), as well as a positive correlation between the L/R ratio and fecal chromogranin A in male participants (r = 0.555). No significant correlations were found between any of the markers and gastrointestinal symptoms, however, perceived exertion correlated with the combination of IL-6, IL-10 and salivary cortisol (r = 0.492). The lack of correlation between intestinal permeability and gastrointestinal symptoms could be due to minor symptoms experienced in lab settings compared to real-life competitions. The correlation between L/R ratio and uric acid might imply a barrier-protective effect of uric acid, and inflammatory processes due to strenuous exercise seem to play an important role regarding physical exhaustion.

Enteroendocrine cell regulation of the gut-brain axis

Enteroendocrine cells (EECs) are an essential interface between the gut and brain that communicate signals about nutrients, pain, and even information from our microbiome. EECs are hormone-producing cells expressed throughout the gastrointestinal epithelium and have been leveraged by pharmaceuticals like semaglutide (Ozempic, Wegovy), terzepatide (Mounjaro), and retatrutide (Phase 2) for diabetes and weight control, and linaclotide (Linzess) to treat irritable bowel syndrome (IBS) and visceral pain. This review focuses on role of intestinal EECs to communicate signals from the gut lumen to the brain. Canonically, EECs communicate information about the intestinal environment through a variety of hormones, dividing EECs into separate classes based on the hormone each cell type secretes. Recent studies have revealed more diverse hormone profiles and communication modalities for EECs including direct synaptic communication with peripheral neurons. EECs known as neuropod cells rapidly relay signals from gut to brain via a direct communication with vagal and primary sensory neurons. Further, this review discusses the complex information processing machinery within EECs, including receptors that transduce intraluminal signals and the ion channel complement that govern initiation and propagation of these signals. Deeper understanding of EEC physiology is necessary to safely treat devastating and pervasive conditions like irritable bowel syndrome and obesity.

Psychosocial and Sensory Factors Contribute to Self-Reported Pain and Quality of Life in Young Adults with Irritable Bowel Syndrome

AIMS

Psychosocial and sensory factors, including anxiety, depression, and pressure pain threshold have been used to cluster chronic symptoms in irritable bowel syndrome (IBS). This study examined the contribution of psychosocial sensory factors on pain interference and quality of life (QOL) in this population.

DESIGN

We performed a cross-sectional analysis of baseline data from a randomized controlled trial.

SETTINGS

Two gastrointestinal clinics, general communities, and two large campuses of a public university in the Northeastern United States.

PARTICIPANTS/SUBJECTS

Eighty young adults with IBS aged 21 ± 2.57 years (76.25% female).

METHODS

Demographic and psychosocial factors including anxiety, depression, fatigue, cognition or general concerns, sleep disturbance, self-efficacy, coping, and food intake were measured as independent variables. Quantitative sensory testing was conducted to measure mechanical, thermal, and pressure pain thresholds. Self-reported pain measured by the brief pain inventory (BPI) and IBS-QOL were assessed as the outcome variables. Regression analysis and mediation analysis were conducted to determine the associated factors of IBS pain and QOL.

RESULTS

Age, sex, and psychosocial factors including coping, self-efficacy, alcohol intake, mechanical pain sensitivity, and cold pain threshold were significantly associated with pain interference (all p < 0.05). Coping, and self-efficacy were significantly associated with IBS-QOL (all p < 0.05). In the mediation analysis, coping catastrophizing and self-efficacy were indirectly associated with IBS-QOL mediated by fatigue.

CONCLUSIONS

Psychosocial factors including coping and self-efficacy, and quantitative sensory testing factors significantly correlate with self-reported pain and QOL among young adults with IBS. This preliminary research calls for further interventional studies that target personalized psychosocial and quantitative sensory factors to improve pain management and quality of life in IBS patients.

A combination of fecal calprotectin and human beta-defensin 2 facilitates diagnosis and monitoring of inflammatory bowel disease

Inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) show a large overlap in clinical presentation, which presents diagnostic challenges. As a consequence, invasive and burdensome endoscopies are often used to distinguish between IBD and IBS. Here, we aimed to develop a noninvasive fecal test that can distinguish between IBD and IBS and reduce the number of endoscopies.We used shotgun metagenomic sequencing to analyze the composition and function of gut microbiota of 169 IBS patients, 447 IBD patients and 1044 population controls and measured fecal Calprotectin (FCal), human beta defensin 2 (HBD2), and chromogranin A (CgA) in these samples. These measurements were used to construct training sets (75% of data) for logistic regression and machine learning models to differentiate IBS from IBD and inactive from active IBD. The results were replicated on test sets (remaining 25% of the data) and microbiome data obtained using 16S sequencing.Fecal HBD2 showed high sensitivity and specificity for differentiating between IBD and IBS (sensitivity = 0.89, specificity = 0.76), while the inclusion of microbiome data with biomarkers (HBD2 and FCal) showed a potential for improvement in predictive power (optimal sensitivity = 0.87, specificity = 0.93). Shotgun sequencing-based models produced comparable results using 16S-sequencing data. HBD2 and FCal were found to have predictive power for IBD disease activity (AUC ≈ 0.7).HBD2 is a novel biomarker for IBD in patients with gastro-intestinal complaints, especially when used in combination with FCal and potentially in combination with gut microbiome data.

Physiological mechanisms of unexplained (functional) gastrointestinal disorders

Functional gastrointestinal disorders (FGIDs) encompass a range of complex conditions with similar clinical characteristics and no overt pathology. Recent recognition of sub-clinical pathologies in FGIDs, in conjunction with physiological and biochemical abnormalities including increased intestinal permeability, microbial profile alterations, differences in metabolites and extra-intestinal manifestations of disease, call into question the designation of these conditions as 'functional'. This is despite significant heterogeneity in both symptom profile and specifics of reported physiological abnormalities hampering efforts to determine defined mechanisms that drive onset and chronicity of symptoms. Instead, the literature demonstrates these conditions are disorders of homeostatic imbalance, with disruptions in both host and microbial function and metabolism. This imbalance is also associated with extraintestinal abnormalities including psychological comorbidities and fatigue that may be a consequence of gastrointestinal disruption. Given the exploitation of such abnormalities will be crucial for improved therapeutic selection, an enhanced understanding of the relationship between alterations in function of the gastrointestinal tract and the response of the immune system is of interest in identifying mechanisms that drive FGID onset and chronicity. Considerations for future research should include the role of sex hormones in regulating physiological functions and treatment responses in patients, as well as the importance of high-level phenotyping of clinical, immune, microbial and physiological parameters in study cohorts. There is opportunity to examine the functional contribution of the microbiota and associated metabolites as a source of mechanistic insight and targets for therapeutic modulation.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

DISCUSSION

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

Biomarkers in Irritable Bowel Syndrome: Biological Rationale and Diagnostic Value

BACKGROUND

Patients with irritable bowel syndrome (IBS) usually suffer from nonspecific and overlapping signs that hamper the diagnostic process. In line with this, biomarkers specific for IBS could be of great benefit for diagnosing and managing patients. In IBS, the need is for apparent distinguishing features linked to the disease that improve diagnosis, differentiate from other organic diseases, and discriminate between IBS subtypes.

