Tachykinins in the gut. Part II. Roles in neural excitation, secretion and inflammation

Updates on treatment of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a highly prevalent gastrointestinal disorder characterized by abdominal pain and discomfort in association with altered bowel habits. It is estimated to affect 10%-15% of the Western population, and has a large impact on quality of life and (in)direct healthcare costs. IBS is a multifactorial disorder involving dysregulation within the brain-gut axis, and it is frequently associated with gastrointestinal motor and sensory dysfunction, enteric and central nervous system irregularities, neuroimmune dysregulation, and post-infectious inflammation. As with other functional medical disorders, the treatment for IBS can be challenging. Conventional therapy for those with moderate to severe symptoms is largely unsatisfactory, and the development of new and effective drugs is made difficult by the complex pathogenesis, variety of symptoms, and lack of objective clinical findings that are the hallmark of this disorder. Fortunately, research advances over the past several decades have provided insight into potential mechanisms responsible for the pathogenesis of IBS, and have led to the development of several promising pharmaceutical agents. In recent years there has been much publicity over several of these new IBS medications (alosetron and tegaserod) because of their reported association with ischemic colitis and cardiovascular disease. While these agents remain available for use under restricted prescribing programs, this highlights the need for continued development of safe and effective medication for IBS. This article provides a physiologically-based overview of recently developed and frequently employed pharmaceutical agents used to treat IBS, and discusses some non-pharmaceutical options that may be beneficial in this disorder.

Utilization of the least shrew as a rapid and selective screening model for the antiemetic potential and brain penetration of substance P and NK1 receptor antagonists

Substance P (SP) is thought to play a cardinal role in emesis via the activation of central tachykinin NK1 receptors during the delayed phase of vomiting produced by chemotherapeutics. Although the existing supportive evidence is significant, due to lack of an appropriate animal model, the evidence is indirect. As yet, no study has confirmed that emesis produced by SP or a selective NK1 receptor agonist is sensitive to brain penetrating antagonists of either NK1, NK2, or NK3 receptors. The goals of this investigation were to demonstrate: 1) whether intraperitoneal (i.p.) administration of either SP, a brain penetrating (GR73632) or non-penetrating (e.g. SarMet-SP) NK1 receptor agonist, an NK2 receptor agonist (GR64349), or an NK3 receptor agonist (Pro7-NKB), would induce vomiting and/or scratching in the least shrew (Cryptotis parva) in a dose-dependent manner; and whether these effects are sensitive to the above selective receptor antagonists; 2) whether an exogenous emetic dose of SP (50 mg/kg, i.p.) can penetrate into the shrew brain stem and frontal cortex; 3) whether GR73632 (2.5 mg/kg, i.p.)-induced activation of NK1 receptors increases Fos-measured neuronal activity in the neurons of both brain stem emetic nuclei and the enteric nervous system of the gut; and 4) whether selective ablation of peripheral NK1 receptors can affect emesis produced by GR73632. The results clearly demonstrated that while SP produced vomiting only, GR73632 caused both emesis and scratching behavior dose-dependently in shrews, and these effects were sensitive to NK1-, but not NK2- or NK3-receptor antagonists. Neither the selective, non-penetrating NK1 receptor agonists, nor the selective NK2- or NK3-receptor agonists, caused a significant dose-dependent behavioral effect. An emetic dose of SP selectively and rapidly penetrated the brain stem but not the frontal cortex. Systemic GR73632 increased Fos expression in the enteric nerve plexi, the medial subnucleus of nucleus tractus solitarius, and the dorsal motor nucleus of the vagus, but not the area postrema. Ablation of peripheral NK1 receptors attenuated the ability of GR73632 to induce a maximal frequency of emesis and shifted its percent animals vomiting dose-response curve to the right. The NK1-ablated shrews exhibited scratching behavior after systemic GR73632-injection. These results, for the first time, affirm a cardinal role for central NK1 receptors in SP-induced vomiting, and a facilitatory role for gastrointestinal NK1 receptors. In addition, these data support the validation of the least shrew as a specific and rapid behavioral animal model to screen concomitantly both the CNS penetration and the antiemetic potential of tachykinin NK1 receptor antagonists.

A randomized, placebo-controlled, crossover, double-blind trial of the NK1 receptor antagonist aprepitant on gastrointestinal motor function in healthy humans

BACKGROUND

Little is known about the role of tachykinins on human gastrointestinal motility and no data exist on the possible effect of an NK1 receptor antagonist.

AIM

To examine the effect of an antiemetic dose of the selective NK1 receptor antagonist aprepitant on gastrointestinal propulsion in healthy humans.

METHODS

Twelve healthy volunteers participated in a crossover, double-blind study. In random order, each volunteer had a 125-mg capsule of aprepitant or placebo on day 1 followed by an 80-mg capsule of aprepitant or placebo on days 2-5. Gamma camera imaging was used to measure gastric emptying, small intestinal transit and colonic transit of a radiolabelled, 1600-kJ mixed liquid and solid meal ingested on day 2.

RESULTS

Aprepitant did not change gastric retention at 15 min, gastric half emptying time, gastric mean transit time, time to small intestinal transit of 10%, small intestinal mean transit time or colonic geometric centre after 24, 48 and 72 h.

CONCLUSION

A 125-mg capsule of aprepitant followed by an 80-mg capsule of aprepitant each of the next 2-5 days did not induce major changes in the propulsive function of the gastrointestinal tract in the small number of healthy volunteers investigated.

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.

Chronic inflammation alters the contribution of neurokinin receptor subtypes to epithelial function in rat colon

We have previously shown that neurokinin-1 (NK1) receptors predominantly mediate substance P-induced secretion of the non-inflamed rat colonic mucosa in vitro with a gradient in the magnitude of these responses. The aim of this study was to examine the effects of chronic inflammation on the contributions of different neurokinin receptor subtypes to colonic mucosal secretion. Colitis was induced by the intracolonic administration of 2,4,6-trinitrobenzene sulfonic acid in rats, reactivated 6 weeks later. Segments of proximal, mid- and distal colon were stripped of muscularis propria and mounted in Ussing chambers for measurement of short-circuit current. Use of selective agonists suggests that in the chronically inflamed rat colon NK1 receptors play a greater role in neurokinin-mediated mucosal secretion than do either NK2 or NK3. Selective antagonism implies that this is region-specific, with the inflammatory process altering the relative contribution of the neurokinin receptor subtypes within each region of the rat colon.

Role of preprotachykinin-A gene products on multiple organ injury in LPS-induced endotoxemia

Endotoxemia is a life-threatening, inflammatory condition that involves multiple organ injury and dysfunction. Preprotachykinin-A (PPT-A) gene products, substance P (SP), and neurokinin-A have been shown to play an important role in neurogenic inflammation. To investigate the role of PPT-A gene products on multiple organ injury in LPS-induced endotoxemia, endotoxemia was induced by LPS administration (10 mg/kg, i.p.) in PPT-A gene-deficient mice (PPTA(-/-)) and the wild-type (WT) control mice (PPT-A+/+). I.p. administration of LPS to WT mice caused a significant increase in circulating levels of SP as well as in liver, lung, and kidney. PPT-A gene deletion significantly protected against liver, pulmonary, and renal injury following LPS-induced endotoxemia, as evidenced by tissue myeloperoxidase activities, plasma alanine aminotransferase, aspartate aminotransferase levels, and histological examination. Furthermore, PPT-A(-/-) mice had significantly attenuated chemokines, proinflammatory cytokines, and adhesion molecule levels in the liver, lung, and kidney. These results show that PPT-A gene products are critical proinflammatory mediators in endotoxemia and the associated multiple organ injury. In addition, the data suggest that deletion of the PPT-A gene protected mice against organ damage in endotoxemia by disruption in neutrophil recruitment.

