GSK962040: a small molecule, selective motilin receptor agonist, effective as a stimulant of human and rabbit gastrointestinal motility

Structural basis for motilin and erythromycin recognition by motilin receptor

Motilin is an endogenous peptide hormone almost exclusively expressed in the human gastrointestinal (GI) tract. It activates the motilin receptor (MTLR), a class A G protein-coupled receptor (GPCR), and stimulates GI motility. To our knowledge, MTLR is the first GPCR reported to be activated by macrolide antibiotics, such as erythromycin. It has attracted extensive attention as a potential drug target for GI disorders. We report two structures of G_q-coupled human MTLR bound to motilin and erythromycin. Our structures reveal the recognition mechanism of both ligands and explain the specificity of motilin and ghrelin, a related gut peptide hormone, for their respective receptors. These structures also provide the basis for understanding the different recognition modes of erythromycin by MTLR and ribosome. These findings provide a framework for understanding the physiological regulation of MTLR and guiding drug design targeting MTLR for the treatment of GI motility disorders.

Deglycosylated Azithromycin Targets Transgelin to Enhance Intestinal Smooth Muscle Function

Azithromycin (AZM) has been widely used as an antibacterial drug for many years. It has also been used to treat delayed gastric emptying. However, it exerts several side effects. We found that deglycosylated AZM (Deg-AZM or CP0119), an AZM metabolite, is a positively strong intestinal agonist that may result in the intestinal mobility experienced by patients after AZM administration. We confirmed that Deg-AZM can function strongly on intestinal peristalsis and identified transgelin as its potential molecular target. Furthermore, our pharmacological studies showed that the binding of Deg-AZM to transgelin enhanced the contractility of intestinal smooth muscle cells by facilitating the assembly of actin filaments into tight bundles and stress fibers. Specifically, Deg-AZM promoted intestinal peristaltic activity in wild-type mice but not in transgelin (-/-) mice. Moreover, Deg-AZM did not exert antibacterial activity and did not disrupt intestinal flora. Thus, Deg-AZM may become a potential drug for slow-transit constipation treatment.

Motilin: from gastric motility stimulation to hunger signalling

After the discovery of motilin in 1972, motilin and the motilin receptor were studied intensely for their role in the control of gastrointestinal motility and as targets for treating hypomotility disorders. The genetic revolution - with the use of knockout models - sparked novel insights into the role of multiple peptides but contributed to a decline in interest in motilin, as this peptide and its receptor exist only as pseudogenes in rodents. The past 5 years have seen a major surge in interest in motilin, as a series of studies have shown its relevance in the control of hunger and regulation of food intake in humans in both health and disease. Luminal stimuli, such as bitter tastants, have been identified as modulators of motilin release, with effects on hunger and food intake. The current state of knowledge and potential implications for therapy are summarized in this Review.

Gastroparesis: pharmacotherapy and cardiac risk

BACKGROUND

Gastroparesis is characterized by abnormal gastric motility and delayed emptying with symptoms of early satiety, postprandial fullness, bloating, nausea, vomiting and abdominal pain. Pharmacological discovery has been lagging because potential drugs often are associated with abnormalities of electrical conduction of the myocardium due to interaction with cardiac ion channels leading to limited pharmaceutical options for development of new drugs.

OBJECTIVE

Addresses the safety of drugs for gastroparesis in terms of cardiotoxicity related to the clinical use of prokinetics and antiemetics.

METHODS

Survey of QT drugs List and review of current literature.

RESULTS

Many prokinetic drugs are associated with cardiac adverse events and manifest as prolongation of ventricular repolarization, i.e., QT-interval prolongation of the electrocardiogram. This disturbance may develop into a potentially fatal polymorphic ventricular tachyarrhythmia; Torsade de Pointes. Co-administration of prokinetics with other drugs affecting the repolarization process, pharmacokinetic interactions leading to increased blood levels, or the presence of clinical risk factors could further increase the risk for cardiac arrhythmias.

CONCLUSIONS

It is important that clinicians managing gastroparesis are aware of the arrhythmogenic potential of drugs used clinically and risk factors that contribute to QT prolongation to safeguard patients at risk for drug-induced cardiac arrhythmia.

Manometric evaluation of the motilin receptor agonist camicinal (GSK962040) in humans

BACKGROUND

The gut hormone motilin stimulates gastrointestinal motility by inducing gastric phase III of the migrating motor complex (MMC) and enhancing the rate of gastric emptying. Camicinal (GSK962040), a small molecule motilin receptor agonist, has been shown to increase gastrointestinal motility.

METHODS

In this proof of concept study the effects of camicinal on MMC activity, esophageal and gastric pH was evaluated in eight healthy volunteers as a secondary endpoint. Doses of 50 and 150 mg were compared to placebo for a period of 24 hours in a double-blinded randomized crossover trial.

KEY RESULTS

The 50 mg dose (n=4) of camicinal had no significant impact on gastroduodenal manometry or pH parameters. A single dose of 150 mg (n=4) induced a gastric phase III after 0:34 h (0:25-0:58), which was significantly faster compared to placebo (18:15 h (4:32-22:16); P=.03). Moreover, the high dose significantly increased the occurrence of gastric phase III contractions compared to placebo (12% vs 39%; P=.0003). This increase in gastric phase III contractions during a period of 24 hour was due to an increased occurrence of gastric phases III during the daytime (5% vs 50%; P=.0001). The same dose however did not affect small bowel manometry parameters or esophageal and gastric pH.

CONCLUSIONS AND INFERENCES

Considering its stimulating effect on the MMC and gastric emptying, camicinal is an attractive candidate for the treatment of gastroparesis and gastroesophageal reflux disease. This trial was registered at clinicaltrials.gov as NCT00562848.

Prokinetics in the Management of Functional Gastrointestinal Disorders

PURPOSE OF REVIEW

The goal of this review is to review the current status of prokinetics and to place it in historical context. Impaired motility and thus propulsion have long been thought to play important roles in the pathogenesis of a number of gastrointestinal disorders including gastroesophageal reflux disease (GERD), gastroparesis, chronic idiopathic pseudo-obstruction, and constipation. Historically, disordered motility was also thought to contribute to a number of functional gastrointestinal disorders such as functional dyspepsia (FD) and irritable bowel syndrome (IBS).

RECENT FINDINGS

As we learn more of the pathophysiology of FD, IBS, GERD, constipation, and gastroparesis, the limitations of a therapeutic strategy based on the stimulation of motility (i.e., the use of a prokinetic) have become apparent and the disappointments of the past explained. The development of prokinetic drugs has also been hampered by the non-selective nature of many of the agents studied to date which resulted in some unexpected side effects. There is still an unmet need for an effective and safe prokinetic, but drug development in this area must be mindful of the challenges of the area and the need for selectivity for a given target receptor.

