Growth Hormone-releasing Hormone Agonist Research Articles

Growth hormone-releasing hormone and its analogues in health and disease.

Growth hormone-releasing hormone (GHRH) and its ability to stimulate the production and release of growth hormone from the pituitary were discovered more than four decades ago. Since then, this hormone has been studied extensively and research into its functions is still ongoing. GHRH has multifaceted roles beyond the originally identified functions that encompass a variety of direct extrapituitary effects. In this Review, we illustrate the different biological activities of GHRH, covering the effects of GHRH agonists and antagonists in physiological and pathological contexts, along with the underlying mechanisms. GHRH and GHRH analogues have been implicated in cell growth, wound healing, cell death, inflammation, immune functions, mood disorders, feeding behaviour, neuroprotection, diabetes mellitus and obesity, as well as cardiovascular, lung and neurodegenerative diseases and some cancers. The positive effects observed in preclinical models in vitro and in vivo strongly support the potential use of GHRH agonists and antagonists as clinical therapeutics.

GHRH and its analogues in central nervous system diseases.

Growth hormone-releasing hormone (GHRH) is primarily produced by the hypothalamus and stimulates the release of growth hormone (GH) in the anterior pituitary gland, which subsequently regulates the production of hepatic insulin-like growth factor-1 (IGF-1). GH and IGF-1 have potent effects on promoting cell proliferation, inhibiting cell apoptosis, as well as regulating cell metabolism. In central nerve system (CNS), GHRH/GH/IGF-1 promote brain development and growth, stimulate neuronal proliferation, and regulate neurotransmitter release, thereby participating in the regulation of various CNS physiological activities. In addition to hypothalamus-pituitary gland, GHRH and GHRH receptor (GHRH-R) are also expressed in other brain cells or tissues, such as endogenous neural stem cells (NSCs) and tumor cells. Alternations in GHRH/GH/IGF-1 axis are associated with various CNS diseases, for example, Alzheimer's disease, amyotrophic lateral sclerosis and emotional disorders manifest GHRH, GH or IGF-1 deficiency, and GH or IGF-1 supplementation exerts beneficial therapeutic effects on these diseases. CNS tumors, such as glioma, can express GHRH and GHRH-R, and activating this signaling pathway promotes tumor cell growth. The synthesized GHRH antagonists have shown to inhibit glioma cell growth and may hold promising as an adjuvant therapy for treating glioma. In addition, we have shown that GHRH agonist MR-409 can improve neurological sequelae after ischemic stroke by activating extrapituitary GHRH-R signaling and promoting endogenous NSCs-derived neuronal regeneration. This article reviews the involvement of GHRH/GH/IGF-1 in CNS diseases, and potential roles of GHRH agonists and antagonists in treating CNS diseases.

#2368 GHRH levels and AhR expression in CKD patients before and after kidney transplantation

Abstract Background and Aims Chronic kidney disease (CKD) is an irreversible decline in renal function where kidney transplantation (KT) is the optimal therapeutic intervention. We aim to investigate the role and activation of the uremic toxin receptor aryl hydrocarbon receptor (AhR) in the microvasculature, particularly its implication in the blood-brain barrier impairment. We will also explore the potential role of growth hormone-releasing hormone (GHRH) as a biomarker reflecting the resolution of uremia-induced inflammation, early vascular ageing (EVA) phenotype, and potential enhancement in central nervous system (CNS) function post-KT. Method Resistance arteries from KT patients and non-CKD controls were isolated and expression of AhR was analysed by immunohistochemistry. The study used plasma samples from 60 KT patients, and levels of GHRH were measured at baseline and two years after transplantation using ELISA. Results Following KT, our initial findings indicate a decrease in levels of DBP, Lp(a), creatinine, homocysteine, phosphate, and troponin T among KT patients. Conversely, there was an increase in albumin, HBA1c, calcium and NfL post-transplantation. The expression of AhR in the resistance arteries of KT patients (2.6%) was notably lower compared to non-CKD controls (9.7%). Plasma concentrations of GHRH were significantly higher (p < 0.0001) in CKD-5 patients two years post-KT (2.94 ng/mL, IQR 2.60-3.43) compared to baseline (2.32 mg/L, IQR 1.84-3.24). This elevated trend in GHRH levels post-KT was observed in both sexes, with males (p < 0.0001) and females (p 0.0084) showing higher levels—males (3.0 ng/mL, IQR 2.6-3.5) and females (2.8 ng/mL, IQR 2.4-3.5)—compared to baseline level of males (2.4 ng/mL, IQR 1.8-3.2) and females (2.2 ng/mL, 1.9-3.3). No significant difference in GHRH levels was observed when assessing extreme EVA phenotypes based on the presence or absence of calcification or fibrosis. Conclusion Contrary to our initial expectation, the preliminary results indicate a downregulation in AhR expression within resistance vessels of CKD patients, implying modifications in AhR signaling within the uremic environment. The observed alteration in GHRH levels presents a promising avenue for further investigation focusing on its possible application as a biomarker for assessing CNS status in CKD patients undergoing KT. Prospective clinical application could involve the administration of GHRH agonists as a protective measure against cognitive impairment, considering its deficiency in CKD. Such supplementation holds promise to prevent further cognitive morbidity. The modulation in the levels of this hormone has the potential to significantly influence the treatment trajectory of CKD patients and enhance clinical outcomes.

