Inter-laboratory comparison of cytogenetic endpoints for the biomonitoring of radiological workers

Biomonitoring findings for occupational lead exposure in battery and ceramic tile workers using biochemical markers, alkaline comet assay, and micronucleus test coupled with fluorescence in situ hybridisation

Manufacture of lead-containing products has long been associated with various health risks. To get an insight into the related genotoxic risks, we conducted a biomonitoring study in 50 exposed workers and 48 matched controls using a battery of endpoints that sensitively detect the extent of genome instability in peripheral blood lymphocytes. The levels of primary DNA damage were estimated with the alkaline comet assay, while cytogenetic abnormalities were determined with the cytokinesis-block micronucleus (CBMN) cytome assay. Additionally, CBMN slides of 20 exposed and 16 control participants were subjected to fluorescence in situ hybridisation (FISH), coupled with pancentromeric probes to establish the incidence of centromere-positive micronuclei, nuclear buds, and nucleoplasmic bridges. Blood lead levels (B-Pb) were measured with atomic absorption spectrometry. To further characterise cumulative effects of occupational exposure, we measured erythrocyte protoporphyrin (EP) concentrations and delta-aminolevulinic acid dehydratase (ALAD) activity in blood. We also assessed the influence of serum folate (S-folate) and vitamin B12 (S-B12) on genome stability. Compared to controls, occupationally exposed workers demonstrated significantly higher B-Pb (298.36±162.07 vs 41.58±23.02), MN frequency (18.71±11.06 vs 8.98±7.50), centromere positive MN (C+ MN) (8.15±1.8 vs 3.69±0.47), and centromere negative MN (C- MN) (14.55±1.80 vs 4.56±0.89). Exposed women had significantly higher comet tail intensity (TI) and length (TL) than control women. Furthermore, workers showed a positive correlation between age and nuclear buds and MN, between MN and years of exposure, and between S-B12 levels and TI and ALAD activity, while a negative correlation was found between TI and B-Pb. These findings suggest that occupational settings in the manufacture of lead-containing products pose significant genotoxic risks, which calls for developing more effective work safety programmes, including periodical monitoring of B-Pb and genetic endpoints.

Development of electronic training and telescoring tools to increase the surge capacity of dicentric chromosome scorers for radiological/nuclear mass casualty incidents

Dicentric chromosome assay (DCA) is most frequently used for estimating the absorbed radiation dose in the peripheral blood lymphocytes of humans after occupational or incidental radiation exposure. DCA is considered to be the "gold standard" for estimating the absorbed radiation dose because the dicentric chromosome formation is fairly specific to ionizing radiation exposure and its baseline frequency is extremely low in non-exposed humans. However, performance of DCA for biodosimetry is labor intensive and time-consuming making its application impractical for radiological/nuclear mass casualty incidents. Realizing the critical need for rapid dose estimation particularly after radiological/nuclear disaster events, several laboratories have initiated efforts to automate some of the procedural steps involved in DCA. Although metaphase image capture and dicentric chromosome analysis have been automated using commercially available platforms, lack or an insufficient number of these platforms may pose a serious bottleneck when hundreds and thousands of samples need to be analyzed for rapid dose estimation. To circumvent this problem, a web-based approach for telescoring was initiated by our laboratory, which enabled the cytogeneticists around the globe to analyze and score digital images. To further increase the surge capacity of dicentric scorers, we recently initiated a dicentric training and scoring exercise involving a total of 50 volunteers at all academic levels without any prerequisite for experience in radiation cytogenetics. Out of the 50 volunteers enrolled thus far, only one outlier was found who overestimated the absorbed radiation dose. Our approach of training the civilians in dicentric chromosome analysis holds great promise for increasing the surge capacity of dicentric chromosome scorers for a rapid biodosimetry in the case of mass casualty scenarios.

The potential for complete automated scoring of the cytokinesis block micronucleus cytome assay using imaging flow cytometry

The lymphocyte Cytokinesis-Block Micronucleus (CBMN) assay was originally developed for the measurement of micronuclei (MN) exclusively in binucleated (BN) cells, which represent the population of cells that can express MN because they completed nuclear division. Recently the assay has evolved into a comprehensive cytome method to include biomarkers that measure chromosomal instability and cytotoxicity by quantification of nuclear buds (NBUDs), nucleoplasmic bridges (NPBs) and apoptotic/necrotic cells. Furthermore, enumeration of mono- and polynucleated cells allows for computation of the nuclear division index (NDI) to assess mitotic activity. Typically performed by manual microscopy, the CBMN cytome assay is laborious and subject to scorer bias and fatigue, leading to inter- and intra-scorer variability. Automated microscopy and conventional flow cytometry methods have been developed to automate scoring of the traditional and cytome versions of the assay. However, these methods have several limitations including the requirement to create high-quality microscope slides, lack of staining consistency and sub-optimal nuclear/cytoplasmic visualization. In the case of flow cytometry, stripping of the cytoplasmic membrane makes it impossible to measure MN in BN cells, calculate the NDI or to quantify apoptotic or necrotic cells. Moreover, the absence of cellular visualization using conventional flow cytometry, makes it impossible to quantify NBUDs and NPBs. In this review, we propose that imaging flow cytometry (IFC), which combines high resolution microscopy with flow cytometry, may overcome these limitations. We demonstrate that by using IFC, images from cells in suspension can be captured, removing the need for microscope slides and allowing visualization of intact cytoplasmic membranes and DNA content. Thus, mono-, bi- and polynucleated cells with and without MN can be rapidly and automatically identified and quantified. Finally, we present high-resolution cell images containing NBUDs and NPBs, illustrating that IFC possesses the potential for completely automated scoring of all components of the CBMN cytome assay.

