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

Mast cell modulation: A novel therapeutic strategy for abdominal pain in irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most prevalent gastrointestinal disorders characterized by recurrent abdominal pain and an altered defecation pattern. Chronic abdominal pain represents the hallmark IBS symptom and is reported to have the most bothersome impact on the patient's quality of life. Unfortunately, effective therapeutic strategies reducing abdominal pain are lacking, mainly attributed to a limited understanding of the contributing mechanisms. In the past few years, exciting new insights have pointed out that altered communication between gut immune cells and pain-sensing nerves acts as a hallmark driver of IBS-related abdominal pain. In this review, we aim to summarize our current knowledge on altered neuro-immune crosstalk as the main driver of altered pain signaling, with a specific focus on altered mast cell functioning herein, and highlight the relevance of targeting mast cell-mediated mechanisms as a novel therapeutic strategy for chronic abdominal pain in IBS patients.

Research Progress of Central and Peripheral Corticotropin-Releasing Hormone in Irritable Bowel Syndrome with Comorbid Dysthymic Disorders

Irritable bowel syndrome (IBS) is considered a stress disorder characterized by psychological and gastrointestinal dysfunction. IBS patients not only suffer from intestinal symptoms such as abdominal pain, diarrhea, or constipation but also, experience dysthymic disorders such as anxiety and depression. Studies have found that corticotropin-releasing hormone plays a key role in IBS with comorbid dysthymic disorders. Next, we will summarize the effects of corticotropin-releasing hormone from the central nervous system and periphery on IBS with comorbid dysthymic disorders and relevant treatments based on published literatures in recent years.

Examination of the role of adrenergic receptor stimulation in the sensitization of neuroinflammatory-based depressive-like behavior in isolated Guinea pig pups

Early-life attachment disruption appears to sensitize neuroinflammatory signaling to increase later vulnerability for stress-related mental disorders, including depression. How stress initiates this process is unknown, but studies with adult rats and mice suggest sympathetic nervous system activation and/or cortisol elevations during the early stress are key. Guinea pig pups isolated from their mothers exhibit an initial active behavioral phase characterized by anxiety-like vocalizing. This is followed by inflammatory-dependent depressive-like behavior and fever that sensitize on repeated isolation. Using strategies that have been successful in adult studies, we assessed whether sympathetic nervous system activity and cortisol contributed to the sensitization process in guinea pig pups. In Experiment 1, the adrenergic agonist ephedrine (3 or 10 mg/kg), either alone or with cortisol (2.5 mg/kg), did not increase depressive-like behavior or fever during initial isolation the following day as might have been expected to if this stimulation was sufficient to account for the sensitization process. In Experiment 2, both depressive-like behavior and fever sensitized with repeated isolation, but beta-adrenergic receptor blockade with propranolol (10 or 20 mg/kg) did not affect either of these responses or their sensitization. The high dose of propranolol did, however, reduce vocalizing. These results suggest sympathetic nervous system activation is neither necessary nor sufficient to induce the presumptive neuroinflammatory signaling underlying sensitization of depressive-like behavioral or febrile responses in developing guinea pigs. Thus, processes mediating sensitization of neuroinflammatory-based depressive-like behavior following early-life attachment disruption in this model appear to differ from those previously found to underlie neuroinflammatory priming in adults.

Apigenin attenuates visceral hypersensitivity in water avoidance stress rats by modulating the microbiota-gut-brain axis and inhibiting mast cell activation

Visceral hypersensitivity (VH) and gut microbiota dysbiosis significantly contribute to the occurrence and development of irritable bowel syndrome (IBS), exacerbated by stress. Apigenin, a natural flavonoid derived from plants, possesses a range of beneficial properties. However, additional research is necessary to investigate its potential in alleviating symptoms of IBS and elucidating its underlying mechanisms of action. Our study confirms that apigenin effectively reverses mast cell and microglial activation, regulates the composition and abundance of the gut microbiota, improves intestinal barrier function in rats induced with water-avoidance stress, and mitigates VH and colonic hypermotility. Furthermore, in vitro studies suggest a potential role of dysbiotic gut microbiota in activating mast cells at the cellular level. Notably, apigenin inhibits mast cell degranulation through the toll-like receptor 4 (TLR4) / myeloid differentiation primary response gene 88 (MyD88) / nuclear factor-kappa B (NF-κB) pathway. In conclusion, this study discusses the potential therapeutic effects of apigenin in alleviating VH and modulating the gut-brain axis in water-avoidance stress rats, providing a novel or alternative treatment approach for IBS.

Psychosocial stress-induced intestinal permeability in healthy humans: What is the evidence?

