Aim: to compare the repair process of DNA double-strand breaks in mammalian cells after acute versus prolonged exposure to X-ray irradiation with different dose rates. Material and methods. Studies were performed on primary human fibroblasts isolated from skin biopsies of healthy volunteers (women, 29 and 30 years). Cells were irradiated using an X-ray machine RUB RUST-M1 (JSC "Ruselectronics", Moscow, Russia) at 37°C temperature with a dose rate of 400 mGy/min (200 kV, 2*2.4 mA, a filter of 1.5mm AI) or 4 mGy/min (50 kV, 2*0.4 mA, a filter of 1.5 mm AI). Immuno-cytochemical protein staining was utilized for yH2AX and Rad51 foci analysis. Results. Phosphorylated histone H2AX (yH2AX) and the key protein of homologous recombination Rad51 foci formation and disappearance kinetics were investigated simultaneously in primary human dermal fibroblasts after acute and prolonged exposure to X-ray radiation at a same dose. It was shown that the relative yield of yH2AX foci per dose reduces with decrease in dose rate, while the relative yield of Rad51 foci conversely increases. Conclusion. Our findings suggest the fundamental differences in the ratio of non-homologous end joining and homologous recombination DNA repair in acute versus prolonged irradiated cells.
Ozerov I.V., Eremin P.S., Osipov A.N., Eremin I.I., Tsvetkova A.D., Guseva S.S., Ivanova K.Yu., Gavrilenko 0.I., Pustovalova M.V., Smetanina N.M., Grekhova A.K., Lazareva N.L., Pullin A.A., Maksimova О.A., Gordeev A.V., Bushmanov A.Yu., Kotenko K.V. Characteristics of changes in the number of yH2AX and Rad51 protein foci in human skin fibroblasts after prolonged exposure to low-dose rate X-ray radiation // Saratov Journal of Medical Scientific Research, Vol. 10, Issue 4, 2014, pp. 739-743

Aim: to study the patterns of changes in the number of DNA double-strand breaks (DSB) in mammalian cells continuously exposed to low dose-rate y- radiation. Material and methods. Chinese hamster lung fibroblasts (V79) were used in this study. The y- irradiation of cells at a dose rate of 0.1 mGy/min was performed using the «Gamma-Panorama» unit (Cs-137). The fluorescence immunoassay of the phosphorylated H2AX-histone (y-H2AX) foci was used to investigate the DNA DSBs formation. Frequency of apoptotic cells was evaluated using «DNA halo» assay. 5 (6) — chloromethyl-2,7-dichlorodihydrofluorescein diacetate was used to estimate the reactive oxygen species (ROS) production. Results, it was showed that continuous low dose-rate irradiation of Chinese hamster V79 cells induces an increase of the y-H2AX foci number and ROS production rate at the early stages of exposure time (6-24 h, doses 3.6-14.4 cGy), while increasing exposition time and, therefore, the radiation dose (48-72 h, 28.8-43.2 cGy) caused a decrease in these endpoints to almost the control level. There was observed no significant changes in the frequency of apoptotic cells. Conclusion. It is assumed that the processes causing the DSB amount changes in mammalian cells continuously exposed to low dose-rate y-radiation are associated with the development of oxidative stress and subsequent activation of cellular antioxidant defense systems.
Ozerov I.V., Bushmanov A.Yu., Anchishkina N.A., Guryev D.V., Pustovalova M.V., Smetanina N.M., Arkhangelskaya E.Yu., Vorobyova N.Y., Osipov A.N. Induction and reparation of double-strand DNA breaks in V79 cells continuously exposed to low dose-rate Y-radiation // Saratov Journal of Medical Scientific Research, Vol. 9, Issue 4, 2013, pp. 787-791