Ghrelin stimulates angiogenesis in human microvascular endothelial cells: Implications beyond GH release

Desacylghrelin modulates GHS-R1 receptor expression and cell differentiation in placental BeWo cells

BACKGROUND

and purpose: Ghrelin is the endogenous ligand of the growth hormone secretagogue receptor (GHS-R1). Ghrelin, and GHS-R1, may have a role in placental growth and function, and its unacylated form desacylghrelin (DAG) could be involved in fetal growth. Nevertheless, the effects of DAG on placental function, and the receptor involved in its actions, remain to be determined. We aimed to investigate the effect of DAG in placental BeWo cells viability, proliferation, differentiation, and GSH-R1 expression.

METHODS

BeWo cells, a human trophoblast cell line, was cultured with 3 nM DAG during 12, 24, 48, and 72 h. Cell viability, proliferation, differentiation (assessed by human Chorionic Gonadotropin quantification), and GSH-R1 expression were analyzed. To evaluate the mechanism of DAG effect on GSH-R1, 30 nM receptor antagonist ([D-Lys3]-GHRP-6) was added alone or in combination with 3 nM DAG during 12 h and 24 h.

RESULTS

DAG has no effect on cell proliferation or viability, but it has an inhibitory effect on cell differentiation. DAG had a stimulatory effect on GSH-R1 expression at 12 and 24 h (p = 0.029 and p = 0.025, respectively). On the contrary, culture with 48 h DAG inhibits GSH-R1 expression compared to the control (p = 0.005), while GSH-R1 antagonist inhibited the effect of DAG on GSH-R1 expression. DAG also reduces intracellular (p = 0.020) and secreted (p = 0.011) hCG concentration in BeWo cells.

CONCLUSION

DAG increases GHS-R1 expression, potentially mediated through GHS-R1 itself. DAG may also inhibit placental BeWo cell differentiation, suggesting a possible role of DAG in placental and fetal physiology.

The effects and mechanisms of ghrelin upon angiogenesis in human coronary artery endothelial cells under hypoxia

Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor (GHSR), has been found to stimulate angiogenesis both in vivo and in vitro. However, the effect of ghrelin upon angiogenesis, and the corresponding mechanisms of ghrelin therein, in human coronary artery endothelial cells (HCAECs) under hypoxia is still unknown. Our study found that ghrelin significantly increased HCAECs proliferation, migration, in vitro angiogenesis, and microvessel sprouting from the aortic ring under hypoxic conditions. The ghrelin-induced angiogenic process was accompanied by vascular endothelial growth factor (VEGF), angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2) and endothelial-specific receptor tyrosine kinase (Tie2) expressions. In addition, this angiogenic effect was almost completely inhibited by Ang-2 RNAi and Tie2 RNAi. Pretreatment with the GHSR1a blocker [D-Lys3]-GHRP-6 abolished ghrelin-induced VEGF, Ang-1, Ang-2 and Tie2 expressions and in vitro angiogenesis. In conclusion, this is the first demonstration that ghrelin stimulates HCAECs in vitro angiogenesis through GHSR1a-mediated VEGF, Ang-1, Ang-2 and Tie2 pathways under hypoxic conditions. It indicated that ghrelin might play an important role in myocardial angiogenesis after ischemic injury.

Effect of ghrelin on hypoxia-related cardiac angiogenesis: involvement of miR-210 signalling pathway

OBJECTIVE

Hypoxia is the main stimulus for angiogenesis. Hypoxia-inducible factor (HIF)-1α, vascular endothelial growth factor (VEGF), and miR-210 are involved in the hypoxia-induced angiogenesis. This study examined the effects of hypoxia and/or ghrelin on miR-210, HIF-1α, and VEGF levels in the heart of rats.

METHODS

Wistar rats were randomly divided into 4 groups (n = 6): control; ghrelin, received daily intraperitoneal injections of ghrelin; hypoxia, was exposed to hypoxic condition; hypoxia + ghrelin, was exposed to hypoxic condition and received intraperitoneal injections of ghrelin, for 2 weeks. Myocardial angiogenesis, the expression level of miR-210, and protein levels of HIF-1α and VEGF were assayed in the heart samples.

RESULTS

Hypoxia increased myocardial angiogenesis and cardiac levels of miR-210, HIF-1α, and VEGF. However, ghrelin inhibited these hypoxia-induced changes. Interestingly, ghrelin had no significant effect on miR-210, HIF-1α, and VEGF levels in normoxic condition.

CONCLUSION

Ghrelin may be useful as an anti-angiogenic factor.

Another Weapon against Cancer and Metastasis: Physical-Activity-Dependent Effects on Adiposity and Adipokines

Physically active behavior has been associated with a reduced risk of developing certain types of cancer and improved psychological conditions for patients by reducing anxiety and depression, in turn improving the quality of life of cancer patients. On the other hand, the correlations between inactivity, sedentary behavior, and overweight and obesity with the risk of development and progression of various cancers are well studied, mainly in middle-aged and elderly subjects. In this article, we have revised the evidence on the effects of physical activity on the expression and release of the adipose-tissue-derived mediators of low-grade chronic inflammation, i.e., adipokines, as well as the adipokine-mediated impacts of physical activity on tumor development, growth, and metastasis. Importantly, exercise training may be effective in mitigating the side effects related to anti-cancer treatment, thereby underlining the importance of encouraging cancer patients to engage in moderate-intensity activities. However, the strong need to customize and adapt exercises to a patient’s abilities is apparent. Besides the preventive effects of physically active behavior against the adipokine-stimulated cancer risk, it remains poorly understood how physical activity, through its actions as an adipokine, can actually influence the onset and development of metastases.

Research progress of ghrelin on cardiovascular disease

Ghrelin, a 28-aminoacid peptide, was isolated from the human and rat stomach and identified in 1999 as an endogenous ligand for the growth hormone secretagogue-receptor (GHS-R). In addition to stimulating appetite and regulating energy balance, ghrelin and its receptor GHS-R1a have a direct effect on the cardiovascular system. In recent years, it has been shown that ghrelin exerts cardioprotective effects, including the modulation of sympathetic activity and hypertension, enhancement of the vascular activity and angiogenesis, inhibition of arrhythmias, reduction in heart failure and inhibition of cardiac remodeling after myocardial infarction (MI). The cardiovascular protective effect of ghrelin may be associated with anti-inflammation, anti-apoptosis, inhibited sympathetic nerve activation, regulated autophagy, and endothelial dysfunction. However, the molecular mechanisms underlying the effects of ghrelin on the cardiovascular system have not been fully elucidated, and no specific therapeutic agent has been established. It is important to further explore the pharmacological potential of ghrelin pathway modulation for the treatment of cardiovascular diseases.

Dysregulation of ghrelin in diabetes impairs the vascular reparative response to hindlimb ischemia in a mouse model; clinical relevance to peripheral artery disease

Type 2 diabetes is a prominent risk factor for peripheral artery disease (PAD). Yet, the mechanistic link between diabetes and PAD remains unclear. This study proposes that dysregulation of the endogenous hormone ghrelin, a potent modulator of vascular function, underpins the causal link between diabetes and PAD. Moreover, this study aimed to demonstrate the therapeutic potential of exogenous ghrelin in a diabetic mouse model of PAD. Standard ELISA analysis was used to quantify and compare circulating levels of ghrelin between (i) human diabetic patients with or without PAD (clinic) and (ii) db/db diabetic and non-diabetic mice (lab). Db/db mice underwent unilateral hindlimb ischaemia (HLI) for 14 days and treated with or without exogenous ghrelin (150 µg/kg/day.) Subsequently vascular reparation, angiogenesis, hindlimb perfusion, structure and function were assessed using laser Doppler imaging, micro-CT, microangiography, and protein and micro-RNA (miRNA) analysis. We further examined hindlimb perfusion recovery of ghrelin KO mice to determine whether an impaired vascular response to HLI is linked to ghrelin dysregulation in diabetes. Patients with PAD, with or without diabetes, had significantly lower circulating levels of endogenous ghrelin, compared to healthy individuals. Diabetic db/db mice had ghrelin levels that were only 7% of non-diabetic mice. The vascular reparative capacity of diabetic db/db mice in response to HLI was impaired compared to non-diabetic mice and, importantly, comparable to ghrelin KO mice. Daily therapeutic treatment of db/db mice with ghrelin for 14 days post HLI, stimulated angiogenesis, and improved skeletal muscle architecture and cell survival, which was associated with an increase in pro-angiogenic miRNAs-126 and -132. These findings unmask an important role for endogenous ghrelin in vascular repair following limb ischemia, which appears to be downregulated in diabetic patients. Moreover, these results implicate exogenous ghrelin as a potential novel therapy to enhance perfusion in patients with lower limb PAD, especially in diabetics.

