The cytogenetic indication of irradiation in persons exposed to the action of the factors in the Chernobyl accident]

363 men who have been working under conditions of additional irradiation in terms from few hours to some months were cytogenetically examined to define individual irradiation. In 111 men with the known dose of irradiation (5-140 cGy), the results of cytogenetic evaluation indicated, as a rule, a less intensive irradiation than physical dosimetry. This could be caused by elimination of chromosome aberrations, individual sensitivity, peculiar irradiation situation, or in some cases by incorrect evaluation of dose. In 252 men with the unknown dose of irradiation a tentative level was determined as based on frequency of metaphases with chromosome type aberrations. According to the study the absorbed dose was below 25 cGy in 209 cases, 26-50 cGy in 39 cases, and reached 51-90 cGy in 4 cases.     

Effects of low-dose neutrons applied at reduced dose rate on human melanoma cells

Human melanoma cells that are resistant to gamma rays were irradiated with 14 MeV neutrons given at low doses ranging from 5 cGy to 1.12 Gy at a very low dose rate of 0.8 mGy min(-1) or a moderate dose rate of 40 mGy min(-1). The biological effects of neutrons were studied by two different methods: a cell survival assay after a 14-day incubation and an analysis of chromosomal aberrations in metaphases collected 20 h after irradiation. Unusual features of the survival curve at very low dose rate were a marked increase in cell killing at 5 cGy followed by a plateau for survival from 10 to 32.5 cGy. The levels of induced chromosomal aberrations showed a similar increase for both dose rates at 7.5 cGy and the existence of a plateau at the very low dose rate from 15 to 30 cGy. The existence of a plateau suggests that a repair process after low-dose neutrons might be induced after a threshold dose of 5-7.5 cGy which compensates for induced damage from doses as high as 32.5 cGy. These findings may be of interest for understanding the relative biological effectiveness of neutrons and the effects of environmental low-dose irradiation.     

Cytogenetic effects of low-dose radiation with different LET in human peripheral blood lymphocytes

Chromosome damage and the spectrum of aberrations induced by low doses of γ-irradiation, X-rays and accelerated carbon ions (195 MeV/u, LET 16.6 keV/μm) in peripheral blood lymphocytes of four donors were studied. G₀-lymphocytes were exposed to 1–100 cGy, stimulated by PHA, and analyzed for chromosome aberrations at 48 h post-irradiation by the metaphase method. A complex nonlinear dose–effect dependence was observed over the range of 1 to 50 cGy. At 1–7 cGy, the cells showed the highest radiosensitivity per unit dose (hypersensitivity, HRS), which was mainly due to chromatid-type aberration. According to the classical theory of aberration formation, chromatid-type aberrations should not be induced by irradiation of unstimulated lymphocytes. With increasing dose, the frequency of aberrations decreased significantly, and in some cases it even reached the control level. At above 50 cGy the dose–effect curves became linear. In this dose range, the frequency of chromatid aberrations remained at a low constant level, while the chromosome-type aberrations increased linearly with dose. The high yield of chromatid-type aberrations observed in our experiments at low doses confirms the idea that the molecular mechanisms which underlie the HRS phenotype may differ from the classical mechanisms of radiation-induced aberration formation. The data presented, as well as recent literature data on bystander effects and genetic instability expressed as chromatid-type aberrations on a chromosomal level, are discussed with respect to possible common mechanisms underlying all low-dose phenomena.     

The dose dependence of cytogenetic damages and the adaptive response of mammalian cells under the action of ionizing radiation at low doses

The dose-effect dependence of cytogenetic damage after single dose irradiation in the dose range of 0.1-2 Gy and the adaptive response after double-dose irradiation were studied on Chinese hamster and human melanoma cells in culture. The non-linear dose dependencies were found for the induction of chromosome aberrations with decrease in cell radiosensitivity in the definite dose range. This decrease started at 10 and 20 cGy for melanoma and Chinese hamster cells respectively. The maximal adaptive response was induced at 1 cGy for melanoma cells and at 20 cGy for Chinese hamster cells. It can be supposed that the same inducible repair processes are responsible for non-linearity of dose-effect curves and induction of the adaptive response. These processes are similar in mechanisms and different in quantitative proportion for different cell types.     

