Activation of flavin-containing oxidases underlies light-induced production of H₂O₂ in mammalian cells

Violet-blue light is toxic to mammalian cells, and this toxicity has been linked with cellular production of H₂O₂. In this report, we show that violet-blue light, as well as UVA, stimulated H₂O₂ production in cultured mouse, monkey, and human cells. We found that H₂O₂ originated in peroxisomes and mitochondria, and it was enhanced in cells over-expressing flavin-containing oxidases. These results support the hypothesis that photoreduction of flavoproteins underlies light-induced production of H₂O₂ in cells. Because H₂O₂ and its metabolite, hydroxyl radicals, can cause cellular damage, these reactive oxygen species may contribute to pathologies associated with exposure to UVA, violet, and blue light. They may also contribute to phototoxicity often encountered during light microscopy. Because multiphoton excitation imaging with 1,047-nm wavelength prevented light-induced H₂O₂ production in cells, possibly by minimizing photoreduction of flavoproteins, this technique may be useful for decreasing phototoxicity during fluorescence microscopy.