A 5-HT4 agonist mosapride enhances rectorectal and rectoanal reflexes in guinea pigs

Disorders of gastrointestinal hypomotility

Ingestion and digestion of food as well as expulsion of residual material from our gastrointestinal tract requires normal propulsive, i.e. motor, function. Hypomotility refers to inherited or acquired changes that come with decreased contractile forces or slower transit. It not only often causes symptoms but also may compromise nutritional status or lead to other complications. While severe forms, such as pseudo-obstruction or ileus, may have a tremendous functional impact, the less severe forms of hypomotility may well be more relevant, as they contribute to common disorders, such as functional dyspepsia, gastroparesis, chronic constipation, and irritable bowel syndrome (IBS). Clinical testing can identify changes in contractile activity, defined by lower amplitudes or abnormal patterns, and the related effects on transit. However, such biomarkers show a limited correlation with overall symptom severity as experienced by patients. Similarly, targeting hypomotility with pharmacological interventions often alters gut motor function but does not consistently improve symptoms. Novel diagnostic approaches may change this apparent paradox and enable us to obtain more comprehensive information by integrating data on electrical activity, mechanical forces, patterns, wall stiffness, and motions with information of the flow of luminal contents. New drugs with more selective effects or more specific delivery may improve benefits and limit adverse effects. Lastly, the complex regulation of gastrointestinal motility involves the brain-gut axis as a reciprocal pathway for afferent and efferent signaling. Considering the role of visceral input in emotion and the effects of emotion on visceral activity, understanding and managing hypomotility disorders requires an integrative approach based on the mind-body continuum or biopsychosocial model of diseases.

Constitutively Active 5-HT Receptors: An Explanation of How 5-HT Antagonists Inhibit Gut Motility in Species Where 5-HT is Not an Enteric Neurotransmitter?

Antagonists of 5-Hydroxytryptamine (5-HT) receptors are well known to inhibit gastrointestinal (GI)-motility and transit in a variety of mammals, including humans. Originally, these observations had been interpreted by many investigators (including us) as evidence that endogenous 5-HT plays a major role in GI motility. This seemed a logical assumption. However, the story changed dramatically after recent studies revealed that 5-HT antagonists still blocked major GI motility patterns (peristalsis and colonic migrating motor complexes) in segments of intestine depleted of all 5-HT. Then, these results were further supported by Dr. Gershons' laboratory, which showed that genetic deletion of all genes that synthesizes 5-HT had minor, or no inhibitory effects on GI transit in vivo. If 5-HT was essential for GI motility patterns and transit, then one would expect major disruptions in motility and transit when 5-HT synthesis was genetically ablated. This does not occur. The inhibitory effects of 5-HT antagonists on GI motility clearly occur independently of any 5-HT in the gut. Evidence now suggests that 5-HT antagonists act on 5-HT receptors in the gut which are constitutively active, and don't require 5-HT for their activation. This would explain a long-standing mystery of how 5-HT antagonists inhibit gut motility in species like mice, rats, and humans where 5-HT is not an enteric neurotransmitter. Studies are now increasingly demonstrating that the presence of a neurochemical in enteric neurons does not mean they function as neurotransmitters. Caution should be exercised when interpreting any inhibitory effects of 5-HT antagonists on GI motility.

The 5-hydroxytryptamine 4 Receptor Agonist-induced Actions and Enteric Neurogenesis in the Gut

We explored a novel effect of 5-hydroxytryptamine 4 receptor (5-HT4R) agonists in vivo to reconstruct the enteric neural circuitry that mediates a fundamental distal gut reflex. The neural circuit insult was performed in guinea pigs and rats by rectal transection and anastomosis. A 5-HT4R-agonist, mosapride citrate (MOS) applied orally and locally at the anastomotic site for 2 weeks promoted the regeneration of the impaired neural circuit or the recovery of the distal gut reflex. MOS generated neurofilament-, 5-HT4R- and 5-bromo-2'-deoxyuridine-positive cells and formed neural network in the granulation tissue at the anastomosis. Possible neural stem cell markers increased during the same time period. These novel actions by MOS were inhibited by specific 5-HT4R-antagonist such as GR113808 (GR) or SB-207266. The activation of enteric neural 5-HT4R promotes reconstruction of an enteric neural circuit that involves possibly neural stem cells. We also succeeded in forming dense enteric neural networks by MOS in a gut differentiated from mouse embryonic stem cells. GR abolished the formation of enteric neural networks. MOS up-regulated the expression of mRNA of 5-HT4R, and GR abolished this upregulation, suggesting MOS differentiated enteric neural networks, mediated via activation of 5-HT4R. In the small intestine in H-line: Thy1 promoter green fluorescent protein (GFP) mice, we obtained clear 3-dimensional imaging of enteric neurons that were newly generated by oral application of MOS after gut transection and anastomosis. All findings indicate that treatment with 5-HT4R-agonists could be a novel therapy for generating new enteric neurons to rescue aganglionic disorders in the whole gut.

