Ghrelin/motilin-related peptide is a potent prokinetic to reverse gastric postoperative ileus in rat

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.

Phlorizin attenuates postoperative gastric ileus in rats

BACKGROUND

Postoperative ileus (POI) is a major complication of abdominal surgery (AS). Impaired gut barrier mediated via Toll-like receptor 4 (TLR4) and interleukin-1 (IL-1) receptor is involved in the development of POI. Phlorizin is a nonselective inhibitor of sodium-linked glucose transporters (SGLTs) and is known to improve lipopolysaccharide (LPS)-induced impaired gut barrier. This study aimed to clarify our hypothesis that AS-induced gastric ileus is mediated via TLR4 and IL-1 signaling, and phlorizin improves the ileus.

METHODS

AS consisted of a celiotomy and manipulation of the cecum for 1 min. Gastric emptying (GE) in 20 min with liquid meal was determined 3 h after the surgery in rats. The effect of subcutaneous (s.c.) injection of LPS (1 mg kg-1 ) was also determined 3 h postinjection.

KEY RESULTS

AS delayed GE, which was blocked by TAK-242, an inhibitor of TLR4 signaling and anakinra, an IL-1 receptor antagonist. LPS delayed GE, which was also mediated via TLR4 and IL-1 receptor. Phlorizin (80 mg kg-1 , s.c.) significantly improved delayed GE induced by both AS and LPS. However, intragastrical (i.g.) administration of phlorizin did not alter it. As gut mainly expresses SGLT1, SGLT2 may not be inhibited by i.g. phlorizin. The effect of phlorizin was blocked by ghrelin receptor antagonist in the LPS model.

CONCLUSIONS & INFERENCES

AS-induced gastric ileus is mediated via TLR4 and IL-1 signaling, which is simulated by LPS. Phlorizin improves the gastric ileus via activation of ghrelin signaling, possibly by inhibition of SGLT2. Phlorizin may be useful for the treatment of POI.

Understanding the potential causes of gastrointestinal dysfunctions in multiple system atrophy

Multiple system atrophy (MSA) is a rare, progressive neurodegenerative disorder characterised by autonomic, pyramidal, parkinsonian and/or cerebellar dysfunction. Autonomic symptoms of MSA include deficits associated with the gastrointestinal (GI) system, such as difficulty swallowing, abdominal pain and bloating, nausea, delayed gastric emptying, and constipation. To date, studies assessing GI dysfunctions in MSA have primarily focused on alterations of the gut microbiome, however growing evidence indicates other structural components of the GI tract, such as the enteric nervous system, the intestinal barrier, GI hormones, and the GI-driven immune response may contribute to MSA-related GI symptoms. Here, we provide an in-depth exploration of the physiological, structural, and immunological changes theorised to underpin GI dysfunction in MSA patients and highlight areas for future research in order to identify more suitable pharmaceutical treatments for GI symptoms in patients with MSA.

The ghrelin agonist, HM01 activates central vagal and enteric cholinergic neurons and reverses gastric inflammatory and ileus responses in rats

BACKGROUND

Electrical vagal stimulation alleviates abdominal surgery (AS)-induced intestinal inflammation. Ghrelin receptors (GHS-Rs) are expressed in the brain and peripheral tissues. We investigated the influence of HM01, an orally active ghrelin agonist crossing the blood-brain barrier, on AS-induced gastric inflammation and emptying (GE) in rats.

METHODS

HM01 (6 mg/kg) or saline pretreatment was administered per orally (po) or intraperitoneally (ip). We assessed GE, gastric cytokine mRNA, and Fos positive cells in the dorsal motor nucleus of the vagus (DMN) and gastric corpus myenteric plexus (MP) in sham (anesthesia alone) and AS groups. The transcripts of GHS-R1 variants were determined in the medulla oblongata and gastric corpus of naïve rats.

KEY RESULTS

In vehicle pretreated rats, HM01 (ip) significantly increased the number of Fos immunoreactive cells in the MP and DMN in 55% and 52% of cholinergic neurons respectively. Hexamethonium did not modify HM01-induced Fos expression in the DMN while reducing it in the MP by 2-fold with values still significantly higher than that in control groups. AS upregulated gastric IL-1β and TNFα expression and inhibited GE by 66.6%. HM01 (po) abolished AS-induced gastric ileus and increased cytokine expression and elevated IL-10 by 4.0-fold versus vehicle/sham. GHS-R1a mRNA level was 5.4-fold higher than the truncated GHS-R1b isoform in the brain medulla and 40-fold higher in the gastric submucosa/muscle layers than in the mucosa.

CONCLUSIONS AND INFERENCE

Peripheral HM0 activates central vagal and myenteric cholinergic pathways that may influence both central and peripheral targets to prevent AS-induced gastric inflammatory and ileus.

Yeokwisan, a Standardized Herbal Formula, Enhances Gastric Emptying via Modulation of the Ghrelin Pathway in a Loperamide-induced Functional Dyspepsia Mouse Model

Background: Yeokwisan, a standardized herbal formula, has exhibited clinical benefit for patients suffering from refractory functional dyspepsia (FD) in Korea since 2016. However, data about the mechanism of action of this formula are yet not available. Aim of the study: To evaluate and explore the effects of Yeokwisan on gastric emptying, a major symptom of functional dyspepsia, and its underlying mechanisms of action using a mouse model. Materials and methods: BALB/C mice were pretreated with Yeokwisan (100, 200, and 400 mg/kg, po) or mosapride (3 mg/kg, po) for 5 days and then treated with loperamide (10 mg/kg, ip) after 20 h of fasting. A solution of 0.05% phenol red (500 μL) or diet of 5% charcoal (200 μL) was orally administered, followed by assessment of gastric emptying or intestinal transit. Plasma acyl-ghrelin (ELISA), C-kit (immunofluorescence and western blotting), nNOS (western blotting) and gastric contraction- and ghrelin-related gene/protein expression levels were examined in stomach and small intestine tissues. Results: Loperamide injection substantially delayed gastric emptying, while Yeokwisan pretreatment (especially 200 and 400 mg/kg Yeokwisan) significantly attenuated this peristaltic dysfunction, as evidenced by the quantity of phenol red retained in the stomach (p < 0.05 or 0.01) and stomach weight (p < 0.05 or 0.01). The levels of plasma acyl-ghrelin and expression of gastric ghrelin-related genes, such as growth hormone secretagogue receptor (GHSR), ghrelin-O-acyltransferase (GOAT), adrenergic receptor β1 (ADRB1) and somatostatin receptor (SSTR), were significantly normalized (p < 0.05 or 0.01) by Yeokwisan (400 mg/kg). Yeokwisan (400 mg/kg) significantly tempered the loperamide-induced alterations in the c-kit and nNOS levels (p < 0.01) as well as the expression of contraction- and ghrelin-related genes, such as 5-HT4 receptor (5-HT4R), anoctamin-1 (ANO1), ryanodine receptor 3 (RYR3) and smooth muscle myosin light chain kinase (smMLCK), in the stomach, but not in the small intestine. Conclusion: The present results showed the clinical relevance of Yeokwisan, in treating FD, especially in promoting gastric emptying but not small intestinal transit. The main mechanisms corresponding to these effects may involve the modulation of the ghrelin pathway and activation of interstitial cells of Cajal in stomach tissue.

Postoperative ileus-An ongoing conundrum

BACKGROUND

Postoperative ileus is common and is a major clinical problem. It has been widely studied in patients and in experimental models in laboratory animals. A wide variety of treatments have been tested to prevent or modify the course of this disorder.

PURPOSE

This review draws together information on animal studies of ileus with studies on human patients. It summarizes some of the conceptual advances made in understanding the mechanisms that underlie paralytic ileus. The treatments that have been tested in human subjects (both pharmacological and non-pharmacological) and their efficacy are summarized and graded consistent with current clinical guidelines. The review is not intended to provide a comprehensive overview of ileus, but rather a general understanding of the major clinical problems associated with it, how animal models have been useful to elucidate key mechanisms and, finally, some perspectives from both scientists and clinicians as to how we may move forward with this debilitating yet common condition.

