In vitro percutaneous absorption of all-trans retinoic acid applied in free form or encapsulated in stratum corneum lipid liposomes

The objective of this study was to design an all-trans retinoic acid (RA) topical release system that modifies drug diffusion parameters in the vehicle and the skin in order to reduce systemic absorption and the side-effects associated with topical application of the drug to skin. Three cases of application of hydrogels containing RA either in free form or encapsulated in stratum corneum lipid liposomes (SCLLs) have been considered. For this purpose, we have evaluated the RA in formulations with combinations of Carbopol® Ultrez™ 10 (U10) and hyaluronic acid (HA) for percutaneous absorption. In vitro permeability experiments with [3H]-t-RA were carried out using a Franz-type diffusion cell in abdominal rat skin samples. Accumulation of the drug in the surface and skin layers was evaluated by both the tape stripping method and a dissection technique, and subsequently, all the radiolabelled samples were analyzed by liquid scintillation counting. The results show that RA encapsulation not only prolongs drug release but also promotes drug retention by the viable skin. At the same time, interaction between RA and HA has an obstructive effect on diffusion, which contributes to the formation of a reservoir of the latter.