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

Illuminating the neuropeptide Y4 receptor and its ligand pancreatic polypeptide from a structural, functional, and therapeutic perspective

The neuropeptide Y4 receptor (Y4R), a rhodopsin-like G protein-coupled receptor (GPCR) and the hormone pancreatic polypeptide (PP) are members of the neuropeptide Y family consisting of four receptors (Y1R, Y2R, Y4R, Y5R) and three highly homologous peptide ligands (neuropeptide Y, peptide YY, PP). In this family, the Y4R is of particular interest as it is the only subtype with high affinity to PP over NPY. The Y4R, as a mediator of PP signaling, has a pivotal role in appetite regulation and energy homeostasis, offering potential avenues for the treatment of metabolic disorders such as obesity. PP as anorexigenic peptide is released postprandial from the pancreas in response to food intake, induces satiety signals and contributes to hamper excessive food intake. Moreover, this system was also described to be associated with different types of cancer: overexpression of Y4R have been found in human adenocarcinoma cells, while elevated levels of PP are related to the development of pancreatic endocrine tumors. The pharmacological relevance of the Y4R advanced the search for potent and selective ligands for this receptor subtype, which will be significantly progressed through the elucidation of the active state PP-Y4R cryo-EM structure. This review summarizes the development of novel PP-derived ligands, like Obinepitide as dual Y2R/Y4R agonist in clinical trials or UR-AK86c as small hexapeptide agonist with picomolar affinity, as well as the first allosteric modulators that selectively target the Y4R, e.g. VU0506013 as potent Y4R positive allosteric modulator or (S)-VU0637120 as allosteric antagonist. Here, we provide valuable insights into the complex physiological functions of the Y4R and PP and the pharmacological relevance of the system in appetite regulation to open up new avenues for the development of tool compounds for targeted therapies with potential applications in metabolic disorders.

PET Imaging of the Neuropeptide Y System: A Systematic Review

Neuropeptide Y (NPY) is a vastly studied biological peptide with numerous physiological functions that activate the NPY receptor family (Y₁, Y₂, Y₄ and Y₅). Moreover, these receptors are correlated with the pathophysiology of several diseases such as feeding disorders, anxiety, metabolic diseases, neurodegenerative diseases, some types of cancers and others. In order to deepen the knowledge of NPY receptors' functions and molecular mechanisms, neuroimaging techniques such as positron emission tomography (PET) have been used. The development of new radiotracers for the different NPY receptors and their subsequent PET studies have led to significant insights into molecular mechanisms involving NPY receptors. This article provides a systematic review of the imaging biomarkers that have been developed as PET tracers in order to study the NPY receptor family.

Crystal structures of human neuropeptide Y (NPY) and peptide YY (PYY)

Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) form the evolutionarily conserved pancreatic polypeptide family. While the fold is widely utilized in nature, crystal structures remain elusive, particularly for the human forms, with only the structure of a distant avian form of PP reported. Here we utilize a crystallization chaperone (antibody Fab fragment), specifically recognizing the amidated peptide termini, to solve the structures of human NPY and human PYY. Intriguingly, and despite limited sequence identity (~50%), the structure of human PYY closely resembles that of avian PP, highlighting the broad structural conservation of the fold throughout evolution. Specifically, the PYY structure is characterized by a C-terminal amidated α-helix, preceded by a backfolded poly-proline N-terminus, with the termini in close proximity to each other. In contrast, in the structure of human NPY the N-terminal component is disordered, while the helical component of the peptide is observed in a four-helix bundle type arrangement, consistent with a propensity for multimerization suggested by NMR studies.

N-Terminus to Arginine Side-Chain Cyclization of Linear Peptidic Neuropeptide Y Y4 Receptor Ligands Results in Picomolar Binding Constants

The family of neuropeptide Y (NPY) receptors comprises four subtypes (Y₁R, Y₂R, Y₄R, Y₅R), which are addressed by at least three endogenous peptides, i.e., NPY, peptide YY, and pancreatic polypeptide (PP), the latter showing a preference for Y₄R. A series of cyclic oligopeptidic Y₄R ligands were prepared by applying a novel approach, i.e., N-terminus to arginine side-chain cyclization. Most peptides acted as Y₄R partial agonists, showing up to 60-fold higher Y₄R affinity compared to the linear precursor peptides. Two cyclic hexapeptides (18, 24) showed higher Y₄R potency (Ca²⁺ aequorin assay) and, with pK_i values >10, also higher Y₄R affinity compared to human pancreatic polypeptide (hPP). Compounds such as 18 and 24, exhibiting considerably lower molecular weight and considerably more pronounced Y₄R selectivity than PP and previously described dimeric peptidic ligands with high Y₄R affinity, represent promising leads for the preparation of labeled tool compounds and might support the development of drug-like Y₄R ligands.

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

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

Towards improved receptor targeting: anterograde transport, internalization and postendocytic trafficking of neuropeptide Y receptors

The neuropeptide Y system is known to be involved in the regulation of many central physiological and pathophysiological processes, such as energy homeostasis, obesity, cancer, mood disorders and epilepsy. Four Y receptor subtypes have been cloned from human tissue (hY1, hY2, hY4 and hY5) that form a multiligand/multireceptor system together with their three peptidic agonists (NPY, PYY and PP). Addressing this system for medical application requires on the one hand detailed information about the receptor-ligand interaction to design subtype-selective compounds. On the other hand comprehensive knowledge about alternative receptor signaling, as well as desensitization, localization and downregulation is crucial to circumvent the development of undesired side-effects and drug resistance. By bringing such knowledge together, highly potent and long-lasting drugs with minimized side-effects can be engineered. Here, current knowledge about Y receptor export, internalization, recycling, and degradation is summarized, with a focus on the human Y receptor subtypes, and is discussed in terms of its impact on therapeutic application.

Manipulating Y receptor subtype activation of short neuropeptide Y analogs by introducing carbaboranes

Short selective neuropeptide Y (NPY) analogs are highly attractive because of their facile synthesis. Based on the reduced-size NPY analog [Pro(30), Nle(31), Bpa(32), Leu(34)]NPY 28-36 position 32 was identified as a key position to alter the preferential activation pattern of the human neuropeptide Y receptors (hYRs). By replacing benzoylphenylalanine (Bpa) by a biphenylalanine (Bip) the photostability was first improved while the biological activity was maintained. SAR-studies showed that both aromatic rings have a high influence on the preferential hYR subtype activation. Interestingly, replacement of Bpa(32) by a strongly hydrophobic moiety changed the hYR subtype preference of the analog. Whereas the parent compound is able to activate the human neuropeptide Y1 receptor (hY1R) subtype, the introduction of an N(ε)-ortho-carbaboranyl propionic acid modified lysine resulted in a loss of activity at the hY1R but in an increased activity at both the hY2R and the hY4R. However, subsequent receptor internalization studies with this novel analog revealed that receptor internalization can neither be triggered at the hY2R nor at the hY4R suggesting a biased ligand. Surprisingly, investigations by (1)H NMR spectroscopy revealed structural changes in the side chains of residues Pro(30) and Leu(34) which nicely correlates with the shift from hY1R/hY4R to hY2R/hY4R activation preference. Thus, position 32 has been identified to switch the bioactive conformation and subsequently influences receptor subtype activation behavior.

Neuropeptide Y receptors: how to get subtype selectivity

The neuropeptide Y (NPY) system is a multireceptor/multiligand system consisting of four receptors in humans (hY(1), hY(2), hY(4), hY(5)) and three agonists (NPY, PYY, PP) that activate these receptors with different potency. The relevance of this system in diseases like obesity or cancer, and the different role that each receptor plays influencing different biological processes makes this system suitable for the design of subtype selectivity studies. In this review we focus on the latest findings within the NPY system, we summarize recent mutagenesis studies, structure activity relationship studies, receptor chimera, and selective ligands focusing also on the binding mode of the native agonists.

Therapeutic potential of neuropeptide Y (NPY) receptor ligands

Neuropeptide Y (NPY) is widely distributed in the human body and contributes to a vast number of physiological processes. Since its discovery, NPY has been implicated in metabolic regulation and, although interest in its role in central mechanisms related to food intake and obesity has somewhat diminished, the topic remains a strong focus of research concerning NPY signalling. In addition, a number of other uses for modulators of NPY receptors have been implied in a range of diseases, although the development of NPY receptor ligands has been slow, with no clinically approved receptor therapeutics currently available. Nevertheless, several interesting small molecule compounds, notably Y2 receptor antagonists, have been published recently, fueling optimism in the field. Herein we review the role of NPY in the pathophysiology of a number of diseases and highlight instances where NPY receptor signalling systems are attractive therapeutic targets.

