Fructo-oligosaccharide intensifies visceral hypersensitivity and intestinal inflammation in a stress-induced irritable bowel syndrome mouse model

AIM To determine whether fructo-oligosaccharide(FOS) affects visceral sensitivity, inflammation, and production of intestinal short-chain fatty acids(SCFA) in an irritable bowel syndrome(IBS) mouse model.METHODS Mice were randomly assigned to daily oral gavage of saline solution with or without FOS(8 g/kg body weight) for 14 d. Mice were further assigned to receive either daily one-hour water avoidance stress(WAS) or sham-WAS for the first 10 d. After 2 wk, visceral sensitivity was measured by abdominal withdrawal reflex in response to colorectal distension and mucosal inflammation was evaluated. Gas chromatography, real-time reverse transcription PCR, and immunohistochemistry assays were used to quantify cecal concentrations of SCFA, intestinal cytokine expression, and number of intestinal mast cells per high-power field(HPF), respectively.RESULTS Mice subjected to WAS exhibited visceral hypersensitivity and low-grade inflammation. Among mice subjected to WAS, FOS increased visceral hypersensitivity and led to higher cecal concentrations of acetic acid(2.49 ± 0.63 mmol/L vs 1.49 ± 0.72 mmol/L, P < 0.05), propionic acid(0.48 ± 0.09 mmol/L vs 0.36 ± 0.05 mmol/L, P < 0.01), butyric acid(0.28 ± 0.09 mmol/L vs 0.19 ± 0.003 mmol/L, P < 0.05), as well as total SCFA(3.62 ± 0.87 mmol/L vs 2.27 ± 0.75 mmol/L, P < 0.01) compared to saline administration. FOS also increased ileal interleukin(IL)-23 mR NA(4.71 ± 4.16 vs 1.00 ± 0.99, P < 0.05) and colonic IL-1β mR NA(2.15 ± 1.68 vs 0.88 ± 0.53, P < 0.05) expressions as well as increased mean mast cell counts in the ileum(12.3 ± 2.6 per HPF vs 8.3 ± 3.6 per HPF, P < 0.05) and colon(6.3 ± 3.2 per HPF vs 3.4 ± 1.2 per HPF, P < 0.05) compared to saline administration in mice subjected to WAS. No difference in visceral sensitivity, intestinal inflammation, or cecal SCFA levels was detected with or without FOS administration in mice subjected to sham-WAS.CONCLUSION FOS administration intensifies visceral hypersensitivity and gut inflammation in stress-induced IBS mice, but not in the control mice, and is also associated with increased intestinal SCFA production.

Hewei Jiangni granule alleviates visceral hypersensitivity in a rat model of non-erosive reflux disease via transient receptor potential channel signaling

Objective:To uncover the underlying mechanism of Hewei Jiangni granule(HWJNG)on non-erosive reflux disease(NERD)treatment by examining histological changes,gastrointestinal neurochemicals release and visceral hypersensitivity-related receptor expression in NERD model rats.Methods:A NERD rat model was established via a combination of basal sensitization and acid perfusion.HWJNG treatments at different doses were then administered.Pathological changes to tissues,mast cell(MC)activation,serum levels of esophageal visceral hypersensitivity-related neurochemicals,and transient receptor potential(TRP)receptor mRNA and protein levels were investigated.Results:Compared with the control group,the expression of tryptase in MCs,the changes of intercellular space,and the serum levels of substance P(SP),calcitonin gene-related peptides(CGRP)and proteinaseactivated receptor 2(PAR2)increased in the model group(all P<.05).The expression of TRP vanilloid 1(Trpv1)mRNA decreased in esophagus and dorsal root ganglia(DRG)of the model group(P=.030&P=.013),and the expression of TRP melastatin channel subfamily member 8(Trpm8)mRNA decreased in the esophagus of model group(P<.01).The level of esophageal TRPV1 protein increased in the model group(P<.01)and the level of TRPM8 protein decreased in esophagus and DRG of the model group(both P<.05).Compared with the model group,the serum levels of SP,CGRP,and PAR2 in the mediumdose HWJNG group showed significant decreases(all P<.05).The expression of Trpv1 mRNA in esophagus and DRG of the HWJNG groups and the Omeprazole group remarkably decreased(all P<.05),as was the expression of Trpm8 mRNA in esophagus of the HWJNG groups(all P<.05).Conclusion:HWJNG alleviated visceral hypersensitivity in NERD model rats by regulating TRP-mediated signaling.Our results indicate that HWJNG has potential as a therapeutic agent for NERD.

