5-HT4 receptor agonists enhance both cholinergic and nitrergic activities in human isolated colon circular muscle

The Relationship Between Autonomic Dysfunction and Mood Symptoms in De Novo Parkinson's Disease Patients Over Time

BACKGROUND

Autonomic dysfunction is prevalent in Parkinson's disease (PD) and can worsen quality of life. We examined: (a) whether specific autonomic symptoms were more strongly associated with anxiety or depression in PD and (b) whether overall autonomic dysfunction predicted mood trajectories over a 5-year period.

METHODS

Newly diagnosed individuals with PD (N = 414) from the Parkinson's Progression Markers Initiative completed self-report measures of depression, anxiety, and autonomic symptoms annually. Cross-sectional linear regressions examined relationships between specific autonomic subdomains (gastrointestinal, cardiovascular, thermoregulatory, etc.) and mood. Multilevel modeling examined longitudinal relationships with total autonomic load.

RESULTS

Gastrointestinal symptoms were associated with both higher anxiety (b = 1.04, 95% CI [.55, 1.53], P < .001) and depression (b = .24, 95% CI [.11, .37], P = .012), as were thermoregulatory symptoms (anxiety: b = 1.06, 95% CI [.46, 1.65], P = .004; depression: b = .25, 95% CI [.09, .42], P = .013), while cardiovascular (b = .36, 95% CI [.10, .62], P = .012) and urinary symptoms (b = .10, 95% CI [.01, .20], P = .037) were associated only with depression. Longitudinally, higher total autonomic load was associated with increases in both depression (b = .01, 95% CI [.00, .02], P = .015) and anxiety (b = .04, 95% CI [.01, .06], P < .001) over time, as well as occasion-to-occasion fluctuations (depression: b = .08, 95% CI [.05, .10], P < .001; anxiety: b = .24, 95% CI [.15, .32], P < .001).

CONCLUSION

Findings suggest autonomic dysfunction, particularly gastrointestinal and thermoregulatory symptoms, may be an indicator for elevated anxiety/depression and a potential treatment target early on in PD.

Hyoscine butylbromide mode of action on bowel motility: From pharmacology to clinical practice

BACKGROUND

Hyoscine butylbromide (HBB) has been available for use as an antispasmodic since 1951 and is indicated for the treatment of abdominal pain associated with cramps. A previous review in 2007 summarized the evidence on the mode of action of HBB in vitro and in vivo in both animal and human studies. However, since then, novel publications have appeared within the literature and also our knowledge of what represents normal motility in humans has evolved.

PURPOSE

This review is the result of the collaboration between a basic scientist and clinicians with the aim of providing an updated overview of the mechanisms of action of HBB and its clinical efficacy to guide not only use in clinical practice, but also future research.

The effects of loperamide on excitatory and inhibitory neuromuscular function in the human colon

BACKGROUND

In most animal species, opioids alter colonic motility via the inhibition of excitatory enteric motor neurons. The mechanisms by which opioids alter human colonic motility are unclear. The aim of this study was to describe the effects of loperamide on neuromuscular function in the human colon.

METHODS

Tissue specimens of human colon from 10 patients undergoing an anterior resection were divided into three inter-taenial circular muscle strips. Separate organ baths were used to assess: (1) excitatory transmission (selective blockade of inhibitory transmission: L-NOARG/MRS2179); (2) inhibitory transmission (selective blockade of excitatory transmission: hyoscine hydrobromide); and (3) a control bath (no drug additions). Neuromuscular function was assessed using force transducer recordings and electrical field stimulation (EFS; 20 V, 10 Hz, 0.5 ms, 10 s) prior to and following loperamide and naloxone.

KEY RESULTS

In human preparations with L-NOARG/MRS2179, loperamide had no significant effects on isometric contractions. In preparations with hyoscine hydrobromide, loperamide reduced isometric relaxation during EFS (median difference + 0.60 g post-loperamide, Z = -2.35, p = 0.019).

CONCLUSIONS AND INFERENCES

Loperamide had no effect on excitatory neuromuscular function in human colonic circular muscle. These findings suggest that loperamide alters colonic function by acting primarily on inhibitory motor neurons, premotor enteric neurons, or via alternative non-opioid receptor pathways.

Antispasmodic Effect of Bergamot Essential Oil on Rat Isolated Gut Tissues

Preclinical data indicate that bergamot essential oil (BEO) can modulate the synaptic functions within the central nervous system (CNS). Particularly, several data shows that essential oil is endowed with reproducible analgesic and anxiolytic effects that may derived from the ability to modulate the excitatory and inhibitory neurotransmission in the CNS. Although there are differences in the functional complexity of the enteric nervous system (ENS), it is likely that the phytocomplex has biological properties in gut superimposable to those showed in the CNS. Accordingly, the aim of this study was to investigate ex-vivo the effect of bergamot essential oil and its main constituents on the contractile activity of rat isolated colon, jejunum and ileum induced by different muscle stimulants such as acetylcholine (10⁻⁶ M) and potassium chloride (80 mM). Our present data demonstrate that BEO inhibits cholinergically- and non cholinergically-mediated contractions in rat isolated gut and that linalool is the most active component. These results suggest that the phytocomplex might be useful in the treatment of spastic disorders in ENS mainly characterized by the presence of pain; incidentally, irritable bowel syndrome (IBS) is a painful condition in which a role for neurotransmitter dysfunction has been envisaged. More investigation is required for clinical translation of the present data.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

The 5-HT4 Receptor Agonist Prucalopride Stimulates Mucosal Growth and Enhances Carbohydrate Absorption in the Ileum of the Mouse

BACKGROUND

Enteric serotonin may function as a mucosal growth factor. Previous work demonstrated increased crypt cell proliferation and intestinal mucosal surface area with potentiation of serotonin. While an indirect mechanism was postulated to explain these effects, the presence of 5-HT4 receptors on enterocytes raises the possibility of a direct action of serotonin. We hypothesized that a 5-HT4 specific agonist, prucalopride, would stimulate intestinal mucosal growth and enhance absorptive function in the murine small intestine.

METHODS

Adult wild-type mice were treated parenterally with prucalopride for 14 days via surgically implanted osmotic pumps. In vivo D-xylose absorption was assessed by oral gavage and serum D-xylose measurements. On day 14, glucose absorption was assessed by instilling a glucose solution into isolated segments of small intestine. The bowel was harvested and examined for morphologic parameters and crypt cell proliferation.

RESULTS

Villus height, crypt depth, and crypt proliferation were significantly increased in the distal small bowel of prucalopride-treated mice compared with control animals. Crypt depth was also increased in the proximal and middle small intestine in treated mice. There was no difference in D-xylose absorption throughout the study period; however, glucose absorption was significantly increased in the distal small intestine of prucalopride-treated mice.

CONCLUSION

Parenteral administration of the 5-HT4 receptor specific agonist, prucalopride, results in morphologic and functional changes in the murine small intestine that are most prominent in the distal small bowel. While further studies are necessary to delineate the mechanism, it is plausible that the effects are mediated by 5-HT4 receptors on enterocytes.

Targeting phosphocreatine metabolism in relapsing-remitting multiple sclerosis: evaluation with brain MRI, 1H and 31P MRS, and clinical and cognitive testing

BACKGROUND/OBJECTIVES

Fluoxetine and prucalopride might change phosphocreatine (PCr) levels via the cAMP-PKA pathway, an interesting target in the neurodegenerative mechanisms of MS.

METHODS

We conducted a two-center double-blind, placebo-controlled, randomized trial including 48 relapsing-remitting MS patients. Patients were randomized to receive placebo (n = 13), fluoxetine (n = 15), or prucalopride (n = 14) for 6 weeks. Proton (¹H) and phosphorus (³¹P) magnetic resonance spectroscopy (MRS) as well as volumetric and perfusion MR imaging were performed at weeks 0, 2, and 6. Clinical and cognitive testing were evaluated at weeks 0 and 6.

RESULTS

No significant changes were observed for both ³¹P and ¹H MRS indices. We found a significant effect on white matter volume and a trend towards an increase in grey matter and whole brain volume in the fluoxetine group at week 2; however, these effects were not sustained at week 6 for white matter and whole brain volume. Fluoxetine and prucalopride showed a positive effect on 9-HPT, depression, and fatigue scores.

