Biodosimetry after accidental radiation exposure by conventional chromosome analysis and FISH

Translocation dose-response curve for 137Cs γ-rays: Dose validation at various dose rate and changing dose rate conditions

A Fluorescence In-Situ Hybridization (FISH) based translocation dose-response curve has been constructed for biodosimetry application in our nuclear establishment at Kalpakkam, India. Peripheral blood sample from a healthy male donor (27 years) was exposed to nine different doses (0.1 Gy-5 Gy) of ¹³⁷Cs γ-rays (100 mGy/min) in an automated calibration facility with a linear distancing system and subjected to FISH assay using chromosome 1, 2 and 4 specific fluorescent probes. Validation of the dose-response curve was done following three different approaches i) by blind test method ii) using blood samples exposed to γ doses (0.5, 1 & 2 Gy) at different dose rates (124, 23 & 10 mGy/min) and iii) with blood samples exposed to 0.5, 1 & 2 Gy γ doses at changing dose rates (increasing and decreasing dose rates). Results showed that a predefined dose-response curve constructed at a particular acute dose rate can be used for dose estimation in exposures involving varying dose rates and changing dose rate scenarios.

Retrospective biodosimetry techniques: Focus on cytogenetics assays for individuals exposed to ionizing radiation

In the absence of physical data, biodosimetry tools are required for fast dose and risk assessment in the event of radiological or nuclear mass accidents or attacks to triage exposed humans and take immediate medical countermeasures. Biodosimetry tools have mostly been developed for retrospective dose assessment and the follow-up of victims of irradiation. Among them, cytogenetics analyses, to reveal chromosome damage, are the most developed and allow the determination of doses from blood samples as low as 100 mGy. Various cytogenetic tests have already allowed retrospective dose assessment of Chernobyl liquidators and military personnel exposed to nuclear tests after decades. In this review, we discuss the properties of various biodosimetry techniques, such as their sensitivity and limitations as a function of the time from exposure, using multiple examples of nuclear catastrophes or working exposure. Among them, chromosome FISH hybridization, which reveals chromosome translocations, is the most reliable due to the persistence of translocations for decades, whereas dicentric chromosome and micronuclei assays allow rapid and accurate dose assessment a short time after exposure. Both need to be adjusted through mathematical algorithms for retrospective analyses, accounting for the time since exposure and the victims' age. The goal for the future will be to better model chromosome damage, reduce the time to result, and develop new complementary biodosimetry approaches, such as mutation signatures.

Human Lymphocyte Metaphase Chromosome Preparation for Radiation-Induced Chromosome Aberration Analysis

Radiation-induced chromosomal aberration analysis for metaphase chromosomes is well established and the golden standard for human biodosimetry. This method can estimate doses of human radiation exposure after nuclear accident and unwanted radiation exposure from their lymphocytes. The natural background frequency of dicentric chromosome for human lymphocytes is less than 1% and any increase in dicentric and centric ring chromosomes may be highly associated with radiation exposure. With the appropriate number of metaphase cells, one can detect the exposure of more than 0.1 Gy by observing dicentric and centric ring chromosomes. Dicentric chromosome analysis is relying on morphological changes and may be difficult for researchers without appropriate training. This method is time consuming and labor intensive, but still currently the most reliable technique and analysis needs only light microscopes with high magnification objectives and trained personnel. Recent research enables us to visualize dicentric chromosomes clearly with fluorescent markers for easy detection of dicentric and centric ring chromosomes. This chapter will introduce classical dicentric analysis of human lymphocyte cells with Giemsa staining.

