Effect of a novel 5-HT3 receptor agonist MKC-733 on upper gastrointestinal motility in humans

Mechanisms underlying the laxative effect of lactulose: A randomized placebo-controlled trial showing increased small bowel water and motility unaltered by the 5-HT3 receptor antagonist, ondansetron

BACKGROUND

Lactulose is a laxative which accelerates transit and softens stool. Our aim was to investigate its mechanism of action and use this model of diarrhea to investigate the anti-diarrheal actions of ondansetron.

METHODS

A double-blind, randomized, placebo-controlled crossover study of the effect of ondansetron 8 mg in 16 healthy volunteers. Serial MRI scans were performed fasted and 6 h after a meal. Participants then received lactulose 13.6 g twice daily and study drug for a further 36 h. On Day 3, they had further serial MRI scans for 4 h. Measurements included small bowel water content (SBWC), colonic volume, colonic gas, small bowel motility, whole gut transit, and ascending colon relaxation time (T1AC), a measure of colonic water content.

KEY RESULTS

Lactulose increased area under the curve (AUC) of SBWC from 0 to 240 min, mean difference 14.2 L · min (95% CI 4.1, 24.3), p = 0.009, and substantially increased small bowel motility after 4 h (mean (95% CI) 523 (457-646) a.u. to 852 (771-1178) a.u., p = 0.007). There were no changes in T1AC after 36 h treatment. Ondansetron did not significantly alter SBWC, small bowel motility, transit, colonic volumes, colonic gas nor T1AC, with or without lactulose.

CONCLUSION & INFERENCES

Lactulose increases SBWC and stimulates small bowel motility; however, unexpectedly it did not significantly alter colonic water content, suggesting its laxative effect is not osmotic but due to stimulation of motility. Ondansetron's lack of effect on intestinal water suggests its anti-diarrheal effect is not due to inhibition of secretion but more likely altered colonic motility.

Exercise is inversely associated with functional dyspepsia among a sample of Chinese male armed police recruits

BACKGROUND

There is no study evaluating the association between exercise and functional dyspepsia (FD) based on the Rome IV criteria. We aimed to investigate the prevalence of FD and evaluate the association between exercise and FD based on Rome IV criteria among a sample of Chinese armed police recruits.

METHODS

An on-site questionnaire survey on FD among a sample of Chinese armed police recruits was conducted based on the Rome IV criteria in 2021. Potential confounders included age, body mass index (BMI), race, marriage, education, smoking, and drinking variables were adjusted.

RESULTS

A total of 2594 recruits were enrolled, including 46 FD participants and 2548 non-FD participants. In the model adjusted for all demographic variables among participants excluding irritable bowel syndrome (IBS) and functional constipation (FC), compared with no exercise participants, 1 h < each exercise time ≤ 2 h (OR = 0.15, 95% CI: 0.03-0.77, P = 0.0230) was inversely associated with FD and compared with no exercise participants, mild exercise (OR = 0.09, 95% CI: 0.01-0.71, P = 0.0220) was significantly inversely associated with FD.

CONCLUSIONS

The incidence rate of FD in this sample Chinese armed police recruits was 1.77%, and 1 h < each exercise time ≤ 2 h and mild intensity exercise were independently inversely associated with FD. However, the causal relationship needs to be verified by further randomized controlled trials.

The Ketogenic Diet Improves Gut-Brain Axis in a Rat Model of Irritable Bowel Syndrome: Impact on 5-HT and BDNF Systems

Altered gut-brain communication can contribute to intestinal dysfunctions in the intestinal bowel syndrome. The neuroprotective high-fat, adequate-protein, low-carbohydrate ketogenic diet (KD) modulates the levels of different neurotransmitters and neurotrophins. The aim was to evaluate the effects of KD on levels of 5-HT, the receptors 5-HT_3B and 5-HT₄, the 5-HT transporter SERT, the neurotrophin BDNF, and its receptor TrkB in the colon and brain of a rat model of irritable bowel syndrome (IBS). Samples from Wistar rats exposed to maternal deprivation as newborns and then fed with a standard diet (IBS-Std) or KD (IBS-KD) for ten weeks were analyzed. As controls, unexposed rats (Ctrl-Std and Ctrl-KD) were studied. IBS-Std rats had a disordered enteric serotoninergic signaling shown by increased mucosal 5-HT content and reduced SERT, 5-HT_3B, and 5-HT₄ levels compared to controls. In the brain, these animals showed up-regulation of the BDNF receptor TrkB as a counteracting response to the stress-induced reduction of the neurotrophin. KD showed a dual effect in improving the altered 5-HT and BDNF systems. It down-regulated the increased mucosal 5-HT without affecting transporter and receptor levels. KD improved brain BDNF levels and established negative feedback, leading to a compensatory downregulation of TrkB to maintain a physiological steady state.

A link between gastrointestinal disorders and migraine: Insights into the gut-brain connection

Background

Migraine is a complex, multifaceted, and disabling headache disease that is often complicated by gastrointestinal (GI) conditions, such as gastroparesis, functional dyspepsia, and cyclic vomiting syndrome (CVS). Functional dyspepsia and CVS are part of a spectrum of disorders newly classified as disorders of gut–brain interaction (DGBI). Gastroparesis and functional dyspepsia are both associated with delayed gastric emptying, while nausea and vomiting are prominent in CVS, which are also symptoms that commonly occur with migraine attacks. Furthermore, these gastric disorders are comorbidities frequently reported by patients with migraine. While very few studies assessing GI disorders in patients with migraine have been performed, they do demonstrate a physiological link between these conditions.

Objective

To summarize the available studies supporting a link between GI comorbidities and migraine, including historical and current scientific evidence, as well as provide evidence that symptoms of GI disorders are also observed outside of migraine attacks during the interictal period. Additionally, the importance of route of administration and formulation of migraine therapies for patients with GI symptoms will be discussed.

Methods

A literature search of PubMed for articles relating to the relationship between the gut and the brain with no restriction on the publication year was performed. Studies providing scientific support for associations of gastroparesis, functional dyspepsia, and CVS with migraine and the impact these associations may have on migraine treatment were the primary focus. This is a narrative review of identified studies.

Results

Although the association between migraine and GI disorders has received very little attention in the literature, the existing evidence suggests that they may share a common etiology. In particular, the relationship between migraine, gastric motility, and vomiting has important clinical implications in the treatment of migraine, as delayed gastric emptying and vomiting may affect oral dosing compliance, and thus, the absorption and efficacy of oral migraine treatments.

Conclusions

There is evidence of a link between migraine and GI comorbidities, including those under the DGBI classification. Many patients do not find adequate relief with oral migraine therapies, which further necessitates increased recognition of GI disorders in patients with migraine by the headache community.

Does Intravenous Ondansetron Affect the Intestinal Motility Pattern in Healthy Donkeys (Equus asinus)?

