Combined effects of ghrelin and higher food intake enhance skeletal muscle mitochondrial oxidative capacity and AKT phosphorylation in rats with chronic kidney disease

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.

Sarcopenia and cardiovascular disease in patients with and without kidney disease: what do we know?

Cardiovascular disease (CVD) incidence is high in patients with chronic kidney disease (CKD) and is the most frequent cause of mortality in this population. Advanced age, hypertension, uremic toxins, endothelial dysfunction, atherosclerosis, hyperhomocysteinemia, oxidative stress, and inflammation are among the leading causes of increased CVD in advanced stages of CKD. Although defined as a decrease in muscle strength associated with aging, sarcopenia is also prevalent in CKD patients. Sarcopenia causes physical disability, low quality of life, and mortality. Regular exercise and nutritional supplementation may slow the progression of sarcopenia. Recent studies have shown that sarcopenia increases the risk of CVD and mortality in people with or without kidney disease. This review discusses the relationship between sarcopenia and CVD in light of the current literature.

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

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

Growth hormone secretagogue receptor-1a mediates ghrelin's effects on attenuating tumour-induced loss of muscle strength but not muscle mass

BACKGROUND

Ghrelin may ameliorate cancer cachexia (CC) by preventing anorexia, muscle, and fat loss. However, the mechanisms mediating these effects are not fully understood. This study characterizes the pathways involved in muscle mass and strength loss in the Lewis lung carcinoma (LLC)-induced cachexia model, and the effects of ghrelin in mice with or without its only known receptor: the growth hormone secretagogue receptor-1a ((GHSR-1a), Ghsr+/+ and Ghsr-/- ).

METHODS

Five to 7-month-old male C57BL/6J Ghsr+/+ and Ghsr-/- mice were inoculated with 1 × 106 heat-killed (HK) or live LLC cells (tumour implantation, TI). When tumours were palpable (7 days after TI), tumour-bearing mice were injected with vehicle (T + V) or ghrelin twice/day for 14 days (T + G, 0.8 mg/kg), while HK-treated mice were given vehicle (HK + V). Body weight and grip strength were evaluated before TI and at termination (21 days after TI). Hindlimb muscles were collected for analysis.

RESULTS

Less pronounced body weight (BW) loss (87.70 ± 0.98% vs. 83.92 ± 1.23%, percentage of baseline BW in tumour-bearing Ghsr+/+ vs. Ghsr-/- , P = 0.008), and lower upregulation of ubiquitin-proteasome system (UPS, MuRF1/Trim63, 5.71 ± 1.53-fold vs. 9.22 ± 1.94-fold-change from Ghsr+/+ HK + V in tumour-bearing Ghsr+/+ vs. Ghsr-/- , P = 0.036) and autophagy markers (Becn1, Atg5, Atg7, tumour-bearing Ghsr+/+  < Ghsr-/- , all P < 0.02) were found in T + V Ghsr+/+ vs. Ghsr-/- mice. Ghrelin attenuated LLC-induced UPS marker upregulation in both genotypes, [Trim63 was decreased from 5.71 ± 1.53-fold to 1.96 ± 0.47-fold in Ghsr+/+ (T + V vs. T + G: P = 0.032) and 9.22 ± 1.94-fold to 4.72 ± 1.06-fold in Ghsr-/- (T + V vs. T + G: P = 0.008)]. Only in Ghsr+/+ mice ghrelin ameliorated LLC-induced grip strength loss [improved from 89.24 ± 3.48% to 97.80 ± 2.31% of baseline (T + V vs. T + G: P = 0.042)], mitophagy markers [Bnip3 was decreased from 2.28 ± 0.56 to 1.38 ± 0.14-fold (T + V vs. T + G: P ≤ 0.05)], and impaired mitochondrial respiration [State 3u improved from 698.23 ± 73.96 to 934.37 ± 95.21 pmol/min (T + V vs. T + G: P ≤ 0.05)], whereas these markers were not improved by ghrelin Ghsr-/- . Compared with Ghsr+/+ , Ghsr-/- tumour-bearing mice also showed decreased response to ghrelin in BW [T + G-treated Ghsr+/+ vs. Ghsr -/- : 91.75 ± 1.05% vs. 86.18 ± 1.13% of baseline BW, P < 0.001)], gastrocnemius (T + G-treated Ghsr+/+ vs. Ghsr-/- : 96.9 ± 2.08% vs. 88.15 ± 1.78% of Ghsr+/+ HK + V, P < 0.001) and quadriceps muscle mass (T + G-treated Ghsr+/+ vs. Ghsr-/- : 96.12 ± 2.31% vs. 88.36 ± 1.94% of Ghsr+/+ HK + V, P = 0.01), and gastrocnemius type IIA (T + G-treated Ghsr+/+ vs. Ghsr-/- : 1250.49 ± 31.72 vs. 1017.62 ± 70.99 μm2 , P = 0.027) and IIB fibre cross-sectional area (T + G-treated Ghsr+/+ vs. Ghsr-/- : 2496.48 ± 116.88 vs. 2183.04 ± 103.43 μm2 , P = 0.024).

CONCLUSIONS

Growth hormone secretagogue receptor-1a mediates ghrelin's effects on attenuating LLC-induced weakness but not muscle mass loss by modulating the autophagy-lysosome pathway, mitophagy, and mitochondrial respiration.

Sarcopenia in chronic kidney disease: what have we learned so far?