Determination of Affinity and Activity of Ligands at the Human Neuropeptide Y Y4Receptor by Flow Cytometry and Aequorin Luminescence

Fluorescence-labeled neuropeptide Y (NPY) has been used in flow cytometric binding assays for the determination of affinity constants of NPY Y1, Y2, and Y5 receptor ligands. Because the binding of fluorescent NPY is insufficient for competition studies at the human Y4 receptor (hY4R), we replaced Glu-4 in hPP with Lys for the derivatization with cyanine-5. Because cy5-[K(4)]hPP has high affinity (Kd 5.6 nM) to the hY4R, it was used as a probe in a flow cytometric binding assay. Specific binding of cy5-[K(4)]hPP to hY4R was visualized by confocal microscopy. The hY(4)R, the chimeric G protein G(qi5) and mitochondrially targeted apoaequorin were stably coexpressed in CHO cells. Aequorin luminescence was quantified in a microplate reader and by a CCD camera. By application of these methods 3-cyclohexyl-N-[(3-1H-imidazol-4-ylpropylamino)(imino)methyl]propanamide (UR-AK49) was discovered as the first nonpeptidic Y4R antagonist (pKi 4.17), a lead to be optimized in terms of potency and selectivity.

Neuropeptide y receptor selective ligands in the treatment of obesity

Obesity is a serious public health problem throughout the world, affecting both developed societies and developing countries. The central nervous system has developed a meticulously interconnected circuitry in order to keep us fed and in an adequate nutritional state. One of these consequences is that an energy-dense environment favors the development of obesity. Neuropeptide Y (NPY) is one of the most abundant and widely distributed peptides in the central nervous system of both rodents and humans and has been implicated in a variety of physiological actions. Within the hypothalamus, NPY plays an essential role in the control of food intake and body weight. Centrally administered NPY causes robust increases in food intake and body weight and, with chronic administration, can eventually produce obesity. NPY activates a population of at least six G protein-coupled Y receptors. NPY analogs exhibit varying degrees of affinity and specificity for these Y receptors. There has been renewed speculation that ligands for Y receptors may be of benefit for the treatment of obesity. This review highlights the therapeutic potential of Y(1), Y(2), Y(4), and Y(5) receptor agonists and antagonists as additional intervention to treat human obesity.

Mechanisms and emerging treatments of the metabolic complications of chronic pancreatitis

OBJECTIVES

Exocrine and endocrine abnormalities in chronic pancreatitis contribute to the morbidity and mortality risks of the disease. Complications of exocrine insufficiency include malabsorption, vitamin deficiency syndromes, and weight loss. Oral enzyme replacement therapy is usually effective if attention is paid to factors that affect the bioavailability of enzyme preparations. Complications of endocrine insufficiency can be more difficult to treat due in part to an incomplete knowledge of their etiology.

METHODS

This review focuses on the endocrine aspects of chronic pancreatitis and highlights the observations of our laboratory on the pathogenesis of the metabolic complications of the disease.

RESULTS

In addition to decreased insulin secretory capacity, pancreatogenic (or apancreatic) diabetes is characterized by decreased or absent glucagon and pancreatic polypeptide (PP) secretion, a loss of hepatic insulin receptor (IR) expression/availability, and an impairment in hepatic IR function (phosphorylation and endocytosis). Diminished hepatic IR expression in chronic pancreatitis appears to be because of PP deficiency; laboratory animals and patients with PP deficiency demonstrate decreased hepatic IR availability that is reversed by prolonged (8-hour) PP administration. The impairment in hepatic IR function appears independent of PP deficiency but is reversed by prolonged (28-day) treatment with the insulinotropic/insulinomimetic hormone glucagon-like peptide 1. The endocytosis of hepatic IR is linked to the endocytosis of the glucose transporter 2 from the hepatocyte plasma membrane, and studies suggest that the 2 plasma membrane-bound proteins are complexed noncovalently to function and translocate as a unit after insulin binding to the hepatic IR. The process appears vigorous and sensitive enough to account for a significant reduction in hepatic glucose output and may represent a major mechanism for insulin regulation of hepatic glucose production.

CONCLUSIONS

The regulatory mechanisms of PP-mediated hepatic IR expression and combined IR and GLUT2 endocytosis after insulin binding are defective in chronic pancreatitis and contribute to the apancreatic diabetes, which characterizes this disease.

Self-regulation of agonist activity at the Y receptors

Neuropeptide Y (NPY) is one of the most abundant neuropeptides, and is likely to be present at nanomolar levels over extended periods in the synaptic space of many forebrain areas. This might be linked to an evolved generalized toning activity through a number of other peptide receptors that use C-terminally amidated agonists (with LHRH and orexin receptors and GIR as examples). However, the Y1 and Y2 receptors (which constitute the bulk of Y receptors active in the neural matrix) possess subnanomolar affinities that, at saturating NPY levels, could produce excessive signaling, as well as receptor losses via repeated endocytosis. The related Y4 receptor shows an even higher agonist affinity, and faces the same problem in visceral and neural locations accessible to pancreatic polypeptide (PP). An examination of agonist peptide interaction with Y receptors shows that Y1 and Y4 receptors in particular (as located on either the intact cells, or on particulates derived from various cell types) develop a blockade dependent on ligand concentration, with the blocking ranks of [NPY]>>[peptide YY] (PYY) for the Y1, and [human PP]>>>[PYY-related Y4 agonist] for the Y4 receptor. This blockade is also echoed in a concentration-related reduction in biological activity of primary agonists (NPY and PP), resembling a partial agonism, and is influenced especially by the allosteric interactivity of agonists. With the Y2 receptor, the blocking by agonists is less pronounced, but the signaling by NPY-related peptides is apparently less than with PYY-related agonists. The extended occupancy and self-attenuation of primary agonist activity at Y receptors could represent an evolutionary solution contributing to a balancing of metabolic signaling, agonist clearance and receptor conservation.

Neuropeptides and their receptors: innovative science providing novel therapeutic targets

This review examines our current understanding of the roles of some of the best known neuropeptides that have played major roles in our combined research programmes. Evidence obtained from over 75 years of research shows involvement of these transmitters in a wide range of organs relevant to cardiovascular, respiratory, cutaneous, neuronal and intestinal systems. There is an increasing understanding of the mechanisms involved in the release of the peptides (substance P and calcitonin gene-related peptide (CGRP)) from sensory nerves or, neuropeptide Y (NPY) from sympathetic, parasympathetic and nonadrenergic, noncholinergic (NANC) neurons. Responses in target tissues result from interactions of the neuropeptides, or related forms, with specific G-protein coupled receptors (GPCRs or 7 transmembrane-spanning, 7TM proteins) that belong to either rhodopsin-like, class 1 (neurokinin (NK) and NPY Y receptors) or secretin-like, class 2 GPCRs (CGRP receptors). The majority of receptors activated by our chosen neuropeptides are now cloned, with knowledge of preferred agonists and selective antagonists for many receptor subtypes within these families. The study of neuropeptides in animal models has additionally revealed physiological and pathophysiological roles that in turn have led to the ongoing development of new drugs, through utilization predominantly of antagonist activities.

