Colonic mucosal mediators from patients with irritable bowel syndrome excite enteric cholinergic motor neurons

BACKGROUND

Mediators released in the mucosal milieu have been suggested to be involved in visceral hypersensitivity and abdominal pain in patients with irritable bowel syndrome (IBS). However, their impact on myenteric neurons remains unsettled.

METHODS

Mucosal biopsies were obtained from the descending colon of patients with IBS and controls. Mucosal mast cells were identified immunohistochemically. The impact of spontaneously released mucosal mediators on guinea pig electrically stimulated longitudinal muscle myenteric plexus (LMMP) preparations was assessed in vitro by means of selective receptor antagonists and inhibitors.

KEY RESULTS

Patients with IBS showed an increased mast cell count compared with controls. Application of mucosal mediators of IBS to LMMPs potentiated cholinergic twitch contractions, an effect directly correlated with mast cell counts. Enhanced contractions were inhibited by 50.3% with the prostaglandin D2 antagonist BW A868C, by 31.3% and 39% with the TRPV1 antagonists capsazepine and HC-030031, respectively, and by 60.5% with purinergic P2X antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid. Conversely, the serotonin1-4, histamine1-3, tachykinin1-3 receptor blockade, and serine protease inhibition had no significant effect.

CONCLUSIONS & INFERENCES

Colonic mucosal mediators from patients with IBS excite myenteric cholinergic motor neurons. These effects were correlated with mast cell counts and mediated by activation of prostanoid receptors, TRPV1, and P2X receptors. These results support the role of mucosal inflammatory mediators and mast cell activation in altered motor function of IBS.

Functional and neurochemical changes of the gastrointestinal tract in a rodent model of Parkinson's disease

Patients with Parkinson's disease develop motor disturbances often accompanied by peripheral autonomic dysfunctions, including gastrointestinal disorders, such as dysphagia, gastric stasis and constipation. While the mechanisms subserving enteric autonomic dysfunctions are not clearly understood, they may involve the enteric dopaminergic and/or nitrergic systems. In the present study, we demonstrate that rats with unilateral 6-hydroxydopamine lesion of nigrostriatal dopaminergic neurons develop a marked inhibition of propulsive activity compared to sham-operated controls, as indicated by a 60% reduction of daily fecal output at the 4th week of observation. Immunohistochemical data revealed that 6-hydroxydopamine treatment did not affect the total number of HuC/D-positive myenteric neurons in both the proximal and distal segments of ileum and colon. Conversely, in the distal ileum and proximal colon the number of nitrergic neurons was significantly reduced. These results suggest that a disturbed distal gut transit, reminiscent of constipation in the clinical setting, may occur as a consequence of a reduced propulsive motility, likely due to an impairment of a nitric oxide-mediated descending inhibition during peristalsis.

JC virus infects the enteric glia of patients with chronic idiopathic intestinal pseudo-obstruction

BACKGROUND AND AIMS

Chronic idiopathic intestinal pseudo-obstruction (CIIP) is characterised by severe impairment of intestinal propulsive motility that mimics bowel obstruction. JC virus (JCV) is a polyomavirus that can infect brain glial cells causing a fatal disease, but may also be found throughout the normal gastrointestinal tract. The hypothesis that JCV infects the myenteric plexuses of patients with CIIP was tested.

METHODS

10 patients with CIIP and 61 normal specimens (30 ascending colon and 31 ileum) from patients with uncomplicated colon cancer were studied. DNA was extracted from the myenteric plexuses, and JCV T antigen (TAg) DNA and the viral regulatory region were detected by PCR and sequencing. Immunohistochemistry was performed to detect JCV viral protein expression, neuronal and glial markers. Fluorescence in situ hybridisation was performed for cellular localisation of the JCV infection.

RESULTS

Clinical studies demonstrated neurogenic impairment, and pathological analyses showed neuropathy in each patient with CIIP. JCV TAg DNA was found in the myenteric plexuses of 8/10 (80%) of the patients with CIIP and 3/31 (9.7%) of the control patients (p<0.001). All samples were JCV Mad-1 strains. Seven of the 10 CIIP specimens expressed both JCV TAg and the JCV viral protein VP1, while none of the controls expressed either. JCV infection co-localised with glial fibrillary acidic protein expression, a marker of enteric glial cells.

CONCLUSION

JCV infection occurs in the myenteric plexuses of patients with CIIP. The JCV localisation in enteroglial cells suggests a possible pathological role for this virus in enteric neuropathy.

Review article: molecular, pathological and therapeutic features of human enteric neuropathies

BACKGROUND

Considerable information has been gathered on the functional organization of enteric neuronal circuitries regulating gastrointestinal motility. However, little is known about the neuropathophysiological mechanisms underlying gastrointestinal motor disorders.

AIM

To analyse the most important pathological findings, clinical implications and therapeutic management of idiopathic enteric neuropathies.

METHODS

PubMed searches were used to retrieve the literature inherent to molecular determinants, pathophysiological bases and therapeutics of gastrointestinal dysmotility, such as achalasia, gastroparesis, chronic intestinal pseudo-obstruction, Hirschsprung's disease and slow transit constipation, to unravel advances on digestive disorders resulting from enteric neuropathies.

RESULTS

Current data on molecular and pathological features of enteric neuropathies indicate that degenerative and inflammatory abnormalities can compromise the morpho-functional integrity of the enteric nervous system. These alterations lead to a massive impairment in gut transit and result in severe abdominal symptoms with associated high morbidity, poor quality of life for patients and established mortality. Many pathophysiological aspects of these severe conditions remain obscure, and therefore treatment options are quite limited and often unsatisfactory.

CONCLUSIONS

This review of enteric nervous system abnormalities provides a framework to better understand the pathological processes underlying gut dysmotility, to translate this knowledge into clinical management and to foster the development of targeted therapeutic strategies.

