Imeglimin prevents visceral hypersensitivity and colonic hyperpermeability in irritable bowel syndrome rat model.

Visceral hypersensitivity and leaky gut, which are mediated via corticotropin-releasing factor (CRF) and Toll-like receptor 4 are key pathophysiology of irritable bowel syndrome (IBS). Metformin was reported to improve these gastrointestinal (GI) changes. In this study, we attempted to determine the effects of imeglimin, which was synthesized from metformin on GI function in IBS rat models. Imeglimin blocked lipopolysaccharide- or CRF-induced visceral hypersensitivity and colonic hyperpermeability. These effects were prevented by compound C or naloxone. These results suggest that imeglimin may be effective for the treatment of IBS by improved visceral sensation and colonic barrier via AMPK and opioid receptor.

EMA401, an angiotensin II type 2 receptor antagonist blocks visceral hypersensitivity and colonic hyperpermeability in rat model of irritable bowel syndrome.

Visceral hypersensitivity and impaired gut barrier are crucial pathophysiology of irritable bowel syndrome (IBS), and injection of lipopolysaccharide or corticotropin-releasing factor, and repeated water avoidance stress simulate these gastrointestinal changes in rat (IBS models). We previously demonstrated that losartan, an angiotensin II type 1 (AT1) receptor antagonist prevented these changes, and we attempted to determine the effects of EMA401, an AT2 receptor antagonist in the current study. EMA401 blocked visceral hypersensitivity and colonic hyperpermeability in these models, and naloxone reversed the effects by EMA401. These results suggest that EMA401 may improve gut function via opioid signaling in IBS.

Pioglitazone improves visceral sensation and colonic permeability in a rat model of irritable bowel syndrome.

Visceral hypersensitivity and impaired gut barrier with minor inflammation are considered to play an important role in the pathophysiology of irritable bowel syndrome (IBS). Since pioglitazone is known to have anti-inflammatory property, we hypothesized that pioglitazone is beneficial for treating IBS. In this study, the effect was tested in rat IBS models such as lipopolysaccharide or repeated water avoidance stress-induced visceral allodynia and increased colonic permeability. Pioglitazone blocked these visceral changes, and GW9662, a peroxisome proliferator-activated receptor gamma (PPAR-γ) antagonist fully reversed the effect by pioglitazone. These results suggest that PPAR-γ activation by pioglitazone may be useful for IBS treatment.

Metformin inhibits visceral allodynia and increased gut permeability induced by stress in rats.

BACKGROUND AND AIM: Metformin has been shown to have anti-cytokine property. Lipopolysaccharide (LPS)-induced or repeated water avoidance stress (WAS)-induced visceral allodynia and increased gut permeability were pro-inflammatory cytokine-dependent responses, which were considered to be animal models of irritable bowel syndrome (IBS). We hypothesized that metformin improves symptoms in the patients with IBS by attenuating these visceral changes and tested the hypothesis in rats. METHODS: The threshold of the visceromotor response induced by colonic balloon distention was measured. Colonic permeability was determined in vivo by quantifying the absorbed Evans blue for 15 min spectrophotometrically. RESULTS: Subcutaneously injected LPS (1 mg/kg) reduced the threshold of visceromotor response, and metformin (5-50 mg/kg for 3 days) intraperitoneally attenuated this response in a dose-dependent manner. Repeated WAS (1 h daily for 3 days) induced visceral allodynia, which was also blocked by metformin. The antinociceptive effect of metformin on the LPS-induced allodynia was reversed by compound C, an adenosine monophosphate-activated protein kinase inhibitor or NG -nitro-L-arginine methyl ester, a nitric oxide synthesis inhibitor but not modified by naloxone. Additionally, it was blocked by sulpiride, a dopamine D2 receptor antagonist, but domperidone, a peripheral dopamine D2 receptor antagonist, did not alter it. Metformin also blocked the LPS-induced or repeated WAS-induced increased colonic permeability. CONCLUSIONS: Metformin attenuated the visceral allodynia and increased gut permeability in animal IBS models. These actions may be evoked via activation of adenosine monophosphate-activated protein kinase, nitric oxide, and central dopamine D2 pathways. These results indicate the possibility that metformin can be useful for treating IBS.

