[D-TRP32]neuropeptide Y: a competitive antagonist of NPY in rat hypothalamus

Importance of Orexigenic Counter-Regulation for Multiple Targeted Feeding Inhibition

OBJECTIVE

Central feeding regulation involves both anorectic and orexigenic pathways. This study examined whether targeting both systems could enhance feeding inhibition induced by anorectic neuropeptides.

RESEARCH METHODS AND PROCEDURES

Experiments were carried out in 24-hour fasted rats. Intracerebroventricular (ICV) injections were accomplished through stereotaxically implanted cannulae aimed at the lateral cerebral ventricle. Food intake of standard rat chow pellets was subsequently recorded for 2 hours.

RESULTS

Blockade of orexigenic central opioids and neuropeptide Y (NPY) by ICV naloxone (25 microg) or the NPY receptor antagonist [D-Trp32]NPY (NPY-Ant; 10 micro g) powerfully augmented the feeding suppression induced by ICV glucagon-like peptide 1 (7-36)-amide (GLP-1; 10 microg) or xenin-25 (xenin; 15 microg) in 24-hour fasted rats. Most importantly, in combination with naloxone or NPY-Ant, even a low and ineffective dose of GLP-1 (5 microg) caused a 40% reduction of food intake, which was augmented further when both antagonists were given in combination with GLP-1. The combination of GLP-1 (5 microg) and xenin (10 microg) at individually ineffective doses caused a 46% reduction of food intake, which was abolished at a 10-fold lower dose. This ineffective dose, however, reduced food intake by 72% when administered in combination with naloxone and NPY-Ant.

DISCUSSION

Targeting up to four pathways of feeding regulation in the central nervous system by blockade of endogenous feeding stimuli and simultaneous administration of anorectic neuropeptides potentiated reduction of food intake. This raises a promising perspective for treatment of obesity.

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.

Investigational therapies in the treatment of obesity

Obesity is a major public health concern and environmental factors are involved in its development. The hypothalamus is a primary site for the integration of signals for the regulation of energy homeostasis. Dysregulation of these pathways can lead to weight loss or gain. Some drugs in development can have favourable effects on body weight, acting on some of these pathways and leading to responses resulting in weight loss. Strategies for the management of weight reduction include exercise, diet, behavioural therapy, drug therapy and surgery. Investigational antiobesity medications can modulate energy homeostasis by stimulating catabolic or inhibiting anabolic pathways. Investigational drugs stimulating catabolic pathways consist of leptin, agonists of melanocortin receptor-4, 5-HT and dopamine; bupropion, growth hormone fragments, cholecystokinin subtype 1 receptor agonist, peptide YY3-36, oxyntomodulin, ciliary neurotrophic factor analogue, beta3-adrenergic receptor agonists, adiponectin derivatives and glucagon-like peptide-1. On the other hand, investigational drugs inhibiting anabolic pathways consist of the ghrelin receptor, neuropeptide Y receptor and melanin-concentrating hormone-1 antagonists; somatostatin analogues, peroxisome proliferator-activated receptor-gamma and -beta/delta antagonists, gastric emptying retardation agents, pancreatic lipase inhibitors, topiramate and cannabinoid-1 receptor antagonists. These differing approaches are reviewed and commented on in this article.

Chronic neuropeptide Y infusion into the lateral ventricle induces sustained feeding and obesity in mice lacking either Npy1r or Npy5r expression

Neuropeptide Y (NPY) is a powerful orexigenic neurotransmitter. The NPY Y1 and Y5 receptors have been implicated in mediating the appetite-stimulating activity of NPY. To further investigate the importance of these two receptors in NPY-induced hyperphagia after chronic central administration, we used mice lacking either Npy1r or Npy5r expression. NPY infusion into the lateral ventricle of wild-type mice stimulated food intake and induced obesity over a 7-d period. Fat pad weight as well as plasma insulin, leptin, and corticosterone levels were strongly increased in NPY-treated mice. In addition, NPY infusion resulted in a significant decrease in hypothalamic NPY and proopiomelanocortin expression. Interestingly, the lack of either Npy1r or Npy5r expression in knockout mice did not affect such feeding response to chronic NPY infusion. Moreover, the obesity syndrome that developed in these animals was similar to that in wild-type animals. Taken together, these data strongly suggest biological redundancies between Y1 and Y5 receptor signaling in the NPY-mediated control of food intake.

Involvement of peripheral neuropeptide y receptors in sympathetic modulation of acute cutaneous flare induced by intradermal capsaicin

In a recent study, we have demonstrated that the dorsal root reflex (DRR)-mediated acute cutaneous neurogenic inflammation following intradermal injection of capsaicin (CAP) is sympathetically dependent and subject to modulation by peripheral alpha(1)-adrenoceptors. Postganglionic sympathetic neurons contain not only adrenergic neurotransmitters, but also non-adrenergic substances, including neuropeptide Y (NPY). In this study, we examined if peripheral NPY receptors participate in the flare following CAP injection. Different NPY receptor subtypes were studied by using relatively specific agonists and antagonists for the Y(1) and Y(2) subtypes. Changes in cutaneous blood flow on the plantar surface of the foot were measured using a laser Doppler flowmeter. Following CAP injection, cutaneous flare spread more than 20 mm away from the site of CAP injection. Removal of the postganglionic sympathetic nerves by surgical sympathectomy reduced dramatically the CAP-evoked flare. If the foot of sympathectomized rats was pretreated with either NPY or Y(2) receptor agonists by intra-arterial injection, the spread of flare induced by CAP injection could be restored and prolonged. However, if the spinal cord was pretreated with a GABA(A) receptor antagonist, bicuculline, to prevent DRRs, NPY or an Y(2) receptor agonist no longer restored the CAP-evoked flare. A Y(1) receptor agonist did not affect the CAP-evoked flare in sympathectomized rats. In sympathetically intact rats, blockade of either peripheral NPY or Y(2) receptors with [D-Trp(32)]-NPY or BIIE0246 markedly reduced the flare induced by CAP injection, whereas blockade of peripheral Y(1) receptors by BIBP3226 did not obviously affect the flare. It is suggested that NPY is co-released with NE from the postganglionic sympathetic terminals to activate NPY Y(2) and alpha(1) receptors following CAP injection. Both substances are involved, at least in part, in modulation of the responses of CAP sensitive afferents thereby affecting their ability to evoke the release of inflammatory agents from primary afferents.

Recent developments in our understanding of the physiological role of PP-fold peptide receptor subtypes

The three peptides pancreatic polypeptide (PP), peptide YY (PYY), and neuropeptide Y (NPY) share a similar structure known as the PP-fold. There are four known human G-protein coupled receptors for the PP-fold peptides, namely Y1, Y2, Y4, and Y5, each of them being able to bind at least two of the three endogenous ligands. All three peptides are found in the circulation acting as hormones. Although NPY is only released from neurons, PYY and PP are primarily found in endocrine cells in the gut, where they exert such effects as inhibition of gall bladder secretion, gut motility, and pancreatic secretion. However, when PYY is administered in an experimental setting to animals, cloned receptors, or tissue preparations, it can mimic the effects of NPY in essentially all studies, making it difficult to study the effects of PP-fold peptides and to delineate what receptor and peptide accounts for a particular effect. Initial studies with transgenic animals confirmed the well-established action of NPY on metabolism, food-intake, vascular systems, memory, mood, neuronal excitability, and reproduction. More recently, using transgenic techniques and novel antagonists for the Y1, Y2, and Y5 receptors, NPY has been found to be a key player in the regulation of ethanol consumption and neuronal development.

