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

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.

The ghrelin-GHSR-1a pathway inhibits high glucose-induced retinal angiogenesis in vitro by alleviating endoplasmic reticulum stress

Background

To investigate the effect of ghrelin, a brain-gut peptide hormone, on high glucose-induced retinal angiogenesis in vitro and explore its association with endoplasmic reticulum (ER) stress.

Methods

Human retinal microvascular endothelial cells (HRMECs) were first divided into control and high-glucose groups, and the mRNA and protein expression levels of the receptor for ghrelin [growth hormone secretin receptor 1a, (GHSR-1a)] in cells were determined. HRMECs were then treated with high glucose alone or in combination with ghrelin or siGHSR-1a, and cell viability, migration, tube formation and the expression of the ER stress-related proteins PERK, ATF4 and CHOP were detected. Finally, to clarify whether the effects of ghrelin are related to ER stress, tunicamycin, an inducer of ER stress, was used to treat HRMECs, and cell viability, cell migration, and tube formation were evaluated.

Results

GHSR-1a expression in HRMECs at both the mRNA and protein levels was inhibited by high-glucose treatment. Under high-glucose conditions, ghrelin promoted cell viability and inhibited migration and tube formation, which were blocked by siGHSR-1a treatment. Ghrelin inhibited the increases in the protein levels of p-PERK, ATF4 and CHOP induced by high-glucose treatment, and combination treatment with siGHSR-1a reversed this effect of ghrelin. When tunicamycin was added, the effects of ghrelin on cell viability, migration and tube formation were all weakened.

Conclusions

This study experimentally revealed that ghrelin can inhibit high glucose-induced retinal angiogenesis in vitro through GHSR-1a, and alleviation of ER stress may be one of the mechanisms underlying this effect.

Effect of Ghrelin on the Cardiovascular System

Simple Summary

Ghrelin is an octanoylated peptide that was initially isolated from rat and human stomachs in the process of searching for an endogenous ligand to the orphan growth hormone secretagogue receptor (GHS-R), a G-protein-coupled receptor. Exogenous or endogenous ghrelin secreted from the stomach binds to GHS-R on gastric vagal nerve terminals, and the signals are transmitted to the central nervous system via the vagal afferent nerve to facilitate growth hormone (GH) secretion, feeding, sympathetic inhibition, parasympathetic activation, and anabolic effects. Ghrelin also binds directly to the pituitary GHS-R and stimulates GH secretion. Ghrelin has beneficial effects on the cardiovascular system, including cardioprotective effects such as anti-heart failure, anti-arrhythmic, and anti-inflammatory actions, and it enhances vascular activity via GHS-R-dependent stimulation of GH/IGF-1 (insulin-like growth factor-1) and modulation of the autonomic nervous system. The anti-heart failure effects of ghrelin could be useful as a new therapeutic strategy for chronic heart failure.

Abstract

Ghrelin, an n-octanoyl-modified 28-amino-acid-peptide, was first discovered in the human and rat stomach as an endogenous ligand for the growth hormone secretagogue receptor (GHS-R). Ghrelin-GHS-R1a signaling regulates feeding behavior and energy balance, promotes vascular activity and angiogenesis, improves arrhythmia and heart failure, and also protects against cardiovascular disease by suppressing cardiac remodeling after myocardial infarction. Ghrelin’s cardiovascular protective effects are mediated by the suppression of sympathetic activity; activation of parasympathetic activity; alleviation of vascular endothelial dysfunction; and regulation of inflammation, apoptosis, and autophagy. The physiological functions of ghrelin should be clarified to determine its pharmacological potential as a cardiovascular medication.

Perivascular Adipose Tissue Inflammation: The Anti-Inflammatory Role of Ghrelin in Atherosclerosis Progression

Perivascular adipose tissue (PVAT) and its adipokines engage in bidirectional crosstalk with the vascular wall. Atherosclerosis disrupts this interaction through inflammation, rupture-prone plaques, and subsequent thrombosis. The cardioprotective effects of ghrelin are in contradiction to its adipogenic properties. The concurrent research of anti-/pro-atherogenic mechanisms of ghrelin and PVAT-derived adipokines provides a better understanding of atherosclerosis progression in metabolic disorders. In-depth coverage of the characteristic features of PVAT concerning vascular dysfunction, with a survey of ghrelin-induced anti-inflammatory effects on adipose tissue macrophage infiltration and the inhibitory activity of ghrelin on the proinflammatory adipokine secretion, show that the impact of ghrelin on the endothelial function should be studied in relation to PVAT.

FGF/FGFR-Dependent Molecular Mechanisms Underlying Anti-Cancer Drug Resistance

Simple Summary

Deregulation of the FGF/FGFR axis is associated with many types of cancer and contributes to the development of chemoresistance, limiting the effectiveness of current treatment strategies. There are several mechanisms involved in this phenomenon, including cross-talks with other signaling pathways, avoidance of apoptosis, stimulation of angiogenesis, and initiation of EMT. Here, we provide an overview of current research and approaches focusing on targeting components of the FGFR/FGF signaling module to overcome drug resistance during anti-cancer therapy.

Abstract

Increased expression of both FGF proteins and their receptors observed in many cancers is often associated with the development of chemoresistance, limiting the effectiveness of currently used anti-cancer therapies. Malfunctioning of the FGF/FGFR axis in cancer cells generates a number of molecular mechanisms that may affect the sensitivity of tumors to the applied drugs. Of key importance is the deregulation of cell signaling, which can lead to increased cell proliferation, survival, and motility, and ultimately to malignancy. Signaling pathways activated by FGFRs inhibit apoptosis, reducing the cytotoxic effect of some anti-cancer drugs. FGFRs-dependent signaling may also initiate angiogenesis and EMT, which facilitates metastasis and also correlates with drug resistance. Therefore, treatment strategies based on FGF/FGFR inhibition (using receptor inhibitors, ligand traps, monoclonal antibodies, or microRNAs) appear to be extremely promising. However, this approach may lead to further development of resistance through acquisition of specific mutations, metabolism switching, and molecular cross-talks. This review brings together information on the mechanisms underlying the involvement of the FGF/FGFR axis in the generation of drug resistance in cancer and highlights the need for further research to overcome this serious problem with novel therapeutic strategies.

