Interactions of elastic and rigid vesicles with human skin in vitro: electron microscopy and two-photon excitation microscopy

Abstract

Interactions between vesicle formulations and human skin were studied, in vitro, in relation to their composition and elasticity. The skin ultrastructure was investigated using transmission electron microscopy (TEM), freeze-fracture electron microscopy (FFEM) and two-photon fluorescence microscopy (TPE). The main difference between the vesicle formulations was their elasticity. Elastic vesicle formulations contained bilayer forming surfactants/lipids and single-chain surfactant octaoxyethylenelaurate-ester (PEG-8-L), whereas rigid vesicles contained bilayer surfactants in combination with cholesterol. TEM results showed three types of interactions after non-occlusive application of elastic PEG-8-L containing vesicle formulations on human skin: (1) the presence of spherical lipid structures containing or surrounded by electron dense spots; (2) oligolamellar vesicles were observed between the corneocytes in the upper part of the stratum corneum; and (3) large areas containing lipids, surfactants and electron dense spots were observed deeper down into the stratum corneum. Furthermore, after treatment with vesicles containing PEG-8-L and a saturated C12-chain surfactant, small stacks of bilayers were found in intercellular spaces of the stratum corneum. Rigid vesicles affected only the most apical corneocytes to some extent. FFEM observations supported the TEM findings. Major morphological changes in the intercellular lipid bilayer structure were only observed after treatment with PEG-8-L containing elastic vesicles. TPE showed a distinctdifference in penetration pathways after non-occlusive application of elastic or rigid vesicles. After treatment with elastic vesicles, thread-like channels were formed within the entire stratum corneum and the polygonal cell shape of corneocytes could not be distinguished. Fluorescent label incorporated in rigid vesicles was confined to the intercellular spaces of the upper 2-5 micrometer of the stratum corneum and the cell contours could still be distinguished.

In Vitro Cutaneous Application of ISCOMs on Human Skin Enhances Delivery of Hydrophobic Model Compounds Through the Stratum Corneum

“…Similar electron-dense spots in the lipid areas in the stratum corneum have also previously been observed by van den Bergh et al after treatment with elastic vesicles and fixation with osmium tetroxide (11). In that study, the spots were concluded to originate from the vesicle material.…”

“…Lamellar stacks similar to the contents of lamellar bodies in the stratum granulosum were observed by van den Bergh et al after application of elastic vesicles onto human and mouse skin (11,13). In the same studies, disorganized intercellular lipids were also observed.…”

“…The transcutaneous penetration pathway of either fluorescent drugs or various nanoparticles has previously been indentified using confocal laser scanning microscopy (CLSM) (9)(10)(11)(12). Supplementary to this, transmission electron microscopy (TEM) provides a higher resolution and has previously been used to evaluate the mechanism of penetration of elastic vesicles into both human and mice skin in vitro and to study interactions between vesicles and skin (11,13). The results of those studies showed the location of intact elastic vesicles in the upper three layers of the stratum corneum and that the intercellular lipid layer was disturbed by the application of elastic vesicles.…”

Application of in vivo Laser Scanning Microscopy to Visualise the Penetration of a Fluorescent Dye in Solution and in Liposomes into the Skin after Pre-Treatment with Microneedles

“…Therefore, it is highly probable that the conduits formed by microneedles can be monitored over time using CLSM. The information obtained from CLSM studies of skin penetration can be used to optimise formulations for delivery of substances into the skin in general or into special parts of the skin, for example, transport through hair follicles or sebaceous glands (Grams et al, 2005, Lademann et al, 2009, van den Bergh et al, 1999. Often, these investigations were performed in vitro on porcine ear skin or excised human skin.…”

Highly deformable and highly fluid vesicles as potential drug delivery systems: theoretical and practical considerations

“…23,24 Elastic vesicles from nonionic surfactants These are elastic (deformable) vesicles prepared from the bilayer-forming surfactant L-595 (100% sucrose laurate ester, 30% mono-, 40% di-, and 30% triester) and the micelle-forming nonionic surfactant PEG-8-L (polyoxyethylene laurate ester) with sulfosuccinate as stabilizer (50/50/5 molar ratio). 25 Vesicles facilitate drug transport by a fast partitioning into the SC, thereby carrying vesicle-bound drug molecules into the SC. 26 The transport is via a fine meshwork of thread-like channels.…”