A single low dose of Fe ions can cause long-term biological responses in NL20 human bronchial epithelial cells
Space radiation cancer risk may be a potential obstacle for long-duration spaceflight. Among all types of cancer space radiation may induce, lung cancer has been estimated to be the largest potential risk. Although previous animal study has shown that Fe ions, the most important contributor to the total dose equivalent of space radiation, induced a higher incidence of lung tumorigenesis per dose than X-rays, the underlying mechanisms at cellular level remained unclear. Therefore, in the present study, we investigated long-term biological changes in NL20 human bronchial epithelial cells after exposure to Fe ion or X-ray irradiation. We found that compared with sham control, the progeny of NL20 cells irradiated with 0.1 Gy of Fe ions showed slightly increased micronucleus formation, significantly decreased cell proliferation, disturbed cell cycle distribution, and obviously elevated intracellular ROS levels accompanied by reduced SOD1 and SOD2 expression, but the progeny of NL20 cells irradiated with 0.9 Gy of X-rays did not show any significant changes. More importantly, Fe ion exposure caused much greater soft-agar colony formation than X-rays did in the progeny of irradiated NL20 cells, clearly suggesting higher cell transformation potential of Fe ions compared with X-rays. These data may shed the light on the potential lung tumorigenesis risk from Fe ion exposure. In addition, ATM inhibition by Ku55933 reversed some of the changes in the progeny of Fe ion-irradiated cells but not others such as soft-agar colony formation, suggesting complex processes from DNA damage to carcinogenesis. These data indicate that even a single low dose of Fe ions can induce long-term biological responses such as cell transformation, etc., suggesting unignorable health risk from space radiation to astronauts.
KeywordsSpace radiation Lung cancer Fe ions X-rays NL20 human bronchial epithelial cells
This research was supported by the National Natural Science Foundation of China (Grant Nos. 11335011 and U1632270), the Key Research and Development Program of China (2016YFC0904702), the Renowned City and University Program of Suzhou (MCMX201603) and the Priority Academic Program Development of Jiangsu Higher Education Institution (PARD). The authors acknowledge the assistance from the support teams of Institute of Modern Physics (IMP), Chinese Academy of Sciences for Fe ion exposure.
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Conflict of interest
The authors declare no conflicts of interests. The authors are responsible for the content and writing of this paper.
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