Abstract
In human epidemiological studies, a significant increase in the cancer incidence rate has been reported by exposure to 100 mSv or higher doses of ionizing radiation.
However, the relationship between lower doses of ionizing radiation and cancer incidence is still unclear. In general, oxidative DNA damage is closely related to cancer generation. We studied the oxidative DNA damage elicited by low dose ionizing irradiation. Mice were irradiated with X-rays, and the 8-hydroxydeoxyguanosine (8-OHdG) levels in the tissue DNA and urine were measured by HPLC-ECD. The γ-ray irradiation of a dG or DNA solution caused a linear increase in the 8-OHdG levels, in the range of 20 – 300 mGy. Thus, 8-OHdG seems to be a good marker of the oxidative DNA damage caused by ionizing radiation. In contrast, in the case of the whole body irradiation of mice, the 8-OHdG levels in liver DNA and urine increased from about 0.5 Gy irradiation. These results indicate that living organisms have a defense mechanism against the oxidative damage caused by ionizing radiation. Considering the 8-OHdG level as an ionizing radiation effect marker for living organisms, a threshold level of irradiation seems to exist for oxidative damage and tumorigenesis. Detailed results with lower irradiation doses will also be discussed.