Glucagon-like peptide-1 analog, liraglutide, improves visceral sensation and gut permeability in rats.

BACKGROUND AND AIM: A glucagon-like peptide-1 analog, liraglutide, has been reported to block inflammatory somatic pain. We hypothesized that liraglutide attenuates lipopolysaccharide (LPS)-induced and repeated water avoidance stress (WAS)-induced visceral hypersensitivity and tested the hypothesis in rats. METHODS: The threshold of the visceromotor response induced by colonic balloon distention was measured to assess visceral sensation. Colonic permeability was determined in vivo by quantifying the absorbed Evans blue spectrophotometrically, which was instilled in the proximal colon for 15 min. The interleukin-6 level in colonic mucosa was also quantified using ELISA. RESULTS: Subcutaneously injected LPS (1 mg/kg) reduced the visceromotor response threshold after 3 h. Liraglutide (300 µg/kg subcutaneously) at 15 h and 30 min before injecting LPS eliminated LPS-induced allodynia. It also blocked the allodynia induced by repeated water avoidance stress for 1 h for three consecutive days. Neither vagotomy nor naloxone altered the antinociceptive effect of liraglutide, but NG -nitro-L-arginine methyl ester, a nitric oxide synthesis inhibitor, blocked it. LPS increased colonic permeability and the interleukin-6 level, and the analog significantly inhibited these responses. CONCLUSIONS: This study suggests that liraglutide blocked LPS-induced visceral allodynia, which may be a nitric oxide-dependent response, and was probably mediated by inhibiting pro-inflammatory cytokine production and attenuating the increased gut permeability. Because the LPS-cytokine system is considered to contribute to altered visceral sensation in irritable bowel syndrome, these results indicate the possibility that liraglutide can be useful for treating this disease.

Repeated water avoidance stress induces visceral hypersensitivity: Role of interleukin-1, interleukin-6, and peripheral corticotropin-releasing factor.

BACKGROUND AND AIM: Repeated water avoidance stress (WAS) induces visceral hypersensitivity. Additionally, it is also known to activate corticotropin-releasing factor (CRF), mast cells, and pro-inflammatory cytokines systems, but their precise roles on visceral sensation have not been determined definitely. The aim of the study was to explore this issue. METHODS: Abdominal muscle contractions induced by colonic balloon distention, that is, visceromotor response (VMR) was detected electrophysiologically in conscious rats. WAS or sham stress as control for 1 h daily was loaded, and the threshold of VMR was determined before and at 24 h after the stress. RESULTS: Repeated WAS for three consecutive days reduced the threshold of VMR, but sham stress did not induce any change. Astressin, a CRF receptor antagonist (50 µg/kg) intraperitoneally (ip) at 10 min before each WAS session, prevented the visceral allodynia, but the antagonist (200 µg/kg) ip at 30 min and 15 h before measurement of the threshold after completing 3-day stress session did not modify the response. Ketotifen, a mast cell stabilizer (3 mg/kg), anakinra, an interleukin (IL)-1 receptor antagonist (20 mg/kg) or IL-6 antibody (16.6 µg/kg) ip for two times before the measurement abolished the response. CONCLUSIONS: Repeated WAS for three consecutive days induced visceral allodynia, which was mediated through mast cells, IL-1, and IL-6 pathways. Inhibition of peripheral CRF signaling prevented but did not reverse this response, suggesting that peripheral CRF may be an essential trigger but may not contribute to the maintenance of repeated WAS-induced visceral allodynia.

Levodopa acts centrally to induce an antinociceptive action against colonic distension through activation of D2 dopamine receptors and the orexinergic system in the brain in conscious rats.

