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Bousquet P, Hudson A, García-Sevilla JA, Li JX. Imidazoline Receptor System: The Past, the Present, and the Future. Pharmacol Rev 2020; 72:50-79. [PMID: 31819014 DOI: 10.1124/pr.118.016311] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Imidazoline receptors historically referred to a family of nonadrenergic binding sites that recognize compounds with an imidazoline moiety, although this has proven to be an oversimplification. For example, none of the proposed endogenous ligands for imidazoline receptors contain an imidazoline moiety but they are diverse in their chemical structure. Three receptor subtypes (I1, I2, and I3) have been proposed and the understanding of each has seen differing progress over the decades. I1 receptors partially mediate the central hypotensive effects of clonidine-like drugs. Moxonidine and rilmenidine have better therapeutic profiles (fewer side effects) than clonidine as antihypertensive drugs, thought to be due to their higher I1/α 2-adrenoceptor selectivity. Newer I1 receptor agonists such as LNP599 [3-chloro-2-methyl-phenyl)-(4-methyl-4,5-dihydro-3H-pyrrol-2-yl)-amine hydrochloride] have little to no activity on α 2-adrenoceptors and demonstrate promising therapeutic potential for hypertension and metabolic syndrome. I2 receptors associate with several distinct proteins, but the identities of these proteins remain elusive. I2 receptor agonists have demonstrated various centrally mediated effects including antinociception and neuroprotection. A new I2 receptor agonist, CR4056 [2-phenyl-6-(1H-imidazol-1yl) quinazoline], demonstrated clear analgesic activity in a recently completed phase II clinical trial and holds great promise as a novel I2 receptor-based first-in-class nonopioid analgesic. The understanding of I3 receptors is relatively limited. Existing data suggest that I3 receptors may represent a binding site at the Kir6.2-subtype ATP-sensitive potassium channels in pancreatic β-cells and may be involved in insulin secretion. Despite the elusive nature of their molecular identities, recent progress on drug discovery targeting imidazoline receptors (I1 and I2) demonstrates the exciting potential of these compounds to elicit neuroprotection and to treat various disorders such as hypertension, metabolic syndrome, and chronic pain.
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Affiliation(s)
- Pascal Bousquet
- Faculty of Medicine, University of Strasbourg, Strasbourg, France (P.B.); Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada (A.H.); Laboratory of Neuropharmacology, University Research Institute on Health Sciences, University of the Balearic Islands, Palma de Malllorca, Spain (J.A.G.-S.); and Department of Pharmacology and Toxicology, University at Buffalo, Buffalo, New York (J.-X.L.)
| | - Alan Hudson
- Faculty of Medicine, University of Strasbourg, Strasbourg, France (P.B.); Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada (A.H.); Laboratory of Neuropharmacology, University Research Institute on Health Sciences, University of the Balearic Islands, Palma de Malllorca, Spain (J.A.G.-S.); and Department of Pharmacology and Toxicology, University at Buffalo, Buffalo, New York (J.-X.L.)
| | - Jesús A García-Sevilla
- Faculty of Medicine, University of Strasbourg, Strasbourg, France (P.B.); Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada (A.H.); Laboratory of Neuropharmacology, University Research Institute on Health Sciences, University of the Balearic Islands, Palma de Malllorca, Spain (J.A.G.-S.); and Department of Pharmacology and Toxicology, University at Buffalo, Buffalo, New York (J.-X.L.)
| | - Jun-Xu Li
- Faculty of Medicine, University of Strasbourg, Strasbourg, France (P.B.); Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada (A.H.); Laboratory of Neuropharmacology, University Research Institute on Health Sciences, University of the Balearic Islands, Palma de Malllorca, Spain (J.A.G.-S.); and Department of Pharmacology and Toxicology, University at Buffalo, Buffalo, New York (J.-X.L.)