Y(4) receptors mediate the inhibitory responses of pancreatic polypeptide in human and mouse colon mucosa

The antisecretory effects of several Y agonists, including pancreatic polypeptide (PP), indicate the presence of Y(1), Y(2), and Y(4) receptors in mouse and human (h) colon mucosae. Here, we used preparations from human and from wild-type (WT), Y(4), and Y(1) receptor knockout ((-/-)) mice, alongside Y(4) receptor-transfected cells to define the relative functional contribution of the Y(4) receptor. First, rat (r) PP antisecretory responses were lost in murine Y(4)(-/-) preparations, but hPP and Pro(34) peptide YY (PYY) costimulated Y(4) and Y(1) receptors in WT mucosa. The Y(1) antagonist/Y(4) agonist GR231118 [(Ile,Glu,Pro,Dpr,Tyr,Arg,Leu,Arg,Try-NH(2))-2-cyclic(2,4'),(2',4)-diamide] elicited small Y(4)-mediated antisecretory responses in human tissues pretreated with the Y(1) antagonist, BIBO3304 [(R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N(2)-(diphenylacetyl)-argininamide trifluoroacetate)], and attenuated Y(4)-mediated hPP responses in mouse and human mucosa. GR231118 and rPP were also antisecretory in hY(4)-transfected epithelial monolayers but were partial agonists compared with hPP at this receptor. In Y(4)-transfected human embryonic kidney (HEK) 293 cells, Y(4) ligands displaced [(125)I]hPP binding with orders of affinity (pK(i)) at human (hPP = rPP > GR231118 > Pro(34)PYY = PYY) and mouse (rPP = hPP > GR231118 > Pro(34)PYY > PYY) Y(4) receptors. GR231118- and rPP-stimulated guanosine 5'-3-O-(thio)triphosphate binding through hY(4) receptors with significantly lower efficacy than hPP. GR231118 marginally increased basal but abolished further PP-induced hY(4) internalization to recycling (transferrin-labeled) pathways in HEK293 cells. Taken together, these findings show that Y(4) receptors play a definitive role in attenuating colonic anion transport and may be useful targets for novel antidiarrheal agents due to their limited peripheral expression.

Evidence for the existence of an additional class of neuropeptide Y receptor sites in rat brain

Five distinct neuropeptide Y (NPY) receptors have been cloned thus far. Selective agonists and antagonists have recently been developed allowing for detailed functional studies as to the pathophysiological role of a given subtype as well as receptor binding characteristics and distribution. To precisely investigate the discrete localization and ligand selectivity profile of Y4 and Y5 receptors, a series of selective molecules were used as radioligands and competitors in rat brain tissues. Binding data revealed that Y4 and Y5 receptor-related agonists and antagonists competed with high affinity for specific 125I-[Leu31,Pro34]human peptide YY (hPYY) binding in the presence of BIBO3304 [(R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]-methyl]-N2-(diphenylacetyl)-argininamide trifluoroacetate] to mask Y1 sites as well as specific 125I-labeled human pancreatic polypeptide (hPP) binding. Competition binding profiles were best fitted to a two-site model for both radioligands, suggesting the likely recognition of the Y4 and Y5 subtypes. We were surprised to find that the visualization of these specific binding sites by receptor autoradiography clearly revealed the distinct distribution of specific 125I-[Leu31,Pro34]hPYY (in presence of Y1 and Y5 blockers) and 125I-hPP (in presence of Y5 blocker) binding sites. Moreover, significant amounts of specific 125I-hPP binding were observed in the medial preoptic area, paraventricular nucleus of the hypothalamus, interpeduncular nucleus, and various brainstem nuclei, even after masking Y4 and Y5 receptors. Similar results were obtained using 125I-hPYY(3-36) in presence of Y2 and Y5 blockers. These results suggest the possible existence of at least one additional subtype of NPY receptor sites in the rat brain, with enrichment seen in midbrain and brainstem areas involved in the regulation of food intake and cardiorespiratory parameters.

Heterogeneity of the neuropeptide Y (NPY) contractile and relaxing receptors in horse penile small arteries

The distribution of neuropeptide Y (NPY)-immunorective nerves and the receptors involved in the effects of NPY upon electrical field stimulation (EFS)- and noradrenaline (NA)-elicited contractions were investigated in horse penile small arteries. NPY-immunoreactive nerves were widely distributed in the erectile tissues with a particularly high density around penile intracavernous small arteries. In small arteries isolated from the proximal part of the corpora cavernosa, NPY (30 nM) produced a variable modest enhancement of the contractions elicited by both EFS and NA. At the same concentration, the NPY Y(1) receptor agonist, [Leu(31), Pro(34)]NPY, markedly potentiated responses to EFS and NA, whereas the NPY Y(2) receptor agonist, NPY(13-36), enhanced exogenous NA-induced contractions. In arteries precontracted with NA, NPY, peptide YY (PYY), [Leu(31), Pro(34)]NPY and the NPY Y(2) receptor agonists, N-acetyl[Leu(28,31)]NPY (24-36) and NPY(13-36), elicited concentration-dependent contractile responses. Human pancreatic polypeptide (hPP) evoked a biphasic response consisting of a relaxation followed by contraction. NPY(3-36), the compound 1229U91 (Ile-Glu-Pro-Dapa-Tyr-Arg-Leu-Arg-Tyr-NH2, cyclic(2,4')diamide) and eventually NPY(13-36) relaxed penile small arteries. The selective NPY Y(1) receptor antagonist BIBP3226 ((R)-N(2)-(diphenacetyl)-N-[(4-hydroxyphenyl)methyl]D-arginineamide) (0.3 microM) shifted to the right the concentration-response curves to both NPY and [Leu(31), Pro(34)]NPY and inhibited the contractions induced by the highest concentrations of hPP but not the relaxations observed at lower doses. In the presence of the selective NPY Y(2) receptor antagonist BIIE0246 ((S)-N2-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6h)-oxodibenz[b,e]azepin-11-y1]-1-piperazinyl]-2-oxoethyl]cyclo-pentyl-N-[2-[1,2-dihydro-3,5 (4H)-dioxo-1,2-diphenyl-3H-1,2, 4-triazol-4-yl]ethyl]-argininamide) (0.3 microM), the Y(2) receptor agonists NPY(13-36) and N-acetyl[Leu(28,31)]NPY (24-36) evoked potent slow relaxations in NA-precontracted arteries, under conditions of nitric oxide (NO) synthase blockade. Mechanical removal of the endothelium markedly enhanced contractions of NPY on NA-precontracted arteries, whereas blockade of the neuronal voltage-dependent Ca(2+) channels did not alter NPY responses. These results demonstrate that NPY can elicit dual contractile/relaxing responses in penile small arteries through a heterogeneous population of postjunctional NPY receptors. Potentiation of the contractions evoked by NA involve both NPY Y(1) and NPY Y(2) receptors. An NO-independent relaxation probably mediated by an atypical endothelial NPY receptor is also shown and unmasked in the presence of selective antagonists of the NPY contractile receptors.

Receptor autoradiography as mean to explore the possible functional relevance of neuropeptides: focus on new agonists and antagonists to study natriuretic peptides, neuropeptide Y and calcitonin gene-related peptides

Over the past 20 years, receptor autoradiography has proven most useful to provide clues as to the role of various families of peptides expressed in the brain. Early on, we used this method to investigate the possible roles of various brain peptides. Natriuretic peptide (NP), neuropeptide Y (NPY) and calcitonin (CT) peptide families are widely distributed in the peripheral and central nervous system and induced multiple biological effects by activating plasma membrane receptor proteins. The NP family includes atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). The NPY family is composed of at least three peptides NPY, peptide YY (PYY) and the pancreatic polypeptides (PPs). The CT family includes CT, calcitonin gene-related peptide (CGRP), amylin (AMY), adrenomedullin (AM) and two newly isolated peptides, intermedin and calcitonin receptor-stimulating peptide (CRSP). Using quantitative receptor autoradiography as well as selective agonists and antagonists for each peptide family, in vivo and in vitro assays revealed complex pharmacological responses and radioligand binding profile. The existence of heterogeneous populations of NP, NPY and CT/CGRP receptors has been confirmed by cloning. Three NP receptors have been cloned. One is a single-transmembrane clearance receptor (NPR-C) while the other two known as CG-A (or NPR-A) and CG-B (or NPR-B) are coupled to guanylate cyclase. Five NPY receptors have been cloned designated as Y(1), Y(2), Y(4), Y(5) and y(6). All NPY receptors belong to the seven-transmembrane G-protein coupled receptors family (GPCRs; subfamily type I). CGRP, AMY and AM receptors are complexes which include a GPCR (the CT receptor or CTR and calcitonin receptor-like receptor or CRLR) and a single-transmembrane domain protein known as receptor-activity-modifying-proteins (RAMPs) as well as an intracellular protein named receptor-component-protein (RCP). We review here tools that are currently available in order to target each NP, NPY and CT/CGRP receptor subtype and establish their respective pathophysiological relevance.

