Fluorescence in situ hybridization analysis of chromosomal aberrations in mouse splenocytes at one- and two-months after total body exposure to iron-56 (Fe) ion particles or X-rays.

High atomic number and energy (HZE) particles such as iron-56 (Fe) ions are a major contributor to health risks in long-term manned space exploration. The aim of this study is to understand radiation-induced differential genotoxic effects between HZE particles and low linear energy transfer (LET) photons. C57BL/6J Jms female mice of 8 weeks old were exposed to total body irradiation of accelerated Fe-particles with a dose ranging from 0.1 to 3.0 Gy or of X-rays with a dose ranging from 0.1 to 5.0 Gy. Chromosomal aberrations (CAs) in splenocytes were examined by fluorescence in situ hybridization at 1- and 2-months after exposure. Clonal expansions of cells with CAs were found to be induced only by X-rays but not by Fe-particles. Dose-dependent increase in the frequencies of stable-type CAs was observed at 1- as well as 2-months after exposure to both radiation types. The frequencies of stable-type CAs in average were much higher in mice exposed to X-rays than those to Fe-particles and did not change significantly between 1- and 2-months after exposure to both radiation types. On the other hand, the frequencies of unstable-type CAs induced by X-rays and Fe-particles were not much different, and they appeared to decrease with time from 1- to 2-months after exposure. These results suggested that larger fraction of stable-type CAs induced by Fe-particles might be non-transmissible than those by X-rays because of some associating lethal alterations on themselves or on other chromosomes in the same cells and that these cells might be removed by 1-month after Fe-TBI. We also demonstrated that exposure to Fe-particles induced insertions at relatively higher frequency to other stable-type CAs than X-rays. Our findings suggest that insertions can be used as indicators of past exposure to high-LET particle radiation.

Enhanced Effects of Chronic Restraint-Induced Psychological Stress on Total Body Fe-Irradiation-Induced Hematopoietic Toxicity in Trp53-Heterozygous Mice.

Humans are exposed to both psychological stress (PS) and radiation in some scenarios such as manned deep-space missions. It is of great concern to verify possible enhanced deleterious effects from such concurrent exposure. Pioneer studies showed that chronic restraint-induced PS (CRIPS) could attenuate Trp53 functions and increase gamma-ray-induced carcinogenesis in Trp53-heterozygous mice while CRIPS did not significantly modify the effects on X-ray-induced hematopoietic toxicity in Trp53 wild-type mice. As high-linear energy transfer (LET) radiation is the most important component of space radiation in causing biological effects, we further investigated the effects of CRIPS on high-LET iron-particle radiation (Fe)-induced hematopoietic toxicity in Trp53-heterozygous mice. The results showed that CRIPS alone could hardly induce significant alteration in hematological parameters (peripheral hemogram and micronucleated erythrocytes in bone marrow) while concurrent exposure caused elevated genotoxicity measured as micronucleus incidence in erythrocytes. Particularly, exposure to either CRISP or Fe-particle radiation at a low dose (0.1 Gy) did not induce a marked increase in the micronucleus incidence; however, concurrent exposure caused a significantly higher increase in the micronucleus incidence. These findings indicated that CRIPS could enhance the deleterious effects of high-LET radiation, particularly at a low dose, on the hematopoietic toxicity in Trp53-heterozygous mice.

Recombinant cell-detecting RaDR-GFP in mice reveals an association between genomic instability and radiation-induced-thymic lymphoma.

