Structure and function of ghrelin. Results Probl Cell Differ. 2008;46:89-115. [PMID: 18193177 DOI: 10.1007/400_2007_049]

Circulating profile of the appetite-regulating hormone ghrelin during moult-fast and chick provisioning in southern rockhopper penguins (Eudyptes chrysocome chrysocome)

A multitude of animal species undergo prolonged fasting events at regularly occurring life history stages. During such periods of food deprivation, individuals need to suppress their appetite. The satiety signalling gut hormone ghrelin has received much attention in this context in studies looking at mammalian systems. In wild birds, however, knowledge on the ghrelin system and its role during extended fasts is still scarce. In this study, we collected plasma samples for measurements of circulating ghrelin concentrations from adult southern rockhopper penguins (Eudyptes chrysocome chrysocome) during the three to four week-long moult-fast that they repeat annually to replace their feathers. We further sampled chicks before and after feeding bouts and non-moulting adults. Circulating ghrelin levels did not differ significantly between fed and unfed chicks but chicks had significantly lower plasma ghrelin levels compared to adults. Furthermore, penguins in late moult (i.e. individuals at the end of the prolonged fasting bout) had higher ghrelin levels compared to non-moulting adults. Our results show elevated levels of circulating ghrelin during moult and generally lower levels of ghrelin in chicks than in adults regardless of feeding state. Given the scarcity or absence of knowledge on the function of ghrelin in seabirds and in fasting birds in general, our results add greatly to our understanding of the avian ghrelin system.

Gut-Brain Axis Modulation of Metabolic Disorders: Exploring the Intertwined Neurohumoral Pathways and Therapeutic Prospects

A significant rise in metabolic disorders, frequently brought on by lifestyle choices, is alarming. A wide range of preliminary studies indicates the significance of the gut-brain axis, which regulates bidirectional signaling between the gastrointestinal tract and the cognitive system, and is crucial for regulating host metabolism and cognition. Intimate connections between the brain and the gastrointestinal tract provide a network of neurohumoral transmission that can transmit in both directions. The gut-brain axis successfully establishes that the wellness of the brain is always correlated with the extent to which the gut operates. Research on the gut-brain axis has historically concentrated on how psychological health affects how well the gastrointestinal system works. The latest studies, however, revealed that the gut microbiota interacts with the brain via the gut-brain axis to control phenotypic changes in the brain and in behavior. This study addresses the significance of the gut microbiota, the role of the gut-brain axis in management of various metabolic disorders, the hormonal and neural signaling pathways and the therapeutic treatments available. Its objective is to establish the significance of the gut-brain axis in metabolic disorders accurately and examine the link between the two while evaluating the therapeutic strategies to be incorporated in the future.

Effect of Continuous Positive Airway Pressure on Changes of Plasma/Serum Ghrelin and Evaluation of These Changes between Adults with Obstructive Sleep Apnea and Controls: A Meta-Analysis

BACKGROUND AND OBJECTIVE

Obstructive sleep apnea (OSA) can be related to high ghrelin hormone levels that may encourage additional energy intake. Herein, a new systematic review and meta-analysis were performed to check the changes in serum/plasma levels of ghrelin in adults with OSA compared to controls, as well as before compared after continuous positive airway pressure (CPAP) therapy in adults with OSA.

MATERIALS AND METHODS

Four main databases were systematically and comprehensively searched until 17 October 2022, without any restrictions. For assessing the quality, we used the Joanna Briggs Institute (JBI) critical appraisal checklist adapted for case-control studies and the National Institutes of Health (NIH) quality assessment tool for before-after studies. The effect sizes were extracted by the Review Manager 5.3 software for the blood of ghrelin in adults with OSA compared with controls, as well as before and after CPAP therapy.

RESULTS

Fifteen articles involving thirteen studies for case-control studies and nine articles for before-after studies were included. The pooled standardized mean differences were 0.30 (95% confidence interval (CI): -0.02, 0.61; p = 0.07; I² = 80%) and 0.10 (95% CI: -0.08, 0.27; p = 0.27; I² = 42%) for case-control and before-after studies, respectively. For thirteen case-control studies, nine had moderate and four high qualities, whereas for nine before-after studies, five had good and four fair qualities. Based on the trial sequential analysis, more studies are needed to confirm the pooled results of the analyses of blood ghrelin levels in case-control and before-after studies. In addition, the radial plot showed outliers for the analysis of case-control studies that they were significant factors for high heterogeneity.

CONCLUSIONS

The findings of the present meta-analysis recommended that the blood levels of ghrelin had no significant difference in the adults with OSA compared with the controls, nor did they have significant difference in adults with OSA before compared with after CPAP therapy. The present findings need to be confirmed in additional studies with more cases and higher qualities.

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.

Involvement of the ghrelin system in the maintenance and reinstatement of cocaine-motivated behaviors: a role of adrenergic action at peripheral β1 receptors

Cocaine addiction is a significant medical and public concern. Despite decades of research effort, development of pharmacotherapy for cocaine use disorder remains largely unsuccessful. This may be partially due to insufficient understanding of the complex biological mechanisms involved in the pathophysiology of this disorder. In the present study, we show that: (1) elevation of ghrelin by cocaine plays a critical role in maintenance of cocaine self-administration and cocaine-seeking motivated by cocaine-conditioned stimuli; (2) acquisition of cocaine-taking behavior is associated with the acquisition of stimulatory effects of cocaine by cocaine-conditioned stimuli on ghrelin secretion, and with an upregulation of ghrelin receptor mRNA levels in the ventral tegmental area (VTA); (3) blockade of ghrelin signaling by pretreatment with JMV2959, a selective ghrelin receptor antagonist, dose-dependently inhibits reinstatement of cocaine-seeking triggered by either cocaine or yohimbine in behaviorally extinguished animals with a history of cocaine self-administration; (4) JMV2959 pretreatment also inhibits brain stimulation reward (BSR) and cocaine-potentiated BSR maintained by optogenetic stimulation of VTA dopamine neurons in DAT-Cre mice; (5) blockade of peripheral adrenergic β1 receptors by atenolol potently attenuates the elevation in circulating ghrelin induced by cocaine and inhibits cocaine self-administration and cocaine reinstatement triggered by cocaine. These findings demonstrate that the endogenous ghrelin system plays an important role in cocaine-related addictive behaviors and suggest that manipulating and targeting this system may be viable for mitigating cocaine use disorder.

Involvement of the ghrelin system in the maintenance of oxycodone self-administration: converging evidence from endocrine, pharmacologic and transgenic approaches

Ghrelin, an orexigenic hormone, has emerged as a critical biological substrate implicated in drug reward. However, the response of the ghrelin system to opioid-motivated behaviors and the role of ghrelin in oxycodone self-administration remain to be studied. Here, we investigated the reciprocal interactions between the endogenous ghrelin system and oxycodone self-administration behaviors in rats and the role of the ghrelin system in brain stimulation reward (BSR) driven by optogenetic stimulation of midbrain reward circuits in mice. Oxycodone self-administration significantly elevated plasma ghrelin, des-acyl ghrelin and growth hormone and showed no effect on plasma LEAP2, a newly identified endogenous ghrelin receptor (GHS-R1a) antagonist. Oxycodone self-administration produced significant decreases in plasma gastric inhibitory polypeptide and insulin. Acquisition of oxycodone self-administration significantly upregulated GHS-R1a mRNA levels in dopamine neurons in the ventral tegmental area (VTA), a brain region critical in drug reward. Pretreatment with JMV2959, a selective GHS-R1a antagonist, dose-dependently reduced oxycodone self-administration and decreased the breakpoint for oxycodone under a progressive ratio reinforcement in Long-Evans rats. The inhibitory effects of JMV2959 on oxycodone self-administration is selectively mediated by GHS-R1a as JMV2959 showed a similar effect in Wistar wildtype but not in GHS-R knockout rats. JMV2959 pretreatment significantly inhibited BSR driven by selective stimulation of VTA dopamine neurons, but not by stimulation of striatal GABA neurons projecting to the VTA in mice. These findings suggest that elevation of ghrelin signaling by oxycodone or oxycodone-associated stimuli is a causal process by which oxycodone motivates oxycodone drug-taking and targeting the ghrelin system may be a viable treatment approach for opioid use disorders.