Effects of esomeprazole on glutathione levels and mitochondrial oxidative phosphorylation in the gastric mucosa of rats treated with indomethacin

Proton pump inhibitors exert their preventive and healing effects on gastropathy induced by nonsteroidal anti-inflammatory drug (NSAIDs) by a dual action: the antisecretory and the antioxidant effect. The latter was investigated by using esomeprazole against indomethacin-induced gastric mucosa lesions in rats and assessed by a histomorphometric analysis. Treatment by intragastric gavage were 1% methocel as vehicle; esomeprazole 10, 30, or 60 micromol/kg; indomethacin 100 micromol/kg; and esomeprazole 10, 30, or 60 micromol/kg plus indomethacin 100 micromol/kg. The evaluation of glutathione (GSH) levels and respiratory chain complex activities [nicotinamide adenine dinucleotide, reduced (NADH)-ubiquinone oxidoreductase, succinate dehydrogenase, cytochrome C reductase, cytochrome oxidase] was performed in the isolated gastric mucosa. Esomeprazole (10-60 micromol/kg) dose dependently reversed, up to complete recovery, the inhibitory effect of indomethacin on GSH levels (approximately 60% inhibition) and mitochondrial enzyme activities (inhibition ranging from 60% to 75%). Indomethacin-induced mucosal injuries were reduced by esomeprazole. Thus, in addition to inhibiting acid secretion, the gastroprotective effect of esomeprazole can be ascribed to a reduction in gastric oxidative injury.

Isolated porcine bronchi provide a reliable model for development of bronchodilator anti-muscarinic agents for human use

BACKGROUND AND PURPOSE

In human airways, muscarinic acetylcholine receptors (mAChRs) exert a predominant role in the control of airways resistance and anti-muscarinic agents are currently included in the pharmacological treatment of chronic obstructive pulmonary disease (COPD). However, the development of more effective mAChR antagonists is hampered by considerable species variability in the ultrastrucural and functional control of airway smooth muscle, making extrapolation of any particular animal model questionable. This study was designed to characterize the mAChRs in a bronchial preparation from pigs, animals considered to provide close models of human biology.

EXPERIMENTAL APPROACH

Smooth muscle bronchial strips were examined by electron microscopy in order to compare their neuromuscular structure with that of human bronchi and used to study the affinity of a series of selective mAChR antagonists, estimated as pKis in competition binding assays with NMS and pA2, by Schild analysis, in contractile experiments.

KEY RESULTS

Pharmacodynamic binding parameters and affinity profiles of a series of antagonists were consistent with the presence of a majority of M2 mAChRs along with a minor population of M3 mAChRs. Functionally, the highly significant correlation between postjunctional pA2 affinities and corresponding affinity constants at human recombinant M1-M5 subtypes indicated that smooth muscle contraction in porcine bronchi, as in human bronchi, was dependent on the M3 subtype.

CONCLUSION AND IMPLICATIONS

Based on the characterization of mAChRs, isolated porcine bronchi provide an additional experimental model for development of mAChR antagonists for the treatment of human airway dysfunctions.

Systematic review: gastro-oesophageal reflux disease and dental lesions

BACKGROUND

Dental erosion (DE), which is the irreversible loss of tooth substance that does not involve bacteria ranging from a minimal loss of surface enamel to the partial or complete exposure of dentine by a chemical process, is acknowledged as an established extra-oesophageal manifestation of gastro-oesophageal reflux disease (GERD). However, the real impact of GERD in the genesis of this lesion remains unclear.

AIM

To review the existing literature to assess the relationship between DE and GERD.

METHODS

Studies that assessed the prevalence of DE in individuals with GERD or vice versa were identified in Medline and the Cochrane Controlled Trials Register via a systematic research strategy.

RESULTS

Seventeen studies met the selection criteria. Studies, however, differed greatly as far as design, population methods of diagnosing GERD, duration of follow-up and, consequently, findings. The median prevalence of DE in GERD patients was 24%, with a large range (5-47.5%), and the median prevalence of GERD in DE adults patients was 32.5% (range: 21-83%) and in paediatric population 17% (range: 14-87%). Children with GERD are found by a majority of studies at increased risk of developing DEs in comparison with healthy subjects, as are intellectually disabled people.

CONCLUSIONS

This systematic review shows that there is a strong association between GERD and DE. The severity of DEs seems to be correlated with the presence of GERD symptoms, and also, at least in adults, with the severity of proximal oesophageal or oral exposure to an acidic pH. The inspection of the oral cavity in search for DEs should become a routine manoeuvre in patients with GERD.

Potential options to optimize therapy of gastroesophageal reflux disease with proton pump inhibitors

Proton pump inhibitors (PPIs) are antisecretory agents that are widely used in the short- and long-term management of gastroesophageal reflux disease (GERD) to relieve symptoms, heal esophagitis, and prevent complications, such as strictures and Barrett's esophagus. The total healthcare costs of GERD are high, especially for maintenance treatment. Therefore, the choice of cost-effective therapeutic options is an ineluctable challenge for public health authorities, third-party payers, and patients. In some European Union countries, a recent trend of public health authorities is to promote the choice of less expensive PPIs, regardless of their antisecretory potency--this in spite of the evidence that newer PPIs provide superior symptom relief and esophageal erosion healing compared to earlier drugs. Several large clinical trials have demonstrated the superiority of esomeprazole over other PPIs at standard doses for both initial and continuous maintenance therapy in patients with moderate/severe erosive esophagitis. The non-erosive GERD poses a major challenge as this condition appears more frequently to be less responsive to PPIs. The use of PPIs with the strongest antisecretory properties might reveal to be more adequate and cost-effective, particularly for this indication.

