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Photobiology| Volume 139, ISSUE 5, SUPPLEMENT , S129, May 2019

747 The coexistence of riboflavin and tryptophan is responsible for the production of H2O2 in the UVA-induced cytotoxicity of dermal fibroblasts

      We previously reported that H2O2 plays a pivotal role in the UVA-induced cellular senescence of normal human fibroblasts in vitro using culture medium containing various kinds of UVA chromophores. In this study, we investigated possible candidates for UVA chromophores in the culture medium by assaying cell viability. Cell viability was dramatically reduced when riboflavin and tryptophan coexisted during UVA irradiation, while little or no change in cell viability was observed in the presence of riboflavin or tryptophan alone. In addition, an increase of H2O2 level in the medium was detected in a dose-dependent manner after UVA irradiation only when riboflavin and tryptophan coexisted. Interestingly, the reduced cell viability induced by UVA irradiation in the presence of both riboflavin and tryptophan was restored by simultaneous treatment with N-acetyl-L-cysteine that increases the intracellular amount of reduced glutathione, however, there was no significant change in the amount of H2O2 in the culture medium. These results suggested that the coexistence of riboflavin and tryptophan is principally responsible for the production of H2O2 in the UVA-induced cytotoxicity of cultured dermal fibroblasts and that cysteine compounds may alleviate H2O2-induced cell toxicity by activating the intracellular anti-H2O2 ability, leading to the prevention of UVA-induced cellular senescence.