SUMMARY

Some biomarkers are associated with a possible pathophysiologic mechanism of IBS; others are used for differentiating IBS from non-IBS patients. Implementation of IBS biomarkers in everyday clinical practice is critical for early diagnosis and treatment. However, our knowledge about their efficient use is still scarce. Key Messages: This review discusses the biomarkers implemented for IBS diagnosis and management, such as blood (serum), fecal, immunological, related to the microbiome, microRNAs, and some promising novel biomarkers associated with imaging and psychological features of the disease. We focus on the most commonly studied and validated biomarkers and their biological rationale, diagnostic, and clinical value.

Evidence-based clinical practice guidelines for irritable bowel syndrome 2020

Managing irritable bowel syndrome (IBS) has attracted international attention because single-agent therapy rarely relieves bothersome symptoms for all patients. The Japanese Society of Gastroenterology (JSGE) published the first edition of evidence-based clinical practice guidelines for IBS in 2015. Much more evidence has accumulated since then, and new pharmacological agents and non-pharmacological methods have been developed. Here, we report the second edition of the JSGE-IBS guidelines comprising 41 questions including 12 background questions on epidemiology, pathophysiology, and diagnostic criteria, 26 clinical questions on diagnosis and treatment, and 3 questions on future research. For each question, statements with or without recommendations and/or evidence level are given and updated diagnostic and therapeutic algorithms are provided based on new evidence. Algorithms for diagnosis are requisite for patients with chronic abdominal pain or associated symptoms and/or abnormal bowel movement. Colonoscopy is indicated for patients with one or more alarm symptoms/signs, risk factors, and/or abnormal routine examination results. The diagnosis is based on the Rome IV criteria. Step 1 therapy consists of diet therapy, behavioral modification, and gut-targeted pharmacotherapy for 4 weeks. For non-responders, management proceeds to step 2 therapy, which includes a combination of different mechanistic gut-targeted agents and/or psychopharmacological agents and basic psychotherapy for 4 weeks. Step 3 therapy is for non-responders to step 2 and comprises a combination of gut-targeted pharmacotherapy, psychopharmacological treatments, and/or specific psychotherapy. These updated JSGE-IBS guidelines present best practice strategies for IBS patients in Japan and we believe these core strategies can be useful for IBS diagnosis and treatment globally.

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

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

Prospects for the use of biomarkers in the diagnosis of irritable bowel syndrome

Irritable bowel syndrome is a chronic functional disorder of the intestine, manifested by altered intestinal habits and recurrent abdominal pain in combination with two or more criteria: association with defecation, association with a change in the frequency of defecation, association with a change in the appearance of the stool. To date, IBS remains a diagnosis of exclusion that needs to be differentiated from a wide range of organic diseases. In recent years, a large number of publications have appeared on the research of etiopathogenesis, diagnosis and treatment of IBS. This literary review highlights the problems of searching for biomarkers of IBS as a way to solve the problem of diagnosis of this pathology and understanding the causes of its occurrence.

Irritable Bowel Syndrome between Molecular Approach and Clinical Expertise-Searching for Gap Fillers in the Oxidative Stress Way of Thinking

Irritable bowel syndrome (IBS) remains to date an intriguing functional gastrointestinal disorder. Recent studies described a multitude of exogenous factors that work together in IBS, gradually impairing intestinal lining cellular metabolism, including oxidative status balance, with or without a genetic background. Although the current biomarkers support the differentiation between IBS subtypes and other functional gastrointestinal disorder, they are mostly non-specific, referring to clinical, biochemical, and inflammatory imbalances. Since IBS could be also the result of deficient signaling pathways involving both gastrointestinal secretion and neuro-vegetative stimulation, IBS makes no exception from the oxidative hypothesis in the pathological mechanisms. Regarding the oxidative stress implication in IBS, the previous research efforts showed controversial results, with some animal models and patient studies reporting clear oxidative imbalance both on systemic and local levels, but still with no concrete evidence to point to a direct correlation between oxidative stress and IBS. Additionally, it seems that a major role could be also attributed to gut microbiota and their ability to shape our bodies and behaviors. Moreover, the genetic features study in IBS patients showed that several genetic similarities point to a possible correlation of IBS with affective spectrum disorders. Thus, we focus here the discussion on the assumption that IBS could in fact be more likely a stress-related disorder rather than a gastrointestinal one.

Biomarkers in Stress Related Diseases/Disorders: Diagnostic, Prognostic, and Therapeutic Values

Various internal and external factors negatively affect the homeostatic equilibrium of organisms at the molecular to the whole-body level, inducing the so-called state of stress. Stress affects an organism's welfare status and induces energy-consuming mechanisms to combat the subsequent ill effects; thus, the individual may be immunocompromised, making them vulnerable to pathogens. The information presented here has been extensively reviewed, compiled, and analyzed from authenticated published resources available on Medline, PubMed, PubMed Central, Science Direct, and other scientific databases. Stress levels can be monitored by the quantitative and qualitative measurement of biomarkers. Potential markers of stress include thermal stress markers, such as heat shock proteins (HSPs), innate immune markers, such as Acute Phase Proteins (APPs), oxidative stress markers, and chemical secretions in the saliva and urine. In addition, stress biomarkers also play critical roles in the prognosis of stress-related diseases and disorders, and therapy guidance. Moreover, different components have been identified as potent mediators of cardiovascular, central nervous system, hepatic, and nephrological disorders, which can also be employed to evaluate these conditions precisely, but with stringent validation and specificity. Considerable scientific advances have been made in the detection, quantitation, and application of these biomarkers. The present review describes the current progress of identifying biomarkers, their prognostic, and therapeutic values.

Biomarkers in Stress Related Diseases/Disorders: Diagnostic, Prognostic, and Therapeutic Values

Various internal and external factors negatively affect the homeostatic equilibrium of organisms at the molecular to the whole-body level, inducing the so-called state of stress. Stress affects an organism's welfare status and induces energy-consuming mechanisms to combat the subsequent ill effects; thus, the individual may be immunocompromised, making them vulnerable to pathogens. The information presented here has been extensively reviewed, compiled, and analyzed from authenticated published resources available on Medline, PubMed, PubMed Central, Science Direct, and other scientific databases. Stress levels can be monitored by the quantitative and qualitative measurement of biomarkers. Potential markers of stress include thermal stress markers, such as heat shock proteins (HSPs), innate immune markers, such as Acute Phase Proteins (APPs), oxidative stress markers, and chemical secretions in the saliva and urine. In addition, stress biomarkers also play critical roles in the prognosis of stress-related diseases and disorders, and therapy guidance. Moreover, different components have been identified as potent mediators of cardiovascular, central nervous system, hepatic, and nephrological disorders, which can also be employed to evaluate these conditions precisely, but with stringent validation and specificity. Considerable scientific advances have been made in the detection, quantitation, and application of these biomarkers. The present review describes the current progress of identifying biomarkers, their prognostic, and therapeutic values.

