Erythromycin derivatives ABT 229 and GM 611 act on motilin receptors in the rabbit duodenum

Prokinetics-safety and efficacy: The European Society of Neurogastroenterology and Motility/The American Neurogastroenterology and Motility Society expert review

BACKGROUND

Prokinetics are a class of pharmacological drugs designed to improve gastrointestinal (GI) motility, either regionally or across the whole gut. Each drug has its merits and drawbacks, and based on current evidence as high-quality studies are limited, we have no clear recommendation on one class or other. However, there remains a large unmet need for both regionally selective and/or globally acting prokinetic drugs that work primarily intraluminally and are safe and without systemic side effects.

PURPOSE

Here, we describe the strengths and weaknesses of six classes of prokinetic drugs, including their pharmacokinetic properties, efficacy, safety and tolerability and potential indications.

Butyrlycholine esterase inhibitory activity and effects of extracts (fruit, bark and leaf) from Zanthoxylum armatum DC in gut, airways and vascular smooth muscles

BACKGROUND

Fruit, bark and leaves of Zanthoxylum armatum DC are popular remedies for gastrointestinal, cardiovascular and respiratory disorders in the subcontinent traditional practices. The aim of the study was to individually probe the profile of methanol extracts from three different parts of Zanthoxylum armatum.

METHODS

The ex-vivo muscle relaxant effects of extracts were assessed in the isolated intestine, trachea and thoracic aortic rings and were compared with the positive controls and CRC were constructed. The anti-diarrheal effect of extracts was evaluated in mice by inducing diarrhea with castor oil. The extracts were also studied for acute toxicity and butyrylcholine esterase inhibition.

RESULTS

The extracts from fruit, bark and leaves of Z. armatum showed inhibitory effect against the butyrylcholine esterase enzyme with percent inhibition of 50.75 ± 1.23, 82.57 ± 1.33, and 37.52 ± 1.11respectively, compared to standard serine (IC₅₀: 0.04 ± 0.001 μmol/L). The fruit and bark extracts provided 75, and 52% diarrheal protection, compared to verapamil (96%). In isolated rabbit jejunum strips, increasing addition of the extracts inhibited the spontaneous and high K⁺ precontractions with EC₅₀ values of 0.71 and 3 mg/mL for fruit, EC₅₀ values of 0.61 and 0.5 mg/mL for bark, EC₅₀ 0.81 and 3.1 mg/mL for leaves, like verapamil. The extracts induced a concentration-dependent relaxation of the carbachol (1 μM) and high K⁺ (80 mM) precontractions with EC₅₀ values of 2.4 and 0.9 mg/mL for fruit, EC₅₀ values of 1.2 and 3 for leaves. The bark extract was equipotent against both contractions with EC₅₀ 3.1 and 0.7 mg/mL, respectively. In the aortic rings, the fruit extract completely relaxed the phenylephrine (1 μM)-induced contractions with (EC₅₀ value = 0.8 mg/ml) and a partial inhibition of high K⁺ induced contractions. The leaves extract completely relaxed the aortic contractions with (EC₅₀ values = 1.0 and 8.5 mg/ml). The extracts caused no acute toxicity up to 3 g/kg dose.

CONCLUSIONS

The experiments revealed that the extracts of aerial parts of Z. armatum have antidiarrheal properties in vivo and showed spasmolytic effect in intestinal and tracheal preparations with possible mechanism involving the blockage of Ca⁺⁺ channels. These experiments provide enough justification for use of this plant in ethnomedicine in diarrhea, gut and bronchial spasms.

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.

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.

Motilides: a long and winding road: lessons from mitemcinal (GM-611) on diabetic gastroparesis

Mitemcinal (GM-611) is a macrolide motilin receptor agonist with acid-resistance and without antibiotic activity. Since ABT-229 (a first generation of motilin receptor agonist) had failed to demonstrate symptomatic relief in functional dyspepsia and diabetic gastroparesis, there is a controversy for which of prokinetics or relaxants is clinically beneficial. Currently, oral mitemcinal has been focused on diabetic gastroparesis under clinical development. It showed to accelerate gastric-emptying in diabetic animals and in patients with gastroparesis. The latest double-blind, placebo-controlled study demonstrated to be effective at improving diabetes-related gastroparesis symptoms. A sub-group analysis, which included patients with BMI < 35 kg/m2 and hemoglobin A1c < 10%, there were significantly more symptomatic relieves in the 10 mg mitemcinal group than in the placebo group. The frequency of adverse events did not differ between groups. Mitemcinal shows promise in the subset of patients who should be confirmed in future studies.

