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Romero A, Sanchez A, Jones JD, Ledesma K, El-Halawany MS, Hamouda AK, Bill BR. Optimization of Zebrafish Larvae 6-OHDA Exposure for Neurotoxin Induced Dopaminergic Marker Reduction. Zebrafish 2024. [PMID: 38608227 DOI: 10.1089/zeb.2023.0098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/14/2024] Open
Abstract
Parkinson's disease (PD) is a neurodegenerative disorder that is clinically assessed by motor symptoms associated with the loss of midbrain dopaminergic neurons affecting the quality of life for over 8.5 million people worldwide. The neurotoxin 6-hydroxydopamine (6-OHDA) has been used to chemically induce a PD-like state in zebrafish larvae by several laboratories; however, highly variable concentration, methodology, and reagents have resulted in conflicting results suggesting a need to investigate these issues of reproducibility. We propose a protocol that addresses the differences in methodology and induces changes in 6 days postfertilization (dpf) larvae utilizing a 24-h exposure at 3 dpf with 30 μM 6-OHDA. Despite ∼50% lethality, no morphological or development differences in surviving fish are observed. Definition of our model is defined by downregulation of the expression of th1 by reverse transcriptase-quantitative polymerase chain reaction, a marker for dopaminergic neurons and a reduction in movement. Additionally, we observed a downregulation of pink1 and an upregulation of sod1 and sod2, indicators of mitochondrial dysfunction and response to reactive oxygen species, respectively.
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Affiliation(s)
- Adrian Romero
- The University of Texas at Tyler College of Arts and Sciences Department of Biology, Tyler, Texas, USA
- The University of Texas Tyler Ben and Maytee Fisch College of Pharmacy, Tyler, Texas, USA
| | - Armando Sanchez
- The University of Texas at Tyler College of Arts and Sciences Department of Biology, Tyler, Texas, USA
| | - Jocelyn D Jones
- The University of Texas at Tyler College of Arts and Sciences Department of Biology, Tyler, Texas, USA
| | - Kristel Ledesma
- The University of Texas at Tyler College of Arts and Sciences Department of Biology, Tyler, Texas, USA
| | - Medhat S El-Halawany
- The University of Texas Tyler Ben and Maytee Fisch College of Pharmacy, Tyler, Texas, USA
| | - Ayman K Hamouda
- The University of Texas Tyler Ben and Maytee Fisch College of Pharmacy, Tyler, Texas, USA
| | - Brent R Bill
- The University of Texas at Tyler College of Arts and Sciences Department of Biology, Tyler, Texas, USA
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2
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Alkhlaif Y, El-Halawany M, Toma W, Park A, Hamouda AK, Imad Damaj M. L-theanine attenuates nicotine reward and withdrawal signs in mice. Neurosci Lett 2023; 807:137279. [PMID: 37105354 DOI: 10.1016/j.neulet.2023.137279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Revised: 04/22/2023] [Accepted: 04/24/2023] [Indexed: 04/29/2023]
Abstract
BACKGROUND L-theanine, 2-amino-4-(ethylcarbamoyl) butyric acid, an amino acid detected in green tea leaves, is used as a dietary supplement to attenuate stress and enhance mood and cognition. Furthermore, L-theanine induces anxiolytic effects in humans. Recently, L-theanine was reported to reduce morphine physical dependence in primates, suggesting the potential usefulness of L-theanine for drug dependence intervention. OBJECTIVE The aim of this study is to determine whether L-theanine attenuates nicotine-withdrawal (somatic and affective signs) and nicotine reward in mice. We also investigated the effects of L-theanine on nicotinic receptors binding and function. METHODS ICR male mice rendered dependent to nicotine through implanted subcutaneous osmotic minipumps for 14 days undertook precipitated nicotine withdrawal by mecamylamine on day 15. Anxiety-like behaviors using LDB, somatic signs observation and hot plate latency were assessed consecutively after treatment with L-theanine. Furthermore, we examined the effect of L-theanine on acute nicotine responses and nicotine conditioned reward in mice and on expressed nicotinic receptors in oocytes. KEY FINDINGS L-theanine reduced in a dose-dependent manner anxiety-like behavior, hyperalgesia and somatic signs during nicotine withdrawal. Also, L-theanine decreased the nicotine CPP, but it did not affect the acute responses of nicotine. Finally, L-theanine did not alter the binding or the function of expressed α4β2 and α7 nAChRs. CONCLUSION Our results support the potential of L-theanine as a promising candidate for treating nicotine dependence.
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Affiliation(s)
- Yasmin Alkhlaif
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, United States
| | - Medhat El-Halawany
- Department of Pharmaceutical Sciences and Health Outcomes, College of Pharmacy, The University of Texas at Tyler, Tyler, TX, United States
| | - Wisam Toma
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, United States
| | - Abigail Park
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, United States
| | - Ayman K Hamouda
- Department of Pharmaceutical Sciences and Health Outcomes, College of Pharmacy, The University of Texas at Tyler, Tyler, TX, United States
| | - M Imad Damaj
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, United States.
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3
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Gaona J, Mohiuddin M, Hamouda AK. Examining the effect of a substituted carbamate positive allosteric modulator on the (α4)3(β2)2 and (α4)2(β2)3 nicotinic acetylcholine receptors. Biophys J 2023; 122:395a. [PMID: 36784010 DOI: 10.1016/j.bpj.2022.11.2157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2023] Open
Affiliation(s)
- Josue Gaona
- The University of Texas at Tyler, Tyler, TX, USA
| | | | - Ayman K Hamouda
- Ben and Maytee Fisch College of Pharmacy, The University of Texas at Tyler, Tyler, TX, USA
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Appiani R, Pallavicini M, Hamouda AK, Bolchi C. Pyrrolidinyl benzofurans and benzodioxanes: Selective α4β2 nicotinic acetylcholine receptor ligands with different activity profiles at the two receptor stoichiometries. Bioorg Med Chem Lett 2022; 65:128701. [PMID: 35346843 DOI: 10.1016/j.bmcl.2022.128701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2022] [Revised: 03/17/2022] [Accepted: 03/23/2022] [Indexed: 11/28/2022]
Abstract
A series of racemic benzofurans bearing N-methyl-2-pyrrolidinyl residue at C(2) or C(3) has been synthesized and tested for affinity at the α4β2 and α3β4 nicotine acetylcholine receptors (nAChRs). As previously reported for the benzodioxane based analogues, hydroxylation at proper position of benzene ring results in high α4β2 nAChR affinity and α4β2 vs. α3β4 nAChR selectivity. 7-Hydroxy-N-methyl-2-pyrrolidinyl-1,4-benzodioxane (2) and its 7- and 5-amino benzodioxane analogues 3 and 4, which are all α4β2 nAChR partial agonists, and 2-(N-methyl-2-pyrrolidinyl)-6-hydroxybenzofuran (12) were selected for functional characterization at the two α4β2 stoichiometries, the high sensitivity (α4)2(β2)3 and the low sensitivity (α4)3(β2)2. The benzene pattern substitution, which had previously been found to control α4β2 partial agonist activity and α4β2 vs. α3β4 selectivity, proved to be also involved in stoichiometry-selectivity. The 7-hydroxybenzodioxane derivative 2 selectively activates (α4)2(β2)3 nAChR, which cannot be activated by its 5-amino analogue 4. A marginal structural modification, not altering the base pyrrolidinyl benzodioxane scaffold, resulted in opposite activity profiles at the two α4β2 nAChR isoforms providing an interesting novel case study.
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Affiliation(s)
- Rebecca Appiani
- Dipartimento di Scienze Farmaceutiche, Università degli Studi di Milano, via Mangiagalli 25, I-20133 Milano, Italy.
| | - Marco Pallavicini
- Dipartimento di Scienze Farmaceutiche, Università degli Studi di Milano, via Mangiagalli 25, I-20133 Milano, Italy.
| | - Ayman K Hamouda
- Department of Pharmaceutical Sciences and Health Outcomes, Fisch College of Pharmacy, The University of Texas at Tyler, Tyler, TX, USA.
| | - Cristiano Bolchi
- Dipartimento di Scienze Farmaceutiche, Università degli Studi di Milano, via Mangiagalli 25, I-20133 Milano, Italy.
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Romero A, Hunt JC, Bill BR, Hamouda AK. Optimizing 6‐Hydroxydopamine Concentrations for induction of a Parkinson’s Disease Like Behavior in Zebrafish. FASEB J 2022. [DOI: 10.1096/fasebj.2022.36.s1.r5750] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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6
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Deba F, Munoz K, Peredia E, Akk G, Hamouda AK. Assessing potentiation of the (α4)3(β2)2 nicotinic acetylcholine receptor by the allosteric agonist CMPI. J Biol Chem 2021; 298:101455. [PMID: 34861241 PMCID: PMC8715118 DOI: 10.1016/j.jbc.2021.101455] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 11/20/2021] [Accepted: 11/29/2021] [Indexed: 12/11/2022] Open
Abstract
The extracellular domain of the nicotinic acetylcholine receptor isoforms formed by three α4 and two β2 subunits ((α4)3(β2)2 nAChR) harbors two high-affinity “canonical” acetylcholine (ACh)-binding sites located in the two α4:β2 intersubunit interfaces and a low-affinity “noncanonical” ACh-binding site located in the α4:α4 intersubunit interface. In this study, we used ACh, cytisine, and nicotine (which bind at both the α4:α4 and α4:β2 interfaces), TC-2559 (which binds at the α4:β2 but not at the α4:α4 interface), and 3-(2-chlorophenyl)-5-(5-methyl-1-(piperidin-4-yl)-1H-pyrrazol-4-yl)isoxazole (CMPI, which binds at the α4:α4 but not at the α4:β2 interface), to investigate the binding and gating properties of CMPI at the α4:α4 interface. We recorded whole-cell currents from Xenopus laevis oocytes expressing (α4)3(β2)2 nAChR in response to applications of these ligands, alone or in combination. The electrophysiological data were analyzed in the framework of a modified Monod–Wyman–Changeux allosteric activation model. We show that CMPI is a high-affinity, high-efficacy agonist at the α4:α4 binding site and that its weak direct activating effect is accounted for by its inability to productively interact with the α4:β2 sites. The data presented here enhance our understanding of the functional contributions of ligand binding at the α4:α4 subunit interface to (α4)3(β2)2 nAChR-channel gating. These findings support the potential use of α4:α4 specific ligands to increase the efficacy of the neurotransmitter ACh in conditions associated with decline in nAChRs activity in the brain.
