Tretyakova N, Sangaiah R, Yen T Y, Gold A, Swenberg J A
Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill 27599, USA.
Chem Res Toxicol. 1997 Oct;10(10):1171-9. doi: 10.1021/tx9700681.
1,3-Butadiene (BD) is a high-volume industrial chemical and a common environmental pollutant. Although BD is classified as a "probable human carcinogen", only limited evidence is available for its tumorigenic effects in occupationally exposed populations. Animal studies show a surprisingly high sensitivity of mice to the carcinogenic effects of BD compared to rats (approximately 10(3)-fold), making interspecies extrapolations difficult. Identification and quantitation of specific BD-induced DNA adducts are important for improving our understanding of the mechanisms of BD biological effects and for explaining the observed species differences. Covalent binding of BD to DNA is probably due to its two epoxy metabolites: 3,4-epoxy-1-butene (EB) and 1,2:3,4-diepoxybutane (DEB). Both EB and DEB are direct mutagens producing frameshift and point mutations at both A:T and G:C base pairs. DEB is 100 times more mutagenic than EB and is found in quantity only in tissues of the most sensitive species (mouse). This has led to the suggestion that the higher sensitivity of mice to BD could be due to greater exposure to DEB. The present work was initiated in order to isolate and structurally characterize DEB-induced adenine adducts. The adducts were formed by reacting DEB with free adenine (Ade), 2'-deoxyadenosine (2'-dAdo), and calf thymus DNA followed by HPLC separation and analysis of the products by UV spectrophotometry, electrospray ionization mass spectrometry, and nuclear magnetic resonance. The adenine reaction resulted in three products which were identified as N-3-, N-7-, and N-9-(2'-hydroxy-3',4'-epoxybut-1'-yl)adenine. These adducts underwent acid-catalyzed hydrolysis to their corresponding (2',3',4'-trihydroxybut-1'-yl)adenines upon heating or storage. The 2'-dAdo reaction with DEB followed by acid hydrolysis yielded a single adduct, N6-(2',3',4'-trihydroxybut-1'-yl)adenine (N6-DEB-Ade). N-3-DEB-Ade and N6-DEB-Ade were also found in hydrolysates of calf thymus DNA exposed to DEB. The amounts of N-3-DEB-Ade (13/10(3) normal Ade) and N6-DEB-Ade (5/10(3) normal Ade) were slightly lower than those of the corresponding EB-induced adducts in similar experiments, suggesting comparable reactivity of the two epoxy metabolites of BD toward adenine in DNA. The findings of this study provide a basis for future analyses of BD-induced adenyl DNA adducts in vitro and in vivo.
1,3 - 丁二烯（BD）是一种大量生产的工业化学品，也是一种常见的环境污染物。尽管BD被归类为“可能的人类致癌物”，但关于其在职业暴露人群中的致癌作用，仅有有限的证据。动物研究表明，与大鼠相比，小鼠对BD的致癌作用具有惊人的高敏感性（约10³倍），这使得种间推断变得困难。鉴定和定量特定的BD诱导的DNA加合物，对于增进我们对BD生物学效应机制的理解以及解释观察到的物种差异很重要。BD与DNA的共价结合可能归因于其两种环氧代谢产物：3,4 - 环氧 - 1 - 丁烯（EB）和1,2:3,4 - 二环氧丁烷（DEB）。EB和DEB都是直接诱变剂，在A:T和G:C碱基对处产生移码突变和点突变。DEB的诱变性比EB高100倍，并且仅在最敏感物种（小鼠）的组织中大量存在。这导致有人提出，小鼠对BD的较高敏感性可能是由于更多地接触DEB。开展本研究是为了分离并对DEB诱导的腺嘌呤加合物进行结构表征。这些加合物通过使DEB与游离腺嘌呤（Ade）、2'-脱氧腺苷（2'-dAdo）以及小牛胸腺DNA反应形成，然后通过高效液相色谱法分离产物，并通过紫外分光光度法、电喷雾电离质谱法和核磁共振对产物进行分析。腺嘌呤反应产生了三种产物，它们被鉴定为N - 3 - 、N - 7 - 和N - 9 - （2'-羟基 - 3',4'-环氧丁 - 1'-基）腺嘌呤。这些加合物在加热或储存时会发生酸催化水解，生成相应的（2',3',4'-三羟基丁 - 1'-基）腺嘌呤。2'-dAdo与DEB反应后经酸水解产生单一加合物，即N6 - （2',3',4'-三羟基丁 - 1'-基）腺嘌呤（N6 - DEB - Ade）。在暴露于DEB的小牛胸腺DNA水解产物中也发现了N - 3 - DEB - Ade和N6 - DEB - Ade。在类似实验中，N - 3 - DEB - Ade（13/10³正常Ade）和N6 - DEB - Ade（5/10³正常Ade）的量略低于相应的EB诱导加合物，这表明BD的两种环氧代谢产物对DNA中腺嘌呤的反应性相当。本研究结果为未来体外和体内分析BD诱导的腺苷DNA加合物提供了基础。
