Change of nitric oxide in experimental colitis and its inhibition by melatonin in vivo and in vitro

Protective effect of Dulaglutide, a GLP1 agonist, on acetic acid-induced ulcerative colitis in rats: involvement of GLP-1, TFF-3, and TGF-β/PI3K/NF-κB signaling pathway

A chronic inflammatory condition of the colon called ulcerative colitis (UC) is characterized by mucosal surface irritation that extends from the rectum to the near proximal colon portions. The rationale of this work was to conclude if dulaglutide (Dula) could protect rats from developing colitis caused by exposure to acetic acid (AA). Rats were randomly divided into seven groups (each with eight rats): Normal control, Dula control, AA (received 2 milliliters of 3% v/v AA through the rectum), Sulfasalazine (SLZ); given SLZ (100 mg/kg) orally from day 11 to day 21 then AA intrarectally on day 22 and Dula groups ( pretreated with 50, 100 or 150 μg/kg subcutaneous injection of Dula - once weekly for three weeks and AA on day 22 to induce ulcerative colitis, colon tissues and blood samples were taken on day 23. By generating colonic histological deviations such as inflammatory processes, goblet cell death, glandular hyperplasia, and mucosa ulcers, Dula dropped AA-induced colitis. Additionally, these modifications diminished blood lactate dehydrogenase (LDH), C-reactive protein (CRP), colon weight, and the weight/length ratio of the colon. In addition, Dula decreased the oxidative stress biomarker malondialdehyde (MDA) and increased the antioxidant enzymes (total antioxidant capacity (TAC), reduced glutathione (GSH), and superoxide dismutase (SOD) concentrations). Dula also significantly reduced the expression of transforming growth factor-1 (TGF-β1), phosphatidylinositol-3-kinase (PI3K), protein kinase B (AKT) signaling pathway, and the inflammatory cytokines: nuclear factor kappa B (NF-κB), interleukin-6 (IL-6), and interferon-γ (IFN-γ) in colonic cellular structures. In addition, Dula enforced the levels of glucagon-like peptide-1 (GLP-1) and trefoil factor-3 (TFF-3) that were crucial to intestinal mucosa regeneration and healing of wounds. By modulating TGF-β1 in conjunction with other inflammatory pathways like PI3K/AKT and NF-κB, regulating the oxidant/antioxidant balance, and improving the integrity of the intestinal barrier, Dula prevented AA-induced colitis in rats.

Therapeutic applications of melatonin in disorders related to the gastrointestinal tract and control of appetite

Most animals have large amounts of the special substance melatonin, which is controlled by the light/dark cycle in the suprachiasmatic nucleus. According to what is now understood, the gastrointestinal tract (GIT) and other areas of the body are sites of melatonin production. According to recent studies, the GIT and adjacent organs depend critically on a massive amount of melatonin. Not unexpectedly, melatonin's many biological properties, such as its antioxidant, anti-inflammatory, pro-apoptotic, anti-proliferative, anti-metastasis, and antiangiogenic properties, have drawn the attention of researchers more and more. Because melatonin is an antioxidant, it produces a lot of secretions in the GIT's mucus and saliva, which shields cells from damage and promotes the development of certain GIT-related disorders. Melatonin's ability to alter cellular behavior in the GIT and other associated organs, such as the liver and pancreas, is another way that it functions. This behavior alters the secretory and metabolic activities of these cells. In this review, we attempted to shed fresh light on the many roles that melatonin plays in the various regions of the gastrointestinal tract by focusing on its activities for the first time.

Tiron ameliorates acetic acid-induced colitis in rats: Role of TGF-β/EGFR/PI3K/NF-κB signaling pathway

BACKGROUND

Ulcerative colitis (UC), an ongoing inflammatory disorder of the colon, is marked by persistent mucosal surface irritation extending from the rectum to the near-proximal colon. Tiron is a synthetic analogue of vitamin E which is known to have antioxidant and anti-inflammatory effects in various animal models, so the goal of this study was to find out whether Tiron had any preventive impacts on UC inflicted by acetic acid (A.A) exposure in rats.

METHOD

Tiron (235 and 470 mg/kg) was administered intra-peritoneally for 2 weeks, and A.A (2 ml, 3 % v/v) was injected intra-rectally to cause colitis. Colon tissues and blood samples were then collected for measurement of various inflammatory and oxidative stress biomarkers.

RESULTS

Tiron administration significantly diminished lactate dehydrogenase (LDH), C-reactive protein (CRP), colon weight, and the weight/length ratio of the colon as compared to A.A-injected rats. Additionally, Tiron attenuated oxidative stress biomarkers. Tiron also enforced the levels of Glucagon-like peptide-1 (GLP-1) and trefoil factor-3 (TFF-3), while it greatly lowered the expression of nuclear factor kappa B (NF-κB), interleukin-6 (IL-6), interferon-γ (IFN-γ), and transforming growth factor-1(TGF-β1), phosphorylated epidermal growth factor receptor (P-EGFR), phosphatidylinositol-3-kinase (PI3K) and protein kinase B (AKT) expression in colonic cellular structures. Furthermore, colonichistopathologic damages, revealed by hematoxylin and eosin (H&E) and Alcian Blue stain, were significantly decreased upon Tiron administration.

CONCLUSION

Tiron prevented A.A-induced colitis in rats via modulating inflammatory pathway TGF-β1/P-EGFR/PI3K/AKT/NF-κB, alongside managing the oxidant/antioxidant equilibrium, and boosting the reliability of the intestinal barrier.

