Cardiac effects of hexarelin in hypopituitary adults

Acylated ghrelin prevents doxorubicin-induced cardiac intrinsic cell death and fibrosis in rats by restoring IL-6/JAK2/STAT3 signaling pathway and inhibition of STAT1

This study investigated if JAK/STAT signaling pathway mediates doxorubicin (DOX)-induced cell death and fibrosis in left ventricles (LVs) of rats and examined if acylated ghrelin affords protection by modulating this pathway. Male rats (120 ± 5 g) were divided into 6 groups (10 rats each) as follows: control; control + AG (10 ng/kg, s.c.); DOX (an accumulative dose 15 mg/kg, i.p.); DOX + AG, DOX + AG + AG490, a JAK2 inhibitor (5 mg/kg, i.p.); and DOX + AG + [D-Lys3]-GHRP-6; an AG receptor antagonist (3.75 mg/kg, i.p.). All treatments were carried out for 35 days. In rats' LVs, DOX significantly impaired the systolic and diastolic functions, enhanced levels of ROS and MDA, reduced levels of GSH and Bcl-2, and increased mRNA and protein levels of collagen I/III and TGF-β and cleaved caspase-3. In addition, although DOX did not affect JAK1 or JAK2 activity, it significantly increased protein levels of IL-6, decreased STAT3 and p-STAT3 (Tyr701&Ser727), and increased STAT1 and p-STAT1 (Tyr701&Ser727) levels, with a concomitant decrease in ERK1/2 activity and an increase in P38 activity. However, without affecting IL-6 and JAK1/2, AG reversed all of the observed alterations with a significant increase in the levels and activities of JAK2. Similar effects of AG were also seen in control rats. Interestingly, all the beneficial effects afforded by AG were abolished by AG490 and AG + [D-Lys3]-GHRP-6. In conclusion, DOX-induced cardiac toxicity involves stimulation of IL-6, P38, and STAT1 signaling levels whereas the protective effect afforded by AG involves the activation of ERK1/2 and JAK2/STAT3 and inhibition of STAT1.

Improvement of cardiomyocyte function by in vivo hexarelin treatment in streptozotocin-induced diabetic rats

Diabetic cardiomyopathy is characterized by diastolic and systolic cardiac dysfunction, yet no therapeutic drug to specifically treat it. Hexarelin has been demonstrated to improve heart function in various types of cardiomyopathy via its receptor GHS-R. This experiment aims to test the effect of hexarelin on cardiomyocytes under experimental diabetes. Streptozotocin (STZ, 65 mg/kg)-induced diabetic rat model was employed with vehicle injection group as control. Daily hexarelin (100 μg/kg) treatment was performed for 2 weeks after 4-week STZ-induced diabetes. Cardiomyocytes were isolated by enzyme treatment under O2 -saturated perfusion for single-cell shortening, [Ca2+ ]i transient, and electrophysiology recordings. GHS-R expression and apoptosis-related signaling proteins Bax, Bcl-2, caspase-3 and 9, were assessed by western blot. Experimental data demonstrated a reduced cell contraction and relaxation in parallel with depressed rise and fall of [Ca2+ ]i transients in diabetic cardiomyocytes. Hexarelin reversed the changes in both contraction and [Ca2+ ]i . Action potential duration and transient outward potassium current (Ito ) density were dramatically increased in diabetic cardiomyocytes and hexarelin treatment reverse such changes. Upregulated GHS receptor (GHS-R) expression was observed in both control and diabetic groups after hexarelin treatment, which also caused antiapoptotic changes of Bax, Bcl-2, caspase-3 and 9 expression. In STZ-induced diabetic rats, hexarelin is able to improve cardiomyocyte function through recovery of Ito K+ currents, intracellular Ca2+ homeostasis and antiapoptotic signaling pathways.

Synthetic Growth Hormone-Releasing Peptides (GHRPs): A Historical Appraisal of the Evidences Supporting Their Cytoprotective Effects

BACKGROUND

Growth hormone-releasing peptides (GHRPs) constitute a group of small synthetic peptides that stimulate the growth hormone secretion and the downstream axis activity. Mounting evidences since the early 1980s delineated unexpected pharmacological cardioprotective and cytoprotective properties for the GHRPs. However, despite intense basic pharmacological research, alternatives to prevent cell and tissue demise before lethal insults have remained as an empty niche in the clinical armamentarium. Here, we have rigorously reviewed the investigational development of GHRPs and their clinical niching perspectives.

METHODOLOGY

PubMed/MEDLINE databases, including original research and review articles, were explored. The search design was date escalated from 1980 and included articles in English only.

RESULTS AND CONCLUSIONS

GHRPs bind to two different receptors (GHS-R1a and CD36), which redundantly or independently exert relevant biological effects. GHRPs' binding to CD36 activates prosurvival pathways such as PI-3K/AKT1, thus reducing cellular death. Furthermore, GHRPs decrease reactive oxygen species (ROS) spillover, enhance the antioxidant defenses, and reduce inflammation. These cytoprotective abilities have been revealed in cardiac, neuronal, gastrointestinal, and hepatic cells, representing a comprehensive spectrum of protection of parenchymal organs. Antifibrotic effects have been attributed to some of the GHRPs by counteracting fibrogenic cytokines. In addition, GHRP family members have shown a potent myotropic effect by promoting anabolia and inhibiting catabolia. Finally, GHRPs exhibit a broad safety profile in preclinical and clinical settings. Despite these fragmented lines incite to envision multiple pharmacological uses for GHRPs, especially as a myocardial reperfusion damage-attenuating candidate, this family of "drugable" peptides awaits for a definitive clinical niche.

