Ghrelin improves body weight loss and skeletal muscle catabolism associated with angiotensin II-induced cachexia in mice

Ghrelin Promotes Lipid Uptake into White Adipose Tissue via Endothelial Growth Hormone Secretagogue-Receptor in Mice

Background/Objectives: Endothelial peroxisome proliferator-activated receptor gamma (PPARγ) regulates adipose tissue by facilitating lipid uptake into white adipocytes, but the role of endothelial lipid transport in systemic energy balance remains unclear. Ghrelin conveys nutritional information through the central nervous system and increases adiposity, while deficiency in its receptor, growth hormone secretagogue-receptor (GHSR), suppresses adiposity on a high-fat diet. This study aims to examine the effect of ghrelin/GHSR signaling in the endothelium on lipid metabolism. Methods: We compared the effects of ghrelin on adiposity and lipid uptake into adipocytes in wild-type and GHSR-null mice. Transgenic mice expressing GHSR selectively in endothelial cells were also generated and compared with global GHSR-null and wild-type mice. The impact of ghrelin on lipid uptake-related genes was assessed in cultured endothelial cells. Results: Ghrelin increased adiposity and triglyceride clearance in wild-type but not in GHSR-null mice. GHSR-null mice showed higher serum triglyceride after olive oil gavage and lower white adipose tissue (WAT) weight on a high-fat diet, suggesting impaired lipid uptake. Restoring GHSR expression in endothelial cells increased lipoprotein lipase activity, lipid uptake into WAT, and WAT weight. Ghrelin enhanced free fatty acid uptake and the expression of lipid uptake genes in cultured endothelial cells, whereas these effects were absent in GHSR-null mice-derived endothelial cells. Knockdown of PPARγ revealed that ghrelin/GHSR signaling in endothelial cells promoted lipid uptake via endothelial PPARγ. Conclusions: Endothelial GHSR is key for regulating lipid metabolism via PPARγ in response to ghrelin and for the role of endothelium in regulating white adipocyte metabolism. Targeting endothelial ghrelin signaling may be a promising therapeutic approach for managing excessive adiposity and associated metabolic disorders.

Molecular characterization and distribution of motilin and motilin receptor in the Japanese medaka Oryzias latipes

Motilin (MLN) is a peptide hormone originally isolated from the mucosa of the porcine intestine. Its orthologs have been identified in various vertebrates. Although MLN regulates gastrointestinal motility in tetrapods from amphibians to mammals, recent studies indicate that MLN is not involved in the regulation of isolated intestinal motility in zebrafish, at least in vitro. To determine the unknown function of MLN in teleosts, we examined the expression of MLN and the MLN receptor (MLNR) at the cellular level in Japanese medaka (Oryzias latipes). Quantitative PCR revealed that mln mRNA was limitedly expressed in the gut, whereas mlnr mRNA was not detected in the gut but was expressed in the brain and kidney. By in situ hybridization and immunohistochemistry, mlnr mRNA was detected in the dopaminergic neurons of the area postrema in the brain and the noradrenaline-producing cells in the interrenal gland of the kidney. Furthermore, we observed efferent projections of mlnr-expressing dopaminergic neurons in the lobus vagi (XL) and nucleus motorius nervi vagi (NXm) of the medulla oblongata by establishing a transgenic medaka expressing the enhanced green fluorescence protein driven by the mlnr promoter. The expression of dopamine receptor mRNAs in the XL and cholinergic neurons in NXm was confirmed by in situ hybridization. These results indicate novel sites of MLN activity other than the gastrointestinal tract. MLN may exert central and peripheral actions through the regulation of catecholamine release in medaka.

Lacticaseibacillus paracasei PS23 increases ghrelin levels and modulates microbiota composition: a post-hoc analysis of a randomized controlled study

Muscle damage can occur due to excessive, high-intensity, or inappropriate exercise. It is crucial for athletes and sports enthusiasts to have access to ways that expedite their recovery and alleviate discomfort. Our previous clinical trial demonstrated the anti-inflammatory and muscle damage-ameliorating properties of Lacticaseibacillus paracasei PS23 (PS23), prompting us to further explore the role of this probiotic in muscle damage recovery. This post-hoc analysis of a randomized controlled study investigated potential mediators between the intake of PS23 and the prevention of strength loss after muscle damage. We recruited 105 students from a sports university who had participated in the previously published clinical trial. These participants were randomly allocated to three groups, receiving capsuled live PS23 (L-PS23), heat-treated PS23 (HT-PS23), or a placebo over a period of six weeks. Baseline and endpoint measurements were taken for the levels of circulating ghrelin and other blood markers, stress, mood, quality of life, and the fecal microbiota. A significant increase in ghrelin levels was recorded in the L-PS23 group compared to the other groups. Additionally, both L-PS23 and HT-PS23 interventions led to positive shifts in the gut microbiota composition, particularly in elevated Lacticaseibacillus, Blautia, and Lactobacillus populations. The abundance of these bacteria was positively correlated with exercise performance and inversely correlated with inflammatory markers. In conclusion, dietary supplementation with PS23 may enhance exercise performance and influence muscle damage by increasing ghrelin levels and modulating the gut microbiota composition. Further clarification of the possible mechanisms and clinical implications is required.

