Heavy ion carcinogenesis and human space exploration

Exploring the LET dependence of DNA DSB repair kinetics using the DR DNA database

The repair of DNA double-strand breaks is a crucial yet delicate process which is affected by a multitude of factors. In this study, our goal is to analyse the influence of the linear energy transfer (LET) on the DNA repair kinetics. By utilizing the database of repair of DNA and aggregating the results of 84 experiments, we conduct various model fits to evaluate and compare different hypothesis regarding the effect of LET on the rejoining of DNA ends. Despite the considerable research efforts dedicated to this topic over the past decades, our findings underscore the complexity of the relationship between LET and DNA repair kinetics. This study leverages big data analysis to capture overall trends that single experimental studies might miss, providing a valuable model for understanding how radiation quality impacts DNA damage and subsequent biological effects. Our results highlight the gaps in our current understanding, emphasizing the pressing need for further investigation into this phenomenon.

Synergistic effect of Gemcitabin-loaded metal organic frameworks nanoparticles with particle therapy

Combination of nanoagents with radiations has opened up new perspectives in cancer treatment, improving both tumor diagnosis and therapeutic index. This work presents the first investigation of an innovative strategy that combines porous metal-organic frameworks (nanoMOFs) loaded with the anti-cancer drug Gemcitabine monophosphate (GemMP) and particle therapy-a globally emerging technique that offers more precise radiation targeting and enhanced biological efficacy compared to conventional radiotherapy. This radiochemotherapy has been confronted with two major obstacles limiting the efficacy of therapeutics when tested in vivo: (i) the presence of hypoxia, one of the most important causes for radiotherapy failure and (ii) the presence of a microenvironment, main biological barrier to the direct penetration of nanoparticles into cancer cells. On the one hand, this study explore the effects of hypoxia on drug delivery systems in combination with radiation, demonstrating that GemMP-loaded nanoMOFs significantly enhance the anticancer efficacy of particle therapy under both normoxic (pO2 = 20 %) and hypoxic (pO2 = 0.5 %) conditions. Notably, the presence of GemMP-loaded nanoMOFs allows the irradiation dose to be reduced by 1.4-fold in normoxia and at least 1.6-fold in hypoxia, achieving the same cytotoxic effect (SF=10 %) as carbon or helium ions alone. Synergistic effects between GemMP-loaded nanoMOFs and radiations have been observed and quantified. On the other hand, we also highlighted the ability of the nanoMOFs to diffuse through an extracellular matrix and accumulate in cells. An higher effect of the encapsulated GemMP than the free drug was observed, confirming the key role of the nanoMOFs in transporting the active substance to the cancer cells as a Trojan horse. This paves the way to the design of "all-in-one" nanodrugs where each component plays a role in the optimization of cancer therapy to maximize cytotoxic effects on hypoxic tumor cells while minimizing toxicity on healthy tissue.

Differential network analysis reveals the key role of the ECM-receptor pathway in α-particle-induced malignant transformation

Space particle radiation is a major environmental factor in spaceflight, and it is known to cause body damage and even trigger cancer, but with unknown molecular etiologies. To examine these causes, we developed a systems biology approach by focusing on the co-expression network analysis of transcriptomics profiles obtained from single high-dose (SE) and multiple low-dose (ME) α-particle radiation exposures of BEAS-2B human bronchial epithelial cells. First, the differential network and pathway analysis based on the global network and the core modules showed that genes in the ME group had higher enrichment for the extracellular matrix (ECM)-receptor interaction pathway. Then, collagen gene COL1A1 was screened as an important gene in the ME group assessed by network parameters and an expression study of lung adenocarcinoma samples. COL1A1 was found to promote the emergence of the neoplastic characteristics of BEAS-2B cells by both in vitro experimental analyses and in vivo immunohistochemical staining. These findings suggested that the degree of malignant transformation of cells in the ME group was greater than that of the SE, which may be caused by the dysregulation of the ECM-receptor pathway.

Effects of simulated space conditions on CD4+ T cells: a multi modal analysis

Introduction

The immune system is an intricate network of cellular components that safeguards against pathogens and aberrant cells, with CD4+ T cells playing a central role in this process. Human space travel presents unique health challenges, such as heavy ion ionizing radiation, microgravity, and psychological stress, which can collectively impede immune function. The aim of this research was to examine the consequences of simulated space stressors on CD4+ T cell activation, cytokine production, and gene expression.

Methods

CD4+ T cells were obtained from healthy individuals and subjected to Fe ion particle radiation, Photon irradiation, simulated microgravity, and hydrocortisone, either individually or in different combinations. Cytokine levels for Th1 and Th2 cells were determined using multiplex Luminex assays, and RNA sequencing was used to investigate gene expression patterns and identify essential genes and pathways impacted by these stressors.

Results

Simulated microgravity exposure resulted in an apparent Th1 to Th2 shift, evidenced on the level of cytokine secretion as well as altered gene expression. RNA sequencing analysis showed that several gene pathways were altered, particularly in response to Fe ions irradiation and simulated microgravity exposures. Individually, each space stressor caused differential gene expression, while the combination of stressors revealed complex interactions.

Discussion

The research findings underscore the substantial influence of the space exposome on immune function, particularly in the regulation of T cell responses. Future work should focus expanding the limited knowledge in this field. Comprehending these modifications will be essential for devising effective strategies to safeguard the health of astronauts during extended space missions.

Conclusion

The effects of simulated space stressors on CD4+ T cell function are substantial, implying that space travel poses a potential threat to immune health. Additional research is necessary to investigate the intricate relationship between space stressors and to develop effective countermeasures to mitigate these consequences.

Cognitive Effects of Simulated Galactic Cosmic Radiation Are Mediated by ApoE Status, Sex, and Environment in APP Knock-In Mice

Cosmic radiation experienced during space travel may increase the risk of cognitive impairment. While simulated galactic cosmic radiation (GCRsim) has led to memory deficits in wildtype (WT) mice, it has not been investigated whether GCRsim in combination with genetic risk factors for Alzheimer's disease (AD) worsens memory further in aging mice. Here, we investigated the central nervous system (CNS) effects of 0 Gy (sham) or 0.75 Gy five-ion GCRsim or 2 Gy gamma radiation (IRR) in 14-month-old female and male APPNL-F/NL-F knock-in (KI) mice bearing humanized ApoE3 or ApoE4 (APP;E3F and APP;E4F). As travel to a specialized facility was required for irradiation, both traveled sham-irradiated C57BL/6J WT and KI mice and non-traveled (NT) KI mice acted as controls for potential effects of travel. Mice underwent four behavioral tests at 20 months of age and were euthanized for pathological and biochemical analyses 1 month later. Fecal samples were collected pre- and post-irradiation at four different time points. GCRsim seemed to impair memory in male APP;E3F mice compared to their sham counterparts. Travel tended to improve cognition in male APP;E3F mice and lowered total Aβ in female and male APP;E3F mice compared to their non-traveled counterparts. Sham-irradiated male APP;E4F mice accumulated more fibrillar amyloid than their APP;E3F counterparts. Radiation exposure had only modest effects on behavior and brain changes, but travel-, sex-, and genotype-specific effects were seen. Irradiated mice had immediate and long-term differences in their gut bacterial composition that correlated to Alzheimer's disease phenotypes.

Simulated microgravity impairs human NK cell cytotoxic activity against space radiation-relevant leukemic cells

Natural killer (NK) cells are an important first-line of defense against malignant cells. Because of the potential for increased cancer risk from astronaut exposure to space radiation, we determined whether microgravity present during spaceflight affects the body's defenses against leukemogenesis. Human NK cells were cultured for 48 h under normal gravity and simulated microgravity (sμG), and cytotoxicity against K-562 (CML) and MOLT-4 (T-ALL) cells was measured using standard methodology or under continuous sμG. This brief exposure to sμG markedly reduced NK cytotoxicity against both leukemias, and these deleterious effects were more pronounced in continuous sμG. RNA-seq performed on NK cells from two additional healthy donors provided insight into the mechanism(s) by which sμG reduced cytotoxicity. Given our prior report of space radiation-induced human T-ALL in vivo, the reduced cytotoxicity against MOLT-4 is striking and raises the possibility that μG may increase astronaut risk of leukemogenesis during prolonged missions beyond LEO.