Intracoronary Des-Acyl Ghrelin Acutely Increases Cardiac Perfusion Through a Nitric Oxide-Related Mechanism in Female Anesthetized Pigs

Des-acyl ghrelin (DAG), the most abundant form of ghrelin in humans, has been found to reduce arterial blood pressure and prevent cardiac and endothelial cell apoptosis. Despite this, data regarding its direct effect on cardiac function and coronary blood flow, as well as the related involvement of autonomic nervous system and nitric oxide (NO), are scarce. We therefore examined these issues using both in vivo and in vitro studies. In 20 anesthetized pigs, intracoronary 100 pmol/mL DAG infusion with a constant heart rate and aortic blood pressure, increased coronary blood flow and NO release, whereas reducing coronary vascular resistances (P < .05). Dose responses to DAG were evaluated in five pigs. No effects on cardiac contractility/relaxation or myocardial oxygen consumption were observed. Moreover, whereas the blockade of muscarinic cholinoceptors (n = 5) or α- and β-adrenoceptors (n = 5 each) did not abolish the observed responses, NO synthase inhibition (n = 5) prevented the effects of DAG on coronary blood flow and NO release. In coronary artery endothelial cells, DAG dose dependently increased NO release through cAMP signaling and ERK1/2, Akt, and p38 MAPK involvement as well as the phosphorylation of endothelial NO synthase. In conclusion, in anesthetized pigs, DAG primarily increased cardiac perfusion through the involvement of NO release. Moreover, the phosphorylation of ERK1/2 and Akt appears to play roles in eliciting the observed NO production in coronary artery endothelial cells.

Implications of ghrelin and hexarelin in diabetes and diabetes-associated heart diseases

Ghrelin and its synthetic analog hexarelin are specific ligands of growth hormone secretagogue (GHS) receptor. GHS have strong growth hormone-releasing effect and other neuroendocrine activities such as stimulatory effects on prolactin and adrenocorticotropic hormone secretion. Recently, several studies have reported other beneficial functions of GHS that are independent of GH. Ghrelin and hexarelin, for examples, have been shown to exert GH-independent cardiovascular activity. Hexarelin has been reported to regulate peroxisome proliferator-activated receptor gamma (PPAR-γ) in macrophages and adipocytes. PPAR-γ is an important regulator of adipogenesis, lipid metabolism, and insulin sensitization. Ghrelin also shows protective effects on beta cells against lipotoxicity through activation of phosphatidylinositol-3 kinase/protein kinase B, c-Jun N-terminal kinase (JNK) inhibition, and nuclear exclusion of forkhead box protein O1. Acylated ghrelin (AG) and unacylated ghrelin (UAG) administration reduces glucose levels and increases insulin-producing beta cell number, and insulin secretion in pancreatectomized rats and in newborn rats treated with streptozotocin, suggesting a possible role of GHS in pancreatic regeneration. Therefore, the discovery of GHS has opened many new perspectives in endocrine, metabolic, and cardiovascular research areas, suggesting the possible therapeutic application in diabetes and diabetic complications especially diabetic cardiomyopathy. Here, we review the physiological roles of ghrelin and hexarelin in the protection and regeneration of beta cells and their roles in the regulation of insulin release, glucose, and fat metabolism and present their potential therapeutic effects in the treatment of diabetes and diabetic-associated heart diseases.

The cardiovascular action of hexarelin

Hexarelin, a synthetic growth hormone-releasing peptide, can bind to and activate the growth hormone secretagogue receptor (GHSR) in the brain similar to its natural analog ghrelin. However, the peripheral distribution of GHSR in the heart and blood vessels suggests that hexarelin might have direct cardiovascular actions beyond growth hormone release and neuroendocrine effects. Furthermore, the non-GHSR CD36 had been demonstrated to be a specific cardiac receptor for hexarelin and to mediate its cardioprotective effects. When compared with ghrelin, hexarelin is chemically more stable and functionally more potent. Therefore, it may be a promising therapeutic agent for some cardiovascular conditions. In this concise review, we discuss the current evidence for the cardiovascular action of hexarelin.

Lipid, adipokine and ghrelin levels in myocardial infarction patients with insulin resistance

Background

Insulin resistance (IR) is a risk factor for ischaemic heart disease and myocardial infarction (MI). IR often manifests in MI and is regarded as an independent predictor of in-hospital mortality, which can provide early risk stratification for recurrent acute coronary events.

Methods

The study enrolled 200 patients (130 males and 70 females aged 61.4 ± 1.12 years) diagnosed with ST elevation MI. At days 1 and 12 from the MI onset, IR levels and lipid profiles, as well as serum glucose, insulin, adipokine and ghrelin levels, were measured.

Results

Free fatty acid (FFA) levels had the most pronounced changes: IR patients had a 9-fold increase in FFA levels at day 1, and patients without IR had a 6-fold increase. Leptin levels at days 1 and 12, in IR patients were, on average, 1.5- and 2-fold higher compared to the controls and patients with no IR (р < 0.05). Leptin levels in IR patients were increased throughout the entire hospital stay. Resistin levels in IR patients were, on average, 1.4-fold higher throughout the entire hospital stay, while in non-IR patients, resistin levels were similar to the controls. Adiponectin levels in IR patients were decreased compared to the controls, while in patients with IR, they were similar to the controls. Both IR and non-IR MI patients had 3-fold and 3.7-fold lower ghrelin levels at day 1, respectively, compared to the controls. The correlation analysis showed a negative correlation between ghrelin and FFA (r = −0.48 р = 0.007), ghrelin and leptin (r = −0.4 р = 0.003), ghrelin and insulin (r = −0.54 р = 0.002), and ghrelin and glucose (r = −0.31 р = 0.002) in MI patients.

Conclusion

Dyslipidaemia, along with insulinaemia and glycaemia, is one of the most significant IR risk factors in the acute and early recovery phases of MI. Dyslipidaemia is characterised by a high FFA level; an imbalance of leptin, resistin, and adiponectin; and a deficiency of ghrelin in the acute and early recovery periods of MI. FFA and ghrelin can be used as promising molecular markers to stratify the risk of recurrent acute coronary events and diabetes mellitus in MI patients.

Ghrelin in cardiovascular disease and atherogenesis

Although initially associated with regulation of appetite, the cardiovascular system has also been recognized as a potentially important target for ghrelin. Moreover, a limited number of clinical studies suggest a role for ghrelin in the treatment of congestive heart failure. So far reported cardiovascular effects of growth hormone secretagogues and/or ghrelin include lowering of peripheral resistance, either direct at the vascular level and/or by modulating sympathetic nervous activity. Other observed effects indicate possible improvement of contractility and cardioprotective effects both in vivo and in vitro.Taken together, these results offer an interesting perspective on the future where further studies aiming at evaluating a role of GHS and ghrelin in the treatment of cardiovascular disease are warranted.

