Corticotropin-releasing hormone receptor 1 gene variants in irritable bowel syndrome

Single Nucleotide Polymorphisms, Associated with Increased Risk of Irritable Bowel Syndrome with Predominant Constipation: A Meta Analysis

Introduction. Genetic predisposition in combination with environmental factors and the patient’s psychological and emotional state play a key role in the development of irritable bowel syndrome (IBS). Studies of association between genetic polymorphisms and IBS can help in understanding the key pathophysiological mechanisms. To date, 11 meta-analyses on this issue have been published, however, none of them comprehensively summarize the data on the prevalence of genetic polymorphisms in IBS with predominant constipation (IBS-C).

Aim: to summarize the published data on the impact of genetic polymorphisms on the risk of IBS-C.

Materials and methods. A literature search was performed in the PubMed and Scopus databases. Identified studies were used for a meta-analysis according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Publications investigating genetic polymorphisms in patients with IBS-C were included in this analysis.

Results. A total of 34 studies met the inclusion criteria. The collected data were sufficient to conduct a meta-analysis on polymorphisms of three of the listed genes: SLC6A4 (10 articles), GNB3 (5 articles), ADRA2A (4 articles). No significant association was found between the SLC6A4 (5-HTTLPR) polymorphism, GNB3 c.825C > T (rs5443) polymorphism and either IBS or IBS-C. It was found that ADRA2A 1291C>G polymorphism was significantly associated with both IBS and IBS-C.

Conclusions. Our meta-analysis revealed that ADRA2A 1291C>G polymorphism was significantly associated with both IBS and IBS-C in the mixed population. Neither homozygous nor heterozygous variants of the SLC6A4 (5-HTTLPR) polymorphism and GNB3 C825T polymorphism were associated with either IBS-C or IBS as a whole.

Neural circuits regulating visceral pain

Visceral hypersensitivity, a common clinical manifestation of irritable bowel syndrome, may contribute to the development of chronic visceral pain, which is a major challenge for both patients and health providers. Neural circuits in the brain encode, store, and transfer pain information across brain regions. In this review, we focus on the anterior cingulate cortex and paraventricular nucleus of the hypothalamus to highlight the progress in identifying the neural circuits involved in visceral pain. We also discuss several neural circuit mechanisms and emphasize the importance of cross-species, multiangle approaches and the identification of specific neurons in determining the neural circuits that control visceral pain.

Gene polymorphisms and serum levels of BDNF and CRH in vitiligo patients

Background

Vitiligo is one of the most common hypomelanoses, in which the destruction of functioning melanocytes causes depigmentation of the skin, hair and mucous membranes. The genes encrypting brain-derived neurotrophic factor (BDNF) and corticotropin releasing hormone (CRH) might be the conceivable contributors to the development of vitiligo. This study was aimed at investigation of the serum levels of BDNF and CRH as well as their selected single nucleotide polymorphisms (SNPs) in vitiligo patients in comparison with the healthy controls.

Methods

The cross-sectional study was carried out between October 2020 and June 2021 in 93 vitiligo patients (age range from 23 to 48 years) and 132 healthy controls (age range from 24 to 52 years). The psychological status of study participants was evaluated using the Generalized Anxiety Disorder-7 (GAD-7) scale. Serum levels of BDNF and CRH were measured with the help of a commercially available sandwich enzyme-linked immunosorbent assay (ELISA) kit. Genotyping for the rs11030094 polymorphism of the BDNF gene and for the rs242924 polymorphism of the corticotropin releasing hormone receptor 1 (CRH-R1) gene was performed by a real-time polymerase chain reaction (PCR).

Results

There was a significant relationship between the CRH-R1 rs242924 and BDNF rs11030094 polymorphisms and vitiligo. Moreover, serum levels of neurotransmitters differed significantly between vitiligo and control groups and were associated with the CRH-R1 rs242924 and BDNF rs11030094 SNPs.

Conclusions

Our findings demonstrated the association between CRH-R1 rs242924 and BDNF rs11030094 polymorphisms and vitiligo. Further studies need to be carried out in vitiligo patients to confirm the results observed.

