Low Doses of Gamma-Radiation Induce Nonlinear Dose Responses in Mammalian and Plant Cells

The percentage of cells with chromosome aberrations or micronuclei induced by low doses of acute (dose rate of 47 cGy/min) or chronic (dose rate of 0.01 cGy/min) gamma-irradiation was studied in vitro in Chinese hamster fibroblasts, human lymphocytes, and Vicia faba seeds and seedlings. The sensitivity of the indicated biological entities to low doses was greater than expected based on linear extrapolation from higher doses. The dose-response curves for cytogenetic damage that were obtained were nonlinear when evaluated over the full range of the doses used. At very low doses, the dose-response curves appeared linear, followed by a plateau region at intermediate doses. At high doses the dose response curves again appeared linear with a slope different from that for the low-dose region. There was no statistically significant difference between the yields of cells with micronuclei induced by low doses of acute versus chronic irradiation. Similar data were obtained both for human lymphocyte culture and for roots and seeds of Vicia faba. Our experiments revealed that the dose range over which the plateau occurs depends on the type of cells irradiated. We have also shown that the modifying effects of the repair inhibitor caffeine and the radioprotector mercaptoethylenamine (MEA) are absent at low doses of gamma irradiation and that caffeine increased the number of cells with cytogenetic damage when evaluated over the plateau region. In the presence of MEA, the upper end of the plateau region was extended from just above 1 Gy to about 2 Gy. We therefore provide direct evidence that a plateau exists in the dose-response curve for the indicated radiation-induced stochastic effects. Furthermore, our results suggest that, for low linear energy transfer radiation, the induction of DNA repair occurs only after a threshold level of cytogenetic damage and that the higher yield of cytogenetic damage per unit dose at low radiation doses is attributable to an insignificant contribution or the absence of DNA repair processes

Assessing ICT Competency in Teachers In Relation to Requirements of the Professional Standard for Teachers

The paper describes conceptual approaches to the assessment of ICT competency in teachers following requirements of the professional standard for teachers. It provides an analysis of the existing approaches. ICT competency is considered as a teacher’s ability to plan, organize and implement teaching/learning activity in an educational context according to the requirements of the Federal State Educational Standard in General Education, to actively participate in the development of an educational organization, and to continue to develop professionally. The paper outlines the authors’ approach to designing test frameworks for ICT competency assessment. The materials of this paper represent the outcomes of a research carried out by the Federal Institute for Education Development on the topic “Conceptual Approaches to Assessing ICT Competency in Teachers with Regard to the Professional Standard”. This paper was written as a part of work carried out for the Ministry of Education and Science № 27.302.2016/НМ on the topic «Conceptual Approaches to Assessing ICT Competency in Teachers with Regard to the Professional Standard»

Non-Linear Effects In The Formation Of DNA Damage In Medaka Fish Fibroblast Cells Caused by Combined Action of Cadmium And Ionizing Radiation

Ionizing radiation-induced formation of genomic DNA damage can be modulated by nearby chemical species such as heavy metal ions, which can lead to non-linear dose response. To investigate this phenomenon, we studied cell survival and formation of 8-hydroxyguanine (8-OHG) base modifications and double strand breaks (DSB) caused by combined action of cadmium (Cd) and gamma radiation in cultured medaka fish (Oryzias latipes) fibroblast cells. Our data show that the introduction of Cd leads to a significant decrease in the fraction of surviving cells and to increased sensitivity of cells to ionizing radiation (IR). Cd also appears to cause non-linear increases in radiation-induced yields of 8-OHG and DSB as dose-yield plots of these lesions exhibit non-linear S-shaped curves with a sharp increase in the yields of lesions in the 10–20 μM range of Cd concentrations. The combined action of ionizing radiation and Cd leads to increased DNA damage formation compared to the effects of the individual stressors. These results are consistent with a hypothesis that the presence of Cd modulates the efficiency of DNA repair systems thus causing increases in radiation-induced DNA damage formation and decreases in cell survival

Comparison in vivo Study of Genotoxic Action of High- Versus Very Low Dose-Rate γ-Irradiation

The aim of the present study was to compare genotoxicity induced by high- versus very low dose-rate exposure of mice to γ-radiation within a dose range of 5 to 61 cGy using the single-cell gel electrophoresis (comet) assay and the micronucleus test. CBA/lac male mice were irradiated at a dose rate of 28.2 Gy/h (high dose rate) or 0.07 mGy/h (very low dose rate). The comet assay study on spleen lymphocytes showed that very low dose-rate irradiation resulted in a statistically significant increase in nucleoid relaxation (DNA breaks), starting from a dose of 20 cGy. Further prolongation of exposure time and, hence, increase of a total dose did not, however, lead to further increase in the extent of nucleoid relaxation. Doses of 20 and 61 cGy were equal in inducing DNA breaks in mouse spleen lymphocytes as assayed by the comet assay. Of note, the level of DNA damage by 20–61 cGy doses of chronic irradiation (0.07 mGy/h) was similar to that an induced by an acute (28.2 Gy/h) dose of 14 cGy. The bone marrow micronucleus test revealed that an increase in polychromatic erythrocytes with micronuclei over a background level was induced by very low-level γ-irradiation with a dose of 61 cGy only, with the extent of the cytogenetic effect being similar to that of 10 cGy high-dose-rate exposure. In summary, presented results support the hypothesis of the nonlinear threshold nature of mutagenic action of chronic low dose-rate irradiation