The current study was undertaken to investigate the effect of intravenous administration of ondansetron on the small and large intestinal motility in donkeys (Equus asinus) using non-invasive transabdominal ultrasonography. The current prospective, randomized, placebo-controlled, crossover study was conducted on thirty healthy donkeys (15 males and 15 females). The selected donkeys underwent two trials; the first was performed by intravenous administration of saline solution as a placebo, while the second was carried out by intravenous administration of ondansetron hydrochloride. The contractility of selected portions of both the small intestine (duodenum and jejunum) and the large intestine (left colon, right colon, and cecum) was counted over a period of 3 minutes before administration (zero time) and at 15, 30, 60, 90, 120, 180, and 240 minutes after administration. The results of this study showed that ondansetron significantly altered the small and large intestinal contractility compared to normal saline. Intravenous administration of ondansetron induced a significant decrease in the duodenal, jejunal and cecal contractility compared to placebo at 30, 60, 90, and 120 minutes after administration. Likewise, ondansetron induced a significant decrease in the left colon and right colon contractility when compared with placebo at 30, 60, 90, 120, and 180 minutes following administration. Ondansetron can be used as a highly specific and selective serotonin 5-HT₃ receptor antagonist for reducing the small and large intestinal motility in donkeys, and is therefore highly suggested for treating spasmodic colic in equine.

Gastric Motor Functions in Patients With Mood Disorders and Functional Gastroduodenal Symptoms

OBJECTIVE

Functional gastroduodenal symptoms (FGDSs) may result from perturbations in gastric emptying (GE) and gastric accommodation (GA), which are variably affected by acute stress. This study aimed to examine whether individuals who have both mood disorder and FGDS exhibit differences in GE and GA using standardized, validated, and reproducible noninvasive methods.

METHODS

Using a data retrieval program, 1554 individuals at a single center were identified after having undergone measurements of GE by scintigraphy of a 99mTc-radiolabeled egg (320 kcal, 30% fat meal) and GA by single-photon emission computed tomography to assess the underlying pathophysiology in FGDS. An extensive medical record review identified 267 of these individuals as having diagnoses of depression, anxiety, or comorbid anxiety/depression (CAD). Differences in GE and GA as related to the presence of anxiety or depressive disorders were analyzed using one-way analysis of variance on ranks and Mann-Whitney tests for the two-group comparisons.

RESULTS

Sixty-three patients with anxiety, 134 with depression, and 70 with CAD were identified. GE at 1 hour was slower (p = .04) and GE at 2 hours numerically decreased (p = .07) for depression compared with anxiety. GA was diminished for CAD compared with anxiety (p = .04) and depression (p = .009). There were no differences in fasting gastric volume or GE at 4 hours.

CONCLUSIONS

In this study examining GE and GA in anxiety and depressive disorders among patients with FGDS, the combined presence of anxiety and depression was associated with impaired GA compared with patients with depression or anxiety alone, and early GE seemed to be slower in those with depression compared with patients with anxiety.

CSTI-300 (SMP-100); a Novel 5-HT3 Receptor Partial Agonist with Potential to Treat Patients with Irritable Bowel Syndrome or Carcinoid Syndrome

The 5-hydroxytryptamine (5-HT) (serotonin) 5-HT₃ receptor represents a clinical target for antagonists to deliver symptomatic relief to patients with diarrhea-predominant irritable bowel syndrome (IBS-d) or carcinoid syndrome. Unfortunately, this pharmacological strategy can present side effects (e.g., severe constipation). The present study investigates the potential of a novel 5-HT₃ receptor partial agonist, CSTI-300, to treat patients with IBS-d and other conditions associated with discomfort from colonic distension, with a predicted reduced side-effect profile. The in vitro and in vivo preclinical pharmacology of the drug CSTI-300 was investigated to explore the potential to treat patients with IBS-d. CSTI-300 displayed selective high affinity for the human and rat 5-HT₃ receptor (K_i approximately 2.0 nM) and acted as a partial agonist (approximately 30%-50% intrinsic efficacy) in vitro. In an in vivo model of IBS-d, the rat colon distension model, CSTI-300 displayed dose-dependent efficacy. In addition, oral administration of CSTI-300 to dogs that achieved plasma levels of the drug exceeding the K_i value for the 5-HT₃ receptor failed to either evoke emesis or alter the state of feces. Pharmacokinetics for CSTI-300 in rat and dog identified high levels of oral availability with t _1/2 range of 1.6-4.4 hours. The preclinical pharmacology of the lead candidate drug, CSTI-300, supports the potential of this novel drug to offer symptomatic relief to patients with irritable bowel syndrome and carcinoid syndrome with a rationale for a reduced "on-target" side-effect profile relative to 5-HT₃ receptor antagonists, such as alosetron. SIGNIFICANCE STATEMENT: There is a lack of effective current treatment for diarrhea-predominant irritable bowel syndrome and carcinoid syndrome, and in both conditions, overactivity of the 5-hydroxytryptamine (5-HT) 5-HT₃ receptor is thought to be implicated in the pathophysiology. Because 5-HT₃ receptor blockade with antagonists results in significant side effects, we present evidence that treatment with a suitable 5-HT₃ receptor partial agonist will alleviate some symptoms associated with these conditions yet, without fully inhibiting the receptor, predict a less pronounced side-effect profile associated with this therapeutic strategy.

Enhancing our understanding of small bowel function using modern imaging techniques

Small intestinal function is critical to digestive health and patients believe an abnormal reaction to food is responsible for many of their symptoms. Despite this, our ability to assess disturbed function in clinical practice has been limited, particularly after ingestion of the complex nutrients which make up normal food. Recent advances in both wireless capsules and magnetic resonance imaging have provided new insights. This review will briefly describe the limitations of past techniques and focus on how these newer techniques are changing our understanding, particularly of how patients' gastrointestinal tracts respond to food.

Advances in understanding relationship between 5-hydroxytryptamine and its receptors and intestinal dysmotility in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common clinical functional gastrointestinal disease, which seriously affects the quality of life of patients. The pathogenesis of this disorder is unclear and may be related to the changes of visceral sensitivity, gastrointestinal motility, and the function of the brain-gut axis. 5-hydroxytryptamine (5-HT) is an important neurotransmitter, which exhibits a variety of biological effects including gastrointestinal secretion and motility regulation by binding to its receptors. The changes in the synthesis and release of 5-HT and in the expression and function of corresponding receptors are all involved in the pathophysiological process of IBS. In this paper, we will review the role of 5-HT and its receptors in intestinal dysmotility in IBS.

Novel investigational drugs for constipation-predominant irritable bowel syndrome: a review

INTRODUCTION

Constipation-predominant irritable bowel syndrome (IBS-C) is a functional gastrointestinal (GI) disorder with an unknown etiology. A number of the drugs tested for IBS-C have also been applied to chronic constipation and chronic idiopathic constipation. Unfortunately, due to severe adverse effects, many drugs envisioned for IBS-C had been withdrawn from the market. Nevertheless, a number of potential new agents for this indication are now under development.

AREAS COVERED

The following review describes the most recently developed agents in preclinical as well as Phase 1 and Phase 2 clinical studies. Information was obtained from published literature, abstracts and the latest results found in Clinicaltrial.gov database. The authors put a special interest on glucagon-like peptide 1 analogue, bile acid modulators, serotonergic agents, guanylate cyclase C and cannabinoid antagonists.

EXPERT OPINION

To enter the market, a newly-developed drug has to meet several criteria, such as good bioavailability or the absence of drug-related adverse events. Taking into account constipation and abdominal pain as the main symptoms in IBS-C, a novel successful drug is usually able to improve both at the same time. Four out of fifteen investigational drugs described in this paper belong to the serotonergic family and have a good prognosis to reach the market; still, more long-term clinical studies are warranted.

