The prokinetic face of ghrelin

Role of the Ghrelin System in Colorectal Cancer

The ghrelin system contains several components (e.g., ghrelin with growing number of alternative peptides, growth hormone secretagogue receptors (GHS-Rs), and ghrelin-O-acyl-transferase (GOAT) and participates in regulation of a number of key processes of gastrointestinal (GI) tract cancer progression, including cell proliferation, migration, invasion, apoptosis, inflammation, and angiogenesis. However, its exact role in promoting or inhibiting cancer progression is still unclear. Colorectal cancer (CRC) is one of the most common human malignancies worldwide. Molecular studies suggest an autocrine/paracrine mechanism for the secretion of ghrelin in colorectal carcinogenesis and its contribution to its initial stages. However, the signalling pathways of CRC development involving the ghrelin system are poorly understood. Potential mechanisms of colon carcinogenesis involving components of the ghrelin system were previously described in an animal model and in in vitro studies. However, the diagnostic–prognostic role of serum ghrelin concentrations, tissue expression, or genetic changes of this system in various stages of CRC progression remains an open case. Thus, the aim of this study is to discuss the role of the ghrelin system in colon carcinogenesis, diagnostics and CRC prognostics, as well as the results of studies on the use of ghrelin and its analogues in the therapy of CRC-related syndromes (e.g., cachexia and sarcopenia).

Ghrelin Levels in Children With Intestinal Failure Receiving Long-Term Parenteral Nutrition

Background

Children with intestinal failure (IF) require parenteral nutrition (PN). Transition to oral and enteral nutrition (EN) can be difficult also due to abnormal gastrointestinal motility. The gut hormone ghrelin is increased in states of negative energy balance, functioning to preserve euglycemia, and also has appetite stimulating and prokinetic properties. We aimed to evaluate and compare ghrelin levels in children with IF, and to assess the relationship with PN-dependency.

Methods

In this exploratory prospective multicenter study, plasma acylated (AG) and unacylated (UAG) ghrelin levels were measured in children with short bowel syndrome (SBS) and with functional IF (pseudo-obstruction or any enteropathy) and compared with healthy control subjects. Spearman’s rho (r_s) was used to assess correlations of AG and UAG with PN-dependency (%PN) and parenteral glucose intake.

Results

Sixty-four samples from 36 IF-patients were analyzed. Median baseline AG and UAG levels were respectively 279.2 and 101.0 pg/mL in children with SBS (n = 16), 126.4 and 84.5 pg/mL in children with functional IF (n = 20) and 82.4 and 157.3 pg/mL in healthy children (n = 39). AG levels were higher in children with SBS and functional IF than in healthy children (p = 0.002 and p = 0.023, respectively). In SBS, AG positively correlated with %PN (r_s = 0.5, p = 0.005) and parenteral glucose intake (r_s = 0.6, p = 0.003). These correlations were not observed in functional IF.

Conclusion

Children with IF had raised AG levels which could be related to starvation of the gut. The positive correlation between AG and glucose infusion rate in SBS suggests an altered glucoregulatory function.

Ghrelin abates bacterial translocation following burn injury by improving gastric emptying

BACKGROUND

In severe burns, increased intestinal permeability facilitates bacterial translocation, resulting in systemic endotoxemia and multi^- organ failure. We investigated the role of burn-induced gastrointestinal dysmotility (BIGD) in promoting bacterial translocation following burn injury, and the protective effect of ghrelin in this process.

METHODS

We assessed gastric emptying (GE%) and intestinal transit (IT by geometric center "GC") in a 60% total body surface area scald burn rat model and measured bacterial counts in mesenteric lymph nodes (MLN) and distal small intestine by colony-forming unit per gram of tissue (CFU/g). A group of animals was treated with ghrelin or saline after burn.

KEY RESULTS

Scald burn was associated with a significant delay in GE (62% ± 4% vs 74% ± 4%; P = .02) and a trend of delay in intestinal transit (GC: 5.5 ± 0.1 vs 5.8 ± 0.2; P = .09). Concurrently, there was a marginal increase in small intestinal bacterial overgrowth (6 × 10⁵ vs 2 × 10⁵  CFU/g; P = .05) and significant translocation to MLN (2 × 10² vs 4 × 10¹ ; P = .03). We observed a negative correlation between GE and intestinal bacterial overgrowth (r_s  = -0.61; P = .002) and between IT and translocation (r_s  = -0.63; P = .004). Ghrelin administration significantly accelerated GE following burn injury (91% ± 3% vs 62% ± 4; P = .03), reduced small intestinal bacterial overgrowth, and completely inhibited translocation to MLN (0.0 vs 5 × 10² ; P = .01).