Molecular identification and characterization of the dog motilin receptor

Motilin, a 22-amino acid peptide hormone secreted by endocrine cells of the intestinal mucosa, plays an important role in the regulation of gastrointestinal motility. The actions of motilin agonists have been extensively investigated in dogs due to physiological similarities between the dog and human alimentary tracts. The amino acid sequence of the dog motilin receptor, however, was previously unknown. We have cloned a cDNA from dog stomach corresponding to the motilin receptor. The deduced protein shared 71% and 72% sequence identity with the human and rabbit motilin receptors, respectively. Expression of the dog motilin receptor in CHO cells promoted the typical cellular responses to the agonists, motilin and erythromycin. The rank order of potency determined for these agonists was similar to that found for the human motilin receptor, with motilin being more potent than erythromycin. Immunohistochemistry of the dog stomach revealed that the motilin receptor was localized in neuronal cell bodies and fibers. This is the first study detailing the cloning, expression, and functional characterization of the dog motilin receptor. Determination of the full sequence and functional properties of the dog motilin receptor will provide useful information enabling us to interpret previous and future studies of motilin agonists in dogs.

Effects of motilin and mitemcinal (GM-611) on gastrointestinal contractile activity in rhesus monkeys in vivo and in vitro

Neither the presence of motilin receptors nor their action has been investigated in monkeys. The object of this study was to determine the effects of motilin and mitemcinal (GM-611), an erythromycin derivative, on the gastrointestinal tract in rhesus monkeys in vivo and in vitro. In in vivo investigations in conscious monkeys, both motilin and mitemcinal induced migrating motor complex-like contractions in the interdigestive state and also accelerated gastric emptying. In in vitro investigations, the presence of motilin receptors in the gastrointestinal tract was demonstrated by receptor binding assays. Motilin and mitemcinal contracted isolated duodenum strips in a concentration-dependent manner. In conclusion, rhesus monkeys may be useful for studying the physiological and pharmacological roles of the motilin agonistic mechanism because they show reactivity to motilin both in vivo and in vitro.

Standardized concept for the treatment of gastrointestinal dysmotility in critically ill patients--current status and future options

Inhibition of gastrointestinal motility is a major problem in critically ill patients. Motor stasis gives rise to subsequent complications including intolerance to enteral feeding, enhanced permeability of the atrophic intestinal mucosa and conditions as severe as systemic inflammatory response syndrome, sepsis and multiple organ failure. Although the diagnosis of motility disturbances in critically ill patients is difficult, the type and site of the disturbance are important to consider in the analysis of the condition and in the choice of therapeutic approach. The pharmacological treatment of impaired gastrointestinal motility is difficult to handle for the clinician, because the underlying mechanisms are complex and not fully understood and the availability of pharmacological treatment options is limited. In addition, there is a lack of controlled studies on which to build an evidence-based treatment concept for critically ill patients. Notwithstanding this situation, there has been remarkable progress in the understanding of the integrated regulation of gastrointestinal motility in health and disease. These advances, which largely relate to the organization of the enteric nervous system and its signaling mechanisms, enable the intensivist to develop a standardized concept for the use of prokinetic agents in the treatment of impaired gastrointestinal motility in critically ill patients.

Efficacy of mitemcinal, a motilin agonist, on gastrointestinal symptoms in patients with symptoms suggesting diabetic gastropathy: a randomized, multi-center, placebo-controlled trial

BACKGROUND

Mitemcinal, an oral motilin agonist, accelerates gastric emptying.

AIM

To investigate if mitemcinal was superior to placebo in relief of symptoms attributed to gastroparesis.

METHODS

In a randomized, double-blind design, 392 insulin-requiring diabetics with symptoms attributable to gastroparesis were treated for 3 months with placebo, mitemcinal 5 or 10 mg bid. On a weekly basis, patients assessed whether there was adequate relief of their gastroparesis symptoms. Patients were classified as Complete Responders (CR) if there were three consecutive positive monthly responses, which required at least 50% of their weekly responses in a month being positive. An Overall Responder (OR) had at least 75% positive weekly responses for the whole treatment period.