Bis(31/31')[[Cys(31), Nva(34)]NPY(27-36)-NH(2)]: a neuropeptide Y (NPY) Y(5) receptor selective agonist with a latent stimulatory effect on food intake in rats

The actions of neuropeptide Y (NPY) are mediated by at least six G-protein coupled receptors denoted as Y(1), Y(2), Y(3), Y(4), Y(5), and y(6). Investigations using receptor selective ligands and receptor knock-out mice suggest that NPY effects on feeding are mediated by both Y(1) and Y(5) receptors. We have previously shown that Cys-dimers of NPY C-terminal peptides exhibit Y(1) selectivity relative to Y(2) receptors. Re-investigation of their selectivity with respect to the newly cloned receptors, has identified bis(31/31') [[Cys(31), Nva(34)]NPY(27-36)-NH(2)] (BWX-46) as a Y(5) receptor selective agonist. BWX-46 selectively bound Y(5) receptors, and inhibited cAMP synthesis by Y(5) cells with potencies comparable to that of NPY. Moreover, BWX-46 (10 microM) exhibited no significant effect on the cAMP synthesis by Y(1), Y(2), and Y(4) cells. Thus, BWX-46 constitutes the lowest molecular weight Y(5) selective agonist reported to date. Intrahypothalamic (i.h.t)-injection of 30 and 40 microg of BWX-46 stimulated the food intake by rats in a gradual manner, reaching maximal level 8 h after injection. This response was similar to that exhibited by other Y(5) selective agonists, but differed from that of NPY, which exhibited a rapid orexigenic stimulus within 1 h. It is suggested that the differences in the orexigenic stimuli of NPY and Y(5) agonists may be due to their differences in the signal transduction mechanisms.

The neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y

This review aims to give a brief overview of NPY receptor distribution and physiology in the brain and summarizes series of studies, test by test and region by region, aimed at identification receptor subtypes and neuronal circuitry mediating anxiolytic-like effects of NPY. We conclude that from four known NPY receptor subtypes in the rat (Y(1), Y(2), Y(4), Y(5)), only the NPY Y(1) receptor can be linked to anxiety-regulation with certainty in the forebrain, and that NPY Y(2) receptor may have a role in the pons. Microinjection studies with NPY and NPY receptor antagonists support the hypothesis that the amygdala, the dorsal periaqueductal gray matter, dorsocaudal lateral septum and locus coeruleus form a neuroanatomical substrate that mediates anxiolytic-like effects of NPY. The release of NPY in these areas is likely phasic, as NPY receptor antagonists are silent on their own. However, constant NPY-ergic tone seems to exist in the dorsal periaqueductal gray, the only brain region where NPY Y(1) receptor antagonists had anxiogenic-like effects. We conclude that endogenous NPY has an important role in reducing anxiety and serves as a physiological stabilizer of neural activity in circuits involved in the regulation of arousal and anxiety.

Characterisation of a new chimeric ligand for galanin receptors: galanin(1-13)-[D-Trp(32)]-neuropeptide Y(25-36)amide

In this work, we studied a novel chimeric peptide, M242, galanin(1-13)-[D-Trp(32)]-neuropeptide Y(25-36)amide, and examined its properties in comparison with its parent peptide, M32, galanin(1-13)-neuropeptide Y(25-36)amide, a previously known high-affinity ligand for galanin receptors, and galanin itself. Binding assays performed in Bowes cells known to express human galanin receptor type 1 (hGalR1) and in Chinese hamster ovary cells overexpressing human galanin receptor type 2 (hGalR2) revealed that all three ligands had comparable affinities: at hGalR1<1 nM and at hGalR2<10 nM. However, in rat hippocampal membranes M242 had a 24-fold lower affinity than galanin (9.4 vs. 0.4 nM) and 134-fold lower affinity than M32 (9.4 vs. 0.07 nM). In the same tissue, we also examined the effects of these peptides on adenylate cyclase activity. M32 showed a weak antagonistic behaviour but M242 acted as a potent biphasic regulator of adenylate cyclase. In conclusion, we present and characterise a new peptide M242, which could be a useful tool in studies of galaninergic signalling.

Binding of chimeric NPY/galanin peptides M32 and M242 to cloned neuropeptide Y receptor subtypes Y1, Y2, Y4, and Y5

Ligand binding to neuropeptide Y (NPY) receptors Y1, Y2, Y4, and Y5 from guinea-pig was investigated using the two NPY-galanin hybrids M32 (galanin1-13-NPY25-36-amide) and M242 ([D-Trp(32)]M32). The affinity of M32 for Y1, Y2, and Y4 receptors was 13, 4, and 30nM, respectively, similar to that of NPY18-36 and NPY22-36 but 40-fold to 300-fold lower than the affinity of intact porcine NPY. M242 bound to the Y1, Y2, and Y4 receptors with 9-fold to 20-fold lower affinity than did M32. The affinities of M32 and M242 for Y5 were 400 and 800 nM, respectively. Thus, M32 seems to gain affinity relative to both of its constituent peptide portions although the NPY25-36 part may be sufficient for NPY-receptor recognition, especially at the Y2 receptor. This suggests that the galanin portion of M32 influences and/or stabilizes the conformation of the NPY portion, similar to the effect seen for the NPY portion of M32 in binding to galanin receptors.

The role of neuropeptide Y in orexin-induced hypothalamic-pituitary-adrenal activation

The role of neuropeptide Y (NPY) in the mediation of orexin-induced hypothalamic-pituitary-adrenal (HPA) activation was investigated in the rat. The HPA system was stimulated by intracerebroventricular (i.c.v.) administration of orexin-A or orexin-B (140 or 280 pmol, respectively) and the plasma concentration of corticosterone was used as an index of the degree of activation. i.c.v. pretreatment with NPY antagonist or NPY antiserum (30 min or 24 h before orexin administration, respectively) inhibited the orexin-induced corticosterone release. The inhibitory actions of the antagonist and the antiserum were revealed by the dose-response curve; the highest concentrations practically abolished the HPA activation evoked by the orexins. These data suggest that the HPA system-stimulating effect of the orexins may be mediated by NPY.

The first selective agonist for the neuropeptide YY5 receptor increases food intake in rats

The first Y(5) receptor-selective analog of neuropeptide Y (NPY), [Ala(31),Aib(32)]NPY, has been developed and biologically characterized. Using competition binding assays on cell lines that express different Y receptors, we determined the affinity of this analog to be 6 nm at the human Y(5) receptor, >500 nm at the Y(1) and Y(2) receptors, and >1000 nm at the Y(4) receptor. Activity studies performed in vitro using a cAMP enzyme immunoassay, and in vivo using food intake studies in rats, showed that the peptide acted as an agonist. Further peptides obtained by the combination of the Ala(31)-Aib(32) motif with chimeric peptides containing segments of NPY and pancreatic polypeptide displayed the same selectivity and even higher affinity (up to 0.2 nm) for the Y(5) receptor. In vivo administration of the new Y(5) receptor-selective agonists significantly stimulated feeding in rats. The NMR solution structures of NPY and [Ala(31),Aib(32)]NPY showed a different conformation in the C-terminal region, where the alpha-helix of NPY was substituted by a more flexible, 3(10)-helical turn structure.

