domain: sdv.sp chim sdv

text:
Zahraa Hammoud

Nathalie Khreich

Lizette Auezova

Sophie Fourmentin

Abdelhamid Elaissari

Hélène Greige-Gerges
email: greigegeorges@yahoo.com

Cyclodextrin-membrane interaction in drug delivery and membrane structure maintenance

Keywords: cholesterol, cyclodextrin, liposome, membrane, phospholipid

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Introduction

Liposomes are phospholipid (PL) vesicles containing one or more lipid bilayers and an aqueous internal cavity. They can encapsulate hydrophilic and hydrophobic drugs in their aqueous core and lipid bilayer, respectively, constituting an effective drug delivery system [START_REF] Gharib | Liposomes incorporating cyclodextrin-drug inclusion complexes: Current state of knowledge[END_REF]. Another drug delivery system is based on cyclodextrins (CDs), oligosaccharides formed of glucopyranose units. CDs have a truncated funnel shape with a hydrophobic internal cavity and a hydrophilic outer surface [START_REF] Gharib | Liposomes incorporating cyclodextrin-drug inclusion complexes: Current state of knowledge[END_REF]. Thus, CDs can entrap hydrophobic drugs in their cavities forming CD/drug inclusion complexes that improve drug solubility and bioavailability, enhance physical and thermal stability of drugs, and limit drug toxic effects [START_REF] Baek | Enhanced transdermal drug delivery of zaltoprofen using a novel formulation[END_REF][START_REF] Loftsson | Cyclodextrins in topical drug formulations: theory and practice[END_REF][START_REF] Zhang | Synthesis and evaluation of a novel β-cyclodextrin derivative for oral insulin delivery and absorption[END_REF].

Drug-in-CD-in-liposome (DCL), a combined system made of CD and liposome, was proposed by [START_REF] Mccormack | Drugs-in-cyclodextrins-in liposomes: a novel concept in drug delivery[END_REF] to increase loading rates of hydrophobic molecules and to provide their prolonged release compared to conventional liposomes and CD/drug inclusion complexes. In DCL, hydrophobic drugs are loaded into the aqueous phase of liposome in the form of CD/drug inclusion complex.

CDs boost drug delivery by interacting with membrane components [START_REF] Babu | Effect of cyclodextrins on the complexation and transdermal delivery of bupranolol through rat skin[END_REF][START_REF] Mura | Development of liposomal and microemulsion formulations for transdermal delivery of clonazepam: effect of randomly methylated β-cyclodextrin[END_REF][START_REF] Nakanishi | Effect of cyclodextrins on biological membrane. II. Mechanism of enhancement on the intestinal absorption of non-absorbable drug by cyclodextrins[END_REF][START_REF] Tilloy | Methylated beta-cyclodextrin as Pgp modulators for deliverance of doxorubicin across an in vitro model of blood-brain barrier[END_REF][START_REF] Ventura | Biomembrane model interaction and percutaneous absorption of papaverine through rat skin: effects of cyclodextrins as penetration enhancers[END_REF]. This interaction may induce a perturbation in the lipid bilayer affecting the membrane properties such as fluidity (Gharib et al., 2018a;[START_REF] Grammenos | ESR technique for noninvasive way to quantify cyclodextrins effect on cell membranes[END_REF] and permeability [START_REF] Piel | Study of the relationship between lipid binding properties of cyclodextrins and their effect on the integrity of liposomes[END_REF][START_REF] Wang | Evaluation of cholesterol depletion as a marker of nephrotoxicity in vitro for novel β-cyclodextrin derivatives[END_REF]. A deep understanding of CD interaction with biomimetic, i.e. liposomal, and biological membranes is crucial in pharmacology for controlling CD-mediated drug delivery and release.

Freeze-drying of liposomes is essential to extend their shelf life (Gharib et al., 2018b). Also, sperm cryopreservation has been extensively applied in artificial insemination programs [START_REF] Mocé | Use of cholesterol in sperm cryopreservation: present moment and perspectives to future[END_REF]. However, the freezing process can cause membrane damage [START_REF] Drobnis | Cold shock damage is due to lipid phase transitions in cell membranes: A demonstration using sperm as a model[END_REF]; therefore, suitable cryoprotectants should be added. CDs are able to form hydrogen bonds with polar groups of membrane lipids, thereby stabilizing the ordered conformation of liposomes and spermatozoa during freeze-drying. Furthermore, CD/cholesterol inclusion complexes serve as cholesterol (Chol) donors to load membranes with Chol for membrane stabilization. Consequently, free CDs (Gharib et al., 2018b;[START_REF] Madison | The Effect of 2-Hydroxypropyl-β-Cyclodextrin on Post-Thaw Parameters of Cryopreserved Jack and Stallion Semen[END_REF][START_REF] Zeng | Freezability of boar spermatozoa is improved by exposure to 2-hydroxypropyl-betacyclodextrin[END_REF] and Chol-loaded CDs [START_REF] Salmon | Cholesterol-Loaded Cyclodextrin Increases the Cholesterol Content of Goat Sperm to Improve Cold and Osmotic Resistance and Maintain Sperm Function after Cryopreservation1[END_REF] are capable to maintain the integrity of a membrane during freeze-drying, thereby ensuring its protection.

To the best of our knowledge, this is the first review that focuses on CD interaction with biomimetic and biological membranes considering the factors that may affect this interaction such as the type and concentration of CD as well as the membrane structure and composition.

The main techniques applied to study the CD-membrane interaction are introduced, and the literature data are resumed into conclusive tables. Furthermore, the literature data on CDmediated extraction of membrane components (PLs, Chol, and proteins) are discussed. We also summarize the effects of CDs on the membrane properties such as permeability, fluidity, and stability. In addition, an overview of the beneficial effects of CDs as membrane cryoprotectants is presented. The last section of this review discusses recent data on DCLs development.

Biological membranes

Membrane structure based on fluid mosaic model

The fluid mosaic model of cell membranes is a fundamental concept in membrane biology.

According to this model, the basic structure of a biological membrane is a lipid bilayer associated with proteins, often glycosylated [START_REF] Singer | THE FLUID MOSAIC MODEL OF THE STRUCTURE OF CELL MEMBRANES Reprinted with permission from Science[END_REF]. The variety of lipids and proteins experience both rotational and translational freedom within the bilayer plane and are asymmetrically distributed between the membrane leaflets [START_REF] Holthuis | Lipid traffic: floppy drives and a superhighway[END_REF].

Membrane composition 1.2.1. Phospholipids and sphingolipids

PLs are amphiphilic molecules comprising a glycerol backbone esterified at first and second positions with two fatty acids; the third alcohol of glycerol is esterified by a phosphoric acid which, in turn, is esterified by a polar group such as choline, ethanolamine, glycerol, inositol, or serine. The membrane surface charge depends on the polar head groups of PLs and sphingolipids constituting the membrane. The PLs phosphatidylcholine (PC) and phosphatidylethanolamine (PE) containing, respectively, positively charged groups choline and ethanolamine, are neutral. On the contrary, when the polar group is zwitterionic (serine) or nonionizable (glycerol, hydrogen, or inositol), the resulting PL is negatively charged. Furthermore, the fatty acids which esterify the primary and secondary alcohols of glycerol vary in their length and degree of saturation [START_REF] Li | A review on phospholipids and their main applications in drug delivery systems[END_REF]. Like PLs, sphingolipids are composed of a polar head group and a nonpolar moiety, which is a fatty acid linked to a long-chain amino alcohol, sphingosine. They include sphingomyelins (SM) and glycosphingolipids: cerebrosides, sulfatides, globosides, and gangliosides. Gangliosides and sulfatides are negatively charged due to the presence of sialic acid and sulfate groups, respectively, contributing to the global membrane charge. Sphingolipids have generally much more saturated hydrocarbon chains than PLs allowing them to be packed tightly together [START_REF] Brown | Structure and Function of Sphingolipid-and Cholesterol-rich Membrane Rafts[END_REF].

The structure of a lipid influences its geometry and membrane curvature. Thus, PC and SM both possess a cylindrical shape based on the head-to-tail ratio (the same head and tail cross sectional areas) resulting in a lamella (bilayer) when mixed in an aqueous medium. However, lysophosphatidylcholine (LPC) and phosphatidylinositol (PI) are of inverted conical shape (higher head-to-tail ratio) and form micelles in an aqueous environment. Conversely, PE, phosphatidic acid (PA), and phosphatidylserine (PS), containing relatively small head groups, are cone-shaped lipids which adopt in water an inverted micellar structure. The fact that biological membranes have a lamellar structure explains the choice of PC for the preparation of biomimetic lipid bilayers.

As mentioned earlier, membrane components are asymmetrically distributed between the inner and outer leaflets of membrane. In general, the inner leaflet is rich in PLs containing amine or serine moieties and the signaling lipids such as PI and PA, whereas PC and SM are densely located in the outer leaflet [START_REF] Zalba | Cell membrane modulation as adjuvant in cancer therapy[END_REF].

Cholesterol

Cellular membranes contain up to 40 % sterols (Chol in mammals) in relation to the total membrane lipids. Chol has a four-ring nucleus with a double bond between C-5 and C-6, an iso-octyl side chain at C-17, two methyl groups at C-18 and C-19, and a hydroxyl group at C-3.

Its hydroxyl group is oriented toward the aqueous phase while the hydrophobic moiety is located alongside PL acyl chains. Chol plays an essential role in controlling membrane fluidity, permeability, receptors function, and ion transport [START_REF] Burger | Regulation of receptor function by cholesterol[END_REF][START_REF] Cooper | Influence of increased membrane cholesterol on membrane fluidity and cell function in human red blood cells[END_REF][START_REF] Kabouridis | Cholesterol depletion disrupts lipid rafts and modulates the activity of multiple signaling pathways in T lymphocytes[END_REF][START_REF] Simons | Lipid rafts and signal transduction[END_REF].

Proteins

Membrane proteins are classified into integral (or intrinsic) and peripheral (or extrinsic). Integral proteins intercalate into the membrane hydrophobic matrix where they are tightly bound by hydrophobic interactions. Integral proteins are also suggested to be amphipathic with their hydrophobic domains embedded in the hydrophobic interior and their hydrophilic domains protruding from the hydrophobic region of the lipid bilayer into the surrounding aqueous environments. Peripheral proteins are loosely bound to hydrophilic parts of membranes by electrostatic and other non-hydrophobic interactions [START_REF] Nicolson | The Fluid-Mosaic Model of Membrane Structure: Still relevant to understanding the structure, function and dynamics of biological membranes after more than 40years[END_REF].

Lipid rafts

Lipids are not only asymmetrically distributed between the membrane leaflets but also heterogeneously dispersed within a single layer. Cellular membranes contain highly ordered stable structures called "lipid rafts" surrounded by a liquid disordered matrix. Lipid rafts are small-sized domains rich in sphingolipids and Chol, closely packed, functional, and dynamic.

They are resistant to solubilization by mild detergents [START_REF] Brown | FUNCTIONS OF LIPID RAFTS IN BIOLOGICAL MEMBRANES[END_REF][START_REF] Simons | Functional rafts in cell membranes[END_REF]. Also, rafts contain a specific group of membrane proteins linked to saturated acyl chains either using glycosylphosphatidylinositol (GPI) anchor or through acylation with myristate or palmitate [START_REF] Brown | FUNCTIONS OF LIPID RAFTS IN BIOLOGICAL MEMBRANES[END_REF]. Lipid rafts were proved to be implicated in many cellular processes such as sorting of lipids and proteins [START_REF] Mcintosh | Sorting of Lipids and Transmembrane Peptides Between Detergent-Soluble Bilayers and Detergent-Resistant Rafts[END_REF], signal transduction and trafficking [START_REF] Hanzal-Bayer | Lipid rafts and membrane traffic[END_REF][START_REF] Stauffer | Compartmentalized IgE Receptor-mediated Signal Transduction in Living Cells[END_REF], and transmission of viral and bacterial infections [START_REF] Wang | Lipid rafts play an important role in the vesicular stomatitis virus life cycle[END_REF].

Biomimetic membranes

Due to the complex organization of biological membranes, simple biomimetic membranes are used as models. In the case of CD-membrane interaction studies, lipid monolayers and liposomes are utilized [START_REF] Grauby-Heywang | Study of the interaction of beta-cyclodextrin with phospholipid monolayers by surface pressure measurements and fluorescence microscopy[END_REF][START_REF] Milles | Organization of fluorescent cholesterol analogs in lipid bilayers -lessons from cyclodextrin extraction[END_REF][START_REF] Ohvo-Rekilä | Cyclodextrin-catalyzed extraction of fluorescent sterols from monolayer membranes and small unilamellar vesicles[END_REF].