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Venkataraman AV, Keat N, Myers JF, Turton S, Mick I, Gunn RN, Rabiner EA, Passchier J, Parker CA, Tyacke RJ, Nutt DJ. First evaluation of PET-based human biodistribution and radiation dosimetry of 11C-BU99008, a tracer for imaging the imidazoline 2 binding site. EJNMMI Res 2018; 8:71. [PMID: 30062395 PMCID: PMC6066589 DOI: 10.1186/s13550-018-0429-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Accepted: 07/18/2018] [Indexed: 12/04/2022] Open
Abstract
BACKGROUND We measured whole body distribution of 11C-BU99008, a new PET biomarker for non-invasive identification of the imidazoline2 binding site. The purpose of this phase I study was to evaluate the biodistribution and radiation dosimetry of 11C-BU99008 in healthy human subjects. METHODS A single bolus injection of 11C-BU99008 (296 ± 10.5 MBq) was administered to four healthy subjects who underwent whole-body PET/CT over 120 min from the cranial vertex to the mid-thigh. Volumes of interest were drawn around visually identifiable source organs to generate time-activity curves (TAC). Residence times were determined from time-activity curves. Absorbed doses to individual organs and the whole body effective dose were calculated using OLINDA/EXM 1.1 for each subject. RESULTS The highest measured activity concentration was in the kidney and spleen. The longest residence time was in the muscle at 0.100 ± 0.023 h, followed by the liver at 0.067 ± 0.015 h and lungs at 0.052 ± 0.010 h. The highest mean organ absorbed dose was within the heart wall (0.028 ± 0.002 mGy/MBq), followed by the kidneys (0.026 ± 0.005 mGy/MBq). The critical organ was the heart wall. The total mean effective dose averaged over subjects was estimated to be 0.0056 ± 0.0004 mSv/MBq for an injection of 11C-BU99008. CONCLUSIONS The biodistribution of 11C-BU99008 has been shown here for the first time in humans. Our dosimetry data showed the total mean effective dose over all subjects was 0.0056 ± 0.0004 mSv/MBq, which would result in a total effective dose of 1.96 mSv for a typical injection of 350 MBq of 11C-BU99008. The effective dose is not appreciably different from those obtained with other 11C tracers.
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Affiliation(s)
- Ashwin V. Venkataraman
- Neuropsychopharmacology Unit, Centre for Psychiatry, Division of Brain Sciences, Imperial College London, 5th Floor Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, W12 0NN UK
- Restorative Neurosciences, Imperial College London, Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, W12 0NN UK
| | - Nicholas Keat
- Imanova Limited, Imperial College London, Hammersmith Hospital, Burlington Danes Building, Du Cane Road, London, W12 0NN UK
| | - James F. Myers
- Neuropsychopharmacology Unit, Centre for Psychiatry, Division of Brain Sciences, Imperial College London, 5th Floor Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, W12 0NN UK
| | - Samuel Turton
- Neuropsychopharmacology Unit, Centre for Psychiatry, Division of Brain Sciences, Imperial College London, 5th Floor Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, W12 0NN UK
| | - Inge Mick
- Neuropsychopharmacology Unit, Centre for Psychiatry, Division of Brain Sciences, Imperial College London, 5th Floor Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, W12 0NN UK
| | - Roger N. Gunn
- Imanova Limited, Imperial College London, Hammersmith Hospital, Burlington Danes Building, Du Cane Road, London, W12 0NN UK
- Restorative Neurosciences, Imperial College London, Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, W12 0NN UK
| | - Eugenii A. Rabiner
- Imanova Limited, Imperial College London, Hammersmith Hospital, Burlington Danes Building, Du Cane Road, London, W12 0NN UK
| | - Jan Passchier
- Imanova Limited, Imperial College London, Hammersmith Hospital, Burlington Danes Building, Du Cane Road, London, W12 0NN UK
| | - Christine A. Parker
- Neuropsychopharmacology Unit, Centre for Psychiatry, Division of Brain Sciences, Imperial College London, 5th Floor Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, W12 0NN UK
- Experimental Medicine Imaging, GlaxoSmithKline Research & Development Limited, Gunnels Wood Road, Stevenage, SG1 2NY UK
| | - Robin J. Tyacke
- Neuropsychopharmacology Unit, Centre for Psychiatry, Division of Brain Sciences, Imperial College London, 5th Floor Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, W12 0NN UK
| | - David J. Nutt
- Neuropsychopharmacology Unit, Centre for Psychiatry, Division of Brain Sciences, Imperial College London, 5th Floor Burlington Danes Building, Hammersmith Hospital campus, 160 Du Cane Road, London, W12 0NN UK