Cardiovascular actions of the ghrelin gene-derived peptides and growth hormone-releasing hormone

In 1976, small peptide growth hormone secretagogues (GHSs) were discovered and found to promote growth hormone (GH) release from the pituitary. The GHS receptor (GHS-R) was subsequently cloned, and its endogenous ligand ghrelin was later isolated from the stomach. Ghrelin is a 28-amino acid peptide, whose acylation is essential for binding to GHS-R type 1a and for the endocrine functions, including stimulation of GH secretion and subsequent food intake. Unacylated ghrelin, the other ghrelin form, although devoid of GHS-R binding is an active peptide, sharing many peripheral effects with acylated ghrelin (AG). The ghrelin system is broadly expressed in myocardial tissues, where it exerts different functions. Indeed, ghrelin inhibits cardiomyocyte and endothelial cell apoptosis, and improves left ventricular (LV) function during ischemia–reperfusion (I/R) injury. In rats with heart failure (HF), ghrelin improves LV dysfunction and attenuates the development of cardiac cachexia. Similarly, ghrelin exerts vasodilatory effects in humans, improves cardiac function and decreases systemic vascular resistance in patients with chronic HF. Obestatin is a recently identified ghrelin gene peptide. The physiological role of obestatin and its binding to the putative GPR39 receptor are still unclear, although protective effects have been demonstrated in the pancreas and heart. Similarly to AG, the hypothalamic peptide growth hormone-releasing hormone (GHRH) stimulates GH release from the pituitary, through binding to the GHRH-receptor. Besides its proliferative effects in different cell types, at the cardiovascular level GHRH inhibits cardiomyocyte apoptosis, and reduces infarct size in both isolated rat heart after I/R and in vivo after myocardial infarction. Therefore, both ghrelin and GHRH exert cardioprotective effects, which make them candidate targets for therapeutic intervention in cardiovascular dysfunctions.

Ghrelin protects H9c2 cells from hydrogen peroxide-induced apoptosis through NF-κB and mitochondria-mediated signaling

Oxidative stress is a major mechanism underlying the pathogenesis of cardiovascular disease. Herein we investigate the protective effects of ghrelin in H(2)O(2)-induced apoptosis of H9c2 cells, as well as the possible molecular mechanisms involved. To study apoptosis, the cells were assessed by morphologic examination, MTS assay, Annexin V-propidium iodide dual staining and TUNEL analysis. Intracellular reactive oxygen species (ROS) production and mitochondrial membrane potential were also measured. To investigate the underlying molecular mechanisms, the expression of Bcl-2, Bax, active caspase-9 and NF-κB were assessed by Western blotting, and caspase-3 activity was determined by a colorimetric activity assay kit. After stimulation with H(2)O(2) for 18h, H9c2 cells viability decreased significantly; a large fraction of cells underwent apoptosis. We observed a dose-dependent rescue of H9c2 cells from H(2)O(2)-induced apoptosis in the presence of different ghrelin concentrations. Preincubation with ghrelin also restored the ROS and mitochondrial membrane potential levels that had been altered by H(2)O(2) treatment. Moreover, ghrelin decreased H(2)O(2)-induced Bax production and caspase-9 activation, and increased Bcl-2 levels. NF-κB phosphorylation was also significantly inhibited by ghrelin in H(2)O(2)-treated cells. Caspase-3 activation was suppressed by ghrelin in H(2)O(2)-treated H9c2 cells in a dose-dependent manner. In summary, ghrelin protects H9c2 cells from oxidative stress-induced apoptosis through downregulation of Bax expression, caspase-9 activation and NF-κB phosphorylation, and upregulation of Bcl-2 expression. Caspase-3 activation was also reduced in a dose-dependent manner. These data suggest that ghrelin might protect against cardiovascular disease by protecting the mitochondria.

Hexarelin suppresses cardiac fibroblast proliferation and collagen synthesis in rat

Abnormal growth of cardiac fibroblasts is critically involved in the pathophysiology of cardiac hypertrophy/remodeling. Hexarelin is a synthetic growth hormone secretagogue (GHS), which possesses a variety of cardiovascular protective activities mediated via the GHS receptor (GHSR), including improving cardiac dysfunction and remodeling. The cellular and molecular mechanisms underlying the effect of GHS on cardiac fibrosis are, however, not clear. In this report, cultured cardiac fibroblasts from 8-day-old rats were stimulated with ANG II or FCS to induce proliferation. The fibroblast proliferation and DNA and collagen synthesis were evaluated utilizing 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay,3H-thymidine incorporation, and3H-proline incorporation. The level of mRNA of transforming growth factor (TGF)-β was evaluated by RT-PCR, and the active TGF-β1 release from cardiac fibroblasts was evaluated by ELISA. The level of cellular cAMP was measured by radioimmunoassay. In addition, the effects of 3,7-dimethyl-l-propargylxanthine (DMPX; a specific adenosine receptor A2R antagonist) and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; a specific A1R antagonist) were tested. It was found that incubation with 10−7mol/l hexarelin for 24 h 1) inhibited the ANG II-induced proliferation and collagen synthesis and the 5% FCS- and TGF-β-induced increase of DNA synthesis in cardiac fibroblast and 2) reduced ANG II-induced upregulation of TGF-β mRNA expression and active TGF-β1 release from fibroblasts. Hexarelin increased the cellular level of cAMP in cardiac fibroblasts. DMPX (10−8mol/l) but not DPCPX abolished the effect of hexarelin on cardiac fibroblast DNA synthesis. It is concluded that hexarelin inhibits DNA and collagen synthesis and proliferation of cardiac fibroblasts through activation of both GHSR and A2R and diminishment of ANG II-induced increase in TGF-β expression and release.

