Inflammation in irritable bowel syndrome: Myth or new treatment target?

Overlapping irritable bowel syndrome and inflammatory bowel disease

The pathogenesis of irritable bowel-type symptoms occurring in patients with inflammatory bowel disease who are in apparent remission continues to generate scientific controversy and the interpretation and management of these symptoms, so distressing to the sufferer, represent major challenges for the clinician. On the one hand, these symptoms often satisfy Rome IV criteria for IBS and their occurrence correlates highly with anxiety, a known trigger for IBS. On the other hand, recent studies have shown that many of these patients exhibit subtle inflammatory changes. These observations beg the question: are these symptoms "true" IBS superimposed on IBD, or an active but subclinical form of IBD? While it is certain that earlier studies failed to detect subclinical inflammation, it is also evident that even with the use of sensitive biomarkers for inflammation, such as calprotectin and lactoferrin backed up by pan-endoscopy and biopsy to exclude ongoing inflammatory activity in its most subtle form, the prevalence of IBS-type symptoms remains higher than expected in the IBD patient. Pending further definition of its etiology and pathology, we coined the term irritable inflammatory bowel syndrome (IIBS) to refer to this phenomenon. Here we explore the risk factors for this entity, sift through clues to its pathogenesis and attempt to provide, albeit bereft of a robust evidence base, an approach to its management.

Metformin inhibits visceral allodynia and increased gut permeability induced by stress in rats

BACKGROUND AND AIM

Metformin has been shown to have anti-cytokine property. Lipopolysaccharide (LPS)-induced or repeated water avoidance stress (WAS)-induced visceral allodynia and increased gut permeability were pro-inflammatory cytokine-dependent responses, which were considered to be animal models of irritable bowel syndrome (IBS). We hypothesized that metformin improves symptoms in the patients with IBS by attenuating these visceral changes and tested the hypothesis in rats.

METHODS

The threshold of the visceromotor response induced by colonic balloon distention was measured. Colonic permeability was determined in vivo by quantifying the absorbed Evans blue for 15 min spectrophotometrically.

RESULTS

Subcutaneously injected LPS (1 mg/kg) reduced the threshold of visceromotor response, and metformin (5-50 mg/kg for 3 days) intraperitoneally attenuated this response in a dose-dependent manner. Repeated WAS (1 h daily for 3 days) induced visceral allodynia, which was also blocked by metformin. The antinociceptive effect of metformin on the LPS-induced allodynia was reversed by compound C, an adenosine monophosphate-activated protein kinase inhibitor or N^G -nitro-L-arginine methyl ester, a nitric oxide synthesis inhibitor but not modified by naloxone. Additionally, it was blocked by sulpiride, a dopamine D2 receptor antagonist, but domperidone, a peripheral dopamine D2 receptor antagonist, did not alter it. Metformin also blocked the LPS-induced or repeated WAS-induced increased colonic permeability.

CONCLUSIONS

Metformin attenuated the visceral allodynia and increased gut permeability in animal IBS models. These actions may be evoked via activation of adenosine monophosphate-activated protein kinase, nitric oxide, and central dopamine D2 pathways. These results indicate the possibility that metformin can be useful for treating IBS.

Association of irritable bowel syndrome and venous thromboembolism

OBJECTIVE

Inflammatory bowel disease (IBD) is associated with venous thromboembolism (VTE). Whether functional gastrointestinal disorders, such as irritable bowel syndrome (IBS), are associated with VTE has not been determined. This nationwide study aimed to determine the risk of VTE in IBS outpatients in primary and specialist care.

