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Valérie Audinot

Publications and source records attributed to Valérie Audinot.

18 recordsLinked to original sources
PubMed2006

New ligands at the melatonin binding site MT(3).

The third melatonin binding site, MT3 is a non-classical one since it is not a seven transmembrane domains receptor, but an enzyme, quinone reductase 2. A major concern for the study of the physiological role of this site is the lack of specific ligands, permitting to more accurately dissect the pathways linked to the activation of MT3. Indeed, in the course of finding new ligands, we identified a new series of compounds with affinity to the binding site in the nM range, particularly 2,3-dimethoxy 7-hydroxy 10-methyl 5H 10H indeno(1,2-b)indol-10-one (DMHMIO), with a Ki of 190 pM. Based on slightly different and novel synthons compared to most of the compounds used in melatonin pharmacology studies, these compounds offer new perspective for the description of the melatonin pathways, so much more by not having any affinity towards the MT1 and MT2 'classical' melatonin receptors.

Animals↗
PubMed2005

Functional characterization of human neuropeptide Y receptor subtype five specific antagonists using a luciferase reporter gene assay.

Neuropeptide Y (NPY) has several receptors; one of them, the neuropeptide Y5 receptor (NPY5) seems involved in feeding behavior in mammals. Although this particular receptor has been extensively studied in the literature, the difficulties encountered to obtain a stable cell line expressing this recombinant receptor have impaired the development of tools necessary to establish its molecular pharmacology. We thus established a method for the functional study of new ligands. It is based upon the cotransfection in human melatonin receptor 1 (MT1)-overexpressing HEK293 cells of three plasmids encoding melanocortin receptor (MC5), neuropeptide Y5 receptor (NPY5) and a cyclic AMP response element-controlled luciferase. Once challenged with alphaMSH, the MC5 receptor activates the cyclic AMP response, through the coupling protein subunit G(s). In contrast, NPY5 agonists, through the NPY5 receptor which is negatively coupled to the same pathway, counteract the alphaMSH-mediated effect on cyclic AMP level. Using appropriate controls, this method can pinpoint compounds with antagonistic activity. Simple and straightforward, this system permits reproducible measurements of agonist or antagonist effects in the presence of neuropeptide Y, the natural agonist. This method has the advantage over already existing methods and beyond its apparent complexity, to enhance the cyclic AMP concentration at a 'physiological' level, by opposition to a forskolin-induced adenylate cyclase activation. Finally, to further validate this assay, we showed results from (1) a series of natural peptidic agonists that permitted the standardization and (2) a series of potent nonpeptidic antagonists (affinity >10(-9) M) that form a new class of active NPY5 receptor antagonists.

Biological Assay↗
PubMed2005

Molecular tools to study melatonin pathways and actions.

Melatonin, an indoleamine neurohormone that is synthesized mainly in the pineal gland and derived from 5-HT, has many effects on a wide range of physio-pathological functions. Some of these effects are mediated by the interactions of melatonin with the two melatonin MT1 and MT2 receptors. Other effects are often suggested to be due to the chemical antioxidant nature of this indoleamine, and are observed at high, non-physiological concentrations. However, it is increasingly believed that some of these effects are due to interactions with other protein targets. In this review, we summarize the molecular pharmacology of melatonin, including the main enzymes involved in its synthesis and catabolism, and the proteins that mediate its actions. Furthermore, various compounds, mainly inhibitors and antagonists, that can be used to dissect these functions and pathways are presented.

Animals↗
PubMed2004

Molecular pharmacology of the ovine melatonin receptor: comparison with recombinant human MT1 and MT2 receptors.

The variations of the pharmacological properties of melatonin receptors between different mammalian species in transfected cell lines have been poorly investigated. In the present study, melatonin analogues have been used to characterize the pharmacology of the recombinant ovine melatonin receptor (oMT1) expressed in CHO cell lines and the native oMT1 from the pars tuberalis (PT). Studies with selective ligands on native and transfected oMT1 showed similar properties for binding affinities [r2(PT/CHO) = 0.85]. The affinities and the functional activities of these ligands were compared with the human receptors (hMT1 or hMT2) expressed in CHO cells as well. The oMT1 and hMT1 receptors had similar pharmacological profiles (r2=0.82). Nevertheless, some of the selective compounds at the human receptor presented a reduced affinity at the ovine receptor. Furthermore, some compounds showed marked different functional activities at oMT1 vs. hMT1 receptors. Our findings demonstrated differences in the pharmacological properties of melatonin receptors in ovine and human species.