Cytogenetic Adaptive Response and Genetic Instability Induced by Low-Dose Rate High-LET Radiation in Mice

In the present work, we investigated the effect of a low-dose rate of high-energy radiation that simulates the radiation fields formed in the conditions of a high-altitude flight on mice in vivo. Adaptive response (AR) and genetic instability in generations F1, F2, F3 born from males irradiated under these conditions were examined by the micronucleus test in polychromatic erythrocytes of bone marrow. Two-month-old males of SHK mice were used. Irradiation was performed for 24h a day in the radiation field behind the concrete shield of the accelerator of 70 GeV protons (Serpukhov), which adequately simulates the component and spectral composition of the field formed in the atmosphere at a height of 10 km, to accumulate doses of 11.5, 21.5 and 31.5 cGy (1 cGy/day). For induction of AR, mice were exposed to irradiation according to the following scheme: an adapting doses of 11.5, 21.5, 31.5 cGy, followed after a day by a challenging dose of 1.5 Gy (28.2 Gy/h). To reveal the genetic instability, one group of males, descendants of chronically irradiated and unirradiated parents, at an age of two months were subjected to additional irradiation with a dose of 1.5 Gy from a 60Co source. Another group of males were exposed to chronic γ-irradiation by the scheme of AR: an adapting dose of 10 cGy (1 cGy/day) followed after a day by a challenging dose of 1.5 Gy. Bone marrow specimens for calculating micronuclei were prepared by the conventional method. The experiments demonstrated that: 1) irradiation of mice with all doses of high-LET radiation leads to an increase in cytogenetic damage in erythrocytes; 2) irradiation of mice with these doses induces no AR as opposite to γ-radiation; and 3) in mice of the F1 generation born from males irradiated with doses of 11.5, 21.5 and 31.5 cGy, an increase in sensitivity to additional irradiation with a dose of 1.5 Gy of γ-radiation and the absence of AR compared with the descendants of unirradiated males occur; 4) in mice of the F2 and F3 generations born from males irradiated with doses of 21.5 and 31.5 cGy, an increase in sensitivity to additional irradiation with a dose of 1.5 Gy of γ-radiation and the absence of AR take place too. The data obtained indicate the genetic instability in F1, F2 and F3 generations born from irradiated males. These findings may be used to assess the radiation risks from long-term high-altitude flights

Study of cytogenetic effects induced by accelerated 12C ions with energy of 200 MeV/n in Mice

In present work we investigated the cytogenetic effects induced by accelerated 12C ions with energy of 200 MeV/n on mice. Dose dependence, ability of the adaptive response (AR) induction and genetic instability in the generation F1 were studied by the micronucleus test in polychromatic erythrocytes (PCE) of bone marrow. Two-month-old males of SHK mice were irradiated by 12C ions with energy of 200 MeV/n (Nuclotron, Joint Institute for Nuclear Research, Dubna, Russia). A control group was exposed to X-rays. The dose dependences of the frequency of PCE with micronucleus (MN) induced with doses of 10, 15, 50 100 and 150 cGy of both types of radiation were studied. For adaptive response detection mice were exposed to irradiation according to the following scheme: an adapting doses of 10 cGy of 12C ions, followed after a day by a challenging dose of 1.5 Gy of X-rays (1Gy/min). To obtain generation F1, 15 days after the irradiation, males from the irradiated and control groups were mated in separate cages with unirradiated females for two weeks. This period of time was chosen because it is sufficient for the formation of spermatides, which then take part in the impregnation of the ovule. Dendants of irradiated and unirradiated parents were exposed to additional X-radiation with a dose of 1.5 Gy or by the scheme of AR to reveal the genetic instability. Bone marrow specimens for calculating micronuclei were prepared by the conventional method. The experiments demonstrated that: 1) at low doses (0-50 cGy) both dose-dependencies of cytogenetic damage induction can be fitted by a linear regression and almost coincide, i.e. RBE value is equal 1; at higher doses RBE value rises to 1.4; 2) irradiation of mice with dose of 10 cGy of accelerated 12C ions induces AR as X-radiation; and 3) the levels of spontaneous and radiation-induced PCE with MN in mice born from both males irradiated with a dose of 10 cGy of accelerated 12C ions and unirradiated animals is the same. The F1 generation born from irradiated males is unable to induce the AR, as distinct from their parents. The offsprings of unirradiated males reserves this ability. Obtained data indicate the genetic instability in F1 generation born from 12C-irradiated males. These findings may be used to assess the delayed radiation effect from low-dose of high-LET radiation and for developing basic foundation of adaptive medicine