Hemostatic effect of acylated ghrelin in control and sleeve gastrectomy-induced rats: mechanisms of action

This study investigated the effect of acylated ghrelin (AG) deficiency after sleeve gastrectomy (SG) or chronic administration in control and SG-indiuced rats on platelet function, coagulation, and fibrinolysis. Administration of AG (100 µg/kg, subcutaneously) to control or SG rats significantly inhibited platelets aggregation and lowered levels of Von-Willebrand factor (vWF), fibrinogen, and thromboxane B2. Concomitantly, it decreased circulatory levels and aortic expression levels of plasminogen activator inhibitor-1 (PAI-1) and tissue factor (TF) and increased the aortic expression of the endothelial nitric oxidase (eNOS). However, AG inhibited angiotensin-II (ANGII)-induced upregulation of tissue factor pathway inhibitor (TPAI) and TF and increased activity of TF and increases eNOS expression in cultured endothelial cells, an effect that was abolished by the addition of D-[lys3]-GHRP-6, a selective AG receptor (GHSR-1a) blocker or L-Name, a potent eNOS inhibitor. In conclusion, AG has an anti-platelet, anti-coagulant, and fibrinolytic roles mediated through GHSR-1a to enhance nitric oxide synthesis.

Physiological Effect of Ghrelin on Body Systems

Ghrelin is a relatively novel multifaceted hormone that has been found to exert a plethora of physiological effects. In this review, we found/confirmed that ghrelin has effect on all body systems. It induces appetite; promotes the use of carbohydrates as a source of fuel while sparing fat; inhibits lipid oxidation and promotes lipogenesis; stimulates the gastric acid secretion and motility; improves cardiac performance; decreases blood pressure; and protects the kidneys, heart, and brain. Ghrelin is important for learning, memory, cognition, reward, sleep, taste sensation, olfaction, and sniffing. It has sympatholytic, analgesic, antimicrobial, antifibrotic, and osteogenic effects. Moreover, ghrelin makes the skeletal muscle more excitable and stimulates its regeneration following injury; delays puberty; promotes fetal lung development; decreases thyroid hormone and testosterone; stimulates release of growth hormone, prolactin, glucagon, adrenocorticotropic hormone, cortisol, vasopressin, and oxytocin; inhibits insulin release; and promotes wound healing. Ghrelin protects the body by different mechanisms including inhibition of unwanted inflammation and induction of autophagy. Having a clear understanding of the ghrelin effect in each system has therapeutic implications. Future studies are necessary to elucidate the molecular mechanisms of ghrelin actions as well as its application as a GHSR agonist to treat most common diseases in each system without any paradoxical outcomes on the other systems.

Attribution of Ghrelin to Cancer; Attempts to Unravel an Apparent Controversy

Ghrelin is an endogenous peptide hormone mainly produced in the stomach. It has been known to regulate energy homeostasis, stimulate secretion of growth hormone, and mediate many other physiologic effects. Various effects attributed to ghrelin contribute to many aspects of cancer development and progression. Accordingly, a large body of evidence has emerged about the association of ghrelin with several types of cancer in scales of cell-line, animal, and human studies. However, existing data are controversial. This controversy occurs in two main domains: one is the controversial results in local effects of ghrelin on different types of human cancer cell-lines; the second is the apparent disagreement in the results of in-vitro and clinical studies that investigated ghrelin association to one type of cancer. These inconsistencies have hampered the indications to consider ghrelin as a potential tumor biomarker or therapeutic agent in cancer patients. Previous studies have reviewed different parts of current literature about the ghrelin-cancer relationship. Although they have highlighted these controversial results in various ways, no specific recommendations have been given to address it. In this study, we comprehensively reviewed in-vitro, in-vivo, and clinical studies and attempted to use the following approaches to unravel the inconsistencies detected: (a) to distinguish local and systemic effects of ghrelin in interpreting its summary clinical role in each cancer; (b) scrutinizing factors that regulate local effects of ghrelin and could justify different effects of ghrelin on different cancer cell-lines. These approaches could have notable implications for future in-vitro and clinical studies.

Acylated ghrelin protects aorta damage post-MI via activation of eNOS and inhibition of angiotensin-converting enzyme induced activation of NAD(P)H-dependent oxidase

NAD(P)H dependent oxidase derived-reactive oxygen species (ROS) due to activation of the renin-angiotensin-aldosterone system (RAAS) in blood vessels postmyocardial infarction MI or during the HF leads to endothelium dysfunction and enhanced apoptosis. Acylated ghrelin (AG) is a well-reported cardioprotective and antiapoptotic agent for the heart. AG receptors are widely distributed in most of blood vessels, suggesting a role in the regulation of endothelial function and survival. This study investigated if AG can protect aorta of rats' postmyocardial infarction (MI)-induced damage and endothelial dysfunction. Adult male rats were divided into four groups of (1) Sham, (2) Sham + AG, (3) MI, and (4) MI + AG. Vehicle (normal saline) or AG (100 µ/kg) was administered to rats for 21 consecutive days, after which, numerous biochemical markers were detected by blot. Both histological and electron microscope studies were carried on aortic samples from MI-induced rats. AG increased protein levels of both total and phosphorylated forms of endothelial nitric oxide synthase (eNOS and p-eNOS, respectively). Only in MI-treated rats, AG prevented the decreases in the levels of reduced glutathione (GSH) and superoxide dismutase (SOD) and lowered levels of malondialdehyde (MDA) and glutathione disulfide (GSSG). Concomitantly, it lowered the increased protein levels of angiotensin-converting enzyme (ACE), p22phox and cleaved caspase-3 and prevented the aorta histological and ultrustructural abnormalities induced by MI.

Ghrelin Stimulates Endothelial Cells Angiogenesis through Extracellular Regulated Protein Kinases (ERK) Signaling Pathway

Adipose tissue is hyper-vascularized. Vessels in adipose tissue not only supply nutrients and oxygen to nourish adipocytes, but also provide cytokines that regulate mass and function of adipose tissue. Understanding the fundamental mechanisms how vessels modulate adipocyte functions would provide new therapeutic options for treatment of metabolic disease and obesity. In recent years, researches about ghrelin are focused on glucose and lipid metabolism, but its effect on vascular function remains uncharacterized. In the present study, ghrelin receptor gene deletion mice (Ghsr^-/- mice) were used to study ghrelin-regulated vascular metabolism in white adipose tissue. Ghsr^-/- mice demonstrated lower food intake, lower body weight, and resistance to high-fat diet-induced obesity. The number of vessels in white adipose tissue was decreased in Ghsr^-/- mice when compared with wild type mice fed with high-fat diet. To further define ghrelin effects in vitro, we used endothelial progenitor cells from wild type and Ghsr^-/- mice as well as human umbilical vein endothelial cells in our experiments. We found that ghrelin stimulated endothelial cells angiogenesis and migration through the MEK-ERK signaling pathway. [d-Lys3]-GHRP-6 and PD98059 could reverse the effects of ghrelin on endothelial cells. Our study indicates that ghrelin activates its receptor on endothelial cells to promote angiogenesis and migration via a mechanism involving the extracellular regulated protein kinases (ERK) signaling pathway.

Receptor of ghrelin is expressed in cutaneous neurofibromas of individuals with neurofibromatosis 1

BACKGROUND

Multiple cutaneous neurofibromas are a hallmark of neurofibromatosis 1 (NF1). They begin to appear during puberty and increase in number and volume during pregnancy, suggesting a hormonal influence. Ghrelin is a hormone that acts via growth hormone secretagogue receptor (GHS-R), which is overexpressed in many neoplasms and is involved in tumorigenesis. We aimed to investigate GHS-R expression in NF1 cutaneous neurofibromas and its relationship with tumors volume, and patient's age and gender.

RESULTS

Sample comprised 108 cutaneous neurofibromas (55 large and 53 small tumors) from 55 NF1 individuals. GHS-R expression was investigated by immunohistochemistry in tissue micro and macroarrays and quantified using a digital computer-assisted method. All neurofibromas expressed GHS-R, with a percentage of positive cells ranging from 4.9% to 76.1%. Large neurofibromas expressed more GHS-R than the small ones. The percentage of GHS-R-positive cells and intensity of GHS-R expression were positively correlated with neurofibromas volume. GHS-R expression was more common in female gender.