Cumulative Effects of Psychologic Distress, Visceral Hypersensitivity, and Abnormal Transit on Patient-reported Outcomes in Irritable Bowel Syndrome

BACKGROUND & AIMS

Little is known about the link between pathophysiologic factors and symptoms of irritable bowel syndrome (IBS), or whether these factors have cumulative effects on patient-reported outcomes (PROs). We investigated whether pathophysiologic alterations associated with IBS have cumulative or independent effects on PROs.

METHODS

We performed a retrospective analysis of data from 3 cohorts of patients with IBS (n = 407; 74% female; mean age, 36 ± 12 years), based on Rome II or Rome III criteria, seen at a specialized unit for functional gastrointestinal disorders in Sweden from 2002 through 2014. All patients underwent assessments of colonic transit time (radiopaque markers); compliance, allodynia, and hyperalgesia (rectal barostat); anxiety and depression (Hospital Anxiety and Depression scale), as pathophysiologic factors. Dysfunction was defined by available normal values. PROs included IBS symptom severity, somatic symptom severity, and disease-specific quality of life.

RESULTS

Allodynia was observed in 36% of patients, hyperalgesia in 22%, accelerated colonic transit in 18%, delayed transit in 7%, anxiety in 52%, and depression in 24%: each of these factors was associated with severity of at least 1 symptom of IBS. Rectal compliance was not associated with more severe symptoms of IBS. At least 3 pathophysiologic factors were present in 20% of patients, 2 in 30%, 1 in 31%, and none in 18%. With increasing number of pathophysiologic abnormalities, there was a gradual increase in IBS symptom severity (P < .0001) and somatic symptom severity (P < .0001), and a gradual reduction in quality of life (P < .0001).

CONCLUSION

Visceral hypersensitivity, including allodynia and hyperalgesia, abnormal colonic transit, and psychologic factors are all associated with IBS symptoms. These factors have a cumulative effect on gastrointestinal and nongastrointestinal symptoms, as well as on quality of life, in patients with IBS and are therefore relevant treatment targets.

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.

Evidence of increased fecal granins in children with irritable bowel syndrome and correlates with symptoms

BACKGROUND

Granins have been implicated in the pathophysiology of irritable bowel syndrome (IBS) in adults. We sought to determine whether fecal granins are altered in children with IBS and associated with symptoms.

METHODS

Children (7-12 years of age) with IBS and healthy controls (HC) kept daily pain and stool diaries for 2 weeks. Stool samples were analyzed for chromogranins A and B (CgA, CgB) and secretogranins II and III (SgII, SgIII). Children also completed psychological measures to assess anxiety, depression, somatization, and internalizing symptoms.

KEY RESULTS

Fecal CgB and SgIII concentrations were higher in all the boys (IBS plus HC, n = 48) than in all the girls (IBS plus HC, n = 75) (P = 0.02 and P = 0.046, respectively). CgA and SgIII were greater in children with IBS (n = 52) vs HC (n = 69) (P = 0.01, P = 0.017, respectively). CgB and SgII did not differ between groups. In children with IBS, the number of pain episodes per week and mean daily pain rating correlated positively with all four granins. The number of stools per day correlated positively with CgB and SgII, and the percent of diarrheal stools (6 or 7 on the Bristol Scale) correlated inversely with all four granins in boys but not in girls. Fecal granins did not correlate with psychological measures.

CONCLUSIONS AND INFERENCES

As measured by fecal granins, there is evidence of neuroimmune activation in children with IBS. Granins are related to abdominal pain symptoms, stooling frequency, and stool form in children with IBS. Sex influences the fecal concentration of CgB and SgIII.

Fecal chromogranins and secretogranins are linked to the fecal and mucosal intestinal bacterial composition of IBS patients and healthy subjects

Altered fecal levels of chromogranins (Cg) and secretogranins (Sg) are demonstrated in irritable bowel syndrome (IBS), but their role in IBS pathophysiology remains unknown. This study aimed to determine if granins are associated with bacterial composition, immune activation and IBS symptoms. Protein levels of fecal granins (CgA, CgB, SgII and SgIII) were analysed with immunoassays. Mucosal mRNA expression of granins, TPH1 and immune markers were evaluated with RT-qPCR. 16S rRNA gene sequencing was performed on fecal and mucosal bacteria. The intestinal granin profile, based on fecal protein levels and mucosal mRNA expression, could not discriminate between IBS patients (n = 88) and healthy subjects (HS, n = 33). IBS patients dominated by high fecal or mucosal granin levels, respectively, did not differ in symptom or immune profiles. Fecal-dominated and mucosal-dominated granin clusters of IBS patients and HS, demonstrated separate fecal and mucosal bacterial profiles and high fecal abundance of granins were associated with a less diverse bacterial composition and the Bacteroides enterotype. The intestinal granin profiles of IBS patients and HS are linked to the intestinal bacterial composition, diversity and enterotypes. These findings suggest that granins may be one of several host-produced factors regulating the microbiota composition of the intestine.

Pain self-management plus nurse-led support in young adults with irritable bowel syndrome: Study protocol for a pilot randomized control trial

Irritable bowel syndrome (IBS) is a functional gut disorder that typically manifests in early adult years. IBS patients report that pain is the most distressing symptom with the greatest impact on quality of life. Pain-sensitivity genes and the gut microbiome may influence severity of symptoms as well as response to self-management (SM) interventions. Based on current understanding of the science of SM, pain neurophysiology, and the gut-brain axis, our team developed a pain SM intervention to be added to evidence-based self-management instruction to increase the individual's SM knowledge and skills (self-efficacy, self-regulation, and goal-setting). The purpose of this randomized controlled longitudinal pilot study is to examine the feasibility, acceptability, and preliminary effectiveness of the IBS-pain SM intervention on IBS-pain SM behaviors and related health outcomes. A sample of 80 young adults (age 18-29 years old) will be recruited and randomly assigned to the experimental or control group. Both groups will receive 10 electronic video modules focused on IBS-pain SM knowledge and skills. The experimental group also will receive nurse-led one-on-one phone consultations to facilitate monitoring and problem-solving. All participants will be followed over 12 weeks. Primary outcomes will be measured at baseline, 6 weeks, and 12 weeks, including IBS-pain SM behaviors, quality of life, and well-being. The influence of pain-sensitivity genes and the gut microbiome on IBS-pain SM behaviors and health outcomes also will be assessed.

Biomarkers for visceral hypersensitivity in patients with irritable bowel syndrome

BACKGROUND

Increased visceral sensitivity is observed in up to 60% of patients with Irritable Bowel Syndrome (IBS). Mucosal inflammation, altered neuroendocrine activity and intraluminal metabolic processes may contribute to the development of visceral hypersensitivity. Previously, we demonstrated that biomarkers, indicative for these biological processes, were altered in IBS patients compared to healthy controls. However, how these processes relate to visceral hypersensitivity is unknown.

AIM

The aim of this study was to provide insight in biological processes associated with visceral hypersensitivity. Fecal and plasma biomarkers were measured in normosensitive and hypersensitive IBS patients.

