title: Repair kinetics of DNA-DSB induced by X-rays or carbon ions under oxic and hypoxic conditions.
abstract: We studied the relation between initial DNA double-strand breaks (DNA-DSB) and the rejoining kinetics of the strand breaks, as well as the OER (oxygen enhancement ratio) after low- and high-LET (linear energy transfer) radiations. CHO cells were exposed to 200 kVp X-rays or 80 keV/microm carbon ions under oxic and hypoxic conditions. DNA-DSB in the cells were analyzed by a static-field gel electrophoresis (SFGE). The kinetics of the rejoining could be described by a sum of fast and slow components. The initial released DNA after X-ray irradiation was higher for cells irradiated under an oxic condition than that under a hypoxic condition. The OER of DNA-DSB after X-ray irradiation was 5.7. This value decreased rapidly to be 3.4 with the fast component by 15 minutes. On the other hand, the OER of DNA-DSB after carbon ion irradiation was 2.2, and this value was not changed by rejoining incubation. The OER values for cell killing were 2.8 and 1.8 after X-ray and carbon ion irradiations, respectively. These values matched to the OER for DNA-DSB with complete rejoining. We conclude that the rejoining of DNA-DSB is an important factor in the mechanism of the oxygen effect.
authors.affiliation: Graduate School of Science and Technology, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 163-8522, Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Hirayama
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Furusawa
authors.forename: Takeshi
authors.initials: T
authors.lastname: Fukawa
authors.forename: Koichi
authors.initials: K
authors.lastname: Ando
mesh_terms: D000818:Animals; D016466:CHO Cells; D002247:Carbon Isotopes; D015687:Cell Hypoxia / Q000235:genetics* / Q000528:radiation effects*; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D007477:Ions; D007700:Kinetics; D010100:Oxygen / Q000378:metabolism*; D011829:Radiation Dosage; D014965:X-Rays
chemical_list: D002247:Carbon Isotopes; D007477:Ions; D004247:DNA; D010100:Oxygen