Retrospective dose estimation in remote period after exposure using different biological methods

Investigation of application of chromosome aberrations of lymphocytes in peripheral blood for biological dosimetry purposes in remote (up to 40 years) period after acute exposure to doses of 1 Gy and more was carried out. The comparative analysis of frequency of unstable and stable (using FISH and G-banding methods) aberrations was performed for 24 subjects accidentally exposed to radiation on nuclear submarines during 1961-1985. Statistically significant increasing of frequency of dicentrics and centric rings was determined in the exposed subjects in remote period after exposure to compare with controls. Their sum frequency in the exposed group varied depending on ARS heaviness from 0.1 to 1.0 aberrations per 100 cells. In control group it was from 0 to 0.2 correspondingly. Translocation frequency (complete + incomplete) fixed by FISH method (2, 4, and 12 chromosomes) varied within the limits of 0.2-16.0 for exposed subjects and 0.3-1.26 translocations per genome per 100 cells for controls. Some examined persons (5 subjects) exposed to accident in 1985 had results of analysis of unstable chromosome aberration in acute period after exposure that allow to estimate obtained doses by dicentrics frequency which having good correlation with ARS heaviness. Individual dosed using traslocation frequency were defined retrospectively in 11 from 21 exposed persons. They correlate with calculated physics doses and doses estimated by haematolotical parameters in acute period and also doses obtained by ESR spectroscopy of tooth enamel in remote period.     

Results of dynamic cytogenetic study of children and teenagers living in areas, radioactive by contaminated after the Chernobyl accident

Results of multiyear cytogenetic study of children and teenagers living in areas, radioactive by contaminated after Chernobyl accident, were adduced. Mean density of 137Cs contamination in two compared living areas were 111 and 200 kBq/m2 and mean external doses accumulated for 1986-2001 were 6.7 and 11.4 mGy correspondingly. Averaged thyroid doses receives by subjects of all age groups in the second area were approximately 1.5 times higher than in the first area; in the youngest group (0-1 year) the doses were 114.3 and 174.3 mGy. During 17 years cytogenetic investigation approximately from 30% to 60% of examined persons were observed the increased level of chromosome aberrations in lymphocytes of peripheral blood. Average frequency of unstable aberrations (acentrics, dicentrics and centric rings) constituted about 0.4 per 100 cells (0.22 per 100 cells in controls) during all period of observation. Level of marker aberrations (dicentrics and centric rings) was increased almost all times of study and varied within 0.04-0.19 per 100 cell (0.03 in control group). The parallel investigation of frequency of stable aberrations by FISH method showed up their level about 3 times exceeding observed dicentrics level. Comparably higher indexes of cytogenetic disturbances were revealed in group exposed in utero during period of accident.     

The cytogenetic effect in a group of settlers from a 30-kilometer area of right of way

One of the critical human group of potential risk is the group of population from 30-km zone around the Chernobyl nuclear power plant. The cytogenetical examination of 12 persons (8 man, 4 woman, 30-60 years old) from 5 villages situated in north-west and south-east directions from the ChNPP in the frame of this zone was conducted. The data of the conventional analysis showed relatively low cytogenetic effects comparable with the effects in exposed people out of the zone (the mean level of unstable cytogenetic markers in different villages was 0.21-0.35 per 100 cells). The level of stable translocations in one case (woman, 59 years old) determined using FISH (16.62 per 100 cells for the whole genome) exceeded their spontaneous aged frequency and confirmed the high sensitivity of this method for the evaluation of real radiation exposure.     

Cytogenetic effect in peripheral blood lymphocytes of children living in villages in the Ovruch District, Zhitomir Region of the Ukraine contaminated by radionuclides]

For the purpose of genetic indication of low level of chronic radiation exposure the cytogenetic monitoring of some critical children groups living in two contaminated Ukrainian villages was carried out. In all the groups the mean frequency of aberrant cells and chromosome type aberrations (including dicentrics, centric rings, chromosome translocations as well as polyploid cells) significantly exceeded control level. During the repeated examination of children from Vistupovichi (in 13 months after the first one) the striking increase of cytogenetic effect was revealed. Dicentrics and rings were registered in 79% of persons with the individual rate 0.5-1.5 and mean group frequency 0.57 per 100 cells. The authors tried to evaluate the average cumulative doses of radiation for examined groups using G. Littlefield equation for dicentric outcome under the low dose rate Cs-137 source and taking into account the assumption about the reducing of 50% dicentrics per year. According to this rough calculation, the revealed cytogenetic effect can correspond to the mean total dose of 33 cSv for Vistupovichi children.     

