14 DAY TRIAL // You might have seen the trick in SF movies: hibernating space navigators go to their target locations, located at distances of light years, while asleep, in an arrested animation, just like bacteria and tardigrades do. But an arrested metabolism could save lives not only in space, but on Earth too.
Now, the secret was found in the stench of rotten eggs, farts, bad breath and swamp mud: hydrogen sulfide (H2S). A new research to be published in the journal Anesthesiology shows this gas can decrease a mouse's metabolism without lowering its blood flow.
"A little hydrogen sulfide gas is a way to reversibly and, apparently, safely cut metabolism in mice. There seemed to be no side harmful effects to the mice after hours of breathing it in. They got sluggish, but still responded to a pinch on the tail," lead researcher Dr. Warren Zapol, a medical researcher at Massachusetts General Hospital, told LiveScience.
It was known that hydrogen sulfide plummets the metabolism, but its effect on blood circulation was not known. The research team watched how hydrogen sulfide affected heart activity in mice by using ultrasound technology. 6 hours later, the heart rate of the mice decreased by 50%, but their blood pressure did not, which means that the blood supply to the tissues was not interrupted. Moreover, the breathing failure did not occur.
"When you make everything sluggish, you'd think the heart would become sluggish, but it didn't. You'd think poisoning the metabolism would dangerously slow it down, but it didn't really seem to interfere," said Zapol.
The team points that hydrogen sulfide added to body chilling (another way of cutting down cell activity), could drop the metabolism by up to 90 %.
"Nine months in a spaceship heading out to Mars takes a lot of oxygen to burn, food and water to consume, and produces a lot of waste (carbon dioxide, urine and feces)," said Zapol, also a member on the Institute of Medicine's Committee on Aerospace Medicine and the Medicine of Extreme Environments.
A low metabolism would reduce consumption and waste production, fact that would enable longer space journeys and faster, lighter spacecrafts. But the discovery could have very earthly applications, too, like in the case of severe injuries.
"If someone loses a lot of blood, we might be able to safely reduce their need for oxygen. That would feasibly extend limited windows to perform life-saving operations," said Zapol.
But all these applications require first a lot of research, as larger animals react very differently to this toxic gas.
"The next thing we need to do is scale this up to animals bigger than a mouse," said Zapol.
In humans, this gas can induce headaches and nausea at levels 2,700 times lower than those employed by the research team. Even in the case of the mice involved in this study, 10 weeks of continuous exposure at the same concentration of H2S induced nose lesions and ulcers. Still, the toxic hydrogen sulfide could be skipped in getting the same effect of arrested metabolism.
"H2S may not be the key ingredient for inducing a suspended animation-like state in mice - a less-toxic compound may form after the gas is inhaled. We need to find out what, exactly, is circulating in the blood and causing what we've observed," explained Zapol.