Lipid monolayers

Lipid monolayers, also referred as Langmuir monolayers, are formed by spreading amphiphilic molecules at the surface of a liquid; they consist of a single lipid type or a mixture of lipids. This system displays many advantages in comparison with other biomimetic membranes allowing control of parameters such as temperature, nature and packing of lipids, and compositions of the liquid medium (pH, ionic strength) (Maget-Dana, 1999).

Liposomes

Liposomes are spherical self-closed structures where a lipid bilayer encloses an aqueous inner cavity. Liposomes are mainly prepared from PLs, with or without Chol. They are generally classified according to their size and number of bilayers. Small unilamellar vesicles (SUV) range between 20 and 100 nm while large unilamellar vesicles (LUV) are greater than 100 nm, and giant unilamellar vesicles (GUV) exceed 1000 nm; all these types having a single lamella.

Multilamellar vesicles (MLV) are large vesicles (> 0.5 µm) possessing more than 5 concentric lamellae [START_REF] Gharib | Liposomes incorporating cyclodextrin-drug inclusion complexes: Current state of knowledge[END_REF].

Liposomes are biocompatible, biodegradable, non-immunogenic, and non-toxic structures. All these characteristics make them suitable for drug delivery. Hydrophobic and hydrophilic substances can be entrapped, respectively, within the lipid bilayer and the aqueous internal cavity, and amphiphilic molecules are located at the water-bilayer interface (Figure 1). These properties make liposomes effective as carriers of bioactive molecules in cosmetic, pharmaceutical, food, and farming industries [START_REF] Sherry | Essential oils encapsulated in liposomes: a review[END_REF].

Membrane fluidity

The fluidity of a membrane is one of its important properties; it strongly depends on the temperature and the membrane composition, in particular the presence of Chol and its content.

Depending on the temperature, a lipid bilayer can adopt distinct physical states (Figure 2) which are characterized by different lateral organization, molecular order, and mobility of lipids constituting the bilayer (Eeman and Deleu, 2010). At low temperatures, the lamellar gel phase (also called 'solid ordered' (So) phase) is formed where the hydrocarbon chains are elongated to the maximum in all-trans configuration. Upon temperature elevation, a lipid bilayer demonstrates structural changes called 'thermotropic transitions': the pre-transition in which the lipid bilayer passes from the lamellar gel phase to the rippled gel phase, and the main transition which represents the transition from the rippled gel phase to the 'liquid disordered' (Ld) phase.

Ld phase is characterized by the presence of numerous gauche conformers along the acyl chains; therefore, it shows a great increase in membrane fluidity and molecular disorder compared to the rippled gel phase [START_REF] Abboud | Biophysical methods: Complementary tools to study the influence of human steroid hormones on the liposome membrane properties[END_REF].

In the presence of Chol, a lipid bilayer can acquire a new phase, called 'liquid ordered' (Lo) phase. In this case, the acyl chains have intermediate properties between those of So and Ld phases. [START_REF] Vist | Phase equilibria of cholesterol/dipalmitoylphosphatidylcholine mixtures: deuterium nuclear magnetic resonance and differential scanning calorimetry[END_REF] presented the dynamic of DPPC membrane at various temperatures and Chol levels. The authors showed that for intermediate membrane content of Chol (7-30 %), the So phase coexists with the Lo phase below the transition temperature.

Above the transition temperature, the Lo phase coexists with the Ld phase. Beyond 30 mol % membrane Chol content and whatever the temperature, the Lo phase is reached.

Figure 2: The different physical states of a lipid bilayer in an aqueous environment. At low temperature, the solid ordered phase exists. At pre-transition temperature (Tp), a lipid bilayer passes from the solid ordered phase to the rippled phase (left). At main transition temperature (Tm), a lipid bilayer passes to the liquid disordered phase (down). Adding Chol (green) to a lipid bilayer induces the formation of the liquid ordered phase (right).

Membrane fluidity is also influenced by the membrane PL composition. First, the nature of polar head group affects the membrane lateral organization; membrane lipids with small polar heads allow a more compact lipid assembly due to a reduced steric hindrance (Eeman and Deleu, 2010). Additionally, saturation status of acyl chains strongly affects the membrane lateral organization; namely, saturated lipids have straight tails, thus promoting their tight packing.

However, the cis double bonds of unsaturated lipids prohibit their tight packing through steric hindrance resulting in a more fluid membrane. In addition, membrane fluidity depends on the length of the acyl chains; longer alkyl chains are easily held together via Van der Walls and hydrophobic interactions in comparison to those with shorter ones [START_REF] Zalba | Cell membrane modulation as adjuvant in cancer therapy[END_REF].

Cyclodextrins

Structure

Cyclodextrins (CDs) are non-toxic cyclic oligosaccharides formed of α-1,4-linked Dglucopyranose units. They are obtained from starch by means of enzymatic degradation. Due to the 4 C1 chair conformation of glucopyranose, CDs have a bottomless bowl shape (truncated cone) of various sizes according to the number of glucose units. The most common native CDs are formed of 6 (α-CD), 7 (β-CD), or 8 (γ-CD) glucose subunits, with a respective cavity size of approximately 0.5, 0.6, and 0.8 nm (Figure 3) [START_REF] Gharib | Liposomes incorporating cyclodextrin-drug inclusion complexes: Current state of knowledge[END_REF]. Based on X-ray studies, CDs dispose their hydroxyl functional groups to the cone exterior extending the primary hydroxyl group (C6) of glucopyranose from the narrow edge of the ring and the secondary hydroxyl groups (C2 and C3) from the wider edge as shown in Figure 4 (Del [START_REF] Valle | Cyclodextrins and their uses: a review[END_REF]. This arrangement provides CD a hydrophilic outer surface, whereas the interior cavity is hydrophobic.

Derivatives

Natural CDs, especially β-CD, have limited solubility in water because of their relatively strong intermolecular hydrogen bonding in the crystal state. The aqueous solubility of CDs determined at 25 ºC is 0.1211, 0.0163, and 0.1680 mol/L for α-CD, β-CD, and γ-CD, respectively [START_REF] Connors | The Stability of Cyclodextrin Complexes in Solution[END_REF]. Chemical modifications such as amination, etherification, methylation, and esterification of the primary and secondary hydroxyl groups are applied to synthesize various hydrophobic, hydrophilic, and ionic CD derivatives with an improved aqueous solubility compared to the native CDs [START_REF] Gharib | Liposomes incorporating cyclodextrin-drug inclusion complexes: Current state of knowledge[END_REF].

In addition to the native CDs, various CD derivatives have been used to study their interaction with membranes. They include the hydroxypropyl derivatives (HP-α-CD, HP-β-CD, and HP-γ-CD), maltosylated derivatives (G2-α-CD and G2-β-CD), sulfobutylether-β-CD (SBE-β-CD), carboxyethylated-γ-CD (CE-γ-CD), and the methylated derivatives (Me-α-CD, DM-α-CD, Me-β-CD, dimeb, trimeb, Me-γ-CD). The latters also include the randomly methylated β-CD derivatives (rameb) and the partially methylated crystallized-β-CD (crysmeb). Recently, interest in multi-substituted-β-CDs such as hydroxypropyl-sulfobutyl-ether-β-cyclodextrin (HPn-SBEm-β-CD), which is substituted by hydroxypropyl and sulfobutyl groups: n-(2,3,6-O-2-hydroxypropyl)m- [START_REF] Wang | A comparison between conventional liposome and drug-cyclodextrin complex in liposome system[END_REF]3,6-O-sulfobutyl)-β-CD has emerged. Two HPn-SBEm-β-CDs (HP2-SBE3-β-CD and HP3-SBE2-β-CD) were evaluated for their effects on biological membranes [START_REF] Wang | Evaluation of cholesterol depletion as a marker of nephrotoxicity in vitro for novel β-cyclodextrin derivatives[END_REF].

Cyclodextrins used as drug delivery enhancers

CDs are able to entrap hydrophobic drugs in their cavities forming CD/drug inclusion complexes. As a result, CDs favor drug dissolution in the aqueous phase, making them suitable to diffuse in an aqueous medium, to come in contact with membrane surface, and to permeate through membrane. Moreover, encapsulation in CD protects the drug from chemical and enzymatic degradation [START_REF] Babu | Effect of cyclodextrins on the complexation and transdermal delivery of bupranolol through rat skin[END_REF][START_REF] Rong | Hydroxypropyl-sulfobutyl-β-cyclodextrin improves the oral bioavailability of edaravone by modulating drug efflux pump of enterocytes[END_REF][START_REF] Rosa Teixeira | Ultrastructural changes in bacterial membranes induced by nano-assemblies β-cyclodextrin chlorhexidine: SEM, AFM, and TEM evaluation[END_REF].

Drug-in-cyclodextrin-in-liposome

Van der Waal forces, hydrogen bonds, and hydrophobic interactions are involved in the CD/drug inclusion complex formation [START_REF] Gidwani | A Comprehensive Review on Cyclodextrin-Based Carriers for Delivery of Chemotherapeutic Cytotoxic Anticancer Drugs[END_REF]. Therefore, the inclusion complex will rapidly dissociate following intravenous administration where blood components may displace the encapsulated drug. As for liposomes, highly lipophilic drugs incorporated in the liposomal PL bilayer would be also rapidly released after intravenous and transdermal administration [START_REF] Kirby | The effect of lipid composition of small unilamellar liposomes containing melphalan and vincristine on drug clearance after injection into mice[END_REF][START_REF] Maestrelli | Preparation and characterisation of liposomes encapsulating ketoprofen-cyclodextrin complexes for transdermal drug delivery[END_REF][START_REF] Takino | Long Circulating Emulsion Carrier Systems for Highly Lipophilic Drugs[END_REF]. To ensure a stable encapsulation of hydrophobic drugs, an approach has been proposed [START_REF] Mccormack | Drugs-in-cyclodextrins-in liposomes: a novel concept in drug delivery[END_REF] where the drugs are encapsulated in the aqueous phase of liposomes in the form of CD/drug inclusion complexes. This approach combines the relative advantages of both carriers in a single "drug-in-CD-in-liposome" (DCL) system. Indeed, the entrapment of a water-soluble CD/drug inclusion complex into liposomes would allow accommodation of insoluble drugs in the aqueous phase of vesicles (Figure 5) [START_REF] Gharib | Drug-in-cyclodextrin-in-liposomes as a carrier system for volatile essential oil components: Application to anethole[END_REF].

Figure 5: Schematic representation of drug-in-cyclodextrin-in-liposome system composed of lipid bilayer and an aqueous inner cavity. The drug in the form of CD/drug inclusion complex is loaded in the aqueous phase.

Cyclodextrin-lipid membrane interaction

The interaction of native and modified CDs with fatty acids, Chol and PLs was recently reviewed by [START_REF] Szente | Cyclodextrin-Lipid Complexes: Cavity Size Matters[END_REF]. In the sections below, we will focus, in particular, on the interaction between CDs and both biomimetic and biological membranes, with respect to the composition of biomimetic membrane, the type of biological membrane, the lipid to CD molar ratio, as well as the CD type and concentration.

The effect of cyclodextrins on membrane fluidity

The effect of CDs on the fluidity and stability of liposome membranes and biological systems (stratum corneum and colon carcinoma cells) was evaluated using differential scanning calorimetry (DSC), fluorescence anisotropy, and electron spin resonance (ESR) techniques.

DSC is used in lipid membrane research to study the thermal behavior of lipid bilayers in the presence of active agents, i.e. CDs. The thermodynamic parameters such as pre-transition temperature (Tp), main transition temperature (Tm), main transition enthalpy (∆Hm), and temperature width at half peak height (∆T1/2) can be determined using DSC [START_REF] Demetzos | Differential Scanning Calorimetry (DSC): A Tool to Study the Thermal Behavior of Lipid Bilayers and Liposomal Stability[END_REF].

Tp is represented by a flat endothermic peak and its disappearance reflects drug interaction with the polar head groups of PLs. Tm is a sharp endotherm represented by the apex of the peak [START_REF] Demetzos | Differential Scanning Calorimetry (DSC): A Tool to Study the Thermal Behavior of Lipid Bilayers and Liposomal Stability[END_REF]Gharib et al., 2018a). ∆Hm is the heat required for the entire transition; it is calculated from the area under the main transition peak. The decrease in ∆Hm suggests an increase in the membrane fluidity and disorder (increase in the number of acyl chains in the gauche conformation) while its increase reflects an interaction of the drug with the upper glycerol head group region of the lipid bilayer. Furthermore, ∆T1/2 reflects the cooperativity of the transition, being inversely proportional to it. It is very sensitive to the presence of additives (Gharib et al., 2018a).

