Orexigenic Effect Research Articles

A phase 1, single-blind, placebo-controlled, 3-arm cross-over trial assessing the appetite enhancing effects of potentially ghrelinergic dairy-derived peptides

AbstractMethods to stimulate appetite in the sick or elderly remains a challenge with few safe therapeutic options. Ghrelin is an orexigenic hormone, increasing appetite and subsequent food intake. It has received considerable attention as a therapeutic target to stimulate food intake in patients with anorexia. The identification of food-grade bioactives with proven orexigenic effects would mark significant progress in the treatment of disease-related malnutrition. This study therefore investigated the effects of two milk-derived ghrelinergic peptides on appetite and energy intake in healthy humans.A single-blind, placebo-controlled, 3-arm (placebo, casein bioactive MF1145 and whey bioactive UL-2-141) cross-over trial was conducted in healthy male volunteers. Participants received 26 mg/kg of both the bioactives and placebo. The main outcome measures were energy & protein intake from a set breakfast and ad libitum lunch and subjective appetite sensations as assessed by visual analogue scale (VAS). Basal and postprandial levels of active ghrelin (AG) were measured. Dietary intakes were analysed using Nutritics software. Statistical analyses were performed in R.Overall, 22 male participants (mean age 27 years) were included, average BMI was 24.6 kg/m2, (19.8 to 30.2 kg/m2). Mean energy and protein intakes at lunch when treated with placebo were 1343 kcal (95% CI: 1215–1471 kcal) and 74 g (95% CI: 66–81 g), respectively. Energy and protein intakes were not significantly different from placebo for either treatment (p = 0.918, p = 0.319 for UL-2-141 and p = 0.889, p = 0.959 for MF1145, respectively). Similarly, appetite, hunger and satiety responses on VAS were not significantly different from placebo for either treatment. AG peak post-lunch on placebo was 653 pg/ml (95% CI: 511–794 pg/ml). Treatment with UL-2-141 resulted in 139 pg/ml reduction in post-prandial AG compared to placebo and treatment with MF1145 resulted in 114 pg/ml reduction compared to placebo. This pattern was significant for both treatments (p = 0.021 and p = 0.045, respectively) however when controlling for fasting-AG, the pattern was no longer significant (p = 0.590 and p = 0.877 respectively). Pre-prandial AG peaks were not significantly different across treatments.While these peptides have previously demonstrated ghrelinergic effects in rats, no effect on appetite or food intake in humans was identified by this study. This may be attributable to the small sample size or low dose. However, since healthy adults are often not in tune with their own physiological hunger, they may not respond strongly to simple physiological modulators and repeating the study in subjects with established anorexia may be prudent.

Neuropeptide Y Signaling in the Lateral Hypothalamus Modulates Diet Component Selection and is Dysregulated in a Model of Diet-Induced Obesity

The preclinical multicomponent free-choice high-fat high-sucrose (fcHFHS) diet has strong validity to model diet-induced obesity (DIO) and associated maladaptive molecular changes in the central nervous system. fcHFHS-induced obese rats demonstrate increased sensitivity to intracerebroventricular infusion of the orexigenic Neuropeptide Y (NPY). The brain region-specific effects of NPY signaling on fcHFHS diet component selection are not completely understood. For example, fcHFHS-fed rats have increased intake of chow and fat following intracerebroventricular NPY infusion, whereas NPY administration in the nucleus accumbens, a key hub of the reward circuitry, specifically increases fat intake. Here, we investigated whether NPY infusion in the lateral hypothalamic area (LHA), which is crucially involved in the regulation of intake, regulates fcHFHS component selection, and if LHA NPY receptor subtypes 1 or 5 (NPYR1/5) are involved. Male Wistar rats were fed a chow or fcHFHS diet for at least seven days, and received intra-LHA vehicle or NPY infusions in a cross-over design. Diet component intake was measured two hours later. Separate experimental designs were used to test the efficacy of NPY1R- or NPY5R antagonism to prevent the orexigenic effects of intra-LHA NPY. Intra-LHA NPY increased caloric intake in chow- and fcHFHS-fed rats. This effect was mediated specifically by chow intake in fcHFHS-fed rats. The orexigenic effects of intra-LHA NPY were prevented by NPY1R and NPY5R antagonism in chow-fed rats, but only by NPY5R antagonism in fcHFHS-fed rats. Thus, NPY signaling has brain region-specific effects on fcHFHS component selection and LHA NPYR sensitivity is dysregulated during consumption of a fcHFHS diet.