CONCLUSION

Both fluoxetine and prucalopride had a symptomatic effect on upper limb function, fatigue, and depression, but this should be interpreted with caution. No effect of treatment was found on ³¹P and ¹H MRS parameters, suggesting that these molecules do not influence the PCr metabolism.

cAMP Catalyzing Phosphodiesterases Control Cholinergic Muscular Activity But Their Inhibition Does Not Enhance 5-HT4 Receptor-Mediated Facilitation of Cholinergic Contractions in the Murine Gastrointestinal Tract

Background: As the signal transduction of 5-HT₄ receptors on cholinergic neurons innervating smooth muscle is controlled by phosphodiesterase (PDE) 4 in porcine stomach and colon, and human large intestine, the in vivo gastroprokinetic effects of a 5-HT₄ receptor agonist might be enhanced by combination with a selective PDE4 inhibitor. The presence of 5-HT₄ receptors on cholinergic neurons towards murine gastrointestinal circular muscle was recently shown. If the control of this receptor pathway by PDE4 is also present in mice, this might be a good model for in vivo testing of the combination therapy. Therefore this study investigates the role of cAMP catalyzing PDEs in smooth muscle cell activity and in the intraneuronal signal transduction of the 5-HT₄ receptors in the gastrointestinal tract of C57Bl/6J mice.

Methods: In circular smooth muscle strips from murine fundus, jejunum, and colon, submaximal cholinergic contractions were induced by either electrical field stimulation (EFS) or by carbachol (muscarinic receptor agonist). The influence of the PDE inhibitors IBMX (non-selective), vinpocetine (PDE1), EHNA (PDE2), cilostamide (PDE3), and rolipram (PDE4) was tested on these contractions and on the facilitating effect of a submaximal concentration of prucalopride (5-HT₄ receptor agonist) on EFS-induced contractions.

Results: In the three gastrointestinal regions, IBMX and cilostamide concentration-dependently decreased carbachol- as well as EFS-induced contractions. Some inhibitory effect was also observed with rolipram. In the fundus a non-significant trend for an enhancement of the facilitating effect of prucalopride on EFS-induced contractions was observed with IBMX, but none of the selective PDE inhibitors enhanced the facilitating effect of prucalopride in fundus, jejunum or colon.

Conclusion: In analogy with the porcine gastrointestinal tract, in murine fundus, jejunum, and colon circular smooth muscle PDE3 is the main regulator of the cAMP turnover, with some contribution of PDE4. In contrast to the porcine gastrointestinal tract, the in vitro facilitation of electrically induced cholinergic contractions by 5-HT₄ receptor stimulation could not be enhanced by specific PDE inhibition. The C57Bl/6J murine model is thus not suitable for in vivo testing of a 5-HT₄ receptor agonist combined with a selective PDE4 inhibitor.

Synergy between 5-HT4 receptor stimulation and phosphodiesterase 4 inhibition in facilitating acetylcholine release in human large intestinal circular muscle

BACKGROUND

Gastroprokinetic properties of 5-HT₄ receptor agonists, such as prucalopride, are attributed to activation of 5-HT₄ receptors on cholinergic nerves innervating smooth muscle in the gastrointestinal smooth muscle layer, increasing acetylcholine release and muscle contraction. In porcine stomach and colon, phosphodiesterase (PDE) 4 has been shown to control the signaling pathway of these 5-HT₄ receptors. The aim of this study was to investigate the PDE-mediated control of these 5-HT₄ receptors in human large intestine.

METHODS

Circular smooth muscle strips were prepared from human large intestine; after incubation with [³H]-choline, electrically induced tritium outflow was determined as a measure for acetylcholine release. The influence of PDE inhibition on the facilitating effect of prucalopride on electrically induced acetylcholine release was studied.

KEY RESULTS

The non-selective PDE inhibitor IBMX enhanced the facilitating effect of prucalopride on electrically induced acetylcholine release. The selective inhibitors vinpocetine (PDE1), EHNA (PDE2) and cilostamide (PDE3) did not influence, while rolipram and roflumilast (PDE4) enhanced the prucalopride-induced facilitation to the same extent as IBMX.

CONCLUSIONS & INFERENCES

In human large intestinal circular muscle, the intracellular pathway of 5-HT₄ receptors facilitating cholinergic neurotransmission to large intestinal circular smooth muscle is controlled by PDE4. If the synergy between 5-HT₄ receptor agonism and PDE4 inhibition is confirmed in a functional assay with electrically induced cholinergic contractions of human large intestinal circular smooth muscle strips, combination of a selective 5-HT₄ receptor agonist with a selective PDE4 inhibitor might enhance the in vivo prokinetic effect of the 5-HT₄ receptor agonist in the large intestine.

Parkinson disease with constipation: clinical features and relevant factors

Constipation is one of the most frequent non-motor symptoms of Parkinson disease (PD) and it may be ignored by PD patients, leading to this problem not to be reported in time. The relationships between constipation and demographic variables, motor symptoms and other non-motor symptoms of PD are still unknown. PD patients were evaluated by diagnostic criteria of functional constipation in Rome III and divided into PD with constipation (PD-C) and PD with no constipation (PD-NC) groups. PD patients were assessed by rating scales of motor symptoms and other non-motor symptoms, activity of daily living and quality of life. The frequency of constipation in PD patients was 61.4%, and 24.5% of PD patients had constipation before the onset of motor symptoms. PD-C group had older age and age of onset, longer disease duration, more advanced disease stage, and more severe motor symptoms and non-motor symptoms, including worse cognition and emotion, poorer sleep quality, severer autonomic symptoms, fatigue and apathy. Binary Logistic regression analysis showed that the age, H-Y stage, depression, anxiety and autonomic dysfunction increased the risk of constipation in PD patients. Constipation exerted serious impact on the activity of daily living and quality of life in PD patients.

The novel, potent and highly selective 5-HT4 receptor agonist YH12852 significantly improves both upper and lower gastrointestinal motility

BACKGROUND AND PURPOSE

5-HT₄ receptor agonists have been shown to be effective at treating various gastrointestinal tract disorders. However, a lack of selectivity against off-targets has been a limiting factor for their clinical use.

EXPERIMENTAL APPROACH

The binding affinity and selectivity of YH12852 for human 5-HT_4(a) receptor in CHO-K1 cells were evaluated using radioligand binding assays, and agonistic activity was assessed using a β-lactamase reporter system. Contractile activity and propulsive motility were measured in the guinea pig isolated distal colon. Its prokinetic effect on the gastrointestinal tract was evaluated in guinea pigs, dogs and monkeys. Its tissue distribution was evaluated in rats.

KEY RESULTS

YH12852 exhibited high affinity and potency for human recombinant 5-HT_4(a) receptor with high selectivity over other 5-HT and non-5-HT receptors, ion channels, enzymes and transporters. YH12852 induced contractions and increased propulsive motility in guinea pig isolated colon. These effects were abolished by the 5-HT₄ receptor antagonist GR113808. YH12852 increased defecation more effectively than prucalopride in guinea pigs and dogs and improved gastric emptying more effectively than mosapride in guinea pigs, dogs and monkeys. YH12852 was highly distributed to the gastrointestinal tract as the target organ.

CONCLUSION AND IMPLICATIONS

The high in vitro potency and selectivity of YH12852 for 5-HT₄ receptor translated into potent in vivo efficacy with good tolerability. YH12852 significantly improved both upper and lower bowel motility in the animal models tested and has the potential to address considerable unmet needs in patients with functional constipation, gastroparesis or both.

5-HT4 receptors facilitate cholinergic neurotransmission throughout the murine gastrointestinal tract

BACKGROUND

In the gastrointestinal tract of several species, facilitating 5-HT₄ receptors were proposed on myenteric cholinergic neurons innervating smooth muscle by in vitro study of the effect of the selective 5-HT₄ receptor agonist prucalopride on submaximal cholinergic contractions. This was not yet established in the murine gastrointestinal tract.

METHODS

In circular smooth muscle strips from murine fundus, jejunum and colon, contractions were induced by electrical field stimulation in the presence of guanethidine, L-NAME and for colon also MRS 2500. Submaximal contractions were induced to study the influence of prucalopride.

KEY RESULTS

Electrical field stimulation at reduced voltage induced reproducible submaximal neurogenic and cholinergic contractions as the contractions were abolished by tetrodotoxin and atropine. Hexamethonium had no systematic inhibitory effect but mecamylamine reduced the responses, suggesting that part of the cholinergic response is due to activation of preganglionic neurons. Prucalopride concentration-dependently increased the submaximal cholinergic contractions in the three tissue types, reaching maximum from 0.03 μmol/L onwards. The facilitation in the different series with 0.03 μmol/L prucalopride ranged from 41% to 104%, 30% to 76% and 24% to 74% in fundus, jejunum, and colon, respectively. The effect of 0.03 μmol/L prucalopride was concentration-dependently inhibited by GR 113808.