Animals↗
PubMed2004

Preparation of 4-azaindole and 7-azaindole dimers with a bisalkoxyalkyl spacer in order to preferentially target melatonin MT1 receptors over melatonin MT2 receptors.

Several 4-azaindole and 7-azaindole dimer analogues of melatonin with a bisalkoxyalkyl spacer between the position 5 of each heterocycle were synthetized. Our aim was to investigate the influence of the spacers length on the selectivity of such compounds for the MT(1) receptors over the MT(2) receptors. Our results suggest the distance between indole ring seems to be an important parameter in determining the potency of binding with melatonin receptor site.

Aza Compounds↗
PubMed2003

New selective ligands of human cloned melatonin MT1 and MT2 receptors.

Melatonin has a key role in the circadian rhythm relay to periphery organs. Melatonin exerts its multiple roles mainly through two seven transmembrane domain, G-coupled receptors, namely MT1 or MT2 receptors. A pharmacological characterization of these human cloned melatonin hMT1 and hMT2 receptors stably expressed in HEK-293 or CHO cells is presented using a 2-[125I]-iodo-melatonin binding assay and a [35S]-GTPgammaS functional assay. Both reference compounds and new chemically diverse ligands were evaluated. Binding affinities at each receptor were found to be comparable on either HEK-293 or CHO cell membranes. Novel non-selective or selective hMT1 and hMT2 ligands are described. The [35S]-GTPgammaS functional assay was used to define the functional activity of these compounds which included partial, full agonist and/or antagonist activity. None of the compounds acted as an inverse agonist. We report new types of selective antagonists, such as S 25567 and S 26131 for MT1 and S 24601 for MT2. These studies brought other new molecular tools such as the selective MT1 agonist, S 24268, as well as the non-selective antagonist, S 22153. Finally, we also discovered S 25150, the most potent melatonin receptor agonist, so far reported in the literature.

Animals↗
PubMed2003

Design and synthesis of naphthalenic dimers as selective MT1 melatoninergic ligands.

We report the synthesis and binding properties at MT(1) and MT(2) receptors of the first example of agomelatine (N-[2-(7-methoxynaphth-1-yl)ethyl]acetamide) dimers in which two agomelatine moieties are linked together through their methoxy substituent by a polymethylene side chain according to the "bivalent ligand" approach. Some of these compounds behave as MT(1)-selective ligands. The most selective one (5) behaves as an antagonist.

Acetamides↗
PubMed2003

Design and synthesis of 3-phenyl tetrahydronaphthalenic derivatives as new selective MT2 melatoninergic ligands.

Tetrahydronaphthalenic analogues of melatonin have been synthesized and evaluated as melatonin receptor ligands. Introduction of a phenyl substituent in the 3-position of the tetraline ring allows to obtain MT(2) selective ligands. Activity and MT(2) selectivity can be modulated with suitable modifications of the N-acyl substituent. The (+)-(RR)-cis enantiomer of the N-[2-(7-methoxy-3-phenyl-1,2,3,4-tetrahydro-naphthalen-1-yl)ethyl]cyclobutyl carboxamide (14) is one of the most MT(2) selective ligands described until now and behaves as an antagonist.

Animals↗
PubMed2003

Molecular identification of the long isoform of the human neuropeptide Y Y5 receptor and pharmacological comparison with the short Y5 receptor isoform.

The neuropeptide Y Y5 receptor gene generates two splice variants, referred to here as Y5(L) (long isoform) and Y5(S) (short isoform). Y5(L) mRNA differs from Y5(S) mRNA in its 5' end, generating a putative open reading frame with 30 additional nucleotides upstream of the initiator AUG compared with the Y5(S) mRNA. The purpose of the present work was to investigate the existence of the Y5(L) mRNA. The authenticity of this transcript was confirmed by isolating part of its 5' untranslated region through 5' rapid amplification of cDNA ends and analysing its tissue distribution. To study the initiation of translation on Y5(L) mRNA, we cloned the Y5(L) cDNA and two Y5(L) cDNA mutants lacking the first or the second putative initiation start codon. Transient expression of the three plasmids in COS-7 cells and saturation binding experiments using (125)I-labelled polypeptide YY (PYY) as a ligand showed that initiation of translation on Y5(L) mRNA could start at the first AUG, giving rise to a Y5(L) receptor with an N-terminal 10-amino-acid extension when compared with the Y5(S) receptor. The human Y5(L) and Y5(S) receptor isoforms displayed similar affinity constants (1.3 nM and 1.5 nM respectively). [(125)I]PYY binding to COS-7 cells expressing either the Y5(L) or the Y5(S) isoform was inhibited with the same rank order of potency by a selection of six chemically diverse compounds: PYY>neuropeptide Y>pancreatic polypeptide>CGP71683A>Synaptic 34>Banyu 6. Comparison of the tissue distribution of Y5(L) and Y5(S) mRNAs, as determined by reverse transcription-PCR analysis, indicated that expression of Y5(L) mRNA occurs in a tissue-specific manner. Finally, we have shown that the two AUG triplets contained in the 5' untranslated region of Y5(L) mRNA did not affect receptor expression.