Investigational drug therapies for the treatment of gastroparesis

INTRODUCTION

Gastroparesis is defined by nausea, vomiting, pain, early satiety and bloating, and characterized by delayed gastric emptying without obvious structural abnormalities. Metoclopramide is widely used, increasing gastric emptying and inhibiting nausea and vomiting. Other drugs are available in certain countries and some are used 'off-label' because they increase gastric emptying or inhibit emesis. However, correlation between gastroparesis symptoms and rates of gastric emptying is poor. For anti-emetic drugs, dose-ranging and Phase III trials in gastroparesis are lacking. Areas covered: Gastric motility may still be disordered, leading to nausea, even though gastric emptying is unchanged. One hypothesis is that interstitial cells of Cajal (ICC) are damaged by diabetes leading to gastric dysrhythmia and nausea. Novel approaches to treatment of nausea also include the use of ghrelin receptor agonists, highlighting a link between appetite and nausea. Expert opinion: There is an urgent need to diversify away from historical drug targets. In particular, there is a need to control nausea by regulating ICC functions and/or by facilitating appetite via ghrelin receptor agonists. It is also important to note that different upper gastrointestinal disorders (gastroparesis, chronic unexplained nausea and vomiting, functional dyspepsia) are difficult to distinguish apart, suggesting wider therapeutic opportunity.

The effect of camicinal (GSK962040), a motilin agonist, on gastric emptying and glucose absorption in feed-intolerant critically ill patients: a randomized, blinded, placebo-controlled, clinical trial

Background

The promotility agents currently available to treat gastroparesis and feed intolerance in the critically ill are limited by adverse effects. The aim of this study was to assess the pharmacodynamic effects and pharmacokinetics of single doses of the novel gastric promotility agent motilin agonist camicinal (GSK962040) in critically ill feed-intolerant patients.

Methods

A prospective, randomized, double-blind, parallel-group, placebo-controlled, study was performed in mechanically ventilated feed-intolerant patients [median age 55 (19–84), 73 % male, APACHE II score 18 (5–37) with a gastric residual volume ≥200 mL]. Gastric emptying and glucose absorption were measured both pre- and post-treatment after intragastric administration of 50 mg (n = 15) camicinal and placebo (n = 8) using the ¹³C-octanoic acid breath test (BTt_1/2), acetaminophen concentrations, and 3-O-methyl glucose concentrations respectively.

Results

Following 50 mg enteral camicinal, there was a trend to accelerated gastric emptying [adjusted geometric means: pre-treatment BTt_1/2 117 minutes vs. post- treatment 76 minutes; 95 % confidence intervals (CI; 0.39, 1.08) and increased glucose absorption (AUC_240min pre-treatment: 28.63 mmol.min/L vs. post-treatment: 71.63 mmol.min/L; 95 % CI (1.68, 3.72)]. When two patients who did not have detectable plasma concentrations of camicinal were excluded from analysis, camicinal accelerated gastric emptying (adjusted geometric means: pre-treatment BTt_1/2 121 minutes vs. post-treatment 65 minutes 95 % CI (0.32, 0.91) and increased glucose absorption (AUC_240min pre-treatment: 33.04 mmol.min/L vs. post-treatment: 74.59 mmol.min/L; 95 % CI (1.478, 3.449). In those patients receiving placebo gastric emptying was similar pre- and post-treatment.

Conclusions

When absorbed, a single enteral dose of camicinal (50 mg) accelerates gastric emptying and increases glucose absorption in feed-intolerant critically ill patients.

Trial registration

The study protocol was registered with the US NIH clinicaltrials.gov on 23 December 2009 (Identifier NCT01039805).

Functional Dyspepsia and Gastroparesis

BACKGROUND

Upper gastrointestinal disorders typically present with common symptoms. The most relevant non-mucosal diseases are gastroparesis, functional dyspepsia and rumination syndrome. The literature pertaining to these 3 conditions was reviewed.

KEY MESSAGES

Gastroparesis is characterized by delayed gastric emptying in the absence of mechanical obstruction of the stomach. The cardinal symptoms include postprandial fullness (early satiety), nausea, vomiting and bloating. The most frequently encountered causes of these symptoms are mechanical obstruction (pyloric stenosis), iatrogenic disease, gastroparesis, functional dyspepsia, cyclical vomiting and rumination syndrome. The most common causes of gastroparesis are neuropathic disorders such as diabetes, idiopathic, post-vagotomy and scleroderma among myopathic disorders. Principles of management of gastroparesis include exclusion of mechanical obstruction with imaging and iatrogenic causes with careful medication and past surgical history. Prokinetics and anti-emetics are the mainstays of treatment. Functional dyspepsia is characterized by the same symptoms as gastroparesis; in addition to delayed gastric emptying, pathophysiological abnormalities include accelerated gastric emptying, impaired gastric accommodation and gastric or duodenal hypersensitivity to distension and nutrients. Novel treatments include tricyclic antidepressants in patients with normal gastric emptying, acotiamide (acetyl cholinesterase inhibitor) and 5-HT1A receptor agonists such as buspirone. Rumination syndrome is characterized by repetitive regurgitation of gastric contents occurring within minutes after a meal. Episodes often persist for 1-2 h after the meal, and the regurgitant consists of partially digested food that is recognizable in its taste. Regurgitation is typically effortless or preceded by a sensation of belching. This has been summarized as a 'meal in, meal out, day in, day out' behavior for weeks or months, differentiating rumination from gastroparesis. Patients often have a background of psychological disorder or a prior eating disorder. Treatment is based on behavioral modification.

CONCLUSION

Precise identification of the cause and pathophysiology of upper gastrointestinal symptoms is essential for optimal management.

