Reiko Kanda

Dynamic analysis of chromosome aberrations in three victims of the Tokai-mura criticality accident.

Purpose : To investigate the dynamics of chromosome aberrations in the blood cells of three workers severely exposed to neutrons and γ-rays in a criticality accident that occurred in Tokai-mura, Japan, in 1999. Materials and methods : The change with time of the frequency of chromosome aberrations in the three patients was examined using a new analysis to score drug-induced prematurely condensed ring chromosomes (PCC-R) and a conventional metaphase analysis. Results : The frequencies and cellular distributions of PCC-R, dicentrics and rings did not change significantly among the samples obtained at 9-48 h after the accident while the first depletion of lymphocytes occurred. The distributions of these aberrations in the cells of two patients showed a slight overdispersion compared with a Poisson distribution reflecting neutron and non-uniform exposures. The dose-response curve of rings paralleled that of dicentrics, but not PCC-R. The half-lives of PCC-R (8.5 months) and of rings (8.7 months) were shorter than that of dicentrics (13.5 months). Conclusions : In the three patients of the Tokai-mura accident, lymphocytes in the circulating and extravascular pools had reached equilibrium at 9h, and highly damaged lymphocytes did not selectively move away from the circulatory system during the first rapid depletion of lymphocytes after exposure. Data on the in vivo half-life of PCC-R as well as dicentrics and rings obtained in the present study may be useful for retrospective dosimetry.

Perceived risk of nuclear power and other risks during the last 25 years in Japan.

Abstract The present study described the results of three “fixed-point” surveys on perceived risk related to a list of social and individual risk events during 25 years in Japan. Female clerical staff and researchers were asked to rank 30 items related to various types of technologies and human activities according to their subjective judgments on the order of perceived magnitude of risk in 1983, 1992, and 2007. A similar survey was undertaken for Japanese citizens using web-based questionnaires in 2007. In general, the risk perceptions of the Japanese people, irrespective of gender, age, and occupation, have been uniform during the last 25 years. The female clerical staffs have consistently judged nuclear power as most risky during the last 25 years, whereas researchers’ judgment fluctuated with events such as the Chernobyl accident. The ranking of the risk of motor vehicles fell during the 25-y period, whereas those of health risks with food preservatives, x-rays, and antibiotics rose transiently in the 1992 survey. During the 15 years from 1992 to 2007, people tended to learn how to accommodate themselves to these technologies with low risks in exchange for high benefits, except in the case of nuclear power. Nuclear power was regarded as a high-risk item by the Japanese even before the Fukushima nuclear power plant accident in March 2011. This partly explains that the crisis inevitably provokes further high risk perception in Japan, although the overall health threat to the human population in Japan is estimated to be relatively limited so far.

Sister chromatid exchanges in ring chromosomes following X-irradiation of human lymphocytes.

Purpose: To examine whether X‐rays induce sister chromatid exchanges (SCE). Materials and methods: Peripheral lymphocytes irradiated in vitro or in vivo were cultured and treated with okadaic acid to generate premature chromosome condensation (PCC). When identical spreads were analysed using conventional Giemsa staining and pan‐centromeric fluorescence in situ hybridization painting, ring chromosomes were observed. Results: In PCC preparations, cells in the late G2 phase and late M phase were observed. In late M phase cells, 17–20% of ring chromosomes lacked one chromatid (single‐chromatid ring), irrespective of dose. Both the distribution patterns of centromeres in rings and intercentromere distances in dicentric rings indicate that a considerable number of single‐chromatid rings might be formed by SCE occurring in a chromosome‐type ring, thereby joining strands of two rings, followed by a transformation into one ring. These single‐chromatid rings were less stable in vivo than chromosome‐type rings. Conclusion: Single‐chromatid rings visualized clearly using PCC techniques indicate SCE in the respective rings. Contrary to the conventional SCE‐detecting technique, this approach does not require the use of bromodeoxyuridine, which itself leads to SCE. Some of the observed SCE might be secondary products resulting from the repair of radiation‐induced DNA damage, while others may be spontaneous.

Brief Communication: Chemically Induced Premature Chromosome Condensation in Human Fibroblast Cell Lines: Fundamental Study for Applications to the Biodosimetry of Local Exposure

The premature chromosome condensation (PCC) of human peripheral lymphocytes treated with inhibitors of protein phosphatase has been demonstrated to be an excellent tool for the estimation of high-dose whole-body exposure. To develop a new biodosimetry for local exposure, the cytogenetical reaction of human fibroblast lines to PCC inducers was examined and compared with that of lymphocytes. The efficiency of the induction by calyculin A was greater than that by okadaic acid in both cell types. Calyculin A induced PCC in 5-Gy-irradiated and unirradiated samples at almost the same frequency in the lymphocytes, whereas the efficacy was considerably lower in irradiated fibroblasts than in unirradiated ones. Calcium ionophore enhanced the induction of PCC in irradiated fibroblasts, although PCC frequencies were still much lower than those in the lymphocytes. The frequency of ring chromosomes observed in 2- and 5-Gy-irradiated fibroblasts was too low to be used as a marker for cytogenetic dosimetry, and that of excess fragments, scored as the observed chromosome number minus 46, might be substituted. The frequency of excess fragments for 2-, 5-, and 10-Gy-irradiated fibroblasts was less than 0.75, about 1 and a few per cell, respectively, although these values changed with the culture period. The prospects and limitations of the application of PCC techniques to fibroblasts are discussed.

