QUANTIFICATION OF OXIDATIVE DNA MODIFICATIONS IN MITOCHONDRIA

Specific repair endonucleases were used to quantify oxidative modifica tions in mitochondrial DNA (mtDNA) from rat liver and from porcine liv er and kidney by means of a relaxation assay. In rat fiver mitochondri a the number of modifications sensitive to formamidopyrimidine - DNA g lycosylase (FPG protein), which include 8-hydroxyguanine (8-oxo-7,8-di hydroguanine) residues, was only 0.8 +/- 0.2 per 105 base pairs (bp). Even lower values were observed in porcine kidney (0.5 +/- 0.3 per 105 bp) and liver (0.4 +/- 0.2 per 105 bp). The numbers of sites of base loss (AP sites) sensitive to T4 endonuclease V and of 5,6-dihydropyrim idines sensitive to endonuclease III were less than 0.2 per 105 bp in all cases. The data provide evidence that the steady-state levels of o xidative mtDNA modifications are low under physiological conditions, e ither because reactive oxygen species generated in the mitochondria ar e instantly inactivated or because of efficient DNA repair processes i nside mitochondria.