Retrospective cytogenetic analysis of unstable and stable chromosome aberrations in the victims of radiation accident in Bulgaria

Five occupational workers in an industrial sterilization unit at Stamboliyski in Bulgaria were accidentally exposed to a very high specific activity of Cobalt-60 source on June 14, 2011. Initial cytogenetic analysis performed on days 2 and 7 after radiation exposure revealed the whole body absorbed radiation doses of 5.32 Gy for patient 1, 3.40 Gy for patient 2, 2.50 Gy for patient 3, 1.91 Gy for patient 4 and 1.24 Gy for patient 5 [1]. Here, a retrospective multicolor FISH analysis was performed on three patients (patients 1, 2 and 3) using the blood samples collected over a period of 4 years from 2012 through 2015. In all the three patients, cells with stable chromosome aberrations (simple and complex chromosome translocations) were 3-4 folds more than cells with unstable chromosome aberrations (dicentric, rings and excess acentric chromosome fragments). In corroboration with the results reported in the literature, we observed that the time dependent decline of dicentrics, rings and excess acentric fragments occurred much more rapidly than chromosome translocations in the blood samples of the three victims. Further, inter-individual variation in the decline of radiation induced chromosome aberrations was also noticed among the three victims. The reason for the increased persistence of balanced chromosome translocations is not entirely clear but may be attributed to certain subsets of long-lived T-lymphocytes. The retrospective cytogenetic follow up studies on radiation-exposed victims may be useful for determining the extent of genomic/chromosomal instability in the hematopoietic system.

Persistence of radiation-induced aberrations in patients after radiotherapy with C-ions and IMRT

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A follow-up of aberrations in lymphocytes of cancer patients was performed.

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The ratio of dicentrics to translocations declined indicating bone marrow damage.

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Bone marrow exposure was verified by examination of treatment plans.

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Clonal aberrations were also present before therapy and thus not radiation induced.

Background and purpose

Chromosomal aberrations in peripheral blood lymphocytes are a biomarker for radiation exposure and are associated with an increased risk for malignancies. To determine the long-term cytogenetic effect of radiotherapy, we analyzed the persistence of different aberration types up to 2.5 years after the treatment.

Materials and methods

Cytogenetic damage was analyzed in lymphocytes from 14 patients that had undergone C-ion boost + IMRT treatment for prostate cancer. Samples were taken immediately, 1 year and 2.5 years after therapy. Aberrations were scored using the multiplex fluorescence in situ hybridization technique and grouped according to their transmissibility to daughter cells.

Results

Dicentric chromosomes (non-transmissible) and translocations (transmissible) were induced with equal frequencies. In the follow-up period, the translocation yield remained unchanged while the yield of dicentrics decreased to ≈40% of the initial value (p = 0.011 and p = 0.001 for 1 and 2.5 years after compared to end of therapy). In 2 patients clonal aberrations were observed; however they were also found in samples taken before therapy and thus were not radiotherapy induced.

Conclusion

The shift in the aberrations spectrum towards a higher fraction of translocations indicates the exposure of hematopoietic stem and progenitor cells underlining the importance of a careful sparing of bone marrow during radiotherapy to minimize the risk for secondary cancers.

Chromosome Damage Caused by Accidental Chronic Whole-Body Gamma Radiation Exposure in Thailand

In February 2000, a radiation incident involving a medical ⁶⁰Co source occurred in a metal scrapyard in Thailand. Several individuals were suspected to have received chronic or fractionated exposures ranging from a few mGy to a several Gy. Using fluorescence in situ hybridization to paint chromosomes, we determined the frequencies of chromosome aberrations in peripheral blood lymphocytes of 13 people who entered the scrapyard, 3 people who involved in recovering the source, and 9 nearby residents. Aberration frequencies greater than controls were observed in 13 of the donors at 3 months postexposure. The predominant form of aberration observed was simple, complete, symmetrical translocations. An approximate 50% decrease in these aberrations and in total color junctions was observed in 7 donors resampled at 16 months postexposure. Although high, acute exposures are known to have detrimental effects, the biological consequences of chronic, low dose-rate radiation exposures are unclear. Thirteen of the donors had elevated aberration frequencies, and 6 also had symptoms of acute radiation syndrome. If there are any long-term health consequences of this incident, it will most likely occur among this group of individuals. The consequences for the remaining donors, who presumably received lower total doses delivered at lower dose rates, are less clear.