An impaired intestinal barrier function can be detrimental to the host as it may allow the translocation of luminal antigens and toxins into the subepithelial tissue and bloodstream. In turn, this may cause local and systemic immune responses and lead to the development of pathologies. In vitro and animal studies strongly suggest that psychosocial stress is one of the factors that can increase intestinal permeability via mast-cell dependent mechanisms. Remarkably, studies have not been able to yield unequivocal evidence that such relation between stress and intestinal permeability also exists in (healthy) humans. In the current Review, we discuss the mechanisms that are involved in stress-induced intestinal permeability changes and postulate factors that influence these alterations and that may explain the translational difficulties from in vitro and animal to human studies. As human research differs highly from animal research in the extent to which stress can be applied and intestinal permeability can be measured, it remains difficult to draw conclusions about the presence of a relation between stress and intestinal permeability in (healthy) humans. Future studies should bear in mind these difficulties, and more research into in vivo methods to assess intestinal permeability are warranted.

Dietary monosodium glutamate increases visceral hypersensitivity in a mouse model of visceral pain

BACKGROUND

Monosodium glutamate (MSG) has been identified as a trigger of abdominal pain in irritable bowel syndrome (IBS), but the mechanism is unknown. This study examined whether MSG causes visceral hypersensitivity using a water-avoidance stress (WAS) mouse model of visceral pain.

METHODS

Mice were divided into four groups receiving treatment for 6 days: WAS + MSG gavage, WAS + saline gavage, sham-WAS + MSG gavage, and sham-WAS + saline gavage. The acute effects of intraluminal administration of 10 μM MSG on jejunal extrinsic afferent nerve sensitivity to distension (0-60 mmHg) were examined using ex vivo extracellular recordings. MSG was also applied directly to jejunal afferents from untreated mice. Glutamate concentration was measured in serum, and in the serosal compartment of Ussing chambers following apical administration.

KEY RESULTS

Acute intraluminal MSG application increased distension responses of jejunal afferent nerves from mice exposed to WAS + MSG. This effect was mediated by wide dynamic range and high-threshold units at both physiologic and noxious pressures (10-60 mmHg, p < 0.05). No effect of MSG was observed in the other groups, or when applied directly to the jejunal afferent nerves. Serum glutamate was increased in mice exposed to WAS + MSG compared to sham-WAS + saline, and serosal glutamate increased using WAS tissue (p = 0.0433).

CONCLUSIONS AND INFERENCES

These findings demonstrate that repeated exposure to MSG in mice leads to sensitization of jejunal afferent nerves to acute ex vivo exposure to MSG. This may contribute to visceral hypersensitivity reported in response to MSG in patients with IBS.

Irritable bowel syndrome: treatment based on pathophysiology and biomarkers

OBJECTIVE

To appraise the evidence that pathophysiological mechanisms and individualised treatment directed at those mechanisms provide an alternative approach to the treatment of patients with irritable bowel syndrome (IBS).

DESIGN

A PubMED-based literature review of mechanisms and treatment of IBS was conducted independently by the two authors, and any differences of perspective or interpretation of the literature were resolved following discussion.

RESULTS

The availability of several noninvasive clinical tests can appraise the mechanisms responsible for symptom generation in IBS, including rectal evacuation disorders, abnormal transit, visceral hypersensitivity or hypervigilance, bile acid diarrhoea, sugar intolerances, barrier dysfunction, the microbiome, immune activation and chemicals released by the latter mechanism. The basic molecular mechanisms contributing to these pathophysiologies are increasingly recognised, offering opportunities to intervene with medications directed specifically to food components, receptors and potentially the microbiome. Although the evidence supporting interventions for each mechanism is not at the same level of proof, the current state-of-the-art provides the opportunity to advance the practice from treatment based on symptoms to individualisation of treatment guided by pathophysiology and clinically identified biomarkers.

CONCLUSION

These advances augur well for the implementation of evidence-based individualised treatment for patients with IBS based on actionable biomarkers or psychological disturbances.