DESIGN

We performed two matched case-control studies. Cases (n = 90,502) were individuals in Sweden aged 18-80 years with a first hospital diagnosis of VTE between 2001 and 2010. Five controls (n = 452,510) from the Swedish Total Population Register were matched to each case for birth, sex, country of birth, and education level. Diagnosis of IBS was determined in the Swedish hospital outpatient register. This procedure was replicated for the primary care population. As the Primary Care data did not have nationwide coverage, we only included individuals that were registered in the Primary Care database. A total of 9766 cases of hospital diagnosed VTE individuals could be found in the Primary Care population and they were matched to 48,830 controls also from the Primary health care population. Conditional logistic regression was used to determine odds ratio (OR) for first VTE diagnosis. Results The adjusted OR for VTE when IBS was diagnosed in hospital outpatient care was 1.49 (95% confidence interval 1.33-1.67). The crude OR for VTE was 1.18 (0.94-1.48) when IBS was diagnosed in primary care.

CONCLUSIONS

This is the first study describing an association between VTE and IBS. The results suggest that specialist treated IBS patients have increased risk of VTE.

Elevated serum neopterin levels in children with functional constipation: association with systemic proinflammatory cytokines

BACKGROUND

Functional constipation is a clinical problem with an incompletely understood etiology. Functional bowel diseases have been shown to be related to inflammation in many studies in adults. In this study, we aimed to evaluate leukocytes, C-reactive protein, proinflammatory and anti-inflammatory cytokines, and neopterin levels in children with functional constipation.

METHODS

Seventy-six children with constipation and 71 healthy controls (mean age 7.12 ± 3.46 years and 7.32 ± 4.33 years, respectively, P = 0.991) were included in the study. Leukocytes, C-reactive protein, interleukin (IL)-1β, IL-6, IL-10, IL-12, tumor necrosis factor-alpha (TNF-α) and neopterin levels were assessed in patients and healthy controls. Parameters were measured in the serum using enzyme-linked immunosorbent assay methods.

RESULTS

Mean IL-6 (20.31 ± 12.05 vs. 16.2 ± 10.25 pg/mL, respectively, P = 0.003), IL-12 (181.42 ± 133.45 vs. 135.6 ± 83.67 pg/mL, respectively, P = 0.018) and neopterin levels (2.08 ± 1.12 vs. 1.52 ± 1.02 pg/mL, respectively, P = 0.001) were significantly higher in constipated children than healthy controls. Leukocyte and thrombocyte counts, C-reactive protein, and IL-1β, IL-10 and TNF-α levels did not show any difference between the two groups.

CONCLUSIONS

In this study, IL-6, IL-12 and neopterin levels of constipated patients were found to be higher than those of controls. These results indicate the presence of subclinical inflammation in children with functional constipation.

The Food-Specific Serum IgG Reactivity in Major Depressive Disorder Patients, Irritable Bowel Syndrome Patients and Healthy Controls

There is an increasing amount of evidence which links the pathogenesis of irritable bowel syndrome (IBS) with food IgG hyperreactivity. Some authors have suggested that food IgG hyperreactivity could be also involved in the pathophysiology of major depressive disorder (MDD). The aim of this study was to compare levels of serum IgG against 39 selected food antigens between three groups of participants: patients with MDD (MDD group), patients with IBS (IBS group) and healthy controls (HC group). The study included 65 participants (22 in the MDD group, 22 in the IBS group and 21 in the HC group). Serum IgG levels were examined using enzyme-linked immunosorbent assay (ELISA). Medical records, clinical data and laboratory results were collected for the analysis. IgG food hyperreactivity (interpreted as an average of levels of IgG antibodies above 7.5 µg/mL) was detected in 28 (43%) participants, including 14 (64%) from the MDD group, ten (46%) from the IBS group and four (19%) from the HC group. We found differences between extreme IgG levels in MDD versus HC groups and in IBS versus HC groups. Patients with MDD had significantly higher serum levels of total IgG antibodies and IgG against celery, garlic and gluten compared with healthy controls. The MDD group also had higher serum IgG levels against gluten compared with the IBS group. Our results suggest dissimilarity in immune responses against food proteins between the examined groups, with the highest immunoreactivity in the MDD group. Further studies are needed to repeat and confirm these results in bigger cohorts and also examine clinical utility of IgG-based elimination diet in patients with MDD and IBS.

