In vivo changes in the intestinal reflexes and the response to CCK in the inflamed small intestine of the rat

Effects of probiotic supplementation on post-infectious irritable bowel syndrome in rodent model

BACKGROUND

Probiotics have been reported to be the active component used in the treatment of many functional gastrointestinal symptoms and syndromes. Lactobacillus and yeast culture are extensively used in probiotic supplements and traditional treatments for irritable bowel syndrome (IBS). The aim of this study was to investigate the effects of probiotic treatments (Lactobacillus acidophilus LA5, Bifidobacterium animalis subsp. lactis BB12 and Saccharomyces cerevisiae var. boulardii) on the behavioral response, targeted gene expression and pro-inflammatory cytokine levels of Pi (Post infectious)-IBS -induced mice.

METHODS

Pathogen-free male C57L/B6 mice and the Trichinella-infected mice were used to measure the score of abdominal withdrawal reflex (AWR). To compare molecular, biological and biochemical evidences of given probiotics with normal and positive control groups in mice, we conducted quantitative reverse transcription polymerase chain reaction (RT-qPCR), western blotting, and cytokine analysis.

RESULTS

Pi-IBS-induced immune response was confirmed that PAR-2 mRNA level was significantly increased by Trichinella infection (P < 0.05). The reduction of Pi-IBS symptoms through Trichinella infection and the effects of given probiotics were confirmed by a change in the protein levels of cytokines (P < 0.05). In addition, the administration of DW (Daewon) probiotics significantly decreased serum levels of IL-1 and IL-6 (P < 0.05).

CONCLUSIONS

We have demonstrated that the given probiotics decreased pro-inflammatory cytokine levels in both the control and Pi-IBS induced mice. Taken all the results together, the results support that DW probiotics has a potential as a probiotic medication for patient with IBS via regulating TNF-α and IL-6 protein levels and serum IL-1 and IL-6 levels.

Heat shock protein 70 protects mouse against post-infection irritable bowel syndrome via up-regulating intestinal γδ T cell's Th17 response

Background

This study investigated the role of HSP70 in modulating intestinal γδ T cells’ Th17 response in Trichinella spiralis-induced PI-IBS mice model.

Methods

The intestinal HSP70’s expression and mRNA level were measured by Western blot and RT-PCR. The intestinal γδ T cell’s morphological changes were analyzed using immunofluorescence staining and confocal laser scanning microscope. The pro-inflammatory cytokines’ level was detected by ELISA. The isolated and purified γδ T cells were pre-incubated with HSP70 and their functions including proliferation, apoptosis, activation and production of IL-17 were also detected.

Results

Heat treatment augmented intestinal HSP70 expression and alleviated the clinical presentations in PI-IBS mice. Meanwhile, intestinal γδ T cells and local IL-17 level were increased by pre-induction of HSP70. HSP70 promoted the proliferation of PI-IBS mice’s intestinal γδ T cells, inhibited the apoptosis and stimulated these cells to secret IL-17 rather than IFN-γ.

Conclusion

Our results suggest that HSP70 plays a protective role via up-regulating intestinal γδ T cell’s Th17 response in PI-IBS mice.

Enteroendocrine cells-sensory sentinels of the intestinal environment and orchestrators of mucosal immunity

The intestinal epithelium must balance efficient absorption of nutrients with partitioning commensals and pathogens from the bodies' largest immune system. If this crucial barrier fails, inappropriate immune responses can result in inflammatory bowel disease or chronic infection. Enteroendocrine cells represent 1% of this epithelium and have classically been studied for their detection of nutrients and release of peptide hormones to mediate digestion. Intriguingly, enteroendocrine cells are the key sensors of microbial metabolites, can release cytokines in response to pathogen associated molecules and peptide hormone receptors are expressed on numerous intestinal immune cells; thus enteroendocrine cells are uniquely equipped to be crucial and novel orchestrators of intestinal inflammation. In this review, we introduce enteroendocrine chemosensory roles, summarize studies correlating enteroendocrine perturbations with intestinal inflammation and describe the mechanistic interactions by which enteroendocrine and mucosal immune cells interact during disease; highlighting this immunoendocrine axis as a key aspect of innate immunity.

