Modification of radiation-induced strand breaks by glutathione: Comparison of single- and double-strand breaks in SV40 DNA
- Univ. of Pennsylvania School of Medicine, Philadelphia, PA (United States)
A number of investigations have suggested that the widely observed oxygen enhancement of radiation-induced cell killing or intracellular DNA damage requires the presence of glutathione (GSH) or other thiols. We have adapted an in vitro model system to investigate the effects of GSH on radiation-induced DNA double-strand breaks (DSBs), lesions felt to be critical to cell death. Superhelical SV40 DNA, 25 {mu}g/ml, was irradiated in air or nitrogen in the presence of 0-20 mM GSH and single-strand breaks (SSBs) and DSBs were measured using neutral gel electrophoresis/ethidium bromide fluorescence. Control experiments demonstrated that a substantial concentration of free SH was still present after irradiation. Dose-response curves for SSBs and DSBs in air or nitrogen were predominantly linear at all GSH concentrations tested from 0-20 mM, except for 20 mM GSH in nitrogen, indicating that both SSBs and DSBs in nitrogen at 20 mM GSH, suggesting additional damage, rather than the expected additional protection. The possible mechanism for a damaging effect from GSH is discussed. Oxygen enhancement ratios (OERs) were calculated from the slopes of dose-response curves. The OERs for SSBs did not differ substantially from those for DSBs at the same [GSH], contrary to the observations of Prise. The OERs for SSBs and DSBs peaked at 6.5 and 8, respectively, at 5 mM GSH. These similarities suggest that the much lower OERs (2.5-3.0) generally reported for radiation killing of cells, which also typically contain about 5 mM GSH, cannot be accounted for by differences in OER between lethal lesions, represented by DSBs, and nonlethal lesions, represented by SSBs. In view of the present results, another possible explanation, that intracellular compounds other than reduced thiols are important in the chemical modification of the response of DNA to radiation, seems to be much more likely. 41 refs., 5 figs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 160178
- Journal Information:
- Radiation Research, Vol. 144, Issue 1; Other Information: PBD: Oct 1995
- Country of Publication:
- United States
- Language:
- English
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