Persistent intestinal neuromuscular dysfunction after acute nematode infection in mice

The gut microbiome in disorders of gut-brain interaction

Functional gastrointestinal disorders (FGIDs), chronic disorders characterized by either abdominal pain, altered intestinal motility, or their combination, have a worldwide prevalence of more than 40% and impose a high socioeconomic burden with a significant decline in quality of life. Recently, FGIDs have been reclassified as disorders of gut-brain interaction (DGBI), reflecting the key role of the gut-brain bidirectional communication in these disorders and their impact on psychological comorbidities. Although, during the past decades, the field of DGBIs has advanced significantly, the molecular mechanisms underlying DGBIs pathogenesis and pathophysiology, and the role of the gut microbiome in these processes are not fully understood. This review aims to discuss the latest body of literature on the complex microbiota-gut-brain interactions and their implications in the pathogenesis of DGBIs. A better understanding of the existing communication pathways between the gut microbiome and the brain holds promise in developing effective therapeutic interventions for DGBIs.

Modulation of the microbiota across different intestinal segments by Rifaximin in PI-IBS mice

BACKGROUND

Rifaximin has been increasingly applied in irritable bowel syndrome (IBS) treatment. Whether there were differences in the effects of rifaximin on microbiota from different intestinal segments, especially the small intestine where rifaximin predominantly acted, has not been confirmed.

METHODS

In this study, we used Trichinella spiralis infection to induce post infectious irritable bowel syndrome (PI-IBS) and measured visceral sensitivity of mice by means of abdominal withdrawal reflex (AWR) tests to colorectal distention (CRD). We compared the effects of rifaximin on the composition of ileal, colonic mucosal and fecal microbiota in PI-IBS mice.

RESULTS

Rifaximin significantly reduced AWR scores and increased pain threshold in PI-IBS mice, and this effect was associated with the change in the relative abundance of ileal mucosal microbiota. Rifaximin could obviously decrease ileum mucosal microbiota alpha diversity assessed by Shannon microbial diversity index. Meanwhile, the analysis of beta diversity and relative abundance of microbiota at phylum, family and genus levels showed that rifaximin could improve the microbiota structure of ileal mucosa. However, for colonic mucosal and fecal microbiota, this effect of rifaximin was not obvious. Rifaximin could reshape the correlation of genera between different intestinal segments.

CONCLUSION

Rifaximin improved visceral hypersensitivity in PI-IBS mice. Rifaximin mainly affected ileal mucosal microbiota, and its improvement effect on IBS might be closely related to the improvement of ileal microbiota structure.

Gut Microbiota Shifting in Irritable Bowel Syndrome: The Mysterious Role of Blastocystis sp

Irritable bowel syndrome (IBS) is a chronic disorder, which its causative agent is not completely clear; however, the interaction between microorganisms and gastrointestinal (GI) epithelial cells plays a critical role in the development of IBS and presenting symptoms. During recent decades, many studies have highlighted the high prevalence of Blastocystis sp. in patients with IBS and suggested a probable role for this protist in this disease. Recent studies have documented changes in the gut microbiota composition in patients with IBS regarding the presence of Blastocystis sp., but it is not clear that either disturbance of the gut during GI disorders is a favorable condition for Blastocystis sp. colonization or the presence of this protist may lead to alteration in the gut microbiota in IBS patients. In this review, we comprehensively gather and discuss scientific findings covering the role of Blastocystis sp. in IBS via gut microbiota shifting.

Prevalence of irritable bowel syndrome-like symptoms using Rome IV criteria in patients with inactive inflammatory bowel disease and relation with quality of life

Irritable bowel syndrome (IBS)-like symptoms tend to be common in inflammatory bowel disease (IBD) patients even during the long-standing remission phase, and quality of life (QOL) seem to reduce in IBD patients with such symptoms. Thus, the aim of this study was to define the prevalence of IBS-like symptoms in inactive IBD patients using Rome IV criteria and evaluate the effect of IBS-like symptoms on QOL.Total 137 patients with IBD (56 with ulcerative colitis (UC) and 81 with Crohn disease (CD), who had been in long-standing remission according to the clinical scoring system and 123 control participants were included. These patients completed questionnaires to evaluate IBS-like symptoms according to Rome IV criteria, and the impact of these symptoms on the QOL of inactive IBD patients was compared with and without IBS-like symptoms according to disease-specific inflammatory bowel disease questionnaire (IBDQ).Depending on our research, IBS-like symptoms were found in 32% (18/56) of patients with inactive UC, 35% (29/81) of patients with inactive CD, and 13.8% (17/123) of control participants (P < .001). The QOL seemed to be significantly lower in both inactive UC and CD patients with IBS-like symptoms than in those without such symptoms (P < .001).In conclusion, we defined that the prevalence of IBS-like symptoms in IBD patients in remission is 2 to 3 times higher than that in healthy control participants, and significantly lower IBDQ scores showed QOL was reduced in inactive IBD patients with IBS-like symptoms as compared with patients without IBS-like symptoms.

Irritable Bowel Syndrome and Neurological Deficiencies: Is There A Relationship? The Possible Relevance of the Oxidative Stress Status

Background: Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders, exhibiting complex and controversial pathological features. Both oxidative stress and inflammation-related reactive oxygen species production may be involved in IBS pathological development. Thus, we focused on several aspects regarding the causes of oxidative stress occurrence in IBS. Additionally, in the molecular context of oxidative changes, we tried to discuss these possible neurological implications in IBS. Methods: The literature search included the main available databases (e.g., ScienceDirect, Pubmed/Medline, Embase, and Google Scholar). Articles in the English language were taken into consideration. Our screening was conducted based on several words such as “irritable bowel syndrome”, “gut brain axis”, “oxidative stress”, “neuroendocrine”, and combinations. Results: While no consistent evidence suggests clear pathway mechanisms, it seems that the inflammatory response may also be relevant in IBS. The mild implication of oxidative stress in IBS has been described through clinical studies and some animal models, revealing changes in the main markers such as antioxidant status and peroxidation markers. Moreover, it seems that the neurological structures involved in the brain-gut axis may be affected in IBS rather than the local gut tissue and functionality. Due to a gut-brain axis bidirectional communication error, a correlation between neurological impairment, emotional over-responsiveness, mild inflammatory patterns, and oxidative stress can be suggested. Conclusions: Therefore, there is a possible correlation between neurological impairment, emotional over-responsiveness, mild inflammatory patterns, and oxidative stress that are not followed by tissue destruction in IBS patients. Moreover, it is not yet clear whether oxidative stress, inflammation, or neurological impairments are key determinants or in which way these three interact in IBS pathology. However, the conditions in which oxidative imbalances occur may be an interesting research lead in order to find possible explanations for IBS development.

Protease Activated Receptor-2 Induces Immune Activation and Visceral Hypersensitivity in Post-infectious Irritable Bowel Syndrome Mice

BACKGROUND

The role of protease activated receptor-2 (PAR-2) in the pathogenesis of abdominal pain in irritable bowel syndrome (IBS) is not well defined.

AIMS

To investigate the role of PAR-2-mediated visceral hypersensitivity in a post-infectious IBS (PI-IBS) mouse model.

METHODS

T. spiralis-infected PI-IBS mouse model was used. Fecal serine protease activity and intestinal mast cells were evaluated. Intestinal permeability was assessed by urine lactulose/mannitol ratio, and colonic expressions of PAR-2 and tight junction (TJ) proteins were examined by Western blot. Intestinal immune profile was assessed by measuring Th (T helper) 1/Th2 cytokine expression. Visceral sensitivity was evaluated by abdominal withdrawal reflex in response to colorectal distention.