CONCLUSIONS & INFERENCES

In the murine gastrointestinal tract, activation of 5-HT₄ receptors with prucalopride enhances cholinergic contractions, illustrating facilitation of myenteric cholinergic neurotransmission. The degree of enhancement with prucalopride is of similar magnitude as previously reported in other species, but the effective concentrations are lower than those needed in the gastrointestinal tract of other species.

Localization of the 5-hydroxytryptamine 4 receptor in equine enteric neurons and extrinsic sensory fibers

BACKGROUND

Serotonin plays a pivotal role in regulating gut motility, visceral sensitivity, and fluid secretion via specific receptors. Among these receptors, 5-HT₄ exerts a prominent control on gut motor function. Although the prokinetic effect exerted by 5-HT₄ agonists is well known, the cellular sites of 5-HT₄ expression remain poorly understood in large mammals, e.g., horses. In this study, we evaluated the distribution of 5-HT₄ in the horse intestine and in foals with enteric aganglionosis, reminiscent of human Hirschsprung's disease.

METHODS

The intestine and spinal ganglia were obtained from three healthy horses and two foals with hereditary ileocolonic aganglionosis. Tissues were processed for immunohistochemistry using a specific antibody to 5-HT₄ and a variety of neuronal markers. Myenteric and submucosal plexus 5-HT₄ -immunoreactive (IR) neurons were quantified as relative percentage (mean±SD) to the total number of neurons counted. Furthermore, the density of 5-HT₄ -IR nerve fibers was evaluated in the mucosa and tunica muscularis.

KEY RESULTS

The 5-HT₄ immunoreactivity was localized to large percentages of myenteric neurons ranging from 28±9% (descending colon) to 63±19% (ileum), and submucosal neurons ranging from 54±6% (ileum) to 68±14% (duodenum). The 5-HT₄ -immunoreactivity was co-expressed by some substance P-IR (SP-IR) spinal ganglion neurons and extrinsic sensory fibers of aganglionic foals.

CONCLUSIONS & INFERENCES

The presence of 5-HT₄ in many enteric and extrinsic sensory neurons and nerve fibers provides solid morphological evidence of the cellular sites of 5-HT₄ expression in horses. The evidence of SP-IR sensory neurons positive for 5-HT₄ suggests its role in visceral sensitivity.

Changes in cholinergic and nitrergic systems of defunctionalized colons after colostomy in rabbits

BACKGROUND

This study was designed to assess smooth muscle function and motility in defunctionalized colonic segments and subsequent changes in pathways responsible for gastrointestinal motility.

METHODS

Two-month-old New Zealand rabbits were randomly allocated into control and study groups. Sigmoid colostomies were performed in the study group. After a 2-month waiting period, colonic segments were harvested in both groups. For the in vitro experiment, the isolated circular muscle strips which were prepared from the harvested distal colon were used. First, contraction responses were detected using KCl and carbachol; relaxation responses were detected using papaverine, sodium nitroprusside, sildenafil, and l-arginine. The neurologic responses of muscle strips to electrical field stimulation (EFS) were evaluated in an environment with guanethidine and indomethacin. EFS studies were then repeated with atropine, Nω-nitro-l-arginine methyl ester, atropine, and Nω-nitro-l-arginine methyl ester-added environments.

RESULTS

Although macroscopic atrophy had developed in the distal colonic segment of the colostomy, the contraction and relaxation capacity of the smooth muscle did not change. EFS-induced nitrergic-peptidergic, cholinergic-peptidergic, and noncholinergic nonnitrergic responses significantly decreased at all frequencies (0.5-32 Hz) in the study group compared with those in the control group (P < 0.05).

CONCLUSIONS

Although the contraction capacity of the smooth muscle was not affected, the motility of the distal colon deteriorated owing to the defective secretion of presynaptic neurotransmitters such as acetylcholine, nitric oxide, and neuropeptides.

The effect of levosulpiride on in vitro motor patterns in the human gastric fundus, antrum, and jejunum

BACKGROUND

Levosulpiride is a 5HT4 agonist/D2 antagonist prokinetic agent used to improve gastric emptying in patients with functional dyspepsia or gastroparesis. The aim of this study was to characterize its effect on the main in vitro motility patterns in the human fundus, antrum, and jejunum.

METHODS

Circular muscle strips from human stomach (antrum and fundus) and jejunum, obtained from 46 patients undergoing bariatric surgery, were studied using organ baths. Enteric motor neurons (EMNs) were stimulated by electrical field stimulation (EFS).

KEY RESULTS

Levosulpiride, caused an increase in the EFS-induced cholinergic contractions in the gastric antrum (+37 ± 15.18% at 100 μM, pEC50 = 4.46 ± 0.14; p < 0.05, n = 8) and jejunum (+45.4 ± 22.03% at 100 μM, pEC50 = 3.78 ± 6.81; p < 0.05, n = 5), but not in the gastric fundus. It also caused a slight decrease in tone and frequency of spontaneous contractions in the jejunum, but did not have any major effect on tone or spontaneous contractions in the stomach. It did not have any effect on EFS-induced relaxations mediated by nitric oxide (NO) in the stomach (antrum and fundus) and by NO and ATP in the jejunum.

CONCLUSIONS & INFERENCES

Our results suggest that the prokinetic effects of levosulpiride in humans are mainly due to the facilitation of the release of acetylcholine by enteric motor neurons in the gastric antrum and the jejunum.

Distribution of 5-HT3, 5-HT4, and 5-HT7 Receptors Along the Human Colon

Background/Aims

Several disorders of the gastrointestinal tract are associated with abnormal serotonin (5-HT) signaling or metabolism where the 5-HT₃ and 5-HT₄ receptors are clinically relevant. The aim was to examine the distribution of 5-HT₃, 5-HT₄, and 5-HT₇ receptors in the normal human colon and how this is associated with receptor interacting chaperone 3, G protein coupled receptor kinases, and protein LIN-7 homologs to extend previous observations limited to the sigmoid colon or the upper intestine.

Methods

Samples from ascending, transverse, descending, and sigmoid human colon were dissected into 3 separate layers (mucosa, longitudinal, and circular muscles) and ileum samples were dissected into mucosa and muscle layers (n = 20). Complementary DNA was synthesized by reverse transcription from extracted RNA and expression was determined by quantitative or end point polymerase chain reaction.

Results

The 5-HT₃ receptor subunits were found in all tissues throughout the colon and ileum. The A subunit was detected in all samples and the C subunit was expressed at similar levels while the B subunit was expressed at lower levels and less frequently. The 5-HT₃ receptor E subunit was mainly found in the mucosa layers. All splice variants of the 5-HT₄ and 5-HT₇ receptors were expressed throughout the colon although the 5-HT₄ receptor d, g, and i variants were expressed less often.

Conclusions

The major differences in 5-HT receptor distribution within the human colon are in relation to the mucosa and muscular tissue layers where the 5-HT₃ receptor E subunit is predominantly found in the mucosal layer which may be of therapeutic relevance.

Efficacy and safety of prucalopride in adults and children with chronic constipation

INTRODUCTION

Chronic constipation (CC) is a debilitating condition with high prevalence rates both in children and adults. Despite the broad range of medical and pharmaceutical treatments, the bowel function does not restore in a fair amount of patients. Prucalopride is a first-in-class selective, high affinity serotonin 5-hydroxytryptamine type 4 (5-HT4) receptor agonist promoting gastro-intestinal prokinetic activity and has been evaluated for the treatment of CC.

AREAS COVERED

A PubMed search (1965 - 2014) using the following terms alone or in combination: prucalopride, 5-HT4, R093877, safety, toxicity, pharmacokinetics, pharmacodynamics, transit, cardiac, human ether-a-go-go related gene (hERG), arrhythmia, potassium current, elderly, children.

EXPERT OPINION

Prucalopride, a highly selective 5-HT4 receptor agonist, stimulates gastrointestinal motility and has been proven to be effective in the treatment of CC in adults by increasing stool frequency, reducing constipation-related symptoms and improving quality of life (QoL). The safety and tolerability have been proven to be excellent. More research would be preferable on the effect of prucalopride on men, children and in other gastrointestinal motility disorders.

Cholinergic interactions between donepezil and prucalopride in human colon: potential to treat severe intestinal dysmotility

BACKGROUND AND PURPOSE

Cholinesterase inhibitors such as neostigmine are used for acute colonic pseudo-obstruction, but cardio-bronchial side-effects limit use. To minimize side-effects, lower doses could be combined with a 5-HT4 receptor agonist, which also facilitates intestinal cholinergic activity. However, safety concerns, especially in the elderly, require drugs with good selectivity of action. These include the AChE inhibitor donepezil (used for Alzheimer's disease, with reduced cardio-bronchial liability) and prucalopride, the first selective, clinically available 5-HT4 receptor agonist. This study examined their individual and potential synergistic activities in human colon.

