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Proudman RGW, Akinaga J, Baker JG. The signaling and selectivity of α-adrenoceptor agonists for the human α2A, α2B and α2C-adrenoceptors and comparison with human α1 and β-adrenoceptors. Pharmacol Res Perspect 2022; 10:e01003. [PMID: 36101495 PMCID: PMC9471048 DOI: 10.1002/prp2.1003] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 08/05/2022] [Accepted: 08/15/2022] [Indexed: 11/11/2022] Open
Abstract
α2‐adrenoceptors, (α2A, α2B and α2C‐subtypes), are Gi‐coupled receptors. Central activation of brain α2A and α2C‐adrenoceptors is the main site for α2‐agonist mediated clinical responses in hypertension, ADHD, muscle spasm and ITU management of sedation, reduction in opiate requirements, nausea and delirium. However, despite having the same Gi‐potency in functional assays, some α2‐agonists also stimulate Gs‐responses whilst others do not. This was investigated. Agonist responses to 49 different α‐agonists were studied (CRE‐gene transcription, cAMP, ERK1/2‐phosphorylation and binding affinity) in CHO cells stably expressing the human α2A, α2B or α2C‐adrenoceptor, enabling ligand intrinsic efficacy to be determined (binding KD/Gi‐IC50). Ligands with high intrinsic efficacy (e.g., brimonidine and moxonidine at α2A) stimulated biphasic (Gi‐Gs) concentration responses, however for ligands with low intrinsic efficacy (e.g., naphazoline), responses were monophasic (Gi‐only). ERK1/2‐phosphorylation responses appeared to be Gi‐mediated. For Gs‐mediated responses to be observed, both a system with high receptor reserve and high agonist intrinsic efficacy were required. From the Gi‐mediated efficacy ratio, the degree of Gs‐coupling could be predicted. The clinical relevance and precise receptor conformational changes that occur, given the structural diversity of compounds with high intrinsic efficacy, remains to be determined. Comparison with α1 and β1/β2‐adrenoceptors demonstrated subclass affinity selectivity for some compounds (e.g., α2:dexmedetomidine, α1:A61603) whilst e.g., oxymetazoline had high affinity for both α2A and α1A‐subtypes, compared to all others. Some compounds had subclass selectivity due to selective intrinsic efficacy (e.g., α2:brimonidine, α1:methoxamine/etilefrine). A detailed knowledge of these agonist characteristics is vital for improving computer‐based deep‐learning and drug design.
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Affiliation(s)
- Richard G W Proudman
- Cell Signalling Research Group, Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, C Floor Medical School, Queen's Medical Centre, University of Nottingham, Nottingham, UK
| | - Juliana Akinaga
- Cell Signalling Research Group, Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, C Floor Medical School, Queen's Medical Centre, University of Nottingham, Nottingham, UK
| | - Jillian G Baker
- Cell Signalling Research Group, Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, C Floor Medical School, Queen's Medical Centre, University of Nottingham, Nottingham, UK
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2
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Seyedabadi M, Ghahremani MH, Albert PR. Biased signaling of G protein coupled receptors (GPCRs): Molecular determinants of GPCR/transducer selectivity and therapeutic potential. Pharmacol Ther 2019; 200:148-178. [PMID: 31075355 DOI: 10.1016/j.pharmthera.2019.05.006] [Citation(s) in RCA: 82] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Accepted: 04/26/2019] [Indexed: 02/07/2023]
Abstract
G protein coupled receptors (GPCRs) convey signals across membranes via interaction with G proteins. Originally, an individual GPCR was thought to signal through one G protein family, comprising cognate G proteins that mediate canonical receptor signaling. However, several deviations from canonical signaling pathways for GPCRs have been described. It is now clear that GPCRs can engage with multiple G proteins and the line between cognate and non-cognate signaling is increasingly blurred. Furthermore, GPCRs couple to non-G protein transducers, including β-arrestins or other scaffold proteins, to initiate additional signaling cascades. Receptor/transducer selectivity is dictated by agonist-induced receptor conformations as well as by collateral factors. In particular, ligands stabilize distinct receptor conformations to preferentially activate certain pathways, designated 'biased signaling'. In this regard, receptor sequence alignment and mutagenesis have helped to identify key receptor domains for receptor/transducer specificity. Furthermore, molecular structures of GPCRs bound to different ligands or transducers have provided detailed insights into mechanisms of coupling selectivity. However, receptor dimerization, compartmentalization, and trafficking, receptor-transducer-effector stoichiometry, and ligand residence and exposure times can each affect GPCR coupling. Extrinsic factors including cell type or assay conditions can also influence receptor signaling. Understanding these factors may lead to the development of improved biased ligands with the potential to enhance therapeutic benefit, while minimizing adverse effects. In this review, evidence for ligand-specific GPCR signaling toward different transducers or pathways is elaborated. Furthermore, molecular determinants of biased signaling toward these pathways and relevant examples of the potential clinical benefits and pitfalls of biased ligands are discussed.
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Affiliation(s)
- Mohammad Seyedabadi
- Department of Pharmacology, School of Medicine, Bushehr University of Medical Sciences, Iran; Education Development Center, Bushehr University of Medical Sciences, Iran
| | | | - Paul R Albert
- Ottawa Hospital Research Institute, Neuroscience, University of Ottawa, Canada.
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3
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Evans NJ, Bayliss AL, Reale V, Evans PD. Characterisation of Signalling by the Endogenous GPER1 (GPR30) Receptor in an Embryonic Mouse Hippocampal Cell Line (mHippoE-18). PLoS One 2016; 11:e0152138. [PMID: 26998610 PMCID: PMC4801207 DOI: 10.1371/journal.pone.0152138] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 03/09/2016] [Indexed: 01/14/2023] Open
Abstract
Estrogen can modulate neuronal development and signalling by both genomic and non-genomic pathways. Many of its rapid, non-genomic effects on nervous tissue have been suggested to be mediated via the activation of the estrogen sensitive G-protein coupled receptor (GPER1 or GPR30). There has been much controversy over the cellular location, signalling properties and endogenous activators of GPER1. Here we describe the pharmacology and signalling properties of GPER1 in an immortalized embryonic hippocampal cell line, mHippoE-18. This cell line does not suffer from the inherent problems associated with the study of this receptor in native tissue or the problems associated with heterologously expression in clonal cell lines. In mHippoE-18 cells, 17β-Estradiol can mediate a dose-dependent rapid potentiation of forskolin-stimulated cyclic AMP levels but does not appear to activate the ERK1/2 pathway. The effect of 17β-Estradiol can be mimicked by the GPER1 agonist, G1, and also by tamoxifen and ICI 182,780 which activate GPER1 in a variety of other preparations. The response is not mimicked by the application of the classical estrogen receptor agonists, PPT, (an ERα agonist) or DPN, (an ERβ agonist), further suggesting that this effect of 17β-Estradiol is mediated through the activation of GPER1. However, after exposure of the cells to the GPER1 specific antagonists, G15 and G36, the stimulatory effects of the above agonists are replaced by dose-dependent inhibitions of forskolin-stimulated cyclic AMP levels. This inhibitory effect is mimicked by aldosterone in a dose-dependent way even in the absence of the GPER1 antagonists. The results are discussed in terms of possible "Biased Antagonism" whereby the antagonists change the conformation of the receptor resulting in changes in the agonist induced coupling of the receptor to different second messenger pathways.
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Affiliation(s)
- Nicholas J. Evans
- The Signalling Laboratory, The Babraham Institute, Cambridge, CB22 3AT, United Kingdom
| | - Asha L. Bayliss
- The Signalling Laboratory, The Babraham Institute, Cambridge, CB22 3AT, United Kingdom
| | - Vincenzina Reale
- The Signalling Laboratory, The Babraham Institute, Cambridge, CB22 3AT, United Kingdom
| | - Peter D. Evans
- The Signalling Laboratory, The Babraham Institute, Cambridge, CB22 3AT, United Kingdom
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Yuliana ND, Korthout H, Wijaya CH, Kim HK, Verpoorte R. Plant-derived food ingredients for stimulation of energy expenditure. Crit Rev Food Sci Nutr 2014; 54:373-88. [PMID: 24188308 DOI: 10.1080/10408398.2011.586739] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The development of obesity is related to the regulation of energy intake, energy expenditure, and energy storage in the body. Increasing energy expenditure by inducing lipolysis followed by fat oxidation is one of the alternatives which could help to reverse this increasingly widespread condition. Currently, there is no approved drug targeting on stimulation of energy expenditure available. The use of herbal medicines has become a preferred alternative, supported by the classical consensus on the innocuity of herbal medicine vs synthetic drugs, something that often lacks a scientific basis (ban on Ephedra, for example). The inclusion of functional food in the daily diet has also been promoted although its efficacy requires further investigation. This review summarizes the results of recent work focused on the investigation of edible plant materials targeted at various important pathways related to stimulation of energy expenditure. The aim is to evaluate a number of plants that may be of interest for further studies because of their potential to provide novel lead compounds or functional foods which may be used to combat obesity, but require further studies to evaluate their antiobesity activity in humans.
