Mechanisms of hypersensitivity in IBS and functional disorders

Relieving visceral hyperalgesia effect of Kangtai capsule and its potential mechanisms via modulating the 5-HT and NO level in vivo

Kangtai capsule (KT) is one type of traditional Chinese medicine preparation derived from the proved recipe, which was frequently applied as an effective clinical treatment of IBS. However, there still lack the reasonable and all-round analytical approach and the scientific studies on its underlying mechanisms. Therefore, our study aimed to develop the novel method for evaluating its quality as well as to interpret the potential mechanisms. In our study, high performance liquid chromatography (HPLC) fingerprint was applied to provide a chemical profile of KT. The neonatal maternal separation (NMS) on Sprague-Dawley pups was employed to evaluate the therapeutic effect of KT by virtue of various parameters including visceral hyperalgesia, serum nitric oxide (NO) level, and tissue 5-hydroxytryptamine (5-HT) level. Consequently, a chromatographic condition, which was carried at 30°C with a flow rate of 0.5 ml/min on AQUA 3μ C18 column with mobile phase of acetonitrile and water-phosphoric acid (100:0.1, v/v), was established to give a common fingerprint chromatography under 254 nm with a similarity index of 0.963 within ten batches of KT samples. On the NMS model, KT markedly elevated the pain threshold of NMS rats. Furthermore, KT at three doses significantly decreased 5-HT content from distal colon of visceral hyperalgesia rats induced by NMS, while the significant decrease of 5-HT content in serum was only observed in the group with KT at high dose. However, compared with that in NMS rats without KT, there was no apparent difference of 5-HT level from brain issue in the rats with various doses. Besides, KT could substantially elevate the concentration of NO in the serum. The results showed our study developed the simple, rapid, accurate, reproducible qualitative and quantitative analysis by HPLC fingerprint for the quality control for KT. Data from the pharmacological investigation suggested that the curative effect of KT to the visceral hypersensitivity may be concerned with the level of 5-HT and NO in vivo, promising its potential in irritable bowel syndrome treatment.

Life course study of the etiology of self-reported irritable bowel syndrome in the 1958 British birth cohort

OBJECTIVE

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder with unknown etiology. This is the first study to use a life course approach to examine premorbid risk markers for self-reported IBS in a UK birth cohort.

METHODS

Cohort study using the 1958 British birth cohort, which included 98.7% of births in 1 week in England, Wales, and Scotland. The outcome was self-reported IBS by the age of 42 years, classified with onset after 24 years and onset after 34 years. Childhood psychopathology was assessed by the Rutter scales, and adulthood psychopathology was assessed by the Malaise Inventory.

RESULTS

The prevalence of self-reported IBS in this cohort was 8.4% by 42 years (95% confidence interval [CI]=8.2-8.6). In multivariate analyses, being female (odds ratio [OR]=2.00, 95% CI=1.67-2.36), reporting 1 week to 1 month of school absence for ill health at 16 years (OR=1.27, 95% CI=1.03-1.56) and psychopathology at 23 years (OR=1.25, 95% CI=1.01-1.54) and 33 years (OR=2.20, 95% CI=1.74-2.76) were associated with an increased odds for IBS. Prospectively measured childhood adversity showed no significant association.

CONCLUSIONS

This is the first study to show a long-term prospective link between premorbid psychopathology and later self-reported IBS, in agreement with previous findings on chronic fatigue syndrome. There is no evidence that prospective measures of childhood adversity are risk markers for IBS, and there is weak evidence that prospective measures of childhood illness at 16 years are risk markers for IBS, differing to results from the same cohort for psychopathology, chronic fatigue syndrome, and chronic widespread pain. This study also does not replicate the findings of retrospective studies examining the etiology of IBS.

Upregulation of cystathionine β-synthetase expression contributes to visceral hyperalgesia induced by heterotypic intermittent stress in rats

Background

Hydrogen sulfide (H₂S) functions as a neuromodulator, but whether it modulates visceral pain is not well known. This study was designed to determine the role for the endogenous H₂S producing enzyme cystathionine β-synthetase (CBS) and cystathionine γ-lyase (CSE) in a validated rat model of visceral hyperalgesia (VH).

Methods

VH was induced by nine-day heterotypic intermittent stress (HIS). Abdominal withdrawal reflex (AWR) scores were determined by measuring the visceromoter responses to colorectal distension (CRD). Dorsal root ganglia (DRG) neurons innervating the colon were labeled by injection of DiI (1,1'-dioleyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate) into the colon wall. Patch clamp recording techniques were employed to examine excitability and sodium channel currents of colon specific DRG neurons. Tissues from colon related thoracolumbar DRGs were analyzed for CBS, CSE and sodium channel expression.

Results

HIS significantly increased the visceromotor responses to CRD in association with an upregulated expression of CBS not CSE proteins in colon related DRGs. Administration of O-(Carboxymethyl)hydroxylamine hemihydrochloride (AOAA), an inhibitor of CBS, attenuated the AWR scores in HIS-treated rats, in a dose dependent fashion. In contrast, AOAA did not produce any effect on AWR scores in healthy control rats. AOAA reversed the potentiation of sodium channel current densities of colon specific DRG neurons of HIS rats. To further confirm the role for CBS-H₂S signaling, NaHS was used to mimic the production of H₂S by CBS. Application of NaHS significantly enhanced neuronal excitability and potentiated sodium channel current densities of colon DRG neurons from healthy control rats. Furthermore, AOAA reversed the upregulation of Na_V1.7 and Na_V1.8 in colon related DRGs of HIS rats.

Conclusion

Our results suggest that upregulation of CBS expression might play an important role in developing VH via sensitization of sodium channels in peripheral nociceptors, thus identifying a specific neurobiological target for the treatment of VH in functional bowel syndromes.

Experimental endotoxemia as a model to study neuroimmune mechanisms in human visceral pain

The administration of bacterial endotoxin (i.e., lipopolysaccharide, LPS) constitutes a well-established experimental approach to study the effects of an acute and transient immune activation on physiological, behavioral, and emotional aspects of sickness behavior in animals and healthy humans. However, little is known about possible effects of experimental endotoxemia on pain in humans. This knowledge gap is particularly striking in the context of visceral pain in functional as well as chronic-inflammatory gastrointestinal disorders. Although inflammatory processes have been implicated in the pathophysiology of visceral pain, it remains incompletely understood how inflammatory mediators interact with bottom-up (i.e., increased afferent input) and top-down (i.e., altered central pain processing) mechanisms of visceral hyperalgesia. Considering the recent findings of visceral hyperalgesia after LPS application in humans, in this review, we propose that experimental endotoxemia with its complex peripheral and central effects constitutes an experimental model to study neuroimmune communication in human pain research. We summarize and attempt to integrate relevant animal and human studies concerning neuroimmune communication in visceral and somatic pain, discuss putative mechanisms, and conclude with future research directions.

Rectal hyposensitivity

Impaired or blunted rectal sensation, termed rectal hyposensitivity (RH), which is defined clinically as elevated sensory thresholds to rectal balloon distension, is associated with disorders of hindgut function, characterised primarily by symptoms of constipation and fecal incontinence. However, its role in symptom generation and the pathogenetic mechanisms underlying the sensory dysfunction remain incompletely understood, although there is evidence that RH may be due to 'primary' disruption of the afferent pathway, 'secondary' to abnormal rectal biomechanics, or to both. Nevertheless, correction of RH by various interventions (behavioural, neuromodulation, surgical) is associated with, and may be responsible for, symptomatic improvement. This review provides a contemporary overview of RH, focusing on diagnosis, clinical associations, pathophysiology, and treatment paradigms.