[D-Trp(34)] neuropeptide Y is a potent and selective neuropeptide Y Y(5) receptor agonist with dramatic effects on food intake

The neuropeptide Y (NPY) Y(5) receptor has been proposed to mediate several physiological effects of NPY, including the potent orexigenic activity of the peptide. However, the lack of selective NPY Y(5) receptor ligands limits the characterization of the physiological roles of this receptor. Screening of several analogs of NPY revealed that [D-Trp(34)]NPY is a potent and selective NPY Y(5) receptor agonist. Unlike the prototype selective NPY Y(5) receptor agonist [D-Trp(32)]NPY, [D-Trp(34)]NPY markedly increases food intake in rats, an effect that is blocked by the selective NPY Y(5) receptor antagonist CGP 71683A. These data demonstrate that [D-Trp(34)]NPY is a useful tool for studies aimed at determining the physiological roles of the NPY Y(5) receptor.

Characterization of the cloned atlantic cod neuropeptide Y-Yb receptor: peptide-binding requirements distinct from known mammalian Y receptors

Five members of the neuropeptide Y (NPY) receptor family have been cloned in mammals. The recently cloned NPY receptor in the Atlantic cod seems to be distinct from the mammalian subtypes as it has only 50% identity to Y1, Y4, and y6 and only 30% to Y2 and Y5. In most of the other families of G-protein-coupled receptors, species homologues have 65-90% identity between fishes and mammals. The functional expression and detailed pharmacological characterization of this cod NPY receptor, designated Yb, is reported. Membranes of cells transiently transfected with cod Yb showed saturable [(125)I]PYY binding with a K(d) of 45 pM. The pharmacological profile is similar to those of both the zebrafish Yb and Yc receptors and distinct from those of the mammalian NPY receptors. In competition experiments the cod Yb receptor had the following rank order of potencies: porcine PYY = porcine NPY = p[Leu(31), Pro(34)]NPY > zebrafish PYY > zebrafish NPY >> NPY2-36 = NPY3-36 > NPY18-36 > bovine PP = [D-Trp(32)]NPY > BIBP3226. This is in sharp contrast to the high selectivity of BIBP3226 for the Y1 receptor from all mammalian species. Together with the low amino acid identity of cod Yb with the mammalian Y1, Y4, and y6 receptors, this is further support for the notion that fish Yb constitutes a distinct NPY receptor subtype.

Chemistry, nutrition, and microbiology of D-amino acids

Exposure of food proteins to certain processing conditions induces two major chemical changes: racemization of all L-amino acids to D-isomers and concurrent formation of cross-linked amino acids such as lysinoalanine. Racemization of L-amino acids residues to their D-isomers in food and other proteins is pH-, time-, and temperature-dependent. Although racemization rates of the 18 different L-amino acid residues in a protein vary, the relative rates in different proteins are similar. The diet contains both processing-induced and naturally formed D-amino acids. The latter include those found in microorganisms, plants, and marine invertebrates. Racemization impairs digestibility and nutritional quality. The nutritional utilization of different D-amino acids varies widely in animals and humans. In addition, some D-amino acids may be both beneficial and deleterious. Thus, although D-phenylalanine in an all-amino-acid diet is utilized as a nutritional source of L-phenylalanine, high concentrations of D-tyrosine in such diets inhibit the growth of mice. Both D-serine and lysinoalanine induce histological changes in the rat kidney. The wide variation in the utilization of D-amino acids is illustrated by the fact that whereas D-methionine is largely utilized as a nutritional source of the L-isomer, D-lysine is totally devoid of any nutritional value. Similarly, although L-cysteine has a sparing effect on L-methionine when fed to mice, D-cysteine does not. Because D-amino acids are consumed by animals and humans as part of their normal diets, a need exists to develop a better understanding of their roles in nutrition, food safety, microbiology, physiology, and medicine. To contribute to this effort, this multidiscipline-oriented overview surveys our present knowledge of the chemistry, nutrition, safety, microbiology, and pharmacology of D-amino acids. Also covered are the origin and distribution of D-amino acids in the food chain and in body fluids and tissues and recommendations for future research in each of these areas. Understanding of the integrated, beneficial effects of D-amino acids against cancer, schizophrenia, and infection, and overlapping aspects of the formation, occurrence, and biological functions of D-amino should lead to better foods and improved human health.

Evidence that the inhibition of luteinizing hormone secretion exerted by central administration of neuropeptide Y (NPY) in the rat is predominantly mediated by the NPY-Y5 receptor subtype

A number of studies have indicated that neuropeptide Y (NPY) is a central regulator of the gonadotropic axis, and the Y1 receptor was initially suggested to be implicated. As at least five different NPY receptor subtypes have now been characterized, the aim of the present study was to reinvestigate the pharmacological profile of the receptor(s) mediating the inhibitory action of NPY on LH secretion by using a panel of NPY analogs with different selectivity toward the five NPY receptor subtypes. When given intracerebroventricularly (icv) to castrated rats, a bolus injection of native NPY (0.7-2.3 nmol) dose-dependently decreased plasma LH. Peptide YY (PYY; 2.3 nmol) was as potent as NPY, suggesting that the Y3 receptor is not implicated. Confirming previous data, the mixed Y1, Y4, and Y5 agonist [Leu31,Pro34]NPY (0.7-2.3 nmol) inhibited LH release with potency and efficacy equal to those of NPY. Neither the selective Y2 agonist C2-NPY (2.3 nmol) nor the selective Y4 agonist rat pancreatic polypeptide affected plasma LH, excluding Y2 and Y4 subtypes for the action of NPY on LH secretion. The mixed Y4-Y5 agonist human pancreatic polypeptide (0.7-7 nmol) as well as the mixed Y2-Y5 agonist PYY3-36 (0.7-7 nmol) that displayed very low affinity for the Y1 receptor, thus practically representing selective Y5 agonists in this system, decreased plasma LH with potency and efficacy similar to those of NPY, indicating that the Y5 receptor is mainly involved in this inhibitory action of NPY on LH secretion. [D-Trp32]NPY, a selective, but weak, Y5 agonist, also inhibited plasma LH at a dose of 7 nmol. Furthermore, the inhibitory action of NPY (0.7 nmol) on LH secretion could be fully prevented, in a dose-dependent manner (6-100 microg, icv), by a nonpeptidic Y5 receptor antagonist. This antagonist (60 microg, icv) also inhibited the stimulatory action of NPY (0.7 nmol) on food intake. The selectivity of PYY3-36, human PP, [D-Trp32]NPY, and the Y5 antagonist for the Y5 receptor subtype was further confirmed by their ability to inhibit the specific [125I][Leu31,Pro34]PYY binding to rat brain membrane homogenates in the presence of the Y1 receptor antagonist BIBP3226, a binding assay system that was described as being highly specific for Y5-like receptors. With the exception of [D-Trp32]NPY, all analogs able to inhibit LH secretion were also able to stimulate food intake. Taken together, these results indicate that the Y5 receptor is involved in the negative control by NPY of the gonadotropic axis.