5-HT3 and 5-HT4 antagonists inhibit peristaltic contractions in guinea-pig distal colon by mechanisms independent of endogenous 5-HT

Recent studies have shown that endogenous serotonin is not required for colonic peristalsis in vitro, nor gastrointestinal (GI) transit in vivo. However, antagonists of 5-Hydroxytryptamine (5-HT) receptors can inhibit peristalsis and GI-transit in mammals, including humans. This raises the question of how these antagonists inhibit GI-motility and transit, if depletion of endogenous 5-HT does not cause any significant inhibitory changes to either GI-motility or transit? We investigated the mechanism by which 5-HT3 and 5-HT4 antagonists inhibit distension-evoked peristaltic contractions in guinea-pig distal colon. In control animals, repetitive peristaltic contractions of the circular muscle were evoked in response to fixed fecal pellet distension. Distension-evoked peristaltic contractions were unaffected in animals with mucosa and submucosal plexus removed, that were also treated with reserpine (to deplete neuronal 5-HT). In control animals, peristaltic contractions were blocked temporarily by ondansetron (1–10 μM) and SDZ-205–557 (1–10 μM) in many animals. Interestingly, after this temporary blockade, and whilst in the continued presence of these antagonists, peristaltic contractions recovered, with characteristics no different from controls. Surprisingly, similar effects were seen in mucosa-free preparations, which had no detectable 5-HT, as detected by mass spectrometry. In summary, distension-evoked peristaltic reflex contractions of the circular muscle layer of the guinea-pig colon can be inhibited temporarily, or permanently, in the same preparation by selective 5-HT3 and 5-HT4 antagonists, depending on the concentration of the antagonists applied. These effects also occur in preparations that lack any detectable 5-HT. We suggest caution should be exercised when interpreting the effects of 5-HT3 and 5-HT4 antagonists; and the role of endogenous 5-HT, in the generation of distension-evoked colonic peristalsis.

Serotonin: from top to bottom

Serotonin is a monoamine neurotransmitter, which is phylogenetically conserved in a wide range of species from nematodes to humans. In mammals, age-related changes in serotonin systems are known risk factors of age-related diseases, such as diabetes, faecal incontinence and cardiovascular diseases. A decline in serotonin function with aging would be consistent with observations of age-related changes in behaviours, such as sleep, sexual behaviour and mood all of which are linked to serotonergic function. Despite this little is known about serotonin in relation to aging. This review aims to give a comprehensive analysis of the distribution, function and interactions of serotonin in the brain; gastrointestinal tract; skeletal; vascular and immune systems. It also aims to demonstrate how the function of serotonin is linked to aging and disease pathology in these systems. The regulation of serotonin via microRNAs is also discussed, as are possible applications of serotonergic drugs in aging research and age-related diseases. Furthermore, this review demonstrates that serotonin is potentially involved in whole organism aging through its links with multiple organs, the immune system and microRNA regulation. Methods to investigate these links are discussed.

Efficacy of mosapride citrate with polyethylene glycol solution for colonoscopy preparation

AIM: To evaluate the efficacy and safety of adjunctive mosapride citrate for bowel preparation before colonoscopy.

METHODS: We conducted a randomized, double-blind, placebo-controlled study with mosapride in addition to polyethylene glycol (PEG)-electrolyte solution. Of 250 patients undergoing colonoscopy, 124 were randomized to receive 2 L PEG plus 15 mg of mosapride citrate (mosapride group), and 126 received 2 L PEG plus placebo (placebo group). Patients completed a questionnaire reporting the acceptability and tolerability of the bowel preparation process. The efficacy of bowel preparation was assessed by colonoscopists using a 5-point scale based on Aronchick’s criteria. The primary end point was optimal bowel preparation rates (scores of excellent/good/fair vs poor/inadequate).

