Space-like 56Fe irradiation manifests mild, early sex-specific behavioral and neuropathological changes in wildtype and Alzheimer's-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-ß 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.

Space radiation triggers persistent stress response, increases senescent signaling, and decreases cell migration in mouse intestine.

Proliferative gastrointestinal (GI) tissue is radiation-sensitive, and heavy-ion space radiation with its high-linear energy transfer (high-LET) and higher damaging potential than low-LET γ-rays is predicted to compromise astronauts' GI function. However, much uncertainty remains in our understanding of how heavy ions affect coordinated epithelial cell migration and extrusion, which are essential for GI homeostasis. Here we show using mouse small intestine as a model and BrdU pulse labeling that cell migration along the crypt-villus axis is persistently decreased after a low dose of heavy-ion 56Fe radiation relative to control and γ-rays. Wnt/ß-catenin and its downstream EphrinB/EphB signaling are key to intestinal epithelial cell (IEC) proliferation and positioning during migration, and both are up-regulated after 56Fe radiation. Conversely, factors involved in cell polarity and adhesion and cell-extracellular matrix interactions were persistently down-regulated after 56Fe irradiation-potentially altering cytoskeletal remodeling and cell extrusion. 56Fe radiation triggered a time-dependent increase in γH2AX foci and senescent cells but without a noticeable increase in apoptosis. Some senescent cells acquired the senescence-associated secretory phenotype, and this was accompanied by increased IEC proliferation, implying a role for progrowth inflammatory factors. Collectively, this study demonstrates a unique phenomenon of heavy-ion radiation-induced persistently delayed IEC migration involving chronic sublethal genotoxic and oncogenic stress-induced altered cytoskeletal dynamics, which were seen even a year later. When considered along with changes in barrier function and nutrient absorption factors as well as increased intestinal tumorigenesis, our in vivo data raise a serious concern for long-duration deep-space manned missions.

Simulated space radiation-induced mutants in the mouse kidney display widespread genomic change.

Exposure to a small number of high-energy heavy charged particles (HZE ions), as found in the deep space environment, could significantly affect astronaut health following prolonged periods of space travel if these ions induce mutations and related cancers. In this study, we used an in vivo mutagenesis assay to define the mutagenic effects of accelerated 56Fe ions (1 GeV/amu, 151 keV/µm) in the mouse kidney epithelium exposed to doses ranging from 0.25 to 2.0 Gy. These doses represent fluences ranging from 1 to 8 particle traversals per cell nucleus. The Aprt locus, located on chromosome 8, was used to select induced and spontaneous mutants. To fully define the mutagenic effects, we used multiple endpoints including mutant frequencies, mutation spectrum for chromosome 8, translocations involving chromosome 8, and mutations affecting non-selected chromosomes. The results demonstrate mutagenic effects that often affect multiple chromosomes for all Fe ion doses tested. For comparison with the most abundant sparsely ionizing particle found in space, we also examined the mutagenic effects of high-energy protons (1 GeV, 0.24 keV/µm) at 0.5 and 1.0 Gy. Similar doses of protons were not as mutagenic as Fe ions for many assays, though genomic effects were detected in Aprt mutants at these doses. Considered as a whole, the data demonstrate that Fe ions are highly mutagenic at the low doses and fluences of relevance to human spaceflight, and that cells with considerable genomic mutations are readily induced by these exposures and persist in the kidney epithelium. The level of genomic change produced by low fluence exposure to heavy ions is reminiscent of the extensive rearrangements seen in tumor genomes suggesting a potential initiation step in radiation carcinogenesis.

Neurochemical differences in learning and memory paradigms among rats supplemented with anthocyanin-rich blueberry diets and exposed to acute doses of 56Fe particles.