The relationship between physical activity, body fatness and metabolic syndrome in urban South African school teachers: The sympathetic activity and ambulatory blood pressure in Africans study

BACKGROUND

 Globally, the prevalence of metabolic syndrome (MS) is rising because of increased levels of physical inactivity and obesity. In South Africa, information about teachers' physical activity (PA), body fatness and MS is limited.

AIM

 To assess the relationship between PA, body fatness and MS in urban South African teachers.

SETTING

 The study setting was in Dr Kenneth Kaunda District in the North West province of South Africa.

METHODS

 A cross-sectional study was conducted using secondary data drawn from the sympathetic activity and ambulatory blood pressure in Africans (SABPA) study of 216 teachers (aged 25-65 years). Variables included anthropometry, biochemical measurements, objectively measured PA and lifestyle behaviours.

RESULTS

 Twenty-nine percent of the total participants were classified with MS, with 46% in men compared to 13% in women; 33% were sedentary and 67% participated in light activity. A weak significant negative relationship was found between the mean 7-day awake metabolic equivalent of tasks (METs) and triglycerides (r = -0.29; p = 0.02) and gamma-glutamyl transferase (r = -0.25; p = 0.06), activity energy expenditure (r = -0.24; p = 0.06) and PA level (r = -0.23; p = 0.07). After adjusting for age, self-reported smoking and alcohol use or consumption, a weak significant negative relationship between mean 7-day awake METs and triglycerides (r = -0.28; p  0.01) was observed.

CONCLUSION

 In the teachers with MS, only one MS marker (triglycerides) showed a negative association with PA. Physical activity could therefore be beneficial in the regulation of triglycerides. Participation in regular PA could be beneficial in the regulation of triglycerides. Focused PA interventions in school teachers that advocate the benefits of PA and healthy lifestyle choices to reduce dietary fat intake (and alcohol) are recommended.

Irritable bowel syndrome and microbiome; Switching from conventional diagnosis and therapies to personalized interventions

The human microbiome has been linked to several diseases. Gastrointestinal diseases are still one of the most prominent area of study in host-microbiome interactions however the underlying microbial mechanisms in these disorders are not fully established. Irritable bowel syndrome (IBS) remains as one of the prominent disorders with significant changes in the gut microbiome composition and without definitive treatment. IBS has a severe impact on socio-economic and patient’s lifestyle. The association studies between the IBS and microbiome have shed a light on relevance of microbial composition, and hence microbiome-based trials were designed. However, there are no clear evidence of potential treatment for IBS. This review summarizes the epidemiology and socioeconomic impact of IBS and then focus on microbiome observational and clinical trials. At the end, we propose a new perspective on using data-driven approach and applying computational modelling and machine learning to design microbiome-aware personalized treatment for IBS.

Oxytocin antagonist induced visceral pain and corticotropin-releasing hormone neuronal activation in the central nucleus of the amygdala during colorectal distention in mice

Activation of neurons containing oxytocin and corticotropin-releasing hormone (CRH) in the paraventricular nucleus (PVN) of the hypothalamus, the anterior cingulate cortex (ACC), and the central nucleus of the amygdala (CeA) during colorectal distention (CRD) is likely to play a crucial role in animal models of irritable bowel syndrome (IBS). Earlier studies in rodents showed that the microbiome is involved in social behavior via oxytocin expression in the brain. However, the detailed mechanism of visceral sensation and oxytocin is largely unknown. We tested the following hypotheses: (1) that oxytocin neurons in the PVN are activated by CRD, and (2) that the activation of oxytocin neurons by CRD is related to anxiety-like behavior, visceral perception, and an activation of CRH CeA neurons or ACC neurons. Oxytocin antagonist caused visceral hypersensitivity and anxiety-like behavior. In the PVN, oxytocin neurons were activated by CRD. Noxious CRD activated the CeA, basolateral nucleus of the amygdala (BLA), and ACC. High-dose oxytocin antagonist suppressed ACC activity and activated CRH CeA neurons. These results support our hypotheses. Oxytocin likely regulates CRH CeA neurons in an inhibitory manner and the ACC in an excitatory manner. Further research into the interaction of oxytocin and CRH in visceral pain and anxiety is warranted.

