Manned space travel has been taking place for decades, yet there remains the uncertainty of the lingering effects of radiation and gravity on the human body. Residents, human and mice, of past space shuttle missions and the International Space Station make helpful test subjects. A recent study deals with issues arising from gravity in space.
Researchers recently studied the biological affects of space travel on mice that were aboard the space shuttle Atlantis. They uncovered disturbing metabolic changes in the liver that could translate to issues in humans on prolonged space journeys. NASA, though aware of the effects of gravity fields on humans, has not reported liver damage, yet.
Prior to this study, we really didn’t have much information on the impact of spaceflight on the liver. We knew that astronauts often returned with diabetes-like symptoms, but they were usually resolved quickly.
Mice flown aboard Atlantis’s final mission lost weight but redistributed lipids, particularly in the liver. Activated liver cells caused liver scarring. This early sign of liver damage occurred faster than expected.
We saw the beginning of nascent liver damage in just 13.5 days. The mice also lost lean muscle mass. We have seen this same phenomenon in humans on bed rest – muscles atrophy and proteins break down into amino acids. The question is, how does that affect your liver?
The study compared space-faring mice and earth-bound mice. Samples taken from the space mice indicated fat storage in their livers with lower levels of retinol (animal based form of Vitamin A). They lose retinol from lipid droplets. There are also changes in the level of genes that break down fats. Signs of non-alcoholic fatty liver disease, the start of fibrosis, were evident.
It generally takes a long time, months to years, to induce fibrosis in mice, even when eating an unhealthy diet. If a mouse is showing nascent signs of fibrosis without a change in diet after 13.5 days, what is happening to the humans?
Further research is needed to determine if the potential liver damage relates to humans. Perhaps Scott Kelly, who spent a year on the International Space Station could provide future information, along with his earthbound twin? With 150 day flights to Mars looming in the near future, learning about the biological effects on the body are paramount.
Jonscher sums up,
Whether or not this is a problem is an open question. We need to look at mice involved in longer duration space flight to see if there are compensatory mechanisms that come into play that might protect them from serious damage.