Therapeutic effects of ghrelin on endotoxic shock in rats

Generation of a mouse model of thyroid storm and preliminary investigation of the therapeutic effects of ghrelin

BACKGROUND

Thyroid storm (TS), a life-threatening condition that can damage multiple organs, has limited therapeutic options. Hypercytokinemia is a suggested background, but the pathological condition is unclear and there are no appropriate animal models. We aimed to develop a TS mouse model by administration of triiodothyronine and lipopolysaccharide, and then to examine the effects of ghrelin on this model.

METHODS

We evaluated the use of serum IL-6 levels as a representative marker of hypercytokinemia in patients with TS. To establish the mouse model, preliminary experiments were conducted to determine the non-lethal doses of triiodothyronine and lipopolysaccharide when administered individually. As a TS model, C57BL/6 mice were administered with triiodothyronine 1.0 mg/kg (subcutaneously, once daily for seven consecutive days) and lipopolysaccharide 0.5 mg/kg (intraperitoneally, on day 7) to develop a lethal model with approximately 30% survival on day 8. We assessed the survival ratio, mouse sepsis scores and blood biomarkers (IL-6, metanephrine, alanine aminotransferase) and evaluated the effects of ghrelin 300 µg/kg on these parameters in TS model.

RESULTS

Serum IL-6 was increased in patients with TS compared with those with Graves' disease as the diseased control (18.2 vs. 2.85 pg/mL, P < .05, n = 4 each). The dosage for the murine TS model was triiodothyronine 1.0 mg/kg and lipopolysaccharide 0.5 mg/kg. The TS model group had increased mouse sepsis score, serum IL-6, metanephrine and alanine aminotransferase. In this model, the ghrelin improved the survival rate to 66.7% (P < .01, vs. 0% [saline-treated group]) as well as the mouse sepsis score, and it decreased the serum IL-6 and metanephrine.

CONCLUSION

We established an animal model of TS that exhibits pathophysiological states similar to human TS with induction of serum IL-6 and other biomarkers by administration of T3 and LPS. The results suggest the potential effectiveness of ghrelin for TS in humans.

Changes in Circulating Acylated Ghrelin and Neutrophil Elastase in Diabetic Retinopathy

Background and Objectives: The role and the levels of ghrelin in diabetes-induced retinal damage have not yet been explored. The present study aimed to measure the serum levels of total ghrelin (TG), and its acylated (AG) and des-acylated (DAG) forms in patients with the two stages of diabetic retinopathy (DR), non-proliferative (NPDR) and proliferative (PDR). Moreover, the correlation between serum ghrelin and neutrophil elastase (NE) levels was investigated. Materials and Methods: The serum markers were determined via enzyme-linked immunosorbent assays in 12 non-diabetic subjects (CTRL), 15 diabetic patients without DR (Diabetic), 15 patients with NPDR, and 15 patients with PDR. Results: TG and AG serum levels were significantly decreased in Diabetic (respectively, p < 0.05 and p < 0.01 vs. CTRL), NPDR (p < 0.01 vs. Diabetic), and in PDR patients (p < 0.01 vs. NPDR). AG serum levels were inversely associated with DR abnormalities (microhemorrhages, microaneurysms, and exudates) progression (r = -0.83, p < 0.01), serum neutrophil percentage (r = -0.74, p < 0.01), and serum NE levels (r = -0.73, p < 0.01). The latter were significantly increased in the Diabetic (p < 0.05 vs. CTRL), NPDR (p < 0.01 vs. Diabetic), and PDR (p < 0.01 vs. PDR) groups. Conclusions: The two DR stages were characterized by decreased AG and increased NE levels. In particular, serum AG levels were lower in PDR compared to NPDR patients, and serum NE levels were higher in the PDR vs. the NPDR group. Together with the greater presence of retinal abnormalities, this could underline a distinctive role of AG in PDR compared to NPDR.

Ghrelin Alleviates Experimental Ulcerative Colitis in Old Mice and Modulates Colonocyte Metabolism via PPARγ Pathway

There is a growing prevalence of inflammatory bowel disease (IBD), a chronic inflammatory condition of the gastrointestinal tract, among the aging population. Ghrelin is a gut hormone that, in addition to controlling feeding and energy metabolism, has been shown to exert anti-inflammatory effects; however, the effect of ghrelin in protecting against colitis in old mice has not been assessed. Here, we subjected old female C57BL/6J mice to dextran sulfate sodium (DSS) in drinking water for six days, then switched back to normal drinking water, administered acyl-ghrelin or vehicle control from day 3 to 13, and monitored disease activities throughout the disease course. Our results showed that treatment of old mice with acyl-ghrelin attenuated DSS-induced colitis. Compared to the DSS group, ghrelin treatment decreased levels of the inflammation marker S100A9 in the colons collected on day 14 but not on day 8, suggesting that the anti-inflammatory effect was more prominent in the recovery phase. Ghrelin treatment also significantly reduced F4/80 and interleukin-17A on day 14. Moreover, acyl-ghrelin increased mitochondrial respiration and activated transcriptional activity of the peroxisome proliferator-activated receptor gamma (PPARγ) in Caco-2 cells. Together, our data show that ghrelin alleviated DSS-induced colitis, suggesting that ghrelin may promote tissue repair in part through regulating epithelial metabolism via PPARγ mediated signaling.

An insight into the multifunctional role of ghrelin and structure activity relationship studies of ghrelin receptor ligands with clinical trials

Ghrelin is a multifunctional gastrointestinal acylated peptide, primarily synthesized in the stomach and regulates the secretion of growth hormone and energy homeostasis. It plays a central role in modulating the diverse biological, physiological and pathological functions in vertebrates. The synthesis of ghrelin receptor ligands after the finding of growth hormone secretagogue developed from Met-enkephalin led to reveal the endogenous ligand ghrelin and the receptors. Subsequently, many peptides, small molecules and peptidomimetics focusing on the ghrelin receptor, GHS-R1a, were derived. In this review, the key features of ghrelin's structure, forms, its bio-physiological functions, pathological roles and therapeutic potential have been highlighted. A few peptidomimetics and pseudo peptide synthetic perspectives have also been discussed to make ghrelin receptor ligands, clinical trials and their success.

Targeting the Ghrelin Receptor as a Novel Therapeutic Option for Epilepsy

Epilepsy is a neurological disease affecting more than 50 million individuals worldwide. Notwithstanding the availability of a broad array of antiseizure drugs (ASDs), 30% of patients suffer from pharmacoresistant epilepsy. This highlights the urgent need for novel therapeutic options, preferably with an emphasis on new targets, since “me too” drugs have been shown to be of no avail. One of the appealing novel targets for ASDs is the ghrelin receptor (ghrelin-R). In epilepsy patients, alterations in the plasma levels of its endogenous ligand, ghrelin, have been described, and various ghrelin-R ligands are anticonvulsant in preclinical seizure and epilepsy models. Up until now, the exact mechanism-of-action of ghrelin-R-mediated anticonvulsant effects has remained poorly understood and is further complicated by multiple downstream signaling pathways and the heteromerization properties of the receptor. This review compiles current knowledge, and discusses the potential mechanisms-of-action of the anticonvulsant effects mediated by the ghrelin-R.