Detection of Inter-chromosomal Stable Aberrations by Multiple Fluorescence In Situ Hybridization (mFISH) and Spectral Karyotyping (SKY) in Irradiated Mice

Ionizing radiation (IR) induces numerous stable and unstable chromosomal aberrations. Unstable aberrations, where chromosome morphology is substantially compromised, can easily be identified by conventional chromosome staining techniques. However, detection of stable aberrations, which involve exchange or translocation of genetic materials without considerable modification in the chromosome morphology, requires sophisticated chromosome painting techniques that rely on in situ hybridization of fluorescently labeled DNA probes, a chromosome painting technique popularly known as fluorescence in situ hybridization (FISH). FISH probes can be specific for whole chromosome/s or precise sub-region on chromosome/s. The method not only allows visualization of stable aberrations, but it can also allow detection of the chromosome/s or specific DNA sequence/s involved in a particular aberration formation. A variety of chromosome painting techniques are available in cytogenetics; here two highly sensitive methods, multiple fluorescence in situ hybridization (mFISH) and spectral karyotyping (SKY), are discussed to identify inter-chromosomal stable aberrations that form in the bone marrow cells of mice after exposure to total body irradiation. Although both techniques rely on fluorescent labeled DNA probes, the method of detection and the process of image acquisition of the fluorescent signals are different. These two techniques have been used in various research areas, such as radiation biology, cancer cytogenetics, retrospective radiation biodosimetry, clinical cytogenetics, evolutionary cytogenetics, and comparative cytogenetics.

Profiling of low molecular weight proteins in plasma from locally irradiated individuals

In studies reported in the 1960s and since, blood plasma from radiation-exposed individuals has been shown to induce chromosome damage when transferred into lymphocyte cultures of non-irradiated persons. This effect has been described to occur via clastogenic factors, whose nature is still mostly unknown. We have previously examined clastogenic factors from irradiated individuals by looking at plasma-induced DNA damage in reporter cells. Plasma was tested from ca. 30 locally exposed clinical patients receiving fractionated radiation treatment, as well as from three radiological accident victims exposed in 1994, albeit sampled 14 years post-accident. In the current work, proteome changes in the plasma from all subjects were examined with 2D gel electrophoresis-based proteomics techniques, in order to evaluate the level of protein expression with respect to the findings of a clastogenic factor effect. No differences were observed in protein expression due to local radiation exposure (pre- vs post-exposure). In contrast, plasma from the radiation accident victims showed alterations in the expression of 18 protein spots (in comparison with plasma from the control group). Among these, proteins such as haptoglobin, serotransferrin/transferrin, fibrinogen and ubiquitin-60S ribosomal protein L40 were observed, none of them likely to be clastogenic factors. In conclusion, the proteomics techniques applied were unable to identify changes in the proteome of the locally irradiated patients, whereas such differences were observed for the accident victims. However, association with the clastogenic effect or any specific clastogenic factor remains unresolved and thus further studies with more sensitive techniques are warranted.

A modified system for analyzing ionizing radiation-induced chromosome abnormalities

The analysis of dicentric chromosomes in human peripheral blood lymphocytes (PBLs) by Giemsa staining is the most established method for biological dosimetry. However, this method requires a well-trained person because of the difficulty in detecting aberrations rapidly and accurately. Here, we applied a fluorescence in situ hybridization (FISH) technique, using telomere and centromere peptide nucleic acid (PNA) probes, to solve the problem of biological dosimetry in radiation emergency medicine. A comparison by a well-trained observer found that FISH analysis of PBLs for the dose estimation was more accurate than the conventional Giemsa analysis, especially in samples irradiated at high doses. These results show that FISH analysis with centromeric/telomeric PNA probes could become the standard method for biological dosimetry in radiation emergency medicine.

