Hibernating astronauts—science or fiction?

Abstract

For long-duration manned space missions to Mars and beyond, reduction of astronaut metabolism by torpor, the metabolic state during hibernation of animals, would be a game changer: Water and food intake could be reduced by up to 75% and thus reducing payload of the spacecraft. Metabolic rate reduction in natural torpor is linked to profound changes in biochemical processes, i.e., shift from glycolysis to lipolysis and ketone utilization, intensive but reversible alterations in organs like the brain and kidney, and in heart rate control via Ca 2+. This state would prevent degenerative processes due to organ disuse and increase resistance against radiation defects. Neuro-endocrine factors have been identified as main targets to induce torpor although the exact mechanisms are not known yet. The widespread occurrence of torpor in mammals and examples of human hypometabolic states support the idea of human torpor and its beneficial applications in medicine and space exploration.

Oxygen and brain death; back from the brink

“…Hibernation and cerebral hypometabolism have recently been documented in primates [dwarf lemurs (Blanco et al, 2013;Dausmann et al, 2004)], with torpor not confined solely to cold-blooded mammals. Indirectly, this implies that perhaps we humans might have the ability to hibernate, which has beneficial applications, from medicine to long-term space exploration (Chouker et al, 2019). Several species take advantage of active brain cooling (upper right inset) to induce cerebral hypometabolism consistent with the Q 10 effect, forming the basis for therapeutic hypothermia as a neuroprotective intervention in human patients after cardiac arrest/ischaemic stroke (Duan, Huber, Ding, Huber, & Geng, 2019) as 10-fold (Frerichs, Kennedy, Sokoloff, & Hallenbeck, 1994).…”

“…Originally thought to be restricted to cold-adapted mammals, hibernation has also been observed in primates (dwarf lemurs; Blanco, Dausmann, Ranaivoarisoa, & Yoder, 2013;Dausmann, Glos, Ganzhorn, & Heldmaier, 2004), implying that perhaps we humans have the ability to hibernate, which has beneficial applications in medicine and longterm space exploration (Chouker, Bereiter-Hahn, Singer, & Heldmaier, 2019). Central metabolic roles for pyruvate dehydrogenase kinase isoenzyme 4 (Faherty, Villanueva-Canas, Blanco, Alba, & Yoder, 2018) and hibernation-specific protein (HP20 complex; Kondo et al, 2006) have been suggested as ancestral 'hibernation signatures' that contribute to mammalian brain signalling and neuroprotection.…”

Do critical care patients hibernate? Theoretical support for less is more

“…Torpor is widespread but not ubiquitous among mammals; humans do not spontaneously enter torpor and no known interventions induce it. This is not due to phylogenetic distance from torpor species as it is described in primates, nor size as torpor can be present in bears but absent in rats [2].…”

Cold‐induced chromatin compaction and nuclear retention of clock mRNAs resets the circadian rhythm

“…Bastide et al, 2017) and its potential to provide solutions to overcome the physiological challenges of long duration space flight (Choukèr et al, 2019;Jackson & Kochanek, 2019;Nordeen & Martin, 2019) expose the need to understand the cellular response to cooling at the molecular level. Elucidating these processes will ultimately provide solutions to pharmacologically activate beneficial pathways without the need for cooling and inactivate detrimental pathways to expand the remit of controlled cooling for medical applications.…”