A murine model of hypertensive heart disease in older women

We propose a new mouse (C57Bl6/J) model combining several features of heart failure with preserved ejection fraction encountered in older women, including hypertension from Angiotensin II infusion (AngII), menopause, and advanced age. To mimic menopause, we delayed ovariectomy (Ovx) at 12 months of age. We also studied the effects of AngII infusion for 28 days in younger animals and the impact of losing gonadal steroids earlier in life. We observed that AngII effects on heart morphology were different in younger and adult mice (3- and 12-month-old; 20 and 19% increase in heart weight. P < 0.01 for both) than in older animals (24-month-old; 6%; not significant). Ovariectomy at 12 months restored the hypertrophic response to AngII in elderly females (23%, p = 0.0001). We performed a bulk RNA sequencing study of the left ventricle (LV) and left atrial gene expression in elderly animals, controls, and Ovx. AngII modulated (|Log2 fold change| ≥ 1) the LV expression of 170 genes in control females and 179 in Ovx ones, 64 being shared. In the left atrium, AngII modulated 235 genes in control females and 453 in Ovx, 140 shared. We observed many upregulated genes associated with the extracellular matrix regulation in both heart chambers. Many of these upregulated genes were shared between the ventricle and the atrium as well as in control and Ovx animals, namely for the most expressed Ankrd1, Nppb, Col3a1, Col1a1, Ctgf Col8a1, and Cilp. Several circadian clock LV genes were modulated differently by AngII between control and Ovx females (Clock, Arntl, Per2, Cry2, and Ciart). In conclusion, sex hormones, even in elderly female mice, modulate the heart's hypertrophic response to AngII. Our study identifies potential new markers of hypertensive disease in aging female mice and possible disturbances of their cardiac circadian clock.

Unlocking the Potential of Obestatin: A Novel Peptide Intervention for Skeletal Muscle Regeneration and Prevention of Atrophy

Obestatin is derived from the same gene as that of ghrelin and their functions were perceived to be antagonistic. Recent developments have shown that although they are known to have contradictory functions, effect of obestatin on skeletal muscle regeneration is similar to that of ghrelin. Obestatin works through a receptor called GPR39, a ghrelin and motilin family receptor and transduces signals in skeletal muscle similar to that of ghrelin. Not only there is a similarity in the receptor family, but also obestatin targets similar proteins and transcription factors as that of ghrelin (for example, FoxO family members) for salvaging skeletal muscle atrophy. Moreover, like ghrelin, obestatin also works by inducing the transcription of Pax7 which is required for muscle stem cell mobilisation. Hence, there are quite some evidences which points to the fact that obestatin can be purposed as a peptide intervention to prevent skeletal muscle wasting and induce myogenesis. This review elaborates these aspects of obestatin which can be further exploited and addressed to bring obestatin as a clinical intervention towards preventing skeletal muscle atrophy and sarcopenia.

Advancing cancer cachexia diagnosis with -omics technology and exercise as molecular medicine

Muscle atrophy exacerbates disease outcomes and increases mortality, whereas the preservation of skeletal muscle mass and function play pivotal roles in ensuring long-term health and overall quality-of-life. Muscle atrophy represents a significant clinical challenge, involving the continued loss of muscle mass and strength, which frequently accompany the development of numerous types of cancer. Cancer cachexia is a highly prevalent multifactorial syndrome, and although cachexia is one of the main causes of cancer-related deaths, there are still no approved management strategies for the disease. The etiology of this condition is based on the upregulation of systemic inflammation factors and catabolic stimuli, resulting in the inhibition of protein synthesis and enhancement of protein degradation. Numerous necessary cellular processes are disrupted by cachectic pathology, which mediate intracellular signalling pathways resulting in the net loss of muscle and organelles. However, the exact underpinning molecular mechanisms of how these changes are orchestrated are incompletely understood. Much work is still required, but structured exercise has the capacity to counteract numerous detrimental effects linked to cancer cachexia. Primarily through the stimulation of muscle protein synthesis, enhancement of mitochondrial function, and the release of myokines. As a result, muscle mass and strength increase, leading to improved mobility, and quality-of-life. This review summarises existing knowledge of the complex molecular networks that regulate cancer cachexia and exercise, highlighting the molecular interplay between the two for potential therapeutic intervention. Finally, the utility of mass spectrometry-based proteomics is considered as a way of establishing early diagnostic biomarkers of cachectic patients.