Neuropeptide Y Y4 receptor homodimers dissociate upon agonist stimulation

The pancreatic polypeptide-fold family of peptides consists of three 36-amino acid peptides, namely neuropeptide Y (NPY), peptide YY, and pancreatic polypeptide (PP). These peptides regulate important functions, including food intake, circadian rhythms, mood, blood pressure, intestinal secretion, and gut motility, through four receptors: Y1, Y2, Y4, and Y5. Additional receptor subtypes have been proposed based on pharmacology observed in native tissues. Recent studies with other G-protein-coupled receptors have shown that homo- and heterodimerization may be important in determining receptor function and pharmacology. In the present study, the recently cloned rhesus (rh) Y4 receptor was evaluated using radioligand binding, and the pharmacological profile was found to be very similar to the human Y4 receptor. To study homo- and heterodimerization involving the Y4 receptor using bioluminescence resonance energy transfer 2 (BRET(2)), the carboxy termini of the rhesus Y1, Y2, Y4, and Y5 receptors were fused to Renilla luciferase, and rhY4 was also fused to green fluorescent protein. Dimerization was also studied using Western blot analysis. Using both BRET(2) and Western analysis, we found that the rhY4 receptor is present at the cell surface as a homodimer. Furthermore, agonist stimulation using the Y4-selective agonists PP and 1229U91 can dissociate these dimers in a concentration-dependent manner. In contrast, rhY4 did not heterodimerize with other members of the NPY receptor family or with human opioid delta and mu receptors. Therefore, homodimerization is an important component in the regulation of the Y4 receptor.

Development and characterization of a highly selective neuropeptide Y Y5 receptor agonist radioligand: [125I][hPP1-17, Ala31, Aib32]NPY

(1) The existence of multiple classes of neuropeptide Y (NPY) receptors (Y(1), Y(2), Y(4), Y(5) and y(6)) is now well established. However, one of the major difficulties in the study of these various receptor subtypes is the current lack of highly selective probes to investigate a single receptor class. Up to most recently, this was particularly true for the Y(4) and Y(5) subtypes. (2) [hPP(1-17), Ala(31), Aib(32)]NPY, the first highly selective Y(5) agonist, was iodinated using the chloramine T method and purified by high-pressure liquid chromatography. (3) Binding performed in rat brain homogenates revealed that equilibrium was reached after 120 min (t(1/2)=21 min) and 60 min (t(1/2)=12 min) at 25 and 100 pM [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY, respectively. (4) Isotherm saturation binding experiments demonstrated that [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY binds to an apparent single population with high-affinity (K(D) of 1.2 and 1.7 nM) and low-capacity (B(max) of 14+/-3 fmol/100,000 cells and 20+/-5 fmol/mg protein) sites in Y(5) receptor HEK293-transfected cells and rat brain membrane homogenates, respectively. No specific [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY binding sites could be detected in Y(1), Y(2) or Y(4) receptors transfected HEK293 cells, demonstrating the high selectivity of this ligand for the Y(5) subtype. (5) Competition binding experiments performed in rat brain membrane homogenates and Y(5)-receptor transfected HEK293 cells demonstrated that specific [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY binding was competed with high affinity by Y(5) agonists and antagonists such as [Ala(31), Aib(32)]NPY, [hPP(1-17), Ala(31), Aib(32)]NPY, hPP, CGP71683A and JCF109, but not by Y(1) (BIBP3226), Y(2) (BIIE0246) and Y(1)/Y(4) (GR231118) preferential ligands. (6) Taken together, these data demonstrate that [(125)I][hPP(1-17), Ala(31), Aib(32)]NPY is the first highly selective Y(5) radioligand to be developed. This new probe should prove most useful for further detailed studies of the molecular and pharmacological properties of this receptor subtype in brain and peripheral tissues.

The use of bioluminescence resonance energy transfer 2 to study neuropeptide Y receptor agonist-induced beta-arrestin 2 interaction

The neuropeptide Y (NPY) family peptides NPY, peptide YY (PYY), and pancreatic polypeptide (PP) bind to four G protein-coupled receptors (GPCRs): Y1, Y2, Y4, and Y5. A key step in the desensitization and internalization of GPCRs is the association of the receptor with beta-arrestins. In the present study, these receptors were analyzed with respect to their ability to interact with GFP2-tagged beta-arrestin 2 using the new bioluminescence resonance energy transfer 2 method. Agonists induced a concentration-dependent association of beta-arrestin 2 with all four receptors. Whereas the Y1 receptor exhibited the highest maximum response and rapid association (t(1/2) = 3.4 min), the maximal signals for the association of Y2 and Y4 receptors were less than half of that of Y1, and the association rates were much slower. Interestingly, when evaluated at the Y4 receptor, the Y4 agonist 1229U91 [(Ile,Glu,Pro,Dpr,Tyr,Arg, Leu,Arg,Try-NH2)-2-cyclic(2,4'),(2',4)-diamide] was unable to provoke the same maximal response as human PP, suggesting that 1229U91 is a partial agonist. When stimulated by PYY, the Y5 receptor responded with a t(1/2) of 4.6 min and a maximal response approximately 60% of what was observed with Y1. Because beta-arrestins are key components in GPCR internalization, it is interesting to note that the receptor that is known to internalize rapidly (Y1) exhibits the most rapid association with beta-arrestin 2, whereas the receptor that is known to internalize slowly, or not at all (Y2) associates slowly with beta-arrestin 2.

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.

Neuropeptide Y and its receptors as potential therapeutic drug targets

Neuropeptide Y (NPY) is a 36-amino-acid peptide that exhibits a large number of physiological activities in the central and peripheral nervous systems. NPY mediates its effects through the activation of six G-protein-coupled receptor subtypes named Y(1), Y(2), Y(3), Y(4), Y(5), and y(6). Evidence suggests that NPY is involved in the pathophysiology of several disorders, such as the control of food intake, metabolic disorders, anxiety, seizures, memory, circadian rhythm, drug addiction, pain, cardiovascular diseases, rhinitis, and endothelial cell dysfunctions. The synthesis of agonists and antagonists for these receptors could be useful to treat several of these diseases.

Internalization of pancreatic polypeptide Y4 receptors: correlation of receptor intake and affinity

Unlike neuropeptide Y receptors, the pancreatic polypeptide Y4 receptors display considerable differences in sequence and ligand-binding affinity across mammalian species. This could produce different receptor turnover rates in the same cellular membrane environment. Comparing rat, human and guinea-pig Y4 receptors expressed in Chinese hamster ovary (CHO) cells (K(d) with human pancreatic polypeptide 14, 45 and 116 pM, respectively), we indeed found human pancreatic polypeptide internalization in the rank order of receptor affinities. A large fraction of the internalized human pancreatic polypeptide, similar across the Y4 species, was associated with secondary endosomes (density approximately 1.05 in Percoll gradients) and lysosomes (density approximately 1.11). For all Y4 receptors examined, this intake was potently and selectively inhibited by cholesterol-complexing polyene antibiotic filipin III and also by clathrin lattice formation inhibitor, phenylarsine oxide. Internalization differences found across Y4 receptor species to a degree compare with those observed for the cloned guinea-pig neuropeptide Y Y1 and human neuropeptide Y Y5 receptors and, generally, support ligand-binding affinities as important determinants of internalization for neuropeptide receptors.

Pharmacological characterization of human NPFF1 and NPFF2 receptors expressed in CHO cells by using NPY Y1 receptor antagonists

Neuropeptide FF (NPFF) belongs to an opioid-modulatory system including two precursors (pro-NPFF(A) and pro-NPFF(B)) and two G-protein coupled receptors (NPFF(1) and NPFF(2)). The pharmacological and functional profiles of human NPFF(1) and NPFF(2) receptors expressed in Chinese hamster ovary (CHO) cells were compared by determining the affinity of several peptides derived from both NPFF precursors and by measuring their abilities to inhibit forskolin-induced cAMP accumulation. Each NPFF receptor recognizes peptides from both precursors with nanomolar affinities, however, with a slight preference of pro-NPFF(A) peptides for NPFF(2) receptors and of pro-NPFF(B) peptides for NPFF(1) receptors. BIBP3226 ((R)-N(2)-(diphenylacetyl)-N-[(4-hydroxyphenyl)-methyl]-argininamide) and BIBO3304 ((R)-N(2)-(diphenylacetyl)-N-[4-(aminocarbonylaminomethyl)-benzyl]-argininamide trifluoroacetate), two selective neuropeptide Y (NPY) Y(1) receptor antagonists, display relative high affinities for NPFF receptors and exhibit antagonist properties towards hNPFF(1) receptors. The structural determinants responsible for binding of these molecules to NPFF receptors were investigated and led to the synthesis of hNPFF(1) receptor antagonists with affinities from 40 to 80 nM. Our results demonstrate differences in pharmacological characteristics between NPFF(1) and NPFF(2) receptors and the feasibility of subtype-selective antagonists.