CONCLUSIONS

GHS-R is expressed in cutaneous neurofibromas. Larger neurofibromas have a higher percentage of positive cells and higher GHS-R intensity. Based on our results we speculate that ghrelin may have an action on the tumorigenesis of cutaneous neurofibromas. Future studies are required to understand the role of ghrelin in the pathogenesis of NF1-associated cutaneous neurofibroma.

Saliva/serum ghrelin, obestatin and homocysteine levels in patients with ischaemic heart disease

BACKGROUND

We aimed to compare ghrelin, obestatin, homocysteine (Hcy), vitamin B₁₂ and folate levels in the serum and saliva of ischaemic heart disease patients.

METHODS

Serum and saliva were collected from 33 ischaemic heart disease (IHD) patients and 28 age- and body mass index-matched healthy individuals. Levels of acylated and desacylated ghrelin, obestatin and Hcy were determined using the ELISA method.

RESULTS

Acylated ghrelin, desacylated ghrelin and obestatin levels in the saliva were found to be higher than those in the serum of the control group, while acylated and desacylated ghrelin levels in the saliva were significantly lower than those in the serum. Obestatin levels were higher in IHD patients (p = 0.001). Saliva and serum vitamin B₁₂ and folate levels in IHD patients were significantly lower than in the control group (p = 0.001).

CONCLUSIONS

It was determined that serum ghrelin levels increased in ischaemic heart disease patients, while serum levels of obestatin decreased.

Ghrelin inhibits atherosclerotic plaque angiogenesis and promotes plaque stability in a rabbit atherosclerotic model

Intraplaque angiogenesis associates with the instability of atherosclerotic plaques. In the present study, we investigated the effects of ghrelin on intraplaque angiogenesis and plaque instability in a rabbit model of atherosclerosis. The rabbits were randomly divided into three groups, namely, the control group, atherosclerotic model group, and ghrelin-treated group, with treatments lasting for 4 weeks. We found that the thickness ratio of the intima to media in rabbits of the ghrelin-treated group was significantly lower than that in rabbits of the atherosclerotic model group. The number of neovessels and the levels of vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor 2 (VEGFR2) decreased dramatically in rabbits of the ghrelin-treated group compared to those of the atherosclerotic model group. Ghrelin significantly decreased the plaque content of macrophages, matrix metalloproteinase (MMP)-2, and MMP-9, in a rabbit model of atherosclerosis. In addition, the level of the pro-inflammatory factor monocyte chemoattractant protein (MCP)-1 was significantly lower in rabbits of the ghrelin-treated group than in rabbits of the atherosclerotic model group. In summary, ghrelin can inhibit intraplaque angiogenesis and promote plaque stability by down-regulating VEGF and VEGFR2 expression, inhibiting the plaque content of macrophages, and reducing MCP-1 expression at an advanced stage of atherosclerosis in rabbits.

Ghrelin, MicroRNAs, and Critical Limb Ischemia: Hungering for a Novel Treatment Option

Critical limb ischemia (CLI) is the most severe manifestation of peripheral artery disease. It is characterized by chronic pain at rest, skin ulcerations, and gangrene tissue loss. CLI is a highly morbid condition, resulting in a severely diminished quality of life and a significant risk of mortality. The primary goal of therapy for CLI is to restore blood flow to the affected limb, which is only possible by surgery, but is inadvisable in up to 50% of patients. This subset of patients who are not candidates for revascularisation are referred to as "no-option" patients and are the focus of investigation for novel therapeutic strategies. Angiogenesis, arteriogenesis and vasculogenesis are the processes whereby new blood vessel networks form from the pre-existing vasculature and primordial cells, respectively. In therapeutic angiogenesis, exogenous stimulants are administered to promote angiogenesis and augment limb perfusion, offering a potential treatment option for "no option" patients. However, to date, very few clinical trials of therapeutic angiogenesis in patients with CLI have reported clinically significant results, and it remains a major challenge. Ghrelin, a 28-amino acid peptide, is emerging as a potential novel therapeutic for CLI. In pre-clinical models, exogenous ghrelin has been shown to induce therapeutic angiogenesis, promote muscle regeneration, and reduce oxidative stress via the modulation of microRNAs (miRs). miRs are endogenous, small, non-coding ribonucleic acids of ~20-22 nucleotides which regulate gene expression at the post-transcriptional level by either translational inhibition or by messenger ribonucleic acid cleavage. This review focuses on the mounting evidence for the use of ghrelin as a novel therapeutic for CLI, and highlights the miRs which orchestrate these physiological events.

Is there an effect of ghrelin/ghrelin analogs on cancer? A systematic review

Ghrelin is a hormone with multiple physiologic functions, including promotion of growth hormone release, stimulation of appetite and regulation of energy homeostasis. Treatment with ghrelin/ghrelin-receptor agonists is a prospective therapy for disease-related cachexia and malnutrition. In vitro studies have shown high expression of ghrelin in cancer tissue, although its role including its impact in cancer risk and progression has not been established. We performed a systematic literature review to identify peer-reviewed human or animal in vivo original research studies of ghrelin, ghrelin-receptor agonists, or ghrelin genetic variants and the risk, presence, or growth of cancer using structured searches in PubMed database as well as secondary searches of article reference lists, additional reviews and meta-analyses. Overall, 45 (73.8%) of the 61 studies reviewed, including all 11 involving exogenous ghrelin/ghrelin-receptor agonist treatment, reported either a null (no statistically significant difference) or inverse association of ghrelin/ghrelin-receptor agonists or ghrelin genetic variants with cancer risk, presence or growth; 10 (16.7%) studies reported positive associations; and 6 (10.0%) reported both negative or null and positive associations. Differences in serum ghrelin levels in cancer cases vs controls (typically lower) were reported for some but not all cancers. The majority of in vivo studies showed a null or inverse association of ghrelin with risk and progression of most cancers, suggesting that ghrelin/ghrelin-receptor agonist treatment may have a favorable safety profile to use for cancer cachexia. Additional large-scale prospective clinical trials as well as basic bioscientific research are warranted to further evaluate the safety and benefits of ghrelin treatment in patients with cancer.

Ghrelin Promotes Functional Angiogenesis in a Mouse Model of Critical Limb Ischemia Through Activation of Proangiogenic MicroRNAs

Current therapeutic strategies for the treatment of critical limb ischemia (CLI) have only limited success. Recent in vitro evidence in the literature, using cell lines, proposes that the peptide hormone ghrelin may have angiogenic properties. In this study, we aim to investigate if ghrelin could promote postischemic angiogenesis in a mouse model of CLI and, further, identify the mechanistic pathway(s) that underpin ghrelin's proangiogenic properties. CLI was induced in male CD1 mice by femoral artery ligation. Animals were then randomized to receive either vehicle or acylated ghrelin (150 μg/kg sc) for 14 consecutive days. Subsequently, synchrotron radiation microangiography was used to assess hindlimb perfusion. Subsequent tissue samples were collected for molecular and histological analysis. Ghrelin treatment markedly improved limb perfusion by promoting the generation of new capillaries and arterioles (internal diameter less than 50 μm) within the ischemic hindlimb that were both structurally and functionally normal; evident by robust endothelium-dependent vasodilatory responses to acetylcholine. Molecular analysis revealed that ghrelin's angiogenic properties were linked to activation of prosurvival Akt/vascular endothelial growth factor/Bcl-2 signaling cascade, thus reducing the apoptotic cell death and subsequent fibrosis. Further, ghrelin treatment activated proangiogenic (miR-126 and miR-132) and antifibrotic (miR-30a) microRNAs (miRs) while inhibiting antiangiogenic (miR-92a and miR-206) miRs. Importantly, in vitro knockdown of key proangiogenic miRs (miR-126 and miR-132) inhibited the angiogenic potential of ghrelin. These results therefore suggest that clinical use of ghrelin for the early treatment of CLI may be a promising and potent inducer of reparative vascularization through modulation of key molecular factors.

Ghrelin ameliorates impaired angiogenesis of ischemic myocardium through GHSR1a-mediated AMPK/eNOS signal pathway in diabetic rats

OBJECTIVES

Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor (GHSR), has been found to stimulate angiogenesis in vivo and in vitro. However, the effect and the corresponding mechanisms of ghrelin on impaired myocardial angiogenesis in diabetic and myocardial infarction (MI) rat model are still unknown.

