Journal
RADIATION RESEARCH
Volume 170, Issue 3, Pages 365-371Publisher
RADIATION RESEARCH SOC
DOI: 10.1667/RR1255.1
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Funding
- Japan Science Society
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Phosphorylated ATM immunofluorescence staining was used to investigate the dose-response relationship for the number of DNA double-strand breaks (DSBs) induced in primary normal human fibroblasts irradiated with doses from 1.2 to 200 mGy. The induction of DSBs showed a supralinear dose-response relationship. Radiation-induced bystander effects may explain these findings. To test this hypothesis, the number of DSBs in cells treated with lindane, an inhibitor of radiation-induced bystander effects, prior to X irradiation was assessed; a supralinear dose-response relationship was not observed. Moreover, the number of DSBs obtained by subtracting the number of phosphorylated ATM foci in lindane-treated cells from the number of phosphorylated ATM foci in untreated cells was proportional to the dose at low doses (1.2-5 mGy) and was saturated at doses from 10-200 mGy. Thus the increase in the number of DSBs in the range of 1.2-5 mGy was largely due to radiation-induced bystander effects, while at doses > 10 mGy, the DSBs may be induced mainly by dose-dependent direct radiation effects and partly by dose-independent radiation-induced bystander effects. The findings in our present study provide direct evidence of the dose-response relationship for radiation-induced bystander effects from broad-beam X rays. (c) 2008 by Radiation Research Society.
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