Protective alleles and precision healthcare in crewed spaceflight

Common and rare alleles are now being annotated across millions of human genomes, and omics technologies are increasingly being used to develop health and treatment recommendations. However, these alleles have not yet been systematically characterized relative to aerospace medicine. Here, we review published alleles naturally found in human cohorts that have a likely protective effect, which is linked to decreased cancer risk and improved bone, muscular, and cardiovascular health. Although some technical and ethical challenges remain, research into these protective mechanisms could translate into improved nutrition, exercise, and health recommendations for crew members during deep space missions.

Synergistic interplay between radiation and microgravity in spaceflight-related immunological health risks

Spaceflight poses a myriad of environmental stressors to astronauts´ physiology including microgravity and radiation. The individual impacts of microgravity and radiation on the immune system have been extensively investigated, though a comprehensive review on their combined effects on immune system outcomes is missing. Therefore, this review aims at understanding the synergistic, additive, and antagonistic interactions between microgravity and radiation and their impact on immune function as observed during spaceflight-analog studies such as rodent hindlimb unloading and cell culture rotating wall vessel models. These mimic some, but not all, of the physiological changes observed in astronauts during spaceflight and provide valuable information that should be considered when planning future missions. We provide guidelines for the design of further spaceflight-analog studies, incorporating influential factors such as age and sex for rodent models and standardizing the longitudinal evaluation of specific immunological alterations for both rodent and cellular models of spaceflight exposure.

Insights into the radioprotective efficacy of Pterocarpus santalinus L. aqueous extract

In the present study, we have attempted a comprehensive assessment of the possible radioprotective efficacy of Pterocarpus santalinus aqueous extract (PSAE). All the studied models were gamma-irradiated with prior treatment with PSAE. First, the content of total phenols (4.061 μg/mg gallic acid equivalents), flavonoids (6.616 μg/mg quercetin equivalents), and tannins (0.008 mg/L of PSAE) were determined spectrophotometrically. Second, UHPLC-HRMS analysis was performed to identify the possible radioprotectors. Of those, santalins A & B are known for their usage as natural color in foods and alcoholic beverages identified in PSAE. Treatment was well tolerated with no side effects from PSAE. Later, it was shown that radiation-induced lethality significantly amended in PSAE-treated spleen lymphocytes as evidenced by reduced elevated levels of ROS and lipid peroxidation, restored total thiols and GSH: GSSG, inhibited DNA DSBs and cell death. Furthermore, an immunomodulation study was carried out because radiation exposure induces an inflammatory response. Our study shows that PSAE suppressed concanavalin A-induced T-cell proliferation as evidenced by CFSE dye dilution and CD69 antibody staining methods. Taken together, the current study explored the protective efficacy of PSAE from gamma radiation-inflicted injuries and hence we recommend PSAE as a potent radioprotective formulation.

Galactic Cosmic Ray Particle Exposure Does Not Increase Protein Levels of Inflammation or Oxidative Stress Markers in Rat Microglial Cells In Vitro

Astronauts on exploratory missions will be exposed to galactic cosmic rays (GCR), which can induce neuroinflammation and oxidative stress (OS) and may increase the risk of neurodegenerative disease. As key regulators of inflammation and OS in the CNS, microglial cells may be involved in GCR-induced deficits, and therefore could be a target for neuroprotection. This study assessed the effects of exposure to helium (4He) and iron (56Fe) particles on inflammation and OS in microglia in vitro, to establish a model for testing countermeasure efficacy. Rat microglia were exposed to a single dose of 20 cGy (300 MeV/n) 4He or 2 Gy 56Fe (600 MeV/n), while the control cells were not exposed (0 cGy). Immediately following irradiation, fresh media was applied to the cells, and biomarkers of inflammation (cyclooxygenase-2 [COX-2], nitric oxide synthase [iNOS], phosphorylated IκB-α [pIκB-α], tumor necrosis factor-α [TNFα], and nitrite [NO2-]) and OS (NADPH oxidase [NOX2]) were assessed 24 h later using standard immunochemical techniques. Results showed that radiation did not increase levels of NO2- or protein levels of COX-2, iNOS, pIκB-α, TNFα, or NOX2 compared to non-irradiated control conditions in microglial cells (p > 0.05). Therefore, microglia in isolation may not be the primary cause of neuroinflammation and OS following exposures to helium or iron GCR particles.

Chromosomal damage, gene expression and alternative transcription in human lymphocytes exposed to mixed ionizing radiation as encountered in space

Astronauts travelling in space will be exposed to mixed beams of particle radiation and photons. Exposure limits that correspond to defined cancer risk are calculated by multiplying absorbed doses by a radiation-type specific quality factor that reflects the biological effectiveness of the particle without considering possible interaction with photons. We have shown previously that alpha radiation and X-rays may interact resulting in synergistic DNA damage responses in human peripheral blood lymphocytes but the level of intra-individual variability was high. In order to assess the variability and validate the synergism, blood from two male donors was drawn at 9 time points during 3 seasons of the year and exposed to 0-2 Gy of X-rays, alpha particles or 1:1 mixture of both (half the dose each). DNA damage response was quantified by chromosomal aberrations and by mRNA levels of 3 radiation-responsive genes FDXR, CDKN1A and MDM2 measured 24 h post exposure. The quality of response in terms of differential expression of alternative transcripts was assessed by using two primer pairs per gene. A consistently higher than expected effect of mixed beams was found in both donors for chromosomal aberrations and gene expression with some seasonal variability for the latter. No synergy was detected for alternative transcription.

Radiation-induced DNA double-strand breaks in cortisol exposed fibroblasts as quantified with the novel foci-integrated damage complexity score (FIDCS)

Without the protective shielding of Earth's atmosphere, astronauts face higher doses of ionizing radiation in space, causing serious health concerns. Highly charged and high energy (HZE) particles are particularly effective in causing complex and difficult-to-repair DNA double-strand breaks compared to low linear energy transfer. Additionally, chronic cortisol exposure during spaceflight raises further concerns, although its specific impact on DNA damage and repair remains unknown. This study explorers the effect of different radiation qualities (photons, protons, carbon, and iron ions) on the DNA damage and repair of cortisol-conditioned primary human dermal fibroblasts. Besides, we introduce a new measure, the Foci-Integrated Damage Complexity Score (FIDCS), to assess DNA damage complexity by analyzing focus area and fluorescent intensity. Our results show that the FIDCS captured the DNA damage induced by different radiation qualities better than counting the number of foci, as traditionally done. Besides, using this measure, we were able to identify differences in DNA damage between cortisol-exposed cells and controls. This suggests that, besides measuring the total number of foci, considering the complexity of the DNA damage by means of the FIDCS can provide additional and, in our case, improved information when comparing different radiation qualities.

A method to predict space radiation biological effectiveness for non-cancer effects following intense Solar Particle Events

In addition to the continuous exposure to cosmic rays, astronauts in space are occasionally exposed to Solar Particle Events (SPE), which involve less energetic particles but can deliver much higher doses. The latter can exceed several Gy in a few hours for the most intense SPEs, for which non-stochastic effects are thus a major concern. To identify adequate shielding conditions that would allow respecting the dose limits established by the various space agencies, the absorbed dose in the considered organ/tissue must be multiplied by the corresponding Relative Biological Effectiveness (RBE), which is a complex quantity depending on several factors including particle type and energy, considered biological effect, level of effect (and thus absorbed dose), etc. While in several studies only the particle-type dependence of RBE is taken into account, in this work we developed and applied a new approach where, thanks to an interface between the FLUKA Monte Carlo transport code and the BIANCA biophysical model, the RBE dependence on particle energy and absorbed dose was also considered. Furthermore, we included in the considered SPE spectra primary particles heavier than protons, which in many studies are neglected. This approach was then applied to the October 2003 SPE (the most intense SPE of solar cycle 23, also known as "Halloween event") and the January 2005 event, which was characterized by a lower fluence but a harder spectrum, i.e., with higher-energy particles. The calculation outcomes were then discussed and compared with the current dose limits established for skin and blood forming organs in case of 30-days missions. This work showed that the BIANCA model, if interfaced to a radiation transport code, can be used to calculate the RBE values associated to Solar Particle Events. More generally, this work emphasizes the importance of taking into account the RBE dependence on particle energy and dose when calculating equivalent doses.

