RESUMEN
Cyclodextrins (CDs) are known for their ability to extract lipid components from synthetic and biological membranes and therefore to induce an increase of membrane permeability. However, the effect of cholesterol (CHOL) content in the membrane on the CD permeabilizing effect was not considered yet. Given that an increase in CHOL content reduces the membrane permeability, the aim of this work was to reveal how CHOL would modulate the CDs effect on the membrane. Hence, liposomes made of dipalmitoyl phosphatidylcholine (DPPC) and various CHOL contents (DPPC/CHOL 100:10, 100:25, 100:50, and 100:100) encapsulating the hydrophilic fluorophore, sulforhodamine B (SRB), were prepared and exposed to the native CDs (α-CD, ß-CD, γ-CD) and four ß-CD derivatives: the randomly methylated-ß-CD (RAMEB), the low methylated-ß-CD (CRYSMEB), the hydroxypropyl-ß-CD (HP-ß-CD) and the sulfobutyl ether-ß-CD (SBE-ß-CD) at different CD/DPPC molar ratios (1:1, 10:1, and 100:1). The membrane permeability was monitored following the release of SRB with time. The results demonstrated that the CDs effect on the membrane depends on the CD type, CD concentration, and membrane CHOL content. The investigated CDs exhibited an instantaneous permeabilizing effect promoting vesicle leakage of SRB from the various membranes; this effect increased with CDs concentration. Among the studied CDs, α-CD, ß-CD, and RAMEB were the most permeabilizing CDs on the different membranes. Similar modifications of SRB release from the various liposomal formulations were obtained with HP-ß-CD, CRYSMEB, and SBE-ß-CD. γ-CD was the less potent CD in affecting the membrane permeability. The CDs effect also depended on the CHOL content: at the CD/DPPC molar ratio (100:1), RAMEB and ß-CD considerably permeabilized the membrane of high CHOL content (50%, 100%) while the remaining CDs showed a decreasing permeabilizing effect upon CHOL content membrane increase.
RESUMEN
Encapsulation in liposomes has been an efficient strategy to improve the stability of sensitive bioactive compounds such as essential oils (EOs). However, the stability of liposomal formulations remains a key parameter controlling the delivery of encapsulated ingredients. Cholesterol (Chol) modulates the membrane properties conferring stability to the lipid bilayer. Thus, the Chol content in the liposome formulations encapsulating EO components should be carefully chosen. In this work, various liposome formulations differing by Chol content (DPPC:Chol 100:10; 100:25; 100:50; 100:75; 100:100) were exposed to a series of 22 EO components at DPPC/EO 100/25. The formulations were characterized for their final composition and their permeability to the hydrophilic fluorophore, sulforhodamine B (SRB), was monitored. Results showed that the Chol content experimentally determined for the various formulations (above 10% Chol) was below the theoretical weighed Chol. Among the tested components, 13 molecules displayed a significant permeabilizing effect on 10% Chol membranes. Most of these possess a hydroxyl group. The EO induced permeability was dependent on the Chol content which affects the membrane phase: their effect was reduced upon increasing Chol content keeping five EOs components effective at 40% Chol. The EO's effect was also linked to the hydrophobicity of the molecule. Hence, the DPPC:Chol ratio of the formulation is chosen considering the structure of the compound, its hydrophobicity and its effect on the permeability at different Chol content: a formulation comprising 40% Chol is suggested for highly hydrophobic molecules whereas a formulation with higher Chol content could be selected for less hydrophobic compounds.
Asunto(s)
Liposomas , Aceites Volátiles , 1,2-Dipalmitoilfosfatidilcolina/química , Colesterol/química , Membrana Dobles de Lípidos , Liposomas/química , PermeabilidadRESUMEN
Liposomes are lipid vesicles made of one or multiple lipid bilayers surrounding an internal aqueous core. They are broadly employed as models to study membrane structure and properties. Among these properties, liposome membrane permeability is crucial and widely assessed by fluorescence techniques. The first part of this review is devoted to describe the various techniques used for membrane permeability assessment. Attention is paid to fluorescence techniques based on vesicle leakage of self-quenching probes, dye/quencher pair or cation/ligand pair. Secondly, the membrane-active agents inducing membrane permeabilization is presented and details on their mechanisms of action are given. Emphasis is also laid on the intrinsic and extrinsic factors that can modulate the membrane permeability. Hence, a suitable liposomal membrane should be formulated according to the aim of the study and its application.