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Impact of low-dose low-energy proton radiation on mice

Project Full Title:

Understanding the impact of chronic low-dose, low energy, proton radiation on systemic inflammation and anxiety-like behaviors in mice

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Project Description:

This interdisciplinary project will incorporate the disciplines of Biology and Physics. However the project is specifically housed within the Hope College Department of Biology. A major component of NASA’s 2018 strategic plan is to send astronauts to the moon and to Mars within the next couple of decades (NASA Strategic Plan 2018). As part of the strategic plan for NASA, an asteroid will be sequestered from outer space and brought to lunar orbit. During this time, astronauts will spend long-term missions on the moon and asteroid. Additional, long-term missions include traveling to Mars for eventual human habitation. However, one major risk to mission success is the space radiation that astronauts will receive during a long-term mission flight outside of lower Earth orbit (LEO) (Chancellor, Scott, et al.; Zeitlin et al.). The space radiation environment is comprised of a mixture of galactic cosmic radiation that originates from outside the solar system, solar particle events (SPE) that originate from solar flares from the Sun, and solar wind (originates from the Sun) (Chancellor, Blue, et al.). Astronauts either in a moon-base habitat or spacecraft travelling to Mars will be shielded from protons; however, they will be exposed to a complex mixture of chronic low-dose, high-energy, high-charge (HZE) ion particles from galactic cosmic radiation (GCR) (Kim et al.; Spence et al.; Zeitlin et al.). Additionally, while not protected and outside the spacecraft or habitat performing extravehicular activities (EVA), astronauts are likely to be exposed to high and low energy protons found in SPE and solar wind,respectively, in addition to GCR (Cucinotta; Chancellor, Scott, et al.). Given the complexity surrounding the ions, energies, and doses of radiation found outside of LEO, it is difficult to fully understand the impact of space radiation on astronauts and assess risks (Chancellor, Blue, et al.). Therefore, a better understanding and characterization of individual ions, energies, and doses are needed until better methods are developed (Norbury et al.). One of the best methods to examine the effects of space radiation on animal models and biological samples is to mimic it on Earth using particle accelerators (Kim et al.; Norbury et al.). Of particular interest are low-dose, low-energy protons due to their high abundance normally found in the space environment (Stone et al.; Zeitlin et al.). Interestingly, acute low-dose, high energy proton studies in rodents show deficits in cardiac physiology (Coleman et al.), brain electrophysiology, and memory (Bellone et al.; Suresh Kumar et al.). Additionally, in humans treated with high-dose, high energy proton therapy for uveal melanomas, approximately one-third developed lasting inflammation in the eye (Lumbroso et al.). Given the detrimental physiological and cognitive impact on rodents and humans after high-energy proton studies and a lack of low-energy proton studies on skin and inflammation, knowledge of how inflammation might respond to chronic low-dose, low-energy proton radiation is warranted. Understanding if inflammation is induced by low-dose, low-energy proton radiation is of particular importance for the long-term mental health of astronauts. Previous research found that an increase inflammatory cytokines, such as tumor necrosis factor (TNF), were associated with increased depression (Reichenberg et al.), bipolar disorder, and schizophrenia (Hope et al.). The potential risk to mental health has recently been noted in an evidence report indicating that “psychological stressors of space as more salient over longer duration” (Evidence Report: Risk of Adverse Cognitive or Behavioral Conditions and Psychiatric Disorders). Therefore, the proposed study aims to test the hypothesis that chronic low-dose, low-energy proton radiation negatively impacts mental health due to lasting systemic inflammation.

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