Irritable bowel syndrome and endometriosis: New insights for old diseases

Irritable bowel syndrome and endometriosis are two diseases affecting a significant part of the female population, either together or individually, with remarkable consequences in the quality of life. Several studies suggest an epidemiological association between them. Their association may not be just an epidemiological phenomenon, but the manifestation of a pathophysiological correlation, which probably generates a mutual promotion phenomenon. In particular, both clinical entities share the presence of a chronic low-grade inflammatory state at the basis of the disease persistence. Recognizing this association is highly significant due to their prevalence and the common clinical manifestation occurring with a chronic abdominal pain. A further multi disciplinary approach is suggested in these patients' management in order to achieve an adequate diagnostic work up and a targeted therapy. This paper analyses some common pathophysiological mechanisms, such as activation of mast cell line, neuronal inflammation, dysbiosis and impaired intestinal permeability. The aim was to investigate their presence in both IBS and endometriosis, and to show the complexity of their relationship in the generation and maintenance of chronic inflammation.

Glucagon-like peptide-1 analog, liraglutide, improves visceral sensation and gut permeability in rats

BACKGROUND AND AIM

A glucagon-like peptide-1 analog, liraglutide, has been reported to block inflammatory somatic pain. We hypothesized that liraglutide attenuates lipopolysaccharide (LPS)-induced and repeated water avoidance stress (WAS)-induced visceral hypersensitivity and tested the hypothesis in rats.

METHODS

The threshold of the visceromotor response induced by colonic balloon distention was measured to assess visceral sensation. Colonic permeability was determined in vivo by quantifying the absorbed Evans blue spectrophotometrically, which was instilled in the proximal colon for 15 min. The interleukin-6 level in colonic mucosa was also quantified using ELISA.

RESULTS

Subcutaneously injected LPS (1 mg/kg) reduced the visceromotor response threshold after 3 h. Liraglutide (300 μg/kg subcutaneously) at 15 h and 30 min before injecting LPS eliminated LPS-induced allodynia. It also blocked the allodynia induced by repeated water avoidance stress for 1 h for three consecutive days. Neither vagotomy nor naloxone altered the antinociceptive effect of liraglutide, but N^G -nitro-L-arginine methyl ester, a nitric oxide synthesis inhibitor, blocked it. LPS increased colonic permeability and the interleukin-6 level, and the analog significantly inhibited these responses.

CONCLUSIONS

This study suggests that liraglutide blocked LPS-induced visceral allodynia, which may be a nitric oxide-dependent response, and was probably mediated by inhibiting pro-inflammatory cytokine production and attenuating the increased gut permeability. Because the LPS-cytokine system is considered to contribute to altered visceral sensation in irritable bowel syndrome, these results indicate the possibility that liraglutide can be useful for treating this disease.

Inflammatory cell distribution in colon mucosa as a new tool for diagnosis of irritable bowel syndrome: A promising pilot study

BACKGROUND

Currently, there are no histological criteria to diagnose irritable bowel syndrome (IBS). Our aims were (i) to examine the distribution of inflammatory cells in the colon of healthy and IBS subjects and (ii) to find histological diagnosis criteria for IBS.

METHODS

Colonic biopsies were taken from four distinct regions of the colon from 20 controls (HC) and 11 patients with IBS (4 with constipation (IBS-C) and 7 with diarrhea (IBS-D) and embedded in paraffin. Macrophages, mast cells, eosinophils, and T lymphocytes were immunostained and positive cells counted.

KEY RESULTS

In both HC and IBS patients, global cellularity decreased from the cecum to the rectum (P < .01) which is attributed to reduced number of macrophages (P < .05) and eosinophils (P < .001) but not T cells. Mast cells were reduced in IBS (P < .05) but not in HC, particularly in IBS-D (P < .05). Results showed higher number of macrophages in the left colon of IBS subjects than HC (P < .05).