The protective effects of anthocyanin-rich blueberries (BB) on brain health are well documented and are particularly important under conditions of high oxidative stress, which can lead to "accelerated aging." One such scenario is exposure to space radiation, consisting of high-energy and -charge particles (HZE), which are known to cause cognitive dysfunction and deleterious neurochemical alterations. We recently tested the behavioral and neurochemical effects of acute exposure to HZE particles such as 56Fe, within 24-48h after exposure, and found that radiation primarily affects memory and not learning. Importantly, we observed that specific brain regions failed to upregulate antioxidant and anti-inflammatory mechanisms in response to this insult. To further examine these endogenous response mechanisms, we have supplemented young rats with diets rich in BB, which are known to contain high amounts of antioxidant-phytochemicals, prior to irradiation. Exposure to 56Fe caused significant neurochemical changes in hippocampus and frontal cortex, the two critical regions of the brain involved in cognitive function. BB supplementation significantly attenuated protein carbonylation, which was significantly increased by exposure to 56Fe in the hippocampus and frontal cortex. Moreover, BB supplementation significantly reduced radiation-induced elevations in NADPH-oxidoreductase-2 (NOX2) and cyclooxygenase-2 (COX-2), and upregulated nuclear factor erythroid 2-related factor 2 (Nrf2) in the hippocampus and frontal cortex. Overall results indicate that 56Fe particles may induce their toxic effects on hippocampus and frontal cortex by reactive oxygen species (ROS) overload, which can cause alterations in the neuronal environment, eventually leading to hippocampal neuronal death and subsequent impairment of cognitive function. Blueberry supplementation provides an effective preventative measure to reduce the ROS load on the CNS in an event of acute HZE exposure.

Cardiovascular risks associated with low dose ionizing particle radiation.

Previous epidemiologic data demonstrate that cardiovascular (CV) morbidity and mortality may occur decades after ionizing radiation exposure. With increased use of proton and carbon ion radiotherapy and concerns about space radiation exposures to astronauts on future long-duration exploration-type missions, the long-term effects and risks of low-dose charged particle irradiation on the CV system must be better appreciated. Here we report on the long-term effects of whole-body proton ((1)H; 0.5 Gy, 1 GeV) and iron ion ((56)Fe; 0.15 Gy, 1GeV/nucleon) irradiation with and without an acute myocardial ischemia (AMI) event in mice. We show that cardiac function of proton-irradiated mice initially improves at 1 month but declines by 10 months post-irradiation. In AMI-induced mice, prior proton irradiation improved cardiac function restoration and enhanced cardiac remodeling. This was associated with increased pro-survival gene expression in cardiac tissues. In contrast, cardiac function was significantly declined in (56)Fe ion-irradiated mice at 1 and 3 months but recovered at 10 months. In addition, (56)Fe ion-irradiation led to poorer cardiac function and more adverse remodeling in AMI-induced mice, and was associated with decreased angiogenesis and pro-survival factors in cardiac tissues at any time point examined up to 10 months. This is the first study reporting CV effects following low dose proton and iron ion irradiation during normal aging and post-AMI. Understanding the biological effects of charged particle radiation qualities on the CV system is necessary both for the mitigation of space exploration CV risks and for understanding of long-term CV effects following charged particle radiotherapy.

Effects of (56)Fe radiation on hippocampal function in mice deficient in chemokine receptor 2 (CCR2).

(56)Fe irradiation affects hippocampus-dependent cognition. The underlying mechanisms may involve alterations in neurogenesis, expression of the plasticity-related immediate early gene Arc, and inflammation. Chemokine receptor-2 (CCR2), which mediates the recruitment of infiltrating and resident microglia to sites of CNS inflammation, is upregulated by (56)Fe irradiation. CCR2 KO and wild-type mice were used to compare effects of (56)Fe radiation (600MeV, 0.25Gy) on hippocampal function using contextual fear conditioning involving tone shock pairing during training (+/+) and exposure to the same environment without tone shock pairings (-/-). In the -/- condition, irradiation enhanced habituation in WT mice, but not CCR2 KO mice, suggesting that a lack of CCR2 was associated with reduced cognitive performance. In the +/+ condition, irradiation reduced freezing but there was no genotype differences. There were no significant correlations between the number of Arc-positive cells in the dentate gyrus and freezing in either genotype. While measures of neurogenesis and gliogenesis appeared to be modulated by CCR2, there were no effects of genotype on the total numbers of newly born activated microglia before or after irradiation, indicating that other mechanisms are involved in the genotype-dependent radiation response.

Genetic background and lymphocyte populations after total-body exposure to iron ion radiation.

