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

N-Terminal Pro-Brain Natriuretic Peptide Correlates with Ghrelin and Acyl-Ghrelin in Pre-Dialysis Chronic Kidney Disease

Pro-B amino-terminal natriuretic peptide (NT-proBNP) is a diagnostic marker for heart failure (HF), a severe complication of chronic kidney disease (CKD). However, its significance in CKD is not clear, as other factors, such as renal function, may also have an impact. Recent studies have shown that ghrelin treatment is effective in HF in the general population, but the impact of ghrelin on cardiac function in CKD patients is still unknown. Our study aimed to investigate the factors associated with NT-proBNP in pre-dialysis CKD patients and to evaluate the correlation between NT-proBNP and ghrelin and acyl-ghrelin, molecules determined using ELISA methods. In a cross-sectional observational study, we included 80 patients with pre-dialysis CKD, with a mean age of 68 years and 50% men. The median values for NT-proBNP were 351.8 pg/mL, for acyl ghrelin 16.39 pg/mL, and for ghrelin 543.32 pg/mL. NT-proBNP was correlated with ghrelin (p = 0.034, r = 0.24), acyl-ghrelin (p = 0.033, r = -0.24), estimated glomerular filtration rate (p = 0.027, r = -0.25), serum urea (p = 0.006, r = 0.31), and ferritin (p = 0.041, r = 0.28). In multivariate analysis, ghrelin (p = 0.040) and blood urea (p = 0.040) remained significant predictors for NT-proBNP levels. NT-proBNP was a significant predictor for acyl-ghrelin (p = 0.036). In conclusion, in pre-dialysis CKD patients, a high value of NT-proBNP was associated with a high value of total ghrelin and a low value of acyl-ghrelin.

Genome-Wide Association and Two-Sample Mendelian Randomization Analyses of Plasma Ghrelin and Gastrointestinal Cancer Risk

BACKGROUND

Observational studies have suggested that the gut hormone ghrelin is an early marker of future risk of developing gastrointestinal cancer. However, whether ghrelin is a causal risk factor remains unclear. We conducted a genome-wide association study (GWAS) of plasma ghrelin and used Mendelian randomization (MR) to investigate the possible causal association between ghrelin and gastrointestinal cancer risk.

METHODS

Genetic variants associated with plasma ghrelin were identified in a GWAS comprising 10,742 Swedish adults in the discovery (N = 6,259) and replication (N = 4,483) cohorts. The association between ghrelin and gastrointestinal cancer was examined through a two-sample MR analysis using the identified genetic variants as instruments and GWAS data from the UK Biobank, FinnGen, and a colorectal cancer consortium.

RESULTS

GWAS found associations between multiple genetic variants within ±200 kb of the GHRL gene and plasma ghrelin. A two-sample MR analysis revealed that genetically predicted higher plasma ghrelin levels were associated with a lower risk of gastrointestinal cancer in UK Biobank and in a meta-analysis of the UK Biobank and FinnGen studies. The combined OR per approximate doubling of genetically predicted plasma ghrelin was 0.91 (95% confidence interval, 0.85-0.99; P = 0.02). Colocalization analysis revealed limited evidence of shared causal variants for plasma ghrelin and gastrointestinal cancer at the GHRL locus (posterior probability H4 = 24.5%); however, this analysis was likely underpowered.

CONCLUSIONS

Our study provides evidence in support of a possible causal association between higher plasma ghrelin levels and a reduced risk of gastrointestinal cancer.

IMPACT

Elevated plasma ghrelin levels might reduce the risk of gastrointestinal cancer.

Acyl ghrelin improves cardiac function in heart failure and increases fractional shortening in cardiomyocytes without calcium mobilization

BACKGROUND AND AIMS

Ghrelin is an endogenous appetite-stimulating peptide hormone with potential cardiovascular benefits. Effects of acylated (activated) ghrelin were assessed in patients with heart failure and reduced ejection fraction (HFrEF) and in ex vivo mouse cardiomyocytes.

METHODS AND RESULTS

In a randomized placebo-controlled double-blind trial, 31 patients with chronic HFrEF were randomized to synthetic human acyl ghrelin (0.1 µg/kg/min) or placebo intravenously over 120 min. The primary outcome was change in cardiac output (CO). Isolated mouse cardiomyocytes were treated with acyl ghrelin and fractional shortening and calcium transients were assessed. Acyl ghrelin but not placebo increased cardiac output (acyl ghrelin: 4.08 ± 1.15 to 5.23 ± 1.98 L/min; placebo: 4.26 ± 1.23 to 4.11 ± 1.99 L/min, P < 0.001). Acyl ghrelin caused a significant increase in stroke volume and nominal increases in left ventricular ejection fraction and segmental longitudinal strain and tricuspid annular plane systolic excursion. There were no effects on blood pressure, arrhythmias, or ischaemia. Heart rate decreased nominally (acyl ghrelin: 71 ± 11 to 67 ± 11 b.p.m.; placebo 69 ± 8 to 68 ± 10 b.p.m.). In cardiomyocytes, acyl ghrelin increased fractional shortening, did not affect cellular Ca2+ transients, and reduced troponin I phosphorylation. The increase in fractional shortening and reduction in troponin I phosphorylation was blocked by the acyl ghrelin antagonist D-Lys 3.

CONCLUSION

In patients with HFrEF, acyl ghrelin increased cardiac output without causing hypotension, tachycardia, arrhythmia, or ischaemia. In isolated cardiomyocytes, acyl ghrelin increased contractility independently of preload and afterload and without Ca2+ mobilization, which may explain the lack of clinical side effects. Ghrelin treatment should be explored in additional randomized trials.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05277415.

Potential Applications for Growth Hormone Secretagogues Treatment of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) arises from neuronal death due to complex interactions of genetic, molecular, and environmental factors. Currently, only two drugs, riluzole and edaravone, have been approved to slow the progression of this disease. However, ghrelin and other ligands of the GHS-R1a receptor have demonstrated interesting neuroprotective activities that could be exploited in this pathology. Ghrelin, a 28-amino acid hormone, primarily synthesized and secreted by oxyntic cells in the stomach wall, binds to the pituitary GHS-R1a and stimulates GH secretion; in addition, ghrelin is endowed with multiple extra endocrine bioactivities. Native ghrelin requires esterification with octanoic acid for binding to the GHS-R1a receptor; however, this esterified form is very labile and represents less than 10% of circulating ghrelin. A large number of synthetic compounds, the growth hormone secretagogues (GHS) encompassing short peptides, peptoids, and non-peptidic moieties, are capable of mimicking several biological activities of ghrelin, including stimulation of GH release, appetite, and elevation of blood IGF-I levels. GHS have demonstrated neuroprotective and anticonvulsant effects in experimental models of pathologies both in vitro and in vivo. To illustrate, some GHS, currently under evaluation by regulatory agencies for the treatment of human cachexia, have a good safety profile and are safe for human use. Collectively, evidence suggests that ghrelin and cognate GHS may constitute potential therapies for ALS.

The expression and function of growth hormone secretagogue receptor in immune cells: A current perspective

The orexigenic hormone ghrelin and its receptor, growth hormone secretagogue receptor (GHS-R), have been extensively studied in the last two decades, revealing that ghrelin signaling has important implications in health and disease. Metabolic diseases, such as obesity and diabetes, are often accompanied by low-grade chronic inflammation, that has been coined as "meta-inflammation." Immune cells are key cellular mediators of meta-inflammation, controlling both initiation and resolution of inflammation. Immune cells exhibit dynamic changes in cellular characteristics and functional output in response to the stimuli/insults from their surrounding microenvironment. Emerging evidence shows that ghrelin has an important effect on inflammation, in addition to its well-known effects on metabolism. However, the cellular/molecular mechanism of ghrelin signaling in immunity is largely unknown because the knowledge in regard to the expression and function of GHS-R in immune cells is currently sparse. In this review, we have accumulated the recent findings related to the expression and functions of GHS-R in various immune cells under different physiological and pathological states. This review aims to inspire further investigation of the immunological roles of ghrelin signaling and advance the therapeutic applications of ghrelin signaling in meta-inflammation.