The term sarcopenia was first introduced in 1988 by Irwin Rosenberg to define a condition of muscle loss that occurs in the elderly. Since then, a broader definition comprising not only loss of muscle mass, but also loss of muscle strength and low physical performance due to ageing or other conditions, was developed and published in consensus papers from geriatric societies. Sarcopenia was proposed to be diagnosed based on operational criteria using two components of muscle abnormalities, low muscle mass and low muscle function. This brought awareness of an important nutritional derangement with adverse outcomes for the overall health. In parallel, many studies in patients with chronic kidney disease (CKD) have shown that sarcopenia is a prevalent condition, mainly among patients with end stage kidney disease (ESKD) on hemodialysis (HD). In CKD, sarcopenia is not necessarily age-related as it occurs as a result of the accelerated protein catabolism from the disease and from the dialysis procedure per se combined with low energy and protein intakes. Observational studies showed that sarcopenia and especially low muscle strength is associated with worse clinical outcomes, including worse quality of life (QoL) and higher hospitalization and mortality rates. This review aims to discuss the differences in conceptual definition of sarcopenia in the elderly and in CKD, as well as to describe etiology of sarcopenia, prevalence, outcome, and interventions that attempted to reverse the loss of muscle mass, strength and mobility in CKD and ESKD patients.

Melanocortin-4 receptor antagonist TCMCB07 ameliorates cancer- and chronic kidney disease-associated cachexia

Cachexia, a devastating wasting syndrome characterized by severe weight loss with specific losses of muscle and adipose tissue, is driven by reduced food intake, increased energy expenditure, excess catabolism, and inflammation. Cachexia is associated with poor prognosis and high mortality and frequently occurs in patients with cancer, chronic kidney disease, infection, and many other illnesses. There is no effective treatment for this condition. Hypothalamic melanocortins have a potent and long-lasting inhibitory effect on feeding and anabolism, and pathophysiological processes increase melanocortin signaling tone, leading to anorexia, metabolic changes, and eventual cachexia. We used 3 rat models of anorexia and cachexia (LPS, methylcholanthrene sarcoma, and 5/6 subtotal nephrectomy) to evaluate efficacy of TCMCB07, a synthetic antagonist of the melanocortin-4 receptor. Our data show that peripheral treatment using TCMCB07 with intraperitoneal, subcutaneous, and oral administration increased food intake and body weight and preserved fat mass and lean mass during cachexia and LPS-induced anorexia. Furthermore, administration of TCMCB07 diminished hypothalamic inflammatory gene expression in cancer cachexia. These results suggest that peripheral TCMCB07 treatment effectively inhibits central melanocortin signaling and therefore stimulates appetite and enhances anabolism, indicating that TCMCB07 is a promising drug candidate for treating cachexia.

Double burden of malnutrition in persons with obesity

A paradoxical double challenge has emerged in the last decades with respect to nutrition and nutrition-related clinical conditions. Hunger-related undernutrition continues to represent an unacceptable burden, although its prevalence has been encouragingly reduced worldwide. On the other hand, the prevalence of overweight and obesity, defined as fat excess accumulation with negative impact on individual health, has dramatically increased due to increasingly pervasive obesogenic lifestyle changes. Undernutrition and obesity may coexist in world regions, Countries and even smaller communities and households, being referred to as double burden of malnutrition. It is however important to point out that fat accumulation and obesity may also induce additional nutritional derangements in affected individuals, both directly through metabolic and body composition changes and indirectly through acute and chronic diseases with negative impact on nutritional status. In the current narrative review, associations between fat accumulation in obesity and malnutrition features as well as their known causes will be reviewed and summarized. These include risk of loss of skeletal muscle mass and function (sarcopenia) that may allow for malnutrition diagnosis also in overweight and obese individuals, thereby introducing a new clinically relevant perspective to the obesity-related double burden of malnutrition concept.

Physiological Effect of Ghrelin on Body Systems

Ghrelin is a relatively novel multifaceted hormone that has been found to exert a plethora of physiological effects. In this review, we found/confirmed that ghrelin has effect on all body systems. It induces appetite; promotes the use of carbohydrates as a source of fuel while sparing fat; inhibits lipid oxidation and promotes lipogenesis; stimulates the gastric acid secretion and motility; improves cardiac performance; decreases blood pressure; and protects the kidneys, heart, and brain. Ghrelin is important for learning, memory, cognition, reward, sleep, taste sensation, olfaction, and sniffing. It has sympatholytic, analgesic, antimicrobial, antifibrotic, and osteogenic effects. Moreover, ghrelin makes the skeletal muscle more excitable and stimulates its regeneration following injury; delays puberty; promotes fetal lung development; decreases thyroid hormone and testosterone; stimulates release of growth hormone, prolactin, glucagon, adrenocorticotropic hormone, cortisol, vasopressin, and oxytocin; inhibits insulin release; and promotes wound healing. Ghrelin protects the body by different mechanisms including inhibition of unwanted inflammation and induction of autophagy. Having a clear understanding of the ghrelin effect in each system has therapeutic implications. Future studies are necessary to elucidate the molecular mechanisms of ghrelin actions as well as its application as a GHSR agonist to treat most common diseases in each system without any paradoxical outcomes on the other systems.

Ghrelin forms in the modulation of energy balance and metabolism

Ghrelin is a gastric hormone circulating in acylated (AG) and unacylated (UnAG) forms. This narrative review aims at presenting current emerging knowledge on the impact of ghrelin forms on energy balance and metabolism. AG represents ~ 10% of total plasma ghrelin, has an appetite-stimulating effect and is the only form for which a receptor has been identified. Moreover, other metabolic AG-induced effects have been reported, including the modulation of glucose homeostasis with stimulation of liver gluconeogenesis, the increase of fat mass and the improvement of skeletal muscle mitochondrial function. On the other hand, UnAG has no orexigenic effects, however recent reports have shown that it is directly involved in the modulation of skeletal muscle energy metabolism by improving a cluster of interlinked functions including mitochondrial redox activities, tissue inflammation and insulin signalling and action. These findings are in agreement with human studies which show that UnAG circulating levels are positively associated with insulin sensitivity both in metabolic syndrome patients and in a large cohort from the general population. Moreover, ghrelin acylation is regulated by a nutrient sensor mechanism, specifically set on fatty acids availability. These recent findings consistently point towards a novel independent role of UnAG as a regulator of muscle metabolic pathways maintaining energy status and tissue anabolism. While a specific receptor for UnAG still needs to be identified, recent evidence strongly supports the hypothesis that the modulation of ghrelin-related molecular pathways, including those involved in its acylation, may be a potential novel target in the treatment of metabolic derangements in disease states characterized by metabolic and nutritional complications.Level of evidence Level V, narrative review.