Simulated Microgravity Impairs Human NK Cell Cytotoxic Activity Against Space Radiation-Relevant Leukemic Cells

Natural killer (NK) cells are important effectors of the innate immune system. Unlike T cells, NK cells do not require antigen-priming, making them an important first-line of defense against malignant cells. Because of the potential for increased cancer risk as a result of astronaut exposure to space radiation, we performed studies to determine whether conditions of microgravity present during spaceflight affects the body's natural defenses against leukemogenesis. Human NK cells were cultured for 48 hours under normal gravity and simulated microgravity (sµG), and cytotoxicity against K-562 (CML) and MOLT-4 (T-ALL) cell lines was measured using standard methodology or under continuous conditions of sµG. Even this brief exposure to sµG markedly reduced NK cytotoxicity against both leukemic cells using standard assay procedures, and these deleterious effects were even more pronounced in continuous sµG. RNA-seq performed on NK cells from two healthy donors provided insight into the mechanism(s) by which sµG reduced cytotoxicity. Given our prior report that human HSC exposed to simulated space radiation gave rise to T-ALL in vivo , the reduced cytotoxicity against MOLT-4 is striking and raises the possibility that µG may add to astronaut risk of leukemogenesis during prolonged missions beyond LEO.

Using single-sample networks to identify the contrasting patterns of gene interactions and reveal the radiation dose-dependent effects in multiple tissues of spaceflight mice

Transcriptome profiles are sensitive to space stressors and serve as valuable indicators of the biological effects during spaceflight. Herein, we transformed the expression profiles into gene interaction patterns by single-sample networks (SSNs) and performed the integrated analysis on the 301 spaceflight and 290 ground control samples, which were obtained from the GeneLab platform. Specifically, an individual SSN was established for each sample. Based on the topological structures of 591 SSNs, the differentially interacted genes (DIGs) were identified between spaceflights and ground controls. The results showed that spaceflight disrupted the gene interaction patterns in mice and resulted in significant enrichment of biological processes such as protein/amino acid metabolism and nucleic acid (DNA/RNA) metabolism (P-value < 0.05). We observed that the mice exposed to radiation doses within the three intervals (4.66-7.14, 7.592-8.295, 8.49-22.099 mGy) exhibited similar gene interaction patterns. Low and medium doses resulted in changes to the circadian rhythm, while the damaging effects on genetic material became more pronounced in higher doses. The gene interaction patterns in response to space stressors varied among different tissues, with the spleen, lung, and skin being the most responsive to space radiation (P-value < 0.01). The changes observed in gene networks during spaceflight conditions might contribute to the development of various diseases, such as mental disorders, depression, and metabolic disorders, among others. Additionally, organisms activated specific gene networks in response to virus reactivation. We identified several hub genes that were associated with circadian rhythms, suggesting that spaceflight could lead to substantial circadian rhythm dysregulation.

Kaplan lecture 2023: lymphopenia in particle therapy

PURPOSE

Lymphopenia is now generally recognized as a negative prognostic factor in radiotherapy. Already at the beginning of the century we demonstrated that high-energy carbon ions induce less damage to the lymphocytes of radiotherapy patients than X-rays, even if heavy ions are more effective per unit dose in the induction of chromosomal aberrations in blood cells irradiated ex-vivo. The explanation was based on the volume effect, i.e. the sparing of larger volumes of normal tissue in Bragg peak therapy. Here we will review the current knowledge about the difference in lymphopenia between particle and photon therapy and the consequences.

CONCLUSIONS

There is nowadays an overwhelming evidence that particle therapy reduces significantly the radiotherapy-induced lymphopenia in several tumor sites. Because lymphopenia turns down the immune response to checkpoint inhibitors, it can be predicted that particle therapy may be the ideal partner for combined radiation and immunotherapy treatment and should be selected for patients where severe lymphopenia is expected after X-rays.

Integrating evolutionarily conserved mechanism of response to radiation for exploring novel Caenorhabditis elegans radiation-responsive genes for estimation of radiation dose associated with spaceflight

During space exploration, space radiation is widely recognized as an inescapable perilous stressor, owing to its capacity to induce genomic DNA damage and escalate the likelihood of detrimental health outcomes. Rapid and reliable estimation of space radiation dose holds paramount significance in accurately assessing the health risks associated with spaceflight. However, the identification of space radiation-responsive genes, with their potential to serve as early indicators for diagnosing radiation dose associated with spaceflight, continues to pose a significant challenge. In this study, based on the evolutionarily conserved mechanism of radiation response, an in silico analysis method of homologous comparison was performed to identify the Caenorhabditis elegans orthologues of human radiation-responsive genes with possible roles in the major processes of response to radiation, and thereby to explore the potential C. elegans radiation-responsive genes for evaluating the levels of space radiation exposure. The results showed that there were 60 known C. elegans radiation-responsive genes and 211 C. elegans orthologues of human radiation-responsive genes implicated in the major processes of response to radiation. Through an investigation of all available transcriptomic datasets obtained from space-flown C. elegans, it was observed that the expression levels of the majority of these putative C. elegans radiation-responsive genes identified in this study were notably changed across various spaceflight conditions. Furthermore, this study indicated that within the identified genes, 19 known C. elegans radiation-responsive genes and 40 newly identified C. elegans orthologues of human radiation-responsive genes exhibited a remarkable positive correlation with the duration of spaceflight. Moreover, a noteworthy presence of substantial multi-collinearity among the majority of these identified genes was observed. This observation lends support to the possibility of treating each identified gene as an independent indicator of radiation dose in space. Ultimately, a subset of 15 potential radiation-responsive genes was identified, presenting the most promising indicators for estimation of radiation dose associated with spaceflight in C. elegans.

The human biology of spaceflight

To expand the human exploration footprint and reach Mars in the 2030s, we must explore how humans survive and thrive in demanding, unusual, and novel ecologies (i.e., extreme environments). In the extreme conditions encountered during human spaceflight, there is a need to understand human functioning and response in a more rigorous theoretically informed way. Current models of human performance in space-relevant environments and human space science are often operationally focused, with emphasis on acute physiological or behavioral outcomes. However, integrating current perspectives in human biology allows for a more holistic and complete understanding of how humans function over a range of time in an extreme environment. Here, we show how the use of evolution-informed frameworks (i.e., models of life history theory to organize the adaptive pressures of spaceflight and biocultural perspectives) coupled with the use of mixed-methodological toolkits can shape models that better encompass the scope of biobehavioral human adjustment to long-duration space travel and extra-terrestrial habitation. Further, we discuss how we can marry human biology perspectives with the rigorous programmatic structures developed for spaceflight to model other unknown and nascent extremes.

Ion beam processing of DNA origami nanostructures

DNA origami nanostructures are emerging as a bottom-up nanopatterning approach. Direct combination of this approach with top-down nanotechnology, such as ion beams, has not been considered because of the soft nature of the DNA material. Here we demonstrate that the shape of 2D DNA origami nanostructures deposited on Si substrates is well preserved upon irradiation by ion beams, modeling ion implantation, lithography, and sputtering conditions. Structural changes in 2D DNA origami nanostructures deposited on Si are analyzed using AFM imaging. The observed effects on DNA origami include structure height decrease or increase upon fast heavy ion irradiation in vacuum and in air, respectively. Slow- and medium-energy heavy ion irradiation results in the cutting of the nanostructures or crater formation with ion-induced damage in the 10 nm range around the primary ion track. In all these cases, the designed shape of the 2D origami nanostructure remains unperturbed. Present stability and nature of damages on DNA origami nanostructures enable fusion of DNA origami advantages such as shape and positioning control into novel ion beam nanofabrication approaches.

Radiation cataract in Heterogeneous Stock mice after γ-ray or HZE ion exposure

Health effects of space radiation are a serious concern for astronauts on long-duration missions. The lens of the eye is one of the most radiosensitive tissues in the body and, therefore, ocular health risks for astronauts is a significant concern. Studies in humans and animals indicate that ionizing radiation exposure to the eye produces characteristic lens changes, termed "radiation cataract," that can affect visual function. Animal models of radiation cataractogenesis have previously utilized inbred mouse or rat strains. These studies were essential for determining morphological changes and dose-response relationships between radiation exposure and cataract. However, the relevance of these studies to human radiosensitivity is limited by the narrow phenotypic range of genetically homogeneous animal models. To model radiation cataract in genetically diverse populations, longitudinal cataract phenotyping was nested within a lifetime carcinogenesis study in male and female heterogeneous stock (HS/Npt) mice exposed to 0.4 Gy HZE ions (n = 609) or 3.0 Gy γ-rays (n = 602) and in unirradiated controls (n = 603). Cataractous change was quantified in each eye for up to 2 years using Merriam-Focht grading criteria by dilated slit lamp examination. Virtual Optomotry™ measurement of visual acuity and contrast sensitivity was utilized to assess visual function in a subgroup of mice. Prevalence and severity of posterior lens opacifications were 2.6-fold higher in HZE ion and 2.3-fold higher in γ-ray irradiated mice compared to unirradiated controls. Male mice were at greater risk for spontaneous and radiation associated cataracts. Risk for cataractogenesis was associated with family structure, demonstrating that HS/Npt mice are well-suited to evaluate genetic determinants of ocular radiosensitivity. Last, mice were extensively evaluated for cataract and tumor formation, which revealed an overlap between individual susceptibility to both cancer and cataract.