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Affiliation(s)
- Farah Deba
- Department of Pharmaceutical Sciences, The University of Texas at Tyler, Tyler, Texas, USA
| | - Kemburli Munoz
- Department of Pharmaceutical Sciences, Texas A&M HSC, Kingsville, Texas, USA
| | - Eloisa Peredia
- Department of Pharmaceutical Sciences, The University of Texas at Tyler, Tyler, Texas, USA
| | - Gustav Akk
- Department of Anesthesiology, Washington University in St. Louis, St. Louis, Missouri, USA; The Taylor Family Institute for Innovative Psychiatric Research, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Ayman K Hamouda
- Department of Pharmaceutical Sciences, The University of Texas at Tyler, Tyler, Texas, USA.
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7
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Pinheiro NM, Banzato R, Tibério I, Prado MAM, Prado VF, Hamouda AK, Prado CM. Acute Lung Injury in Cholinergic-Deficient Mice Supports Anti-Inflammatory Role of α7 Nicotinic Acetylcholine Receptor. Int J Mol Sci 2021; 22:ijms22147552. [PMID: 34299169 PMCID: PMC8303767 DOI: 10.3390/ijms22147552] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Revised: 07/05/2021] [Accepted: 07/07/2021] [Indexed: 11/16/2022] Open
Abstract
(1) Background: The lung cholinergic pathway is important for controlling pulmonary inflammation in acute lung injury, a condition that is characterized by a sudden onset and intense inflammation. This study investigated changes in the expression levels of nicotinic and muscarinic acetylcholine receptors (nAChR and mAChR) in the lung during acute lung injury. (2) Methods: acute lung injury (ALI) was induced in wild-type and cholinergic-deficient (VAChT-KDHOM) mice using intratracheal lipopolysaccharide (LPS) instillation with or without concurrent treatment with nicotinic ligands. Bronchoalveolar lavage fluid was collected to evaluate markers of inflammation, and then the lung was removed and processed for isolation of membrane fraction and determination of acetylcholine receptors level using radioligand binding assays. (3) Results: LPS-induced increase in lung inflammatory markers (e.g., neutrophils and IL-1β) was significantly higher in VAChT-KDHOM than wild-type mice. In contrast, LPS treatment resulted in a significant increase in lung’s α7 nicotinic receptor level in wild-type, but not in VAChT-KDHOM mice. However, treatment with PNU 282987, a selective α7 nicotinic receptor agonist, restored VAChT-KDHOM mice’s ability to increase α7 nicotinic receptor levels in response to LPS-induced acute lung injury and reduced lung inflammation. LPS also increased muscarinic receptors level in VAChT-KDHOM mice, and PNU 282987 treatment reduced this response. (4) Conclusions: Our data indicate that the anti-inflammatory effects of the lung cholinergic system involve an increase in the level of α7 nicotinic receptors. Pharmacological agents that increase the expression or the function of lung α7 nicotinic receptors have potential clinical uses for treating acute lung injury.
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Affiliation(s)
- Nathalia M. Pinheiro
- Department of Bioscience, Federal University of Sao Paulo, Santos 11015-020, SP, Brazil;
- College of Pharmacy, University of Texas at Tyler, Tyler, TX 75799, USA;
| | - Rosana Banzato
- Department of Medicine, School of Medicine, University of Sao Paulo, Sao Paulo 01246-903, SP, Brazil; (R.B.); (I.T.); (V.F.P.)
| | - Iolanda Tibério
- Department of Medicine, School of Medicine, University of Sao Paulo, Sao Paulo 01246-903, SP, Brazil; (R.B.); (I.T.); (V.F.P.)
| | - Marco A. M. Prado
- Molecular Medicine Group, Robarts Research Institute, London, ON N6A 5B7, Canada;
- Department of Physiology & Pharmacology, University of Western Ontario, London, ON N6A 5B7, Canada
- Department of Anatomy & Cell Biology, University of Western Ontario, London, ON N6A 5B7, Canada
| | - Vânia F. Prado
- Department of Medicine, School of Medicine, University of Sao Paulo, Sao Paulo 01246-903, SP, Brazil; (R.B.); (I.T.); (V.F.P.)
- Molecular Medicine Group, Robarts Research Institute, London, ON N6A 5B7, Canada;
| | - Ayman K. Hamouda
- College of Pharmacy, University of Texas at Tyler, Tyler, TX 75799, USA;
| | - Carla M. Prado
- Department of Bioscience, Federal University of Sao Paulo, Santos 11015-020, SP, Brazil;
- Correspondence: ; Tel.: +55-13-3229-0118
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8
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Hamouda AK, Bautista MR, Akinola LS, Alkhlaif Y, Jackson A, Carper M, Toma WB, Garai S, Chen YC, Thakur GA, Fowler CD, Damaj MI. Potentiation of (α4)2(β2)3, but not (α4)3(β2)2, nicotinic acetylcholine receptors reduces nicotine self-administration and withdrawal symptoms. Neuropharmacology 2021; 190:108568. [PMID: 33878302 DOI: 10.1016/j.neuropharm.2021.108568] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 02/28/2021] [Accepted: 04/10/2021] [Indexed: 11/26/2022]
Abstract
The low sensitivity (α4)3(β2)2 (LS) and high sensitivity (α4)2(β2)3 (HS) nAChR isoforms may contribute to a variety of brain functions, pathophysiological processes, and pharmacological effects associated with nicotine use. In this study, we examined the contributions of the LS and HS α4β2 nAChR isoforms in nicotine self-administration, withdrawal symptoms, antinociceptive and hypothermic effects. We utilized two nAChR positive allosteric modulators (PAMs): desformylflustrabromine (dFBr), a PAM of both the LS and HS α4β2 nAChRs, and CMPI, a PAM selective for the LS nAChR. We found that dFBr, but not CMPI, decreased intravenous nicotine self-administration in male mice in a dose-dependent manner. Unlike dFBr, which fully reverses somatic and affective symptoms of nicotine withdrawal, CMPI at doses up to 15 mg/kg in male mice only partially reduced nicotine withdrawal-induced somatic signs, anxiety-like behavior and sucrose preference, but had no effects on nicotine withdrawal-induced hyperalgesia. These results indicate that potentiation of HS α4β2 nAChRs is necessary to modulate nicotine's reinforcing properties that underlie nicotine intake and to reverse nicotine withdrawal symptoms that influence nicotine abstinence. In contrast, both dFBr and CMPI enhanced nicotine's hypothermic effect and reduced nicotine's antinociceptive effects in male mice. Therefore, these results indicate a more prevalent role of HS α4β2 nAChR isoforms in mediating various behavioral effects associated with nicotine, whereas the LS α4β2 nAChR isoform has a limited role in mediating body temperature and nociceptive responses. These findings will facilitate the development of more selective, efficacious, and safe nAChR-based therapeutics for nicotine addiction treatment.
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Affiliation(s)
- Ayman K Hamouda
- Department of Pharmaceutical Sciences, College of Pharmacy, The University of Texas at Tyler, Tyler, TX, USA.
| | - Malia R Bautista
- Department of Neurobiology and Behavior, University of California Irvine, Irvine, CA, USA
| | - Lois S Akinola
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA, USA
| | - Yasmin Alkhlaif
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA, USA
| | - Asti Jackson
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA, USA
| | - Moriah Carper
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA, USA
| | - Wisam B Toma
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA, USA
| | - Sumanta Garai
- Department of Pharmaceutical Sciences, Northeastern University, Boston, MA, USA
| | - Yen-Chu Chen
- Department of Neurobiology and Behavior, University of California Irvine, Irvine, CA, USA
| | - Ganesh A Thakur
- Department of Pharmaceutical Sciences, Northeastern University, Boston, MA, USA
| | - Christie D Fowler
- Department of Neurobiology and Behavior, University of California Irvine, Irvine, CA, USA
| | - M Imad Damaj
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA, USA.
