1
|
Effects of I 2 -imidazoline receptor (IR) alkylating BU99006 in the mouse brain: Upregulation of nischarin/I 1 -IR and μ-opioid receptor proteins and modulation of associated signalling pathways. Neurochem Int 2017; 108:169-176. [DOI: 10.1016/j.neuint.2017.03.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 03/16/2017] [Accepted: 03/21/2017] [Indexed: 12/12/2022]
|
2
|
Abstract
Since first introduced more than two decades ago, the research in imidazoline I2 receptors has been steadily increasing. This review provides an update on the current status of I2 receptor pharmacology. Imidazoline I2 receptors or I2 binding sites refer to several (at least four) different proteins that bind to [3H]-idazoxan and [3H]-2-BFI with high affinity. The molecular identities of the proteins remain elusive. One of the proteins (45kD) seems to be consistent with the identity of brain creatine kinase. The biological functions of I2 receptors have been primarily unveiled by the studies of selective I2 receptor ligands. Accumulating evidence suggests that I2 receptor ligands are effective analgesics for persistent and chronic painful conditions such as inflammatory, neuropathic and postoperative pain. One selective I2 receptor ligand, CR4056, has been advanced to phase II clinical trial with the therapeutic indication of chronic inflammatory pain (osteoarthritis). The expansion to the treatment of other chronic pain conditions should be expected if CR4056 could eventually be approved as a new drug. I2 receptor ligands also demonstrate robust discriminative stimulus activity and induce a characteristic discriminative cue in animals. Biochemical and preclinical in vivo investigations also suggest that I2 receptor ligands have neuroprotective activity and modulate body temperature. The emerging discrepancies of a range of purported selective I2 receptor ligands suggest different pharmacological effects mediated by discrete I2 receptor components which likely attribute to the I2 receptor-related proteins. It is proposed that the I2 receptors represent an emerging drug target for the treatment of neurological disorders such as pain and stroke, and deserve more research attention to translate preclinical findings to pharmacotherapies.
Collapse
Affiliation(s)
- Jun-Xu Li
- School of Pharmacy, Nantong University, Nantong, Jiangsu Province, China; Department of Pharmacology and Toxicology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, New York, USA.
| |
Collapse
|
3
|
Keller B, García-Sevilla JA. Immunodetection and subcellular distribution of imidazoline receptor proteins with three antibodies in mouse and human brains: Effects of treatments with I1- and I2-imidazoline drugs. J Psychopharmacol 2015; 29:996-1012. [PMID: 26038110 DOI: 10.1177/0269881115586936] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Various imidazoline receptor (IR) proteins have been proposed to mediate the effects of selective I1- and I2-IR drugs. However, the association of these IR-binding proteins with classic I1- and I2-radioligand binding sites remains somewhat controversial. In this study, three IR antibodies (anti-NISCH and anti-nischarin for I1-IRs; and anti-IRBP for I1/I2-IRs) were used to immunodetect, characterize and compare IR protein patterns in brain (mouse and human; total homogenate, subcellular fractionation, grey and white matter) and some cell systems (neurones, astrocytes, human platelets). Various immunoreactive IRs (specific molecular weight bands coincidently detected with the different antibodies) were related to I1-IR (167 kDa, 105/115 kDa and 85 kDa proteins) or I2-IR (66 kDa, 45 kDa and 30 kDa proteins) types. The biochemical characterization of cortical 167 kDa protein, localized in the membrane/cytosol but not in the nucleus, indicated that this I1-IR also forms part of higher order nischarin-related complexes. The contents of I1-IR (167 kDa, 105/115 kDa, and 85 kDa) proteins in mouse brain cortex were upregulated by treatment with I1-drugs (moxonidine, efaroxan) but not with I2-drugs (BU-224, LSL 61122). Conversely, the contents of I2-IR (66 kDa, 45 kDa and 30 kDa) proteins in mouse brain cortex were modulated by treatment with I2-drugs (decreases after BU-224 and LSL 61122, and increases after idazoxan) but not with I1-drugs (with the exception of moxonidine). These findings further indicate that brain immunoreactive IR proteins exist in multiple forms that can be grouped in the already known I1- and I2-IR types, which are expressed both in neurones and astrocytes.
