Differential Regulation of Bilastine Affinity for Human Histamine H1

International Journal of Molecular Sciences Article Differential Regulation of Bilastine Affinity for Human Histamine H1 Receptors by Lys 179 and Lys 191 via Its Binding Enthalpy and Entropy Hayato Akimoto 1, Minoru Sugihara 2 and Shigeru Hishinuma 1,* 1 Department of Pharmacodynamics, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan; [email protected] 2 Pharmaceutical Education and Research Center, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan; [email protected] * Correspondence: [email protected] Abstract: Bilastine, a zwitterionic second-generation antihistamine containing a carboxyl group, has higher selectivity for H1 receptors than first-generation antihistamines. Ligand-receptor docking simulations have suggested that the electrostatic interaction between the carboxyl group of second- ECL2 5.39 generation antihistamines and the amino group of Lys179 and Lys191 of human H1 receptors might contribute to increased affinity of these antihistamines to H1 receptors. In this study, we evaluated the roles of Lys179ECL2 and Lys1915.39 in regulating the electrostatic and hydrophobic binding of bilastine to H1 receptors by thermodynamic analyses. The binding enthalpy and entropy of bilastine were estimated from the van ’t Hoff equation using the dissociation constants. These 3 constants were obtained from the displacement curves against the binding of [ H] mepyramine to membrane preparations of Chinese hamster ovary cells expressing wild-type human H1 receptors and Citation: Akimoto, H.; Sugihara, M.; their Lys179ECL2 or Lys1915.39 mutants to alanine at various temperatures. We found that the binding Hishinuma, S. Differential Regulation of bilastine to wild-type H1 receptors occurred by enthalpy-dependent binding forces and, more of Bilastine Affinity for Human dominantly, entropy-dependent binding forces. The mutation of Lys179ECL2 and Lys1915.39 to alanine Histamine H1 Receptors by Lys 179 reduced the affinity of bilastine to H receptors by reducing enthalpy- and entropy-dependent binding and Lys 191 via Its Binding Enthalpy 1 ECL2 5.39 and Entropy. Int. J. Mol. Sci. 2021, 22, forces, respectively. These results suggest that Lys179 and Lys191 differentially contribute to 1655. https://doi.org/10.3390/ijms the increased binding affinity to bilastine via electrostatic and hydrophobic binding forces. 22041655 Keywords: affinity; antihistamine; bilastine; enthalpy; entropy; histamine H1 receptor Academic Editors: Paul Chazot and Ilona Obara Received: 22 December 2020 Accepted: 5 February 2021 1. Introduction Published: 6 February 2021 It is known that Gq/11-protein-coupled H1 receptors are involved in mediating allergic and inflammatory responses in peripheral tissues and the state of arousal in the central Publisher’s Note: MDPI stays neutral nervous system [1–8]. Various first- and second-generation antihistamines have been with regard to jurisdictional claims in developed for the treatment of type I hypersensitivity, such as allergic rhinitis [9–13]. published maps and institutional affil- Some second-generation antihistamines have zwitterionic properties owing to the presence iations. of carboxyl groups, which help reduce their side effects such as sedation and impaired performance resulting from the blockade of H1 receptors in the central nervous system via their penetration into the brain through the blood–brain barrier. Bilastine (Figure1), a zwitterionic second-generation antihistamine, has non-sedative properties as well as an Copyright: © 2021 by the authors. increased selectivity for H1 receptors than first-generation antihistamines [13–19]. Licensee MDPI, Basel, Switzerland. 3.32 The human H1 receptor possesses Asp107 (superscripts indicate Ballesteros-Weinstein This article is an open access article numbering [20]), a highly conserved amino acid in aminergic G protein-coupled receptors, distributed under the terms and deep in the ligand-binding pocket, whereas Lys179ECL2 and Lys1915.39, located at the conditions of the Creative Commons entrance of the ligand-binding pocket, are anion-binding sites unique to the H1 receptor Attribution (CC BY) license (https:// (Figure2a) [ 21]. Ligand-receptor docking simulations based on the crystal structure of creativecommons.org/licenses/by/ 4.0/). human H1 receptor indicated that the carboxyl group of second-generation antihistamines, Int. J. Mol. Sci. 2021, 22, 1655. https://doi.org/10.3390/ijms22041655 https://www.mdpi.com/journal/ijms Int. J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 2 of 8 COO– Int. J. Mol. Sci. 2021, 22, 1655 2 of 8 N + such as olopatadine,N levocetirizine, fexofenadine, and acrivastine, appeared to form a salt bridgeN with Lys179ECL2 and/or Lys1915.39. This bridge might have contributed