In this study, the frequency and spectrum of chromosomal aberrations were analysed in samples of peripheral blood from 372 (mean age = 12.24 ± 2.60 years old) long-term resident children in a boarding school (Tashtagol city, Kemerovo Region, Russian Federation) under conditions of high exposure to radon and its decay products. As a control group, we used blood samples from people living in Zarubino village (Kemerovo Region, Russian Federation). We discovered that the average frequencies of single and double fragments, chromosomal exchanges, total number of aberrations, chromatid type, chromosome type and all types of aberrations were significantly increased in the exposed group. This is evidence of considerable genotoxicity to children living under conditions of high exposure to radon compared to children living under ecological conditions without increased radon radiation.
The genotypic associations of the frequencies of spontaneous and radiation-induced chromosome aberrations in human lymphocytes were studied to develop genetic tests for elevated and reduced radiosensitivity. Cytogenetic analysis and genotyping (19 sites of detoxification and DNA repair genes) were carried out for a sample of Chernobyl cleanup workers (n = 83) and for a homogenous control sample of volunteers (n = 99). In both groups, the frequency of chromosome-type aberrations proved to be elevated in carriers of minor alleles in the XPD gene (sites T2251G (Lys751Gln) and G862A (Asp312Asn)) and a combination of GSTM1-GSTT1-positive genotypes. The polymorphism of these gene did not affect the frequency of gamma-radiation-induced aberrations in the controls (1 Gy in vitro), which was associated with the alleles of the OGG1, XRCC1, and CYP1A1 genes. Thus, the frequencies of spontaneous and in vitro induced chromosome-type aberrations are associated with the alleles of different xenobiotic detoxification and DNA repair genes. At the same time, among the cleanup workers (irradiated in vivo), the elevated frequency of aberrations was observed in the carriers of the genotypes associated with the higher rate of spontaneous (but not induced in vitro) cytogenetic damages in the controls.
When the adaptive response (AR) was studied on human blood lymphocytes, a new dependence was discovered. This dependence defines the direction of the radiosensitivity change after a low dose of irradiation. Using micronucleus (MN) test with cytochalasin B the dependence between the cell reaction after low level irradiation and radiosensititvity (the effect after irradiation at the dose of 1 Gy) was observed. The negative correlation between the frequency of AR manifestation, sensibilization, intermediate links and radiosensitivity was discovered. This regularity is observed in the population of Moscow, Obninsk, Chelyabinsk region (irradiated and control) inhabitants, Chernobyl accident liquidators, Moscow children, in individuals with Hodgkin's lymphoma before and during treatment. The negative correlation is also noted by AR determination with two irradiation schemes: in one or two different cell cycle phases (G1-G1 or G1-G2). Similar links are observed using the chromosome methaphase analysis (the frequency of cells with chromosome aberrations). So, the results of the experiments conducted allow us to suppose that the connection between the cell radiosensitivity and a different type of reaction after low dose irradiation--from AR to the increase in radiosensitivity (sensibilization) is a general regularity. AR is induced by low level irradiation and high cell radiosensitivity, while sensibilization is induced by low radiosensitivity. Since AR and sensibilization can be induced not only by irradiation, but many different chemicals and physical agents, the described correlation can be observed in the case of different exposures. Cellular AR and sensibilization are integral indexes depending on many genetic and epigenetic factors, as well as on the initiation of a large number of events. However, the discovered mechanisms of interrelations are still difficult to explain.
Suggestions that the induction of genomic instability could play a role in radiation-induced carcinogenesis and heritable disease prompted the investigation of chromosome instability in relation to radiotherapy for childhood cancer. Chromosome analysis of peripheral blood lymphocytes at their first in vitro division was undertaken on 25 adult survivors of childhood cancer treated with radiation, 26 partners who acted as the non-irradiated control group and 43 offspring. A statistically significant increase in the frequency of dicentrics in the cancer survivor group compared with the partner control group was attributed to the residual effect of past radiation therapy. However, chromatid aberrations plus chromosome gaps, the aberrations most associated with persistent instability, were not increased. Therefore, there was no evidence that irradiation of the bone marrow had resulted in instability being transmitted to descendant cells. Frequencies of all aberration categories were significantly lower in the offspring group, compared to the partner group, apart from dicentrics for which the decrease did not reach statistical significance. The lower frequencies in the offspring provide no indication of transmissible instability being passed through the germline to the somatic cells of the offspring. Thus, in this study, genomic instability was not associated with radiotherapy in those who had received such treatment, nor was it found to be a transgenerational radiation effect.
