Characterization of a selective antagonist of neuropeptide Y at the Y2 receptor. Synthesis and pharmacological evaluation of a Y2 antagonist

Agrp-negative arcuate NPY neurons drive feeding under positive energy balance via altering leptin responsiveness in POMC neurons

Neuropeptide Y (NPY) in the arcuate nucleus (ARC) is known as one of the most critical regulators of feeding. However, how NPY promotes feeding under obese conditions is unclear. Here, we show that positive energy balance, induced by high-fat diet (HFD) or in genetically obese leptin-receptor-deficient mice, leads to elevated Npy2r expression especially on proopiomelanocortin (POMC) neurons, which also alters leptin responsiveness. Circuit mapping identified a subset of ARC agouti-related peptide (Agrp)-negative NPY neurons that control these Npy2r expressing POMC neurons. Chemogenetic activation of this newly discovered circuitry strongly drives feeding, while optogenetic inhibition reduces feeding. Consistent with that, lack of Npy2r on POMC neurons leads to reduced food intake and fat mass. This suggests that under energy surplus conditions, when ARC NPY levels generally drop, high-affinity NPY2R on POMC neurons is still able to drive food intake and enhance obesity development via NPY released predominantly from Agrp-negative NPY neurons.

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.

Counteracting Health Risks by Modulating Homeostatic Signaling

Homeostasis was initially conceptualized by Bernard and Cannon around a century ago as a steady state of physiological parameters that vary within a certain range, such as blood pH, body temperature, and heart rate^1,2. The underlying mechanisms that maintain homeostasis are explained by negative feedbacks that are executed by the neuronal, endocrine, and immune systems. At the cellular level, homeostasis, such as that of redox and energy steady state, also exists and is regulated by various cell signaling pathways. The induction of homeostatic mechanism is critical for human to adapt to various disruptive insults (stressors); while on the other hand, adaptation occurs at the expense of other physiological processes and thus runs the risk of collateral damages, particularly under conditions of chronic stress. Conceivably, anti-stress protection can be achieved by stressor-mimicking medicinals that elicit adaptive responses prior to an insult and thereby serve as health risk countermeasures; and in situations where maladaptation may occur, downregulating medicinals could be used to suppress the responses and prevent subsequent pathogenesis. Both strategies are preemptive interventions particularly suited for individuals who carry certain lifestyle, environmental, or genetic risk factors. In this article, we will define and characterize a new modality of prophylactic intervention that forestalls diseases via modulating homeostatic signaling. Moreover, we will provide evidence from the literature that support this concept and distinguish it from other homeostasis-related interventions such as adaptogen, hormesis, and xenohormesis.

Neuropeptide Y Y2 antagonist treated ovariectomized mice exhibit greater bone mineral density

Osteoporosis, a disease characterized by progressive bone loss and increased risk of fracture, often results from menopausal loss of estrogen in women. Neuropeptide Y has been shown to negatively regulate bone formation, with amygdala specific deletion of the Y2 receptor resulting in increased bone mass in mice. In this study, ovariectomized (OVX) mice were injected once daily with JNJ-31020028, a brain penetrant Y2 receptor small molecule antagonist to determine the effects on bone formation. Antagonist treated mice had reduced weight and showed increased whole-body bone mineral density compared to vehicle-injected mice. Micro computerized tomography (micro-CT) demonstrated increased vertebral trabecular bone volume, connectivity density and trabecular thickness. Femoral micro-CT analysis revealed increased bone volume within trabecular regions and greater trabecular number, without significant difference in other parameters or within cortical regions. A decrease was seen in serum P1NP, a measure used to confirm positive treatment outcomes in bisphosphonate treated patients. C-terminal telopeptide 1 (CTX-1), a blood biomarker of bone resorption, was decreased in treated animals. The higher bone mineral density observed following Y2 antagonist treatment, as determined by whole-body DEXA scanning, is indicative of either enhanced mineralization or reduced bone loss. Additionally, our findings that ex vivo treatment of bone marrow cells with the Y2 antagonist did not affect osteoblast and osteoclast formation suggests the inhibitor is not affecting these cells directly, and suggests a central role for compound action in this system. Our results support the involvement of Y2R signalling in bone metabolism and give credence to the hypothesis that selective pharmacological manipulation of Y2R may provide anabolic benefits for treating osteoporosis.

NPY receptors as potential targets for anti-obesity drug development

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

Anticonvulsant neuropeptides as drug leads for neurological diseases

Anticonvulsant neuropeptides are best known for their ability to suppress seizures and modulate pain pathways. Galanin, neuropeptide Y, somatostatin, neurotensin, dynorphin, among others, have been validated as potential first-in-class anti-epileptic or/and analgesic compounds in animal models of epilepsy and pain, but their therapeutic potential extends to other neurological indications, including neurodegenerative and psychatric disorders. Disease-modifying properties of neuropeptides make them even more attractive templates for developing new-generation neurotherapeutics. Arguably, efforts to transform this class of neuropeptides into drugs have been limited compared to those for other bioactive peptides. Key challenges in developing neuropeptide-based anticonvulsants are: to engineer optimal receptor-subtype selectivity, to improve metabolic stability and to enhance their bioavailability, including penetration across the blood–brain barrier (BBB). Here, we summarize advances toward developing systemically active and CNS-penetrant neuropeptide analogs. Two main objectives of this review are: (1) to provide an overview of structural and pharmacological properties for selected anticonvulsant neuropeptides and their analogs and (2) to encourage broader efforts to convert these endogenous natural products into drug leads for pain, epilepsy and other neurological diseases.

In vitro and in vivo characterization of JNJ-31020028 (N-(4-{4-[2-(diethylamino)-2-oxo-1-phenylethyl]piperazin-1-yl}-3-fluorophenyl)-2-pyridin-3-ylbenzamide), a selective brain penetrant small molecule antagonist of the neuropeptide Y Y(2) receptor

RATIONALE

The lack of potent, selective, brain penetrant Y(2) receptor antagonists has hampered in vivo functional studies of this receptor.

OBJECTIVE

Here, we report the in vitro and in vivo characterization of JNJ-31020028 (N-(4-{4-[2-(diethylamino)-2-oxo-1-phenylethyl]piperazin-1-yl}-3-fluorophenyl)-2-pyridin-3-ylbenzamide), a novel Y(2) receptor antagonist.

METHODS

The affinity of JNJ-31020028 was determined by inhibition of the PYY binding to human Y(2) receptors in KAN-Ts cells and rat Y(2) receptors in rat hippocampus. The functional activity was determined by inhibition of PYY-stimulated calcium responses in KAN-Ts cells expressing a chimeric G protein Gqi5 and in the rat vas deferens (a prototypical Y(2) bioassay). Ex vivo receptor occupancy was revealed by receptor autoradiography. JNJ-31020028 was tested in vivo with microdialysis, in anxiety models, and on corticosterone release.

