Visceral hyperalgesia and intestinal dysmotility in a mouse model of postinfective gut dysfunction

Vasoactive Intestinal Polypeptide Plays a Key Role in the Microbial-Neuroimmune Control of Intestinal Motility

BACKGROUND & AIMS

Although chronic diarrhea and constipation are common, the treatment is symptomatic because their pathophysiology is poorly understood. Accumulating evidence suggests that the microbiota modulates gut function, but the underlying mechanisms are unknown. We therefore investigated the pathways by which microbiota modulates gastrointestinal motility in different sections of the alimentary tract.

METHODS

Gastric emptying, intestinal transit, muscle contractility, acetylcholine release, gene expression, and vasoactive intestinal polypeptide (VIP) immunoreactivity were assessed in wild-type and Myd88-/-Trif-/- mice in germ-free, gnotobiotic, and specific pathogen-free conditions. Effects of transient colonization and antimicrobials as well as immune cell blockade were investigated. VIP levels were assessed in human full-thickness biopsies by Western blot.

RESULTS

Germ-free mice had similar gastric emptying but slower intestinal transit compared with specific pathogen-free mice or mice monocolonized with Lactobacillus rhamnosus or Escherichia coli, the latter having stronger effects. Although muscle contractility was unaffected, its neural control was modulated by microbiota by up-regulating jejunal VIP, which co-localized with and controlled cholinergic nerve function. This process was responsive to changes in the microbial composition and load and mediated through toll-like receptor signaling, with enteric glia cells playing a key role. Jejunal VIP was lower in patients with chronic intestinal pseudo-obstruction compared with control subjects.

CONCLUSIONS

Microbial control of gastrointestinal motility is both region- and bacteria-specific; it reacts to environmental changes and is mediated by innate immunity-neural system interactions. By regulating cholinergic nerves, small intestinal VIP plays a key role in this process, thus providing a new therapeutic target for patients with motility disorders.

Post-infectious irritable bowel syndrome following a diagnosis of traveller's diarrhoea: a comprehensive characterization of clinical and laboratory parameters

BACKGROUND

Prolonged or recurrent gastrointestinal symptoms may persist after acute traveller's diarrhoea (TD), even after adequate treatment of the primary cause. This study aims to describe the epidemiological, clinical and microbiological characteristics of patients with post-infectious irritable bowel syndrome (PI-IBS) after returning from tropical or subtropical areas.

METHODS

We conducted a retrospective study of patients presenting between 2009 and 2018 at the International Health referral centre in Barcelona with persistent gastrointestinal symptoms following a diagnosis of TD. PI-IBS was defined as the presence of persistent or recurrent gastrointestinal manifestations for at least 6 months after the diagnosis of TD, a negative stool culture for bacterial pathogens and a negative ova and parasite exam after targeted treatment. Epidemiological, clinical and microbiological variables were collected.

RESULTS

We identified 669 travellers with a diagnosis of TD. Sixty-eight (10.2%) of these travellers, mean age 33 years and 36 (52.9%) women, developed PI-IBS. The most frequently visited geographical areas were Latin America (29.4%) and the Middle East (17.6%), with a median trip duration of 30 days (IQR 14-96). A microbiological diagnosis of TD was made in 32 of these 68 (47%) patients, 24 (75%) of whom had a parasitic infection, Giardia duodenalis being the most commonly detected parasite (n = 20, 83.3%). The symptoms persisted for a mean of 15 months after diagnosis and treatment of TD. The multivariate analysis revealed that parasitic infections were independent risk factors for PI-IBS (OR 3.0, 95%CI 1.2-7.8). Pre-travel counselling reduced the risk of PI-IBS (OR 0.4, 95%CI 0.2-0.9).

CONCLUSIONS

In our cohort, almost 10% of patients with travellers' diarrhoea developed persistent symptoms compatible with PI-IBS. Parasitic infections, mainly giardiasis, seem to be associated with PI-IBS.

Role of inflammation in pediatric irritable bowel syndrome

BACKGROUND

IBS affects a large number of children throughout the world and is thought to be the result of disturbed neuroimmune function along with the brain-gut axis. Although the underlying pathophysiologic mechanisms are not clear, the role of low-grade inflammation and mucosal immune activation in IBS symptom generation has become evident also in subsets of pediatric patients. Animal models provided meaningful insight in the causal relationship between abnormal mucosal immune activation and changes in gastrointestinal (GI) sensory-motor function. Likewise, the development of long-standing GI symptoms fulfilling the current criteria for functional GI disorders after infection gastroenteritis and in patients with IBD or celiac disease in remission further supports this hypothesis. Immune activation, its impact on gut sensory-motor function, and potential implications for symptom generation emerged in both children and adults with IBS.

PURPOSE

The aim of this review is to summarize the main evidence on the presence of low-grade inflammation and immune activation in children with IBS, its possible role in symptom generation, and its potential implication for new therapeutic strategies.

Effect of altered gut microbiota on visceral hypersensitivity of postinfectious irritable bowel syndrome mice

OBJECTIVE

Irritable bowel syndrome (IBS) is a common functional bowel disorder characterized with visceral hypersensitivity. Previous studies indicated gut microbiota alteration associated short-chain fatty acids (SCFAs) dysregulation is associated with IBS development. The aim of the study is to explore the potential role of microbiota dysbiosis mediated visceral hypersensitivity in postinfectious-IBS (PI-IBS) mouse model.

METHODS

Four-week-old NIH mice were randomly allocated into four groups: control mice, PI-IBS mice, PI-IBS mice co-housing with normal mice, and PI-IBS mice were administrated with a cocktail of antibiotics. Trichinella spiralis infection established PI-IBS mouse model. Microbiota in cecal contents and feces were analyzed by 16S rDNA sequencing. SCFAs were detected by gas chromatography. 5-hydroxytryptamine (5-HT) was evaluated by ELISA, and N-methyl-D-aspartate receptors (NMDARs) were examined by western blot. Visceral sensitivity was determined by abdominal withdrawal reflex in response to colorectal distention.

RESULTS

Increased SCFAs were observed in cecal contents and feces in PI-IBS mice accompanied with higher 5-HT and NMDAR subunits expressions in ileum and colon. Visceral hypersensitivity was observed in PI-IBS mice compared to control mice. When administrated with antibiotics cocktails and co-housing with normal mice, PI-IBS mice showed decreased SCFAs, 5-HT, NMDAR subunits expressions, and improved visceral hypersensitivity.

CONCLUSION

Gut microbiota alteration induced increased SCFAs, 5-HT and NMDAR subunits expressions were associated with visceral hypersensitivity in PI-IBS mice. The critical role of gut microbiota in improving visceral hypersensitivity was further identified by treatment of antibiotics cocktail and co-housing.

Long-lasting visceral hypersensitivity in a model of DSS-induced colitis in rats

BACKGROUND

Persistent visceral hypersensitivity is a key component of functional and inflammatory gastrointestinal diseases. Current animal models fail to fully reproduce the characteristics of visceral pain in humans, particularly as it relates to persistent hypersensitivity. This work explores the validity of DSS-induced colitis in rats as a model to mimic chronic intestinal hypersensitivity.

METHODS

Exposure to DSS (5% for 7 days) was used to induce colitis in rats. Thereafter, changes in viscerosensitivity (visceromotor responses to colorectal distension-CRD), the presence of somatic referred pain (mechanosensitivity of the hind paws, von Frey test) and the expression (qRT-PCR) of sensory-related markers (colon, lumbosacral DRGs, and lumbosacral spinal cord) were assessed at different times during the 35 days period after colitis induction.