RESULTS

Colonic PAR-2 expression as well as fecal serine protease activity and intestinal mast cell counts were elevated in PI-IBS compared to the control mice. Decreased colonic TJ proteins expression, increased lactulose/mannitol ratio, elevated colonic Th1/Th2 cytokine ratio, and visceral hypersensitivity were observed in PI-IBS compared to the control mice. Administration of PAR-2 agonist in control mice demonstrated similar changes observed in PI-IBS mice, while PAR-2 antagonist normalized the increased intestinal permeability and reduced visceral hypersensitivity observed in PI-IBS mice.

CONCLUSIONS

PAR-2 activation increases intestinal permeability leading to immune activation and visceral hypersensitivity in PI-IBS mouse model.

Rome Foundation Working Team Report on Post-Infection Irritable Bowel Syndrome

BACKGROUND & AIMS

The existence of postinfection irritable bowel syndrome (PI-IBS) has been substantiated by epidemiology studies conducted in diverse geographic and clinical settings. However, the available evidence has not been well summarized, and there is little guidance for diagnosis and treatment of PI-IBS. The ROME Foundation has produced a working team report to summarize the available evidence on the pathophysiology of PI-IBS and provide guidance for diagnosis and treatment, based on findings reported in the literature and clinical experience.

METHODS

The working team conducted an evidence-based review of publication databases for articles describing the clinical features (diagnosis), pathophysiology (intestinal sensorimotor function, microbiota, immune dysregulation, barrier dysfunction, enteroendocrine pathways, and genetics), and animal models of PI-IBS. We used a Delphi-based consensus system to create guidelines for management of PI-IBS and a developed treatment algorithm based on published findings and experiences of team members.

RESULTS

PI-IBS develops in about 10% of patients with infectious enteritis. Risk factors include female sex, younger age, psychological distress during or before acute gastroenteritis, and severity of the acute episode. The pathogenesis of PI-PBS appears to involve changes in the intestinal microbiome as well as epithelial, serotonergic, and immune system factors. However, these mechanisms are incompletely understood. There are no evidence-based, effective pharmacologic strategies for treatment of PI-IBS. We provide a consensus-based treatment algorithm, based on clinical presentation and potential disease mechanisms.

CONCLUSIONS

Based on a systematic review of the literature and team experience, we summarize the clinical features, pathophysiology (from animal models and human studies), and progression of PI-IBS. Based on these findings, we present an algorithm for diagnosis and treatment of PI-IBS based on team consensus. We also propose areas for future investigation.

MLCK-mediated intestinal permeability promotes immune activation and visceral hypersensitivity in PI-IBS mice

BACKGROUND

Alterations in intestinal permeability regulated by tight junctions (TJs) are associated with immune activation and visceral hypersensitivity in irritable bowel syndrome (IBS). Myosin light chain kinase (MLCK) is an important mediator of epithelial TJ. The aim of this study is to investigate the role of MLCK in the pathogenesis of IBS using a post infectious IBS (PI-IBS) mouse model.

METHODS

Trichinella spiralis-infected PI-IBS mouse model was used. Urine lactulose/mannitol ratio was measured to assess intestinal epithelial permeability. Western blotting was used to evaluate intestinal TJ protein (zonula occludens-1) and MLCK-associated protein expressions. Immune profile was assessed by measuring Th (T helper) 1/Th2 cytokine expression. Visceral sensitivity was determined by abdominal withdrawal reflex in response to colorectal distension.

RESULTS

Eight weeks after inoculation with T. spiralis, PI-IBS mice developed decreased pain and volume thresholds during colorectal distention, increased urine lactulose/mannitol ratio, elevated colonic Th1/Th2 cytokine ratio, and decreased zonula occludens-1 expression compared to the control mice. MLCK expression was dramatically elevated in the colonic mucosa of PI-IBS mice compared to the control mice, alongside increased pMLC/MLC and decreased MLCP expression. Administration of MLCK inhibitor and TJ blocker both reversed the increased intestinal permeability, visceral hypersensitivity, and Th1-dominant immune profile in PI-IBS mice.

CONCLUSION

MLCK is a pivotal step in inducing increased intestinal permeability promoting low-grade intestinal immune activation and visceral hypersensitivity in PI-IBS mice. MLCK inhibitor may provide a potential therapeutic option in the treatment of IBS.

Pathogenesis, Experimental Models and Contemporary Pharmacotherapy of Irritable Bowel Syndrome: Story About the Brain-Gut Axis

Background

Although the precise pathophysiology of irritable bowel syndrome (IBS) remains unknown, it is generally considered to be a disorder of the brain-gut axis, representing the disruption of communication between the brain and the digestive system. The present review describes advances in understanding the pathophysiology and experimental approaches in studying IBS, as well as providing an update of the therapies targeting brain-gut axis in the treatment of the disease.

Methods

Causal factors of IBS are reviewed. Following this, the preclinical experimental models of IBS will be introduced. Besides, both current and future therapeutic approaches of IBS will be discussed.

Results

When signal of the brain-gut axis becomes misinterpreted, it may lead to dysregulation of both central and enteric nervous systems, altered intestinal motility, increased visceral sensitivity and consequently contributing to the development of IBS. Interference of the brain-gut axis can be modulated by various psychological and environmental factors. Although there is no existing animal experiment that can represent this complex multifactorial disease, these in vivo models are clinically relevant readouts of gastrointestinal functions being essential to the identification of effective treatments of IBS symptoms as well as their molecular targets. Understanding the brain-gut axis is essential in developing the effective therapy for IBS. Therapies include improvement of GI motor functions, relief of visceral hypersensitivity and pain, attenuation of autonomic dysfunctions and suppression of mucosal immune activation.

Conclusion

Target-oriented therapies that provide symptomatic, psychological and physiological benefits could surely help to improve the quality of life of IBS patients.

Pathophysiology and Therapeutic Strategies for Symptomatic Uncomplicated Diverticular Disease of the Colon

Colonic diverticulosis imposes a significant burden on industrialized societies. The current accepted causes of diverticula formation include low fiber content in the western diet with decreased intestinal content and size of the lumen, leading to the transmission of muscular contraction pressure to the wall of the colon, inducing the formation of diverticula usually at the weakest point of the wall where penetration of the blood vessels occurs. Approximately 20 % of the patients with colonic diverticulosis develop abdominal symptoms (i.e., abdominal pain and discomfort, bloating, constipation, and diarrhea), a condition which is defined as symptomatic uncomplicated diverticular disease (SUDD). The pathogenesis of SUDD symptoms remains uncertain and even less is known about how to adequately manage bowel symptoms. Recently, low-grade inflammation, altered intestinal microbiota, visceral hypersensitivity, and abnormal colonic motility have been identified as factors leading to symptom development, thus changing and improving the therapeutic approach. In this review, a comprehensive search of the literature regarding on SUDD pathogenetic hypotheses and pharmacological strategies was carried out. The pathogenesis of SUDD, although not completely clarified, seems to be related to an interaction between colonic microbiota alterations, and immune, enteric nerve, and muscular system dysfunction (Cuomo et al. in United Eur Gastroenterol J 2:413-442, 2014). Greater understanding of the inflammatory pathways and gut microbiota composition in subjects affected by SUDD has increased therapeutic options, including the use of gut-directed antibiotics, mesalazine, and probiotics (Bianchi et al. in Aliment Pharmacol Ther 33:902-910, 2011; Comparato et al. in Dig Dis Sci 52:2934-2941, 2007; Tursi et al. in Aliment Pharmacol Ther 38:741-751, 2013); however, more research is necessary to validate the safety, effectiveness, and cost-effectiveness of these interventions.

