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Durham-Lee JC, Mokkapati VUL, Johnson KM, Nesic O. Amiloride improves locomotor recovery after spinal cord injury. J Neurotrauma 2011; 28:1319-26. [PMID: 21534729 PMCID: PMC3136742 DOI: 10.1089/neu.2011.1921] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Amiloride is a drug approved by the United States Food and Drug Administration, which has shown neuroprotective effects in different neuropathological conditions, including brain injury or brain ischemia, but has not been tested in spinal cord injury (SCI). We tested amiloride's therapeutic potential in a clinically relevant rat model of contusion SCI inflicted at the thoracic segment T10. Rats receiving daily administration of amiloride from 24 h to 35 days after SCI exhibited a significant improvement in hindlimb locomotor ability at 21, 28, and 35 days after injury, when compared to vehicle-treated SCI rats. Rats receiving amiloride treatment also exhibited a significant increase in myelin oligodendrocyte glycoprotein (MOG) levels 35 days after SCI at the site of injury (T10) when compared to vehicle-treated controls, which indicated a partial reverse in the decrease of MOG observed with injury. Our data indicate that higher levels of MOG correlate with improved locomotor recovery after SCI, and that this may explain the beneficial effects of amiloride after SCI. Given that amiloride treatment after SCI caused a significant preservation of myelin levels, and improved locomotor recovery, it should be considered as a possible therapeutic intervention after SCI.
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Affiliation(s)
- Julieann C. Durham-Lee
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
| | - Venkata Usha L. Mokkapati
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
| | - Kathia M. Johnson
- Department of Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas
| | - Olivera Nesic
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas
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Gao ZG, Kim SK, Ijzerman AP, Jacobson KA. Allosteric modulation of the adenosine family of receptors. Mini Rev Med Chem 2005; 5:545-53. [PMID: 15974932 PMCID: PMC3431557 DOI: 10.2174/1389557054023242] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Allosteric modulators for adenosine receptors (ARs) are of an increasing interest and may have potential therapeutic advantage over orthosteric ligands. Benzoylthiophene derivatives (including PD 81,723), 2-aminothiazolium salts, and related allosteric modulators of the A(1) AR have been studied. The benzoylthiophene derivatives were demonstrated to be selective enhancers for the A(1) AR, with little or no effect on other subtypes of ARs. Allosteric modulation of the A(2A) AR has also been reported. A(3) allosteric enhancers may be predicted to be useful against ischemic conditions. We have recently characterized two classes of A(3) AR allosteric modulators: 3-(2-pyridinyl)isoquinolines (e.g. VUF5455) and 1H-imidazo-[4,5-c]quinolin-4-amines (e.g. DU124183), which selectively decreased the agonist dissociation rate at the human A(3)AR but not at A(1) and A(2A) ARs. DU124183 left-shifted the agonist conc.-response curve for inhibition of forskolin-stimulated cAMP accumulation in intact cells expressing the human A(3)AR with up to 30% potentiation of the maximal efficacy. The increased potency of A(3) agonists was evident only in the presence of an A(3) antagonist, since VUF5455 and DU124183 also antagonized, i.e. displaced binding at the orthosteric site, with K(i) values of 1.68 and 0.82 microM, respectively. A(3)AR mutagenesis studies implicated F182(5.43) and N274(7.45) in the action of the enhancers and was interpreted using a rhodopsin-based A(3)AR molecular model, suggesting multiple binding modes. Amiloride analogues, SCH-202676 (N-(2,3-diphenyl-1,2,4-thiadiazol-5(2H)-ylidene)methanamine), and sodium ions were demonstrated to be common allosteric modulators for at least three subtypes (A(1), A(2A), and A(3)) of ARs.
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MESH Headings
- Animals
- Humans
- Models, Molecular
- Mutagenesis
- Receptor, Adenosine A1/chemistry
- Receptor, Adenosine A1/drug effects
- Receptor, Adenosine A2A/chemistry
- Receptor, Adenosine A2A/drug effects
- Receptor, Adenosine A2B/chemistry
- Receptor, Adenosine A2B/drug effects
- Receptors, Purinergic P1/chemistry
- Receptors, Purinergic P1/drug effects
- Receptors, Purinergic P1/genetics
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Affiliation(s)
- Zhan-Guo Gao
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, NIDDK, National Inst. of Health, Bethesda, Maryland 20892-0810, USA.