Combined ROS Sensitive PEG-PPS-PEG with Peptide Agonist for Effective Target Therapy in Mouse Model.

Growth hormone-releasing hormone (GHRH) agonist, a 29-amino acid peptide, shows significant potential in treating myocardial infarction (MI) by aiding the repair of injured heart tissue. The challenge lies in the effective on-site delivery of GHRH agonist. This study explores the use of a targetable delivery system employing ROS-responsive PEG-PPS-PEG polymers to encapsulate and deliver GHRH agonist MR409 for enhanced therapeutic efficacy. We synthesized a self-assembling poly (ethylene glycol)-poly (propylene sulfide)-poly (ethylene glycol) polymer (PEG-PPS-PEG) amphiphilic polymer responsive to reactive oxygen species (ROS). The hydrophilic peptide GHRH agonist MR409 was encapsulated within these polymers to form nano PEG-PPS-PEG@MR409 vesicles (NPs). Cardiomyocyte apoptosis was induced under hypoxia and serum-free culture condition for 24 hours, and their production of ROS was detected by fluorescence dye staining. The cellular uptake of PEG-PPS-PEG@MR409 NPs was observed using fluorescence-labeled MR409. Targeting ability and therapeutic efficacy were evaluated using a mouse MI model. PEG-PPS-PEG@MR409 NPs were efficiently internalized by cardiomyocytes, reducing ROS levels and apoptosis. These NPs exhibited superior targeting to the infarcted heart compared to naked MR409 peptide. With a reduced injection frequency (once every three days), PEG-PPS-PEG@MR409 NPs significantly promoted cardiac function recovery post-MI, matching the efficacy of daily MR409 injections. ROS-responsive PEG-PPS-PEG polymers provide a novel and effective platform for the targeted delivery of GHRH agonist peptides, improving cardiac function and offering a new approach for peptide therapy in MI treatment.

Abstract 18614: Growth Hormone Releasing Hormone Agonists Reverse the Cardiometabolic Heart Failure With Preserved Ejection Fraction Phenotype via the Hypoxia-Inducible Factor 1 Alpha

Introduction: Heart failure (HF) with preserved ejection fraction (HFpEF) treatment is limited due in large part to lack of understanding of the underlying mechanisms involved. Recently, we showed that growth hormone-releasing hormone-agonist (GHRH-agonist) has cardioprotective effects in a cardiometabolic HFpEF model; however, the mechanism of these therapeutic effects is still unclear. Here, we hypothesize that the anti-HFpEF properties of GHRH-receptor activation are mediated by hypoxia-induced factor (HIF)-1α pathway. Methods: Wild-type (WT) and HIF-1α cardiomyocyte knockout (HIF-1α CM KO) mice received a high-fat diet (HFD) plus the nitric oxide synthase inhibitor (L-NAME) for 9 weeks. After 5 weeks of HFD+L-NAME regimen, animals receive daily injections of GHRH-agonist, MR-356, or placebo during a 4-week period. Control animals received no HFD+L-NAME or MR-356 treatment. Echocardiography, blood pressure, glucose tolerance test, and hemodynamic measurements were evaluated. Results: The HFD+L-NAME diet produced a HFpEF phenotype, which was reversed in mice with intact HIF-1α treated with MR-356 (Figure 1 A-E). In contrast, following cardiac-specific deletion of HIF-1α CM , MR-356 no longer reversed (A) the elevated isovolumetric relaxation time (IVRT), (B) increased E/E’ ratio and (C) reduced global longitudinal strain (GLS). EF was preserved (D) while the slope of the end-diastolic pressure-volume relationship (EDPVR, E) was increased in the placebo group and restored by MR-356 in WT mice but not HIF-1α CM KO mice. Figure 1F shows representative pressure-volume loops from WT placebo, HIF-1α CM treated with placebo or MR-356. Conclusions: Our findings show that cardiac-specific HIF-1α deletion blocks cardioprotective effects of MR-356 suggesting that HIF-1α is necessary for its anti-HFpEF effects.