Acute Stress Regulates Sex-Related Molecular Responses in the Human Jejunal Mucosa: Implications for Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a prevalent gastrointestinal disorder linked to intestinal barrier dysfunction and life stress. We have previously reported that female sex per se determines an increased susceptibility to intestinal barrier dysfunction after cold pain stress (CPS). We aimed to identify sex-related molecular differences in response to CPS in healthy subjects to understand the origin of sex bias predominance in IBS. In 13 healthy males and 21 females, two consecutive jejunal biopsies were obtained using Watson's capsule, at baseline, and ninety minutes after CPS. Total mucosal RNA and protein were isolated from jejunal biopsies. Expression of genes related to epithelial barrier (CLDN1, CLDN2, OCLN, ZO-1, and ZO-3), mast cell (MC) activation (TPSAB1, SERPINA1), and the glucocorticoid receptor (NR3C1) were analyzed using RT-qPCR. NR3C1, ZO-1 and OCLN protein expression were evaluated through immunohistochemistry and western blot, and mucosal inflammation through MC, lymphocyte, and eosinophil numbering. Autonomic, hormonal, and psychological responses to CPS were monitored. We found an increase in jejunal MCs, a reduced CLDN1 and OCLN expression, and an increased CLDN2 and SERPINA1 expression 90 min after CPS. We also found a significant decrease in ZO-1, OCLN, and NR3C1 gene expression, and a decrease in OCLN protein expression only in females, when compared to males. CPS induced a significant increase in blood pressure, plasma cortisol and ACTH, and subjective stress perception in all participants. Specific and independent sex-related molecular responses in epithelial barrier regulation are unraveled by acute stress in the jejunum of healthy subjects and may partially explain female predominance in IBS.

A Novel Mast Cell Stabilizer JM25-1 Rehabilitates Impaired Gut Barrier by Targeting the Corticotropin-Releasing Hormone Receptors

Mast cell (MC) plays a central role in intestinal permeability; however, few MC-targeting drugs are currently available for protection of the intestinal barrier in clinical practice. A nonfluorinated Lidocaine analog 2-diethylamino-N-2,5-dimethylphenyl acetamide (JM25-1) displays anti-allergic effect, but its impact on MC remains elusive. In this study, we explored whether JM25-1 has therapeutic potential on intestinal barrier defect through stabilizing MC. JM25-1 alleviated release of β-hexosaminidase and cytokine production of MC. The paracellular permeability was redressed by JM25-1 in intestinal epithelial cell monolayers co-cultured with activated MC. In vivo, JM25-1 diminished intestinal mucosal MC amount and cytokine production, especially downregulating the expression of CRHR1, accompanied by an increase of CRHR2. Protective effects appeared in JM25-1-treated stress rats with a recovery of weight and intestinal barrier integrity. Through network pharmacology analysis, JM25-1 showed a therapeutic possibility for irritable bowel syndrome (IBS) with predictive targeting on PI3K/AKT/mTOR signaling. As expected, JM25-1 reinforced p-PI3K, p-AKT, p-mTOR signaling in MC, while the mTOR inhibitor Rapamycin reversed the action of JM25-1 on the expression of CRHR1 and CRHR2. Moreover, JM25-1 successfully remedied intestinal defect and declined MC and CRHR1 expression in rat colon caused by colonic mucus of IBS patients. Our data implied that JM25-1 possessed therapeutic capacity against intestinal barrier defects by targeting the CRH receptors of MC through PI3K/AKT/mTOR signaling.

Progress in research of low-grade inflammation in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common intestinal disease with a prevalence of 10%-15%. However, its pathophysiology is still not completely clear, and it has long been considered as a functional disease. In recent years, it has been found that low-grade inflammation plays a pathogenic role in IBS. Studies have confirmed that there is persistent mucosal inflammation at the microscopic and molecular levels. This review discusses the evidence, role, and clinical relevance of mucosal inflammation in IBS. In addition to mucosal inflammation, neuroinflammation may lead to changes in neuroendocrine pathways and glucocorticoid receptor genes through the "gut-brain" axis, and thus cause IBS through proinflammatory phenotype and hypothalamic pituitary adrenal axis and 5-hydroxytryptamine dysfunction. The observation that IBS patients can benefit from anti-inflammatory therapy also confirms that IBS is associated with inflammation.

Immune responses in the irritable bowel syndromes: time to consider the small intestine

BACKGROUND

Irritable bowel syndrome (IBS) is considered a disorder of gut-brain interaction (DGBI), presenting as chronic abdominal pain and altered defaecation. Symptoms are often food related. Much work in the field has focused on identifying physiological, immune and microbial abnormalities in the colon of patients; however, evidence of small intestinal immune activation and microbial imbalance has been reported in small studies. The significance of such findings has been largely underappreciated despite a growing body of work implicating small intestinal homeostatic imbalance in the pathogenesis of DGBIs.

MAIN TEXT

Small intestinal mechanosensation is a characteristic feature of IBS. Furthermore, altered small intestinal barrier functions have been demonstrated in IBS patients with the diarrhoea-predominant subtype. Small intestinal bacterial overgrowth and increased populations of small intestinal mast cells are frequently associated with IBS, implicating microbial imbalance and low-grade inflammation in the pathogenesis of IBS. Furthermore, reports of localised food hypersensitivity responses in IBS patients implicate the small intestine as the site of immune-microbial-food interactions.