Agonist internalization by cloned Y1 neuropeptide Y (NPY) receptor in Chinese hamster ovary cells shows strong preference for NPY, endosome-linked entry and fast receptor recycling

In Chinese hamster ovary (CHO) cells expressing the cloned guinea-pig Y1 receptor, the saturable, receptor-linked internalization of NPY (NPY)-related peptides showed the rank order of human/rat neuropeptide Y (hNPY)>pig/rat peptide YY (pPYY)>=(Pro(34))human PYY>(Leu(31),Pro(34))hNPY>(Leu(31),Pro(34))hPYY>>BVD-11 (a selective Y1 antagonist). All agonists accessed similar numbers of Y1 sites in particulates from disrupted cells, with relatively small affinity variation. The rate of internalization could significantly depend on the overall interactivity of the agonist peptide (reflected in sensitivity to chaotropic agents, as well as in the level of non-saturable binding and internalization). Concentration-dependent inhibition of the agonist-driven CHO-Y1 internalization was found with filipin III (a cholesterol-complexing macrolide), and confirmed with inhibitors of clathrin lattice formation, phenylarsine oxide (PAO) and sucrose. In the concentration range affecting Y1 internalization, none of the above treatments or agents significantly alter agonist affinity for Y1 cell surface or particulate receptors. Largely similar responses to the above inhibitors were observed in CHO-Y1 cells for internalization of human transferrin. Internalization of CHO-Y1 receptor apparently is driven by NPY in strong preference to other naturally encountered agonists. At 37 degrees C, most of the internalized receptor is rapidly recycled through endosome-like membrane elements, detectable in Percoll gradients.

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.

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.

Y4 receptor knockout rescues fertility in ob/ob mice

Hypothalamic neuropeptide Y (NPY) has been implicated in the regulation of energy balance and reproduction, and chronically elevated NPY levels in the hypothalamus are associated with obesity and reduced reproductive function. However, it is not known which one of the five cloned Y receptors mediates these effects. Here we show that crossing the Y4 receptor knockout mouse (Y4(-/-)) onto the ob/ob background restores the reduced plasma testosterone levels of ob/ob mice as well as the reduced testis and seminal vesicle size and morphology to control values. Fertility in the sterile ob/ob mice was greatly improved by Y4 receptor deletion, with 100% of male and 50% of female Y4(-/-),ob/ob double knockout mice producing live offspring. Development of the mammary ducts and lobuloalveoli was significantly enhanced in pregnant Y4(-/-) and Y4(-/-),ob/ob females. Consistent with the improved fertility and enhanced mammary gland development, gonadotropin releasing hormone (GnRH) expression was significantly increased in Y4(-/-) and Y4(-/-),ob/ob animals. Y4(-/-) mice displayed lower body weight and reduced white adipose tissue mass accompanied by increased plasma levels of pancreatic polypeptide (PP). However, Y4 deficiency had no beneficial effects to reduce body weight or excessive adiposity of ob/ob mice. These data suggest that central Y4 receptor signaling specifically inhibits reproductive function under conditions of elevated central NPY-ergic tonus.

Roles of pancreatic polypeptide in regulation of food intake

Pancreatic polypeptide (PP) is produced in pancreatic islets of Langerhans and released into the circulation after ingestion of a meal. Peripherally administered PP suppresses food intake and gastric emptying. On the other hand, central administration of PP elicits food intake and gastric emptying. Therefore, PP actions on food intake may be, in part, attributable to gastric emptying. PP transgenic mice exhibit decreases in both food intake and gastric emptying rate that were clearly reversed by anti-PP antiserum. PP is an anorexigenic signal in the periphery and an orexigenic signal in the central nervous system.

The hypothalamus and the control of energy homeostasis: different circuits, different purposes

The hypothalamus regulates many aspects of energy homeostasis, adjusting both the drive to eat and the expenditure of energy in response to a wide range of nutritional and other signals. It is becoming clear that various neural circuits operate to different degrees and probably serve specific functions under particular conditions of altered feeding behaviour. This review will discuss this functional diversity by illustrating hypothalamic neurones that express neuropeptide Y (NPY), the melanocortin-4 receptor (MC4-R) and the orexins. NPY neurones in the arcuate nucleus (ARC) release NPY, a powerful inducer of feeding and obesity, in the paraventricular nucleus (PVN) and the lateral hypothalamic area (LHA). ARC-NPY neurones are inhibited by leptin and insulin and become overactive when levels of these hormones fall during undernutrition. They may function physiologically to protect against starvation. With disruption of the inhibitory leptin signals due to gene mutations, the NPY neurones are overactive, which contributes to hyperphagia and obesity in the ob/ob and db/db mice and fa/fa Zucker rat. The MC4-R is activated by alpha-melanocyte-stimulating hormone [alpha-MSH; a cleavage product of pro-opiomelanocortin (POMC), which is expressed in the other ARC neurones] and inhibits feeding. This effect is antagonised by agouti gene-related peptide (AGRP), which is coexpressed by the ARC-NPY neurones only. Activation of MC4-R, possibly mediated by blockade of AGRP release, appears to restrain overeating of a palatable diet. This response may be programmed by a transient rise in leptin soon after presentation of palatable food, and rats that fail to do this will overeat and become obese. Orexin-A and -B (corresponding to hypocretins 1 and 2) are expressed in specific LHA neurones. These have extensive reciprocal connections with many areas involved in appetite control, including the nucleus of the solitary tracts (NTS), which relays vagal afferent satiety signals from the viscera. Orexin neurones also have close anatomical connections with LHA glucose-sensitive neurones. Orexin-A induces acute feeding but does not cause obesity. Orexin neurones are stimulated by hypoglycaemia partly via the NTS and inhibited by food ingestion. These neurones may therefore be involved in the severe hyperphagia of hypoglycaemia and short-term control of feeding.

Novel analogues of neuropeptide Y with a preference for the Y1-receptor

Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the mammalian brain and acts in humans via at least three receptor subtypes: Y1, Y2, and Y5. Whereas selective agonists and antagonists are known for the Y2- and Y5-receptors, the Y1-receptor still lacks a highly selective agonist. This work presents the first NPY-based analogues with Y1-receptor preference and agonistic properties. Furthermore, the importance of specific amino acids of NPY for binding to the Y-receptor subtypes is presented. Amongst the analogues tested, [Phe7,Pro34]pNPY (where pNPY is porcine neuropeptide Y) showed the most significant Y1-receptor preference (> 1 : 3000-fold), with subnanomolar affinity to the Y1-receptor, and Ki values of approximately 30 nM for the Y2- and Y5-subtype, respectively. Variations of position 6, especially [Arg6,Pro34]pNPY and variations within positions 20-23 of NPY were found to result in further analogues with significant Y1-receptor preference (1 : 400-1 : 2000). In contrast, cyclo S-S [Cys20,Cys24]pNPY was found to be a highly selective ligand at the Y2-receptor, binding only threefold less efficiently than NPY. Analogues containing variations of positions 31 and 32 showed highly reduced affinity to the Y1-receptor, while binding to the Y5-receptor was affected less. Inhibition of cAMP-accumulation of selected peptides with replacements within position 20-23 of NPY showed preserved agonistic properties. The NPY analogues tested give insights into ligand-receptor interaction of NPY at the Y1-, Y2- and Y5-receptor and contribute to our understanding of subtype selectivity. Furthermore, the Y1-receptor-preferring peptides are novel tools that will provide insight into the physiological role of the Y1-receptor.