The GPCR accessory protein MRAP2 regulates both biased signaling and constitutive activity of the ghrelin receptor GHSR1a

Ghrelin is a hormone secreted by the stomach during fasting periods and acts through its receptor, the growth hormone secretagogue 1a (GHSR1a), to promote food intake and prevent hypoglycemia. As such, GHSR1a is an important regulator of energy and glucose homeostasis and a target for the treatment of obesity. Here, we showed that the accessory protein MRAP2 altered GHSR1a signaling by inhibiting its constitutive activity, as well as by enhancing its G protein-dependent signaling and blocking the recruitment and signaling of β-arrestin in response to ghrelin. In addition, the effects of MRAP2 on the Gα_q and β-arrestin pathways were independent and involved distinct regions of MRAP2. These findings may have implications for the regulation of ghrelin function in vivo and the role of MRAP2 in energy homeostasis. They also show that accessory proteins can bias signaling downstream of GPCRs in response to their endogenous agonist.

Cyclic vomiting syndrome: an overview for clinicians

Introduction: Cyclic vomiting syndrome (CVS) is an under recognized entity causing significant impact on patient's lifestyle. CVS is characterized by recurrent episodes of abdominal pain, nausea, and vomiting leading to many emergency department presentations prior to diagnosis. Patients often have lengthy delays in starting appropriate therapy leading to significant physical and financial hardship. Most cases of cyclic vomiting syndrome are reversible by managing risk factors and starting on appropriate treatment.Areas covered: This review covers the diagnostic criteria, pathophysiology, risk factors, and treatment for CVS and provides a valuable resource for clinicians to review and help with managing this challenging syndrome. The latest literature regarding the diagnosis and management of CVS is summarized.Expert Opinion: The direction for future research in CVS and insights to managing CVS are summarized. The role of pain that can be frequently controlled by tricyclic antidepressants and lorazepam suggests a central nervous system (CNS) origin. A standardized treatment regimen for CVS must be implemented as patients do respond to current therapies but there is often a significant delay in initiation of treatment. Reviewed recent data looking at MRI brain changes in patients with CVS that may lead to a better understanding of the pathophysiology of this disease.

A novel 86-bp indel of the motilin receptor gene is significantly associated with growth and carcass traits in Gushi-Anka F2 reciprocal cross chickens

1. A previous whole-genome association analysis has identified the motilin receptor gene (MLNR), which regulates gastrointestinal motility and gastric emptying, as a candidate gene related to chicken growth.2. MLNR mRNA was expressed in all tissues tested, and the expression level in digestive tissues was greater than in other tissues. Expression levels in the pancreas, duodenum and glandular stomach at day old and one, two and three weeks of age indicated a possible correlation with the digestive system. This suggested that the MLNR gene plays a central role in gastrointestinal tract function and affects the growth and development of chickens. Moreover, there was a significant difference in expression in the glandular stomach tissue between Ross 308 and Gushi chickens at six weeks of age.3. Re-sequencing revealed an 86-bp insertion/deletion polymorphism in the downstream region of the MLNR gene. The mutation locus was genotyped in 2,261 individuals from nine different chicken breeds. MLNR expression levels in the glandular stomach of chickens with DD genotypes were greater than those in chickens with the ID and II genotypes. The DD genotype was the most dominant genotype in commercial broiler's (Ross 308 and Arbor Acres broilers), and the D allele frequency in these breeds exceeded 91%. The deletion mutation tended towards fixation in commercial broilers.4. Association with growth and carcass traits analysed in a Gushi-Anka F₂ intercrossed population, showed that the DD genotype was significantly associated with the greatest growth and carcass trait values, whereas values associated with the II genotype were the lowest in the F₂ reciprocal cross chickens.5. The results suggest that the mutation is strongly associated with growth related traits and it is likely to be useful for marker-assisted selection of chickens.

Protective effect of silkworm pupa oil on hydrochloric acid/ethanol-induced gastric ulcers

BACKGROUND

Silkworm pupae are a traditional Chinese food, rich in various saturated and unsaturated fatty acids. Unsaturated fatty acids have a certain protective effect against oxidative damage. The present study used an animal model to determine the protective effect of silkworm pupa oil on hydrochloric acid / ethanol-induced gastric ulcer.

RESULTS

Silkworm pupa oil is rich in unsaturated fatty acids, including palmitoleic acid 63.4 g kg^-1 , oleic acid 249.1 g kg^-1 , linoleic acid 47.0 g kg^-1 , and linolenic acid 337.8 g kg^-1 , whereas its unsaturated fatty acid content is 700 g kg^-1 . Compared to a gastric ulcer control group, high and low doses of pupa oil reduced gastric ulcer area and gastric secretion, whereas gastric pH increased. It also increased serum antioxidant superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) levels, somatostatin (SST), and vasoactive intestinal peptide (VIP) levels, and reduced serum interleukin-6 (IL-6), interleukin-12 (IL-12), tumor necrosis factor (TNF-α), and interferon-γ (IFN-γ), motilin (MTL), and gastrin (GT) levels. RT-qPCR and western blot analyses indicated that silkworm pupa oil significantly increased CAT, GSH-Px, epidermal growth factor (EGF), Epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), Cu/Zn-SOD, Mn-SOD, and NF-kappa-B inhibitor-α (IκB-α) expression and lowered nuclear factor-kappa B (NF-κB), B-cell lymphoma-2 (Bcl-2), cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS) expression.

CONCLUSION

Silkworm pupa oil treatment reduced oxidative damage and inflammation in mice, and high-dose silkworm pupa oil was superior to low-dose silkworm pupa oil, following ranitidine. © 2018 Society of Chemical Industry.

Alpha-melanocyte stimulating hormone in ghrelin-elicited feeding and gut motility

This review evaluates published studies regarding alpha-melanocyte stimulating hormone (α-MSH) in ghrelin-elicited feeding and gut motility. We have sought to integrate all available evidences to provide a complete review on the properties of melanocortin receptors (MCR) and the potential clinical treatment of α-MSH after ghrelin-elicited feeding and gut motility. The available studies were grouped into four categories: food intake, gastric emptying, small intestinal transit, and colonic transit. As we describe, the literature provides evidence of the ability of ghrelin to increase food intake, gastric emptying, small intestinal transit, and colonic transit. α-MSH, which displays high affinity for the MC3 and MC4 receptors, can competitively activate MCRs with agouti-related protein stimulated by ghrelin, and partly attenuates the effect of acyl ghrelin on food intake. Central ghrelin-induced acceleration of gastric emptying is not mediated by MCRs, but the acceleration of the small intestinal transit is at least partly mediated via MCRs in the brain. Similar to fecal pellets and total fecal weight, distal colonic motility and secretion are partly mediated by MCRs in the brain. The interplay between acyl ghrelin and MCRs may provide a new therapeutic avenue to ameliorate anorexia and constipation.

A Comparison of the Central versus Peripheral Gastrointestinal Prokinetic Activity of Two Novel Ghrelin Mimetics

The gastrointestinal (GI) prokinetic effects of ghrelin occur through direct peripheral effects on ghrelin receptors within the enteric nervous system and via the ghrelin receptor on the vagus nerve, which activate a centrally mediated mechanism. However, the relative contribution of peripheral versus central effects to the overall prokinetic effect of ghrelin agonists requires further investigation. Here, we investigated the central versus peripheral prokinetic effect of ghrelin by using two novel ghrelin agonists: HM01 (N'-[(1S)-1-(2,3-dichloro-4-methoxyphenyl)ethyl]-N-methyl-N-[1,3,3-trimethyl-(4R)-piperidyl]-urea HCL) with high brain penetration compared with HM02 (N'-[(1S)-1-(2,3-dichloro-4-methoxyphenyl)ethyl]-N-hydroxy-N-(1-methyl-4-piperidinyl)-urea), a more peripherally acting ghrelin agonist. The pharmacokinetic profiles of both ghrelin agonists were evaluated after intravenous and oral administration in rats. The efficacy of HM01 and HM02 was assessed in a rat model of postoperative ileus (POI) induced by abdominal surgery and in a rodent defecation assay. Pharmacokinetic results in our models confirmed that HM01, but not HM02, was a brain-penetrant ghrelin agonist. Administration of either HM01 or HM02 reversed the delayed upper and lower gastrointestinal transit induced by abdominal surgery to levels resembling the non-POI controls. In the defecation test, HM01, but not HM02, significantly increased the weight of fecal pellets. Our findings suggest that, in a rodent model of POI, synthetic ghrelin agonists stimulate GI transit through a peripheral site of action. However, in the defecation assay, our data suggest that a ghrelin-mediated mechanism is located at a central site. Taken together, a ghrelin agonist with both central and peripheral prokinetic activity may show therapeutic potential to treat delayed GI transit disorders.

