Effects of Low-Dose Irradiation Using Unsealed Caesium-137 on Cultured Normal Human Cells

Caesium-137 (Cs-137) is one of the major radionuclides appearing in the natural environment after nuclear power plant accidents. However, the biological effects of low-dose internal irradiation with this radionuclide remain unclear. We developed an experimental model for studying low-dose internal irradiation using cultured human cells. The cells were incubated in the culture medium supplemented with unsealed Cs-137 chloride. We used the Monte Carlo simulation method for measuring internal irradiation because making direct measurements was not possible. The simulation revealed that 96.40%?99.70% of the internal irradiation involved ?-particles and other electrons. During the experiment, a gradual incorporation of Cs-137 in the cells, and the absorbed dose rate increased in a time-dependent manner. In addition, the number of ?-H2AX and 53BP1 nuclear foci in the cells increased by internal irradiation in a dose-dependent manner. Microarray analysis revealed time-dependent alterations in gene expression caused by the radiation. These results demonstrate that our experimental system can be useful in the investigation of the effects of low-dose internal irradiation. HUVECs synchronized in G1 cell cycle phase were irradiated by unsealed cesium-137 in culture medium at 0.0146 mGy per minute (0.675 mGy) externally and 0.0152 mGy per minute (2.09 mGy/ hr), 0.0159 mGy per minute (4.66 mGy/ hr)for 1, 3 and 6 h, respectively. Experiments were biologically duplicated.