Orexins/Hypocretins: Key Regulators of Energy Homeostasis.

Originally described to be involved in feeding regulation, orexins/hypocretins are now also considered as major regulatory actors of numerous biological processes, such as pain, sleep, cardiovascular function, neuroendocrine regulation, and energy expenditure. Therefore, they constitute one of the most pleiotropic families of hypothalamic neuropeptides. Although their orexigenic effect is well documented, orexins/hypocretins also exert central effects on energy expenditure, notably on the brown adipose tissue (BAT) thermogenesis. A better comprehension of the underlying mechanisms and potential interactions with other hypothalamic molecular pathways involved in the modulation of food intake and thermogenesis, such as AMP-activated protein kinase (AMPK) and endoplasmic reticulum (ER) stress, is essential to determine the exact implication and pathophysiological relevance of orexins/hypocretins on the control of energy balance. Here, we will review the actions of orexins on energy balance, with special focus on feeding and brown fat function.

Activation of Kappa Opioid Receptor Regulates the Hypothermic Response to Calorie Restriction and Limits Body Weight Loss.

Mammals maintain a nearly constant core body temperature (Tb) by balancing heat production and heat dissipation. This comes at a high metabolic cost that is sustainable if adequate calorie intake is maintained. When nutrients are scarce or experimentally reduced such as during calorie restriction (CR), endotherms can reduce energy expenditure by lowering Tb [1-6]. This adaptive response conserves energy, limiting the loss of body weight due to low calorie intake [7-10]. Here we show that this response is regulated by the kappa opioid receptor (KOR). CR is associated with increased hypothalamic levels of the endogenous opioid Leu-enkephalin, which is derived from the KOR agonist precursor dynorphin [11]. Pharmacological inhibition of KOR, but not of the delta or the mu opioid receptor subtypes, fully blocked CR-induced hypothermia and increased weight loss during CR independent of calorie intake. Similar results were seen with DIO mice subjected to CR. In contrast, inhibiting KOR did not change Tb in animals fed ad libitum (AL). Chemogenetic inhibition of KOR neurons in the hypothalamic preoptic area reduced the CR-induced hypothermia, whereas chemogenetic activation of prodynorphin-expressing neurons in the arcuate or the parabrachial nucleus lowered Tb. These data indicate that KOR signaling is a pivotal regulator of energy homeostasis and can affect body weight during dieting by modulating Tb and energy expenditure.

Marijuana Use in Patients with Symptoms of Gastroparesis: Prevalence, Patient Characteristics, and Perceived Benefit.

Marijuana may be used by some patients with gastroparesis (Gp) for its potential antiemetic, orexigenic, and pain-relieving effects. The aim of this study was to describe the use of marijuana by patients for symptoms of Gp, assessing prevalence of use, patient characteristics, and patients' perceived benefit on their symptoms of Gp. Patients with symptoms of Gp underwent history and physical examination, gastric emptying scintigraphy, and questionnaires assessing symptoms. Patients were asked about the current use of medications and alternative medications including marijuana. Fifty-nine of 506 (11.7%) patients with symptoms of Gp reported current marijuana use, being similar among patients with delayed and normal gastric emptying and similar in idiopathic and diabetic patients. Patients using marijuana were younger, more often current tobacco smokers, less likely to be a college graduate, married or have income > $50,000. Patients using marijuana had higher nausea/vomiting subscore (2.7 vs 2.1; p = 0.002), higher upper abdominal pain subscore (3.5 vs 2.9; p = 0.003), more likely to be using promethazine (37 vs 25%; p = 0.05) and dronabinol (17 vs 3%; p < 0.0001). Of patients using marijuana, 51% had been using it for more than 2years, 47% were using this once or more per day, and 81% of marijuana users rated their benefit from marijuana as better or much better. A subset of patients (12%) with symptoms of Gp use marijuana. Patients with severe nausea and abdominal pain were more likely to use marijuana and perceive it to be beneficial for their symptoms. ClinicalTrials.gov Identifier: NCT01696747.