RESULTS

Following colitis, a sustained increase in visceromotor responses to CRD were observed, indicative of the presence of visceral hypersensitivity. Responses in animals without colitis remained stable over time. In colitic animals, somatic referred hypersensitivity was also detected. DSS-induced colitis was associated to a differential expression of sensory-related markers (with both pro- and anti-nociceptive action) in the colon, lumbosacral DRGs and lumbosacral spinal cord; indicating the presence of peripheral and central sensitization.

CONCLUSIONS AND INFERENCES

DSS-induced colitis in rats is associated to the generation of a long-lasting state of visceral (colonic) hypersensitivity, despite clinical colitis resolution. This model reproduces the changes in intestinal sensitivity characteristics of inflammatory and functional gastrointestinal disorders in humans and can be used in the characterization of new pharmacological treatments against visceral pain.

In Vitro Efficacy of Targeted Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols Enzymatic Digestion in a High-Fidelity Simulated Gastrointestinal Environment

Background and Aims

Irritable bowel syndrome (IBS) is characterized by abdominal pain and changes in bowel habits. Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) are poorly absorbed short-chain carbohydrates that may drive commensal microbial gas production, promoting abdominal pain in IBS. Low-FODMAP diet can result in symptomatic improvement in 50%-80% of IBS patients. However, this diet is not meant to be sustained long term, with concern for downstream nutrition and microbial issues. In this study, we evaluate the function of a targeted FODMAP enzymatic digestion food supplement FODMAP enzymatic digestion (FODZYME) containing a fructan-hydrolase enzyme (with significant inulinase activity) in a simulated gastrointestinal environment.

Methods

Using SHIME (Simulator of the Human Intestinal Microbial Ecosystem), a multi-compartment simulator of the human gut, FODZYME dose finding assay in modeled gastrointestinal conditions assessed enzymatic ability to hydrolyze 3 g of inulin. Full intestinal modeling assessing digestion of inulin, absorption of fructose, gas production, and other measures of commensal microbial behavior was completed using 1.125 g of FODZYME.

Results

After 30 minutes, 90% of the inulin was converted to fructose by 1.125 g of FODZYME. Doubling dosage showed no significant improvement in conversion, whereas a half dose decreased performance to 77.2%. Seventy percent of released fructose was absorbed during simulated small intestinal transit, with a corresponding decrease in microbial gas production, and a small decrease in butyrate and short-chain fatty acid production.

Conclusion

FODZYME specifically breaks down inulin in representative gastrointestinal conditions, resulting in decreased gas production while substantially preserving short-chain fatty acid and butyrate production in the model colon. Our results suggest dietary supplementation with FODZYME would decrease intestinal FODMAP burden and gas production.

Histamine production by the gut microbiota induces visceral hyperalgesia through histamine 4 receptor signaling in mice

The gut microbiota has been implicated in chronic pain disorders, including irritable bowel syndrome (IBS), yet specific pathophysiological mechanisms remain unclear. We showed that decreasing intake of fermentable carbohydrates improved abdominal pain in patients with IBS, and this was accompanied by changes in the gut microbiota and decreased urinary histamine concentrations. Here, we used germ-free mice colonized with fecal microbiota from patients with IBS to investigate the role of gut bacteria and the neuroactive mediator histamine in visceral hypersensitivity. Germ-free mice colonized with the fecal microbiota of patients with IBS who had high but not low urinary histamine developed visceral hyperalgesia and mast cell activation. When these mice were fed a diet with reduced fermentable carbohydrates, the animals showed a decrease in visceral hypersensitivity and mast cell accumulation in the colon. We observed that the fecal microbiota from patients with IBS with high but not low urinary histamine produced large amounts of histamine in vitro. We identified Klebsiella aerogenes, carrying a histidine decarboxylase gene variant, as a major producer of this histamine. This bacterial strain was highly abundant in the fecal microbiota of three independent cohorts of patients with IBS compared with healthy individuals. Pharmacological blockade of the histamine 4 receptor in vivo inhibited visceral hypersensitivity and decreased mast cell accumulation in the colon of germ-free mice colonized with the high histamine-producing IBS fecal microbiota. These results suggest that therapeutic strategies directed against bacterial histamine could help treat visceral hyperalgesia in a subset of patients with IBS with chronic abdominal pain.

Ojeok-san ameliorates visceral and somatic nociception in a mouse model of colitis induced colorectal cancer

Cancer patients can develop visceral, somatic, and neuropathic pain, largely due to the malignancy itself and its treatments. Often cancer patients and survivors turn to the use of complementary and alternative medicine (CAM) to alleviate pain and fatigue. Thus, it is necessary to investigate how CAM therapies work as novel analgesics to treat cancer pain. Ojeok-san (OJS) is an herbal formula consisting of seventeen herbs. This herbal formula has been shown to possess anti-inflammatory, immunoregulatory, and analgesic properties. In this study, we examined the potential beneficial effects and mechanism of action of OJS in a preclinical model of colitis-associated colorectal cancer. Male and female C57BL/6J mice were exposed to the carcinogen, azoxymethane (AOM, 10 mg/kg) and a chemical inflammatory driver, dextran sulfate sodium (DSS1-2%), to promote tumorigenesis in the colorectum. OJS was given orally (500, 1000, and 2000 mg/kg) to determine its influence on disease activity, tumor burden, nociception, sedation, Erk signaling, and behavioral and metabolic outcomes. In addition, in vitro studies were performed to assess CT-26 cell viability, dorsal root ganglia (DRG) activation, and bone-marrow-derived macrophage (BMDM) inflammatory response to lipopolysaccharide stimulation after OJS treatment. We found that administration of 2000 mg/kg of OJS was able to mitigate mechanical somatic and visceral nociception via Erk signaling without affecting symptom score and polyp number. Moreover, we discovered that OJS has sedative properties and elicits prolonged total sleeping time in AOM/DSS mice. Our in vitro experiments showed that OJS has the capacity to reduce TNFα gene expression in LPS-stimulated BMDM, but no changes were observed in DRG spike number and CT-26 cell proliferation. Taken together, these data suggest that OJS ameliorates nociception in mice and warrants further examination as a potential CAM therapy to promote analgesia.

Analysis of Intestinal Movements with Spatiotemporal Maps: Beyond Anatomy and Physiology

Over 150 years ago, methods for quantitative analysis of gastrointestinal motor patterns first appeared. Graphic representations of physiological variables were recorded with the kymograph after the mid-1800s. Changes in force or length of intestinal muscles could be quantified, however most recordings were limited to a single point along the digestive tract.In parallel, photography and cinematography with X-Rays visualised changes in intestinal shape, but were hard to quantify. More recently, the ability to record physiological events at many sites along the gut in combination with computer processing allowed construction of spatiotemporal maps. These included diameter maps (DMaps), constructed from video recordings of intestinal movements and pressure maps (PMaps), constructed using data from high-resolution manometry catheters. Combining different kinds of spatiotemporal maps revealed additional details about gut wall status, including compliance, which relates forces to changes in length. Plotting compliance values along the intestine enabled combined DPMaps to be constructed, which can distinguish active contractions and relaxations from passive changes. From combinations of spatiotemporal maps, it is possible to deduce the role of enteric circuits and pacemaker cells in the generation of complex motor patterns. Development and application of spatiotemporal methods to normal and abnormal motor patterns in animals and humans is ongoing, with further technical improvements arising from their combination with impedance manometry, magnetic resonance imaging, electrophysiology, and ultrasonography.

