Nitric oxide is a central component in neuropeptide regulation of appetite

Ghrelin Action in the PVH of Male Mice: Accessibility, Neuronal Targets, and CRH Neurons Activation

The hormone ghrelin displays several well-characterized functions, including some with pharmaceutical interest. The receptor for ghrelin, the growth hormone secretagogue receptor (GHSR), is expressed in the hypothalamic paraventricular nucleus (PVH), a critical hub for the integration of metabolic, neuroendocrine, autonomic, and behavioral functions. Here, we performed a neuroanatomical and functional characterization of the neuronal types mediating ghrelin actions in the PVH of male mice. We found that fluorescent ghrelin mainly labels PVH neurons immunoreactive for nitric oxide synthase 1 (NOS1), which catalyze the production of nitric oxide [NO]). Centrally injected ghrelin increases c-Fos in NOS1 PVH neurons and NOS1 phosphorylation in the PVH. We also found that a high dose of systemically injected ghrelin increases the ghrelin level in the cerebrospinal fluid and in the periventricular PVH, and induces c-Fos in NOS1 PVH neurons. Such a high dose of systemically injected ghrelin activates a subset of NOS1 PVH neurons, which do not express oxytocin, via an arcuate nucleus-independent mechanism. Finally, we found that pharmacological inhibition of NO production fully abrogates ghrelin-induced increase of calcium concentration in corticotropin-releasing hormone neurons of the PVH whereas it partially impairs ghrelin-induced increase of plasma glucocorticoid levels. Thus, plasma ghrelin can directly target a subset of NO-producing neurons of the PVH that is involved in ghrelin-induced activation of the hypothalamic-pituitary-adrenal neuroendocrine axis.

Metabolic Hormone Action in the VTA: Reward-Directed Behavior and Mechanistic Insights

Dysfunctional signaling in midbrain reward circuits perpetuates diseases characterized by compulsive overconsumption of rewarding substances such as substance abuse, binge eating disorder, and obesity. Ventral tegmental area (VTA) dopaminergic activity serves as an index for how rewarding stimuli are perceived and triggers behaviors necessary to obtain future rewards. The evolutionary linking of reward with seeking and consuming palatable foods ensured an organism's survival, and hormone systems that regulate appetite concomitantly developed to regulate motivated behaviors. Today, these same mechanisms serve to regulate reward-directed behavior around food, drugs, alcohol, and social interactions. Understanding how hormonal regulation of VTA dopaminergic output alters motivated behaviors is essential to leveraging therapeutics that target these hormone systems to treat addiction and disordered eating. This review will outline our current understanding of the mechanisms underlying VTA action of the metabolic hormones ghrelin, glucagon-like peptide-1, amylin, leptin, and insulin to regulate behavior around food and drugs of abuse, highlighting commonalities and differences in how these five hormones ultimately modulate VTA dopamine signaling.

Ghrelin activates the mesolimbic dopamine system via nitric oxide associated mechanisms in the ventral tegmental area

Besides enhanced feeding, the orexigenic peptide ghrelin activates the mesolimbic dopamine system to cause reward as measured by locomotor stimulation, dopamine release in nucleus accumbens shell (NAcS), and conditioned place preference. Although the ventral tegmental area (VTA) appears to be a central brain region for this ghrelin-reward, the underlying mechanisms within this area are unknown. The findings that the gaseous neurotransmitter nitric oxide (NO) modulate the ghrelin enhanced feeding, led us to hypothesize that ghrelin increases NO levels in the VTA, and thereby stimulates reward-related behaviors. We initially demonstrated that inhibition of NO synthesis blocked the ghrelin-induced activation of the mesolimbic dopamine system. We then established that antagonism of downstream signaling of NO in the VTA, namely sGC, prevents the ability of ghrelin to stimulate the mesolimbic dopamine system. The association of ghrelin to NO was further strengthened by in vivo electrochemical recordings showing that ghrelin enhances the NO release in the VTA. Besides a GABA_B -receptor agonist, known to reduce NO and cGMP, blocks the stimulatory properties of ghrelin. The present series of experiments reveal that ablated NO signaling, through pharmacologically inhibiting the production of NO and/or cGMP, prevents the ability of ghrelin to induced reward-related behaviors.

Inhibition of nitric oxide synthase or cystathionine gamma-lyase abolishes leptin-induced fever in male rats

Leptin is an adipokine that regulates energy balance and immune function. Peripheral leptin administration elicits prostaglandin E₂-dependent fever in rats. The gasotransmitters nitric oxide (NO) and hydrogen sulfide (H₂S) are also involved in lipopolysaccharide (LPS)-induced fever response. However, there is no data in the literature indicating if these gasotransmitters have a role in leptin-induced fever response. Here, we investigate the inhibition of NO and H₂S enzymes neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS), and cystathionine γ-lyase (CSE) in leptin-induced fever response, respectively. Selective nNOS inhibitor 7-nitroindazole (7-NI), selective iNOS inhibitor aminoguanidine (AG), and CSE inhibitor dl-propargylglycine (PAG) were administered intraperitoneally (ip). Body temperature (Tb), food intake, and body mass were recorded in fasted male rats. Leptin (0.5 mg/kg ip) induced a significant increase in Tb, whereas AG (50 mg/kg ip), 7-NI (10 mg/kg ip), or PAG (50 mg/kg ip) caused no changes in Tb. AG, 7-NI, or PAG abolished leptin increase in Tb. Our results highlight the potential involvement of iNOS, nNOS, and CSE in leptin-induced febrile response without affecting anorexic response to leptin in fasted male rats 24 h after leptin injection. Interestingly, all the inhibitors alone had the same anorexic effect induced by leptin. These findings have implications for understanding the role of NO and H₂S in leptin-induced febrile response.

