Malins Donald C, Hellstrom Karl Erik, Anderson Katie M, Johnson Paul M, Vinson Mark A
Biochemical Oncology Program and Tumor Immunology Program, Pacific Northwest Research Institute, 720 Broadway, Seattle, WA 98122, USA.
Proc Natl Acad Sci U S A. 2002 Apr 30;99(9):5937-41. doi: 10.1073/pnas.082111199. Epub 2002 Apr 23.
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.
N-乙酰半胱氨酸（NAC）是一种强效抗氧化剂，具有抗原毒性和抗癌特性，目前正在临床试验中进行研究。NAC可清除自由基（如羟基自由基·OH），这些自由基会导致与疾病（如癌症）相关的DNA变化。·OH与嘌呤反应形成诱变的8-羟基嘌呤（8-OH）和可能无诱变作用的甲酰胺嘧啶（Fapy）损伤。Fapy损伤抑制DNA合成，可能调节8-OH损伤的诱变潜力，这表明这些氧化碱基的比例具有生物学重要性。然而，关于NAC如何修饰氧化的DNA结构或这种修饰如何影响细胞过程（如复制和转录），人们知之甚少。通过使用气相色谱-质谱联用仪和傅里叶变换红外光谱仪，我们发现饮食中的NAC（饮食中含5%，持续14天）会影响·OH诱导的BALB/c小鼠后腿DNA的结构变化。例如，与对照组相比，喂食NAC的小鼠中诱变的8-羟基鸟嘌呤（8-OH-Gua）减少了约50%（P = 0.02）。NAC将log(10)（8-OH-Gua/FapyGua）比值从0.58±0.15降至基本为零，即几乎呈中性的氧化还原状态。与喂食NAC的小鼠相比，对照小鼠的DNA具有显著更高的变异性。此外，处理组和对照组小鼠的DNA在碱基结构和垂直碱基堆积相互作用方面存在差异。这些结果表明NAC降低了8-OH-Gua的浓度、对数比值和变异性（以前与肿瘤变化相关），表明NAC降低了氧化DNA的诱变潜力。NAC暴露后发现的其他结构变化可能会抵消这些益处，这些变化可能会影响DNA合成的保真度。
