Traditional phototoxicity testing compares the cytotoxicity of test substances in the presence and absence of ultraviolet A (UV-A) light according to the OECD 432 guideline. Although UV-A activation is the primary factor responsible for phototoxicity of substances present either on the surface of, or within, the skin, activation of certain classes of compound has also been observed with lower energy light in the blue spectrum. This is of increasing relevance with the use of electronic devices and LED lighting, and blue light is also being widely used for a variety of treatments. Dental, dermatological and some anti-cancer treatments utilise blue light to convert inactive molecules into active ones. Despite the obvious benefits of this approach, it is now becoming apparent that, like UV-A light, blue light has the ability to induce toxicity of certain co-administered therapies.
Our research in this area has focused on the development of an in vitro method suitable for testing blue light activation (475 nm wavelength) of chemicals and subsequent toxic effects in gingival tissue using the human-derived EpiGingivalTM-FT 3D model from MatTek. The EpiGingivalTM-FT model was chosen because of its applicability to blue light exposure in dental use.
Interestingly, and in contrast to UV-A, exposure to increasing doses of blue light alone had no effect on tissue viability. However, exposure to the anti-cancer drugs, 5-amino-levulinic acid and protoporphyrin IX, prior to blue light exposure significantly reduced tissue viability when compared with dark conditions. These data suggest that these compounds may act as suitable positive controls for future testing of blue-light induced toxicity in this model.
Our research on blue light-mediated toxicity was presented at the SOT conference in Baltimore in March 2017.