Complex cytogenetic characteristic of people suffered from Chernobyl accident

A cytogenetic study was performed on Chernobyl cleanup workers, on their children, on persons evacuated from contaminated aeria (adult and children), on so named "veterans of particular risk" irradiated due to the accidents on the nuclear plant, testing of nuclear weapons etc. and on control donors. The yield of stable (FISH analysis) and of unstable chromosome aberrations, micronuclei in both lymphocytes and erythrocytes, HPRT mutations was found to be increased in exposed groups as compared to control ones. In children of liquidators and in evacuated children we observed genomic instability and increased in vitro chromosomal radiosensitivity. Acceleration of age accumulation of translocations characterized the exposed population in comparison with control group. People with the highest level of routine chromosome aberrations had cardiovascular and digestive diseases more often likely than those with the lowest level. In frame of International Project ECP-6--"Biological dosimetry" the dose-responses for dicentrics and translocations were constructed in dose range 0-100 cGy of gamma-irradiation on the base of data of 8 laboratories. On cancer patients undergone whole-body gamma-irradiation (every day at the dose 11.5 cGy to a total of dose 57.5 cGy) we constructed the dose-responses for the dicentrics and translocations and compared them with the dose-responses for these aberrations after the in vitro irradiation of lymphocytes of the same patients. For the dicentrics the effectiveness of the in vivo irradiation was less than of the in vitro one. No differences were found for translocations.     

2-[(Aminopropyl)amino] ethanethiol-mediated reductions in 60Co gamma-ray and fission-spectrum neutron-induced chromosome damage in V79 cells

The radioprotector 2-[aminopropyl)amino] ethanethiol (WR1065), which has been reported to reduce the cytotoxic and mutagenic effects of low LET radiation, was investigated for its ability to protect against low LET (60Co gamma ray) and high LET (fission-spectrum neutron)-induced chromosome damage in V79 cells. Cells were irradiated in G2 phase in the presence or absence of 4 mM WR1065 and were harvested and analyzed 2 h later for chromatid-type aberrations. Irradiation of G2-phase V79 cells in the presence of WR1065 resulted in a 30 to 50% reduction in the frequency of gamma-ray and neutron-induced chromatid-type breaks and exchanges. The effects were found only after exposures of greater than 200 cGy gamma-ray or 50 cGy neutron irradiation. The radioprotector was effective at reducing neutron-induced aberrations after exposures at dose rates of both 10 and 43 cGy/min. Thus the radioprotector WR1065 is an effective anti-clastogenic agent in V79 cells, protecting against both 60Co gamma-ray and fission-spectrum neutron-induced aberrations, when present during irradiation.     

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.     

Transformation of C3H 10T1/2 cells with 4.3 MeV alpha particles at low doses: effects of single and fractionated doses.

Oncogenic transformation of C3H 10T1/2 cells was determined after exposure to graded doses of 4.3-MeV alpha particles LET = 101 keV/microns. The source of alpha particles was 244Cm and the irradiation was done in an irradiation chamber built for the purpose. Graded doses in the range of 0.2 to 300 cGy were studied with special emphasis on the low-dose region, with as many as seven points in the interval up to 10 cGy. The dose-effect relationship was a complex function. Transformation frequency increased with dose up to 2 cGy; it seemed to flatten at doses between 2 and 20 cGy but increased again at higher doses. A total of 21 cGy was delivered in a single dose or in 3 or 10 equal fractions at an interval of 1.5 h. An inverse dose-protraction effect of 1.4 was found with both fractionation schemes. Measurements of the mitotic index of the population immediately before the various fractions revealed a strong effect on the rate of cell division even after very low doses of radiation. Mitotic yield decreased markedly with the total dose delivered, and it was as low as 50% of the control value after 4.2 cGy and 20% after 14 cGy with both fractionation schemes.     