Systematic review: maintenance treatment of gastro-oesophageal reflux disease with proton pump inhibitors taken 'on-demand'

BACKGROUND

Proton pump inhibitors (PPI) therapy 'on-demand' is often used as an alternative to continuous maintenance therapy in gastro-oesophageal reflux disease (GERD).

AIM

We conducted a systematic review with the specific objectives to ascertain whether on-demand PPI therapy was effective in preventing symptomatic relapse and to assess the relative efficacy of on-demand vs. continuous PPI maintenance strategy.

METHODS

Randomized-controlled clinical trials comparing on-demand PPI vs. placebo or on-demand vs. continuous PPI therapy in GERD patients were identified by searching the Medline database and the Cochrane Controlled Trials Register.

RESULTS

Seventeen studies were found which met inclusion criteria. Out of the 17 studies: five investigated exclusively patients with non-erosive reflux disease (NERD), four patients with NERD and mild oesophagitis, two patients with erosive oesophagitis only, and two patients with uninvestigated GERD symptoms, respectively. Four further studies were not investigating the effectiveness of the therapies but primarily pharmacoeconomic or quality of life parameters.

CONCLUSIONS

On the basis of the analysis of 17 studies, we can conclude that on-demand therapy with currently available PPI appears to be effective in the long-term management of patients with NERD or mild and uninvestigated forms of GERD, but not in patients with (severe) erosive oesophagitis.

Role of carbon monoxide in electrically induced non-adrenergic, non-cholinergic relaxations in the guinea-pig isolated whole trachea

BACKGROUND AND PURPOSE

Nitric oxide (NO) and vasoactive intestinal peptide (VIP) are considered transmitters of non-adrenergic, non-cholinergic (NANC) relaxations in guinea-pig trachea, whereas the role of carbon monoxide (CO) is unknown. This study was designed to assess the participation of CO, and to investigate the localization of haem oxygenase-2 (HO-2), the CO-producing enzyme, in tracheal neurons.

EXPERIMENTAL APPROACH

NANC responses to electrical field stimulation (EFS) at 3 and 10 Hz were evaluated in epithelium-free whole tracheal segments as intraluminal pressure changes. Drugs used were: L-nitroarginine methyl ester (L-NAME, 100 microM) to inhibit NO synthase (NOS), alpha-chymotrypsin (2 U ml(-1)) to inactivate VIP, zinc protoporphyrin-IX (ZnPP-IX, 10 microM) to inhibit HO-2, and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microM), a soluble guanylyl cyclase inhibitor. For immunohistochemistry, tissues were exposed to antibodies to PGP 9.5, a general neuronal marker, HO-2 and NOS, and processed with an indirect immunofluorescence method.

KEY RESULTS

alpha-Chymotrypsin did not affect NANC relaxations. ODQ inhibited NANC responses by about 60%, a value similar to that obtained by combining L-NAME and ZnPP-IX. The combination of ODQ, L-NAME and ZnPP-IX reduced the responses by 90%. Subpopulations of HO-2 positive neurons containing NOS were detected in tracheal sections.

CONCLUSIONS AND IMPLICATIONS

In the guinea-pig trachea, NANC inhibitory responses at 3 and 10 Hz use NO and CO as main transmitters. Their participation is revealed following inhibition of NOS, HO-2 and soluble guanylyl cyclase. The involvement of CO as a relaxing transmitter paves the way for novel therapeutic approaches in the treatment of airway obstruction.

Identification of galanin receptor 1 on excitatory motor neurons in the guinea pig ileum

Exogenously administered galanin inhibits cholinergic transmission to the longitudinal muscle and reduces peristaltic efficiency in the guinea pig ileum with a mechanism partially mediated by galanin receptor 1 (GAL-R1). We investigated the effect of exogenous galanin 1-16, which has high affinity for GAL-R1, on the ascending excitatory reflex of the circular muscle elicited by radial distension in isolated segments of guinea pig ileum. We used a three-compartment bath that allows dissecting the ascending pathway into the oral (site of excitatory motor neurons), intermediate (site of ascending interneurons) and caudal compartment (site of intrinsic primary afferent neurons). Galanin 1-16 (0.3-3 micromol L(-1)) applied to the oral compartment inhibited in a concentration-dependent manner the ascending excitatory reflex elicited by the wall distension in the caudal compartment. This effect was antagonized by the GAL-R1 antagonist, RWJ-57408 (1 and 10 micromol L(-1)). By contrast, galanin 1-16 was ineffective when added to the intermediate or caudal compartment up to 3 micromol L(-1). GAL-R1 immunoreactive neurons did not contain neuron-specific nuclear protein, a marker for intrinsic primary afferent neurons. These findings indicate that GAL-R1s are present on motor neurons responsible for the ascending excitatory reflex, but not on ascending interneurons and intrinsic primary afferent neurons.

Role of galanin receptor 1 in gastric motility in rat

Galanin actions are mediated by distinct galanin receptors (GAL-R), GAL-R1, -R2 and -R3. We investigated the role of GAL-R1 in gastric motility and the expression of GAL-R1 in the rat stomach. In vivo, in urethane-anaesthetized rats, galanin (equipotent for all GAL-Rs) induced a short inhibition of gastric motility, followed by increase in tonic and phasic gastric motility; the latter was significantly reduced by the GAL-R1 antagonist, RWJ-57408. Galanin 1-16 (high affinity for GAL-R1 and -R2) induced a long-lasting decrease of intragastric pressure, which was not modified by RWJ-57408. In vitro, galanin and galanin 1-16 induced increase of intragastric pressure that was not affected by RWJ-57408. Tetrodotoxin (TTX) did not suppress the galanin excitatory effect, whereas the effect of galanin 1-16 on gastric contraction was increased by TTX- or N-nitro-L-arginine, an inhibitor of nitric oxide synthase. GAL-R1 immunoreactivity was localized to cholinergic and tachykinergic neurons and to neurons immunoreactive for nitric oxide synthase or vasoactive intestinal polypeptide. This study suggests that an extrinsic GAL-R1 pathway mediates the galanin excitatory action, whereas an extrinsic, non GAL-R1 pathway is likely to mediate the galanin inhibitory effect in vivo. GAL-R1 intrinsic neurons do not appear to play a major role in the control of gastric motility.

