Receptor binding profiles of NPY analogues and fragments in different tissues and cell lines

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.

Structural basis of neuropeptide Y signaling through Y1 receptor

Neuropeptide Y (NPY) is highly abundant in the brain and involved in various physiological processes related to food intake and anxiety, as well as human diseases such as obesity and cancer. However, the molecular details of the interactions between NPY and its receptors are poorly understood. Here, we report a cryo-electron microscopy structure of the NPY-bound neuropeptide Y1 receptor (Y1R) in complex with Gi1 protein. The NPY C-terminal segment forming the extended conformation binds deep into the Y1R transmembrane core, where the amidated C-terminal residue Y36 of NPY is located at the base of the ligand-binding pocket. Furthermore, the helical region and two N-terminal residues of NPY interact with Y1R extracellular loops, contributing to the high affinity of NPY for Y1R. The structural analysis of NPY-bound Y1R and mutagenesis studies provide molecular insights into the activation mechanism of Y1R upon NPY binding.

Activation of neuropeptide Y receptors is neuroprotective against excitotoxicity in organotypic hippocampal slice cultures

Glutamate and NPY have been implicated in hippocampal neuropathology in temporal lobe epilepsy. Thus, we investigated the involvement of NPY receptors in mediating neuroprotection against excitotoxic insults in organotypic cultures of rat hippocampal slices. Exposure of hippocampal slice cultures to 2 microM AMPA (alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate) induced neuronal degeneration, monitored by propidium iodide uptake, of granule cells and CA1 pyramidal cells. For dentate granule cells, selective activation of Y1, Y2, or Y5 receptors with 1 microM [Leu31,Pro34]NPY, 300 nM NPY13-36 or 1 microM 500 nM NPY(19-23)-(Gly1,Ser3,Gln4,Thr6,Ala31,Aib32,Gln34)-PP, respectively, had a neuroprotective effect against AMPA, whereas only the activation of Y2 receptors was effective for CA1 pyramidal cells. When the slice cultures were exposed to 6 microM kainate, the CA3 pyramidal cells displayed significant degeneration, and in this case the activation of Y1, Y2, and Y5 receptors was neuroprotective. For the kainic acid-induced degeneration of CA1 pyramidal cells, it was again found that only the Y2 receptor activation was effective. Based on the present findings, it was concluded that Y1, Y2, and Y5 receptors effectively can modify glutamate receptor-mediated neurodegeneration in the hippocampus.

Marked neuropeptide Y-induced contractions via NPY-Y1 receptor and its desensitization in rat veins

The aim of this study was to investigate neuropeptide Y (NPY)-induced vasoconstrictions in rat blood vessels and which NPY receptor subtype is involved in vasoconstrictions. NPY produced marked contractions in rat common jugular, brachial, portal, femoral and tail veins, and vena cava inferior, whereas it produced little or no contractions in rat common carotid, brachial, femoral and tail arteries, and thoracic and abdominal aortae. The maximal NPY-induced contractions were larger than maximal phenylephrine (PE)-induced contractions in the veins. These NPY-induced contractions were blocked by the Y1 antagonists, SRL-21, and BIBP3226 but not by the Y5 antagonist, L-152804. A Y2 agonist, NPY (13-36), did not produce contractions. RT-PCR showed that NPY-Y1 was the only receptor subtype in the veins indicating that NPY-induced contractions are mediated through the Y1 receptor. Pretreatment with NPY showed a rapid and long-lasting desensitization of these contractions. The marked NPY-induced contractions and its desensitization in the veins suggest the physiological relevance of NPY in the venous circulation.

