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神崎 訓枝; 土肥 輝美
no journal, ,
地衣類は放射性セシウムを蓄積し、バイオモニタリングにも活用されているが、その蓄積能と種間差の有無や要因については不明点が多い。本研究では、自己組織化マップ(Self-Organizing Map)を用い、地衣類の放射性セシウム蓄積に関する非系統的な類似性に基づくクラスタリングを行った。ウメノキゴケ類の地衣類では、セシウムは下部組織に蓄積が認められ、その場所はメラニン様物質の沈着位置と一致したことから、福島第一原子力発電所事故に由来する放射性セシウム濃度とメラニン様物質の色調との関連を解析した。その結果、分類学的には遠い種でも、蓄積能とメラニン様物質の性質が類似する種が確認され、地衣類の応用可能性を広げる知見が得られた。
佐藤 達彦; 松谷 悠佑; 浜田 信行*
no journal, ,
In 2021, the International Commission on Radiation Units and Measurements (ICRU) and the International Commission on Radiological Protection (ICRP) jointly proposed the use of absorbed dose instead of equivalent dose for specifying dose limits to prevent tissue reactions (formerly referred to as deterministic effects). However, no recommendations have yet been provided on how to address exposure scenarios involving mixed radiation fields, including both low- and high-linear energy transfer (LET) radiations. To address these issues, ICRP recently launched a new task group on relative biological effectiveness (RBE) to review past studies on RBE and to discuss evaluation procedures for determining appropriate radiation weighting factors for both stochastic effects and tissue reactions. As part of this task group, we recently developed a microdosimetry-based model for evaluating the mean and uncertainty of RBE for various types of tissue reactions and applied it to skin reactions and diseases of the circulatory system (DCS). Our results suggest that the mean RBE values for these biological endpoints tend to be lower than the corresponding radiation weighting factors, thereby supporting the recent decision by ICRU and ICRP. At the meeting, we will present the details of the developed model, along with proposed future research directions aimed at contributing to ICRP's evaluation of radiation weighting factors for tissue reactions.
松谷 悠佑; 佐藤 達彦; 浜田 信行*
no journal, ,
ヒト水晶体上皮細胞(HLEC)の電離放射線に対する細胞応答は、放射線白内障のメカニズムを理解する上で極めて重要である。1950年、国際放射線防護委員会(ICRP)は白内障を放射線障害の一つとして特定し、その後、線量限度を複数回改訂し、2011年には線量限度の引き下げを勧告した。一方、HLECに対して利用可能なin vitro生物学的データは限られており、長期被ばく後の生物学的影響は依然として不明確となっている。そこで様々な線量率(1.82, 0.1, 0.033, 0.00461, 0.00081Gy/min)に対する光子線照射後のHLECの細胞生存率やDNA損傷応答など、基本的な細胞応答について発表する。本発表は、HLECへの生物学的影響の理解を深め、眼水晶体への放射線影響の評価に貢献するものである。
光安 優典*; 岡 壽崇; 高橋 温*; 木野 康志*; 奥津 賢一*; 関根 勉*; 山下 琢磨*; 清水 良央*; 千葉 美麗*; 鈴木 敏彦*; et al.
no journal, ,
野生ニホンザルの被ばく線量を計算で推定する場合、サルの捕獲地点の空間線量率と個体の年齢の情報だけを利用することがほとんどである。一方、捕獲個体の筋肉などをGe半導体検出器で測定すると体内にCs-134やCs-137が含まれているので、正しい推定にはこれらの放射性核種からの放射線による被ばくも考慮する必要がある。そこで本研究では、空間線量率と年齢から推定した被ばく線量に加え、体内のCsからの被ばくも考慮することで計算推定値がどのように変化するかを検討し、ESRを用いた被ばく線量の実測値との比較を行った。
廣瀬 エリ; 別部 光里*; 横谷 明徳*; 望月 陽人; 天野 由記
no journal, ,
Understanding microbial responses to ionizing radiation contributes to ensuring the long-term safety of underground geological disposal systems for radioactive waste. This study investigates the effects of gamma radiation (5-50 kGy) on microorganisms sampled from groundwater at depths of 140 m, 185 m, and 350 m, within the Horonobe Underground Research Laboratory, using boreholes. Viability assays showed that the number of live cells gradually decreased up to 15 kGy, while total cell counts decreased sharply up to 10 kGy but remained detectable at higher doses, indicating that some microbial populations have structural resilience to radiation. Consistent with this, gene analysis revealed dose-dependent changes in microbial community composition due to radiation exposure. Notably, ATP levels were not correlated with live or total cell counts. At each depth, the energy metabolism decreased significantly at 5 kGy, remained relatively stable between 5 and 10 kGy, and then gradually declined at higher doses. This suggests an ATP peak near 5 kGy, possibly related to energy demands for DNA repair processes, oxidative stress management, or metabolic changes. These findings suggest that certain radiation-resistant microorganisms can survive high-dose radiation exposure with sustained energy metabolism and may remain functionally active. Their continued energy metabolic activity under high-radiation may contribute to processes such as metal corrosion, gas generation, and radionuclide mobility, which are relevant to the long-term safety performance of geological disposal systems.