Role of galanin receptor 1 in peristaltic activity in the guinea pig ileum

Galanin effects are mediated by distinct receptors, galanin receptor 1 (GAL-R1), GAL-R2 and GAL-R3. Here, we analyzed 1) the role of GAL-R1 in cholinergic transmission and peristalsis in the guinea-pig ileum using longitudinal muscle-myenteric plexus preparations and intact segments of the ileum in organ bath, and 2) the distribution of GAL-R1 immunoreactivity in the myenteric plexus with immunohistochemistry and confocal microscopy. Galanin inhibited electrically stimulated contractions of longitudinal muscle-myenteric plexus preparations with a biphasic curve. Desensitization with 1 microM galanin suppressed the high potency phase of the curve, whereas the GAL-R1 antagonist, RWJ-57408 (1 microM), inhibited the low potency phase. Galanin (3 microM) reduced the longitudinal muscle contraction and the peak pressure, and decreased the compliance of the circular muscle. All these effects were antagonized by RWJ-57408 (1 or 10 microM). RWJ-57408 (10 microM) per se did not affect peristalsis parameters in normal conditions, nor when peristalsis efficiency was reduced by partial nicotinic transmission blockade with hexamethonium. In the myenteric plexus, GAL-R1 immunoreactivity was localized to neurons and to fibers projecting within the plexus and to the muscle. GAL-R1 was expressed mostly by cholinergic neurons and by some neurons containing vasoactive intestinal polypeptide or nitric oxide synthase. This study indicates that galanin inhibits cholinergic transmission to the longitudinal muscle via two separate receptors; GAL-R1 mediates the low potency phase. The reduced peristalsis efficiency could be explained by inhibition of the cholinergic drive, whereas the decreased compliance is probably due to inhibition of descending neurons and/or to the activation of an excitatory muscular receptor. Endogenous galanin does not appear to affect neuronal pathways subserving peristalsis in physiologic conditions via GAL-R1.

Improvement of vestibular compensation by Levo-sulpiride in acute unilateral labyrinthine dysfunction

L-sulpiride is the levorotatory enantiomer of sulpiride, a neuroleptic of the family of benzamide derivatives; it has a characteristic antagonist effect on central DA2 dopaminergic receptors and dopamine DA1 "autoreceptors". Its efficacy in the symptomatic control of acute vertigo spells has been recognized, apart from its well-known antiemetic, antidyspeptic and anti-depressant properties, at high dosages. To establish objective parameters of the results of its clinical application, a randomized prospective study was started comparing the effects of the drug in a group of 87 patients with vertigo of peripheral origin, with those in a control group treated with other vestibular suppressants. The drug was administered via the intravenous route, 25 mg t.i.d., for the first 3 days, then by oral administration, with the same schedule and dosage, for a further 7 days. After clinical evaluation of vestibular signs and symptoms, electronystagmographic recordings of rotatory tests were obtained, at admission and were then controlled after 6 months. A subjective Visual Analogue Scale was also delivered daily to the patients in order to monitor symptomatic improvements. When compared to conventional treatments, L-sulpiride appeared to induce a statistically significant faster recovery in unilateral vestibular lesions. An unexpected favourable outcome of treatment was the facilitation of spontaneous vestibular compensation, in terms of lesser residual labyrinthine dysfunction and reduction of recurrent vertigo attacks during the 6 months follow-up. The mechanisms of action of the drug and its interaction with the vestibular system are discussed.

Review article: clinical implications of enteric and central D2 receptor blockade by antidopaminergic gastrointestinal prokinetics

Antidopaminergic gastrointestinal prokinetics (bromopride, clebopride, domperidone, levosulpiride and metoclopramide) have been exploited clinically for the management of motor disorders of the upper gastrointestinal tract, including functional dyspepsia, gastric stasis of various origins and emesis. The prokinetic effect of these drugs is mediated through the blockade of enteric (neuronal and muscular) inhibitory D2 receptors. The pharmacological profiles of the marketed compounds differ in terms of their molecular structure, affinity at D2 receptors, ability to interact with other receptor systems [5-hydroxytryptamine-3 (5-HT3) and 5-HT4 receptors for metoclopramide; 5-HT4 receptors for levosulpiride) and ability to permeate the blood-brain barrier (compared with the other compounds, domperidone does not easily cross the barrier). It has been suggested that the serotonergic (5-HT4) component of some antidopaminergic prokinetics may enhance their therapeutic efficacy in gastrointestinal disorders, such as functional dyspepsia and diabetic gastroparesis. The antagonism of central D2 receptors may lead to both therapeutic (e.g. anti-emetic effect due to D2 receptor blockade in the area postrema) and adverse (including hyperprolactinaemia and extrapyramidal dystonic reactions) effects. As the pituitary (as well as the area postrema) is outside the blood-brain barrier, hyperprolactinaemia is a side-effect occurring with all antidopaminergic prokinetics, although to different extents. Extrapyramidal reactions are most commonly observed with compounds crossing the blood-brain barrier, although with some differences amongst the various agents. Prokinetics with a high dissociation constant compared with that of dopamine at the D2 receptor (i.e. compounds that bind loosely to D2 receptors in the nigrostriatal pathway) elicit fewer extrapyramidal signs and symptoms. A knowledge of central and peripheral D2 receptor pharmacology can help the clinician to choose between the antidopaminergic prokinetics to obtain a more favourable risk/benefit ratio.

