Motilin Receptor Research Articles

The hungry stomach: physiology, disease, and drug development opportunities.

During hunger, a series of high-amplitude contractions of the stomach and small intestine (phase III), which form part of a cycle of quiescence and contractions (known as the migrating motor complex, MMC), play a “housekeeping” role prior to the next meal, and may contribute toward the development of hunger. Several gastrointestinal (GI) hormones are associated with phase III MMC activity, but currently the most prominent is motilin, thought to at least partly mediate phase III contractions of the gastric MMC. Additional GI endocrine and neuronal systems play even more powerful roles in the development of hunger. In particular, the ghrelin-precursor gene is proving to have a complex physiology, giving rise to three different products: ghrelin itself, which is formed from a post-translational modification of des-acyl-ghrelin, and obestatin. The receptors acted on by des-acyl-ghrelin and by obestatin are currently unknown but both these peptides seem able to exert actions which oppose that of ghrelin, either indirectly or directly. An increased understanding of the actions of these peptides is helping to unravel a number of different eating disorders and providing opportunities for the discovery of new drugs to regulate dysfunctional gastric behaviors and appetite. To date, ghrelin and motilin receptor agonists and antagonists have been described. The most advanced are compounds which activate the ghrelin and motilin receptors which are being progressed for disorders associated with gastric hypomotility.

Diabetic gastroparesis: Therapeutic options

Gastroparesis is a condition characterized by delayed gastric emptying and the most common known underlying cause is diabetes mellitus. Symptoms include nausea, vomiting, abdominal fullness, and early satiety, which impact to varying degrees on the patient’s quality of life. Symptoms and deficits do not necessarily relate to each other, hence despite significant abnormalities in gastric emptying, some individuals have only minimal symptoms and, conversely, severe symptoms do not always relate to measures of gastric emptying. Prokinetic agents such as metoclopramide, domperidone, and erythromycin enhance gastric motility and have remained the mainstay of treatment for several decades, despite unwanted side effects and numerous drug interactions. Mechanical therapies such as endoscopic pyloric botulinum toxin injection, gastric electrical stimulation, and gastrostomy or jejunostomy are used in intractable diabetic gastroparesis (DG), refractory to prokinetic therapies. Mitemcinal and TZP-101 are novel investigational motilin receptor and ghrelin agonists, respectively, and show promise in the treatment of DG. The aim of this review is to provide an update on prokinetic and mechanical therapies in the treatment of DG.

Erythromycin inhibited glycinergic inputs to gastric vagal motoneurons in brainstem slices of newborn rats

Motilin has been known to stimulate the motility of digestive organs peripherally via activation of motilin receptors located at gastrointestinal (GI) cholinergic nerve endings and/or smooth muscle cells. Recent studies have indicated that motilin may also promote GI motility via actions in the central nervous system; however the sites of action and the mechanisms are not clear yet. The present study aimed to test the hypothesis that motilin receptor agonist erythromycin alters the synaptic inputs of preganglionic gastric vagal motoneurons (GVMs) located in the dorsal motor nucleus of the vagus (DMV). Gastric vagal motoneurons were retrogradely labeled by fluorescent tracer from the stomach wall of newborn rats. Fluorescently labeled GVMs in DMV were recorded using whole-cell patch-clamp in brainstem slices and the effects of motilin receptor agonist erythromycin on the synaptic inputs were examined. Erythromycin (100 nmol L(-1), 1 μmol L(-1), 10 μmol L(-1)) significantly inhibited the frequency of glycinergic spontaneous inhibitory postsynaptic currents (sIPSCs) of GVMs and significantly inhibited the amplitude at the concentration of 10 μmol L(-1). These responses were prevented by GM-109, a selective motilin receptor antagonist. In the pre-existence of tetradotoxin (TTX, 1 μmol L(-1)), erythromycin (10 μmol L(-1)) caused significant decreases of the glycinergic miniature inhibitory postsynaptic currents (mIPSCs), in both the frequency and the amplitude. However, erythromycin (10 μmol L(-1)) didn't cause significant changes of the GABAergic sIPSCs. Erythromycin selectively inhibits the glycinergic inputs of GVMs.