EXPERIMENTAL APPROACH

Neuronally mediated muscle contractions and relaxations of human colon were evoked by electrical field stimulation (EFS) and defined phenotypically as cholinergic, nitrergic or tachykinergic using pharmacological tools; the effects of drugs were determined as changes in 'area under the curve'.

KEY RESULTS

Prucalopride increased cholinergically mediated contractions (EC50 855 nM; 33% maximum increase), consistent with its ability to stimulate intestinal motility; donepezil (477%) and neostigmine (2326%) had greater efficacy. Concentrations of donepezil (30-100 nM) found in venous plasma after therapeutic doses had minimal ability to enhance cholinergic activity. However, donepezil (30 nM) together with prucalopride (3, 10 μM) markedly increased EFS-evoked contractions compared with prucalopride alone (P = 0.04). For example, the increases observed with donepezil and prucalopride 10 μM together or alone were, respectively, 105 ± 35%, 4 ± 6% and 35 ± 21% (n = 3-7, each concentration).

CONCLUSIONS AND IMPLICATIONS

Potential synergy between prucalopride and donepezil activity calls for exploration of this combination as a safer, more effective treatment of colonic pseudo-obstruction.

Regionally dependent neuromuscular functions of motilin and 5-HT₄ receptors in human isolated esophageal body and gastric fundus

BACKGROUND

Motilin agonists promote human gastric motility and cholinergic activity, but excitatory and inhibitory actions are reported in the esophagus. The effect of 5-HT₄ agonists in esophagus is also unclear. Perhaps the use of drugs with additional actions explains the variation. The aim, therefore, was to examine how motilin and prucalopride, selective motilin and 5-HT₄ receptor agonists, modulate neuromuscular functions in human esophagus and gastric fundus.

METHODS

Electrical field stimulation (EFS) evoked nerve-mediated contractions of circular and longitudinal muscle from human esophageal body and circular muscle from gastric fundus.

KEY RESULTS

In esophageal circular muscle EFS evoked brief contraction, followed by another contraction on termination of EFS, each prevented by atropine. Nitric oxide synthase inhibition facilitated contraction during EFS and the overall contraction became monophasic. In esophagus longitudinal muscle and gastric fundus, EFS evoked cholinergically mediated, monophasic contractions, attenuated by simultaneous nitrergic activation. Motilin (100-300 nM) reduced esophagus circular muscle contractions during EFS, unaffected by L-NAME or apamin. Motilin 300 nM also reduced EFS-evoked contractions of longitudinal muscle. Similar concentrations of motilin facilitated cholinergic activity in the fundus and increased baseline muscle tension. Prucalopride facilitated EFS-evoked contractions in esophagus (tested at 30 μM) and fundus (0.1-30 μM).

CONCLUSIONS & INFERENCES

Selective motilin and 5-HT₄ agonists have different, region-dependent abilities to modulate human esophageal and stomach neuromuscular activity, exemplified by weak inhibition (motilin) or excitation (5-HT₄) in esophageal body and excitation for both in stomach. In different patients with motility dysfunctions, motilin and 5-HT₄ agonists may reduce gastro-esophageal reflux in different ways.

Drugs acting at 5-HT4 , D2 , motilin, and ghrelin receptors differ markedly in how they affect neuromuscular functions in human isolated stomach

BACKGROUND

Progress in identifying safer, effective drugs to increase gastric emptying is impeded by failed clinical trials. One potential reason for failure is lack of translation from animal models to the human condition. To make progress, the actions of existing drugs and new therapeutic candidates need to be understood in human isolated stomach.

METHODS

Neuromuscular activities were evoked in human gastric antrum circular muscle by electrical field stimulation (EFS), defined phenotypically using pharmacological tools.

KEY RESULTS

EFS evoked cholinergically mediated contractions, attenuated by simultaneous nitrergic activation. The 5-HT4 receptor agonist/D2 antagonist metoclopramide and the selective 5-HT4 agonist prucalopride, facilitated contractions in the absence (respectively, Emax 95 ± 29% and 42 ± 9%, n = 3-6 each concentration) and presence (139 ± 38%, 55 ± 13%, n = 3-5) of the NO synthase inhibitor L-NAME, without affecting submaximal contractions to carbachol; the 5-HT4 antagonist SB204070 prevented facilitation by metoclopramide 100 μM (respectively, -5 (range -26 to 34) and 167 (12-1327)% in presence and absence; n = 5-6). The selective motilin receptor agonist camicinal provided considerably greater facilitation (478 (12-2080)% at 30 μM, n = 8). Domperidone (0.001-100 μM; n = 3-6) and acylated or des-acylated ghrelin (1-300 nM; n = 2-4) had no consistent activity, even with protease inhibitors.

CONCLUSIONS & INFERENCES

5-HT4 receptor agonists show different efficacies. Motilin receptor activation has greater potential to increase gastric emptying, whereas ghrelin and D2 receptor antagonism have no direct activity. Drugs stimulating human gastric motility directly can act regardless of disease mechanisms, whereas drugs without direct activity but an ability to block nausea/vomiting may be effective only if these symptoms exist.

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

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

New pharmacological treatment options for chronic constipation

INTRODUCTION

A number of new medications were recently demonstrated to be more effective than placebo in treating chronic constipation, including the intestinal chloride channel activator lubiprostone, the prokinetic selective 5-HT4 receptor agonist prucalopride and the guanylate cyclase-C agonist linaclotide. Recent publications have also revisited traditional laxatives like PEG. Moreover, a number of pharmacological treatments are in development and these include another guanylate cyclase-C agonist, plecanatide and an ileal bile acid transporter inhibitor, elobixibat.

AREAS COVERED

This review focuses on the pharmacology, efficacy and safety profile of prucalopride, linaclotide, plecanatide and elobixibat.

EXPERT OPINION

The possible present or future clinical application of prucalopride, linaclotide, plecanatide and elobixibat in both chronic constipation and irritable bowel syndrome with constipation is reported, and some considerations on the possible role of PEG taking into account recent literature are advanced.

Translational neuropharmacology: the use of human isolated gastrointestinal tissues

Translational sciences increasingly emphasize the measurement of functions in native human tissues. However, such studies must confront variations in patient age, gender, genetic background and disease. Here, these are discussed with reference to neuromuscular and neurosecretory functions of the human gastrointestinal (GI) tract. Tissues are obtained after informed consent, in collaboration with surgeons (surgical techniques help minimize variables) and pathologists. Given the difficulties of directly recording from human myenteric neurones (embedded between muscle layers), enteric motor nerve functions are studied by measuring muscle contractions/relaxations evoked by electrical stimulation of intrinsic nerves; responses are regionally dependent, often involving cholinergic and nitrergic phenotypes. Enteric sensory functions can be studied by evoking the peristaltic reflex, involving enteric sensory and motor nerves, but this has rarely been achieved. As submucosal neurones are more accessible (after removing the mucosa), direct neuronal recordings are possible. Neurosecretory functions are studied by measuring changes in short-circuit current across the mucosa. For all experiments, basic questions must be addressed. Because tissues are from patients, what are the controls and the influence of disease? How long does it take before function fully recovers? What is the impact of age- and gender-related differences? What is the optimal sample size? Addressing these and other questions minimizes variability and raises the scientific credibility of human tissue research. Such studies also reduce animal use. Further, the many differences between animal and human GI functions also means that human tissue research must question the ethical validity of using strains of animals with unproved translational significance.

Effect of hyoscine butylbromide (Buscopan®) on cholinergic pathways in the human intestine

BACKGROUND

Hyoscine butylbromide (HBB, Buscopan(®) ) is clinically used to treat intestinal cramps and visceral pain. Various studies, mainly on animal tissues, suggested that its antimuscarinic action is responsible for its spasmolytic effect. However, functional in vitro studies with human tissue have not been performed so far.

METHODS

We wanted to provide a comprehensive study on the mode of action of HBB in human intestinal samples and investigated HBB (1 nmol L(-1) -10 μmol L(-1)) effects on muscle activity with isometric force transducers and calcium imaging, on epithelial secretion with Ussing chamber technique and on enteric neurons using fast neuroimaging.