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9
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Deba F, Ramos K, Vannoy M, Munoz K, Akinola LS, Damaj MI, Hamouda AK. Examining the Effects of (α4)3(β2)2 Nicotinic Acetylcholine Receptor-Selective Positive Allosteric Modulator on Acute Thermal Nociception in Rats. Molecules 2020; 25:molecules25122923. [PMID: 32630476 PMCID: PMC7355939 DOI: 10.3390/molecules25122923] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Revised: 06/19/2020] [Accepted: 06/22/2020] [Indexed: 12/14/2022] Open
Abstract
Neuronal nicotinic acetylcholine receptor (nAChR)-based therapeutics are sought as a potential alternative strategy to opioids for pain management. In this study, we examine the antinociceptive effects of 3-(2-chlorophenyl)-5-(5-methyl-1-(piperidin-4-yl)-1H-pyrazol-4-yl)isoxazole (CMPI), a novel positive allosteric modulator (PAM), with preferential selectivity to the low agonist sensitivity (α4)3(β2)2 nAChR and desformylflustrabromine (dFBr), a PAM for α4-containing nAChRs. We used hot plate and tail flick tests to measure the effect of dFBr and CMPI on the latency to acute thermal nociceptive responses in rats. Intraperitoneal injection of dFBr, but not CMPI, dose-dependently increased latency in the hot plate test. In the tail flick test, the effect achieved at the highest dFBr or CMPI dose tested was only <20% of the maximum possible effects reported for nicotine and other nicotinic agonists. Moreover, the coadministration of dFBr did not enhance the antinociceptive effect of a low dose of nicotine. Our results show that the direct acute effect of dFBr is superior to that for CMPI, indicating that selectivity to (α4)3(β2)2 nAChR is not advantageous in alleviating responses to acute thermal nociceptive stimulus. However, further studies are necessary to test the suitability of (α4)3(β2)2 nAChR-selective PAMs in chronic pain models.
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Affiliation(s)
- Farah Deba
- Department of Pharmaceutical Sciences, College of Pharmacy, The University of Texas at Tyler, Tyler, TX 75799, USA;
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center MS 131, 1010 W. Ave. B, Kingsville, TX 78363, USA; (K.R.); (M.V.); (K.M.)
| | - Kara Ramos
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center MS 131, 1010 W. Ave. B, Kingsville, TX 78363, USA; (K.R.); (M.V.); (K.M.)
| | - Matthew Vannoy
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center MS 131, 1010 W. Ave. B, Kingsville, TX 78363, USA; (K.R.); (M.V.); (K.M.)
| | - Kemburli Munoz
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center MS 131, 1010 W. Ave. B, Kingsville, TX 78363, USA; (K.R.); (M.V.); (K.M.)
| | - Lois S. Akinola
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Kontos Medical Science Building, 1217 E. Marshall St., P.O. Box 980613, Richmond, VA 23298, USA; (L.S.A.); (M.I.D.)
| | - M. Imad Damaj
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Kontos Medical Science Building, 1217 E. Marshall St., P.O. Box 980613, Richmond, VA 23298, USA; (L.S.A.); (M.I.D.)
| | - Ayman K. Hamouda
- Department of Pharmaceutical Sciences, College of Pharmacy, The University of Texas at Tyler, Tyler, TX 75799, USA;
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center MS 131, 1010 W. Ave. B, Kingsville, TX 78363, USA; (K.R.); (M.V.); (K.M.)
- Correspondence: ; Tel.: +1-903-565-6578
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Deba F, Akk G, Hamouda AK. Assessing CMPI potentiation of (α4)3(β2)2 nicotinic acetylcholine receptor using the Monod‐Wyman‐Changeux allosteric model. FASEB J 2020. [DOI: 10.1096/fasebj.2020.34.s1.03706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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11
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Wilkerson JL, Deba F, Crowley ML, Hamouda AK, McMahon LR. Advances in the In vitro and In vivo pharmacology of Alpha4beta2 nicotinic receptor positive allosteric modulators. Neuropharmacology 2020; 168:108008. [PMID: 32113032 DOI: 10.1016/j.neuropharm.2020.108008] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 02/08/2020] [Accepted: 02/11/2020] [Indexed: 11/29/2022]
Abstract
Receptors containing α4 and β2 subunits are a major neuronal nicotinic acetylcholine receptor (nAChR) subtype in the brain. This receptor plays a critical role in nicotine addiction, with potential smoking cessation therapeutics producing modulation of α4β2 nAChR. In addition, compounds that act as agonists at α4β2 nAChR may be useful for the treatment of pathological pain. Further, as the α4β2 nAChR has been implicated in cognition, therapeutics that act as α4β2 nAChR agonists are also being examined as treatments for cognitive disorders and neurological diseases that impact cognitive function, such as Alzheimer's disease and schizophrenia. This review will cover the molecular in vitro evidence that allosteric modulators of the α4β2 neuronal nAChR provide several advantages over traditional α4β2 nAChR orthosteric ligands. Specifically, we explore the concept that nAChR allosteric modulators allow for greater pharmacological selectivity, while minimizing potential deleterious off-target effects. Further, here we discuss the development and preclinical in vivo behavioral assessment of allosteric modulators at the α4β2 neuronal nAChR as therapeutics for smoking cessation, pathological pain, as well as cognitive disorders and neurological diseases that impact cognitive function. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.
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Affiliation(s)
- Jenny L Wilkerson
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, 32610, United States.
| | - Farah Deba
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Texas at Tyler, Tyler, TX, 75799, United States
| | - Morgan L Crowley
- Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL, 32610, United States
| | - Ayman K Hamouda
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Texas at Tyler, Tyler, TX, 75799, United States.
| | - Lance R McMahon
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, 32610, United States.
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12
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Hamouda AK, Jackson A, Bagdas D, Imad Damaj M. Reversal of Nicotine Withdrawal Signs Through Positive Allosteric Modulation of α4β2 Nicotinic Acetylcholine Receptors in Male Mice. Nicotine Tob Res 2019; 20:903-907. [PMID: 29059422 DOI: 10.1093/ntr/ntx183] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Accepted: 08/15/2017] [Indexed: 01/03/2023]
Abstract
Introduction Nicotine withdrawal symptoms are important factors in determining the relapse rate to tobacco smoking and drugs that diminish these symptoms would potentially have a higher success rate as smoking cessation aids. Unlike US Food and Drug administration approved smoke cessation aids (nicotine and varenicline) which act as nicotinic acetylcholine receptors (nAChRs) agonists, desformylflustrabromine (dFBr) acts as a nAChR positive allosteric modulator with higher selectivity to the α4β2 nAChR. In animal studies, dFBr was well tolerated and reduced intravenous nicotine self-administration. In this study, we use behavioral test in mouse model of spontaneous nicotine withdrawal to assess the effect of dFBr on nicotine withdrawal symptoms. Methods Spontaneous nicotine withdrawal in nicotine-dependent ICR male mice was established 18-24 h after termination (minipump removal) of 14 days infusion of nicotine. After that (day 15), spontaneous signs of nicotine withdrawal were examined in the following order: anxiety-like behaviors, somatic signs, and then hyperalgesia using previously published behavioral protocols. Fifteen minutes before withdrawal signs testing, mice received a subcutaneous acute injection of vehicle or dFBr at the doses of 0.02, 0.1, and 1 mg/kg to determine the effect of dFBr on nicotine withdrawal symptoms. Results dFBr produced dose-dependent reversal of nicotine withdrawal signs in mouse model of spontaneous nicotine withdrawal. Implications Positive allosteric modulators of nAChR such as dFBr reduce nicotine withdrawal symptoms supporting the potential clinical use of this novel class of nAChR-based therapeutics as smoking cessation aid.
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Affiliation(s)
- Ayman K Hamouda
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center MS, Kingsville, TX
| | - Asti Jackson
- Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA
| | - Deniz Bagdas
- Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA.,Experimental Animals Breeding and Research Center, Faculty of Medicine, Uludag University, Bursa, Turkey
| | - M Imad Damaj
- Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA
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Deba F, Munoz K, Peterson SL, Hamouda AK. Assessing the cognitive‐enhancing effect of desformylflustrabromine in rat model of Aβ‐induced cognitive impairment. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.806.10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Kemburli Munoz
- Department of Pharmaceutical SciencesRangel College of Pharmacy, Texas A&M Health Sciences CenterKingsvilleTX
| | - Steven L Peterson
- Department of Pharmaceutical SciencesRangel College of Pharmacy, Texas A&M Health Sciences CenterKingsvilleTX
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Abstract
Disposition of beta-amyloid peptide 1-42 (Aβ1-42) in the space around the synapses and formation of Aβ-containing aggregates known as neuritic or senile plaques are hallmark features of neurodegenerative pathologies associated with Alzheimer's disease (AD). While AD is a multifactorial disease that includes other proteinopathies (e.g., hyperphosphorylated tau aggregates) and neurotransmitter disturbances (e.g., loss of cortical cholinergic innervation), Aβ (soluble or in senile plaques) remains the major undisputed factor that contributes to the pathological and behavior presentation of AD. Overproduction of Aβ and mutations in Aβ precursor (amyloid precursor protein) or enzymes involved in Aβ1-42 production and removal (γ secretase/presenilins) have been shown in cases of early onset of AD and produced AD-like pathologies in animal models. In addition, the level of soluble Aβ1-42 has been shown to correlate with cognitive impairment in animal models before the presence of senile plaques or other histological features of AD. However, much still is unknown about the biochemical processes leading to amyloid formation and its relation to the pathogenesis, neuronal damage/dysfunction, and behavioral changes associated with AD. In this article, we review animal models that have been developed to study AD-like pathologies and then provide detailed methodology to develop an acute rat model of Aβ-induced cognitive impairment. We use this model to examine the cognitive-enhancing effect of novel pharmacological interventions targeting nicotinic acetylcholine receptors.