Actions of probiotics on trinitrobenzenesulfonic acid-induced colitis in rats

We investigated the actions of probiotics, Streptococcus faecalis 129 BIO 3B (SF3B), in a trinitrobenzenesulfonic acid- (TNBS-) induced colitis model in rats. After TNBS was administered into the colons of rats for induction of colitis, the rats were divided into two groups: one group was given a control diet and the other group was given a diet containing SF3B for 14 days. There were no apparent differences in body weight, diarrhea period, macroscopic colitis score, and colonic weight/length ratio between the control group and SF3B group, suggesting that induction of colitis was not prevented by SF3B. Next, we investigated whether SF3B-containing diet intake affects the restoration of enteric neurotransmissions being damaged during induction of colitis by TNBS using isolated colonic preparations. Recovery of the nitrergic component was greater in the SF3B group than in the control group. A compensatory appearance of nontachykininergic and noncholinergic excitatory components was less in the SF3B group than in the control group. In conclusion, the present study suggests that SF3B-containing diet intake can partially prevent disruptions of enteric neurotransmissions induced after onset of TNBS-induced colitis, suggesting that SF3B has therapeutic potential.

Changes of cytokine levels in a mouse model of post-infectious irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a highly prevalent functional gastrointestinal disorder. Post-infectious IBS (PI-IBS) is caused by an acute gastrointestinal infection preceding the onset of symptoms. However, the pathophysiology of PI-IBS is not clear, and the purpose of this study was to investigate the probable immune mechanisms of PI-IBS.

METHODS

C57BL/6 mice were randomly assigned to either an infection group or a control group. Mice in the infection group were infected with Trichinella spiralis to establish a model of PI-IBS (500 Trichinella), while control mice received only salt solution. Visceral sensitivity of colorectal distention in mice was evaluated by abdominal withdrawal reflex scores and intestinal inflammation was assessed using hematoxylin-eosin staining; at day 56 post-infection, the mRNA and protein levels of specific cytokines in the gut segments were detected using reverse-transcription polymerase chain reaction and enzyme-linked immunoabsorbent assay.

RESULTS

Levels of interferon γ and interleukin (IL)-17 in the PI-IBS group were significantly increased in the duodenum and ileum, and IL-10 was decreased in the jejunum, ileum, and colon compared with control mice. However, the expression level of IL-1β was not significantly different between the two groups.

CONCLUSIONS

The present study suggests that the local low-grade inflammation and immune activation that are an important component of the pathophysiology of PI-IBS are primarily induced and maintained by specific cytokines.

Is fecal microbiota transplantation (FMT) an effective treatment for patients with functional gastrointestinal disorders (FGID)?

BACKGROUND

Despite its high prevalence and significant effect on quality of life, the etiology of functional gastrointestinal disorders (FGID), and specifically irritable bowel syndrome (IBS), has yet to be fully elucidated. While alterations in immunity, motility, and the brain-gut axis have been implicated in disease pathogenesis, the intestinal microbiota are increasingly being shown to play a role and numerous studies have demonstrated significant differences from normal in the intestinal flora of patients with FGID, and between types of FGID. Fecal microbiota transplantation (FMT) is a curative therapy for Clostridium difficile infection (CDI), a disease hallmarked by intestinal dysbiosis, and FMT is now being explored as a means to also restore intestinal homeostasis in FGID.

PURPOSE

This review aims to investigate the role of intestinal microbiota in the pathogenesis of FGID, the implications of FMT for the treatment of FGID, and the challenges encountered in measuring response to a specific intervention in patients with FGID.

Experimental model of tympanic colic (acute abdomen) in chinchillas (Chinchilla lanigera)

Digestive disorders caused by sudden changes in diet or inappropriate diet are among the most common disorders of the digestive system. Cecal or intestinal tympany, one consequence of inappropriate diet, is characterized by the accumulation of gases, marked distension of the cecum and colon and the induction of inflammatory processes. To know the effects of intestinal tympany on the enteric plexuses, we developed a method of experimental tympanic colic (TC) in the Chinchilla lanigera. This species was used in view of its susceptibility to TC. TC was induced with a diet rich in alfalfa associated with grain overload for two weeks. Physical and clinical examination including the von Frey test confirmed the diagnosis. The chinchillas with acute abdomen were treated with 1% ketoprofen and resumption of a balanced diet. Necropsy and histopathological analysis showed tympany-induced alterations mainly in the cecum and colon. After treatment, the control conditions were restored. The TC protocol is proposed as an experimental approach designed to aid the study of the effects of acute intestinal inflammation and obstruction caused by an inappropriate diet.

WE. Motility response to colonic distention is increased in postinfectious irritable bowel syndrome (PI-IBS)

BACKGROUND

Acute intestinal infection leads to persistent intestinal smooth muscle hypercontractility and pain hypersensitivity after resolution of the infection in animal models. We investigated whether postinfectious irritable bowel syndrome (PI-IBS) is associated with abnormalities in phasic contractions of the colon, smooth muscle tone, and pain sensitivity compared to non-PI-IBS (NI-IBS) or healthy controls (HC).

METHODS

Two hundred and eighteen Rome III-positive IBS patients and 43 HC participated. IBS patients were designated PI-IBS, if their IBS symptoms began following an episode of gastroenteritis characterized by two or more of: fever, vomiting, or diarrhea. Pain threshold to phasic distentions of the descending colon was assessed using a barostat. Colonic motility was assessed with the barostat bag minimally inflated to the individual operating pressure (IOP), at 20 mmHg above the IOP, and following a test meal. IBS symptom severity and psychological symptoms were assessed by the IBS Severity Scale (IBS-SS) and the Brief Symptom Inventory-18 (BSI-18).

KEY RESULTS

Twenty two (10.1%) met criteria for PI-IBS. Both IBS and HC groups showed a significant increase in motility index during intraluminal distention and following meals. The magnitude of the response to distention above (orad to) the balloon was significantly greater in PI-IBS compared with NI-IBS (p < 0.05) or HC (p < 0.01). Differences between PI-IBS and NI-IBS were not significant for IBS symptom severity, pain threshold, barostat bag volumes, or any psychological score on the BSI-18.

CONCLUSIONS & INFERENCES

Patients with PI-IBS have greater colonic hypercontractility than NI-IBS. We speculate that sustained mild mucosal inflammation may cause this colonic irritability.

Experimental gastritis leads to anxiety- and depression-like behaviors in female but not male rats

Human and animals studies support the idea that there is a gender-related co-morbidity of pain-related and inflammatory gastrointestinal (GI) diseases with psychological disorders. This co-morbidity is the evidence for the existence of GI-brain axis which consists of immune (cytokines), neural (vagus nerve) and neuroendocrine (HPA axis) pathways. Psychological stress causes disturbances in GI physiology, such as altered GI barrier function, changes in motility and secretion, development of visceral hypersensitivity, and dysfunction of inflammatory responses. Whether GI inflammation would exert impact on psychological behavior is not well established. We examined the effect of experimental gastritis on anxiety- and depression-like behaviors in male and female Sprague-Dawley rats, and evaluated potential mechanisms of action. Gastritis was induced by adding 0.1% (w/v) iodoacetamide (IAA) to the sterile drinking water for 7 days. Sucrose preference test assessed the depression-like behavior, open field test and elevated plus maze evaluated the anxiety-like behavior. IAA treatment induced gastric inflammation in rats of either gender. No behavioral abnormality or dysfunction of GI-brain axis was observed in male rats with IAA-induced gastritis. Anxiety- and depression-like behaviors were apparent and the HPA axis was hyperactive in female rats with IAA-induced gastritis. Our results show that gastric inflammation leads to anxiety- and depression-like behaviors in female but not male rats via the neuroendocrine (HPA axis) pathway, suggesting that the GI inflammation can impair normal brain function and induce changes in psychological behavior in a gender-related manner through the GI-to-brain signaling.