METHODS

In the present study, adult SD rats were randomly divided into 4 groups: control, DM, DM+ghrelin, DM+ghrelin+[D-Lys3]-GHRP-6 groups. DM was induced by streptozotocin (STZ) 60 mg/kg body weight. 12 weeks post STZ injection all groups were subjected to MI, which was induced by ligation left anterior descending artery (LAD). Ghrelin and [D-Lys3]-GHRP-6 were administered via intraperitoneal injection at the doses 200 μg/kg and 50mg/kg for 4 weeks, respectively. Left ventricular function, microvascular density (MVD), myocardial infarct size, the expression of hypoxia-inducible factor (HIF1α), vascular endothelial growth factor (VEGF), fetal liver kinase-1 (Flk-1) and fms-like tyrosine kinase-1 (Flt-1), AMPK and endothelial nitric oxide synthase (eNOS) phosphorylation were examined.

RESULTS

Compared with the DM group, left ventricular ejection fraction (LVEF), fractional shortening (FS), and MVD were increased, whereas myocardial infarct size decreased remarkably in DM+ghrelin group. For the mechanism study, we found that ghrelin promoted the HIF1α, VEGF, Flk-1 and Flt-1 expression, AMPK and eNOS phosphorylation in diabetic rats. However, the above biochemical events in ghrelin treated diabetic rats were completely inhibited by GHSR-1a blocker [D-Lys3]-GHRP-6.

CONCLUSIONS

These results suggest that administration of ghrelin ameliorates impaired angiogenesis in diabetic MI rats. And these beneficial effects derive from regulating GHSR1a-mediated AMPK/eNOS signal pathway by upregulating of HIF1α, VEGF and its receptors Flk-1, Flt-1 expressions.

Octanoylated ghrelin attenuates angiogenesis induced by oxLDL in human coronary artery endothelial cells via the GHSR1a-mediated NF-κB pathway

OBJECTIVE

Low concentrations of oxidized low-density lipoprotein (oxLDL) promote the in vitro angiogenesis of endothelial cells and play an important role in plaque angiogenesis, which may cause plaque vulnerability and enhance the risk of intravascular thrombosis. The aim of this research was to investigate the effects of octanoylated ghrelin on oxLDL-induced angiogenesis and the underlying molecular mechanisms involved in this process.

MATERIALS/METHODS

Human coronary artery endothelial cells (HCAECs) were incubated with 5 μg/ml oxLDL and treated with various concentrations of octanoylated ghrelin (10(-9)-10(-6)M) with or without inhibitors for 24h. Cell proliferation, migration, and in vitro angiogenesis were analyzed by bromodeoxyuridine (BrdU) staining and BrdU enzyme-linked immunosorbent assay (ELISA), transwell assay, and tube formation on Matrigel, respectively. NF-κB (nuclear factor κB) expression was determined by Western-blot analysis.

RESULTS

Treatment with oxLDL at 5 μg/ml enhanced the proliferation, migration and tube formation of HCAECs. In contrast, pretreatment with octanoylated ghrelin significantly attenuated in vitro angiogenesis in oxLDL-induced HCAECs. In addition, Western blot analysis indicated that NF-κB expression was increased after oxLDL treatment, and that this effect was significantly reversed by pretreatment with octanoylated ghrelin. However, the NF-κB inhibitor PDTC or the GHSR1a inhibitor [D-Lys3]-GHRP-6 abolished the effects of octanoylated ghrelin on the inhibition of angiogenesis and NF-κB p65 expression induced by oxLDL.

CONCLUSIONS

These findings suggest that octanoylated ghrelin attenuates angiogenesis induced by oxLDL in HCAECs via the inhibition of GHSR1a-mediated NF-κB pathway. Furthermore, octanoylated ghrelin may promote the stability of vulnerable plaques by inhibiting plaque angiogenesis.

Ghrelin Decreases Angiogenesis, HIF-1α and VEGF Protein Levels in Chronic Hypoxia in Lung Tissue of Male Rats

PURPOSE

Hypoxia is a condition of decreased availability of oxygen. When cells are exposed to a low oxygen environment, they impel the hypoxia responses to adapt to new situation. The hypoxia response leads to the activation of various cellular signaling pathways. The aim of this study was to evaluate the effect of ghrelin on angiogenesis, Hypoxia-Inducible-Factor-1α (HIF-1) and Vascular endothelial growth factor (VEGF) levels in normobaric hypoxia situation.

METHODS

Twenty four animals were divided into 4 groups (n=6): control (C), ghrelin (Gh), hypoxia (H), and hypoxic animals that received ghrelin (H+Gh). Hypoxia (11%) was induced by an Environmental Chamber System GO2 Altitude. Animals in ghrelin groups received a subcutaneous injection of ghrelin (150 μg/kg/day) for 14 days.

RESULTS

Our results showed that hypoxia significantly (p<0.05) increased angiogenesis without any significant changes on HIF-1 and VEGF levels, whereas ghrelin significantly (p<0.05) decreased angiogenesis, expression of HIF-1 and VEGF in this condition. Ghrelin administration did not show any significant changes in normal conditions.

CONCLUSION

Ghrelin had no effect on angiogenesis, expression of HIF-1 and VEGF in normal oxygen conditions but it reduced angiogenesis process in lung tissue with reducing the level of HIF and VEGF in hypoxic condition. Therefore, effect of ghrelin on angiogenesis could be related to blood oxygen level.

The Role of Ghrelin in Senescence: A Mini-Review

Ghrelin, a 28-amino acid hormone produced mainly by the X/A-like endocrine cells in gastric mucosa, has a widespread tissue distribution and diverse physiological functions such as hormonal, orexigenic, metabolic, cardiovascular, neurological, and immunological activities. Considerable evidence has suggested that ghrelin plays an important role in organism senescence or aging. The present review provides a comprehensive picture of this new development. We first reviewed the aging (senescence)-dependent reduction of ghrelin signaling, and then highlighted its relationship with the aging-associated alteration in food intake, energy metabolism, cardiovascular function, neurological activity, and adaptive immunity. Our literature review suggests that ghrelin is an innovative and promising agent in the treatment of these pathophysiological conditions associated with senescence.

Angiogenesis in gastric mucosa: an important component of gastric erosion and ulcer healing and its impairment in aging

Angiogenesis (also referred to as neovascularization-formation of new blood vessels from existing vessels) is a fundamental process essential for healing of tissue injury and ulcers because regeneration of blood microvessels is a critical requirement for oxygen and nutrient delivery to the healing site. This review article updates the current views on angiogenesis in gastric mucosa following injury and during ulcer healing, its sequential events, the underlying mechanisms, and the impairment of angiogenesis in aging gastric mucosa. We focus on the time sequence and ultrastructural features of angiogenesis, hypoxia as a trigger, role of vascular endothelial growth factor signaling (VEGF), serum response factor, Cox2 and prostaglandins, nitric oxide, and importin. Recent reports indicate that gastric mucosa of aging humans and experimental animals exhibits increased susceptibility to injury and delayed healing. Gastric mucosa of aging rats has increased susceptibility to injury by a variety of damaging agents such as ethanol, aspirin, and other non-steroidal anti-inflammatory drugs because of structural and functional abnormalities including: reduced gastric mucosal blood flow, hypoxia, reduced expression of vascular endothelial growth factor and survivin, and increased expression of early growth response protein 1 (egr-1) and phosphatase and tensin homolog (PTEN). Until recently, postnatal neovascularization was assumed to occur solely through angiogenesis sprouting of endothelial cells and formation of new blood vessels from pre-existing blood vessels. New studies in the last decade have challenged this paradigm and indicate that in some tissues, including gastric mucosa, the homing of bone marrow-derived endothelial progenitor cells to the site of injury can also contribute to neovascularization by a process termed vasculogenesis.

Ghrelin augments murine T-cell proliferation by activation of the phosphatidylinositol-3-kinase, extracellular signal-regulated kinase and protein kinase C signaling pathways

Thymic atrophy occurs during normal aging, and is accelerated by exposure to chronic stressors that elevate glucocorticoid levels and impair the naïve T cell output. The orexigenic hormone ghrelin was recently shown to attenuate age-associated thymic atrophy. Here, we report that ghrelin enhances the proliferation of murine CD4+ primary T cells and a CD4+ T-cell line. Ghrelin induced activation of the ERK1/2 and Akt signaling pathways, via upstream activation of phosphatidylinositol-3-kinase and protein kinase C, to enhance T-cell proliferation. Moreover, ghrelin induced expression of the cell cycle proteins cyclin D1, cyclin E, cyclin-dependent kinase 2 (CDK2) and retinoblastoma phosphorylation. Finally, ghrelin activated the above-mentioned signaling pathways and stimulated thymocyte proliferation in young and older mice in vivo.