Changes in Circulating Acylated Ghrelin and Neutrophil Elastase in Diabetic Retinopathy

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

Augmentation of Growth Hormone by Chewing in Females

Sarcopenia is an age-related condition characterized by progressive loss of muscle mass and strength. Age-related decline in the secretion of growth hormone (GH), a condition called somatopause, is thought to play a role in sarcopenia. As pharmacological GH has adverse effects, we attempted to increase physiological GH. While the relationship between chewing and ghrelin levels has been studied, there are no reports on the relationship between chewing and GH. The aim of this study was to clarify the effects of chewing on the muscle anabolic hormones serum GH and plasma ghrelin. Thirteen healthy adults ingested a chewy nutrition bar containing 5.56 g of protein, 12.71 g of carbohydrate, and 0.09 g of fat on two different days, chewing before swallowing in one trial and swallowing without chewing in the other. Blood samples were taken before and after ingestion (0, 15, 30, and 60 min); GH, acylated ghrelin, glucose, insulin, amino acids, and lactate were measured. Two-way repeated ANOVA revealed a significant difference in the GH concentrations between the "Chew trial" and "Swallow trial" in females (p = 0.0054). However, post-hoc analyses found no statistically significant difference at each time point. The area under the curve of the percentage increase in GH was significantly increased in the "Chew trial" compared with the "Swallow trial" in females (12,203 ± 15,402% min vs. 3735 ± 988% min, p = 0.0488). Chewing had no effect on glucose, insulin, amino acids, or lactate concentrations. Thus, we found that chewing a protein supplement rather than swallowing it without chewing elevates the blood GH concentration. These results serve as a rationale for larger research and longitudinal studies to confirm the impacts of chewing on GH secretion.

Cancer cachexia: molecular mechanisms and treatment strategies

Muscle wasting is a consequence of physiological changes or a pathology characterized by increased catabolic activity that leads to progressive loss of skeletal muscle mass and strength. Numerous diseases, including cancer, organ failure, infection, and aging-associated diseases, are associated with muscle wasting. Cancer cachexia is a multifactorial syndrome characterized by loss of skeletal muscle mass, with or without the loss of fat mass, resulting in functional impairment and reduced quality of life. It is caused by the upregulation of systemic inflammation and catabolic stimuli, leading to inhibition of protein synthesis and enhancement of muscle catabolism. Here, we summarize the complex molecular networks that regulate muscle mass and function. Moreover, we describe complex multi-organ roles in cancer cachexia. Although cachexia is one of the main causes of cancer-related deaths, there are still no approved drugs for cancer cachexia. Thus, we compiled recent ongoing pre-clinical and clinical trials and further discussed potential therapeutic approaches for cancer cachexia.

Potential Applications for Growth Hormone Secretagogues Treatment of Amyotrophic Lateral Sclerosis

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

Diverse and Complementary Effects of Ghrelin and Obestatin

Ghrelin and obestatin are two "sibling proteins" encoded by the same preproghrelin gene but possess an array of diverse and complex functions. While there are ample literature documenting ghrelin's functions, the roles of obestatin are less clear and controversial. Ghrelin and obestatin have been perceived to be antagonistic initially; however, recent studies challenge this dogma. While they have opposing effects in some systems, they function synergistically in other systems, with many functions remaining debatable. In this review, we discuss their functional relationship under three "C" categories, namely complex, complementary, and contradictory. Their functions in food intake, weight regulation, hydration, gastrointestinal motility, inflammation, and insulin secretion are complex. Their functions in pancreatic beta cells, cardiovascular, muscle, neuroprotection, cancer, and digestive system are complementary. Their functions in white adipose tissue, thermogenesis, and sleep regulation are contradictory. Overall, this review accumulates the multifaceted functions of ghrelin and obestatin under both physiological and pathological conditions, with the intent of contributing to a better understanding of these two important gut hormones.