Agonist and antagonist activities on human NPFF(2) receptors of the NPY ligands GR231118 and BIBP3226

Neuropeptide FF (NPFF) is a part of a neurotransmitter system acting as a modulator of endogenous opioid functions. At this time, no non-peptide or peptide NPFF-antagonists have been discovered. Here, we demonstrate that Neuropeptide Y (NPY) ligands, in fact possess significant ability to interact with the human NPFF(2) receptors. NPY Y(1) antagonist BIBP3226 and mixed Y(1) antagonist/Y(4) agonist GR231118 are able to displace with low affinity, 50 -- 100 nM, the specific binding on NPFF receptors expressed in CHO cells as well as in rat dorsal spinal cord, an affinity however superior to those determined against Y(2), Y(4) or Y(5) receptors. Furthermore, BIBP3226 which is unable to inhibit the forskolin-stimulated cyclic AMP production mediated by NPFF(2) receptors, antagonizes the effect of NPFF, revealing the first antagonist of NPFF receptors. These properties of NPY ligands on Neuropeptide FF receptors must be considered when evaluating pharmacological activities of these drugs.

A GABA-neuropeptide Y (NPY) interplay in LH release

Neuropeptide Y (NPY) stimulates and gamma-amino butyric acid (GABA) inhibits LH release in the rat. Since a sub-population of NPY-producing neurons in the arcuate nucleus (ARC) of the hypothalamus co-express GABA, the possibility of an interplay between NPY and GABA in the release of LH was investigated in two ways. First by employing light and electron microscopic double staining for NPY and GABA, using pre and post-immunolabeling on rat brain sections, we detected GABA in NPY immunoreactive axon terminals in the MPOA, one of the primary sites of action of these neurotransmitters/neuromodulators in the regulation of LH release. These morphological findings raised the possibility that inhibitory GABA co-released with NPY may act to restrain the excitatory effects of NPY on LH release. Muscimol (MUS, 0.44 or 1.76 nmol/rat), a GABA(A) receptor agonist, administered intracerebroventricularly (icv), alone failed to affect LH release, but NPY (0.47 nmol/rat icv) alone stimulated LH release in ovarian steroid-primed ovariectomized rats. On the other hand, administration of MUS blocked the NPY-induced stimulation of LH release in a dose-dependent manner. Similarly, administration of MUS abolished the excitatory effects on LH release of 1229U91, a selective NPY Y4 receptor agonist. These results support the possibility that in the event of co-release of these neurotransmitters/neuromodulators, GABA may act to restrain stimulation of LH release by NPY during the basal episodic and cyclic release of LH in vivo.

Constitutive neuropeptide Y Y(4) receptor expression in human colonic adenocarcinoma cell lines

1. Three human adenocarcinoma cell lines, Colony-24 (Col-24), Col-6 and Col-1 have been studied as confluent epithelial layers able to transport ions vectorially in response to basolateral vasoactive intestinal polypeptide (VIP) and pancreatic polypeptides (PP). 2. Different species PP stimulated responses in Col-24 with Y(4)-like pharmacology. Bovine (b)PP, human (h)PP and porcine (p)PP were equipotent (EC(50) values 3.0--5.0 nM) while rat (r)PP, avian (a)PP and [Leu(31), Pro(34)]PYY (Pro(34)PYY) were significantly less potent. PYY was inactive. The PP pharmacology in Col-1 was comparable with Col-24. However, Col-6 cells were different; pPP had an EC(50) intermediate (22.0 nM) between that of bPP (3.0 nM) and hPP (173.2 nM), with aPP and rPP being at least a further fold less potent. 3. Deamidation of Tyr(36) in bPP (by O-methylation or hydroxylation) or removal of the residue resulted in significant loss of activity in Col-24. 4. GR231118 (1 microM) had no PP-like effects. In Col-24 and Col-1, GR231118 significantly attenuated bPP (30 nM) or hPP (100 nM) responses, but it did not alter bPP responses in Col-6. BIBP3226 and GR231118 both inhibited Y(1)-mediated responses which were only present in Col-6. 5. RT--PCR analysis confirmed the presence of hY(4) receptor mRNA in Col-24 and Col-1 epithelia but a barely visible hY(4) product was observed in Col-6 and we suggest that an atypical Y(4) receptor is expressed in this cell line.

Sympathetic and parasympathetic interaction in vascular and secretory control of salivary glands in anaesthetised dogs

The present study was undertaken to examine sympathetic-parasympathetic interactions in the regulation of salivary gland function, with special reference to the possible role of the sympathetic cotransmitter neuropeptide Y (NPY). In dogs anaesthetised with pentobarbitone, electrical stimulation of the parasympathetic nerve to the submandibular gland evoked an increase in glandular blood flow and salivary secretion. Sympathetic nerve stimulation evoked a significant prolonged attenuation of vasodilator and secretory responses to subsequent parasympathetic stimulation. This attenuation was not significantly altered by alpha- and beta-adrenoceptor blockade. Systemic administration of the sympathetic cotransmitter, NPY, mimicked the effect of the sympathetic stimulation by significantly attenuating vasodilatation and salivary secretion. The NPY Y1 receptor agonist, [Leu31, Pro34]NPY and the specific NPY Y2 receptor agonist N-acetyl[Leu28, Leu31]NPY 24-36 both significantly attenuated the vasodilatation and salivary secretion evoked by stimulation of the parasympathetic nerve. The NPY Y1 receptor antagonist, GR231118 significantly antagonised the attenuation of vasodilatation caused by both sympathetic stimulation and the NPY Y1 receptor agonist. GR231118 also inhibited the pressor response of NPY. Intra-arterial injection of methacholine and stimulation of the parasympathetic nerve both caused local vasodilatation in the gland which was significantly attenuated by pretreatment with sympathetic stimulation or the NPY Y1 agonist. The NPY Y2-specific agonist did not attenuate methacholine-induced vasodilatation but did attenuate vasodilatation evoked by parasympathetic stimulation. The results indicate that NPY as a sympathetic cotransmitter may have a role in the regulation of vascular secretory function of salivary glands.

Pharmacological characterization of the cloned neuropeptide Y y(6) receptor

Neuropeptide Y has potent appetite stimulating effects which are mediated by hypothalamic receptors believed to be of the neuropeptide Y Y(1) and/or neuropeptide Y Y(5) subtype. In mice, the neuropeptide Y y(6) receptor is also expressed in the hypothalamus, suggesting that it too may function as a feeding receptor in this species. Several laboratories have studied the pharmacology of the neuropeptide Y y(6) receptor, but their results are not in agreement. Using neuropeptide Y and a variety of peptide analogs and small molecule antagonists, we have determined that the pharmacology of the cloned mouse neuropeptide Y y(6) receptor is distinct from that of the other known neuropeptide Y receptors. The rank order of binding affinity for the mouse neuropeptide Y y(6) receptor is [(Ile, Glu,Pro,Dpr,Tyr,Arg,Leu,Arg,Tyr-NH(2))(2)human peptide YY=human, rat neuropeptide Y=human, rat neuropeptide Y-(2-36)=human, rat [Leu(31), Pro(34)porcine (Cys(2))-neuropeptide Y-(1-4)-8-aminooctanoyl-(D-Cys(27)porcine [D-Trp(32)rat pancreatic polypeptide=human pancreatic polypeptide. A similar rank order of potency is seen for inhibition of forskolin-stimulated cyclic AMP. The neuropeptide Y Y(5) receptor antagonist trans-naphthalene-1-sulfonic acid ¿4-[4-amino-quinazolin-2-ylamino)-methyl]-cyclohexylmethy l¿-amide hydrochloride (CGP 71683A) and the neuropeptide Y Y(1) receptor antagonist ((R)-N(2)-diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-argininam ide) (BIBP3226) bind weakly to the neuropeptide Y y(6) receptor (K(i)10, 000 nM, respectively). Although the function of the neuropeptide Y y(6) receptor remains to be elucidated, its pharmacology is not consistent with a role in appetite regulation.