Mutational analysis of predicted extracellular domains of human growth hormone secretagogue receptor 1a

The Class A family of guanine nucleotide-binding protein (G protein)-coupled receptors that includes receptors for motilin, ghrelin, and growth hormone secretagogue (GHS) has substantial potential importance as drug targets. Understanding of the molecular basis of hormone binding and receptor activation should provide insights helpful in the development of such drugs. We previously reported that Cys residues and the perimembranous residues in the extracellular loops and amino-terminal tail of the motilin receptor are critical for peptide ligand, motilin, binding and biological activity. In the current work, we focused on the predicted extracellular domains of the human GHS receptor 1a, and identified functionally important residues by using sequential deletions ranging from one to twelve amino acid residues and site-directed replacement mutagenesis approach. Each construct was transiently expressed in COS cells, and characterized for ghrelin- and growth hormone releasing peptide (GHRP)-6-stimulated intracellular calcium responses and ghrelin radioligand binding. Cys residues in positions 116 and 198 in the first and second extracellular loops and the perimembranous Glu 187 residue in the second extracellular loop were critical for ghrelin and GHRP-6 biological activity. These results suggest that Cys residues in the extracellular domains in this family of Class A G protein-coupled receptor is likely involved in the highly conserved and functionally important disulfide bond, and that the perimembranous residues contribute peptide ligand binding and signaling.

9-Dihydroerythromycins as non-antibiotic motilin receptor agonists

A series of 9-dihydroerythromycin A and B analogues with modification of the desosamine nitrogen have been synthesized and screened for motilin agonist activity, antibiotic activity, tachyphylaxis and hERG channel current inhibition. Small alkyl groups resulted in the potency while compounds with a primary or secondary amine resulted in the low motilin agonist potency. Several compounds were identified as non-antibiotic motilin receptor agonists with minimal tachyphylaxis and low hERG interaction.

Diabetic gastroparesis: Therapeutic options

Gastroparesis is a condition characterized by delayed gastric emptying and the most common known underlying cause is diabetes mellitus. Symptoms include nausea, vomiting, abdominal fullness, and early satiety, which impact to varying degrees on the patient’s quality of life. Symptoms and deficits do not necessarily relate to each other, hence despite significant abnormalities in gastric emptying, some individuals have only minimal symptoms and, conversely, severe symptoms do not always relate to measures of gastric emptying. Prokinetic agents such as metoclopramide, domperidone, and erythromycin enhance gastric motility and have remained the mainstay of treatment for several decades, despite unwanted side effects and numerous drug interactions. Mechanical therapies such as endoscopic pyloric botulinum toxin injection, gastric electrical stimulation, and gastrostomy or jejunostomy are used in intractable diabetic gastroparesis (DG), refractory to prokinetic therapies. Mitemcinal and TZP-101 are novel investigational motilin receptor and ghrelin agonists, respectively, and show promise in the treatment of DG. The aim of this review is to provide an update on prokinetic and mechanical therapies in the treatment of DG.

Systematic Analysis of G Protein-Coupled Receptor Gene Expression in Adrenocorticotropin-Independent Macronodular Adrenocortical Hyperplasia Identifies Novel Targets for Pharmacological Control of Adrenal Cushing’s Syndrome

Stimulation of cortisol secretion through abnormally expressed G protein-coupled receptors (GPCRs) is a frequent feature of ACTH-independent macronodular adrenal hyperplasia (AIMAH). This has opened a pharmacological strategy that targets GPCRs for the treatment of Cushing's syndrome in AIMAH. However, only few drugs are available for the presently described GPCRs. The objective of the study was to identify new GPCR targets for the pharmacological treatment of adrenal Cushing's syndrome. We designed a cDNA chip containing 865 nucleotidic sequences of GPCRs. mRNAs were extracted from three normal adrenals, 18 AIMAHs, four adrenals from Cushing's disease patients, and 13 cortisol-secreting adenomas. A set of GPCR mRNAs that showed significantly higher or lower expression in AIMAH than in normal adrenal were studied by quantitative RT-PCR analysis. Analysis of protein expression and function were performed on selected GPCRs. The study was conducted at a tertiary care center and basic research laboratories. The ACTH MC2 receptor showed a low expression in 15 of 18 AIMAHs samples, whereas several previously undescribed GPCR genes were found highly expressed in a subset of AIMAH, such as the receptors for motilin (MLNR; three of 18 AIMAHs) and γ-aminobutyric acid (GABBR1; five of 18 AIMAHs), and the α2A adrenergic receptor (ADRA2A; 13 of 18 AIMAHs), on which we focused our attention. Western blot and immunochemistry analyses showed expression of ADRA2A protein in AIMAH but not in normal adrenal cortex. The ADRA2A agonist clonidine enhanced both basal and stimulated cortisol production. Clonidine-induced increase in basal cortisol levels was blocked by the ADRA2A antagonist yohimbine. ADRA2A is a potential target for pharmacological treatment of Cushing's syndrome linked to AIMAH.