In this study, we aimed to investigate how homologous recombinant (HR)-related genomic instability is involved in ionizing radiation (IR)-induced thymic lymphoma in mice. We divided five-week-old Rosa26 Direct Repeat-GFP (RaDR-GFP) transgenic mice into non-IR control and IR groups and exposed the mice in the IR group to a 7.2 Gy dose of γ-rays, delivered in 1.8 Gy fractions, once a week for four weeks. We then estimated mouse survival and recorded their body, thymus, and spleen weights. The frequency of HR events in the chromosomes of the thymus, bone marrow, and spleen cells and the phenotype of thymic lymphoma cells were analyzed using fluorescence-activated cell sorting (FACS). We found that most mice in the IR group developed thymic lymphoma, their survival rate decreasing to 20% after 180 days of IR exposure, whereas no mice died in the non-IR control group until day 400. The thymus and spleen weighed significantly more in the IR-4-month group than that in the non-IR group; however, we observed no significant differences between the body weights of the control and IR mice. FACS analysis indicated that the frequency of HR events significantly increased at two and four months after the last IR dose in the bone marrow and thymus cells, but not in the spleen cells of RaDR-GFP transgenic mice, suggesting that recombinant cells accumulated in the thymus upon IR exposure. This suggests that IR induces genome instability, revealed as increased HR, that drives the development of thymic lymphoma. Additionally, phenotypic analysis of lymphoma cells showed an increase in the CD4-/CD8+ (CD8SP) cell population and a decrease in the CD4+/CD8- (CD4SP) cell population in the IR-4-month group compared to that in the non-IR group, indicating that IR induces an aberrant cell phenotype characteristic of lymphoma. In conclusion, we observed a significant increase in HR events and abnormal phenotype in thymic lymphoma cells at two and four months after IR exposure in both the thymus and bone marrow tissues, suggesting that genomic instability is involved in the early stages of thymic lymphomagenesis. Our study indicates that HR-visualizing RaDR-GFP transgenic mice can help explore the links between the molecular mechanisms of genome instability and IR-induced tumorigenesis.

Mitigation of Iron Irradiation-Induced Genotoxicity and Genomic Instability by Postexposure Dietary Restriction in Mice.

Background and Purpose. Postexposure onset of dietary restriction (DR) is expected to provide therapeutic nutritional approaches to reduce health risk from exposure to ionizing radiation (IR) due to such as manned space exploration, radiotherapy, or nuclear accidents as IR could alleviate radiocarcinogenesis in animal models. However, the underlying mechanisms remain largely unknown. This study is aimed at investigating the effect from postexposure onset of DR on genotoxicity and genomic instability (GI) induced by total body irradiation (TBI) in mice. Materials and Methods. Mice were exposed to 2.0 Gy of accelerated iron particles with an initial energy of 500 MeV/nucleon and a linear energy transfer (LET) value of about 200 keV/µm. After TBI, mice were either allowed to free access to a standard laboratory chow or treated under DR (25% cut in diet). Using micronucleus frequency (MNF) in bone marrow erythrocytes, induction of acute genotoxicity and GI in the hematopoietic system was, respectively, determined 1 and 2 months after TBI. Results and Conclusions. TBI alone caused a significant increase in MNF while DR alone did not markedly influence the MNF. DR induced a significant decrease in MNF compared to the treatment by TBI alone. Results demonstrated that postexposure onset of DR could relieve the elevated MNF induced by TBI with high-LET iron particles. These findings indicated that reduction in acute genotoxicity and late GI may be at least a part of the mechanisms underlying decreased radiocarcinogenesis by DR.

Altered Induction of Reactive Oxygen Species by X-rays in Hematopoietic Cells of C57BL/6-Tg (CAG-EGFP) Mice.

Previous work pointed to a critical role of excessive production of reactive oxygen species (ROS) in increased radiation hematopoietic death in GFP mice. Meanwhile, enhanced antioxidant capability was not demonstrated in the mouse model of radio-induced adaptive response (RAR) using rescue of radiation hematopoietic death as the endpoint. ROS induction by ex vivo X-irradiation at a dose ranging from 0.1 to 7.5 Gy in the nucleated bone marrow cells was comparatively studied using GFP and wild type (WT) mice. ROS induction was also investigated in the cells collected from mice receiving a priming dose (0.5 Gy) efficient for RAR induction in WT mice. Significantly elevated background and increased induction of ROS in the cells from GFP mice were observed compared to those from WT mice. Markedly lower background and decreased induction of ROS were observed in the cells collected from WT mice but not GFP mice, both receiving the priming dose. GFP overexpression could alter background and induction of ROS by X-irradiation in hematopoietic cells. The results provide a reasonable explanation to the previous study on the fate of cells and mice after X-irradiation and confirm enhanced antioxidant capability in RAR. Investigations involving GFP overexpression should be carefully interpreted.

Evaluation of sodium orthovanadate as a radioprotective agent under total-body irradiation and partial-body irradiation conditions in mice.

