Synergistic interaction between neuropeptide Y1 and Y5 receptor pathways in regulation of energy homeostasis

Hormonal Gut-Brain Signaling for the Treatment of Obesity

The brain, particularly the hypothalamus and brainstem, monitors and integrates circulating metabolic signals, including gut hormones. Gut-brain communication is also mediated by the vagus nerve, which transmits various gut-derived signals. Recent advances in our understanding of molecular gut-brain communication promote the development of next-generation anti-obesity medications that can safely achieve substantial and lasting weight loss comparable to metabolic surgery. Herein, we comprehensively review the current knowledge about the central regulation of energy homeostasis, gut hormones involved in the regulation of food intake, and clinical data on how these hormones have been applied to the development of anti-obesity drugs. Insight into and understanding of the gut-brain axis may provide new therapeutic perspectives for the treatment of obesity and diabetes.

Heterozygous Genetic Variants in Autosomal Recessive Genes of the Leptin-Melanocortin Signalling Pathway Are Associated With the Development of Childhood Obesity

Monogenic obesity is a severe, genetically determined disorder that affects up to 1/1000 newborns. Recent reports on potential new therapeutics and innovative clinical approaches have highlighted the need for early identification of individuals with rare genetic variants that can alter the functioning of the leptin-melanocortin signalling pathway, in order to speed up clinical intervention and reduce the risk of chronic complications. Therefore, next-generation DNA sequencing of central genes in the leptin-melanocortin pathway was performed in 1508 children and adolescents with and without obesity, aged 2-19 years. The recruited cohort comprised approximately 5% of the national paediatric population with obesity. The model-estimated effect size of rare variants in the leptin-melanocortin signalling pathway on longitudinal weight gain between carriers and non-carriers was derived. In total, 21 (1.4%) participants had known disease-causing heterozygous variants (DCVs) in the genes under investigation, and 62 (4.1%) participants were carriers of rare variants of unknown clinical significance (VUS). The estimated frequency of potential genetic variants associated with obesity (including rare VUS) ranged between 1/150 (VUS and DCV) and 1/850 (DCV) and differed significantly between participants with and without obesity. On average, the variants identified would result in approximately 7.6 kg (7.0-12.9 kg at the 95th percentile of body weight) (girls) and 8.4 kg (8.2-14.4 kg) (boys) of additional weight gain in carriers at age 18 years compared with subjects without obesity. In conclusion, children with a genetic predisposition to obesity can be promptly identified and may account for more than 6% of obesity cases. Early identification of genetic variants in the LEPR, PCSK1, POMC, MC3R and MC4R genes could reduce the societal burden and improve the clinical management of early severe childhood obesity and its implementation should be further investigated.

Sex differences in behavioral and metabolic effects of gene inactivation: The neuropeptide Y and Y receptors in the brain

Brain and gonadal hormones interplay controls metabolic and behavioral functions in a sex-related manner. However, most translational neuroscience research related to animal models of endocrine and psychiatric disorders are often carried out in male animals only. The Neuropeptide Y (NPY) system shows sex-dependent differences and is sensitive to gonadal steroids. Based on published data from our and other laboratories, in this review we will discuss the sex related differences of NPY action on energy balance, bone homeostasis and behavior in rodents with the genetic manipulation of genes encoding NPY and its Y1, Y2 and Y5 cognate receptors. Comparative analyses of the phenotype of transgenic and knockout NPY and Y receptor rodents unravels sex dependent differences in the functions of this neurotransmission system, potentially helping to develop therapeutics for a variety of sex-related disorders including metabolic syndrome, osteoporosis and ethanol addiction.

Multi-Target Drugs Against Metabolic Disorders

BACKGROUND

Metabolic disorders are a major cause of illness and death worldwide. Metabolism is the process by which the body makes energy from proteins, carbohydrates, and fats; chemically breaking these down in the digestive system towards sugars and acids which constitute the human body's fuel for immediate use, or to store in body tissues, such as the liver, muscles, and body fat.

OBJECTIVE

The efficiency of treatments for multifactor diseases has not been proved. It is accepted that to manage multifactor diseases, simultaneous modulation of multiple targets is required leading to the development of new strategies for discovery and development of drugs against metabolic disorders.

METHODS

In silico studies are increasingly being applied by researchers due to reductions in time and costs for new prototype synthesis; obtaining substances that present better therapeutic profiles.

DISCUSSION

In the present work, in addition to discussing multi-target drug discovery and the contributions of in silico studies to rational bioactive planning against metabolic disorders such as diabetes and obesity, we review various in silico study contributions to the fight against human metabolic pathologies.

CONCLUSION

In this review, we have presented various studies involved in the treatment of metabolic disorders; attempting to obtain hybrid molecules with pharmacological activity against various targets and expanding biological activity by using different mechanisms of action to treat a single pathology.

