Astronauts traveling to the Moon, Mars, and other future deep space destinations will likely make new and amazing discoveries. Undertaking these exploration missions will not be possible without increased risk to crew members from exposure to the space environment. To reduce risks of the hazards of spaceflight and protect astronauts from space radiation, NASA is using the International Space Station to develop capabilities to predict space radiation exposure for future exploration missions.
Published in the journal Nature-Scientific Reports, results from an ISS Medical Monitoring study of International Space Station astronauts demonstrate how the sensitivity of an individual astronaut's DNA to radiation exposure on Earth can predict their DNA's response during spaceflight as measured by changes to their chromosomes.
"We wanted to know if it is possible to detect and measure radiation exposure damage in the bodies of astronauts, and if there were differences based on age, sex, and other factors that could be measured before they go into space," said senior scientist Honglu Wu from NASA's Johnson Space Center in Houston. "We hope to use these measurements to help develop and compare methods of protecting astronauts from radiation."
Space radiation originates from three primary sources: particles trapped in the Earth's magnetic field, particles shot into space during solar flares, and galactic cosmic rays, which originate outside our solar system. Exposure to radiation can increase the risk of developing cancer, alterations to the central nervous system, cardiovascular disease, and other adverse health effects. Life on Earth is protected from most space radiation by the planet's atmosphere and magnetic field.
On missions in low-Earth orbit, astronauts are also protected from some of the space radiation exposure by a combination of Earth's magnetic field, spacecraft shielding, and limiting the astronaut's time in space. NASA's Human Research Program seeks to conduct research in the field of medical countermeasures such as pharmaceuticals and early disease detection technology to help mitigate the consequences of space radiation exposure. During exploration missions beyond Earth's orbit, it may not be possible to provide the same level of protection from shielding or limit mission exposure time.
As we prepare for these longer missions and a permanent human presence in space, NASA's Human Research Program seeks to conduct research in the field of medical countermeasures such as pharmaceuticals and early disease detection technology to help mitigate the consequences of space radiation exposure. A key part of that is figuring out ways to estimate the sensitivity of astronauts to radiation prior to flight and continually assess long-term health for the remainder of their lifetimes.
As people age and live their lives, their chromosomes accumulate alterations. These changes can result from normal bodily processes or due to exposure to environmental factors. Chromosomes contain the DNA building blocks of our bodies and altering them can increase the risk of developing cancer and other diseases.
During the ISS Medical Monitoring experiment, researchers studied blood samples from 43 space station crew members to measure their levels of chromosome alterations from radiation and other factors before and after a mission. These alterations to chromosomes are observed in a very small percentage of individual cells within a person's blood.
The study involved three key measurements. Before astronauts flew to the station, researchers examined their blood cells to assess their baseline chromosomal status against which any future alterations could be measured. Next, these blood samples were intentionally exposed to gamma-ray radiation on Earth to measure how easily their cells accumulated chromosomal changes. This measurement established each astronaut's inherent sensitivity to radiation. Finally, after the astronauts returned from their missions, the study team again took blood samples from the individuals to assess their level of chromosomal alterations.
Wu and retired NASA statistician Alan Feiveson then compared each astronaut's levels of post-flight alterations to their corresponding background levels established before launching into space. In addition, the investigators checked to see if any of this increase could also be explained by age, sex, or individual sensitivity.
"It was an intriguing challenge to develop a statistical method for analyzing all of the blood samples to see if an astronaut's pre-flight levels of radiosensitivity actually plays a role in predicting their spaceflight-induced chromosome alterations," said Feiveson.
After analyzing all of the data, the researchers found that, similar to people on Earth:
+ Older crew members had higher levels of baseline chromosomal irregularities, and
+ The blood cells of older astronauts were more sensitive to developing chromosomal alterations compared to younger crew members.
These results indicated that:
+ Crew members with higher inherent sensitivity, as determined by gamma radiation on the ground, were more likely to see higher levels of changes to their chromosomes in their post-flight blood samples compared to those with lower sensitivity.
+ Individuals who showed higher baseline chromosomal alterations in their pre-flight blood samples tended to also be more sensitive to developing additional chromosomal changes compared to astronauts with low baseline levels.
"The findings suggest that if older astronauts indeed have higher sensitivities to radiation, they might be at higher risk of chromosome alterations," said Wu. "While experiencing chromosome alterations does not automatically mean someone will develop cancer, it does raise the question of whether they are at increased risk for it."
Younger astronauts are thought to be more susceptible than older astronauts to the long-term health consequences resulting from space radiation exposure. This is partly because younger astronauts have more lifespan remaining and could live long enough to develop a cancer from the radiation exposure; it usually takes five to 20 years or more after the radiation exposure for cancer to occur.
"When thinking about going to Mars, we typically have thought it might be better to send older astronauts because of their experience and lower risk of developing cancer in their lifetime," said Wu. "Now, based on this new research, we know that we should study the age effects of radiation exposure more."
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