Biodosimetry of Persons Chronically Exposed to Low and Therapeutic Doses of Ionizing Radiation

Dynamic changes of the chromosomal aberrations and the DNA damage were analyzed in individuals exposed to low and therapeutic doses of radiation. The investigation included 37 persons living in areas where the radioactive sources were discovered 10–12 years ago. It was established by biodosimetry methods that the examined persons had absorbed dose of 0.2–0.7 Gy or had increased number of chromosomal aberrations, though insufficient to determine a dose. Clinical examination, chromosomal analysis, and assay of DNA damage by the comet (single-cell gel electrophoresis) assay were carried out. There was no correlation between the doses received 10 years ago and the cytogenetic changes with clinical outcome. The effect of the local fractionated gamma-irradiation with doses of 40–70 Gy was studied in cancer patients with localized head and neck tumors. The study of chromosomal abnormalities, the DNA damages by the comet assay, and the micronuclei detection of the buccal cells revealed a statistically significant correlation between the initial cytogenetic indices in cancer patients and their dynamic changes during and after the radiation exposure. In addition, the correlation was detected between the initial cytogenetic parameters and the functional stage of red blood system. Our results allow us to conclude that there is a need for further research to estimate the individual radiation risk to optimize and individualize the subsequent medical management of radiotherapy.

Establishment of a Dose-response Curve for X-ray-Induced Micronuclei in Human Lymphocytes

The cytokinesis-block micronucleus assay in peripheral blood lymphocytes is an established technique for biodosimetry. The aim of this project was to generate a X-ray induced micronuclei (MN) curve for peripheral blood lymphocytes taken from five healthy donors. The blood samples were irradiated with X-rays of 122 KeV at a dose rate of 0.652 Gy/min to doses of 0.5, 1, 2, 3, and 4 Gy. The blood samples were then cultured for 72 h at 37°C and processed following the International Atomic Energy Agency standard procedure with slight modifications. The result showed that the yields of MN frequencies were increased with the increase of radiation dose. Reconstruction of the relationship of MN with dose was fitted to a linear-quadratic model using Chromosome Aberration Calculation Software version 2.0. Due to their advantages, mainly, the dependence on radiation dose and dose rate, despite their limitation, these curves will be useful as alternative method for in vitro dose reconstruction and can support the preparedness for public or occupational radiation overexposure and protection. The results reported here also give us confidence to apply the obtained calibration curve of MN for future biological dosimetry requirements in Indonesia.

The micronucleus assay as a biological dosimeter in hospital workers exposed to low doses of ionizing radiation

The health risk associated with low levels of ionizing radiation is still a matter of debate. A number of factors, such as non-target effects, adaptive responses and low-dose hypersensitivity, affect the long-term outcome of low-dose exposures. Cytogenetic bio-dosimetry provides a measure of the absorbed dose, taking into account the individual radiation sensitivity. The aim of the present study is to evaluate the value of the micronucleus (MN) test as a bio-dosimeter in hospital workers exposed to low doses of ionizing radiation. Blood samples were obtained from 30 subjects selected among workers exposed to X- and gamma-radiation, and 30 controls matched for sex, age and smoking from the same hospital. Micronucleus frequencies were analyzed by use of the cytokinesis-block method. The MN frequency was compared among the groups considering the confounding factors and the length of employment. No increase in the number of bi-nucleated cells with MN (BNMN), but a significant increase in the number of mono-nucleated cells with micronuclei (MOMN) was observed in exposed subjects compared with the controls. The relationship between MN frequency and accumulated dose (mSv) was evaluated. The length of employment did not affect the extent of MN frequency, but an increase of BNMN and MOMN cells was observed based on the accumulated radiation dose. Our study shows the sensitivity of the MN test in the detection of cytogenetic effects of cumulative exposure levels, suggesting the potential usefulness of this assay in providing a biological index in medical surveillance programs.

No threshold for the induction of chromosomal damage at clinically relevant low doses of X rays

The recent steep increase in population dose from radiation-based medical diagnostics, such as computed tomography (CT) scans, requires insight into human health risks, especially in terms of cancer development. Since the induction of genetic damage is considered a prominent cause underlying the carcinogenic potential of ionizing radiation, we quantified the induction of micronuclei and loss of heterozygosity events in human cells after exposure to clinically relevant low doses of X rays. A linear dose-response relationship for induction of micronuclei was observed in human fibroblasts with significantly increased frequencies at doses as low as 20 mGy. Strikingly, cells exposed during S-phase displayed the highest induction, whereas non S-phase cells showed no significant induction below 100 mGy. Similarly, the induction of loss of heterozygosity in human lymphoblastoid cells quantified at HLA loci, was linear with dose and reached significance at 50 mGy. Together the findings favor a linear-no-threshold model for genetic damage induced by acute exposure to ionizing radiation. We speculate that the higher radiosensitivity of S-phase cells might relate to the excessive cancer risk observed in highly proliferative tissues in radiation exposed organisms.