METHODS

A total of 167 IBS patients underwent a rectal barostat procedure to assess visceral sensitivity to pain. Based on the outcome, patients were classified into a normosensitive or hypersensitive group. Calprotectin, human β-defensin 2 (HBD2), chromogranin A (CgA), and short chain fatty acids (SCFAs) were measured in feces, citrulline in plasma, and serotonin and its main metabolite 5-hydroxyindoleacetic acid (5-HIAA) in platelet-poor plasma.

KEY RESULTS

Fecal markers and plasma citrulline were measured in 83 hypersensitive and 84 normosensitive patients, while platelet-poor plasma for the assessment of serotonin and 5-HIAA was available for a subgroup, i.e. 53 hypersensitive and 42 normosensitive patients. No statistically significant differences were found in concentrations of biomarkers between groups. Adjustment of the analyses for potential confounders, such as medication use, did not alter this conclusion.

CONCLUSIONS & INFERENCES

Our findings do not support a role for the biological processes as ascertained by biomarkers in visceral hypersensitivity in IBS patients. This study is registered in the US National Library of Medicine (clinicaltrials.gov, NCT00775060).

Biomarkers as a diagnostic tool for irritable bowel syndrome: where are we?

Irritable bowel syndrome (IBS) is a common condition in clinical practice. There are currently no objective tests to rule in the disease, but rather tests to rule out other diseases. Biomarkers in IBS may provide the tools needed for diagnosis, prognosis and therapy. These include identification of differences in microbial composition, immune activation, bile acid composition, colonic transit, and alteration in sensation in subgroups of IBS patients. Areas covered: Studies included in our review were chosen based on a PubMed search for 'biomarkers' and 'IBS'. We have reviewed the literature on biomarkers to appraise their accuracy, validity and whether they are actionable. We have not covered genetic associations as biomarkers in this review. Expert commentary: There is significant promise in the usefulness of biomarkers for IBS. The most promising actionable biomarkers are markers of changes in bile acid balance, such as elevated bile acid in the stool, and altered colonic transit. However, there is also potential for microbial studies and mucosal proteases as future actionable biomarkers.

Derivation and validation of a diagnostic test for irritable bowel syndrome using latent class analysis

BACKGROUND

The accuracy of symptom-based diagnostic criteria for irritable bowel syndrome (IBS) is modest.

AIMS

To derive and validate a new test that utilises latent class analysis.

METHODS

Symptom, colonoscopy, and histology data were collected from 1981 patients and 360 patients in two cohorts referred to secondary care for investigation of their gastrointestinal symptoms in Canada and the UK, respectively. Latent class analysis was used to identify naturally occurring clusters in patient-reported symptoms in the Canadian dataset, and the latent class model derived from this was then applied to the UK dataset in order to validate it. Sensitivity, specificity, and positive and negative likelihood ratios (LRs) were calculated for the latent class models.

RESULTS

In the Canadian cohort, the model had a sensitivity of 44.7% (95% CI 40.0-50.0) and a specificity of 85.3% (95% CI 83.4-87.0). Positive and negative LRs were 3.03 (95% CI 2.57-3.56) and 0.65 (95% CI 0.59-0.71) respectively. A maximum positive LR of 3.93 was achieved following construction of a receiver operating characteristic curve. The performance in the UK cohort was similar, with a sensitivity and specificity of 52.5% (95% CI 42.2-62.7) and 84.3% (95% CI 79.3-88.6), respectively. Positive and negative LRs were 3.35 (95% CI 2.38-4.70) and 0.56 (95% CI 0.45-0.68), respectively, with a maximum positive LR of 4.15.

CONCLUSIONS

A diagnostic test for IBS, utilising patient-reported symptoms incorporated into a latent class model, performs as accurately as symptom-based criteria. It has potential for improvement via addition of clinical markers, such as coeliac serology and faecal calprotectin.

Pathophysiology, Evaluation, and Management of Chronic Watery Diarrhea

Chronic watery diarrhea poses a diagnostic and therapeutic challenge and is often a disabling condition for patients. Although acute diarrhea is likely to be caused by infection, the causes of chronic diarrhea (>4 weeks in duration) are more elusive. We review the pathophysiology, diagnosis, and treatment of chronic diarrhea. Drawing on recent insights into the molecular mechanisms of intestinal epithelial transport and barrier function, we discuss how diarrhea can result from a decrease in luminal solute absorption, an increase in secretion, or both, as well as derangements in barrier properties. We also describe the various extraepithelial factors that activate diarrheal mechanisms. Finally, clinical evaluation and tests used in the assessment of patients presenting with chronic diarrhea are reviewed, and an algorithm guiding therapeutic decisions and pharmacotherapy is presented.

Biomarkers of Irritable Bowel Syndrome

Traditionally, irritable bowel syndrome (IBS) has not been regarded as an organic disease, and the pathophysiology of IBS is heterogeneous. Currently, the diagnosis of IBS is based upon the Rome diagnostic criteria. The performance of these criteria is only modest in predicting IBS, and moreover their validation is lacking. Additionally, as functional symptoms are common in the general population, healthy controls or volunteers are difficult to define and there is currently no definition of “normal” in the Rome criteria. Due to the weaknesses of the current diagnostic criteria, patients and doctors expect new gold standard diagnostic tools. Various etiologic mechanisms result in potential biomarkers. The focus of this research has been to find non-invasive biomarkers from serum, breath gas, and fecal materials. Though biomarkers should be based on biological and pathogenic processes, most biomarkers for IBS have been developed to identify organic diseases and therefore eliminate IBS. To date, these types of biomarkers for IBS have been disappointing. The purposes of developing biomarkers include improvement of diagnosis, differentiation from other organic diseases, and discrimination of IBS subtypes. A true mechanistic biomarker would make it possible to rule in IBS, rather than to rule out other organic diseases. New serologic biomarkers for diarrhea-predominant IBS have been introduced based on the pathophysiologic findings from a rat model and validation in a large-scale clinical trial. Further investigations of abnormal organic findings from each subtype of IBS would enable the development of new, simple subtype-specific biomarkers.

Irritable Bowel Syndrome: Pathophysiology and Current Therapeutic Approaches

Irritable bowel syndrome (IBS) is a prevalent condition affecting 10-20% of adults in most countries; IBS results in significant morbidity and health care costs. IBS is a disorder of the brain-gut axis, and recent insights into the pathophysiological mechanisms include altered bile acid metabolism, neurohormonal regulation, immune dysfunction, alterations in the epithelial barrier, and secretory properties of the gut. There remains a significant unmet need for effective treatments, particularly for the pain component of IBS, although the introduction of drugs directed at secretion, motility, and a nonabsorbable antibiotic provides an option for the bowel dysfunction in IBS.