Migraine and obesity: what is the real direction of their association?

INTRODUCTION

In recent decades, studies have addressed the issue of how migraine and obesity are related and have suggested obesity as a risk factor for migraine headache. However, the exact direction of this relationship remains under debate. In this review, the authors summarize the evidence that have suggested migraine as a risk factor for obesity and overweightness.

AREAS COVERED

This article reviews the results of the previous research published on PubMed and Scopus databases (from 2000 to 2020) concerning the association between migraine and obesity to determine the actual direction of their association. Special attention has been given to the common mechanistic pathways involved in the pathophysiology of migraine and obesity.

EXPERT OPINION

The majority of research conducted thus far has considered obesity as a risk factor for migraine. However, because of the cross-sectional design of available research, we cannot be certain of the proposed direction of this association. There is evidence supporting the hypothesis that obesity can serve as a consequence of migraine through the effects of neuropeptides, inflammatory mediators, adipokines, gut microbiota and modifications in eating behavior and lifestyle. However, the real direction of the relationship between migraine and obesity should be further investigated in large prospective studies.

Lipopolysaccharide-induced inflammation increases nitric oxide production in taste buds

Inducible nitric oxide synthase (iNOS) is expressed when cells are induced or stimulated by proinflammatory cytokines and/or bacterial lipopolysaccharide (LPS). iNOS is a downstream gene of the NF-κB pathway. Our previous studies demonstrated that five Nfkb genes are expressed in mouse taste epithelium and taste organoids. However, it is unclear whether activation of the NF-κB pathway could induce iNOS gene expression and increase nitric oxide (NO) production in taste buds. In this study, we investigated the expression of iNOS mRNA and protein after LPS stimulation. Our results showed that a subset of taste bud cells and taste neurons express iNOS proteins after LPS stimulation. In addition, isolated mouse taste epithelium can release NO after exposure to LPS ex vivo. In taste behavioral tests, the NO donor nitroprusside enhanced mouse aversive responses to salty, bitter, and sour taste compounds. The enhanced aversive responses were especially strong for salty taste. In conclusion, our results suggest that iNOS and NO may play a role in the inflammation-associated taste disturbances.

Growth hormone secretagogue receptor signaling in the supramammillary nucleus targets nitric oxide-producing neurons and controls recognition memory in mice

Ghrelin is a stomach-derived hormone that acts via the growth hormone secretagogue receptor (GHSR). Recent evidence suggests that some of ghrelin's actions may be mediated via the supramammillary nucleus (SuM). Not only does ghrelin bind to cells within the mouse SuM, but ghrelin also activates SuM cells and intra-SuM ghrelin administration induces feeding in rats. In the current study, we aimed to further characterize ghrelin action in the SuM. We first investigated a mouse model expressing enhanced green fluorescent protein (eGFP) under the promoter of GHSR (GHSR-eGFP mice). We found that the SuM of GHSR-eGFP mice contains a significant amount of eGFP cells, some of which express neuronal nitric oxide synthase. Centrally-, but not systemically-, injected ghrelin reached the SuM, where it induced c-Fos expression. Furthermore, a 5-day 40% calorie restriction protocol, but not a 2-day fast, increased c-Fos expression in non-eGFP+ cells of the SuM of GHSR-eGFP mice, whereas c-Fos induction by calorie restriction was not observed in GHSR-deficient mice. Exposure of satiated mice to a binge-like eating protocol also increased c-Fos expression in non-eGFP+ cells of the SuM of GHSR-eGFP mice in a GHSR-dependent manner. Finally, intra-SuM-injected ghrelin did not acutely affect food intake, locomotor activity, behavioral arousal or spatial memory but increased recognition memory. Thus, we provide a compelling neuroanatomical characterization of GHSR SuM neurons and its behavioral implications in mice.

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

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

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

The Role of Gasotransmitters in Gut Peptide Actions

Although gasotransmitters nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) receive a bad connotation; in low concentrations these play a major governing role in local and systemic blood flow, stomach acid release, smooth muscles relaxations, anti-inflammatory behavior, protective effect and more. Many of these physiological processes are upstream regulated by gut peptides, for instance gastrin, cholecystokinin, secretin, motilin, ghrelin, glucagon-like peptide 1 and 2. The relationship between gasotransmitters and gut hormones is poorly understood. In this review, we discuss the role of NO, CO and H₂S on gut peptide release and functioning, and whether manipulation by gasotransmitter substrates or specific blockers leads to physiological alterations.

The Role of the Gut Microbiome, Immunity, and Neuroinflammation in the Pathophysiology of Eating Disorders

There is a growing recognition that both the gut microbiome and the immune system are involved in a number of psychiatric illnesses, including eating disorders. This should come as no surprise, given the important roles of diet composition, eating patterns, and daily caloric intake in modulating both biological systems. Here, we review the evidence that alterations in the gut microbiome and immune system may serve not only to maintain and exacerbate dysregulated eating behavior, characterized by caloric restriction in anorexia nervosa and binge eating in bulimia nervosa and binge eating disorder, but may also serve as biomarkers of increased risk for developing an eating disorder. We focus on studies examining gut dysbiosis, peripheral inflammation, and neuroinflammation in each of these eating disorders, and explore the available data from preclinical rodent models of anorexia and binge-like eating that may be useful in providing a better understanding of the biological mechanisms underlying eating disorders. Such knowledge is critical to developing novel, highly effective treatments for these often intractable and unremitting eating disorders.