The micronucleus assay as a biological dosimeter of in vivo ionising radiation exposure

Biological dosimetry, based on the analysis of micronuclei (MN) in the cytokinesis-block micronucleus (CBMN) assay can be used as an alternative method for scoring dicentric chromosomes in the field of radiation protection. Biological dosimetry or Biodosimetry, is mainly performed, in addition to physical dosimetry, with the aim of individual dose assessment. Many studies have shown that the number of radiation-induced MN is strongly correlated with dose and quality of radiation. The CBMN assay has become, in the last years, a thoroughly validated and standardised technique to evaluate in vivo radiation exposure of occupational, medical and accidentally exposed individuals. Compared to the gold standard, the dicentric assay, the CBMN assay has the important advantage of allowing economical, easy and quick analysis. The main disadvantage of the CBMN assay is related to the variable micronucleus (MN) background frequency, by which only in vivo exposures in excess of 0.2-0.3 Gy X-rays can be detected. In the last years, several improvements have been achieved, with the ultimate goals (i) of further increasing the sensitivity of the CBMN assay for low-dose detection by combining the assay with a fluorescence in situ hybridisation centromere staining technique, (ii) of increasing the specificity of the test for radiation by scoring nucleoplasmic bridges in binucleated cells and (iii) of making the assay optimally suitable for rapid automated analysis of a large number of samples, viz. in case of a large-scale radiation accident. The development of a combined automated MN-centromere scoring procedure remains a challenge for the future, as it will allow systematic biomonitoring of radiation workers exposed to low-dose radiation.

Chromosomal radiosensitivity of HIV positive individuals

PURPOSE

Radiosensitivity in relation to the human immunodeficiency virus (HIV) status is important in South Africa as the prevalence of HIV infections is high. In this study the in vitro chromosomal radiosensitivity of HIV positive individuals was investigated and compared with that of HIV negative individuals.

MATERIALS AND METHODS

Blood samples from 59 HIV positive and 39 HIV negative individuals were exposed in vitro to doses of 6MV X-rays ranging from 1-4 Gy. Chromosomal radiosensitivity was assessed with the micronucleus assay. Micronuclei are a measure of chromosomal damage and were quantified in at least 500 binucleated lymphoblasts (BN) per sample. Un-irradiated control samples from each donor were also analysed.

RESULTS

In 47% of HIV positive individuals difficulties with cell stimulation by adding phytohaemagglutinin (PHA) to blood cultures were noticed which resulted in insufficient yield of BN for microscopic analysis. Micronuclei frequencies were consistently higher in irradiated lymphocytes obtained from HIV positive individuals compared to that observed in cells from HIV negative donors. Data for both groups were fitted to the linear-quadratic equation Y = alphaD + betaD(2) where Y is the number of micronuclei in 500 binucleated cells and D is the dose in Gy. The fitted parameters for respectively HIV positive and HIV negative lymphocytes are alpha = 80.17 Gy(-1), beta = 14 Gy(-2) and alpha = 54.5 Gy(-1), beta = 16.2 Gy(-2). The confidence ellipses of these parameters are separated indicating that the increase in radiosensitivity is statistically significant.

CONCLUSION

T-lymphocytes of HIV infected individuals were considerably more sensitive to X-rays compared to that of HIV negative donors. This may have implications for normal tissue tolerance during radiotherapy as well as for the radiological health of radiation workers.

Assessment of radiation damage-the need for a multiparametric and integrative approach with the help of both clinical and biological dosimetry

Accidental exposure to ionizing radiation leads to damage on different levels of the biological organization of an organism. Depending on exposure conditions, such as the nature of radiation, time and affected organs and organ systems, the clinical endpoint of radiation damage and the resulting acute and chronic radiation syndromes may vary to a great extent. Exposure situations range from purely localized radiation scenarios and partial-body exposures to whole-body exposures. Therefore, clinical pictures vary from localized radiation injuries up to the extreme situation of radiation-induced multi-organ involvement and failure requiring immediate, intensive, and interdisciplinary medical treatment. These totally different and complex clinical situations not only appear most different in clinical diagnostic and therapeutic aspects, but also, due to different levels of underlying biological damage, biological indicators of effects may vary to a wide extent. This fact means that an exact assessment of the extent of radiation damage within individual patients can only be performed when taking into consideration clinical as well as different biological indicators. Among the clinical indicators, routine laboratory parameters such as blood counts and the documentation of clinical signs and symptoms (using such methods as the METREPOL system) are the key parameters, but dicentric assay, the gold standard for biological dosimetry, and other methods under development, such as the gamma-H2AX focus assay or gene expression analysis of radiosensitive genes, must also be taken into account. Each method provides best results in different situations, or, in other words, there are methods that work better in a specific exposure condition or at a given time of examination (e.g., time after exposure) than others. Some methods show results immediately; others require days to weeks until results are available for clinical decision-making. Therefore, to provide the best basis for triage and planning and to provide medical treatment after accidental radiation exposure, different and independent diagnostic procedures integrating all clinical aspects as well as different biological indicators have to be applied. This multiparametric approach has been suggested after recent radiation accidents but needs to be adopted and standardized worldwide. A new integrative concept is shown and discussed.