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.

Neuroimmune connections between corticotropin-releasing hormone and mast cells: novel strategies for the treatment of neurodegenerative diseases

Corticotropin-releasing hormone is a critical component of the hypothalamic–pituitary–adrenal axis, which plays a major role in the body’s immune response to stress. Mast cells are both sensors and effectors in the interaction between the nervous and immune systems. As first responders to stress, mast cells can initiate, amplify and prolong neuroimmune responses upon activation. Corticotropin-releasing hormone plays a pivotal role in triggering stress responses and related diseases by acting on its receptors in mast cells. Corticotropin-releasing hormone can stimulate mast cell activation, influence the activation of immune cells by peripheral nerves and modulate neuroimmune interactions. The latest evidence shows that the release of corticotropin-releasing hormone induces the degranulation of mast cells under stress conditions, leading to disruption of the blood-brain barrier, which plays an important role in neurological diseases, such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, autism spectrum disorder and amyotrophic lateral sclerosis. Recent studies suggest that stress increases intestinal permeability and disrupts the blood-brain barrier through corticotropin-releasing hormone-mediated activation of mast cells, providing new insight into the complex interplay between the brain and gastrointestinal tract. The neuroimmune target of mast cells is the site at which the corticotropin-releasing hormone directly participates in the inflammatory responses of nerve terminals. In this review, we focus on the neuroimmune connections between corticotropin-releasing hormone and mast cells, with the aim of providing novel potential therapeutic targets for inflammatory, autoimmune and nervous system diseases.

Functional abdominal pain disorders and asthma: two disorders, but similar pathophysiology?

INTRODUCTION

Functional abdominal pain disorders (FAPDs) and asthma are common ailments affecting both children and adults worldwide. Multiple studies have demonstrated an association between these two disorders. However, the exact reason for this observed association is not apparent.

AREAS COVERED

The current review has explored available literature and outlined multiple underlying pathophysiological mechanisms, common to both asthma and FAPDs, as possible reasons for this association.

EXPERT OPINION

Smooth muscle dysfunction, hypersensitivity and hyper-responsiveness, mucosal inflammation, and barrier dysfunction involving gastrointestinal and respiratory tracts are the main underlying pathophysiological mechanisms described for the generation of symptoms in FAPDs and asthma. In addition, alterations in neuroendocrine regulatory functions, immunological dysfunction, and microbial dysbiosis have been described in both disorders. We believe that the pathophysiological processes that were explored in this article would be able to expand the mechanisms of the association. The in-depth knowledge is needed to be converted to therapeutic and preventive strategies to improve the quality of care of children suffering from FAPDs and asthma.

Peripheral Corticotropin-Releasing Factor Triggers Jejunal Mast Cell Activation and Abdominal Pain in Patients With Diarrhea-Predominant Irritable Bowel Syndrome

INTRODUCTION

To determine the effect of peripheral CRF on intestinal barrier function in diarrhea-predominant IBS (IBS-D). Irritable bowel syndrome (IBS) pathophysiology has been linked to life stress, epithelial barrier dysfunction, and mast cell activation. Corticotropin-releasing factor (CRF) is a major mediator of stress responses in the gastrointestinal tract, yet its role on IBS mucosal function remains largely unknown.

METHODS

Intestinal response to sequential i.v. 5-mL saline solution (placebo) and CRF (100 μg) was evaluated in 21 IBS-D and 17 healthy subjects (HSs). A 20-cm jejunal segment was perfused with an isosmotic solution and effluents collected at baseline, 30 minutes after placebo, and 60 minutes after CRF. We measured water flux, albumin output, tryptase release, stress hormones, cardiovascular and psychological responses, and abdominal pain. A jejunal biopsy was obtained for CRF receptor expression assessment.

RESULTS

Water flux did not change after placebo in IBS-D and HS but significantly increased after CRF in IBS-D (P = 0.007). Basal luminal output of albumin was higher in IBS-D and increased further after CRF in IBS-D (P = 0.042). Basal jejunal tryptase release was higher in IBS-D, and CRF significantly increased it in both groups (P = 0.004), the response being higher in IBS-D than in HS (P = 0.0023). Abdominal pain worsened only in IBS-D after CRF and correlated with jejunal tryptase release, water flux, and albumin output. IBS-D displayed jejunal up-regulation of CRF2 and down-regulation of CRF1 compared with HS.

