RADIATION DAMAGE TO DNA--EFFECTS OF MODIFIERS AND LET

本研究的目的是测试直接机制的模型 不同 LET 辐射对 DNA 的辐射损伤以及损伤修复 辐射防护剂。 DNA 损伤和硫醇的最新模型 我们的实验室已开发出自动氧化作用。 第一个描述了 DNA 辐射事件从最初的 DNA 离子自由基到形成 次级自由基，最后形成抗磁性产物。 第二个 描述硫醇从硫基自由基到磺酰基的自动氧化循环 过氧自由基。 我们的研究将测试硫醇对 DNA 的影响 含氧和缺氧系统中的自由基过程，以寻求 更好地了解化学增氧效应和硫醇 辐射防护。 这些研究是在以下条件下进行的 强调辐射的直接影响，将利用电子自旋 共振光谱 (ESR)，使用从头开始的理论建模 分子轨道理论（MO计算）和气相色谱-质量 光谱（GC-MS）技术。 高LET重离子的影响 DNA 辐射及其硫醇修复将通过使用 密歇根州立大学国家超导回旋加速器。 具体来说，在目标 I 中，研究重要的根本机制 DNA辐射防护和化学氧增强作用将 调查了。 包括： 1.糖自由基与硫醇的反应 在缺氧和有氧系统中。 2. 硫磺侵蚀的调查- DNA 和 DNA 成分上的氧（磺酰基）自由基。 3. 的 特定 DNA 碱基自由基与硫醇反应的研究 通过实验确定哪些特定自由基与硫醇反应。 在 目标 II 从头开始 MO 计算也将用于预测哪一个 许多已知的 DNA 自由基中间体能够参与 硫醇的辐射防护作用的比较和阐明 实验结果。 使用等糖反应将允许 准确的反应能量计算。 在目标 III 的调查中 DNA-硫醇系统的高 LET 照射将检验以下假设： 高 LET 辐射造成的损害比低 LET 辐射造成的损害更复杂 辐射，正是这种复杂的损害导致了辐射的减少 在 OER 和 LET 中。 在 Aim IV 样品中，通过 ESR 进行辐照和研究 目标 I 和 III 将通过以下方法分析 DNA 碱基损伤和碱基释放： GC-MS 和 HPLC。 产品分析将与 Wake 联合进行 森林大学。 这些分析的结果将用于测试和 进一步阐明 ESR 实验提出的机制。

The goal of this research is to test models for mechanisms of direct radiation damage to DNA for radiations of varying LET and damage repair by radioprotective agents. Recent models for DNA damage and thiol autoxidation have been developed in our laboratory. The first describes DNA radiation events from the initial DNA ion radicals to the formation of secondary radicals and finally to diamagnetic products. The second describes the autoxidation cycle of thiols from thiyl radical to sulfonyl peroxyl radical. Our investigations will test the effect of thiols on DNA free radical processes in both oxic and anoxic systems in order to seek a better understanding of the chemical oxygen enhancement effect and thiol radioprotection. These studies, which are performed under conditions that emphasize the direct effect of radiation, will employ electron spin resonance spectroscopy (ESR), theoretical modeling using ab initio molecular orbital theory (MO calculations), and gas chromatography--mass spectroscopy (GC-MS) techniques. The effects of high LET heavy ion radiation on DNA and its repair by thiols will be investigated by use of the National Superconducting Cyclotron at Michigan State University. Specifically, in Aim I investigations of radical mechanisms important to DNA radioprotection and the chemical oxygen enhancement effect will be investigated. Included are: 1. The reaction of sugar radicals with thiols in anoxic and oxic systems. 2. The investigation of the attack of sulfur- oxygen (sulfoxyl) radicals on DNA and DNA components. 3. The investigation of the reaction of specific DNA base radicals with thiols to experimentally ascertain which specific radicals react with thiols. In Aim II ab initio MO calculations will also be employed to predict which of the many known DNA radical intermediates are able to participate in radioprotection by thiols for comparison to and elucidation of experimental results. Use of isodesmic reactions will allow for calculation of accurate reactions energies. In Aim III investigations of high LET irradiation on DNA-thiol systems will test the hypothesis that damage by high LET radiation is more complex than that caused by low LET radiation and that it is this complex damage which results in the decrease in OER with LET. In Aim IV samples irradiated and investigated by ESR in Aims I and III will be analyzed for DNA base damage and base release by GC-MS and HPLC. Product analyses will be performed jointly with Wake Forest University. Results of these analyses will serve to test and further elucidate mechanisms proposed by ESR experiments.