Comparative investigation of structural and gene somatic mutations in workers of nuclear chemical plants. II. Frequency of lymphocytes mutant in T-cell receptor loci

Frequency of lymphocytes mutant at T-cell receptor (TCR) loci was defined in 42 workers of nuclear chemical plants. In 11 persons mainly exposed to external radiation the mean frequency of TCR-mutant lymphocytes was statistically significant by higher compared with control group of unexposed donors: 9.1 x 10(-4) vs 3.5 x 10(-4) correspondently (p < 0.01). Frequency of TCR-mutant lymphocytes did not correlate neither the frequency of structural mutations non doses of external exposure. In group of workers exposed to combined external and internal radiation (n = 31) the average frequency of TCR-mutant lymphocytes was higher compared with control level: 8.9 x 10(-4) vs 3.5 x 10(-4) correspondently (p < 0.01). Correlations between the frequency of TCR-mutant cells and Pu content in organism (r = 0.5; p = 0.005) and between the frequency of chromosome aberration of unstable and stable types (r = 0.5; p = 0.002 and r = 0.6; p = 0.036, correspondently) were set. Comparison of results of analysis of structural and gene mutations allows us to supose that in case of external exposure the observed disturbances can result from genome instability in remote period after irradiation. In case of combined exposure the genetic changes were possibly caused by the constant action of alpha-radiation from Pu containing in the body.     

Induction of chromatid-type aberrations in peripheral lymphocytes of hospital workers exposed to very low doses of radiation

Radiological personnel represent workers exposed to low cumulative doses of radiation. As their surveillance is generally based on physical dosimetry, there is little or inconclusive information on biological effects due to radiation exposure at these doses. We aimed to explore the extent of chromosomal damage in circulating lymphocytes of hospital workers (technicians, nurses and physicians) chronically exposed to a very low level of radiation using conventional and molecular cytogenetic analyses (chromosome painting with chromosomes #2, #3 and #10 as probe cocktail). Compared with controls, exposed workers displayed a significant increase in the frequency of aberrant lymphocytes (1.26+/-0.11/100 cells versus 1.63+/-0.17/100 cells). In particular, exposed technicians showed significantly higher mean values than nurses or physicians (3.68+/-1.17/100 cells versus 1.36+/-0.18/100 cells and 1.36+/-0.09/100 cells, respectively). Interestingly, we found that the chromosomal damage was prevalently expressed as chromatid-type aberrations. Chromosome painting indicated that the frequency of chromosome rearrangements (CR; translocations and dicentrics pooled together) was approximately comparable between radiological workers and the control group. Moreover, we did not detect any significant difference due to radiation exposure when CR rates were considered separately for each of the three chromosomes in the probe cocktail.     

Remote effects at cell and subcell level in the hemopoietic system after chronic radiation exposure in man

The parameters characterizing the state of hemopoietic cells obtained from chronically exposed residents of the Techa riverside villages studied at late time after the exposure included: the level of somatic mutations in the TCR gene, the level of chromosome aberrations, the intensity of peripheral blood lymphocyte apoptosis. Exposed versus unexposed subjects (controls) showed an increased frequency of CD3-CD4+ T-lymphocytes, chromosome aberrations of stable type (translocations) and unstable type (dicentrics, rings), and also increased intensity of lymphocyte apoptosis. The findings of tests using a standard additional gamma-irradiation (1 Gy) accompanied by 24-hour incubation indicated that the rate of apoptosis of lymphocytes was significantly higher in exposed individuals in comparison with unexposed ones. It was suggested basing on the obtained data that at late time the chronic (for over 50 years) exposure at RBM doses from 0.01 to 3.22 Sv was a factor inducing the damage to the genetic apparatus of hemopoietic cells. Evidently, the initial chronic low-intensity irradiation in the above-indicated dose range activates adaptive processes at the cellular level in hemopoietic cells. Late time after the onset of exposure the adaptation reserves are depleted in chronically exposed persons which brings about its failure in the case of a challenge by additional external exposures.     

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.     