Role of the Ghrelin System in Colitis and Hepatitis as Risk Factors for Inflammatory-Related Cancers

It is not known exactly what leads to the development of colorectal cancer (CRC) and hepatocellular carcinoma (HCC), but there are specific risk factors that increase the probability of their occurrence. The unclear pathogenesis, too-late diagnosis, poor prognosis as a result of high recurrence and metastasis rates, and repeatedly ineffective therapy of both cancers continue to challenge both basic science and practical medicine. The ghrelin system, which is comprised of ghrelin and alternative peptides (e.g., obestatin), growth hormone secretagogue receptors (GHS-Rs), and ghrelin-O-acyl-transferase (GOAT), plays an important role in the physiology and pathology of the gastrointestinal (GI) tract. It promotes various physiological effects, including energy metabolism and amelioration of inflammation. The ghrelin system plays a role in the pathogenesis of inflammatory bowel diseases (IBDs), which are well known risk factors for the development of CRC, as well as inflammatory liver diseases which can trigger the development of HCC. Colitis-associated cancer serves as a prototype of inflammation-associated cancers. Little is known about the role of the ghrelin system in the mechanisms of transformation of chronic inflammation to low- and high-grade dysplasia, and, finally, to CRC. HCC is also associated with chronic inflammation and fibrosis arising from different etiologies, including alcoholic and nonalcoholic fatty liver diseases (NAFLD), and/or hepatitis B (HBV) and hepatitis C virus (HCV) infections. However, the exact role of ghrelin in the progression of the chronic inflammatory lesions into HCC is still unknown. The aim of this review is to summarize findings on the role of the ghrelin system in inflammatory bowel and liver diseases in order to better understand the impact of this system on the development of inflammatory-related cancers, namely CRC and HCC.

Ghrelin and Obestatin in Adolescent Patients with Anorexia Nervosa: Is There an Association with Disordered Eating, Depression, and Obsessive-Compulsive Symptoms?

Anorexia nervosa (AN) is an eating disorder characterized by restrictive eating and significant weight loss. In the course of AN, changes are observed in appetite regulation, including orexigenic ghrelin and potentially anorexigenic obestatin. The study aimed to determine if any changes in serum ghrelin and obestatin levels during treatment of AN are observed, while investigating the correlations between these peptides and the severity of disturbed eating attitudes, depression, and anxiety. Thirty adolescent inpatients with AN (examined twice: before hospitalization treatment AN-BT and after treatment AN-AT) and thirty healthy age- and height-matched girls (CG) participated in the study. Anthropometric, serum ghrelin and obestatin concentrations and psychometric evaluations (Eating Attitudes Test 26 Item-EAT-26, Beck Depression Inventory-BDI, Hamilton Depression Rating Scale-HDRS, and Yale Brown Obsessive-Compulsive Scale-Y-BOCS) were performed. The study revealed significantly higher ghrelin and obestatin levels in AN-BT than in AN-AT. A trend toward lower levels during treatment provided partial normalizations. Analyzing correlations in the AN-BT vs. CG group, correlations of peptides with EAT-26, BDI, and HDRS scores were detected. These results suggest a potential role for ghrelin and obestatin in the context of defense mechanisms regulating appetite and body weight in the course of AN and in terms of psychopathological changes co-occurring with this eating disorder.

Role of the Ghrelin System in Colorectal Cancer

The ghrelin system contains several components (e.g., ghrelin with growing number of alternative peptides, growth hormone secretagogue receptors (GHS-Rs), and ghrelin-O-acyl-transferase (GOAT) and participates in regulation of a number of key processes of gastrointestinal (GI) tract cancer progression, including cell proliferation, migration, invasion, apoptosis, inflammation, and angiogenesis. However, its exact role in promoting or inhibiting cancer progression is still unclear. Colorectal cancer (CRC) is one of the most common human malignancies worldwide. Molecular studies suggest an autocrine/paracrine mechanism for the secretion of ghrelin in colorectal carcinogenesis and its contribution to its initial stages. However, the signalling pathways of CRC development involving the ghrelin system are poorly understood. Potential mechanisms of colon carcinogenesis involving components of the ghrelin system were previously described in an animal model and in in vitro studies. However, the diagnostic–prognostic role of serum ghrelin concentrations, tissue expression, or genetic changes of this system in various stages of CRC progression remains an open case. Thus, the aim of this study is to discuss the role of the ghrelin system in colon carcinogenesis, diagnostics and CRC prognostics, as well as the results of studies on the use of ghrelin and its analogues in the therapy of CRC-related syndromes (e.g., cachexia and sarcopenia).

Ghrelin Alleviates Endoplasmic Reticulum Stress in MC3T3E1 Cells by Inhibiting AMPK Phosphorylation

Ghrelin is a gastric endocrine peptide that has been found to be involved in the process of energy homeostasis and bone physiology in recent years. To explore the effects of ghrelin on endoplasmic reticulum stress (ERS) in MC3T3E1 cells and its possible mechanism, an ERS model was induced by tunicamycin (TM) in the osteoblast line MC3T3E1. TM at 1.5 μg/mL was selected as the experimental concentration found by CCK8 assay. Through the determination of apoptosis, reactive oxygen species production, and endoplasmic reticulum stress-related gene expression, we found that ERS induced by TM can be relieved by ghrelin in a concentration-dependent manner (P < 0.001). Compared with the TM group, ghrelin reduced the expression of ERS-related marker genes induced by TM. Compared with the GSK621 + TM group without ghrelin pretreatment, the mRNA expression of genes in the ghrelin pretreatment group decreased significantly (P < 0.001). The results of protein analysis showed that the levels of BIP, p-AMPK, and cleaved-caspase3 in the TM group increased significantly, while the levels decreased after ghrelin pretreatment. In group GSK621 + TM compared with group GSK621 + ghrelin+TM, ghrelin pretreatment significantly reduced the level of p-AMPK, which is consistent with the trend of the ERS-related proteins BIP and cleaved-caspase3. In conclusion, ghrelin alleviates the ERS induced by TM in a concentration-dependent manner and may or at least partly alleviate the apoptosis induced by ERS in MC3T3E1 cells by inhibiting the phosphorylation of AMPK.

Relationships between Ghrelin and Obestatin with MDA, Proinflammatory Cytokines, GSH/GSSG Ratio, Catalase Activity, and Semen Parameters in Infertile Patients with Leukocytospermia and Varicocele

Ghrelin and obestatin are involved in many biological functions including reproduction. Growing evidences suggest that both peptides could exert protective and antioxidant activities. In this study, the relationships between ghrelin/obestatin, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), malondialdehyde (MDA), reduced glutathione (GSH), oxidized glutathione (GSSG), expressed as the GSH/GSSG ratio, catalase (CAT), and semen parameters in infertile patients with varicocele or leukocytospermia and controls were investigated. Fifty-six infertile patients (32 with leukocytospermia and 24 with varicocele) and 14 controls participated in this study. Semen analysis was performed following the WHO guidelines. Apoptotic and necrotic sperm were scored by annexin V/propidium iodide assay. Seminal plasma samples were used for the following determinations: ghrelin, obestatin, IL-6, and TNF-α were measured by an immunological method, GSH/GSSG by an enzymatic method, and CAT by spectrophotometric determination. With respect to controls, both the leukocytospermia and varicocele groups showed altered sperm parameters, significantly increased sperm apoptosis (P = 0.009 and P = 0.011, respectively), IL-6 (P = 0.0001 and P = 0.004, respectively), and TNF-α levels (P = 0.0001 and P = 0.002, respectively); both groups had significantly decreased levels of ghrelin (P = 0.0001), obestatin (P = 0.0001 and P = 0.006, respectively), and GSH/GSSG ratio (P = 0.003 and P = 0.0001, respectively). The MDA concentration was significantly increased in the leukocytospermia group vs. controls (P = 0.0001), in the varicocele group vs. controls (P = 0.011), and in the leukocytospermia group vs. the varicocele group (P = 0.008). CAT activity was augmented in both the leukocytospermia and varicocele groups (P = 0.0001)vs. controls. The results indicate that both ghrelin and obestatin may play a protective role in human semen and this effect is probably due to their antioxidant properties.

