Matsuya Yusuke, Tsutsumi Kaori, Sasaki Kohei, Yoshii Yuji, Kimura Takaaki, Date Hiroyuki
Graduate School of Health Sciences, Hokkaido University, Kita-12, Nishi-5, Kita-ku, Sapporo 060-0812, Japan.
Faculty of Health Sciences, Hokkaido University, Kita-12, Nishi-5, Kita-ku, Sapporo 060-0812, Japan.
J Radiat Res. 2017 May 1;58(3):302-312. doi: 10.1093/jrr/rrw110.
Hyper-radiosensitivity (HRS) is a well-known bioresponse under low-dose or low-dose-rate exposures. Although disorder of the DNA repair function, non-targeted effects and accumulation of cells in G2 have been experimentally observed, the mechanism for inducing HRS by long-term irradiation is still unclear. On the basis of biological experiments and a theoretical study, we have shown that change in the amount of DNA associated with accumulation of cells in G2 enhances radiosensitivity. To demonstrate continuous irradiation with 250 kVp X-rays, we adopted a fractionated regimen of 0.186 or 1.00 Gy per fraction at intervals of 1 h (i.e. 0.186 Gy/h, 1.00 Gy/h on average) to Chinese Hamster Ovary (CHO)-K1 cells. The change in the amount of DNA during irradiation was quantified by flow cytometric analysis with propidium iodide (PI). Concurrently, we attempted a theoretical evaluation of the DNA damage by using a microdosimetric-kinetic (MK) model that was modified to incorporate the change in the amount of DNA. Our experimental results showed that the fraction of the cells in G2/M phase increased by 6.7% with 0.186 Gy/h and by 22.1% with 1.00 Gy/h after the 12th irradiation. The MK model considering the change in amount of DNA during the irradiation exhibited a higher radiosensitivity at a high dose range, which could account for the experimental clonogenic survival. The theoretical results suggest that HRS in the high dose range is associated with an increase in the total amount of DNA during irradiation.
超敏反应（HRS）是低剂量或低剂量率照射下一种众所周知的生物反应。尽管在实验中观察到了DNA修复功能紊乱、非靶向效应以及细胞在G2期的积累，但长期照射诱导HRS的机制仍不清楚。基于生物学实验和理论研究，我们发现与细胞在G2期积累相关的DNA量的变化会增强放射敏感性。为了用250 kVp X射线进行连续照射，我们采用了每1小时一次、每次0.186或1.00 Gy的分次照射方案（即平均每小时0.186 Gy、1.00 Gy）处理中国仓鼠卵巢（CHO）-K1细胞。用碘化丙啶（PI）通过流式细胞术分析定量照射期间DNA量的变化。同时，我们尝试用一个经过修改以纳入DNA量变化的微剂量动力学（MK）模型对DNA损伤进行理论评估。我们的实验结果表明，在第12次照射后，G2/M期细胞比例在0.186 Gy/h照射时增加了6.7%，在1.00 Gy/h照射时增加了22.1%。考虑到照射期间DNA量变化的MK模型在高剂量范围内表现出更高的放射敏感性，这可以解释实验性克隆存活情况。理论结果表明，高剂量范围内的HRS与照射期间DNA总量的增加有关。