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Affiliation(s)
- Nancy Dewi Yuliana
- a Department of Pharmacognosy, Section of Metabolomics , Leiden University , Einsteinweg 55, 2333 CC , Leiden , The Netherlands
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5
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Shawky E. Determination of Synephrine and Octopamine in Bitter Orange Peel by HPTLC with Densitometry. J Chromatogr Sci 2013; 52:899-904. [DOI: 10.1093/chromsci/bmt113] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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6
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Verpeut JL, Walters AL, Bello NT. Citrus aurantium and Rhodiola rosea in combination reduce visceral white adipose tissue and increase hypothalamic norepinephrine in a rat model of diet-induced obesity. Nutr Res 2013; 33:503-12. [PMID: 23746567 DOI: 10.1016/j.nutres.2013.04.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Revised: 03/29/2013] [Accepted: 04/02/2013] [Indexed: 01/02/2023]
Abstract
Extracts from the immature fruit of Citrus aurantium are often used for weight loss but are reported to produce adverse cardiovascular effects. Root extracts of Rhodiola rosea have notable antistress properties. The hypothesis of these studies was that C aurantium (6% synephrine) and R rosea (3% rosavins, 1% salidroside) in combination would improve diet-induced obesity alterations in adult male Sprague-Dawley rats. In normal-weight animals fed standard chow, acute administration of C aurantium (1-10 mg/kg) or R rosea (2-20 mg/kg) alone did not reduce deprivation-induced food intake, but C aurantium (5.6 mg/kg) + R rosea (20 mg/kg) produced a 10.5% feeding suppression. Animals maintained (13 weeks) on a high-fat diet (60% fat) were exposed to 10-day treatments of C aurantium (5.6 mg/kg) or R rosea (20 mg/kg) alone or in combination. Additional groups received vehicle (2% ethanol) or were pair fed to the C aurantium + R rosea group. Although high-fat diet intake and weight loss were not influenced, C aurantium + R rosea had a 30% decrease in visceral fat weight compared with the other treatments. Only the C aurantium group had an increased heart rate (+7%) compared with vehicle. In addition, C aurantium + R rosea administration resulted in an elevation (+15%) in hypothalamic norepinephrine and an elevation (+150%) in frontal cortex dopamine compared with the pair-fed group. These initial findings suggest that treatments of C aurantium + R rosea have actions on central monoamine pathways and have the potential to be beneficial for the treatment of obesity.
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Affiliation(s)
- Jessica L Verpeut
- Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ, USA
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7
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Bayliss A, Evans PD. Characterisation of AmphiAmR4, an amphioxus (Branchiostoma floridae) α₂-adrenergic-like G-protein-coupled receptor. INVERTEBRATE NEUROSCIENCE 2012. [PMID: 23183848 DOI: 10.1007/s10158-012-0145-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Little is known about the evolutionary relationship between vertebrate adrenergic receptors and invertebrate octopamine and tyramine receptors. The complexity of the adrenergic signalling system is believed to be an innovation of the vertebrate lineage but the presence of noradrenaline has been reported in some invertebrate species. The cephalochordate, amphioxus (Branchiostoma floridae), is an ideal model organism for studying the evolution of vertebrate GPCRs, given its unique position at the base of the chordate lineage. Here, we describe the pharmacological characterisation and second messenger coupling abilities of AmphiAmR4, which clusters with α₂-adrenergic receptors in a phylogenetic tree but also shares a high sequence similarity to invertebrate octopamine/tyramine receptors in both BLAST and Hidden Markov Model analyses. Thus, it was of particular interest to determine if AmphiAmR4 displayed similar functional properties to the vertebrate α₂-adrenergic receptors or to invertebrate octopamine or tyramine receptors. When stably expressed in Chinese hamster ovary (CHO) cells, noradrenaline couples the receptor to both the activation of adenylyl cyclase and to the activation of the MAPKinase pathway. Pharmacological studies with a wide range of agonists and antagonists suggest that AmphiAmR4 functions as an α₂-adrenergic-like receptor when expressed in CHO cells.
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Affiliation(s)
- Asha Bayliss
- The Inositide Laboratory, The Babraham Institute, The Babraham Research Campus, Cambridge CB22 3AT, UK
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8
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Differential modulation of Beta-adrenergic receptor signaling by trace amine-associated receptor 1 agonists. PLoS One 2011; 6:e27073. [PMID: 22073124 PMCID: PMC3205048 DOI: 10.1371/journal.pone.0027073] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Accepted: 10/09/2011] [Indexed: 11/19/2022] Open
Abstract
Trace amine-associated receptors (TAAR) are rhodopsin-like G-protein-coupled receptors (GPCR). TAAR are involved in modulation of neuronal, cardiac and vascular functions and they are potentially linked with neurological disorders like schizophrenia and Parkinson's disease. Subtype TAAR1, the best characterized TAAR so far, is promiscuous for a wide set of ligands and is activated by trace amines tyramine (TYR), phenylethylamine (PEA), octopamine (OA), but also by thyronamines, dopamine, and psycho-active drugs. Unfortunately, effects of trace amines on signaling of the two homologous β-adrenergic receptors 1 (ADRB1) and 2 (ADRB2) have not been clarified yet in detail. We, therefore, tested TAAR1 agonists TYR, PEA and OA regarding their effects on ADRB1/2 signaling by co-stimulation studies. Surprisingly, trace amines TYR and PEA are partial allosteric antagonists at ADRB1/2, whereas OA is a partial orthosteric ADRB2-antagonist and ADRB1-agonist. To specify molecular reasons for TAAR1 ligand promiscuity and for observed differences in signaling effects on particular aminergic receptors we compared TAAR, tyramine (TAR) octopamine (OAR), ADRB1/2 and dopamine receptors at the structural level. We found especially for TAAR1 that the remarkable ligand promiscuity is likely based on high amino acid similarity in the ligand-binding region compared with further aminergic receptors. On the other hand few TAAR specific properties in the ligand-binding site might determine differences in ligand-induced effects compared to ADRB1/2. Taken together, this study points to molecular details of TAAR1-ligand promiscuity and identified specific trace amines as allosteric or orthosteric ligands of particular β-adrenergic receptor subtypes.
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9
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Gatti R, Lotti C. Development and validation of a pre-column reversed phase liquid chromatographic method with fluorescence detection for the determination of primary phenethylamines in dietary supplements and phytoextracts. J Chromatogr A 2011; 1218:4468-73. [DOI: 10.1016/j.chroma.2011.05.044] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Revised: 12/07/2010] [Accepted: 05/11/2011] [Indexed: 11/28/2022]
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10
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Wang H, Li SY, Zhao CK, Zeng X. A system for screening agonists targeting beta2-adrenoceptor from Chinese medicinal herbs. J Zhejiang Univ Sci B 2009; 10:243-50. [PMID: 19353741 DOI: 10.1631/jzus.b0820340] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In order to develop a model for screening the agonists of human beta(2)-adrenoceptor from Chinese medicinal herbs extracts, we used a cell-based functional assay based on a common G protein-coupled receptor (GPCR) regulation mechanism and destabilized enhanced green fluorescent protein (d(2)EGFP) reporter gene technique. The positive cell clone was confirmed by real-time polymerase chain reaction (PCR) and imaging analysis. To assess the value of this model, we screened over 2000 high performance liquid chromatography (HPLC)-fractionated samples from the ethanol extracts of Chinese medicinal herbs. Six fractions (isolated from Panax japonicus, Veratrum nigrum, Phellodendron amurense, Fructus Aurantii Immaturus, Chaenomeles speciosa, and Dictamnus dasycarpus) showed significant effects on active reporter gene expression, three of which (isolated from Phellodendron amurense, Fructus Aurantii Immaturus, and Chaenomeles speciosa) were selected for further concentration response analysis and the half maximal effective concentration (EC(1/2 max)) values were 4.2, 2.7, and 4.8 microg/ml, respectively. Therefore, this reporter gene assay was suitable for screening beta(2)-adrenoceptor agonists. The results suggest that the six herbal extracts are the possible agonists of beta(2)-adrenoceptor.
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Affiliation(s)
- Hui Wang
- Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
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11
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Cornil CA, Ball GF. Interplay among catecholamine systems: dopamine binds to alpha2-adrenergic receptors in birds and mammals. J Comp Neurol 2008; 511:610-27. [PMID: 18924139 PMCID: PMC2858410 DOI: 10.1002/cne.21861] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Dopaminergic and adrenergic receptors are G-protein-coupled receptors considered to be different based on their pharmacology and signaling pathways. Some receptor subtypes that are members of one family are actually closer in phylogenetic terms to some subtypes belonging to the other family, suggesting that the pharmacological specificity among these receptors from different families is not perfect. Indeed, evidence is accumulating that one amine can cross-talk with receptors belonging to the other system. However, most of these observations were collected in vitro using artificial cell models transfected with cloned receptors, so that the occurrence of this phenomenon in vivo as well as its distribution in the central nervous system is not known. In this study the pharmacological basis of possible in vivo interactions between dopamine and alpha(2)-adrenergic receptors was investigated in quail, zebra finches, and rats. Binding competitions showed that dopamine displaces the binding of the selective alpha(2)-adrenergic ligand, [(3)H]RX821002, in the brain of the three species with an affinity approximately 10-28-fold lower than that of norepinephrine. Dopamine also displaces with an affinity 3-fold lower than norepinephrine the binding of [(3)H]RX821002 to human alpha(h2A)-adrenergic receptors expressed in Sf9 cells. The anatomical distribution of this interaction was assessed in brain slices of quail and rat based on autoradiographic methods. Both norepinephrine and dopamine significantly displace [(3)H]RX821002 binding in all brain nuclei considered. Together, these data provide evidence for an interaction between the dopaminergic and noradrenergic systems in the vertebrate brain, albeit with species variations.