Functionally biased signalling properties of 7TM receptors - opportunities for drug development for the ghrelin receptor

The ghrelin receptor is a 7 transmembrane (7TM) receptor involved in a variety of physiological functions including growth hormone secretion, increased food intake and fat accumulation as well as modulation of reward and cognitive functions. Because of its important role in metabolism and energy expenditure, the ghrelin receptor has become an important therapeutic target for drug design and the development of anti-obesity compounds. However, none of the compounds developed so far have been approved for commercial use. Interestingly, the ghrelin receptor is able to signal through several different signalling pathways including Gαq , Gαi/o , Gα12/13 and arrestin recruitment. These multiple signalling pathways allow for functionally biased signalling, where one signalling pathway may be favoured over another either by selective ligands or through mutations in the receptor. In the present review, we have described how ligands and mutations in the 7TM receptor may bias the receptors to favour either one G-protein over another or to promote G-protein independent signalling pathways rather than G-protein-dependent pathways. For the ghrelin receptor, both agonist and inverse agonists have been demonstrated to signal more strongly through the Gαq -coupled pathway than the Gα12/13 -coupled pathway. Similarly a ligand that promotes Gαq coupling over Gαi coupling has been described and it has been suggested that several different active conformations of the receptor may exist dependent on the properties of the agonist. Importantly, ligands with such biased signalling properties may allow the development of drugs that selectively modulate only the therapeutically relevant physiological functions, thereby decreasing the risk of side effects.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Ghrelin in ocular pathophysiology: from the anterior to the posterior segment

Ghrelin is a 28 amino acid acylated peptide produced in several organs that binds the growth hormone secretagogues receptor type 1a (GHSR-1a). It acts over a wide range of systems, e.g. the endocrine, cardiovascular, musculoskeletal and immune systems and the eye. The aim of this work is to review the physiologic and pathologic implications of the ghrelin-GHSR-1a in the eye. A systematic revision of studies published between 2000 and 2013 in English, Spanish or Portuguese in MEDLINE, EMBASE and Scopus was performed. Search words used included: ghrelin, GHSR-1a, ocular production, iris muscular kinetics, ciliary body, glaucoma, retinopathy and uvea. The production of ghrelin by the ocular tissue has been detected both in the anterior and posterior segments, as well as the presence of GHSR-1a. This peptide promotes the relaxation of the iris sphincter and dilator muscles, being this effect independent from GHSR-1a and dependent on prostaglandins release in the first case and dependent on GHSR-1a in the second. Regarding ocular pathology, ghrelin levels in the aqueous humor appear to be decreased in individuals with glaucoma. Moreover, ghrelin has been shown to decrease the intraocular pressure in animal models of ocular hypertension through GHSR-1a. In the posterior segment, the ghrelin-GHSR-1a system interferes with the development of oxygen-induced retinopathy, being protective in the vaso-obliterative phase and deleterious in the vaso-proliferative stage of the disease. Thus, the ghrelin-GHSR-1a system presents as a possible local regulatory mechanism in the eye, with pathophysiological implications, constituting a target for future clinical and therapeutic research and interventions.

Ghrelin induces cell migration through GHSR1a-mediated PI3K/Akt/eNOS/NO signaling pathway in endothelial progenitor cells

OBJECTIVE

The purpose of this research was to investigate the effects of ghrelin on circulating endothelial progenitor cells (EPC) directional migration and its underlying molecular mechanisms involved in this process.

MATERIALS/METHODS

EPC were isolated from bone marrow of SD rats by using Percoll density gradient centrifugation, and characterized by double positive for acLDL-Dil uptake and FITC-UEA-1 binding and immunocytochemistry for CD34, CD133, vWF and Flk-1. EPC were treated with different concentrations of ghrelin (10(-9)~10(-6)M) with or without GHSR1a inhibitor [D-Lys3]-GHRP-6, PI3K inhibitor LY294002 and endothelial nitric oxide synthase (eNOS) inhibitor L-NAME, migration of EPC was detected by transwell assay, levels of phosphorylated and total Akt and eNOS were determined by Western-blot analysis and Nitric Oxide (NO) production was measured by Griess assay, respectively.

RESULTS

EPC were successfully obtained by Percoll density gradient centrifugation and ghrelin at 10(-8)M~10(-7)M promoted EPC migration. Ghrelin-induced EPC migration was accompanied by phosphorylation of Akt and eNOS, as well as an increase in NO production. These biochemical events and EPC directional migration induced by ghrelin were completely inhibited by GHSR-1a blocker [D-Lys3]-GHRP-6. PI3K inhibitor LY294002 attenuated ghrelin-induced EPC migration, phosphorylation of Akt and eNOS, and NO production. eNOS inhibitor L-NAME blocked ghrelin-induced EPC migration, phosphorylation of eNOS, and NO production, but had no effect on Akt phosphorylation.

CONCLUSIONS

These findings suggest that ghrelin stimulates EPC directional migration via GHSR1a-mediated PI3K/Akt/eNOS/NO signal pathway. It indicates that ghrelin may be used as a therapeutic strategy to treat ischemic diseases by promoting EPC directional migration.

The ghrelin axis--does it have an appetite for cancer progression?

Ghrelin, the endogenous ligand for the GH secretagogue receptor (GHSR), is a peptide hormone with diverse physiological roles. Ghrelin regulates GH release, appetite and feeding, gut motility, and energy balance and also has roles in the cardiovascular, immune, and reproductive systems. Ghrelin and the GHSR are expressed in a wide range of normal and tumor tissues, and a fluorescein-labeled, truncated form of ghrelin is showing promise as a biomarker for prostate cancer. Plasma ghrelin levels are generally inversely related to body mass index and are unlikely to be useful as a biomarker for cancer, but may be useful as a marker for cancer cachexia. Some single nucleotide polymorphisms in the ghrelin and GHSR genes have shown associations with cancer risk; however, larger studies are required. Ghrelin regulates processes associated with cancer, including cell proliferation, apoptosis, cell migration, cell invasion, inflammation, and angiogenesis; however, the role of ghrelin in cancer is currently unclear. Ghrelin has predominantly antiinflammatory effects and may play a role in protecting against cancer-related inflammation. Ghrelin and its analogs show promise as treatments for cancer-related cachexia. Further studies using in vivo models are required to determine whether ghrelin has a role in cancer progression.

D-Lys(3)-GHRP-6 antagonizes the effect of unacylated but not of acylated ghrelin on the growth of HECa10 murine endothelial cells

Recent studies demonstrate that ghrelin can be an endogenous regulator of angiogenesis. We studied direct effects of human acylated (hAG) and unacylated (hUAG) ghrelin, as well as of rat acylated ghrelin (rAG) on the growth of HECa10 murine endothelial cells. Ghrelin was applied separately or together with D-Lys(3)-GHRP-6, which is commonly used as an antagonist of ghrelin receptor type 1a - GHS-R1a. The growth of HECa10 cells was assessed with Mosmann and in selected study conditions also with BrdU and TUNEL methods. Both hAG and hUAG (10(-5) M to 10(-12) M) inhibited the growth of HECa10 cells in 24h and 72 h cultures. Similarly, rAG decreased the growth of the cells after 24h (10(-7) M and 10(-11) M), and after 72 h (10(-7) M, 10(-8) M and 10(-11) M). Unexpectedly, D-Lys(3)-GHRP-6 itself also inhibited the growth of these cells at 10(-4) to 10(-6) M in 24h, 48 h (dose-response effect) and 72 h cultures. D-Lys(3)-GHRP-6 did not modify the inhibitory effect of rAG. However, D-Lys(3)-GHRP-6 at the concentration of 10(-4) M diminished, abolished or even reversed the inhibitory effect of hUAG in 72 h culture and this was dependent on ghrelin concentrations. These data indicate that both AG and UAG have antiangiogenic properties at least at the level of endothelial growth, through decreased metabolic activity of the cells or stimulation of apoptosis. D-Lys(3)-GHRP-6 (inhibitor of GHS-R1a) seems not to be an appropriate antagonist in this experimental condition. Similar effects of these substances on HECa10 cells suggest that they are not mediated by GHS-R1a.