Levodopa possesses antinociceptive actions against several somatic pain conditions. However, we do not know at this moment whether levodopa is also effective to visceral pain. The present study was therefore performed to clarify whether levodopa is effective to visceral pain and its mechanisms. Visceral sensation was evaluated by colonic distension-induced abdominal withdrawal reflex (AWR) in conscious rats. Subcutaneously (80 mg/rat) or intracisternally (2.5 µg/rat) administered levodopa significantly increased the threshold of colonic distension-induced AWR in conscious rats. The dose difference to induce the antinociceptive action suggests levodopa acts centrally to exert its antinociceptive action against colonic distension. While neither sulpiride, a D2 dopamine receptor antagonist, nor SCH23390, a D1 dopamine receptor antagonist by itself changed the threshold of colonic distension-induced AWR, the intracisternally injected levodopa-induced antinociceptive action was significantly blocked by pretreatment with subcutaneously administered sulpiride but not SCH23390. Treatment with intracisternal SB334867, an orexin 1 receptor antagonist, significantly blocked the subcutaneously administered levodopa-induced antinociceptive action. These results suggest that levodopa acts centrally to induce an antinociceptive action against colonic distension through activation of D2 dopamine receptors and the orexinergic system in the brain.

Tranilast alleviates visceral hypersensitivity and colonic hyperpermeability by suppressing NLRP3 inflammasome activation in irritable bowel syndrome rat models.

Visceral hypersensitivity resulting from compromised gut barrier with activated immune system is a key feature of irritable bowel syndrome (IBS). Corticotropin-releasing factor (CRF) and Toll-like receptor 4 (TLR4) activate proinflammatory cytokine signaling to induce these changes, which is one of the mechanisms of IBS. As activation of the NLRP3 inflammasome by lipopolysaccharide (LPS) or TLR4 leads to release interleukin (IL)-1ß, the NLRP3 inflammasome may be involved in the pathophysiology of IBS. Tranilast, an anti-allergic drug has been demonstrated to inhibit the NLRP3 inflammasome, and we evaluated the impact of tranilast on visceral hypersensitivity and colonic hyperpermeability induced by LPS or CRF (IBS rat model). Visceral pain threshold caused by colonic balloon distention was measured by monitoring abdominal muscle contractions electrophysiologically. Colonic permeability was determined by quantifying the absorbed Evans blue within the colonic tissue. Colonic protein levels of NLRP3 and IL-1ß were assessed by immunoblot or ELISA. Intragastric administration of tranilast (20-200 mg/kg) for 3 days inhibited LPS (1 mg/kg)-induced visceral hypersensitivity and colonic hyperpermeability in a dose-dependent manner. Simultaneously, tranilast also abolished these alterations induced by CRF (50 µg/kg). LPS increased colonic protein levels of NLRP3 and IL-1ß, and tranilast inhibited these changes. ß-hydroxy butyrate, an NLRP3 inhibitor, also abolished visceral hypersensitivity and colonic hyperpermeability caused by LPS. In contrast, IL-1ß induced similar GI alterations to LPS, which were not modified by tranilast. In conclusion, tranilast improved visceral pain and colonic barrier by suppression of the NLRP3 inflammasome in IBS rat models. Tranilast may be useful for IBS treating.

Brain histamine improves colonic hyperpermeability through the basal forebrain cholinergic neurons, adenosine A2B receptors and vagus nerve in rats.

Intestinal barrier dysfunction, leaky gut, is implicated in various diseases, including irritable bowel syndrome (IBS) and neurodegenerative conditions like Alzheimer's disease. Our recent investigation revealed that basal forebrain cholinergic neurons (BFCNs), critical for cognitive function, receive signals from butyrate and orexin, playing a role in regulating intestinal barrier function through adenosine A2B signaling and the vagus. This study explores the involvement and function of brain histamine, linked to BFCNs, in the regulation of intestinal barrier function. Colonic permeability, assessed by quantifying absorbed Evans blue in rat colonic tissue, showed that histamine did not affect increased colonic permeability induced by LPS when administered subcutaneously. However, intracisternal histamine administration improved colonic hyperpermeability. Elevating endogenous histamine levels in the brain with SKF91488, a histamine N-methyltransferase inhibitor, also improved colonic hyperpermeability. This effect was abolished by intracisternal chlorpheniramine, an histamine H1 receptor antagonist, not ranitidine, an H2 receptor antagonist. The SKF91488-induced improvement in colonic hyperpermeability was blocked by vagotomy, intracisternal pirenzepine (suppressing BFCNs activity), or alloxazine (an adenosine A2B receptor antagonist). Additionally, intracisternal chlorpheniramine injection eliminated butyrate-induced improvement in colonic hyperpermeability. These findings suggest that brain histamine, acting via the histamine H1 receptor, regulates intestinal barrier function involving BFCNs, adenosine A2B signaling, and the vagus. Brain histamine appears to centrally regulate intestinal barrier function influenced by butyrate, differentiating its actions from peripheral histamine in conditions like IBS, where mast cell-derived histamine induces leaky gut. Brain histamine emerges as a potential pharmacological target for diseases associated with leaky gut, such as dementia and IBS.