Effects of burns on gut motor and mucosa functions

This review analyzed the published studies on the effects of thermal injury on gastrointestinal motility and mucosal damage. Our strategy was to integrate all available evidence to provide a complete review on the prokinetic properties of variable reagents and the potential clinical treatment of mucosal damage and gastrointestinal dysmotility after thermal injury. We classified the studies into two major groups: studies on gastrointestinal dysmotility and studies on mucosal damage. We also subclassified the studies into 3 parts: stomach, small intestine, and colon. This review shows evidence that ghrelin can recover burn-induced delay in gastric emptying and small intestinal transit, and can protect the gastric mucosa from burn-induced injury. Oxytocin and β-glucan reduced the serum inflammatory mediators, and histological change and mucosal damage indicators, but did not show evidence of having the ability to recover gastrointestinal motility. Using a combination of different reagents to protect the gastrointestinal mucosa against damage and to recover gastrointestinal motility is an alternative treatment for thermal injury.

Diminished gastric prokinetic response to ghrelin in a rat model of spinal cord injury

BACKGROUND

Patients with cervical or high-thoracic spinal cord injury (SCI) often present reduced gastric emptying and early satiety. Ghrelin provokes motility via gastric vagal neurocircuitry and ghrelin receptor agonists offer a therapeutic option for gastroparesis. We have previously shown that experimental high-thoracic injury (T3-SCI) diminishes sensitivity to another gastrointestinal peptide, cholecystokinin. This study tests the hypothesis that T3-SCI impairs the vagally mediated response to ghrelin.

METHODS

We investigated ghrelin sensitivity in control and T3-SCI rats at 3-days or 3-weeks after injury utilizing: (i) acute (3-day post-injury) fasting and post-prandial serum levels of ghrelin; (ii) in vivo gastric reflex recording following intravenous or central brainstem ghrelin; and (iii) in vitro whole cell recording of neurons within the dorsal motor nucleus of the vagus (DMV).

KEY RESULTS

The 2-day food intake of T3-SCI rats was reduced while fasting serum ghrelin levels were higher than in controls. Intravenous and fourth ventricle ghrelin increased in vivo gastric motility in fasted 3-day control rats but not fasted T3-SCI rats. In vitro recording of DMV neurons from 3-day T3-SCI rats were insensitive to exogenous ghrelin. For each measure, vagal responses returned after 3-weeks.

CONCLUSIONS AND INFERENCES

Hypophagia accompanying T3-SCI produces a significant and physiologically appropriate elevation in serum ghrelin levels. However, higher ghrelin levels did not translate into increased gastric motility in the acute stage of T3-SCI. We propose that this may reflect diminished sensitivity of peripheral vagal afferents to ghrelin or a reduction in the responsiveness of medullary gastric vagal neurocircuitry following T3-SCI.

Evaluation of mTOR signaling pathway proteins in rat gastric mucosa exposed to sulfite and ghrelin

BACKGROUND/AIMS

Mammalian target of rapamycin (mTOR) signaling serves as a central regulator of cell growth, proliferation, and survival. In this study, we planned to evaluate the expressions of mTOR signaling constituents (p-p70S6K, p-mTOR, and p-Tuberin) in rat gastric mucosa and to compare the results in sulfite- and sulfite+ghrelin-exposed groups.

MATERIALS AND METHODS

Rats were divided into three groups: the control group (C), the sodium metabisulfite (Na2S2O5) (S) group, and sulfite+ghrelin (SG) group. Sodium metabisulfite at 100 mg/kg/day was administered via gavage, and ghrelin at 20 μg/kg/day was administered intraperitoneally for 35 days. We have used immunohistochemistry for mTOR signaling pathway components.

RESULTS

There were no significant differences for p-p70S6K and p-mTOR expression among the C, S, and SG groups. Tuberin expression was significantly increased in the S group compared to the C group. Furthermore, tuberin expression was found to be significantly decreased in the SG group.

CONCLUSION

This study is the first one in the literature that shows the expression of mTOR signaling proteins in gastric mucosa of rats exposed to sulfite and ghrelin. Furthermore, it demonstrates that ghrelin treatment reduces p-Tuberin expression induced by ingested sulfite.

Ardipusilloside-I stimulates gastrointestinal motility and phosphorylation of smooth muscle myosin by myosin light chain kinase

Ardipusilloside-I is a natural triterpenoid saponin, which was isolated from Ardisia pusilla A. DC. The aim of the study was to evaluate the stimulation of ardipusilloside-I on gastrointestinal motility in vitro and in vivo. The experiment of smooth muscle contraction directly monitored the contractions of the isolated jejunal segment (IJS) in different contractile states, and the effects of ardipusilloside-I on myosin were measured in the presence of Ca²⁺-calmodulin using the activities of 20 kDa myosin light chain (MLC₂₀) phosphorylation and myosin Mg²⁺-ATPase. The effects of ardipusilloside-I on gastro emptying and intestinal transit in constipation-predominant rats were observed, and the MLCK expression in jejuna of constipated rats was determined by western blot. The results showed that, ardipusilloside-I increased the contractility of IJS in a dose-dependent manner and reversed the low contractile state (LCS) of IJS induced by low Ca²⁺, adrenaline, and atropine respectively. There were synergistic effects on contractivity of IJS between ardipusilloside-I and ACh, high Ca²⁺, and histamine, respectively. Ardipusilloside-I could stimulate the phosphorylation of MLC₂₀ and Mg²⁺-ATPase activities of Ca²⁺- dependent phosphorylated myosin. Ardipusilloside-I also stimulated the gastric emptying and intestinal transit in normal and constipated rats in vivo, respectively, and increased the MLCK expression in the jejuna of constipation-predominant rats. Briefly, the findings demonstrated that ardipusilloside-I could effectively excite gastrointestinal motility in vitro and in vivo.

Gastrointestinal motility dysfunction in critically ill patients: Pathogenesis, clinical assessment, and treatment

Gastrointestinal motility dysfunction is a common clinical complication in ICU patients, which can lead to difficulty in enteral nutrition, vomiting, diarrhea, increased intra-abdominal pressure, ventilator associated pneumonia, intestinal flora displacement, and other adverse reactions. The clinical features of gastrointestinal dysfunction mainly include gastric emptying disturbance, intestinal dysfunction, and gastrointestinal motility disorders. The causes of gastrointestinal motility dysfunction in ICU patients are complex and the clinical evaluation of gastrointestinal dysfunction is difficult. These factors have led to the fact that gastrointestinal motility monitoring techniques have not been widely used in clinical practice. Timely detection and correction of gastrointestinal motility dysfunction in ICU patients can improve outcomes. This article reviews the etiology, clinical evaluation, and treatment of gastrointestinal motility dysfunction in ICU patients.

Relamorelin for the treatment of gastrointestinal motility disorders

INTRODUCTION

Current treatments for gastroparesis are limited. Chronic idiopathic constipation (CIC) has more treatment options, but none are efficacious for severe cases. Areas covered: Molecular targets to accelerate GI motility are being identified, and relamorelin, a synthetic ghrelin analog, has been promising. In humans, relamorelin increases growth hormone levels and accelerates gastric emptying. Relamorelin was superior to placebo for symptom relief in phase IIA studies for diabetic gastroparesis (DG) and CIC. In phase IIB studies in DG, relamorelin did not significantly reduce vomiting frequency when compared to placebo, but it reduced four symptoms of DG (nausea, fullness, bloating and abdominal pain) and accelerated gastric emptying. To date, relamorelin has been well tolerated and safe in humans without cardiac or neurologic adverse effects. It is still in clinical trial stages and not yet approved by the Food and Drug Administration. Phase III studies are underway. Expert opinion: Relamorelin shows promise in treating DG, with a reduction in core symptoms. Relative to available treatments, it appears to be efficacious and well tolerated. The absence of neurological or cardiovascular adverse effects places it at an advantage over other available therapies. Once approved, it will likely become the drug of first choice for DG.