Sarcopenia and Ghrelin System in the Clinical Outcome and Prognosis of Gastroenteropancreatic Neuroendocrine Neoplasms

Simple Summary

Malnutrition and sarcopenia affect clinical outcomes in cancer patients. Nutritional evaluation in patients with neuroendocrine neoplasms (NENs) is not routinely performed. Currently, the evaluation of sarcopenia using CT scans is the gold standard in cancer patients, additionally, anthropometric, biochemical and molecular analysis of patients with gastroenteropancreatic NENs at diagnosis was perfomed. The expression levels of key ghrelin system components were assessed in 63 tumor samples. Results: Nutritional parameters were similar in GEP-NEN tumors of different origin. Relapsed disease was associated with decreased BMI. Patients who presented with weight loss at diagnosis had significantly lower overall survival (108 (25–302) vs. 263 (79–136) months). Ghrelin O-acyltransferase (GOAT) enzyme expression was higher in these patients. The prevalence of sarcopenia using CT images reached 87.2%. Mortality was observed only in patients with sarcopenia. Muscle evaluation was correlated with biochemical parameters but not with the expression of ghrelin system components. Conclusion: Survival is related to the nutritional status of patients with GEP-NENs and also to the molecular expression of some relevant ghrelin system components. Routine nutritional evaluation should be performed in these patients, in order to prescribe appropriate nutritional support, when necessary, for increasing quality of life and improving clinical outcomes.

Abstract

Background: Malnutrition and sarcopenia affect clinical outcomes and treatment response in cancer patients. Patients with neuroendocrine neoplasms (NENs) may present with additional symptoms related to tumor localization in the gastrointestinal tract and hormone secretion, increasing the risk and effects of sarcopenia. Aim: To explore the presence of malnutrition and sarcopenia in gastroenteropancreatic (GEP)-NEN patients, their relation to tumor characteristics, patient outcomes, survival and the molecular expression of ghrelin system components in the tumor. Patients and methods: One-hundred-and-four patients were included. Anthropometric, biochemical and CT-scans at diagnosis were evaluated. The expression levels of key ghrelin system components were assessed in 63 tumor samples. Results: Nutritional parameters were similar in GEP-NEN tumors of different origin. Relapsed disease was associated with decreased BMI. Patients who presented with weight loss at diagnosis had significantly lower overall survival (108 (25–302) vs. 263 (79–136) months). Ghrelin O-acyltransferase (GOAT) enzyme expression was higher in these patients. The prevalence of sarcopenia using CT images reached 87.2%. Mortality was observed only in patients with sarcopenia. Muscle evaluation was correlated with biochemical parameters but not with the expression of ghrelin system components. Conclusion: Survival is related to the nutritional status of patients with GEP-NENs and also to the molecular expression of some relevant ghrelin system components. Routine nutritional evaluation should be performed in these patients, in order to prescribe appropriate nutritional support, when necessary, for increasing quality of life and improving clinical outcomes.

Temporal changes and prognostic value of plasma ghrelin level in patients with acute heart failure: a prospective study

BACKGROUND

Plasma ghrelin levels can be elevated in patients with acute heart failure (AHF). This study aimed to analyze the temporal changes and prognostic value of ghrelin levels in patients with AHF.

METHODS

This prospective study included patients with AHF at the Cardiology Department, Weifang People's Hospital (May 2018-October 2019), and age- and sex-matched healthy controls. Plasma ghrelin levels were measured. Multivariable logistic regression and receiver operating characteristic (ROC) curve analyses were used to evaluate whether ghrelin levels could predict major cardiac adverse events (MACEs) during a 1-year follow-up.

RESULTS

Finally, 92 patients with AHF and 50 healthy controls were enrolled. Ghrelin levels were higher in patients with AHF at 1, 3, 12, and 24 h compared with controls (all P < 0.01). Ghrelin levels in the AHF group were higher at 3 and 12 h than at 1 and 24 h (P < 0.001). Ghrelin level at 3 h in patients with AHF was negatively correlated with the left ventricular end-diastolic diameter and left ventricular ejection fraction (both P < 0.05). MACEs occurred in 48 patients with AHF. Ghrelin levels were higher in the MACE group than in the non-MACE group at 1 (P = 0.011) and 3 h (P = 0.034). Multivariable regression showed that ghrelin level at 3 h was independently associated with MACEs [OR = 0.629, 95% confidence interval (CI): 0.515-0.742, P = 0.010], but the area under the ROC curve was only 0.629 (95% CI 0.515-0.742).

CONCLUSIONS

Plasma ghrelin levels are elevated in AHF and patients with MACEs during follow-up.

Measurement of serial serum total and acylated ghrelin levels in critically ill patients: A prospective and observational pilot study

BACKGROUND

Ghrelin is a hormone that regulates appetite and energy metabolism. The change of serial serum total and acylated ghrelin levels during hospital stays of critical patients are unknown. In addition, the relationship of this change with the clinical results of patients in the intensive care unit (ICU) is also unknown. The aim of this study was to determine serum total and acylated ghrelin levels serially in critically ill patients.

METHODS

This prospective study was performed in the ICU. Patients who were >18 years old and stayed in ICU for >48 h were included in the study. Serum total and acylated ghrelin concentrations were measured at baseline in all participants and serially on the 2nd, 5th, and 10th day after entry into the study in those who remained in the ICU.

RESULTS

A total of 60 participants were included. The mean age was 56 ± 21 years. (Baseline, 2nd, 5th, and 10th day median serum total ghrelin levels were 3551 (1651-3995), 3485.20 (1379-4071), 3359 (1167-3919), and 3355 pg/ml (2207-3843), respectively. Baseline, 2nd, 5th, and 10th day acylated ghrelin levels were 47 (0-673), 50 (0-730), 73 (0-808), and 125 pg/ml (0-689), respectively. There was no significant difference between total ghrelin/acylated ghrelin levels and mortality (P > .05). ICU mortality was 30%.

CONCLUSION

Ghrelin levels were decreased slightly and acylated ghrelin levels increased substantially over time in critically ill patients. There were no differences between serum total ghrelin/acylated ghrelin levels and ICU mortality .

Endocrinopathies and cancer cachexia

PURPOSE OF REVIEW

Cancer cachexia cannot be easily reversed by standard nutritional support and interventions directed at underlying metabolic derangements may be needed to prevent or reverse cachexia and maintain healthy body composition. The following review will highlight the contribution and potential therapeutic interventions for insulin resistance, alterations in ghrelin signaling, and hypogonadism in cancer patients.

RECENT FINDINGS

In addition to decreased caloric intake, chronic inflammation, and altered metabolism of glucose, proteins and lipids, endocrine abnormalities can propagate weight loss or changes in body composition in cancer patients.

SUMMARY

Cancer cachexia, loss of muscle mass with or without the loss of fat mass, is a multifactorial syndrome, which is associated with increased morbidity and mortality. Currently, limited therapeutic options for the treatment of weight loss in cancer patients exist, which lead to clinically meaningful improvements in weight gain and performance status. Treatment directed at underlying insulin resistance, low testosterone, and altered ghrelin sensitivity, in the future, may lead to potential therapeutic options for loss of lean body mass and cancer cachexia.

