Micronuclei-biological indicator for retrospective dosimetry after exposure to ionizing radiation

Micronuclei and Cancer

Chromosome-containing micronuclei are a feature of human cancer. Micronuclei arise from chromosome mis-segregation and characterize tumors with elevated rates of chromosomal instability. Although their association with cancer has been long recognized, only recently have we broadened our understanding of the mechanisms that govern micronuclei formation and their role in tumor progression. In this review, we provide a brief historical account of micronuclei, depict the mechanisms underpinning their creation, and illuminate their capacity to propel tumor evolution through genetic, epigenetic, and transcriptional transformations. We also posit the prospect of leveraging micronuclei as biomarkers and therapeutic targets in chromosomally unstable cancers.

SIGNIFICANCE

Micronuclei in chromosomally unstable cancer cells serve as pivotal catalysts for cancer progression, instigating transformative genomic, epigenetic, and transcriptional alterations. This comprehensive review not only synthesizes our present comprehension but also outlines a framework for translating this knowledge into pioneering biomarkers and therapeutics, thereby illuminating novel paths for personalized cancer management.

Furazolidone Increases Survival of Mice Exposed to Lethal Total Body Irradiation through the Antiapoptosis and Antiautophagy Mechanism

Exposure to total body irradiation (TBI) causes dose- and tissue-specific lethality. However, there are few effective and nontoxic radiation countermeasures for the radiation injury. In the current study, mice were pretreated with a traditional antimicrobial agent, FZD, before TBI; the protective effects of FZD on radiation injury were evaluated by using parameters such as the spleen index and thymus index, immunohistochemical staining of intestinal tissue, and frequency of micronuclei in polychromatophilic erythrocytes of bone marrow. The intestinal epithelial cell line IEC-6 was used to investigate the underlying mechanisms. Our results indicated that FZD administration significantly improved the survival of lethal dose-irradiated mice, decreased the number of micronuclei, upregulated the number of leukocytes and immune organ indices, and restored intestinal integrity in mice after TBI. TUNEL and western blot showed that FZD protected intestinal tissue by downregulating radiation-induced apoptosis and autophagy. Meanwhile, FZD protected IEC-6 cells from radiation-induced cell death by inhibiting apoptosis and autophagy. To sum up, FZD protected against radiation-induced cell death both in vitro and in vivo through antiapoptosis and antiautophagy mechanisms.

Evaluation of oxidative DNA damage in pigeon erythrocytes using DNA breakage detection-fluorescence in situ hybridization (DBD-FISH)

DNA breakage detection-fluorescence in situ hybridization (DBD-FISH) enables detection and quantification of DNA breakage in the entire genome or within specific DNA sequences in single cells. We used this method to visualize and evaluate DNA damage in pigeon erythrocytes that were induced by elevated temperature and hydrogen peroxide. We also examined morphological changes in the cell nuclei. DBD-FISH demonstrated a significant increase of DNA damage in a temperature dependent manner, which resulted in nuclear abnormalities associated with apoptotic cells. These cells gave strong nuclear fluorescent signals that indicated cell death.

Chromosomal Aberrations in Human Peripheral Blood Lymphocytes after Exposure to Ionizing Radiation

Biological dosimetry using chromosome aberration analyses in human peripheral blood lymphocytes is suitable and useful tool for estimating the dose when a nuclear or radiological emergency is investigated. Blood samples from five healthy donors were obtained to establish dose-response calibration curves for chromosomal aberrations after exposure to ionizing radiation. In this work, dicentric assay and CBMN assay were compared considering the sensitivity and accuracy of dose estimation. In a total of 21,688 analyzed metaphase spreads, 10,969 dicentric chromosomes, 563 centric rings and 11,364 acentric chromosomes were found. The number of metaphase cells decreased with increasing radiation dose. The centric rings were not found in the non-irradiated control. There was no relationship between radiation dose and acentric ring induction. The frequency of total MN increased in a dose-dependent manner. In comparison with the control value, MN increased about 9, 32, 75, 87, and 52 fold higher after treatment with 1, 2, 3, 4, and 5 Gy, respectively. The results revealed that the mean frequency of chromosomal aberrations, both in dicentric and in micronuclei analyses increased with increasing radiation dose.

Micronucleus frequencies in groups receiving external or internal radiation

OBJECTIVE

In the current study, we aimed to explore whether there is alteration between pre- and post-treatment micronucleus (MN) frequencies induced by internal and external ionizing radiation.