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Nikolic K, Agbaba D. Imidazoline antihypertensive drugs: selective i(1) -imidazoline receptors activation. Cardiovasc Ther 2011; 30:209-16. [PMID: 21884004 DOI: 10.1111/j.1755-5922.2011.00269.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Involvement of imidazoline receptors (IR) in the regulation of vasomotor tone as well as in the mechanism of action of some centrally acting antihypertensives has received tremendous attention. To date, pharmacological studies have allowed the characterization of three main imidazoline receptor classes, the I(1) -imidazoline receptor which is involved in central inhibition of sympathetic tone to lower blood pressure, the I(2) -imidazoline receptor which is an allosteric binding site of monoamine oxidase B (MAO-B), and the I(3) -imidazoline receptor which regulates insulin secretion from pancreatic β-cells. All three imidazoline receptors represent important targets for cardiovascular research. The hypotensive effect of clonidine-like centrally acting antihypertensives was attributed both to α(2) -adrenergic receptors and nonadrenergic I(1) -imidazoline receptors, whereas their sedative action involves activation of only α(2) -adrenergic receptors located in the locus coeruleus. Since more selective I(1) -imidazoline receptors ligands reduced incidence of typical side effects of other centrally acting antihypertensives, there is significant interest in developing new agents with higher selectivity and affinity for I(1) -imidazoline receptors. The selective imidazoline receptors agents are also more effective in regulation of body fat, neuroprotection, inflammation, cell proliferation, epilepsy, depression, stress, cell adhesion, and pain. New agonists and antagonists with high selectivity for imidazoline receptor subtypes have been recently developed. In the present review we provide a brief update to the field of imidazoline research, highlighting some of the chemical diversity and progress made in the theoretical studies of imidazoline receptor ligands.
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Affiliation(s)
- K Nikolic
- Faculty of Pharmacy, Institute of Pharmaceutical Chemistry, University of Belgrade, Vojvode Stepe, Belgrade, Serbia.
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Friedrich VL, Martinelli GP, Prell GD, Holstein GR. Distribution and cellular localization of imidazoleacetic acid-ribotide, an endogenous ligand at imidazol(in)e and adrenergic receptors, in rat brain. J Chem Neuroanat 2007; 33:53-64. [PMID: 17210242 PMCID: PMC1907380 DOI: 10.1016/j.jchemneu.2006.11.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2006] [Revised: 11/21/2006] [Accepted: 11/23/2006] [Indexed: 10/23/2022]
Abstract
Imidazoleacetic acid-ribotide (IAA-RP) is a putative neurotransmitter/modulator recently discovered in mammalian brain. The present study examines the distribution of IAA-RP in the rat CNS using a highly specific antiserum raised in rabbit against IAA-RP with immunostaining of aldehyde-fixed rat CNS. IAA-RP-immunoreactive neurons were present throughout the neuraxis; neuroglia were not labeled. In each region, only a subset of the neuronal pool was immunostained. In the forebrain, ribotide-immunolabeled neurons were common in neocortex, in hippocampal formation, and in subcortical structures including basal ganglia, thalamus and hypothalamus. Labeling was prominent in limbic areas including olfactory bulb, basal forebrain, pyriform cortex and amygdala. In the mid- and hindbrain, immunolabeled neurons were concentrated in specific nuclei and, in some areas, in specific subregions of those nuclei. Structures of the motor system, including cranial nerve motor nuclei, precerebellar nuclei, the substantia nigra, and the red nucleus were clearly labeled. Staining was intense in cells and/or puncta in the rostral and caudal ventrolateral medullary reticular formation, nucleus tractus solitarius and the caudal vestibular nuclear complex. Within neurons, the ribotide was found predominantly in somata and dendrites; some myelinated axons and occasional synaptic terminals were also immunostained. These data indicate that IAA-RP contributes to the neurochemical phenotype of many neuronal populations and further supports our suggestion that, in autonomic structures, IAA-RP may serve as a chemical mediator in complex circuits involved in blood pressure regulation and, more generally, sympathetic drive.
