Artificial background and induced levels of oxidative base damage in DNA from human cells.

The pre-mutagenic oxidative DNA base damage of 8-hydroxy-guanine is present in DNA isolated from cells and the amount present increases with exposure of cells to oxidative stress. The oxidative DNA base damage may be present before isolation of DNA or it may be produced during isolation and processing of DNA. We have found that the amount of oxidative base damage measured in DNA can be reduced to a stable lower level by adding increasing concentrations of the antioxidants desferrioxamine, histidine and reduced glutathione immediately before cell lysis. Inclusion of these antioxidants after cell lysis did not affect the level of DNA damage. Oxidative DNA base damage produced by ultraviolet A irradiation of human cells was also reduced by adding antioxidants after irradiation and before cell lysis. Thus, unidentified oxidants induced by ultraviolet A irradiation may damage DNA significantly during extractions of DNA from cells subsequent to ultraviolet A irradiation.