Cardiovascular effects of intravenous ghrelin infusion in healthy young men

Ghrelin infusion improves cardiac function in patients suffering from cardiac failure, and bolus administration of ghrelin increases cardiac output in healthy subjects. The cardiovascular effects of more continuous intravenous ghrelin exposure remain to be studied. We therefore studied the cardiovascular effects of a constant infusion of human ghrelin at a rate of 5 pmol/kg per minute for 180 min. Fifteen healthy, young (aged 23.2 +/- 0.5 yr), normal-weight (23.0 +/- 0.4 kg/m(2)) men volunteered in a randomized double-blind, placebo-controlled crossover study. With the subjects remaining fasting, peak myocardial systolic velocity S', tissue tracking TT, left ventricular ejection fraction EF, and endothelium-dependent flow-mediated vasodilatation were measured. Ghrelin infusion increased S' 9% (P = 0.002) and TT 10% (P < 0.001), whereas EF, resting blood flow velocity, and endothelium-dependent flow-mediated vasodilatation did not change (P = 0.13). This was associated with a peak in serum growth hormone after 60 min of infusion (37.77 +/- 5.27 ng/ml, P < 0.001), a doubling of free fatty acid levels (P = 0.001), and a 1.6-fold increase in cortisol levels (P < 0.05), whereas glucose and catecholamine levels were constant. In conclusion, supraphysiological levels of ghrelin stimulate left ventricular function in terms of S' and TT in healthy young normal-weight men without changing resting blood flow velocity and endothelium-dependent flow-mediated vasodilatation. The effects did not translate into detectable increments in EF.

Effects of ghrelin and synthetic GH secretagogues on the cardiovascular system

Ghrelin, a newly discovered endogenous hormone that is produced by the stomach, and synthetic peptides have been identified recently as potent growth-hormone secretagogues. This effect is exerted through interaction with a specific G-protein-coupled receptor, GHS-R1a, which is expressed mainly in the hypothalamus-pituitary complex. A study of the peripheral distribution of GHS receptors has shown that it is also present in cardiovascular tissue, which has led to the exploration of the cardiovascular functions of ghrelin and synthetic, growth-hormone-releasing peptides. These ligands have several cardiovascular activities, including a cardioprotective effect against myocardial ischemia, and vasoactive and cardiotropic effects in both experimental models and humans. These effects are mediated by the interaction of these ligands with binding sites, including GHS-1Ra, for which the signalling pathways are not documented fully. Identification of the cardiac and vascular binding sites for ghrelin and synthetic, growth-hormone-releasing peptides will provide new perspectives for treating cardiovascular diseases with these ligands.

Ghrelin and GHS on cardiovascular applications/functions

Although initially recognised for their GH-releasing properties, the cardiovascular system has been recognised as a potentially important target for GH secretagogues (GHS). Moreover, a limited number of studies also indicate cardiovascular effects of ghrelin. So far reported cardiovascular effects of GHS and/or ghrelin include lowering of peripheral resistance, possible improvement of contractility and cardioprotective effects both in vivo and in vitro. Taken together, these results offer an interesting perspective on the future where further studies aiming at evaluating a role of GHS and ghrelin in the treatment of cardiovascular disease are warranted.

La ghréline, un exemple saisissant de pléïotropie des peptides neuroendocriniens

Ghrelin, a peptide predominantly produced by the stomach, has been discovered as a natural ligand of the growth hormone secretagogue receptor (GHS-R) type 1a. Shortly there after, it attracted enormous interest since it appeared as the first peripheral orexigenic factor. Besides, ghrelin exerts other neuroendocrine metabolic and non-endocrine actions (e.g. cardiovascular activities) that may rely on the widespread distribution of ghrelin and its receptor (GHS-R). The existence of several GHS-R subtypes and evidences that neuroendocrine and metabolic but not all other ghrelin actions are dependent on acylation on serine 3 add further complexity to the system whose major physiological role remains to be definitely elucidated. Ghrelin knockout(-/-) mice are neither anorectic nor dwarf though GHS-R-/- are slightly underweight and do not respond to ghrelin with increased GH secretion or appetite. Thus, the continuation of the fascinating ghrelin story as well as its potential pathophysiological implications in endocrinology and internal medicine remain open avenues for future investigations.

Ghrelin inhibits FGF-2-mediated angiogenesis in vitro and in vivo

Recent evidence indicates that ghrelin, an endogenous ligand of the growth hormone secretagogue receptor (GHS-R), is highly expressed in the cardiovascular system, and in this study we addressed the possibility that ghrelin may affect angiogenesis in vitro and in vivo. Reverse transcription-polymerase chain reaction showed that human umbilical vein endothelial cells (HUVECs) express ghrelin and GHS-R mRNAs. Ghrelin inhibited FGF-2-induced proliferation of HUVECs cultured in vitro, the maximal effective concentration being 10(-8) M, and this effect was annulled by the GHS-R antagonist D-Lys3-growth hormone releasing peptide-6. FGF-2 stimulated HUVEC cultured on Matrigel to form capillary-like structures, and ghrelin (10(-8) M) suppressed this effect. In the chick embryo chorioallantoic membrane in vivo assay, FGF-2 induced a strong angiogenic response, which was counteracted by ghrelin (500 ng). Taken together, these findings suggest that ghrelin acts as an angiostatic molecule and indicate that its activity is comparable to that of a well-known angiostatic agent, i.e., vinblastine. The antiangiogenic activity of ghrelin deserves further investigations, alone or together with other antiangiogenic agents, for the treatment of pathological conditions characterized by enhanced angiogenesis.