Exploiting Common Aspects of Obesity and Alzheimer's Disease

Alzheimer’s disease (AD) is an example of age-related dementia, and there are still no known preventive or curative measures for this disease. Obesity and associated metabolic changes are widely accepted as risk factors of age-related cognitive decline. Insulin is the prime mediator of metabolic homeostasis, which is impaired in obesity, and this impairment potentiates amyloid-β (Aβ) accumulation and the formation of neurofibrillary tangles (NFTs). Obesity is also linked with functional and morphological alterations in brain mitochondria leading to brain insulin resistance (IR) and memory deficits associated with AD. Also, increased peripheral inflammation and oxidative stress due to obesity are the main drivers that increase an individual’s susceptibility to cognitive deficits, thus doubling the risk of AD. This enhanced risk of AD is alarming in the context of a rapidly increasing global incidence of obesity and overweight in the general population. In this review, we summarize the risk factors that link obesity with AD and emphasize the point that the treatment and management of obesity may also provide a way to prevent AD.

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.

Proteomic analysis of hypothalamus and liver proteins affected by dietary l-arginine supplementation in laying hens

The goal of this study was to investigate the influence of l-arginine (l-Arg) supplementation on diet-induced changes in hypothalamus and liver proteome of laying hens. Layers were fed either an isonitrogenous control diet or a l-Arg diet. The test included a 2-week acclimation period and a 12-week experimental period. Eight layers per group were sacrificed at terminal of the experiment underwent 12 fasting. Blood and tissue samples of hypothalamus and liver were collected for further analysis. The levels of serum nitric oxide and hypothalamus neuropeptide Y of layers in l-Arg group were increased in comparison with those in control group. Quantitative proteomic analyses showed that a total of 3,715 hypothalamus proteins (235 differentially expressed) and 3797 liver proteins (373 differentially expressed) were detected between control and l-Arg-fed groups. A further enriched Gene Ontology term analysis of proteins found that 17 hypothalamus proteins (11 upregulated and six downregulated) and 29 liver proteins (14 upregulated and 15 downregulated) were altered differentially between the two groups. Our findings revealed the changes in metabolic and hormonal signals in central nervous system and peripheral tissues by responding to l-Arg feeding, which provides a possible way to gain a better understanding of l-Arg function in laying hens.

NO involvement in the inhibition of ghrelin on voltage-dependent potassium currents in rat hippocampal cells

Ghrelin is a peptide hormone that plays an important role in promoting appetite, regulating distribution and rate of use of energy, cognition, and mood disorders, but the relevant neural mechanisms of these function are still not clear. In this study, we examined the effect of ghrelin on voltage-dependent potassium (K⁺) currents in hippocampal cells of 1-3 days SD rats by whole-cell patch-clamp technique, and discussed whether NO was involved in this process. The results showed that ghrelin significantly inhibited the voltage-dependent K⁺ currents in hippocampal cells, and the inhibitory effect was more significant when l-arginine was co-administered. In contrast, N-nitro- l-arginine methyl ester increased the ghrelin inhibited K⁺ currents and attenuated the inhibitory effect of ghrelin. While d-arginine (D-AA) showed no significant impact on the ghrelin-induced decrease in K⁺ current. These results show that ghrelin may play a physiological role by inhibiting hippocampal voltage dependent K⁺ currents, and the NO pathway may be involved in this process.

Endogenous Nitric Oxide and Dopamine Regulate Feeding Behavior in Neonatal Layer-type Chickens

Evidence from animal studies suggests that endogenous nitric oxide and dopamine (DA) have a regulatory role in the rewarding system, but their interaction(s) have not been studied in avian species. In this study, 4 experiments were performed to determine the effects of central administration of L-arginine (nitric oxide precursor; 200 nmol), NG-nitro-L-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor; 100 nmol), amphetamine (an indirect DA agonist; 125 pmol) and DA (40 pmol) on feeding behavior in neonatal layer-type chickens (each experiment included 4 groups, n=12 birds in each group). Prior to the initiation of the treatments, birds were fasted for 3 hours (FD3). In experiment 1, chickens received intracerebroventricular (ICV) injection of saline, L-NAME (100 nmol), amphetamine (125 pmol), and combination of L-NAME + amphetamine. In experiment 2, chickens received the ICV injection of saline, L-arginine (200 nmol), amphetamine (125 pmol) and their combination. In experiment 3, chickens received ICV injection of saline, L-arginine (200 nmol), DA (40 pmol) and L-arginine + DA. In experiment 4, chickens received ICV injection of saline, L-NAME (100 nmol), DA (40 pmol) and L-NAME + DA. Thereafter, the cumulative food intake (on the basis of metabolic body weight) was recorded until 2-h post injection. The results showed that ICV injection of amphetamine or DA significantly decreased food intake (P<0.05). Also, co-administration of L-NAME + amphetamine attenuated the hypophagic effect of amphetamine (P<0.05), while combined administration of L-NAME and DA had no effect on DA-induced hypophagia. Additionally, the hypophagic effect of amphetamine was significantly amplified by L-arginine (P<0.05), but the combination of L-arginine and DA did not alter feeding behavior which was induced by DA. These results suggest an interaction between DAergic and nitrergic systems via a presynaptic mechanism on food intake regulation in layer-type chicken.

