Stink bomb gas puts mice into suspended animation


By Andy Coghlan Suspended animation has been deliberately induced in a species of mouse which does not naturally hibernate. It is the first time such a feat has been achieved, say the procedure’s pioneers. If a similar response could be triggered in humans, there would be major healthcare benefits and the futuristic idea of putting astronauts into suspended animation on long-haul space flights could move a step closer to reality. The mice were induced to fall into their deep sleep after being exposed to hydrogen sulphide – the gas which gives rotten eggs and stink bombs their characteristic foul odour. The animals later revived in ordinary air. Mark Roth, head of the team which pioneered the procedure at the Fred Hutchinson Cancer Research Center in Seattle, US, explains that hydrogen sulphide all but shuts down the body’s usual demand for the oxygen it needs to keep cells ticking over. Usually, cells denied oxygen – after a heart attack or stroke, for example – die quickly. But hydrogen sulphide instead sends cells into a state of dormancy. “You’re shutting down the cellular hunger for oxygen,” says Roth, delaying the cells’ oxygen-starvation and buying time for medical treatment. Roth and his colleagues exposed ordinary mice to air containing 80 parts per million of hydrogen sulphide, plunging the creatures into suspended animation for up to 6 hours. They were then revived with fresh air, having suffered no ill effects. While hibernating, their metabolic rates plummeted by about 90% as their cells dropped their usual demand for oxygen. Core body temperatures dropped from the normal 37°C to 15°C. “Once down to around 15°C, instead of 150 breaths per minute, they were down to just a couple of really shallow breaths a minute,” says Roth. High levels of hydrogen sulphide have been known to kill people working in sewers and petrochemical plants. But research on rodents showed that certain low levels appeared to kill the animals, only for them to recover later. Roth notes that a similar “Lazarus effect” has been witnessed in patients pronounced dead after exposure to extreme cold. Body cells naturally make hydrogen sulphide and Roth believes the chemical enables warm-blooded animals to stay at the same temperature by regulating oxygen demand in cells. “It’s our chemical thermostat,” he says. So providing a slight excess of the gas, he reasoned, might interfere with metabolic rates and depress demand for oxygen. In the future, Roth foresees agents which reduce metabolic rate in the same routine way that anaesthetics are used today to dull pain. It could provide a new way to help prevent tissue damage and death in stroke or heart attack victims, he suggests. It could also help to preserve transplantable organs for longer. “Space applications may also appear in the future, but our primary goal is to think about the medical applications in the here-and-now,” he says. But it will take careful experiments to develop safe and effective agents. Roth doubts whether it would be practical to place emergency patients in special chambers containing the gas, instead favouring injected agents which do the same job. “This work is exciting and incredibly creative,” says Samuel Tisherman of the University of Pittsburg’s Safar Center for Resuscitation Research. He says the procedure could complement approaches his own team are developing to prevent tissue damage by rapidly flushing the body with ice-cold saline. Large-animal experiments have already achieved up to 20 minutes in suspended animation before revival with this procedure – Tisherman’s team is aiming for 3 hours. Researchers at the European Space Agency described the breakthrough as “amazing”, but wondered if extra measures beyond the hydrogen sulphide would be needed to keep astronauts alive. “And I’m not sure astronauts would appreciate the smell as they’re trying to nod off,” joked Mark Ayres of ESA’s Advanced Concepts Team in Noordwijk, the Netherlands. Journal reference: Science (vol 308,
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