Cyclooxygenase inhibition attenuates brain angiogenesis and independently decreases mouse survival under hypoxia

Although cyclooxygenase (COX) role in cancer angiogenesis has been studied, little is known about its role in brain angioplasticity. In the present study, we chronically infused mice with ketorolac, a non‐specific COX inhibitor that does not cross the blood–brain barrier (BBB), under normoxia or 50% isobaric hypoxia (10% O₂ by volume). Ketorolac increased mortality rate under hypoxia in a dose‐dependent manner. Using in vivo multiphoton microscopy, we demonstrated that chronic COX inhibition completely attenuated brain angiogenic response to hypoxia. Alterations in a number of angiogenic factors that were reported to be COX‐dependent in other models were assayed at 24‐hr and 10‐day hypoxia. Intriguingly, hypoxia‐inducible factor 1 was unaffected under COX inhibition, and vascular endothelial growth factor receptor type 2 (VEGFR2) and C‐X‐C chemokine receptor type 4 (CXCR4) were significantly but slightly decreased. However, a number of mitogen‐activated protein kinases (MAPKs) were significantly reduced upon COX inhibition. We conclude that additional, angiogenic factor‐independent mechanism might contribute to COX role in brain angioplasticity, probably including mitogenic COX effect on endothelium. Our data indicate that COX activity is critical for systemic adaptation to chronic hypoxia, and BBB COX is essential for hypoxia‐induced brain angioplasticity. These data also indicate a potential risk for using COX inhibitors under hypoxia conditions in clinics. Further studies are required to elucidate a complete mechanism for brain long‐term angiogenesis regulation through COX activity.

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.

Temporospatial effects of acyl-ghrelin on activation of astrocytes after ischaemic brain injury

The protective mechanisms of astrocyte signalling are based on the release of neurotrophic factors and the clearing of toxic substances in the early stages of cerebral ischaemia. However, astrocytes are also responsible for the detrimental effects that occur during the later stages of ischaemia, in which glial scars are formed, thereby impeding neural recovery. Acyl-ghrelin has been found to be neuroprotective after stroke, although the influence of acyl-ghrelin on astrocytes after ischaemic injury is yet to be clarified. In the present study, we used permanent middle cerebral arterial occlusion to establish a brain ischaemia model in vivo, as well as oxygen and glucose deprivation (OGD) to mimic ischaemic insults in vitro. We found that acyl-ghrelin injection significantly increased the number of activated astrocytes in the peri-infarct area at day 3 after brain ischaemia and decreased the number of activated astrocytes after day 9. Moreover, the expression of fibroblast growth factor 2 (FGF2) in the ischaemic hemisphere increased markedly after day 3, and i.c.v. injection of SU5402, an inhibitor of FGF2 signalling, abolished the suppression effects of acyl-ghrelin on astrocyte activation in the peri-infarct region during the later stages of ischaemia. The results from in vitro studies also showed the dual effect of acyl-ghrelin on astrocyte viability. Acyl-ghrelin increased the viability of uninjured astrocytes in an indirect way by stimulating the secretion from OGD-injured astrocytes. It also inhibited the astrocyte viability in the presence of FGF2 in a dose-dependent manner. Furthermore, the expression of acyl-ghrelin receptors on astrocytes was increased after acyl-ghrelin and FGF2 co-treatment. In conclusion, acyl-ghrelin promoted astrocyte activation in the early stages of ischaemia but suppressed the activation in later stages of ischaemic injury. These later effects were likely to be triggered by the increased expression of endogenous FGF2 after brain ischaemia.

Identification of the S100 fused-type protein hornerin as a regulator of tumor vascularity

Sustained angiogenesis is essential for the development of solid tumors and metastatic disease. Disruption of signaling pathways that govern tumor vascularity provide a potential avenue to thwart cancer progression. Through phage display-based functional proteomics, immunohistochemical analysis of human pancreatic ductal carcinoma (PDAC) specimens, and in vitro validation, we reveal that hornerin, an S100 fused-type protein, is highly expressed on pancreatic tumor endothelium in a vascular endothelial growth factor (VEGF)-independent manner. Murine-specific hornerin knockdown in PDAC xenografts results in tumor vessels with decreased radii and tortuosity. Hornerin knockdown tumors have significantly reduced leakiness, increased oxygenation, and greater apoptosis. Additionally, these tumors show a significant reduction in growth, a response that is further heightened when therapeutic inhibition of VEGF receptor 2 (VEGFR2) is utilized in combination with hornerin knockdown. These results indicate that hornerin is highly expressed in pancreatic tumor endothelium and alters tumor vessel parameters through a VEGF-independent mechanism.Angiogenesis is essential for solid tumor progression. Here, the authors interrogate the proteome of pancreatic cancer endothelium via phage display and identify hornerin as a critical protein whose expression is essential to maintain the pancreatic cancer vasculature through a VEGF-independent mechanism.

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.

Exploration of Serum Proteomic Profiling and Diagnostic Model That Differentiate Crohn's Disease and Intestinal Tuberculosis

AIM

To explore the diagnostic models of Crohn's disease (CD), Intestinal tuberculosis (ITB) and the differential diagnostic model between CD and ITB by analyzing serum proteome profiles.