Changes in Epithelial Barrier Function in Response to Parasitic Infection: Implications for IBD Pathogenesis

BACKGROUND AND AIMS

Mast cells [MCs] are implicated in epithelial barrier alterations that characterize inflammatory and functional bowel disorders. In this study, we describe mast cell proteinases [chymases and tryptases] and tight junction [TJ] proteins kinetics in a rat model of postinfectious gut dysfunction.

METHODS

Jejunal tissues of control and -infected rats were used. Inflammation-related changes in MCs and the expression of TJ-related proteins were evaluated by immunostaining and reverse transcription-quantitative polymerase chain reaction. Epithelial barrier function was assessed in vitro (Ussing chambers) and in vivo.

RESULTS

After infection, intestinal inflammation was associated with a generalized overexpression of MC chymases, peaking between Days 6 and 14. Thereafter, a mucosal MC hyperplasia and a late increase in connective tissue MC counts were observed. From Day 2 post-infection, TJ proteins occludin and claudin-3 expression was down-regulated whereas the pore-forming protein claudin-2 was overexpressed. The expression of proglucagon, precursor of the barrier-enhancing factor glucagon-like peptide-2, was reduced. These changes were associated with an increase in epithelial permeability, both in vitro and in vivo.

CONCLUSIONS

Proteinases expression and location of mucosal and connective tissue MCs indicate a time-related pattern in the maturation of intestinal MCs following infection. Altered expression of TJ-related proteins is consistent with a loss of epithelial tightness, and provides a molecular mechanism for the enhanced epithelial permeability observed in inflammatory conditions of the gut.

Changes of cytokine levels in a mouse model of post-infectious irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a highly prevalent functional gastrointestinal disorder. Post-infectious IBS (PI-IBS) is caused by an acute gastrointestinal infection preceding the onset of symptoms. However, the pathophysiology of PI-IBS is not clear, and the purpose of this study was to investigate the probable immune mechanisms of PI-IBS.

METHODS

C57BL/6 mice were randomly assigned to either an infection group or a control group. Mice in the infection group were infected with Trichinella spiralis to establish a model of PI-IBS (500 Trichinella), while control mice received only salt solution. Visceral sensitivity of colorectal distention in mice was evaluated by abdominal withdrawal reflex scores and intestinal inflammation was assessed using hematoxylin-eosin staining; at day 56 post-infection, the mRNA and protein levels of specific cytokines in the gut segments were detected using reverse-transcription polymerase chain reaction and enzyme-linked immunoabsorbent assay.

RESULTS

Levels of interferon γ and interleukin (IL)-17 in the PI-IBS group were significantly increased in the duodenum and ileum, and IL-10 was decreased in the jejunum, ileum, and colon compared with control mice. However, the expression level of IL-1β was not significantly different between the two groups.

CONCLUSIONS

The present study suggests that the local low-grade inflammation and immune activation that are an important component of the pathophysiology of PI-IBS are primarily induced and maintained by specific cytokines.

PAR-2-mediated control of barrier function and motility differs between early and late phases of postinfectious gut dysfunction in the rat

Proteinase-activated receptor-2 (PAR-2) and mast cell (MC) mediators contribute to inflammatory and functional gastrointestinal disorders. We aimed to characterize jejunal PAR-2-mediated responses and the potential MC involvement in the early and late phases of a rat model of postinfectious gut dysfunction. Jejunal tissues of control and Trichinella spiralis-infected (14 and 30 days postinfection) rats, treated or not with the MC stabilizer, ketotifen, were used. Histopathology and immunostaining were used to characterize inflammation, PAR-2 expression, and mucosal and connective tissue MCs. Epithelial barrier function (hydroelectrolytic transport and permeability) and motility were assessed in vitro in basal conditions and after PAR-2 activation. Intestinal inflammation on day 14 postinfection (early phase) was significantly resolved by day 30 (late phase) although MC counts and epithelial permeability remained increased. PAR-2-mediated ion transport (Ussing chambers, in vitro) and epithelial surface PAR-2 expression were reduced in the early phase, with a trend toward normalization during the late phase. In control conditions, PAR-2 activation (organ bath) induced biphasic motor responses (relaxation followed by excitation). At 14 days postinfection, spontaneous contractility and PAR-2-mediated relaxations were enhanced; motor responses were normalized on day 30. Postinfectious changes in PAR-2 functions were not affected by ketotifen treatment. We concluded that, in the rat model of Trichinella spiralis infection, alterations of intestinal PAR-2 function and expression depend on the inflammatory phase considered. A lack of a ketotifen effect suggests no interplay between MCs and PAR-2-mediated motility and ion transport alterations. These observations question the role of MC mediators in PAR-2-modulating postinfectious gut dysfunction.