RESULTS

Mitemcinal 10 mg produced a significantly better response rate than placebo with a 10.6% increase in the OR (P < 0.05 vs. placebo). Mitemcinal 10 mg also produced statistically significant increases in the CR and OR in the subgroup identified by baseline body mass index (<35 kg/m(2)) and haemoglobin A(1c) (<10%) (P < 0.01 vs. placebo). Adverse events did not differ from placebo frequency levels.

CONCLUSIONS

Mitemcinal can induce a statistically significant response to treatment in a subset of diabetic gastroparesis where future prokinetic clinical trials should be focused.

Promotility medications--now and in the future

Gastrointestinal promotility drugs stimulate smooth muscle contractions to enhance gastric emptying and small and large bowel transit. Currently available drug classes with prokinetic properties include antidopaminergic agents, serotonergic agents, and motilin-receptor agonists. Due to moderate prokinetic effects, poor symptomatic responses and the presence of adverse effects, there is a clear need for new classes of prokinetics. Several newer prokinetic drugs and drug classes are currently under evaluation. Selecting candidate agents and designing the appropriate therapeutic trials is hampered by the lack of insight in the pathophysiology of motility-related symptoms. As gastrointestinal motor disorders are chronic, relapsing, and remitting disorders, it seems desirable that studies with candidate prokinetic drugs establish a long-term efficacy and not only short-term effects on gastrointestinal functions.

Natural products to drugs: natural product derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or in registration (current 31 December 2004) have been reviewed. Natural product derived drugs launched in the United States of America, Europe and Japan since 1998 and new natural product templates discovered since 1990 are discussed.

Effects of Nitric Oxide Synthase Inhibitor on the Digestive System Measured by Simultaneous Monitoring of Gastric Motility, Gastric Emptying Activity and Postprandial Pancreaticobiliary Secretion in Dogs

Relationships between the NO synthase inhibitor and gastric and pancreaticobiliary functions measured simultaneously in the digestive state have been little studied. The aim of this study was to estimate the effect of NO synthase inhibitor on integrated digestive function in conscious dogs. A strain gauge force transducer was implanted on the gastric antrum of 6 mongrel dogs to measure gastric contractile activity and two duodenal cannulas were inserted into the proximal and distal sites to measure the gastric emptying rate and the pancreaticobiliary output into the duodenum using our novel method. Postprandial pancreatic and biliary secretion were presented as amylase and bile acid activity, respectively. Furthermore, a cervical cannula was placed into the superior vena cava as a route for the administration of NO synthase inhibitor, N omega-nitro-L-arginine (L-NNA), at a dose of 2.5 mg/kg-h. In a group given L-NNA, gastric contractile activity after ingestion was significantly enhanced, but the emptying rates of gastric solids and liquids were significantly suppressed in comparison with the control. The mean 0-1 h amylase integrated output was significantly (P < 0.05) decreased in comparison with the control, and the mean bile acid integration of 0-1 h output was also significantly (P < 0.01) decreased. A possible explanation for this observation is that smaller volumes of nutrient are delivered into the duodenum; however, it could also be that postprandial pancreaticobiliary secretion is inhibited by an alteration of blood flow or by a change in contractions of the sphincter of Oddi after the administration of L-NNA.

Progress with novel pharmacological strategies for gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GORD) is a chronic disorder characterised by an increased exposure of the oesophagus to intragastric contents. Currently, GORD symptoms are maintained under control with antisecretory agents, mainly gastric proton pump inhibitors (PPIs). Although impaired oesophageal motility may partly underlie the pathophysiology of GORD, the use of prokinetic agents has been found to be unsatisfactory. To date, novel pharmacological approaches for GORD are mainly related to the control of transient lower oesophageal sphincter (LOS) relaxations (TLOSRs). The majority of patients with GORD have reflux episodes during TLOSRs, which are evoked by gastric distension, mainly occurring after ingestion of a meal. Patients with reflux disease with normal peristalsis and without or with mild erosive disease could potentially benefit from anti-TLOSR therapy. This therapy might also be of value to treat some severe forms of esophagitis in combination with PPIs. GABA-B-receptor agonists are the most promising class of agents identified so far for TLOSR control. The GABA-B-receptor agonist, baclofen, is the most effective compound in inhibiting TLOSRs in humans. Since baclofen has several CNS adverse effects, novel orally available GABA-B agonists are needed for effective and well tolerated treatment of GORD. Endogenous or exogenous cholecystokinin (CCK) causes a reduction in LOS pressure, an increase in TLOSR frequency and a reduction in gastric emptying. In healthy volunteers and patients with GORD, loxiglumide, a selective CCK1-receptor antagonist, was found to reduce the rate of TLOSRs, although its effect on postprandial acid reflux may be modest. Orally effective CCK antagonists are not marketed to date. The anticholinergic agent atropine, given to healthy volunteers and patients with GORD, markedly reduced the rate of TLOSRs. Because of severe gastrointestinal (and other) adverse effects of anticholinergics, including worsening of supine acid clearance and constipation, it is unlikely that this class of drugs will have a future as anti-TLOSR agents on a routine basis. In spite of their effectiveness in reducing TLOSR rate, untoward adverse effects, such as addiction and severe constipation, currently limit the use of morphine and other opioid mu-receptor agonists. The same applies to nitric oxide synthase inhibitors, which are associated with marked gastrointestinal, cardiovascular, urinary and respiratory adverse effects. Animal studies provide promising evidence for the use of cannabinoid receptor 1 agonists, by showing potent inhibition of TLOSRs in the dog, thus opening a new route for clinical investigation in humans. A better understanding of TLOSR pathophysiology is a necessary step for the further development of novel drugs effective for anti-reflux therapy.