Prokineticin-2 and ghrelin robustly influence the sexual and ingestive behaviors of female Syrian hamsters

Prokineticins are involved in many physiological processes including circadian rhythms, neurogenesis, angiogenesis, and cancer. Recently, they have been found to play a role in regulating food intake. Historically, proteins that increase feeding behavior in mammals decrease reproductive behavior to prevent pregnancy and lactation when food is scarce. In the current study, prokineticin-2 (PK2) had pronounced effects on reproductive and ingestive behaviors when given to female Syrian hamsters. Administration of PK2 prevented ingestive behaviors induced by food restriction, such as the amount of time spent with food and eating. Hamsters given PK2 preferred to engage in reproductive behaviors, including spending time with a male and lordosis. Furthermore, analysis of blood plasma revealed that changes to behavior persisted despite similar levels of des-acyl ghrelin (DAG) and reduced glucose concentrations in the blood. Additionally, administering 10 mg/kg of acyl ghrelin (AG) to a different cohort of animals significantly decreased the amount of time females spent with a potential mating partner, increased the amount of time females spent with food, decreased the duration of lordosis, and increased the duration of eating. Results from the current study support the need for further research investigating the reproductive and ingestive roles of PK2 and ghrelin.

Cinnamomum osmophloeum Kanehira ethanol extracts prevents human liver-derived HepG2 cell death from oxidation stress by induction of ghrelin gene expression

Diabetes patients associated with liver disease carry a significant risk of morbidity and mortality. Cinnamon has been reported to reduce fructose-induced oxidative stress in the rat liver. However, the mechanism by which cinnamon protects the liver in a high-saccharide environment remains to be investigated. HepG2 cells were cultured with 30 mM D-ribose to mimic the high-oxidative-stress environment, typical of a liver in a diabetic patient. Three different chemical types of C. osmophloeum ethanol extracts (CEEs) were added in HepG2 culture media and the administration of all three CEEs protected HepG2 cells from D-ribose damage and increased cell survival by approximately 20 percent. Exclusively, the transcript variant 1 of the ghrelin gene, but not variant 3, was 2-3 times induced by the addition of these CEEs. Moreover, the mRNAs of ghrelin processing enzyme, furin, and mboat4 were detected in HepG2 cells. The ghrelin hormones in the culture media were increased 4-9 times by the addition of CEEs. The protective effects of ghrelin on HepG2 cells in D-ribose environment were further confirmed by recombinant ghrelin transfection. We conclude that the CEEs induce ghrelin gene expression and protect HepG2 cells from D-ribose-induced oxidative damage through ghrelin signalling.

Dietary Polysaccharide from Enteromorpha Clathrata Modulates Gut Microbiota and Promotes the Growth of Akkermansia muciniphila, Bifidobacterium spp. and Lactobacillus spp

Recently, accumulating evidence has suggested that Enteromorpha clathrata polysaccharide (ECP) could contribute to the treatment of diseases. However, as a promising candidate for marine drug development, although ECP has been extensively studied, less consideration has been given to exploring its effect on gut microbiota. In this light, given the critical role of gut microbiota in health and disease, we investigated here the effect of ECP on gut microbiota using 16S rRNA high-throughput sequencing. As revealed by bioinformatic analyses, ECP considerably changed the structure of the gut microbiota and significantly promoted the growth of probiotic bacteria in C57BL/6J mice. However, interestingly, ECP exerted different effects on male and female microbiota. In females, ECP increased the abundances of Bifidobacterium spp. and Akkermansia muciniphila, a next-generation probiotic bacterium, whereas in males, ECP increased the population of Lactobacillus spp. Moreover, by shaping a more balanced structure of the microbiota, ECP remarkably reduced the antigen load from the gut in females. Altogether, our study demonstrates for the first time a prebiotic effect of ECP on gut microbiota and forms the basis for the development of ECP as a novel gut microbiota modulator for health promotion and disease management.

Serum Obestatin: A Biomarker of Cardiovascular and All-Cause Mortality in Hemodialysis Patients

BACKGROUND

Recent experimental studies have suggested that obestatin, a proposed anorexigenic gut hormone and a physiological opponent of acyl-ghrelin, has protective cardiovascular effects. We tested the hypothesis that obestatin is independent of inflammatory mediators and/or acyl-ghrelin in predicting outcomes of the maintenance hemodialysis (MHD) population.

METHODS

It was a 6-year cohort study on 261 MHD patients. Obestatin, acyl-ghrelin, adipokines (leptin and adiponectin), markers of inflammation and nutrition, prospective all-cause and cardiovascular mortality were studied.

RESULTS

During the follow-up, 160 patients died in total, with 74 deaths due to cardiovascular causes. For each ng/mL increase in baseline obestatin level in fully adjusted models (including malnutrition-inflammation score, Interleukin-6 [IL-6], adipokines and acyl-ghrelin), the hazard for death from all causes was 0.90 (95% CI 0.81-0.99) and for cardiovascular death 0.85 (95% CI 0.73-0.99). However, these associations were more robust in the subgroup of patients aged above 71 years: 0.85 (95% CI 0.73-0.98) for all-cause death and 0.66 (95% CI 0.52-0.85) for cardiovascular death. An interaction between high IL-6 (above median) and low obestatin (below median) levels for increased risk of all-cause mortality (synergy index [SI] 5.14, p = 0.001) and cardiovascular mortality (SI 4.81, p = 0.02) emerged in the development of multivariable adjusted models. Interactions were also observed between obestatin, Tumor necrosis factor-alpha, adipokines and acyl-ghrelin, which were associated with mortality risk.

CONCLUSION

Serum obestatin behaves as a biomarker for cardiovascular and all-cause mortality in MHD patients. The prognostic ability of obestatin in this regard is independent of inflammation, nutritional status, acyl-ghrelin's and adipokines' activity and is modified by age being very prominent in patients older than 71 years.

Associations of serum leptin, ghrelin and peptide YY levels with physical activity and cardiorespiratory fitness in adolescent boys with different BMI values

The aim of this study was to investigate the differences in associations of serum acylated and des-acylated ghrelin, peptide YY (PYY) and leptin levels with physical activity (PA) and cardiorespiratory fitness (CReF) in adolescent boys (mean age of 14.0 years) with overweight (OWB; n=55) and with normal weight (NWB; n=154).

METHODS

Total PA was measured by 7-day accelerometry (counts/min) and CReF by peak oxygen consumption (VO²peak/kg).

RESULTS

No differences were found in serum PYY, acylated ghrelin or des-acyl ghrelin levels, whereas mean leptin (11.6±10.6 vs. 2.0±2.7 ng/ml; p<0.05) and insulin (18.1±8.7 vs. 11.0±6.2 mU/l; p<0.05) levels were significantly higher in OWB compared to NWB. Mean CReF was significantly lower in OWB compared to NWB (39.7±8.7 vs. 50.5±6.8 ml/min/kg; p<0.05). Leptin was negatively correlated with CReF in both groups (r=-0.43; p<0.05), des-acylated ghrelin with CReF only in OWB (r =-0.36; p<0.05). In OWB leptin was negatively correlated with total PA (r=-0.32; p<0.05) and positively with sedentary time of PA (r=0.35; p<0.05). In NWB 28.1% of the variability of CReF was determined by leptin and insulin resistance index (HOMA-IR), whereas in OWB 71.9% was determined by trunk FM and BMI.

CONCLUSIONS

Leptin concentration was inversely associated with CReF in adolescent boys independently of BMI in both groups, while des-acylated ghrelin was associated with CReF only in OWB. Low PA in OWB was associated with high serum leptin level.

Similar effects of lysine deficiency in muscle biochemical characteristics of fatty and lean piglets

The main objective of this work was to investigate the effects of feeding Lys-deficient diets on muscle biochemical characteristics, particularly intramuscular fat concentration and fatty acid profile, in a fatty (Iberian) and a conventional pig genotype (Landrace × Large White [LDW]) maintained in identical experimental conditions. Performance and plasma metabolite changes were also monitored. Twenty-eight barrows of 10 kg initial BW, 14 of Iberian and 14 of LDW breed, were randomly assigned to each of 2 experimental diets in a 2 × 2 factorial arrangement (2 breeds × 2 diets). Seven pigs were allocated to each treatment combination. Diets (isonitrogenous and isoenergetic; 200 g CP/kg DM and 14.7 MJ ME) based on barley, corn, corn gluten meal, and soybean meal, with identical composition, except for their Lys content (10.9 g/kg for the diet adequate in Lys and 5.2 g/kg for the diet deficient in Lys), were assayed. Pigs were housed in individual 2 m pens and fed at 85% of ad libitum intake of the Iberian genotype, of greater intake capacity. Daily feed allowance was based on BW individually measured each week. At 25 kg BW, pigs were slaughtered by exsanguination after electrical stunning. Blood samples were taken and longissimus dorsi and biceps femoris muscles were rapidly dissected and stored frozen prior to analysis. Performance was reduced in both pig breeds when fed Lys-deficient diets, particularly in LDW pigs (breed × diet interaction, < 0.05). Intramuscular fat content increased in longissimus dorsi of Iberian ( < 0.05) and in biceps femoris of both pig genotypes ( < 0.01) when fed Lys-deficient diets. Oleic acid increased ( < 0.05) and PUFA acid decreased ( < 0.01) in longissiumus dorsi and biceps femoris of pigs of both genotypes fed Lys-deficient diets. The proportion of oxidative fibers ( < 0.001) and free carnitine content ( < 0.05) increased in longissimus dorsi of both pigs types fed Lys-deficient diets. Plasma creatinine was greater in LDW pigs compared with Iberian pigs ( < 0.01). Urea and total cholesterol increased in pigs consuming Lys-deficient diets ( < 0.01). The plasma free carnitine concentration was higher in Iberian pigs than in LDW pigs ( < 0.059). No changes in plasma carnitine status due to dietary Lys supply were detected. Feeding Lys-deficient diets could be a suitable strategy for increasing intramuscular fat content in fatty and lean pigs.