Neuropeptide Y effects on vasorelaxation and intestinal contraction in the Atlantic cod Gadus morhua

Neuropeptide Y (NPY) has prominent cardiovascular effects in mammals and sharks, but no such effect has previously been demonstrated in any teleost fish. In the Atlantic cod, we found that cod NPY (10(-10)-10(-6) M) relaxed celiac arteries precontracted with epinephrine, and weak contractions were elicited in intestinal ring preparations. A few NPY-immunoreactive nerve fibers were present along small gut arteries. The results suggest that cod NPY produces vasorelaxation both by a direct action on smooth muscle and by release of prostaglandins, but with no involvement of nitric oxide, leukotrienes, or endothelium-derived relaxing factors. An additional indirect effect involving another neurotransmitter may occur. Cod NPY (10(-7) M) and human NPY (10(-7) M) had identical effects on the vessels. Small differences only in the effects of porcine [Leu(31),Pro(34)]NPY, NPY-(13-36), and cod NPY suggest the presence of a Y(1) subfamily receptor, similar to the zebrafish Ya receptor. A physiological role for NPY in teleost vasculature is concluded, but surprisingly the effect, a vasodilation, is opposite to that in mammals and is mediated by prostaglandins.

Structure and receptor binding of PYY analogs

Differences in the structure of PYY and two important analogs, PYY [3-36] and [Pro34]PYY, are evaluated. Y-receptor subtype ligand binding data are used in conjunction with structural data to develop a model for receptor subtype selective agonists. For PYY it is proposed that potent binding to Y1, Y4 and Y5 receptors requires the juxtaposition of the two termini while Y2 binding only requires the C-terminal helix. Further experiments that delineate between primary and tertiary structure contributions for receptor binding and activation are required to support the hypothesis that tertiary structure is stable enough to influence the expression of PYY's bioactivity.

Structure and dynamics of micelle-bound neuropeptide Y: comparison with unligated NPY and implications for receptor selection

The biological importance of the neuropeptide Y (NPY) has steered a number of investigations about its solution structure over the last 20 years. Here, we focus on the comparison of the structure and dynamics of NPY free in solution to when bound to a membrane mimetic, dodecylphosphocholine (DPC) micelles, as studied by 2D (1)H NMR spectroscopy. Both, free in solution and in the micelle-bound form, the N-terminal segment (Tyr1-Glu15) is shown to extend like a flexible tail in solution. This is not compatible with the PP-fold model for NPY that postulates backfolding of the flexible N terminus onto the C-terminal helix. The correlation time (tau(c)) of NPY in aqueous solution, 5.5 (+/-1.0) ns at 32 degrees C, is only consistent with its existence in a dimeric form. Exchange contributions especially enhancing transverse relaxation rates (R(2)) of residues located on one side of the C-terminal helix of the molecule are supposed to originate from dimerization of the NPY molecule. The dimerization interface was directly probed by looking at (15)N-labeled NPY/spin-labeled [TOAC34]-[(14)N]-NPY heterodimers and revealed both parallel and anti-parallel alignment of the helices. The NMR-derived three-dimensional structure of micelle-bound NPY at 37 degrees C and pH 6.0 is similar but not identical to that free in solution. The final set of 17 lowest-energy DYANA structures is particularly well defined in the region of residues 21-31, with a mean pairwise RMSD of 0.23 A for the backbone heavy atoms and 0.85 A for all heavy atoms. The combination of NMR relaxation data and CD measurements clearly demonstrates that the alpha-helical region Ala18-Thr32 is more stable, and the C-terminal tetrapeptide becomes structured only in the presence of the phosphocholine micelles. The position of NPY relative to the DPC micelle surface was probed by adding micelle integrating spin labels. Together with information from (1)H,(2)H exchange rates, we conclude that the interaction of NPY with the micelle is promoted by the amphiphilic alpha-helical segment of residues Tyr21-Thr32. NPY is located at the lipid-water interface with its C-terminal helix parallel to the membrane surface and penetrates the hydrophobic interior only via insertions of a few long aliphatic or aromatic side-chains. From these data we can demonstrate that the dimer interface of neuropeptide Y is similar to the interface of the monomer binding to DPC-micelles. We speculate that binding of the NPY monomer to the membrane is an essential key step preceeding receptor binding, thereby pre-orientating the C-terminal tetrapeptide and possibly inducing the bio-active conformation.

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.

