Neuropeptide Y receptors as targets for anti-obesity drug development: perspective and current status

Neuropeptide Y is a widely distributed neuropeptide that elicits a plethora of physiological effects via interaction with six different receptors (Y₁–y₆). Recent attention has focused on the role of neuropeptide Y in the regulation of energy homeostasis. Neuropeptide Y stimulates food intake, inhibits energy expenditure, increases body weight and increases anabolic hormone levels by activating the neuropeptide Y Y₁ and Y₅ receptors in the hypothalamus. Based on these findings, several neuropeptide Y Y₁ and Y₅ receptor antagonists have been developed recently as potential anti-obesity agents. In addition, mice lacking neuropeptide Y, the neuropeptide Y Y₁ receptor or the neuropeptide Y Y₅ receptor have been generated. The data obtained to date with these newly developed tools suggests that neuropeptide Y receptor antagonists, particularly neuropeptide Y Y₁ receptor antagonists, may be useful anti-obesity agents. However, the redundancy of the neurochemical systems regulating energy homeostasis may limit the effect of ablating a single pathway. In addition, patients in whom the starvation response is activated, such as formerly obese patients who have lost weight or patients with complete or partial leptin deficiency, may be the best candidates for treatment with a neuropeptide Y receptor antagonist.     

Neuropeptide Y and energy homeostasis: insights from Y receptor knockout models

A complex system has evolved to regulate food intake and to maintain energy homeostasis. A series of short-term hormonal and neural signals that derive from the gastrointestinal tract, such as cholecystokinin (CCK), pancreatic polypeptide (PP) and peptide YY-(3–36), recently discovered to regulate meal size. Others such as ghrelin initiate meals, and insulin and leptin, together with circulating nutrients, indicate long-term energy stores. All these signals act on central nervous system sites which converge on the hypothalamus, an area that contains a large number of peptide and other neurotransmitters that influence food intake with neuropeptide Y (NPY) being one of the most prominent ones. Five Y receptors are known which mediate the action of neuropeptide Y and its two other family members, peptide YY and pancreatic polypeptide. Elevated neuropeptide Y expression in the hypothalamus leads to the development of obesity and its related phenotypes, Type II diabetes and cardiovascular disease. The limited availability of specific pharmacological tools and the considerable number of Y receptors have made it difficult to delineate their individual contributions to the regulation of energy homeostasis. However, recent studies analysing transgenic and knockout neuropeptide Y and Y receptor mouse models have started to unravel some of the individual functions of these Y receptors potentially also helping to develop novel therapeutics for a variety of physiological disorders including obesity.     

Orphan G-protein-coupled receptors : strategies for identifying ligands and potential for use in eating disorders

G-protein-coupled receptors (GPCRs) are key regulators of intercellular interactions, participating in almost every physiological response. They exert their effects by being activated by a variety of endogenous ligands. Traditionally, these ligands were identified first, providing tools to characterise the receptors. However, since the late 1980s, homology screening approaches have allowed the GPCRs to be found first, and in turn used as orphan targets to identify their ligands. Over the last decade this method has led to the identification of 12 novel neuropeptide families. Interestingly, four of these deorphanised GPCR systems, melanin-concentrating hormone, ghrelin, orexin and neuropeptide B/neuropeptide W, have been found to play a role in the control of energy balance. This article reviews the role of these GPCR systems in the control of food intake and energy expenditure, and discusses their potential use in therapies directed at eating disorders. As obesity has reached epidemic proportions across the developed world, pharmacotherapy has focused on this condition. However, difficulties in weight control also characterise disorders of binge eating such as bulimia and binge-eating disorder. Consequently, hypophagic treatments may be of potential benefit in normal, overweight or obese individuals displaying aberrant (out of control) eating behaviour.     