MATERIALS AND METHODS

The study enrolled a total of 67 patients including patients admitted to our hospital for treatment of hyperthyroidism (n = 17), scanning with low-dose I-131 (n = 15), and ablative therapy with high-dose I-131 (n = 15) at Department of Nuclear Medicine as well as patients with different diagnoses receiving external radiotherapy with various doses and durations at Department of Radiation Oncology (n = 20). Thirty-two patients who received radioactive iodine and returned for a follow-up visit at 1 month.

RESULTS

Considering both pre- and post-treatment MN frequencies of each group, lowest MN frequencies were detected for patients undergoing screening with low-dose I-131, and highest MN frequencies were found in radiotherapy patients. Comparison of pre- and post-treatment MN frequencies among hyperthyroidism, when pre- and post-treatment MN frequencies compared among hyperthyroidism, I-131 whole body scanning, ablation, and radiotherapy patient groups differences between MN frequencies were significant for each group (P < 0.05).

CONCLUSION

Our study showed that MN analysis might be of value in determining chromosome damage that could potentially occur in patients exposed to internal and external radiation.

Dose-dependent micronuclei formation in normal human fibroblasts exposed to proton radiation

Micronuclei are small extranuclear bodies resulting from chromosome fragments or the whole chromosomes secluded from daughter nuclei during mitosis. The number of radiation-induced micronuclei reflects the level of chromosomal damage and relates to an absorbed dose and quality of incident ionizing radiation. The aim of the present study was to determine the micronucleus formation as a specific biological marker for acute radiation-induced DNA damage in normal human fibroblasts exposed to 30-MeV protons and Co-60 gamma radiation. We found a linear increase in binuclear cells containing micronuclei for absorbed doses from 1 to 5 Gy for both radiation modalities. However, the total number of micronuclei in binuclear cells follows a linear-quadratic dose dependence. In case of human exposure to mixed radiation fields or high LET radiation, the proportion of binuclear cells containing micronuclei from all binuclear cells can thus serve as a good biomarker of radiation-induced DNA damage.

Response of human lymphocytes to proton radiation of 60 MeV compared to 250 kV X-rays by the cytokinesis-block micronucleus assay

Particle radiotherapy such as protons provides a new promising treatment modality to cancer. However, studies on its efficacy and risks are relatively sparse. Using the cytokinesis-blocked micronucleus assay, we characterized response of human peripheral blood lymphocytes, obtained from health donors irradiated in vitro in the dose range: 0-4. 0 Gy, to therapeutic proton radiation of 60 MeV from AIC-144 isochronous cyclotron, by studying nuclear division index and DNA damage and compared them with X-rays. Peripheral blood lymphocytes show decreased ability to proliferate with increasing radiation doses for both radiation types, however, in contrast to X-rays, irradiation with protons resulted in a higher proliferation index at lower doses of 0.75 and 1.0 Gy. Protons are more effective in producing MN at doses above 1.75 Gy compared to X-rays. Dose-response curves for micronucleus incidence can be best described by a cubic model for protons, while for X-rays the response was linear. The differences in the energy spectrum and intracellular distribution of energy between radiation types are also apparent at the intracellular distribution of cytogenetic damage as seen by the distribution of various numbers of micronuclei in binucleated cells. Our studies, although preliminary, further contribute to the understanding of the mechanistic differences in the response of HPBL in terms of cellular proliferation and cytogenetic damage induced by protons and X-rays as well as intra-cellular distribution of energy and thus radiobiological effectiveness.

Evaluation of DNA damage in lymphocytes of radiology personnel by comet assay

OBJECTIVES

The importance of X-rays as a diagnostic medical tool cannot be denied. However, continuous exposure to X-rays can cause DNA damage. This study aimed to use the comet assay technique to investigate the level of DNA damage in lymphocytes due to X-rays in occupationally exposed personnel.

METHODS

Blood samples were collected from 74 exposed and 70 control subjects for analysis. A total of 100 randomly captured cells from each slide were examined using an epifluorescent microscope. The comets were analyzed by a visual scoring method according to comet tail length.

RESULTS

The results indicated a significant increase (p<0.05) in DNA damage in X-rays technicians (129.8 ± 17.2) as compared with the control group (53.0 ± 25.0). A significant increase (p<0.02) in DNA damage was also observed with an increase in exposure duration of technicians because of their service length.