Overexpression of NOX2 Exacerbates AngII-Mediated Cardiac Dysfunction and Metabolic Remodelling

The present study aimed to examine the effects of low doses of angiotensin II (AngII) on cardiac function, myocardial substrate utilization, energetics, and mitochondrial function in C57Bl/6J mice and in a transgenic mouse model with cardiomyocyte specific upregulation of NOX2 (csNOX2 TG). Mice were treated with saline (sham), 50 or 400 ng/kg/min of AngII (AngII₅₀ and AngII₄₀₀) for two weeks. In vivo blood pressure and cardiac function were measured using plethysmography and echocardiography, respectively. Ex vivo cardiac function, mechanical efficiency, and myocardial substrate utilization were assessed in isolated perfused working hearts, and mitochondrial function was measured in left ventricular homogenates. AngII₅₀ caused reduced mechanical efficiency despite having no effect on cardiac hypertrophy, function, or substrate utilization. AngII₄₀₀ slightly increased systemic blood pressure and induced cardiac hypertrophy with no effect on cardiac function, efficiency, or substrate utilization. In csNOX2 TG mice, AngII₄₀₀ induced cardiac hypertrophy and in vivo cardiac dysfunction. This was associated with a switch towards increased myocardial glucose oxidation and impaired mitochondrial oxygen consumption rates. Low doses of AngII may transiently impair cardiac efficiency, preceding the development of hypertrophy induced at higher doses. NOX2 overexpression exacerbates the AngII -induced pathology, with cardiac dysfunction and myocardial metabolic remodelling.

Ubiquitin Ligases at the Heart of Skeletal Muscle Atrophy Control

Skeletal muscle loss is a detrimental side-effect of numerous chronic diseases that dramatically increases mortality and morbidity. The alteration of protein homeostasis is generally due to increased protein breakdown while, protein synthesis may also be down-regulated. The ubiquitin proteasome system (UPS) is a master regulator of skeletal muscle that impacts muscle contractile properties and metabolism through multiple levers like signaling pathways, contractile apparatus degradation, etc. Among the different actors of the UPS, the E3 ubiquitin ligases specifically target key proteins for either degradation or activity modulation, thus controlling both pro-anabolic or pro-catabolic factors. The atrogenes MuRF1/TRIM63 and MAFbx/Atrogin-1 encode for key E3 ligases that target contractile proteins and key actors of protein synthesis respectively. However, several other E3 ligases are involved upstream in the atrophy program, from signal transduction control to modulation of energy balance. Controlling E3 ligases activity is thus a tempting approach for preserving muscle mass. While indirect modulation of E3 ligases may prove beneficial in some situations of muscle atrophy, some drugs directly inhibiting their activity have started to appear. This review summarizes the main signaling pathways involved in muscle atrophy and the E3 ligases implicated, but also the molecules potentially usable for future therapies.

Molecular mechanisms of cancer cachexia‑induced muscle atrophy (Review)

Muscle atrophy is a severe clinical problem involving the loss of muscle mass and strength that frequently accompanies the development of numerous types of cancer, including pancreatic, lung and gastric cancers. Cancer cachexia is a multifactorial syndrome characterized by a continuous decline in skeletal muscle mass that cannot be reversed by conventional nutritional therapy. The pathophysiological characteristic of cancer cachexia is a negative protein and energy balance caused by a combination of factors, including reduced food intake and metabolic abnormalities. Numerous necessary cellular processes are disrupted by the presence of abnormal metabolites, which mediate several intracellular signaling pathways and result in the net loss of cytoplasm and organelles in atrophic skeletal muscle during various states of cancer cachexia. Currently, the clinical morbidity and mortality rates of patients with cancer cachexia are high. Once a patient enters the cachexia phase, the consequences are difficult to reverse and the treatment methods for cancer cachexia are very limited. The present review aimed to summarize the recent discoveries regarding the pathogenesis of cancer cachexia-induced muscle atrophy and provided novel ideas for the comprehensive treatment to improve the prognosis of affected patients.

Cisplatin-Induced Skeletal Muscle Dysfunction: Mechanisms and Counteracting Therapeutic Strategies

Among the severe side effects induced by cisplatin chemotherapy, muscle wasting is the most relevant one. This effect is a major cause for a clinical decline of cancer patients, since it is a negative predictor of treatment outcome and associated to increased mortality. However, despite its toxicity even at low doses, cisplatin remains the first-line therapy for several types of solid tumors. Thus, effective pharmacological treatments counteracting or minimizing cisplatin-induced muscle wasting are urgently needed. The dissection of the molecular pathways responsible for cisplatin-induced muscle dysfunction gives the possibility to identify novel promising therapeutic targets. In this context, the use of animal model of cisplatin-induced cachexia is very useful. Here, we report an update of the most relevant researches on the mechanisms underlying cisplatin-induced muscle wasting and on the most promising potential therapeutic options to preserve muscle mass and function.