Non-targeted effects and space radiation risks for astronauts on multiple International Space Station and lunar missions

Future space travel to the earth's moon or the planet Mars will likely lead to the selection of experienced International Space Station (ISS) or lunar crew persons for subsequent lunar or mars missions. Major concerns for space travel are galactic cosmic ray (GCR) risks of cancer and circulatory diseases. However large uncertainties in risk prediction occur due to the quantitative and qualitative differences in heavy ion microscopic energy deposition leading to differences in biological effects compared to low LET radiation. In addition, there are sparse radiobiology data and absence of epidemiology data for heavy ions and other high LET radiation. Non-targeted effects (NTEs) are found in radiobiology studies to increase the biological effectiveness of high LET radiation at low dose for cancer related endpoints. In this paper the most recent version of the NASA Space Cancer Risk model (NSCR-2022) is used to predict mission risks while considering NTEs in solid cancer risk predictions. I discuss predictions of space radiation risks of cancer and circulatory disease mortality for US Whites and US Asian-Pacific Islander (API) populations for 6-month ISS, 80-day lunar missions, and combined ISS-lunar mission. Model predictions suggest NTE increase cancer risks by about ∼2.3 fold over a model that ignores NTEs. US API are predicted to have a lower cancer risks of about 30% compared to US Whites. Cancer risks are slightly less than additive for multiple missions, which is due to the decease of risk with age of exposure and the increased competition with background risks as radiation risks increase. The inclusion of circulatory risks increases mortality estimates about 25% and 37% for females and males, respectively in the model ignoring NTEs, and 20% and 30% when NTEs are assumed to modify solid cancer risk. The predictions made here for combined ISS and lunar missions suggest risks are within risk limit recommendations by the National Council on Radiation Protection and Measurements (NCRP) for such missions.

Genome-scale metabolic modelling of extremophiles and its applications in astrobiological environments

Metabolic modelling approaches have become the powerful tools in modern biology. These mathematical models are widely used to predict metabolic phenotypes of the organisms or communities of interest, and to identify metabolic targets in metabolic engineering. Apart from a broad range of industrial applications, the possibility of using metabolic modelling in the contexts of astrobiology are poorly explored. In this mini-review, we consolidated the concepts and related applications of applying metabolic modelling in studying organisms in space-related environments, specifically the extremophilic microbes. We recapitulated the current state of the art in metabolic modelling approaches and their advantages in the astrobiological context. Our review encompassed the applications of metabolic modelling in the theoretical investigation of the origin of life within prebiotic environments, as well as the compilation of existing uses of genome-scale metabolic models of extremophiles. Furthermore, we emphasize the current challenges associated with applying this technique in extreme environments, and conclude this review by discussing the potential implementation of metabolic models to explore theoretically optimal metabolic networks under various space conditions. Through this mini-review, our aim is to highlight the potential of metabolic modelling in advancing the study of astrobiology.

Space agency-specific standards for crew dose and risk assessment of ionising radiation exposures for the International Space Station

The Partner Agencies of the International Space Station (ISS) maintain separate career exposure limits and shared Flight Rules that control the ionising radiation exposures that crewmembers can experience due to ambient environments throughout their space missions. In low Earth orbit as well as further out in space, energetic ions referred to as galactic cosmic radiation (GCR) easily penetrate spacecraft and spacecraft contents and consequently are always present at low dose rates. Protons and electrons that are trapped in the Earth's geomagnetic field are encountered intermittently, and a rare energetic solar particle event (SPE) may expose crew to (mostly) energetic protons. Space radiation protection goals are to optimize radiation exposures to maintain deleterious late effects at known and acceptable levels and to prevent any early effects that might compromise crew health and mission success. The conventional radiation protection metric effective dose provides a basic framework for limiting exposures associated with human spaceflight and can be communicated to all stakeholders. Additional metrics and uncertainty analyses are required to understand more completely and to convey nuanced information about potential impacts to an individual astronaut or to a space mission. Missions to remote destinations well beyond low Earth orbit (BLEO) are upcoming and bestow additional challenges that shape design and radiation protection needs. NASA has recently adopted a more permissive career exposure limit based upon effective dose and new restrictions on mission exposures imposed by nuclear technologies. This manuscript reviews the exposure limits that apply to the ISS crewmembers. This work was performed in collaboration with the advisory and guidance efforts of International Commission on Radiological Protection (ICRP) Task Group 115 and will be summarized in an upcoming ICRP Report.

Chromosomal positioning and epigenetic architecture influence DNA methylation patterns triggered by galactic cosmic radiation

Despite surging interest in space travel in recent decades, the impacts of prolonged, elevated exposure to galactic cosmic radiation (GCR) on human health remain poorly understood. This form of ionizing radiation causes significant changes to biological systems including damage to DNA structure by altering epigenetic phenotype with emphasis on DNA methylation. Building on previous work by Kennedy et al. (Sci Rep 8(1): 6709. 10.1038/S41598-018-24755-8), we evaluated spatial DNA methylation patterns triggered by high-LET (56Fe, 28Si) and low-LET (X-ray) radiation and the influence of chromosome positioning and epigenetic architecture in distinct radial layers of cell nucleus. Next, we validated our results using gene expression data of mice irradiated with simulated GCR and JAXA astronauts. We showed that primarily 56Fe induces a persistent DNA methylation increase whereas 28Si and X-ray induce a decrease DNA methylation which is not persistent with time. Moreover, we highlighted the role of nuclear chromatin architecture in cell response to external radiation. In summary, our study provides novel insights towards epigenetic and transcriptomic response as well as chromatin multidimensional structure influence on galactic cosmic radiation damage.

Neurovascular dysfunction associated with erectile dysfunction persists after long-term recovery from simulations of weightlessness and deep space irradiation

There has been growing interest within the space industry for long-duration manned expeditions to the Moon and Mars. During deep space missions, astronauts are exposed to high levels of galactic cosmic radiation (GCR) and microgravity which are associated with increased risk of oxidative stress and endothelial dysfunction. Oxidative stress and endothelial dysfunction are causative factors in the pathogenesis of erectile dysfunction, although the effects of spaceflight on erectile function have been unexplored. Therefore, the purpose of this study was to investigate the effects of simulated spaceflight and long-term recovery on tissues critical for erectile function, the distal internal pudendal artery (dIPA), and the corpus cavernosum (CC). Eighty-six adult male Fisher-344 rats were randomized into six groups and exposed to 4-weeks of hindlimb unloading (HLU) or weight-bearing control, and sham (0Gy), 0.75 Gy, or 1.5 Gy of simulated GCR at the ground-based GCR simulator at the NASA Space Radiation Laboratory. Following a 12-13-month recovery, ex vivo physiological analysis of the dIPA and CC tissue segments revealed differential impacts of HLU and GCR on endothelium-dependent and -independent relaxation that was tissue type specific. GCR impaired non-adrenergic non-cholinergic (NANC) nerve-mediated relaxation in the dIPA and CC, while follow-up experiments of the CC showed restoration of NANC-mediated relaxation of GCR tissues following acute incubation with the antioxidants mito-TEMPO and TEMPOL, as well as inhibitors of xanthine oxidase and arginase. These findings indicate that simulated spaceflight exerts a long-term impairment of neurovascular erectile function, which exposes a new health risk to consider with deep space exploration.

Lost in Space? Unmasking the T Cell Reaction to Simulated Space Stressors

The space environment will expose astronauts to stressors like ionizing radiation, altered gravity fields and elevated cortisol levels, which pose a health risk. Understanding how the interplay between these stressors changes T cells' response is important to better characterize space-related immune dysfunction. We have exposed stimulated Jurkat cells to simulated space stressors (1 Gy, carbon ions/1 Gy photons, 1 µM hydrocortisone (HC), Mars, moon, and microgravity) in a single or combined manner. Pro-inflammatory cytokine IL-2 was measured in the supernatant of Jurkat cells and at the mRNA level. Results show that alone, HC, Mars gravity and microgravity significantly decrease IL-2 presence in the supernatant. 1 Gy carbon ion irradiation showed a smaller impact on IL-2 levels than photon irradiation. Combining exposure to different simulated space stressors seems to have less immunosuppressive effects. Gene expression was less impacted at the time-point collected. These findings showcase a complex T cell response to different conditions and suggest the importance of elevated cortisol levels in the context of space flight, also highlighting the need to use simulated partial gravity technologies to better understand the immune system's response to the space environment.

