Assessment of DNA damage in multiple organs of mice after whole body X-irradiation using the comet assay.

The comet assay was performed to elucidate the linearity of calibration curves and detection limits for DNA damage in multiple organs of whole body X-irradiated mice, and rates of reduction in DNA damage by DNA repair during the irradiation period were estimated in the respective organs by comparing the rates of increase in DNA damage at different absorbed dose rates of X-rays. Of the assay parameters, tail length and the percentage DNA in the tail showed a higher sensitivity to DNA damage in most organs than Olive tail moment. Data at the higher absorbed dose rates (2.22 or 1.44 Gy/min) showed good correlations between absorbed doses and these two parameters, with correlation coefficients of more than 0.7 in many organs. However, this assay had difficulty detecting DNA damage at the lower absorption dose rate (0.72 Gy/min). The estimated rates of increase in DNA damage and those of DNA repair during the irradiation period in the respective organs suggested differences in the radiosensitivity of nuclear DNA and DNA repair capacity among organs. Our results indicated that absorbed dose rates of 1.0-1.3 Gy/min or greater were needed to induce detectable DNA damages by the comet assay in many organs.