CONCLUSIONS

The present study suggests that the exposed radiology personnel should carefully comply with radiation protection procedures such as wearing of lead apron during diagnostic procedures and minimize radiation exposure where possible to avoid potential genotoxic effects due to X-rays.

Use of the DBD-FISH technique for detecting DNA breakage in response to high doses of X-rays

The aim of this study was to generate a dose-response curve using the DNA breakage detection-fluorescent in situ hybridization (DBD-FISH) test as a biomarker of initial genetic effects induced by high doses of X-rays. A dose-response curve was obtained by measuring the ex vivo responses to increasing doses (0-50 Gy) of X-rays in the peripheral blood lymphocytes of ten healthy donors. The overall dose-response curve was constructed using integrated density (ID; area × fluorescence intensity) as a measure of genetic damage induced by irradiation. The correlation coefficient was high (r = 0.934, b(0) = 10.408, and b(1) = 0.094). One-way ANOVA with the Student-Newman-Keuls test for multiple comparisons showed significant differences among the average ln ID values according to dose. Our results suggest the usefulness of the DBD-FISH technique for measuring intrinsic individual cellular radio sensitivity ex vivo.

A cytogenetic approach to the effects of low levels of ionizing radiation (IR) on the exposed Tunisian hospital workers

OBJECTIVES

The aim of this study is to assess chromosomal damage in Tunisian hospital workers occupationally exposed to low levels of ionizing radiation (IR).

MATERIALS AND METHODS

The cytokinesis-block micronucleus (CBMN) assay in the peripheral lymphocytes of 67 exposed workers compared to 43 controls matched for gender, age and smoking habits was used. The clastogenic/aneugenic effect of IR was evaluated using the CBMN assay in combination with fluorescence in situ hybridization with human pan-centromeric DNA in all the exposed subjects and controls.

RESULTS

The study showed a significant increase of the micronucleus (MN) frequency in the lymphocytes of the exposed workers compared to the control group (13.63 ± 4.9‰ vs. 6.52 ± 4.21‰, p < 0.05). The centromere analysis performed in our study showed that MNs in hospital staff were predominantly centromere negative (72%) and the mean negative labeled micronucleus (C-MN) frequency was significantly higher in the exposed subjects than in the controls (9.04 ± 4.57‰ vs. 1.17 ± 0.77‰). The multivariate regression analysis, taking into account all confounding factors, showed that only the time of exposure to IR had a significant effect on the level of MNs and C-MN.

CONCLUSION

The present study shows that chromosomal damage leading to the formation of micronucleated lymphocytes is more frequent in the hospital workers exposed to IR than in the controls, despite the low levels of exposure. The results of the study confirm the well-known clastogenic properties of ionizing radiation. In regards to health monitoring, detection of early genotoxic effects may allow for the adoption of preventive biological control measures, such as hygienic improvements in the workplace or reduction of hours of occupational exposure.

Radiation-induced biomarkers for the detection and assessment of absorbed radiation doses

Radiation incident involving living organisms is an uncommon but a very serious situation. The first step in medical management including triage is high-throughput assessment of the radiation dose received. Radiation exposure levels can be assessed from viability of cells, cellular organelles such as chromosome and different intermediate metabolites. Oxidative damages by ionizing radiation result in carcinogenesis, lowering of the immune response and, ultimately, damage to the hematopoietic system, gastrointestinal system and central nervous system. Biodosimetry is based on the measurement of the radiation-induced changes, which can correlate them with the absorbed dose. Radiation biomarkers such as chromosome aberration are most widely used. Serum enzymes such as serum amylase and diamine oxidase are the most promising biodosimeters. The level of gene expression and protein are also good biomarkers of radiation.

Assessment of genetic damage in peripheral blood of human volunteers exposed (whole-body) to a 200 muT, 60 Hz magnetic field

AIM

To investigate the extent of damage in nucleated cells in peripheral blood of healthy human volunteers exposed to a whole-body 60 Hz, 200 microT magnetic field.

MATERIALS AND METHODS

In this study, 10 male and 10 female healthy human volunteers received a 4 h whole-body exposure to a 200 microT, 60 Hz magnetic field. In addition, five males and five females were treated in a similar fashion, but were exposed to sham conditions. For each subject, a blood sample was obtained prior to the exposure period and aliquots were used as negative- (pre-exposure) and positive- [1.5 Gray (Gy) (60)Cobalt ((60)Co) gamma-irradiation] controls. At the end of the 4 h exposure period, a second blood sample was obtained. The extent of DNA damage was assessed in peripheral human blood leukocytes from all samples using the alkaline comet assay. To detect possible clastogenic effects, the incidence of micronuclei was assessed in phytohemagglutinin (PHA)-stimulated lymphocytes using the cytokinesis-block micronucleus assay.

