Rectal hypersensitivity as hallmark for irritable bowel syndrome: defining the optimal cutoff

Overactive bladder syndrome symptoms in youth with abdominal pain-associated disorders of gut-brain interaction

The purpose of the current study was to assess the frequency of overactive bladder syndrome (OBS) symptoms and their relationship to gastrointestinal symptoms in youth with abdominal pain-associated disorders of gut-brain interaction (AP-DGBI). This is a retrospective study of 226 youth diagnosed with an AP-DGBI. As part of standard care, all patients completed a symptom questionnaire regarding gastrointestinal and non-gastrointestinal symptoms including increased urinary frequency, nighttime urination, and urinary urgency. Overall, 54% of patients reported at least one OBS symptom. Increased frequency of urination was reported by 19%, urinary urgency by 34%, and nighttime urination by 36%. Increased frequency of urination and urinary urgency were associated with a change in stool form, a change in stool frequency, and in those fulfilling criteria for IBS. Increased frequency of urination was reported more frequently in those reporting predominantly loose stools (33% vs. 12%). Urinary symptoms are common in youth with AP-DGBI. Increased urinary frequency and urinary urgency are specifically associated with IBS, with increased urinary frequency being primarily associated with diarrhea predominant IBS. Further studies are needed to determine the impact of OBS on AP-DGBI severity and quality of life, and whether they impact DGBI treatment.

Piezo2 regulates colonic mechanical sensitivity in a sex specific manner in mice

The mechanosensitive ion channel Piezo2 in mucosa and primary afferents transduces colonic mechanical sensation. Here we show that chemogenetic activation or nociceptor-targeted deletion of Piezo2 is sufficient to regulate colonic mechanical sensitivity in a sex dependent manner. Clozapine N-oxide-induced activation of Piezo2;hM3Dq-expressing sensory neurons evokes colonic hypersensitivity in male mice, and causes dyspnea in female mice likely due to effects on lung sensory neurons. Activation of Piezo2-expressing colonic afferent neurons also induces colonic hypersensitivity in male but not female mice. Piezo2 levels in nociceptive neurons are higher in female than in male mice. We also show that Piezo2 conditional deletion from nociceptive neurons increases body weight growth, slows colonic transits, and reduces colonic mechanosensing in female but not male mice. Piezo2 deletion blocks colonic hypersensitivity in male but not female mice. These results suggest that Piezo2 in nociceptive neurons mediates innocuous colonic mechanosensing in female mice and painful sensation in male mice, suggesting a sexual dimorphism of Piezo2 function in the colonic sensory system.

Impact of Saccharomyces boulardii CNCM I-745 on Bacterial Overgrowth and Composition of Intestinal Microbiota in Diarrhea-Predominant Irritable Bowel Syndrome Patients: Results of a Randomized Pilot Study

BACKGROUND

Small intestinal bacterial overgrowth (SIBO) is associated with diarrhea-predominant irritable bowel syndrome (IBS-D). Probiotics like Saccharomyces boulardii CNCM I-745 (Sb) may be efficacious in balancing the microbiota. This randomized open label study assessed the effect of Sb in patients with bacterial overgrowth associated with IBS-D and its impact on the intestinal microbiota.

METHODS

Patients were randomized to receive Sb + dietary advice (Sb + DA) or dietary advice (DA) only for 15 days. SIBO was assessed by the lactulose hydrogen breath test (LHBT). Symptoms were assessed with the IBS Symptom Severity Scale (IBS-SSS) and stool consistency with the Bristol Stool Form Scale. Microbiota and mycobiota were analyzed by 16S rDNA and ITS2.

RESULTS

54 patients were included, among whom 48 (27 Sb + DA, 21 DA) were evaluated. Decrease of hydrogen excretion was slightly higher in Sb + DA group, 41% versus 29% in DA group, and IBS-SSS total score were reduced by -134 and -93, respectively. The proportion of patients with diarrhea was lower in the Sb + DA group than in the DA group (25.9% compared to 47.6%). Bacterial and fungal microbiota showed that Sb treatment was associated with several modifications. Interestingly, F. prausnitzii was more abundant in Sb-treated patients with marked clinical improvement. The safety of S. boulardii CNCM I-745 was excellent.

CONCLUSIONS

In patients with SIBO, S. boulardii CNCM I-745 associated with dietary advice reduced bacterial overgrowth and improved digestive symptoms while restoring the intestinal microbiota. The increased abundance of F. prausnitzii coupled with symptom improvement merits further research.

Type of Rectal Barostat Protocol Affects Classification of Hypersensitivity and Prediction of Symptom Severity in Irritable Bowel Syndrome

Background/Aims

Visceral hypersensitivity is an important pathophysiologic mechanism in irritable bowel syndrome (IBS). We compared 2 barostat distension protocols and their ability to distinguish between IBS patients and healthy controls, identify subjects with rectal hypersensitivity, and their associations with gastrointestinal symptom severity.

Methods

We retrospectively reviewed all patients at our unit that had undergone barostat investigations 2002-2014. Protocol 1 (n = 369) used phasic isobaric distensions with stepwise increments in pressure and protocol 2 (n = 153) used pressure controlled ramp inflations. Both protocols terminated when subjects reported pain or maximum pressure was reached. Thresholds for first sensation, urgency, discomfort and pain were established. Age- and gender-matched controls were used for comparison. The gastrointestinal symptom rating scale-IBS, and the hospital anxiety and depression scale were used for symptom reports.

Results

A significantly higher proportion of patients was classified as having hypersensitivity in protocol 1 vs protocol 2 for all thresholds (P < 0.001). Patients with visceral hypersensitivity, defined based on rectal pain thresholds in protocol 1 had more severe gastrointestinal symptoms overall as well as anxiety, whereas these associations were weaker or in most cases absent when visceral hypersensitivity was defined based on rectal pain thresholds in protocol 2.

Conclusion

Our study indicates that a rectal barostat protocol using phasic isobaric distensions with stepwise pressure increments is more sensitive in IBS patients with respect to identifying subjects with rectal hypersensitivity and a link with IBS symptoms.

Unraveling the role of Epac1-SOCS3 signaling in the development of neonatal-CRD-induced visceral hypersensitivity in rats

Aims

Visceral hypersensitivity in irritable bowel syndrome (IBS) is widespread, but effective therapies for it remain elusive. As a canonical anti‐inflammatory protein, suppressor of cytokine signaling 3 (SOCS3) reportedly relays exchange protein 1 directly activated by cAMP (Epac1) signaling and inhibits the intracellular response to inflammatory cytokines. Despite the inhibitory effect of SOCS3 on the pro‐inflammatory response and neuroinflammation in PVN, the systematic investigation of Epac1‐SOCS3 signaling involved in visceral hypersensitivity remains unknown. This study aimed to explore Epac1‐SOCS3 signaling in the activity of hypothalamic paraventricular nucleus (PVN) corticotropin‐releasing factor (CRF) neurons and visceral hypersensitivity in adult rats experiencing neonatal colorectal distension (CRD).

Methods

Rats were subjected to neonatal CRD to simulate visceral hypersensitivity to investigate the effect of Epac1‐SOCS3 signaling on PVN CRF neurons. The expression and activity of Epac1 and SOCS3 in nociceptive hypersensitivity were determined by western blot, RT‐PCR, immunofluorescence, radioimmunoassay, electrophysiology, and pharmacology.

Results

In neonatal‐CRD‐induced visceral hypersensitivity model, Epac1 and SOCS3 expressions were downregulated and IL‐6 levels elevated in PVN. However, infusion of Epac agonist 8‐pCPT in PVN reduced CRF neuronal firing rates, and overexpression of SOCS3 in PVN by AAV‐SOCS3 inhibited the activation of PVN neurons, reduced visceral hypersensitivity, and precluded pain precipitation. Intervention with IL‐6 neutralizing antibody also alleviated the visceral hypersensitivity. In naïve rats, Epac antagonist ESI‐09 in PVN increased CRF neuronal firing. Consistently, genetic knockdown of Epac1 or SOCS3 in PVN potentiated the firing rate of CRF neurons, functionality of HPA axis, and sensitivity of visceral nociception. Moreover, pharmacological intervention with exogenous IL‐6 into PVN simulated the visceral hypersensitivity.

Conclusions

Inactivation of Epac1‐SOCS3 pathway contributed to the neuroinflammation accompanied by the sensitization of CRF neurons in PVN, precipitating visceral hypersensitivity and pain in rats experiencing neonatal CRD.