The association between ghrelin levels and markers of arterial stiffness and inflammatory markers in Saudi subjects with metabolic syndrome

BACKGROUND

Arterial stiffness is a principal cardiovascular risk factor. Metabolic syndrome (MetS) is a predisposing factor to arterial stiffness and persistent MetS circumstances can deteriorate the arterial stiffness severity. Low concentrations of plasma ghrelin are meticulously connected to arterial stiffness. This work targeted to judge the relationship between plasma ghrelin levels and intima-media thickness (IMT) and brachial-ankle pulse wave velocity (baPWV) as markers of arterial stiffness and inflammatory markers and in Saudi subjects with MetS.

PATIENTS AND METHODS

Eighty-four young adults were recruited from the visitors of the outpatient clinics of Taif hospitals, and then they were divided into a control group that involves subjects without MetS and a study group involving those with MetS. Anthropometric measurements, blood pressure, plasma ghrelin levels, fasting plasma glucose levels (FPG) and lipid profile were assessed. baPWV was measured by a volume plethysmograph while IMT was evaluated by ultrasonography.

RESULTS

Plasma ghrelin values were significantly (P<0.001) decreased in the MetS group versus control group. Arterial stiffness was noticed in MetS group by significantly (P<0.01) increased IMT and baPWV (P<0.001) matched with control group. Plasma ghrelin concentrations were negatively associated with age, smoking, FPG, HbA1c, CRP, TNF-alpha, baPWV, and Lt Carotid IMT.

CONCLUSIONS

Depending on our outcomes showing the valuable properties of ghrelin in the cardiovascular system in patients with metabolic syndrome, it can be postulated that ghrelin may be associated with markers of atherosclerosis.

Ghrelin and Motilin Control Systems in GI Physiology and Therapeutics

Ghrelin and motilin are released from gastrointestinal endocrine cells during hunger, to act through G protein-coupled receptors that have closely related amino acid sequences. The actions of ghrelin are more complex than motilin because ghrelin also exists outside the GI tract, it is processed to des-acyl ghrelin which has activity, ghrelin can exist in truncated forms and retain activity, the ghrelin receptor can have constitutive activity and is subject to biased agonism and finally additional ghrelin-like and des-acyl ghrelin receptors are proposed. Both ghrelin and motilin can stimulate gastric emptying, acting via different pathways, perhaps influenced by biased agonism at the receptors, but research is revealing additional pathways of activity. For example, it is becoming apparent that reduction of nausea may be a key therapeutic target for ghrelin receptor agonists and perhaps for compounds that modulate the constitutive activity of the ghrelin receptor. Reduction of nausea may be the mechanism through which gastroparesis symptoms are reduced. Intriguingly, a potential ability of motilin to influence nausea is also becoming apparent. Ghrelin interacts with digestive function through its effects on appetite, and ghrelin antagonists may have a place in treating Prader-Willi syndrome. Unlike motilin, ghrelin receptor agonists also have the potential to treat constipation by acting at the lumbosacral defecation centres. In conclusion, agonists of both ghrelin and motilin receptors hold potential as treatments for specific subsets of digestive system disorders.

Obestatin regulates cardiovascular function and promotes cardioprotection through the nitric oxide pathway

Patients with ischaemic heart disease or chronic heart failure show altered levels of obestatin, suggesting a role for this peptide in human heart function. We have previously demonstrated that GH secretagogues and the ghrelin gene-derived peptides, including obestatin, exert cardiovascular effects by modulating cardiac inotropism and vascular tone, and reducing cell death and contractile dysfunction in hearts subjected to ischaemia/reperfusion (I/R), through the Akt/nitric oxide (NO) pathway. However, the mechanisms underlying the cardiac actions of obestatin remain largely unknown. Thus, we suggested that obestatin-induced activation of PI3K/Akt/NO and PKG signalling is implicated in protection of the myocardium when challenged by adrenergic, endothelinergic or I/R stress. We show that obestatin exerts an inhibitory tone on the performance of rat papillary muscle in both basal conditions and under β-adrenergic overstimulation, through endothelial-dependent NO/cGMP/PKG signalling. This pathway was also involved in the vasodilator effect of the peptide, used both alone and under stress induced by endothelin-1. Moreover, when infused during early reperfusion, obestatin reduced infarct size in isolated I/R rat hearts, through an NO/PKG pathway, comprising ROS/PKC signalling, and converging on mitochondrial ATP-sensitive potassium [mitoK(ATP)] channels. Overall, our results suggest that obestatin regulates cardiovascular function in stress conditions and induces cardioprotection by mechanisms dependent on activation of an NO/soluble guanylate cyclase (sGC)/PKG pathway. In fact, obestatin counteracts exaggerated β-adrenergic and endothelin-1 activity, relevant factors in heart failure, suggesting multiple positive effects of the peptide, including the lowering of cardiac afterload, thus representing a potential candidate in pharmacological post-conditioning.

Preclinical evidence of ghrelin as a therapeutic target in epilepsy

Ghrelin, an orexigenic peptide synthesized by endocrine cells of the gastric mucosa, plays a major role in inhibiting seizures. However, the underlying mechanism of ghrelin's anticonvulsant action is still unclear. Nowadays, there are considerable evidences showing that ghrelin is implicated in various neurophysiological processes, including learning and memory, neuroprotection, neurogenesis, and inflammatory effects. In this review, we will summarize the effects of ghrelin on epilepsy. It may provide a comprehensive picture of the role of ghrelin in epilepsy.

Obestatin Plays Beneficial Role in Cardiomyocyte Injury Induced by Ischemia-Reperfusion In Vivo and In Vitro

BACKGROUND Obestatin, primarily recognized as a peptide within the gastrointestinal system, has been shown to benefit the cardiovascular system. We designed this experiment to study the protective role and underlying mechanism of obestatin against ischemia-reperfusion(I/R) injury in myocardial cells. MATERIAL AND METHODS In an In vivo experiment, LAD was ligated for 0.5 h and then opened for reperfusion with obestatin for 24 h. Then, the infarction area was shown with TTC staining, and inflammation factors in serum were analyzed by qRT-PCR. In primary cultured cardiomyocytes, we measured the level of LDH, MDA, GSH, and SOD. Finally, we assessed cells apoptosis using flow cytometry and detected the concentrations of caspase-3, Bax, and Bcl-2 using Western blot analysis. RESULTS TTC staining showed that in the 3 obestatin groups, the infarct area became smaller with the increase of obestatin concentration. Obestatin also inhibited LDH expression in rat serum and decreased mRNA levels of TNF-α, IL-6, ICAM-1, and iNOS in rat cardiomyocytes after reperfusion. In primary cultured cardiomyocytes, obestatin decreased LDH content and increased GSH level after I/R injury. Obestatin was also found to antagonize the apoptosis of cardiomyocytes in a dose-dependent manner. Western blot analysis showed that obestatin downregulated the expression of caspase-3 and Bax and upregulated the expression of Bcl-2. CONCLUSIONS Obestatin can protect cardiomyocyte from I/R-induced injury in vitro and in vivo. This beneficial effect is closely related with its properties of anti-inflammation, anti-cytotoxicity, and anti-apoptosis. The protective effect of obestatin might be associated with activation of Bcl-2 and inhibition of caspase-3 and Bax.

