Early results from NASA’s of astronaut Scott Kelly and his earthbound identical twin Mark Kelly have so far raised no serious concerns about the effects of long-term space travel on health, said scientists at the 2019 AAAS Annual Meeting.
Craig Kundrot, director of NASA’s space life and physical sciences research and applications division, said so far there are no “red flags” in the data coming out of the twins’ study, but that the team will continue to study the changes that were unexpected.
These changes “could be a good adaptive response to space flight with no permanent consequences, because you expect the body to make some adjustments or it could be sending things down a path that could be a concern, and we just don’t know yet,” he said.
A year in space does change a man, however. Scott Kelly’s time in low earth orbit onboard the International Space Station revved up his immune system and caused an unexpected shed of mitochondrial DNA fragments into his bloodstream. But these and other molecular changes may be temporary and reversible signs of the body adapting to the stresses of low gravity, radiation and higher than normal levels of carbon dioxide in the air, among other challenges, the researchers said.
Long-term space flight produces thousands of changes in an astronaut’s genes, small molecules and microbial companions, said Chris Mason, a physiology and biophysics professor at Weill Cornell Medical College, “but over 91 percent of genes return back to normal very quickly, upon coming back to Earth, and we see that for the most part the body has this extraordinary plasticity and adaptation to being in zero gravity, at least for a year.”
Since the study includes only two individuals, “we don’t regard any of this as conclusive, but on the whole it’s encouraging,” said Kundrot.
Mason, who is part of a larger team studying changes in cells, genes and gene expression in the Kelly twins, said the distribution of different types of immune cells and immune system activity changed dramatically in Scott after a week of being in space. “It appears that the body is almost on a kind of high alert, which you would imagine if your body suddenly went zero gravity,” he said.
The researchers also saw a spike in freely-circulating mitochondrial DNA, not contained within cells, in Scott’s blood at the beginning and at the end of the mission. Levels of this type of free DNA can be “an indicator of overall health and of which cells are dying at which speed,” Mason said, explaining that the phenomenon occurs on Earth in healthy people as well.
Mason said the scientists aren’t sure yet how the mitochondrial DNA is being released from cells, but he noted that this free DNA may be one trigger of the immune system, priming it to cope with the stress of spaceflight.
Conducting rigorously controlled experiments on two humans 240 vertical miles apart has its challenges, said Mason, including the “repatriation” of Scott’s blood samples that were returned to Earth in Kazakhstan. The scientists tried to control one more variable when they asked Mark to eat the same meals as Scott during the experiment.
“He politely declined, and I think stuck to the nachos and margaritas, and kept a food log of that,” Mason said.
Research on microbes, plants and animals conducted through NASA’s project can help fill in the details of what happens across a variety of biological systems during long-haul space flights, said Sylvain Costes, the project’s manager and principle investigator. GeneLab is the world’s first database to contain gene, gene expression, protein and metabolism data on organisms sent to space, along with comparative data from Earth.
The unique database allows scientists to uncover space-related changes that may not have been obvious at first, said Costes, who discussed an ongoing study in mice that revealed unexpected changes in the liver. “We see some changes at the mitochondrial level in animals that seems to be having profound effects on the liver, and then the liver itself sends signals to the entire tissue of the mice, and it seems to affect the eyes and muscle,” he said. “We’re not really sure yet what it means, but it was a surprise, because liver has really never been on the list” of key organs studied in human space research.
Much of the data gathered in GeneLab comes from low orbit experiments on the International Space Station, but conditions in deep space will be different, said Kundrot, noting that rate of radiation doses will be two times higher than in low orbit.
Kundrot said on Friday that NASA will soon announce experimental payloads for Exploration Mission-1, a 26-day uncrewed mission that will push beyond the Moon, to explore the biological impacts on deep space.