The lymphocyte cytokinesis-block micronucleus cytome assay and its application in radiation biodosimetry

The cytokinesis-block micronucleus cytome (CBMN Cyt) assay is one of the best-validated methods for measuring chromosome damage in human lymphocytes. This paper describes the methodology, biology, and mechanisms underlying the application of this technique for biodosimetry following exposure to ionizing radiation. Apart from the measurement of micronuclei, it is also possible to measure other important biomarkers within the CBMN Cyt assay that are relevant to radiation biodosimetry. These include nucleoplasmic bridges, which are an important additional measure of radiation-induced damage that originate from dicentric chromosomes as well as the proportion of dividing cells and cells undergoing cell death. A brief account is also given of current developments in the automation of this technique and important knowledge gaps that need attention to further enhance the applicability of this important method for radiation biodosimetry.

Cytogenetic damage in human blood lymphocytes exposed in vitro to radon

The effect of radon in inducing DNA damage was investigated in vitro by two well-established cytogenetic assays. Blood samples were irradiated with radon using a novel irradiation assembly. Doses varied between 0 and 127 mGy for chromosome aberration (CA) assay and 0 and 120 mGy for cytokinesis blocked micronucleus (CBMN) assay. Dose-rates varied between 0.000054 and 0.708 mGy/min. After the irradiation period of 3h, excess radon gas was released and cultures were initiated using standard procedures. Chromosome aberrations such as dicentrics, excess acentric fragments, acentric rings, centric rings, chromatid breaks were observed. Micronuclei, nucleoplasmic bridges and nuclear buds were scored by the CBMN assay. A significant increase in the frequency of dicentrics, excess acentric fragments and centric rings was observed with increasing radon dose, whereas total acentric rings plus double minute and chromatid breaks/cell were not significantly elevated. In CBMN assay, the frequency of micronuclei was found to be significantly raised whereas that of nucleoplasmic bridges and nuclear buds were not. Nucleoplasmic bridges and nuclear buds tended to increase with dose but did not achieve statistical significance. There was a strong positive correlation between nucleoplasmic bridges and dicentrics (P<0.028) or rings (P<0.0001) and between micronuclei and acentric fragments (P<0.0005). The study shows that radon is capable of inducing significant chromosome damage at very low doses and dose-rates.

The cytokinesis-block micronucleus assay as a biological dosimeter for targeted alpha therapy

Ionizing radiation causes structural chromosomal aberrations, a proportion of which give rise to chromosome fragments without spindle attachment organelles. When a cell divides, some of these fragments are excluded from the main daughter nuclei and form small nuclei within the cytoplasm. The cytokinesis-block micronucleus assay allows these micronuclei (MN) to be counted, providing an in situ biological dosimeter. In this study, we evaluated the micronucleus frequency in peripheral blood lymphocytes after in vitro incubation with the alpha conjugates (213)BiI(3) and (213)Bi-9.2.27 (AIC). Lymphocytes were inoculated in vitro AIC for 3 h. Further, we report the first MN measurements in melanoma patients after targeted alpha therapy (TAT) with (213)Bi-9.2.27. Patients were injected with 260-360 MBq of AIC, and blood samples taken at 3 h, 2 weeks and 4 weeks post-treatment. Absorbed dose (MIRD) and effective total body dose (PED) were calculated. The MN frequency in lymphocytes was similar for equal in vitro incubation activities of (213)BiI(3) and (213)Bi-9.2.27 (P=0.5), indicating that there is no selective targeting of lymphocytes by the alpha conjugates. After inoculation with 10-1200 kBq mL-1 of AIC, there was a substantial activity-related increase in MN. The number of MN in the blood of treated patients peaked at 3 h post-TAT, slowly returning to baseline levels by 4 weeks. The mean photon equivalent dose (PED) is 0.43 Gy (SD 0.15) and the mean MIRD calculated absorbed dose is 0.11 Gy (SD 0.03), giving an RBE=4+/-0.4 for this study.

The genotoxic effects in lymphocyte cultures of children treated with radiosynovectomy by using yttrium-90 citrate colloid

The aim of this study was to investigate the genotoxic effect on the peripheral blood lymphocytes potentially induced by yttrium-90 citrate colloid (Y-90) in children who were undergoing radiosynovectomy for hemophilic synovitis, using chromosomal aberration analysis (CA) and the micronuclei (MN) assay for detecting chromosomal aberrations, as well as the sister chromatid exchanges (SCE) technique for assessed DNA damage.

MATERIALS AND METHODS

Cytogenetic analyses were undertaken in 18 boys (mean age, 14.5 +/- 2.1 years) with hemophilic synovitis who underwent radiosynovectomy with Y-90. CA, MN, and SCE were evaluated just prior to, then at 2 and 90 days following radiosynovectomy from the peripheral lymphocytes of the children. An activity of 185 MBq of Y-90 was injected into the 18 knee joints under aseptic conditions. To check the possibility of leakage from the joint and its migration within the body, the patients underwent scanning under a dual-headed gamma camera at the hours 2 and 48 following the procedure.

