Diffusion of [2-14C]diazepam across isolated hairless mouse stratum corneum/epidermal tissues

The objective of this study was to develop a method of preparing mouse stratum corneum/epidermal (SCE) tissue without the dermis for use in drug diffusion studies. The diffusion of radiolabeled diazepam across this new preparation has been studied and the effect of the dermis on diffusion evaluated. Incubation of large pieces of mouse skin in a 20mM EDTA, 15 mM sodium phosphate buffer, pH 7.2, in normal saline for 3-4 h at 37 degrees C resulted in a tissue which easily separated at the epidermal-dermal junction. The resulting tissue contains stratum corneum and epidermis, which are the same layers used in studies with human skin in vitro. The EDTA treatment did not effect diffusion of [2-14C]diazepam across whole mouse skin (SCE and dermis) used as controls. The rate of drug diffusion was greater across SCE than SCE and dermis, however, 0.48-1.12 micrograms/cm2/h versus 0.11-0.52 microgram/cm/h, respectively. The permeability coefficients for mouse SCE ranged from 1.92-4.48 X 10(-2) cm/h. The lag times and diffusion coefficients were 0.36-0.91 h and 0.1-0.6 X 10(-6) cm2/h, respectively. The presence of the dermis decreased the diffusion rate or flux of diazepam. The dermis appears to accumulate drug until it is saturated and then the drug diffuses into the receiving chamber.