Abstract P2085: Growth Hormone Releasing Hormone Agonist Counteracts The Cardiometabolic Heart Failure With Preserved Ejection Fraction Phenotype In Vivo Via The Hypoxia Inducible Factor 1 Alpha

Heart failure (HF) with preserved ejection fraction (HFpEF) treatment is limited due in large part to a lack of understanding of the underlying mechanisms. Recently, we showed that growth hormone-releasing hormone-agonist (GHRH-agonist) has cardioprotective effects in a murine model of cardiometabolic HFpEF; however, the mechanism of these therapeutic effects is still unclear. Here, we hypothesize that the therapeutic effects of GHRH-agonist in HFpEF are mediated by GHRH-receptor activation of the hypoxia-induced factor (HIF)-1α pathway. Methods: Wild-type (WT) and HIF-1α cardiomyocyte knockout (HIF-1α CM KO) mice were fed a high-fat diet (HFD) plus the nitric oxide synthase inhibitor (L-NAME) for 9 weeks. After 5 weeks of HFD+L-NAME regimen, animals received daily injections of placebo or the GHRH-agonist, MR-356, for the remaining 4-week period. Control animals received no HFD+L-NAME or MR-356 treatment. Echocardiography, blood pressure, glucose tolerance test, and hemodynamic measurements were evaluated. Results: The HFD+L-NAME diet produced a HFpEF phenotype, which was reversed in mice with intact HIF-1α treated with MR-356. In contrast, in mice with a cardiac-specific deletion of HIF-1α CM , MR-356 treatment failed to reverse the elevated relative wall thickness in diastole (RWTd), increased E/E’ ratio and reduced global longitudinal strain (GLS). The slope of end-diastolic pressure-volume relationship (EDPVR) was increased in the placebo group and restored by MR-356 in WT mice but not HIF-1α CM KO mice, while EF was preserved. Conclusion: Our findings suggest that HIF-1α is necessary for the cardioprotective and anti-HFpEF effects MR-356.

Abstract 449: Growth Hormone-releasing Hormone Agonist Attenuates Vascular Calcification and Vascular Injury in Diabetic Db/db Mice

Vascular calcification (VC) is an independent risk factor for cardiovascular diseases. VC increases mortality of all-causes. VC is one of most common cardiovascular complications in type II diabetes. So far, no therapy has been proven to be effective in treatment of clinical VC. The present study investigated the therapeutic effects of MR409, an agonistic analog of growth hormone-releasing hormone (GHRH-A), on VC in diabetic db/db mice. Diabetic mice were injected with MR409 subcutaneously every day for 8 weeks. Long-term treatment with MR409 improved serum lipid profile and endothelium-dependent relaxation to acetylcholine, and reduced vascular structural injury in diabetic mice without affecting serum growth hormone level. Echocardiography showed that calcium plaques present in heart valve of diabetic mice disappeared in diabetic mice after treatment with MR409. MR409 inhibited vascular calcium deposition associated with a marked reduction in the expressions of osteogenic-regulated alkaline phosphatase (ALP) and transcription osteogenic marker gene Runx2 in diabetic mice. MR409 also inhibited vascular reactive oxygen species (ROS) generation and upregulated the expressions of anti-calcifying protein Klotho in diabetic mice. Our results demonstrate that GHRH-A MR409 can effectively attenuate VC and heart valve calcification, and protect against endothelial dysfunction and vascular injury in diabetic mice without significantly affecting pituitary-growth hormone axis. The mechanisms may involve upregulation of anti-calcifying protein Klotho and reduction in vascular ROS and the expression of redox sensitive osteogenic genes Runx2 and ALP. GHRH-A may represent a new pharmacological strategy for treatment of VC and diabetics associated cardiovascular complications.

Efficacy of a growth hormone-releasing hormone agonist in a murine model of cardiometabolic heart failure with preserved ejection fraction.