The rabbit motilin receptor: molecular characterisation and pharmacology

Following identification of the human motilin receptor, we isolated the rabbit orthologue by PCR amplification and found this to be 85% identical to the open reading frame of the human receptor. The protein encoded was 84% identical to the human polypeptide. In HEK293T cells transfected with the rabbit receptor, motilin concentration-dependently increased intracellular calcium mobilisation (pEC50=9.25). After transfection with Go1alpha, motilin similarly stimulated [35S]GTPgammaS binding (pEC50=8.87). Using both systems, similar values were obtained with the human receptor, with rank-order potencies of motilin=[Nle13]-motilin>erythromycin; ghrelin was ineffective. In circular muscle preparations of rabbit gastric antrum, [Nle13]-motilin 0.1-30 nM concentration-dependently increased the amplitude of electrically-evoked, neuronally-mediated contractions (pEC50=8.3); higher concentrations increased the muscle tension (30-3000 nM). Both responses to [Nle13]-motilin faded rapidly during its continual presence. Rat or human ghrelin 0.01-10 microM were without activity. Erythromycin 30-3000 nM and 10 microM, respectively, increased neuronal activity and muscle tension in rabbit stomach. Unlike [Nle13]-motilin, the increase in neuronal activity did not fade during continual presence of submaximally-effective concentrations of erythromycin; some fade was observed at higher concentrations. We conclude that the pharmacology of the rabbit motilin receptor is similar to the human orthologue and, when expressed as a recombinant, comparable to the native receptor. However, in terms of their ability to increase neuronal activity in rabbit stomach, [Nle13]-motilin and erythromycin are distinguished by different response kinetics, reflecting different rates of ligand degradation and/or interaction with the receptor.

New developments in the treatment of functional dyspepsia

Functional dyspepsia is a clinical syndrome defined by chronic or recurrent pain or discomfort in the upper abdomen of unknown origin. Although generally accepted, investigators differently interpret this definition and clinical trials are often biased by inhomogeneous inclusion criteria. The poorly defined multifactorial pathogenesis of dyspeptic symptoms has hampered efforts to develop effective treatments. A general agreement exists on the irrelevant role played by Helicobacter pylori in the pathophysiology of functional dyspepsia. Gastric acid secretion is within normal limits in patients with functional dyspepsia but acid related symptoms may arise in a subgroup of them. Proton pump inhibitors appear to be effective in this subset of patients with dyspepsia. Non-painful dyspeptic symptoms are suggestive of underlying gastrointestinal motor disorders and such abnormalities can be demonstrated in a substantial proportion of patients. Postprandial fullness and vomiting have been associated with delayed gastric emptying of solids, and early satiety and weight loss to postcibal impaired accommodation of the gastric fundus. Prokinetics have been shown to exert beneficial effects, at least in some patients with dyspepsia. In contrast, drugs enhancing gastric fundus relaxation have been reported to improve symptoms, although conflicting results have also been published. An overdistended antrum may also generate symptoms, but its potential pathogenetic role and the effects of drugs on this abnormality have never been investigated formally. Visceral hypersensitivity plays a role in some dyspeptic patients and this abnormality is also a potential target for treatment. Both chemo- and mechanoreceptors can trigger hyperalgesic responses. Psychosocial abnormalities have been consistently found in functional digestive syndromes, including dyspepsia. Although useful in patients with irritable bowel syndromes (IBS), antidepressants have been only marginally explored in functional dyspepsia. Among the new potentially useful agents for the treatment of functional dyspepsia, serotonin 5-HT(4) receptor agonists have been shown to exert a prokinetic effect. Unlike motilides, 5-HT(4) receptor agonists do not appear to increase the gastric fundus tone and this may contribute to improve symptoms. 5-HT(3) receptor antagonists have been investigated mainly in the IBS and the few studies performed in functional dyspepsia have provided conflicting results. Also, kappa-opioid receptor agonists might be useful for functional digestive syndromes because of their antinociceptive effects, but available results in functional dyspepsia are scanty and inconclusive. Other receptors that represent potential clinical targets for antagonists include purinoceptors (i. e., P2X2/3 receptors), NMDA receptors (NR2B subtype), protease-activated receptor-2, the vanilloid receptor-1, tachykinin receptors (NK(1)/NK(2)) and cholecystokinin (CCK)(1) receptors.