DISCUSSION

Stress via CRF-driven mast cell activation seems to be relevant in the pathophysiology of IBS-D.

Global burden of irritable bowel syndrome: trends, predictions and risk factors

Irritable bowel syndrome (IBS) is one of the most common disorders of gut-brain interaction worldwide, defined according to patterns of gastrointestinal symptoms as described by the Rome diagnostic criteria. However, these criteria, developed with reference to research conducted largely in Western populations, might be limited in their applicability to other countries and cultures. Epidemiological data show a wide variation in the prevalence of IBS globally and more rigorous studies are needed to accurately determine any differences that might exist between countries as well as the potential explanations. The effects of IBS on the individual, in terms of their quality of life, and on health-care delivery and society, in terms of economic costs, are considerable. Although the magnitude of these effects seems to be comparable between nations, their precise nature can vary based on the existence of societal and cultural differences. The pathophysiology of IBS is complex and incompletely understood; genetics, diet and the gut microbiome are all recognized risk factors, but the part they play might be influenced by geography and culture, and hence their relative importance might vary between countries. This Review aims to provide an overview of the burden of IBS in a global context, to discuss future implications for the care of people with IBS worldwide, and to identify key areas for further research.

The Increased Level of Depression and Anxiety in Irritable Bowel Syndrome Patients Compared with Healthy Controls: Systematic Review and Meta-analysis

BACKGROUND/AIMS

Irritable bowel syndrome (IBS) patients commonly experience psychiatric disorders, such as depression and anxiety. This meta-analysis sought to compare depression and anxiety levels between IBS patients and healthy controls.

METHODS

We searched major electronic databases (PubMed, EMBASE, MEDLINE, and Cochrane library) to find comparative studies on IBS patients and healthy controls. The primary outcome was a standardized mean difference (SMD) of anxiety and depression levels; sub-group analyses were conducted according to IBS-subtypes.

RESULTS

In total, 2293 IBS patients and 4951 healthy controls from 27 studies were included. In random effect analysis, depression and anxiety levels were significantly higher in IBS patients (pooled SMD = 0.76; 95% CI, 0.62-0.90; P < 0.001; I2 = 77.2% and pooled SMD = 0.84; 95% CI, 0.67-1.01; P < 0.001; I2 = 85.6%, respectively). Both analyses' funnel plots showed symmetry. In meta-regression analysis, heterogeneity was due to the studied region and questionnaire type for both depression and anxiety. In sub-group analyses of IBS-subtype, the pooled SMDs of depression and anxiety levels (IBS with predominant constipation: 0.83 and 0.81, IBS with predominant diarrhea: 0.73 and 0.65, and IBS with mixed bowel habits: 0.62 and 0.75; P < 0.001, respectively) were significantly higher in all IBS-subtypes.

CONCLUSIONS

The present meta-analysis showed depression and anxiety levels to be higher in IBS patients than in healthy controls, regardless of IBS-subtype. However, the gender effect on psychological factors among IBS patients could not be determined and should be evaluated in prospective studies.

Corticotropin-releasing hormone receptor 1 (CRH-R1) polymorphisms are associated with irritable bowel syndrome and acoustic startle response

BACKGROUND

Corticotropin-releasing hormone receptor 1 (CRH-R1) in the amygdala and the stria terminalis plays an important role in the activation of central stress circuits. Genetic factors may contribute to the hyperresponsiveness of these circuits in irritable bowel syndrome (IBS).

AIMS

To determine if CRH-R1 SNPs are associated with: (1) a diagnosis of IBS, (2) gastrointestinal (GI) symptoms, and (3) acoustic startle response (ASR) to threat, which is mediated by the amygdala via CRH.