Collapse
Affiliation(s)
- Benjamin Keller
- Laboratori de Neurofarmacologia, IUNICS-IdISPa, Universitat de les Illes Balears, Palma de Mallorca, Spain and Redes Temáticas de Investigación Cooperativa en Salud-Red de Trastornos Adictivos (RETICS-RTA), ISCIII, Madrid, Spain
| | - Jesús A García-Sevilla
- Laboratori de Neurofarmacologia, IUNICS-IdISPa, Universitat de les Illes Balears, Palma de Mallorca, Spain and Redes Temáticas de Investigación Cooperativa en Salud-Red de Trastornos Adictivos (RETICS-RTA), ISCIII, Madrid, Spain
| |
Collapse
|
4
|
Abstract
The imidazoline I2 receptor ligand BU99006 binds to and attenuates effects mediated by I2 receptors in vitro, although its effects in vivo have not been studied previously. This study examined the effects of BU99006 in two behavioral assays in rats: hypothermia and 2-BFI discrimination. BU99006 (3.2-15 mg/kg, intraperitoneally) produced a dose-dependent hypothermic effect (rectal temperature), which was antagonized by the I2 receptor antagonist idazoxan. BU99006 (3.2 or 10 mg/kg administered 10 min or 2 h before the session, respectively) did not significantly alter hypothermia produced by the I2 receptor agonist 2-BFI (10 mg/kg). In rats discriminating 5.6 mg/kg 2-BFI, BU99006 (1.78-17.8 mg/kg, intraperitoneally) produced 40 and 82% responding on the 2-BFI-associated lever when it was administered immediately or 2 h before the test sessions, respectively. BU99006 enhanced the discriminative stimulus and rate-suppressing effects of 2-BFI. Collectively, these data suggest that BU99006 is an imidazoline I2 receptor agonist with no evidence of I2 receptor antagonism in rats.
Collapse
|
5
|
Tyacke RJ, Fisher A, Robinson ESJ, Grundt P, Turner EM, Husbands SM, Hudson AL, Parker CA, Nutt DJ. Evaluation and initial in vitro and ex vivo characterization of the potential positron emission tomography ligand, BU99008 (2-(4,5-dihydro-1H-imidazol-2-yl)-1- methyl-1H-indole), for the imidazoline₂ binding site. Synapse 2012; 66:542-51. [PMID: 22290740 DOI: 10.1002/syn.21541] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Revised: 01/12/2012] [Accepted: 01/23/2012] [Indexed: 11/06/2022]
Abstract
The density of the Imidazoline₂ binding site (I₂BS) has been shown to change in psychiatric conditions such as depression and addiction, along with neurodegenerative disorders such as Alzheimer's disease and Huntington's chorea. The presence of I₂BS on glial cells and the possibility that they may in some way regulate glial fibrillary acidic protein has led to increased interest into the role of I₂BS and I₂BS ligands in conditions characterized by marked gliosis. In addition, it has been suggested that I₂BS may be a marker for human glioblastomas. Therefore, the development of a positron emission tomography (PET) radioligand for the I₂BS would be of major benefit in our understanding of these conditions. We now report the successful synthesis and initial pharmacological evaluation of potential PET radioligands for the I₂BS as well as the tritiation and characterization of the most favorable of the series, BU99008 (6), both in vitro and ex vivo in rat. The series as a whole demonstrated excellent affinity and selectivity for the I₂BS, with BU99008 (6) selected as the lead candidate to be taken forward for in vivo assessment. BU99008 (6) showed very good affinity for the I₂BS (K(i) of 1.4 nM; K(d) = 1.3 nM), good selectivity compared with the α₂ -adrenoceptor (909-fold). In addition, following peripheral administration, [³H]BU99008 demonstrated a heterogenous uptake into the rat brain consistent with the known distribution of the I₂BS in vivo. This, and the amenability of BU99008 (6) to radiolabeling with a positron-emitting radioisotope, indicates its potential as a PET radioligand for imaging the I₂BS in vivo.
Collapse
Affiliation(s)
- Robin J Tyacke
- Neuropsychopharmacology Unit, Centre for Pharmacology and Therapeutics, Hammersmith Hospital Campus, Imperial College London, London W12 0NN, United Kingdom.
| | | | | | | | | | | | | | | | | |
Collapse
|
6
|
Edwards LP, Brown-Bryan TA, McLean L, Ernsberger P. Pharmacological Properties of the Central Antihypertensive Agent, Moxonidine. Cardiovasc Ther 2011; 30:199-208. [DOI: 10.1111/j.1755-5922.2011.00268.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
|
7
|
Kimura A, Tyacke RJ, Robinson JJ, Husbands SM, Minchin MC, Nutt DJ, Hudson AL. Identification of an imidazoline binding protein: creatine kinase and an imidazoline-2 binding site. Brain Res 2009; 1279:21-8. [PMID: 19410564 PMCID: PMC2722693 DOI: 10.1016/j.brainres.2009.04.044] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2009] [Revised: 03/28/2009] [Accepted: 04/22/2009] [Indexed: 12/11/2022]
Abstract
Drugs that bind to imidazoline binding proteins have major physiological actions. To date, three subtypes of such proteins, I(1), I(2) and I(3), have been proposed, although characterisations of these binding proteins are lacking. I(2) binding sites are found throughout the brain, particularly dense in the arcuate nucleus of the hypothalamus. Selective I(2) ligands demonstrate antidepressant-like activity and the identity of the proteins that respond to such ligands remained unknown until now. Here we report the isolation of a approximately 45 kDa imidazoline binding protein from rabbit and rat brain using a high affinity ligand for the I(2) subtype, 2-BFI, to generate an affinity column. Following protein sequencing of the isolated approximately 45 kDa imidazoline binding protein, we identified it to be brain creatine kinase (B-CK). B-CK shows high binding capacity to selective I(2) ligands; [(3)H]-2-BFI (5 nM) specifically bound to B-CK (2330+/-815 fmol mg protein(-1)). We predicted an I(2) binding pocket near the active site of B-CK using molecular modelling. Furthermore, B-CK activity was inhibited by a selective I(2) irreversible ligand, where 20 microM BU99006 reduced the enzyme activity by 16%, confirming the interaction between B-CK and the I(2) ligand. In summary, we have identified B-CK to be the approximately 45 kDa imidazoline binding protein and we have demonstrated the existence of an I(2) binding site within this enzyme. The importance of B-CK in regulating neuronal activity and neurotransmitter release may well explain the various actions of I(2) ligands in brain and the alterations in densities of I(2) binding sites in psychiatric disorders.
