SAVING the lives of people who have been seriously injured or suffered a stroke or heart attack can be a race against time. As soon as cells are deprived of oxygen they start dying. In the brain, that triggers a disastrous cascade of events in which cells can continue to die even after the oxygen supply is restored.
That鈥檚 why doctors have long sought ways of protecting oxygen-deprived cells (New Scientist, 8 March 2003, p 46). The longer they can keep cells alive without oxygen, the more time they have to patch up the patient, perhaps by closing a gaping wound or removing a blood clot blocking an artery. Slowing down cells鈥� metabolism by cooling tissue has been standard practice during heart operations for decades.
The discovery that mice can be placed in a state of suspended animation for up to 6 hours by exposing them to hydrogen sulphide (see main story) could open up a whole new avenue of research. 鈥淲hat you鈥檙e looking at here is the beginnings of an attempt to create a state of hibernation in non-hibernating animals,鈥� says Mark Roth of the Fred Hutchinson Cancer Research Center in Seattle, whose team discovered the effect.
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If it lives up to its promise, drugs designed to shut down metabolism could one day be used as routinely as we now use anaesthetics to shut down consciousness. Ideally, such a treatment would be simple enough to be applied by paramedics at an accident scene.
Sam Tisherman, associate director of the University of Pittsburgh鈥檚 Safar Center for Resuscitation Research in Philadelphia, says that the hydrogen sulphide approach could complement his team鈥檚 attempts to improve cooling techniques. They are experimenting with a radical method that involves 鈥減ickling鈥� the body with icy salt water. 鈥淲e鈥檝e utilised a rapid flush of the entire body with ice-cold saline to preserve the organism until repair of bleeding blood vessels could be accomplished,鈥� says Tisherman.
His team has kept animals who have had heart attacks in a state of suspended animation for up to two hours, with no pulse, breathing or movement. Not all of them recover after resuscitation, but Tisherman hopes that using something like hydrogen sulphide to reduce oxygen demand might allow less extreme cooling. 鈥淐ooling an average-sized human is difficult and brings with it potential complications, such as coagulation and infection,鈥� he says.
The ultimate use of such a method, if it ever becomes possible to slow metabolism for extended periods, would be to put people with untreatable diseases in stasis until a cure is developed.
'This is your captain speaking. Please prepare to enter stasis鈥�'
The advantages are huge. Putting astronauts in a state of suspended animation during a trip to Mars, for instance, would greatly reduce the demand for vital oxygen as well as food, water and power 鈥� and no doubt help preserve their mental well-being.
Unlike NASA, the European Space Agency is actively investigating ways of inducing a state of hibernation, including gradually reducing oxygen levels, attempting to reset the body鈥檚 core temperature, and trying to identify the natural triggers in animals that hibernate. One substance showing promise is a small protein called DADLE, which slows down the metabolism of cells in the lab.
The finding that hydrogen sulphide gas can apparently shut down metabolism in a non-hibernating animal (see main story) boosts the idea that mammals have a common hibernating ancestor, says Mark Ayre of the ESA鈥檚 Advanced Concepts Team in Noordwijk, the Netherlands. We might still have vestiges of that ability, he says. Some genes that are active in hibernators are also found in people and could perhaps be switched on.
鈥淚f inducing and maintaining torpor in astronauts would require nothing more than exposure to atmospheric hydrogen sulphide, it would be almost too simple,鈥� Ayre says. 鈥淣o doubt other mechanisms would have to be used for maintaining physiological conditioning and so on鈥ut the reduction in metabolic rate and core body temperature is very impressive.鈥�
Those other mechanisms might include ways of maintaining bone and muscle mass, and dealing with waste products. Animals like ground squirrels also rev up their metabolism every two or three weeks during hiberation, perhaps to allow their immune system to deal with any invaders.
But as far as the effect鈥檚 discoverers are concerned, the idea of adapting it for space travel can wait. They are focusing on the possible medical applications.