Neuropeptide Y receptor subtype with unique properties cloned in the zebrafish: the zYa receptor

Neuropeptide Y (NPY) belongs to a family of structurally related neuroendocrine peptides for which five different G-protein-coupled receptor subtypes have been cloned in mammals. To identify additional subtypes we have performed PCR with degenerate primers in different species. We describe here the cloning and pharmacological profile of a unique NPY receptor subtype in the zebrafish that has tentatively been called the zYa receptor. It has 46-50% amino acid identity to the mammalian Y1, Y4 and y6 receptors and the previously cloned zebrafish receptors zYb and zYc, and only about 27% to Y2 and Y5. The zYa receptor binds NPY and PYY from mammals as well as zebrafish with high affinities and has a K(d) of 28 pM for porcine (125)I-PYY. It has a unique binding profile displaying some features in common with each of the mammalian Y1, Y2 and Y5 receptors. In a microphysiometer assay the receptor responds with extracellular acidification. Chromosomal mapping in the zebrafish genome of zYa, zYb and zYc receptor genes indicates a possible orthologous relationship between zYc and mammalian y6, but identifies no obvious mammalian ortholog for zYa (zYb is a recent copy of zYc in the fish lineage). These results imply that previous studies of NPY in fishes, which have striven to interpret the effects within the framework of mammalian Y1, Y2, and Y5 receptors, need to be reevaluated. Thus, the sequence comparisons, pharmacological properties, and chromosomal localization suggest that the zYa receptor is a novel NPY receptor subtype which is likely to be present also in mammals.

Increased NPY activity in the PVN contributes to food-restriction induced reductions in blood pressure in aortic coarctation hypertensive rats

We hypothesized that hypothalamic NPYergic mechanisms mediate the blood pressure lowering effect of caloric restriction in hypertensive rats. Aortic coarctation-induced (AC) hypertensive rats (n=25) were assigned to either an ad libitum fed control group (AL) or food restricted group (FR; 60% of AL consumption) for 3 weeks. Rats were instrumented chronically with vascular catheters and bilateral guide cannulae directed at the paraventricular hypothalamic nuclei (PVN). Blood pressure (BP) and heart rate (HR) responses to bilateral PVN microinjection of saline (200 nl) or the putative NPY receptor antagonists [D-Trp32]NPY(1-36) (3.3 micrograms/200 nl) and [D-Tyr27,36 Thr32]NPY(27-36) (D-NPY(27-36); 3.3 micrograms/200 nl) were determined. The FR rats were then refed and cardiovascular responses to PVN injections of NPY receptor antagonists were again determined. FR rats had significantly reduced resting BP (159+/-4 vs. 129+/-4 mmHg) and HR (360+/-11 vs. 326+/-9 bpm) compared to AL controls. Refeeding restored BP and HR of FR rats to levels similar to AL (BP=153+/-4 mmHg, HR=359+/-11 bpm). PVN administration of [D-Trp32]NPY produced foraging behavior and concurrent increases in BP and HR in FR, AL and Re-fed rats. The behavioral activation suggests that [D-Trp32]NPY(1-36) produced activation of NPY receptors. In contrast, D-NPY (27-36) did not produce any behavioral response or affect BP or HR in AL or Re-fed rats. In FR rats, D-NPY (27-36) produced significant increases in BP (peak=15+/-3 mmHg) which partially reversed the effect of FR on BP. Thus, in FR rats with reduced BP, PVN administration of an NPY receptor antagonist increases BP. NPY blockade in the PVN accounted for about 50% of the BP effect of food restriction, thus other mechanisms are likely to be involved. These findings are consistent with the hypothesis that NPYergic mechanisms may contribute to the reduction of BP produced by food restriction.

Characterization of the neuropeptide Y5 receptor in the human hypothalamus: a lack of correlation between Y5 mRNA levels and binding sites

Neuropeptide Y (NPY) is a 36-amino-acid peptide that appears to play a central role in the control of feeding behavior. Recently, a cDNA encoding a novel NPY receptor subtype (Y5) was cloned from the rat and human hypothalamus, and shown to have a pharmacology consistent with NPY-induced feeding. We have subsequently cloned this cDNA from human hypothalamus and stably expressed it in CHO cells. Consistent with earlier reports, hY5 has a high affinity for NPY, [Leu31, Pro34]NPY, and NPY(3-36), but low affinity for larger C-terminal deletions of NPY and BIBP3226. High levels of hY5 mRNA were found in the human testis, brain, spleen and pancreas, with lower levels in several other tissues. In the human brain, hY5 mRNA levels were typically higher than hY2, but lower in comparison to hY1 receptor mRNA. To quantify the relative amounts of hY1, hY2 and hY5 mRNA in the human hypothalamus, we employed competitive RT-PCR. Interestingly, the relative amount of hY5 mRNA was substantially higher than either hY1 or hY2. However, pharmacological characterization of NPY binding sites in human hypothalamus membranes revealed predominantly the hY2 subtype. These data establish that while hY5 mRNA levels are very high in the human hypothalamus, conventional radioligand binding techniques do not detect hY5-like binding site. Whether hY5-like binding sites exist in the other human tissues that express hY5 mRNA (and what function hY5 has in those tissues) awaits future investigation.

NPY receptor subtypes involved in the contraction of the proximal colon of the rat

Experiments were designed to determine the receptor subtype(s) involved in the contraction of the rat proximal colon to NPY. In this tissue, mRNA of Y2 and Y4 NPY receptor subtypes were highly expressed, whereas Y5 mRNA levels were very low and Y1 mRNA levels were intermediate. NPY analogues induced contractions with the following order of potency: rPP > hPP = PYY = NPY = [Leu31,Pro34]NPY > NPY(2-36) = [D-Trp32]NPY > NPY(33-36). Responses to NPY, PYY and NPY(13-36) were not or partially affected by tetrodotoxin, in contrast to the responses to [Leu31,Pro34]NPY, rPP, hPP and [D-Trp32]NPY which were fully blocked. Atropine did not inhibit the contractions to NPY, PYY and [Leu31,Pro34]NPY but significantly affected those to NPY(13-36), [D-Trp32]NPY, rPP and hPP. The specific Y1 receptor antagonist BIBP 3226 was ineffective but JCF 104 and JCF 105 (two compounds with preferential affinity toward the hY5 receptor versus the hY1 or hY2 receptor) abolished the contractions provoked by the NPY analogues. These results suggest that NPY activates three receptor subtypes, a Y2 subtype possibly by a direct action on the smooth muscle cells, as well as a Y4 and a Y5 (or 'Y5-like') subtype which, respectively, release acetylcholine and an unknown neurotransmitter.