KEY RESULTS

Hyoscine butylbromide concentration dependently reduced muscle contractions, calcium mobilization, and epithelial secretion induced by the muscarinic agonist bethanechol with IC50 values of 429, 121, and 224 nmol L(-1), respectively. Forskolin-induced secretion was not altered by HBB. Cholinergic muscarinic muscle and epithelial responses evoked by electrical nerve stimulation were inhibited by 1-10 μmol L(-1) HBB. Moreover, HBB significantly reduced the bethanechol-induced action potential discharge in enteric neurons. Interestingly, we observed that high concentrations of HBB (10 μmol L(-1)) moderately decreased nicotinic receptor-mediated secretion, motility, and nerve activity.

CONCLUSIONS & INFERENCES

The results demonstrated the strong antimuscarinic action of HBB whereas the nicotinic antagonism at higher concentrations plays at most a moderate modulatory role. The muscle relaxing effect of HBB and its inhibition of muscarinic nerve activation likely explain its clinical use as an antispasmodic drug. Our results further highlight a so far unknown antisecretory action of HBB which warrants further clinical studies on its use in secretory disorders.

Predominant mucosal expression of 5-HT4(+h) receptor splice variants in pig stomach and colon

AIM: To investigate cellular 5-HT_4(-h/+h) receptor distribution, particularly in the epithelial layer, by laser microdissection and polymerase chain reaction (PCR) in porcine gastrointestinal (GI) tissues.

METHODS: A stepwise approach was used to evaluate RNA quality and to study cell-specific 5-HT₄ receptor mRNA expression in the porcine gastric fundus and colon descendens. After freezing, staining and laser microdissection and pressure catapulting (LMPC), RNA quality was evaluated by the Experion automated electrophoresis system. 5-HT₄ receptor and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expressions were examined by endpoint reverse transcription (RT)-PCR in mucosal and muscle-myenteric plexus (MMP) tissue fractions, in mucosal and MMP parts of hematoxylin and eosin (HE) stained tissue sections and in microdissected patches of the epithelial and circular smooth muscle cell layer in these sections. Pig gastric fundus tissue sections were also stained immunohistochemically (IHC) for enterochromaffin cells (EC cells; MAB352); these cells were isolated by LMPC and examined by endpoint RT-PCR.

RESULTS: After HE staining, the epithelial and circular smooth muscle cell layer of pig colon descendens and the epithelial cell layer of gastric fundus were identified morphologically and isolated by LMPC. EC cells of pig gastric fundus were successfully stained by IHC and isolated by LMPC. Freezing, HE and IHC staining, and LMPC had no influence on RNA quality. 5-HT₄ receptor and GAPDH mRNA expressions were detected in mucosa and MMP tissue fractions, and in mucosal and MMP parts of HE stained tissue sections of pig colon descendens and gastric fundus. In the mucosa tissue fractions of both GI regions, the expression of h-exon containing receptor [5-HT_4(+h) receptor] mRNA was significantly higher (P < 0.01) compared to 5-HT_4(-h) receptor expression, and a similar trend was obtained in the mucosal part of HE stained tissue sections. Large microdissected patches of the epithelial and circular smooth muscle cell layer of pig colon descendens and of the epithelial cell layer of pig gastric fundus, also showed 5-HT₄ receptor and GAPDH mRNA expression. No 5-HT₄ receptor mRNA expression was detected in gastric LMPC-isolated EC cells from IHC stained tissues, which cells were positive for GAPDH.

CONCLUSION: Porcine GI mucosa predominantly expresses 5-HT_4(+h) receptor splice variants, suggesting their contribution to the 5-HT₄ receptor-mediated mucosal effects of 5-HT.

Regional- and agonist-dependent facilitation of human neurogastrointestinal functions by motilin receptor agonists

BACKGROUND AND PURPOSE

Delayed gastric emptying is poorly managed. Motilin agonists are potential treatments but inadequate understanding into how enteric nerve functions are stimulated compromises drug/dose selection. Resolution is hampered by extreme species dependency so methods were developed to study human gastrointestinal neuromuscular activities and the neurobiology of motilin.

EXPERIMENTAL APPROACH

Protocols to study neuromuscular activities were developed for different regions of human stomach and intestine (71 patients) using circular muscle preparations and electrical field stimulation (EFS) of intrinsic nerves. Other tissues were fixed for immunohistochemistry.

KEY RESULTS

EFS evoked contractions and/or relaxations via cholinergic and nitrergic neurons, with additional tachykinergic activity in colon; these were consistent after 154 min (longer if stored overnight). Motilin 1-300 nM and the selective motilin agonist GSK962040 0.1-30 µM acted pre-junctionally to strongly facilitate cholinergic contractions of the antrum (E(max) ≈ 1000% for motilin), with smaller increases in fundus, duodenum and ileum; high concentrations increased baseline muscle tension in fundus and small intestine. There were minimal effects in the colon. In the antrum, cholinergic facilitation by motilin faded irregularly, even with peptidase inhibitors, whereas facilitation by GSK962040 was long lasting. Motilin receptor immunoreactivity was identified in muscle and myenteric plexus predominantly in the upper gut, co-expressed with choline acetyltransferase in neurons.

CONCLUSIONS AND IMPLICATIONS

Motilin and GSK962040 strongly facilitated cholinergic activity in the antrum, with lower activity in fundus and small intestine only. Facilitation by motilin was short lived, consistent with participation in migrating motor complexes. Long-lasting facilitation by GSK962040 suggests different receptor interactions and potential for clinical evaluation.

Prucalopride: evaluation of the pharmacokinetics, pharmacodynamics, efficacy and safety in the treatment of chronic constipation

INTRODUCTION

Prucalopride is the first member of a novel class of 5-HT(4) receptor agonist which has been extensively evaluated for the treatment of chronic constipation. Predominantly, prucalopride is currently used to treat patients that show an insufficient response to laxatives as an alternative form of therapy.

AREAS COVERED

The following article provides the reader with a systematic review of the literature on prucalopride. Specifically, the article reviews the currently literature on the pharmacokinetics and the pharmacodynamics of the drugs as well as reviewing literature on its efficacy. Furthermore, the authors also highlight the safety and tolerability of the drug that have been demonstrated in its clinical development.

EXPERT OPINION

Prucalopride is an important addition to the therapeutic abilities for treating chronic constipation, especially in females poorly responding to laxatives. The safety profile of the drug, to date, is favorable. There is also the possibility that prucalopride might be of benefit to other disorders of gastrointestinal motility with a number of studies currently in progress, which are evaluating alternative applications.

Prokinetics in diabetic gastroparesis

Within the last 50 years, diabetic gastroparesis has become a well recognized complication of type 1 and type 2 diabetes. It is a syndrome characterized by abnormal gastric function, resulting in delayed emptying of the stomach in the absence of any evident mechanical obstruction, predominantly manifested by early satiety, postprandial fullness, nausea, vomiting, and weight loss. The past five years have shown significant advances in its pathophysiology and in new diagnostic tests. Prokinetic medications remain the therapeutic focus for improving clinical symptoms of gastroparesis through enhanced gastric emptying. This article summarizes the present knowledge of prokinetics, with emphasis on medications currently available, as well as drugs under clinical investigation, including some agents in advanced clinical trials that are likely to be used in the treatment of diabetic gastroparesis in the future. These include the ghrelin agonists and newer 5-HT4 agonists devoid of cardiac side effects.

Origin and modulation of circular smooth muscle layer contractions in the porcine esophagus

BACKGROUND

The origin and modulation mechanisms controlling timing and amplitude of esophageal body peristalsis are not fully understood. We aimed to characterize the neurotransmitters involved in the origin and modulation of circular smooth muscle esophageal body (EB) contractions.

METHODS

Responses of porcine EB strips to electrical stimulation of motor neurons (MNs) were assessed in organ baths and with microelectrodes. The effect of antagonists of inhibitory (L-NAME 1 mmol L(-1) , MRS2179 10 μmol L(-1) ) and excitatory neurotransmitters (atropine 1 μmol L(-1) ; SR140333 1 μmol L(-1) -NK(1) ra-, GR94800 1 μmol L(-1) -NK(2) ra-) and of ganglionic neurotransmitters (hexamethonium 100 μmol L(-1) , ondansetron 1 μmol L(-1) , NF279 10 μmol L(-1) ) were characterized.