Ghrelin protects H9c2 cardiomyocytes from angiotensin II-induced apoptosis through the endoplasmic reticulum stress pathway

Ghrelin, a gastric hormone, exerts cardioprotective function by increasing myocardial contractility and vasodilation. Previous studies have reported that angiotensin II (Ang II) production increased in heart failure, which can induce cardiomyocyte apoptosis. In this study, we investigated the effect of ghrelin on Ang II-induced H9c2 cardiomyocyte apoptosis. The results showed that Ang II inhibited H9c2 cell viability, which was blocked by ghrelin. By annexin V-propidium iodide dual staining and 2'-deoxyuridine 5'-triphosphate nick end-labeling analysis, we found that Ang II induced H9c2 cell apoptosis, whereas coincubation of ghrelin with Ang II significantly reduced H9c2 cell apoptosis induced by Ang II. Simultaneously, the results revealed that ghrelin regulated the Ang II-induced imbalance of Bax and Bcl-2 expression and reduced Ang II-induced caspase-3 expression. Moreover, mRNA expressions of endoplasmic reticulum stress-related molecules GRP78, caspase-12, and C/EBP homologous protein were significantly upregulated by Ang II. However, their expressions were significantly inhibited by ghrelin. In addition, we found that ghrelin markedly inhibited Ang II-induced Ang II type 1 receptor expression. These data suggest that ghrelin may play an antagonistic role in Ang II-induced cardiomyocyte apoptosis via decreasing Ang II type 1 receptor expression and inhibiting the activation of endoplasmic reticulum stress pathway.

Myocardial angiogenesis after chronic ghrelin treatment in a rat myocardial infarction model

Ghrelin has a protective role in a rat model of myocardial infarction (MI), but the underlying mechanism is not clear. Here, we investigated the effects of ghrelin treatment on angiogenesis in an experimental rat MI model. Adult male Sprague-Dawley rats were subjected to MI by ligating the anterior descending coronary artery. The rats were then treated with a subcutaneous injection of ghrelin (100 μg/kg) or saline (control group) for 4 weeks. Sham animals underwent thoracotomy and pericardiotomy, but not LAD ligation. At 28 days after ligation, the ghrelin treatment group showed a higher density of α-SMA positive vessels than the saline treatment MI group in myocardial infarct (6±2.1/mm(2) vs 4±1.8/mm(2), P<0.05) and peri-infarct zones (25±9.5/mm(2) vs 15±5.7/mm(2), P<0.05). RT-PCR and western-blot analyses showed that ghrelin significantly increased vascular endothelial growth factor (VEGF) expression in the peri-infarct zone compared with the control group. Moreover, there was a two-fold increase of Bcl-2 and a 3.5-fold reduction of the Bax protein in the ghrelin-treated MI group compared to the saline treatment MI group. Taken together, ghrelin could induce angiogenesis in rats after MI, the process that may be associated with the enhancement of VEGF and an anti-apoptosis effect.

Ghrelin protects musculocutaneous tissue from ischemic necrosis by improving microvascular perfusion

Persistent ischemia in musculocutaneous tissue may lead to wound breakdown and necrosis. The objective of this experimental study was to analyze, whether the gastric peptide ghrelin prevents musculocutaneous tissue from necrosis and to elucidate underlying mechanisms. Thirty-two C57BL/6 mice equipped with a dorsal skinfold chamber containing ischemic musculocutaneous tissue were allocated to four groups: 1) ghrelin; 2) Nω-nitro-l-arginine methyl ester (l-NAME); 3) ghrelin and l-NAME; and 4) control. Microcirculation, inflammation, angiogenesis, and tissue survival were assessed by fluorescence microscopy. Inducible and endothelial nitric oxide synthase (iNOS I and eNOS), vascular endothelial growth factor (VEGF), as well as nuclear factor κB (NF-κB) were assessed by Western blot analysis. Ghrelin-treated animals showed an increased expression of iNOS and eNOS in critically perfused tissue compared with controls. This was associated with arteriolar dilation, increased arteriolar perfusion, and a sustained functional capillary density. Ghrelin further upregulated NF-κB and VEGF and induced angiogenesis. Finally, ghrelin reduced microvascular leukocyte-endothelial cell interactions, apoptosis, and overall tissue necrosis ( P < 0.05 vs. control). Inhibition of nitric oxide by l-NAME did not affect the anti-inflammatory and angiogenic action of ghrelin but completely blunted the ghrelin-induced tissue protection by abrogating the arteriolar dilation, the improved capillary perfusion, and the increased tissue survival. Ghrelin prevents critically perfused tissue from ischemic necrosis. Tissue protection is the result of a nitric oxide synthase-mediated improvement of the microcirculation but not due to induction of angiogenesis or attenuation of inflammation. This might represent a promising, noninvasive, and clinically applicable approach to protect musculocutaneous tissue from ischemia.

Ghrelin stimulates angiogenesis via GHSR1a-dependent MEK/ERK and PI3K/Akt signal pathways in rat cardiac microvascular endothelial cells

Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor (GHSR), is thought to exert a protective effect on the cardiovascular system, specifically by promoting vascular endothelial cell function such as cell proliferation, migration, survival and angiogenesis. However, the effect of ghrelin on angiogenesis and the corresponding mechanisms have not yet been extensively studied in cardiac microvascular endothelial cells (CMECs) isolated from left ventricular myocardium of adult Sprague-Dawley (SD) rats. In our study, we found that ghrelin and GHSR are constitutively expressed in CMECs. Ghrelin significantly increases CMECs proliferation, migration, and in vitro angiogenesis. The ghrelin-induced angiogenic process was accompanied by phosphorylation of ERK and Akt. MEK inhibitor PD98059 abolished ghrelin-induced phosphorylation of ERK, but had no effect on Akt phosphorylation. PI3K inhibitor LY294002 abolished ghrelin-induced phosphorylation of Akt, but had no effect on ERK phosphorylation. Ghrelin-induced angiogenesis was partially blocked by treatment with PD98059 or LY294002. In addition, this angiogenic effect was almost completely inhibited by PD98059+LY294002. Pretreatment with GHSR1a blocker [D-Lys3]-GHRP-6 abolished ghrelin-induced phosphorylation of ERK, Akt and in vitro angiogenesis. In conclusion, this is the first demonstration that ghrelin stimulates CMECs angiogenesis through GHSR1a-mediated MEK/ERK and PI3K/Akt signal pathways, indicating that two pathways are required for full angiogenic activity of ghrelin. This study suggests that ghrelin may play an important role in myocardial angiogenesis.

Ghrelin in the fetal pancreas - a digital quantitation study

Ghrelin is a hormone produced by specialized neuroendocrine cells located in the fetal pancreas. In the adult, ghrelin has multiple effects, but in the fetus the role of ghrelin and the distribution of ghrelin-producing cells is not well documented. The aim of this study was to describe and quantitate the number of ghrelin positive cells in the pancreas during gestation. The material consisted of pancreatic tissue from 19 fetuses at different gestational ages. Immunohistochemical staining was performed, and the expression was quantitated using an automated digital image analysis system. The results showed ghrelin-producing cells as scattered single cells in ductular structures and acini throughout the gestation. From midgestation they were also found in the periphery of the islets as a rim of cells. A tendency towards a high ghrelin expression during early gestation and a stable expression from midgestation to term was observed. In conclusion, the effects of fetal ghrelin are not fully understood, but the varying distribution of ghrelin positive cells indicates different effects of ghrelin during development.

Expression and possible immune-regulatory function of ghrelin in oral epithelium

Originally found in stomach mucosa, ghrelin is a peptide appetite hormone that has been implicated as an immuno-modulatory factor. Ghrelin has also been found in salivary glands and saliva; however, its expression patterns and biological properties in the oral cavity remain unclear. Therefore, we investigated the expression patterns of ghrelin in saliva, gingival crevicular fluid (GCF), and gingival tissue, as well as its in vitro effects on IL-8 production by TNF-α or LPS-stimulated oral epithelial cells. In the clinical samples obtained from 12 healthy volunteers, the concentration of ghrelin in GCF remarkably exceeded that detected in saliva. The expression of ghrelin mRNAs and growth hormone secretagogue (GHS) receptors could be detected in human oral epithelial cells. Immunohistochemical analysis revealed the expression of ghrelin in gingival epithelium, as well as in fibroblasts in the lamina propria. Ghrelin increased intracellular calcium mobilization and cAMP levels in oral epithelial cells, suggesting that ghrelin acts on epithelial cells to induce cell signaling. Furthermore, synthetic ghrelin inhibited the production of IL-8 from TNF-α or LPS-stimulated oral epithelial cells. These results indicate that ghrelin produced in the oral cavity appears to play a regulatory role in innate immune responses to inflammatory infection.