Oxidative stress in exercise training: the involvement of inflammation and peripheral signals

The evidence about the health benefits of regular physical activity is well established. Exercise intensity is a significant variable and structured high-intensity interval training (HIIT) has been demonstrated to improve both whole-body and skeletal muscle metabolic health in different populations. Conversely, fatigue accumulation, if not resolved, leads to overwork, chronic fatigue syndrome (CFS), overtraining syndrome up to alterations of endocrine function, immune, systemic inflammation, and organic diseases with health threat. In response to temporary increases in stress during training, some athletes are unable to maintain sufficient caloric intake, thus suffering a negative energy balance that causes further stress. The regulation of the energy balance is controlled by the central nervous system through an elaborate interaction of the signalling that involves different tissues such as leptin, adiponectin and ghrelin whose provide important feedback to the hypothalamus to regulate the energy balance. Although exercise-induced reactive oxygen species are required for normal force production in muscle, high levels of ROS appear to promote contractile dysfunction. However, a high level of oxidative stress in may induce a rise in inflammatory markers and a disregulation in expression of adiponectin, leptin and grelin.

Placental extract suppresses cardiac hypertrophy and fibrosis in an angiotensin II-induced cachexia model in mice

Cachexia is an intractable metabolic disorder that causes extreme weight loss. It is a symptom of many chronic diseases, including cancer, liver failure, congestive heart failure and chronic kidney disease, and there is as yet no effective treatment. While the mechanisms underlying cachexia are complex, it is often accompanied by elevated angiotensin II (Ang II). Human placental extract (HPE) is a source of numerous biologically active molecules and has been used clinically to treat chronic hepatitis, liver cirrhosis and other chronic diseases. Here, we investigated the effects of HPE in an Ang II-induced cachexia model in mice. HPE treatment preserved both fat mass and lean body mass and suppressed weight loss in the cachexia model, though food intake was unaffected. Ang II infusion also caused cardiac hypertrophy and fibrosis. HPE suppressed these effects as well as Ang II-induced cardiac expression of genes related to heart failure and cardiac remodeling. HPE also reversed Ang II-induced downregulation of mitochondria-related molecules and suppressed cardiac inflammation and oxidative stress. HPE administration may thus be an effective approach to the treatment of cachexia, cardiac hypertrophy and fibrosis.

The expressions of some metabolic hormones (leptin, ghrelin and obestatin) in the tissues of sheep tongue

In this study, we aimed to observe the localization and expression of peptide hormones-leptin, ghrelin and obestatin-in the sheep tongue by immunohistochemistry. For that purpose, tongues of ten adult sheep were used. Leptin expression of moderate intensity was observed in the basal and parabasal epithelial cells of the luminal epithelium, and leptin was strongly expressed in the taste buds of the circumvallate and fungiform papillae and in von Ebner's glands. Ghrelin was primarily expressed in some of the skeletal muscle cells and the smooth muscle cells of the middle layer of blood vessels. A strong expression was observed in the epithelial cells lining the base of the groove surrounding the circumvallate papillae. Obestatin expression was particularly strong in the epithelial cells of the salivary ducts. It was also stronger in the von Ebner's glands than in the seromucous glands. Leptin, ghrelin and obestatin were shown to be produced at varying levels in different cell types, including epithelial, stromal and skeletal muscle cells, as well as in ganglion neurons, neural plexuses and blood vessels in the sheep tongue. Cellular localization and expression of these peptide hormones have not been investigated in many species including sheep.

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.

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.

Ghrelin mediates exercise endurance and the feeding response post-exercise

Objective

Exercise training has several well-established health benefits, including many related to body weight, appetite control, and blood glucose homeostasis. However, the molecular mechanisms and, in particular, the hormonal systems that mediate and integrate these beneficial effects are poorly understood. In the current study, we aimed to investigate the role of the hormone ghrelin and its receptor, the growth hormone secretagogue receptor (GHSR; ghrelin receptor), in mediating the effects of exercise on food intake and blood glucose following exercise as well as in regulating exercise endurance capacity.

Methods

We used two mouse models of treadmill running to characterize the changes in plasma ghrelin with exercise. We also assessed the role of the ghrelin system to influence food intake and blood glucose after exercise, exercise endurance, and parameters potentially linked to responses to exercise. Mice lacking GHSRs (GHSR-null mice) and wild-type littermates were studied.

