Impaired capsaicin and neurokinin-evoked colonic motility in inflammatory bowel disease

Radioprotective Effects of Carvacrol and/or Thymol against Gamma Irradiation-Induced Acute Nephropathy: In Silico and In Vivo Evidence of the Involvement of Insulin-like Growth Factor-1 (IGF-1) and Calcitonin Gene-Related Peptide

Radiotherapy (RT) is an effective curative cancer treatment. However, RT can seriously damage kidney tissues resulting in radiotherapy nephropathy (RN) where oxidative stress, inflammation, and apoptosis are among the common pathomechanisms. Carvacrol and thymol are known for their antioxidative, anti-inflammatory, and radioprotective activities. Therefore, this study investigated the nephroprotective potentials of carvacrol and/or thymol against gamma (γ) irradiation-induced nephrotoxicity in rats along with the nephroprotection mechanisms, particularly the involvement of insulin-like growth factor-1 (IGF-1) and calcitonin gene-related peptide (CGRP). Methods: Male rats were injected with carvacrol and/or thymol (80 and 50 mg/kg BW in the vehicle, respectively) for five days and exposed to a single dose of irradiation (6 Gy). Then, nephrotoxicity indices, oxidative stress, inflammatory, apoptotic biomarkers, and the histopathological examination were assessed. Also, IGF-1 and CGRP renal expressions were measured. Results: Carvacrol and/or thymol protected kidneys against γ-irradiation-induced acute RN which might be attributed to their antioxidative, anti-inflammatory, and antiapoptotic activities. Moreover, both reserved the γ -irradiation-induced downregulation of CGRP- TNF-α loop in acute RN that might be involved in the pathomechanisms of acute RN. Additionally, in Silico molecular docking simulation of carvacrol and thymol demonstrated promising fitting and binding with CGRP, IGF-1, TNF-α and NF-κB through the formation of hydrogen, hydrophobic and alkyl bonds with binding sites of target proteins which supports the reno-protective properties of carvacrol and thymol. Collectively, our findings open a new avenue for using carvacrol and/or thymol to improve the therapeutic index of γ-irradiation.

CGRP physiology, pharmacology, and therapeutic targets: migraine and beyond

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse physiological functions. Its two isoforms (α and β) are widely expressed throughout the body in sensory neurons as well as in other cell types, such as motor neurons and neuroendocrine cells. CGRP acts via at least two G protein-coupled receptors that form unusual complexes with receptor activity-modifying proteins. These are the CGRP receptor and the AMY1 receptor; in rodents, additional receptors come into play. Although CGRP is known to produce many effects, the precise molecular identity of the receptor(s) that mediates CGRP effects is seldom clear. Despite the many enigmas still in CGRP biology, therapeutics that target the CGRP axis to treat or prevent migraine are a bench-to-bedside success story. This review provides a contextual background on the regulation and sites of CGRP expression and CGRP receptor pharmacology. The physiological actions of CGRP in the nervous system are discussed, along with updates on CGRP actions in the cardiovascular, pulmonary, gastrointestinal, immune, hematopoietic, and reproductive systems and metabolic effects of CGRP in muscle and adipose tissues. We cover how CGRP in these systems is associated with disease states, most notably migraine. In this context, we discuss how CGRP actions in both the peripheral and central nervous systems provide a basis for therapeutic targeting of CGRP in migraine. Finally, we highlight potentially fertile ground for the development of additional therapeutics and combinatorial strategies that could be designed to modulate CGRP signaling for migraine and other diseases.

Constipation Caused by Anti-calcitonin Gene-Related Peptide Migraine Therapeutics Explained by Antagonism of Calcitonin Gene-Related Peptide's Motor-Stimulating and Prosecretory Function in the Intestine

The development of small-molecule calcitonin gene-related peptide (CGRP) receptor antagonists (gepants) and of monoclonal antibodies targeting the CGRP system has been a major advance in the management of migraine. In the randomized controlled trials before regulatory approval, the safety of these anti-CGRP migraine therapeutics was considered favorable and to stay within the expected profile. Post-approval real-world surveys reveal, however, constipation to be a major adverse event which may affect more than 50% of patients treated with erenumab (an antibody targeting the CGRP receptor), fremanezumab or galcanezumab (antibodies targeting CGRP). In this review article we address the question whether constipation caused by inhibition of CGRP signaling can be mechanistically deduced from the known pharmacological actions and pathophysiological implications of CGRP in the digestive tract. CGRP in the gut is expressed by two distinct neuronal populations: extrinsic primary afferent nerve fibers and distinct neurons of the intrinsic enteric nervous system. In particular, CGRP is a major messenger of enteric sensory neurons which in response to mucosal stimulation activate both ascending excitatory and descending inhibitory neuronal pathways that enable propulsive (peristaltic) motor activity to take place. In addition, CGRP is able to stimulate ion and water secretion into the intestinal lumen. The motor-stimulating and prosecretory actions of CGRP combine in accelerating intestinal transit, an activity profile that has been confirmed by the ability of CGRP to induce diarrhea in mice, dogs and humans. We therefore conclude that the constipation elicited by antibodies targeting CGRP or its receptor results from interference with the physiological function of CGRP in the small and large intestine in which it contributes to the maintenance of peristaltic motor activity, ion and water secretion and intestinal transit.

