Influence of cosmic radiation and/or microgravity on development of Carausius morosus

"Modeled microgravity" affects cell response to ionizing radiation and increases genomic damage

The aim of this work was to assess whether "modeled microgravity" affects cell response to ionizing radiation, increasing the risk associated with radiation exposure. Lymphoblastoid TK6 cells were irradiated with various doses of gamma rays and incubated for 24 h in a modeled microgravity environment obtained by the Rotating Wall Vessel bioreactor. Cell survival, induction of apoptosis and cell cycle alteration were compared in cells irradiated and then incubated in 1g or modeled microgravity conditions. Modulation of genomic damage induced by ionizing radiation was evaluated on the basis of HPRT mutant frequency and the micronucleus assay. A significant reduction in apoptotic cells was observed in cells incubated in modeled microgravity after gamma irradiation compared with cells maintained in 1g. Moreover, in irradiated cells, fewer G2-phase cells were found in modeled microgravity than in 1g, whereas more G1-phase cells were observed in modeled microgravity than in 1g. Genomic damage induced by ionizing radiation, i.e. frequency of HPRT mutants and micronucleated cells, increased more in cultures incubated in modeled microgravity than in 1g. Our results indicate that modeled microgravity incubation after irradiation affects cell response to ionizing radiation, reducing the level of radiation-induced apoptosis. As a consequence, modeled microgravity increases the frequency of damaged cells that survive after irradiation.

Critical issues in connection with human missions to Mars: protection of and from the Martian environment

Human missions to Mars are planned to happen within this century. Activities associated therewith will interact with the environment of Mars in two reciprocal ways: (i) the mission needs to be protected from the natural environmental elements that can be harmful to human health, the equipment or to their operations; (ii) the specific natural environment of Mars should be protected so that it retains its value for scientific and other purposes. The following environmental elements need to be considered in order to protect humans and the equipment on the planetary surface: (i) cosmic ionizing radiation, (ii) solar particle events; (iii) solar ultraviolet radiation; (iv) reduced gravity; (v) thin atmosphere; (vi) extremes in temperatures and their fluctuations; and (vii) surface dust. In order to protect the planetary environment, the requirements for planetary protection as adopted by COSPAR for lander missions need to be revised in view of human presence on the planet. Landers carrying equipment for exobiological investigations require special consideration to reduce contamination by terrestrial microorganisms and organic matter to the greatest feasible extent. Records of human activities on the planet's surface should be maintained in sufficient detail that future scientific experimenters can determine whether environmental modifications have resulted from explorations.

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.

Effects on ontogenesis of Carausius morosus hit by cosmic heavy ions

Among the biological problems that arise in long duration spaceflights, the effects of weightlessness and ionizing radiation appear to be the two main risk factors. Eggs of the stick insect Carausius morosus were exposed to spaceflight conditions during the 12.56 day Biosatellite mission Cosmos 1887. Five different ages were used, representing different sensitivities to radiation and different capacities for regeneration. During spaceflight the eggs continued their development. Already, in the Spacelab D1 mission in 1985, it has been shown that microgravity leads to a reduced hatching rate of eggs exposed during the early steps of development. When the eggs were hit by a heavy ion, a further but not significant reduction of the hatching rate was observed. Hatching was normal for eggs which were exposed on a 1 g reference centrifuge in space. Heavy ion hits caused body anomalies. The combined action of heavy ions and microgravity resulted in an unexpectedly high rate of anomalies. In the experiment on Cosmos 1887 these results were confirmed. Studies on the embryonic development before hatching showed no major difference between flight and ground control specimen, neither in speed of development nor in morphological anomalies. Hatching therefore seems to be the critical point in insect ontogenesis.

Critical issues in connection with human planetary missions: protection of and from the environment

Activities associated with human missions to the Moon or to Mars will interact with the environment in two reciprocal ways: (i) the mission needs to be protected from the natural environmental elements that can be harmful to human health, the equipment or to their operations: (ii) the specific natural environment of the Moon or Mars should be protected so that it retains its value for scientific and other purposes. The following environmental elements need to be considered in order to protect humans and the equipment on the planetary surface: (i) cosmic ionizing radiation, (ii) solar particle events; (iii) solar ultraviolet radiation; (iv) reduced gravity; (v) thin atmosphere; (vi) extremes in temperatures and their fluctuations; (vii) surface dust; (viii) impacts by meteorites and micrometeorites. In order to protect the planetary environment. the requirements for planetary protection as adopted by COSPAR for lander missions need to be revised in view of human presence on the planet. Landers carrying equipment for exobiological investigations require special consideration to reduce contamination by terrestrial microorganisms and organic matter to the Greatest feasible extent. Records of human activities on the planet's surface should be maintained in sufficient detail that future scientific experimenters can determine whether environmental modifications have resulted from explorations. Grant numbers: 14056/99/NL/PA.