Search for clastogenic factors in the plasma of locally irradiated individuals

In studies reported in the 1960s and in several investigations since, plasma from irradiated individuals was shown to induce chromosomal aberrations when transferred into normal blood cultures. In the present study, the aim was to investigate the occurrence of these clastogenic factors (CF) using markers representing DNA damage produced in reporter lymphocytes that are treated with plasma from locally exposed individuals. Blood plasma was obtained from clinical patients with benign conditions before and after they had received radiation to small treatment volumes. Three patient groups were studied: (I) marginal resected basal cell carcinoma, (II) painful osteoarthritis of the knee, and (III) painful tendinitis of the elbow or the heel. Patients in each treatment group obtained the same fractionated treatment regimen, ranging from a total dose of 40 Gy (8 × 5 Gy, 2 factions/week) to a very small volume (1-3.5 cm³) in group I to a total dose of 6 Gy (6 × 1 Gy, 2 fractions/week) for groups II and III (treatment volumes 800-1150 cm³ and 80-160 cm³, respectively). The presence of CF in the plasma was investigated through cytogenetic (chromosomal aberrations, micronuclei) assays and kinetics of early DNA damage (γ-H2AX foci) in reporter cells. With the experimental settings applied, local radiation exposure had no apparent effect on the induction of CF in patient plasma; no deviations in chromosomal aberrations or micronucleus or focus induction were observed in reporter cells treated with postexposure plasma with respect to pre-exposure samples when the mean values of the groups were compared. However, there was a large interindividual variation in the plasma-induced DNA-damaging effects. Steroid treatment of patients was demonstrated to be the most influential factor affecting the occurrence of plasma factors; plasma from patients treated with steroids led to significant reductions of γ-H2AX foci and reduced numbers of chromatid aberrations in reporter cells. In addition to the locally exposed patients, newly obtained plasma samples from three radiological accident victims exposed in 1994 were examined. In contrast to the patient data, a significant increase in chromosomal aberrations was induced with plasma from two accident victims.

Chromosome aberration measurements in mitotic and G2-PCC lymphocytes at the standard sampling time of 48 h underestimate the effectiveness of high-LET particles

The relationship between heavy-ion-induced cell cycle delay and the time-course of aberrations in first-cycle metaphases or prematurely condensed G(2)-cells (G(2)-PCC) was investigated. Lymphocytes of the same donor were irradiated with X-rays or various charged particles (carbon, iron, xenon, and chromium) covering an LET range of 2-3,160 keV/μm. Chromosome aberrations were measured in samples collected at 48, 60, 72, and 84 h postirradiation. Linear-quadratic functions were fitted to the data, and the fit parameters α and β were determined. At any sampling time, α values derived from G(2)-cells were higher than those from metaphases. The α value derived from metaphase analysis at 48 h increased with LET, reached a maximum around 155 keV/μm, and decreased with a further rise in LET. At the later time-points, higher α values were estimated for particles with LET > 30 keV/μm. Estimates of α values from G(2)-cells showed a similar LET dependence, yet the time-dependent increase was less pronounced. Altogether, our data demonstrate that heavily damaged lymphocytes suffer a prolonged G(2)-arrest that is clearly LET dependent. For this very reason, the standard analysis of aberrations in metaphase cells 48 h postirradiation will considerably underestimate the effectiveness of high-LET radiation. Scoring of aberrations in G(2)-PCC at 48 h as suggested by several authors will result in higher aberration yields. However, when particles with a very high-LET value (LET > 150 keV/μm) are applied, still a fraction of multiple damaged cells escape detection by G(2)-analysis 48 h postirradiation.

Alpha particles induce different F values in monocellular layers of settled and attached human lymphocytes

There is rapidly increasing information on the issue of three-dimensional nuclear architecture, according to which chromosomes are organized in localized territories and chromosome arms in exclusive domains within a given territory. The aim of the present study was to investigate the impact of different cell exposure conditions on cytogenetic damage induced by high-LET radiation. To this end the yield ratio of dicentrics to centric rings (F value) induced by (241)Am α particles was analyzed in monolayer cultures of human lymphocytes that were either settled or attached to foils, simulating a rounded or spread out cellular geometry, respectively. Monolayers were exposed in special irradiation chambers to 0.1 and 1.0 Gy and subsequently analyzed for chromosome aberrations. Independent of these different dose levels, significantly different F values of 10.07 ± 1.73 and 4.27 ± 0.44 have been determined in attached and settled lymphocytes, respectively. Since the diameter of nuclei vertically traversed by α particles in attached cells is about one-half that in settled cells, these F values support the postulate that proximity effects regarding the chromatin geometry in flattened or spherical human lymphocytes influence the formation of high-LET radiation-induced dicentrics and centric rings. A comparison with our earlier data sets obtained for both in vitro and in vivo exposure of human lymphocytes to α particles or (137)Cs γ rays supports the notion that the F value depends on the radiation quality when investigations are confined to spherical human lymphocytes. Thus the F value should not be ruled out as a practical chromosomal "fingerprint" for past exposure to high-LET radiation.