KEY RESULTS

Electrical field stimulation (EFS) induced a frequency-dependent off-contraction (16.8 ± 0.8 g) following a latency period. Latency was significantly reduced by L-NAME (-66.1 ± 4.1%) and MRS2179 (-25.9 ± 5.6%), and strongly increased by atropine (+36.8 ± 5.8%). Amplitude was reduced by L-NAME (-69.9 ± 10.4%), MRS2179 (-34.1 ± 6.0%), atropine (-42.3 ± 4.7%), hexamethonium (-18.9 ± 3.3%), NF279 (-20.7 ± 3.5%), ondansetron (-16.3 ± 3.2%), GR94800 (-28.0 ± 4.8%) SR140333 (-20.9 ± 7.1%), and α-chymotrypsin (-31.3 ± 7.0%). The EFS induced a monophasic nitrergic inhibitory junction potential.

CONCLUSIONS & INFERENCES

Our results suggest that timing (latency) and amplitude of esophageal contractions are determined by a balance of complex interactions between excitatory and inhibitory MNs. Latency depends on the activation of inhibitory MNs releasing NO and a minor purinergic contribution through P2Y(1) receptors, and excitatory MNs releasing ACh. Amplitude depends on a major contribution of excitatory MNs releasing ACh and tachykinins, and also on inhibitory MNs releasing NO, ATP or related purines, and peptidergic neurotransmitters acting as strong modulators of the excitatory neuroeffector transmission.

The facilitating effect of prucalopride on cholinergic neurotransmission in pig gastric circular muscle is regulated by phosphodiesterase 4

The influence of the selective 5-HT(4) receptor agonist prucalopride on acetylcholine release from cholinergic nerve endings innervating pig gastric circular muscle and the possible regulation of this effect by phosphodiesterases (PDEs) was investigated, as PDEs have been shown to control the response to 5-HT(4) receptor activation in pig left atrium. Circular muscle strips were prepared from pig proximal stomach and either submaximal cholinergic contractions or tritium outflow after incubation with [(3)H]-choline, induced by electrical field stimulation, were studied. Prucalopride concentration-dependently increased the amplitude of submaximal cholinergic contractions and of acetylcholine release induced by electrical field stimulation. The effect of the highest concentration tested (0.3 μM) on cholinergic contractions was antagonized by the selective 5-HT(4) receptor antagonist GR113808 but not by granisetron or methysergide; the antagonism of prucalopride by GR113808 was confirmed in the release assay. The non-selective PDE-inhibitor 3-isobutyl-methyl-xanthine (IBMX) concentration-dependently reduced the amplitude of the cholinergic contractions; 3 μM IBMX reduced the cholinergic contractions maximally by 16% but it enhanced the facilitating effect of prucalopride from 51 to 83%. IBMX (10 μM) induced and enhanced the facilitating effect of prucalopride on electrically induced acetylcholine release. The selective inhibitors vinpocetine (PDE1), EHNA (PDE2) and cilostamide (PDE3) did not influence the effect of prucalopride on acetylcholine release but the PDE4-inhibitor rolipram (1 μM) enhanced the facilitating effect of prucalopride to the same extent as IBMX. These results demonstrate that 5-HT(4) receptors are present on the cholinergic nerves towards the pig gastric circular muscle, facilitating acetylcholine release; the intracellular transduction pathway of this facilitation is regulated by PDE4. Combination of a 5-HT(4) receptor agonist with selective inhibition of the PDE involved in this regulation of transmitter release might enhance the prokinetic effect of the 5-HT(4) receptor agonist.

Investigation of neurogenic excitatory and inhibitory motor responses and their control by 5-HT(4) receptors in circular smooth muscle of pig descending colon

The aim of this study was to investigate whether the pig colon descendens might be a good model for the responses mediated via the different locations of human colonic 5-HT(4) receptors. The intrinsic excitatory and inhibitory motor neurotransmission in pig colon descendens was therefore first characterized. In circular smooth muscle strips, electrical field stimulation (EFS) at basal tone induced only in the combined presence of the NO synthase inhibitor N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME) and the SK channel blocker apamin voltage-dependent on-contractions. These on-contractions were largely reduced by the neuronal conductance blocker tetrodotoxin (TTX) and by the muscarinic receptor antagonist atropine, illustrating activation of cholinergic neurons. The 5-HT(4) receptor agonist prucalopride facilitated submaximal EFS-evoked cholinergic contractions and this effect was prevented by the 5-HT(4) receptor antagonist GR113808, supporting the presence of facilitating 5-HT(4) receptors on the cholinergic nerve endings innervating circular muscle in pig colon descendens. Relaxations were induced by EFS in strips pre-contracted with substance P in the presence of atropine. The responses at lower stimulation voltages were abolished by TTX. L-NAME or apamin alone did not influence or only moderately reduced the relaxations, but L-NAME plus apamin abolished the relaxations at lower stimulation voltages, suggesting that NO and ATP act as inhibitory neurotransmitters in a redundant way. Prucalopride did not influence the EFS-induced relaxations at lower stimulation voltage, nor did it per se relax contracted circular muscle strips. No evidence for relaxing 5-HT(4) receptors, either on inhibitory neurons or on the muscle cells was thus obtained in pig colon descendens circular muscle.

Constipation, IBs and the 5-HT4 Receptor: What Role for Prucalopride?

After the problems associated with the non-selective 5-HT4 receptor agonists cisapride and tegaserod, the 5-HT4 receptor is now beginning to come in from the cold. Thus, prucalopride is now the first of a new class of drug defined by selectivity and high intrinsic activity at the 5-HT4 receptor. Prucalopride has been developed for treatment of chronic constipation rather than constipation-predominant irritable bowel syndrome (IBS). This follows the trend of first evaluating new gastrointestinal (GI) prokinetic drugs in disorders where disrupted GI motility is known to exist, rather than in a functional bowel disorder where changes in motility are uncertain. If prucalopride is not progressed towards the IBS indication, it has at least shown the way for other selective 5-HT4 receptor agonists. Most notable among these is TD-5108 (velusetrag), also characterized by good selectivity at the 5-HT4 receptor, high intrinsic activity and efficacy in patients with chronic constipation.

Challenges and prospects for pharmacotherapy in functional gastrointestinal disorders

Functional gastrointestinal disorders, such as irritable bowel syndrome and functional dyspepsia, are complex conditions with multiple factors contributing to their pathophysiology. As a consequence they are difficult to treat and have posed significant challenges to the pharmaceutical industry when trying to develop new and effective treatments. This review provides an overview of these difficulties and how the industry is reshaping its drug developmental strategies. It describes some of the more significant and encouraging advances that have occurred, and discusses how future research might embrace the opportunities provided by advances in genetic and in particular, epigenetic research.

Influence of 5-HT4 receptor activation on acetylcholine release in human large intestine with endometriosis

BACKGROUND

The 5-HT(4) receptor agonist prucalopride enhances large intestinal contractility by facilitating acetylcholine release through activation of 5-HT(4) receptors on cholinergic nerves and is effective in patients with constipation. Patients with intestinal endometriosis can present with constipation. We investigated in vitro whether large intestinal endometriotic infiltration influences contractility and facilitation of acetylcholine release by prucalopride.

METHODS

Sigmoid colon or rectum circular muscle strips were obtained at the level of an endometriotic nodule with infiltration of the Auerbach plexus, and at a macroscopically healthy site at least 5 cm cranially from the nodule, in patients undergoing laparoscopic colorectal resection because of symptomatic bowel endometriosis. Responses to muscarinic receptor stimulation and to electrical field stimulation (EFS), and the facilitating effect of prucalopride on acetylcholine release were evaluated.

KEY RESULTS

The EC50 and E(max) of the contractile responses to the muscarinic receptor agonist carbachol did not differ between healthy and lesioned strips. EFS-induced on-contractions were not different between the healthy and lesioned strips, while the non-nitrergic relaxant responses induced by EFS were decreased in the lesioned strips. The facilitating effect of prucalopride on acetylcholine release in healthy strips was similar to that reported before in macroscopically healthy colon tissue of patients with colon cancer; in lesioned strips, the effect of prucalopride was fully maintained in 6/8 patients and absent in two.

CONCLUSIONS & INFERENCES

Large intestinal endometriosis does not lead to a systematic interference with the cholinergic facilitating effect of prucalopride.