METHODS

Serum proteome profiles from 30 CD patients, 21 ITB patients and 30 healthy controls (HCs) were analyzed by using weak cationic magnetic beads combined with MALDI-TOF-MS technique to detect the differentially expressed proteins of serum samples. Three groups were made and compared accordingly: group of CD patients and HCs, group of ITB patients and HCs, group of CD patients and ITB patients. Wilcoxon rank sum test was used to screen the ten most differentiated protein peaks (P < 0.05). Genetic algorithm combining with support vector machine (SVM) was utilized to establish the optimal diagnostic models for CD, ITB and the optimal differential diagnostic model between CD and ITB. The predictive effects of these models were evaluated by Leave one out (LOO) cross validation method.

RESULTS

There were 236 protein peaks differently expressed between group of CD patients and HCs, 305 protein peaks differently expressed between group of ITB patients and HCs, 332 protein peaks differently expressed between group of CD patients and ITB patients. Ten most differentially expressed peaks were screened out between three groups respectively (P < 0.05) to establish diagnostic models and differential diagnostic model. A diagnostic model comprising of four protein peaks (M/Z 4964, 3029, 2833, 2900) can well distinguish CD patients and HCs, with a specificity and sensitivity of 96.7% and 96.7% respectively. A diagnostic model comprising four protein peaks (M/Z 3030, 2105, 2545, 4210) can well distinguish ITB patients and HCs, with a specificity and sensitivity of 93.3% and 95.2% respectively. A differential diagnostic model comprising three potential biomarkers protein peaks (M/Z 4267, 4223, 1541) can well distinguish CD patients and ITB patients, with a specificity and sensitivity of 76.2% and 80.0% respectively. Among the eleven protein peaks from the diagnostic models and differential diagnostic model, two have been successfully purified and identified, Those two peaks were M/Z 2900 from the diagnostic model between CD and HCs and M/Z 1541 from the differential diagnostic model between CD and ITB. M/Z 2900 was identified as appetite peptide, M/Z 1541 was identified as Lysyl oxidase-like 2 (LOXL-2).

CONCLUSION

The differently expressed protein peaks analyzed by serum proteome with weak cationic magnetic beads combined MALDI-TOF-MS technique can effectively distinguish CD patients and HCs, ITB patients and HCs, CD patients and ITB patients. The diagnostic model between CD patients and HCs consisting of four protein peaks (M/Z 4964, 3029, 2833, 2900), the diagnostic model between ITB patients and HCs comprising four protein peaks (M/Z 3030, 2105, 2545, 4210) and the differential diagnostic model between CD patients and ITB patients comprising three protein peaks (M/Z 4267, 4223, 1541) had high specificity and sensitivity and can contribute to diagnoses of CD, ITB and the differential diagnosis between CD and ITB. Two proteins from the diagnostic model of CD and the differential diagnostic model between CD and ITB were identified. Further experiments are required using a larger cohort of samples.

Effects of sleeve gastrectomy and rs9930506 FTO variants on angiopoietin/Tie-2 system in fat expansion and M1 macrophages recruitment in morbidly obese subjects

Angiogenesis in inflammation are hallmarks for adipose tissue expansion in obesity. The role of angiopoietin/Tie-2 system in adipose tissue expansion and immune cell recruitment is unclear. We studied the effect of sleeve gastrectomy and the influence of FTO rs9930506 polymorphism on Tie-2, angiopoietin-1 and angiopoietin-2 expression in morbid obesity. Fifteen morbidly obese subjects (4 men and 11 women) aged 24-55 years were followed-up 3 and 6 months after sleeve gastrectomy. Serum sTie-2, angiopoietin-1, angiopoietin-2, and hypoxia-inducible factor-1α concentrations were determined by ELISA. Tie-2 and its ligands in visceral and subcutaneous adipose tissue were localized by immunohistochemistry. Tie-2 expression was measured by flow cytometry in circulating monocytes and infiltrated macrophages. Comparisons before and after sleeve gastrectomy were carried out using ANOVA for repeated measures. rs9930506FTO genotyping was performed by PCR-RFLP. Circulating sTie-2 and angiopoietin-2 were higher before sleeve gastrectomy. Tie-2 and angiopoietin-2 mRNA levels were higher in subcutaneous adipose tissue than visceral and both decreased after surgery. Monocytes and infiltrated macrophages showed a pro-inflammatory phenotype, with increased Tie-2 expression that decreased 3 and 6 months after sleeve gastrectomy. Baseline sTie-2 correlated inversely with adiponectin levels. At baseline the rs9930506FTO AG ó GG genotypes carriers had more 34 kg than genotype carriers of rs9930506 AA. Weight and body mass index decreased at 6 months. We found that angiopoietin/Tie-2 system is mainly expressed in subcutaneous adipose tissue, contributing to expandability, fat accumulation, and monocytes attachment in obesity. Bariatric surgery favorably modifies the pro-angiogenic profile, allowed a reduced angiogenic expression in the circulation and adipose tissue.

Increased ghrelin signaling prolongs survival in mouse models of human aging through activation of sirtuin1

Caloric restriction (CR) is known to retard aging and delay functional decline as well as the onset of diseases in most organisms. Ghrelin is secreted from the stomach in response to CR and regulates energy metabolism. We hypothesized that in CR ghrelin has a role in protecting aging-related diseases. We examined the physiological mechanisms underlying the ghrelin system during the aging process in three mouse strains with different genetic and biochemical backgrounds as animal models of accelerated or normal human aging. The elevated plasma ghrelin concentration was observed in both klotho-deficient and senescence-accelerated mouse prone/8 (SAMP8) mice. Ghrelin treatment failed to stimulate appetite and prolong survival in klotho-deficient mice, suggesting the existence of ghrelin resistance in the process of aging. However, ghrelin antagonist hastened death and ghrelin signaling potentiators rikkunshito and atractylodin ameliorated several age-related diseases with decreased microglial activation in the brain and prolonged survival in klotho-deficient, SAMP8 and aged ICR mice. In vitro experiments, the elevated sirtuin1 (SIRT1) activity and protein expression through the cAMP-CREB pathway was observed after ghrelin and ghrelin potentiator treatment in ghrelin receptor 1a-expressing cells and human umbilical vein endothelial cells. Furthermore, rikkunshito increased hypothalamic SIRT1 activity and SIRT1 protein expression of the heart in the all three mouse models of aging. Pericarditis, myocardial calcification and atrophy of myocardial and muscle fiber were improved by treatment with rikkunshito. Ghrelin signaling may represent one of the mechanisms activated by CR, and potentiating ghrelin signaling may be useful to extend health and lifespan.