Anxiogenic-like effect of the NPY Y1 receptor antagonist BIBP3226 administered into the dorsal periaqueductal gray matter in rats

Exogenous neuropeptide Y (NPY) administered intracerebroventricularly or into the central nucleus of amygdala has anxiolytic-like effects in animal models of anxiety. These effects are probably mediated by the NPY Y1 receptor. The role of the NPY Y1 receptor activation by endogenous NPY in this and other brain areas has not been fully elucidated. The selective NPY Y1 receptor antagonist (R)-N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)methyl]-D-arginine amide (BIBP3226) was microinjected into various brain sites implicated in the regulation of anxiety-related behaviour and resultant behavioural changes were assessed using the elevated plus-maze (EPM) and open-field test in rats. Intracerebroventricular application of BIBP3226 (5.0 microg) which caused an anxiogenic-like effect in the EPM did not affect exploratory activity in the open-field test. A decrease in EPM exploration was observed also when BIBP3226 (0.5 microg) was microinjected into the dorsal periaqueductal gray matter (DPAG). Intra-DPAG BIBP3226 did not change open-field behaviour suggesting that the effects of BIBP3226 in the EPM test were not related to changes in locomotor activity in general. Bilateral application of BIBP3226 into the central nucleus of amygdala (0.5 and 2.5 microg/side) and unilateral injections into the locus coeruleus and the paraventricular nucleus of the hypothalamus (both 0.5 microg) were ineffective in modifying the plus-maze exploration. These data suggest that endogenous NPY may regulate anxiety-related behaviour in rats by acting via the NPY Y1 receptors in DPAG.

The pharmacology of neuropeptide Y (NPY) receptor-mediated feeding in rats characterizes better Y5 than Y1, but not Y2 or Y4 subtypes

Thirteen neuropeptide Y (NPY) agonists were administered intracerebroventricularly (i.c.v.) in rats (full dose-response curves) to estimate their half-effective dose (ED50) on feeding. These values were compared to their binding affinities (IC50) for rat NPY receptor subtypes Y1, Y2, Y4 and Y5 in vitro. Correlations between in vivo ED50 and in vitro IC50 were strong for the Y5 (r = 0.87; P < 0.01), weak for the Y1 (r = 0.48; P < 0.04) and non-significant for the Y2 and Y4 receptor subtypes. In vitro, h[D-Trp32]NPY was found to be a Y5-selective ligand and a full agonist in Y5-expressing cells. In vivo, it dose-dependently stimulated feeding, but failed to induce the full maximal response observed with pNPY. It did not antagonize pNPY-induced feeding and overfeeding in 24 h fasted rats. These findings demonstrate a role for the Y5, or possibly Y5 in combination with Y1, but not Y2 or Y4 receptor subtypes in feeding. No evidence was found for the existence of an additional, as yet undescribed, NPY feeding receptor.

The NPY Y1 receptor antagonist BIBP 3226 blocks NPY induced feeding via a non-specific mechanism

We have previously shown that intracerebroventricular BIBP 3226 inhibits NPY induced feeding in rats. However, this was associated with abnormal behaviour, likely to be due to interaction with Y1 receptors involved in mechanisms other than the control of food intake. In order to minimise such interactions we investigated the effects of paraventricular nucleus (PVN) injections of BIBP 3226 and its inactive enantiomer BIBP 3435. Intra-PVN injection of NPY (0.1-2.5 nmol/animal) increased food intake, with an EC50 of approximately 0.15 nmol/animal. Injections of BIBP 3226 and BIBP 3435 (0.25-25 nmol) reduced NPY-induced food intake in a dose responsive manner, with BIBP 3226 reducing food intake by 95%, and BIBP 3435 by 65% at the highest dose tested. The reversibility of the effect of BIBP 3226 was investigated by measuring the feeding response to NPY (0.5 nmol) in animals 1 week after BIBP 3226 injection. The response to NPY was less in animals which had received high doses of BIBP 3226. Animals previously injected with saline vehicle alone showed a normal NPY feeding response. These results suggest that BIBP 3226 may be inhibiting NPY-induced food intake in a non-specific manner, not secondary to inhibition of the Y1 receptor. This does not, however rule out a role for the Y1 receptor in the control of food intake by NPY.

Characterisation of the neuropeptide Y receptor that mediates feeding in the rat: a role for the Y5 receptor?

Food intake was measured in freely fed rats following intracerebroventricular administration of neuropeptide Y (NPY) and several of its analogues and antagonists to investigate the hypothesis that the NPY Y5 receptor mediates feeding. Rat NPY (rNPY), rNPY(2-36) and rNPY(3-36) produced similar feeding responses over the dose range 0.7-7.0 nmol. Rat peptide YY (rPYY) was more potent and at least as efficacious as rNPY. [Leu31 Pro34]-rNPY (agonist potency: Y1 > Y5 > Y4 = y6) and human pancreatic polypeptide (hPP) produced flatter dose-response curves, suggesting partial agonism at the receptor(s). rNPY(13-36) (agonist potency: Y2 > Y5) had little activity and rPP was inactive. [D-Trp32]-NPY was a weak orexigenic agent given alone and, consistent with partial agonism, it markedly antagonised the response to porcine NPY (pNPY). Similarly, the receptor antagonist (Y1 > Y4) 1229U91 stimulated feeding slightly, and markedly inhibited rNPY-induced feeding. In contrast to a previous report, BIBP 3226 (70 nmol), another Y1 receptor antagonist, failed to inhibit the response to rNPY. Our data in vivo are inconsistent with findings that hPP, [Leu31 Pro34]-rNPY and [D-Trp32]-rNPY are full agonists at the rat cloned Y5 receptor. Thus, whilst the Y5 receptor may be involved, its participation as the sole receptor mediating the orexigenic action of NPY in the rat remains unproven.

WRYamide, a NPY-based tripeptide that antagonizes feeding in rats

Modifications of (D-Trp32) neuropeptide Y (NPY) led to the development of potential peptide-based lower molecular weight (500-800 Da) NPY feeding antagonists. One compound, WRYamide (N-Ac-Trp-Arg-Tyr-NH2), blocked NPY-induced feeding for 1 to 4 h when injected intrahypothalamically (i.h.t.) at 1 to 40 microgram. Schedule-induced feeding was also antagonized for up to 24 h by 20 microgram of WRYamide, i.h.t. Injection of 2.5 mg/kg (1 mg/rat) of WRYamide, i.v., also reduced significantly schedule-induced feeding for 4 h. A conditioned taste aversion could not be classically conditioned to saccharin using WRYamide as the unconditioned stimulus. These results may lead to the development of systemically active anti-obesity drugs.

Evidence for involvement of neuropeptide Y receptors in the regulation of food intake: studies with Y1-selective antagonist BIBP3226

1. Experiments were conducted to evaluate the effects of the novel non-peptide neuropeptide Y Y1 receptor antagonist, BIBP3226 (N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)methyl]-D-arginine amide) on spontaneous, fasting-induced and NPY-induced food intake in rats. In addition to consumption of regular chow, the effects of BIBP3226 on consumption of highly palatable sweetened mash were monitored in a 1 h test on first exposure and after familiarization with novel food. 2. BIBP3226 (10.0 nmol, i.c.v.) had no effect on the consumption of regular chow, but reduced significantly the intake of highly palatable diet and the food intake stimulated by fasting (24 h). Neuropeptide Y (NPY, 1.0 nmol, i.c.v.) significantly increased the consumption of regular rat chow. This orexigenic effect of NPY was blocked by BIBP3226 (10.0 nmol, administered i.c.v. 5 min before NPY) at 30 min and 4 h, but not at 1 and 2 h. When animals were pretreated with diazepam (0.5 mg kg(-1), i.p., 20 min before NPY), BIBP3226 failed to suppress NPY-induced feeding. 3. An NPY Y1 and Y3 receptor agonist, [Leu31,Pro34]NPY and a Y5 receptor agonist human peptide YY3-36 (hPYY3-36, both 30 pmol), microinjected into the paraventricular nucleus of the hypothalamus (PVN) increased the consumption of regular rat chow. BIBP3226 (0.4 nmol, into the PVN) completely blocked the stimulatory effect of [Leu31,Pro34]NPY but not that of hPYY3-36. BIBP3226 (0.4 nmol) alone failed to modify the consumption of the regular chow. Higher doses of BIBP3226 (1.0 and 2.0 nmol) injected into the vicinity of the PVN reduced the consumption of the sweetened mash. 4. These results suggest that both the NPY Y1 and Y5 receptors in the PVN are involved in the regulation of food intake. The stimulatory effect of exogenous NPY is probably mediated through an NPY receptor subtype that is not identical with the Y1 receptor (possibly Y5 receptor). However, the NPY Y1 receptors may mediate the effect of endogenous NPY in conditions of increased energy demand or on intake of highly palatable diets.