Targeting the endocannabinoid system for gastrointestinal diseases: future therapeutic strategies

Cannabinoids extracted from the marijuana plant (Cannabis sativa) and synthetic cannabinoids have numerous effects on gastrointestinal (GI) functions. Recent experimental data support an important role for cannabinoids in GI diseases. Genetic studies in humans have proven that defects in endocannabinoid metabolism underlie functional GI disorders. Mammalian cells have machinery, the so-called endocannabinoid system (ECS), to produce and metabolize their own cannabinoids in order to control homeostasis of the gut in a rapidly adapting manner. Pharmacological manipulation of the ECS by cannabinoids, or by drugs that raise the levels of endogenous cannabinoids, have shown beneficial effects on GI pathophysiology. This review gives an introduction into the functions of the ECS in the GI tract, highlights the role of the ECS in GI diseases and addresses its potential pharmacological exploitation.

Intestinal gas: has diet anything to do in the absence of a demonstrable malabsorption state?

PURPOSE OF REVIEW

To summarize the relevant publications during the last 12 months supporting that diet can influence gas-related symptoms in the absence of a malabsorption state.

RECENT FINDINGS

Gas symptoms during carbohydrate fermentation: a diet incorporating beans is well tolerated by a majority of individuals involved in a program of heart disease biomarkers. By contrast, in patients with irritable bowel syndrome, a diet avoiding fermentable carbohydrates improved gas-related abdominal symptoms. The rate of fermentation determines the production of abdominal symptoms, and many slowly fermentable fibers have a rapid fermentation profile that can generate abdominal symptoms. Modulation of visceral sensitivity: diet can influence gas symptoms by increasing the tolerability of the intestine to gas. Capsaicin decreases visceral hyperalgesia and improved bloating in patients with irritable bowel syndrome. Changes in gas-producing bacteria: different strains of Lactobacillus have antimicrobial properties against gas-forming coliforms. New clinical studies show beneficial effects of prebiotics and probiotics on abdominal bloating.

SUMMARY

Actual data suggest that diet could improve gas-related abdominal symptoms acting on several mechanisms: gas production, visceral hypersensitivity and modulation of gas-producing enteric bacteria.

Irritable bowel syndrome: methods, mechanisms, and pathophysiology. Methods to assess visceral hypersensitivity in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder, characterized by recurrent abdominal pain or discomfort in combination with disturbed bowel habits in the absence of identifiable organic cause. Visceral hypersensitivity has emerged as a key hypothesis in explaining the painful symptoms in IBS and has been proposed as a "biological hallmark" for the condition. Current techniques of assessing visceral perception include the computerized barostat using rectal distensions, registering responses induced by sensory stimuli including the flexor reflex and cerebral evoked potentials, as well as brain imaging modalities such as functional magnetic resonance imaging and positron emission tomography. These methods have provided further insight into alterations in pain processing in IBS, although the most optimal method and condition remain to be established. In an attempt to give an overview of these methods, a literature search in the electronic databases PubMed and MEDLINE was executed using the search terms "assessment of visceral pain/visceral nociception/visceral hypersensitivity" and "irritable bowel syndrome." Both original articles and review articles were considered for data extraction. This review aims to discuss currently used modalities in assessing visceral perception, along with advantages and limitations, and aims also to define future directions for methodological aspects in visceral pain research. Although novel paradigms such as brain imaging and neurophysiological recordings have been introduced in the study of visceral pain, confirmative studies are warranted to establish their robustness and clinical relevance. Therefore, subjective verbal reporting following rectal distension currently remains the best-validated technique in assessing visceral perception in IBS.

Brain-Gut Interactions in IBS

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder with an estimated prevalence of 10–20%. Current understanding of the pathophysiology of IBS is incomplete due to the lack of a clearly identified pathological abnormality and due to the lack of reliable biomarkers. Possible mechanisms believed to contribute to IBS development and IBS like symptoms include physical stressors, such as infection or inflammation, psychological, and environmental factors, like anxiety, depression, and significant negative life events. Some of these mechanisms may involve the brain-gut axis (BGA). In this article we review the current knowledge on the possible involvement of the BGA in IBS and discuss new directions for potential future therapies of IBS.

Activation of the alpha-7 nicotinic acetylcholine receptor (α7 nAchR) reverses referred mechanical hyperalgesia induced by colonic inflammation in mice

In the current study, we investigated the effect of the activation of the alpha-7 nicotinic acetylcholine receptor (α7 nAchR) on dextran sulphate sodium (DSS)-induced colitis and referred mechanical hyperalgesia in mice. Colitis was induced in CD1 male mice through the intake of 4% DSS in tap water for 7 days. Control mice received unadulterated water. Referred mechanical hyperalgesia was evaluated for 7 days after the beginning of 4% DSS intake. Referred mechanical hyperalgesia started within 1 day after beginning DSS drinking, peaked at 3 days and persisted for 7 days. This time course profile perfectly matched with the appearance of signs of colitis. Both acute and chronic oral treatments with nicotine (0.1-1.0 mg/kg, p.o.) were effective in inhibiting the established referred mechanical hyperalgesia. The antinociceptive effect of nicotine was completely abrogated by cotreatment with the selective α7 nAchR antagonist methyllycaconitine (MLA) (1.0 mg/kg). Consistent with these results, i.p. treatment with the selective α7 nAchR agonist PNU 282987 (0.1-1.0 mg/kg) reduced referred mechanical hyperalgesia at all periods of evaluation. Despite their antinociceptive effects, nicotinic agonists did not affect DSS-induced colonic damage or inflammation. Taken together, the data generated in the present study show the potential relevance of using α7 nAchR agonists to treat referred pain and discomfort associated with inflammatory bowel diseases.

JCM-16021, a Chinese Herbal Formula, Attenuated Visceral Hyperalgesia in TNBS-Induced Postinflammatory Irritable Bowel Syndrome through Reducing Colonic EC Cell Hyperplasia and Serotonin Availability in Rats

The present study aimed to investigate the analgesic effect of JCM-16021, a revised traditional Chinese herbal formula, on postinflammatory irritable bowel syndrome (PI-IBS) in rats. The trinitrobenzene sulfonic (TNBS) acid-induced PI-IBS model rats were orally administrated with different doses of JCM-16021 (1.2, 2.4, and 4.8 g/kg/d) for 14 consecutive days. The results showed that JCM-16021 treatment dose-dependently attenuated visceral hyperalgesia in PI-IBS rats. Further, the colonic enterochromaffin (EC) cell number, serotonin (5-HT) content, tryptophan hydroxylase expression, and mechanical-stimuli-induced 5-HT release were significantly ameliorated. Moreover, the decreased levels of mucosal cytokines in PI-IBS, especially the helper T-cell type 1- (T(h)1-) related cytokine TNF-α, were also elevated after JCM-16021 treatment. These data demonstrate that the analgesic effect of JCM-16021 on TNBS-induced PI-IBS rats may be medicated via reducing colonic EC cell hyperplasia and 5-HT availability.

Clustering and stability of functional lower gastrointestinal symptom after enteric infection

BACKGROUND

Current diagnostic criteria for functional gut disorder are based on symptom clusters observed after sporadic onset. It remains unclear whether symptoms group similarly in functional disorders of postinfectious etiology. We utilized observational data from the Walkerton Health Study (WHS) to: (i) determine groupings of functional gastrointestinal symptoms among patients exposed to acute gastroenteritis (GE), and (ii) assess the stability of these symptoms grouping over time.

METHODS

WHS participants 16 years of age and older at the time of the outbreak were included, if they had completed a modified Talley's Bowel Disease Questionnaire (BDQ) and responded 'yes' to a screening question as to whether they had experienced abdominal pain in the last 2 weeks. Exploratory factor analysis (EFA) using tetrachoric correlations was undertaken to identify symptom constructs. Hierarchical cluster analysis using the k-means method was used to create cluster groupings of patients based on these factors. Confirmatory factors analysis using responses to BDQ questionnaire administered at 4, 6, and 8 years after the outbreak was performed to assess stability of symptom domains over time.