Substance P receptor expression in patients with inflammatory bowel disease. Determination by three different techniques, i.e., storage phosphor autoradiography, RT-PCR and immunohistochemistry

Inflammatory bowel disease (IBD) is characterized by chronic intestinal inflammation accompanied by changes in motility. It is known that regulatory peptides like substance P (SP) are important pro-inflammatory peptides which are also involved in neuronal conduction. To get clues for new diagnostic and therapeutic approaches we describe the SP receptor (NK-1) distribution in IBD compared to control intestinal tissue, on mRNA and protein level by three complementary techniques. Autoradiography showed differences within the intestinal wall of control patients; mucosal binding was 17 fmol/g and muscular binding was significantly (p=0.01) higher (98 fmol/g). In inflamed specimens of patients with IBD mucosal SP binding was increased compared to controls (55+/-10 vs 18+/-4 fmol/g mucosa, p=0.002). However RT-PCR showed that the mRNA content of the NK-1 receptor in these samples was not increased. In non-inflamed samples of patients with Crohn's disease (CD) and ulcerative colitis (UC) SP binding was similar as in controls, while mRNA was significantly decreased in CD patients (0.7+/-0.02 vs 4.4+/-0.7, p=0.01) but not in UC patients (4.4+/-0.7 vs 4.1+/-1.4). Immunohistochemistry identified a broad spectrum of NK-1 receptor locations in control intestine. No aberrant expression in IBD was found. This study showed that although there was no difference in location of the SP receptors in IBD patients versus controls, the quantity of SP binding was significantly increased in the inflamed mucosa of IBD patients, while the mRNA level was not increased. Further a difference in mRNA level between non-inflamed tissue of CD and UC patients was shown, with mRNA in CD being lower. These changes in SP receptor expression during chronic inflammation suggest that SP receptors are a potential target for therapeutic regulation of the inflammatory response.

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 of neuropeptides in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing condition involving complex interactions between genes and the environment. The mechanisms triggering the initial attack and relapses, however, are not well understood. In the past several years the enteric nervous system (ENS) has been implicated in the pathophysiology of IBD. Both the ENS and the central nervous system (CNS) can amplify or modulate aspects of intestinal inflammation through secretion of neuropeptides that serve as a link between the ENS and CNS. Neuropeptides are defined as any peptide released from the nervous system that serves as an intercellular signaling molecule. Neuropeptides thought to play a potentially key role in IBD include substance P, corticotropin-releasing hormone, neurotensin, vasoactive intestinal peptide, mu-opioid receptor agonists, and galanin. This review focuses on the role of these neuropeptides in the pathophysiology of IBD and discusses the cell types and mechanisms involved in this process. The available evidence that neuropeptide blockade may be considered a therapeutic approach in both Crohn's disease and ulcerative colitis will also be discussed.

Stimulation of neuronal receptors, neuropeptides and cytokines during experimental oil of mustard colitis

Oil of mustard (OM), administered intracolonically, produces severe colitis in mice that is maximized within 3 days. The purpose of this study was to characterize the cytokine response, and to establish expression patterns of enteric neuronal mediators and neuronal receptors affected during active colitis. We measured the changes in the mRNA levels for neuronal receptors and mediators by real-time PCR, and cytokine and chemokine protein levels in the affected tissue. Significant increases in neuronal receptors, such as transient receptor potential A1 (TRPA1), cannabinoid type 1 receptor, neurokinin 1 receptor (NK1R) and delta-opioid receptor; prokineticin-1 receptor; and soluble mediators, such as prodynorphin, proenkephalin1, NK1, prokineticin-1 and secretory leukocyte protease inhibitor, occurred. Significant increases in cytokines, such as interleukin (IL)-1beta, IL-6 and granulocyte macrophage colony stimulating factor (GM-CSF), and in chemokines, such as macrophage chemotactic protein 1 (MCP-1), macrophage inflammatory protein 1 (MIP-1alpha) and Kupffer cell derived chemokine (KC), were detected, with no changes in T-cell-derived cytokines. Furthermore, immunodeficient C57Bl/6 RAG2(-/-) mice exhibited OM colitis of equal severity as seen in wt C57Bl/6 and CD-1 mice. The results demonstrate rapidly increased levels of mRNA for neuronal receptors and soluble mediators associated with pain and inflammation, and increases in cytokines associated with macrophage and neutrophil activation and recruitment. Collectively, the data support a neurogenic component in OM colitis coupled with a myeloid cell-related, T- and B-cell-independent inflammatory component.

Alterations of neuropeptides in the human gut during peritonitis

BACKGROUND AND AIMS

Gastrointestinal motility is reduced during sepsis but the pathomechanism involved is poorly understood. We investigated the expression of substance P (SP) and vasoactive intestinal peptide (VIP) in the myenteric plexus during peritonitis in human small bowel.

MATERIALS AND METHODS

Tissue samples of the small bowel were gathered from healthy patients and from patients with peritonitis. Immunohistochemistry for myeloperoxidase (MPO), SP, and VIP was performed in whole mount sections. To determine the level of inflammation, MPO-positive cells were counted in the circular muscle layer. SP and VIP immunoreactivity was analyzed in myenteric plexus neurons. The area of positive immunoreactivity for either neuropeptide within the plexus was analyzed and set in relation to the total area of the plexus and consecutively expressed as percentage.

RESULTS

During peritonitis, MPO-positive cells significantly increased by approximately fourfold as compared to healthy tissue. The immunoreactivity for SP was significantly reduced by approximately 80% in myenteric plexus neurons during peritonitis. In contrast, the immunoreactivity for VIP significantly increased by nearly twofold during peritonitis.

CONCLUSIONS

During peritonitis, the inflammatory reaction within the gut is increased. The neuropeptide expression in myenteric plexus neurons was observed as shifting towards increased expression of VIP, known to inhibit intestinal motility, and towards decreased expression of the prokinetic neuropeptide SP.

Changes of the different neuropeptide-containing nerve fibers and immunocells in the diabetic rat's alimentary tract

Peripheral neuropathy is a common complication of diabetes mellitus, where neuropeptides and immunocells might play important roles in the pathogenesis of the disease. In this article we have quantified the different neuropeptide-containing nerve fibers and immunocells in the streptozotocin-induced diabetic rat's alimentary tract (tongue, duodenum, colon) using immunohistochemical and immunocytochemical methods. The immunoreactive (IR) nerve fibers were found in all layers of the alimentary tract and their distribution pattern was similar in both control and diabetic groups. Mast cell-nerve fiber contacts were rarely found in the controls. However, after 4 weeks duration of diabetes the number of IR nerve fibers and the immunocompetent cells increased significantly (P < 0.05), and the number of mast cell-nerve fiber contacts was even more significantly increased (P < 0.001). The distance between nerve fibers and immunocells was about 1 mum or even less. Some of the mast cells were degranulated in the vicinity of nerve fibers. No immunocompetent cells were IR for any antisera in the control. However, after the streptozotocin treatment, a large number of the immunocompetent cells showed immunoreactivity for SP and NPY. Counting all immunocompetent cells in whole sections showed that 12.3% of them were IR for SP and 25.4% were IR for NPY. Increased number of SP-containing nerve fibers and immunocells in diabetes mellitus might be the reason for painful neuropathy and might amplify the inflammatory reaction in an axon reflex manner; the released histamine and leukotrienes, cytokines, and chemokines might cause inflammations and lesions of the mucosa.

A neurokinin 1 receptor antagonist decreases adhesion reformation after laparoscopic lysis of adhesions in a rat model of adhesion formation

BACKGROUND

Up to 94% of patients experience fibrous adhesions after abdominal surgery, and a significant number of these patients require a second operation for open or laparoscopic lysis of adhesions (LOA). The authors have previously shown that inhibition of the binding of tachykinin ligands to the neurokinin 1 receptor (NK-1R) using the neurokinin 1 receptor antagonist (NK-1RA) CJ-12,255 decreases primary adhesion formation and upregulates the peritoneal fibrinolytic system in a rat model. Whereas most studies have focused on the prevention of primary adhesions, few have addressed adhesion reformation after LOA. This study aimed to determine the effects of NK-1RA administration on adhesion reformation and peritoneal fibrinolytic activity after laparoscopic LOA.