Sensory nerves promote corneal inflammation resolution via CGRP mediated transformation of macrophages to the M2 phenotype through the PI3K/AKT signaling pathway

OBJECTIVES

To explore the role of the corneal sensory nerves in Pseudomonas aeruginosa (P. aeruginosa) keratitis, the synergistic effect between the sensory neurons and macrophages in calcitonin gene-related peptide (CGRP) release, and the functional mechanisms of CGRP-mediated transformation of macrophages to the M2 phenotype.

METHODS

Corneal nerve loss, macrophage recruitment, and CGRP expression were evaluated. To explore the synergistic effect between the sensory neurons and macrophages, RAW 264.7 cells were challenged with lipopolysaccharide (LPS), then trigeminal ganglion (TG) sensory neurons were isolated and co-incubated with macrophages, and CGRP expression was tested. To investigate the biological function of cornea neuron-initiated immune responses mediated by CGRP, BIBN 4096BS was used to inhibit CGRP in vivo and α-CGRP was used to simulate CGRP in vitro. The expressions of inflammatory cytokines (IL-1β, IL-6, TNF-α, and IL-10), M1 (CD80/CD86), M2 (CD163/CD206) macrophage markers, and signal transducers (PI3K/AKT) were detected.

RESULTS

P. aeruginosa infection induced corneal nerve loss, macrophage recruitment, and CGRP up-expression. CGRP was co-localized with macrophages. Co-culture showed that sensory neurons and macrophages can mediate CGRP release. More CGRP was released when the two types of cells were combined to respond to LPS. BIBN 4096BS promoted pro-inflammatory cytokines and inhibited the anti-inflammatory cytokines and signal transducers, while, α-CGRP inhibited the pro-inflammatory cytokines and M1 markers and promoted the anti-inflammatory cytokine, M2 markers, and signal transducers.

CONCLUSIONS

P. aeruginosa infection induces corneal sensory neuron activation, macrophage recruitment, and CGRP up-expression. The synergistic effect between the sensory neurons and macrophages promotes CGRP release. CGRP inhibits corneal inflammation and promotes the transformation of macrophages to the M2 phenotype through the PI3K/AKT signaling pathway.

Eosinophils in Inflammatory Bowel Disease

Clinical investigations in inflammatory bowel disease (IBD) patients have provided increasing evidence that eosinophils contribute to chronic intestinal inflammation. Accumulation of eosinophils in the gastrointestinal tract correlates with the variations of eosinophil regulatory molecules; however, their role in gastrointestinal dysfunction in IBD has not been fully elucidated. This review will describe the development and characterization of gastrointestinal eosinophils, mechanisms of eosinophil recruitment to the gastrointestinal tract. Moreover, the eosinophil-induced changes to the enteric nervous system associated with disease severity and gastrointestinal dysfunction will be analyzed with suggestive molecular pathways for enteric neuronal injury. Current and potential therapeutic interventions targeting eosinophils will be discussed.

Impairment of Small Intestinal Function in Ulcerative Colitis: Role of Enteric Innervation

Small intestinal dysfunction has been described in patients with ulcerative colitis and in experimental animal models of colitis. This is demonstrated by a decrease in fluid, electrolyte, amino acid, fat and carbohydrate absorption as well as by deranged intestinal motility. Histopathological changes in the small intestines in colitis have not been consistently demonstrated, but there is evidence of structural and biochemical alterations as shown by increased intestinal permeability and a decrease in the expression of multiple brush border membrane enzymes such as disaccharidases and aminopetidases, in both humans and experimental animals. The pathophysiology of this dysfunction has not been elucidated, but it is thought to include alterations in neural circuitry such as increased neuronal excitability, neuronal damage and changes of neuropeptidergic innervation and receptors as well as an increase in local production of pro-inflammatory cytokines and alterations in the production of some neurohumoral mediators. In the following, we provide an update on the advancement of clinical and scientific contributions to elucidate the underlying mechanisms of the alteration of the functions of apparently intact small intestinal segments, induced by ulcerative colitis.