Most studies in the literature evaluated the effect of CDs on DPPC liposome membrane. The latter, in the absence of CD, displayed a pre-transition at approximately 35 ºC and a main transition at around 41 ºC (Gharib et al., 2018a). The interaction of CDs with liposomal membranes induced alterations in the membrane calorimetric parameters. Table 1 summarizes the literature data on the DSC results obtained with CD-loaded liposomes, showing the liposomal membrane composition, CD type and concentration as well as lipid:CD molar ratio.

As can be seen from Table 1, CDs influence the membrane fluidity.

Table 1: The effect of cyclodextrins on the thermotropic parameters of the liposome membranes determined by DSC

[CD]: Cyclodextrin concentration, Chol: cholesterol, DMPC: dimyristoyl phosphatidylcholine; DPPC: dipalmitoyl phosphatidylcholine, NI: not indicated. Indeed, β-CD [START_REF] Castelli | Differential Scanning Calorimetry Evidence of the Enhancement of β-Sitosterol Absorption across Biological Membranes Mediated by β-Cyclodextrins[END_REF] and HP-β-CD (Gharib et al., 2018a) the pre-transition peak was abolished -Tm was increased as a function of

[CD] an increase in ∆Hm at low molar ratios (100:181 and 100:454) but it was decreased at high ratios (100:909 and 100:1363) -∆T1/2 was increased.

Gharib et al., 2018a

reported that dimeb, β-CD, trimeb [START_REF] Puglisi | Interaction of Natural and Modified β-Cyclodextrins with a Biological Membrane Model of Dipalmitoylphosphatidylcholine[END_REF], and HP-β-CD (Gharib et al., 2018a) increased the Tm of DPPC membranes as a function of lipid:CD molar ratio (Figure 6). In addition, β-CD, at a concentration of 167 mM, increased the Tm of DMPC liposome membrane [START_REF] Castelli | Differential Scanning Calorimetry Evidence of the Enhancement of β-Sitosterol Absorption across Biological Membranes Mediated by β-Cyclodextrins[END_REF]. Thus, CDs appear to stabilize the liposome lipid bilayer by hydrogen bonding to polar lipids. In contrast, [START_REF] Nishijo | Interactions of cyclodextrins with DPPC liposomes. Differential scanning calorimetry studies[END_REF] showed that the Tm value of DPPC membrane was reduced in the presence of trimeb, while β-CD, γ-CD, and HP-β-CD barely influenced the Tm of this membrane model. The authors suggested that CDs exhibit a membrane fluidizing effect and may extract PLs from the membrane. On the other side, Liossi et al ( 2017) showed a lowering effect of HP-β-CD towards DPPC membrane. The ∆Hm of DPPC membrane was significantly decreased in the presence of α-CD [START_REF] Nishijo | Interactions of cyclodextrins with DPPC liposomes. Differential scanning calorimetry studies[END_REF], dimeb [START_REF] Nishijo | Interactions of cyclodextrins with DPPC liposomes. Differential scanning calorimetry studies[END_REF][START_REF] Puglisi | Interaction of Natural and Modified β-Cyclodextrins with a Biological Membrane Model of Dipalmitoylphosphatidylcholine[END_REF], or HP-β-CD [START_REF] Liossi | Exploring the interactions of irbesartan and irbesartan-2-hydroxypropyl-β-cyclodextrin complex with model membranes[END_REF] suggesting an increase in the membrane fluidity and disorder. Conversely, Gharib et al. (2018a) demonstrated an increase in ΔHm of DPPC liposome at low HP-ß-CD molar fraction (1.81 and 4.54); an HP-β-CD interaction with the upper chain/glycerol/head group region of the lipid bilayer was proposed. However, at higher molar fraction (9.09 and 13.63), HP-ß-CD exerted a lowering effect on the ΔHm; HP-β-CD was suggested to interact with the hydrophobic core of the lipid bilayer leading to perturbation of DPPC packing order. Furthermore, adding Chol appears to modulate the effect of CDs on DPPC membranes. Thus, β-CD and trimeb increased the ∆Hm of DPPC:Chol (90:10) membrane at all the studied lipid to CD molar ratios. Whereas the effect of dimeb differed depending on its molar fraction; the ∆Hm increased to its maximal value (4.94 ± 0.18 kcal/mol) at lipid:CD molar ratio of 1:7; however, a further increase in its molar fraction (1:32) led to a decrease in ∆Hm (2.88 ± 0.31 kcal/mol). According to the authors, dimeb is able to extract both DPPC and Chol at higher CD molar fraction [START_REF] Puglisi | Interaction of Natural and Modified β-Cyclodextrins with a Biological Membrane Model of Dipalmitoylphosphatidylcholine[END_REF].

Few studies have determined the effect of CD on the cooperativity of transition. The presence of dimeb, trimeb [START_REF] Puglisi | Interaction of Natural and Modified β-Cyclodextrins with a Biological Membrane Model of Dipalmitoylphosphatidylcholine[END_REF], or HP-β-CD (Gharib et al., 2018a) induced an increase in the ∆T1/2 of DPPC vesicles. This could be explained by the interaction between CD and the hydrophobic region of DPPC bilayer which causes membrane disruption (Gharib et al., 2018a). The anisotropy value is known to be inversely proportional to the membrane fluidity. To our knowledge, the study of Gharib et al. (2018a) is the only one using fluorescence anisotropy to evaluate the CD effect on the membrane fluidity. The authors used 1,6-diphenyl-1,3-5hexatriene (DPH) as a probe since membranes do not exhibit a natural intrinsic fluorescence.

Due to its low aqueous solubility, DPH inserts in the bilayer core; the depolarization property of DPH depends on the packing of the acyl chains. Thus, the fluorescence anisotropy of DPH in liposomes gives information about the organization of the membrane environment around the fluorescent probe (Gharib et al., 2018a). The authors determined the DPH anisotropy values of blank and HP-ß-CD-loaded DPPC liposomes prepared at different DPPC:HP-ß-CD molar ratios (100:181, 100:454, 100:909, and 100:1363) at 28, 41, and 50 ºC. The results showed that HPβ-CD reduced the DPH anisotropy of DPPC membrane at all the studied temperatures in a concentration-dependent manner (Figure 7), suggesting an increase in the membrane fluidity of DPPC liposomes in the presence of HP-β-CD (Gharib et al., 2018a).

Figure 7: DPH anisotropy values for blank and HP-ß-CD-loaded DPPC liposomes prepared at different DPPC:HP-ß-CD molar ratios at 28, 41, and 50 ºC (Gharib et al., 2018a).

Moreover, Gharib et al. (2018a) determined the anisotropy values of DPH inserted in liposomes composed of saturated PLs and Chol or unsaturated PLs and Chol; in addition, different PL:Chol:HP-β-CD molar ratios were used in this study. HP-β-CD was found to increase the membrane fluidity of liposome membranes composed of unsaturated PLs, while no effect was exerted on those composed of saturated lipids. Thus, the packing state of PLs can modulate the CD effect on membrane model systems.

ESR spectroscopy is another technique used to provide information about the structure and dynamic of biological membranes. The fatty acid spin-label agents, 5-doxyl stearate (5-DSA) and 16-doxyl stearate (16-DSA), are generally used as paramagnetic probes. 5-DSA is located at the lipid-aqueous interface of the membrane while 16-DSA is inserted into its hydrophobic core. The nitroxide group of the spin probes moves around the point of attachment. Hence, the ESR spectra allow the identification of changes in the probe rotational mobility in biological membranes and can be further correlated with membrane fluidity [START_REF] Abboud | Biophysical methods: Complementary tools to study the influence of human steroid hormones on the liposome membrane properties[END_REF][START_REF] Grammenos | ESR technique for noninvasive way to quantify cyclodextrins effect on cell membranes[END_REF].

ESR was applied to examine the effect of rameb (0-10 mM) on the microviscosity of human colon carcinoma cell membrane. In the absence of rameb, the microviscosity was found to be 298 cP. This value decreased with increasing CD concentration and stabilized at 265 cP for a rameb concentration of 2.5 mM. Then, the values remained constant until 10 mM [START_REF] Grammenos | ESR technique for noninvasive way to quantify cyclodextrins effect on cell membranes[END_REF]. Finally, it is worthy to note that the membrane Chol content was not considered in the above mentioned studies. Nevertheless, it is well known that Chol has a key role in maintaining the membrane fluidity; its content can modulate CD-induced membrane fluidity changes.

Extraction of lipid membrane components from biomimetic and biological membranes

Several studies evaluated the extent of lipid extraction mediated by CDs. Following the incubation of membrane with CD, the suspension is subjected to centrifugation, and the supernatant is collected to determine the amount of extracted PLs and Chol in the suspension.

In general, CDs enable rapid extraction of membrane lipids. Alpha-CDs were found to extract mainly PLs; β-CDs, in particular methylated β-CDs, extract preferably Chol; γ-CDs are less lipid selective compared to the other CDs (Figure 8). concentration in the membrane, resulting in a decrease of FRET signals [START_REF] Denz | Interaction of fluorescent phospholipids with cyclodextrins[END_REF].

Table 2 resumes the literature data regarding CD-mediated extraction of lipid components from biomimetic and biological membranes; the studies on biomimetic membranes are presented first (liposomes then monolayers) followed by those on biological membranes. Furthermore, Table 2 shows the lipid composition of liposomes and monolayers, the cell type from which membranes are extracted as well as the type and concentration of CD used in each study. Generally, Chol release from liposomes and biological membranes displayed a rapid exponential kinetics [START_REF] Iborra | Cholesterol Efflux Promotes Acrosome Reaction in Goat Spermatozoa1[END_REF][START_REF] Milles | Organization of fluorescent cholesterol analogs in lipid bilayers -lessons from cyclodextrin extraction[END_REF]. However, [START_REF] Yancey | Cellular cholesterol efflux mediated by cyclodextrins. Demonstration Of kinetic pools and mechanism of efflux[END_REF] reported that HP-β-CD-mediated Chol release from mouse L-cell fibroblasts, human fibroblasts, and rat hepatoma cells followed a bi-exponential kinetics, revealing a fast pool with half-times of 19-23 s and a slow pool with half-times ranging from 15 to 35 min.

Moreover, [START_REF] Kilsdonk | Cellular cholesterol efflux mediated by cyclodextrins[END_REF] demonstrated that HP-β-CD-induced a rapid Chol release from mouse L-cell fibroblasts over an initial period (up to about 2 h) until the equilibrium between Chol in the outer medium and in the membrane compartment was reached. Also, the kinetics of the PL extraction from liposomes by Me-α-CD and Me-β-CD was fitted to a biexponential equation [START_REF] Denz | Interaction of fluorescent phospholipids with cyclodextrins[END_REF].

The factors affecting lipid extraction from membranes

The data presented in Table 2 show that CDs have a potential to extract lipid components from biomimetic and biological membranes; the extent of extraction depends on CD type and concentration, PL structure, overall lipid membrane composition, and cell type.

Cyclodextrin type and concentration

The interaction of methylated CDs such as Me-α-CD, Me-β-CD, and Me-γ-CD, with liposome membrane containing NBD-labeled PLs was examined by detecting FRET between the NBD and Rh-PE as described earlier [START_REF] Denz | Interaction of fluorescent phospholipids with cyclodextrins[END_REF]. Me-α-CD and Me-ß-CD were similarly efficient in inducing a high efflux of fluorescent-labeled PLs embedded in the membrane, whereas Me-γ-CD produced no effect. Also, the interaction of different CDs (α-CD, β-CD, HP-β-CD, Me-β-CD, and γ-CD) with NBD and BODIPY-labeled Chol was characterized [START_REF] Milles | Organization of fluorescent cholesterol analogs in lipid bilayers -lessons from cyclodextrin extraction[END_REF]. The results demonstrated that Me-β-CD induced the greatest Chol extraction while α-CD had no effect.

Moreover, many studies analyzed the effect of CDs on the erythrocyte membrane. Beta-CD induced greater Chol extraction from human erythrocytes relative to other native CDs [START_REF] Irie | Cyclodextrin-induced hemolysis and shape changes of human erythrocytes in vitro[END_REF][START_REF] Ohtani | Differential effects of alpha-, beta-and gammacyclodextrins on human erythrocytes[END_REF]. On the other hand, α-CD was more potent in inducing PL extraction [START_REF] Ohtani | Differential effects of alpha-, beta-and gammacyclodextrins on human erythrocytes[END_REF]. The influence of diverse CD derivatives on rabbit erythrocyte membrane was studied; α-CD and DM-α-CD were shown to extract PLs while HP-α-CD had no effect [START_REF] Motoyama | Effect of 2,6-di-O-methyl-αcyclodextrin on hemolysis and morphological change in rabbit's red blood cells[END_REF]. In addition, methylated β-CD derivatives caused a greater Chol efflux from the erythrocyte membrane, as compared to β-CD (Motoyama et al., 2009b).