METHODS

Three CRH-R1 SNPS (rs110402, rs242924, and rs7209436) were genotyped using salivary DNA from IBS and healthy control subjects (HCs). Eye blink ASR was obtained during safe (no shock), anticipation (abdominal shock may soon occur) and threat (abdominal shock likely) conditions in a subset of subjects. Associations between each SNP with IBS status, clinical traits and ASR were measured.

RESULTS

235 IBS patients (mean age 37.5 yrs, 74% F) and 264 HCs (mean age 32.1 yrs, 70% F) were studied. Of these, 57 IBS and 41 HCs underwent the ASR protocol. The presence of IBS was associated with the major allele for all three CRH-R1 SNPs (p=0.009-0.025). Within IBS, the major allele for all three SNPs (p=0.017-0.065) was associated with GI symptom anxiety scores. Within subjects with at least one copy of the major allele for the CRH-R1 SNPs, IBS had significantly lower ASR compared to HCs during threat conditions (p=0.001-0.002). Within IBS, CRH-R1 SNPs were associated with a graded increase in ASR to threat (p=0.007-0.008).

CONCLUSION

These findings support that CRH-R1 contributes to the dysregulated stress responsiveness in IBS.

Activation of corticotropin-releasing factor neurons and microglia in paraventricular nucleus precipitates visceral hypersensitivity induced by colorectal distension in rats

Visceral hypersensitivity is a major contributor to irritable bowel syndrome and other disorders with visceral pain. Substantial evidence has established that glial activation and neuro-glial interaction play a key role in the establishment and maintenance of visceral hypersensitivity. We recently demonstrated that activation of spinal microglial toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88)/nuclear factor κB (NF-κB) signaling facilitated the development of visceral hypersensitivity in a rat model developed by neonatal and adult colorectal distensions (CRDs). Hypothalamic paraventricular nucleus (PVN) plays a pivotal role in the pathogenesis of chronic pain. In this study, we examined the mechanism by which microglia and neurons in PVN establish and maintain visceral hypersensitivity and the involvement of TLR4 signaling. Visceral hypersensitivity was precipitated by adult colorectal distension (CRD) only in rats that experienced neonatal CRDs. Visceral hypersensitivity was associated with an increase in the expression of c-fos, corticotropin-releasing factor (CRF) protein and mRNA in PVN, which could be prevented by intra-PVN infusion of lidocaine or small interfering RNA targeting the CRF gene. These results suggest PVN CRF neurons modulate visceral hypersensitivity. Adult CRD induced an increase in the expression of Iba-1 (a microglial marker), TLR4 protein, and its downstream effectors MyD88, NF-κB, as well as proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) only in rats that experienced neonatal CRDs. Intra-PVN infusion of minocycline, a nonselective microglial inhibitor, attenuated the hyperactivity of TLR4 signaling cascade, microglial activation, and visceral hypersensitivity. Taken together, these data suggest that neonatal CRDs induce a glial activation in PVN. Adult CRD potentiates the glial and CRF neuronal activity, and precipitates visceral hypersensitivity and pain. TLR4 signaling and proinflammatory cytokines TNF-α and IL-1β may participate in neuro-glial interaction during the pathogenesis of visceral hypersensitivity.

Associations between Single-Nucleotide Polymorphisms in Corticotropin-Releasing Hormone-Related Genes and Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a common functional disorder with distinct features of stress-related pathophysiology. A key mediator of the stress response is corticotropin-releasing hormone (CRH). Although some candidate genes have been identified in stress-related disorders, few studies have examined CRH-related gene polymorphisms. Therefore, we tested our hypothesis that single-nucleotide polymorphisms (SNPs) in CRH-related genes influence the features of IBS.

METHODS

In total, 253 individuals (123 men and 130 women) participated in this study. They comprised 111 IBS individuals and 142 healthy controls. The SNP genotypes in CRH (rs28364015 and rs6472258) and CRH-binding protein (CRH-BP) (rs10474485) were determined by direct sequencing and real-time polymerase chain reaction. The emotional states of the subjects were evaluated using the State-Trait Anxiety Inventory, Perceived Stress Scale, and the Self-rating Depression Scale.