Ghrelin modulates physiologic and pathologic retinal angiogenesis through GHSR-1a

PURPOSE

Vascular degeneration and the ensuing abnormal vascular proliferation are central to proliferative retinopathies. Given the metabolic discordance associated with these diseases, the authors explored the role of ghrelin and its growth hormone secretagogue receptor 1a (GHSR-1a) in proliferative retinopathy.

METHODS

In a rat model of oxygen-induced retinopathy (OIR), the contribution of ghrelin and GHSR-1a was investigated using the stable ghrelin analogs [Dap3]-ghrelin and GHRP6 and the GSHR-1a antagonists JMV-2959 and [D-Lys3]-GHRP-6. Plasma and retinal levels of ghrelin were analyzed by ELISA, whereas retinal expression and localization of GHSR-1a were examined by immunohistochemistry and Western blot analysis. The angiogenic and vasoprotective properties of ghrelin and its receptor were further confirmed in aortic explants and in models of vaso-obliteration.

RESULTS

Ghrelin is produced locally in the retina, whereas GHSR-1a is abundantly expressed in retinal endothelial cells. Ghrelin levels decrease during the vaso-obliterative phase and rise during the proliferative phase of OIR. Intravitreal delivery of [Dap3]-ghrelin during OIR significantly reduces retinal vessel loss when administered during the hyperoxic phase. Conversely, during the neovascular phase, ghrelin promotes pathologic angiogenesis through the activation of GHSR-1a. These angiogenic effects were confirmed ex vivo in aortic explants.

CONCLUSIONS

New roles were disclosed for the ghrelin-GHSR-1a pathway in the preservation of retinal vasculature during the vaso-obliterative phase of OIR and during the angiogenic phase of OIR. These findings suggest that the ghrelin-GHSR-1a pathway can exert opposing effects on retinal vasculature, depending on the phase of retinopathy, and thus holds therapeutic potential for proliferative retinopathies.

Integrating GHS into the Ghrelin System

Oligopeptide derivatives of metenkephalin were found to stimulate growth-hormone (GH) release directly by pituitary somatotrope cells in vitro in 1977. Members of this class of peptides and nonpeptidyl mimetics are referred to as GH secretagogues (GHSs). A specific guanosine triphosphatate-binding protein-associated heptahelical transmembrane receptor for GHS was cloned in 1996. An endogenous ligand for the GHS receptor, acylghrelin, was identified in 1999. Expression of ghrelin and homonymous receptor occurs in the brain, pituitary gland, stomach, endothelium/vascular smooth muscle, pancreas, placenta, intestine, heart, bone, and other tissues. Principal actions of this peptidergic system include stimulation of GH release via combined hypothalamopituitary mechanisms, orexigenesis (appetitive enhancement), insulinostasis (inhibition of insulin secretion), cardiovascular effects (decreased mean arterial pressure and vasodilation), stimulation of gastric motility and acid secretion, adipogenesis with repression of fat oxidation, and antiapoptosis (antagonism of endothelial, neuronal, and cardiomyocyte death). The array of known and proposed interactions of ghrelin with key metabolic signals makes ghrelin and its receptor prime targets for drug development.

Ghrelin modulates insulin sensitivity and tau phosphorylation in high glucose-induced hippocampal neurons

Ghrelin, a 28-amino acid brain-gut peptide expressed in periphery tissues and the central nervous system, has been demonstrated to increase insulin sensitivity in adipocytes. Recent data have indicated that insulin resistance exists in the brain and is related to Alzheimer's Disease (AD). The aim of this study was to investigate whether ghrelin increased high glucose-induced hippocampal neuron insulin sensitivity, and further modulated tau phosphorylation. Hippocampal neurons were cultured in concentrations of 25 mM and 75 mM glucose. The effect of ghrelin on hippocampal neuronal insulin sensitivity was detected by [(3)H]-2-deoxy-D-glucose uptake. The expression of Akt, glycogen synthase kinase-3beta (GSK-3beta) and tau phosphorylation was determined via Western blotting. Culturation in 75 mM glucose resulted in decreased neuronal glucose uptake and an increase in the level of tau phosphorylation at Ser 199. In neurons treated with ghrelin for 1 h, neuronal glucose uptake was increased and tau hyperphosphorylation was improved. Ghrelin activated Akt and GSK-3beta phosphorylation, whereas phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin eliminated ghrelin's effect on neuronal glucose uptake and tau phosphorylation. This study demonstrated that ghrelin increased insulin-stimulated neuronal glucose uptake in 25 mM or 75 mM glucose, raised insulin sensitivity, improved insulin resistance and decreased tau abnormal phosphorylation via the PI3-K/Akt-GSK pathway. Ghrelin is a potential new medicine in the treatment of AD.

Low serum acylated ghrelin levels are associated with the development of cardiovascular disease in hemodialysis patients

BACKGROUND

Ghrelin has a protective effect on endothelial cells. Endothelial cell dysfunction is associated with cardiovascular disease (CVD) and CVD remains the leading cause of morbidity in hemodialysis (HD) patients. Acylated ghrelin (A-Ghr) is the functional form of ghrelin, so we hypothesized that A-Ghr is associated with the occurrence of CVD in HD patients.

METHODS

We conducted a prospective cohort study in 412 HD patients. The cohort was sub-grouped into low and high A-Ghr groups according to the median A-Ghr level of 4.88 pg/mL. The association between the low/high A-Ghr groups and the incidence of CVD were analyzed.

RESULTS

The HD patients in a low A-Ghr group had a greater risk of incidental CVD than those in a high A-Ghr ghrelin. This association remained significant after the adjustment for possible confounding factors, including age, gender, HD duration, BMI, diabetes, albumin, nPCR and Charlson's comorbidity index score.

CONCLUSION

It appears that a low serum A-Ghr level is associated with the development of CVD in HD patients.

A concerted kinase interplay identifies PPARgamma as a molecular target of ghrelin signaling in macrophages

The peroxisome proliferator-activator receptor PPARγ plays an essential role in vascular biology, modulating macrophage function and atherosclerosis progression. Recently, we have described the beneficial effect of combined activation of the ghrelin/GHS-R1a receptor and the scavenger receptor CD36 to induce macrophage cholesterol release through transcriptional activation of PPARγ. Although the interplay between CD36 and PPARγ in atherogenesis is well recognized, the contribution of the ghrelin receptor to regulate PPARγ remains unknown. Here, we demonstrate that ghrelin triggers PPARγ activation through a concerted signaling cascade involving Erk1/2 and Akt kinases, resulting in enhanced expression of downstream effectors LXRα and ABC sterol transporters in human macrophages. These effects were associated with enhanced PPARγ phosphorylation independently of the inhibitory conserved serine-84. Src tyrosine kinase Fyn was identified as being recruited to GHS-R1a in response to ghrelin, but failure of activated Fyn to enhance PPARγ Ser-84 specific phosphorylation relied on the concomitant recruitment of docking protein Dok-1, which prevented optimal activation of the Erk1/2 pathway. Also, substitution of Ser-84 preserved the ghrelin-induced PPARγ activity and responsiveness to Src inhibition, supporting a mechanism independent of Ser-84 in PPARγ response to ghrelin. Consistent with this, we found that ghrelin promoted the PI3-K/Akt pathway in a Gα_q-dependent manner, resulting in Akt recruitment to PPARγ, enhanced PPARγ phosphorylation and activation independently of Ser-84, and increased expression of LXRα and ABCA1/G1. Collectively, these results illustrate a complex interplay involving Fyn/Dok-1/Erk and Gα_q/PI3-K/Akt pathways to transduce in a concerted manner responsiveness of PPARγ to ghrelin in macrophages.