Serotonergic Mechanisms Regulating the GI Tract: Experimental Evidence and Therapeutic Relevance

Serotonin (5-hydroxytryptamine; 5-HT) is best known as a neurotransmitter critical for central nervous system (CNS) development and function. 95% of the body's serotonin, however, is produced in the intestine where it has been increasingly recognized for its hormonal, autocrine, paracrine, and endocrine actions. This chapter provides the most current knowledge of the critical autocrine and paracrine roles of 5-HT in intestinal motility and inflammation as well as its function as a hormone in osteocyte homeostasis. Therapeutic applications in each of these areas are also discussed.

Current and Emerging Medical Therapies for Gastroparesis

OPINION STATEMENT

Gastroparesis likely involves various pathophysiological disorders and is increasingly prevalent as complications of surgeries, medications, and chronic diabetes. Key to diagnosis is evidence of delayed gastric emptying, generally based on standardized scintigraphy, and ruling out distal obstruction or other dysmotilities. Initial medical management includes reviewing potentially exacerbating medications and ruling out other reversible causes, achieving tighter glucose control in diabetics, and implementing dietary and lifestyle changes. While current available medications are limited, symptomatic control is aimed at improving gastric emptying, alleviating nausea and vomiting, and treating associated abdominal pain. Other potential therapies are aimed at reducing acid production, improving gastric accommodation or pyloric dysfunction, and treating bacterial overgrowth. Future studies should be aimed toward identification of subpopulations of gastroparetics who are better responders to the various medications based on differences in underlying pathophysiology and adopting standardized study end point measures that may allow for comparisons across trials. This chapter will review current treatment options, upcoming promising medications, and some of the hurdles in advancing the field forward.

Role of central vagal 5-HT3 receptors in gastrointestinal physiology and pathophysiology

Vagal neurocircuits are vitally important in the co-ordination and modulation of GI reflexes and homeostatic functions. 5-hydroxytryptamine (5-HT; serotonin) is critically important in the regulation of several of these autonomic gastrointestinal (GI) functions including motility, secretion and visceral sensitivity. While several 5-HT receptors are involved in these physiological responses, the ligand-gated 5-HT3 receptor appears intimately involved in gut-brain signaling, particularly via the afferent (sensory) vagus nerve. 5-HT is released from enterochromaffin cells in response to mechanical or chemical stimulation of the GI tract which leads to activation of 5-HT3 receptors on the terminals of vagal afferents. 5-HT3 receptors are also present on the soma of vagal afferent neurons, including GI vagal afferent neurons, where they can be activated by circulating 5-HT. The central terminals of vagal afferents also exhibit 5-HT3 receptors that function to increase glutamatergic synaptic transmission to second order neurons of the nucleus tractus solitarius within the brainstem. While activation of central brainstem 5-HT3 receptors modulates visceral functions, it is still unclear whether central vagal neurons, i.e., nucleus of the tractus solitarius (NTS) and dorsal motor nucleus of the vagus (DMV) neurons themselves also display functional 5-HT3 receptors. Thus, activation of 5-HT3 receptors may modulate the excitability and activity of gastrointestinal vagal afferents at multiple sites and may be involved in several physiological and pathophysiological conditions, including distention- and chemical-evoked vagal reflexes, nausea, and vomiting, as well as visceral hypersensitivity.

Emerging Pharmacologic Therapies for Constipation-predominant Irritable Bowel Syndrome and Chronic Constipation

Irritable bowel syndrome with constipation and chronic functional constipation are common digestive disorders that negatively impact quality of life and account for billions of dollars in health care costs. Related to the heterogeneity of pathogenesis that underlie these disorders and the failure of symptoms to reliably predict underlying pathophysiology, traditional therapies provide relief to only a subset of affected individuals. The evidence surrounding new and emerging pharmacologic treatments, which include both luminally and systemically acting drugs, is discussed here. These include agents such as lubiprostone, bile acid modulations, guanylate cyclase-C receptor agonists, serotonin receptor modulators and herbal therapies.

Novel partial 5HT3 agonist pumosetrag reduces acid reflux events in uninvestigated GERD patients after a standard refluxogenic meal: a randomized, double-blind, placebo-controlled pharmacodynamic study

BACKGROUND

Low basal lower esophageal sphincter (LES) pressure and transient LES relaxations are major causes of gastroesophageal reflux disease (GERD). Pumosetrag, a novel selective partial 5HT3 receptor agonist, showed a promising effect on reducing reflux events in health. We aimed to evaluate the effect of pumosetrag on changes in reflux episodes, lower esophageal sphincter pressure (LESP), and specific symptoms in patients with GERD receiving a refluxogenic meal.

METHODS

Patients with GERD, who developed heartburn and/or regurgitation after ingestion of a refluxogenic meal, were randomized to 1 of 3 dose levels of pumosetrag (0.2, 0.5, or 0.8 mg) or placebo. Before and after 7 days of treatment, patients underwent manometry, intraesophageal multichannel, intraluminal impedance and pH after a standard refluxogenic meal.

KEY RESULTS

A total of 223 patients with GERD [125 (56%) women, mean (SD) age = 36 (12) years] were enrolled. No overall treatment effects were detected for the total number of reflux episodes (acidic and weakly acidic) (p > 0.5); however, significant treatment effects (p < 0.05) on the number of acid reflux episodes were observed with lower values on pumosetrag 0.2 mg (10.8 ± 1.1), 0.5 mg (9.5 ± 1.1), and 0.8 mg (9.9 ± 1.1) compared with placebo (13.3 ± 1.1). Significant treatment effects (p < 0.05) were also observed for the percentage of time pH was <4, with less time for pumosetrag at 0.5 mg (10%) and 0.8 mg (10%) compared with placebo (16%).

CONCLUSIONS & INFERENCES

In GERD, the partial 5HT3 agonist pumosetrag significantly reduced the rate of acid reflux events but did not result in a significant change in LESP or symptomatic improvement over a 1-week treatment period.

Effects of 5-HT2B, 5-HT3 and 5-HT4 receptor antagonists on gastrointestinal motor activity in dogs

AIM: To study the effects of 5-hydroxytryptamine (5-HT) receptor antagonists on normal colonic motor activity in conscious dogs.

METHODS: Colonic motor activity was recorded using a strain gauge force transducer in 5 dogs before and after 5-HT2B, 5-HT3 and 5-HT4 receptor antagonist administration. The force transducers were implanted on the serosal surfaces of the gastric antrum, terminal ileum, ileocecal sphincter and colon. Test materials or vehicle alone was administered as an intravenous bolus injection during a quiescent period of the whole colon in the interdigestive state. The effects of these receptor antagonists on normal gastrointestinal motor activity were analyzed.

RESULTS: 5-HT2B, 5-HT3 and 5-HT4 receptor antagonists had no contractile effect on the fasting canine terminal ileum. The 5-HT3 and 5-HT4 receptor antagonists inhibited phase III of the interdigestive motor complex of the antrum and significantly inhibited colonic motor activity. In the proximal colon, the inhibitory effect was dose dependent. Dose dependency, however, was not observed in the distal colon. The 5-HT2B receptor antagonist had no contractile effect on normal colonic motor activity.

CONCLUSION: The 5-HT3 and 5-HT4 receptor antagonists inhibited normal colonic motor activity. The 5-HT2B receptor antagonist had no contractile effect on normal colonic motor activity.