Serotonin receptor 2B induces visceral hyperalgesia in rat model and patients with diarrhea-predominant irritable bowel syndrome

BACKGROUND Serotonin receptor 2B(5-HT2B receptor)plays a critical role in many chronic pain conditions.The possible involvement of the 5-HT2B receptor in the altered gut sensation of irritable bowel syndrome with diarrhea(IBS-D)was investigated in the present study.AIM To investigate the possible involvement of 5-HT2B receptor in the altered gut sensation in rat model and patients with IBS-D.METHODS Rectosigmoid biopsies were collected from 18 patients with IBS-D and 10 patients with irritable bowel syndrome with constipation who fulfilled the Rome IV criteria and 15 healthy controls.The expression level of the 5-HT2B receptor in colon tissue was measured using an enzyme-linked immunosorbent assay and correlated with abdominal pain scores.The IBS-D rat model was induced by intracolonic instillation of acetic acid and wrap restraint.Alterations in visceral sensitivity and 5-HT2B receptor and transient receptor potential vanilloid type 1(TRPV1)expression were examined following 5-HT2B receptor antagonist adminis-tration.Changes in visceral sensitivity after administration of the TRPV1 antago-INTRODUCTION Irritable bowel syndrome(IBS)is a chronic functional bowel disorder characterized by recurrent abdominal pain with altered bowel habits that affects approximately 15%of the population worldwide[1].IBS significantly impacts the quality of life of patients.Although the pathogenesis of IBS is not completely understood,the role of abnormal visceral sensitivity in IBS has recently emerged[2,3].5-Hydroxytryptamine(5-HT)is known to play a key role in the physiological states of the gastrointestinal tract.Plasma 5-HT levels in IBS with diarrhea(IBS-D)patients were greater than those in healthy controls[4],suggesting a possible role of 5-HT in the pathogenesis of IBS-D.The serotonin receptor 2(5-HT2 receptor)family comprises three subtypes:5-HT2A,5-HT2B,and 5-HT2c.All 5-HT2 receptors exhibit 46%-50%overall sequence identity,and all of these receptors preferentially bind to Gq/11 to increase inositol phosphates and intracellular calcium mobilization[5].5-HT2B receptors are widely expressed throughout the gut,and experimental evidence suggests that the primary function of 5-HT2B receptors is to mediate contractile responses to 5-HT through its action on smooth muscle[6].The 5-HT2B receptor is localized to both neurons of the myenteric nerve plexus and smooth muscle in the human colon.The 5-HT2B receptor mediates 5-HT-evoked contraction of longitudinal smooth muscle[6].These findings suggest that the 5-HT2B receptor could play an important role in modulating colonic motility,which could affect sensory signaling in the gut.Other laboratories have shown that the 5-HT2B receptor participates in the development of mechanical and formalin-induced hyperalgesia[7,8].A 5-HT2B receptor antagonist reduced 2,4,6-trinitrobenzene sulfonic acid(TNBS)and stress-induced visceral hyperalgesia in rats[9,10].However,the role of the 5-HT2B receptor in IBS-D patients and in acetic acid-and wrap restraint-induced IBS-D rat models was not investigated.

Pharmacological evaluation of NSAID-induced gastropathy as a “Translatable” model of referred visceral sensitivity

AIM To evaluate whether non-steroidal anti-inflammatory drugs(NSAIDs)-induced gastropathy is a clinically predictive model of referred visceral hypersensitivity.METHODS Gastric ulcer pain was induced by the oral administration of indomethacin to male,CD1 mice(n = 10/group) and then assessed by measuring referred abdominal hypersensitivity to tactile application. A diverse range of pharmacological mechanisms contributing to the pain were subsequently investigated. These mechanisms included: transient receptor potential(TRP),sodium and acid-sensing ion channels(ASICs) as well as opioid receptors and guanylate cyclase C(GC-C). RESULTS Results showed that two opioids and a GC-C agonist,morphine,asimadoline and linaclotide,respectively,the TRP antagonists,AMG9810 and HC-030031 and the sodium channel blocker,carbamazepine,elicited a dose-and/or time-dependent attenuation of referred visceral hypersensitivity,while the ASIC blocker,amiloride,was ineffective at all doses tested. CONCLUSION Together,these findings implicate opioid receptors,GC-C,and sodium and TRP channel activation as possible mechanisms associated with visceral hypersensitivity. More importantly,these findings also validate NSAID-induced gastropathy as a sensitive and clinically predictive mouse model suitable for assessing novel molecules with potential pain-attenuating properties.

