Cataractogenesis from high-LET radiation and the Casarett model.

Space radiations, especially heavy ions, constitute significant hazards to astronauts. These hazards will increase as space missions lengthen. Moreover, the dangers to astronauts will be enhanced by the persistence, or even the progression, of biological damage throughout their subsequent life spans. To assist in the assessment of risks to astronauts, we are investigating the long-term effects of heavy ions on specific animal tissues. In one study, the eyes of rabbits of various ages were exposed to a single dose of Bragg plateau 20Ne ions (LET infinity approximately equals 30 keV/micrometer). The development of cataracts has shown a pronounced age-related response during the first year after irradiation, and will be followed for two more years. In other studies, mice were exposed to single or fractionated doses of 12C ions (4-cm spread-out Bragg peak; dose-averaged LET infinity = 70-80 keV/micrometer) or 60Co gamma-photons (LET infinity = 0.3 keV/micrometer). Measurements of the frequency of posterior lens opacification have shown that the tissue sparing observed with dose fractionation of gamma-photons was absent when 12C-ion doses were fractionated. Development of posterior lens cataracts was also followed for long periods (up to 21 months) in mice exposed to single doses of Bragg plateau HZE particles (40Ar, 20Ne and 12C ions: LET infinity approximately equals 100, 30 and 10 keV/micrometer, respectively) or 225 kVp X-rays. Based on average cataract levels at the different observation times, the RBE's (RBE = relative biological effectiveness) for the ions were circa 5, 3 and 1-2, respectively, over the range of doses used (0.05-0.9 Gy). Investigations of cataractogenesis are useful for exploring the model of radiation damage proposed by Casarett and by Rubin and Casarett with a tissue not connected directly to the vasculature.     

Helium-ion-induced human cataractogenesis.

Retrospective and ongoing analyses of clinical records from 347 primary intraocular melanoma patients treated with helium ions at LBL will allow examination of the exposure-response data for human cataract; which is a complication of the therapy from incidental exposure of the lens. Direct particle beam traversal of at least a portion of the lens usually is unavoidable in treatment of posterior intraocular tumors. The precise treatment planned for each patient permits quantitative assessment of the lenticular dose and its radiation quality. We are reporting our preliminary results on the development of helium-ion-induced lens opacifications and cataracts in 54 of these patients who had 10% or less of their lens in the treatment field. We believe these studies will be relevant to estimating the human risk for cataract in space flight.     

Mice heterozygous for the ATM gene are more sensitive to both X-ray and heavy ion exposure than are wildtypes

Previous studies have shown that the eyes of ATM heterozygous mice exposed to low-LET radiation (X-rays) are significantly more susceptible to the development of cataracts than are those of wildtype mice. The findings, as well as others, run counter to the assumption underpinning current radiation safety guidelines, that individuals are all equally sensitive to the biological effects of radiation. A question, highly relevant to human space activities is whether or not, in similar fashion there may exist a genetic predisposition to high-LET radiation damage.Mice haplodeficient for the ATM gene and wildtypes were exposed to 325 mGy of 1 GeV/amu ⁵⁶Fe ions at the AGS facility of Brookhaven National Laboratory. The fluence was equivalent to 1 ion per lens epithelial cell nuclear area. Controls consisted of irradiated wildtype as well as unirradiated wildtype and heterozygous mice. Prevalence analyses for stage 0.5–3.0 cataracts indicated that not only cataract onset but also progression were accelerated in the mice haplo-deficient for the ATM gene.The data show that heterozygosity for the ATM gene predisposes the eye to the cataractogenic influence of heavy ions and suggest that ATM heterozygotes in the human population may also be radiosensitive. This may have to be considered in the selection of individuals who will be exposed to both HZE particles and low-LET radiation as they may be predisposed to increased late normal tissue damage.     

Induction and repair of DNA strand breaks in bovine lens epithelial cells after high LET irradiation.

