ArticlePDF AvailableLiterature Review

The cardiovascular action of hexarelin

September 2014
Journal of Geriatric Cardiology 11(3):253-8

DOI:10.11909/j.issn.1671-5411.2014.03.007

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PubMed

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CC BY-NC-SA 3.0

Authors:

Yuanjie Mao

Ohio University

Takeshi Tokudome

Yokohama City University

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.

. In vivo studies of the cardiovascular action of hexarelin.

…

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Journal of Geriatric Cardiology (2014) 11: 253−258

http://www.jgc301.com; jgc@jgc301.com | Journal of Geriatric Cardiology

Review • Open Access •

The cardiovascular action of hexarelin

Yuanjie MAO1,2, Takeshi Tokudome1, Ichiro Kishimoto1,3

1Department of Biochemistry, National Cerebral and Cardiovascular Center, Suita, Osaka 565-8565, Japan

2Department of Medicine, Prince George’s Hospital Center, Cheverly, Maryland 20785, USA

3Department of Endocrinology and Metabolism, National Cerebral and Cardiovascular Center, Suita, Osaka 565-8565, Japan

Abstract

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 car-

diovascular conditions. In this concise review, we discuss the current evidence for the cardiovascular action of hexarelin.

J Geriatr Cardiol 2014; 11: 253−258. doi:10.11909/j.issn.1671-5411.2014.03.007

Keywords: Hexarelin; Cardiovascular disease; Growth hormone secretagogue receptor; CD36

1 Introduction

Growth hormone secretagogues (GHS) are a class of

small synthetic peptides that stimulate growth hormone (GH)

release through binding to the growth hormone secre-

tagogue receptor (GHSR) 1a. Moreover, GHSR 1a is a

G-protein-coupled receptor originally identified in the hy-

pothalamus and pituitary,[1] and later recognized as the re-

ceptor for the endogenous hormone ghrelin.[2] The periph-

eral distribution of GHSR 1a in the heart, adrenals, fat,

prostate, bone, and digestive tract has supported physio-

logical roles of GHSs and ghrelin independent of GH re-

lease and neuroendocrine stimulation. For example, GH-in-

dependent effects on orexigenic properties, fat metabolism,

immune, gastrointestinal, and cardiovascular activities have

been reported for GHSs and ghrelin.[3–6 ]

Previous studies have revealed that ghrelin administra-

tion can improve cardiac function in rats and patients with

chronic heart failure, as indicated by increased left ventricle

ejection fraction (LVEF), cardiac output, and exercise ca-

pacity.[7–9 ] In rodents with acute myocardial infarction (MI),

ghrelin administration prevented malignant arrhythmias and

reduced mortality in the acute phase, while improving left

Correspondence to: Ichiro Kishimoto, MD, Department of Biochemistry,

National Cerebral and Cardiovascular Center Research Institute, 5-7-1 Fuji-

shiro-dai, Suita, Osaka 565-8565, Japan. E-mail: kishimot@hsp.ncvc.go.jp

Telephone: +81-668-335015 Fax: +81-668-355402

Received: April 2, 2014 Revised: May 25, 2014

Accepted: July 10, 2014 Published online: September 10, 2014

ventricle (LV) dysfunction and attenuating cardiac remod-

eling in the subacute phase.[10–13] However, ghrelin is an

unstable natural peptide that is transformed and degraded,

which limits its clinical use. The GHS hexarelin is a chemi-

cally stable and potent synthetic hexapeptide that can be

administered orally, making it a potential alternative to

ghrelin.[14] It is comparable to ghrelin with respect to the

half-maximal effective concentration for their common re-

ceptor, GHSR 1a; although the cardiac action of hexarelin

was reported to be mediated in part by GHSR 1a and largely

by activation of the CD36 receptor, in isolated working

hearts.[15,16] In this concise review, we discuss the current

evidence for the cardiovascular action of hexarelin.

2 Cardiovascular action

2.1 Inotropic effect

Acute intravenous administration of hexarelin had a

short-lasting, positive inotropic effect. Cardiac performance

was studied by radionuclide angiocardiography in seven

male volunteers. Hexarelin administration increased LVEF

(70.7 ± 3.0% vs. 64.0 ± 1.5%, P < 0.03) without affecting

mean blood pressure and heart rate. LVEF was significantly

increased after 15 min and peaked at 30 min, and the effect

lasted for up to 60 min after administration.[17] In 24 male

patients with coronary artery disease undergoing by-pass

surgery under general anesthesia, LVEF, cardiac output,

and cardiac index were evaluated by transoesophageal

echocardiography while wedge pressure, central venous

254 MAO YJ, et al. Cardiovascular action of hexarelin

Journal of Geriatric Cardiology | jgc@jgc301.com; http://www.jgc301.com

pressure, mean arterial pressure, and systemic vascular re-

sistance index were determined by systemic and pulmonary

arterial catheterization. Acute intravenous administration

of hexarelin (2 µg/kg) induced a rapid increase in LVEF,

cardiac output, and cardiac index, while reducing wedge

pressure. It also increased mean arterial pressure and tran-

siently decreased central venous pressure, but did not

change the systemic vascular resistance index and heart

rate.[18] Furthermore, hexarelin induced time- and concen-

tration-dependent inotropic effects in rat papillary muscle,[19]

and increased the amplitude of intracellular Ca2+ transients

and L-type Ca2+ current to produce positive inotropic effects

in freshly isolated adult Wistar rat ventricular myocytes

through protein kinase C signaling cascade.[20].

2.2 Inhibition of apoptosis

Treatment of neonatal rat cardiomyocytes with hexarelin

significantly decreased angiotensin II-induced apoptosis and

DNA fragmentation, and increased myocyte viability.[21]

Hexarelin treatment also inhibited doxorubicin-induced

apoptosis and promoted survival of H9c2 cardiomyocytes

and endothelial cells.[22] The anti-apoptosis activity of hex-

arelin in cardiomyocytes and endothelial cells may partially

explain its cardioprotective effects. Chronic administration

of hexarelin alleviates LV dysfunction, pathological remod-

eling, and cardiac cachexia in rats with congestive heart

failure by suppressing stress-induced neurohormonal activa-

tion and cardiomyocyte apoptosis.[23]