Exogenous Ghrelin Accelerates the Healing of Acetic Acid-Induced Colitis in Rats

Previous studies have shown that ghrelin reduces colonic inflammation induced by trinitrobenzene sulfonic acid and dextran sodium sulfate. In the present study we determined the effect of treatment with ghrelin on the course of acetic acid-induced colitis in rats. Rectal administration of 3% acetic acid solution led to induction of colitis in all animals. Damage of the colonic wall was accompanied by an increase in mucosal concentration of pro-inflammatory interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), as well mucosal activity of myeloperoxidase. Moreover, induction of colitis led to a reduction in colonic blood flow and DNA synthesis. Administration of ghrelin after induction of colitis led to faster regeneration of the colonic wall and reduction in colonic levels of IL-1β, TNF-α, and myeloperoxidase. In addition, treatment with ghrelin improved mucosal DNA synthesis and blood flow. Our study disclosed that ghrelin exhibits a strong anti-inflammatory and healing effect in acetic acid-induced colitis. Our current observation in association with previous findings that ghrelin exhibits curative effect in trinitrobenzene sulfonic acid- and dextran sodium sulfate-induced colitis suggest that therapeutic effect of ghrelin in the colon is universal and independent of the primary cause of colitis.

The Anti-apoptotic Effect of Ghrelin on Restraint Stress-Induced Thymus Atrophy in Mice

Thymic atrophy is a complication that results from exposure to many environmental stressors, disease treatments, and microbial challenges. Such acute stress-associated thymic loss can have a dramatic impact on the host's ability to replenish the necessary naïve T cell output to reconstitute the peripheral T cell numbers and repertoire to respond to new antigenic challenges. We have previously reported that treatment with the orexigenic hormone ghrelin results in an increase in the number and proliferation of thymocytes after dexamethasone challenge, suggesting a role for ghrelin in restraint stress-induced thymic involution and cell apoptosis and its potential use as a thymostimulatory agent. In an effort to understand how ghrelin suppresses thymic T cell apoptosis, we have examined the various signaling pathways induced by receptor-specific ghrelin stimulation using a restraint stress mouse model. In this model, stress-induced apoptosis in thymocytes was effectively blocked by ghrelin. Western blot analysis demonstrated that ghrelin prevents the cleavage of pro-apoptotic proteins such as Bim, Caspase-3, and PARP. In addition, ghrelin stimulation activates the Akt and Mitogen-activated protein kinases (MAPK) signaling pathways in a time/dose-dependent manner. Moreover, we also revealed the involvement of the FoxO3a pathway in the phosphorylation of Akt and ERK1/2. Together, these findings suggest that ghrelin inhibits apoptosis by modulating the stress-induced apoptotic signal pathway in the restraint-induced thymic apoptosis.

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.

Ghrelin-related peptides exert protective effects in the cerebral circulation of male mice through a nonclassical ghrelin receptor(s)

The ghrelin-related peptides, acylated ghrelin, des-acylated ghrelin, and obestatin, are novel gastrointestinal hormones. We firstly investigated whether the ghrelin gene, ghrelin O-acyltransferase, and the ghrelin receptor (GH secretagogue receptor 1a [GHSR1a]) are expressed in mouse cerebral arteries. Secondly, we assessed the cerebrovascular actions of ghrelin-related peptides by examining their effects on vasodilator nitric oxide (NO) and superoxide production. Using RT-PCR, we found the ghrelin gene and ghrelin O-acyltransferase to be expressed at negligible levels in cerebral arteries from male wild-type mice. mRNA expression of GHSR1a was also found to be low in cerebral arteries, and GHSR protein was undetectable in GHSR-enhanced green fluorescent protein mice. We next found that exogenous acylated ghrelin had no effect on the tone of perfused cerebral arteries or superoxide production. By contrast, exogenous des-acylated ghrelin or obestatin elicited powerful vasodilator responses (EC50 < 10 pmol/L) that were abolished by the NO synthase inhibitor N(ω)-nitro-L-arginine methyl ester. Furthermore, exogenous des-acylated ghrelin suppressed superoxide production in cerebral arteries. Consistent with our GHSR expression data, vasodilator effects of des-acylated ghrelin or obestatin were sustained in the presence of YIL-781 (GHSR1a antagonist) and in arteries from Ghsr-deficient mice. Using ghrelin-deficient (Ghrl(-/-)) mice, we also found that endogenous production of ghrelin-related peptides regulates NO bioactivity and superoxide levels in the cerebral circulation. Specifically, we show that NO bioactivity was markedly reduced in Ghrl(-/-) vs wild-type mice, and superoxide levels were elevated. These findings reveal protective actions of exogenous and endogenous ghrelin-related peptides in the cerebral circulation and show the existence of a novel ghrelin receptor(s) in the cerebral endothelium.