Genetic and phenotypic diversity of fecal Candida albicans strains in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common disorder characterized by chronic abdominal pain and changes in bowel movements. Visceral hypersensitivity is thought to be responsible for pain complaints in a subset of patients. In an IBS-like animal model, visceral hypersensitivity was triggered by intestinal fungi, and lower mycobiota α-diversity in IBS patients was accompanied by a shift toward increased presence of Candida albicans and Saccharomyces cerevisiae. Yet, this shift was observed in hypersensitive as well as normosensitive patients and diversity did not differ between IBS subgroups. The latter suggests that, when a patient changes from hyper- to normosensitivity, the relevance of intestinal fungi is not necessarily reflected in compositional mycobiota changes. We now confirmed this notion by performing ITS1 sequencing on an existing longitudinal set of fecal samples. Since ITS1 methodology does not recognize variations within species, we next focused on heterogeneity within cultured healthy volunteer and IBS-derived C. albicans strains. We observed inter- and intra-individual genomic variation and partial clustering of strains from hypersensitive patients. Phenotyping showed differences related to growth, yeast-to-hyphae morphogenesis and gene expression, specifically of the gene encoding fungal toxin candidalysin. Our investigations emphasize the need for strain-specific cause-and-effect studies within the realm of IBS research.

Latest Insights on the Pathogenesis of Irritable Bowel Syndrome

The pathogenesis of irritable bowel syndrome is multifactorial and complex. Our understanding of its pathophysiology has evolved, but remains incompletely understood. Symptoms result from a dysregulation of brain-gut interactions. Evidence has identified alterations in central and peripheral (gut) mechanisms in irritable bowel syndrome and the bidirectional communication between the brain and the gut. Pertinent mechanisms include disturbed gut motility, visceral hypersensitivity, altered mucosal and immune function, altered gut microbiota, and altered central nervous system processing. This review addresses factors that increase the risk of irritable bowel syndrome and the central and peripheral mechanisms thought to underlie its symptoms.

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.

Sensory Adaptation Training or Escitalopram for IBS With Constipation and Rectal Hypersensitivity: A Randomized Controlled Trial

INTRODUCTION

Rectal hypersensitivity is an important pathophysiological dysfunction in irritable bowel syndrome with predominant constipation (IBS-C), whose treatment remains challenging. In a randomized controlled trial, we compared the efficacy and safety of a novel sensori-behavioral treatment, sensory adaptation training (SAT) with escitalopram.

METHODS

Patients with IBS-C (Rome III) with rectal hypersensitivity received 6 biweekly sessions of SAT or escitalopram 10 mg daily for 3 months. SAT was performed by repetitive gradual distension of 10-cm long highly compliant rectal balloon above tolerability thresholds using barostat. Treatment effects on sensory thresholds and symptoms were compared. Coprimary outcome measures were those achieving improvements in rectal hypersensitivity (≥20% increase in ≥2/3 sensory thresholds) and pain (≥30% decrease).

RESULTS

We randomized 49 patients; 26 received SAT and 23 escitalopram. SAT significantly improved desire to defecate (Δ 13.5 ± 2.3 vs 2.2 ± 1.1 mm Hg, P = 0.0006) and maximum tolerability (Δ 14.8 ± 1.9 vs 1.6 ± 0.9 mm Hg, P < 0.0001) thresholds compared with escitalopram. There were significantly greater percentage of hypersensitivity responders with SAT than escitalopram (69% vs 17%, P < 0.001), but not pain responders (58% vs 44%, P = 0.4). Daily pain scores did not differ between groups (P = 0.8) or escitalopram (P = 0.06) but decreased with SAT (P = 0.0046) compared with baseline. SAT significantly increased rectal compliance (P < 0.019) and complete spontaneous bowel movements per week than escitalopram (P = 0.04). Five withdrew from adverse events with escitalopram and none with SAT.

DISCUSSION

SAT was significantly more efficacious in improving hypersensitivity and bowel symptoms in IBS-C than escitalopram. SAT is a promising novel treatment for IBS with rectal hypersensitivity.

Supraspinal Mechanisms of Intestinal Hypersensitivity

Gut inflammation or injury causes intestinal hypersensitivity (IHS) and hyperalgesia, which can persist after the initiating pathology resolves, are often referred to somatic regions and exacerbated by psychological stress, anxiety or depression, suggesting the involvement of both the spinal cord and the brain. The supraspinal mechanisms of IHS remain to be fully elucidated, however, over the last decades the series of intestinal pathology-associated neuroplastic changes in the brain has been revealed, being potentially responsible for the phenomenon. This paper reviews current clinical and experimental data, including the authors' own findings, on these functional, structural, and neurochemical/molecular changes within cortical, subcortical and brainstem regions processing and modulating sensory signals from the gut. As concluded in the review, IHS can develop and maintain due to the bowel inflammation/injury-induced persistent hyperexcitability of viscerosensory brainstem and thalamic nuclei and sensitization of hypothalamic, amygdala, hippocampal, anterior insular, and anterior cingulate cortical areas implicated in the neuroendocrine, emotional and cognitive modulation of visceral sensation and pain. An additional contribution may come from the pathology-triggered dysfunction of the brainstem structures inhibiting nociception. The mechanism underlying IHS-associated regional hyperexcitability is enhanced NMDA-, AMPA- and group I metabotropic receptor-mediated glutamatergic neurotransmission in association with altered neuropeptide Y, corticotropin-releasing factor, and cannabinoid 1 receptor signaling. These alterations are at least partially mediated by brain microglia and local production of cytokines, especially tumor necrosis factor α. Studying the IHS-related brain neuroplasticity in greater depth may enable the development of new therapeutic approaches against chronic abdominal pain in inflammatory bowel disease.

The Potential Role of Gut Mycobiome in Irritable Bowel Syndrome

The human gut is inhabited by diverse microorganisms that play crucial roles in health and disease. Gut microbiota dysbiosis is increasingly considered as a vital factor in the etiopathogenesis of irritable bowel syndrome (IBS), which is a common functional gastrointestinal disorder with a high incidence all over the world. However, investigations to date are primarily directed to the bacterial community, and the gut mycobiome, another fundamental part of gut ecosystem, has been underestimated. Intestinal fungi have important effects on maintaining gut homeostasis just as bacterial species. In the present article, we reviewed the potential roles of gut mycobiome in the pathogenesis of IBS and the connections between the fungi and existing mechanisms such as chronic low-grade inflammation, visceral hypersensitivity, and brain-gut interactions. Moreover, possible strategies targeted at the gut mycobiome for managing IBS were also described. This review provides a basis for considering the role of the mycobiome in IBS and offers novel treatment strategies for IBS patients; moreover, it adds new dimensions to researches on microorganism.

Repeated transcutaneous electrical nerve stimulation of nonspecific acupoints of the upper body attenuates stress-induced visceral hypersensitivity in rats

Irritable bowel syndrome (IBS) is a common stress-related gastrointestinal disorder and visceral hypersensitivity (VH) is characteristically found in IBS patients. Transcutaneous electrical nerve stimulation (TENS) applied to certain acupoints has been shown to benefit IBS patients. Here, we investigated whether nonspecific acupoint is involved in the efficacy of TENS treatment for IBS. Twenty-five male rats were randomly assigned to four experimental groups and one sham-control group. The four experimental groups were defined as TENS-RR, TENS-RL, TENS-LR, and TENS-LL based on the location of the two TENS patches [right (R) or left (L)]. The former and latter letter pairs indicate that the patch locations were the upper chest and upper back, respectively. The heterotypic intermittent stress (HIS) protocol was performed for 16 days. VH was assessed by electromyography to evaluate response to rectal distention (RD). Modulated medium-frequency TENS, sweep range 1-10 Hz, amplitude slightly above the supra motor threshold, was applied 30 min per day followed by RD every second day for the final 7 days of the 16-day HIS period. VH was induced after the rats had been subjected to HIS for 10 days. A significant reduction of VH was observed only in the TENS-LL group compared with that in the sham-control group. These data suggest that repeated TENS treatment can alleviate stress-induced VH in rats. Further, whether TENS patches are attached to the left or right side of the body, which are nonspecific acupoints for gastrointestinal functions, may be an important factor in the treatment of stress-associated gastrointestinal symptoms.

Visceral sensitivity remains stable over time in patients with irritable bowel syndrome, but with individual fluctuations

BACKGROUND

Visceral hypersensitivity in irritable bowel syndrome (IBS), measured with rectal balloon distensions, using a barostat, has been suggested to be a phenomenon that is reduced due to habituation at repeated investigations. We investigated the stability of rectal sensitivity in patients with IBS who had undergone a previous rectal barostat study and assessed variations in symptom pattern and severity in relation to rectal sensory function.

