Des-acyl ghrelin exhibits pro-anabolic and anti-catabolic effects on C2C12 myotubes exposed to cytokines and reduces burn-induced muscle proteolysis in rats

Unacylated Ghrelin Protects Against Age-Related Loss of Muscle Mass and Contractile Dysfunction in Skeletal Muscle

Sarcopenia, the progressive loss of muscle mass and function, universally affects older adults and is closely associated with frailty and reduced quality of life. Despite the inevitable consequences of sarcopenia and its relevance to healthspan, no pharmacological therapies are currently available. Ghrelin is a gut-released hormone that increases appetite and body weight through acylation. Acylated ghrelin activates its receptor, growth hormone secretagogue receptor 1a (GHSR1a), in the brain by binding to it. Studies have demonstrated that acyl and unacylated ghrelin (UnAG) both have protective effects against acute pathological conditions independent of receptor activation. Here, we investigated the long-term effects of UnAG in age-associated muscle atrophy and contractile dysfunction in mice. Four-month-old and 18-month-old mice were subjected to either UnAG or control treatment for 10 months. UnAG did not affect food consumption or body weight. Gastrocnemius and quadriceps muscle weights were reduced by 20%-30% with age, which was partially protected against by UnAG. Specific force, force per cross-sectional area, measured in isolated extensor digitorum longus muscle was diminished by 30% in old mice; however, UnAG prevented the loss of specific force. UnAG also protected from decreases in mitochondrial respiration and increases in hydrogen peroxide generation of skeletal muscle of old mice. Results of bulk mRNA-seq analysis and our contractile function data show that UnAG reversed neuromuscular junction impairment that occurs with age. Collectively, our data revealed the direct role of UnAG in mitigating sarcopenia in mice, independent of food consumption or body weight, implicating UnAG treatment as a potential therapy against sarcopenia.

Metabolic underpinnings of cancer-related fatigue

Cancer-related fatigue (CRF) is one of the most prevalent and detrimental complications of cancer. Emerging evidence suggests that obesity and insulin resistance are associated with CRF occurrence and severity in cancer patients and survivors. In this narrative review, we analyzed recent studies including both preclinical and clinical research on the relationship between obesity and/or insulin resistance and CRF. We also describe potential mechanisms for these relationships, though with the caveat that because the mechanisms underlying CRF are incompletely understood, the mechanisms mediating the association between obesity/insulin resistance and CRF are similarly incompletely delineated. The data suggest that, in addition to their effects to worsen CRF by directly promoting tumor growth and metastasis, obesity and insulin resistance may also contribute to CRF by inducing chronic inflammation, neuroendocrinological disturbance, and metabolic alterations. Furthermore, studies suggest that patients with obesity and insulin resistance experience more cancer-induced pain and are at more risk of emotional and behavioral disruptions correlated with CRF. However, other studies implied a potentially paradoxical impact of obesity and insulin resistance to reduce CRF symptoms. Despite the need for further investigation utilizing interventions to directly elucidate the mechanisms of cancer-related fatigue, current evidence demonstrates a correlation between obesity and/or insulin resistance and CRF, and suggests potential therapeutics for CRF by targeting obesity and/or obesity-related mediators.

Role and molecular mechanism of ghrelin in degenerative musculoskeletal disorders

Ghrelin is a brain-gut peptide, and the first 28-peptide that was found in the gastric mucosa. It has a growth hormone (GH)-releasing hormone-like effect and can potently promote the release of GH from pituitary GH cells; however, it is unable to stimulate GH synthesis. Therefore, ghrelin is believed to play a role in promoting bone growth and development. The correlation between ghrelin and some degenerative diseases of the musculoskeletal system has been reported recently, and ghrelin may be one of the factors influencing degenerative pathologies, such as osteoporosis, osteoarthritis, sarcopenia and intervertebral disc degeneration. With population ageing, the risk of health problems caused by degenerative diseases of the musculoskeletal system gradually increases. In this article, the roles of ghrelin in musculoskeletal disorders are summarized to reveal the potential effects of ghrelin as a key target in the treatment of related bone and muscle diseases and the need for further research.

Desacyl-ghrelin, not just an inactive form of ghrelin?-A review of current knowledge on the biological actions of desacyl-ghrelin

Desacyl-ghrelin is a form of ghrelin which lacks acyl-modification of the third serine residue of ghrelin. Originally, desacyl-ghrelin was considered to be just an inactive form of ghrelin. More recently, however, it has been suggested to have various biological activities, including control of food intake, growth hormone, glucose metabolism, and gastric movement, and is involved in cell survival. In this review, we summarize the current knowledge of the biological actions of desacyl-ghrelin and the proposed mechanisms by which it exerts the effects.

Association between fat-free mass loss, changes in appetite and weight regain in individuals with obesity

BACKGROUND

The role of fat-free mass loss (FFML) in modulating weight regain, in individuals with obesity, as well as the potential mechanisms involved, remain inconsistent.

AIMS

To determine if % FFML following weight loss (WL) is a predictor of weight regain, and to investigate the association between %FFML and changes in appetite markers.

METHODS

Seventy individuals with obesity (BMI: 36±4kg/m²; age: 44±9 years; 29 males) underwent 8 weeks of a very low-energy diet (550-660 kcal/day), followed by 4 weeks of gradual refeeding and weight stabilization, and a 9-month maintenance program (eucaloric diet). Body weight and body composition (fat mass (FM) and FFM) (primary outcomes), as well as ß-hydroxybutyrate (ßHB) plasma concentration (a marker of ketosis) in fasting and appetite-related hormones (ghrelin, glucagon-like peptide 1, peptide YY, and cholecystokinin) and subjective appetite feelings, in fasting and every 30 minutes after a fixed breakfast for 2.5h (secondary outcomes), were measured at baseline, week 9 and 1 year (and week 13 in 35 subjects (25 males)). The association between FFML, weight regain and changes in appetite was assessed by linear regression.

RESULTS

WL at week 9 was 17.5±4.3kg and %FFML 20.4±10.6%. Weight regain at 1 year was 1.7±8.2kg (8.8±45.0%). After adjusting for WL and FM at baseline, %FFML at week 9 was not a significant predictor of weight regain. Similar results were seen at week 13. The greater the %FFML at week 9, but not 13, the smaller the reduction, or greater the increase in basal ghrelin concentration (ß:-3.2; 95% CI: -5.0, -1.1; P=0.003), even after adjusting for WL and ß-hydroxybutyrate.

CONCLUSION

%FFML was not a significant predictor of weight regain at 1-year in individuals with obesity. However, a greater %FFML was accompanied by a greater increase in ghrelin secretion under ketogenic conditions, suggesting a link between FFM and appetite regulation.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT01834859.