Charge Characteristics of Agouti-Related Protein Implicate Potent Involvement of Heparan Sulfate Proteoglycans in Metabolic Function.

SummaryThe endogenous melanocortin peptide agouti-related protein (AgRP) plays a well-known role in foraging, but its contribution to metabolic regulation is less understood. Mature AgRP(83-132) has distinct residues for melanocortin receptor binding and heparan sulfate interactions. Here, we show that AgRP increases ad libitum feeding and operant responding for food in mice, decreases oxygen consumption, and lowers body temperature and activity, indicating lower energy expenditure. AgRP increased the respiratory exchange ratio, indicating a reduction of fat oxidation and a shift toward carbohydrates as the primary fuel source. The duration and intensity of AgRP's effects depended on the density of its positively charged amino acids, suggesting that its orexigenic and metabolic effects depend on its affinity for heparan sulfate. These findings may have major clinical implications by unveiling the critical involvement of interactions between AgRP and heparan sulfate to the central regulation of energy expenditure, fat utilization, and possibly their contribution to metabolic disease.

A model of emotional stress‐induced binge eating in female mice with no history of food restriction

Overeating is a major contributing factor to obesity and related health complications. For women, in particular, negative emotions such as stress strongly influence eating behavior and bingeing episodes. Modeling this type of binge eating in rodents presents challenges: firstly, stress-induced anorexia is commonly observed in rodents therefore a mild stressor is required in order to observe an orexigenic effect. Second, many studies report using calorie restriction to observe the required behavior; yet this does not necessarily reflect the human condition. Thus, the aim of this study was to develop a model of emotional stress-induced bingeing independent of caloric restriction. Female and male C57BL/6J mice were divided into ad libitum (n = 20 per sex) and food-restricted (n = 20 per sex) groups which were both further split into a control group and a group exposed to frustration stress (n = 10 per group). All mice were provided intermittent access to a highly palatable food in 2 cycles. At the end of each cycle the stress group was subjected to a 15-minute frustration episode where highly palatable food was within the home cage but inaccessible. Both groups were then given free access for 15 minutes. Frustrated female mice from the ad libitum displayed binge-like behavior compared with controls (P = .0001). Notably, this behavior was absent in males. Ovariectomy had no impact on binge-like behavior. Collectively, these data validate a novel model of emotional stress-induced binge eating specific to female mice which does not require caloric restriction and is not driven by ovarian hormones.

Intranasal administration of a stapled relaxin-3 mimetic has anxiolytic- and antidepressant-like activity in rats.

Background and PurposeDepression and anxiety are common causes of disability, and innovative tools and potential pharmacological targets are actively sought for prevention and treatment. Therapeutic strategies targeting the relaxin‐3 peptide or its primary endogenous receptor, RXFP3, for the treatment of major depression and anxiety disorders have been limited by a lack of compounds with drug‐like properties. We proposed that a hydrocarbon‐stapled mimetic of relaxin‐3, when administered intranasally, might be uniquely applicable to the treatment of these disorders.Experimental ApproachWe designed a series of hydrocarbon‐stapled relaxin‐3 mimetics and identified the most potent compound using in vitro receptor binding and activation assays. Further, we assessed the effect of intranasal delivery of relaxin‐3 and the lead stapled mimetic in rat models of anxiety and depression.Key ResultsWe developed an i,i+7 stapled relaxin‐3 mimetic that manifested a stabilized α‐helical structure, proteolytic resistance, and confirmed agonist activity in receptor binding and activation in vitro assays. The stapled peptide agonist enhanced food intake after intracerebral infusion in rats, confirming in vivo activity. We showed that intranasal delivery of the lead i,i+7 stapled peptide or relaxin‐3 had orexigenic effects in rats, indicating a potential clinically translatable route of delivery. Further, intranasal administration of the lead i,i+7 stapled peptide exerted anxiolytic and antidepressant‐like activity in anxiety‐ and depression‐related behaviour paradigms.Conclusions and ImplicationsOur preclinical findings demonstrate that targeting the relaxin‐3/RXFP3 receptor system via intranasal delivery of an i,i+7 stapled relaxin‐3 mimetic may represent an effective treatment approach for depression, anxiety, and related neuropsychiatric disorders.