Trypsin induces biphasic muscle contraction and relaxation via transient receptor potential vanilloid 1 and neurokinin receptors 1/2 in porcine esophageal body

Duodenal reflux of fluids containing trypsin relates to refractory gastroesophageal reflux disease (GERD). Esophageal peristalsis and clearance are important factors in GERD pathogenesis. However, the function of trypsin in esophageal body contractility is not fully understood. In this study, effects of trypsin on circular smooth muscle (CSM) and longitudinal smooth muscle (LSM) of the porcine esophageal body were examined. Trypsin elicited a concentration dependent biphasic response, a major contraction and a subsequent relaxation only in CSM. In CSM, contraction occurred at trypsin concentrations of 100nM and relaxation at 1μM. A proteinase-activated receptor (PAR)2 activating peptide, SLIGKV-NH₂ (1mM), induced a monophasic contraction. Those responses were unaffected by tetrodotoxin though abolished by the gap junction uncouplers carbenoxolone and octanol. They were also partially inhibited by a transient receptor potential vanilloid type 1 (TRPV1) antagonist and abolished by combination of neurokinin receptor 1 (NK₁) and NK₂ antagonists, but not by an NK₃ antagonist, suggesting a PAR2-TRPV1-substance P pathway in sensory neurons. Substance P (100nM), an agonist for various NK receptors (NK₁, NK₂ and NK₃) with differing affinities, induced significant contraction in CSM, but not in LSM. The contraction was also blocked by the combination of NK₁ and NK₂ antagonists, but not by the NK₃ antagonist. Moreover, substance P-induced contractions were unaffected by the TRPV1 antagonist, but inhibited by a gap junction uncoupler. In conclusion, trypsin induced a biphasic response only in CSM and this was mediated by PAR2, TRPV1 and NK_1/2. Gap junctions were indispensable in this tachykinin-induced response.

Alterations of colonic function in the Winnie mouse model of spontaneous chronic colitis

The Winnie mouse, carrying a missense mutation in Muc2, is a model for chronic intestinal inflammation demonstrating symptoms closely resembling inflammatory bowel disease (IBD). Alterations to the immune environment, morphological structure, and innervation of Winnie mouse colon have been identified; however, analyses of intestinal transit and colonic functions have not been conducted. In this study, we investigated in vivo intestinal transit in radiographic studies and in vitro motility of the isolated colon in organ bath experiments. We compared neuromuscular transmission using conventional intracellular recording between distal colon of Winnie and C57BL/6 mice and smooth muscle contractions using force displacement transducers. Chronic inflammation in Winnie mice was confirmed by detection of lipocalin-2 in fecal samples over 4 wk and gross morphological damage to the colon. Colonic transit was faster in Winnie mice. Motility was altered including decreased frequency and increased speed of colonic migrating motor complexes and increased occurrence of short and fragmented contractions. The mechanisms underlying colon dysfunctions in Winnie mice included inhibition of excitatory and fast inhibitory junction potentials, diminished smooth muscle responses to cholinergic and nitrergic stimulation, and increased number of α-smooth muscle actin-immunoreactive cells. We conclude that diminished excitatory responses occur both prejunctionally and postjunctionally and reduced inhibitory purinergic responses are potentially a prejunctional event, while diminished nitrergic inhibitory responses are probably due to a postjunction mechanism in the Winnie mouse colon. Many of these changes are similar to disturbed motor functions in IBD patients indicating that the Winnie mouse is a model highly representative of human IBD.

NEW & NOTEWORTHY

This is the first study to provide analyses of intestinal transit and whole colon motility in an animal model of spontaneous chronic colitis. We found that cholinergic and purinergic neuromuscular transmission, as well as the smooth muscle cell responses to cholinergic and nitrergic stimulation, is altered in the chronically inflamed Winnie mouse colon. The changes to intestinal transit and colonic function we identified in the Winnie mouse are similar to those seen in inflammatory bowel disease patients.

Targeting tachykinin receptors for the treatment of functional gastrointestinal disorders with a focus on irritable bowel syndrome

BACKGROUND

Tachykinins (TKs) are a family of endogenous peptides widely expressed in the central and in the peripheral nervous systems as well as in the gastrointestinal (GI) tract. They act as full agonists at three different membrane receptors neurokinin (NK) 1, NK2, and NK3, which are G protein-coupled receptors and in the GI tract are expressed both on neurons and effector cells.