The lens epithelium is the initiation site for the development of radiation induced cataracts. Radiation in the cortex and nucleus interacts with proteins, while in the epithelium, experimental results reveal mutagenic and cytotoxic effects. It is suggested that incorrectly repaired DNA damage may be lethal in terms of cellular reproduction and also may initiate the development of mutations or transformations in surviving cells. The occurrence of such genetically modified cells may lead to lens opacification. For a quantitative risk estimation for astronauts and space travelers it is necessary to know the relative biological effectiveness (RBE), because the spacial and temporal distribution of initial physical damage induced by cosmic radiation differ significantly from that of X-rays. RBEs for the induction of DNA strand breaks and the efficiency of repair of these breaks were measured in cultured diploid bovine lens epithelial cells exposed to different LET irradiation to either 300 kV X-rays or to heavy ions at the UNILAC accelerator at GSI. Accelerated ions from Z=8 (O) to Z=92 (U) were used. Strand breaks were measured by hydroxyapatite chromatography of alkaline unwound DNA (overall strand breaks). Results showed that DNA damage occurs as a function of dose, of kinetic energy and of LET. For particles having the same LET the severity of the DNA damage increases with dose. For a given particle dose, as the LET rises, the numbers of DNA strand breaks increase to a maximum and then reach a plateau or decrease. Repair kinetics depend on the fluence (irradiation dose). At any LET value, repair is much slower after heavy ion exposure than after X-irradiation. For ions with an LET of less than 10,000 keV micrometers-1 more than 90 percent of the strand breaks induced are repaired within 24 hours. At higher particle fluences, especially for low energetic particles with a very high local density of energy deposition within the particle track, a higher proportion of non-rejoined breaks is found, even after prolonged periods of incubation. At the highest LET value (16,300 keV micrometers-1) no significant repair is observed. These LET-dependencies are consistent with the current mechanistic model for radiation induced cataractogenesis which postulates that genomic damage to the surviving fraction of epithelial cells is responsible for lens opacification.     

Simultaneous measurement of multiple radiation-induced protein expression profiles using the Luminex(TM) system.

Space flight results in the exposure of astronauts to a mixed field of radiation composed of energetic particles of varying energies, and biological indicators of space radiation exposure provides a better understanding of the associated long-term health risks. Current methods of biodosimetry have employed the use of cytogenetic analysis for biodosimetry, and more recently the advent of technological progression has led to advanced research in the use of genomic and proteomic expression profiling to simultaneously assess biomarkers of radiation exposure. We describe here the technical advantages of the Luminex(TM) 100 system relative to traditional methods and its potential as a tool to simultaneously profile multiple proteins induced by ionizing radiation. The development of such a bioassay would provide more relevant post-translational dynamics of stress response and will impart important implications in the advancement of space and other radiation contact monitoring.     

Countermeasures for space radiation induced adverse biologic effects

Radiation exposure in space is expected to increase the risk of cancer and other adverse biological effects in astronauts. The types of space radiation of particular concern for astronaut health are protons and heavy ions known as high atomic number and high energy (HZE) particles. Recent studies have indicated that carcinogenesis induced by protons and HZE particles may be modifiable. We have been evaluating the effects of proton and HZE particle radiation in cultured human cells and animals for nearly a decade. Our results indicate that exposure to proton and HZE particle radiation increases oxidative stress, cytotoxicity, cataract development and malignant transformation in in vivo and/or in vitro experimental systems. We have also shown that these adverse biological effects can be prevented, at least partially, by treatment with antioxidants and some dietary supplements that are readily available and have favorable safety profiles. Some of the antioxidants and dietary supplements are effective in preventing radiation induced malignant transformation in vitro even when applied several days after the radiation exposure. Our recent progress is reviewed and discussed in the context of the relevant literature.     

Cataract analysis and the assessment of radiation risk in space.

Radiation cataract, a non-stochastic effect on the lens, is readily amenable to non-invasive analysis. Thus, it provides the means to assess radiation risk in space and for long-term monitoring of those who frequent that environment. The importance of such evaluations are underscored by the uncertainties associated with the assignment of quality factors for the effects of heavy charged particles constituting cosmic and solar radiation. Experimental studies were conducted using albino rats to evaluate the cataractogenic potential of 570 MeV/amu Argon ions administered as both single and protracted doses. The cataract studies and investigations of quantitative cytopathological changes associated with them indicate that as the dose of heavy particles decreases, the relative biological effectiveness, compared to X rays, increases. Fractionating the exposures not only failed to reduce the cataractogenic effect but caused a dose-dependent enhancement in the time of onset of opacification. Cytopathologically, the damage caused by heavy particles, when compared to low-LET radiation was found to be quantitatively dissimilar but qualitatively identical. In addition, damage which might be consistent with microlesions was not evident. The data indicates that as regards the cataractogenic potential of heavy particles at low doses an assignment of a Quality Factor (QF) of at least 40 may be in order.     