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Affiliation(s)
- Charlotte A Cornil
- Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA.
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12
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Farooqui T. Octopamine-mediated neuronal plasticity in honeybees: implications for olfactory dysfunction in humans. Neuroscientist 2007; 13:304-22. [PMID: 17644763 DOI: 10.1177/10738584070130040501] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Biogenic amines, such as norepinephrine (in vertebrates) and octopamine (in invertebrates), have structural and functional similarities. These amines play crucial roles in animal behavior by modifying the synaptic output of relevant neurons. Increased levels of norepinephrine in the olfactory bulb preferentially increase mitral cell excitatory responses to olfactory nerve inputs, suggesting its critical role in modulating olfactory function including memory formation and/or recall of specific olfactory memories. Increased levels of octopamine in the antennal lobe play an important role in a reinforcement pathway involved in olfactory learning and memory in honeybees. Similar to adrenergic receptors in the human brain, activation of octopaminergic receptors in the honeybee brain induces specific second messenger pathways that change protein phosphorylation and/or gene expression, altering the activity and/or abundance of proteins responsible for neuronal signaling leading to changes in olfactory behavior. The author's studies in honeybees Apis mellifera indicate that oxidative stress plays a major role in olfactory dysfunction. A similar mechanism has been proposed for olfactory abnormalities in patients of Alzheimer disease and Parkinson disease. Due to similarities in cellular and molecular processes, which govern neuronal plasticity in humans and honeybees, the author proposes that the honeybee can be used as a potential and relatively simple model system for understanding human olfactory dysfunction during aging and in neurodegenerative diseases.
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Affiliation(s)
- Tahira Farooqui
- Department of Entomology, The Ohio State University, Columbus, Ohio 43210, USA.
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13
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Putzbach K, Rimmer CA, Sharpless KE, Sander LC. Determination of Bitter Orange alkaloids in dietary supplements standard reference materials by liquid chromatography with ultraviolet absorbance and fluorescence detection. J Chromatogr A 2007; 1156:304-11. [PMID: 17524413 DOI: 10.1016/j.chroma.2006.12.027] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Revised: 12/01/2006] [Accepted: 12/06/2006] [Indexed: 11/26/2022]
Abstract
Four adrenergic amines [synephrine, octopamine, tyramine, and n-methyltyramine] were determined in a variety of Bitter Orange containing dietary supplements. Two extraction techniques were evaluated in detail: Soxhlet extraction and sonication extraction. A liquid chromatographic separation using a reversed-phase C(18) stationary phase and the ion-pairing reagent sodium dodecyl sulfate was developed to separate the Bitter Orange alkaloids. Ultraviolet absorbance detection at 220 nm and fluorescence detection with excitation at 273 nm and emission at 304 nm were used for the alkaloid detection. The method described was used for the assignment of the levels of the predominant alkaloids in three candidate standard reference materials containing Bitter Orange.
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Affiliation(s)
- Karsten Putzbach
- Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
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14
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Burman C, Maqueira B, Coadwell J, Evans PD. Eleven new putative aminergic G-protein coupled receptors from Amphioxus (Branchiostoma floridae): identification, sequence analysis and phylogenetic relationship. INVERTEBRATE NEUROSCIENCE 2007; 7:87-98. [PMID: 17225134 DOI: 10.1007/s10158-006-0041-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2006] [Accepted: 12/19/2006] [Indexed: 11/29/2022]
Abstract
We have identified eleven novel aminergic-like G-protein coupled receptor (GPCRs) sequences (named AmphiAmR1-11) by searching the genomic trace sequence database for the amphioxus species, Branchiostoma floridae. They share many of the structural motifs that have been used to characterize vertebrate and invertebrate aminergic GPCRs. A preliminary classification of these receptors has been carried out using both BLAST and Hidden Markov Model analyses. The amphioxus genome appears to express a number of D1-like dopamine receptor sequences, including one related to insect dopamine receptors. It also expresses a number of receptors that resemble invertebrate octopamine/tyramine receptors and others that resemble vertebrate alpha-adrenergic receptors. Amphioxus also expresses receptors that resemble vertebrate histamine receptors. Several of the novel receptor sequences have been identified in amphioxus cDNA libraries from a number of tissues.
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Affiliation(s)
- Chloe Burman
- The Inositide Laboratory, The Babraham Institute, Cambridge, UK
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15
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Xhaard H, Rantanen VV, Nyrönen T, Johnson MS. Molecular evolution of adrenoceptors and dopamine receptors: implications for the binding of catecholamines. J Med Chem 2006; 49:1706-19. [PMID: 16509586 DOI: 10.1021/jm0511031] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We derived homology models for all human catecholamine-binding GPCRs (CABRs; the alpha-1, alpha-2, and beta-adrenoceptors and the D1-type and D2-type dopamine receptor) using the bovine rhodopsin-11-cis-retinal X-ray structure. Interactions were predicted from the endogenous ligands norepinephrine or dopamine and from the binding site and were used to optimize receptor-ligand interactions. Similar binding modes in the complexes agree with a large "binding core" conserved across the CABRs, that is, D3.32, V(I)3.33, T3.37, S5.42, S(A/C)5.43, S5.46, F6.51, F6.52, and W6.48. Model structures and docking simulations suggest that extracellular loop 2 could provide a common attachment point for the ligands' beta-hydroxyl via a hydrogen bond donated by the main-chain NH group of residue xl2.52. The modeled CABRs and docking modes are in good agreement with published experimental studies. Complementarity between the ligand and the binding site suggests that the bovine rhodopsin structure is a suitable template for modeling agonist-bound CABRs.
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Affiliation(s)
- Henri Xhaard
- Department of Biochemistry and Pharmacy, Abo Akademi University, FI-20520 Turku, Finland
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16
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Srivastava DP, Yu EJ, Kennedy K, Chatwin H, Reale V, Hamon M, Smith T, Evans PD. Rapid, nongenomic responses to ecdysteroids and catecholamines mediated by a novel Drosophila G-protein-coupled receptor. J Neurosci 2006; 25:6145-55. [PMID: 15987944 PMCID: PMC6725065 DOI: 10.1523/jneurosci.1005-05.2005] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Nongenomic response pathways mediate many of the rapid actions of steroid hormones, but the mechanisms underlying such responses remain controversial. In some cases, cell-surface expression of classical nuclear steroid receptors has been suggested to mediate these effects, but, in a few instances, specific G-protein-coupled receptors (GPCRs) have been reported to be responsible. Here, we describe the activation of a novel, neuronally expressed Drosophila GPCR by the insect ecdysteroids ecdysone (E) and 20-hydroxyecdysone (20E). This is the first report of an identified insect GPCR interacting with steroids. The Drosophila melanogaster dopamine/ecdysteroid receptor (DmDopEcR) shows sequence homology with vertebrate beta-adrenergic receptors and is activated by dopamine (DA) to increase cAMP levels and to activate the phosphoinositide 3-kinase pathway. Conversely, E and 20E show high affinity for the receptor in binding studies and can inhibit the effects of DA, as well as coupling the receptor to a rapid activation of the mitogen-activated protein kinase pathway. The receptor may thus represent the Drosophila homolog of the vertebrate "gamma-adrenergic receptors," which are responsible for the modulation of various activities in brain, blood vessels, and pancreas. Thus, DmDopEcR can function as a cell-surface GPCR that may be responsible for some of the rapid, nongenomic actions of ecdysteroids, during both development and signaling in the mature adult nervous system.
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Affiliation(s)
- Deepak P Srivastava
- The Inositide Laboratory, The Babraham Institute, Cambridge CB2 4AT, United Kingdom
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Morita M, Susuki J, Amino H, Yoshiki F, Moizumi S, Kudo Y. Use of the exogenous Drosophila octopamine receptor gene to study Gq-coupled receptor-mediated responses in mammalian neurons. Neuroscience 2006; 137:545-53. [PMID: 16289891 DOI: 10.1016/j.neuroscience.2005.09.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2004] [Revised: 08/31/2005] [Accepted: 09/03/2005] [Indexed: 10/25/2022]
Abstract
Diverse excitatory and inhibitory neuronal responses are mediated via Gq-coupled receptors, but the lack of a systematic comparison of different receptors or neurons has hindered a better understanding of these responses. Such a comparison may be provided by an exogenous receptor that is activated by compounds that have no effect on endogenous receptors. We therefore expressed an invertebrate biogenic amine receptor, the Drosophila octopamine receptor, in rat cortical neurons and compared octopamine receptor-mediated responses with those mediated by the group I metabotropic glutamate receptor, the endogenous Gq-coupled receptor in rat cortical neurons. Stimulation of either receptor did not result in a calcium response in octopamine receptor-expressing neurons, although octopamine preferentially elicited a calcium increase in octopamine receptor-expressing PC12h cells, while enhancing the neuronal depolarization-induced calcium increase and the electrical excitability. The increased excitability was caused by inward currents resulting from a reduction in the leak current, which was voltage-independent and blocked by genistein, a non-selective tyrosine kinase inhibitor. These results show that, in cortical neurons, exogenous octopamine receptor in mushroom bodies activated the same cell signaling pathway as endogenous metabotropic glutamate receptor, suggesting that the diverse neuronal responses mediated by Gq-coupled receptors are due to the properties of different neurons, rather than to the properties of the receptors.