Phlorizin attenuates postoperative gastric ileus in rats.

BACKGROUND: Postoperative ileus (POI) is a major complication of abdominal surgery (AS). Impaired gut barrier mediated via Toll-like receptor 4 (TLR4) and interleukin-1 (IL-1) receptor is involved in the development of POI. Phlorizin is a nonselective inhibitor of sodium-linked glucose transporters (SGLTs) and is known to improve lipopolysaccharide (LPS)-induced impaired gut barrier. This study aimed to clarify our hypothesis that AS-induced gastric ileus is mediated via TLR4 and IL-1 signaling, and phlorizin improves the ileus. METHODS: AS consisted of a celiotomy and manipulation of the cecum for 1 min. Gastric emptying (GE) in 20 min with liquid meal was determined 3 h after the surgery in rats. The effect of subcutaneous (s.c.) injection of LPS (1 mg kg-1 ) was also determined 3 h postinjection. KEY RESULTS: AS delayed GE, which was blocked by TAK-242, an inhibitor of TLR4 signaling and anakinra, an IL-1 receptor antagonist. LPS delayed GE, which was also mediated via TLR4 and IL-1 receptor. Phlorizin (80 mg kg-1 , s.c.) significantly improved delayed GE induced by both AS and LPS. However, intragastrical (i.g.) administration of phlorizin did not alter it. As gut mainly expresses SGLT1, SGLT2 may not be inhibited by i.g. phlorizin. The effect of phlorizin was blocked by ghrelin receptor antagonist in the LPS model. CONCLUSIONS & INFERENCES: AS-induced gastric ileus is mediated via TLR4 and IL-1 signaling, which is simulated by LPS. Phlorizin improves the gastric ileus via activation of ghrelin signaling, possibly by inhibition of SGLT2. Phlorizin may be useful for the treatment of POI.

Peripheral apelin mediates visceral hypersensitivity and impaired gut barrier in a rat irritable bowel syndrome model.

Growing evidence indicates that visceral hypersensitivity and impaired gut barrier play an important role in the pathophysiology of irritable bowel syndrome (IBS). In animal models, these changes are known to be mediated via corticotropin-releasing factor (CRF)-Toll like receptor 4 (TLR4)-proinflammatory cytokine signaling. Apelin, an endogenous ligand of APJ, was reported to modulate CRF-induced enhanced colonic motility. In this context, we hypothesized that apelin also modulates visceral sensation and gut barrier, and tested this hypothesis. We measured visceral pain threshold in response to colonic balloon distention by abdominal muscle contractions assessed by electromyogram in rats. Colonic permeability was estimated by quantifying the absorbed Evans blue in colonic tissue. Intraperitoneal (ip) administration of [Ala13]-apelin-13, an APJ antagonist, blocked lipopolysaccharide (LPS)- or CRF-induced visceral hypersensitivity and colonic hyperpermeability (IBS model) in a dose-response manner. These inhibitory effects were blocked by compound C, an AMPK inhibitor, NG-nitro-L-arginine methyl ester, a nitric oxide (NO) synthesis inhibitor or naloxone in the LPS model. On the other hand, ip [Pyr1]-apelin-13, an APJ agonist, caused visceral hypersensitivity and colonic hyperpermeability, and these effects were reversed by astressin, a CRF receptor antagonist, TAK-242, a TLR4 antagonist or anakinra, an interleukin-1 receptor antagonist. APJ system modulated CRF-TLR4-proinflammatory cytokine signaling to cause visceral hypersensitivity and colonic hyperpermeability. APJ antagonist blocked these GI changes in IBS models, which were mediated via AMPK, NO and opioid signaling. Apelin may contribute to the IBS pathophysiology, and the inhibition of apelinergic signaling may be a promising therapeutic option for IBS.