Genistein and/or sulfasalazine ameliorate acetic acid-induced ulcerative colitis in rats via modulating INF-γ/JAK1/STAT1/IRF-1, TLR-4/NF-κB/IL-6, and JAK2/STAT3/COX-2 crosstalk

Ulcerative Colitis (UC) is a chronic idiopathic inflammatory bowel disease in which the colon's lining becomes inflamed. Exploring herbal remedies that can recover mucosal damage is becoming popular in UC. The study aims to investigate the probable colo-protective effect of a natural isoflavone, genistein (GEN), and/or a drug, sulfasalazine (SZ), against acetic acid (AA)-induced UC in rats, in addition to exploring the possible underlying mechanisms. UC was induced by the intrarectal installation of 1-2 ml of 5% diluted AA for 24 hours. Ulcerated rats were allocated into the disease group and three treated groups, with SZ (100 mg/kg), GEN (100 mg/kg), and their combination for 14 days, besides the control groups. The anti-colitic efficacy of GEN and/or SZ was evidenced by hindering the AA-induced weight loss, colon edema, and macroscopic scores, besides reduced disease activity index and weight/length ratio. Furthermore, treatments attenuated the colon histopathological injury scores, increased the number of goblet cells, and lessened fibrosis. Both treatments reduced the up-regulation of INF-γ/JAK1/STAT1 and INF-γ /TLR-4/ NF-κB signaling pathways and modulated the IRF-1/iNOS/NO and IL-6/JAK2/STAT3/COX-2 pathways and consequently, reduced the levels of TNF-α and IL-1β. Moreover, both treatments diminished oxidative stress, which appeared by reducing the MPO level and elevating the SOD activity, and hindered apoptosis; by decreasing the immunohistochemical expression of caspase-3. The current findings offer novel insights into the protective effects of GEN and suggest a superior benefit of combining GEN with SZ, over either drug alone, in the UC management.

Targeting SIRT1/FoxO3a/Nrf2 and PI3K/AKT Pathways with Rebamipide Attenuates Acetic Acid-Induced Colitis in Rats

Rebamipide is a quinolone derivative that has been commonly used for the treatment of gastric and duodenal ulcers. However, the molecular mechanisms of rebamipide against acetic acid-evoked colitis have not been adequately examined. Hence, the current study aimed to investigate the ameliorative effect of rebamipide in a rat model of acetic acid-evoked ulcerative colitis and the linked mechanisms pertaining to SIRT1/FoxO3a/Nrf2 and PI3K/AKT pathways. Herein, colitis was induced by the intrarectal administration of 3% acetic acid solution in saline (v/v) while rebamipide was administered by oral gavage (100 mg/kg/day) for seven days before the colonic insult. The colonic injury was examined by macroscopical and microscopical examination. The current findings demonstrated that rebamipide significantly improved the colonic injury by lowering the colonic disease activity index and macroscopic mucosal injury score. Moreover, it mitigated the histopathological aberrations and microscopical damage score. The favorable outcomes of rebamipide were driven by combating inflammation evidenced by dampening the colonic expression of NF-κBp65 and the pro-inflammatory markers CRP, TNF-α, and IL-6. In the same context, rebamipide curtailed the colonic pro-inflammatory PI3K/AKT pathway as seen by downregulating the immunostaining of PI3K and p-AKT(Ser473) signals. In tandem, rebamipide combated the colonic pro-oxidant events and augmented the antioxidant milieu by significantly diminishing the colonic TBARS and replenishing GSH, SOD, GST, GPx, and CAT. In the same regard, rebamipide stimulated the colonic upstream SIRT1/FoxO3a/Nrf2 axis by upregulating the expression of SIRT1, FoxO3a, and Nrf2, alongside downregulating Keap-1 gene expression. These antioxidant actions were accompanied by upregulation of the protein expression of the cytoprotective signal PPAR-γ in the colons of rats. In conclusion, the present findings suggest that the promising ameliorative features of rebamipide against experimental colitis were driven by combating the colonic inflammatory and oxidative responses. In perspective, augmentation of colonic SIRT1/FoxO3a/Nrf2 and inhibition of PI3K/AKT pathways were engaged in the observed favorable outcomes.

Icosapent ethyl alleviates acetic acid-induced ulcerative colitis via modulation of SIRT1 signaling pathway in rats

Ulcerative colitis (UC) is a global inflammatory bowel disease. This study aimed to assess the effects of icosapent ethyl on acetic acid-induced colitis in rats as well as the underlying mechanisms involved. 36 male Wister rats were equally divided into six groups: control, UC, mesalamine 100 mg/kg, icosapent 150mg/kg, icosapent 300 mg/kg, and EX527-icosapent 300 mg/kg groups. Except for control group, UC was induced by acetic acid instillation into colon. Drugs were administered once daily for one week then under thiopental anaesthesia, colons were excised. Colitis macroscopic and microscopic scores were assessed. A part of colon was homogenized for detection of malondialdehyde (MDA), inerleukin1 (IL-1β), tumor necrosis factor (TNF-α), superoxide dismutase (SOD), phosphorylated Akt (pAkt) and caspase 3 levels. Silent information regulator 1 (SIRT1), heme oxygenase 1 (HO-1), and nuclear factor erythroid 2 (Nrf2) mRNA expressions were detected. Mallory-stained colonic sections were examined for collagen fibres detection. Immunohistochemistry of NF-κB and p53 expressionsin colonic sections were assessed. Acetic acid induced colitis with increments in MDA, IL-1β, TNF-α, and caspase 3 levels while decreased SOD, pAkt, SIRT1, HO-1, and Nrf2 with increased collagen fibres as well as NF-κB and p53. Icosapent decreased macro& microscopic colitis scores, MDA, IL-1β, TNF-α, and caspase 3 levels while increased SOD, pAkt, SIRT1, HO-1, and Nrf2 with decreased collagen fibres as well as NF-κB and p53. The effects of icosapent 300 mg/kg were similar to mesalamine. Icosapent effects were antagonized by EX527. Icosapent alleviated acetic acid-induced colitis via its anti-inflammatory, antioxidant, and anti-apoptotic effects mediated in part by SIRT1 pathway activation.

Pre-clinical Investigation of Protective Effect of Nutraceutical D-Glucosamine on TNBS-induced Colitis

The level of precursors involved in the biosynthesis of glycosaminoglycan (GAG), glucosamine synthase, and N-acetyl glucosamine (NAG), are significantly reduced in inflammatory bowel disease (IBD). This results in deficient GAG content in mucosa, which eventually disrupts the gut wall integrity, provoking abnormal immunological responses. This is characterized by colossal liberation of inflammatory mediators including tumor necrosis factor-alpha (TNF-α), interleukins (IL), and reactive oxygen species provoking colonic inflammation. D-glucosamine (D-GLU) is reported to suppress oxidative stress, and pro-inflammatory cytokines and acts as a starting material for biosynthesis of NAG. The potential of D-GLU and its combination with mesalamine (5-ASA) was investigated in 2,4,6-trinitrobenzene sulfonic acid (TNBS)-instigated IBD in Wistar rats. Standard and test drugs were given orally for five days to separate groups of rats. Colonic inflammation was evaluated by disease activity score rate (DASR), colon/body weight ratio, colon length, diameter, colon pH, histological injury and score. Inflammatory biomarkers IL-1β, TNF-α, along with reduced glutathione (GSH), and malondialdehyde (MDA) were assessed. Combination of D-GLU +5-ASA significantly ameliorated severity of colonic inflammation by lowering DASR (P < 0.001) and colon/body weight ratio (P < 0.001), restored the colonic architecture and suppressed the histopathological score (P < 0.001), along with the absence of major adverse reactions. The combination suppressed the levels of inflammatory markers (P < 0.001) and MDA (P < 0.001) while enhancing GSH level (P < 0.001). In comparison to individual 5-ASA and D-GLU, combination of drugs significantly diminished colitis severity through their combined anti-inflammatory and antioxidant effects by acting on multiple targets simultaneously. The combination holds remarkable potential in the management of IBD.