RESULTS

Direct sequencing of the rs28364015 SNP of CRH revealed no genetic variation among the study subjects. There was no difference in the genotype distributions and allele frequencies of rs6472258 and rs10474485 between IBS individuals and controls. However, IBS subjects with diarrhea symptoms without the rs10474485 A allele showed a significantly higher emotional state score than carriers.

CONCLUSIONS

These results suggest that the CRH and CRH-BP genes have no direct effect on IBS status. However, the CRH-BP SNP rs10474485 has some effect on IBS-related emotional abnormalities and resistance to psychosocial stress.

Corticotropin-Releasing Hormone Receptor 2 Gene Variants in Irritable Bowel Syndrome

Background

Corticotropin-releasing hormone (CRH) plays an important role in the pathophysiology of irritable bowel syndrome (IBS) and regulates the stress response through two CRH receptors (R1 and R2). Previously, we reported that a CRHR1 gene polymorphism (rs110402, rs242924, and rs7209436) and haplotypes were associated with IBS. However, the association between the CRHR2 gene and IBS was not investigated. We tested the hypothesis that genetic polymorphisms and haplotypes of CRHR2 are associated with IBS pathophysiology and negative emotion in IBS patients.

Methods

A total of 142 IBS patients and 142 healthy controls participated in this study. Seven single nucleotide polymorphisms (SNPs) of the CRHR2 gene (rs4722999, rs3779250, rs2240403, rs2267710, rs2190242, rs2284217, and rs2284220) were genotyped. Subjects' psychological states were evaluated using the Perceived-Stress Scale, the State-Trait Anxiety Inventory, and the Self-Rating Depression Scale.

Results

We found that rs4722999 and rs3779250, located in intronic region, were associated with IBS in terms of genotype frequency (rs4722999: P = 0.037; rs3779250: P = 0.017) and that the distribution of the major allele was significantly different between patients and controls. There was a significant group effect (controls vs. IBS), and a CRHR2 genotype effect was observed for three psychological scores, but the interaction was not significant. We found a haplotype of four SNPs (rs4722999, rs3779250, rs2240403, and rs2267710) and two SNPs (rs2284217 and rs2284220) in strong linkage disequilibrium (D′ > 0.90). We also found that haplotypes of the CRHR2 gene were significantly different between IBS patients and controls and that they were associated with negative emotion.

Conclusion

Our findings support the hypothesis that genetic polymorphisms and haplotypes of CRHR2 are related to IBS. In addition, we found associations between CRHR2 genotypes and haplotypes and negative emotion in IBS patients and controls. Further studies on IBS and the CRH system are warranted.

Genetic epidemiology of irritable bowel syndrome

Irritable bowel syndrome (IBS) is the most common functional gastrointestinal disorder characterized by presence of abdominal pain or discomfort associated with altered bowel habits. It has three main subtypes - constipation predominant IBS (C-IBS), diarrhea predominant IBS (D-IBS) and IBS with mixed features of both diarrhea as well as constipation (M-IBS). Its pathophysiology and underlying mechanisms remain elusive. It is traditionally believed that IBS is a result of multiple factors including hypersensitivity of the bowel, altered bowel motility, inflammation and stress. Initial studies have shown familial aggregation of IBS suggesting shared genetic or environmental factors. Twin studies of IBS from different parts of world have shown higher concordance rates among monozygotic twins than dizygotic twins, and thus suggesting a genetic component to this disorder. Multiple studies have tried to link single-nucleotide polymorphisms (SNPs) to IBS but there is little evidence that these SNPs are functional. Various molecules have been studied and investigated by the researchers. Serotonin, a known neurotransmitter and a local hormone in the enteric nervous system, has been most extensively explored. At this time, the underlying gene pathways, genes and functional variants linked with IBS remain unknown and the promise of genetically-determined risk prediction and personalize medicine remain unfulfilled. However, molecular biological technologies continue to evolve rapidly and genetic investigations offer much promise in the intervention, treatment and prevention of IBS.