Intestinal microbiota and immune function in the pathogenesis of irritable bowel syndrome

The pathophysiology of irritable bowel syndrome (IBS) is believed to involve alterations in the brain-gut axis; however, the etiological triggers and mechanisms by which these changes lead to symptoms of IBS remain poorly understood. Although IBS is often considered a condition without an identified "organic" etiology, emerging evidence suggests that alterations in the gastrointestinal microbiota and altered immune function may play a role in the pathogenesis of the disorder. These recent data suggest a plausible model in which changes in the intestinal microbiota and activation of the enteric immune system may impinge upon the brain-gut axis, causing the alterations in gastrointestinal function and the clinical symptoms observed in patients with IBS. This review summarizes the current evidence for altered intestinal microbiota and immune function in IBS. It discusses the potential etiological role of these factors, suggests an updated conceptual model for the pathogenesis of the disorder, and identifies areas for future research.

Early Trichinella spiralis and Trichinella nativa infections induce similar gene expression profiles in rat jejunal mucosa

Trichinella spiralis causes a significantly higher parasite burden in rat muscle than Trichinella nativa. To assess whether the difference in infectivity is due to the early intestinal response, we analyzed gene expression changes in the rat jejunum during Trichinella infection with a whole-genome microarray. The rats were euthanized on day five of infection, and their jejunal mucosa was sampled for microarray analysis. In addition, intestinal histology and hematology were examined. Against our expectations, the gene expression changes were similar in both T.nativa- and T. spiralis-infected groups. The two groups were hence pooled, and in the combined Trichinella-infected group, 551 genes were overexpressed and 427 underexpressed when compared to controls (false discovery rate ≤ 0.001 and fold change at least 2 in either direction). Pathway analysis identified seven pathways significantly associated with Trichinella infection (p < 0.05). The microarray data suggested nonspecific damage and an inflammatory response in the jejunal mucosa. Histological findings, including hyperemia, hemorrhage and a marked infiltration of inflammatory cells, supported the microarray data. Trichinella infection caused complex gene expression changes that indicate a host response to tissue damage in the mucosa of the jejunum, but the changes were not notably dependent on the studied species of Trichinella.

An Update on Post-infectious Irritable Bowel Syndrome: Role of Genetics, Immune Activation, Serotonin and Altered Microbiome

The literature on post-infectious irritable bowel syndrome (IBS) is reviewed with special emphasis on recent new data. Further accounts of this phenomenon continue to be reported following a range of infections including giardiasis as well as viral and bacterial gastroenteritis. Risk factors such as severity of initial illness, female gender together with adverse psychological factors have been confirmed. Recent evidence of a genetic predisposition needs replication. Animal studies suggest activation of mast cells and inflammation driven impairment of serotonin transporter may be important, which are findings supported by some recent human studies in IBS with diarrhoea. Experimentally induced inflammation leads to damage and remodelling of enteric nerves. Similar changes have been reported in IBS patients with increase in nerves expressing transient receptor potential cation channel V1. While changes in microbiota are very likely this area has yet to be explored using modern techniques. Since the prognosis is for slow improvement, treatments should currently target the key symptoms of diarrhoea and abdominal pain. Future therapies aimed at correcting underlying mechanisms including immune activation and serotonin excess are currently being explored and may provide better treatments in the future.

Chronic gastrointestinal consequences of acute infectious diarrhea: evolving concepts in epidemiology and pathogenesis

Acute infectious diarrhea is a frequent occurrence both in the developing world, where it results in considerable mortality, and in developed countries, where it accounts for a significant number of health visits, hospitalizations, and medical and non-medical losses. Recent evidence in basic, clinical, and epidemiological science domains has emerged that suggest that the burden caused by these infections is not limited to the acute illness, but may result in triggering or contributing to the pathogenesis of a number of chronic health problems. This review considers the breadth of this information for the purpose of consolidating what is currently known, identifying gaps in knowledge, and describing future directions and policy implications related to the chronic consequences of acute infectious diarrhea. A unifying hypothesis of this review is that infections may trigger a number of long-lasting changes in gut physiology and immunity that can increase the risk to a variety of chronic gastrointestinal diseases, particularly in genetically susceptible individuals.

Characteristics of intestinal lamina propria dendritic cells in a mouse model of postinfectious irritable bowel syndrome

BACKGROUND AND AIM

Postinfectious irritable bowel syndrome (PI-IBS), which results from inflammation has been emphasized a lot recently. Dendritic cells (DCs) may contribute to intestinal mucosal immune activation in the pathogenesis of PI-IBS. This study tested the hypothesis that phenotype and function of intestinal lamina propria DCs (LPDCs) changed in the development of a PI-IBS mouse model.

METHODS

Mice infected with Trichinella spiralis underwent abdominal withdrawal reflex (AWR) to evaluate visceral sensitivity. LPDCs were isolated and purified by intestine digestion and magnetic label-based technique. Surface markers were analyzed by flow cytometry. Endocytic activity, mixed lymphocyte reaction (MLR) and chemotaxis were studied. Cytokine production of the LPDCs cocultured with CD4(+) T cells was determined.

RESULTS

Intestinal inflammation resolved after 8 weeks infection with sustained visceral hyperalgesia. Surface markers CD86 and MHCII were lower in the acute infection group, but increased in the PI-IBS stage. Enhanced ability of endocytic activity and decreased abilities to attract and stimulate CD4(+) T cell proliferation were in the acute infection group. However, LPDCs in the PI-IBS stage showed weakened endocytic ability with enhanced abilities to attract and stimulate CD4(+) T cell proliferation. Cocultured LPDCs with CD4(+) T cells showed a predominant Th2 response in the acute infection stage, and more important roles of Th1, Th17 responses in the PI-IBS stage.

CONCLUSIONS

The hypothesis was supported that the phenotype and function of LPDCs changed in the development of PI-IBS, which induced the maintenance of intestinal mucosal immune activation and might provide a clue for the treatment of the disease.

Mechanisms underlying visceral hypersensitivity in irritable bowel syndrome

Visceral hypersensitivity is currently considered a key pathophysiological mechanism involved in pain perception in large subgroups of patients with functional gastrointestinal disorders, including irritable bowel syndrome (IBS). In IBS, visceral hypersensitivity has been described in 20%-90% of patients. The contribution of the central nervous system and psychological factors to visceral hypersensitivity in patients with IBS may be significant, although still debated. Peripheral factors have gained increasing attention following the recognition that infectious enteritis may trigger the development of persistent IBS symptoms, and the identification of mucosal immune, neural, endocrine, microbiological, and intestinal permeability abnormalities. Growing evidence suggests that these factors play an important role in pain transmission from the periphery to the brain via sensory nerve pathways in large subsets of patients with IBS. In this review, we will report on recent data on mechanisms involved in visceral hypersensitivity in IBS, with particular attention paid to peripheral mechanisms.