Designing a dynamic dissolution method: a review of instrumental options and corresponding physiology of stomach and small intestine

Development of new pharmaceutical compounds and dosage forms often requires in vitro dissolution testing with the closest similarity to the human gastrointestinal (GI) tract. To create such conditions, one needs a suitable dissolution apparatus and the appropriate data on the human GI physiology. This review discusses technological approaches applicable in biorelevant dissolutions as well as the physiology of stomach and small intestine in both fasted and fed state, that is, volumes of contents, transit times for water/food and various solid oral dosage forms, pH, osmolality, surface tension, buffer capacity, and concentrations of bile salts, phospholipids, enzymes, and Ca(2+) ions. The information is aimed to provide clear suggestions on how these conditions should be set in a dynamic biorelevant dissolution test.

Effects of pregnane glycosides on food intake depend on stimulation of the melanocortin pathway and BDNF in an animal model

Pregnane glycosides appear to modulate food intake by possibly affecting the hypothalamic feeding circuits; however, the mechanisms of the appetite-regulating effect of pregnane glycosides remain obscure. Here, we show that pregnane glycoside-enriched extracts from swamp milkweed Asclepias incarnata at 25-100 mg/kg daily attenuated food intake (up to 47.1 ± 8.5% less than controls) and body weight gain in rats (10% for males and 9% for females, respectively) by activating melanocortin signaling and inhibiting gastric emptying. The major milkweed pregnane glycoside, ikemagenin, exerted its appetite-regulating effect by decreasing levels of agouti-related protein (0.6-fold) but not NPY satiety peptides. Ikemagenin treatment also increased secretion of brain-derived neurotropic factor (BDNF) downstream of melanocortin receptors in the hypothalamus (1.4-fold) and in the C6 rat glioma cell culture in vitro (up to 6-fold). These results support the multimodal effects of pregnane glycosides on feeding regulation, which depends on the activity of the melanocortin signaling pathway and BDNF.

Glucose-dependent trafficking of 5-HT3 receptors in rat gastrointestinal vagal afferent neurons

BACKGROUND

Intestinal glucose induces gastric relaxation via vagally mediated sensory-motor reflexes. Glucose can alter the activity of gastrointestinal (GI) vagal afferent (sensory) neurons directly, via closure of ATP-sensitive potassium channels, and indirectly, via the release of 5-hydroxytryptamine (5-HT) from mucosal enteroendocrine cells. We hypothesized that glucose may also be able to modulate the ability of GI vagal afferent neurons to respond to the released 5-HT, via regulation of neuronal 5-HT(3) receptors.

METHODS

Whole-cell patch clamp recordings were made from acutely dissociated GI-projecting vagal afferent neurons exposed to equiosmolar Krebs' solution containing different concentrations of d-glucose (1.25-20 mmol L(-1)) and the response to picospritz application of 5-HT assessed. The distribution of 5-HT(3) receptors in neurons exposed to different glucose concentrations was also assessed immunohistochemically.

KEY RESULTS

Increasing or decreasing extracellular d-glucose concentration increased or decreased, respectively, the 5-HT-induced inward current and the proportion of 5-HT(3) receptors associated with the neuronal membrane. These responses were blocked by the Golgi-disrupting agent Brefeldin-A (5 μmol L(-1)) suggesting involvement of a protein-trafficking pathway. Furthermore, l-glucose did not mimic the response of d-glucose implying that metabolic events downstream of neuronal glucose uptake are required to observe the modulation of 5-HT(3) receptor mediated responses.

CONCLUSIONS & INFERENCES

These results suggest that, in addition to inducing the release of 5-HT from enterochromaffin cells, glucose may also increase the ability of GI vagal sensory neurons to respond to the released 5-HT, providing a means by which the vagal afferent signal can be amplified or prolonged.

Influence of the 5-HT3 receptor antagonist ondansetron on gastric sensorimotor function and nutrient tolerance in healthy volunteers

BACKGROUND

Serotonin is believed to be involved in the regulation of the gastric accommodation reflex in man however which receptor subtype(s) are involved remains to be elucidated.

METHODS

Eleven healthy subjects (nine men, age 19-30) underwent a gastric barostat and a drinking test after treatment with either placebo or ondansetron (8 mg intravenously). During the barostat protocol an intragastric flaccid bag was stepwise distended (2 mmHg increments 2 min) to determine gastric compliance and sensitivity to distention. Subsequently, the pressure level was set at intra-abdominal pressure +2 mmHg while volume was followed before and after administration of a liquid meal (200 mL; 300 kcal). During the drink test volunteers drank at a rate of 15 mL min(-1) until maximal satiation. Results (mean ± SEM) were compared using t-tests and mixed model analysis.

KEY RESULTS

Gastric compliance was not significantly altered by ondansetron (51.5 ± 5.6 vs 49.2 ± 5.2 mL mmHg(-1)), neither were the pressure thresholds for first perception or discomfort. Ondansetron treatment did not affect basal gastric tone (173 ± 14 vs 156 ± 12 mL), neither did it affect the amplitude of the meal-induced relaxation (160 ± 52 vs 131 ± 43 mL) or the maximum volume increase after the meal (264 ± 54 mL vs 234 ± 51 mL). During the drinking test the amount of liquid meal ingested at maximum satiation was significantly increased by ondansetron (784 ± 74 vs 907 ± 64 mL, P < 0.05).

CONCLUSIONS & INFERENCES

These data suggest that 5-HT acting at 5-HT(3) receptors is not involved in the control of gastric sensorimotor function, but contributes to the regulation of hunger and satiation in man.

Assessment of gastrointestinal motor functions by MRI: a comprehensive review

BACKGROUND

Magnetic resonance imaging (MRI) is a useful technique for evaluating gastrointestinal (GI) motor functions because it provides multi-planar imaging capability, high imaging speed, good spatial resolution and excellent soft tissue contrast. Moreover, multiple parameters of GI function can be assessed non-invasively during a single study.

PURPOSE

This critical review of the literature discusses the strengths and limitations of MRI for evaluating GI motor functions.

Classification and functions of enteroendocrine cells of the lower gastrointestinal tract

With over thirty different hormones identified as being produced in the gastrointestinal (GI) tract, the gut has been described as 'the largest endocrine organ in the body' (Ann. Oncol., 12, 2003, S63). The classification of these hormones and the cells that produce them, the enteroendocrine cells (EECs), has provided the foundation for digestive physiology. Furthermore, alterations in the composition and function of EEC may influence digestive physiology and thereby associate with GI pathologies. Whilst there is a rapidly increasing body of data on the role and function of EEC in the upper GI tract, there is a less clear-cut understanding of the function of EEC in the lower GI. Nonetheless, their presence and diversity are indicative of a role. This review focuses on the EECs of the lower GI where new evidence also suggests a possible relationship with the development and progression of primary adenocarcinoma.

Emerging pharmacological therapies for the irritable bowel syndrome

The irritable bowel syndrome (IBS) is a symptom-based disorder defined by the presence of abdominal pain and altered bowel habits. Clinical presentations of IBS are diverse, with some patients reporting diarrhea, some constipation, and others a mixture of both. Like the varied clinical phenotypes, the pathogenesis of IBS is also diverse. IBS is not a single disease entity, but rather likely consists of several different disease states. This fact has important implications for the choices and efficacy of IBS treatment. This article reviews the IBS drugs that have reached phase II or III clinical trials.

The effects of acute citalopram dosing on gastric motor function and nutrient tolerance in healthy volunteers

BACKGROUND

It is unclear whether endogenous serotonin release is involved in the regulation of gastric motility and food intake.

AIM

To study the effect of acute administration of the selective serotonin reuptake inhibitor citalopram on gastric motor function in man.