Activation of basal forebrain cholinergic neurons improves colonic hyperpermeability through the vagus nerve and adenosine A2B receptors in rats.

Intestinal barrier dysfunction, a leaky gut, contributes to the pathophysiology of various diseases such as dementia and irritable bowel syndrome (IBS). We recently clarified that orexin, ghrelin, or adenosine A2B signaling in the brain improved leaky gut through the vagus nerve. The present study was performed to clarify whether basal forebrain cholinergic neurons (BFCNs) are implicated in the central regulation of intestinal barrier function. We activated BFCNs using benzyl quinolone carboxylic acid (BQCA), a positive muscarinic M1 allosteric modulator, and evaluated colonic permeability by quantifying the absorbed Evans blue in rat colonic tissue. Intracisternal (not intraperitoneal) injection of BQCA blocked the increased colonic permeability in response to lipopolysaccharide. Vagotomy blocked BQCA-induced improvement of colonic hyperpermeability. Intracisternally administered pirenzepine, a muscarinic M1 selective antagonist, prevented intestinal barrier function improvement by intravenously administered 2-deoxy-d-glucose, central vagal stimulant. Adenosine A2B receptor antagonist but not dopamine or opioid receptor antagonist prevented BQCA-induced blockade of colonic hyperpermeability. Additionally, intracisternal injection of pirenzepine blocked orexin- or butyrate-induced intestinal barrier function improvement. These results suggest that BFCNs improve leaky gut through adenosine A2B signaling and the vagal pathway. Furthermore, BFCNs mediate orexin- or butyrate-induced intestinal barrier function improvement. Since BFCNs play a role in cognitive function and a leaky gut is associated with dementia, the present finding may lead us to speculate that BFCNs are involved in the development of dementia by regulating intestinal barrier function.

Phlorizin attenuates visceral hypersensitivity and colonic hyperpermeability in a rat model of irritable bowel syndrome.

Visceral hypersensitivity and impaired gut barrier are crucial contributors to the pathophysiology of irritable bowel syndrome (IBS), and those are mediated via corticotropin-releasing factor (CRF)-Toll like receptor 4-pro-inflammatory cytokine signaling. Phlorizin is an inhibitor of sodium-linked glucose transporters (SGLTs), and known to have anti-cytokine properties. Thus, we hypothesized that phlorizin may improve these gastrointestinal changes in IBS, and tested this hypothesis in rat IBS models, i.e., lipopolysaccharide (LPS) or CRF-induced visceral hypersensitivity and colonic hyperpermeability. The visceral pain threshold in response to colonic balloon distention was estimated by abdominal muscle contractions by electromyogram, and colonic permeability was measured by quantifying the absorbed Evans blue in colonic tissue. Subcutaneous (s.c.) injection of phlorizin inhibited visceral hypersensitivity and colonic hyperpermeability induced by LPS in a dose-dependent manner. Phlorizin also blocked CRF-induced these gastrointestinal changes. Phlorizin is known to inhibit both SGLT1 and SGLT2, but intragastric administration of phlorizin may only inhibit SGLT1 because gut mainly expresses SGLT1. We found that intragastric phlorizin did not display any effects, but ipragliflozin, an orally active and selective SGLT2 inhibitor improved the gastrointestinal changes in the LPS model. Compound C, an adenosine monophosphate-activated protein kinase (AMPK) inhibitor, NG-nitro-L-arginine methyl ester, a nitric oxide (NO) synthesis inhibitor and naloxone, an opioid receptor antagonist reversed the effects of phlorizin. In conclusions, phlorizin improved visceral hypersensitivity and colonic hyperpermeability in IBS models. These effects may result from inhibition of SGLT2, and were mediated via AMPK, NO and opioid pathways. Phlorizin may be effective for the treatment of IBS.