Ghrelin enhances food intake and carbohydrate oxidation in a nitric oxide dependent manner

In the present study we sought to investigate interactions between hypothalamic nitric oxide (NO) and ghrelin signaling on food intake and energy substrate utilization as measured by the respiratory exchange ratio (RER). Guide cannulae were unilaterally implanted in either the arcuate (ArcN) or paraventricular (PVN) nuclei of male Sprague-Dawley rats. Animals were pretreated with subcutaneous (2.5-10mg/kg/ml) or central (0-100pmol) N-nitro-l-Arginine methyl ester (l-NAME) followed by 50pmol of ghrelin administered into either the ArcN or PVN. Both l-NAME and ghrelin were microinjected at the onset of the active cycle and food intake and RER were assessed 2h postinjection. RER was measured as the ratio of the volume of carbon dioxide expelled relative to the volume of oxygen consumed (VCO₂/VO₂) using an open-circuit indirect calorimeter. Our results demonstrated that peripheral and central l-NAME pretreatment dose-dependently attenuated ghrelin induced increases in food intake and RER in either the ArcN or PVN. In fact the 100pmol dose largely reversed the metabolic effects of ghrelin in both anatomical regions. These findings suggest that ghrelin enhancement of food intake and carbohydrate oxidation in the rat ArcN and PVN is NO-dependent.

Hypothalamic expression of inflammatory mediators in an animal model of binge eating

Binge eating episodes are characterized by uncontrollable, distressing eating of a large amount of highly palatable food and represent a central feature of bingeing related eating disorders. Research suggests that inflammation plays a role in the onset and maintenance of eating-related maladaptive behavior. Markers of inflammation can be selectively altered in discrete brain regions where they can directly or indirectly regulate food intake. In the present study, we measured expression levels of different components of cytokine systems (IL-1, IL-6, IL-18, TNF-α and IFN-ɣ) and related molecules (iNOS and COX2) in the preoptic and anterior-tuberal parts of the hypothalamus of a validated animal model of binge eating. In this animal model, based on the exposure to both food restriction and frustration stress, binge-like eating behavior for highly palatable food is not shown when animals are exposed to the frustration stress during the estrus phase. We found a characteristic down-regulation of the IL-18/IL-18 receptor system (with increased expression of the inhibitor of the pro-inflammatory cytokine IL-18, IL-18BP, together with a decreased expression of the binding chain of the IL-18 receptor) and a three-fold increase in the expression of iNOS specifically in the anterior-tuberal region of the hypothalamus of animals that develop a binge-like eating behavior. Differently, when food restricted animals were stressed during the estrus phase, IL-18 expression increased, while iNOS expression was not significantly affected. Considering the role of this region of the hypothalamus in controlling feeding related behavior, this can be relevant in eating disorders and obesity. Our data suggest that by targeting centrally selected inflammatory markers, we may prevent that disordered eating turns into a full blown eating disorder.

Behind melanocortin antagonist overexpression in the zebrafish brain: A behavioral and transcriptomic approach

Melanocortin signaling is regulated by the binding of naturally occurring antagonists, agouti-signaling protein (ASIP) and agouti-related protein (AGRP) that compete with melanocortin peptides by binding to melanocortin receptors to regulate energy balance and growth. Using a transgenic model overexpressing ASIP, we studied the involvement of melanocortin system in the feeding behaviour, growth and stress response of zebrafish. Our data demonstrate that ASIP overexpression results in enhanced growth but not obesity. The differential growth is explained by increased food intake and feeding efficiency mediated by a differential sensitivity of the satiety system that seems to involve the cocaine- and amphetamine- related transcript (CART). Stress response was similar in both genotypes. Brain transcriptome of transgenic (ASIP) vs wild type (WT) fish was compared using microarrays. WT females and males exhibited 255 genes differentially expressed (DEG) but this difference was reduced to 31 after ASIP overexpression. Statistical analysis revealed 1122 DEG when considering only fish genotype but 1066 and 981 DEG when comparing ASIP males or females with their WT counterparts, respectively. Interaction between genotype and sex significantly affected the expression of 97 genes. Several neuronal systems involved in the control of food intake were identified which displayed a differential expression according to the genotype of the fish that unravelling the flow of melanocortinergic information through the central pathways that controls the energy balance. The information provided herein will help to elucidate new central systems involved in control of obesity and should be of invaluable use for sustaining fish production systems.

Nitric Oxide Exerts Basal and Insulin-Dependent Anorexigenic Actions in POMC Hypothalamic Neurons

The arcuate nucleus of the hypothalamus represents a key center for the control of appetite and feeding through the regulation of 2 key neuronal populations, notably agouti-related peptide/neuropeptide Y and proopimelanocortin (POMC)/cocaine- and amphetamine-regulated transcript neurons. Altered regulation of these neuronal networks, in particular the dysfunction of POMC neurons upon high-fat consumption, is a major pathogenic mechanism involved in the development of obesity and type 2 diabetes mellitus. Efforts are underway to preserve the integrity or enhance the functionality of POMC neurons in order to prevent or treat these metabolic diseases. Here, we report for the first time that the nitric oxide (NO(-)) donor, sodium nitroprusside (SNP) mediates anorexigenic actions in both hypothalamic tissue and hypothalamic-derived cell models by mediating the up-regulation of POMC levels. SNP increased POMC mRNA in a dose-dependent manner and enhanced α-melanocortin-secreting hormone production and secretion in mHypoA-POMC/GFP-2 cells. SNP also enhanced insulin-driven POMC expression likely by inhibiting the deacetylase activity of sirtuin 1. Furthermore, SNP enhanced insulin-dependent POMC expression, likely by reducing the transcriptional repression of Foxo1 on the POMC gene. Prolonged SNP exposure prevented the development of insulin resistance. Taken together, the NO(-) donor SNP enhances the anorexigenic potential of POMC neurons by promoting its transcriptional expression independent and in cooperation with insulin. Thus, increasing cellular NO(-) levels represents a hormone-independent method of promoting anorexigenic output from the existing POMC neuronal populations and may be advantageous in the fight against these prevalent disorders.