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Affiliation(s)
- M Morita
- Laboratory of Cellular Neurobiology, School of Life Science, Tokyo University of Pharmacy and Life Science, 1432-1, Horinouchi, Hachioji, 192-0392, Japan.
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18
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Zhang WP, Ouyang M, Thomas SA. Potency of catecholamines and other L-tyrosine derivatives at the cloned mouse adrenergic receptors. Neuropharmacology 2004; 47:438-49. [PMID: 15275833 DOI: 10.1016/j.neuropharm.2004.04.017] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2004] [Accepted: 04/30/2004] [Indexed: 11/28/2022]
Abstract
The adrenergic system is a neuromodulatory system whose endogenous ligands are considered to be the catecholamines norepinephrine (NE) and epinephrine (E). Evidence suggests that the catecholamine dopamine (DA) may also activate adrenergic signaling. Further, tyramine (TA) and octopamine (OA) are other monoamines that can be produced in catecholaminergic cells when tyrosine hydroxylase activity is low or absent, as in some genetic mouse models of adrenergic function. Here, we systematically examine the ability of these L-tyrosine-derived monoamines to activate all 10 known isoforms of the cloned mouse adrenergic receptors expressed in Chinese hamster ovary cells. In comparison to NE or E, DA is nearly as efficacious in this system but is from 1 to 4 orders of magnitude less potent. In comparison to DA, OA has roughly equivalent potency but is usually only a partial agonist. TA is either very weak or lacks agonism. Of note, all three mouse alpha(1) receptors increase cAMP, in contrast to results reported for human alpha(1d) receptors. In addition, a 12-amino acid hemagglutinin epitope tag added to the N-terminus of alpha(2) receptors selectively enhances the potency of NE approximately 10- to 100-fold, indicating that caution should be applied when interpreting physiological results from experiments using modified receptors.
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Affiliation(s)
- Wei-Ping Zhang
- Department of Pharmacology, University of Pennsylvania, 3620 Hamilton Walk, Philadelphia, PA 19104-6084 USA
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19
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Fugh-Berman A, Myers A. Citrus aurantium, an ingredient of dietary supplements marketed for weight loss: current status of clinical and basic research. Exp Biol Med (Maywood) 2004; 229:698-704. [PMID: 15337824 DOI: 10.1177/153537020422900802] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Seville orange (Citrus aurantium) extracts are being marketed as a safe alternative to ephedra in herbal weight-loss products, but C. aurantium may also have the potential to cause adverse health effects. C. aurantium contains synephrine (oxedrine), which is structurally similar to epinephrine. Although no adverse events have been associated with ingestion of C. aurantium products thus far, synephrine increases blood pressure in humans and other species, and has the potential to increase cardiovascular events. Additionally, C. aurantium contains 6',7'-dihydroxybergamottin and bergapten, both of which inhibit cytochrome P450-3A, and would be expected to increase serum levels of many drugs. There is little evidence that products containing C. aurantium are an effective aid to weight loss. Synephrine has lipolytic effects in human fat cells only at high doses, and octopamine does not have lipolytic effects in human adipocytes.
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Affiliation(s)
- Adriane Fugh-Berman
- Department of Physiology & Biophysics, Georgetown University, Box 571460, Washington, District of Columbia 20057-1460, USA.
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20
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Cordeaux Y, IJzerman AP, Hill SJ. Coupling of the human A1 adenosine receptor to different heterotrimeric G proteins: evidence for agonist-specific G protein activation. Br J Pharmacol 2004; 143:705-14. [PMID: 15302686 PMCID: PMC1575922 DOI: 10.1038/sj.bjp.0705925] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The present study investigates the effect of varying ligand structure on the ability of agonists to activate guanine nucleotide-binding proteins of the Gi, Gs and Gq families via the A(1) adenosine receptor. In CHO cells expressing this receptor, inhibition or potentiation of forskolin-stimulated cAMP accumulation was used as an end point to measure the activation of Gi and, in Pertussis toxin (PTX)-treated cells, Gs, respectively. Stimulation of inositol phosphate accumulation in PTX-treated cells was used as an index of Gq activation. CPA (N(6)-cyclopentyladenosine), NECA (5'-N-ethyl-carboxyamidoadenosine) and eight analogues of these ligands presented a range of guanine nucleotide-binding protein (G-protein)-activating profiles. Some ligands could only activate Gi (e.g. 2'deoxyCPA), some primarily Gi and Gs (and only weakly Gq) (e.g. 3'deoxyCPA), highlighting the importance of the ribose hydroxyls in agonist activation of multiple G proteins. CHA (N(6)-cyclohexyladenosine) activated Gi, Gs and Gq, but was more efficacious than CPA in activating Gs. The NECA analogues 5'-N-cyclopropyl-carboxamidoadenosine, 5'-N-cyclobutyl-carboxamidoadenosine and 5'-N-cyclopentyl-carboxamidoadenosine (CPeCA) also activated all three G proteins, although their ability to activate Gs and Gq (relative to CPA) was reduced with increasing substituent size, such that CPeCA produced only a small stimulation (at 100 microM) at Gq, but was a full agonist, relative to CPA, at Gi and Gs. This study suggests that the A(1) adenosine receptor can adopt agonist-specific conformations, arising from small changes in ligand structure, which lead to the differential activation of Gi, Gs and Gq.
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Affiliation(s)
- Yolande Cordeaux
- Institute of Cell Signalling, Medical School, University of Nottingham, Nottingham NG7 2UH
| | - Adriaan P IJzerman
- Leiden/Amsterdam Centre for Drug research, Division of Medicinal Chemistry, Leiden, Netherlands
| | - Stephen J Hill
- Institute of Cell Signalling, Medical School, University of Nottingham, Nottingham NG7 2UH
- Author for correspondence:
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21
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Bour S, Visentin V, Prévot D, Carpéné C. Moderate weight-lowering effect of octopamine treatment in obese Zucker rats. J Physiol Biochem 2004; 59:175-82. [PMID: 15000448 DOI: 10.1007/bf03179913] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Octopamine is proposed as a substitution product of synephrine by diverse drug industries that advertise new weight-lowering products or medicinal plants enriched in this biogenic amine. We have already reported that octopamine is able to activate in vitro lipolysis in rat adipocytes via beta3-adrenergic receptor activation, while it activates glucose uptake in human fat cells via its oxidation by amine oxidases. In this work, we tested whether a chronic challenge with octopamine could exert anti-obesity effects. A treatment consisting in daily i.p. administration of octopamine (81 micromol/kg) was compared on a four-week period with calorie restriction in the genetically obese Zucker rat. Octopamine treatment resulted in a 19% decrease in body weight gain, when compared to the 177 g gained by controls during the same period. The decrease in body weight gain was detectable only after three weeks of treatment and was apparently not due to a pronounced and sustainable anorectic effect of octopamine since: 1) cumulated food consumption was only reduced by 10%; 2) the experimental 18% reduction of food intake provoked a rapid decrease in body weight gain, significant in less than two weeks. The lipolytic responses to isoprenaline or octopamine and the stimulation of glucose transport by insulin or by the amine oxidase substrate tyramine were unmodified by the treatments. Noteworthy, the elevated plasma insulin of obese rats was lowered by octopamine. This study shows that octopamine can reduce body weight gain in obese rats, without apparent adverse effects, but with less efficacy than beta3-AR agonists.
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Affiliation(s)
- S Bour
- Institut National de la Santé et de la Recherche Médicale, U586, CHU Rangueil, Université Paul Sabatier, 31043 Toulouse, France
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22
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Peltonen JM, Nyrönen T, Wurster S, Pihlavisto M, Hoffrén AM, Marjamäki A, Xhaard H, Kanerva L, Savola JM, Johnson MS, Scheinin M. Molecular mechanisms of ligand-receptor interactions in transmembrane domain V of the alpha2A-adrenoceptor. Br J Pharmacol 2003; 140:347-58. [PMID: 12970108 PMCID: PMC1574035 DOI: 10.1038/sj.bjp.0705439] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. The structural determinants of catechol hydroxyl interactions with adrenergic receptors were examined using 12 alpha2-adrenergic agonists and a panel of mutated human alpha2A-adrenoceptors. The alpha2ASer201 mutant had a Cys --> Ser201 (position 5.43) amino-acid substitution, and alpha2ASer201Cys200 and alpha2ASer201Cys204 had Ser --> Cys200 (5.42) and Ser --> Cys204 (5.46) substitutions, respectively, in addition to the Cys --> Ser201 substitution. 2. Automated docking methods were used to predict the receptor interactions of the ligands. Radioligand-binding assays and functional [35S]GTPgammaS-binding assays were performed using transfected Chinese hamster ovary cells to experimentally corroborate the predicted binding modes. 3. The hydroxyl groups of phenethylamines were found to have different effects on ligand affinity towards the activated and resting forms of the wild-type alpha2A-adrenoceptor. Substitution of Ser200 or Ser204 with cysteine caused a deterioration in the capability of catecholamines to activate the alpha2A-adrenoceptor. The findings indicate that (i) Cys201 plays a significant role in the binding of catecholamine ligands and UK14,304 (for the latter, by a hydrophobic interaction), but Cys201 is not essential for receptor activation; (ii) Ser200 interacts with the meta-hydroxyl group of phenethylamine ligands, affecting both catecholamine binding and receptor activation; while (iii) substituting Ser204 with a cysteine interferes both with the binding of catecholamine ligands and with receptor activation, due to an interaction between Ser204 and the para-hydroxyl group of the catecholic ring.