5' Untranslated Regions↗
PubMed2002

Peroxisome proliferator-activated receptor gamma (PPARgamma ) as a molecular target for the soy phytoestrogen genistein.

The principal soy phytoestrogen genistein has an array of biological actions. It binds to estrogen receptor (ER) alpha and beta and has ER-mediated estrogenic effects. In addition, it has antiestrogenic effects as well as non-ER-mediated effects such as inhibition of tyrosine kinase. Because of its complex biological actions, the molecular mechanisms of action of genistein are poorly understood. Here we show that genistein dose-dependently increases estrogenic transcriptional activity in mesenchymal progenitor cells, but its biological effects on osteogenesis and adipogenesis are different. At low concentrations (< or =1 microm), genistein acts as estrogen, stimulating osteogenesis and inhibiting adipogenesis. At high concentrations (>1 microm), however, genistein acts as a ligand of PPARgamma, leading to up-regulation of adipogenesis and down-regulation of osteogenesis. Transfection experiments show that activation of PPARgamma by genistein at the micromolar concentrations down-regulates its estrogenic transcriptional activity, while activation of ERalpha or ERbeta by genistein down-regulates PPARgamma transcriptional activity. Genistein concurrently activates two different transcriptional factors, ERs and PPARgamma, which have opposite effects on osteogenesis or adipogenesis. As a result, the balance between activated ERs and PPARgamma determines the biological effects of genistein on osteogenesis and adipogenesis. Our findings may explain distinct effects of genistein in different tissues.

Adipocytes↗
PubMed2002

SVK14 cells express an MCH binding site different from the MCH1 or MCH2 receptor.

Melanin-concentrating hormone (MCH) is a cyclic peptide, mainly involved in the regulation of skin pigmentation in teleosts and feeding behavior in mammals. The human keratinocyte SVK14 cell line has been previously shown to express binding sites for the MCH analog [125I]-[Phe13,3-iodo-Tyr19]MCH. We report here that: (1) this binding site similarly recognized [125I]-[3-iodo-Tyr13]MCH; (2) its pharmacological profile clearly differed from those observed at the two human MCH receptor subtypes, MCH1-R and MCH2-R; (3) MCH did not induce any effect on second messenger systems (including cAMP, calcium, and MAP kinase signaling pathways), and (4) no mRNAs corresponding to the MCH receptors were found. In conclusion, the binding site characterized in the SVK14 cell line is distinct from the MCH1 and MCH2 receptors and deserves therefore further investigation.

Binding Sites↗
PubMed2002

Synthesis and structure-affinity-activity relationships of novel benzofuran derivatives as MT(2) melatonin receptor selective ligands.

A series of N-(2-phenylbenzofuran-3-yl) ethyl amide and N-(2-arylalkylbenzofuran-3-yl) ethyl amide derivatives were synthesized and evaluated as melatonin receptor ligands. The affinity of each compound for the two MT(1) and MT(2) melatonin receptor subtypes was determined by binding studies using 2-[(125)I]iodomelatonin on human embryonic kidney cell line HEK293 membrane homogenates. The intrinsic activity of the most interesting compounds was evaluated on the [(35)S]GTPgammaS binding assay. Introduction of a 2-phenyl substituent in the C-2 benzofuran position leads to an agonist compound, 10q, which binds more strongly than melatonin itself to both MT(1) and MT(2) subtypes. On the other hand, a 2-benzyl group in the same position allows MT(2) antagonist selective ligands to be obtained. The MT(2) selectivity and antagonist potency can be modulated with suitable modifications on the N-acyl and benzyl substituents, and the most selective compounds 10c and 19 show affinity ratios of 123 and 192, respectively, and bind to the MT(2) subtype similarly to melatonin itself (0.1 nM). Nevertheless, 10c acts as an MT(1) and MT(2) antagonist, whereas 19 is a partial agonist.

