Changes in the repair of radiation-induced DNA damage to bone marrow cells in mice injected with 90Sr

Male CCBA mice used in the experiment were given intraperitoneal injections of 592 kBq/animal 90Sr. Animals were examined at 1, 3, 6, 13, 21, 30, 100, 400 days after injection. Bone marrow cells were studied using alkaline Single Cell Gel technique (Comet assay). For DNA repair evaluation, animals were exposed to additional external γ-irradiation (3 Gy) each time they were examined, and DNA migration was measured immediately following additional irradiation, 15 and 120 minutes later. Changes in DNA migration damage level and repair character is manifested in following way: a marked increase in DNA migration length was observed at the peak of cell death (at day 13) and less pronounced at days 30 and 100 after 90Sr injection. A decrease in DNA damage induction by additional γ-irradiation was noted to occur parallel to bone marrow cell devastation. At the time of cell death peak this value was the lowest; the dynamic of fast reduction of DNA migration length was accelerated at 1 day of 90Sr exposure and at day 100 after the isotope injection; the dynamic of slow reduction in DNA migration was significantly delayed beginning from the 1 day of exposure to 90Sr with lowest value being registered at peak of cell death; at day 400 of exposure to 90Sr bone marrow cells displayed only a reduction in DNA damage due to additional γ-irradiation. (authors)