METHOD

Irritable bowel syndrome patients, who had previously been undergone a rectal barostat study, were included. All patients underwent a second study 8-12 years later. Symptoms were characterized by use of questionnaires.

KEY RESULTS

We included 26 subjects (17 females, median age at the index investigation 44.5 (21-61) years). Pressure and volume sensory thresholds were unchanged at the follow-up compared with the index investigation (P > 0.05 for all). At the index investigation, 8/26 patients had rectal hypersensitivity of which four were reclassified as normosensitive, and sixfrom normo- to hypersensitive, meaning that 10/26 patients were hypersensitive at the follow-up investigation. IBS-QOL had improved significantly in six of nine domains at follow-up (P < 0.05 for all). There were no differences in anxiety, depression, IBS symptom severity, or somatization (P > 0.05) at follow-up. None of these were associated with change in rectal sensitivity at follow-up.

CONCLUSIONS AND INFERENCES

Rectal hypersensitivity and IBS symptoms remained stable at the group level over 8-12 years in IBS patients, even though individual fluctuations were noted. Our findings contradict previous findings indicating that visceral hypersensitivity is an unstable trait.

Conditioned Pain Modulation (CPM) is Reduced in Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis of CPM and the Role of Psychological Factors

This systematic review summarises evidence assessing endogenous pain inhibition in people with irritable bowel syndrome (IBS) compared with healthy controls using conditioned pain modulation (CPM) and offset analgesia (OA). Evidence regarding the role of psychological variables is also examined. The review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Four electronic databases were searched to retrieve studies assessing CPM or OA in adults diagnosed with IBS according to the ROME II/III criteria. Standardized mean differences were calculated for each study and a random effects model was used for meta-analysis. Eleven studies were included, 5 of which reported results on the relationship between CPM and psychological variables. None of the studies assessed OA. The risk of bias assessment found a lack of assessor blinding in all studies. The pooled effect estimate was 0.90 (95% CI, 0.40-1.40) indicating a significantly lower CPM effect in people with IBS compared with controls. This effect was reduced to 0.51 when 1 outlier was excluded from the analysis. In addition, reduced CPM responses were significantly correlated with higher anxiety (r=0.17 to 0.64), stress (r=0.63), and pain catastrophizing (r=0.38) in people with IBS; however, the evidence available was limited and the strength of these associations variable. Depression was not found to be associated with CPM in these IBS cohorts. The results of this review suggest that people with IBS, as a group, demonstrate reduced pain inhibition measured by CPM. The preliminary evidence about the association between psychological factors and CPM warrants further investigations.

Prospective study evaluating immune-mediated mechanisms and predisposing factors underlying persistent postinfectious abdominal complaints

BACKGROUND

The role of persistent immune activation in postinfectious irritable bowel syndrome (PI-IBS) remains controversial. Here, we prospectively studied healthy subjects traveling to destinations with a high-risk to develop infectious gastroenteritis (IGE) in order to identify immune-mediated mechanisms and risk factors of PI-IBS.

METHODS

One hundred and one travelers were asked to complete questionnaires on psychological profile and gastrointestinal (GI) symptoms before travel, 2 weeks, 6 months and 1 year after travel. At each visit, blood was collected for PBMC isolation and rectal biopsies were taken. PI-IBS was diagnosed using the Rome III criteria and subjects with persistent postinfectious abdominal complaints (PI-AC) were identified using 3 GSRS symptoms (ie, loose stools, urgency and abdominal pain).

RESULTS

Forty-seven of the 101 subjects reported IGE during travel. After 1 year, two subjects were diagnosed with PI-IBS and eight subjects were presented with PI-AC versus two subjects with IBS and two with abdominal complaints in the non-infected group. PBMC analysis showed no differences in T and B cell populations in subjects with PI-AC vs healthy. Additionally, no differences in gene expression were observed in the early postinfectious phase or after 1 year. Regression analysis identified looser stools, higher anxiety and somatization before infection and several postinfectious GI symptoms as risk factors for PI-AC.

CONCLUSIONS

The incidence of PI-IBS is low following travelers' diarrhea and there is need for larger studies investigating the role of immune activation in PI-IBS. Psychological factors before infection and the severity of symptoms shortly after infection are risk factors for the persistence of PI-AC.

Effects of Vitamin D Supplementation in Patients with Irritable Bowel Syndrome: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

Objective:

There are some evidence that Vitamin D supplementation may be beneficial for patients with irritable bowel syndrome (IBS). The aim of this study was to evaluate the effects of Vitamin D supplementation on symptoms and quality of life (QOL) in patients with IBS.

Methods:

In a randomized, double-blind, placebo-controlled clinical trial, 116 patients with IBS were supplemented weekly with either a pearl of 50,000 IU Vitamin D or an identical pearl of placebo containing medium chain triglyceride for 6 weeks.

Results:

Mean age of patients was 42.24 ± 12.26, and 40.06 ± 13.37 in Vitamin D and placebo groups, respectively. Dietary intakes were similar between and within groups. Serum concentration of 25-hydroxy Vitamin D increased significantly from 21.10 ± 5.23 to 36.43 ± 12.34 in the Vitamin D group (P < 0.001), while it was not significantly different before and after the trial in placebo group. The IBS symptoms severity scores (SSSs), disease-specific QOL, and total score were evaluated at weeks 0 and 6. IBS-SSS, IBS-QOL, and the total score were improved significantly more in Vitamin D group in comparison to the placebo group (P < 0.05).

Conclusions:

This study indicates that Vitamin D therapy can improve the severity of symptoms and QOL in patients with IBS; however, the long-term effects remained to be elucidated. Trial registration at IRCT: IRCT201402234010N11 IRB Number: 116/3976

Sera with anti-enteric neuronal antibodies from patients with irritable bowel syndrome promote apoptosis in myenteric neurons of guinea pigs and human SH-Sy5Y cells

BACKGROUND

Sera anti-enteric neuronal antibodies (AENA), neuronal inflammation, and degeneration in myenteric plexus in patients with irritable bowel syndrome (IBS) were reported. Effects of sera AENA in patients with IBS are unclear.

METHODS

Patients with IBS met Rome III criteria were enrolled. Controls included healthy subjects (HS) and patients with slow transit functional constipation, inflammatory bowel disease, chronic intestinal pseudo-obstruction, and autoimmune diseases. Indirect immunofluorescence was used to detect AENA. Anti-enteric neuronal antibodies intensities were termed as "1" = weak fluorescence (mild positive); "2" = moderate fluorescence (moderate positive); "3" = very high fluorescence (intensive positive). Intensities of ≥1 were defined as positive and ≥2 were defined as obvious positive. Cultured myenteric neurons of small intestine from guinea pigs and human SH-Sy5Y cells were incubated with fetal bovine serum (FBS), HS sera, or IBS sera with or without AENA. Indirect immunofluorescence with anti-PGP9.5/DAPI/anti-active caspase-3 or TUNEL, Western blot, and flow cytometry were used to detect apoptosis.

KEY RESULTS

Overall, 293 patients with IBS were enrolled (41.7 ± 11.5 years). AENA-positive and obvious positive rates in IBS were higher than HS (76.8% vs 33%; 43.7% vs 7%; all P < 0.001). Myenteric neurons incubated with AENA moderate or intensive positive IBS sera showed higher rates of anti-active caspase-3 and TUNEL-positive cells than HS or FBS (20% ± 7.3% and 35% ± 13.3% vs 4.3% ± 1.5% and 0.9% ± 0.4%, respectively; 6.2% ± 2.0% and 10.2% ± 4.6% vs 1.3% ± 1.9% and 0.5%±0.5%, respectively; all P < 0.05). Human SH-Sy5Y cells incubated with AENA moderate or intensive positive IBS sera showed increased cleaved caspase-3 and Bax expression and decreased Bcl-2 expression. Flow cytometry showed apoptosis rates of these two groups were higher than that of AENA mild positive, negative, HS, and FBS (7.6%±0.8% and 10.7%±1.3% vs 5.0%±0.8%, 3.8%±0.3%, 3.4%±0.2% and, 2.8%±0.2%, P < 0.05).

CONCLUSIONS AND INFERENCES

The AENA obvious positive rate in patients with IBS was higher than HS, and sera with higher levels of AENA promoted neuronal apoptosis. AENA-mediated neuropathy might exist in a subset of patients with IBS.

