Abstract
Recent accumulating evidence including epidemiologic study of atomic bomb survivors suggests that chronic incidence of non-cancer diseases such as cardiovascular diseases increases by the exposure of low dose radiation, which is going to be taken into account in radioprotection regulation. It is, however, controversial that risk estimation model based on data obtained by high dose/high dose rate radiation can be applied to risk estimation for low dose/low dose rate radiation as in the case of risk estimation for cancer. Inflammation is one of the biggest risk factors for non-cancer diseases. We have demonstrated that continuous exposure of low dose rate gamma-radiation ameliorates type II diabetes and rheumatoid arthritis in mouse models. Through meta-analysis, we detected significant reduction of gene expression such as IL-1alpha, CD80, and iNOS by continuous low dose rate irradiation for 17 days, in mice implanted with allogeneic tumor cells, while that of p53-downstream targets such as p21 and mdm2 was significantly reduced. Continuous low dose rate irradiation significantly reduced footpad swelling evoked by concanavalin A, and suppressed pulmonary metastasis of Lewis lung carcinoma that is know to depend on inflammatory response. These results suggest that biological responses to continuous low dose/low dose rate radiation are qualitatively different from those to high dose/high dose rate radiation. We propose that dose rate effect should be taken into account for the risk estimation of non-cancer diseases for low dose/low dose rate radiation.
