The ionizing radiation exposure to crew on current and future space missions can significantly increase their health risks for cancers, degenerative diseases, and other acute and late effects. A common approach for estimating risk to crew is by completing stochastic (e.g., Monte Carlo) or deterministic particle transport simulations. Within the simulated environment, a small fraction of the particle histories tracked will interact with the astronaut or detector, particularly for larger spacecraft such as the International Space Station, Tiangong Space Station or Lunar Gateway. These simulations can be computationally intensive as they require a very large number of particle histories to achieve a low statistical uncertainty. Variance reduction techniques are applied to simulations to reduce the computational time of the simulation while maintaining the same (or less) statistical uncertainty. The variance reduction technique developed herein involves applying a directional source bias to an isotropic radiation field, such as galactic cosmic rays, to reduce the quantity of particles that have a low probability of interacting with the astronaut or detector. A custom application has been developed utilizing the Geant4 Toolkit that computes the trajectories and energies of particles in three dimensions in the International Space Station using the Monte Carlo method. The results demonstrate the impact of our variance reduction technique on effective dose equivalence depending on: primary and secondary particle type (proton, neutron, photon, heavy ion, etc.), geometric volumes and spacecraft materials. Our variance reduction technique can be tuned by the user to optimize the simulation time depending on their objectives and enables rapid testing of different shield configurations and materials. This variance reduction technique is implemented easily using several input parameters for boundary conditions. Recommended values are presented for rapid implementation in simulations.

Astronauts on exploratory missions will be exposed to particle radiation of high energy and charge (HZE particles), which have been shown to produce neurochemical and performance deficits in animal models. Exposure to HZE particles can produce both targeted effects, resulting from direct ionization of atoms along the particle track, and non-targeted effects (NTEs) in cells that are distant from the track, extending the range of potential damage beyond the site of irradiation. While recent work suggests that NTEs are primarily responsible for changes in cognitive function after HZE exposures, the relative contributions of targeted and non-targeted effects to neurochemical changes after HZE exposures are unclear. The present experiment was designed to further explore the role of targeted and non-targeted effects on HZE-induced neurochemical changes (inflammation and oxidative stress) by evaluating the effects of exposure location and particle energy/linear energy transfer (LET). Forty-six male Sprague-Dawley rats received head-only or body-only exposures to ⁵⁶Fe particles [600 MeV/n (75 cGy) or 1,000 MeV/n (100 cGy)] or ⁴⁸Ti particles [500 MeV/n (50 cGy) or 1,100 MeV/n (75 cGy)] or no irradiation (0 cGy). Twenty-four h after irradiation, rats were euthanized, and the brain was dissected for analysis of HZE-particle-induced neurochemical changes in the hippocampus and frontal cortex. Results showed that exposure to ⁵⁶Fe and ⁴⁸Ti ions produced changes in measurements of brain inflammation [glial fibrillary astrocyte protein (GFAP)], oxidative stress [NADPH-oxidoreductase-2 (NOX2)] and antioxidant enzymes [superoxide dismutase (SOD), glutathione S-transferase (GST), nuclear factor erythroid 2-related factor 2 (Nrf2)]. However, radiation effects varied depending upon the specific measurement, brain region, and exposure location. Although overall exposures of the head produced more detrimental changes in neuroinflammation and oxidative stress than exposures of the body, body-only exposures also produced changes relative to no irradiation, and the effect of particle energy/LET on neurochemical changes was minimal. Results indicate that both targeted and non-targeted effects are important contributors to neurochemical changes after head-only exposure. However, because there were no consistent neurochemical changes as a function of changes in track structure after head-only exposures, the role of direct effects on neuronal function is uncertain. Therefore, these findings, although in an animal model, suggest that NTEs should be considered in the estimation of risk to the central nervous system (CNS) and development of countermeasures.