There are no acute cardiac effects of a single iv dose of human ghrelin in severe growth hormone deficient patients

It has previously been suggested that ghrelin mediates GH-independent biologic activities on the heart. We investigated the acute effects on cardiac contraction of a single iv administration of human ghrelin (in a dose of 1 microg/kg) in severe untreated GH deficient subjects. Prior to the ghrelin infusion, an echocardiographic examination was performed at rest (baseline), after physiologic saline and during dobutamine stress echocardiography (DSE) to exclude a preexisting (subclinical) myocardial dysfunction. To evaluate the acute cardiac effect of infusion and during DSE the velocity of left ventricular (LV) wall contraction was measured continuously by echocardiography. Despite severe GH deficiency we observed in all subjects a normal cardiac function at rest after physiologic saline and during DSE. No acute changes in cardiac performance or cardiac parameters could be observed after a single iv dose of ghrelin. Also, no important increase in GH secretion was detected after ghrelin administration. Our study suggests that, in contrast to hexarelin, a single iv administration of ghrelin in a physiological dose has no acute effects on cardiac function in severe GH deficiency. This suggests that GH-independent effects of ghrelin play no important role in the acute regulation of cardiac function in man.

Biological, physiological, pathophysiological, and pharmacological aspects of ghrelin

Ghrelin is a peptide predominantly produced by the stomach. Ghrelin displays strong GH-releasing activity. This activity is mediated by the activation of the so-called GH secretagogue receptor type 1a. This receptor had been shown to be specific for a family of synthetic, peptidyl and nonpeptidyl GH secretagogues. Apart from a potent GH-releasing action, ghrelin has other activities including stimulation of lactotroph and corticotroph function, influence on the pituitary gonadal axis, stimulation of appetite, control of energy balance, influence on sleep and behavior, control of gastric motility and acid secretion, and influence on pancreatic exocrine and endocrine function as well as on glucose metabolism. Cardiovascular actions and modulation of proliferation of neoplastic cells, as well as of the immune system, are other actions of ghrelin. Therefore, we consider ghrelin a gastrointestinal peptide contributing to the regulation of diverse functions of the gut-brain axis. So, there is indeed a possibility that ghrelin analogs, acting as either agonists or antagonists, might have clinical impact.

Activation of GABAA and opioid receptors reduce penile erection induced by hexarelin peptides

The effect of muscimol, a GABA(A) receptor agonist, and of morphine, an opioid receptor agonist, on penile erection induced by the hexarelin analogue peptide EP 80661 (GAB-D-Trp(2-Me)-D-Trp(2-Me)-LysNH(2)) and on the increase in the concentration of NO(2)(-) and NO(3)(-) that occurs concomitantly in the dialysate obtained from the paraventricular nucleus (PVN) of the hypothalamus by intracerebral microdialysis, was studied in male rats. Muscimol (50, 100 and 200 ng) and morphine (0.1, 0.5, 1 and 5 microg) given into the PVN dose-dependently reduced penile erection induced by EP 80661 (1 microg) injected into the PVN. The reduction of penile erection was parallel to a decrease of the concomitant NO(2)(-) and NO(3)(-) increase that occurs in the paraventricular dialysate in these experimental conditions. Muscimol and morphine effects on EP 80661-induced penile erection and NO(2)(-) increase were prevented by the prior administration into the PVN of bicuculline (250 ng) and naloxone (5 microg), respectively. The present results show that the activation of GABA(A) receptors and of opioid receptors in the PVN reduces penile erection induced by hexarelin analogue peptides by reducing the increase in NO activity that occurs in this hypothalamic nucleus in these experimental conditions.

Cardiac effects of ghrelin and its endogenous derivatives des-octanoyl ghrelin and des-Gln14-ghrelin

The mechanisms underlying the cardiac activities of synthetic growth hormone secretagogues (GHS) are still unclear. The natural ligand of the GHS receptors, i.e. ghrelin, classically binds the GHS receptor and exerts endocrine actions in acylated forms only; its cardiovascular actions still need to be investigated further. In order to clarify these aspects, we studied the effects of either the synthetic peptidyl GHS hexarelin (1 microM), or the natural ghrelin (50 nM) and the endogenous ghrelin derivatives des-Gln14-ghrelin (1-100 nM) and des-octanoyl ghrelin (50 nM), on the tension developed by guinea pig papillary muscle and on L-type Ca2+ current (ICa) of isolated ventricular cells. The binding of these molecules to ventricular cell membrane homogenates was also studied. We observed that all peptides reduced the tension developed at low frequencies (60-120 beats/min) in a dose-dependent manner. No alteration in cardiac contractility was induced by des-Gln14-ghrelin or des-octanoylated ghrelin when the endocardial endothelium had been removed or after cyclooxygenase blockade. Pretreatment with tyramine (2 microM) had no effect on the inotropic response induced by des-Gln(14)-ghrelin. No significant effect on I(Ca) of isolated ventricular cells was observed in the presence of des-Gln14-ghrelin (100 nM). The order of potency on the tension of papillary muscle was: des-octanoyl ghrelin > ghrelin = des-Gln14-ghrelin > hexarelin. This gradient of potency was consistent with the binding experiments performed on ventricular membranes where either acylated or unacylated ghrelin forms, and hexarelin, recognized a common high-affinity binding site. In conclusion, ghrelin, des-Gln14-ghrelin and des-octanoyl ghrelin, show similar negative inotropic effect on papillary muscle; as des-octanoyl ghrelin is peculiarly devoid of any GH-releasing activity, the cardiotropic action of these molecules is independent of GH release. The binding studies and the experiments performed both on the isolated cells and on papillary muscle after endothelium removal or cyclooxygenase blockade indicate that the cardiotropic action of natural and synthetic ghrelin analogues reflects the interaction with a novel GHS receptor (peculiarly common for ghrelin and des-octanoyl ghrelin), leading to release of cyclooxygenase metabolites from endothelial cells, as indicated by direct measurement of prostacyclin metabolite 6-keto-PGF(1alpha).