Comparison of cytogenic response of human lymphocytes to in vivo and in vitro exposure to low doses of gamma-rays. Unstable chromosomal exchanges detected by FPG techniques

On peripheral lymphocytes of eight cancer patients undergone whole-body therapeutic irradiation (at daily dose of 10 cGy up to total dose of 50 cGy of 60Co gamma-rays) the dose-response of unstable chromosome exchanges (dicentrics and centric rings) was studied. This dose response fitted well linear function. The lower slope of dose-response curve was found for in vivo irradiated lymphocytes as compared to the dose response curve obtained for in vitro irradiated lymphocytes of the same patients. This finding seems to provide evidence that in case of protracted irradiation of individuals an absorbed dose could be underestimated if for biological dosimetry an in vitro dose response curve for unstable chromosome aberrations is used as referent one.     

Dose responses for chromosome aberrations produced in noncycling primary human fibroblasts by alpha particles,and by gamma rays delivered at sublimiting low dose rates

As the total dose of X or gamma rays is delivered at lower and lower rates, the yield of chromosome aberrations progressively diminishes. Simultaneously, the shape of the dose response changes from one exhibiting pronounced upward curvature at high dose rates to one approaching linearity at low dose rates. Although the maximum sparing effect caused by lowering the dose rate can be predicted from classical cytogenetic theory, it has yet to be verified experimentally. Here, noncycling normal human fibroblasts were exposed to graded doses of (137)Cs gamma rays at chronic dose rates of 6.3 and 2.8 cGy h(-1), dose rates that we reasoned should be lower than those required to achieve maximal sparing. This was indeed shown to be the case, after it was determined that the two chronic dose rates produced identical linear dose responses of 0.05 total aberrations per cell Gy(-1). Consistent with cytogenetic theory, this value was statistically indistinguishable from the linear coefficient derived from a fit to aberration frequencies produced by high-dose-rate exposure. Exposure to (238)Pu alpha particles also produced a linear dose response for total aberrations, whose slope-with respect to (137)Cs gamma rays as a reference radiation-implied a maximum RBE of 35 +/- 2.     

Comparison of cytogenetic response of human lymphocytes to in vivo and in vitro exposure to low-dose gamma rays. Translocations and dicentrics detected by the FISH technique

On peripheral lymphocytes of 5 cancer patients undergone wholebody therapeutic irradiation (at daily dose of 10 cGy up to total dose 50 cGy of 60Co gamma-rays) the dose response of unstable and stable chromosomal exchanges detected by FISH was compared with the dose response of the some aberrations in lymphocytes irradiated in vitro. The dose response fitted well to linear function. For dicentrics the lower slope of dose-response curve was found for in vivo irradiated lymphocytes as compared to the dose-response curve obtained for in vitro irradiated lymphocytes of the same patients. No difference between in vivo and in vitro irradiation of lymphocytes was found for translocations. The frequency of translocations increased faster with the dose than the frequency of dicentrics only in lymphocytes irradiated in vivo.     

Genetic efficacy of low doses of ionizing radiation in chronically-irradiated small mammals

Earlier we have established the genetic effects of low dose chronic irradiation in bank vole (somatic and germ cells, embryos), in pond carp (fertilized eggs, embryos, fry) and in laboratory mice (somatic and germ cells) in the range of doses from near-background to 10 cGy. These low dose effects observed in mammals and fish are not expected from extrapolation of high dose experiments. For understanding reasons this discrepancy the comparative analysis of genetic efficiency of low dose chronic irradiation and the higher doses of acute irradiation was carried out with natural populations of bank vole which inhabited the two sites differing in ground of radionuclide deposition. For comparing efficiency the linear regression model of dose-effect curve was used. Dose-effect equations were obtained for animals from two chronically irradiated bank vole populations. The mean population absorbed doses were in the range 0.04-0.68 cGy, the main part of absorbed doses consisted of external radiation of animals exposed to 137Cs gamma-rays. Dose-effect equations for acute irradiation to 137Cs gamma-rays (10-100 cGy) were determined for the same populations. Comparison of genetic efficiency was made by extrapolation, using regression coefficient beta and doubling dose estimation. For chronic exposure the doubling doses calculated from low-dose experiments are 0.1-2 cGy and the doubling doses determined from high-dose experiments are in the range of 5-20 cGy. Our hypothesis that the doubling dose estimate is calculated in higher-dose ionizing radiation experiments should be much higher than the deduced from the low dose line regression equation was verified. The doubling dose estimates for somatic cells of bank vole and those for germ cells of laboratory mice are in close agreement. The radiosensitivity of bank vole chromosomes were shown is practically the same as that for human lymphocytes since doubling dose estimates for acute irradiation close to each other. For low LET radiation a higher genetic efficiency of chronic low doses in comparison with the higher doses of acute gamma-irradiation (137Cs source) was proved by three methods.     