Intermediate LET-like effect in distal part of proton Bragg peak revealed by track-ends imaging during super-Fricke radiolysis

Upstream of the efficiency of proton or carbon ion beams in cancer therapy, and to optimize hadrontherapy results, we analysed the chemistry of Fricke solutions in track-end of 64-MeV protons and 1.14-GeV carbon ions. An original optical setup is designed to determine the primary track-segment yields along the last millimetres of the ion track with a sub-millimetre resolution. The Fe3+-yield falls in the Bragg peak to (4.9 ± 0.4) × 10-7 mol/J and 1.9 × 10-7 mol/J, under protons and carbon ions respectively. Beyond the Bragg peak, a yield recovery is observed over 1 mm for proton beams. It is attributed to the intermediate-LET of protons in this region where their energy decreases and energy distribution becomes broader, in relation with the longitudinal straggling of the beam. Consequently to this LET decrease in the distal part of the Bragg peak, Fe3+-yield increases. For the first time, this signature is highlighted at the chemical level under proton irradiation. Nevertheless, this phenomenon is not identified for carbon ion beams since their straggling is lower. It would need a greater spatial resolution to be observed.

Simulating Space Conditions Evokes Different DNA Damage Responses in Immature and Mature Cells of the Human Hematopoietic System

The impact of space radiation and microgravity on DNA damage responses has been discussed controversially, largely due to the variety of model systems engaged. Here, we performed side-by-side analyses of human hematopoietic stem/progenitor cells (HSPC) and peripheral blood lymphocytes (PBL) cultivated in a 2D clinostat to simulate microgravity before, during and after photon and particle irradiation. We demonstrate that simulated microgravity (SMG) accelerates the early phase of non-homologous end joining (NHEJ)-mediated repair of simple, X-ray-induced DNA double-strand breaks (DSBs) in PBL, while repair kinetics in HSPC remained unaltered. Repair acceleration was lost with increasing LET of ion exposures, which increases the complexity of DSBs, precluding NHEJ and requiring end resection for successful repair. Such cell-type specific effect of SMG on DSB repair was dependent on the NF-кB pathway pre-activated in PBL but not HSPC. Already under unperturbed growth conditions HSPC and PBL suffered from SMG-induced replication stress associated with accumulation of single-stranded DNA and DSBs, respectively. We conclude that in PBL, SMG-induced DSBs promote repair of radiation-induced damage in an adaptive-like response. HSPC feature SMG-induced single-stranded DNA and FANCD2 foci, i.e., markers of persistent replication stress and senescence that may contribute to a premature decline of the immune system in space.

TLR4 Agonist MPLA Ameliorates Heavy-Ion Radiation Damage via Regulating DNA Damage Repair and Apoptosis

Heavy-ion radiation received during radiotherapy as well as the heavy-ion radiation received during space flight are equally considered harmful. Our previous study showed that TLR4 low toxic agonist, monophosphoryl lipid A (MPLA), alleviated radiation injury resulting from exposure to low-LET radiation. However, the role and mechanism of MPLA in heavy-ion-radiation injury are unclear. This study aimed to investigate the role of MPLA on radiation damage. Our data showed that MPLA treatment alleviated the heavy-ion-induced damage to microstructure and the spleen and testis indexes. The number of karyocytes in the bone marrow from the MPLA-treated group was higher than that in the irradiated group. Meanwhile, western blotting analysis of intestine proteins showed that pro-apoptotic proteins (cleaved-caspase3 and Bax) were downregulated while anti-apoptotic proteins (Bcl-2) were upregulated in the MPLA-treated group. Our in vitro study demonstrated that MPLA significantly improved cell proliferation and inhibited cell apoptosis after irradiation. Moreover, immunofluorescence staining and quantification of nucleic γ-H2AX and 53BP1 foci also suggested that MPLA significantly attenuated cellular DNA damage repair. Collectively, the above evidence supports the potential ability of MPLA to protect against heavy-ion-radiation injury by inhibiting apoptosis and alleviating DNA damage in vivo and vitro, which could be a promising medical countermeasure for the prevention of heavy-ion-radiation injury.

A Dusty Road for Astronauts

The lunar dust problem was first formulated in 1969 with NASA's first successful mission to land a human being on the surface of the Moon. Subsequent Apollo missions failed to keep the dust at bay, so exposure to the dust was unavoidable. In 1972, Harrison Schmitt suffered a brief sneezing attack, red eyes, an itchy throat, and congested sinuses in response to lunar dust. Some additional Apollo astronauts also reported allergy-like symptoms after tracking dust into the lunar module. Immediately following the Apollo missions, research into the toxic effects of lunar dust on the respiratory system gained a lot of interest. Moreover, researchers believed other organ systems might be at risk, including the skin and cornea. Secondary effects could translocate to the cardiovascular system, the immune system, and the brain. With current intentions to return humans to the moon and establish a semi-permanent presence on or near the moon's surface, integrated, end-to-end dust mitigation strategies are needed to enable sustainable lunar presence and architecture. The characteristics and formation of Martian dust are different from lunar dust, but advances in the research of lunar dust toxicity, mitigation, and protection strategies can prove strategic for future operations on Mars.

Microbial applications for sustainable space exploration beyond low Earth orbit

With the construction of the International Space Station, humans have been continuously living and working in space for 22 years. Microbial studies in space and other extreme environments on Earth have shown the ability for bacteria and fungi to adapt and change compared to "normal" conditions. Some of these changes, like biofilm formation, can impact astronaut health and spacecraft integrity in a negative way, while others, such as a propensity for plastic degradation, can promote self-sufficiency and sustainability in space. With the next era of space exploration upon us, which will see crewed missions to the Moon and Mars in the next 10 years, incorporating microbiology research into planning, decision-making, and mission design will be paramount to ensuring success of these long-duration missions. These can include astronaut microbiome studies to protect against infections, immune system dysfunction and bone deterioration, or biological in situ resource utilization (bISRU) studies that incorporate microbes to act as radiation shields, create electricity and establish robust plant habitats for fresh food and recycling of waste. In this review, information will be presented on the beneficial use of microbes in bioregenerative life support systems, their applicability to bISRU, and their capability to be genetically engineered for biotechnological space applications. In addition, we discuss the negative effect microbes and microbial communities may have on long-duration space travel and provide mitigation strategies to reduce their impact. Utilizing the benefits of microbes, while understanding their limitations, will help us explore deeper into space and develop sustainable human habitats on the Moon, Mars and beyond.

56 Fe ion exposure increases the incidence of lung and brain tumors at a similar rate in male and female mice

The main deterrent to long-term space travel is the risk of Radiation Exposure Induced Death (REID). The National Aeronautics and Space Administration (NASA) has adopted Permissible Exposure Levels (PELs) to limit the probability of REID to 3% for the risk of death due to radiation-induced carcinogenesis. The most significant contributor to current REID estimates for astronauts is the risk of lung cancer. Recently updated lung cancer estimates from Japan's atomic bomb survivors showed that the excess relative risk of lung cancer by age 70 is roughly four-fold higher in females compared to males. However, whether sex differences may impact the risk of lung cancer due to exposure to high charge and energy (HZE) radiation is not well studied. Thus, to evaluate the impact of sex differences on the risk of solid cancer development post-HZE radiation exposure, we irradiated Rb fl/fl ; Trp53 fl/+ male and female mice infected with Adeno-Cre with various doses of 320 kVp X-rays or 600 MeV/n 56 Fe ions and monitored them for any radiation-induced malignancies. We observed that lung adenomas/carcinomas and esthesioneuroblastomas (ENBs) were the most common primary malignancies in X-ray and 56 Fe ion-exposed mice, respectively. In addition, 1 Gy 56 Fe ion exposure compared to X-rays led to a significantly higher incidence of lung adenomas/carcinomas (p=0.02) and ENBs (p<0.0001). However, we did not find a significantly higher incidence of any solid malignancies in female mice as compared to male mice, regardless of radiation quality. Furthermore, gene expression analysis of ENBs suggested a distinct gene expression pattern with similar hallmark pathways altered, such as MYC targets and MTORC1 signaling, in X-ray and 56 Fe ion-induced ENBs. Thus, our data revealed that 56 Fe ion exposure significantly accelerated the development of lung adenomas/carcinomas and ENBs compared to X-rays, but the rate of solid malignancies was similar between male and female mice, regardless of radiation quality.