RESULTS

The procedure was well tolerated in all the children, and there was no extra-articular activity owing to extra-articular leakage of radioactive material in whole-body imaging. The mean frequency of CA in lymphocytes determined prior to the onset of therapy (0.31 +/- 0.48/900 cells) was not significantly increased, in comparison to the control values obtained 2 (0.30 +/- 0.48/900 cells) and 90 days (0.15 +/- 0.37/900 cells) after radiosynovectomy (p = 1.0 and 0.625, respectively). We observed that MN frequency was mildly increased in lymphocytes 2 days after therapy (8.30 +/- 1.89 MN/1000 binucleated cells vs. 9.23 +/- 1.79 MN/1000 binucleated cells; p = 0.013). But there was no significant difference between the baseline and the day 90 control levels of MN (p = 0.196). In the analysis of SCE frequency, there were no significant differences between the baseline (8.11 +/- 0.77) and the control analysis performed 2 and 90 days following radiosynovectomy (8.18 +/- 0.77 and 8.07 +/- 0.74; p = 0.710 and 0.662, respectively).

CONCLUSIONS

The results of this study indicated that high radiation doses are not obtained by peripheral lymphocytes of children who undergo Y-90 radiosynovectomy and, therefore, they contradict a high cancer risk.

Cytogenetic monitoring by use of the micronucleus assay among hospital workers exposed to low doses of ionizing radiation

The aim of this study was to assess occupationally induced chromosomal damage in a large population of hospital workers exposed to low doses of ionizing radiation. We used the cytokinesis-block micronucleus (CBMN) assay in the peripheral lymphocytes of 132 exposed workers compared with 69 controls matched for gender, age and smoking habits. The CBMN assay was combined with fluorescence in situ hybridization with a human pan-centromeric DNA probe in 32 exposed subjects and 30 controls randomly chosen from the initial populations. Occupational dosimetry records were collected over the last 10-year period and revealed very low exposure levels. The average binucleated micronucleated cell rate (BMCR) was significantly higher in the exposed subjects than in the controls (14.9 per thousand+/-8.1 versus 11.8 per thousand+/-6.5; P=0.011). About one-third of the micronuclei were centromere-negative in the exposed and control groups. BMCR significantly positively correlated with donor age in the exposed population; this correlation was at the border of significance in the control group. In the two groups, BMCR was significantly greater in females than in males, and the significant correlation between age and BMCR was observed in the female population, but not in the male one. No effect of smoking habits emerged. Univariate analysis revealed a possible influence of familial cancer history and diagnostic medical radiation dose (estimated from examinations reported in the questionnaire) on BMCR. Multiple regression analysis, taking into account all the previous confounding factors, showed that only occupational exposure status, gender and age had a significant effect on BMCR. In conclusion, the present study shows that chromosomal damage leading to micronucleated lymphocytes is more frequent in hospital workers exposed to ionizing radiation than in controls, despite the very low levels of exposure.

Automated human blood micronucleated reticulocyte measurements for rapid assessment of chromosomal damage

This study evaluated the utility of human blood micronucleated reticulocyte (MNCD71+) frequency measurement as a cytogenetic damage biomarker. The analytical methodology was flow cytometry in conjunction with a previously described three color fluorescence labeling technique that includes anti-CD71 to focus analyses on the most immature fraction of reticulocytes [S.D. Dertinger, K. Camphausen, J.T. MacGregor, M.E. Bishop, D.K. Torous, S. Avlasevich, et al., Three-color labeling method for flow cytometric measurement of cytogenetic damage in rodent and human blood, Environ. Mol. Mutagen. 44 (2004) 427-435]. Blood specimens from 50 self-reported healthy adult volunteers were studied. In addition to MNCD71+ measurements, blood plasma folate and B12 levels were assessed, since these variables tend to influence other indices of cytogenetic damage. Time-course data are also provided for 10 cancer patients undergoing treatment. For these subjects, frequency of MNCD71+ was measured immediately before therapy, and daily during the first week of chemotherapy and/or fractionated radiotherapy. For the group of healthy volunteers, the variables of age, and folate and B12 levels demonstrated no significant effect on MNCD71+ frequency. In addition, no difference was observed between pre-treatment MNCD71+ values for cancer patients compared with healthy volunteers. Regarding chemotherapy and/or partial body radiotherapy, elevated frequencies were observed upon initiation of treatment for 9 of the 10 patients studied. Maximal effects were observed 3-5 days following initiation of therapy. The largest increases in frequency of MNCD71+ (up to 25.9-fold) were observed in those patients exposed to anti-neoplastic drugs, presumably due to the systemic red marrow exposure provided by these agents. Taken together, these data support the hypothesis that the MNCD71+ endpoint represents a valuable biomarker of cytogenetic damage that does not require cell culture or microscopy-based scoring.

Perspectives of micronuclear test in human lymphocytes cultivated in cytogenetic block conditions. Part 1: Cell proliferation

Cultivation of human blood lymphocytes under the conditions of cytokinetic block with cytochalasin B creates unique opportunity to analyze the total spectrum of the changes describing genome instability. The main task of the present publication is the analysis of a modern state, opportunities and outlooks of the micronuclear test on human blood lymphocytes. The special attention is given those directions of researches which are rather seldom present in the literature - to laws of cellular proliferation, to existence of physiological conditionality and genetic predisposition to development of effects of genome instability; to effects of emotional stress and the adaptive response to action of ionizing irradiation, etc. The material is presented in 2 consecutive publications. It is finished with discussion of methodical features of statement of culture, results of the microscopic analysis and ideology of creation of the conclusions of the study.

