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.     

In vitro transmission of chromosomal aberrations through mitosis in human lymphocytes

Stable and unstable chromosome aberrations in human lymphocytes exposed to 2 and 4Gy of X-rays in G(0) were analyzed in M1 and M2 cells harvested at 72h to investigate how the scoring protocol influences the yields of aberrations transmitted through one mitosis. Metaphase chromosomes 2, 3, and 5 were painted using fluorescence in situ hybridization (FISH) whole chromosome probes, together with a pan-centromeric probe and stained by the harlequin-FISH method, to allow the cell cycle status of each cell to be determined as it was scored. A strict scoring criterion was adopted so that each metaphase had to contain 46 centromeres and each dicentric/centric ring had to have an acentric present. In addition to scoring the painted material, unstable aberrations in the whole genome were also recorded. The yield of complete dicentrics decreased by more than a factor of 2 in going from M1 to M2. The decrease was greater at the lower dose. Two-way translocations appeared stable, but one-way translocations decreased. This suggests that if translocation yields are to be used for biological dosimetry purposes, then the two-way type should be used.     

A study to verify a reported excess of chromosomal aberrations in blood lymphocytes of Namibian uranium miners

This report describes a study to verify an earlier report of excess chromosomal damage in the blood lymphocytes of uranium miners. Coded blood samples from 10 miners and 10 controls were analyzed conventionally for unstable aberrations and by FISH for translocations. Conventional analysis, scoring 1000 metaphases per subject, showed no significant difference between miners and controls in the frequencies of chromosome- and chromatid-type aberrations. Investigators at two laboratories undertook FISH analyses, each scoring 4000 metaphases per subject. When the data from each laboratory were examined separately, one found slightly more translocations in the miners while the other found fewer. In neither case was the difference significant at the 95% level of confidence. Combining the data likewise showed no significant excess of damage in the miners. This applied to simple one- and two-way translocations and to cells with complex exchanges. There was no correlation between levels of translocations and total lifetime doses from occupational and/or background irradiation. A borderline significant excess of rogue cells was found in the miners. This may be a chance observation, as these rare, highly abnormal cells are considered to be unrelated to radiation exposure and are probably due to a virus. The overall conclusion is that the frequency of chromosomal damage in the miners did not exceed that in the controls. Therefore, the result of the earlier study was not confirmed.     

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.     

High frequency of spontaneous translocations revealed by FISH in cells from patients with the cancer-prone syndromes ataxia telangiectasia and Nijmegen breakage syndrome.

The application of fluorescence in situ hybridization (FISH) using whole-chromosome paints (WCPs) is proving to be a very powerful technique for revealing chromosomal instability that, for the most part, has gone undetected by conventional cytogenetic analysis. We have analyzed the frequency of translocations in lymphocytes and lymphoblastoid cell lines from ataxia telangiectasia (AT) and Nijmegen breakage syndrome (NBS) homozygotes and heterozygotes using a three-color chromosome-painting technique (WCP 1, 2, 4). With this assay we were able to detect an increased frequency of spontaneous translocations in AT homozygotes (median, 18.47 +/- 10.82 translocations per 1,000 metaphase cells; 10 patients) and AT heterozygotes (median, 7.87 +/- 3.15 translocations per 1,000 cells; 7 patients), in comparison to controls (median, 2.26 +/- 1.75 translocations per 1,000 cells; 10 controls). Analysis of NBS homozygotes (median, 19.05 +/- 11.27 translocations per 1,000 cells; 5 patients) and NBS heterozygotes (median, 6.93 +/- 3.04 translocations per 1,000 cells; 6 patients) also showed an increased frequency of translocations in these patients compared to controls. The presence of such hitherto undetected chromosomal aberrations corroborate previous findings of spontaneous chromosomal instability in AT and NBS patients, as manifested by an increased rate of open breaks and rearrangements involving chromosomes 7 and 14. Moreover, we show that the degree of genomic instability in AT and NBS patients is even higher than previously established and that some AT and NBS heterozygotes evidence spontaneous chromosomal instability as well. These increased levels of nonspecific translocations could be an important risk factor for the development of malignancies in homozygotes and heterozygotes for ATM or NBS1 gene mutations.     

