In the field of in vitro tests, IEC (l’Institut d’Expertise Clinique – Lyon) has, among others, actively worked on the phototoxicity model with reconstructed skin (IFSCC 2014, Paris, poster No. 298, Phototoxicity on Human Reconstructed Epidermis (Episkin® model): Development and validation of the Method).
There is indeed no in vitro method validated to date for the phototoxic potential of finished products. Only the in vitro 3T3 NRU method(1) validated to assess the phototoxic potential of chemical ingredients is commonly performed for both finished products and cosmetic ingredients.
This test is based on the comparison of the cytotoxicity (with and without irradiation with simulated sunlight ) of the product applied at different concentrations on a monolayer cell (continuous cell line of mouse fibroblasts – Balb / c 3T3 , clone 31). Although validated for chemical ingredients, this method has limitations which do not allow it to be effectively implemented to finished products.
IEC has therefore worked on the demonstration of the relevance and interest of the use of reconstructed skin model EpiSkinTM, according to GLP standards.
Various molecules known to be photo-toxic or non- phototoxic in vivo were tested on human reconstructed epidermis: a very good predictability of this method has been demonstrated based on a protocol which proves to be very close to the in vivo protocol TCFS PT(2) (Final Clinical Safety Test, Phototoxic Potential, published by Afssaps and still widely used) especially regarding the time of contact and the dose exposure to UV; this method shows multiple interests:
- confirm or invalidate “probable phototoxicity” result with 3T3 NRU
- overcome problems of solubilization (use of oil as a solvent, impossible with 3T3 NRU)
- closely match normal conditions of use of a finished product , since it will be tested as such
- perform additional analyzes (eg histology).
(1) OCDE, Test Guidelines for the testing of chemicals / Section 4: health effects, test n° 432: in vitro photo-toxicity test 3T3 NRU – 13 April 2004.
(2) Afssaps Recommendation, TCFS PT – finale version of December 2009.
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