Nanoemulsions as vehicles for topical administration of glycyrrhetic acid: characterization and in vitro and in vivo evaluation.

Nano-emulsions are innovative colloidal systems characterized by high kinetic stability, low viscosity, and optical transparency, which make them very attractive in many dermatological applications. Furthermore their small size seems to favor the topical administration of actives which scarcely cross the skin. In the light of these interesting features, the present study was aimed to the evaluation, in vitro and in vivo, of glycyrrhetic acid (GA) release through the skin from the nanoemulsion system. GA-loaded nanoemulsion (GA(N)) was prepared by phase inversion temperature (PIT) method, and was characterized in order to determine mean droplet size and its stability during a well-defined storage period. Further Cryo-TEM studies were performed to obtain information regarding nanoemulsion structure. The GA release pattern from nanoemulsion was evaluated in vitro, to determine its percutaneous absorption through excised human skin (stratum corneum and epidermis, SCE), and in vivo evaluating GA topical anti-inflammatory activity on healthy human volunteers by the UVB-induced erythema model. Nanoemulsions prepared by PIT method showed a mean droplet diameter of 210 nm that drastically changed during a storage of 5 weeks at room temperature. In vitro and in vivo evidence showed that the nanoemulsion system significantly increased the transdermal permeability of GA in comparison to a control O/W emulsion (GA(O/W)) containing the same amount of active compound.