Effects of chronic low-dose-rate gamma irradiation on the antitumor activity and chemokine system in mice

Daisaku Takai, Akiko Todate, Kazuaki Ichinohe, Jun-ichiro Komura


Introduction: There has been a growing interest in the carcinogenic effects of low-dose-rate radiation following the exposure of many people after the nuclear power plant accidents in Chernobyl and Fukushima. However, estimating cancer risk is more difficult for low-dose radiation than for high-dose radiation. This study aimed to clarify the effects of chronic low-dose-rate gamma irradiation on antitumor activity in mice and the possible involvement of chemokine systems in this.
Methods: Mice were exposed to gamma rays for 400 days at low-dose rates of 0.05, 1.0, and 20 mGy/22 h/day, giving total accumulated doses of 20, 400, and 8000 mGy, respectively. The antitumor activity to a syngeneic tumor cell line and the expression levels of 84 genes involved in the chemokine system in recipient mice were analyzed.
Results: Reduced antitumor activity was reproducibly observed in the mice irradiated at a dose rate of 20 mGy/22 h/day but not in the mice irradiated at 0.05 or 1.0 mGy/22 h/day. Enhanced antitumor activity, previously reported for acute low-dose irradiation, was not detected under conditions of chronic irradiation. The expression levels of some genes involved in the chemokine systems were altered after low-dose-rate irradiation.
Conclusion: No apparent effects were revealed in mice with chronic irradiation at dose rates of 0.05 or 1.0 mGy/22 h/day. The suppression of antitumor activity observed after chronic irradiation at 20 mGy/22 h/day could be explained, at least in part, by alterations in chemokine/chemokine receptor systems.

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