Fe Irradiation Research Articles

The effect of hydrogen-helium synergism on dislocation loops in RAFM steel at different temperatures by dual-beam ion irradiation

Simultaneous Fe+H ion irradiation (denoted as Fe+H) and Fe+H ion irradiation with pre-implantation of He (denoted as He/Fe+H) were carried out on Chinese Low-Activation Martensitic (CLAM) steels at 350 ℃-550 ℃ to investigate the synergistic effect between H and He. The peak dose was 15 dpa, the He concentration in the observation area was 11 appm/dpa and the H concentration was 44 appm/dpa. The microstructure and hardening of the irradiated samples were evaluated by TEM and nanoindentation, respectively. Bubbles were not observed in irradiated CLAM steels at all temperatures, which implies that the promotion of bubbles by H may not be as strong as that by He and that H attenuates the promotion of bubbles by He. The hardening induced by He/Fe+H irradiation at 450 °C is about 1.6 times that of Fe+H irradiation, the synergistic effect of H and He is most significant at this temperature. Comparison with Fe+He irradiation and single Fe irradiation reveals that Fe+H irradiation at 350 °C induces lower interstitial defect damage than Fe+He irradiation, but the level of interstitial defects induced by the synergistic effect of both H and He with displacement damage is comparable at higher temperatures. The average size of dislocation loops induced by Fe+H irradiation is between that of single Fe irradiation and Fe+He irradiation, but the number density of dislocation loops induced by Fe+H irradiation is higher than that of Fe+He irradiation. The synergistic effect of He with displacement damage tends to promote the growth of dislocation loops, while the synergistic effect of H tends to promote the nucleation of dislocation loops.

Modification of the band gap of Ruddlesden‒Popper perovskites Srn+1TinO3n+1 (n=1, 2, 3, and ∞) by Fe ion irradiation doping

Ruddlesden‒Popper (RP)-type perovskite materials Srn+1TinO3n+1 (n = 1, 2, 3, and ∞) have important application prospects in photocatalysis. However, their wide band gap limits their visible light absorption ability. Doping is an efficient method that can be used to reduce the band gap and improve its light absorption range. In this work, irradiation doping with the advantages of compulsivity and controllability, rather than a chemical doping method, is used to manipulate the band gaps of Srn+1TinO3n+1 to understand the respective contributions of the substitution of the Sr and Ti sites to the band gap reduction as a function of the n value. The solid-state reaction-prepared RP-type perovskites Srn+1TinO3n+1 (n = 1, 2, 3, and ∞) irradiated by a 270 keV Fe ion beam with 0–1 × 1016 ions/cm2 doses were characterized by SEM, XRD and UV–vis diffuse reflectance spectra. Tauc plot analysis showed that the band gaps of Srn+1TinO3n+1 decreased with an increase in Fe doping dose, which was confirmed by DFT calculations. Meanwhile, the effects of the perovskite and rock-salt layers of the RP-type perovskite on the band gap modification were demonstrated, showing that the band gap of Srn+1TinO3n+1 with smaller n values decreases less when the Fe irradiation dose increases. This is explained by more salt SrO layers found in Srn+1TinO3n+1 for smaller n values, which prevents the substitution of Sr and Ti atoms in perovskite layers, significantly influencing the band gap.

Ground-based selected ionizing space radiation effects on stability of APIs and their formulations

Primary goal of any space mission is to keep astronauts healthy and fit during entire mission. One of the important challenges for that is providing a safe and effective pharmacy with the capabilities to address both scheduled and unanticipated medical conditions that may arise during spaceflight. Extended exposure to space environmental conditions may trigger drug deterioration, impacting quality, effectiveness, and safety. To assess the influence of space ionizing radiations on the stability of medicines launched aboard spacecraft, a preliminary ground-based ionizing radiation drug interaction study was carried out at different doses in the present work. Four different types of radiations - proton, neutron (thermal, fast), gamma and heavy ions (56Fe) were used to irradiate selected drugs namely diclofenac, ciprofloxacin and metoprolol along with their formulations. Chemical stability of each irradiated sample was checked using high performance liquid chromatographic method. Significant degradation was observed in even solid-state during proton irradiation in both Active Pharmaceutical Ingredient (API) and tablet dosage form. Solution of active pharmaceutical ingredient and liquid dosage forms were prone to degradation in presence of gamma radiation. No physical and chemical changes observed after neutron and 56Fe irradiation. Irradiation of the same drug with different radiations demonstrated varying HPLC chromatographic profiles in terms of %degradation as well as proportion of same degradation products. This indicates possibility of different degradation pathways to generate degradation products.