KEY RESULTS

A total of 773 participants were eligible for inclusion [62.2% female, mean age 43.1 years (SD = 16.9)]. Eighty-four percent were exposed to acute GE during the outbreak. Two symptom groupings of abdominal pain with either diarrhea or constipation together explained 85.7% of the total variance. Cluster analysis identified four patients groupings based on these factors. These clusters could be qualitatively described as diarrhea- and constipation-predominant, mixed bowel pattern, and no predominance of bowel movements abnormalities. Results of the confirmatory factor analysis validating symptom domains identified in Year 1 showed that the baseline model was acceptable at 4 and 6 years after the outbreak and approached acceptability at 8 years. Values of root mean square error of approximation were 0.071 (90% CI: 0.053, 0.089) at 4 and 0.071 (90% CI: 0.049, 0.092) at 6 years and 0.089 (90% CI: 0.065, 0.114) at 8 years.

CONCLUSIONS & INFERENCES

The majority of subjects with postinfectious functional bowel disorders belong to groups with symptoms of abdominal pain and either diarrhea or constipation. These symptom groupings were stable across time.

Synesthesia, pseudo-synesthesia, and irritable bowel syndrome

BACKGROUND AND AIMS

Synesthesia is a sensory disorder where the stimulation of one sensory modality can lead to a reaction in another which would not usually be expected to respond; for instance, someone might see a color on hearing a word such as a day of the week. Disordered perception of sensory information also appears to contribute to the pathophysiology of irritable bowel syndrome (IBS). The purpose of this exploratory study was to ascertain whether these two conditions might be linked in any way.

METHODS

Two hundred consecutive IBS outpatients were screened for synesthesia and compared with 200 matched healthy volunteers (controls). Positive responders were tested for two types of synesthesia (grapheme-color and music-color/shape) using a questionnaire which was repeated after 3 months to test for reproducibility.

RESULTS

Of the 200 IBS outpatients screened, 26 (13%) patients and six (3%) controls claimed to be synesthetic (P < 0.001). Reproducibility was more variable in IBS patients than controls but despite this variability, 15 (7.5%) patients compared with 5 (2.5%) controls had greater than 75% consistency (P = 0.036), and 19 (9.5%) patients and 6 (3%) controls had greater than 50% consistency (P = 0.012). A reproducibility of less than 50% was observed in seven (3.5%) patients and no controls (0%) (P = 0.015), and these individuals were classified as having pseudo-synesthesia.

CONCLUSION

IBS patients clearly differ from controls in terms of claiming to have synesthetic experiences. These results justify additional studies on the relationship between IBS and synesthesia to further understand the neural mechanisms underpinning these two conditions and to establish whether they may be linked.

Relationship among food intolerance, severity of symptoms and the number of mast cells in the ileocecal junction in patients with diarrhea-predominant irritable bowel syndrome

AIM: To analyze the relationship among food intolerance, severity of symptoms and the number of mucosal mast cells (MCs) in the ileocecal junction (ICJ) in patients with diarrhea-predominant irritable bowel syndrome (D-IBS), and to explore the influence of food intolerance on the pathogenesis of D-IBS.

METHODS: Twenty-two patients with D-IBS fulfilling the Rome III criteria and 21 asymptomatic healthy controls underwent colonoscopy in which two adjacent biopsy samples were taken from the ICJ. Mucosal MCs were detected by toluidine blue staining. The Food Intolerance Questionnaire was used to evaluate the perceived food intolerance status of D-IBS patients and controls. The Functional Bowel Disorder Severity Index (FBDSI) and IBS Symptom Severity Scale (IBS-SSS) were used to evaluate the severity of symptoms in D-IBS patients. The relationship among the scores of FBDSI and IBS-SSS, the number of MCs and the scores of food intolerance in D-IBS patients was analyzed.

RESULTS: The number of mucosal MCs in the ICJ was significantly higher in patients with D-IBS than in controls (4.68 ± 0.55/HP vs 1.33 ± 0.54/HP, P < 0.001). Compared to controls, perceived FI was more frequent in patients with D-IBS (P < 0.05). The scores of FBDSI and IBS-SSS were positively correlated with that of food intolerance in D-IBS patients (FBDSI: r = 0.992, P < 0.001; IBS-SSS: r = 0.970, P < 0.001), and with the number of mucosal MCs in the ICJ (FBDSI: r = 0.957, P < 0.001; IBS-SSS: r = 0.985, P < 0.001). The scores of food intolerance in D-IBS patients were positively correlated with the number of mucosal MCs in the ICJ (r = 0.964, P < 0.001). The number of mucosal MCs in the ICJ were significantly higher in healthy subjects with self-reported food intolerance than in those without food intolerance (P < 0.05).

CONCLUSION: The symptoms of D-IBS are positively correlated with increased number of enteric mucosal MCs which might be caused by food antigen. Food intolerance is more frequent in D-IBS patients than in controls. D-IBS symptoms may be caused or exacerbated by food intolerance.

Functional dysbiosis within the gut microbiota of patients with constipated-irritable bowel syndrome

BACKGROUND

The role of the gut microbiota in patho-physiology of irritable bowel syndrome (IBS) is suggested by several studies. However, standard cultural and molecular methods used to date have not revealed specific and consistent IBS-related groups of microbes.

AIM

To explore the constipated-IBS (C-IBS) gut microbiota using a function-based approach.

METHODS

The faecal microbiota from 14 C-IBS women and 12 sex-match healthy subjects were examined through a combined strictly anaerobic cultural evaluation of functional groups of microbes and fluorescent in situ hybridisation (16S rDNA gene targeting probes) to quantify main groups of bacteria. Starch fermentation by C-IBS and healthy faecal samples was evaluated in vitro.

RESULTS

In C-IBS, the numbers of lactate-producing and lactate-utilising bacteria and the number of H(2) -consuming populations, methanogens and reductive acetogens, were at least 10-fold lower (P < 0.05) compared with control subjects. Concomitantly, the number of lactate- and H(2) -utilising sulphate-reducing population was 10 to 100 fold increased in C-IBS compared with healthy subjects. The butyrate-producing Roseburia - E. rectale group was in lower number (0.01 < P < 0.05) in C-IBS than in control. C-IBS faecal microbiota produced more sulphides and H(2) and less butyrate from starch fermentation than healthy ones.

CONCLUSIONS

A major functional dysbiosis was observed in constipated-irritable bowel syndrome gut microbiota, reflecting altered intestinal fermentation. Sulphate-reducing population increased in the gut of C-IBS and were accompanied by alterations in other microbial groups. This could be responsible for changes in the metabolic output and enhancement in toxic sulphide production which could in turn influence gut physiology and contribute to IBS pathogenesis.

Oxytocin prolongs the gastric emptying time in patients with diabetes mellitus and gastroparesis, but does not affect satiety or volume intake in patients with functional dyspepsia

Background

Oxytocin is released in response to a fatty meal. Blockage of the oxytocin receptor led to slower gastric emptying whereas stimulation resulted in less satiety in healthy volunteers. Patients with diabetes mellitus and gastroparesis lack oxytocin elevation, and dyspepsia is partly caused by reduced fundus accommodation causing early satiety and related symptoms. The aim of this study was thus to examine the effect of oxytocin on gastric emptying, satiety and volume intake in patients with gastrointestinal pathology.