Acylated Ghrelin Receptor Agonist HM01 Decreases Lean Body and Muscle Mass, but Unacylated Ghrelin Protects against Redox-Dependent Sarcopenia

Sarcopenia, the progressive loss of muscle mass and dysfunction, universally affects the elderly and is closely associated with frailty and reduced quality of life. Despite the inevitable consequences of sarcopenia and its relevance to healthspan, no pharmacological therapies are currently available. Ghrelin is a gut-released hormone that increases appetite and body weight upon acylation, which activates its receptor GHSR1a. Recent studies have demonstrated that acyl and unacylated ghrelin are protective against acute pathological conditions of skeletal muscle. We hypothesized that both acyl ghrelin receptor agonist (HM01) and unacylated ghrelin ameliorate muscle atrophy and contractile dysfunction in oxidative stress-induced sarcopenia. HM01, unacylated ghrelin, or saline was delivered via osmotic pump. HM01 increased food consumption transiently, while the body weight remained elevated. It also decreased lean body mass and muscle mass of wildtype and Sod1KO. In contrast, unacylated ghrelin ameliorated loss of muscle mass by 15-30% in Sod1KO mice without changes in food consumption or body weights. Contractile force was decreased by ~30% in Sod1KO mice, but unacylated ghrelin prevented the force deficit by ~80%. We identified downregulation of transcription factor FoxO3a and its downstream E3 ligase MuRF1 by unacylated ghrelin. Our data show a direct role of unacylated ghrelin in redox-dependent sarcopenia independent of changes of food consumption or body weight.

Antagonization of Ghrelin Suppresses Muscle Protein Deposition by Altering Gut Microbiota and Serum Amino Acid Composition in a Pig Model

Simple Summary

This study investigated the effects of the antagonization of ghrelin on muscle protein deposition, eating patterns and gut microbiota in pigs by injecting ghrelin antagonist ([D-Lys3]-GHRP-6) in a short term. We found that the antagonization of ghrelin affected the eating patterns of animals, which resulted in changes in the absorption of amino acids and gut microbiota, and it reduced protein deposition in muscles. We emphasize the important role of ghrelin in promoting muscle protein deposition and provide new clues for future research on improving muscle loss.

Abstract

Ghrelin is an appetite-stimulating hormone that can increase food intake and has been reported to prevent muscle loss; however, the mechanism is not yet fully understood. In this study, [D-Lys3]-GHRP-6 (GHRP) was used to investigate the effects of the antagonization of ghrelin on muscle protein deposition, eating patterns and gut microbiota in a pig model. We found that the growth performance and muscle fiber cross-sectional area of pigs treated with GHRP were significantly reduced compared with the control (CON) group. Moreover, the levels of serum isoleucine, methionine, arginine and tyrosine in the GHRP group were lower than that of the CON group. The abundance of acetate-producing bacteria (Oscillospiraceae UCG-005, Parabacteroides and Oscillospiraceae NK4A214 group) and acetate concentration in the colons of pigs treated with GHRP were significantly reduced. In addition, the injection of GHRP down-regulated the mRNA expression of MCT-1 and mTOR, and it up-regulated the mRNA expression of HDAC1, FOXO1 and Beclin-1. In summary, the antagonization of ghrelin reduced the concentration of important signal molecules (Arg, Met and Ile) that activate the mTOR pathway, concurrently reduce the concentration of HDAC inhibitors (acetate), promote autophagy and finally reduce protein deposition in muscles.

Sarcopenia in Children with Solid Organ Tumors: An Instrumental Era

Sarcopenia has recently been studied in both adults and children and was found to be a prognostic marker for adverse outcome in a variety of patient groups. Our research showed that sarcopenia is a relevant marker in predicting outcome in children with solid organ tumors, such as hepatoblastoma and neuroblastoma. This was especially true in very ill, high-risk groups. Children with cancer have a higher likelihood of ongoing loss of skeletal muscle mass due to a mismatch in energy intake and expenditure. Additionally, the effects of cancer therapy, hormonal alterations, chronic inflammation, multi-organ dysfunction, and a hypermetabolic state all contribute to a loss of skeletal muscle mass. Sarcopenia seems to be able to pinpoint this waste to a high degree in a new and objective way, making it an additional tool in predicting and improving outcome in children. This article focuses on the current state of sarcopenia in children with solid organ tumors. It details the pathophysiological mechanisms behind sarcopenia, highlighting the technical features of the available methods for measuring muscle mass, strength, and function, including artificial intelligence (AI)-based techniques. It also reviews the latest research on sarcopenia in children, focusing on children with solid organ tumors.

Understanding the molecular basis of anorexia and tissue wasting in cancer cachexia

Cancer cachexia syndrome is a major cause of morbidity and mortality in cancer patients in the advanced stage. It is a devastating disorder characterized by nutritional impairment, weakness, and wasting, and it affects treatment success and quality of life. Two major symptoms of cancer cachexia are anorexia and weight loss. Weight loss in cachexia is not reversed through increased food intake, suggesting that anorexia and weight loss in cancer patients are regulated by independent molecular mechanisms. Although the wasting phenotype mostly occurs in skeletal muscle and adipose tissue, other organs, such as the brain, liver, pancreas, heart, and gut, are also involved in cachexia. Thus, cachexia is a multiorgan syndrome. Although the molecular basis of cancer cachexia-induced weight loss is known, the mechanism underlying anorexia is poorly understood. Here, we highlight our recent discovery of a new anorexia mechanism by which a tumor-derived humoral factor induces cancer anorexia by regulating feeding-related neuropeptide hormones in the brain. Furthermore, we elucidated the process through which anorexia precedes tissue wasting in cachexia. This review article aims to provide an overview of the key molecular mechanisms of anorexia and tissue wasting caused by cancer cachexia.

Tumors can release factors that cause anorexia and weight loss in cancer patients, negatively impacting quality of life and treatment success. Patients with this condition, known as cachexia, can lose their appetite and be unable to gain weight even if they eat more. Although cancer cachexia directly causes the death of up to 20% of cancer patients, the mechanisms are poorly understood. Eunbyul Yeom and Kweon Yu at The Korea Research Institute of Bioscience and Biotechnology, Daejon, South Korea have reviewed the causes of cancer cachexia, highlighting their recent discovery that tumors produce a signaling molecule that induces anorexia by disrupting hunger signaling in the brain. Improving our understanding of the mechanisms underlying cancer cachexia may help in development of treatments.

Ghrelin and its role in gastrointestinal tract tumors (Review)

Ghrelin, an orexigenic hormone, is a peptide that binds to the growth hormone secretagogue receptor; it is secreted mainly by enteroendocrine cells in the oxyntic glands of the stomach. Ghrelin serves a role in both local and systemic physiological processes, and is implicated in various pathologies, including neoplasia, with tissue expression in several types of malignancies in both in vitro and in vivo studies. However, the precise implications of the ghrelin axis in metastasis, invasion and cancer progression regulation has yet to be established. In the case of gastrointestinal (GI) tract malignancies, ghrelin has shown potential to become a prognostic factor or even a therapeutic target, although data in the literature are inconsistent and unsystematic, with reports untailored to a specific histological subtype of cancer or a particular localization. The evaluation of immunohistochemical expression shows a limited outlook owing to the low number of cases analyzed, and in vivo analyses have conflicting data regarding differences in ghrelin serum levels in patients with cancer. The aim of this review was to examine the relationship between ghrelin and GI tract malignancies to demonstrate the inconsistencies in current results and to highlight its clinical significance in the outcome of these patients.