Effect of a prebiotic galactooligosaccharide mixture (B-GOS®) on gastrointestinal symptoms in adults selected from a general population who suffer with bloating, abdominal pain, or flatulence

BACKGROUND

Prebiotics exert beneficial effects upon gastrointestinal (GI) environment, but this is not always accompanied with a positive effect on GI symptoms. B-GOS® is a prebiotic with high selectivity toward bifidobacteria and a variety of other beneficial effects in humans. Here, we investigated its effect on GI symptoms in adults who suffer with bloating, abdominal pain, and flatulence.

METHODS

In a double-blind, placebo-controlled, crossover study, 83 subjects from the general population who presented with GI symptoms during screening period and had a predicted probability of functional bowel disorder of more than 75% were randomized to receive either a placebo or the B-GOS® treatment (2.75 g/d). Subjects were screened for the presence of GI symptoms for 1 week, they consumed the treatments for 2 weeks, and then went through a 2-week washout period, before switching to the other treatment for the final 2 weeks. GI symptoms, bowel movements, and stool consistency were assessed in daily and weekly questionnaires. Quality of life was assessed weekly and depression and anxiety at the end of each treatment period.

RESULTS

B-GOS® resulted in significantly (P < 0.001) lower scores for bloating, flatulence, and abdominal pain both from baseline and placebo at the end of first week. The effect was sustained at the end of second week. It had no effect on the number of bowel movements, consistency of stools, quality of life, or mood throughout the study.

CONCLUSION

Results suggest that B-GOS® could possibly be used in the management of bloating, flatulence, or abdominal pain and warrant further investigation.

Plausibility criteria for putative pathophysiological mechanisms in functional gastrointestinal disorders: a consensus of experts

BACKGROUND AND AIMS

The functional gastrointestinal disorders (FGIDs) are extremely common conditions associated with a considerable personal, social and health economic burden. Managing FGIDs in clinical practice is challenging because of the uncertainty of symptom-based diagnosis, the high frequency of overlap between these conditions and the limited efficacy of available therapies. It has often been argued that successful drug development and management of FGIDs requires knowledge of the underlying pathophysiology. Numerous and highly variable candidate pathophysiological mechanisms have been implicated in the generation of FGID symptoms, but there is no current consensus on how to best define the relevance of these disturbances.

METHODS

A group of international experts on FGIDs developed plausibility criteria that should be fulfilled by relevant pathophysiological mechanisms in FGIDs.

RESULTS

Five criteria are proposed: (1) the presence of the abnormality in a subset of patients, (2) temporal association between proposed mechanism and symptom(s), (3) correlation between the level of impairment of the mechanism and symptom(s), (4) induction of the symptom(s) by provoking the pathophysiological abnormality in healthy subjects and (5) treatment response by a therapy specifically correcting the underlying disorder or congruent natural history of symptoms and dysfunction in the absence of specific therapy. Based on strength of evidence for these five criteria according to the Grading of Recommendations Assessment, Development and Evaluation system, a plausibility score can be calculated for each mechanism.

CONCLUSION

Evaluation of the strength of evidence for candidate pathophysiological abnormalities fulfilling these five plausibility criteria will help to identify the most relevant mechanisms to target for novel diagnostic approaches and for the development of new therapies.

Identification of experimental bladder sensitivity among dysmenorrhea sufferers

BACKGROUND

Dysmenorrhea is a common risk factor for chronic pain conditions including bladder pain syndrome. Few studies have formally evaluated asymptomatic bladder pain sensitivity in dysmenorrhea, and whether this largely reflects excess pelvic symptom reporting due to comorbid psychological dysfunction.

OBJECTIVE

We sought to determine whether bladder hypersensitivity is more common among women reporting moderate or greater dysmenorrhea, without chronic pain elsewhere, after accounting for anxiety and depression. Demonstrating this would suggest that dysmenorrhea might be an early clue for visceral or widespread pain hypersensitivity and improve understanding of potential precursors to bladder pain syndrome.

STUDY DESIGN

We compared cohorts of regularly menstruating women, without symptoms of chronic pain elsewhere, reporting (1) moderate-to-severe dysmenorrhea (n = 98) and (2) low levels or no menstrual pain (n = 35). Participants underwent rapid bladder filling following a standard water ingestion protocol, serially rating bladder pain and relative urgency during subsequent distension. Potential differences in bladder volumes were controlled for by sonographic measurement at standard cystometric thresholds. Bladder sensitivity was also measured with complementary measures at other times separately including a simplified rapid filling test, palpation of the bladder wall, and through ambulatory self-report. Anxiety and depression were evaluated with the National Institutes of Health Patient-Reported Outcomes Measurement Information System measures.

RESULTS

Women with moderate-to-severe dysmenorrhea reported more urinary symptoms than controls and had a lower maximum capacity (498 ± 18 mL vs 619 ± 34 mL, P < .001) and more evoked bladder filling pain (0-100 visual analog scale: 25 ± 3 vs 12 ± 3, P < .001). The dysmenorrhea-bladder capacity relationship remained significant irrespective of menstrual pain severity, anxiety, depression, or bladder pain (R² = 0.13, P = .006). Severity of menstrual pain predicted evoked bladder pain (R² = 0.10, P = .008) independent of anxiety (P = .21) and depression (P = .21). Women with moderate-to-severe dysmenorrhea exhibiting provoked bladder pain (24/98, 24%) also reported higher pain during the screening rapid bladder test (P < .001), in response to transvaginal bladder palpation (P < .015), and on prospective daily diaries (P < .001) than women with dysmenorrhea without provoked bladder pain.

CONCLUSION

Women experiencing moderate-to-severe dysmenorrhea also harbor a higher pain response to naturally evoked bladder distension. Noninvasive bladder provocation needs to be tested further longitudinally in those with dysmenorrhea to characterize the course of visceral sensitivity and determine if it may help predict individuals at risk for developing subsequent pain in the bladder or elsewhere.

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.

Rome III vs Rome IV criteria for irritable bowel syndrome: A comparison of clinical characteristics in a large cohort study

BACKGROUND

The Rome criteria for irritable bowel syndrome (IBS) have been revised and are expected to apply only to the subset of Rome III IBS subjects with abdominal pain as predominant symptom, occurring at least once a week. The aim of this study was to determine the percentage of Rome III IBS subjects that fulfills Rome IV criteria and to evaluate differences between Rome IV-positive and Rome IV-negative subjects.

METHODS

Four hundred and four Rome III IBS subjects completed a 14-day end-of-day symptom diary, the Gastrointestinal Symptom Rating Scale (GSRS), Hospital Anxiety and Depression Scale, and RAND 36-item Short-Form Health Survey (SF-36). Diary-based surrogate Rome IV criteria were defined as occurrence of abdominal pain at least 1 day each week with a severity of ≥2 (mild; definition 1) or ≥3 (considerable; definition 2).

KEY RESULTS

Using surrogate Rome IV criteria, 353 (87.4%, definition 1) and 249 (61.6%, definition 2) subjects were defined as Rome IV positive. These patients were more often female, younger, and recruited from secondary/tertiary care compared with Rome IV-negative subjects. They also presented with higher abdominal pain scores and gastrointestinal (GI) symptom severity on both end-of-day diary and GSRS, higher psychological symptom scores, and lower quality of life compared with Rome IV-negative subjects.

CONCLUSIONS AND INFERENCES

The Rome IV IBS population likely reflects a subgroup of Rome III IBS patients with more severe GI symptomatology, psychological comorbidities, and lower quality of life. This implies that results from Rome III IBS studies may not be directly comparable to those from Rome IV IBS populations.

Mechanisms of Stress-induced Visceral Pain

Evidence suggests that long-term stress facilitates visceral pain through sensitization of pain pathways and promotes chronic visceral pain disorders such as the irritable bowel syndrome (IBS). This review will describe the importance of stress in exacerbating IBS-induced abdominal pain. Additionally, we will briefly review our understanding of the activation of the hypothalamic-pituitary-adrenal axis by both chronic adult stress and following early life stress in the pathogenesis of IBS. The review will focus on the glucocorticoid receptor and corticotropin-releasing hormone-mediated mechanisms in the amygdala involved in stress-induced visceral hypersensitivity. One potential mechanism underlying persistent effects of stress on visceral sensitivity could be epigenetic modulation of gene expression. While there are relatively few studies examining epigenetically mediated mechanisms involved in stress-induced visceral nociception, alterations in DNA methylation and histone acetylation patterns within the brain, have been linked to alterations in nociceptive signaling via increased expression of pro-nociceptive neurotransmitters. This review will discuss the latest studies investigating the long-term effects of stress on visceral sensitivity. Additionally, we will critically review the importance of experimental models of adult stress and early life stress in enhancing our understanding of the basic molecular mechanisms of nociceptive processing.