METHODS

Nineteen healthy volunteers underwent a gastric barostat, gastric emptying and/or a drinking test after dosing with either placebo or citalopram (20 mg intravenously). In the barostat protocol, a flaccid bag was introduced in the stomach and inflated at intra-abdominal pressure +2 mmHg, volume was recorded before and after administration of a liquid meal (300 kcal). Gastric emptying for solids and liquids was simultaneously assessed using the ¹⁴C-octanoic acid/¹³C-glycine breath test. During the drink test, volunteers drank at a rate of 15 mL/min until maximal satiation. Citalopram was compared with placebo using t-tests and mixed model analysis.

RESULTS

Citalopram induced a significant preprandial gastric relaxation (volume increase of 154 ± 55 mL vs. -38 ± 33 mL after placebo dosing; P < 0.05), whereas the postprandial volume increase was significantly decreased after citalopram treatment (F₁₂.₈₀ = 4.78, P < 0.0001; maximum volume increase was 304 ± 40 vs. 201 ± 54 mL after placebo and citalopram treatment respectively). Citalopram enhanced solid (123 ± 17 vs. 77 ± 6 min, P < 0.05) but not liquid emptying (62 ± 6 vs. 57 ± 4 min). Satiation scores during the drink test were lower after citalopram (F₁₉.₁₅₃ = 2.02, P = 0.01; volunteers drank 998 ± 129 vs. 765 ± 79 mL after citalopram and placebo treatment respectively).

CONCLUSION

The observed effects indicate a role for serotonin in the control of gastric motility and food intake.

Influence of acute tryptophan depletion on gastric sensorimotor function in humans

Peripheral serotonin (5-hydrodytryptamine; 5-HT) is involved in the regulation of gastrointestinal motility and sensation, whereas centrally it plays a role in mood regulation. A dysfunctional serotonergic system may provide a plausible link between functional dyspepsia symptoms and its high psychosocial comorbidity such as anxiety and depression. The aim of this study was to evaluate the effect of decreased 5-HT synthesis by acute tryptophan depletion (ATD) on gastric sensorimotor function and nutrient tolerance, anxiety scores, and gastrointestinal mucosal 5-HT concentrations in healthy volunteers. All subjects were studied under a control condition and during ATD. Gastric sensorimotor function and nutrient tolerance were assessed using a barostat (n = 16, mean age 28.8 ± 1.4 yr) and a satiety drinking test (n = 13, mean age 27.3 ± 1.4 yr). Anxiety during the barostat was evaluated using State-Trait Anxiety Inventory (STAI) questionnaire. 5-HT concentrations were measured in fundic and duodenal mucosal biopsies by means of ELISA and immunohistochemistry. ATD significantly decreased plasma tryptophan levels compared with control in every experiment. ATD did not affect gastric sensitivity and compliance but decreased the sensation of nausea during balloon distension (AUC: 17.4 ± 4.3 vs. 11.4 ± 3.4 mm·mmHg, P = 0.030). ATD enhanced the postprandial volume increase (ANOVA, P < 0.05), but this was not accompanied by augmented nutrient tolerance (848 ± 110 vs. 837 ± 99 ml, nonsignificant). ATD had no effect on STAI state anxiety scores. No evidence was found for an effect on the number of enterochromaffin cells, but ATD reduced 5-HT levels in the duodenal mucosa. ATD alters gastric postprandial motor function and distension-induced nausea. These findings confirm involvement of 5-HT in the control of gastric accommodation and sensitivity.

Novel serotonin type 3 receptor partial agonists for the potential treatment of irritable bowel syndrome

Serotonin type 3 (5-HT(3)) receptor partial agonists are being targeted as potential new drugs for the treatment of irritable bowel syndrome (IBS). Two new chemical series bearing indazole and indole cores have exhibited nanomolar binding affinity for the h5-HT(3)A receptor. A range of partial agonist activities in HEK cells heterologously expressing the h5-HT(3)A receptor were measured for the indazole series. Excellent 5-HT(3) receptor selectivity, favorable in vitro metabolic stability and CYP inhibition properties, and good oral in vivo potency in the murine von Bezold-Jarisch reflex model is exemplified thereby indicating the series to have potential utility as improved IBS agents.

Physiological parameters for oral delivery and in vitro testing

Pharmaceutical solid oral dosage forms must undergo dissolution in the intestinal fluids of the gastrointestinal tract before they can be absorbed and reach the systemic circulation. Therefore, dissolution is a critical part of the drug-delivery process. The rate and extent of drug dissolution and absorption depend on the characteristics of the active ingredient as well as properties of the dosage form. Just as importantly, characteristics of the physiological environment such as buffer species, pH, bile salts, gastric emptying rate, intestinal motility, and hydrodynamics can significantly impact dissolution and absorption. While significant progress has been made since 1970 when the first compendial dissolution test was introduced (USP apparatus 1), current dissolution testing does not take full advantage of the extensive physiologic information that is available. For quality control purposes, where the question is one of lot-to-lot consistency in performance, using nonphysiologic test conditions that match drug and dosage form properties with practical dissolution media and apparatus may be appropriate. However, where in vitro-in vivo correlations are desired, it is logical to consider and utilize knowledge of the in vivo condition. This publication critically reviews the literature that is relevant to oral human drug delivery. Physiologically relevant information must serve as a basis for the design of dissolution test methods and systems that are more representative of the human condition. As in vitro methods advance in their physiological relevance, better in vitro-in vivo correlations will be possible. This will, in turn, lead to in vitro systems that can be utilized to more effectively design dosage forms that have improved and more consistent oral bioperformance.

Effects of a 5-HT(3) antagonist, ondansetron, on fasting and postprandial small bowel water content assessed by magnetic resonance imaging

BACKGROUND

5-HT(3) antagonists have been shown to be effective in relieving the symptoms of irritable bowel syndrome with diarrhoea (IBS-D). Using a recently validated magnetic resonance imaging (MRI) method, we have demonstrated reduced fasting small bowel water content (SBWC) in IBS-D associated with accelerated small bowel transit. We hypothesized that slowing of transit with ondansetron would lead to an increase in SBWC by inhibiting fasting motility.

AIM

To assess the effects of ondansetron compared with placebo in healthy volunteers on SBWC and motility in two different groups of subjects, one studied using MRI and another using manometry.

METHODS

Healthy volunteers were given either a placebo or ondansetron on the day prior to and on the study day. Sixteen volunteers underwent baseline fasting and postprandial MRI scans for 270 min. In a second study, a separate group of n = 18 volunteers were intubated and overnight migrating motor complex (MMC) recorded. Baseline MRI scans were carried out after the tube was removed.

RESULTS

Fasting SBWC was markedly increased by ondansetron (P < 0.0007). Ondansetron reduced the overall antroduodenal Motility Index (P < 0.04). The subjects who were intubated had significantly lower fasting SBWC (P < 0.0002) compared with the group of subjects who were not intubated.

CONCLUSIONS

The 5-HT(3) receptor antagonism increased fasting small bowel water. This was associated with reduced fasting antroduodenal Motility Index which may explain the clinical benefit of such drugs.

Pharmacological management of constipation

The approach of this review is to give a pragmatic approach to using laxatives, based on a combination of what is known about mechanism of action and the available literature on evidence.

