biomolecules Article Clotrimazole Fluidizes Phospholipid Membranes and Localizes at the Hydrophobic Part near the Polar Part of the Membrane Alessio Ausili, Illya Yakymenko , José A. Teruel and Juan C. Gómez-Fernández * Department of Biochemistry and Molecular Biology (A), Faculty of Veterinary Science, International Campus of Excellence Mare Nostrum, Universidad de Murcia, Apartado. 4021, E-30100 Murcia, Spain; [email protected] (A.A.); [email protected] (I.Y.); [email protected] (J.A.T.) * Correspondence: [email protected] Abstract: Clotrimazole (1-[(2-chlorophenyl)-diphenylmethyl]-imidazole) is an azole antifungal drug belonging to the imidazole subclass that is widely used in pharmacology and that can be incorporated in membranes. We studied its interaction with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) phospholipid vesicles by using differential scanning calorimetry and found that the transition temperature decreases progressively as the concentration of clotrimazole increases. However, the temperature of completion of the transition remained constant despite the increase of clotrimazole concentration, suggesting the formation of fluid immiscibility. 1H-NMR and 1H NOESY MAS-NMR were employed to investigate the location of clotrimazole in 1-palmitoyl-2-oleoyl-sn-glycero-3- phosphocholine (POPC) phospholipid membranes. In the presence of clotrimazole, all the resonances Citation: Ausili, A.; Yakymenko, I.; originating from POPC were shifted upfield, but mainly those corresponding to C2 and C3 of the Teruel, J.A.; Gómez-Fernández, J.C. fatty acyl, chains suggesting that clotrimazole aromatic rings preferentially locate near these carbons. Clotrimazole Fluidizes Phospholipid In the same way, 2D-NOESY measurements showed that the highest cross-relaxation rates between Membranes and Localizes at the protons of clotrimazole and POPC were with those bound to the C2 and C3 carbons of the fatty acyl Hydrophobic Part near the Polar Part chains. Molecular dynamics simulations indicated that clotrimazole is located near the top of the of the Membrane. Biomolecules 2021, hydrocarbon-chain phase, with the nitrogen atoms of the imidazole ring of clotrimazole being closest 11, 1304. https://doi.org/10.3390/ to the polar group of the carbonyl moiety. These results are in close agreement with the NMR and biom11091304 the conclusion is that clotrimazole is located near the water–lipid interface and in the upper part of the hydrophobic bilayer. Academic Editors: Jose Manuel Lorenzo Rodriguez, Keywords: clotrimazole; model membrane; location; membrane fluidity Vito Verardo and Adrián Velázquez Campoy Received: 1 August 2021 Accepted: 30 August 2021 1. Introduction Published: 2 September 2021 Clotrimazole (1-[(2-chlorophenyl)-diphenylmethyl]-imidazole) is an azole antifun- gal drug belonging to the imidazole subclass with a molecular weight of 344.8 g/mol. Publisher’s Note: MDPI stays neutral The clotrimazole molecule consists of a quaternary carbon substituted with an imidazole with regard to jurisdictional claims in group, two phenyl rings and a phenyl ring with a chloro-substitution at the ortho-position. published maps and institutional affil- Its spatial conformation is tetrahedral (Figure1). iations. Its principal medicinal use is for the treatment of vaginal and oral candidiasis [1,2] and athlete’s foot [3], caused by Candida albicans and different fungi, respectively, although it is also used for infections caused by other fungi. Its mechanism of action involves the inhibition of Cyp51p (cytochrome P450 14alpha-demethylase), which causes the demethy- Copyright: © 2021 by the authors. lation of 14-α-lanosterol, Cyp51p. This enzyme is involved in the synthesis of ergosterol, Licensee MDPI, Basel, Switzerland. which is the major component of fungal cytoplasmic membranes. Blocking the ergosterol This article is an open access article synthesis pathway leads to the accumulation of 14-α-methylated sterols, resulting in a distributed under the terms and structural and functional defect of the membrane [4]. conditions of the Creative Commons In addition to effects on Cyp51p, an influence on Ca2+-related metabolism has been ob- Attribution (CC BY) license (https:// served. These effects include inhibition of sarcoplasmic reticulum Ca2+-ATPase (SERCA) [5], creativecommons.org/licenses/by/ gastric H+-K+-ATPase [6] and Na+-K+-ATPase [7], but it is not known if it has a specific 4.0/). Biomolecules 2021, 11, 1304. https://doi.org/10.3390/biom11091304 https://www.mdpi.com/journal/biomolecules Biomolecules 2021, 11, 1304 2 of 13 Biomolecules 2021, 11, 1304 2 of 13 binding site on these proteins, so its mechanism of action could be based on its perturbation of membrane structure and dynamics. Figure 1. Structure of clotrimazole. Protons