Non-fluorescent chromosome painting using the peroxidase/diaminobenzidine (DAB) reaction

PURPOSE To develop and validate non-fluorescent chromosome painting for bright-field microscopy using the peroxidase/diaminobenzidine (DAB) reaction. MATERIALS AND METHODS Peripheral blood lymphocytes were taken from patients with uterine cancer who had received heavy-ion radiation therapy. Chromosome slides were treated with RNase and pepsin, denatured mildly, hybridized with a biotinylated DNA probe specific for whole-chromosome 4 and stained using the peroxidase/DAB reaction with an avidin-biotin amplification. The slides were analysed under a bright-field microscope and an atomic force microscope. The detection rate of chromosome aberrations by DAB painting was compared with that obtained by dual analysis of Giemsa staining and FISH painting. RESULTS When chromosomes 4 were painted, 11.5% of unstable aberrations were detected by DAB painting, while 10.8% of them were found by dual analysis of Giemsa staining and FISH painting. CONCLUSION A DAB painting method that can effectively detect rearranged aberrations was established. It has advantages over FISH painting: the preparations can be analysed by bright-field microscope, can be preserved permanently and are suitable for analysis by an automated system.

Rapid and reliable diagnosis of murine myeloid leukemia (ML) by FISH of peripheral blood smear using probe of PU. 1, a candidate ML tumor suppressor

BackgroundMurine myeloid leukemia (ML) provides a good animal model to study the mechanisms of radiation-induced leukemia in humans. This disease has been cytogenetically characterized by a partial deletion of chromosome 2 with G-banding. For the rapid diagnosis of ML, this study reports a FISH method using spleen cells and peripheral blood smears from ML mice exposed to gamma rays and neutrons with PU.1, a candidate ML tumor suppressor, as a probe.ResultsAmong mice that were tentatively diagnosed with ML by clinical findings and blood smear examination, 85% carried spleen cells showing the loss of PU.1 although the frequency of these abnormal cells varied among individuals. Mice with very low frequencies of cells showing the loss of one copy of PU.1 (one-PU.1 frequency) were later diagnosed pathologically not with ML but with blastic or eosinophilic leukemia. Some neutron-irradiated mice had cells showing translocated PU.1, although no pathological features differentiated these ML mice from ML mice expressing the simple loss of PU.1.The one-PU.1 frequency can be detected from spleen metaphase cells, spleen interphase cells, and blood smears. There was a good correlation between the one-PU.1 frequency in spleen metaphase cells and that in spleen interphase cells (r = 0.96) and between one-PU.1 frequency in spleen interphase cells and that in blood cells (r = 0.83).ConclusionThe FISH method was capable of detecting aberration of copy number of the PU.1 gene on murine chromosome 2, and using a peripheral blood smear is more practical and less invasive than conventional pathological diagnosis or the cytogenetic examination of spleen cells.

Investigation of new cytogenetic biomarkers specific to high-LET radiation using in vivo and in vitro exposed human lymphocytes

Purpose: To find detectable cytogenetic biomarkers that can offer information about the radiation quality of in vivo exposure retrospectively. Materials and methods: Chromosome-type aberrations of peripheral lymphocytes of uterine cancer patients that received internal γ- and external X-ray therapy or carbon beam therapy and of victims severely exposed to neutrons and γ-rays in a criticality accident that occurred in Tokai-mura, Japan were analysed. Data obtained from in vitro irradiation experiments using 60Co γ-rays and 10 MeV neutrons were compared with the in vivo exposure data. Results: The ratio of acentric rings to dicentric chromosomes (termed RaD ratio) and that of excess fragments to dicentrics (termed EfD ratio) showed significant (p < 0.05) differences between the two groups of cancer patients, and these ratios for accidental victims were in between the values of the two groups of cancer patients. The in vitro studies using doses equivalent to 1 – 3 Gy of γ-rays have confirmed that the EfD ratios were increased with the high LET (linear energy transfer) and RaD ratios decreased. Conclusion: The present data show that the RaD and EfD ratios can be used as cytogenetic biomarkers of exposure to high-LET radiation at least within a few years of exposure.

Investigation of Natural Radioactivity in a Monazite Processing Plant in Japan

Abstract Monazite is a naturally occurring radioactive material that is processed for use in a variety of domestic applications. At present, there is little information available on potential radiation doses experienced by people working with monazite. The ambient dose rate and activity concentration of natural radionuclides in raw materials, products, and dust in work sites as well as the 222Rn and 220Rn concentrations in work sites were measured in a monazite processing plant in Japan. Dose estimations for plant workers were also conducted. The activity concentration of the 238U series in raw materials and products for the monazite processing plant was found to be higher than the relevant values described in the International Atomic Energy Agency Safety Standards. The ambient dose rates in the raw material yard were higher than those in other work sites. Moreover, the activity concentrations of dust in the milling site were higher than those in other work sites. The 222Rn concentrations in all work sites were almost the same as those in regular indoor environments in Japan. The 220Rn concentrations in all work sites were much higher than those in regular indoor environments in Japan. The maximum value of the effective dose for workers was 0.62 mSv y−1, which is lower than the reference level range (1–20 mSv y−1) for abnormally high levels of natural background radiation published in the International Commission of Radiological Protection Publication 103.

Brief Communication: Allocyclic X Chromosome Visualized by Drug-Induced Premature Chromosome Condensation

Calyculin A, an inhibitor of serine/threonine protein phosphatases, can induce premature chromosome condensation (PCC) in human peripheral lymphocytes. In female lymphocytes treated with calyculin, one highly condensed chromosome per nucleus was frequently observed at early to middle S phase. When these PCC spreads were hybridized with a whole chromosome-painting probe for the X chromosome, one large spot and a cluster of small spots were observed in a cell. Judging from the Giemsa stained image, the former seemed to have finished DNA replication, while the latter was in the process of replication. Because this large spot was seldom observed in male PCC spreads, it was considered an inactive X chromosome. The inconsistency of this observation with earlier reports that the inactive X chromosome replicates later than autosomes and the active homolog is discussed.