Long-Term Sex- and Genotype-Specific Effects of 56Fe Irradiation on Wild-Type and APPswe/PS1dE9 Transgenic Mice.

Space radiation presents a substantial threat to travel beyond Earth. Relatively low doses of high-energy particle radiation cause physiological and behavioral impairments in rodents and may pose risks to human spaceflight. There is evidence that 56Fe irradiation, a significant component of space radiation, may be more harmful to males than to females and worsen Alzheimer’s disease pathology in genetically vulnerable models. Yet, research on the long-term, sex- and genotype-specific effects of 56Fe irradiation is lacking. Here, we irradiated 4-month-old male and female, wild-type and Alzheimer’s-like APP/PS1 mice with 0, 0.10, or 0.50 Gy of 56Fe ions (1GeV/u). Mice underwent microPET scans before and 7.5 months after irradiation, a battery of behavioral tests at 11 months of age and were sacrificed for pathological and biochemical analyses at 12 months of age. 56Fe irradiation worsened amyloid-beta (Aβ) pathology, gliosis, neuroinflammation and spatial memory, but improved motor coordination, in male transgenic mice and worsened fear memory in wild-type males. Although sham-irradiated female APP/PS1 mice had more cerebral Aβ and gliosis than sham-irradiated male transgenics, female mice of both genotypes were relatively spared from radiation effects 8 months later. These results provide evidence for sex-specific, long-term CNS effects of space radiation.

Multi-Domain Touchscreen-Based Cognitive Assessment of C57BL/6J Female Mice Shows Whole-Body Exposure to 56Fe Particle Space Radiation in Maturity Improves Discrimination Learning Yet Impairs Stimulus-Response Rule-Based Habit Learning.

Astronauts during interplanetary missions will be exposed to galactic cosmic radiation, including charged particles like 56Fe. Most preclinical studies with mature, “astronaut-aged” rodents suggest space radiation diminishes performance in classical hippocampal- and prefrontal cortex-dependent tasks. However, a rodent cognitive touchscreen battery unexpectedly revealed 56Fe radiation improves the performance of C57BL/6J male mice in a hippocampal-dependent task (discrimination learning) without changing performance in a striatal-dependent task (rule-based learning). As there are conflicting results on whether the female rodent brain is preferentially injured by or resistant to charged particle exposure, and as the proportion of female vs. male astronauts is increasing, further study on how charged particles influence the touchscreen cognitive performance of female mice is warranted. We hypothesized that, similar to mature male mice, mature female C57BL/6J mice exposed to fractionated whole-body 56Fe irradiation (3 × 6.7cGy 56Fe over 5 days, 600 MeV/n) would improve performance vs. Sham conditions in touchscreen tasks relevant to hippocampal and prefrontal cortical function [e.g., location discrimination reversal (LDR) and extinction, respectively]. In LDR, 56Fe female mice more accurately discriminated two discrete conditioned stimuli relative to Sham mice, suggesting improved hippocampal function. However, 56Fe and Sham female mice acquired a new simple stimulus-response behavior and extinguished this acquired behavior at similar rates, suggesting similar prefrontal cortical function. Based on prior work on multiple memory systems, we next tested whether improved hippocampal-dependent function (discrimination learning) came at the expense of striatal stimulus-response rule-based habit learning (visuomotor conditional learning). Interestingly, 56Fe female mice took more days to reach criteria in this striatal-dependent rule-based test relative to Sham mice. Together, our data support the idea of competition between memory systems, as an 56Fe-induced decrease in striatal-based learning is associated with enhanced hippocampal-based learning. These data emphasize the power of using a touchscreen-based battery to advance our understanding of the effects of space radiation on mission critical cognitive function in females, and underscore the importance of preclinical space radiation risk studies measuring multiple cognitive processes, thereby preventing NASA’s risk assessments from being based on a single cognitive domain.

Effect of Three Types of Ion Beam Irradiation on Gerbera (Gerbera hybrida) In Vitro Shoots with Mutagenesis Efficiency.