The role of eosinophils and mast cells in intestinal functional disease

Functional gastrointestinal disorders (FGIDs) are common and currently defined by a symptom-based classification with no discernable pathology. In functional dyspepsia (FD), the duodenum is now implicated as a key area where symptoms originate.This is attributed to immune activation with increasing evidence indicating a role for duodenal eosinophilia. In irritable bowel syndrome (IBS), mastocytosis has been documented throughout the small and large intestine. Eosinophils and mast cells are an important link between innate and adaptive immunity, and are important in allergic type TH2 inflammation. Eosinophils may give rise to symptoms due to release of preformed cytokine proteins, which trigger neural excitation, muscle spasm, and pain. The close relationship of mast cells to nerves in IBS may similarly give rise to symptoms. Genetic studies also support of the role of innate immunity in FGIDs. The data supporting a prime role for eosinophils and mast cells in subsets of FD and IBS has become credible, and these data should be used to implement advances in diagnosis and therapeutic trials.

Effect of probiotics on gastrointestinal function: evidence from animal models

The digestive tract works through a complex net of integrative functions. At the level of the gut, this integration occurs between the immune, neuromotor and endocrine systems, the intestinal barrier and gut luminal contents. Gastrointestinal function is controlled and coordinated by the central nervous system to ensure effective motility, secretion, absorption and mucosal immunity. Thus, it is clear that the gut keeps a tightly regulated equilibrium between luminal stimuli, epithelium, immunity and neurotransmission in order to maintain homeostasis. It follows that perturbations of any of these systems may lead to gut dysfunction. While we acknowledge that the gut-brain axis is crucial in determining coordinated gut function, in this review we will focus on peripheral mechanisms that influence gastrointestinal physiology and pathophysiology. We will discuss the general hypothesis that the intestinal content is crucial in determining what we consider normal gastrointestinal physiology, and consequently that alteration in luminal content by dietary, antibiotic or probiotic manipulation can result in changes in gut function. This article focuses on lessons learned from animal models of gut dysfunction.

Inflammation and microflora

Irritable bowel syndrome (IBS) is the most common gastrointestinal condition, affecting 10% to 20% of adults in developed countries. Over the last few years, growing evidence has supported a new hypothesis for IBS based on alterations in intestinal bacterial composition. This article reviews the evidence for a bacterial concept in IBS and begins to formulate a hypothesis of how these bacterial systems could integrate in a new pathophysiologic mechanism in the development of IBS. Data suggesting an interaction between this gut flora and inflammation in the context of IBS is also presented.

Systematic review of animal models of post-infectious/post-inflammatory irritable bowel syndrome

AIMS

Post-infectious irritable bowel syndrome (PI-IBS) is a subset of IBS which occurs after an episode of acute gastrointestinal infections. The mechanisms of PI-IBS are not fully understood. Currently, numerous animal models have been used in the study of PI-IBS. This article reviews the strengths and weaknesses of these models.

METHODS

All relevant articles were identified by searching in Ovid SP from 1962, the year the term PI-IBS was coined, up to December 31, 2009. The types of model were categorized as either post-infectious or post-inflammatory, and the characteristics of each kind of model were listed.

RESULTS

Based on our literature search, 268 articles were identified. Of those articles, 50 were included in this review. The existing PI-IBS models include infection with bacteria (e.g., Campylobacter jejuni, Salmonella enterica, and Campylobacter rodentium), and infection with parasites (e.g., Trichinella spiralis, Nippostrongylus brasiliensis, and Cryptosporidium parvum). The post-inflammatory IBS models are commonly induced with chemical agents, such as acetic acid, deoxycholic acid, dextran sulfate sodium, mustard oil, zymosan, and trinitrobenzene sulfonic acid (TNBS). TNBS is the most commonly used agent for post-inflammatory IBS models, but the experimental protocol varies. These models have one or more aspects similar to IBS patients.

CONCLUSIONS

Different methods have been used for the development of post-infectious or post-inflammatory IBS models. Each model has its weaknesses and strengths. More studies are needed to establish post-infection IBS models using more common pathogens. A standard protocol in developing TNBS-induced post-inflammatory IBS model is needed.

Mechanisms underlying gut dysfunction in a murine model of chronic parasitic infection

Irritable bowel syndrome (IBS) is common in countries where chronic parasitic infestations are endemic. However, the relationship between parasitic infection and IBS is not clear. The aim of this study was to examine whether chronic parasitic infection is accompanied by gut dysfunction and whether the continued presence of the parasite is required for the maintenance of the dysfunction. We used chronic Trichuris muris infection in Th1-biased susceptible AKR mice to evaluate this relationship. AKR mice were infected with T. muris and were euthanized on various days postinfection (pi) to examine worm burden, muscle function, and immune and inflammatory responses. Mice were treated with the anthelmintic oxantel pamoate to assess the effect of eradication of infection on muscle function. Infection resulted in persistence of the parasite, elevated IFN-γ, and increased MPO activity evident at 45 days pi. This was accompanied by a reduction in muscle contractility and excitatory innervation. Whereas parasite eradication at 7 days pi normalized IFN-γ and muscle contractility, eradication at 28 days pi failed to normalize muscle contractility. Administration of dexamethasone after parasite eradication normalized all parameters. Anthelmintic treatment improved histology except for eosinophils, which were normalized by subsequent dexamethasone therapy. Persistent gut dysfunction is independent of the continued presence of the parasite and is maintained by inflammatory process that includes eosinophils. Thus data in this preclinical model suggest that parasitic infection could be a cause of IBS, and the lack of symptomatic improvement following eradication is insufficient evidence to refute a causal relationship between the infection and IBS.

Low-grade mucosal inflammation induces colonic PAR-2 activation and visceral hypersensitivity in mice

AIM: To detect the expression of protease-activated receptor-2 (PAR-2) in the colon and substance P (SP) and calcitonin gene-related peptide (CGRP) in the cornu dorsale medullae spinalis and to explore the relationship between the activation of PAR-2 and visceral hypersensitivity in mice with dextran sulfate sodium (DSS)-induced low-glade colonic mucosal inflammation (LGI).

METHODS: Thirty-six C57BL/6 mice were randomly divided into two groups: LGI group and control group. The LGI group was given 1.5% DSS solution for 5 d and distilled water for another 10 d, while the control group was given distilled water only. After treatment, the myoelectric activity of the abdominal wall at different levels of colorectal distension (CRD) was recorded. The expression of SP and CGRP in the cornu dorsale medullae spinalis and PAR-2 in the colonic mucosa was detected by immunohistochemistry.

RESULTS: After treatment, colonic histological index (HI) in the LGI group was 1.500 ± 0.926. When the colon was distended to a pressure of 15 mmHg, the myoelectric activity of the abdominal wall in the LGI group was comparable to that in the control group (27.958 μV ± 1.660 μV vs 26.947 μV ± 0.854 μV, P > 0.05). However, the myoelectric activity of the abdominal wall was significantly higher in the LGI group than in the control group when the colon was distended to a pressure of 30, 45 or 60 mmHg (33.455 μV ± 3.786 μV vs 31.253 μV ± 3.842 μV; 46.848 μV ± 4.038 μV vs 37.267 μV ± 2.542 μV; 47.207 μV ± 18.151 μV vs 33.798 μV ± 8.415 μV, all P < 0.05). The integrated optical density (IA) of PAR-2 staining in the distal colon was significantly higher in the LGI group than in the control group. The IA of SP and CGRP staining in the spine cord was also significantly higher in the LGI group than in the control group (40.769 ± 8.422 vs 21.718 ± 4.131; 30.288 ± 13.530 vs 10.788 ± 4.490; 46.829 ± 26.261 vs 13.997 ± 3.340, all P < 0.05). There is a positive correlation between the expression of PAR-2 and SP and between the expression of PAR-2 and CGRP in the LGI group (r = 0.622, P < 0.05, r = 0.588, P < 0.05). The expression of PAR-2, SP or CGRP was closely correlated with the myoelectric activity of the abdominal wall in the LGI group (r = 0.439-0.835, P < 0.05).