RESULTS

JNJ-31020028 bound with high affinity (pIC(50) = 8.07 +/- 0.05, human, and pIC(50) = 8.22 +/- 0.06, rat) and was >100-fold selective versus human Y(1), Y(4), and Y(5) receptors. JNJ-31020028 was demonstrated to be an antagonist (pK(B) = 8.04 +/- 0.13) in functional assays. JNJ-31020028 occupied Y(2) receptor binding sites (approximately 90% at 10 mg/kg) after subcutaneous administration in rats. JNJ-31020028 increased norepinephrine release in the hypothalamus, consistent with the colocalization of norepinephrine and neuropeptide Y. In a variety of anxiety models, JNJ-31020028 was found to be ineffective, although it did block stress-induced elevations in plasma corticosterone, without altering basal levels, and normalized food intake in stressed animals without affecting basal food intake.

CONCLUSION

These results suggest that Y(2) receptors may not be critical for acute behaviors in rodents but may serve modulatory roles that can only be elucidated under specific situational conditions.

Selective and brain penetrant neuropeptide y y2 receptor antagonists discovered by whole-cell high-throughput screening

The role of neuropeptide Y Y2 receptor (Y2R) in human diseases such as obesity, mood disorders, and alcoholism could be better resolved by the use of small-molecule chemical probes that are substantially different from the currently available Y2R antagonist, N-[(1S)-4-[(aminoiminomethyl)amino]-1-[[[2-(3,5-dioxo-1,2-diphenyl-1,2,4-triazolidin-4-yl)ethyl]amino]carbonyl]butyl]-1-[2-[4-(6,11-dihydro-6-oxo-5H-dibenz[b,e]azepin-11-yl)-1-piperazinyl]-2-oxoethyl]-cyclopentaneacetamide) (BIIE0246). Presented here are five potent, selective, and publicly available Y2R antagonists identified by a high-throughput screening approach. These compounds belong to four chemical scaffolds that are structurally distinct from the peptidomimetic BIIE0246. In functional assays, IC(50) values between 199 and 4400 nM against the Y2R were measured, with no appreciable activity against the related NPY-Y1 receptor (Y1R). Compounds also displaced radiolabeled peptide YY from the Y2R with high affinity (K(i) values between 1.55 and 60 nM) while not displacing the same ligand from the Y1R. In contrast to BIIE0246, Schild analysis with NPY suggests that two of the five compounds behave as competitive antagonists. Profiling against a panel of 40 receptors, ion channels, and transporters found in the central nervous system showed that the five Y2R antagonists demonstrate greater selectivity than BIIE0246. Furthermore, the ability of these antagonists to penetrate the blood-brain barrier makes them better suited for pharmacological studies of Y2R function in both the brain and periphery.

Kinetic study of neuropeptide Y (NPY) proteolysis in blood and identification of NPY3-35: a new peptide generated by plasma kallikrein

There is little information on how neuropeptide Y (NPY) proteolysis by peptidases occurs in serum, in part because reliable techniques are lacking to distinguish different NPY immunoreactive forms and also because the factors affecting the expression of these enzymes have been poorly studied. In the present study, LC-MS/MS was used to identify and quantify NPY fragments resulting from peptidolytic cleavage of NPY(1-36) upon incubation with human serum. Kinetic studies indicated that NPY(1-36) is rapidly cleaved in serum into 3 main fragments with the following order of efficacy: NPY(3-36) >> NPY(3-35) > NPY(2-36). Trace amounts of additional NPY forms were identified by accurate mass spectrometry. Specific inhibitors of dipeptidyl peptidase IV, kallikrein, and aminopeptidase P prevented the production of NPY(3-36), NPY(3-35), and NPY(2-36), respectively. Plasma kallikrein at physiological concentrations converted NPY(3-36) into NPY(3-35). Receptor binding assays revealed that NPY(3-35) is unable to bind to NPY Y1, Y2, and Y5 receptors; thus NPY(3-35) may represent the major metabolic clearance product of the Y2/Y5 agonist, NPY(3-36).

Neuropeptide Y expression, localization and cellular transducing effects in HUVEC

BACKGROUND INFORMATION

NPY (neuropeptide Y) may have an effect on the properties of vascular endothelial cells such as pro-angiogenic effects and potentiation of noradrenaline-induced vasoconstriction. In HUVEC (human umbilical-vein endothelial cells), immunoreactive neuropeptide Y has been detected, but NPY synthesis, storage and secretion have not been studied. The aim of the present study was to establish NPY expression, storage and cellular transducing effects in HUVEC.

RESULTS

HUVEC contain 0.19 fmol of NPY/microg of protein and 0.46 fmol of pro-NPY/microg of protein, as measured by ELISA. RT (reverse transcriptase)-PCR confirmed the expression of NPY in HUVEC. Immunofluorescence revealed the presence of NPY in small punctate structures, with a fluorescence pattern different from that observed for von Willebrand factor, indicating distinct storage compartments. Double labelling for NPY and Rab3A demonstrated similar granular patterns, with at least partial co-localization. Electron microscopy showed NPY immunoreactivity in vesicle-like cytoplasmic structures, of a fine fibrillar texture, as well as in mitochondria and in the nucleus. A similar general distribution pattern was also obtained for Rab3A. Y1 and Y2 receptors were expressed in HUVEC as assessed by RT-PCR, and they were functional since NPY induced a 42 nM intracellular calcium increase within 100 s, representing 22% of the histamine-induced response. In contrast with histamine, NPY did not induce acute von Willebrand factor secretion.

CONCLUSIONS

HUVEC produce, store and respond to NPY, suggesting an autocrine regulatory role for NPY in the endothelium.

Novel non-peptidic neuropeptide Y Y2 receptor antagonists

Through SAR studies of a piperidinylindoline cinnamide HTS lead, the first potent, non-peptide, low molecular weight selective Neuropeptide Y Y2 (NPY Y2) antagonists have been synthesized. The SAR studies around the piperidinyl, the indolinyl, and the cinnamyl moieties are discussed.

NPY, NPY receptors, and DPP IV activity are modulated by LPS, TNF-alpha and IFN-gamma in HUVEC

Since NPY increases endothelial cell (EC) stickiness for leukocytes, we studied the effects of LPS, TNF-alpha and IFN-gamma on its expression and action in HUVEC. Cytokines raised NPY and pro-NPY intracellular content and dipeptidyl peptidase IV (DPP IV) activity. Y1 and Y2 receptors were expressed in basal conditions, and LPS, TNF-alpha and IFN-gamma induced Y5 receptor expression with a concomitant extinction of Y2 receptor expression. NPY induced an intracellular calcium increase mainly mediated by Y2 and Y5 receptors in basal conditions. After stimulation with LPS, TNF-alpha and IFN-gamma, calcium increase was mainly caused by Y5 receptor. The modulation of the NPY system by LPS, TNF-alpha and IFN-gamma, and the NPY-induced calcium signaling suggest a role for NPY during the inflammatory response.