PURPOSE: Our previous study indicated that sodium orthovanadate (vanadate), a strong inhibitor of p53, effectively suppressed the lethality from the hematopoietic (HP) and gastrointestinal (GI) syndromes after 12 Gy total-body irradiation (TBI) in mice. This conclusion, however, was inconsistent with the fact that p53 plays a radioprotective role in the intestinal epithelium. The death after TBI of around 12 Gy was attributed to a combined effect of HP and GI syndromes. To verify the effect from prophylactic administration of p53 inhibitor on protection of HP and GI syndromes, in this study, the radioprotective effects from vanadate were investigated in TBI and lower half-body irradiation (partial-body irradiation: PBI) mouse models. METHODS: Female ICR mice were given a single injection of vanadate or vehicle, followed by a lethal dose of TBI or PBI. Radioprotective effects of vanadate against the irradiations were evaluated by analyzing survival rate, body weight, hematopoietic parameters, and histological changes in the bone marrow and intestinal epithelium. RESULTS: TBI-induced HP syndrome was effectively suppressed by vanadate treatment. After TBI, the vanadate-treated mice retained better bone marrow cellularity and showed markedly higher survival rate compared to the vehicle-treated animals. In contrast, vanadate did not relieve loss of intestinal crypts and failed to rescue mice from GI death after PBI. CONCLUSION: Vanadate is a p53 inhibitor that has been shown to be beneficial as a radiation protective agent against HP but was not effective in protecting against acute GI radiation injury.

Synergistic Effects of Chronic Restraint-Induced Stress and Low-Dose 56Fe-particle Irradiation on Induction of Chromosomal Aberrations in Trp53-Heterozygous Mice.

Astronauts can develop psychological stress (PS) during space flights due to the enclosed environment, microgravity, altered light-dark cycles, and risks of equipment failure or fatal mishaps. At the same time, they are exposed to cosmic rays including high atomic number and energy (HZE) particles such as iron-56 (Fe) ions. Psychological stress or radiation exposure can cause detrimental effects in humans. An earlier published pioneering study showed that chronic restraint-induced psychological stress (CRIPS) could attenuate Trp53 functions and increase carcinogenesis induced by low-linear energy transfer (LET) γ rays in Trp53-heterozygous (Trp53+/-) mice. To elucidate possible modification effects from CRIPS on high-LET HZE particle-induced health consequences, Trp53+/- mice were received both CRIPS and accelerated Fe ion irradiation. Six-week-old Trp53+/- C57BL/6N male mice were restrained 6 h per day for 28 consecutive days. On day 8, they received total-body Fe-particle irradiation (Fe-TBI, 0.1 or 2 Gy). Metaphase chromosome spreads prepared from splenocytes at the end of the 28-day restraint regimen were painted with the fluorescence in situ hybridization (FISH) probes for chromosomes 1 (green), 2 (red) and 3 (yellow). Induction of psychological stress in our experimental model was confirmed by increase in urinary corticosterone level on day 7 of restraint regimen. Regardless of Fe-TBI, CRIPS reduced splenocyte number per spleen at the end of the 28-day restraint regimen. At 2 Gy, Fe-TBI alone induced many aberrant chromosomes and no modifying effect was detected from CRIPS on induction of aberrant chromosomes. Notably, neither Fe-TBI at 0.1 Gy nor CRIPS alone induced any increase in the frequency of aberrant chromosomes, while simultaneous exposure resulted in a significant increase in the frequency of chromosomal exchanges. These findings clearly showed that CRIPS could enhance the frequency of chromosomal exchanges induced by Fe-TBI at a low dose of 0.1 Gy.

Reduced High-Dose Radiation-Induced Residual Genotoxic Damage by Induction of Radioadaptive Response and Prophylactic Mild Dietary Restriction in Mice.

Radioadaptive response (RAR) describes a phenomenon in a variety of in vitro and in vivo systems that a low-dose of priming ionizing radiation (IR) reduces detrimental effects of a subsequent challenge IR at higher doses. Among in vivo investigations, studies using the mouse RAR model (Yonezawa Effect) showed that RAR could significantly extenuate high-dose IR-induced detrimental effects such as decrease of hematopoietic stem cells and progenitor cells, acute radiation hematopoietic syndrome, genotoxicity and genomic instability. Meanwhile, it has been demonstrated that diet intervention has a great impact on health, and dietary restriction shows beneficial effects on numerous diseases in animal models. In this work, by using the mouse RAR model and mild dietary restriction (MDR), we confirmed that combination of RAR and MDR could more efficiently reduce radiogenotoxic damage without significant change of the RAR phenotype. These findings suggested that MDR may share some common pathways with RAR to activate mechanisms consequently resulting in suppression of genotoxicity. As MDR could also increase resistance to chemotherapy and radiotherapy in normal cells, we propose that combination of MDR, RAR, and other cancer treatments (i.e., chemotherapy and radiotherapy) represent a potential strategy to increase the treatment efficacy and prevent IR risk in humans.