Enteric Tuft Cells in Host-Parasite Interactions

Enteric tuft cells are chemosensory epithelial cells gaining attention in the field of host-parasite interactions. Expressing a repertoire of chemosensing receptors and mediators, these cells have the potential to detect lumen-dwelling helminth and protozoan parasites and coordinate epithelial, immune, and neuronal cell defenses against them. This review highlights the versatility of enteric tuft cells and sub-types thereof, showcasing nuances of tuft cell responses to different parasites, with a focus on helminths reflecting the current state of the field. The role of enteric tuft cells in irritable bowel syndrome, inflammatory bowel disease and intestinal viral infection is assessed in the context of concomitant infection with parasites. Finally, the review presents pertinent questions germane to understanding the enteric tuft cell and its role in enteric parasitic infections. There is much to be done to fully elucidate the response of this intriguing cell type to parasitic-infection and there is negligible data on the biology of the human enteric tuft cell—a glaring gap in knowledge that must be filled.

The α isoform of cGMP-dependent protein kinase 1 (PKG1α) is expressed and functionally important in intrinsic primary afferent neurons of the guinea pig enteric nervous system

BACKGROUND

Intrinsic primary afferent neurons (IPANs) enable the gut to manifest reflexes in the absence of CNS input. PKG1α is selectively expressed in a subset of neurons in dorsal root ganglia (DRG) and has been linked to nociception and long-term hyperexcitability.

METHODS

We used immunoblotting, immunocytochemistry, and in vitro assays of IPAN-dependent enteric functions to test hypotheses that subsets of primary neurons of the ENS and DRG share a reliance on PKG1α expression.

KEY RESULTS

PKG1α immunoreactivity was demonstrated in immunoblots from isolated myenteric ganglia. PKG1α, but not PKG1β, immunoreactivity, was coincident with that of neuronal markers (HuC/D; β3-tubulin) in both enteric plexuses. PKG1α immunoreactivity also co-localized with the immunoreactivities of the IPAN markers, calbindin (100%; myenteric plexus) and cytoplasmic NeuN (98 ± 1% submucosal plexus). CGRP-immunoreactive DRG neurons, identified as visceral afferents by retrograde transport, were PKG1α-immunoreactive. We used intraluminal cholera toxin to determine whether PKG1α was necessary to enable stimulation of the mucosa to activate Fos in enteric neurons. Tetrodotoxin (1.0 µM), low Ca2+ /high Mg2+ media, and the PKG inhibitor, N46 (100 µM), all inhibited Fos activation in myenteric neurons. N46 also concentration dependently inhibited peristaltic reflexes in isolated preparations of distal colon (IC50  = 83.3 ± 1.3 µM).

CONCLUSIONS & INFERENCES

These data suggest that PKG1α is present and functionally important in IPANs and visceral afferent nociceptive neurons.

Animal models of visceral pain and the role of the microbiome

Visceral pain refers to pain arising from the internal organs and is distinctly different from the expression and mechanisms of somatic pain. Diseases and disorders with increased visceral pain are associated with significantly reduced quality of life and incur large financial costs due to medical visits and lost work productivity. In spite of the notable burden of illness associated with those disorders involving increased visceral pain, and some knowledge regarding etiology, few successful therapeutics have emerged, and thus increased attention to animal models of visceral hypersensitivity is warranted in order to elucidate new treatment opportunities. Altered microbiota-gut-brain (MGB) axis communication is central to the comorbid gastrointestinal/psychiatric diseases of which increased visceral (intestinal) sensitivity is a hallmark. This has led to a particular focus on intestinal microbiome disruption and its potential role in the etiology of heightened visceral pain. Here we provide a review of studies examining models of heightened visceral pain due to altered bidirectional communication of the MGB axis, many of which are conducted on a background of stress exposure. We discuss work in which the intestinal microbiota has either been directly manipulated (as with germ-free, antibiotic, and fecal microbial transplantation studies) or indirectly affected through early life or adult stress, inflammation, and infection. Animal models of visceral pain alterations with accompanying changes to the intestinal microbiome have the highest face and construct validity to the human condition and are the focus of the current review.

Post-infection Irritable Bowel Syndrome

Epidemiologic data support that acute gastrointestinal infection is one of the strongest risk factors for development of irritable bowel syndrome (IBS). Risk of post-infection IBS (PI-IBS) seems to be greater with bacterial and protozoal than viral enterocolitis. Younger individuals, women, and those with severe enterocolitis are more likely to develop PI-IBS. Disease mechanisms in animal models and humans involve chronic perturbation of intestinal microbiome, epithelial and neuronal remodeling, and immune activation. These mechanisms can lead to luminal (increased proteolytic activity, altered bile acid composition) and physiologic (increased permeability, transit changes, and visceral hypersensitivity) alterations that can mediate PI-IBS symptoms.

Updates on the epidemiology, pathogenesis, diagnosis, and management of postinfectious irritable bowel syndrome

PURPOSE OF REVIEW

With its impact on quality of life and increasing awareness, postinfectious irritable bowel syndrome (PI-IBS) is now gaining attention as one of the major health problems commonly encountered in gastrointestinal practice. Literature investigating the various pathogenic mechanisms involved is rapidly emerging. The objective of the current review is to provide an update on recent evidence published in the past 2 years describing advances in our understanding of the epidemiology, pathogenesis, diagnosis, and treatment of PI-IBS.

RECENT FINDINGS

Significant proportion of research in the recent past was preclinical in nature. Epidemiological studies continue to highlight the risk of IBS after infection, with recent studies documenting postprotozoal effects. Advances in pathogenic mechanisms included clinical studies, which documented micro-RNA down-regulation and Peroxiredoxin-1 up-regulation in colonic mucosa of PI-IBS patients. Protease-activated receptor-2 (PAR-2) activation in PI-IBS mice models resulted in increase in epithelial permeability, mucosal inflammation, visceral hypersensitivity. Moxibustion and rifamycin reduced intestinal inflammation by inhibiting cytokine and chemokine release via different mechanisms. Miltefosine reduced mast cell degranulation and TRPV1 activation, thereby reducing visceral hypersensitivity.

SUMMARY

At present, generalization of limited diagnostic and therapeutic strategies across a heterogeneous prevalent patient population impedes the ability to provide effective personalized care in PI-IBS. Further development in pathogenesis discovery, diagnostic tool development are needed in order to design well tolerated and effective therapies that guide treatments based on distinct pathways of disease.

Fecal dysbiosis associated with colonic hypersensitivity and behavioral alterations in chronically Blastocystis-infected rats

BACKGROUND

Infectious gastroenteritis is a risk factor for the development of post-infectious Irritable Bowel Syndrome (PI-IBS). Recent clinical studies reported a higher prevalence of the intestinal parasite Blastocystis in IBS patients. Using a rat model, we investigated the possible association between Blastocystis infection, colonic hypersensitivity (CHS), behavioral disturbances and gut microbiota changes.

METHODS

Rats were orally infected with Blastocystis subtype 4 (ST4) cysts, isolated from human stool samples. Colonic sensitivity was assessed by colorectal distension and animal behavior with an automatic behavior recognition system (PhenoTyper), the Elevated Plus Maze test and the Forced Swimming tests. Feces were collected at different time points after infection to study microbiota composition by 16 S rRNA amplicon sequencing and for short-chain fatty acid (SFCA) analysis.

RESULTS

Blastocystis-infected animals had non-inflammatory CHS with increased serine protease activity. Infection was also associated with anxiety- and depressive-like behaviors. Analysis of fecal microbiota composition showed an increase in bacterial richness associated with altered microbiota composition. These changes included an increase in the relative abundance of Oscillospira and a decrease in Clostridium, which seem to be associated with lower levels of SCFAs in the feces from infected rats.