Analysis of FISH-painted chromosomes in individuals living near the Semipalatinsk nuclear test site

The Semipalatinsk nuclear test site (STS) is located in the Republic of Kazakhstan. A total of 498 nuclear weapons tests were conducted in this area between 1949 and 1989. The radiation exposure to people who lived close to the STS resulted mostly from the above-ground explosions. Blood samples for chromosome analysis were obtained from 10 subjects who were born before the first explosion in August 1949 and lived continuously in the village of Dolon. The individual calculated effective doses were about 3 Sv. Chromosomes 2, 4 and 8 were painted by means of the FISH technique. In total, 22,240 cells were analyzed. The mean frequency of translocations in the subjects who were irradiated during childhood (2.4/1000 cells) did not differ from the control value (3.1 translocations/1000 cells). It is assumed, therefore, that the calculated physical dose is too high. A significantly increased level of complex cells was determined, however, and this was assumed to have been induced in circulating lymphocytes. The reason for this may be the incorporation of radionuclides from fallout which were not distributed homogeneously within the body, but accumulated instead in tissues that were well supplied with peripheral blood.     

Dose dependency of FISH-detected translocations in stable and unstable cells after Cs gamma irradiation of human lymphocytes in vitro

Human peripheral lymphocytes were exposed to 137Cs gamma-rays (0-4.3 Gy) in order to check the impact of unstable cells on the dose-response curve for translocations. Chromosomes 2, 4 and 8 were FISH-painted. 17,720 first dividing cells were analysed. For the discrimination between stable and unstable cells the painted and the counter-stained chromosomes were analysed at doses of 1 Gy and higher. The cell distribution of translocations follows a Poisson distribution. The data were fitted to the linear-quadratic function, y = c + alphaD + betaD2. As expected, the alpha coefficients of the dose-response curves for translocations in stable cells or in total cells do not differ. However, at doses >1 Gy, the frequency of all translocations in stable cells seems to be lower than the frequency in total cells. For the establishment of calibration curves for past dose assessment purposes, only complete translocations should be scored, in order to estimate reliable doses.     

Persistence of chromosomal alterations affecting the 1cen-q12 region in a human lymphoblastoid cell line exposed to diepoxybutane and mitomycin C

Multicolor fluorescence in situ hybridization (FISH) with tandem-labeling probes for the 1cen-q12 region is a potential biomarker for the detection of structural chromosomal aberrations (CAs) in human cells. To determine the suitability of this technique for biomonitoring humans exposed to 1,3-butadiene (BD) and to characterize the alterations induced as well as their stability over time, the human lymphoblastoid cell line AZH-1 was treated with 5 μM diepoxybutane (DEB) or the positive control mitomycin C (MMC; 0.1 μM) for 24 h. Following the removal of the test chemicals, cell cultures were grown for an additional 19 days in the absence of the test compound. Using the tandem FISH technique, aliquots from the main cultures were examined for the induction of CAs affecting the 1cen-q12 region at various intervals. A significant increase in chromosomal breakage/exchanges affecting the 1cen-q12 region was seen in both the DEB- and MMC-treated interphase and metaphase cells. The damage peaked at approximately 48 h following the addition of the test compound and declined with time. However, at day 20, the frequency of aberrant cells was still significantly higher than the control levels. For comparison, the frequency of micronuclei (MN) formed and their origin was determined using the cytochalasin B-modified MN assay and FISH with a pancentromeric probe. Showing a similar pattern, the frequency of centronere-negative MN peaked at 48 h, but however was not significantly elevated above control levels at 20 days. At early time points, aberrations detected using the FISH assay consisted of nearly equal proportions of unstable- and stable-type aberrations, while at the later time points, translocations were the predominant aberration type. In addition, the use of tandem-label FISH in combination with BrdU-immunfluorescence staining, showed that almost identical frequencies of structural aberrations could be seen in actively replicating and non-replicating cell populations. These studies indicate that a small but significant proportion of the alterations detected using this FISH technique persists over time and that this technique may be valuable for biomonitoring chromosomal alterations in BD-exposed populations.     