Mitochondrial Activity and Skeletal Muscle Insulin Resistance in Kidney Disease

Insulin resistance is a key feature of the metabolic syndrome, a cluster of medical disorders that together increase the chance of developing type 2 diabetes and cardiovascular disease. In turn, type 2 diabetes may cause complications such as diabetic kidney disease (DKD). Obesity is a major risk factor for developing systemic insulin resistance, and skeletal muscle is the first tissue in susceptible individuals to lose its insulin responsiveness. Interestingly, lean individuals are not immune to insulin resistance either. Non-obese, non-diabetic subjects with chronic kidney disease (CKD), for example, exhibit insulin resistance at the very onset of CKD, even before clinical symptoms of renal failure are clear. This uraemic insulin resistance contributes to the muscle weakness and muscle wasting that many CKD patients face, especially during the later stages of the disease. Bioenergetic failure has been associated with the loss of skeletal muscle insulin sensitivity in obesity and uraemia, as well as in the development of kidney disease and its sarcopenic complications. In this mini review, we evaluate how mitochondrial activity of different renal cell types changes during DKD progression, and discuss the controversial role of oxidative stress and mitochondrial reactive oxygen species in DKD. We also compare the involvement of skeletal muscle mitochondria in uraemic and obesity-related muscle insulin resistance.

Unacylated Ghrelin: A Novel Regulator of Muscle Intermediate Metabolism With Potential Beneficial Effects in Chronic Kidney Disease

In patients with chronic kidney disease (CKD), malnutrition with loss of skeletal muscle mass has a negative impact on morbidity and mortality. Emerging evidence indicates that a cluster of oxidative stress, inflammation, and insulin resistance directly contributes to skeletal muscle catabolism by favoring protein breakdown over synthesis. Ghrelin is a gastric hormone discovered and initially studied in its acylated orexigenic form. More recently, a role of unacylated ghrelin (UnAG) has been described to reduce skeletal muscle mitochondrial reactive oxygen species generation, inflammation, and insulin resistance both in experimental models and in clinical studies. UnAG administration could therefore represent a potential comprehensive therapeutic approach for CKD-related metabolic and nutritional complications. Studies of UnAG administration in experimental and clinical CKD are needed to test the hypothesis that UnAG may chronically improve nutritional status and outcome in CKD patients.

Acylated ghrelin treatment normalizes skeletal muscle mitochondrial oxidative capacity and AKT phosphorylation in rat chronic heart failure

BACKGROUND

Chronic heart failure (CHF) is associated with skeletal muscle abnormalities contributing to exercise intolerance, muscle loss, and negative impact on patient prognosis. A primary role has been proposed for mitochondrial dysfunction, which may be induced by systemic and tissue inflammation and further contribute to low insulin signalling. The acylated form of the gastric hormone ghrelin (AG) may improve mitochondrial oxidative capacity and insulin signalling in both healthy and diseased rodent models.

METHODS

We investigated the impact of AG continuous subcutaneous administration (AG) by osmotic minipump (50 nmol/kg/day for 28 days) compared with placebo (P) on skeletal muscle mitochondrial enzyme activities, mitochondrial biogenesis regulators transcriptional expression and insulin signalling in a rodent post-myocardial infarction CHF model.

RESULTS

No statistically significant differences (NS) were observed among the three group in cumulative food intake. Compared with sham-operated, P had low mitochondrial enzyme activities, mitochondrial biogenesis regulators transcripts, and insulin signalling activation at AKT level (P < 0.05), associated with activating nuclear translocation of pro-inflammatory transcription factor nuclear factor-κB. AG completely normalized all alterations (P < 0.05 vs P, P = NS vs sham-operated). Direct AG activities were strongly supported by in vitro C2C12 myotubes experiments showing AG-dependent stimulation of mitochondrial enzyme activities. No changes in mitochondrial parameters and insulin signalling were observed in the liver in any group.

CONCLUSIONS

Sustained peripheral AG treatment with preserved food intake normalizes a CHF-induced tissue-specific cluster of skeletal muscle mitochondrial dysfunction, pro-inflammatory changes, and reduced insulin signalling. AG is therefore a potential treatment for CHF-associated muscle catabolic alterations, with potential positive impact on patient outcome.

Impact of ghrelin on body composition and muscle function in a long-term rodent model of critical illness

Background

Patients with multiple injuries or sepsis requiring intensive care treatment invariably develop a catabolic state with resultant loss of lean body mass, for which there are currently no effective treatments. Recovery can take months and mortality is high. We hypothesise that treatment with the orexigenic and anti-inflammatory gastric hormone, ghrelin may attenuate the loss of body mass following critical illness and improve recovery.

Methods

Male Wistar rats received an intraperitoneal injection of the fungal cell wall derivative zymosan to induce a prolonged peritonitis and consequent critical illness. Commencing at 48h after zymosan, animals were randomised to receive a continuous infusion of ghrelin or vehicle control using a pre-implanted subcutaneous osmotic mini-pump, and continued for 10 days.