Model-based dietary optimization for late-stage, levodopa-treated, Parkinson's disease patients

Levodopa has been the gold standard for Parkinson’s disease treatment for more than 40 years. Its bioavailability is hindered by dietary amino acids, leading to fluctuations in the motor response particularly in late-stage (stage 3 and 4 on Hoehn and Yahr scale) patients. The routine dietary intervention consists of low-protein (<0.8 g/kg) diets or the redistribution of daily protein allowance to the last meal. Computational modeling was used to examine the fluctuation of gastrointestinal levodopa absorption under consideration of the diet by (i) identifying the group of patients that could benefit from dietary interventions, (ii) comparing existing diet recommendations for their impact on levodopa bioavailability, and (iii) suggesting a mechanism-based dietary intervention. We developed a multiscale computational model consisting of an ordinary differential equations-based advanced compartmentalized absorption and transit (ACAT) gut model and metabolic genome-scale small intestine epithelial cell model. We used this model to investigate complex spatiotemporal relationship between dietary amino acids and levodopa absorption. Our model predicted an improvement in bioavailability, as reflected by blood concentrations of levodopa with protein redistribution diet by 34% compared with a low-protein diet and by 11% compared with the ante cibum (a.c.) administration. These results are consistent with the reported better outcome in late-stage patients. A systematic analysis of the effect of different amino acids in the diet suggested that a serine-rich diet could improve the bioavailability by 22% compared with the a.c. administration. In addition, the slower gastric emptying rate in PD patients exacerbates the loss of levodopa due to competition. Optimizing dietary recommendations in quantity, composition, and intake time holds the promise to improve levodopa efficiency and patient’s quality of life based on highly detailed, mechanistic models of gut physiology endowed with improved extrapolative properties, thus paving the way for precision medical treatment.

The pharmacodynamics, safety and pharmacokinetics of single doses of the motilin agonist, camicinal, in type 1 diabetes mellitus with slow gastric emptying

BACKGROUND AND PURPOSE

Here we have investigated the pharmacokinetics, pharmacodynamics and safety of single doses of camicinal in type 1 diabetes mellitus (T1DM) patients with a history of slow gastric emptying with symptoms consistent with gastroparesis.

EXPERIMENTAL APPROACH

In a randomized, double-blind, placebo-controlled, incomplete block, three-period, two-centre crossover study, patients received oral administration of placebo and two of the three possible doses of camicinal (25, 50 or 125 mg). Gastric emptying ((13) C-octanoic acid breath test), pharmacokinetics and safety were primary outcomes.

KEY RESULTS

Nine of the 10 patients enrolled completed the study. Gastric half-emptying time decreased by -95 min (95% CI: -156.8, -34.2) after a single dose of camicinal 125 mg compared with placebo (52 vs. 147 min, P < 0.05), representing a 65% improvement. A decrease of the gastric half-emptying time compared with placebo (approximately 39 min) was observed with camicinal 25 and 50 mg, representing a 27% reduction for both doses (not statistically significant). A positive exposure-response relationship was demonstrated across all doses. The effects of camicinal on gastric half-emptying time were not influenced by fasting glucose levels. Single doses up to 125 mg were well tolerated. Camicinal was well absorbed, exhibiting linear and approximately dose-proportional pharmacokinetic characteristics and a clear exposure-response relationship with gastric emptying.

CONCLUSIONS AND IMPLICATIONS

Camicinal significantly accelerated gastric emptying of solids in T1DM patients following administration of a single oral dose. Camicinal was well tolerated and exhibited similar pharmacokinetic characteristics in diabetic patients to those previously reported in healthy volunteers.

Pharmacological, Pharmacokinetic, and Pharmacogenomic Aspects of Functional Gastrointestinal Disorders

This article reviews medications commonly used for the treatment of patients with functional gastrointestinal disorders. Specifically, we review the animal models that have been validated for the study of drug effects on sensation and motility; the preclinical pharmacology, pharmacokinetics, and toxicology usually required for introduction of new drugs; the biomarkers that are validated for studies of sensation and motility endpoints with experimental medications in humans; the pharmacogenomics applied to these medications and their relevance to the FGIDs; and the pharmacology of agents that are applied or have potential for the treatment of FGIDs, including psychopharmacologic drugs.

Early investigational therapeutics for gastrointestinal motility disorders: from animal studies to Phase II trials

INTRODUCTION

The most common gastrointestinal disorders that include evidence of dysmotility include: gastroparesis, the lower functional gastrointestinal disorders associated with altered bowel function (such as chronic [functional] diarrhea, chronic idiopathic constipation) and opioid-induced constipation. These conditions, which are grouped as gastrointestinal motility and functional disorders, are characterized by abnormal motor, sensory or secretory functions that alter bowel function and result in a significant disease burden, since currently available treatments do not completely alleviate symptoms. New drugs are being developed for these disorders, targeting mechanisms involved in the pathophysiology of these diseases, specifically, motor function, intestinal secretion and bile acid modulation.

AREAS COVERED

The article provides a brief overview of motility disorders and the drugs approved and currently available for these indications. It also provides an evaluation of the efficacy, safety and possible mechanisms of the drugs currently under investigation for the treatment of gastroparesis, chronic diarrhea, chronic idiopathic constipation and opioid-induced constipation, based on animal to Phase II studies. Medications with complete Phase III trials are excluded from this discussion.

EXPERT OPINION

Treatment of gastrointestinal motility disorders requires the understanding of the pathophysiological mechanisms, biomarkers to identify subgroups of these disorders and robust pharmacological studies from animal to Phase II studies. These are prerequisites for the development of efficacious medications and individualizing therapy in order to enhance the treatment of these patients.

Ghrelin and motilin receptors as drug targets for gastrointestinal disorders

The gastrointestinal tract is the major source of the related hormones ghrelin and motilin, which act on structurally similar G protein-coupled receptors. Nevertheless, selective receptor agonists are available. The primary roles of endogenous ghrelin and motilin in the digestive system are to increase appetite or hedonic eating (ghrelin) and initiate phase III of gastric migrating myoelectric complexes (motilin). Ghrelin and motilin also both inhibit nausea. In clinical trials, the motilin receptor agonist camicinal increased gastric emptying, but at lower doses reduced gastroparesis symptoms and improved appetite. Ghrelin receptor agonists have been trialled for the treatment of diabetic gastroparesis because of their ability to increase gastric emptying, but with mixed results; however, relamorelin, a ghrelin agonist, reduced nausea and vomiting in patients with this disorder. Treatment of postoperative ileus with a ghrelin receptor agonist proved unsuccessful. Centrally penetrant ghrelin receptor agonists stimulate defecation in animals and humans, although ghrelin itself does not seem to control colorectal function. Thus, the most promising uses of motilin receptor agonists are the treatment of gastroparesis or conditions with slow gastric emptying, and ghrelin receptor agonists hold potential for the reduction of nausea and vomiting, and the treatment of constipation. Therapeutic, gastrointestinal roles for receptor antagonists or inverse agonists have not been identified.

The effects of camicinal, a novel motilin agonist, on gastro-esophageal function in healthy humans-a randomized placebo controlled trial

BACKGROUND

A proportion of patients with foregut dysmotility fail to respond to standard interventions. Motilin agonists may be beneficial in this group. We aimed to determine the effect of camicinal, a novel motilin agonist, on gastrointestinal physiology in healthy volunteers.