Pathophysiology and Individualized Treatment of Hypothalamic Obesity Following Craniopharyngioma and Other Suprasellar Tumors: A Systematic Review

The development of hypothalamic obesity (HO) following craniopharyngioma (CP) and other suprasellar tumors leads to reduced patient quality of life. No treatment algorithms are currently available for management of HO. Depending on which hypothalamic nuclei are destroyed, the pathophysiologic mechanisms and clinical symptoms that contribute to HO differ among patients. Herein, we review the contribution of the hypothalamus to the pathophysiologic mechanisms and symptoms underlying CP-associated HO. Additionally, we performed a systematic search of MEDLINE and Embase to identify all intervention studies for weight management in patients with CP or other suprasellar tumors published until September 2017. The search yielded 1866 publications, of which 40 were included. Of these 40 studies, we identified four modalities for intervention (i.e., lifestyle, dietary, pharmacotherapeutic, or surgical) within six clinical domains (i.e., psychosocial disorders, hyperphagia, sleep disturbances, decreased energy expenditure, hyperinsulinemia, and hypopituitarism). We used the findings from our systematic review, in addition to current knowledge on the pathophysiology of HO, to develop an evidence-based treatment algorithm for patients with HO caused by CP or other suprasellar tumors. Although the individual effects of the HO interventions were modest, beneficial individual effects may be achieved when the pathophysiologic background and correct clinical domain are considered. These two aspects can be combined in an individualized treatment algorithm with a stepwise approach for each clinical domain. Recently elucidated targets for HO intervention were also explored to improve future management of HO for patients with CP and other suprasellar tumors.

Adipose Y5R mRNA is higher in obese than non-obese humans and is correlated with obesity parameters

Neuropeptide Y is mainly expressed in the central nervous system to regulate food intake via its receptors, Y receptors, and in various peripheral tissues including adipose tissue. The objectives of this study were to compare Y5R mRNA and adipocyte parameters consisting of area, width, height, and perimeter either between obese and non-obese subjects or between subcutaneous and visceral fat as well as to compare between NPY, Y1R, Y2R, and Y5R mRNA expressions in subcutaneous and visceral adipose tissues. In subcutaneous and visceral adipose tissues, Y5R was greater in obese than in non-obese humans (both P < 0.05). Y1R mRNA expression was highest followed by Y5R, Y2R, and NPY mRNA expressions, respectively, in subcutaneous and visceral adipose tissues. Visceral Y5R mRNA had positive correlations with body weight, body mass index, waist circumference, hip circumference (R ≍ 0.4), and visceral Y1R mRNA (R = 0.773), but had a negative correlation with the quantitative insulin sensitivity check index (R=-0.421) (all P < 0.05). Subcutaneous and visceral adipocyte parameters were positively correlated with body weight, waist circumference, hip circumference, and waist-to-hip ratio, with greater values of correlation coefficient shown in visceral (R ≍ 0.5-0.8) than in subcutaneous adipocytes (R ≍ 0.4-0.6, all P < 0.05). The parameters of visceral adipocytes had positive correlations with serum NPY levels (R ≍ 0.4, all P < 0.05). Y5R mRNA in visceral adipose tissue is related to increased obesity and reduced insulin sensitivity. The dominant Y receptors in subcutaneous and visceral adipose tissue might be the Y1R and Y5R. Visceral adipocytes show higher correlations with obesity parameters than subcutaneous adipocytes, suggestive of an increased risk of metabolic syndrome in visceral obesity. Y1R and Y5R in visceral adipose tissue might be targets of drug development in prevention or treatment of adiposity. Impact statement Obesity, defined as excess fat accumulation, has been increasingly diagnosed worldwide causing adverse health consequences. The novel findings of this study were that Y5R mRNA expression in both subcutaneous and visceral fat was higher in obese than non-obese subjects. Furthermore, Y5R only in visceral fat, not subcutaneous fat, was positively correlated with visceral Y1R and obesity parameters but it was negatively correlated with the QUICKI. Moreover, we found that Y1R expression was highest followed by Y5R and Y2R, respectively, in both subcutaneous and visceral fat. Our results suggested that Y5R in visceral fat was associated with increased obesity and decreased insulin sensitivity. Y1R and Y5R might be the dominant receptors that mediate the effect of NPY-induced fat accumulation in both subcutaneous and visceral adipose tissues. Y1R and Y5R in visceral adipose tissue might be targets of drug development in prevention or treatment of obesity.