Sepsis as a Pan-Endocrine Illness-Endocrine Disorders in Septic Patients

Sepsis is defined as "life-threatening organ dysfunction caused by a dysregulated host response to infection". One of the elements of dysregulated host response is an endocrine system disorder. Changes in its functioning in the course of sepsis affect almost all hormonal axes. In sepsis, a function disturbance of the hypothalamic-pituitary-adrenal axis has been described, in the range of which the most important seems to be hypercortisolemia in the acute phase. Imbalance in the hypothalamic-pituitary-thyroid axis is also described. The most typical manifestation is a triiodothyronine concentration decrease and reverse triiodothyronine concentration increase. In the somatotropic axis, a change in the secretion pattern of growth hormone and peripheral resistance to this hormone has been described. In the hypothalamic-pituitary-gonadal axis, the reduction in testosterone concentration in men and the stress-induced "hypothalamic amenorrhea" in women have been described. Catecholamine and β-adrenergic stimulation disorders have also been reported. Disorders in the endocrine system are part of the "dysregulated host response to infection". They may also affect other components of this dysregulated response, such as metabolism. Hormonal changes occurring in the course of sepsis require further research, not only in order to explore their potential significance in therapy, but also due to their promising prognostic value.

In silico strategy for detailing the binding modes of a novel family of peptides proven as ghrelin receptor agonists

Ghrelin is a peptide hormone involved in multiple functions, including growth hormone release stimulation, food intake regulation, and metabolic and cytoprotective effect. A novel family of peptides with internal cycles was designed as ghrelin analogs and the biological activity of two of them (A228 and A233) was experimentally studied in-depth. In this work, an in silico strategy was developed for describing and assessing the binding modes of A228 and A233 to GHS-R1a (ghrelin receptor) comparing it with ghrelin and GHRP-6 peptides. Several reported structures of different G protein coupled receptors were used as templates, to obtain a good quality model of GHS-R1a. The best model was selected by preliminary molecular docking with ghrelin and GHRP-6. Docking was used to estimate peptide orientations in the binding site of the best model, observing a superposition of its N-terminal and its first aromatic residue. To test the complex stability in time, the C-terminal fragments of each peptide were added and the complexes were inserted a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane, performing a molecular dynamic simulation for 100 ns using the CHARMM36 force field. Despite of the structural differences, the studied peptides share a common binding mode; the N-terminal interacts with E124 and the aromatic residue close to it, with the aromatic cluster (F279, F309, and F312). A preliminary pharmacophore model, consisting in a positive charged amine and an aromatic ring at an approximate distance of 0.79 nm, can be proposed. The results here described could represent a step forward in the efficient search of new ghrelin analogs.

Conserved function of zebrafish (Danio rerio) Gdf15 as a sepsis tolerance mediator

GDF15 is frequently detected in patients suffering from various diseases, especially those associated with pro-inflammatory processes and/or metabolic disorders. Accordingly, sepsis, whose major complications are related to metabolic alterations and systemic inflammation, significantly increases the secretion of GDF15. Indeed, this cytokine could be considered a marker of sepsis severity. However, until the last several years, the involvement of GDF15 in these disorders had not been widely characterized. In mice, GDF15 was recently described as a pivotal inducer of sepsis tolerance by mediating metabolic alterations that reduce tissue damage. In this work we describe a zebrafish gdf15 gene. We found that gdf15 follows an expression pattern similar to that observed in mammals, being highly expressed in the liver and kidney and induced after pro-inflammatory stimuli. Moreover, larvae overexpressing gdf15 were more resistant to bacterial and viral challenges without affecting the pathogen load. Consequently, Gdf15 also protected zebrafish larvae against LPS-induced mortality. As in mice, zebrafish Gdf15 seems to induce sepsis tolerance by altering the metabolic parameters of the individuals.

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

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

Protective Effects of Ghrelin on Fasting-Induced Muscle Atrophy in Aging Mice

Sarcopenia is the aging-associated progressive loss of skeletal muscle; however, the pathogenic mechanism of sarcopenia is not clear. The orexigenic hormone ghrelin stimulates growth hormone secretion, increases food intake, and promotes adiposity. Here we showed that fasting-induced muscle loss was exacerbated in old ghrelin-null (Ghrl-/-) mice, exhibiting decreased expression of myogenic regulator MyoD and increased expression of protein degradation marker MuRF1, as well as altered mitochondrial function. Moreover, acylated ghrelin and unacylated ghrelin treatments significantly increased mitochondrial respiration capacity in muscle C2C12 cells. Consistently, acylated ghrelin and unacylated ghrelin treatments effectively increased myogenic genes and decreased degradation genes in the muscle in fasted old Ghrl-/- mice, possibly by stimulating insulin and adenosine monophosphate-activated protein kinase pathways. Furthermore, Ghrl-/- mice showed a profile of pro-inflammatory gut microbiota, exhibiting reduced butyrate-producing bacteria Roseburia and ClostridiumXIVb. Collectively, our results showed that ghrelin has a major role in the maintenance of aging muscle via both muscle-intrinsic and -extrinsic mechanisms. Acylated ghrelin and unacylated ghrelin enhanced muscle anabolism and exerted protective effects for muscle atrophy. Because unacylated ghrelin is devoid of the obesogenic side effect seen with acylated ghrelin, it represents an attractive therapeutic option for sarcopenia.

Ghrelin alterations during experimental and human sepsis

BACKGROUND

Ghrelin is a hormone mainly produced by cells of the gastric mucosa, which has been shown to possess anti-inflammatory and immunomodulatory properties. The objective of the study was to investigate ghrelin levels during sepsis, as well as in an experimental sepsis model.

METHODS

All consecutive admissions to the ICU of a tertiary hospital in Athens, Greece were screened for eligibility during the study. Thirty four non-septic patients upon ICU admission who subsequently developed sepsis were enrolled. Clinical data and scores were recorded, and blood samples were obtained at baseline (upon ICU admission), and at sepsis development. Total and active ghrelin, leptin, and cytokines were measured. Moreover, lipopolysaccharide (LPS) was administered to mice in order to induce endotoxemia and at specified time points, blood and tissue samples were collected.

RESULTS

In patients, serum total and active ghrelin concentrations were significantly elevated in sepsis compared to baseline (553.8 ± 213.4 vs 193.5 ± 123.2, p < 0.001; 254.3 ± 70.6 vs 56.49 ± 16.3, p < 0.001). Active ghrelin levels at the sepsis stage were inversely correlated with SOFA score and length of stay in the ICU (p = 0.023 and p = 0.027 respectively). In the mouse endotoxemia model ghrelin levels were elevated following LPS treatment, and the same trend was observed for leptin, TNFα and IL-6. Ghrelin administration managed to reduce IL-6 levels in mouse serum and in BALF. Pulmonary expression of ghrelin and its receptor GHSR1a was found decreased in LPS-treated mice.

CONCLUSIONS

In a well-defined cohort of ICU patients, we have demonstrated that active and total ghrelin increase in sepsis. The same is true for the experimental sepsis model used in the study. The inverse correlation of active ghrelin levels with SOFA score and length of ICU stay among septic patients is indicative of a potential protective role of active ghrelin during the septic process.