Molecular Ghrelin System in the Pancreatic Acinar Cells: The Role of the Polypeptide, Caerulein and Sensory Nerves

Ghrelin (GHRL) is an endogenous ligand for the growth hormone secretagogue receptor (GHS-R). Experimental studies showed that GHRL protects the stomach and pancreas against acute damage, but the effect of GHRL on pancreatic acinar cells was still undetermined. Aim: To investigate the effect of GHRL and caerulein on the functional ghrelin system in pancreatic acinar cells taking into account the role of sensory nerves (SN). Methods: Experiments were carried out on isolated pancreatic acinar cells and AR42J cells. Before acinar cells isolation, GHRL was administered intraperitoneally at a dose of 50 µg/kg to rats with intact SN or with capsaicin deactivation of SN (CDSN). After isolation, pancreatic acinar cells were incubated in caerulein-free or caerulein containing solution. AR42J cells were incubated under basal conditions and stimulated with caerulein, GHRL or a combination of the above. Results: Incubation of isolated acinar cells with caerulein inhibited GHS-R and GHRL expression at the level of mRNA and protein in those cells. Either in rats with intact SN or with CDSN, administration of GHRL before isolation of acinar cells increased expression of GHRL and GHS-R in those cells and reversed the caerulein-induced reduction in expression of those parameters. Similar upregulation of GHS-R and GHRL was observed after administration of GHRL in AR42J cells. Conclusions: GHRL stimulates its own expression and expression of its receptor in isolated pancreatic acinar cells and AR42J cells on the positive feedback pathway. This mechanism seems to participate in the pancreatoprotective effect of GHRL in the course of acute pancreatitis.

Ghrelin affects stopover decisions and food intake in a long-distance migrant

Billions of birds migrate long distances to either reach breeding areas or to spend the winter at more benign places. On migration, most passerines frequently stop over to rest and replenish their fuel reserves. To date, we know little regarding how they decide that they are ready to continue their journey. What physiological signals tell a bird's brain that its fuel reserves are sufficient to resume migration? A network of hormones regulates food intake and body mass in vertebrates, including the recently discovered peptide hormone, ghrelin. Here, we show that ghrelin reflects body condition and influences migratory behavior of wild birds. We measured ghrelin levels of wild garden warblers (Sylvia borin) captured at a stopover site. Further, we manipulated blood concentrations of ghrelin to test its effects on food intake and migratory restlessness. We found that acylated ghrelin concentrations of garden warblers with larger fat scores were higher than those of birds without fat stores. Further, injections of unacylated ghrelin decreased food intake and increased migratory restlessness. These results represent experimental evidence that appetite-regulating hormones control migratory behavior. Our study lays a milestone in migration physiology because it provides the missing link between ecologically dependent factors such as condition and timing of migration. In addition, it offers insights in the regulation of the hormonal system controlling food intake and energy stores in vertebrates, whose disruption causes eating disorders and obesity.

From Belly to Brain: Targeting the Ghrelin Receptor in Appetite and Food Intake Regulation

Ghrelin is the only known peripherally-derived orexigenic hormone, increasing appetite and subsequent food intake. The ghrelinergic system has therefore received considerable attention as a therapeutic target to reduce appetite in obesity as well as to stimulate food intake in conditions of anorexia, malnutrition and cachexia. As the therapeutic potential of targeting this hormone becomes clearer, it is apparent that its pleiotropic actions span both the central nervous system and peripheral organs. Despite a wealth of research, a therapeutic compound specifically targeting the ghrelin system for appetite modulation remains elusive although some promising effects on metabolic function are emerging. This is due to many factors, ranging from the complexity of the ghrelin receptor (Growth Hormone Secretagogue Receptor, GHSR-1a) internalisation and heterodimerization, to biased ligand interactions and compensatory neuroendocrine outputs. Not least is the ubiquitous expression of the GHSR-1a, which makes it impossible to modulate centrally-mediated appetite regulation without encroaching on the various peripheral functions attributable to ghrelin. It is becoming clear that ghrelin’s central signalling is critical for its effects on appetite, body weight regulation and incentive salience of food. Improving the ability of ghrelin ligands to penetrate the blood brain barrier would enhance central delivery to GHSR-1a expressing brain regions, particularly within the mesolimbic reward circuitry.

Interaction between acyl-ghrelin and BMI predicts clinical outcomes in hemodialysis patients

Background

Ghrelin, a gastric orexigenic peptide, and body mass index (BMI) are known as inversely associated to each other and are both linked to cardiovascular (CV) risk and mortality in maintenance hemodialysis (MHD) patients. However, it is unclear whether the interaction between ghrelin and BMI is associated with a risk of all-cause and CV death in this population.

Methods

A prospective observational study was performed on 261 MHD outpatients (39% women, mean age 68.6 ± 13.6 years) recruited from October 2010 through April 2012, and were followed until November 2014 (median follow-up-28 months, interquartile range-19–34 months). We measured acyl-ghrelin (AG) levels, appetite, nutritional and inflammatory markers, prospective all-cause and cardiovascular (CV) mortality.

Results

During follow-up, 109 patients died, 51 due to CV causes. A significant interaction effect of high BMI and high AG (defined as levels higher than median) on all-cause mortality was found. Crude Cox HR for the product termed BMI x AG was 0.52, with a 95% confidence interval (CI): 0.29 to 0.95 (P = 0.03). Evaluating the interaction on an additive scale revealed that the combined predictive value of BMI and AG is larger than the sum of their individual predictive values (synergy index was 1.1). Across the four BMI-AG categories, the group with high BMI and high AG exhibited better all-cause and cardiovascular mortality irrespective of appetite and nutritional status (multivariable adjusted hazard ratios were 0.31, 95% CI 0.16 to 0.62, P = 0.001, and 0.35, 95% CI 0.13 to 0.91, P = 0.03, respectively). Data analyses made by dividing patients according to fat mass-AG, but not to lean body mass-AG categories, provided similar results.

Conclusions

Higher AG levels enhance the favourable association between high BMI and survival in MHD patients irrespective of appetite, nutritional status and inflammation.

Effect of ghrelin and leptin receptors genes polymorphisms on production results and physicochemical characteristics of M. pectoralis superficialis in broiler chickens

Ghrelin and leptin and their receptors GHSR and LEPR regulate food intake, the processes in adipose tissue, and the body’s energy homeostasis in mammals. The aim of the present study was to determine the effect of GHSR/Csp6I and LEPR/Bsh1236I polymorphisms on the meat production parameters of broiler chickens reared to 42 days of age. In 318 fast-growing Hubbard Flex and Ross 308 chickens, g.3051C > T substitution at the GHSR locus and a GGTCAA deletion at positions g.3407_3409del and g.3411_3413del were identified. The use of restriction enzyme Bsh1236I showed the presence of two transitions g.352C > T and g.427G > A in LEPR locus. The chickens were classified into four GHSR/Csp6I and into five LEPR/Bsh1236I diplotypes. GHSR and LEPR polymorphisms were found to influence final bodyweight, daily gain, dressing percentage without giblets, proportion of giblets and the quality characteristics of M. pectoralis superficialis. GHSR/Csp6I and LEPR/Bsh1236I had an effect on pH24 h (P < 0.05) and lightness (L*) of M. pectoralis superficialis (P < 0.05), whereas GHSR/Csp6I influenced shear force (P < 0.05) and thawing loss (P < 0.05). GHSR/Csp6I and LEPR/Bsh1236I were found to have no effect on the abdominal fat content in chicken carcasses. Single nucleotide polymorphisms reported in the present study could be used in breeding programs as selection markers for growth traits and poultry meat quality.

Effect of aerobic exercise on leptin and ghrelin in patients with colorectal cancer

OBJECTIVES

Aerobic exercise can improve the levels of leptin and ghrelin in healthy people, but the effect of aerobic exercise on these proteins in colorectal cancer patients is not well known. The purpose of this study was to investigate plasma leptin and ghrelin concentrations in male patients with colorectal cancer after 8 weeks aerobic exercise and after a week of detraining.