Gerbera in vitro shoots were irradiated using three types of ion beams with different line energy transfers (LETs) to investigate the effective LET and absorbed doses for mutagenesis. Furthermore, genomic mutation analyses were conducted on the obtained mutants. Survival rate analysis showed a lower lethal dose 50% (LD50) with ion beams with higher LETs. Trait/morphological mutations exhibited changes in the color and shape of petals and male sterility. Irradiation conditions with the highest growth change and trait/morphological mutation rates in each ion were C irradiation at 10 Gy, Ar irradiation at 5 Gy, and Fe irradiation at 5 Gy, with a range of absorbed dose of around LD50 to about 10 Gy lower. The highest trait/morphological mutation rate was 14.1% with Ar irradiation at 5 Gy, which was one of the criteria for ion beam irradiation of gerbera in vitro shoots. Furthermore, the genomic mutation in the flower color, petal shape, and male sterile mutants were confirmed by genotype analysis using Genotyping by Random Amplicon Sequencing-Direct technology. This is the first study to report the efficient production of gerbera mutants that could be analyzed. Our findings may lead to more efficient gerbera mutant production and analysis technology.

Effects of Heavy Ion Particle Irradiation on Spore Germination of Bacillus spp. from Extremely Hot and Cold Environments.

Extremophiles are optimal models in experimentally addressing questions about the effects of cosmic radiation on biological systems. The resistance to high charge energy (HZE) particles, and helium (He) ions and iron (Fe) ions (LET at 2.2 and 200 keV/µm, respectively, until 1000 Gy), of spores from two thermophiles, Bacillus horneckiae SBP3 and Bacillus licheniformis T14, and two psychrotolerants, Bacillus sp. A34 and A43, was investigated. Spores survived He irradiation better, whereas they were more sensitive to Fe irradiation (until 500 Gy), with spores from thermophiles being more resistant to irradiations than psychrotolerants. The survived spores showed different germination kinetics, depending on the type/dose of irradiation and the germinant used. After exposure to He 1000 Gy, D-glucose increased the lag time of thermophilic spores and induced germination of psychrotolerants, whereas L-alanine and L-valine increased the germination efficiency, except alanine for A43. FTIR spectra showed important modifications to the structural components of spores after Fe irradiation at 250 Gy, which could explain the block in spore germination, whereas minor changes were observed after He radiation that could be related to the increased permeability of the inner membranes and alterations of receptor complex structures. Our results give new insights on HZE resistance of extremophiles that are useful in different contexts, including astrobiology.

Comparative RNA-Seq transcriptome analyses reveal dynamic time-dependent effects of 56Fe, 16O, and 28Si irradiation on the induction of murine hepatocellular carcinoma

BackgroundOne of the health risks posed to astronauts during deep space flights is exposure to high charge, high-energy (HZE) ions (Z > 13), which can lead to the induction of hepatocellular carcinoma (HCC). However, little is known on the molecular mechanisms of HZE irradiation-induced HCC.ResultsWe performed comparative RNA-Seq transcriptomic analyses to assess the carcinogenic effects of 600 MeV/n 56Fe (0.2 Gy), 1 GeV/n 16O (0.2 Gy), and 350 MeV/n 28Si (0.2 Gy) ions in a mouse model for irradiation-induced HCC. C3H/HeNCrl mice were subjected to total body irradiation to simulate space environment HZE-irradiation, and liver tissues were extracted at five different time points post-irradiation to investigate the time-dependent carcinogenic response at the transcriptomic level. Our data demonstrated a clear difference in the biological effects of these HZE ions, particularly immunological, such as Acute Phase Response Signaling, B Cell Receptor Signaling, IL-8 Signaling, and ROS Production in Macrophages. Also seen in this study were novel unannotated transcripts that were significantly affected by HZE. To investigate the biological functions of these novel transcripts, we used a machine learning technique known as self-organizing maps (SOMs) to characterize the transcriptome expression profiles of 60 samples (45 HZE-irradiated, 15 non-irradiated control) from liver tissues. A handful of localized modules in the maps emerged as groups of co-regulated and co-expressed transcripts. The functional context of these modules was discovered using overrepresentation analysis. We found that these spots typically contained enriched populations of transcripts related to specific immunological molecular processes (e.g., Acute Phase Response Signaling, B Cell Receptor Signaling, IL-3 Signaling), and RNA Transcription/Expression.ConclusionsA large number of transcripts were found differentially expressed post-HZE irradiation. These results provide valuable information for uncovering the differences in molecular mechanisms underlying HZE specific induced HCC carcinogenesis. Additionally, a handful of novel differentially expressed unannotated transcripts were discovered for each HZE ion. Taken together, these findings may provide a better understanding of biological mechanisms underlying risks for HCC after HZE irradiation and may also have important implications for the discovery of potential countermeasures against and identification of biomarkers for HZE-induced HCC.