RESULTS: A total of 249 patients were included in the analysis. In the mosapride group, optimal bowel preparation rates were significantly higher in the left colon compared with the placebo group (78.2% vs 65.6%, P < 0.05), but not in the right colon (76.5% vs 66.4%, P = 0.08). After excluding patients with severe constipation, there was a significant difference in bowel preparation in both the left and right colon (82.4% vs 66.7%, 80.8% vs 67.5%, P < 0.05, P < 0.01). The incidence of adverse events was similar in both groups. Among the subgroup who had previous colonoscopy experience, a significantly higher number of patients in the mosapride group felt that the current preparation was easier compared with patients in the placebo group (34/72 patients vs 24/74 patients, P < 0.05).

CONCLUSION: Mosapride citrate may be an effective and safe adjunct to PEG-electrolyte solution that leads to improved quality of bowel preparation, especially in patients without severe constipation.

Comparison of effects of a selective 5-HT reuptake inhibitor versus a 5-HT4 receptor agonist on in vivo neurogenesis at the rectal anastomosis in rats

It was recently reported that activation of enteric neural 5-HT(4) receptors (SR4) promotes reconstruction of enteric neural circuit injury in distal gut of guinea pigs and that this reconstruction involves neural stem cells. We aimed to explore a novel approach using a selective serotonin reuptake inhibitor (SSRI), which increases endogenous 5-HT, to repair enteric nerve fiber injury in the rat distal gut. Enteric nerve fiber injury was performed by rectal transection and subsequent end-to-end one-layer anastomosis. The SSRI fluvoxamine maleate (100 μmol/l) was applied locally at the anastomotic site to compare with the 5-HT(4) agonist mosapride citrate (100 μmol/l) (applied for patent) applied locally and orally. Unlike mosapride, fluvoxamine failed to promote the regeneration of the nerve fiber tract across the anastomosis. Furthermore, fluvoxamine did not generate anti-distal-less homeobox 2 (DLX2)- and anti-SR4-positive cells (neural stem cells) and/or anti-neurofilament (NF)-positive cells (neural cells) in newly formed granulation tissue at the anastomosis, whereas these cell types were observed in mosapride-treated preparations. In contrast to its effects in guinea pigs, mosapride generated 5-bromo-2'-deoxyuridine (BrdU)-positive neural cells in ganglia sites 3 mm oral and anal from the anastomosis 2 wk after nerve fiber injury. All actions of mosapride were observed after local and or oral applications. These findings indicate that local SSRI treatment does not induce in vivo nerve fiber tract growth across the anastomosis in the rat distal gut. Mosapride induces nerve fiber tract growth across the anastomosis, mediated through enteric neural stem cells possibly from neural crest-derived stem cells or mesenchymal stem cells in the bone marrow.

Mosapride citrate improves postoperative ileus of patients with colectomy

BACKGROUND AND AIMS

Postoperative ileus is a transient bowel dysmotility that occurs following many types of operations and is a common complication of gastrointestinal surgery. Mosapride citrate is an agonist of the 5-hydroxytryptamine 4 receptor and accelerates upper gut motility. No study has evaluated its effect on gastrointestinal motility after surgery. The aim of this study was to investigate whether mosapride citrate reduces the duration of postoperative ileus.

METHODS

Thirty patients with colon cancer who underwent colectomy were divided into two groups: the mosapride group and the control group. The mosapride group received mosapride 15 mg by mouth with a minimal amount of water three times a day, starting on postoperative day 1. The control group received only a minimal amount of water on the same schedule. Patients were allowed to resume oral feeding on postoperative day 4. Postoperative time to first flatus and defecation were evaluated, and the amount of food intake was observed. Gastrointestinal motility was recorded on postoperative day 8.

RESULTS

The appearance ratio of interdigestive migrating contractions and the motility index at the antrum and duodenum were significantly higher in the mosapride group than in the control group. The time to first flatus and defecation were significantly shorter in the mosapride group than in the control group. The amount of food intake on postoperative days 6 and 7 was significantly larger in the mosapride group than in the control group.