Melatonin mediated inhibition of EZH2-NOS2 crosstalk attenuates inflammatory bowel disease in preclinical in vitro and in vivo models

AIMS

Inflammatory Bowel Disease is characterised by abdominal pain, diarrhoea, rectal bleeding and weight loss. Sometimes it may leads to severe health complications resulting in death of an individual. Current research efforts to highlight the role of melatonin in regulating EZH2, a master epigenetic regulator and its beneficiary effect in case of IBD management.

MATERIAL METHODS

Murine macrophages (RAW 264.7) were treated with lipopolysaccharides (LPS) to activate them for generating inflammatory response to investigate efficacy of melatonin in-vitro models. Similarly, for developing in vivo models, Dextran sodium sulphate (36-50 kDa) was used. Evaluations of anti-inflammatory activities were carried out by nitrite assay, western blotting, q-PCR, immunofluorescence, and histological studies.

KEY FINDINGS

Reduction of epigenetic target, EZH2 by melatonin significantly improves the clinical symptoms of dextran sodium sulphate induced colitis and may be implicated as a potential therapeutic target in IBD management. The present study evaluates the efficacy of melatonin by epigenetic regulation in IBD models. Down regulation of EZH2 by melatonin reduced the chemical induced inflammatory insults in in vitro and in vivo models. Exploration of molecular pathways has revealed interlink of EZH2 and NOS2, a hallmark of inflammation. Molecular mechanistic action of melatonin is attributed to inhibition of the expression and physical interaction of EZH2 and NOS2.

SIGNIFICANCE

Our study highlights melatonin therapeutic effect via attenuating interaction between EZH2 and NOS2 which is beneficial in managing IBD treatment.

Preventive empagliflozin activity on acute acetic acid-induced ulcerative colitis in rats via modulation of SIRT-1/PI3K/AKT pathway and improving colon barrier

BACKGROUND

Ulcerative colitis (UC) is a chronic colon inflammation that is linked to exposure to environmental factors leading to improper immune responses to enteric microbes in genetically susceptible individuals. This study was designed to explore the possible protective impact of Empagliflozin (EMPA), an anti-diabetic sodium-glucose cotransporter-2 (SGLT2) inhibitor, on acetic acid (AA)-induced UC in rats.

METHOD

Intrarectal instillation of AA (2 ml, 3% v/v) was used to induce UC. EMPA (10 & 30 mg/kg) was administered orally for 11 days.

RESULTS

EMPA successfully counteracted AA-induced UC that was manifested by improving colonic histopathological architecture concomitant with a marked decrease in disease activity index (DAI), colon weight, weight/length ratio, serum lactate dehydrogenase (LDH) activity, and C-reactive protein (CRP) level. Additionally, EMPA successfully restored the disrupted oxidant/antioxidants balance induced by AA. Moreover, EMPA significantly induced silent information regulator-1(SIRT-1) expression along with a significant reduction in phosphatidylinositol-3-Kinase (PI3K), Protein Kinase B (AKT), nuclear factor kappa B (NF-κB), tumor necrosis factor (TNF)-α and interleukins (IL-1β and IL-6) expression in colonic tissues. Furthermore, EMPA successfully improved the colonic barrier that was appeared from the marked induction of tight junction proteins level (occludin and claudin-1).

CONCLUSION

EMPA successfully counteracted AA-induced UC in rats via the modulation of SIRT1/PI3K/AKT/NF-κB inflammatory pathway, normalizing oxidant/antioxidants balance, and improving the integrity of colon barrier.

6,7-Dihydroxy-2,4-Dimethoxyphenanthrene from Chinese Yam Peels Alleviates DSS-Induced Intestinal Mucosal Injury in Mice via Modulation of the NF-κB/COX-2 Signaling Pathway

In this study, we evaluated the protective effect and molecular mechanism of a dominant phenanthrene, (6,7-dihydroxy-2,4-dimethoxyphenanthrene, CYP4), from Chinese yam peels on intestinal epithelial integrity. Three doses of Chinese yam phenolic extract (CYPE) and Chinese yam phenanthrene 4 (CYP4) were administered to BALB/c mice for 7 days before dextran sulfate sodium (DSS) treatment, with berberine hydrochloride as a positive control (PC). Results showed that both disease activity indexes (DAIs), histological damage score (HDS) and survival rate in DSS mice, were improved with preintervention of CYPE and CYP4, which exhibited better efficiency than PC. Further studies showed that administration of CYP4 downregulated the oxidative stress-associated factors, MPO and NO, and improved tight junction protein occludin. Besides, the CYP4 treatment substantially downregulated the caspase-3 expression and the apoptosis rate of intestinal epithelial cells. In addition, the CYP4 treatment ameliorated the production of inflammatory cytokines including TNF-α, IFN-γ, IL-10, and IL-23 in the colon. Furthermore, the protein expression of ERK1/2, NF-κB p65, pNF-κB, and COX-2 was suppressed in CYE4 groups as compared with that in model control (MC). These findings suggested that CHP4 could effectively inhibit the activation of NF-κB/COX-2 in an experimental UC model in vivo. It was demonstrated for the first time that CYPE and CYP4 protected intestinal mucosa from damage and prevented DSS-induced colitis in mice. CYP4 was one of the active principles obligatory for the biological effect of Chinese yam in protecting intestinal health. These findings indicated that CYP4 might be a promising and useful approach for treatment of UC in humans.