Multi-domain cognitive assessment of male mice shows space radiation is not harmful to high-level cognition and actually improves pattern separation

Astronauts on interplanetary missions - such as to Mars - will be exposed to space radiation, a spectrum of highly-charged, fast-moving particles that includes 56Fe and 28Si. Earth-based preclinical studies show space radiation decreases rodent performance in low- and some high-level cognitive tasks. Given astronaut use of touchscreen platforms during training and space flight and given the ability of rodent touchscreen tasks to assess functional integrity of brain circuits and multiple cognitive domains in a non-aversive way, here we exposed 6-month-old C57BL/6J male mice to whole-body space radiation and subsequently assessed them on a touchscreen battery. Relative to Sham treatment, 56Fe irradiation did not overtly change performance on tasks of visual discrimination, reversal learning, rule-based, or object-spatial paired associates learning, suggesting preserved functional integrity of supporting brain circuits. Surprisingly, 56Fe irradiation improved performance on a dentate gyrus-reliant pattern separation task; irradiated mice learned faster and were more accurate than controls. Improved pattern separation performance did not appear to be touchscreen-, radiation particle-, or neurogenesis-dependent, as 56Fe and 28Si irradiation led to faster context discrimination in a non-touchscreen task and 56Fe decreased new dentate gyrus neurons relative to Sham. These data urge revisitation of the broadly-held view that space radiation is detrimental to cognition.

Space-like 56Fe irradiation manifests mild, early sex-specific behavioral and neuropathological changes in wildtype and Alzheimer\u2019s-like transgenic mice

Space travel will expose people to high-energy, heavy particle radiation, and the cognitive deficits induced by this exposure are not well understood. To investigate the short-term effects of space radiation, we irradiated 4-month-old Alzheimer’s disease (AD)-like transgenic (Tg) mice and wildtype (WT) littermates with a single, whole-body dose of 10 or 50 cGy 56Fe ions (1 GeV/u) at Brookhaven National Laboratory. At ~1.5 months post irradiation, behavioural testing showed sex-, genotype-, and dose-dependent changes in locomotor activity, contextual fear conditioning, grip strength, and motor learning, mainly in Tg but not WT mice. There was little change in general health, depression, or anxiety. Two months post irradiation, microPET imaging of the stable binding of a translocator protein ligand suggested no radiation-specific change in neuroinflammation, although initial uptake was reduced in female mice independently of cerebral blood flow. Biochemical and immunohistochemical analyses revealed that radiation reduced cerebral amyloid-β levels and microglia activation in female Tg mice, modestly increased microhemorrhages in 50 cGy irradiated male WT mice, and did not affect synaptic marker levels compared to sham controls. Taken together, we show specific short-term changes in neuropathology and behaviour induced by 56Fe irradiation, possibly having implications for long-term space travel.

Simulated space radiation: Investigating ionizing radiation effects on the stability of amlodipine besylate API and tablets