The presence of β-CD and its derivatives, HP-β-CD and Me-β-CD, did not modify the PL content of mouse L-cell fibroblast membrane but reduced the Chol content in the order of Me-β-CD > β-CD > HP-β-CD [START_REF] Kilsdonk | Cellular cholesterol efflux mediated by cyclodextrins[END_REF]. Moreover, the impact of CD type on the lipid release was demonstrated using a blood brain barrier model. Indeed, α-CD preferentially promoted PL extraction, β-CD selectively extracted Chol, while both CD types induced SM release [START_REF] Monnaert | Behavior of -, -, and -Cyclodextrins and Their Derivatives on an in Vitro Model of Blood-Brain Barrier[END_REF]. Using various β-CD derivatives, it was shown that CDs enhanced Chol efflux from human umbilical vein endothelial cells, with rameb inducing the greatest effect [START_REF] Castagne | Study of the cholesterol extraction capacity of β-cyclodextrin and its derivatives, relationships with their effects on endothelial cell viability and on membrane models[END_REF]. In addition, β-CD derivatives (HP2-SBE3-β-CD, HP3-SBE2-β-CD, SBEβ-CD, Me-β-CD, and dimeb) caused Chol extraction from human embryonic kidney cells with dimeb exerting the strongest effect [START_REF] Wang | Evaluation of cholesterol depletion as a marker of nephrotoxicity in vitro for novel β-cyclodextrin derivatives[END_REF]. The impact of the three native CDs as well as G2-α-CD and G2-β-CD on Caco-2 cell membrane was also investigated [START_REF] Ono | A moderate interaction of maltosyl-alpha-cyclodextrin with Caco-2 cells in comparison with the parent cyclodextrin[END_REF]; the authors demonstrated that β-CD and G2-β-CD did not affect the PL content while α-CD extracted most of the PLs from cell membrane, and γ-CD produced no effect. According to [START_REF] Szente | Cyclodextrins: Assessing the Impact of Cavity Size, Occupancy, and Substitutions on Cytotoxicity and Cholesterol Homeostasis[END_REF], the cavity size and the substitution groups of CDs influenced their ability to extract Chol from biological membranes and to evoke cell damage. Methylated CDs (dimeb and rameb) were more potent in solubilizing Chol compared to HP-β-CD and SBE-β-CD, whereas HP-γ-CD was not found to extract Chol.

CD concentration can also influence the CD-mediated lipid extraction. All studies on this subject, both on biomimetic and biological membranes, highlight the importance of CD concentration. Indeed, increasing the CD concentration increases the extent of lipid release from membranes [START_REF] Denz | Interaction of fluorescent phospholipids with cyclodextrins[END_REF][START_REF] Milles | Organization of fluorescent cholesterol analogs in lipid bilayers -lessons from cyclodextrin extraction[END_REF][START_REF] Ohvo | Cyclodextrin-mediated removal of sterols from monolayers: effects of sterol structure and phospholipids on desorption rate[END_REF][START_REF] Ohvo-Rekilä | Cyclodextrin-catalyzed extraction of fluorescent sterols from monolayer membranes and small unilamellar vesicles[END_REF][START_REF] Yancey | Cellular cholesterol efflux mediated by cyclodextrins. Demonstration Of kinetic pools and mechanism of efflux[END_REF].

Phospholipid type

The effect of PL acyl chain length and saturation as well as PL head group type on the strength of CD-mediated PL extraction have been discussed in the literature [START_REF] Denz | Interaction of fluorescent phospholipids with cyclodextrins[END_REF][START_REF] Grauby-Heywang | Study of the interaction of beta-cyclodextrin with phospholipid monolayers by surface pressure measurements and fluorescence microscopy[END_REF]. Short chain lipids are better extracted than long ones from liposome membrane when various methylated CDs were applied. In addition, PC was more effectively removed from liposome membrane in comparison with PE and PS [START_REF] Denz | Interaction of fluorescent phospholipids with cyclodextrins[END_REF]. Moreover, β-CD was capable to release PC from monolayers without any effect on phosphatidylglycerol (PG) monolayers (Grauby-Heywang and Turlet, 2008).

Concerning the saturation status of acyl chains, the presence of an unsaturated acyl chain was reported to favor the β-CD-induced PLs desorption from monolayers (Grauby-Heywang and Turlet, 2008); a double bond creates a kink in the carbon chain rendering the structure less tightly packed. In addition, the lipid backbone influences its extraction; thus, SM (sphingosine backbone) was easier extracted from biomimetic membranes than PLs (glycerol backbone) [START_REF] Grauby-Heywang | Study of the interaction of beta-cyclodextrin with phospholipid monolayers by surface pressure measurements and fluorescence microscopy[END_REF]. This difference can be explained by the fact that SM can act as both H-bond donor and acceptor while PC is only a H-bond acceptor; H-bonds between lipids and CDs stabilize lipid-CD complex, thereby favoring lipid extraction [START_REF] Boggs | Lipid intermolecular hydrogen bonding: influence on structural organization and membrane function[END_REF].

Membrane lipid composition

CD-mediated Chol desorption from pure Chol monolayer was studied and compared to those composed of Chol mixed with PLs or SM. The results showed that CDs induced minimal efflux of Chol from mixed monolayers in comparison with pure Chol monolayers [START_REF] Ohvo | Cyclodextrin-mediated removal of sterols from monolayers: effects of sterol structure and phospholipids on desorption rate[END_REF][START_REF] Ohvo-Rekilä | Cyclodextrin-catalyzed extraction of fluorescent sterols from monolayer membranes and small unilamellar vesicles[END_REF], and SM exerted a greater effect in lowering Chol desorption rate compared to PLs [START_REF] Ohvo | Cyclodextrin-mediated removal of sterols from monolayers: effects of sterol structure and phospholipids on desorption rate[END_REF]. The rate of HP-β-CD-mediated sterol extraction was higher from POPC:sterol vesicles than that from SM:sterol vesicles [START_REF] Ohvo-Rekilä | Cyclodextrin-catalyzed extraction of fluorescent sterols from monolayer membranes and small unilamellar vesicles[END_REF]. [START_REF] Besenicar | Kinetics of cholesterol extraction from lipid membranes by methyl-beta-cyclodextrin--a surface plasmon resonance approach[END_REF] reported that the addition of SM to dioleoylphosphatidylcholine:Chol (DOPC:Chol) vesicles slowed the Me-β-CD-mediated Chol extraction.

These findings are corroborated by the study of [START_REF] Ohvo | Effects of sphingomyelin and phosphatidylcholine degradation on cyclodextrin-mediated cholesterol efflux in cultured fibroblasts[END_REF]. The authors stated that reducing SM content in human skin fibroblasts by about 76 %, using sphingomyelinase, stimulated the HP-β-CD-induced Chol removal from the plasma membrane (23 % compared to 13 % from untreated cells), while reducing PC content by about 12 % using PC-phospholipase C, had no effect on membrane Chol level. Hence, Chol interaction with other membrane components may retard its CD-induced extraction.

Cell type

Two studies compared the effect of CDs on the Chol extraction rate from three different cell types: mouse L-cell fibroblast, human skin fibroblast, and rat hepatoma cells [START_REF] Kilsdonk | Cellular cholesterol efflux mediated by cyclodextrins[END_REF][START_REF] Yancey | Cellular cholesterol efflux mediated by cyclodextrins. Demonstration Of kinetic pools and mechanism of efflux[END_REF]. [START_REF] Kilsdonk | Cellular cholesterol efflux mediated by cyclodextrins[END_REF] (1996) found that Chol release rate varied between the cells as follows: rat hepatoma cells > mouse L-cell fibroblasts > human skin fibroblasts. This difference might be due to the disparate CD concentrations tested; at high concentrations such as 200 mM, HP-β-CD might have various Chol efflux capacities towards different cell types.

The mechanisms of cyclodextin-mediated lipid extraction

The mechanisms of Chol and PL extraction by CDs were discussed in several studies. Thus,

Cyclodextrin-mediated lipid exchange between membranes

Based on the capacity of natural CDs and their derivatives to extract membrane lipid components, they had been widely used to catalyze the lipid exchange between different membrane vesicles or between a lipid vesicle membrane and a biological cell membrane. CDmediated lipid exchange has been mainly performed to build up lipid vesicles with lipid asymmetry (Figure 9); indeed, in natural biological membranes, the lipid composition of the inner and the outer leaflets is different [START_REF] Huang | Effect of Cyclodextrin and Membrane Lipid Structure upon Cyclodextrin-Lipid Interaction[END_REF]. CDs promote the lipid molecule efflux from a donor membrane surface partially or fully forming a soluble complex with this lipid in aqueous medium and carrying it to an acceptor membrane [START_REF] Tanhuanpää | γ-Cyclodextrins Greatly Enhance Translocation of Hydrophobic Fluorescent Phospholipids from Vesicles to Cells in Culture: IMPORTANCE OF MOLECULAR HYDROPHOBICITY IN PHOSPHOLIPID TRAFFICKING STUDIES[END_REF]. Table 3 summarizes the literature regarding the CD-induced lipid exchange between membranes. The membrane lipid compositions of donor and acceptor vesicles, the type and concentration of CD used in each study are presented as well. 3, CDs are able to mediate efficient transfer of PLs and Chol between lipid vesicles or between a lipid vesicle and a cell; the transfer is controlled by several parameters. First, the level of CD-mediated lipid exchange between vesicles is directly proportional to the CD concentration [START_REF] Huang | Effect of Cyclodextrin and Membrane Lipid Structure upon Cyclodextrin-Lipid Interaction[END_REF][START_REF] Kainu | Introduction of phospholipids to cultured cells with cyclodextrin[END_REF][START_REF] Leventis | Use of cyclodextrins to monitor transbilayer movement and differential lipid affinities of cholesterol[END_REF][START_REF] Mccauliff | Sterol Transfer between Cyclodextrin and Membranes: Similar but Not Identical Mechanism to NPC2-Mediated Cholesterol Transfer[END_REF][START_REF] Tanhuanpää | γ-Cyclodextrins Greatly Enhance Translocation of Hydrophobic Fluorescent Phospholipids from Vesicles to Cells in Culture: IMPORTANCE OF MOLECULAR HYDROPHOBICITY IN PHOSPHOLIPID TRAFFICKING STUDIES[END_REF]. However, at high CD concentrations, it may induce membrane damage and vesicle solubilization [START_REF] Huang | Effect of Cyclodextrin and Membrane Lipid Structure upon Cyclodextrin-Lipid Interaction[END_REF]. Second, the level of lipid exchange between membranes is affected by the CD type. Me-β-CD is more efficient towards lipid exchange between liposomes compared to HP-β-CD and HP-α-CD [START_REF] Huang | Effect of Cyclodextrin and Membrane Lipid Structure upon Cyclodextrin-Lipid Interaction[END_REF]. Moreover, Me-β-CD and α-CD are found to be more potent in mediating DPPC transfer between vesicles compared to that of Chol; on the contrary, β-CD and γ-CD are more efficient transfer inducers of Chol in comparison with DPPC [START_REF] Leventis | Use of cyclodextrins to monitor transbilayer movement and differential lipid affinities of cholesterol[END_REF]. Another factor affecting the lipid exchange is the type of PL. For instance, Me-α-CD induced the transport of SM (75 %), PC and PE (10-15 %) but not PI and PS. Also, SM molecules with shorter acyl chains (fewer than 36 C) were exchanged to a greater extent than the longer ones [START_REF] Li | Efficient replacement of plasma membrane outer leaflet phospholipids and sphingolipids in cells with exogenous lipids[END_REF]. These findings are consistent with those of [START_REF] Kainu | Introduction of phospholipids to cultured cells with cyclodextrin[END_REF] reporting that the transport of PLs triggered by Me-β-CD depends on length of their acyl chains; at the same time, there was no consistent relation with the PLs head group.

Similarly, the lipid transport rate mediated by CE-γ-CD (5 mM) decreased as the acyl chain length of PC increased from 6 to 14 C atoms [START_REF] Tanhuanpää | γ-Cyclodextrins Greatly Enhance Translocation of Hydrophobic Fluorescent Phospholipids from Vesicles to Cells in Culture: IMPORTANCE OF MOLECULAR HYDROPHOBICITY IN PHOSPHOLIPID TRAFFICKING STUDIES[END_REF].