Results

Zymosan peritonitis induced significant weight loss and reduced food intake with a nadir at Day 2 and gradual recovery thereafter. Supra-physiologic plasma ghrelin levels were achieved in the treated animals. Ghrelin-treated rats ate more food and gained more body mass than controls. Ghrelin increased adiposity and promoted carbohydrate over fat metabolism, but did not alter total body protein, muscle strength nor muscle morphology. Muscle mass and strength remained significantly reduced in all zymosan-treated animals, even at ten days post-insult.

Conclusions

Continuous infusion of ghrelin increased body mass and food intake, but did not increase muscle mass nor improve muscle function, in a long-term critical illness recovery model. Further studies with pulsatile ghrelin delivery or additional anabolic stimuli may further clarify the utility of ghrelin in survivors of critical illness.

Unacylated ghrelin normalizes skeletal muscle oxidative stress and prevents muscle catabolism by enhancing tissue mitophagy in experimental chronic kidney disease

Unacylated ghrelin (UnAG) may lower skeletal muscle oxidative stress, inflammation, and insulin resistance in lean and obese rodents. UnAG-induced autophagy activation may contribute to these effects, likely involving removal of dysfunctional mitochondria (mitophagy) and redox state maintenance. In chronic kidney disease (CKD) oxidative stress, inflammation and insulin resistance may negatively influence patient outcome by worsening nutritional state through muscle mass loss. Here we show in a 5/6 nephrectomy (Nx) CKD rat model that 4 d s.c. UnAG administration (200 µg twice a day) normalizes CKD-induced loss of gastrocnemius muscle mass and a cluster of high tissue mitochondrial reactive oxygen species generation, high proinflammatory cytokines, and low insulin signaling activation. Consistent with these results, human uremic serum enhanced mitochondrial reactive oxygen species generation and lowered insulin signaling activation in C2C12 myotubes while concomitant UnAG incubation completely prevented these effects. Importantly, UnAG enhanced muscle mitophagy in vivo and silencing RNA-mediated autophagy protein 5 silencing blocked UnAG activities in myotubes. UnAG therefore normalizes CKD-induced skeletal muscle oxidative stress, inflammation, and low insulin signaling as well as muscle loss. UnAG effects are mediated by autophagy activation at the mitochondrial level. UnAG administration and mitophagy activation are novel potential therapeutic strategies for skeletal muscle metabolic abnormalities and their negative clinical impact in CKD.-Gortan Cappellari, G., Semolic, A., Ruozi, G., Vinci, P., Guarnieri, G., Bortolotti, F., Barbetta, D., Zanetti, M., Giacca, M., Barazzoni, R. Unacylated ghrelin normalizes skeletal muscle oxidative stress and prevents muscle catabolism by enhancing tissue mitophagy in experimental chronic kidney disease.

Does H2 Alter Mitochondrial Bioenergetics via GHS-R1α Activation?

More than 400 original articles have been published from 2007 onwards evaluating therapeutic potential of molecular hydrogen (H₂), the youngest member of medical gases family with selective anti-oxidative properties. However, recent studies suggest that H₂ may tackle other mitochondrial processes besides oxidative stress, including metabolic pathways that drive cellular energy.

Curcumin prevents mitochondrial dynamics disturbances in early 5/6 nephrectomy: Relation to oxidative stress and mitochondrial bioenergetics

Five-sixths nephrectomy (5/6NX) is a widely used model to study the mechanisms leading to renal damage in chronic kidney disease (CKD). However, early alterations on renal function, mitochondrial dynamics, and oxidative stress have not been explored yet. Curcumin is an antioxidant that has shown nephroprotection in 5/6NX-induced renal damage. The aim of this study was to explore the effect of curcumin on early mitochondrial alterations induced by 5/6NX in rats. In isolated mitochondria, 5/6NX-induced hydrogen peroxide production was associated with decreased activity of complexes I and V, decreased activity of antioxidant enzymes, alterations in oxygen consumption and increased MDA-protein adducts. In addition, it was found that 5/6NX shifted mitochondrial dynamics to fusion, which was evidenced by increased optic atrophy 1 and mitofusin 1 (Mfn1) and decreased fission 1 and dynamin-related protein 1 expressions. These data were confirmed by morphological analysis and immunoelectron microscopy of Mfn-1. All the above-described mechanisms were prevented by curcumin. Also, it was found that curcumin prevented renal dysfunction by improving renal blood flow and the total antioxidant capacity induced by 5/6NX. Moreover, in glomeruli and proximal tubules 5/6NX-induced superoxide anion production by uncoupled nitric oxide synthase (NOS) and nicotinamide adenine dinucleotide phosphate oxidase (NOX) dependent way, this latter was associated with increased phosphorylation of serine 304 of p47phox subunit of NOX. In conclusion, this study shows that curcumin pretreatment decreases early 5/6NX-induced altered mitochondrial dynamics, bioenergetics, and oxidative stress, which may be associated with the preservation of renal function. © 2016 BioFactors, 43(2):293-310, 2017.

Ghrelin treatment improves physical decline in sarcopenia model mice through muscular enhancement and mitochondrial activation

Chronic kidney disease (CKD) impairs physical performance in humans, which leads to a risk of all-cause mortality. In our previous study, we demonstrated that a reduction in muscle mitochondria rather than muscle mass was a major cause of physical decline in 5/6 nephrectomized CKD model mice. Because ghrelin administration has been reported to enhance oxygen utilization in skeletal muscle, we examined the usefulness of ghrelin for a recovery of physical decline in 5/6 nephrectomized C57Bl/6 mice, focusing on the epigenetic modification of peroxisome proliferator activated receptor gamma coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis. The mice were intraperitoneally administered acylated ghrelin (0.1 nmol/gBW; three times per week) for a month. Muscle strength and exercise endurance were measured by using a dynamometer and treadmill, respectively. Mitochondrial DNA copy number was determined by quantitative PCR. The methylation levels of the cytosine residue at 260 base pairs upstream of the translation initiation point (C-260) of PGC-1α, which has been demonstrated to decrease the expression, was evaluated by methylation-specific PCR and bisulfite genomic sequencing methods after the ghrelin administration. Ghrelin administration improved both muscle strength and exercise endurance in the mice and was associated with an increase in muscle mass and muscle mitochondrial content. Ghrelin administration decreased the methylation ratio of C-260 of PGC-1α in the skeletal muscle and increased the expression. Therefore, ghrelin administration effectively reduced the physical decline in 5/6 nephrectomized mice and was accompanied with an increased mitochondrial content through de-methylation of the promoter region of PGC-1α in the muscle.

