The influence of very low dose rate gamma-radiation on genetic structures of mice: molecular and cytogenetic study

Abstract

The results of investigation of molecular genetic and cytogenetic characteristics of CBA/lac male mice exposed to continuous very low dose rate gamma-radiation (0.17 cGy/day) during 40, 80, 120, and 210 days are presented in this study. Total accumulated doses were 6.8, 13.6, 20.4, 35.7 cGy, respectively. The parameters studied were levels of DNA-protein cross-links (DPCs) and DNA breaks in spleen lymphocytes (SLs), as well as percentage of bone marrow polychromatic erythrocytes with micronuclei (MNPCEs) and peripheral blood normochromatic erythrocytes with micronuclei (MNNCEs), using the DNA precipitation, the DNA alkali unwinding, the single cell gel electrophoresis (comet) assays and the micronucleus test, respectively. In addition, the induction of DNA damage in SLs after incubation with hydrogen peroxide (H2O2 at 0.1–5 mM) was studied. An increase in the sensitivity of SLs to H2O2 was revealed at 40 days of irradiation (6.7 cGy) as compared to SLs from non-irradiated control animals. However, after 120 days of exposure to radiation (20.4 cGy), SLs became more resistant to H2O2 treatment. This effect could be attributed to a development of adaptation processes triggered upon accumulation of a certain dose (in our experiments it is ∼20 cGy). Beginning from 80 days of irradiation (13.6 cGy), an increased level of DNA relaxation was observed, most likely indicating the induction of proliferation of SLs. Noteworthy is that populations of cells with markedly high level of DNA damage and apoptotic cells were registered. A level of DPCs in SLs was increased at 40 days of point only. No increase in bone marrow MNPCE or peripheral blood MNCCE in mice continuously exposed to very low-dose rate radiation was registered as compared with non-irradiated mice.