Current and novel therapeutic options for irritable bowel syndrome management

Irritable bowel syndrome is a functional gastrointestinal disorder affecting up to 3-15% of the general population in western countries. It is characterised by unexplained abdominal pain, discomfort, and bloating in association with altered bowel habits. The pathophysiology of irritable bowel syndrome is multifactorial involving disturbances of the brain-gut axis. The pathophysiology provides the rationale for pharmacotherapy: abnormal gastrointestinal motor functions, visceral hypersensitivity, psychosocial factors, autonomic dysfunction, and mucosal immune activation. Understanding the mechanisms, and their mediators or modulators including neurotransmitters and receptors have led to several therapeutic approaches including agents acting on the serotonin receptor or serotonin transporter system, antidepressants, novel selective anticholinergics, alpha-adrenergic agonists, opioid agents, cholecystokinin-antagonists, neurokinin-antagonists, somatostatin receptor agonists, corticotropin releasing factor antagonists, chloride channel activators, guanylate cyclase-c agonists, melatonin, atypical benzodiazepines, antibiotics, immune modulators and probiotics. The mechanisms and current evidence regarding efficacy of these agents are reviewed.

Challenges to the therapeutic pipeline for irritable bowel syndrome: end points and regulatory hurdles

Recent advances in our understanding of basic neuroenteric mechanisms and the role of effectors and transmitters in the brain-gut axis have provided opportunities to develop new therapeutic agents for irritable bowel syndrome (IBS). Furthermore, human pharmacodynamic studies utilizing transit, colonic, or rectal sensitivity and brain imaging have been useful in determining therapeutic efficacy (particularly for drugs that act on motor function). This review provides an overview of medications that have not yet been approved for treatment of patients with IBS yet have shown promise in phase IIB trials. These include drugs that act on the serotonin receptor and transporter system: antidepressants, norepinephrine reuptake inhibitors, opioids, cholecystokinin antagonists, neurokinin-antagonists, chloride channel activators, guanylate cyclase C agonists, atypical benzodiazepines, probiotics, and antibiotics. The changing landscape in the regulatory approval process has impacted the development of IBS drugs. Guidance documents from regulatory agencies in Europe and the United States have focused on patients' reported outcomes and associated quality of life. After a decade of experience with different end points that have generated some data on psychometric validation and unprecedented information about responsiveness of the binary or global end points to drug therapy, it is necessary to pursue further validation studies before or during pivotal phase IIB or III trials. The hope of providing relief to patients should galvanize all parties to achieve these goals.

Glucose increases synaptic transmission from vagal afferent central nerve terminals via modulation of 5-HT3 receptors

Acute hyperglycemia has profound effects on vagally mediated gastrointestinal functions. We have reported recently that the release of glutamate from the central terminals of vagal afferent neurons is correlated directly with the extracellular glucose concentration. The present study was designed to test the hypothesis that 5-HT(3) receptors present on vagal afferent nerve terminals are involved in this glucose-dependent modulation of glutamatergic synaptic transmission. Whole-cell patch-clamp recordings were made from neurons of the nucleus tractus solitarius (NTS) in thin rat brainstem slices. Spontaneous and evoked glutamate release was decreased in a concentration-dependent manner by the 5-HT(3) receptor selective antagonist, ondansetron. Alterations in the extracellular glucose concentration induced parallel shifts in the ondansetron-mediated inhibition of glutamate release. The changes in excitatory synaptic transmission induced by extracellular glucose concentration were mimicked by the serotonin uptake inhibitor, fenfluramine. These data suggest that glucose alters excitatory synaptic transmission within the rat brainstem via actions on tonically active 5-HT(3) receptors, and the number of 5-HT(3) receptors on vagal afferent nerve terminals is positively correlated with the extracellular glucose concentration. These data indicate that the 5-HT(3) receptors present on synaptic connections between vagal afferent nerve terminals and NTS neurons are a strong candidate for consideration as one of the sites where glucose acts to modulate vagovagal reflexes.

Serotonin and GI clinical disorders

Serotonin is widely distributed throughout the gut within both the enteric nerves and enterochromaffin (EC) cells. EC cells are located in the gut mucosa with maximal numbers in the duodenum and rectum where they act as signal transducers, responding to pressure and luminal substances both bacterial and dietary. Activation leads to serotonin release which acts on a range of receptors on mucosal afferent and myenteric interneurones to initiate secretomotor reflexes. These cause nausea and vomiting as well as intestinal secretion, propulsion and if pronounced, diarrhoea. Inflammation in animal models acts via T lymphocytes to increase EC cell numbers and mucosal serotonin (5-HT) content while inflammatory cytokines decrease serotonin transporter (SERT) function. Inflammation due to coeliac disease and following gastrointestinal infection increases mucosal 5-HT availability by a combination of increased EC cells and depressed SERT. Irritable bowel syndrome (IBS) developing after gastrointestinal infection and IBS with diarrhoea is associated with excess 5-HT. The associated diarrhoeal symptoms respond well to 5-HT(3) receptor antagonists. These drugs also inhibit the nausea and vomiting occurring in patients undergoing chemotherapy which cause a marked increase in release of 5-HT as well as other mediators. Other conditions including IBS-C and constipation may have inadequate 5-HT release and benefit from both 5-HT(3) and 5-HT(4) receptor agonists.

Serotonergic signalling in the stomach and duodenum of patients with gastroparesis

Serotonin (5-HT) is involved in the regulation of motoric and sensory functions of the upper gastrointestinal tract. The aim of the current study was to determine whether serotonergic signalling is altered in patients with idiopathic gastroparesis. Mucosal biopsy specimens were collected from the duodenum, antrum and fundus of 11 patients with idiopathic gastroparesis and 11 healthy controls. Neuroendocrine cells, specifically 5-HT producing cells, were counted after immunohistochemistry, and non-neuronal mRNA expression levels of tryptophan hydroxylase (TPH)-1, 5-HT transport protein (SERT), 5-HT3 and 5-HT4 receptor were quantified by real time RT-PCR. The number of 5-HT producing cells was comparable between patients and controls. No difference in expression of TPH-1 (rate limiting enzyme in 5-HT biosynthetic pathway) and SERT (responsible for 5-HT uptake) was found between patients and controls (P > 0.05). In the duodenum, the expression of the 5-HT3 receptor subunits and the 5-HT4 receptor was comparable between both groups. However, the 5-HT4(c) splice variant was expressed more abundantly in healthy controls compared to patients (P = 0.015). This study suggests that the delayed gastric emptying and upper abdominal symptoms in idiopathic gastroparesis do not result from altered mucosal 5-HT biosynthetic and uptake capacity.

Serotonin pharmacology in the gastrointestinal tract: a review

Serotonin (5-hydroxytryptamine or 5-HT) plays a critical physiological role in the regulation of gastrointestinal (GI) function. 5-HT dysfunction may also be involved in the pathophysiology of a number of functional GI disorders, such as chronic constipation, irritable bowel syndrome and functional dyspepsia. This article describes the role of 5-HT in the enteric nervous system (ENS) of the mammalian GI tract and the receptors with which it interacts. Existing serotonergic therapies that have proven effective in the treatment of GI functional disorders and the potential of drugs currently in development are also highlighted. Advances in our understanding of the physiological and pathophysiological roles of 5-HT in the ENS and the identification of selective receptor ligands bodes well for the future development of more efficacious therapies for patients with functional GI disorders.

A novel partial 5HT3 agonist DDP733 after a standard refluxogenic meal reduces reflux events: a randomized, double-blind, placebo-controlled pharmacodynamic study

BACKGROUND

DDP733, a selective partial 5HT(3) receptor agonist, increases lower oesophageal sphincter pressure in experimental animal models. However, its effect on gastro-oesophageal reflux or lower oesophageal sphincter pressure in humans remains unknown.