Imipramine improves visceral sensation and gut barrier in rat models of irritable bowel syndrome.

An impaired gut barrier, possibly leading to visceral hypersensitivity has been recently recognized to be one of the pivotal pathophysiology of irritable bowel syndrome (IBS). We previously showed that lipopolysaccharide (LPS), corticotropin-releasing factor (CRF), and repeated water avoidance stress (WAS) induce visceral hypersensitivity and colonic hyperpermeability via pro-inflammatory cytokine signaling (rat IBS models). Although the precise mechanisms of action are unclear, imipramine, a tricyclic antidepressant, improves IBS symptoms, and also has anticytokine properties. In this study, we hypothesized that imipramine improves the gut barrier to ameliorate IBS symptoms. To test this hypothesis, we determined its effects on visceral hypersensitivity and colonic hyperpermeability in rat IBS models. The visceral pain threshold in response to colonic balloon distention was electrophysiologically estimated by abdominal muscle contractions, and colonic permeability was measured by quantifying the absorbed Evans blue in colonic tissue in vivo. Subcutaneous imipramine injection (7, 20, 50 mg/kg) dose-dependently inhibited LPS-induced (1 mg/kg, subcutaneously) visceral hypersensitivity and colonic hyperpermeability. Imipramine also blocked these gastrointestinal (GI) changes induced by CRF (50 µg/kg, intraperitoneally) or repeated WAS (1 h daily for 3 days). Yohimbine (an α2-adrenoceptors antagonist), sulpiride (a dopamine D2 receptor antagonist), and naloxone hydrochloride (an opioid receptor antagonist) reversed these effects of imipramine in the LPS model. Therefore, imipramine may block GI changes in IBS via α2-adrenoceptors, dopamine D2, and opioid signaling. The improvement in the gut barrier resulting in inhibition of visceral pain is considered a valid mechanism of imipramine to ameliorate IBS symptoms.

Losartan improves visceral sensation and gut barrier in a rat model of irritable bowel syndrome.

BACKGROUND: Lipopolysaccharide (LPS) or repeated water avoidance stress (WAS) induces visceral allodynia and colonic hyperpermeability via corticotropin-releasing factor (CRF) and proinflammatory cytokines, which is considered to be a rat irritable bowel syndrome (IBS) model. As losartan is known to inhibit proinflammatory cytokine release, we hypothesized that it improves these visceral changes. METHODS: The threshold of visceromotor response (VMR), that is, abdominal muscle contractions induced by colonic balloon distention was electrophysiologically measured in rats. Colonic permeability was determined in vivo by quantifying the absorbed Evans blue in colonic tissue for 15 minutes spectrophotometrically. KEY RESULTS: Lipopolysaccharide (1 mg kg-1 ) subcutaneously (s.c.) reduced the threshold of VMR and increased colonic permeability. Losartan (5-25 mg kg-1  s.c.) for 3 days inhibited these changes in a dose-dependent manner. Moreover, repeated WAS (1 hour daily for 3 days) or intraperitoneal injection of CRF (50 µg kg-1 ) induced the similar visceral changes as LPS, which were also eliminated by losartan. These effects by losartan in LPS model were reversed by GW9662 (a peroxisome proliferator-activated receptor-γ [PPAR-γ] antagonist), NG -nitro-L-arginine methyl ester (a nitric oxide [NO] synthesis inhibitor), or naloxone (an opioid receptor antagonist). Moreover, it also inhibited by sulpiride (a dopamine D2 receptor antagonist) or domperidone (a peripheral dopamine D2 antagonist). CONCLUSION & INFERENCES: Losartan prevented visceral allodynia and colonic hyperpermeability in rat IBS models. These actions may be PPAR-γ-dependent and also mediated by the NO, opioid, and dopamine D2 pathways. Losartan may be useful for IBS treatment.

Dehydroepiandrosterone sulfate improves visceral sensation and gut barrier in a rat model of irritable bowel syndrome.