Molecular characterization of the ligand-receptor interaction of the neuropeptide Y family

Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) belong to the NPY hormone family and activate a class of receptors called the Y-receptors, and also belong to the large superfamily of the G-protein coupled receptors. Structure-affinity and structure-activity relationship studies of peptide analogs, combined with studies based on site-directed mutagenesis and anti-receptor antibodies, have given insight into the individual characterization of each receptor subtype relative to its interaction with the ligand, as well as to its biological function. A number of selective antagonists at the Y1-receptor are available whose structures resemble that of the C-terminus of NPY. Some of these compounds, like BIBP3226, BIBO3304 and GW1229, have recently been used for in vivo investigations of the NPY-induced increase in food intake. Y2-receptor selective agonists are the analog cyclo-(28/32)-Ac-[Lys28-Glu32]-(25-36)-pNPY and the TASP molecule containing two units of the NPY segment 21-36. Now the first antagonist with nanomolar affinity for the Y2-receptor is also known, BIIE0246. So far, the native peptide PP has been shown to be the most potent ligand at the Y4-receptor. However, by the design of PP/NPY chimera, some analogs have been found that bind not only to the Y4-, but also to the Y5-receptor with subnanomolar affinities, and are as potent as NPY at the Y1-receptor. For the characterization of the Y5-receptor in vitro and in vivo, a new class of highly selective agonists is now available. This consists of analogs of NPY and of PP/NPY chimera which all contain the motif Ala31-Aib32. This motif has been shown to induce a 3(10)-helical turn in the region 28-31 of NPY and is suggested to be the key motif for high Y5-receptor selectivity. The results of feeding experiments in rats treated with the first highly specific Y5-receptor agonists support the hypothesis that this receptor plays a role in the NPY-induced stimulation of food intake. In conclusion, the selective compounds for the different Y receptor subtypes known so far are promising tools for a better understanding of the physiological properties of the hormones of the NPY family and related receptors.

BIIE0246, a potent and highly selective non-peptide neuropeptide Y Y(2) receptor antagonist

1. BIIE0246, a newly synthesized non-peptide neuropeptide Y (NPY) Y(2) receptor antagonist, was able to compete with high affinity (8 to 15 nM) for specific [(125)I]PYY(3 - 36) binding sites in HEK293 cells transfected with the rat Y(2) receptor cDNA, and in rat brain and human frontal cortex membrane homogenates. 2. Interestingly, in rat brain homogenates while NPY, C2-NPY and PYY(3 - 36) inhibited all specific [(125)I]PYY(3 - 36) labelling, BIIE0246 failed to compete for all specific binding suggesting that [(125)I]PYY(3 - 36) recognized, in addition to the Y(2) subtype, another population of specific NPY binding sites, most likely the Y(5) receptor. 3. Quantitative receptor autoradiographic data confirmed the presence of [(125)I]PYY(3 - 36)/BIIE0246-sensitive (Y(2)) and-insensitive (Y(5)) binding sites in the rat brain as well as in the marmoset monkey and human hippocampal formation. 4. In the rat vas deferens and dog saphenous vein (two prototypical Y(2) bioassays), BIIE0246 induced parallel shifts to the right of NPY concentration-response curves with pA(2) values of 8.1 and 8.6, respectively. In the rat colon (a Y(2)/Y(4) bioassay), BIIE0246 (1 microM) completely blocked the contraction induced by PYY(3 - 36), but not that of [Leu(31), Pro(34)]NPY (a Y(1), Y(4) and Y(5) agonist) and hPP (a Y(4) and Y(5) agonist). Additionally, BIIE0246 failed to alter the contractile effects of NPY in prototypical Y(1) in vitro bioassays. 5. Taken together, these results demonstrate that BIIE0246 is a highly potent, high affinity antagonist selective for the Y(2) receptor subtype. It should prove most useful to establish further the functional role of the Y(2) receptor in the organism.

2-36[K4,RYYSA(19-23)]PP a novel Y5-receptor preferring ligand with strong stimulatory effect on food intake

Members of the neuropeptide Y (NPY) family regulate many physiological processes via interaction with at least four functional, pharmacologically distinct Y-receptors. However, selective antagonists developed for several subtypes have not been useful in defining particular Y-receptor functions in vivo. To identify critical residues within members of the NPY family required for Y-receptor subtype-selectivity we have determined the contribution of each residue within NPY to receptor binding by replacing them with L-alanine. In a second study, chimeric peptides where single or stretches of residues were interchanged between members of the NPY family were generated and tested in radioligand binding studies. Overall, substituted alanine analogues exhibited similar orders of affinities at each Y-receptor subtype with no obvious subtype-selectivity. Residues of particular interest are Leu30 which exhibited selectivity for the Y4-receptor, whereas Asp16 does not appear to play any role in ligand binding. Several chimeric peptides, e.g., [K4]pancreatic polypeptide ([K4]PP) and [RYYSA(19-23)]PP clearly showed higher affinity at the Y4 and Y5 subtypes compared to the Y1 and Y2 subtypes. In addition, the transfer of a proline residue from position 14 to 13 in peptide YY decreases its affinity at the Y1-, Y4- and Y5-receptors but is unchanged at the Y2 subtype. Combining these results, and with the help of molecular modelling, second generation chimeras were designed. The most significant improvement was achieved in chimera 2-36[K4,RYYSA(19-23)]PP where the affinity for the Y5 subtype increased by ninefold over that from NPY. Several of these compounds were also tested for their ability to stimulate food intake in a rat model. Interestingly, again 2-36[K4,RYYSA(19-23)]PP showed the most dramatic effect with a major increase on food intake over a range of doses compared to NPY suggesting a possible synergistic effect of several Y-receptors on feeding behaviour.

Evidence that NPY Y1 receptors are involved in stimulation of feeding by orexins (hypocretins) in sated rats

Neuropeptide Y (NPY) produced in the arcuate nucleus (ARC) of the hypothalamus stimulates feeding both directly by activating NPY receptors and indirectly through release of the orexigenic peptides, galanin and beta-endorphin (beta-END), in the paraventricular nucleus (PVN) and surrounding neural sites. Orexin A and orexin B, produced outside the ARC in the lateral hypothalamic area (LH), have recently been shown to stimulate feeding. In the present studies we tested the hypothesis that NPYergic signaling may mediate feeding stimulated by orexins. In adult male rats injected intracerebroventricularly (i.c.v.) with orexin A (3, 10, 15 nmol) or orexin B (3, 10, 30 nmol) feeding was stimulated in a dose-dependent manner; maximal feeding was seen after 15 nmol orexin A and 30 nmol orexin B. To determine whether NPY may mediate this orexin stimulated feeding, we used 1229U91, a selective NPY Y1 receptor antagonist (NPY-A). Whereas NPY-A on its own was ineffective, it suppressed NPY-induced feeding. Furthermore, NPY-A completely blocked the feeding evoked by either orexin A (15 nmol) or orexin B (30 nmol). These results show that orexin A and B stimulate feeding and further suggest that these excitatory effects may be mediated by NPYergic signaling through Y1 receptors. These findings are in accord with the view that the orexin-NPY pathway may comprise a functional link upstream from NPY within the hypothalamic appetite regulating network.

Orexigenic effect of the melanocortin MC4 receptor antagonist HS014 is inhibited only partially by neuropeptide Y Y1 receptor selective antagonists

Neuropeptide Y (NPY) and melanocortin (MC) peptides have opposite effects on food intake: NPY-like peptides and MC receptor antagonists stimulate feeding and increase body weight, whereas melanocortins and NPY antagonists inhibit food intake. In this study we tested whether the orexigenic effect of the selective MC4 receptor antagonist HS014 (1 nmol) could be inhibited by three different NPY antagonists, (R)-N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)methyl]- D-argininamide (BIBP3226), (R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N2-(diphenylacetyl)-argininamide-trifluoroacetate (BIBO3304), and decapeptide [D-Tyr27,36D-Thr32]NPY27-36, after icv administration in freely feeding male rats. All three NPY receptor antagonists inhibited the orexigenic effects of HS014 partially and with markedly different potency. [D-Tyr27,36D-Thr32]NPY27-36 was active only in subconvulsive dose. The NPY Y1 selective antagonist BIBP3226 was more effective in inhibiting the effect of HS014 than BIBO3304 despite in vitro data indicating that BIBP3226 is about 10 times less potent than BIBO3304 at NPY Y1 receptor. An enantiomer of BIBO3304, BIBO3457, failed to inhibit HS014-induced feeding, indicating that the effects of BIBO3304 were stereoselective. These results suggest that stimulation of food intake caused by weakening of melanocortinergic tone at the MC4 receptor is partially but not exclusively related to NPY Y1 receptor activation.Key words: neuropeptide Y, NPY Y1 receptor antagonist, BIBO3304, BIBP3226, [D-Tyr27,36D-Thr32]NPY(27-36), 1229U91, food intake, MC4 receptor antagonist, HS014.

