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Identification of ultimate DNA damaging oxygen species
1Institute of Pharmacology and Toxicology, University of Würzburg, Federal Republic of Germany.
Abstract:
DNA damage induced by various reactive oxygen species can be characterized using a set of repair endonucleases with defined substrate specificities. DNA damage profiles thus obtained in a cell-free system can be compared with those observed in cellular DNA. Using this approach, we have demonstrated that an illumination of Salmonella typhimurium cells with visible light in the presence of methylene blue gives rise to a DNA damage profile very similar to that of singlet oxygen in a cell-free system. Therefore, the genotoxicity observed under these conditions most probably is attributable to the direct action of this species. The damage consists mainly of base modifications that are subject to repair by uvrABC-independent pathways. Revertant frequencies observed in parallel in the strains TA100 and TA2638 indicate a pronounced mutagenicity of the lesions induced. Exposure of Salmonella typhimurium to tert-butylhydroperoxide gives rise to another form of damage profile that is also different from that produced by hydroxyl radicals in a cell-free system. However, the latter dissimilarity does not exclude hydroxyl radicals as ultimate reactive species, as a very rapid repair of the induced base modifications is observed, which might have distorted the damage profile despite immediate work up.
Insights
Visible light and methylene blue induce DNA damage in Salmonella typhimurium, primarily base modifications. This damage is mutagenic and likely caused by singlet oxygen, independent of uvrABC repair pathways.
Area of Science:
- Molecular Biology
- Genetics
- Toxicology
Background:
- Reactive oxygen species (ROS) cause DNA damage.
- Characterizing DNA damage profiles helps understand genotoxicity.
- Repair endonucleases can identify specific DNA lesions.
Purpose of the Study:
- To characterize DNA damage profiles induced by visible light/methylene blue and tert-butylhydroperoxide in Salmonella typhimurium.
- To compare in vivo DNA damage profiles with cell-free systems.
- To investigate the role of singlet oxygen and hydroxyl radicals in DNA damage and mutagenicity.
Main Methods:
- Illumination of Salmonella typhimurium with visible light in the presence of methylene blue.
- Exposure of Salmonella typhimurium to tert-butylhydroperoxide.
- Analysis of DNA damage profiles using repair endonucleases.
- Assessment of mutagenicity using revertant frequencies in strains TA100 and TA2638.
- Comparison of in vivo damage profiles with cell-free ROS-induced damage.
Main Results:
- Visible light/methylene blue treatment produced a DNA damage profile similar to singlet oxygen in cell-free systems.
- The induced DNA damage primarily involved base modifications repaired by uvrABC-independent pathways.
- The lesions exhibited pronounced mutagenicity.
- tert-butylhydroperoxide exposure generated a different damage profile, distinct from hydroxyl radical damage.
- Rapid repair of tert-butylhydroperoxide-induced damage may have altered its profile.
Conclusions:
- Genotoxicity from visible light/methylene blue in Salmonella typhimurium is likely due to direct singlet oxygen action.
- The induced base modifications are mutagenic and repaired via non-uvrABC pathways.
- Hydroxyl radicals may still be involved in tert-butylhydroperoxide-induced damage, with rapid repair obscuring the initial profile.