METHODS

Adhesions were induced in 31 rats using our previously described ischemic button model. The rats underwent laparoscopy 7 days later, during which adhesions were scored and lysed followed by administration of the NK-1RA or saline. Then 7 days after LOA, 23 rats were killed and adhesions were scored. Eight rats also were killed 24 h after the LOA to obtain peritoneal tissue and fluid, which were analyzed for tissue plasminogen activator (tPA) mRNA expression and peritoneal fibrinolytic activity by reverse transcriptase-polymerase chain reaction (RT-PCR) and bioassay, respectively.

RESULTS

At laparoscopy, 79% +/- 3% of the buttons formed adhesions. In the saline-administered control animals, 42% +/- 3.2% of the buttons reformed adhesions after LOA (p < 0.05), whereas in the animals that received the NK-1RA, 18.2% +/- 3.5% of the buttons reformed adhesions (p < 0.05). As compared with control animals, NK-1RA administration increased tPA mRNA levels by 38% and fibrinolytic activity sixfold (p < 0.05; 7.0 +/- 2.1 U/ml vs 1.2 +/- 0.54 U/ml).

CONCLUSIONS

When administered during laparoscopic LOA, an NK-1RA significantly upregulates peritoneal fibrinolytic activity and decreases adhesion reformation.

Immunomodulatory properties of substance P: the gastrointestinal system as a model

Communication between nerves and immune and inflammatory cells of the small and large intestine plays a major role in the modulation of several intestinal functions, including intestinal motility, ion transport, and mucosal permeability. Neuroimmune interactions at intestinal sites have been associated with the pathophysiology of infectious and enterotoxin-mediated diarrhea and intestinal inflammation, including inflammatory bowel disease (IBD). During the past 20 years the neuropeptide substance P (SP) has been identified as an important mediator in the development and progress of intestinal inflammation by binding to its high-affinity neurokinin-1 receptor (NK-1R). This peptide, released from enteric nerves, sensory neurons, and inflammatory cells of the lamina propria during intestinal inflammation, participates in gut inflammation by interacting, directly or indirectly, with NK-1R expressed on nerves, epithelial cells, and immune and inflammatory cells, such as mast cells, macrophages, and T cells. SP-dependent activation of these cells leads to the release of cytokines and chemokines as well as other neuropeptides that modulate diarrhea, inflammation, and motility associated with the pathophysiology of several intestinal disease states. The recent development of specific nonpeptide NK-1R antagonists and NK-1R-deficient mice helped us understand the functional importance of the SP-NK-1R system in mediating intestinal neuroimmune interactions and to identify the particular cells and signaling pathways involved in this response. This review summarizes our understanding on the immunomodulatory properties of SP and its receptor in the intestinal tract with particular focus on their involvement in intestinal physiology as well as in the pathophysiology of several intestinal disease states at the in vivo and cell signaling level.

Anti-inflammatory effects of 4-phenyl-3-butenoic acid and 5-(acetylamino)-4-oxo-6-phenyl-2-hexenoic acid methyl ester, potential inhibitors of neuropeptide bioactivation

Substance P (SP) and calcitonin gene-related peptide (CGRP) are well established mediators of inflammation. Therefore, inhibition of the biosynthesis of these neuropeptides is an attractive potential strategy for pharmacological intervention against a number of inflammatory diseases. The final step in the biosynthesis of SP and CGRP is the conversion of their glycine-extended precursors to the active amidated peptide, and this process is catalyzed by sequential action of the enzymes peptidylglycine alpha-monooxygenase (PAM) and peptidylamidoglycolate lyase. We have demonstrated previously that 4-phenyl-3-butenoic acid (PBA) is a PAM inhibitor, and we have also shown that in vivo inhibition of serum PAM by PBA correlates with this compound's ability to inhibit carrageenan-induced edema in the rat. Here we demonstrate the ability of PBA to inhibit all three phases of adjuvant-induced polyarthritis (AIP) in rats; this represents the first time that an amidation inhibitor has been shown to be active in a model of chronic inflammation. We recently introduced 5-(acetylamino)-4-oxo-6-phenyl-2-hexenoic acid (AOPHA) as one of a new series of mechanism-based amidation inhibitors. We now report for the first time that AOPHA and its methyl ester (AOPHA-Me) are active inhibitors of serum PAM in vivo, and we show that AOPHA-Me correspondingly inhibits carrageenan-induced edema in rats in a dose-dependent manner. Neither PBA nor AOPHA-Me exhibits significant cyclooxygenase (COX) inhibition in vitro; thus, the anti-inflammatory activities of PBA and AOPHA-Me are apparently not a consequence of COX inhibition. We discuss possible pharmacological mechanisms that may account for the activities of these new anti-inflammatory compounds.

Recent insights into digestive motility in functional dyspepsia

Functional gastrointestinal disorders, such as functional dyspepsia (FD) and irritable bowel syndrome, are common pathologies of the gut. FD is a clinical syndrome defined as chronic or recurrent pain or discomfort of unknown origin in the upper abdomen. The pathophysiological mechanisms responsible for FD have not been fully elucidated, but new ideas regarding its pathophysiology and the significance of the pathophysiology with respect to the symptom pattern of FD have emerged. In particular, there is growing interest in alterations in gastric motility, such as accommodation to a meal or gastric emptying, and visceral sensation in FD. The mechanisms underlying impaired gastroduodenal motor function are unclear, but possible factors include abnormal neurohormonal function, autonomic dysfunction, visceral hypersensitivity to acid or mechanical distention, Helicobacter pylori infection, acute gastrointestinal infection, psychosocial comorbidity, and stress. Although the optimum treatment for FD is not yet clearly established, acid-suppressive drugs, prokinetic agents, eradication of H. pylori, and antidepressants have been widely used in the management of patients with FD. The therapeutic efficacy of prokinetics such as itopride hydrochloride and mosapride citrate in the treatment of FD is supported by the results of relatively large and well-controlled studies. In addition, recent research has yielded new therapeutic agents and modalities for dysmotility in FD, including agonists/antagonists of various sensorimotor receptors, activation of the nitrergic pathway, kampo medicine, acupuncture, and gastric electric stimulation. This review discusses recent research on the pathophysiology of and treatment options for FD, with special attention given to digestive dysmotility.

Beneficial effect of tachykinin NK1 receptor antagonism in the development of hapten-induced colitis in mice

The gastro-intestinal tract is highly innervated by both intrinsic and extrinsic sensory nerves and this neuronal component is thought to play a role in local inflammatory responses. This in vivo study was designed to determine the function of substance P and the tachykinin NK1 receptor in the pathogenesis of inflammatory bowel disease by the use of the specific antagonist RP 67580. The dinitrofluorobenzene (DNFB)-induced colonic hypersensitivity model is associated with increased levels of substance P in the colon. The tachykinin NK1 receptor antagonist RP 67580 was used to investigate the role of substance P on the development of diarrhea, mast cell infiltration and activation, colonic tissue damage, hypertrophy of colonic lymphoid structures and leukocyte infiltration. The formation of watery diarrhea could completely be abrogated by treatment with RP 67580 in DNFB-sensitized animals 72 h after challenge. Antagonizing the tachykinin NK1 receptor in these animals also resulted in significantly reduced colonic patch hypertrophy, leukocyte recruitment and tissue damage. Total levels of substance P in the colon of DNFB-sensitized mice treated with the inactive enantiomer of the tachykinin NK1 receptor antagonist were significantly higher compared to DNFB-sensitized mice treated with RP 67580 72 h after challenge. Although RP 67580 was capable of reducing the total number of mast cells present in the colon, mast cell activation was not affected by this treatment. In conclusion, in this chemically-induced immunological model for inflammatory bowel disease we demonstrated an important role for tachykinin NK1 receptors, and its ligand substance P, in the development of colitis downstream from mast cell activation.