CONCLUSION

Mosapride citrate reduces the duration of postoperative ileus and may improve outcomes after gastrointestinal surgery.

Effects of mosapride citrate, a 5-HT4-receptor agonist, on gastric distension-induced visceromotor response in conscious rats

Mosapride citrate (mosapride), a prokinetic agent with 5-HT(4)-receptor agonistic activity, is known to enhance gastric emptying and alleviate symptoms in patients with functional dyspepsia (FD). As hyperalgesia and delayed gastric emptying play an important role in the pathogenesis of FD, we used in this study balloon gastric distension to enable abdominal muscle contractions and characterized the visceromotor response (VMR) to such distension in conscious rats. We also investigated the effects of mosapride on gastric distension-induced VMR in the same model. Mosapride (3-10 mg/kg, p.o.) dose-dependently inhibited gastric distension-induced VMR in rats. However, itopride even at 100 mg/kg failed to inhibit gastric distension-induced VMR in rats. Additionally, a major metabolite M1 of mosapride, which possesses 5-HT(3)-receptor antagonistic activity, inhibited gastric distension-induced VMR. The inhibitory effect of mosapride on gastric distension-induced visceral pain was partially, but significantly inhibited by SB-207266, a selective 5-HT(4)-receptor antagonist. This study shows that mosapride inhibits gastric distension-induced VMR in conscious rats. The inhibitory effect of mosapride is mediated via activation of 5-HT(4) receptors and blockage of 5-HT(3) receptors by a mosapride metabolite. This finding indicates that mosapride may be useful in alleviating FD-associated gastrointestinal symptoms via increase in pain threshold.

Investigational agents for the irritable bowel syndrome

IMPORTANCE OF THE FIELD

Irritable bowel syndrome (IBS) is a common disorder with significant health and economic consequences. The etiology of IBS is complex and appears to be multifactorial. Traditional IBS therapies have been directed primarily at the relief of individual symptoms but have been largely disappointing. This has triggered the search for newer treatment strategies with improved patient outcomes.

AREAS COVERED IN THIS REVIEW

Enhanced knowledge about the putative pathophysiology of IBS has allowed the identification of new mechanistic targets for treatment. Our aim is to review emerging and promising drugs in the treatment of IBS based on disease pathophysiology. Data were extracted using Medline and PubMed search engines until January 2010. Abstracts were identified through 'Web of Science' and abstract supplements of major gastrointestinal scientific meetings. Drugs were classified according to mechanism of action and those with efficacy in trials involving human subjects examined.

WHAT THE READER WILL GAIN

Additional insight into the pathophysiology as well as current and prospective treatments of IBS.

TAKE HOME MESSAGE

A multitude of putative drug targets have been identified and some novel treatments have progressed through to human clinical trials, but very few will be approved for the market in the near future. Moreover, and in keeping with the complex and multifactorial nature of this syndrome, it is unlikely that there will be one dominant and universally effective form of therapy for all IBS patients.

A 5-HT(4)-receptor activation-induced neural plasticity enhances in vivo reconstructs of enteric nerve circuit insult

BACKGROUND

It was recently reported that some 5-HT(4)-receptor agonists increased neuronal numbers and length of neurites in enteric neurons developing in vitro from immunoselected neural crest-derived precursors. We aimed to explore a novel approach in vivo to reconstruct the enteric neural circuitry that mediates a fundamental distal gut reflex.

METHODS

The neural circuit insult was performed in guinea pigs by rectal transection and subsequent end-to-end one layer anastomosis. A 5-HT(4)-receptor agonist, mosapride citrate (10-100 micromol L(-1)) (applied for a patent) was applied locally at the anastomotic site.

KEY RESULTS

Mosapride promoted the regeneration of the neural circuit in the impaired myenteric plexus and the recovery of the defecation reflex in the distal gut. Furthermore, mosapride generated neurofilament (NF)-, 5-HT(4)-receptor- and 5-bromo-2'-deoxyuridine (BrdU)-positive cells and surprisingly formed neural network in the newly formed granulation tissue at the anastomotic site 2 weeks after enteric nerve circuit insult. Possible neural stem cell markers, anti-distal less homeobox 2 (DLX2)- and p75-positive and NF-positive cells increased during the same time period. All actions by mosapride were inhibited by the specific 5-HT(4)-receptor antagonist, GR113808 (10 micromol L(-1)).