An overview of anamorelin as a treatment option for cancer-associated anorexia and cachexia

INTRODUCTION

Cancer cachexia is a complex multifaceted syndrome involving functional impairment, changes in body composition, and nutritional disorders. The treatment of cancer cachexia can be based on these three domains of the syndrome. Phase II and III trials of anamorelin, a ghrelin mimetic agent, have been shown to increase body weight in patients with cancer cachexia, mainly by increasing muscle and fat mass. Anamorelin has been shown to improve anorexia scores.

AREAS COVERED

This review aims to outline the effect of anamorelin on body composition and functional parameters as well as to discuss the clinical importance of these alterations in patients with cancer cachexia.

EXPERT OPINION

To date, there is no treatment approved to enhance body composition and functional parameters in patients with cancer cachexia. Anamorelin, the most advanced therapy to treat cachexia, has not yielded convincing results in all aspects of the syndrome. In particular, no effect has been noted on physical function and long-term survival. Along with these essential improvements for future interventions with anamorelin, subsequent studies must address other etiologies of cancer, rather than non-small cell lung cancer, and add complementary therapies, such as exercise training and nutritional interventions, in an attempt to overcome cancer cachexia.

Ghrelin, via corticotropin-releasing factor receptors, reduces glucose uptake and increases lipid content in mouse myoblasts cells

Ghrelin and the corticotropin-releasing factor (CRF) family are known regulators of cellular metabolism and energy balance. We previously demonstrated that myoblast glucose metabolism is regulated by ghrelin and that this effect is mediated by CRF receptor type 2 (CRF-R2). Here we explored the effect of des-acyl ghrelin, the major circulating isoform of ghrelin, on cellular metabolism in mouse myoblast C2C12 cells, and examined whether CRF family receptors mediate its metabolic effects in muscle cells. C2C12 cells were exposed to des-acyl ghrelin with or without the CRF-R1- and CRF-R2-specific antagonists antalarmin or antisauvagine-30, respectively. Des-acyl ghrelin reduced glucose uptake and expression of the glucose transporter GLUT4, but induced retinol-binding protein 4 (RBP4) expression. Antalarmin and antisauvagine-30 inhibited the induction of glucose uptake by des-acyl ghrelin and its effect on GLUT4 and RBP4 expression. Moreover, treating C2C12 cells with des-acyl ghrelin resulted in cAMP activation in response to the CRF-R1-specific ligand stressin, and the CRF-R2-specific ligand Ucn3. Furthermore, des-acyl ghrelin reduced the expression of uncoupling proteins UCP2 and UCP3. Adding antalarmin or antisauvagine-30 to the medium reversed this effect. Finally, des-acyl ghrelin elevated lipid content and acetyl-CoA carboxylase expression in C2C12 cells. Our results suggest that during food deprivation, des-acyl ghrelin signals the muscle cells that glucose levels are low and that they should switch to fatty acids for their metabolic fuel.

Acylated and unacylated ghrelin relieve cancer cachexia in mice through multiple mechanisms

Cancer cachexia is a wasting syndrome resulting from decreased protein synthesis and increased protein degradation. Calpain-dependent cleavage of myofilament is the initial step of myofilament degradation and plays a critical role in muscle atrophy. Ghrelin is a multifunctional hormone known to improve protein synthesis and inhibit protein degradation. However, its mechanism of action is not fully understood. Here we investigated whether acylated ghrelin (AG) and unacylated ghrelin (UnAG) could protect against cancer cachexia in mice bearing CT26 colorectal adenocarcinoma. We found for the first time that both AG and UnAG could inhibit calpain activity in skeletal muscle of cancer cachectic mice. AG and UnAG also improved tumor-free body weight, grip strength, muscle mass, epididymal fat mass, and nutritional state in tumor-bearing (TB) mice. Moreover, AG and UnAG reduced serum tumor necrosis factor-± concentration, increased Akt activity, and downregulated atrogin-1 expression in TB mice. Our results may contribute to the development of an AG/UnAG-based therapy for cancer cachexia.

Cancer cachexia and its pathophysiology: links with sarcopenia, anorexia and asthenia

Cancer cachexia is a multifactorial syndrome characterized by a progressive loss of skeletal muscle mass, along with adipose tissue wasting, systemic inflammation and other metabolic abnormalities leading to functional impairment. Cancer cachexia has long been recognized as a direct cause of complications in cancer patients, reducing quality of life and worsening disease outcomes. Some related conditions, like sarcopenia (age-related muscle wasting), anorexia (appetite loss) and asthenia (reduced muscular strength and fatigue), share some key features with cancer cachexia, such as weakness and systemic inflammation. Understanding the interplay and the differences between these conditions is critical to advance basic and translational research in this field, improving the accuracy of diagnosis and contributing to finally achieve effective therapies for affected patients.

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

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

The influence of skeletal muscle on appetite regulation

INTRODUCTION

Fat-free mass, of which skeletal muscle is amajor component, correlates positively with energy intake at energy balance. This is due to the effects of metabolically active tissue on energy expenditure which in itself appears to signal to the brain adrive to eat to ensure cellular energy homeostasis. The mechanisms responsible for this drive to eat are unknown but are likely to be related to energy utilization. Here muscle imparts an indirect influence on hunger. The drive to eat is also enhanced after muscle loss secondary to intentional weight loss. The evidence suggests loss of both fat mass and skeletal muscle mass directly influences the trajectory and magnitude of weight regain highlighting their potential role in long-termappetite control. The mechanisms responsible for the potential direct drive to eat stemming from muscle loss are unknown.

AREAS COVERED

The literature pertaining to muscle and appetite at energy balance and after weight loss was examined. Aliterature search was conducted to identify studies related to appetite, muscle, exercise, and weight loss.

EXPERT OPINION

Understanding the mechanisms which link energy expenditure and muscle loss to hunger has the potential to positively impact both the prevention and the treatment of obesity.

Ghrelin knockout mice display defective skeletal muscle regeneration and impaired satellite cell self-renewal

PURPOSE

Muscle regeneration depends on satellite cells (SCs), quiescent precursors that, in consequence of injury or pathological states such as muscular dystrophies, activate, proliferate, and differentiate to repair the damaged tissue. A subset of SCs undergoes self-renewal, thus preserving the SC pool and its regenerative potential. The peptides produced by the ghrelin gene, i.e., acylated ghrelin (AG), unacylated ghrelin (UnAG), and obestatin (Ob), affect skeletal muscle biology in several ways, not always with overlapping effects. In particular, UnAG and Ob promote SC self-renewal and myoblast differentiation, thus fostering muscle regeneration.

METHODS

To delineate the endogenous contribution of preproghrelin in muscle regeneration, we evaluated the repair process in Ghrl^-/- mice upon CTX-induced injury.