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Affiliation(s)
- Farah Deba
- Department of Pharmaceutical Science, Fisch College of Pharmacy, University of Texas at Tyler, Tyler, TX, USA
| | - Steven Peterson
- Department of Pharmaceutical Sciences, Irma Lerma Rangel College of Pharmacy, Texas A&M University, Kingsville, TX, USA.
| | - Ayman K Hamouda
- Department of Pharmaceutical Science, Fisch College of Pharmacy, University of Texas at Tyler, Tyler, TX, USA.
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15
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Munoz K, Deba F, Hamouda AK. Agonist-Specific Pharmacological Effects of CMPI and NS9283 at (α4)3(β2)2 Neuronal Nicotinic. Acetylcholine Receptors. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.1690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Deba F, Ali HI, Tairu A, Ramos K, Ali J, Hamouda AK. LY2087101 and dFBr share transmembrane binding sites in the (α4)3(β2)2 Nicotinic Acetylcholine Receptor. Sci Rep 2018; 8:1249. [PMID: 29352227 PMCID: PMC5775429 DOI: 10.1038/s41598-018-19790-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 01/08/2018] [Indexed: 12/17/2022] Open
Abstract
Positive allosteric modulators (PAMs) of nicotinic acetylcholine receptors (nAChRs) have potential therapeutic application in neuropathologies associated with decrease in function or loss of nAChRs. In this study, we characterize the pharmacological interactions of the nAChRs PAM, LY2087101, with the α4β2 nAChR using mutational and computational analyses. LY2087101 potentiated ACh-induced currents of low-sensitivity (α4)3(β2)2 and high-sensitivity (α4)2(β2)3 nAChRs with similar potencies albeit to a different maximum potentiation (potentiation I max = ~840 and 450%, respectively). Amino acid substitutions within the α4 subunit transmembrane domain [e.g. α4Leu256 and α4Leu260 within the transmembrane helix 1 (TM1); α4Phe316 within the TM3; and α4Gly613 within TM4] significantly reduced LY2087101 potentiation of (α4)3(β2)2 nAChR. The locations of these amino acid residues and LY2087101 computational docking analyses identify two LY2087101 binding sites: an intrasubunit binding site within the transmembrane helix bundle of α4 subunit at the level of α4Leu260/α4Phe316 and intersubunit binding site at the α4:α4 subunit interface at the level of α4Leu256/α4Ile315 with both sites extending toward the extracellular end of the transmembrane domain. We also show that desformylflustrabromine (dFBr) binds to these two sites identified for LY2087101. These results provide structural information that are pertinent to structure-based design of nAChR allosteric modulators.
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Affiliation(s)
- Farah Deba
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, TX, 78363, USA
| | - Hamed I Ali
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, TX, 78363, USA
| | - Abisola Tairu
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, TX, 78363, USA
| | - Kara Ramos
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, TX, 78363, USA
| | - Jihad Ali
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, TX, 78363, USA
| | - Ayman K Hamouda
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, TX, 78363, USA.
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Wang ZJ, Deba F, Mohamed TS, Chiara DC, Ramos K, Hamouda AK. Unraveling amino acid residues critical for allosteric potentiation of (α4)3(β2)2-type nicotinic acetylcholine receptor responses. J Biol Chem 2017; 292:9988-10001. [PMID: 28446611 DOI: 10.1074/jbc.m116.771246] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 04/20/2017] [Indexed: 01/29/2023] Open
Abstract
Neuronal nicotinic acetylcholine receptors (nAChRs) are promising drug targets to manage several neurological disorders and nicotine addiction. Growing evidence indicates that positive allosteric modulators of nAChRs improve pharmacological specificity by binding to unique sites present only in a subpopulation of nAChRs. Furthermore, nAChR positive allosteric modulators such as NS9283 and CMPI have been shown to potentiate responses of (α4)3(β2)2 but not (α4)2(β2)3 nAChR isoforms. This selective potentiation underlines that the α4:α4 interface, which is present only in the (α4)3(β2)2 nAChR, is an important and promising drug target. In this report we used site-directed mutagenesis to substitute specific amino acid residues and computational analyses to elucidate CMPI's binding mode at the α4:α4 subunit extracellular interface and identified a unique set of amino acid residues that determined its affinity. We found that amino acid residues α4Gly-41, α4Lys-64, and α4Thr-66 were critical for (α4)3(β2)2 nAChR potentiation by CMPI, but not by NS9283, whereas amino acid substitution at α4His-116, a known determinant of NS9283 and of agonist binding at the α4:α4 subunit interface, did not reduce CMPI potentiation. In contrast, substitutions at α4Gln-124 and α4Thr-126 reduced potentiation by CMPI and NS9283, indicating that their binding sites partially overlap. These results delineate the role of amino acid residues contributing to the α4:α4 subunit extracellular interface in nAChR potentiation. These findings also provide structural information that will facilitate the structure-based design of novel therapeutics that target selectively the (α4)3(β2)2 nAChR.
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Affiliation(s)
- Ze-Jun Wang
- From the Department of Pharmaceutical Sciences, Texas A&M Health Sciences Center, Kingsville, Texas 78363
| | - Farah Deba
- From the Department of Pharmaceutical Sciences, Texas A&M Health Sciences Center, Kingsville, Texas 78363
| | - Tasnim S Mohamed
- From the Department of Pharmaceutical Sciences, Texas A&M Health Sciences Center, Kingsville, Texas 78363
| | - David C Chiara
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
| | - Kara Ramos
- From the Department of Pharmaceutical Sciences, Texas A&M Health Sciences Center, Kingsville, Texas 78363
| | - Ayman K Hamouda
- From the Department of Pharmaceutical Sciences, Texas A&M Health Sciences Center, Kingsville, Texas 78363, .,Department of Neuroscience and Experimental Therapeutics, Texas A&M Health Sciences Center, Bryan, Texas 77807, and
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Ang G, Deba F, Pandhare A, Blanton MP, Cohen JB, Hamouda AK. Photoaffinity Labeling of A4B2 Nicotinic Acetylcholine Receptor using [ 3 H]-Labeled Positive Allosteric Modulators. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.1736] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Jayakar SS, Ang G, Chiara DC, Hamouda AK. Photoaffinity Labeling of Pentameric Ligand-Gated Ion Channels: A Proteomic Approach to Identify Allosteric Modulator Binding Sites. Methods Mol Biol 2017; 1598:157-197. [PMID: 28508361 DOI: 10.1007/978-1-4939-6952-4_7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Photoaffinity labeling techniques have been used for decades to identify drug binding sites and to study the structural biology of allosteric transitions in transmembrane proteins including pentameric ligand-gated ion channels (pLGIC). In a typical photoaffinity labeling experiment, to identify drug binding sites, UV light is used to introduce a covalent bond between a photoreactive ligand (which upon irradiation at the appropriate wavelength converts to a reactive intermediate) and amino acid residues that lie within its binding site. Then protein chemistry and peptide microsequencing techniques are used to identify these amino acids within the protein primary sequence. These amino acid residues are located within homology models of the receptor to identify the binding site of the photoreactive probe. Molecular modeling techniques are then used to model the binding of the photoreactive probe within the binding site using docking protocols. Photoaffinity labeling directly identifies amino acids that contribute to drug binding sites regardless of their location within the protein structure and distinguishes them from amino acids that are only involved in the transduction of the conformational changes mediated by the drug, but may not be part of its binding site (such as those identified by mutational studies). Major limitations of photoaffinity labeling include the availability of photoreactive ligands that faithfully mimic the properties of the parent molecule and protein preparations that supply large enough quantities suitable for photoaffinity labeling experiments. When the ligand of interest is not intrinsically photoreactive, chemical modifications to add a photoreactive group to the parent drug, and pharmacological evaluation of these chemical modifications become necessary. With few exceptions, expression and affinity-purification of proteins are required prior to photolabeling. Methods to isolate milligram quantities of highly enriched pLGIC suitable for photoaffinity labeling experiments have been developed. In this chapter, we discuss practical aspects of experimental strategies to identify allosteric modulator binding sites in pLGIC using photoaffinity labeling.
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Affiliation(s)
- Selwyn S Jayakar
- Department of Neurobiology, Harvard Medical School, Boston, MA, USA
| | - Gordon Ang
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, TX, USA
| | - David C Chiara
- Department of Neurobiology, Harvard Medical School, Boston, MA, USA
| | - Ayman K Hamouda
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, TX, USA. .,Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M Health Science Center, Bryan, TX, USA. .,Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M Health Science Center, Kingsville, TX, USA.