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Affiliation(s)
- Victor L. Friedrich
- Department of Neuroscience, Mount Sinai School of Medicine, One Gustave Levy Place, New York, NY 10029
| | - Giorgio P. Martinelli
- Department of Neurology, Mount Sinai School of Medicine, One Gustave Levy Place, New York, NY 10029
| | - George D. Prell
- Department of Pharmacology, Mount Sinai School of Medicine, One Gustave Levy Place, New York, NY 10029
| | - Gay R. Holstein
- Department of Neuroscience, Mount Sinai School of Medicine, One Gustave Levy Place, New York, NY 10029
- Department of Neurology, Mount Sinai School of Medicine, One Gustave Levy Place, New York, NY 10029
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Parker CA, Anderson NJ, Robinson ESJ, Price R, Tyacke RJ, Husbands SM, Dillon MP, Eglen RM, Hudson AL, Nutt DJ, Crump MP, Crosby J. Harmane and harmalan are bioactive components of classical clonidine-displacing substance. Biochemistry 2005; 43:16385-92. [PMID: 15610033 DOI: 10.1021/bi048584v] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Elucidation of the structure of the endogenous ligand(s) for imidazoline binding sites, clonidine-displacing substance (CDS), has been a major goal for many years. Crude CDS from bovine lung was purified by reverse-phase high-pressure liquid chromatography. Electrospray mass spectrometry (ESMS) and nuclear magnetic resonance ((1)H NMR) analysis revealed the presence of L-tryptophan and 1-carboxy-1-methyltetrahydro-beta-carboline in the active CDS extract. Competition radioligand binding studies, however, failed to show displacement of specific [(3)H]clonidine binding to rat brain membranes for either compound. Further purification of the bovine lung extract allowed the isolation of the beta-carbolines harmane and harmalan as confirmed by ESMS, (1)H NMR, and comparison with synthetic standards. Both compounds exhibited a high (nanomolar) affinity for both type 1 and type 2 imidazoline binding sites, and the synthetic standards were shown to coelute with the active classical CDS extracts. We therefore propose that the beta-carbolines harmane and harmalan represent active components of classical CDS. The identification of these compounds will allow us to establish clear physiological roles for CDS.
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Prell GD, Martinelli GP, Holstein GR, Matulić-Adamić J, Watanabe KA, Chan SLF, Morgan NG, Haxhiu MA, Ernsberger P. Imidazoleacetic acid-ribotide: an endogenous ligand that stimulates imidazol(in)e receptors. Proc Natl Acad Sci U S A 2004; 101:13677-82. [PMID: 15365189 PMCID: PMC518812 DOI: 10.1073/pnas.0404846101] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2004] [Indexed: 11/18/2022] Open
Abstract
We identified the previously unknown structures of ribosylated imidazoleacetic acids in rat, bovine, and human tissues to be imidazole-4-acetic acid-ribotide (IAA-RP) and its metabolite, imidazole-4-acetic acid-riboside. We also found that IAA-RP has physicochemical properties similar to those of an unidentified substance(s) extracted from mammalian tissues that interacts with imidazol(in)e receptors (I-Rs). ["Imidazoline," by consensus (International Union of Pharmacology), includes imidazole, imidazoline, and related compounds. We demonstrate that the imidazole IAA-RP acts at I-Rs, and because few (if any) imidazolines exist in vivo, we have adopted the term "imidazol(in)e-Rs."] The latter regulate multiple functions in the CNS and periphery. We now show that IAA-RP (i) is present in brain and tissue extracts that exhibit I-R activity; (ii) is present in neurons of brainstem areas, including the rostroventrolateral medulla, a region where drugs active at I-Rs are known to modulate blood pressure; (iii) is present within synaptosome-enriched fractions of brain where its release is Ca(2+)-dependent, consistent with transmitter function; (iv) produces I-R-linked effects in vitro (e.g., arachidonic acid and insulin release) that are blocked by relevant antagonists; and (v) produces hypertension when microinjected into the rostroventrolateral medulla. Our data also suggest that IAA-RP may interact with a novel imidazol(in)e-like receptor at this site. We propose that IAA-RP is a neuroregulator acting via I-Rs.