METHODS

Healthy male subjects were randomly assigned to receive a single dose of 125 mg camicinal or placebo in a double-blind cross-over design. Esophageal function and reflux indices were assessed using high-resolution manometry (pre and 1.5-h post dose) and 24-h ambulatory multichannel intraluminal impedance/pH. After a standardized meal, subjects ingested a wireless motility capsule from which compartmental transit times and motility indices were derived. Subjects were restudied with the alternate intervention after 7 days.

KEY RESULTS

The study subjects (12 male, mean age 47.4 years, range 22-55) tolerated the drug well, except one who exhibited mild abdominal pain on both placebo and camicinal. In comparison to placebo, gastric emptying time (GET) was accelerated following camicinal (-115.4 min, 95% confidence interval -194.4, -36.4, p = 0.009). No effect was demonstrable on esophageal function, small bowel, colonic, or whole bowel transit times and motility indices. With camicinal, as part of a post hoc analysis, there was a trend association between the percentage reduction in GET and total number of acidic reflux events (r = 0.56, p = 0.09).

CONCLUSIONS & INFERENCES

Camicinal decreases GET and was generally well-tolerated. In health, the direct effects of camicinal are on accelerating GET with a potential secondary benefit of reducing reflux events, which warrant further exploration in patient cohorts.

Drug-drug interactions in pharmacologic management of gastroparesis

BACKGROUND

Gastroparesis is a disorder characterized by delayed gastric emptying due to chronic abnormal gastric motility. The treatment of the disease often entails the co-administration of several classes of pharmacological agents. These agents may be metabolized via the same pathway. Inhibition or induction of a shared metabolic pathway leads to change in the systemic levels of prescribed drugs, possibly leading to undesired clinical outcomes.

PURPOSE

This review discusses different pharmacological treatment for gastroparesis patients and describes the potential for drug-drug interactions (DDIs) in some of the combinations that are currently used. Prokinetic agents such as metoclopramide and domperidone are the cornerstone in treatment of gastroparesis. Antiemetic agents such as promethazine and ondansetron are frequently administered to gastroparesis patients to reduce nausea and vomiting. Gastroparesis is prevalent in diabetic patients and therefore antidiabetic agents are also prescribed. Many of these co-administered drugs are metabolized via common drug metabolizing enzymes and this can trigger potential DDIs. The scientific literature was reviewed from the years 1975-2014 for original research articles and reviews that evaluated DDIs in gastroparesis. Many commonly prescribed combinations were predicted to cause potential DDIs in gastroparesis patients. This review will help inform about potential hazardous combinations. This information will hopefully lead to less adverse effects and more successful gastroparesis management.

Current advances in treatment of gastroparesis

INTRODUCTION

Gastroparesis is a syndrome defined by delayed gastric emptying in the absence of mechanical obstruction. Gastroparesis has significant symptomatology and negative impacts on the patient's quality of life.

AREAS COVERED

This article reviews current treatment options for gastroparesis, recent advances in treatment and future directions that treatment may head. Current options are broadly divided into prokinetics and symptom modulators. Within each group, current modalities as well as recent advances are discussed according to agent mechanism of action. Lastly, findings regarding the cellular pathophysiology involved in gastroparesis will be briefly reviewed along with their implications for future treatments.

EXPERT OPINION

The numerous motor functions and neural inputs that control gastric motility are complex and not fully understood. Our lack of understanding of its pathophysiology has led to treatment options which are empirical, palliative and often ineffective. Newly intensified interest in the cellular pathophysiology behind gastroparesis provides promise for a new era of treatments. Identification of common cellular changes in gastroparesis has provided targets for treatment that may allow us to one day better treat the symptoms of gastroparesis related to its underlying pathophysiology. This is the future of gastroparesis therapy.

The antibiotic azithromycin is a motilin receptor agonist in human stomach: comparison with erythromycin

BACKGROUND AND PURPOSE

The antibiotic azithromycin is a suggested alternative to erythromycin for treating patients with delayed gastric emptying. However, although hypothesized to activate motilin receptors, supportive evidence is unavailable. This was investigated using recombinant and naturally expressed motilin receptors in human stomach, comparing azithromycin with erythromycin.

EXPERIMENTAL APPROACH

[(125)I]-motilin binding and calcium flux experiments were conducted using human recombinant motilin receptors in CHO cells. Neuromuscular activities were studied using circular muscle of human gastric antrum, after electrical field stimulation (EFS) of intrinsic nerves.

KEY RESULTS

Azithromycin (1-100 μM) and erythromycin (3-30 μM) concentration-dependently displaced [(125)I]-motilin binding to the motilin receptor (52 ± 7 and 58 ± 18% displacement at 100 and 30 μM respectively). Azithromycin, erythromycin and motilin concentration-dependently caused short-lived increases in intracellular [Ca(2+)] in cells expressing the motilin receptor. EC50 values were, respectively, 2.9, 0.92 and 0.036 μM (n = 3 each); and maximal activities were similar. In human stomach, EFS evoked cholinergically mediated contractions, attenuated by simultaneous nitrergic activation. Azithromycin and erythromycin lactobionate (30-300 μM each) facilitated these contractions (apparent E(max) values of 2007 ± 396 and 1924 ± 1375%, n = 3-4 each concentration, respectively). These actions were slow in onset and faded slowly. The higher concentrations also evoked short-lived muscle contraction. Contractions to a submaximally effective concentration of carbachol were unaffected by either drug.

CONCLUSIONS AND IMPLICATIONS

Azithromcyin activates human recombinant motilin receptors in therapeutically relevant concentrations, similar to erythromycin. In humans, gastric antrum azithromycin caused long-lasting facilitation of cholinergic activity. These actions explain the gastric prokinetic activity of azithromycin.

Differential expression of motilin receptor in various parts of gastrointestinal tract in dogs

Objectives. The presence of motilin receptor in the GI tract of different animal species has been verified. However, the quantitation of motilin receptor expression in different regions of the GI tract remains unclear. The aim of this study was to investigate the expression of motilin receptor in the GI tract and semiquantitatively compare the expression difference in different GI regions in dogs. Methods. Antrum, duodenum, jejunum, ileum, proximal colon, middle colon, and distal colon were obtained from various parts of the GI tract of six sacrificed dogs. The distribution of motilin receptor was determined by immunohistochemistry. The expression levels of motilin receptor mRNA in different regions were measured by RT-PCR. Results. Motilin receptor was expressed throughout the GI tract in dogs. Multiple comparisons of the mean motilin receptor mRNA expression among various regions were significant (P < 0.05). Motilin receptor mRNA was extensively expressed in duodenum, followed by ileum, jejunum, proximal colon, antrum, middle colon, and distal colon. Immunohistochemistry revealed that motilin receptor immunoreactivity was observed only in the enteric nervous system. Conclusion. Motilin receptor is expressed differentially along the GI tract in dogs. The significantly high expression of motilin receptor mRNA is found in the duodenum.

