A reliable assessment of 8-oxo-2-deoxyguanosine levels in nuclear and mitochondrial DNA using the sodium iodide method to isolate DNA

A major controversy in the area of DNA biochemistry concerns the actual in vivo levels of oxidative damage in DNA. We show here that 8-oxo-2-deoxyguan osine (oxo8dG) generation during DNA isolation is eliminated using the sodi um iodide (Nal) isolation method and that the level of oxo8dG in nuclear DN A (nDNA) is almost one-hundredth of the level obtained using the classical phenol method. We found using Nal that the ratio of oxo8dG/10(5) deoxyguano sine (dG) in nDNA isolated from mouse tissues ranged from 0.032 +/- 0.002 f or liver to 0.015 +/- 0.003 for brain. We observed a significant increase ( 10-fold) in oxo8dG in nDNA isolated from liver tissue after 2 Gy of gamma - irradiation when Nal was used to isolate DNA. The turnover of oxo8da in nDN A was rapid, e.g. disappearance of oxo8da in the mouse liver in vivo after gamma -irradiation had a half-life of 11 min. The levels of oxo8da in mitoc hondrial DNA isolated from liver, heart and brain were 6-, 16- and 23-fold higher than nDNA from these tissues. Thus, our results showed that the stea dy-state levels of oxo8da in mouse tissues range from 180 to 360 lesions in the nuclear genome and from one to two lesions in 100 mitochondrial genome s.