2.3 Ischemia-reperfusion injury

In hearts subjected to 30 min of ischemia followed by

120 min of reperfusion, hexarelin (1 µmol/L) significantly

reduced infarct size, as determined by using triphenyltetra-

zolium chloride staining, and the protection provided by

hexarelin was partly abolished by the protein kinase C in-

hibitor chelerythrine.[24] Hexarelin treatment not only pre-

served the electrophysiological properties of cardiomyo-

cytes after ischemia-reperfusion injury but also inhibited

cardiomyocyte apoptosis and promoted cell survival by

modification of mitogen-activated protein kinase path-

ways,[25] and produced a positive inotropic effect on

ischemic cardiomyocytes.[26] Hexarelin administration for

30 days counteracted the ischemic heart damage in Zucker

rats subjected to low flow ischemia and reperfusion. The

recovery of LV pressure developed at reperfusion was sig-

nificantly greater in hexarelin-treated rats than in controls

and the increase in coronary resistance was minimal.[27] The

chronic administration of hexarelin to GH-deficient rats had

a pronounced protective effect against ischemic and

post-ischemic ventricular dysfunction, and prevented hy-

per-responsiveness of the coronary vascular bed to angio-

tensin II in perfused hearts.[28]

2.4 Myocardial infarction

Four weeks after ligation of the left coronary artery, male

rats were treated with hexarelin (100 µg/kg per day) or

normal saline subcutaneously for two weeks. Transthoracic

echocardiography was performed before and after the

treatment period. Compared with normal saline, hexarelin

treatment increased stroke volume, stroke volume in-

dex, cardiac output, and cardiac index, and decreased total

peripheral resistance.[29]

2.5 Cardiac fibrosis

Hexarelin treatment of spontaneously hypertensive rats

for five weeks significantly reduced cardiac fibrosis by de-

creasing interstitial and perivascular myocardial collagen

deposition and myocardial hydroxyproline content, and re-

ducing collagen I and III mRNA and protein expression. In

addition, hexarelin treatment increased matrix metallopro-

teinase-2 and -9 activities and decreased myocardial mRNA

expression of the tissue inhibitor of metalloproteinase-1.

Furthermore, hexarelin treatment significantly attenuated

LV hypertrophy, LV diastolic dysfunction, and high blood

pressure.[30] Treatment of cultured cardiac fibroblasts with

hexarelin (0.1 µmol/L) inhibited angiotensin II-induced

proliferation and collagen synthesis, and transforming

growth factor (TGF)-β-induced DNA synthesis, and re-

duced the angiotensin II-mediated upregulation of TGF-β

expression and release.[31]

2.6 Atherosclerosis

Anti-atherosclerotic activity of hexarelin was observed in

adult Sprague-Dawley rats. Treatment with hexarelin sup-

pressed the formation of atherosclerotic plaques and neoin-

tima, partially reversed serum high-density lipoprotein cho-

lesterol/low-density lipoprotein cholesterol ratio, and in-

creased serum nitric oxide levels and aortic mRNA expres-

sion of endothelial nitric oxide synthase, GHSRs, and CD36

in atherosclerotic rats. Hexarelin treatment also decreased

tritiated thymidine incorporation in cultured vascular smooth

muscle cells, calcium sedimentation in the aortic wall, and

foam cell formation induced by oxidized low-density lipo-

protein.[32] Furthermore, chronic treatment with hexarelin

unaltered the high triglyceride levels and significantly de-

creased plasma cholesterol concentrations in obese rats.[27]

3 Cardiac receptor

The cardiovascular action of hexarelin has been regarded

MAO YJ, et al. The cardiovascular action of hexarelin 255

http://www.jgc301.com; jgc@mail.sciencep.com | Journal of Geriatric Cardiology

as GH-independent and occurs through activation of cardiac

receptors. Previous studies showed that the cardiovascular

effects of hexarelin are not shared by recombinant human

GH or by GH-releasing hormone, indicating that they are

not mediated by an increase in circulating GH levels.[17,18,33]

Moreover, hexarelin significantly increased LVEF in nor-

mal and in GH-deficient patients[34–36] and prevented cardiac

damage after ischemia-reperfusion in hypophysectomized

rats,[37] indicating that its cardioprotective activity is not due

to stimulation of the GH axis.[27]

Hexarelin can bind to specific cardiac sites. Specific

125I-Tyr-Ala-hexarelin binding was observed in the human

cardiovascular system, and the highest 125I-Tyr-Ala-hex-

arelin levels were detected in the ventricles, followed by

atria, aorta, coronaries, carotid, endocardium, and vena ca-

va.[38] Specific hexarelin binding has also been shown in

H9c2 myocytes.[39] Currently, two cardiac receptor subtypes

have been proposed for hexarelin.

3.1 Cardiac GHSR 1a receptor

GHSR mRNA expression in cardiomyocytes was upre-

gulated after treatment with hexarelin,[21] and GHSR 1a

protein was expressed primarily in the heart as compared to

all other organs.[40] Fluorescein-conjugated ghrelin (1–18)

bound specifically to heart tissue in situ and was displaced

by both excess ghrelin and hexarelin.[40] Further, hexarelin

significantly prolonged action potential duration, produced

positive inotropic effects, and preserved electrophysiologi-

cal properties after ischemia-reperfusion injury in isolated

myocytes. These effects were abolished in the presence of

the GHSR antagonist d-Lys-3-GH-releasing peptide-6 or the

GHSR 1a-specific antagonist BIM28163.[20,25,26,41] The ef-

fects of hexarelin on cardiac function, cardiac fibrosis, and

blood pressure were also mediated by GHSRs, since GHSR

expression was upregulated by hexarelin treatment and a

selective GHSR antagonist inhibited hexarelin activity.[30]

3.2 Cardiac CD36 receptor

The presence of specific GHS binding sites was demon-

strated in three different human breast carcinoma cell lines

(MCF7, T47D, and MDA-MB-231), which lacked detect-

able GHSR 1a mRNA expression. However, hexarelin

treatment significantly inhibited proliferation of these cell

lines at concentrations close to the binding affinity.[42] A

photoactivatable derivative of hexarelin was developed to

label and characterize binding sites in anterior pituitary

membranes. The differential binding affinity for car-

diac tissue raised the possibility of the existence of distinct

receptor subtypes in the pituitary and the cardiovascular

system.[43] GHSRs were detected mainly in the myocardium

by using a radioreceptor assay with 125I-Tyr-Ala-hexarelin,

but they were also present in the adrenals, gonads, arteries,

lungs, liver, skeletal muscle, kidneys, pituitary, thyroid,

adipose tissue, veins, uterus, skin, and lymph nodes. Hex-

arelin and human ghrelin completely displaced the radioli-

gand from binding sites in endocrine tissues, but ghrelin was

less potent than hexarelin. In non-endocrine tissues, such as

heart, ghrelin did not displace 125I-Tyr-Ala-hexarelin,

whereas hexarelin had the same displacement activity as in

endocrine tissues. This suggested that there is a hex-

arelin-specific receptor subtype in the heart and in other

non-endocrine tissues.[44] Finally, the specific cardiac re-

ceptor for hexarelin was identified. The N-terminal se-

quence of the deglycosylated protein was identical to rat

CD36, a multifunctional glycoprotein, which is expressed in

cardiomyocytes and microvascular endothelial cells. Hex-

arelin-mediated activation of CD36 in perfused hearts in-

creased coronary perfusion pressure in a dose-dependent

manner. This effect was not observed in hearts from

CD36-null mice and from spontaneously hypertensive rats

genetically deficient in CD36.[45, 46]

4 Hexarelin vs. ghrelin

Hexarelin has more potent beneficial effects on the car-

diovascular system compared with its natural analog ghrelin.