Ghrelin acts as energy status sensor of male reproduction by modulating Sertoli cells glycolytic metabolism and mitochondrial bioenergetics

Ghrelin is a growth hormone-releasing peptide that has been suggested to interfere with spermatogenesis, though the underling mechanisms remain unknown. We studied the effect of ghrelin in human Sertoli cells (hSCs) metabolic phenotype. For that, hSCs were exposed to increasing concentrations of ghrelin (20, 100 and 500 pM) mimicking the levels reported in obese, normal weight, and severely undernourished individuals. The metabolite production/consumption was determined. The protein levels of key glycolysis-related transporters and enzymes were assessed. The lactate dehydrogenase (LDH) activity was measured. Mitochondrial complexes protein levels and mitochondria membrane potential were also measured. We showed that hSCs express the growth hormone secretagogue receptor. At the concentration present in the plasma of normal weight men, ghrelin caused a decrease of glucose consumption and mitochondrial membrane potential in hSCs, though LDH activity and lactate production remained unchanged, illustrating an alteration of glycolytic flux efficiency. Exposure of hSCs to levels of ghrelin found in the plasma of severely undernourished individuals decreased pyruvate consumption and mitochondrial complex III protein expression. All concentrations of ghrelin decreased alanine and acetate production by hSCs. Notably, the effects of ghrelin levels found in severely undernourished individuals were more pronounced in hSCs metabolic phenotype highlighting the importance of a proper eating behavior to maintain male reproductive potential. In conclusion, ghrelin acts as an energy status sensor for hSCs in a dose-dependent manner, showing an inverse association with the production of lactate, thus controlling the nutritional support of spermatogenesis.

Unacylated Ghrelin Reduces Skeletal Muscle Reactive Oxygen Species Generation and Inflammation and Prevents High-Fat Diet-Induced Hyperglycemia and Whole-Body Insulin Resistance in Rodents

Excess reactive oxygen species (ROS) generation and inflammation may contribute to obesity-associated skeletal muscle insulin resistance. Ghrelin is a gastric hormone whose unacylated form (UnAG) is associated with whole-body insulin sensitivity in humans and may reduce oxidative stress in nonmuscle cells in vitro. We hypothesized that UnAG 1) lowers muscle ROS production and inflammation and enhances tissue insulin action in lean rats and 2) prevents muscle metabolic alterations and normalizes insulin resistance and hyperglycemia in high-fat diet (HFD)-induced obesity. In 12-week-old lean rats, UnAG (4-day, twice-daily subcutaneous 200-µg injections) reduced gastrocnemius mitochondrial ROS generation and inflammatory cytokines while enhancing AKT-dependent signaling and insulin-stimulated glucose uptake. In HFD-treated mice, chronic UnAG overexpression prevented obesity-associated hyperglycemia and whole-body insulin resistance (insulin tolerance test) as well as muscle oxidative stress, inflammation, and altered insulin signaling. In myotubes, UnAG consistently lowered mitochondrial ROS production and enhanced insulin signaling, whereas UnAG effects were prevented by small interfering RNA-mediated silencing of the autophagy mediator ATG5. Thus, UnAG lowers mitochondrial ROS production and inflammation while enhancing insulin action in rodent skeletal muscle. In HFD-induced obesity, these effects prevent hyperglycemia and insulin resistance. Stimulated muscle autophagy could contribute to UnAG activities. These findings support UnAG as a therapeutic strategy for obesity-associated metabolic alterations.

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.

Insulin resistance in chronic kidney disease: new lessons from experimental models

Insulin resistance (IR) is a common feature of chronic kidney disease (CKD), but the underlying mechanisms still remain unclear. A growing body of evidence suggests that IR and its associated metabolic disorders are important contributors for the cardiovascular burden of these patients. In recent years, the modification of the intestinal flora and activation of inflammation pathways have been implicated in the pathogenesis of IR in obese and diabetic patients. All these pathways ultimately lead to lipid accumulation in ectopic sites and impair insulin signalling. These important discoveries have led to major advances in understanding the mechanisms of uraemia-induced IR. Indeed, recent studies show impairment of the intestinal barrier function and changes in the composition of the gut microbiome during CKD that can contribute to the prevailing inflammation, and the production and absorption of toxins generated from bacterial metabolism. The specific role of individual uraemic toxins in the pathogenesis of IR has been highlighted in rodents. Moreover, correcting some uraemia-associated factors by modulating the intestinal flora improves insulin sensitivity. This review outlines potential mechanisms by which important modifications of body homeostasis induced by the decline in kidney function can affect insulin sensitivity, and the relevance of recent advances in the field to provide novel therapeutic approaches to reduce IR associated cardiovascular mortality.

