Ultrasound-induced hibernation in mice makes it possible in humans

By Mayank Chhaya-

Having for decades been in the realm of science fiction novels and books, human hibernation has moved a step closer.

Over six decades after it was first proposed as a biomedical solution to reduce energy consumption during long-term human spaceflight, human hibernation may no longer be an altogether an outlandish science fiction fantasy.

Scientists have now managed to induce torpor, a sort of hibernation, among mice, perhaps opening doors to induce that among larger animals and eventually even humans. What is extraordinary about this breakthrough is that it has been achieved using a noninvasive technique like ultrasound.

A paper published in Nature Metabolism by Hong Chen, a professor of biomedical engineering at Washington University in St. Louis and others, says, “We report noninvasive, precise and safe induction of a torpor-like state in mice through remote ultrasound stimulation.”

For decades noninvasive and safe induction of a torpor-like state, says the paper, has been considered science fiction confined to movies and novels. Part of the reason it had not been attained until now is because it was believed that hibernation is regulated by endogenous blood substances or substances produced inside blood cells that suppress metabolism. That made inducing hibernation is next to impossible without invasive methods. However, with the realization that torpor is controlled by the central nervous system, noninvasive possibilities have opened.

“Ultrasound is the only available energy form that can noninvasively penetrate the skull and focus on any location within the brain with millimeter precision and without ionizing radiation16,17. These capabilities, along with its safety, portability and low cost, have made ultrasound a promising technology for neuromodulation in small animals, non-human primates and humans, although its mechanism remains elusive,” the paper says.

“Torpor, like hibernation, is a physiological state in which mammals actively suppress metabolism, reduce body temperature and slow down other live processes to conserve energy and survive fatal conditions and cold environmental temperatures,” it says.

This has profound implications for increasing survival for patients under life-threatening conditions by slowing down their metabolism and in the process slowing down the progress of those conditions.

At a grander level this has the potential to help put astronauts on long duration spaceflights, say for instance to Mars and eventually even on intergalactic travels, into extended hibernation quite like what is often seen in sci-fi movies such as Stanley Kubrick’s space masterpiece ‘2001 A Space Odyssey.’

Of course, that breakthrough is still some time away, especially long-duration hibernation for space travel since it is not yet known what happens when subjects are awakened from such hibernation. What is exciting is that ultrasound-induced torpor or hibernation is no longer just a theory. It has been achieved.

The Nature Metabolism paper says, “We designed a ‘plug-and-play’ wearable ultrasound transducer to remotely deliver ultrasound to the POA (preoptic area) region of freely moving mice that had ad libitum access to food and water. We first recorded mouse body temperature change by a thermal infrared camera and found a profound decrease in skin temperature in the interscapular area where brown adipose tissue (BAT).”

Long-duration human spaceflights face a host of other challenges for the astronauts, particularly the Galactic Cosmic Radiation (GCR), which as NASA explains is “a dominant source of radiation that must be dealt with aboard current spacecraft and future space missions within our solar system. GCR comes from outside the solar system but primarily from within our Milky Way galaxy. GCR is composed of the nuclei of atoms that have had their surrounding electrons stripped away and are traveling at nearly the speed of light.”

“Another way to think of GCR would be to imagine the nucleus of any element in the periodic table from hydrogen to uranium. Now imagine that same nucleus moving at an incredibly high speed. The high-speed nucleus you are imagining is GCR. These particles were probably accelerated within the last few million years by magnetic fields of supernova remnants,” it says.

“GCR are heavy, high-energy ions of elements that have had all their electrons stripped away as they journeyed through the galaxy at nearly the speed of light. They can cause atoms they pass through to ionize. They can pass practically unimpeded through a typical spacecraft or the skin of an astronaut, the agency explains.

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