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MESH Headings
- Adrenergic Agonists/metabolism
- Adrenergic Agonists/pharmacology
- Amino Acid Sequence
- Amino Acid Substitution
- Animals
- Binding Sites/genetics
- Binding, Competitive/drug effects
- Brimonidine Tartrate
- CHO Cells
- Catecholamines/chemistry
- Catecholamines/metabolism
- Cricetinae
- Guanosine 5'-O-(3-Thiotriphosphate)/metabolism
- Idazoxan/analogs & derivatives
- Idazoxan/metabolism
- Ligands
- Membrane Proteins/chemistry
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Models, Molecular
- Molecular Structure
- Mutation
- Protein Structure, Tertiary
- Quinoxalines/chemistry
- Quinoxalines/metabolism
- Radioligand Assay
- Receptors, Adrenergic, alpha-2/chemistry
- Receptors, Adrenergic, alpha-2/genetics
- Receptors, Adrenergic, alpha-2/metabolism
- Sequence Homology, Amino Acid
- Sulfur Radioisotopes
- Tritium
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Affiliation(s)
- Juha M Peltonen
- Department of Pharmacology and Clinical Pharmacology, University of Turku, Finland
- Turku Graduate School of Biomedical Sciences, University of Turku, Finland
| | - Tommi Nyrönen
- Department of Biochemistry and Pharmacy, Åbo Akademi University, Turku, Finland
- Center for Scientific Computing, Espoo
| | | | - Marjo Pihlavisto
- Department of Pharmacology and Clinical Pharmacology, University of Turku, Finland
| | | | - Anne Marjamäki
- Department of Pharmacology and Clinical Pharmacology, University of Turku, Finland
| | - Henri Xhaard
- Department of Biochemistry and Pharmacy, Åbo Akademi University, Turku, Finland
| | - Liisa Kanerva
- Departments of Chemistry and Biomedicine, University of Turku, Turku, Finland
| | | | - Mark S Johnson
- Department of Biochemistry and Pharmacy, Åbo Akademi University, Turku, Finland
| | - Mika Scheinin
- Department of Pharmacology and Clinical Pharmacology, University of Turku, Finland
- Author for correspondence:
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23
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Pauwels PJ, Rauly I, Wurch T. Dissimilar pharmacological responses by a new series of imidazoline derivatives at precoupled and ligand-activated alpha 2A-adrenoceptor states: evidence for effector pathway-dependent differential antagonism. J Pharmacol Exp Ther 2003; 305:1015-23. [PMID: 12649300 DOI: 10.1124/jpet.102.048215] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Whereas agonist-directed differential signaling at a single receptor subtype has become an accepted pharmacological concept, distinct behaviors by ligands that are assumed to be antagonists is less documented. The intrinsic activity and capacity of antagonism for a new series of imidazoline-derived adrenergic ligands analogous to dexefaroxan were investigated by measuring two distinct signaling pathways at the recombinant human alpha 2A-adrenoceptor (alpha 2A AR): 1) pertussis toxin-resistant guanosine 5'-O-(3-[35S]thio)triphosphate ([35S]GTP gamma S) binding responses mediated by either a recombinant G alpha oCys351Ile or G alpha i2Cys352Ile protein in CHO-K1 cells, and 2) inhibition of cAMP formation in a stably transfected C6-glial cell line. Ligands could be differentiated as inverse agonists [i.e., 2-(4-methoxy-2-ethyl-2,3-dihydrobenzofuran-2-yl)-4,5-dihydro-1H-imidazole; RX 851062], neutral antagonists [i.e., 2-(4-hydroxy-2-ethyl-2,3-dihydrobenzofuran-2-yl)-4,5-dihydro-1H-imidazole; RX 851057], partial [i.e., 2-(4-chloro-2,3-dihydrobenzofuran-2-yl)-4,5-dihydro-1H-imidazole; RX 821008], and high-efficacy [i.e., 2-(6,7-dichloro-2,3-dihydrobenzofuran-2-yl)-4,5-dihydro-1H-imidazole; RX 821010] agonists at a precoupled alpha 2A AR state in the copresence of a G alpha oCys351Ile protein but not G alpha i2Cys352Ile protein by monitoring [35S]GTP gamma S binding responses. Neither positive nor negative efficacy was observed for these compounds by monitoring the adenylate cyclase pathway at a presumably low-affinity alpha 2A AR state. The capacity of the dexefaroxan analogs to antagonize the (-)-epinephrine-mediated [35S]GTP gamma S binding response at a G alpha oCys351Ile protein was inversely correlated with their magnitude of intrinsic activity and unrelated to their ligand binding affinity for the alpha 2A AR. On the other hand, their capacity to antagonize either (-)-epinephrine or 5-bromo-6-(2-imidazolin-2-ylamino)quinoxaline tartrate (UK 14304)-mediated inhibition of forskolin-stimulated cAMP formation was not related with the rank order of antagonist capacity for the (-)-epinephrine-mediated [35S]GTP gamma S binding response. In conclusion, these data demonstrate that certain alpha2 AR ligands that are assumed to be antagonists, may yield dissimilar pharmacological responses, dependent on the investigated agonist-stimulated effector pathway.
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Affiliation(s)
- Petrus J Pauwels
- Department of Cellular and Molecular Biology, Centre de Recherche Pierre Fabre, 17, avenue Jean Moulin, 81106 Castres Cédex, France.
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24
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Richardson J, Chatwin H, Hirasawa A, Tsujimoto G, Evans PD. Agonist-specific coupling of a cloned human alpha1A-adrenoceptor to different second messenger pathways. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 2003; 367:333-41. [PMID: 12690424 DOI: 10.1007/s00210-003-0703-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2002] [Accepted: 01/23/2003] [Indexed: 11/30/2022]
Abstract
The agonist-specific coupling properties of the three cloned human alpha(1)-adrenoceptor subtypes have been compared, when expressed at similar levels in Chinese hamster ovary (CHO) cell lines, using noradrenaline and the (+/-)- meta- and (+/-)- para- structural isomers of octopamine as agonists. The alpha(1A)- and the alpha(1B)-adrenoceptor subtypes coupled to both the release of arachidonic acid and to the accumulation of inositol phosphates, whereas the alpha(1D)-adrenoceptor subtype only coupled effectively to the accumulation of inositol phosphates. The rank order of potencies of the three agonists tested was the same for all the three receptor subtypes when coupled to either signalling pathway: noradrenaline > meta-octopamine > para-octopamine. Meta-octopamine was a partial agonist of the alpha(1A)-adrenoceptor subtype when coupled to arachidonic acid release, whereas para-octopamine was a full agonist of this pathway. In contrast, meta-octopamine was a full agonist at the alpha(1B)-adrenoceptor subtype when coupled to arachidonic acid release, whereas para-octopamine was a partial agonist of this pathway. Neither meta-octopamine, nor para-octopamine acted as full agonists when coupling any of the three alpha(1)-adrenoceptor subtypes to the accumulation of inositol phosphates. Para-octopamine was only a weak partial agonist of this pathway for all three receptor subtypes. The results show that the modulation of arachidonic acid release and inositol 1,4,5-trisphosphate production occurs in both a subtype- and agonist-specific manner for the alpha(1A)-, alpha(1B)- and alpha(1D)-adrenoceptor subtypes. In addition, the alpha(1A)-adrenoceptor exhibits agonist-specific coupling (agonist trafficking) to the different second messenger pathways.
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Affiliation(s)
- Joanna Richardson
- The Laboratory of Receptor Signalling, The Babraham Institute, Cambridge, UK
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25
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Chatwin HM, Rudling JE, Patel D, Reale V, Evans PD. Site-directed mutagenesis studies on the Drosophila octopamine/tyramine receptor. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2003; 33:173-184. [PMID: 12535676 DOI: 10.1016/s0965-1748(02)00188-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The cloned Drosophila octopamine/tyramine receptor can be coupled to second messenger pathways in an agonist-specific fashion by the endogenously occurring biogenic amines, octopamine and tyramine, when expressed in Chinese hamster ovary cells. We have mutated to alanine a range of receptor amino acids that could potentially form hydrogen bonds with the beta-hydroxyl group of octopamine based on homologies with alpha- and beta-adrenergic receptor subtypes. After stable expression of the mutant receptors in CHO cells we have compared the ability of octopamine and tyramine to displace [(3)H]yohimbine binding to membrane fractions from the mutant cell lines with their ability to modulate adenylyl cyclase activity in intact cells. The results suggest that none of the mutated amino acids residues, at least in isolation, are likely to be involved in interactions with the beta-hydroxyl group of the octopamine side chain. It is possible that amino acids not mutated in the present study are somehow involved in this interaction. Alternatively, it is also possible that the beta-hydroxyl group of the octopamine side chain is capable of interacting with more than one of the amino acids mutated in the present study.