CONCLUSIONS

Given the association of IBS symptoms with food intake in a large proportion of patients and the emerging evidence of immune activation in these patients, the current literature suggests the pathogenesis of IBS is not limited to the colon but rather may involve dysfunction of the entire intestinal tract. It remains unclear if regional variation in IBS pathology explains the various symptom phenotypes and further work should consider the intestinal tract as a whole to answer this question.

The Role of Leaky Gut in Functional Dyspepsia

Patients with functional dyspepsia (FD) complain of epigastric symptoms with no identifiable cause. Increased intestinal permeability has been described in these patients, especially in the proximal small bowel or duodenum, and was associated with mucosal immune activation and symptoms. In this review, we discuss duodenal barrier function, including techniques currently applied in FD research. We summarize the available data on duodenal permeability in FD and factors associated to increased permeability, including mucosal eosinophils, mast cells, luminal and systemic factors. While the increased influx of antigens into the duodenal mucosa could result in local immune activation, clinical evidence for a causal role of permeability is lacking in the absence of specific barrier-protective treatments. As both existing and novel treatments, including proton pump inhibitors (PPI) and pre- or probiotics may impact duodenal barrier function, it is important to recognize and study these alterations to improve the knowledge and management of FD.

Potential Roles of Enterochromaffin Cells in Early Life Stress-Induced Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders, also known as disorders of the gut–brain interaction; however, the pathophysiology of IBS remains unclear. Early life stress (ELS) is one of the most common risk factors for IBS development. However, the molecular mechanisms by which ELS induces IBS remain unclear. Enterochromaffin cells (ECs), as a prime source of peripheral serotonin (5-HT), play a pivotal role in intestinal motility, secretion, proinflammatory and anti-inflammatory effects, and visceral sensation. ECs can sense various stimuli and microbiota metabolites such as short-chain fatty acids (SCFAs) and secondary bile acids. ECs can sense the luminal environment and transmit signals to the brain via exogenous vagal and spinal nerve afferents. Increasing evidence suggests that an ECs-5-HT signaling imbalance plays a crucial role in the pathogenesis of ELS-induced IBS. A recent study using a maternal separation (MS) animal model mimicking ELS showed that MS induced expansion of intestinal stem cells and their differentiation toward secretory lineages, including ECs, leading to ECs hyperplasia, increased 5-HT production, and visceral hyperalgesia. This suggests that ELS-induced IBS may be associated with increased ECs-5-HT signaling. Furthermore, ECs are closely related to corticotropin-releasing hormone, mast cells, neuron growth factor, bile acids, and SCFAs, all of which contribute to the pathogenesis of IBS. Collectively, ECs may play a role in the pathogenesis of ELS-induced IBS. Therefore, this review summarizes the physiological function of ECs and focuses on their potential role in the pathogenesis of IBS based on clinical and pre-clinical evidence.

Functional Nausea Is Real and Makes You Sick

Functional nausea is a condition that severely impairs the quality of life of affected individuals. Only recently, it has been added to the pediatric list of disorders of gut-brain interaction. In most cases, only minimal testing is needed to diagnose functional nausea. Hypnotherapy has been shown to be a very effective treatment and there are several other medical and non-medical interventions which have the potential to benefit sub-groups of patients with chronic nausea.

Duodenum at a crossroads: Key integrator of overlapping and psychological symptoms in functional dyspepsia?

The study of the interaction between gastrointestinal (GI) function and psychological features is a complex and developing field. The bidirectional communication between the gut and the brain or gut-brain axis is considered as a pivotal player in the pathogenesis of the highly prevalent functional GI disorders, including irritable bowel syndrome and functional dyspepsia (FD), which have been redefined as disorders of gut-brain interaction. However, the mechanisms through which changes in the gut alter brain functioning, feelings, and behavior remain unclear. Based on the presence of duodenal pathology in adult FD patients, Ronkainen et al. provide the first prospective evidence for duodenal eosinophils potentially driving anxiety. Also in this edition, associations between gastroduodenal pathology and rumination syndrome, which may coexist with FD, have now been confirmed in children by Friesen et al. Together these findings confirm not only the potential role of duodenal alterations in determining overlapping upper GI but also psychological symptoms, which result from bidirectional and complex interactions. In this review, we provide an overview of the recent advances in this field and highlight the novel contributions of the original studies of Ronkainen et al. and Friesen et al. to this topic.

