Influence of liposomal encapsulation on the penetration of retinoic acid through human skin in vitro
Delphine Imbert , Gerald B. Kasting , R. Randall Wickett

Synopsis

The penetration of liposome-encapsulated trans -retinoic acid ( t -RA) through the different strata of the skin was investigated using in vitro diffusion experiments on human cadaver skin. Simple phospholipid liposomes and a more complex pH-sensitive preparation containing 0.05% t -RA were applied to isolated human stratum corneum, isolated human epidermis, and dermatomed human skin, along with one of two non-liposomal controls. The control solutions were either 0.05% t -RA in ethanol (for small-dose experiments) or saturated solutions of t -RA in Transcutol®\/water mixtures (for large-dose experiments and some small-dose experiments). Skin-specific interactions were differentiated from solution thermodynamic effects by repeating some experiments using a silicone rubber membrane. The influence of dose volume and occlusion was investigated. The results showed no evidence of enhanced epidermal penetration, nor of decreased percutaneous absorption from liposomal t -RA vs unencapsulated controls under realistic dose conditions. However, under one set of exaggerated dose conditions (consisting of a large, non-occluded dose of t -RA in PC liposomes), there was a suggestion that diffusion of t -RA across the lower skin layers may have been retarded by the liposomal components.

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