SFTG international collaborative study on in vitro micronucleus test

This study on the in vitro micronucleus assay, comprising 11 laboratories using human lymphocytes, was coordinated by an organizing committee supported by the SFTG (the French branch of the European Environmental Mutagen Society). Nine coded substances were assessed for their ability to induce micronuclei in human lymphocytes in vitro, mitomycin C being used as a positive control. Cultures were exposed to the test substances for a short (early or late) time or for a long time, followed by a short or long recovery period, in the presence of cytochalasin B. Each chemical was evaluated, generally in two laboratories, using three treatment schedules at least twice. The data were assessed for acceptability, and then classified as negative, positive or equivocal. Two of seven genotoxic compounds, namely colchicine and bleomycin, clearly induced micronuclei. Reproducible results were difficult to obtain for some substances, which tended to be those acting at specific stages of the cell cycle. Cytosine arabinoside, diethylstilboestrol and 5-fluorouracil were classified as equivocal. Urethane and thiabendazole were classified as negative. The two presumed non-genotoxic compounds, mannitol and clofibrate, did not induce micronuclei. Repeat testing, exposing cells at both an early and late time after mitogenic stimulation, was needed to detect substances classified as equivocal. These results show the importance of achieving sufficient inhibition of nuclear division to avoid the possibility of missing an effect. The evaluation of micronuclei in mononucleated as well as binucleated cells was particularly useful to detect aneugens. There were no false positive results using lymphocytes, indicating a high specificity. It is concluded that the clastogenic or aneugenic potential in vitro of the substances tested was correctly identified in this study, but that refining the protocol to take into account factors such as the stages of the cell cycle exposed to the compound, or the duration of recovery would be likely to improve the sensitivity of detection using lymphocytes.

SFTG international collaborative study on in vitro micronucleus test I. General conditions and overall conclusions of the study

This study, coordinated by the SFTG (French branch of European Environmental Mutagen Society), included 38 participants from Europe, Japan and America. Clastogens (bleomycin, urethane), including base and nucleoside analogs (5-fluorouracil and cytosine arabinoside), aneugens and/or polyploidy inducers (colchicine, diethylstilboestrol, griseofulvin and thiabendazole), as well as non-genotoxic compounds (mannitol and clofibrate), were tested. Four cell types were used, i.e. human lymphocytes in the presence of cytochalasin B and CHO, CHL and L5178Y cell lines, in the presence or absence of cytochalasin B, with various treatment-recovery schedules. Mitomycin C was used as a positive control for all cell types. Mannitol and clofibrate were consistently negative in all cell types and with all treatment-recovery conditions. Urethane, known to induce questionable clastogenicity, was not found as positive. Bleomycin and mitomycin C were found positive in all treatment-recovery conditions. The base and nucleoside analogs were less easy to detect, especially 5-fluorouracil due to the interference with cytotoxicity, while cytosine arabinoside was detected in all cell types depending on the treatment-recovery schedule. Aneugens (colchicine, diethylstilboestrol and griseofulvin) were all detected in all cell types. In this study, the optimal detection was ensured when a short treatment followed by a long recovery was associated with a long continuous treatment without recovery. There was no impact of the presence or absence of cytochalasin B on the detection of micronucleated cells on cell lines. Scoring micronucleated cells in both mononucleated and binucleated cells when using cytochalasin B was confirmed to be useful for the detection and the identification of aneugens. In conclusion, these results, together with previously published validation studies, provide a useful contribution to the optimisation of a study protocol for the detection of both clastogens and aneugens in the in vitro micronucleus test.

Adverse event reporting and developments in radiation biology after normal tissue injury: International Atomic Energy Agency consultation

PURPOSE

Recent research has enhanced our understanding of radiation injury at the molecular-cellular and tissue levels; significant strides have occurred in standardization of adverse event reporting in clinical trials. In response, the International Atomic Energy Agency, through its Division of Human Health and its section for Applied Radiation Biology and Radiotherapy, organized a consultation meeting in Atlanta (October 2, 2004) to discuss developments in radiobiology, normal tissue reactions, and adverse event reporting.

METHODS AND MATERIALS

Representatives from cooperative groups of African Radiation Oncology Group, Curriculo Radioterapeutica Ibero Latino Americana, European Organization for Research and Treatment of Cancer, National Cancer Institute of Canada Clinical Trials Group, Radiation Therapy Oncology Group, and Trans-Tasman Radiation Oncology Group held the meeting discussion.

RESULTS

Representatives of major radiotherapy groups/organizations and prominent leaders in radiotherapy discussed current understanding of normal tissue radiobiologic effects, the design and implementation of future clinical and translational projects for normal tissue injury, and the standardization of adverse-event reporting worldwide.

CONCLUSIONS

The consensus was to adopt NCI comprehensive adverse event reporting terminology and grading system (CTCAE v3.0) as the new standard for all cooperative group trials. Future plans included the implementation of coordinated research projects focusing on normal tissue biomarkers and data collection methods.

