Synergistic topical photoprotection by a combination of the iron chelator 2-furildioxime and sunscreen.

Iron is a factor in skin photodamage, apparently by way of its participation in oxygen radical production. Certain topical iron chelators are photoprotective. Our purpose was to determine the level of topical photoprotection provided by the iron chelator 2-furildioxime (FDO) in combination with sunscreen in short- and long-term photoprotection models. Guinea pigs were treated topically with FDO, sunscreen, and a combination of the two and were then exposed to varying doses of UV radiation to determine the sun protection factor (SPF). Hairless mice were treated topically with FDO, sunscreen, and a combination of the two and then subjected to long-term exposure to a suberythemal dose of UV radiation. The mice were evaluated for skin wrinkling and skin tumors. In guinea pigs, topical FDO combined with sunscreen provided more than additive protection; 5% FDO alone provides approximately SPF 4, whereas 5% FDO combined with an SPF 4 sunscreen product yielded an SPF of more than 30. In hairless mice exposed long term to UV radiation, 5% FDO and sunscreen delayed tumor onset by a mean of 8 and 12 weeks, respectively. The combination of FDO and sunscreen delayed tumor onset by a mean of 58 weeks. A similar more than additive level of protection was observed for skin wrinkling. Topical FDO combined with sunscreen is a potent photoprotection system against both short- and long-term UV radiation exposure.