Pharmacological characterization and appetite suppressive properties of BMS-193885, a novel and selective neuropeptide Y(1) receptor antagonist

Treatment of obesity is still a large unmet medical need. Neuropeptide Y is the most potent orexigenic peptide in the animal kingdom. Its five cloned G-protein couple receptors are all implicated in the regulation of energy homeostasis evidenced by overexpression or deletion of neuropeptide Y or its receptors. Neuropeptide Y most likely exerts its orexigenic activity via the neuropeptide Y(1) and neuropeptide Y(5) receptors, although the involvement of the neuropeptide Y(2) and neuropeptide Y(4) receptors are also gaining importance. The lack of potent, selective, and brain penetrable pharmacologic agents at these receptors made our understanding of the modulation of food intake by neuropeptide Y-ergic agents elusive. BMS-193885 (1,4-dihydro-[3-[[[[3-[4-(3-methoxyphenyl)-1-piperidinyl]propyl]amino] carbonyl]amino]phenyl]-2,6-dimethyl-3,5-pyridinedicarboxylic acid, dimethyl ester) is a potent and selective neuropeptide Y(1) receptor antagonist. BMS-193885 has 3.3 nM affinity at the neuropeptide Y(1) receptor, acting competitively at the neuropeptide Y binding site. BMS-193885 increased the K(d) of [(125)I]PeptideYY from 0.35 nM to 0.65 nM without changing the B(max) (0.16 pmol/mg of protein) in SK-N-MC cells that endogenously express the neuropeptide Y(1) receptor. It is also found to be a full antagonist with an apparent K(b) of 4.5 nM measured by reversal of forskolin (FK)-stimulated inhibition of cAMP production by neuropeptide Y. Pharmacological profiling showed that BMS-193885 has no appreciable affinity at the other neuropeptide Y receptors, and is also 200-fold less potent at the alpha(2) adrenergic receptor. Testing the compound in a panel of 70 G-protein coupled receptors and ion channels resulted in at least 200-fold or greater selectivity, with the exception of the sigma(1) receptor, where the selectivity was 100-fold. When administered intracerebroventricularly or directly into the paraventricular nucleus of the hypothalamus, it blocked neuropeptide Y-induced food intake in rats. Intraperitoneal administration of BMS-193885 (10 mg/kg) also reduced one-hour neuropeptide Y-induced food intake in satiated rats, as well as spontaneous overnight food consumption. Chronic administration of BMS-193885 (10 mg/kg) i.p. for 44 days significantly reduced food intake and the rate of body weight gain compared to vehicle treated control without developing tolerance or affecting water intake. These results provide supporting evidence that BMS-193885 reduces food intake and body weight via inhibition of the central neuropeptide Y(1) receptor. BMS-193885 has no significant effect of locomotor activity up to 20 mg/kg dose after 1 h of treatment. It also showed no activity in the elevated plus maze when tested after i.p. and i.c.v. administration, indicating that reduction of food intake is unrelated to anxious behavior. BMS-193885 has good systemic bioavailability and brain penetration, but lacks oral bioavailability. The compound had no serious cardiovascular adverse effect in rats and dogs up to 30 and 10 mg/kg dose, respectively, when dosed intravenously. These data demonstrate that BMS-193885 is a potent, selective, brain penetrant Y(1) receptor antagonist that reduces food intake and body weight in animal models of obesity both after acute and chronic administration. Taken together the data suggest that a potent and selective neuropeptide Y(1) receptor antagonist might be an efficacious treatment for obesity in humans.     

神经肽Y与脂肪细胞增殖分化的研究进展

神经肽Y（NPY）在中枢和外周神经系统的神经组织中合成,除了调节食欲和能量的平衡,还具有许多重要功能。本文对NPY通过其受体介导,作用于脂肪细胞,促进脂肪细胞增殖和分化的机制研究情况作一简要的概述。     

Neuropeptides in learning and memory processes with focus on galanin

Neuropeptides represent by far the most common signalling molecules in the central nervous system. They are involved in a wide range of physiological functions and can act as neurotransmitters, neuromodulators or hormones in the central nervous system and in the periphery. Accumulating evidence during the past 40 years has implicated a number of neuropeptides in various cognitive functions including learning and memory. A major focus has been on the possibility that neuropeptides, by coexisting with classical neurotransmitters, can modulate classical transmitter function of importance for cognition. It has become increasingly clear that most transmitter systems in the brain can release a cocktail of signalling molecules including classical transmitters and several neuropeptides. However, the neuropeptides seem to come into action mainly under conditions of severe stress or aversive events, which have linked their action also to regulation of affective components of behaviour. This paper summarises some of the results of three neuropeptides, which can impact on hippocampal cognition by intrinsic (dynorphins, nociceptin) or extrinsic (galanin) modulation. The results obtained with these neuropeptides in rodent studies indicate that they are important for various aspects of hippocampal learning and memory as well as hippocampal plasticity. Recent studies in humans have also shown that dysregulation of these neuropeptides may be of importance for both neurodegenerative and neuropsychiatric disorders associated with cognitive impairments. It is concluded that compounds acting on neuropeptide receptor subtypes will represent novel targets for a number of disorders, which involve cognitive deficiencies.     