Acylated ghrelin suppresses the cytokine response to lipopolysaccharide and does so independently of the hypothalamic-pituitary-adrenal axis

Ghrelin, one of the major metabolic hormones involved in controlling energy balance, has recently been shown to have other properties including regulating the hypothalamic-pituitary-adrenal (HPA) axis response to psychological stress and being a potent anti-inflammatory agent. Ghrelin's HPA axis and anti-inflammatory actions have previously been identified as principally due to the acylated form (AG). However, our recent work has also suggested a role for des-acylated ghrelin (DAG) in these functions. Here we hypothesized ghrelin's anti-inflammatory activity is mediated by the HPA axis and this effect is differentially executed by AG and DAG. We gave adult male Wistar rats a concomitant injection of AG or DAG and lipopolysaccharide (LPS) and measured their effects on circulating cytokines, stress hormones and neuronal activation of the paraventricular nucleus of the hypothalamus (PVN). AG, but not DAG significantly suppressed the pro- and anti-inflammatory cytokine response induced by LPS in vivo. DAG also had no effects on any components of the HPA axis. AG, despite stimulating neuronal activation in the PVN in vivo and stimulating ACTH release from the pituitary in vitro, did not affect the HPA axis response to LPS. These findings suggest AG's anti-inflammatory effects are independent of its actions on the HPA axis and have implications for the potential use of this peptide for treatment of inflammatory conditions without compromising HPA axis activity.

Adipokines in critical illness: A review of the evidence and knowledge gaps

Adipose tissue products or adipokines play a major role in chronic endocrine and metabolic disorders; however, little is known about critical conditions. In this article, the experimental and clinical evidence of alterations of adipokines, adiponectin, leptin, resistin, visfatin, asymmetric dimethylarginine (ADMA), and ghrelin in critical illness, their potential metabolic, diagnostic, and prognostic value, and the gaps in the field have been reviewed. The results showed considerable changes in the concentration of the adipokines; while the impact of adipokines on metabolic disorders such as insulin resistance and inflammation has not been well documented in critically ill patients. There is no consensus about the circulatory and functional changes of leptin and adiponectin. However, it seems that lower concentrations of adiponectin at admission with gradual consequent increase might be a useful pattern in determining better outcomes of critical illness. Some evidence has suggested the adverse effects of elevated resistin concentration, potential prognostic importance of visfatin, and therapeutic value of ghrelin. High ADMA levels and low arginine:ADMA ratio were also proposed as predictors of ICU mortality and morbidities. However, there is no consensus on these findings. Although primary data indicated the role of adipokines in critical illness, further studies are required to clarify whether the reason of these changes is pathophysiological or compensatory. The relationship of pathophysiological background, disease severity, baseline nutritional status and nutrition support during hospitalization, and variations in body fat percentage and distribution with adipokines, as well as the potential prognostic or therapeutic role of these peptides should be further investigated in critically ill patients.

Metabolomic analysis for the protective effects of mangiferin on sepsis-induced lung injury in mice

This study aimed to investigate the efficacy of mangiferin, including its known antioxidant and anti-inflammatory effects on sepsis-induced lung injury induced by a classical cecal ligation and puncture (CLP) models in mouse using a metabolomics approach. A total of 24 mice were randomly divided into four groups: the sham group was given saline before sham operation. The CLP group received the CLP operation only. HMF and LMF groups were given mangiferin treatment of high dose and low dose of mangiferin, respectively, before the CLP operation. One week after treatment, the mice were sacrificed and their lungs were collected for metabolomics analysis. We developed ultra-performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry to perform lung metabolic profiling analysis. With the methods of principal component analysis and partial least squares discriminant analysis, 58 potential metabolites associated with amino acid metabolism, purine metabolism, lipid metabolism and energy regulation were observed to be increased or reduced in HMF and LMF groups compared with the CLP group. Conclusively, our results suggest that mangiferin plays a protective role in the moderation of sepsis-induced lung injury through reducing oxidative stress, regulating lipid metabolism and energy biosynthesis.

Influence of a diet enriched with virgin olive oil or butter on mouse gut microbiota and its correlation to physiological and biochemical parameters related to metabolic syndrome

The type of fat in the diet determinates the characteristics of gut microbiota, exerting a major role in the development of metabolic syndrome. We hypothesize that a diet enriched with extra virgin olive oil (EVOO) has a distinctive effect on the intestinal microbiome in comparison with an enriched butter diet (BT) and this effect is related to the physiological benefits exerted by EVOO. Swiss Webster mice were fed standard (SD) or two high fat diets enriched with EVOO or butter. Hormonal, physiological and metabolic parameters were evaluated. At the end of the feeding period, DNA was extracted from faeces and the 16S rRNA genes were pyrosequenced. Among the main significant differences found, BT triggered the highest values of systolic blood pressure, correlating positively with the percentage of Desulfovibrio sequences in faeces, which in turn showed significantly higher values in BT than in EVOO. EVOO had the lowest values of plasmatic insulin, correlating inversely with Desulfovibrio, and had the lowest plasmatic values of leptin which correlated inversely with Sutterellaceae, Marispirillum and Mucilaginibacter dageonensis, the three showing significantly higher percentages in EVOO. The lowest total cholesterol levels in plasma were detected in SD, correlating positively with Prevotella and Fusicatenibacter, both taxa with significantly greater presence in SD. These results may be indicative of a link between specific diets, certain physiological parameters and the prevalence of some taxa, supporting the possibility that in some of the proposed effects of virgin olive oil the modulation of intestinal microbiota could be involved.

Endocrine and Metabolic Alterations in Sepsis and Implications for Treatment

Sepsis induces profound neuroendocrine and metabolic alterations. During the acute phase, the neuroendocrine changes are directed toward restoration of homeostasis, and also limit unnecessary energy consumption in the setting of restricted nutrient availability. Such changes are probably adaptive. In patients not recovering quickly, a prolonged critically ill phase may ensue, with different neuroendocrine changes, which may represent a maladaptive response. Whether stress hyperglycemia should be aggressively treated or tolerated remains a matter of debate. Until new evidence from randomized controlled trials becomes available, preventing severe hyperglycemia is recommended. Evidence supports withholding parenteral nutrition in the acute phase of sepsis.

The activation of α2-adrenergic receptor in the spinal cord lowers sepsis-induced mortality

The effect of clonidine administered intrathecally (i.t.) on the mortality and the blood glucose level induced by sepsis was examined in mice. To produce sepsis, the mixture of D-galactosamine (GaLN; 0.6 g/10 ml)/lipopolysaccharide (LPS; 27 µg/27 µl) was treated intraperitoneally (i.p.). The i.t. pretreatment with clonidine (5 µg/5 µl) increased the blood glucose level and attenuated mortality induced by sepsis in a dose-dependent manner. The i.t. post-treatment with clonidine up to 3 h caused an elevation of the blood glucose level and protected sepsis-induced mortality, whereas clonidine post-treated at 6, 9, or 12 h did not affect. The pre-treatment with oral D-glucose for 30 min prior to i.t. post-treatment (6 h) with clonidine did not rescue sepsis-induced mortality. In addition, i.t. pretreatment with pertussis toxin (PTX) reduced clonidine-induced protection against mortality and clonidine-induced hyperglycemia, suggesting that protective effect against sepsis-induced mortality seems to be mediated via activating PTX-sensitive G-proteins in the spinal cord. Moreover, pretreatment with clonidine attenuated the plasma tumor necrosis factor α (TNF-α) induced by sepsis. Clonidine administered i.t. or i.p. increased p-AMPKα1 and p-AMPKα2, but decreased p-Tyk2 and p-mTOR levels in both control and sepsis groups, suggesting that the up-regulations of p-AMPKα1 and p-AMPKα2, or down-regulations of p-mTOR and p-Tyk2 may play critical roles for the protective effect of clonidine against sepsis-induced mortality.