In one study, either ghrelin (320 μg/kg per day) or equimo-

lar hexarelin (80 μg/kg per day) was administered to hy-

pophysectomized rats for seven days and their hearts were

then subjected to ischemia and reperfusion in vitro. Hex-

arelin was more potent than ghrelin in preventing increases

in LV end-diastolic pressure, coronary perfusion pressure,

and creatine kinase release in the heart perfusate.[15] In an-

other study, chronic hexarelin administration improved

heart function in ghrelin-null mice to a greater extent than

equimolar ghrelin administration after experimental MI.[47]

Given the fact that the half-maximal effective concentration

of hexarelin for GHSR 1a (1.7 nmol/L) is comparable to

that of ghrelin (1.0 nmol/L),[16] the higher potency of hex-

arelin was considered to be mediated largely by interactions

with CD36 in the heart, and in part by GHSRs.[15,47]

However, other studies reported that when GHSR 1a ac-

tivation was identical hexarelin and ghrelin had similar car-

diac effects, although the dosage of ghrelin was 10 times

higher than that of hexarelin in molar terms. Ghrelin (10

nmol/L) or hexarelin (1 nmol/L) addition to the perfusion

system after ischemia had a positive inotropic effect on

ischemic cardiomyocytes through activation of the GHSR

1a receptor, thereby protecting them from ischemia-re-

perfusion injury.[20,26] Another study suggested that ghrelin-

256 MAO YJ, et al. Cardiovascular action of hexarelin

Journal of Geriatric Cardiology | jgc@jgc301.com; http://www.jgc301.com

and hexarelin-mediated activation of GHSR 1a had a similar

protective effect on cardiomyocytes after ischemia-reper-

fusion injury by inhibiting cardiomyocyte apoptosis and

promoting cell survival.[25] The common features of the two

peptides were compared in Table 1.

5 Conclusions

Hexarelin has cardioprotective activity in common car-

diovascular conditions such as cardiac fibrosis, ischemic

heart disease, cardiac dysfunction, and atherosclerosis. The

important in vivo studies of hexarelin in cardiovascular con-

ditions are summarized in Table 2. These beneficial effects

seem to be mediated through the direct binding and activa-

tion of its cardiac receptors CD36 and GHSR 1a. Since

hexarelin is a chemically stable synthetic GHS with more

potent cardiac effects than its natural analog ghrelin, it can

be a potential alternative to ghrelin as a promising

Table 1. Comparison of hexarelin and ghrelin.

Hexarelin Ghrelin

Source Synthetic Natural

Chemical structure 6 Amino acids 28 Amino acids

Amino acid sequence His-D-2-methyl-Trp-Ala-Trp-

D-Phe-Lys-NH2

Gly-Ser-Ser(octanoyl)-Phe-Leu-Ser-Pro-Glu-His-Gln-Arg-Val-Gln-Gln-

Arg-Lys-Glu-Ser-Lys- Lys-Pro-Pro-Ala-Lys-Leu-Gln-Pro-Arg-OH

Half life 57–71 min[48] 11–17 min,[49] 27–31 min[50]

Receptor GHSR1a; CD36 GHSR1a

Receptor affinity for GHSR1a (EC50) 1.7 nmol/L[16] 1.0 nmol/L[16]

GHSR1a: growth hormone secretagogue receptor; EC50: half-maximal effective concentration.

Table 2. In vivo studies of the cardiovascular action of hexarelin.

First author, date Species Model Dose, duration, initiation of treatment Main outcomes

Mao, et al, 2013[47] Ghrelin-

null mice

Experimental myocardial infarction

by coronary artery ligation

300μg/kg per day for 14 days, from 30 min

after ligation (s.c.)

Improved heart failure

better than ghrelin

Xu, et al, 2012[30] Rats Spontaneous hypertension 100 μg/kg per day for 5 weeks, from an age o

16 weeks (s.c.) Reduced cardiac fibrosis

Pang, et al, 2010[32] Rats

High lipid diet and vitamin D3-

induced atherosclerosis

200 μg/kg per day for 30 days, in the last

month after high lipid diet (s.c.)

Alleviated the development

of atherosclerosis

Xu, et al, 2005 [23] Rats

Pressure-overload heart failure by

abdominal aortic banding

200 μg/kg per day for 3 weeks, from 9 weeks

after heart failure (s.c.)

Alleviated LV dysfunction, pathological

remodeling, and cardiac cachexia

Torsello, et al,

2003 [15] Rats Hypophysectomized 80 μg/kg per day for 7 days, before in vitro

ischemia and reperfusion procedure (s.c.)

Far more effective than ghrelin in the

control of heart function

Broglio, et al,

2002 [18] Humans Coronary artery disease during

by-pass surgery 2 μg/kg acute administration (i.v.) Increased LVEF, cardiac index

and cardiac output

Imazio, et al,

2002 [34] Humans Normal, dilated, and ischemic

cardiomyopathy 2 μg/kg acute administration (i.v.)

Increased LVEF in ischemic cardio-

myopathy patients and in normals but

not in dilated cardiomyopathy patients

Broglio, et al,

2001 [35] Humans

Normal adults, growth hormone-

deficient patients, and severe dilated

cardiomyopathy patients

2 μg/kg acute administration (i.v.) Produced a positive inotropic effect

De Gennaro-Colonna,

et al, 2000 [27]

Zucker

rats Obese 160 μg/kg per day for 30 days, at 30

weeks of age (s.c.)

Induced cardioprotective effect after is-

chemia and decreased plasma cholesterol

Tivesten, et al,

2000 [29] Rats Experimental myocardial infarction

by coronary artery ligation

10 μg/kg per day or 100μg/kg per day for 2

weeks, from 4 weeks after ligation (s.c.)

Improved cardiac function and

decreased peripheral resistance

Bisi, et al, 1999[36] Humans Growth hormone deficiency 2μg/kg acute administration (i.v.) Increased LVEF

Locatelli, et al,

1999[37] Rats Hypophysectomized 80 μg/kg per day for 7 days, be-

fore ischemia-reperfusion damage (s.c.)