Increased frequency of chromosome translocations in airline pilots with long-term flying experience

BACKGROUND

Chromosome translocations are an established biomarker of cumulative exposure to external ionising radiation. Airline pilots are exposed to cosmic ionising radiation, but few flight crew studies have examined translocations in relation to flight experience.

METHODS

We determined the frequency of translocations in the peripheral blood lymphocytes of 83 airline pilots and 50 comparison subjects (mean age 47 and 46 years, respectively). Translocations were scored in an average of 1039 cell equivalents (CE) per subject using fluorescence in situ hybridisation (FISH) whole chromosome painting and expressed per 100 CE. Negative binomial regression models were used to assess the relationship between translocation frequency and exposure status and flight years, adjusting for age, diagnostic x ray procedures, and military flying.

RESULTS

There was no significant difference in the adjusted mean translocation frequency of pilots and comparison subjects (0.37 (SE 0.04) vs 0.38 (SE 0.06) translocations/100 CE, respectively). However, among pilots, the adjusted translocation frequency was significantly associated with flight years (p = 0.01) with rate ratios of 1.06 (95% CI 1.01 to 1.11) and 1.81 (95% CI 1.16 to 2.82) for a 1- and 10-year incremental increase in flight years, respectively. The adjusted rate ratio for pilots in the highest compared to the lowest quartile of flight years was 2.59 (95% CI 1.26 to 5.33).

CONCLUSIONS

Our data suggests that pilots with long-term flying experience may be exposed to biologically significant doses of ionising radiation. Epidemiological studies with longer follow-up of larger cohorts of pilots with a wide range of radiation exposure levels are needed to clarify the relationship between cosmic radiation exposure and cancer risk.

Canadian Cytogenetic Emergency network (CEN) for biological dosimetry following radiological/nuclear accidents

PURPOSE

To test the ability of the cytogenetic emergency network (CEN) of laboratories, currently under development across Canada, to provide rapid biological dosimetry using the dicentric assay for triage assessment, that could be implemented in the event of a large-scale radiation/nuclear emergency.

MATERIALS AND METHODS

A workshop was held in May 2004 in Toronto, Canada, to introduce the concept of CEN and recruit clinical cytogenetic laboratories at hospitals across the country. Slides were prepared for dicentric assay analysis following in vitro irradiation of blood to a range of gamma-ray doses. A minimum of 50 metaphases per slide were analyzed by 41 people at 22 different laboratories to estimate the exposure level.

RESULTS

Dose estimates were calculated based on a dose response curve generated at Health Canada. There were a total of 104 dose estimates and 96 (92.3%) of them fell within the expected range using triage scoring criteria. Half of the laboratories analyzed 50 metaphases in </= 1 hour and the time to score them was proportional to dose. The capacity and scoring expertise of the various participating laboratories were found to be generally acceptable.

CONCLUSIONS

The dose estimates generated through triage scoring by this network were acceptable for emergency biological dosimetry. When this network is fully operational, it will be the first of its kind in Canada able to respond to radiological/nuclear emergencies by providing triage quality biological dosimetry for a large number of samples. This network represents an alternate expansion of existing international emergency biological dosimetry cytogenetic networks.