Cilostazol protects against acetic acid-induced colitis in rats: Possible role for cAMP/SIRT1 pathway

The phosphodiesterase-3 inhibitor, cilostazol has been recently shown to protect against chemically induced colitis in animal models. However, whether cyclic adenosine monophosphate (cAMP) contributes to the anti-inflammatory activity of cilostazol in colitis is still unknown. In the current study, we investigated the role of cAMP/silent information regulator-1 (SIRT-1) pathway in the protective effect of cilostazol using rat model of acetic acid-induced colitis. Upregulation of SIRT1 activity and expression has been recently shown to protect against chemically induced colitis. Our results demonstrated that cilostazol alleviated the histopathological changes associated with acetic acid-induced colitis. Interestingly, pre-administration of cilostazol increased cAMP concentration and SIRT1 expression in colonic mucosa to levels similar to that observed in control animals without induction of colitis. In addition, cilostazol inhibited the SIRT1 targets; NF-κB, Akt and MAPK inflammatory pathways as demonstrated by suppression of acetic acid-induced upregulation of NF-κB activity, p-AKT levels and the expression of p38 MAPK. NF-κB activity and the levels of p-AKT, tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β) were similar in rats pretreated with cilostazol prior to induction of colitis and the control rats without colitis. Furthermore, cilostazol reduced acetic acid-induced oxidative stress and apoptosis. In conclusion, the protective effect of cilostazol against acetic acid-induced colitis may be attributed to activation of SIRT1 expression by cAMP. SIRT1 is suggested to contribute to cilostazol-induced suppression of NF-κB, Akt and MAPK inflammatory pathways, oxidative stress and apoptosis.

Synbiotic supplementation with prebiotic green banana resistant starch and probiotic Bacillus coagulans spores ameliorates gut inflammation in mouse model of inflammatory bowel diseases

Purpose

The research goal is to develop dietary strategies to help address the growing incidence of inflammatory bowel diseases (IBD). This study has investigated the effectiveness of green banana resistant starch (GBRS) and probiotic Bacillus coagulans MTCC5856 spores for the amelioration of dextran-sulfate sodium (DSS)-induced colitis in mice.

Methods

Eight-week-old C57BL/6 mice were fed standard rodent chow diet supplemented with either B. coagulans, GBRS or its synbiotic combination. After 7 days supplementation, colitis was induced by adding 2% DSS in drinking water for 7 days while continuing the supplemented diets. Animal health was monitored and after 14 days all animals were sacrificed to measure the biochemical and histochemical changes associated with each supplement type.

Results

The disease activity index and histological damage score for DSS-control mice (6.1, 17.1, respectively) were significantly higher (p < 0.0001) than the healthy mice. Synbiotic supplementation alleviated these markers (− 67%, − 94% respectively) more adequately than B. coagulans (− 52%, − 58% respectively) or GBRS (− 57%, − 26%, respectively) alone. Compared to DSS-control synbiotic supplementation significantly (p < 0.0001) maintained expressions of tight junction proteins. Moreover, synbiotic effects accounted for ~ 40% suppression of IL-1β and ~ 29% increase in IL-10 levels in serum while also reducing C-reactive protein (− 37%) compared to that of the DSS-control. While, B. coagulans alone could not induce additional levels of short-chain fatty acid (SCFA) production beyond the caecum, the synbiotic combination with GBRS resulted in substantial increased SCFA levels across the whole length of the colon.

Conclusion

The synbiotic supplementation with B. coagulans and GBRS ameliorated the overall inflammatory status of the experimental IBD model via synergistic functioning. This supports researching its application in mitigating inflammation in human IBD.

Electronic supplementary material

The online version of this article (10.1007/s00394-020-02200-9) contains supplementary material, which is available to authorized users.

Preventive effects of pectin with various degrees of esterification on ulcerative colitis in mice

Low esterified or amidated low esterified pectin displayed better preventive effects on acute colitis over high esterified pectin.

Evaluation of the therapeutic activity of melatonin and resveratrol in Inflammatory Bowel Disease: A longitudinal PET/CT study in an animal model

Inflammatory Bowel Disease (IBD) is a group of chronic disorders of the gastrointestinal tract, which two main types are Crohn's disease and ulcerative colitis. Although conventional therapeutic strategies have demonstrated to be effective in the IBD treatment, it is necessary to incorporate novel therapeutic agents that target other mechanisms involved in the pathogenesis of the disease, such as oxidative stress. For this reason, the efficacy in vivo of two antioxidant compounds, melatonin and resveratrol, has been investigated in an animal model of TNBS (2, 4, 6-trinitrobenzenesulfonic acid) induced colitis. PET/CT (Positron emission tomography/Computer Tomography) scans were performed to assess disease activity and evaluate treatment response. SUV_max (Standardized Uptake Value) values, body weight changes and histological evaluation were used as inflammatory indices to measure the efficacy of both treatments. SUV_max values increased rapidly after induction of colitis, but after the beginning of the treatment (day 3) a statistically significant decrease was observed on days 7 and 10 in treated animals compared to the non-treated group. This remission of the disease was also confirmed by histological analysis of the colon tissue using the Nancy histological index (p value < 0.05 for differences between non-treated and both groups of treated animals). Moreover, statistical analysis showed a correlation (R² = 65.52%) between SUV_max values and weight changes throughout the treatment. Overall, this study demonstrates the potential of resveratrol, and melatonin in lower extent, as therapeutic agents in the IBD treatment.

Synbiotic Supplementation Containing Whole Plant Sugar Cane Fibre and Probiotic Spores Potentiates Protective Synergistic Effects in Mouse Model of IBD

Inflammatory bowel diseases (IBD) are a chronic inflammatory disorders with increasing global incidence. Synbiotic, which is a two-point approach carrying probiotic and prebiotic components in mitigating inflammation in IBD, is thought to be a pragmatic approach owing to the synergistic outcomes. In this study, the impacts of dietary supplementation with probiotic Bacillus coagulans MTCC5856 spores (B. coagulans) and prebiotic whole plant sugar cane fibre (PSCF) was assessed using a murine model of IBD. Eight-week-old C57BL/6 mice were fed a normal chow diet supplemented with either B. coagulans, PSCF or its synbiotic combination. After seven days of supplementation, colitis was induced with dextran sulfate sodium (DSS) in drinking water for seven days during the continuation of the supplemented diets. Synbiotic supplementation ameliorated disease activity index and histological score (-72%, 7.38, respectively), more effectively than either B. coagulans (-47%, 10.1) and PSCF (-53%, 13.0) alone. Synbiotic supplementation also significantly (p < 0.0001) prevented the expression of tight junction proteins and modulated the altered serum IL-1β (-40%), IL-10 (+26%), and C-reactive protein (CRP) (-39%) levels. Synbiotic supplementations also raised the short-chain fatty acids (SCFA) profile more extensively compared to the unsupplemented DSS-control. The synbiotic health outcome effect of the probiotic and prebiotic combinations may be associated with a synergistic direct immune-regulating efficacy of the components, their ability to protect epithelial integrity, stimulation of probiotic spores by the prebiotic fibre, and/or with stimulation of greater levels of fermentation of fibres releasing SCFAs that mediate the reduction in colonic inflammation. Our model findings suggest synbiotic supplementation should be tested in clinical trials.

