The use of reconstructed human skin to evaluate UV-induced modifications and sunscreen efficacy.

Biological and clinical effects of sun exposures are characterized by short-term reactions, i.e. sunburn reaction and suntan, as well as long-term consequences corresponding to photoaging and photocancers. We have developed several human in vitro three-dimensional models in order to assess both the photodamage and the photoprotection afforded by sunscreens. Using a full thickness reconstructed skin comprising a differentiated epidermis and a living dermal equivalent, UVB- and UVA-induced biological markers could be found at both the keratinocyte and the fibroblast level. Typical markers of the sunburn reaction could be reproduced in that model as well as dermal damages related to the photoaging process. Another model of reconstructed epidermis, comprising keratinocytes but also melanocytes and Langerhans cells, has been developed. The study of the UV-induced pigmentation as possible using the pigmented reconstructed epidermis and allowing to reproduce the epidermal melanin unit. The assessment of cellular parameters related to UV-induced immunosuppression could be performed using the reconstructed epidermis containing Langerhans cells. Exposure to solar-simulated radiation provokes morphological alterations and the reduction in numbers of Langerhans cells within the exposed epidermis. Using all these models, the efficiency of sunscreens could be envisaged after topical application. The results showed that appropriate sunscreens could efficiently prevent the damage described above.