Recent advances in feeding suppressing agents: potential therapeutic strategy for the treatment of obesity

Obesity is an increasingly prevalent health problem for which no ideal treatments are available, especially for long-term maintenance of body loss. The only approved drugs are centrally acting appetite suppressants that modulate monoamine neurotransmitters in the brain. Since the discovery of leptin, and the fact it modulates neuropeptide systems in the CNS, attention has shifted from amines to peptides. Many researchers have focused on these neuropeptide systems in the CNS and their involvement in energy balance. With an effort to identify molecules involved in feeding behaviour and energy expenditure in the brain, especially in the hypothalamic nuclei, a series of novel potential targets for the development of anti-obesity agents, as well as potential drug candidates, are being given attention. Many pharmaceutical companies have large programmes directed at the development of new modulators of neuropeptide receptors, antagonists of appetite enhancing peptides and agonists of appetite suppressing peptides, including neuropeptide Y receptors and melanocortin receptors. This review covers recent targets for drug discovery of anti-obesity agents and patents focusing on the receptors.     

Pharmacology of neuropeptide Y receptor antagonists. Focus on cardiovascular functions

Neuropeptide Y is one of the most abundant mammalian neuropeptides identified to date. The possible actions of neuropeptide Y, that is co-localized and released with noradrenaline, as a sympathetic co-transmitter has attracted much attention during the last decade. In recent years, several non-peptide antagonists with high subtype selectivity for neuropeptide Y receptors have been introduced. With them, the status of neuropeptide Y as a sympathetic transmitter has been established, and so have profound cardiovascular effects mediated by neuropeptide Y Y(1) and Y(2) receptors. Significant release of neuropeptide Y occurs especially upon stronger sympathetic activation, and recent data suggest that the importance of neuropeptide Y seems enhanced in stress-related cardiovascular disorders. The true significance of neuropeptide Y has thus started to unfold, owing to the presence of the first generation of selective neuropeptide Y receptor antagonists. This review concerns the pharmacology of these agents, what we have learnt from them, and might find out in the future.     

Cardiovascular and sympathoadrenal responses to intrathecal injection of neuropeptide K in the conscious rat

Summary In the conscious freely moving rat, the intrathecal (i.t.) injection of neuropeptide K (NPK; 0.65 to 6.5 nmol), at T-9 spinal cord level, produced dose-dependent and prolonged (> 3 h) increases in mean arterial blood pressure (MAP) and heart rate (HR). The cardiovascular response to 3.25 nmol NPK was less sustained when injected at T-2 level. The cardiovascular response to 3.25 nmol NPK (T-9 level) was correlated with increases in plasma levels of noradrenaline, adrenaline and neuropeptide Y (NPY), and was significantly reduced by the prior i.v. administration of inhibitors of either -adrenoceptors (1 mg/kg, phentolamine), ₁-adrenoceptors (1 mg/kg, prazosin), ₁-adrenoceptors (1 mg/kg, metoprolol) or angiotensin converting enzyme (10 mg/kg, captopril). The cardiovascular response to NPK was also significantly reduced in rats that had undergone, 48 h earlier, bilateral adrenalectomy or to a greater extent sympathectomy with 6-hydroxydopamine. Whereas NPK-induced release of adrenaline was abolished by adrenalectomy, that of neuropeptide Y and noradrenaline was blunted by either treatment. The results suggest that the cardiovascular effect of i.t. NPK is mediated by the stimulation of the sympathoadrenal system and the release of angiotensin. Sympathetic fibers may play a greater role than the adrenal medulla in the cardiovascular response to NPK. It appears that neuropeptide Y derives from both sympathetic fibers and adrenal medullae. Hence, if released in the spinal cord, NPK may play an important role in cardiovascular and sympathoadrenal regulation.Correspondence to R. Couture at the above address     