CONCLUSION & INFERENCES

Here we report a decreasing gradient of immune cells from the cecum to the rectum of the human colon. Although global cellularity cannot be used to distinguish between IBS and HC, closer analysis of macrophages and mast cells may be useful markers to confirm IBS histologically and to differentiate between IBS-C and IBS-D when clinical presentation alternates between constipation and diarrhoea. This pilot study remains to be confirmed with greater number of patients.

Clinical and symptom scores are significantly correlated with fecal microbiota features in patients with symptomatic uncomplicated diverticular disease: a pilot study

BACKGROUND

There is growing consensus that symptomatic uncomplicated diverticular disease is a chronic inflammatory condition, and that alterations in the fecal microbiota may contribute to its pathogenesis.

OBJECTIVE

The aim of this study was to relate the fecal microbiota composition in symptomatic uncomplicated diverticular disease to measures of inflammation, symptoms, and history of previous acute diverticulitis.

PARTICIPANTS AND METHODS

Fecal microbiota composition in 28 individuals with symptomatic uncomplicated diverticular disease was characterized by 16S RNA gene amplicon sequencing. Microbiota composition was related to clinical history, symptom and inflammation measures, and demographic variables.

RESULTS

Previous acute diverticulitis was associated with higher relative abundance of Pseudobutyrivibrio, Bifidobacterium, Christensenellaceae family, and Mollicutes RF9 order (P=0.004, 0.006, 0.010, and 0.019, respectively), but not microbiota alpha or beta diversity. A higher bloating severity score was significantly correlated with a higher relative abundance of Ruminococcus (P=0.032), and significantly inversely correlated with the relative abundance of the Roseburia (P=0.002). Fecal calprotectin levels were positively correlated with alpha diversity (Shannon index, P=0.005) and the relative abundance of Lactobacillus (P=0.004). Pain score was positively correlated with the relative abundance of Cyanobacterium (adjusted P=0.032).

CONCLUSION

Patient symptoms in symptomatic diverticular disease are significantly correlated with features of the fecal microbiota. Our findings suggest the potential utility of therapies that target intestinal microbiology, such as dietary prebiotic supplements.

Effects of urban coarse particles inhalation on oxidative and inflammatory parameters in the mouse lung and colon

Background

Air pollution is a recognized aggravating factor for pulmonary diseases and has notably deleterious effects on asthma, bronchitis and pneumonia. Recent studies suggest that air pollution may also cause adverse effects in the gastrointestinal tract. Accumulating experimental evidence shows that immune responses in the pulmonary and intestinal mucosae are closely interrelated, and that gut-lung crosstalk controls pathophysiological processes such as responses to cigarette smoke and influenza virus infection. Our first aim was to collect urban coarse particulate matter (PM) and to characterize them for elemental content, gastric bioaccessibility, and oxidative potential; our second aim was to determine the short-term effects of urban coarse PM inhalation on pulmonary and colonic mucosae in mice, and to test the hypothesis that the well-known antioxidant N-acetyl-L-cysteine (NAC) reverses the effects of PM inhalation.

Results

The collected PM had classical features of urban particles and possessed oxidative potential partly attributable to their metal fraction. Bioaccessibility study confirmed the high solubility of some metals at the gastric level. Male mice were exposed to urban coarse PM in a ventilated inhalation chamber for 15 days at a concentration relevant to episodic elevation peak of air pollution. Coarse PM inhalation induced systemic oxidative stress, recruited immune cells to the lung, and increased cytokine levels in the lung and colon. Concomitant oral administration of NAC reversed all the observed effects relative to the inhalation of coarse PM.

Conclusions

Coarse PM-induced low-grade inflammation in the lung and colon is mediated by oxidative stress and deserves more investigation as potentiating factor for inflammatory diseases.