嵯峨 涼*; 岩森 賢大*; 松谷 悠佑
no journal, ,
放射線抵抗性を示すがん幹細胞(cancer stem cell, CSC)を考慮した細胞殺傷予測モデルにより、生物学的効果(生存率や腫瘍制御確率)をより正確に推定することが可能である。しかしながら、酸素濃度がCSCの放射線感受性に与える影響は依然として不明である。本研究では、酸素増感効果比(oxygen enhancement ratio, OER)とCSC割合を考慮した細胞殺傷予測モデル(integrated microdosimetric-kinetic (IMK)モデル)を使用してin vitro実験を行い、CSCと酸素効果の関係を分析した。細胞選別装置(BD FACS Aria)を使用して、前立腺がん細胞集団からのCSCを豊富に含むside population (SP)細胞を、Hoechst 33342排出能とDNA量に基づいて抽出した。SP細胞のDNA二本鎖切断(DSB)と細胞生存を、有酸素および低酸素条件の両方で測定した。その結果、他のmain population (MP)細胞と比較して、SP細胞ではDSBが減少する一方、生存率が増加することが示された。モデル解析では、MP細胞とSP細胞のOER値はそれぞれ1.42と1.30であることが示された。これらの結果は、CSCが豊富に含むSP細胞は、その固有の放射線抵抗性により酸素による放射線影響が低下することを示唆している。
江田 脩真*; 櫻井 滉也*; 小畑 結衣*; 廣瀬 エリ; 横谷 明徳*
no journal, ,
We are developing a new experimental method to investigate the efficiency of cellular repair of radiation-induced DNA damage by transfecting radiation-damaged EGFP plasmid DNA into non-irradiated cells and recovering the plasmid from the cells after a certain period of repair time. First, using non-irradiated plasmid as a sample, we introduced plasmid DNA into human breast cancer cells MCF7 by lipofection, and after a certain time had passed, we extracted the nuclear DNA from all cells, including those expressing EGFP, using a standard kit. The obtained DNA samples were subjected to agarose gel electrophoresis, and bands located at positions different from genomic DNA were sliced out and recovered. The sample was confirmed to be EGFP plasmid via real-time PCR. This result suggests that closed circular EGFP plasmid DNA may exist independently of genomic DNA within the cell nucleus. We are also investigating the in vivo recombination potential of enzymatically linearized EGFP plasmid DNA as a model for double-strand breaks, and will discuss these results as well.
野口 実穂*; 横谷 明徳*; 鈴木 啓司*; 廣瀬 エリ; Liu, C.*; 平山 亮一*
no journal, ,
Radiation-induced senescence is caused by irreversible growth arrest due to a sustained response to severe damage to nuclear DNA. Radiation deposits energy randomly in cells, and it is thought to cause severe damage to some organelles other than the nucleus, such as mitochondria, which are distributed throughout the cell. In senescent cells that are capable of perpetual survival, it is speculated that mitochondrial homeostasis may be maintained to a certain degree by some mechanism. However, the mechanisms involved in the maintenance of mitochondrial homeostasis in senescent cells are not well understood. In this study, we focus on mitophagy, mitochondrial morphology, and the mitochondrial UPR, and elucidate how these multiple systems interact to contribute to maintaining mitochondrial homeostasis in radiation-induced senescent cells. We investigated the time-dependent induction of mitophagy and changes in mitochondrial morphology. In immortalized human fibroblasts irradiated with 20 Gy of X-rays, the mitophagy adaptor protein NDP52 accumulated in punctate forms on mitochondria within several hours after irradiation, persisted for two days, and then disappeared. At the same time, mitochondrial morphology was examined based on the distribution and accumulation of the mitochondrial outer membrane protein TOM20. For 24 to 48 hours after irradiation, mitochondria were fragmented in almost all cells, but 3 days after irradiation, the number of cells with fused mitochondria increased, and after 5 days postirradiation, almost all cells showed fused mitochondria. These results suggest that mitochondrial homeostasis in radiation-induced senescent cells may be maintained by the removal of abnormal mitochondria by mitophagy followed by equilibration of normal mitochondrial components through fusion. Next, we investigated the nuclear translocation of transcription factor, ATF5, which is related to induction of mitochondrial UPR. We confirmed that ATF5 was diffused throughout the cytoplasm before irradiation, at 24 hours after irradiation, it translocated to the nucleus and formed foci, and these foci were observed for up to 7 days. In the future, we plan to investigate the relationship between ATF5 nuclear translocation and mitochondrial morphology, and clarify the role that ATF5 nuclear translocation plays in maintaining mitochondrial homeostasis in radiation induced senescent cells.
岡 壽崇
no journal, ,
After the Tokyo Electric Power Company Holdings' Fukushima Daiichi Nuclear Power Station accident, radionuclides were released into the environment. From the viewpoint of biological effects of radiation from radionuclides, dosimetry of wild animals in Fukushima Prefecture has attracted public concern. In this work, we estimated the radiation dose from the teeth of the wild animals using electron spin resonance (ESR) spectrometer. CO
radicals generated in tooth enamel by radiation have a very long lifetime (10
years) and are used as indicators for estimating individual radiation doses. Teeth of large Japanese field mice and wild Japanese macaques captured in the contaminated area of Fukushima Prefecture were collected and subjected to dose estimation. Teeth were washed, ground into granules, and then enamel and dentine were separated using the heavy-liquid separation method. Doses for young and old groups of Japanese field mice were estimated to be 
57 mGy and 270 mGy, respectively. The dose estimated by ESR for the older group was much higher than that estimated from environmental radiation levels at the capture site and from the accumulation of 
Cs in the mice. This discrepancy may be due to the tendency of older individuals to move farther away from the capture site, thus, dose did not reflect the environmental conditions at the capture location. On the other hand, dose estimation for 18 Japanese macaques suggests that the maximum environmental radiation dose they received was 300 mGy.