Glucose Homeostasis in Obese Women Is Not Associated to Unacylated Ghrelin Plasma Levels

Introduction:

Unacylated ghrelin (UAG) is the major form of circulating ghrelin. Initially considered as a nonfunctional peptide, soon after, UAG has been associated to an insulin sensitizing action and to a negative action on energy balance. The aim of this study was to analyze the association between the serum levels of UAG and glucose metabolism parameters in obese women, independently from eventual influence of anthropometrics.

Methods:

One hundred lean and 254 obese Caucasian women were studied. Each woman was characterized for anthropometrics, fasting glucose, insulin, HbA1c, and UAG. In addition, obese women were subjected to a classic oral glucose tolerance test (oGTT) to assess glucose and insulin at 120 minutes. Insulin resistance was assessed by the homeostasis model assessment (HOMA-IR). Obese women were classified in 3 glycemic status subgroups (normoglycemia, prediabetes, and diabetes) according to HbA1c and to fasting and oGTT glucose values.

Results:

In comparison with the lean group, significantly lower levels of UAG were observed in obese women. However, no significant difference was observed through obesity classes I to III. UAG levels were not significantly different among glycemic status subgroups and did not show any association with glucose, insulin, HOMA-IR, or HbA1c.

Conclusions:

Although anthropometry can influence the level of the unacylated form of ghrelin, UAG plasma levels do not associate to glucose homeostasis parameters.

Leptin and ghrelin expressions in the gastrointestinal tracts of calves and cows

This study aims to investigate and compare the expressions of leptin and ghrelin in the gastrointestinal tracts of calves and cows. The mRNA expression of leptin in the rumen, abomasum, and jejunum of calves was significantly higher than that in cows. In both calves and cows, abomasum ghrelin mRNA expression was significantly higher than that in other gastrointestinal tracts. In calves, leptin protein expression in the abomasum was the highest. In addition, leptin protein expression in the abomasum and jejunum of calves was significantly higher than that in cows. Results indicated that leptin in the abomasum and jejunum plays an important role during the suckling period in a ruminant.

Ghrelin acylation by ghrelin- O-acyltransferase can occur in healthy part of oncological liver in humans

Activation of ghrelin is controlled by the enzyme ghrelin- O-acyl transferase (GOAT). In humans, localization of this acylation is poorly understood. The aim of this study is to explore GOAT localization and activation in the human liver by evaluating both bioactive and non-bioactive ghrelin in the bloodstream entering and leaving the liver and to simultaneously evaluate GOAT mRNA expression in the liver. A healthy part of oncologic hepatic tissue collected from nine patients undergoing hepatectomy was used to evaluate GOAT mRNA expression by quantitative real-time polymerase chain reaction (RT-qPCR). Simultaneously, blood from the portal vein, the suprahepatic vein, the subclavicular vein, and the radial artery was also sampled to assay total and acylated ghrelin. Acylated ghrelin level was significantly increased in the suprahepatic vein compared with the portal vein level (385 ± 42 ng/ml vs. 268 ± 24 ng/ml, P = 0.04). Suprahepatic-to-portal vein ratio for acylated ghrelin (acylation ratio) is 1.4 ± 0.1. Mean expression of GOAT mRNA in the liver, expressed as 2^-∆Ct·µg total RNA^-1·1 µl of liver tissue^-1 was at 0.042 ± 0.021 arbitrary units. GOAT mRNA expression in the liver was correlated with acylated-to-total ghrelin ratio in the suprahepatic vein ( P = 0.016, R = 0.75) and with the acylation liver ratio ( P = 0.05, R = 0.61). Blood concentration of acylated ghrelin was found significantly increased after its passage through the liver, suggesting that acylation can occur in the liver. RT-qPCR data confirmed the presence of GOAT in the liver, with a positive correlation between GOAT expression and acylated ghrelin liver ratio. This study strongly suggests that the liver is a site of ghrelin acylation in humans. NEW & NOTEWORTHY Although the activation of ghrelin by the enzyme ghrelin- O-acyl transferase (GOAT) is yet well demonstrated, its localization, especially in humans, remains poorly understood. We explored GOAT localization and activation in the human liver by simultaneously evaluating both bioactive and non-bioactive ghrelin in the bloodstream entering and leaving the liver and also GOAT mRNA expression in the liver. We therefore showed for the first time, to our knowledge, that GOAT localized in the liver is active and takes part in ghrelin activation.

Functional group and stereochemical requirements for substrate binding by ghrelin O-acyltransferase revealed by unnatural amino acid incorporation

Ghrelin is a small peptide hormone that undergoes a unique posttranslational modification, serine octanoylation, to play its physiological roles in processes including hunger signaling and glucose metabolism. Ghrelin O-acyltransferase (GOAT) catalyzes this posttranslational modification, which is essential for ghrelin to bind and activate its cognate GHS-R1a receptor. Inhibition of GOAT offers a potential avenue for modulating ghrelin signaling for therapeutic effect. Defining the molecular characteristics of ghrelin that lead to binding and recognition by GOAT will facilitate the development and optimization of GOAT inhibitors. We show that small peptide mimics of ghrelin substituted with 2,3-diaminopropanoic acid in place of the serine at the site of octanoylation act as submicromolar inhibitors of GOAT. Using these chemically modified analogs of desacyl ghrelin, we define key functional groups within the N-terminal sequence of ghrelin essential for binding to GOAT and determine GOAT's tolerance to backbone methylations and altered amino acid stereochemistry within ghrelin. Our study provides a structure-activity analysis of ghrelin binding to GOAT that expands upon activity-based investigations of ghrelin recognition and establishes a new class of potent substrate-mimetic GOAT inhibitors for further investigation and therapeutic interventions targeting ghrelin signaling.

Ghrelin for the management of cachexia associated with cancer

BACKGROUND

Cancer sufferers are amongst the most malnourished of all the patient groups. Studies have shown that ghrelin, a gut hormone can be a potential therapeutic agent for cachexia (wasting syndrome) associated with cancer. A variety of mechanisms of action of ghrelin in people with cancer cachexia have been proposed. However, safety and efficacy of ghrelin for cancer-associated cachexia have not been systematically reviewed. The aim of this review was to assess whether ghrelin is associated with better food intake, body composition and survival than other options for adults with cancer cachexia.

OBJECTIVES

To assess the efficacy and safety of ghrelin in improving food intake, body composition and survival in people with cachexia associated with cancer.

SEARCH METHODS

We searched CENTRAL, MEDLINE and Embase without language restrictions up to July 2017. We also searched for ongoing studies in trials registers, performed handsearching, checked bibliographic references of relevant articles and contacted authors and experts in the field to seek potentially relevant research. We applied no restrictions on language, date, or publication status.

SELECTION CRITERIA

We included randomised controlled (parallel-group or cross-over) trials comparing ghrelin (any formulation or route of administration) with placebo or an active comparator in adults (aged 18 years and over) who met any of the international criteria for cancer cachexia.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility. Two review authors then extracted data and assessed the risk of bias for individual studies using standard Cochrane methodology. For dichotomous variables, we planned to calculate risk ratio with 95% confidence intervals (CI) and for continuous data, we planned to calculate mean differences (MD) with 95% CI. We assessed the evidence using GRADE and created 'Summary of findings' tables.

