The biological effects of space radiation during long stays in space.

Many space experiments are scheduled for the International Space Station (ISS). Completion of the ISS will soon become a reality. Astronauts will be exposed to low-level background components from space radiation including heavy ions and other high-linear energy transfer (LET) radiation. For long-term stay in space, we have to protect human health from space radiation. At the same time, we should recognize the maximum permissible doses of space radiation. In recent years, physical monitoring of space radiation has detected about 1 mSv per day. This value is almost 150 times higher than that on the surface of the Earth. However, the direct effects of space radiation on human health are currently unknown. Therefore, it is important to measure biological dosimetry to calculate relative biological effectiveness (RBE) for human health during long-term flight. The RBE is possibly modified by microgravity. In order to understand the exact RBE and any interaction with microgravity, the ISS centrifugation system will be a critical tool, and it is hoped that this system will be in operation as soon as possible.     

Radiobiological problems in space

Summary An overview is presented on radiation problems in space, with emphasis on aspects of major interest for manned space exploration. A classification of the radiation hazards is presented and strategies for their evaluation are discussed. Space radiation problems are compared with characteristic aspects of radiation research in other disciplines, in order to provide further insight into those aspects that are unique to space.The research described in this paper was carried out while the author was a NASA VisitingThe research described in this paper was carried out while the author was a NASA VisitingThe research described in this paper was carried out while the author was a NASA VisitingThe research described in this paper was carried out while the author was a NASA Visiting     

Enzymic chemical reaction under microgravity environment in space

In recent years, some papers have reported synergism in the biological effects of space radiation and microgravity. However, there is no direct evidence for these phenomena. As one possible mechanism, we investigated whether DNA ligation in the final step of DSBs repair of DNA molecules induced by radiation is depressed by microgravity. Therefore, we have scheduled the space experiments of the effects of microgravity on repair activity of T4 DNA ligase for DSBs prepared with digestion of a restriction enzyme (Sma I) to plasmid DNA. As another possible mechanism, the high mutation frequency may be induced from abnormal base-incorporation during DNA replication under microgravity. Using the Taq polymerase and polymerase III, we have also scheduled whether mutation frequency is affected by microgravity during DNA replication for a damaged DNA base induced by an alkylating agent (N-methyl-N-nitrosourea, MNU).     

Emphasis of biological research for space radiation]

The paper summarized issues, current status and the recent topics in biological research of space radiation. Researches to estimate a risk associated with space radiation exposure during a long-term manned space flight, such as in the International Space Station, is emphasized because of the large uncertainty of biological effects and a complexity of the radiation environment in space. The Issues addressed are; 1) biological effects and end points in low dose radiation, 2) biological effects under low dose rate and long-term radiation exposure, 3) modification of biological responses to radiation under space environments, 4) various aspects of biological end points vs. cellular and molecular mechanisms, 5) estimation of human risk associated with radiation exposure in space flight, 6) regulations for radiation exposure limits for space workers. The paper also summarized and introduced recent progress in space related radiation researches with various biological systems.     

增强UV-B辐射与其它因子复合作用对植物生长的影响研究

增强UV-B辐射与其它因子复合作用对植物的影响研究是扩展UV-B辐射效应研究的重要途径,有着广阔的研究空间,并已成为目前UV-B辐射研究新的发展趋势.本文较为全面地综述了目前国内外有关增强UV-B辐射与其它因子（包括CO2、O3、水分、温度、有效辐射、重金属、盐分、矿质营养、酸雨、铈、镧、硒以及某些物理因子）复合作用对植物影响的研究进展,提出了目前该领域研究的一些不足并对未来发展提出了展望.     

Proposal from space radiation biologists. Importance of Centrifuge Facility in the study of biological effect by space radiation]

In microgravity, astronauts were constantly exposed to space radiation containing various kinds of radiation with a low-dose rate during long-term stays in space. It is very difficult to define the relative biological effectiveness (RBE) of space radiation under microgravity. In order to understand correct the RBE of space radiation, therefore, utilization of Centrifuge Facility is desired as a control experiment at orbit for removing other factors such as microgravity except space radiation. Here, we summarized the importance of Centrifuge Facility in the study of biological effect of space radiation.     