RESULTS

There was no evidence of either increased DNA damage, as indicated by the alkaline comet assay, or increased incidence of micronuclei (MN) in the magnetic field exposed group. However, an in vitro exposure of 1.5 Gy gamma-irradiation caused a significant increase in both DNA damage and MN induction.

CONCLUSIONS

This study found no evidence that an acute, whole-body exposure to a 200 microT, 60 Hz magnetic field for 4 hours could cause DNA damage in human blood.

Fifty years of cytogenetics: a parallel view of the evolution of cytogenetics and genotoxicology

A parallelism exists between human cytogenetics and cytogenetic toxicology. The breakthroughs, mostly coming from and used in clinical genetics, are widely used in genetic toxicology. The birth of human cytogenetics occurred in 1956 when it was published that the diploid number of chromosomes in humans is 46. The first stage in chromosome-induced mutagenesis began in 1938 when Sax published the effects of X-rays on the chromosomes of Drosophila. In 1959, the cytogenetic anomalies for Down, Klinefelter, and Turner syndromes were described, and parallelly in 1960, the first publication on chromosomal aberrations in man caused by ionizing radiation appeared. The cytogenetic analysis of chromosomal aberrations in cell cultures is considered one of the primary methods to evaluate induced mutagenesis. At the end of the 1960s, banding techniques allowed chromosomes to be individually identified, in parallel, the sister chromatid exchange analysis technology was described. Another milestone in the history of induced mutagenesis was the discovery that mutagenic agents were able to alter chromosomal division and segregation in gonads inducing meiotic nondisjunction. Here we review new approaches and applications such as biological dosimetry, translocation scoring using FISH, and micronucleus test. Chromosomal aberrations and micronucleus test are now effective cytogenetic biomarkers of early effect used as cancer predictors. Human cytogenetics has proven to be effective over its 50-year lifespan and, although each new technique that has appeared seemed to announce its end, the fact is that the current state of cytogenetics is in reality a collection of techniques that, while common, are cheap, fast, and wide-ranging. Therefore, in genotoxicology, they continue to be useful to identify mutagenic agents as well as to evaluate and analyze exposed populations.

The micronucleus frequency in cytokinesis-blocked lymphocytes of cattle in the vicinity of a nuclear power plant

Cytogenetic and hematological analyses were performed on the peripheral blood lymphocytes (PBLs) obtained from Korean native cattle bred in the vicinity of three nuclear power plants (Wolsong, Uljin and Yeonggwang) and in a control area. The micronucleus (MN) rates for the cattle from the Wolsong, Uljin and Yeonggwang nuclear power plants and for the control area were 9.87 +/- 2.64, 8.90 +/- 3.84, 9.20 +/- 3.68 and 9.60 +/- 3.91 per 1,000 cytokinesis-blocked lymphocytes, respectively. The apparent difference is not statistically significant. The MN frequencies of PBLs from cattle bred in the four areas are within the background variation for this study. The MN frequencies and hematological values were similar regardless of whether the cattle were bred near a nuclear power plant or in the control area.

Cytogenetic analysis in lymphocytes from workers occupationally exposed to low levels of ionizing radiation

The aim of the present study was to perform a cytogenetic analysis in peripheral lymphocytes of 36 individuals occupationally exposed to low levels of ionizing radiation, and compare the results with 36 controls, using the chromosomal aberrations test (CA), sensitivity to bleomycin and cytokinesis-blocked micronucleus assay (MN). The frequencies of CA/100 cells observed for the exposed workers were not significantly higher than in controls (P>0.05). The mean break/cell (b/c) for the controls and exposed workers was 0.59±0.39 and 0.57±0.29, respectively (P>0.01). The MN frequencies were significantly increased (P<0.01) in exposed workers (6.13±3.18) in comparison with controls (5.11±3.85). The mean MN was also statistically higher in the non-smoker exposed when compared with non-smoker controls, 5.80±3.09 and 5.15±4.08, respectively (P<0.01). The cytogenetic analysis of MN proved to be the most sensitive biological marker to assess the cellular response to low levels of irradiation.