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Hamouda AK, Deba F, Wang ZJ, Cohen JB. Photolabeling a Nicotinic Acetylcholine Receptor (nAChR) with an (α4)3(β2)2 nAChR-Selective Positive Allosteric Modulator. Mol Pharmacol 2016; 89:575-84. [PMID: 26976945 DOI: 10.1124/mol.116.103341] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Accepted: 03/09/2016] [Indexed: 01/25/2023] Open
Abstract
Positive allosteric modulators (PAMs) of nicotinic acetylcholine (ACh) receptors (nAChRs) have potential clinical applications in the treatment of nicotine dependence and many neuropsychiatric conditions associated with decreased brain cholinergic activity, and 3-(2-chlorophenyl)-5-(5-methyl-1-(piperidin-4-yl)-1H-pyrrazol-4-yl)isoxazole (CMPI) has been identified as a PAM selective for neuronal nAChRs containing theα4 subunit. In this report, we compare CMPI interactions with low-sensitivity (α4)3(β2)2 and high-sensitivity (α4)2(β2)3 nAChRs, and with muscle-type nAChRs. In addition, we use the intrinsic reactivity of [(3)H]CMPI upon photolysis at 312 nm to identify its binding sites inTorpedonAChRs. Recording fromXenopusoocytes, we found that CMPI potentiated maximally the responses of (α4)3(β2)2nAChR to 10μM ACh (EC10) by 400% and with anEC50of ∼1µM. CMPI produced a left shift of the ACh concentration-response curve without altering ACh efficacy. In contrast, CMPI inhibited (∼35% at 10µM) ACh responses of (α4)2(β2)3nAChRs and fully inhibited human muscle andTorpedonAChRs with IC50values of ∼0.5µM. Upon irradiation at 312 nm, [(3)H]CMPI photoincorporated into eachTorpedo[(α1)2β1γδ] nAChR subunit. Sequencing of peptide fragments isolated from [(3)H]CMPI-photolabeled nAChR subunits established photolabeling of amino acids contributing to the ACh binding sites (αTyr(190),αTyr(198),γTrp(55),γTyr(111),γTyr(117),δTrp(57)) that was fully inhibitable by agonist and lower-efficiency, state-dependent [(3)H]CMPI photolabeling within the ion channel. Our results establish that CMPI is a potent potentiator of nAChRs containing anα4:α4 subunit interface, and that its intrinsic photoreactivy makes it of potential use to identify its binding sites in the (α4)3(β2)2nAChR.
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Affiliation(s)
- Ayman K Hamouda
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, Texas (A.K.H., F.D., Z.-J.W.); and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., J.B.C.)
| | - Farah Deba
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, Texas (A.K.H., F.D., Z.-J.W.); and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., J.B.C.)
| | - Ze-Jun Wang
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, Texas (A.K.H., F.D., Z.-J.W.); and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., J.B.C.)
| | - Jonathan B Cohen
- Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville, Texas (A.K.H., F.D., Z.-J.W.); and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., J.B.C.)
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Wang ZJ, Deba F, Trevino TR, Ramos K, Hamouda AK. Interaction of the Positive Allosteric Modulator LY2087101 with α4β2 Nicotinic Acetylcholine Receptor. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.3229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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22
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Mohamed TS, Jayakar SS, Hamouda AK. Orthosteric and Allosteric Ligands of Nicotinic Acetylcholine Receptors for Smoking Cessation. Front Mol Neurosci 2015; 8:71. [PMID: 26635524 PMCID: PMC4658446 DOI: 10.3389/fnmol.2015.00071] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 11/06/2015] [Indexed: 12/23/2022] Open
Abstract
Nicotine addiction, the result of tobacco use, leads to over six million premature deaths world-wide per year, a number that is expected to increase by a third within the next two decades. While more than half of smokers want and attempt to quit, only a small percentage of smokers are able to quit without pharmacological interventions. Therefore, over the past decades, researchers in academia and the pharmaceutical industry have focused their attention on the development of more effective smoking cessation therapies, which is now a growing 1.9 billion dollar market. Because the role of neuronal nicotinic acetylcholine receptors (nAChR) in nicotine addiction is well established, nAChR based therapeutics remain the leading strategy for smoking cessation. However, the development of neuronal nAChR drugs that are selective for a nAChR subpopulation is challenging, and only few neuronal nAChR drugs are clinically available. Among the many neuronal nAChR subtypes that have been identified in the brain, the α4β2 subtype is the most abundant and plays a critical role in nicotine addiction. Here, we review the role of neuronal nAChRs, especially the α4β2 subtype, in the development and treatment of nicotine addiction. We also compare available smoking cessation medications and other nAChR orthosteric and allosteric ligands that have been developed with emphasis on the difficulties faced in the development of clinically useful compounds with high nAChR subtype selectivity.
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Affiliation(s)
- Tasnim S Mohamed
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center Kingsville, TX, USA
| | - Selwyn S Jayakar
- Department of Neurobiology, Harvard Medical School Boston, MA, USA
| | - Ayman K Hamouda
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center Kingsville, TX, USA ; Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M Health Sciences Center Bryan, TX, USA
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Hamouda AK, Wang ZJ, Stewart DS, Jain AD, Glennon RA, Cohen JB. Desformylflustrabromine (dFBr) and [3H]dFBr-Labeled Binding Sites in a Nicotinic Acetylcholine Receptor. Mol Pharmacol 2015; 88:1-11. [PMID: 25870334 PMCID: PMC4468644 DOI: 10.1124/mol.115.098913] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 04/13/2015] [Indexed: 12/11/2022] Open
Abstract
Desformylflustrabromine (dFBr) is a positive allosteric modulator (PAM) of α4β2 and α2β2 nAChRs that, at concentrations >1 µM, also inhibits these receptors and α7 nAChRs. However, its interactions with muscle-type nAChRs have not been characterized, and the locations of its binding site(s) in any nAChR are not known. We report here that dFBr inhibits human muscle (αβεδ) and Torpedo (αβγδ) nAChR expressed in Xenopus oocytes with IC50 values of ∼ 1 μM. dFBr also inhibited the equilibrium binding of ion channel blockers to Torpedo nAChRs with higher affinity in the nAChR desensitized state ([(3)H]phencyclidine; IC50 = 4 μM) than in the resting state ([(3)H]tetracaine; IC50 = 60 μM), whereas it bound with only very low affinity to the ACh binding sites ([(3)H]ACh, IC50 = 1 mM). Upon irradiation at 312 nm, [(3)H]dFBr photoincorporated into amino acids within the Torpedo nAChR ion channel with the efficiency of photoincorporation enhanced in the presence of agonist and the agonist-enhanced photolabeling inhibitable by phencyclidine. In the presence of agonist, [(3)H]dFBr also photolabeled amino acids in the nAChR extracellular domain within binding pockets identified previously for the nonselective nAChR PAMs galantamine and physostigmine at the canonical α-γ interface containing the transmitter binding sites and at the noncanonical δ-β subunit interface. These results establish that dFBr inhibits muscle-type nAChR by binding in the ion channel and that [(3)H]dFBr is a photoaffinity probe with broad amino acid side chain reactivity.
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Affiliation(s)
- Ayman K Hamouda
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Ze-Jun Wang
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Deirdre S Stewart
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Atul D Jain
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Richard A Glennon
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
| | - Jonathan B Cohen
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.S.S., J.B.C.); Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (A.D.J., R.A.G.); and Department of Pharmaceutical Sciences, Rangel College of Pharmacy, Texas A&M Health Sciences Center, Kingsville,Texas (A.K.H., Z.-J.W.)
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Hamouda AK, Stewart DS, Chiara DC, Savechenkov PY, Bruzik KS, Cohen JB. Identifying barbiturate binding sites in a nicotinic acetylcholine receptor with [3H]allyl m-trifluoromethyldiazirine mephobarbital, a photoreactive barbiturate. Mol Pharmacol 2014; 85:735-46. [PMID: 24563544 DOI: 10.1124/mol.113.090985] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
At concentrations that produce anesthesia, many barbituric acid derivatives act as positive allosteric modulators of inhibitory GABAA receptors (GABAARs) and inhibitors of excitatory nicotinic acetylcholine receptors (nAChRs). Recent research on [(3)H]R-mTFD-MPAB ([(3)H]R-5-allyl-1-methyl-5-(m-trifluoromethyldiazirinylphenyl)barbituric acid), a photoreactive barbiturate that is a potent and stereoselective anesthetic and GABAAR potentiator, has identified a second class of intersubunit binding sites for general anesthetics in the α1β3γ2 GABAAR transmembrane domain. We now characterize mTFD-MPAB interactions with the Torpedo (muscle-type) nAChR. For nAChRs expressed in Xenopus oocytes, S- and R-mTFD-MPAB inhibited ACh-induced currents with IC50 values of 5 and 10 µM, respectively. Racemic mTFD-MPAB enhanced the equilibrium binding of [(3)H]ACh to nAChR-rich membranes (EC50 = 9 µM) and inhibited binding of the ion channel blocker [(3)H]tenocyclidine in the nAChR desensitized and resting states with IC50 values of 2 and 170 µM, respectively. Photoaffinity labeling identified two binding sites for [(3)H]R-mTFD-MPAB in the nAChR transmembrane domain: 1) a site within the ion channel, identified by photolabeling in the nAChR desensitized state of amino acids within the M2 helices of each nAChR subunit; and 2) a site at the γ-α subunit interface, identified by photolabeling of γMet299 within the γM3 helix at similar efficiency in the resting and desensitized states. These results establish that mTFD-MPAB is a potent nAChR inhibitor that binds in the ion channel preferentially in the desensitized state and binds with lower affinity to a site at the γ-α subunit interface where etomidate analogs bind that act as positive and negative nAChR modulators.
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Affiliation(s)
- Ayman K Hamouda
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts (A.K.H., D.C.C., J.B.C.); Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, Massachusetts (D.S.S.); and Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois (P.Y.S., K.S.B.)