Environmental radiation exposure at Chornobyl has not systematically affected the genomes or mutagen tolerance phenotypes of local worms

The 1986 disaster at the Chornobyl Nuclear Power Plant transformed the surrounding region into the most radioactive landscape known on the planet. Questions remain regarding whether this sudden environmental shift selected for species, or even individuals within a species, that are naturally more resistant to radiation exposure. We collected, cultured, and cryopreserved 298 wild nematodes isolates from areas varying in radioactivity within the Chornobyl Exclusion Zone. We sequenced and assembled genomes de novo for 20 Oschieus tipulae strains, analyzed their genomes for evidence of recent mutation acquisition in the field and saw no evidence of an association between mutation and radiation level at the sites of collection. Multigenerational exposure of each of these strains to several mutagens in the lab revealed that strains vary heritably in tolerance to each mutagen, but mutagen tolerance cannot be predicted based on the radiation levels at collection sites.

Modeling of ionizing radiation-induced chromosome aberration and tumor prevalence based on two classes of DNA double-strand breaks clustering in chromatin domains

There has been some controversy over the use of radiobiological models when modeling the dose-response curves of ionizing radiation (IR)-induced chromosome aberration and tumor prevalence, as those curves usually show obvious non-targeted effects (NTEs) at low doses of high linear energy transfer (LET) radiation. The lack of understanding the contribution of NTEs to IR-induced carcinogenesis can lead to distinct deviations of relative biological effectiveness (RBE) estimations of carcinogenic potential, which are widely used in radiation risk assessment and radiation protection. In this work, based on the initial pattern of two classes of IR-induced DNA double-strand breaks (DSBs) clustering in chromatin domains and the subsequent incorrect repair processes, we proposed a novel radiobiological model to describe the dose-response curves of two carcinogenic-related endpoints within the same theoretical framework. The representative experimental data was used to verify the consistency and validity of the present model. The fitting results indicated that, compared with targeted effect (TE) and NTE models, the current model has better fitting ability when dealing with the experimental data of chromosome aberration and tumor prevalence induced by multiple types of IR with different LETs. Notably, the present model without introducing an NTE term was adequate to describe the dose-response curves of IR-induced chromosome aberration and tumor prevalence with NTEs in low-dose regions. Based on the fitting parameters, the LET-dependent RBE values were calculated for three given low doses. Our results showed that the RBE values predicted by the current model gradually decrease with the increase of doses for the endpoints of chromosome aberration and tumor prevalence. In addition, the calculated RBE was also compared with those evaluated from other models. These analyses show that the proposed model can be used as an alternative tool to well describe dose-response curves of multiple carcinogenic-related endpoints and effectively estimate RBE in low-dose regions.

Immediate effects of acute Mars mission equivalent doses of SEP and GCR radiation on the murine gastrointestinal system-protective effects of curcumin-loaded nanolipoprotein particles (cNLPs)

Introduction

Missions beyond low Earth orbit (LEO) will expose astronauts to ionizing radiation (IR) in the form of solar energetic particles (SEP) and galactic cosmic rays (GCR) including high atomic number and energy (HZE) nuclei. The gastrointestinal (GI) system is documented to be highly radiosensitive with even relatively low dose IR exposures capable of inducing mucosal lesions and disrupting epithelial barrier function. IR is also an established risk factor for colorectal cancer (CRC) with several studies examining long-term GI effects of SEP/GCR exposure using tumor-prone APC mouse models. Studies of acute short-term effects of modeled space radiation exposures in wildtype mouse models are more limited and necessary to better define charged particle-induced GI pathologies and test novel medical countermeasures (MCMs) to promote astronaut safety.

Methods

In this study, we performed ground-based studies where male and female C57BL/6J mice were exposed to γ-rays, 50 MeV protons, or 1 GeV/n Fe-56 ions at the NASA Space Radiation Laboratory (NSRL) with histology and immunohistochemistry endpoints measured in the first 24 h post-irradiation to define immediate SEP/GCR-induced GI alterations.

Results

Our data show that unlike matched γ-ray controls, acute exposures to protons and iron ions disrupts intestinal function and induces mucosal lesions, vascular congestion, epithelial barrier breakdown, and marked enlargement of mucosa-associated lymphoid tissue. We also measured kinetics of DNA double-strand break (DSB) repair using gamma-H2AX- specific antibodies and apoptosis via TUNEL labeling, noting the induction and disappearance of extranuclear cytoplasmic DNA marked by gamma-H2AX only in the charged particle-irradiated samples. We show that 18 h pre-treatment with curcumin-loaded nanolipoprotein particles (cNLPs) delivered via IV injection reduces DSB-associated foci levels and apoptosis and restore crypt villi lengths.

Discussion

These data improve our understanding of physiological alterations in the GI tract immediately following exposures to modeled space radiations and demonstrates effectiveness of a promising space radiation MCM.

Space radiation quality factor for Galactic Cosmic Rays and typical space mission scenarios using a microdosimetric approach

Space radiation exposure from omnipresent Galactic Cosmic Rays (GCRs) in interplanetary space poses a serious carcinogenic risk to astronauts due to the-limited or absent-protective effect of the Earth's magnetosphere and, in particular, the terrestrial atmosphere. The radiation risk is directly influenced by the quality of the radiation, i.e., its pattern of energy deposition at the micron/DNA scale. For stochastic biological effects, radiation quality is described by the quality factor, [Formula: see text], which can be defined as a function of Linear Energy Transfer (LET) or the microdosimetric lineal energy ([Formula: see text]). In the present work, the average [Formula: see text] of GCR for different mission scenarios was calculated using a modified version of the microdosimetric Theory of Dual Radiation Action (TDRA). NASA's OLTARIS platform was utilized to generate the radiation environment behind different aluminum shielding (0-30 g/cm²) for a typical mission scenario in low-earth orbit (LEO) and in deep space. The microdosimetric lineal energy spectra of ions ([Formula: see text]) in 1 μm liquid water spheres were calculated by a generalized analytical model which considers energy-loss fluctuations and δ-ray transport inside the irradiated medium. The present TDRA-based [Formula: see text]-values for the LEO and deep space missions were found to differ by up to 10% and 14% from the corresponding ICRP-based [Formula: see text]-values and up to 3% and 6% from NASA's [Formula: see text]-model. In addition, they were found to be in good agreement with the [Formula: see text]-values measured in the International Space Station (ISS) and by the Mars Science Laboratory (MSL) Radiation Assessment Detector (RAD) which represent, respectively, a LEO and deep space orbit.

Microgravity alters the expressions of DNA repair genes and their regulatory miRNAs in space-flown Caenorhabditis elegans

During spaceflight, multiple unique hazardous factors, particularly microgravity and space radiation, can induce different types of DNA damage, which pose a constant threat to genomic integrity and stability of living organisms. Although organisms have evolved different kinds of conserved DNA repair pathways to eliminate this DNA damage on Earth, the impact of space microgravity on the expressions of these DNA repair genes and their regulatory miRNAs has not been fully explored. In this study, we integrated all existing datasets, including both transcriptional and miRNA microarrays in wild-type (WT) Caenorhabditis elegans that were exposed to the treatments of spaceflight (SF), spaceflight control with a 1g centrifugal device (SC), and ground control (GC) in three space experiments with the periods of 4, 8 and 16.5 days. The results of principal component analysis showed the gene expression patterns for five major DNA repair pathways (i.e., non-homologous end joining (NHEJ), homologous recombination (HR), mismatch repair (MMR), nucleotide excision repair (NER), and base excision repair (BER)) were well separated and clustered between SF/GC and SC/GC treatments after three spaceflights. In the 16.5-days space experiment, we also selected the datasets of dys-1 mutant and ced-1 mutant of C. elegans, which respectively presented microgravity-insensitivity and radiosensitivity. Compared to the WT C. elegans flown in the 16.5-days spaceflight, the separation distances between SF and SC samples were significantly reduced in the dys-1 mutant, while greatly enhanced in the ced-1 mutant for five DNA repair pathways. By comparing the results of differential expression analysis in SF/GC versus SC/GC samples, we found the DNA repair genes annotated in the pathways of BER and NER were prominently down-regulated under microgravity during both the 4- and 8-days spaceflights. While, under microgravity, the genes annotated in MMR were dominatingly up-regulated during the 4-days spaceflight, and those annotated in HR were mainly up-regulated during the 8-days spaceflight. And, most of the DNA repair genes annotated in the pathways of BER, NER, MMR, and HR were up-regulated under microgravity during the 16.5-days spaceflight. Using miRNA-mRNA integrated analysis, we determined the regulatory networks of differentially expressed DNA repair genes and their regulatory miRNAs in WT C. elegans after three spaceflights. Compared to GC conditions, the differentially expressed miRNAs were analyzed under SF and SC treatments of three spaceflights, and some altered miRNAs that responded to SF and SC could regulate the expressions of corresponding DNA repair genes annotated in different DNA repair pathways. In summary, these findings indicate that microgravity can significantly alter the expression patterns of DNA repair genes and their regulatory miRNAs in space-flown C. elegans. The alterations of the expressions of DNA repair genes and the dominating DNA repair pathways under microgravity are possibly related to the spaceflight period. In addition, the key miRNAs are identified as the post-transcriptional regulators to regulate the expressions of various DNA repair genes under microgravity. These altered miRNAs that responded to microgravity can be implicated in regulating diverse DNA repair processes in space-flown C. elegans.