CONCLUSIONS & INFERENCES

These results indicate that activation of enteric neural 5-HT(4)-receptors promotes reconstruction of an enteric neural circuit leading to the recovery of the defecation reflex in the distal gut, and that this reconstruction involves possibly neural stem cells. These findings indicate that treatment with 5-HT(4) agonists could be a novel therapy for generating new enteric neurons to rescue aganglionic gut disorders.

The effect of mosapride citrate on constipation in patients with diabetes

OBJECTIVE

Constipation is one of the most common gastrointestinal complications suspected to degrade the quality of life in diabetic patients. Mosapride citrate is a novel selective 5-HT4 receptor agonist, which enhances gastric emptying and motility in the upper gastrointestinal tract facilitating acetylcholine release from the enteric cholinergic neurons. Since the receptors of 5-HT4 have been recently found in the lower intestine including the rectum in humans, we tested if mosapride improves constipation in diabetic patients.

PATIENTS AND METHODS

Diabetic patients with constipation were treated with mosapride citrate (15 mg/day, n=20) or domperidone (30 mg/day, n=12) as controls for 8 weeks. Bowel frequency was monitored and gastrointestinal symptoms were evaluated by Gastrointestinal Symptoms Rating Scale (GSRS).

RESULTS

Administration of mosapride resulted in increased bowel frequency after 4 and 8 weeks of administration, while no change was seen in the control group. Mosapride increased bowel frequency in even patients with diabetic polyneuropathy. Mosapride improved reflux and constipation evaluated by GSRS. As previously reported, glycemic control also improved by mosapride in these patients.

CONCLUSIONS

Administration of mosapride increased bowel frequency and ameliorated symptoms of reflux and constipation possibly stimulating the lower intestine. Given that mosapride has those beneficial aspects, it may be a useful prokinetic agent in treating diabetic patients with constipation.

A new possibility for repairing the anal dysfunction by promoting regeneration of the reflex pathways in the enteric nervous system

Moderate rectal distension elicits recto-rectal reflex contractions and simultaneous recto-internal anal sphincter reflex relaxations that together comprise the defecation reflex. Both reflexes are controlled by 1) pelvic nerves, 2) lumbar colonic nerves, and 3) enteric nervous system. The aim of the present study was to explore a novel approach to repairing the defecation reflex dysfunction by using the plasticity of enteric nervous pathways. Experiments were performed in anesthetized guinea pigs with ethyl carbamate. The rectum 30 mm oral from the anal verge was transected without damage to extrinsic nerves, and subsequent end-to-end one-layer anastomosis was performed. Recovery of the defecation reflex and associated reflex pathways were evaluated. Eight weeks after sectioning of intrinsic reflex nerve pathways in the rectum, the defecation reflex recovered to the control level, accompanied with regeneration of reflex pathways. The 5-HT(4)-receptor agonist mosapride (0.5 and 1.0 mg/kg) significantly (P < 0.01) enhanced the recovered defecation reflex 8 wk after surgery. Two weeks after local treatment with brain-derived neurotrophic factor (BDNF: 10(-6) g/ml) at the rectal anastomotic site, the recto-internal anal sphincter reflex relaxations recovered and some bundles of fine nerve fibers were shown to interconnect the oral and anal ends of the myenteric plexus. These results suggested a possibility for repairing the anal dysfunction by promoting regeneration of the reflex pathways in the enteric nervous system with local application of BDNF.

5-Hydroxytryptamine2C receptors on pudendal motoneurons innervating the external anal sphincter

The aim of this study was to determine the localization of 5-hydroxytryptamine2C (5-HT2C) receptors on the motoneurons innervating the external anal sphincter (EAS) of male rats. Motoneurons were retrogradely labeled after percutaneous intramuscular injection of Fluorogold (FG) into the EAS. Using fluorescent immunohistochemistry, FG-positive EAS motoneurons that were immunoreactive for the 5-HT2C receptor (5-HT2C-IR) were targeted for specific examination with widefield microscopy or confocal laser scanning microscopy with spectral separation. Widefield microscopy revealed distributions of FG-positive EAS motoneurons in the L5-S1 gray matter corresponding to the dorsomedial cell group. 5-HT2C-IR positive cells were distributed in the intermediolateral cell column and the ventral horn. Ventral horn 5-HT2C-IR labeling included the dorsomedial cell group as well as the dorsolateral, ventromedial and ventrolateral areas. Confocal analysis of FG-positive EAS motoneurons and 5-HT2C-IR positive motoneuron profiles adjacent to EAS motoneurons that were not labeled with FG but presumably innervate the bulbospongiosus muscle confirmed that EAS motoneurons were immunopositive for the 5-HT2C receptor. These data suggest that previously identified descending serotonergic immunopositive fibers observed terminating on EAS motoneurons might mediate their input through the activation of 5-HT2C receptors.