Prevented cardiac damage after

ischemia-reperfusion

Bisi, et al, 1999[17] Humans Volunteers 2μg/kg acute administration (i.v.) Increased LVEF without significant chan-

ges in mean blood pressure and heart rate

De Gennaro Colonna,

et al, 1997[51] Rats Anti-GHRH serum-treated 160 μg/kg per day for 15 days, after administra-

tion of an anti-GHRH serum for 20 days (s.c.)Counteracted the ischemic damage

LV: left ventricle; LVEF: left ventricular ejection fraction; GHRH: growth hormone releasing hormone.

MAO YJ, et al. The cardiovascular action of hexarelin 257

http://www.jgc301.com; jgc@mail.sciencep.com | Journal of Geriatric Cardiology

therapeutic agent for the treatment of cardiovascular dis-

eases. However, as current evidence is mainly from experi-

mental animal models or in vitro cell lines, clinical trials

aimed to extend the application of hexarelin in human sub-

jects and observe its efficacy and potential side effects are

warranted.

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Using Synchrotron Radiation Imaging Techniques to Elucidate the Actions of Hexarelin in the Heart of Small Animal Models

Article

Full-text available

Jan 2022

The majority of the conventional techniques that are utilized for investigating the pathogenesis of cardiovascular disease in preclinical animal models do not permit microlevel assessment of in situ cardiomyocyte and microvascular functions. Therefore, it has been difficult to establish whether cardiac dysfunction in complex multiorgan disease states, such as heart failure with preserved ejection fraction and pulmonary hypertension, have their origins in microvascular dysfunction or rather in the cardiomyocyte. Herein, we describe our approach of utilizing synchrotron radiation microangiography to, first, ascertain whether the growth hormone secretagogue (GHS) hexarelin is a vasodilator in the coronary circulation of normal and anesthetized Sprague-Dawley rats, and next investigate if hexarelin is able to prevent the pathogenesis of right ventricle (RV) dysfunction in pulmonary hypertension in the sugen chronic hypoxia model rat. We show that acute hexarelin administration evokes coronary microvascular dilation through GHS-receptor 1a and nitric oxide, and through endothelium-derived hyperpolarization. Previous work indicated that chronic exogenous administration of ghrelin largely prevented the pathogenesis of pulmonary hypertension in chronic hypoxia and in monocrotaline models. Unexpectedly, chronic hexarelin administration prior to sugen chronic hypoxia did not prevent RV hypertrophy or RV cardiomyocyte relaxation impairment. Small-angle X-ray scattering revealed that super relaxed myosin filaments contributed to diastolic dysfunction, and that length-dependent activation might contribute to sustained contractility of the RV. Thus, synchrotron-based imaging approaches can reveal novel insights into cardiac and coronary functions in vivo.

Hexarelin targets neuroinflammatory pathways to preserve cardiac morphology and function in a mouse model of myocardial ischemia-reperfusion

Article

Full-text available

Jul 2020
BIOMED PHARMACOTHER

Acute myocardial ischemia and reperfusion injury (IRI) underly the detrimental effects of coronary heart disease on the myocardium. Despite the ongoing advances in reperfusion therapies, there remains a lack of effective therapeutic strategies for preventing IRI. Growth hormone secretagogues (GHS) have been demonstrated to improve cardiac function, attenuate inflammation and modulate the autonomic nervous system (ANS) in models of cardiovascular disease. Recently, we demonstrated a reduction in infarct size after administration of hexarelin (HEX), in a murine model of myocardial infarction. In the present study we employed a reperfused ischemic (IR) model, to determine whether HEX would continue to have a cardioprotective influence in a model of higher clinical relevance. Myocardial ischemia was induced by transient ligation of the left descending coronary artery (tLAD) in C57BL/6 J mice followed by HEX (0.3 mg/kg/day; n = 20) or vehicle (VEH) (n = 18) administration for 21 days, first administered immediately prior-to reperfusion. IR-injured and sham mice were subjected to high-field magnetic resonance imaging to assess left ventricular (LV) function, with HEX-treated mice demonstrating a significant improvement in LV function compared with VEH-treated mice. A significant decrease in interstitial collagen, TGF-β1 expression and myofibroblast differentiation was also seen in the HEX-treated mice after 21 days. HEX treatment shifted the ANS balance towards a parasympathetic predominance; combined with a significant decrease in cardiac troponin-I and TNF-α levels, these findings were suggestive of an anti-inflammatory action on the myocardium mediated via HEX. In this model of IR, HEX appeared to rebalance the deregulated ANS and activate vagal anti-inflammatory pathways to prevent adverse remodelling and LV dysfunction. There are limited interventions focusing on IRI that have been successful in improving clinical outcome in acute myocardial infarction (AMI) patients, this study provides compelling evidence towards the translational potential of HEX where all others have largely failed.

Hexarelin modulates lung mechanics, inflammation, and fibrosis in acute lung injury

Article

Full-text available

Nov 2021

Introduction: Acute respiratory distress syndrome (ARDS) is an acute form of diffuse lung injury characterized by (i) an intense inflammatory response, (ii) increased pulmonary vascular permeability, and (iii) the loss of respiratory pulmonary tissue. In this article we explore the therapeutic potential of hexarelin, a synthetic hexapeptide growth hormone secretagogue (GHS), in an experimental model of ARDS. Hexarelin has anti-inflammatory properties and demonstrates cardiovascular-protective activities including the inhibition of cardiomyocyte apoptosis and cardiac fibrosis, both of which may involve the angiotensin-converting enzyme (ACE) system. Methods: In our experimental model, ARDS was induced by the instillation of 100 mM HCl into the right bronchus; these mice were treated with hexarelin (320 μg/kg, ip) before (Pre) or after (Post) HCl challenge, or with vehicle. Respiratory system compliance, blood gas analysis, and differential cell counts in a selective bronchoalveolar lavage (BAL) were determined 6 or 24 hours after HCl instillation. In an extended study, mice were observed for a subsequent 14 days in order to assess lung fibrosis. Results: Hexarelin induced a significant improvement in lung compliance and a reduction of the number of total immune cells in BAL 24 hours after HCl instillation, accompanied with a lower recruitment of neutrophils compared with the vehicle group. At day 14, hexarelin-treated mice presented with less pulmonary collagen deposition compared with vehicle-treated controls. Conclusions: Our data suggest that hexarelin can inhibit the early phase of the inflammatory response in a murine model of HCl-induced ARDS, thereby blunting lung remodeling processes and fibrotic development.