Underlying molecular and cellular mechanisms in childhood irritable bowel syndrome

Irritable bowel syndrome (IBS) affects a large number of children throughout the world. The symptom expression of IBS is heterogeneous, and several factors which may be interrelated within the IBS biopsychosocial model play a role. These factors include visceral hyperalgesia, intestinal permeability, gut microbiota, psychosocial distress, gut inflammation, bile acids, food intolerance, colonic bacterial fermentation, and genetics. The molecular and cellular mechanisms of these factors are being actively investigated. In this mini-review, we present updates of these mechanisms and, where possible, relate the findings to childhood IBS. Mechanistic elucidation may lead to the identification of biomarkers as well as personalized childhood IBS therapies.

[Current Status of Translational Research on Irritable Bowel Syndrome]

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder. The pathophysiology of IBS is not completely understood. Genetic, immune, environmental, inflammatory, neurological and psychological factors contribute to the risk of this condition. Traditional research explored gastrointestinal motor abnormalities, central neural dysregulation, abnormal psychological features, and visceral hypersensitivity. More recent investigations consider bacterial overgrowth, abnormal serotonin pathways, altered gut flora, immune activation and mucosal inflammation. The purpose of this article is to review recent translational research concerning the pathophysiology, biomarker and genetic factors of IBS and to encourage IBS research in Korea.

Pilot study of small bowel mucosal gene expression in patients with irritable bowel syndrome with diarrhea

Prior studies in with irritable bowel syndrome with diarrhea (IBS-D) patients showed immune activation, secretion, and barrier dysfunction in jejunal or colorectal mucosa. We measured mRNA expression by RT-PCR of 91 genes reflecting tight junction proteins, chemokines, innate immunity, ion channels, transmitters, housekeeping genes, and controls for DNA contamination and PCR efficiency in small intestinal mucosa from 15 IBS-D and 7 controls (biopsies negative for celiac disease). Fold change was calculated using 2((-ΔΔCT)) formula. Nominal P values (P < 0.05) were interpreted with false detection rate (FDR) correction (q value). Cluster analysis with Lens for Enrichment and Network Studies (LENS) explored connectivity of mechanisms. Upregulated genes (uncorrected P < 0.05) were related to ion transport (INADL, MAGI1, and SONS1), barrier (TJP1, 2, and 3 and CLDN) or immune functions (TLR3, IL15, and MAPKAPK5), or histamine metabolism (HNMT); downregulated genes were related to immune function (IL-1β, TGF-β1, and CCL20) or antigen detection (TLR1 and 8). The following genes were significantly upregulated (q < 0.05) in IBS-D: INADL, MAGI1, PPP2R5C, MAPKAPK5, TLR3, and IL-15. Among the 14 nominally upregulated genes, there was clustering of barrier and PDZ domains (TJP1, TJP2, TJP3, CLDN4, INADL, and MAGI1) and clustering of downregulated genes (CCL20, TLR1, IL1B, and TLR8). Protein expression of PPP2R5C in nuclear lysates was greater in patients with IBS-D and controls. There was increase in INADL protein (median 9.4 ng/ml) in patients with IBS-D relative to controls (median 5.8 ng/ml, P > 0.05). In conclusion, altered transcriptome (and to lesser extent protein) expression of ion transport, barrier, immune, and mast cell mechanisms in small bowel may reflect different alterations in function and deserves further study in IBS-D.

A novel biomarker panel for irritable bowel syndrome and the application in the general population

Biological markers that measure gut health and diagnose functional gastro-intestinal (GI) disorders, such as irritable bowel syndrome (IBS), are lacking. The objective was to identify and validate a biomarker panel associated with the pathophysiology of IBS that discriminates IBS from healthy controls (HC), and correlates with GI symptom severity. In a case-control design, various plasma and fecal markers were measured in a cohort of 196 clinical IBS patients and 160 HC without GI symptoms. A combination of biomarkers, which best discriminates between IBS and HC was identified and validated in an independent internal validation set and by permutation testing. The correlation between the biomarker panel and GI symptom severity was tested in IBS patients and in a general population cohort of 958 subjects. A set of 8 biomarker panel was identified to discriminate IBS from HC with high sensitivity (88.1%) and specificity (86.5%). The results for the IBS subtypes were comparable. Moreover, a moderate correlation was found between the biomarker panel and GI symptom scores in the IBS (r = 0.59, p < 0.001) and the general population cohorts (r = 0.51, p = 0.003). A novel multi-domain biomarker panel has been identified and validated, which correlated moderately to GI symptom severity in IBS and general population subjects.

Population-based metagenomics analysis reveals markers for gut microbiome composition and diversity

Deep sequencing of the gut microbiomes of 1135 participants from a Dutch population-based cohort shows relations between the microbiome and 126 exogenous and intrinsic host factors, including 31 intrinsic factors, 12 diseases, 19 drug groups, 4 smoking categories, and 60 dietary factors. These factors collectively explain 18.7% of the variation seen in the interindividual distance of microbial composition. We could associate 110 factors to 125 species and observed that fecal chromogranin A (CgA), a protein secreted by enteroendocrine cells, was exclusively associated with 61 microbial species whose abundance collectively accounted for 53% of microbial composition. Low CgA concentrations were seen in individuals with a more diverse microbiome. These results are an important step toward a better understanding of environment-diet-microbe-host interactions.

The influence of a short-term gluten-free diet on the human gut microbiome

Background

A gluten-free diet (GFD) is the most commonly adopted special diet worldwide. It is an effective treatment for coeliac disease and is also often followed by individuals to alleviate gastrointestinal complaints. It is known there is an important link between diet and the gut microbiome, but it is largely unknown how a switch to a GFD affects the human gut microbiome.

Methods

We studied changes in the gut microbiomes of 21 healthy volunteers who followed a GFD for four weeks. We collected nine stool samples from each participant: one at baseline, four during the GFD period, and four when they returned to their habitual diet (HD), making a total of 189 samples. We determined microbiome profiles using 16S rRNA sequencing and then processed the samples for taxonomic and imputed functional composition. Additionally, in all 189 samples, six gut health-related biomarkers were measured.

Results

Inter-individual variation in the gut microbiota remained stable during this short-term GFD intervention. A number of taxon-specific differences were seen during the GFD: the most striking shift was seen for the family Veillonellaceae (class Clostridia), which was significantly reduced during the intervention (p = 2.81 × 10⁻⁰⁵). Seven other taxa also showed significant changes; the majority of them are known to play a role in starch metabolism. We saw stronger differences in pathway activities: 21 predicted pathway activity scores showed significant association to the change in diet. We observed strong relations between the predicted activity of pathways and biomarker measurements.

Conclusions

A GFD changes the gut microbiome composition and alters the activity of microbial pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-016-0295-y) contains supplementary material, which is available to authorized users.

Gut microbiota as potential orchestrators of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a multifactorial functional disorder with no clearly defined etiology or pathophysiology. Modern culture-independent techniques have improved the understanding of the gut microbiota’s composition and demonstrated that an altered gut microbiota profile might be found in at least some subgroups of IBS patients. Research on IBS from a microbial perspective is gaining momentum and advancing. This review will therefore highlight potential links between the gut microbiota and IBS by discussing the current knowledge of the gut microbiota; it will also illustrate bacterial-host interactions and how alterations to these interactions could exacerbate, induce or even help alleviate IBS.