Prucalopride

Prucalopride, a first-in-class dihydrobenzofuran-carboxamide derivative, is a potent, selective and specific serotonin 5-HT(4) receptor agonist with enterokinetic properties. Over a 12-week treatment period, prucalopride 2 and 4 mg once daily significantly improved bowel habit assessments (based on patient diary data) relative to placebo in three large, randomized, double-blind, multicentre trials in patients (aged 17-95 years) with severe chronic constipation, the majority of whom were women who experienced inadequate relief with previous therapies. There was no additional benefit with the 4 mg/day over the 2 mg/day dosage of prucalopride. Patient assessments of constipation symptoms and severity, treatment efficacy, satisfaction with bowel habit and treatment, and health-related quality of life were also significantly improved with prucalopride compared with placebo. The improvement in patient satisfaction with bowel habit and treatment was maintained for up to 24 months in open-label, multicentre, long-term follow-up studies. Prucalopride therapy was generally well tolerated; most adverse events in the 12-week studies were transient and of mild to moderate severity. In terms of cardiovascular tolerability, the incidence of QT interval prolongation with prucalopride at dosages of 2 and 4 mg/day was low and similar to that with placebo. Moreover, prucalopride at dosages up to 20 mg/day (10-fold higher than the recommended therapeutic dosage) had no clinically relevant effects on cardiovascular parameters in healthy volunteers.

Hexane extract of Poncirus trifoliata (L.) Raf. stimulates the motility of rat distal colon

AIM OF THE STUDY

Poncirus trifoliata (L.) Raf. (Rutaceae, PT) has been commonly used for treating gastrointestinal (GI) disorders in Korean traditional medicine, but its pharmacological roles in the regulation of colonic motility have not been clarified. This study investigated the regulatory effects of PT on the colonic motility.

MATERIALS AND METHODS

Immature fruits of PT were sequentially partitioned with MeOH, n-hexane, CHCl(3), EtOAc, n-BuOH and H(2)O, and the effects of PT extracts on the contractility of colonic strips and colonic luminal transit in rats were measured in vitro and in vivo, respectively.

RESULTS

Among six different extracts, only hexane extract of PT (PTHE) dose-dependently increased the low frequency contraction of longitudinal muscle in distal colonic strips, and the ED(50) value was revealed to be 0.71 microg/ml. The contractile patterns induced by PTHE were remarkably different from those caused by acetylcholine (ACh) and serotonin (5-HT). The stimulatory effects of PTHE on the whole distal colonic strips were more prominent than on the mucosa/submucosa-denuded segments. The M(2) receptor-preferring, methoctramine (0.5 microM), and M(3) receptor-preferring antagonist, 4-DAMP (0.5 microM) significantly blocked the PTHE (1 microg/ml)-induced contraction of distal colon longitudinal muscles, whereas the 5-HT receptor antagonists (1.0 microM, alone or in combination) selective for 5-HT(3) (ondansetron), 5-HT(4) (GR113808) and 5-HT(1, 2, 5-7) (methysergide) receptors did not change the PTHE (1 microg/ml)-induced contractility of distal colon longitudinal muscles. SNAP (0.1mM), a NO donor, enhanced the stimulatory effects of PTHE on the longitudinal muscle of distal colon, but l-NAME (0.1mM), a NO synthesis inhibitor, had no effects. PTHE (10-100mg/kg) caused a dose-dependent increase of colonic luminal transit.

CONCLUSIONS

Collectively, these findings suggest that PTHE specifically acts on the longitudinal muscle of distal colon in rats, and these stimulatory effects are likely mediated, at least, by activation of acetylcholinergic M(2) and M(3) receptors.

Translating 5-HT receptor pharmacology

Since metoclopramide was first described (in 1964) there have been several attempts to develop compounds which retained gastrointestinal prokinetic activity (via 5-HT(4) receptor activation) but without the limiting side effects associated with dopamine D(2) receptor antagonism. Early compounds (mosapride, cisapride, renzapride, tegaserod) were identified before several of the 5-HT receptors were even described (including 5-HT(4) and 5-HT(2B)), whereas prucalopride came later. Several compounds were hampered by non-selectivity, introducing cardiac liability (cisapride: activity at human Ether-a-go-go Related Gene) or potentially, a reduced intestinal prokinetic activity caused by activity at a second 5-HT receptor (renzapride: antagonism at the 5-HT(3) receptor; tegaserod: antagonism at the 5-HT(2B) receptor). Poor intrinsic activity at gastrointestinal 5-HT(4) receptors has also been an issue (mosapride, tegaserod). Perhaps prucalopride has now achieved the profile of good selectivity of action and high intrinsic activity at intestinal 5-HT(4) receptors, without clinically-meaningful actions on 5-HT(4) receptors in the heart. The progress of this compound for treatment of chronic constipation, as well as competitor molecules such as ATI-7505 and TD-5108, will now be followed with interest as each attempts to differentiate themselves from each other. Perhaps at last, 5-HT(4) receptor agonists are being given the chance to show what they can do.

Different stimulatory effects of methylisogermabullone on the spontaneous contractility of rat gastrointestinal segments

Using rat gastrointestinal (GI) strips, this study investigated the stimulatory effects of methylisogermabullone (MIGB) purified from radish on the spontaneous contractility of GI smooth muscles and pharmacological mechanisms involved in the MIGB-induced GI contraction. MIGB at 30 microM differently regulated the tone and amplitude of spontaneous GI contractility according to the region (fundus through distal colon) and orientation (longitudinal and circular) of smooth muscles: a significant increase in both tone and amplitude of spontaneous contraction in the ileum longitudinal and distal colon circular muscles and in amplitude only in the fundus, jejunum and distal colon longitudinal muscles. Pretreatment of ileum longitudinal muscles with atropine (0.5 microM) or 4-DAMP (0.5 microM) significantly inhibited the acetylcholine (ACh, 1 microM)- and MIGB (30 microM)-stimulated contraction, and methoctramine (0.5 microM) also obviously reduced the tone and amplitude increased by ACh and MIGB, respectively. In the presence of methysergide (1 microM), pretreatment of ileum longitudinal muscles with both ondansetron (0.1 microM) and GR113808 (0.1 microM) significantly inhibited the contraction stimulated by 5-HT (10 microM), but not by MIGB. Taken together, it is concluded that MIGB differently regulates the spontaneous contractility (tone and/or amplitude) of GI segments according to the region of gut and orientation of smooth muscles, and these contractile responses of GI tracts to MIGB are likely mediated, at least, by activation of acetylcholinergic M2 and M3 receptors.

Neurotransmission in Parkinson's disease: beyond dopamine

Parkinson's disease (PD) is most frequently associated with characteristic motor symptoms that are known to arise with degeneration of dopaminergic neurons. However, patients with this disease also experience a multitude of non-motor symptoms, such as sleep disturbances, fatigue, apathy, anxiety, depression, cognitive impairment, dementia, olfactory dysfunction, pain, sweating and constipation, some of which can be at least as debilitating as the movement disorders and have a major impact on patients' quality of life. Many of these non-motor symptoms may be evident prior to the onset of motor dysfunction. The neuropathology of PD has shown that complex, interconnected neuronal systems, regulated by a number of different neurotransmitters in addition to dopamine, are involved in the aetiology of motor and non-motor symptoms. This review focuses on the non-dopaminergic neurotransmission systems associated with PD with particular reference to the effect that their modulation and interaction with dopamine has on the non-motor symptoms of the disease. PD treatments that focus on the dopaminergic system alone are unable to alleviate both motor and non-motor symptoms, particularly those that develop at early stages of the disease. The development of agents that interact with several of the affected neurotransmission systems could prove invaluable for the treatment of this disease.

Translating 5-HT receptor pharmacology

Since metoclopramide was first described (in 1964) there have been several attempts to develop compounds which retained gastrointestinal prokinetic activity (via 5-HT(4) receptor activation) but without the limiting side effects associated with dopamine D(2) receptor antagonism. Early compounds (mosapride, cisapride, renzapride, tegaserod) were identified before several of the 5-HT receptors were even described (including 5-HT(4) and 5-HT(2B)), whereas prucalopride came later. Several compounds were hampered by non-selectivity, introducing cardiac liability (cisapride: activity at human Ether-a-go-go Related Gene) or potentially, a reduced intestinal prokinetic activity caused by activity at a second 5-HT receptor (renzapride: antagonism at the 5-HT(3) receptor; tegaserod: antagonism at the 5-HT(2B) receptor). Poor intrinsic activity at gastrointestinal 5-HT(4) receptors has also been an issue (mosapride, tegaserod). Perhaps prucalopride has now achieved the profile of good selectivity of action and high intrinsic activity at intestinal 5-HT(4) receptors, without clinically-meaningful actions on 5-HT(4) receptors in the heart. The progress of this compound for treatment of chronic constipation, as well as competitor molecules such as ATI-7505 and TD-5108, will now be followed with interest as each attempts to differentiate themselves from each other. Perhaps at last, 5-HT(4) receptor agonists are being given the chance to show what they can do.