α-melanocyte stimulating hormone modulates the central acyl ghrelin-induced stimulation of feeding, gastrointestinal motility, and colonic secretion

Background

Acyl ghrelin-induced intake depends on hypothalamic neuropeptide Y and agouti-related protein (AgRP) neurotransmitters. Intracerebroventricular (ICV) injection of AgRP increases feeding through competitive antagonism at melanocortin receptors. ICV administration of α-melanocyte stimulating hormone (α-MSH), a natural antagonist of AgRP, may modulate the acyl ghrelin-induced orexigenic effect.

Objective

This study aimed to investigate the modulating effect of α-MSH on the central acyl ghrelin-induced food intake, gastrointestinal motility, and colonic secretion in rats.

Methods and procedures

We examined the effects of α-MSH and acyl ghrelin on food intake, gastric emptying, small intestinal transit, colonic motility, and secretion in conscious rats with a chronic implant of ICV catheters.

Results

ICV injection of O-n-octanoylated ghrelin (0.1 nmol/rat) significantly increased the cumulative food intake up to 8 h (P<0.01), enhanced non-nutrient semi-liquid gastric emptying (P<0.001), increased the geometric center and running percentage of small intestinal transit (P<0.001), accelerated colonic transit time (P<0.05), and increased fecal pellet output (P<0.01) and total fecal weight (P<0.01). Pretreatment with ICV injection of α-MSH (1.0 and 2.0 nmol/rat) attenuated the acyl ghrelin-induced hyperphagic effect, fecal pellet output, and total fecal weight, while higher dose of α-MSH (2.0 nmol/rat) attenuated the increase in the geometric center of small intestinal transit (P<0.01). However, neither dose of α-MSH altered acyl ghrelin-stimulated gastroprokinetic effect, increase in the running percentage of small intestinal transit, nor accelerated colonic transit time.

Conclusion

α-MSH is involved in central acyl ghrelin-elicited feeding, small intestinal transit, fecal pellet output, and fecal weight. α-MSH does not affect central acyl ghrelin-induced acceleration of gastric emptying and colonic transit time in rats.

Gastrointestinal Peptides During Chronic Gastric Electrical Stimulation in Patients With Intractable Vomiting

OBJECTIVES

Gastric electrical stimulation (GES) is an alternative therapy to treat patients with intractable vomiting. A preclinical study has demonstrated the modulation of the gastrointestinal (GI) peptide ghrelin by GES but such mechanism has never been investigated in patients. The aim of this work was to assess the effect of GES on GI peptide levels in patients with intractable vomiting.

MATERIALS AND METHODS

Twenty-one patients were randomized to receive either ON or OFF GES, 14 completed the study (10 ON, 4 OFF stimulation). Vomiting episodes, gastric emptying, and gastrointestinal quality of life index (GIQLI) were assessed. Gastric and blood samples were collected before and four months after the ON period of gastric stimulation. mRNA and/or peptide levels were assessed in gastric biopsies for ghrelin, leptin, and NUCB2/nesfatin-1 and in duodenal biopsies for glucagon-like peptide 1 (GLP-1) and peptide YY (PYY) using RT-qPCR and multiplex technology. Ghrelin, leptin, GLP-1, PYY, gastric inhibitory peptide (GIP), and NUCB2/nesfatin-1 levels also were quantified in blood samples.

RESULTS

Among clinical parameters, vomiting episodes were slightly reduced by GES (p = 0.09). In tissue, mRNA or protein levels were not modified following chronic GES. In blood, a significant reduction of postprandial PYY levels (p < 0.05) was observed at M4 and a reduction of NUCB2/nesfatin-1 levels in fasted patients (p < 0.05). Increased plasma leptin levels after GES were correlated with reduction of vomiting and improvement of GIQLI.

CONCLUSIONS

GES reduces NUCB2/nesfatin-1 levels under fasting conditions and postprandial PYY levels in patients suffering from nausea and/or vomiting refractory to pharmacological therapies.

Therapeutic Potential of Targeting the Ghrelin Pathway

Ghrelin was discovered in 1999 as the endogenous ligand of the growth-hormone secretagogue receptor 1a (GHSR1a). Since then, ghrelin has been found to exert a plethora of physiological effects that go far beyond its initial characterization as a growth hormone (GH) secretagogue. Among the numerous well-established effects of ghrelin are the stimulation of appetite and lipid accumulation, the modulation of immunity and inflammation, the stimulation of gastric motility, the improvement of cardiac performance, the modulation of stress, anxiety, taste sensation and reward-seeking behavior, as well as the regulation of glucose metabolism and thermogenesis. Due to a variety of beneficial effects on systems’ metabolism, pharmacological targeting of the endogenous ghrelin system is widely considered a valuable approach to treat metabolic complications, such as chronic inflammation, gastroparesis or cancer-associated anorexia and cachexia. The aim of this review is to discuss and highlight the broad pharmacological potential of ghrelin pathway modulation for the treatment of anorexia, cachexia, sarcopenia, cardiopathy, neurodegenerative disorders, renal and pulmonary disease, gastrointestinal (GI) disorders, inflammatory disorders and metabolic syndrome.

Nesfatin-1 regulates the lateral hypothalamic area melanin-concentrating hormone-responsive gastric distension-sensitive neurons and gastric function via arcuate nucleus innervation

Nesfatin-1, a recently discovered neuropeptide involved in satiety. Recent studies have revealed that central nesfatin-1 inhibits gastric emptying and gastric acid secretion, though the mechanisms involved in these processes are not known. We aim to explore the effects of nesfatin-1 on a population of gastric distension (GD)-sensitive neurons in the lateral hypothalamus (LHA), gastric motility, and gastric secretion and the role for an arcuate nucleus (Arc)-LHA neural pathway in these processes. Single unit extracellular discharge recordings were made in of LHA. Further, gastric motility and gastric secretion in rats were monitored. Retrograde tracing and fluorescent immunohistochemical staining were used to explore nesfatin-1 neuron projection. The results revealed that administration of nesfatin-1 to the LHA or electric stimulation of the Arc could alter the neuronal activity of melanin-concentrating hormone (MCH)-responsive, GD-responsive neurons in LHA, which could be blocked by pretreatment with MCH receptor-1 antagonist PMC-3881-PI or weakened by pretreatment of a nesfatin-1 antibody in LHA. Administration of nesfatin-1 into LHA could inhibit gastric motility and gastric secretion, and these effects could be enhanced by administration of PMC-3881-PI. Electrical stimulation of Arc promoted the gastric motility and gastric secretion. Nesfatin-1 antibody or PMC-3881-PI pretreatment to LHA had no effect on Arc stimulation-induced gastric motility, but these pretreatments did alter Arc stimulation-induced effects on gastric secretion. Our findings suggest that nesfatin-1 signaling in LHA participates in the regulation of efferent information from the gastrointestinal tract and gastric secretion which also involve MCH signaling. Further, they show that a nesfatin-1-positive Arc to LHA pathway is critical for these effects.

From Belly to Brain: Targeting the Ghrelin Receptor in Appetite and Food Intake Regulation

Ghrelin is the only known peripherally-derived orexigenic hormone, increasing appetite and subsequent food intake. The ghrelinergic system has therefore received considerable attention as a therapeutic target to reduce appetite in obesity as well as to stimulate food intake in conditions of anorexia, malnutrition and cachexia. As the therapeutic potential of targeting this hormone becomes clearer, it is apparent that its pleiotropic actions span both the central nervous system and peripheral organs. Despite a wealth of research, a therapeutic compound specifically targeting the ghrelin system for appetite modulation remains elusive although some promising effects on metabolic function are emerging. This is due to many factors, ranging from the complexity of the ghrelin receptor (Growth Hormone Secretagogue Receptor, GHSR-1a) internalisation and heterodimerization, to biased ligand interactions and compensatory neuroendocrine outputs. Not least is the ubiquitous expression of the GHSR-1a, which makes it impossible to modulate centrally-mediated appetite regulation without encroaching on the various peripheral functions attributable to ghrelin. It is becoming clear that ghrelin’s central signalling is critical for its effects on appetite, body weight regulation and incentive salience of food. Improving the ability of ghrelin ligands to penetrate the blood brain barrier would enhance central delivery to GHSR-1a expressing brain regions, particularly within the mesolimbic reward circuitry.