Space radiation research in Europe: flight experiments and ground-based studies

Exposure to space radiation has long been acknowledged as a potential showstopper for long-duration manned interplanetary missions. In an effort to gain more information on space radiation risk and to develop countermeasures, NASA initiated several years ago a Space Radiation Health Program, which is currently supporting biological experiments performed at the Brookhaven National Laboratory. Accelerator-based radiobiology research in the field of space radiation research is also under way in Russia and Japan. The European Space Agency (ESA) supports research in the field in three main directions: spaceflight experiments on the International Space Station; modeling and simulations of the space radiation environment and transport; and, recently, ground-based radiobiology experiments exploiting the high-energy SIS18 synchrotron at GSI in Germany (IBER program). Several experiments are currently under way within IBER, and so far, beams of C and Fe-ions at energies between 11 and 1,000 MeV/n have been used in cell and tissue targets.     

Broad-Spectrum Antibiotic or G-CSF as Potential Countermeasures for Impaired Control of Bacterial Infection Associated with an SPE Exposure during Spaceflight

A major risk for astronauts during prolonged space flight is infection as a result of the combined effects of microgravity, situational and confinement stress, alterations in food intake, altered circadian rhythm, and radiation that can significantly impair the immune system and the body’s defense systems. We previously reported a massive increase in morbidity with a decrease in the ability to control a bacterial challenge when mice were maintained under hindlimb suspension (HS) conditions and exposed to solar particle event (SPE)-like radiation. HS and SPE-like radiation treatment alone resulted in a borderline significant increase in morbidity. Therefore, development and testing of countermeasures that can be used during extended space missions in the setting of exposure to SPE radiation becomes a serious need. In the present study, we investigated the efficacy of enrofloxacin (an orally bioavailable antibiotic) and Granulocyte colony stimulating factor (G-CSF) (Neulasta) on enhancing resistance to Pseudomonas aeruginosa infection in mice subjected to HS and SPE-like radiation. The results revealed that treatment with enrofloxacin or G-CSF enhanced bacterial clearance and significantly decreased morbidity and mortality in challenged mice exposed to suspension and radiation. These results establish that antibiotics, such as enrofloxacin, and G-CSF could be effective countermeasures to decrease the risk of bacterial infections after exposure to SPE radiation during extended space flight, thereby reducing both the risk to the crew and the danger of mission failure.     

Tardigrades in Space Research - Past and Future

To survive exposure to space conditions, organisms should have certain characteristics including a high tolerance for freezing, radiation and desiccation. The organisms with the best chance for survival under such conditions are extremophiles, like some species of Bacteria and Archea, Rotifera, several species of Nematoda, some of the arthropods and Tardigrada (water bears). There is no denying that tardigrades are one of the toughest animals on our planet and are the most unique in the extremophiles group. Tardigrada are very small animals (50 to 2,100 μm in length), and they inhabit great number of Earth environments. Ever since it was proven that tardigrades have high resistance to the different kinds of stress factors associated with cosmic journeys, combined with their relatively complex structure and their relative ease of observation, they have become a perfect model organism for space research. This taxon is now the focus of astrobiologists from around the world. Therefore, this paper presents a short review of the space research performed on tardigrades as well as some considerations for further studies.     

