Effects of low-dose gamma radiation on DNA damage, chromosomal aberration and expression of repair genes in human blood cells

Exposure to low-dose gamma radiation is common in certain occupations but the biological and health effects from such exposure remain to be determined. The aim of this study was to investigate the effects of low-dose gamma radiation on DNA damage, chromosomal aberration and DNA repair gene expressions in whole blood and peripheral lymphocytes. The study revealed a dose-dependent effect of gamma radiation on DNA damage. Significant increases in DNA strand breaks and oxidative base damage, determined as formamidopyrimidine-DNA-glycosylase (FPG)-sensitive sites, were observed at absorbed doses of 5 and 10 cGy, respectively. However, gamma radiation at doses up to 500 cGy did not significantly increase the level of 8-oxo-7, 8-dihydro-2′-deoxyguanosine (8-oxodG) determined by HPLC with electrochemical detection (HPLC-ECD). Gamma radiation as low as 5 cGy caused chromosomal aberrations determined as dicentric and deletion frequencies. This finding is significant since the genotoxic effects of gamma radiation can be observed even at a low dose of 5 cGy. Furthermore, gamma radiation decreased the mRNA expression of both hOGG1 and XRCC1 repair genes determined by reverse transcriptase-polymerase chain reaction (RT-PCR), with a significant decrease of expression being observed at 20 cGy. The expression levels of hOGG1 and XRCC1 mRNA were inversely correlated with the levels of FPG-sensitive sites and DNA strand breaks. The finding of decreased expression levels for hOGG1 and XRCC1 in gamma-irradiated lymphocytes has not been reported elsewhere. Our observations suggest that the genotoxic effects of gamma radiation may be due to a combination of DNA-damaging effects and reduced DNA repair capacity, and may explain the significant increase in health risk from high doses of ionizing radiation.