Hopcia K L, McCarey Y L, Sylvester F C, Held K D
Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Radiat Res. 1996 Mar;145(3):315-23.
Apoptosis in HL60 human leukemia cells irradiated in vitro was quantified using a DNA fragmentation assay. Dose-response curves for induction of apoptosis in HL60 cells 6 h after irradiation with 280 kVp X rays in air and hypoxia give an oxygen enhancement ratio (OER) of 2.7. This is similar to the OER of 2.8 obtained from survival curves for HL60 cells using a soft agar clonogenic assay. However, HL60 cells are much more sensitive to radiation-induced loss of clonogenicity than to induction of apoptosis at 6 h. For example, 12 Gy in air reduces the surviving fraction to about 0.002 in a clonogenic assay, but 12 Gy does not cause any significant increase in the percentage of apoptosis-like DNA fragmentation 6 h after irradiation compared to unirradiated controls. However, if apoptosis is assayed 2-4 days after irradiation, the HL60 cells show greater sensitivity, with 5 Gy in air causing 45-50% apoptosis at 3 days. When apoptosis is measured 3 days after irradiation, the OER is similar to that obtained for survival and for apoptosis at 6 h. Although the HL60 cells exhibit radiation-induced apoptosis if one waits 2-4 days after low doses of radiation, rather than just 6 h, to conduct the assay, the amount of cells undergoing apoptosis is still not sufficient to account for all the loss of clonogenicity seen when HL60 cells are exposed to ionizing radiation.
采用DNA片段化分析法定量检测体外照射的HL60人白血病细胞中的凋亡情况。用280 kVp X射线在空气中和缺氧条件下照射HL60细胞6小时后诱导凋亡的剂量反应曲线得出氧增强比（OER）为2.7。这与使用软琼脂克隆形成试验从HL60细胞存活曲线获得的OER为2.8相似。然而，HL60细胞对辐射诱导的克隆形成能力丧失比在6小时时对凋亡诱导更为敏感。例如，在克隆形成试验中，空气中12 Gy可使存活分数降至约0.002，但与未照射的对照相比，12 Gy在照射后6小时并未导致凋亡样DNA片段化百分比有任何显著增加。然而，如果在照射后2 - 4天检测凋亡情况，HL60细胞表现出更高的敏感性，空气中5 Gy在3天时可导致45 - 50%的凋亡。当在照射后3天测量凋亡时，OER与6小时时存活和凋亡所获得的OER相似。尽管如果在低剂量辐射后等待2 - 4天而不是仅6小时进行检测，HL60细胞会表现出辐射诱导的凋亡，但发生凋亡的细胞数量仍不足以解释HL60细胞暴露于电离辐射时所观察到的所有克隆形成能力的丧失。