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.

Adaptive response of blood lymphocytes of inhabitants residing in high background radiation areas of ramsar- micronuclei, apoptosis and comet assays

The hot springs in certain areas of Ramsar contain (226)Ra and (222)Rn. The effects of natural radiation on the inhabitants of these areas and the inhabitant's radiosensitivity or adaptive responses were studied. One group of volunteers from areas with high natural background radiation and another group from areas with normal background radiation were chosen as the case and control group respectively. The frequency of micronuclei, apoptosis, and DNA damage in peripheral blood mononuclear cells were measured following gamma irradiation (4 Gy). The incidence of micronuclei in the case group was significantly lower than that in the control group while their frequency of apoptosis was higher (P < 0.05). However, the rates of induced DNA damage and repair were significantly higher in the case group (P < 0.05). Smaller number of micronuclei and higher levels of apoptosis in the case group could be the result of higher resistance to radiation stress and a more rigorous checkpoint at cell division. However, regarding the alkaline labile sites, the individuals in the case group are more sensitive and susceptible to DNA damage. The results of micronuclei, apoptosis and repair studies suggest that an adaptive response might be induced in people residing in areas with high background radiation.

Novel Microarray-Based Method for Estimating Exposure to Ionizing Radiation

Accurate estimation of the dose of ionizing radiation to which individuals have been exposed is critical for therapeutic treatment. We investigated whether gene expression profiles could be used to evaluate the dose received, thereby serving as a biological dosimeter. We used cDNA microarrays to monitor changes in gene expression profiles induced by ionizing radiation in mouse total blood. The subsets of genes best characterizing each dose were identified by resampling the original data set and calculating the intersection of the dose signatures. This analytical strategy minimizes the impact of potential genetic/epigenetic variation between mice and overcomes the bias in gene selection inherent to microarray technology. The significance of the identified signatures was evaluated by monitoring the type I error rate by in silico negative control simulation. Based on the distribution of the mean ratios of the selected probes, we were able to identify transcription profiles giving 83% to 100% correct estimation of the dose received by test mice, demonstrating that the selected probes could be used to determine the dose of radiation to which the animals had been exposed. This method could potentially be generalized to determine the level of exposure to other toxins and could be used to develop new related clinical applications.

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.

Assessment of DNA damage in nuclear medicine personnel--comparative study with the alkaline comet assay and the chromosome aberration test

Despite much research over the last few decades, there still remains considerable uncertainty as to the genetic impact of ionizing radiation on human populations, particularly at low levels. The aim of the present study was to provide data on the genetic hazards due to occupational exposure of low doses of ionizing radiation in nuclear medicine departments. The assessment of primary DNA damage in peripheral blood leukocytes of medical staff was performed using the alkaline comet assay and the data obtained were compared with the results of conventional cytogenetic biodosimetry using the chromosome aberration (CA) test. Altogether 120 subjects (60 exposed and 60 controls) participated in the study. Statistically significant increases in primary DNA damage and increased frequencies of CAs compared to controls were observed. Within the exposed population, significant inter-individual differences in DNA damage were found, indicating differences in genome sensitivity. Age and gender were not confounding factors, while smoking enhanced the levels of primary DNA damage only in control subjects, as revealed by both biomarkers studied. The present study suggests that genotoxic damage results from exposure to chronic low doses of ionizing radiation in nuclear medicine departments. Therefore, the exposed medical personnel should carefully comply with the radiation protection procedures and should minimize radiation exposure where possible to avoid potential genotoxic effects. The results obtained in this study point to the significance of biological indicators providing information on the actual risk to the radiation exposed individuals. According to our results, the alkaline comet assay and CA test are sensitive biomarkers that can be used as additional complements to physical dosimetry for assessing exposure to radiation in nuclear medicine personnel.

A cytogenetic study of Korean native goat bred in the nuclear power plant using the micronucleus assay

Cytogenetic and hematological analysis was performed on the peripheral blood lymphocytes (PBLs) obtained from Korean native goats bred in two nuclear power plants (Wolsong and Uljin) and a control area. The frequencies of gamma-ray-induced micronuclei (MN) in the cytokinesis-blocked (CB) lymphocytes at several doses were measured in three Korean native goats. The measurements performed after irradiation showed dose-related increases in the MN frequency in each of the donors. The results were analyzed using a linear-quadratic model with a line of best fit of y=0.1019D+0.0045D2+0.0093 (y=number of MN/CB cells and D=irradiation dose in Gy). The MN rates in the goats from the Wolsong and Uljin nuclear power plant, and the control area were 9.60+/-2.88, 6.83+/-1.47 and 9.88+/-4.32 per 1,000 CB lymphocytes, respectively. The apparent difference is not statistically significant. The MN frequencies of PBLs from goats bred in three areas means that the values are within the background variation in this experiment. The MN frequencies and hematological values were similar regardless of whether the goats were bred in the nuclear power plant or the control area.

