title: Targeting the γ-Aminobutyric Acid A Receptor α4 Subunit in Airway Smooth Muscle to Alleviate Bronchoconstriction.
abstract: We previously demonstrated that airway smooth muscle (ASM) cells express γ-aminobutyric acid A receptors (GABA(A)Rs), and that GABA(A)R agonists acutely relax ASM. Among the GABA(A)R α subunits, human ASM cells express only α4 and α5, providing the opportunity for selective pharmacologic targeting. Novel GABA(A)R-positive allosteric modulators designed for enhanced α4/α6 subunit selectivity were synthesized using iterative computational analyses (CMD-45 and XHe-III-74). Studies using oocyte heterologous expression systems confirmed that CMD-45 and XHe-III-74 led to significantly greater augmentation of currents induced by a 3% maximal effective concentration (EC3) of GABA [EC3]-induced currents in oocytes expressing α4 or α6 subunits (along with β3 and γ2) compared with other α subunits. CMD-45 and XHe-III-74 also led to greater ex vivo relaxation of contracted wild-type mouse tracheal rings compared with tracheal rings from GABA(A)R α4 subunit (Gabra4) knockout mice. Furthermore, CMD-45 and XHe-III-74 significantly relaxed precontracted human ASM ex vivo, and, at a low concentration, both ligands led to a significant leftward shift in albuterol-mediated ASM relaxation. In vivo, inhaled XHe-III-74 reduced respiratory system resistance in an asthmatic mouse model. Pretreatment of human ASM cells with CMD-45 and XHe-III-74 inhibited histamine-induced increases in intracellular calcium concentrations in vitro, an effect that was lost when calcium was omitted from the extracellular buffer, suggesting that inhibition of calcium influx due to alterations in plasma membrane potential may play a role in the mechanism of ASM relaxation. Selective targeting of the GABA(A)R α4 subunit with inhaled ligands may be a novel therapeutic pathway to treat bronchoconstriction, while avoiding sedative central nervous system effects, which are largely mediated by α1-3 subunit-containing GABA(A)Rs in the brain.
authors.affiliation: 1 Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York.
authors.forename: Gene T
authors.initials: GT
authors.lastname: Yocum
authors.affiliation: 1 Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York.
authors.forename: George
authors.initials: G
authors.lastname: Gallos
authors.affiliation: 1 Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: 2 Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; and.
authors.forename: Rajwana
authors.initials: R
authors.lastname: Jahan
authors.affiliation: 2 Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; and.
authors.forename: Michael Rajesh
authors.initials: MR
authors.lastname: Stephen
authors.affiliation: 3 Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria.
authors.forename: Zdravko
authors.initials: Z
authors.lastname: Varagic
authors.affiliation: 3 Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria.
authors.forename: Roshan
authors.identifier: http://orcid.org/0000-0002-8928-2133
authors.initials: R
authors.lastname: Puthenkalam
authors.affiliation: 3 Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria.
authors.forename: Margot
authors.identifier: http://orcid.org/0000-0002-9809-2649
authors.initials: M
authors.lastname: Ernst
authors.affiliation: 2 Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; and.
authors.forename: James M
authors.initials: JM
authors.lastname: Cook
authors.affiliation: 1 Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York.
authors.forename: Charles W
authors.initials: CW
authors.lastname: Emala
mesh_terms: D000818:Animals; D001249:Asthma / Q000378:metabolism / Q000503:physiopathology; D016084:Bronchoconstriction / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009130:Muscle, Smooth / Q000378:metabolism* / Q000503:physiopathology; D011963:Receptors, GABA-A / Q000378:metabolism*; D014132:Trachea / Q000378:metabolism* / Q000503:physiopathology; D014982:Xenopus laevis
chemical_list: D011963:Receptors, GABA-A; D002118:Calcium
keywords: CMD-45; GABAA receptor; XHe-III-74; asthma; flexiVent