Review of the implications of dietary tryptophan intake in patients with irritable bowel syndrome and psychiatric disorders

In this review, we address the possible role of the essential amino acid L-tryptophan or its metabolic derivative 5-hydroxytryptophan in the modulation of serotonin (5-hydroxytryptamine) synthesis and thereby in affecting the pathophysiology of central and peripheral nervous system disorders, including depression and irritable bowel syndrome. L-Tryptophan may represent a link between apparently disparate functional disorders and is of interest for general gastroenterologists, neurogastroenterologists, and neurologists. On the basis of estimates showing that approximately 20% of patients with functional bowel disorders seeking care in referral centres have psychiatric comorbidity, we attempt to provide a conceptual framework for defining the possible role of L-tryptophan in this population.

Ligand-induced mu opioid receptor endocytosis and recycling in enteric neurons

Immunohistochemistry and confocal microscopy were used to investigate endocytosis and recycling of the native mu opioid receptor (muOR) in enteric neurons. Isolated segments of the guinea-pig ileum were exposed to increasing concentrations of muOR agonists at 4 degrees C to allow ligand binding and warming to 37 degrees C for 0 min (baseline) to 6 h in ligand-free medium to allow receptor internalization and recycling. The endogenous ligand, [Met]enkephalin, and [D-Ala(2),MePhe(4),Gly-ol(5)] enkephalin (DAMGO), an opioid analog, and the alkaloids, etorphine and fentanyl, induced rapid internalization of muOR immunoreactivity in enteric neurons, whereas morphine did not. muOR internalization was prevented by muOR antagonists. Basal levels of muOR immunoreactivity in the cytoplasm were 10.52+/-2.05%. DAMGO (1 nM-100 microM) induced a concentration-dependent increase of muOR immunofluorescence density in the cytoplasm to a maximum of 84.37+/-2.26%. Translocation of muOR immunoreactivity in the cytoplasm was detected at 2 min, reached the maximum at 15-30 min, remained at similar levels for 2 h, began decreasing at 4 h, and was at baseline values at 6 h. A second exposure to DAMGO (100 nM) following recovery of internalized muOR immunoreactivity at the cell surface induced a translocation of muOR immunoreactivity in the cytoplasm comparable to the one observed following the first exposure (46.89+/-3.11% versus 43.31+/-3.80%). muOR internalization was prevented by hyperosmolar sucrose, phenylarsine oxide or potassium depletion, which inhibit clathrin-mediated endocytosis. muOR recycling was prevented by pre-treatment with bafilomycin A1, an acidotropic agent that inhibits endosomal acidification, but not by the protein synthesis inhibitor, cycloheximide. This study shows that native muOR in enteric neurons undergoes ligand-selective endocytosis, which is primarily clathrin-mediated, and recycles following endosomal acidification. Following recycling, muOR is activated and internalized by DAMGO indicating that recycled receptors are functional.

5-HT4 receptors contribute to the motor stimulating effect of levosulpiride in the guinea-pig gastrointestinal tract

BACKGROUND

The dopamine D2 receptor antagonist levosulpiride is a substituted benzamide derivative, whose gastrokinetic properties are exploited clinically for the management of functional dyspepsia. However, for other benzamide derivatives, such as cisapride and mosapride, agonism towards serotonin 5-HT4 receptors is considered the main mechanism leading to gastrointestinal prokinesia.

AIMS

To assess whether levosulpiride is able to activate 5-HT4 receptors in the guinea-pig isolated gastrointestinal tract.

MATERIALS AND METHODS

Circular muscle strips from gastric antrum, and colonic longitudinal muscle strips were used to detect electrically stimulated neurogenic contractions. The effect of levosulpiride was assessed in the absence and presence of GR125487, a selective 5-HT4 receptor antagonist. Furthermore, potential interaction of levosulpiride with 5-HT3 receptors and tissue cholinesterases was assessed in unstimulated ileal longitudinal muscle-myenteric plexus preparations.

RESULTS

Antral and colonic strip contractions were cholinergic/tachykinergic in nature. Micromolar concentrations of levosulpiride potentiated submaximal responses, through a mechanism competitively antagonized by GR125487 (pKB=9.4). In LMMPs, levosulpiride slightly affected contractions caused by the 5-HT, receptor agonist 2-methyl-5-HT, and had no effect on contractions to exogenous acetylcholine.

CONCLUSIONS

Our results indicate that levosulpiride acts as a moderate agonist at the 5-HT4 receptor. This property, together with antagonism at D2 receptors, may contribute to its gastrointestinal prokinetic effect.

Twenty-four hour recordings of colonic motility in patients with diverticular disease: evidence for abnormal motility and propulsive activity

INTRODUCTION

Diverticular disease of the colon is one of the most common pathologic entities in western countries. Although altered motility of the large bowel is commonly believed to be one of the major pathophysiologic mechanisms, no convincing evidence has been reported yet. In fact, only a few conflicting studies concerning distal colonic motility (with no information on forceful propulsive activity) are available in the literature.

PURPOSE

The purpose of the present study was to investigate basal and stimulated (postprandial) colonic motility from the transverse (not affected), descending, and sigmoid colon in patients with diverticular disease, together with detection of high-amplitude propagated contractions (mass movements). Motility data from patients were compared with those obtained in healthy control subjects.

METHODS

Ten patients and 16 control subjects of both sexes were recruited for the study. In all subjects, colonic motility was recorded for a 24-hour period by a colonoscopically positioned manometric catheter. Two 1000-kcal mixed meals were served during the study.

RESULTS

Compared with control subjects, patients with diverticular disease displayed significantly increased amounts of motility in the affected segments; the response to a physiologic stimulus (meal) was also abnormal in the patients' group. Diverticular disease patients also had a significant increase of forceful propulsive activity compared with control subjects (average = 10.3 +/- 2.7/subject/day high-amplitude propagated contractions for patients and 5.5 +/- 0.8/subject/day for control subjects; P = 0.051); interestingly, about 20 percent of such activity was abnormal, being propagated in a retrograde fashion.