Neuroimmune link in the mucosa of chronic gastritis with Helicobacter pylori infection

It is suggested that different neuropeptides regulate gastric mucosal integrity and participate in the development of chronic gastritis. The aim of this study was to examine the roles and changes of immunoreactive (IR) nerves and immunocompetent cells in human gastritis. Immunohistochemical, immunocytochemical, and confocal laser microscopic methods were used. All investigated nerve fibers were found in different quantities in the mucosa of both control and gastritis samples. The number of SP, NPY, and VIP IR nerve fibers increased significantly (P < 0.05) in gastritis. No IR immunocompetent cells (lymphocytes, plasma cells, mast cells) were found in the control, however, some showed NPY (16.8%) and SP (9.4%) immunoreactivity in chronic gastritis. The distance between nerve fibers and immunocompetent cells was 200 nm to 1 microm. In conclusion, the increased number of SP, NPY, and VIP IR nerves and IR immunocytes suggests that they participate in development of neurogenic inflammation, repairing processes of chronic gastritis.

Altered tachykinergic influence on gastric mechanical activity in mdx mice

This study investigated whether alterations in gastric activity in dystrophic mdx mouse can be attributed to dysfunctions of tachykinins. Endoluminal pressure was recorded and the expression of neuronal nitric oxide synthase (nNOS), NK1 and NK2 neurokinin receptors was investigated by immunohistochemistry. SR48968, NK2 receptor antagonist, but not SR140333, NK1 receptor antagonist, decreased the tone only in mdx gastric preparations. In the presence of N(omega)-nitro-l-arginine methyl ester (l-NAME), inhibitor of NOS, SR48968 reduced the tone also in normal stomach. [Sar(9), Met(O(2))(11)]-SP, agonist of NK1 receptors, caused tetrodotoxin-sensitive relaxations, antagonized by SR140333 or l-NAME, with no difference in the potency or efficacy between normal and mdx preparations. [beta-Ala(8)]-NKA(4-10), an NK2 receptor agonist, induced SR48968-sensitive contractions in both types of preparations, although the maximal response of mdx tissues was significantly lower than normal preparations. Immunohistochemistry demonstrated a consistent reduction of nNOS and NK2 receptor expression in mdx stomach smooth muscle cells and no change in nNOS and NK1 receptor expression in neurones. In conclusion, in mdx stomach the activation of NK2 receptors plays a role in the development of the tone, associated with a reduced NO production by muscular nNOS. The hypo-responsiveness to NK2 receptors could depend on the reduced expression of these receptors.

Irritable bowel syndrome and chronic constipation: emerging drugs, devices, and surgical treatments

Irritable bowel syndrome (IBS) and chronic constipation (CC) are two of the most common functional disorders of the gut. CC and IBS are estimated to affect up to 20% and 27% of the North American population respectively. Although not life-threatening, CC and IBS can profoundly and negatively affect quality of life and are associated with a significant economic burden related to direct and indirect annual health-care costs. Possible etiologies for IBS and CC include alterations in visceral sensation and gastrointestinal motility. IBS may be caused by disturbances in brain-gut interactions affecting gastrointestinal motility and visceral sensitivity. Research efforts in CC have begun to identify abnormalities in myenteric neurons, alterations in neurotransmitters and their receptors, and incoordination of the muscles of the pelvic floor or anorectum. Both disorders may be influenced by genetic predisposition, environmental factors, and stress. In this article, the safety and efficacy of traditional and emerging therapies for CC and IBS are examined. In addition, their pathophysiology and symptoms are briefly reviewed.

The role of tachykinins in circular muscle contractility of the murine ileum: A functional investigation

We investigated the participation of different tachykinin receptors in contractility of circular muscle strips of the mouse ileum using selective NK receptor agonists and antagonists. The NK1 receptor agonist septide (1-100 nM) induced dose-dependent contractions which were reduced by atropine and augmented by L-NNA. L-NNA increased and TTX consecutively reduced contractions to the NK2 receptor agonist beta-A-NKA (1-100 nM). Senktide, agonist of NK3 receptors, failed to induce contractions. NANC contractions to EFS were decreased after NK1 receptor blockade with RP67580. This inhibitory effect was more pronounced after additional blockade of NK2 and NK3 receptors. NK3 receptor antagonism alone reduced contractions at higher frequencies of stimulation. When the duration of the EFS stimulus was increased, the participation of all NK receptor subtypes became more evident. Our results suggest that excitatory NANC transmission in the circular muscle layer of the mouse ileum is mediated by tachykinins acting principally on NK1 receptors on cholinergic nerves and smooth muscle cells. Also NK2 receptors, located on smooth muscle cells and nitrergic neurons, and NK3 receptors on enteric neurons are involved.

Tachykinin Receptor Expression and Function in Human Esophageal Smooth Muscle

Tachykinins are present in enteric nerves of the gastrointestinal tract and cause contraction of esophageal smooth muscle; however, the mechanisms involved are not understood. Our aim was to characterize tachykinin signaling in human esophageal smooth muscle. We investigated functional effects of tachykinins on human esophageal smooth muscle using tension recordings and isolated cells, receptor expression with reverse transcription (RT)-polymerase chain reaction (PCR) and immunoblotting, intracellular Ca2+ responses using fluorescent indicator dyes, and membrane currents with patch-clamp electrophysiology. The mammalian tachykinins [substance P and neurokinin (NK) A and NKB] elicited concentration-dependent contractions of human esophageal smooth muscle. These responses were not affected by muscarinic receptor or neuronal blockade indicating a direct effect on smooth muscle cells (SMCs). Immunofluorescence and RT-PCR identified tachykinin receptors (NK1, NK2, and NK3) on SMCs. Contraction was mediated through a combination of Ca2+ release from intracellular stores and influx through L-type Ca2+ channels. NK2 receptor blockade inhibited the largest proportion of tachykinin-evoked responses. NKA evoked a nonselective cation current (I(NSC)) with properties similar to that elicited by muscarinic stimulation. The following paradigm is suggested: tachykinin receptor binding to SMCs releases Ca2+ from stores along with activation of I(NSC), which in turn results in membrane depolarization, L-type Ca2+ channel opening, rise of Ca2+ concentration, and contraction. These studies reveal new aspects of tachykinin signaling in human esophageal SMCs. Excitatory tachykinin pathways may represent targets for pharmacological intervention in disorders of esophageal dysmotility.

Role of NK1 and NK2 receptors in mouse gastric mechanical activity

1. The aim of the present study was to examine the role of NK1 and NK2 receptors in the control of mechanical activity of mouse stomach. In this view, the motor effects induced by NK1 and NK2 receptor agonists and antagonists were analyzed, measuring motility as intraluminal pressure changes in mouse-isolated stomach preparations. In parallel, immunohistochemical studies were performed to identify the location of NK1 and NK2 receptors on myenteric neurons and smooth muscle cells. 2. Substance P (SP) induced biphasic effects: a contraction followed by relaxation; neurokinin A (NKA) and [beta-Ala8]-NKA(4-10), selective agonist of NK2 receptors, evoked concentration-dependent contractions, whereas [Sar9, Met(O2)11]-SP, selective agonist of NK1 receptors, induced concentration-dependent relaxation. 3. SR48968, NK2 receptor antagonist, did not modify the spontaneous activity and reduced the contractile effects induced by tachykinins without affecting the relaxation. SR140333, NK1 receptor antagonist, did not modify the spontaneous activity and antagonized the relaxant response to tachykinins, failing to affect the contractile effects. 4. The relaxation to SP or to [Sar9, Met(O2)11]-SP was abolished by tetrodotoxin (TTX) and significantly reduced by N(omega)-nitro-L-arginine methyl ester (L-NAME). 5. NK2-immunoreactivity (NK2-IR) was seen at the level of the smooth muscle cells of both circular and longitudinal muscle layers. NK1-immunoreactive (NK1-IR) neurons were seen in the myenteric ganglia and NK1/nNOS double labeling revealed that some neurons were both NK1-IR and nNOS-IR. 6. These results suggest that, in mouse stomach, NK1 receptors, causing relaxant responses, are present on nitrergic inhibitory myenteric neurons, whereas NK2 receptors, mediating contractile responses, are present at muscular level.

