Renal and sympathoadrenal responses in space

Cosmic kidney disease: an integrated pan-omic, physiological and morphological study into spaceflight-induced renal dysfunction

Missions into Deep Space are planned this decade. Yet the health consequences of exposure to microgravity and galactic cosmic radiation (GCR) over years-long missions on indispensable visceral organs such as the kidney are largely unexplored. We performed biomolecular (epigenomic, transcriptomic, proteomic, epiproteomic, metabolomic, metagenomic), clinical chemistry (electrolytes, endocrinology, biochemistry) and morphometry (histology, 3D imaging, miRNA-ISH, tissue weights) analyses using samples and datasets available from 11 spaceflight-exposed mouse and 5 human, 1 simulated microgravity rat and 4 simulated GCR-exposed mouse missions. We found that spaceflight induces: 1) renal transporter dephosphorylation which may indicate astronauts' increased risk of nephrolithiasis is in part a primary renal phenomenon rather than solely a secondary consequence of bone loss; 2) remodelling of the nephron that results in expansion of distal convoluted tubule size but loss of overall tubule density; 3) renal damage and dysfunction when exposed to a Mars roundtrip dose-equivalent of simulated GCR.

The kidney, volume homeostasis and osmoregulation in space: current perspective and knowledge gaps

Although we have sent humans into space for more than 50 years crucial questions regarding kidney physiology, volume regulation and osmoregulation remain unanswered. The complex interactions between the renin-angiotensin-aldosterone system, the sympathetic nervous system, osmoregulatory responses, glomerular function, tubular function, and environmental factors such as sodium and water intake, motion sickness and ambient temperature make it difficult to establish the exact effect of microgravity and the subsequent fluid shifts and muscle mass loss on these parameters. Unfortunately, not all responses to actual microgravity can be reproduced with head-down tilt bed rest studies, which complicates research on Earth. Better understanding of the effects of microgravity on kidney function, volume regulation and osmoregulation are needed with the advent of long-term deep space missions and planetary surface explorations during which orthostatic intolerance complaints or kidney stone formation can be life-threatening for astronauts. Galactic cosmic radiation may be a new threat to kidney function. In this review, we summarise and highlight the current understandings of the effects of microgravity on kidney function, volume regulation and osmoregulation and discuss knowledge gaps that future studies should address.

Physiological adaptations affecting drug pharmacokinetics in space: what do we really know? A critical review of the literature

As human spaceflight progresses with extended mission durations, the demand for effective and safe drugs will necessarily increase. To date, the accepted medications used during missions (for space motion sickness, sleep disturbances, allergies, pain, and sinus congestion) are administered under the assumption that they act as safely and efficaciously as on Earth. However, physiological changes have been documented in human subjects in spaceflight involving fluid shifts, muscle and bone loss, immune system dysregulation, and adjustments in the gastrointestinal tract and metabolism. These alterations may change the pharmacokinetics (PK) and pharmacodynamics of commonly used medications. Frustratingly, the information gained from bed rest studies and from in‐flight observations is incomplete and also demonstrates a high variability in drug PK. Therefore, the objectives of this review are to report (i) the impact of the space environmental stressors on human physiology in relation to PK; (ii) the state‐of‐the‐art on experimental data in space and/or in ground‐based models; (iii) the validation of ground‐based models for PK studies; and (iv) the identification of research gaps.

Integrated RNA-seq Analysis Indicates Asynchrony in Clock Genes between Tissues under Spaceflight

Rodent models have been widely used as analogs for estimating spaceflight-relevant molecular mechanisms in human tissues. NASA GeneLab provides access to numerous spaceflight omics datasets that can potentially generate novel insights and hypotheses about fundamental space biology when analyzed in new and integrated fashions. Here, we performed a pilot study to elucidate space biological mechanisms across tissues by reanalyzing mouse RNA-sequencing spaceflight data archived on NASA GeneLab. Our results showed that clock gene expressions in spaceflight mice were altered compared with those in ground control mice. Furthermore, the results suggested that spaceflight promotes asynchrony of clock gene expressions between peripheral tissues. Abnormal circadian rhythms are associated not only with jet lag and sleep disorders but also with cancer, lifestyle-related diseases, and mental disorders. Overall, our findings highlight the importance of elucidating the causes of circadian rhythm disruptions using the unique approach of space biology research to one day potentially develop countermeasures that benefit humans on Earth and in space.

