量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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We examined OH radical-mediated indirect actions from X
irradiation on cell killing in wild-type Chinese hamster ovary
cell lines (CHO and AA8) under oxic and hypoxic conditions,
and compared the contribution of direct and indirect actions
under both conditions. The contribution of indirect action on
cell killing can be estimated from the maximum degree of
protection by dimethylsulfoxide, which suppresses indirect
action by quenching OH radicals without affecting the direct
action of X rays on cell killing. The contributions of indirect
action on cell killing of CHO cells were 76% and 50% under
oxic and hypoxic conditions, respectively, and those for AA8
cells were 85% and 47%, respectively. Therefore, the indirect
action on cell killing was enhanced by oxygen during X
irradiation in both cell lines tested. Oxygen enhancement
ratios (OERs) at the 10% survival level (D10 or LD90) for CHO
and AA8 cells were 2.68 6 0.15 and 2.76 6 0.08, respectively.
OERs were evaluated separately for indirect and direct
actions, which gave the values of 3.75 and 2.01 for CHO, and
4.11 and 1.32 for AA8 cells, respectively. Thus the generally
accepted OER value of 3 is best understood as the average
of the OER values for both indirect and direct actions. These
results imply that both indirect and direct actions on cell
killing require oxygen for the majority of lethal DNA
damage, however, oxygen plays a larger role in indirect than
for direct effects. Conversely, the lethal damage induced by
the direct action of X rays are less affected by oxygen
concentration.
OH Radicals from the Indirect Actions of X-Rays Induce Cell Lethality and Mediate the Majority of the Oxygen Enhancement Effect
