Yasushi Mariya

Activity concentrations of environmental samples collected in Fukushima Prefecture immediately after the Fukushima nuclear accident

Radionuclide concentrations in environmental samples such as surface soils, plants and water were evaluated by high purity germanium detector measurements. The contribution rate of short half-life radionuclides such as 132I to the exposure dose to residents was discussed from the measured values. The highest values of the 131I/137Cs activity ratio ranged from 49 to 70 in the environmental samples collected at Iwaki City which is located to the south of the F1-NPS. On the other hand, the 132I/131I activity ratio in the same environmental samples had the lowest values, ranging from 0.01 to 0.02. By assuming that the 132I/131I activity ratio in the atmosphere was equal to the ratio in the environmental samples, the percent contribution to the thyroid equivalent dose by 132I was estimated to be less than 2%. Moreover, the contribution to the thyroid exposure by 132I might be negligible if 132I contamination was restricted to Iwaki City.

Estimation of internal exposure of the thyroid to 131I on the basis of 134Cs accumulated in the body among evacuees of the Fukushima Daiichi Nuclear Power Station accident

Namie Town was heavily contaminated by the Fukushima Daiichi Nuclear Power Station accident. The thyroid equivalent dose for residents who lived in Namie was estimated using results of whole body counting examinations which were carried out by the Japan Atomic Energy Agency a few months after the nuclear accident. Photon peaks of (131)I and (134)Cs were previously measured by the authors using a NaI(Tl) scintillation spectrometer and that information was used to estimate the (131)I/(134)Cs activity ratio of total intake in the present study. The maximum values of (131)I/(134)Cs activity ratio corresponding to thyroid uptake factors of 0.3, 0.1 and 0.03 were evaluated to be 0.9, 2.6 and 8.7, respectively. The maximum value of the (131)I/(134)Cs activity ratio was used to obtain the most conservative thyroid equivalent dose estimation. The maximum internal exposure of the thyroid to (131)I on the basis of (134)Cs accumulated in the body measured by the whole body counter was estimated to be 18mSv. This value was much smaller than 50mSv that the International Atomic Energy Agency recommends as the dose at which exposed persons should take stable iodine tablets.

Correlations between the detection of stress‐associated hormone/oxidative stress markers in umbilical cord blood and the physical condition of the mother and neonate

Aim:  The objective of this study was to assess the correlations between the detection of stress‐associated hormone/oxidative stress markers in umbilical cord blood (CB) and the physical condition of the mother and neonate.

Impact of time interval and dose rate on cell survival following low-dose fractionated exposures

Abstract Enhanced cell lethality, also known as hyper-radiosensitivity, has been reported at low doses of radiation (≤0.5 Gy) in various cell lines, and is expected to be an effective cancer therapy. We conducted this study to examine the impact of time interval and dose rate of low-dose fractionated exposures with a short time interval. We evaluated the cell-survival rates of V79 and A549 cells using clonogenic assays. We performed fractionated exposures in unit doses of 0.25, 0.5, 1.0 and 2.0 Gy. We exposed the cells to 2 Gy of X-rays (i) at dose-rates of 1.0, 1.5 and 2.0 Gy/min at 1-min intervals and (ii) at a dose-rate of 2.0 Gy/min at 10-s, 1-min and 3-min intervals by fractionated exposures. Apoptosis and cell cycle analyses were also evaluated in the fractionated exposures (unit dose 0.25 Gy) and compared with single exposures by using flow cytometry. Both cell-type survival rates with fractionated exposures (unit dose 0.25 Gy) with short time intervals were markedly lower than those for single exposures delivering the same dose. When the dose rates were lower, the cytotoxic effect decreased compared with exposure to a dose-rate of 2.0 Gy/min. On the other hand, levels of apoptosis and cell cycle distribution were not significantly different between low-dose fractionated exposures and single exposures in either cell line. These results indicate that a stronger cytotoxic effect was induced with low-dose fractionated exposures with a short time interval for a given dose due to the hyper-radiosensitivity phenomenon, suggesting that dose rates are important for effective low-dose fractionated exposures.

Serum miR-375-3p increase in mice exposed to a high dose of ionizing radiation

Exposure to high-doses of ionizing radiation (IR) leads to development of a strong acute radiation syndrome (ARS) in mammals. ARS manifests after a latency period and it is important to develop fast prognostic biomarkers for its early detection and assessment. Analysis of chromosomal aberrations in peripheral blood lymphocytes is the gold standard of biological dosimetry, but it fails after high doses of IR. Therefore, it is important to establish novel biomarkers of exposure that are fast and reliable also in the high dose range. Here, we investigated the applicability of miRNA levels in mouse serum. We found significantly increased levels of miR-375-3p following whole body exposure to 7 Gy of X-rays. In addition, we analyzed their levels in various organs of control mice and found them to be especially abundant in the pancreas and the intestine. Following a dose of 7 Gy, extensive cell death occurred in these tissues and this correlated negatively with the levels of miR-375-3p in the organs. We conclude that high expressing tissues of miR-375-3p may secrete this miRNA in serum following exposure to 7 Gy. Therefore, elevated miR-375-3p in serum may be a predictor of tissue damage induced by exposure to a high radiation dose.