Induction of Cell Death through Alteration of Oxidants and Antioxidants in Lung Epithelial Cells Exposed to High Energy Protons

Radiation affects several cellular and molecular processes, including double strand breakage and modifications of sugar moieties and bases. In outer space, protons are the primary radiation source that poses a range of potential health risks to astronauts. On the other hand, the use of proton irradiation for tumor radiation therapy is increasing, as it largely spares healthy tissues while killing tumor tissues. Although radiation-related research has been conducted extensively, the molecular toxicology and cellular mechanisms affected by proton irradiation remain poorly understood. Therefore, in this study, we irradiated rat lung epithelial cells with different doses of protons and investigated their effects on cell proliferation and death. Our data show an inhibition of cell proliferation in proton-irradiated cells with a significant dose-dependent activation and repression of reactive oxygen species and antioxidants glutathione and superoxide dismutase, respectively, compared with control cells. In addition, the activities of apoptosis-related genes such as caspase-3 and -8 were induced in a dose-dependent manner with corresponding increased levels of DNA fragmentation in proton-irradiated cells compared with control cells. Together, our results show that proton irradiation alters oxidant and antioxidant levels in cells to activate the apoptotic pathway for cell death.     

In vitro cultured cells as probes for space radiation effects on biological systems

Near future scenarios of long-term and far-reaching manned space missions, require more extensive knowledge of all possible biological consequences of space radiation, particularly in humans, on both a long-term and a short-term basis. In vitro cultured cells have significantly contributed to the tremendous advancement of biomedical research. It is therefore to be expected that simple biological systems such as cultured cells, will contribute to space biomedical sciences. Space represents a novel environment, to which life has not been previously exposed. Both microgravity and space radiation are the two relevant components of such an environment, but biological adaptive mechanisms and efficient countermeasures can significantly minimize microgravity effects. On the other hand, it is felt that space radiation risks may be more relevant and that defensive strategies can only stem from our deeper knowledge of biological effects and of cellular repair mechanisms. Cultured cells may play a key role in such studies. Particularly, thyroid cells may be relevant because of the exquisite sensitivity of the thyroid gland to radiation. In addition, a clone of differentiated, normal thyroid follicular cells (FRTL5 cells) is available in culture, which is well characterized and particularly fit for space research.     

地球熔岩管道微生物研究对天体生物学的启示

天体生物学作为与深空探测相结合的交叉学科,旨在从地球极端环境类比、古代生命载体信息发掘和模拟等方面揭示地外行星体是否适合生命生存和繁衍,其中适宜的环境条件是评价所有天体是否宜居的重要条件。近年来在月球和火星等行星表面发现了大量由火山熔岩流形成的熔岩管道,这些巨型管状地下空间具有稳定的温度和防辐射等环境条件,为生物在地外星体上的生存提供了潜在的庇护场所。基于地球熔岩管道的天体生物学的类比研究可以为探索地外生命痕迹提供重要线索,本文综述了现阶段地球熔岩管道内微生物的研究进展、微生物痕量气体代谢在天体生物学研究中的潜力及天体生物学的研究进展,旨在为后续开展地球及地外熔岩管道的天体生物学研究提供思路。     

Radiation risk in manned space flights

This paper addresses some of the pertinent questions relating to the assessment of radiation risk for humans in space; the paper is not intended as a comprehensive review. The radiation field is briefly summarised and doses to be expected are given based on recent on-board measurements. The problems in adapting terrestrial epidemiological data to the space situation are outlined. Apart from the intrinsic uncertainties in deriving risk factors the specific difficulties are mainly concerned with the effects of energetic charged particles for which no human data exist. The necessity for continuing ground-based research is stressed. Also discussed is whether the principles of radiation protection successfully applied on Earth are really suitable for the space situation or whether they should be replaced by a different approach.     

三维辐射传输模型在森林生态系统研究中的应用与展望

太阳辐射是森林生态系统功能与服务得以维持并发展的基础, 对森林中的辐射传输过程进行建模对于理解森林生态系统过程具有重要意义。近年来, 三维辐射传输模型的迅速发展使得冠层辐射能量分布格局与动态的准确模拟成为可能。为更好地理解三维辐射传输模型以使其更有效地服务于森林生态系统研究, 该文从模型的原理、应用及发展趋势3个角度展开论述。首先简要介绍了辐射度方法、光线追踪法等森林三维辐射传输模型常用的原理及目前代表性的模型, 然后总结了三维辐射传输模型在森林生态系统研究中的应用, 最后对模型未来如何通过提高易用性、增加多模型耦合等方式更好地应用于森林生态系统研究进行了展望。随着森林生态系统大数据的积累与过程模型的不断完善, 三维辐射传输模型将在未来森林生态理论研究与实践中发挥更加重要的作用。     

