Absorption and metabolism of topically applied testosterone in an organotypic skin culture

The Living Skin Equivalent (LSE) is an organotypic coculture of human dermal fibroblasts in a collagen-containing matrix and a stratified epidermis composed of human epidermal keratinocytes. In order to establish the feasibility of using this in vitro system as a model for cutaneous biotransformation, the metabolic fate of topically applied testosterone (T) was monitored in the LSE. After a 24-hour exposure period (37 degrees C) to radiolabelled T, LSE extracts analyzed by high-performance thin-layer chromatography showed that approximately 50% of the applied T had been metabolized. Identified metabolites included bands which comigrated with polar metabolites and products of T 5 alpha-reductase. The general distribution of the observed metabolites was similar to that obtained using biopsied human skin. The rates of T penetration (32 degrees C) through the LSE were monitored after application of T in two vehicles (water and petrolatum) and yielded permeability constants (Kps) of 29 and 1.6 x 10(-3) cm/h, respectively. These Kp values were 4- to 6-fold higher than those reported for human abdominal skin, and reflect the vehicle-related shift in penetration seen in human skin. The Kp values for two additional steroids, estradiol and hydrocortisone, and for T were also determined at 22 degrees C and compared to published Kp values. These Kp values in the LSE were, respectively, 63-, 187- and 35-fold higher than those reported for human skin. The data suggest that compared to human skin the LSE has only a partial barrier function to the passage of test chemicals.(ABSTRACT TRUNCATED AT 250 WORDS)