Effects of the neuropeptide Y Y(2) receptor antagonist BIIE0246 on presynaptic inhibition by neuropeptide Y in rat hippocampal slices

We previously reported that (S)-N(2)-[[1-[2-[4-[(R,S)-5, 11-dihydro-6(6h)-oxodibenz[b, e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cylopentyl]a cetyl]-N-[2-[1, 2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2, 4-triazol-4-yl]ethyl]argininamid, BIIE0246, is a potent and highly selective neuropeptide Y Y(2) receptor antagonist. Neuropeptide Y Y(2) receptors have been proposed to mediate the inhibition by neuropeptide Y of excitatory synaptic transmission in rat hippocampus. Therefore, we investigated the effects of BIIE0246 on the electrophysiological properties of neuropeptide Y in rat hippocampal slices and determined the affinity of this novel antagonist for rat hippocampal neuropeptide Y Y(2) receptors. BIIE0246 displayed an affinity of IC(50)=4.0+/-1.6 (n=4) for neuropeptide Y receptor binding sites labelled by 125I-neuropeptide Y in rat hippocampal membranes. At a concentration of 1 microM, BIIE0246 completely antagonized the inhibitory effects of 300 nM neuropeptide Y on synaptic transmission in rat hippocampal slices. This is the first study showing that a selective neuropeptide Y Y(2) receptor antagonist is able to block neuropeptide Y mediated effects in the hippocampus and unambiguously characterizes the presynaptic receptor in the rat hippocampus as the neuropeptide Y Y(2) receptor.

The role of NPY in metabolic homeostasis: implications for obesity therapy

Neuropeptide Y (NPY) is a 36 amino acid amidated peptide which has now emerged as an important regulator of feeding behaviour. Upon intracerebroventricular (icv.) administration, NPY produces a pronounced feeding response in a variety of species. The actions of NPY are believed to be mediated by a family of receptor subtypes named Y1 - y6. Recent studies suggest that the Y1 and Y5 receptor subtypes are intimately involved in NPY induced feeding. This review presents preclinical data obtained with receptor subtype selective agonists and antagonists as well as findings from knockout mice. These new data suggest that NPY receptor antagonists may become an additional option for treating human obesity.

Association of neuropeptide Y Y1 receptors with glutamate-positive and NPY-positive neurons in rat hippocampal cultures

The hippocampus is particularly enriched with neuropeptide tyrosine (NPY) and NPY receptors including the Y1, Y2 and Y5 subtypes. We have previously reported on the enrichment of cultured rat hippocampal neurons in specific [125I][Leu31, Pro34]PYY/BIBP3226-sensitive (Y1) binding sites and Y1 receptor mRNAs [St-Pierre et al. (1998) Br. J. Pharmacol., 123, p183]. We have now identified which cell types express the Y1 receptor. The majority of Y1 receptors, visualized using either the radiolabeled probe [125I][Leu31,Pro34]PYY or two antibodies directed against distinct domains of the Y1 receptor, was expressed in neurons as revealed by neuron-specific enolase (NSE) immunostaining. One antibody was directed against the second extracelllular loop of the Y1 receptor (amino acids 185-203) whereas the second was directed against the intracellular C-terminal loop (amino acids 355-382). The labelling was evident over both perikarya and processes. Neurons labelled by the various Y1 receptor probes were mostly glutamate-positive as revealed by double immunostaining. Most interestingly, a number of NPY-positive cultured hippocampal neurons were also enriched with the Y1 receptor, suggesting that this subtype may act as an autoreceptor to regulate NPY release in the hippocampus. These results thus provide an anatomical basis for the modulation of glutamate and NPY release by the Y1 receptor in the hippocampus.

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.

Neuropeptide Y-related compounds and feeding

Neuropeptide Y (NPY) and related compounds increase short-term feeding. Previous studies have used different animal models, feeding schedules, sources of the compounds, and time and routes of administration. These differences in methodology are important in the variability reported on the potency of NPY-related compounds. To obtain reliable data on the relative efficacy, we tested NPY, NPY 3-36, and pancreatic polypeptide (PP) using an identical protocol and the same commercial source. These three NPY-related compounds were tested using the intracerebroventricular (i.c.v., into the third ventricle) administration, and the profile of the feeding enhancement including the dose response and potency was determined. Compounds were tested in parallel on at least 2 successive days. NPY, NPY 3-36, and PP exhibited different potencies in enhancing 2-h food intake. Comparison of their dose responses (using 0.1, 0.25, 0.5, 1.0, 2.5, and 5.0 microg/rat) demonstrated an overall potency of NPY 3-36 > NPY > PP for the high doses. To study ligand interactions, we examined the effects of various combinations of NPY-related compounds administered concomitantly. These combinations were justified based on the data obtained from the individual dose responses. The data show that the effects of NPY plus NPY 3-36 or NPY 3-36 plus PP were less than additive. When compared to the individual responses, the effects of NPY 3-36 were almost identical to those induced by the combinations using low doses of NPY plus NPY 3-36, or low and high doses of PP plus NPY 3-36. The results support the notion that NPY and its analogues induce a short-term feeding response by activating multiple receptor subtypes.