Unraveling astrocyte behavior in the space brain: Radiation response of primary astrocytes

Introduction

Exposure to space conditions during crewed long-term exploration missions can cause several health risks for astronauts. Space radiation, isolation and microgravity are major limiting factors. The role of astrocytes in cognitive disturbances by space radiation is unknown. Astrocytes' response toward low linear energy transfer (LET) X-rays and high-LET carbon (12C) and iron (56Fe) ions was compared to reveal possible effects of space-relevant high-LET radiation. Since astronauts are exposed to ionizing radiation and microgravity during space missions, the effect of simulated microgravity on DNA damage induction and repair was investigated.

Methods

Primary murine cortical astrocytes were irradiated with different doses of X-rays, 12C and 56Fe ions at the heavy ion accelerator GSI. DNA damage and repair (γH2AX, 53BP1), cell proliferation (Ki-67), astrocytes' reactivity (GFAP) and NF-κB pathway activation (p65) were analyzed by immunofluorescence microscopy. Cell cycle progression was investigated by flow cytometry of DNA content. Gene expression changes after exposure to X- rays were investigated by mRNA-sequencing. RT-qPCR for several genes of interest was performed with RNA from X-rays- and heavy-ion-irradiated astrocytes: Cdkn1a, Cdkn2a, Gfap, Tnf, Il1β, Il6, and Tgfβ1. Levels of the pro inflammatory cytokine IL-6 were determined using ELISA. DNA damage response was investigated after exposure to X-rays followed by incubation on a 2D clinostat to simulate the conditions of microgravity.

Results

Astrocytes showed distinct responses toward the three different radiation qualities. Induction of radiation-induced DNA double strand breaks (DSBs) and the respective repair was dose-, LET- and time-dependent. Simulated microgravity had no significant influence on DNA DSB repair. Proliferation and cell cycle progression was not affected by radiation qualities examined in this study. Astrocytes expressed IL-6 and GFAP with constitutive NF-κB activity independent of radiation exposure. mRNA sequencing of X-irradiated astrocytes revealed downregulation of 66 genes involved in DNA damage response and repair, mitosis, proliferation and cell cycle regulation.

Discussion

In conclusion, primary murine astrocytes are DNA repair proficient irrespective of radiation quality. Only minor gene expression changes were observed after X-ray exposure and reactivity was not induced. Co-culture of astrocytes with microglial cells, brain organoids or organotypic brain slice culture experiments might reveal whether astrocytes show a more pronounced radiation response in more complex network architectures in the presence of other neuronal cell types.

Radioprotection for Astronauts’ Missions: Numerical Results on the Nomex Shielding Effectiveness

Space missions with humans expose the crews to ionizing radiation, mainly due to the galactic cosmic radiation (GCR). All radiation protection programs in space aim to minimize crews’ exposure to radiation. The radiation protection of astronauts can be achieved through the use of shields. The shields could serve as a suit to reduce GCR exposure and, in an emergency, as a radiation shelter to perform necessary interventions outside the space habitat in case of a solar proton event (SPE). A space radiation shielding that is suitable for exploration during space missions requires particular features and a proper knowledge of the radiation type. This study shows the results of numerical simulations performed with the Geant4 toolkit-based code DOSE. Calculations to evaluate the performance of Nomex, an aramidic fiber with high mechanical resistance, in terms of dose reduction to crews, were performed considering the interaction between protons with an energy spectrum ranging from 50 to 1100 MeV and a target slab of 20 g/cm2. This paper shows the properties of secondary products obtained as a result of the interaction between space radiation and a Nomex target and the properties of the secondary particles that come out the shield. The results of this study show that Nomex can be considered a good shield candidate material in terms of dose reductions. We also note that the secondary particles that provide the greatest contribution to the dose are protons, neutrons and, in a very small percentage, α-particles and Li ions.

Prospective Use of Probiotics to Maintain Astronaut Health during Spaceflight

Maintaining an astronaut's health during space travel is crucial. Multiple studies have observed various changes in the gut microbiome and physiological health. Astronauts on board the International Space Station (ISS) had changes in the microbial communities in their gut, nose, and skin. Additionally, immune system cell alterations have been observed in astronauts with changes in neutrophils, monocytes, and T-cells. Probiotics help tackle these health issues caused during spaceflight by inhibiting pathogen adherence, enhancing epithelial barrier function by reducing permeability, and producing an anti-inflammatory effect. When exposed to microgravity, probiotics demonstrated a shorter lag phase, faster growth, improved acid tolerance, and bile resistance. A freeze-dried Lactobacillus casei strain Shirota capsule was tested for its stability on ISS for a month and has been shown to enhance innate immunity and balance intestinal microbiota. The usage of freeze-dried spores of B. subtilis proves to be advantageous to long-term spaceflight because it qualifies for all the aspects tested for commercial probiotics under simulated conditions. These results demonstrate a need to further study the effect of probiotics in simulated microgravity and spaceflight conditions and to apply them to overcome the effects caused by gut microbiome dysbiosis and issues that might occur during spaceflight.

Mouse genomic associations with in vitro sensitivity to simulated space radiation

Exposure to ionizing radiation is considered by NASA to be a major health hazard for deep space exploration missions. Ionizing radiation sensitivity is modulated by both genomic and environmental factors. Understanding their contributions is crucial for designing experiments in model organisms, evaluating the risk of deep space (i.e. high-linear energy transfer, or LET, particle) radiation exposure in astronauts, and also selecting therapeutic irradiation regimes for cancer patients. We identified single nucleotide polymorphisms in 15 strains of mice, including 10 collaborative cross model strains and 5 founder strains, associated with spontaneous and ionizing radiation-induced in vitro DNA damage quantified based on immunofluorescent tumor protein p53 binding protein (53BP1) positive nuclear foci. Statistical analysis suggested an association with pathways primarily related to cellular signaling, metabolism, tumorigenesis and nervous system damage. We observed different genomic associations in early (4 and 8 h) responses to different LET radiation, while later (24 hour) DNA damage responses showed a stronger overlap across all LETs. Furthermore, a subset of pathways was associated with spontaneous DNA damage, suggesting 53BP1 positive foci as a potential biomarker for DNA integrity in mouse models. Our results suggest several mouse strains as new models to further study the impact of ionizing radiation and validate the identified genetic loci. We also highlight the importance of future human in vitro studies to refine the association of genes and pathways with the DNA damage response to ionizing radiation and identify targets for space travel countermeasures.

Towards sustainable human space exploration-priorities for radiation research to quantify and mitigate radiation risks

Human spaceflight is entering a new era of sustainable human space exploration. By 2030 humans will regularly fly to the Moon's orbit, return to the Moon's surface and preparations for crewed Mars missions will intensify. In planning these undertakings, several challenges will need to be addressed in order to ensure the safety of astronauts during their space travels. One of the important challenges to overcome, that could be a major showstopper of the space endeavor, is the exposure to the space radiation environment. There is an urgent need for quantifying, managing and limiting the detrimental health risks and electronics damage induced by space radiation exposure. Such risks raise key priority topics for space research programs. Risk limitation involves obtaining a better understanding of space weather phenomena and the complex radiation environment in spaceflight, as well as developing and applying accurate dosimetric instruments, understanding related short- and long-term health risks, and strategies for effective countermeasures to minimize both exposure to space radiation and the remaining effects post exposure. The ESA/SciSpacE Space Radiation White Paper identifies those topics and underlines priorities for future research and development, to enable safe human and robotic exploration of space beyond Low Earth Orbit.