The neuropeptide Y Y1 antagonist, 1229U91, a potent agonist for the human pancreatic polypeptide-preferring (NPY Y4) receptor

Recently, a novel high-affinity peptide antagonist, 1229U91, was published as a selective neuropeptide Y Y1 antagonist. The selectivity of 1229U91 was evaluated in the human NPY Y1 receptor containing cell line, SK-N-MC, and cells containing the cloned human NPY Y2, the pancreatic polypeptide-preferring (NPY Y4), and the NPY Y5 receptors. 1229U91 potently displaced [125I]-peptide YY (PYY) binding to human NPY Y1 receptors (IC50 = 0.245+/-0.004 nM, n = 4). but displayed little affinity for the human NPY Y2 and Y5 receptors (IC50 > 1000 nM). Interestingly, 1229U91 displaced [125I]-PYY with even greater affinity at the human NPY Y4 receptor (IC50 = 0.081+/-0.009 nM, n = 4). Using a cyclic AMP accumulation assay, 1229U91 blocked NPY inhibition of forskolin-induced adenylate cyclase activity in NPY Y1 receptor containing SK-N-MC cells. In the human NPY Y4 receptor expressing cell line, 1229U91 did not block pancreatic polypeptide (PP) inhibition of forskolin stimulated adenylate cyclase. However, in the absence of PP, 1229U91 was able to inhibit forskolin stimulated cyclic AMP accumulation (IC50 = 7.16+/-2.8 nM, n = 4). We conclude that 1229U91 binds non-selectively with high affinity to both human NPY Y1 and Y4 receptors. Furthermore, 1229U91 displays antagonist activity at the NPY Y1 receptor, while having agonist activity at the NPY Y4 receptor.

Peptide analogue studies of the hypothalamic neuropeptide Y receptor mediating pituitary adrenocorticotrophic hormone release

Hypothalamic neuropeptide Y (NPY) is thought to be important in the regulation of feeding and also in the release of Adrenocorticotrophic hormone (ACTH). Intracerebroventricular administration of NPY to male rats significantly increased plasma ACTH 10 min after injection and stimulated 2-h food intake. A series of analogues of NPY that have a greatly reduced affinity for the Y1 [human pancreatic polypeptide (human PP), NPY(3-36)], the Y2 ([Pro34]NPY, human PP), the Y3 (peptide YY), and the Y6 (human PP) receptor, all markedly stimulated ACTH release. Rat PP, which binds with high affinity to the Y4 receptor, was unable to stimulate ACTH release. A novel analogue fragment [Pro34]NPY(13-36) was synthesized as a ligand with low Y1 and Y2 receptor affinity. Interestingly, neither [Pro34]NPY(13-36) nor the selective Y5 receptor agonist [D-Trp32]NPY stimulated food intake, whereas both significantly increased plasma ACTH. Thus the hypothalamic NPY receptor mediating increases in plasma ACTH has a fragment activation profile unlike the Y1-Y4 or Y6 receptors and appears distinct from the NPY receptor controlling food intake.

The bioactive conformation of neuropeptide Y analogues at the human Y2-receptor

Several attempts to investigate the bioactive conformation of neuropeptide Y have been made so far. As cyclic peptides are much more rigid than linear ones, we decided to synthesise cyclic analogues of the C-terminal dodekapeptide amide neuropeptide Y Ac-25-36. Cyclisation was performed by side chain lactamisation of ornithine or lysine and glutamic or aspartic acid. The affinity of the 19 peptides ranged from Ki 0.6 nM to greater than 10,000 nM. We found that the size, position, orientation, configuration. and the location of the cycle plays an important role for receptor recognition. Circular dichroic studies have been performed to characterise the secondary structure of each peptide. Receptor binding studies were carried out on human neuroblastoma cell lines SK-N-MC (Y1) and SMS-KAN (Y2), and on rabbit kidney membranes (Y2). The pharmacological and spectral data showed that the alpha-helix content was not the predominant factor for high Y2-receptor affinity. Instead, the location and the size of the hydrophobic lactam bridge, and the conserved C-terminal tetrapeptide (Arg-Glu-Arg-Tyr) seemed to be the main parameters. Using molecular dynamics, the structures of four cyclic peptides (i,i+4) have been investigated and compared with the previously published NMR structure of one of the cyclic peptide analogues. Significant differences have been found in the overall three-dimensional fold of the peptides. The distances between the N- and the C-terminus allow discrimination between peptides with high binding affinity and those with low binding affinity, because of the correlation that was found with the measured affinity. Thus, this study suggests that a turn-like structure and the orientation of the C-terminus towards the N-terminus play major roles for high affinity binding of cyclic dodecapeptides to the Y2-receptor. None of the cyclic segments exhibits significant affinity to the Y1-receptor. Thus, these results support the hypothesis of a discontinuous binding site of neuropeptide Y at the Y1-receptor.

Regulation of neurotransmission in the arcuate nucleus of the rat by different neuropeptide Y receptors

We examined the effects of peptides of the neuropeptide Y (NPY)/pancreatic polypeptide (PP) family on synaptic transmission in the arcuate nucleus in rat hypothalamic slices. Application of NPY produced two effects. In some cells NPY produced an outward current that had the properties of a K+ current. NPY also inhibited the evoked glutamatergic EPSC recorded in these arcuate neurons by a presynaptic mechanism. Although the effects of NPY on the K+ current reversed within a few minutes of washout of the peptide, its effects on the EPSC frequently were longer lasting (>30 min). Similar effects were observed using peptide YY or the NPY analog [Leu31, Pro34]NPY. Although K+ current activation by [Leu31,Pro34]NPY was blocked by the selective Y1 antagonist BIBP 3226, inhibition of the EPSC was blocked only partially. Other NPY-related peptides such as NPY(13-36), PP, and [D-Trp32]NPY also inhibited the EPSC. However, none of these peptides produced activation of the K+ current. Thus, activation of more than one NPY receptor produces synaptic inhibition in the arcuate nucleus. A Y1 receptor activates a K+ current postsynaptically, and several receptor types appear to inhibit the EPSC by a presynaptic mechanism.