Heart failure (HF) with preserved ejection fraction (HFpEF) represents a major unmet medical need owing to its diverse pathophysiology and lack of effective therapies. Potent synthetic, agonists (MR-356 and MR-409) of growth hormone-releasing hormone (GHRH) improve the phenotype of models of HF with reduced ejection fraction (HFrEF) and in cardiorenal models of HFpEF. Endogenous GHRH exhibits a broad range of regulatory influences in the cardiovascular (CV) system and aging and plays a role in several cardiometabolic conditions including obesity and diabetes. Whether agonists of GHRH can improve the phenotype of cardiometabolic HFpEF remains untested and unknown. Here we tested the hypothesis that MR-356 can mitigate/reverse the cardiometabolic HFpEF phenotype. C57BL6N mice received a high-fat diet (HFD) plus the nitric oxide synthase inhibitor (l-NAME) for 9 wk. After 5 wk of HFD + l-NAME regimen, animals were randomized to receive daily injections of MR-356 or placebo during a 4-wk period. Control animals received no HFD + l-NAME or agonist treatment. Our results showed the unique potential of MR-356 to treat several HFpEF-like features including cardiac hypertrophy, fibrosis, capillary rarefaction, and pulmonary congestion. MR-356 improved cardiac performance by improving diastolic function, global longitudinal strain (GLS), and exercise capacity. Importantly, the increased expression of cardiac pro-brain natriuretic peptide (pro-BNP), inducible nitric oxide synthase (iNOS), and vascular endothelial growth factor-A (VEGF-A) was restored to normal levels suggesting that MR-356 reduced myocardial stress associated with metabolic inflammation in HFpEF. Thus, agonists of GHRH may be an effective therapeutic strategy for the treatment of cardiometabolic HFpEF phenotype.NEW & NOTEWORTHY This randomized study used rigorous hemodynamic tools to test the efficacy of a synthetic GHRH agonist to improve cardiac performance in a cardiometabolic HFpEF. Daily injection of the GHRH agonist, MR-356, reduced the HFpEF-like effects as evidenced by improved diastolic dysfunction, reduced cardiac hypertrophy, fibrosis, and pulmonary congestion. Notably, end-diastolic pressure and end-diastolic pressure-volume relationship were reset to control levels. Moreover, treatment with MR-356 increased exercise capacity and reduced myocardial stress associated with metabolic inflammation in HFpEF.

Growth hormone-releasing hormone agonist attenuates vascular calcification in diabetic db/db mice.

Vascular calcification (VC) is an independent risk factor for cardiovascular diseases. VC increases mortality of all-causes. VC is one of most common cardiovascular complications in type II diabetes. So far, no therapy has been proven to be effective in treatment of clinical VC. The present study investigated the therapeutic effects of MR409, an agonistic analog of growth hormone-releasing hormone (GHRH-A), on VC in diabetic db/db mice. Diabetic mice were injected with MR409 subcutaneously every day for 8 weeks. Long-term treatment with MR409 improved serum lipid profile and endothelium-dependent relaxation to acetylcholine, and reduced vascular structural injury in diabetic mice without affecting serum growth hormone level. Echocardiography showed that calcium plaques present in heart valve of diabetic mice disappeared in diabetic mice after treatment with MR409. MR409 inhibited vascular calcium deposition associated with a marked reduction in the expressions of osteogenic-regulated alkaline phosphatase (ALP) and transcription osteogenic marker gene Runx2 in diabetic mice. MR409 also inhibited vascular reactive oxygen species (ROS) generation and upregulated the expressions of anti-calcifying protein Klotho in diabetic mice. Our results demonstrate that GHRH-A MR409 can effectively attenuate VC and heart valve calcification, and protect against endothelial dysfunction and vascular injury in diabetic mice without significantly affecting pituitary-growth hormone axis. The mechanisms may involve upregulation of anti-calcifying protein Klotho and reduction in vascular ROS and the expression of redox sensitive osteogenic genes Runx2 and ALP. GHRH-A may represent a new pharmacological strategy for treatment of VC and diabetics associated cardiovascular complications.