RESULTS

Although muscles from Ghrl^-/- mice do not visibly differ from WT muscles in term of weight, structure, and SCs content, muscle regeneration after CTX-induced injury is impaired in Ghrl^-/- mice, indicating that ghrelin-derived peptides actively participate in muscle repair. Remarkably, the lack of ghrelin gene impacts SC self-renewal during regeneration.

CONCLUSIONS

Although we cannot discern the specific Ghrl-derived peptide responsible for such activities, these data indicate that Ghrl contributes to a proper muscle regeneration.

Phosphodiesterase 4B knockout prevents skeletal muscle atrophy in rats with burn injury

The phosphodiesterase 4 (PDE4)-cAMP pathway plays a predominant role in mediating skeletal muscle proteolysis in burn injury. The present investigations to determine the PDE4 isoform(s) involved in this action revealed that burn injury increased the expression of rat skeletal muscle PDE4B mRNA by sixfold but had little or no effect on expression of other PDE4 isoforms. These observations led us to study the effects of burn in PDE4B knockout (KO) rats. As reported by us previously, burn injury significantly increased extensor digitorum longus (EDL) muscle total and myofibrillar proteolysis in wild-type (WT) rats, but there were no significant effects on either total or myofibrillar protein breakdown in EDL muscle of PDE4B KO rats with burn injury. Moreover, burn injury increased PDE4 activity in the skeletal muscle of WT rats, but this was reduced by >80% in PDE4B KO rats. Also, burn injury decreased skeletal muscle cAMP concentration in WT rats but had no significant effects in the muscles of PDE4B KO rats. Incubation of the EDL muscle of burn-PDE4B KO rats with an inhibitor of the exchange factor directly activated by cAMP, but not with a protein kinase A inhibitor, eliminated the protective effects of PDE4B KO on EDL muscle proteolysis and increased muscle proteolysis to the same extent as in the EDL of burn-WT rats. These novel findings confirm a major role for PDE4B in skeletal muscle proteolysis in burn injury and suggest that an innovative therapy based on PDE4B-selective inhibitors could be developed to treat skeletal muscle cachexia in burn injury without the fear of causing emesis, which is associated with PDE4D inhibition.

β-Hydroxy-β-methyl Butyrate Is More Potent Than Leucine in Inhibiting Starvation-Induced Protein Degradation in C2C12 Myotubes

Leucine (Leu) and its metabolites α-ketoisocaproate (KIC) and β-hydroxy-β-methyl butyrate (HMB) are potent regulators of protein turnover. The aim of this study was to compare the inhibitory effects of Leu, KIC, and HMB on protein degradation and to investigate the mechanisms involved. The results showed that the inhibitory effect of HMB (0.38 ± 0.04) was more potent than that of Leu (0.76 ± 0.04) and KIC (0.56 ± 0.04, P < 0.01), and was significantly abolished in the presence of LY294002 (1.48 ± 0.02) and rapamycin (1.96 ± 0.02, P < 0.01). In the presence of insulin, the inhibitory effect of HMB (0.34 ± 0.03) was still more effective than that of Leu (0.60 ± 0.04) and KIC (0.57 ± 0.08, P < 0.05). Interestingly, LY294002 treatment markedly attenuated the effect of HMB, while rapamycin treatment failed to exert the same effect. Thus, HMB appears to be more potent than Leu and KIC in inhibiting protein degradation in the absence or presence of insulin, and this inhibitory effect may be dependent on PI3K/Akt signaling pathway regardless of insulin, and mTOR signaling was only involved in this effect of HMB in the absence of insulin.

Protective Effect of Unacylated Ghrelin on Compression-Induced Skeletal Muscle Injury Mediated by SIRT1-Signaling

Unacylated ghrelin, the predominant form of circulating ghrelin, protects myotubes from cell death, which is a known attribute of pressure ulcers. In this study, we investigated whether unacylated ghrelin protects skeletal muscle from pressure-induced deep tissue injury by abolishing necroptosis and apoptosis signaling and whether these effects were mediated by SIRT1 pathway. Fifteen adult Sprague Dawley rats were assigned to receive saline or unacylated ghrelin with or without EX527 (a SIRT1 inhibitor). Animals underwent two 6-h compression cycles with 100 mmHg static pressure applied over the mid-tibialis region of the right limb whereas the left uncompressed limb served as the intra-animal control. Muscle tissues underneath the compression region, and at the similar region of the opposite uncompressed limb, were collected for analysis. Unacylated ghrelin attenuated the compression-induced muscle pathohistological alterations including rounding contour of myofibers, extensive nucleus accumulation in the interstitial space, and increased interstitial space. Unacylated ghrelin abolished the increase in necroptosis proteins including RIP1 and RIP3 and attenuated the elevation of apoptotic proteins including p53, Bax, and AIF in the compressed muscle. Furthermore, unacylated ghrelin opposed the compression-induced phosphorylation and acetylation of p65 subunit of NF-kB. The anti-apoptotic effect of unacylated ghrelin was shown by a decrease in apoptotic DNA fragmentation and terminal dUTP nick-end labeling index in the compressed muscle. The protective effects of unacylated ghrelin vanished when co-treated with EX527. Our findings demonstrated that unacylated ghrelin protected skeletal muscle from compression-induced injury. The myoprotective effects of unacylated ghrelin on pressure-induced tissue injury were associated with SIRT1 signaling.

Ghrelin Ameliorates Asthma by Inhibiting Endoplasmic Reticulum Stress

BACKGROUND

This study aimed to confirm the ameliorative effect of ghrelin on asthma and investigate its mechanism.

MATERIALS AND METHODS

The murine model of asthma was induced by ovalbumin (OVA) treatment and assessed by histological pathology and airway responsiveness to methacholine. The total and differential leukocytes were counted. Tumor necrosis factor α, interferon γ, interleukin-5 and interleukin-13 levels in bronchoalveolar lavage fluid were quantified by commercial kits. The protein levels in pulmonary tissues were measured by Western blot analysis.

RESULTS

Ghrelin ameliorated the histological pathology and airway hyperresponsiveness in the OVA-induced asthmatic mouse model. Consistently, OVA-increased total and differential leukocytes and levels of tumor necrosis factor α, interferon γ, interleukin-5 and interleukin-13 in bronchoalveolar lavage fluid were significantly attenuated by ghrelin. Ghrelin prevented the increased protein levels of the endoplasmic reticulum stress markers glucose regulated protein 78 and CCAAT/enhancer binding protein homologous protein and reversed the reduced levels of p-Akt in asthmatic mice.

CONCLUSIONS

Ghrelin might prevent endoplasmic reticulum stress activation by stimulating the Akt signaling pathway, which attenuated inflammation and ameliorated asthma in mice. Ghrelin might be a new target for asthma therapy.