The novel cannabinoid CB1 receptor agonist AM11101 increases food intake in female rats.

Δ9 -tetrahydrocannabinol (THC) acts via cannabinoid CB1 receptors to increase feeding. Here, we assessed the orexigenic effect of AM11101, a novel CB1 receptor agonist designed to have a more favourable pharmacodynamic profile than THC. The acute, orexigenic effects of AM11101 and THC were compared in female rats. Food intake and meal patterns were also examined following once daily treatment with AM11101 and THC for 7days. AM11101 (0.01-0.1mg·kg-1 ) increased food intake during the first hour following both acute and chronic treatments in pre-fed and freely feeding animals. This orexigenic effect persisted for up to 4hr, with no compensatory decrease in feeding during the subsequent 4-22hr. THC (1mg·kg-1 ) increased 1-hr food intake in pre-fed animals, but was less reliable than AM11101 in increasing 1-hr food intake in freely feeding animals following both acute and chronic administration. The orexigenic effect of both compounds was due to an increase in meal size, not meal number. Our study provides the first demonstration that AM11101 increases short-term food intake via a selective increase in meal size. AM11101 promotes a more reliable orexigenic effect than THC in freely feeding animals, with no subsequent compensatory decrease in feeding. AM11101 may offer a greater efficacy than THC and its congeners in stimulating food intake in underweight clinical populations.

Exposure to chlorpyrifos at different ages triggers APOE genotype-specific responses in social behavior, body weight and hypothalamic gene expression

To date, we have shown that apolipoprotein E (APOE) polymorphisms differentially modulate the neurobehavioral and metabolic effects of chlorpyrifos (CPF), a widely used pesticide, which is detected as residue in food. We previously reported that, after being exposed to CPF, APOE3 subjects exhibit metabolic dysfunctions while APOE4 subjects undergo changes in behavior. In the current study, we investigated the effects of a double exposure to CPF on social behavior and hypothalamic gene expression in apoE-targeted replacement (TR) mice. Male apoE3-and apoE4-TR mice were exposed to CPF at 0 or 1 mg/kg/day on postnatal days 10–15 and then, during adulthood (5 months of age), fed a CPF-supplemented diet (0 or 2 mg/kg/day) for 15 days. During adult exposure to CPF, body weight gain and food intake were monitored. At the end of the adult exposure period, we evaluated social behavior in a three-chamber test, as well as mRNA levels of hypothalamic neuropeptides and receptors related to social behavior and feeding control. Adult CPF exposure increased food intake in general, but only apoE4 mice increased their body weight. Postnatal CPF exposure improved preference for the social contexts in apoE4 mice while adult CPF exposure did the same in apoE3 mice. Anorexigenic-peptide and social-related behavior gene expression decreased as a result of adult CPF exposure in apoE4 mice, and neuropeptide Y was more expressed in apoE4 mice. These results indicate that CPF exposure produces orexigenic and metabolic effects and enlarges individual differences in social behavior, especially in apoE3 mice.

Signal Transduction and Pathogenic Modifications at the Melanocortin-4 Receptor: A Structural Perspective.

The melanocortin-4 receptor (MC4R) can be endogenously activated by binding of melanocyte-stimulating hormones (MSH), which mediates anorexigenic effects. In contrast, the agouti-related peptide (AgRP) acts as an endogenous inverse agonist and suppresses ligand-independent basal signaling activity (orexigenic effects). Binding of ligands to MC4R leads to the activation of different G-protein subtypes or arrestin and concomitant signaling pathways. This receptor is a key protein in the hypothalamic regulation of food intake and energy expenditure and naturally-occurring inactivating MC4R variants are the most frequent cause of monogenic obesity. In general, obesity is a growing problem on a global scale and is of social, medical, and economic relevance. A significant goal is to develop optimized pharmacological tools targeting MC4R without adverse effects. To date, this has not been achieved because of inter alia non-selective ligands across the five functionally different MCR subtypes (MC1-5R). This motivates further investigation of (i) the three-dimensional MC4R structure, (ii) binding mechanisms of various ligands, and (iii) the molecular transfer process of signal transduction, with the aim of understanding how structural features are linked with functional-physiological aspects. Unfortunately, experimentally elucidated structural information is not yet available for the MC receptors, a group of class A G-protein coupled receptors (GPCRs). We, therefore, generated MC4R homology models and complexes with interacting partners to describe approximate structural properties associated with signaling mechanisms. In addition, molecular insights from pathogenic mutations were incorporated to discriminate more precisely their individual malfunction of the signal transfer mechanism.