Collapse
Key Words
- 2-bfi, 2-(2-benzofuranyl)2-imidazoline
- bu224, 2-(4,5-dihydroimidaz-2-yl)quinoline
- bu99006, 5-isothiocyanoato-2-benzofuranyl-2-imidazoline
- b-ck, brain creatine kinase
- ck, creatine kinase
- gold, genetic optimisation for ligand docking
- gr, glucose-responsive
- i2, imidazoline-2 subtype
- katp channel, atp sensitive potassium channel
- mao, monoamine oxidase
- moe, molecular operating environment
- imidazoline binding protein
- creatine kinase
- 2-bfi
- harmane and psychiatric disorders
Collapse
Affiliation(s)
- Atsuko Kimura
- Psychopharmacology Unit, University of Bristol, BS1 3NY, UK
| | | | - James J. Robinson
- Department of Pharmacy and Pharmacology, University of Bath, BA2 7AY, UK
| | | | | | - David J. Nutt
- Psychopharmacology Unit, University of Bristol, BS1 3NY, UK
| | - Alan L. Hudson
- Department of Pharmacology, 9-70 Medical Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| |
Collapse
|
8
|
Paterson LM, Tyacke RJ, Robinson ESJ, Nutt DJ, Hudson AL. In vitro and in vivo effect of BU99006 (5-isothiocyanato-2-benzofuranyl-2-imidazoline) on I2 binding in relation to MAO: Evidence for two distinct I2 binding sites. Neuropharmacology 2007; 52:395-404. [PMID: 17045310 DOI: 10.1016/j.neuropharm.2006.08.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Revised: 08/02/2006] [Accepted: 08/03/2006] [Indexed: 10/24/2022]
Abstract
BU99006 is an irreversible I(2) ligand which selectively inactivates I(2) binding sites, making it an ideal tool with which to study I(2) site mechanism. We sought to determine the effects of BU99006 on I(2) binding in relation to monoamine oxidase (MAO), and the time course of these effects. In vitro, rat brain membranes that were pre-treated with 10 microM BU99006 showed no change in MAO activity, despite suffering a significant reduction in [(3)H]2BFI binding (52.5+/-19.6 to 8.5+/-3.8 fmol mg(-1), 84%). Furthermore, reversible I(2) ligands 2BFI and BU224 were able to inhibit MAO, whether treated with BU99006 or not. In vivo, a 5 mg kg(-1) i.v. dose of BU99006 in rats rapidly reduced [(3)H]2BFI binding with similar magnitude (85%, maximal reduction after 20 min), without effect on either MAO activity or the specific binding of selective MAO-A and MAO-B radioligands. Moreover, following this irreversible treatment, recovery of central [(3)H]2BFI binding occurred with a rapid half-life of 4.3 h in rat brain (2.0 h in mouse), which is not consistent with a site on MAO. These data indicate that the high affinity site which is occupied by [(3)H]2BFI and irreversibly binds BU99006, is not the same as that which causes inhibition of MAO, and may point to the existence of another I(2) binding site.
Collapse
Affiliation(s)
- Louise M Paterson
- Psychopharmacology Unit, Dorothy Hodgkin Building, University of Bristol, Whitson Street, Bristol, BS1 3NY, UK
| | | | | | | | | |
Collapse
|
9
|
Dardonville C, Rozas I. Imidazoline binding sites and their ligands: an overview of the different chemical structures. Med Res Rev 2004; 24:639-61. [PMID: 15224384 DOI: 10.1002/med.20007] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Since Bousquet et al. discovered the imidazoline binding sites (IBS) two decades ago, when they realized that the antihypertensive drug clonidine interacts not only with the alpha2-adrenenoceptors (alpha2-AR) but also with a distinct imidazoline preferring binding site, these receptors have been paid a great deal of attention. At least two subtypes, I1 and I2, have been characterised based on their binding affinity for different radioligands, but their structures still remain unknown. The pharmacological profile of these IBSs has been the objective of several and very thorough reviews. However, a medicinal chemistry overview of the different IBS ligands prepared to date has never been attempted. In this study, we attempt to compile all the different chemical structures reported to date as IBS ligands and classify them in function of their chemical structure and binding affinity for the different IBS subtypes. Thus, we comment on the different endogenous IBS ligands known as well as the drugs described to interact with the I1-IBS which have found application as antihypertensive drugs. Then, we review those compounds described in the literature to interact with the I2-IBS, classifying them by their chemical families (imidazolines, guanidines, 2-aminoimidazolines, beta-carbolines). Finally, some conclusions are drawn.
Collapse
|