CONCLUSIONS

Our findings suggest that experimental infection of rats with Blastocystis mimics IBS symptoms with the establishment of CHS related to microbiota and metabolic shifts.

Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome - An Update

Small intestinal bacterial overgrowth (SIBO) is one manifestation of gut microbiome dysbiosis and is highly prevalent in IBS (Irritable Bowel Syndrome). SIBO can be diagnosed either by a small bowel aspirate culture showing ≥10³ colony-forming units (CFU) per mL of aspirate, or a positive hydrogen lactulose or glucose breath test. Numerous pathogenic organisms have been shown to be increased in subjects with SIBO and IBS, including but not limited to Enterococcus, Escherichia coli, and Klebsiella. In addition, Methanobrevibacter smithii, the causal organism in a positive methane breath test, has been linked to constipation predominant irritable bowel syndrome (IBS-C). As M. smithii is an archaeon and can overgrow in areas outside of the small intestine, it was recently proposed that the term intestinal methanogen overgrowth (IMO) is more appropriate for the overgrowth of these organisms. Due to gut microbiome dysbiosis, patients with IBS may have increased intestinal permeability, dysmotility, chronic inflammation, autoimmunity, decreased absorption of bile salts, and even altered enteral and central neuronal activity. As a consequence, SIBO and IBS share a myriad of symptoms including abdominal pain, distention, diarrhea, and bloating. Furthermore, gut microbiome dysbiosis may be associated with select neuropsychological symptoms, although more research is needed to confirm this connection. This review will focus on the role of the gut microbiome and SIBO in IBS, as well as novel innovations that may help better characterize intestinal overgrowth and microbial dysbiosis.

Animal Models for Functional Gastrointestinal Disorders

Functional gastrointestinal disorders (FGID), such as functional dyspepsia (FD) and irritable bowel syndrome (IBS) are characterized by chronic abdominal symptoms in the absence of an organic, metabolic or systemic cause that readily explains these complaints. Their pathophysiology is still not fully elucidated and animal models have been of great value to improve the understanding of the complex biological mechanisms. Over the last decades, many animal models have been developed to further unravel FGID pathophysiology and test drug efficacy. In the first part of this review, we focus on stress-related models, starting with the different perinatal stress models, including the stress of the dam, followed by a discussion on neonatal stress such as the maternal separation model. We also describe the most commonly used stress models in adult animals which brought valuable insights on the brain-gut axis in stress-related disorders. In the second part, we focus more on models studying peripheral, i.e., gastrointestinal, mechanisms, either induced by an infection or another inflammatory trigger. In this section, we also introduce more recent models developed around food-related metabolic disorders or food hypersensitivity and allergy. Finally, we introduce models mimicking FGID as a secondary effect of medical interventions and spontaneous models sharing characteristics of GI and anxiety-related disorders. The latter are powerful models for brain-gut axis dysfunction and bring new insights about FGID and their comorbidities such as anxiety and depression.

Chang'an II Decoction ( II )-Containing Serum Ameliorates Tumor Necrosis Factor-α-Induced Intestinal Epithelial Barrier Dysfunction via MLCK-MLC Signaling Pathway in Rats

OBJECTIVE

To investigate the effect of Chang'an II Decoction ( II ))-containing serum on intestinal epithelial barrier dysfunction in rats.

METHODS

Tumor necrosis factor (TNF)-α-induced injury of Caco-2 monolayers were established as an inflammatory model of human intestinal epithelium. Caco-2 monolayers were treated with blank serum and Chang'an II Decoction-containing serum that obtained from the rats which were treated with distilled water and Chang'an II Decoction intragastrically at doses of 0.49, 0.98, 1.96 g/(kg·d) for 1 week, respectively. After preparation of containing serum, cells were divided into the normal group, the model group, the Chang'an II-H, M, and L groups (treated with 30 ng/mL TNF-α and medium plus 10% high, middle-, and low-doses Chang'an II serum, respectively). Epithelial barrier function was assessed by transepithelial electrical resistance (TER) and permeability of fluorescein isothiocyanate (FITC)-labeled dextran. Transmission electron microscopy was used to observe the ultrastructure of tight junctions (TJs). Immunofluorescence of zonula occludens-1 (ZO-1), claudin-1 and nuclear transcription factor-kappa p65 (NF-κ Bp65) were measured to determine the protein distribution. The mRNA expression of myosin light chain kinase (MLCK) was measured by real-time polymerase chain reaction. The expression levels of MLCK, myosin light chain (MLC) and p-MLC were determined by Western blot.

RESULTS

Chang'an II Decoction-containing serum significantly attenuated the TER and paracellular permeability induced by TNF-α. It alleviated TNF-α-induced morphological alterations in TJ proteins. The increases in MLCK mRNA and MLCK, MLC and p-MLC protein expressions induced by TNF-α were significantly inhibited in the Chang'an II-H group. Additionally, Chang'an II Decoction significantly attenuated translocation of NF-κ Bp65 into the nucleus.

CONCLUSION

High-dose Chang'an II-containing serum attenuates TNF-α-induced intestinal barrier dysfunction. The underlying mechanism may be involved in inhibiting the MLCK-MLC phosphorylation signaling pathway mediated by NF-κ Bp65.

Effects of probiotic supplementation on post-infectious irritable bowel syndrome in rodent model

BACKGROUND

Probiotics have been reported to be the active component used in the treatment of many functional gastrointestinal symptoms and syndromes. Lactobacillus and yeast culture are extensively used in probiotic supplements and traditional treatments for irritable bowel syndrome (IBS). The aim of this study was to investigate the effects of probiotic treatments (Lactobacillus acidophilus LA5, Bifidobacterium animalis subsp. lactis BB12 and Saccharomyces cerevisiae var. boulardii) on the behavioral response, targeted gene expression and pro-inflammatory cytokine levels of Pi (Post infectious)-IBS -induced mice.

METHODS

Pathogen-free male C57L/B6 mice and the Trichinella-infected mice were used to measure the score of abdominal withdrawal reflex (AWR). To compare molecular, biological and biochemical evidences of given probiotics with normal and positive control groups in mice, we conducted quantitative reverse transcription polymerase chain reaction (RT-qPCR), western blotting, and cytokine analysis.

RESULTS

Pi-IBS-induced immune response was confirmed that PAR-2 mRNA level was significantly increased by Trichinella infection (P < 0.05). The reduction of Pi-IBS symptoms through Trichinella infection and the effects of given probiotics were confirmed by a change in the protein levels of cytokines (P < 0.05). In addition, the administration of DW (Daewon) probiotics significantly decreased serum levels of IL-1 and IL-6 (P < 0.05).

CONCLUSIONS

We have demonstrated that the given probiotics decreased pro-inflammatory cytokine levels in both the control and Pi-IBS induced mice. Taken all the results together, the results support that DW probiotics has a potential as a probiotic medication for patient with IBS via regulating TNF-α and IL-6 protein levels and serum IL-1 and IL-6 levels.

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.

The Pathophysiology of Colonic Diverticulosis: Inflammation versus Constipation?

Background

Diverticulosis of the colon is the most common anatomic alteration of the human colon, but the pathophysiologic mechanisms of its occurrence are not completely understood.

Summary

Constipation has been considered the key factor for diverticulosis occurrence. However, several fine papers questioned this pathogenetic hypothesis, showing on the contrary an inverse relationship between low number of bowel movements and diverticulosis occurrence. In the last years, several papers have showed the role of low-grade inflammation in the occurrence of symptoms in people having diverticulosis, as well as its role on symptom persistence following acute diverticulitis, even if the evidence available is not so strong. Although the trigger of this low-grade inflammation is currently under debate, some preliminary evidence found colonic dysbiosis linked to symptom occurrence in those patients.