Results

An acute bout of exercise transiently elevated plasma acyl-ghrelin. Without the action of this increased ghrelin on GHSRs (as in GHSR-null mice), high intensity interval exercise markedly reduced food intake compared to control mice. The effect of exercise to acutely raise blood glucose remained unmodified in GHSR-null mice. Exercise-induced increases in plasma ghrelin positively correlated with endurance capacity, and time to exhaustion was reduced in GHSR-null mice as compared to wild-type littermates. In an effort to mechanistically explain their reduced exercise endurance, exercised GHSR-null mice exhibited an abrogated sympathoadrenal response, lower overall insulin-like growth factor-1 levels, and altered glycogen utilization.

Conclusions

Exercise transiently increases plasma ghrelin. GHSR-null mice exhibit decreased food intake following high intensity interval exercise and decreased endurance when submitted to an exercise endurance protocol. These data suggest that an intact ghrelin system limits the capacity of exercise to restrict food intake following exercise, although it enhances exercise endurance.

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High intensity exercise transiently increases plasma ghrelin.

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Without ghrelin action on its receptors (growth hormone secretagogue receptors), exercise markedly reduces food intake.

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An intact ghrelin system enhances exercise endurance.

JMV2894, a novel growth hormone secretagogue, accelerates body mass recovery in an experimental model of cachexia

Oncologic patients subjected to chemotherapy frequently present aphagia, malnutrition, and cachexia. The purpose of this study was to investigate whether selected growth hormone secretagogues including hexarelin, JMV2894 and JMV2951 could antagonize body weight loss and wasting induced by cisplatin administration in rats. The three growth hormone secretagogues behaved as full agonists of the growth hormone secretagogues receptor both in terms of ability to stimulate calcium mobilization in Chinese hamster ovary cells and stimulation of growth hormone release in neonatal rats. Adult rats were (i) treated with vehicle throughout (controls), or (ii) treated with cisplatin (days 1-3) and a growth hormone secretagogues or vehicle, (days 1-12). Body weight and food consumption were measured daily. Although all growth hormone secretagogues caused initial transient acute increases in food intake, the total amount of food eaten by controls and growth hormone secretagogues treated groups over the 12 experimental days was not significantly different. All groups pre-treated with cisplatin lost up to 5-10 % body weight in the first 4 days; they subsequently gained weight at a rate comparable with controls. Interestingly, rats which received JMV2894 demonstrated a faster gain in body weight than any other growth hormone secretagogues treated group and at the end of the protocol reached a weight similar to that of controls. JMV2894 did not stimulate perirenal and epididymal fat accumulation but reduced MuRF mRNA levels in skeletal muscles. In conclusion, our findings demonstrate that JMV2894 antagonizes cisplatin induced weight loss in rats and may prove useful in antagonizing cachexia associated with cancer and chemotherapy in humans.

Therapeutic Potential of Targeting the Ghrelin Pathway

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

Effects of GHRP-2 and Cysteamine Administration on Growth Performance, Somatotropic Axis Hormone and Muscle Protein Deposition in Yaks (Bos grunniens) with Growth Retardation

The objective of this study was to investigate the effects of growth hormone-releasing peptide-2 (GHRP-2) and cysteamine (CS) administration on growth performance in yaks with growth retardation and try to elucidate its regulatory mechanisms. Trial 1, thirty-six 1-year-old Qinghai high plateau yaks (body weight 38–83.2 kg) were randomly chosen for body weight and jugular blood samples collection. The relationship between body weight and serum GHRH (P < 0.05, R = 0.45), GH (P < 0.05, R = 0.47), IGF-1 (P < 0.05, R = 0.62) was significantly correlated in yaks colonies with lighter body weights. Trial 2, fifteen 1-year-old Qinghai high plateau yaks with growth retardation (average body weight 54.8 ± 8.24 kg) were randomly selected and assigned to negative control group (NG), GHRP-2 injection group (GG) and cysteamine feeding group (CG), with 5 yaks per group. Another five 1-year-old Qinghai high plateau yaks with normal growth performance (average body weight 75.3 ± 2.43 kg) were selected as positive control group (PG). The average daily gain (ADG) of the GG and CG were significantly higher than those in the PG and NG (P < 0.05). Both GHRP-2 and CS administration significantly enhanced the myofiber diameter and area of skeletal muscle (P<0.05). GHRP-2 significantly enhanced the serum GH and IGF-1 levels (P < 0.05), and up-regulated GHR, IGF-1 and IGF-1R mRNA expression in the liver and skeletal muscle (P < 0.05), enhanced the mRNA expression of PI₃K, AKt and mTOR in the skeletal muscle (P<0.05). CS significantly reduced the serum SS levels and the hypothalamus SS mRNA expression (P < 0.05), and enhanced GHR and IGF-1 mRNA expression in the liver (P < 0.05), decreased the mRNA expression of muscle atrophy F-box (Atrogin-1) and muscle ring finger 1 (MuRF1) mRNA (P < 0.05). Conclusions: Growth retardation in yaks was primarily due to somatotropic axis hormones secretion deficiency. Both GHRP-2 and CS administration can accelerate growth performance and GH, IGF-1 secretion in yaks with growth retardation. GHRP-2 enhanced muscle protein deposition mainly by up-regulated the protein synthesis pathways, whereas CS worked mainly by down-regulated the ubiquitin-proteasome pathway.