Heal the heart through gut (hormone) ghrelin: a potential player to combat heart failure

Article

Full-text available

Mar 2021
HEART FAIL REV

Ghrelin, a small peptide hormone (28 aa), secreted mainly by X/A-like cells of gastric mucosa, is also locally produced in cardiomyocytes. Being an orexigenic factor (appetite stimulant), it promotes release of growth hormone (GH) and exerts diverse physiological functions, viz. regulation of energy balance, glucose, and/or fat metabolism for body weight maintenance. Interestingly, administration of exogenous ghrelin significantly improves cardiac functions in CVD patients as well as experimental animal models of heart failure. Ghrelin ameliorates pathophysiological condition of the heart in myocardial infarction, cardiac hypertrophy, fibrosis, cachexia, and ischemia reperfusion injury. This peptide also exerts significant impact at the level of vasculature leading to lowering high blood pressure and reversal of endothelial dysfunction and atherosclerosis. However, the molecular mechanism of actions elucidating the healing effects of ghrelin on the cardiovascular system is still a matter of conjecture. Some experimental data indicate its beneficial effects via complex cellular cross talks between autonomic nervous system and cardiovascular cells, some other suggest more direct receptor–mediated molecular actions via autophagy or ionotropic regulation and interfering with apoptotic and inflammatory pathways of cardiomyocytes and vascular endothelial cells. Here, in this review, we summarise available recent data to encourage more research to find the missing links of unknown ghrelin receptor–mediated pathways as we see ghrelin as a future novel therapy in cardiovascular protection.

Pharmacological targeting of the hyper-inflammatory response to SARS-CoV-2-infected K18-hACE2 mice using a cluster of differentiation 36 receptor modulator

Article

Full-text available

Feb 2024

The scientific and medical community faced an unprecedented global health hazard that led to nearly 7 million deaths attributable to the rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In spite of the development of efficient vaccines against SARS-CoV-2, many people remain at risk of developing severe symptoms as the virus continues to spread without beneficial patient therapy. The hyper-inflammatory response to SARS-CoV-2 infection progressing to acute respiratory distress syndrome remains an unmet medical need for improving patient care. The viral infection stimulates alveolar macrophages to adopt an inflammatory phenotype regulated, at least in part, by the cluster of differentiation 36 receptor (CD36) to produce unrestrained inflammatory cytokine secretions. We suggest herein that the modulation of the macrophage response using the synthetic CD36 ligand hexarelin offers potential as therapy for halting respiratory failure in SARS-CoV-2-infected patients.

Hexarelin alleviates apoptosis on ischemic acute kidney injury via MDM2/p53 pathway

Article

Full-text available

Sep 2023

Introduction Hexarelin exhibits significant protection against organ injury in models of ischemia/reperfusion (I/R)-induced injury (IRI). Nevertheless, the impact of Hexarelin on acute kidney injury (AKI) and its underlying mechanism remains unclear. In this study, we investigated the therapeutic potential of Hexarelin in I/R-induced AKI and elucidated its molecular mechanisms. Methods We assessed the protective effects of Hexarelin through both in vivo and in vitro experiments. In the I/R-induced AKI model, rats were pretreated with Hexarelin at 100 μg/kg/d for 7 days before being sacrificed 24 h post-IRI. Subsequently, kidney function, histology, and apoptosis were assessed. In vitro, hypoxia/reoxygenation (H/R)-induced HK-2 cell model was used to investigate the impact of Hexarelin on apoptosis in HK-2 cells. Then, we employed molecular docking using a pharmmapper server and autodock software to identify potential target proteins of Hexarelin. Results In this study, rats subjected to I/R developed severe kidney injury characterized by tubular necrosis, tubular dilatation, increased serum creatinine levels, and cell apoptosis. However, pretreatment with Hexarelin exhibited a protective effect by mitigating post-ischemic kidney pathological changes, improving renal function, and inhibiting apoptosis. This was achieved through the downregulation of conventional apoptosis-related genes, such as Caspase-3, Bax and Bad, and the upregulation of the anti-apoptotic protein Bcl-2. Consistent with the in vivo results, Hexarelin also reduced cell apoptosis in post-H/R HK-2 cells. Furthermore, our analysis using GSEA confirmed the essential role of the apoptosis pathway in I/R-induced AKI. Molecular docking revealed a strong binding affinity between Hexarelin and MDM2, suggesting the potential mechanism of Hexarelin’s anti-apoptosis effect at least partially through its interaction with MDM2, a well-known negative regulator of apoptosis-related protein that of p53. To validate these findings, we evaluated the relative expression of MDM2 and p53 in I/R-induced AKI with or without Hexarelin pre-administration and observed a significant suppression of MDM2 and p53 by Hexarelin in both in vivo and in vitro experiments. Conclusion Collectively, Hexarelin was identified as a promising medication in protecting apoptosis against I/R-induced AKI.

CD36 as a target for metabolic modulation therapy in cardiac disease

Article

Full-text available

Jun 2021

Introduction: Disturbances in myocardial lipid metabolism are increasingly being recognized as drivers of the development and progression of heart disease. Therefore, there is a need for treatments that can directly target lipid metabolic defects in heart failure. The membrane-associated glycoprotein CD36 plays a pivotal role in governing myocardial lipid metabolism by mediating lipid signaling and facilitating the cellular uptake of long-chain fatty acids. Emerging evidence suggests that CD36 is a prominent target in the treatment of heart failure. Areas covered: This article provides an overview of the key role of CD36 for proper contractile functioning of the healthy heart, its implication in the development of cardiac disease (ischemia/reperfusion, cardiac hypertrophy, diabetic cardiomyopathy) and its application as target to normalize cardiac metabolism as part of so-called metabolic modulation therapy. Expert opinion: CD36 appears a promising and effective therapeutic target in the treatment of heart failure. Natural compounds and chemical agents known to alter the amount or subcellular distribution of CD36, or inhibit its functioning, should be evaluated for their potency to correct cardiac metabolism and cure heart disease.

Hexarelin Modulation of MAPK and PI3K/Akt Pathways in Neuro-2A Cells Inhibits Hydrogen Peroxide—Induced Apoptotic Toxicity

Article

Full-text available

May 2021

Hexarelin, a synthetic hexapeptide, exerts cyto-protective effects at the mitochondrial level in cardiac and skeletal muscles, both in vitro and in vivo, may also have important neuroprotective bioactivities. This study examined the inhibitory effects of hexarelin on hydrogen peroxide (H2O2)-induced apoptosis in Neuro-2A cells. Neuro-2A cells were treated for 24 h with various concentrations of H2O2 or with the combination of H2O2 and hexarelin following which cell viability and nitrite (NO2−) release were measured. Cell morphology was also documented throughout and changes arising were quantified using Image J skeleton and fractal analysis procedures. Apoptotic responses were evaluated by Real-Time PCR (caspase-3, caspase-7, Bax, and Bcl-2 mRNA levels) and Western Blot (cleaved caspase-3, cleaved caspase-7, MAPK, and Akt). Our results indicate that hexarelin effectively antagonized H2O2-induced damage to Neuro-2A cells thereby (i) improving cell viability, (ii) reducing NO2− release and (iii) restoring normal morphologies. Hexarelin treatment also reduced mRNA levels of caspase-3 and its activation, and modulated mRNA levels of the BCL-2 family. Moreover, hexarelin inhibited MAPKs phosphorylation and increased p-Akt protein expression. In conclusion, our results demonstrate neuroprotective and anti-apoptotic effects of hexarelin, suggesting that new analogues could be developed for their neuroprotective effects.