Persistent epithelial barrier alterations in a rat model of postinfectious gut dysfunction

BACKGROUND

Mucosal mast cells (MMCs), epithelial barrier function (EBF) and the enteric nervous system (ENS) are interactive factors in the pathophysiology of functional gastrointestinal disorders. We characterized postinfectious EBF alterations in the Trichinella spiralis infection model of MMC-dependent intestinal dysfunction in rats.

METHODS

Sprague-Dawley rats were infected with T. spiralis. 30 ± 2 days postinfection, jejunal EBF (electrophysiological parameters, fluorescein isothiocyanate-dextran fluxes and responses to secretagogues and MMC degranulators) was evaluated (Ussing chamber). In some experiments, participation of secretomotor neurons was examined by tetrodotoxin (TTX) pretreatment. Jejunal histology and MMC count and activity were also assessed.

KEY RESULTS

30 ± 2 days postinfection, when only a low grade inflammation was observed, increased MMC number and activity were associated with altered EBF. EBF alterations were characterized by increased mucosal permeability and ion secretion. In T. spiralis-infected animals, secretory responses to serotonin (5-HT) and immunoglobulin E (IgE)-dependent activation of MMCs were reduced. In contrast, responses to substance P (SP) and capsaicin were similar in infected and noninfected animals. Neuronal blockade with TTX altered secretory responses to SP and capsaicin only in infected rats.

CONCLUSIONS & INFERENCES

Trichinella spiralis infection in rats, at late stages, results in persistent postinfectious intestinal barrier dysfunctions and mucosal mastocytosis, with other signs suggestive of a low grade inflammation. The altered permeability and the TTX-independent hyporesponsiveness to 5-HT and IgE indicate epithelial alterations. Changes in responses to SP and capsaicin after neuronal blockade suggest an ENS remodeling during this phase. Similar long-lasting neuro-epithelial alterations might contribute to the pathophysiology of functional and postinfectious gastrointestinal disorders.

Purinergic and nitrergic neuromuscular transmission mediates spontaneous neuronal activity in the rat colon

Nitric oxide (NO) and ATP mediate smooth muscle relaxation in the gastrointestinal tract. However, the involvement of these neurotransmitters in spontaneous neuronal activity is unknown. The aim of the present work was to study spontaneous neuromuscular transmission in the rat midcolon. Microelectrode experiments were performed under constant stretch both in circular and longitudinal directions. Spontaneous inhibitory junction potentials (sIJP) were recorded. Tetrodotoxin (1 microM) and apamin (1 microM) depolarized smooth muscle cells and inhibited sIJP. N(omega)-nitro-l-arginine (l-NNA, 1 mM) depolarized smooth muscle cells but did not modify sIJP. In contrast, the P2Y(1) antagonist MRS-2500 (1 microM) did not modify the resting membrane potential (RMP) but reduced sIJP (IC(50) = 3.1 nM). Hexamethonium (200 microM), NF-023 (10 microM), and ondansetron (1 microM) did not modify RMP and sIJP. These results correlate with in vitro (muscle bath) and in vivo (strain gauges) data where l-NNA but not MRS-2500 induced a sustained increase of spontaneous motility. We concluded that, in the rat colon, inhibitory neurons regulate smooth muscle RMP and cause sIJP. In vitro, the release of inhibitory neurotransmitters is independent of nicotinic, P2X, and 5-hydroxytryptamine type 3 receptors. Neuronal NO causes a sustained smooth muscle hyperpolarization that is responsible for a constant inhibition of spontaneous motility. In contrast, ATP acting on P2Y(1) receptors is responsible for sIJP but does not mediate inhibitory neural tone. ATP and NO have complementary physiological functions in the regulation of gastrointestinal motility.