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Gao ZG, Melman N, Erdmann A, Kim SG, Müller CE, IJzerman AP, Jacobson KA. Differential allosteric modulation by amiloride analogues of agonist and antagonist binding at A(1) and A(3) adenosine receptors. Biochem Pharmacol 2003; 65:525-34. [PMID: 12566079 PMCID: PMC8607904 DOI: 10.1016/s0006-2952(02)01556-3] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The diuretic drug amiloride and its analogues were found previously to be allosteric modulators of antagonist binding to A(2A) adenosine receptors. In this study, the possibility of the allosteric modulation by amiloride analogues of antagonist binding at A(1) and A(3) receptors, as well as agonist binding at A(1), A(2A), and A(3) receptors, was explored. Amiloride analogues increased the dissociation rates of two antagonist radioligands, [3H]8-cyclopentyl-1,3-dipropylxanthine ([3H]DPCPX) and [3H]8-ethyl-4-methyl-2-phenyl-(8R)-4,5,7,8-tetrahydro-1H-imidazo[2,1-i]purin-5-one ([3H]PSB-11), from A(1) and A(3) receptors, respectively. Amiloride and 5-(N,N-dimethyl)amiloride (DMA) were more potent at A(1) receptors than at A(3) receptors, while 5-(N,N-hexamethylene)amiloride (HMA) was more potent at A(3) receptors. Thus, amiloride analogues are allosteric inhibitors of antagonist binding at A(1), A(2A), and A(3) adenosine receptor subtypes. In contrast to their effects on antagonist-occupied receptors, amiloride analogues did not affect the dissociation rates of the A(1) agonist [3H]N(6)-[(R)-phenylisopropyl]adenosine ([3H]R-PIA) from A(1) receptors or the A(2A) agonist [3H]2-[p-(2-carboxyethyl)phenyl-ethylamino]-5'-N-ethylcarboxamidoadenosine ([3H]CGS21680) from A(2A) receptors. The dissociation rate of the A(3) agonist radioligand [125I]N(6)-(4-amino-3-iodobenzyl)adenosine-5'-N-methyluronamide ([125I]I-AB-MECA) from A(3) receptors was decreased significantly by amiloride analogues. The binding modes of amiloride analogues at agonist-occupied and antagonist-occupied receptors differed markedly, which was demonstrated in all three subtypes of adenosine receptors tested in this study. The effects of the amiloride analogues on the action of the A(3) receptor agonist were explored further using a cyclic AMP functional assay in intact CHO cells expressing the human A(3) receptor. Both binding and functional assays support the allosteric interactions of amiloride analogues with A(3) receptors.
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Affiliation(s)
- Zhan-Guo Gao
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bldg. 8A, Rm. B1A-19, Bethesda, MD 20892-0810, USA
| | - Neli Melman
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bldg. 8A, Rm. B1A-19, Bethesda, MD 20892-0810, USA
| | - Andreas Erdmann
- Experimental Transplantation and Immunology Branch, NCI, National Institutes of Health, Bethesda, MD 20892, USA
| | - Seong Gon Kim
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bldg. 8A, Rm. B1A-19, Bethesda, MD 20892-0810, USA
| | - Christa E. Müller
- Pharmaceutical Institute, University of Bonn, Kreuzbergweg 26, D-53115 Bonn, Germany
| | - Adriaan P. IJzerman
- Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Leiden University, P.O. Box 9502, 2300 RA, Leiden, The Netherlands
| | - Kenneth A. Jacobson
- Molecular Recognition Section, Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bldg. 8A, Rm. B1A-19, Bethesda, MD 20892-0810, USA
- Corresponding author. Tel.: +1-301-496-9024; fax: +1-301-480-8422. (K.A. Jacobson)
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Gao ZG, Ijzerman AP. Allosteric modulation of A(2A) adenosine receptors by amiloride analogues and sodium ions. Biochem Pharmacol 2000; 60:669-76. [PMID: 10927025 DOI: 10.1016/s0006-2952(00)00360-9] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Allosteric regulation of rat A(2A) adenosine receptors by amiloride, amiloride analogues, and sodium ions was studied by investigating their ability to influence the dissociation of [(3)H]4-2-[7-amino-2-(2-furyl)-1,2,4-triazolo[1,5-a][1,3, 5]triazin-5-yl-amino]ethylphenol ([(3)H]ZM241385) from receptors in rat striatal membranes. Both amiloride and its analogues accelerated the dissociation, the analogues being more potent than amiloride itself. In contrast, sodium ions decreased the rate of [(3)H]ZM241385 dissociation in a concentration-dependent manner, and this rate was not influenced by guanosine triphosphate, N-ethylmaleimide, suramin, or the selective A(2A) adenosine receptor antagonist, 5-amino-2-(2-furyl)-7(2-phenylethyl)pyrazolo[4,3-e]-1,2, 4-triazolo[1,5-c]pyrimidine (SCH58261). The effect of competition between the amiloride analogue 5-(N,N-hexamethylene)amiloride (HMA) and sodium ions on [(3)H]ZM241385 dissociation was also explored. The addition of sodium ions resulted in a concentration-dependent rightward shift of the HMA response curve. The slopes of the HMA concentration-response curves in the presence and absence of sodium ions were not significantly different, which suggests that sodium ions and amiloride analogues act at a common allosteric site on the A(2A) adenosine receptor. There was a lack of correlation between the displacement of ligand binding and the allosteric potencies of the amiloride analogues.
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Affiliation(s)
- Z G Gao
- Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Leiden University, P.O. Box 9502, 2300 RA, Leiden, The Netherlands
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Abstract
Interactions of amiloride with GABAB receptors have been examined using spontaneously discharging rat neocortical slices. These discharges were suppressed by the GABAB receptor agonist baclofen (10 microM), and were prevented by amiloride and its analogs 5-(N,N-dimethyl)-amiloride, 5-(N-methyl-N-isobutyl)-amiloride and benzamil, but not by triamterene (100-500 microM). Each of these also increased the spontaneous discharge rate and reduced the discharge amplitude. The action of amiloride and its analogs in preventing the action of baclofen, may involve allosteric modification of the receptor binding sites via guanine nucleotide-binding proteins, or an indirect effect through antagonism of co-activated adenosine A1 receptors.
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Affiliation(s)
- J Ong
- Department of Anaesthesia and Intensive Care, University of Adelaide, Australia
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