Electronic supplementary material

The online version of this article (10.1186/s12989-017-0227-z) contains supplementary material, which is available to authorized users.

Alterations of Food-specific Serum IgG4 Titers to Common Food Antigens in Patients With Irritable Bowel Syndrome

Background/Aims

The role of dietary factors in the pathogenesis of irritable bowel syndrome (IBS) is still unclear. The aim of this study was to compare IgG4 levels to common food antigens between patients with IBS and healthy controls.

Methods

Thirty-two patients diagnosed as IBS according to the Rome III criteria (12 diarrhea subgroup; 20 non-diarrhea subgroup) and 32 sex and age-matched healthy controls participated in the study. Serum IgG4 titers to 90 common foods were measured in each subject. The number of subjects with positivity defined as the cut-off value ≥ 0.7 U/mL was compared.

Results

Patients with IBS had significantly higher IgG4 titers to wheat, leek and taro compared to those of controls. Serum IgG4 titers to ginger, cocoa, walnut, white radish, onion, and lettuce in IBS patients tended to be higher than controls. IgG4 titers to wheat, gluten and gliadin in the diarrhea subgroup, and lettuce, leek and taro in the non-diarrhea subgroup tended to be higher compared with controls. The number of subjects with positivity to apple, orange, lettuce, and leek was significantly higher in IBS patients than controls. The number of subjects with positivity to apple, orange, gluten, and gliadin in the diarrhea subgroup, and egg white, pineapple, soybean, lettuce, and leek in the non-diarrhea subgroup was significantly higher compared with controls.

Conclusions

Serum IgG4 antibody levels to some common foods are abnormally elevated in IBS patients. The type of foods with abnormally elevated serum IgG4 titers in the diarrhea subgroup may be different from that in the non-diarrhea subgroup.

Epidemiological and clinical perspectives on irritable bowel syndrome in India, Bangladesh and Malaysia: A review

Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder, common in clinic and in the community. It has a significant impact on both society and patients' quality of life. The epidemiology, clinical presentation, and management of IBS may vary in different geographical regions due to differences in diet, gastrointestinal infection, socio-cultural and psycho-social factors, religious and illness beliefs, symptom perception and reporting. Although previous reviews and consensus reports on IBS in Asia have been published, Asia is quite diverse socio-demographically. In this context, India, Bangladesh and Malaysia share some similarities, including: (1) large proportion of the population living in rural areas; (2) rapid development and associated lifestyle changes in urban areas; and (3) dietary, cultural and religious practices. The present review explores the clinical and epidemiological data on IBS from these three major nations in South and South-East Asia. In-depth review of the literature revealed important differences between IBS in the East, as revealed by studies from these three countries, and the West; these include a predominantly rural profile, differences in bowel habit and symptom profile, raising concern with regards to diagnostic criteria and subtyping of IBS, higher dietary fiber consumption, frequent lactose malabsorption, parasitosis, and possible overlap between post-infectious IBS and tropical sprue. Moreover, the current perception on difference in prevalence of the disorder in these countries, as compared to the West, might be related to variation in survey methods.

New therapeutic perspectives in irritable bowel syndrome: Targeting low-grade inflammation, immuno-neuroendocrine axis, motility, secretion and beyond

Irritable bowel syndrome (IBS) is a chronic, recurring, and remitting functional disorder of the gastrointestinal tract characterized by abdominal pain, distention, and changes in bowel habits. Although there are several drugs for IBS, effective and approved treatments for one or more of the symptoms for various IBS subtypes are needed. Improved understanding of pathophysiological mechanisms such as the role of impaired bile acid metabolism, neurohormonal regulation, immune dysfunction, the epithelial barrier and the secretory properties of the gut has led to advancements in the treatment of IBS. With regards to therapies for restoring intestinal permeability, multiple studies with prebiotics and probiotics are ongoing, even if to date their efficacy has been limited. In parallel, much progress has been made in targeting low-grade inflammation, especially through the introduction of drugs such as mesalazine and rifaximin, even if a better knowledge of the mechanisms underlying the low-grade inflammation in IBS may allow the design of clinical trials that test the efficacy and safety of such drugs. This literature review aims to summarize the findings related to new and investigational therapeutic agents for IBS, most recently developed in preclinical as well as Phase 1 and Phase 2 clinical studies.