Substitution of D-Trp32 in NPY destabilizes the binding transition state to the Y1 receptor site in SK-N-MC cell membranes

The retention rate of the spin label 3-isothiocyanto methyl-2,2,5,5-tetramethyl-1-pyrrolidinyl oxyl spin label (proxyl) attached to the porcine N-acetyl-NPY peptide and the porcine N-acetyl-D-Trp32-NPY peptide at Lys4 was investigated using SK-N-MC neuroblastoma cell membranes containing the Y1 receptor. The release rate of the spin labeled peptides was monitored by electron spin resonance and the KD was determined by a direct radiolabeled NPY displacement binding assay. The analyses show that for the porcine [Ac-Tyr1N epsilon 4-proxyl]-NPY, the KD was 8 x 10(-10) M and koff was 2.7 x 10(-4) sec-1 yielding a value for kon of 3.3 x 10(5) sec-1 M-1. The [Ac-Tyr1, N epsilon 4-proxyl,-D-Trp32]-NPY antagonist ligand had a value of KD equal to 1.35 x 10(-7) M and koff was 1.7 x 10(-4) sec-1 leading to a value for kon of 1.2 x 10(3) sec-1 M-1. The difference in the kon rates of two orders of magnitude is interpreted as demonstrating the N-acetyl-N epsilon 4 proxyl-D-Trp32-NPY ligand binding transition state to be of higher energy then for the unmodified NPY amino acid sequence.

Neuropeptide Y family of hormones: receptor subtypes and antagonists

Neuropeptide Y (NPY) is the most abundant peptide present in the mammalian central and peripheral nervous system. NPY exhibits a variety of potent central and peripheral effects including those on feeding, memory, blood pressure, cardiac contractility and intestinal secretions. Classical pharmacological studies have shown that NPY effects are mediated by four different receptor subtypes, Y-1, Y-1-like, Y-2, and Y-3. However, the existence of numerous atypical activities provide strong evidence for the occurrence of additional NPY receptor subtypes. Pharmacological studies have further been facilitated by the recent cloning and expression of Y-1, Y-2, Y-4 (PP-1) and Y-5 receptors. Moreover, the cloned Y-5 receptor has been suggested to be the long awaited Y-1-like receptor involved in feeding. Structure-activity studies have laid a good foundation towards the development of receptor selective compounds, and to date potent Y-1 selective peptide and nonpeptide antagonists have been developed. The need to clone numerous receptor subtypes and to develop receptor selective compounds for physiological and perhaps clinical use is expected to keep NPY research active for many years to come.

Effects of neuropeptide Y (NPY) and [D-Trp32]NPY on monoamine and metabolite levels in dialysates from rat hypothalamus during feeding behavior

Administration of neuropeptide Y (NPY) into hypothalamic areas or into the cerebral ventricles induces marked increases in food consumption in satiated rats. Since monoamines have been suggested to be involved in NPY-induced feeding, we investigated the effects of NPY and [D-Trp32]NPY, a putative NPY antagonist, on extracellular levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4-dihydroxyphenyl acetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindole-3-acetic acid (5-HIAA) in the hypothalamus, including the paraventricular hypothalamic nuclei (PVN), during feeding behavior. Intracerebroventricular (i.c.v.) injections of NPY (20 microg) significantly increased extracellular NE (1.5-fold), DA (2.5-fold), DOPAC (2-fold) and HVA (3-fold), and did not change 5-HT or 5-HIAA levels. This dose of NPY significantly increased food intake over a 2 h period. The putative NPY antagonist [D-Trp32]NPY (40 microg, i.c.v.) produced similar neurochemical changes to NPY: it increased dialysate levels of NE (1.7-fold), DA (2.5-fold), DOPAC (1.6-fold) and HVA (2.2-fold) and did not change 5-HT or 5-HIAA levels. [D-Trp32]NPY also produced a significant increase in food intake. I.c.v. administration of [D-Trp32]NPY 5 min before NPY did not significantly change the increase in NE, DA, HVA and DOPAC induced by NPY. In these animals, food consumption was also significantly increased. These data indicate that NPY-induced feeding is associated with activation of the hypothalamic monoaminergic system and that [D-Trp32]NPY, at the dose given, acts as an agonist and not as an antagonist at NPY receptors in vivo.

A receptor subtype involved in neuropeptide-Y-induced food intake

Neuropeptide Y (NPY) is a powerful stimulant of food intake and is proposed to activate a hypothalamic 'feeding' receptor distinct from previously cloned Y-type receptors. This receptor was first suggested to explain a feeding response to NPY and related peptides, including NPY2-36, that differed from their activities at the Y1 receptor. Here we report the expression cloning of a novel Y-type receptor from rat hypothalamus, which we name Y5. The complementary DNA encodes a 456-amino-acid protein with less than 35% overall identity to known Y-type receptors. The messenger RNA is found primarily in the central nervous system, including the paraventricular nucleus of the hypothalamus. The extent to which selected peptides can inhibit adenylate cyclase through the Y5 receptor and stimulate food intake in rats correspond well. Our data support the idea that the Y5 receptor is the postulated 'feeding' receptor, and may provide a new method for the study and treatment of obesity and eating disorders.

Antinociceptive effects of neuropeptide Y and related peptides in mice

This study compares the antinociceptive and orexigenic activities of NPY and analogs after intracerebroventricular administration in mice. NPY had an antinociceptive action in the mouse writhing test which was not affected by prior treatment with naltrexone, yohimbine, idazoxan or reserpine. A detailed examination revealed that NPY (0.023-0.7 nmol), PYY (0.007-0.07 nmol), NPY2-36 (0.023-0.23 nmol) and the Y1 agonist [Leu31, Pro34]-NPY (0.07-0.7 nmol) all produced a dose-dependent and complete suppression of acetic acid-induced writhing. In contrast, the Y2 agonist, NPY13-36, had little or no antinociceptive effect. As shown by their ED50 values, the relative potency of the peptides was PYY > NPY2-36 > or = NPY > [Leu31, Pro34]-NPY > > NPY13-36, suggesting that a Y1 rather than a Y2 or Y3 receptor subtype was implicated in the antinociceptive action. Thereafter, all peptides were assessed for their effects on food intake. With respect to dose and peptide specificity, the hyperphagic effects of NPY and related peptides paralleled those on nociception, suggesting a common receptor mechanism. However, a purported NPY antagonist, [D-Trp32]-NPY, attenuated NPY's effect on feeding yet this same peptide elicited a dose-dependent inhibition of acetic acid-induced writhing, suggesting some molecular distinction between antinociception and stimulation of food intake.

Hemodynamic characterization of a novel neuropeptide Y receptor antagonist

Defining the roles of the vasoconstrictor peptide neuropeptide Y (NPY) in the cardiovascular system is difficult due to lack of availability of specific NPY receptor antagonists. We report the in vivo NPY receptor blocking actions of a novel nonapeptide dimer, 1229U91 {(IleGluProDprTyrArgLeuArgTyrNH(2)(2)}, and describe its hemodynamic effects. In anesthetized normotensive rats, 1229U91 produced significant and dose-dependent reductions in NPY-reduced hemodynamic responses. 1229U91 (3-30 nmol/kg intravenously, i.v.) attenuated the pressor response (34 +/- 6-84 +/- 1%) and the increases in renal vascular resistance (RVR, 56 +/- 9-94 +/- 2%) produced by NPY (1 nmol/kg i.v.). Intravenous norepinephrine (NE)-induced hemodynamic responses were not altered by 1229U91. 1229U91 also produced dose-dependent inhibition of NPYinduced vasoconstrictor responses in anesthetized dogs and spontaneously hypertensive rats (SHR). These data demonstrate that 1229U91 is a selective NPY receptor antagonist. 1229U91 had no effect on resting hemodynamic variables in these preparations. In conscious SHR, 1229U91 did not produce significant changes in blood pressure (BP) or heart rate (HR) over a wide dose-range (15-1,500 nmol/kg i.v.). Lack of effect of the NPY receptor antagonist in SHR suggests that NPY does not contribute to the maintenance of BP in this hypertension model.