Differences in genetic predisposition to high anxiety in two inbred rat strains: role of substance P, diazepam binding inhibitor fragment and neuropeptide Y

RATIONALE: Regulatory neuropeptide systems appear to modulate anxiety and emotionality, since anxiety in rats can be increased by intracerebroventricular (ICV) administration of diazepam-binding-inhibitor fragment (DBI) and decreased by ICV administration of neuropeptide Y (NPY) or substance P (SP). OBJECTIVE: Involvement of these three neuropeptides in genetic predisposition to anxiety was studied in two inbred rat strains. METHODS: Levels of anxiety to novel environments were first measured in Fischer-344 (F-344/N) and Wistar Albino Glaxo (WAG/G) rats using open-field conflict, hole-board, black and white box, elevated-plus maze and Vogel lick suppression procedures. Levels of SP, DBI and NPY in the hippocampus, midbrain and hypothalamus of F-344/N and WAG/G rats were then measured without stress (basal levels) or after stress induced by shuttle-box, shock-avoidance testing. Finally, effects of ICV injection of SP or NPY rats were measured in F-344/N and WAG/G rats using the hole-board test. RESULTS: F-344/N rats had elevated level of anxiety compare to WAG/G rats with all five procedures. Levels of SP in the hippocampus, midbrain and hypothalamus of F-344/N rats were significantly lower than in WAG/G rats and levels of SP decreased in WAG/G, but not F-344/N, rats after stress. Levels of DBI in the hippocampus and midbrain of F-344/N rats were also lower than in WAG/G rats, but they increased in F-344/N rats after stress. In contrast, levels of NPY were higher in the midbrain of F-344/N rats than in WAG/G rats, especially after stress. ICV injection of SP or NPY decreased anxiety in the black and white box in both F-344/N and WAG/G rats, but F-344/N rats were more sensitive. CONCLUSIONS: These findings support the hypothesis that decreased levels of SP in certain brain regions may contribute to high levels of anxiety in rats. Decreased levels of DBI and increased levels of NPY in high-anxiety animals may act as compensatory mechanisms.     

Both overexpression of agouti-related peptide or neuropeptide Y in the paraventricular nucleus or lateral hypothalamus induce obesity in a neuropeptide- and nucleus specific manner

Both reduction of melanocortin signaling and increase in neuropeptide Y signaling in the brain result in obesity. However, where in the brain reduced melanocortin or increased neuropeptide Y signaling mediate these effects is poorly understood. In separate experiments we have injected recombinant adeno-associated viral vectors that overexpressed agouti-related peptide or neuropeptide Y in specific brain regions namely the paraventricular nucleus and the lateral hypothalamus. In this review we compare the results from these studies and discuss these data with previous data from intracerebroventricular or local brain injections. This review shows that the effects of agouti-related peptide clearly differ from those of neuropeptide Y. In addition, these data suggests complementary roles for these neuropeptides in energy balance.     

Metallocarboxypeptidases: emerging drug targets in biomedicine

Metallocarboxypeptidases (MCPs) are commonly regarded as exopeptidases that actively participate in the digestion of proteins and peptides. In the recent years, however, novel MCPs comprising a wide range of physiological roles have been found in different mammalian extra-pancreatic tissues and fluids. Among them, CPU, also known as thrombin-activatable fibrinolysis inhibitor (TAFI), has been shown to cleave C-terminal Lys residues from partially degraded fibrin, acting as inhibitor of clot fibrinolysis and therefore constituting an important drug target for thrombolytic therapies. Other MCPs such as CPE, CPN, CPM, and CPD function as pro-hormone and neuropeptide processors and display several structural differences with the pancreatic-like enzymes. In addition, important advances have been made in the discovery and characterization of new endogenous and exogenous proteinaceous inhibitors; the structural determination of their complexes with several MCPs has revealed novel binding modes. Finally, the use of MCPs in antibody-directed enzyme pro-drug therapy (ADEPT) has proved to be an efficient approach for the delivery of lethal levels of chemotherapeutic drugs specifically at tumor tissues. Taken together, these recent developments may help to understand potential biomedical implications of MCPs. Future perspectives for the regulation of these enzymes through the use of more selective and potent inhibitors are also discussed in this review and combined with earlier observations in the field.     

