Diffusion of E and Z Urocanic Amphiphiles through Skin and Their Insertion in a Membrane Model

The incorporation of synthetic urocanic amphiphiles into a membrane model is described. A monomolecular film of dipalmitoyl phosphatidylcholine (DPPC) and cholesterol was formed at the air-water interface and used as a model. In parallel, diffusion of these derivatives through the skin was studied using rat skin on flow-through diffusion cells. The flux and the cumulative amount were determined. Although the structure and the composition of the DPPC/cholesterol monolayer differed greatly from multilayers of epidermal lipids, the results obtained in the incorporation and diffusion studies were similar. The structure of the urocanic amphiphiles was very close, but the membranes led to the following flux or insertion classification: Ester E > Ester Z >> Amide E. From the results obtained and for simplicity, the technique of Langmuir monolayers seems to be highly suited to the primary screening of amphiphilic compounds.