Nesfatin-1 influences the excitability of gastric distension-responsive neurons in the ventromedial hypothalamic nucleus of rats

The present study investigated the effects of nesfatin-1 on gastric distension (GD)-responsive neurons via an interaction with corticotropin-releasing factor (CRF) receptor signaling in the ventromedial hypothalamic nucleus (VMH), and the potential regulation of these effects by hippocampal projections to VMH. Extracellular single-unit discharges were recorded in VHM following administration of nesfatin-1. The projection of nerve fibers and expression of nesfatin-1 were assessed by retrograde tracing and fluoro-immunohistochemical staining, respectively. Results showed that there were GD-responsive neurons in VMH; Nesfatin-1 administration and electrical stimulation of hippocampal CA1 sub-region altered the firing rate of these neurons. These changes could be partially blocked by pretreatment with the non-selective CRF antagonist astressin-B or an antibody to NUCB2/nesfatin-1. Electrolytic lesion of CA1 hippocampus reduced the effects of nesfatin-1 on VMH GD-responsive neuronal activity. These studies suggest that nesfatin-1 plays an important role in GD-responsive neuronal activity through interactions with CRF signaling pathways in VMH. The hippocampus may participate in the modulation of nesfatin-1-mediated effects in VMH.

Effects of ghrelin receptor agonist, relamorelin, on gastric motor functions and satiation in healthy volunteers

BACKGROUND

Synthetic human ghrelin accelerates gastric emptying, reduces gastric accommodation, and results in numerical increases in postprandial symptom scores. The ghrelin receptor agonist, relamorelin, accelerates gastric emptying in patients with diabetic gastroparesis.

AIM

To measure pharmacological effects of relamorelin on gastric accommodation, distal antral motility, and satiation in healthy volunteers.

METHODS

In a placebo-controlled, double-blind, randomized study of 16 healthy volunteers, we compared effects of 30 μg subcutaneous (s.c.) relamorelin to placebo on: (i) gastric volumes measured by single photon emission computed tomography, (ii) 1-h postprandial distal antral motility index (MI) by 15-lumen perfusion gastroduodenal manometry, and (iii) satiation tested by Ensure nutrient drink test. Primary endpoints were: fasting and postprandial gastric volumes, distal antral phasic pressure activity (number of contractions, mean amplitude, and MI), and maximum tolerated volume. Results were normally distributed and the two treatment groups were compared using t-test.

KEY RESULTS

Relamorelin, 30 μg s.c., significantly increased the number of contractions in the distal antrum during 0-60 min postmeal when compared to placebo (p = 0.022); this was also observed in the first two 15-min periods (p = 0.005 and 0.015 for number of contractions 0-15 and 16-30). There was borderline increase in MI_0-15 (p = 0.055) and numerically increased MI_0-60 (p = 0.139) and MI_16-30 (p = 0.116). The amplitude of contractions was not significantly increased. Relamorelin did not significantly alter fasting or postprandial gastric volumes, gastric accommodation, or satiation volumes and symptoms.

CONCLUSIONS & INFERENCES

Relamorelin increases frequency of distal antral motility contractions without significant effects on amplitude of contractions. The lack of inhibition of accommodation and absence of increase in satiation symptoms support relamorelin for the treatment of symptomatic gastroparesis (ClinicalTrials.gov NCT02466711).

Hesperidin alleviates rat postoperative ileus through anti-inflammation and stimulation of Ca(2+)-dependent myosin phosphorylation

AIM

Postoperative ileus (POI) is a postoperative dysmotility disorder of gastrointestinal tract, which remains one of the most perplexing problems in medicine. In the present study we investigated the effects of hesperidin, a major flavonoid in sweet oranges and lemons, on POI in rats.

METHODS

SD rats were administered hesperidin (5, 20, and 80 mg·kg(-1)·d(-1), ig) for 3 consecutive days. POI operation (gently manipulating the cecum for 1 min) was performed on d 2. The gastrointestinal motility and isolated intestinal contraction were examined 1 d after the operation. Then the myosin phosphorylation and inflammatory responses in cecum tissue were assessed. Smooth muscle cells were isolated from rat small intestine for in vitro experiments.

RESULTS

The gastric emptying and intestinal transit were significantly decreased in POI rats, which were reversed by administration of hesperidin. In ileum and cecum preparations of POI rats in vitro, hesperidin (2.5-160 μmol/L) dose-dependently increased the spontaneous contraction amplitudes without affecting the contractile frequency, which was blocked by the myosin light chain kinase (MLCK) inhibitor ML-7 or verapamil, but not by TTX. Furthermore, administration of hesperidin increased the phosphorylation of MLC20 in the cecum tissue of POI rats. Moreover, administration of hesperidin reversed the increased levels of inflammatory cytokines, iNOS and COX-2 in cecum tissue of POI rats. In freshly isolated intestinal smooth muscle cells, hesperidin (5-80 μmol/L) dose-dependently increased the intracellular Ca(2+) concentration as well as the phosphorylation of MLC20, which was abrogated by ML-7 or siRNA that knocked down MLCK.

CONCLUSION

Oral administration of hesperidin effectively alleviates rat POI through inhibition of inflammatory responses and stimulation of Ca(2+)-dependent MLC phosphorylation.

Orexin-A affects gastric distention sensitive neurons in the hippocampus and gastric motility and regulation by the perifornical area in rats

Orexin-A is mainly produced in the lateral hypothalamus (LHA) and the perifornical area (PeF). Here, we aim to elucidate the effects of orexin-A in the hippocampus (Hi) on gastric distention (GD)-sensitive neurons and gastric motility, and potential regulation mechanisms by the PeF. Retrograde tracing and fluorescent-immunohistochemical staining were used to determine orexin-A neuronal projections. Single unit discharges in the Hi were recorded extracellularly and gastric motility in conscious rats was monitored during administration of orexin-A to the Hi or electrical stimulation of the PeF. Orexin-A administration to the Hi excited most of the GD-excitatory (GD-E) neurons and GD-inhibitory (GD-I) neurons, and increased gastric motility in a dose-dependent manner. All of effects induced by orexin-A could be partly blocked by pretreatment with orexin-A antagonist, SB-334867. Electrical stimulation of the PeF excited the majority of the orexin-A-responsive GD neurons in the Hi and promoted gastric motility. Additionally, pretreatment with SB-334867 in the Hi increased the firing rate of GDI and GDE neurons following electrical stimulation of the PeF. These findings suggest that orexin-A could regulate activities of GD-sensitive neurons and gastric motility. Furthermore, the PeF may be involved in this regulatory pathway.

Short-Term Effects of Relamorelin on Descending Colon Motility in Chronic Constipation: A Randomized, Controlled Trial

BACKGROUND

The pentapeptide ghrelin agonist, relamorelin, accelerates colonic transit in patients with chronic constipation (CC). In a murine model, relamorelin decreased excitability of colonic circular smooth muscle cells and colonic intraluminal pressure.

AIM

To determine short-term effects of relamorelin on colonic motility measured by barostat and multilumen manometry in CC.

METHODS

In a placebo-controlled, single-dose, double-blind, randomized study in patients with CC, we investigated the motor effects of relamorelin, 100 μg, SQ (12 patients) compared to placebo SQ (six patients). A motility-barostat balloon assembly was used to measure colonic compliance; tone and phasic pressure activity were measured before and after a 1000-kcal milkshake meal (administered ~60 min post-medication). Overall "background" phasic pressure activity was assessed by: average amplitude and motility index (MI = ln[sum amplitudes × #contractions + 1]) over defined periods. High-amplitude propagating contractions (HAPCs) were characterized by amplitude >75 mmHg and propagating contractions >50 mmHg; both were propagated over at least 10 cm. Postprandial HAPCs were the primary end point. The study sample had 80% power to detect an increase of 3.3 HAPCs in the hour post-meal.

RESULTS

Relamorelin, 100 μg, significantly induced more pre-meal propagated contractions [PCs of either >50 or >75 mmHg] compared to placebo (p < 0.05). Relamorelin also induced more post-meal PCs >50 or >75 mmHg than placebo. Relamorelin did not significantly alter colonic compliance, fasting or postprandial phasic pressure activity (20 min pre-meal fasting MI) or tone, and 60 min postprandial phasic pressure amplitude or MI, or tone.