Dietary therapies for functional bowel symptoms: Recent advances, challenges, and future directions

BACKGROUND

Functional gastrointestinal symptoms in irritable bowel syndrome (IBS) and quiescent inflammatory bowel disease (IBD) cause significant morbidity and a reduction in quality of life. Multiple dietary therapies are now available to treat these symptoms, but supporting evidence for many is limited. In addition to a further need for studies demonstrating efficacy and mechanism of action of dietary therapies, the risk of nutritional inadequacy, alterations to the microbiome and changes in quality of life are key concerns requiring elucidation. Identifying predictors of response to dietary therapy is an important goal as management could be tailored to the individual to target specific dietary components, and thereby reduce the level of dietary restriction necessary.

PURPOSE

This review discusses the available dietary therapies to treat symptoms in patients with IBS and patients with quiescent IBD suffering from IBS symptoms, with the aim to understand where current dietary evidence lies and how to move forward in dietary research in this field.

Paneth Cell Defects Induce Microbiota Dysbiosis in Mice and Promote Visceral Hypersensitivity

BACKGROUND & AIMS

Separation of newborn rats from their mothers induces visceral hypersensitivity and impaired epithelial secretory cell lineages when they are adults. Little is known about the mechanisms by which maternal separation causes visceral hypersensitivity or its relationship with defects in epithelial secretory cell lineages.

METHODS

We performed studies with C3H/HeN mice separated from their mothers as newborns and mice genetically engineered (Sox9^flox/flox-vil-cre on C57BL/6 background) to have deficiencies in Paneth cells. Paneth cell deficiency was assessed by lysozyme staining of ileum tissues and lysozyme activity in fecal samples. When mice were 50 days old, their abdominal response to colorectal distension was assessed by electromyography. Fecal samples were collected and microbiota were analyzed using Gut Low-Density Array quantitative polymerase chain reaction.

RESULTS

Mice with maternal separation developed visceral hypersensitivity and defects in Paneth cells, as reported from rats, compared with mice without maternal separation. Sox9^flox/flox-vil-Cre mice also had increased visceral hypersensitivity compared with control littermate Sox9^flox/flox mice. Fecal samples from mice with maternal separation and from Sox9^flox/flox-vil-cre mice had evidence for intestinal dysbiosis of the microbiota, characterized by expansion of Escherichia coli. Daily gavage of conventional C3H/HeN adult mice with 10⁹ commensal E coli induced visceral hypersensitivity. Conversely, daily oral administration of lysozyme prevented expansion of E coli during maternal separation and visceral hypersensitivity.

CONCLUSIONS

Mice with defects in Paneth cells (induced by maternal separation or genetically engineered) have intestinal expansion of E coli leading to visceral hypersensitivity. These findings provide evidence that Paneth cell function and intestinal dysbiosis are involved in visceral sensitivity.

Isomalto-oligosaccharides ameliorate visceral hyperalgesia with repair damage of ileal epithelial ultrastructure in rats

Background

Treatment of irritable bowel syndrome (IBS) with probiotics has achieved effectiveness to a certain extent. Whether prebiotics will work is still unclear. This study aimed to investigate the therapeutic effects of the prebiotic isomalto-oligosaccharides (IMO) on visceral hypersensitivity (VHS) in rats and to explore potential mechanism.

Methods

Water avoidance stress (WAS) was used to induce VHS in rats. The score for the abdominal withdrawal reflex (AWR) was determined while colorectal distension and compared between VHS group and control group in order to validate VHS preparation. Rats with VHS were then divided into an IMO-treated group (intragastric 5% IMO, 2 mL/d, 14 days) and a water-control group (intragastric water). After treatment, AWR score and intestinal transit rate (ITR) were determined, stool culture was performed, the ultrastructure of the ileum epithelium was observed with scanning electron microscopy (SEM), and serum cytokines were measured.

Results

WAS significantly increased AWR score responding to colorectal distension, and lowered the pain threshold. IMO treatment improved VHS with a reduction in AWR score on graded colorectal distension and an increase in pain threshold. SEM showed damages on the ileal epithelial ultrastructure in VHS rats, which was attenuated by IMO treatment. ITR, fecal microbiota and serum cytokine levels were comparable among control group, water-control group, and IMO-treated rats.

Conclusion

In this randomized placebo-controlled study, the results showed that IMO ameliorated WAS-induced visceral hyperalgesia in rats, this effect may be attributed to the repair of damages on intestinal epithelial ultrastructure.

When the low FODMAP diet does not work

Irritable bowel syndrome (IBS) is heterogeneous. Patients need proper assessment and explanation of IBS pathophysiology and appropriate therapies. A low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet effectively reduces symptoms in 75% of patients. Best treatment for those nonresponsive will depend on the pathophysiological basis for symptom genesis, with the following possible abnormalities: (i) Visceral hypersensitivity and/or enhanced gut-brain communication: a low FODMAP diet is mainly targeted for this patient group. A dietitian may also recommend antispasmodic agents, including peppermint oil. Another dietary treatment is a low food chemical diet, although this diet is often extremely limited, and therefore, not suited for some populations. Psychological therapies are also clinically beneficial. (ii) Altered motility: in patients with fast transit, a dietitian may recommend a reduction in all FODMAPs or targeted monosaccharides and disaccharides, which are more osmotic in nature. If not effective, patients may benefit from psyllium, which has an exceptional water-holding capacity aimed to promote more formed stools. Patients with slow or uncoordinated transit are often more difficult to treat. Dietary interventions have some success and usually comprise a combination of adequate fiber and fluid, osmotic laxatives, and stimulating agents such as caffeine, senna, and exercise. (iii) Altered microbiome: supplementary probiotics and prebiotics have weak evidence of efficacy with some notable exceptions. A dietitian may trial supplementary Bifidobacterium infantis or oligosaccharides, usually as an adjunct therapy. Guidance from a dietitian will encompass dietary methods to treat IBS but additionally identify where dietary treatment is not indicated to ensure that diet is correctly used and patients are not nutritionally or psychologically compromised.

Biomarkers of Irritable Bowel Syndrome

Traditionally, irritable bowel syndrome (IBS) has not been regarded as an organic disease, and the pathophysiology of IBS is heterogeneous. Currently, the diagnosis of IBS is based upon the Rome diagnostic criteria. The performance of these criteria is only modest in predicting IBS, and moreover their validation is lacking. Additionally, as functional symptoms are common in the general population, healthy controls or volunteers are difficult to define and there is currently no definition of “normal” in the Rome criteria. Due to the weaknesses of the current diagnostic criteria, patients and doctors expect new gold standard diagnostic tools. Various etiologic mechanisms result in potential biomarkers. The focus of this research has been to find non-invasive biomarkers from serum, breath gas, and fecal materials. Though biomarkers should be based on biological and pathogenic processes, most biomarkers for IBS have been developed to identify organic diseases and therefore eliminate IBS. To date, these types of biomarkers for IBS have been disappointing. The purposes of developing biomarkers include improvement of diagnosis, differentiation from other organic diseases, and discrimination of IBS subtypes. A true mechanistic biomarker would make it possible to rule in IBS, rather than to rule out other organic diseases. New serologic biomarkers for diarrhea-predominant IBS have been introduced based on the pathophysiologic findings from a rat model and validation in a large-scale clinical trial. Further investigations of abnormal organic findings from each subtype of IBS would enable the development of new, simple subtype-specific biomarkers.

The Role of Visceral Hypersensitivity in Irritable Bowel Syndrome: Pharmacological Targets and Novel Treatments

Irritable bowel syndrome (IBS) is the most common disorder referred to gastroenterologists and is characterized by altered bowel habits, abdominal pain, and bloating. Visceral hypersensitivity (VH) is a multifactorial process that may occur within the peripheral or central nervous systems and plays a principal role in the etiology of IBS symptoms. The pharmacological studies on selective drugs based on targeting specific ligands can provide novel therapies for modulation of persistent visceral hyperalgesia. The current paper reviews the cellular and molecular mechanisms underlying therapeutic targeting for providing future drugs to protect or treat visceroperception and pain sensitization in IBS patients. There are a wide range of mediators and receptors participating in visceral pain perception amongst which substances targeting afferent receptors are attractive sources of novel drugs. Novel therapeutic targets for the management of VH include compounds which alter gut-brain pathways and local neuroimmune pathways. Molecular mediators and receptors participating in pain perception and visceroperception include histamine-1 receptors, serotonin (5-hydrodytryptamine) receptors, transient receptor potential vanilloid type I, tachykinins ligands, opioid receptors, voltage-gated channels, tyrosine receptor kinase receptors, protease-activated receptors, adrenergic system ligands, cannabinoid receptors, sex hormones, and glutamate receptors which are discussed in the current review. Moreover, several plant-derived natural compounds with potential to alleviate VH in IBS have been highlighted. VH has an important role in the pathology and severity of complications in IBS. Therefore, managing VH can remarkably modulate the symptoms of IBS. More preclinical and clinical investigations are needed to provide efficacious and targeted medicines for the management of VH.