Effects of ABT-229, a motilin agonist, on acid reflux, oesophageal motility and gastric emptying in patients with gastro-oesophageal reflux disease

AIM

The effect of ABT-229, a new macrolide with no antibacterial activity, on gastro-oesophageal reflux, oesophageal motility and gastric emptying in patients with gastro-oesophageal reflux disease was investigated.

METHODS

Twenty-one patients were treated with a placebo and ABT-229 (2.5, 5 or 10 mg b.d.) in a randomized, incomplete crossover study design. Ambulatory 24-h pH manometry was performed and gastric emptying was assessed by the 13C-octanoic acid breath test on the seventh day of treatment.

RESULTS

A significant decrease was found in the mean (+/- s.e.) percentage of reflux time (intra-oesophageal pH < 4) for ABT-229 5 mg b.d. and 10 mg b.d., but not for 2.5 mg b.d., compared with placebo. For ABT-229 5 mg, it was 8.5 +/- 0.5% vs. 10.7 +/- 0.7% (P < 0.038) and, for ABT-229 10 mg, it was 6.6 +/- 0.5% vs. 8.4 +/- 0.5% (P < 0.019). There were no significant differences in any of the analysed manometric parameters. In addition, the gastric half-emptying time for all doses of ABT-229 did not differ significantly from that after placebo.

CONCLUSIONS

ABT-229 is able to reduce slightly, but significantly, acid reflux in patients with gastro-oesophageal reflux disease. This effect does not appear to be due to a measurable improvement in oesophageal motility or gastric emptying.

Failure of a motilin receptor agonist (ABT-229) to relieve the symptoms of functional dyspepsia in patients with and without delayed gastric emptying: a randomized double-blind placebo-controlled trial

INTRODUCTION

Motilin-receptor agonists are prokinetics; whether they relieve the symptoms of functional dyspepsia is unknown. We aimed to test the efficacy of the motilin agonist ABT-229 in functional dyspepsia patients with and without delayed gastric emptying.

METHODS

Patients were randomized with postprandial symptoms and documented functional dyspepsia by endoscopy (n=589 in intention-to-treat analysis). Patients were assigned to either the delayed or normal gastric emptying strata, based on a validated 13C octanoic acid breath test. Patients were then further randomized within each strata, to receive one of four doses of ABT-229 (1.25, 2. 5, 5 or 10 mg b.d. before breakfast and dinner) or placebo for 4 weeks, following a 2-week baseline. The primary outcome was the assessment of change in symptom severity over the 2 weeks from baseline to final visit, based on a self-report questionnaire measuring severity on visual analogue scales.

RESULTS

Baseline characteristics across the treatment arms were very similar. No significant differences in the upper abdominal discomfort severity score (maximum 800 mm) were observed for any active treatment arm vs. placebo (mean change from baseline -139, -141, -145, -160 and -134 mm for placebo, 1.25, 2.5, 5, and 10 mg, respectively, at 4 weeks by intention-to-treat). More patients on placebo reported a good or excellent global response than patients on 1.25 or 5 mg of active therapy (both P < 0.05). The results were very similar in those with and without delayed gastric emptying. Helicobacter pylori status did not predict response. Excluding patients with any baseline heartburn (total remaining n=240), ABT-229 10 mg was inferior to placebo in relief of upper abdominal discomfort.

CONCLUSIONS

ABT-229 was of no value for relief of symptoms in functional dyspepsia, compared with placebo.