Agonist of growth hormone-releasing hormone improves the disease features of spinal muscular atrophy mice

Spinal muscular atrophy (SMA) is a severe autosomal recessive neuromuscular disease affecting children and young adults, caused by mutations of the survival motor neuron 1 gene (SMN1). SMA is characterized by the degeneration of spinal alpha motor neurons (αMNs), associated with muscle paralysis and atrophy, as well as other peripheral alterations. Both growth hormone-releasing hormone (GHRH) and its potent agonistic analog, MR-409, exert protective effects on muscle atrophy, cardiomyopathies, ischemic stroke, and inflammation. In this study, we aimed to assess the protective role of MR-409 in SMNΔ7 mice, a widely used model of SMA. Daily subcutaneous treatment with MR-409 (1 or 2 mg/kg), from postnatal day 2 (P2) to euthanization (P12), increased body weight and improved motor behavior in SMA mice, particularly at the highest dose tested. In addition, MR-409 reduced atrophy and ameliorated trophism in quadriceps and gastrocnemius muscles, as determined by an increase in fiber size, as well as upregulation of myogenic genes and inhibition of proteolytic pathways. MR-409 also promoted the maturation of neuromuscular junctions, by reducing multi-innervated endplates and increasing those mono-innervated. Finally, treatment with MR-409 delayed αMN death and blunted neuroinflammation in the spinal cord of SMA mice. In conclusion, the present study demonstrates that MR-409 has protective effects in SMNΔ7 mice, suggesting that GHRH agonists are promising agents for the treatment of SMA, possibly in combination with SMN-dependent strategies.

Scavenging of reactive oxygen species can adjust the differentiation of tendon stem cells and progenitor cells and prevent ectopic calcification in tendinopathy

Tendinopathy is a common disorder that leads to pain and impaired quality of life. Recent studies revealed that osteogenic differentiation of tendon stem/progenitor cells (TSPCs) played an important role in the pathogenesis of tendon calcification and tendinopathy. In this study, we found that the growth hormone-releasing hormone agonist (GA) can prevent matrix degradation and osteogenic differentiation in TSPCs. As oxidative stress is a key factor in the osteogenic differentiation of TSPCs, we used bovine serum albumin/heparin nanoparticles (BHNPs), which have biocompatibility and drug loading capacity, to scavenge reactive oxygen species (ROS) and achieve sustained release of GA at the site of inflammation. The newly developed BHNPs@GA had a synergetic effect on reducing ROS production in TSPCs. In addition, BHNPs@GA effectively inhibited tendon calcification and promoted collagen formation in a rat model of tendinopathy. Focusing on the ROS underlying the differentiation and dedifferentiation of TSPCs, this work demonstrated that sustained release of GA targeting ROS and ectopic ossification is a practical therapeutic strategy for treating tendinopathy. Statement of SignificanceOsteogenic differentiation of tendon stem/progenitor cells (TSPCs) plays an important role in the pathogenesis of ectopic calcification in tendinopathy. In this study, we found that growth hormone-releasing hormone agonist (GA) can reduce reactive oxygen species (ROS) production and adjust TSPCs differentiation. Bovine serum albumin/heparin nanoparticles (BHNPs) were developed to encapsulate GA and achieve sustained release of GA at the site of inflammation. The developed compound, BHNPs@GA, with a synergistic effect of inhibiting ROS and thus, can effectively adjust TSPCs differentiation, inhibit tendon calcification, and promote collagen formation in tendinopathy. This study highlighted the role of ROS underlying the differentiation and dedifferentiation of TSPCs in tendinopathy, and findings may help to identify new therapeutic targets and develop novel strategy for treating tendinopathy.

Synthetic growth hormone-releasing hormone agonist ameliorates the myocardial pathophysiology characteristic of heart failure with preserved ejection fraction.

To test the hypothesis that the activation of the growth hormone-releasing hormone (GHRH) receptor signalling pathway within the myocardium both prevents and reverses diastolic dysfunction and pathophysiologic features consistent with heart failure with preserved ejection fraction (HFpEF). Impaired myocardial relaxation, fibrosis, and ventricular stiffness, among other multi-organ morbidities, characterize the phenotype underlying the HFpEF syndrome. Despite the rapidly increasing prevalence of HFpEF, few effective therapies have emerged. Synthetic agonists of the GHRH receptors reduce myocardial fibrosis, cardiomyocyte hypertrophy, and improve performance in animal models of ischaemic cardiomyopathy, independently of the growth hormone axis. CD1 mice received 4- or 8-week continuous infusion of angiotensin-II (Ang-II) to generate a phenotype with several features consistent with HFpEF. Mice were administered either vehicle or a potent synthetic agonist of GHRH, MR-356 for 4-weeks beginning concurrently or 4-weeks following the initiation of Ang-II infusion. Ang-II-treated animals exhibited diastolic dysfunction, ventricular hypertrophy, interstitial fibrosis, and normal ejection fraction. Cardiomyocytes isolated from these animals exhibited incomplete relaxation, depressed contractile responses, altered myofibrillar protein phosphorylation, and disturbed calcium handling mechanisms (ex vivo). MR-356 both prevented and reversed the development of the pathological phenotype in vivo and ex vivo. Activation of the GHRH receptors increased cAMP and cGMP in cardiomyocytes isolated from control animals but only cAMP in cardiac fibroblasts, suggesting that GHRH-A exert differential effects on cardiomyocytes and fibroblasts. These findings indicate that the GHRH receptor signalling pathway(s) represents a new molecular target to counteract dysfunctional cardiomyocyte relaxation by targeting myofilament phosphorylation and fibrosis. Accordingly, activation of GHRH receptors with potent, synthetic GHRH agonists may provide a novel therapeutic approach to management of the myocardial alterations associated with the HFpEF syndrome.