Involvement of tryptophan W276 and of two surrounding amino acid residues in the high constitutive activity of the ghrelin receptor GHS-R1a

The human ghrelin receptor (GHS-R1a) is known to display a high level of signaling in the absence of ligand. The Trp276, located in the fully conserved CWXP motif of G protein-coupled receptors, is believed to function as a rotameric switch in these receptors. A comparative modelling of GHS-R1a with the motilin receptor, the most related G protein-coupled receptor to GHS-R1a known to date, but characterized by a very low ligand-independent signaling level, revealed that only two surrounding residues of Trp276, that are Val131 and Ile134, were different from these receptors. We mutated them at once in GHS-R1a to create a “motilin receptor-like” environment of Trp276 in order to study the consequences on GHS-R1a activation. We studied the pharmacological properties of the W276A, V131L-I134M GHS-R1a mutants. Basal as well as maximal ghrelin-induced signaling was assessed both by inositol-phosphate accumulation and SRE pathways. As compared to the wild type receptor, the SRE-luciferase assay displayed a markedly impaired basal activity for W276A whereas that of V131L-I134M was, strikingly, two fold increased. Nevertheless, the efficacy of ghrelin to bind or to stimulate mutant receptors remained unchanged. It is concluded that Trp276, Val131 and Ile134 have a significant impact on constitutive signaling of GHS-R1a, V131L-I134M being the first example of a GHS-R1a mutant with a higher basal activity than the wild type receptor.

S1701 A Cross-Talk Between Motilin Receptor and Growth Hormone Secretagogue Receptor Using Chimeric Constructs' Expression and Co-Expression

S1701 A Cross-Talk Between Motilin Receptor and Growth Hormone Secretagogue Receptor Using Chimeric Constructs' Expression and Co-Expression

W1390 Characterization of a Novel, Potent, and Selective Small Molecule Motilin Receptor Agonist, RQ-00201894

W1390 Characterization of a Novel, Potent, and Selective Small Molecule Motilin Receptor Agonist, RQ-00201894

Colitis affects the smooth muscle and neural response to motilin in the rabbit antrum

The underlying mechanisms of gastric dysfunction during or after an episode of intestinal inflammation are poorly understood. This study investigated the effects of colitis on the contractile effects of motilin, an important endocrine regulator of gastric motility, in the antrum. Myeloperoxidase (MPO) activity, NF-kappaB activity and motilin receptor density were determined in the antrum of rabbits 5 days after the induction of 2,4,6-trinitrobenzenesulphonic acid colitis. Smooth muscle and neural responses to motilin were studied in antral smooth muscle strips in vitro. Colitis did not affect MPO activity, but increased NF-kappaB activity in the antrum. Motilin receptor density in the antrum was not affected. Under control conditions, motilin induced a slowly developing tonic smooth muscle contraction. Five days post-inflammation, tonic contractions to motilin were reduced and preceded by a rapid initial contraction. Other kinases were recruited for the phosphorylation of myosin light chain (MLC) (a multi-functional MLC kinase), and for the inhibition of MLC phosphatase (Rho kinase in addition to protein kinase C) to mediate the motilin-induced contractions during inflammation. Colitis potentiated the cholinergic neural on-contractions in the antrum. This was associated with a hyper-reactivity to motilin and an increased muscle response to ACh. Colitis altered the course of the motilin-induced smooth muscle contraction in the antrum. This involved changes in the kinases phosphorylating MLC. Increased cholinergic excitability to motilin in the antrum may play a role in the pathogenesis of inflammation-associated gastric motility disorders.

