Wavelength dependence of oxidative DNA damage induced by UV and visible light.

‐ ) and a Fenton reaction — could be involved. endonuclease V (i.e. cyclobutane pyrimidine dimers) was Yet another possibility is a release of Ca 21 from intracellular constant (~1:200), indicating that the direct excitation of stores which could activate cellular nucleases and thus induce DNA is responsible for both types of damage in this range DNA damage (18,19). of the spectrum. While the yield of pyrimidine dimers per The ratio of pyrimidine dimers and oxidative DNA modiunit dose continued to decrease exponentially beyond 315 fications at various wavelengths depends on the relative connm, the yield of Fpg-sensitive modifications increased to a tribution of direct and indirect mechanisms and is of major second maximum between 400 and 450 nm. The damage interest for the estimation of the mutagenic risk associated spectrum in this wavelength range consisted of only a with solar irradiation and the impact of spectral changes caused few other modifications (strand breaks, abasic sites and by ozone layer depletion. Here, we report a quantification of pyrimidine modifications sensitive to endonuclease III) cyclobutane pyrimidine dimers and various types of oxidative and is attributed to endogenous photosensitizers that give modifications induced in cultured cells by wavelengths between rise to oxidative DNA damage via singlet oxygen and/or 290 and 500 nm. The lesions were quantified by means of type I reactions. The generation of Fpg-sensitive modifica- several repair endonucleases (Table I) and an alkaline elution tions by visible light was not linear with dose but followed technique (28). a saturation curve. It is calculated that the exposure of the The results indicate that the generation of oxidative DNA cells to low doses of solar radiation results in the formation base modifications by solar radiation has a second maximum of cyclobutane pyrimidine dimers and Fpg-sensitive modi- between 400 and 450 nm due to the excitation of (unidentified) fications in a ratio of 10:1. endogenous photosensitizers and that in cells exposed to sunlight these indirectly induced base modifications account for ~10% of the total endonuclease-sensitive base damage.