Characterization of N-(1-Acetyl-2,3-dihydro-1H-indol-6-yl)-3-(3-cyano-phenyl)-N-[1-(2-cyclopentyl-ethyl)-piperidin-4yl]acrylamide (JNJ-5207787), a small molecule antagonist of the neuropeptide Y Y2 receptor

The in vitro pharmacological properties of N-(1-Acetyl-2,3-dihydro-1H-indol-6-yl)-3-(3-cyano-phenyl)-N-[1-(2-cyclopentyl-ethyl)-piperidin-4yl]-acrylamide (JNJ-5207787), a novel neuropeptide Y Y(2) receptor (Y(2)) antagonist, were evaluated. JNJ-5207787 inhibited the binding of peptide YY (PYY) to human Y(2) receptor in KAN-Ts cells (pIC(50) = 7.00 +/- 0.10) and to rat Y(2) receptors in rat hippocampus (pIC(50) = 7.10 +/- 0.20). The compound was >100-fold selective versus human Y(1),Y(4), and Y(5) receptors as evaluated by radioligand binding. In vitro receptor autoradiography data in rat brain tissue sections confirmed the selectivity of JNJ-5207787. [(125)I]PYY binding sites sensitive to JNJ-5207787 were found in rat brain regions known to express Y(2) receptor (septum, hypothalamus, hippocampus, substantia nigra, and cerebellum), whereas insensitive binding sites were observed in regions known to express Y(1) receptor (cortex and thalamus). JNJ-5207787 was demonstrated to be an antagonist via inhibition of PYY-stimulated guanosine 5'-O-(3-[(35)S]thio)triphosphate binding ([(35)S]GTPgammaS) in KAN-Ts cells (pIC(50) corrected = 7.20 +/- 0.12). This was confirmed auto-radiographically in rat brain sections where PYY-stimulated guanosine 5'-O-(3-[(35)S]thio)triphosphate binding was inhibited by JNJ-5207787 (10 microM) in hypothalamus, hippocampus, and substantia nigra. After intraperitoneal administration in rats (30 mg/kg), JNJ-5207787 penetrated into the brain (C(max) = 1351 +/- 153 ng/ml at 30 min) and occupied Y(2) receptor binding sites as revealed by ex vivo receptor autoradiography. Hence, JNJ-5207787 is a potent and selective pharmacological tool available to establish the potential role of central and peripheral Y(2) receptors in vivo.

Angiotensin II mediates catecholamine and neuropeptide Y secretion in human adrenal chromaffin cells through the AT1 receptor

The aim of the present work was to study the effect of angiotensin II (Ang II) on catecholamines and neuropeptide Y (NPY) release in primary cultures of human adrenal chromaffin cells. Ang II stimulates norepinephrine (NE), epinephrine (EP) and NPY release from perifused chromaffin cells by 3-, 2- and 12-fold, respectively. The NPY release is more sustained than that of catecholamines. We found that the receptor-AT(2) agonist, T(2)-(Ang II 4-8)(2) has no effect on NE, EP and NPY release from chromaffin cells. We further showed that Ang II increases intracellular Ca(2+) concentration ([Ca(2+)](i)). The selective AT(1)-receptor antagonist Candesartan blocked [Ca(2+)](i) increase by Ang II, while T(2)-(Ang II 4-8)(2) was ineffective. These findings demonstrate that AT(1) stimulation induces catecholamine secretion from human adrenal chromaffin cells probably by raising cytosolic calcium.

Impaired angiogenesis in neuropeptide Y (NPY)-Y2 receptor knockout mice

Which of Y1-Y5 receptors (Rs) mediate NPY's angiogenic activity was studied using Y2R-null mice and R-specific antagonists. In Y2R-null mice, NPY-induced aortic sprouting and in vivo Matrigel capillary formation were decreased by 50%; Y1R-antagonist blocked the remaining response. NPY-induced sprouting was equally inhibited by Y2R- (and Y5R- but less by Y1R-) antagonists in wild type mice. Spontaneous and NPY-induced revascularization of ischemic gastrocnemius muscles were similarly reduced in Y2R-null mice. Thus, NPY-induced angiogenesis, spontaneous and ischemic, is primarily mediated by Y2Rs. However, Y5Rs and, to a lesser degree Y1Rs, also may play a role in NPY-mediated angiogenesis.

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.

Induction of hypertrophic responsiveness of cardiomyocytes to neuropeptide Y in response to pressure overload

To determine whether neuropeptide Y (NPY)-related mechanisms become activated with progression of cardiac hypertrophy in vivo, protein mass and de novo protein synthesis (incorporation of [(14)C]Phe, 0.1 muCi ml(-1)) were assessed in cardiomyocytes, obtained from spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto rats (8, 12, 16, 20, and 24 weeks of age), and cultured for 24 h. NPY (10(-8) M) increased protein mass of cardiomyocytes from 16-week-old SHRs by 9.2 +/- 2.1% (n = 8, P < 0.05). De novo protein synthesis was increased maximally in SHRs at 12, 16, and 20 weeks (P < 0.05, n = 8) in response to NPY by 12.6 +/- 2.1% (10(-6) M), 20.1 +/- 4.2% (10(-8) M), and 9.4 +/- 1.8% (10(-7) M), respectively. Peptide YY(3-36), (PYY(3-36)), which displays selectivity for NPY Y(2) and NPY Y(5) receptors, and the NPY Y(5)-selective agonist [D-Trp(34)]-NPY increased de novo protein synthesis maximally by 16.2 +/- 5.1% (10(-7) M; n = 4, P < 0.05) and 17.8 +/- 5.2% (10(-6) M; n = 7, P < 0.05), respectively, in SHRs at 16 weeks, whereas [Leu(31)Pro(34)]-NPY (< or =10(-6) M), which displays some activity at NPY Y(1) and NPY Y(4) receptors, did not. The NPY Y(1)-selective antagonist BVD-42 (2 x 10(-7) M) and the NPY Y(2)-selective antagonist BIIE0246 (2 x 10(-7) M) did not attenuate responses to NPY (10(-7) M) and PPY(3-36) (10(-7) M). These data indicate that hypertrophic responsiveness to NPY, mediated via NPY Y(5) receptors, is induced transiently in SHR cardiomyocytes subsequent to onset of cardiomyocyte hypertrophy in response to pressure overload.

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.