Protective Effects of p53 Regulatory Agents Against High-LET Radiation-Induced Injury in Mice.

Radiation damage to normal tissues is one of the most serious concerns in radiation therapy, and the tolerance dose of the normal tissues limits the therapeutic dose to the patients. p53 is well known as a transcription factor closely associated with radiation-induced cell death. We recently demonstrated the protective effects of several p53 regulatory agents against low-LET X- or γ-ray-induced damage. Although it was reported that high-LET heavy ion radiation (>85 keV/µm) could cause p53-independent cell death in some cancer cell lines, whether there is any radioprotective effect of the p53 regulatory agents against the high-LET radiation injury in vivo is still unclear. In the present study, we verified the efficacy of these agents on bone marrow and intestinal damages induced by high-LET heavy-ion irradiation in mice. We used a carbon-beam (14 keV/µm) that was shown to induce a p53-dependent effect and an iron-beam (189 keV/µm) that was shown to induce a p53-independent effect in a previous study. Vanadate significantly improved 60-day survival rate in mice treated with total-body carbon-ion (p < 0.0001) or iron-ion (p < 0.05) irradiation, indicating its effective protection of the hematopoietic system from radiation injury after high-LET irradiation over 85 keV/µm. 5CHQ also significantly increased the survival rate after abdominal carbon-ion (p < 0.02), but not iron-ion irradiation, suggesting the moderate relief of the intestinal damage. These results demonstrated the effectiveness of p53 regulators on acute radiation syndrome induced by high-LET radiation.

Altered Response to Total Body Irradiation of C57BL/6-Tg (CAG-EGFP) Mice.

Application of green fluorescent protein (GFP) in a variety of biosystems as a unique bioindicator or biomarker has revolutionized biological research and made groundbreaking achievements, while increasing evidence has shown alterations in biological properties and physiological functions of the cells and animals overexpressing transgenic GFP. In this work, response to total body irradiation (TBI) was comparatively studied in GFP transgenic C57BL/6-Tg (CAG-EGFP) mice and C57BL/6 N wild type mice. It was demonstrated that GFP transgenic mice were more sensitive to radiation-induced bone marrow death, and no adaptive response could be induced. In the nucleated bone marrow cells of GFP transgenic mice exposed to a middle dose, there was a significant increase in both the percentage of cells expressing pro-apoptotic gene Bax and apoptotic cell death. While in wild type cells, lower expression of pro-apoptotic gene Bax and higher expression of anti-apoptotic gene Bcl-2, and significant lower induction of apoptosis were observed compared to GFP transgenic cells. Results suggest that presence of GFP could alter response to TBI at whole body, cellular and molecular levels in mice. These findings indicate that there could be a major influence on the interpretation of the results obtained in GFP transgenic mice.

Space Radiation Biology for "Living in Space".

Space travel has advanced significantly over the last six decades with astronauts spending up to 6 months at the International Space Station. Nonetheless, the living environment while in outer space is extremely challenging to astronauts. In particular, exposure to space radiation represents a serious potential long-term threat to the health of astronauts because the amount of radiation exposure accumulates during their time in space. Therefore, health risks associated with exposure to space radiation are an important topic in space travel, and characterizing space radiation in detail is essential for improving the safety of space missions. In the first part of this review, we provide an overview of the space radiation environment and briefly present current and future endeavors that monitor different space radiation environments. We then present research evaluating adverse biological effects caused by exposure to various space radiation environments and how these can be reduced. We especially consider the deleterious effects on cellular DNA and how cells activate DNA repair mechanisms. The latest technologies being developed, e.g., a fluorescent ubiquitination-based cell cycle indicator, to measure real-time cell cycle progression and DNA damage caused by exposure to ultraviolet radiation are presented. Progress in examining the combined effects of microgravity and radiation to animals and plants are summarized, and our current understanding of the relationship between psychological stress and radiation is presented. Finally, we provide details about protective agents and the study of organisms that are highly resistant to radiation and how their biological mechanisms may aid developing novel technologies that alleviate biological damage caused by radiation. Future research that furthers our understanding of the effects of space radiation on human health will facilitate risk-mitigating strategies to enable long-term space and planetary exploration.

Diallyl Disulfide Mitigates DNA Damage and Spleen Tissue Effects After Irradiation.