Elucidation of the Binding Mode of the Carboxyterminal Region of Peptide YY to the Human Y2 Receptor

Understanding the agonist-receptor interactions in the neuropeptide Y (NPY)/peptide YY (PYY) signaling system is fundamental for the design of novel modulators of appetite regulation. We report here the results of a multidisciplinary approach to elucidate the binding mode of the native peptide agonist PYY to the human Y₂ receptor, based on computational modeling, peptide chemistry and in vitro pharmacological analyses. The preserved binding orientation proposed for full-length PYY and five analogs, truncated at the amino terminus, explains our pharmacological results where truncations of the N-terminal proline helix showed little effect on peptide affinity. This was followed by receptor mutagenesis to investigate the roles of several receptor positions suggested by the modeling. As a complement, PYY-(3-36) analogs were synthesized with modifications at different positions in the common PYY/NPY C-terminal fragment (³²TRQRY³⁶-amide). The results were assessed and interpreted by molecular dynamics and Free Energy Perturbation (FEP) simulations of selected mutants, providing a detailed map of the interactions of the PYY/NPY C-terminal fragment with the transmembrane cavity of the Y₂ receptor. The amidated C-terminus would be stabilized by polar interactions with Gln288^6.55 and Tyr219^5.39, while Gln130^3.32 contributes to interactions with Q³⁴ in the peptide and T³² is close to the tip of TM7 in the receptor. This leaves the core, α-helix of the peptide exposed to make potential interactions with the extracellular loops. This model agrees with most experimental data available for the Y₂ system and can be used as a basis for optimization of Y₂ receptor agonists.

The role of pancreatic polypeptide in the regulation of energy homeostasis

Imbalances in normal regulation of food intake can cause obesity and related disorders. Inadequate therapies for such disorders necessitate better understanding of mechanisms that regulate energy homeostasis. Pancreatic polypeptide (PP), a robust anorexigenic hormone, effectively modulates food intake and energy homeostasis, thus potentially aiding anti-obesity therapeutics. Intra-gastric and intra-intestinal infusion of nutrients stimulate PP secretion from the gastrointestinal tract, leading to vagal stimulation that mediates complex actions via the neuropeptide Y4 receptor in arcuate nucleus of the hypothalamus, subsequently activating key hypothalamic nuclei and dorsal vagal complex of the brainstem to influence energy homeostasis and body composition. Novel studies indicate affinity of PP for the relatively underexplored neuropeptide y6 receptor, mediating actions via the suprachiasmatic nucleus and pathways involving vasoactive intestinal polypeptide and insulin like growth factor 1. This review highlights detailed mechanisms by which PP mediates its actions on energy balance through various areas in the brain.

NPY-Y1 coexpressed with NPY-Y5 receptors modulate anxiety but not mild social stress response in mice

The Y1 and Y5 receptors for neuropeptide Y have overlapping functions in regulating anxiety. We previously demonstrated that conditional removal of the Y1 receptor in the Y5 receptor expressing neurons in juvenile Npy1r(Y5R-/-) mice leads to higher anxiety but no changes in hypothalamus-pituitary-adrenocortical axis activity, under basal conditions or after acute restraint stress. In the present study, we used the same conditional system to analyze the specific contribution of limbic neurons coexpressing Y1 and Y5 receptors on the emotional and neuroendocrine responses to social chronic stress, using different housing conditions (isolation vs. group-housing) as a model. We demonstrated that control Npy1r(2lox) male mice housed in groups show increased anxiety and hypothalamus-pituitary-adrenocortical axis activity compared with Npy1r(2lox) mice isolated for six weeks immediately after weaning. Conversely, Npy1r(Y5R-/-) conditional mutants display an anxious-like behavior but no changes in hypothalamus-pituitary-adrenocortical axis activity as compared with their control littermates, independently of housing conditions. These results suggest that group housing constitutes a mild social stress for our B6129S mouse strain and they confirm that the conditional inactivation of Y1 receptors specifically in Y5 receptor containing neurons increases stress-related anxiety without affecting endocrine stress responses.

Regulation of energy homeostasis by the NPY system

Obesity develops when energy intake exceeds energy expenditure over time. Numerous neurotransmitters, hormones, and factors have been implicated to coordinately control energy homeostasis, centrally and peripherally. However, the neuropeptide Y (NPY) system has emerged as the one with the most critical functions in this process. While NPY centrally promotes feeding and reduces energy expenditure, peptide YY (PYY) and pancreatic polypeptide (PP), the other family members, mediate satiety. Importantly, recent research has uncovered additional functions for these peptides that go beyond the simple feeding/satiety circuits and indicate a more extensive function in controlling energy homeostasis. In this review, we will discuss the actions of the NPY system in the regulation of energy balance, with a particular focus on energy expenditure.

