Radiation exposure during deep-space missions could increase astronauts’ long-term risk of heart disease, a study in rats suggests. Rats exposed to radiation levels that astronauts might encounter on a round trip to Mars developed about twice as much scar tissue around the heart’s small blood vessels as unexposed rats, and the damage was still visible 360 days later. The finding points to a possible risk of cardiac fibrosis, a condition associated with heart failure, although it is not yet known whether the same effect occurs in humans.
The study was published Sept. 30 in PLoS ONE. Because the research involved rats rather than people, its results cannot establish that astronauts will develop the same condition. However, the authors said the findings emphasize the importance of monitoring astronauts’ health for many years after they return to Earth.
Radiation damage remained visible nearly a year later
The scar tissue observed in the study is a sign of cardiac fibrosis, which can make it harder for the heart to relax and can increase the risk of heart failure.
“The message we’re trying to get across is … that follow-up time is extremely important,” study co-author John Baker, a professor of surgery in the Radiobiological Sciences Laboratory at the Medical College of Wisconsin, told Live Science. “When astronauts come back to Earth, they expect, and so do we, to live long lives. I think we need to be wary that they may develop at least some type of heart disease.”
Humans generally live much longer than rats — about 80 years compared with roughly 2 to 4 years for rats. As a result, the equivalent effects in humans could take decades to appear, the researchers said.
Simulating a journey to Mars
The relationship between radiation exposure and heart problems is well documented, but determining exactly how galactic cosmic radiation affects the heart is difficult. “No astronaut has ever been exposed to galactic cosmic radiation for long periods of time,” Baker said.
Baker and his colleagues had previously identified heart problems in rats exposed to radiation. For the new study, they used NASA’s Simulated Galactic Cosmic Ray Simulation, or SimGCRSim, which is designed to more accurately reproduce the mixture and intensity of cosmic radiation astronauts could experience during deep-space missions lasting more than a year.
The researchers exposed rats to radiation for several minutes, with the precise exposure time depending on each animal’s size. The dose was intended to resemble the radiation an astronaut might receive during a round trip to Mars — approximately 18 months with current technology. The rats’ hind legs were also partially suspended to simulate weightlessness.
After 360 days, the irradiated rats had twice as much scar tissue around the small blood vessels in their hearts as rats that had not been exposed to radiation. This buildup of tissue can prevent the heart from relaxing properly, increasing the risk of heart failure, Baker said.
Radiation and weightlessness had different effects
The researchers did not observe the same cardiac-fibrosis effect in rats exposed only to simulated weightlessness. This suggested that radiation, rather than the simulated weightlessness, caused the heart damage observed in the experiment.
However, the weightlessness-only group had lower levels of some important immune cells in long-term analyses. That result suggests that microgravity could also have lasting effects on health, even though many of its known effects are short term.
“It was only the radiation that caused damage to the heart,” Baker said of the scar-tissue finding.
More research is needed
Rupak Pathak, an associate professor of pharmacy at the University of Arkansas for Medical Sciences who was not involved in the study, described the research as “an extremely valuable contribution to astrobiology.” Pathak, who holds a doctorate in radiobiology, told Live Science that rats and humans have obvious biological differences but “share over 90% of their genetic information” and have very similar cardiac systems.
Still, Pathak noted that the rats were exposed to radiation only once. He said further experiments should investigate whether chronic radiation exposure affects the function of the heart and other vital organs.
The researchers also cautioned that the study cannot determine how the findings translate to people. Differences in lifespan, biology and exposure patterns could all affect when — or whether — similar heart problems emerge in astronauts.
Baker and his colleagues hope future experiments will help NASA develop protective measures for long-duration missions. Possible countermeasures could include heart medications for astronauts and improved spacecraft shielding.
“The more we know before we start, the better NASA will be able to consider what kinds of countermeasures we can develop,” Baker said.
Source: www.livescience.com