BACKGROUND Several factors found in foods are beneficial to human health and they may contribute to radiation protection. Taking food factors could be an easy way to reduce the effects of radiation after nuclear accidents, as well as secondary radiation risks after cancer radiotherapy or space missions. Here, diallyl disulfide (DADS), a component of garlic oil, was studied for its ability to mitigate radiation damage. MATERIAL AND METHODS We investigated the effects of DADS on micronucleus (MN) formation and apoptosis in HepG2 cells by use of 4-Gy X-ray irradiation. We also assessed the effects of DADS on radiation damage in vivo by evaluating MN formation in bone marrow cells in mice (BALB/c, 8-week-old females) after oral intake of DADS prior to irradiation with 4 Gy. Several tissue effects were also investigated. RESULTS The presence of DADS inhibited MN formation, whereas DADS had no influence on the radiation-induced inhibition of cell cycle progression in HepG2 cells. An increase in apoptosis in HepG2 cells was induced after irradiation, and this effect was stronger in the presence of DADS than in its absence. In mice, when DADS was administered daily for 3 days prior to irradiation, MN formation in irradiated mice was decreased. The decrease in MN formation in mice was greater with 0.5% DADS compared to 1% DADS. Moreover, an increase in spleen weight observed 3 weeks after irradiation was suppressed in mice administered DADS. CONCLUSIONS DADS is a potential radiation-protective agent that effectively mitigates DNA damage, and its effects in the spleen observed after irradiation may be related to inflammation and carcinogenesis.

Reduction of Delayed Homologous Recombination by Induction of Radioadaptive Response in RaDR-GFP Mice (Yonezawa Effect): An Old Player With a New Role.

Radiotherapy (RT) treats cancer effectively with high doses of ionizing radiation (IR) to killing cancer cells and shrinking tumors while bearing the risk of developing different side effects, including secondary cancer, which is most concerning for long-term health consequences. Genomic instability (GI) is a characteristic of most cancer cells, and IR-induced GI can manifest as delayed homologous recombination (HR). Radioadaptive response (RAR) is capable of reducing genotoxicity, cell transformation, mutation, and carcinogenesis, but the rational evidence describing its contributions to the reduction of radiation risk, in particular, carcinogenesis, remains fragmented. In this work, to investigate the impact of RAR on high-dose, IR-induced GI measured as delayed HR, the frequency of recombinant cells was comparatively studied under RAR-inducible and -uninducible conditions in the nucleated cells in hematopoietic tissues (bone marrow and spleen) using the Rosa26 Direct Repeat-green fluorescent protein (RaDR-GFP) homozygote mice. Results demonstrated that the frequency of recombinant cells was significantly lower in hematopoietic tissues under RAR-inducible condition. These findings suggest that reduction in delayed HR may be at least a part of the mechanisms underlying decreased carcinogenesis by RAR, and application of RAR would contribute to a more rigorous and scientifically grounded system of radiation protection in RT.

Radiation-Induced Reactions in The Liver - Modulation of Radiation Effects by Lifestyle-Related Factors.

Radiation has a wide variety of effects on the liver. Fibrosis is a concern in medical fields as one of the acute effects of high-dose irradiation, such as with cancer radiotherapies. Cancer is also an important concern following exposure to radiation. The liver has an active metabolism and reacts to radiations. In addition, effects are modulated by many environmental factors, such as high-calorie foods or alcohol beverages. Adaptations to other environmental conditions could also influence the effects of radiation. Reactions to radiation may not be optimally regulated under conditions modulated by the environment, possibly leading to dysregulation, disease or cancer. Here, we introduce some reactions to ionizing radiation in the liver, as demonstrated primarily in animal experiments. In addition, modulation of radiation-induced effects in the liver due to factors such as obesity, alcohol drinking, or supplements derived from foods are reviewed. Perspectives on medical applications by modulations of radiation effects are also discussed.

Increased Hematopoietic Stem Cells/Hematopoietic Progenitor Cells Measured as Endogenous Spleen Colonies in Radiation-Induced Adaptive Response in Mice (Yonezawa Effect).