Th17: a new participant in gut dysfunction in mice infected with Trichinella spiralis

Trichinella spiralis infection in rodents is a well-known model of intestinal inflammation associated with hypermotility. Our aim was to elucidate if Th17 cells were involved in the development of gastrointestinal hypermotility in this experimental model. Intestinal inflammation was observed by hematoxylin-eosin (HE) staining. Jejunal smooth muscle contractility was investigated in response to acetylcholine (Ach). The effects of IL-17 on jejunum smooth muscle contractility were explored. Flow cytometry was used to analyze the proportion of Th17 cells in jejunum. The levels of IL-17, IL-23, and TGF-β1 in jejunum were measured by Western blot. Our results showed that the inflammation in jejunum was severe at 2 weeks postinfection (PI), which was not discernible at 8 weeks PI. Jejunal smooth muscle contractility was increased at 2 weeks PI and kept higher at 12 weeks PI. The proportion of Th17 cells and the expression of IL-17 were upregulated in jejunum at 2 weeks PI and normalized at 8 weeks PI. When jejunual smooth muscle strips were cultured with IL-17, contractions elicited by Ach were enhanced in a concentration-dependent manner. Our data suggest that Th17 cells are increased during acute infection with Trichinella spiralis and IL-17 may contribute to jejunal muscle contractility in mice.

Synaptic plasticity: the new explanation of visceral hypersensitivity in rats with Trichinella spiralis infection?

BACKGROUND AND AIM

Synaptic plasticity plays an important role in affecting the intensity of visceral reflex. It may also be involved in the development of visceral hypersensitivity. The aim of this study was to investigate the role of synaptic plasticity on visceral hypersensitivity of rats infected by Trichinella spiralis.

METHODS

Thirty male Sprague-Dawley (SD) rats were randomly divided into control, acute, and chronic infection groups, and were investigated at 1 week after adaptive feeding and at 2 and 8 weeks post infection (PI) by oral administration of 1 ml phosphate-buffered saline (PBS) containing 8,000 Trichinella spiralis larvae. Visceral sensitivity was evaluated by electromyography (EMG) recording during colorectal distension. Intestinal inflammation was observed by hematoxylin-eosin (HE) staining. Synaptic ultrastructure parameters, such as postsynaptic density (PSD) length, synaptic cleft, and number of synaptic vesicles, were examined by transmission electron microscopy (TEM). The expression of protein associated with synaptic plasticity, including postsynaptic density-95 (PSD-95), synaptophysin, calbindin-28 K, N-methyl-D-aspartate receptor-1 (NMDA-R1), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPA-R), and glial cell line-derived neurotrophic factor (GDNF), were analyzed by Western blot.

RESULTS

(1) Visceral hypersensitivity was noted in the chronic infection group, although the inflammation was nearly eliminated (P<0.05). Severe inflammation and downregulation of visceral sensitivity were observed in the acute infection group (P<0.05). (2) There were many more synaptic vesicles and longer PSD in the chronic infection group than in the control group (P<0.05, respectively). However, in comparison with control rats, disappearance of mitochondria cristae in the synapses, and decrease of synaptic vesicles and length of PSD were observed in the acute infection group. There was no significant difference in width of synaptic cleft among the three groups. (3) Compared with the control, the expression of proteins associated with synaptic plasticity was significantly upregulated during chronic infection phase (P<0.05), and downregulated during acute infection phase.

CONCLUSION

Synaptic plasticity was observed in SD rats infected by Trichinella spiralis and was associated with visceral sensitivity, which suggests that it may play an important role in the formation of visceral hypersensitivity.