Blockade of neuropeptide Y(2) receptors and suppression of NPY's anti-epileptic actions in the rat hippocampal slice by BIIE0246

Neuropeptide Y (NPY) has been shown to suppress synaptic excitation in rat hippocampus by a presynaptic action. The Y(2) (Y(2)R) and the Y(5) (Y(5)R) receptors have both been implicated in this action. We used the non-peptide, Y(2)R-selective antagonist, BIIE0246, to test the hypothesis that the Y(2)R mediates both the presynaptic inhibitory and anti-epileptic actions of NPY in rat hippocampus in vitro. NPY and the Y(2)R-selective agonist, [ahx(5-24)]NPY, both inhibited the population excitatory postsynaptic potential (pEPSP) evoked in area CA1 by stratum radiatum stimulation in a concentration-dependent manner. BIIE0246 suppressed the inhibitory effects of both agonists, suppressing the maximal inhibition without causing a change in the agonist EC(50), in a manner inconsistent with competitive antagonism. BIIE0246 washed out from hippocampal slices extremely slowly. Application of agonist at high concentrations (1 - 3 microM) for prolonged periods did not alter the rate of washout, but did partially overcome the antagonism, inconsistent with an insurmountable antagonism by BIIE0246. In the stimulus train-induced bursting (STIB) model of ictal activity in hippocampal slices, both NPY and [ahx(5-24)]NPY inhibited primary afterdischarge (1 degrees AD) activity. BIIE0246 (100 nM) completely suppressed the actions of NPY and [ahx(5-24)]NPY in this model. In contrast, the potent Y(5)R-selective agonist, Ala(31)Aib(32)NPY, affected neither 1 degrees AD activity in the presence of BIIE0246, nor, by itself, even the pEPSP in CA1. BIIE0246 potently suppresses NPY actions in rat hippocampus, suggesting a dominant role for Y(2)R there. The apparently insurmountable antagonism observed may result from the lipophilic nature of the antagonist.

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.

Neuropeptide Y Y(1) receptor regulates protein turnover and constitutive gene expression in hypertrophying cardiomyocytes

Increased levels of neuropeptide Y correlate with severity of left ventricular hypertrophy in vivo. At cardiomyocyte level, hypertrophy is characterised by increased mass and altered phenotype. The aims were to determine the contributions of increased synthesis and reduced degradation of protein to neuropeptide Y-mediated increase in mass, assess effects on gene expression, and characterise neuropeptide Y Y receptor subtype involvement. Neuropeptide Y (10 nM) increased protein mass of adult rat ventricular cardiomyocytes maintained in culture (24 h) (16%>basal) and de novo protein synthesis (incorporation of [(14)C]phenylalanine) (18%>basal). Neuropeptide Y (100 nM) prevented degradation of existing protein at 8 h. Actinomycin D (5 microM) attenuated increases in protein mass to neuropeptide Y (< or = 1 nM) but not to neuropeptide Y (10 nM). [Leu(31), Pro(34)]neuropeptide Y (10 nM), an agonist at neuropeptide Y Y(1) receptors, increased protein mass (25%>basal) but did not stimulate protein synthesis. Neuropeptide Y-(3-36) (10 nM), an agonist at neuropeptide Y Y(2) receptors, increased protein mass (29%>basal) and increased protein synthesis (13%>basal), respectively. Actinomycin D (5 microM) abolished the increase in protein mass elicited by neuropeptide Y-(3-36) but not that by [Leu(31), Pro(34)]neuropeptide Y. BIBP3226 [(R)-N2-(diphenylacetyl)-N-(4-hydroxyphenylmethyl)-D-arginine amide] (1 microM), a neuropeptide Y Y(1) receptor subtype-selective antagonist, and T(4) [neuropeptide Y-(33-36)](4), a neuropeptide Y Y(2) receptor subtype-selective antagonist, attenuated the increase in protein mass to 100 nM neuropeptide Y by 68% and 59%, respectively. Neuropeptide Y increased expression of the constitutive gene, myosin light chain-2 (MLC-2), maximally at 12 h (4.7-fold>basal) but did not induce (t< or = 36 h) expression of foetal genes (atrial natriuretic peptide (ANP), skeletal-alpha-actin and myosin heavy chain-beta). This increase was attenuated by 86% and 51%, respectively, by BIBP3226 (1 microM) and T(4) [neuropeptide Y-(33-36)](4) (100 nM). [Leu(31), Pro(34)]neuropeptide Y (100 nM) (2.4-fold>basal) and peptide YY-(3-36) (100 nM) (2.3 fold>basal) increased expression of MLC-2 mRNA at 12 h. In conclusion, initiation of cardiomyocyte hypertrophy by neuropeptide Y requires activation of both neuropeptide Y Y(1) and neuropeptide Y Y(2) receptors and is associated with enhanced synthesis and attenuated degradation of protein together with increased expression of constitutive genes but not reinduction of foetal genes.

Modulation of intracellular calcium changes and glutamate release by neuropeptide Y1 and Y2 receptors in the rat hippocampus: differential effects in CA1, CA3 and dentate gyrus

In the present work, we investigated the role of pre- and post-synaptic neuropeptide Y1 (NPY1) and Y2 receptors on the calcium responses and on glutamate release in the rat hippocampus. In cultured hippocampal neurones, we observed that only NPY1 receptors are involved in the modulation of intracellular free calcium concentration ([Ca(2+)](i)). In 88% of the neurones analysed, the increase in the [Ca(2+)](i), in response to depolarization with 50 mM KCl, was inhibited by 1 microM [Leu31,Pro34]NPY, whereas 300 nM NPY13-36 was without effect. However, studies with hippocampal synaptosomes showed that both NPY1 and Y2 receptors can modulate the [Ca(2+)](i) and glutamate release. The pharmacological characterization of the NPY-induced inhibition of glutamate release indicated that Y2 receptors play a predominant role, both in the modulation of Ca(2+)-dependent and -independent glutamate release. However, we could distinguish between Y1 and Y2 receptors by using [Leu31,Pro34]NPY and NPY13-36. Active pre-synaptic Y1 receptors are present in the dentate gyrus (DG) as well as in the CA3 subregion, but its activity was not revealed by using the endogenous agonist, NPY. Concerning the Y2 receptors, they are present in the three subregions (CA1, CA3 and DG) and were activated by either NPY13-36 or NPY. The present data support a predominant role for NPY2 receptors in mediating NPY-induced inhibition of glutamate release in the hippocampus, but the physiological relevance of the presently described DG and CA3 pre-synaptic NPY1 receptors remains to be clarified.