The Role of Mast Cells in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders, but its treatment is unsatisfactory as its pathophysiology is multifactorial. The putative factors of IBS pathophysiology are visceral hypersensitivity and intestinal dysmotility, also including psychological factors, dysregulated gut-brain axis, intestinal microbiota alterations, impaired intestinal permeability, and mucosal immune alterations. Recently, mucosal immune alterations have received much attention with the role of mast cells in IBS. Mast cells are abundant in the intestines and function as intestinal gatekeepers at the interface between the luminal environment in the intestine and the internal milieu under the intestinal epithelium. As a gatekeeper at the interface, mast cells communicate with the adjacent cells such as epithelial, neuronal, and other immune cells throughout the mediators released when they themselves are activated. Many studies have suggested that mast cells play a role in the pathophysiology of IBS. This review will focus on studies of the role of mast cell in IBS and the limitations of studies and will also consider future directions.

Increased Intestinal Permeability and Decreased Barrier Function: Does It Really Influence the Risk of Inflammation?

Background

Increased intestinal permeability due to barrier dysfunction is supposed to cause microbial translocation which may induce low-grade inflammation in various diseases. However, this series of events has not been comprehensively evaluated yet.

Summary

Intestinal epithelial barrier dysfunction and increased permeability have been described in patients with inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), alcoholic liver disease, nonalcoholic steatohepatitis (NASH), liver cirrhosis, acute pancreatitis, primary biliary cholangitis (PBC), type 1 and type 2 diabetes, chronic kidney disease, chronic heart failure (CHF), depression, and other diseases. Most clinical reports used either permeability assays of challenge tests or measurement of circulating bacterial markers like endotoxin for assessment of 'the leaky gut'. The intestinal permeability assessed by the challenge tests has often been related to the changes of tight junction proteins in the epithelium or circulating endotoxin levels. In patients with IBD, alcoholic liver disease, NASH, liver cirrhosis, PBC, obstructive jaundice, severe acute pancreatitis, and CHF, endotoxemia and proinflammatory cytokinemia have been found in addition to increased permeability. In the serum of patients with IBS and depression, antiflagellin antibodies and antilipid A antibodies were detected, respectively, together with increased permeability and proinflammatory cytokinemia. The site of infection, which is localized to the intestine in IBD and IBS, includes various extraintestinal organs in other diseases. The relation of gut dysbiosis to intestinal barrier dysfunction has gradually been clarified.

Key Messages

Although no direct cause-and-effect relationship has been confirmed, all clinical and experimental data suggest the importance of intestinal hyperpermeability in the inflammatory changes of various diseases. Increased intestinal permeability is a new target for disease prevention and therapy. Considering the close relationship of 'the leaky gut' and gut dysbiosis to the major diseases, we can conclude that meticulous dietetic and probiotic approaches to recover healthy microbiota have the potential to make a breakthrough in the management of these diseases tomorrow.

Increased Intestinal Permeability and Decreased Barrier Function: Does It Really Influence the Risk of Inflammation?

Background

Increased intestinal permeability due to barrier dysfunction is supposed to cause microbial translocation which may induce low-grade inflammation in various diseases. However, this series of events has not been comprehensively evaluated yet.