The existence of radiation-induced adaptive response (AR) was reported in varied biosystems. In mice, the first in vivo AR model was established using X-rays as both the priming and the challenge doses and rescue of bone marrow death as the end point. The underlying mechanism was due to the priming radiation-induced resistance in the blood-forming tissues. In a series of investigations, we further demonstrated the existence of AR using different types of ionizing radiation (IR) including low linear energy transfer (LET) X-rays and high LET heavy ion. In this article, we validated hematopoietic stem cells/hematopoietic progenitor cells (HSCs/HPCs) measured as endogenous colony-forming units-spleen (CFU-S) under AR inducible and uninducible conditions using combination of different types of IR. We confirmed the consistency of increased CFU-S number change with the AR inducible condition. These findings suggest that AR in mice induced by different types of IR would share at least in part a common underlying mechanism, the priming IR-induced resistance in the blood-forming tissues, which would lead to a protective effect on the HSCs/HPCs and play an important role in rescuing the animals from bone marrow death. These findings provide a new insight into the mechanistic study on AR in vivo.

A Chemical Modulator of p53 Transactivation that Acts as a Radioprotective Agonist.

Inhibiting p53-dependent apoptosis by inhibitors of p53 is an effective strategy for preventing radiation-induced damage in hematopoietic lineages, while p53 and p21 also play radioprotective roles in the gastrointestinal epithelium. We previously identified some zinc(II) chelators, including 8-quinolinol derivatives, that suppress apoptosis in attempts to discover compounds that target the zinc-binding site in p53. We found that 5-chloro-8-quinolinol (5CHQ) has a unique p53-modulating activity that shifts its transactivation from proapoptotic to protective responses, including enhancing p21 induction and suppressing PUMA induction. This p53-modulating activity also influenced p53 and p53-target gene expression in unirradiated cells without inducing DNA damage. The specificity of 5CHQ for p53 and p21 was demonstrated by silencing the expression of each protein. These effects seem to be attributable to the sequence-specific alteration of p53 DNA-binding, as evaluated by chromatin immunoprecipitation and electrophoretic mobility shift assays. In addition, 5-chloro-8-methoxyquinoline itself had no antiapoptotic activity, indicating that the hydroxyl group at the 8-position is required for its antiapoptotic activity. We applied this remarkable agonistic activity to protecting the hematopoietic and gastrointestinal system in mouse irradiation models. The dose reduction factors of 5CHQ in total-body and abdominally irradiated mice were about 1.2 and 1.3, respectively. 5CHQ effectively protected mouse epithelial stem cells from a lethal dose of abdominal irradiation. Furthermore, the specificity of 5CHQ for p53 in reducing the lethality induced by abdominal irradiation was revealed in Trp53-KO mice. These results indicate that the pharmacologic upregulation of radioprotective p53 target genes is an effective strategy for addressing the gastrointestinal syndrome. Mol Cancer Ther; 17(2); 432-42. ©2017 AACRSee all articles in this MCT Focus section, "Developmental Therapeutics in Radiation Oncology."

Trends of Training Courses Conducted in the Human Resources Development Center of the National Institute for Quantum and Radiological Science and Technology After the Fukushima Dai-Ichi Nuclear Power Plant Accident.

Environmental contamination with radioactive materials caused by the Fukushima Dai-ichi Nuclear Power Plant (NPP) accident in 2011 raised a serious health concern among residents in Japan, and the demand for radiation experts who can handle the radiation-associated problems has increased. The Human Resources Development Center (HRDC) of the National Institute of for Quantum and Radiological Science and Technology in Japan has offered a variety of training programs covering a wide range of technologies associated with radiation since 1959. In this study, the time-course change in the number and age of the applicants for training programs regularly scheduled at HRDC were analyzed to characterize the demand after the NPP accident. The results suggested that the demand for the training of industrial radiation experts elevated sharply after the NPP accident followed by a prompt decrease, and that young people were likely stimulated to learn the basics of radiation. The demand for the training of medical radiation experts was kept high regardless of the NPP accident. The demand for the training of radiation emergency experts fluctuated apparently with three components: a terminating demand after the criticality accident that occurred in 1999, an urgent demand for handling of the NPP accident, and a sustained demand from local governments that undertook reinforcement of their nuclear disaster prevention program. The demand for the training of school students appeared to be increasing after the NPP accident. It could be foreseen that the demand for training programs targeting young people and medical radiation experts would be elevated in future.

Differences in sustained alterations in protein expression between livers of mice exposed to high-dose-rate and low-dose-rate radiation.