Melatonin ameliorates TNBS-induced colitis in rats through the melatonin receptors: involvement of TLR4/MyD88/NF-κB signalling pathway

AIM

The aim of the present study is to investigate the anti-inflammatory effect of melatonin in trinitrobenzene sulfonic acid (TNBS)-induced rat colitis through the inhibition of Toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) signalling pathway and activation of melatonin receptor.

METHODS

Colitis was induced in Wistar rats by administration of 100 mg/kg TNBS dissolved in 0.25 ml of 50% ethanol solution using a flexible plastic rubber catheter into the colon via the anus. This resulted in incidence of colitis on the first day, and all treatments were conducted for 10 days after induction of colitis. Melatonin was administered intraperitoneally (i.p.) at doses of 1, 5, and 10 mg/kg/day. Luzindole (non-selective MT1/MT2 receptor antagonist) was administered i.p. at dose of 5 mg/kg/day 15 min prior to melatonin injection. During the experiment, animals were monitored for the appearance of diarrhoea, body weight loss, and rectal bleeding. Myeloid peroxidase enzyme and tumour necrosis factor-α (TNF-α) activities were detected by immunohistochemistry. The protein expression level of TLR4, myeloid differentiation factor 88 (MyD88), NF-κB p65, and inhibitor of kappa B (I-κB) were detected by western blotting analysis.

RESULTS

Treatment with melatonin improved weight loss, mucosal, and histological damage compared with TNBS group. In addition, melatonin decreased TNBS-induced up-regulation of TLR4, MyD88, and NF-κB p65, and increased down-regulation of I-κB proteins. On the other hand, the administration of luzindole resulted in the inhibition of melatonin effects.

CONCLUSIONS

It seems that the inhibition of TLR4/NF-κB signalling pathway may mediate the anti-inflammatory effects of melatonin in TNBS-induced rat colitis.

Ziziphus spina-christi fruit extract suppresses oxidative stress and p38 MAPK expression in ulcerative colitis in rats via induction of Nrf2 and HO-1 expression

In this study, we aimed to evaluate the anti-inflammatory and protective effects of Ziziphus spina-christi fruit extract (ZFE) against acetic acid (AcOH)-induced colitis in rats. Before a single AcOH instillation, ZFE (100, 200, and 400 mg/kg/day) was administered for 5 days by oral gavage. Pretreatment with ZFE at different doses suppressed the spread of inflammation and inhibited mucosal damage; in addition, it reduced ulcer size and mitigated colitis markers. Administration of ZFE (400 mg/kg) resulted in a greater reduction of inflammatory colonic injury than that after reference drug, mesalazine (MLZ), administration. In addition, ZFE not only histopathologically ameliorated AcOH-induced colitis but also restored the balance between the oxidants and antioxidants. Furthermore, ZFE effectively modulated the mRNA expression of redox-sensitive transcription factors, such as nuclear factor (erythroid-derived 2)-like 2 and heme oxygenase-1, downregulated the expression of p38 mitogen-activated protein kinase, and upregulated that of vascular endothelial growth factor A and interleukin-1β in AcOH-induced colitis in rats. In conclusion, our results suggested that ZFE could prevent the development of chronic experimental colitis in rats; therefore, it could be considered as an alternative and/or additive therapeutic approach for the management of inflammatory bowel disease.

Melatonin's role as a co-adjuvant treatment in colonic diseases: A review

Melatonin is produced in the pineal gland as well as many other organs, including the enterochromaffin cells of the digestive mucosa. Melatonin is a powerful antioxidant that resists oxidative stress due to its capacity to directly scavenge reactive species, to modulate the antioxidant defense system by increasing the activities of antioxidant enzymes, and to stimulate the innate immune response through its direct and indirect actions. In addition, the dysregulation of the circadian system is observed to be related with alterations in colonic motility and cell disruptions due to the modifications of clock genes expression. In the gastrointestinal tract, the activities of melatonin are mediated by melatonin receptors (MT2), serotonin (5-HT), and cholecystokinin B (CCK2) receptors and via receptor-independent processes. The levels of melatonin in the gastrointestinal tract exceed by 10-100 times the blood concentrations. Also, there is an estimated 400 times more melatonin in the gut than in the pineal gland. Gut melatonin secretion is suggested to be influenced by the food intake. Low dose melatonin treatment accelerates intestinal transit time whereas high doses may decrease gut motility. Melatonin has been studied as a co-adjuvant treatment in several gastrointestinal diseases including irritable bowel syndrome (IBS), constipation-predominant IBS (IBS-C), diarrhea-predominant IBS (IBS-D), Crohn's disease, ulcerative colitis, and necrotizing enterocolitis. The purpose of this review is to provide information regarding the potential benefits of melatonin as a co-adjuvant treatment in gastrointestinal diseases, especially IBS, Crohn's disease, ulcerative colitis, and necrotizing enterocolitis.

Sleep disorders and inflammatory disease activity: chicken or the egg?

Sleep dysfunction is a highly prevalent condition that has long been implicated in accelerating disease states characterized by having an inflammatory component such as systemic lupus erythematosus, HIV, and multiple sclerosis. Inflammatory bowel disease (IBD) is a chronic, debilitating disease that is characterized by waxing and waning symptoms, which are a direct result of increased circulating inflammatory cytokines. Recent studies have demonstrated sleep dysfunction and the disruption of the circadian rhythm to result in an upregulation of inflammatory cytokines. Not only does this pose a potential trigger for disease flares but also an increased risk of malignancy in this subset of patients. This begs to question whether or not there is a therapeutic role of sleep cycle and circadian rhythm optimization in the prevention of IBD flares. Further research is needed to clarify the role of sleep dysfunction and alterations of the circadian rhythm in modifying disease activity and also in reducing the risk of malignancy in patients suffering from IBD.