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.

Muscle wasting as main evidence of energy impairment in cancer cachexia: future therapeutic approaches

The present review aimed at discussing the impact, pathogenesis and therapeutic approaches of muscle wasting, which is a major clinical feature of cancer-related cachexia syndrome. The pathogenesis of muscle wasting in cancer cachexia lies in a discrepancy between anabolic and catabolic pathways mediated by chronic inflammation. Effective interventions specifically aimed at hampering muscle loss and enhancing muscle function are still lacking. Promising agents include anti-inflammatory, orexigenic and anabolic drugs, alongside with nutritional supplements that influence the STAT3 and PI3K/Akt/mTOR pathways involved in muscle wasting. Personalized physical activity combined with pharmacological and nutritional support hold promise. A greater understanding of the pathogenetic processes of cancer cachexia-related muscle wasting will enable the development of an early and effective targeted mechanism-based multimodal approach.

The Role of Ghrelin in Senescence: A Mini-Review

Ghrelin, a 28-amino acid hormone produced mainly by the X/A-like endocrine cells in gastric mucosa, has a widespread tissue distribution and diverse physiological functions such as hormonal, orexigenic, metabolic, cardiovascular, neurological, and immunological activities. Considerable evidence has suggested that ghrelin plays an important role in organism senescence or aging. The present review provides a comprehensive picture of this new development. We first reviewed the aging (senescence)-dependent reduction of ghrelin signaling, and then highlighted its relationship with the aging-associated alteration in food intake, energy metabolism, cardiovascular function, neurological activity, and adaptive immunity. Our literature review suggests that ghrelin is an innovative and promising agent in the treatment of these pathophysiological conditions associated with senescence.

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.

Ghrelin ameliorates catabolic conditions and respiratory dysfunction in a chronic obstructive pulmonary disease model of chronic cigarette smoke-exposed rats

Cigarette smoking, which is a well-known major risk factor for chronic obstructive pulmonary disease (COPD), causes both pulmonary and extrapulmonary abnormalities. Ghrelin is a gastric peptide that regulates energy homeostasis. In the present study, we investigated the effects of ghrelin on the catabolic changes, respiratory function and emphysema in an animal model of COPD induced by chronic exposure to cigarette smoke. Rats were exposed to cigarette smoke, and they were administered human ghrelin (0.1 or 1 mg/kg, subcutaneous, twice daily) for 12 weeks. Compared with air-exposed rats, body weight gain, food intake, food efficiency, tidal volume, peak expiratory flow rate, and forced expiratory volume at 100 ms were significantly lower, while functional residual capacity, lung capacity, and neutrophils in bronchoalveolar lavage fluid were significantly higher in cigarette smoke-exposed rats. These indicated that the systemic abnormalities associated with COPD developed after the exposure to cigarette smoke. Ghrelin significantly and dose-dependently increased the body weight gain and food efficiency in cigarette smoke-exposed rats. In ghrelin-treated rats, skeletal muscle strength, which tended to be lowered by cigarette smoke exposure, was improved. Ghrelin ameliorated respiratory function and emphysema in a dose-dependent manner, but did not inhibit the increase in neutrophils in the bronchoalveolar lavage fluid. The respiratory functional parameters and lung capacity were significantly correlated with body weight gain. These results suggest that ghrelin inhibited the development of the catabolic changes, respiratory dysfunction, and emphysema that were induced by cigarette smoke exposure in rats, at least in part, through the amelioration of nutritional status.