Targeting the Neuropeptide Y System in Stress-related Psychiatric Disorders

Repeated, extreme, or traumatic stressors can elicit pathological effects leading to many negative physical and psychological outcomes. Stressors can precipitate the onset of psychiatric diseases, or exacerbate pre-existing disorders including various anxiety and mood disorders. As stressors can negatively impact human psychiatric health, it is essential to identify neurochemicals that may confer protection from the negative sequelae of repeated or extreme stress exposure. Elucidating the neurobiological underpinnings of stress resilience will enhance our ability to promote resilience to, or recovery from, stress-related psychiatric disease. Herein, we will review the evidence for neuropeptide Y as an endogenous mediator of resilience and its potential relevance for the treatment of stress-related psychiatric diseases.

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Overview of neuropeptide Y and receptor subtypes in the central nervous system.

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Alterations of neuropeptide Y in human stress-related psychiatric disorders.

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Evidence for neuropeptide Y in resilience to stress-related emotionality in rodent behavioral models.

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Pharmacotherapeutic implications for neuropeptide Y in the treatment of stress-related psychiatric disorders.

Conditional inactivation of neuropeptide Y Y1 receptors unravels the role of Y1 and Y5 receptors coexpressing neurons in anxiety

BACKGROUND

The Y1 receptor (Y1R) and Y5 receptor (Y5R) for neuropeptide Y share similar actions in the regulation of anxiety. Previously demonstrated that conditional removal of the Y1R during postnatal development in the forebrain excitatory neurons leads to higher anxiety, increased hypothalamus-pituitary-adrenocortical axis activity, and decreased body growth rate in male mice raised by foster mothers that exhibit high levels of maternal care. In the present study, we used the same conditional system to analyze the specific contribution to emotional behavior and stress response of the Y1R coexpressed with the Y5R.

METHODS

Using the Cre-loxP recombination system, we investigated anxious behavior, spatial memory, and metabolic functions of conditional knockout mice in which the inactivation of the Npy1r gene was induced in the Y5Rs expressing neurons of juvenile mice (Npy1r(Y5R-/-) ).

RESULTS

Npy1r(Y5R-/-) mice show increased anxiety-related behavior but no changes in hypothalamus-pituitary-adrenocortical axis activity or in body weight growth, independently of gender and mouse strain used as foster mothers. Also, Npy1r(Y5R-/-) mice of both genders display increased spatial reference memory in the Morris water maze test.

CONCLUSIONS

The results suggest that neuropeptide Y Y1R differentially expressed in the limbic system regulates anxiety and stress responses via distinct neurochemical circuits. In addition, we provide the first experimental genetic evidence that the Y1Rs coexpressed with the Y5R are involved in retention of spatial memory in male and female mice.

Can neuropeptides treat obesity? A review of neuropeptides and their potential role in the treatment of obesity

Obesity is a major worldwide public health issue. The physiological systems that regulate body weight are thus of great interest as targets for anti-obesity agents. Peptidergic systems are critical to the regulation of energy homeostasis by key regions in the hypothalamus and brainstem. A number of neuropeptide systems have therefore been investigated as potential treatments for obesity. Blocking orexigenic peptide signals such as neuropeptide Y, melanin-concentrating hormone, orexins, relaxin-3 and galanin-like peptide or stimulating anorectic signalling pathways used by peptides such as the melanocortins, ciliary neurotrophic factor and brain-derived neurotrophic factor, are approaches that have shown some promise, but which have also highlighted possible concerns. Manipulation of central peptidergic systems poses a number of therapeutic problems, including brain access and side effects. Given that the homeostatic defence of body weight may limit the effectiveness of any single-target therapy developed, a combination therapy approach may offer the best hope for the effective prevention and treatment of obesity.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

The neuropeptide Y Y1 receptor knockdown modulates activator protein 1-involved feeding behavior in amphetamine-treated rats

BACKGROUND

Hypothalamic neuropeptide Y (NPY) and two immediate early genes, c-fos and c-jun, have been found to be involved in regulating the appetite-suppressing effect of amphetamine (AMPH). The present study investigated whether cerebral catecholamine (CA) might regulate NPY and POMC expression and whether NPY Y1 receptor (Y1R) participated in activator protein-1 (AP-1)-mediated feeding.

METHODS

Rats were given AMPH daily for 4 days. Changes in the expression of NPY, Y1R, c-Fos, c-Jun, and AP-1 were assessed and compared.

RESULTS

Decreased CA could modulate NPY and melanocortin receptor 4 (MC4R) expressions. NPY and food intake decreased the most on Day 2, but Y1R, c-Fos, and c-Jun increased by approximately 350%, 280%, and 300%, respectively, on Day 2. Similarly, AP-1/DNA binding activity was increased by about 180% on Day 2. The expression patterns in Y1R, c-Fos, c-Jun, and AP-1/DNA binding were opposite to those in NPY during AMPH treatment. Y1R knockdown was found to modulate the opposite regulation between NPY and AP-1, revealing an involvement of Y1R in regulating NPY/AP-1-mediated feeding.