Stress-induced altered visceral sensation and impaired gut barrier play an important role in the pathophysiology of irritable bowel syndrome (IBS). These responses were demonstrated to be peripheral corticotropin-releasing factor (CRF) dependent and also mediated via proinflammatory cytokine in animal IBS model. Dehydroepiandrosterone sulfate (DHEA-S) is known to have anti-inflammatory properties by suppressing proinflammatory cytokine release. We hypothesized that DHEA-S improves stress-induced visceral changes and is beneficial for IBS treatment. We explored the effects of DHEA-S on lipopolysaccharide (LPS)- or repeated water avoidance stress (WAS)-induced visceral allodynia and increased colonic permeability (rat IBS models). The threshold of visceromotor response, i.e. abdominal muscle contractions induced by colonic balloon distention was electrophysiologically measured. Colonic permeability was estimated in vivo by quantifying the absorbed Evans blue in colonic tissue. DHEA-S abolished visceral allodynia and colonic hyperpermeability induced by LPS in a dose-dependent manner. It also blocked repeated WAS- or peripheral injection of CRF-induced visceral changes. These effects by DHEA-S in LPS model were reversed by bicuculline, a γ-aminobutyric acid (GABA)A receptor antagonist, NG-nitro-L-arginine methyl ester, a nitric oxide (NO) synthesis inhibitor, naloxone, an opioid receptor antagonist, or sulpiride, a dopamine D2 receptor antagonist. However, domperidone, a peripheral dopamine D2 receptor antagonist did not modify the effects. Peripheral injection of astressin2-B, a selective CRF receptor subtype 2 (CRF2) antagonist also reversed these effects. In conclusion, DHEA-S blocked stress-induced visceral changes via GABAA, NO, opioid, central dopamine D2 and peripheral CRF2 signaling. DHEA-S may be useful for IBS treating.

Butyrate inhibits visceral allodynia and colonic hyperpermeability in rat models of irritable bowel syndrome.

Lipopolysaccharide (LPS) or repeated water avoidance stress (WAS) induces visceral allodynia and gut hyperpermeability via corticotropin-releasing factor (CRF) and proinflammatory cytokines, which is a rat irritable bowel syndrome (IBS) model. As butyrate is known to suppress the release of proinflammatory cytokine, we hypothesized that butyrate alleviates these colonic changes in IBS models. The visceral pain was assessed by electrophysiologically measuring the threshold of abdominal muscle contractions in response to colonic distention. Colonic permeability was determined by measuring the absorbance of Evans blue in colonic tissue. Colonic instillation of sodium butyrate (SB; 0.37-2.9 mg/kg) for 3 days inhibited LPS (1 mg/kg)-induced visceral allodynia and colonic hyperpermeability dose-dependently. Additionally, the visceral changes induced by repeated WAS (1 h for 3 days) or CRF (50 µg/kg) were also blocked by SB. These effects of SB in the LPS model were eliminated by compound C, an AMPK inhibitor, or GW9662, a PPAR-γ antagonist, NG-nitro-L-arginine methyl ester, a NO synthesis inhibitor, naloxone or sulpiride. SB attenuated visceral allodynia and colonic hyperpermeability in animal IBS models. These actions may be AMPK and PPAR-γ dependent and also mediated by the NO, opioid and central dopamine D2 pathways. Butyrate may be effective for the treatment of IBS.

Grape Seed Extract Eliminates Visceral Allodynia and Colonic Hyperpermeability Induced by Repeated Water Avoidance Stress in Rats.