Antagonistic properties of centrally truncated analogs of [D-Trp(32)]NPY

We have previously shown that [D-Trp(32)]NPY can competitively antagonize NPY-induced feeding in rats (Balasubramaniam et al. J. Med. Chem. 1994, 37, 811-815). This peptide, however, did not bind to SK-N-MC cells with Y-1 receptors. Since centrally truncated NPY analogs have been shown to bind Y-1 receptors, we synthesized similar analogs of [D-Trp(32)]NPY and investigated their Y-1 (SK-N-MC) and Y-2 (SK-N-BE2) receptor affinities and their properties in human erythroleukemia (HEL) cells. None of the analogs with D-Trp(32) mobilized intracellular calcium, [Ca2]i, in HEL cells. Although Des-AA(6-24)[Aoc(6)]NPY and the corresponding D-Trp(32) analog exhibited no affinity to Y-1 receptors, Des-AA(7-24)[Aoc(6),D-Trp(32)] NPY(6) exhibited weak binding. Replacing Pro(5) in 6 with D-Ala to stabilize the central chain reversal, and hence the antiparallel alignment of the N- and C-terminal regions known to be important for Y-1 binding, resulted in an analog, Des-AA(7-24)[D-Ala(5),Aoc(6),D-Trp(32)]NPY (7), which exhibited moderate antagonist potency in attenuating NPY effects on cAMP and [Ca2+]i, in SK-N-MC and HEL cells, respectively. This analog also shifted the dose-response curve of NPY on blood pressure in anesthetized rats. Deletion of only the 7-17 and/or the incorporation of N-Me-Ala(5), superior beta-turn stabilizer, in 7 did not improve the Y-1 receptor affinity. Des-AA(7-24)[D-Ala(5), Gly(6),D-Trp(32)]NPY exhibited an affinity similar to that of 7, suggesting that a long spacer arm is not necessary for efficient Y-1 receptor interaction. Locking the antiparallel alignment via a 2/26 or 2/27 lactam bridge did not improve the binding. Finally, replacement of D-Ala(5) in 7 with D-Trp dramatically increased both the binding and the antagonistic potencies. Modeling based on the avian pancreatic polypeptide X-ray structure suggested that analogs which have the N- and C-terminal regions in close proximity might exhibit good binding, and that the D-Trp(32) substitution may induce a beta-turn that could be important for exhibiting antagonism. A systematic investigation has resulted in the development of relatively potent Y-1 receptor antagonists. Further structure-activity studies with these compounds and those previously reported by us and other investigators should result in the development of long-acting and receptor selective antagonists.

Synthesis, structure, and antagonistic properties of des-Asn29[D-Trp28,32]NPY(27-36)

We have previously reported that [D-Trp32]NPY and its centrally truncated analogues such as des-AA7-24[D-Trp5,32,Aoc6]NPY can competitively antagonize NPY effects on rat hypothalamus and Y1 (SK-N-MC AND HEL) cells, respectively. In continuation of this work, we performed structure-activity studies with C-terminal decapeptide sequence keeping D-Trp at position 32 to develop lower molecular weight Y1-selective antagonists. This study led to the development of des-Asn29[D-Trp28,32]NPY(27-36), which bound to both Y1 (SK-N-MC, Ki > or = 10 microM) and Y2 (SK-N-BE2, Ki = 1.01 +/- 0.03 microM) receptors. This peptide did not exhibit any agonist activity at Y1 receptors, and exhibited comparable potencies in antagonizing the effects of NPY on the synthesis of cAMP and mobilization of [Ca2+]i in HEL cells. However, in SK-N-MC cells, it was more potent in antagonizing the mobilization of [Ca2+]i than inhibition of cAMP synthesis. Substitution of Nva for Gln34 to increase the hydrophobicity without altering the carbon skeleton substantially increased Y1 affinity (Ki = 0.33 +/- 0.15 microM) and imparted Y1 selectivity (Ki for Y2 affinity = 3.16 +/- 0.50). Moreover, this peptide exhibited good antagonistic potency in HEL cells. 2D NMR studies of des-Asn29[D-Trp28,32]NPY(27-36) revealed the existence of a fairly stable loop-like structure between residues 27 and 32 and a less stable one between residues 32 and 36. The increased Y1 affinity of des-Asn29[D-Trp28,32,Nva34]NPY(27-36) may be due to the stabilization of the 32-36 loop by Nva34. It appears therefore that stabilization of the loop structures in these peptides should result in the development of more potent Y1 receptor antagonists. Our investigations also suggest that HEL cells express a homogeneous population of NPY Y1 receptors whereas SK-N-MC cells express high- and low-affinity Y1 receptors coupled to Ca2+ and cAMP, respectively.

Cloning and functional expression of a cDNA encoding a human type 2 neuropeptide Y receptor

Neuropeptide Y (NPY) is a 36-amino acid polypeptide that is widely distributed in the central nervous system and periphery. Pharmacological studies have suggested that there are at least three receptor subtypes, Y1, Y2, and Y3. Cloning of the Y1 subtype has been reported previously. Here we report the isolation by expression cloning of a cDNA encoding a human NPY receptor displaying a pharmacology typical of a Y2 receptor. COS-7 cells transfected with the cDNA express high affinity binding sites for NPY, peptide YY, and NPY13-36, whereas [Leu31,Pro34]NPY binds with lower affinity. The receptor is 381 amino acids in length and has seven putative transmembrane regions typical of G-protein-coupled receptors. Comparison of the amino acid sequence of this Y2 receptor to that of the human Y1 receptor indicates that the two receptors are 31% identical at the amino acid level. Northern blot analyses reveal a single 4-kilobase mRNA species and indicate that the messenger RNA is present in many areas of the central nervous system. NPY induced calcium mobilization and inhibited forskolin-stimulated cAMP accumulation in Chinese hamster ovary cells that stably express the Y2 receptor cDNA, indicating that the recombinant Y2 receptor is functionally coupled to second messenger systems.

High-affinity neuropeptide Y receptor antagonists

Neuropeptide Y (NPY) is one of the most abundant peptide transmitters in the mammalian brain. In the periphery it is costored and coreleased with norepinephrine from sympathetic nerve terminals. However, the physiological functions of this peptide remain unclear because of the absence of specific high-affinity receptor antagonists. Three potent NPY receptor antagonists were synthesized and tested for their biological activity in in vitro, ex vivo, and in vivo functional assays. We describe here the effects of these antagonists inhibiting specific radiolabeled NPY binding at Y1 and Y2 receptors and antagonizing the effects of NPY in human erythroleukemia cell intracellular calcium mobilization perfusion pressure in the isolated rat kidney, and mean arterial blood pressure in anesthetized rats.