A growth hormone secretagogue prevents ischemic-induced mortality independently of the growth hormone pathway in dogs with chronic dilated cardiomyopathy

To determine the functional role of growth hormone (GH) secretagogue in myocardium with ischemia, left ventricular (LV) pressure gauge, wall thickness crystals, coronary occluder, pacers, and catheters were implanted in 26 dogs. Beginning 1 week after ventricular pacing (240 beats/min) was initiated, dogs were treated (s.c.) with GH releasing peptide-6 (GHRP-6, n = 8, 0.2 mg/kg/day), GH (n = 7, 0.06 mg/kg/day), or vehicle (n = 11). Two weeks of pacing was associated with similar decreases in LV pressure, rate of change of LV pressure, systolic wall thickening (WT), and an increase in left atrial pressure in all groups. Coronary artery occlusion (CAO) resulted in a similar loss of WT in ischemic regions, which did not recover during reperfusion period in all groups. WT in nonischemic regions, however, was enhanced in the GHRP-6 group compared with the GH and vehicle groups, e.g., increase of WT after 1 h of reperfusion was greater (p <0.05) in the GHRP-6 (+53 +/- 8%) than in the GH (+14 +/- 12%) or (+14 +/- 6%). There were no differences in myocardial blood flow, hemodynamics, or arrhythmic beats among all groups during CAO and reperfusion periods. Strikingly, no dogs in the GHRP-6 group died during CAO, whereas the survival rates for GH and vehicle groups were 57 and 55%, respectively. Our data demonstrate, for the first time, that chronic therapy with a GH secretagogue prevents sudden death in dogs with dilated cardiomyopathy subjected to acute ischemia. This seems to be related to an enhanced nonischemic compensatory mechanism mediated by the GH secretagogue receptors rather than via the GH/insulin growth factor-1 pathway.

Ghrelin and des-acyl ghrelin inhibit cell death in cardiomyocytes and endothelial cells through ERK1/2 and PI 3-kinase/AKT

Ghrelin is an acyl-peptide gastric hormone acting on the pituitary and hypothalamus to stimulate growth hormone (GH) release, adiposity, and appetite. Ghrelin endocrine activities are entirely dependent on its acylation and are mediated by GH secretagogue (GHS) receptor (GHSR)-1a, a G protein-coupled receptor mostly expressed in the pituitary and hypothalamus, previously identified as the receptor for a group of synthetic molecules featuring GH secretagogue (GHS) activity. Des-acyl ghrelin, which is far more abundant than ghrelin, does not bind GHSR-1a, is devoid of any endocrine activity, and its function is currently unknown. Ghrelin, which is expressed in heart, albeit at a much lower level than in the stomach, also exerts a cardio protective effect through an unknown mechanism, independent of GH release. Here we show that both ghrelin and des-acyl ghrelin inhibit apoptosis of primary adult and H9c2 cardiomyocytes and endothelial cells in vitro through activation of extracellular signal-regulated kinase-1/2 and Akt serine kinases. In addition, ghrelin and des-acyl ghrelin recognize common high affinity binding sites on H9c2 cardiomyocytes, which do not express GHSR-1a. Finally, both MK-0677 and hexarelin, a nonpeptidyl and a peptidyl synthetic GHS, respectively, recognize the common ghrelin and des-acyl ghrelin binding sites, inhibit cell death, and activate MAPK and Akt.These findings provide the first evidence that, independent of its acylation, ghrelin gene product may act as a survival factor directly on the cardiovascular system through binding to a novel, yet to be identified receptor, which is distinct from GHSR-1a.

Effects of acute hexarelin administration on cardiac performance in patients with coronary artery disease during by-pass surgery

Growth hormone (GH) secretagogues are synthetic molecules with neuroendocrine but also cardiovascular activities mediated by specific GH secretagogue-receptors. The acute administration of hexarelin, a peptidyl GH secretagogue, increases left ventricular ejection fraction in normal subjects and even in patients with severe GH deficiency. We evaluated cardiac performances in patients with coronary artery disease after acute administration of hexarelin (2.0 microg/kg, i.v.) compared to that in patients given with GH-releasing hormone (GHRH; 2.0 microg/kg, i.v.), recombinant human (rh)-GH (10.0 microg/kg, i.v.) or placebo. Cardiac performance was studied in 24 male patients (age [mean +/- S.E.M.]: 59.5 +/- 1.1 years; body mass index: 24.6 +/- 0.9 kg/m(2); left ventricular ejection fraction: 57.2 +/- 1.4%) with coronary artery disease undergoing by-pass surgery during general anesthesia. Left ventricular ejection fraction, left ventricular end diastolic volume, cardiac index and cardiac output were evaluated by intraoperative omniplane transoesophageal echocardiography while wedge pressure, central venous pressure, mean arterial pressure and systemic vascular resistance index were evaluated by systemic and pulmonary arterial catheterization. RhGH, GHRH and placebo did not exert any hemodynamic effect while hexarelin induced a prompt (after +10 min) increase in left ventricular ejection fraction (P < 0.001), cardiac index (P < 0.001) and cardiac output (P < 0.001) lasting up to +90 min without any variation in left ventricular end diastolic volume. Accordingly, hexarelin induced a reduction of wedge pressure (P < 0.01). These changes occurred in the presence of increased mean arterial pressure (P < 0.05) and transient decrease of central venous pressure (P < 0.05 at +30 min only) but no change in systemic vascular resistance index. Heart rate after hexarelin was similar to that after placebo. Hexarelin induced a slight increase in GH levels which was similar to that after GHRH but far lower (P < 0.01) than that after rhGH. Thus, in patients with coronary artery disease undergoing by-pass surgery, the acute administration of hexarelin clearly improves cardiac performance without any relevant variation in systemic vascular resistance. The cardiotropic effect of hexarelin is not shared by GHRH or by rhGH, indicating that it is not mediated by the increase in circulating GH levels but more likely reflects activation of specific cardiovascular GH secretagogue receptors.

Neuroendocrine and peripheral activities of ghrelin: implications in metabolism and obesity

Ghrelin, a 28-amino acid acylated peptide predominantly produced by the stomach, displays strong growth hormone (GH)-releasing activity mediated by the hypothalamus-pituitary GH secretagogue (GHS)-receptors specific for synthetic GHS. The discovery of ghrelin definitely changes our understanding of GH regulation but it is also already clear that ghrelin is much more than simply a natural GHS. Ghrelin acts also on other central and peripheral receptors and shows other actions including stimulation of lactotroph and corticotroph secretion, orexia, influence on gastro-entero-pancreatic functions, metabolic, cardiovascular and anti-proliferative effects. GHS were born more than 20 years ago as synthetic molecules suggesting the option that GH deficiency could be treated by orally active GHS as an alternative to recombinant human GH (rhGH). Up to now, this has not been the case and also their usefulness as anabolic anti-aging intervention restoring GH/insulin-like growth factor-I axis in somatopause is still unclear. We are now confronted with the theoretical possibility that GHS analogues could become candidate drugs for treatment of pathophysiological conditions in internal medicine totally unrelated to disorders of GH secretion. Particularly, GHS receptor agonists or antagonists acting on appetite could represent new drug intervention in eating disorders.

