Triamcinolone permeation from different liposome formulations through rat skin in vitro

Liposome-skin interactions and their effects on the skin permeation of drugs

The aim of the study was to evaluate the interaction of phospholipid liposomes with skin and stratum corneum lipid liposomes (SCLLs). The influence of phospholipid liposomes on the skin permeability of model drugs was also studied. The transdermal flux of the drugs applied in various phospholipid containing formulations through human epidermis was studied in diffusion chambers. Liposomes in water solutions did not enhance the skin permeability of the drugs, but when ethanol (32% w/v) was present in the donor with EPC (egg yolk lecithin), permeabilities of some model drugs were substantially increased. Confocal microscopy studies revealed that EPC do not penetrate into the skin from water solutions, while from ethanol solutions, EPC penetrates deeply into the stratum corneum. Also, resonance energy transfer between different liposome compositions and the release of calcein from SCLLs showed that interactions between phospholipid liposomes and SCLLs increased with increasing ethanol concentration in the liposome solutions.

Application of vesicles to rat skin in vivo: a confocal laser scanning microscopy study

A major problem in (trans)dermal drug delivery is the low penetration rate of most substances through the barrier of the skin, the stratum corneum. One of the methods to increase the penetration rate across the skin is encapsulation of a (model) drug in lipid vesicles. In this study fluorescently labelled liposomes were applied on rat skin, in vivo. Bilayer labelled gel-state and liquid-state liposomes (conventional or with flexible bilayers) were non-occlusively applied on the dorsal area in the neck of the rat for 1, 3 or 6 h. Micelles were used as a control formulation. The penetration pathway and penetration depth of the lipophilic fluorescent label into the skin was visualised by confocal laser scanning microscopy (CLSM). During the first 3 h of application almost no differences in penetration depth were observed, when the label was applied in the various formulations. After 6 h application, it was clear that the label applied in micelles and gel-state liposomes did not penetrate as deep into the skin as the label applied in liquid-state vesicles. Among the liquid-state vesicles, the suspension with the most flexible bilayers showed the highest fluorescence intensity in the viable epidermis and dermis, 6 h post-application. Thus the vesicular form and the thermodynamic state of the bilayer and to a smaller extent the flexibility of the bilayer influence the penetration depth of the label into the skin at longer application periods. These results are in good agreement with CLSM results obtained from in vitro experiments with human skin.

Interactions between liposomes and human skin in vitro, a confocal laser scanning microscopy study

One major problem in (trans)dermal drug delivery is the low penetration rate of drugs through the barrier of the skin. Encapsulation of a drug in lipid vesicles is one strategy to increase the penetration rate of a drug across the skin. In this study, the interactions between fluorescent-labelled liposomes and skin are visualized by confocal laser scanning microscopy (CLSM). Bilayer labelled gel-state and liquid-state liposomes (conventional or with flexible bilayers) were non-occlusively applied on human skin in vitro. The penetration pathway and penetration depth of the lipophilic fluorescent label into the skin were visualized. From the CLSM images, it was clear that the label applied in micelles and gel-state liposomes did not penetrate as deep into the skin as the label applied in liquid-state vesicles. Among the liquid-state vesicles, the suspensions with the flexible bilayers showed the highest fluorescence intensity in the dermis. Thus, the thermodynamic state of the bilayer and, to a smaller extent, the flexibility of the bilayer influence, strongly the penetration depth of the label into the skin. The label applied non-occlusively in flexible liposomes penetrated deeper into the skin than after occlusive application.