CONCLUSIONS

These results point to a molecular mechanism of CA/NPY/Y1R/AP-1 signaling in the control of AMPH-mediated anorexia and may advance the medical research of anorectic and anti-obesity drugs.

Genetic association analysis of 30 genes related to obesity in a European American population

OBJECTIVE

Obesity, which is frequently associated with diabetes, hypertension and cardiovascular diseases, is primarily the result of a net excess of caloric intake over energy expenditure. Human obesity is highly heritable, but the specific genes mediating susceptibility in non-syndromic obesity remain unclear. We tested candidate genes in pathways related to food intake and energy expenditure for association with body mass index (BMI).

METHODS

We reanalyzed 355 common genetic variants of 30 candidate genes in seven molecular pathways related to obesity in 1982 unrelated European Americans from the New York Cancer Project. Data were analyzed by using a Bayesian hierarchical generalized linear model. The BMIs were log-transformed and then adjusted for covariates, including age, age(2), gender and diabetes status. The single-nucleotide polymorphisms (SNPs) were modeled as additive effects.

RESULTS

With the stipulated adjustments, nine SNPs in eight genes were significantly associated with BMI: ghrelin (GHRL; rs35683), agouti-related peptide (AGRP; rs5030980), carboxypeptidase E (CPE; rs1946816 and rs4481204), glucagon-like peptide-1 receptor (GLP1R; rs2268641), serotonin receptors (HTR2A; rs912127), neuropeptide Y receptor (NPY5R;Y5R1c52), suppressor of cytokine signaling 3 (SOCS3; rs4969170) and signal transducer and activator of transcription 3 (STAT3; rs4796793). We also found a gender-by-SNP interaction (rs1745837 in HTR2A), which indicated that variants in the gene HTR2A had a stronger association with BMI in males. In addition, NPY1R was detected as having a significant gene effect even though none of the SNPs in this gene was significant.

CONCLUSION

Variations in genes AGRP, CPE, GHRL, GLP1R, HTR2A, NPY1R, NPY5R, SOCS3 and STAT3 showed modest associations with BMI in European Americans. The pathways in which these genes participate regulate energy intake, and thus these associations are mechanistically plausible in this context.

Inhibiting neuropeptide Y Y1 receptor modulates melanocortin receptor- and NF-κB-mediated feeding behavior in phenylpropanolamine-treated rats

Neuropeptide Y (NPY) and nuclear factor-kappa B (NF-κB) are involved in regulating anorexia elicited by phenylpropanolamine (PPA), a sympathomimetic drug. This study explored whether NPY Y1 receptor (Y1R) is involved in this process, and a potential role for the proopiomelanocortin system was identified. Rats were given PPA once a day for 4days. Changes in the hypothalamic expression of the NPY, Y1R, NF-κB, and melanocortin receptor 4 (MC4R) levels were assessed and compared. The results indicated that food intake and NPY expression decreased, with the largest reductions observed on Day 2 (approximately 50% and 45%, respectively), whereas NF-κB, MC4R, and Y1R increased, achieving maximums on Day 2 (160%, 200%, and 280%, respectively). To determine the role of Y1R, rats were pretreated with Y1R antisense or a Y1R antagonist via intracerebroventricular injection 1h before the daily PPA dose. Y1R knockdown and inhibition reduced PPA anorexia and partially restored the normal expression of NPY, MC4R, and NF-κB. The data suggest that hypothalamic Y1R participates in the appetite-suppression from PPA by regulating MC4R and NF-κB. The results of this study increase our understanding of the molecular mechanisms in PPA-induced anorexia.

New advances in models and strategies for developing anti-obesity drugs

INTRODUCTION

Obesity is a worldwide pandemic. Obesity-related health and economic costs are staggering. Existing strategies to combat obesity through lifestyle improvements and medical intervention have had limited success. Pharmacotherapy, in combination with lifestyle modification, may play a vital role in reversing the disease burden. However, past and current weight-loss medications have had serious safety risks, notably cardiovascular and psychiatric events.

AREAS COVERED

The authors review the strategies for designing new anti-obesity drugs by describing those currently in development. They describe their target, mechanism of action and developmental or regulatory status. Furthermore, they discuss the problem of weight regain following weight loss, and its relevance to the long-term success of anti-obesity pharmacotherapy.

EXPERT OPINION

For weight management drugs to achieve the safety and efficacy required to be impactful, current studies are uncovering and characterizing new targets, including new signaling circuits and hormones regulating appetite and metabolism, and re-evaluating the role of pharmacotherapy in weight management. To avoid the safety failures of many past weight-loss drugs, the models and strategies covered in this article incorporate recent advances in knowledge and technology. We discuss the emergence of cGMP signaling as a potentially transformative target in weight management. Modulating cGMP signaling may represent an ideal goal for an anti-obesity pharmacotherapy, reflecting some of the major themes described in the present review: targeting pathways that are newly realized as relevant for weight management; promoting safety by re-purposing drugs that are safe, proven, and approved for clinical use; and having a synergistic effect on multiple, reinforcing pathways.