A pegylated leptin antagonist ameliorates CKD-associated cachexia in mice

Elevated serum leptin levels correlate with inflammation and predict changes in lean body mass in patients with CKD, and activation of the melanocortin system by leptin signaling mediates the pathophysiology of CKD-associated cachexia. We tested whether treatment with a pegylated leptin receptor antagonist (PLA) attenuates cachexia in mice with CKD. CKD and Sham mice received vehicle or PLA (2 or 7 mg/kg per day). At these doses, PLA did not influence serum leptin levels in mice. Treatment with 7 mg/kg per day PLA stimulated appetite and weight gain, improved lean mass and muscle function, reduced energy expenditure, and normalized the levels of hepatic TNF-α and IL-6 mRNA in mice with CKD. Furthermore, treatment with 7 mg/kg per day PLA attenuated the CKD-associated increase in the transcriptional and protein abundance of uncoupling proteins that mediates thermogenesis, and it normalized the molecular signatures of processes associated with muscle wasting in CKD, including proteolysis, myogenesis and muscle regeneration, and expression of proinflammatory muscle cytokines, such as IL-1α, -1β, and -6 and TNF-α. Our results suggest that leptin antagonism may represent a viable therapeutic strategy for cachexia in CKD.

Association of plasma des-acyl ghrelin levels with CKD

BACKGROUND AND OBJECTIVES

There are no effective therapies for malnutrition in CKD/ESRD patients. This study hypothesized that ghrelin, an endogenous orexigenic hormone, would correlate with renal function and might suggest therapeutic interventions for CKD/ESRD malnutrition.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Fifty-one CKD and 15 hemodialysis patients were enrolled. Acyl ghrelin (AG) and des-acyl ghrelin (DG) were determined using separate two-site-specific assays. Leptin, insulin, growth hormone, insulin-link growth factor-1, C-reactive protein, TNF-α, and IL-6 were also measured.

RESULTS

Univariate correlation analyses showed that CKD stage was highly, positively correlated with the levels of preprandial and postprandial DG and positively correlated with TNF-α, IL-6, leptin, and age. Multivariate partial-correlation analyses showed that CKD was independently associated with the proportion of preprandial and postprandial DG, whereas TNF-α, IL-6, leptin, insulin, and age were not independently associated with either. Geometric mean (GM) preprandial and postprandial AG were comparable between CKD stages ≤2 and >2, whereas GM preprandial DG and postprandial DG were 1.95-fold and 2.17-fold greater, respectively, for CKD stage >2 versus stage ≤2. DG was the dominant form of ghrelin preprandially and postprandially for both CKD stages ≤2 and >2. Dialysis had no effect on AG, but reduced DG by 73% to levels even lower (GM 48.7 pg/ml) than those seen postprandially in CKD stage ≤2 patients (GM 77.0 pg/ml).

CONCLUSIONS

This study shows a strong and independent correlation of DG with CKD stage. Postprandial suppression of ghrelin is impaired with reduced renal function. Hemodialysis selectively removes DG but not AG.

Ghrelin and cachexia in chronic kidney disease

Ghrelin is a growth hormone (GH) secretagogue and a potent orexigenic factor that stimulates feeding by interacting with hypothalamic feeding-regulatory nuclei. Its multifaceted effects are potentially beneficial as a treatment in human disease states. In both adult and pediatric chronic kidney disease (CKD) patients, decreased appetite plays a major role in wasting, which in turn is linked to morbidity and mortality; wasting has also been linked to high levels of leptin and proinflammatory cytokines. The beneficial effects of ghrelin treatment in CKD are potentially mediated by multiple concurrent actions, including the stimulation of appetite-regulating centers, anti-inflammatory effects, and direct kidney effects. Further evaluation of this appetite-regulating hormone in CKD is needed to confirm previous findings and to determine the underlying mechanisms.

Insulin resistance in patients with chronic kidney disease

Metabolic syndrome and its components are associated with chronic kidney disease (CKD) development. Insulin resistance (IR) plays a central role in the metabolic syndrome and is associated with increased risk for CKD in nondiabetic patients. IR is common in patients with mild-to-moderate stage CKD, even when the glomerular filtration rate is within the normal range. IR, along with oxidative stress and inflammation, also promotes kidney disease. In patients with end stage renal disease, IR is an independent predictor of cardiovascular disease and is linked to protein energy wasting and malnutrition. Systemic inflammation, oxidative stress, elevated serum adipokines and fetuin-A, metabolic acidosis, vitamin D deficiency, depressed serum erythropoietin, endoplasmic reticulum stress, and suppressors of cytokine signaling all cause IR by suppressing insulin receptor-PI3K-Akt pathways in CKD. In addition to adequate renal replacement therapy and correction of uremia-associated factors, thiazolidinedione, ghrelin, protein restriction, and keto-acid supplementation are therapeutic options. Weight control, reduced daily prednisolone dosage, and the use of cyclosporin decrease the risk of developing new-onset diabetes after kidney transplantation. Improved understanding of the pathogenic mechanisms underlying IR in CKD may lead to more effective therapeutic strategies to reduce uremia-associated morbidity and mortality.

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

Ghrelin is a gastric peptide that regulates energy homeostasis. Angiotensin II (Ang II) is known to induce body weight loss and skeletal muscle catabolism through the ubiquitin-proteasome pathway. In this study, we investigated the effects of ghrelin on body weight and muscle catabolism in mice treated with Ang II. The continuous subcutaneous administration of Ang II to mice for 6 days resulted in cardiac hypertrophy and significant decreases in body weight gain, food intake, food efficiency, lean mass, and fat mass. In the gastrocnemius muscles of Ang II-treated mice, the levels of insulin-like growth factor 1 (IGF-1) were decreased, and the levels of mRNA expression of catabolic factors were increased. Although the repeated subcutaneous injections of ghrelin (1.0mg/kg, twice daily for 5 days) did not affect cardiac hypertrophy, they resulted in significant body weight gains and improved food efficiencies and tended to increase both lean and fat mass in Ang II-treated mice. Ghrelin also ameliorated the decreased IGF-1 levels and the increased mRNA expression levels of catabolic factors in the skeletal muscle. IGF-1 mRNA levels in the skeletal muscle significantly decreased 24h after Ang II infusion, and this was reversed by two subcutaneous injections of ghrelin. In C2C12-derived myocytes, the dexamethasone-induced mRNA expression of atrogin-1 was decreased by IGF-1 but not by ghrelin. In conclusion, we demonstrated that ghrelin improved body weight loss and skeletal muscle catabolism in mice treated with Ang II, possibly through the early restoration of IGF-1 mRNA in the skeletal muscle and the amelioration of nutritional status.

