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Hirayama, Ryoichi*; Uzawa, Akiko*; Takase, Nobuhiro*; Matsumoto, Yoshitaka*; Noguchi, Miho; Koda, Kana*; Ozaki, Masakuni*; Yamashita, Kei*; Li, H.*; Kase, Yuki*; et al.
Mutation Research; Genetic Toxicology And Environmental Mutagenesis, 756(1-2), p.146 - 151, 2013/08
Times Cited Count：24 Percentile：62.77(Biotechnology & Applied Microbiology)Hirayama, Ryoichi*; Uzawa, Akiko*; Matsumoto, Yoshitaka*; Noguchi, Miho; Kase, Yuki*; Takase, Nobuhiro*; Ito, Atsushi*; Koike, Sachiko*; Ando, Koichi*; Okayasu, Ryuichi*; et al.
Radiation Protection Dosimetry, 143(2-4), p.508 - 512, 2011/02
Times Cited Count：14 Percentile：71.96(Environmental Sciences)We studied double-strand breaks (DSB) induction and rejoining in clamped and non-clamped transplanted tumours in mice leg after exposure to 80 keV/
m carbon ions and X-rays. The yields of DSB in the tumours were analysed by a static-field gel electrophoresis. The OER of DSB after X-rays was 1.68, and this value was not changed after 1 h rejoining time (1.40). These damages in oxygenated conditions were rejoined 60-70% within 1 h in situ. No difference was found between the exposure to X-rays and carbon ions for the induction and rejoining of DSB. Thus, the values of OER and rejoined fraction after exposure to carbon ions were similar to those after X-rays, and the calculated relative biological effectivenesses of carbon ion were around 1 under both oxygen conditions. The yields of DSB in vivo depend on exposure doses, oxygen conditions and rejoining time, but not on the types of radiation quality.
Hirayama, Ryoichi*; Matsumoto, Yoshitaka*; Uzawa, Akiko*; Takase, Nobuhiro*; Tsuruoka, Chizuru*; Wada, Mami*; Noguchi, Miho; Kase, Yuki*; Matsufuji, Naruhiro*; Ito, Atsushi*; et al.
no journal, ,
The contribution of indirect action mediated by OH radicals in cell killing can be estimated from the maximum degree of protection by dimethylsulfoxide (DMSO), which suppresses indirect action of radiation without affecting direct action. Exponentially growing Chinese hamster ovary cells under oxic and hypoxic conditions were exposed to X-rays and iron ions having a dose-averaged LET at 200 keV/micrometer in the presence or absence of DMSO, and the cell survival was determined using the colony formation assay. The contributions of indirect action of 76% and 50% were found for X-rays under oxic and hypoxic conditions, respectively. In contrast, the contributions of indirect action for iron ions were estimated to be 42% and 32%. The RBE values were 2.8 for oxic and 5.3 for hypoxic, and the OER values were 2.8 for X-rays and 1.5 for iron ions. When the RBE and OER were estimated separately for direct action (RBE(D) and OER(D)) and indirect action (RBE(I) and OER(I)); the RBE(D) was larger than RBE(I) under both normal and low oxygen concentrations. The OER(D) values for both X-rays and iron ions were lower than that for OER(I). Thus, direct action of radiation gives a remarkably higher RBE and lower OER for cell killing than indirect action. It is possible that particle beams may be highly effective in treating cancer if the particle therapy can only use the portion of direct action out of total radiation actions; this would be exemplified by the usage of radioactive 9C-ion beams and boron neutron capture.
Hirayama, Ryoichi*; Matsumoto, Yoshitaka*; Noguchi, Miho; Uzawa, Akiko*; Koda, Kana*; Furusawa, Yoshiya*
no journal, ,
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.