Enhanced effect of neuropeptide Y on food intake caused by blockade of the V1A vasopressin receptor

Food intake is regulated by various factors such as neuropeptide Y. Neuropeptide Y potently induces an increase in food intake, and simultaneously stimulates arginine-vasopressin (AVP) secretion in the brain. Recently, we reported that V_1A vasopressin receptor-deficient (V_1AR^−/−) mice exhibited altered daily food intake accompanied with hyperglycemia and hyperleptinemia. Here, we further study the involvement of the AVP/V_1A receptor in the appetite regulation of neuropeptide Y with V_1AR^−/− mice and antagonists for the AVP receptor. The intra-cerebral-ventricle administration of neuropeptide Y induced greater food consumption in V_1AR^−/− mice than wild-type (WT) mice, whereas an anorexigenic effect of leptin was not different between the two groups. This finding suggests that the orexigenic effect of neuropeptide Y was enhanced in V_1AR^−/− mice, leading to the increased food intake in response to the neuropeptide Y stimulation. In addition, the neuropeptide Y-induced orexigenic effect was enhanced by co-administration of OPC-21268, an antagonist for the V_1A vasopressin receptor, into the cerebral ventricle in WT mice, whereas the neuropeptide Y-induced orexigenic effect was not affected by co-administration of SSR-149415, an antagonist for the V_1B vasopressin receptor. These results indicate that AVP could suppress the neuropeptide Y-induced orexigenic effect via the V_1A vasopressin receptor, and that blockade or inhibition of the AVP/V_1A receptor signal resulted in the enhanced neuropeptide Y-induced orexigenic effect. Thus, we show that the AVP/V_1A receptor is involved in appetite regulation as an anorexigenic factor for the neuropeptide Y-induced orexigenic effect.     

The role of the endocannabinoid system in the neuroendocrine regulation of energy balance

Animal and human studies carried out so far have established a role for the endocannabinoid system (ECS) in the regulation of energy balance. Here we critically discuss the role of the endocannabinoid signalling in brain structures, such as the hypothalamus and reward-related areas, and its interaction with neurotransmitter and neuropeptide systems involved in the regulation of food intake and body weight. The ECS has been found to interact with peripheral signals, like leptin, insulin, ghrelin and satiety hormones and the resulting effects on both central and peripheral mechanisms affecting energy balance and adiposity will be described. Furthermore, ECS dysregulation has been associated with the development of dyslipidemia, glucose intolerance and obesity; phenomena that are often accompanied by a plethora of neuroendocrine alterations which might play a causal role in determining ECS dysregulation. Despite the withdrawal of the first generation of cannabinoid type 1 receptor (CB1) antagonists from the pharmaceutical market due to the occurrence of psychiatric adverse events, new evidence suggests that peripherally restricted CB1 antagonists might be efficacious for the treatment of obesity and its associated metabolic disorders. Thus, a perspective on new promising strategies to selectively target the ECS in the context of energy balance regulation is given.     

Increased hypothalamic neuropeptide Y concentration or hyperphagia in streptozotocin-diabetic rats are not mediated by glucocorticoids

Hypothalamic neuropeptide Y containing neurones are overactive and may mediate hyperphagia in insulin-deficient diabetic rats, but the factors stimulating them remain uncertain. To determine the possible role of glucocorticoids, we investigated the effects of the glucocorticoid receptor blocker mifepristone (RU486) on food intake and regional hypothalamic neuropeptide Y concentrations in streptozotocin-diabetic rats. RU486 (30 mg/kg) or corn oil vehicle control was given orally for 3 weeks to diabetic rats. Food intake and neuropeptide Y levels in the hypothalamic arcuate and paraventricular nuclei were increased in untreated diabetic rat groups (P<0.01), and though RU486 did increase plasma corticosterone levels (P<0.01) it did not have any effect on either feeding or neuropeptide Y levels (P=NS). These negative findings suggest that glucocorticoids may not be responsible for increasing hypothalamic neuropeptide Y or for hyperphagia in insulin-deficient diabetes.     

