Controlled oxidation of calf thymus DNA to produce standard samples for 8-oxodeoxyguanosine analysis; effects of freeze-drying, storage and hydrolysis conditions

Calf thymus DNA containing defined levels of 8-hydroxy-2'-deoxyguanosine (8-oxodG) was prepared by treatment with visible light in the presence of photosensitiser Ro 19-8022. The DNA was checked for stability; after freeze-drying, the amount of 8-oxodG did not increase during 6 weeks' storage at room temperature. However, freeze-drying itself can introduce additional oxidative damage. Two enzymic hydrolysis regimes (DNase I, phosphodiesterases I and II, and alkaline phosphatase; or P1 nuclease and alkaline phosphatase) give similar values for 8-oxodG.