FISH chromosome analysis of plutonium workers from the Sellafield nuclear facility

Chromosome analysis using a single-color FISH technique to paint three pairs of chromosomes was undertaken on a group of 46 retired plutonium workers with assessed bone marrow doses >60 mSv, 34 of whom were categorized as having robust dosimetry and 12 for whom internal doses were considered less reliable. Comparisons were made with a group of 34 workers with negligible radiation exposure and a group of 34 workers with similar recorded external gamma-ray doses but negligible internal dose. The simple translocation frequency of 17.65 +/- 1.96 x 10(-3) per genome equivalent for the 34 plutonium workers with robust dosimetry was significantly increased in comparison with that of 10.06 +/- 1.16 x 10(-3) per genome equivalent for the unirradiated control group (P = <0.001) and that of 13.55 +/- 1.43 x 10(-3) per genome equivalent for the group with similar external gamma-ray exposure (P = 0.012). Thus, although in vitro studies have indicated that the majority of alpha-particle-irradiated cells suffer complex non-transmissible chromosome damage, in vivo a significant proportion survive with simple exchanges that can be passed on to descendant cells. In contrast, the three groups demonstrated no significant differences in stable complex aberrations. No evidence of an increase in dicentrics or unstable complex aberrations associated with plutonium exposure was observed, and it can therefore be assumed that there is little, if any, ongoing irradiation of mature lymphocytes. The translocation frequency of 12.08 +/- 1.92 x 10(-3) per genome equivalent for the group of 12 plutonium workers with less reliable internal dosimetry could adequately be accounted for by age and external dose and indicates that the internal bone marrow doses are likely to have been overestimated. Cytogenetic analysis can therefore make a valuable contribution to the validation of internal doses from plutonium deposition.     

The characterization and transmissibility of chromosome aberrations induced in peripheral blood lymphocytes by in vitro alpha-particle radiation

Peripheral blood lymphocytes were irradiated in vitro with (213)Bi alpha particles at doses of 0, 10, 20, 50, 100, 200 and 500 mGy. Chromosome analysis was performed on 47-h cultures using single-color fluorescence in situ hybridization (FISH) to paint chromosomes 1, 3 and 5. The whole genome was analyzed for unstable aberrations to derive aberration frequencies and determine cell stability. The dose response for dicentrics was 33.60 +/- 0.47 x 10(-2) per Gy. A more detailed analysis revealed that the majority of aberrations scored as dicentrics were part of complex/multiple aberrations, with the proportion of cells containing complexes increasing with dose. Cells containing aberrations involving painted chromosomes (FISH aberrations) were further classified according to cell stability and complexity. The majority of cells with FISH aberrations were unstable. The proportion of aberrant FISH cells with complex/multiple aberrations ranged from 56% at 10 mGy to 89% at 500 mGy. A linear dose response for genomic frequencies of translocations in stable cells fitted the data from 0 to 200 mGy with a dose response of 7.90 +/- 0.98 x 10(-2) per Gy, thus indicating that they are likely to be observed in peripheral blood lymphocytes from individuals with past or chronic exposure to high-LET radiation. Comparisons with the dose response for low-LET radiation suggest an RBE of 13.6 for dicentrics in all cells and 3.2 for translocations in stable cells. Since stochastic effects of radiation are attributable to genetic changes in viable cells, translocations in stable cells may be a better measure when considering the comparative risks of different qualities of radiation.     

Variation in the frequencies of spontaneous and in vitro induced chromosome aberrations in human lymphocytes during natural and radiation-induced aging

The frequency of translocations detected by FISH in lymphocytes of control donors increases with age as a quadratic function. This process is faster in persons previously exposed to low doses of radiation. It means that translocation frequency can be used as a measure of biological age. Moreover, translocation frequency should be taken into account in biological reconstruction of absorbed doses. The frequencies of dicentrics detected by FIGH and FPG linearly increase with age in both groups, and this process occurs at equal rates during natural and radiation-induced aging. The age-dependent increase in the frequency of translocations exceeds the increase in dicentrics. The radiation sensitivity of lymphocytes estimated from the frequency of in vitro induced chromosomal aberrations tends to increase with age in the control group and decreases significantly in the group exposed to radiation; i.e., low-dose preexposure alters the pattern of the age dependence of radiation sensitivity in lymphocytes in vitro.     

Chromosome aberrations in relation to radiation dose following partial-body exposures in three populations

Structural chromosome aberrations were evaluated in peripheral blood samples obtained from three populations exposed to partial-body irradiation. These included 143 persons who received radiotherapy for enlarged thymus glands during infancy and 50 sibling controls; 79 persons irradiated for enlarged tonsils and 81 persons surgically treated for the same condition during childhood; and 77 women frequently exposed as young adults to fluoroscopic chest X rays during lung collapse treatment for tuberculosis (TB) and 66 women of similar ages treated for TB with other therapies. Radiation exposures occurred 30 and more years before blood was drawn. Doses to active bone marrow averaged over the entire body were 21, 6, and 14 cGy for the exposed thymic, tonsil, and TB subjects, respectively. Two hundred metaphases were scored for each subject, and the frequencies of symmetrical (stable) and asymmetrical (unstable) chromosome aberrations were quantified in 97,200 metaphases. Cells with stable aberrations were detected with greater frequency in the irradiated subjects compared with nonirradiated subjects in all three populations, and an overall test for an association between stable aberrations and partial-body ionizing radiation was highly significant (P less than 0.001). We found no evidence that radiation-induced aberrations varied by age at exposure. These data show that exposure of children or young adults to partial-body fractionated radiation can result in detectable increased frequencies of stable chromosome aberrations in circulating lymphocytes 30 years later, and that these aberrations appear to be informative as biological markers of population exposure.     