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Affiliation(s)
- George D Prell
- Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, New York, NY 10029, USA.
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Cooper EJ, Hudson AL, Parker CA, Morgan NG. Effects of the beta-carbolines, harmane and pinoline, on insulin secretion from isolated human islets of Langerhans. Eur J Pharmacol 2004; 482:189-96. [PMID: 14660022 DOI: 10.1016/j.ejphar.2003.09.039] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It is well known that certain imidazoline compounds can stimulate insulin secretion and this has been attributed to the activation of imidazoline I(3) binding sites in the pancreatic beta-cell. Recently, it has been proposed that beta-carbolines may be endogenous ligands having activity at imidazoline sites and we have, therefore, studied the effects of beta-carbolines on insulin secretion. The beta-carbolines harmane, norharmane and pinoline increased insulin secretion two- to threefold from isolated human islets of Langerhans. The effects of harmane and pinoline were dose-dependent (EC(50): 5 and 25 microM, respectively) and these agents also blocked the inhibitory effects of the potassium channel agonist, diazoxide, on glucose-induced insulin release. Stimulation of insulin secretion by harmane was glucose-dependent but, unlike the imidazoline I(3) receptor agonist efaroxan, it increased the rate of insulin release beyond that elicited by 20 mM glucose (20 mM glucose alone: 253+/-34% vs. basal; 20 mM glucose plus 100 microM harmane: 327+/-15%; P<0.01). Stimulation of insulin secretion by harmane was attenuated by the imidazoline I(3) receptor antagonist KU14R (2 (2-ethyl 2,3-dihydro-2-benzofuranyl)-2-imidazole) and was reduced when islets were treated with efaroxan for 18 h, prior to the addition of harmane. The results reveal that beta-carbolines can potentiate the rate of insulin secretion from human islets and suggest that these agents may be useful prototypes for the development of novel insulin secretagogues.
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Affiliation(s)
- E Jane Cooper
- Cellular Pharmacology Group, School of Life Sciences, Keele University, Staffs ST5 5BG, UK
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Abstract
It was long thought that the prototypical centrally acting antihypertensive drug clonidine lowers sympathetic tone by activating alpha(2)-adrenoceptors in the brain stem. Supported by the development of two new centrally acting drugs, rilmenidine and moxonidine, the imidazoline hypothesis evolved recently. It assumes the existence of a new group of receptors, the imidazoline receptors, and attributes the sympathoinhibition to activation of I(1) imidazoline receptors in the medulla oblongata. This review analyzes the mechanism of action of clonidine-like drugs, with special attention given to the imidazoline hypothesis. Two conclusions are drawn. The first is that the arguments against the imidazoline hypothesis outweigh the observations that support it and that the sympathoinhibitory effects of clonidine-like drugs are best explained by activation of alpha(2)-adrenoceptors. The second conclusion is that this class of drugs lowers sympathetic tone not only by a primary action in cardiovascular regulatory centres in the medulla oblongata. Peripheral presynaptic inhibition of transmitter release from postganglionic sympathetic neurons contributes to the overall sympathoinhibition.
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Affiliation(s)
- Bela Szabo
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Albert-Ludwigs-Universität, Albertstrasse 25, D-79104 Freiburg i. Br., Germany.
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Raasch W, Schäfer U, Chun J, Dominiak P. Biological significance of agmatine, an endogenous ligand at imidazoline binding sites. Br J Pharmacol 2001; 133:755-80. [PMID: 11454649 PMCID: PMC1572857 DOI: 10.1038/sj.bjp.0704153] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Affiliation(s)
- W Raasch
- Institute of Experimental and Clinical Pharmacology and Toxicology, Medical University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany.
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