Molecular and cellular mechanisms of action of mixed gamma-neutron irradiation at various dose rates

Exposures to mixed gamma-neutron radiation were performed using a BARS-6 pulsed reactor (PEI, RF, Obninsk) either in a regimen of one 100-μsec pulse or in a regimen of continuous 60-min irradiation at dose rates distinguished in 3.6-107 times. The average energy of neutrons was 1.4 MeV. The obtained data testify to differential sensitivity of the investigated parameters to damaging action of mixed gamma-neutron radiation with various of dose rates. It was shown, that irradiation of mice with pulse radiation was 1.3-1.8 times more effective in the induction of chromosome aberrations in bone marrow cells in comparison with continuous regimen of irradiation. At the same time, other biological tests (yield of chromosome aberrations in human lymphocytes, decreasing of the number of cells in thymus) demonstrated that pulsed and continuous regimens have almost equal biological effectiveness. Analysis of chromosome aberration spectra showed that over 90 % of aberrations induced in cultured human blood lymphocytes were chromosome-type aberrations, whereas the proportion of chromosome-type aberrations induced in mice bone marrow cells was 46-58 %. These results suggest that the population of bone marrow cells was represented by cells which were at various cell cycle stages. The increased effectiveness of pulsed gamma-neutron radiation in induction of chromosome aberrations in mice bone marrow may be due to an increase in the proportion of dividing cells in the bone marrow cell population. It was shown that the continuous mode of an irradiating is more effective in rise of polyploidy cells and injury of membranous frames. The obtained experimental results evidence about availability of usage of impulse gamma-neutron radiation for therapy of malignant neoplasm.