MATERIALS AND METHODS

Thirty men with colorectal cancer (aged: 51.56 ± 11.28 years; ± standard deviation ( SD)) were randomly assigned to training group (n = 15) or control group (n = 15). Before the experiment, Rockport walking test was conducted in order to measure peak aerobic capacity (VO2peak) of all subjects. Exercise training program consisted of 8 weeks walking and three 45-min sessions in each week with 50-60% of target heart rate. After 8 weeks of training, subjects underwent a week of detraining. A repeated measure analysis of variance (ANOVA) was used to evaluate time-course change in variables.

RESULTS

The results showed that body fat percentage was decreased and VO2peak was increased in the training group compared to the control group (P < 0.05). Ghrelin concentration was increased significantly in the training group compared to the control group (P < 0.05), while plasma leptin concentration and insulin resistance did not change significantly. After a week of detraining, the variables did not change significantly in the training group.

CONCLUSION

VO2peak and ghrelin levels increased after 8 weeks aerobic exercise; however, plasma leptin and insulin resistance were not affected by this protocol in male patients with colorectal cancer.

Exendin-4 decreases ghrelin levels through mTOR signaling

Exendin-4 (EX-4), a long-acting glucagon-like peptide-1 receptor (GLP-1R) agonist, regulates feeding behavior through its ability to inhibit gastric emptying. Ghrelin, a gastric hormone, provides a hunger signal to the central nervous system to stimulate appetite. Here, we report that EX-4 suppresses ghrelin production through the mTORC1-dependent mechanism. Central administration of EX-4 reduces gastric, hypothalamic and plasma ghrelin in both C57BL/6J mice and diet induced obese mice. These changes were associated with a significant increase in mTORC1 activity. Both GLP-1 and EX-4 suppressed the expression and secretion of ghrelin in cultured mHypoE-42 cells, a hypothalamic cell line. These effects were associated with significant changes in mTOR signaling. Inhibition of mTORC1 activity by mTOR siRNA or rapamycin abolished the suppression of ghrelin production induced by GLP-1 and EX-4 in mHypoE-42 cells. Our results identify mTORC1 as a critical signaling pathway for the downregulation of ghrelin induced by activation of GLP-1R.

Ghrelin binding to serum albumin and its biological impact

Ghrelin is an octanoylated peptide hormone that plays a key role in the regulation of the body weight and glucose homeostasis. In plasma, ghrelin circulates bound to larger proteins whose identities are partially established. Here, we used size exclusion chromatography, mass spectrometry and isothermal titration microcalorimetry to show that ghrelin interacts with serum albumin. Furthermore, we found that such interaction displays an estimated dissociation constant (KD) in the micromolar range and involves albumin fatty-acid binding sites as well as the octanoyl moiety of ghrelin. Notably, albumin-ghrelin interaction reduces the spontaneous deacylation of the hormone. Both in vitro experiments-assessing ghrelin ability to inhibit calcium channels-and in vivo studies-evaluating ghrelin orexigenic effects-indicate that the binding to albumin affects the bioactivity of the hormone. In conclusion, our results suggest that ghrelin binds to serum albumin and that this interaction impacts on the biological activity of the hormone.

Associations between Bone Mineral Characteristics and Serum Levels of Ghrelin and Peptide YY in Overweight Adolescent Boys

BACKGROUND/AIMS

The role of ghrelin and peptide YY (PYY) in bone mineralization is not fully known. The aim of this study was to determine whether acylated and des-acyl ghrelin and PYY in addition to leptin are related to bone mineral density (BMD) in adolescent overweight boys (OWB) and normal-weight boys (NWB).

PARTICIPANTS AND METHODS

Fifty- five OWB (BMI >85th percentile) and 154 NWB (BMI <85th percentile) aged 12-16 years participated in this study. Fasting serum acylated and des-acyl ghrelin, PYY, leptin, testosterone levels, total body (TB) and lumbar spine (LS) bone mineral content (BMC), and BMD were measured. TB BMC for height and TB and LS bone mineral apparent density (BMAD) were calculated.

RESULTS

No differences were seen in acylated and des-acyl ghrelin or PYY levels, while the leptin levels were significantly higher in the OWB compared to the NWB. In the OWB, TB BMAD was positively correlated with acylated ghrelin and leptin, and TB BMC for height was positively correlated with PYY. In the OWB, the variability of TB BMD was determined by TB fat-free mass and des-acyl ghrelin, whereas the variability of TB BMAD was determined by leptin.

CONCLUSIONS

Des-acyl ghrelin and PYY are involved in the bone mineralization process in puberty, and the impact can vary between normal and overweight subjects.

Localization of ghrelin-like peptide in the gastrointestinal tract of the golden apple snail (Pomacea canaliculata) and changing of its concentration during fasting

Ghrelin is an endogenous hormone detected in the gastrointestinal tracts (GI) of various species. In the present study, ghrelin-like peptide (ghrelin-LP) was identified in the GI tract of the golden apple snail, Pomacea canaliculata. Using immunohistochemistry, the result revealed an immunoreactivity (-ir) of ghrelin-LP in regions of the GI tract. The ghrelin-LP-ir was observed in both opened-type and closed-type cells of the esophagus, stomach, and small and large intestines. The highest density of ghrelin-LP immunoreactive cells was found in the esophagus and the least density was detected in the stomach. The highest percentages of the opened-type and closed-type cells were present in the esophagus and small intestine, respectively. In immunoblotting, the molecular weight of ghrelin-LP was related to the human ghrelin peptide (∼13kDa). Moreover, the concentration of ghrelin-LP was significantly higher in snails that were fasted for 24h compared with fed snails. The concentration decreased after refeeding. The present study could be useful for understanding the physiological role of ghrelin-LP in mollusk species.

Ghrelin and its correlation with leptin, energy related metabolites and thyroidal hormones in dairy cows in transitional period

The transition from late gestation to early lactation is a critical period in a dairy cow’s life so that dairy cows undergo tremendous changes during this period.

The aim of this study was to determine blood levels of ghrelin, leptin, glucose, β-ydroxybutyrate (BHB), non-esterified fatty acids (NEFA), triglycerides (TG), triiodothyronine (T3) and thyroxine (T4) in dairy Holstein cows (n = 20) and their correlations during the transition period.

Blood samples were collected weekly from 3 wk antepartum to 6 wk postpartum from 20 high-yielding Holstein-Friesian cows. Ghrelin and leptin of plasma and glucose, BHB, NEFA, TG, T3, T4 of serum were then measured.

Early lactation cows showed significantly higher (p<0.05) values of ghrelin, BHB and NEFA, and lower levels of leptin, TG, T3 and T4 (p<0.05) compared to late dry cows. Serum concentrations of glucose did not differ significantly at any time (P>0.05).

Plasma ghrelin concentrations showed positive correlations with the serum BHB and NEFA (p<0.01), while plasma ghrelin had negative correlations (p<0.01) with leptin, TG, T3 and T4. In addition, no significant correlation (p>0.05) was found between ghrelin and glucose.

The results of the study showed that blood ghrelin, leptin, BHB and NEFA levels are sensitive indicators of the energy balance during the peri-partum period in dairy cows and glucose values may not be considered as a precise indicator of negative energy balance in dairy cows.

Energy homeostasis and appetite regulating hormones as predictors of weight loss in men and women

Sex differences in weight loss are often seen despite using the same weight loss program. There has been relatively little investigation of physiological influences on weight loss success in males and females, such as energy homeostasis and appetite regulating hormones. The aims were to 1) characterise baseline plasma leptin, ghrelin and adiponectin concentrations in overweight and obese males and females, and 2) determine whether baseline concentrations of these hormones predict weight loss in males and females. Subjects were overweight or obese (BMI 25-40 kg/m(2)) adults aged 18-60 years. Weight was measured at baseline, and after three and six months participation in a weight loss program. Baseline concentrations of leptin, adiponectin and ghrelin were determined by enzyme-linked immunosorbent assay (ELISA). An independent t-test or non-parametric equivalent was used to determine any differences between sex. Linear regression determined whether baseline hormone concentrations were predictors of six-month weight change. Females had significantly higher baseline concentrations of leptin, adiponectin and unacylated ghrelin as well as ratios of leptin:adiponectin and leptin:ghrelin. The ratio of acylated:unacylated ghrelin was significantly higher in males. In males and females, a higher baseline concentration of unacylated ghrelin predicted greater weight loss at six months. Additionally in females, higher baseline total ghrelin predicted greater weight loss and a higher ratio of leptin:ghrelin predicted weight gain at six months. A higher pre-weight-loss plasma concentration of unacylated ghrelin is a modest predictor of weight loss success in males and females, while a higher leptin:ghrelin ratio is a predictor of weight loss failure in females. Further investigation is required into what combinations and concentrations of these hormones are optimal for weight loss success.

