Characterization of DNA Damage Inflicted by Free Radicals from a Mutagenic Sunscreen Ingredient and Its Location Using an in vitro Genetic Reversion Assay

We describe an in vitro approach to assessing the potential genotoxicity of illuminated sunscreens. The photomutagenic sunscreen Padimate-O attacks DNA on illumination with simulated sunlight, producing strand breaks and lesions that are labile to N, N'-dimethylethy-lenediamine but few, if any, cyclobutane dimers or other direct photoproducts. The damage can be completely suppressed by the free radical quenchers Tris, ethanol, mannitol and dimethylsulfoxide, which is commonly used as a solvent in conventional photomutagenicity assays. Using a genetic reversion assay that depends on regenerating P-galactosidase activity in photodamaged plas-mids we find that GC base pairs are particularly susceptible to attack by Padimate-O.