@misc{oai:repo.qst.go.jp:00062568,
 author = {Hirayama, Ryoichi and Furusawa, Yoshiya and Ito, Atsushi and Noguchi, Miho and Matsumoto, Yoshitaka and Uzawa, Akiko and Ando, Koichi and Okayasu, Ryuichi and 平山 亮一 and 古澤 佳也 and 伊藤 敦 and 松本 孔貴 and 鵜澤 玲子 and 安藤 興一 and 岡安 隆一},
 month = {Jun},
 note = {We examined the contribution of indirect action of X-irradiation under oxic and hypoxic conditions in cell killing of a CHO line and its NHEJ-defective xrs6 mutant line (a Ku80 mutant of CHO).  X-irradiation was performed at a dose rate of 4.9 Gy/min using a generator operating at 200 kVp and 20 mA. For oxic and hypoxic conditions, irradiation chambers were flushed for more than 1 hour with air + 5% CO2 and 95% N2 + 5% CO2, respectively, prior to irradiation at room temperature.  Protective effect of DMSO which specifically scavenges OH radicals was evaluated from cell survivals.  Fractions of cell killing by the OH mediated indirect action were calculated by the method of Shinohara et al. (Acta Oncol., 35, 869-75. 1996).  The fractions for CHO were 80% and 60% under oxic and hypoxic conditions, respectively.  The fractions for xrs6 were 50% and 30% under oxic and hypoxic conditions, respectively.  Thus, our data indicate that the indirect action of OH radicals in cell killing is dependent of the oxygen concentration and the repair capacity of the cells. However, radiolysis study of liquid water demonstrated previously that the G(OH) value was independent of oxygen concentration (C. V. Sonntag, The Chemical Basis of Radiation Biology, 33. 1987).  
When the repair proficient and deficient cells were compared, the contribution of the indirect action in cell killing was higher for the former than for the latter.  In other words, the contribution of direct action was more pronounced in xrs6 cells.  When the actual numbers of damages contributing for the cell killing were estimated, it was found that the repair deficient cells were more sensitive to the damage produced under hypoxia.  It is our hypothesis that DNA damage produced under hypoxia is more complex and less likely to be repaired.  This type of damage is especially problematic for NHEJ deficient xrs6 cells.  Taken together, DNA damage due to direct action of X-rays was more akin to those by high LET radiations., 10th International Workshop Radiation Damage to DNA},
 title = {Contribution of indirect action of X-irradiation under oxic and hypoxic conditions in different radiosensitivity cells},
 year = {2008}
}