PURPOSE

This article reviews the literature concerning the role of TKs in the GI tract function in physiological and pathological conditions and their potential relevance in the treatment of functional GI disorders with particular reference to irritable bowel syndrome (IBS). The efficacy of NK1 antagonists in chemotherapy-induced and postoperative nausea and vomiting is well established. While pharmacodynamic studies have reported conflicting and negative results concerning the effects of NK1 and of NK3 antagonists, respectively, on the GI tract function in humans, clinical studies applying the NK3 antagonist talnetant in IBS-D were negative. Pharmacodynamic studies applying NK2 antagonists have suggested a role for antagonism of NK2 receptors in modulation of GI chemical-induced altered motility and of stress-induced altered bowel habits. Clinical studies and in particular a recently completed Phase 2 study have reported that the NK2 antagonist ibodutant is effective and safe in treating symptoms of D-IBS, especially in females.

Melatonin Attenuates Noise Stress-induced Gastrointestinal Motility Disorder and Gastric Stress Ulcer: Role of Gastrointestinal Hormones and Oxidative Stress in Rats

BACKGROUND/AIMS

There are increasing evidences for gastrointestinal motility disorder (GIMD) and gastric stress ulcer induced by noise stress. The present study was to investigate the reversed effect of melatonin on GIMD and gastric stress ulcer induced by noise stress and potential mechanism.

METHODS

Noise stress was induced on rats, and melatonin (15 mg/kg) was administered to rats by intraperitoneal injection. Differences were assessed in gastric residual rate (GRR), small intestine propulsion rate (SPR), Guth injury score, cortisol, gastrointestinal hormones (calcitonin-gene-related peptide and motilin) and oxidative stress markers (superoxide dismutase and malondialde hyde) in blood plasma as well as gastric mucosa homogenate with or without melatonin. The pathological examination of gastric mucosa was also performed.

RESULTS

The GRR and SPR were improved by noise stress compared with control (P < 0.05). The pathological examination and Guth injury score revealed gastric stress ulcer. Moreover, the levels of cortisol, motilin and malondialdehyde in blood plasma and ma-londialdehyde in gastric mucosa homogenate were increased by noise stress (P < 0.05). CGRP and superoxide dismutase activ-ity in both of blood plasma and gastric mucosa homogenate were significantly decreased (P< 0.05). Furthermore, melatonin reversed changes in GRR, SPR, pathological examination, Guth injury score, cortisol, motilin, CGRP, superoxide dismutase activity and malondialdehyde (P < 0.05).

CONCLUSIONS

Melatonin is effective in reversing the GIMD and gastric stress ulcer induced by noise stress. The underlying mechanism may be involved in oxidative stress and gastrointestinal hormones.

Colonic motility in ulcerative colitis

BACKGROUND

Inflammatory conditions affecting the gut may cause motility disturbances, and ulcerative colitis - one of the main disorders among the inflammatory bowel diseases - may display abnormal colonic motility.

AIM

To review the abnormalities of the large bowel in ulcerative colitis, by considering the motility, laboratory (in vitro) and pathological studies dealing with this topic.

METHODS

A comprehensive online search of Medline and the Science Citation Index was carried out.

RESULTS

Patients with ulcerative colitis frequently display colonic motor abnormalities, including lack of contractility, an increase of propulsive contractile waves, an excessive production of nitric oxide, vasoactive intestinal polypeptide nerves, interleukin 1 beta, neurotensin, tachykinins levels and the weaker action of substance P, likely related to a neuromuscular dysfunction due to the inflammatory process.

CONCLUSIONS

A better understanding of the pathophysiological grounds of altered colonic motility in ulcerative colitis may lead to a more in-depth knowledge of the accompanying symptoms and to better and more targeted therapeutic approaches.

Cross-talk between neural and immune receptors provides a potential mechanism of homeostatic regulation in the gut mucosa

The relationship between elements of the immune system and the nervous system in the presence of bacteria has been addressed recently. In particular, the sensory vanilloid receptor 1 (transient receptor potential cation channel subfamily V member 1 (TRPV1)) and the neuropeptide calcitonin gene-related peptide (CGRP) have been found to modulate cytokine response to lipopolysaccharide (LPS) independently of adaptive immunity. In this review we discuss mucosal homeostasis in the gastrointestinal tract where bacterial concentration is high. We propose that the Gram-negative bacterial receptor Toll-like receptor 4 (TLR4) can activate TRPV1 via intracellular signaling, and thereby induce the subsequent release of anti-inflammatory CGRP to maintain mucosal homeostasis.