Pharmacological ascorbate (P-AscH^-, high dose, intravenous vitamin C) preferentially sensitizes human pancreas ductal adenocarcinoma (PDAC) cells to radiation-induced toxicity compared to non-tumorigenic epithelial cells. Radiation-induced G₂-checkpoint activation contributes to the resistance of cancer cells to DNA damage induced toxicity. We hypothesized that P-AscH^- induced radio-sensitization of PDAC cells is mediated by perturbations in the radiation induced activation of the G₂-checkpoint pathway. Both non-tumorigenic pancreatic ductal epithelial and PDAC cells display decreased clonogenic survival and increased doubling times after radiation treatment. In contrast, the addition of P-AscH^- to radiation increases clonogenic survival and decreases the doubling time of non-tumorigenic epithelial cells but decreasing clonogenic survival and increasing the doubling time of PDAC cells. Results from the mitotic index and propidium iodide assays showed that while the P-AscH^- treatments did not affect radiation-induced G₂-checkpoint activation, it enhanced G₂accumulation. The addition of catalase reverses the increases in G₂-accumulation, indicating a peroxide-mediated mechanism. In addition, P-AscH^- treatment of PDAC cells suppresses radiation-induced accumulation of cyclin B1 protein levels. Both translational and post-translational pathways appear to regulate cyclin B1 protein levels after the combination treatment of PDAC cells with P-AscH^- and radiation. The protein changes seen are reversed by the addition of catalase suggesting that hydrogen peroxide mediates P-AscH^- induced radiation sensitization of PDAC cells by enhancing G₂-accumulation and reducing cyclin B1 protein levels.

Diffuse intrinsic pontine gliomas (DIPG) are an aggressive type of pediatric brain tumor with a very high mortality rate. Surgery has a limited role given the tumors location. Palliative radiation therapy alleviates symptoms and prolongs survival, but median survival remains less than 1 year. There is no clear role for chemotherapy in DIPGs as trials adding chemotherapy to palliative radiation therapy have failed to improve survival compared to radiation alone. Thus, there is a critical need to identify tissue-specific radiosensitizers to improve clinical outcomes for patients with DIPGs. Pharmacologic (high dose) ascorbate (P-AscH^–) is a promising anticancer therapy that sensitizes human tumors, including adult high-grade gliomas, to radiation by acting selectively as a generator of hydrogen peroxide (H₂O₂) in cancer cells. In this study we demonstrate that in contrast to adult glioma models, P-AscH– does not radiosensitize DIPG. DIPG cells were sensitive to bolus of H₂O₂ but have faster H₂O₂ removal rates than GBM models which are radiosensitized by P-AscH^–. These data support the hypothesis that P-AscH– does not enhance DIPG radiosensitivity, likely due to a robust capacity to detoxify and remove hydro-peroxides.

The effect of autophagy on the radiation-induced bystander effect (RIBE) in vivo is unclear. Here, the whole brains of microtubule-associated protein 1A/1B-light chain 3 (LC3) and C57BL/6 (B6) mice were irradiated once (10 Gy)(IR1), given 3 fractions in three weeks (IR3), or 6 fractions in six weeks (IR6). The median survival of LC3 mice was 56.5 days, and that of B6 mice was 65 days after IR6. LC3 mice showed more congestion and fibrosis in the lung after the IR3 and IR6 irradiation protocols than B6 mice. Quantitative proteomics of serum samples and lung RNA sequencing of the LC3 group showed that the common most clustered pathway of the IR3 group was the elastic fiber formation pathway, which contained Periostin (POSTN). POSTN in the motoneurons increased with increasing number of radiation fractions in LC3 mice. A 1 lg/g POSTN neutralizing antibody reduced the lung fibrosis of LC3 mice exposed to IR3 by one-third, and significantly prolonged the survival time of LC3 mice exposed to IR6. LDN-214117 and LRRK2-in-1 were the best two of sixteen transforming growth factor-beta1 (TGF-b) receptor and autophagy mediators to decrease Postn mRNA. These data led us to conclude that LC3 accelerated motoneuron secretion of POSTN and aggravated the RIBE in the lung after brain irradiation.