Na+/K+-ATPase is involved in the regulation of food intake in rainbow trout but apparently not through brain glucosensing mechanisms

To assess the hypothesis that Na+/K+-ATPase (NKA) is involved in the central regulation of food intake in fish, we observed in a first experiment with rainbow trout (Oncorhynchus mykiss) that intracerebroventricular (ICV) treatment with ouabain decreased food intake. We hypothesized that this effect relates to modulation of glucosensing mechanisms in brain areas (hypothalamus, hindbrain, and telencephalon) involved in food intake control. Therefore, we evaluated in a second experiment, the effect of ICV administration of ouabain, in the absence or in the presence of glucose, on NKA activity, mRNA abundance of different NKA subunits, parameters related to glucosensing, transcription factors, and appetite-related neuropeptides in brain areas involved in the control of food intake. NKA activity and mRNA abundance of nkaα1a and nkaα1c in brain were inhibited by ouabain treatment and partially by glucose. The anorectic effect of ouabain is opposed to the orexigenic effect reported in mammals. The difference might relate to the activity of glucosensing as well as downstream mechanisms involved in food intake regulation. Ouabain inhibited glucosensing mechanisms, which were activated by glucose in hypothalamus and telencephalon. Transcription factors and neuropeptides displayed responses comparable to those elicited by glucose when ouabain was administered alone, but not when glucose and ouabain were administered simultaneously. Ouabain might therefore affect other processes, besides glucosensing mechanisms, generating changes in membrane potential and/or intracellular pathways finally modulating transcription factors and neuropeptide mRNA abundance leading to modified food intake.

RhoA in tyrosine hydroxylase neurones regulates food intake and body weight via altered sensitivity to peripheral hormones.

Dopamine-producing tyrosine hydroxylase (TH) neurones in the hypothalamic arcuate nucleus (ARC) have recently been shown to be involved in ghrelin signalling and body weight homeostasis. In the present study, we investigate the role of the intracellular regulator RhoA in hypothalamic TH neurones in response to peripheral hormones. Diet-induced obesity was found to be associated with increased phosphorylation of TH in ARC, indicating obesity-associated increased activity of ARC TH neurones. Mice in which RhoA was specifically knocked out in TH neurones (TH-RhoA-/- mice) were more sensitive to the orexigenic effect of peripherally administered ghrelin and displayed an abolished response to the anorexigenic hormone leptin. When TH-RhoA-/- mice were challenged with a high-fat high-sucrose (HFHS) diet, they became hyperphagic and gained more body weight and fat mass compared to wild-type control mice. Importantly, lack of RhoA prevented development of ghrelin resistance, which is normally observed in wild-type mice after long-term HFHS diet feeding. Patch-clamp electrophysiological analysis demonstrated increased ghrelin-induced excitability of TH neurones in lean TH-RhoA-/- mice compared to lean littermate control animals. Additionally, increased expression of the orexigenic hypothalamic neuropeptides agouti-related peptide and neuropeptide Y was observed in TH-RhoA-/- mice. Overall, our data indicate that TH neurones in ARC are important for the regulation of body weight homeostasis and that RhoA is both a central effector in these neurones and important for the development of obesity-induced ghrelin resistance. The obese phenotype of TH-RhoA-/- mice may be a result of increased sensitivity to ghrelin and decreased sensitivity to leptin, resulting in increased food intake.

