Antioxidant-induced changes in oxidized DNA.
N-acetylcysteine (NAC), a strong antioxidant, has antigenotoxic and anticarcinogenic properties currently being investigated in clinical trials. NAC detoxifies free radicals (e.g., the hydroxyl radical,.OH) that cause DNA changes implicated in disease (e.g., cancer). The.OH reacts with purines to form mutagenic 8-hydroxypurine (8-OH) and putatively nonmutagenic formamidopyrimidine (Fapy) lesions. Fapy lesions inhibit DNA synthesis likely modulating the mutagenic potential of the 8-OH lesions, which would suggest that the ratio of these oxidized bases is biologically important. However, little is known about how NAC modifies oxidized DNA structure or how such modifications may affect cellular processes, such as replication and transcription. By using gas chromatography-mass spectrometry and Fourier transform-infrared spectroscopy, we found that dietary NAC (5% in the diet for 14 days) affected.OH-induced structural changes in DNA of the hind leg of the BALB/c mouse. For example, mutagenic 8-hydroxyguanine (8-OH-Gua) was reduced approximately 50% (P = 0.02) in mice fed NAC compared with controls. NAC reduced the log(10) (8-OH-Gua/FapyGua) ratio from 0.58 +/- 0.15 to essentially zero, a virtually neutral redox status. DNA from control mice had a remarkably high variance compared with mice fed NAC. Moreover, the DNA from treated and control mice was distinct with respect to base structure and vertical base-stacking interactions. The findings showing that NAC lowered the concentration of 8-OH-Gua, the log ratio, and the variance (previously associated with neoplastic changes) suggest that NAC reduces the mutagenic potential of oxidized DNA. These benefits could be offset by the other structural changes found after NAC exposure, which may affect the fidelity of DNA synthesis.
Malins
Donald C
DC
Biochemical Oncology Program and Tumor Immunology Program, Pacific Northwest Research Institute, 720 Broadway, Seattle, WA 98122, USA. dmalins@pnri.org
Hellstrom
Karl Erik
KE
Anderson
Katie M
KM
Johnson
Paul M
PM
Vinson
Mark A
MA
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D004247:DNA / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D004249:DNA Damage; D005260:Female; D016166:Free Radical Scavengers / Q000494:pharmacology; D008401:Gas Chromatography-Mass Spectrometry; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D009690:Nucleic Acid Conformation; D010100:Oxygen / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared
D000975:Antioxidants; D016166:Free Radical Scavengers; C024829:8-hydroxyguanine; D006147:Guanine; D004247:DNA; D010100:Oxygen; D000111:Acetylcysteine