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Hamouda AK, Jayakar SS, Chiara DC, Cohen JB. Photoaffinity Labeling of Nicotinic Receptors: Diversity of Drug Binding Sites! J Mol Neurosci 2013; 53:480-6. [DOI: 10.1007/s12031-013-0150-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 10/10/2013] [Indexed: 12/11/2022]
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Pandhare A, Hamouda AK, Staggs B, Aggarwal S, Duddempudi PK, Lever JR, Lapinsky DJ, Jansen M, Cohen JB, Blanton MP. Bupropion binds to two sites in the Torpedo nicotinic acetylcholine receptor transmembrane domain: a photoaffinity labeling study with the bupropion analogue [(125)I]-SADU-3-72. Biochemistry 2012; 51:2425-35. [PMID: 22394379 DOI: 10.1021/bi300101r] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bupropion, a clinically used antidepressant and smoking-cessation drug, acts as a noncompetitive antagonist of nicotinic acetylcholine receptors (nAChRs). To identify its binding site(s) in nAChRs, we developed a photoreactive bupropion analogue, (±)-2-(N-tert-butylamino)-3'-[(125)I]-iodo-4'-azidopropiophenone (SADU-3-72). Based on inhibition of [(125)I]SADU-3-72 binding, SADU-3-72 binds with high affinity (IC(50) = 0.8 μM) to the Torpedo nAChR in the resting (closed channel) state and in the agonist-induced desensitized state, and bupropion binds to that site with 3-fold higher affinity in the desensitized (IC(50) = 1.2 μM) than in the resting state. Photolabeling of Torpedo nAChRs with [(125)I]SADU-3-72 followed by limited in-gel digestion of nAChR subunits with endoproteinase Glu-C established the presence of [(125)I]SADU-3-72 photoincorporation within nAChR subunit fragments containing M1-M2-M3 helices (αV8-20K, βV8-22/23K, and γV8-24K) or M1-M2 helices (δV8-14). Photolabeling within βV8-22/23K, γV8-24K, and δV8-14 was reduced in the desensitized state and inhibited by ion channel blockers selective for the resting (tetracaine) or desensitized (thienycyclohexylpiperidine (TCP)) state, and this pharmacologically specific photolabeling was localized to the M2-9 leucine ring (δLeu(265), βLeu(257)) within the ion channel. In contrast, photolabeling within the αV8-20K was enhanced in the desensitized state and not inhibited by TCP but was inhibited by bupropion. This agonist-enhanced photolabeling was localized to αTyr(213) in αM1. These results establish the presence of two distinct bupropion binding sites within the Torpedo nAChR transmembrane domain: a high affinity site at the middle (M2-9) of the ion channel and a second site near the extracellular end of αM1 within a previously described halothane (general anesthetic) binding pocket.
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Affiliation(s)
- Akash Pandhare
- Department of Pharmacology and Neuroscience and the Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, United States
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Pandhare A, Hamouda AK, Staggs B, Duddempudi PK, Lever JR, Cohen JB, Lapinsky DJ, Jansen M, Blanton MP. Bupropion Binds in the Middle (M2-9) of the Torpedo Nicotinic Acetylcholine Receptor Ion Channel. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.661] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Hamouda AK, Stewart DS, Husain SS, Cohen JB. Multiple transmembrane binding sites for p-trifluoromethyldiazirinyl-etomidate, a photoreactive Torpedo nicotinic acetylcholine receptor allosteric inhibitor. J Biol Chem 2011; 286:20466-77. [PMID: 21498509 DOI: 10.1074/jbc.m111.219071] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Photoreactive derivatives of the general anesthetic etomidate have been developed to identify their binding sites in γ-aminobutyric acid, type A and nicotinic acetylcholine receptors. One such drug, [(3)H]TDBzl-etomidate (4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzyl-[(3)H]1-(1-phenylethyl)-1H-imidazole-5-carboxylate), acts as a positive allosteric potentiator of Torpedo nACh receptor (nAChR) and binds to a novel site in the transmembrane domain at the γ-α subunit interface. To extend our understanding of the locations of allosteric modulator binding sites in the nAChR, we now characterize the interactions of a second aryl diazirine etomidate derivative, TFD-etomidate (ethyl-1-(1-(4-(3-trifluoromethyl)-3H-diazirin-3-yl)phenylethyl)-1H-imidazole-5-carboxylate). TFD-etomidate inhibited acetylcholine-induced currents with an IC(50) = 4 μM, whereas it inhibited the binding of [(3)H]phencyclidine to the Torpedo nAChR ion channel in the resting and desensitized states with IC(50) values of 2.5 and 0.7 mm, respectively. Similar to [(3)H]TDBzl-etomidate, [(3)H]TFD-etomidate bound to a site at the γ-α subunit interface, photolabeling αM2-10 (αSer-252) and γMet-295 and γMet-299 within γM3, and to a site in the ion channel, photolabeling amino acids within each subunit M2 helix that line the lumen of the ion channel. In addition, [(3)H]TFD-etomidate photolabeled in an agonist-dependent manner amino acids within the δ subunit M2-M3 loop (δIle-288) and the δ subunit transmembrane helix bundle (δPhe-232 and δCys-236 within δM1). The fact that TFD-etomidate does not compete with ion channel blockers at concentrations that inhibit acetylcholine responses indicates that binding to sites at the γ-α subunit interface and/or within δ subunit helix bundle mediates the TFD-etomidate inhibitory effect. These results also suggest that the γ-α subunit interface is a binding site for Torpedo nAChR negative allosteric modulators (TFD-etomidate) and for positive modulators (TDBzl-etomidate).
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Affiliation(s)
- Ayman K Hamouda
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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daCosta CJB, Michel Sturgeon R, Hamouda AK, Blanton MP, Baenziger JE. Structural characterization and agonist binding to human α4β2 nicotinic receptors. Biochem Biophys Res Commun 2011; 407:456-60. [PMID: 21396349 DOI: 10.1016/j.bbrc.2011.03.026] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Accepted: 03/03/2011] [Indexed: 01/19/2023]
Abstract
The Cys-loop receptor super-family of neurotransmitter-gated ion channels mediates fast synaptic transmission throughout the human nervous system. These receptors exhibit widely varying pharmacologies, yet their structural characterization has relied heavily on their homology with the naturally abundant muscle-type Torpedo nicotinic acetylcholine receptor. Here we examine for the first time the structure of a human α4β2 neuronal nicotinic acetylcholine receptor. We show that human α4β2 nicotinic receptors adopt a secondary/tertiary fold similar to that of the Torpedo nicotinic receptor with a large proportion of both α-helix and β-sheet, but exhibit a substantially increased thermal stability. Both receptors bind agonist, but with different patterns of agonist recognition - particularly in the nature of the interactions between aromatic residues and the agonist quaternary amine functional group. By comparing α4β2 and Torpedo receptors, we begin to delineate their structural similarities and differences.
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Affiliation(s)
- Corrie J B daCosta
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, 451 Smyth Rd., Ottawa, Ontario, Canada K1H 8M5
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Husain SS, Stewart D, Desai R, Hamouda AK, Li SGD, Kelly E, Dostalova Z, Zhou X, Cotten JF, Raines DE, Olsen RW, Cohen JB, Forman SA, Miller KW. p-Trifluoromethyldiazirinyl-etomidate: a potent photoreactive general anesthetic derivative of etomidate that is selective for ligand-gated cationic ion channels. J Med Chem 2010; 53:6432-44. [PMID: 20704351 DOI: 10.1021/jm100498u] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
We synthesized the R- and S-enantiomers of ethyl 1-(1-(4-(3-((trifluoromethyl)-3H-diazirin-3-yl)phenyl)ethyl)-1H-imidazole-5-carboxylate (trifluoromethyldiazirinyl-etomidate), or TFD-etomidate, a novel photoactivable derivative of the stereoselective general anesthetic etomidate (R-(2-ethyl 1-(phenylethyl)-1H-imidazole-5-carboxylate)). Anesthetic potency was similar to etomidate's, but stereoselectivity was reversed and attenuated. Relative to etomidate, TFD-etomidate was a more potent inhibitor of the excitatory receptors, nAChR (nicotinic acetylcholine receptor) ((alpha1)(2)beta1delta1gamma1) and 5-HT(3A)R (serotonin type 3A receptor), causing significant inhibition at anesthetic concentrations. S- but not R-TFD-etomidate enhanced currents elicited from inhibitory alpha1beta2gamma2L GABA(A)Rs by low concentrations of GABA, but with a lower efficacy than R-etomidate, and site-directed mutagenesis suggests they act at different sites. [(3)H]TFD-etomidate photolabeled the alpha-subunit of the nAChR in a manner allosterically regulated by agonists and noncompetitive inhibitors. TFD-etomidate's novel pharmacology is unlike that of etomidate derivatives with photoactivable groups in the ester position, which behave like etomidate, suggesting that it will further enhance our understanding of anesthetic mechanisms.