Results

Gastric emptying scintigraphy was performed twice in 12 patients with diabetic gastroparesis, once with oxytocin and once with saline as intravenous infusions. The patients scored their sensation of satiety using a visual analogue scale (VAS). The gastric emptying in patients with gastroparesis was prolonged during oxytocin infusion (p = 0.034) without affecting satiety. A slow satiety drinking test was performed in 14 patients with functional dyspepsia. The patients scored their satiety every five minutes until maximal satiety was reached, and the total volume was determined. The VAS was also completed 30 minutes afterwards. The test was performed twice, once with oxytocin and once with saline as intravenous infusions. There was no difference in satiety scores or volume of nutrient intake between saline and oxytocin infusions, either before, during or after the meal.

Conclusions

Oxytocin prolongs gastric emptying in patients with diabetes mellitus and gastroparesis, but has no effect on volume of nutrient intake or satiety and other related symptoms in patients with functional dyspepsia.

Brain responses to visceral stimuli reflect visceral sensitivity thresholds in patients with irritable bowel syndrome

BACKGROUND & AIMS

Only a fraction of patients with irritable bowel syndrome (IBS) have increased perceptual sensitivity to rectal distension, indicating differences in processing and/or modulation of visceral afferent signals. We investigated the brain mechanisms of these perceptual differences.

METHODS

We analyzed data from 44 women with IBS and 20 female healthy subjects (controls). IBS symptom severity was determined by a severity scoring system. Anxiety and depression symptoms were assessed using the hospital anxiety and depression score. Blood oxygen level-dependent signals were measured by functional magnetic resonance imaging during expectation and delivery of high (45 mmHg) and low (15 mmHg) intensity rectal distensions. Perception thresholds to rectal distension were determined in the scanner. Brain imaging data were compared among 18 normosensitive and 15 hypersensitive patients with IBS and 18 controls. Results were reported significant if peak P-values were ≤.05, with family-wise error correction in regions of interest.

RESULTS

The subgroups of patients with IBS were similar in age, symptom duration, psychological symptoms, and IBS symptom severity. Although brain responses to distension were similar between normosensitive patients and controls, hypersensitive patients with IBS had greater activation of insula and reduced deactivation in pregenual anterior cingulate cortex during noxious rectal distensions, compared to controls and normosensitive patients with IBS. During expectation of rectal distension, normosensitive patients with IBS had more activation in right hippocampus than controls.

CONCLUSIONS

Despite similarities in symptoms, hyper- and normosensitive patients with IBS differ in cerebral responses to standardized rectal distensions and their expectation, consistent with differences in ascending visceral afferent input.

Carbohydrate Elimination or Adaptation Diet for Symptoms of Intestinal Discomfort in IBD: Rationales for "Gibsons' Conundrum"

Therapeutic use of carbohydrates in inflammatory bowel diseases (IBDs) is discussed from two theoretical, apparent diametrically opposite perspectives: regular ingestion of prebiotics or withdrawal of virtually all carbohydrate components. Pathogenesis of IBD is discussed connecting microbial flora, host immunity, and genetic interactions. The best studied genetic example, NOD2 in Crohn's disease, is highlighted as a model which encompasses these interactions and has been shown to depend on butyrate for normal function. The role of these opposing concepts in management of irritable bowel syndrome (IBS) is contrasted with what is known in IBD. The conclusion reached is that, while both approaches may alleviate symptoms in both IBS and IBD, there is insufficient data yet to determine whether both approaches lead to equivalent bacterial effects in mollifying the immune system. This is particularly relevant in IBD. As such, caution is urged to use long-term carbohydrate withdrawal in IBD in remission to control IBS-like symptoms.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Abdominal bloating and distension: what is the role of the microbiota

Most patients with irritable bowel syndrome complain of a sensation of an increase in pressure within their abdomen during the course of the day which is called bloating and, in approximately half of these individuals, this symptom is accompanied by an actual increase in abdominal girth, which is referred to as distension. The pathophysiology of these two phenomena is somewhat different and it is now recognised that a whole variety of overlapping mechanisms are involved. Some of these are potentially amenable to treatment by modification of the bacterial flora of the gut and this article reviews the evidence for this.

Gut memories: towards a cognitive neurobiology of irritable bowel syndrome

The brain and the gut are engaged in continual crosstalk along a number of pathways collectively termed the 'brain-gut axis'. Over recent years it has become increasingly clear that dysregulation of the axis at a number of levels can result in disorders such as irritable bowel syndrome (IBS). With recent advances in neuroimaging technologies, insights into the neurobiology of IBS are beginning to emerge. However the cognitive neurobiology of IBS has remained relatively unexplored to date. In this review we summarise the available data on cognitive function in IBS. Moreover, we specifically address three key pathophysiological factors, namely; stress, immune activation and chronic pain, together with other factors involved in the manifestation of IBS, and explore how each of these components may impact centrally, what neurobiological mechanisms might be involved, and consider the implications for cognitive functioning in IBS. We conclude that each factor addressed could significantly impinge on central nervous system function, supporting the view that future research efforts must be directed towards a detailed assessment of cognitive function in IBS.

Effects of octreotide on jejunal hypersensitivity triggered by Cryptosporidium parvum intestinal infection in an immunocompetent suckling rat model

BACKGROUND

Similar to other bacterial or protozoan infections, human cryptosporidiosis may trigger postinfectious irritable bowel syndrome (IBS)-like symptoms, a condition in which enhanced visceral perception of pain during intestinal distension plays a pivotal role. In an immunocompetent suckling rat model which mimicks features of postinfectious IBS, Cryptosporidium parvum infection induces long-lasting jejunal hypersensitivity to distension in association with intestinal activated mast cell accumulation. The aim of the present study was to explore in this model whether octreotide, a somatostatin agonist analog, could prevent the development of jejunal hypersensitivity and intestinal mast cell/nerve fiber accumulation.

METHODS

Five-day-old Sprague-Dawley rats were infected with C. parvum and treated 10 days later with octreotide (50 g kg(-1) day(-1), i.p.) for 7 days.

KEY RESULTS

Compared with untreated infected rats, octreotide treatment of infected rats resulted in increased weight gain [day 23 postinfection (PI)], decreased food intake (day 16 PI), and a reduction in jejunal villus alterations (day 14 PI), CD3(+) IEL (day 37 PI) and mast cell (days 37 and 50 PI) accumulations, nerve fiber densities (day 50 PI), and hypersensitivity to distension (day 120 PI). In uninfected rats, the effects of octreotide treatment were limited to higher weight gain (days 16 and 23 PI) and decreased food intake (day 23 PI) compared with uninfected-untreated rats.

CONCLUSIONS & INFERENCES

Data confirms the relevance of the present rat model to postinfectious IBS studies and prompt further investigation of somatostatin-dependent regulatory interactions in cryptosporidiosis.

Molecular analysis of the luminal- and mucosal-associated intestinal microbiota in diarrhea-predominant irritable bowel syndrome

Alterations in the intestinal microbiota have been suggested as an etiological factor in the pathogenesis of irritable bowel syndrome (IBS). This study used a molecular fingerprinting technique to compare the composition and biodiversity of the microbiota within fecal and mucosal niches between patients with diarrhea-predominant IBS (D-IBS) and healthy controls. Terminal-restriction fragment (T-RF) length polymorphism (T-RFLP) fingerprinting of the bacterial 16S rRNA gene was used to perform microbial community composition analyses on fecal and mucosal samples from patients with D-IBS (n = 16) and healthy controls (n = 21). Molecular fingerprinting of the microbiota from fecal and colonic mucosal samples revealed differences in the contribution of T-RFs to the microbiota between D-IBS patients and healthy controls. Further analysis revealed a significantly lower (1.2-fold) biodiversity of microbes within fecal samples from D-IBS patients than healthy controls (P = 0.008). No difference in biodiversity in mucosal samples was detected between D-IBS patients and healthy controls. Multivariate analysis of T-RFLP profiles demonstrated distinct microbial communities between luminal and mucosal niches in all samples. Our findings of compositional differences in the luminal- and mucosal-associated microbiota between D-IBS patients and healthy controls and diminished microbial biodiversity in D-IBS fecal samples further support the hypothesis that alterations in the intestinal microbiota may have an etiological role in the pathogenesis of D-IBS and suggest that luminal and mucosal niches need to be investigated.