Ghrelin receptor activity amplifies hippocampal N-methyl-d-aspartate receptor-mediated postsynaptic currents and increases phosphorylation of the GluN1 subunit at Ser896 and Ser897

Although ghrelin and its cognate receptor growth hormone secretagogue receptor (GHSR1a) are highly localized in the hypothalamic nuclei for the regulation of metabolic states and feeding, GHSR1a is also highly localized in the hippocampus, suggesting its involvement in extra-hypothalamic functions. Indeed, exogenous application of ghrelin has been reported to improve hippocampal learning and memory. However, the underlying mechanism of ghrelin regulation of hippocampal functions is poorly understood. Here, we report ghrelin-promoted phosphorylation of GluN1 and amplified N-methyl-d-aspartate receptor (NMDAR)-mediated excitatory postsynaptic currents in the CA1 pyramidal cells of the hippocampus in slice preparations. The ghrelin-induced responses were sensitive to a GHSR1a antagonist and inverse agonist, and were absent in GHSR1a homozygous knock-out mice. These results indicated that activation of GHSR1a was critical in the ghrelin-induced enhancement of the NMDAR function. Interestingly, heterozygous mouse hippocampi were also insensitive to ghrelin treatment, suggesting that a slight reduction in the availability of GHSR1a may be sufficient to negate the effect of ghrelin on GluN1 phosphorylation and NMDAR channel activities. In addition, NMDAR-mediated spike currents, which are of dendritic origin, were blocked by the GHSR1a antagonist, suggesting the presence of GHSR1a on the pyramidal cell dendrites in physical proximity to NMDAR. Together with our findings on the localization of GHSR1a in the CA1 region of the hippocampus, which was shown by fluorescent ghrelin binding, immunoreactivity, and enhanced green fluorescent protein reporter gene expression, we conclude that the activation of GHSR1a favours rapid modulation of the NMDAR-mediated glutamatergic synaptic transmission by phosphorylating GluN1 in the hippocampus.

Ghrelin receptors as targets for novel motility drugs

Constipation arises from a multitude of causes, including aging, spinal cord injury (SCI), and dietary issues. The heterogeneity of inciting factors has made the treatment of constipation particularly challenging. Agonists of ghrelin receptors have beneficial effects on delayed gastric emptying, but less is known about their ability to improve colorectal motility. Recent publications indicate that the activation of the ghrelin receptors in the spinal cord can alleviate constipation due to dietary causes, Parkinsonism, and SCI in rodents. Ghrelin-responsive neurons in the intermediolateral cell column of the lumbosacral spinal cord can activate enteric microcircuits that coordinate propulsive colorectal contractions, leading to defecation. Learning more about the properties of neurons in the spinal defecation center and the roles of ghrelin receptors in the defecation reflex will accelerate the development of improved treatments of constipation.

Identification, tissue distribution and functional characterization of the ghrelin receptor in West African lungfish, Protopterus annectens

We identified two ghrelin receptor isoforms, the ghrelin receptor type-1a (GHS-R1a) and its alternative splice form (GHS-R1b) for West African lungfish, Protopterus annectens. Lungfish GHS-R1a and 1b comprised 361 and 281 amino acids, respectively. Lungfish GHS-R1a showed the highest identity to coelacanth GHS-R1a (80.4%). The highest expression of GHS-R1a mRNAs was seen in the brain, liver, ovary, heart, intestine, and gills. GHS-R1b mRNAs were also detected in the same tissues with GHS-R1a, but their expression level was 1/20 that of GHS-R1a. In human embryonic kidney 293 cells transiently expressing lungfish GHS-R1a, rat and bullfrog ghrelin, and two GHS-R1a agonists, GHRP-6 and hexarelin, increased intracellular Ca(2+) concentrations. The intensity of the Ca(2+) increases induced by GHS-R1a agonists was twice when compared to that induced by ghrelin, although the median effective doses (ED50) were similar, suggesting a long-lasting effect of GHS-R1a agonists with similar affinity. We also examined changes in the GHS-R gene expression during an eight-week estivation. Body weight was slightly lowered, but plasma sodium and glucose concentrations decreased; plasma urea concentration increased significantly 4weeks after the start of estivation. Overall, expression of GHS-R1a mRNA decreased, but changes in GHS-R1b mRNA expression were inconsistent with those of GHS-R1a during estivation, suggesting an involvement of GHS-R in energy homeostasis, as seen in mammals. Our results suggest that the ghrelin-GHS-R1a system is present in this lungfish although ghrelin has not yet been found. The structure of GHS-R1a is closer to that of tetrapods than Actinopterygian fish, indicating a process of evolution that follows the Crossopterygii such as coelacanth.

Genetic manipulation of the ghrelin signaling system in male mice reveals bone compartment specificity of acylated and unacylated ghrelin in the regulation of bone remodeling

Ghrelin receptor-deficient (Ghsr-/-) mice that lack acylated ghrelin (AG) signaling retain a metabolic response to unacylated ghrelin (UAG). Recently, we showed that Ghsr-deficiency affects bone metabolism. The aim of this study was to further establish the impact of AG and UAG on bone metabolism. We compared bone metabolism in Ghsr-/- (lacking only AG signaling) and ghrelin-deficient (Ghrl-/-; both AG and UAG deficient) male mice. Ghrl-/- mice had lower cortical bone mass, whereas Ghsr-/- mice had lower trabecular bone mass. This demonstrates bone compartment-specific effects of AG and a role for UAG in bone metabolism. Also, Ghrl-/- but not Ghsr-/- mice had increased bone formation rate and increased osteogenic stem cell numbers in their bone marrow. In ex vivo bone marrow cultures both AG and UAG inhibited osteoblast differentiation. This indicated that bone resorption must be increased in these mice. Accordingly, osteoclastogenesis rate was faster in bone marrow cultures from Ghsr-/- and Ghrl-/- mice, and osteoclast formation was inhibited by AG signaling and partially suppressed by UAG. In osteoblast cultures, AG markedly induced osteoprotegerin gene expression and both peptides reduced RANKL/osteoprotegerin ratio. These data describe unique cell-type specific effects of AG and UAG within a single tissue, supporting a tight and complex control of bone formation and resorption as well as a link between nutrition and bone metabolism. The balance between AG and UAG actions in the bone marrow may lead to bone compartmental-specific effects.

Novel and conventional receptors for ghrelin, desacyl-ghrelin, and pharmacologically related compounds

The only molecularly identified ghrelin receptor is the growth hormone secretagogue receptor GHSR1a. Its natural ligand, ghrelin, is an acylated peptide whose unacylated counterpart (UAG) is almost inactive at GHSR1a. A truncated, nonfunctional receptor, GHSR1b, derives from the same gene. We have critically evaluated evidence for effects of ghrelin receptor ligands that are not consistent with actions at GHSR1a. Effects of ghrelin are observed in cells or tissues where the expression of GHSR1a is not detectable or after the Ghsr gene has been inactivated. In several, effects of ghrelin are mimicked by UAG, and ghrelin binding is competitively reduced by UAG. Effects in the absence of GHSR1a and sites at which ghrelin and UAG have similar potency suggest the presence of novel nonspecific ghrelin receptors (ghrelin receptor-like receptors [GRLRs]). A third class of receptor, the UAG receptors, at which UAG, but not ghrelin, is an agonist has been proposed. None of the novel receptors, with the exception of the glycoprotein CD36, which accounts for ghrelin action at a limited number of sites, have been identified. GHSR1a and GHSR1b combine with other G protein-coupled receptors to form heterodimers, whose pharmacologies differ from their components. Thus, it is feasible some GRLRs and some UAG receptors are heterodimers. Effects mediated through GRLRs or UAG receptors include adipocyte lipid accumulation, myoblast differentiation, osteoblast proliferation, insulin release, cardioprotection, coronary artery constriction, vascular endothelial cell proliferation, and tumor cell proliferation. The molecular identification and pharmacologic characterization of novel ghrelin receptors are thus important objectives.