Neuropeptide Y Y1 receptor knockdown can modify glutathione peroxidase and c-AMP response element-binding protein in phenylpropanolamine-treated rats

It has been reported that antioxidative enzymes, neuropeptide Y (NPY), and c-AMP response element-binding protein (CREB) are involved in regulating phenylpropanolamine (PPA)-mediated appetite suppression. Here, we investigated whether Y1 receptor (Y1R) might be involved in this regulation. Rats were daily treated with PPA for 4 days. Changes in the contents of NPY, Y1R, glutathione peroxidase (GP), and CREB were assessed and compared. Results showed that Y1R, GP, and CREB increased, with a maximal increase about 100, 200, and 150 %, respectively, on Day 2. By contrast, NPY decreased with a biggest reduction about 48 % on Day 2 and the pattern of expression during PPA treatment was opposite to those of Y1R, GP, and CREB. Central knockdown (using antisense) or inhibition (using antagonist) of Y1R expression modulated the anorectic response of PPA and the reciprocal regulation between NPY and GP (or CREB), revealing an essential role of Y1R in regulating NPY, GP, and CREB. These results suggest that Y1R participates in the reciprocal regulation of NPY, GP, and CREB in the hypothalamus during PPA treatment in conscious rats. The present results may aid the therapeutic research of PPA and related antiobesity drugs.

Mechanisms underlying current and future anti-obesity drugs

Regulation of body weight is organized by distributed brain circuits that use a variety of neuropeptides and transmitters, and that are responsive to endocrine and metabolic signals. Targeting of these circuits with novel pharmaceutical drugs would be helpful additions to lifestyle interventions for the treatment of obesity. The recent FDA approval of two anti-obesity drugs holds promise in a field in which previous drugs were removed from clinical use because of unacceptable psychiatric and cardiovascular side effects. Here, the modes of action of anti-obesity drugs are reviewed.

The identification of neuropeptide Y receptor subtype involved in phenylpropanolamine-induced increase in oxidative stress and appetite suppression

Hypothalamic neuropeptide Y (NPY) and superoxide dismutase (SOD) have been reported to participate in the regulation of appetite-suppressing effect of phenylpropanolamine (PPA), a sympathomimetic agent. This study explored whether Y1 receptor (Y1R) and/or Y5 receptor (Y5R) was involved in this regulation. Wistar rats were treated with PPA for 24 h. Changes in food intake and hypothalamic NPY, Y1R, Y5R, and SOD contents were assessed and compared. Results showed that food intake and NPY contents were decreased following PPA treatment, while Y1R and SOD contents were increased and Y5R contents remained unchanged. Moreover, although Y1R or Y5R knockdown by themselves could modify the food intake, Y1R but not Y5R knockdown could modify PPA-induced anorexia as well as NPY and SOD contents. In addition, selective inhibition of Y1R but not Y5R could modulate PPA-induced anorexia. It is suggested that Y1R but not Y5R participates in the anorectic response of PPA via the modulation of NPY and SOD. Results provide molecular mechanism of NPY-mediated PPA anorexia and may aid the understanding of the toxicology of PPA.

Obesity pharmacotherapy: what is next?

The increase in obesity in the Unites States and around the world in the last decade is overwhelming. The number of overweight adults in the world surpassed 1 billion in 2008. Health hazards associated with obesity are serious and include heart disease, sleep apnea, diabetes, and cancer. Although lifestyle modifications are the most straightforward way to control weight, a large portion of the population may not be able to rely on this modality alone. Thus, the development of anti-obesity therapeutics represents a major unmet medical need. Historically, anti-obesity pharmacotherapies have been unsafe and minimally efficacious. A better understanding of the biology of appetite and metabolism provides an opportunity to develop drugs that may offer safer and more effective alternatives for weight management. This review discusses drugs that are currently on the market and in development as anti-obesity therapeutics based on their target and mechanism of action. It should serve as a roadmap to establish expectations for the near future for anti-obesity drug development.

Regulation of appetite to treat obesity

Obesity has escalated into a pandemic over the past few decades. In turn, research efforts have sought to elucidate the molecular mechanisms underlying the regulation of energy balance. A host of endogenous mediators regulate appetite and metabolism, and thereby control both short- and long-term energy balance. These mediators, which include gut, pancreatic and adipose neuropeptides, have been targeted in the development of anti-obesity pharmacotherapy, with the goal of amplifying anorexigenic and lipolytic signaling or blocking orexigenic and lipogenic signaling. This article presents the efficacy and safety of these anti-obesity drugs.

