Rejoining of DNA double-strand breaks in hypoxic cells following irradiation by X-rays and heavy ions

Hirayama, Ryoichi*; Matsumoto, Yoshitaka*; Noguchi, Miho; Uzawa, Akiko*; Koda, Kana*; Furusawa, Yoshiya*

The presence or absence of molecular oxygen dramatically influences the biological effect of low LET radiations. To produce oxygen effect, molecular oxygen must be present during the radiation exposure or at least during the lifetime of the free radicals generated by the radiation. Little study has been done to actually investigate the influence of oxygen after the radiation exposure. The present study was undertaken in order to explore the rejoining activity of DNA-DSB induced by anaerobic X-ray or carbon ion (80 keV/m) irradiations under oxic and hypoxic holdings (37 C). DNA-DSB in CHO cells were analyzed by a static-field gel electrophoresis. The kinetics of the rejoining could be described by a sum of fast and slow components. The slow component of DNA-DSB induced by X-ray under oxic incubation was faster than that under hypoxic incubation. Furthermore, the percentages of non-reparable DNA damage were 5% and 20% under oxic and hypoxic incubation conditions, respectively. However, no difference between oxic and hypoxic incubation conditions was found for carbon ion irradiation. There results indicate that molecular oxygen influences the rejoining of DNA-DSB after low LET radiation exposure.