Heavy ion contributions to organ dose equivalent for the 1977 galactic cosmic ray spectrum

Estimates of organ dose equivalents for the skin, eye lens, blood forming organs, central nervous system, and heart of female astronauts from exposures to the 1977 solar minimum galactic cosmic radiation spectrum for various shielding geometries involving simple spheres and locations within the Space Transportation System (space shuttle) and the International Space Station (ISS) are made using the HZETRN 2010 space radiation transport code. The dose equivalent contributions are broken down by charge groups in order to better understand the sources of the exposures to these organs. For thin shields, contributions from ions heavier than alpha particles comprise at least half of the organ dose equivalent. For thick shields, such as the ISS locations, heavy ions contribute less than 30% and in some cases less than 10% of the organ dose equivalent. Secondary neutron production contributions in thick shields also tend to be as large, or larger, than the heavy ion contributions to the organ dose equivalents.     

Adaptive response studies may help choose astronauts for long-term space travel.

Long-term manned exploratory missions are planned for the future. Exposure to high-energy neutrons, protons and high charge and energy particles during a deep space mission, needs protection against the detrimental effects of space radiation. It has been suggested that exposure to unpredictable extremely large solar particle events would kill the astronauts without massive shielding. To reduce this risk to astronauts and to minimize the need for shielding, astronauts with highest significant adaptive responses should be chosen. It has been demonstrated that some humans living in very high natural radiation areas have acquired high adaptive responses to external radiation. Therefore, we suggest that for a deep space mission the adaptive response of all potential crew members be measured and only those with high adaptive response be chosen. We also proclaim that chronic exposure to elevated levels of radiation can considerably decrease radiation susceptibility and better protect astronauts against the unpredictable exposure to sudden and dramatic increase in flux due to solar flares and coronal mass ejections.     

Radiation effects in space.

The radiation protection guidelines of the National Aeronautics and Space Administration (NASA) are under review by Scientific Committee 75 of the National Council Protection and Measurements. The re-evaluation of the current guidelines is necessary, first, because of the increase in information about radiation risks since 1970 when the original recommendations were made and second, the population at risk has changed. For example, women have joined the ranks of the astronauts. Two types of radiation, protons and heavy ions, are of particular concern in space. Unfortunately, there is less information about the effects on tissues and cancer by these radiations than by other radiations. The choice of Quality Factors (Q) for obtaining dose equivalents for these radiations, is an important aspect of the risk estimate for space travel. There are not sufficient data for the induction of late effects by either protons or by heavy ions. The current information suggests a RBE for the relative protons of about 1, whereas, a RBE of 20 for tumor induction by heavy ions, such as iron-56, appears appropriate. The recommendations for the dose equivalent career limits for skin and the lens of the eye have been reduced but the 30-day and annual limits have been raised.     

载人深空探测任务的空间环境工程关键问题

对载人深空探测过程中将遭受的太阳宇宙射线、银河宇宙射线、微重力、尘与尘暴、深空微生物等环境进行分析。对不同深空环境给航天员带来的威胁进行了探讨。从物理屏蔽防护、辐射风险的监测和预警、辐射防护药物、航天员选拨等角度对采取的措施进行了阐述。从空间辐射对航天员的损伤机理、抗辐射和微重力药物开发、空间辐射屏蔽防护结构与材料、航天服自清洁、抗微生物侵蚀材料的研发等多个角度对需要进一步开展的工作进行了讨论。     

Materials trade study for lunar/gateway missions.