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.

Alternative targets within the endocannabinoid system for future treatment of gastrointestinal diseases

Many beneficial effects of herbal and synthetic cannabinoids on gut motility and inflammation have been demonstrated, suggesting a vast potential for these compounds in the treatment of gastrointestinal disorders. These effects are based on the so-called 'endocannabinoid system' (ECS), a cooperating network of molecules that regulate the metabolism of the body's own and of exogenously administered cannabinoids. The ECS in the gastrointestinal tract quickly responds to homeostatic disturbances by de novo synthesis of its components to maintain homeostasis, thereby offering many potential targets for pharmacological intervention. Of major therapeutic interest are nonpsychoactive cannabinoids or compounds that do not directly target cannabinoid receptors but still possess cannabinoid-like properties. Drugs that inhibit endocannabinoid degradation and raise the level of endocannabinoids are becoming increasingly promising alternative therapeutic tools to manipulate the ECS.

Decreased pain inhibition in irritable bowel syndrome depends on altered descending modulation and higher-order brain processes

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder involving abdominal pain and bowel dysfunction. IBS pain symptoms have been hypothesized to depend on peripheral and central mechanisms, but the pathophysiology is still unclear. The aim of the present study was to assess the contribution of cerebral and cerebrospinal processes to pain inhibition deficits in IBS. Fourteen female patients with diarrhea-predominant IBS (IBS-D) and 14 healthy female volunteers were recruited. Acute pain and the nociceptive withdrawal reflex (RIII reflex) were evoked by transcutaneous electrical stimulation of the right sural nerve with modulation by hetero-segmental counter-irritation produced by sustained cold pain applied on the left forearm. Psychological symptoms were assessed by questionnaires. Shock pain decreased significantly during counter-irritation in the controls (P<0.001) but not in IBS patients (P=0.52). Similarly, RIII-reflex amplitude declined during counter-irritation in the controls (P=0.009) but not in IBS patients (P=0.11). Furthermore, pain-related anxiety increased during counter-irritation in IBS patients (P=0.003) but not in the controls (P=0.74). Interestingly, across all subjects, counter-irritation analgesia was positively correlated with RIII-reflex inhibition (r=0.39, P=0.04) and negatively with pain-related anxiety (r=-0.61, P<0.001). In addition, individual differences in counter-irritation analgesia were predicted independently by the modulation of RIII responses (P=0.03) and by pain catastrophizing (P=0.01), with the latter mediating the effect of pain-related anxiety. In conclusion, these results demonstrate that pain inhibition deficits in female IBS-D patients depend on two potentially separable mechanisms reflecting: (1) altered descending modulation and (2) higher-order brain processes underlying regulation of pain and affect.

Outcome of biofeedback therapy in dyssynergic defecation patients with and without irritable bowel syndrome

AIM

The Rome II and III diagnostic criteria for dyssynergic defecation require the exclusion of irritable bowel syndrome (IBS). To prospectively study whether the presence of IBS affects the outcome of biofeedback therapy in dyssynergic defecation patients.

METHODS

Consecutive patients with dyssynergic defecation underwent biofeedback therapy. Dyssynergic defecation was diagnosed based on symptoms, anorectal manometries, balloon expulsion tests, and colonic transit studies. The defecation dynamics and balloon expulsion time were evaluated at the end of the biofeedback therapy in all patients. IBS symptoms were graded before and 4 weeks after the biofeedback therapy using a 4-point Likert scale. Failure of the biofeedback therapy was defined as <50% improvement of constipation symptoms, which were evaluated using a 10 cm long visual analog scale before and 4 weeks after biofeedback therapy.

RESULTS

Fifty patients completed the study. The biofeedback therapy was successful in 30 patients. Twenty-nine patients fulfilled the Rome II criteria for IBS. Patients with or without IBS demonstrated similar responses to the biofeedback therapy (16 of 29 vs. 14 of 21, P>0.05). The disappearance of IBS symptoms was observed more frequently in patients with an improved defecation index compared with those with no improvement (8 of 12 vs 4 of 17, P<0.05). A high pretreatment constipation symptom score, a high rectal sensory threshold, and a delayed colonic transit time were associated with a poor treatment outcome.

CONCLUSIONS

The presence of IBS in dyssynergic defecation did not affect the outcome of biofeedback therapy. In addition, treating dyssynergic defecation patients with IBS by biofeedback therapy improved both constipation and IBS symptoms.

Spinal cord plasticity and acid-sensing ion channels involvement in a rodent model of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastro-intestinal disorder characterized by intractable chronic abdominal pain. In this study, we examined the possible spinal mechanisms underlying colonic hypersensitivity (CHS) using a non-inflammatory rat model of IBS induced by rectal enemas of butyrate, a short-chain fatty acid. We hypothesized that spinal plasticity could be responsible for CHS and that ASIC channels, which are known to support pain-elicited currents in the spinal cord, could contribute to central sensitization in our model of IBS. First, in order to determine if visceral pain relies on changes in spinal activity, we analyzed Fos expression in the spinal cord of rats treated with butyrate following a challenge with repetitive noxious colorectal distension. We found that Fos immunoreactivity was increased in thoracic T10-11-12, lumbar L1-2-6 and sacral S1 spinal segments. In control rats treated with saline, noxious repetitive colorectal distensions evoked Fos expression only in L1-2-6 and S1 spinal segments. Secondly, intrathecal injection of PcTx1, a specific ASIC1A antagonist, in the lumbar spinal cord completely prevented the development of CHS induced by butyrate. ASIC1 and 2 mRNAs, especially ASIC1A, were upregulated in the lumbar spinal cord. ASIC1A could thus contribute to spinal sensitization in our model of IBS, as it is supported by spinal colocalization of ASIC1A and Fos proteins. The whole data pinpoint a potential critical role of thoracic spinal cord in non-inflammatory pain states such as IBS and suggest that ASIC channels are part of the molecular effectors of central sensitization leading to visceral pain.

Biologic properties and clinical uses of rifaximin

INTRODUCTION

Rifaximin is increasingly being used to treat acute and chronic gastrointestinal infections and disorders. The drug exerts its beneficial effect through a variety of gut-selective mechanisms involving the host intestinal microbiota.

AREAS COVERED

Abstracts of all publications listed in PubMed on the topic of rifaximin are reviewed to determine their potential value in the understanding of mechanisms of rifaximin activity. The author's extensive file on the drug is also used in the review.

EXPERT OPINION

Rifaximin inhibits a broad spectrum of bacteria in the bile-rich small bowel and susceptible bacteria in the aqueous colon, and alters microbial virulence and epithelial cell function. The different mechanisms of action of rifaximin potentially explain the use of the drug in widely varied diseases and syndromes.

Relationships among the lactulose breath test, intestinal gas volume, and gastrointestinal symptoms in patients with irritable bowel syndrome

BACKGROUND AND AIMS

Irritable bowel syndrome (IBS) patients frequently complain of gas-related symptoms, and the lactulose breath test (LBT) is a test that assesses the amount of fermented gas generated by bacteria in the bowel. We aimed to assess the relationship among intestinal gas volume, LBT result, and gastrointestinal symptom score in healthy control and functional bowel disorder (FBD) subjects.

