Mechanism of mutagenicity by 5-hydroperoxymethyl-2'-deoxyuridine, an intermediate product of ionizing radiation, in bacteria. HPMdU bacterial mutagenicity and oxidation of DNA bases.
The specific objective was to find what processes are responsible for the mutagenicity of 5-hydroperoxymethyl-2'-deoxyuridine (HPMdU), which is a product of ionizing radiation, and what role transition metal ions play in those processes. We found that HPMdU is a more potent mutagen than its decomposition products 5-hydroxymethyl-2'-deoxyuridine (HMdU) and 5-formyl-2'-deoxyuridine (FdU) in the Salmonella typhimurium strains tested, with the TA100 strain being the most sensitive. HMdU exerted intermediate mutagenicity and FdU was the weakest of the three compounds. At 50 nmoles/plate, HPMdU increased the number of revertants by 4-fold, whereas 1000 nmoles HMdU was required to enhance the number of revertants by 5-fold. Pretreatment of TA100 with o-phenanthroline, a membrane-permeable Fe and Cu chelator, caused an increase in mutagenicity of the low HPMdU doses but inhibited that of the 50 nmoles HPMdU/plate, while desferal, a membrane-impermeable Fe chelator, had virtually no effect. Azide (a catalase inhibitor) enhanced HPMdU mutagenicity, whereas 3-amino-1,2,4-triazole (a catalase and peroxidase inhibitor) and ammonium formate (a hydroxyl radical scavenger) were protective. Preincubation of TA100 cells with 20 and 40 nM HPMdU caused dose-dependent formation of the oxidized DNA base derivatives HMdU, thymidine glycol and 8-hydroxyl-2'-deoxyguanosine (8-OHdG), known hydroxyl radical-mediated oxidation products. Cumulatively, these results suggest that the genetic effects of HPMdU are due to its hydroperoxide moiety, which upon reacting with Fe generates hydroxyl radicals that in turn oxidize neighboring bases in cellular DNA. This also may be a mechanism by which ionizing radiation exerts its long-term effects.
Patel
U
U
Department of Environmental Medicine, New York University Medical Center, NY 10016-6451.
Bhimani
R
R
Frenkel
K
K
D004249:DNA Damage; D004269:DNA, Bacterial / Q000187:drug effects / Q000528:radiation effects; D003857:Deoxyuridine / Q000031:analogs & derivatives / Q000633:toxicity; D005609:Free Radicals; D007501:Iron / Q000633:toxicity; D007502:Iron Chelating Agents / Q000494:pharmacology; D016296:Mutagenesis; D009152:Mutagenicity Tests; D009153:Mutagens; D016877:Oxidants / Q000633:toxicity*; D010084:Oxidation-Reduction; D012486:Salmonella typhimurium; D013936:Thymidine / Q000031:analogs & derivatives* / Q000633:toxicity; D013941:Thymine / Q000528:radiation effects
D004269:DNA, Bacterial; D005609:Free Radicals; D007502:Iron Chelating Agents; D009153:Mutagens; D016877:Oxidants; C061518:5-hydroperoxymethyl-2'-deoxyuridine; C061519:5-formyl-2'-deoxyuridine; C018080:5-hydroxymethyl-2'-deoxyuridine; D007501:Iron; D013941:Thymine; D013936:Thymidine; D003857:Deoxyuridine