Regulation of hindbrain Pyy expression by acute food deprivation, prolonged caloric restriction, and weight loss surgery in mice

PYY is a gut-derived putative satiety signal released in response to nutrient ingestion and is implicated in the regulation of energy homeostasis. Pyy-expressing neurons have been identified in the hindbrain of river lamprey, rodents, and primates. Despite this high evolutionary conservation, little is known about central PYY neurons. Using in situ hybridization, PYY-Cre;ROSA-EYFP mice, and immunohistochemistry, we identified PYY cell bodies in the gigantocellular reticular nucleus region of the hindbrain. PYY projections were present in the dorsal vagal complex and hypoglossal nucleus. In the hindbrain, Pyy mRNA was present at E9.5, and expression peaked at P2 and then decreased significantly by 70% at adulthood. We found that, in contrast to the circulation, PYY-(1-36) is the predominant isoform in mouse brainstem extracts in the ad libitum-fed state. However, following a 24-h fast, the relative amounts of PYY-(1-36) and PYY-(3-36) isoforms were similar. Interestingly, central Pyy expression showed nutritional regulation and decreased significantly by acute starvation, prolonged caloric restriction, and bariatric surgery (enterogastroanastomosis). Central Pyy expression correlated with body weight loss and circulating leptin and PYY concentrations. Central regulation of energy metabolism is not limited to the hypothalamus but also includes the midbrain and the brainstem. Our findings suggest a role for hindbrain PYY in the regulation of energy homeostasis and provide a starting point for further research on gigantocellular reticular nucleus PYY neurons, which will increase our understanding of the brain stem pathways in the integrated control of appetite and energy metabolism.

Involvement of neuropeptide Y Y1 receptor in the regulation of amphetamine-mediated appetite suppression

Recently, we reported that an initial decrease followed by recovery of food intake was observed during four days of amphetamine (AMPH) treatment and suggested that these changes in response were mediated by changes in neuropeptide Y (NPY) and proopiomelanocortin (POMC). Here we investigated if Y1 receptor (Y1R) and/or Y5 receptor (Y5R) might be involved in this regulation. Rats were treated daily with AMPH for four days. Changes in the expression levels of Y1R, Y5R, melanocortin receptor 3 (MC3R), and NPY were assessed and compared. Results showed that Y1R and MC3R increased, with a maximal increase of about 210% on Day 2 but with a restoration to the normal level on Day 4. In contrast, NPY decreased with a biggest reduction of about 45% on Day 2 and the pattern of expression during AMPH treatment was opposite to those of Y1R and MC3R, while the expression of Y5R was not changed. Central inhibitions of NPY formation or Y1R activity modulated the anorectic response of AMPH and the reciprocal regulation of NPY and MC3R, revealing a crucial role of Y1R in this action. It is suggested that Y1R participates in the reciprocal regulation of NPY- and MC3R-containing neurons in the hypothalamus during the anorectic effect of AMPH. These results may further the understanding of Y1R in the control of eating.

A role for neuropeptide Y Y5 but not the Y1-receptor subtype in food deprivation-induced reinstatement of heroin seeking in the rat

RATIONAL AND OBJECTIVES

Neuropeptide Y (NPY), an orexigenic peptide that is released during periods of food restriction, has been shown to have a significant modulatory impact on drug-related behaviors. We have previously reported that both acute food deprivation (FD) and NPY injections can reinstate extinguished drug-seeking behavior, a proposed animal model of relapse to drug abuse. However, it is not clear whether the FD effect on drug seeking is dependent on NPY transmission. Here, we used the reinstatement model to assess the role of NPY Y1 and Y5-receptor-mediated transmission in FD-induced reinstatement of heroin seeking.

METHODS

Rats were trained to self-administer heroin for 10-12 days (0.1 mg/kg/infusion/intravenous). Animals then underwent extinction training followed by drug-seeking reinstatement tests under 21 h of FD and sated conditions.

RESULTS

Injections of a novel NPY Y5-receptor antagonist, Lu AA33810 (0.0, 1.0, or 30.0 mg/kg/IP), resulted in a significant attenuation of FD-induced reinstatement of extinguished heroin seeking. However, no significant effects on reinstatement were found for the Y1-receptor antagonist, BIBO 3304 (0.0, 5.0, or 10.0 nmol/intracerebroventricular).

CONCLUSIONS

These results suggest that while signals mediated through NPY Y1 receptors play a modest role in reinstatement, activation of Y5 receptors has a critical function in FD-induced reinstatement of heroin-seeking behavior.