Molecular evolution of GPCRs: Ghrelin/ghrelin receptors

After the discovery in 1996 of the GH secretagogue-receptor type-1a (GHS-R1a) as an orphan G-protein coupled receptor, many research groups attempted to identify the endogenous ligand. Finally, Kojima and colleagues successfully isolated the peptide ligand from rat stomach extracts, determined its structure, and named it ghrelin. The GHS-R1a is now accepted to be the ghrelin receptor. The existence of the ghrelin system has been demonstrated in many animal classes through biochemical and molecular biological strategies as well as through genome projects. Our work, focused on identifying the ghrelin receptor and its ligand ghrelin in laboratory animals, particularly nonmammalian vertebrates, has provided new insights into the molecular evolution of the ghrelin receptor. In mammals, it is assumed that the ghrelin receptor evolution is in line with the plate tectonics theory. In contrast, the evolution of the ghrelin receptor in nonmammalian vertebrates differs from that of mammals: multiplicity of the ghrelin receptor isoforms is observed in nonmammalian vertebrates only. This multiplicity is due to genome duplication and polyploidization events that particularly occurred in Teleostei. Furthermore, it is likely that the evolution of the ghrelin receptor is distinct from that of its ligand, ghrelin, because only one ghrelin isoform has been detected in all species examined so far. In this review, we summarize current knowledge related to the molecular evolution of the ghrelin receptor in mammalian and nonmammalian vertebrates.

Ghrelin at the interface of obesity and reward

The prevalence of obesity continues to increase and has reached epidemic proportions. Accumulating data over the past few decades have given us key insights and broadened our understanding of the peripheral and central regulation of energy homeostasis. Despite this, the currently available pharmacological treatments, reducing body weight, remain limited due to poor efficacy and side effects. The gastric peptide ghrelin has been identified as the only orexigenic hormone from the periphery to act in the hypothalamus to stimulate food intake. Recently, a role for ghrelin and its receptor at the interface between homeostatic control of appetite and reward circuitries modulating the hedonic aspects of food has also emerged. Nonhomeostatic factors such as the rewarding and motivational value of food, which increase with food palatability and caloric content, can override homeostatic control of food intake. This nonhomeostatic decision to eat leads to overconsumption beyond nutritional needs and is being recognized as a key component in the underlying causes for the increase in obesity incidence worldwide. In addition, the hedonic feeding behavior has been linked to food addiction and an important role for ghrelin in the development of addiction has been suggested. Moreover, plasma ghrelin levels are responsive to conditions of stress, and recent evidence has implicated ghrelin in stress-induced food-reward behavior. The prominent role of the ghrelinergic system in the regulation of feeding gives rise to it as an effective target for the development of successful antiobesity pharmacotherapies that not only affect satiety but also selectively modulate the rewarding properties of food and reduce the desire to eat.

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 could be a candidate for the prevention of in-stent restenosis

Percutaneous coronary intervention is a revolutionary treatment for ischemic heart disease, but in-stent restenosis (ISR) remains a clinical challenge. Inflammation, smooth muscle proliferation, endothelial function impairment, and local thrombosis have been identified as the main mechanisms for ISR. Considering the multifactorial mechanisms of ISR, a novel therapeutic agent with multiple bioactivities is required. Ghrelin is a novel gut-brain peptide predominantly produced by the stomach, and has been shown to play a role in various cardiovascular activities, such as increasing myocardial contractility, improving cardiac output, and inhibiting ventricular remodeling, as well as attenuating cardiac ischemia-reperfusion injury. Recent studies have demonstrated that ghrelin effectively inhibits vascular inflammation and vascular smooth muscle cell proliferation, repairs endothelial cells, promotes vascular endothelial function, inhibits platelet aggregation, and exerts antithrombotic effects. These findings suggest that ghrelin may be an innovative therapeutic candidate for the prevention and treatment of ISR.

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.

Ghrelin and adipokines as circulating markers of disease activity in patients with Takayasu arteritis

Introduction

The current markers of disease activity in Takayasu arteritis (TA) are insufficient for proper assessment. We investigated circulating levels of unacylated and acylated ghrelin, leptin and adiponectin and their relationships with disease activity in patients with TA.

Methods

This study included 31 patients with TA and 32 sex-, age- and body mass index-matched healthy controls. Disease activity was assessed in TA patients using various tools, including Kerr's criteria, disease extent index-Takayasu, physician's global assessment, radiological parameters, and laboratory markers. Plasma unacylated and acylated ghrelin, and serum leptin and adiponectin levels were measured using an enzyme-linked immunosorbent assay.

Results

Unacylated and acylated ghrelin levels were found to be significantly lower in TA patients than that in healthy controls. Patients with active disease had lower unacylated ghrelin levels than those with inactive disease and had lower acylated ghrelin levels than healthy controls. Ghrelin levels were negatively correlated with various parameters of disease activity. The leptin/ghrelin ratio was significantly higher in TA patients than controls. It was positively correlated with disease activity. There was a positive correlation between unacylated and acylated ghrelin and a negative correlation between leptin and ghrelin. There was no statistical difference in adiponectin levels between TA patients and controls. The radiological activity markers were positively correlated with other parameters of disease activity.

Conclusions

This study suggests that plasma unacylated and acylated ghrelin levels may be useful in monitoring disease activity and planning treatment strategies for patients with TA. The serum leptin level and leptin/ghrelin ratio may also be used to help assess the disease activity.