Stable and unstable chromosome aberrations in humans and other mammals in relation to the problems of biological dosimetry

Literature data of long-term cytogenetic follow-up of people exposed to radiation as a results of different radiation accidents are considered for the purpose of discussing of some problems of biological dosimetry. The results obtained for mammals are also presented. Of particular interest is a decrease in the level of dicentrics and symmetrical translocations in peripheral blood lymphocytes with the time after acute exposure depending on the dose of irradiation. The frequency of dicentrics decreases in accordance to the exponential law passing the fast and slow phases of elimination. In different radiation situations the values of the parameter which defines the half-life period of lymphocytes characterizing 50% reduction of cells with dicentrics markedly vary. However a general regularity is a decrease in the parameter value as the exposure dose increases. The level of stable translocations estimates by the EISH method remains relatively constant at doses below 1-2 Gy. At higher doses their level in peripheral blood lymphocytes declines with time due to which the retrospective dose appears to be underestimated. The reasons of such regularity, the role of various factors affecting the scoring of translocations, criteria of analysis of the given chromosome aberrations are discussed in the context of common agreements between leading European laboratories on the use of FISH for improving biological dosimetric estimates.     

Suitability of FISH painting techniques for the detection of partial-body irradiations for biological dosimetry

Peripheral blood was irradiated with 2, 3, 4 or 5 Gy of X rays and was mixed with nonirradiated blood at five different dilutions to simulate partial-body irradiations. Analysis by FISH was performed using whole-chromosome painting probes for chromosomes 1, 4 and 11 in combination with a pancentromeric probe. Chromosome aberrations affecting the painted fraction were classified according to the PAINT nomenclature; other unstable aberrations affecting the unpainted material were also recorded. To evaluate the suitability of painting for dose assessment in partial-body irradiations, the ability of the u test and a proposed s test to detect the expected overdispersion and the similarity between the real doses and the doses estimated using Dolphin's approach were considered. For short-term biodosimetry, compared with solid-stained dicentric analyses, the suitability of FISH painting techniques for the detection of partial-body exposures is reduced, because of the decrease in the frequency of aberrations detected by FISH and in the number of cells with two or more aberrations. For reconstruction of past doses, when only complete apparently simple translocations in cells free of unstable aberrations were considered, the detection of the overdispersion and the accuracy of dose estimations were dramatically reduced. In a partial-body exposure, as the original dose increased, the whole-body dose estimated a long time after irradiation would tend to be lower, and the difference from the original dose would tend to be greater.     

Analysis of translocations in stable cells and their implications in retrospective biological dosimetry

The aim of the present study was to evaluate the influence of the exclusion of cells with unstable aberrations in the elaboration of dose-effect curves for translocations and their implications in biological dosimetry of past exposures. To establish dose-effect curves, peripheral blood samples were irradiated with 60Co gamma rays at ten different doses and the yield of translocations analyzed by FISH was considered in all cells and in stable cells (those without dicentrics, acentrics or rings). To discriminate transmissible translocations, the dose- effect curve for total apparently simple translocations in stable cells was chosen as the reference. In stable cells, dose- effect curves for apparently simple translocations without pseudosimple and complex-derived one-way patterns, tAbtBa and total translocations were obtained. None of these curves differed from the reference curve. When all cells were considered, only the curve for total translocations was significantly different from the reference curve. From the results obtained it can be concluded that the use of dose-effect curves for apparently simple translocations in stable cells and in all cells will give similar dose estimates in retrospective biological dosimetry studies. However, the use of dose-effect curves for total translocations in all cells will lead to underestimations of the dose mainly at high doses.     

The cellular lethality of radiation-induced chromosome translocations in human lymphocytes

Recent evidence has shown that translocation frequencies decline over time. This phenomenon might be explained by the co-occurrence of translocations in cells that also contain dicentrics, in which case translocations would be eliminated as a by-product of selection against dicentrics. Alternatively, a fraction of translocations may themselves be lethal. Here we describe our initial approaches to develop mathematical models to test whether the decline in translocation frequencies results from the first, the second, or a combination of these two possibilities. The models assumed that all chromosome exchanges were simple, i.e., were comprised of dicentrics as well as one-way and two-way translocations. Complex aberrations (three or more breaks in two or more chromosomes) were not modeled, nor were fragments or intrachromosomal exchanges (rings, inversions). We tested the models using Monte Carlo simulations, and then we fitted the models to data describing chromosome aberration frequencies induced by a single acute in vitro exposure to (137)Cs gamma rays in human peripheral blood lymphocytes from two donors. Chromosome painting was used to enumerate translocations and dicentrics from 2 to 7 days after exposure. Our results indicate that in donor no. 2, the decline in translocation frequencies occurs as a by-product of selection against dicentrics. However, in donor no. 1, whose cells appeared more radiosensitive than cells from donor no. 2, up to 40% of the one-way translocations may themselves be lethal at high doses, although calculations indicate that two-way translocations do not cause lymphocyte mortality. Individual variation in the probability that translocations are lethal to cells appears to be important, and one-way translocations appear to be lethal more often than two-way translocations. Within the limits of these models, these findings indicate that both postulated mechanisms, i.e. inherent lethality and selection against dicentrics in the same cells, contribute to the loss of both one-way and two-way translocations.     