The additive effect of allopregnanolone on ghrelin's orexigenic effect in rats

The progesterone metabolite, allopregnanolone (AlloP), is a GABAA receptor modulating steroid and is known to have orexigenic and pro-obesity effects. The neurobiological mechanisms underpinning these effects are most likely due to enhanced GABAergic signaling in the lateral arcuate nucleus (ARC) and medial paraventricular nucleus (PVN) of the hypothalamus. Inspired by the finding that GABAergic signaling is also important for the orexigenic effects of the circulating hormone, ghrelin, we sought to determine the extent to which AlloP (one of the most potent endogenous GABAA-receptor modulators) operates alongside ghrelin to enhance food intake. Male rats with ad libitum access to standard chow were injected intravenously with AlloP and/or ghrelin, alone or in combination. The intake of the standard chow was greater after AlloP 1 mg/kg together with ghrelin 30 μg/kg than with 30 μg/kg ghrelin alone. Food intake was also increased for the combined treatment of AlloP 0.5 mg/kg + ghrelin 10 μg/kg, AlloP 1 mg/kg + ghrelin 10 μg/kg, and AlloP 0.5 mg/kg + ghrelin 30 μg/kg. There was no significant difference in food intake between the two ghrelin doses or between the two doses of AlloP and the vehicle. In electrophysiological studies, physiologically relevant concentrations of AlloP prolonged the current decay time of spontaneous inhibitory post-synaptic current of dissociated cells of the ARC and PVN. We conclude that AlloP enhances the hyperphagic effect of ghrelin, findings of potential relevance for the hyperphagia associated with the luteal phase of the reproductive cycle.

Amygdala NPY Circuits Promote the Development of Accelerated Obesity under Chronic Stress Conditions

Neuropeptide Y (NPY) exerts a powerful orexigenic effect in the hypothalamus. However, extra-hypothalamic nuclei also produce NPY, but its influence on energy homeostasis is unclear. Here we uncover a previously unknown feeding stimulatory pathway that is activated under conditions of stress in combination with calorie-dense food; NPY neurons in the central amygdala are responsible for an exacerbated response to a combined stress and high-fat-diet intervention. Central amygdala NPY neuron-specific Npy overexpression mimics the obese phenotype seen in a combined stress and high-fat-diet model, which is prevented by the selective ablation of Npy. Using food intake and energy expenditure as readouts, we demonstrate that selective activation of central amygdala NPY neurons results in increased food intake and decreased energy expenditure. Mechanistically, it is the diminished insulin signaling capacity on central amygdala NPY neurons under combined stress and high-fat-diet conditions that leads to the exaggerated development of obesity.

Kisspeptin and RFRP3 modulate body mass in Phodopus sungorus via two different neuroendocrine pathways.

Many animals exhibit remarkable metabolic and reproductive adaptations to seasonal changes in their environment. When day length shortens, Djungarian hamsters (Phodopus sungorus) reduce their body weight and inhibit their reproductive activity, whereas the opposite occurs in springtime. These physiological adaptations are considered to depend on photoperiodic changes in hypothalamic genes encoding the peptides kisspeptin (Kp) and RFamide-related peptide 3 (RFRP3) for the control of reproduction, as well as pro-opiomelanocortin and somatostatin for metabolic regulation. The present study investigates the effect of Kp and RFRP3 on long-term body weight regulation, aiming to establish whether metabolic and reproductive hypothalamic networks may interact during adaptation to seasonal physiology. We found that chronic central administration of both Kp and RFRP3 in short photoperiod-adapted male Djungarian hamsters increased body weight, although via different pathways. The effect of Kp was dependent on testicular activity because castration prevented the body weight increase and was associated with an increase in pro-opiomelanocortin and neuropeptide Y expression. On the other hand, the orexigenic effect of RFRP3 was associated with an increase in circulating insulin and leptin levels, although it had no effect on any of the hypothalamic metabolic genes investigated, and did not change circulating levels of sex steroids. Notably, neither Kp, nor RFRP3 altered female hamster metabolic parameters. Thus, using a rodent model exhibiting seasonal changes in reproduction and metabolism, the present study demonstrates that, in addition to its role in the central control of reproduction, Kp also participates in body weight control in a sex-dependent manner via an anabolic action of testosterone. Conversely, RFRP3 affects body weight control in males mostly by acting on adiposity, with no overt effect on the reproductive system in both sexes.

Mas Receptor Activation Slows Tumor Growth and Attenuates Muscle Wasting in Cancer.