Oncology Update: Anamorelin

Background:

Cancer cachexia is a catabolic syndrome associated with uncontrolled muscle breakdown. There may be associated fat loss. Occurring in high frequency in advanced cancer, it is an indicator of poor prognosis. Besides weight loss, patients experience a cluster of symptoms including anorexia, early satiety, and weakness. The 3 stages of cachexia include stages of precachexia, cachexia, and refractory cachexia. Refractory cachexia is associated with active catabolism or the presence of factors that make active management of weight loss no longer possible. Patients with refractory cachexia often receive glucocorticoids or megasterol acetate. Glucocorticoid effect is short and responses to megasterol are variable. Anamorelin is a new agent for cancer anorexia-cachexia, with trials completed in advanced lung cancer. Acting as an oral mimetic of ghrelin, it improves appetite and muscle mass. This article reviews the pharmacology, pharmacodynamics, and effect on cancer cachexia.

Methods:

A PubMed search was done using the Medical Subject Headings term anamorelin. Articles were selected to provide a pharmacologic characterization of anamorelin.

Results:

Anamorelin increases muscle mass in patients with advanced cancer in 2-phase 3 trials.

Conclusions:

Anamorelin improves anorexia-cachexia symptoms in patients with advanced non–small-cell lung cancer.

Acylated and unacylated ghrelin inhibit atrophy in myotubes co-cultured with colon carcinoma cells

Cancer cachexia is a result of increased protein degradation and decreased protein synthesis. The multifunctional circulating hormone ghrelin promotes synthesis and inhibits degradation of muscle protein, but its mechanism of action is not fully understood. Here, we investigated whether co-culturing C2C12 myotubes with CT26 colon carcinoma cells induces myotube atrophy, and whether acylated ghrelin (AG) and unacylated ghrelin (UnAG) had anti-atrophic effects. We found that co-culture induced myotube atrophy and increased tumor necrosis factor-alpha (TNF-α) and myostatin concentrations in the culture medium. Moreover, co-culture down-regulated myogenin and MyoD expression, inhibited the Akt signaling, up-regulated ubiquitin E3 ligase expression, and activated the calpain system and autophagy in myotubes. Both AG and UnAG inhibited these changes. Our study describes a novel in vitro model that can be employed to investigate cancer cachexia, and our findings suggest a possible use for AG and UnAG in treating cancer cachexia.

Unacylated Ghrelin Enhances Satellite Cell Function and Relieves the Dystrophic Phenotype in Duchenne Muscular Dystrophy mdx Model

Muscle regeneration depends on satellite cells (SCs), quiescent precursors that, in consequence of injury or in pathological states such as muscular dystrophies, activate, proliferate, and differentiate to repair the damaged tissue. A subset of SCs undergoes self-renewal, thus preserving the SC pool and its regenerative potential. Unacylated ghrelin (UnAG) is a circulating hormone that protects muscle from atrophy, promotes myoblast differentiation, and enhances ischemia-induced muscle regeneration. Here we show that UnAG increases SC activity and stimulates Par polarity complex/p38-mediated asymmetric division, fostering both SC self-renewal and myoblast differentiation. Because of those activities on different steps of muscle regeneration, we hypothesized a beneficial effect of UnAG in mdx dystrophic mice, in which the absence of dystrophin leads to chronic muscle degeneration, defective muscle regeneration, fibrosis, and, at later stages of the pathology, SC pool exhaustion. Upregulation of UnAG levels in mdx mice reduces muscle degeneration, improves muscle function, and increases dystrophin-null SC self-renewal, maintaining the SC pool. Our results suggest that UnAG has significant therapeutic potential for preserving the muscles in dystrophies. Stem Cells 2017;35:1733-1746.

[Ghrelin: a gastric hormone at the crossroad between growth and appetite regulation]

Ghrelin is a 28 amino acid peptide hormone synthesized within the gastrointestinal tract. Initially identified as the endogenous ligand of the GHS-R1a (Growth Hormone Secretagogue Receptor 1a), ghrelin is a powerful stimulator of growth hormone (GH) secretion. At the crossroad between nutrition, growth and long-term energy metabolism, ghrelin also plays a unique role as the first identified gastric hormone increasing appetite and adiposity. However, the role of the ghrelin/GHS-R system in the physiology of growth, feeding behaviour and energy homeostasis needs to be better understood. Utilization of pharmacological tools and complementary animal models with deficiency in preproghrelin, ghrelin-O-acyl-transferase (GOAT - the enzyme that acylates ghrelin -) or GHS-R in situations of chronic undernutrition or high fat diet gives a more precise overview of the role of ghrelin in the pathophysiology of eating and metabolic disorders.

Improvement of Physical Decline Through Combined Effects of Muscle Enhancement and Mitochondrial Activation by a Gastric Hormone Ghrelin in Male 5/6Nx CKD Model Mice

Because a physical decline correlates with an increased risk of a wide range of disease and morbidity, an improvement of physical performance is expected to bring significant clinical benefits. The primary cause of physical decline in 5/6 nephrectomized (5/6Nx) chronic kidney disease model mice has been regarded as a decrease in muscle mass; however, our recent study showed that a decrease in muscle mitochondria plays a critical role. In the present study, we examined the effects of a gastric hormone ghrelin, which has been reported to promote muscle mitochondrial oxidation, on the physical decline in the chronic kidney disease model mice, focusing on the epigenetic modulations of a mitochondrial activator gene, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). Ghrelin treatment improved a decline in exercise endurance of 5/6Nx mice, associated with an increase in both of the muscle mass and mitochondrial amount. The expression level of PGC-1α was decreased in the skeletal muscle of 5/6Nx mice, which was associated with an increase in the methylation ratio of the cytosine residue at 260 base pairs upstream of the initiation point. Conversely, ghrelin treatment de-methylated the cytosine residue and increased the expression of PGC-1α. A representative muscle anabolic factor, IGF-1, did not affect the expression of PGC-1α and muscle mitochondrial amount, although it increased muscle mass. As a result, IGF-1 treatment in 5/6Nx mice did not increase the decreased exercise endurance as effectively as ghrelin treatment did. These findings indicate an advantage of ghrelin treatment for a recovery of physical decline.

Ghrelin prevents tumour- and cisplatin-induced muscle wasting: characterization of multiple mechanisms involved

BACKGROUND

Cachexia and muscle atrophy are common consequences of cancer and chemotherapy administration. The novel hormone ghrelin has been proposed as a treatment for this condition. Increases in food intake and direct effects on muscle proteolysis and protein synthesis are likely to mediate these effects, but the pathways leading to these events are not well understood.

METHODS

We characterized molecular pathways involved in muscle atrophy induced by Lewis lung carcinoma (LLC) tumour implantation in c57/bl6 adult male mice and by administration of the chemotherapeutic agent cisplatin in mice and in C2C12 myotubes. The effects of exogenous ghrelin administration and its mechanisms of action were examined in these settings.

RESULTS

Tumour implantation and cisplatin induced muscle atrophy by activating pro-inflammatory cytokines, p38-C/EBP-β, and myostatin, and by down-regulating Akt, myoD, and myogenin, leading to activation of ubiquitin-proteasome-mediated proteolysis and muscle weakness. Tumour implantation also increased mortality. In vitro, cisplatin up-regulated myostatin and atrogin-1 by activating C/EBP-β and FoxO1/3. Ghrelin prevented these changes in vivo and in vitro, significantly increasing muscle mass (P < 0.05 for LLC and P < 0.01 for cisplatin models) and grip strength (P = 0.038 for LLC and P = 0.001 for cisplatin models) and improving survival (P = 0.021 for LLC model).

