Cell‐Free Mitochondrial DNA as a Potential Biomarker for Astronauts' Health

BACKGROUND: Space travel–associated stressors such as microgravity or radiation exposure have been reported in astronauts after short‐ and long‐duration missions aboard the International Space Station. Despite risk mitigation strategies, adverse health effects remain a concern. Thus, there is a need to develop new diagnostic tools to facilitate early detection of physiological stress. METHODS AND RESULTS: We measured the levels of circulating cell‐free mitochondrial DNA in blood plasma of 14 astronauts 10 days before launch, the day of landing, and 3 days after return. Our results revealed a significant increase of cell‐free mitochondrial DNA in the plasma on the day of landing and 3 days after return with vast ~2 to 355‐fold interastronaut variability. In addition, gene expression analysis of peripheral blood mononuclear cells revealed a significant increase in markers of inflammation, oxidative stress, and DNA damage. CONCLUSIONS: Our study suggests that cell‐free mitochondrial DNA abundance might be a biomarker of stress or immune response related to microgravity, radiation, and other environmental factors during space flight.