Alpha-Particle-Induced Complex Chromosome Exchanges Transmitted through Extra-Thymic Lymphopoiesis In Vitro Show Evidence of Emerging Genomic Instability

Human exposure to high-linear energy transfer α-particles includes environmental (e.g. radon gas and its decay progeny), medical (e.g. radiopharmaceuticals) and occupational (nuclear industry) sources. The associated health risks of α-particle exposure for lung cancer are well documented however the risk estimates for leukaemia remain uncertain. To further our understanding of α-particle effects in target cells for leukaemogenesis and also to seek general markers of individual exposure to α-particles, this study assessed the transmission of chromosomal damage initially-induced in human haemopoietic stem and progenitor cells after exposure to high-LET α-particles. Cells surviving exposure were differentiated into mature T-cells by extra-thymic T-cell differentiation in vitro. Multiplex fluorescence in situ hybridisation (M-FISH) analysis of naïve T-cell populations showed the occurrence of stable (clonal) complex chromosome aberrations consistent with those that are characteristically induced in spherical cells by the traversal of a single α-particle track. Additionally, complex chromosome exchanges were observed in the progeny of irradiated mature T-cell populations. In addition to this, newly arising de novo chromosome aberrations were detected in cells which possessed clonal markers of α-particle exposure and also in cells which did not show any evidence of previous exposure, suggesting ongoing genomic instability in these populations. Our findings support the usefulness and reliability of employing complex chromosome exchanges as indicators of past or ongoing exposure to high-LET radiation and demonstrate the potential applicability to evaluate health risks associated with α-particle exposure.

Retrospective biodosimetry using translocation frequency in a stable cell of occupationally exposed to ionizing radiation

Two cases of hematological malignancies were reported in an industrial radiography company over a year, which were reasonably suspected of being consequences of prolonged exposure to ionizing radiation because of the higher incidence than expected in the general population. We analyzed chromosomal aberrations in the peripheral blood lymphocytes from the other workers who had been working under similar circumstances as the patients in the company. Among the subjects tested, 10 workers who belonged to the highest band were followed up periodically for 1.5 years since the first analysis. The aim of this study was to clarify pertinence of translocation analysis to an industrial set-up where chronic exposure was commonly expected. To be a useful tool for a retrospective biodosimetry, the aberrations need to be persistent for a decade or longer. Therefore we calculated the decline rates and half-lives of frequency for both a reciprocal translocation and a dicentric chromosome and compared them. In this study, while the frequency of reciprocal translocations was maintained at the initial level, dicentric chromosomes were decreased to 46.9% (31.0-76.5) of the initial frequency over the follow-up period. Our results support the long-term stability of reciprocal translocation through the cell cycle and validate the usefulness of translocation analysis as a retrospective biodosimetry for cases of occupational exposure.

Reduced chromosome aberration complexity in normal human bronchial epithelial cells exposed to low-LET γ-rays and high-LET α-particles

Purpose:

Cells of the lung are at risk from exposure to low and moderate doses of ionizing radiation from a range of environmental and medical sources. To help assess human health risks from such exposures, a better understanding of the frequency and types of chromosome aberration initially-induced in human lung cell types is required to link initial DNA damage and rearrangements with transmission potential and, to assess how this varies with radiation quality.

Materials and methods:

We exposed normal human bronchial lung epithelial (NHBE) cells in vitro to 0.5 and 1 Gy low-linear energy transfer (LET) γ-rays and a low fluence of high-LET α-particles and assayed for chromosome aberrations in premature chromosome condensation (PCC) spreads by 24-color multiplex-fluorescence in situ hybridization (M-FISH).