MAIN RESULTS

We screened 926 individual references and identified three studies that satisfied the inclusion criteria. Fifty-nine participants (37 men and 22 women) aged between 54 and 78 years were randomised initially, 47 participants completed the treatment. One study had a parallel design and two had a cross-over design. The studies included people with a variety of cancers and also differed in the dosage, route of administration, frequency and duration of treatment.One trial, which compared ghrelin with placebo, found that ghrelin improved food intake (very low-quality evidence) and had no adverse events (very low-quality evidence). Due to unavailability of data we were unable to report on comparisons for ghrelin versus no treatment or alternative experimental treatment modalities, or ghrelin in combination with other treatments or ghrelin analogues/ghrelin mimetics/ghrelin potentiators. Two studies compared a higher dose of ghrelin with a lower dose of ghrelin, however due to differences in study designs and great diversity in the treatment provided we did not pool the results. In both trials, food intake did not differ between participants on higher-dose and lower-dose ghrelin. None of the included studies assessed data on body weight. One study reported higher adverse events with a higher dose as compared to a lower dose of ghrelin.All studies were at high risk of attrition bias and bias for size of the study. Risk of bias in other domains was unclear or low.We rated the overall quality of the evidence for primary outcomes (food intake, body weight, adverse events) as very low. We downgraded the quality of the evidence due to lack of data, high or unclear risk of bias of the studies and small study size.

AUTHORS' CONCLUSIONS

There is insufficient evidence to be able to support or refute the use of ghrelin in people with cancer cachexia. Adequately powered randomised controlled trials focusing on evaluation of safety and efficacy of ghrelin in people with cancer cachexia is warranted.

Synthetic Triterpenoid Inhibition of Human Ghrelin O-Acyltransferase: The Involvement of a Functionally Required Cysteine Provides Mechanistic Insight into Ghrelin Acylation

The peptide hormone ghrelin plays a key role in regulating hunger and energy balance within the body. Ghrelin signaling presents a promising and unexploited target for development of small molecule therapeutics for treatment of obesity, diabetes, and other health conditions. Inhibition of ghrelin O-acyltransferase (GOAT), which catalyzes an essential octanoylation step in ghrelin maturation, offers a potential avenue for controlling ghrelin signaling. Through screening a small molecule library, we have identified a class of synthetic triterpenoids that efficiently inhibit ghrelin acylation by the human isoform of GOAT (hGOAT). These compounds function as covalent reversible inhibitors of hGOAT, providing the first evidence of the involvement of a nucleophilic cysteine residue in substrate acylation by a MBOAT family acyltransferase. Surprisingly, the mouse form of GOAT does not exhibit susceptibility to cysteine-modifying electrophiles, revealing an important distinction in the activity and behavior between these closely related GOAT isoforms. This study establishes these compounds as potent small molecule inhibitors of ghrelin acylation and provides a foundation for the development of novel hGOAT inhibitors as therapeutics targeting diabetes and obesity.

Ghrelin Octanoylation Is Completely Stabilized in Biological Samples by Alkyl Fluorophosphonates

Ghrelin is a peptide hormone involved in multiple physiological processes related to energy homeostasis. This hormone features a unique posttranslational serine octanoylation modification catalyzed by the enzyme ghrelin O-acyltransferase, with serine octanoylation essential for ghrelin to bind and activate its cognate receptor. Ghrelin deacylation rapidly occurs in circulation, with both ghrelin and desacyl ghrelin playing important roles in biological signaling. Understanding the regulation and physiological impact of ghrelin signaling requires the ability to rapidly protect ghrelin from deacylation in biological samples such as blood serum or cell lysates to preserve the relative concentrations of ghrelin and desacyl ghrelin. In in vitro ghrelin O-acyltransferase activity assays using insect microsomal protein fractions and mammalian cell lysate and blood serum, we demonstrate that alkyl fluorophosphonate treatment provides rapid, complete, and long-lasting protection of ghrelin acylation against serine ester hydrolysis without interference in enzyme assay or ELISA analysis. Our results support alkyl fluorophosphonate treatment as a general tool for stabilizing ghrelin and improving measurement of ghrelin and desacyl ghrelin concentrations in biochemical and clinical investigations and suggest current estimates for active ghrelin concentration and the ghrelin to desacyl ghrelin ratio in circulation may underestimate in vivo conditions.

Endoglin and obestatin levels, cardiometabolic risk factors and subclinical atherosclerosis in children aged 10-18 years

BACKGROUND

The aim of this study was to investigate the early signs of atherosclerosis and to evaluate serum endoglin and obestatin levels as predictors of subclinical atherosclerosis in obese children.

METHODS

A total of 95 children (60 obese and 35 controls) aged 10-18 years were included in the study. Their endoglin and obestatin levels and biochemical parameters were measured. The carotid intima media thickness (cIMT) and brachial artery flow-mediated dilatation (FMD) responses were evaluated.

RESULTS

The cIMT values were higher (p < 0.001) and FMD responses were lower (p = 0.003) in the obese group than in the control group. A logistic regression multivariate analysis revealed that cIMT was independently associated with the body mass index (BMI) Z-score (β = 0.323, p = 0.003) and low density lipoprotein (LDL) (β = 0.29, p = 0.008), while FMD % was independently associated with waist circumference (β = -0.36, p = 0.002). The obese and control groups were similar in endoglin (p = 0.67) and obestatin levels (p = 0.70). The endoglin level was inversely correlated with the cholesterol and LDL levels (r = -0.23, p = 0.032; rho = -0.25, p = 0.019).

CONCLUSIONS

The cIMT and brachial artery FMD response in obese children are significantly different compared to healthy controls. Circulating endoglin and obestatin levels are not predictive markers for subclinical atherosclerosis in obese children aged 10-18 years old.

Plasma ghrelin levels in association with left ventricular function and nutritional status in dialysis patients

The present study investigated the association between ghrelin levels and the cardiac function and malnutrition of dialysis patients. The aim was to examine the conducive use of exogenous ghrelin to improve the malnutrition, protect the cardiovascular function with dialysis patients in the future. The study included 30 continuous ambulatory peritoneal dialysis (CAPD) patients and 30 hemodialysis (HD) patients undertaking treatment between March 2013 and March 2014. The control group included a total of 30 healthy physical examinees. The plasma ghrelin levels were measured by the enzyme-linked immunosorbent assay to collect the clinical materials and biochemical parameters. The plasma ghrelin levels were 4.28±1.07, 4.63±1.08 and 2.00±0.48 ng/ml in the CAPD, HD and control groups, respectively, and statistical significance was identified between the three groups; F=75.106, P<0.0001. The plasma ghrelin levels in the CAPD group were positively correlated with left ventricular ejection fraction (LVEF) (r=0.506, P=0.004) and were negatively correlated with body mass index (BMI) (r=−0.556, P=0.001). The plasma ghrelin levels in the CAPD and HD groups were positively correlated with serum creatinine (Scr) and blood urea nitrogen (BUN). In conclusion, the plasma ghrelin levels of patients in the CAPD and HD groups were higher compared to those of the control group, which demonstrated that dialysis patients could not effectively remove the plasma ghrelin. The present study found that the plasma ghrelin levels were positively correlated with LVEF, and high levels of ghrelin will exhibit protective effects on the cardiovascular function of CAPD patients. Plasma ghrelin levels were positively correlated with Scr and BUN levels in CAPD and HD patients, and were negatively correlated with BMI in CAPD patients, which showed that ghrelin was correlated with malnutrition of dialysis patients.

Ghrelin attenuates the growth of HO-8910 ovarian cancer cells through the ERK pathway

Ovarian cancer is one of the most common causes of death from gynecologic tumors and is an important public health issue. Ghrelin is a recently discovered bioactive peptide that acts as a natural endogenous ligand of the growth hormone secretagogue receptor (GHSR). Several studies have identified the protective effects of ghrelin on the mammalian reproductive system. However, little research has been done on the effects of ghrelin on ovarian cancer cells, and the underlying mechanisms of these effects. We sought to understand the potential involvement of mitogen-activated protein kinases (MAPKs) in ghrelin-mediated inhibition of growth of the ovarian line HO-8910. We applied different concentrations of ghrelin and an inhibitor of the ghrelin receptor (D-Lys3-GHRP-6) to HO-8910 cells and observed the growth rate of cells and changes in phosphorylation of the MAPKs ERK1/2, JNK and p38. We discovered that ghrelin-induced apoptosis of HO-8910 cells was though phosphorylated ERK1/2, and that this phosphorylation (as well as p90rsk phosphorylation) was mediated by the GHSR. The ERK1/2 pathway is known to play an essential part in the ghrelin-mediated apoptosis of HO-8910 cells. Hence, our study suggests that ghrelin inhibits the growth of HO-8910 cells primarily through the GHSR/ERK pathway.