Application of cell sorting for enhancing the performance of the cytokinesis-block micronucleus assay

Among the numerous methods available to assess genotoxicity, the cytokinesis-block micronucleus (CBMN) assay is very popular due its relative simplicity and power to detect both clastogenic and aneugenic compounds. A problem with the CBMN assay is that all DNA damaging agents also inhibit the ability of cells to progress through mitosis, leading to a low number of binucleated cells (BNCs). One method to resolve this issue is to ensure a sufficient proportion of BNCs in the samples. In the current study, the applicability of a cell sorting system capable of isolating cell fractions containing abundant BNCs was investigated. Furthermore, to investigate the relationship between the cell division delay due to radiation exposure and the generation of BNCs and micronuclei (MN), we assessed a series of lag times between radiation exposure and addition of cytochalasin-B (Cyt-B). Cells from the human chronic myelogenous leukemia cell line K562 were exposed to X-rays (2 Gy and 4 Gy), and Cyt-B was subsequently added at 0, 6 and 12 h following irradiation. After treatment with Cyt-B for 24 h, the percentage of BNCs, the MN frequency and the cell cycle distribution were analyzed. In addition, cells displaying the DNA contents corresponding to BNCs were isolated and analyzed. The results indicate that applying the cell sorter to the CBMN assay increased the percentage of BNCs compared with the standard method. Thus, this technique is a promising way of enhancing the capacity of the CBMN assay.

Mental and physical stress of the Fukushima disaster evacuees as estimated by the measurement of urinary 8‑hydroxy‑2'‑deoxyguanosine

Following the accident at the Fukushima Daiichi Nuclear Power Plant in 2011, a number of evacuees were forced to live in temporary housing and suffered mental and physical stress. However, few reports have used objective or quantitative indicators to determine the evacuees level of stress. The aim of the present study was to serially estimate the mental and physical stress of the evacuees from 2013 to 2015 by using the oxidative stress marker, urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG). A total of 773 evacuees from Namie town in Fukushima prefecture participated in the study. In the first year, 486 evacuees participated (age, 62.8±18.2 years; male/female, 217/269). Of these, 127 continually participated in the study for 3 years (age, 69.5±13.5 years; males/female 52/75) and 18.1% had no chronic disease after the first year. Urine samples were collected once per year. Urinary 8-OHdG was measured using immunochromatography and corrected by the concentration of urinary creatinine. For all the participants examined each year, mean values of urinary 8-OHdG significantly increased over time. For the 127 continual participants, mean values of urinary 8-OHdG were significantly higher in 2014 and 2015 than those in 2013. Age, gender and presence of chronic disease did not significantly influence the 8-OHdG values, suggesting that the stress level of the evacuees was not associated with these factors. The stress level of the individuals increased with the length of time spent living in the temporary housing. The evacuees in radiation disasters have different stressors from other natural disasters, which may accelerate mental and physical stress.

Estimation of effective doses in pediatric X‑ray computed tomography examination

X-ray computed tomography (CT) images are used for diagnostic and therapeutic purposes in various medical disciplines. In Japan, the number of facilities that own diagnostic CT equipment, the number of CT examinations and the number of CT scanners increased by ~1.4-fold between 2005 and 2011. CT operators (medical radiological technologists, medical physicists and physicians) must understand the effective doses for examinations at their own institutions and carefully approach each examination. In addition, the patients undergoing the examination (as well as his/her family) must understand the effective dose of each examination in the context of the cumulative dose. In the present study, the numbers of pediatric patients (aged 0-5 years) and total patients who underwent CT at Hirosaki University Hospital (Hirosaki, Japan) between January 2011 and December 2013 were surveyed, and effective doses administered to children aged 0, 1 and 5 years were evaluated. Age- and region-specific conversion factors and dose-length products obtained from the CT scanner were used to estimate the effective doses. The numbers of CT examinations performed in 2011, 2012 and 2013 were 16,662, 17,491 and 17,649, respectively, of which 613 (1.2%) of the overall total involved children aged 0-5 years. The estimated effective doses per examination to children aged 0, 1 and 5 years were 6.3±4.8, 4.9±3.8 and 2.7±3.0 mSv, respectively. This large variation was attributed to several factors associated with scan methods and ranges in actual setting. In conclusion, the requirement for individual patient prospective exposure management systems and estimations of low-dose radiation exposure should be considered in light of the harmful effects of exposure.

Cytogenetic dosimetry by micronucleus assay using peripheral blood cells is modified by thyroid hormones

Cytokinesis-block micronucleus (CBMN) assay is a convenient and easy method of radiation biodosimetry that uses peripheral blood (PB) cells. However, for micronuclei (MN) frequency induced by ionising radiation, a dose-response relationship in abnormal condition, such as in cancer patients, has not been assessed. To clarify the difference between the dose-response curve generated by the CBMN assay in conditions when thyroid hormone levels were normal and during thyroid hormone withdrawal (THW) prior to (131)I treatment, 12 thyroid cancer patients who underwent thyroidectomy were studied. The collected PB mononuclear cells were exposed to 0.5-3.0 Gy X-ray irradiation. Under normal conditions, dose dependency and independency of MN frequency were observed in 92 % and 8 %, respectively. In contrast, during THW, the number of patients who showed dose independency significantly increased to 42 % in comparison with control. Furthermore, a higher concentration of serum thyroglobulin in dose-independent patients was observed. These results suggest that MN frequency in cytogenetic dosimetry is affected by thyroid hormones.