Furthermore, CE-γ-CD enhanced the PI transport rate by about twice compared to PG, PE, PS, and PC; besides, the SM transport mediated by this CD was about 3 folds more rapid than that of PC. The authors concluded that the overall molecular hydrophobicity of PLs is an essential factor controlling their CE-γ-CD-mediated transport. [START_REF] Mccauliff | Sterol Transfer between Cyclodextrin and Membranes: Similar but Not Identical Mechanism to NPC2-Mediated Cholesterol Transfer[END_REF] studied the mechanism of transfer of DHE, a fluorescent Chol analogue, from HP-β-CD/DHE complex to PL membranes. They demonstrated that the DHE transfer occurred by a collisional transfer mechanism involving a direct interaction of HP-β-CD with the membrane. HP-β-CD acts like Niemann-Pick C2 protein; the latter is involved in Chol transport and metabolism.

The effects of cyclodextrins on signal transduction pathways

To the best of our knowledge, CDs do not interact with specific membrane receptors. They act through a non-classical mechanism which is based on the extraction of membrane components (Chol, PL, lipid metabolites, and proteins), and/or the disruption of raft domains [START_REF] Kabouridis | Cholesterol depletion disrupts lipid rafts and modulates the activity of multiple signaling pathways in T lymphocytes[END_REF][START_REF] Matassoli | Hydroxypropyl-Beta-Cyclodextrin Reduces Inflammatory Signaling from Monocytes: Possible Implications for Suppression of HIV Chronic Immune Activation[END_REF]. This may result in the alteration of signaling pathways; for example, Chol extraction by CDs leads to several changes including: i) the activation of phosphatidylinositol-3-kinase/protein kinase B/ Bcl-2-associated death promoter (PI3K/Akt/Bad) pathways (Motoyama et al., 2009); ii) the stimulation of ERK (extracellular signal-regulated kinase) phosphorylation and the inhibition of PI3K/Akt phosphorylation, thereby reducing the expression of the transcription factor c-Jun in colon carcinoma cells [START_REF] Scheinman | Cholesterol affects gene expression of the Jun family in colon carcinoma cells using different signaling pathways[END_REF];

iii) the suppression of resveratrol-induced activation of kinase-dependent signaling pathways (c-Jun NH2-terminal kinase/ERK/Akt) and caspase-dependent apoptosis in colon cancer cells [START_REF] Colin | Endocytosis of Resveratrol via Lipid Rafts and Activation of Downstream Signaling Pathways in Cancer Cells[END_REF]; iv) the activation of Wnt/β-catenin pathway which plays multiple roles at different stages of development of Xenopus laevis [START_REF] Reis | Cholesterol-rich membrane microdomains modulate Wnt/β-catenin morphogen gradient during Xenopus development[END_REF]; v) the activation of protein kinase A and tyrosine kinase resulting in protein phosphorylation and sperm capacitation [START_REF] Osheroff | Regulation of human sperm capacitation by a cholesterol efflux-stimulated signal transduction pathway leading to protein kinase A-mediated up-regulation of protein tyrosine phosphorylation[END_REF][START_REF] Visconti | Cholesterol Efflux-Mediated Signal Transduction in Mammalian Sperm: Cholesterol Release Signals an Increase in Protein Tyrosine Phosphorylation during Mouse Sperm Capacitation[END_REF]; vi) the enhancement of antigen receptor-mediated intracellular calcium release in Ramos B cells [START_REF] Awasthi-Kalia | Differential effects of filipin and methyl-beta-cyclodextrin on B cell receptor signaling[END_REF], and its inhibition in Jurkat T cells [START_REF] Kabouridis | Cholesterol depletion disrupts lipid rafts and modulates the activity of multiple signaling pathways in T lymphocytes[END_REF]; vii) the enhancement of signaling pathways associated with β1-adrenergic receptors resulting in compartmentalized cyclic adenosine monophosphate (cAMP) response in cardiac monocytes [START_REF] Agarwal | Effects of cholesterol depletion on compartmentalized cAMP responses in adult cardiac myocytes[END_REF]; viii) the suppression of cAMP-dependent protein kinase (PKA) modulation of voltage-gated potassium channel (Kv) current in rat mesenteric artery smooth muscle cells [START_REF] Brignell | Steady-State Modulation of Voltage-Gated K+ Channels in Rat Arterial Smooth Muscle by Cyclic AMP-Dependent Protein Kinase and Protein Phosphatase 2B[END_REF]; ix) the suppression of signaling pathways associated with chemokine receptor (CCR5), leading to the inhibition of calcium release and abrogation of inhibition of forskolin-stimulated cAMP accumulation in Chinese hamster ovary cells and human embryonic kidney cells [START_REF] Cardaba | CCR5 internalisation and signalling have different dependence on membrane lipid raft integrity[END_REF], x) the suppression of insulin-stimulated Akt phosphorylation in mice hepatocytes [START_REF] Key | Hepatocyte ABCA1 Deletion Impairs Liver Insulin Signaling and Lipogenesis[END_REF]; xi) other signaling pathways may also be involved. Additionally, CD-induced extraction of other membrane components (PLs or proteins) may affect several signal transduction pathways. For instance, DM-α-CD suppressed nitric oxide and tumor necrosis factor-α (TNF-α) production as well as nuclear factor-KB (NF-KB) activation in stimulated macrophages due to the efflux of PLs and cluster of differentiation 14 from lipid rafts [START_REF] Motoyama | Involvement of CD14 in the inhibitory effects of dimethyl-α-cyclodextrin on lipopolysaccharide signaling in macrophages[END_REF].

The signaling pathways changes would depend on the cell line [START_REF] Awasthi-Kalia | Differential effects of filipin and methyl-beta-cyclodextrin on B cell receptor signaling[END_REF][START_REF] Kabouridis | Cholesterol depletion disrupts lipid rafts and modulates the activity of multiple signaling pathways in T lymphocytes[END_REF][START_REF] Motoyama | Involvement of CD14 in the inhibitory effects of dimethyl-α-cyclodextrin on lipopolysaccharide signaling in macrophages[END_REF], the CD type and concentration [START_REF] Colin | Endocytosis of Resveratrol via Lipid Rafts and Activation of Downstream Signaling Pathways in Cancer Cells[END_REF][START_REF] Motoyama | Involvement of CD14 in the inhibitory effects of dimethyl-α-cyclodextrin on lipopolysaccharide signaling in macrophages[END_REF], the CD forms (free or CD/guest complex) [START_REF] Key | Hepatocyte ABCA1 Deletion Impairs Liver Insulin Signaling and Lipogenesis[END_REF], etc. This illustrates the vastness of this topic and requires separate consideration in a special review.

Protein extraction

Table 4 resumes the results of several studies, as examples, on the ability of CDs to extract proteins from different cell membranes. The type and concentration of CD are also presented. As shown in Table 4, CDs are able to solubilize membrane proteins; the CD concentration and type are modulating factors of the process [START_REF] Ono | A moderate interaction of maltosyl-alpha-cyclodextrin with Caco-2 cells in comparison with the parent cyclodextrin[END_REF][START_REF] Ohtani | Differential effects of alpha-, beta-and gammacyclodextrins on human erythrocytes[END_REF][START_REF] Motoyama | Effect of 2,6-di-O-methyl-αcyclodextrin on hemolysis and morphological change in rabbit's red blood cells[END_REF]Motoyama et al., 2009). Thus, β-CD was more potent in inducing protein extraction from human erythrocytes compared to the other native CDs [START_REF] Ohtani | Differential effects of alpha-, beta-and gammacyclodextrins on human erythrocytes[END_REF]. On the other side, α-CD was more effective in inducing protein extraction from Caco-2 cell membrane, and no effect was exerted by β-CD [START_REF] Ono | A moderate interaction of maltosyl-alpha-cyclodextrin with Caco-2 cells in comparison with the parent cyclodextrin[END_REF]. Furthermore, DM-α-CD [START_REF] Motoyama | Effect of 2,6-di-O-methyl-αcyclodextrin on hemolysis and morphological change in rabbit's red blood cells[END_REF] and the methylated derivatives of β-CD (Me-β-CD and dimeb), unlike the native α-and β-CDs (Motoyama et al., 2009b), were found to induce the extraction of proteins spanning rabbit erythrocytes membranes.

Table 4: Some examples of cyclodextrin-induced protein extraction

It is worthy to note that Me-β-CD was the only CD used in the literature to selectively extract membrane proteins from T lymphocytes [START_REF] Ilangumaran | Effects of cholesterol depletion by cyclodextrin on the sphingolipid microdomains of the plasma membrane[END_REF] and B lymphocytes [START_REF] Awasthi-Kalia | Differential effects of filipin and methyl-beta-cyclodextrin on B cell receptor signaling[END_REF]. Also, it was observed to selectively extract prenylated proteins GRK1 and PDE6 from rod outer segment membrane. These proteins were demonstrated to have different EC50 values (effective concentration to extract 50 % of total protein amount); it depends on the strength of protein-membrane association. For GRK1, EC50 was 0.17 mM while for PDE6 it was 5.1 mM [START_REF] Saito | Methyl-β-cyclodextrin is a useful compound for extraction and purification of prenylated enzymes from the retinal disc membrane[END_REF]. Moreover, [START_REF] Elliott | Cholesterol-Dependent Association of Caveolin-1 with the Transducin α Subunit in Bovine Photoreceptor Rod Outer Segments: Disruption by Cyclodextrin and Guanosine 5'-O -(3-Thiotriphosphate) †[END_REF] reported that adding Me-β-CD resulted in the extraction of the peripheral protein transducin α subunit (Tα) from the detergent resistant domains of rod outer segment membrane without any effect on caveolin-1.

The effect of cyclodextrins on the membrane permeability

Cell membrane permeability is essential for many biological processes. Therefore, liposome membrane permeability was examined in the presence of various CDs by analyzing the release of fluorescent dyes incorporated into liposomes such as carboxyfluorescein [START_REF] Nishijo | Interactions of cyclodextrins with dipalmitoyl, distearoyl, and dimyristoyl phosphatidyl choline liposomes. A study by leakage of carboxyfluorescein in inner aqueous phase of unilamellar liposomes[END_REF] and calcein [START_REF] Besenicar | Kinetics of cholesterol extraction from lipid membranes by methyl-beta-cyclodextrin--a surface plasmon resonance approach[END_REF][START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF][START_REF] Piel | Study of the relationship between lipid binding properties of cyclodextrins and their effect on the integrity of liposomes[END_REF]. Regarding cellular membranes, permeability was evaluated by analyzing the release of intracellular components such as hemoglobin [START_REF] Ohtani | Differential effects of alpha-, beta-and gammacyclodextrins on human erythrocytes[END_REF] and the enzyme lactate dehydrogenase [START_REF] Wang | Evaluation of cholesterol depletion as a marker of nephrotoxicity in vitro for novel β-cyclodextrin derivatives[END_REF]. Table 5 summarizes the results of the literature search regarding the effect CDs on the membrane permeability with respect to the membrane lipid composition or cell type, CD type and concentration, and intravesicular fluorescent dye or intracellular component used to assess the membrane permeability.

Table 5: The effect of cyclodextrins on liposomal and biological membrane permeability The interaction of CDs with lipid membrane components increased the membrane permeability;

the extent of increase in permeability is directly proportional to the CD concentration [START_REF] Kilsdonk | Cellular cholesterol efflux mediated by cyclodextrins[END_REF][START_REF] Nishijo | Interactions of cyclodextrins with dipalmitoyl, distearoyl, and dimyristoyl phosphatidyl choline liposomes. A study by leakage of carboxyfluorescein in inner aqueous phase of unilamellar liposomes[END_REF][START_REF] Ohtani | Differential effects of alpha-, beta-and gammacyclodextrins on human erythrocytes[END_REF][START_REF] Piel | Study of the relationship between lipid binding properties of cyclodextrins and their effect on the integrity of liposomes[END_REF][START_REF] Wang | Evaluation of cholesterol depletion as a marker of nephrotoxicity in vitro for novel β-cyclodextrin derivatives[END_REF]. On the other side, [START_REF] Besenicar | Kinetics of cholesterol extraction from lipid membranes by methyl-beta-cyclodextrin--a surface plasmon resonance approach[END_REF] showed that Me-β-CD (0-4 mM) did not influence the membrane permeability of DOPC and DOPC:Chol liposomes. This is probably due to relatively low CD concentrations (0-4 mM) unlike other studies using higher CD concentrations up to 10 mM [START_REF] Kilsdonk | Cellular cholesterol efflux mediated by cyclodextrins[END_REF][START_REF] Nishijo | Interactions of cyclodextrins with dipalmitoyl, distearoyl, and dimyristoyl phosphatidyl choline liposomes. A study by leakage of carboxyfluorescein in inner aqueous phase of unilamellar liposomes[END_REF], 20 mM [START_REF] Wang | Evaluation of cholesterol depletion as a marker of nephrotoxicity in vitro for novel β-cyclodextrin derivatives[END_REF], and 100 mM [START_REF] Piel | Study of the relationship between lipid binding properties of cyclodextrins and their effect on the integrity of liposomes[END_REF].