CONCLUSIONS

Relamorelin stimulates propagated colonic contractions without alteration of background irregular contractions in CC. ClinicalTrial.Gov registration number: NCT 01781104.

Ghrelin and Neurodegenerative Disorders-a Review

Ghrelin, the endogenous ligand of the growth hormone secretagogue receptor 1a (GHS-R1a), is a gut-derived, orexigenic peptide hormone that primarily regulates growth hormone secretion, food intake, and energy homeostasis. With the wide expression of GHS-R1a in extra-hypothalamic regions, the physiological role of ghrelin is more extensive than solely its involvement in metabolic function. Ghrelin has been shown to be involved in numerous higher brain functions, such as memory, reward, mood, and sleep. Some of these functions are disrupted in neurodegenerative disorders, including Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease (HD). This link between ghrelin and these neurodegenerative diseases is supported by numerous studies. This review aims to provide a comprehensive overview of the most recent evidence of the novel neuromodulatory role of ghrelin in PD, AD, and HD. Moreover, the changes in circulating and/or central ghrelin levels that are associated with disease progression are also postulated to be a biomarker for clinical diagnosis and therapy.

Ghrelin O-acyltransferase (GOAT) and energy metabolism

Ghrelin O-acyltransferase (GOAT), a member of MBOATs family, is essential for octanoylation of ghrelin, which is required for active ghrelin to bind with and activate its receptor. GOAT is expressed mainly in the stomach, pancreas and hypothalamus. Levels of GOAT are altered by energy status. GOAT contains 11 transmembrane helices and one reentrant loop. Its invariant residue His-338 and conserved Asn-307 are located in the endoplasmic reticulum lumen and cytosol respectively. GOAT contributes to the regulation of food intake and energy expenditure, as well as glucose and lipids homeostasis. Deletion of GOAT blocks the acylation of ghrelin leading to subsequent impairment in energy homeostasis and survival when mice are challenged with high energy diet or severe caloric restriction. GO-CoA-Tat, a peptide GOAT inhibitor, attenuates acyl-ghrelin production and prevents weight gain induced by a medium-chain triglycerides-rich high fat diet. Further, GO-CoA-Tat increases glucose- induced insulin secretion. Overall, inhibition of GOAT is a novel strategy for treatment of obesity and related metabolic disorders.

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.

Relamorelin Relieves Constipation and Accelerates Colonic Transit in a Phase 2, Placebo-Controlled, Randomized Trial

BACKGROUND & AIMS

Ghrelin receptors are located in the colon. Relamorelin is a pentapeptide selective agonist of ghrelin receptor 1a with gastric effects, but its effects in the colon are not known. We aimed to evaluate the effects of relamorelin on bowel movements (BMs) and gastrointestinal and colonic transit (CT) in patients with chronic constipation.

METHODS

We performed a study of 48 female patients with chronic constipation who fulfilled the Rome III criteria and had 4 or fewer spontaneous BMs (SBMs)/wk. In a randomized (1:1), double-blind, parallel-group, placebo-controlled trial, the effects of relamorelin (100 μg/d, given subcutaneously) were tested during 14 days after a 14-day baseline, single-blind phase in which patients were given placebo at 2 Mayo Clinic sites. The participants' mean age was 40.6 ± 1.5 y, with a mean body mass index of 25.7 ± 0.6 kg/m(2), with 1.7 ± 0.1 SBM/wk, and a mean stool consistency of 1.2 ± 0.1 on the Bristol scale during this baseline period. The effect of treatment on transit was measured in 24 participants with colonic transit of less than 2.4 (geometric center at 24 h) during the baseline period. Gastric emptying, small-bowel transit, and CT were measured during the last 2 days that patients received relamorelin or placebo. Bowel function was determined from daily diaries kept by patients from days 1 through 28. Study end points were time to first BM, SBMs/wk, complete SBMs/wk, stool form, and ease of stool passage. Effects of relamorelin were assessed by analysis of covariance.

RESULTS

Compared with placebo, relamorelin accelerated gastric emptying half-time (P = .027), small-bowel transit (P = .051), and CT at 32 hours (P = .040) and 48 hours (P = .017). Relamorelin increased the number of SBMs (P < .001) and accelerated the time to first BM after the first dose was given (P = .004) compared with placebo, but did not affect stool form. Adverse events associated with relamorelin included increased appetite, fatigue, and headache.

CONCLUSIONS

Relamorelin acts in the colon to significantly reduce symptoms of constipation and accelerate CT in patients with chronic constipation, compared with placebo. ClinicalTrial.Gov registration number: NCT01781104.

Therapeutic applications of ghrelin agonists in the treatment of gastroparesis

There remains an unmet need for effective pharmacologic treatments for gastroparesis. Ghrelin is the endogenous ligand for the growth hormone secretagogue receptor and has been shown to regulate energy homeostasis and exert prokinetic effects on gastrointestinal motility. In recent years, several ghrelin receptor agonists have been studied in clinical trials of patients with diabetic gastroparesis. The intravenous macrocyclic peptidomimetic, TZP-101, initially suggested improvement in gastroparesis symptoms with intravenous administration when compared to placebo. However, in subsequent studies of oral preparations, TZP-102 failed to confirm these results. Another ghrelin receptor agonist, RM-131, was recently shown to significantly accelerate gastric emptying (GE) in patients with type 1 and type 2 diabetes and delayed GE. RM-131 reduced total Gastroparesis Cardinal Symptom Index-Daily Diary (GCSI-DD) and composite scores among type 1 diabetics. Continued development of ghrelin agonists should be explored in attempts to expand therapeutic options for the treatment of gastroparesis.

Review of gastroesophageal reflux disease (GERD) in the diabetic patient

This article reviews the known pathophysiological mechanisms of comorbid gastroesophageal reflux disease (GERD) in the diabetic patient, discusses therapeutic options in care, and provides an approach to its evaluation and management. We searched for review articles published in the past 10 years through a PubMed search using the filters diabetes mellitus, GERD, pathophysiology, and management. The search only yielded a handful of articles, so we independently included relevant studies from these review articles along with related citations as suggested by PubMed. We found diabetic patients are more prone to developing GERD and may present with atypical manifestations. A number of mechanisms have been proposed to elucidate the connection between these two diseases. Studies involving treatment options for comorbid disease suggest conflicting drug-drug interactions. Currently, there are no published guidelines specifically for the evaluation and management of GERD in the diabetic patient. Although there are several proposed mechanisms for the higher prevalence of GERD in the diabetic patient, this complex interrelationship requires further research. Understanding the pathophysiology will help direct diagnostic evaluation. In our review, we propose a management algorithm for GERD in the diabetic patient.

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.

Nesfatin-1 signaling in the basom edial amygdala modulates the gastric distension-sensitive neurons discharge and decreases gastric motility via melanocortin 3/4 receptors and modified by the arcuate nucleus

Nesfatin-1 is a novel anorexigenic peptide that regulates feeding behavior and gastrointestinal function. This study aimed to explore the effects of nesfatin-1 on gastric distension (GD)-sensitive neurons in the basomedial amygdala (BMA) and the potential mechanism for nesfatin-1 to regulate gastric motility through the arcuate nucleus (Arc). The projection of nerve fiber and expression of nesfatin-1 were observed by retrograde tracing and fluo-immunohistochemistry staining. Single-unit discharges in the BMA were recorded extracellularly, and gastric motility in conscious rats was monitored. Results showed that the nesfatin-1/ fluorogold-double labeled neurons were observed in the Arc. Nesfatin-1 could excite the GD-excitatory neurons and inhibit the GD-inhibitory neurons in the BMA. Gastric motility and gastric emptying were significantly reduced by nesfatin-1 administration to the BMA in a dose-dependent manner. The effects of nesfatin-1 could be partially blocked by melanocortin 3/4 receptors antagonist, SHU9119. Electrical stimulation of the Arc significantly excited the response of GD neurons to nesfatin-1 and promoted gastric motility. Nevertheless, these effects could be mitigated by pretreatment with anti-NUCB2/nesfatin-1 antibody. It is suggested that nesfatin-1 in the BMA plays an important role in decreasing gastric motility and the Arc may be involved in this regulation process.