Evaluation of the reticulocyte micronucleus assay in patients treated with radioiodine for thyroid cancer

In the case of accidental radiation exposure, biological dosimetry has an important role. Previous studies have indicated that the flow cytometric micronucleus (MN) assay in human transferrin receptor positive reticulocytes (Tf-Ret) in blood could be a sensitive biomarker for chromosome damage. In the present investigation, the utility and sensitivity of this method was studied in 44 young patients from Belarus, who were treated with 131I for thyroid cancer. Red marrow (RM) is the critical organ in radioiodine therapy (RIT). In our patients, it was exposed to 100-700 mSv low-dose rate irradiation within 2-4 days. About 3 days after 131I administration, the frequency of micronucleated-Tf-Ret (f(MN-Tf-Ret)) increases within 1 day to a maximum and declines in the following 2-5 days to its value before treatment. A total dose of 100 mSv was easily detectable. The sensitivity of the assay after acute irradiation may be 50 mSv. The method should be useful for monitoring individuals after a radiation accident, provided blood samples can be obtained within a few days after exposure. The time-course of f(MN-Tf-Ret) is interpreted using a model, which considers the exponential exposure of red marrow in RIT as well as the kinetics of erythroblast maturation and reticulocyte migration into the peripheral circulation. Similar modelling was done on published data of MN in immature mouse erythrocytes. Striking similarities in the kinetic and in the yield of MN-induction were found between these two species. This lends support for the use of the mouse as a model for the MN-induction in humans.

Individual responsiveness to induction of micronuclei in human lymphocytes after exposure in vitro to 1800-MHz microwave radiation

The widespread application of microwaves is of great concern in view of possible consequences for human health. Many in vitro studies have been carried out to detect possible effects on DNA and chromatin structure following exposure to microwave radiation. The aim of this study is to assess the capability of microwaves, at different power densities and exposure times, to induce genotoxic effects as evaluated by the in vitro micronucleus (MN) assay on peripheral blood lymphocytes from nine different healthy donors, and to investigate also the possible inter-individual response variability. Whole blood samples were exposed for 60, 120 and 180 min to continuous microwave radiation with a frequency of 1800 MHz and power densities of 5, 10 and 20 mW/cm(2). Reproducibility was tested by repeating the experiment 3 months later. Multivariate analysis showed that lymphocyte proliferation indices were significantly different among donors (p<0.004) and between experiments (p<0.01), whereas the applied power density and the exposure time did not have any effect on them. Both spontaneous and induced MN frequencies varied in a highly significant way among donors (p<0.009) and between experiments (p<0.002), and a statistically significant increase of MN, although rather low, was observed dependent on exposure time (p=0.0004) and applied power density (p=0.0166). A considerable decrease in spontaneous and induced MN frequencies was measured in the second experiment. The results show that microwaves are able to induce MN in short-time exposures to medium power density fields. Our data analysis highlights a wide inter-individual variability in the response, which was confirmed to be a characteristic reproducible trait by means of the second experiment.

Micronuclei in humans induced by exposure to low level of ionizing radiation: influence of polymorphisms in DNA repair genes

Understanding the risks deriving from protracted exposure to low doses of ionizing radiation has remarkable societal importance in view of the large number of work settings in which sources of IR are encountered. To address this question, we studied the frequency of micronuclei (MN), which is an indicator of DNA damage, in a population exposed to low levels of ionizing radiation and in matched controls. In both exposed population and controls, the possible influence of single nucleotide polymorphisms in XRCC1, XRCC3 and XPD genes on the frequency of micronuclei was also evaluated. We also considered the effects of confounding factors, like smoking status, age and gender. The results indicated that MN frequency was significantly higher in the exposed workers than in the controls [8.62+/-2.80 versus 6.86+/-2.65; P=0.019]. Radiological workers with variant alleles for XRCC1 or XRCC3 polymorphisms or wild-type alleles for XPD exon 23 or 10 polymorphisms showed a significantly higher MN frequency than controls with the same genotypes. Smoking status did not affect micronuclei frequency either in exposed workers or controls, while age was associated with increased MN frequency in the exposed only. In the combined population, gender but not age exerted an influence on the yield of MN, being higher in females than in males. Even though there is a limitation in this study due to the small number of subjects, these results suggest that even exposures to low level of ionizing radiation could have genotoxic effects and that XRCC3, XRCC1 and XPD polymorphisms might contribute to the increased genetic damage in susceptible individuals occupationally exposed to chronic low levels of ionizing radiation. For a clear conclusion on the induction of DNA damage caused by protracted exposure to low doses of ionizing radiation and the possible influence of genetic polymorphism in DNA repair genes larger studies are needed.

