Oxidative DNA damage and mutations induced by a polar photosensitizer, Ro19-8022.

The oxidative DNA damage induced by the polar photosensitizer Ro19-8022 in the presence of light was studied and correlated with the associated mutagenicity. Both in isolated DNA and AS52 Chinese hamster ovary cells, photoexcited Ro19-8022 gave rise to a DNA damage profile that was similar to that caused by singlet oxygen: base modifications sensitive to the repair endonuclease Fpg protein, which according to high-performance liquid chromatography (HPLC) analysis were predominantly 8-hydroxyguanine (8-oxoG) residues, were generated in much higher yield than single-strand breaks, sites of base loss (AP sites) and oxidative pyrimidine modifications sensitive to endonuclease III. Fifty percent…

Determination of steady-state levels of oxidative DNA base modifications in mammalian cells by means of repair endonucleases

The alkaline elution technique in combination with various repair endonucleases (Fpg protein, endonuclease III, exonuclease III, T4 endonuclease V) was used to quantify steady-state (background) levels of oxidative base modifications in various types of mammalian cells. In human lymphocytes the number of base modifications sensitive to Fpg protein, which include 8-hydroxyguanine, was 0.25 +/- 0.05 per 10(6) base pairs. Even lower levels (0.07 +/- 0.02 per 10(6) bp) were observed in HeLa cells. The numbers of sites sensitive to the other repair endonucleases were below the detection limit (0.05 per 10(6) bp). In a direct comparison, the background level of Fpg-sensitive modifications determi…

Fanconi's anaemia cells have normal steady-state levels and repair of oxidative DNA base modifications sensitive to Fpg protein

Abstract Cells from Fanconi's anaemia (FA) patients are abnormally sensitive to oxygen. However, a distinct genetic defect in either the cellular defence against reactive oxygen species (ROS) or in their metabolic generation has not been identified to date. Recently, the gene for the human 8-hydroxyguanine (8-oxoG) glycosylase, which removes this oxidative base modification from the genome, has been localized on chromosome 3p25, i.e., in the same region as the FA complementation group D (FAD) gene. We therefore studied the removal of photosensitization-induced 8-oxoG residues from the DNA of FA cells, using Fpg protein, the bacterial 8-oxoG glycosylase, to quantify the lesions by alkaline e…

Contributions - C: Carcinogenic Factors: Endogenous

Influence of glutathione levels and heat-shock on the steady-state levels of oxidative DNA base modifications in mammalian cells

The effects of thiols, ascorbic acid and thermal stress on the basal (steady-state) levels of oxidative DNA base modifications were studied. In various types of untreated cultured mammalian cells, the levels of total glutathione were found to be inversely correlated with the levels of DNA base modifications sensitive to the repair endonuclease Fpg protein, which include 8-hydroxyguanine (8-oxoG). A depletion of glutathione by treatment with buthionine sulphoximine increased the steady-state level in AS52 Chinese hamster cells by approximately 50%. However, additional thiols in the culture medium did not reduce the level of Fpg-sensitive base modifications: 0-10 mM N-acetylcysteine had no ef…

DNA oxidation products determined with repair endonucleases in mammalian cells: Types, basal levels and influence of cell proliferation

Purified repair endonucleases such as Fpg protein, endonuclease III and IV allow a very sensitive quantification of various types of oxidative DNA modifications in mammalian cells. By means of these assays, the numbers of base modifications sensitive to Fpg protein, which include 8-hydroxyguanine (8-oxoG), were determined to be less than 0.3 per 10(6) bp in several types of untreated cultured mammalian cells and human lymphocytes and less than 10 per 10(6) bp in mitochondrial DNA from rat and porcine liver. Oxidative 5,6-dihydropyrimidine derivatives sensitive to endonuclease III and sites of base loss sensitive to endonuclease IV or exonuclease III were much less frequent than Fpg-sensitiv…