The interaction of central nitrergic and GABAergic systems on food intake in neonatal layer-type chicks

Most physiological behaviors such as food intake are controlled by the hypothalamus and its nuclei. It has been demonstrated that injection of the paraventricular nucleus of the hypothalamus with nitric oxide (NO) donors elicited changes in the concentration of some amino acids, including GABA. Also, central nitrergic and GABAergic systems are known to provide inputs to the paraventricular nucleus and are involved in food intake control. Therefore, the present study examines the probable interaction of central nitrergic and GABAergic systems on food intake in neonatal layer-type chicks. The results of this study showed that intracerebroventricular (ICV) injection of L-arginine (400 and 800 nmol), as a NO donor, significantly decreased food intake (P < 0.001), but ICV injection of Nω-Nitro-L-arginine methyl ester (L-NAME) (200 and 400 nmol), a NO synthesis inhibitor, increased food intake (P < 0.001). In addition, the orexigenic effect of gaboxadol (0.2 µg), a GABAA agonist, was significantly attenuated in ICV co-injection of L-arginine (200 nmol) and gaboxadol (0.2 µg) (P < 0.001), but it was significantly amplified in ICV co-injection of L-NAME (100 nmol) and gaboxadol (0.2 µg) (P < 0.001). On the other hand, the orexigenic effect of baclofen (0.2 µg), a GABAB agonist, did not change in ICV co-injection of L-arginine (200 nmol) or L-NAME (100 nmol) with baclofen (0.2 µg) (P > 0.05). Also, the hypophagic effect of L-arginine (800 nmol) was significantly amplified in ICV co-injection of picrotoxin (0.5 µg), a GABAA antagonist, or CGP54626 (21 ng), a GABAB antagonist, with L-arginine (800 nmol) (P < 0.001). These results probably suggest an interaction of central nitrergic and GABAergic systems on food intake in neonatal layer-type chicks and GABAA receptors play a major role in this interaction.

Pathophysiology of anorexia in the cancer cachexia syndrome

Anorexia is commonly present in persons with cancer and a major component of cancer cachexia. There are multiple causes of anorexia in cancer. Peripherally, these can be due to (i) substances released from or by the tumour, e.g. pro-inflammatory cytokines, lactate, and parathormone-related peptide; (ii) tumours causing dysphagia or altering gut function; (iii) tumours altering nutrients, e.g. zinc deficiency; (iv) tumours causing hypoxia; (v) increased peripheral tryptophan leading to increased central serotonin; or (vi) alterations of release of peripheral hormones that alter feeding, e.g. peptide tyrosine tyrosine and ghrelin. Central effects include depression and pain, decreasing the desire to eat. Within the central nervous system, tumours create multiple alterations in neurotransmitters, neuropeptides, and prostaglandins that modulate feeding. Many of these neurotransmitters appear to produce their anorectic effects through the adenosine monophosphate kinase/methylmalonyl coenzyme A/fatty acid system in the hypothalamus. Dynamin is a guanosine triphosphatase that is responsible for internalization of melanocortin 4 receptors and prostaglandin receptors. Dynamin is up-regulated in a mouse model of cancer anorexia. A number of drugs, e.g. megestrol acetate, cannabinoids, and ghrelin agonists, have been shown to have some ability to be orexigenic in cancer patients.

Serum nitric oxide metabolites are associated with the risk of hypertriglyceridemic-waist phenotype in women: Tehran Lipid and Glucose Study

BACKGROUND AND AIM

There are some controversial issues regarding the association of nitric oxide and obesity-related states. This study was conducted to investigate whether serum nitric oxide metabolites (NOx) could predict the occurrence of visceral lipid accumulation, defined as hypertriglyceridemic-waist (HTW) phenotype.

METHODS

We used a prospective approach for this study conducted on participants of the Tehran Lipid and Glucose Study, 2243 adult men and women were followed for a median of 6.3 years. Serum NOx concentrations were measured at baseline (2006-2008), and demographics, anthropometrics and biochemical variables were evaluated at baseline and again after a 3-year (2009-2011) and a 6-year follow-up (2012-2014). The occurrence of HTW phenotype, defined as waist circumference ≥90 cm in men and ≥85 cm in women, along with serum triglyceride levels ≥177 mg/dL, were assessed across serum NOx tertiles.

RESULTS

Mean age of participants was 41.5 ± 14.5 years at baseline and 39.4% were male. The cumulative incidence of HTW phenotype was 37.6% (33.2% in men, 40.5% in women). There was no significant association between serum NOx and the occurrence of HTW phenotype in men. After adjustment of confounding variables, risk of HTW phenotype in women, in the highest compared to the lowest tertile of serum NOx (≥30.9 vs. <19.9 μmol/L), increased by 39% (OR = 1.39, 95% CI = 1.05-1.93, P for trend = 0.053).

CONCLUSION

Serum NOx level was an independent predictor of HTW phenotype in women.