Systematic review with meta-analysis: the accuracy of diagnosing irritable bowel syndrome with symptoms, biomarkers and/or psychological markers

BACKGROUND

Irritable bowel syndrome (IBS) is a complex, heterogeneous disease which can be challenging to diagnose. No study has identified and assessed the accuracy of all available methods of diagnosing IBS.

AIM

To conduct a systematic review of the literature to identify and assess accuracy of symptom-based diagnostic criteria, biomarkers, psychological markers or combinations thereof.

METHODS

MEDLINE, EMBASE and EMBASE Classic were searched (until April 2015) to identify studies reporting accuracy of available methods to diagnose IBS in adult populations. Eligible studies assessed accuracy of these diagnostic tests against an accepted reference standard. Data were extracted to calculate positive and negative likelihood ratios, with 95% confidence intervals (CIs), of the diagnostic test utilised. Where more than one study used the same test, data were pooled in a meta-analysis.

RESULTS

Twenty-two studies (7106 patients) were eligible. Positive and negative likelihood ratios of the current gold standard, the Rome III criteria, were 3.35 (95% CI: 2.97-3.79) and 0.39 (95% CI: 0.34-0.46), similar to other symptom-based criteria. Eleven biomarkers performed no better than symptom-based criteria. Psychological markers performed well in one study. Five different combinations were assessed. The best in terms of positive likelihood ratio was faecal calprotectin, intestinal permeability and Rome I criteria (26.4; 95% CI: 11.4-61.9), and in terms of negative likelihood ratio serum-based biomarkers and psychological markers (0.18; 95% CI: 0.12-0.25).

CONCLUSIONS

Symptom-based diagnostic criteria, biomarkers and psychological markers performed modestly in predicting IBS. Combining symptoms with markers appears more effective, and may represent the way forward in the diagnosis of IBS.

Immunological Biomarkers in Postinfectious Irritable Bowel Syndrome

BACKGROUND

There is a recognized need for biological markers to facilitate diagnoses of irritable bowel syndrome (IBS) and to distinguish it from other functional and organic disorders. As postinfectious IBS (PI-IBS) is believed to account for as many as one third of all IBS cases, here we sought to identify differences in specific cytokines and serologic responses across patients with idiopathic IBS and PI-IBS and healthy controls.

METHODS

At total of 120 US military personnel were identified from the Defense Medical Surveillance System-based International Classification of Diseases, 9th Revision, Clinical Modification (ICD9-CM) codes recorded during medical encounters and were grouped based on infectious gastroenteritis (IGE) episode (Shigella, Campylobacter, Salmonella, or an unspecified pathogen) followed by IBS, IBS without antecedent IGE, or IGE without subsequent IBS within 2 years of the IGE exposure. Sera from subjects were assayed for cytokine levels and antibodies against a panel of microbiome antigens.

RESULTS

In total, 10 of 118 markers considered were shown to differ between IBS patients and healthy controls, including cytokines interleukin-6 (IL-6), IL-8, IL-1β, and macrophage inflammatory protein-1β (MIP-1β), as well as antibody responses to microbial antigens. Antimicrobial antibody response profiles also differed between PI-IBS cases compared with IBS cases without an antecedent episode of acute IGE. Comparisons also suggest that immunoglobulin A (IgA) and IgG profiles may point to pathogen-specific origins among PI-IBS cases.

CONCLUSION

Taken together, these results provide further evidence as to the molecular distinctness of classes of IBS cases and that serum biomarkers may prove useful in elucidating their pathobiological pathways.

Colonic mucosal gene expression and genotype in irritable bowel syndrome patients with normal or elevated fecal bile acid excretion

The mucosal gene expression in rectosigmoid mucosa (RSM) in irritable bowel syndrome with diarrhea (IBS-D) is unknown. Our objectives were, first, to study mRNA expression [by RT(2) PCR of 19 genes pertaining to tight junctions, immune activation, intestinal ion transport and bile acid (BA) homeostasis] in RSM in IBS-D patients (n = 47) and healthy controls (n = 17) and study expression of a selected protein (PDZD3) in 10 IBS-D patients and 4 healthy controls; second, to assess RSM mRNA expression according to genotype and fecal BA excretion (high ≥ 2,337 μmol/48 h); and third, to determine whether genotype or mucosal mRNA expression is associated with colonic transit or BA parameters. Fold changes were corrected for false detection rate for 19 genes studied (P < 0.00263). In RSM in IBS-D patients compared with controls, mRNA expression of GUC2AB, PDZD3, and PR2Y4 was increased, whereas CLDN1 and FN1 were decreased. One immune-related gene was upregulated (C4BP4) and one downregulated (CCL20). There was increased expression of a selected ion transport protein (PDZD3) on immunohistochemistry and Western blot in IBS-D compared with controls (P = 0.02). There were no significant differences in mucosal mRNA in 20 IBS-D patients with high compared with 27 IBS-D patients with normal BA excretion. GPBAR1 (P < 0.05) was associated with colonic transit. We concluded that mucosal ion transport mRNA (for several genes and PDZD3 protein) is upregulated and barrier protein mRNA downregulated in IBS-D compared with healthy controls, independent of genotype. There are no differences in gene expression in IBS-D with high compared with normal fecal BA excretion.

Fecal Calprotectin and serum chromogranin A as potential biomarkers of irritable bowel syndrome symptom severity

Irritable bowel syndrome (IBS) is a disorder of the lower gastrointestinal (GI) tract, which manifests as abdominal pain and/or discomfort accompanied by altered bowel function, in the absence of structural pathology. The onset and precipitation of IBS is the result of an interaction among several factors, including psychological distress, altered GI sensation and processing of sensory information as well as GI inflammation. These factors have varying contributions to disorder etiology in different patients, and in line with that, there is now emerging evidence about a low-grade inflammation in a subgroup of IBS patients. Because IBS diagnosis is based on the ROME III criteria, with the exclusion of structural pathology, patients are often exposed to numerous invasive and unpleasant tests. In order to decrease the cost of repeated testing, while simultaneously alleviating patients' anxiety, research should be aimed at detecting cost-effective biomarkers. We hypothesize chromogranin A (CgA) and fecal Calprotectin (FC) could be used to eliminate possible organic causes of IBS symptoms. Also, we hypothesize FC could be helpful in detecting IBS patients with low-grade inflammation. Forty-eight outpatients with IBS (76% females) completed a set of psychosocial measures (HRQoL, STAI, BDI, VSI, SF-36), and their FC and CgA levels were obtained. We found elevated CgA levels in 4 patients, but CgA levels were not related to any of the psychological measures used. Elevated FC levels were found in 12 patients. FC levels significantly correlated with the physical component of health related quality of life (HRQoL) (r48=-.42, p<.01). In addition, one-way ANOVA's were performed to test possible differences in psychosocial measures depending on the patient's FC status. The analysis showed only one significant difference. Patients with the highest levels of FC had significantly lower physical component of HRQoL compared to the other two groups of patients.