CONCLUSION: Low-grade mucosal inflammation induces visceral hypersensitivity in mice possibly by activating colonic PAR-2.

ICC density predicts bacterial overgrowth in a rat model of post-infectious IBS

AIM: To investigate the interstitial cells of Cajal (ICC) number using a new rat model.

METHODS: Sprague-Dawley rats were assigned to two groups. The first group received gavage with Campylobacter jejuni (C. jejuni) 81-176. The second group was gavaged with placebo. Three months after clearance of Campylobacter from the stool, precise segments of duodenum, jejunum, and ileum were ligated in self-contained loops of bowel that were preserved in anaerobic bags. Deep muscular plexus ICC (DMP-ICC) were quantified by two blinded readers assessing the tissue in a random, coded order. The number of ICC per villus was compared among controls, Campylobacter recovered rats without small intestinal bacterial overgrowth (SIBO), and Campylobacter recovered rats with SIBO.

RESULTS: Three months after recovery, 27% of rats gavaged with C. jejuni had SIBO. The rats with SIBO had a lower number of DMP-ICC than controls in the jejunum and ileum. Additionally there appeared to be a density threshold of 0.12 DMP-ICC/villus that was associated with SIBO. If ileal density of DMP-ICC was < 0.12 ICC/villus, 54% of rats had SIBO compared to 9% among ileal sections with > 0.12 (P < 0.05). If the density of ICC was < 0.12 DMP-ICC/villus in more than one location of the bowel, 88% of these had SIBO compared to 6% in those who did not (P < 0.001).

CONCLUSION: In this post-infectious rat model, the development of SIBO appears to be associated with a reduction in DMP-ICC. Further study of this rat model might help understand the pathophysiology of post-infectious irritable bowel syndrome.

Increased feelings with increased body signals

Since the beginning of psychology as a scientific endeavour, the question of whether the body plays a role in how a person experiences emotion has been the centre of emotion research. Patients with structural gastrointestinal disorders, such as Crohn's disease, provide an intriguing opportunity to study the influence of body signals on emotions and feelings. In the present study, emotionally salient films were presented to participants with Crohn's disease in either the active state (Crohn's-active, CA) or silent state (Crohn's-silent, CS), and to normal comparison (NC) participants. We hypothesized that CA participants would have increased feelings, compared with CS and NC participants, when viewing emotional films designed to elicit happiness, disgust, sadness and fear. Gastric myoelectrical activity (electrogastrogram, or EGG) was measured during the films, and after each film was presented, participants rated emotion intensity (arousal) and pleasantness (valence). All groups labelled the emotions similarly. In support of the hypothesis, CA participants showed an increase in subjective arousal for negative emotions compared with CS and NC participants. The CA participants also showed increased EGG during emotional film viewing, as well as a strong positive correlation of EGG with arousal ratings. Together, these findings can be taken as evidence that aberrant feedback from the gastrointestinal system up-regulates the intensity of feelings of negative emotions.

Effectiveness of trimebutine maleate on modulating intestinal hypercontractility in a mouse model of postinfectious irritable bowel syndrome

Trimebutine maleate, which modulates the calcium and potassium channels, relieves abdominal pain in patients with irritable bowel syndrome. However, its effect on postinfectious irritable bowel syndrome is not clarified. The aim of this study was to investigate the effectiveness of trimebutine maleate on modulating colonic hypercontractility in a mouse model of postinfectious irritable bowel syndrome. Mice infected up to 8 weeks with T. spiralis underwent abdominal withdrawal reflex to colorectal distention to evaluate the visceral sensitivity at different time points. Tissues were examined for histopathology scores. Colonic longitudinal muscle strips were prepared in the organ bath under basal condition or to be stimulated by acetylcholine and potassium chloride, and consecutive concentrations of trimebutine maleate were added to the bath to record the strip responses. Significant inflammation was observed in the intestines of the mice infected 2 weeks, and it resolved in 8 weeks after infection. Visceral hyperalgesia and colonic muscle hypercontractility emerged after infection, and trimebutine maleate could effectively reduce the colonic hyperreactivity. Hypercontractility of the colonic muscle stimulated by acetylcholine and high K(+) could be inhibited by trimebutine maleate in solution with Ca(2+), but not in Ca(2+) free solution. Compared with 8-week postinfectious irritable bowel syndrome group, 2-week acute infected strips were much more sensitive to the stimulators and the drug trimebutine maleate. Trimebutine maleate was effective in reducing the colonic muscle hypercontractility of postinfectious irritable bowel syndrome mice. The findings may provide evidence for trimebutine maleate to treat postinfectious irritable bowel syndrome patients effectively.

Intestinal bacteria and the regulation of immune cell homeostasis

The human intestine is colonized by an estimated 100 trillion bacteria. Some of these bacteria are essential for normal physiology, whereas others have been implicated in the pathogenesis of multiple inflammatory diseases including IBD and asthma. This review examines the influence of signals from intestinal bacteria on the homeostasis of the mammalian immune system in the context of health and disease. We review the bacterial composition of the mammalian intestine, known bacterial-derived immunoregulatory molecules, and the mammalian innate immune receptors that recognize them. We discuss the influence of bacterial-derived signals on immune cell function and the mechanisms by which these signals modulate the development and progression of inflammatory disease. We conclude with an examination of successes and future challenges in using bacterial communities or their products in the prevention or treatment of human disease.

The putative role of the intestinal microbiota in the irritable bowel syndrome

The irritable bowel syndrome (IBS) is a chronic abdominal symptom complex that is heterogeneous in terms of its clinical presentation and underlying pathophysiology and pathogenesis. It is now established that enteric infection can trigger the syndrome in at least a subset of patients. In addition, there is growing evidence of low grade inflammation and immune activation in the distal bowel of some IBS patients. These observations now prompt the question as to what maintains gut dysfunction in these patients. The intestinal microbiota influences a broad array of host organs that include the gut and the brain, and is an important determinant of normal function in these systems. Disruption of the delicate balance between the host and its intestinal microbiota (termed dysbiosis) results in changes in the mucosal immune system that range from overt inflammation as seen in Crohn's Disease, to low grade inflammation without tissue injury, as seen in a subset of IBS patients. Under experimental conditions, disruption of the microbiota also produces changes in gut sensory-motor function and immune activity. Thus, dysbiosis induced by infection, dietary change or drugs such as antibiotics could produce low grade inflammation and chronic gut dysfunction, reminiscent of that seen in IBS. Fluctuations in gut physiology destabilize the habitat of commensal bacteria and provide a basis for chronic dysbiosis. Recent observations in animal models that changes in gut flora influence behavior provide a basis for a novel unifying hypothesis that accommodates both gut dysfunction and behavioral changes that characterize many IBS patients. This hypothesis states that dysbiosis exists in at least a subset of IBS patients, as a result of infection, dietary change or drugs and contributes to gut inflammatory and functional change in addition to psychiatric co-morbidity.