IL-1β directly suppress ghrelin mRNA expression in ghrelin-producing cells

In animal models, ghrelin production is suppressed by LPS administration. To elucidate the detailed molecular mechanisms involved in the phenomenon, we investigated the effects of LPS and LPS-inducible cytokines, including TNF-α, IL-1β, and IL-6, on the expression of ghrelin in the ghrelin-producing cell line MGN3-1. These cells expressed IL-1R, and IL-1β significantly suppressed ghrelin mRNA levels. The suppressive effects of IL-1β were attenuated by knockdown of IKKβ, suggesting the involvement of the NF-κB pathway. These results suggested that IL-1β is a major regulator of ghrelin expression during inflammatory processes.

Therapeutic Potential of Targeting the Ghrelin Pathway

Ghrelin was discovered in 1999 as the endogenous ligand of the growth-hormone secretagogue receptor 1a (GHSR1a). Since then, ghrelin has been found to exert a plethora of physiological effects that go far beyond its initial characterization as a growth hormone (GH) secretagogue. Among the numerous well-established effects of ghrelin are the stimulation of appetite and lipid accumulation, the modulation of immunity and inflammation, the stimulation of gastric motility, the improvement of cardiac performance, the modulation of stress, anxiety, taste sensation and reward-seeking behavior, as well as the regulation of glucose metabolism and thermogenesis. Due to a variety of beneficial effects on systems’ metabolism, pharmacological targeting of the endogenous ghrelin system is widely considered a valuable approach to treat metabolic complications, such as chronic inflammation, gastroparesis or cancer-associated anorexia and cachexia. The aim of this review is to discuss and highlight the broad pharmacological potential of ghrelin pathway modulation for the treatment of anorexia, cachexia, sarcopenia, cardiopathy, neurodegenerative disorders, renal and pulmonary disease, gastrointestinal (GI) disorders, inflammatory disorders and metabolic syndrome.

The Impact of Ghrelin in Metabolic Diseases: An Immune Perspective

Obesity and insulin resistance have reached epidemic proportions. Obesogenic conditions are associated with increased risk for the development of other comorbidities and obesity-related diseases. In metabolic disorders, there is chronic low-grade inflammation induced by the activation of immune cells, especially in metabolic relevant organs such as white adipose tissue (WAT). These immune cells are regulated by environmental and systemic cues. Ghrelin is a peptide secreted mainly by X/A-like gastric cells and acts through the growth hormone secretagogue receptor (GHS-R). This receptor is broadly expressed in the central nervous system (CNS) and in several cell types, including immune cells. Studies show that ghrelin induces an orexigenic state, and there is increasing evidence implicating an immunoregulatory role for ghrelin. Ghrelin mainly acts on the innate and adaptive immune systems to suppress inflammation and induce an anti-inflammatory profile. In this review, we discuss the immunoregulatory roles of ghrelin, the mechanisms by which ghrelin acts and potential pharmacological applications for ghrelin in the treatment of obesity-associated inflammatory diseases, such as type 2 diabetes (T2D).

Effects of ghrelin on the apoptosis of human neutrophils in vitro

Acute respiratory distress syndrome (ARDS) is characterized by lung inflammation and the diffuse infiltration of neutrophils into the alveolar space. Neutrophils are abundant, short-lived leukocytes that play a key role in immune defense against microbial infections. These cells die via apoptosis following the activation and uptake of microbes, and will also enter apoptosis spontaneously at the end of their lifespan if they do not encounter pathogens. Apoptosis is essential for the removal of neutrophils from inflamed tissues and for the timely resolution of neutrophilic inflammation. Ghrelin is an endogenous ligand for the growth hormone (GH) secretagogue receptor, produced and secreted mainly from the stomach. Previous studies have reported that ghrelin exerts anti-inflammatory effects in lung injury through the regulation of the apoptosis of different cell types; however, the ability of ghrelin to regulate alveolar neutrophil apoptosis remains largely undefined. We hypothesized that ghrelin may have the ability to modulate neutrophil apoptosis. In this study, to examine this hypothesis, we investigated the effects of ghrelin on freshly isolated neutrophils in vitro. Our findings demonstrated a decrease in the apoptotic ratio (as shown by flow cytometry), as well as in the percentage of cells with decreased mitochondrial membrane potential (ΔΨm) and in the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick-end labeling-positive rate, accompanied by an increased B-cell lymphoma 2/Bax ratio and the downregulation of cleaved caspase-3 in neutrophils following exposure to lipopolysaccharide (100 ng/ml). However, pre-treatment with ghrelin at a physiological level (100 nM) did not have a notable influence on the neutrophils in all the aforementioned tests. Our findings suggest that ghrelin may not possess the ability to modulate the neutrophil lifespan in vitro.

Effect of D-glucose feeding on mortality induced by sepsis

Sepsis is the life-threatening response to infection which can lead to tissue damage, organ failure, and death. In the current study, the effect of orally administered D-glucose on the mortality and the blood glucose level induced by D-Galactosamine (GaLN)/lipopolysaccharide (LPS)-induced sepsis was examined in ICR mice. After various amounts of D-glucose (from 1 to 8 g/kg) were orally fed, sepsis was induced by injecting intraperitoneally (i.p.) the mixture of GaLN /LPS. Oral pre-treatment with D-glucose dose-dependently increased the blood glucose level and caused a reduction of sepsis-induced mortality. The oral post-treatment with D-glucose (8 g/kg) up to 3 h caused an elevation of the blood glucose level and protected the mortality observed in sepsis model. However, D-glucose post-treated at 6, 9, or 12 h after sepsis induction did not affect the mortality and the blood glucose level induced by sepsis. Furthermore, the intrathecal (i.t.) pretreatment once with pertussis toxin (PTX; 0.1 µg/5 ml) for 6 days caused a reduction of D-glucose-induced protection of mortality and hyperglycemia. Furthermore, once the hypoglycemic state is continued up to 6 h after sepsis initiated, sepsis-induced mortality could not be reversed by D-glucose fed orally. Based on these findings, it is assumed that the hypoglycemic duration between 3 and 6 h after the sepsis induction may be a critical time of period for the survival. D-glucose-induced protective effect against sepsis-induced mortality appears to be mediated via activating PTX-sensitive G-proteins in the spinal cord. Finally, the production of hyperglycemic state may be critical for the survival against the sepsis-induced mortality.

Anti-inflammatory role of obestatin in autoimmune myocarditis

Obestatin is a popular endogeneous peptide, known to have an autoimmune regulatory effect on energy metabolism and the gastrointestinal system. Studies regarding the anti-inflammatory effects of obestatin are scarce. The aim of this study was to show the anti-inflammatory effect of obestatin in an experimental model of autoimmune myocarditis in rats. Experimental autoimmune myocarditis was induced in Lewis rats by immunization with subcutaneous administration of porcine cardiac myosin, twice at 7-day intervals. Intraperitoneal pretreatment with obestatin (50 μg/kg) was started before the induction of myocarditis and continued for 3 weeks. The severity of myocarditis was evidenced by clinical, echocardiographic and histological findings. In addition, by-products of neutrophil activation, lipid peroxidation, inflammatory and anti-inflammatory cytokines were measured in serum. Obestatin significantly ameliorated the clinical and histopathological severity of autoimmune myocarditis. Therapeutic effects of obestatin in myocarditis were associated with reduced lipid peroxidation, suppression of polymorphonuclear leukocyte infiltration and enhancement of glutathione synthesis, inhibition of serum inflammatory and activation of anti-inflammatory cytokines. Histopathologically, the left ventricle was significantly dilated, and its wall thickened, along with widespread lymphocytic and histocytic infiltration. The myocardium was severely infiltrated with relatively large mononuclear cells. These histopathological changes were observed in lesser degrees in obestatin-treated rats. This study demonstrated a novel anti-inflammatory effect of obestatin in an experimental model of autoimmune myocarditis. Consequently, obestatin administration may represent a promising therapeutic approach for myocarditis and dilated cardiomyopathy in the future.