Cytogenetic methods for biodosimetry and risk individualisation after exposure to ionising radiation

Measurement of dicentric chromosomes in human lymphocytes has been applied to assess dose received by potentially overexposed people and estimate risk for health effects. Since the dicentrics in exposed people decrease with time, the introduction of fluorescent in situ hybridisation enables to measure stable translocations for biodosimetry and address old or long-term exposures. In addition, premature chromosome condensation, which enables analysis in interphase, offers several advantages for biodosimetry. However, dose and risk estimates derived using cytogenetics and adequate calibration curves are based on the assumption that all individuals respond equally to radiation. Since increased radiosensitivity has been associated with cancer proneness, there is particular interest for risk assessment at the individual level. Towards this end, the efficiency of dynamics that govern DNA repair and apoptosis, as well as the conserved cellular processes that have evolved to facilitate DNA damage recognition using signal transduction pathways to activate cell cycle arrest and preserve genomic integrity, are being investigated. Recent work in cancer cytogenetics and on the modulation of radiation effects at the chromosome level using changes in gene expression associated with proteins or factors such as caffeine or amifostine treatment during G(2) to M-phase transition, reconfirmed the importance of G(2) chekpoint in determining radiosensitivity and of the cdk1/cyclin-B activity in the conversion of DNA damage into chromatid breaks. G(2)-chromosomal radiosensitivity may offer, therefore, a basis for the identification or testing of key genetic targets for modulation of radiation effects and the establishment of a screening method to detect intrinsic radiosensitivity.

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.

Micronucleus Frequency is Increased in Peripheral Blood Lymphocytes of Nuclear Power Plant Workers

Nuclear power plant workers are exposed to ionizing radiation at relatively low doses and for prolonged periods of time. To investigate the extent of genetic damage in these workers, a group of 133 nuclear power plant workers and 39 healthy controls were compared using the cytokinesis-block micronucleus assay. The frequency of micronuclei was significantly increased in peripheral lymphocytes of nuclear power plant workers (20.5 +/- 9.7% compared to 13.7 +/- 5.9%). A significant dose-response relationship was observed between micronucleus (MN) frequency and both the accumulated dose and the duration of employment (P < 0.01 for both variables after adjusting for age, gender and cigarette smoking) with an evident leveling off for exposures over 200 mSv. Accumulated dose and duration of employment were significantly correlated but exerted independent effects on MN frequency. For non-occupational parameters, age was significantly associated with the frequency of micronuclei, while gender was not. Smoking habit showed no overall effect, whereas increased chromosome damage was evident in smokers of more than 20 cigarettes per day. In conclusion, a dose-related association between MN frequency and exposure to ionizing radiation was evident in nuclear power plant workers, encouraging the application of the cytokinesis-block micronucleus assay in biomonitoring studies of human populations with prolonged exposure to ionizing radiation.

Patient dosimetry for 131I-lipiodol therapy

Patient dosimetry data for intra-arterial()iodine-131 lipiodol therapy for hepatocellular carcinoma (HCC) are scarce. The aim of this study was to determine the absorbed dose (D) to the tumour and healthy tissues, as well as the effective dose (E), by different methods for 17 therapies in 15 patients who received a mean activity of 1.9 GBq (SD 0.2) (131)I-lipiodol. Eight patients received thyroid blocking by potassium iodide (KI). Patient dosimetry was performed based on bi-planar total body scans using the Monte Carlo simulation program MCNP-4B and the MIRDOSE-3 standard software program. CT images of each patient were used to determine liver and tumour volume and position. The total body dose to the patient was also determined by biological dosimetry with the in vitro micronucleus (MN) assay. From the increase in micronucleus yield after therapy, the equivalent total body dose (ETBD) was calculated. Results for D and E were comparable between MCNP and MIRDOSE (liver: mean 7.8 Gy, SD 1.8, lungs: 6.8 Gy, SD 2.9, E: 2.01 Gy, SD 0.58). MIRDOSE gave a systematic overestimation for the tumour dose, especially for tumours <3 cm (15%). The MCNP method is more accurate since the dose contributions from tumour to organs and vice versa can be accounted for. The absorbed dose to the thyroid was significantly lower for patients who received KI (7.2 Gy, SD 2.2) than for the other patients (13.8 Gy, SD 5.0). MN yields could be obtained for only 12 of the 17 therapies due to hypersplenism. A mean ETBD of 1.66 Gy (SD 0.73) was obtained, but the MN results showed no correlation between the ETBD and the total body dose values of the physical dosimetry. Also, in all except one of the patients, no further reduction in the number of thrombocytes was observed after therapy, probably due to the existing hypersplenism. It is concluded that in view of the high E values, patient dosimetry is necessary for patients receiving (131)I-lipiodol therapy. Except in the case of the smaller tumours, comparable results were obtained with MCNP and MIRDOSE. Due to hypersplenism, biological dosimetry results based on the MN assay are not reliable.