Endocannabinoid and nitric oxide interaction mediates food intake in neonatal chicken

The aim of the current study was to investigate the interaction of the nitric oxide and cannabinoidergic systems on feeding behaviour in neonatal chicken. A total of 6 experiments were designed to evaluate the interaction between cannabinoidergic and nitrergic systems on food intake in 3-h food-deprived (FD3) neonatal chickens. In Experiment 1, chickens received intracerebroventricular (ICV) injections of saline, 2-arachidonoylglycerol (2-AG) (a CB1 receptor agonist, 2 µg), l-arginine (nitric oxide precursor, 200 nmol) and co-administration of 2-AG + l-arginine. In Experiment 2, ICV injection of saline, 2-AG (2 µg), l-NAME (a nitric oxide synthesis inhibitor, 100 nmol) and their combination (2-AG + l-NAME) were applied to the birds. In Experiment 3, injections were saline, CB65 (a CB2 receptor agonist, 1.25 µg), l-arginine (200 nmol) and CB65 + l-arginine. In Experiment 4, birds received ICV injection of saline, CB65 (1.25 µg), l-NAME (100 nmol) and CB65 + l-NAME. In Experiment 5, chickens were ICV injected with saline, l-arginine (800 nmol), SR141716A (a selective CB1 receptor antagonist, 6.25 µg) and l-arginine + SR141716A. In Experiment 6, birds were injected with saline, l-arginine (800 nmol), AM630 (a selective CB2 receptor antagonist, 5 µg) and l-arginine + AM630. Cumulative food intake was recorded until 2-h post injection. ICV injection of CB1 and CB2 receptor agonists increased food intake. Co-injection of 2-AG + l-NAME increased the hyperphagic effects of CB1 receptors. CB2 receptor-induced food intake was not affected by co-administration of CB65 + l-NAME. l-Arginine decreased food intake and this effect was amplified by co-injection of l-arginine + SR141716A. However; CB2 receptor antagonists had no effect on l-arginine-induced hypophagia. The results suggest that there is an interaction between endogenous nitric oxide and the cannabinoidergic system on feeding behaviour which is mediated via CB1 receptors in the neonatal chicken.

Modulation of opioid-induced feeding behavior by endogenous nitric oxide in neonatal layer-type chicks

The current study was designed to evaluate the effects of central administration of L-arginine (The precursor of nitric oxide), N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, selective opioid receptor agonists and involvement of central nitrergic/opioidergic systems on feeding behavior in neonatal layer-type chicks. The results of this study showed that the intracerebroventricular (ICV) injection of L-arginine (400 and 800 nmol) significantly decreased food intake (P < 0.001) but the injection of 200 nmol L-arginine had no effect on cumulative food intake in FD3 chickens (P > 0.05). The ICV injection of L-NAME (200 and 400 nmol) increased food intake (P < 0.001) but 100 nmol of L-NAME had no significant effect (P > 0.05). On the other hand, the co-injection of 100 nmol L-NAME significantly attenuated the anorexigenic effect of 800 nmol L-arginine (P < 0.001). Moreover, the food intake of chicks was significantly decreased by ICV injection of DAMGO (μ-opioid receptor agonist, 125 pmol) (P < 0.001) while both DPDPE (δ-opioid receptor agonist, 40 pmol) and U-50488H (κ-opioid receptor agonist, 30 nmol) significantly stimulated food intake (P < 0.001). In addition, the hypophagic effect of DAMGO was significantly amplified by administration of L-arginine (P < 0.001) while the administration of L-NAME attenuated the hypophagic effect of DAMGO (P < 0.001). In contrast, co-injection of L-arginine or L-NAME with DPDPE had no effect on the hyperphagia induced by DPDPE as well as the hyperphagic effect of U-50488H on food intake was not affected by concurrent injection of L-arginine or L-NAME (P > 0.05). These results suggest that nitrergic and opioidergic systems have an important role on feeding behavior in the CNS of neonatal layer-type chicks and it seems that interaction between them is mediated by μ-opioid receptor.

Acute hypothalamic administration of L-arginine increases feed intake in rats

Objective: This study investigated the chronic (oral) and acute (hypothalamic infusion) effects of L-arginine supplementation on feed intake, body composition, and behavioral changes in rats. Methods: Twenty rats were divided into two groups treated orally for 60 days; one group received L-arginine (1 g/kg body weight) and one group received saline (1 mL/NaCl 0.9%). Daily consumption of water and food were evaluated, and weight monitored. After the oral treatment, the rats underwent stereotactic biopsy and a group was injected with 2 µL of L-arginine (0.5 mM) and another received an injection of saline (0.9% NaCl), in the hypothalamic route, through micro infusion. Immediately after micro infusion, the animal behavior was evaluated through tests in the open field. Food and water consumption were evaluated at 12 and 24 hours after the micro infusion. Daily water consumption and weight gain evolution were evaluated. At the end of treatments, rats were euthanized and blood was collected for glucose, glycerol, and cholesterol evaluation, and histological analysis of vital organs. Results: Oral supplementation with L-arginine increased water intake (11%, p<0.05) and promoted weight gain (3%, p<0.05). However, hypothalamic infusion promoted a significant increase in chow intake (30%, p<0.05) after 24 hours of L-arginine administration. Conclusion: Chronic oral treatment with L-arginine was not effective on appetite modulation; however, an effect was observed when L-arginine was administered directly into the hypothalamus, suggesting a central regulation on appetite through nNOS sensitization. Chronic use of L-arginine did not cause substantial changes in anthropometric, biochemical, behavioral, or histological variables.

Effect of anorexigenic peptide obestatin on platelet aggregation and osmotic resistance of erythrocytes

We studied the effects of the anorexigenic peptide obestatin on the coagulation system and blood rheology (by the parameters of platelet aggregation and osmotic resistance of erythrocytes) in vitro and in vivo. Obestatin inhibited in vitro platelet aggregation in the entire dose range and reduced osmotic resistance of erythrocytes in all doses except 300 nmol/kg (obestatin in a dose of 300 nmol/kg had no effect on this parameter). Similar to the results of in vitro experiments, intranasal, intraperitoneal, and subcutaneous administration of obestatin in a dose of 300 nmol/kg inhibited platelet aggregation and had no effect on the osmotic resistance of erythrocytes.