In vitro and in vivo study of a colon-targeting pH-sensitive hydrocortisone sodium succinate hydrogel

The aim of this study was to prepare and characterize a novel pH-sensitive hydrocortisone sodium succinate loaded hydrogel (HSS-GEL) for specifically delivering HSS to the colon, and evaluate its targeting properties.

Investigation of the effect of intracolonic melatonin gel formulation on acetic acid-induced colitis

The aims of the present study were to develop a colon-specific gel formulation of melatonin with sodium alginate and to evaluate its in vitro characteristics and intracolonic performance on oxidative stress parameters, such as nitric oxide (NOx), malondialdehyde (MDA) and glutathione (GSH) levels in rats with acetic acid-induced colitis. The melatonin-alginate gel formulations were prepared and their physico-pharmaceutical properties were determined. Formulation M5, which contained 3% of sodium alginate and 20% polyethylene glycol, was used for in vivo studies. The in vivo studies were conducted in rats with acetic acid-induced colitis. NOx, MDA and GSH levels were determined and histological investigations were performed. It was found that formulation M5 was the most suitable formulation for the colon-specific melatonin gel, in terms of pH, viscosity, drug release and mucoadhesion properties. The MDA levels in the tissues of Group 2 (treated with an intracolonic gel formulation without melatonin) were found to be significantly higher than in Group 1 (the untreated group). NOx levels decreased with the intracolonic and systemic melatonin treatment in the colitis-induced rats. Neither intracolonic nor intra-peritoneal (IP) melatonin treatment affected GSH levels. The epitelization of the colon tissues in groups administered with intracolonic melatonin, IP melatonin, and the intracolonic gel formulation without melatonin was much better than that found in the untreated group. It was concluded that melatonin participated in various defense mechanisms against the colonic inflammatory process, and that the dose, route and formulation type were the most important parameters in the effectiveness of melatonin.

Protective efficacy of ursodeoxycholic acid nanoparticles in animal model of inflammatory bowel disease

Abstract Context: Ursodeoxycholic acid (UDCA) exerts dose-dependent chemoprevention in colonic inflammation. Polycationic UDCA nanoparticles (UNPs) are envisaged for solubility enhancement and site directed drug delivery.

OBJECTIVE

The objective was to study the ameliorative efficacy of UNPs through localized delivery of the drug.

METHODS

UNPs were prepared through nanoprecipitation technique. Particle size, morphology, in vitro drug release and in vivo protective efficacy in inflammatory bowel disease (IBD) of these nanoparticles were studied.

RESULTS AND DISCUSSION

The average particle size was around 100 nm, and the average drug encapsulation was about 99%. In vitro drug release study shows optimal drug release in simulated colonic fluid. The lowering of tissue nitric oxide, malondialdehyde, myeloperoxidase and histology of the colon tissue supported the protective efficacy of the nanoparticles.

CONCLUSION

This study presents the improved efficacy of UNPs in animal model of IBD due to complete release of drug at the desired site of action.

Melatonin reduces ulcerative colitis-associated local and systemic damage in mice: investigation on possible mechanisms

BACKGROUND AND AIMS

Ulcerative colitis (UC) is a chronic gastrointestinal disorder. Substantial research reveals that melatonin has beneficial effects in ulcerative colitis both experimentally and clinically. We have previously reported that ulcerative colitis was associated with local and systemic damage in mice. The purpose of this study was to reveal the novel targets of melatonin in its protective mechanism against ulcerative colitis in mice. We also wished to determine whether or not melatonin protected against ulcerative colitis-induced systemic damage in mice.

METHODS

Ulcerative colitis was induced in mice by use of 3% (w/v) dextran sulfate sodium for two cycles. One cycle comprised 7 days of DSS-treated water followed by 14 days of normal drinking water. Melatonin was administered at doses of 2, 4, or 8 mg/kg bw/day, po throughout. The effect of melatonin in mice with UC was evaluated by use of biochemical data, histological evaluation, comet and micronucleus assays, immunohistochemistry, and western blot analysis.

RESULTS

The results indicated that melatonin treatment ameliorated the severity of ulcerative colitis by modulating a variety of molecular targets, for example nuclear factor kappa B, cyclooxygenase-2, interleukin 17, signal transducer and activator of transcription 3, nuclear erythroid 2-related factor 2, matrix metalloproteinase-9, and connective tissue growth factor. Further, ulcerative colitis increased gut permeability, plasma lipopolysaccharide level, systemic inflammation, and genotoxicity. Melatonin treatment led to mucosal healing and reduced ulcerative colitis-induced elevated gut permeability and reduced the plasma LPS level, systemic inflammation, and genotoxicity.

CONCLUSION

Melatonin ameliorated ulcerative colitis-associated local and systemic damage in mice.

The effect of melatonin on plasma markers of inflammation and on expression of nuclear factor-kappa beta in acetic acid-induced colitis in the rat

BACKGROUND AND AIMS

Melatonin may be involved in gastrointestinal tract physiology and could affect inflammation-related gastrointestinal disorders. Rat models of ulcerative colitis imply melatonin is beneficial. To determine potential pathophysiological mechanisms, we assessed colonic nuclear factor-kappa beta expression and measured serum levels of pentraxin-3, lipid peroxides, and total thiols in an acetic acid model of this disease.

MATERIALS AND METHODS

Thirty rats were divided into five groups: a control group, an acetic acid-induced colitis group, a group treated with melatonin before colitis induction, a group treated short-term after colitis induction, and a group treated long-term after colitis induction. After four weeks, blood samples were taken for measurement of pentraxin-3, lipid peroxide, and total thiols. Sections of the colon were taken for histopathological examination and immunohistochemical detection of nuclear factor-kappa beta expression.

RESULTS

Melatonin administration reduced nuclear factor-kappa beta immunohistochemical expression, reduced serum levels of lipid peroxide and pentraxin-3, and maintained serum levels of total thiols. However, in long-term treatment the protective effect of melatonin was not as marked.