Identification of biosynthetic intermediates of teaghrelins and teaghrelin-like compounds in oolong teas, and their molecular docking to the ghrelin receptor

Teaghrelins are unique acylated flavonoid tetraglycosides found in Chin-shin oolong tea, and have been demonstrated to be promising oral ghrelin analogues. The biosynthetic pathway of teaghrelins from quercetin-3-O-rutinoside (rutin) or kaempferol-3-O-rutinoside (nicotiflorin) was proposed to comprise three enzymatic steps according to the identification of putative intermediates in Chin-shin oolong tea. In addition to the two known teaghrelins in Chin-shin oolong tea, four teaghrelin-like compounds with different attachments of glycosides were identified in various oolong teas. Molecular modeling and docking were used to evaluate theoretically whether the putative biosynthetic intermediates of teaghrelins and the four teaghrelin-like compounds could be potential candidates of ghrelin analogues. The results showed that the attachment of a coumaroyl group was crucial for these tea compounds to bind to the ghrelin receptor. However, the additional attachment of a rhamnosyl glycoside to the flavonoid backbone of teaghrelin-like compounds at C-7 significantly reduced their binding affinity with the ghrelin receptor.

Serum inflammatory markers in obese mice: Effect of ghrelin

Background:

Ghrelin is involved in modulation of food intake and energy homeostasis; however, it may play a role in cardiovascular system and atherosclerosis process. This study aimed to investigate the effect of ghrelin on serum inflammatory markers in control and obese mice.

Materials and Methods:

Ghrelin (100 mg/kg/day, twice daily) was administered interaperitoneally to control and diet-induced obese mice. After 10 days, blood samples were taken.

Results:

Results showed that administration of ghrelin did not change serum hsCRP level; however, it reduced serum IL-6 concentration in obese mice (P < 0.05).

Conclusion:

It seems that the exact role and mechanism of ghrelin in prevention or treatment of atherosclerosis needs more studies.

Ghrelin accelerates the growth and osteogenic differentiation of rabbit mesenchymal stem cells through the ERK1/2 pathway

Background

Mesenchymal stem cells (MSCs) can differentiate into chondroblasts, adipocytes, or osteoblasts under appropriate stimulation. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor (GHSR), stimulates growth hormone (GH) secretion, and has both orexigenic and adipogenic effects. This study sought to understand the potential involvement of members of MAPK serine/threonine kinases in the ghrelin-induced growth of rabbit MSCs ( rBMSC).

Methods

We applied various concentrations of ghrelin to cultured rBMSC and observed the growth rate of the cells by MTT, changes in the phosphorylation state of ERK1/2, JNK and p38, and the expression levels of ALP, Runx2, and Osterix by wetern blot.

Results

We found that the growth and osteogenic differentiation of ghrelin-treated rBMSC are promoted primarily by phosphorylated ERK1/2, and that this phosphorylation, as well p38 phosphorylation, is mediated by GHSR.

Conclusions

Our study suggests that ghrelin promotes the growth and osteogenic differentiation of rBMSC primarily through the ERK1/2 pathway.

A new class of ghrelin O-acyltransferase inhibitors incorporating triazole-linked lipid mimetic groups

Inhibitors of ghrelin O-acyltransferase (GOAT) have untapped potential as therapeutics targeting obesity and diabetes. We report the first examples of GOAT inhibitors incorporating a triazole linkage as a biostable isosteric replacement for the ester bond in ghrelin and amide bonds in previously reported GOAT inhibitors. These triazole-containing inhibitors exhibit sub-micromolar inhibition of the human isoform of GOAT (hGOAT), and provide a foundation for rapid future chemical diversification and optimization of hGOAT inhibitors.

Ghrelin improves functional survival of engrafted adipose-derived mesenchymal stem cells in ischemic heart through PI3K/Akt signaling pathway

Mesenchymal stem cells (MSCs) have been proposed as a promising cell population for cell therapy and regenerative medicine applications. However, the low retention and poor survival of engrafted cells hampered the therapeutic efficacy of engrafted MSCs. Ghrelin is a 28-amino-acid peptide hormone and is proved to exert a protective effect on the cardiovascular system. This study is designed to investigate the protective effects of ghrelin on engrafted adipose-derived mesenchymal stem cells (ADMSCs) and its beneficial effects with cellular therapy in mice myocardial infarction (MI). Results showed that intramyocardial injection of ADMSCs combining with ghrelin administration inhibited host cardiomyocyte apoptosis, reduced fibrosis, and improved cardiac function. To reveal possible mechanisms, ADMSCs were subjected to hypoxia/serum deprivation (H/SD) injury to simulate ischemic conditions in vivo. Ghrelin (10⁻⁸ M, 33712 pg/ml) improved ADMSCs survival under H/SD condition. Western blot assay revealed that ghrelin increased AKT phosphorylation both in vivo and in vitro, decreased the proapoptotic protein Bax, and increased the antiapoptotic protein Bcl-2 in vitro, while these effects were abolished by PI3K inhibitor LY294002. These revealed that ghrelin may serve as a promising candidate for hormone-driven approaches to improve the efficacy of mesenchymal stem cell-based therapy for cardiac ischemic disease via PI3K/AKT pathway.

Teaghrelins, unique acylated flavonoid tetraglycosides in Chin-shin oolong tea, are putative oral agonists of the ghrelin receptor

Chin-shin oolong tea, a popular tea in Taiwan, was empirically perceived to induce hunger and accelerate gastric emptying in a manner similar to the physiological effects of ghrelin, an endogenous acylated peptide known as the hunger hormone. Two unique acylated flavonoid tetraglycosides previously identified in Chin-shin oolong tea were demonstrated to induce hunger of rats in a food intake assay and, thus, named teaghrelin-1 and teaghrelin-2. Similar to GHRP-6, a synthetic analogue of ghrelin, teaghrelin-1 stimulated growth hormone secretion of rat primary anterior pituitary cells in a dose-dependent manner, and the stimulation was inhibited by [D-Arg(1),D-Phe(5),D-Trp(7,9),Leu(11)]-substance P, an antagonist of the ghrelin receptor. While teaghrelin-2 remained unmodified, a meta-O-methylated metabolite of teaghrelin-1 was detected in bile of rats after intravenous injection. Presumably, teaghrelins are promising oral agonists of the ghrelin receptor.

Acupuncture for functional dyspepsia: study protocol for a two-center, randomized controlled trial

Background

Functional dyspepsia (FD) is a common health problem currently without any optimal treatments. Acupuncture has been traditionally sought as a treatment for FD. The aim of this study is to investigate whether acupuncture treatment helps improve symptoms of FD.

Methods/design

A two-center, randomized, waitlist-controlled trial will be carried out to evaluate whether acupuncture treatment improves FD symptoms. Seventy six participants aged 18 to 75 years with FD as diagnosed by Rome III criteria will be recruited from August 2013 to January 2014 at two Korean Medicine hospitals. They will be randomly allocated either into eight sessions of partially individualized acupuncture treatment over 4 weeks or a waitlist group. The acupuncture group will then be followed-up for 3 weeks with six telephone visits and a final visit will be paid at 8 weeks. The waitlist group will receive the identical acupuncture treatment after a 4-week waiting period. The primary outcome is the proportion of responders with adequate symptom relief and the secondary outcomes include Nepean dyspepsia index, EQ-5D, FD-related quality of life, Beck’s depression inventory, state-trait anxiety inventory questionnaire, and level of ghrelin hormone. The protocol was approved by the participating centers’ Institutional Review Boards.