METHOD

In 84 IBS subjects, 24 FBD subjects other than IBS, and 25 healthy controls, a symptom questionnaire that enquired about seven main symptoms, plain abdominal radiography and a LBT were checked on the same day. The intestinal gas volume was calculated as the gas volume score (GVS) with a digitalized image of plain supine abdominal radiographs.

RESULTS

The GVS was greater in the LBT (+) group compared to the LBT (-) group (P = 0.02). The GVS was greater in the FBD and IBS groups than in the control group (P < 0.01). The GVS showed low but positive correlations with the severity and frequency of bloating, flatulence, abdominal pain, constipation, and tenesmus (P < 0.05). The severity of flatulence (P = 0.02) and the frequency of bloating (P = 0.02) in the LBT (+) group were significantly higher than those in the LBT (-) group.

CONCLUSIONS

Subjects with positive LBT had more gas-related symptoms and greater gas volume scores. Gas-related symptoms, positive LBT and increased GVS were significantly associated to each other. These findings can broaden the understanding of the pathophysiologic mechanisms of gas-related symptoms in IBS.

Stress-related alterations of visceral sensation: animal models for irritable bowel syndrome study

Stressors of different psychological, physical or immune origin play a critical role in the pathophysiology of irritable bowel syndrome participating in symptoms onset, clinical presentation as well as treatment outcome. Experimental stress models applying a variety of acute and chronic exteroceptive or interoceptive stressors have been developed to target different periods throughout the lifespan of animals to assess the vulnerability, the trigger and perpetuating factors determining stress influence on visceral sensitivity and interactions within the brain-gut axis. Recent evidence points towards adequate construct and face validity of experimental models developed with respect to animals' age, sex, strain differences and specific methodological aspects such as non-invasive monitoring of visceromotor response to colorectal distension as being essential in successful identification and evaluation of novel therapeutic targets aimed at reducing stress-related alterations in visceral sensitivity. Underlying mechanisms of stress-induced modulation of visceral pain involve a combination of peripheral, spinal and supraspinal sensitization based on the nature of the stressors and dysregulation of descending pathways that modulate nociceptive transmission or stress-related analgesic response.

Symptoms in patients with ulcerative colitis in remission are associated with visceral hypersensitivity and mast cell activity

OBJECTIVE

Patients with ulcerative colitis in remission (UCR) frequently report irritable bowel syndrome (IBS)-like symptoms. Recent studies have pointed to the role of mast cells in mediating visceral hypersensitivity in IBS. We hypothesized that visceral hypersensitivity is frequently present in patients with UCR and is related to the quantity and activity of mast cells in the sigmoid mucosa.

MATERIAL AND METHODS

A group of 17 controls and 19 patients with UCR were studied. Rectal compliance and perception were measured by electronic barostat. Sigmoid biopsies were taken to quantify the amount of mast cells, degranulating mast cells and mast cells in close proximity to mucosal nerve endings.

RESULTS

Visceroperception significantly increased in UCR (p < 0.05) versus controls. Rectal perception correlated positively with IBS-like symptoms in UCR (r = 0.969; p < 0.05). The amount of mucosal mast cells (per 100 crypts) was significantly increased in UCR versus controls: 228 ± 20 versus 163 ± 18 (p < 0.05). In the UCR patients a higher percentage of mucosal mast cells was in close proximity to nerve endings (58 ± 4 vs. 38 ± 3% in controls; p < 0.05) or was degranulating (40 ± 7 vs. 16 ± 4% in controls; p < 0.05). There was a significant but weak correlation between quantity of mucosal mast cells and pain perception (r = 0.32; p < 0.05).

CONCLUSION

Rectal hypersensitivity is associated with mucosal presence and activation of mast cells and with IBS-like symptoms in patients with UCR.

Interstitial cells of Cajal: a novel hypothesis for the pathophysiology of irritable bowel syndrome

Irritable bowl syndrome (IBS) affects a large proportion of the world's population, and accounts for a considerable number of visits to gastroenterologists and general practitioners. Despite its high prevalence, the precise mechanism of IBS has not been identified to date. The interstitial cells of Cajal (ICC) participate in the production of slow waves and the regulation of their propagation through the gastrointestinal system; thus, they are important components of gastrointestinal motility. The present review proposes that ICC play a central role in the pathophysiology of IBS. This hypothesis is based on many links between ICC and currently proposed mechanisms of IBS pathophysiology. It appears that ICC may be involved in almost all of the previously explained pathogenic mechanisms of IBS. If proven, this hypothesis may provide a key to solving the IBS mystery.

T-type calcium channels contribute to colonic hypersensitivity in a rat model of irritable bowel syndrome

The symptoms of irritable bowel syndrome (IBS) include significant abdominal pain and bloating. Current treatments are empirical and often poorly efficacious, and there is a need for the development of new and efficient analgesics aimed at IBS patients. T-type calcium channels have previously been validated as a potential target to treat certain neuropathic pain pathologies. Here we report that T-type calcium channels encoded by the Ca(V)3.2 isoform are expressed in colonic nociceptive primary afferent neurons and that they contribute to the exaggerated pain perception in a butyrate-mediated rodent model of IBS. Both the selective genetic inhibition of Ca(V)3.2 channels and pharmacological blockade with calcium channel antagonists attenuates IBS-like painful symptoms. Mechanistically, butyrate acts to promote the increased insertion of Ca(V)3.2 channels into primary sensory neuron membranes, likely via a posttranslational effect. The butyrate-mediated regulation can be recapitulated with recombinant Ca(V)3.2 channels expressed in HEK cells and may provide a convenient in vitro screening system for the identification of T-type channel blockers relevant to visceral pain. These results implicate T-type calcium channels in the pathophysiology of chronic visceral pain and suggest Ca(V)3.2 as a promising target for the development of efficient analgesics for the visceral discomfort and pain associated with IBS.

The effects of gabapentin in two animal models of co-morbid anxiety and visceral hypersensitivity

Visceral hypersensitivity and an increased response to stress are two of the main symptoms of irritable bowel syndrome. Thus efforts to develop animal models of irritable bowel syndrome have centred on both of these parameters. The anticonvulsant gabapentin, which is widely used as an analgesic agent, also reduces anxiety. No data exists to our knowledge of the effects of gabapentin in animal models of co-morbid exaggerated stress response and visceral pain. Our aim was to assess the effect of gabapentin on stress and visceral hypersensitivity in two different animal models of irritable bowel syndrome. The animal models employed were the genetically susceptible Wistar Kyoto rat and the neonatally stressed maternal separation model. These animals were subjected to the open field paradigm to assess stress-induced defecation rates and colorectal distension to assess the level of visceral sensitivity. Gabapentin (30 mg/kg) prevented the stress-induced increase in faecal pellet output in the maternally separated rat, but not the Wistar Kyoto animals. On the other hand gabapentin (30 mg/kg) reduced the number of pain behaviours in response to colorectal distension in both models. These results show that whilst both models have similar responses to gabapentin in terms of visceral pain they differ in terms of their physiological response to stress. This indicates that the origin of anxiety and perhaps then visceral hypersensitivity differs in these models. Overall, these data suggest that gabapentin may be a useful treatment in disorders of co-morbid pain and an overactive stress system such as irritable bowel syndrome.

Oral baclofen reduces visceral pain-related pseudo-affective responses to colorectal distension in rats: relation between plasma exposure and efficacy

OBJECTIVE

We previously showed that activation of GABA(B) receptors by intravenous baclofen reduces pseudo-affective responses to colorectal distension in rats. Here we evaluate the potential clinical significance of these observations.