CONCLUSION

Ghrelin prevents muscle atrophy by down-regulating inflammation, p38/C/EBP-β/myostatin, and activating Akt, myogenin, and myoD. These changes appear, at least in part, to target muscle cells directly. Ghrelin administration in this setting is associated with improved muscle strength and survival.

Antifibrotic activity of acylated and unacylated ghrelin

Fibrosis can affect almost all tissues and organs, it often represents the terminal stage of chronic diseases, and it is regarded as a major health issue for which efficient therapies are needed. Tissue injury, by inducing necrosis/apoptosis, triggers inflammatory response that, in turn, promotes fibroblast activation and pathological deposition of extracellular matrix. Acylated and unacylated ghrelin are the main products of the ghrelin gene. The acylated form, through its receptor GHSR-1a, stimulates appetite and growth hormone (GH) release. Although unacylated ghrelin does not bind or activate GHSR-1a, it shares with the acylated form several biological activities. Ghrelin peptides exhibit anti-inflammatory, antioxidative, and antiapoptotic activities, suggesting that they might represent an efficient approach to prevent or reduce fibrosis. The aim of this review is to summarize the available evidence regarding the effects of acylated and unacylated ghrelin on different pathologies and experimental models in which fibrosis is a predominant characteristic.

Cancer cachexia: understanding the molecular basis

Cancer cachexia is a devastating, multifactorial and often irreversible syndrome that affects around 50-80% of cancer patients, depending on the tumour type, and that leads to substantial weight loss, primarily from loss of skeletal muscle and body fat. Since cachexia may account for up to 20% of cancer deaths, understanding the underlying molecular mechanisms is essential. The occurrence of cachexia in cancer patients is dependent on the patient response to tumour progression, including the activation of the inflammatory response and energetic inefficiency involving the mitochondria. Interestingly, crosstalk between different cell types ultimately seems to result in muscle wasting. Some of the recent progress in understanding the molecular mechanisms of cachexia may lead to new therapeutic approaches.

Des-acyl-ghrelin (DAG) normalizes hyperlactacidemia and improves survival in a lethal rat model of burn trauma

Critical illness, including burn injury, results in elevated plasma lactate levels. Dysregulation of PI3K/Akt signaling has been shown to play a predominant role in the inactivation of skeletal muscle PDC and, hence, in hyperlactacidemia in rat models of sepsis and endotoxemia. This observation, and our previous finding that DAG can reverse burn-induced skeletal muscle proteolysis through the activation of PI3K/Akt pathway, led us to hypothesize that DAG may also attenuate hyperlactacidemia in burn injury. Our investigations revealed that burn injury significantly elevated both skeletal muscle lactate production and plasma lactate levels. Moreover, this was accompanied in skeletal muscle by a 5-7 fold increase in mRNA expression of pyruvate dehydrogenase kinases (PDK) 2 and 4, and a ∼30% reduction in PDC activity. DAG treatment of burn rats completely normalized not only the mRNA expression of the PDKs and PDC activity, but also hyperlactacidemia within 24h of burn injury. DAG also normalized epinephrine-induced lactate production by isolated skeletal muscles from normal rats. Moreover, DAG also improved survival in a lethal rat model of burn trauma. These findings with DAG may have clinical implications because chances of survival for critically ill patients are greatly improved if plasma lactate levels are normalized within 24h of injury.

Transcriptional regulation of important cellular processes in skeletal myogenesis through interferon-γ

The purpose of the present study was to investigate the effect of interferon (IFN)-γ on the transcriptomic profile of differentiating mouse C2C12 myogenic cells. Global gene expression was evaluated using whole mouse genome oligonucleotide microarrays, and the results were validated through real-time PCR. IFN-γ (1 ng/mL) increased myoblast proliferation but decreased cell respiration and myosin heavy chain content and slightly decreased the fusion index in differentiating C2C12 cell cultures. The genes upregulated through IFN-γ were involved in cell cycle; regulation of cell proliferation; programmed cell death; chemotaxis; and cytokine, growth factor, and peptidase activity, whereas the genes downregulated through IFN-γ primarily contributed to the regulation of transcription, cell-cell signaling, nitrogen compound biosynthesis, ser/thr protein kinase signaling, and regulation of the Wnt pathway. In conclusion, IFN-γ affects the expression of numerous genes associated with the regulation of several processes in myogenesis. The effects of IFN-γ on cellular transcription include (1) alteration of cytokine/growth factor expression, promoting cell proliferation and migration but inhibiting differentiation, (2) impairment of pro-myogenic transcription, (3) disruption of cell adhesion and sarcolemma/cytoskeleton organization, and (4) increased peptidase activity leading to enhanced proteolysis and apoptosis.

Ghrelin: from discovery to cancer cachexia therapy

PURPOSE OF REVIEW

Despite the high prevalence of cancer cachexia, a condition that negatively impacts patients' prognosis and quality of life, effective therapies are still lacking. Ghrelin is a peptide hormone involved in anabolic and homeostatic functions, whose mechanisms of action are still only partially clarified, but with promising positive effects in cancer cachexia. Recently, the therapeutic administration of ghrelin in cancer has been shown to counteract loss of body mass and function, including muscle, and we specifically focus on this novel evidence.

RECENT FINDINGS

Recent research aimed at developing new pharmacological therapies to prevent muscle wasting has used ghrelin and molecules acting as synthetic ghrelin receptor agonists with different modalities of administration and with high selectivity for specific targeted tissues. Positive effects of these therapies were described in cancer cachexia and chemotherapy-induced muscle wasting. New insights into the mechanisms of action of ghrelin revealed how its pleiotropic effects should be ascribed both to systemic anti-inflammation effect and to muscle-specific action through the activation of the antiatrophic molecular cascade.

SUMMARY

Growing interest arises from the identification of ghrelin as a valid and well tolerated therapeutic option to counteract structural and functional wasting derived from tumour growth.

Phosphodiesterase (PDE) inhibitor torbafylline (HWA 448) attenuates burn-induced rat skeletal muscle proteolysis through the PDE4/cAMP/EPAC/PI3K/Akt pathway

Treatment of rats after burn-injury with the cyclic AMP phosphodiesterase (PDE) inhibitor, torbafylline (also known as HWA 448) significantly reversed changes in rat skeletal muscle proteolysis, PDE4 activity, cAMP concentrations and mRNA expression of TNFα, IL-6, ubiquitin and E3 ligases. Torbafylline also attenuated muscle proteolysis during in vitro incubation, and this effect was blocked by the inhibitor Rp-cAMPS. Moreover, torbafylline significantly increased phospho-Akt levels, and normalized downregulated phospho-FOXO1 and phospho-4E-BP1 in muscle of burn rats. Similarly, torbafylline also normalized phosphorylation levels of Akt and its downstream elements in TNFα+IFNγ treated C2C12 myotubes. Torbafylline enhanced protein levels of exchange protein directly activated by cAMP (Epac) both in skeletal muscle of burn rats and in TNFα+IFNγ treated C2C12 myotubes. Pretreatment with a specific antagonist of PI3K or Epac significantly reversed the inhibitory effects of torbafylline on TNFα+IFNγ-induced MAFbx mRNA expression and protein breakdown in C2C12 myotubes. Torbafylline inhibits burn-induced muscle proteolysis by activating multiple pathways through PDE4/cAMP/Epac/PI3K/Akt.