Physical and biological organ dosimetry analysis for international space station astronauts

In this study, we analyzed the biological and physical organ dose equivalents for International Space Station (ISS) astronauts. Individual physical dosimetry is difficult in space due to the complexity of the space radiation environment, which consists of protons, heavy ions and secondary neutrons, and the modification of these radiation types in tissue as well as limitations in dosimeter devices that can be worn for several months in outer space. Astronauts returning from missions to the ISS undergo biodosimetry assessment of chromosomal damage in lymphocyte cells using the multicolor fluorescence in situ hybridization (FISH) technique. Individual-based pre-flight dose responses for lymphocyte exposure in vitro to gamma rays were compared to those exposed to space radiation in vivo to determine an equivalent biological dose. We compared the ISS biodosimetry results, NASA's space radiation transport models of organ dose equivalents, and results from ISS and space shuttle phantom torso experiments. Physical and biological doses for 19 ISS astronauts yielded average effective doses and individual or population-based biological doses for the approximately 6-month missions of 72 mSv and 85 or 81 mGy-Eq, respectively. Analyses showed that 80% or more of organ dose equivalents on the ISS are from galactic cosmic rays and only a small contribution is from trapped protons and that GCR doses were decreased by the high level of solar activity in recent years. Comparisons of models to data showed that space radiation effective doses can be predicted to within about a +/-10% accuracy by space radiation transport models. Finally, effective dose estimates for all previous NASA missions are summarized.     

Problems of component discrimination in space radiation dosimetry

Resolving the LET spectrum of environmental radiation in space for assessing dose equivalents creates special problems due to superposition effects. Three components of the radiation field in space, trapped protons, tissue disintegration stars, and neutrons, contribute the bulk of the total dose equivalent. While lack of discrimination of neutron recoil and trapped primary protons does not interfere with correct determination of the combined dose equivalent as such, the simultaneous bursts of several low-energy protons and alpha particles from tissue disintegration stars completely defy LET-resolution with conventional instrumentation. So far, the tissue star dose has been determined only semiquantitatively from nuclear emulsion data. The neutron spectrum in space shows a markedly higher relative fluence in the region beyond 5 MeV than the fission neutron spectrum. Therefore, its LET spectrum centers less heavily on LET values near the proton Bragg Peak. This would call for assigning a QF value of less than 10 to the neutron dose in space. Still more serious shortcomings exist with regard to LET interpretation of heavy primaries.     

Enhanced intestinal tumor multiplicity and grade in vivo after HZE exposure: mouse models for space radiation risk estimates

Carcinogenesis induced by space radiation is considered a major risk factor in manned interplanetary and other extended missions. The models presently used to estimate the risk for cancer induction following deep space radiation exposure are based on data from A-bomb survivor cohorts and do not account for important biological differences existing between high-linear energy transfer (LET) and low-LET-induced DNA damage. High-energy and charge (HZE) radiation, the main component of galactic cosmic rays (GCR), causes highly complex DNA damage compared to low-LET radiation, which may lead to increased frequency of chromosomal rearrangements, and contribute to carcinogenic risk in astronauts. Gastrointestinal (GI) tumors are frequent in the United States, and colorectal cancer (CRC) is the third most common cancer accounting for 10% of all cancer deaths. On the basis of the aforementioned epidemiological observations and the frequency of spontaneous precancerous GI lesions in the general population, even a modest increase in incidence by space radiation exposure could have a significant effect on health risk estimates for future manned space flights. Ground-based research is necessary to reduce the uncertainties associated with projected cancer risk estimates and to gain insights into molecular mechanisms involved in space-induced carcinogenesis. We investigated in vivo differential effects of γ-rays and HZE ions on intestinal tumorigenesis using two different murine models, ApcMin/+ and Apc1638N/+. We showed that γ- and/or HZE exposure significantly enhances development and progression of intestinal tumors in a mutant-line-specific manner, and identified suitable models for in vivo studies of space radiation–induced intestinal tumorigenesis.     