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 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 inhibits AGEs-induced apoptosis in human endothelial cells involving ERK1/2 and PI3K/Akt pathways

Endothelial dysfunction caused by cell apoptosis is thought to be a major cause of diabetic vascular complications. Advanced glycation end products (AGEs) play an important role in the pathogenesis of diabetic vascular complications by inducing apoptosis of endothelial cells. The aim of this study was to explore the effect of ghrelin on AGEs-induced apoptosis in cultured human umbilical vein endothelial cells (HUVECs) and the potential mechanisms involved in this process. Exposure to AGEs (200 mg l(-1) ) for 48 h caused a significant increase in cell apoptosis, while pretreatment with ghrelin eliminated AGEs-induced apoptosis in HUVECs, as evaluated by MTT assays, flow cytometry and Hoechst 33258 staining. The induction of caspase-3 activation was also prevented by ghrelin in cells incubated with AGEs. Exposure to ghrelin (10(-6)  M) resulted in a rapid activation of extracellular signal-regulated protein kinase (ERK)1/2 and Akt. The inhibitory effect of ghrelin on caspase-3 activity was attenuated by inhibitors of ERK1/2 (PD98059), PI3K/Akt (LY294002) and growth hormone secretagogue receptor (GHSR)-1a (D-Lys(3) -growth hormone releasing peptide-6). The results of this study indicated that ghrelin could inhibit AGEs-mediated cell apoptosis via the ERK1/2 and PI3K/Akt pathways and GHSR-1a was also involved in the protective action of ghrelin in HUVECs. As such, ghrelin demonstrates significant potential for preventing diabetic cardiovascular complications.

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.

The Chick Embryo Chorioallantoic Membrane as an In Vivo Assay to Study Antiangiogenesis

Antiangiogenesis, e.g., inhibition of blood vessel growth, is being investigated as a way to prevent the growth of tumors and other angiogenesis-dependent diseases. Pharmacological inhibition interferes with the angiogenic cascade or the immature neovasculature with synthetic or semi-synthetic substances, endogenous inhibitors or biological antagonists.The chick embryo chorioallantoic membrane (CAM) is an extraembryonic membrane, which serves as a gas exchange surface and its function is supported by a dense capillary network. Because its extensive vascularization and easy accessibility, CAM has been used to study morphofunctional aspects of the angiogenesis process in vivo and to study the efficacy and mechanism of action of pro- and anti-angiogenic molecules. The fields of application of CAM in the study of antiangiogenesis, including our personal experience, are illustrated in this review article.

Lean mean fat reducing "ghrelin" machine: hypothalamic ghrelin and ghrelin receptors as therapeutic targets in obesity

Obesity has reached epidemic proportions not only in Western societies but also in the developing world. Current pharmacological treatments for obesity are either lacking in efficacy and/or are burdened with adverse side effects. Thus, novel strategies are required. A better understanding of the intricate molecular pathways controlling energy homeostasis may lead to novel therapeutic intervention. The circulating hormone, ghrelin represents a major target in the molecular signalling regulating food intake, appetite and energy expenditure and its circulating levels often display aberrant signalling in obesity. Ghrelin exerts its central orexigenic action mainly in the hypothalamus and in particular in the arcuate nucleus via activation of specific G-protein coupled receptors (GHS-R). In this review we describe current pharmacological models of how ghrelin regulates food intake and how manipulating ghrelin signalling may give novel insight into developing better and more selective anti-obesity drugs. Accumulating data suggests multiple ghrelin variants and additional receptors exist to play a role in energy metabolism and these may well play an important role in obesity. In addition, the recent findings of hypothalamic GHS-R crosstalk and heterodimerization may add to the understanding of the complexity of bodyweight regulation.

Ghrelin and obestatin: different role in fetal lung development?

Ghrelin and obestatin are two proteins that originate from post-translational processing of the preproghrelin peptide. Various authors claim an opposed role of ghrelin and obestatin in several systems. Preproghrelin mRNA is significantly expressed in airway epithelium throughout lung development, predominantly during the earliest stages. The aim of this study was to evaluate the role of ghrelin and obestatin in fetal lung development in vitro. Immunohistochemistry studies were performed at different gestational ages in order to clarify the expression pattern of ghrelin, GHS-R1a, obestatin and GPR39 during fetal lung development. Fetal rat lung explants were harvested at 13.5 days post-conception (dpc) and cultured during 4 days with increasing doses of total ghrelin, acylated ghrelin, desacyl-ghrelin, ghrelin antagonist (D-Lys(3)-GHRP-6) or obestatin. Immunohistochemistry studies demonstrated that ghrelin, GHS-R1a, obestatin and GPR39 proteins were expressed in primitive rat lung epithelium throughout all studied gestational ages. Total and acylated ghrelin supplementation significantly increased the total number of peripheral airway buds, whereas desacyl-ghrelin induced no effect. Moreover, GHS-R1a antagonist significantly decreased lung branching. Finally, obestatin supplementation induced no significant effect in the measured parameters. The present study showed that ghrelin has a positive effect in fetal lung development through its GHS-R1a receptor, whereas obestatin has no effect on lung branching.

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.

Ghrelin, des-acyl ghrelin and obestatin: three pieces of the same puzzle

The major active product of ghrelin gene is a 28-amino acid peptide acylated at the serine 3 position with an octanoyl group, called simply ghrelin. Ghrelin has a multiplicity of physiological functions, affecting GH release, food intake, energy and glucose homeostasis, gastrointestinal, cardiovascular, pulmonary and immune function, cell proliferation and differentiation and bone physiology. Nevertheless, recent developments have shown that ghrelin gene can generate various bioactive molecules besides ghrelin, mainly des-acyl ghrelin and obestatin, obtained from alternative splicing or from extensive post-translational modification. Although their receptors have not yet been identified, they have already proven to be active, having intriguingly subtle but opposite physiological actions to ghrelin. This suggests the existence of a novel endocrine system with multiple effector elements which not only may have opposite actions but may regulate the action of each other. In this review, we summarize the steps which lead to the production of the different ghrelin gene products and examine the most significant differences between them in terms of structure and actions.

Ghrelin in vitro modulates vasoactive factors in human umbilical vein endothelial cells

OBJECTIVE

To determine whether Ghrelin could affect prostaglandins (PGs) and nitric oxide synthesis in human umbilical vein endothelial cells (HUVEC). The effect of Ghrelin on endothelial cell proliferation was also evaluated.

DESIGN

In vitro research report.

SETTING

Third-level referral academic centers, including molecular and cellular biology laboratories.