Seventeen-year follow-up study on chromosomal aberrations in five victims accidentally exposed to several Gy of <Superscript>60</Superscript>Co γ-rays

On 25 June 1990, a radiation accident occurred in a ⁶⁰Co source radiation unit in Shanghai, due to violations in operation regulations. This accident resulted in the exposure of seven individuals to acute high-dose and dose-rate whole-body external irradiation. Conventional chromosomal aberration analysis, G-banding automatic karyotype analysis and/or fluorescent in situ hybridization (FISH) painting methods were used to analyze chromosomal aberrations in peripheral blood lymphocytes from five of the victims 24 h to 17 years after accidental exposure to 1.9–5.1 Gy of ⁶⁰Co γ-rays. The frequency of unstable chromosomal aberrations (dicentrics and rings) remained at constant levels 1 month after exposure. Three months after exposure, the frequency was reduced by 20–40% in three victims, while no reduction was seen in the other two victims. Twelve years after exposure, the number of dicentrics and rings decreased by more than 90%, and did not reveal a dose-dependent relationship. However, even at 12–17 years after exposure, stable chromosome aberrations, dominated by translocations, remained at a high level in a dose-dependent manner. The frequency of stable chromosomal aberrations detected by FISH showed a similar dose-dependent relationship as that detected by karyotype analysis of G-banding chromosomes. The G-banding analysis also suggested that the pattern of chromosome breakpoints is random. The FISH data showed a decreasing tendency with time for chromosome translocation frequency in the peripheral lymphocytes, and the rate of reduction varied among different individuals. It is likely that the higher dose the victim received, the lesser the translocation frequency decreased with time. The G-banding data also showed that the rate of reduction of translocations is different among individuals. From 5 to 17 years after accidental irradiation, a very small reduction (~10%) of translocation frequency was observed in victims C and D, while there was about a 35% reduction (the highest among the victims) for victim G who received the smallest dose (1.9 Gy). These observations can be used to validate the existence of chromosomal aberrations in peripheral blood lymphocytes as a biological dosimeter for radiation exposures.     

Clastogenic effect of ethanol in chronic and abstinent alcoholics

Alcoholism is one of the main causes of damage for human health, being relevant to study the induction of chromosomal aberrations (CA) by ethanol, and to investigate the individual susceptibility to diseases caused by alcoholism. A cytogenetic study was performed in human peripheral blood lymphocytes of 29 heavy chronic alcoholics, 11 alcoholics in abstinence, and 10 controls. The values of the chromosomal aberrations, mitotic indexes (MI) and proliferation indexes (PI) were determined. A molecular cytogenetic study was also carried out using fluorescence in situ hybridization (FISH) method with DNA library probes for chromosomes 1, 3 and 6, in lymphocytes from chronic alcoholic individuals in comparison with a control group. The results showed that the CA frequencies for chronic alcoholics (5.15 CA/100 cells) and alcoholics in abstinence (3.87 CA/100 cells) were higher than those obtained for control individuals (1.72 CA/100 cells). The mean translocation frequencies (equivalent to the genome) were calculated for six chronic alcoholics (0.267 translocations/100 cells) and six alcoholics in abstinence (0.167 translocations/100 cells), whose values were significantly higher than those observed for six control individuals (0.067 translocations/100 cells). The CA frequencies were not statistically different when smoker and non-smoker alcoholics were compared, indicating that although the smoking habit had significantly increased (four-fold) the CA frequency in healthy control individuals, a lack of interaction effect was observed within the group of alcoholics when smokers and non-smokers were compared. The CA frequencies presented by alcoholics in abstinence were similar to those obtained for chronic alcoholics. Therefore, chronic ethanol intoxication can lead to chromosome damage and disturbances in the metabolism of endogenous and exogenous compounds, which may persist for a long time, and constitute a relevant factor of risk for the development of neoplasias.     