Neuropeptide Y Y2 receptor signalling mechanisms in the human glioblastoma cell line LN319

Neuropeptide Y (NPY) regulates neurotransmitter release through activation of the Y2 receptor subtype. We have recently characterized a human glioblastoma cell line, LN319, that expresses exclusively NPY Y2 receptors and have demonstrated that NPY triggers transient decreases in cAMP and increases in intracellular calcium responses. The present study was designed to further characterize calcium signalling by NPY and bradykinin (BK) in LN319 cells. Both agonists elevated free intracellular calcium ([Ca(2+)](i)) without soliciting calcium influx. NPY appeared to activate two distinct signalling cascades that liberate calcium from thapsigargin- and ryanodine-insensitive compartments. One pathway proceeded through phospholipase C (PLC)-dependent phosphatidylinositol turnover, while the other triggered calcium release through a so far unidentified mediator. Part of the response was sensitive to pertussis toxin (PTX) under conditions where the toxin totally abolished the NPY-mediated effects on cAMP. The calcium release induced by BK on the other hand was largely PTX-insensitive, PLC-dependent, and from both thapsigargin- and ryanodine-sensitive stores. Following stimulation with NPY, subsequent [Ca(2+)](i) responses to NPY were strongly depressed. Partial heterologous desensitization occurred, when BK was used as the first agonist, whereas NPY had no effect on a subsequent stimulation with BK. These data suggest that NPY-induced calcium mobilization in LN319 cells involves two different G proteins and signalling mediators, and a hitherto unidentified calcium compartment. Homologous desensitization of NPY signalling might be explained by receptor-G protein uncoupling, while heterologous desensitization by BK could be the result of either transient depletion or inhibition of a mediator in the calcium signalling cascades activated by NPY.

Neuropeptide Y-Y1 receptor antisense oligodeoxynucleotide increases the infarct volume after middle cerebral artery occlusion in rats

An antisense oligodeoxynucleotide selective for the rat neuropeptide Y1 receptor gene was given into the left lateral ventricle in the experimental group of rats, whereas a missense oligodeoxynucleotide or saline was given in the control groups. Some rats were decapitated at 1-2h after the last injection of the oligodeoxynucleotides to examine their effects on the Y1 receptor density in the insular cortex. When compared to the Y1 and Y2 binding density of the untreated rats, the antisense-treated rats had reduced Y1 binding in the insular cortex but the Y2 binding was unaffected; treatment with missense oligodeoxynucleotide had no effect. Other rats underwent a right-sided middle cerebral artery occlusion at 1-2h after the last injection of the oligodeoxynucleotides or saline to examine the effect on the infarction volume at three days following stroke. The antisense treatment resulted in a doubling of the mean infarction volume when compared to the missense or saline treatment.Thus, reducing the Y1 receptor density prior to middle cerebral artery occlusion is harmful. Neuropeptide Y may mediate neuroprotection against focal ischemia via the cortical Y1 receptor, since the immunoreactivity for neuropeptide Y has been shown to increase within the peri-infarct cortex after middle cerebral artery occlusion.

A novel high throughput chemiluminescent assay for the measurement of cellular cyclic adenosine monophosphate levels

The second messenger 3', 5'-cyclic AMP (cAMP) is a highly regulated molecule that is governed by G protein-coupled receptor activation and other cellular processes. Measurement of cAMP levels in cells is widely used as an indicator of receptor function in drug discovery applications. We have developed a nonradioactive ELISA for the accurate quantitation of cAMP levels produced in cell-based assays. This novel competitive assay utilizes chemiluminescent detection that affords both a sensitivity and a dynamic assay range that have not been previously reported with any other assay methodologies. The assay has been automated in 96- and 384-well formats, providing assay data that are equivalent to, if not better than, data generated by hand. This report demonstrates the application of this novel assay technology to the functional analysis of a specific G protein-coupled receptor, neuropeptide receptor Y1, on SK-N-MC cells. Our data indicate the feasibility of utilizing this assay methodology for monitoring cAMP levels in a wide range of functional cell-based assays for high throughput screening.

Sympathetic innervation alters activation of pacemaker current (If) in rat ventricle

Pacemaker current (If) exists in both neonatal and adult ventricles, but activates at more negative voltages in the adult. This study uses whole-cell patch clamp to investigate the factors that may contribute to the maturational shift of If, comparing neonatal rat ventricular myocytes that were cultured for 4-6 days either alone, in co-culture with sympathetic nerves, or with neurotransmitters chronically present in culture. If recorded from nerve-muscle co-cultures had a significantly more negative and shallower activation-voltage relation than that from control muscle cultures, which was reflected in the midpoint potential (V50) and slope factor (K) of activation. This effect of innervation was prevented by the sustained presence in the culture of the alpha1-adrenergic antagonist prazosin (Pz) at 10(-7) M. In parallel experiments, myocytes treated with noradrenaline (NA) at 10(-7) M or neuropeptide Y (NPY) at 10(-7) M during culture had the same If activation as control cells, but cells treated with NA and NPY together had a significantly more negative and shallower activation curve. Maximum conductance and reversal potential were unchanged. The effect of chronic exposure to NA + NPY was prevented by the sustained presence of either Pz or the NPY Y2 selective antagonist T4-[NPY(33-36)]4 (3.5 x 10(-7) M) in the culture, indicating a requirement for both alpha1-adrenergic and NPY Y2 activation. Substituting NA with the alpha1A-adrenergic selective agonist A61603 (5(-10) x 10(-9) M), in the presence of NPY, did not alter If, suggesting the involvement of alpha1B- rather than alpha1A-adrenoceptors. Further, sequential exposure to NPY followed by NA was effective in reproducing the action of chronic simultaneous exposure to these agonists, but sequential exposure to NA followed by NPY was ineffective. The results are consistent with past studies indicating that NPY affects the functional expression of the alpha1B-adrenergic cascade and suggest that sympathetic innervation induces a negative shift of If in ventricle via a combined action at alpha1B-adrenergic and NPY Y2 receptors. This effect of innervation probably contributes to the developmental maturation of If activation.

Effect of a selective neuropeptide Y Y(2) receptor antagonist, BIIE0246 on neuropeptide Y release

We have examined the selective neuropeptide Y Y(2) receptor antagonist, (S)-N(2)-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6h)-oxodibenz[b, e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cyclopentyl]acetyl ]-N-[2-[1 ,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3-H-1,2, 4-triazol-4-yl]ethyl]-argininamid (BIIE0246) on neuropeptide release from rat hypothalamic slices in vitro. BIIE0246 prevented neuropeptide Y-(13-36)-induced reduction in basal and K(+)-stimulated neuropeptide Y release. Addition of BIIE0246 alone enhanced K(+)-stimulated neuropeptide release, without affecting basal release. These data are consistent with anatomical and functional studies suggesting a pre-synaptic role for neuropeptide Y Y(2) receptors in regulating rat hypothalamic neuropeptide Y release in the rat.

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.