Prokinetics in gastroparesis

Prokinetic agents are medications that enhance coordinated gastrointestinal motility and transit of content in the gastrointestinal tract, mainly by amplifying and coordinating the gastrointestinal muscular contractions. In addition to dietary therapy, prokinetic therapy should be considered as a means to improve gastric emptying and symptoms of gastroparesis, balancing benefits and risks of treatment. In the United States, metoclopramide remains the first-line prokinetic therapy, because it is the only approved medication for gastroparesis. Newer agents are being developed for the management of gastroparesis. This article provides detailed information about prokinetic agents for the treatment of gastroparesis.

Management of gastroparesis: beyond basics

OPINION STATEMENT

Gastroparesis is defined as the presence of delayed gastric emptying in the absence of mechanical obstruction, with a variety of upper gastrointestinal symptoms. Although measurement of gastric emptying is necessary for the diagnostic labeling, this finding has little impact in terms of explaining the symptom pattern and determining the prognosis and therapeutic approach. Clinical management is based on ruling out of mechanical causes and serum electrolyte imbalances, followed by initial medical treatment with a gastroprokinetic agent in most cases. However, the evidence that these drugs provide substantial symptomatic benefit is weak. Recent attempts to establish efficacy with newer prokinetics, including serotonin-4, motilin, and ghrelin receptor agonists, have seen few successes, but a new group of agents is under evaluation. More recently, also, no benefit was found with treatment with a tricyclic antidepressant in idiopathic gastroparesis. In refractory cases, especially when there is weight loss, invasive therapeutics such as insertion of feeding tubes, intrapyloric injection of botulinum toxin, implantable gastric electrical stimulation, or surgical (partial) gastrectomy are occasionally considered, but there is little evidence of efficacy, and these are not devoid of potentially major complications. Gastroparesis is likely to remain a challenging condition in the clinic in the foreseeable future.

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

BACKGROUND

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

METHODS

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

KEY RESULTS

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

CONCLUSIONS & INFERENCES

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

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

BACKGROUND

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

METHODS

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

KEY RESULTS

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

CONCLUSIONS & INFERENCES

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

Therapeutic options for functional dyspepsia

Functional dyspepsia (FD) is defined by the presence of chronic gastroduodenal symptoms in the absence of organic or systemic disease that explains them, and a negative upper endoscopy. According to the Rome III consensus, FD can be subdivided into PDS (postprandial distress syndrome) and EPS (epigastric pain syndrome). In patients with mild symptoms, reassurance and lifestyle adjustments are often sufficient. Pharmacotherapy, for those with more severe or persisting symptoms, includes the use of proton pump inhibitors (PPIs), prokinetics and psychotropic agents. In those diagnosed with Helicobacter pylori infection, eradication is recommended, although the symptom impact is often limited. PPIs are the initial therapy of choice for EPS, while prokinetics can be used in PDS. Tricyclic antidepressants can be used for refractory symptoms, especially in EPS. Emerging therapies include the novel gastroprokinetic agent acotiamide for PDS, fundus-relaxing 5-HT(1A) agonists in patients with PDS/early satiation and mirtazapine for FD with weight loss.

Gastroparesis: from concepts to management

While the symptoms of gastroparesis are common, an accurate diagnosis is based on a combination of those symptoms with a documented delay in gastric emptying. Typical symptoms include nausea, vomiting, early satiety, postprandial fullness, bloating, and abdominal discomfort. Patients with gastroparesis face many diagnostic and therapeutic challenges. The most common origins of gastroparesis are idiopathic causes and diabetes mellitus. The increased use of certain medications in medicine today, including opiates and drugs with anticholinergic properties, can alter gastrointestinal functions and mimic symptoms of gastroparesis. Accordingly, alternative explanations for symptoms and altered gastrointestinal function need to be considered. Numerous clinical sequelae, including weight loss and severe protein-calorie malnutrition, may be seen in advanced stages of gastroparesis. This article provides an overview of gut sensorimotor function to help the reader better understand the clinical presentation of patients with dyspepsia and those who may have accompanying delayed gastric emptying that meets criteria for gastroparesis. Techniques available for diagnosing motor dysfunction and the principles of gastroparesis management are reviewed. Nutrition recommendations and a review of pharmacologic agents, nonpharmacologic techniques, and novel treatment modalities are provided.

Translational neuropharmacology: the use of human isolated gastrointestinal tissues

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

Ghrelin and motilin receptor agonists: time to introduce bias into drug design

Ghrelin and motilin receptor agonists increase gastric motility and are attractive drug targets. However, 14 years after the receptors were described (18-24 years since ligands became available) the inactivity of the ghrelin agonist TZP-102 in patients with gastroparesis joins the list of unsuccessful motilin agonists. Fundamental questions must be asked. Pustovit et al., have now shown that the ghrelin agonist ulimorelin evokes prolonged increases in rat colorectal propulsion yet responses to other ghrelin agonists fade. Similarly, different motilin agonists induce short- or long-lasting effects in a cell-dependent manner. Together, these and other data create the hypothesis that the receptors can be induced to preferentially signal ('biased agonism') via particular pathways to evoke different responses with therapeutic advantages/disadvantages. Biased agonism has been demonstrated for ghrelin. Are motilin agonists which cause long-lasting facilitation of human stomach cholinergic function (compared with motilin) biased agonists (e.g., camicinal, under development for patients with gastric hypo-motility)? For ghrelin, additional complications exist because the therapeutic aims/mechanisms of action are uncertain, making it difficult to select the best (biased) agonist. Will ghrelin agonists be useful treatments of nausea and/or as suggested by Pustovit et al., chronic constipation? How does ghrelin increase gastric motility? As gastroparesis symptoms poorly correlate with delayed gastric emptying (yet gastro-prokinetic drugs can provide relief: e.g., low-dose erythromycin), would low doses of ghrelin and motilin agonists relieve symptoms simply by restoring neuromuscular rhythm? These questions on design and functions need addressing if ghrelin and motilin agonists are to reach patients as drugs.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Motilin: towards a new understanding of the gastrointestinal neuropharmacology and therapeutic use of motilin receptor agonists