Ghrelin and muscle metabolism in chronic uremia

Patients with chronic kidney disease (CKD) are prone to nutritional complications with negative prognostic impact. In particular, protein-energy wasting is a major CKD-associated clinical burden, and emerging evidence indicates that clustered metabolic alterations, including inflammation, oxidative stress, and insulin resistance, contribute to loss of skeletal muscle mass. Ghrelin is a gastric hormone discovered in its acylated form and extensively studied for its appetite-stimulating effect. Further studies have shown that ghrelin may positively modulate systemic inflammation and insulin action. In addition, a role of ghrelin in the regulation of redox state has been described in vitro. Ghrelin treatment could therefore represent a potential comprehensive therapeutic approach for CKD-related metabolic and nutritional complications, and evidence supporting this hypothesis has emerged in clinical and experimental CKD. Clinical trials of ghrelin administration are needed to test the hypothesis that ghrelin may chronically improve nutritional status and outcome in CKD patients.

Neuroendocrine and metabolic activities of ghrelin gene products

Acylated ghrelin (AG) is a 28 amino acid gastric peptide a natural ligand for the growth hormone secretagogue (GHS) receptor type 1a (GHS-R1a), endowed with GH-secreting and orexigenic properties. Besides, ghrelin exerts several peripheral metabolic actions, including modulation of glucose homeostasis and stimulation of adipogenesis. Notably, AG administration causes hyperglycemia in rodents as in humans. Ghrelin pleiotropy is supported by a widespread expression of the ghrelin gene, of GHS-R1a and other unknown ghrelin binding sites. The existence of alternative receptors for AG, of several natural ligands for GHS-R1a and of acylation-independent ghrelin non-neuroendocrine activities, suggests that there might be a complex 'ghrelin system' not yet completely explored. Moreover, the patho-physiological implications of unacylated ghrelin (UAG), and obestatin (Ob), the other two ghrelin gene-derived peptides, need to be clarified. Within the next few years, we may better understand the 'ghrelin system', where we might envisage clinical applications.

High-fat diet with acyl-ghrelin treatment leads to weight gain with low inflammation, high oxidative capacity and normal triglycerides in rat muscle

Obesity is associated with muscle lipid accumulation. Experimental models suggest that inflammatory cytokines, low mitochondrial oxidative capacity and paradoxically high insulin signaling activation favor this alteration. The gastric orexigenic hormone acylated ghrelin (A-Ghr) has antiinflammatory effects in vitro and it lowers muscle triglycerides while modulating mitochondrial oxidative capacity in lean rodents. We tested the hypothesis that A-Ghr treatment in high-fat feeding results in a model of weight gain characterized by low muscle inflammation and triglycerides with high muscle mitochondrial oxidative capacity. A-Ghr at a non-orexigenic dose (HFG: twice-daily 200-µg s.c.) or saline (HF) were administered for 4 days to rats fed a high-fat diet for one month. Compared to lean control (C) HF had higher body weight and plasma free fatty acids (FFA), and HFG partially prevented FFA elevation (P<0.05). HFG also had the lowest muscle inflammation (nuclear NFkB, tissue TNF-alpha) with mitochondrial enzyme activities higher than C (P<0.05 vs C, P = NS vs HF). Under these conditions HFG prevented the HF-associated muscle triglyceride accumulation (P<0.05). The above effects were independent of changes in redox state (total-oxidized glutathione, glutathione peroxidase activity) and were not associated with changes in phosphorylation of AKT and selected AKT targets. Ghrelin administration following high-fat feeding results in a novel model of weight gain with low inflammation, high mitochondrial enzyme activities and normalized triglycerides in skeletal muscle. These effects are independent of changes in tissue redox state and insulin signaling, and they suggest a potential positive metabolic impact of ghrelin in fat-induced obesity.

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

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

Fighting protein-energy wasting in chronic kidney disease: a challenge of complexity

Chronic uremia is often characterized by wasting of muscle and fat mass, which has been defined as protein-energy wasting (PEW), and is responsible for substantial worsening of patient outcome in terms of morbidity and mortality, mostly from cardiovascular events. Despite major advances in patient treatment, nutritional outcome in patients with end-stage renal disease has not improved substantially in recent years. Extensive research in this field has provided plausible explanations for this limitation by indicating that the pathogenesis of PEW in kidney disease is complex and multifactorial. Complexity involves underlying metabolic alterations, including inflammation, oxidative stress, and insulin resistance. In addition, patient heterogeneity is increasing with large numbers of obese individuals as a result of the ongoing obesity epidemics. Several tissues are involved in cross-talk and contribute to metabolic derangements, including adipose tissue, the gut, and the central nervous system, with novel mediators including the gastric hormone ghrelin. Acknowledging its complex pathogenesis may favor the development of novel and more effective therapeutic tools for PEW. These should ideally be effective in treating the underlying common mechanisms of wasting, which appear to include oxidative stress, inflammation, and insulin resistance.

