A REPRODUCIBLE, STRUCTURALLY APPROPRIATE SKIN MODEL FOR DERMAL IRRITANCY AND EFFICACY TESTING.

The ability to determine, in vitro, the efficacy and irritancy of materials contacting the skin critically depends on the accuracy of the skin model in emulating native epidermis’ structure and biochemistry. In addition, for any toxicology or efficacy model to be useful, it is important to know that the model is reproducible both within a given lot and between lots. For this reason, the structure, biochemical nature, and reproducibility of an organotypic skin model, EpiDerm™, was investigated. Using light microscopy, histological cross-sections showed basal, spinous, granular, and stratum corneum layers, similar to epidermis. Using immunohistochemistry techniques, epidermis-specific proteins such as pro-filaggrin, cytokeratins K1 and K10, keratohyalin, transglutaminase, and gluco-cerebrosidase were localized within the model in the appropriate cellular layers; lipid analysis of EpiDerm and native epidermis showed very similar lipid profiles. Ultrastructurally, transmission electron microscopy revealed lamellar lipid bilayers spaced in the two patterns characteristic of in vivo stratum corneum. In order to assess the model’s reproducibility, each lot of tissue was exposed to 2 commonly used surfactants, Triton X-100 (TX) and sodium dodecyl sulfate (SDS), and a negative control, ultrapure water. Using the MTT assay and 3 exposure times for each surfactant, N=2 tissues, a dose response curve was constructed and an effective time which reduces the metabolic activity by 50% (ET-50) was interpolated. The average ET-50’s for TX and SDS for 114 lots produced in 1995 were 6.64 ± 0.79 and 0.92 ± 0.23 hours, respectively; the negative control had a coefficient of variation (c.v.) of 8.6% for the same lots. Within individual lots, the MTT response for the negative control had an average c.v. of 3.6% (N=114) and for all positive and negative controls an average c.v. of 10.3%. Based on these results, the EpiDerm skin model appears well suited to answer numerous dermal efficacy and/or safety questions without the use of laboratory animals or costly human clinical panels.