AIM

To evaluate the effect of DDP733 on reflux episodes in healthy volunteers receiving a refluxogenic meal.

METHODS

A randomized, double-blind, placebo-controlled cross-over study evaluated the pharmacodynamic effects of DDP733 (0.5, 0.8 and 1.4 mg). Healthy subjects underwent oesophageal manometry and intra-oesophageal multichannel intraluminal impedance and pH after a refluxogenic meal.

RESULTS

DDP733 0.5 mg significantly (P = 0.013) reduced the rate of reflux episodes after a refluxogenic meal from 10 (+/-2.2) on placebo to 6 (+/-1.2) on drug over a 2-h period. DDP733 0.8 and 1.4 mg had no significant effect on reducing the number of reflux episodes. Significant differences in resting lower oesophageal sphincter pressure and the proportion of time pH was <4 (placebo minus drug) after a refluxogenic meal were not observed. No serious adverse events were reported.

CONCLUSION

In healthy subjects, the partial 5HT(3) agonist DDP733 at a dose of 0.5 mg significantly reduces the rate of reflux events, but did not result in a significant change in lower oesophageal sphincter pressure at 1 h postdosing.

Effects of ondansetron on gastric tone and motility changes induced by a prolonged intraduodenal infusion of nutrients. Results of a placebo-controlled study

Our aim was to study the 5-HT3 antagonist, ondansetron, on gastric motility changes induced by duodenal infusion of nutrients. First, the effects of a 2-hr intraduodenal infusion (IDI) of a caloric diet on antral motility were assessed. Second, a crossed-over placebo-controlled study assessed 3-day oral intake of ondansetron (8 mg bid) on gastric motility changes induced by the IDI. During the IDI, antral numbers of waves (NW) as area under curve (AUC) were lower than fasting values. After infusion, antral NW and AUC increased to return to basal values. The antral area increased slightly shortly after the start of the IDI, then remained stable. When subjects received ondansetron, the only significant motor effect was a higher antral NW and AUC during the first 30 min of the IDI (P < 0.05). After the end of the IDI, the AUC and NW increased in both the distal and the proximal antrum. The increase was lower by ondansetron in the proximal antrum. Proximal stomach relaxation induced was not influenced by ondansetron. In conclusion, an IDI of nutrients decreased antral motility, increased the antral area, and promoted fundic relaxation. This inhibitory effect was rapidly reversible. Ondansetron induced only minor motility changes in the antrum and had no effect on fundic relaxation promoted by IDI.

Mechanisms of serotonergic agents for treatment of gastrointestinal motility and functional bowel disorders

Most of the body's serotonin is released in the gut where it plays an important role in the control of gastrointestinal (GI) motility, sensitivity and muscle tone by activating different receptor subtypes. This review focuses on the known effects of selective serotonin reuptake inhibitor and serotonin receptor agonists and antagonists on the sensorimotor function of the GI tract and describes the therapeutic potential of these actions for GI motility and functional bowel disorders.

Regional differences in expression of TPH-1, SERT, 5-HT(3) and 5-HT(4) receptors in the human stomach and duodenum

The aim of this study was to increase the understanding of the role of serotonergic signalling in normal gastroduodenal function at a molecular level. Mucosal biopsy specimens were collected from the fundus, antrum and duodenum of 11 healthy subjects. Serotonin (5-HT)-positive cells were counted and the mRNA levels of tryptophan hydroxylase (TPH), serotonin transporter (SERT), 5-HT(4) receptor and 5-HT(3) receptor subunits were quantified by real-time reverse transcription polymerase chain reaction. The number of 5-HT-positive cells was larger in the duodenum compared with the stomach (P < 0.001). Serotonin transport protein expression was 19-fold higher in the duodenum compared with the antrum and 457-fold higher compared with the fundus (P < 0.001). Tryptophan hydroxylase-1 expression was lower in the duodenum compared with the antrum and fundus (regional differences -2.3 and -3.6, respectively). The 5-HT(4) receptor and the 5-HT(3C) and 5-HT(3E) receptor subunits were more abundantly expressed in duodenum compared with the stomach (P < 0.001). The larger number of 5-HT-positive cells, the higher expression of 5-HT(3) and 5-HT(4) receptors, and in particularly the higher uptake capacity of 5-HT in the duodenum, point out to a more prominent role of serotonergic signalling at the mucosal level in the duodenum compared with the stomach.

The serotonin signaling system: from basic understanding to drug development for functional GI disorders

Serotonin is an important gastrointestinal signaling molecule. It is a paracrine messenger utilized by enterochromaffin (EC) cells, which function as sensory transducers. Serotonin activates intrinsic and extrinsic primary afferent neurons to, respectively, initiate peristaltic and secretory reflexes and to transmit information to the central nervous system. Serotonin is also a neurotransmitter utilized by a system of long descending myenteric interneurons. Serotonin is synthesized through the actions of 2 different tryptophan hydroxylases, TpH1 and TpH2, which are found, respectively, in EC cells and neurons. Serotonin is inactivated by the serotonin reuptake transporter (SERT)-mediated uptake into enterocytes or neurons. The presence of many serotonin receptor subtypes enables selective drugs to be designed to therapeutically modulate gastrointestinal motility, secretion, and sensation. Current examples include tegaserod, a 5-HT(4) partial agonist, which has been approved for treatment of irritable bowel syndrome (IBS) with constipation in women and for chronic constipation in men and women. The 5-HT(3) antagonists, granisetron and ondansetron, are useful in combating the nausea associated with cancer chemotherapy, and alosetron is employed in the treatment of IBS with diarrhea. Serotonergic signaling abnormalities have also been putatively implicated in the pathogenesis of functional bowel diseases. Other compounds, for which efficacy has not been rigorously established, but which may have value, include tricyclic antidepressants and serotonin selective reuptake inhibitors to combat IBS, and 5-HT(1) agonists, which enhance gastric accommodation, to treat functional dyspepsia. The initial success encountered with serotonergic agents holds promise for newer and more potent insights and therapies of brain-gut disorders.

Role of motility in chronic diarrhoea

Patients complaining of 'chronic diarrhoea' usually mean the passage of loose, urgent stools. Chronic diarrhoea is a feature of malabsorption; it may also be seen in the 'dumping syndrome' which follows gastric surgery, small intestinal bacterial overgrowth, bile salt malabsorption and in malabsorption of simple sugars including most commonly lactose, fructose and sorbitol. Excessively rapid entry of chyme into the small or large intestine generates propulsive motor patterns leading to accelerated transit. Inflammation is associated with decreased normal mixing motor patterns but increased propulsive motility including high amplitude propagated contractions (HAPCs). Evidence for abnormal small intestinal motility in the diarrhoea associated with irritable bowel syndrome (IBS) is conflicting and any difference appears small. Increased colonic HAPCs with increased propulsion is seen in IBS with diarrhoea (IBS-D). Stress-induced colonic motility is increased in IBS-D with hyper-responsiveness to corticotrophin releasing factor (CRF). Long-lasting increases in mucosal serotonin availability may contribute to the chronic diarrhoea seen in IBS-D and coeliac disease. Treatments for abnormal motility in chronic diarrhoea include those designed to correct specific underlying abnormalities including octreotide, antibiotics, colestyramine, specific food avoidance and anti-inflammatory agents. There are also treatments aimed primarily at altering motility directly including opiates, 5HT3 receptor antagonists and amitriptyline.

