NUNDO: a numerical model of a human torso phantom and its application to effective dose equivalent calculations for astronauts at the ISS

Long term food stability for extended space missions: a review

At present, human spaceflight is confined to low Earth orbit but, in future, will again go to the Moon and, beyond, to Mars. The provision of food during these extended missions will need to meet the special nutritional and psychosocial needs of the crew. Terrestrially grown and processed food products, currently provided for consumption by astronauts/cosmonauts, have not yet been systematically optimised to maintain their nutritional integrity and reach the shelf-life necessary for extended space voyages. Notably, space food provisions for Mars exploration will be subject to extended exposure to galactic cosmic radiation and solar particle events, the impact of which is not fully understood. In this review, we provide a summary of the existing knowledge about current space food products, the impact of radiation and storage on food composition, the identification of radiolytic biomarkers and identify gaps in our knowledge that are specific in relation to the effect of the cosmic radiation on food in space.

[From human terrestrial models to new preventive measures for ocular changes in astronauts : Results of the German Aerospace Center studies]

BACKGROUND

Ocular changes in astronauts, particularly the spaceflight associated neuro-ocular syndrome (SANS), pose a medical challenge for which no suitable preventive measures exist. During long-duration spaceflight missions, e.g. to the Moon and Mars, SANS and radiation-induced cataract could affect the health and performance of crews and jeopardize the success of missions. Mechanistic studies and development of preventive measures require suitable terrestrial models.

OBJECTIVE

Overview on the most recent research and future plans in space medicine.

MATERIAL AND METHODS

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RESULTS

Bed rest studies at the German Aerospace Center (DLR) demonstrated that strict bed rest in a -6° head down tilt position reproduces changes just like SANS on Earth. This model including creation of optic disc edema is applied in human studies testing influences of artificial gravity through short arm centrifugation as a preventive method. The unique research facility :envihab provides the opportunity to also simulate the ambient conditions of the International Space Station during bed rest studies.

CONCLUSION

Future head down tilt bed rest studies will serve to systematically test preventive measures for SANS. Similar investigations would be difficult to realize under real space conditions. Through close collaboration between space medicine and terrestrial ophthalmology, this research can benefit patients on Earth.

The Role of the Nuclear Factor κB Pathway in the Cellular Response to Low and High Linear Energy Transfer Radiation

Astronauts are exposed to considerable doses of space radiation during long-term space missions. As complete shielding of the highly energetic particles is impracticable, the cellular response to space-relevant radiation qualities has to be understood in order to develop countermeasures and to reduce radiation risk uncertainties. The transcription factor Nuclear Factor κB (NF-κB) plays a fundamental role in the immune response and in the pathogenesis of many diseases. We have previously shown that heavy ions with a linear energy transfer (LET) of 100–300 keV/µm have a nine times higher potential to activate NF-κB compared to low-LET X-rays. Here, chemical inhibitor studies using human embryonic kidney cells (HEK) showed that the DNA damage sensor Ataxia telangiectasia mutated (ATM) and the proteasome were essential for NF-κB activation in response to X-rays and heavy ions. NF-κB’s role in cellular radiation response was determined by stable knock-down of the NF-κB subunit RelA. Transfection of a RelA short-hairpin RNA plasmid resulted in higher sensitivity towards X-rays, but not towards heavy ions. Reverse Transcriptase real-time quantitative PCR (RT-qPCR) showed that after exposure to X-rays and heavy ions, NF-κB predominantly upregulates genes involved in intercellular communication processes. This process is strictly NF-κB dependent as the response is completely absent in RelA knock-down cells. NF-κB’s role in the cellular radiation response depends on the radiation quality.

COMPARISON OF ORGAN DOSES IN HUMAN PHANTOMS: VARIATIONS DUE TO BODY SIZE AND POSTURE

Organ dose calculations performed using human phantoms can provide estimates of astronauts' health risks due to cosmic radiation. However, the characteristics of such phantoms strongly affect the estimation precision. To investigate organ dose variations with body size and posture in human phantoms, a non-uniform rational B-spline boundary surfaces model was constructed based on cryosection images. This model was used to establish four phantoms with different body size and posture parameters, whose organs parameters were changed simultaneously and which were voxelised with 4 × 4 × 4 mm3 resolution. Then, using Monte Carlo transport code, the organ doses caused by ≤500 MeV isotropic incident protons were calculated. The dose variations due to body size differences within a certain range were negligible, and the doses received in crouching and standing-up postures were similar. Therefore, a standard Chinese phantom could be established, and posture changes cannot effectively protect astronauts during solar particle events.

