Held K D, Hopcia K L
Department of Radiation Oncology, Massachusetts General Hospital, Boston 02114.
Mutat Res. 1993 May;299(3-4):261-9. doi: 10.1016/0165-1218(93)90102-j.
Previous data have been consistent with the hypothesis that the thiol depleter dimethyl fumarate (DMF) increases radiation sensitivity of hypoxic mammalian cells by a combination of two actions: depletion of glutathione (GSH) which interferes with the chemical competition between damage fixation and repair and depletion of protein thiol (PSH) which causes inhibition of enzymatic repair processes. However, one cannot rule out the possibility that PSH also acts in the chemical competition to restitute damaged DNA. The studies presented here have addressed this question by studying the effects of ionizing radiation on isolated nuclei which contain very low levels of GSH, but substantial amounts of PSH, compared to intact cells. The results show that DNA damage, measured using the non-denaturing filter elution assay, is increased about 1.6-fold in isolated nuclei irradiated in air, compared to whole cells, and about 4.3-fold in nuclei irradiated in N2. Thus, the OER for DNA damage decreases from about 3 in whole cells to 1 in isolated nuclei. Also, although DMF increases radiation-induced DNA damage in whole cells irradiated in hypoxia about 2-fold, it does not increase DNA damage in isolated nuclei irradiated in hypoxia. These data do not support the idea that PSH can act in the chemical competition reaction to chemically repair radiation-induced DNA radicals. The data are discussed in relation to the effect that various procedures for nuclei isolation can have on radiation sensitivity of DNA and on the OER. We also address the question of whether radiation-induced DNA damage measured by non-denaturing elution correlates with cell killing.
硫醇消耗剂富马酸二甲酯（DMF）通过两种作用的组合增加缺氧哺乳动物细胞的辐射敏感性，一是消耗谷胱甘肽（GSH），这会干扰损伤固定和修复之间的化学竞争；二是消耗蛋白质硫醇（PSH），这会导致酶促修复过程受到抑制。然而，不能排除PSH也在化学竞争中发挥作用以修复受损DNA的可能性。此处呈现的研究通过研究电离辐射对分离细胞核的影响来解决这个问题，与完整细胞相比，分离细胞核中GSH水平极低，但PSH含量可观。结果表明，使用非变性滤膜洗脱测定法测量，与完整细胞相比，在空气中辐照的分离细胞核中的DNA损伤增加约1.6倍，在氮气中辐照的细胞核中增加约4.3倍。因此，DNA损伤的氧增强比（OER）从完整细胞中的约3降至分离细胞核中的1。此外，尽管DMF使缺氧辐照的完整细胞中辐射诱导的DNA损伤增加约2倍，但它并未增加缺氧辐照的分离细胞核中的DNA损伤。这些数据不支持PSH可在化学竞争反应中对辐射诱导的DNA自由基进行化学修复的观点。讨论了这些数据与各种细胞核分离程序对DNA辐射敏感性和OER的影响之间的关系。我们还探讨了通过非变性洗脱测量的辐射诱导的DNA损伤是否与细胞杀伤相关的问题。