Diagnosis of Irritable Bowel Syndrome: Role of Potential Biomarkers

Irritable bowel syndrome is a disorder diagnosed on symptom-based criteria without inclusion of any objective parameter measurable by known diagnostic methods. Heterogeneity of the disorder and overlapping with more serious organic diseases increase uncertainty for the physician's work and increase the cost of confirming the diagnosis. This paper is an attempt to summarize the efforts to find adequate biomarkers for irritable bowel syndrome, which should shorten the time to diagnosis and reduce the cost. Most of the reviewed papers were observational studies from secondary care institutions. Since publication of the Rome III criteria in 2006, most recent studies use these for the recruitment of IBS patients. This is a positive step forward as future studies should use the same criteria, facilitating comparison of their results. Among the studied biomarkers, most evidence is provided for fecal calprotectin. Cutoff values for fecal calprotectin have still to be investigated prior to inclusion in the irritable bowel syndrome diagnostic algorithm.

Intestinal secretory mechanisms in irritable bowel syndrome-diarrhea

Although diarrhea is the predominant bowel dysfunction in as many as one-third of patients with irritable bowel syndrome (IBS), it is unclear whether there is a specific disorder of intestinal fluid or electrolyte secretion in IBS. Diarrhea is generally considered a result of accelerated colonic transit in patients with IBS. Although a primary secretory diathesis has not been well-documented in patients with IBS with diarrhea (IBS-D), several mechanisms that could potentially contribute to intestinal secretion have been reported. Some of these mechanisms also influence motor and secretory dysfunctions that contribute to the pathophysiology of IBS-D. We review the evidence supporting secretion in IBS-D caused by peptides and amines produced by enteroendocrine cells or submucosal neurons, enterocyte secretory processes, and intraluminal factors (bile acids and short-chain fatty acids). Understanding these mechanisms and developing clinical methods for their identification could improve management of patients with IBS-D.

Crosstalk at the mucosal border: importance of the gut microenvironment in IBS

The aetiology and pathology of IBS, a functional bowel disorder thought to lack an organic cause, is largely unknown. However, studies suggest that various features, such as altered composition of the gut microbiota, together with increased intestinal permeability, a changed balance in the enteroendocrine system and a dysregulated immune system in the gut, most likely have an important role in IBS. Exactly how these entities act together and give rise to symptoms is still unknown, but an altered gut microbiota composition could lead to dysregulation of the intestinal barrier as well as the enteroendocrine and the immune systems, which (through interactions with the nervous system) might generate symptoms. This Review highlights the crosstalk between the gut microbiota, the enteroendocrine system, the immune system and the role of intestinal permeability in patients with IBS.

The quest for biomarkers in IBS-where should it lead us?

Irritable bowel syndrome (IBS) is a prevalent functional gastrointestinal disorder which represents a major cost to health-care services. The diagnosis of IBS is currently performed by means of symptom-based diagnostic criteria, but there has been an ongoing interest in developing biomarkers which could simplify the diagnosis and/or evaluating the effect of treatments. This article reviews the current literature concerning the proposed biomarkers including those of altered gut motility, of visceral hypersensitivity, of abnormal brain mechanisms, of serum, fecal and mucosal inflammation and of increased intestinal permeability.

Validating biomarkers of treatable mechanisms in irritable bowel syndrome

BACKGROUND

A valid biomarker is 'an indicator of normal biologic or pathogenic processes, or pharmacological responses to a therapeutic intervention'. There is no validated biomarker for irritable bowel syndrome (IBS). The aim of the study was to assess ability of three quantitative traits to identify treatable processes to discriminate between IBS-diarrhea (IBS-D) patients, IBS-constipation (IBS-C) patients and healthy volunteers (HV).

METHODS

In 30 HV, 30 IBS-C patients and 64 IBS-D patients, we characterized bowel symptoms and quantitated pathophysiological mechanisms: bile acid (BA) synthesis (serum C4 and FGF19), fecal BA and fat, colonic transit (CT), and intestinal permeability (IP). We used multiple logistic regression and receiver-operating characteristic (ROCAUC ) to appraise three factors (fecal BA, CT, and IP) individually and in combination to identify discriminant targets for treatment in IBS.

KEY RESULTS

There were significant associations between the three subgroups and symptoms reflecting bowel function and the quantitative traits. There were significant associations between fecal BA and CT at 48 h (r = 0.43; p < 0.001) and between fecal BA and IP (r = 0.23; p = 0.015). Individually, fecal BA and CT48 (but not IP) were significant independent predictors for distinguishing HV from IBS. In combination, they discriminated HV from IBS-D patients (ROCAUC 0.70), HV from IBS-C patients (ROCAUC 0.73), and IBS-C patients from IBS-D patients (ROCAUC 0.86). Colonic transit and fecal BA excretion together discriminate between healthy volunteers and IBS-C patients or IBS-D patients, or between the IBS subgroups with 75-90% specificity at 60% sensitivity.

CONCLUSIONS & INFERENCES

Colonic transit and fecal BA individually and together constitute useful biomarkers to identify treatable mechanisms in IBS and to differentiate subgroups of IBS.

Diagnosis of IBS: symptoms, symptom-based criteria, biomarkers or 'psychomarkers'?

IBS is estimated to have a prevalence of up to 20% in Western populations and results in substantial costs to health-care services worldwide, estimated to be US$1 billion per year in the USA. IBS remains difficult to diagnose due to its multifactorial aetiology, heterogeneous nature and overlap of symptoms with organic pathologies, such as coeliac disease and IBD. As a result, IBS often continues to be a diagnosis of exclusion, resulting in unnecessary investigations. Available methods for the diagnosis of IBS-including the current gold standard, the Rome III criteria-perform only moderately well. Visceral hypersensitivity and altered pain perception do not discriminate between IBS and other functional gastrointestinal diseases or health with any great accuracy. Attention has now turned to developing novel biomarkers and using psychological markers (so-called psychomarkers) to aid the diagnosis of IBS. This Review describes how useful symptoms, symptom-based criteria, biomarkers and psychomarkers, and indeed combinations of all these approaches, are in the diagnosis of IBS. Future directions in diagnosing IBS could include combining demographic data, gastrointestinal symptoms, biomarkers and psychomarkers using statistical methods. Latent class analysis to distinguish between IBS and non-IBS symptom profiles might also represent a promising avenue for future research.