Clastogenic effect of ethanol in chronic and abstinent alcoholics

Alcoholism is one of the main causes of damage for human health, being relevant to study the induction of chromosomal aberrations (CA) by ethanol, and to investigate the individual susceptibility to diseases caused by alcoholism. A cytogenetic study was performed in human peripheral blood lymphocytes of 29 heavy chronic alcoholics, 11 alcoholics in abstinence, and 10 controls. The values of the chromosomal aberrations, mitotic indexes (MI) and proliferation indexes (PI) were determined. A molecular cytogenetic study was also carried out using fluorescence in situ hybridization (FISH) method with DNA library probes for chromosomes 1, 3 and 6, in lymphocytes from chronic alcoholic individuals in comparison with a control group. The results showed that the CA frequencies for chronic alcoholics (5.15 CA/100 cells) and alcoholics in abstinence (3.87 CA/100 cells) were higher than those obtained for control individuals (1.72 CA/100 cells). The mean translocation frequencies (equivalent to the genome) were calculated for six chronic alcoholics (0.267 translocations/100 cells) and six alcoholics in abstinence (0.167 translocations/100 cells), whose values were significantly higher than those observed for six control individuals (0.067 translocations/100 cells). The CA frequencies were not statistically different when smoker and non-smoker alcoholics were compared, indicating that although the smoking habit had significantly increased (four-fold) the CA frequency in healthy control individuals, a lack of interaction effect was observed within the group of alcoholics when smokers and non-smokers were compared. The CA frequencies presented by alcoholics in abstinence were similar to those obtained for chronic alcoholics. Therefore, chronic ethanol intoxication can lead to chromosome damage and disturbances in the metabolism of endogenous and exogenous compounds, which may persist for a long time, and constitute a relevant factor of risk for the development of neoplasias.     

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.     

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.     

Cytogenetic analyses by fluorescence in situ hybridization (FISH) in hospital workers occupationally exposed to low levels of ionizing radiation

An occupationally exposed population has been studied to evaluate the suitability of FISH painting techniques to detect chronic exposures to very low doses of ionizing radiation by the analysis of translocations. Whole-chromosome painting probes for chromosomes 1, 4 and 11 in combination with a pancentromeric probe have been employed. For comparison, a matched control population has also been studied. The mean genomic frequencies per 100 cells of total translocations in the control and exposed populations were 0.90 +/- 0.12 and 1.04 +/- 0.11, respectively. In the occupationally exposed population, no correlation between the frequencies of translocations and the doses received was found. When the two populations were compared, no significant differences were observed for the frequencies of the different chromosomal abnormalities examined. The absence of differences between control and exposed populations could be attributed to the very low-dose exposures recorded in the occupationally exposed population and to the wide range of individual frequencies of translocations observed.     

A combination of the micronucleus assay and a FISH technique for evaluation of the genotoxicity of 1,2,4-benzenetriol

The cytokinesis-block micronucleus (CBMN) assay has emerged as one of the preferred methods for assessing chromosome damage. Micronuclei (MN) are small, extranuclear bodies that are formed in mitosis from acentric chromosomal fragments or chromosomes that are not included in each daughter nucleus. Thus, MN contain either chromosomal fragments or whole chromosomes. The CBMN assay, together with a fluorescence in situ hybridization (FISH) technique using specific centromeric probes for chromosomes 7 and 8, were employed in mitogen-stimulated human lymphocytes pretreated with the benzene metabolite, 1,2,4-benzenetriol (BT). Treatment of human lymphocytes resulted in the induction of MN in a dose-dependent manner. The frequency of MN in control lymphocytes was 4.5 per 1000 binucleated (BN) cells and this increased to 9.5, 14, 28 and 40 per 1000 BN cells at 10, 25, 50 and 100 microM BT, respectively. The frequency of aneuploidy 7 and 8 in BN cells also increased at each concentration. Aneuploidy 8 was more frequent than aneuploidy 7, suggesting that chromosome 8 is more sensitive to aneuploidy induction by BT. The frequency of MN containing centromere positive signals for chromosomes 7 and 8 increased with the concentration of BT. The frequency of MN with centromere positive signals was higher for chromosome 8 than for chromosome 7, also suggesting a greater sensitivity of chromosome 8 to this agent. These results suggest that combined application of the CBMN assay with a FISH technique, using chromosome-specific centromeric probes, would allow the detection of aneuploidy in human lymphocytes and identify the mechanistic origin of MN induced by a clastogen or aneugen.     

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.