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Affiliation(s)
- Heather M Chatwin
- The Laboratory of Receptor Signalling, The Babraham Institute, Babraham, Cambridge CB2 4AT, UK
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26
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Kukkonen JP, Näsman J, Akerman KE. Modelling of promiscuous receptor-Gi/Gs-protein coupling and effector response. Trends Pharmacol Sci 2001; 22:616-22. [PMID: 11730971 DOI: 10.1016/s0165-6147(00)01864-2] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
A single G-protein-coupled receptor might activate multiple G-protein species. This multiplex coupling ability can be used by tissues to regulate signalling; for the pharmacologist, such multiplex coupling might cause difficulties in the interpretation of experimental data. In this article, we present mathematical models for the activation of two separate G-protein species by a single receptor. Issues addressed concern mutual antagonism between the G proteins and the availability of an already activated receptor for interaction with a new G protein (receptor-G-protein-effector complexing versus free diffusion of G proteins) in addition to receptor-G-protein precoupling at different G-protein and receptor expression levels. The output from the receptor models uses, as readout, a new model for adenylyl cyclase regulation by two allosteric regulators (i.e. G(s) and G(i)).
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Affiliation(s)
- J P Kukkonen
- Dept of Physiology, Division of Cell Physiology, Uppsala University, BMC,PO Box 572,SE-75123, Uppsala, Sweden.
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27
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Nasman J, Kukkonen JP, Ammoun S, Akerman KE. Role of G-protein availability in differential signaling by alpha 2-adrenoceptors. Biochem Pharmacol 2001; 62:913-22. [PMID: 11543726 DOI: 10.1016/s0006-2952(01)00730-4] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The impact of G-protein expression on the coupling specificity of the human alpha(2B)-adrenergic receptor (alpha(2B)-AR) was studied in Sf9 cells. The alpha(2B)-AR was shown to activate both coexpressed G(s)- and G(i)-proteins in a [(35)S]GTPgammaS binding assay. Noradrenaline and the synthetic agonist UK14,304 were equally potent and efficacious in stimulating G(i) activation. At the effector level (adenylyl cyclase), both ligands stimulated cAMP production. In the presence of forskolin, the effects of the agonists were more complex. Noradrenaline stimulated cAMP production, while UK14,304 showed a biphasic concentration-response curve with inhibition of stimulated cAMP production at low agonist concentrations and further stimulation at high agonist concentrations. G(s) coexpression caused a monophasic stimulatory response with both ligands. Coexpression with G(i) resulted in a biphasic concentration-response curve for noradrenaline and a monophasic inhibition with UK14,304. Experiments with a panel of agonists demonstrated that the more efficacious an agonist is in stimulating cAMP production, the weaker is its ability to couple to inhibition of cAMP accumulation via exogenous G(i). To be able to explain the mechanistic consequences of dual G-protein coupling described above, we developed a mathematical model based on the hypothesis that an agonist induces different conformations of the receptor having different affinity for different G-proteins. The model reproduced the profiles seen in the concentration-response curves with G(s) and G(i) coexpression. The model predicts that the affinity of the receptor conformation for G-proteins as well as the availability of G-proteins will determine the ultimate response of the receptor.
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Affiliation(s)
- J Nasman
- Department of Physiology, Division of Cell Physiology, Uppsala University, BMC, Box 572, SE-75123, Uppsala, Sweden.
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28
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Cordeaux Y, Nickolls SA, Flood LA, Graber SG, Strange PG. Agonist regulation of D(2) dopamine receptor/G protein interaction. Evidence for agonist selection of G protein subtype. J Biol Chem 2001; 276:28667-75. [PMID: 11369753 DOI: 10.1074/jbc.m008644200] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The D(2) dopamine receptor has been expressed in Sf21 insect cells together with the G proteins G(o) and G(i2), using the baculovirus system. Expression levels of receptor and G protein (alpha, beta, and gamma subunits) in the two preparations were similar as shown by binding of [(3)H]spiperone and quantitative Western blot, respectively. For several agonists, binding data were fitted best by a two-binding site model in either preparation, showing interaction of expressed receptor and G protein. For some agonists, binding to the higher affinity site was of higher affinity in D(2)/G(o) than in the D(2)/G(i2) preparation. Some agonists exhibited binding data that were best fitted by a two-binding site model in D(2)/G(o) and a one-binding site model in D(2)/G(i2). Therefore, receptor/G protein interaction seemed to be stronger in the D(2)/G(o) preparation. Agonist stimulation of [(35)S]GTP gamma S (guanosine 5'-3-O-(thio)triphosphate) binding in the two preparations also gave evidence for higher affinity D(2)/G(o) interaction. In the D(2)/G(o) preparation, agonist stimulation of [(35)S]GTP gamma S binding occurred at higher potency for several agonists, and a higher stimulation (relative to dopamine) was achieved in D(2)/G(o) compared with D(2)/G(i2). Some agonists were able to stimulate [(35)S]GTP gamma S binding in the D(2)/G(o) preparation but not in D(2)/G(i2). The extent of D(2) receptor selectivity for G(o) over G(i2) is therefore dependent on the agonist used, and thus agonists may stabilize different conformations of the receptor with different abilities to couple to and activate G proteins.
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Affiliation(s)
- Y Cordeaux
- School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading, Berkshire RG6 6AJ, United Kingdom
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29
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Pauwels PJ, Tardif S, Colpaert FC, Wurch T. Modulation of ligand responses by coupling of alpha(2A)-adrenoceptors to diverse G(alpha)-proteins. Biochem Pharmacol 2001; 61:1079-92. [PMID: 11301041 DOI: 10.1016/s0006-2952(01)00575-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The hypothesis that different signalling may be mediated via a single alpha(2A)-adrenoceptor (alpha(2A) AR) subtype was investigated by challenging alpha(2) AR ligands in combination with diverse recombinant wt, mutant, and chimeric G(alpha)-proteins. Possible coupling of alpha(2A) AR to endogenous G(alphai/o)-proteins in CHO-K1 cells was excluded by measuring pertussis toxin (PTX)-resistant [(35)S]GTPgammaS-binding responses as a common functional response to alpha(2A) AR activation. (-)-Adrenaline (10 microM) displayed the highest magnitude of [(35)S]GTPgammaS-binding response in the co-presence of a PTX-resistant G(alphao)Cys(351)Ile protein, whereas a decreased response was obtained with the mutant G(alphai1/2)-proteins. Replacement of the last six amino acids at the C-terminal portion of the G(alphao)-protein by the corresponding amino acid region of either the G(alphaz)-, G(alphas)-, G(alphaq)-, or G(alpha15)-protein and co-expression with the alpha(2A) AR resulted in similar maximal (-)-adrenaline-mediated [(35)S]GTPgammaS-binding responses with these chimeric G(alphao)-proteins. The ligands D-medetomidine, BHT 920 (6-allyl-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepin-2-ylamine) and (+)-RX 811059 (2-(2-ethoxy-2,3-dihydro-benzo[1,4]dioxin-2-yl)-4,5-dihydro-1H-imidazole) were weakly active or virtually inactive at the chimeric G(alphao/s)-, G(alphao/q)-, and G(alphao/15)-proteins in contrast to the G(alphao/z)-protein. Furthermore, combining the constitutively active mutant Thr(373)Lys alpha(2A) AR with these chimeric G(alphao)-proteins enhanced the apparent intrinsic activity of d-medetomidine and BHT 920. A similar observation was made using the corresponding fusion proteins, where the stoichiometry of the mutant alpha(2A) AR to the chimeric G(alphao)-protein was fixed at 1.0. These data indicate that a single ligand may display different magnitudes of activation at the alpha(2A) AR subtype coupled to chimeric G(alphao) proteins under controlled conditions of alpha(2A) AR: G(alphao)-protein expression.
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Affiliation(s)
- P J Pauwels
- Department of Cellular and Molecular Biology, Centre de Recherche Pierre Fabre, 17 Avenue Jean Moulin, F-81106, Castres Cédex, France.