Nucleoplasmic bridges are a sensitive measure of chromosome rearrangement in the cytokinesis-block micronucleus assay

We have performed experiments using the WIL2-NS human B lymphoblastoid cell line and primary human lymphocytes to: (i). determine the importance of including measurements of nucleoplasmic bridges (NPB) in the cytokinesis-block micronucleus (CBMN) assay; (ii). provide evidence that NPB originate from dicentric chromosomes and centric ring chromosomes. In addition, we describe theoretical models that explain how dicentric chromosomes and centric ring chromosomes may result in the formation of NPB at anaphase. The results with WIL2-NS showed that it was possible to distinguish genotoxic effects induced by different oxidizing agents in terms of the NPB/micronucleus frequency ratio. The results with lymphocytes indicated a strong correlation: (i). between NPB, centric ring chromosomes and dicentric chromosomes in metaphases (r > 0.93, P < 0.0001); (ii). between micronuclei (MNi), acentric chromosome fragments and acentric ring chromosomes (r > 0.93, P < 0.0001). The dose-response curves with gamma-rays were very similar for NPB, ring chromosomes and dicentric chromosomes, as were the dose-response curves for MNi, acentric rings and fragments. However, not all acentric chromosomes and dicentric chromosomes/centric rings were converted to MNi and NPB respectively, depending on the dose of radiation. Preliminary data, using FISH, suggest that NPB often represent DNA from a structural rearrangement involving only one or two homologous chromosomes. The results from this study validate the inclusion of NPB in the CBMN assay which provides a valuable measure of chromosome breakage/rearrangement that was otherwise not available in the micronucleus assay. The CBMN assay allows NPB measurement to be achieved reliably because inhibition of cytokinesis prevents the loss of NPB that would otherwise occur if cells were allowed to divide.

Cytogenetic monitoring of industrial radiographers using the micronucleus assay

Industrial radiography is the process of using either gamma-emitting radionuclide sources or X-ray machines to examine the safety of industrial materials. Industrial radiographers are among the radiation workers who receive the highest individual occupational radiation doses. To assess occupationally induced chromosomal damage, we performed the cytokinesis-block micronucleus (CBMN) assay in peripheral lymphocytes of 29 male industrial radiographers, exposed to ionizing radiation for 12.8 years+/-11.2, in comparison with 24 gender-, age-, and smoking habits-matched controls. The CBMN assay was combined with fluorescent in situ hybridization with a pan-centromeric DNA probe in 17 exposed subjects and 17 controls randomized from the initial populations. The mean cumulative equivalent dose, recorded by film dosimeters, was 67.2 mSv+/-49.8 over the past 5 years. The mean micronucleated binucleated cell rate (MCR) was significantly higher in the industrial radiographers than in the controls (10.7 per thousand +/-5.2 versus 6.6 per thousand +/-3.1, P=0.009); this difference was due to a significantly higher frequency of centromere-negative micronuclei (C-MN) in exposed subjects than in controls (8.5 per thousand +/-4.9 versus 2.2 per thousand +/-1.6, P<0.001). The two populations did not significantly differ in centromere-positive micronuclei (C+MN) frequency. These findings demonstrate a clastogenic effect in lymphocytes of industrial radiographers. MCR significantly positively correlated with age in the two groups. After correction for the age effect, MCR did not correlate with duration of occupational exposure. No correlation between radiation doses and MCR, C-MN, and C+MN frequencies was observed. In addition to physical dosimetry records, the enhanced chromosomal damage in lymphocytes of industrial radiographers emphasizes the importance of radiation safety programs.

Micronucleus assay reveals no radiation effects among nuclear power plant workers

The micronucleus assay was applied as biomarker for exposure effect and radiosensitivity in a group of 99 radiation workers of the Nuclear Power Plant Doel (Belgium). The difference in micronucleus frequency between the group of radiation workers with annual dose exceeding 2 mSv and a non-exposed control population was statistically not significant. With respect to the micronucleus frequency after an in vitro challenge dose of 2 Gy, which can be considered as biomarker for radiosensitivity, the data of present study can be represented by a normal distribution without a high frequency tail. This means that a subpopulation of workers with elevated radiosensitivity could not be identified in the population under study.

Non-disjunction and chromosome loss in gamma-irradiated human lymphocytes: a fluorescence in situ hybridization analysis using centromere-specific probes

Centromere-specific DNA probes for chromosomes 4, 7 and 18 were used to simultaneously analyze chromosome loss, non-disjunction, breaks within the labeled region, and nucleoplasmic bridges induced by gamma rays in binucleated human lymphocytes. The doses used were 0, 1, 2 and 4 Gy, and approximately 1000 cells were scored per dose. Micronucleus frequency increased in a linear-quadratic fashion. For chromosome loss, significant increases were observed at 2 and 4 Gy, whereas for non-disjunction significant increases were observed at 1 Gy; thus non-disjunction allowed us to detect the effects of radiation at a lower dose than chromosome loss. The use of centromere-specific probes allowed discrimination between the clastogenic and aneugenic effects of ionizing radiation. The analysis of chromosome loss, not taking fragmented signals into account, ensures the detection of an aneugenic effect, which was not possible using pancentromeric probes. The frequency of chromosome breakage within the labeled regions was higher in nuclei than in micronuclei, suggesting an increase in the engulfment of chromosomal material by nuclei as a consequence of the presence of cytochalasin B in the cultures. Chromatin filaments connecting main nuclei, the so-called nucleoplasmic bridges, were observed in irradiated samples, and are a manifestation of rearranged chromosomes producing anaphase bridges.