Chromosome aberration analysis and the influence of mitotic delay after simulated partial-body exposure with high doses of sparsely and densely ionising radiation

The influence of high doses of sparsely and densely ionising radiation on the yield of aberrant human peripheral lymphocytes in simulated partial-body exposures was studied by investigating radiation-induced chromosome aberration frequencies, namely dicentric and centric ring chromosomes. Peripheral blood samples from two volunteers were irradiated with high doses of 200 kV X-rays or neutrons with a mean energy of <E (n)> or =2.1 MeV and partial-body exposure was simulated by mixing irradiated and non-irradiated blood from the same two donors in proportions of 25, 50, and 75%. Lymphocytes were cultured and first-division metaphase cells were collected after culture times of 48, 56, and 72 h. A significant underrepresentation of dicentric and centric ring chromosomes was observed at the three highest doses of X-rays between the different culture times for nearly all proportions. After neutron irradiation, some significant differences were observed at all doses and all culture times, without however, revealing any systematic pattern. The distribution of dicentric and ring chromosomes showed overdispersion for both radiation types. After simulated partial-body exposures with 200 kV X-rays and <E (n)> or =2.1 MeV neutrons, strong mitotic delays could be observed, which depended on both the irradiated volume and the applied dose: the smaller the irradiated volume and the higher the dose, the higher was the selective advantage of non-irradiated cells. For the purpose of biological dosimetry after partial body exposure, an extension of the lymphocyte culture time is suggested at least for doses > or =3.0 Gy of 200 kV X-rays and > or =0.5 Gy of <E (n)> or =2.1 MeV neutrons in order to prevent a systematic underestimation of cytogenetic damage.

Measurements of metaphase and interphase chromosome aberrations transmitted through early cell replication rounds in human lymphocytes exposed to low-LET protons and high-LET 12C ions

Inheritable chromosome aberrations (CA) are of concern because cytogenetic damage may trigger the carcinogenic process. Moreover, stability of radiation-induced CA is a prerequisite for meaningful biological dosimetry. CA inheritability arguably depends on the aberration structure, with symmetrical exchanges being favoured over asymmetrical rearrangements, but it is also affected by radiation quality. CA induced by low-LET protons and high-LET 12C ions in G0 peripheral blood lymphocytes were measured in first- , second- and third-generation by combined FISH/harlequin staining of metaphase as well as prematurely condensed interphase chromosomes 1 and 2. As expected, the frequency of non-transmissible (NT) aberrations declined through replication rounds. A radiation-induced arrest occurred prior to first post-irradiation mitosis that prevalently affected aberrant cells. Aberrant cells incurred cycle delays also at subsequent cycles following proton-irradiation but not 12C ion-irradiation. As expected, the frequency of reciprocal translocations remained fairly stable while that of dicentrics was halved at each mitotic round. A significant fraction of complex-type exchanges was found in third-generation cells following both irradiations and appeared to be transmitted relatively more efficiently after protons than 12C ions. A low but stably transmitted frequency of transmissible (T)-type insertions were detected after 12C ions but not after low LET-irradiation. Our data support a differential ability by aberrant cells to progress through post-irradiation mitoses that is influenced by the aberration burden and radiation quality.

Cytogenetic biodosimetry of an accidental exposure of a radiological worker using multiple assays

A technician involved in the maintenance of X-ray equipment visited the occupational medicine service with complaints of skin lesions, apparently caused by an accidental exposure three months earlier. To estimate the dose received by the technician in the accident, biodosimetry was performed 6 and 18 months post-exposure with the dicentric and micronucleus assays. Part of the latest blood sample was also used for retrospective dosimetry by fluorescence in situ hybridisation (FISH) analysis for translocations. The data obtained 6 and 18 months post-exposure indicate that both dicentrics and micronuclei disappear with a half-time of 1 y. After correction for delayed blood sampling, dose values of 0.75 Gy (95% confidence limits 0.56-1.05 Gy) from dicentrics and 0.96 Gy (95% confidence limits 0.79-1.18 Gy) from micronuclei were obtained. FISH analysis of translocations resulted in a dose estimate of 0.79 Gy (95% confidence limits 0.61-0.99 Gy). The satisfactory agreement between the three cytogenetic endpoints supports the use of the micronucleus assay for triage purposes in the case of large scale radiological accidents and provides further evidence for the valid use of FISH for translocations as a reliable retrospective biological dosimeter.