Localisation and activation of the neurokinin 1 receptor in the enteric nervous system of the mouse distal colon

The substance P neurokinin 1 receptor (NK1R) regulates motility, secretion, inflammation and pain in the intestine. The distribution of the NK1R is a key determinant of the functional effects of substance P in the gut. Information regarding the distribution of NK1R in subtypes of mouse enteric neurons is lacking and is the focus of the present study. NK1R immunoreactivity (NK1R-IR) is examined in whole-mount preparations of the mouse distal colon by indirect immunofluorescence and confocal microscopy. The distribution of NK1R-IR within key functional neuronal subclasses was determined by using established neurochemical markers. NK1R-IR was expressed by a subpopulation of myenteric and submucosal neurons; it was mainly detected in large multipolar myenteric neurons and was colocalized with calcitonin gene-related peptide, neurofilament M, choline acetyltransferase and calretinin. The remaining NK1R-immunoreactive neurons were positive for nitric oxide synthase. NK1R was expressed by most of the submucosal neurons and was exclusively co-expressed with vasoactive intestinal peptide, with no overlap with choline acetyltransferase. Treatment with substance P resulted in the concentration-dependent internalisation of NK1R from the cell surface into endosome-like structures. Myenteric NK1R was mainly expressed by intrinsic primary afferent neurons, with minor expression by descending interneurons and inhibitory motor neurons. Submucosal NK1R was restricted to non-cholinergic secretomotor neurons. These findings highlight key differences in the neuronal distribution of NK1R-IR between the mouse, rat and guinea-pig, with important implications for the functional role of NK1R in regulating intestinal motility and secretion.

Calcitonin gene-related peptide is a key neurotransmitter in the neuro-immune axis

The question of how the neural and immune systems interact in host defense is important, integrating a system that senses the whole body with one that protects. Understanding the mechanisms and routes of control could produce novel and powerful ways of promoting and enhancing normal functions as well as preventing or treating abnormal functions. Fragmentation of biological research into specialities has resulted in some failures in recognizing and understanding interactions across different systems and this is most striking across immunology, hematology, and neuroscience. This reductionist approach does not allow understanding of the in vivo orchestrated response generated through integration of all systems. However, many factors make the understanding of multisystem cross-talk in response to a threat difficult, for instance the nervous and immune systems share communication molecules and receptors for a wide range of physiological signals. But, it is clear that physical, hard-wired connections exist between the two systems, with the key link involving sensory, unmyelinated nerve fibers (c fibers) containing the neuropeptide calcitonin gene-related peptide (CGRP), and modified macrophages, mast cells and other immune and host defense cells in various locations throughout the body. In this review we will therefore focus on the induction of CGRP and its key role in the neuroimmune axis.

Activated eosinophils in association with enteric nerves in inflammatory bowel disease

Enteric neural dysfunction leads to increased mucous production and dysmotility in inflammatory bowel disease (IBD). Prior studies have shown that tissue eosinophilia is related to disease activity. We hypothesized that interactions between eosinophils and nerves contribute to neural dysfunction in IBD. Tissue from patients with intractable IBD, endoscopic biopsies from patients with steroid responsive IBD, both when active and quiescent, and control tissue were studied. Immunohistochemical studies showed that eosinophils localize to nerves in the mucosal layer of patients with Crohn’s disease (CD) (p<0.001) and ulcerative colitis (UC), (p<0.01). Eosinophils localized to substance P and choline acetyltransferase (ChAT) immunostained nerves. Real time PCR of laser capture micro-dissected enteric ganglia demonstrated Intercellular Adhesion Molecule 1 (ICAM-1) mRNA was increased 7-fold in UC (n = 4), (p = 0.03), and 10-fold in CD (n = 3), (p = 0.05). Compared with controls, eotaxin-3 (CCL-26) mRNA was increased 9-fold in UC (p = 0.04) and 15-fold in CD (p = 0.06). Eosinophil numbers correlated with disease activity, while deposition of major basic protein (MBP) and eosinophil Transforming Growth Factor β -1 (TGFβ-1) expression were seen in therapeutically responsive disease. These data indicate a significant localization of eosinophils to nerves in IBD, mediated through neurally expressed ICAM-1 and eotaxin-3. This cell/neural interaction may influence the function of nerves and contribute to symptoms in IBD.

Calcitonin gene-related peptide is a promising marker in ulcerative colitis

BACKGROUND

Assessment of the severity and extent of disease activity continues to present challenges for physicians in the treatment of ulcerative colitis. Standard markers that can objectively reflect disease activity are useful for physicians to both evaluate the course of ulcerative colitis and monitor the effectiveness of therapy for any given patient.

AIMS

We hypothesize that calcitonin gene-related peptide (CGRP) can reflect the activity and severity of ulcerative colitis and be used as a marker to assess the effectiveness of various therapies.

METHODS

We examined the expression levels of CGRP by reverse transcription polymerase chain reaction (RT-PCR) and semi-quantitative immunohistochemisty in mucosal biopsies from 38 patients with UC and 18 controls. Levels of CGRP mRNA and protein expression were compared between patients and controls with the clinical activity index (CAI) and the endoscopic activity index (EAI) for various levels of UC severity.