Efficacious pharmaceuticals with the adequate shelf life are essential for the well-being of the space explorers and successful completion of a space mission. Space is brimming with different types of radiations, which penetrate inside the spacecraft despite the shielding material. Such radiations can alter the stability of the pharmaceuticals during long duration space missions. The literature reporting the space radiation effects on the pharmaceuticals is scarce in a public domain. Ground-based simulation studies can be useful to predict the influence of the space radiations on the stability of the pharmaceuticals. Based upon these facts, the main objective of the present preliminary work was to investigate the effect of different types of ionizing radiations on the stability of amlodipine besylate API and tablets. Amlodipine besylate samples were irradiated by protons, neutrons (thermal and fast), gamma and heavy ion (56Fe) radiations with their different doses. The samples were also irradiated with UV–visible radiation to compare the effect of selected ionizing radiations with photodegradation. The physical stability was examined through organoleptic evaluation and the chemical stability was evaluated by FTIR and HPLC. The results of the organoleptic evaluation showed colour changes from colourless to yellow in proton irradiated solid API and gamma irradiated API aqueous solution. The FTIR spectrum of proton irradiated API showed one additional absorption band at 1728 cm−1 due to degradation products. HPLC analysis revealed that amlodipine degraded up to 10% and 21% after the highest doses of proton and gamma irradiation, respectively. No physical or chemical changes were observed after neutron and 56Fe irradiation. The structures of major radiolytic products were elucidated using LC-MS/MS. Two new impurities were found in the API aqueous solution as a result of gamma irradiation. The drug degradation pathways were postulated by proposing the plausible mechanism of formation.

Surface morphology correlated with sputtering yield measurements of laser-ablated iron

AbstractIron (Fe) targets are exposed to 100 pulses of Nd: YAG laser (532 nm, 6 ns, 10 Hz) at various fluences ranging from 4.8 to 38.5 J/cm2. In order to explore the effect of background environment, targets have been exposed under vacuum as well as under five different pressures ranging from 5 to 100 Torr of various background gases like Ar, Ne, O2, and air. The sputtering yield measurements and surface modifications of laser-ablated Fe are explored by quartz crystal microbalance (QCM) and scanning electron microscopy (SEM) analysis, respectively. QCM measurements reveal that the sputtering yield of Fe is strongly affected by laser fluence, pressure and nature of gas. By increasing laser fluence, the sputtering yield initially increases due to enhanced energy deposition and then saturates due to self-regulating regime. However, with increasing pressures of background gases, the sputtering yield of Fe initially increases and then decreases. Owing to thermal conductivity, ionization potential, and mass of background gas, the sputtering yield of Fe varies in accordance with the sequence vacuum >Ar>Ne>O2> air. The SEM analysis reveals the formation of several features like laser-induced periodic surface structures, cones, cavities, channels, multiple ablative craters, and dot-like structures. The difference in the periodicity, size, and shape of features is explained on the basis of confinement and shielding effects of plasma and various energy deposition mechanisms. The surface profilometry analysis reveals that the crater depth increases with increasing the laser fluence in inert environments, while in case of reactive environments, it tends to decrease initially and afterwards it increases. X-ray diffraction and energy-dispersive X-ray analyses confirm the oxide formation in case of Fe treatment in O2 and air; however, no additional phases are observed for Fe irradiation under inert environments.

Abstract 4163: Space radiation-induced persistent DNA damage and alterations in cytoskeletal remodeling pathways affect intestinal epithelial cell migration in mice

Abstract Lombardi Comprehensive Cancer Center, and Department of Biochemistry and Molecular & Cellular Biology Georgetown University, Washington, DC 20057, USA. Heavy ion space radiation is considered as a risk factor of gastrointestinal (GI) cancer and perturbed intestinal epithelial cell (IEC) migration has been implicated in GI carcinogenesis. The purpose of the current study was to assess rate of IEC migration as well as dissect key IEC migration signaling events after exposure to heavy ion 56Fe irradiation and compare the results to sham- and γ-irradiation. Male C57BL/6J mice were exposed to 0.5 Gy of either γ or 56Fe radiation and control mice were sham irradiated. IEC migration distance was measured 7 and 60 d after exposure using BrdU pulse labeling. We also analyzed cell polarity, microtubule dynamics, and adhesion dynamics using immunoblots and immunofluorescence. Measure of IEC migration rate showed a greater decrease after 56Fe relative to γ radiation at both the time points. At the molecular level, compared to sham and γ radiation, 56Fe radiation exhibited significantly greater impairment of cell adhesion dynamics evidenced by altered integrins and Rock1 as well as cytoskeletal dynamics evidenced by altered MLCK expression. Similarly, perturbed cell polarity, tight junction, and microtubule dynamics was revealed by the deregulation of Par3, Claudin1, Scribble, Occludin, ZO-1, phospho-Tau and MAP1B. Also, the Wnt/β-catenin and EphB/EphrinB pathways critical for IEC migration consistently showed greater deregulation at both the time points tested after 56Fe radiation relative to γ -rays. Taken together, our molecular findings correlate with the BrdU pulse labeling data, and demonstrate greater effects of heavy ion 56Fe on IEC migration relative to γ -rays. In summary, our results have demonstrated for the first time that radiation can disrupt cell migration dynamics through alteration of signaling molecules involved in crucial cellular processes and these results have implications for heavy ion space radiation-induced gastrointestinal homeostatic deregulation and carcinogenesis. Citation Format: Santosh Kumar, Shubhankar Suman, Albert Fornace, Kamal Datta. Space radiation-induced persistent DNA damage and alterations in cytoskeletal remodeling pathways affect intestinal epithelial cell migration in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4163.