Mast cell stabilizer ketotifen [4-(1-methyl-4-piperidylidene)-4h-benzo[4,5]cyclohepta[1,2-b]thiophen-10(9H)-one fumarate] prevents mucosal mast cell hyperplasia and intestinal dysmotility in experimental Trichinella spiralis inflammation in the rat

Trichinella spiralis infection in rats induces hypermotility and an abnormal response to cholecystokinin (CCK) similar to motor disturbances observed in irritable bowel syndrome. Mast cell hyperplasia is also characteristic of this experimental model. The aim of our study was to correlate mast cell activity with the development of dysmotility and to demonstrate whether the mast cell stabilizer ketotifen [4-(1-methyl-4-piperidylidene)-4H-benzo[4,5]cyclohepta[1,2-b]thiophen-10(9H)-one fumarate] could prevent the development of intestine hypermotility. Sprague-Dawley rats were infected with T. spiralis and, 5 days after infection, treated with the mast-cell stabilizer ketotifen (10 mg/kg/day). Twelve days after infection, intestinal spontaneous motor activity and response to CCK were evaluated by means of strain-gauge transducers. Immunohistochemistry for rat mast cell protease II (RMCPII), cyclooxygenase (COX)-2, and inducible nitric-oxide synthase (iNOS) was performed in intestinal specimens. In addition, RMCPII and myeloperoxidase were determined in serum. Infected control rats showed hypermotility, mast cell hyperplasia, increased RMCPII levels, increased myeloperoxidase, and overexpression of COX-2 and iNOS. In contrast, ketotifen-treated rats showed spontaneous intestinal motility and CCK response similar to the noninfected control rats. Mast cell hyperplasia and RMCPII were reduced in ketotifen-treated rats. Inflammatory parameters were less modified by ketotifen, but those animals that received the longest ketotifen treatment showed a slight amelioration in these parameters. These results indicate that mast cells are implicated in the development of hypermotility. The treatment with ketotifen prevented hypermotility and mast cell hyperplasia and diminished mucosal mast cell activity.

Cyclical upregulated iNOS and long-term downregulated nNOS are the bases for relapse and quiescent phases in a rat model of IBD

We previously reported that indomethacin induces a chronic intestinal inflammation in the rat where the cyclical characteristic phases of Crohn's disease are manifested with a few days' interval and lasting for several months: active phase (high inflammation, hypomotility, bacterial translocation) and reactive phase (low inflammation, hypermotility, no bacterial translocation). In this study, we investigated the possible role of both constitutive and inducible isoforms of nitric oxide (NO) synthase (NOS) and cyclooxygenase (COX) in the cyclicity of active and reactive phases in rats with chronic intestinal inflammation. Rats selected at either active or reactive phases and from 2 to 60 days after indomethacin treatment were used. mRNA expression of both constitutive and inducible NOS and COX isoforms in each phase was evaluated by RT-PCR and cellular enzyme localization by immunohistochemistry. The effects of different COX and NOS inhibitors on the intestinal motor activity were tested. mRNA expression of COX-1 was not modified by inflammation, whereas mRNA expression of neuronal NOS was reduced in all indomethacin-treated rats. In contrast, NOS and COX inducible forms showed a cyclical oscillation. mRNA expression and protein of both iNOS and COX-2 increased only during active phases. The intestinal hypomotility associated with active phases was turned into hypermotility after the administration of selective iNOS inhibitors. Sustained downregulation of constitutive NOS caused hypermotility, possibly as a defense mechanism. However, this reaction was masked during the active phases due to the inhibitory effects of NO resulting from the increased levels of the inducible NOS isoform.

Intestinal motor disorders associated with cyclical bacterial overgrowth in a rat model of enteritis