CONCLUSIONS

We concluded that patients with diverticular disease of the colon have abnormal motor and propulsive activities of the large bowel, which are confined to the affected segments.

Improving opportunities for effective management of gastro-oesophageal reflux disease

The recent introduction of proton pump inhibitors has extraordinarily improved the therapeutic approach to gastro-oesophageal reflux disease. The concept of decreasing gastric acid secretion and increasing the pH in the lower oesophagus has been demonstrated to be therapeutically effective and the higher the level of pH achieved, the better the results. In spite of the evident efficacy of these molecules, there are still many patients who will continue to have symptoms despite medical treatment. Proton pump inhibitors suppress gastric acidity, but this effect shows a remarkable interindividual variation depending on different reasons. Thus, it is still possible to optimise medical therapy for gastro-oesophageal reflux disease. Esomeprazole, the S-isomer of omeprazole, has an advantageous metabolism and this particular feature translates into superior clinical efficacy. Clinical trials for initial and long-term treatment across the gastro-oesophageal reflux disease spectrum, have clearly demonstrated the superiority of esomeprazole over omeprazole, even if tolerability and safety are very similar.

Review article: the pharmacological treatment of acute colonic pseudo-obstruction

Acute colonic pseudo-obstruction (Ogilvie's syndrome) can be defined as a clinical condition with symptoms, signs and radiological appearance of acute large bowel obstruction unrelated to any mechanical cause. Recent reports of the efficacy of cholinesterase inhibitors in relieving acute colonic pseudo-obstruction have fuelled interest in the pharmacological treatment of this condition. The aim of the present review is to outline current perspectives in the pharmacological treatment of patients with acute colonic pseudo-obstruction. The best documented pharmacological treatment of Ogilvie's syndrome is intravenous neostigmine (2-2.5 mg), which leads to quick decompression in a significant proportion of patients after a single infusion. However, the search for new colokinetic agents for the treatment of lower gut motor disorders has made available a number of drugs that may also be therapeutic options for Ogilvie's syndrome. Among these agents, the potential of 5-hydroxytryptamine-4 receptor agonists and motilin receptor agonists is discussed.

Clinical pharmacology and safety profile of esomeprazole, the first enantiomerically pure proton pump inhibitor

Awareness of important differences in the pharmacological profile of individual optical isomers of chiral drugs led to the development of esomeprazole, the S-isomer of omeprazole, a new pharmacological entity designed to improve the clinical outcome of available proton pump inhibitors in the management of acid-related disorders. The superior acid control achieved by esomeprazole is mainly due to an advantageous metabolism compared with racemate omeprazole, leading to improved bioavailability and to enhanced delivery of the drug to the gastric proton pump.

Irritable bowel syndrome: new agents targeting serotonin receptor subtypes

Although the past few years have seen an exponential growth of compounds of potential interest for the treatment of functional gastrointestinal (GI) tract disorders, the gap that still exists between basic and clinical research is easily noticed if one considers the relative paucity of drugs that have received marketing authorisation for the treatment of irritable bowel syndrome (IBS). Traditional efficacy outcomes in drug development for IBS include the ability of the compound to affect GI tract motility (i.e. to exert a prokinetic or an antispasmodic effect), which is thought to be of importance if a motor disorder is the underlying pathophysiological mechanism. More recently, altered visceral sensitivity to a distending stimulus has been suggested to be a key pathophysiological feature, at least in some patients, and has become a target for therapeutic interventions. However, there is now growing consensus that the primary outcome measure in the treatment of functional disorders are those that reflect overall control of the patient's symptoms (pain, diarrhoea, constipation) in everyday situations such as the clinical global improvement scales. Although, in general, guidelines on the design of treatment trials for functional GI tract disorders advise against subcategorisation of patients according to the main symptom (because of symptom instability), subcategorisation indeed makes sense especially in IBS (constipation- or diarrhoea-predominant). Compounds with a specific indication for each subpopulation of patients are now emerging. The rationale for investigations on serotonin (5-hydroxytryptamine; 5-HT) receptor ligands in IBS rests mainly on the fact that serotonin, which may be released by enterochromaffin-like cells in the GI tract as well as from other sources, has a number of well documented motor effects on the GI tract and can produce hyperalgesia in several experimental models. Serotonin receptors belonging to the 5-HT3 and 5-HT4 subtype are the most extensively studied in gastroenterology, although hitherto 'orphan' receptor subtypes, such as the 5-HT7 and the 5-HT(1B/D) receptors, are now emerging. Among 5-HT3 receptor antagonists, alosetron was recently approved for the treatment of diarrhoea-predominant IBS and is an example of a compound that, at least theoretically, may act at multiple levels: by inhibiting visceral sensitivity, by increasing compliance, and by inhibiting excitatory 5-HT3 receptors located on both ascending and descending neuronal pathways involved in peristalsis. For this reason, 5-HT3 receptor antagonists may slow transit, hence the specific indication of alosetron in diarrhoea-predominant IBS. However, alosetron has been recently withdrawn by the manufacturer because of safety concerns. Hypomotility remains an attractive therapeutic target in IBS and the new generation of prokinetics includes several partial agonists at the 5-HT4 receptor, such as tegaserod (HTF-919) and prucalopride (R0-93877). In addition, preliminary evidence suggests that 5-HT4 receptors may also be involved in the modulation of visceral sensitivity. Second-generation 5-HT4 receptor agonists seem to be devoid of the QT-prolonging effects observed in some clinical circumstances with cisapride and may be more active at the colonic level. Piboserod (SB-207266A) is a 5-HT4 receptor antagonist under development for the treatment of diarrhoea-predominant IBS. Finally, interest in 5-HT7 and 5-HT(1B/D) receptor subtypes stems from the observation that the former receptors mediate smooth muscle relaxation (at least in the human colon), whereas sumatriptan (a 5-HT(1B/D) receptor agonist) can affect GI tract motility and visceral sensitivity.