Agonistic analog of growth hormone–releasing hormone promotes neurofunctional recovery and neural regeneration in ischemic stroke

Ischemic stroke can induce neurogenesis. However, most stroke-generated newborn neurons cannot survive. It has been shown that MR-409, a potent synthetic agonistic analog of growth hormone-releasing hormone (GHRH), can protect against some life-threatening pathological conditions by promoting cell proliferation and survival. The present study shows that long-term treatment with MR-409 (5 or 10 μg/mouse/d) by subcutaneous (s.c.) injection significantly reduces the mortality, ischemic insult, and hippocampal atrophy, and improves neurological functional recovery in mice operated on for transient middle cerebral artery occlusion (tMCAO). Besides, MR-409 can stimulate endogenous neurogenesis and improve the tMCAO-induced loss of neuroplasticity. MR-409 also enhances the proliferation and inhibits apoptosis of neural stem cells treated with oxygen and glucose deprivation-reperfusion. The neuroprotective effects of MR-409 are closely related to the activation of AKT/CREB and BDNF/TrkB pathways. In conclusion, the present study demonstrates that GHRH agonist MR-409 has remarkable neuroprotective effects through enhancing endogenous neurogenesis in cerebral ischemic mice.

Agonist of growth hormone–releasing hormone enhances retinal ganglion cell protection induced by macrophages after optic nerve injury

Optic neuropathies are leading causes of irreversible visual impairment and blindness, currently affecting more than 100 million people worldwide. Glaucoma is a group of optic neuropathies attributed to progressive degeneration of retinal ganglion cells (RGCs). We have previously demonstrated an increase in survival of RGCs by the activation of macrophages, whereas the inhibition of macrophages was involved in the alleviation on endotoxin-induced inflammation by antagonist of growth hormone-releasing hormone (GHRH). Herein, we hypothesized that GHRH receptor (GHRH-R) signaling could be involved in the survival of RGCs mediated by inflammation. We found the expression of GHRH-R in RGCs of adult rat retina. After optic nerve crush, subcutaneous application of GHRH agonist MR-409 or antagonist MIA-602 promoted the survival of RGCs. Both the GHRH agonist and antagonist increased the phosphorylation of Akt in the retina, but only agonist MR-409 promoted microglia activation in the retina. The antagonist MIA-602 reduced significantly the expression of inflammation-related genes Il1b, Il6, and Tnf Moreover, agonist MR-409 further enhanced the promotion of RGC survival by lens injury or zymosan-induced macrophage activation, whereas antagonist MIA-602 attenuated the enhancement in RGC survival. Our findings reveal the protective effect of agonistic analogs of GHRH on RGCs in rats after optic nerve injury and its additive effect to macrophage activation, indicating a therapeutic potential of GHRH agonists for the protection of RGCs against optic neuropathies especially in glaucoma.

Effects of growth hormone-releasing hormone agonistic analog MR-409 on insulin-secreting cells under cyclopiazonic acid-induced endoplasmic reticulum stress

The endoplasmic reticulum (ER) stress is one of the mechanisms related to decreased insulin secretion and beta cell death, contributing to the progress of type 2 diabetes mellitus (T2D). Thus, investigating agents that can influence this process would help prevent the development of T2D. Recently, the growth-hormone-releasing hormone (GHRH) action has been demonstrated in INS-1E cells, in which it increases cell proliferation and insulin secretion. As the effects of GHRH and its agonists have not been fully elucidated in the beta cell, we proposed to investigate them by evaluating the role of the GHRH agonist, MR-409, in cells under ER stress. Our results show that the agonist was unable to ameliorate or prevent ER stress. However, cells exposed to the agonist showed less oxidative stress and greater survival even under ER stress. The mechanisms by which GHRH agonist, MR-409, leads to these outcomes require further investigation.