CONCLUSION

Melatonin is effective in prevention and short-term treatment of the inflammatory process in acetic-acid induced colitis whereas the benefit of long-term treatment is unclear. Benefit may be linked to protection mechanisms against inflammatory processes by inhibiting the nuclear factor-kappa beta and conserving endogenous antioxidant reserves of total thiols, thus reducing the level of colonic damage possibly caused by lipid peroxides.

Modulation by melatonin of the pathogenesis of inflammatory autoimmune diseases

Melatonin is the major secretory product of the pineal gland during the night and has multiple activities including the regulation of circadian and seasonal rhythms, and antioxidant and anti-inflammatory effects. It also possesses the ability to modulate immune responses by regulation of the T helper 1/2 balance and cytokine production. Autoimmune diseases, which result from the activation of immune cells by autoantigens released from normal tissues, affect around 5% of the population. Activation of autoantigen-specific immune cells leads to subsequent damage of target tissues by these activated cells. Melatonin therapy has been investigated in several animal models of autoimmune disease, where it has a beneficial effect in a number of models excepting rheumatoid arthritis, and has been evaluated in clinical autoimmune diseases including rheumatoid arthritis and ulcerative colitis. This review summarizes and highlights the role and the modulatory effects of melatonin in several inflammatory autoimmune diseases including multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, type 1 diabetes mellitus, and inflammatory bowel disease.

Protective effects of 3,4-oxo-isopropylidene-shikimic acid on experimental colitis induced by trinitrobenzenesulfonic acid in rats

BACKGROUND

3,4-Oxo-isopropylidene-shikimic acid (ISA) is a derivative of shikimic acid (SA). SA is extracted from Illicium verum Hook.fil., which has been used in traditional Chinese medicine and used for treating vomiting, stomach aches, insomnia, skin inflammation, and rheumatic pain.

AIMS

To investigate the effects and the protective mechanism of 3,4-oxo-isopropylidene-shikimic acid on experimental colitis model induced by 2,4,6-trinitrobenzenesulfonic acid (TNBS) in rats.

METHODS

Colitis in rats was induced by colonic administration with TNBS. ISA (50, 100, and 200 mg/kg) was administered for 12 days to experimental colitis rats. The inflammatory degree was assessed by macroscopic damage score, colon weight/length ratios (mg/cm), and myeloperoxidase (MPO) activity. Malondialdehyde (MDA), glutathione (GSH), and nitric oxide (NO) levels, and superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), inducible nitric oxide synthase (iNOS) activities were measured with biochemical methods.

RESULTS

ISA significantly ameliorated macroscopic damage, reduced colon weight/length ratios and the activity of MPO, depressed MDA and NO levels and iNOS activity, and enhanced GSH level, and GSH-Px and SOD activities in the colon tissues of experimental colitis in a dose-dependent manner. Moreover, the effect of ISA (200 mg/kg) was as effective as sulfasalazine (500 mg/kg).

CONCLUSIONS

The findings of this study demonstrate the protective effect of ISA on experimental colitis, probably due to an antioxidant action.

Effects of curcumin and Ginkgo biloba on matrix metalloproteinases gene expression and other biomarkers of inflammatory bowel disease

Treatment of inflammatory bowel disease (IBD) by synthetic active ingredients leads to many side effects. The objective of this study was to manage IBD using natural products as curcumin and Ginkgo biloba. Rats were divided into four groups (control, IBD, curcumin treated, and ginkgo treated). Inflammation was assessed by determination of myeloperoxidase, matrix metalloproteinases, metalloproteinase-1 inhibitor, nitric oxide, hydroxyproline, tumor necrosis factor-alpha, ceruloplasmin, and histopathological scoring. IBD induction significantly increased all measured parameters. Treated groups had significantly lower levels when compared with the IBD group. In conclusion, curcumin and ginkgo were effective in prevention and treatment of IBD.

Detection of melatonin and homocysteine simultaneously in ulcerative colitis

BACKGROUND

Oxidative stress could be a major contributing factor to the tissue injury that characterize inflammatory bowel disease (IBD). Homocysteine (HCY) could cause oxidative damage to the colon tissue in ulcerative colitis (UC) patients, melatonin (MLT) supplementation could reduce oxidative damage that caused by HCY in vitro and in vivo. In this study, we aimed to determine the levels of plasma HCY and MLT simultaneously in UC patients.

METHODS

Collected the clinical data of 112 UC patients and 110 healthy controls (HC). The levels of plasma HCY and MLT were detected by HPLC-FD method. The levels of plasma folate, vitamin B(12) (VitB(12)) were detected by ELISA method.

RESULTS

The levels of plasma HCY in UC patients were significantly higher than that in HC (11.27±7.26 μmol/L vs. 8.19±4.81 μmol/L, P=0.000). The levels of plasma MLT in UC patients were significantly lower than that in HC (49.06±31.40 pg/ml vs. 64.28±41.16 pg/ml, P=0.008). The levels of plasma folate and VitB(12) in UC patients were lower than that in HC (7.64±1.95 nmol/L vs. 9.14±1.23 nmol/L, 108.64±32.22 pmol/L vs. 112.64±33.33 pmol/L, P<0.05). The levels of plasma HCY and MLT in UC patients were not correlated with either the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) or the disease activity, localization and duration of UC (P>0.05). The change of increasing levels of plasma MLT but decreasing levels of plasma HCY was shown in UC patients, however, the association between the levels of plasma MLT and HCY were not statistically significant (P>0.05).

CONCLUSIONS

The levels of plasma HCY were increased whereas the levels of plasma MLT were decreased in UC patients.

New paradigms in chronic intestinal inflammation and colon cancer: role of melatonin

In intestinal bowel disease (IBD), immune-mediated conditions exert their effects through various cells and proinflammatory mediators. Recent data support a participation of the endoplasmic reticulum stress and mitochondrial dysfunctions in IBD. Moreover, it is evident that chronic degenerative pathologies, including IBD, share comparable disease mechanisms with alteration in the autophagy mechanisms. Chronic inflammation in IBD exposes these patients to a number of signals known to have tumorigenic effects. This circuitry of inflammation and cancer modifies apoptosis and autophagy, and promotes cellular cycle progression, invasion, and angiogenesis. Melatonin has been shown as a specific antioxidant reducing oxidative damage in both lipid and aqueous cell environments. However, several studies provide further insight into the molecular mechanisms of melatonin action in the colon. In this line, recent data suggest that melatonin modulates autophagy and sirtuin activity. An anti-autophagic property of melatonin has been demonstrated, and it could contribute to its anti-oncogenic activity. Nevertheless, there is no information about whether antitumoral effects of melatonin on colon cancer are dependent on autophagy. Sirtuins have pleiotropic effects on cancer development, being reported both as facilitator and as suppressor of colon cancer development. Sirtuins and melatonin are connected through the circadian clock machinery, and melatonin seems able to correct the alterations in sirtuin activity associated with several pathological conditions. Autophagy and sirtuin activities are linked through 5'AMP-activated protein kinase (AMPK) activation, which switches on autophagy and increases sirtuin. The effect of melatonin on AMPK and the impact of this effect on IBD and colon cancer remain an open question.