Evaluation of Hexarelin Effects on Epileptic Seizures, Hippocampal Neuronal Damage and Memory Impairment after Pentylenetetrazole-Induced Acute Model in Rat

Article

Full-text available

Oct 2019

Recent studies have demonstrated that ghrelin receptors have antiepileptic effects. The aim of this study was to investigate the effect of ghrelin receptor agonist hexarelin on pentylenetetrazole (PTZ)-induced seizures and post-seizure hippocampal damage. In our study, we used 42 male 230-250 g Wistar Albino rats. Animals were divided into seven groups as control, saline (PTZ; 1 ml/kg serum physiologic), positive control (5 mg/kg diazepam), 50 µg/kg, 100 µg/kg, 200 µg/kg and 400 µg/kg hexarelin. 30 min after drugs administration at the indicated doses, PTZ was administered 45 mg/kg to induce an epileptic seizure. The animals were observed for 30 min. Seizure stages (according to the Racine Scale) and first myoclonic jerk times (FMJ). 24 hours after PTZ injection, passive avoidance test was performed, and then brain tissues were removed. After the routine histological process, serial sections from brain tissues were stained with toluidine blue to determine neuronal damage. The hippocampal Cornu Ammonis CA1, CA3 and dentate gyrus regions were evaluated histopathologically. Statistical evaluation of the data was performed by oneway ANOVA, and multiple comparisons were determined by the Tukey test. Statistical significance was defined at p<0.05. Obtained data suggest that 200 µg/kg and 400 µg/kg hexarelin decreased seizure stages and increased FMJ compared to PTZ group (p<0,05). In addition, 200 µg/kg and 400 µg/kg hexarelin improved retention time in passive avoidance compared to PTZ group (p<0,05). Furthermore, 200 µg/kg and 400 µg/kg hexarelin reduced neuronal damage in hippocampal CA1, CA3, and DG regions compared to PTZ group (p<0,05). However, all these effects of hexarelin were not observed at 50 µg/kg and 100 µg/kg (p>0,05). In conclusion, we suggest that hexarelin has protective effects on epileptic seizures and neuronal damage after PTZ dose-dependently

Hexarelin exerts neuroprotective and antioxidant effects against hydrogen peroxide-induced toxicity through the modulation of MAPK and PI3K/Akt patways in Neuro-2A cells

Preprint

Full-text available

Nov 2020

Hexarelin, a synthetic hexapeptide, protects cardiac and skeletal muscles by inhibiting apoptosis, both in vitro and in vivo . Moreover, evidence suggests that hexarelin could have important neuroprotective bioactivity. Oxidative stress and the generation of free radicals has been implicated in the etiologies of several neurodegenerative diseases, including amyotrophic lateral sclerosis, Parkinson’s disease, Alzheimer’s disease, Huntington’s disease and multiple sclerosis. In addition to direct oxidative stress, exogenous hydrogen peroxide (H 2 O 2 ) can penetrate biological membranes and enhance the formation of other reactive oxygen species. The aim of this study was to examine the inhibitory influence of hexarelin on H 2 O 2 -induced apoptosis in Neuro-2A cells, a mouse neuroblastoma cell line. Our results indicate that H 2 O 2 reduced the viability of Neuro-2A cells in a dose-related fashion. Furthermore, H 2 O 2 induced significant changes in the morphology of Neuro-2A cells, reflected in the formation of apoptotic cell bodies, and an increase of nitric oxide (NO) production. Hexarelin effectively antagonized H 2 O 2 oxidative damage to Neuro-2A cells as indicated by improved cell viability, normal morphology and reduced nitrite (NO 2 ⁻ ) release. Hexarelin treatment of Neuro-2A cells also reduced mRNA levels of caspases−3 and −7 and those of the pro-apoptotic molecule Bax; by contrast, hexarelin treatment increased anti-apoptotic Bcl-2 mRNA levels. Hexarelin also reduced MAPKs phosphorylation induced by H 2 O 2 and concurrently increased p-Akt protein expression. In conclusion, our results identify several neuroprotective and anti-apoptotic effects of hexarelin. These properties suggest that further investigation of hexarelin as a neuroprotective agent in an investigational and therapeutic context are merited.

Hexarelin Treatment in Male Ghrelin Knockout Mice after Myocardial Infarction

Article

Full-text available

Jul 2013
ENDOCRINOLOGY

Both ghrelin and the synthetic analogue hexarelin are reported to possess cardioprotective actions that are mainly exerted through different receptors. However, their effects on acute myocardial infarction have not been compared in vivo. This study aimed to clarify whether hexarelin treatment can compensate for ghrelin deficiency in ghrelin knockout mice, and to compare the effects of hexarelin (400 nmol/kg per day, s.c.) and equimolar ghrelin treatment after myocardial infarction. Myocardial infarction was produced by left coronary artery ligation in male ghrelin-knockout mice, which then received ghrelin, hexarelin, or vehicle treatment for 2 weeks. The mortality within 2 weeks was significantly lower in the hexarelin group (6.7%) and ghrelin group (14.3%) than in the vehicle group (50%) (P < 0.05). A comparison of cardiac function 2 weeks post-infarction showed that in the ghrelin and hexarelin treatment groups, cardiac output were greater, while systolic function, represented by ejection fraction, and diastolic function, represented by dP/dt min, were significantly superior compared to the vehicle group (P < 0.05). Hexarelin treatment was more effective than ghrelin treatment, as indicated by the ejection fraction, dP/dt max, and dP/dt min. Telemetry recording and heart rate variability analysis demonstrated that sympathetic nervous activity was clearly suppressed in the hexarelin and ghrelin groups relative to the vehicle group. Our data demonstrated that hexarelin treatment can result in better heart function than ghrelin treatment 2 weeks after myocardial infarction in ghrelin knockout mice, although both hormones have similar effects on heart rate variability and mortality.