Summary

Intestinal epithelial barrier dysfunction and increased permeability have been described in patients with inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), alcoholic liver disease, nonalcoholic steatohepatitis (NASH), liver cirrhosis, acute pancreatitis, primary biliary cholangitis (PBC), type 1 and type 2 diabetes, chronic kidney disease, chronic heart failure (CHF), depression, and other diseases. Most clinical reports used either permeability assays of challenge tests or measurement of circulating bacterial markers like endotoxin for assessment of 'the leaky gut'. The intestinal permeability assessed by the challenge tests has often been related to the changes of tight junction proteins in the epithelium or circulating endotoxin levels. In patients with IBD, alcoholic liver disease, NASH, liver cirrhosis, PBC, obstructive jaundice, severe acute pancreatitis, and CHF, endotoxemia and proinflammatory cytokinemia have been found in addition to increased permeability. In the serum of patients with IBS and depression, antiflagellin antibodies and antilipid A antibodies were detected, respectively, together with increased permeability and proinflammatory cytokinemia. The site of infection, which is localized to the intestine in IBD and IBS, includes various extraintestinal organs in other diseases. The relation of gut dysbiosis to intestinal barrier dysfunction has gradually been clarified.

Key Messages

Although no direct cause-and-effect relationship has been confirmed, all clinical and experimental data suggest the importance of intestinal hyperpermeability in the inflammatory changes of various diseases. Increased intestinal permeability is a new target for disease prevention and therapy. Considering the close relationship of 'the leaky gut' and gut dysbiosis to the major diseases, we can conclude that meticulous dietetic and probiotic approaches to recover healthy microbiota have the potential to make a breakthrough in the management of these diseases tomorrow.

Electrophysiological Mechanisms of Gastrointestinal Arrhythmogenesis: Lessons from the Heart

Disruptions in the orderly activation and recovery of electrical excitation traveling through the heart and the gastrointestinal (GI) tract can lead to arrhythmogenesis. For example, cardiac arrhythmias predispose to thromboembolic events resulting in cerebrovascular accidents and myocardial infarction, and to sudden cardiac death. By contrast, arrhythmias in the GI tract are usually not life-threatening and much less well characterized. However, they have been implicated in the pathogenesis of a number of GI motility disorders, including gastroparesis, dyspepsia, irritable bowel syndrome, mesenteric ischaemia, Hirschsprung disease, slow transit constipation, all of which are associated with significant morbidity. Both cardiac and gastrointestinal arrhythmias can broadly be divided into non-reentrant and reentrant activity. The aim of this paper is to compare and contrast the mechanisms underlying arrhythmogenesis in both systems to provide insight into the pathogenesis of GI motility disorders and potential molecular targets for future therapy.

Mechanisms of Electrical Activation and Conduction in the Gastrointestinal System: Lessons from Cardiac Electrophysiology

The gastrointestinal (GI) tract is an electrically excitable organ system containing multiple cell types, which coordinate electrical activity propagating through this tract. Disruption in its normal electrophysiology is observed in a number of GI motility disorders. However, this is not well characterized and the field of GI electrophysiology is much less developed compared to the cardiac field. The aim of this article is to use the established knowledge of cardiac electrophysiology to shed light on the mechanisms of electrical activation and propagation along the GI tract, and how abnormalities in these processes lead to motility disorders and suggest better treatment options based on this improved understanding. In the first part of the article, the ionic contributions to the generation of GI slow wave and the cardiac action potential (AP) are reviewed. Propagation of these electrical signals can be described by the core conductor theory in both systems. However, specifically for the GI tract, the following unique properties are observed: changes in slow wave frequency along its length, periods of quiescence, synchronization in short distances and desynchronization over long distances. These are best described by a coupled oscillator theory. Other differences include the diminished role of gap junctions in mediating this conduction in the GI tract compared to the heart. The electrophysiology of conditions such as gastroesophageal reflux disease and gastroparesis, and functional problems such as irritable bowel syndrome are discussed in detail, with reference to ion channel abnormalities and potential therapeutic targets. A deeper understanding of the molecular basis and physiological mechanisms underlying GI motility disorders will enable the development of better diagnostic and therapeutic tools and the advancement of this field.