PURPOSE: Particle radiations could significantly impact astronaut health during space missions. This study quantified the effects of iron ion radiation on lymphocytes in two strains of mice differing in susceptibility to radiation-induced acute myeloid leukemia (AML) and thymic lymphoma (TL): C57BL/6 (AML resistant, TL sensitive) and CBA/Ca (AML sensitive, TL resistant). MATERIALS AND METHODS: The animals (n = 60/strain) were irradiated with 56Fe(26+) (1 GeV) to total doses of 0, 0.5, 2 and 3 Gray (Gy) at an average dose rate of 1 Gy/min and euthanised on days 4 and 30 thereafter; blood, spleen, and bone marrow were collected for flow cytometry analyses. Cells expressing the following molecules were quantified: Cluster of differentiation (CD) 4, CD8, CD25, CD34, CD71, B220 (isoform of CD45 on B cells), NK1.1 (marker on natural killer or NK cells, C57B mice), panNK (marker on NK cells, CBA mice), and Sca1 (stem cell antigen 1). RESULTS: Exposure to radiation resulted in different distribution patterns in lymphocyte populations and leukocytes expressing activation and progenitor markers in the two mouse strains. Significant main effects were dependent upon strain, as well as radiation dose, body compartment, and time of assessment. Especially striking differences were noted on day 4 after 3 Gy irradiation, including in the CD4:CD8 ratio [blood, C57 (2.83 ±â€Š0.25) vs. CBA (6.19 ±â€Š0.24); spleen, C57 (2.29 ±â€Š0.12) vs. CBA (4.98 ±â€Š0.22)], %CD25(+) mononuclear cells in bone marrow [C57 (5.62 ±â€Š1.19) vs. CBA (12.45 ±â€Š0.93)] and %CD34(+)Sca1(+) cells in bone marrow [CD45¹° gate, C57 (2.72 ±â€Š0.74) vs. CBA (21.44 ±â€Š0.73)]. CONCLUSION: The results show that genetic background, as well as radiation dose and time post-exposure, had a profound impact on lymphocyte populations, as well as other leukocytes, after exposure to iron ion radiation.

Transgenerational effects of preconception paternal contamination with (55)Fe.

The conjecture that germline mutations induced by radiation exposure before conception may predispose subsequent offspring to cancer remains contentious. Previous experimental studies have shown that preconception paternal irradiation with (239)Pu induces perturbations in the hemopoietic systems of offspring and influences sensitivity to a secondary carcinogen. In the present study, male DBA2 mice were injected intravenously with the Auger electron emitter (55)Fe (4 kBq g(-1)) 18 or 84 days before mating with normal females. Comet analysis showed an increased incidence of DNA strand breaks in sperm from contaminated animals after 84 days, but not after 18 days, indicating spermatogonial rather than spermatid damage. Offspring were either assayed for changes in bone marrow stem cells and committed progenitors or challenged with the chemical carcinogen methyl nitrosourea (MNU, 50 mg/kg) at 10 weeks of age and monitored for the onset of malignancy. Offspring from irradiated fathers had normal peripheral blood profiles, although the stem cell population was amplified in offspring arising from those exposed to (55)Fe at 84 days before conception. Exposure to MNU significantly increased the incidence of lympho-hemopoietic malignancies in offspring from the 84-day group, but not in those from the 18-day group. These findings support the hypothesis that aberrations that are potentially leukemogenic may be transmitted to offspring after radiation damage to the paternal germline.

Evaluation of uncertainties in estimates of fetal doses from 59Fe kinetic studies at Vanderbilt University.

In a 1997 paper, Stabin et al. published estimates of the fetal radiation doses for women who received oral administrations of 59Fe at Vanderbilt University in the 1940's. These authors concluded that there was "considerable uncertainty... in the amount of radioactive material administered to these subjects." In an effort to quantify this uncertainty, the underlying factors in the input data used in the Stabin et al. dose estimates have been examined in detail. Such factors include (a) an absence of detailed information on, and discrepancies in, the amounts of 59Fe reported to have been administered; (b) the probability that the radioactive iron included 55Fe as well as 59Fe; (c) uncertainties as to the period of time that elapsed between the administration of the radioiron and the taking of the maternal blood samples, and the accompanying impacts of radioactive decay; (d) possible losses of 59Fe in the procedures used in preparing the blood samples; and (e) questions as to the reported efficiency of the counting equipment. Our principal conclusion is that, due to the significant uncertainties and the lack of key information, it is not possible to estimate the doses accurately. An ancillary conclusion, however, is that the doses were probably significantly higher than previously estimated. This latter possibility should be carefully considered by any investigators who subsequently seek to use these estimates to quantify the relationship between the doses to the fetus and the resulting health effects.

