CYTOTOXIC EFFECTS OF UVA-IRRADIATED RIBOFLAVIN SOLUTION AND THE DEGENERATION OF ELASTIC FIBER

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Irradiation of riboflavin solution produced strong cytotoxicity which was eliminated by the treatment of the irradiated solution with catalase, suggesting that the cytotoxicity was derived from hydrogen peroxide (HP) . This suggestion was supported by the similar cytotoxicities between the irradiated riboflavin solution and the same concentration of HP as the irradiated solution contained. Measurement of HP was carried out with horseradish peroxidase whose absorption spectrum changes when it binds to HP.The cytotoxicity of riboflavin solution increased when the solution was irradiated under hypoxic conditions. The increase was due to sooner production of HP at the early phase of exposure. If riboflavin solution was irradiated at sufficient doses under either hypoxic or normoxic conditions, the cytotoxicities of either solution were similar.Riboflavin was irradiated with a glass-filtered mercury lamp. Induced radicals were detected with DMPO.Hydroxyl radicals, ribofravin radicals, and superoxide were trapped. Hydroxyl radicals were produced much more at the early phase and riboflavin radicals constatly from about 2 min irradiation period.Elastin was exposed to UVA in the presence of riboflavin or to HP.These treatments did not affect the rate of elastase digestion of the treated elastin. After elastin was solubilized with elastase, it was treated with HP at various concentration. Solubilized elastin changed its pattern of absorption spectrum faster at the higher concentration. The final absorption spectrum of solubilized elastin was very similar to that which was allowed to change spontaneously.