Effect of Atilmotin, a Motilin Receptor Agonist, on Esophageal, Lower Esophageal Sphincter, and Gastric Pressures

Motilin, an endogenous gastrointestinal (GI) hormone, increases upper gastrointestinal tract motility and is associated with phase III of the gastric migrating motor complex. The motilin receptor agonist, atilmotin, at doses of 6, 30 or 60 microg intravenously (IV), increases the early phase of gastric emptying. Prior studies at higher doses of 100-450 microg IV demonstrated that some subjects developed noncardiac chest pain. The aim of this study is to determine the effects of atilmotin on esophageal, lower esophageal sphincter (LES), and gastric contractility and the development of esophageal-related symptoms. Ten healthy volunteers underwent esophageal manometry to study the effects of atilmotin on upper GI motility. Five subjects were studied on three separate days following administration of saline placebo and subsequent IV bolus dose of atilmotin (6, 30 or 150 microg). Another five subjects were studied at the highest dose (150 microg). Atilmotin at 150 microg increased proximal gastric pressure by 6.5 mmHg (P = 0.001 compared with placebo). Atilmotin increased LES pressure at all studied doses; LES pressure increased from 24 +/- 2 mmHg following placebo injection to 34 +/- 4 mmHg following a 30 microg dose of atilmotin (P = 0.007). In the esophagus, atilmotin increased the percentage of failed swallows at the highest dose studied. Failed swallows increased from 17 +/- 7% following placebo injection to 36 +/- 7% following a 150 microg dose of atilmotin (P = 0.016). Atilmotin decreased distal esophageal contractile amplitude only at the highest dose studied, from 69 +/- 8 mmHg (placebo) to 50 +/- 5 mmHg following 150 microg atilmotin (P = 0.018). There were no serious adverse effects or episodes of chest pain with atilmotin. Atilmotin affects esophageal, LES, and gastric motility. LES and gastric pressures were increased, whereas there was disruption of esophageal peristalsis characterized by lower amplitude and failed contractions.

The Safety of Macrolides During Lactation

Infantile exposure to macrolides has been associated with hypertrophic pyloric stenosis causing projectile vomiting, dehydration, electrolyte abnormalities, and in rare cases death possibly via macrolide interaction with gastric motilin receptors. Large population-based cohorts have suggested that exposure to macrolides via breastmilk may be associated with pyloric stenosis. In this prospective, controlled observational study designed to assess the safety of macrolides during lactation, we followed infants whose mothers contacted our Drug Consultation Center at the Assaf Harofeh Medical Center (Zerrifin, Israel) inquiring about safety of macrolides during lactation and compared them to a cohort of infants exposed to amoxicillin during breastfeeding. Fifty-five infants exposed to macrolide antibiotics were compared to a control cohort of 36 infants exposed to amoxicillin via lactation. The infants in the macrolide group were all exposed to erythromycin and the newer macrolides: azithromycin, clarithromycin, and roxithromycin. The rate of adverse reactions the infant experienced while being exposed to both antibiotics was comparable. Seven (12.7%) infants in the macrolide group experienced adverse reactions versus three infants (8.3%) in the amoxicillin group (odds ratio = 1.6, 95% confidence interval, 0.38-6.65, p = 0.73). The adverse reactions in the infants exposed to macrolides were rash, diarrhea, loss of appetite, and somnolence, whereas the infants exposed to amoxicillin experienced rashes and somnolence. Factors such as gestational age, age and weight at exposure, maternal age, or type of macrolide were not associated with the infant's adverse reaction in multivariate regression analysis. Rates and types of minor adverse reactions in breastfed infants exposed to a macrolide or amoxicillin in breastmilk were comparable. Macrolide exposure during breastfeeding was not associated with pyloric stenosis, although larger prospective studies are required to confirm our observation.

The discovery and optimisation of benzazepine sulfonamide and sulfones as potent agonists of the motilin receptor

Optimisation of a series of benzazepine sulfonamide hit compounds identified from high throughput screening led to the discovery of a new series of tractable, potent motilin receptor agonists.