Comparison of magnetic properties of austenitic stainless steel after ion irradiation

Abstract Specimens of austenitic stainless steel (ASS) were irradiated with H, Fe and Xe ions at room temperature. The vibrating sample magnetometer (VSM) and grazing incidence X-ray diffraction (GIXRD) were used to analyze the magnetic properties and martensite formation. The magnetic hysteresis loops indicated that higher irradiation damage causes more significant magnetization phenomenon. Under the same damage level, Xe irradiation causes the most significant magnetization, Fe irradiation is the second, and H irradiation is the least. A similar martensite amount variation with irradiation can be obtained. The coercivity Hc increases first to 2 dpa and then decreases continuously with irradiation damage for Xe irradiation. At the same damage lever, H irradiation causes a largest Hc and Xe irradiation causes a minimal one.

Characterization of ion irradiation effects on the microstructure, hardness, deformation and crack initiation behavior of austenitic stainless steel:Heavy ions vs protons

Irradiation Assisted Stress Corrosion Cracking (IASCC) is a complex phenomenon of degradation which can have a significant influence on maintenance time and cost of core internals of a Pressurized Water Reactor (PWR). Hence, it is an issue of concern, especially in the context of lifetime extension of PWRs. Proton irradiation is generally used as a representative alternative of neutron irradiation to improve the current understanding of the mechanisms involved in IASCC. This study assesses the possibility of using heavy ions irradiation to evaluate IASCC mechanisms by comparing the irradiation induced modifications (in microstructure and mechanical properties) and cracking susceptibility of SA 304 L after both type of irradiations: Fe irradiation at 450 °C and proton irradiation at 350 °C. Irradiation-induced defects are characterized and quantified along with nano-hardness measurements, showing a correlation between irradiation hardening and density of Frank loops that is well captured by Orowan's formula. Both irradiations (iron and proton) increase the susceptibility of SA 304 L to intergranular cracking on subjection to Constant Extension Rate Tensile tests (CERT) in simulated nominal PWR primary water environment at 340 °C. For these conditions, cracking susceptibility is found to be quantitatively similar for both irradiations, despite significant differences in hardening and degree of localization.

Bi-directional and shared epigenomic signatures following proton and 56Fe irradiation

The brain’s response to radiation exposure is an important concern for patients undergoing cancer therapy and astronauts on long missions in deep space. We assessed whether this response is specific and prolonged and is linked to epigenetic mechanisms. We focused on the response of the hippocampus at early (2-weeks) and late (20-week) time points following whole body proton irradiation. We examined two forms of DNA methylation, cytosine methylation (5mC) and hydroxymethylation (5hmC). Impairments in object recognition, spatial memory retention, and network stability following proton irradiation were observed at the two-week time point and correlated with altered gene expression and 5hmC profiles that mapped to specific gene ontology pathways. Significant overlap was observed between DNA methylation changes at the 2 and 20-week time points demonstrating specificity and retention of changes in response to radiation. Moreover, a novel class of DNA methylation change was observed following an environmental challenge (i.e. space irradiation), characterized by both increased and decreased 5hmC levels along the entire gene body. These changes were mapped to genes encoding neuronal functions including postsynaptic gene ontology categories. Thus, the brain’s response to proton irradiation is both specific and prolonged and involves novel remodeling of non-random regions of the epigenome.