Co-Administration of Soy Isoflavones and Vitamin D in Management of Irritable Bowel Disease

BACKGROUND AND AIMS

The substantial characteristics of Irritable Bowel Syndrome (IBS) are associated with estrogens in women. Both soy isoflavones and vitamin D can modulate estrogen receptors in the colonic smooth muscles. The aim of this study was to investigate the effects of soy isoflavones, vitamin D and their probable interactions in women with IBS.

METHODS

In a factorial blinded randomized clinical trial, 100 women with IBS (age:18-75yr, were randomly assigned in 4 arms to receive either placebo of vitamin D and placebo of soy isoflavones (P+P), or placebo of vitamin D and soy isoflavones (P+S), or vitamin D and placebo of soy isoflavones (D+P), or vitamin D and soy isoflavones (D+S) for 6 weeks. Dosage of soy isoflavone was 2 capsules of 20 mg soy isoflavones per day, and dosage of vitamin D was one pearl of 50'000 IU biweekly. The clinical outcomes were IBS symptoms severity scores (IBS-SSS), disease- specific quality of life (IBS-QOL) and total score (IBS-TS) that evaluated at weeks 0, 6, and 10, and compared to each other.

RESULTS

IBS-TS improved significantly in both S+P and D+P groups (p- value = 0.004, 0.015). The interaction effect of soy isoflavones and vitamin D on IBS-TS was significant (p<0.05). The interaction effect of soy isoflavones with vitamin D and the main effect of vitamin D on IBS-SSS were not statistically significant, whereas IBS-SSS decreased significantly in S+P and D+P groups (p-value = 0.001, 0.047 respectively).

CONCLUSION

Our results indicate that co-administration of soy isoflavones with vitamin D did not improve the IBS- SSS and IBS- QOL; however, it improved the IBS-TS.

TRIAL REGISTRATION

Clinical Trials.gov NCT02026518.

Systematic review: instruments to assess abdominal pain in irritable bowel syndrome

BACKGROUND

Consensus on standard methods to assess chronic abdominal pain in patients with irritable bowel syndrome (IBS) is currently lacking.

AIM

To systematically review the literature with respect to instruments of measurement of chronic abdominal pain in IBS patients.

METHODS

Systematic literature search was performed in PubMed/Medline databases for studies using pain measurement instruments in patients with IBS.

RESULTS

One hundred and ten publications were reviewed. A multitude of different instruments is currently used to assess chronic abdominal pain in IBS patients. The single-item methods, e.g. the validated 10-point numeric rating scale (NRS), and questionnaires assessing gastrointestinal symptoms severity, focus mostly on the assessment of only the intensity of abdominal pain. Of these questionnaires, the validated IBS-Symptom Severity Scale includes the broadest measurement of pain-related aspects. General pain questionnaires and electronic momentary symptom assessment tools have been used to study abdominal pain in IBS patients, but have not yet been validated for this purpose. The evidence for the use of provocation tests, e.g. the rectal barostat with balloon distention, for measurement of abdominal pain in IBS is weak, due to the poor correlation between visceral pain thresholds assessed by provocation tests and abdominal pain as assessed by retrospective questionnaires.

CONCLUSIONS

The multitude of different instruments to measure chronic abdominal pain in IBS makes it difficult to compare endpoints of published studies. There is need for validated instruments to assess chronic abdominal pain in IBS patients, that overcome the limitations of the currently available methods.

Visceral hypersensitivity in irritable bowel syndrome: evidence for involvement of serotonin metabolism--a preliminary study

BACKGROUND

Altered serotonergic (5-HT) metabolism and visceral perception have been associated with the pathogenesis of irritable bowel syndrome (IBS). Aim of this preliminary study was to assess the effect of the direct precursor of 5-HT, 5-hydroxytryptophan (5-HTP), on systemic 5-HT metabolites and visceral perception and to assess potential differential responses between IBS and controls.

METHODS

15 IBS patients and 15 healthy volunteers participated in this randomized double-blind placebo controlled study. Visceroperception was measured by rectal barostat. The 100 mg 5-HTP or placebo was ingested orally. Serotonergic metabolites were assessed in platelet poor plasma.

KEY RESULTS

5-HTP induces rectal allodynia in a significant number of healthy controls; IBS patients exhibit lowered pain thresholds in both placebo and 5-HTP conditions. 5-HTP induces rectal hyperalgesia in hypersensitive but not in non-hypersensitive IBS patients. Administration of 5-HTP significantly increased plasma 5-HTP levels (p < 0.001), did not affect 5-HT levels (p > 0.05), while levels of the main metabolite of 5-HT, 5-hydroxyindoleacetic acid, increased significantly (p < 0.05) in both groups. The magnitude of these changes observed in 5-HT metabolites was significantly greater in IBS patients.

CONCLUSIONS & INFERENCES

Oral administration of 5-HTP induced significant alterations in systemic 5-HT metabolites that were accompanied by increased visceroperception of pain in controls and hypersensitive IBS patients. Changes in 5-HT metabolism appear to be important factors involved in visceral hypersensitivity as the 5-HTP-induced pro-nociceptive response was observed in all hypersensitive IBS patients and to a lesser magnitude in a significant number of healthy controls but in none of the non-hypersensitive IBS patients.

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.

Placebo analgesia in patients with functional and organic abdominal pain: a fMRI study in IBS, UC and healthy volunteers

OBJECTIVE

Understanding the neural circuitry of placebo analgesia in the context of visceral pain is increasingly important given evidence of clinical benefit of placebo treatment in IBS. This functional MRI study addressed placebo analgesia in IBS, UC and healthy control (HC) volunteers.

DESIGN

Painful rectal distensions were delivered in N=17 patients with IBS , N=15 patients with UC in remission, and sex-matched and age-matched HCs in an adaptation phase followed by intravenous application of saline combined with either positive instructions of pain relief (placebo) or neutral instructions (control). Neural activation during cued-pain anticipation and pain was analysed along with ratings of expected and perceived pain and measures of negative affectivity and salivary cortisol concentrations. Correlational analyses between placebo analgesia responses and negative affect were accomplished.

RESULTS

HC and UC revealed significant pain inhibition during placebo analgesia, as evidenced by reduced neural activation in pain-related brain areas. In contrast, patients with IBS failed to effectively engage neural downregulation of pain, as evidenced by the absence of placebo-induced changes in distension-induced brain activation, resulting in a significant group difference in the cingulate cortex compared with HC. Depression scores correlated with weaker placebo analgesia, whereas state and trait anxiety were not associated.

CONCLUSIONS

Patients with IBS failed to effectively engage neural downregulation of rectal distension-induced pain during placebo analgesia, indicating a specific deficit in cognitive pain inhibition, which may in part be mediated by depression.

The quest for biomarkers in IBS-where should it lead us?

Irritable bowel syndrome (IBS) is a prevalent functional gastrointestinal disorder which represents a major cost to health-care services. The diagnosis of IBS is currently performed by means of symptom-based diagnostic criteria, but there has been an ongoing interest in developing biomarkers which could simplify the diagnosis and/or evaluating the effect of treatments. This article reviews the current literature concerning the proposed biomarkers including those of altered gut motility, of visceral hypersensitivity, of abnormal brain mechanisms, of serum, fecal and mucosal inflammation and of increased intestinal permeability.

Diagnosis of IBS: symptoms, symptom-based criteria, biomarkers or 'psychomarkers'?