studied by 1H-NMR are symbolised as follows, according Figure 1. Structure of clotrimazole. Protons studied by 1H-NMR are symbolised as follows, to the carbon to which they are linked: atom 4, A; atom 12, B; atom 5, C; atoms 5, 14, 18, 20 and 24, D; according to the carbon to which they are linked: atom 4, A; atom 12, B; atom 5, C; atoms 5, 14, 18, atoms 11, 15, 16, 17, 21, 22 and 23, E; atoms 9 and 10, F; atom 2, G. 20 and 24, D; atoms 11, 15, 16, 17, 21, 22 and 23, E; atoms 9 and 10, F; atom 2, G. It is also worthwhile mentioning that clotrimazole has been associated with lipid particlesIts principal for pharmacological medicinal use applications.is for the treatment Clotrimazole of vaginal is orally and administered oral candidiasis for the [1,2] and treatmentathlete’s offoot systemic [3], caused candidiasis by (pulmonaryCandida albicans and disseminated and different cryptococcosis fungi, respectively, and as- althoughpergillosis). it is also However, used becausefor infections of its adverse caused effects by other following fungi. systemic Its mechanism administration, of action involvesit is mainly the inhibition used for of the Cy treatmentp51p (cytochrome of localized P450 topical 14alpha-demethylase), candidiasis. Further, itswhich topical causes the demethylationeffectiveness seems of 14- toα be-lanosterol, strongly affected Cyp51p. by the This formulation enzyme is [8 involved,9], which in may the play synthesis a key of role in ensuring the permanence and promoting the penetration of drugs in the skin and ergosterol, which is the major component of fungal cytoplasmic membranes. Blocking the biofilm’s matrix [10]. To reach this goal, over the past few decades new topical delivery ergosterolsystems synthesis have been pathway explored [11leads,12]. to In particular,the accumulation it has recently of 14- beenα-methylated shown that lipo-sterols, resultingsomal in formulations a structural in and the formfunctional of three-dimensionally defect of the membrane structured [4]. hybrid vesicles clearly improveIn addition the cutaneous to effects delivery on Cyp51p, of clotrimazole an influence for the on treatment Ca2+-related of topical metabolism candidiasis has [13 ].been observed.Given theThese hydrophobic effects natureinclude of clotrimazoleinhibition andof sarcoplasmic its capacity to insertreticulum into membranes, Ca2+-ATPase (SERCA)it would [5], be gastric interesting H+-K to+-ATPase understand [6] its and interaction Na+-K+-ATPase with membranes [7], but and it is its not location known within if it has a specificphospholipid binding bilayers. site on Inthese this study,proteins, we used so its 1,2-dimyristoyl-sn-glycero-3-phosphocholine mechanism of action could be based on its perturbation(DMPC) and of membrane 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine structure and dynamics. (POPC) vesicles. DMPC wasIt is used also for worthwhile the differential mentioning scanning calorimetry that clotrimazole studies. Thishas phospholipidbeen associated is one with of the lipid most commonly used phospholipids for this purpose. POPC was used for the 1H-NMR particles for pharmacological applications. Clotrimazole is orally administered for the studies. POPC is widely used because it is considered a model of the most common treatmentphospholipids of systemic in animal candidiasis tissues. However, (pulmo sincenary itsand transition disseminated temperature cryptococcosis is below zero, and aspergillosis).DMPC, with However, a transition because temperature of its atadverse 23.5 ◦C, effects is preferred. following Nevertheless, systemic anadministration, important it is advantagemainly used of using for POPCthe treatment for 1H-NMR of studieslocalized is that topical the double candidiasis. bond of theFurther, oleoyl residueits topical effectivenessprovides aseems resonance to be that strongly serves asaffected a reference by the at theformulation middle of [8,9], the monolayer which may due play to the a key role protonsin ensuring related the to permanence the double bond. and Afterpromoting usingdifferential the penetration scanning of drugs calorimetry in the (DSC), skin and 1 1 biofilm’sH-NMR matrix and [10].H NOESY To reach MAS-NMR this goal, to locate over thethe clotrimazole past few decades molecule new in POPC topical vesicles, delivery systemswe determined have been that explored it could be [11,12]. mainly foundIn pa inrticular, the part it of has the hydrophobicrecently been bilayer shown that it that is close to the lipid–water interface. These results are in very good agreement with studies liposomal formulations in the form of three-dimensionally structured hybrid vesicles using molecular dynamics simulations clearly improve the cutaneous delivery of clotrimazole for the treatment of topical