Grape seed extract (GSE) is rich in polyphenols composed mainly of proanthocyanidins, which are known to attenuate proinflammatory cytokine production. Repeated water avoidance stress (WAS) induces visceral allodynia and colonic hyperpermeability via toll-like receptor 4 (TLR4) and proinflammatory cytokine pathways, which is a rat irritable bowel syndrome (IBS) model. Thus, we explored the effects of GSE on repeated WAS (1 h for 3 days)-induced visceral allodynia and colonic hyperpermeability in Sprague-Dawley rats. Paracellular permeability, as evaluated by transepithelial electrical resistance and flux of carboxyfluorescein, was analyzed in Caco-2 cell monolayers treated with interleukin-6 (IL-6) and IL-1ß. WAS caused visceral allodynia and colonic hyperpermeability, and intragastric administration of GSE (100 mg/kg, once daily for 11 days) inhibited these changes. Furthermore, GSE also suppressed the elevated colonic levels of IL-6, TLR4, and claudin-2 caused by WAS. Paracellular permeability was increased in Caco-2 cell monolayers in the presence of IL-6 and IL-1ß, which was inhibited by GSE. Additionally, GSE suppressed the claudin-2 expression elevated by cytokine stimulation. The effects of GSE on visceral changes appear to be evoked by suppressing colonic TLR4-cytokine signaling and maintaining tight junction integrity. GSE may be useful for treating IBS.

Altered colonic sensory and barrier functions by CRF: roles of TLR4 and IL-1.

Visceral allodynia and increased colonic permeability are considered to be crucial pathophysiology of irritable bowel syndrome (IBS). Corticotropin-releasing factor (CRF) and immune-mediated mechanisms have been proposed to contribute to these changes in IBS, but the precise roles have not been determined. We explored these issues in rats in vivo. The threshold of visceromotor response, i.e., abdominal muscle contractions induced by colonic balloon distention was electrophysiologically measured. Colonic permeability was estimated by quantifying the absorbed Evans blue in colonic tissue. Intraperitoneal injection of CRF increased the permeability, which was blocked by astressin, a non-selective CRF receptor antagonist, but astressin2-B, a selective CRF receptor subtype 2 (CRF2) antagonist did not modify it. Urocortin 2, a selective CRF2 agonist inhibited the increased permeability by CRF. Eritoran, a toll-like receptor 4 (TLR4) antagonist or anakinra, an interleukin-1 receptor antagonist blocked the visceral allodynia and the increased gut permeability induced by CRF. Subcutaneous injection of lipopolysaccharide (immune stress) or repeated water avoidance stress (WAS, psychological stress), 1 h daily for 3 days induced visceral allodynia and increased gut permeability (animal IBS models), which were also blocked by astressin, eritoran or anakinra. In conclusion, stress-induced visceral allodynia and increased colonic permeability were mediated via peripheral CRF receptors. CRF induced these visceral changes via TLR4 and cytokine system, which were CRF1 dependent, and activation of CRF2 inhibited these CRF1-triggered responses. CRF may modulate immune system to alter visceral changes, which are considered to be pivotal pathophysiology of IBS.

Lovastatin inhibits visceral allodynia and increased colonic permeability induced by lipopolysaccharide or repeated water avoidance stress in rats.

Statins have been reported to block inflammatory somatic pain and have an anti-cytokine property. Lipopolysaccharide (LPS) or repeated water avoidance stress (WAS) induces visceral hypersensitivity and increases gut permeability in rats, which are mediated through proinflammatory cytokine-dependent pathways. Since visceral hypersensitivity with increased gut permeability plays a crucial role in the pathophysiology of irritable bowel syndrome (IBS), these above animal models are considered to simulate IBS. We hypothesized that lovastatin improves symptoms in the patients with IBS by attenuating these visceral changes. The threshold of visceromotor response (VMR) induced by colonic balloon distention was measured for the assessment of visceral sensation in rats. Colonic permeability was determined in vivo by quantifying the absorbed Evans blue in colonic tissue for 15min using a spectrophotometer. Subcutaneously (s.c.) injected LPS (1mg/kg) reduced the threshold of VMR after 3h. Pretreatment with lovastatin (20mg/kg s.c. daily for 3 days) abolished this response by LPS. Repeated WAS (1h daily for 3 days) induced visceral allodynia, which was also blocked by repeated injection of lovastatin before each stress session. The antinociceptive effect of lovastatin on the LPS-induced allodynia was reversed by mevalonolactone, NG-nitro-L-arginine methyl ester or naloxone. Lovastatin also blocked the LPS- or repeated WAS-induced increased gut permeability. These results indicate the possibility that lovastatin can be useful for treating IBS.