Additionally, several studies stated that the CD-induced membrane permeability increase depends on the type of CD, namely its hydrophobicity and the cavity size. For instance, α-CD, dimeb, and trimeb were shown to induce carboxyfluorescein release from DPPC, distearoylphosphatidylcholine (DSPC), and dimyristoyl-phosphatidylcholine (DMPC) liposomes while no effect was produced by β-CD, HP-β-CD, and γ-CD [START_REF] Nishijo | Interactions of cyclodextrins with dipalmitoyl, distearoyl, and dimyristoyl phosphatidyl choline liposomes. A study by leakage of carboxyfluorescein in inner aqueous phase of unilamellar liposomes[END_REF]. Besides, the permeability of soybean phosphatidylcholine (SPC):stearylamine (SA) liposome, assessed by studying the kinetics of calcein release, was found to increase after exposure to methylated β-CDs such as dimeb, rameb, and trimeb [START_REF] Piel | Study of the relationship between lipid binding properties of cyclodextrins and their effect on the integrity of liposomes[END_REF]. However, other CDs used in this work, β-CD, crysmeb, HP-β-CD, SBE-β-CD, γ-CD, and HP-γ-CD, did not significantly induce calcein leakage from liposomes. As suggested by the authors, calcein molecules may escape from the liposomes as a result of the interaction of methylated CDs with membrane lipids.

Moreover, the same authors showed that the methylated CDs increased the permeability of liposomes containing or not Chol; this result allowed them to conclude that Chol does not protect membranes from the effect of CDs [START_REF] Piel | Study of the relationship between lipid binding properties of cyclodextrins and their effect on the integrity of liposomes[END_REF]. Furthermore, [START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF] demonstrated that the CD-mediated membrane permeability increase was greater for Me-β-CD than for HP-β-CD or HP-γ-CD; thus, the effect of CD on the membrane permeability depends on the lipophilicity of CD rather than its cavity size.

Concerning the effect of CDs on the permeability of biological membranes, the native CDs were able to increase the permeability of human erythrocytes, with β-CD exerting the greatest effect [START_REF] Ohtani | Differential effects of alpha-, beta-and gammacyclodextrins on human erythrocytes[END_REF]. In addition, methylated CDs such as Me-β-CD [START_REF] Kilsdonk | Cellular cholesterol efflux mediated by cyclodextrins[END_REF][START_REF] Wang | Evaluation of cholesterol depletion as a marker of nephrotoxicity in vitro for novel β-cyclodextrin derivatives[END_REF] and dimeb [START_REF] Wang | Evaluation of cholesterol depletion as a marker of nephrotoxicity in vitro for novel β-cyclodextrin derivatives[END_REF] were demonstrated to be more potent in enhancing the membrane permeability of mouse L cell fibroblasts [START_REF] Kilsdonk | Cellular cholesterol efflux mediated by cyclodextrins[END_REF] and human embryonic kidney 293A cells [START_REF] Wang | Evaluation of cholesterol depletion as a marker of nephrotoxicity in vitro for novel β-cyclodextrin derivatives[END_REF] compared to other β-CD derivatives.

Other factors controlling the CD-induced membrane permeability are the type of PL constituting the liposomal membrane and the size of liposomal vesicles [START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF]. Indeed, liposomes composed of saturated PLs (HPC) were found to be less affected by CDs in relation to the unsaturated ones. Moreover, the presence of Chol in the membrane lowered the permeability of unsaturated PC liposomes, while it increased or did not affect that of HPC or DSPC liposomes [START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF].

Moreover, for the same membrane lipid composition, the CD-induced calcein release from MLV was greater relative to SUV. The greater SUV stability is evidently due to the curvature of lipid molecules which does not allow lipids to establish an optimal contact angle to interact with CDs [START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF].

Furthermore, [START_REF] Monnaert | Behavior of -, -, and -Cyclodextrins and Their Derivatives on an in Vitro Model of Blood-Brain Barrier[END_REF] measured the endothelial permeability coefficient (Pe) of [ 14 C]sucrose across blood brain barrier at 0-5 mM for α-CD and β-CD, and at 0-50 mM for γ-CD.

The sucrose permeability was determined to be dependent of CD concentration; the effect of CDs was in the order of α-CD > Me-α-CD= HP-α-CD = β-CD= Me-β-CD= HP-β-CD > γ-CD, Meγ-CD > HP-γ-CD.

Table 5 presents the data on the kinetics of intravesicular components release from liposomes induced by different CDs. We can notice that most CDs induced an instant release of intravesicular components after CD adding to liposomes followed by a slow [START_REF] Nishijo | Interactions of cyclodextrins with dipalmitoyl, distearoyl, and dimyristoyl phosphatidyl choline liposomes. A study by leakage of carboxyfluorescein in inner aqueous phase of unilamellar liposomes[END_REF] or negligible [START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF] release stage. This finding can be explained by the fact that at the initial stage, the CD-induced extraction of membrane lipids results in membrane permeabilization. Following this stage, CD/lipid complexes may act as lipid donors towards membrane allowing its re-organization [START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF].

Vesicles solubilization upon cyclodextrinmembrane interaction

The particle size analysis by dynamic light scattering [START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF] and turbidity measurements [START_REF] Boulmedarat | Cyclodextrin-Mediated Drug Release from Liposomes Dispersed Within a Bioadhesive Gel[END_REF][START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF] revealed that CDs, in particular methylated β-CDs, induced vesicle solubilization due to the CDs ability to draw PLs and Chol out of the liposome membrane [START_REF] Anderson | Calorimetric measurement of phospholipid interaction with methyl-beta-cyclodextrin[END_REF]. [START_REF] Hatzi | Integrity of liposomes in presence of cyclodextrins: effect of liposome type and lipid composition[END_REF] showed that Me-β-CD was more potent in solubilizing PC and PC:Chol Based on the data discussed in this section and in the preceding sections, we can conclude that CDs are inactive at concentrations below 0.5 mM. In contrast, at moderate concentrations, they can induce lipid extraction and catalyze lipid exchange between membranes. CDs can also promote vesicles solubilization at relatively high concentrations (> 50 mM). It is worthy to mention the "shuttle-sink" model for lipid efflux described by [START_REF] Atger | Cyclodextrins as catalysts for the removal of cholesterol from macrophage foam cells[END_REF]. According to this model, the rate of Chol exchange (influx and efflux) between cell membrane and medium compartment, as it is the case with serum lipoproteins, increases in the presence of low CD concentrations; the equilibrium is not changed and there is no clear change in the membrane and medium Chol pools. However, in the presence of lipid vesicles and CDs, the vesicles act as a sink shifting the equilibrium to favor net efflux of Chol from the cell membranes.

Cyclodextrins act as cryoprotectants during freeze-drying

Freeze-drying, also known as lyophilization, is essential to ensure the long-term storage of liposomes and biological cells. Nevertheless, it may cause membrane disruption owing to ice crystal formation, membrane phase transition, and osmotic dehydration [START_REF] Chen | An overview of liposome lyophilization and its future potential[END_REF][START_REF] Ingvarsson | Stabilization of liposomes during drying[END_REF][START_REF] Wolkers | 085 Freeze-dried cells and tissues[END_REF]. Freeze-drying appeared to be effective for storage of several cell types including erythrocytes (Arav, 2013), platelets [START_REF] Crowe | Freeze-dried platelets: Moving towards clinical use[END_REF], and sperms [START_REF] Keskintepe | Freeze-Drying of Mammalian Sperm[END_REF]. It was mostly applied on spermatozoa; cryopreservation may promote damage in all sperm compartments, resulting in the loss of sperm motility, viability, acrosomal integrity, and the fertilizing capacity of the frozen-thawed sperms [START_REF] Mocé | Use of cholesterol in sperm cryopreservation: present moment and perspectives to future[END_REF].

Hence, maintaining the integrity of the lipid bilayer structure during freezing of liposomes and biological cells (particularly sperm cell) is highly recommended. Several papers studied the effect of CD as a cryoprotectant to preserve liposomal and biological membranes during the aforementioned process.

Cryopreservation of sperm cells using cyclodextrins as cryoprotectants

The effect of CDs on sperm cell cryopreservation was documented in a set of studies. In general, HP-β-CD and Me-β-CD, at optimal concentrations, have an ability to increase sperm cell viability after thawing, as compared to the control. However, CD-induced resistance of spermatozoa to the damage caused by freezing and thawing was shown to vary between species; the variation is due to membrane PL:Chol ratio that differs between species [START_REF] Madison | The Effect of 2-Hydroxypropyl-β-Cyclodextrin on Post-Thaw Parameters of Cryopreserved Jack and Stallion Semen[END_REF].

The study of [START_REF] Madison | The Effect of 2-Hydroxypropyl-β-Cyclodextrin on Post-Thaw Parameters of Cryopreserved Jack and Stallion Semen[END_REF] on jack and stallion sperm cells demonstrated that adding HP-β-CD (60 mM) resulted in an improved cell viability and motility of both sperm cell types. In the presence of HP-β-CD, the post thaw motility was 23 ± 0.7 % for jack and 17 ±0.4 % for stallion relative to control (20 ± 0.7 % for jack; 15 ± 0.4 % for stallion). Moreover, for both species, HP-β-CD induced the sperm post thaw acrosome reaction. Zeng and coworkers studied the effects of HP-β-CD [START_REF] Zeng | Freezability of boar spermatozoa is improved by exposure to 2-hydroxypropyl-betacyclodextrin[END_REF] and Me-β-CD [START_REF] Zeng | Effects of methyl-beta-cyclodextrin on cryosurvival of boar spermatozoa[END_REF] on boar sperm cell viability, motility, and acrosomal status during freeze-drying.

According to the authors, the pretreatment with HP-β-CD (up to 40 mM) and Me-β-CD (up to 20 mM) increased the number of sperm cells with intact acrosomes and enhanced the sperm motility compared to untreated cells. However, further elevation of CD concentration up to 80 mM and 40 mM for HP-β-CD and Me-β-CD, respectively, lowered the sperm viability and motility.

Cryopreservation of sperm cells pretreated with cyclodextrin/cholesterol complex

Chol-loaded CDs were suggested to facilitate Chol transfer into the sperm plasma membrane.

The effect of Me-β-CD/Chol inclusion complex applied prior to the freeze-drying procedure, on sperm membrane integrity, sperm motility, acrosome reaction, and sperm fertility was extensively studied in the literature. [START_REF] Purdy | Effect of cholesterol-loaded cyclodextrin on the cryosurvival of bull sperm[END_REF] showed that pretreating bull sperm with Me-β-CD/Chol can increase the number of survived sperm cells and preserve their fertilizing potential. In addition, adding treated or untreated sperm to oocytes gave similar percentages of oocytes able to cleave and develop into embryos. Similarly, Salmon et al.

(2016) reported that Me-β-CD/Chol, added prior to the cryopreservation procedure, improved the goat sperm cryosurvival rate showing greater percentages of motile and live sperms with intact acrosomes relative to untreated samples. However, contradictory results were published by [START_REF] Pinho | Effect of cyclodextrin-loaded cholesterol conjugates on plasma membrane viability of Piau swine breed frozen/thawed spermatozoa[END_REF] who demonstrated that Me-β-CD/Chol application did not improve, it even decreases, the quality of Piau swine sperm.

The effect of Me-β-CD/Chol inclusion complex was concentration dependent. Pretreating boar sperm with Me-β-CD/Chol (1 mg/120 x 10 6 sperm) increased the percentages of viable (40 ± 3 %) and total motile sperm (25 ± 3%) determined after 1 h, in comparison with untreated samples (viability 32 ± 3 % and total motility 19 ± 3 %). However, higher concentrations of Meβ-CD/Chol (above 3 mg/120 x 10 6 sperm) resulted in lower percentages of viable and motile sperm; thus, at the concentration of 6 mg/120 x 10 6 sperm, the cell viability and total motility were 24 ± 3 % and 11 ± 3 %, respectively [START_REF] Blanch | Response of Boar Sperm to the Treatment with Cholesterol-Loaded Cyclodextrins Added Prior to Cryopreservation: Effect of Cholesterol on Boar Sperm Cryosurvival[END_REF]. Furthermore, freezing stallion sperm in the presence of Me-β-CD/Chol (0-7.5mg/ 120 x 10 6 sperm) enhanced sperm membrane integrity, as compared to the control; the optimal Chol-Me-β-CD concentration being 1.5 mg/120 ×10 6 sperm [START_REF] Moore | Adding cholesterol to the stallion sperm plasma membrane improves cryosurvival[END_REF].