Research on Correlation Between Psychological Factors, Mast Cells, and PAR-2 Signal Pathway in Irritable Bowel syndrome

PURPOSE

The study aimed to explore the level of psychological stress factors, mast cell (MC), and neuropeptide in the occurrence of irritable bowel syndrome (IBS) and the correlation among them, and to identify representative and effective indicators for the pathogenesis and clinical medication development of IBS.

SUBJECTS AND METHODS

Twenty-eight patients (20-64 years old) with diarrhea-predominant IBS (IBS-D) were included in the IBS-D group and 8 healthy subjects (35-63 years old) were enrolled in the control group. All subjects accepted the colonoscopic biopsies, self-rating depression scale (SDS) and self-rating anxiety scale (SAS) assessment. MC degranulation, neuropeptide S (NPS), neuropeptide Y (NPY), NPY receptor 2 (NPY2R) and Protease-activated receptor 2 (PAR-2) in colon tissues were performed by Strept Avidin-Biot complex (SABC) immunohistochemistry. Enzyme-linked immunosorbent assay (ELISA) detection was used to test the expression of NPS and NPY in peripheral blood plasma and colon tissues. Western blot was applied to examine the level of NPY2R and PAR-2.

RESULTS

The level of anxiety and depression of patients with IBS-D was more serious than that in the control. The expression of NPS, NPY and NPY2R was down-regulated in the IBS-D. The total MC and tryptase-positive MC increased significantly in the colon tissue of IBS-D and the expression level of PAR-2 was significantly up-regulated.

CONCLUSION

There has been a close connection among those indicators that the activated MC may up-regulate the function of PAR-2, resulting in the change of neuropeptide (NPS and NPY), successively leading to clinical symptoms and psychological negative changes in the IBS.

Puerarin from Pueraria lobata alleviates the symptoms of irritable bowel syndrome-diarrhea

As a functional bowel disorder, irritable bowel syndrome (IBS), especially IBS-diarrhea (IBS-D), affects approximately 9-20% of the population worldwide. Classical treatments for IBS usually result in some side effects and intestinal microbial disorders, which inhibit the clinical effects. Natural edible medicines with beneficial effects and few side effects have received more attention in recent years. Puerarin is the main active ingredient in pueraria and has been used in China to treat splenasthenic diarrhea and as a natural food in folk medicine for hundreds of years. However, there have been no reports of using puerarin in the treatment of IBS-D, and the underlying mechanism is also still unclear. In this study, a comprehensive model that could reflect the symptoms of IBS-D was established by combining neonatal maternal separation (NMS) and adult colonic acetic acid stimulation (ACAAS) in rats. The results showed that puerarin could reverse the abdominal pain and diarrhea in IBS-D rats. The therapeutic effect was realized by regulating the richness of the gut microbiota to maintain the stabilization of the intestinal micro-ecology. Furthermore, the possible mechanism might be related to the activity of the hypothalamic-pituitary-adrenal (HPA) axis by the suppressed expression of corticotropin-releasing hormone receptor (CRF) 1. At the same time, intestinal function was improved by enhancing the proliferation of colonic epithelial cells by upregulating the expression of p-ERK/ERK and by repairing the colonic mucus barrier by upregulating occludin expression. All these results suggest that puerarin could exert excellent therapeutic effects on IBS-D.

Overexpression of corticotropin-releasing factor in intestinal mucosal eosinophils is associated with clinical severity in Diarrhea-Predominant Irritable Bowel Syndrome

Corticotropin-releasing factor (CRF) has been identified in intestinal mucosal eosinophils and associated with psychological stress and gut dysfunction. Irritable bowel syndrome (IBS) is commonly characterized by altered intestinal motility, immune activation, and increased gut barrier permeability along with heightened susceptibility to psychosocial stress. Despite intensive research, the role of mucosal eosinophils in stress-associated gut dysfunction remains uncertain. In this study, we evaluated eosinophil activation profile and CRF content in the jejunal mucosa of diarrhea-predominant IBS (IBS-D) and healthy controls (HC) by gene/protein expression and transmission electron microscopy. We also explored the association between intestinal eosinophil CRF and chronic stress, and the potential mechanisms underlying the stress response by assessing eosinophil response to neuropeptides. We found that mucosal eosinophils displayed higher degranulation profile in IBS-D as compared to HC, with increased content of CRF in the cytoplasmic granules, which significantly correlated with IBS clinical severity, life stress background and depression. Eosinophils responded to substance P and carbachol by increasing secretory activity and CRF synthesis and release, without promoting pro-inflammatory activity, a profile similar to that found in mucosal eosinophils from IBS-D. Collectively, our results suggest that intestinal mucosal eosinophils are potential contributors to stress-mediated gut dysfunction through CRF production and release.