A pharmacological composition for induction of a reversible torpor-like state and hypothermia in rats

Mechanistic Implications of GSK and CREB Crosstalk in Ischemia Injury

Ischemia-reperfusion (IR) injury is a damage to an organ when the blood supply is less than the demand required for normal functioning, leading to exacerbation of cellular dysfunction and death. IR injury occurs in different organs like the kidney, liver, heart, brain, etc., and may not only involve the ischemic organ but also cause systemic damage to distant organs. Oxygen-glucose deprivation in cells causes oxidative stress, calcium overloading, inflammation, and apoptosis. CREB is an essential integrator of the body's various physiological systems, and it is widely accepted that dysfunction of CREB signaling is involved in many diseases, including ischemia-reperfusion injury. The activation of CREB can provide life to a cell and increase the cell's survival after ischemia. Hence, GSK/CREB signaling pathway can provide significant protection to cells of different organs after ischemia and emerges as a futuristic strategy for managing ischemia-reperfusion injury. Different signaling pathways such as MAPK/ERK, TLR4/MyD88, RISK, Nrf2, and NF-κB, get altered during IR injury by the modulation of GSK-3 and CREB (cyclic AMP response element (CRE)-binding protein). GSK-3 (protein kinase B) and CREB are the downstream targets for fulfilling the roles of various signaling pathways. Calcium overloading during ischemia increases the expression of calcium-calmodulin-dependent protein kinase (CaMK), which subsequently activates CREB-mediated transcription, thus promoting the survival of cells. Furthermore, this review highlights the crosstalk between GSK-3 and CREB, promoting survival and rendering the cells resistant to subsequent severe ischemia.

Solid Xenon Carrier Based on α-Cyclodextrin: Properties, Preparation, and Application

The inert gas xenon (Xe) is increasingly used in medicine as a universal anesthetic, a regulator of cellular metabolism, and a broad-spectrum organoprotector. Commonly utilized Xe inhalation requires expensive equipment that is not universally available. Here we describe the production process and physical characteristics of a solid, highly stable xenon carrier based on α-cyclodextrin (α-CD), developed for oral administration. It was found, that the interaction of α-CD with Xe in an aqueous solution and elevated pressure leads to precipitation of the α-CD-Xe complex. We have discovered three new properties of the resulting complex that promote long-term storage and oral delivery of Xe. (i) At temperatures below 0 °C, the precipitated α-CD-Xe complex containing water is so stable that it allows the removal of water by vacuum freeze-drying (lyophilization). (ii). Lyophilized α-CD-Xe remains stable for months at room temperature. (iii) Upon contact with water, α-CD-Xe rapidly releases gaseous Xe. As revealed in the forced swim test, after oral administration of lyophilized α-CD-Xe to rats, the duration of swimming was significantly increased. The obtained data open up prospects for the development of drugs based on the lyophilized α-CD-Xe complex suitable for storage, transportation, and medical use, including outside the hospital.

Be cool to be far: Exploiting hibernation for space exploration

In mammals, torpor/hibernation is a state that is characterized by an active reduction in metabolic rate followed by a progressive decrease in body temperature. Torpor was successfully mimicked in non-hibernators by inhibiting the activity of neurons within the brainstem region of the Raphe Pallidus, or by activating the adenosine A1 receptors in the brain. This state, called synthetic torpor, may be exploited for many medical applications, and for space exploration, providing many benefits for biological adaptation to the space environment, among which an enhanced protection from cosmic rays. As regards the use of synthetic torpor in space, to fully evaluate the degree of physiological advantage provided by this state, it is strongly advisable to move from Earth-based experiments to 'in the field' tests, possibly on board the International Space Station.

Pharmacological torpor prolongs rat survival in lethal normobaric hypoxia

Resistance to hypoxia is one of the most prominent features of natural hibernation and is expected to be present in the pharmacological torpor (PT) that simulates hibernation. We studied resistance to lethal hypoxia (3.5% oxygen content) in rats under PT. To initiate PT, we used the previously developed pharmacological composition (PC) which, after a single intravenous injection, can induce a daily decrease in Tb by 7 °C-8 °C at the environmental temperature of 22 °C-23 °C. Half-survival (median) time of rats in lethal hypoxia was found to increase from 5 ± 0.8 min in anesthetized control rats to 150 ± 12 min in rats injected with PC, which is a 30-fold increase. Behavioral tests after PT and hypoxia, including the traveling distance, the number of rearing and grooming episodes, revealed that animal responses are significantly restored within a week. It is assumed that the discovered unprecedented resistance of artificially torpid rats to lethal hypoxia may open up broad prospects for the therapeutic use of PT for preconditioning to various damaging factors, treatment of diseases, and extend the so-called "golden hour" for lifesaving interventions.

Long-term pharmacological torpor of rats with feedback-controlled drug administration

The maintenance of pharmacological torpor and hypothermia (body temperature 28 °C - 33 °C) in rats for a week is presented. For this purpose, our laboratory has developed a device (BioFeedback-2) for the feed-back controlled multiple injections of small doses of a pharmacological composition that we created earlier. On the 7th day, the rat spontaneously come out of the pharmacological torpor, the body temperature returned to normal, and on the 8th day, the animal could consume food and water. The proposed approach for maintaining multi-day pharmacological torpor can be applied in medicine, as well as for protecting astronauts during long missions in space.