Stimulatory action of mitemcinal (GM‐611), an acid‐resistant non‐peptide motilin receptor agonist, on colonic motor activity and defecation: spontaneous and mitemcinal‐induced giant migrating contractions during defecation in dogs

The aim of this study was to characterize giant migrating contractions (GMCs) during spontaneous defecation in dogs and to investigate the effect of mitemcinal (an orally active and highly acid-resistant motilin receptor agonist) on colonic motility to assess the possibility of using it for the treatment of colonic motility disorders. To assess colonic motility, strain-gauge force transducers were implanted on the gastrointestinal tract of five dogs, and the behaviour of the dogs was monitored with a noctovision-video camera system. The effect of mitemcinal (0, 3, 10 or 30 mg per dog) and sennoside (300 mg per dog) on colonic motility was assessed 24 h after oral administration. During a 39-day period, the starting point of most of the 140 GMCs was between the transverse colon and the descending colon, but some variation was observed. In the daytime, the GMCs originated from somewhat more proximal positions than at night. Mitemcinal caused an increase in the GMC-index (integration of contractile amplitude and duration) and proximal translocation of the GMC starting point, but did not cause an increase in the number of defecations 12 h after administration. Sennoside, however, caused a significant increase in the number of defecations, an increase in the GMC-index, and prolongation of the duration of GMCs. The GMC starting point in the canine colon varied during spontaneous defecation. Mitemcinal was a potent prokinetic drug to mimic a spontaneous defecation compared with sennoside. Mitemcinal evacuates more intestinal luminal contents during the defecation than does sennoside.

Re: Myocardial Infarction Associated with Adderall XR and Alcohol Use in a Young Man

<i>Background</i>—Animal studies have shown that motilin affects gall bladder motility. In humans, no effect has been shown, but erythromycin, a motilin receptor agonist, induces gall bladder emptying. <i>Aims</i>—To explore the effect of increasing doses of exogenous motilin on gall bladder volume and antral contractility in the fasted state in humans. <i>Methods</i>—After an overnight fast, eight healthy men received increasing intravenous doses of Leu¹³-motilin (KW-5139) or 0.9% NaCl in a double blind, randomised fashion. Gall bladder volume and antral contraction frequency were determined by ultrasonography. <i>Results</i>—Infusion of motilin increased plasma motilin levels. Motilin induced a reduction in gall bladder volume of 8.0 (5.0)%, 17.1 (5.0)%, 18.5 (4.7)%, and 16.1 (4.9)% of baseline volume at the end of infusion of 2, 4, ,8 and 16 pmol/kg/min respectively, compared with mean stable gall bladder volumes during placebo infusion (p&lt;0.05). Antral contraction frequency increased during motilin infusion, but not during placebo infusion (p&lt;0.05). <i>Conclusions</i>—Exogenous motilin reducted fasting gall bladder volume and increased antral contractions. After reaching maximal reduction, the gall bladder volume did not decrease further during continuous motilin infusion at higher doses and stayed at the same reduced volume. The degree of gall bladder volume reduction during motilin infusion mimicked gall bladder emptying preceding antral phase III activity of the migrating motor complex in humans. This study indicates that motilin may play a physiological role in the regulation of gall bladder emptying in the fasted state.

Stepwise loss of motilin and its specific receptor genes in rodents

Specific interactions among biomolecules drive virtually all cellular functions and underlie phenotypic complexity and diversity. Biomolecules are not isolated particles, but are elements of integrated interaction networks, and play their roles through specific interactions. Simultaneous emergence or loss of multiple interacting partners is unlikely. If one of the interacting partners is lost, then what are the evolutionary consequences for the retained partner? Taking advantages of the availability of the large number of mammalian genome sequences and knowledge of phylogenetic relationships of the species, we examined the evolutionary fate of the motilin (MLN) hormone gene, after the pseudogenization of its specific receptor, MLN receptor (MLNR), on the rodent lineage. We speculate that the MLNR gene became a pseudogene before the divergence of the squirrel and other rodents about 75 mya. The evolutionary consequences for the MLN gene were diverse. While an intact open reading frame for the MLN gene, which appears functional, was preserved in the kangaroo rat, the MLN gene became inactivated independently on the lineages leading to the guinea pig and the common ancestor of the mouse and rat. Gain and loss of specific interactions among biomolecules through the birth and death of genes for biomolecules point to a general evolutionary dynamic: gene birth and death are widespread phenomena in genome evolution, at the genetic level; thus, once mutations arise, a stepwise process of elaboration and optimization ensues, which gradually integrates and orders mutations into a coherent pattern.