Corticotropin-releasing factor receptor type 1 and type 2 interaction in irritable bowel syndrome

Irritable bowel syndrome (IBS) displays chronic abdominal pain or discomfort with altered defecation, and stress-induced altered gut motility and visceral sensation play an important role in the pathophysiology. Corticotropin-releasing factor (CRF) is a main mediator of stress responses and mediates these gastrointestinal functional changes. CRF in brain and periphery acts through two subtype receptors such as CRF receptor type 1 (CRF1) and type 2 (CRF2), and activating CRF1 exclusively stimulates colonic motor function and induces visceral hypersensitivity. Meanwhile, several recent studies have demonstrated that CRF2 has a counter regulatory action against CRF1, which may imply that CRF2 inhibits stress response induced by CRF1 in order to prevent it from going into an overdrive state. Colonic contractility and sensation may be explained by the state of the intensity of CRF1 signaling. CRF2 signaling may play a role in CRF1-triggered enhanced colonic functions through modulation of CRF1 activity. Blocking CRF2 further enhances CRF-induced stimulation of colonic contractility and activating CRF2 inhibits stress-induced visceral sensitization. Therefore, we proposed the hypothesis, i.e., balance theory of CRF1 and CRF2 signaling as follows. Both CRF receptors may be activated simultaneously and the signaling balance of CRF1 and CRF2 may determine the functional changes of gastrointestinal tract induced by stress. CRF signaling balance might be abnormally shifted toward CRF1, leading to enhanced colonic motility and visceral sensitization in IBS. This theory may lead to understanding the pathophysiology and provide the novel therapeutic options targeting altered signaling balance of CRF1 and CRF2 in IBS.

Effects of electroacupuncture on corticotropin-releasing hormone in rats with chronic visceral hypersensitivity

AIM: To investigate the effect of electroacupuncture on corticotropin-releasing hormone (CRH) in the colon, spinal cord, and hypothalamus of rats with chronic visceral hypersensitivity.

METHODS: A rat model of chronic visceral hypersensitivity was generated according to the internationally accepted method of colorectal balloon dilatation. In the 7^th week after the procedure, rats were randomly divided into a model group (MG), electroacupuncture group (EA), and sham electroacupuncture group (S-EA). After treatment, the abdominal withdrawal reflex (AWR) score was used to assess the behavioral response of visceral hyperalgesia. Immunohistochemistry (EnVision method), ELISA, and fluorescence quantitative PCR methods were applied to detect the expression of CRH protein and mRNA in the colon, spinal cord, and hypothalamus.

RESULTS: The sensitivity of the rats to the colorectal distension stimulus applied at different strengths (20-80 mmHg) increased with increasing stimulus strength, resulting in increasing AWR scores in each group. Compared with NG, the AWR score of MG was significantly increased (P < 0.01). After conducting EA, the AWR scores of the rats were decreased compared with MG rats. The relative expression of CRH mRNA in the colon, spinal cord, and hypothalamus of MG rats was significantly increased compared with NG rats (P < 0.01). CRH mRNA in the colon and spinal cord of EA and S-EA rats was decreased to varying degrees (P > 0.05) compared with normal rats (NG). However, the decrease in EA compared with MG rats was statistically significant (P < 0.01). The average optical density of CRH expression in the colon of the MG rats was significantly enhanced compared with NG (P < 0.05), while the average optical density of CRH expression in the EA and S-EA rats was significantly decreased compared with MG rats (P < 0.01, P < 0.05, respectively). Compared with MG rats, the CRH concentration in the spinal cord of EA rats was significantly reduced (P < 0.01), but there was no significant change in S-EA rats (P > 0.05).

CONCLUSION: Electroacupuncture at the Shangjuxu acupoint was able to significantly reduce the visceral hypersensitivity in rats, and regulated the expression of CRH protein and mRNA in the colon, spinal cord and hypothalamus at different levels, playing a therapeutic role in this model of irritable bowel syndrome.

Genetic polymorphism in pathogenesis of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a complex symptom-based disorder without established biomarkers or putative pathophysiology. IBS is a common functional gastrointestinal disorder which is defined as recurrent abdominal pain or discomfort that has at least two of the following symptoms for 3 d per month in the past 3 mo according to ROME III: relief by defecation, onset associated with a change in stool frequency or onset with change in appearance or form of stool. Recent discoveries revealed genetic polymorphisms in specific cytokines and neuropeptides may possibly influence the frequencies and severity of symptoms, as well as the therapeutic responses in treating IBS patients. This review gives new insights on how genetic determinations influence in clinical manifestations, treatment responses and potential biomarkers of IBS.