Results of a cytogenetic study of populations with different radiation risks in the Semipalatinsk region

A cytogenetic study was conducted for the first time on human populations neighboring the Semipalatinsk nuclear test site (STS) and exposed to ionizing radiation for a long period of time. In populations with the extreme and maximum radiation risks, high frequencies of radiation-induced chromosomal markers, including acentric fragments (1.99 +/- 0.10 per 100 cells), dicentrics (0.23 +/- 0.01), ring chromosomes (0.38 +/- 0.14), and stable chromosomal aberrations (1.17 +/- 0.02), were found. These frequencies significantly exceeded those in control populations. The spectrum of chromosomal aberrations and the frequencies of the aberrations of different types in persons living in the areas with the highest radionuclide contamination confirmed the mutagenic effect of radiation on chromosomes in the human populations studied.     

Results of a Cytogenetic Study of Populations with Different Radiation Risks in the Semipalatinsk Region

A cytogenetic study was conducted for the first time on human populations neighboring the Semipalatinsk nuclear test site (STS) and exposed to ionizing radiation for a long period of time. In populations with the extreme and maximum radiation risks, high frequencies of radiation-induced chromosomal markers, including acentric fragments (1.99 ± 0.10 per 100 cells), dicentrics (0.23 ± 0.01), ring chromosomes (0.38 ± 0.14), and stable chromosomal aberrations (1.17 ± 0.02), were found. These frequencies significantly exceeded those in control populations. The spectrum of chromosomal aberrations and the frequencies of the aberrations of different types in persons living in the areas with the highest radionuclide contamination confirmed the mutagenic effect of radiation on chromosomes in the human populations studied.     

Cytogenetic analyses in peripheral lymphocytes of persons living in houses with increased levels of indoor radon concentrations

Published data concerning the effects of indoor radon exposure on the frequency of chromosome aberrations in peripheral lymphocytes of residents are contradictory. Possible reasons for this may be the low radon concentration in dwellings and/or the limited number of investigated persons. We therefore studied the relationship of domestic radon exposure and the occurrence of chromosome aberrations in peripheral lymphocytes in 61 persons living in houses with radon concentrations from 80 up to 13,000 Bq/m3. We analyzed 60,000 cells from fluorescence plus Giemsa (FPG)-stained slides. It could be clearly demonstrated that in groups of persons living in dwellings with indoor radon concentrations >200 Bq/m3 the number of cells containing dicentrics and/or centric rings (C(dic + cr)) (2.45 +/- 0.50 x 10(-3)) was significantly increased (p < 0.05) in comparison to the control level (1.03 +/- 0.15 x 10(-3)). However, there was no difference in the mean frequency of C(dic + cr) between the groups living in dwellings with higher radon concentrations. Using the fluorescence in situ hybridization (FISH) technique for the detection of translocations, we analyzed 23,315 cells in 16 persons of the highest exposed group (>5,000 Bq/m3). The observed frequency of translocations was 3.9 +/- 0.64 x 10(-3). In comparison to the control group (2.02 +/- 0.18 x 10(-3)), there was a slight but not statistically significant increase in the exposed group (P = 0.055). If, however, the age of the examined persons is taken into account, the values are significantly increased (P < 0.05) in the exposed persons older than 40 years in comparison to the age-matched controls. Since most of the translocations were found in stable cells, it is concluded that translocations are also induced in blood-forming tissue and are transmitted to peripheral blood.     

mFISH analysis of chromosome aberrations in workers occupationally exposed to mixed radiation