Molecular mechanisms of radiation dose-rate effects are not well understood. Among many possibilities, long-lasting sustained alterations in protein levels would provide critical information. To evaluate sustained effects after acute and chronic radiation exposure, we analyzed alterations in protein expression in the livers of mice. Acute exposure consisted of a lethal dose of 8 Gy and a sublethal dose of 4 Gy, with analysis conducted 6 days and 3 months after irradiation, respectively. Chronic irradiation consisted of a total dose of 8 Gy delivered over 400 days (20 mGy/day). Analyses following chronic irradiation were done immediately and at 3 months after the end of the exposure. Based on antibody arrays of protein expression following both acute lethal and sublethal dose exposures, common alterations in the expression of two proteins were detected. In the sublethal dose exposure, the expression of additional proteins was altered 3 months after irradiation. Immunohistochemical analysis showed that the increase in one of the two commonly altered proteins, MyD88, was observed around blood vessels in the liver. The alterations in protein expression after chronic radiation exposure were different from those caused by acute radiation exposures. Alterations in the expression of proteins related to inflammation and apoptosis, such as caspase 12, were observed even at 3 months after the end of the chronic radiation exposure. The alterations in protein expression depended on the dose, the dose rate, and the passage of time after irradiation. These changes could be involved in long-term effects of radiation in the liver.

Effects of chronic restraint-induced stress on radiation-induced chromosomal aberrations in mouse splenocytes.

Both ionizing radiation (IR) and psychological stress (PS) cause detrimental effects on humans. A recent study showed that chronic restraint-induced PS (CRIPS) diminished the functions of Trp53 and enhanced radiocarcinogenesis in Trp53-heterozygous (Trp53+/-) mice. These findings had a marked impact on the academic field as well as the general public, particularly among residents living in areas radioactively contaminated by nuclear accidents. In an attempt to elucidate the modifying effects of CRIPS on radiation-induced health consequences in Trp53 wild-type (Trp53+/+) animals, investigations involving multidisciplinary analyses were performed. We herein demonstrated that CRIPS induced changes in the frequency of IR-induced chromosomal aberrations (CAs) in splenocytes. Five-week-old male Trp53+/+ C57BL/6J mice were restrained for 6h per day for 28 consecutive days, and total body irradiation (TBI) at a dose of 4Gy was performed on the 8th day. Metaphase chromosome spreads prepared from splenocytes at the end of the 28-day restraint regimen were painted with fluorescence in situ hybridization (FISH) probes for chromosomes 1, 2, and 3. The results obtained showed that CRIPS alone did not induce CAs, while TBI caused significant increases in CAs, mostly translocations. Translocations appeared at a lower frequency in mice exposed to TBI plus CRIPS than in those exposed to TBI alone. No significant differences were observed in the frequencies of the other types of CAs (insertions, dicentrics, and fragments) visualized with FISH between these experimental groups (TBI+CRIPS vs. TBI). These results suggest that CRIPS does not appear to synergize with the clastogenicity of IR.

Revisiting the health effects of psychological stress-its influence on susceptibility to ionizing radiation: a mini-review.

Both psychological stress (PS) and ionizing radiation (IR) cause varied detrimental effects on humans. There has been no direct evidence so far showing PS alone could cause cancer; however, long-lasting PS may affect our overall health and ability to cope with cancer. Due to their living conditions and occupations, some people may encounter concurrent exposure to both PS and IR to a high extent. In addition to possible health effects resulting directly from exposure to IR on these people, fear of IR exposure is also a cause of PS. The question of whether PS would influence susceptibility to IR, radiocarcinogenesis in particular, is of great concern by both the academic world and the public. Recently, investigations using animal PS models demonstrated that PS could modulate susceptibility to IR, causing increased susceptibility to radiocarcinogenesis in Trp53-heterozygous mice, hematological toxicity in peripheral blood and elevated chromosome aberration (dicentrics) frequency in splenocytes of Trp53-wild-type mice. To actively reduce health risk from exposure to IR, further studies are needed to cumulate more evidence and provide insights into the mechanisms underlying the alterations in susceptibility due to PS modulation. This mini-review gives a general overview of the significance of PS effects on humans and experimental animals, with a special focus on summarizing the latest weight-of-evidence approaches to radiobiological studies on PS-induced alterations in susceptibility in experimental animal models. The susceptibility being investigated is mainly in the context of the impact of the modulatory effect of PS on radiocarcinogenesis; we seek to improve understanding of the combined effects of exposure to both PS and IR in order to facilitate, via active intervention, strategies for radiation risk reduction.