Key Messages

Constipation no longer seems the leading cause for diverticulosis occurrence, while low-grade inflammation could play a role in symptom occurrence.

Altered Intestinal Microbiota with Increased Abundance of Prevotella Is Associated with High Risk of Diarrhea-Predominant Irritable Bowel Syndrome

Alterations in gut microbiota are postulated to be an etiologic factor in the pathogenesis of irritable bowel syndrome (IBS). To determine whether IBS patients in China exhibited differences in their gut microbial composition, fecal samples were collected from diarrhea-predominant IBS (IBS-D) and healthy controls and evaluated by 16S ribosomal RNA gene sequence and quantitative real-time PCR. A mouse model of postinfectious IBS (PI-IBS) was established to determine whether the altered gut microbiota was associated with increased visceral hypersensitivity. The results indicated that there were significant differences in the bacterial community profiles between IBS-D patients and healthy controls. Prevotella was more abundant in fecal samples from IBS-D patients compared with healthy controls (p < 0.05). Meanwhile, there were significant reductions in the quantity of Bacteroides, Bifidobacteria, and Lactobacillus in IBS-D patients compared with healthy controls (p < 0.05). Animal models similarly showed an increased abundance of Prevotella in fecal samples compared with control mice (p < 0.05). Finally, after the PI-IBS mice were cohoused with control mice, both the relative abundance of Prevotella and visceral hypersensitivity of PI-IBS mice were decreased. In conclusion, the altered intestinal microbiota is associated with increased visceral hypersensitivity and enterotype enriched with Prevotella may be positively associated with high risk of IBS-D.

Beneficial effects of Rifaximin in post-infectious irritable bowel syndrome mouse model beyond gut microbiota

BACKGROUND AND AIMS

Rifaximin is a minimally absorbed antibiotic, which has shown efficacy in irritable bowel syndrome (IBS) patients. However, the mechanism on how it effects in IBS is still incompletely defined. In this study, Trichinella spiralis-infected post-infectious (PI) IBS mouse model was used, to assess the action of rifaximin on visceral hypersensitivity, barrier function, gut inflammation, and microbiota.

METHODS

Post-infectious IBS model was established by T. spiralis infection in mice. Rifaximin were administered to PI-IBS mice for seven consecutive days. The abdominal withdrawal reflex and threshold of colorectal distention were employed to evaluate visceral sensitivity. Smooth muscle contractile response was recorded in the organ bath. Intestinal permeability was measured by Ussing chamber. Expression of tight junction protein and cytokines were measured by Western blotting. Ilumina miseq platform was used to analyze bacterial 16S ribosomal RNA.

RESULTS

Post-infectious IBS mice treated with rifaximin exhibited decreased abdominal withdrawal reflex score, increased threshold, reduced contractile response, and intestinal permeability. Rifaximin also suppressed the expression of interleukin-12 and interleukin-17 and promoted the expression of the major tight junction protein occludin. Furthermore, rifaximin did not change the composition and diversity, and the study reavealed that rifaximin had a tiny effect on the relative abundance of Lactobacillus and Bifidobacterium in this PI-IBS model.

CONCLUSIONS

Rifaximin alleviated visceral hypersensitivity, recovered intestinal barrier function, and inhibited low-grade inflammation in colon and ileum of PI-IBS mouse model. Moreover, rifaximin exerts anti-inflammatory effects with only a minimal effect on the overall composition and diversity of the gut microbiota in this model.

The Present Status of Fecal Microbiota Transplantation and Its Value in the Elderly

OPINION STATEMENT

PURPOSE OF REVIEW: This article will review current literature describing fecal microbiota transplantation (FMT) in the treatment of various diseases, and its potential role in elderly patients (age ≥ 65 years).

RECENT FINDINGS

Research on FMT has blossomed in the last decade and its pivotal role in the treatment of recurrent Clostridium difficile infection (CDI) has been recognized by the American College of Gastroenterology in the latest guidelines. There is also emerging evidence that FMT may be beneficial in the treatment of severe and/or complicated CDI refractory to medical therapy, resulting in decreased rates of colectomy and mortality. In the elderly, CDI is associated with markedly higher rates of mortality and colectomy; outcomes are even worse when patients have underlying inflammatory bowel disease (IBD). While the majority of patients who receive FMT for CDI are older, only a handful of studies focused specifically on FMT treatment outcomes and safety in this age group. Current data corroborate the efficacy and safety profile of FMT, while also supporting its use for recurrent, severe, and/or complicated CDI in the elderly population. FMT is recommended for the treatment of recurrent, severe, and/or complicated CDI in patients older than 65 years of age. It may be prudent to offer FMT earlier in the disease course, possibly after just the second recurrence and for the first episode of severe CDI to avert complications including colectomy and end-organ failure that elderly patients are more prone to developing.

Novel Indications for Fecal Microbial Transplantation: Update and Review of the Literature

BACKGROUND AND AIMS

Fecal microbial transplantation (FMT) is an established successful treatment modality for recurrent Clostridium difficile infection (CDI). The safety profile and potential therapeutic advantages of FMT for diseases associated with dysbiosis and immune dysfunction have led to many publications, mainly case series, and while many studies and reviews have been published on the use of FMT for inflammatory bowel disease (IBD), its potential use for other disease conditions has not been thoroughly reviewed. The aim of this review was to investigate the evidence surrounding the use of FMT in conditions other than IBD and CDI.

METHODS

A PubMed search was performed using the terms "Fecal microbiota transplantation" OR "FMT" OR "Bacteriotherapy."

RESULTS

A total of 26 articles describing the use of FMT in a variety of both intra-and extraintestinal disease conditions including gastrointestinal, hematologic, neurologic, metabolic, infectious, and autoimmune disorders have been included in this review and have demonstrated some positive results. The studies included were case reports, case series, controlled trials, and cohort studies.

CONCLUSIONS

The findings of these studies demonstrate that FMT, particularly in conditions associated with gastrointestinal dysbiosis, shows promise to provide another effective tool in the therapeutic armament of the practicing physician. FMT was found to be possibly effective in various diseases, mostly associated with enteric dysbiosis or with immune dysfunction. Randomized clinical studies on large populations should be performed to explore the effectiveness of this therapy, and basic research studies should be designed to gain understanding of the mechanisms through which impact these disorders.

Transfer of CD11c+ lamina propria mononuclear phagocytes from post-infectious irritable bowel syndrome causes mucosal barrier dysfunction and visceral hypersensitivity in recipient mice

The role of low-grade inflammation in the development of post‑infectious irritable bowel syndrome (PI‑IBS) has attracted increasing attention. Abnormal CD11c+ mononuclear phagocytes, such as dendritic cells (DCs), macrophages, and monocytes, are involved in the disruption of immune tolerance in organisms, which can lead to the development of chronic inflammatory diseases. The present study tested the hypothesis that CD11c+ lamina propria mononuclear phagocytes (CD11c+ LPMPs) contribute to increased mucosal permeability and visceral hypersensitivity in a PI‑IBS mouse model. CD11c+ LPMPs were isolated and purified via the digestion of intestinal tissues and magnetic‑activated cell sorting. We detected increased mucosal permeability, visceral hypersensitivity and intestinal inflammation during both the acute and chronic stages of Trichinella infection. Following the transfer of CD11c+ LPMPs from PI‑IBS mice into normal mice, low‑grade inflammation was detected, as demonstrated by increased IL‑4 expression in the ileum, as well as enhanced mucosal permeability, as indicated by decreased transepithelial electrical resistance and the pre-sence of ultrastructural alterations. More importantly, the mice that underwent adoptive transfer of CD11c+ LPMPs from the PI‑IBS mice also exhibited increased abdominal withdrawal reflex scores and a decreased threshold. Our data demonstrated that the CD11c+ LPMPs from this PI‑IBS mouse model were not only able to transfer enteric inflammation to the normal mice but also caused abnormal intestinal function, characterized by epithelial barrier disruption and visceral hyperalgesia.