An objective method for detecting time-dependent effects in graft survival

The proportional hazards model has become increasingly important in the analysis of censored survival data after transplantation. Neverthless, in clinical transplantation it is still undefined how the influence of covariates changes over time. The additive regression model is an alternative (or extension) to the Cox model. It results in plots (Aalen plots) that may give information on the effect of covariates over time by way of the cumulative regression function plots. A total of 386 primary cadaveric kidney transplants performed between 1984 and 1996 were included in our analysis. The follow-up period ranged from 24 to 156 months. According to Aalen, an additive regression model was used and plots for the detection of time-dependent effects of covariates were determined. Patients dying with functioning grafts were classed as graft failures. Factors potentially affecting graft outcome, such as sex, donor and recipient's age, HLA A-B match, cold ischaemia time (CIT), delayed graft function (DGF), serum creatinine at 1 month (Cr1), rejection episodes within 3 months (R3), and type of brain death (BD), were considered. The slopes of the plots by donor age, DGF, HLA A-B match, R3, Cr1 and BD appear to have a significant influence throughout the observation period, with different time-dependent effects on graft survival. Slopes for DGF, Cr1, and age of donor are positive (increased hazard), while slopes for HLA match and BD are negative (decreased hazard). Estimated regression functions for DGF, donor age and Cr1 show a prompt slope (within 3 months); the covariate R3 has a clear influence for about 5 years, and then seems to disappear; and BD appears to have a consistent effect over the entire period. The additive regression model with Aalen plots represents a useful technique in the analysis of survival data after kidney transplantation. Some covariates, such as R3, may often lose their effects on graft survival, with a relevant clinical impact. Others have a clear and additive influence over the entire period (BD), while the effects of donor age, DGF and CR1 each appear to have a prompt effect in the outcome.

Contribution of NK3 tachykinin receptors to propulsion in the rabbit isolated distal colon

The role of NK3 receptors in rabbit colonic propulsion has been investigated in vitro with the selective agonist, senktide, and two selective antagonists, SR142801 and SB222200. Peristalsis was elicited by distending a rubber balloon with 0.3 and 1.0 mL of water leading to a velocity of 2.2 and 2.8 mm s-1, respectively. At concentrations of 1 nM, senktide inhibited propulsion evoked by both distensions (range 25-40%), whereas at 6 and 60 nmol L-1 facilitated 'submaximal' propulsion by 30%. In the presence of Nomega-nitro-L-arginine (L-NNA, 200 micromol L-1), which per se caused a slight prokinetic effect, 1 nmol L-1 senktide markedly accelerated propulsion (range 35-50%). Hexamethonium (200 micromol L-1) had minor effects on propulsion. In its presence, 60 nmol L-1 senktide significantly inhibited propulsion induced by both stimuli (range 20-50%). SR142801 (0.3, 3 nmol L-1) and SB222200 (30, 300 nmol L-1) facilitated 'submaximal' propulsion (range 20-40%). Conversely, higher antagonist concentrations (SR142801: 30, 300 nM; SB222200: 1, 10 micromol L-1) inhibited propulsion to both distensions by 20%. A combination of SR142801 (300 nmol L-1) plus hexamethonium (200 micromol L-1) induced an approximately four-fold greater inhibition of propulsion than that induced by SR142801 alone. In conclusion, in the rabbit-isolated distal colon, a subset of NK3 receptors located on descending pathways mediates an inhibitory effect on propulsion by activating a NO-dependent mechanism. Another subset of NK3 receptors, located on ascending pathways mediates a facilitative effect involving a synergistic interaction with cholinergic nicotinic receptors.

Tachykinin-dependent and -independent components of peristalsis in the guinea pig isolated distal colon

BACKGROUND & AIMS

In the intestine, tachykinins regulate motility by participating in neuromuscular and neuro-neuronal transmission. The aim of this study was to test the hypothesis that colonic propulsion is regulated by an interplay between tachykinergic and cholinergic transmission.

METHODS

Propulsion was elicited by intraluminal distention of a thin rubber balloon, which traveled from the oral to the anal end of guinea pig isolated distal colon segments. The overall contribution of endogenous tachykinins to colonic propulsion was examined by blocking NK1, NK2, and NK3 receptors simultaneously.

RESULTS

NK2-receptor blockade by MEN 11420 inhibited propulsion, whereas blockade of NK(1) by SR 140333 or of NK3 receptors by SR 142801 had minor effects on motility. Blockade of muscarinic or nicotinic receptors by hyoscine or hexamethonium decelerated peristalsis up to propulsion arrest. In the presence of partial muscarinic receptor blockade, the NK1-receptor antagonist SR 140333 and the NK2-receptor antagonist MEN 11420 markedly inhibited propulsion. Propulsion was also inhibited by the NK3-receptor antagonist SR 142801 in the presence of partial nicotinic receptor blockade. The simultaneous administration of the 3 tachykinin antagonists inhibited propulsion by 50%.

CONCLUSIONS

This study demonstrates the existence of an interplay between tachykinergic and cholinergic pathways during peristalsis and the importance of endogenous tachykinins acting at multiple receptor sites in the control of colonic propulsion.

Low-amplitude propagated contractile waves: a relevant propulsive mechanism of human colon

BACKGROUND

Human colonic motility is still poorly understood, especially as far as concerns its propulsive function. Available data refer almost exclusively to the forceful propulsive activity, which is recognized as high-amplitude propagated contractions, the manometric equivalent of mass movements. By contrast, information on less vigorous propulsive contractions is still lacking.

AIMS

To investigate the presence and behaviour of low-amplitude propagated contractile waves (less than 50 mmHg in amplitude) in the colon of healthy humans during a 24-hour study period.