MATERIAL AND METHODS

Clinically relevant colorectal distension protocols were used to assess the effects of oral baclofen on visceromotor and autonomic cardiovascular responses in conscious rats. Plasma levels of baclofen were monitored to provide clinical relevance to the doses used. Conscious female Sprague-Dawley rats were subjected to repeated noxious colorectal distension (12 × 80 mmHg), ascending-phasic colorectal distension (10-80 mmHg, 10 mmHg increments) or ramp colorectal distension (10 min ramp at 8 mmHg/min). Visceromotor and cardiovascular responses (mean arterial blood pressure and heart rate) were monitored. Pain-related response thresholds were assessed using ascending-phasic and ramp colorectal distension.

RESULTS

Baclofen (1-10 μmol/kg, p.o.) reduced the visceromotor response to colorectal distension, reaching a 40% maximal inhibition (p < 0.05). The highest dose (10 μmol/kg, p.o.) also inhibited pain-related cardiovascular responses in telemetrized rats (50-55% reduction in colorectal distension-evoked hypertensive and tachycardic responses; p < 0.05). Similar thresholds for pain-related visceromotor responses were determined during ramp or ascending-phasic colorectal distension (34.1 ± 1.9 and 31.7 ± 3.2 mmHg, respectively). Baclofen (10 μmol/kg, p.o.) increased thresholds to 71.1 ± 3.7 and 77.5 ± 1.8 mmHg during ramp and ascending-phasic colorectal distension, respectively (p < 0.001). Plasma levels of baclofen were 3.3 ± 0.2 μmol/l at 90 min post-dosing, corresponding to the end of the colorectal distension procedure.

CONCLUSIONS

Oral baclofen, at plasma levels similar to those reported safe and within a therapeutic range in humans, produced significant visceral anti-nociceptive effects in rats.

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Abdomino-phrenic dyssynergia in patients with abdominal bloating and distension

OBJECTIVES

The abdomen normally accommodates intra-abdominal volume increments. Patients complaining of abdominal distension exhibit abnormal accommodation of colonic gas loads (defective contraction and excessive protrusion of the anterior wall). However, abdominal imaging demonstrated diaphragmatic descent during spontaneous episodes of bloating in patients with functional gut disorders. We aimed to establish the role of the diaphragm in abdominal distension.

METHODS

In 20 patients complaining of abdominal bloating and 15 healthy subjects, we increased the volume of the abdominal cavity with a colonic gas load, while measuring abdominal girth and electromyographic activity of the anterior abdominal muscles and of the diaphragm.

RESULTS

In healthy subjects, the colonic gas load increased girth, relaxed the diaphragm, and increased anterior wall tone. With the same gas load, patients developed significantly more abdominal distension; this was associated with paradoxical contraction of the diaphragm and relaxation of the internal oblique muscle.

CONCLUSIONS

In this experimental provocation model, abnormal accommodation of the diaphragm is involved in abdominal distension.

Visceral hypersensitivity in irritable bowel syndrome

Altered central processing, abnormal gastrointestinal motility and visceral hypersensitivity may be possible major pathophysiology of irritable bowel syndrome (IBS). These factors affect each other and are probably associated with development of IBS symptoms. It has been confirmed that lower pain threshold to colonic distention was observed in most of patients with IBS than healthy subjects. We have investigated pain perception of the descending colon among different subtypes of IBS. There was no difference in pain threshold to colonic distention between IBS with diarrhea and constipation. Some brain regions such as the anterior cingulate cortex (ACC) may play a major role for generating pain and/or pain-related emotion in humans. IBS patients showed greater activation in the perigenual ACC during painful rectal distention compared with healthy subjects. Inflammation, stress and the combination of both stimuli can induce significant increase in visceral sensitivity in animal models. Serotonin (5-HT) can modulate visceral perception. It has been thought that 5-HT(3) receptors may play an important role for conveying visceral sensation from the gut. Corticotropin-releasing hormone (CRH) may also modulate visceral pain hypersensitivity in IBS. CRH receptor-1 antagonist significantly prevented an increase in gut sensitivity in rats. It has been demonstrated that non-specific CRH receptor antagonist α-helical CRH significantly reduced abdominal pain score during gut stimulus in patients with IBS. In conclusion, visceral hypersensitivity is common in IBS patients and probably plays a major role in development of the symptoms and both central and peripheral factors may enhance the pain sensitivity.

'Gut health': a new objective in medicine?

'Gut health' is a term increasingly used in the medical literature and by the food industry. It covers multiple positive aspects of the gastrointestinal (GI) tract, such as the effective digestion and absorption of food, the absence of GI illness, normal and stable intestinal microbiota, effective immune status and a state of well-being. From a scientific point of view, however, it is still extremely unclear exactly what gut health is, how it can be defined and how it can be measured. The GI barrier adjacent to the GI microbiota appears to be the key to understanding the complex mechanisms that maintain gut health. Any impairment of the GI barrier can increase the risk of developing infectious, inflammatory and functional GI diseases, as well as extraintestinal diseases such as immune-mediated and metabolic disorders. Less clear, however, is whether GI discomfort in general can also be related to GI barrier functions. In any case, methods of assessing, improving and maintaining gut health-related GI functions are of major interest in preventive medicine.

Modulation of visceral hypersensitivity by glial cell line-derived neurotrophic factor family receptor &alpha;-3 in colorectal afferents

Irritable bowel syndrome is characterized by colorectal hypersensitivity and contributed to by sensitized mechanosensitive primary afferents and recruitment of mechanoinsensitive (silent) afferents. Neurotrophic factors are well known to orchestrate dynamic changes in the properties of sensory neurons. Although pain modulation by proteins in the glial cell line-derived neurotrophic factor (GDNF) family has been documented in various pathophysiological states, their role in colorectal hypersensitivity remains unexplored. Therefore, we investigated the involvement of the GDNF family receptor α-3 (GFRα3) signaling in visceral hypersensitivity by quantifying visceromotor responses (VMR) to colorectal distension before and after intracolonic treatment with 2,4,6-trinitrobenzene sulfonic acid (TNBS). Baseline responses to colorectal distension did not differ between C57BL/6 and GFRα3 knockout (KO) mice. Relative to intracolonic saline treatment, TNBS significantly enhanced the VMR to colorectal distension in C57BL/6 mice 2, 7, 10, and 14 days posttreatment, whereas TNBS-induced visceral hypersensitivity was significantly suppressed in GFRα3 KO mice. The proportion of GFRα3 immunopositive thoracolumbar and lumbosacral colorectal dorsal root ganglion neurons was significantly elevated 2 days after TNBS treatment. In single fiber recordings, responses to circumferential stretch of colorectal afferent endings in C57BL/6 mice were significantly increased (sensitized) after exposure to an inflammatory soup, whereas responses to stretch did not sensitize in GFRα3 KO mice. These findings suggest that enhanced GFRα3 signaling in visceral afferents may contribute to development of colorectal hypersensitivity.

Traditional thoughts on the pathophysiology of irritable bowel syndrome

The pathogenesis of symptoms in irritable bowel syndrome (IBS) is multifactorial and varies from patient to patient. Disturbances of motor function in the small intestine and colon and smooth-muscle dysfunction in other gut and extraintestinal regions are prominent. Abnormalities of sensory function in visceral and somatic structures are detected in most patients with IBS, which may relate to peripheral sensitization or altered central nervous system processing of afferent information. Contributions from psychosocial disturbances are observed in patients from tertiary centers and primary practice. Proof of causation of symptom genesis for most of these factors is limited.