Subtype selectivity of the novel nonpeptide neuropeptide Y Y1 receptor antagonist BIBO 3304 and its effect on feeding in rodents

1. The novel Y1-selective argininamide derivative BIBO 3304 ((R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N2-(diphen ylacetyl)-argininamide trifluoroacetate) has been synthesized and was examined for its subtype selectivity, its in vitro antagonistic properties and its food intake inhibitory properties. 2. BIBO 3304 displayed subnanomolar affinity for both the human and the rat Y1 receptor (IC50 values 0.38+/-0.06 nM and 0.72+/-0.42 nM, respectively). The inactive enantiomer of BIBO 3304 (BIBO 3457) had low affinity for both the human and rat Y1 receptor subtype (IC50> 1000 nM). BIBO 3304 showed low affinity for the human Y2 receptor, human and rat Y4 receptor as well as for the human and rat Y5 receptor (IC50 values > 1000 nM). 3. 30 microg BIBO 3304 administered into the paraventricular nucleus inhibited the feeding response induced by 1 microg NPY as well as the hyperphagia induced by a 24 h fast implying a role for Y1 receptors in NPY mediated feeding. The inactive enantiomer had no effect. 4. BIBO 3304 inhibits neither the galanin nor the noradrenaline induced orexigenic response. but it blocked feeding behaviour elicited by both [Leu31, Pro24]NPY and NPY (3 36) suggesting an interplay between different NPY receptor subtypes in feeding behavior. 5. The present study reveals that BIBO 3304 is a subtype selective nonpeptide antagonist with subnanomolar affinity for the Y1 receptor subtype that significantly inhibits food intake induced by application of NPY or by fasting.

Bioassays for NPY receptors: old and new

Classical pharmacology performed on isolated organ preparations is an essential tool for receptor characterization and classification. Basic pharmacological parameters (e.g. ED50, ID50, pD2, pA2 as measures of apparent affinities) obtained by relating the agent concentration with the biological effect are the final results of the various steps required for drug action and necessarily reflect the complex mechanisms of cell function. Results obtained with bioassays are therefore a useful and essential part in the assessment of endogenous systems, in the present case, the NPY family of peptides and their receptors. An attempt has been made, in the present review, to present a choice of isolated organs that may provide a starting point towards the construction of a solid classical pharmacology of receptors for NPY and congeners. Some of these organs appear to be 'monoreceptor systems' (e.g. the rabbit saphenous vein) whose response is contributed by a single receptor type, others (e.g. the rat colon) are 'multiple receptor systems' and their pharmacology is much too complex and requires the use of a variety of compounds from the naturally occuring peptides, to some selective agonists and when available, specific and selective antagonists. Such compounds have been utilised by us and other workers to detect specific biological responses to NPY and congeners in peripheral tissues: such responses have been quantified, carefully analysed in pharmacological terms and characterized as biological effects mediated by Y1 (the rabbit saphenous vein), Y2 (dog saphenous vein, rat vas deferens, rat colon), Y4 (rat colon) and Y5 (rabbit ileum) receptors. Compared to findings obtained with binding assays and molecular biology experiments, the results of the bioassays show very interesting similarities. Much remains however to be done in view of providing the classical pharmacological bases that are needed in the field of NPY.