Role of NPY Y1 receptors in cardiovascular control in the conscious rabbit

Prejunctional neuropeptide Y (NPY) Y1 receptors on cardiac sympathetic neurons mediate transient inhibition of chronotropic responses in rabbit isolated right atria. The function of these receptors remains speculative. We investigated a possible functional role for these receptors in modulation of the baroreceptor-heart rate (HR) reflex in the conscious rabbit. Mean arterial pressure (MAP) responses to a range of doses of the Y1 receptor agonist [Leu31,Pro34]NPY (1-8 microg/kg, i.v.) were constructed in ganglion-blocked rabbits. After administration of the selective Y1 receptor antagonist GR231118(150 microg/kg, i.v.), two-point [Leu31,Pro34]NPY dose-pressor responses were assessed. Linear regression analysis of the relation between the shift in the [Leu31,Pro34]NPY dose-pressor response lines against time was used as an estimate of the functional half-life of GR231118. GR231118 shifted the two-point [Leu31,Pro34]NPY dose-pressor response relation by 10- to 30-fold. A single estimate of the functional half-life of a bolus dose of GR231118 was 25 +/- 2 min. This determination allowed a steady-state Y1-receptor blockade to be established by a bolus and infusion. In a separate group of rabbits, the baroreceptor-HR reflex was assessed before and 30 min after administration of GR231118 (150 microg/kg bolus, then 150 microg/ kg/h, i.v.). GR231118 caused an initial transient pressor response and bradycardia, followed by a depressor response and a more sustained tachycardia. Infusion of GR231118 had no effect on the baroreceptor-HR reflex. Prejunctional Y1 receptors appear not to mediate a tonic inhibition of cardiac sympathetic neurotransmission in the conscious rabbit during physiological manipulations in MAP. However, activation of postjunctional Y1 receptors by neuronal or circulating NPY may be important in maintenance of vascular tone in the conscious rabbit.

Potent and selective tools to investigate neuropeptide Y receptors in the central and peripheral nervous systems: BIBO3304 (Y1) and CGP71683A (Y5)

We have evaluated 3 newly developed neuropeptide Y receptor antagonists in various in vitro binding and bioassays: BIBO3304 (Y1), T4[NPY33-36]4 (Y2), and CGP71683A (Y5). In rat brain homogenates, BIBO3304 competes for the same population of [125I][Leu31,Pro34] peptide YY (PYY) binding sites (75%) as BIBP3226, but with a 10 fold greater affinity (IC50 of 0.2 ± 0.04 nM for BIBO3304 vs. 2.4 ± 0.07 nM for BIBP3226),while CGP71683A has high affinity for 25% of specific [125I][Leu31,Pro34]PYY binding sites. Both BIBO3304 and CGP71683A (at 1.0 µM) were unable to compete for a significant proportion of specific [125I]PYY3-36/Y2 sites. The purported Y2 antagonist T4[NPY33-36]4 competed against [125I]PYY3-36 binding sites with an affinity of 750 nM. These results were confirmed in HEK 293 cells transfected with either the rat Y1, Y2, Y4, or Y5 receptor cDNA. BIBO3304, but not CGP71683A, competed with high affinity for [125I][Leu31,Pro34]PYY binding sites in HEK 293 cells transfected with the rat Y1 receptor cDNA, whereas the reverse profile was observed upon transfection with the rat Y5 receptor cDNA. Additionally, both molecules were inactive at Y2 and Y4 receptor subtypes expressed in HEK 293 cells. Receptor autoradiographic studies revealed the presence of [125I][Leu31,Pro34]PYY/BIBO3304-insensitive sites in the rat brain as reported previously for BIBP3226. Finally, the selective antagonistic properties of BIBO3304 were demonstrated in a Y1 bioassay (rabbit saphenous vein; pA2 value of 9.04) while being inactive in Y2 (rat vas deferens) and Y4 (rat colon) bioassays. These results confirm the high affinity and selectivity of BIBO3304 and CGP71683A for the Y1 and Y5 receptor subtypes, respectively, while the purported Y2 antagonist, T4[NPY33-36]4 possesses rather low affinity for this receptor.Key words: NPY receptor antagonist, receptor subtypes, bioassays, receptor binding assays, autoradiographic studies, receptor distribution.

PYY preference is a common characteristic of neuropeptide Y receptors expressed in human, rat, and mouse gastrointestinal epithelia

This investigation describes the relative potencies of four peptide agonists, namely, peptide YY (PYY), [Leu31,Pro34]PYY (Pro34PYY), neuropeptide Y (NPY), and [Leu31,Pro34]NPY (Pro34NPY), as antisecretory agents in human, rat, and mouse gastrointestinal preparations. The inhibition of agonist responses by the Y1-receptor antagonist BIBP 3226 was also tested in each preparation. An unexpectedly pronounced preference for PYY and Pro34PYY was observed in functional studies of two human epithelial lines stably transfected with the rat Y1 receptor (Y1-7 and C1Y1-6). NPY and Pro34NPY were at least an order of magnitude less effective than PYY in these functional studies but were only marginally less potent in displacement binding studies using membrane preparations of the same clonal lines. The orders of agonist potency obtained in Y1-7 and C1Y1-6 epithelia were compared with those obtained from a single human colonic adenocarcinoma cell line (Colony-6, which constitutively expresses Y1 receptors) and also from mucosal preparations of rat and mouse descending colon. Similar peptide orders of potency were obtained in rat and mouse colonic mucosae and Colony-6 epithelia, all of which exhibited PYY preference (although less pronounced than with Y1-7 and C1Y1-6 epithelia) and significant sensitivity to the Y1 receptor antagonist, BIBP 3226. We have compared the pharmacology of these five mammalian epithelial preparations and provide cautionary evidence against the reliance upon agonist concentration-response relationships alone, in the characterization of NPY receptor types.Key words: Y receptors, neuropeptide Y, gastrointestinal epithelia, ion transport.

BIIE0246: a selective and high affinity neuropeptide Y Y(2) receptor antagonist

The in vitro biological characterisation of the first potent and selective non-peptide neuropeptide Y Y(2) receptor antagonist, (S)-N(2)-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6h)-oxodibenz[b, e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl] cylopentyl] acetyl]-N-[2-[1,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2, 4-triazol-4-yl]ethyl]-argininamid (BIIE0246) is reported. BIIE0246 displaced [125I]neuropeptide Y with high affinity (IC(50)=3.3 nM) from the human neuropeptide Y Y(2) receptor and proved to be highly selective. BIIE0246 displayed antagonistic properties and thus represents the first selective non-peptide neuropeptide Y Y(2) receptor antagonist.

Neuropeptide Y contributes to innervation-dependent increase in I(Ca, L) via ventricular Y2 receptors

The developmental increase in L-type Ca current (I(Ca,L)) density in the rat ventricle is reproduced in vitro by culturing neonatal myocytes with sympathetic neurons. We tested whether this effect of sympathetic innervation results from a chronic or sustained action of neurally released neuropeptide Y (NPY). Ventricular myocytes from newborn rats were cultured in serum-free medium with or without sympathetic neurons, NPY, or NPY analogs. Ca currents were measured in single myocytes at room temperature using the perforated patch clamp. In all cell groups (control, innervated, or NPY treated), the current-voltage relation for I(Ca,L) was represented by a bell-shaped curve with maximal value near 0 mV. The current density at 0 mV normalized to that of corresponding mean control values was 1.63 +/- 0.12 and 1.52 +/- 0.16 for innervated and NPY-treated myocytes, respectively. Both groups differed significantly from control (P < 0.05). NPY analogs exhibited the following rank order of effectiveness: NPY >/= NPY-(13-36) >/= PYY >> [Leu31Pro34]NPY, suggesting that the NPY effect occurs via a Y2-receptor subtype. In confirmation, chronic treatment of innervated cultures with a Y2-selective NPY antagonist prevented the innervation-dependent increase in I(Ca,L). These results indicate that sympathetic innervation contributes to the developmental increase in I(Ca,L) via neurally released NPY acting at Y2 receptors on the ventricular myocytes.