Impact of microgravity on radiobiological processes and efficiency of DNA repair

To study the influence of microgravity on radiobiological processes in space, space experiments have been performed, using an on-board 1xg reference centrifuge as in-flight control. The trajectory of individual heavy ions was localized in relation to the biological systems by use of the Biostack concept, or an additional high dose of radiation was applied either before the mission or during the mission from an on-board radiation source. In embryonic systems, such as early developmental stages of Drosophila melanogaster and Carausius morosus, the occurrence of chromosomal translocations and larval malformations was dramatically increased in response to microgravity and radiation. It has been hypothesized that these synergistic effects might be caused by an interference of microgravity with DNA repair processes. However, recent studies on bacteria, yeast cells and human fibroblasts suggest that a disturbance of cellular repair processes in the microgravity environment might not be a complete explanation for the reported synergism of radiation and microgravity. As an alternative explanation, an impact of microgravity on signal transduction, on the metabolic/physiological state or on the chromatin structure at the cellular level, or modification of self-assembly, intercellular communication, cell migration, pattern formation or differentiation at the tissue and organ level should be considered.

Neurobiological problems in long-term deep space flights

Future missions in space may involve long-term travel beyond the magnetic field of the Earth, subjecting astronauts to radiation hazards posed by solar flares and galactic cosmic rays, altered gravitation fields and physiological stress. Thus, it is critical to determine if there will be any reversible or irreversible, detrimental neurological effects from this prolonged exposure to space. A question of particular importance focuses on the long-term effects of the space environment on the central nervous system (CNS) neuroplasticity, with the potential acute and/or delayed effects that such perturbations might entail. Although the short-term effects of microgravity on neural control were studied on previous low earth orbit missions, the late consequences of stress in space, microgravity and space radiation have not been addressed sufficiently at the molecular, cellular and tissue levels. The possibility that space flight factors can interact influencing the neuroplastic response in the CNS looms critical issue not only to understand the ontogeny of the CNS and its functional integrity, but also, ultimately the performance of astronauts in extended space forays. The purpose of this paper is to review the neurobiological modifications that occur in the CNS exposed to the space environment, and its potential consequences for extended deep space flight.

Results of space experiments

Life science research in space was started in Europe with the first Biostack experiment flown onboard Apollo 16 in 1972. Biostack was designed to investigate the biological effects of single heavy ions of cosmic radiation. Among several undertakings towards this goal, the Biostack achieved the highest precision in the determination of the spatial correlation of the observed biological response of single test organisms to the passage of single heavy ions, which is the mandatory requirement. It also provided information on the influence of additional spaceflight factors, such as microgravity, on radiation effects and measurements of the spectrum of charge and energy of the cosmic radiation. The experiment was performed as an international cooperation effort. This report gives a summary of the biological data accumulated in this and the follow-on experiments of the Biostack program.

HZE particle effects in space

Among the various particulate components of ionizing radiation in space, heavy ions (the so-called HZE particles) have been of special concern to radiobiologists. To understand the ways by which HZE particles of cosmic radiation interact with biological systems, methods have been developed to precisely localize the trajectory of an HZE particle relative to the biological object and to correlate the physical data of the particle with the biological effects observed along its path. In a variety of test systems, injuries were traced back to the traversal of a single HZE particle, such as somatic mutations, and chromosomal aberrations in plant seeds, development disturbances and malformations in insect and salt shrimp embryos, or cell death in bacterial spores. In the latter case, a long-ranging killing effect around the particle's track was observed. Whereas, from spaceflight experiments, substantial infomation has been accumulated on single HZE particle effects in resting systems and in a few embryonic systems, there is a paucity of data on cosmic radiation effects in whole tissues or animals, especially mammalians.

Comparison of measured cosmic ray LET spectra with models and predictions

Radiation effects of cosmic ray nuclei are generally described as a function of the particle LET. For a large number of space missions LET spectra have been measured and models have been developed to calculate these spectra that include the effects of geomagnetic shielding and shielding provided by material. In this paper we compare measured and calculated LET spectra. For low earth orbits events with high local energy deposition, i.e., short range secondaries, contribute significantly to the measured spectra. These events are produced by nuclear interactions, mainly induced by protons from the south atlantic anomaly. The technique to include these contributions in the models depends on the size of radiation sensitive volumes. For sizes comparable to or larger than the range of target secondaries it is essential to separate contributions by target interactions from those of cosmic rays. This separation is possible in experiments which use stacks of plastic nuclear track detectors. The yield of short range events generated by protons and measured in the detector can be calibrated from accelerator experimental data. We present first results for CR-39 detectors.

Possible mechanism of microgravity impact on Carausius morosus ontogenesis

Experiments aboard "Spacelab-D1" and "Cosmos-1887" revealed an adverse effect of space flight on Carausius morosus embryos. The main influencing factor for stick insect eggs turned out to be microgravity, while the contribution of HZE particles of cosmic radiation was relatively low. Flight experiments indicated an increased vulnerability of stick insect eggs to microgravity at intermediate stages of development, that could support the "convection" hypothesis.

Possible actions of gravity on the cellular machinery

Since the first flight of the ESA Biorack on the German Spacelab Mission D1 in 1985 evidence has been obtained that biological cells and small unicellular organisms function differently under conditions of microgravity. However, there is still lack of scientific proof that these effects are caused by a direct influence on the cells in the weightlessness condition. The question how normal gravity may play a role in cellular activity is being addressed and the results show that gravity may provide important signals during certain state transitions in the cell. These would be gravity-sensitive windows in the biological process. Also, by amplification mechanisms inside the cell, the cell may assume a state that is typical for normal gravity conditions and would change in microgravity. Experimental tools are discussed that would provide the conditions to obtain evidence for direct action of gravity and for the possible existence of gravity-sensitive windows.