@article{oai:repo.qst.go.jp:00046685,
 author = {Hirayama, Ryoichi and Ito, Atsushi and Noguchi, Miho and Matsumoto, Yoshitaka and Uzawa, Akiko and Kobashi, Gen and Okayasu, Ryuichi and Furusawa, Yoshiya and Hirayama, Ryoichi and Ito, Atsushi and Matsumoto, Yoshitaka and Uzawa, Akiko and Kobashi, Gen and Okayasu, Ryuichi and Furusawa, Yoshiya},
 issue = {5},
 journal = {Radiation Research},
 month = {Nov},
 note = {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.},
 pages = {514--523},
 title = {OH Radicals from the Indirect Actions of X-Rays Induce Cell Lethality and Mediate the Majority of the Oxygen Enhancement Effect},
 volume = {180},
 year = {2013}
}