Discussion

Results of this trial will help clarify not only whether the acupuncture treatment is beneficial for symptom improvement in FD patients but also to elucidate the related mechanisms of how acupuncture might work.

Trial registration

ClinicalTrials.gov Identifier: NCT01921504.

Structure and physiological actions of ghrelin

Ghrelin is a gastric peptide hormone, discovered as being the endogenous ligand of growth hormone secretagogue receptor. Ghrelin is a 28 amino acid peptide presenting a unique n-octanoylation modification on its serine in position 3, catalyzed by ghrelin O-acyl transferase. Ghrelin is mainly produced by a subset of stomach cells and also by the hypothalamus, the pituitary, and other tissues. Transcriptional, translational, and posttranslational processes generate ghrelin and ghrelin-related peptides. Homo- and heterodimers of growth hormone secretagogue receptor, and as yet unidentified receptors, are assumed to mediate the biological effects of acyl ghrelin and desacyl ghrelin, respectively. Ghrelin exerts wide physiological actions throughout the body, including growth hormone secretion, appetite and food intake, gastric secretion and gastrointestinal motility, glucose homeostasis, cardiovascular functions, anti-inflammatory functions, reproductive functions, and bone formation. This review focuses on presenting the current understanding of ghrelin and growth hormone secretagogue receptor biology, as well as the main physiological effects of ghrelin.

Changes in the ghrelin hormone pathway maybe part of an unusual gastric system in monotremes

Ghrelin is a growth hormone (GH)-releasing and appetite-regulating peptide predominately released from the stomach. Ghrelin is evolutionarily highly conserved and known to have a wide range of functions including the regulation of metabolism by maintaining an insulin-glucose balance. The peptide is produced as a single proprotein, which is later proteolytically cleaved. Ghrelin exerts its biological function after O-n-octanoylation at residue serine 3, which is catalyzed by ghrelin O-acyl transferase (GOAT) and allows binding to the growth hormone secretagogue receptor (GHS-R 1a). Genes involved in the ghrelin pathway have been identified in a broad range of vertebrate species, however, little is known about this pathway in the basal mammalian lineage of monotremes (platypus and echidna). Monotremes are particularly interesting in this context, as they have undergone massive changes in stomach anatomy and physiology, accompanied by a striking loss of genes involved in gastric function. In this study, we investigated genes in the ghrelin pathway in monotremes. Using degenerate PCR, database searches and synteny analysis we found that genes encoding ghrelin and GOAT are missing in the platypus genome, whilst, as has been reported in other species, the GHSR is present and expressed in brain, pancreas, kidney, intestine, heart and stomach. This is the first report suggesting the loss of ghrelin in a mammal. The loss of this gene may be related to changes to the platypus digestive system and raises questions about the control of blood glucose levels and insulin response in monotreme mammals. In addition, the conservation of the ghrelin receptor gene in platypus indicates that another ligand(s) maybe acting via this receptor in monotremes.

Differential modulation of ghrelin-induced GH and LH release by PACAP and dopamine in goldfish pituitary cells

Ghrelin (GRLN) participates in multiple physiological processes, including the regulation of growth hormone (GH) and luteinizing hormone (LH) release. In the goldfish, neuroendocrine control of GH and LH release are multifactorial. In this system, pituitary adenylate cyclase-activating polypeptide (PACAP)-stimulated GH and LH secretion, as well as dopamine (DA)-induced GH release, are mediated by protein kinase A (PKA)-dependent, but protein kinase C (PKC)-independent, mechanisms. In addition, DA inhibits LH secretion by actions at sites along both PKA and PKC signaling pathways. Recently, goldfish GRLN (gGRLN19) has been shown to induce GH release via PKC, and LH secretion via both PKC and PKA. To further understand the neuroendocrine regulation of goldfish GH and LH release, we examined the effects of DA and PACAP on gGRLN19 actions in primary cultures of goldfish pituitary cells in perifusion and in Ca(2+)-imaging experiments. Consistent with their known intracellular signaling mechanisms in gonadotrophs, DA inhibited gGRLN19-induced LH release while cotreatment of PACAP and gGRLN19 did not produce additive LH responses. When applied prior to gGRLN19, PACAP potentiated gGRLN19-induced GH release and Ca(2+) signals within somatotrophs. In contrast, neither prior treatment with DA followed by gGRLN19 nor pretreatment with gGRLN19 prior to PACAP produced an enhanced GH release response. These observations suggest that PKA activators positively modulate gGRLN19 actions on goldfish somatotrophs in a ligand- and treatment order-specific manner. Results add to our understanding of the complexity of neuroendocrine control of GH and LH release at the pituitary cell level, and our understanding of GRLN action.

Role of ghrelin in the pathophysiology of gastrointestinal disease

Ghrelin is a 28-amino-acid peptide that plays multiple roles in humans and other mammals. The functions of ghrelin include food intake regulation, gastrointestinal (GI) motility, and acid secretion by the GI tract. Many GI disorders involving infection, inflammation, and malignancy are also correlated with altered ghrelin production and secretion. Although suppressed ghrelin responses have already been observed in various GI disorders, such as chronic gastritis, Helicobacter pylori infection, irritable bowel syndrome, functional dyspepsia, and cachexia, elevated ghrelin responses have also been reported in celiac disease and inflammatory bowel disease. Moreover, we recently reported that decreased fasting and postprandial ghrelin levels were observed in female patients with functional dyspepsia compared with healthy subjects. These alterations of ghrelin responses were significantly correlated with meal-related symptoms (bloating and early satiation) in female functional dyspepsia patients. We therefore support the notion that abnormal ghrelin responses may play important roles in various GI disorders. Furthermore, human clinical trials and animal studies involving the administration of ghrelin or its receptor agonists have shown promising improvements in gastroparesis, anorexia, and cancer. This review summarizes the impact of ghrelin, its family of peptides, and its receptors on GI diseases and proposes ghrelin modulation as a potential therapy.

Growth hormone-releasing hormone stimulates GH release while inhibiting ghrelin- and sGnRH-induced LH release from goldfish pituitary cells

Goldfish GH-releasing hormone (gGHRH) has been recently identified and shown to stimulate GH release in goldfish. In goldfish, neuroendocrine regulation of GH release is multifactorial and known stimulators include goldfish ghrelin (gGRLN19) and salmon gonadotropin-releasing hormone (sGnRH), factors that also enhance LH secretion. To further understand the complex regulation of pituitary hormone release in goldfish, we examined the interactions between gGHRH, gGRLN19, and sGnRH on GH and LH release from primary cultures of goldfish pituitary cells in perifusion. Treatment with 100nM gGHRH for 55min stimulated GH release. A 5-min pulse of either 1nM gGRLN19 or 100nM sGnRH induced GH release in naïve cells, and these were just as effective in cells receiving gGHRH. Interestingly, gGHRH abolished both gGRLN19- and sGnRH-induced LH release and reduced basal LH secretion levels. These results suggest that gGHRH does not interfere with sGnRH or gGRLN19 actions in the goldfish somatotropes and further reveal, for the first time, that GHRH may act as an inhibitor of stimulated and basal LH release by actions at the level of pituitary cells.

