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B. Epe
Role of Endogenous Oxidative DNA Damage in Carcinogenesis: What Can We Learn from Repair-Deficient Mice?
Basal steadystate levels of oxidative DNA base modifications such as 7,8-dihydro-8-oxo-2deoxyguanosine (8-oxoG) are observed in all types of cells, most probably due to a continuous generation of reactive oxygen species (ROS) in the cellular oxygen metabolism, and it has long been suspected that they might play an important role in the initiation of carcinogenesis. Experimental evidence for this assumption can be obtained by studying the effects of a modulation the steadystate levels, either by in or decreasing the generation of oxidative DNA damage, on spontaneous mutation rates and cancer incidence. However, clear answers have not yet been obtained by these strategies. It is still doubtful whether an efficient reduction of the in vivo steadystate levels can achieved by application of antioxidants, and effects observed under oxidative stress conditions (i.e. increased oxidative DNA damage) are inconclusive due to the pronounced epigenetic effects of ROS on signal transduction and gene expression (tumor promotion). In addition, the reliable quantification of the basal levels of oxidative DNA modifications is still major problem. Recently, the generation of mice deficient in the repair 8-oxoG (ogg1/ mice) has opened the door for an alternative approach. Results obtained so far indicate that an increase by less than five 8-oxoG residues per 106 bp in the liver of the knockout animals is associated with a two to threefold higher spontaneous mutation frequency in transgenic genes. However, the increase in the ogg1/ mice of the steadystate level of 8-oxoG and the spontaneous mutation frequency was only observed in the liver and apparently too small to enhance the spontaneous cancer incidence significantly. The limited effect seems to be due to a backup repair system for 8-oxoG in the ogg1/ mice, and it can be expected that the inactivation of this pathway doubleknockout mice will lead to higher effects and a better assessment of the risk associated with endogenous oxidative DNA damage.
Biological Chemistry, Walter de Gruyter
Print ISSN: 1431-6730
Volume: 383, 04/2002
Pages: 467 - 475