[(125)I]-GR231118: a high affinity radioligand to investigate neuropeptide Y Y(1) and Y(4) receptors

GR231118 (also known as 1229U91 and GW1229), a purported Y(1) antagonist and Y(4) agonist was radiolabelled using the chloramine T method. [(125)I]-GR231118 binding reached equilibrium within 10 min at room temperature and remained stable for at least 4 h. Saturation binding experiments showed that [(125)I]-GR231118 binds with very high affinity (K(d) of 0.09 - 0.24 nM) in transfected HEK293 cells with the rat Y(1) and Y(4) receptor cDNA and in rat brain membrane homogenates. No specific binding sites could be detected in HEK293 cells transfected with the rat Y(2) or Y(5) receptor cDNA demonstrating the absence of significant affinity of GR231118 for these two receptor classes. Competition binding experiments revealed that specific [(125)I]-GR231118 binding in rat brain homogenates is most similar to that observed in HEK293 cells transfected with the rat Y(1), but not rat Y(4), receptor cDNA. Autoradiographic studies demonstrated that [(125)I]-GR231118 binding sites were fully inhibited by the Y(1) antagonist BIBO3304 in most areas of the rat brain. Interestingly, high percentage of [(125)I]-GR231118/BIBO3304-insensitive binding sites were detected in few areas. These [(125)I]-GR231118/BIBO3304-insensitive binding sites likely represent labelling to the Y(4) receptor subtype. In summary, [(125)I]-GR231118 is a new radiolabelled probe to investigate the Y(1) and Y(4) receptors; its major advantage being its high affinity. Using highly selective Y(1) antagonists such as BIBO3304 or BIBP3226 it is possible to block the binding of [(125)I]-GR231118 to the Y(1) receptor allowing for the characterization and visualization of the purported Y(4) subtype. British Journal of Pharmacology (2000) 129, 37 - 46

Evidence that stimulation of two modalities of pituitary luteinizing hormone release in ovarian steroid-primed ovariectomized rats may involve neuropeptide Y Y1 and Y4 receptors

A large body of evidence indicates that neuropeptide Y (NPY) is involved in stimulation of basal and cyclic release of hypothalamic LHRH and pituitary LH. To identify the NPY receptor subtypes that mediate the excitatory effects of NPY in these two modalities of LH release, we studied the effects of 1229U91, a selective Y1 receptor antagonist and Y4 receptor agonist, in two experimental paradigms that reproduce the two modalities of LH secretion in steroid-primed ovariectomized (OVX) rats. Rats were ovariectomized and implanted with a permanent cannula into the lateral cerebroventricle. In the first experiment, rats received estradiol benzoate (EB, 30 microg/rat) on day 5, followed 2 days later with progesterone (2 mg/rat) at 1000 h to induce an afternoon LH surge. 1229U91 (30 microg/3 microl) or vehicle (control) was injected intracerebroventricularly into these rats either once at 1300 h or twice (15 microg/injection) at 1100 and 1200 h. Blood samples were collected before progesterone injection at 1000 h and at hourly intervals from 1300 -1800 h via an intrajugular cannula implanted on the previous day. In control rats, serum LH levels rose significantly at 1400 h, and these high levels were maintained until 1700 h. After two injections of 1229U91, LH levels displayed a tendency to rise at 1300-1400 h, as in controls, but thereafter, decreased rapidly below the control range. In the second experiment, the acute effect of 1229U91 on LH release was evaluated in OVX rats pretreated with EB alone. Saline alone or saline containing 1, 3, 10, or 30 microg 1229U91 was injected intracerebroventricularly at 1000 h, and the effects on LH release were analyzed at 10, 20, 30, and 60 min. 1229U91 elicited a dose-dependent stimulation of LH release, with maximal response (950% of basal levels) occurring at 10 min after the 30-microg dose; elevated levels were maintained for 1 h. Because 1229U91 is a potent Y4 agonist with some affinity for Y5 receptors, these results raised the possibility that activation of Y4/Y5 receptors by 1229U91 may augment LH release. Therefore, we examined the effects of icv administration of rat pancreatic polypeptide, a Y4-selective agonist, and [D-Trp32]-NPY, a Y5 agonist on LH release in EB-primed rats. Rat pancreatic polypeptide (0.5-2 microg/rat) stimulated LH release in a dose-related manner, and peak levels (280% of basal levels) were seen at 10-20 min; the response evoked by a higher dose (10 microg) was smaller than that induced by 0.5 or 2 microg. [D-Trp32]-NPY was relatively less effective, because only the highest (10-microg) dose elicited a modest stimulation (244% of basal levels). These results demonstrate that 1229U91, a Y1 antagonist and Y4 agonist, evokes two types of responses; it suppresses the protracted ovarian steroid-induced LH surge, and acutely, it also stimulates LH. These results imply that normally two different types of NPY receptors may mediate the stimulation of LH release. Because 1229U91 is a Y1 receptor antagonist, inhibition of the steroid-induced LH surge by 1229U91 suggests that Y1 receptors may mediate the cyclic release of LH. On the other hand, acute stimulation of LH by 1229U91 implies that the Y4 agonist-like activity of 1229U91 may mediate the basal release of LH and that either NPY or a yet-to-be-identified endogenous Y4 receptor agonist may activate Y4 receptors in the hypothalamus to stimulate LH release.

1,3-Disubstituted benzazepines as novel, potent, selective neuropeptide Y Y1 receptor antagonists

A novel series of potent and selective non-peptide neuropeptide Y (NPY) Y1 receptor antagonists, having benzazepine nuclei, have been designed, synthesized, and evaluated for activity. Chemical modification of the R(1) and R(3) substituents in structure 1 (Chart 1) yields several compounds that show high affinity for the Y1 receptor (K(i) values of less than 10 nM). SAR studies revealed that introduction of an isopropylurea group at R(1) and a 3-(benzo-condensed-urea) group, 3-(fluorophenylurea) group, or a 3-(N-(4-hydroxyphenyl)guanidine) group at R(3) in structure 1 afforded potent and subtype-selective NPY Y1 receptor antagonists. 3-(3-(Benzothiazol-6-yl)ureido)-1-N-(3-(N'-(3-isopropylureido++ +))benzyl )-2,3,4,5-tetrahydro-1H-1-benzazepin-2-one (21), which was one of the most potent derivatives, competitively inhibited specific [(125)I]peptide YY (PYY) binding to Y1 receptors in human neuroblastoma SK-N-MC cells (K(i) = 5.1 nM). 21 not only inhibited the Y1 receptor-mediated increase in cytosolic free Ca(2+) concentration in SK-N-MC cells but also antagonized the Y1 receptor-mediated inhibitory effect of peptide YY on gastrin-induced histamine release in rat enterochromaffin-like cells. 21 showed no significant affinity in 17 receptor binding assays including Y2, Y4, and Y5 receptors.

NPY receptor subtype in the rabbit isolated ileum

1. The purpose of this work was to verify the hypothesis that the rabbit ileum is a selective preparation for the NPY Y5 receptor by using new selective antagonists recently synthesized. Spontaneous contractions of the rabbit isolated ileum were recorded and binding experiments were performed in cells expressing the human NPY Y1, Y2, Y4 or Y5 receptor subtype. 2. NPY analogues produced a concentration-dependent transient inhibition of the spontaneous contractions of the rabbit ileum with the following order of potency hPP > rPP > PYY > or = [Leu31,-Pro34]-NPY > NPY >> NPY13-36. Pre-exposure to rPP, PYY, [Leu31,Pro34]-NPY or NPY (but not NPY13-36) inhibited the effect of subsequent administration of hPP suggesting cross-desensitization of the preparation. The apparent affinity of the various agonists studied was correlated to the affinity reported for the human Y4 receptor subtype (and to a lesser extent for the rat Y4 subtype) but not to the affinity for the Y5 receptor subtype. 3. BIBO 3304, a selective NPY Y1 receptor antagonist, and CGP 71683A, a selective NPY Y5 receptor antagonist, did not affect the response to hPP. JCF 109, another NPY Y5 receptor antagonist, produced an inhibition of the response to hPP but only at the highest dose tested (10 microM) which also, by itself, produced intrinsic inhibitory effects. 4. 1229U91, a non-selective ligand for Y1, Y2, Y4 and Y5 receptors with high affinity toward the Y1 and Y4 receptor subtypes, produced a concentration-dependent transient inhibition of the spontaneous contractions of the rabbit ileum and a dose-dependent inhibition of the response to hPP (apparent pKB: 7.2). 5. These results suggest that in the rabbit ileum, the NPY receptor involved in the inhibition of the spontaneous contractile activity is a NPY Y4 receptor subtype.