Diet-dependent modulation of gastro-oesphageal vagal afferent mechanosensitivity by endogenous nitric oxide

Neuronal nitric oxide (NO) plays an important role in gastric motor activity and modulates the mechanosensitivity of gastro-oesophageal vagal afferents. Effects of NO on food intake are dependent on feeding status. We sought to determine the effect of NO on gastro-oesophageal vagal afferent activity in the normally fed and food-restricted states and the second messenger pathways mediating these effects. Eight week old female C56BL/6 mice were fed ad libitum or food restricted for 14 h. An in vitro preparation was used to determine the functional effects of NO and the second messenger pathways involved. Expression of NO signal transduction molecules in vagal afferents was determined by reverse-transcription polymerase chain reaction (RT-PCR). Endogenous NO and the NO donor S-nitroso-N-acetylpenicillamine (SNAP) inhibited vagal mucosal afferent responses to tactile stimuli in mice fed ad libitum. After a 14 h fast endogenous NO and SNAP potentiated tension and mucosal afferent responses to mechanical stimulation. The excitatory effect of NO was blocked by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin. After a 14 h fast expression of NADPH oxidase 2 (NOX2) mRNA in whole nodose ganglia was significantly reduced and the excitatory effect of NO on gastro-oesophageal vagal afferents was lost. Under fasting conditions the inhibitory effect of NO was blocked with the hyperpolarisation-activated cyclic nucleotide-gated (HCN) channel blocker ivabradine and mRNA expression of HCN3 in the nodose ganglia was elevated. In conclusion, the role of NO in the peripheral modulation of gastro-oesophageal vagal afferents is dynamic and dependent on feeding status.

Role of ghrelin in fertilization, early embryo development, and implantation periods

In order to clarify the physiological role of ghrelin in gestation, we evaluated the effects of administration of exogenous ghrelin (2 or 4 nmol/animal per day) or its antagonist (6 nmol/animal per day of (d-Lys3)GHRP6) on fertilization, early embryo development, and implantation periods in mice. Three experiments were performed, treating female mice with ghrelin or its antagonist: i) starting from 1 week before copulation to 12 h after copulation, mice were killed at day 18 of gestation; ii) since ovulation induction until 80 h later, when we retrieved the embryos from oviducts/uterus, and iii) starting from days 3 to 7 of gestation (peri-implantation), mice were killed at day 18. In experiments 1 and 3, the antagonist and/or the highest dose of ghrelin significantly increased the percentage of atrophied fetuses and that of females exhibiting this finding or a higher amount of corpora lutea compared with fetuses (nCL/nF) (experiment 3: higher nCL/nF-atrophied fetuses: ghrelin 4, 71.4-71.4% and antagonist, 75.0-62.5% vs ghrelin 2, 46.2-15.4% and control, 10-0.0%; n=7-13 females/group; P<0.01). In experiment 2, the antagonist diminished the fertilization rate, and both, ghrelin and the antagonist, delayed embryo development (blastocysts: ghrelin 2, 62.5%; ghrelin 4, 50.6%; and antagonist, 61.0% vs control 78.4%; n=82-102 embryos/treatment; P<0.0001). In experiment 3, additionally, ghrelin (4 nmol/day) and the antagonist significantly diminished the weight gain of fetuses and dams during pregnancy. Our results indicate that not only hyperghrelinemia but also the inhibition of the endogenous ghrelin effects exerts negative effects on the fertilization, implantation, and embryo/fetal development periods, supporting the hypothesis that ghrelin (in 'adequate' concentrations) has a physiological role in early gestational events.

The role of nitric oxide signaling in food intake; insights from the inner mitochondrial membrane peptidase 2 mutant mice

Reactive oxygen species have been implicated in feeding control through involvement in brain lipid sensing, and regulating NPY/AgRP and pro-opiomelanocortin (POMC) neurons, although the underlying mechanisms are unclear. Nitric oxide is a signaling molecule in neurons and it stimulates feeding in many species. Whether reactive oxygen species affect feeding through interaction with nitric oxide is unclear. We previously reported that Immp2l mutation in mice causes excessive mitochondrial superoxide generation, which causes infertility and early signs of aging. In our present study, reduced food intake in mutant mice resulted in significantly reduced body weight and fat composition while energy expenditure remained unchanged. Lysate from mutant brain showed a significant decrease in cGMP levels, suggesting insufficient nitric oxide signaling. Thus, our data suggests that reactive oxygen species may regulate food intake through modulating the bioavailability of nitric oxide.

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Mature adult Immp2l mutant mice have reduced body weight and fat composition.

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Reduced body weight and fat composition is caused by reduced food intake.

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Energy expenditure is not affected in mutant mice.

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Brain cGMP level is lower in mutant mice.