Acute stress inhibits food intake and alters ghrelin signaling in the brain of tilapia (Oreochromis mossambicus)

This study investigated the effect of an acute stress on food intake and on the expression of neuropeptide Y (NPY), corticotropin-releasing hormone (CRH), and ghrelin and its receptors, growth hormone secretagogue receptors (GHSRs) in the tilapia (Oreochromis mossambicus). Food intake was significantly (P < 0.01) reduced in fish after a 30-min crowding and handling stress. In a second group of animals exposed to the same 30-min stressor, tissue samples were collected immediately after the stressor to determine changes in the neuroendocrine regulators of food intake. Although CRH and NPY are considered the major mediators of appetite during stress, both mRNA levels were unaltered in the telencephalon/pre-optic area and in the hypothalamic/optic tectum. Interestingly, there was an elevation in the ghrelin transcript (P < 0.05) in the telencephalon/pre-optic area and elevation of its functional receptor (GHSR1a-LR) (P < 0.001) in the hypothalamic/optic tectum. Elevation of GHSR-LR heteronuclear RNA (P < 0.01) in the telencephalon/pre-optic area and suppression in the hypothalamic/optic tectum (P < 0.001) suggest rapid control of the ghrelin regulatory system in response to acute stress. These results suggest that ghrelin signaling is altered during acute stress. It is not clear if these changes result in altered feeding behavior because no changes in CRH or NPY mRNA expression were observed or if ghrelin is playing a role in regulating overall metabolic changes after acute stress.

Orphan GPCRs and neuromodulation

Most G protein-coupled receptors (GPCRs) started as orphan GPCRs. Matching them to known neuromodulators led to the elucidation of the broad diversity of the neuroreceptor families. Moreover, orphan GPCRs have also been used as targets to discover novel neuromodulators. These discoveries have had profound impact on our understanding of brain function. Here, I present an overview of how some of the novel neuropeptides have enlarged our comprehension of responses that direct sleep/wakefulness, the onset of obesity and the feeding response. I also discuss other advances gained from orphan GPCR studies such as the concept of specificity in neuromodulation or of receptors acting as sensors instead of synaptic transmitters. Finally, I suggest that the recently discovered neuromodulators may hold the keys to our understanding of higher brain functions and psychiatric disorders.

Ghrelin, leptin and insulin in cirrhotic children and adolescents: relationship with cirrhosis severity and nutritional status

OBJECTIVE

Ghrelin, leptin, and insulin concentrations are involved in the control of food intake and they seem to be associated with anorexia-cachexia in cirrhotic patients. The present study aimed to investigate the relationship between the nutritional status and fasting ghrelin, leptin and insulin concentrations in pediatric cirrhotic patients.

METHODS

Thirty-nine patients with cirrhosis and 39 healthy controls aged 0-15 years matched by sex and age were enrolled. Severity of liver disease was assessed by Child-Pugh classification, and Pediatric for End Stage Liver Disease (PELD) or Model for End-stage Liver Disease (MELD) scores. Blood samples were collected from patients and controls to assay total ghrelin, acyl ghrelin, leptin and insulin by using a commercial ELISA kit. Anthropometry parameters used were standard deviation score of height-for-age and triceps skinfold thickness-for-age ratio. A multiple linear regression analysis was used to determine the correlation between dependent and independent variables.

RESULTS

Acyl ghrelin was significantly lower in cirrhotic patients than in controls [142 (93-278) pg/mL vs 275 (208-481) pg/mL, P=0.001]. After multiple linear regression analysis, total ghrelin and acyl ghrelin showed an inverse correlation with age; acyl ghrelin was associated with the severity of cirrhosis and des-acyl ghrelin with PELD or MELD scores ≥15. Leptin was positively correlated with gender and anthropometric parameters. Insulin was not associated with any variable.

CONCLUSION

Low acyl ghrelin and high des-acyl ghrelin concentrations were associated with cirrhosis severity, whereas low leptin concentration was associated with undernourishment in children and adolescents with cirrhosis.

Ghrelin-induced growth hormone release from goldfish pituitary cells is nitric oxide dependent

Ghrelin (GRLN) is an important neuroendocrine regulator of growth hormone (GH) release in vertebrates. Previous studies show goldfish (g)GRLN(19)-induced GH from the goldfish pituitary involves voltage sensitive Ca(2+) channels, increases in intracellular Ca(2+) and the PKC signalling pathway. We set out to examine the role of the nitric oxide (NO) pathway in gGLRN(19)-induced GH release from primary cultures of goldfish pituitary cells using pharmacological regulators in cell column perifusion systems. The NO scavenger PTIO abolished gGRLN(19)-induced GH release and co-treatment with the NO donor SNP and GRLN did not produce additive GH release responses. Nitric oxide synthase (NOS) inhibitors 1400 W and 7-Ni abolished GRLN-induced GH release while treatment with another NOS inhibitor, AGH, had no significant effect. Taken together, these results demonstrate that the NOS/NO is an integral component of gGRLN(19)-induced signalling within the goldfish pituitary cells, and given the relative specificity of AGH for inducible NOS and endothelial NOS isoforms, suggests that neuronal NOS is the likely NOS isoform utilized in goldfish somatotropes by this physiological regulator.

G protein-coupled receptor deorphanizations

G protein-coupled receptors (GPCRs) are major regulators of intercellular interactions. They initiate these actions by being activated by a wide variety of natural ligands. Historically, ligands were discovered first, but the advent of molecular biology reversed this trend. Most GPCRs are identified on the basis of their DNA sequences and thus are initially unmatched to known natural ligands. They are termed orphan GPCRs. Discovering their ligands-i.e., "deorphanizing" the GPCRs-gave birth to the field of reverse pharmacology. This review discusses the present status of GPCR deorphanization, presents a few examples of successes and surprises, and highlights difficulties encountered in these efforts.

Plasma ghrelin levels in patients with familial Mediterranean fever

BACKGROUND

Familial Mediterranean fever (FMF) is an auto-inflammatory disorder characterized by febrile attacks. Increased acute-phase reactants are characteristic during febrile attacks. Ghrelin is a natural G-protein that decreases secretion of pro-inflammatory cytokines and acts as anti-inflammatory agent. The aim of this study was to investigate whether there is any change in ghrelin levels and whether increases in ghrelin levels can be used as a marker in these patients.

SUBJECTS AND METHODS

Thirty-seven male patients and 30 healthy men as a control group were included in the study. Blood samples were obtained for ghrelin measurements both before the attacks (pre-attack period; ghrelin 1 group) and during the attacks (ghrelin 2 group). Samples were kept at -80°C until the analysis was conducted and plasma ghrelin levels were measured using an immune-sorbent assay method.

RESULTS

Mean ghrelin levels measured during the attacks were significantly higher (11.01 ± 4.78 pg/ml) as compared to pre-attack levels (5.78 ± 2.17 pg/ml; p < 0.001). Similarly, mean ghrelin levels measured in FMF patients during an attack were significantly different from that of the control group (6.57 ± 4.13 pg/ml; p < 0.001).

CONCLUSIONS

In this study, high ghrelin levels were measured during attacks in FMF patients. This finding is in line with previous results regarding the fact that inflammatory response arising during an FMF attack is an acute inflammatory event. Our findings suggest that ghrelin levels measured during FMF attacks could be used as a biochemical indicator for the FMF attack in FMF patients and that it could be used for support of the diagnosis of the disease.

The role of ghrelin in the control of energy balance

Ghrelin is the only potent orexigenic peptide in circulation. It stimulates food intake and leads to positive energy balance, adipogenesis, and body weight gain. However, the physiological significance of ghrelin in the regulation of energy homeostasis is controversial, since loss of ghrelin function in rodents does not necessarily lead to anorexia and weight loss. In this chapter, we discuss the metabolic function of ghrelin and are highlighting recent findings including the discovery and function of ghrelin-acylating enzyme ghrelin O-acyltransferase (GOAT). Based on available published data, we conclude that ghrelin is a principally important endogenous regulator of energy balance, which however may affect both food intake and systemic metabolism via independent mechanisms. Importantly, ghrelin, when acylated by GOAT, might represent a key molecular link between the sensing of consumed calories and the neuroendocrine control of energy homeostasis. Thus, agents antagonizing the action of ghrelin may have therapeutic potential in the therapy of obesity.