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.

Emerging treatments in Neurogastroenterology: relamorelin: a novel gastrocolokinetic synthetic ghrelin agonist

BACKGROUND

Synthetic ghrelin agonists, predominantly small molecules, are being developed as prokinetic agents that may prove useful in the treatment of gastrointestinal motility disorders. Relamorelin (RM-131) is a pentapeptide synthetic ghrelin analog that activates the growth hormone secretagogue (GHS)-1a (also called the ghrelin) receptor with approximately sixfold greater potency than natural ghrelin. The ability of relamorelin to stimulate growth hormone (GH) release is comparable to that of native ghrelin. Relamorelin has enhanced efficacy and plasma stability compared to native ghrelin.

PURPOSE

In this review, we discuss the pharmacokinetics, pharmacodynamics and potential indications for relamorelin. Relamorelin is administered subcutaneously, dosed daily or twice daily. Relamorelin is being studied for the treatment of patients with gastrointestinal motility disorders. Phase IIA pharmacodynamic studies have demonstrated acceleration of gastric emptying in patients with type 1 diabetes mellitus (T1DM) and type 2 DM (T2DM) and upper gastrointestinal symptoms. In a phase IIA study in patients with diabetic gastroparesis, relamorelin accelerated gastric emptying and significantly improved vomiting frequency compared to placebo and improved other symptoms of gastroparesis in a prespecified subgroup of patients with vomiting at baseline. In patients with chronic idiopathic constipation with defined transit profile at baseline, relamorelin relieved constipation and accelerated colonic transit compared to placebo. These characteristics suggest that this new ghrelin analog shows great promise to relieve patients with upper or lower gastrointestinal motility disorders.

The regulation of circulating ghrelin - with recent updates from cell-based assays

Ghrelin is a stomach-derived orexigenic hormone with a wide range of physiological functions. Elucidation of the regulation of the circulating ghrelin level would lead to a better understanding of appetite control in body energy homeostasis. Earlier studies revealed that circulating ghrelin levels are under the control of both acute and chronic energy status: at the acute scale, ghrelin levels are increased by fasting and decreased by feeding, whereas at the chronic scale, they are high in obese subjects and low in lean subjects. Subsequent studies revealed that nutrients, hormones, or neural activities can influence circulating ghrelin levels in vivo. Recently developed in vitro assay systems for ghrelin secretion can assess whether and how individual factors affect ghrelin secretion from cells. In this review, on the basis of numerous human, animal, and cell-based studies, we summarize current knowledge on the regulation of circulating ghrelin levels and enumerate the factors that influence ghrelin levels.

Postoperative ileus: mechanisms and future directions for research

Postoperative ileus (POI) is an abnormal pattern of gastrointestinal motility characterized by nausea, vomiting, abdominal distension and/or delayed passage of flatus or stool, which may occur following surgery. Postoperative ileus slows recovery, increases the risk of developing postoperative complications and confers a significant financial load on healthcare institutions. The aim of the present review is to provide a succinct overview of the clinical features and pathophysiological mechanisms of POI, with final comment on selected directions for future research.Terminology used when describing POI is inconsistent, with little differentiation made between the obligatory period of gut dysfunction seen after surgery ('normal POI') and the more clinically and pathologically significant entity of a 'prolonged POI'. Both normal and prolonged POI represent a fundamentally similar pathophysiological phenomenon. The aetiology of POI is postulated to be multifactorial, with principal mediators being inflammatory cell activation, autonomic dysfunction (both primarily and as part of the surgical stress response), agonism at gut opioid receptors, modulation of gastrointestinal hormone activity and electrolyte derangements. A final common pathway for these effectors is impaired contractility and motility and gut wall oedema. There are many potential directions for future research. In particular, there remains scope to accurately characterize the gastrointestinal dysfunction that underscores an ileus, development of an accurate risk stratification tool will facilitate early implementation of preventive measures and clinical appraisal of novel therapeutic strategies that target individual pathways in the pathogenesis of ileus warrant further investigation.

New ghrelin agonist, HM01 alleviates constipation and L-dopa-delayed gastric emptying in 6-hydroxydopamine rat model of Parkinson's disease

BACKGROUND

Constipation and L-dopa-induced gastric dysmotility are common gastrointestinal (GI) symptoms in Parkinson's disease (PD). We investigated the novel ghrelin agonist, HM01 influence on GI motor dysfunctions in 6-hydroxydopamine (6-OHDA) rats.

METHODS

HM01 pharmacological profiles were determined in vitro and in vivo in rats. We assessed changes in fecal output and water content, and gastric emptying (GE) in 6-OHDA rats treated with orogastric (og) HM01 and L-dopa/carbidopa (LD/CD, 20/2 mg/kg). Fos immunoreactivity (ir) cells in specific brain and lumbosacral spinal cord were quantified.

KEY RESULTS

HM01 displayed a high binding affinity to ghrelin receptor (Ki: 1.42 ± 0.36 nM), 4.3 ± 1.0 h half-life and high brain/plasma ratio. 6-OHDA rats had reduced daily fecal output (22%) and water intake (23%) compared to controls. HM01 (3 and 10 mg/kg) similarly reversed the decreased 4-h fecal weight and water content in 6-OHDA rats. Basal GE was not modified in 6-OHDA rats, however, LD/CD (once or daily for 8 days) delayed GE in 6-OHDA and control rats that was prevented by HM01 (3 mg/kg acute or daily before LD/CD). HM01 increased Fos-ir cell number in the area postrema, arcuate nucleus, nucleus tractus solitarius, and lumbosacral intermediolateral column of 6-OHDA rats where 6-OHDA had a lowering effect compared to controls.

CONCLUSIONS & INFERENCES

6-OHDA rats display constipation- and adipsia-like features of PD and L-dopa-inhibited GE. The new orally active ghrelin agonist, HM01 crosses the blood-brain barrier and alleviates these alterations suggesting a potential benefit for PD with GI disorders.

The effects of nesfatin-1 in the paraventricular nucleus on gastric motility and its potential regulation by the lateral hypothalamic area in rats

The current study investigated the effects of nesfatin-1 in the hypothalamic paraventricular nucleus (PVN) on gastric motility and the regulation of the lateral hypothalamic area (LHA). Using single unit recordings in the PVN, we show that nesfatin-1 inhibited the majority of the gastric distention (GD)-excitatory neurons and excited more than half of the GD-inhibitory (GD-I) neurons in the PVN, which were weakened by oxytocin receptor antagonist H4928. Gastric motility experiments showed that administration of nesfatin-1 in the PVN decreased gastric motility, which was also partly prevented by H4928. The nesfatin-1 concentration producing a half-maximal response (EC50) in the PVN was lower than the value in the dorsomedial hypothalamic nucleus, while nesfatin-1 in the reuniens thalamic nucleus had no effect on gastric motility. Retrograde tracing and immunofluorescent staining showed that nucleobindin-2/nesfatin-1 and fluorogold double-labeled neurons were observed in the LHA. Electrical LHA stimulation changed the firing rate of GD-responsive neurons in the PVN. Pre-administration of an anti- nucleobindin-2/nesfatin-1 antibody in the PVN strengthened gastric motility and decreased the discharging of the GD-I neurons induced by electrical stimulation of the LHA. These results demonstrate that nesfatin-1 in the PVN could serve as an inhibitory factor to inhibit gastric motility, which might be regulated by the LHA.

Brain peptides and the modulation of postoperative gastric ileus

Postoperative ileus (POI) develops after abdominal surgery irrespective of the site of surgery. When prolonged, POI can lead to longer hospitalization times and higher healthcare costs. Moreover, it is associated with complaints for the patient. In order to develop new strategies to treat this condition, a deeper understanding of the pathophysiology of the POI is necessary. This review will focus on brain peptides (ghrelin, nesfatin-1, somatostatin, corticotropin-releasing factor, thyrotropin-releasing hormone and calcitonin gene-related peptide) involved in the mediation of POI and the possible modulation of these pathways to shorten the time of POI. Lastly, the role of vagal signaling or chewing gum as potential treatment strategies of alleviating symptoms of POI is discussed.