Animals↗
PubMed2002

Ligand modulation of [35S]GTPgammaS binding at human alpha(2A), alpha(2B) and alpha(2C) adrenoceptors.

Affinities and efficacies of chemically diverse ligands--some of them used as clinical agents--were examined, employing [3H]RX821,002 and [35S]GTPgammaS binding assays, respectively, at human (h) cloned, halpha(2A), halpha(2B) and halpha(2C) adrenoceptors (AR) expressed in Chinese hamster ovary (CHO) cells. As compared to noradrenaline (NA, efficacy defined as 100%), the majority of the 13 agonists tested generally behaved as partial agonists. Amongst 18 antagonists, pK(B) and pK(i) values, which were highly correlated for each alpha(2)-AR subtype, failed to reveal any strikingly selective agents. Inverse agonist properties were not detected for any antagonist, consistent with a lack of constitutive activity suggested by the monophasic inhibition of [35S]GTPgammaS binding by GTPgammaS. These data should facilitate interpretation of experimental and clinical actions of adrenergic agonists. Moreover, they emphasize the continuing need for alpha(2)-AR subtype-selective antagonists in order to define further the roles and therapeutic relevance of halpha(2A)-, halpha(2B)-, and halpha(2C)-AR.

Adrenergic alpha-Agonists↗
PubMed2002

Differential actions of antiparkinson agents at multiple classes of monoaminergic receptor. I. A multivariate analysis of the binding profiles of 14 drugs at 21 native and cloned human receptor subtypes.

Because little comparative information is available concerning receptor profiles of antiparkinson drugs, affinities of 14 agents were determined at diverse receptors implicated in the etiology and/or treatment of Parkinson's disease: human (h)D(1), hD(2S), hD(2L), hD(3), hD(4), and hD(5) receptors; human 5-hydroxytryptamine (5-HT)(1A), h5-HT(1B), h5-HT(1D), h5-HT(2A), h5-HT(2B), and h5-HT(2C) receptors; halpha(1A)-, halpha(1B)-, halpha(1D)-, halpha(2A)-, halpha(2B)-, halpha(2C)-, rat alpha(2D)-, hbeta(1)-, and hbeta(2)-adrenoceptors (ARs); and native histamine(1) receptors. A correlation matrix (294 pK(i) values) demonstrated substantial "covariance". Correspondingly, principal components analysis revealed that axis 1, which accounted for 76% variance, was associated with the majority of receptor types: drugs displaying overall high versus modest affinities migrated at opposite extremities. Axis 2 (7% of variance) differentiated drugs with high affinity for hD(4) and H(1) receptors versus halpha(1)-AR subtypes. Five percent of variance was attributable to axis 3, which distinguished drugs with marked affinity for hbeta(1)- and hbeta(2)-ARs versus hD(5) and 5-HT(2A) receptors. Hierarchical (cluster) analysis of global homology generated a dendrogram differentiating two major groups possessing low versus high affinity, respectively, for multiple serotonergic and hD(5) receptors. Within the first group, quinpirole, quinerolane, ropinirole, and pramipexole interacted principally with hD(2), hD(3), and hD(4) receptors, whereas piribedil and talipexole recognized dopaminergic receptors and halpha(2)-ARs. Within the second group, lisuride and terguride manifested high affinities for all sites, with roxindole/bromocriptine, cabergoline/pergolide, and 6,7-dihydroxy-N,N-dimethyl-2-ammotetralin (TL99)/apomorphine comprising three additional subclusters of closely related ligands. In conclusion, an innovative multivariate analysis revealed marked heterogeneity in binding profiles of antiparkinson agents. Actions at sites other than hD(2) receptors likely participate in their (contrasting) functional profiles.

Animals↗
PubMed2002

Differential actions of antiparkinson agents at multiple classes of monoaminergic receptor. II. Agonist and antagonist properties at subtypes of dopamine D(2)-like receptor and alpha(1)/alpha(2)-adrenoceptor.