Possible synergism of physical exercise and ghrelin-agonists in patients with cachexia associated with chronic heart failure

The occurrence of cachexia of multifactorial etiology in chronic heart failure (CHF) is a common and underestimated condition that usually leads to poor outcome and low survival rates, with high direct and indirect costs for the Health Care System. Recently, a consensus definition on cachexia has been reached, leading to a growing interest by the scientific community in this condition, which characterizes the last phase of many chronic diseases (i.e., cancer, acquired immunodeficiency syndrome). The etiology of cachexia is multifactorial and the underlying pathophysiological mechanisms are essentially the following: anorexia and malnourishment; immune overactivity and systemic inflammation; and endocrine disorders (anabolic/catabolic imbalance and resistance to growth hormone). In this paper, we review the main pathophysiological mechanisms underlying CHF cachexia, focusing also on the broad spectrum of actions of ghrelin and ghrelin agonists, and their possible use in combination with physical exercise to contrast CHF cachexia.

Ghrelin gene products in acute and chronic inflammation

Ghrelin gene products--the peptides ghrelin, unacylated ghrelin, and obestatin--have several actions on the immune system, opening new perspectives within neuroendocrinology, metabolism and inflammation. The aim of this review is to summarize the available evidence regarding the less known role of these peptides in the machinery of inflammation and autoimmunity, outlining some of their most promising therapeutic applications.

Sickness behaviour after lipopolysaccharide treatment in ghrelin deficient mice

Ghrelin is an orexigenic hormone produced mainly by the gastrointestinal system and the brain. Much evidence also indicates a role for ghrelin in sleep and thermoregulation. Further, ghrelin was recently implicated in immune system modulation. Administration of bacterial lipopolysaccharide (LPS) induces fever, anorexia, and increased non-rapid-eye movement sleep (NREMS) and these actions are mediated primarily by proinflammatory cytokines. Ghrelin reduces LPS-induced fever, suppresses circulating levels of proinflammatory cytokines and reduces the severity and mortality of various models of experimental endotoxemia. In the present study, we determined the role of intact ghrelin signaling in LPS-induced sleep, feeding, and thermoregulatory responses in mice. Sleep-wake activity was determined after intraperitoneal, dark onset administration of 0.4, 2 and 10 μg LPS in preproghrelin knockout (KO) and wild-type (WT) mice. In addition, body temperature, motor activity and changes in 24-h food intake and body weight were measured. LPS induced dose-dependent increases in NREMS, and suppressed rapid-eye movement sleep, electroencephalographic slow-wave activity, motor activity, food intake and body weight in both Ppg KO and WT mice. Body temperature changes showed a biphasic pattern with a decrease during the dark period followed by an increase in the light phase. The effects of the low and middle doses of LPS were indistinguishable between the two genotypes. Administration of 10 μg LPS, however, induced significantly larger changes in NREMS and wakefulness amounts, body temperature, food intake and body weight in the Ppg KO mice. These findings support a role for ghrelin as an endogenous modulator of inflammatory responses and a central component of arousal and feeding circuits.

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.

Cardioprotective effect of ghrelin in cardiopulmonary bypass involves a reduction in inflammatory response

Background

Ghrelin has been reported to protect the cardiovascular system; however, the cardioprotective effect of ghrelin against cardiopulmonary bypass (CPB) induced myocardial injury are unclear. In this study, the protective effect of ghrelin on CPB induced myocardial injury and the underlying mechanisms were investigated.

Methods and Results

Adult male rats were subjected to CPB and randomly to receive vehicle (n = 8), ghrelin (n = 8), ghrelin plus [D-Lys3]-GHRP-6, a GHSR-1a inhibitor (n = 8), or ghrelin plus wortmannin, a phosphoinositide 3′-kinase (PI3K) inhibitor (n = 8). In vitro study was performed on cultured cardiomyocytes subjected to simulated cardiopulmonary bypass (SCPB). Ghrelin attenuated the inflammatory response, as evidenced by reduced induction of TNF-α, IL-6 and myocardial myeloperoxidase activity and concurrent reduction in apoptosis, oxidative stress, and levels of myocardial injury markers following CPB. Moreover, ghrelin significantly increased cardiac function after CPB. In cultured cardiomyocytes subjected to simulated CPB, ghrelin increased cell viability and decreased the percentage of apoptotic myocytes. Inhibition of ghrelin downstream signaling blocked the cardioprotective effects both in vivo and vitro.

Conclusions

Ghrelin could provide an effective approach to the attenuation of CPB induced myocardial injury. The cardioprotective effects elicited by ghrelin may contribute to the inhibition of inflammatory response through the Akt-activated pathway.

Impact of ghrelin on vitreous cytokine levels in an experimental uveitis model

Background

The purpose of this study was to investigate the effect of intraperitoneal ghrelin on vitreous levels of interleukin (IL)-1, IL-6, and tumor necrosis factor-alpha (TNF-α) and to compare its effects with those of intraperitoneal infliximab in an experimental uveitis model.

Methods

Twenty-four male rats were assigned to four groups of six rats in each. All the rats, except for those in group 1 (controls), were injected intravitreally with concanavalin A to induce experimental uveitis. Rats in group 2 (sham) were not given any treatment after uveitis was induced. Rats in group 3 were given intraperitoneal infliximab 0.5 mg/100 mL on days 0, 1, 3, 5, and 7 following induction of uveitis on day 14 of the study. Rats in group 4 were given intraperitoneal ghrelin 10 ng/kg/day for 7 days following induction of uveitis. On day 21 of the study, enucleated globes were subjected to histopathologic examination. Vitreous levels of IL-1, IL-6, and TNF-α were measured by enzyme-linked immunosorbent assay.

Results

Vitreous levels of IL-1, IL-6, and TNF-α were significantly increased in the sham group relative to the control group (P < 0.05), but showed a significant decrease in the group treated with infliximab (P < 0.05). Cytokine levels also decreased in the ghrelin-treated group, but the decrease was not statistically significant (P > 0.05).

Conclusion

Ghrelin failed to decrease the IL-1, IL-6, and TNF-α levels that play a critical role in the pathogenesis of uveitis.

The effects of ghrelin on colonic anastomosis healing in rats

OBJECTIVES

In addition to its roles in the stimulation of growth hormone secretion and the regulation of appetite and metabolism, ghrelin exerts immunomodulatory, anti-inflammatory and antioxidant actions in several organ systems. In this study, we investigated the effects of ghrelin on the healing of experimental colonic anastomoses.

METHODS

Wistar rats were randomly divided into two groups (n = 10 in each). A segment of colon was excised, and an end-to-end anastomosis was performed in the distal colon. The Ghrelin Group received 10 ng/kg/day IP ghrelin for seven days postoperatively, whereas the Control Group received an identical volume of saline. On the seventh postoperative day, the anastomotic bursting pressures and hydroxyproline levels were measured, and adhesion formation around the anastomoses was examined. Histopathological analyses were performed to evaluate inflammatory cell infiltration, fibroblast infiltration, collagen density and neovascularization.

RESULTS

In the Ghrelin Group, the bursting pressure and hydroxyproline levels were significantly higher than in the Control Group. The adhesion formation scores were lower in the Ghrelin Group than in the Control Group. Although the inflammatory cell infiltration was diminished in the Ghrelin Group, the degrees of fibroblast infiltration, collagen density and neovascularization were not significantly different between the groups.