Long-term persistence of translocations in stable lymphocytes from victims of a radiological accident

PURPOSE

To investigate whether translocations in 'stable' lymphocytes, i.e. those not containing unstable aberrations in any chromosome including counterstained ones, would have a longer persistence with time compared with those measured in all cells.

MATERIALS AND METHODS

The time-course of chromosomal aberrations in the three most highly exposed radiation victims of an Estonian accident in November 1994 was followed for 7 post-accident years encompassing 15 samples. Chromosome painting was performed using probes for chromosomes 1, 2 and 4 with a pan-centromeric probe, and chromosomal aberrations involving the painted chromosomes were scored using a developed version of the Protocol for Aberration Identification and Nomenclature Terminology (PAINT) nomenclature. Metaphases containing aberrations were captured with an image analyser and stored on a computer. An earlier analysis of aberrations in the painted portion of the genome was performed in all cells, irrespective of the possible aberrations in the unpainted part of the genome. The present analysis has taken into account the 'stable/unstable' nature of the complete cell. Evaluation was performed on images, counting all chromosomes and checking the counterstained chromosomes for unstable aberrations, i.e. dicentrics, acentrics or ring chromosomes.

RESULTS

In the original analyses of all cells, a decrease in translocation frequency in the early samples was observed. In the present study of stable cells, the results showed that the yield of translocations is constant with time.

CONCLUSIONS

The results show that translocations observed in stable cells are persistent with time. This implies that retrospective dosimetry and calibration should be performed using stable cells. To obtain more information on this issue, the stability status of all cells in any future fluorescence in situ hybridization follow-up of a radiation accident should be noted.

ESTRO Breur Gold Medal Award Lecture 2001: irradiation accidents-- lessons for oncology?

Considering the number of radioactive sources in use all over the world (both in industry and medicine) irradiation accidents are exceedingly rare, as demonstrated by the main databases registering such cases: UNSCEAR, IAEA, REAC/TS (Oak Ridge, USA), the German group in Ulm and the Paris Institut Curie. The precise causes of most accidents have been openly analyzed, allowing to reduce the risk of subsequent identical accidental exposures. In addition, a rapid retrospective overview shows that positive lessons could be drawn from such accidents: 1)Lessons for patient management: one should keep in mind that the first ever allogeneic bone marrow transplantations were performed in 1958, on scientists from Yugoslavia who had been severely irradiated in a nuclear Research laboratory. Apart from what was learned from such accidents for the management of severe aplasia, the treatment of superficial accidental exposures has also benefited radiotherapy patients in certain specific situations. 2) Lessons for technology: the efforts to improve safety in nuclear plants are well known; the (successful) efforts to reduce the once-elevated risks when changing the therapeutic Cobalt 60 sources are less well known. Today, most irradiation accidents (by far) are related to misuse or loss of radioactive sources from industrial radiography sets. However, here again, various technological improvements significantly reduced the risks. 3) Lessons for radiobiology: the need for more and more sophisticated biological dosimetry has led to studies allowing better understanding of the short- and long-term effects of radiation on human cells. Analyses of samples taken in areas which were heavily accidentally irradiated also helped to identify, in particular, the cardinal role of TGF beta and TNF alpha in the development of fibrosis and necrosis after irradiation. 4) Lessons for prevention of accidents in radiotherapy: only three large-scale accidents involving external radiotherapy have been registered in the last decade, but deciphering the cause(s) of such problems clearly participated in the setting of demanding Quality Assurance programmes and strict national and international recommendations. Such open circulation of the information about these (fortunately rare) accidents appears to be one of the ways to improve Quality Assurance in Radiotherapy.