The accompanying multivariate analysis of the binding profiles of antiparkinson agents revealed contrasting patterns of affinities at diverse classes of monoaminergic receptor. Herein, we characterized efficacies at human (h)D(2SHORT(S)), hD(2LONG(L)), hD(3), and hD(4.4) receptors and at halpha(2A)-, halpha(2B)-, halpha(2C)-, and halpha(1A)-adrenoceptors (ARs). As determined by guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding, no ligand displayed "full" efficacy relative to dopamine (100%) at all "D(2)-like" sites. However, at hD(2S) receptors quinpirole, pramipexole, ropinirole, quinerolane, pergolide, and cabergoline were as efficacious as dopamine (E(max)100%); TL99, talipexole, and apomorphine were highly efficacious (79-92%); piribedil, lisuride, bromocriptine, and terguride showed intermediate efficacy (40-55%); and roxindole displayed low efficacy (11%). For all drugs, efficacies were lower at hD(2L) receptors, with terguride and roxindole acting as antagonists. At hD(3) receptors, efficacies ranged from 33% (roxindole) to 94% (TL99), whereas, for hD(4) receptors, highest efficacies (approximately 70%) were seen for quinerolane, quinpirole, and TL99, whereas piribedil and terguride behaved as antagonists and bromocriptine was inactive. Although efficacies at hD(2S) versus hD(2L) sites were highly correlated (r = 0.79), they correlated only modestly to hD(3)/hD(4) sites (r = 0.44-0.59). In [(35)S]GTPgammaS studies of halpha(2A)-ARs, TL99 (108%), pramipexole (52%), talipexole (51%), pergolide (31%), apomorphine (16%), and quinerolane (11%) were agonists and ropinirole and roxindole were inactive, whereas piribedil and other agents were antagonists. Similar findings were obtained at halpha(2B)- and halpha(2C)-ARs. Using [(3)H]phosphatidylinositol depletion, roxindole, bromocriptine, lisuride, and terguride displayed potent antagonist properties at halpha(1A)-ARs. In conclusion, antiparkinson agents display diverse agonist and antagonist properties at multiple subtypes of D(2)-like receptor and alpha(1)/alpha(2)-AR, actions, which likely contribute to their contrasting functional profiles.

Adrenergic alpha-1 Receptor Agonists↗
PubMed2002

Appetite-boosting property of pro-melanin-concentrating hormone(131-165) (neuropeptide-glutamic acid-isoleucine) is associated with proteolytic resistance.

Melanin-concentrating hormone (MCH) is a cyclic neuropeptide, with a major role in stimulation of feeding behavior in mammals. MCH signals in the brain occur via two seven-transmembrane G protein-coupled receptors, namely MCH1 (SLC-1, MCH(1), MCH-R1, or MCH-1R) and MCH2 (SLT, MCH(2), MCH-R2, or MCH-2R). In this study, we demonstrate that the pro-MCH(131-165) peptide neuropeptide-glutamic acid-isoleucine (NEI)-MCH is more potent than MCH in stimulating feeding in the rat. Using rat MCH1-expressed human embryonic kidney 293 cells, we show that NEI-MCH exhibits 5-fold less affinity in a binding assay and 2-fold less potency in a cAMP assay than MCH. A similar 7- to 8-fold shift in potency was observed in a Ca(2+)(i) assay using rat MCH1 or human MCH2-transfected Chinese hamster ovary cell models. This demonstrates that NEI-MCH is not a better agonist than MCH at either of the MCH receptors. Then, we compared the proteolysis resistance of MCH and NEI-MCH to rat brain membrane homogenates and purified proteases. Kinetics of peptide degradation using brain extracts indicated a t(1/2) of 34.8 min for MCH and 78.5 min for NEI-MCH with a specific pattern of cleavage of MCH but not NEI-MCH by exo- and endo-proteases. Furthermore, MCH was found highly susceptible to degradation by aminopeptidase M and endopeptidase 24.11, whereas NEI-MCH was fully resistant to proteolysis by these enzymes. Therefore, our results strongly suggest that reduced susceptibility to proteases of NEI-MCH compared with MCH account for its enhanced activity in feeding behavior. NEI-MCH represents therefore the first MCH natural functional "superagonist" so far described.

Amino Acid Sequence↗
PubMed2002

Melanin-concentrating hormone and its receptors: state of the art.

Melanin-concentrating hormone (MCH) is a cyclic neuropeptide of nineteen amino acids in mammals. Its involvement in the feeding behaviour has been well established during the last few years. A first receptor subtype, now termed MCHIR, was discovered in 1999, following the desorphanisation of the SLCI orphan receptor, using either reverse pharmacology or systematic screening of agonist candidates. A second MCH receptor, MCH2R, has been discovered recently, by several groups working on data mining of genomic banks. The molecular pharmacology of these two receptors is only described on the basis of the action of peptides derived from MCH. The present review tentatively summarizes the knowledge on these two receptors and presents the first attempts to discover new classes of antagonists that might have major roles in the control of obesity and feeding behaviour.

Amino Acid Sequence↗