We performed a study on the presence of chromosome aberrations in a cohort of plutonium workers of the Mayak production association (PA) with a mean age of 73.3 ± 7.2 years to see whether by multi-color fluorescence in situ hybridization (mFISH) translocation analysis can discriminate individuals who underwent occupational exposure with internal and/or external exposure to ionizing radiation 40 years ago. All Mayak PA workers were occupationally exposed to chronic internal alpha-radiation due to incorporated plutonium-239 and/or to external gamma-rays. First, we obtained the translocation yield in control individuals by mFISH to chromosome spreads of age-matched individuals and obtained background values that are similar to previously published values of an international study (Sigurdson et al. in Mutat Res 652:112–121, 2008). Workers who had absorbed a total dose of >0.5 Gy external gamma-rays to the red bone marrow (RBM) displayed a significantly higher frequency of stable chromosome aberrations relative to a group of workers exposed to <0.5 Gy gamma-rays total absorbed RBM dose. Thus, the translocation frequency may be considered to be a biological marker of external radiation exposure even years after the exposure. In a group of workers who were internally exposed and had incorporated plutonium-239 at a body burden >1.48 kBq, mFISH revealed a considerable number of cells with complex chromosomal rearrangements. Linear associations were observed for translocation yield with the absorbed RBM dose from external gamma-rays as well as for complex chromosomal rearrangements with the plutonium-239 body burden.     

Cytogenetic monitoring of hospital workers exposed to low-level ionizing radiation

In the present study the cytogenetic effects in hospital workers exposed to low-level radiation were evaluated. Samples of peripheral blood were collected from 63 subjects working in radiodiagnostics and from 30 subjects, working in the same hospitals, who were used as controls. A higher number of cells with chromosome-type aberrations (CA) was observed in the exposed workers vs. the controls and the difference was statistically significant (p less than 0.05). No correlation was, on the contrary, found between CA and years of exposure. A significant difference was observed in the incidence of cells with CA between smokers and non-smokers, but in the control group only. In contrast, in the workers exposed to ionizing radiation, the frequency of cells with CA was very similar in smokers and non-smokers.     

A survey of lymphocyte chromosomal damage in Slovenian workers exposed to occupational clastogens.

Assays for sister-chromatid exchanges (SCE), unstable chromosome and chromatid aberrations and micronuclei were performed on blood lymphocytes from persons exposed protractedly to radiation or chemical hazards in the workplace. There was a general tendency with all endpoints examined for the yields to increase with years of working in the industry. This was especially marked for SCE. By comparison with a control group of administrative workers the levels of damage were higher, usually significantly so, in the occupational groups. These comprised workers at a nuclear research reactor, a hospital diagnostic X-ray department, a coal mine and a mercury ore mine.     

Chromosomal aberrations in peripheral lymphocytes of train engine drivers.

Studies of Swedish railway employees have indicated that railroad engine drivers have an increased cancer morbidity and incidence of chronic lymphatic leukemia. The drivers are exposed to relatively high magnetic fields (MF), ranging from a few to over a hundred microT. Although the possible genotoxic potential of MF is unclear, some earlier studies have indicated that occupational exposure to MF may increase chromosome aberrations in blood lymphocytes. Since an increased level of chromosomal aberrations has been suggested to predict elevated cancer risk, we performed a cytogenetic analysis on cultured (48 h) peripheral lymphocytes of Swedish train engine drivers. A pilot study of 18 engine drivers indicated a significant difference in the frequency of cells with chromosomal aberrations (gaps included or excluded) in comparison with seven concurrent referents (train dispatchers) and a control group of 16 office workers. The engine drivers had about four times higher frequency of cells with chromosome-type aberrations (excluding gaps) than the office workers (P < 0.01) and the dispatchers (P < 0.05). Seventy-eight percent of the engine drivers showed at least one cell per 100 with chromosome-type aberrations compared with 29% among the dispatchers and 31% among the office workers. In a follow-up study, another 30 engine drivers showed an increase (P < 0.05) in the frequency of cells with chromosome-type aberrations (gaps excluded) as compared with 30 referent policemen. Sixty percent of the engine drivers had one or more cells (per 100 cells) with chromosome-type aberrations compared with 30% among the policemen. In conclusion, the results of the two studies support the hypothesis that exposure to MF at mean intensities of 2-15 microT can induce chromosomal damage.     

Regularities in forming chromosome aberrations in cattle lymphocytes in external and combined radiation exposure

Aberrations in lymphocytes of cattle blood exposed to gamma-radiation and combined radiation were found. It was shown that seven days after the exposure to doses from 64.5 to 103.3 mC/kg a number of aberration varied in the range from 16.1 to 37.7 per 100 cells, whereas a frequency of aberrated cells was from 13.5 to 29.8. After the exposure to 77.3 mC/h and the following inclusion of fused radioactive particles into the fodder (48.1-762.2 Mbq/kg of the live weight), the number of aberrations increased from 25.5 up to 55.0 per 100 cells and the number of aberrated cells increased from 21 up to 43%.