Improvement of cardiac and systemic function in old mice by agonist of growth hormone-releasing hormone.

Age-related diseases such as cardiovascular diseases portend disability, increase health expenditures, and cause late-life mortality. Synthetic agonists of growth hormone-releasing hormone (GHRH) exhibit several favorable effects on heart function and remodeling. Here we assessed whether GHRH agonist MR409 can modulate heart function and systemic parameters in old mice. Starting at the age of 15 months, mice were injected subcutaneously with MR409 (10 µg/day, n = 8) or vehicle (n = 7) daily for 6 months. Mice treated with MR409 showed improvements in exercise activity, cardiac function, survival rate, immune function, and hair growth in comparison with the controls. More stem cell colonies were grown out of the bone marrow recovered from the MR409-treated mice. Mitochondrial functions of cardiomyocytes (CMs) from the MR409-treated mice were also significantly improved with more mitochondrial fusion. Fewer β-gal positive cells were observed in endothelial cells after 10 passages with MR409. In Doxorubicin-treated H9C2 cardiomyocytes, cell senescence marker p21 and reactive oxygen species were significantly reduced after cultured with MR409. MR409 also improved cellular ATP production and oxygen consumption rate in Doxorubicin-treated H9C2 cells. Mitochondrial protein OPA1 long isoform was significantly increased after treatment with MR409. The effects of MR409 were mediated by GHRH receptor and protein kinase A (PKA). In short, GHRH agonist MR409 reversed the aging-associated changes with respect of heart function, mobility, hair growth, cellular energy production, and senescence biomarkers. The improvement of heart function may be related to a better mitochondrial functions through GHRH receptor/cAMP/PKA/OPA1 signaling pathway and relieved cardiac inflammation.

Growth hormone-releasing hormone antagonistic analog MIA-690 stimulates food intake in mice

In addition to its metabolic and endocrine effects, growth hormone-releasing hormone (GHRH) was found to modulate feeding behavior in mammals. However, the role of recently synthetized GHRH antagonist MIA-690 and MR-409, a GHRH agonist, on feeding regulation remains to be evaluated. We investigated the effects of chronic subcutaneous administration of MIA-690 and MR-409 on feeding behavior and energy metabolism, in mice. Compared to vehicle, MIA-690 increased food intake and body weight, while MR-409 had no effect. Both analogs did not modify locomotor activity, as well as subcutaneous, visceral and brown adipose tissue (BAT) mass. A significant increase of hypothalamic agouti-related peptide (AgRP) gene expression and norepinephrine (NE) levels, along with a reduction of serotonin (5-HT) levels were found after MIA-690 treatment. MIA-690 was also found able to decrease gene expression of leptin in visceral adipose tissue. By contrast, MR-409 had no effect on the investigated markers. Concluding, chronic peripheral administration of MIA-690 could play an orexigenic role, paralleled by an increase in body weight. The stimulation of feeding could be mediated, albeit partially, by elevation of AgRP gene expression and NE levels and decreased 5-HT levels in the hypothalamus, along with reduced leptin gene expression, in the visceral adipose tissue.

Protective effects of growth hormone-releasing hormone analogs in DSS-induced colitis in mice

Besides its metabolic and endocrine effects, growth hormone (GH)-releasing hormone (GHRH) is involved in the modulation of inflammation. Recently synthetized GHRH antagonist MIA-690 and MR-409, GHRH agonist, developed by us have shown potent pharmacological effects in various experimental paradigms. However, whether their administration modify resistance to chronic inflammatory stimuli in colon is still unknown. Ex vivo results demonstrated that MIA-690 and MR-409 inhibited production of pro-inflammatory and oxidative markers induced by lipopolysaccharide on isolated mouse colon specimens. In vivo, both MIA-690 and MR-409 have also been able to decrease the responsiveness to nociceptive stimulus, in hot plate test. Additionally, both peptides also induced a decreased sensitivity to acute and persistent inflammatory stimuli in male mice, in formalin test and dextran sodium sulfate (DSS)-induced colitis model, respectively. MIA-690 and MR-409 attenuate DSS-induced colitis with particular regard to clinical manifestations, histopathological damage and release of pro-inflammatory and oxidative markers in colon specimens. Respect to MR-409, MIA-690 showed higher efficacy in inhibiting prostaglandin (PG)E2, 8-iso-PGF2α and serotonin (5-HT) levels, as well as tumor necrosis factor (TNF)-α, interleukin (IL)-6 and nitric oxide synthase gene expression in colon specimens of DSS-induced colitis. Furthermore, MIA-690 decreased serum insulin-like growth factor (IGF)-1 levels in mice DSS-treated, respect to MR-409. Thus, our findings highlight the protective effects of MIA-690 and MR-409 on inflammation stimuli. The higher antinflammatory and antioxidant activities observed with MIA-690 could be related to decreased serum IGF-1 levels.