Innervation of the mammalian esophagus

Understanding the innervation of the esophagus is a prerequisite for successful treatment of a variety of disorders, e.g., dysphagia, achalasia, gastroesophageal reflux disease (GERD) and non-cardiac chest pain. Although, at first glance, functions of the esophagus are relatively simple, their neuronal control is considerably complex. Vagal motor neurons of the nucleus ambiguus and preganglionic neurons of the dorsal motor nucleus innervate striated and smooth muscle, respectively. Myenteric neurons represent the interface between the dorsal motor nucleus and smooth muscle but they are also involved in striated muscle innervation. Intraganglionic laminar endings (IGLEs) represent mechanosensory vagal afferent terminals. They also establish intricate connections with enteric neurons. Afferent information is implemented by the swallowing central pattern generator in the brainstem, which generates and coordinates deglutitive activity in both striated and smooth esophageal muscle and orchestrates esophageal sphincters as well as gastric adaptive relaxation. Disturbed excitation/inhibition balance in the lower esophageal sphincter results in motility disorders, e.g., achalasia and GERD. Loss of mechanosensory afferents disrupts adaptation of deglutitive motor programs to bolus variables, eventually leading to megaesophagus. Both spinal and vagal afferents appear to contribute to painful sensations, e.g., non-cardiac chest pain. Extrinsic and intrinsic neurons may be involved in intramural reflexes using acetylcholine, nitric oxide, substance P, CGRP and glutamate as main transmitters. In addition, other molecules, e.g., ATP, GABA and probably also inflammatory cytokines, may modulate these neuronal functions.

An association of multiple endocrine neoplasia 2B, a RET mutation; constipation; and low substance P-nerve fiber density in colonic circular muscle

BACKGROUND

Multiple endocrine neoplasia (MEN) 2B is a rare hereditary syndrome that results from an activating mutation of the RET proto-oncogene. The RET gene is involved in the development of the enteric nervous system. Patients with MEN 2B have enlarged enteric ganglia and may be affected by gastrointestinal dysmotility. A deficiency of the neurotransmitter substance P (SP) has been identified in both pediatric and adult patients with chronic constipation.

METHODS

Three patients, in whom constipation was the presenting symptom and MEN 2B had been provisionally diagnosed, underwent genetic analysis. Seromuscular colonic biopsies were taken for immunofluorescence imaging in all 3 patients. A retrospective review of the patient notes was undertaken.

RESULTS

All 3 patients had constipation refractory to conservative treatment. Genetic analyses in the 3 patients confirmed an identical RET mutation (Met918Thr). Immunofluorescence imaging in all 3 patients identified grossly enlarged myenteric plexus ganglia but surprisingly a low density of SP-labeled nerve fibers in the colonic circular muscle. Nitric oxide synthase and vasoactive intestinal peptide labeling were not reduced.

CONCLUSION

The results show an association between MEN 2B and its most common RET mutation, colonic dysmotility, and low density of SP in the colonic circular muscle. Larger numbers of patients need to be studied to investigate whether low SP is primarily associated with the constipation or RET mutation and if it is a common feature of MEN 2B.

Tachykinin receptors as drug targets for motility disorders

The tachykinins and their receptors are strategically distributed within the gut wall, spinal cord, and central nervous system to be potential targets of therapeutic agents for gastrointestinal motility disorders. However, the development of effective tachykinin receptor agonists or antagonists to treat these disorders has had very limited success so far. This is, in part, due to the complex and multilevel of regulation of gastrointestinal motility function and the challenges faced in targeting the specific type of gut contraction to normalize function in disease state.

Expression of the neurokinin type 1 receptor in the human colon

The distribution of the neurokinin type 1 receptor (NK1r) in human intestine, mapped in a few immunohistochemical investigations in the antrum and the duodenum, is comparable to that widely studied in rodents. Importantly, despite pharmacological evidence of their presence in mammalian intestinal muscle, their immunohistochemical visualization in smooth muscle cells remains to be determined in human digestive tract. In the present work, we studied the distribution of NK1r in the human colon, with a particular view to visualize their expression in muscle cells. With this aim, part of colonic segments were incubated with nicardipine and TTX in order to induce accumulation of the NK1r on cell membrane. NK1r were visualized by using immunohistochemistry combined with fluorescence and confocal microscopy. Without incubation, NK1r-IR was clearly observed on the membrane and the cytoplasm of myenteric and submucous neurons and interstitial cells of Cajal, but could not be clearly determined in the longitudinal and circular muscle. NK1r-IR-expressing neurons and interstitial cells were closely surrounded by substance P (SP) immunoreactive nerves. Incubation of colonic segments with nicardipine and TTX at 4 degrees C for 1 h with SP allowed to reveal a strong NK1r-IR at the surface of muscle cells. Incubation with SP (10(-6) M) at 37 degrees C for 1 min induced a relocation of NK1r-IR into the cytoplasm of muscle. This is interpreted as an internalization of NK1r induced by the binding of SP on muscular NK1r. The present data contribute to emphasize the role of NK1r in tachykinin-mediated neuronal processes regulating intestinal motility.

Vanilloid receptor (TRPV1)-deficient mice show increased susceptibility to dinitrobenzene sulfonic acid induced colitis

In the human colon, vanilloid receptor TRPV1 is overexpressed both in afferent nerve terminals and in epithelial cells during inflammation. In the past years, pharmacological experiments using TRPV1 agonists and antagonists revealed that TRPV1 receptors may play proinflammatory and protective roles in the gastrointestinal tract. Here, we applied a genetic approach to define the role of TRPV1 and analyzed the effects of dinitrobenzene sulfonic acid (DNBS)-induced colitis in TRPV1-deficient (TRPV1-/-) mice. Intrarectal infusion of DNBS induced increased inflammation in TRPV1-/- mice compared to wild-type littermates (TRPV1+/+) as evaluated by macroscopic scoring and myeloperoxidase assays. This finding indicates that TRPV1 receptors are required for the protection within sensory pathways that regulate the response following the initiation of colonic inflammation. Electrophysiological recordings from circular smooth-muscle cells, performed 8 and 24 h after DNBS treatment, revealed strong spontaneous oscillatory action potentials in TRPV1-/- but not in TRPV1+/+ colons, indicating an early TRPV1-mediated control of inflammation-induced irritation of smooth-muscle activities. These unexpected results suggest that TRPV1 receptors mediate endogenous protection against experimentally induced colonic inflammation.

Functional characterisation of tachykinin receptors in the circular muscle layer of the mouse ileum

OBJECTIVES

Tachykinins are important mediators in neuromuscular signalling but have not been thoroughly characterised in the mouse gut. We investigated the participation of tachykinin receptors in contractility of circular muscle strips of the mouse ileum.

RESULTS

Electrical field stimulation (EFS) of excitatory nonadrenergic noncholinergic (NANC) nerves induced frequency-dependent contractions which were mimicked by substance P (SP). Desensitisation of SP and NK(1), NK(2) or NK(3) receptors significantly reduced contractions to EFS. The NK(1) receptor blocker RP67580 significantly inhibited NANC contractions to EFS. The NK(2) and NK(3) receptor blockers nepadutant and SR142801 did not affect NANC contractions per se but increased the RP67580-induced inhibition of NANC contractions to EFS. Contractions to SP were significantly reduced by RP67580 but not affected by nepadutant or SR142801. The NK(1) and NK(2) receptor agonists, septide and [beta-ala(8)]-NKA 4-10 (beta-A-NKA), respectively, but not the NK(3) receptor agonist senktide-induced dose-dependent contractions. Atropine inhibited and l-NNA augmented contractions to septide. Contractions to beta-A-NKA were insensitive to atropine but augmented by l-NNA.

CONCLUSIONS

Tachykinins mediate NANC contractions to EFS in the mouse small intestine. Endogenously released tachykinins activate mainly NK(1) receptors, located on cholinergic nerves and smooth muscle cells and, to a lesser degree, NK(2) and NK(3) receptors, most likely located presynaptically.