CONCLUSION

Our results indicate that ghrelin improves the healing of colonic anastomoses in rats.

Ghrelin, appetite and critical illness

PURPOSE OF REVIEW

Recovery and rehabilitation after critical illness is a vital part of intensive care management. The role of feeding and nutritional intervention is the subject of many recent studies. The gastric hormone ghrelin has effects on appetite and food intake and on immunomodulatory functions. Here we review the interactions between critical illness, appetite regulation, nutrition and ghrelin.

RECENT FINDINGS

Critical illness results in significant loss of lean body mass; strategies to prevent this have so far proven unsuccessful. Ghrelin has been shown to reduce catabolic protein loss in animal models of critical illness and improve body composition in chronic cachectic illnesses in humans.

SUMMARY

Enhancing recovery from critical illness will improve both short-term and long-term outcomes. Ghrelin may offer an important means of improving appetite, muscle mass and rehabilitation in the period after critical illness, although studies are needed to see whether this potential is realized.

Ghrelin - a pleiotropic hormone secreted from endocrine x/a-like cells of the stomach

The gastric X/A-like endocrine cell receives growing attention due to its peptide products with ghrelin being the best characterized. This peptide hormone was identified a decade ago as a stimulator of food intake and to date remains the only known peripherally produced and centrally acting orexigenic hormone. In addition, subsequent studies identified numerous other functions of this peptide including the stimulation of gastrointestinal motility, the maintenance of energy homeostasis and an impact on reproduction. Moreover, ghrelin is also involved in the response to stress and assumed to play a role in coping functions and exert a modulatory action on immune pathways. Our knowledge on the regulation of ghrelin has markedly advanced during the past years by the identification of the ghrelin acylating enzyme, ghrelin-O-acyltransferase, and by the description of changes in expression, activation, and release under different metabolic as well as physically and psychically challenging conditions. However, our insight on regulatory processes of ghrelin at the cellular and subcellular levels is still very limited and warrants further investigation.

Exogenous ghrelin attenuates endotoxin fever in rats

Ghrelin is a gut-derived peptide that plays a role in energy homeostasis. Recent studies have implicated ghrelin in systemic inflammation, showing increased plasma ghrelin levels after endotoxin (lipopolysaccharide, LPS) administration. The aims of this study were (1) to test the hypothesis that ghrelin administration affects LPS-induced fever; and (2) to assess the putative effects of ghrelin on plasma corticosterone secretion and preoptic region prostaglandin (PG) E(2) levels in euthermic and febrile rats. Rats were implanted with a temperature datalogger capsule in the peritoneal cavity to record body core temperature. One week later, they were challenged with LPS (50 μg/kg, intraperitoneal, i.p.) alone or combined with ghrelin (0.1mg/kg, i.p.). In another group of rats, plasma corticosterone and preoptic region PGE(2) levels were measured 2h after injections. In euthermic animals, systemic administration of ghrelin failed to elicit any thermoregulatory effect, and caused no significant changes in basal plasma corticosterone and preoptic region PGE(2) levels. LPS caused a typical febrile response, accompanied by increased plasma corticosterone and preoptic PGE(2) levels. When LPS administration was combined with ghrelin fever was attenuated, corticosterone secretion further increased, and the elevated preoptic PGE(2) levels were relatively reduced, but a correlation between these two variables (corticosterone and PGE(2)) failed to exist. The present data add ghrelin to the neurochemical milieu controlling the immune/thermoregulatory system acting as an antipyretic molecule. Moreover, our findings also support the notion that ghrelin attenuates fever by means of a direct effect of the peptide reducing PGE(2) production in the preoptic region.

Stress-related alterations of acyl and desacyl ghrelin circulating levels: mechanisms and functional implications

Ghrelin is the only known peripherally produced and centrally acting peptide hormone that stimulates food intake and digestive functions. Ghrelin circulates as acylated and desacylated forms and recently the acylating enzyme, ghrelin-O-acyltransferase (GOAT) and the de-acylating enzyme, thioesterase 1/lysophospholipase 1 have been identified adding new layers of complexity to the regulation of ghrelin. Stress is known to alter gastrointestinal motility and food intake and was recently shown to modify circulating ghrelin and GOAT levels with differential responses related to the type of stressors including a reduction induced by physical stressors (abdominal surgery and immunological/endotoxin injection, exercise) and elevation by metabolic (cold exposure, acute fasting and caloric restriction) and psychological stressors. However, the pathways underlying the alterations of ghrelin under these various stress conditions are still largely to be defined and may relate to stress-associated autonomic changes. There is evidence that alterations of circulating ghrelin may contribute to the neuroendocrine and behavioral responses along with sustaining the energetic requirement needed upon repeated exposure to stressors. A better understanding of these mechanisms will allow targeting components of ghrelin signaling that may improve food intake and gastric motility alterations induced by stress.

Voluntary exercise attenuates obesity-associated inflammation through ghrelin expressed in macrophages

Chronic low-level inflammation is associated with obesity and a sedentary lifestyle, causing metabolic disturbances such as insulin resistance. Exercise training has been shown to decrease chronic low-level systemic inflammation in high-fat diet (HFD)-induced obesity. However, the molecular mechanisms mediating its beneficial effects are not fully understood. Ghrelin is a peptide hormone predominantly produced in the stomach that stimulates appetite and induces growth hormone release. In addition to these well-known functions, recent studies suggest that ghrelin localizes to immune cells and exerts an anti-inflammatory effect. The purpose of the current study was to investigate the role of ghrelin expressed in macrophages in the anti-inflammatory effects of voluntary exercise training. Expression of tumor necrosis factor-α (TNF-α), monocyte chemotactic protein (MCP)-1 and F4/80 was increased in adipose tissue from mice fed a HFD (HFD mice) compared with mice fed a standard diet (SD mice), whereas the expression of these inflammatory cytokines was markedly decreased in mice performing voluntary wheel running during the feeding of a HFD (HFEx mice). The expression of TNF-α was also increased in peritoneal macrophages by a HFD and exercise training inhibited the increase of TNF-α expression. Interestingly, expression of ghrelin in peritoneal macrophages was decreased by a HFD and recovered by exercise training. Suppression of ghrelin expression by siRNA increased TNF-α expression and LPS-stimulated NF-κB activation in RAW264 cells, which is a macrophage cell line. TNF-α expression by stimulation with LPS was significantly suppressed in RAW264 cells cultured in the presence of ghrelin. These results suggest that ghrelin exerts potent anti-inflammatory effects in macrophages and functions as a mediator of the beneficial effects of exercise training.