Increased colonic transit in rats produced by a combination of a cholinesterase inhibitor with a 5-HT4 receptor agonist

Increased cholinergic stimulation and accelerated gastrointestinal (GI) transit may be produced by direct stimulation of the acetylcholine (ACh) receptor with an appropriate agonist by increased release of ACh from cholinergic nerve terminals or by a decreased removal or breakdown of ACh within cholinergic synapses. The acetylcholinesterase inhibitor, neostigmine, and the 5-HT(4) receptor partial agonist tegaserod, are two agents with known prokinetic activity which work by different mechanisms that result in increased levels of ACh at cholinergic synapses innervating intestinal smooth muscle. Here, we aimed to investigate the potential synergistic effect on colonic transit that may occur with concomitant use of these two agents. Colonic transit was indirectly assessed in rats via measurements of fecal pellet output every 30 min for 2.5 h following administration of neostigmine (0.003-0.1 mg kg(-1), i.p.), tegaserod (0.01-1.0 mg kg(-1), i.p.), or a combination of both compounds. When administered alone, neostigmine or tegaserod caused a dose-dependent increase in fecal pellet output. In combination, low doses of the two agents which did not produce statistically significant effects alone, compared to the vehicle, caused a significant increase in fecal pellet output. Combinations of higher doses of neostigmine and tegaserod did not display synergy. In summary, when combined at low doses, neostigmine and tegaserod produce synergistic effects manifested by a statistically significant increase in the expulsion of fecal pellets. A combination of an anticholinesterase agent with a 5-HT(4) receptor agonist may prove to be a useful therapeutic approach to treat conditions associated with slow GI transit.

Prucalopride: a new drug for the treatment of chronic constipation

Prucalopride belongs to a novel class of 5-hydroxytryptamine-4 receptor agonists, and has been evaluated extensively for the treatment of chronic constipation. Prucalopride has a stimulatory effect on gastrointestinal motility and transit, as established by in vivo and in vitro studies in animals and humans. Its therapeutic efficacy, tolerability and safety have been evaluated in Phase II and Phase III studies in chronic constipation. The cardiovascular safety profile of the drug was studied in vitro and in vivo in animal studies, in clinical studies in chronic constipation patients, as well as in specific additional clinical cardiovascular studies. Phase II studies identified a dose-dependent effect of prucalopride on bowel pattern and associated symptoms in chronic constipation. The Phase III studies mainly recruited patients with insufficient response to laxatives, and showed consistent efficacy and excellent tolerability for prucalopride.

Distribution of serotonin receptors and interacting proteins in the human sigmoid colon

This study aimed to examine the distribution of 5-HT receptors in the human colon. 5-HT induces desensitization of the circular muscle and as this is facilitated by G-protein coupled receptor kinases (GRKs) and other proteins, we also examined their distribution. Human sigmoid colon samples were dissected into three separate layers (mucosa, taeniae coli and intertaenial strips) and RNA was amplified by RT-PCR. The 5-HT(2B) receptor and all 5-HT(7) receptor splice variants were expressed in all tissues. 5-HT(4) a,b,c and n splice variants were also expressed in all tissues and 5-HT(4d), 5-HT(4g) and 5-HT(4i) were only detected in some samples. The 5-HT(2A) receptor was seen predominantly in the intertaenial strips of the colon. Only one transcript of the serotonin transporter (SERT) was detected in the muscle layers. Variation was seen in GRK expression with GRK2 and 3 predominantly expressed in the mucosa, while GRK5 and 6 were found more commonly in the taeniae coli. PDZ (named after postsynaptic density protein, Drosophila disc large tumour suppressor and tight junction protein ZO-1) domain containing proteins, which may be involved in 5-HT receptor trafficking, were also detected throughout the sigmoid colon. The 5-HT(3A) subunit was expressed in all tissues, whereas the 5-HT(3E) subunit was mainly found in the mucosa layer while the 5-HT(3B) subunit was more common in the muscle layers. Receptor interacting chaperone (RIC-3), which is involved in transporting 5-HT(3) receptor subunits, is expressed less in mucosa compared to muscle layers. In conclusion, these results show that there is variation in distribution of 5-HT receptors and interacting proteins within the sigmoid colon that may contribute to colonic function.

Pharmacotherapy of gastroparesis

Gastroparesis is a relatively common and often disabling condition that is characterized by a broad range of clinical presentation ranging from dyspeptic symptoms to nausea, vomiting, abdominal pain, malnutrition, frequent hospitalizations and incapacitation. The treatment of gastroparetic symptoms can be challenging to the gastroenterologist and the intensity of therapy varies with the physician's knowledge. Hence the determination that a patient is refractory to 'standard medical therapy' is an assessment that is subspeciality-based and could differ around the world depending on medications available. In this article, we review the use of available prokinetics, antiemetic agents, the approach for analgesia in the context of gastroparesis, and also discuss potential and evolving pharmacotherapies. The progress has been relatively limited as far as availability of new medications for gastroparesis is concerned; however, active research in developing newer prokinetics holds great promise for the future of management of this challenging entity.

Selective desensitization of the 5-HT4 receptor-mediated response in pig atrium but not in stomach

BACKGROUND AND PURPOSE

The time dependency of the effect of 5-HT(4) receptor agonists depends on many specific regulatory mechanisms, which vary between tissues. This has important implications with regard to the effects of endogenous 5-HT, as well as to the clinical use of 5-HT(4) receptor agonists, and might contribute to tissue selectivity of agonists.

EXPERIMENTAL APPROACH

The progression and desensitization of 5-HT(4) receptor-mediated responses were evaluated in an organ bath set-up using two, clinically relevant, porcine in vitro models: gastric cholinergic neurotransmission and atrial contractility.

KEY RESULTS

Exposure of gastric tissue to 5-HT or to the selective 5-HT(4) receptor agonists prucalopride and M0003 results in a sustained non-transient effect during exposure; after washout, the response to a subsequent challenge with 5-HT shows no clear desensitization. Incubation of left atrial tissue with 5-HT resulted in a transient response, leading after washout to a marked desensitization of the subsequent response to 5-HT. The selective 5-HT(4) receptor agonists prucalopride and M0003 induce only very weak atrial responses whereas they are very effective in desensitizing the atrial response to 5-HT. The observations also suggest that the properties of prucalopride and M0003 to bind to and/or activate the 5-HT(4) receptor differ from those of 5-HT. This difference might have contributed to the observed desensitization.

CONCLUSIONS AND IMPLICATIONS

The high potency of prucalopride and M0003 in desensitizing the response to 5-HT together with their low efficacy in the atrium emphasizes the cardiac safety of this class of 5-HT(4) receptor agonists.

Effects of excitatory and inhibitory neurotransmission on motor patterns of human sigmoid colon in vitro

BACKGROUND AND PURPOSE

To characterize the in vitro motor patterns and the neurotransmitters released by enteric motor neurons (EMNs) in the human sigmoid colon.

EXPERIMENTAL APPROACH

Sigmoid circular strips were studied in organ baths. EMNs were stimulated by electrical field stimulation (EFS) and through nicotinic ACh receptors.

KEY RESULTS

Strips developed weak spontaneous rhythmic contractions (3.67+/-0.49 g, 2.54+/-0.15 min) unaffected by the neurotoxin tetrodotoxin (TTX; 1 microM). EFS induced strong contractions during (on, 56%) or after electrical stimulus (off, 44%), both abolished by TTX. Nicotine (1-100 microM) inhibited spontaneous contractions. Latency of off-contractions and nicotine responses were reduced by N(G)-nitro-L-arginine (1 mM) and blocked after further addition of apamin (1 microM) or the P2Y(1) receptor antagonist MRS 2179 (10 microM) and were unaffected by the P2X antagonist NF279 (10 microM) or alpha-chymotrypsin (10 U mL(-1)). Amplitude of on- and off-contractions was reduced by atropine (1 microM) and the selective NK(2) receptor antagonist Bz-Ala-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH(2) (1 microM). MRS 2179 reduced the amplitude of EFS on- and off-contractions without altering direct muscular contractions induced by ACh (1 nM-1 mM) or substance P (1 nM-10 microM).

CONCLUSIONS AND IMPLICATIONS

Latency of EFS-induced off-contractions and inhibition of spontaneous motility by nicotine are caused by stimulation of inhibitory EMNs coreleasing NO and a purine acting at muscular P2Y(1) receptors through apamin-sensitive K(+) channels. EFS-induced on- and off-contractions are caused by stimulation of excitatory EMNs coreleasing ACh and tachykinins acting on muscular muscarinic and NK(2) receptors. Prejunctional P2Y(1) receptors might modulate the activity of excitatory EMNs. P2Y(1) and NK(2) receptors might be therapeutic targets for colonic motor disorders.