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Affiliation(s)
- S Shaukat Husain
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, 32 Fruit Street, Boston, Massachusetts 02114, USA
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Srivastava S, Hamouda AK, Talley TT, Pandhare A, Duddempudi PK, Hsiao H, Taylor P, Cohen JB, Blanton MP. Photoaffinity Labeling the Agonist Binding Sites of Torpedo and α4β2 Nicotinic Acetylcholine Receptors and Acetylcholine Binding Proteins (AChBPs) with [3H]Cytisine. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Hamouda AK, Stewart D, Husain SS, Cohen JB. A Transmembrane Binding Site at a Subunit Interface for Torpedo Nicotinic Acetylcholine Receptor Potentiators And Inhibitors. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Chiara DC, Hamouda AK, Ziebell MR, Mejia LA, Garcia G, Cohen JB. [(3)H]chlorpromazine photolabeling of the torpedo nicotinic acetylcholine receptor identifies two state-dependent binding sites in the ion channel. Biochemistry 2009; 48:10066-77. [PMID: 19754159 DOI: 10.1021/bi901271w] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Chlorpromazine (CPZ), a potent nicotinic acetylcholine receptor (nAChR) noncompetitive antagonist, binds with higher affinity in the ion channel in the desensitized state than in the closed channel state and with low affinity to additional sites in nAChR-rich membranes. For nAChR equilibrated with agonist, we confirm previous reports that [(3)H]CPZ occupies a site near the cytoplasmic end of the M2 ion channel domain, photolabeling positions M2-2, M2-6, and/or M2-9 in each subunit. We find that [(3)H]CPZ also binds at the extracellular end of the channel, photolabeling amino acids at positions M2-16 (alpha,gamma), M2-17 (alpha,beta,delta), and M2-20 (alpha,beta,delta). The photolabeling at the cytoplasmic end of the channel is fully inhibitable by phencyclidine or proadifen, whereas neither drug inhibits [(3)H]CPZ photolabeling at the extracellular end, establishing that positively charged drugs can bind simultaneously at the cytoplasmic and extracellular ends of the ion channel. [(3)H]CPZ photolabeling is not detected in the transmembrane domain outside the ion channel, but it photolabels alphaMet-386 and alphaSer-393 in the cytoplasmic alphaMA helix. In the nAChR equilibrated with alpha-bungarotoxin to stabilize the nAChR in a closed state, [(3)H]CPZ photolabels amino acids at M2-5 (alpha), M2-6 (alpha,beta,delta), and M2-9 (beta,delta), with no labeling at M2-2. These results provide novel information about the modes of drug binding within the nAChR ion channel and indicate that within the nAChR transmembrane domain, the binding of cationic aromatic amine antagonists can be restricted to the ion channel domain, in contrast to the uncharged, allosteric potentiators and inhibitors that also bind within the delta subunit helix bundle and at subunit interfaces.
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Affiliation(s)
- David C Chiara
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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Sanghvi M, Hamouda AK, Davis MI, Morton RA, Srivastava S, Pandhare A, Duddempudi PK, Machu TK, Lovinger DM, Cohen JB, Blanton MP. Hydrophobic photolabeling studies identify the lipid-protein interface of the 5-HT3A receptor. Biochemistry 2009; 48:9278-86. [PMID: 19715355 DOI: 10.1021/bi901208j] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
A HEK-293 cell line that stably expresses mouse 5-HT(3A)Rs containing a C-terminal extension that confers high-affinity binding of alpha-bungarotoxin (alphaBgTx) was established (alphaBgTx-5-HT(3A)Rs) and used to purify alphaBgTx-5-HT(3A)Rs in a lipid environment for use in structural studies using photoaffinity labeling. alphaBgTx-5-HT(3A)Rs were expressed robustly (60 pmol of [(3)H]BRL-43694 binding sites (approximately 3 microg of receptor) per milligram of protein) and displayed the same functional properties as wild-type receptors (serotonin EC(50) = 5.3 +/- 0.04 microM). While [(125)I]alphaBgTx bound to the alphaBgTx-5-HT(3A)Rs with high affinity (K(d) = 11 nM), application of nonradioactive alphaBgTx (up to 300 microM) had no effect on serotonin-induced current responses. alphaBgTx-5-HT(3A)Rs were purified on an alphaBgTx-derivatized affinity column from detergent extracts in milligram quantities and at approximately 25% purity. The hydrophobic photolabel 3-trifluoromethyl-3-(m-[(125)I]iodophenyl)diazirine ([(125)I]TID) was used to identify the amino acids at the lipid-protein interface of purified and lipid-reconstituted alphaBgTx-5-HT(3A)Rs. [(125)I]TID photoincorporation into the alphaBgTx-5-HT(3A)R subunit was initially mapped to subunit proteolytic fragments of 8 kDa, containing the M4 transmembrane segment and approximately 60% of incorporated (125)I, and 17 kDa, containing the M1-M3 transmembrane segments. Within the M4 segment, [(125)I]TID labeled Ser(451), equivalent to the [(125)I]TID-labeled residue Thr(422) at the lipid-exposed face of the Torpedo nicotinic acetylcholine receptor (nAChR) alpha1M4 alpha-helix. These results provide a first definition of the surface of the 5-HT(3A)R M4 helix that is exposed to lipid and establish that this surface is equivalent to the surface exposed to lipid in the Torpedo nAChR.
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Affiliation(s)
- Mitesh Sanghvi
- Department of Pharmacology and Neuroscience and Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA
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Srivastava S, Hamouda AK, Pandhare A, Duddempudi PK, Sanghvi M, Cohen JB, Blanton MP. [(3)H]Epibatidine photolabels non-equivalent amino acids in the agonist binding site of Torpedo and alpha4beta2 nicotinic acetylcholine receptors. J Biol Chem 2009; 284:24939-47. [PMID: 19620239 DOI: 10.1074/jbc.m109.019083] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nicotinic acetylcholine receptor (nAChR) agonists, such as epibatidine and its molecular derivatives, are potential therapeutic agents for a variety of neurological disorders. In order to identify determinants for subtype-selective agonist binding, it is important to determine whether an agonist binds in a common orientation in different nAChR subtypes. To compare the mode of binding of epibatidine in a muscle and a neuronal nAChR, we photolabeled Torpedo alpha(2)betagammadelta and expressed human alpha4beta2 nAChRs with [(3)H]epibatidine and identified by Edman degradation the photolabeled amino acids. Irradiation at 254 nm resulted in photolabeling of alphaTyr(198) in agonist binding site Segment C of the principal (+) face in both alpha subunits and of gammaLeu(109) and gammaTyr(117) in Segment E of the complementary (-) face, with no labeling detected in the delta subunit. For affinity-purified alpha4beta2 nAChRs, [(3)H]epibatidine photolabeled alpha4Tyr(195) (equivalent to Torpedo alphaTyr(190)) in Segment C as well as beta2Val(111) and beta2Ser(113) in Segment E (equivalent to Torpedo gammaLeu(109) and gammaTyr(111), respectively). Consideration of the location of the photolabeled amino acids in homology models of the nAChRs based upon the acetylcholine-binding protein structure and the results of ligand docking simulations suggests that epibatidine binds in a single preferred orientation within the alpha-gamma transmitter binding site, whereas it binds in two distinct orientations in the alpha4beta2 nAChR.
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Affiliation(s)
- Shouryadeep Srivastava
- Department of Pharmacology and Neuroscience and the Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA
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Hamouda AK, Jin X, Sanghvi M, Srivastava S, Pandhare A, Duddempudi PK, Steinbach JH, Blanton MP. Photoaffinity labeling the agonist binding domain of alpha4beta4 and alpha4beta2 neuronal nicotinic acetylcholine receptors with [(125)I]epibatidine and 5[(125)I]A-85380. Biochim Biophys Acta 2009; 1788:1987-95. [PMID: 19545536 DOI: 10.1016/j.bbamem.2009.06.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2009] [Revised: 06/15/2009] [Accepted: 06/16/2009] [Indexed: 11/26/2022]
Abstract
The development of nicotinic acetylcholine receptor (nAChR) agonists, particularly those that discriminate between neuronal nAChR subtypes, holds promise as potential therapeutic agents for many neurological diseases and disorders. To this end, we photoaffinity labeled human alpha4beta2 and rat alpha4beta4 nAChRs affinity-purified from stably transfected HEK-293 cells, with the agonists [(125)I]epibatidine and 5[(125)I]A-85380. Our results show that both agonists photoincorporated into the beta4 subunit with little or no labeling of the beta2 and alpha4 subunits respectively. [(125)I]epibatidine labeling in the beta4 subunit was mapped to two overlapping proteolytic fragments that begin at beta4V102 and contain Loop E (beta4I109-P120) of the agonist binding site. We were unable to identify labeled amino acid(s) in Loop E by protein sequencing, but we were able to demonstrate that beta4Q117 in Loop E is the principal site of [(125)I]epibatidine labeling. This was accomplished by substituting residues in the beta2 subunit with the beta4 homologs and finding [(125)I]epibatidine labeling in beta4 and beta2F119Q subunits with little, if any, labeling in alpha4, beta2, or beta2S113R subunits. Finally, functional studies established that the beta2F119/beta4Q117 position is an important determinant of the receptor subtype-selectivity of the agonist 5I-A-85380, affecting both binding affinity and channel activation.
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Affiliation(s)
- Ayman K Hamouda
- Department of Pharmacology and Neuroscience and the Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, 3601 4th Street, Lubbock, TX 79430, USA
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Hamouda AK, Chiara DC, Blanton MP, Cohen JB. Probing the structure of the affinity-purified and lipid-reconstituted torpedo nicotinic acetylcholine receptor. Biochemistry 2009; 47:12787-94. [PMID: 18991407 DOI: 10.1021/bi801476j] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Torpedo nicotinic acetylcholine receptor (nAChR) is the only member of the Cys-loop superfamily of ligand-gated ion channels (LGICs) that is available in high abundance in a native membrane preparation. To study the structure of the other LGICs using biochemical and biophysical techniques, detergent solubilization, purification, and lipid reconstitution are usually required. To assess the effects of purification on receptor structure, we used the hydrophobic photoreactive probe 3-trifluoromethyl-3-(m-[(125)I]iodophenyl)diazirine ([(125)I]TID) to compare the state-dependent photolabeling of the Torpedo nAChR before and after purification and reincorporation into lipid. For the purified nAChR, the agonist-sensitive photolabeling within the M2 ion channel domain of positions M2-6, M2-9, and M2-13, the agonist-enhanced labeling of deltaThr274 (deltaM2-18) within the delta subunit helix bundle, and the labeling at the lipid-protein interface (alphaMu4) were the same as for the nAChR in native membranes. However, addition of agonist did not enhance [(125)I]TID photolabeling of deltaIle288 within the deltaM2-M3 loop. These results indicate that after purification and reconstitution of the Torpedo nAChR, the difference in structure between the resting and desensitized states within the M2 ion channel domain was preserved, but not the agonist-dependent change of structure of the deltaM2-M3 loop. To further characterize the pharmacology of [(125)I]TID binding sites in the nAChR in the desensitized state, we examined the effect of phencyclidine (PCP) on [(125)I]TID photolabeling. PCP inhibited [(125)I]TID labeling of amino acids at the cytoplasmic end of the ion channel (M2-2 and M2-6) while potentiating labeling at M2-9 and M2-13 and allosterically modulating the labeling of amino acids within the delta subunit helix bundle.