IBS is estimated to have a prevalence of up to 20% in Western populations and results in substantial costs to health-care services worldwide, estimated to be US$1 billion per year in the USA. IBS remains difficult to diagnose due to its multifactorial aetiology, heterogeneous nature and overlap of symptoms with organic pathologies, such as coeliac disease and IBD. As a result, IBS often continues to be a diagnosis of exclusion, resulting in unnecessary investigations. Available methods for the diagnosis of IBS-including the current gold standard, the Rome III criteria-perform only moderately well. Visceral hypersensitivity and altered pain perception do not discriminate between IBS and other functional gastrointestinal diseases or health with any great accuracy. Attention has now turned to developing novel biomarkers and using psychological markers (so-called psychomarkers) to aid the diagnosis of IBS. This Review describes how useful symptoms, symptom-based criteria, biomarkers and psychomarkers, and indeed combinations of all these approaches, are in the diagnosis of IBS. Future directions in diagnosing IBS could include combining demographic data, gastrointestinal symptoms, biomarkers and psychomarkers using statistical methods. Latent class analysis to distinguish between IBS and non-IBS symptom profiles might also represent a promising avenue for future research.

The severity of irritable bowel syndrome or the presence of fibromyalgia influencing the perception of visceral and somatic stimuli

BACKGROUND

Fibromyalgia Syndrome (FMS) is a frequent comorbidity in Irritable Bowel Syndrome (IBS) patients with a higher functional bowel disorder severity index (FBDSI). We tested the possibility that mild to severe IBS patients without FMS would have a graduated visceral and somatic perception, and the presence of FMS would further enhance somatic, but conversely attenuate visceral perception.Our aim was to study visceral and somatic sensitivity in mild IBS patients and in severe IBS patients with or without FMS.

METHODS

Eleven mild IBS and 19 severe IBS with and without FMS patients were studied. Somatic and visceral stimuli were applied in each patient by means of electrical stimulations at active and control sites and by means of an electronic barostat in the rectum. Thresholds for discomfort and perception cumulative scores were measured.

RESULTS

Mild and severe IBS patients without FMS demonstrated a significantly lower somatic perception cumulative score than severe IBS patients with FMS at active site. Conversely only severe IBS patients without FMS had significantly lower visceral thresholds for discomfort than mild IBS patients and severe IBS patients with FMS.

CONCLUSIONS

The presence of co-existing FMS or greater FBDSI affects somatic and visceral perception in a graded fashion across IBS patients.

Interaction between preprandial and postprandial rectal sensory and motor abnormalities in IBS

BACKGROUND AND AIMS

Rectal sensory and motor interactions in patients with IBS have not been studied in detail. The aim of this study was to evaluate fasting and postprandial rectal sensorimotor characteristics and their interactions in IBS compared with healthy controls.

DESIGN

We included 274 patients with IBS and 34 controls. All subjects underwent a rectal barostat study before and 60 min after a standardised liquid meal (800 kcal; 60% fat). Sensory thresholds, intensity of sensations, viscerosomatic referral and compliance were measured. During 15 min before the first distension sequence and until 50 min after meal intake, rectal balloon volumes were registered in 5 min intervals at operating pressure to quantify rectal tone. Mixed models were used to analyse the rectal tone response over time.

RESULTS

Rectal sensory thresholds and compliance were decreased and viscerosomatic referral areas increased in patients with IBS compared with controls. Meal intake increased rectal sensitivity, compliance and referral areas in patients and controls and the same proportions of patients were hypersensitive to distension before and after meal intake. There was a higher basal rectal tone in IBS and a significantly different rectal tone response after meal intake in patients with IBS compared with controls and, interestingly, also in IBS with rectal hypersensitivity (defined in the preprandial state), compared with normosensitive patients.

CONCLUSIONS

Meal intake affects rectal sensorimotor function in IBS and health. Importantly, the rectal tone responses to a high-caloric meal are different between patients with IBS and controls, as well as between hypersensitive and normosensitive patients with IBS.

Fermentable oligosaccharides, disaccharides, monosaccharides and polyols: role in irritable bowel syndrome

Irritable bowel syndrome (IBS) was previously left poorly treated despite its high prevalence and cost. Over the past decade, significant research has been conducted providing new dietary strategies for IBS management. The 'low fermentable oligosaccharides, disaccharides, monosaccharides and polyols diet' has shown symptom improvement in 68-76% of patients. Randomized, controlled trials have now proven its efficacy. The diet, low in poorly absorbed and fermentable carbohydrates, uses dietary restriction and re-challenge to determine individual tolerance to various short-chain carbohydrates. However there may be potential detrimental effects of the diet in the long term, due to potential changes to the gastrointestinal microbiota. Appropriate dietary education and management of the diet is imperative. Future research should focus on the relevance of changes to the microbiota and ways to liberalize the dietary restrictions.

Markers for visceral hypersensitivity in patients with irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a heterogenous disorder with visceral hypersensitivity as important hallmark. It is not known whether IBS patients with visceral hypersensitivity have different epidemiological and clinical characteristics compared with IBS patients without visceral hypersensitivity. Aim of our study was to compare in detail a large group of hyper- vs normosensitive IBS patients with respect to epidemiological and clinical characteristics.

METHODS

IBS patients (Rome III criteria) have been recruited for a large-scale cohort study. All patients from this cohort who underwent a rectal barostat procedure were included and allocated based on those with and without visceral hypersensitivity. Patient demographics, and symptoms were collected using questionnaires (GSRS, HADS, SF-36) and a 14-day symptom diary for IBS-related symptoms. A multivariate logistic regression model was used to identify risk markers for having visceral hypersensitivity.

KEY RESULTS

Ninety-five normosensitive and 93 hypersensitive IBS patients participated in this study. Hypersensitive patients had significantly higher scores for GSRS abdominal pain (p < 0.05), indigestion, reflux and constipation syndrome (all p < 0.01), and IBS symptom intensity, discomfort (both p < 0.05) and mean symptom composite score (p < 0.01). Age, female sex, and the use of SSRI medication were significantly different between the normo- and the hypersensitive IBS patients. However, after adjustment for other risk markers, only increasing age was found to be significantly associated with lower odds for having hypersensitivity (OR 0.97 [95% CI: 0.94; 0.99]).

CONCLUSIONS & INFERENCES

Apart from more severe symptomatology, hypersensitive IBS patients are characterized by significantly younger age compared with normosensitive IBS patients. The study has been registered in the US National Library of Medicine (http://www.clinicaltrials.gov, NCT00702026).

Mild moxibustion decreases the expression of prokineticin 2 and prokineticin receptor 2 in the colon and spinal cord of rats with irritable bowel syndrome

It has been proven that prokineticin 2 (PK2) and its receptor PKR2 play an important role in hyperalgesia, while mild moxibustion can relieve visceral hypersensitivity in a rat model of irritable bowel syndrome (IBS). The goal of the present study was to determine the effects of mild moxibustion on the expression of PK2 and PKR2 in colon and spinal cord in IBS rat model, which was induced by colorectal distension using inflatable balloons. After mild moxibustion treatment, abdominal withdrawal reflex (AWR) scores were assessed by colorectal distension; protein and mRNA expression of PK2 and PKR2 in rat colon and spinal cord was determined by immunohistochemistry and fluorescence quantitative PCR. Compared with normal rats, the AWR scores of rats and the expressions of PK2/PKR2 proteins and mRNAs in colon and spinal cord tissue were significantly increased in the model group; compared with the model group, the AWR scores of rats and the expressions of PK2/PKR2 proteins and mRNAs in colon and spinal cord tissue were significantly decreased in the mild moxibustion group. These findings suggest that the analgesia effect of mild moxibustion may be associated with the reduction of the abnormally increased expression of the PK2/PKR2 proteins and mRNAs in the colon and spinal cord.

Predictors of early postoperative pain after stapled haemorrhoidopexy

AIM

Moderate to severe pain after stapled haemorrhoidopexy (SH) is not uncommon. This study was designed to identify the predictors of postoperative pain after SH in a single centre.

METHOD

Seventy-six patients with Grade II to IV haemorrhoids who underwent SH were selected from a prospectively compiled database. Preoperative data, including patient characteristics, manometry results and surgical data, were documented. Pain was evaluated during the first 24 h after the operation. Its intensity was classified into three grades according to the visual analogue scale (VAS) score: mild (VAS ≤ 3), moderate (VAS >3 to <5) and severe (VAS ≥ 5). Analgesics were not routinely given but were administered if the patient had moderate or severe pain. Both univariate and multivariate analyses were used to determine the predictors of postoperative pain.