Cultivation of Staphylococcus epidermidis in the Human Spaceflight Environment Leads to Alterations in the Frequency and Spectrum of Spontaneous Rifampicin-Resistance Mutations in the rpoB Gene

Bacteria of the genus Staphylococcus are persistent inhabitants of human spaceflight habitats and represent potential opportunistic pathogens. The effect of the human spaceflight environment on the growth and the frequency of mutations to antibiotic resistance in the model organism Staphylococcus epidermidis strain ATCC12228 was investigated. Six cultures of the test organism were cultivated in biological research in canisters-Petri dish fixation units for 122 h on orbit in the International Space Station (ISS) as part of the SpaceX-3 resupply mission. Asynchronous ground controls (GCs) consisted of identical sets of cultures cultivated for 122 h in the ISS Environmental Simulator at Kennedy Space Center. S. epidermidis exhibited significantly lower viable counts but significantly higher frequencies of mutation to rifampicin (Rif) resistance in space vs. GC cultures. The spectrum of mutations in the rpoB gene leading to Rif(R) was altered in S. epidermidis isolates cultivated in the ISS compared to GCs. The results suggest that the human spaceflight environment induces unique physiologic stresses on growing bacterial cells leading to changes in mutagenic potential.

Radiation environment at aviation altitudes and in space

On the Earth, protection from cosmic radiation is provided by the magnetosphere and the atmosphere, but the radiation exposure increases with increasing altitude. Aircrew and especially space crew members are therefore exposed to an increased level of ionising radiation. Dosimetry onboard aircraft and spacecraft is however complicated by the presence of neutrons and high linear energy transfer particles. Film and thermoluminescent dosimeters, routinely used for ground-based personnel, do not reliably cover the range of particle types and energies found in cosmic radiation. Further, the radiation field onboard aircraft and spacecraft is not constant; its intensity and composition change mainly with altitude, geomagnetic position and solar activity (marginally also with the aircraft/spacecraft type, number of people aboard, amount of fuel etc.). The European Union Council directive 96/29/Euroatom of 1996 specifies that aircrews that could receive dose of >1 mSv y(-1) must be evaluated. The dose evaluation is routinely performed by computer programs, e.g. CARI-6, EPCARD, SIEVERT, PCAire, JISCARD and AVIDOS. Such calculations should however be carefully verified and validated. Measurements of the radiation field in aircraft are thus of a great importance. A promising option is the long-term deployment of active detectors, e.g. silicon spectrometer Liulin, TEPC Hawk and pixel detector Timepix. Outside the Earth's protective atmosphere and magnetosphere, the environment is much harsher than at aviation altitudes. In addition to the exposure to high energetic ionising cosmic radiation, there are microgravity, lack of atmosphere, psychological and psychosocial components etc. The milieu is therefore very unfriendly for any living organism. In case of solar flares, exposures of spacecraft crews may even be lethal. In this paper, long-term measurements of the radiation environment onboard Czech aircraft performed with the Liulin since 2001, as well as measurements and simulations of dose rates on and outside the International Space Station were presented. The measured and simulated results are discussed in the context of health impact.

Constitutive expression of tdTomato protein as a cytotoxicity and proliferation marker for space radiation biology

The radiation risk assessment for long-term space missions requires knowledge on the biological effectiveness of different space radiation components, e.g. heavy ions, on the interaction of radiation and other space environmental factors such as microgravity, and on the physical and biological dose distribution in the human body. Space experiments and ground-based experiments at heavy ion accelerators require fast and reliable test systems with an easy readout for different endpoints. In order to determine the effect of different radiation qualities on cellular proliferation and the biological depth dose distribution after heavy ion exposure, a stable human cell line expressing a novel fluorescent protein was established and characterized. tdTomato, a red fluorescent protein of the new generation with fast maturation and high fluorescence intensity, was selected as reporter of cell proliferation. Human embryonic kidney (HEK/293) cells were stably transfected with a plasmid encoding tdTomato under the control of the constitutively active cytomegalovirus (CMV) promoter (ptdTomato-N1). The stably transfected cell line was named HEK-ptdTomato-N1 8. This cytotoxicity biosensor was tested by ionizing radiation (X-rays and accelerated heavy ions) exposure. As biological endpoints, the proliferation kinetics and the cell density reached 100 h after irradiation reflected by constitutive expression of the tdTomato were investigated. Both were reduced dose-dependently after radiation exposure. Finally, the cell line was used for biological weighting of heavy ions of different linear energy transfer (LET) as space-relevant radiation quality. The relative biological effectiveness of accelerated heavy ions in reducing cellular proliferation peaked at an LET of 91 keV/μm. The results of this study demonstrate that the HEK-ptdTomato-N1 reporter cell line can be used as a fast and reliable biosensor system for detection of cytotoxic damage caused by ionizing radiation.