Recent advances in potential clinical application of ghrelin in obesity

Ghrelin is the natural ligand of the growth hormone secretagogue receptor (GHS-R1a). Ghrelin is a 28 amino acid peptide possessing a unique acylation on the serine in position 3 catalyzed by ghrelin O-acyltransferase (GOAT). Ghrelin stimulates growth hormone secretion, but also appetite, food intake, weight gain, and gastric emptying. Ghrelin is involved in weight regulation, obesity, type 2 diabetes, and metabolic syndrome. Furthermore, a better understanding of ghrelin biology led to the identification of molecular targets modulating ghrelin levels and/or its biological effects: GOAT, ghrelin, and GHS-R1a. Furthermore, a recent discovery, showing the involvement of bitter taste receptor T2R in ghrelin secretion and/or synthesis and food intake, suggested that T2R could represent an additional interesting molecular target. Several classes of ghrelin-related pharmacological tools for the treatment of obesity have been or could be developed to modulate the identified molecular targets.

Differential involvement of protein kinase C and protein kinase A in ghrelin-induced growth hormone and gonadotrophin release from goldfish (Carassius auratus) pituitary cells

Ghrelin (GRLN) and its receptor have been identified and characterised in goldfish brain and the pituitary, and recent evidence shows that goldfish (g)GRLN(19) induces both growth hormone (GH) and maturational gonadotrophin (LH) release through an extracellular Ca(2+) -dependent mechanism in goldfish. To further understand the role of GRLN in hormone release, the present study examined the involvement of protein kinase C (PKC) and protein kinase A (PKA) in gGRLN(19) -induced GH and LH release and corresponding Ca(2+) signals in primary cultures of goldfish pituitary cells. Treatments with PKC inhibitors, Bis-II and Gö 6976, significantly reduced gGRLN(19) -induced GH and LH release and their corresponding intracellular Ca(2+) signals in identified somatotrophs and gonadotrophs, respectively. gGRLN(19) was unable to further stimulate hormone release or Ca(2+) signals when cells were pretreated with the PKC agonist, DiC8. PKA inhibitors, H-89 and KT 5720, inhibited gGRLN(19) -induced LH release and Ca(2+) signals in gonadotrophs but not GH release or Ca(2+) signals in somatotrophs. Interestingly, pretreatment of pituitary cells with the adenylate cyclase activator forskolin potentiated gGRLN(19) -induced GH, but not LH, release, although it had no effect on intracellular Ca(2+) signals in either cell type. Taken together, the results suggest that PKC is an important intracellular component in gGRLN(19) -induced GH and LH release, whereas PKA is involved in gGRLN(19) -elicited LH release. Furthermore, the PKA pathway potentiates gGRLN(19) -induced GH release via a Ca(2+) -independent mechanism. Overall, the present study provides insight into the neuroendocrine regulation of GH and LH release by elucidating the mechanistic aspects of GRLN, a hormone involved in many critical physiological processes, including pituitary functions.

Beyond the metabolic role of ghrelin: a new player in the regulation of reproductive function

Ghrelin is a gastric peptide, discovered by Kojima et al. (1999) [55] as a result of the search for an endogenous ligand interacting with the "orphan receptor" GHS-R1a (growth hormone secretagogue receptor type 1a). Ghrelin is composed of 28 aminoacids and is produced mostly by specific cells of the stomach, by the hypothalamus and hypophysis, even if its presence, as well as that of its receptors, has been demonstrated in many other tissues, not least in gonads. Ghrelin potently stimulates GH release and participates in the regulation of energy homeostasis, increasing food intake, decreasing energy output and exerting a lipogenetic effect. Furthermore, ghrelin influences the secretion and motility of the gastrointestinal tract, especially of the stomach, and, above all, profoundly affects pancreatic functions. Despite of these previously envisaged activities, it has recently been hypothesized that ghrelin regulates several aspects of reproductive physiology and pathology. In conclusion, ghrelin not only cooperates with other neuroendocrine factors, such as leptin, in the modulation of energy homeostasis, but also has a crucial role in the regulation of the hypothalamic-pituitary gonadal axis. In the current review we summarize the main targets of this gastric peptide, especially focusing on the reproductive system.

Ghrelin and cardiovascular diseases

Ghrelin, a newly discovered bioactive peptide, is a natural endogenous ligand of the growth hormone (GH) secretagogue receptor and initially identified as a strong stimulant for the release of GH. Subsequent research has shown that ghrelin and its various receptors are ubiquitous in many other organs and tissues. Moreover, they participate in the regulation of appetite, energy, bodyweight, metabolism of glucose and fat, as well as modulation of gastrointestinal, cardiovascular, pulmonary, immune functions and cell proliferation/apoptosis. Increasing evidence has demonstrated that ghrelin has a close relationship with cardiovascular system. Ghrelin and its receptors are widely distributed in cardiovascular tissues, and there is no doubt that the effects of ghrelin in the cardiovascular system are mediated not only via its growth-hormone-releasing effect but also by its direct effects on the heart. Exogenous administration of ghrelin can dilate peripheral blood vessels, constrict coronary artery, improve endothelial function, as well as inhibit myocardial cell apoptosis. So, ghrelin may have cardiovascular protective effect, including lowering of blood pressure, regulation of atherosclerosis, and protection from ischemia/reperfusion injury as well as improving the prognosis of myocardial infarction and heart failure. Some of these new functions of ghrelin may provide new potential therapeutic opportunities for ghrelin in cardiovascular medicine. In this paper, we will review the existing evidence for cardiovascular effects of ghrelin, including the cardiovascular function, the variations in ghrelin plasma levels in pathophysiologicalogical conditions, the possible protective mechanisms of ghrelin, as well as its future potential therapeutic roles.

Short-,moderate-, and long-term treadmill training protocols reduce plasma, fundus, but not small intestine ghrelin concentrations in male rats

BACKGROUND

It has been suggested that circulating ghrelin levels are upregulated by fasting, hypoglycemic status, and a physical exercise-induced energy deficit.

AIM

The purpose of the present study was to investigate the timecourse adaptations of the plasma, fundus, and small intestine ghrelin concentrations as well as related hormones and liver ATP levels to 3, 6, and 12 weeks of treadmill endurance running.

MATERIAL/SUBJECTS AND METHODS

Thirty-nine male Wistar rats (12-14 weeks old) were randomly assigned to 3 control (C3, no.=5; C6, no.=7 and C12, no.=7) and 3 training groups (E3, no.=6; E6, no.=7 and E12, no.=7). The rats in the 3 training groups were exercised on a motor-driven treadmill at 25 m/min (0% grade) for 60 min/day, 5 days/week for 3, 6, and 12 weeks, respectively. The animals were sacrificed 48 h after the last session of each training program and tissues were analyzed.

RESULTS

Total ghrelin concentrations were significantly (p<0.05) lower in trained rat plasma and fundus tissue after all treadmill endurance running programs. Small intestine ghrelin concentrations remained unchanged. Plasma GH concentrations and liver ATP content were significantly higher in E6 and E12 groups.

CONCLUSION

Data indicate that as little as 3 weeks of moderate treadmill exercise reduces plasma and fundus total ghrelin concentrations with elevated plasma GH and liver ATP content occurring after 6 and 12 weeks of training. Exercise training-induced improvement of energy source availability and negative feedback from increased GH levels may play a role in reducing plasma and fundus ghrelin levels.