[3H]-BIBP3226 and [3H]-NPY binding to intact SK-N-MC cells and CHO cells expressing the human Y1 receptor

We have studied the binding of [3H]-NPY and the newly developed non-peptide Y1 receptor antagonist [3H]-BIBP3226 to intact SK-N-MC cells and CHO-K1 cells transfected with the human NPY Y1 receptor gene i.e. CHO-Y1 cells. Whereas the association and dissociation of the specific [3H]-NPY binding was slow, the binding kinetics of [3H]-BIBP3226 binding was very rapid. Saturation binding of both radioligands reveal the presence of an apparently homogeneous population of high affinity binding sites in both cell lines. The corresponding equilibrium dissociation constants are similar for the two cell lines and are close to those obtained from previous competition binding experiments. The specific binding of both radioligands was completely and with high affinity displaced by BIBP3226 and its inactive (S)-enantiomer BIBP3435 was much less potent. Whilst the NPY Y1 agonists NPY, PYY and [Leu31-Pro34]-NPY completely and potently displaced [3H]-NPY binding, they could only displace 70 to 80% of the [3H]-BIBP3226 binding sites in CHO-Y1 and SK-N-MC cells. A possible explanation can be that only part of the receptors are G-protein coupled. In agreement pertussis toxin was found to reduce high affinity [3H]-NPY binding sites in CHO-Y1 cells whereas [3H]-BIBP3226 binding parameters remained unchanged.

A role for neuropeptide Y in rat iridial arterioles

A role for neuropeptide Y (NPY) in neurotransmission in rat iridial arterioles has been investigated. Reverse transcription-polymerase chain reaction analysis has demonstrated mRNA expression for both Y1 and Y2 receptors in the superior cervical ganglion and iris. The Y1 agonist [Leu31,Pro34]NPY caused a dose-dependent constriction of iris arterioles (50% effective concentration of 10(-8) M), but, at low concentrations (10(-9) and 10(-10) M), it failed to potentiate either submaximal responses to norepinephrine (10(-6) M) or submaximal, noradrenergic responses to nerve stimulation. In contrast, 10(-7) M [Leu31,Pro34]NPY potentiated submaximal, noradrenergic responses to nerve stimulation (10 Hz, < or = 1 s) and to a concentration of norepinephrine (10(-7) M) which produced only small contractions. The Y1 antagonist 1229U91 blocked contractions induced by [Leu31,Pro34]NPY. Stimulation of the nerves for longer periods (10 or 20 Hz; 5, 30, or 60 s) revealed a component of the response which was reduced by 1229U91. This component was not apparent after brief stimuli (10 Hz, < or = 1 s), even when opposing receptor pathways were blocked. The Y2 agonist N-acetyl-[Leu28,Leu31]NPY24-36 had little effect on arterioles preconstricted with either high potassium or an alpha 2-adrenoceptor agonist, or on nerve-mediated contractions. Results suggest that NPY, released from sympathetic nerves during long-duration, high-frequency stimulation, activates Y1 receptors on iris arterioles to produce vasoconstriction and to potentiate responses to low concentrations of norepinephrine.

Identification of multiple neuropeptide Y receptor subtypes in the human frontal cortex

Recently, we found abundant mRNA and binding sites for neuropeptide Y Y1-like receptors in the human cerebral cortex. However, an earlier study using indirect labeling methods failed to detect substantial neuropeptide Y1-like receptor binding in numerous areas of the human brain, including the cerebral cortex. To resolve the disparity in these findings, we characterized the neuropeptide Y receptor subtypes labeled with [125I]peptide YY in homogenates of human frontal cortex. Competition experiments using 100 pM [125I]peptide YY binding to human frontal cortex homogenates indicated predominantly neuropeptide Y Y2 receptors are labeled with this concentration of ligand. However, saturation analysis of [125I]peptide YY binding to frontal cortex membranes resulted in isotherms best characterized by a two-site fit. Binding of [125I]peptide YY to the high affinity (Kd = 40 pM) binding site was prevented using a 100 nM concentration of the neuropeptide Y Y2 receptor agonist peptide YY-(3-36). By masking the higher affinity site, we found a low affinity [125I]peptide YY binding site (Kd = 1.4 nM) exhibiting a pharmacology consistent with a neuropeptide Y Y1-like receptor. It appears that neuropeptide Y Y2 receptors are the predominant subtype labeled with low concentrations of[125I]peptide YY and that the neuropeptide Y Y1 receptor is a low affinity [125I]peptide YY binding site in the human frontal cortex.

