Bioactivation of Halogenated Hydrocarbons

说明(申请人提供)：烷基和乙烯基卤化物因其大量生产、广泛的人体暴露以及已知的遗传毒性和致癌性而令人感兴趣。继续研究的是这一组中的双功能亲电体(包括氧化产物)和相关化合物丁二烯二环氧化物，这是另一种商品化学品(1，3-丁二烯)的氧化产物。这些研究集中在硫醇依赖的1，2-二溴乙烷(二溴乙烷)和丁二烯二环氧化物的激活机制，特别是通过谷胱甘肽(GSH)转移酶(GST)和DNA修复蛋白O6-烷基鸟嘌呤DNA-烷基转移酶(AGT)。第一个具体目标涉及1，2-二溴乙烷和丁二烯二环氧化物衍生的DNA-AGT交联物的突变机理的表征。除了N7-鸟基以外的其他交联物的进一步表征将被完成，一个主要的假设是来自AGT的多肽是诱变加合物。第二个具体目标涉及丁二烯二环氧化物的GSH结合物，并假设这是一种显著的亲电物种，参与了丁二烯二环氧化物的DNA烷基化和遗传毒性(与解毒产品相反)。还提出了一种方法来评估这些化学物质在啮齿动物体内的AGT和GST途径。第三个具体目标是利用一种新的化学方法来合成具有不稳定的糖苷键的DNA加合物，包括几个来自烷基和乙烯基卤化物的加合物，特别是N7-(2-氧乙基)-鸟嘌呤、S-[N7-(2-鸟乙基)]谷胱甘肽和N，3-亚乙基(5)鸟嘌呤。我们的假设是，这些加合物是错误编码的。这些和其他不稳定加合物的错误编码潜力将用几种微生物和人类DNA聚合酶进行评估，并进行比较。总的来说，这些研究应该为这些加合物的毒性和致癌性提供新的机械性见解，并提供可能改变风险评估范式的重要信息。

DESCRIPTION (provided by applicant): Alkyl and vinyl halides are of interest because of their high volumes of production, extensive human exposure, and known genotoxicity and carcinogenicity. Continuing studies are directed toward bifunctional electrophiles in this group (including oxidation products) and the related compound butadiene diepoxide, an oxidation product of another commodity chemical (1,3-butadiene). The proposed studies are focused on thiol- dependent activation mechanisms of 1,2-dibromoethane (ethylene dibromide) and butadiene diepoxide, particularly by glutathione (GSH) transferases (GSTs) and the DNA repair protein O6-alkylguanine DNA- alkyltransferase (AGT). The first Specific Aim involves the characterization of mechanisms of mutation of DNA-AGT crosslinks derived from 1,2-dibromoethane and butadiene diepoxide. Further characterization of crosslinks other than the N7-guanyl ones will be done, and a major hypothesis is that peptides derived from AGT are the mutagenic adducts. The second Specific Aim involves the GSH conjugate of butadiene diepoxide and the hypothesis that this is a prominent electrophilic species involved in DNA alkylation and genotoxicity of butadiene diepoxide (as opposed to a detoxication product). An approach is also proposed to evaluate the AGT and GST pathways for these chemicals in rodents in vivo. The third Specific Aim utilizes a new chemical approach to the synthesis of DNA adducts with unstable glycosidic bonds, including several derived from alkyl and vinyl halides, especially N7-(2-oxoethyl)-guanine, S-[N7-(2-guanylethyl)]glutathione, and N2,3-etheno(5)guanine. Our hypothesis is that these adducts are miscoding. The miscoding potentials of these and other unstable adducts will be evaluated with several microbial and human DNA polymerases, and comparisons will be made. Collectively these studies should provide new mechanistic insight into the toxicity and carcinogenicity of these adducts and important information that may alter paradigms in risk assessment.