PATIENT(S)

Human umbilical cords were obtained from healthy female volunteers at term of uncomplicated pregnancies.

INTERVENTION(S)

HUVEC were cultured with Ghrelin (from 10(-11) to 10(-7) M). After 24 hours supernatants were collected and HUVEC were treated for total RNA extraction.

MAIN OUTCOME MEASURE(S)

In the culture medium PGs release was evaluated by RIA. Prostaglandin-endoperoxide synthase 2 (COX2) and both the constitutive and the inducible isoforms of nitric oxide synthases (ECNOS and INOS) mRNA expressions were evaluated by retrotranscriptase polymerase chain reaction. Endothelial cell proliferation was evaluated by bromo-deoxy-uridine incorporation and by cell counting.

RESULT(S)

Ghrelin negatively affected PGs release as well as COX2, ECNOS, and INOS mRNA expressions in HUVEC. Furthermore, Ghrelin increased bromo-deoxy-uridine incorporation in HUVEC without affecting cell counting.

CONCLUSION(S)

Our in vitro results allowed to hypothesize that Ghrelin could be involved in the modulation of vascular tone by affecting nitric oxide-related protein synthesis and PGs production in endothelial cells.

Ghrelin alleviates biliary obstruction-induced chronic hepatic injury in rats

BACKGROUND

Reactive oxygen species and oxidative stress are implicated in hepatic stellate cell activation and liver fibrosis, which are initiated by recruitment of inflammatory cells and by activation of cytokines.

OBJECTIVE

The possible anti-oxidant and anti-inflammatory effects of ghrelin were evaluated in a hepatic fibrosis model in rats with bile duct ligation (BDL).

METHODS

Under anesthesia, bile ducts of Sprague Dawley rats were ligated, and half of the rats were subcutaneously administered with ghrelin (10 ng/kg/day) and the rest with saline for 28 days. Sham-operated control groups were administered saline or ghrelin. On the 28th day of the study, rats were decapitated and malondialdehyde (MDA) content--an index of lipid peroxidation, and myeloperoxidase (MPO) activity--an index of neutrophil infiltration--were determined in the liver tissues. Oxidant-induced tissue fibrosis was determined by collagen contents, while the hepatic injury was analyzed microscopically. Serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) levels and lactate dehydrogenase (LDH) levels were determined to assess liver function and tissue damage, respectively. Pro-inflammatory cytokines; TNF-alpha, IL-1beta and IL-6 were also assayed in plasma samples.

RESULTS

In the saline-treated BDL group, hepatic MDA levels, MPO activity and collagen content were increased (p<0.001), suggesting oxidative organ damage, as confirmed histologically. In the ghrelin-treated BDL group, however, all of the oxidant responses were reversed significantly (p<0.05-p<0.001). Serum AST, ALT, LDH levels, and cytokines were elevated in the BDL group as compared to the control group, while this increase was significantly decreased by ghrelin treatment.

CONCLUSION

Owing to the anti-inflammatory and anti-oxidant effect as demonstrated in our study, it is possible to speculate that exogenously administered ghrelin may possess an antifibrotic effect against biliary obstruction-induced liver fibrosis. Thus, it seems likely that ghrelin may be of potential therapeutic value in protecting the liver fibrosis and oxidative injury due to biliary obstruction.

Tissue concentration of transforming growth factor beta1 and basic fibroblast growth factor in skin wounds created with a CO2 laser and scalpel: a comparative experimental study, using an animal model of skin resurfacing

Although a number of ablative-laser techniques based on CO(2) and Er: YAG laser devices have been successfully developed and used in the clinical setting, the bio-molecular processes influencing wound healing after exposure to laser energy are not well elucidated. In this study, we aim to assess the impact of the mechanism of injury on the secretion of transforming growth factor beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) in various stages of wound healing, in wounds created with a CO(2) laser and scalpel. Ten Wistar rats were used to determine the levels of growth factor proteins TGF-beta1 and bFGF after CO(2) laser- and scalpel-induced skin injury. Tissue was excised on day 0 for untreated skin (control sites), and on days 1, 10, 30, and 90 following laser and scalpel surgery. Specimens were processed for histopathological analysis and for determining the concentration of growth factors by a Western blot technique. The concentration of TGF-beta1 increased markedly, at day 1 postinjury, from a baseline of 130+/-16 mm(2) (mean surface area of blotted-protein lanes) to 261+/-23 mm(2) and 394+/-22 mm(2) for laser-inflicted injury and scalpel wounds, respectively; the latter values were found to differ significantly (p<0.001). The concentration of b-FGF on day 10 postinjury differed significantly (p<0.001) between the laser sites (553+/-45 mm(2)) and the corresponding scalpel sites (418+/-41 mm(2)). Laser energy alters local tissue secretion of TGF-beta1 and bFGF of skin injuries created with the CO(2) laser compared with wounds created with a scalpel. These differences might have an impact on various aspects of wound healing of skin injuries created by a laser.

Nonclassic Endogenous Novel Regulators of Angiogenesis

Angiogenesis, the process through which new blood vessels arise from preexisting ones, is regulated by several "classic" factors, among which the most studied are vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2). In recent years, investigations showed that, in addition to the classic factors, numerous endogenous peptides play a relevant regulatory role in angiogenesis. Such regulatory peptides, each of which exerts well-known specific biological activities, are present, along with their receptors, in the blood vessels and may take part in the control of the "angiogenic switch." An in vivo and in vitro proangiogenic effect has been demonstrated for erythropoietin, angiotensin II (ANG-II), endothelins (ETs), adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide (PAMP), urotensin-II, leptin, adiponectin, resistin, neuropeptide-Y, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and substance P. There is evidence that the angiogenic action of some of these peptides is at least partly mediated by their stimulating effect on VEGF (ANG-II, ETs, PAMP, resistin, VIP and PACAP) and/or FGF-2 systems (PAMP and leptin). AM raises the expression of VEGF in endothelial cells, but VEGF blockade does not affect the proangiogenic action of AM. Other endogenous peptides have been reported to exert an in vivo and in vitro antiangiogenic action. These include somatostatin and natriuretic peptides, which suppress the VEGF system, and ghrelin, that antagonizes FGF-2 effects. Investigations on "nonclassic" regulators of angiogenesis could open new perspectives in the therapy of diseases coupled to dysregulation of angiogenesis.

