Characterization and comparison of reconstructed skin models: morphological and immunohistochemical evaluation

Reconstructed human skin equivalents are currently being investigated as in vitro models for the prediction of human skin toxicity and irritation responses. Three different industrial reconstructed skin models (EpiDerm, Episkin and SkinEthic) and one in-house equivalent were characterized and compared using light microscopy, immunohistochemistry and reduction of (3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyl tetrazolium bromide) (MTT). Their inter- and intra-batch variation was evaluated. Histological examination showed a completely stratified epithelium in all skin models, which closely resembled normal human epidermis. Low intra-batch variation in tissue architecture was observed in all skin models, but moderate to considerable inter-batch variation was noticed. Evaluation of the expression and localization of a number of differentiation-specific protein markers revealed that all skin models showed an aberrant expression of keratin 6, skin-derived antileukoproteinase, small proline rich proteins, involucrin and transglutaminase. Although variation within batches was low, in particular keratin 6, involucrin and skin-derived antileukoproteinase expression demonstrated some inter-batch variation. Reduction of MTT in vehicle-treated cultures showed high similarities between skin models, but marked differences were observed when 1.0% sodium lauryl sulfate was applied topically for 3 or 16 h. Most pronounced effects were noticed in SkinEthic cultures. Intra-batch variations were low and moderate variations were observed between batches. All skin models tested reproduced many of the characteristics of normal human epidermis and therefore provide a morphologically relevant in vitro means to assess skin irritation and other skin-related studies.