Efficacy of a growth hormone-releasing peptide mimetic in cardiac ischemia/reperfusion injury

The cardioprotective efficacy of the pyrazolinone-piperidine dipeptide growth hormone secretagogue (GHS) CP-424,391 was studied in an in vivo rabbit model of ischemia and reperfusion. CP-424,391 was administered at 25 mg/kg p.o. x 7 days. Ischemia was induced by left coronary artery occlusion for 30 min, after which the heart was reperfused for 2 h. At the end of reperfusion, animals were euthanized and the infarct size was determined. The area at risk of infarct was not different between the control (45.8+/-3.7%, n=6) and CP-424,391-treated groups (36.9+/-4.3%, n=11). The infarct size of the control animals was 49.5+/-7.1% and was significantly (P<0.05) lower in the CP-424,391-treated group (infarct size=17.3+/-3.0). There was a trend, albeit not significant, for the left ventricular function to recover to a greater extent in CP-424,391-treated rabbits. Thus, the treatment of rabbits for 7 days with CP-424,391 was cardioprotective against ischemia/reperfusion injury.

EP 91073 prevents EP 80661-induced penile erection: new evidence for the existence of specific EP peptide receptors mediating penile erection

The effect of EP 91073, EP 51389, EP 70555 and EP 51216, peptide analogues of the growth hormone releasing peptide hexarelin, on penile erection induced by EP 80661 or EP 60761 injected into the paraventricular nucleus of the hypothalamus, was studied in male rats. Of the above peptides only EP 91073 (0.2-1 microg) was found capable of reducing penile erection induced by EP 80661 or EP 60761, when given into the paraventricular nucleus. Despite its ability to prevent EP peptide-induced penile erection, EP 91073 (1 microg) was unable to prevent penile erection induced by the dopamine receptor agonist apomorphine (50 ng), oxytocin (30 ng) and N-methyl-D-aspartic acid (50 ng), when given into the paraventricular nucleus 10 min prior to the above substances. The EP 91073-induced prevention of penile erection occurred with a reduction in the increase in nitric oxide production that occurs in the paraventricular nucleus concomitant to penile erection induced by EP 80661 and EP 60761, as measured by intracerebral vertical microdialysis. The present results are in line with the hypothesis that EP 80661 and EP 60761 induce penile erection by activating specific receptors in the paraventricular nucleus, located possibly in oxytocinergic neurons mediating penile erection, and show that EP 91073 acts as an antagonist of these EP peptide receptors mediating penile erection.

Growth hormone and the heart

Impaired cardiovascular function has recently been demonstrated to potentially reduce life expectancy both in GH deficiency and excess. Experimental and clinical studies have supported the evidence that GH and IGF-I are implicated in cardiac development. In most patients with acromegaly a specific cardiomyopathy, characterized by myocardial hypertrophy with interstitial fibrosis, lympho-mononuclear infiltration and areas of monocyte necrosis, results in biventricular concentric hypertrophy. In contrast, patients with childhood or adulthood-onset GH deficiency (GHD) may suffer both from structural cardiac abnormalities, such as narrowing of cardiac walls, and functional impairment, that combine to reduce diastolic filling and impair left ventricular response to peak exercise. In addition, GHD patients may have an increase in vascular intima-media thickness and a higher occurrence of atheromatous plaques, that can further aggravate the haemodynamic conditions and contribute to increased cardiovascular and cerebrovascular risk. However, several lines of evidence have suggested that the cardiovascular abnormalities can be partially reversed by suppressing GH and IGF-I levels in acromegaly or after GH replacement therapy in GHD patients. Recently, much attention has been focussed on the ability of GH to increase cardiac mass suggesting its possible use in the treatment of chronic nonendocrine heart failure. In fact, GH administration can induce an improvement in haemodynamic and clinical status in some patients. Although these data need to be confirmed in more extensive studies, such promising results seem to open new perspectives for GH treatment in humans.

Penile erection induced by EP 80661 and other hexarelin peptide analogues: involvement of paraventricular nitric oxide

The effect of GAB-D-Trp(2-Me)-D-Trp(2-Me)-LysNH(2) (EP 80661), GAB-D-Trp(2-Me)-D-Trp(2-Me)-D-Trp(2-Me)-LysNH(2) (EP 60761), GAB-D-Trp(2-Me)-LysNH(2) (EP 91071) and GAB-D-Trp(2-Me)-D-beta Nal-Phe-LysNH(2) (EP 50885), four hexarelin peptide analogues that induce penile erection when injected into the paraventricular nucleus of the hypothalamus of male rats, on the concentration of NO(2)(-) and NO(3)(-) in the paraventricular dialysate was studied in male rats. EP peptides (1 microg) induced penile erection and increased the concentration of NO(2)(-) and NO(3)(-) in the paraventricular dialysate. In contrast, hexarelin (1 microg) was ineffective on either penile erection or paraventricular NO(2)(-) and NO(3)(-). EP peptide-induced penile erection was prevented by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methylester given into the paraventricular nucleus (20 microg), which also reduced the concomitant increase of NO(2)(-) and NO(3)(-) concentration in the paraventricular dialysate. In contrast, the oxytocin receptor antagonist [d(CH(2))(5)Tyr(Me)(2)-Orn(8)]vasotocin (1 microg) given into the paraventricular nucleus, was ineffective on penile erection and on the NO(2)(-) and NO(3)(-) increase induced by EP peptides, despite its ability to prevent the sexual response induced by the above peptides when given into the lateral ventricles. The present results show that EP peptides induce penile erection by activating nitric oxide synthase in the paraventricular nucleus of the hypothalamus, possibly in the cell bodies of oxytocinergic neurons that control penile erection.