Craft v. Vanderbilt University.

KIE: Court Decision: 18 Federal Supplement, 2d Series 786; 1998 Aug 19 (date of decision). In a memorandum opinion, the U.S. District Court for the Middle District of Tennessee detailed the reasoning behind an earlier decision to allow the research subjects of radiation experiments to continue their case against a private university, a private foundation, and the state. The subjects were pregnant women who were not informed of the risks of ingesting radioactive iron isotopes in a series of experiments at Vanderbilt University between 1945-1947. Nor were they informed in a later follow-up study about the involuntary exposure, nor contacted later when another follow-up study showed a disproportionately high incidence of cancer among the subjects. Because actions by both Vanderbilt and the Rockefeller Foundation in this joint project were so entwined with those by Tennessee, they could be found liable under federal civil rights law. The claims were not time-barred under Tennessee's medical malpractice statutes, because "the experiments did not constitute medical care." Instead the court concluded that the statute of limitations may be tolled because of fraudulent concealment, noting that "[w]here a confidential relationship exists, as between a physician and a patient, there is an affirmative duty to disclose, and that duty renders silence or failure to disclose known facts fraudulent.^ieng

Additional myeloablation with 52Fe before bone marrow transplantation.

For many hematological malignancies, high-dose chemoradiotherapy followed by bone marrow transplantation offers the best and sometimes the only chance for cure. However, the main causes of failure of this therapy are relapse and toxicity. In order to selectively deliver higher doses of radiotherapy to the bone marrow and to spare normal organs, we explored 52Fe therapy before a conventional BMT conditioning regimen. Twenty-four patients at high risk for relapse after BMT were included in a phase II study. The median follow-up was 42 months. The median 52Fe dose was 59 mCi. This resulted in a median radiation-absorbed dose (RAD) to the BM of 626 rad. The median RAD to the liver was 338 rad. No untoward effects were noted after the injections of 52Fe. The patients recovered hematopoiesis without toxicity in excess of that expected with conventional conditioning alone. The 3-year DFS probability was 49% (95% CI: 20-78%). Eight patients have relapsed, three of them in extramedullary sites. 52Fe should provide a way to boost the radiation dose to marrow-based diseases before bone marrow transplantation without excessive toxicity.

52Fe for additional marrow ablation before bone marrow transplantation.

The effectiveness of bone marrow transplantation (BMT) for malignant blood diseases remains limited by the inability of the preparative regimen to eliminate the disease without causing toxicity to normal organs. We have used 52Fe to deliver radiotherapy selectively to the BM. Fourteen patients with hematologic malignancies received 52Fe before a conventional BMT conditioning regimen. The median 52Fe dose was 58 mCi (range, 32 to 85 mCi). As evaluated by quantitative scanning, the median percentage of 52Fe taken up by the BM was 82% (range, 36% to 90%). This resulted in a median radiation-absorbed dose to the BM of 632 rad (range, 151 to 1,144 rad). The median uptake of 52Fe by the liver was 18% (range, 10% to 64%) and the median radiation-absorbed dose to the liver was 239 rad (range, 82 to 526 rad). The median whole body radiation-absorbed dose was 46 rad (range, 22 to 68 rad). No untoward effects were noted after the injections of 52Fe. The patients recovered hematopoiesis without toxicity in excess of that expected with conventional conditioning alone. The median follow-up was 8 months and three patients have relapsed. 52Fe should provide a way to boost the radiation dose to marrow-based diseases before marrow transplantation without increasing toxicity.

Emesis in ferrets following exposure to different types of radiation: a dose-response study.

Ferrets were exposed to gamma rays (60Co), fission neutrons, high-energy electrons (18.5 MeV) or iron particles (56Fe, 600 MeV/amu) in order to establish the dose-response relationships for emesis following exposure to different types of radiation. The results showed that the mean effective doses (ED50s) for iron particles (35 cGy) and neutrons (40 cGy) were similar. High-energy electrons were the least effective radiation, with an ED50 of 138 cGy. Gamma rays, with an ED50 of 95 cGy, showed an intermediate effectiveness. The results suggest that the relative effectiveness of different types of radiation generally increases with an increase in linear energy transfer (LET), although LET is not completely predictive of relative behavioral effectiveness.