Cohort Profile: Sympathetic activity and Ambulatory Blood Pressure in Africans (SABPA) prospective cohort study

Adapting to an over-demanding stressful urban environment may exhaust the psychophysiological resources to cope with these demands, and lead to sympathetic nervous system dysfunction. The evidence that an urban-dwelling lifestyle may be detrimental to the cardiometabolic health of Africans motivated the design of the Sympathetic activity and Ambulatory Blood Pressure in African Prospective cohort study. We aimed to determine neural mechanistic pathways involved in emotional distress and vascular remodelling. The baseline sample included 409 teachers representing a bi-ethnic sex cohort from South Africa. The study was conducted in 2008–09 and repeated after 3-year follow-up in 2011–12, with an 87.8% successful follow-up rate. Seasonal changes were avoided and extensive clinical assessments were performed in a well-controlled setting. Data collection included sociodemographics, lifestyle habits, psychosocial battery and genetic analysis, mental stress responses mimicking daily life stress (blood pressure and haemostatic, cardiometabolic, endothelial and stress hormones). Target organ damage was assessed in the brain, heart, kidney, blood vessels and retina. A unique highly phenotyped cohort is presented that can address the role of a hyperactive sympathetic nervous system and neural response pathways contributing to the burden of cardiometabolic diseases in Africans.

Irritable bowel syndrome: The evolution of multi-dimensional looking and multidisciplinary treatments

Irritable bowel syndrome (IBS) is common in the society. Among the putative pathogeneses, gut dysmotility results in pain and disturbed defecation. The latter is probably caused by the effect of abnormal gut water secretion. The interaction between abnormal gas accumulation, abdominal pain and bloating remains controversial. Visceral hypersensitivity and its modification along with the central transmission are the characteristics of IBS patients. The identification of biologic markers based on genetic polymorphisms is undetermined. Imbalanced gut microbiota may alter epithelial permeability to activate nociceptive sensory pathways which in turn lead to IBS. Certain food constituents may exacerbate bowel symptoms. The impact of adult and childhood abuses on IBS is underestimated. Using the concept of biopsychosocial dysfunction can integrate multidimensional pathogeneses. Antispasmodics plus stool consistency modifiers to treat the major symptoms and defecation are the first-line drug treatment. New drugs targeting receptors governing bowel motility, sensation and secretion can be considered, but clinicians must be aware of their potential serious side effects. Psychiatric drugs and modalities may be the final options for treating intractable subjects. Probiotics of multi-species preparations are safe and worth to be considered for the treatment. Antibiotics are promising but their long-term safety and effectiveness are unknown. Diet therapy including exclusion of certain food constituents is an economic measure. Using relatively safe complementary and alternative medicines (CAMs) may be optional to those patients who failed classical treatment. In conclusion, IBS is a heterogeneous disorder with multidimensional pathogeneses. Personalized medicines with multidisciplinary approaches using different classes of drugs, psychiatric measures, probiotics and antibiotics, dietary therapy, and finally CAMs, can be considered.

Molecular basis of the irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional disorder characterized by abdominal pain, discomfort and bloating. The pathophysiology of IBS is poorly understood, but the presence of psychosocial basis is now known. There is an increasing number of publications supporting the role of genetics in IBS. Most of the variations are found in genes associated with the brain-gut axis, revealing the strong correlation of brain-gut axis and IBS. miRNAs, which play critical roles in physiological processes, are not well studied in IBS. However, so far there is found an involvement of alterations in miRNA expression or sequence, in IBS symptoms. IBS phenotype is affected by epigenetic alteration and environment. Changes in DNA and histone methylation are observed in patients who suffered childhood trauma or abuse, resulting in altered gene expression, such as the glucocorticoid receptor gene. Finally, diet is another factor associated with IBS, which may contribute to symptom onset. Certain foods may affect on bacterial metabolism and epigenetic modifications, predisposing to IBS.