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

Abstract There is an urgent clinical need for a safe, efficacious stimulant of gastric emptying; current therapies include erythromycin (an antibiotic with additional properties which preclude chronic use) and metoclopramide (a 5‐hydroxytryptamine type 4 receptor agonist and an antagonist at brain D2 receptors, associated with movement disorders). To move away from the complex motilide structure of erythromycin, a small molecule motilin receptor agonist, GSK962040, was identified and characterized. The compound was evaluated using recombinant human receptors, rabbit and human isolated stomach preparations known to respond to motilin and in vivo, by measuring its ability to increase defecation in conscious rabbits. At the human motilin receptor, the pEC50 (the negative logarithm to base 10 of the EC50 value, the concentration of agonist that produces 50% of the maximal response) values for GSK962040 and erythromycin as agonists were, respectively, 7.9 and 7.3; GSK962040 had no significant activity at a range of other receptors (including ghrelin), ion channels and enzymes. In rabbit gastric antrum, GSK962040 300 nmol L−1–10 μmol L−1 caused a prolonged facilitation of the amplitude of cholinergically mediated contractions, to a maximum of 248 ± 47% at 3 μmol L−1. In human‐isolated stomach, GSK962040 10 μmol L−1, erythromycin 10 μmol L−1 and [Nle13]‐motilin 100 nmol L−1, each caused muscle contraction of similar amplitude. In conscious rabbits, intravenous doses of 5 mg kg−1 GSK962040 or 10 mg kg−1 erythromycin significantly increased faecal output over a 2‐h period. Together, these data show that GSK962040, a non‐motilide structure, selectively activates the motilin receptor. Simplification of the structural requirements to activate this receptor greatly facilitates the design of potentially new medicines for gastroparesis.

An orally active motilin receptor antagonist, MA-2029, inhibits motilin-induced gastrointestinal motility, increase in fundic tone, and diarrhea in conscious dogs without affecting gastric emptying

The pharmacological properties of MA-2029, a selective and competitive motilin receptor antagonist, were investigated in conscious dogs after oral administration. Gastrointestinal contractile activity was recorded by chronically implanted force transducers. The proximal gastric volume was measured with a barostat under constant pressure. Gastric emptying was examined using the paracetamol absorption test. MA-2029 (0.3–10 mg/kg, p.o.) administered in the interdigestive state inhibited gastrointestinal contractions induced by motilin (3 µg/kg, i.v.) in a dose-dependent manner. MA-2029 (0.3–3 mg/kg, p.o.) also inhibited the occurrence of spontaneous phase III contractions, even though MA-2029 had no effect on basal gastrointestinal motility or basal gastric emptying even at 10 and 30 mg/kg p.o. The inhibitory effect of MA-2029 on motilin-induced gastrointestinal motility corresponded to its plasma concentration. Motilin (0.3 µg/kg/h, i.v. infusion) reduced the proximal gastric volume by about 50% of control during isobaric distension. This effect was also inhibited by MA-2029 (1–10 mg/kg, p.o.) in a dose-dependent manner. In the digestive state, injection of motilin (3 µg/kg, i.v.) induced diarrhea in 9 of 11 dogs. MA-2029 (1–30 mg/kg, p.o.) reduced the incidence of diarrhea induced by motilin in a dose-dependent manner. The results indicate that MA-2029 inhibits hypermotility induced by motilin in conscious dogs without having an effect on the basal gastrointestinal tone or gastric emptying rate. MA-2029 may be useful in treating gastrointestinal disorders in which the pathogenesis involves the elevation of circulating motilin.

235 PF-04548043, a Novel Motilin Receptor Agonist, Increases Gastric Emptying in Healthy Volunteers and Does Not Undergo Tachyphylaxis

235 PF-04548043, a Novel Motilin Receptor Agonist, Increases Gastric Emptying in Healthy Volunteers and Does Not Undergo Tachyphylaxis