Humans evolved to thrive here on Earth, so as soon as you take us away from that environment, all sorts of health problems arise. Now, researchers from the University of California Riverside and San Diego have found evidence of a new problem. Microgravity simulations show that our guts can become “leaky” after a stint in space, increasing the chances of certain infections and diseases for weeks afterwards.
The human digestive system is a pretty extreme place. Not only is it full of stomach acid that would dissolve other organs, but it contains a vast ecosystem of microorganisms that can cause dangerous infections if they escape into other parts of the body.
To keep us safe, our intestines are lined with epithelial cells that form an impermeable barrier against bacteria and other nasties. At least, it’s supposed to be impermeable – sometimes it’s weakened by illness or poor diet, allowing things to get through that really shouldn’t. This in turn can cause chronic conditions like type 1 diabetes, inflammatory bowel disease, and liver disease.
For the new study, the team wanted to investigate whether the microgravity of space affects this barrier in the human gut. Already, studies have shown that thanks to low gravity and high radiation, space travel can potentially weaken astronauts’ bones and muscles, induce symptoms of dementia, increase chances of cardiovascular disease, and even change gene expression.
To study the effects on the gut, the researchers cultured intestinal epithelial cells in a bioreactor that spins quickly, to simulate the effects of microgravity. After 18 days in this environment, the team stopped the spinning and examined the cells.
It was found that these epithelial cells had delayed formation of “tight junctions,” which connect individual cells together. With these connections weakened, the wall becomes permeable, or “leaky,” which was demonstrated by exposing them to acetaldehyde. This alcohol metabolite is known to normally weaken the barrier, and the microgravity cells had a harder time shrugging off those effects.
“Our study shows for the first time that a microgravity environment makes epithelial cells less able to resist the effects of an agent that weakens the barrier properties of these cells,” says Declan McCole, lead researcher on the study. “Importantly, we observed that this defect was retained up to 14 days after removal from the microgravity environment.”
The team says these findings could have implications for the health of astronauts in space and even after they return to Earth. Unfortunately the gut seems particularly problem-prone – another recent study on mice found that cosmic radiation can affect the ability of intestinal cells to absorb nutrients, and increase cancer risk.
All up, it seems that space travel is pretty taxing on the human body. For now, it seems safer for the majority of us to stay here on Earth – so we had better start looking after it.
The research was published in the journal Scientific Reports.