The National Aeronautics and Space Administration (NASA) administrator has identified protection from radiation hazards as one of the two biggest problems of the agency with respect to human deep space missions. The intensity and strength of cosmic radiation in deep space makes this a 'must solve' problem for space missions. The Moon and two Earth-Moon Lagrange points near Moon are being proposed as hubs for deep space missions. The focus of this study is to identify approaches to protecting astronauts and habitats from adverse effects from space radiation both for single missions and multiple missions for career astronauts to these destinations. As the great cost of added radiation shielding is a potential limiting factor in deep space missions, reduction of mass, without compromising safety, is of paramount importance. The choice of material and selection of the crew profile play major roles in design and mission operations. Material trade studies in shield design over multi-segmented missions involving multiple work and living areas in the transport and duty phase of space mission's to two Earth-Moon co-linear Lagrange points (L1) between Earth and the Moon and (L2) on back side of the moon as seen from Earth, and to the Moon have been studied. It is found that, for single missions, current state-of-the-art knowledge of material provides adequate shielding. On the other hand, the choice of shield material is absolutely critical for career astronauts and revolutionary materials need to be developed for these missions. This study also provides a guide to the effectiveness of multifunctional materials in preparation for more detailed geometry studies in progress.     

航天员受银河宇宙线辐射的剂量计算

在近地空间(LEO)和深空探测中,航天员遭受的辐射风险主要来自于银河宇宙线(GCR)照射.银河宇宙线的辐射剂量是航天员辐射风险评价的基础.国际放射防护委员会(ICRP)于2013年提出了新的航天员空间辐射剂量估算方法,以更准确给出空间重离子辐射的剂量.基于此方法,开发了宇宙线粒子在物质中输运的蒙特卡罗程序,并在程序中实现用中国成年男性人体数字模型来仿真航天员.采用该程序计算了粒子(Z=1~92)各向同性照射航天员时器官的通量-器官剂量转换因数,并估算出航天员在近地轨道空间受银河宇宙线辐射的剂量.     

The SOS-LUX-LAC-FLUORO-Toxicity-test on the International Space Station (ISS).

In the 21st century, an increasing number of astronauts will visit the International Space Station (ISS) for prolonged times. Therefore it is of utmost importance to provide necessary basic knowledge concerning risks to their health and their ability to work on the station and during extravehicular activities (EVA) in free space. It is the aim of one experiment of the German project TRIPLE-LUX (to be flown on the ISS) to provide an estimation of health risk resulting from exposure of the astronauts to the radiation in space inside the station as well as during extravehicular activities on one hand, and of exposure of astronauts to unavoidable or as yet unknown ISS-environmental genotoxic substances on the other. The project will (i) provide increased knowledge of the biological action of space radiation and enzymatic repair of DNA damage, (ii) uncover cellular mechanisms of synergistic interaction of microgravity and space radiation and (iii) examine the space craft milieu with highly specific biosensors. For these investigations, the bacterial biosensor SOS-LUX-LAC-FLUORO-Toxicity-test will be used, combining the SOS-LUX-Test invented at DLR Germany (Patent) with the commercially available LAC-FLUORO-Test. The SOS-LUX-Test comprises genetically modified bacteria transformed with the pBR322-derived plasmid pPLS-1. This plasmid carries the promoterless lux operon of Photobacterium leiognathi as a reporter element under control of the DNA-damage dependent SOS promoter of ColD as sensor element. This system reacts to radiation and other agents that induce DNA damages with a dose dependent measurable emission of bioluminescence of the transformed bacteria. The analogous LAC-FLUORO-Test has been developed for the detection of cellular responses to cytotoxins. It is based on the constitutive expression of green fluorescent protein (GFP) mediated by the bacterial protein expression vector pGFPuv (Clontech, Palo Alto, USA). In response to cytotoxic agents, this system reacts with a dose-dependent reduction of GFP-fluorescence. Currently, a fully automated miniaturized hardware system for the bacterial set up, which includes measurements of luminescence and fluorescence or absorption and the image analysis based evaluation is under development. During the first mission of the SOS-LUX-LAC-FLUORO-Toxicity-Test on the ISS, a standardized, DNA-damaging radiation source still to be determined will be used as a genotoxic inducer. A panel of recombinant Salmonella typhimurium strains carrying either the SOS-LUX plasmid or the fluorescence-mediating lac-GFPuv plasmid will be used to determine in parallel on one microplate the genotoxic and the cytotoxic action of the applied radiation in combination with microgravity. Either in addition to or in place of the fluorometric measurements of the cytotoxic agents, photometric measurements will simultaneously monitor cell growth, giving additional data on survival of the cells. The obtained data will be available on line during the TRIPLE-LUX mission time. Though it is the main goal during the TRIPLE-LUX mission to measure the radiation effect in microgravity, the SOS-LUX-LAC-FLUORO-Toxicity-test in principle is also applicable as a biomonitor for the detection and measurement of genotoxic substances in air or in the (recycled) water system on the ISS or on earth in general.     

