Sunscreen protection against ultraviolet radiation-induced pyrimidine dimers in mouse epidermal DNA

Pyrimidine dimers were measured in epidermal DNA of SKH:HR1 mice following exposure to solar-simulated UV radiation (SSUV, 290-400 nm) or to UVA (320-400 nm). Mice were exposed to SSUV or UVA after topical application (2 mg/cm(2)) of vehicle, a UVB absorber (5% 2-ethylhexyl p-methoxycinnamate [2-EHMC]), or broad-spectrum UVA absorber (5% Mexoryl(R)SX). The rates of induction of pyrimidine dimers in untreated animals were 5.4 +/- 0.57 x 10(-4) (mean +/- SEM) and 7.6 +/- 0.95 x 10(-6) dimers per 10(8) Da of epidermal DNA per J/m(2) of SSUV and UVA, respectively. Topical application of Mexoryl(R)SX reduced the rate of induction of pyrimidine dimers in SSUV-exposed animals to 4.7 +/- 0.44 x 10(-5) dimers per 10(8) Da per J/m(2) for a dimer induction protection factor (PF) of 11.5 (5.4 x 10(-4)/4.7 x 10(-5)). The rate of dimer induction in Mexoryl(R)SX-treated, UVA-exposed mice was 0.95 +/- 0.2 x 10(-6) dimers per 10(8) Da per J/m(2) (PF = 8.0). The 2-EHMC at a concentration of 5% (wt/wt) was significantly less effective than Mexoryl(R)SX in preventing the induction of pyrimidine dimers in animals exposed to either SSUV or UVA. The rates of dimer induction in 2-EHMC-treated mice were 8.2 +/- 1.1 x 10(-5) and 3.8 +/- 0.33 x 10(-6) dimers per Da per J/m(2) of SSUV (PF = 6.6) and UVA (PF = 2.0), respectively, Upon normalizing to the efficacy for edema induction, UVA induced approximately one-fourth the number of pyrimidine dimers per equivalent edematous response when compared to SSUV.