Neuropeptides and Alzheimer''s disease

Numerous neuropeptides have been isolated from the human brain and postulated as neurotransmitter candidates. Their biochemical characteristics and anatomical distribution have been elucidated in some detail, but their possible physiological and pathophysiological roles, as well as their utility as diagnostic markers in brain disorders, have been more difficult to establish. The concentrations of several neuropeptides have been measured in postmortem human brain studies and in cerebrospinal fluid (CSF) of patients with Alzheimer's disease. Here we critically review these findings with focus on: (1) the relation between brain tissue and CSF neuropeptide alterations; (2) the specificity of neuropeptide alterations in Alzheimer's disease in relation to other degenerative brain diseases; (3) possible functional implications.     

Small molecules for interference with cell-cell-communication systems in Gram-negative bacteria

Quorum sensing (QS) systems are bacterial cell-to-cell communication systems that use small molecules as signals. Since QS is involved in the regulation of virulence and biofilm formation in several pathogenic bacteria, it has been suggested as a new target for the development of novel antibacterial therapies. As such, interference with the signal receptors by using chemical compounds has been proposed as an alternative strategy for treatment of bacterial infections and has already shown promising results in combination with traditional antibiotic treatments. In Gram-negative bacteria, the best studied QS systems use N-acyl homoserine lactones (AHLs) as signal molecules. This review provides an overview of all new chemical structure types that inhibit AHL-mediated QS systems as reported during the last three years in scientific journals and in the patent literature. The compounds were classified into three main groups depending on their structure: AHL analogues, 2(5H)-furanones, and compounds that are not structurally related to AHLs. We discuss the biological assays used and the different strategies applied to discover these molecules, including new approaches such as molecular docking for in silico identification of lead structures and random high-throughput screening of large libraries of chemicals. Finally, we elaborate on structure-activity relationships and on the new insights in the mechanisms of action of the identified inhibitors, highlighting the potential of these small molecules in medicine.     

A review of neuropeptide and neuroendocrine dysregulation in anorexia and bulimia nervosa

Neuropeptides play an important role in the regulation of feeding behavior and obesity. The mechanisms for controlling food intake involve a complicated interplay between peripheral systems (including gustatory stimulation, gastrointestinal peptide secretion, and vagal afferent nerve responses) and central nervous system (CNS) neuropeptides and/or monoamines. These neuronal systems include neuropeptides (CRH, opioids, neuropeptide-Y (NPY) and peptide YY (PYY), vasopressin and oxytocin, CCK, and leptin) and monamines (serotonin, dopamine, norepinephrine). In addition to regulating eating behavior, a number of CNS neuropeptides participate in the regulation of neuroendocrine pathways. Thus, clinical studies have evaluated the possibility that CNS neuropeptide alterations may contribute to dysregulated secretion of the gonadal hormones, cortisol, thyroid hormones and growth hormone in the eating disorders. Most of the neuroendocrine and neuropeptide alterations apparent during symptomatic episodes of AN and BN tend to normalize after recovery. This observation suggests that most of the disturbances are consequences rather than causes of malnutrition, weight loss and/or altered meal patterns. Still, an understanding of these neuropeptide disturbances may shed light on why many people with AN or BN cannot easily "reverse" their illness and even after weight gain and normalized eating patterns, many individuals who have recovered from AN or BN have physiological, behavioral and psychological symptoms that persist for extended periods of time.     

Connectomics of orexin-producing neurons: analysis using mouse models

Orexin A and orexin B (also known as hypocretin 1 and hypocretin 2) are hypothalamic neuropeptides that we discovered thirteen years ago. Initially, these peptides were recognized as regulators of feeding behavior. Subsequently, several studies suggested that orexin deficiency causes narcolepsy in humans and other mammalian species, highlighting roles of this hypothalamic neuropeptide in the regulation of sleep and wakefulness. Studies of efferent and afferent systems of orexin-producing neurons have shown that the orexin neuronal system has close interactions with systems that regulate emotion, energy homeostasis, reward, and arousal. These observations suggest that orexin neurons are involved in sensing the body's external and internal environments, and regulate vigilance states accordingly.