Analysis of cellular effects by continuous exposure AT low concentration of tritium

This study investigated the induction of DNA double-strand breaks (DSBs) in the hTERT-immortalized normal human diploid epithelial cells (RPE1-hTERT) continuously exposed to 6000 Bq/ml of tritiated water (HTO) and organically bound tritium (OBT). The relationship of the DSBs induction with the intracellular amount as well as the localization of tritium was also examined. Tritium-labeled thymidine (3H-Thy) and palmitic acid (3H-PA) were used as OBT. The average number of DSBs, which were indicated as co-localized foci of 53BP1 with phosphorylated H2AX, per cell was higher in the order of treatments with 3H-Thy, 3H-PA, and HTO. This order was consistent with that of tritium localization in the insoluble nuclear fraction but not with the intracellular amount of tritium. In addition to the intracellular amount of tritium, we showed that the subcellular localization of tritium is an important factor in cellular effects stimulated by DSBs.