The gastrointestinal hormone motilin has been known about for >40 years, but after identification of its receptor and subsequent development of new tools and methods, a reappraisal of its actions is required. Firstly, it is important to note that motilin and ghrelin receptors are members of the same family (similar genomic organization, gastrointestinal distribution and abilities to stimulate gastrointestinal motility), yet each fails to recognize the ligand of the other; and whereas ghrelin and ghrelin receptors are widespread outside the gastrointestinal tract, motilin and its receptors are largely restricted to the gastrointestinal tract. Secondly, although some studies suggest motilin has activity in rodents, most do not, and receptor pseudogenes exist in rodents. Thirdly, motilin preferentially operates by facilitating enteric cholinergic activity rather than directly contracting the muscle, despite the relatively high expression of receptor immunoreactivity in muscle. This activity is ligand-dependent, with short-lasting actions of motilin contrasting with longer-lasting actions of the non-selective and selective motilin receptor agonists erythromycin and GSK962040. Finally, the use of erythromycin (also an antibiotic drug) to treat patients requiring acceleration of gastric emptying has led to concerns over safety and potential exacerbation of antibiotic resistance. Replacement motilin receptor agonists derived from erythromycin (motilides) have been unsuccessful. New, non-motilide, small molecule receptor agonists, designed to minimize self-desensitization, are now entering clinical trials for treating patients undergoing enteral feeding or with diabetic gastroparesis. Thus, for the translational pharmacologist, the study of motilin illustrates the need to avoid overreliance on artificial systems, on structural information and on animal studies.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

A ghrelin agonist fails to show benefit in patients with diabetic gastroparesis: let's not throw the baby out with the bath water

Ghrelin is the endogenous ligand for the growth hormone secretagogue-1a receptor and is a potential target for treatment of gastroparesis. This viewpoint assesses the potential role of ghrelin agonists in the treatment of gastroparesis through a review of the early phase, randomized, controlled trials of ghrelin agonists in patients with diabetes and, either, delayed gastric emptying at the time of the trial or symptoms at the time of the trial, and prior documentation of delayed gastric emptying of solids. Whereas recent experience with ghrelin agonists that have a macrocycle structure (TZP-101, TZP-102) has not confirmed earlier promising results, there is little evidence that ghrelin receptors downregulate with repeated treatment, in contrast to motilin receptors. Phase IIa clinical trials performed with a different agent (RM-131, which is a small molecule ghrelin agonist) suggest that, as a class, ghrelin agonists may be efficacious in stimulating gastric emptying. It is premature to dismiss ghrelin agonists as potential therapies for gastroparesis.

The ghrelin agonist RM-131 accelerates gastric emptying of solids and reduces symptoms in patients with type 1 diabetes mellitus

BACKGROUND & AIMS

RM-131, a synthetic ghrelin agonist, greatly accelerates gastric emptying of solids in patients with type 2 diabetes and delayed gastric emptying (DGE). We investigated the safety and effects of a single dose of RM-131 on gastric emptying and upper gastrointestinal (GI) symptoms in patients with type 1 diabetes and previously documented DGE.

METHODS

In a double-blind cross-over study, 10 patients with type 1 diabetes (age, 45.7 ± 4.4 y; body mass index, 24.1 ± 1.1 kg/m(2)) and previously documented DGE were assigned in random order to receive a single dose of RM-131 (100 μg, subcutaneously) or placebo. Thirty minutes later, they ate a radiolabeled solid-liquid meal containing EggBeaters (ConAgra Foods, Omaha, NE), and then underwent 4 hours of gastric emptying and 6 hours of colonic filling analyses by scintigraphy. Upper GI symptoms were assessed using a daily diary, gastroparesis cardinal symptom index (total GCSI-DD) and a combination of nausea, vomiting, fullness, and pain (NVFP) scores (each rated on a 0-5 scale).

RESULTS

At screening, participants' mean level of hemoglobin A1c was 9.1% ± 0.5%; their total GCSI-DD score was 1.66 ± 0.38 (median, 1.71), and their total NVFP score was 1.73 ± 0.39 (median, 1.9). The t1/2 of solid gastric emptying was 84.9 ± 31.6 minutes when subjects were given RM-131 and 118.7 ± 26.7 when they were given a placebo. The median difference (Δ)was 33.9 minutes (interquartile range [IQR] -12, -49), or -54.7% (IQR, -21%,-110%). RM-131 decreased gastric retention of solids at 1 hour (P = .005) and 2 hours (P = .019). Numeric differences in t1/2 for gastric emptying of liquids, solid gastric emptying lag time, and colonic filling at 6 hours were not significant. Total GCSI-DD scores were 0.79 on placebo (IQR, 0.75, 2.08) and 0.17 on RM-131 (IQR, 0.00, 0.67; P = .026); NVFP scores were lower on RM-131 (P = .041). There were no significant adverse effects.

CONCLUSIONS

RM-131 significantly accelerates gastric emptying of solids and reduces upper GI symptoms in patients with type 1 diabetes and documented DGE.

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

BACKGROUND AND PURPOSE

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

EXPERIMENTAL APPROACH

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

KEY RESULTS

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

CONCLUSIONS AND IMPLICATIONS

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

Diabetic gastroparesis: recent insights into pathophysiology and implications for management

Delayed gastric emptying affects a substantial proportion of patients with long-standing diabetes, and when associated with symptoms and/or disordered glycemic control, affects quality of life adversely. Important clinicopathological insights have recently been gained by the systematic analysis of gastric biopsies from patients with severe diabetic gastroparesis, which may stimulate the development of new therapies in the coming decade. Experience with prokinetic therapies and treatments, such as pyloric botulinum toxin injection and gastric electrical stimulation, has established that relief of symptoms does not correlate closely with acceleration of delayed gastric emptying, and that well-designed controlled trials are essential to determine the efficacy of emerging therapies.

Anxiolytic actions of motilin in the basolateral amygdala

Motilin is a 22-amino-acid gastrointestinal polypeptide that was first isolated from the porcine intestine. We identified that motilin receptor is highly expressed in GABAergic interneurons in the basolateral nucleus (BLA) of the amygdala, the structure of which is closely involved in assigning stress disorder and anxiety. However, little is known about the role of motilin in BLA neuronal circuits and the molecular mechanisms of stress-related anxiety. Whole-cell recordings from amygdala slices showed that motilin depolarized the interneurons and facilitated GABAergic transmission in the BLA, which is mimicked by the motilin receptor agonist, erythromycin. BLA local injection of erythromycin or motilin can reduce the anxiety-like behavior in mice after acute stress. Therefore, motilin is essential in regulating interneuron excitability and GABAergic transmission in BLA. Moreover, the anxiolytic actions of motilin can partly be explained by modulating the BLA neuronal circuits. The present data demonstrate the importance of motilin in anxiety and the development of motilin receptor non-peptide agonist as a clear target for the potential treatment of anxiety disorders.