The Effects of Galactic Cosmic Radiation Exposure on Hematopoietic Stem Cell Dysfunction and Oncogenesis

Natural sources of radiation in space include galactic cosmic rays (GCR), solar energetic particles (SPE) and trapped energetic particles in a planetary magnetic field. These different sources of space radiation consist of protons of various energies, particle nuclei of high energy and charge (HZE) and neutrons of different energies. These sources are difficult to shield because of their high energies and dense ionization patterns, thus posing significant health risks to astronauts on long term inter-planetary missions. Efforts to protect astronauts from harmful cosmic radiation require a deeper understanding of the effects of GCR on human health. In particular, very little is known about the effects of GCR exposure on the hematopoietic stem cell (HSC) population and whether disruptions in genetic stability in HSCs could result in the development of hematopoietic malignancies in astronauts on deep space missions.The average age of shuttle crew has risen above 46 years, and our work and others have shown that HSCs display diminished function with age. Recent data from our group has demonstrated that middle-aged individuals show frequent defects in DNA mismatch repair (MMR) in HSCs. MMR corrects DNA mismatches generated by DNA polymerase during replication which prevents mutations from becoming permanent in dividing cells. Thus, MMR plays a crucial role in the DNA damage response pathway to prevent short-term mutagenesis and long-term tumorigenesis. Several human MMR proteins have been identified as MutS and MutL homologues consisting of MSH2 and MLH1 heterodimers that functions in DNA mismatch/damage recognition, endonuclease activity and termination of mismatch-provoked excision. Our group has shown that humans accumulate microsatellite instability (MSI) with acquired loss of MLH1 protein in hematopoietic stem and progenitor cells as a function of age. Therefore, we employed a DNA mismatch repair deficient mouse model (MLH1+/- and MLH1-/-) to study the effects of different radiation sources including 56Fe, 28Si, 4He, 1H and γ-rays on HSCs to examine HSCs of potential astronaut population under GCR conditions. The complete blood count (CBC) data after 5 months and 9 months of whole body irradiation with different ions showed a slight dose-dependent decrease in all blood counts but absence of any significant difference in CBC of MLH1+/+ vs MLH1+/- mice. In addition, CFU and competitive repopulation data demonstrated a radiation quality effects on HSC function, but not an MLH1 effect. These results demonstrate that hematopoietic stem cell function is normal and that a MLH1 defect does not differentiate progenitor and mature effector cells following HZE radiation.To study long term effects of different ions on the potential for disease progression in a MLH1 dependent manner, we performed whole body irradiation with 56Fe, 28Si, 1H and γ-rays on MLH1+/+ and MLH1+/- mice and followed them up to 18 months post exposure. We observed that MLH1+/- mice show dramatic increases in lymphomagenesis 10-12 months after 56Fe irradiation compared to wild type mice, with greater than 60 % of MLH1+/- mice developed lymphomas at doses 10 cGy and 100 cGy compared to less than 10 % of wild type. For comparison, roughly 10 % of MLH1+/- mice developed lymphomas when mice were treated with whole body sparsely ionizing γ-rays at 100 cGy compared to none of the control. Thus the date show that MMR defects in HSCs lead to sensitization to radiation induced hematopoietic malignancy and that radiation quality effects exacerbate the sensitivity. The findings could have profound effects on astronaut screening, as well as lead to important questions regarding safety of ion therapy and development of second malignancies for cancer patients who remain on Earth. DisclosuresNo relevant conflicts of interest to declare.

Short- and long-term effects of 56Fe irradiation on cognition and hippocampal DNA methylation and gene expression.

BackgroundAstronauts are exposed to 56Fe ions that may pose a significant health hazard during and following prolonged missions in deep space. We showed previously that object recognition requiring the hippocampus, a structure critical for cognitive function, is affected in 2-month-old mice irradiated with 56Fe ions. Here we examined object recognition in 6-month-old mice irradiated with 56Fe ions, a biological age more relevant to the typical ages of astronauts. Moreover, because the mechanisms mediating the detrimental effects of 56Fe ions on hippocampal function are unclear, we examined changes in hippocampal networks involved in synaptic plasticity and memory, gene expression, and epigenetic changes in cytosine methylation (5mC) and hydroxymethylation (5hmC) that could accompany changes in gene expression. We assessed the effects of whole body 56Fe ion irradiation at early (2 weeks) and late (20 weeks) time points on hippocampus-dependent memory and hippocampal network stability, and whether these effects are associated with epigenetic changes in hippocampal DNA methylation (both 5mC and 5hmC) and gene expression.ResultsAt the two-week time point, object recognition and network stability were impaired following irradiation at the 0.1 and 0.4 Gy dose, but not following irradiation at the 0.2 Gy dose. No impairments in object recognition or network stability were seen at the 20-week time point at any irradiation dose used. Consistent with this pattern, the significance of pathways for gene categories for 5hmC was lower, though not eliminated, at the 20-week time point compared to the 2-week time point. Similarly, significant changes were observed for 5mC gene pathways at the 2-week time point, but no significant gene categories were observed at the 20-week time point. Only the 5hmC changes tracked with gene expression changes.ConclusionsDose- and time-dependent epigenomic remodeling in the hippocampus following 56Fe ion exposure correlates with behavioral changes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3110-7) contains supplementary material, which is available to authorized users.