Changes in micronucleus frequency resulting from preirradiation of cell culture surfaces

We have initiated a series of experiments to quantify the impact of environmental variables on the observed frequency of micronuclei in monolayer cultures. In this paper the influence of preirradiation of cell culture vessels on micronucleus formation in Chinese hamster ovary cells was examined. Dry cell culture vessels were preirradiated with 2 Gy of either alpha particles or X rays and immediately plated with nonirradiated cells. About 48 h later a group of randomly chosen containers was set aside, and the rest of the containers were exposed to a range of doses of X rays or alpha-particle radiation. Nonirradiated cells plated on previously irradiated cell culture surfaces manifested nearly as many micronuclei as the irradiated cells. In all experiments, preirradiation of the cell substrate (the culture dish) led to a significantly increased micronucleus frequency relative to unirradiated substrate. These results suggest that methods of cell culture vessel sterilization and the composition of cell attachment surfaces could be a confounding factor, particularly in low-dose experiments.

Micronuclei in lymphocytes of uranium miners of the former Wismut SDAG

We studied micronucleus frequencies in former German uranium miners of the Wismut SDAG (Sowjetisch-Deutsche Aktiengesellschaft). Various other groups were analyzed for comparison (individuals with lung tumors or lung fibrosis, controls). We had shown previously that micronucleus frequencies were not different among the various groups. Differences were observed, however, when centromere-positive and -negative micronuclei were distinguished. In the analyses presented here, we looked for the effects of smoking habits, alcohol consumption, vitamin uptake, chronic diseases, allergies, doing sports, gamma-GT (gamma-glutamyltranspeptidase), lymphocyte numbers, CEA (carcinoembryonic antigen), X-ray diagnostics, computer tomographies, and scintigraphies. With the exception of more than one scintigraphy carried out during the last four months before micronucleus analysis, none of the factors mentioned above significantly affected micronucleus numbers. One result deserves specific attention: individuals with low percentages of binucleated lymphocytes after in vitro cytochalasin B exposure showed higher micronucleus frequencies than those individuals with high percentages of binucleated cells. The same result was obtained for various other populations that we monitored in the past.

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.

Patient dosimetry after 131I-MIBG therapy for neuroblastoma and carcinoid tumours

AIM

The aim of the study was to determine the equivalent total body dose (ETBD) using the cytokinesis-blocked micronucleus assay in 22 131 I-meta-iodobenzylguanidine (131 I-MIBG) therapies (18 neuroblastoma, mean 5097 MBq, SD 1591; and four carcinoid tumours, mean 7681 MBq, SD 487). The results are correlated with the total body radiation dose according to the Medical Internal Radiation Dosimetry (MIRD) formalism.

METHODS

For each patient, blood samples were taken immediately before and 1 week after 131I-MIBG therapy. The first blood sample was irradiated in vitro with 60Co gamma-rays to determine the dose-response curve. Micronuclei were scored in 1000 binucleated cells. By using the dose-response curve the ETBD was derived from the increase in micronuclei after 131I-MIBG therapy (second blood sample). Based on three consecutive biplanar scans taken at 3, 6 and 9 days post-administration respectively, the total body dose following the MIRD formalism was calculated.