Recent advances in the pathophysiology and treatment of gastroparesis

Gastroparesis is a clinical disorder characterized by upper gastrointestinal symptoms related with delayed gastric emptying of solids and liquids in the absence of mechanical obstruction. Diabetes mellitus has been the most common cause of gastroparesis and idiopathic gastroparesis also accounts for a third of all chronic cases. The most important mechanisms of gastroparesis, as understood to date, are loss of expression of neuronal nitric oxide synthase and loss of the interstitial cells of Cajal. However, the pathogenesis of gastroparesis is poorly understood. There have been several studies on specific molecules related to the pathogenesis of gastroparesis. Additionally, the Gastroparesis Clinical Research Consortium of the National Institutes of Health has achieved several promising results regarding the pathophysiology of gastroparesis. As the progress in the pathophysiology of gastroparesis has been made, a promising new drug therapy has been found. The pathophysiology and drug therapy of gastroparesis are focused in this review. Until now, the real-world medication options for treatment of gastroparesis are limited. However, it is expected to be substantially improved as the pathophysiology of gastroparesis is elucidated.

Anti-emetic and emetic effects of erythromycin in Suncus murinus: role of vagal nerve activation, gastric motility stimulation and motilin receptors

Paradoxically, erythromycin is associated with nausea when used as an antibiotic but at lower doses erythromycin activates motilin receptors and is used to treat delayed gastric emptying and nausea. The aim of this study was to characterise pro- and anti-emetic activity of erythromycin and investigate mechanisms of action. Japanese House musk shrews (Suncus murinus) were used. Erythromycin was administered alone or prior to induction of emesis with abnormal motion or subcutaneous nicotine (10mg/kg). The effects of erythromycin and motilin on vagal nerve activity and on cholinergically mediated contractions of the stomach (evoked by electrical field stimulation) were studied in vitro. The results showed that erythromycin (1 and 5mg/kg) reduced vomiting caused by abnormal motion (e.g., from 10.3 ± 1.8 to 4.0 ± 1.1 emetic episodes at 5mg/kg) or by nicotine (from 9.5 ± 2.0 to 3.1 ± 2.0 at 5mg/kg), increasing latency of onset to emesis; lower or higher doses had no effects. When administered alone, erythromycin 100mg/kg induced vomiting in two of four animals, whereas lower doses did not. In vitro, motilin (1, 100 nM) increased gastric vagal afferent activity without affecting jejunal afferent mesenteric nerve activity. Cholinergically mediated contractions of the stomach (prevented by tetrodotoxin 1 μM or atropine 1 μM, facilitated by l-NAME 300 μM) were facilitated by motilin (1-100 nM) and erythromycin (10-30 μM). In conclusion, low doses of erythromycin have anti-emetic activity. Potential mechanisms of action include increased gastric motility (overcoming gastric stasis) and/ or modulation of vagal nerve pathways involved in emesis, demonstrated by first-time direct recording of vagal activation by motilin.

Diabetic gastrointestinal autonomic neuropathy: current status and new achievements for everyday clinical practice

Gastrointestinal symptoms occur frequently among patients with diabetes mellitus and are associated with considerable morbidity. Diabetic gastrointestinal autonomic neuropathy represents a complex disorder with multifactorial pathogenesis, which is still not well understood. It appears to involve a spectrum of metabolic and cellular changes that affect gastrointestinal motor and sensory control. It may affect any organ in the digestive system. Clinical manifestations are often underestimated, and therefore autonomic neuropathy should be suspected in all diabetic patients with unexplained gastrointestinal symptoms. Advances in technology have now enabled assessment of gastrointestinal motor function. Moreover, novel pharmacological approaches, along with endoscopic and surgical treatment options, contribute to improved outcomes. This review summarises the progress achieved in diabetic gastrointestinal autonomic neuropathy during the last years, focusing on clinical issues of practical importance to the everyday clinician.

Motilin receptor neuropharmacology: revised understanding

Although motilin was identified >40 years ago as a gastrointestinal hormone capable of stimulating gastric emptying, the relatively recent availability of molecular tools and focus on its neuronal activities are now clarifying mechanisms of action. In rodents, only motilin receptor pseudogenes are identified. In human stomach, facilitation of enteric cholinergic activity is identified as the main mechanism by which gastric emptying is increased; some motilin agonists act in a prolonged manner, contrasting with motilin itself and with studies using recombinant receptors. As such, assays using recombinant receptors seem poor predictors of in vivo activity. High-throughput screening enabled selective motilin agonists to be identified, which together with enhanced understanding into neuromuscular actions of motilin, promises to deliver rational treatments of disorders with delayed gastric emptying.

The migrating motor complex: control mechanisms and its role in health and disease

The migrating motor complex (MMC) is a cyclic, recurring motility pattern that occurs in the stomach and small bowel during fasting; it is interrupted by feeding. The MMC is present in the gastrointestinal tract of many species, including humans. The complex can be subdivided into four phases, of which phase III is the most active, with a burst of contractions originating from the antrum or duodenum and migrating distally. Control of the MMC is complex. Phase III of the MMC with an antral origin can be induced in humans through intravenous administration of motilin, erythromycin or ghrelin, whereas administration of serotonin or somatostatin induces phase III activity with duodenal origin. The role of the vagus nerve in control of the MMC seems to be restricted to the stomach, as vagotomy abolishes the motor activity in the stomach, but leaves the periodic activity in the small bowel intact. The physiological role of the MMC is incompletely understood, but its absence has been associated with gastroparesis, intestinal pseudo-obstruction and small intestinal bacterial overgrowth. Measuring the motility of the gastrointestinal tract can be important for the diagnosis of gastrointestinal disorders. In this Review we summarize current knowledge of the MMC, especially its role in health and disease.

