What better way to pass a long stretch of time than by entering a deep sleep to shut down some bodily functions and conserve energy? Bears do it to get through cold winters. So do many smaller mammals, including squirrels and hedgehogs. Even the fat-tailed lemur (a primate cousin of Homo sapiens), living in warm Madagascar, slows down for months when its food supply runs low. But for us humans, hibernation has been an unnecessary and impossible goal. Until now.
Taking lessons from animal hibernators, scientists are using their tricks for medical therapies and may some day adopt them for space travel. Some physicians are employing therapeutic hypothermia – a lowering of the body temperature by a few degrees for several days at a time – to help treat patients with traumatic brain injuries or conditions such as epilepsy. And trials are under way to see if there is a way to lower the body temperature of people, keep them in a sleep-like state for days or weeks and then revive them with no ill effects, something that astronauts may have to do to travel deep into space.
“We see the science has advanced enough to put some of the science fiction into the realm of science reality,” says Leopold Summerer, head of the advanced concepts team of the European Space Agency, one of the operators of the International Space Station. “It doesn’t mean we will have hibernating astronauts any time soon, but we are learning from nature how to understand some of the things that happen to animals during hibernation, such as preventing bone loss or preventing muscle loss.”
A panel of European biomedical researchers, biologists and neuroscientists is expected to deliver recommendations for future lines of human hibernation research and funding soon, according to Summerer. One Italian scientist says he is conducting an experiment to test an animal’s body thermostat for a six-hour period as a precursor to human trials.
Nasa funded a preliminary study that looked at the idea of putting astronauts into a state of torpor, or hibernation, for weeks at a time. The prospective benefits that were reported last year included a cut in the food and water required on their spacecraft, a reduction in waste products, smaller living quarters and less space needed for supplies, exercise and entertainment. And putting the crew to sleep might minimise their psychological challenges. The idea, however, didn’t make it to a second round of funding. John Bradford, head of the company that proposed the human hibernation, says he’s hoping to get funding elsewhere. Nasa says it will be using the year-long sojourn US astronaut Scott Kelly just started at the International Space Station, combined with medical monitoring of his Earthbound twin brother, retired astronaut Mark Kelly, to collect clues about protecting humans who leave Earth’s orbit for months or years at a time.
Biologists aren’t waiting for results from space. They are busy dissecting the neurological and biochemical pathways of such hibernating animals as the Arctic ground squirrel, which sets its internal body temperature at freezing point during the winter, and several kinds of bears that slumber six months at a time without awakening as puny weaklings. “We think that if we understand how they do it, we can replicate it in humans,” said Kelly Drew, a biochemist at the University of Alaska at Fairbanks. Drew and her colleagues at the university’s Institute of Arctic Biology are looking at how the Arctic ground squirrel can get so cold without dying. She believes she has found the molecule that does the job, the A1 adenosine receptor. While she has learned that stimulating this receptor makes the animal get cold, she hasn’t found what triggers it.
“We don’t know what the natural signal is for torpor,” she said. “We don’t know where the signal occurs in the brain – it could be in the brain stem or the hypothalamus.” The next step is to learn how to safely use drugs that stimulate the A1 adenosine receptor and then induce animals that do not normally hibernate to enter and stay in a state of torpor for two to three weeks at a time.
A shorter period of human deep sleep, induced by cooling the body, isalready used to help brain-injury patients at the Johns Hopkins University and many other hospitals. Romergryko Geocadin, a Hopkins professor of neurology and anaesthesiology, has used the treatment, known as therapeutic hypothermia, to help patients with severe epilepsy or brain trauma. “We don’t know why it works,” Geocadin said, “but we know it slows down metabolism and the inflammation” that occurs in the brain with epilepsy. Cooling the body gives the brain a chance to repair itself. “You actually lower the need for energy for the entire body,” he said. “So you give it time to catch up.”
Using ice packs, liquid-filled blankets, caps and even cooling IV fluids, Geocadin lowers a patient’s body temperature from its ordinary level of about 37C to about 33-34C for up to three days at a time. (This involves a handful of patients each month who are comatose because of cardiac arrest or who are experiencing seizures or brain swelling.) Longer than that, “and the whole house of cards starts to fall apart”, increasing the risk of blood clots, pneumonia and other complications.