Acylated and unacylated ghrelin administration to blunt muscle wasting

PURPOSE OF REVIEW

Muscle wasting is a comorbidity often associated with a wide range of disorders that severely affects patient prognosis and quality of life. Ghrelin, through its receptor GHSR-1a, stimulates appetite and growth hormone (GH) release. Several studies indicate that ghrelin administration is a valid treatment for cachexia because it improves muscle mass and function, likely by restoring a positive energy balance.

RECENT FINDINGS

In addition to its GHSR-1a-mediated effects on muscle mass, ghrelin acts directly on skeletal muscle, wherein it exerts a protective activity against muscle wasting. This direct activity is independent of GHSR-1a and is shared by the unacylated form of ghrelin, which does not bind GHSR-1a and is devoid of the effects on appetite and GH release.

SUMMARY

Both the acylated and unacylated forms of ghrelin might have therapeutic potential for the treatment of skeletal muscle wasting.

Acylated and unacylated ghrelin inhibit doxorubicin-induced apoptosis in skeletal muscle

AIM

Doxorubicin, a potent chemotherapeutic drug, has been demonstrated previously as an inducer of apoptosis in muscle cells. Extensive induction of apoptosis may cause excessive loss of muscle cells and subsequent functional decline in skeletal muscle. This study examined the effects of acylated ghrelin, a potential agent for treating cancer cachexia, on inhibiting apoptotic signalling in doxorubicin-treated skeletal muscle. Unacylated ghrelin, a form of ghrelin that does not bind to GHSR-1a, is also employed in this study to examine the GHSR-1a signalling dependency of the effects of ghrelin.

METHODS

Adult C57BL/6 mice were randomly assigned to saline control (CON), doxorubicin (DOX), doxorubicin with treatment of acylated ghrelin (DOX+Acylated Ghrelin) and doxorubicin with treatment of unacylated ghrelin (DOX+Unacylated Ghrelin). Mice in all groups that involved DOX were intraperitoneally injected with 15 mg of doxorubicin per kg body weight, whereas mice in CON group received saline as placebo. Gastrocnemius muscle tissues were harvested after the experimental period for analysis.

RESULTS

The elevation of apoptotic DNA fragmentation and number of TUNEL-positive nuclei were accompanied with the upregulation of Bax in muscle after exposure to doxorubicin, but all these changes were neither seen in the muscle treated with acylated ghrelin nor unacylated ghrelin after doxorubicin exposure. Protein abundances of autophagic markers including LC3 II-to-LC3 I ratio, Atg12-5 complex, Atg5 and Beclin-1 were not altered by doxorubicin but were upregulated by the treatment of either acylated or unacyated ghrelin. Histological analysis revealed that the amount of centronucleated myofibres was elevated in doxorubicin-treated muscle while muscle of others groups showed normal histology.

CONCLUSIONS

Collectively, our data demonstrated that acylated ghrelin administration suppresses the doxorubicin-induced activation of apoptosis and enhances the cellular signalling of autophagy. The treatment of unacylated ghrelin has similar effects as acylated ghrelin on apoptotic and autophagic signalling, suggesting that the effects of ghrelin are probably mediated through a signalling pathway that is independent of GHSR-1a. These findings were consistent with the hypothesis that acylated ghrelin inhibits doxorubicin-induced upregulation of apoptosis in skeletal muscle while treatment of unacylated ghrelin can achieve similar effects as the treatment of acylated ghrelin. The inhibition of apoptosis and enhancement of autophagy induced by acylated and unacylated ghrelin might exert myoprotective effects on doxorubicin-induced toxicity in skeletal muscle.

Ghrelin gene products in acute and chronic inflammation

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

Obestatin is associated to muscle strength, functional capacity and cognitive status in old women

Obestatin has been proposed to have anorexigenic and anti-ghrelin actions. The objective was to study obestatin concentrations in relation to handgrip strength, functional capacity and cognitive state in old women. The prospective study included 110 women (age, 76.93 ± 6.32) from the Mataró Ageing Study. Individuals were characterized by anthropometric variables, grip strength, Barthel and assessment of cognitive impairment [Mini Cognoscitive Examination (MCE) Spanish version], depressive status by the Geriatric Depression Scale (GDS) and frailty by the Fried criteria. Obestatin was measured by IRMA. Obestatin showed negative correlation to handgrip at basal time point (r = -0.220, p = 0.023) and at 2-year follow-up (r = -0.344, p = 0.002). Obestatin, divided into quartiles, showed a negative lineal association with handgrip: 11.03 ± 4.88 kg in first, 8.75 ± 4.08 kg in second, 8.11 ± 3.66 kg in third and 7.61 ± 4.08 kg in fourth quartile (p = 0.018). Higher obestatin levels were associated to increased weakness (categorized by handgrip of frailty criteria): 2.24 ± 0.42 ng/ml in weak vs. 1.87 ± 0.57 ng/ml in non-weak (p = 0.01). The decrease of either MCE or Barthel scores at 2-year follow-up was significantly higher in individuals in the fourth quartile of obestatin in comparison with individuals in the first quartile (p = 0.046 and p = 0.019, respectively). No association was found between obestatin and GDS score and neither with frailty as a condition. Obestatin is associated to low muscle strength, and impaired functional and cognitive capacity in old women participating in the Mataró Ageing Study.

From endocrine to rheumatism: do gut hormones play roles in rheumatoid arthritis?

RA is characterized by chronic inflammation in the musculoskeletal system, in which TNF-α is the key cytokine trigger. TNF-α, previously known as cachectin, is implicated in the modulation of body composition and energy expenditure. Gut hormones, including acyl ghrelin, des-acyl ghrelin, GIP, GLP-1 and PYY, have been known to be the major regulators of appetite, nutrition, energy expenditure and body mass formation. Emerging evidence indicates that blockade of TNF-α by biologics not only ameliorates rheumatoid inflammation, but can affect the secretion and action of gut hormones on appetite, body composition, energy expenditure, muscle catabolism and bone remodelling. A link between the gastrointestinal endocrine axis and the immune system may be established through the interaction of proinflammatory cytokines, including TNF-α and these gut hormones. With the ever-increasing understanding of rheumatoid inflammation and the invention of more biologics to modulate the cytokine network, more attention should be given to the possible immunomodulatory roles of gut hormones in autoimmune inflammatory reactions.