RESULTS

The micronucleus assay was evaluable in only 14 out of 22 131I-MIBG therapies due to cell division inhibition caused by previous chemotherapy treatments and lymphocyte dilution due to blood transfusions given shortly after 131I-MIBG therapy. For these 14 therapies, the mean micronucleus yield after 131I-MIBG therapy was significantly increased (P < 0.01) with a mean of 92 (SD 77) for neuroblastoma patients and with a mean of 35 (SD 8) for carcinoid patients. The increase observed in the present study is greater than previously observed after 131I therapy and 89Sr therapy but much lower than after external beam radiotherapy. For all patients treated with multiple therapies, the initial increase in micronucleus yield had at least partially recovered by the time of the next therapy. This might be explained by an increased turnover of lymphocytes. A mean ETBD of 0.95 Gy (SD 0.55) for neuroblastoma patients and a mean of 0.46 Gy (SD 0.09) for carcinoid patients was calculated. A reasonable correlation (R = 0.87) between the ETBD and the MIRD dose was obtained. The slope value of 0.75 can be explained by the low dose rate effect.

CONCLUSIONS

The observation in the present study of important inter-individual variability in the total body dose, with the possibility of high dose values, suggests the necessity of individual dosimetry when administering 131I-MIBG therapy, especially considering that generally more than one therapy is given to each patient.

HUman MicroNucleus project: international database comparison for results with the cytokinesis-block micronucleus assay in human lymphocytes: I. Effect of laboratory protocol, scoring criteria, and host factors on the frequency of micronuclei

Micronucleus (MN) expression in peripheral blood lymphocytes is well established as a standard method for monitoring chromosome damage in human populations. The first results of an analysis of pooled data from laboratories using the cytokinesis-block micronucleus (CBMN) assay and participating in the HUMN (HUman MicroNucleus project) international collaborative study are presented. The effects of laboratory protocol, scoring criteria, and host factors on baseline micronucleated binucleate cell (MNC) frequency are evaluated, and a reference range of "normal" values against which future studies may be compared is provided. Primary data from historical records were submitted by 25 laboratories distributed in 16 countries. This resulted in a database of nearly 7000 subjects. Potentially significant differences were present in the methods used by participating laboratories, such as in the type of culture medium, the concentration of cytochalasin-B, the percentage of fetal calf serum, and in the culture method. Differences in criteria for scoring micronuclei were also evident. The overall median MNC frequency in nonexposed (i.e., normal) subjects was 6.5 per thousand and the interquartile range was between 3 and 12 per thousand. An increase in MNC frequency with age was evident in all but two laboratories. The effect of gender, although not so evident in all databases, was also present, with females having a 19% higher level of MNC frequency (95% confidence interval: 14-24%). Statistical analyses were performed using random-effects models for correlated data. Our best model, which included exposure to genotoxic factors, host factors, methods, and scoring criteria, explained 75% of the total variance, with the largest contribution attributable to laboratory methods.

Induction of micronuclei in human lymphocytes exposed in vitro to microwave radiation

Increasing applications of electromagnetic fields are of great concern with regard to public health. Several in vitro studies have been conducted to detect effects of microwave exposure on the genetic material leading to negative or questionable results. The micronucleus (MN) assay which is proved to be a useful tool for the detection of radiation exposure-induced cytogenetic damage was used in the present study to investigate the genotoxic effect of microwaves in human peripheral blood lymphocytes in vitro exposed in G(0) to electromagnetic fields with different frequencies (2.45 and 7.7GHz) and power density (10, 20 and 30mW/cm(2)) for three times (15, 30 and 60min). The results showed for both radiation frequencies an induction of micronuclei as compared to the control cultures at a power density of 30mW/cm(2) and after an exposure of 30 and 60min. Our study would indicate that microwaves are able to cause cytogenetic damage in human lymphocytes mainly for both high power density and long exposure time.

A cytogenetic study of nuclear power plant workers using the micronucleus-centromere assay

A cytogenetic study was performed in 215 nuclear power plant workers occupationally exposed to radiation using the micronucleus-centromere assay for peripheral blood lymphocytes. As control population served administrative staff with yearly doses below 1 mSv. The increase of the micronucleus frequency with age, observed in the non-smoking control population, is mainly due to an enhanced number of centromere-positive micronuclei, pointing to an increased chromosome loss. No differences in the number of micronuclei, centromere-positive and centromere-negative micronuclei between smokers and non-smokers are observed. An analysis of the micronucleus data vs. the dose accumulated over the 10 years preceding the venepuncture shows no significant clastogenic or aneuploidogenic effects of the exposure in the studied population which is representative for workers in the nuclear industry at present. According to the linear fits to our data an increase of the micronucleus frequency pro rata 0.5 per 1000 binucleated cells per year, related to the centromere-negative micronuclei, may be expected for workers with the maximal tolerable dose of 20 mSv/year.