Results:

Both simple and complex aberrations were induced in a LET and dose-dependent manner; however, the frequency and complexity observed were reduced in comparison to that previously reported in spherical cell types after exposure to comparable doses or fluence of radiation. Approximately 1–2% of all exposed cells were categorized as being capable of transmitting radiation-induced chromosomal damage to future NHBE cell generations, irrespective of dose.

Conclusion:

One possible mechanistic explanation for this reduced complexity is the differing geometric organization of chromosome territories within ellipsoid nuclei compared to spherical nuclei. This study highlights the need to better understand the role of nuclear organization in the formation of exchange aberrations and, the influence three-dimensional (3D) tissue architecture may have on this in vivo.

High frequency of simple and complex chromosome aberrations detected in the Tokai-mura survivor four and five years after the 1999 criticality accident

In September 1999 a criticality accident occurred in a uranium processing plant in Tokai-mura, Japan. During the accident, three workers (A, B and C) were exposed to high acute doses of neutrons and γ-rays: workers A and B fatally and worker C to an estimated whole body absorbed dose of 0.81 Gy neutrons and 1.3 Gy γ-rays. We obtained fixed peripheral blood lymphocytes (PBL) preparations from worker C approximately four and five years after the accident and assayed by 24 colour karyotyping (M-FISH) to determine the frequency and complexity of chromosome aberrations present. We observed a high frequency of simple reciprocal translocations, which we used to provide a rough estimation of dose and, in addition, for the assessment of the emergence of any clinically-relevant clonal exchanges. We did not observe any evidence of clonality but did find some evidence suggesting chromosome 1 as being preferentially involved in exchanges in stable cells. We also detected a relatively high frequency of damaged cells containing complex chromosome aberrations, of both the stable and unstable types. Qualitatively these complex aberrations were consistent with those observed to be induced after exposure to low doses of high-LET radiation or moderate doses of low-LET radiation, supporting the suggestion that heavily damaged cells can be quite long-lived in vivo.

Inter-chromosomal variation in aberration frequencies in human lymphocytes exposed to charged particles of LET between 0.5 and 55 keV/μm

PURPOSE

To investigate the distribution of chromosomal aberrations in chromosomes 2, 8 and 14 induced by charged particles, using the fluorescence in situ hybridisation (FISH) technique.

METHODS

Irradiation of peripheral blood from six healthy volunteers (four male and two female) was performed at the accelerators of the Joint Institute for Nuclear Research (JINR) in Dubna (Russia). Whole blood samples were irradiated with 2 and 3 Gy of protons (170 MeV/nucleon (n), linear energy transfer (LET) ≈ 0.5 keV/μm), 3.5 Gy of (12)C ions (480 MeV/n, LET = 10.6 keV/μm), 3 Gy of (12)C ions 500 MeV/n, LET = 12 keV/μm), 4 Gy of (7)Li ions (30 MeV/n, LET ≈ 20 keV/μm) and 3 Gy of (11)B ions (32 MeV/n, LET ≈ 55 keV/μm). Chromosomal aberrations were analysed in metaphase and prematurely condensed chromosomes (PCC) induced in G(2)-cells using calyculin A. Chromosomes 2, 8 and 14 were painted in different colours and aberrations scored with the help of an image-analysis system.

RESULTS

Chromosome 2 was generally less sensitive than expected on the basis of its DNA content. A higher than expected frequency of exchanges was found in chromosomes 8 and 14. On average, the dicentric frequency in chromosome 2 was higher than the translocation frequency, whereas variable dicentric to translocation ratios were observed in chromosomes 8 and 14. When aberrations in all painted chromosomes were summed up the ratio was close to 1. The frequency of complex aberrations correlated with LET.

CONCLUSION

In lymphocytes of donors studied in this work chromosome 2 appears to be consistently less sensitive to protons and heavy ions than chromosomes 8 and 14. Complex aberrations appear to be a potential marker of radiation quality.