Inhibition of c-Jun-N-terminal kinase increases cardiac peroxisome proliferator-activated receptor alpha expression and fatty acid oxidation and prevents lipopolysaccharide-induced heart dysfunction

Septic shock results from bacterial infection and is associated with multi-organ failure, high mortality, and cardiac dysfunction. Sepsis causes both myocardial inflammation and energy depletion. We hypothesized that reduced cardiac energy production is a primary cause of ventricular dysfunction in sepsis. The JNK pathway is activated in sepsis and has also been implicated in impaired fatty acid oxidation in several tissues. Therefore, we tested whether JNK activation inhibits cardiac fatty acid oxidation and whether blocking JNK would restore fatty acid oxidation during LPS treatment. LPS treatment of C57BL/6 mice and adenovirus-mediated activation of the JNK pathway in cardiomyocytes inhibited peroxisome proliferator-activated receptor α expression and fatty acid oxidation. Surprisingly, none of the adaptive responses that have been described in other types of heart failure, such as increased glucose utilization, reduced αMHC:βMHC ratio or induction of certain microRNAs, occurred in LPS-treated mice. Treatment of C57BL/6 mice with a general JNK inhibitor (SP600125) increased fatty acid oxidation in mice and a cardiomyocyte-derived cell line. JNK inhibition also prevented LPS-mediated reduction in fatty acid oxidation and cardiac dysfunction. Inflammation was not alleviated in LPS-treated mice that received the JNK inhibitor. We conclude that activation of JNK signaling reduces fatty acid oxidation and prevents the peroxisome proliferator-activated receptor α down-regulation that occurs with LPS.

Use of ghrelin as a treatment for inflammatory bowel disease: mechanistic considerations

Inflammatory bowel diseases (IBD)-and in particular Crohn's disease-are immune-mediated processes that result in denuded intestinal mucosa and can produce decreased appetite, weight loss, and systemic inflammation. Current treatments include anti-inflammatory medications, immunomodulators, and feeding interventions. Ghrelin is an endogenous orexigenic hormone that directly stimulates growth hormone release, increases gut motility, and has cardiovascular and anti-inflammatory properties. Although ghrelin levels are elevated in active IBD, administration of ghrelin in most (but not all) animal models of colitis has produced improvements in disease activity and systemic inflammation. The mechanism for these effects is not known but may relate to decreased inflammation, increased motility, increased appetite, and increased colonic blood flow. Human trials have not been performed, however, and more research is clearly needed.

Ghrelin and cachexia: will treatment with GHSR-1a agonists make a difference for patients suffering from chronic wasting syndromes?

Cachexia is a syndrome of wasting and anorexia that worsens the prognosis of many chronic diseases including cancer, chronic kidney disease, chronic heart disease and chronic obstructive pulmonary disease. Properties of the orexigenic hormone ghrelin-including appetite-stimulation, weight-gain production and increased cardiac output make it a logical treatment for cachexia. While endogenous ghrelin levels are increased in the setting of cachexia, treatment with ghrelin and other GHSR-1a agonists in animal models of cachexia and in humans with cachexia has demonstrated consistent effects of increased appetite and improved weight gain. These positive effects occur in multiple underlying diseases associated with cachexia and appear to be sustained over treatment duration of up to 12 weeks. The mechanism of action in producing these effects is likely related to stimulation of central appetite centers such as the central melanocortin system and to increased growth hormone release, though ghrelin's effects may also relate to decreased systemic inflammation and other direct and indirect actions. Questions regarding the long-term safety of ghrelin treatment are still unanswered, as is the important question of whether successful treatment of cachexia will improve the prognosis of the underlying disease itself.

The effects of ghrelin on inflammation and the immune system

A number of hormones and metabolic mediators signal the brain of changes in the body's energy status and when an imbalance occurs; the brain coordinates the appropriate changes in energy intake and utilization via the control of appetite and food consumption. Under conditions of chronic inflammation and immune activation, there is often a significant loss of body mass and appetite suggesting the presence of shared ligands and signaling pathways mediating "crosstalk" between the immune and neuroendocrine systems. Ghrelin, the endogenous ligand for growth hormone secretagogue receptor (GHS-R), is produced primarily by cells in the stomach and serves as a potent circulating orexigenic hormone controlling food intake, energy expenditure, adiposity and GH secretion. The functional roles of ghrelin and other growth hormone secretagogues (GHS) within the immune system and under states of inflammatory stress and injury are only now coming to light. A number of reports over the past decade have described ghrelin to be a potent anti-inflammatory mediator both in vitro and in vivo and a promising therapeutic agent in the treatment of inflammatory diseases and injury. Moreover, ghrelin has also been shown to promote lymphocyte development in the primary lymphoid organs (bone marrow and thymus) and to ablate age-associated thymic involution. In the current report, we review the literature supporting a role for ghrelin as an anti-inflammatory agent and immunoregulatory hormone/cytokine and its potential use in the treatment of inflammatory diseases and injury.

Hepatoprotective effect of ghrelin on carbon tetrachloride-induced acute liver injury in rats

BACKGROUND & AIMS

Recent studies have revealed that ghrelin may be an antioxidant and antiinflammatory agent. Oxidative stress are considered to play a prominent causative role in the development of various hepatic disorders. We investigated whether ghrelin plays a protective role against carbon tetrachloride (CCl(4))-induced acute liver injury in rats.

METHODS

Forty adult male Sprague-Dawley rats were randomly divided into four equal groups as; control, ghrelin, CCl(4) and ghrelin plus CCl(4). Evaluations were made for lipid peroxidation, enzyme activities and biochemical parameters. Pathological histology was also performed.

RESULTS

CCl(4) treatment increased plasma and liver tissue malondialdehyde (MDA) content and plasma nitric oxide (NO) level, and decreased erythrocyte and liver tissue superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) activities when compared to control group. At the same time, CCl(4) treatment increased the serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alcaline phosphatase (ALP) activities. By contrast, ghrelin pretreatment reduced plasma and liver MDA content and plasma NO level, and increased erythrocyte and liver tissue SOD, CAT and GPx activities when compared with CCl(4)-treated group. Moreover, both ghrelin alone and ghrelin plus CCl(4) treatment elevated serum glucose level. The CCl(4)-induced histopathological changes were also reduced by the ghrelin pretreatment.

CONCLUSION

Our results show that ghrelin can be proposed to protect the liver against CCl(4)-induced oxidative damage in rats, and the hepatoprotective effect may be correlated with its antioxidant and free radical scavenger effects.

Growth hormone releasing peptide-2, a ghrelin agonist, attenuates lipopolysaccharide-induced acute lung injury in rats

Acute lung injury (ALI) and its severe form, acute respiratory distress syndrome (ARDS), are the most common complications of sepsis, and the mortality of sepsis-induced ALI remains high in critically ill patients. Growth hormone releasing peptide-2 (GHRP-2), a ghrelin agonist, has been shown to exert beneficial effects on various inflammatory diseases. We therefore explored whether GHRP-2 possesses anti-inflammatory properties in the pathogenesis of lipopolysaccharide (LPS)-induced ALI. Male Sprague-Dawley rats were intratracheally instilled with LPS (2 mg/kg) to induce ALI. ALI was confirmed with lung tissue injury (histopathological examination), enhanced lung edema (wet-to-dry weight ratio), and neutrophil infiltration (myeloperoxidase activity) at 6 h after LPS exposure. The analyses of bronchoalveolar lavage fluid showed the significant increases in pulmonary permeability (total cells and protein) and the levels of proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). In contrast, these lung injury indexes were attenuated in rats that received a subcutaneous injection of GHRP-2 (100 microg/kg) 0.5 h prior to LPS administration. To further explore the potential anti-inflammatory mechanism of GHRP-2 in LPS-induced ALI, we assessed of nuclear factor-kappaB (NF-kappaB) activity in lung tissues at 6 h after LPS challenge. We thus found that pretreatment with GHRP-2 markedly suppressed the activation of NF-kappaB in lung tissues. These results indicate that GHRP-2 attenuated LPS-induced ALI. Early protection appears to be mediated partly through the inhibition of NF-kappaB pathway activation. The present study indicates that GHRP-2 acts as a potential therapeutic reagent for treating ALI.