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Affiliation(s)
- Ayman K Hamouda
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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Srivastava S, Hamouda AK, Sanghvi M, Pandhare A, Duddempudi PK, Hiyari S, Chiara DC, Cohen JB, Blanton MP. Photoaffinity Labeling the Agonist Binding Sites of nAChRs with [3H]Epibatidine. Biophys J 2009. [DOI: 10.1016/j.bpj.2008.12.773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Hamouda AK, Sanghvi M, Chiara DC, Cohen JB, Blanton MP. Identifying the lipid-protein interface of the alpha4beta2 neuronal nicotinic acetylcholine receptor: hydrophobic photolabeling studies with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine. Biochemistry 2007; 46:13837-46. [PMID: 17994769 DOI: 10.1021/bi701705r] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Using an acetylcholine-derivatized affinity column, we have purified human alpha4beta2 neuronal nicotinic acetylcholine receptors (nAChRs) from a stably transfected HEK-293 cell line. Both the quantity and the quality of the purified receptor are suitable for applying biochemical methods to directly study the structure of the alpha4beta2 nAChR. In this first study, the lipid-protein interface of purified and lipid-reconstituted alpha4beta2 nAChRs was directly examined using photoaffinity labeling with the hydrophobic probe 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine ([125I]TID). [125I]TID photoincorporated into both alpha4 and beta2 subunits, and for each subunit the labeling was initially mapped to fragments containing the M4 and M1-M3 transmembrane segments. For both the alpha4 and beta2 subunits, approximately 60% of the total labeling was localized within fragments that contain the M4 segment, which suggests that the M4 segment has the greatest exposure to lipid. Within M4 segments, [125I]TID labeled homologous amino acids alpha4-Cys582/beta2-Cys445, which are also homologous to the [125I]TID-labeled residues alpha1-Cys418 and beta1-Cys447 in the lipid-exposed face of Torpedo nAChR alpha1M4 and beta1M4, respectively. Within the alpha4M1 segment, [125I]TID labeled residues Cys226 and Cys231, which correspond to the [125I]TID-labeled residues Cys222 and Phe227 at the lipid-exposed face of the Torpedo alpha1M1 segment. In beta2M1, [125I]TID labeled beta2-Cys220, which is homologous to alpha4-Cys226. We conclude from these studies that the alpha4beta2 nAChR can be purified from stably transfected HEK-293 cells in sufficient quantity and purity for structural studies and that the lipid-protein interfaces of the neuronal alpha4beta2 nAChR and the Torpedo nAChR display a high degree of structural homology.
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Affiliation(s)
- Ayman K Hamouda
- Department of Pharmacology and Neuroscience, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA
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Garcia G, Chiara DC, Nirthanan S, Hamouda AK, Stewart DS, Cohen JB. [3H]Benzophenone photolabeling identifies state-dependent changes in nicotinic acetylcholine receptor structure. Biochemistry 2007; 46:10296-307. [PMID: 17685589 DOI: 10.1021/bi7008163] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Interactions of benzophenone (BP) with the Torpedo nicotinic acetylcholine receptor (nAChR) were characterized by electrophysiological analyses, radioligand binding assays, and photolabeling of nAChR-rich membranes with [3H]BP to identify the amino acids contributing to its binding sites. BP acted as a low potency noncompetitive antagonist, reversibly inhibiting the ACh responses of nAChRs expressed in Xenopus oocytes (IC50 = 600 microM) and the binding of the noncompetitive antagonist [3H]tetracaine to nAChR-rich membranes (IC50 = 150 microM). UV irradiation at 365 nm resulted in covalent incorporation of [3H]BP into the nAChR subunits (delta > alpha approximately beta > gamma), with photoincorporation limited to the nAChR transmembrane domain. Comparison of nAChR photolabeling in the closed state (absence of agonist) and desensitized state (equilibrated with agonist) revealed selective desensitized state labeling in the delta subunit of deltaPhe-232 in deltaM1 and deltaPro-286/deltaIle-288 near the beginning of deltaM3 that are within a pocket at the interface between the transmembrane and extracellular domains. There was labeling in the closed state within the ion channel at position M2-13 (alphaVal-255, betaVal-261, and deltaVal-269) that was reduced by 90% upon desensitization and labeling in the transmembrane M3 helices of the beta and gamma subunits (betaMet-285, betaMet-288, and gammaMet-291) that was reduced by 50-80% in the desensitized state. Labeling at the lipid interface (alphaMet-415 in alphaM4) was unaffected by agonist. These results provide a further definition of the regions in the nAChR transmembrane domain that differ in structure between the closed and desensitized states.
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Affiliation(s)
- Galo Garcia
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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Hamouda AK, Sanghvi M, Sauls D, Machu TK, Blanton MP. Assessing the lipid requirements of the Torpedo californica nicotinic acetylcholine receptor. Biochemistry 2006; 45:4327-37. [PMID: 16566607 PMCID: PMC2527474 DOI: 10.1021/bi052281z] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The lipid requirements of the Torpedo californica nicotinic acetylcholine receptor (nAChR) were assessed by reconstituting purified receptors into lipid vesicles of defined composition and by using photolabeling with 3-trifluoromethyl-3-(m-[125I]iodophenyl)diazirine ([125I]TID) to determine functionality. Earlier studies demonstrated that nAChRs reconstituted into membranes containing phosphatidylcholine (PC), the anionic lipid phosphatidic acid (PA), and cholesterol (CH) are particularly effective at stabilizing the nAChR in the resting (closed) state that is capable of undergoing agonist-induced conformational transitions (i.e., functionality). The present studies demonstrate that (1) there is no obligatory requirement for PC, (2) increasing the CH content serves to increase the degree to which nAChRs are stabilized in the resting state, and this effect saturates at approximately 35 mol % (molar lipid percentage), and (3) the effect of increasing levels of PA saturates at approximately 12 mol % and in the absence of PA nAChRs are stabilized in the desensitized state (i.e., nonfunctional). Native Torpedo membranes contain approximately 35 mol % CH but less than 1 mol % PA, suggesting that other anionic lipids may substitute for PA. We report that (1) phosphatidylserine (PS) and phosphatidylinositol (PI), anionic lipids that are abundant in native Torpedo membranes, also stabilize the receptor in the resting state although with reduced efficacy (approximately 50-60%) compared to PA, and (2) for nAChRs reconstituted into PA/CH membranes at different lipid-protein molar ratios, receptor functionality decreases rapidly below approximately 65 lipids per receptor. Collectively, these results are consistent with a functional requirement of a single shell of lipids surrounding the nAChR and specific anionic lipid- and sterol (CH)-protein interactions.
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Affiliation(s)
- Ayman K Hamouda
- Department of Pharmacology and Neuroscience, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA
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Hamouda AK, Chiara DC, Sauls D, Cohen JB, Blanton MP. Cholesterol interacts with transmembrane alpha-helices M1, M3, and M4 of the Torpedo nicotinic acetylcholine receptor: photolabeling studies using [3H]Azicholesterol. Biochemistry 2006; 45:976-86. [PMID: 16411773 PMCID: PMC2564873 DOI: 10.1021/bi051978h] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photoactivatable sterol probe [3alpha-(3)H]6-Azi-5alpha-cholestan-3beta-ol ([3H]Azicholesterol) was used to identify domains in the Torpedo californica nicotinic acetylcholine receptor (nAChR) that interact with cholesterol. [3H]Azicholesterol partitioned into nAChR-enriched membranes very efficiently (>98%), photoincorporated into nAChR subunits on an equal molar basis, and neither the pattern nor the extent of labeling was affected by the presence of the agonist carbamylcholine, consistent with photoincorporation at the nAChR lipid-protein interface. Sites of [3H]Azicholesterol incorporation in each nAChR subunit were initially mapped by Staphylococcus aureus V8 protease digestion to two relatively large homologous fragments that contain either the transmembrane segments M1-M2-M3 (e.g., alphaV8-20) or M4 (e.g., alphaV8-10). The distribution of [3H]Azicholesterol labeling between these two fragments (e.g., alphaV8-20, 29%; alphaV8-10, 71%), suggests that the M4 segment has the greatest interaction with membrane cholesterol. Photolabeled amino acid residues in each M4 segment were identified by Edman degradation of isolated tryptic fragments and generally correspond to acidic residues located at either end of each transmembrane helix (e.g., alphaAsp-407). [3H]Azicholesterol labeling was also mapped to peptides that contain either the M3 or M1 segment of each nAChR subunit. These results establish that cholesterol likely interacts with the M4, M3, and M1 segments of each subunit, and therefore, the cholesterol binding domain fully overlaps the lipid-protein interface of the nAChR.
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Affiliation(s)
- Ayman K Hamouda
- Department of Pharmacology and Neuroscience, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA
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