The dog saphenous vein: a sensitive and selective preparation for the Y2 receptor of neuropeptide Y

The dog saphenous vein responds to neuropeptide Y with a dose-dependent contraction and this vasopressor effect is not altered by the removal of the endothelium nor by the neuropeptide Y Y1 receptor antagonist, BIBP 3226 ((R)-N2-(diphenylacetyl)-N-[(n-hydroxyphenyl)methyl]-argininami de). The dose-response curves obtained with neuropeptide Y, peptide YY and with C-terminal fragments such as neuropeptide Y-(2-26), neuropeptide Y-(13-36) and peptide YY-(3-36) have similar slopes and maxima. EC50 values of these compounds vary between 30 +/- 10 and 89 +/- 47 nM. The neuropeptide Y Y1 receptor-selective agonist [Leu31,Pro34]neuropeptide Y and human pancreatic polypeptide are inactive up to 1 microM. This pharmacological profile suggests that the contraction of the dog saphenous vein induced by neuropeptide Y and its homologues or fragments is mediated by a neuropeptide Y Y2 receptor type. Moreover, this neuropeptide Y Y2 receptor appears to be localized in the venous smooth muscle, where it exerts a direct myotropic effect that may be useful for the pharmacological characterization of new compounds acting as agonists or antagonists of the neuropeptide Y Y2 receptor.

Receptor subtypes Y1 and Y5 are involved in the renal effects of neuropeptide Y

1. Systemic infusion of neuropeptide Y (NPY) reduces renal blood flow and can concomitantly increase diuresis, natriuresis and calciuresis in anaesthetized rats. The present study was designed to investigate whether the apparently contradictory NPY effects on renal blood flow and urine formation and composition are mediated by distinct NPY receptor subtypes. 2. NPY and its analogues, peptide YY (PYY), [Leu31, Pro34]NPY and NPY13-36, were infused in incremental doses of 0.3, 1 and 3 micrograms kg-1 min-1 for 45 min each and the results compared to those obtained in vehicle-infused rats. Renal blood flow was monitored in 1-5 min intervals, while urine excretion and composition were determined in 15 min collection periods. Plasma renin activity and aldosterone concentrations were measured at the end of the final infusion period. 3. Relative to vehicle NPY, PYY and [Leu31, Pro34]NPY dose-dependently reduced renal blood flow and increased diuresis, natriuresis and calciuresis with roughly similar potency; NPY13-36 slightly but significantly increased renal blood flow but had no effect on diuresis, natriuresis and calciuresis. None of the peptides significantly affected endogenous creatinine clearance or kaliuresis. 4. Plasma renin activity was significantly reduced by PYY. Quantitatively similar reductions were observed with NPY and [Leu31, Pro34]NPY but failed to reach statistical significance with the given number of experiments. NPY13-36 did not reduce plasma renin activity. None of the peptides significantly affected plasma aldosterone concentrations. 5. In another series of experiments infusion of PYY3-36 (2 micrograms kg-1 min-1 for 120 min) did not reduce renal blood flow but significantly enhanced diuresis and natriuresis to a similar extent as the NPY 2 micrograms kg-1 min-1. 6. In a final series of experiments the Y1-selective antagonist, BIBP 3226 (1 or 10 micrograms kg-1 min-1) dose-dependently antagonized reductions of renal blood flow elicited by bolus injections of NPY (0.1-30 micrograms kg-1). BIBP 3226 (10 micrograms kg-1 min-1) also inhibited the effects of a 120 min infusion of NPY (2 micrograms kg-1 min-1) on renal blood flow but had only minor inhibitory effects on enhancements of diuresis and did not significantly affect enhancements of natriuresis. 7. We conclude that NPY reduces renal blood via a classical Y1 subtype of NPY receptor. In contrast enhancements of diuresis, natriuresis and calciuresis occur via a distinct subtype which resembles the receptor that mediates NPY-induced enhancement of food intake.

