Key Findings:
This group of investigators is performing interesting and novel research on the effects of flaxseed and its antioxidants on extravehicular activities (EVAs) undertaken by astronauts. These include radiation exposure dangers, decompression illness (DCI) and repeated cycles of 100% O2 exposure. Previous research shows that flaxseed decreased radiation-induced inflammation and oxidative stress in mice. SDG was shown in vitro to have direct hydroxyl radical scavenging properties and to inhibit lipid peroxidation. Using a mouse model of combined effects of repeated exposures to hyperoxia and low-level total body radiation under controlled atmospheric conditions, flaxseed (FS) feeding protected lung tissue from inflammation and oxidative/nitrosative damage. The benefits of flaxseed to reduce the risk of lung cancer (a major risk for space travel) is also of significance to the work of these investigators. The results from the current study are consistent with previous findings of the protective nature of flaxseed antioxidant in hyperoxia. Flaxseed may present a natural supplement for long term tissue radioprotective effects in the setting of repeated cycles of total body radiation and hyperoxia exposure associated with an EVA.
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. (Authors abstract)