Flaxseed Mitigates Acute Oxidative Lung Damage in a Mouse Model of Repeated Radiation and Hyperoxia Exposure Associated with Space Exploration

Abstract

Background Spaceflight missions may require crewmembers to conduct extravehicular activities (EVA). Pre-breathe protocols in preparation for an EVA entail 100% hyperoxia exposure that may last for a few hours and be repeated 2-3 times weekly. Each EVA is associated with additional challenges such as low levels of total body cosmic/galactic radiation exposure that may present a threat to crewmember health. We have developed a mouse model of total body radiation and hyperoxia exposure and identified acute damage of lung tissues. In the current study we evaluated the usefulness of dietary flaxseed (FS) as a countermeasure agent for such double-hit exposures. Methods We evaluated lung tissue changes 2 weeks post-initiation of exposure challenges. Mouse cohorts (n=5/group) were pre-fed diets containing either 0% FS or 10% FS for 3 weeks and exposed to: a) normoxia (Untreated); b) >95% O2 (O2); c) 0.25Gy single fraction gamma radiation (IR); or d) a combination of O2 and IR (O2+IR) 3 times per week for 2 consecutive weeks, where 8-hour hyperoxia treatments were spanned by normoxic intervals. Results At 2 weeks post challenge, while control-diet fed mice developed significant lung injury and inflammation across all challenges, FS protected lung tissues by decreasing bronchoalveolar lavage fluid (BALF) neutrophils (p<0.003) and protein levels, oxidative tissue damage, as determined by levels of malondialdehyde (MDA) (p<0.008) and nitrosative stress as determined by nitrite levels. Lung hydroxyproline levels, a measure of lung fibrosis, were significantly elevated in mice fed 0% FS (p<0.01) and exposed to hyperoxia/radiation or the combination treatment, but not in FS-fed mice. FS also decreased levels of a pro-inflammatory, pro-fibrogenic cytokine (TGF-β1) gene expression levels in lung. Conclusion Flaxseed mitigated adverse effects in lung of repeat exposures to radiation/hyperoxia. This data will provide useful information in the design of countermeasures to early tissue oxidative damage associated with space exploration.

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

“…We have recently developed a novel in vivo murine model of repeated double-hit radiation and hyperoxia exposure relevant to space travel to identify potential acute and long term damaging effects in lung [ 12 , 13 ]. To address mechanisms underlying lung cell damage induced by exposure to radiation and hyperoxia, however, we developed an in vitro model system that permitted cell exposure to combination radiation and hyperoxia.…”

“…Cells exposed to O 2 and IR challenges also displayed increased phosphorylation of H2AX along with elevated levels of DNA damage-induced proteins, cleaved-PARP and GADD45α proteins, correlating with decreased survivin and increased GADD45 α and BAX gene expression. The significant levels of epithelial cell death following exposure to radiation and hyperoxia detected in this study attributed to increased apoptosis, cell cycle arrest, and increased oxidative stress provides, in part, an explanation for the tissue damage and toxicity observed in the lungs of animals exposed to similar cycling exposures to the same challenges [ 12 , 13 ]. The information presented here, in combination with our in vivo findings, provides useful information applicable to ongoing research relevant to human space missions.…”

“…To address the knowledge gap regarding lung complications that result from the combined effects of repeat hyperoxia and radiation exposures, we established an in vitro model system to test these effects at the cellular level. We have recently developed a novel in vivo mouse model to study individual stressors such as hyperoxia or low levels of radiation exposures as well as the combinatorial effects of both stressors and demonstrated that low level radiation and hyperoxia exposure results in lung inflammation, fibrosis and oxidative tissue damage in mice [ 12 , 13 ]. The present study was designed to develop and characterize an in vitro model to investigate the underlying molecular mechanisms of double-hit-induced lung damage using murine pulmonary epithelial cell cultures under controlled atmospheric conditions.…”

Flaxseed lignans enriched in secoisolariciresinol diglucoside prevent acute asbestos-induced peritoneal inflammation in mice

“…In addition to determining significant asbestos-induced nitrosative stress that is blunted by FLC, we evaluated PLF and PLF WBCs for indicators of oxidative stress. Specifically, lipid peroxidation plays a major role in mediating oxidative damage in tissues, is a qualitative indicator of oxidative stress within tissues and cells, and can be measured by determining the amount of MDA, a product of lipid peroxidation ( 27 ). Specifically, in CTL-fed mice, we detected an acute induction of PLF MDA levels (11.26±1.11 compared to 2.08±0.47nM MDA at BL), indicative of lipid peroxidation and oxidative stress following asbestos exposure ( Figure 5C ).…”

“…Our group has reported the protective effect of FS in lung tissue, after repeated radiation and hyperoxia exposure, resulting in significantly decreased bronchoalveolar lavage fluid neutrophils and protein levels, oxidative tissue damage and nitrosative stress as determined by nitrite levels. In addition, lung fibrosis and proinflammatory, profibrogenic cytokine (TGFβ1) gene expression levels were significantly reduced in FS-fed mice ( 27 ). We subsequently identified the lignan component in FS (FLC) as the key mediator of these protective effects ( 15 , 16 ).…”