Irritable bowel syndrome: recent and novel therapeutic approaches

Irritable bowel syndrome (IBS) is a highly prevalent functional gastrointestinal disorder affecting up to 3-15% of the general population in Western countries. It is characterised by unexplained abdominal pain, discomfort and bloating in association with altered bowel habits. The pathophysiology of IBS is considered to be multifactorial, involving disturbances of the brain-gut-axis: IBS has been associated with abnormal gastrointestinal motor functions, visceral hypersensitivity, psychosocial factors, autonomic dysfunction and mucosal inflammation. Traditional IBS therapy is mainly symptom oriented and often unsatisfactory. Hence, there is a need for new treatment strategies. Increasing knowledge of brain-gut physiology, mechanisms, and neurotransmitters and receptors involved in gastrointestinal motor and sensory function have led to the development of several new therapeutic approaches. This article provides a systematic overview of recently approved or novel medications that show promise for the treatment of IBS; classification is based on the physiological systems targeted by the medication. The article includes agents acting on the serotonin receptor or serotonin transporter system, novel selective anticholinergics, alpha-adrenergic agonists, opioid agents, cholecystokinin antagonists, neurokinin antagonists, somatostatin receptor agonists, neurotrophin-3, corticotropin releasing factor antagonists, chloride channel activators, guanylate cyclase-c agonists, melatonin and atypical benzodiazepines. Finally, the role of probiotics and antibacterials in the treatment of IBS is summarised.

The 5-HT4 antagonist R216073 does not affect gastric motor and sensory function in patients with functional dyspepsia

BACKGROUND

Serotonin and the 5-HT4 receptor play an important role in gastrointestinal motor and sensory functions. While 5-HT4 agonists are known for their prokinetics properties, the effect of 5-HT4 antagonists on upper gastrointestinal functions is largely unknown.

AIM

To assess the effect of a 5-HT4 receptor antagonist (R216073) on gastric relaxation and visceral sensitivity in patients with functional dyspepsia. Secondly, the influence of a functional polymorphism in the gene encoding the serotonin transport protein on drug response was determined.

METHODS

A double-blind, randomized, placebo-controlled, two-period crossover study was performed in 20 functional dyspepsia patients. The effect of a single dose of 2,000 mg R216073 on gastric relaxation and sensitivity was tested using three-dimensional ultrasonography and a nutrient drinktest.

RESULTS

R216073 did not affect partial gastric volumes or upper abdominal sensations scored during three-dimensional ultrasonography (P > 0.05). The maximum tolerated volume or upper abdominal sensations induced by the drinktest were not affected by R216073 (P > 0.05). The serotonin transport protein promoter polymorphism was not associated with any of the end-points of the study.

CONCLUSIONS

A single dose of R216073 had no effect on fundic relaxation, drinking capacity, or upper abdominal symptoms in patients with functional dyspepsia.

Emerging drugs for irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most common chronic gastrointestinal disorders, yet its pathophysiology is incompletely understood and pharmacological treatments remain unsatisfactory. Current therapeutic choices include a range of drugs aimed at normalising bowel habits, reducing pain or treating comorbid psychological symptoms. However, this individual symptom-targeted approach remains unsatisfactory in terms of global symptom relief and patient satisfaction. In the last decade, further characterisation of IBS pathophysiology has provided new and exciting targets at different levels of the brain-gut axis for the development of several candidate drugs. Advances in clinical trial design will help to evaluate these compounds in different IBS patient populations.

Abnormalities of serotonin metabolism and their relation to symptoms in untreated celiac disease

BACKGROUND AND AIMS

Serotonin (5-hydroxytryptamine [5-HT]) is a key modulator of gut function that in excess causes nausea, vomiting, and diarrhea. We recently showed that patients with post-infective irritable bowel syndrome have increased postprandial release of 5-HT associated with low-grade T-cell mediated inflammation. Celiac disease is another common disease in which a T-cell enteropathy is associated with increased mucosal 5-HT levels. Our aim was to determine how this inflammatory lesion influenced 5-HT bioavailability and how changes in 5-HT related to the symptoms of nausea, vomiting, and diarrhea seen in untreated celiac patients.

METHODS

Fasting plasma and platelet 5-HT and postprandial plasma 5-HT levels were measured after a high-carbohydrate meal in celiac patients (n = 18) and healthy controls (n = 18) using high-pressure liquid chromatography. Dyspepsia was assessed during the postprandial period using a questionnaire. Finally, we compared the histology and mucosal 5-HT levels in duodenal biopsy specimens from celiac patients and controls.

RESULTS

Celiac patients had increased 5-HT-containing enterochromaffin cell numbers and significantly higher peak plasma 5-HT levels (P = .0002), postprandial area under the curve (P = .0006), and platelet 5-HT stores (P = .031) than controls. Peak 5-HT levels correlated significantly with postprandial dyspepsia scores (P = .005). Celiac patients had higher duodenal 5-HT levels (P = .007) than controls.

CONCLUSIONS

Celiac disease is associated with increased mucosal 5-HT content and enhanced 5-HT release from the upper small bowel, which correlates with postprandial dyspepsia. Serotonin excess may mediate dyspeptic symptoms in untreated celiac disease.

Effect of MKC-733, a 5-HT receptor partial agonist, on bowel motility and symptoms in subjects with constipation: an exploratory study

BACKGROUND

MKC-733, a 5-HT(3) receptor partial agonist, is a novel enteroprokinetic compound.

OBJECTIVE

The aim of this study was to explore the effects of MKC-733 on bowel motility and symptoms in a small group of subjects with constipation. Tolerability was also examined.

METHODS

The study was conducted in a single-blind and dose-escalation manner on 14 male and female subjects with constipation aged 22-67 years. After a 1 week run-in period, subjects were treated with placebo (b.i.d.) for 1 week, and 0.2 and 0.5 mg of MKC-733 (b.i.d.) for 2 weeks sequentially. Geometric mean and per cent elimination of surrogate markers of bowel motility were measured by a radio-opaque marker technique at the end of each treatment period. They were analysed on the whole group and subgroups with low (n = 6) and high (n = 8) bowel motility based upon the geometric mean value after placebo treatment. Subjects kept diaries of their bowel habits and gastrointestinal symptoms.

RESULTS

Percent elimination increased after treatment with 0.5 mg MKC-733 compared with placebo treatment in the whole group (70.4 +/- 33.5% vs. 47.1 +/- 36.6%, mean +/- SD, P < 0.05). In the low bowel motility group, both geometric mean and percent elimination increased after treatment with 0.5 mg MKC-733 compared with placebo (7.1 +/- 0.9 vs. 5.9 +/- 0.5, P < 0.05; 60.0 +/- 35.8% vs. 13.3 +/- 19.4%, P < 0.05). Stool frequency increased after the first-week treatment with MKC-733 compared with placebo (P < 0.05). Numbers of sensation of incomplete evacuation and gastrointestinal symptoms decreased to half and less after the treatment with MKC-733. No serious adverse effect was noted.

CONCLUSION

Multiple doses of 0.5 mg MKC-733 improve bowel motility, which was clearly demonstrated in the subjects with decreased bowel motility. MKC-733 at the doses studied might be effective in increasing stool frequency and reduce gastrointestinal symptoms related to constipation. MKC-733 was well tolerated. Further studies will be needed to clarify efficacy and safety of MKC-733 on a larger population.