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Antioxidant-induced changes in oxidized DNA
Donald C Malins1, Karl Erik Hellstrom, Katie M Anderson
1Biochemical Oncology Program and Tumor Immunology Program, Pacific Northwest Research Institute, 720 Broadway, Seattle, WA 98122, USA. dmalins@pnri.org
Abstract:
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.
Insights
N-acetylcysteine (NAC) reduces DNA damage from hydroxyl radicals, lowering mutagenic 8-hydroxyguanine and its ratio with FapyGua. This suggests NAC decreases oxidized DNA
Area of Science:
- Biochemistry
- Molecular Biology
- Toxicology
Background:
- N-acetylcysteine (NAC) is a potent antioxidant with investigated antigenotoxic and anticarcinogenic properties.
- Hydroxyl radicals (.OH) induce DNA damage, forming mutagenic 8-hydroxypurine (8-OH) and Fapy lesions, crucial in disease etiology.
- The biological significance of the 8-OH to Fapy lesion ratio and NAC's impact on DNA structure remain unclear.
Purpose of the Study:
- To investigate how N-acetylcysteine (NAC) modifies hydroxyl radical-induced structural changes in mouse DNA.
- To assess the effects of NAC on oxidized DNA bases, their ratios, and DNA structural integrity.
- To determine if NAC's modifications to DNA structure influence cellular processes like replication and transcription.
Main Methods:
- Dietary administration of N-acetylcysteine (NAC) to BALB/c mice (5% in diet for 14 days).
- Analysis of DNA structural changes using gas chromatography-mass spectrometry and Fourier transform-infrared spectroscopy.
- Quantification of oxidized DNA bases, specifically 8-hydroxyguanine (8-OH-Gua) and FapyGua.
Main Results:
- Dietary NAC significantly reduced hydroxyl radical-induced 8-hydroxyguanine (8-OH-Gua) by approximately 50% (P = 0.02).
- NAC decreased the log(10) (8-OH-Gua/FapyGua) ratio from 0.58 +/- 0.15 to near zero, indicating a neutral redox status.
- NAC consumption led to distinct DNA base structures and vertical base-stacking interactions, with reduced variance compared to controls.
Conclusions:
- N-acetylcysteine (NAC) demonstrably lowers mutagenic 8-hydroxyguanine and the ratio of oxidized bases, suggesting reduced mutagenic potential of DNA.
- NAC's impact on DNA structure, including base stacking and variance, may influence DNA synthesis fidelity.
- The findings highlight NAC's protective effects against DNA oxidation while noting potential implications for DNA replication and transcription.