The analysis of plutonium production factors has been carried out by using two methodical approaches: assessment of chromosomal aberrations level in routine and G-banded metaphases and molecular-cytogenetic investigation of aneugenic/clastogenic damages in cytokinesis-block binuclear lymphocytes by FISH with centromere specific DNA probes. The obtaining data point out for the first time about both aneugenic and clastogenic influences of incorporated 239Pu with activity range from 0.37 to 6.95 kBq. Correlation analysis of chromosome aberrations with cytome abnormalities allowed finding significant connection between number parameters of metaphase and interphase approaches. The results of this study support the suggestion that aberrant chromosomes are involved preferable in aneugenic events. The FISH technique in binucleated cytokinesis-blocked lymphocytes allows extending of detecting spectrum of chromosome damages and glance of aneugenic mechanisms. Correlations between metaphase and interphase-FISH results point out a high sensitivity of FISH cytome assay, which could be used as an independent test for detection both clastogenic and aneugenic environment influences.
Four children groups with and without thyroid pathology born to fathers exposed to ionizing irradiation in 1986 during Chernobyl accident as liquidators as well as residents of territory with radioactive contamination have been cytogenetically observed. The frequency and spectrum of chromosome aberrations in peripheral blood lymphocytes have been studied using two-termed cultivation (during 48 and 144 hours). Under the short-term incubation the observed groups did not significantly differ on the mean-group integral cytogenetic parameters which corresponded to age norm, but in progeny of parents from radionuclide contaminated territory the increased level of chromosome type exchanges has been revealed. In long-termed lymphocyte cultures of children with chronic thyroiditis the significantly increased cytogenetic effects of both chromatid (single fragments) and chromosome types (abnormal monocentrics, centric rings) have been established. The data received testified the reality of the transmissible chromosome instability phenomenon in progeny of irradiated parents and confirmed the possibility of its expression in consequent mitoses.
Clinical Physiology Laboratory of the Urals Research Center for Radiation Medicine of the Federal Medical-Biological Agency of Russia, 68-A Vorovsky st., Chelyabinsk 454076, Russian Federation. Electronic address: firstname.lastname@example.org.
This paper presents the results of a cytogenetic study conducted among residents of the Techa Riverside communities (Southern Urals, Russia) exposed in the early 1950s as a result of releases of liquid radioactive wastes from the Mayak plutonium-production facility. The study was performed 50-60 years after the beginning of the exposure for those individuals who were predominantly exposed to strontium radioisotopes ((89,90)Sr) through drinking contaminated river water and consumption of local foodstuff. Standard cytogenetic methods were used for evaluation of the frequency of unstable chromosome aberrations in exposed persons as well as in persons from the control group who were of similar age and sex, living in similar socio-economic conditions in non-contaminated territories of the Southern Urals. The exposure doses were reconstructed for the studied donors using the Techa River Dosimetry System developed in 2009. The doses of internal exposure from ingested radionuclides were evaluated using individual or family in vivo measurements of (90)Sr-body burden. Individual cumulative absorbed doses in red bone marrow (RBM) in the studied persons varied in the range of 0.01-4.4Gy. A significantly higher level of unstable chromosome aberrations (UCA) in T-cells was observed in the group of exposed individuals as compared to control group. The highest UCA level was detected in the individuals who were suspected of having chronic radiation syndrome.
Long-lived, sensitive, and specific biomarkers of particular mutagenic agents are much sought after and potentially have broad applications in the fields of cancer biology, epidemiology, and prevention. Many clastogens induce a spectrum of chromosome aberrations, and some of them can be exploited as biomarkers of exposure. Densely ionizing radiation, for example, alpha particle radiation (from radon or plutonium) and neutron radiation, preferentially induces complex chromosome aberrations, which can be detected by the 24-color multifluor fluorescence in situ hybridization (mFISH) technique. We report the detection and quantification of stable complex chromosome aberrations in lymphocytes of healthy former nuclear-weapons workers, who were exposed many years ago to plutonium, gamma rays, or both, at the Mayak weapons complex in Russia. We analyzed peripheral-blood lymphocytes from these individuals for the presence of persistent complex chromosome aberrations. A significantly elevated frequency of complex chromosome translocations was detected in the highly exposed plutonium workers but not in the group exposed only to high doses of gamma radiation. No such differences were found for simple chromosomal aberrations. The results suggest that stable complex chromosomal translocations represent a long-lived, quantitative, low-background biomarker of densely ionizing radiation for human populations exposed many years ago.
A tendency of the increasing frequency of malignant neoplasms in liquidators at low radiation doses was found. The dose-effect dependence of the frequency of radiation markers (dicentric chromosomes) in lymphocytes of peripheral blood was revealed only in a group of liquidators of the ChNPP accident with malignant neoplasms in remote terms.