Novel Double-Hit Model of Radiation and Hyperoxia-Induced Oxidative Cell Damage Relevant to Space Travel

Ralph Pietrofesa,Constantinos Koumenis,Melpo Christofidou-Solomidou,Om Mishra,Pantelis Solomides,Cameron Koch,Thomas Goodwin,Stacey Lehman,Evguenia Arguiri,Anastasia Velalopoulou

doi:10.3390/ijms17060953

Abstract

Spaceflight occasionally requires multiple extravehicular activities (EVA) that potentially subject astronauts to repeated changes in ambient oxygen superimposed on those of space radiation exposure. We thus developed a novel in vitro model system to test lung cell damage following repeated exposure to radiation and hyperoxia. Non-tumorigenic murine alveolar type II epithelial cells (C10) were exposed to >95% O2 for 8 h only (O2), 0.25 Gy ionizing γ-radiation (IR) only, or a double-hit combination of both challenges (O2 + IR) followed by 16 h of normoxia (ambient air containing 21% O2 and 5% CO2) (1 cycle = 24 h, 2 cycles = 48 h). Cell survival, DNA damage, apoptosis, and indicators of oxidative stress were evaluated after 1 and 2 cycles of exposure. We observed a significant (p < 0.05) decrease in cell survival across all challenge conditions along with an increase in DNA damage, determined by Comet analysis and H2AX phosphorylation, and apoptosis, determined by Annexin-V staining, relative to cells unexposed to hyperoxia or radiation. DNA damage (GADD45α and cleaved-PARP), apoptotic (cleaved caspase-3 and BAX), and antioxidant (HO-1 and Nqo1) proteins were increased following radiation and hyperoxia exposure after 1 and 2 cycles of exposure. Importantly, exposure to combination challenge O2 + IR exacerbated cell death and DNA damage compared to individual exposures O2 or IR alone. Additionally levels of cell cycle proteins phospho-p53 and p21 were significantly increased, while levels of CDK1 and Cyclin B1 were decreased at both time points for all exposure groups. Similarly, proteins involved in cell cycle arrest was more profoundly changed with the combination challenges as compared to each stressor alone. These results correlate with a significant 4- to 6-fold increase in the ratio of cells in G2/G1 after 2 cycles of exposure to hyperoxic conditions. We have characterized a novel in vitro model of double-hit, low-level radiation and hyperoxia exposure that leads to oxidative lung cell injury, DNA damage, apoptosis, and cell cycle arrest.

Highlights

Extravehicular activities (EVA) are required by astronauts during space travel and may pose potential health risks [1,2,3,4]
To address mechanisms underlying lung cell damage induced by exposure to radiation and hyperoxia, we developed an in vitro model system that permitted cell exposure to combination radiation and hyperoxia
We have recently identified possible pulmonary toxicity associated with space travel by the use Wofeahcealvl esyrsetceemnttloymidoednetlifireepdeaptoesdsinbdleivpiduulmaloonracroymtobxiniceidtystarsesosocriastseudchwaisthrasdpiactieontraovr ehligbhyotxhyeguesne of a celllesvyesltseamsstoocimateoddwelitrhepspeactedexipnldoirvaitdiouna[l1o2]r. cOoumr bfiinndeidngsstrfreosmsorthsescuucrhreanst rinadvitartoiomnoodrelhsiygshteomxyofgen levelssiamsisloarcicaytceldinwg iltehveslps aocfeheyxppelroorxaiati/orand[i1at2i]o.nOeuxrpofisnudreinigdsenfrtiofimedthdeamcuargreenatt tihnevliutrnogmceoldluellasrylesvteeml, of similar cycling levels of hyperoxia/radiation exposure identified damage at the lung cellular level, showing marked increases in DNA damage and apoptosis, and decreases in cell survival that were especially profound in the double-hit combination challenge group

Summary

Introduction

Extravehicular activities (EVA) are required by astronauts during space travel and may pose potential health risks [1,2,3,4]. Considering that there will be an increased requirement for crew members to perform frequent EVAs as deep space exploration becomes a reality, conditions that could pose a risk to the safety and health of the crew must be identified and prevented by designing modified procedure protocols. Exposure to a unique spectrum of space radiation including galactic cosmic radiation (GCR) and solar particle events (SPE) [9,10] adds an additional environmental risk that may affect lung tissue primed by repeat exposures to hyperoxia during preparation for and during exploration EVAs at hypobaric pressures. With the use of a mouse model to identify potential risks to lung tissues when exposed to conditions associated with space travel, we have characterized significant air space enlargement, lung inflammation, and cellular injury [11]

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