Th17: a new participant in gut dysfunction in mice infected with Trichinella spiralis

Trichinella spiralis infection in rodents is a well-known model of intestinal inflammation associated with hypermotility. Our aim was to elucidate if Th17 cells were involved in the development of gastrointestinal hypermotility in this experimental model. Intestinal inflammation was observed by hematoxylin-eosin (HE) staining. Jejunal smooth muscle contractility was investigated in response to acetylcholine (Ach). The effects of IL-17 on jejunum smooth muscle contractility were explored. Flow cytometry was used to analyze the proportion of Th17 cells in jejunum. The levels of IL-17, IL-23, and TGF-β1 in jejunum were measured by Western blot. Our results showed that the inflammation in jejunum was severe at 2 weeks postinfection (PI), which was not discernible at 8 weeks PI. Jejunal smooth muscle contractility was increased at 2 weeks PI and kept higher at 12 weeks PI. The proportion of Th17 cells and the expression of IL-17 were upregulated in jejunum at 2 weeks PI and normalized at 8 weeks PI. When jejunual smooth muscle strips were cultured with IL-17, contractions elicited by Ach were enhanced in a concentration-dependent manner. Our data suggest that Th17 cells are increased during acute infection with Trichinella spiralis and IL-17 may contribute to jejunal muscle contractility in mice.

Structural changes in the epithelium of the small intestine and immune cell infiltration of enteric ganglia following acute mucosal damage and local inflammation

An acute enteritis is commonly followed by intestinal neuromuscular dysfunction, including prolonged hyperexcitability of enteric neurons. Such motility disorders are associated with maintained increases in immune cells adjacent to enteric ganglia and in the mucosa. However, whether the commonly used animal model, trinitrobenzene sulphonate (TNBS)-induced enteritis, causes histological and immune cell changes similar to human enteric neuropathies is not clear. We have made a detailed study of the mucosal damage and repair and immune cell invasion following intralumenal administration of TNBS. Intestines from untreated, sham-operated and TNBS-treated animals were examined at 3 h to 56 days. At 3 h, the mucosal surface was completely ablated, by 6 h an epithelial covering was substantially restored and by 1 day there was full re-epithelialisation. The lumenal epithelium developed from a squamous cell covering to a fully differentiated columnar epithelium with mature villi at about 7 days. Prominent phagocytic activity of enterocytes occurred at 1-7 days. A surge of eosinophils and T lymphocytes associated with the enteric nerve ganglia occurred at 3 h to 3 days. However, elevated immune cell numbers occurred in the lamina propria of the mucosa until 56 days, when eosinophils were still three times normal. We conclude that the disruption of the mucosal surface that causes TNBS-induced ileitis is brief, a little more than 6 h, and causes a transient immune cell surge adjacent to enteric ganglia. This is much briefer than the enteric neuropathy that ensues. Ongoing mucosal inflammatory reaction may contribute to the persistence of enteric neuropathy.

Probiotics effects on gastrointestinal function: beyond the gut?

The digestive tract works through a complex network of integrative functions. At the level of the gut, this integration occurs between the immune, neuromotor and enteroendocrine systems, coordinating the physical and chemical elements of the intestinal barrier in order to facilitate digestion whilst protecting the gut from unwanted components of the luminal contents. Gastrointestinal function is controlled and coordinated by the central nervous system to ensure effective motility, secretion, absorption and mucosal immunity. It follows that perturbations in this complex network could lead to gut dysfunction and symptom generation. Recently, attention has been focused on the emerging hypothesis that gut luminal content contributes to determine normal GI function and on the therapeutic possibilities arising from modulating its impact on gut physiology and immunity using probiotic bacteria. In this issue of Neurogastroenterology and Motility, two papers explore the effect of specific probiotic bacteria on spinal neuronal activation and in vitro muscle contractility. These papers support the notion that the composition of the intestinal microbiota can influence gut neuro-motor function and enhance our understanding on the mechanisms of action underlying the effects of specific probiotics on gut functional disorders.

Synaptic plasticity: the new explanation of visceral hypersensitivity in rats with Trichinella spiralis infection?

BACKGROUND AND AIM

Synaptic plasticity plays an important role in affecting the intensity of visceral reflex. It may also be involved in the development of visceral hypersensitivity. The aim of this study was to investigate the role of synaptic plasticity on visceral hypersensitivity of rats infected by Trichinella spiralis.

METHODS

Thirty male Sprague-Dawley (SD) rats were randomly divided into control, acute, and chronic infection groups, and were investigated at 1 week after adaptive feeding and at 2 and 8 weeks post infection (PI) by oral administration of 1 ml phosphate-buffered saline (PBS) containing 8,000 Trichinella spiralis larvae. Visceral sensitivity was evaluated by electromyography (EMG) recording during colorectal distension. Intestinal inflammation was observed by hematoxylin-eosin (HE) staining. Synaptic ultrastructure parameters, such as postsynaptic density (PSD) length, synaptic cleft, and number of synaptic vesicles, were examined by transmission electron microscopy (TEM). The expression of protein associated with synaptic plasticity, including postsynaptic density-95 (PSD-95), synaptophysin, calbindin-28 K, N-methyl-D-aspartate receptor-1 (NMDA-R1), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPA-R), and glial cell line-derived neurotrophic factor (GDNF), were analyzed by Western blot.

RESULTS

(1) Visceral hypersensitivity was noted in the chronic infection group, although the inflammation was nearly eliminated (P<0.05). Severe inflammation and downregulation of visceral sensitivity were observed in the acute infection group (P<0.05). (2) There were many more synaptic vesicles and longer PSD in the chronic infection group than in the control group (P<0.05, respectively). However, in comparison with control rats, disappearance of mitochondria cristae in the synapses, and decrease of synaptic vesicles and length of PSD were observed in the acute infection group. There was no significant difference in width of synaptic cleft among the three groups. (3) Compared with the control, the expression of proteins associated with synaptic plasticity was significantly upregulated during chronic infection phase (P<0.05), and downregulated during acute infection phase.

CONCLUSION

Synaptic plasticity was observed in SD rats infected by Trichinella spiralis and was associated with visceral sensitivity, which suggests that it may play an important role in the formation of visceral hypersensitivity.

Basic and clinical aspects of gastrointestinal pain

The gastrointestinal (GI) tract is a system of organs within multicellular animals which facilitates the ingestion, digestion, and absorption of food with subsequent defecation of waste. A complex arrangement of nerves and ancillary cells contributes to the sensorimotor apparatus required to subserve such essential functions that are with the exception of the extreme upper and lower ends of the GI tract normally subconscious. However, it also has the potential to provide conscious awareness of injury. Although this function can be protective, when dysregulated, particularly on a chronic basis, the same system can lead to considerable morbidity. The anatomical and molecular basis of gastrointestinal nociception, conditions associated with chronic unexplained visceral pain, and developments in treatment are presented in this review.

The functional-organic dichotomy: postinfectious irritable bowel syndrome and inflammatory bowel disease-irritable bowel syndrome

Gastroenterologists often encounter situations when the clinical and pathophysiological features that typically distinguish functional from organic disorders overlap. This "blurring of boundaries" can occur with post-infectious irritable bowel syndrome (PI-IBS), a subset of IBS and a newly described entity IBD-IBS. The key associating features include pain and usually diarrheal symptoms that are disproportionate to the observed pathology, microscopic inflammation, and often a co-association with psychological distress. A previous initiating gastrointestinal infection is required for PI-IBS and assumed for IBD-IBS. Using this perspective we discuss the clinical and pathophysiological features of PI-IBS and IBD-IBS and the growing evidence for the overlapping features of these two disorders in terms of alteration of gut flora, immune dysregulation, and role of stress. A unifying model of PI-IBS and IBD-IBS is proposed that may have important clinical and research implications. It obligates us to reframe our understanding of illness and disease from the dualistic biomedical model into a more integrated biopsychosocial (BPS) perspective.

