Substance photo-toxicity is characterized by a chemical irritation of the skin that is induced by ultraviolet (UV) light. Photosensitizing or phototoxic substances reach the skin by topical application, through the circulation system via ingestion or intravenous injection. The reaction can cause rashes, swelling, and inflammation. In some people, symptoms can last for over 20 years after a phototoxic medication has been stopped. Common drugs that are known to cause phototoxic reactions in some people are ibuprofen, doxycycline, and promethazine.
Our human in vitro skin model has significant advantages over the 3T3 Neutral Red Uptake Phototoxicity Assay, currently the most recognized in vitro test method for photo-toxicity. Using human keratinocytes our test method is more species and mechanistically specific than the 3T3 model. The three-dimensional human skin model with a full epidermis is much closer to the human in vivo environment, as opposed to the 3T3 test, which is a simple monolayer model.
Substances and formulations with photosensitizing or phototoxic potential are topically or systemically applied. UV irradiation with a defined, but non-cytotoxic, dose is performed. Parallel testing of a known phototoxic substance serves as positive control.
After substance treatment and UV irradiation with a non-cytotoxic dose, the photo-cytotoxic potential is determined. A substance is considered phototoxic when cell viability of the treated and irradiated skin model is decreased by more than 30% compared to the corresponding non-irradiated control and a cytotoxic effect is excluded.Results are summarized in a detailed test report. The following analytical methods are used
Accreditation – Our in vitro human-based phototoxicity test method (in accordance with the OECD Guideline 432 and the INVITTOX Protocol. 121) was certified in December 2014 as an accredited assay procedure.