Mice put in 'suspended animation'

By Paul Rincon
BBC News science reporter

The mice showed no ill-effects when they were revived

Mice have been placed in a state of near suspended animation, raising the possibility that hibernation could one day be induced in humans.

If so, it might be possible to put astronauts into hibernation-like states for long-haul space flights - as often depicted in science fiction films.

A US team from Seattle reports its findings in Science magazine.

In this case, suspended animation means the reversible cessation of all visible life processes in an organism.

The researchers from the University of Washington and the Fred Hutchinson Cancer Research Center in Seattle put the mice in a chamber filled with air laced with 80 parts per million (ppm) of hydrogen sulphide (H2S) - the malodorous gas that gives rotten eggs their stink.

Hydrogen sulphide can be deadly in high concentrations. But it is also produced normally in humans and animals, and is believed to help regulate body temperature and metabolic activity.

'Widespread uses'

In addition to its possible use in space travel, the ability to induce a hibernation-like state could have widespread uses in medicine.

Lead investigator Dr Mark Roth said this might ultimately lead to new ways of treating cancer, and preventing injury and death from insufficient blood supply to organs and tissues.

During hibernation, activity in the body's cells slows to a near standstill, dramatically cutting the animal's need for oxygen.

If humans could be freed from their dependence on oxygen, it could buy time for critically ill patients on organ-transplant lists and in operating rooms, said Dr Roth.

"Manipulating this molecular mechanism for clinical benefit potentially could revolutionise treatment for a host of human ills related to ischaemia (deficiency of the blood supply), or damage to living tissue from lack of oxygen," he explained.

But he added that any procedure in a clinical setting would likely be administered via injection rather than by getting patients to inhale a gas.

Astonishing drop

In the latest study, Dr Roth and his colleagues found that the mice stopped moving and appeared to lose consciousness within minutes of breathing the air and H2S mixture.

The animals' breathing rates dropped from the normal 120 breaths per minute to less than 10 breaths per minute.

During exposure their metabolic rates dropped by an astonishing 90%, and their core body temperatures fell from 37C to as low as 11C.

After six hours' exposure to the mixture, the mice were given fresh air. Their metabolic rate and core body temperature returned to normal, and tests showed they had suffered no ill effects.

Co-author Eric Blackstone said the next step would be to carry out studies in larger animals.

Mice do not normally hibernate, but they can reach a similar state called clinical torpor in conditions of food deprivation.

"If you can manipulate the metabolism of animals in this way with implications for humans then I could see very widespread applications," commented John Speakman, professor of zoology at the University of Aberdeen.

"There is military interest in short-duration hibernation for battlefield stabilisation of troops. If you have a soldier who is shot down, you want to be able to hibernate them on site until you can get a team in to rescue them."

Space travel

Scientists at the European Space Agency (Esa) are investigating the possibility of inducing hibernation-like states in astronauts sent on long trips to the outer planets such as Jupiter and Saturn. However, like other applications, this one may be some way off.

"The atmospheric approach to inducing torpor is a nice one because it would diffuse very quickly in the body and saves you having to administer something internally," explained Mark Ayre, of Esa's Advanced Concepts Team at Nordwijk in the Netherlands.

"We have been looking at suspended animation to cut consumables - food and water - on a journey that could take five years or longer. That is important because missions are driven by the mass of the spacecraft.

"The other thing is trying to avoid psychological problems. You can have people awake, in which case you need to keep them entertained. That means more volume and potentially a very large mass.

"Or you avoid all that by putting them to sleep."

Inducing hibernation-like states could also have potential in cancer research by allowing patients to tolerate higher radiation doses without damaging healthy tissue.

Cancer cells are not dependent on oxygen to grow, says Dr Roth, so they are more resistant to radiotherapy.

"Right now in most forms of cancer treatment we're killing off the normal cells long before we're killing off the tumour cells. By inducing metabolic hibernation in healthy tissue, we'd at least level the playing field," he explained.