The Pentapeptide RM-131 Promotes Food Intake and Adiposity in Wildtype Mice but Not in Mice Lacking the Ghrelin Receptor

The gastrointestinal peptide hormone ghrelin is the endogenous ligand of the growth hormone secretagogue receptor (a.k.a. ghrelin receptor, GHR). Currently, ghrelin is the only circulating peripheral hormone with the ability to promote a positive energy balance by stimulating food intake while decreasing energy expenditure and body fat utilization, as defined in rodents. Based on these and additional, beneficial effects on metabolism, the endogenous ghrelin system is considered an attractive target to treat diverse pathological conditions including those associated with eating/wasting disorders and cachexia. As the pharmacological potential of ghrelin is hampered by its relatively short half-life, ghrelin analogs with enhanced pharmacokinetics offer the potential to sustainably improve metabolism. One of these ghrelin analogs is the pentapeptide RM-131, which promotes food intake and adiposity with higher potency as compared to native ghrelin in rodents. Whereas, the effect of RM-131 on energy metabolism is solidly confirmed in rodents, it remains elusive whether RM-131 exerts its effect solely via the ghrelin receptor. Accordingly, we assessed the receptor specificity of RM-131 to promote food intake and adiposity in mice lacking the GHR. Our data show that in wildtype mice RM-131 potently promotes weight gain and adiposity through stimulation of food intake. However, RM-131 fails to affect food intake and body weight in mice lacking the GHR, underlining that the anabolic effects of RM-131 are mediated via the ghrelin receptor in mice.

Ghrelin relieves cancer cachexia associated with the development of lung adenocarcinoma in mice

Cancer cachexia is a multifactorial, critical illness syndrome characterized by an ongoing loss of skeletal muscle and adipose tissue. The reductions in body weight and skeletal muscle mass are important prognostic indicators for cancer patients that are refractory to current therapies. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, is produced in the stomach, stimulates food intake and growth hormone secretion, suppresses inflammation, and prevents muscle catabolism. We investigated the pharmacological potential of ghrelin in the treatment of cancer cachexia by using urethane-treated, bronchioalveolar epithelium-specific Pten-deficient mice that developed lung adenocarcinomas. Ghrelin or phosphate-buffered saline was given to mice daily for four weeks beginning at five months after urethane injection, which corresponded to the time point of lung adenocarcinoma formation. Ghrelin inhibited the inductions of C-reactive protein, tumor necrosis factor-α, interleukin-1β, and interleukin-6, mitigated the reduction of food intake and fat mass, and consequently ameliorated body weight loss in the mouse model of lung adenocarcinoma. We also demonstrated that skeletal muscle mass and muscle contraction force in both fast-twitch muscle and slow-twitch muscle were retained in ghrelin-treated mice in conjunction with an upregulation of local insulin-like growth factor 1/Akt signaling. In addition, ghrelin administration reduced the expressions of phosphorylated-p38 mitogen-activated protein kinase, phosphorylated-nuclear factor-kappa B, Forkhead box protein O1, muscle RING-finger protein-1, and F-Box protein 32 in the lysates of skeletal muscle in the tumor-bearing state. Our results indicate that ghrelin administration exerts a protective effect against cancer cachexia by ameliorating skeletal muscle wasting and regulating systemic inflammation.

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.

Ghrelin: much more than a hunger hormone

PURPOSE OF REVIEW

Ghrelin is a multifaceted gut hormone that activates its receptor, growth hormone secretagogue receptor (GHS-R). Ghrelin's hallmark functions are its stimulatory effects on growth hormone release, food intake and fat deposition. Ghrelin is famously known as the 'hunger hormone'. However, ample recent literature indicates that the functions of ghrelin go well beyond its role as an orexigenic signal. Here, we have reviewed some of the most recent findings on ghrelin and its signalling in animals and humans.

RECENT FINDINGS

Ghrelin regulates glucose homeostasis by inhibiting insulin secretion and regulating gluconeogenesis/glycogenolysis. Ghrelin signalling decreases thermogenesis to regulate energy expenditure. Ghrelin improves the survival prognosis of myocardial infarction by reducing sympathetic nerve activity. Ghrelin prevents muscle atrophy by inducing muscle differentiation and fusion. Ghrelin regulates bone formation and metabolism by modulating proliferation and differentiation of osteoblasts.

SUMMARY

In addition to ghrelin's effects on appetite and adiposity, ghrelin signalling also plays crucial roles in glucose and energy homeostasis, cardioprotection, muscle atrophy and bone metabolism. These multifaceted roles of ghrelin make ghrelin and GHS-R highly attractive targets for drug development. Ghrelin mimetics may be used to treat heart diseases, muscular dystrophy/sarcopenia and osteoporosis; GHS-R antagonists may be used to treat obesity and insulin resistance.

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.

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.