Functional aspects and mechanisms of TRPV1 involvement in neurogenic inflammation that leads to thermal hyperalgesia

Neurogenic inflammation is produced by overstimulation of peripheral nociceptor terminals by injury or inflammation of tissues. Excessive activity of sensory neurons produces vasodilation, plasma extravasation and hypersensitivity. Mechanistically, neurogenic inflammation is due to the release of substances from primary sensory nerve terminals that act directly or indirectly at the peripheral terminals, either activating or sensitizing nociceptors, endothelial cells and immunocytes. Notably, small-diameter sensory neurons that are sensitive to capsaicin play a key role in the generation of neurogenic inflammation. The cloning of the vanilloid receptor 1 (TRPV1) has been a breakthrough that has propelled our understanding of the molecular mechanisms involved in neurogenic inflammation. TRPV1 pivotally contributes to the integration of various stimuli and modulates nociceptor excitability, thus making it a true gateway for pain transduction. In addition, TRPV1 is the endpoint target of intracellular signalling pathways triggered by inflammatory mediators. Phosphorylation-induced potentiation of TRPV1 channel activity, along with an incremented TRPV1 surface expression are major events underlying the nociceptor activation and sensitization that leads to thermal hyperalgesia. The important contribution of TRPV1 receptor to the onset and maintenance of neurogenic inflammation has validated it as a therapeutic target for inflammatory pain management. As a result, the development of specific TRPV1 antagonists is a central focus of current drug discovery programs.

Substance P and the neurokinin-1 receptor in relation to eosinophilia in ulcerative colitis

Substance P (SP) has been implicated in the pathophysiology of ulcerative colitis (UC) and it has been suggested that blocking of its effect would be advantageous in this disease. Eosinophils have also been implicated in the pathophysiology of UC. In the present study, specimens from the sigmoid colon of UC patients were investigated by the use of antisera against SP and the neurokinin-1 receptor (NK-1R) and staining for demonstration of eosinophils. The degrees of SP innervation and NK-1R immunoreaction, as well as the levels of eosinophil infiltration, varied between different patients. Interestingly, NK-1R immunoreaction in the epithelium was often seen to be the most marked where there were numerous eosinophils in the underlying mucosa and where the mucosa showed a marked morphologic derangement. The observations suggest that there are marked fluctuations in effects of SP and eosinophils during the disease. The infiltrating eosinophils may be involved in the destruction of the mucosal tissue. Furthermore, for the majority of cases where there is marked derangement of the mucosa, it is apparent that there is an upregulation of the NK-1 receptor in the epithelium in parallel with the infiltration of the eosinophils.

Enteric co-innervation of motor endplates in the esophagus: state of the art ten years after

The existence of a distinct ganglionated myenteric plexus between the two layers of the striated tunica muscularis of the mammalian esophagus represented an enigma for quite a while. Although an enteric co-innervation of vagally innervated motor endplates in the esophagus has been repeatedly suggested, it was not possible until recently to demonstrate this dual innervation. Ten years ago, we were able to demonstrate that motor endplates in the rat esophagus receive a dual innervation from both vagal nerve fibers originating in the brain stem and from varicose enteric nerve fibers originating in the myenteric plexus. Since then, a considerable amount of data could be raised on enteric co-innervation and its occurrence in a variety of species, including humans, its neurochemistry, spatial relationships on motor endplates, ontogeny, and possible roles during esophageal peristalsis. These data underline the significance of this newly discovered innervation component, although its function is still largely unknown. The aim of this review is to summarize current knowledge about enteric co-innervation of esophageal striated muscle and to provide some hints as to its functional significance.

Action of ondansetron and CP-99,994 to modify behavior and antagonize cisplatin-induced emesis in the ferret

The action of ondansetron (1 mg/kg, i.p.) and (+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine (CP-99,994; 10 mg/kg, i.p.) on spontaneous behavior and the emesis induced by cisplatin (10 mg/kg, i.p.) was studied in the ferret. Ondansetron was inactive to modify behavior, but CP-99,994 reduced spontaneous locomotor activity and lip licking by 48% (P<0.01) and 79% (P<0.01), respectively; CP-99,994 also abolished spontaneous burrowing activity (P<0.05). Treatment of animals with cisplatin induced an emetic response that was abolished by both ondansetron and CP-99,994 (P<0.01). However, cisplatin did not significantly modify other behavioral measures although animals that received CP-99,994, cisplatin, or CP-99,994 in combination with cisplatin exhibited more episodes of defecation than animals that received ondansetron (P<0.05). The action of CP-99,994 to modify behavior in this species is discussed in relation to animal models of nausea.

Chronic constipation in children: organic disorders are a major cause

Diagnostic tools for paediatric chronic constipation have been limited, leading to over 90% of patients with treatment-resistant constipation being diagnosed with chronic idiopathic constipation, with no discernible organic cause. Work in our institution suggests that a number of children with intractable symptoms actually have slow colonic transit leading to slow transit constipation. This paper reviews recent data suggesting that a significant number of the children with chronic treatment-resistant constipation may have organic causes (slow colonic transit and outlet obstruction) and suggests new approaches to the management of children with chronic treatment-resistant constipation.

The role of substance P in inflammatory disease

The diffuse neuroendocrine system consists of specialised endocrine cells and peptidergic nerves and is present in all organs of the body. Substance P (SP) is secreted by nerves and inflammatory cells such as macrophages, eosinophils, lymphocytes, and dendritic cells and acts by binding to the neurokinin-1 receptor (NK-1R). SP has proinflammatory effects in immune and epithelial cells and participates in inflammatory diseases of the respiratory, gastrointestinal, and musculoskeletal systems. Many substances induce neuropeptide release from sensory nerves in the lung, including allergen, histamine, prostaglandins, and leukotrienes. Patients with asthma are hyperresponsive to SP and NK-1R expression is increased in their bronchi. Neurogenic inflammation also participates in virus-associated respiratory infection, non-productive cough, allergic rhinitis, and sarcoidosis. SP regulates smooth muscle contractility, epithelial ion transport, vascular permeability, and immune function in the gastrointestinal tract. Elevated levels of SP and upregulated NK-1R expression have been reported in the rectum and colon of patients with inflammatory bowel disease (IBD), and correlate with disease activity. Increased levels of SP are found in the synovial fluid and serum of patients with rheumatoid arthritis (RA) and NK-1R mRNA is upregulated in RA synoviocytes. Glucocorticoids may attenuate neurogenic inflammation by decreasing NK-1R expression in epithelial and inflammatory cells and increasing production of neutral endopeptidase (NEP), an enzyme that degrades SP. Preventing the proinflammatory effects of SP using tachykinin receptor antagonists may have therapeutic potential in inflammatory diseases such as asthma, sarcoidosis, chronic bronchitis, IBD, and RA. In this paper, we review the role that SP plays in inflammatory disease.

Evaluation of acetaminophen P-glycoprotein-mediated salivary secretion by rat submandibular glands

The constant ratio between saliva and plasma acetaminophen concentrations (S/P) during the elimination phase is assumed to result from the equilibrium established among the free-drug concentrations in the arterial blood, venous blood and saliva. Salivary secretion of acetaminophen is assumed to result from a passive diffusion of the drug to saliva from the blood that supplies the salivary glands. However, the constant S/P ratio during acetaminophen disposition and the finding that P-glycoprotein (P-gp), a protein recognized to pump substrates out of the cell, is expressed in duct cells of the submandibular glands questions the mechanisms involved in acetaminophen salivary secretion. Thus, we intended to evaluate the existence of a P-glycoprotein-mediated transport of acetaminophen in rat submandibular glands. Acetaminophen (30 mg/kg, i.v.) pharmacokinetics was assessed in controls and in rats pre-treated with erythromycin (100 mg/kg) as a P-glycoprotein inhibitor. Acetaminophen pharmacokinetic parameters were calculated from saliva and plasma levels considering a non-compartmental analysis. Mean plasma and salivary profiles of control and pre-treated animals were almost superimposable. No difference could be found in S/P ratios in control and erythromycin pre-treated animals (P > 0.05). Moreover, no statistical difference could be found in the kinetic parameters calculated from saliva or plasma drug level (P > 0.05). These observations indicate that acetaminophen salivary secretion in rat submandibular glands is not related to P-glycoprotein-mediated transport under the experimental conditions of the present work.