The mechanisms of adaptive response. Estimation of capacity of human blood lymphocytes to radiation adaptive response using different criteria

Blood lymphocytes of 15 healthy donors have been investigated for the ability to decrease their radiosensitivity after treatment with low dose irradiation named radioinduced adaptive response (AR). The unstable chromosome aberrations were used to evaluate the radiosensitivity change after irradiation of cells with low adaptive dose (5 cGy) and subsequent high challenge dose (1.0 Gy) in comparison with the effect of challenge irradiation only. Three indexes were used: the frequency of cells with aberrations in all analyzed cells (A), the number of chromosome aberrations per cell (B) and the number of chromosome aberrations per one aberrant cell (C). It has been discovered that all donors examined can be divided into four groups: 1--individuals which cells did not show AR by all indexes used; 2--individuals which cells showed AR by indexes A and B, but not C; 3--AR was demonstrated by indexes B and C; 4--AR was confirmed by all three indexes. Generally accepted repair model for AR formation explains only the case of donor groups 3 and 4, but can not explain the mechanism leading to the case of group 2. For understanding this mechanism, the distribution of metaphases by the number of chromosome aberrations per cell was analyzes for each donor. It was shown that the part of cells without aberrations in group 2 donors increased significantly after treatment with the adaptive and challenge irradiation in comparison with that after irradiation with challenge dose only. The conclusion is that in this case AR is formed as a result of change in the frequency 0 cell class--population shift. The analogous shift was observed in the distributions of metaphases for all donors of the group 4, but was absent in the group 3 donors. The data obtained suggest that AR of blood lymphocytes might be a result of several processes: activation of submutational genome damage repair; population shifts manifested by the change in the part of undamaged cells; and, possibly, activation of apoptotic cell death. The complex nature of AR affects each of radiosensitivity evaluation criteria to a different extent.     

Effect of external irradiation with different intensity at 1 Gy dose on the DNA, RNA and total protein content in the testis and liver of rats

The content of DNA, RNA and total protein in the rat testes and liver was studied 1 and 30 days after external chronic gamma-irradiation (dose rate 1.8 and 5.76 cGy/day) and acute gamma-irradiation with relatively low dose rate (5.4 cGy/min) up to a total dose of 1 Gy. The results obtained pointed to the specific metabolic reaction of radiosensitive (testes) and radioresistant (liver) tissues of organism at external irradiation at relatively low dose of different intensity due to unequal cell capacity for proliferation.     

Relative biological effectiveness and dose rate effect of tritiated water on chromosomes in human lymphocytes and bone marrow cells

Tritriated water (HTO) is a major toxic effluent from the nuclear power industry, that is released into the environment in large quantities. The low dose radiation effect and dose rate effect of HTO on human lymphocytes and bone marrow cells have not been well studied. The present study was therefore undertaken to investigate the HTO dose-response relationship for chromosomal aberrations in human lymphocytes and bone marrow cells at low in vitro radiation doses ranging from 0.1 to 1 Gy. Lymphocytes (G₀ stage) and bone marrow cells were incubated for 10–150 min with HTO at a dose rate of 2cGy/min (555 MBq/ml). The relative biological effectiveness (RBE) of HTO was calculated with respect to ₆₀Co γ-rays for the induction of dicentric and centric ring chromosomes at low radiation doses. The RBE value for HTO β-rays relative to ⁶⁰Co γ-rays was 2.7 for lymphocytes and 3.1 for chromatid aberrations in bone marrow cells. Lymphocytes were also chronically exposed to HTO for 6.7–80 h at dose rates of 0.5 cGy/min (138.5 MBq/ml) and 0.02 cGy/min (5.6 MBq/ml). There was a 71.5% decrease in the yield of dicentrics and centric rings at the dose rate of 0.02 cGy/min, indicating a clear dose rate effect of HTO. The RBE value for HTO relative to ¹³⁷Cs γ-rays was 2.0 at a dose rate of 0.02 cGy/min, suggesting that low HTO dose rates produce no increase of the RBE values and that the values may be constant between 2 and 3 within these dose rates. These results should prove useful in assessment of the health risk for humans exposed to low levels of HTO.     