Growth hormone secretagogue binding sites in peripheral human tissues

The family of GH secretagogues (GHS) includes peptidyl (hexarelin) and nonpeptidyl (MK 0677) molecules possessing specific receptors in the brain, pituitary, and thyroid. GHS receptor subtypes have also been identified in the heart; and a gastric-derived peptide, named ghrelin, has recently been proposed as a natural ligand. Our aim was to investigate the presence of GHS receptors in a wide range of human tissues, by radioreceptor assay with [125I]Tyr-Ala-hexarelin. GHS receptors were detected mainly in the myocardium, but they were also present (in order of decreasing binding activity) in adrenal, gonads, arteries, lung, liver, skeletal muscle, kidney, pituitary, thyroid, adipose tissue, veins, uterus, skin, and lymphnode. In contrast, negligible binding was found in parathyroid, pancreas, placenta, mammary gland, prostate, salivary gland, stomach, colon, and spleen. Hexarelin, MK 0677, and human ghrelin completely displaced the radioligand from binding sites of endocrine tissues, but MK 0677 and ghrelin were less potent than hexarelin. In nonendocrine tissues, both MK 0677 and ghrelin were inactive in displacement of [125I]Tyr-Ala-hexarelin, whereas hexarelin was as active as a displacing agent in endocrine tissues. This study provides the first detailed analysis of the tissue localization of GHS receptors and suggests that a still unknown receptor subtype, specific for peptidyl GHS, may exist in the heart and in other tissues.

EP 60761 and EP 50885, two hexarelin analogues, induce penile erection in rats

The effect of hexarelin and four related peptide analogues, EP 40904, EP 40737, EP 50885 and EP 60761, injected into the paraventricular nucleus of the hypothalamus of male rats in doses between 2 and 2000 ng on spontaneous penile erection was studied. Of these peptides, EP 60761 and EP 50885, but not hexarelin, EP 40904 or EP 40737, increased dose-dependently the number of spontaneous penile erections. EP 60761 was active already at the dose of 20 ng, which induced the sexual response in 70% of the treated rats. The maximal response was induced by 200 ng of the peptide. EP 50885 was less potent than EP 60761, with 1000 ng being the minimal effective dose and 2000 ng as the dose required to induce the maximal response. At the doses used, both peptides also increased slightly the number of spontaneous yawning episodes. EP 60761- and EP 50885-induced penile erection was prevented by the oxytocin receptor antagonist [d(CH(2))(5)Tyr(Me)(2)-Orn(8)]vasotocin (0.1-1 microg) given intracerebroventricularly (i.c.v.), but not into the paraventricular nucleus (0.1-1 microg), by the competitive nitric oxide (NO) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) given either into the paraventricular nucleus (10-20 microg) or i.c.v. (75-150 microg), by the N-type Ca(2+) channel blocker omega-conotoxin-GVIA (2-5 ng) or by the opiate morphine (1-10 microg), but not by the dopamine receptor antagonist (Z)-4-[3-[2-(trifluoromethyl)-9H-thioxanthen-9-ylidene]propyl]-1-p ipe razine-ethanol (cis-flupenthixol) (10 microg) or by the N-methyl-D-aspartic acid (NMDA) receptor antagonist (5R, 10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine ((+)-MK-801) (1 microg), all given into the paraventricular nucleus before either peptide. The present results show that EP 60761 and EP 50885 induced penile erection by increasing central oxytocin transmission, possibly by activating NO synthase in the cell bodies of oxytocinergic neurons located in the paraventricular nucleus that control penile erection.

Hexarelin, a growth hormone secretagogue, protects the isolated rat heart from ventricular dysfunction produced by exposure to calcium-free medium

The effect of hexarelin, a potent synthetic growth hormone (GH)-secretagogue, and of human GH were studied on the mechanical and metabolic changes elicited by the calcium-paradox phenomenon in isolated rat hearts submitted to 5 min Ca(2+)-depletion followed by reperfusion with reintegrated Ca(2+)medium. Hexarelin, (80 microg kg(-1)s.c.) administered to normal male young rats for 3 and 7-day, time-dependently antagonized the sudden increase in resting tension of the isolated perfused hearts upon Ca(2+)-repletion. The beneficial effect of hexarelin was particularly evident in the 7-day treatment. In this instance, ventricular contraction peaked at 30 +/- 2 mmHg (controls, 76 +/- 7 mmHg) and the recovery of left ventricular developed pressure (LVDP) was two times higher (P<0.001) than that recorded in controls (LVDP, 29 +/- 2 mmHg). Moreover, the release of creatine kinase into the heart effluent during Ca(2+)-repletion was reduced by 40% (P<0.001) as compared to controls. The protecting activity of hexarelin against the damage induced by calcium-paradox in the heart was apparently divorced from any stimulation of the GH/insulin-like growth factor (IGF) axis, since plasma and heart concentrations of IGF-1 were similar to those measured in control rats. In contrast to hexarelin, administration of GH (400 microg kg(-1) s.c.) for 7 days did not affect the mechanical and metabolic manifestations of calcium-paradox in the perfused rat hearts. Hexarelin (8 microg ml(-1)) perfused for 60 min through the hearts in recirculating conditions did not modify heart contractility and failed to prevent ventricular hypercontractility developed on Ca(2+)-readmission. In conclusion, the mode of action of hexarelin in protecting the rat heart from calcium-paradox events is presently unknown; it would seem, however, that only prolonged exposure to hexarelin makes myocardial cells competent to maintain cytoplasmatic electrolyte balance and to control of Ca(2+)gain, two functions that are impaired during the 'calcium-paradox' phenomenon.

The aging process: where are the drug opportunities?

New data support a role for growth hormone secretagogue receptor agonists as rejuvenating agents. Two enzymes critical for the formation of beta-amyloid plaques in Alzheimer's disease have been identified. Estrogen receptor beta continues to emerge as a potential drug target. The orphan nuclear receptor Nurr1 appears to be a target for treatment of Parkinson's disease, and propargylamines are emerging as inhibitors of oxidative damage in neurons.