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Kukkonen JP, Jansson CC, Akerman KE. Agonist trafficking of G(i/o)-mediated alpha(2A)-adrenoceptor responses in HEL 92.1.7 cells. Br J Pharmacol 2001; 132:1477-84. [PMID: 11264241 PMCID: PMC1572699 DOI: 10.1038/sj.bjp.0703964] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The ability of 19 agonists to elevate Ca(2+) and inhibit forskolin-induced cyclic AMP elevation through alpha(2A)-adrenoceptors in HEL 92.1.7 cells was investigated. Ligands of catecholamine-like- (five), imidazoline- (nine) and non-catecholamine-non-imidazoline-type (five) were included. 2. The relative maximum responses were similar in both assays. Five ligands were full or nearly full agonists, six produced 20 - 70% of the response to a full agonist and the remaining eight gave lower responses (< 20%) so that their potencies were difficult to evaluate. 3. Marked differences in the potencies of the agonists with respect to the two measured responses were seen. The catecholamines were several times less potent in decreasing cyclic AMP than in increasing Ca(2+), whereas the other, both imidazoline and ox-/thiazoloazepine ligands, were several times more potent with respect to the former than the latter response. For instance, UK14,304 was more potent than adrenaline with respect to the cyclic AMP response but less potent than adrenaline with respect to the Ca(2+) response. 4. All the responses were sensitive to pertussis toxin-pretreatment. Also the possible role of PLA(2), beta-adrenoceptors or ligand transport or metabolism as a source of error could be excluded. The results suggest that the active receptor states produced by catecholamines and the other agonists are markedly different and therefore have different abilities to activate different signalling pathways.
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Affiliation(s)
- J P Kukkonen
- Department of Physiology, Division of Cell Physiology, Uppsala University, BMC, P.O. Box 572, S-75123 Uppsala, Sweden.
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Rudling JE, Richardson J, Evans PD. A comparison of agonist-specific coupling of cloned human alpha(2)-adrenoceptor subtypes. Br J Pharmacol 2000; 131:933-41. [PMID: 11053214 PMCID: PMC1572406 DOI: 10.1038/sj.bjp.0703644] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The agonist-specific coupling properties of the three cloned human alpha(2)-adrenoceptor subtypes have been compared, when expressed at similar levels in Chinese hamster ovary (CHO) cell lines, using noradrenaline and (+/-)-meta-octopamine as agonists. Noradrenaline can couple the receptor to both the inhibition and stimulation of forskolin-stimulated cyclic AMP production in all three receptor subtypes, with the relative strength of the coupling to the pathways varying for each of the receptor subtypes. meta-Octopamine selectively couples the alpha(2A)-adrenoceptor only to the inhibition of forskolin-stimulated cyclic AMP production. However, meta-octopamine couples the alpha(2B)- and alpha(2C)-adrenoceptors to both the inhibition and stimulation of forskolin-stimulated cyclic AMP production. The relative potency of meta-octopamine to noradrenaline varies between the different alpha(2)-adrenoceptor subtypes. The effects of meta-octopamine are around two orders of magnitude less potent than those of noradrenaline on both the alpha(2A)- and alpha(2B)-adrenoceptor subtypes. In contrast, in the case of the alpha(2C)-adrenoceptor, meta-octopamine is only one order of magnitude less potent than noradrenaline in the stimulation of forskolin-stimulated cyclic AMP production and, in addition, is equipotent with noradrenaline in the inhibition of forskolin-stimulated cyclic AMP production and has an increased maximal response. This raises the possibility that meta-octopamine may have physiologically important actions via alpha(2C)-adrenoceptors in vivo. The results show that the modulation of cyclic AMP production occurs in both a subtype- and agonist-specific manner for alpha(2A)-adrenoceptors and in a subtype specific manner for alpha(2B)- and alpha(2C)-adrenoceptors.
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Affiliation(s)
- Jane E Rudling
- The Babraham Institute Laboratory of Receptor Signalling, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ
| | - Jo Richardson
- The Babraham Institute Laboratory of Receptor Signalling, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ
| | - Peter D Evans
- The Babraham Institute Laboratory of Receptor Signalling, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ
- Author for correspondence:
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Pauwels PJ, Colpaert FC. Heterogeneous ligand-mediated Ca(++) responses at wt and mutant alpha(2A)-adrenoceptors suggest multiple ligand activation binding sites at the alpha(2A)-adrenoceptor. Neuropharmacology 2000; 39:2101-11. [PMID: 10963753 DOI: 10.1016/s0028-3908(00)00040-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Ligand:receptor interactions were analysed at wild-type, Asp(79)Asn and Thr(373)Lys alpha(2A) AR by measuring Ca(++) responses in the co-presence of a G(alpha 15) protein in CHO-K1 cells. (-)-Adrenaline displayed a time-dependent Ca(++) response with the following magnitude: wt alpha(2A) AR>Thr(373)Lys alpha(2A) AR>Asp(79)Asn alpha(2A) AR. The maximal amplitude of activation by d-medetomidine and clonidine versus that of (-)-adrenaline was not affected by the Asp(79)Asn mutation, whereas it was significantly lower for both UK 14304 (-42%) and oxymetazoline (-35%). BHT 920 induced a higher Ca(++) response (+19%) at the Asp(79)Asn alpha(2A) AR. Some (atipamezole>BRL 44408=idazoxan approximately SKF 86466>dexefaroxan) but not all (RX 811059 and RS 15385) of the putative alpha(2) AR antagonists tested also displayed partial agonist properties at the Asp(79)Asn alpha(2A) AR. At the Thr(373)Lys alpha(2A) AR, high-efficacy responses were produced by each of the agonists, whereas the putative antagonists showed the following rank order of maximal responses: BRL 44408>SKF 86466>atipamezole approximately idazoxan>dexefaroxan. The observed heterogeneity of Ca(++) responses produced by different ligands at wt and mutant alpha(2A) AR may be explained by assuming the existence of multiple ligand activation binding sites at the alpha(2A) AR.
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Affiliation(s)
- P J Pauwels
- Centre de Recherche Pierre Fabre, Department of Cellular and Molecular Biology, 17, avenue Jean Moulin, 81106 Castres Cédex, France.
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Pauwels PJ, Colpaert FC. Disparate ligand-mediated Ca(2+) responses by wild-type, mutant Ser(200)Ala and Ser(204)Ala alpha(2A)-adrenoceptor: G(alpha15) fusion proteins: evidence for multiple ligand-activation binding sites. Br J Pharmacol 2000; 130:1505-12. [PMID: 10928951 PMCID: PMC1572214 DOI: 10.1038/sj.bjp.0703455] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Ligand : receptor interactions were analysed at wt, mutant Ser(200)Ala and Ser(204)Ala alpha(2A) ARs by measuring Ca(2+) responses in CHO-K1 cells either by co-expression with a G(alpha15) protein or at a receptor : G(alpha15) protein stoichiometry of 1.0 using fusion proteins. The magnitude of the UK 14304-mediated Ca(2+) response as elicited by a G(alpha15) protein was largest with both mutant Ser(200)Ala and Ser(204)Ala alpha(2A)ARs compared to the wt alpha(2A) AR in the co-expression and fusion protein experiments. The activation profiles of the wt and both mutant alpha(2A) ARs as analysed by a series of alpha(2) AR agonists differed. d-Medetomidine and clonidine appeared most efficacious at the Ser(204)Ala alpha(2A) AR, whereas oxymetazoline was also partially active at the Ser(200)Ala alpha(2A) AR. Talipexole was silent at both mutant alpha(2A) ARs. The intrinsic activity of (-)-adrenaline was either absent or partial at the Ser(204)Ala and Ser(200)Ala alpha(2A) AR, respectively. This latter observation is related to its lower binding affinity for both mutant alpha(2A) ARs. Ligands characterized as antagonists at wt and Ser(200)Ala alpha(2A) ARs demonstrated either no intrinsic activity (i.e., RX 811059) or positive efficacy with a different rank order of maximal response at the Ser(204)Ala alpha(2A) AR (atipamezole=SKF 86466=idazoxan>dexefaroxan) than Asp(79)Asn alpha(2A) AR (atipamezole>idazoxan approximately SKF 86466>dexefaroxan) and Thr(373)Lys alpha(2A) AR (SKF 86466>atipamezole approximately idazoxan>dexefaroxan). These effects were only observed in the co-expression experiments at concentrations in line with their binding affinities. In conclusion, these Ca(2+) data suggest that multiple activation binding sites exist for these ligands at the alpha(2A) AR, and that their activation may be affected in different ways by the mutations being investigated.
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Affiliation(s)
- P J Pauwels
- Department of Cellular and Molecular Biology, Centre de Recherche Pierre Fabre, 17, avenue Jean Moulin 81106 Castres Cédex, France.
