Damage to Isolated DNA Mediated by Singlet Oxygen

In the present work, we study the reaction of singlet oxygen (¹O₂) with isolated DNA. Emphasis is placed on the identification and quantitative measurement of the DNA modifications that are produced by the reaction of ¹O₂ with DNA. For this purpose, calf‐thymus DNA was incubated with the endoperoxide of N,N′‐di(2,3‐dihydroxypropyl)‐1,4‐naphthalenedipropanamide, a chemical generator of ¹O₂. Thereafter, DNA was digested, and the resulting oxidized nucleosides were measured by means of a recently optimized high‐performance‐liquid‐chromatography tandem‐mass‐spectrometry assay. It was found that, among the different DNA lesions observed, 7,8‐dihydro‐8‐oxo‐2′‐deoxyguanosine is the major ¹O₂‐mediated DNA‐damage product. Interestingly, cyclobutane pyrimidine dimers, oxidized pyrimidine bases, 7,8‐dihydro‐8‐oxo‐2′‐deoxyadenosine, and 2,6‐diamino‐5‐formamido‐4‐hydroxypyrimidine are not formed, at least not in detectable amounts, following treatment of DNA with the ¹O₂ generator. The reported results strongly suggest that the decomposition of the endoperoxide provides a pure source of ¹O₂, and that reaction of ¹O₂ with isolated DNA induces the specific formation of 7,8‐dihydro‐8‐oxo‐2′‐deoxyguanosine.