NPY receptors as potential targets for anti-obesity drug development

The neuropeptide Y system has proven to be one of the most important regulators of feeding behaviour and energy homeostasis, thus presenting great potential as a therapeutic target for the treatment of disorders such as obesity and at the other extreme, anorexia. Due to the initial lack of pharmacological tools that are active in vivo, functions of the different Y receptors have been mainly studied in knockout and transgenic mouse models. However, over recent years various Y receptor selective peptidic and non-peptidic agonists and antagonists have been developed and tested. Their therapeutic potential in relation to treating obesity and other disorders of energy homeostasis is discussed in this review.

Peptides and their potential role in the treatment of diabetes and obesity

It is estimated that 347 million people worldwide have diabetes and that over 1.5 billion adults worldwide are overweight. Predictions suggest these rates are increasing. Diabetes is a common complication in overweight and obese subjects, and in 2004, an estimated 3.4 million people died from consequences of high blood sugar. Thus, there is great interest in revealing the physiological systems that regulate body weight and blood sugar. Several peptidergic systems within the central nervous system and the periphery regulate energy homeostasis. A number of these systems have been investigated as potential treatments for obesity and the metabolic syndrome. However, manipulation of peptidergic systems poses many problems. This review discusses the peptidergic systems currently attracting research interest for their clinical potential to treat obesity. We consider first neuropeptides in the brain, including the orexigenic neuropeptide Y and melanin-concentrating hormone, and anorectic factors such as the melanocortins, ciliary neurotrophic factor, and neuromedin U. We subsequently discuss the utility of targeting peripheral gut peptides, including pancreatic polypeptide, peptide YY, amylin, and the gastric hormone ghrelin. Also, we analyze the evidence that these factors or drugs based on them may be therapeutically useful, while considering the disadvantages of using such peptides in a clinical context.

Neuropeptide Y receptors: ligand binding and trafficking suggest novel approaches in drug development

NPY, PYY and PP constitute the so-called NPY hormone family, which exert its biological functions in humans through YRs (Y₁, Y₂, Y₄ and Y₅). Systematic modulation of YR function became important as this multireceptor/multiligand system is known to mediate various essential physiological key functions and is involved in a variety of major human diseases such as epilepsy, obesity and cancer. As several YRs have been found to be overexpressed on different types of malignant tumors they emerge as promising target in modern drug development. Here, we summarize the current understanding of YRs function and the molecular mechanisms of ligand binding and trafficking. We further address recent advances in YR-based drug design, the development of promising future drug candidates and novel approaches in YR-targeted tumor diagnostics and therapy opportunities.

Current trends in targeting the hormonal regulation of appetite and energy balance to treat obesity

With the eruption of the obesity pandemic over the past few decades, much research has been devoted to understanding the molecular mechanisms by which the human body regulates energy balance. These studies have revealed several mediators, including gut/pancreatic/adipose hormones and neuropeptides that control both short- and long-term energy balance by regulating appetite and/or metabolism. These endogenous mediators of energy balance have been the focus of many anti-obesity drug-development programs aimed at either amplifying endogenous anorexigenic/lipolytic signaling or blocking endogenous orexigenic/lipogenic signaling. Here, we discuss the efficacy and safety of targeting these pathways for the pharmacologic treatment of obesity.

Ghrelin and PYY in the regulation of energy balance and metabolism: lessons from mouse mutants

Effective control of body weight and energy homeostasis requires stringent regulation of caloric intake and energy expenditure. Gut-brain interactions comprise a central axis for the control of energy homeostasis by integrating the intake of nutrients with an effective utilization of ingested calories either by storage or by expenditure as cellular fuel. Ghrelin, a stomach-derived peptide, is the only known circulating orexigenic hormone. It is acylated with a medium-chain fatty acid by the enzyme ghrelin O-acetyltransferase (GOAT) and displays a broad range of activity, from central control of food intake to peripheral functions such as gastric emptying and insulin secretion. PYY, a peptide produced by L cells of the small intestine and rectum, has been shown to inhibit gut motility and is proposed to stimulate a powerful central satiety response. In recent years, pharmacological studies in animals and clinical studies in humans have contributed to our knowledge of principal ghrelin and PYY actions. However, valuable findings from studies using ghrelin-deficient mice, ghrelin receptor [growth hormone secretagogue receptor-1a (GHSR1a)]-deficient mice, double-knockout mice (for ghrelin and GHSR), and GOAT-deficient or -overexpressor mice, as well as mice deficient for PYY or neuropeptide Y receptors have allowed better definition of the actual physiological functions of ghrelin and PYY. This review summarizes findings from mutant mouse studies with emphasis on respective gene knockout and transgenic animals and describes how these studies contribute to the current understanding of how endogenous ghrelin and PYY as two major representatives of endocrine gut-brain communications may regulate energy and glucose homeostasis.