The effect of Hypericum perforatum (St. John's Wort) on experimental colitis in rat

The aim of the present study was to investigate the effect of Hypericum perforatum (HP) on the inflammatory and immune response of colonic mucosa in rat with induced inflammatory bowel disease and that on various enzyme activities in blood and bowel tissue. Male Wistar albino rats were divided into three main groups: control, third day, and seventh day of colitis. Third-day and seventh-day groups were divided into four subgroups. Colitis was induced in all groups except the control group by 2,4,6-trinitrobenzene sulfonic acid (TNBS). The colitis group received saline; treatment groups received HP extract (50, 150, and 300 mg/kg/day, respectively). Glutathione (GSH), catalase (CAT), and malondialdehyde (MDA) activities in blood were measured. Catalase, myeloperoxidase (MPO), glutathione peroxidase (GSH-Px), glutathione reductase (GR), malondialdehyde, and nitric oxide (NO) activities were measured from tissue samples. Colonic damage was significantly reduced by HP extract. Macroscopic scoring of colonic damage significantly reduced in groups given HP extract compared with in the colitis group (P < 0.001). Blood catalase levels were reduced in the HP (150 mg/kg/day) compared with the colitis group (P < 0.01). Blood GSH levels significantly increased in groups treated with HP compared with control (P < 0.001) on the third and seventh day. Tissue GR levels reduced in the colitis and HP (50 mg/kg/day) groups compared with control (P < 0.05). Tissue MPO activity increased in the colitis and treatment groups compared with control (P < 0.007). GSH-Px levels increased in the colitis group compared with control at day 3 (P = 0.006). HP has a protective effect on TNBS-induced inflammatory bowel disease (IBD), probably due to an anti-inflammatory and antioxidant mechanism.

Effect of melatonin on the blood oxygen transport during hypothermia and rewarming in rats

PURPOSE

We aimed to study effect of melatonin on the blood oxygen transport during hypothermia and rewarming in rats.

MATERIAL/METHODS

Cold exposure was performed on male rats (body weight 220-270 g, n=48) for 120 minutes under the box water temperature of 19 degrees C; rewarming took the next 120 min, with a mean rate of 0.06 degrees C/min. Melatonin was administered intraperitoneally 30 min before the cold exposure (bolus doses of 0.1, 1 or 10 mg/kg, or 1 mg/kg*day for 4 days). Haemoglobin-oxygen affinity was evaluated by p50 (blood pO2 at its 50% O2 saturation) determined by the "mixing" method at 37 degrees C, pH 7.4 and pCO2 40 mm Hg (p50stand) and at actual pH, pCO2 and temperature (p50act).

RESULTS

After hypothermia and rewarming, the values of p50stand and p50act were 31.5+/-0.28 and 30.2+/-0.61 mm Hg, respectively. The 0.1 mg/kg of melatonin virtually did not change these values, whereas the larger doses increased them. This effect was maximal after the prolonged (4 days) melatonin administration: p50stand rose by 5.4% (p<0.05) and p50act--by 12.9 (p<0.05) compared with rats without the melatonin treatment. Melatonin affected the mechanisms of O2 transport by decreasing the haemoglobin-oxygen affinity (shifting the oxygen dissociation curve of haemoglobin rightwards) and promoting the tissue oxygenation, thereby enhancing the body's resistance to cold.

CONCLUSIONS

The melatonin effect mediated by haemoglobin-oxygen affinity change may be used for the correction of metabolic disorders and the improvement of the body's resistance to low environmental temperature.

Melatonin and ulcerative colitis: evidence, biological mechanisms, and future research

Ulcerative colitis (UC) is an inflammatory bowel disease that afflicts up to 1 million people in the US. Current treatments for UC are mostly nonspecific, not always effective, and often accompanied by serious side effects. Therefore, there is considerable interest in finding alternative and more tolerable treatments for this disease. Physiologic data suggest that melatonin is an important regulator of both inflammation and motility in the gastrointestinal tract, and data from in vitro studies, animal experiments, and limited studies in humans suggest that supplemental melatonin may have an ameliorative effect on colitis. In this review we summarize the evidence regarding melatonin as a possible therapeutic agent in UC and discuss possible biological mechanisms and directions for future research.

Melatonin inhibits prostaglandin E2- and sodium nitroprusside-induced ion secretion in rat distal colon

Although the gastrointestinal tract is a rich source of melatonin and possesses numerous melatonin-binding sites, the role of melatonin in this tissue has not yet been fully elucidated. In this work we focused on the role of melatonin in the modulation of ion transport in rat distal colon. Whereas melatonin had no effect on colonic secretion or caused only infrequent and small changes in the short circuit current (Isc) due to its solvent ethanol, this mediator significantly modulated the secretion elicited by some secretagogues. Out of the five substances tested (prostaglandin E(2); 5-hydroxytryptamine; bethanechol; histamine; sodium nitroprusside) melatonin inhibited the effect of prostaglandin E(2) (PGE(2)) and sodium nitroprusside (SNP). Melatonin concentration-dependently decreased PGE(2)-evoked Isc and this inhibitory effect was more obvious from the mucosal side. The basal level of cAMP in colonic mucosa was not influenced by melatonin, but this drug prevented a PGE(2)-induced increase in the level of cAMP. The neurotoxin tetrodotoxin blocked the inhibitory effect of melatonin on SNP-induced Isc. Our data suggests that melatonin takes part in the modulation of colonic ion transport. The modulatory effect of melatonin on PGE(2)-induced Isc occurs directly at the level of the epithelium, whereas the effect on SNP-induced Isc is indirect and located in tetrodotoxin-sensitive enteric neurons.