Supernatants of irritable bowel syndrome mucosal biopsies impair human colonic smooth muscle contractility

BACKGROUND

Changes in intestinal motility are likely to contribute to irritable bowel syndrome (IBS) pathophysiology. The aim of the study was to investigate the effects of IBS mucosal supernatants on human colonic muscle contractility.

METHODS

Supernatants were obtained from biopsies of 18 IBS patients-nine with constipation (IBS-C) and nine with diarrhea-predominant IBS (IBS-D)-and nine asymptomatic subjects, used as controls. Colonic circular smooth muscle strips or isolated cells (SMC) were exposed to control or IBS supernatants. Spontaneous phasic contractions on strips and morphofunctional parameters on cells were evaluated in basal conditions and in response to acetylcholine (Ach). Incubation with IBS supernatants was also conducted in the presence of antagonists and inhibitors (namely histamine, protease and prostaglandin antagonists, nuclear factor-kappa B inhibitor, catalase, NADPH oxidase inhibitor, and the cAMP- and/or cGMP-cyclase inhibitors).

KEY RESULTS

Exposure to IBS-C and IBS-D supernatants induced a significant reduction in basal tone and Ach-elicited contraction of muscle strips and a significant shortening and impairment of Ach contraction of SMCs. The NADPH oxidase inhibitor prevented the effect of supernatants, while the protease antagonist only IBS-C effect. No effect was observed with the other antagonists and inhibitors. Dilution of IBS-D supernatants partially restored the effects only on SMCs, whereas dilution of IBS-C supernatants significantly reverted the effects on muscle strips and Ach-elicited response on SMC.

CONCLUSIONS & INFERENCES

Supernatants from mucosal biopsies of IBS patients reduce colonic contractility. The observed impairment was concentration dependent, likely occurring through intracellular oxidative stress damage, involving different neuromotor mechanisms depending on the IBS subtype.

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.

Giardia duodenalis induces paracellular bacterial translocation and causes postinfectious visceral hypersensitivity

Irritable bowel syndrome (IBS) is the most frequent functional gastrointestinal disorder. It is characterized by abdominal hypersensitivity, leading to discomfort and pain, as well as altered bowel habits. While it is common for IBS to develop following the resolution of infectious gastroenteritis [then termed postinfectious IBS (PI-IBS)], the mechanisms remain incompletely understood. Giardia duodenalis is a cosmopolitan water-borne enteropathogen that causes intestinal malabsorption, diarrhea, and postinfectious complications. Cause-and-effect studies using a human enteropathogen to help investigate the mechanisms of PI-IBS are sorely lacking. In an attempt to establish causality between giardiasis and postinfectious visceral hypersensitivity, this study describes a new model of PI-IBS in neonatal rats infected with G. duodenalis At 50 days postinfection with G. duodenalis (assemblage A or B), long after the parasite was cleared, rats developed visceral hypersensitivity to luminal balloon distension in the jejunum and rectum, activation of the nociceptive signaling pathway (increased c-fos expression), histological modifications (villus atrophy and crypt hyperplasia), and proliferation of mucosal intraepithelial lymphocytes and mast cells in the jejunum, but not in the rectum. G. duodenalis infection also disrupted the intestinal barrier, in vivo and in vitro, which in turn promoted the translocation of commensal bacteria. Giardia-induced bacterial paracellular translocation in vitro correlated with degradation of the tight junction proteins occludin and claudin-4. The extensive observations associated with gut hypersensitivity described here demonstrate that, indeed, in this new model of postgiardiasis IBS, alterations to the gut mucosa and c-fos are consistent with those associated with PI-IBS and, hence, offer avenues for new mechanistic research in the field.

Intrinsic Gastrointestinal Macrophages: Their Phenotype and Role in Gastrointestinal Motility

There is an increasing awareness of the role of macrophages in the regulation and maintenance of gastrointestinal function in health and disease. This work has proceeded in the context of an increased understanding of the complex phenotypic variation in macrophages throughout the body and has revealed previously un-identified roles for macrophages in diseases like gastroparesis, post-operative ileus and inflammatory bowel disease. Opportunities for exploiting the phenotypic modulation of tissue resident macrophages have been identified as possible therapies for some of these diseases. In addition, macrophages are an established component of the innate immune system that can respond to variations and changes in the intestinal microbiome and potentially mediate part of the impact of the microbiota on intestinal health. We reviewed the latest work on novel concepts in defining macrophage phenotype, discuss possible mechanisms of action for tissue-resident macrophages in the gut, address the significance of microbiome effects on macrophage phenotype and review the known and possible roles of macrophages in motility disorders of the gastrointestinal tract.

Diverticulosis today: unfashionable and still under-researched

Diverticulosis of the colon is a widespread disease, and its prevalence is increasing especially in the developing world. The underlying pathological mechanisms that cause the formation of colonic diverticula remain unclear but are likely to be the result of complex interactions among age, diet, genetic factors, colonic motility, and changes in colonic structure. The large majority of patients remain asymptomatic throughout their life, one fifth of them become symptomatic (developing the so-called 'diverticular disease') while only a minority of these will develop acute diverticulitis. The factors predicting the development of symptoms remain to be identified. Again, it is generally recognized that diverticular disease occurrence is probably related to complex interactions among colonic motility, diet, lifestyle, and genetic features. Changes in intestinal microflora due to low-fiber diet and consequent low-grade inflammation are thought to be one of the mechanisms responsible for symptoms occurrence of both diverticular disease and acute diverticulitis. Current therapeutic approaches with rifaximin and mesalazine to treat the symptoms seem to be promising. Antibiotic treatment is currently advised only in acute complicated diverticulitis, and no treatment has currently proven effective in preventing the recurrence of acute diverticulitis. Further studies are required in order to clarify the reasons why diverticulosis occurs and the factors triggering occurrence of symptoms. Moreover, the reasons why rifaximin and mesalazine work in symptomatic diverticular disease but not in acute diverticulitis are yet to be elucidated.

Stress and the Microbiota-Gut-Brain Axis in Visceral Pain: Relevance to Irritable Bowel Syndrome

Visceral pain is a global term used to describe pain originating from the internal organs of the body, which affects a significant proportion of the population and is a common feature of functional gastrointestinal disorders (FGIDs) such as irritable bowel syndrome (IBS). While IBS is multifactorial, with no single etiology to completely explain the disorder, many patients also experience comorbid behavioral disorders, such as anxiety or depression; thus, IBS is described as a disorder of the gut-brain axis. Stress is implicated in the development and exacerbation of visceral pain disorders. Chronic stress can modify central pain circuitry, as well as change motility and permeability throughout the gastrointestinal (GI) tract. More recently, the role of the gut microbiota in the bidirectional communication along the gut-brain axis, and subsequent changes in behavior, has emerged. Thus, stress and the gut microbiota can interact through complementary or opposing factors to influence visceral nociceptive behaviors. This review will highlight the evidence by which stress and the gut microbiota interact in the regulation of visceral nociception. We will focus on the influence of stress on the microbiota and the mechanisms by which microbiota can affect the stress response and behavioral outcomes with an emphasis on visceral pain.

