molecules Article Different Classes of Antidepressants Inhibit the Rat α7 Nicotinic Acetylcholine Receptor by Interacting within the Ion Channel: A Functional and Structural Study Yorley Duarte 1,2, Maximiliano Rojas 1, Jonathan Canan 1, Edwin G. Pérez 3, Fernando González-Nilo 1,2 and Jesús García-Colunga 4,* 1 Center for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Av. República 330, Santiago 8370146, Chile; [email protected] (Y.D.); [email protected] (M.R.); [email protected] (J.C.); [email protected] (F.G.-N.) 2 Interdisciplinary Centre for Neuroscience of Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2381850, Chile 3 Department of Organic Chemistry, Faculty of Chemistry and Pharmacy, Pontificia Universidad Católica de Chile, Santiago 7820436, Chile; [email protected] 4 Departamento de Neurobiología Celular y Molecular, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Campus Juriquilla, Boulevard Juriquilla 3001, Juriquilla, Querétaro 76230, Mexico * Correspondence: [email protected]; Tel.: +52-442-238-1063 Abstract: Several antidepressants inhibit nicotinic acetylcholine receptors (nAChRs) in a non- competitive and voltage-dependent fashion. Here, we asked whether antidepressants with a different structure and pharmacological profile modulate the rat α7 nAChR through a similar mechanism by Citation: Duarte, Y.; Rojas, M.; interacting within the ion-channel. We applied electrophysiological (recording of the ion current Canan, J.; Pérez, E.G.; González-Nilo, elicited by choline, ICh, which activates α7 nAChRs from rat CA1 hippocampal interneurons) and in F.; García-Colunga, J. Different silico approaches (homology modeling of the rat α7 nAChR, molecular docking, molecular dynamics Classes of Antidepressants Inhibit the simulations, and binding free energy calculations). The antidepressants inhibited I with the order: Rat α7 Nicotinic Acetylcholine Ch norfluoxetine ~ mirtazapine ~ imipramine < bupropion ~ fluoxetine ~ venlafaxine ~ escitalopram. Receptor by Interacting within the Ion Channel: A Functional and The constructed homology model of the rat α7 nAChR resulted in the extracellular vestibule and Structural Study. Molecules 2021, 26, the channel pore is highly negatively charged, which facilitates the permeation of cations and the 998. https://doi.org/10.3390/ entrance of the protonated form of antidepressants. Molecular docking and molecular dynamics molecules26040998 simulations were carried out within the ion−channel of the α7 nAChR, revealing that the antide- pressants adopt poses along the receptor channel, with slightly different binding-free energy values. Academic Editor: Clelia Dallanoce Furthermore, the inhibition of ICh and free energy values for each antidepressant-receptor complex were highly correlated. Thus, the α7 nAChR is negatively modulated by a variety of antidepressants Received: 19 January 2021 interacting in the ion−channel. Accepted: 11 February 2021 Published: 13 February 2021 Keywords: α7 nicotinic acetylcholine receptors; biological activity; hippocampus; antidepressants; in silico studies; allosteric modulators Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. 1. Introduction Cholinergic pathway dysfunctions have been associated with pathologies, such as Alzheimer’s disease, addiction, depressive disorders, and schizophrenia, among others [1–4]. With regard to depressive disorders, hyperactivation of the cholinergic pathway by nicotinic Copyright: © 2021 by the authors. acetylcholine receptor (nAChR) agonists or acetylcholinesterase inhibitors brings forward Licensee MDPI, Basel, Switzerland. depression in patients, even in adolescents [5–8]. This article is an open access article α α β β distributed under the terms and nAChRs are pentameric proteins made up of the combination of 2– 10 and 2– 4 conditions of the Creative Commons subunits, or forming homomeric receptors with a single subunit. nAChRs are non-selective + + 2+ Attribution (CC BY) license (https:// cation channels permeable to Na ,K , and Ca . The α4β2 and α7 nAChRs are the most creativecommons.org/licenses/by/ abundant subtypes in the brain [9]. Although no model is available for the complete rat α7 4.0/). nAChR, the X-ray structure of the human α4β2 nAChR has been obtained recently, as well Molecules 2021, 26, 998. https://doi.org/10.3390/molecules26040998 https://www.mdpi.com/journal/molecules Molecules 2021, 26, x FOR PEER REVIEW 2 of 15 Molecules 2021, 26, 998 rat α7 nAChR, the X-ray structure of the human α4β2 nAChR has been obtained recently,2 of 15 as well as homology models developed for the human α7 nAChR using protein structures with high sequence identity with this receptor as templates [10,11]. as