Neuropeptides in the pathophysiology and treatment of cachexia

PURPOSE OF REVIEW

Cachexia occurs in various inflammatory diseases and is characterized by weight loss and muscle wasting. Pro-inflammatory cytokines modulate the activity of neuropeptides and hormones that control energy homeostasis and/or illness behaviors. This review summarizes recent (published within the past 18 months) literature regarding neuropeptides and hormones that have been implicated in the pathophysiology of cachexia, and that are likely to have therapeutic potential for preventing or reversing cachexia in various disease states.

RECENT FINDINGS

Hypothalamic pro-opiomelanocortin (POMC) and agouti-related protein (AgRP) neurons are downstream targets for pro-inflammatory cytokines. Genetic or pharmacological blockade of melanocortin receptor signaling preserves lean body mass and attenuates anorexia in experimental models of cachexia. Orally available melanocortin receptor antagonists have been developed and tested in cachectic animals with favorable results. Ghrelin and ghrelin mimetics increase appetite and preserve lean body mass in cachectic patients with diverse underlying diseases. Additional neuropeptide-expressing neurons in the hypothalamus (e.g., orexin neurons) might play a role in cachexia-associated lethargy.

SUMMARY

Promising outcomes from recent preclinical studies and/or early clinical trials with melanocortin receptor antagonists and ghrelin mimetics raise hopes that safe and effective anti-cachexia drugs will soon become available for widespread clinical use.

Pathophysiology and treatment of inflammatory anorexia in chronic disease

Decreased appetite and involuntary weight loss are common occurrences in chronic disease and have a negative impact on both quality of life and eventual mortality. Weight loss in chronic disease comes from both fat and lean mass, and is known as cachexia. Both alterations in appetite and body weight loss occur in a wide variety of diseases, including cancer, heart failure, renal failure, chronic obstructive pulmonary disease and HIV. An increase in circulating inflammatory cytokines has been implicated as a uniting pathogenic mechanism of cachexia and associated anorexia. One of the targets of inflammatory mediators is the central nervous system, and in particular feeding centers in the hypothalamus located in the ventral diencephalon. Current research has begun to elucidate the mechanisms by which inflammation reaches the hypothalamus, and the neural substrates underlying inflammatory anorexia. Research into these neural mechanisms has suggested new therapeutic possibilities, which have produced promising results in preclinical and clinical trials. This review will discuss inflammatory signaling in the hypothalamus that mediates anorexia, and the opportunities for therapeutic intervention that these mechanisms present.

The extra-hypothalamic actions of ghrelin on neuronal function

Ghrelin is a peptide hormone produced and secreted in the stomach. Numerous studies over the past decade demonstrate its importance in food intake, body-weight regulation and glucose homeostasis. These effects are driven largely by the high expression of the ghrelin receptor (GHSR1a) in the hypothalamus. However, GHSR1a is also expressed in numerous extra-hypothalamic neuronal populations, suggesting that ghrelin has physiological functions besides those involved in metabolic functions. In this review, I focus on increasing evidence that ghrelin has important roles in extra-hypothalamic functions, including learning and memory, reward and motivation, anxiety and depression, and neuroprotection. Furthermore, I discuss how the recently demonstrated role of ghrelin in promoting survival during periods of caloric restriction could contribute to its inherent neuroprotective and neuromodulatory properties.

Ghrelin in chronic kidney disease

Patients with chronic kidney disease (CKD) often exhibit symptoms of anorexia and cachexia, which are associated with decreased quality of life and increased mortality. Chronic inflammation may be an important mechanism for the development of anorexia, cachexia, renal osteodystrophy, and increased cardiovascular risk in CKD. Ghrelin is a gastric hormone. The biological effects of ghrelin are mediated through the growth hormone secretagogue receptor (GHSR). The salutary effects of ghrelin on food intake and meal appreciation suggest that ghrelin could be an effective treatment for anorexic CKD patients. In addition to its appetite-stimulating effects, ghrelin has been shown to possess anti-inflammatory properties. The known metabolic effects of ghrelin and the potential implications in CKD will be discussed in this review. The strength, shortcomings, and unanswered questions related to ghrelin treatment in CKD will be addressed.

Chronic renal failure, cachexia, and ghrelin

Protein energy wasting is frequently observed in patients with advanced chronic renal failure and end-stage renal disease. Anorexia and reduced food intake are critical contributing factors and negatively impact on patients' survival. Ghrelin is a prophagic peptide produced by the stomach and acting at the hypothalamic level to increase the activity of orexigenic neurons. In patients with chronic renal disease, plasma levels are increased as a likely effect of reduced renal clearance. Nevertheless, patients' food intake is significantly reduced, suggesting inflammation-mediated resistance of hypothalamic nuclei to peripheral signals. A number of forms of evidence show that ghrelin resistance could be overcome by the administration of exogenous ghrelin. Therefore, ghrelin has been proposed as a potential strategy to improve food intake in chronic renal failure patients with protein energy wasting. Preliminary data are encouraging although larger prospective clinical trials are needed to confirm the results and to identify those patients who are likely to benefit most from the administration of exogenous ghrelin.

Animal models of anorexia and cachexia

BACKGROUND: Cachexia is a devastating syndrome of body wasting that worsens quality of life and survival for patients suffering from diseases such as cancer, chronic kidney disease and chronic heart failure. Successful treatments have been elusive in humans, leaving a clear need for the development of new treatment compounds. Animal models of cachexia are able to recapitulate the clinical findings from human disease and have provided a much-needed means of testing the efficacy of prospective therapies. OBJECTIVE: This review focuses on animal models of cachexia caused by cancer, chronic heart failure and chronic kidney disease, including the features of these models, their implementation, and commonly-followed outcome measures. CONCLUSION: Given a dire clinical need for effective treatments of cachexia, animal models will continue a vital role in assessing the efficacy and safety of potential treatments prior to testing in humans. Also important in the future will be the use of animal models to assess the durability of effect from anti-cachexia treatments and their effect on prognosis of the underlying disease states.