The aims of this study were: 1) to obtain an experimental model reproducing the characteristics of chronicity and spontaneous relapses found in inflammatory bowel disease (IBD) and 2) to correlate these changes with intestinal motility and bacteria translocation. For this purpose, two groups of Sprague-Dawley rats were used: a treated group that received two subcutaneous injections of indomethacin (7.5 mg/kg) 48 h apart and a control group that received saline. Blood leukocytes, TNF, and fecal parameters were monitored for 90 days after treatment. In treated rats, a cyclic oscillation of blood leukocytes and TNF concomitant with an inverse correlation of fecal output was observed. Treated rats were then selected either during their highest or lowest blood leukocyte values for motor activity and microbiological evaluation. Controls were obtained in age-matched rats. Rats with high leukocyte levels showed a decrease of motor activity. In contrast, animals with low leukocyte levels presented hypermotility. Bacterial overgrowth accompanied by bacterial translocation was found in the group with high leukocytes, whereas no differences were observed between the control and indomethacin groups during the lowest leukocyte phase. We obtained a model of IBD characterized by a chronic cyclic oscillation of intestinal motility, flora, and inflammatory blood parameters. During the high-leukocyte stage, motor activity decrease is related to bacterial translocation. This phase is followed by a reactive one characterized by hypermotility associated with a decrease in both bacterial growth and leukocytes. However, as in IBD, this reaction seems unable to prevent a return to relapse.

Changes in the inhibitory responses to electrical field stimulation of intestinal smooth muscle from Trichinella spiralis infected rats

Functional motor changes and morphological alterations have been associated with intestinal inflammation. The aim of this work was to study functional motor changes in inflamed and non-inflamed intestinal segments of Trichinella spiralis infected rats. Thickness of muscle layers and cell infiltration during infection were also evaluated. Segments of rat jejunum and ileum were placed in organ bath and relaxations of the longitudinal muscle in response to electrical field stimulation (EFS) were recorded. During the post-infection (PI) period EFS-induced relaxations in ileum were decreased. Maximal decreases in relaxation were found on day 14-23 PI for ileum, whereas non significant changes were observed in jejunal samples throughout the experimental period. The sensitivity of the EFS-induced relaxations to the NO synthase inhibitor Nomega-nitro-L-arginine (L-NNA) and to the soluble guanylate cyclase inhibitor oxadiazolo-quinoxalin-1-one (ODQ) was decreased on day 14 PI for jejunum, whereas in the ileum it lasted from day 14-23 PI. The sensitivity of EFS-induced relaxations to apamin (a small conductance calcium activated potassium channel blocker) disappeared between day 6-23 PI for both jejunum and ileum. In contrast, the sensitivity of the EFS-induced relaxations to the K(+) channel blockers tetraethylamonium (TEA) and tetrapenthylammonium (TPEA) chloride was similar for healthy tissue and for tissue obtained form infected animals. Distribution and density of NADPH-diaphorase positive neurons was similar in tissue obtained form healthy and infected animals. In conclusion, intestinal inflammation induces functional and structural changes in both worm-free and worm-positive intestinal segments. Increased muscle thickness was similar for both inflamed and noninflamed segments but the most prominent functional changes i.e. a long-lasting decrease of EFS-induced relaxation was found in non-inflamed ileal segments.

Antinerve growth factor treatment prevents intestinal dysmotility in Trichinella spiralis-infected rats

Nerve growth factor (NGF) could be involved in the development of hyperalgesia as well as in nervous remodeling consequence of inflammation. Both dysmotility and increase of visceral sensitivity have been described in functional gastrointestinal disorders such as irritable bowel syndrome. Trichinella spiralis-infected rats show an exacerbated spontaneous motility and a significant increase of the excitatory response to cholecystokinin (CCK), both associated with a reversible inflammatory process and the hypertrophy of the muscle layers. In this study we determined the intestinal expression of NGF mRNA by polymerase chain reaction and NGF by enzyme-linked immunosorbent assay. We implanted serosal strain gauge transducers on duodenum, jejunum, and ileum of anesthetized Sprague-Dawley rats to record circular muscle contractions. The experimental protocol included the evaluation of intestinal spontaneous motor activity (SMA), the response to CCK-8, and the ascending contraction induced by electrical mucosal stimulation. This protocol was performed in healthy and infected nontreated rats, in healthy rats with an NGF antibody treatment (1.6 mg/rat i.p.), and in infected rats with the same treatment applied at 0 or 3 days postinfection. NGF and NGF mRNA levels in the bowel were increased during inflammation. Although anti-NGF treatments did not prevent or reverse inflammatory response, the treatment was effective in preventing the motor alterations induced by the T. spiralis infection, i.e., inhibited increased SMA, reversed altered response to CCK, and reversed in part exacerbated response to electrical stimulation.