RESULTS

Our results showed that the levels of CGRP mRNA and protein expression were significantly reduced in UC patients compared to controls. This effect was more pronounced in patients with more severe cases of UC. There is a statistically significant negative correlation between levels of CGRP mRNA expression and CAI/EAI scores. A statistically significant negative correlation was also found between levels of CGRP protein expression and CAI/EAI scores. Overall, high CAI and EAI scores were accompanied by low CGRP mRNA and protein expression levels.

CONCLUSION

Levels of CGRP protein and mRNA expression in the colonic mucosa of patients are closely associated with UC severity and corroborate traditional indices used to assess the disease.

Decrease of guanylyl cyclase β1 subunit and nitric oxide (NO)-induced relaxation in mouse rectum with colitis and its reproduction on long-term NO treatment

Nitric oxide (NO) influences motility in the colon in patients with ulcerative colitis, but the exact mechanism involved remains unknown. Colitis was induced in mice by the oral administration of 2.5% dextran sodium sulfate (DSS), and the motility in longitudinal preparations from rectum and distal colon and expression of β1 subunit of soluble guanylyl cyclase (sGCβ1) were analyzed. Electrical stimulation (ES) caused a transient relaxation via the NO pathway in both rectum and colon from control mice. Stimulation with sodium nitroprusside (SNP) caused relaxation in the two regions, and the half-time (T (1/2)) of the maximal relaxation induced by 100 μM SNP was 8.1 ± 1.0 s in rectum. DSS treatment (1) abolished the ES-induced relaxation, but not dibutyryl cyclic GMP-induced response, in both regions, (2) decreased the maximal response to SNP accompanied by a loss of immunoreactive sGCβ1 protein in rectum, but did not affect the amplitude of the relaxant response or the protein in distal colon, and (3) caused an increase in the T (1/2) value in response to SNP in both regions. Pretreatment of both preparations from control mice with 600 μM SNP for 30 min decreased both ES- and SNP-induced relaxation, SNP-induced cyclic GMP formation, and immunoreactive sGCβ1 levels. NO-mediated relaxation was impaired by a dysfunctional sGC with and without a loss of immunoreactivity to sGCβ1 in rectum and colon from DSS-treated mice, respectively. Long-term exposure of the tissues with an excess amount of NO changes the sGC-mediated relaxation.

Proinflammatory cytokines suppress the expression level of protease-activated receptor-2 through the induction of iNOS in rat colon

Protease-activated receptor (PAR)-2 plays important roles in intestinal inflammatory responses and also contributes to intestinal digestive motility. In the distal colon of a rat experimental colitis model, expression level of PAR-2 mRNA was decreased, and relaxation through PAR-2 activation was attenuated. This study shows the effects of proinflammatory cytokines on changes to PAR-2 in rat colonic smooth muscle using an organ culture method. Colonic inflammation was induced in rats by administering dextran sodium sulphate in drinking water. Organ culture of distal colonic smooth muscle layer of normal rat was performed for up to 3 days. In the experimental colitis rat, mRNA expression levels of proinflammatory cytokines such as IL-1beta and TNF-alpha increased with inflammation. After the incubation with IL-1beta and TNF-alpha for 3 days, trypsin (PAR-2 agonist)-induced relaxation was attenuated, simultaneous with suppression of PAR-2 mRNA expression. Conversely, in this preparation, mRNA expression levels of iNOS were significantly increased. When l-NMMA was added to the medium with IL-1beta and TNF-alpha, changes to PAR-2 by these cytokine recovered. Moreover, when samples were cultured with NOC-18 (slow-releasing NO donor) for 3 days, relaxation induced by trypsin and expression of PAR-2 mRNA were attenuated. These results suggest that suppression of PAR-2 expression under inflammatory conditions is at least partially induced by NO produced in the colonic muscularis externa by proinflammatory cytokines.

Spatial and temporal expression of tachykinins and NK1- and NK2-receptor gene during TNB induced colitis in rats

The distribution and modification of the tachykinins Substance P (SP) and neurokinin A (NKA), their precursor beta-preprotachykinins (beta-PPT) and the receptors involved in their activity, NK-1 and NK-2, were studied in trinitrobenzensulphonic acid (TNB) colitis. Rats were intrarectally treated with a 120 mg/ml of TNB solution and sacrificed at various times after colitis induction. During the acute phases of colitis, a marked decrease in tissue SP and NKA levels were observed along with an increased transcription of beta-PPT mRNA in the neurons of the myenteric plexus and an increased myeloperoxidase activity, which is an index of the tissue's inflammatory status. De novo expression of both NK(1) and NK(2) receptor mRNA was observed during the acute phase of TNB-colitis in mesenchymal cells around dilated submucosal vessels but their expression in smooth muscle cells of the muscularis mucosae and propria was moderately down-regulated. The peptide levels, myeloperoxidase activity and gene expression of tachykinin receptors were then restored during the late phases (2-4 weeks after the apten administration) while beta-PPT mRNA remained highly expressed in the myenteric plexus ganglia showing that SP and NKA are involved in repair processes. These results point to the enhanced release of tachykinins during the initial phase of colitis and a restoration of this neuropeptide pool in the healing of the tissue.