Functional dyspepsia: drugs for new (and old) therapeutic targets

The therapeutic management of functional dyspepsia remains a major challenge for the gastroenterologist. Current therapies available are based on putative underlying pathophysiologic mechanisms, including gastric acid sensitivity, slow gastric emptying and Helicobacter pylori infection, but only a small proportion of patients achieve symptomatic benefit from these therapeutic approaches. Relatively novel mechanistic concepts under testing include impaired gastric accomodation, visceral hypersensitivity, and central nervous system dysfunction. Serotonergic modulators (e.g. the 5-HT4 agonist tegaserod, the 5-HT3 antagonist alosetron and the 5-HT1P agonist sumatriptan), CCK-1 antagonists (e.g. dexloxiglumide), opioid agonists (e.g. asimadoline), N-methyl-D-aspartate (NMDA) receptor antagonists (e.g dextromethorphan), neurokinin antagonists (e.g. talnetant), capsaicin-like agents and antidepressants are among the agents currently under investigation. It seems unlikely, however, that targeting a single mechanism with an individual drug will result in complete symptom remission in most cases.

A neurokinin 1 receptor antagonist decreases postoperative peritoneal adhesion formation and increases peritoneal fibrinolytic activity

Fibrous adhesions remain a major sequela of abdominal surgery. The proinflammatory peptide substance P (SP), known to participate in inflammatory events, may play a key role in adhesion formation. This hypothesis was tested by using an antagonist, CJ-12,255 (Pfizer), that blocks the binding of SP to the neurokinin 1 receptor (NK-1R). Adhesion formation was surgically induced in the peritoneum of rats receiving daily doses of the NK-1R antagonist (NK-1RA; 5.0 or 10.0 mg/kg per day) or saline. On postoperative day 7, both the low and high doses of NK-1RA significantly (P < 0.05) reduced adhesion formation by 45% and 53%, respectively, compared with controls. Subsequently, the effect of NK-1RA administration on peritoneal fibrinolytic activity was investigated to determine a potential mechanism for SP action in the peritoneum. Samples were collected from nonoperated controls and from animals 24 h postsurgery that were administered either NK-1RA or saline. Fibrinolytic activity in peritoneal fluid was assayed by zymography, and expression of tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1, both regulators of fibrinolytic activity, was assessed in peritoneal tissue and fluid by RT-PCR and bioassay, respectively. NK-1RA administration led to a marked (P < 0.05) increase in tPA mRNA levels in peritoneal tissue compared with nonoperated and saline-administered animals. Likewise, NK-1RA administration significantly (P < 0.05) increased tPA in the peritoneal fluid. These data suggest that activation of the NK-1R promotes peritoneal adhesion formation by limiting fibrinolytic activity in the postoperative peritoneum, thus enabling fibrinous adhesions to persist.

Effects of TAK-637 on NK(1) receptor-mediated mechanisms regulating colonic secretion

This study investigates the effect of a selective NK(1) receptor antagonist TAK-637 on enteric mechanisms involved in regulation of epithelial secretion in the colon. Mucosal sheets isolated from guinea-pig colon were placed in modified Ussing chambers and the net active transport of electrolytes was measured as short-circuit current (Isc). GR-73632, a selective NK(1) receptor agonist, induced an increase in basal Isc, which was inhibited by TAK-637 (IC(50) of 21 nM). The increase in Isc induced by GR-73632 was significantly attenuated by tetrodotoxin (TTX, 1 microM), indicating that TAK-637 inhibits neuronal NK(1) receptors. Moreover, TAK-637 reduced the TTX-resistant component of the response to GR-73632 suggesting that NK(1) receptors expressed by epithelial cells are inhibited by TAK-637. In separate experiments, TAK-637 partially inhibited the submaximal Isc induced by electrical field stimulation (EFS, 0.5 ms, 15 Hz) of enteric nerves or by activation of primary afferent fibers using capsaicin (50 microM). TAK-637 had no significant effect on the basal Isc or on responses induced by neurokinin A (NKA), senktide, or forskolin. The results imply that inhibition of peripheral NK(1) receptors may reduce autonomic epithelial secretion in response to activation of autonomic secretomotor pathways, while having no significant effect on basal epithelial transport.

The endogenous cannabinoid system protects against colonic inflammation

Excessive inflammatory responses can emerge as a potential danger for organisms' health. Physiological balance between pro- and anti-inflammatory processes constitutes an important feature of responses against harmful events. Here, we show that cannabinoid receptors type 1 (CB1) mediate intrinsic protective signals that counteract proinflammatory responses. Both intrarectal infusion of 2,4-dinitrobenzene sulfonic acid (DNBS) and oral administration of dextrane sulfate sodium induced stronger inflammation in CB1-deficient mice (CB1(-/-)) than in wild-type littermates (CB1(+/+)). Treatment of wild-type mice with the specific CB1 antagonist N-(piperidino-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-pyrazole-3-carboxamide (SR141716A) mimicked the phenotype of CB1(-/-) mice, showing an acute requirement of CB1 receptors for protection from inflammation. Consistently, treatment with the cannabinoid receptor agonist R(-)-7-hydroxy-Delta(6)-tetra-hydrocannabinol-dimethylheptyl (HU210) or genetic ablation of the endocannabinoid-degrading enzyme fatty acid amide hydrolase (FAAH) resulted in protection against DNBS-induced colitis. Electrophysiological recordings from circular smooth muscle cells, performed 8 hours after DNBS treatment, revealed spontaneous oscillatory action potentials in CB1(-/-) but not in CB1(+/+) colons, indicating an early CB1-mediated control of inflammation-induced irritation of smooth muscle cells. DNBS treatment increased the percentage of myenteric neurons expressing CB1 receptors, suggesting an enhancement of cannabinoid signaling during colitis. Our results indicate that the endogenous cannabinoid system represents a promising therapeutic target for the treatment of intestinal disease conditions characterized by excessive inflammatory responses.

Colonic smooth muscle responses in patients with diverticular disease of the colon: effect of the NK2 receptor antagonist SR48968

BACKGROUND

Little is known about the pathophysiology of diverticular disease.

AIM

To compare passive and active stress and the response to carbachol of colonic smooth muscle specimens from patients with diverticular disease and patients with colon cancer. The effect of the NK2 receptor antagonist, SR48968, on electrically evoked contractions of circular muscle was also investigated.

PATIENTS

Sigmoid colon segments were obtained from 16 patients (51-83 years) undergoing elective sigmoid resection for diverticular disease and 39 patients (50-88 years) undergoing left hemicolectomy for non-obstructive sigmoid colon cancer.

METHODS

Isometric tension was measured on circular or longitudinal taenial muscle. Strips were stretched gradually to Lo (length allowing the development of optimal active tension with carbachol) and were also exposed to increasing carbachol concentrations. The effects of atropine, tetrodotoxin and SR48968 on electrically evoked (supramaximal strength, 0.3 ms, 0.1-10 Hz) contractions of circular strips from 8 patients with diverticular disease and 19 patients with colon cancer were also studied.

RESULTS

Both passive and active stress in circular muscle strips obtained from patients with diverticular disease was higher than in patients with colon cancer (P < 0.05). Electrically evoked contractions were significantly reduced by atropine in all preparations and were virtually suppressed by combined SR48968 and atropine. Tetrodotoxin suppressed electrically evoked contractions only in patients with colon cancer, whereas a tetrodotoxin-resistant component was identified in patients with diverticular disease.

CONCLUSIONS

The changes in both passive and active stress in specimens from patients with diverticular disease may reflect circular smooth muscle dysfunction. Acetylcholine and tachykinins are the main excitatory neurotransmitters mediating electrically evoked contractions in human sigmoid colon circular muscle.