Obestatin as contractile mediator of excised frog heart

The aim of this study is to investigate the mechanism of positive inotropic effect of obestatin on in vitro heart preparations of Rana ridibunda frog. The application of increasing amounts of obestatin in the concentration range from 1 μmol/l to 1 μmol/l significantly enhances the force of contraction of excised and cannulated frog hearts. This effect was partially reduced in the presence of prazosin (3 μmol/l). Propranolol (30 μmol/l), pertussis toxin (2 ng/ml) and the specific inhibitor of cAMP-dependent protein kinase (PKA) Rp-adenosine 3′,5′-cyclic monophosphothioate triethylamine (30 μmol/l) completely blocked the obestatin-induced increase of the force of frog heart contractions. It is concluded that, via its receptor molecule, obestatin activates neuronal pertussis toxin sensitive G-protein(s) that further enhance the secretion of epinephrine from sympathetic neurons. This epinephrine activates mainly the myocardial β-adrenoreceptors and PKA downstream targets, and is responsible for the observed positive inotropic effect of obestatin. An alternative explanation of our data is that obestatin directly enhances the effect of myocardial β-adrenergic signaling.

The constitutive activity of the ghrelin receptor attenuates apoptosis via a protein kinase C-dependent pathway

The ghrelin receptor (GHS-R1a) displays a high level of constitutive signaling through a phospholipase C/protein kinase C-dependent pathway. Therefore, we have investigated the role of agonist-dependent and agonist-independent signaling of GHS-R1a in apoptosis using the seabream GHS-R1a stably expressed in human embryonic kidney 293 cells (HEK-sbGHS-R1a cells). Cadmium-induced activation of caspase-3 was significantly attenuated in HEK-sbGHS-R1a cells compared to wild-type HEK293 cells, while the apoptotic responses to the protein kinase C inhibitor staurosporine were similar. GHS-R1a ligands had no effect on caspase-3 activation or on cell proliferation. Concentrations of the inverse agonist [d-Arg(1),d-Phe(5),d-Trp(7,9),Leu(11)]-substance P sufficient to inhibit constitutive inositol phosphate generation did not enhance caspase-3 activity, suggesting a possible role of phosphatidylcholine-specific phospholipase C in the anti-apoptotic activity of GHS-R1a. In conclusion, our data suggests that the constitutive activity of sbGHS-R1a may be sufficient alone to attenuate apoptosis via a protein kinase C-dependent pathway.

Effects of weight loss after bariatric surgery for morbid obesity on vascular endothelial growth factor-A, adipocytokines, and insulin

BACKGROUND

Adipocytes regulate blood vessel formation, and in turn endothelial cells promote preadipocyte differentiation through the expression of proangiogenic factors, such as vascular endothelial growth factor (VEGF)-A. Some adipocytokines and hormones also have an effect on vascular development.

OBJECTIVES

Our objectives were to analyze the relationship between weight and circulating VEGF-A in morbidly obese subjects before and after bariatric surgery, and investigate the relationship between circulating VEGF-A and certain adipocytokines and hormones regulating adipocytes.

METHODS

A total of 45 morbidly obese women and nine lean females were included in the study. Patients underwent bariatric surgery: vertical banded gastroplasty (n=17), gastric bypass (n=17), and biliopancreatic diversion (n=11). Serum samples for VEGF-A, adiponectin, leptin, ghrelin, and insulin were obtained preoperatively and 9-12 months after surgery.

RESULTS

Obese patients showed significantly higher VEGF-A levels than controls (306.3+/-170.3 vs. 187.6+/-91.9 pg/ml; P=0.04), decreasing to 246.1+/-160.4 after surgery (P<0.001), with no differences among surgical procedures. In controls there was an inverse correlation between VEGF-A and ghrelin (r=-0.85; P<.01), but not in obese patients. Leptin and insulin concentrations were increased in obese patients, with a significant decrease shown after weight loss with surgery. Conversely, adiponectin concentrations were lower in obese patients, with a significant increase shown after weight loss with surgery. Ghrelin was higher in controls than obese patients, decreasing after gastric bypass and biliopancreatic diversion, but not after vertical banded gastroplasty.

CONCLUSION

Serum VEGF-A levels are significantly higher in obese patients than in lean controls, decreasing after weight loss with bariatric surgery, behaving similarly to other hormones related to adipose mass like leptin and insulin.

Ghrelin induces proliferation in human aortic endothelial cells via ERK1/2 and PI3K/Akt activation

The direct ghrelin (Ghr) involvement in cardiovascular (CV) system homeostasis has been suggested by the expression of its receptor in CV tissues and by evidence that ghrelin mediates CV activities in animals and in humans. Moreover, low Ghr plasma levels have been reported in pathological conditions characterized by high cardiovascular risk. In the present study, we investigated Ghr effect on proliferation of human aortic endothelial cell (HAEC) and involved transduction pathways. Our results indicate that ghrelin elicited proliferation in a dose-dependent manner (EC(50) about of 5nmol/L) in cultured HAEC, and that this effect was inhibited by the receptor antagonist (D-Lys3)-GHRP-6. Western blot experiments documented an activation of external receptor activated kinases (ERK1/2) and Akt in a dose-dependent fashion, as well as involvement of the cAMP pathway in ERK1/2 phosphorylation. Experiments conducted with appropriate pharmacological inhibitors to investigate Ghr-induced HAEC proliferation confirmed the involvement of ERK1/2 and I3P/Akt pathways, as well as the role of AMP cyclase/PKA pathway in ERK1/2 phosphorylation. Our results indicate that Ghr promotes HAEC proliferation, and thus may be a protective factor against vascular damage. The low ghrelin serum levels reported in insulin-resistant states may not be able to effectively counteract endothelial cell injury.

Elevated ghrelin levels in the peritoneal fluid of patients with endometriosis: associations with vascular endothelial growth factor (VEGF) and inflammatory cytokines

OBJECTIVE

To study ghrelin concentrations in the peritoneal fluid of women with endometriosis and of control women without pelvic pathology and its associations with the levels of proinflammatory cytokines and vascular endothelial growth factor (VEGF).

DESIGN

Case-control study.

SETTING

University research institution and hospital.

PATIENT(S)

Forty-six nonobese women with laparoscopically and histopathologically confirmed endometriosis and 20 control women without pelvic pathology.

INTERVENTION(S)

Peritoneal fluid was aspirated during routine diagnostic laparoscopic examination.

MAIN OUTCOME MEASURE(S)

Concentrations of ghrelin and inflammatory cytokines (interleukin [IL]-1 beta, IL-6, tumor necrosis factor [TNF], and VEGF) in the peritoneal fluid were evaluated by specific enzyme immunoassay and enzyme-linked immunosorbent assays, respectively.

RESULT(S)

Ghrelin concentrations in the peritoneal fluid of women with endometriosis were significantly increased as compared with control subjects. Peritoneal ghrelin levels in patients with endometriosis were strongly positively associated with VEGF (r(s) = 0.625). There was no correlation between ghrelin and IL-1 beta, IL-6, or TNF.

CONCLUSION(S)

The results of the present study show that endometriosis is associated with increased peritoneal ghrelin levels. The association between ghrelin and endometriotic lesion vascularization remains to be elucidated.

Genomic variation in myeloma: design, content, and initial application of the Bank On A Cure SNP Panel to detect associations with progression-free survival

BACKGROUND

We have engaged in an international program designated the Bank On A Cure, which has established DNA banks from multiple cooperative and institutional clinical trials, and a platform for examining the association of genetic variations with disease risk and outcomes in multiple myeloma. We describe the development and content of a novel custom SNP panel that contains 3404 SNPs in 983 genes, representing cellular functions and pathways that may influence disease severity at diagnosis, toxicity, progression or other treatment outcomes. A systematic search of national databases was used to identify non-synonymous coding SNPs and SNPs within transcriptional regulatory regions. To explore SNP associations with PFS we compared SNP profiles of short term (less than 1 year, n = 70) versus long term progression-free survivors (greater than 3 years, n = 73) in two phase III clinical trials.

RESULTS

Quality controls were established, demonstrating an accurate and robust screening panel for genetic variations, and some initial racial comparisons of allelic variation were done. A variety of analytical approaches, including machine learning tools for data mining and recursive partitioning analyses, demonstrated predictive value of the SNP panel in survival. While the entire SNP panel showed genotype predictive association with PFS, some SNP subsets were identified within drug response, cellular signaling and cell cycle genes.

CONCLUSION

A targeted gene approach was undertaken to develop an SNP panel that can test for associations with clinical outcomes in myeloma. The initial analysis provided some predictive power, demonstrating that genetic variations in the myeloma patient population may influence PFS.