Cataractogenic potential of ionizing radiations in animal models that simulate man.

Aspects of experiments on radiation-induced lenticular opacification during the life spans of two animal models, the New Zealand white rabbit and the rhesus monkey, are compared and contrasted with published results from a life span study of another animal model, the beagle dog, and the most recent data from the ongoing study of the survivors from radiation exposure at Hiroshima and Nagasaki. An important connection among the three animal studies is that all the measurements of cataract indices were made by one of the authors (A.C.L.), so variation form personal subjectivity was reduced to a minimum. The primary objective of the rabbit experiments (radiations involved: 56Fe, 40Ar and 20Ne ions and 60Co gamma photons) is an evaluation of hazards to astronauts from galactic particulate radiations. An analogous evaluation of hazards from solar flares during space flight is being made with monkeys exposed to 32, 55, 138 and 400 MeV protons. Conclusions are drawn about the proper use of animal models to simulate radiation responses in man and the levels of radiation-induced lenticular opacification that pose risks to man in space.     

光学镜头偏振度测试技术研究

根据斯托克斯参量计算偏振度的方法，设计了光学镜头偏振度测量仪。光学镜头偏振度测量仪采用模块化结构设计，共分为光源系统、准直光学系统、载物转台、探测系统以及后续的信号处理和计算控制系统等五部分。测量透过被测量光学镜头的光分别在0，45，90，135振动方向光信号大小τH，τ45，τV，τ135，以及左旋圆偏振光、右旋圆偏振光信号的大小礼，Jr尺，计算出光学镜头的偏振度；通过对测量装置的分析，找出了影响测试结果的几个因素，并由此分析了不确定度的来源，建立了测量不确定度的数学模型，得到了装置的扩展不确定度约为0．5％。     

Development of human epithelial cell systems for radiation risk assessment.

The most important health effect of space radiation for astronauts is cancer induction. For radiation risk assessment, an understanding of carcinogenic effect of heavy ions in human cells is most essential. In our laboratory, we have successfully developed a human mammary epithelial cell system for studying the neoplastic transformation in vitro. Growth variants were obtained from heavy ion irradiated immortal mammary cell line. These cloned growth variants can grow in regular tissue culture media and maintain anchorage dependent growth and density inhibition property. Upon further irradiation with high-LET radiation, transformed foci were found. Experimental results from these studies suggest that multiexposure of radiation is required to induce neoplastic transformation of human epithelial cells. This multihits requirement may be due to high genomic stability of human cells. These growth variants can be useful model systems for space flight experiments to determine the carcinogenic effect of space radiation in human epithelial cells.     

Active shielding for long duration interplanetary manned missions

For long duration interplanetary manned missions the protection of astronauts from cosmic radiation is an unavoidable problem that has been considered by many space agencies. In Europe, during 2002–2004, the European Space Agency supported two research programs on this thematic: one was the constitution of a dedicated study group (on the thematic ‘Shielding from cosmic radiation for interplanetary missions: active and passive methods’) in the framework of the ‘life and physical sciences’ report, and the other an industrial study concerning the ‘radiation exposure and mission strategies for interplanetary manned missions to Moon and Mars’. Both programs concluded that, outside the protection of the magnetosphere and in the presence of the most intense and energetic solar events, the protection cannot rely solely on the mechanical structures of the spacecraft, but a temporary shelter must be provided. Because of the limited mass budget, the shelter should be based on the use of superconducting magnetic systems. For long duration missions the astronauts must be protected from the much more energetic galactic cosmic rays during the whole mission period. This requires the protection of a large habitat where they could live and work, and not the temporary protection of a small volume shelter. With passive absorbers unable to play any significant role, the use of active shielding is mandatory. The possibilities offered by superconducting magnets are discussed, and recommendations are made about the needed R&D. The technical developments that have occurred in the meanwhile and the evolving panorama of possible near future interplanetary missions, require revising the pioneering studies of the last decades and the adoption of a strategy that considers long lasting human permanence in ‘deep’ space, moreover not only for a relatively small number of dedicated astronauts but also for citizens conducting there ‘normal’ activities.