Abnormal relationships between the neural response to high- and low-calorie foods and endogenous acylated ghrelin in women with active and weight-recovered anorexia nervosa

Evidence contributing to the understanding of neurobiological mechanisms underlying appetite dysregulation in anorexia nervosa draws heavily on separate lines of research into neuroendocrine and neural circuitry functioning. In particular, studies consistently cite elevated ghrelin and abnormal activation patterns in homeostatic (hypothalamus) and hedonic (striatum, amygdala, insula) regions governing appetite. The current preliminary study examined the interaction of these systems, based on research demonstrating associations between circulating ghrelin levels and activity in these regions in healthy individuals. In a cross-sectional design, we studied 13 women with active anorexia nervosa (AN), 9 women weight-recovered from AN (AN-WR), and 12 healthy-weight control women using a food cue functional magnetic resonance imaging paradigm, with assessment of fasting levels of acylated ghrelin. Healthy-weight control women exhibited significant positive associations between fasting acylated ghrelin and activity in the right amygdala, hippocampus, insula, and orbitofrontal cortex in response to high-calorie foods, associations which were absent in the AN and AN-WR groups. Women with AN-WR demonstrated a negative relationship between ghrelin and activity in the left hippocampus in response to high-calorie foods, while women with AN showed a positive association between ghrelin and activity in the right orbitofrontal cortex in response to low-calorie foods. Findings suggest a breakdown in the interaction between ghrelin signaling and neural activity in relation to reward responsivity in AN, a phenomenon that may be further characterized using pharmacogenetic studies.

Devil's Claw to suppress appetite--ghrelin receptor modulation potential of a Harpagophytum procumbens root extract

Ghrelin is a stomach-derived peptide that has been identified as the only circulating hunger hormone that exerts a potent orexigenic effect via activation of its receptor, the growth hormone secretagogue receptor (GHS-R1a). Hence, the ghrelinergic system represents a promising target to treat obesity and obesity-related diseases. In this study we analysed the GHS-R1a receptor activating potential of Harpagophytum procumbens, popularly known as Devil's Claw, and its effect on food intake in vivo. H. procumbens is an important traditional medicinal plant from Southern Africa with potent anti-inflammatory and analgesic effects. This plant has been also used as an appetite modulator but most evidences are anecdotal and to our knowledge, no clear scientific studies relating to appetite modulation have been done to this date. The ghrelin receptor activation potential of an extract derived from the dried tuberous roots of H. procumbens was analysed by calcium mobilization and receptor internalization assays in human embryonic kidney cells (Hek) stably expressing the GHS-R1a receptor. Food intake was investigated in male C57BL/6 mice following intraperitoneal administration of H. procumbens root extract in ad libitum and food restricted conditions. Exposure to H. procumbens extract demonstrated a significant increased cellular calcium influx but did not induce subsequent GHS-R1a receptor internalization, which is a characteristic for full receptor activation. A significant anorexigenic effect was observed in male C57BL/6 mice following peripheral administration of H. procumbens extract. We conclude that H. procumbens root extract is a potential novel source for potent anti-obesity bioactives. These results reinforce the promising potential of natural bioactives to be developed into functional foods with weight-loss and weight maintenance benefits.

Identification of the ghrelin-GHSR 1 system and its influence in the modulation of induced ocular hypertension in rabbit and rat eyes

Recent studies evidenced a decrease in ghrelin's aqueous humor levels in patients with glaucoma. The goal of our investigation was to study the effect of the ghrelin-GHSR-1a system in the modulation of intraocular pressure in acute ocular hypertension models and its expression and distribution in ocular tissues. Two animal models of acute ocular hypertension were used to study the effect of the ghrelin-GHSR-1a system in the modulation of intraocular pressure: the rabbit and the rat. Ocular hypertension was induced by an intravitreal injection of 20% NaCl. Ghrelin or des-acyl ghrelin were delivered subconjunctivally and the intraocular pressure was assessed by a rebound tonometer that was calibrated for each species. In addition, we have studied the influence of nitric oxide and prostaglandins on ghrelin's effect in the rabbit animal model. Finally, we determined by immunofluorescence the expression of ghrelin and GHSR-1 in the rat's ocular tissue. Ghrelin decreased the intraocular pressure in both animal models (maximum decrease: 43.8±12.0% in the rabbit and 29.0±7.46% in the rat). In the rabbit, this effect was blunted in the presence of l-NAME and ketorolac. Des-acyl ghrelin only decreased the intraocular pressure in the rat (maximum decrease: 34.9±8.15%). Ghrelin expression was detected in the ciliary processes and GHSR-1 expression was detected in the trabecular meshwork and ciliary body. The ghrelin-GHSR-1 system is expressed in the anterior segment of the eye. Ghrelin and des-acyl ghrelin are responsible for a hypotensive effect in acute ocular hypertension animal models.

Nicotine administration in healthy non-smokers reduces appetite but does not alter plasma ghrelin

OBJECTIVE

We studied whether suppressed secretion of the orexigenic peptide ghrelin might be involved in the anorexigenic effects of nicotine.

METHODS

Fifty healthy non-smokers chewed gums containing 2 mg nicotine, or no nicotine in a double-blind randomised crossover design in two independent studies.

RESULTS

Plasma nonacylated ghrelin was not significantly affected by nicotine after 30 and 60 min. Increased blood pressure and decreased appetite ratings confirmed a biological nicotine effect.

CONCLUSIONS

These results do not support a key role of peripheral ghrelin secretion in weight changes related to smoking or smoking cessation, but do not rule out that central nervous system ghrelin is involved.

Ghrelin induces apoptosis in colon adenocarcinoma cells via proteasome inhibition and autophagy induction

Ghrelin is a metabolism-regulating hormone recently investigated for its role in cancer survival and progression. Controversially, ghrelin may act as either anti-apoptotic or pro-apoptotic factor in different cancer cells, suggesting that the effects are cell type dependent. Limited data are currently available on the effects exerted by ghrelin on intracellular proteolytic pathways in cancer. Both the lysosomal and the proteasomal systems are fundamental in cellular proliferation and apoptosis regulation. With the aim of exploring if the proteasome and autophagy may be possible targets of ghrelin in cancer, we exposed human colorectal adenocarcinoma cells to ghrelin. Preliminary in vitro fluorimetric assays evidenced for the first time a direct inhibition of 20S proteasomes by ghrelin, particularly evident for the trypsin-like activity. Moreover, 1 μM ghrelin induced apoptosis in colorectal adenocarcinoma cells by inhibiting the ubiquitin-proteasome system and by activating autophagy, with p53 having an "interactive" role.

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.

Unacylated ghrelin promotes skeletal muscle regeneration following hindlimb ischemia via SOD-2-mediated miR-221/222 expression

Background

Surgical treatment of peripheral artery disease, even if successful, does not prevent reoccurrence. Under these conditions, increased oxidative stress is a crucial determinant of tissue damage. Given its reported antioxidant effects, we investigated the potential of unacylated‐ghrelin (UnAG) to reduce ischemia‐induced tissue damage in a mouse model of peripheral artery disease.

Methods and Results

We show that UnAG but not acylated ghrelin (AG) induces skeletal muscle regeneration in response to ischemia via canonical p38/mitogen‐actived protein kinase signaling UnAG protected against reactive oxygen species–induced cell injuries by inducing the expression of superoxide dismutase‐2 (SOD‐2) in satellite cells. This led to a reduced number of infiltrating CD68⁺ cells and was followed by induction of the myogenic process and a reduction in functional impairment. Moreover, we found that miR‐221/222, previously linked to muscle regeneration processes, was up‐regulated and negatively correlated with p57^Kip2 expression in UnAG‐treated mice. UnAG, unlike AG, promoted cell‐cycle entry in satellite cells of mice lacking the genes for ghrelin and its receptor (GHSR1a). UnAG‐induced p38/mitogen‐actived protein kinase phosphorylation, leading to activation of the myogenic process, was prevented in SOD‐2–depleted SCs. By siRNA technology, we also demonstrated that SOD‐2 is the antioxidant enzyme involved in the control of miR‐221/222–driven posttranscriptional p57^Kip2 regulation. Loss‐of‐function experiments targeting miR‐221/222 and local pre–miR‐221/222 injection in vivo confirmed a role for miR‐221/222 in driving skeletal muscle regeneration after ischemia.

Conclusions

These results indicate that UnAG‐induced skeletal muscle regeneration after ischemia depends on SOD‐2–induced miR‐221/222 expression and highlight its clinical potential for the treatment of reactive oxygen species–mediated skeletal muscle damage.