CONCLUSIONS & INFERENCES

Burn-induced gastrointestinal dysmotility is correlated with the systemic translocation of gram-negative gut bacteria that are implicated in multiple organ failure in burn patients. Therapeutic interventions to restore BIGD are warranted (Neurogastroenterol Motil, 2012, 24, 78).

Multiple Beneficial Effects of Ghrelin Agonist, HM01 on Homeostasis Alterations in 6-Hydroxydopamine Model of Parkinson's Disease in Male Rats

Background and objective: Developing therapy for non-motor symptoms of Parkinson’s disease (PD) is important for improving patients’ quality of life. Previously, we reported that the ghrelin receptor agonist, HM01 normalized the decreased 4-h fecal output and levodopa-inhibited gastric emptying in 6-OHDA rats, and activated selective areas in brain and spinal cord. In this study, we evaluated whether chronic HM01 treatment influences motor functions and/or has beneficial effects on non-motor symptoms including alterations of body weight and composition, defecation, feeding and water intake in 6-OHDA rats.

Methods: Male rats were microinjected unilaterally into the medial forebrain bundle with either vehicle or 6-OHDA. Three weeks later, we assessed basal body weight, and 24-h fecal output (pellets, weight, dry weight and water content), water intake and food intake (ingested and spillage). Then, HM01 (3 mg/kg) or vehicle was given per gavage daily for 10–12 days and the same parameters were re-assessed daily. Motor behavior (stepping and rotations tests), body composition were monitored before and after the HM01 treatment.

Results: 6-OHDA rats showed motor deficits in rotation test induced by apomorphine and stepping test. They also displayed a significant reduction in body weight, water consumption, fecal weight and water content and an increase in food spillage compared to vehicle microinjected rats. Daily oral treatment of HM01 did not modify motor alterations compared to vehicle but significantly increased the body weight, fat mass, and 24-h fecal weight, fecal water content, food and water intake in 6-OHDA rats, while HM01 had no significant effect in vehicle microinjected rats. Fecal weight and water content were both correlated with water intake, but not with food intake. Fat mass, but not body weight, was correlated with food intake. HM01 effects were significant after 24 h and remained similar during the treatment.

Conclusions: Chronic treatment with ghrelin agonist, HM01 improved several non-motor symptoms in the rat PD model induced by 6-OHDA lesion including the decrease in body weight, water consumption, fecal weight and water content, and increased food intake while not improving the motor deficits. These findings provide pre-clinical evidence of potential benefits of ghrelin agonists to alleviate non-motor symptoms in PD patients.

Regulation of Gastrointestinal Motility by Motilin and Ghrelin in Vertebrates

The energy balance of vertebrates is regulated by the difference in energy input and energy expenditure. Generally, most vertebrates obtain their energy from nutrients of foods through the gastrointestinal (GI) tract. Therefore, food intake and following food digestion, including motility of the GI tract, secretion and absorption, are crucial physiological events for energy homeostasis. GI motility changes depending on feeding, and GI motility is divided into fasting (interdigestive) and postprandial (digestive) contraction patterns. GI motility is controlled by contractility of smooth muscles of the GI tract, extrinsic and intrinsic neurons (motor and sensory) and some hormones. In mammals, ghrelin (GHRL) and motilin (MLN) stimulate appetite and GI motility and contribute to the regulation of energy homeostasis. GHRL and MLN are produced in the mucosal layer of the stomach and upper small intestine, respectively. GHRL is a multifunctional peptide and is involved in glucose metabolism, endocrine/exocrine functions and cardiovascular and reproductive functions, in addition to feeding and GI motility in mammals. On the other hand, the action of MLN is restricted and species such as rodentia, including mice and rats, lack MLN peptide and its receptor. From a phylogenetic point of view, GHRL and its receptor GHS-R1a have been identified in various vertebrates, and their structural features and various physiological functions have been revealed. On the other hand, MLN or MLN-like peptide (MLN-LP) and its receptors have been found only in some fish, birds and mammals. Here, we review the actions of GHRL and MLN with a focus on contractility of the GI tract of species from fish to mammals.

