Depth-dependent stratum corneum permeability in human skin in vitro.

Abstract

The stratum corneum (SC), a permeable membrane, limits percutaneous penetration. As SC chemical and structural properties responsible for skin barrier function appear depth-related, we conducted an in vitro dermatopharmacokinetic study on intact and adhesive tape-stripped skin samples to clarify whether SC is a homogeneous barrier for chemical transport. SC concentration-thickness profiles were determined for four C-14 labeled model chemicals, panthenol, benzoic acid, paraoxon and butenafine, using the tape-stripping approach. Data analysis with the unsteady-state diffusion equation of Fick's second law permitted a chemical diffusion coefficient in SC. To evaluate the consistency of SC permeability from its surface to lower levels, the skin was tape-stripped five to 10 times to remove the upper cell layers before chemical application, such that diffusion coefficients could be determined from three SC depth levels (0, 5 and 10 tape strips). Results suggested the depth-dependency of SC permeability to panthenol, benzoic acid and butenafine; the diffusion coefficient of panthenol decreased significantly after the first five tape strips and subsequently remained consistent. A progressive increase in diffusion coefficients of benzoic acid and butenafine was observed as tape-stripping levels increased. The removal of superficial SC did not result in a significant difference in the paraoxon diffusion coefficient. For individual chemicals, a variation in the diffusion coefficient from SC surface to deeper layers agreed with the change of the diffusion coefficient over time in intact skin. Characterization of the SC properties contributing to the depth-dependent SC permeability will hopefully provide further insight to skin penetration/decontamination. Copyright © 2016 John Wiley & Sons, Ltd.