SUBJECTS AND METHODS

A series of 16 healthy volunteers of both sexes entered the study, and were investigated by a standard technique involving a colonoscopically-positioned manometric catheter. During the study, two standard 1,000 kcal mixed meal and a 450 kcal breakfast were served. The recordings were, therefore, scanned for the presence of low-amplitude propagated contractile waves (waves of less than 50 mmHg in amplitude, propagated over at least three consecutive recording ports), their daily distribution, and their relationship with physiological events.

RESULTS

Low-amplitude propagated contractile waves were constantly present in all the tracings, with an average of about 61 events/subject/day and a mean amplitude of about 20 mmHg. More than 80% of these events appeared during the day, with a significant (p<0.05) increase after meals and after morning awakening. In 25% of subjects, these waves were accompanied by emission of flatus.

CONCLUSIONS

In the human colon, low-amplitude propagated contractile waves are a constant physiological propulsive pattern, which is generally related to sleep-wake cycles and meal ingestion.

Tumour necrosis factor-alpha gene polymorphism: implications in kidney transplantation

In this study we have analysed the TNFA biallelic polymorphism at the -308 position, in 169 kidney recipients that received the graft in a single Italian transplantation facility and we have then correlated the TNFA genotypes with the post-transplant outcome. To assess the cytokine genotypes, a polymerase chain reaction-sequence specific primer (PCR-SSP) methodology has been utilised. By the analysis of the different genotypes, the corresponding TNF-alpha phenotypes and the level of the TNF-alpha production, were deduced: the TNF(*)1/TNF(*)1 genotype gives a low TNF-alpha production level, TNF(*)1/TNF(*) 2 and TNF(*)2/TNF(*)2 genotypes give a high TNF-alpha production level. Out of the one hundred and sixty-nine patients studied, one hundred and twenty-one recipients (72%) had a low TNF-alpha producer phenotype, whereas forty-eight (28%) had a high TNF-alpha producer phenotype. These frequencies were not statistically different from those of the control group. The incidence of acute rejection episodes, vascular damage (grade III degrees of Banff classification), and serum creatinine levels at 1 month, were significantly greater in high TNF-alpha producers (P=0. 048, 0.031 and 0.007 respectively). The logistical regression model indicated that only the high producer genotype and donor age were significantly and independently correlated with acute graft failure (P=0.02 and P=0.013 respectively). This analysis shows that recipient TNFA polymorphism, previously associated with differential production TNF-alpha by in vitro studies could be related to the clinical outcome of kidney transplantation.

The interaction of antidepressant drugs with enteric 5-HT7 receptors

In this study the functional interaction of the antidepressant drugs amitriptyline, mianserin, maprotiline, imipramine, fluoxetine and the putative antidepressant drug flibanserin has been studied on 5-HT7-mediated responses to 5-carboxamidotryptamine (5-CT) in the guinea-pig ileum. 5-CT induced a concentration-dependent inhibition of the contractile response to substance P (100 nM). Except for fluoxetine and flibanserin, all the antidepressants antagonized by different degrees the 5-CT inhibitory response with the following rank affinity order: mianserin > maprotiline > imipramine > amitriptyline. Mianserin was the only antidepressant to show a profile of competitive antagonism at 5-HT7 receptors in a tenfold range of concentrations (0.1-1 microM), with an affinity (pA2) value of 8.1 +/- 0.6. The antagonism of the other antidepressants was not concentration-dependent (amitriptyline) or was associated with slight or moderate reduction of the maximal 5-CT response (imipramine or maprotiline). The apparent affinity (pKB) values were: amitriptyline, 7.0 +/- 0.2; maprotiline, 7.3 +/- 0.6; imipramine, 7.2 +/- 0.4. Our results show that various antidepressant drugs belonging to different chemical classes behave as antagonists at enteric 5-HT7 receptors through competitive or allosteric mechanisms. This evidence extends our previous findings demonstrating the interaction of antidepressants with other 5-HT receptors, namely 5-HT3 and 5-HT4 receptors.

Role of agonist-dependent receptor internalization in the regulation of mu opioid receptors

Organotypic cultures and ileal neuromuscular preparations were used to determine (i) whether endogenous release of opioids by electrical stimulation induces mu receptor endocytosis, and (ii) whether and under which conditions ligand-induced mu receptor endocytosis influences the responsiveness of neurons expressing native mu receptors. In longitudinal muscle-myenteric plexus preparations, electrical stimulation at 20 Hz induced a prominent endocytosis of mu receptors in enteric neurons, indicating endogenous release of opioids. A similar massive endocytosis was triggered by exogenous application of the mu receptor agonist, [D-Ala(2),MePhe(4), Gly-ol(5)] enkephalin, whereas exogenous application of morphine was ineffective. [D-Ala(2),MePhe(4),Gly-ol(5)] enkephalin and morphine induced a concentration-dependent inhibition of neurogenic cholinergic twitch contractions to electrical stimulation at 0.1 Hz. beta-Chlornaltrexamine shifted to the right the inhibitory curve of both agonists with a concentration-dependent reduction of the maximum agonist response, which is consistent with the existence of spare mu opioid receptors. Under these conditions, the induction of mu receptor endocytosis by exogenously applied [D-Ala(2), MePhe(4),Gly-ol(5)] enkephalin diminished the inhibitory effect of this agonist on twitch contractions and tritiated acetylcholine release. In contrast, there was no reduction of the inhibitory effect of morphine, which failed to induce mu receptor endocytosis, on neurogenic cholinergic response. These results provide the first evidence for the occurrence of mu receptor endocytosis in neurons by endogenously released opioids and show that agonist-dependent mu receptor endocytosis could serve as a mechanism to regulate mu opioid receptor responsiveness to ligand stimulation when the opioid receptor reserve is reduced.