Mice put into "suspended animation" in U.S.

Apr 22 2005

Researchers from the University of Washington and the Fred Hutchinson Cancer Research Centre in Seattle have placed mice in a state of near suspended animation, raising the possibility that in future hibernation could be induced in humans.

Dr Mark Roth, lead investigator, says it might then be possible to put astronauts into a state of hibernation for long-haul space flights, could also lead to new ways of treating cancer, and preventing injury and death from insufficient blood supply to organs and tissues.

Any activity in the body's cells slows to a near standstill during hibernation which dramatically cuts down the animal's need for oxygen.

Roth says that 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.

In the study the mice were put in a chamber filled with air laced with 80 parts per million (PPM) of hydrogen sulphide (H2S) - the foul smelling, gas that gives rotten eggs their stink and the researchers found that the mice stopped moving and appeared to lose consciousness within minutes of breathing the air and H2S mixture. Their breathing rates dropped from the normal 120 breaths per minute to less than 10 breaths per minute.

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

After six hours 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.

Hydrogen sulphide though deadly in high concentrations is produced normally in humans and animals, and is believed to help regulate body temperature and metabolic activity.

Being able to induce a hibernation-like state could have widespread uses in medicine as well as its possible use in space travel.

Treatment for a number of human diseases related to deficiency of the blood supply, or damage to living tissue from lack of oxygen, could be revolutionised by the ability to manipulate molecular mechanisms for clinical benefit.

The next step should be to carry out studies in larger animals, says co-author Eric Blackstone, any procedure in a clinical setting would probably be administered via injection rather than by getting patients to inhale a gas.

Although mice do not normally hibernate, they can reach a similar state called clinical torpor when deprived of food.

John Speakman, professor of zoology at the University of Aberdeen says that if the metabolism of animals can be manipulated in this way with implications for humans, there could be very widespread applications.

The possibility of inducing hibernation-like states in astronauts sent on long trips to the outer planets such as Jupiter and Saturn is being investigated by scientists at the European Space Agency (ESA).

Mark Ayre, of Esa's Advanced Concepts Team at Nordwijk in the Netherlands, says they 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.

When people are awake they need to be kept entertained which means more volume and potentially a very large mass, psychological problems might also be avoided by putting them to sleep.

Induced states of hibernation 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, so they are more resistant to radiotherapy.

Most current forms of cancer treatment kill off the normal cells long before they kill off the tumour cells, and inducing metabolic hibernation in healthy tissue, would at least "level the playing field," says Dr Roth.

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

The findings are published in Science Magazine.