One of the damaging effects during freeze-drying is osmotic stress. The use of a CD/Chol inclusion complex as a cryoprotectant was investigated by evaluating its effect on the osmotic tolerance of sperm cells incubated in both hypo-osmotic and hyper-osmotic conditions. For example, the pretreatment of ram sperm with Chol-loaded Me-β-CD protected membrane integrity after short-term (15 min) exposure to osmotic challenges and significantly increased the percentages of living and intact sperm cells [START_REF] Ahmad | Cholesterol-loaded cyclodextrin pretreatment of ram spermatozoa protects structural integrity of plasma membrane during osmotic challenge and reduces their ability to undergo acrosome reaction in vitro[END_REF]. Also, Me-β-CD/Chol addition increased rabbit sperm cell viability without affecting their functional integrity during a set of osmotic challenges [START_REF] Aksoy | Cholesterol-loaded cyclodextrin enhances osmotic tolerance and inhibits the acrosome reaction in rabbit spermatozoa[END_REF].

Recent data in DCLs development

The DCLs systems have been characterized in many publications for their morphology, size, encapsulation efficiency (EE), and rate of drug release. In this section, the focus is done on the effect of CD/drug inclusion complex on the physiochemical properties and stability (based on membrane integrity and drug retention) of liposomes by comparing the characteristics of DCLs to those of blank and drug-loaded liposomes. In 2015, a review had emerged discussing this topic [START_REF] Gharib | Liposomes incorporating cyclodextrin-drug inclusion complexes: Current state of knowledge[END_REF]. Hence, only the literature data reported between 2015 and 2018 will be presented in this section.

Many studies showed that the incorporation of a drug into liposomes in the form of CD/drug inclusion complex resulted in an improvement of encapsulation efficiency (EE) and/or loading rate values, and in a delay of drug release compared to conventional liposomes. Thus, the loading rate was found to be 31.5 ± 4.2 % for eugenol-loaded phospholipon90H:Chol liposomes and it doubled (63.54 ± 2.28 %) when using the HP-β-CD/eugenol-loaded phospholipon90H:Chol liposomes [START_REF] Sebaaly | Preparation and characterization of clove essential oil-loaded liposomes[END_REF]. Similarly, for anethole, the loading rate was 2 times higher for phospholipon90H:Chol DCLs (0.83 ± 0.15 %) compared to phospholipon90H:Chol conventional liposomes (0.48 ± 0.07 %). Moreover, DCLs demonstrated slower drug release behavior, retaining 38 % of anethole initially present in the vesicles, with respect to 22 % of anethole retained by conventional liposomes [START_REF] Gharib | Drug-in-cyclodextrin-in-liposomes as a carrier system for volatile essential oil components: Application to anethole[END_REF].

Furthermore, the EE values of flurbiprofen-loaded DCLs systems prepared with SBE-β-CD or HP-β-CD, were lower than that of flurbiprofen-loaded liposomes; on the other hand, DCLs delayed the flurbiprofen release [START_REF] Zhang | Drug-in-cyclodextrin-inliposomes: A novel drug delivery system for flurbiprofen[END_REF]. Additionally, nerolidol was efficiently embedded into both lipoid E80 conventional liposomes and DCLs with high EE and loading rate values (> 90 %), and DCLs was more effective to prolong the nerolidol release in comparison to conventional liposomes [START_REF] Azzi | First evaluation of drug-incyclodextrin-in-liposomes as an encapsulating system for nerolidol[END_REF]. DCLs exhibited higher estetrol EE and slower estetrol release rate in comparison with conventional liposomes; nevertheless, both formulations were characterized by a high extent of drug release (80 %) after 6 h [START_REF] Palazzo | Development of injectable liposomes and drug-in-cyclodextrin-in-liposome formulations encapsulating estetrol to prevent cerebral ischemia of premature babies[END_REF]. Conversely, the EE of HP-β-CD/risperidone-loaded SPC:Chol liposomes was less than that of risperidone-loaded SPC:Chol liposomes, and risperidone was released faster from DCLs compared to conventional liposomes [START_REF] Wang | A comparison between conventional liposome and drug-cyclodextrin complex in liposome system[END_REF].

Conclusion

In this review, the interaction of CDs with biomimetic and biological membranes was analyzed.

The CD effect on membranes is mediated by several factors including membrane structure and composition, in particular acyl chain length and saturation of PLs and structure of their head groups, as well as CD type and concentration. CDs can extract membrane lipids; their extraction capacity depends on CD concentration which appears to be efficient above 0.5 mM.

CDs induce vesicle solubilization at concentrations near or above 50 mM. The interaction of CDs with membrane lipids promotes an increase of membrane permeability and fluidity. None of the studies evaluating CD effect on membranes considered the Chol content of lipid bilayer and few studies determined lipid:CD molar ratio. Therefore, these parameters should be analyzed in future studies. Finally, CDs and CD/Chol inclusion complexes were proven to have cryoprotective properties being able to preserve the integrity of liposomal and biological membranes during freeze-drying.

Figure 1 :

 1 Figure 1: Schematic representation of a liposome constituted of a lipid bilayer enclosing an aqueous phase. Hydrophobic drug (red) is entrapped in the lipid bilayer. Hydrophilic drug (green) is embedded in the aqueous phase. Amphiphilic drug (orange) is located at the waterbilayer interphase.

Figure 3 :

 3 Figure 3: The chemical structure of the most common native cyclodextrins.

Figure 4 :

 4 Figure 4: The truncated cone-shaped structure of a cyclodextrin molecule with its hydroxyl groups disposed outside.

  abolished the pretransition peak values of DMPC and DPPC liposomes, respectively, suggesting an interaction of CDs with the polar head groups of PLs. Regarding the effect of CDs on Tm value, it was on DPPC vesicles:-Dimeb, β-CD, and trimeb: Tm was increased with increasing lipid:CD molar ratio -Dimeb: ∆Hm was decreased while ∆T1/2 was increased -Trimeb: an increase in ∆T1/2 without affecting ∆Hm Effects of CDs on DPPC:Chol vesicles: -Trimeb and β-CD: ∆Hm was increased -Dimeb: an increase in ∆Hm up to DPPC:Chol molar ratio of 1:7; after that it was decreased -HP-β-CD: no effect on both vesicles. CD concentration while Tm was not affected -Trimeb: a slight decrease in Tm without affecting ∆Hm β-CD, γ-CD, and HP-β-CD: Tm and ∆Hm were barely affected.

Figure 6 :

 6 Figure 6: DSC scans of blank and HP-ß-CD-loaded DPPC liposomes prepared at DPPC:HP-ß-CD molar ratios of 100:181; 100:454; 100:909 and 100:1363 (Gharib et al., 2018a) Angelini et al. (2017) determined the ratio of pyrene fluorescence intensities in excimer and monomer state for palmityl-oleoyl-phosphatidylcholine (POPC) and β-CD-loaded-POPC liposomes. The results showed that β-CD increased the membrane fluidity in comparison with the control.

  -ß-CD 100:181 DPPC:HP-ß-CD 100:454 DPPC:HP-ß-CD 100:901 DPPC:HP-ß-CD 100:1363

Figure 8 :

 8 Figure 8: A scheme presenting a general technique for evaluating the extent of cyclodextrinmediated lipid extraction The fluorescent analogs of PLs and Chol have been widely used to investigate the structural and dynamic properties of membranes. The interaction of CDs with fluorescent-labeled Chol[START_REF] Milles | Organization of fluorescent cholesterol analogs in lipid bilayers -lessons from cyclodextrin extraction[END_REF] and PLs[START_REF] Denz | Interaction of fluorescent phospholipids with cyclodextrins[END_REF] bearing 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD)

---

  mediated sterol extraction in a concentration dependent manner -Slower sterol extraction rate from SM vesicles compared to POPC vesicles -Better extraction of cholestatrienol compared to DHE. extraction at all CD concentrations used -Fast Chol extraction rate -Reduced Chol extraction rate in the presence of mediated Chol extraction in a concentration dependent manner -Rapid exponential kinetics of Chol efflux with release rate constants ranging from 0.2 to 0.6 s -1 -Greater Chol extraction by Me-β-CD compared to other CDs. Slight extraction of NBD-Chol by HP-β-CD, Milles et al., 2013 β-CD, and γ-CD; no effect was exerted on BODIPY-Chol. -POPC:Rh-PE:C6/C12 NBD-PC (99:0.5:0.5) -POPC:Rh-PE:C6/C12 NBD-PS (99:0.5:0.5) -POPC:Rh-PE:C6/C12 NBD-PE (99:0.5:0.5) -POPC:Rh-PE:C6/C12 NBD-SM (99:0.5:0.5) -Me-α-CD -Me-β-CD -Me-γ-CD 0-10 -CD-mediated PL extraction in a concentration dependent manner -Bi-exponential kinetics of PL efflux -High extraction of PL by Me-α-CD and Me-ß-CD whereas Me-γ-CD was less effective -Better extraction of short chain PLs (C6) compared to the long ones (C12) -Better extraction of NBD-PC and NBD-SM compared to NBD-PS and NBDmediated Chol extraction in a concentration dependent manner -Insignificant PL extraction compared to Chol extraction β-CD-induced disappearance of Chol rich domains in DDPC:chol membranes -Reduced Chol extraction in the presence of PL and SM; SM effect > PL effectin the order: SM > POPC > DPPC -No extraction of DMPG was obtained. membrane Chol extraction in the order: β-CD > γ-CD > α-CD. mediated PLs extraction in the order: α-CD > β-CD >> γ-CD -CD-mediated extraction of Chol in the order: β-CD >> γ-CD; no effect of α-extracted by DM-α-CD and α-CD but no effect of HP-α-CD -No Chol extraction by all CDs used. Only dimeb induced PL and SM release -CD-mediated Chol extraction in the order: dimeb = Me-β-CD > β-CD. mediated Chol extraction in a concentration dependent manner -CD-mediated Chol extraction in the order: Me-β-CD > β-CD > HP-β-CD -HP-β-CD-induced a rapid Chol extraction (up to about 2 hours) -Me-β-CD and HP-β-CD induced cellular release of desmosterol as a function of CD concentration; Me-β-CD effect > HP-β-CD effect -No significant PLs release was obtained -Extent of Chol extraction was the same for all the cell types. Kilsdon k et al., 1995 -Mouse L-cell fibroblast -Human skin fibroblast -Rat hepatoma cells HP-β-CD 0-200 -CD-mediated Chol extraction in a concentration dependent manner till reaching saturation at high CD concentration (50 mM for rat hepatoma cells and 75 mM for L-cell fibroblasts) -Bi-exponential kinetics of Chol efflux. The range of half-times for the fast pool: 19-23 s, and that for the slow pool: 15-35 min -The Chol extraction rate from cells in the order: rat hepatoma cells > mouse L15 -CD-mediated Chol extraction in a concentration dependent manner -Rapid Chol efflux at a single rate; a plateau was reached after 15 min. Selective extraction of PC by α-CD compared to other CDs -Selective Chol extraction by β-CD in a concentration dependent manner α-CD and β-CD mediated extraction of SM γ-CD was less lipid selective. mediated Chol extraction in a concentration dependent manner -For the same CD concentration, the effect of CDs on Chol extraction was in the order: HP 2 -SBE 3 -β-CD < HP3-SBE 2 -β-CD < SBE-β-CD < Me-βNo effect of β-CD and G2-β-CD on PLs extraction at low CD concentrations (< 15 mM) -The majority of membrane PLs were extracted by α-CD -Moderate PLs extraction was obtained at CD 37.5 mM for G2-α-CD and G2-βextraction by CDs was in the order: Dimeb > Rameb >> HP-β-CD > SBE-β-CD -No effect of HP-γ-CD. Szente et al., 2018 BODIPY: dipyrromethene boron difluoride; Chol: cholesterol; DDPC: didecanoylphosphatidylcholine; DHE: dehydroergosterol; Dimeb: dimethylated-β-cyclodextrin; DM-α-CD: : 7-nitrobenz-2-oxa-1,3-diazol-4-yl; PC: phosphatidylcholine; PE: phosphatidylethanolamine; PL: phospholipid; PLC: phospholipase C; POPC: palmitoyl-oleoylphosphatidylcholine; PS: phosphatidylserine; Rh: Rhodamine; SM: sphingomyelin; Trimeb: trimethylated-β-cyclodextrin 6.2.1. Kinetics of cyclodextrin-induced lipid extraction from membranes Several studies examined the ability of CDs to induce lipid extraction from liposomal and biological membranes; the extraction kinetics was determined by monitoring the extraction as a function of time; the release rate constants or half times were evaluated.

  used β-CD, HP-β-CD, and Me-β-CD (in the range of 0-10 mM), and[START_REF] Yancey | Cellular cholesterol efflux mediated by cyclodextrins. Demonstration Of kinetic pools and mechanism of efflux[END_REF] used HP-β-CD (0-200 mM). According to the first study, the rate of Chol release did not differ among the cell types. In contrast,Yancey et al.