A 5-HT4 agonist, mosapride, enhances intrinsic rectorectal and rectoanal reflexes after removal of extrinsic nerves in guinea pigs

Distension-evoked reflex of rectorectal (R-R) contractions and rectointernal anal sphincter (R-IAS) relaxations can be generated in guinea pigs through an extrinsic sacral excitatory neural pathway (pelvic nerves) as well as intrinsic cholinergic excitatory and nitrergic inhibitory pathways. The aim of the present study was to create intrinsic R-R and R-IAS reflex models by pithing (destruction of the lumbar and sacral cords; PITH) and to evaluate whether the prokinetic benzamide mosapride, a 5-HT(4) receptor agonist, enhances these reflexes. The mechanical activities of the R-R and R-IAS were recorded in the anesthetized guinea pig on days 2-9 after PITH. Although the basal rectal pressure at distension after PITH was significantly lower than control, the reflex indexes of R-R contractions and synchronous R-IAS relaxations were unchanged between days 4 and 9 after PITH. The frequency of spontaneous rectal and IAS motility were also unchanged. Immunohistochemical studies revealed that the distribution of myenteric and intramuscular interstitial cells of Cajal (ICC) were not altered after PITH. Mosapride (0.1-1.0 mg/kg iv) dose-dependently increased both intrinsic R-R (maximum: 1.82) and R-IAS reflex indexes (maximum: 2.76) from control (1.0) 6-9 days after PITH. The 5-HT(4) receptor antagonist, GR-113808 (1.0 mg/kg iv) decreased the R-R and R-IAS reflex indexes by approximately 50% and antagonized the effect of mosapride (1.0 mg/kg iv). The present results indicate that mosapride moderately enhanced intrinsic R-R and R-IAS reflexes functionally compensated after deprivation of extrinsic nerves, mediated through endogenously active intrinsic 5-HT(4) receptors.

Mosapride citrate, a novel 5-HT4 agonist and partial 5-HT3 antagonist, ameliorates constipation in parkinsonian patients

Mosapride citrate is a novel selective 5-HT4 receptor agonist. It facilitates acetylcholine release from the enteric cholinergic neurons. In contrast to cisapride, mosapride does not block K(+) channels or D2 dopaminergic receptors. The objective of this study is to perform an open study of mosapride citrate's effects on constipation, a prominent lower gastrointestinal tract disorder in parkinsonian patients. A total of 14 parkinsonian patients (7 with Parkinson's disease, 7 with multiple system atrophy; 10 men, 4 women; mean age, 67 years) with constipation (10 with bowel movement < 3 times/week; 14 with difficulty in defecation) were treated with 15 mg/day of mosapride citrate for 3 months. Pre- and posttreatment objective parameters in colonic transit time (CTT) and rectoanal videomanometry were obtained. Statistical analysis was made by Student's t test. Mosapride was well tolerated by all patients except for 1, who discontinued use of the drug because of epigastric discomfort. None had a worsening of parkinsonism or other adverse events. Thirteen patients reported subjective improvements in bowel frequency (>3 times/week, 13) and difficult defecation (13). Mosapride shortened CTT of the left colon (P < 0.01) and the total colon (P < 0.05). During rectal filling, mosapride lessened the first sensation (P < 0.05) and augmented the amplitude in phasic rectal contraction. During defecation, mosapride augmented the amplitude in rectal contraction (P < 0.05) and lessened the volume of postdefecation residuals. The present study showed for the first time that mosapride citrate augmented lower gastrointestinal tract motility, as shown in CTT and videomanometry, and thereby ameliorated constipation in parkinsonian patients without serious adverse effects.