Preventive effect of rikkunshito on gastric motor function inhibited by L-dopa in rats

We previously reported that ghrelin prevented l-dopa (LD)-induced inhibition of gastric emptying (GE) of a non-nutrient solution in rats. Parkinson's disease treatment involves the combined administration of l-dopa with the enzyme l-amino acid decarboxylase inhibitor, carbidopa (CD) to reduce peripheral formation of dopamine. We investigated the effect LD/CD given orogastrically (og) on GE of a non-nutrient or nutrient meal and whether og pretreatment with rikkunshito, a kampo medicine clinically used to treat gastroparesis, influenced LD/CD effect on GE and postprandial antral and duodenal motility in conscious rats. LD/CD (20/2 mgkg(-1)) decreased significantly GE to 26.3 ± 6.0% compared to 61.2 ± 3.2% in og vehicle monitored 20-min after a non-nutrient meal and to 41.9 ± 5.8% compared to 72.9 ± 5.2% in og vehicle monitored 60 min after a nutrient meal. Rikkunshito (0.5 or 1.0 g kg(-1)) reduced the LD/CD (20/2 mg kg(-1)) inhibition of GE of non-nutrient meal (36.9 ± 7.4% and 46.6 ± 4.8% respectively vs. 12.1 ± 7.4% in og vehicle plus LD/CD) while having no effect alone (56.6 ± 8.5%). The ghrelin antagonist, [d-Lys(3)]-GHRP-6 (1 mg kg(-1)) injected intraperitoneally partially reversed rikkunshito preventive effect on LD/CD-inhibited GE. Rikkunshito (1.0 g kg(-1)) blocked LD/CD (20/2 mg kg(-1))-induced delayed GE of a nutrient meal and the reduction of postprandial antral motility. In 6-hydroxydopamine-induced Parkinson's disease rat model, rikkunshito (1.0 g kg(-1), og) also prevented LD/CD-inhibited gastric emptying of a nutrient meal and enhanced fasting plasma levels of acylated ghrelin. These data indicate that oral rikkunshito alleviates the delayed GE induced by LD/CD in naïve and PD rat model in part through ghrelin-related mechanisms.

Ghrelin contributes to protection of hepatocellular injury induced by ischaemia/reperfusion

BACKGROUND & AIMS

Ghrelin, a gut hormone with pleiotropic effects, may act as a protective signal in parenchymal cells. We investigated the protective effects of ghrelin on hepatocytes after ischaemia/reperfusion (I/R).

METHODS

Hepatic injury was assessed by measurement of plasma alanine aminotransferase (ALT) and lactate dehydrogenase (LDH), histological analysis, and TUNEL assay. Effects of exogenous ghrelin and ghrelin receptor gene deletion on I/R induced injury of liver were evaluated.

RESULTS

Ischaemia/reperfusion induced a profound injury to hepatocytes. This was accompanied by elevations in plasma ALT and LDH. Pretreatment with ghrelin significantly reduced elevations in plasma ALT and LDH, and attenuated tissue damage induced by hepatic I/R in mice. Hepatic injury induced by I/R was more pronounced in ghrelin receptor gene null mice. Ghrelin administration blocked the up-regulation of AMP-activated protein kinase (AMPK) activity induced by hepatic I/R.

CONCLUSIONS

This study demonstrates that ghrelin contributes to the cytoprotection during hepatic I/R.

Effects of ghrelin on gastric distension sensitive neurons and gastric motility in the lateral septum and arcuate nucleus regulation

BACKGROUND

Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor (GHS-R) and a peptide hormone that promotes food intake and gastric motility. Our aims are to explore the effects of ghrelin on gastric distension (GD) sensitive neurons in the lateral septum, and the possible regulation of gastric motility by ghrelin through the hypothalamic arcuate nucleus (ARC).

METHODS

Single-unit discharges were recorded, extracellularly, and the gastric motility was monitored by the administration of ghrelin in the lateral septum. The projection of nerve fiber and expression of ghrelin were observed by retrograde tracer and fluo-immunohistochemistry staining. The expression of GHS-R and ghrelin was determined by real-time polymerase chain reaction and western blotting analysis.

RESULTS

There were GD neurons in the lateral septum. The administration of ghrelin could excite both GD-excitatory (GD-E) and GD-inhibitory (GD-I) neurons in the lateral septum. Gastric motility was significantly enhanced by the administration of ghrelin in the lateral septum in a dose-dependent manner. Pretreatment with [D-Lys-3]-GHRP-6, however, could completely abolish the ghrelin-induced effects. Electrical stimulation of the ARC could significantly excite the response of GD neurons to ghrelin, increase ghrelin protein expression in the lateral septum and promote gastric motility. Nevertheless, these effects could be mitigated by pretreatment of [D-Lys-3]-GHRP-6. Electrical lesion of the lateral septum resulted in decreased gastric motility. The GHS-R and Ghrelin/FG-double labeled neurons were observed in the lateral septum and ARC, respectively.

CONCLUSIONS

It is suggested that the lateral septum may receive afferent information from the gastrointestinal tract and promote gastric motility. Ghrelin plays an important role in promoting gastric motility in the lateral septum. The ARC may be involved in the regulation of the lateral septum's influence on gastric motility.

Ghrelin gene products, receptors, and GOAT enzyme: biological and pathophysiological insight

Ghrelin is a 28-amino acid acylated hormone, highly expressed in the stomach, which binds to its cognate receptor (GHSR1a) to regulate a plethora of relevant biological processes, including food intake, energy balance, hormonal secretions, learning, inflammation, etc. However, ghrelin is, in fact, the most notorious component of a complex, intricate regulatory system comprised of a growing number of alternative peptides (e.g. obestatin, unacylated ghrelin, and In1-ghrelin, etc.), known (GHSRs) and, necessarily unknown receptors, as well as modifying enzymes (e.g. ghrelin-O-acyl-transferase), which interact among them as well as with other regulatory systems in order to tightly modulate key (patho)-physiological processes. This multiplicity of functions and versatility of the ghrelin system arise from a dual, genetic and functional, complexity. Importantly, a growing body of evidence suggests that dysregulation in some of the components of the ghrelin system can lead to or influence the development and/or progression of highly concerning pathologies such as endocrine-related tumors, inflammatory/cardiovascular diseases, and neurodegeneration, wherein these altered components could be used as diagnostic, prognostic, or therapeutic targets. In this context, the aim of this review is to integrate and comprehensively analyze the multiple components and functions of the ghrelin system described to date in order to define and understand its biological and (patho)-physiological significance.

Involvements of the lateral hypothalamic area in gastric motility and its regulation by the lateral septum

Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor (GHS-R) pre-dominantly produced in the stomach. Recent studies have shown that it may promote food intake and gastric motility. We aim to explore effects of ghrelin on the gastric distension (GD) sensitive neurons and gastric motility in the lateral hypothalamic area (LHA), and the possible regulation by the lateral septum. Extracellular single unit discharges were recorded and the gastric motility was monitored by administration of ghrelin into LHA and electrical stimulation of lateral septum. Expression of GHS-R was determined by polymerase chain reaction (PCR), western blot and immunohistochemistry staining. Projection of nerve fiber and expression of ghrelin were observed by retrograde tracer and fluo-immunohistochemistry staining. Results revealed that there were GD neurons in the LHA, and administration of ghrelin could excite both GD-excitatory (GD-E) and GD-inhibited (GD-I) neurons in the LHA. The gastric motility was significantly promoted by administration of ghrelin into LHA with a dose dependent manner, which could be completely abolished by treatment with ghrelin receptor antagonist [D-Lys-3]-GHRP-6 or BIM-28163. c-Fos expression was significantly increased after ghrelin administration to the LHA. Electrical stimulation of the lateral septum could significantly excite GD neurons responsive to ghrelin in the LHA as well as promote gastric motility. However, those effects could be absorbed by pre-treatment of [D-Lys-3]-GHRP-6. GHSR-1a expression in the LHA had no change after ghrelin administration to the LHA or electrical stimulating lateral septum. Electrical lesion of the LHA resulted in the decrease of gastric motility. GHS-R and Ghrelin/FG-double labeled neurons were observed in the LHA and lateral septum, respectively. It is suggested that the LHA may involve in promoting gastric motility via ghrelin. The Lateral septum projects to the LHA and exerts some regulating function on the LHA.