Altered metabolism of bile acids correlates with clinical parameters and the gut microbiota in patients with diarrhea-predominant irritable bowel syndrome

BACKGROUND Bile acids(BAs)have attracted attention in the research of irritable bowel syndrome with predominant diarrhea(IBS-D)due to their ability to modulate bowel function and their tight connection with the gut microbiota.The composition of the fecal BA pool in IBS-D patients is reportedly different from that in healthy populations.We hypothesized that BAs may participate in the pathogenesis of IBS-D and the altered BA profile may be correlated with the gut microbiome.AIM To investigate the role of BAs in the pathogenesis of IBS-D and the correlation between fecal BAs and gut microbiota.METHODS Fifty-five IBS-D patients diagnosed according to the Rome Ⅳ criteria and twentyeight age-,sex-,and body mass index-matched healthy controls(HCs)were enrolled in this study at the gastroenterology department of China-Japan Friendship Hospital.First,clinical manifestations were assessed with standardized questionnaires,and visceral sensitivity was evaluated via the rectal distension test using a high-resolution manometry system.Fecal primary BAs including cholic acid(CA)and chenodeoxycholic acid(CDCA),secondary BAs including deoxycholic acid(DCA),lithocholic acid(LCA),and ursodeoxycholic acid(UDCA)as well as the corresponding tauro-and glyco-BAs were examined by ultraperformance liquid chromatography coupled to tandem mass spectrometry.The gut microbiota was analyzed using 16S rRNA gene sequencing.Correlations between fecal BAs with clinical features and gut microbiota were explored.RESULTS Fecal CA(IBS-D:3037.66[282.82,6917.47]nmol/g,HC:20.19[5.03,1304.28]nmol/g;P<0.001)and CDCA(IBS-D:1721.86[352.80,2613.83]nmol/g,HC:57.16[13.76,1639.92]nmol/g;P<0.001)were significantly increased,while LCA(IBSD:1621.65[58.99,2396.49]nmol/g,HC:2339.24[1737.09,2782.40];P=0.002)and UDCA(IBS-D:8.92[2.33,23.93]nmol/g,HC:17.21[8.76,33.48]nmol/g;P=0.025)were significantly decreased in IBS-D patients compared to HCs.Defecation frequency was positively associated with CA(r=0.294,P=0.030)and CDCA(r=0.290,P=0.032)and negatively associated with DCA(r=−0.332,P=0.013)and LCA(r=−0.326,P=0.015)in IBS-D patients.In total,23 of 55 IBS-D patients and 15 of 28 HCs participated in the visceral sensitivity test.The first sensation threshold was negatively correlated with CDCA(r=−0.459,P=0.028)in IBS-D patients.Furthermore,the relative abundance of the family Ruminococcaceae was significantly decreased in IBS-D patients(P<0.001),and 12 genera were significantly lower in IBS-D patients than in HCs(P<0.05),with 6 belonging to Ruminococcaceae.Eleven of these genera were negatively correlated with primary BAs and positively correlated with secondary BAs in all subjects.CONCLUSION The altered metabolism of BAs in the gut of IBS-D patients was associated with diarrhea and visceral hypersensitivity and might be ascribed to dysbiosis,especially the reduction of genera in Ruminococcaceae.

Bladder-colon chronic cross-sensitization involves neuro-glial pathways in male mice

