Delayed effects of chronic low-dose high linear energy transfer (LET) radiation on mice in vivo.

In the present work, the delayed effects of chronic high linear energy transfer (LET) radiation in polychromatic erythrocytes (PCEs) of mice bone marrow were investigated in vivo. Irradiation of the two-month-old SHK white mongrel random-bred male mice was performed in the radiation field behind the concrete shield of the accelerator of 70 GeV protons to accumulate doses of 0.005-0.16 Gy. The dependence of the biological response on dose, adaptive response (AR) and genomic instability (GI) in F(1) and F(2) generations from males irradiated with doses of 0.005 and 0.16 Gy and from males exposed to combined action of immunomodulator-bendazol hydrochloride (BH) and of 0.16 Gy irradiation, were examined using the micronucleus formation test. The data demonstrated that irradiation of mice with these doses lead to an increase in the level of cytogenetic damage and induces no AR. With analysis of the bone marrow radiosensitivity to 1.5 Gy of X rays and the capacity to AR it was found that the chronic high-LET irradiation of parents induced the GI at least two generations. The combined exposure to BH and the dose of 0.16 Gy induces no AR in F(0) generation but induces AR in F(1) and F(2) offspring.

[Peculiar effects of low doses of high let radiation on mice].

Experiments with exposure of mice to low doses of chronic high-LET radiation were carried out in the radiation field behind the concrete wall of the Serpukhov accelerators of protons with the energy of 70 GeV. The goal was to study dose dependence, radiation adaptive response (AR), and genetic instability. Mice (SHK strain) were irradiated continuously 15, 24 and 31 days which corresponded to the doses of 11.5, 21.5 and 31.5 Gy. Cytogenetic damages were determined using the micronuclear test in marrow polychromatophil erythrocytes. It was shown that all the experimental doses aggravated the cytogenetic damage; however, no AR induction in marrow cells was observed. Males of the F1 generation born from the males irradiated at 11.5 Gy had same level of spontaneous cytogenetic damage as males born from non-irradiated parents. Yet, they displayed an exaggerated sensitivity to additional exposure to 1.5 Gy and no AR induction by the standard gamma-protocol which is indicative of genetic instability.

[The effect of low-dose rate radiation simulating the high-altitude flight conditions on mice in vivo].

In present work, we investigated the peculiarities of the effect of a low-dose rate high-LET radiation that simulates the spectral and component composition of the radiation field formed in the atmosphere at a height of 10 km on mice in vivo. The dose dependence and adaptive response were examined. Irradiation of mice was performed for 24 h a day in the radiation field behind the concrete shield of the Serpukhov accelerator of 70 GeV protons for the time (15-31 days) necessary to accumulate the required doses. The experiments demonstrated that irradiation of mice in vivo in the dose range of 11.5-31.5 cGy leads to an increase in cytogenetic damage to bone marrow cells and induces no adaptive response in bone marrow cells.

Development of genetic instability in mice in response to chronic irradiation simulating high-altitude flight conditions.

The purpose of this work was to study the chronic influence of the high-energy radiation field formed in the atmosphere at an altitude of 10 to 30 km on the level of DNA damage in leukocytes of peripheral blood in mice. The external radiation field (behind the concrete shield) of the U-70 accelerator (Serpukhov, Russia) was used for these studies. This radiation field simulates the components and spectral composition of the high-energy radiation field formed in the atmosphere at an altitude of 10 to 30 km. Two groups of SHK line mice were chronically irradiated with a total dose equivalent to 21.5 and 31.5 cGy. The state of the genome of nucleated blood cells was assessed by the Comet assay (alkaline version) 72 h after completion of chronic irradiation. The level of genome damage in individual peripheral blood leukocytes of irradiated animals was compared with the basal level of DNA lesions in peripheral blood leukocytes of unirradiated control mice. The damage was expressed in %TDNA (the amount of DNA found in the "comet tail" in percent of total DNA in the "comet"). It was found that in mice exposed to the radiation field of the accelerator, the mean value of DNA damage was: %TDNA = 3.88 +/- 0.35% for a dose of 21.5 cGy and % TDNA = 6.00 +/- 0.82% for a dose of 31.5 cGy. In mice irradiated at an X-ray therapeutic device with a dose of 150 cGy 24 h before the examination, %TDNA was 2.27 +/- 0.34% and this did not differ from %TDNA in unirradiated mice, 2.68 +/- 0.56%. We suggest that the increased level of DNA damage observed in mice irradiated with 31.5 cGy from the mixed radiation field at the Serpukhov accelerator points to the development of genetic instability in their leukocytes as a result of chronic exposure of animals to this particular radiation field.

Peculiarities of the effect of low-dose-rate radiation simulating high-altitude flight conditions on mice in vivo.

In the present work, the effect of a low-dose rate of high-LET radiation in polychromatic erythrocytes of mice bone marrow was investigated in vivo. The spectral and component composition of the radiation field used was similar to that present in the atmosphere at an altitude of about 10 km. The dose dependence, adaptive response, and genetic instability in the F1 generation born from males irradiated under these conditions were examined using the micronucleus test. Irradiation of the mice was performed for 24 h per day in the radiation field behind the concrete shield of the Serpukhov accelerator. Protons of 70 GeV were used over a period of 15-31 days, to accumulate doses of 11.5-31.5 cGy. The experiment demonstrated that irradiation of mice in vivo in this dose range leads to an increase in cytogenetic damage to bone marrow cells, but does not induce any adaptive response. In mice pre-irradiated with a dose of 11.5 cGy, an increase in sensitivity was observed after an additional irradiation with a dose of 1.5 Gy. The absence of an adaptive response suggests existence of genetic instability.