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

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.

Effects of Iron Overload and Oxidative Damage on the Musculoskeletal System in the Space Environment: Data from Spaceflights and Ground-Based Simulation Models

“…Space-relevant radiation can induce oxidative damage in various tissues of rodents. Lung tissue from mice showed significant oxidative damage, including DNA damage, protein nitrosative stress, and lipid peroxidation after exposure to radiation, similar to space [ 73 , 74 , 75 ]. Mice exposed to low-doses of ionizing radiation exhibited oxidative damage and apoptosis in the retina [ 76 ].…”

Hyperoxia sensitizes hypoxic HeLa cells to ionizing radiation by downregulating HIF‑1&alpha; and VEGF expression

“…Nordsmark et al ( 17 ) demonstrated that increased tumor partial O 2 pressure enhanced IR response in mammary carcinoma. Pietrofesa et al ( 18 ) reported that exposure to the combination of IR + O 2 increased DNA damage and cell death compared with the individual exposures to IR or O 2 alone. However, how a high concentration of O 2 pretreatment affects the efficacy of cervical cancer radiotherapy has not been fully elucidated.…”

LGM2605 Reduces Space Radiation-Induced NLRP3 Inflammasome Activation and Damage in In Vitro Lung Vascular Networks

“…In further studies using space-relevant radiation (proton radiation), we have shown that LGM2605 (the synthetic version of SDG) acts as a mitigator of radiation-induced increases in inflammatory signals (cytokines, chemokines) in human lung sections (huPCLS) [22]. LGM2605 is a potent scavenger of radiation-induced reactive oxygen species (ROS) and active chlorine species (ACS), and can reduce the ionizing species arising from radiation [23,24,25,26]. However, more importantly, it is also an inhibitor of several proinflammatory signaling pathways that upregulate cytokines, chemokines, and adhesion molecules [24,27].…”