Different effects of morphine and oxycodone in experimentally evoked hyperalgesia: a human translational study

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * Previous studies using short-lasting experimental pain stimulations in healthy volunteers have shown differences in opioid effects regarding visceral pain stimulations. However, these differences can be more pronounced in patients due to a sensitized pain system. Therefore, the aim of the present study was to mimic the clinical situation by investigating opioid effects on experimental pain in healthy volunteers after experimentally evoked hyperalgesia. WHAT THIS STUDY ADDS? * We now know that morphine and oxycodone exerts different effects in the sensitized pain system as we found a greater analgesic effect of oxycodone in response to skin, muscle and oesophageal pain stimulation. This supports clinicians' experiences that oxycodone can be superior to morphine in the treatment of some pain conditions. The evoked hyperalgesia bridged findings from studies in healthy volunteers to patients, and new fundamental knowledge on different analgesic effects in hyperalgesia was found. AIM Similar analgesics may have different analgesic potencies especially in patients in whom the pain system is sensitized. The aim was to investigate different opioid effects on experimental pain after the sensitized pain system was mimicked evoking hyperalgesia in healthy volunteers. METHODS Twenty-four healthy volunteers were randomized to treatment with morphine (30 mg orally) and oxycodone (15 mg orally) or placebo in a double-blind crossover study. Hyperalgesia was induced by oesophageal perfusion with acid and capsaicin. Several exploratory endpoints were studied using skin heat, muscle pressure and oesophageal mechanical, heat and electrical stimulation. Effects on pain from deeper structures were considered most important. RESULTS Different analgesic potencies were found. Oxycodone had a greater analgesic effect than morphine attenuating pain from: (i) heat stimulation of skin (P= 0.016); difference between the means of 0.39 degrees C, 95% CI 0.22, 2.09. (ii) muscle pressure (P < 0.001); difference between the means of 11.93kPa, 95% CI 5.4, 18.5. (iii) oesophageal heat stimulation (P < 0.001); difference between the means of 38.54 cm(2), 95% CI 15.37, 61.71 and (iv) oesophageal electrical stimulation (P= 0.016); difference between the means of 6.69mA, 95% CI 1.23, 12.13. CONCLUSION After sensitization of the pain system different analgesic potencies of morphine and oxycodone were found in response to skin, muscle and oesophageal pain stimulation, in which oxycodone had a greater effect. As similar differential analgesic potencies of the two opioids have been found in patients with chronic pain, the experimental hyperalgesia model bridged findings from studies in healthy volunteers to patients.

Elevated expression of c-fos in central nervous system correlates with visceral hypersensitivity in irritable bowel syndrome (IBS): a new target for IBS treatment

BACKGROUND AND AIMS

Although visceral hypersensitivity is a major pathophysiological feature of irritable bowel syndrome (IBS), its molecular mechanisms are still poorly understood. c-fos is a well-established marker of cell activation. Accumulating evidence demonstrates that norepinephrine (NE) system is dysregulated in IBS; however, very little is known on its mechanism. It is our hypothesis that elevated expression of c-fos in central nervous system (CNS) correlates with visceral hypersensitivity in rat model of IBS. Furthermore, we explored the changes of NE system in IBS patients.

METHODS

The rat model of IBS was induced by heterotypic chronic and acute stress. Tissues obtained from rat model were analyzed for c-fos levels in CNS (frontal lobe, hippocampus, cornu dorsale) and colon by immunohistochemistry. Real-time reverse transcription polymerase chain reaction was used to detect tyrosine hydroxylase (TH) in the colonic tissues obtained from IBS patients.

RESULTS

The rat model of IBS was associated with increased expression of c-fos in different parts of CNS (P = 0.001, P = 0.002, and P = 0.002, respectively), but normal in colon (P = 0.207). The clinical parameters (colonic motility and sensation) of rat model were significantly correlated with elevated c-fos in CNS (P < 0.05). Enterochromaffin cells and serotonin in colon were related to the elevated c-fos in CNS (P < 0.05). The TH messenger ribonucleic acid (mRNA level of IBS-D patients was almost four times as much as that of controls.

CONCLUSIONS

Elevated expression of c-fos in CNS might be one of key mechanisms in etiology of IBS. Therefore, regulation of CNS activation could be a major targeting effect when treating IBS patients.

Biopsychosocial assessment criteria for functional chronic visceral pain: a pilot review of concept and practice

Functional chronic visceral pain (FCVP) is one of the most common causes of morbidity in the general population. Pain perceived within the abdomen may occur due to a range of different mechanisms according to the organ and their afferent pathways. Advances in our understanding of the complexities of FCVP could lead to the exploitation of contemporary research in order to develop and utilize our understanding of neurobiological and psychobiological visceral mechanisms in a clinical setting. This progression, together with increasing amounts of epidemiological and gender based information concerning specific abdominal pain syndromes can allow us to develop assessment tools that go beyond disease only analysis and move toward a more comprehensive assessment model so that patients may have access to expert or multidisciplinary management sooner, rather than later. Based on current evidence, one must consider the main contributors to pain, whether it is nociceptive, neuropathic or psychosocial or as is common with FCVP, a combination of all three.

AIM

This comprehensive assessment model should encompass not only systematic evaluation for reliable communication, but should also progress toward idiographic diagnosis relating to the uniqueness of the patient. This model should be practical in a multidisciplinary setting, taking into account the multi-faceted nature of this presentation.

Luminal and mucosal-associated intestinal microbiota in patients with diarrhea-predominant irritable bowel syndrome

Background

Recent studies have suggested a role for an altered intestinal microbiota in the pathophysiology of irritable bowel syndrome (IBS). However, no consensus has been reached regarding the association between specific enteric bacterial groups and IBS. The aim of this study was to investigate the fecal and mucosal-associated microbiota using two independent techniques in intestinal samples from diarrhea-predominant IBS (D-IBS) and healthy controls.

Methods

Fecal and colonic mucosal biopsy samples were obtained from 10 D-IBS patients and 10 healthy controls. Colonic tissue was collected during a un-sedated un-prepped flexible sigmoidoscopy. Fecal and tissue samples were processed immediately upon collection for culture under aerobic and anaerobic conditions or frozen for further molecular analysis. DNA was extracted from all frozen samples and used to enumerate specific bacterial groups using quantitative real-time PCR (qPCR).

Results

Culture analysis of intestinal samples demonstrated a significant reduction in the concentration of aerobic bacteria in fecal samples from D-IBS patients when compared to healthy controls (1.4 × 10⁷ vs. 8.4 × 10⁸ CFUs/g feces, P = 0.002). qPCR analysis demonstrated a significant 3.6 fold increase (P = 0.02) in concentrations of fecal Lactobacillus species between D-IBS patients and healthy controls.

Conclusions

Our culture and molecular data indicate that quantitative differences exist in specific bacterial groups in the microbiota between D-IBS and healthy subjects.

Anorectal function and visceral hypersensitivity in celiac disease

OBJECTIVE

To evaluate anorectal function and rectal sensitivity thresholds in patients with celiac disease (CD).

METHODS

In 25 unselected patients with CD (16 female, 9 male; mean age 45, range 24 to 75 y) and 20 controls (12 female, 8 male; mean age 41, range 20 to 65 y) anorectal manometry and rectal balloon distension test were conducted using a 4 lumen water perfused catheter with a polyethylene balloon (Zinectics Manometric Catheter, Medtronic).

RESULTS

In celiac patients the maximal anal resting pressure, reflecting the internal anal sphincter function, was significantly higher than that in the controls: 87.8±21.7 mm Hg versus 66.7±15.2 mm Hg (P<0.001). There were no considerable differences between both the groups neither in the maximal anal squeeze nor in the cough pressures. Celiac patients had significantly lower first sensation threshold: 25.6±10.8 mL versus 37.5±12.5 mL (P<0.05). Visceral hypersensitivity (rectal pain/discomfort threshold ≤100 mL) was observed in 36% of celiac patients and in none of the controls (P<0.01).

CONCLUSIONS

The increased anal resting pressure and rectal hypersensitivity are observed in CD. Disturbances in gastrointestinal motility and visceral perception in the course of CD may occur at different levels of the brain-gut axis including direct changes in the enteric nervous system.