A Mission to Mars: Prediction of GCR Doses and Comparison with Astronaut Dose Limits

Long-term human space missions such as a future journey to Mars could be characterized by several hazards, among which radiation is one the highest-priority problems for astronaut health. In this work, exploiting a pre-existing interface between the BIANCA biophysical model and the FLUKA Monte Carlo transport code, a study was performed to calculate astronaut absorbed doses and equivalent doses following GCR exposure under different shielding conditions. More specifically, the interface with BIANCA allowed us to calculate both the RBE for cell survival, which is related to non-cancer effects, and that for chromosome aberrations, related to the induction of stochastic effects, including cancer. The results were then compared with cancer and non-cancer astronaut dose limits. Concerning the stochastic effects, the equivalent doses calculated by multiplying the absorbed dose by the RBE for chromosome aberrations ("high-dose method") were similar to those calculated using the Q-values recommended by ICRP. For a 650-day mission at solar minimum (representative of a possible Mars mission scenario), the obtained values are always lower than the career limit recommended by ICRP (1 Sv), but higher than the limit of 600 mSv recently adopted by NASA. The comparison with the JAXA limits is more complex, since they are age and sex dependent. Concerning the deterministic limits, even for a 650-day mission at solar minimum, the values obtained by multiplying the absorbed dose by the RBE for cell survival are largely below the limits established by the various space agencies. Following this work, BIANCA, interfaced with an MC transport code such as FLUKA, can now predict RBE values for cell death and chromosome aberrations following GCR exposure. More generally, both at solar minimum and at solar maximum, shielding of 10 g/cm2 Al seems to be a better choice than 20 g/cm2 for astronaut protection against GCR.

The Effects of Combined Exposure to Simulated Microgravity, Ionizing Radiation, and Cortisol on the In Vitro Wound Healing Process

Human spaceflight is associated with several health-related issues as a result of long-term exposure to microgravity, ionizing radiation, and higher levels of psychological stress. Frequent reported skin problems in space include rashes, itches, and a delayed wound healing. Access to space is restricted by financial and logistical issues; as a consequence, experimental sample sizes are often small, which limits the generalization of the results. Earth-based simulation models can be used to investigate cellular responses as a result of exposure to certain spaceflight stressors. Here, we describe the development of an in vitro model of the simulated spaceflight environment, which we used to investigate the combined effect of simulated microgravity using the random positioning machine (RPM), ionizing radiation, and stress hormones on the wound-healing capacity of human dermal fibroblasts. Fibroblasts were exposed to cortisol, after which they were irradiated with different radiation qualities (including X-rays, protons, carbon ions, and iron ions) followed by exposure to simulated microgravity using a random positioning machine (RPM). Data related to the inflammatory, proliferation, and remodeling phase of wound healing has been collected. Results show that spaceflight stressors can interfere with the wound healing process at any phase. Moreover, several interactions between the different spaceflight stressors were found. This highlights the complexity that needs to be taken into account when studying the effect of spaceflight stressors on certain biological processes and for the aim of countermeasures development.

Amelioration of Radiation-Induced Cell Death in Neuro2a Cells by Neutralizing Oxidative Stress and Reducing Mitochondrial Dysfunction Using N-Acetyl-L-Tryptophan

The deleterious effects of ionizing radiation on the central nervous system (CNS) are poorly understood. Radiation exposure during an accidental nuclear explosion, nuclear war, or radiotherapy causes severe brain damage. As a result, the current work is carried out to assess the radioprotective potential of N-acetyl-L-tryptophan (L-NAT) in neuronal cells. Radiation-induced cell death and its amelioration by L-NAT pretreatment were investigated using MTT, SRB, CFU, and comet assays. Flow cytometric and microscopic fluorescence assays were used to investigate radiation-induced oxidative stress, alteration in mitochondrial redox, Ca2+ homeostasis, depolarization of mitochondrial membrane potential, and its prevention with L-NAT pretreatment. Western blot analysis of Caspase-3, γ-H2aX, p53, ERK-1/2, and p-ERK-1/2 expression was carried out to identify the effects of L-NAT pretreatment on radiation-induced apoptosis and its regulatory proteins expression. The study demonstrated (MTT, SRB, and CFU assay) significant (~80%; p <0.001%) radioprotection in irradiated (LD50 IR dose) Neuro2a cells that were pretreated with L-NAT. In comparison to irradiated cells, L-NAT pretreatment resulted in significant (p <0.001%) DNA protection. A subsequent study revealed that L-NAT pretreatment of irradiated Neuro2a cells establishes oxidative stress by increasing antioxidant enzymes and mitochondrial redox homeostasis by inhibiting Ca2+ migration from the cytoplasm to the mitochondrial matrix and thus protects the mitochondrial membrane hyperpolarization. Caspase-3 and γ-H2aX protein expression decreased, while p-ERK1/2 and p53 expression increased in L-NAT pretreated irradiated cells compared to irradiated cells. Hence, L-NAT could be a potential radioprotective that may inhibit oxidative stress and DNA damage and maintain mitochondrial health and Ca2+ levels by activating p-ERK1/2 and p53 expression in Neuronal cells.

Armed Forces Radiobiology Research Institute/Uniformed Services University of the Health Sciences perspective on space radiation countermeasure discovery

There is a need to develop and deploy medical countermeasures (MCMs) in order to support astronauts during space missions against excessive exposures to ionizing radiation exposure. The radiation environment of extraterrestrial space is complex and is characterized by nearly constant fluences of elemental atomic particles (protons being a dominant particle type) with widely different energies and ionization potentials. Chronic exposure to such ionizing radiation carries both near- and long-term health risks, which are generally related to the relative intensity and duration of exposure. These radiation-associated health risks can be managed only to a limited extent by physical means, but perhaps they might be more effectively managed biomedically. The Armed Forces Radiobiology Research Institute/Uniformed Services University of the Health Sciences has a long history of researching and developing MCMs specifically designed to support terrestrial-based military missions involving a radiation-threat component. The development of MCMs for both low and high doses of radiation are major aims of current research, and as such can provide lessons learned for the development of countermeasures applicable to future space missions and its extraterrestrial radiation environment.

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.

Comparison of biological measurement and physical estimates of space radiation in the International Space Station

Nowadays, ordinary people can travel in space, and the possibility of extended durations in an environment such as moon of the Earth and Mars with higher space radiation exposures compared to past missions, is increasing. Until now, the physical doses of space radiation have been measured, but measurement of direct biological effects has been hampered by its low dose and low dose-rate effect. To assess the biological effects of space radiation, we launched and kept frozen mouse embryonic stem (ES) cells in minus eighty degree Celsius freezer in ISS (MELFI) on the International Space Station (ISS) for a maximum of 1,584 days. The passive dosimeter for life science experiments in space (PADLES) was attached on the surface of the sample case of the ES cells. The physical dosimeter measured the absorbed dose in water. After return, the frozen cells were thawed and cultured and their chromosome aberrations were analyzed. Comparative experiments with proton and iron ion irradiation were performed at particle accelerators on Earth. The wild-type ES cells showed no differences in chromosomal aberrations between the ground control and ISS exposures. However, we detected an increase of chromosome aberrations in radio-sensitized histone H2AX heterozygous-deficient mouse ES cells and found that the rate of increase against the absorbed dose was 1.54-fold of proton irradiation at an accelerator. On the other hand, we estimated the quality factor of space radiation as 1.48 ± 0.2. using formulas of International Commission of Radiation Protection (ICRP) 60. The relative biological effectiveness (RBE) observed from our experiments (1.54-fold of proton) was almost equal (1.04-fold) to the physical estimation (1.48 ± 0.2). It should be important to clarify the relation between biological effect and physical estimates of space radiation. This comparative study paves a way to reveal the complex radiation environments to reduce the uncertainty for risk assessment of human stay in space.

Carcinogenesis induced by space radiation: A systematic review

The carcinogenic risk from space radiation has always been a health risk issue of great concern during space exploration. In recent years, a large number of cellular and animal experiments have demonstrated that space radiation, composed of high-energy protons and heavy ions, has shown obvious carcinogenicity. However, different from radiation on Earth, space radiation has the characteristics of high energy and low dose rate. It is rich in high-atom-number and high-energy particles and, as it is combined with other space environmental factors such as microgravity and a weak magnetic field, the study of its carcinogenic effects and mechanisms of action is difficult, which leads to great uncertainty in its carcinogenic risk assessment. Here, we review the latest progress in understanding the effects and mechanisms of action related to cell transformation and carcinogenesis induced by space radiation in recent years and summarize the prediction models of cancer risk caused by space radiation and the methods to reduce the uncertainty of prediction to provide reference for the research and risk assessment of space radiation.