Regulation of neuropeptide Y release by neuropeptide Y receptor ligands and calcium channel antagonists in hypothalamic slices

Neuropeptide Y (NPY) is an important regulator of energy balance in mammals through its orexigenic, antithermogenic, and insulin secretagogue actions. We investigated the regulation of endogenous NPY release from rat hypothalamic slices by NPY receptor ligands and calcium channel antagonists. High-potassium stimulation (60 mM) of the slices produced a calcium-dependent threefold increase in NPY release above basal release. The Y2 receptor agonists NPY(13-36) and N-acetyl[Leu28,Leu31]NPY(24-36), the Y4 agonist rat pancreatic polypeptide (rPP), and the Y4/Y5 agonist human pancreatic polypeptide (hPP) significantly reduced both basal and stimulated NPY release. NPY(13-36)-induced reduction of NPY release could be partially prevented in the presence of the weak Y2 antagonist T4-[NPY(33-36)]4, whereas the hPP- and rPP-induced inhibition of release was not affected by the Y5 antagonist CGP71683A or the Y1 antagonist BIBP3226. The selective Y1, Y2, and Y5 antagonists had no effect on either basal or potassium-stimulated release when administered alone. The calcium channel inhibitors omega-conotoxin GVIA (N-type), omega-agatoxin TK (P/Q-type), and omega-conotoxin MVIIC (Q-type) all significantly inhibited potassium-stimulated NPY release, without any effect on basal release, whereas nifedipine had no effect on either basal or stimulated release. Addition of both omega-conotoxin GVIA and omega-agatoxin TK together completely inhibited the potassium-stimulated release. In conclusion, we have demonstrated that NPY release from hypothalamic slices is calcium-dependent, involving N-, P-, and Q-type calcium channels. NPY release is also inhibited by Y2 agonists and rPP/hPP, suggesting that Y2 and Y4 receptors may act as autoreceptors on NPY-containing nerve terminals.

Neuropeptide Y-induced contraction is mediated by neuropeptide Y Y2 and Y4 receptors in the rat colon

Ascending and descending segments of the rat colon were studied to analyze their contractile responses to neuropeptide Y and related peptides. These responses are (a) completely eliminated by tetrodotoxin (1 microM), (b) reduced to a variable extent (20 to 60%) by atropine (1 microM) and (c) not modified by indomethacin, diphenhydramine or methysergide. The order of potency of agonists for peptides related to neuropeptide Y was as follows: human pancreatic polypeptide = rat pancreatic polypeptide > peptide YY = peptide YY-(3-36) = [Leu31,Pro34]neuropeptide Y > neuropeptide Y-(2-36) > C2-neuropeptide Y = neuropeptide Y > neuropeptide Y-(13-36), with minor differences observed between the two parts of the colon. This selectivity pattern does not correspond to the profile of any known cloned neuropeptide Y receptors. BIBP3226, a selective antagonist for the neuropeptide Y Y1 receptor sub-type, was found to be inactive, while a neuropeptide Y Y2 receptor antagonist, T4-[NPY-(33-36)]4, reduced the effects of neuropeptide Y, peptide YY, peptide YY-(3-36) and C2-neuropeptide Y without affecting those of human pancreatic polypeptide, rat pancreatic polypeptide and [Leu31,Pro34]neuropeptide Y. JCF 104 (compound 28), a putative neuropeptide Y Y5 receptor antagonist, showed no effect or a weak inhibition of human pancreatic polypeptide or [Leu31,Pro34]neuropeptide Y-induced contraction. Taken together, these data suggest that: (1) at least two neuropeptide Y receptor types are present in the rat colon autonomic nerve terminals and modulate the release of acetylcholine and possibly other transmitters; (2) a proportion of the receptors mediating the contractile response of the rat colon (especially descending part) to neuropeptide Y and related peptides appears to be of the Y2 type and (3) the significant portion of the response is mediated by a receptor which is insensitive to neuropeptide Y Y1, Y2 and to neuropeptide Y Y5 receptor antagonists. This receptor behaves as a neuropeptide Y Y4 receptor sub-type and appears to be located on enteric nerves.

Metabotropic glutamate receptor modulation of glutamate responses in the suprachiasmatic nucleus

Glutamate is the primary excitatory transmitter in the suprachiasmatic nucleus (SCN). Ionotropic glutamate receptors (iGluRs) mediate transduction of light information from the retina to the SCN, an important circadian clock phase shifting pathway. Metabotropic glutamate receptors (mGluRs) may play a significant modulatory role. mGluR modulation of SCN responses to glutamate was investigated with fura-2 calcium imaging in SCN explant cultures. SCN neurons showed reproducible calcium responses to glutamate, kainate, and N-methyl-D-aspartate (NMDA). Although the type I/II mGluR agonists L-CCG-I and t-ACPD did not evoke calcium responses, they did inhibit kainate- and NMDA-evoked calcium rises. This interaction was insensitive to pertussis toxin. Protein kinase A (PKA) activation by 8-bromo-cAMP significantly reduced iGluR inhibition by mGluR agonists. The inhibitory effect of mGluRs was enhanced by activating protein kinase C (PKC) and significantly reduced in the presence of the PKC inhibitor H7. Previous reports show that L-type calcium channels can be modulated by PKC and PKA. In SCN cells, about one-half of the calcium rise evoked by kainate or NMDA was blocked by the L-type calcium channel antagonist nimodipine. Calcium rises evoked by K+ were used to test whether mGluR inhibition of iGluR calcium rises involved calcium channel modulation. These calcium rises were primarily attributable to activation of voltage-activated calcium channels. PKC activation inhibited K+-evoked calcium rises, but PKC inhibition did not affect L-CCG-I inhibition of these rises. In contrast, 8Br-cAMP had no effect alone but blocked L-CCG-I inhibition. Taken together, these results suggest that activation of mGluRs, likely type II, modulates glutamate-evoked calcium responses in SCN neurons. mGluR inhibition of iGluR calcium rises can be differentially influenced by PKC or PKA activation. Regulation of glutamate-mediated calcium influx could occur at L-type calcium channels, K+ channels, or at GluRs. It is proposed that mGluRs may be important regulators of glutamate responsivity in the circadian system.