Growth Hormone Secretagogues Preserve the Electrophysiological Properties of Mouse Cardiomyocytes Isolated from in Vitro Ischemia/Reperfusion Heart

Article

Full-text available

Sep 2012
ENDOCRINOLOGY

Ischemic heart diseases often induce cardiac arrhythmia with irregular cardiac action potential (AP). This study aims to demonstrate that GH secretagogues (GHS) ghrelin and its synthetic analog hexarelin can preserve the electrophysiological properties of cardiomyocytes experiencing ischemia/reperfusion (I/R). Isolated hearts from adult male mice underwent 20 min global ischemia followed by 30 min reperfusion using a Langendorff apparatus. Ghrelin (10 nm) or hexarelin (1 nm) was administered in the perfusion solution either 10 min before or after ischemia, termed pre- or posttreatments. Cardiomyocytes isolated from these hearts were used for whole-cell patch clamping to measure AP, voltage-gated L-type calcium current (I(CaL)), transient outward potassium current (I(to)), and sodium current (I(Na)). AP amplitude and duration were significantly decreased by I/R, but GHS treatments maintained their normality. GHS treatments prevented the decrease in I(CaL) and I(Na) after I/R, thereby maintaining AP amplitude. Although the significant increase in I(to) after I/R partially explained the shortened AP duration, the normalization of it by GHS treatments might contribute to the preservation of AP duration. Phosphorylated p38 and c-Jun NH(2)-terminal kinase and the downstream active caspase-9 in the cellular apoptosis pathway were significantly increased after I/R but not when GHS treatments were included, whereas phosphorylation of ERK1/2 associated with cell survival showed increase after I/R and a further increase after GHS treatments by binding to its receptor GHS receptor type 1a. These results suggest GHS can not only preserve the electrophysiological properties of cardiomyocytes after I/R but also inhibit cardiomyocyte apoptosis and promote cell survival by modification of MAPK pathways through activating GHS receptor type 1a.

Chronic administration of hexarelin attenuates cardiac fibrosis in the spontaneously hypertensive rat

Article

Full-text available

Jul 2012
AM J PHYSIOL-HEART C

Cardiac fibrosis is a hallmark of heart disease and plays a vital role in cardiac remodeling during heart diseases, including hypertensive heart disease. Hexarelin is one of a series of synthetic growth hormone secretagogues (GHSs) possessing a variety of cardiovascular effects via action on GHS receptors (GHS-Rs). However, the role of hexarelin in cardiac fibrosis in vivo has not yet been investigated. In the present study, spontaneously hypertensive rats (SHRs) were treated with hexarelin alone or in combination with a GHS-R antagonist for 5 wk from an age of 16 wk. Hexarelin treatment significantly reduced cardiac fibrosis in SHRs by decreasing interstitial and perivascular myocardial collagen deposition and myocardial hydroxyproline content and reducing mRNA and protein expression of collagen I and III in SHR hearts. Hexarelin treatment also increased matrix metalloproteinase (MMP)-2 and MMP-9 activities and decreased myocardial mRNA expression of tissue inhibitor of metalloproteinase (TIMP)-1 in SHRs. In addition, hexarelin treatment significantly attenuated left ventricular (LV) hypertrophy, LV diastolic dysfunction, and high blood pressure in SHRs. The effect of hexarelin on cardiac fibrosis, blood pressure, and cardiac function was mediated by its receptor, GHS-R, since a selective GHS-R antagonist abolished these effects and expression of GHS-Rs was upregulated by hexarelin treatment. In summary, our data demonstrate that hexarelin reduces cardiac fibrosis in SHRs, perhaps by decreasing collagen synthesis and accelerating collagen degradation via regulation of MMPs/TIMP. Hexarelin-reduced systolic blood pressure may also contribute to this reduced cardiac fibrosis in SHRs. The present findings provided novel insights and underscore the therapeutic potential of hexarelin as an antifibrotic agent for the treatment of cardiac fibrosis.

Growth Hormone Secretagogues Protect Mouse Cardiomyocytes from in vitro Ischemia/Reperfusion Injury through Regulation of Intracellular Calcium

Article

Full-text available

Apr 2012
PLOS ONE

Ischemic heart disease is a leading cause of mortality. To study this disease, ischemia/reperfusion (I/R) models are widely used to mimic the process of transient blockage and subsequent recovery of cardiac coronary blood supply. We aimed to determine whether the presence of the growth hormone secretagogues, ghrelin and hexarelin, would protect/improve the function of heart from I/R injury and to examine the underlying mechanisms. Isolated hearts from adult male mice underwent 20 min global ischemia and 30 min reperfusion using a Langendorff apparatus. Ghrelin (10 nM) or hexarelin (1 nM) was introduced into the perfusion system either 10 min before or after ischemia, termed pre- and post-treatments. In freshly isolated cardiomyocytes from these hearts, single cell shortening, intracellular calcium ([Ca(2+)](i)) transients and caffeine-releasable sarcoplasmic reticulum (SR) Ca(2+) were measured. In addition, RT-PCR and Western blots were used to examine the expression level of GHS receptor type 1a (GHS-R1a), and phosphorylated phospholamban (p-PLB), respectively. Ghrelin and hexarelin pre- or post-treatments prevented the significant reduction in the cell shortening, [Ca(2+)](i) transient amplitude and caffeine-releasable SR Ca(2+) content after I/R through recovery of p-PLB. GHS-R1a antagonists, [D-Lys3]-GHRP-6 (200 nM) and BIM28163 (100 nM), completely blocked the effects of GHS on both cell shortening and [Ca(2+)](i) transients. Through activation of GHS-R1a, ghrelin and hexarelin produced a positive inotropic effect on ischemic cardiomyocytes and protected them from I/R injury probably by protecting or recovering p-PLB (and therefore SR Ca(2+) content) to allow the maintenance or recovery of normal cardiac contractility. These observations provide supporting evidence for the potential therapeutic application of ghrelin and hexarelin in patients with cardiac I/R injury.

Growth Hormone-Independent Cardioprotective Effects of Hexarelin in the Rat1

Article

Sep 1999
ENDOCRINOLOGY

We previously reported that induction of selective GH deficiency in the rat exacerbates cardiac dysfunction induced by experimental ischemia and reperfusion performed on the explanted heart. In the same model, short-term treatment with hexarelin, a GH-releasing peptide, reverted this effect, as did GH. To ascertain whether hexarelin had non-GH-mediated protective effects on the heart, we compared hexarelin and GH treatment in hypophysectomized rats. Hexarelin (80 μg/kg sc), given for 7 days, prevented exacerbation of the ischemia-reperfusion damage induced by hypophysectomy. We also demonstrate that hexarelin prevents increases in left ventricular end diastolic pressure, coronary perfusion pressure, reactivity of the coronary vasculature to angiotensin II, and release of creatine kinase in the heart perfusate. Moreover, hexarelin prevents the fall in prostacyclin release and enhances recovery of contractility. Treatment with GH (400 μg/kg sc) produced similar results, whereas administration of EP 51389 (8...