Prandial ghrelin attenuation provides evidence that des-acyl ghrelin may be an artifact of sample handling in human plasma

BACKGROUND

Plasma acyl and des-acyl ghrelin are thought of as components of total ghrelin, but this has never been validated using ex vivo spiking experiments, human sample collection comparisons and fit-for-purpose translatable assays.

RESULTS

Acyl ghrelin plasma stability was analyzed by LC-MS/MS and it revealed that acyl ghrelin is enzymatically and chemically converted to des-acyl ghrelin in the presence of active serine proteases and HCl. ELISAs with less than 30% total error were used to assess acyl ghrelin behavior in matched authentic human samples. Acyl and total ghrelin were not statistically different in 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride samples and acyl ghrelin losses in K(2)EDTA plasma were accounted for in des-acyl ghrelin formation.

CONCLUSION

Acyl ghrelin is total ghrelin and des-acyl ghrelin should not be detectible in healthy human plasma under optimal sample handling and assaying conditions.

Acylated and unacylated ghrelin impair skeletal muscle atrophy in mice

Cachexia is a wasting syndrome associated with cancer, AIDS, multiple sclerosis, and several other disease states. It is characterized by weight loss, fatigue, loss of appetite, and skeletal muscle atrophy and is associated with poor patient prognosis, making it an important treatment target. Ghrelin is a peptide hormone that stimulates growth hormone (GH) release and positive energy balance through binding to the receptor GHSR-1a. Only acylated ghrelin (AG), but not the unacylated form (UnAG), can bind GHSR-1a; however, UnAG and AG share several GHSR-1a-independent biological activities. Here we investigated whether UnAG and AG could protect against skeletal muscle atrophy in a GHSR-1a-independent manner. We found that both AG and UnAG inhibited dexamethasone-induced skeletal muscle atrophy and atrogene expression through PI3Kβ-, mTORC2-, and p38-mediated pathways in myotubes. Upregulation of circulating UnAG in mice impaired skeletal muscle atrophy induced by either fasting or denervation without stimulating muscle hypertrophy and GHSR-1a-mediated activation of the GH/IGF-1 axis. In Ghsr-deficient mice, both AG and UnAG induced phosphorylation of Akt in skeletal muscle and impaired fasting-induced atrophy. These results demonstrate that AG and UnAG act on a common, unidentified receptor to block skeletal muscle atrophy in a GH-independent manner.

Ghrelin: a novel neuromuscular recovery promoting factor?

Promoting neuromuscular recovery after neural injury is a major clinical issue. While techniques for nerve reconstruction are continuously improving and most peripheral nerve lesions can be repaired today, recovery of the lost function is usually unsatisfactory. This evidence claims for innovative nonsurgical therapeutic strategies that can implement the outcome after neural repair. Although no pharmacological approach for improving posttraumatic neuromuscular recovery has still entered clinical practice, various molecules are explored in experimental models of neural repair. One of such molecules is the circulating peptide hormone ghrelin. This hormone has proved to have a positive effect on neural repair after central nervous system lesion, and very recently its effectiveness has also been demonstrated in preventing posttraumatic skeletal muscle atrophy. By contrast, no information is still available about its effectiveness on peripheral nerve regeneration although preliminary data from our laboratory suggest that this molecule can have an effect also in promoting axonal regeneration after nerve injury and repair. Should this be confirmed, ghrelin might represent an ideal candidate as a therapeutic agent for improving posttraumatic neuromuscular recovery because of its putative effects at all the various structural levels involved in this regeneration process, namely, the central nervous system, the peripheral nerve, and the target skeletal muscle.

Treatment of cachexia: melanocortin and ghrelin interventions

Cachexia is a condition typified by wasting of fat and LBM caused by anorexia and further endocrinological modulation of energy stores. Diseases known to cause cachectic symptoms include cancer, chronic kidney disease, and chronic heart failure; these conditions are associated with increased levels of proinflammatory cytokines and increased resting energy expenditure. Early studies have suggested the central melanocortin system as one of the main mediators of the symptoms of cachexia. Pharmacological and genetic antagonism of these pathways attenuates cachectic symptoms in laboratory models; effects have yet to be studied in humans. In addition, ghrelin, an endogenous orexigenic hormone with receptors on melanocortinergic neurons, has been shown to ameliorate symptoms of cachexia, at least in part, by an increase in appetite via melanocortin modulation, in addition to its anticatabolic and anti-inflammatory effects. These effects of ghrelin have been confirmed in multiple types of cachexia in both laboratory and human studies, suggesting a positive future for cachexia treatments.

Mechanisms in endocrinology: Ghrelin: the differences between acyl- and des-acyl ghrelin

Des-acyl ghrelin (DAG) is one of the three preproghrelin gene-encoded peptides. Compared with ghrelin and obestatin, it has not received the attention it deserves. DAG has long been considered an inert degradation product of acyl ghrelin (AG). Recent evidence, however, indicates that DAG behaves like a separate hormone. DAG can act together with AG, can antagonize AG, and seems to have AG-independent effects. Therefore, it is believed that DAG must activate its own receptor and that it may also interact with AG at this receptor. Of potential clinical importance is that an increasing number of studies suggest that DAG might be a functional inhibitor of ghrelin and that DAG can suppress ghrelin levels in humans. Therefore, DAG or DAG analogs might be good candidates for future treatment of metabolic disorders or other conditions in which antagonism of AG actions could be beneficial, such as diabetes, obesity, and Prader-Willi syndrome.

Activation of somatostatin 2 receptors in the brain and the periphery induces opposite changes in circulating ghrelin levels: functional implications

Somatostatin is an important modulator of neurotransmission in the central nervous system and acts as a potent inhibitor of hormone and exocrine secretion and regulator of cell proliferation in the periphery. These pleiotropic actions occur through interaction with five G protein-coupled somatostatin receptor subtypes (sst(1) (-) (5)) that are widely expressed in the brain and peripheral organs. The characterization of somatostatin's effects can be investigated by pharmacological or genetic approaches using newly developed selective sst agonists and antagonists and mice lacking specific sst subtypes. Recent evidence points toward a divergent action of somatostatin in the brain and in the periphery to regulate circulating levels of ghrelin, an orexigenic hormone produced by the endocrine X/A-like cells in the rat gastric mucosa. Somatostatin interacts with the sst(2) in the brain to induce an increase in basal ghrelin plasma levels and counteracts the visceral stress-related decrease in circulating ghrelin. By contrast, stimulation of peripheral somatostatin-sst(2) signaling results in the inhibition of basal ghrelin release and mediates the postoperative decrease in circulating ghrelin. The peripheral sst(2)-mediated reduction of plasma ghrelin is likely to involve a paracrine action of D cell-derived somatostatin acting on sst(2) bearing X/A-like ghrelin cells in the gastric mucosa. The other member of the somatostatin family, named cortistatin, in addition to binding to sst(1) (-) (5) also directly interacts with the ghrelin receptor and therefore may simultaneously modulate ghrelin release and actions at target sites bearing ghrelin receptors representing a link between the ghrelin and somatostatin systems.