Ageing and Gastrointestinal Sensory Function

Over the past few decades a combination of electrophysiological, morphological and molecular approaches has enabled the different populations of vagal and spinal afferents that innervate the bowel to be characterized. The sensitivity of these afferents is determined by their location in the gut wall, their relationship with other cells and structures and the receptors and ion channels that they express on their nerve terminals. An important feature of this innervation is that it is upregulated during injury, inflammation and ischaemia through changes in receptors and ion channels that determine excitability and sensitivity. In recent studies we have sought to identify how sensory mechanisms are influenced as part of the normal ageing process. Attenuated signaling was evident in different gastrointestinal afferent subpopulations conveying low and high threshold mechanosensory information and there was impairment in the ability of sensory neurons to sensitize in response to chemical mediators such as 5-HT. These sensory deficits may contribute to altered bowel habits with age and the prevalence of incontinence in the elderly.

Review article: the pathophysiology and medical management of diverticulosis and diverticular disease of the colon

BACKGROUND

The incidence of diverticulosis and diverticular disease of the colon, including diverticulitis, is increasing worldwide, and becoming a significant burden on national health systems. Treatment of patients with diverticulosis and DD is generally based on high-fibre diet and antibiotics, respectively. However, new pathophysiological knowledge suggests that further treatment may be useful.

AIM

To review the current treatment of diverticulosis and diverticular disease.

METHODS

A search of PubMed and Medline databases was performed to identify articles relevant to the management of diverticulosis and diverticular disease. Major international conferences were also reviewed.

RESULTS

Two randomised controlled trials (RCT) found the role of antibiotics in managing acute diverticulitis to be questionable, particularly in patients with no complicating comorbidities. One RCT found mesalazine to be effective in preventing acute diverticulitis in patients with symptomatic uncomplicated diverticular disease. The role of rifaximin or mesalazine in preventing diverticulitis recurrence, based on the results of 1 and 4 RCTs, respectively, remains unclear. RCTs found rifaximin and mesalazine to be effective in treating symptomatic uncomplicated diverticular disease. The use of probiotics in diverticular disease and in preventing acute diverticulitis occurrence/recurrence appears promising but unconclusive. Finally, the role of fibre in treating diverticulosis remains unclear.

CONCLUSIONS

Available evidence suggests that antibiotics have a role only in the treatment of complicated diverticulitis. It appears to be some evidence for a role for rifaximin and mesalazine in treating symptomatic uncomplicated diverticular disease. Finally, there is not currently adequate evidence to recommend any medical treatment for the prevention of diverticulitis recurrence.

Lactobacillus fermentum NS9 restores the antibiotic induced physiological and psychological abnormalities in rats

Gut microbiota play a vital role in maintaining the health of the host. Many factors affect gut microbiota; application of broad range antibiotics disturb microbiota, while probiotic application protects the microbiota. To investigate how probiotics alter the physiological and psychological changes induced by antibiotics, we tested the performance of ampicillin-treated rats in the presence or absence of Lactobacillus fermentum strain NS9, in elevated plus maze and Morris water maze. The results showed that NS9 normalised the composition of gut microbiota and alleviated the ampicillin-induced inflammation in the colon. The levels of the mineralocorticoid and N-methyl-D-aspartate receptors were also elevated in the hippocampus of the ampillicin+NS9 treated group. NS9 administration also reduced the anxiety-like behaviour and alleviated the ampicillin-induced impairment in memory retention. These findings suggest that NS9 is beneficial to the host, because it restores the physiological and psychological abnormalities induced by ampicillin. Our results highlight how gut contents regulate the brain, and shed light on the clinical applications of probiotics to treat the side effect of antibiotics and mental disorders.

Mast Cell-dependent Mesenteric Afferent Activation by Mucosal Supernatant From Different Bowel Segments of Guinea Pigs With Post-infectious Irritable Bowel Syndrome

Background/Aims

Mesenteric afferent nerves (MANs) play a pivotal role in the visceral-nociceptive perception. Inappropriate activation of MANs may be involved in the pathogenesis of post-infectious irritable bowel syndrome (PI-IBS). However, the underlying mechanisms remain unclear. We assessed the effects of mucosal mediators from different bowel segments of guinea pigs with PI-IBS on MAN firing and the role of mast cells.

Methods

PI-IBS was induced in guinea pigs by Trichinella spiralis infection. Inflammation in terminal ileum, proximal and distal colon was scored with hematoxylin-eosin staining, and mast cell infiltration was assessed with immunofluorescence. We determined the effects of supernatant extracted from the mucosa of different bowel segments of PI-IBS on MANs activity, and assessed the role of mast cells in this process.

Results

Eight weeks after infection, intestinal inflammation resolved, whereas mast cell numbers increased significantly in terminal ileum and proximal colon (P < 0.05) compared with findings in controls. Mucosal supernatant from different bowel segments of PI-IBS models, but not from controls, significantly enhanced the frequency of MAN firing (terminal ileum 41.01 ± 7.60 Hz vs. 26.55 ± 0.67 Hz, P = 0.001; proximal colon 45.90 ± 11.20 Hz vs. 30.88 ± 6.92 Hz, P = 0.002; distal colon 48.25 ± 9.70 Hz vs. 29.47 ± 6.13 Hz, P < 0.001). In addition, the excitatory effects were inhibited by mast cell stabilizer Nasmil (terminal ileum, 32.71 ± 2.52 Hz, P = 0.030; proximal colon, 30.94 ± 4.44 Hz, P = 0.002; distal colon, 27.15 ± 5.83 Hz, P < 0.001).

Conclusions

Supernatant from the intestinal mucosa of different bowel segments of PI-IBS models markedly enhanced the MAN firing in a mast cell-dependent manner, indicating that mast cell-mediated MAN activation plays an important role in the pathogenesis of PI-IBS.

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.

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

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

Stress-induced visceral pain: toward animal models of irritable-bowel syndrome and associated comorbidities

Visceral pain is a global term used to describe pain originating from the internal organs, which is distinct from somatic pain. It is a hallmark of functional gastrointestinal disorders such as irritable-bowel syndrome (IBS). Currently, the treatment strategies targeting visceral pain are unsatisfactory, with development of novel therapeutics hindered by a lack of detailed knowledge of the underlying mechanisms. Stress has long been implicated in the pathophysiology of visceral pain in both preclinical and clinical studies. Here, we discuss the complex etiology of visceral pain reviewing our current understanding in the context of the role of stress, gender, gut microbiota alterations, and immune functioning. Furthermore, we review the role of glutamate, GABA, and epigenetic mechanisms as possible therapeutic strategies for the treatment of visceral pain for which there is an unmet medical need. Moreover, we discuss the most widely described rodent models used to model visceral pain in the preclinical setting. The theory behind, and application of, animal models is key for both the understanding of underlying mechanisms and design of future therapeutic interventions. Taken together, it is apparent that stress-induced visceral pain and its psychiatric comorbidities, as typified by IBS, has a multifaceted etiology. Moreover, treatment strategies still lag far behind when compared to other pain modalities. The development of novel, effective, and specific therapeutics for the treatment of visceral pain has never been more pertinent.

