Application of liposomes as potential cutaneous drug delivery systems. In vitro and in vivo investigation with radioactively labelled vesicles.

The potential application of liposomes as dermal delivery systems was investigated, with regard to vesicle composition and size. Liposomes were made up of phospholipids or skin lipids, referred to as phospholipid-based liposomes and stratum corneum lipid-based liposomes, respectively. A stripping procedure from stratum corneum to dermis by means of adhesive tape was carried out to evaluate the extent of accumulation in the superficial layers of the skin. The various liposomes were radiolabelled both in the bilayer structures with [3H]cholesterol, [14C]dipalmitoylphosphatidylcholine and [14C]palmitic acid, depending on vesicle type, and in the aqueous compartments with [14C]inulin. Inulin absorption and elimination was also evaluated. Stratum corneum lipid-based liposomes could permeate the stratum corneum to a greater extent than phospholipid-based liposomes. Stratum corneum lipid-based liposomes could deliver a greater amount of aqueous radiolabelled marker ([14C]inulin) to the deeper skin strata (epidermis and dermis), while avoiding systemic absorption and, hence, organ distribution and renal elimination of [14C]inulin. Another important parameter in determining the extent of absorption is the vesicle size: the greater the mean size of liposomes, the poorer the permeation through stratum corneum layers. When fluid liposomes made up of unsaturated lecithins were used, a percutaneous absorption was obtained instead of dermal delivery. Stratum corneum lipid-based unilamellar liposomes may be suitable devices for dermal delivery.