to the increased selectivity of carboxylated second-generation antihistamines for H1 receptors [21]. Int. J. Mol. Sci. 2021, 22, x FOR PEER REVIEW ECL2 2 5.39of 8 Accordingly,O the electrostatic interaction of bilastine with Lys179 and/or Lys191 may be important in the determination of its binding affinity for H1 receptors. Figure 1. Chemical structure of bilastine. Bilastine is a zwitterionic second-generation antihistamine containing a carboxyl group that contributes to itsCOO non-sedative– properties as well as an increased selectivity for H1 receptors. The human H1 receptor possesses Asp1073.32 (superscripts indicate Ballesteros-Wein- N stein numbering [20]), a highly+ conserved amino acid in aminergic G protein-coupled receptors, deep in the ligand-bindingN pocket, whereas Lys179ECL2 and Lys1915.39, located at N the entrance of the ligand-binding pocket, are anion-binding sites unique to the H1 receptor (Figure 2a) [21]. Ligand-receptor docking simulations based on the crystal structure of human H1 receptor indicatedO that the carboxyl group of second-generation antihistamines, such as olopatadine, levocetirizine, fexofenadine, and acrivastine, appeared to form a salt bridge with Lys179ECL2 and/or Lys1915.39. This bridge might have contributed FigureFigure 1.1. ChemicalChemical structurestructure ofof bilastine.bilastine. BilastineBilastine is is a a zwitterionic zwitterionic second-generation second-generation antihistamine antihista- to the increased selectivity of carboxylated second-generation antihistamines for H1 re- containingmine containing a carboxyl a carboxyl group group that contributes that contributes to its non-sedativeto its non-sedative properties properties as well as aswell an as increased an in- ECL2 ceptorscreased [21]. selectivityAccordingly, for H the1 receptors. electrostatic interaction of bilastine with Lys179 and/or selectivity for H1 receptors. Lys1915.39 may be important in the determination of its binding affinity for H1 receptors. The human H1 receptor possesses Asp1073.32 (superscripts indicate Ballesteros-Wein- stein numbering(a [20]),) a highly conserved amino acid in aminergic(b) G protein-coupled receptors, deep in the ligand-binding pocket, whereas Lys179ECL2 and Lys1915.39, located at Bilastine Lys179ECL2 the entrance of the ligand-binding pocket, are anion-binding sites unique to the H1 recep- 5.39 tor (Figure 2a) [21]. Ligand-receptor docking simulations based on theLys191 crystal structure of ∆G˚(<0) = ∆H˚-T∆S˚ human H1 receptor indicated that the carboxyl group of second-generation antihista- = RTlnK mines,NH2 such as olopatadine,d levocetirizine, fexofenadine, and 4.3Åacrivastine, appeared to ECL2 form a salt bridge withLys179 Lys179ECL2 and/or Lys1915.39. This 3.6Åbridge might have contributed 5.39 to the increased selectivityLys191 of carboxylated second-generation antihistamines for H1 receptors [21]. Accordingly,Asp107 the 3.32electrostatic interaction of bilastine with Lys179ECL2 and/or 3.4Å Lys1915.39 may be important in the determination of its binding affinity for H1 receptors. Bilastine (a) Asp1073.32 (b) COOH Histamine H1 ReceptorBilastine Lys179ECL2 Lys191 5.39 FigureFigure 2. A schematic 2. A schematic structure∆ structureG˚(<0) of human = of∆H human˚- HT1∆ receptorS˚ H1 receptor (a) and (a )docking and docking simulation simulation on the on binding the binding of of bilastine to human H1 receptor (b).= (RTa) lnA Kschematic structure of human H1 receptor is shown bilastine toNH human2 H1 receptor (b). (a) Ad schematic structure of human H1 receptor4.3Å is shown and indi- and indicates that Asp1073.323.32 is a highly conservedECL2 amino acid in the aminergic G-protein-coupled cates that Asp107 is a highly conservedLys179 amino acid in the aminergic G-protein-coupled3.6Å receptors, receptors, and Lys179ECL2 ECL2 and Lys1915.39 5.39 are anion-binding sites unique to the H1 receptor. Ligand- and Lys179 and Lys191 areLys191 anion-binding5.39 sites unique to the H1 receptor. Ligand-receptor receptor interaction is also shown to demonstrate that the binding affinity for ligands (Kd) is deter- interaction is also shown to demonstrate that the binding affinity for ligands (K ) is determined by mined by their thermodynamic bindingAsp107 forces3.32 (∆G° = ∆H° − T∆S° = RTlnKd). (b) Dockingd simula- their thermodynamic binding forces (DG◦ = DH◦ − TDS◦ = RTlnK3.4Åd). (b) Docking simulation was tion was performed to reveal the final position of bilastine binding to human H1 receptor as de- scribedperformed in the materials to reveal and the methods final position section. of The bilastine amino binding group toof humanbilastine H appeared1 receptor to as interact describedBilastine in the 3.32 3.32 with Asp107materials3.32, andand methodsthe carboxyl

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