Neuro-immune interactions in inflammatory bowel disease and irritable bowel syndrome: future therapeutic targets

The gastro-intestinal tract is well known for its largest neural network outside the central nervous system and for the most extensive immune system in the body. Research in neurogastroenterology implicates the involvement of both enteric nervous system and immune system in symptoms of inflammatory bowel disease and irritable bowel syndrome. Since both disorders are associated with increased immune cell numbers, nerve growth and activation of both immune cells and nerves, we focus in this review on the involvement of immune cell-nerve interactions in inflammatory bowel disease and irritable bowel syndrome. Firstly, the possible effects of enteric nerves, especially of the nonadrenergic and noncholinergic nerves, on the intestinal immune system and their possible role in the pathogenesis of chronic intestinal inflammatory diseases are described. Secondly, the possible effects of immunological factors, from the innate (chemokines and Toll-like receptors) as well as the adaptive (cytokines and immunoglobulins) immune system, on gastro-intestinal nerves and its potential role in the development of inflammatory bowel disease and irritable bowel syndrome are reviewed. Investigations of receptor-mediated and intracellular signal pathways in neuro-immune interactions might help to develop more effective therapeutic approaches for chronic inflammatory intestinal diseases.

Mast cells and nerves tickle in the tummy: implications for inflammatory bowel disease and irritable bowel syndrome

Mast cells are well known as versatile cells capable of releasing and producing a variety of inflammatory mediators upon activation and are often found in close proximity of neurons. In addition, inflammation leads to local activation of neurons resulting in the release neuropeptides, which also play an important immune modulatory role by stimulation of immune cells. In intestinal disorders like inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), the number of mast cells is known to be much higher than in the normal intestine. Moreover, both these disorders are also reported to be associated with alterations in neuropeptide content and in neural innervation. Mutual association between mast cells and enteric nerves has been demonstrated to be increased in pathophysiological conditions and contribute to spreading and amplification of the response in IBD and IBS. In this review the focus lies on studies appointed to the direct interaction between mast cells and nerves in IBD, IBS, and animal models for these disorders so far.

Role for NK(1) and NK(2) receptors in the motor activity in mouse colon

The present study examined the effects induced by endogenous and exogenous activation of NK(1) and NK(2) receptors on the mechanical activity of mouse proximal colon. Experiments were performed in vitro recording the changes in intraluminal pressure from isolated colonic segments. Electrical field stimulation in the presence of atropine and guanethidine produced a small relaxation, followed by nonadrenergic noncholinergic (NANC) contraction. SR140333, NK(1) receptor antagonist, or SR48968, NK(2) receptor antagonist, significantly reduced the contraction, although SR48968 appeared more efficacious. The co-administration of SR140333 and SR48968 virtually abolished the NANC contraction. [Sar(9), Met(O(2))(11)]-substance P, selective NK(1) receptor agonist, induced a concentration-dependent biphasic effect, contraction followed by reduction of the mechanical spontaneous activity. Both effects were antagonized by SR140333, but not by SR48968. [beta-Ala(8)]-neurokinin A (4-10), selective NK(2) receptor agonist, evoked concentration-dependent contraction, which was antagonized by SR48968, but not by SR140333. The contraction induced by [Sar(9), Met(O(2))(11)]-substance P, but not by [beta-Ala(8)]-neurokinin A (4-10), was reduced by tetrodotoxin or atropine, and increased by N(omega)-nitro-L-arginine methyl ester (L-NAME), inhibitor of nitric oxide synthase. The inhibitory effects induced by [Sar(9), Met(O(2))(11)]-substance P were abolished by tetrodotoxin or L-NAME. The results of the present study suggest that in mouse colon both NK(1) and NK(2) receptors are junctionally activated by endogenous tachykinins to cause an additive response. NK(1) receptors appear to be located on cholinergic and on nitrergic neurons as well as on smooth muscle cells, whereas NK(2) receptors seem to be present exclusively on smooth muscle cells.