Alterations in the intestinal microbiota and functional bowel symptoms

Functional gastrointestinal disorders (FGIDs) are highly prevalent in Western countries yet no single mechanism or etiological agent that initiates IBS has been identified. Current research has implicated the intestinal microbiota with FGIDs. This article reviews the available literature/data regarding the intestinal microbiota and FGIDS. The possible relationships between the intestinal microbiota and the intestinal function and functional bowel symptoms are discussed.

Physiological changes in the gastrointestinal tract and host protective immunity: learning from the mouse-Trichinella spiralis model

Infection and inflammation in the gastrointestinal (GI) tract induces a number of changes in the GI physiology of the host. Experimental infections with parasites represent valuable models to study the structural and physiological changes in the GI tract. This review addresses research on the interface between the immune system and GI physiology, dealing specifically with 2 major components of intestinal physiology, namely mucin production and muscle function in relation to host defence, primarily based on studies using the mouse-Trichinella spiralis system. These studies demonstrate that the infection-induced T helper 2 type immune response is critical in generating the alterations of infection-induced mucin production and muscle function, and that this immune-mediated alteration in gut physiology is associated with host defence mechanisms. In addition, by manipulating the host immune response, it is possible to modulate the accompanying physiological changes, which may have clinical relevance. In addition to enhancing our understanding of immunological control of GI physiological changes in the context of host defence against enteric infections, the data acquired using the mouse-T. spiralis model provide a basis for understanding the pathophysiology of a wide range of GI disorders associated with altered gut physiology.

The role of humoral autoimmunity in gastrointestinal neuromuscular diseases

Dysfunction of the gastrointestinal neuromuscular apparatus (including interstitial cells of Cajal) is presumed to underlie a heterogeneous group of disorders collectively termed gastrointestinal neuromuscular diseases (GINMDs). There is increasing experimental and clinical evidence that some GINMDs are immune-mediated, with cell-mediated dysfunction relatively well studied. Humoral (antibody)-mediated autoimmunity is associated with several well-established acquired neuromuscular diseases and is now implicated in an increasing number of less well-characterised disorders, particularly of the central nervous system. The role of autoimmunity in GINMDs has been less studied. Whilst most work has focused on the presence of antibodies directed to nuclear antigens, particularly in the context of secondary disorders such as paraneoplastic intestinal pseudo-obstruction, the possibility that 'functional' anti-neuronal antibodies directed to membrane-bound ion channels may cause disease (channelopathy) is now also being realised. The evidence for humoral autoimmunity as an etiologic factor in primary (idiopathic) and secondary GINMDs is systematically presented using the original paradigms previously applied to established autoimmune neuromuscular disorders. The presence of anti-enteric neuronal antibodies, although repeatedly demonstrated, still requires the identification of specific neuronal autoantigens and validated evidence of pathogenicity.

Is irritable bowel syndrome an inflammatory disorder?

Histopathologic data demonstrate low-grade mucosal inflammation in a subset of patients with irritable bowel syndrome (IBS). This inflammatory infiltrate is mainly represented by increased numbers of T lymphocytes and mast cells lying in the lamina propria. The close apposition of immunocytes to gut nerves supplying the mucosa provides a basis for neuroimmune cross-talk, which may explain gut sensorimotor dysfunction and related symptoms in patients with IBS. A previous gastroenteritis (due to Campylobacter jejuni, Salmonella, Shigella, Escherichia coli, and, likely, viruses) is now an established etiologic factor for IBS (hence, postinfectious IBS). Other putative causes, such as undiagnosed food allergies, genetic abnormalities, stress, or bile acid malabsorption, may also promote and maintain a low-grade mucosal inflammation in IBS. The identification of mucosal inflammation in IBS has pathophysiologic implications and paves the way for novel therapeutic options.

Afferent hypersensitivity in a mouse model of post-inflammatory gut dysfunction: role of altered serotonin metabolism

Visceral hypersensitivity is an important clinical feature associated with irritable bowel syndrome which in some patients has been linked to prior infection. Here we employ an animal model in which transient infection leads to persistent gut dysfunction to investigate the role of altered 5-HT metabolism upon afferent mechanosensensitivity in the post-infected gut. Jejunal segments isolated from Trichinella spiralis-infected mice were used to assess 5-HT metabolism whilst afferent activity in T. spiralis-infected mice was studied by extracellular recordings from jejunal mesenteric afferent bundles and patch clamp recordings of isolated nodose ganglion neurons (NGNs). During acute infection, intestinal 5-HT content and release increased, 5-HT turnover decreased and afferent discharge in response to mechanical stimulation was attenuated. By day 28 post infection (PI), 5-HT turnover had normalized, but 5-HT content and release were still elevated. This was associated with afferent mechano-hypersensitivity, which persisted for 8 weeks PI and was susceptible to 5-HT(3) receptor blockade. NGNs from post-infected animals were more excitable than controls but their current densities in response to 2-methyl-5-HT were lower. T. spiralis infection increased mucosal 5-HT bioavailability and affected the spontaneous activity and mechanosensitivity of gastrointestinal sensory nerves. This involved an initial hyposensitivity occurring during acute infection followed by long-term hypersensitivity in the post-infectious period that was in part mediated by 5-HT acting via 5-HT(3) receptors. Functional down-regulation of 5-HT(3) receptors also occurs in the post-infected animals, which may represent an adaptive response to increased mucosal 5-HT bioavailability.

Metabolic profiling of an Echinostoma caproni infection in the mouse for biomarker discovery

BACKGROUND

Metabolic profiling holds promise with regard to deepening our understanding of infection biology and disease states. The objectives of our study were to assess the global metabolic responses to an Echinostoma caproni infection in the mouse, and to compare the biomarkers extracted from different biofluids (plasma, stool, and urine) in terms of characterizing acute and chronic stages of this intestinal fluke infection.

METHODOLOGY/PRINCIPAL FINDINGS

Twelve female NMRI mice were infected with 30 E. caproni metacercariae each. Plasma, stool, and urine samples were collected at 7 time points up to day 33 post-infection. Samples were also obtained from non-infected control mice at the same time points and measured using (1)H nuclear magnetic resonance (NMR) spectroscopy. Spectral data were subjected to multivariate statistical analyses. In plasma and urine, an altered metabolic profile was already evident 1 day post-infection, characterized by reduced levels of plasma choline, acetate, formate, and lactate, coupled with increased levels of plasma glucose, and relatively lower concentrations of urinary creatine. The main changes in the urine metabolic profile started at day 8 post-infection, characterized by increased relative concentrations of trimethylamine and phenylacetylglycine and lower levels of 2-ketoisocaproate and showed differentiation over the course of the infection.

CONCLUSION/SIGNIFICANCE

The current investigation is part of a broader NMR-based metabonomics profiling strategy and confirms the utility of this approach for biomarker discovery. In the case of E. caproni, a diagnosis based on all three biofluids would deliver the most comprehensive fingerprint of an infection. For practical purposes, however, future diagnosis might aim at a single biofluid, in which case urine would be chosen for further investigation, based on quantity of biomarkers, ease of sampling, and the degree of differentiation from the non-infected control group.