The dose and dose-rate effects of paternal irradiation on transgenerational instability in mice: a radiotherapy connection

The non-targeted effects of human exposure to ionising radiation, including transgenerational instability manifesting in the children of irradiated parents, remains poorly understood. Employing a mouse model, we have analysed whether low-dose acute or low-dose-rate chronic paternal γ-irradiation can destabilise the genomes of their first-generation offspring. Using single-molecule PCR, the frequency of mutation at the mouse expanded simple tandem repeat (ESTR) locus Ms6-hm was established in DNA samples extracted from sperm of directly exposed BALB/c male mice, as well as from sperm and the brain of their first-generation offspring. For acute γ-irradiation from 10-100 cGy a linear dose-response for ESTR mutation induction was found in the germ line of directly exposed mice, with a doubling dose of 57 cGy. The mutagenicity of acute exposure to 100 cGy was more pronounced than that for chronic low-dose-rate irradiation. The analysis of transgenerational effects of paternal irradiation revealed that ESTR mutation frequencies were equally elevated in the germ line (sperm) and brain of the offspring of fathers exposed to 50 and 100 cGy of acute γ-rays. In contrast, neither paternal acute irradiation at lower doses (10-25 cGy), nor low-dose-rate exposure to 100 cGy affected stability of their offspring. Our data imply that the manifestation of transgenerational instability is triggered by a threshold dose of acute paternal irradiation. The results of our study also suggest that most doses of human exposure to ionising radiation, including radiotherapy regimens, may be unlikely to result in transgenerational instability in the offspring children of irradiated fathers.     

Frequency of stable chromosomal aberrations determined by FISH in 49 Chernobyl nuclear accident liquidators exposed to various doses of radiation

FISH technique was tested on the 49 liquidators of the Chernobyl Accident. Groups were formed according to average group exposure doses and/or individual ones determined by the method of EPR. The essential variability of spontaneous and irradiation-induced frequencies of reciprocal translocations was observed. In groups with the lowest EPR-doses (below 25 cGy) the average cytogenetic dose was considerably higher then doses determined by EPR-method. The best coincidences between average in-group EPR- and FISH-doses were in the group with 25-50 cGy doses for "acute irradiation" model and in the group with 50-100 cGy and higher for "chronic irradiation" model.     

Changes in the EPR spectra of the nitrosyl complexes of blood proteins in the low-intensity whole-body irradiation of mice

After NO adding to mice blood and isolated erythrocytes ESR signal of nitrozyl complex HbNO (g = 2.07, g = 1.98) and NO-induced MetNg (g = 6.0) were registered. It was shown that the intensity of ESR spectra of these complexes increased after radiation of mice with a dose of 0.06, 0.6 and 5.4 cGy. Low-dose irradiation (0.6 and 0.06 cGy) caused the change in the form of ESR spectra of HbNO (g = 2.07), which is indicative of the shift from T-structure to R-structure and of the preferred formation of R-conformations of oxyhemoglobin in blood. It was found that dependence of NO-induced MetHb signal on irradiation dose is bimodal that may be connected with nonlinear response of the cells to irradiation and retarded adaptive response after radiation with low doses.     

The dynamics of cytogenetic anomalies output in seedling merysteme at the chronic irradiation of seeds

The dynamics of chromosomal aberrations in seedling root merysteme is explored in various terms of irradiation of two genotype corn dry seeds. The effects of chronic irradiation with low rate dose, with acute and with combined irradiation are explored in the different terms of seed storage. It is shown that the output of chromosomal aberrations and of the efficiency of irradiation (1/Gy) change depending on the accumulated dose of chronic irradiation and for both genotypes are described by unmonotonous functions. Efficiency of acute irradiation changes the dependence on the terms of seed storage. The efficiency of chronic irradiation considerably exceeds the efficiency of acute irradiation. Antagonistic effect of combined irradiation dry seeds of one of genotypes is marked.