The Use of Human Keratinocytes in the EU/COLIPA International In Vitro Phototoxicity Test Validation Study and the ECVAM/COLIPA Study on UV Filter Chemicals
Richard Clothier, Angie Willshaw, Helen Cox, Michael Garle, Helen Bowler and Robert Combes
The EU/COLIPA in vitro phototoxicity study involved the testing of 30 chemicals in Phase II, and the ECVAM/COLIPA study on UV filter chemicals involved the testing of 20 chemicals, for which in vivo human and/or animal data were available. Primary human keratinocytes, from four separate male donors, were not found to be sensitive to the 5J/cm2 UVA produced by the SOL500 lamp when assayed by using the neutral red uptake endpoint, as employed with the 3T3 cells used in these international interlaboratory validation studies. The primary human keratinocytes tested in one laboratory alongside the 3T3 fibroblasts gave consistent indications of phototoxicity with all the phototoxicants tested in the Phase II and UV filter studies. The one exception was bithionol, which was predicted to be non-phototoxic in both studies. None of the non-phototoxic chemicals resulted in a positive reaction with the Photoirritation Factor (PIF) version of the prediction model. However, when the Mean Photo Effect (MPE) prediction model version was applied (with a cut-off point of 0.1), one sunscreen agent, octyl salicylate, was deemed to have phototoxic potential. The entire set of negative rated chemicals included in Phase II and in the UV filter study were also rated as non-phototoxic by the MPE prediction model.