homologynAChRs models are regulated developed by a forwide the variety human ofα substances,7 nAChR using including protein antidepressants. structures with In highthis sequenceregard, a identitycommon with effect this of receptor several asantidepressants templates [10, 11with]. different pharmacological profilesnAChRs (including are regulated tricyclic by antidepressants, a wide variety ofserotonin substances,-specific including reuptake antidepressants. inhibitors, and In thisatypical regard, antidepressants) a common effect is a of non several-competitive antidepressants and voltage with-dependent different pharmacologicalinhibition of nA- profilesChRs, consistent (including with tricyclic molecular antidepressants, simulations, serotonin-specific where the antidepressant reuptake- inhibitors,nAChR interac- and atypicaltion takes antidepressants) place within the is aion non-competitive channel (i.e., the and domain voltage-dependent formed by the inhibition M2 transmembrane of nAChRs, consistentsegment of with each molecular subunit) simulations,[12–18]. Furthermore, where the metabolites antidepressant-nAChR of some antidepressants interaction takes, such placeas norfluoxetine within the ion (the channel main (i.e.,metabolite the domain of fluoxetine), formed by the(R, M2S)-dehydronorketamine transmembrane segment, and of(R each,S)-norketamine subunit) [12 (ketamine–18]. Furthermore, metabolites) metabolites inhibit muscle of some and/or antidepressants, neuronal suchnAChRs as norfluoxetine[16,19]. (the main metabolite of fluoxetine), (R,S)-dehydronorketamine, and (R,S)- norketamineIt is well (ketamine documented metabolites) that the inhibitα7 nAChR muscle is a and/or target of neuronal multiple nAChRs substances [16,19 that]. in- cludeIt isselective well documented antagonists that (methyllycaconitine), the α7 nAChR is a target allosteric of multiple modulators, substances and thatanti- includedepres- selectivesants, thereby antagonists, regulating (methyllycaconitine), depressive-like behavior allosteric in modulators, different murine and anti-depressants, models [20–23]. thereby,Furthermore, regulating it is depressive-likeknown that the behavior α7 nAChR in differentis highly murine expressed models in the [20 –hippocampus,23]. Further- more,which it is is associated known that with the depression,α7 nAChR isand highly that expressedcholinergic in signaling the hippocampus, is increased which during is associatedthis condition with [6,23 depression,]. It is well and established that cholinergic over a signalinglong period is increasedof time that during the α7 this nAChR condi- is tiona target [6,23 ].of Itfluoxetine is well established, which inhibits over a longthe functioning period of time of thatthis thereceptorα7 nAChR [24]. Additionally, is a target of fluoxetine,imipramine, which bupropion, inhibits theand functioning mirtazapine of thisalso receptorinhibit rat [24 ].and/or Additionally, human imipramine,α7 nAChRs bupropion,[12,15,17], restoring and mirtazapine the cholinergic also inhibit signaling, rat and/or which human is inα agreement7 nAChRs [with12,15 the,17 ],cholinergic restoring thehypothesis cholinergic of depression signaling, which[18]. Although is in agreement several withclasses the of cholinergic antidepressants hypothesis have ofbeen depres- stud- sionied with [18]. in Although silico methods several on classes different of antidepressants nAChR subtypes have to beensupport studied the existing with in experi- silico methodsmental results on different [25], currently nAChR subtypesnone of the to antidepressants support the existing included experimental here have results been previ- [25], currentlyously studied none on of thethe antidepressantsrat α7 nAChR with included both herefunctional have been and previouslyhigh-resolution studied stru onctural the ratapproaches.α7 nAChR with both functional and high-resolution structural approaches. Thus,Thus, thethe aimsaims ofof this this work work were were (a) (a) to to study study functional functional inhibitory inhibitory effects effects of of several several antidepressantsantidepressants with with different different chemical chemical structures structures and and pharmacological pharmacological profiles profiles (Figure (Figure1) on1) raton rat hippocampal hippocampalα7 α nAChRs,7 nAChRs, (b) (b) to to build build a 3Da 3D structural structural model model of of the the rat ratα α77 nAChR nAChR byby homologyhomology modeling,modeling, and ( (c)c) to to correlate correlate both both functional functional (electrophysiological) (electrophysiological) and and in insilico silico approaches approaches (molecular (molecular docking docking and and