南京市生态系统服务的空间流转

生态系统服务的空间流转研究是生态系统服务研究的重要部分,对于制定区域生态补偿标准具有重要意义。为了衡量地区生态系统服务流转到外部区域的相对价值大小,提出了地区比较生态辐射力概念,利用断裂点公式、指数距离衰减函数,衡量比较生态辐射力的大小。基于南京市主体功能区研究,定量研究南京市各保护型区域的生态系统服务对各开发型区域的辐射力,计算出各开发型区域从不同保护型区域提供的生态系统服务价值比例。结果表明:高淳县、江宁区、溧水县对于白下区、秦淮区比较生态辐射力相对较大,六合区对于鼓楼区、下关区比较生态辐射力相对较大,浦口区对于鼓楼区、秦淮区的比较生态辐射力相对较大。以白下区为例,提出了南京市实施生态补偿建议,根据白下区从外部保护型区域获得的生态系统服务总量,在其提供的生态补偿金中,浦口区、江宁区、六合区、溧水县、高淳县应分别获得总额的22.76%、22.67%、21.50%、17.27%与15.80%。     

A single low dose of Fe ions can cause long-term biological responses in NL20 human bronchial epithelial cells

Space radiation cancer risk may be a potential obstacle for long-duration spaceflight. Among all types of cancer space radiation may induce, lung cancer has been estimated to be the largest potential risk. Although previous animal study has shown that Fe ions, the most important contributor to the total dose equivalent of space radiation, induced a higher incidence of lung tumorigenesis per dose than X-rays, the underlying mechanisms at cellular level remained unclear. Therefore, in the present study, we investigated long-term biological changes in NL20 human bronchial epithelial cells after exposure to Fe ion or X-ray irradiation. We found that compared with sham control, the progeny of NL20 cells irradiated with 0.1 Gy of Fe ions showed slightly increased micronucleus formation, significantly decreased cell proliferation, disturbed cell cycle distribution, and obviously elevated intracellular ROS levels accompanied by reduced SOD1 and SOD2 expression, but the progeny of NL20 cells irradiated with 0.9 Gy of X-rays did not show any significant changes. More importantly, Fe ion exposure caused much greater soft-agar colony formation than X-rays did in the progeny of irradiated NL20 cells, clearly suggesting higher cell transformation potential of Fe ions compared with X-rays. These data may shed the light on the potential lung tumorigenesis risk from Fe ion exposure. In addition, ATM inhibition by Ku55933 reversed some of the changes in the progeny of Fe ion-irradiated cells but not others such as soft-agar colony formation, suggesting complex processes from DNA damage to carcinogenesis. These data indicate that even a single low dose of Fe ions can induce long-term biological responses such as cell transformation, etc., suggesting unignorable health risk from space radiation to astronauts.     

Effect of Solar Particle Event Radiation and Hindlimb Suspension on Gastrointestinal Tract Bacterial Translocation and Immune Activation

The environmental conditions that could lead to an increased risk for the development of an infection during prolonged space flight include: microgravity, stress, radiation, disturbance of circadian rhythms, and altered nutritional intake. A large body of literature exists on the impairment of the immune system by space flight. With the advent of missions outside the Earth''s magnetic field, the increased risk of adverse effects due to exposure to radiation from a solar particle event (SPE) needs to be considered. Using models of reduced gravity and SPE radiation, we identify that either 2 Gy of radiation or hindlimb suspension alone leads to activation of the innate immune system and the two together are synergistic. The mechanism for the transient systemic immune activation is a reduced ability of the GI tract to contain bacterial products. The identification of mechanisms responsible for immune dysfunction during extended space missions will allow the development of specific countermeasures.