Changes in the distribution and function of leukocytes after whole-body iron ion irradiation.

High-energy particle radiation could have a considerable impact on health during space missions. This study evaluated C57BL/6 mice on Day 40 after total-body 56Fe26+ irradiation at 0, 1, 2 and 3 gray (Gy). Radiation consistently increased thymus mass (one-way ANOVA: P < 0.005); spleen, liver and lung masses were similar among all groups. In the blood, there was no radiation effect on the white blood cell (WBC) count or major leukocyte types. However, the red blood cell count, hemoglobin, hematocrit and the CD8+ T cytotoxic (Tc) cell count and percentage all decreased, while both the CD4:CD8 (Th:Tc) cell ratio and spontaneous blastogenesis increased, in one or more irradiated groups compared with unirradiated controls (P < 0.05 vs 0 Gy). In contrast, splenic WBC, lymphocyte, B cell and T helper (Th) counts, %B cells and the CD4:CD8 ratio were all significantly elevated, while Tc percentages decreased, in one or more of the irradiated groups compared with controls (P < 0.05 vs 0 Gy). Although there were trends for minor, radiation-induced increases in %CD11b+ granulocytes in the spleen, cells double-labeled with adhesion markers (CD11b+CD54+, CD11b+CD62E+) were normal. Splenocyte spontaneous blastogenesis and that induced by mitogens (PHA, ConA, LPS) was equivalent to normal. In bone marrow, the percentage of cells expressing stem cell markers, Sca-1 and CD34/Sca-1, were low in one or more of the irradiated groups (P < 0.05 vs 0 Gy). Collectively, the data indicate that significant immunological abnormalities still exist more than a month after 56Fe irradiation and that there are differences dependent upon body compartment.

Genotype differences in anxiety and fear learning and memory of WT and ApoE4 mice associated with enhanced generation of hippocampal reactive oxygen species.

Apolipoprotein E (apoE), involved in cholesterol and lipid metabolism, also influences cognitive function and injury repair. In humans, apoE is expressed in three isoforms. E4 is a risk factor for age-related cognitive decline and Alzheimer's disease, particularly in women. E4 might also be a risk factor for developing behavioral and cognitive changes following (56) Fe irradiation, a component of the space environment astronauts are exposed to during missions. These changes might be related to enhanced generation of reactive oxygen species (ROS). In this study, we compared the behavioral and cognitive performance of sham-irradiated and irradiated wild-type (WT) mice and mice expressing the human E3 or E4 isoforms, and assessed the generation of ROS in hippocampal slices from these mice. E4 mice had greater anxiety-like and conditioned fear behaviors than WT mice, and these genotype differences were associated with greater levels of ROS in E4 than WT mice. The greater generation of ROS in the hippocampus of E4 than WT mice might contribute to their higher anxiety levels and enhanced fear conditioning. In E4, but not WT, mice, phorbol-12-myristate-13-acetate-treated hippocampal slices showed more dihydroxy ethidium oxidation in sham-irradiated than irradiated mice and hippocampal heme oxygenase-1 levels were higher in irradiated than sham-irradiated E4 mice. Mice with apolipoprotein E4 (E4), a risk factor for Alzheimer's disease, have greater anxiety-like and conditioned fear behaviors than wild-type (WT) mice. Generation of reactive oxygen species (ROS, in red) 3months following (56) Fe irradiation, a component of the space environment astronauts are exposed to, is more pronounced in the hippocampus of E4 than WT mice. In E4, but not WT, mice, hippocampal levels of the oxidative stress-relevant marker heme oxygenase-1 are higher in irradiated than sham-irradiated E4 mice.