Scientific hibernation, or induced torpor, is the deliberate attempt to induce a state resembling natural hibernation in non-hibernating species, including humans. This involves a controlled reduction of the body’s metabolic rate and core temperature. The goal is to safely achieve a state of suspended animation, where biological processes slow down significantly, allowing for energy conservation and protection against various stressors.
Natural Hibernation in Animals
Natural hibernation in animals is a biological adaptation for survival during periods of cold temperatures and food scarcity. During this state, animals exhibit profound physiological changes, including a significant drop in body temperature. Heart rates decrease drastically, with some hibernating animals like the European hedgehog experiencing a reduction of up to 90%, from hundreds of beats per minute to as few as 3 to 10 beats per minute. For instance, the Arctic ground squirrel can lower its body temperature to as low as -2.9°C.
The metabolic rate can decrease by as much as 95%, allowing energy conservation through stored fat. Metabolic suppression involves shifts in biochemical processes, like switching from glycolysis to fat and ketone utilization. Despite these extreme physiological changes, hibernators avoid organ damage, muscle atrophy, and bone density loss, which would typically occur in non-hibernators. This resilience is due to molecular strategies that preserve mitochondrial function and prevent cell death during periods of low blood flow and oxygen.
Hibernating animals do not maintain torpor continuously; instead, they undergo periodic “interbout arousals” where their body temperature and metabolic rate return to near-normal levels for a few hours before re-entering torpor. These arousals are energetically costly but are an integral part of the hibernation cycle. Their organs’ ability to withstand repeated cycles of ischemia and reperfusion without injury is a key area of scientific interest.
Potential Human Applications
Scientific hibernation holds significant potential for both space travel and medical treatment. For long-duration space missions, induced hibernation could significantly reduce resource consumption, such as food, water, and oxygen. This metabolic slowdown would also help mitigate physiological challenges like muscle atrophy and bone density loss experienced by astronauts.
Beyond the physical benefits, induced torpor could simplify the psychological challenges of extended confinement in a spacecraft by minimizing psychological stressors. It also offers a protective effect against radiation damage, a concern for deep space travel, as suppressing metabolism and oxygen consumption reduces cell damage from ionizing radiation.
In the medical field, induced hibernation could significantly impact critical care. It holds promise for trauma patients by slowing cellular damage and allowing more time for medical intervention. For instance, lowering a patient’s body temperature to a few degrees above freezing has been used in clinical trials for severe hemorrhage, extending the window for surgeons to operate.
Furthermore, induced torpor could significantly improve organ preservation for transplants. Understanding how hibernating animals keep organs in stasis for extended periods could lead to “organ banks” that vastly extend donor organ viability. This approach could also protect nerves and organs from damage during complex surgeries, cardiac arrest, or strokes by reducing inflammation and promoting an oxidation defense system.
Current Research and Hurdles
Research is exploring ways to induce a hibernation-like state in non-hibernating mammals and humans. Researchers are investigating specific molecular pathways and drug candidates that could safely trigger torpor. One area of focus is the identification of neuro-endocrine factors that regulate metabolism and body temperature. For example, inhibiting activity in the ventromedial periventricular area (VMPA) in rats has induced a state where the body stops producing heat in response to cold.
Breakthroughs include the identification of compounds like hydrogen sulfide (H2S) that have induced hibernation-like states in rodents, though replicating this in larger organisms remains a challenge. Another promising area involves activating adenosine receptors in the brain to induce a similar state. A non-addictive pain relief drug, SNC80, working through the delta opioid pathway, has also shown to rapidly and reversibly slow biochemical and metabolic activities in cells and isolated pig hearts, suggesting potential for organ preservation and trauma treatment.
Despite these advancements, significant challenges remain in safely and effectively inducing and reversing a hibernation-like state in humans. One hurdle is preventing organ damage during rewarming, as tissues can be damaged when blood flow is restored if the body’s metabolic machinery cannot safely handle the rush of oxygenated blood. Understanding how hibernating animals avoid blood clots despite significantly slowed circulation is another complex problem, as immobility in humans can quickly lead to clot formation.
Controlling precise metabolic shifts, such as the ability to switch fuel sources from carbohydrates to lipids, is also a considerable challenge. Researchers are working to understand how the brain functions during prolonged torpor and how memories are retained. While some memories appear preserved, the exact mechanisms for maintaining brain health during extended neuronal depression are still being investigated. Moving from animal research to human application requires extensive clinical studies and a thorough understanding of these intricate biological processes.