Comparison of chronic exposures received by radiation workers using different biological end-points with the doses recorded by TLD

The frequency of different biological end-points such as translocation, dicentrics (DC) and micronuclei (MN) was studied in 14 radiation workers and 21 non-radiation workers. The average frequencies for different types of aberrations were significantly higher in radiation workers compared to those of respective aberrations in non-radiation workers. Out of 14 radiation workers, eight subjects showed a dose above the detection limit as per translocation and seven subjects as per DC frequency and no patient showed a dose above the detection limit as per MN frequency. Regression analysis carried out between the recorded doses according to Thermo Luminescence Dosimeter (TLD) and the dose estimated as per translocation frequency gave a correlation coefficient of 0.32, whereas that obtained with TLD dose and the dose estimated as per DC was 0.81. When the correlation was made between the TLD dose, which was above 0.15 Gy (the detection limit for translocation), and the dose estimated as per translocation frequency in these subjects, a correlation coefficient of 0.98 was found. A similar analysis between the TLD dose above 0.5 Gy (the detection limit for DC) and the dose estimated as per DC frequency in these subjects, a correlation coefficient of 0.26 resulted. This paper discusses the reasons for the poor correlation obtained between TLD dose and dose estimated as per DC and MN frequency.

Biological dosimetry for astronauts: a real challenge

Manned space missions recently increased in number and duration, thus it became important to estimate the biological risks encountered by astronauts. They are exposed to cosmic and galactic rays, a complex mixture of different radiations. In addition to the measurements realized by physical dosimeters, it becomes essential to estimate real biologically effective doses and compare them to physical doses. Biological dosimetry of radiation exposures has been widely performed using cytogenetic analysis of chromosomes. This approach has been used for many years in order to estimate absorbed doses in accidental or chronic overexposures of humans. In addition to conventional techniques (Giemsa or FPG staining, R- or G-banding), faster and accurate means of analysis have been developed (fluorescence in situ hybridization [FISH] painting). As results accumulate, it appears that strong interindividual variability exists in the basal level of aberrations. Moreover, some aberrations such as translocations exhibit a high background level. Radiation exposures seem to induce variability between individual responses. Its extent strongly differs with the mode of exposure, the doses delivered, the kind of radiation, and the cytogenetic method used. This paper aims to review the factors that may influence the reliability of cytogenetic dosimetry. The emphasis is on the exposure to high linear energy transfer (LET) particles in space as recent studies demonstrated interindividual variations in doses estimated from aberration analysis after long-term space missions. In addition to the problem of dose estimates, the heterogeneity of cosmic radiation raises questions relating to the real numbers of damaged cells in an individual, and potential long-term risks. Actually, densely ionizing particles are extremely potent to induce late chromosomal instability, and again, interindividual variability exists in the expression of damage.

Chromosomal instability in in vivo radiation exposed subjects

PURPOSE

To investigate whether delayed chromosomal instability arises in human peripheral T lymphocytes exposed in vivo to gamma-irradiation.

MATERIALS AND METHODS

Long-term cultures were established from lymphocytes obtained from subjects involved in the radiological accident in Estonia in 1994. Two individuals exposed to a high dose, one individual with low exposure and one apparently unexposed person were studied. Two Estonian controls not involved with the accident were also analysed. Cells were grown for 6-42 days and chromosomal aberrations were assessed from G-banded metaphases. In addition, FISH chromosome painting analysis was performed on short-term cultures established from whole blood.

RESULTS

No obvious sign of chromosomal instability was observed in the in vivo follow-up of the frequencies of chromosomal aberrations in lymphocytes of radiation accident victims performed by the FISH technique (48 h cultures established at different time intervals after the exposure). However, when the lymphocytes were cultured long term in vitro, chromosomal instability was observed. There was no dose-response, and the appearance of chromosomally unstable cells in long-term cultures was also observed in a subject exposed to a dose of less than 0.1 Gy. Moreover, in contrast with previous findings, chromosomal instability was also observed in cells from non-exposed control individuals. The chromosomal changes observed in the controls were less complex than the aberrations in the cultures derived from individuals exposed to high doses.

CONCLUSIONS

Chromosomal instability was observed in long-term cultures of donors with in vivo exposure to gamma-radiation. No dose-response was apparent. However, in contrast with previous findings, signs of chromosomal instability were observed also in long-term cultures from non-exposed controls. Further studies are needed to assess possible inter-individual differences in the induction of chromosomal instability.