Commentary: Human Pathophysiological Adaptations to the Space Environment

How the adaptation of the human microbiome to harsh space environment can determine the chances of success for a space mission to Mars and beyond

The ability of human cells to adapt to space radiation is essential for the well-being of astronauts during long-distance space expeditions, such as voyages to Mars or other deep space destinations. However, the adaptation of the microbiomes should not be overlooked. Microorganisms inside an astronaut's body, or inside the space station or other spacecraft, will also be exposed to radiation, which may induce resistance to antibiotics, UV, heat, desiccation, and other life-threatening factors. Therefore, it is essential to consider the potential effects of radiation not only on humans but also on their microbiomes to develop effective risk reduction strategies for space missions. Studying the human microbiome in space missions can have several potential benefits, including but not limited to a better understanding of the major effects space travel has on human health, developing new technologies for monitoring health and developing new radiation therapies and treatments. While radioadaptive response in astronauts' cells can lead to resistance against high levels of space radiation, radioadaptive response in their microbiome can lead to resistance against UV, heat, desiccation, antibiotics, and radiation. As astronauts and their microbiomes compete to adapt to the space environment. The microorganisms may emerge as the winners, leading to life-threatening situations due to lethal infections. Therefore, understanding the magnitude of the adaptation of microorganisms before launching a space mission is crucial to be able to develop effective strategies to mitigate the risks associated with radiation exposure. Ensuring the safety and well-being of astronauts during long-duration space missions and minimizing the risks linked with radiation exposure can be achieved by adopting this approach.

Should Parents Allow Their Children Use Smartphones and Tablets? The Issue of Screen Time for Recreational Activities

Previous research has shown that children are more vulnerable to the adverse effects of radiofrequency electromagnetic fields (RF-EMFs) and blue light emitted from digital screens compared to healthy adults. This paper presents the findings of a cross-sectional study conducted in Yasuj, Iran, to investigate the screen time habits of children and adolescents and its potential impact on their health. A total of 63 participants, including 44 boys and 19 girls, were randomly selected for the study. The results showed that the average daily screen time for the children was 87.38 minutes, with a standard deviation of 49.58. When examining the specific purposes of screen time, it was found that the children spent an average of 17.54 minutes per day on screens for school assignments, 70 minutes per day for recreational purposes, and 23.41 minutes per day for contacting family, friends, and relatives. Our study highlights that a significant portion of the children's screen time was allocated to recreational activities. We observed some differences in screen time between girls and boys. Boys had a slightly higher overall daily screen time, primarily driven by more recreational screen time. However, girls spent slightly more time on screens for school assignments. The screen time for social interactions was similar for both genders. Our findings on the cognitive performance of children with different levels of screen time will be published in a separate paper.

Biological Protection in Deep Space Missions

During deep space missions, astronauts are exposed to highly ionizing radiation, incl. neutrons, protons and heavy ions from galactic cosmic rays (GCR), solar wind (SW) and solar energetic particles (SEP). This increase the risks for cancerogenisis, damages in central nervous system (CNS), cardiovascular diseases, etc. Large SEP events can even cause acute radiation syndrome (ARS). Long term manned deep space missions will therefor require unique radiation protection strategies. Since it has been shown that physical shielding alone is not sufficient, this paper propose pre-flight screening of the aspirants for evaluation of their level of adaptive responses. Methods for boosting their immune system, should also be further investigated, and the possibility of using radiation effect modulators are discussed. In this paper, especially, the use of vitamin C as a promising non-toxic, cost-effective, easily available radiation mitigator (which can be used hours after irradiation), is described. Although it has previously been shown that vitamin C can decrease radiation-induced chromosomal damage in rodents, it must be further investigated before any conclusions about its radiation mitigating properties in humans can be concluded.

rTMS alleviates cognitive and neural oscillatory deficits induced by hindlimb unloading in mice via maintaining balance between glutamatergic and GABAergic systems

Microgravity, as a part of the stress of space flight, has several negative effects on cognitive functions. Repetitive transcranial magnetic stimulation (rTMS), as a novel non-invasive technique, could be an effective approach to alleviated cognitive decline, applied in both preclinical and clinical studies. Neural oscillations and their interactions are involved in cognitive functions and support the communication of neural information. The neural oscillation could be a window from which we may understand what happens in the brain. The current study aimed to explore if 15 Hz rTMS plays a neural modulation role in a mouse model of hindlimb unloading. We hypothezed that rTMS can improve the cognitive and neural oscillatory deficits induced by hindlimb unloading via maintaining the balance between glutamatergic and GABAergic systems. Our data show that rTMS can significantly alleviate behavior deficits, modulate theta oscillation, improve the disturbed power distribution of theta oscillation and the decreased strength of Cross-Frequency Coupling in the dentate gyrus region, and effectively mitigated the blocked communication of neural information in the perforant pathway (PP)-dentate gyrus (DG) neural pathway in Hu mice. Furthermore, biochemical analysis using high-performance liquid chromatography and Western blot assay confirmed that rTMS increases the low expression of glutamate (Glu) and N-Methyl d-Aspartate receptor subtype 2B (NR2B) and decreases the high expression of γ-aminobutyric acid (GABA), 67 KDa isoform of glutamate decarboxylase (GAD67), and GABA type A receptor subunit alpha1 (GABAAR_α1) in the hippocampus of Hu mice. Taken together, the results suggest that rTMS plays a significant neural modulation role in the hippocampal neural activity disorders induced by Hu, which possibly depends on rTMS maintaining the balance of glutamatergic and gamma-aminobutyric acidergic (GABAergic) systems.

Space Medicine: Why Do Recently Published Papers about Telomere Length Alterations Increase our Uncertainty Rather than Reduce it?