Role of tachykinin NK1, NK2 and NK3 receptors in the modulation of visceral hypersensitivity in the rat

Tachykinins are known to be involved in the processing of information leading to central sensitization and nociception. Using an animal model of repetitive colorectal distensions (CRD), we investigated the effect of spinal administration of tachykinin receptor antagonists in the mediation of visceral hypersensitivity. Intrathecal administration of the NK(1) receptor antagonist RP-67,580 (6.5 nmol) and the NK(3) receptor antagonist R-820 (6.5 nmol) completely blocked the CRD-induced hyperalgesia for both noxious and innocuous stimuli. The intrathecal administration of SR-48,968, a tachykinin NK(2) receptor antagonist, did not affect the visceral pain threshold of hypersensitive animals. Thus, the results from the present experiment support the concept that tachykinins with actions at spinal NK(1) and NK(3) but not NK(2) receptor sites are involved in visceral hypersensitivity mediated by nociceptive and non-nociceptive afferent inputs.

Effects of tachykinins and 5-hydroxytryptamine on intestinal secretion

1. The main aim of the present study was to establish the functional in vivo effects of tachykinins on net fluid transport by the jejunum and ileum of anaesthetized rats. Tachykinins were administered by retrograde infusion in saline into the left common carotid artery. The possible involvement of 5-hydroxytryptamine (5-HT) in tachykinin-induced intestinal secretion was also investigated. 2. Some tachykinins were potent at reversing net absorption to secretion, particularly in the jejunum, where the rank order of potency was neurokinin (NK) A > substance P (SP) > NKB. The potency of the NK1 receptor-selective agonist [Sar9,Met(O2)11]-SP was the same as SP. Neurokinin A reduced net fluid absorption from the lumen of the jejunum at an intra-arterial infusion rate of 0.64 microg/kg per min. Infusions of NKA at 1.6 and 4 microg/kg per min induced net secretion into the lumen of the jejunum. These two higher infusion rates also affected fluid transport by the ileum, although not to the same extent as seen in the jejunum. The relative potency of SP was not affected by captopril (10 mg/kg, i.v.). 3. The secretory response of the jejunum to infusion of 4 microg/kg per min SP was blocked in animals administered the NK1 receptor antagonist SR 140 333 (1 mg/kg, i.v.). In addition, SR 140 333 blocked the secretory response to 4 microg/kg per min NKA. However, NKA still induced secretion in animals that had received the NK2 receptor antagonist SR 48 968 (0.3 mg/kg, i.v.). 4. A role for an endogenous tachykinin in the intestinal secretory action of 5-HT was not clearly established using the present model. Although SR 140 333 increased the absorption rate from the jejunum in animals infused intra-arterially with 5-HT, 5-HT itself did not cause a significant reduction in absorption. There were no significant differences in the absorption rates from the ileum between the control group and groups infused with 5-HT with and without SR 140 333. 5. The present study provides functional evidence for the existence of NK1 receptors in the rat small intestine, particularly in the proximal region, where their activation influences fluid transport. It is suggested that the presently used rat model is suitable for screening tachykinin antagonists for potential antidiarrhoeal activity.

Cellular localization and distribution of neurokinin-1 receptors in the rat stomach

In the stomach, the majority of substance P's effects are mediated by the activation of neurokinin-1 (NK1) receptors. The gastric cellular distribution of these receptors in Wistar and Sprague-Dawley rats was determined using immunocytochemistry. The localization of the NK1 receptors with respect to von Willebrand's factor, protein gene product 9.5, substance P, vasoactive intestinal peptide, and calcitonin gene-related peptide was also determined. Results show that NK1 receptor immunoreactivity was dependent on the duration of fixation. In corpus and antrum tissues that were fixed in 4% paraformaldehyde for 30 min, the presence of NK1 receptor immunoreactivity was demonstrated on nerve fibers throughout the stomach, on the surface and in the cytoplasm of myenteric cell bodies, on circular smooth muscle cells, and on vascular endothelial cells. This was observed in tissues from both rodent strains. Overnight fixation in the same fixative, however, demonstrated the presence of NK1 receptor immunoreactivity only on nerve fibers and cell bodies of the myenteric plexus, and on circular smooth muscle cells. In 30-min fixed tissues, the localization of NK1R immunoreactivity on vascular endothelial cells and nerve fibers was confirmed by co-localization with von Willebrand's factor and protein gene product 9.5 immunoreactivity, respectively. In both rodent strains, NK1 receptor immunoreactivity was co-localized with substance P immunoreactivity on nerve fibers of the longitudinal and circular muscle. In the Wistar rat, NK1 receptor immunoreactivity was co-localized with vasoactive intestinal peptide immunoreactivity or calcitonin gene-related peptide immunoreactivity throughout the stomach. However, in the Sprague-Dawley rat, NK1 receptor immunoreactivity was only co-localized with calcitonin gene-related peptide immunoreactivity in a minority of fibers of the circular muscle. The overall results of this study show that the antigenic epitopes of the NK1 receptor are sensitive to overfixation. When tissues were not overfixed, NK1 receptor immunoreactivity was distributed more extensively throughout the rat stomach than has been described previously. The results of this study provide the anatomical basis for many of the actions of substance P in the rat stomach.

The protective and healing effects of a natural antioxidant formulation based on ubiquinol and Aloe vera against dextran sulfate-induced ulcerative colitis in rats

Oxygen/nitrogen reactive species (ROS/RNS) are currently implicated in the pathogenesis of ulcerative colitis, drawing attention on the potential prophylactic and healing properties of antioxidants, scavengers, chelators. We evaluated the possible protective/curative effects of a natural antioxidant preparation based on Aloe vera and ubiquinol, against intestinal inflammation, lesions, and pathological alterations of the intestinal electrophysiological activity and motility, in a rat model of DSS-induced colitis. 5% dextrane sulfate (DDS) (3 days), followed by 1% DSS (4 days) was administered in drinking water. The antioxidant formulation (25 mg/kg) was delivered with a pre-treatment protocol, or simultaneously or post-colitis induction. Spontaneous and acetylcholine-stimulated electrical activity were impaired in the small intestine and in distal colon, upon exposure to DSS only. Severe inflammation occurred, with increased myeloperoxidase activity, and significant alterations of the oxidant/antioxidant status in colonic tissue and peritoneal cells. Lipoperoxidation, superoxide production, glutathione peroxidase and glutathione-S-transferase activities, and reduced glutathione content increased, whilst superoxide dismutase and catalase activities were sharply suppressed in colon tissue. ROS/RNS formation in peritoneal cells was strongly inhibited. Inflammation, electrical/mechanical impairment in the gut, and a great majority of oxidative stress parameters were improved substantially by pre-treatment with the antioxidant preparation, but not by simultaneous administration or post-treatment.

Effect of nepadutant, a neurokinin 2 tachykinin receptor antagonist, on immediate-early gene expression after trinitrobenzenesulfonic acid-induced colitis in the rat

Tachykinins have been implicated in inflammatory responses such as those occurring in inflammatory bowel disease. Accordingly, we investigated the effect of a selective neurokinin (NK) 2 receptor antagonist, nepadutant, on proto-oncogene expression in the L(6)-S(1) spinal cord as well as in dorsal root ganglion (DRG) neurons after either non-noxious colorectal distension (CRD) or trinitrobenzenesulfonic acid (TNBS)-induced colitis in the adult rat. In both preparations, c-fos was expressed in similar spinal cord regions, including medial and lateral dorsal horn, dorsal commissure (DCM; laminae X above the central canal), and the sacral parasympathetic nucleus (SPN, laminae V-VII). However, TNBS-induced colitis produced significantly larger numbers (8-10-fold increase over control) of Fos-positive spinal cord neurons. In addition, there was also a significant increase (3-4-fold) in the number of Jun-positive colon DRG neurons after colitis compared with CRD. Nepadutant had no significant effect on proto-oncogene expression induced by CRD in either spinal cord neurons or DRG neurons. In contrast, nepadutant significantly decreased (70%) the number of Fos-positive neurons in dorsal horn, DCM, and SPN spinal cord regions and significantly decreased (75%) the number of Jun-positive DRG neurons after TNBS-induced irritation of the colon. These findings indicate that nepadutant suppresses the responses of colonic afferent neurons to nociceptive stimuli and that NK2 receptor antagonists may be beneficial in the treatment of sensory symptoms of colitis.