BACKGROUND Irritable bowel syndrome and bladder pain syndrome often overlap and are both characterized by visceral hypersensitivity.Since pelvic organs share common sensory pathways,it is likely that those syndromes involve a cross-sensitization of the bladder and the colon.The precise pathophysiology remains poorly understood.AIM To develop a model of chronic bladder-colon cross-sensitization and to investigate the mechanisms involved.METHODS Chronic cross-organ visceral sensitization was obtained in C57BL/6 mice using ultrasound-guided intravesical injections of acetic acid under brief isoflurane anesthesia.Colorectal sensitivity was assessed in conscious mice by measuring intracolonic pressure during isobaric colorectal distensions.Myeloperoxidase,used as a marker of colorectal inflammation,was measured in the colon,and colorectal permeability was measured using chambers.c-Fos protein expression,used as a marker of neuronal activation,was assessed in the spinal cord(L6-S1 level)using immunohistochemistry.Green fluorescent protein on the fractalkine receptor-positive mice were used to identify and count microglia cells in the L6-S1 dorsal horn of the spinal cord.The expression of NK1 receptors and MAPK-p38 were quantified in the spinal cord using western blot.RESULTS Visceral hypersensitivity to colorectal distension was observed after the intravesical injection of acetic acid vs saline(P<0.0001).This effect started 1 h post-injection and lasted up to 7 d postinjection.No increased permeability or inflammation was shown in the bladder or colon 7 d postinjection.Visceral hypersensitivity was associated with the increased expression of c-Fos protein in the spinal cord(P<0.0001).In green fluorescent protein on the fractalkine receptor-positive mice,intravesical acetic acid injection resulted in an increased number of microglia cells in the L6-S1 dorsal horn of the spinal cord(P<0.0001).NK1 receptor and MAPK-p38 levels were increased in the spinal cord up to 7 d after injection(P=0.007 and 0.023 respectively).Colorectal sensitization was prevented by intrathecal or intracerebroventricular injections of minocycline,a microglia inhibitor,by intracerebroventricular injection of CP-99994 dihydrochloride,a NK1 antagonist,and by intracerebroventricular injection of SB203580,a MAPK-p38 inhibitor.CONCLUSION We describe a new model of cross-organ visceral sensitization between the bladder and the colon in mice.Intravesical injections of acetic acid induced a long-lasting colorectal hypersensitivity to distension,mediated by neuroglial interactions,MAPK-p38 phosphorylation and the NK1 receptor.

FOS EXPRESSION IN LUMBARSACRAL SPINAL CORD AND MEDULLA OBLONGATA INDUCED BY CHRONIC COLONIC INFLAMMATION IN RATS

Objective To investigate Fos expression in rat lumbarsacral spinal cord and medulla oblongata induced by chronic colonic inflammation. Methods Thirty-three male Sprague-Dawley rats were randomly divided into two groups: experimental group: colonic inflammation was induced in seventeen rats by intraluminal administration of trinitrobenzenesulfonic acid (TNBS); control group: saline was administered intraluminally in sixteen rats; After 3, 7, 14 and 28 days of administration, lumbarsacral spinal cord and medulla oblongata were removed and processed for Fos immunohistochemistry. Results Fos-immunoreactive (Fos-IR) neurons induced by TNBS administration were primarily distributed in deep laminae (laminae Ⅲ-Ⅳ,Ⅴ-Ⅵ) in the spinal dorsal horn and in medullary visceral zone (MVZ) in the medulla oblongata. The number of Fos-IR cells in the spinal cord and MVZ in rats after 7 and 14 days of TNBS administration were significantly higher than that in the control rats (P<0.05). After 28 days of TNBS instillation, the number of Fos-IR neurons in MVZ decreased and became comparable to the control group. However, the number of Fos cells in the spinal cord in some rats were still significantly increased compared with the control rats (P<0.05). Conclusion Fos-IR neurons after colonic inflammation recovery may play an important role in the development of visceral hypersensitivity. Medulla oblongata was a less important structure than the spinal cord in inducing visceral hypersensitivity after chronic colonic inflammation.

Adult Stress Promotes Purinergic Signaling to Induce Visceral Pain in Rats with Neonatal Maternal Deprivation

Chronic visceral pain is one of the primary symptoms of patients with irritable bowel syndrome(IBS),which affects up to 15%of the population world-wide.The detailed mechanisms of visceral pain remain largely unclear.Our previous studies have shown that neonatal maternal deprivation(NMD)followed by adult multiple stress(AMS)advances the occurrence of visceral pain,likely due to enhanced norepinephrine(NE)-β2 adrenergic signaling.This study was designed to explore the roles of P2X3 receptors(P2X3Rs)in the chronic visceral pain induced by combined stress.Here,we showed that P2X3 Rs were co-expressed inβ2 adrenergic receptor(β2-AR)-positive dorsal root ganglion neurons and that NE significantly enhanced ATP-induced Ca2+signals.NMD and AMS not only significantly increased the protein expression of P2X3Rs,but also greatly enhanced the ATP-evoked current density,number of action potentials,and intracellular Ca2+concentration of colon-related DRG neurons.Intrathecal injection of the P2X3R inhibitor A317491 greatly attenuated the visceral pain and the ATP-induced Ca2+signals in NMD and AMS rats.Furthermore,theβ2-AR antagonist butoxamine significantly reversed the expression of P2X3Rs,the ATP-induced current density,and the number of action potentials of DRG neurons.Overall,our data demonstrate that NMD followed by AMS leads to P2X3R activation,which is most likely mediated by upregulation ofβ2 adrenergic signaling in primary sensory neurons,thus contributing to visceral hypersensitivity.