There is a growing interest in examining alterations in telomere length as a reliable biomarker of general health, as well as a marker for predicting later morbidity and mortality. Substantial evidence shows that telomere length is associated with aging; telomere shortening acts as a "counting mechanism" that drives replicative senescence by limiting the mitotic potential of normal (but not malignant) cells. In this Correspondence, we attempt to answer the question of why recently published papers about telomere length alterations increase our uncertainty rather than reduce it. This discussion includes three major research areas regarding telomere length: environmental stressors, aging, and life span. Our review suggests that activation of telomerase activity due to stressors in space might be a double-edged sword with both favorable and unfavorable consequences. The selection of an effect's consequence must clearly elucidate the experimental conditions as well as associated stressors. In this Correspondence, we attempt to answer the question of why recently published papers about telomere length alterations increase our uncertainty rather than reduce it. The selection of an effect's consequence must clearly elucidate the experimental conditions as well as associated stressors. Both positive and negative consequences must be clearly addressed in order to bolster the conclusions, as well as identify future research directions.

On the immunological limitations of hibernation and synthetic torpor as a supporting technique for astronauts’ radioprotection in deep space missions

Although human hibernation has been introduced as an effective technique in space exploration, there are concerns regarding the intrinsic risks of the approach (i.e., synthetic torpor) and other factors involved in this procedure. Besides concerns about the brain changes and the state of consciousness during hibernation, an "Achilles heel" of the hibernation is the negative impact of torpor on factors such as the number of circulating leukocytes, complement levels, response to lipopolysaccharides, phagocytotic capacity, cytokine production, lymphocyte proliferation, and antibody production. Moreover, increased virulence of bacteria in deep space can significantly increase the risk of infection. The increased infection risk during long-term space missions with the combined effects of radiation and microgravity affect the astronauts’ immune system. With these additional immune system stressors, torpor-induced extra-immunosuppression can be potentially life threatening for astronauts.

Poor Understanding of Radiation Profiles in Deep Space Causes Inaccurate Findings and Misleading Conclusions

The radiation environment in deep space, where astronauts are behind the shelter provided by the Earth's magnetosphere, is a major health concern. Galactic cosmic rays (GCR) and solar particle events (SPE) are two basic sources of space radiation in the solar system. The health risks of exposure to high levels of space radiation can be observed either as acute and delayed effects. Zhang et al. in their recently published paper entitled "γ-H2AX responds to DNA damage induced by long-term exposure to combined low-dose-rate neutron and γ-ray radiation" have addressed the effects of different cumulative radiation doses on peripheral blood cell, subsets of T cells of peripheral blood lymphocytes and DNA damage repair. These researchers exposed animals to low dose rate ⁶⁰Co-rays at 0.0167 Gy h^-1for 2 h/d and ²⁵²Cf neutrons at 0.028 mGy h^-1for 20 h/d for 15, 30, or 60 consecutive days. They reported that the mRNA of H2AX increased significantly, and showed a positive correlation with dose. Despite strengths, this paper has several shortcomings such as poor definition of low dose radiation as well as space and reactor radiation environments. Another shortcoming of this paper comes from this point that blood cell studies do not represent the biological effects of ionizing radiation on the total body. Moreover, the effects of the human immune system and DNA repair mechanisms are not included in the study. The role of pre-exposures and induction of adaptive response phenomena in decreasing the risk of radiation in deep space missions are also ignored.

Commentary regarding "on-orbit sleep problems of astronauts and countermeasures"

This commentary addresses the article by Wu et al. entitled "On-orbit sleep problems of astronauts and countermeasures". In this article, the authors discussed the sleep problems of astronauts. Despite its challenging topic, the paper authored by Wu et al. has at least one major shortcoming. This issue is related to the observation that the sleep pattern of astronauts can be disturbed by light flash phenomenon. Since the first report by astronaut E.E. Aldrin in 1969, many astronauts have reported light flashes. These visually perceived flashes of light occurred in different shapes but they apparently moved across the visual field of astronauts and possibly caused, at least to some extent, sleep problems. Moreover, the countermeasures proposed by the authors may improve astronauts' sleep pattern, but they do not address the root cause of the light flashes (i.e., heavy ion interactions outside the shielding provided by the Earth's magnetosphere). A possible approach to reducing light flashes is available using the fact that much of the galactic cosmic radiation (GCR) spectrum is composed of ions that can be diverted from the spacecraft using electromagnetic fields. Possible design parameters and the requisite electric and magnetic field strengths to successfully deflect GCR radiation are outlined.

Commentary regarding: "The effect of simulated space radiation on the N-glycosylation of human immunoglobulin G1"

Deep space missions, including Mars voyages, are an important area of research. Protection of astronauts' health during these long-term missions is of paramount importance. The paper authored by Szarka et al. entitled "The effect of simulated space radiation on the N-glycosylation of human immunoglobulin G1" is indeed a step forward in this effort. Despite numerous strengths, there are some shortcomings in this paper including an incomplete description of the space radiation environment as well as discussion of the resulting biological effects. Due to complexity of the space radiation environment, a careful analysis is needed to fully evaluate the spectrum of particles associated with solar particle events and galactic cosmic radiation. The radiation source used in this experiment does not reproduce the range of primary galactic cosmic radiation and solar particle events particles and their associated energies. Furthermore, the effect of radiation interactions within the spacecraft shell and the potential effects of microgravity are not considered. Moreover, the importance of radioadaptation in deep space missions that is confirmed in a NASA report is neither considered. Other shortcomings are also discussed in this commentary. Considering these shortcomings, it can be argued that Szarka et al. draw conclusions based on an incomplete description of the space radiation environment that could affect the applicability of this study.