Influence of TASP-V, a novel neuropeptide Y (NPY) Y2 agonist, on nasal and bronchial responses evoked by histamine in anaesthetized pigs and in humans

1. In nine anaesthetized pigs we have studied the influence of intranasal or intrabronchial pretreatment with TASP-V, a neuropeptide Y (NPY) Y2 agonist formed by the attachment of NPY 21-36 to a template-assembled synthetic peptide (TASP), on the functional responses to subsequent intranasal or intrabronchial histamine challenge. 2. In a parallel study, subjective and objective nasal airway resistance (NAR) increase following intranasal histamine challenge was evaluated in 11 healthy volunteers after TASP-V or placebo pretreatment. 3. In pigs, increase in sphenopalatine blood flow induced by histamine dihydrochloride nasal spray (0.25 mg kg(-1) in 3 ml of saline) was significantly reduced by 65% (P<0.05) following intranasal pretreatment with 10 microg kg(-1) of TASP-V. Bronchoconstriction induced by histamine dihydrochloride nebulization (0.5 mg kg(-1) in 3 ml of saline) was significantly attenuated by 25 and 55% following aerosolized pretreatment with TASP-V analogue at 10 and 20 microg kg(-1), respectively. 4. In healthy volunteers, objective increase in NAR and reduction in nasal minimal cross section area (MCSA) induced by intranasal spray of histamine dihydrochloride (15 microg kg(-1) in 200 microl of saline) were significantly attenuated by 50% following local pretreatment with 1.275 microg kg(-1) of TASP-V when compared with saline. 5. It is concluded that intranasal or intrabronchial pretreatment with TASP-V reduced nasal obstruction and bronchoconstriction evoked by histamine challenge in the pig. In healthy human volunteers, this agent attenuated NAR increase and MCSA reduction induced by intranasal application of histamine.

Mechanisms of vascular growth-promoting effects of neuropeptide Y: role of its inducible receptors

We have previously reported that neuropeptide Y (NPY), a sympathetic cotransmitter and vasoconstrictor, is mitogenic for vascular smooth muscle cells (VSMCs), and now report on the mechanisms mediating these effects. In rat aortic A10 cell line, NPY's potency was greater than that of norepinephrine, and efficacy similar to that of platelet-derived growth factor, but less than that of the full serum, in stimulating cell proliferation; this effect was optimal in cell 60-80% cell density. At lower cell density and serum content, NPY stimulated DNA fragmentation/apoptosis. In rat aortic primary VSMCs (RASMCs), mitogenic effect of NPY was bimodal with the first peak at 1 pM, a decline at 1 nM, and a second peak at 10-100 nM; peptide YY had similar but less efficacious effects. The first NPY's peak was mimicked by Y2 agonists, and blocked by Y2 antagonist (T4-[NPY(33-36]4), and the second mimicked by Y1 agonist and partially blocked by Y1 antagonist, BIBP3226, suggesting a multireceptor mode of action. In A10 and in RASMCs, the expression of NPY receptors, Y1, Y2 and Y5, using RT-PCR was undetectable in quiescent cells but detected after pre-treatment with NPY. The receptor induction was NPY dose-dependent and also affected by incubation time and presence of serum. The NPY mitogenic effects were attenuated by calcium channel blockers, particularly verapamil. In primary cultures of rat coronary endothelial cells (where NPY is also mitogenic), NPY stimulated mitogen-activated protein kinase (MAPK) activity. Thus, the growth-promoting effects of NPY in vascular cells occur at concentrations lower than vasoconstrictive, and appear to be mediated by inducible Y1, Y2, and Y5 receptors, calcium entry and possibly MAPK activation.

HIV envelope protein gp120 induces neuropeptide Y receptor-mediated proliferation of vascular smooth muscle cells: relevance to AIDS cardiovascular pathogenesis

Hyperplasia of vascular smooth muscle cells (VSMCs) occurs during HIV infection, part of a spectrum of HIV-mediated cardiovascular and microvascular pathologies. These changes are not due to direct viral infection but may involve the receptor-mediated action of viral proteins, such as the envelope protein gp120. We sought to identify gp120 receptors which might mediate the vascular smooth muscle cell hyperplasia present in HIV infection. A homology between neuropeptide Y (NPY) and the previously identified receptor-active V2-region of gp120 defined by an octapeptide sequence (Peptide T) related to VIP was noted. Since NPY is mitogenic for VSMCs we therefore determined whether gp120 shares this activity. Rat aortic VSMCs were treated for 24 h with human (h)NPY and gp120 in the presence of 0.5% serum to measure [3H]thymidine incorporation, an index of cell proliferation. NPY increased [3H]thymidine incorporation by 80% after a 24-h treatment in a bimodal fashion, with peak effects at 10(-10) M and 10(-8) M. Gp120 was an even more potent mitogen for VSMCs with peak activity occurring at 10(-12) M. Peptide T was equipotent with gp120, and slightly less efficacious, suggesting that this domain may mediate gp120 effects on VSMCs. When combined, gp120 and NPY acted to antagonize one another, lowering DNA synthesis to basal levels. The profile of pharmacologic inhibition supports a role for NPY receptors since antagonists of Y1 and Y2 subtypes substantially or completely inhibited gp120-mediated VSMC proliferation. This is the first demonstration of the proliferative effects of HIV viral protein gp120 on VSMCs. The effect appears to be mediated via gp120 sequences related to VIP, peptide T, and NPY. These ligands may be competitive inhibitors of binding or gp120 processing. Novel treatments may emerge based upon VIP and NPY receptor antagonists if further work substantiates a role for gp120 in the vascular abnormalities of AIDS.

Neuropeptide Y: a novel angiogenic factor from the sympathetic nerves and endothelium

Sympathetic nerves have long been suspected of trophic activity, but the nature of their angiogenic factor has not been determined. Neuropeptide Y (NPY), a sympathetic cotransmitter, is the most abundant peptide in the heart and the brain. It is released during nerve activation and ischemia and causes vasoconstriction and smooth muscle cell proliferation. Here we report the first evidence that NPY is angiogenic. At low physiological concentrations, in vitro, it promotes vessel sprouting and adhesion, migration, proliferation, and capillary tube formation by human endothelial cells. In vivo, in a murine angiogenic assay, NPY is angiogenic and is as potent as a basic fibroblast growth factor. The NPY action is specific and is mediated by Y1 and Y2 receptors. The expression of both receptors is upregulated during cell growth; however, Y2 appears to be the main NPY angiogenic receptor. Its upregulation parallels the NPY-induced capillary tube formation on reconstituted basement membrane (Matrigel); the Y2 agonist mimics the tube-forming activity of NPY, whereas the Y2 antagonist blocks it. Endothelium contains not only NPY receptors but also peptide itself, its mRNA, and the "NPY-converting enzyme" dipeptidyl peptidase IV (both protein and mRNA), which terminates the Y1 activity of NPY and cleaves the Tyr1-Pro2 from NPY to form an angiogenic Y2 agonist, NPY3-36. Endothelium is thus not only the site of action of NPY but also the origin of the autocrine NPY system, which, together with the sympathetic nerves, may be important in angiogenesis during tissue development and repair.