Effects of UV irradiation on a living skin equivalent.

The Living Skin Equivalent (LSE) is an organotypic coculture composed of human dermal fibroblasts interspersed in a collagen-containing matrix and overlaid with human keratinocytes forming a stratified epidermis. The LSE has a dry, air-exposed epidermal surface suitable for the application of oils, creams and emulsions. These features suggested its feasibility as an in vitro skin model for studying the protective effects of sunscreens. Using the thiazolyl blue (MTT) conversion assay as a measure of mitochondrial function, the extent of cytotoxicity induced by various doses of UV-R (280-400 nm) or UV-A (320-400 nm) was evaluated in the LSE. The doses of UV radiation that caused 50% reductions in MTT conversion (UV-R50 or UV-A50) in different lots of LSE were 0.053 +/- 0.021 J/cm2 (n = 29) and 11.6 +/- 4.9 J/cm2 (n = 17) for UV-R and UV-A, respectively. The protective effects of an 8% homosylate standard and of five UV-A sunscreens, topically applied to the LSE, were determined and compared with their reported protection factors in human skin. Morphological changes and the release of proinflammatory mediators (interleukin-1-alpha, tumor necrosis factor-alpha and prostaglandin E2) implicated in UV-induced erythema were also demonstrated in the LSE exposed to UV-A or UV-B. The data suggest that the LSE can be used for studying the effects of UV radiation on skin and may have utility for assessing the efficacy of certain sunscreens against UV-B and UV-A.