Cancer cachexia is a multifactorial syndrome characterized by a progressive loss of skeletal muscle mass associated with significant functional impairment. Cachexia robs patients of their strength and capacity to perform daily tasks and live independently. Effective treatments are needed urgently. Here, we investigated the therapeutic potential of activating the "alternative" axis of the renin-angiotensin system, involving ACE2, angiotensin-(1-7), and the mitochondrial assembly receptor (MasR), for treating cancer cachexia. Plasmid overexpression of the MasR or pharmacologic angiotensin-(1-7)/MasR activation did not affect healthy muscle fiber size in vitro or in vivo but attenuated atrophy induced by coculture with cancer cells in vitro. In mice with cancer cachexia, the MasR agonist AVE 0991 slowed tumor development, reduced weight loss, improved locomotor activity, and attenuated muscle wasting, with the majority of these effects dependent on the orexigenic and not antitumor properties of AVE 0991. Proteomic profiling and IHC revealed that mechanisms underlying AVE 0991 effects on skeletal muscle involved miR-23a-regulated preservation of the fast, glycolytic fibers. MasR activation is a novel regulator of muscle phenotype, and AVE 0991 has orexigenic, anticachectic, and antitumorigenic effects, identifying it as a promising adjunct therapy for cancer and other serious muscle wasting conditions. SIGNIFICANCE: These findings demonstrate that MasR activation has multiple benefits of being orexigenic, anticachectic, and antitumorigenic, revealing it as a potential adjunct therapy for cancer.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/4/706/F1.large.jpg.See related commentary by Rupert et al., p. 699.

Decreased Plasma Octanoylated Ghrelin Levels in Mice by Oleanolic Acid.

Ghrelin is a stomach-derived peptide hormone with an appetite-stimulating effect. Octanoylation on the serine-3 residue of ghrelin by ghrelin O-acyl transferase (GOAT) is essential for its orexigenic effect. Mature octanoylated ghrelin is generated by the C-terminal cleavage of octanoylated proghrelin via prohormone convertases (furin, PC1/3, or PC2). We previously established an AGS-GHRL8 cell line that produces octanoylated ghrelin in the presence of octanoic acid, and found that oleanolic acid suppresses octanoylated ghrelin production in AGS-GHRL8 cells. Here, we investigated the effects of oleanolic acid in C57BL/6J mice fed a standard, high-fat, or high-glucose diet. Oral administration of oleanolic acid for seven days (20 or 40 mg/kg) reduced plasma octanoylated ghrelin levels and body weight gain in the standard diet-fed mice but not in other two diet-fed mice. There were no significant differences in ghrelin, GOAT, furin, PC1/3, and PC2 gene expression levels between the vehicle- and oleanolic acid-treated mice fed a standard diet. Octanoyl-CoA is a substrate for ghrelin octanoylation by GOAT. We found that oleanolic acid did not affect octanoyl-CoA production in vitro. Hence, the inhibitory effect of oleanolic acid on octanoylated ghrelin production may not be related to the decrease in octanoyl-CoA. The results of this study may provide valuable knowledge for the development of anti-obesity agents with an inhibitory effect on octanoylated ghrelin production.

Effects of Kisspeptin-10 on Hypothalamic Neuropeptides and Neurotransmitters Involved in Appetite Control.

Besides its role as key regulator in gonadotropin releasing hormone secretion, reproductive function, and puberty onset, kisspeptin has been proposed to act as a bridge between energy homeostasis and reproduction. In the present study, to characterize the role of hypothalamic kisspeptin as metabolic regulator, we evaluated the effects of kisspeptin-10 on neuropeptide Y (NPY) and brain-derived neurotrophic factor (BDNF) gene expression and the extracellular dopamine (DA), norepinephrine (NE), serotonin (5-hydroxytriptamine, 5-HT), dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIIA) concentrations in rat hypothalamic (Hypo-E22) cells. Our study showed that kisspeptin-10 in the concentration range 1 nM–10 μM was well tolerated by the Hypo-E22 cell line. Moreover, kisspeptin-10 (100 nM–10 μM) concentration independently increased the gene expression of NPY while BDNF was inhibited only at the concentration of 10 μM. Finally, kisspeptin-10 decreased 5-HT and DA, leaving unaffected NE levels. The inhibitory effect on DA and 5-HT is consistent with the increased peptide-induced DOPAC/DA and 5-HIIA/5-HT ratios. In conclusion, our current findings suggesting the increased NPY together with decreased BDNF and 5-HT activity following kisspeptin-10 would be consistent with a possible orexigenic effect induced by the peptide.

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.