Dyspepsia: organic versus functional

Dyspepsia is the medical term for difficult digestion. It consists of various symptoms in the upper abdomen, such as fullness, discomfort, early satiation, bloating, heartburn, belching, nausea, vomiting, or pain. The prevalence of dyspepsia in the western world is approximately 20% to 25%. Dyspepsia can be divided into 2 main categories: "organic" and "functional dyspepsia" (FD). Organic causes of dyspepsia are peptic ulcer, gastroesophageal reflux disease, gastric or esophageal cancer, pancreatic or biliary disorders, intolerance to food or drugs, and other infectious or systemic diseases. Pathophysiological mechanisms underlying FD are delayed gastric emptying, impaired gastric accommodation to a meal, hypersensitivity to gastric distension, altered duodenal sensitivity to lipids or acids, altered antroduodenojenunal motility and gastric electrical rhythm, unsuppressed postprandial phasic contractility in the proximal stomach, and autonomic nervous system-central nervous system dysregulation. Pathogenetic factors in FD are genetic predisposition, infection from Helicobacter pylori or other organisms, inflammation, and psychosocial factors. Diagnostic evaluation of dyspepsia includes upper gastrointestinal endoscopy, abdominal ultrasonography, gastric emptying testing (scintigraphy, breath test, ultrasonography, or magnetic resonance imaging), and gastric accommodation evaluation (magnetic resonance imaging, ultrasound, single-photon emission computed tomography, and barostat). Antroduodenal manometry can be used for the assessment of the myoelectrical activity of the stomach, whereas sensory function can be evaluated with the barostat, tensostat, and satiety test. Management of FD includes general measures, acid-suppressive drugs, eradication of H. pylori, prokinetic agents, fundus-relaxing drugs, antidepressants, and psychological interventions. This review presents an update on the diagnosis of patients presenting with dyspepsia, with an emphasis on the pathophysiological and pathogenetic mechanisms of FD and the differential diagnosis with organic causes of dyspepsia. The management of uninvestigated and FD, as well as the established and new pharmaceutical agents, is also discussed.

Functional disorders and quality of life after esophagectomy and gastric tube reconstruction for cancer

Functional disorders such as delayed gastric emptying, dumping syndrome or duodeno-gastro-esophageal reflux occur in half of the patients who undergo esophagectomy and gastric tube reconstruction for cancer. The potential role for pyloroplasty in the prevention of functional disorders is still debated. Antireflux fundoplication during esophagectomy can apparently reduce the reflux but at the cost of increasing the complexity of the operation; it is not widely used. The treatment of functional disorders arising after esophagectomy and gastroplasty for cancer is based mainly on dietary measures. Proton pump inhibitors have well documented efficiency and should be given routinely to prevent reflux complications. Erythromycin may prevent delayed gastric emptying, but it should be used with caution in patients with cardiovascular disorders. In the event of anastomotic stricture, endoscopic dilatation is usually efficient. Problems related to gastrointestinal functional disorders after esophageal resection and gastric tube reconstruction do not significantly impair long-term quality of life, which is mainly influenced by tumor recurrence.

GSK962040: a small molecule motilin receptor agonist which increases gastrointestinal motility in conscious dogs

BACKGROUND

GSK962040, a small molecule motilin receptor agonist, was identified to address the need for a safe, efficacious gastric prokinetic agent. However, as laboratory rodents lack a functional motilin system, studies in vivo have been limited to a single dose, which increased defecation in rabbits. Motilin agonists do not usually increase human colonic motility, so gastric prokinetic activity needs to be demonstrated.

METHODS

The effect of intravenous GSK962040 on gastro-duodenal motility was assessed in fasted dogs implanted with strain gauges. Activity was correlated with blood plasma concentrations of GSK962040 (measured by HPLC-MS/MS) and potency of GSK962040 at the dog recombinant receptor [using a Fluorometric Imaging Plate Reader (Molecular Devices, Wokingham, UK) after expression in HEK293 cells].

KEY RESULTS

GSK962040 activated the dog motilin receptor (pEC(50) 5.79; intrinsic activity 0.72, compared with [Nle(13) ]-motilin). In vivo, GSK962040 induced phasic contractions, the duration of which was dose-related (48 and 173 min for 3 and 6 mg kg(-1) ), driven by mean plasma concentrations >1.14 μmol L(-1) . After the effects of GSK962040 faded, migrating motor complex (MMC) activity returned. Migrating motor complex restoration was unaffected by 3 mg kg(-1) GSK962040 but at 6 mg kg(-1) , MMCs returned 253 min after dosing, compared with 101 min after saline (n=5 each).

CONCLUSIONS & INFERENCES

The results are consistent with lower potency for agonists at the dog motilin receptor, compared with humans. They also define the doses of GSK962040 which stimulate gastric motility. Correlation of in vivo and in vitro data in the same species, together with plasma concentrations, guides further studies and translation to other species.

The translational value of rodent gastrointestinal functions: a cautionary tale

Understanding relationships between gene complements and physiology is important, especially where major species-dependent differences are apparent. Molecular and functional differences between rodents (rats, mice, guinea pigs) and humans are increasingly reported. Recently, the motilin gene, which encodes a gastrointestinal hormone widely detected in mammals, was found to be absent in rodents where the receptors are pseudogenes; however, actions of motilin in rodents are sometimes observed. Although ghrelin shares common ancestry with motilin, major species-dependent abberations are not reported. The apparently specific absence of functional motilin in rodents is associated with specialised digestive physiology, including loss of ability to vomit; motilin is functional in mammals capable of vomiting. The exception is rabbit, the only other mammal unable to vomit, in which motilin might be conserved to regulate caecotrophy, another specialised digestive process. Motilin illustrates a need for caution when translating animal functions to humans. Nevertheless, motilin receptor agonists are under development as gastroprokinetic drugs.

Gastroduodenal motility

PURPOSE OF REVIEW

Abnormalities of gastroduodenal motility are considered key players in the pathogenesis of upper gastrointestinal symptoms in disorders such as functional dyspepsia and gastroparesis. Abnormalities of sensory control are considered another important factor that contributes to symptom generation. This review summarizes recent progress in our understanding of gastroduodenal motility and sensitivity in health and in disease.

RECENT FINDINGS

Although gastric and small intestinal motility remain an important focus of research, including the application of the SmartPill (SmartPill Corp., Buffalo, New York, USA) wireless motility monitoring capsule, duodenal sensitivity and low-grade duodenal inflammation are new areas of interest in the pathogenesis of functional dyspepsia. A number of genetic polymorphisms associated with functional dyspepsia are being investigated, but large-scale studies are still lacking. Central processing of visceral stimuli, and its role in the pathogenesis of functional dyspepsia, is another important emerging topic. Therapeutic studies have reported on novel pharmacological approaches in functional dyspepsia and gastroparesis, as well as gastric electrical stimulation in the treatment of refractory gastroparesis.

SUMMARY

There is gradual progress in our understanding of the pathogenesis of gastroduodenal symptoms. Areas of recent advances including the recognition of low-grade duodenal inflammation, the role of central nervous system processing in visceral hypersensitivity and the exploration of novel pharmacotherapeutic approaches.