Journal Article

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

M Pflaum, O Will and B Epe

in Carcinogenesis

Volume 18, issue 11, pages 2225-2231
Published in print November 1997 | ISSN: 0143-3334
Published online November 1997 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/18.11.2225
Determination of steady-state levels of oxidative DNA base modifications in mammalian cells by means of repair endonucleases.

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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 determined by alkaline elution was much lower than the background level of 8-hydroxydesoxyguanosine (8-oxodG) determined after enzymatic DNA hydrolysis by HPLC and electrochemical detection. However, the number of additional Fpg-sensitive modifications induced by a photosensitizer plus light was similar to the additional number of 8-oxodG residues determined by HPLC with electrochemical detection. This indicates that the enzyme assay does not systematically underestimate the number of lesions and points to an artefactual generation of 8-oxodG during DNA isolation and hydrolysis.

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Subjects: Clinical Cytogenetics and Molecular Genetics

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