The autonomic nervous system and inflammatory bowel disease

Crohn's disease and ulcerative colitis, collectively known as inflammatory bowel disease (IBD), are chronic, recurring, inflammatory conditions of the intestine. The precise mechanisms underlying the pathogenesis of IBD are not yet clear but they are believed to involve a number of precipitating factors, most notably genetic susceptibility and environmental influences. The autonomic nervous system (ANS) has long been known as a critical regulator of intestinal function and much evidence now exists to suggest that it also plays an important role in the development of IBD. Dramatic changes in the ANS in IBD are apparent from the cellular to the molecular level ultimately leading to altered communication between the ANS and effector cells of the intestine. This review aims to synthesize the current understanding of the pathogenesis of IBD with a particular emphasis on the role that the ANS plays in the progression of these diseases.

Colonic propulsive and postprandial motor activity in patients with ulcerative colitis in remission

BACKGROUND

Although it is known that colon motility is abnormal in ulcerative colitis, data are still scarce with regard to the underlying mechanisms. Recent evidence suggests that the propulsive activity is highly increased during the active phase of the disease, probably contributing to the diarrhoea. However, data are even scarcer in the quiescent phase of the disease.

AIMS

To assess the colonic high-amplitude and low-amplitude propulsive activity and the colonic motor response to eating in patients with ulcerative colitis in remission.

PATIENTS AND METHODS

Fourteen patients were recruited, all with the disease in remission as documented by clinical and endoscopic criteria. Twenty-four hour manometric recordings were obtained in these patients, and compared to those of 16 healthy controls.

RESULTS

The high-amplitude propagated contractions were similar in both groups (5.8+/-2.6 events in ulcerative colitis patients and 5.5+/-0.8 in controls (P=0.13)), whereas patients tended to display a higher number of low-amplitude propagated events (134.4+/-34 vs. 60.9+/-16 in controls (P=0.058)). No differences were found in the colonic motor response to eating between patients and controls.

CONCLUSIONS

Colonic propulsive activity in ulcerative colitis in remission is almost normal, even though the low-amplitude propagated activity tends to be similar to that observed in patients with the irritable bowel syndrome, thus possibly contributing to the persistence of abdominal symptoms in a subgroup of patients.

Tachykinins and tachykinin receptors in the gut, with special reference to NK2 receptors in human

Tachykinins (TKs), substance P (SP), neurokinin A (NKA) and B (NKB) are important peptide modulators of intestinal motility in animal species studied so far, including humans. Modulation of motility by TKs can occur at various levels, since these peptides are expressed in cholinergic excitatory motor neurons projecting to both circular and longitudinal muscle, interneurons, and intramural and extramural sensory neurons. The effects of SP, NKA and NKB are preferentially mediated through the stimulation of NK1, NK2 and NK3 receptors, respectively; however, the selectivity of natural TKs for their preferred receptors is relative. In addition, SP and NKA are expressed in similar quantities in the human intestine and adequate stimuli can release similar amount of these TKs from enteric nerves. Furthermore, a single anatomical substrate can express more than one TK receptor type, so that the blockade of a single receptor type may not reveal functional effects in integrated models of motility. In isolated human small intestine and colon circular muscle strips, both NK1 and NK2 receptors mediate contractile effects. Indeed, in the human small intestine, smooth muscle electrical and motor events induced by electrical field stimulation (EFS) can involve either or both NK1 and NK2 receptors or these latter receptors predominantly, depending on the experimental conditions. In contrast, in the human colonic smooth muscle, only the NK2 receptor-mediated component of the response to EFS is prominent and some evidence would suggest that this component is the main excitatory motor mechanism at this level. Furthermore, a NK2 receptor-mediated secretory component in the human colonic mucosa has been recently demonstrated. Thus, it could be speculated that the blockade of both NK1 and NK2 receptors will be necessary to antagonise motor effects induced by exogenous administration or endogenous release of TKs in the small intestine, whereas the blockade of the NK2 receptors would be sufficient to disrupt physiological motor and, possibly, secretory activity at the colonic level. Available evidence indicates that, in healthy volunteers, the infusion of NKA (25 pmol/kg/min i.v.) stimulated small intestine motility and precipitated a series of intestinal and non-intestinal adverse events. Nepadutant (8 mg i.v.), a selective NK2 receptor antagonist, antagonised small intestine motility induced by NKA and prevented associated intestinal adverse events. In another study, the same dose of nepadutant increased colo-rectal compliance during isobaric balloon distension in healthy volunteers pretreated with a glycerol enema, disclosing a NK2 receptor-mediated component in the regulation of colonic smooth muscle tone. However, the prolonged blockade of NK2 receptors by nepadutant (16 mg i.v. b.i.d. for 8 days) did not affect bowel habits, neither in term of movements nor of stool consistency. Altogether, these results indicate that, even when there is a significant redundance in the effects of TKs and in the role of their receptors, the selective blockade of tachykinin NK2 receptors can have functional consequences on human intestinal motility and perception, but this can occur without the disruption of the physiological functions.