Analysis of NPY receptor subtypes in the human frontal cortex reveals abundant Y1 mRNA and binding sites

Receptors for neuropeptide Y (NPY) are widely distributed throughout the mammalian brain. Using indirect labeling methods, the human brain was reported to contain predominantly the Y2 receptor subtype, whereas the rat brain contains a mixture of Y1 and Y2 receptor subtypes. To more accurately assess NPY receptors in the human brain, we used type Y1- and Y2-selective radioligands [125I] [Leu31,Pro34]PYY and [125I]PPY (3-36), respectively, to examine NPY receptors in the human frontal cortex. Contrary to an earlier report, abundant Y1 binding sites were found in homogenates of human frontal cortex. Moreover, saturation analysis showed similar densities of both Y1 (Kd = 433 +/- 36 pM, Bmax = 313 +/- 15 fmol/mg protein) and Y2 (Kd = 444 +/- 39 pM, Bmax = 458 +/- 22 fmol/mg protein) receptor subtypes in the human frontal cortex. Subsequently, Northern blot analysis revealed abundant expression of Y1 mRNA, with very low levels of Y2 mRNA, in cerebral cortex and in other areas of the human brain. These findings were confirmed by competitive RT-PCR in the human frontal cortex. Therefore, it appears that Y1 binding sites and mRNA are expressed abundantly in the human frontal cortex and, earlier findings, suggest that the human brain contains a mixture of Y1 and Y2 receptor subtypes.

Fluorescent labelled analogues of neuropeptide Y for the characterization of cells expressing NPY receptor subtypes

Porcine neuropeptide Y (NPY), a 36 amino acid hormone of the pancreatic polypeptide family, and subtype selective analogues have been synthesized by solid phase peptide synthesis. The peptides were labelled with Cy3, a commercially available fluorescent marker based on a cyanine dye, by solid phase strategy. During the cleavage a partial fragmentation of the fluorescent marker occurred. This has been investigated by means of HPLC and electrospray mass spectrometry. The labelled analogues of NPY showed high affinity to the NPY receptor subtypes Y1 and Y2. Thus, Cy3-NPY, Y1-selective Cy3-[Pro34] NPY and Y2 selective Cy3-[Ahx5-24] NPY were used to label SK-N-MC- and SMS-KAN-cells, which are stably expressing the Y1-(SK-N-MC) and the Y2-receptor subtype (SMS-KAN). The binding of the labelled analogues to the receptors was reversible and specific. The photoactivatable analogue, [(Tmd)Phe27] NPY, which showed high affinity to both receptor subtypes was labelled with Cy3 in solution. Whereas the fluorescent labelling of the cells with analogues without photoactivatable amino acid was reversible, successful photocrosslinking could be investigated by the irreversible staining of the cells using Cy3-[(Tmd)Phe27] NPY. These subtype selective analogues are exciting tools to trace receptors in tissues and to identify the pharmacologically characterized subtypes without radioactivity.

BIBP 3226, the first selective neuropeptide Y1 receptor antagonist: a review of its pharmacological properties

Based on the assumption that the pharmacophoric groups interacting with the Y1 receptor are located in the C-terminal part of neuropeptide Y, low molecular weight compounds with high affinity and selectivity for the Y1 receptor were designed and synthesized. The prototype BIBP 3226 possesses affinity for the Y1 receptor in the nanomolar range. In addition, this compound is selective displaying rather low affinity for Y2, Y3, Y4 and a set of 60 other receptors. Both biochemical and pharmacological studies showed that BIBP 3226 behaves as a competitive antagonist. Using BIBP 3226 it was possible to investigate the role of NPY and/or Y1 receptors in blood pressure regulation. The interesting observation was that antagonism to Y1 receptors had no major influence on the basal blood pressure but attenuated stress induced hypertension. This strongly supports the hypothesis that NPY is mainly released during stress involving intense sympathetic nervous system activation. Moreover, BIBP 3226 can be used to characterize NPY receptor subtypes. For instance, we were able to show that presynaptic NPY receptors mediating catecholamine release do not solely belong to the Y2 subtype, but that presynaptic Y1 receptors also exist. In conclusion, BIBP 3226 has been shown to be an important tool for the elucidation of the physiological role of Y1 receptors in the cardiovascular system.