A receptor in pituitary and hypothalamus that functions in growth hormone release

Article

Jan 1996

Excessive Sympathoactivation and Deteriorated Heart Function After Myocardial Infarction in Male Ghrelin Knockout Mice

Article

Mar 2013
ENDOCRINOLOGY

Background: We have previously demonstrated the protective role of endogenous ghrelin against malignant arrhythmias in the very acute phase of myocardial infarction (MI). However, the role of endogenous ghrelin in the chronic phase is unknown. Therefore, the aim of the current study was to focus on the effects of endogenous ghrelin on cardiac function and sympathetic activation after acute MI. Methods and results: In 46 ghrelin-knockout (KO) and 41 wild-type (WT) male mice, MI was produced by left coronary artery ligation. The mortality due to heart failure within 2 weeks was 0% in WT and 10.9% in KO (P < 0.05). At the end of this period, lung weight/tibial length, atrial natriuretic peptide and brain natriuretic peptide transcripts, end-systolic and end-diastolic volumes were all significantly greater in KO mice, whereas systolic function, represented by ejection fraction (16.4 ± 4.7% vs. 25.3 ± 5.1%), end-systolic elastance, and preload-recruitable stroke work, was significantly inferior to that in WT mice (P < 0.05). Telemetry recording and heart rate variability analysis showed that KO mice had stronger sympathetic activation after MI than did WT mice. Metoprolol treatment and ghrelin treatment in KO mice prevented excessive sympathetic activation, decreased plasma epinephrine and norepinephrine levels, and improved heart function and survival rate after MI. Conclusions: Our data demonstrate that endogenous ghrelin plays a crucial role in protecting heart function and reducing mortality after myocardial infarction, and that these effects seem to be partly the result of sympathetic inhibition.

Growth Hormone-Independent Cardiotropic Activities of Growth Hormone-Releasing Peptides in Normal Subjects, in Patients with Growth Hormone Deficiency, and in Patients with Idiopathic or Ischemic Dilated Cardiomyopathy

Article

Feb 2001

Growth hormone releasing peptides (GHRPs) are synthetic molecules endowed with potent neuroendocrine activities mediated by specific receptors in the pituitary and in the central nervous system. GHRPs receptors have been reported even in perpheral tissues, particularly in the myocardium, where they probably mediate growth hormone (GH)-independent activities. We studied in humans the cardiac effects of hexarelin administration in 7 normal adults, in 7 severe GH-deficient patients, and in 12 patients with severe dilated cardiomyopathy. Left ventricular ejection fraction (LVEF), mean blood pressure (MBP), heart rate (HR), and GH levels were evaluated at baseline and every 15 min up to 60 min after acute 2.0 μg/kg iv hexarelin administration. Basal LVEF in dilated cardiomyopathy was impaired and lower (p<0.001) than in GH deficiency, in turn lower (p<0.001) than in normal subjects. Hexarelin significantly (p<0.05) increased LVEF in normal and in GH-deficient subjects, but not in dilated cardiomyopathy, without significant variations in MBP and HR. Hexeralin significantly (p<0.05) increased GH levels in normal subjects and in dilated cardiomyopathy but not in GH deficiency. These findings suggest that, in humans, the acute administration of hexarelin exerts a GH-independent positive inotropic effect likely mediated by specific GHRPs myocardial receptors.

Ghrelin Prevents Incidence of Malignant Arrhythmia after Acute Myocardial Infarction through Vagal Afferent Nerves

Article

Apr 2012
ENDOCRINOLOGY

Ghrelin is a GH-releasing peptide mainly excreted from the stomach. Ghrelin administration has been shown to inhibit cardiac sympathetic nerve activity (CSNA), reduce malignant arrhythmia, and improve prognosis after acute myocardial infarction (MI). We therefore investigated the effects and potential mechanisms of the action of endogenous ghrelin on survival rate and CSNA after MI by using ghrelin-knockout (KO) mice. MI was induced by left coronary artery ligation in 46 KO mice and 41 wild-type mice. On the first day, malignant arrhythmia-induced mortality was observed within 30 min of the ligation and had an incidence of 2.4% in wild-type and 17.4% in KO mice (P < 0.05). We next evaluated CSNA by spectral analysis of heart rate variability. CSNA, represented by the low frequency/high frequency ratio, was higher in KO mice at baseline (2.18 ± 0.43 vs. 0.98 ± 0.09; P < 0.05), and especially after MI (25.5 ± 11.8 vs. 1.4 ± 0.3; P < 0.05), than in wild-type mice. Ghrelin (150 μg/kg, s.c.) 15 min before ligation suppressed the activation of CSNA and reduced mortality in KO mice. Further, this effect of ghrelin was inhibited by methylatropine bromide (1 mg/kg, i.p.) or by perineural treatment of both cervical vagal trunks with capsaicin (a specific afferent neurotoxin). Our data demonstrated that both exogenous and endogenous ghrelin suppressed CSNA, prevented the incidence of malignant arrhythmia, and improved the prognosis after acute MI. These effects are likely to be via the vagal afferent nerves.

Design and characterization of a fluorescent ghrelin analog for imaging the growth hormone secretagogue receptor 1a

Article

Sep 2011

Ghrelin is a 28-amino acid peptide hormone produced in the stomach. It binds to the growth hormone secretagogue receptor 1a (GHS-R1a), a class A G-protein-coupled receptor. In the present study, we describe the design, synthesis and characterization of a truncated, 18-amino acid analog of ghrelin conjugated to a fluorescent molecule, fluorocein isothiocyanate (FITC), through the addition of a lysine at its C terminus ([Dpr(octanoyl)(3), Lys(fluorescein)(19)]ghrelin(1-19)). Receptor binding affinity of this novel fluorescein-ghrelin(1-18) was similar to that of wild-type ghrelin and a synthetic GHS-R1a ligand, hexarelin. Live cell imaging in CHO/GHS-R1a cells demonstrated cell surface receptor labeling and internalization, and agonist activity of fluorescein-ghrelin(1-18) was confirmed by increased phosphorylation of ERK1/2. We also show that GHS-R1a protein is expressed primarily in the heart when compared to all other organs, suggesting high receptor density in the left ventricle. Finally, we demonstrate that fluorescein-ghrelin(1-18) binds specifically to heart tissue in situ, and its binding is displaced by both wt ghrelin and hexarelin. We have therefore developed a novel imaging probe, fluorescein-ghrelin(1-18), that can be used to image GHS-R1a in situ, for the purposes of investigating mechanisms of receptor trafficking or pharmacological agents that target GHS-R1a.

The cardiovascular action of hexarelin

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