Carbon-ion radiation therapy (CIRT) may offer remarkable advantages in cancer treatment with its unique physical and biological characteristics. However, the underlying epigenetic regulatory mechanisms of cancer response to CIRT remain to be identified. In this study, we showed consistent but different degrees of biological effects induced in NSCLC A549 cells by carbon ions of different LET. The genome-wide chromatin accessibility and transcriptional profiles of carbon ion-treated A549 cells were performed using transposase-accessible chromatin sequencing (ATAC-seq) and RNA-seq, respectively, and further gene regulatory network analysis was performed by integrating the two sets of genomic data. Alterations in chromatin accessibility by carbon ions of different LET predominantly occurred in intron, distal intergenic and promoter regions of differential chromatin accessibility regions. The transcriptional changes were mainly regulated by proximal chromatin accessibility. Notably, CCCTC-binding factor (CTCF) was identified as a key transcription factor in the cellular response to carbon ions. The target genes regulated by CTCF in response to carbon ions were found to be closely associated with the LET of carbon ions, particularly in the regulation of gene transcription within the DNA replication- and metabolism-related signaling pathways. This study provides a regulatory profile of genes involved in key signaling pathways and highlighted key regulatory elements in NSCLC A549 cells during CIRT, which expands our understanding of the epigenetic mechanisms of carbon ion-induced biological effects and reveals an important role for LET in the regulation of changes in chromatin accessibility, although further research is needed.

Radiation exposure arising from radiotherapy may induce rapid bone loss and an increase in the extent of bone resorption. Reactive oxygen species (ROS) caused by radiation exposure play a crucial role during the process of osteoclastogenesis. However, the pathological mechanisms underlying radiation-induced osteoclastogenesis have yet to be fully elucidated. CR6-interacting factor-1 (Crif1) as a multifunctional protein is involved in regulating multiple biological functions in cells. Here, we investigated the role of Crif1 in radiation-induced osteoclastogenesis and found that radiation exposure induced an increase in the expression level of Crif1 and enhanced osteoclastogenesis in osteoclast progenitors. Crif1 and NF-jB p65 co-localized in the cytoplasm after radiation exposure. Crif1 knockdown did not affect the phosphorylation and total protein levels of extracellular signal-regulated kinases (ERK), c-Jun amino (N)-terminal kinases (JNK), p38, and IjB-a before and after irradiation. However, Crif1 knockdown did lead to the reduced phosphorylation and nuclear translocation of NF-jB p65 after irradiation and resulted in a reduced level of osteoclastogenesis in RAW264.7 cells after irradiation. In vivo studies involving Lyz2Cre;Crif1^fl/fl mice possessing the myeloid-specific deletion of Crif1 demonstrated the alleviation of bone loss after irradiation when compared with Crif1^fl/fl mice. Our findings demonstrate that Crif1 mediated the phosphorylation and nuclear translocation of NF-jB p65 and promoted osteoclastogenesis via the NF-jB signaling pathway after radiation exposure. Thus, our analysis revealed a specific role for Crif1 in the mediation of radiation-induced bone loss and may provide new insight into potential therapeutic strategies for radiation-induced bone loss.

Although some adverse effects on neurocognitive function have been reported in children and adolescents irradiated prenatally during the atomic bombings and the Chernobyl nuclear accident, little information is available for effects on the elderly. Here we evaluate the effects of prenatal exposure to atomic bomb radiation on subjective neurocognitive function in aged survivors. To evaluate neurocognitive impairment, we mailed the Neurocognitive Questionnaire (NCQ), a self-administered scale, to prenatally exposed survivors, including clinic visitors and non-visitors at the time of the 2011 and 2013 Adult Health Study (AHS) examinations. We received replies from 444 individuals (mean age, 66.9 ± 0.6 years). After adjusting for sex, city, and educational background, we found no significant effects of radiation, clinic visit, or interaction between radiation and clinic visit on the scores of the 4 NCQ factors of metacognition, emotional regulation, motivation/organization, and processing speed. Even in analyses considering gestational age at the time of the bombings, none of the 4 NCQ factor scores was related to maternal uterine dose. There remains the limitation that this study consisted of healthy survivors, but we found no significant radiation effect on late-life cognition in people prenatally exposed to atomic bomb radiation.