ECVAM FEASIBILITY STUDY: CAN THE PRE-VALIDATED IN VITRO SKIN MODEL PHOTOTOXICITY ASSAY BE UPGRADED TO QUANTIFY PHOTOTOXIC POTENCY OF TOPICAL PHOTOTOXINS?

This study by scientists at ZEBET (Germany) and the Czech Republic National Institute of Public Health (SZU) demonstrated that MatTek’s EpiDerm in vitro human skin tissue equivalent can be used in place of animals to accurately predict the phototoxicity of topically applied formulations. The determination of phototoxicity of a chemical in the 3T3-NRU-PT test according to OECD Test Guideline 432 is often the first step in a sequential phototoxicity testing strategy. If the chemical provides a negative result in the 3T3-NRU-PT, in most instances no further testing is required. However, if the result is positive, the chemical may still be applied topically at safe concentrations, depending on the absorption and accumulation of the chemical in the skin. Thus, in addition to the information on inherent phototoxicity potential assessed by the 3T3-NRU-PT, additional testing may be required to obtain combined information on the phototoxicity and bioavailability of the chemical in the skin. Ideally, confirmatory tests should be performed in vivo on human volunteers, but for ethical reasons, this is not acceptable, if the 3T3-NRU-PT has provided a positive result. Thus, to avoid confirmatory testing in vivo in animals, reconstructed human 3-D skin models are offering an attractive in vitro alternative for testing, since such models are characterized by both skin barrier function and viable primary skin cells. In the current study, several substances (mostly cosmetic ingredients) which are known to be safely used in humans, and which provided positive results in the 3T3-NRU-PT, were evaluated using the reconstructed human skin model EpiDerm and the pre-validated EpiDerm Phototoxicity test. In order to clarify the situation in man, human data were generated using a standard photo patch test on a limited group of human volunteers. Study Conclusions: The aim of this study was to demonstrate the importance of the use of a reconstructed human skin model as a supplementary assay to the validated 3T3-NRU-PT test. It has been shown, that a true phototoxic potential of a chemical correctly predicted with the cellular 3T3-NRU-PT may be irrelevant when topically applied to the skin (barrier) at low concentrations (e.g. in a formulation). In our study all four substances were classified by the 3T3-NRU-PT test as clear phototoxins. However, because of the well developed barrier of the EpiDerm model, none of the chemicals was able to penetrate into the deeper (viable) parts of the epidermis and damage the cells by the phototoxic property. All predictions obtained with the EpiDerm Phototoxicity test were subsequently confirmed in the human photo patch test. These first results show that reconstructed human skin models provide valuable information in a sequential approach to assess photo safety (or photo potency) of substances and formulations, as recently suggested by European experts.

3T3-NRU-PT test, 96-well plates, Bioavailability, Cytotoxic effect, Cytotoxicity, ECVAM, EpiDerm, Epiderm phototoxicity test, Eusolex 9020, Human 3-D skin model, Ichthyol pale, In vitro skin model, Irradiation, Litsea cubeba, MTT, MTT assay, Mean photo effect (MPE), Photo irritancy factor (PIF), Photo patch test, Photo potency, Photo safety, Phototoxic potency, Phototoxicity, Phototoxicity assay, Photoxins, Titanium dioxide, Viability

Eusolex 9020, Ichthyol pale, Litsea cubeba, Titanium dioxide