Impact of the alterations in the interstitial cells of Cajal on intestinal motility in post-infection irritable bowel syndrome

The interstitial cells of Cajal (ICC) are basic components of gastrointestinal motility. However, changes in ICC and their role in post‑infection irritable bowel syndrome (PI‑IBS) remain to be elucidated. To observe the impact of alterations in the ICC on intestinal motility in a PI‑IBS mouse model, female C57BL\6 mice were infected by the oral administration of 400 Trichinella spiralis larvae. The abdominal withdrawal reflex, intestine transportation time (ITT), grain numbers, Bristol scores, wet/dry weights and the percentage water content of the mice feces every 2 h were used to assess changes in the intestinal motor function. The intestines were excised and sectioned for pathological and histochemical examination. These intestines were also used to quantify the protein and mRNA expression of c‑kit. The C57BL\6 mouse can act as a PI‑IBS model at day 56 post‑infection. Compared with the control mice, the ITT was shorter, the grain numbers, Bristol scores, wet weights and water contents of the mice feces were higher and the dry weights were unchanged in the PI‑IBS mice. The protein and mRNA expression levels of c‑kit were upregulated in the entire PI‑IBS mouse intestines. Following immunohistochemical staining, the increased number of c‑kit‑positive cells were detected predominantly in the submucosa and myenteron. These results suggested that the alterations of the ICC resulted in the changes of the intestinal motility patterns in the PI‑IBS mouse models induced by Trichinella spiralis infection, which may be the main mechanism underlying intestinal motility disorders in PI‑IBS.

Condition-specific role of colonic inflammatory molecules in persistent functional colorectal hypersensitivity in the mouse

BACKGROUND

A low-level inflammation has been hypothesized to mediate visceral hypersensitivity in functional bowel disorders that persist after or even in the absence of gut inflammation. We aimed to test the efficacy of a steroidal anti-inflammatory treatment, and identify local inflammatory molecules mediating post- and non-inflammatory colorectal hypersensitivity using two mouse models.

METHODS

Visceromotor responses to colorectal distension were quantified as a measure of colorectal sensitivity. On day 1, mice received intracolonic saline (control), trinitrobenzenesulfonic acid (postinflammatory on day 15), or acidified hypertonic saline (non-inflammatory). Colorectal sensitivity before (day 10) and after (day 15) 4-day dexamethasone (Dex) treatment was compared, and colonic gene expression of inflammatory molecules was quantified.

KEY RESULTS

Dexamethasone effectively inhibited gene expression of inflammatory molecules such as interleukin (IL)-1β and mast cell protease-1 in the colon, but did not attenuate colorectal hypersensitivity in either model. Gene expression of inflammatory molecules in the colon did not differ between control and the non-inflammatory model, but the postinflammatory model showed increased IL-10 and tight junction protein 2, and decreased IL-6, transforming growth factor (TGF)-β, a precursor of β-endorphin, occludin, and mucin 2. While no common molecule explained colorectal hypersensitivity in these models, hypersensitivity was positively correlated with TGF-β2 mRNA in control, and with IL-1β, inhibin βA, and prostaglandin E2 synthase in the Dex-treated postinflammatory model. In the non-inflammatory model, cyclooxygenase-2 mRNA was negatively correlated with colorectal sensitivity.

CONCLUSIONS & INFERENCES

These results suggest that persistent functional colorectal hypersensitivity is mediated by condition-specific mediators whose gene expression in the colon is not inevitably sensitive to steroidal anti-inflammatory treatment.

The effects of inflammation, infection and antibiotics on the microbiota-gut-brain axis

Animal studies have demonstrated that the early phase of enteric infection is accompanied by anxiety-like behavior, which is mediated through vagal ascending pathways. Chronic infection alters gut function, including motility and visceral sensitivity, as well as feeding patterns, anxiety and depression-like behavior. These effects are likely immune-mediated, and involve changes in pro-inflammatory cytokines and altered metabolism of kynurenine/tryptophan pathways. Clinical studies have shown that chronic gastrointestinal infections lead to malnutrition and stunting, resulting in impaired cognitive function. Accumulating evidence suggests that in addition to pathogens, the commensal gastrointestinal microbiota also influences gut function and host's behavior. Both animal and clinical studies have demonstrated changes in behavior and brain chemistry after induction of intestinal dysbiosis by administration of antibiotics. This concept of microbiota-gut-brain interactions opens a new field of research aimed at developing microbial-directed therapies to treat a broad spectrum of human conditions, including chronic gastrointestinal and psychiatric disorders.

Bead study: a novel method to measure gastrointestinal transit in mice

BACKGROUND

Intestinal transit assessment in mice using existing methods requires long recording periods or euthanization of animals to localize a tracer. We have developed a novel in vivo method to assess gastrointestinal (GI) transit in mice based on a clinically used 'shapes study'.

METHODS

Mice (n = 70) were gavaged with 5 steel beads and barium 3 h before, with another dose of barium gavaged 10 min before imaging. Mice were fluoroscoped for 20-60 s, and then most of them were euthanized and the GI tract removed to confirm the localization of the beads fluoroscopically. The in vivo and postmortem recordings were analyzed and each bead was scored depending on its location; a total score was calculated by adding individual bead scores. Total scores obtained from the two methods were compared. A group of mice (n = 10) were examined on three occasions, before and after treatment with loperamide or prucalopride.

KEY RESULTS

The stomach and cecum were consistently outlined by barium, serving as reference landmarks. There was an excellent overall correlation between in vivo and postmortem transit scores (r = 0.93). Analysis of scores for individual gut segments revealed high agreement for stomach, cecum, and expelled beads, and moderate agreement for the small bowel and colon. Gastrointestinal transit scores were decreased by loperamide and increased by prucalopride compared with baseline.

CONCLUSIONS & INFERENCES

Metallic beads are reliably localized by videofluoroscopy in vivo within the GI tract. This novel imaging method enables repetitive measurements of GI transit in vivo and detects changes induced by motility-modifying agents.

Associations between IL-1RA polymorphisms and small intestinal bacterial overgrowth among patients with irritable bowel syndrome from India

BACKGROUND

Low-grade inflammation (controlled by pro and anti-inflammatory molecules), induced by gut microbes in patients with small intestinal bacterial overgrowth (SIBO), may be associated with irritable bowel syndrome (IBS). Polymorphisms of IL-RA gene (anti-inflammatory) was evaluated in IBS and healthy subjects (HS); small intestinal mucosal IL-1α and β levels (pro-inflammatory) in relation to the presence of SIBO were evaluated in a subset of patients.

METHODS

Two hundred and twenty-one IBS patients and 273 age- and gender-matched HS were included. Exactly 209 of 221 patients (Rome III) and 273 HS were genotyped (PCR) for IL-1RA polymorphism. Mucosal IL-1α and β levels (pg/mg of biopsy) were estimated (ELISA) in 82/221 patients with and without SIBO (≥10(5)  CFU/mL upper gut aspirate bacteria).

KEY RESULTS

Genotype 1/1 (IL-1RA over-producer) was less frequent among patients than controls (p = 0.007); genotypes 1/3 (p = 0.012, OR = 3.301, 95% CI = 1.31-8.35) and 2/3 (both under-producers; p = 0.009, OR = 7.703, 95% CI = 1.66-35.82) were commoner among IBS. Fifteen of 82 (18.3%) patients had SIBO. Levels of IL-1α and β were higher among patients with SIBO than without (IL-1α: 35.4 [20.1-66.8] vs 25.5 [4.2-65.3], p < 0.001; IL-1β: 206.8 [133.5-365.9] vs 93.1 [25.5-197.7], p < 0.001) and those with bloating than without (p = 0.012; p = 0.015). IL-1β was higher among patients with Bristol stool type 6 than those with type 1-2 (p = 0.002) and type 3-5 (p = 0.007).

CONCLUSIONS & INFERENCES

Polymorphisms 1/1 (IL-1RA over-producer) was infrequent and 1/3 and 2/3 (under-producers) frequent among IBS. Increased IL-1α and β levels were associated with SIBO. Increased IL-1β level was predominantly associated with bloating and loose stools (Bristol type 6).