Gastroesophageal reflux in critically ill patients

Gastroesophageal reflux (GER) is a common occurrence in critically ill, mechanically ventilated patients. Reflux can lead to pulmonary aspiration of gastric contents and subsequent pneumonia. Several characteristics of patients, interventions provided in the intensive care unit setting, and factors associated with feeding increase a patient's risk for reflux. Critical care nurses and clinical nurse specialists can identify patients at highest risk for GER by utilizing the patient's history, reviewing the medications, and assessing the current status to provide interventions to reduce the risk of GER and its sequelae of aspiration pneumonia. This article reviews the physiology of GER, risk factors, and interventions to decrease GER in the critically ill patient.

Ghrelin - a pleiotropic hormone secreted from endocrine x/a-like cells of the stomach

The gastric X/A-like endocrine cell receives growing attention due to its peptide products with ghrelin being the best characterized. This peptide hormone was identified a decade ago as a stimulator of food intake and to date remains the only known peripherally produced and centrally acting orexigenic hormone. In addition, subsequent studies identified numerous other functions of this peptide including the stimulation of gastrointestinal motility, the maintenance of energy homeostasis and an impact on reproduction. Moreover, ghrelin is also involved in the response to stress and assumed to play a role in coping functions and exert a modulatory action on immune pathways. Our knowledge on the regulation of ghrelin has markedly advanced during the past years by the identification of the ghrelin acylating enzyme, ghrelin-O-acyltransferase, and by the description of changes in expression, activation, and release under different metabolic as well as physically and psychically challenging conditions. However, our insight on regulatory processes of ghrelin at the cellular and subcellular levels is still very limited and warrants further investigation.

Ghrelin and gastrointestinal movement

Ghrelin is a potent stimulant for gastric emptying and gastrointestinal (GI) movement. Clinically, it has been reported that the intravenous administration of ghrelin accelerates the rate of gastric emptying and induces gastric phase III contractions of the migrating motor complex in healthy volunteers. Recent technical advances in the measurement of GI motility in conscious small animals, including rats, mice, and the house musk shrew (Suncus murinus), have helped to elucidate the precise mechanism of action of ghrelin. Intravenous administration of ghrelin induces fasted motor activities with phase III-like contractions of the migrating motor complex in the antrum and duodenum in animals. These effects of ghrelin are mediated by activating the hypothalamic orexigenic neuropeptide Y neuron through ghrelin receptors located at the vagal afferent terminal. Stress hormone and anorexigenic peptides cause the disruption of fasted motor activity and induce fed-like motor activity. Ghrelin and the ghrelin signal potentiator rikkunshito successfully restore fed-like motor activities to fasted activities in fenfluramine-treated rats and in a cancer anorexia-cachexia animal model. These findings suggest that ghrelin can be expected to be a therapeutic target for GI disorders.

Ghrelin, des-acyl ghrelin and obestatin on the gastrointestinal motility

Ghrelin, des-acyl ghrelin and obestatin are derived from a common prohormone, preproghrelin by posttranslational processing, originating from endocrine cells in the stomach. Ghrelin exerts stimulatory effects on the motility of antrum and duodenum in both fed and fasted state of animals. On the other hand, des-acyl ghrelin exerts inhibitory effects on the motility of antrum but not on the motility of duodenum in the fasted state of animals. Obestatin exerts inhibitory effects on the motility of antrum and duodenum in the fed state but not in the fasted state of animals. NPY Y2 and Y4 receptors in the brain may mediate the action of ghrelin, CRF type 2 receptor in the brain may mediate the action of des-acyl ghrelin, whereas CRF type 1 and type 2 receptors in the brain may mediate the action of obestatin.

Use of ghrelin as a treatment for inflammatory bowel disease: mechanistic considerations

Inflammatory bowel diseases (IBD)-and in particular Crohn's disease-are immune-mediated processes that result in denuded intestinal mucosa and can produce decreased appetite, weight loss, and systemic inflammation. Current treatments include anti-inflammatory medications, immunomodulators, and feeding interventions. Ghrelin is an endogenous orexigenic hormone that directly stimulates growth hormone release, increases gut motility, and has cardiovascular and anti-inflammatory properties. Although ghrelin levels are elevated in active IBD, administration of ghrelin in most (but not all) animal models of colitis has produced improvements in disease activity and systemic inflammation. The mechanism for these effects is not known but may relate to decreased inflammation, increased motility, increased appetite, and increased colonic blood flow. Human trials have not been performed, however, and more research is clearly needed.