RNA sequencing shows transcriptomic changes in rectosigmoid mucosa in patients with irritable bowel syndrome-diarrhea: a pilot case-control study

Our aim was to conduct a pilot case-control study of RNA expression profile using RNA sequencing of rectosigmoid mucosa of nine females with -diarrhea-predominant irritable bowel syndrome (IBS-D) with accelerated colonic transit and nine female healthy controls. Mucosal total RNA was isolated and purified, and next-generation pair-end sequencing was performed using Illumina TruSeq. Analysis was carried out using a targeted approach toward 12 genes previously associated with IBS and a hypothesis-generating approach. Of the 12 targeted genes tested, patients with IBS-D had decreased mRNA expression of TNFSF15 (fold change controls to IBS-D: 1.53, P = 0.01). Overall, up- and downregulated mRNA expressions of 21 genes (P = 10(-5) to 10(-8); P values with false detection rates are shown) were potentially relevant to IBS-D including the following: neurotransmitters [P2RY4 (P = 0.001), vasoactive intestinal peptide (VIP, P = 0.02)]; cytokines [CCL20 (P = 0.019)]; immune function [C4BPA complement cascade (P = 0.0187)]; interferon-related [IFIT3 (P = 0.016)]; mucosal repair and cell adhesion [trefoil protein (TFF1, P = 0.012)], retinol binding protein [RBP2 (P = 0.017)]; fibronectin (FN1, P = 0.009); and ion channel functions [guanylate cyclase (GUCA2B, P = 0.017), PDZ domain-containing protein 3 (PDZD3, P = 0.029)]. Ten genes associated with functions related to pathobiology of IBS-D were validated by RT-PCR. There was significant correlation in fold changes of the selected genes (Rs = 0.73, P = 0.013). Up- or downregulation of P2RY4, GUC2AB, RBP2, FNI, and C4BPA genes were confirmed on RT-PCR, which also revealed upregulation of farnesoid X receptor (FXR) and apical sodium-coupled bile acid transporter (IBAT/ASBT). RNA-Seq and RT-PCR analysis of rectosigmoid mucosa in IBS-D show transcriptome changes that provide the rationale for validation studies to explore the role of mucosal factors in the pathobiology of IBS-D.

Physiological underpinnings of irritable bowel syndrome: neurohormonal mechanisms

The gastrointestinal tract is a vast neuroendocrine organ with extensive extrinsic and intrinsic neural circuits that interact to control its function. Circulating and paracrine hormones (amine and peptide) provide further control of secretory, absorptive, barrier, motor and sensory mechanisms that are essential to the digestion and assimilation of nutrients, and the transport and excretion of waste products. Specialized elements of the mucosa (including enteroendocrine cells, enterocytes and immune cells) and the microbiome interact with other intraluminal contents derived from the diet, and with endogenous chemicals that alter the gut's functions. The totality of these control mechanisms is often summarized as the brain-gut axis. In irritable bowel syndrome (IBS), which is the most common gastrointestinal disorder, there may be disturbances at one or more of these diverse control mechanisms. Patients present with abdominal pain in association with altered bowel function. This review documents advances in understanding the pathophysiological mechanisms in the brain-gut axis in patients with IBS. It is anticipated that identification of one or more disordered functions in clinical practice will usher in a renaissance in the management of IBS, leading to effective therapy tailored to the needs of the individual patient.

Irritable bowel syndrome: Emerging paradigm in pathophysiology

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders, characterized by abdominal pain, bloating, and changes in bowel habits. These symptoms cannot be explained by structural abnormalities and there is no specific laboratory test or biomarker for IBS. Therefore, IBS is classified as a functional disorder with diagnosis dependent on the history taking about manifested symptoms and careful physical examination. Although a great deal of research has been carried out in this area, the pathophysiology of IBS is complex and not completely understood. Multiple factors are thought to contribute to the symptoms in IBS patients; altered gastrointestinal motility, visceral hypersensitivity, and the brain-gut interaction are important classical concepts in IBS pathophysiology. New areas of research in this arena include inflammation, postinfectious low-grade inflammation, genetic and immunologic factors, an altered microbiota, dietary factors, and enteroendocrine cells. These emerging studies have not shown consistent results, provoking controversy in the IBS field. However, certain lines of evidence suggest that these mechanisms are important at least a subset of IBS patients, confirming that IBS symptoms cannot be explained by a single etiological mechanism. Therefore, it is important to keep in mind that IBS requires a more holistic approach to determining effective treatment and understanding the underlying mechanisms.

Diagnostic utility of faecal biomarkers in patients with irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal (GI) disorder characterized by unspecific symptoms. In clinical practice it is crucial to distinguish between non-inflammatory functional problems and inflammatory, malignant or infectious diseases of the GI tract. Differentiation between these involves the use of clinical, radiological, endoscopic, histological and serological techniques, which are invasive, expensive, time-consuming and/or hindered by inaccuracies arising from subjective components. A range of faecal markers now appears to have the potential to greatly assist in the differentiation of inflammatory bowel disease (IBD) and IBS. Faecal markers of neutrophil influx into the mucosa are reliable indicators of intestinal inflammation and their role has been mainly studied in discriminating IBD from non-IBD conditions (including IBS) rather than organic from non-organic diseases. Phagocyte-specific proteins of the S100 family (S100A12, calprotectin) are amongst the most promising faecal biomarkers of inflammation. Faecal leukocyte degranulation markers (lactoferrin, polymorphonuclear elastase and myeloperoxidase) have also been suggested as diagnostic tools for the differentiation of IBD and IBS. More recently, additional proteins, including granins, defensins and matrix-metalloproteases, have been discussed as differential diagnostic markers in IBD and IBS. In this review, some of the most promising faecal markers, which have the potential to differentiate IBD and IBS and to advance diagnostic practices, will be discussed.

Fecal chromogranins and secretogranins are increased in patients with ulcerative colitis but are not associated with disease activity

BACKGROUND

Little is known of the importance of chromogranins (Cg) and secretogranins (Sg) in ulcerative colitis (UC). We therefore investigated fecal levels of CgA, CgB, SgII and SgIII, and their association with inflammatory activity, disease duration and medical therapy in UC.

METHODS

Analyses of CgA, CgB, SgII, SgIII and calprotectin in stool samples from 41 UC patients and 29 healthy controls were performed. Two stool samples, during relapse and remission, respectively, were obtained from each UC patient.

RESULTS

The levels of fecal CgA and SgII were higher in UC patients with active disease as compared to healthy controls. CgB and SgII were positively correlated with disease duration, but none of the granins were positively correlated with calprotectin, Mayo score, CRP or serum concentrations of TNF in UC patients with active disease. Also UC patients in remission had higher levels of CgA, CgB, SgII, and SgIII as compared to healthy controls. However, levels of fecal CgA, CgB, SgII and SgIII were lower during active disease relative to remission. Moreover, fecal levels of CgA and SgII were higher in UC patients in remission treated with thiopurines than in thiopurine-naïve patients in remission.

CONCLUSION

Fecal chromogranins and secretogranins are increased in UC but are not associated with disease activity, but seem to increase with duration of the disease. Thus, fecal granins might reflect structural changes associated with chronicity of disease, or medical therapy.

Refractory inflammatory bowel disease-could it be an irritable bowel?

Patients with IBD who are apparently in remission-as indicated by normal blood tests, endoscopic findings and ultrasonography results-often continue to experience symptoms. Furthermore, despite these negative findings, there is a temptation to increase their anti-inflammatory medication in the hope that this approach would lead to some improvement. However, this strategy often seems to fail and can sometimes lead to adverse events. Consequently, when evidence of continuing inflammatory activity is lacking it might be appropriate to consider the possibility of co-existent IBS in these patients and to treat them for this condition. Dietary manipulation, antispasmodic agents, antidepressants (especially of the tricyclic variety) and even behavioural treatments might result in a worthwhile improvement of symptoms.