Dietary arginine from 15 to 35 days of age affects feed intake and carcass yield in White Pekin ducks

An experiment was conducted to investigate the effect of dietary arginine (ARG) provided from 15 to 35 days of age on the feed intake and carcass yield of White Pekin ducks. Sixty 14-day-old White Pekin ducks were allotted to one of three dietary treatments, with 10 males and 10 females per treatment. Birds were kept individually and fed diets containing 0.60, 0.85 or 1.70% ARG for 3 weeks. Ducks that were fed the diet containing 1.70% ARG had greater bodyweight gain (P < 0.05), higher feed intake (P < 0.05), and a lower feed conversion ratio (P < 0.05) than those fed the diet containing 0.60% ARG. The hypothalamic contents of neuropeptide Y and leptin at 35 days of age were not affected by dietary ARG levels. Breast muscle yield increased with each increment of dietary ARG content (P < 0.05), and birds fed the diet containing 1.70% ARG had highest leg muscle yield (P < 0.05) and total muscle yield (P < 0.05); in contrast, the abdominal fat yield was not affected (P > 0.05) by dietary ARG. No interaction between dietary ARG level and sex was observed for the above mentioned indices (P > 0.05). In conclusion, dietary ARG supplementation promoted appetite without changing the concentrations of neuropeptide Y or leptin in hypothalamus, and ARG supplementation stimulated muscle growth, especially breast muscle growth, in growing White Pekin ducks of both sexes.

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

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

Lipopolysaccharide inhibits ghrelin-excited neurons of the arcuate nucleus and reduces food intake via central nitric oxide signaling

Lipopolysaccharide (LPS) induces anorexia and expression of inducible nitric oxide synthase (iNOS) in the hypothalamic arcuate nucleus (Arc). Peripheral administration of the iNOS inhibitor 1400 W counteracts the anorectic effects of LPS. Here we investigated the role of central NO signaling in LPS anorexia. In electrophysiological studies we tested whether 1400 W counteracts the iNOS-dependent inhibition of Arc neurons triggered by in vivo or in vitro stimulation with LPS. We used the hormone ghrelin as a functional reference stimulus because ghrelin is known to activate orexigenic Arc neurons. Further, we investigated whether in vitro LPS stimulation induces an iNOS-mediated formation of the second messenger cGMP. Since the STAT1 pathway contributes to the regulation of iNOS expression we investigated whether LPS treatment induces STAT1 phosphorylation in the Arc. Finally we tested the effect of intracerebroventricular injection of 1400 W on LPS-induced anorexia. Superfusion with 1400 W (10(-4) M) increased neuronal activity in 37% of neurons in Arc slices from LPS treated (100 μg/kg ip) but not from saline treated rats. Similarly, 1400 W excited 45% of Arc neurons after in vitro stimulation with LPS (100 ng/ml). In both approaches, a considerable percentage of 1400 W sensitive neurons were excited by ghrelin (10(-8)M; 50% and 75%, respectively). In vitro stimulation with LPS induced cGMP formation in the Arc, which was blocked by co-incubation with 1400 W. LPS treatment elicited a pSTAT1 response in the Arc of mice. Central 1400 W injection (4 μg/rat) attenuated LPS-induced anorexia and counteracted the LPS-dependent decrease in respiratory quotient and energy expenditure. In conclusion, the current findings substantiate a role of central iNOS dependent NO formation in LPS-induced effects on eating and energy homeostasis. A pharmacological blockade of NO formation might be a therapeutic approach to ameliorate disease-related anorexia.

Peripheral neural targets in obesity

Interest in pharmacological treatments for obesity that act in the brain to reduce appetite has increased exponentially over recent years, but failures of clinical trials and withdrawals due to adverse effects have so far precluded any success. Treatments that do not act within the brain are, in contrast, a neglected area of research and development. This is despite the fact that a vast wealth of molecular mechanisms exists within the gut epithelium and vagal afferent system that could be manipulated to increase satiety. Here we discuss mechano- and chemosensory pathways from the gut involved in appetite suppression, and distinguish between gastric and intestinal vagal afferent pathways in terms of their basic physiology and activation by enteroendocrine factors. Gastric bypass surgery makes use of this system by exposing areas of the intestine to greater nutrient loads resulting in greater satiety hormone release and reduced food intake. A non-surgical approach to this system is preferable for many reasons. This review details where the opportunities may lie for such approaches by describing nutrient-sensing mechanisms throughout the gastrointestinal tract.

Hyperleptinemia in obese adolescents deregulates neuropeptides during weight loss

Leptin has emerged over the past decade as a key hormone not only in energy balance regulation but also in neuroendocrine and inflammatory processes. The aim of the present study was to evaluate whether hyperleptinemia deregulates neuropeptides during weight loss. A total of 86 post-pubertal obese adolescents (with or without hyperleptinemia) participated in one year of interdisciplinary weight loss therapy (clinical, nutritional, psychological and exercise-related). Adipokine and neuropeptide concentrations were measured by ELISA, visceral fat was measured by ultrasound and body composition was measured by pletismography. The hyperleptinemic patients presented a lower alpha-MSH concentration and higher NPY/AgRP ratio while the adiponectin/leptin (A/L) ratio was lower compared with the non-hyperleptinemic group. After therapy, significant improvements in BM, BMI, body fat mass, visceral and subcutaneous fat, HOMA-IR, QUICKI, total cholesterol and triglycerides were observed in both groups. Indeed, we observed significant increases in adiponectin and A/L as well as reductions in leptin and NPY/AgRP ratio in the hyperleptinemic group. In the stepwise multiple linear regression analysis with leptin concentration as the dependent variable, α-MSH and body fat mass (%) were the independent predictors to explain leptin concentration. For the entire group, we found positive correlations between leptinemia and BMI and body fat mass (%) as well as a negative correlation with free fat mass (%) and alpha-MSH. Finally, we verified negative correlations between adiponectin/leptin ratio with total cholesterol and LDL-c, only in hyperleptinemic patients. In conclusion, the hyperleptinemia in obese adolescents deregulates neuropeptides during weight loss.