Adiponectin, ghrelin, and leptin differentially influence human platelet and human vascular endothelial cell functions: Implication in obesity-associated cardiovascular diseases

A very strong epidemiological link exists between obesity, the metabolic syndrome, diabetes and diabetes-associated cardiovascular pathologies. For this reason the peripheral effects of the centrally-acting satiety adipokines, adiponectin and leptin, and of non-adipose-derived hormones with similar effects, like ghrelin, have received considerable attention. In this report, we have extended our previous studies of the pro-thrombotic effects of leptin and determined the effects of adiponectin or ghrelin on human platelet activation. Thus, while leptin stimulated human platelet aggregation and adhesion, addition of adiponectin or of ghrelin did not affect either aggregation or adhesion of these cells; even at supra-physiological concentrations. In addition, we compared the impact of these three important hormones on microvascular endothelial cell permeability, an important parameter of endothelial function that when impaired contributes to several vascular pathologies. While physiologically relevant concentrations of either leptin or adiponectin increased the integrity of the diffusion barrier formed by a monolayer of human microvascular endothelial cells, only supra-physiological concentrations of ghrelin had this effect. None of these agents reduced microvascular endothelial barrier function. Taken together, our data are consistent with the ideas that leptin activates human platelets and limits transendothelial cell diffusion but that adiponectin only influences endothelial cell permeability. In contrast, ghrelin had neither of these effects. We propose that these data identify important differences in the effects of leptin, adiponectin or ghrelin on microvascular endothelial cells and platelets and may provide a basis on which to pharmacologically manipulate the selective effects of these peptides on these cell types in human cardiovascular or thrombotic diseases associated with obesity.

Physiological, pathological and potential therapeutic roles of ghrelin

Ghrelin, a hormone that is produced mainly by the stomach, was identified originally as the endogenous ligand of the growth hormone secretagogue (GHS) receptor. Ghrelin might also be synthesized in other organs, where it might have autocrine or paracrine effects. GHS receptors are present in tissues other than the hypothalamus and pituitary, which indicates that ghrelin has other effects in addition to stimulating the release of growth hormone. Recently, it has been suggested that ghrelin might be involved in the pathogenesis of many diseases and be a therapeutic target in these diseases. Here, we provide an overview of the physiological effects of ghrelin and of its pathological and potential therapeutic roles.

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

Ghrelin, a peptide hormone isolated from the stomach, releases growth hormone and stimulates appetite. Ghrelin is also expressed in pancreas, kidneys, cardiovascular system and in endothelial cells. The precise role of ghrelin in endothelial cell functions remains unknown. We examined the expression of ghrelin and its receptor (GHSR1) mRNAs and proteins in human microvascular endothelial cells (HMVEC) and determined whether ghrelin affects in these cells proliferation, migration and in vitro angiogenesis; and whether MAPK/ERK2 signaling is important for the latter action. We found that ghrelin and GHSR1 are constitutively expressed in HMVEC. Treatment of HMVEC with exogenous ghrelin significantly increased in these cells proliferation, migration, in vitro angiogenesis and ERK2 phosphorylation. MEK/ERK2 inhibitor, PD 98059 abolished ghrelin-induced in vitro angiogenesis. This is the first demonstration that ghrelin and its receptor are expressed in human microvascular endothelial cells and that ghrelin stimulates HMVEC proliferation, migration, and angiogenesis through activation of ERK2 signaling.

d-Lys-GHRP-6 does not modify the endocrine response to acylated ghrelin or hexarelin in humans

Acylated ghrelin exerts numerous endocrine and non-endocrine activities via the GH Secretagogue receptor type 1a (GHS-R1a). D-Lys-GHRP-6 has been widely studied in vitro and in vivo in animal studies as GHS-R1a antagonist; its action in humans has, however, never been tested so far. Aim of our study was to verify the antagonistic action of D-Lys-GHRP-6 on the endocrine responses to acylated ghrelin and hexarelin, a peptidyl synthetic GHS, in humans. The effects of different doses of D-Lys-GHRP-6 (2.0microg/kg iv as bolus or 2.0microg/kg/h iv as infusion) on both spontaneous and acylated ghrelin- or hexarelin (1.0microg/kg iv as bolus) -stimulated GH, PRL, ACTH and cortisol levels were studied in six normal volunteers (age [mean+/-SEM]: 25.4+/-1.2yr; BMI: 22.3+/-1.0kg/m(2)). The effects of D-Lys-GHRP-6 (2.0microg/kg iv as bolus+4.0microg/kg/h iv) on the GH response to 0.25microg/kg iv as bolus acylated ghrelin was also studied. During saline, spontaneous ACTH and cortisol decrease was observed while non changes occurred in GH and PRL levels. Acylated ghrelin and hexarelin stimulated (p<0.05) GH, PRL, ACTH and cortisol secretions. D-Lys-GHRP-6 administered either as bolus or a continuous infusion did not modify both spontaneous and acylated ghrelin- or hexarelin-stimulated GH, PRL, ACTH and cortisol secretion. D-Lys-GHRP-6 did not modify even the GH response to 0.25microg/kg iv acylated ghrelin. In conclusion, D-Lys-GHRP-6 does not affect the neuroendocrine response to both ghrelin and hexarelin. These findings question D-Lys-GHRP-6 as an effective GHS-R1a antagonist for human studies.