Growth hormone-releasing hormone agonists ameliorate chronic kidney disease-induced heart failure with preserved ejection fraction

Therapies for heart failure with preserved ejection fraction (HFpEF) are lacking. Growth hormone-releasing hormone agonists (GHRH-As) have salutary effects in ischemic and nonischemic heart failure animal models. Accordingly, we hypothesized that GHRH-A treatment ameliorates chronic kidney disease (CKD)-induced HFpEF in a large-animal model. Female Yorkshire pigs (n = 16) underwent 5/6 nephrectomy via renal artery embolization and 12 wk later were randomized to receive daily subcutaneous injections of GHRH-A (MR-409; n = 8; 30 µg/kg) or placebo (n = 8) for 4 to 6 wk. Renal and cardiac structure and function were serially assessed postembolization. Animals with 5/6 nephrectomy exhibited CKD (elevated blood urea nitrogen [BUN] and creatinine) and faithfully recapitulated the hemodynamic features of HFpEF. HFpEF was demonstrated at 12 wk by maintenance of ejection fraction associated with increased left ventricular mass, relative wall thickness, end-diastolic pressure (EDP), end-diastolic pressure/end-diastolic volume (EDP/EDV) ratio, and tau, the time constant of isovolumic diastolic relaxation. After 4 to 6 wk of treatment, the GHRH-A group exhibited normalization of EDP (P = 0.03), reduced EDP/EDV ratio (P = 0.018), and a reduction in myocardial pro-brain natriuretic peptide protein abundance. GHRH-A increased cardiomyocyte [Ca2+] transient amplitude (P = 0.009). Improvement of the diastolic function was also evidenced by increased abundance of titin isoforms and their ratio (P = 0.0022). GHRH-A exerted a beneficial effect on diastolic function in a CKD large-animal model as demonstrated by improving hemodynamic, structural, and molecular characteristics of HFpEF. These findings have important therapeutic implications for the HFpEF syndrome.

Abstract 15998: Therapeutic Effectiveness Against Heart Failure With Preserved Ejection Fraction by the Activation of the Growth Hormone-releasing Hormone Receptor in a Murine Model

Introduction: Heart failure with preserved ejection fraction (HFpEF) accounts for ~50% of heart failure cases and is characterized by impaired relaxation, ventricular stiffening and fibrosis. Growth hormone releasing hormone-agonists (GHRH-As) reduce fibrosis in rat and swine models of ischemic myocardial injury. However, their therapeutic effect in HFpEF is unknown. Hypothesis: We hypothesized that activation of GHRH receptor signaling prevents pathological remodeling and targets cardio-myocyte (CM) excitation-contraction coupling, ameliorating the compromised myocardial performance associated with HFpEF. Methods: CD1 mice implanted with a mini-osmotic pump (Alzet) to deliver angiotensin-II (Ang-II) for 8 weeks, were randomized at week 4 to receive daily injections of either GHRH-A (MR-356; n=12) or vehicle (n=12). Echocardiographic data and pressure-volume loops were recorded. Biometric measurements and fibrosis were assessed. CMs were isolated and intracellular Ca2 + and sarcomere length acquired. Results: Ang-II-treated mice exhibited functional and morphologic features consistent with HFpEF. CMs exhibited reduced sarcomere length, indicating an inability to relax. The Ca2 + decay rate and sarcomere re-lengthening were delayed. MR-356 treatment reverted the structural remodeling, including fibrosis, improving diastolic function (Figure Top panel). This treatment also abrogated the HFpEF-associated delay in Ca2 + decay and further enhanced sarcomere re-lengthening rate (Figure Bottom panel). Conclusions: Our findings confirm that chronic infusion of Ang-II mediates functional changes in CMs consistent with HFpEF and demonstrate that activation of GHRH receptor signaling pathways targets mechanisms of excitation-contraction coupling, inflammation and fibrosis, thereby preventing HFpEF-associated dysfunctional CM relaxation and myocardial remodeling.