Fauvelle

  et al. (1997) evaluated the effect of α-CD-induced PI extraction using 1 H-NMR, 2 H-NMR, and 31 P-NMR spectroscopy techniques(1997). Fauvelle and coworkers showed that α-CD was attracted to membrane surface by electrostatic interaction between the positively charged primary hydroxyl side of α-CD and the negatively charged PI at the bilayer surface. This promoted the PI molecule extraction; in addition, another α-CD molecule was observed to include the PI unsaturated sn-2 acyl chain.Lopez et al. (2011) applied molecular dynamic (MD) simulations to study the mechanism of Chol extraction by β-CD. It is known that β-CDs in aqueous solution are associated to form dimers which are bound to the membrane surface assuming either a tilted or untilted configuration. Only the untilted configuration was appropriate to extract Chol allowing the formation of a membrane-bound CD/Chol complex. Although Chol is inserted quite deeply within the channel, the dimethyl end of its hydrophobic tail remains in contact with the monolayer surface until the CD/Chol complex tilts by 90º. Finally, the complex is desorbed where each dimer extracts one Chol molecule from membrane. It is worthy to mention that the CD monomer is able to interact with membrane but the strength of this interaction is insufficient to extract Chol. Also,[START_REF] Yancey | Cellular cholesterol efflux mediated by cyclodextrins. Demonstration Of kinetic pools and mechanism of efflux[END_REF] proposed that the CD-mediated Chol extraction occurs by its desorption from the surface directly into CD hydrophobic core (without passage through the aqueous phase). In addition,[START_REF] Steck | Probing red cell membrane cholesterol movement with cyclodextrin[END_REF] suggested that Chol efflux induced by CDs takes place through an activation-collision mechanism where the reversible partial projection of Chol molecules out of the erythrocyte lipid bilayer precedes their collisional capture by CD. Furthermore,[START_REF] Sanchez | Methyl-β-Cyclodextrins Preferentially Remove Cholesterol from the Liquid Disordered Phase in Giant Unilamellar Vesicles[END_REF] used Laurdan generalized polarization to investigate the specificity of Me-β-CD (0.25, 1, and 2 mM) in removing Chol from the coexisting macrodomains (liquid-ordered and liquid-disordered domains) of GUV membranes composed of DOPC:DMPC:Chol (1:1:1). The authors proved that Me-β-CD selectively remove Chol from the liquid disordered phase of the liposome bilayer.

Figure 9 :

 9 Figure 9: A scheme for cyclodextrin-mediated formation of asymmetric vesicles: cyclodextrins can promote lipid efflux (red and green) from symmetric donor membranes, form soluble complexes in aqueous phase, and carry the lipids to acceptor membranes. Various studies were carried out to investigate the transfer of PLs and Chol between donor and acceptor membranes. Donor vesicles, containing unlabeled lipids as well as labeled ones bearing a fluorescent moiety (NBD, BODIPY, pyrene, or other), a heavy isotope, or a radioactive molecule, were incubated with CDs; the unlabeled acceptor membranes are generally cells or lipid vesicles. After incubation, the acceptor membranes were separated from the donor membranes, subjected to lipid extraction, and analyzed. Besides, Huang and London (2013) studied CD-mediated lipid exchange assessing FRET between NBD-labeled lipids and rhodamine-labeled lipids embedded in donor vesicles. FRET was also used to monitor the DHE transfer from CD/DHE complex to lipid vesicles containing dansyl-PE (McCauliff et al., 2011).

  [START_REF] Li | Efficient replacement of plasma membrane outer leaflet phospholipids and sphingolipids in cells with exogenous lipids[END_REF] Chol: cholesterol; DHE: dehydroergosterol; DPPC: dipalmitoyl-phosphatidylcholine; EPC: egg phosphatidylcholine; NBD: 7-nitrobenz-2-oxa-1,3-diazol-4-yl; PC: phosphatidylcholine; PE: phosphatidylethanolamine; PI: phosphatidylinositol; PL: phospholipid; POPA: palmityl-oleoylphosphatidic acid; POPC: palmitoyl-oleoyl-phosphatidylcholine; PS: phosphatidylserine; Rh: rhodamine; SM: sphingomyelin; SOPC: 1-stearoyl-2-oleoyl-phosphatidylcholine; SOPG: 1stearoyl-2-oleoyl-phosphatidylglycerol; TNP-PE: N-trinitrophenyl-PE As it is obvious from Table

--

  α-CD β-CD: -Proteins were randomly extracted, Ono et al., any particular ones -The CD-induced protein extraction was in CD concentration dependent manner -At 150 mM, the CD-induced protein extraction was in the order: γ-CD < G2-β-CD < G2-β-CD << α-CD -At 15 mM, β-CD exhibited no ability for Proteins were randomly extracted, without preference to any particular ones -DM-α-CD induced protein extraction -No extraction was detected with other Proteins were randomly extracted, without preference to any particular ones -Me-β-CD and dimeb induced protein extraction -No extraction was obtained with βcell receptor; GRK1: rhodopsin kinase; Lck: lymphocyte-specific protein tyrosine kinase; MHC 1: major histocompatibility complex 1; PDE 6: cGMP phosphodiesterase 6; PTK: protein tyrosine kinase; Thy-1: Thymocyte antigen 1

-

  Release of CF was proportional to the CD concentration -Release of CF was in the order: DPPC liposome: Dimeb > α-CD > Trimeb DSPC liposome: Dimeb > Trimeb > α-CD Nishijo et al., 2000 DMPC liposome: α-CD> Dimeb > Trimeb Other CDs had no effect α-CD induced the CF release as function of time -Dimeb and Trimeb induced a rapid release of CF at the initial stages followed by a slow release which finally levelled off. -Release was proportional to the CD concentration -Release was in the order: SPC: SA liposome: Dimeb > Rameb > Trimeb SPC:Chol:SA liposome: Dimeb > Rameb > Trimeb > γ-CD Other CDs had no effect -Dimeb induced total release immediately after addition. Other CDs induced the release as a function of time. Release of calcein was in the order: Me-β-CD > HP-β-CD = HP-γ-CD -Release of calcein was in the order: PC > HPC > DSPC -Release of calcein: MLV > SUV -The presence of Chol reduced the permeability of PC liposomes but increased or did not affect that of other liposome types -CDs induced a significant release of calcein immediately after its addition; no further effect was produced. Release was proportional to the CD concentration -Release was in order of β-CD > α-CD > γ-CD -Higher CD concentration was needed for hemoglobin release compared to potassium release. -Release was proportional to the CD concentration -Effect of Me-β-CD > HP-β-CD β-CD had no effect. ; Chol: cholesterol; DMPC: dimyristoyl-phosphatidylcholine; DOPC: dioleoyl-phosphatidylcholine; DPPC: Dipalmitoyl-phosphatidylcholine; DSPC: distearoylphosphatidylcholine; HPC: hydrogenated phosphatidylcholine; LD: lactate dehydrogenase; PC: phosphatidylcholine; SA: stearylamine; SPC: soybean phosphatidylcholine.

  liposomes than HP-β-CD, at a CD concentration starting from 60 mM. This result was attributed to the ability of Me-β-CD to mediate a faster extraction of Chol with respect to HP-β-CD. Also, POPC vesicles were solubilized in a concentration-dependent manner when mixed with rameb solution (15-150 mM); the increase in rameb concentration from 80 to 100 mM led to a 2-fold increase in the amount of extracted POPC[START_REF] Anderson | Calorimetric measurement of phospholipid interaction with methyl-beta-cyclodextrin[END_REF]. In addition, rameb (0-152 mM) caused a progressive decrease in the turbidity of SPC:Chol:SA (60:30:10) liposomes until a transparent solution was obtained (above a CD concentration of 50 mM). Furthermore,[START_REF] Huang | Effect of Cyclodextrin and Membrane Lipid Structure upon Cyclodextrin-Lipid Interaction[END_REF] used FRET to study CD-induced vesicle solubilization. Their results showed that, among different CDs (Me-β-CD, HP-β-CD, and HP-α-CD), a significant vesicle solubilization (abolishment of FRET signals) was achieved by Me-β-CD; the effect was depending on the acyl chain length and saturation degree as well as on the PL head group.

6. 6 . 1 .

 61 Cryopreservation of liposomes using cyclodextrins as cryoprotectants[START_REF] Van Den Hoven | Cyclodextrin as membrane protectant in spray-drying and freeze-drying of PEGylated liposomes[END_REF] demonstrated a stabilizing effect of HP-β-CD, during freeze-drying, towards PEGylated DPPC:Chol liposomes (lipid:CD w:w ratio of 1:6) loaded with prednisolone; its effect was superior to that of sucrose or trehalose, other known cryoprotectants.[START_REF] Sebaaly | Effect of composition, hydrogenation of phospholipids and lyophilization on the characteristics of eugenol-loaded liposomes prepared by ethanol injection method[END_REF] compared the effect of different cryoprotectants (HP-β-CD, sucrose, trehalose, maltodextrin Glucidex6D and 19D, stearylamine, and cetyl alcohol) on phospholipon 90Hliposomes loading eugenol, an essential oil component. HP-β-CD showed the best protective effect; the mean vesicle size, pdI, Zeta potential, and eugenol encapsulation efficiency values were maintained when freeze-drying was conducted in the presence of HP-β-CD.The effects of composition and saturation of soybean PLs on the liposome stability during freeze-drying was evaluated byGharib et al. (2018b) using HP-β-CD as a cryoprotectant. HP-β-CD (10-100 mM) added to suspensions of conventional liposomes or present in the interior aqueous phase of CD-in-liposome system, protected hydrogenated liposomes during freezedrying, while this effect was not observed for liposomes composed of unsaturated PLs. HP-β-CD has a unique structure with numerous H-bond donors and acceptors. It may replace water molecules at the liposome surface during freeze-drying, thereby protecting the liposomal membrane from damage and keeping its structure intact[START_REF] Van Den Hoven | Cyclodextrin as membrane protectant in spray-drying and freeze-drying of PEGylated liposomes[END_REF].

Table 2 :

 2 Extraction of lipid membrane components by cyclodextrins

	Membrane	CDs type	[CD]

Table 3 :

 3 CD-induced lipid exchange between membranes

	595
	Donor	Acceptor	CD type	[CD]	Outcomes	Ref
	membrane	membrane		(mM)
	Liposomes of	-POPC:	CE-γ-CD 0-30	-Rate of lipid transfer was	Tanhuan
	POPC, TNP-	POPA				proportional	to	the	CD	pää and
	PE,	and	(500:20)			concentration	Somerha
	pyrene-		liposomes			-Increasing acyl chain length (6-	rju, 1999
	labelled PL	-Human			14 C) decreased the PL
	with various	fibroblasts			transport rate
	head groups	-Baby				-Transport of PI was enhanced
	and	acyl	hamster			compared to the other PLs
	chain length	kidney cells			-Rate of SM transport was 3
							folds greater than that of PC.
	Negatively	Uncharged	-α-CD	0-1	-CDs, except α-CD, induced Chol	Leventis
	charged		SOPC		-β-CD		transfer. Chol transfer rate was	and
	liposomes	vesicles	-γ-CD		53, 64, 63 folds higher when	Silvius,
	SOPC:SOPG			-Me-β-		treated with 1 mM Me-β-CD, γ-	2001
	(85:15)				CD		CD or	β-CD, respectively,
	containing					compared to untreated samples
	3 H-Chol and 3 H-DPPC					-Rate of Chol transfer was proportional to the CD concentration
							-Me-β-CD and α-CD induced
							DPPC transfer rather than Chol
							transfer
							-β-CD and γ-CD induced Chol
							transfer rather than DPPC
							transfer.
	POPC:Chol:	Baby		Me-β-CD 0-10	-CD induced PL transfer	Kainu et
	heavy		hamster			-Rate of PL transfer was	al., 2010
	isotopes		kidney cell			proportional to CD concentration
	labelled PL of					-Increasing acyl chain length
	various head					decreased the PL transfer rate
	group	and					but the nature of the head group
	acyl	chain					of PL had no effect.
	length
	liposomes
	EPC:DHE	EPC:dansyl-	HP-β-CD		-CD-induced the DHE transfer	McCauliff
	(75:25)		PE	(97:3)			-The rate of DHE transfer was	et	al.,
	liposomes	liposomes			proportional	to	the	CD	2011
							concentration
							-The DHE transfer occurred by a
							collisional transfer mechanism.

Acknowledgments

The research study was supported by the Research Funding Program at the Lebanese University and by the "Agence Universitaire de la Francophonie, Projet de Coopération Scientifique Inter-universitaire (PCSI)" 2018-2020.

Declarations of interest: none.