Hibernation as a Tool for Radiation Protection in Space Exploration

With new and advanced technology, human exploration has reached outside of the Earth's boundaries. There are plans for reaching Mars and the satellites of Jupiter and Saturn, and even to build a permanent base on the Moon. However, human beings have evolved on Earth with levels of gravity and radiation that are very different from those that we have to face in space. These issues seem to pose a significant limitation on exploration. Although there are plausible solutions for problems related to the lack of gravity, it is still unclear how to address the radiation problem. Several solutions have been proposed, such as passive or active shielding or the use of specific drugs that could reduce the effects of radiation. Recently, a method that reproduces a mechanism similar to hibernation or torpor, known as synthetic torpor, has started to become possible. Several studies show that hibernators are resistant to acute high-dose-rate radiation exposure. However, the underlying mechanism of how this occurs remains unclear, and further investigation is needed. Whether synthetic hibernation will also protect from the deleterious effects of chronic low-dose-rate radiation exposure is currently unknown. Hibernators can modulate their neuronal firing, adjust their cardiovascular function, regulate their body temperature, preserve their muscles during prolonged inactivity, regulate their immune system, and most importantly, increase their radioresistance during the inactive period. According to recent studies, synthetic hibernation, just like natural hibernation, could mitigate radiation-induced toxicity. In this review, we see what artificial hibernation is and how it could help the next generation of astronauts in future interplanetary missions.

Cardiac adaptation and cardioprotection against arrhythmias and ischemia-reperfusion injury in mammalian hibernators

Hibernation allows animals to enter an energy conserving state to survive severe drops in external temperatures and a shortage of food. It has been observed that the hearts of mammalian hibernators exhibit intrinsic protection against ischemia-reperfusion (I/R) injury and cardiac arrhythmias in the winter whether they are hibernating or not. However, the molecular and ionic mechanisms for cardioprotection in mammalian hibernators remain elusive. Recent studies in woodchucks (Marmota monax) have suggested that cardiac adaptation occurs at different levels and mediates an intrinsic cardioprotection prior to/in the winter. The molecular/cellular remodeling in the winter (with or without hibernation) includes (1) an upregulation of transcriptional factor, anti-apoptotic factor, nitric oxide synthase, protein kinase C-ε, and phosphatidylinositol-4,5-bisphosphate 3-kinase; (2) an upregulation of antioxidant enzymes (e.g. superoxide dismutase and catalase); (3) a reduction in the oxidation level of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII); and (4) alterations in the expression and activity of multiple ion channels/transporters. Therefore, the cardioprotection against I/R injury in the winter is most likely mediated by enhancement in signaling pathways that are shared by preconditioning, reduced cell apoptosis, and increased detoxification of reactive oxygen species (ROS). The resistance to cardiac arrhythmias and sudden cardiac death in the winter is closely associated with an upregulation of the antioxidant catalase and a downregulation of CaMKII activation. This remodeling of the heart is associated with a reduction in the incidence of afterdepolarizations and triggered activities. In this short review article, we will discuss the seasonal changes in gene and protein expression profiles as well as alterations in the function of key proteins that are associated with the occurrence of cardioprotection against myocardial damage from ischemic events and fatal arrhythmias in a mammalian hibernator. Understanding the intrinsic cardiac adaptive mechanisms that confer cardioprotection in hibernators may offer new strategies to protect non-hibernating animals, especially humans, from I/R injury and ischemia-induced fatal cardiac arrhythmias.

Human torpor: translating insights from nature into manned deep space expedition

During a long-duration manned spaceflight mission, such as flying to Mars and beyond, all crew members will spend a long period in an independent spacecraft with closed-loop bioregenerative life-support systems. Saving resources and reducing medical risks, particularly in mental heath, are key technology gaps hampering human expedition into deep space. In the 1960s, several scientists proposed that an induced state of suppressed metabolism in humans, which mimics 'hibernation', could be an ideal solution to cope with many issues during spaceflight. In recent years, with the introduction of specific methods, it is becoming more feasible to induce an artificial hibernation-like state (synthetic torpor) in non-hibernating species. Natural torpor is a fascinating, yet enigmatic, physiological process in which metabolic rate (MR), body core temperature (T_b ) and behavioural activity are reduced to save energy during harsh seasonal conditions. It employs a complex central neural network to orchestrate a homeostatic state of hypometabolism, hypothermia and hypoactivity in response to environmental challenges. The anatomical and functional connections within the central nervous system (CNS) lie at the heart of controlling synthetic torpor. Although progress has been made, the precise mechanisms underlying the active regulation of the torpor-arousal transition, and their profound influence on neural function and behaviour, which are critical concerns for safe and reversible human torpor, remain poorly understood. In this review, we place particular emphasis on elaborating the central nervous mechanism orchestrating the torpor-arousal transition in both non-flying hibernating mammals and non-hibernating species, and aim to provide translational insights into long-duration manned spaceflight. In addition, identifying difficulties and challenges ahead will underscore important concerns in engineering synthetic torpor in humans. We believe that synthetic torpor may not be the only option for manned long-duration spaceflight, but it is the most achievable solution in the foreseeable future. Translating the available knowledge from natural torpor research will not only benefit manned spaceflight, but also many clinical settings attempting to manipulate energy metabolism and neurobehavioural functions.