Relationship between gut and sepsis: Role of ghrelin

Ghrelin is a growth hormone secretagogue produced by the gut, and is expressed in the hypothalamus and other tissues as well. Ghrelin not only plays an important role in the regulation of appetite, energy balance and glucose homeostasis, but also shows anti-bacterial activity, suppresses pro-inflammatory cytokine production and restores gut barrier function. In experimental animals, ghrelin has shown significant beneficial actions in preventing mortality from sepsis. In the critically ill, corticosteroid insufficiency as a result of dysfunction of the hypothalamic-pituitary-adrenal axis is known to occur. It is therefore possible that both gut and hypothalamus play an important role in the pathogenesis of sepsis by virtue of their ability to produce ghrelin, which, in turn, could be a protective phenomenon to suppress inflammation. It remains to be seen whether ghrelin and its analogues are of benefit in treating patients with sepsis.

Ghrelin Receptor Deficiency does not Affect Diet-Induced Atherosclerosis in Low-Density Lipoprotein Receptor-Null Mice

OBJECTIVE

Ghrelin, a stomach-derived, secreted peptide, and its receptor (growth hormone secretagogue receptor, GHSR) are known to modulate food intake and energy homeostasis. The ghrelin system is also expressed broadly in cardiovascular tissues. Since ghrelin has been associated with anti-inflammatory and anti-atherogenic properties, but is also well known to promote obesity and impair glucose metabolism, we investigated whether ghrelin has any impact on the development of atherosclerosis. The hypothesis that endogenous ghrelin signaling may be involved in atherosclerosis has not been tested previously.

METHODS AND RESULTS

We crossed ghrelin receptor knockout mice (GHSr(-/-)) into a low-density lipoprotein receptor-null (Ldlr(-/-)) mouse line. In this model, atherosclerotic lesions were promoted by feeding a high-fat, high-cholesterol Western-type diet for 13 months, following a standard protocol. Body composition and glucose homeostasis were similar between Ldlr(-/-) and Ldlr/GHSR(-/-)ko mice throughout the study. Absence or presence of GHSr did not alter the apolipoprotein profile changes in response to diet exposure on an LDLRko background. Atherosclerotic plaque volume in the aortic arch and thoracic aorta were also not affected differentially in mice without ghrelin signaling due to GHSR gene disruption as compared to control LDLRko littermates. In light of the associations reported for ghrelin with cardiovascular disease in humans, the lack of a phenotype in these loss-of-function studies in mice suggests no direct role for endogenous ghrelin in either the inhibition or the promotion of diet-induced atherosclerosis.

CONCLUSION

These data indicate that, surprisingly, the complex and multifaceted actions of endogenous ghrelin receptor mediated signaling on the cardiovascular system have minimal direct impact on atherosclerotic plaque progression as based on a loss-of-function mouse model of the disease.

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

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

Ghrelin promotes nuclear factor kappa-B activation in a human B-lymphocyte cell line

Ghrelin, an orexigenic hormone of gastric origin that stimulates growth hormone secretion, may modulate inflammation. This experimental study examines the effect of ghrelin on NFκB (p65 subunit), a transcriptional factor involved in inflammation on a human B-lymphocyte cell (WILCL). After confirming the expression of ghrelin receptor protein using western blotting the cells were transferred to wells maintaining a density of 1 × 10(6) cells per ml and a proportion activated with phytohaemagluttinin. Activated and resting cells were exposed to octanoyl-, desoctanoyl ghrelin and a non-peptide ghrelin agonist (Pfizer CP-464709) in increasing concentrations for 6 h. Cell protein extracts were analyzed for NFκB activation using Trans AM NFκB p65 assay. IL-6, IL-8, IL-10, IL-13 and TNFα were measured in the media using Lincoplex human cytokine assay. In octanoyl ghrelin treated resting cells, NFκB activity (Optical Density OD(450 nm)) (mean ± SEM) in control cells was 0.42 ± 0.10 and increased to 0.61 ± 0.20 (P = 0.044), 0.54 ± 0.10 (P = 0.043), 0.52 ± 0.08 at 1, 10 and 100 nM concentrations respectively. No effect was detected with desoctanoyl ghrelin or ghrelin agonist and no specific change in cytokine production. In conclusion, Octanoyl ghrelin increased NFκB activation by up to 50% in a B-lymphocyte cell line suggesting an effect on the inflammatory process.

Current and emerging strategies for the treatment and management of systemic lupus erythematosus based on molecular signatures of acute and chronic inflammation

Lupus is a chronic, systemic inflammatory condition in which eicosanoids, cytokines, nitric oxide (NO), a deranged immune system, and genetics play a significant role. Our studies revealed that an imbalance in the pro- and antioxidants and NO and an alteration in the metabolism of essential fatty acids exist in lupus. The current strategy of management includes administration of nonsteroidal anti-inflammatory drugs such as hydroxychloroquine and immunosuppressive drugs such as corticosteroids. Investigational drugs include the following: 1) belimumab, a fully human monoclonal antibody that specifically recognizes and inhibits the biological activity of B-lymphocyte stimulator, also known as B-cell-activation factor of the TNF family; 2) stem cell transplantation; 3) rituximab, a chimeric monoclonal antibody against CD20, which is primarily found on the surface of B-cells and can therefore destroy B-cells; and 4) IL-27, which has potent anti-inflammatory actions. Our studies showed that a regimen of corticosteroids and cyclophosphamide, and methods designed to enhance endothelial NO synthesis and augment antioxidant defenses, led to induction of long-lasting remission of the disease. These results suggest that methods designed to modulate molecular signatures of the disease process and suppress inflammation could be of significant benefit in lupus. Some of these strategies could be vagal nerve stimulation, glucose-insulin infusion, and administration of lipoxins, resolvins, protectins, and nitrolipids by themselves or their stable synthetic analogs that are known to suppress inflammation and help in the resolution and healing of the inflammation-induced damage. These strategies are likely to be useful not only in lupus but also in other conditions, such as rheumatoid arthritis, scleroderma, ischemia-reperfusion injury to the myocardium, ischemic heart disease, and sepsis.

Ghrelin improves disturbed myocardial energy metabolism in rats with heart failure induced by isoproterenol

To explore the effects of ghrelin on disturbed myocardial energy metabolism during chronic heart failure (CHF). Rats were subcutaneously injected with isoproterenol (ISO) for 10 days with or without ghrelin for another 10 days. Enzyme immunoassay was to measure ghrelin concentrations. Compared with the control group, ISO-treated rats showed suppressed cardiac function with high ghrelin/GHS-R expressions. These rats also showed the decreases in food consumption and weight. The decreased levels of plasma glucose and myocardial glucogen, but the high lactate in blood and myocardium showed myocardial metabolic disturbance. Compared with the group given ISO alone, the rats with ghrelin (20 and 100 microg/kg/day) improved cardiac dysfunction and increased food intake by 13.5 and 14.2% (both P < 0.01), and rate of weight gain by 95% (P < 0.05) and 1.71-fold (P < 0.01), respectively. The plasma glucose were increased by 49.7 and 50.8% (both P < 0.01), and myocardial glucogen, by 40.5 and 51.7% (both P < 0.01), but blood lactate decreased by 1.56- and 1.96-fold (both P < 0.01), and myocardial lactate by 32.1 and 48.7% (both P < 0.05), respectively. Their MCT1 mRNA and protein expressions increased. The myocardial ghrelin/GHS-R pathway can be upregulated during CHF. The ghrelin can attenuate cardiac dysfunction and energy metabolic disturbance in CHF rats.