RESULTS

Moderate and severe pain was noted in 43 (58.9%) patients. No patient was readmitted due to persistent anal pain during the month following discharge. Postoperative pain was significantly associated with gender (P = 0.017), age (P = 0.014), first initial sensory volume (P = 0.023) and constipation (P = 0.005) in univariate analysis. Multivariate analysis identified male gender as an independent predictor of postoperative moderate to severe pain (P = 0.037, OR = 3.1, 95% CI 1.07-9.09). The initial sensory volume and preoperative coexisting constipation were negative predictors of postoperative moderate to severe pain after SH (P = 0.037, OR = 0.320, 95% CI 0.110-0.934, and P = 0.036, OR = 0.255, 95% CI 0.071-0.913, respectively).

CONCLUSION

Male gender and the initial sensory volume are predictors of postoperative pain after SH. Anal manometry is recommended before the SH procedure. An active analgesia protocol should be considered for male patients with a low initial sensory volume after SH.

Spinal toll-like receptor 4-mediated signalling pathway contributes to visceral hypersensitivity induced by neonatal colonic irritation in rats

BACKGROUND

Although visceral hypersensitivity is a major pathophysiological feature of irritable bowel syndrome (IBS), its underlying mechanisms remain elusive. Toll-like receptor 4 (TLR4) is a critical pattern recognition molecule of the innate immune system. In this study, we investigated whether the TLR4/myeloid differentiation factor 88 (MyD88)/nuclear factor-kappa B (NF-κB) signalling pathway in the spinal cord contributed to the visceral hypersensitivity induced by neonatal colonic irritation (CI) in rats.

METHODS

The Sprague-Dawley rat model of IBS was induced by colon irritation on post-natal day (PND) 8, PND10 and PND12. Experiments were conducted in adult rats. TLR4 mRNA and protein, and its downstream signalling molecules, MyD88, inhibitory nuclear factor-kappa B (IκB) and NF-κB protein expressions in L2-S4 spinal segments were detected by quantitative real-time reverse transcription-polymerase chain reaction as well as Western blotting. TLR4 co-localization was determined by immunohistochemistry. Levels of tumour necrosis factor-alpha (TNF-α) and interleukin 1β (IL-1β) were measured with enzyme-linked immunosorbent assay.

RESULTS

We found that neonatal CI treatment induced long-lasting visceral hypersensitivity without identifiable structural abnormalities in descending colons of adult rats. Neonatal CI treatment evoked a significant up-regulation of the expressions of TLR4 in glia, MyD88, p-IκB-α and NF-κB in adult rats. Neonatal CI treatment also increased the levels of its downstream inflammatory agents TNF-α and IL-1β in the L2-S4 regions of the spinal cord of adult rats.

CONCLUSIONS

These results suggest that neonatal CI stimulates the production of IL-1β and TNF-α through the TLR4/MyD88/NF-κB signalling pathway in the spinal cord, which contributed to visceral hypersensitivity induced by neonatal CI in rats.

Randomized clinical trial on the effect of a multispecies probiotic on visceroperception in hypersensitive IBS patients

BACKGROUND

Irritable bowel syndrome (IBS) is characterized by heterogeneous pathophysiology and low response to treatment. Up to 60% of IBS patients suffers from visceral hypersensitivity, which is associated with symptom severity and underlying pathophysiological mechanisms. Recently, positive effects of probiotics in IBS have been reported, but overall the response was modest. We performed a study in IBS patients, characterized by visceral hypersensitivity measured with the rectal barostat, aiming to assess the effect of 6 weeks of multispecies probiotic mix on visceral pain perception.

METHODS

We conducted a randomized, placebo-controlled, double-blind trial in forty Rome III IBS patients with visceral hypersensitivity. Prior to intake, patients kept a 2-week symptom diary and underwent a rectal barostat measurement. When hypersensitivity was confirmed, participation was allowed and patients received a multispecies probiotic with in vitro proven potential beneficial effects on mechanisms contributing to visceral hypersensitivity (six different probiotic strains; 10(9)  cfu/g), or a placebo product of one sachet (5 g) per day for 6 weeks. At the end of the intervention period, visceroperception and symptoms were reassessed.

KEY RESULTS

Thirty-five patients completed the trial. The percentage of patients with visceral hypersensitivity decreased significantly in the probiotic and placebo group (76.5% and 71.4%, respectively; N.S. between groups). Improvement in pain scores and mean symptom score did not differ between the probiotic and placebo group.

CONCLUSIONS & INFERENCES

In this placebo-controlled trial in IBS patients with visceral hypersensitivity, no significant effect of a multispecies probiotic on viscerperception was observed. The study has been registered in the US National Library of Medicine (http://www.clinicaltrials.gov, NCT00702026).

Mechanisms and efficacy of dietary FODMAP restriction in IBS

IBS is a debilitating condition that markedly affects quality of life. The chronic nature, high prevalence and associated comorbidities contribute to the considerable economic burden of IBS. The pathophysiology of IBS is not completely understood and evidence to guide management is variable. Interest in dietary intervention continues to grow rapidly. Ileostomy and MRI studies have demonstrated that some fermentable carbohydrates increase ileal luminal water content and breath hydrogen testing studies have demonstrated that some carbohydrates also increase colonic hydrogen production. The effects of fermentable carbohydrates on gastrointestinal symptoms have also been well described in blinded, controlled trials. Dietary restriction of fermentable carbohydrates (popularly termed the 'low FODMAP diet') has received considerable attention. An emerging body of research now demonstrates the efficacy of fermentable carbohydrate restriction in IBS; however, limitations still exist with this approach owing to a limited number of randomized trials, in part due to the fundamental difficulty of placebo control in dietary trials. Evidence also indicates that the diet can influence the gut microbiota and nutrient intake. Fermentable carbohydrate restriction in people with IBS is promising, but the effects on gastrointestinal health require further investigation.

Perception and pain thresholds for cutaneous heat and cold, and rectal distension: associations and disassociations

BACKGROUND

Hypersensitivity to somatic or visceral pain has been reported in numerous clinical conditions such as fibromyalgia or the irritable bowel syndrome, and general hypersensitivity has been proposed to be the underlying mechanism. However, cross-modal relationships especially between somatic and visceral pain have rarely been investigated even in healthy volunteers. Furthermore, psychological influences on pain have rarely been characterized across modalities.

METHODS

Sixty-one healthy participants underwent testing of perception and pain thresholds for cutaneous thermode heat and cold, as well as for rectal balloon distension. Psychological testing for anxiety, depression, and pain experience (including catastrophizing and coping) as well as cardiac interoception was performed. Measurement quality and the correlations between the different modalities were examined.

KEY RESULTS

Significant correlations existed between the perception thresholds for cold/heat (τB  = -0.28, p = 0.002) and cold/distension (τB  = -0.21, p = 0.03) and for the pain thresholds for cold/heat (r = -0.61, p < 0.001) and heat/distension (r = 0.33, p = 0.01). No association was found between pain thresholds and anxiety, depression, psychological experience with and processing of pain, or cardiac interoception. Retest reliabilities for pain measurements were satisfying after short intertrial intervals (all intraclass correlation coefficients >0.8), but less so after longer intervals. The individuals contributing to the respective correlations differ between measurements.

CONCLUSIONS & INFERENCES

Moderate associations were found for pain thresholds across modalities. The strength of the associations and their stability over time warrants further investigation and might serve to increase the understanding of conditions affecting multiple pain modalities.

Effects of DA-9701, a novel prokinetic agent, on phosphorylated extracellular signal-regulated kinase expression in the dorsal root ganglion and spinal cord induced by colorectal distension in rats

BACKGROUND/AIMS

DA-9701, a standardized extract of Pharbitis Semen and Corydalis Tuber, is a new prokinetic agent that exhibits an analgesic effect on the abdomen. We investigated whether DA-9701 affects visceral pain induced by colorectal distension (CRD) in rats.

METHODS

A total of 21 rats were divided into three groups: group A (no CRD+no drug), group B (CRD+no drug), and group C (CRD+DA-9701). Expression of pain-related factors, substance P (SP), c-fos, and phosphorylated extracellular signal-regulated kinase (p-ERK) in the dorsal root ganglion (DRG) and spinal cord was determined by immunohistochemical staining and Western blotting.

RESULTS

The proportions of neurons in the DRG and spinal cord expressing SP, c-fos, and p-ERK were higher in group B than in group A. In the group C, the proportion of neurons in the DRG and spinal cord expressing p-ERK was lower than that in group B. Western blot results for p-ERK in the spinal cord indicated a higher level of expression in group B than in group A and a lower level of expression in group C than in group B.

CONCLUSIONS

DA-9701 may decrease visceral pain via the downregulation of p-ERK in the DRG and spinal cord.