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Kalman DS, Colker CM, Shi Q, Swain MA. Effects of a weight-loss aid in healthy overweight adults: double-blind, placebo-controlled clinical trial. Curr Ther Res Clin Exp 2000. [DOI: 10.1016/s0011-393x(00)89034-7] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Fontana E, Morin N, Prévot D, Carpéné C. Effects of octopamine on lipolysis, glucose transport and amine oxidation in mammalian fat cells. Comp Biochem Physiol C Toxicol Pharmacol 2000; 125:33-44. [PMID: 11790328 DOI: 10.1016/s0742-8413(99)00086-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Octopamine is known to exert adrenergic effects in mammals although specific octopamine receptors have been cloned only in invertebrates. It has been shown that octopamine can stimulate alpha(2)-adrenoceptors (ARs) in Chinese hamster ovary cells transfected with human alpha(2)-ARs. More recently, we reported that octopamine stimulates lipolysis through beta(3)-rather than beta(1)-or beta(2)-AR activation in white adipocytes from different mammalian species. The present study was thus undertaken to further characterize the adrenergic properties of octopamine. For this purpose, several biological processes known to be regulated by adrenergic stimulation were studied in response to octopamine, noradrenaline, adrenaline and tyramine in white adipocytes from different mammals. First, octopamine was fully lipolytic in garden dormouse and Siberian hamster while tyramine was ineffective. Although being around one hundred-fold less potent that noradrenaline, octopamine was slightly more potent in these hibernators known for their high sensitivity to beta(3)-AR agonists than in rat and chiefly more active than in human adipocytes known for their limited responses to beta(3)-AR agonists. Second, octopamine reduced insulin-dependent glucose transport in rat fat cells, a response also observed with noradrenaline and selective beta(3)-AR agonists but not with beta(1)-or beta(2)-agonists. Third, human adipocytes, which endogenously express a high level of alpha(2)-ARs, exhibited a clear alpha(2)-adrenergic antilipolytic response to adrenaline but not to octopamine. Moreover, octopamine exhibited only a very weak affinity for the alpha(2A)-ARs labeled by [3H]RX821002 in human adipocyte membranes. In Syrian hamster adipocytes, which also possess alpha(2)-ARs, octopamine induced only a weak antilipolysis. Finally, octopamine was a substrate of fat cell amine oxidases, with an apparent affinity similar to that of noradrenaline. All these results demonstrate that octopamine, tyramine noradrenaline and adrenaline can be degraded by adipocyte amine oxidases. However these biogenic amines interact differently with adipocyte adrenoceptors: tyramine is inactive, adrenaline and noradrenaline activate both beta- and alpha(2)-ARs while octopamine activates only beta(3)-ARs and is devoid of alpha(2)-adrenergic agonism. Thus, octopamine could be considered as an endogenous selective beta(3)-AR agonist.
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Affiliation(s)
- E Fontana
- Institut National de la Santé et de la Recherche Médicale (INSERM), Unité 317, Institut Louis Bugnard Bat L3, CHU Rangueil, 31403, Toulouse, France
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Rudling JE, Kennedy K, Evans PD. The effect of site-directed mutagenesis of two transmembrane serine residues on agonist-specific coupling of a cloned human alpha2A-adrenoceptor to adenylyl cyclase. Br J Pharmacol 1999; 127:877-86. [PMID: 10433494 PMCID: PMC1566090 DOI: 10.1038/sj.bjp.0702614] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The effects of substitution of the Ser200 and Ser204 residues with alanine on the signalling properties of the cloned human alpha2A-adrenoceptor, stably expressed in Chinese hamster ovary (CHO) cell lines, have been investigated using noradrenaline and the structural isomers of octopamine. 2. The Ser-->Ala200 or the Ser-->Ala204 mutant forms of the alpha2A-adrenoceptor, when expressed in cells in the absence of pertussis toxin pretreatment, are two orders of magnitude more sensitive to inhibition of cyclic AMP production by (+/-)-para-octopamine and (+/-)-meta-octopamine, respectively, than cells expressing the wild-type receptor. Binding studies indicate that the effects are not due to an increased agonist affinity for the mutant receptors and that they are likely to be due to agonist-mediated conformational changes in receptor structure. 3. After incubation with pertussis toxin, (+/-)-meta-octopamine (100 microM and above) produced a stimulation of cyclic AMP levels in cells expressing the Ser-->Ala204 mutant form of the alpha2A-adrenoceptor but showed no stimulation in cells expressing the Ser-->Ala200 mutant receptor. Under these conditions (+/-)-para-octopamine did not produce any increases in cyclic AMP production in cells expressing either of the mutant receptor forms or the wild-type receptor. 4. The results emphasise the importance of the Ser200 and Ser204 residues of the alpha2A-adrenoceptor in exerting an inhibitory influence on the ability of (+/-)-para-octopamine and (+/-)-meta-octopamine respectively, to induce a receptor-agonist conformation capable of inhibiting forskolin-stimulation of cyclic AMP levels. 5. It is clear that Ser204 also prevents meta-octopamine from generating a receptor-agonist conformation that can increase cyclic AMP levels, emphasising the importance of this residue in the agonist-specific coupling of this receptor to different second messenger systems.
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Affiliation(s)
- Jane E Rudling
- The Babraham Institute Laboratory of Molecular Signalling, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ
| | - Karen Kennedy
- The Babraham Institute Laboratory of Molecular Signalling, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ
| | - Peter D Evans
- The Babraham Institute Laboratory of Molecular Signalling, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ
- Author for correspondence:
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Effects of Citrus aurantium extract, caffeine, and St. John's Wort on body fat loss, lipid levels, and mood states in overweight healthy adults. CURRENT THERAPEUTIC RESEARCH 1999. [DOI: 10.1016/s0011-393x(00)88523-9] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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38
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Sautel M, Milligan G. Loss of activation of Gs but not Gi following expression of an alpha2A-adrenoceptor-Gi1alpha fusion protein. FEBS Lett 1998; 436:46-50. [PMID: 9771891 DOI: 10.1016/s0014-5793(98)01094-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Both the porcine alpha2A-adrenoceptor and a fusion protein between this receptor and a pertussis toxin-resistant form of Gila were stably expressed in Rat-1 fibroblasts. The agonist UK14304 mediated a biphasic regulation of adenylyl cyclase activity via the isolated receptor with inhibition of the enzyme activity at low concentrations of the compound which was subsequently reversed at higher concentrations. By contrast, stimulation of the fusion protein with this agonist could only produce inhibition of enzyme activity. This inhibition was produced by activation of endogenous Gi rather than the fused alpha subunit of Gi1, as pertussis toxin treatment obliterated inhibitory regulation of adenylyl cyclase via the fusion construct. Pertussis toxin treatment potentiated stimulation of adenylyl cyclase via the isolated receptor but such treatment was unable to uncover capacity of the fusion protein to produce such an effect.
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MESH Headings
- Adenylate Cyclase Toxin
- Adenylyl Cyclases/drug effects
- Adenylyl Cyclases/metabolism
- Adrenergic alpha-Agonists/pharmacology
- Animals
- Binding Sites
- Brimonidine Tartrate
- Cholera Toxin/pharmacology
- Colforsin/pharmacology
- Dose-Response Relationship, Drug
- GTP-Binding Protein alpha Subunits, Gi-Go/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- GTP-Binding Protein alpha Subunits, Gs/genetics
- GTP-Binding Protein alpha Subunits, Gs/metabolism
- Oxymetazoline/pharmacology
- Pertussis Toxin
- Quinoxalines/pharmacology
- Rats
- Receptors, Adrenergic, alpha-2/drug effects
- Receptors, Adrenergic, alpha-2/genetics
- Receptors, Adrenergic, alpha-2/metabolism
- Recombinant Fusion Proteins/drug effects
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Virulence Factors, Bordetella/pharmacology
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Affiliation(s)
- M Sautel
- Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, UK
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Burt AR, Sautel M, Wilson MA, Rees S, Wise A, Milligan G. Agonist occupation of an alpha2A-adrenoreceptor-Gi1alpha fusion protein results in activation of both receptor-linked and endogenous Gi proteins. Comparisons of their contributions to GTPase activity and signal transduction and analysis of receptor-G protein activation stoichiometry. J Biol Chem 1998; 273:10367-75. [PMID: 9553093 DOI: 10.1074/jbc.273.17.10367] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A fusion protein between a pertussis toxin-resistant (C351G) mutant of the alpha subunit of the G protein Gi1 and the porcine alpha2A-adrenoreceptor was stably expressed in Rat 1 fibroblasts. Agonists caused stimulation of high affinity GTPase activity, which was partially prevented by pertussis toxin treatment, demonstrating that the toxin-resistant component of the GTPase activity was derived from the receptor-fused G protein and the remainder from endogenous Gialpha. Half-maximal stimulation of the GTPase activity of endogenous Gi was achieved with lower concentrations of agonist. Although the Km for GTP of the fusion protein-linked Gi was lower than for the endogenous G protein, Vmax measurements demonstrated that adrenaline activated some 5 mol of endogenous Gi/mol of fusion protein-linked Gi. The isolated alpha2A-adrenoreceptor could activate Gs; however, the fusion protein did not. Compared with adrenaline, the efficacy of a range of partial agonists to stimulate endogenous Gialpha was greater than for the fusion protein-constrained C351G Gi1alpha. alpha2A-Adrenoreceptor agonists could stimulate both p44 mitogen-activated protein kinase and p70 S6 kinase and inhibit forskolin-amplified adenylyl cyclase activity in untreated alpha2A-adrenoreceptor-C351G Gi1alpha fusion protein-expressing cells, but these signals were abolished following pertussis toxin treatment. These results demonstrate conclusively, and for the first time, that agonist occupancy of a receptor-G protein fusion protein can result in activation of G proteins other than that physically linked to the receptor. This was selective between G protein classes. Analysis of the contributions of fusion protein-linked and endogenous G proteins to agonist-stimulated GTPase activity provided a direct and original measure of receptor-G protein activation stoichiometry.
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Affiliation(s)
- A R Burt
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom
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