Lethal effect of visible fluorescent light on human cells in culture
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Human D98/AH2 epithelial cells in serum-free Dulbecco’s modified Eagle's culture medium depleted of phenol red were not able to divide and form clones subsequent to illumination by "Daylight," "Special Blue" or "Bilirubin" broad-spectrum visible fluorescent lamps. The dose of light required to produce this inhibition of clonal growth increased with increasing cell density. Irradiation of serum-free medium alone was sufficient to effect trypan blue staining and cell fragmentation within a few hours after treatment with exposed medium. Cell killing was found to be caused by the formation of toxic photoproducts from medium components riboflavin, tryptophan and/or tyrosine. Hydrogen peroxide was determined to be one such photoproduct, responsible for approxiamately half of the medium toxicity. Adjusting riboflavin, tyrosine and phenol red concentrations altered the production rate of products toxic for D98 cells and 3T6-DF8 fibroblasts. When included in the medium during irradiation, the reducing agents cysteine, reduced glutathione and sodium pyruvate also inhibited the formation of toxic photoproducts. In an appendix are results indicating that cells are able to detoxify exposed medium, that irradiation of the serum component bilirubin also yields toxic photoproducts, that generated hydrogen peroxide may induce single strand breaks in cellular DNA, and that D98 cells may become more resistant to toxic photoproducts with the addition of trace amounts of selenium.
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