Abstract
Biological effects of internal radiation exposure have not been well evaluated as compared to the effects of external exposure. As a preliminary study for establishment of the in vitro model for risk estimation by internal exposure, we exposed the cultured H1299 cells to I-125 deoxyuridine (81.4TBq/mmol) or H-3 deoxyuridine (740TBq/mmol) which were present inside (intracellular exposure) or outside (extracellular exposure) the cells for up to 8 weeks in frozen condition. The intracellular irradiation with I-125 exhibited a rapid lethality and reached approximately 40% viability in one week exposure (10.94 total decays/cell), which was comparable to the lethal effect by 4Gy irradiation with external Cs-137source. Phosphorylations of p53, ERK-MEK, and p38 were also observed in cells after the intracellular exposure to I-125. The extracellular irradiation with I-125 caused a gradual decrease in cell viability to approximately 70% of unirradiated cells in 8 weeks. In contrast, no lethality was observed by irradiation with H-3 either in intracellular or in extracellular condition. Based on the methodology shown here, we are about to examine the effects of internal irradiation with I-131 in cultured thyroid cells.