Remote Controlled Autonomous Microgravity Lab Platforms for Drug Research in Space

Research conducted in microgravity conditions has the potential to yield new therapeutics, as advances can be achieved in the absence of phenomena such as sedimentation, hydrostatic pressure and thermally-induced convection. The outcomes of such studies can significantly contribute to many scientific and technological fields, including drug discovery. This article reviews the existing traditional microgravity platforms as well as emerging ideas for enabling microgravity research focusing on SpacePharma's innovative autonomous remote-controlled microgravity labs that can be launched to space aboard nanosatellites to perform drug research in orbit. The scientific literature is reviewed and examples of life science fields that have benefited from studies in microgravity conditions are given. These include the use of microgravity environment for chemical applications (protein crystallization, drug polymorphism, self-assembly of biomolecules), pharmaceutical studies (microencapsulation, drug delivery systems, behavior and stability of colloidal formulations, antibiotic drug resistance), and biological research, including accelerated models for aging, investigation of bacterial virulence , tissue engineering using organ-on-chips in space, enhanced stem cells proliferation and differentiation.

Human Pathophysiological Adaptations to the Space Environment

Space is an extreme environment for the human body, where during long-term missions microgravity and high radiation levels represent major threats to crew health. Intriguingly, space flight (SF) imposes on the body of highly selected, well-trained, and healthy individuals (astronauts and cosmonauts) pathophysiological adaptive changes akin to an accelerated aging process and to some diseases. Such effects, becoming manifest over a time span of weeks (i.e., cardiovascular deconditioning) to months (i.e., loss of bone density and muscle atrophy) of exposure to weightlessness, can be reduced through proper countermeasures during SF and in due time are mostly reversible after landing. Based on these considerations, it is increasingly accepted that SF might provide a mechanistic insight into certain pathophysiological processes, a concept of interest to pre-nosological medicine. In this article, we will review the main stress factors encountered in space and their impact on the human body and will also discuss the possible lessons learned with space exploration in reference to human health on Earth. In fact, this is a productive, cross-fertilized, endeavor in which studies performed on Earth yield countermeasures for protection of space crew health, and space research is translated into health measures for Earth-bound population.

Coronary artery disease and lunar catecholamine cardiomyopathy

OBJECTIVE

Show how lunar catecholamine cardiomyopathy alone, exemplified by Neil Armstrong's single space walk, prior to exposure to inhalation of fine particulate matter, can trigger " Neil Armstrong Syndrome" or by Irwin with coronary, possibly hypertensive heart disease, and catecholamine cardiomyopathy. With space flight, invariably magnesium ion deficits, catecholamine elevations, vicious cycles. Design Use lunar heart rates while configuring rover to show severe tachycardia component of the syndrome. Use Irwin's stress test-" cyanotic fingernails" to support Apollo 15 Space Syndrome. Use Irwin's autobiography to compensate for often incomplete data. Results Paper shows that both Irwin as well as Armstrong meet criteria of my 2nd. Space Syndrome: severe thirst, severe shortness of breath, severe tachycardia, the latter, corrected by replenishing plasma volume. Conclusions Irwin, with a history of hypertension prior to the Apollo 15 mission and classical angina during Earth reentry, may have had coronary as well as hypertensive heart disease whereas there was no evidence that Armstrong had these conditions prior or during his mission. However both, on return to Earth, had abnormal stress tests.

Changes in cerebral oxygenation during parabolic flight

Assessing changes in brain activity under extreme conditions like weightlessness is a desirable, but difficult undertaking. Results from previous studies report specific changes in brain activity connected to an increase or decrease in gravity forces. Nevertheless, so far it remains unclear (1) whether this is connected to a redistribution of blood volume during micro- or hypergravity and (2) whether this redistribution might account for neurocognitive alterations. This study aimed to display changes in brain oxygenation caused by altered gravity conditions during parabolic flight. It was hypothesized that an increase in gravity would be accompanied by a decrease in brain oxygenation, whereas microgravity would lead to an increase in brain oxygenation. Oxygenized and deoxygenized haemoglobin were measured using two near infrared spectroscopy (NIRS) probes on the left and right prefrontal cortex throughout ten parabolas in nine subjects. Results show a decrease of 1.44 μmol/l in oxygenized haemoglobin with the onset of hypergravity, followed by a considerable increase during microgravity (up to 5.34 μmol/l). In contrast, deoxygenized haemoglobin was not altered during the first but only during the second hypergravity phase and showed only minor changes during microgravity. Changes in oxygenized and deoxygenized haemoglobin indicate an increase in arterial flow to the brain and a decrease in venous outflow during microgravity.

Potential renovascular hypertension, space missions, and the role of magnesium

Space flight (SF) and dust inhalation in habitats cause hypertension whereas in SF (alone) there is no consistent hypertension but reduced diurnal blood pressure (BP) variation instead. Current pharmaceutical subcutaneous delivery systems are inadequate and there is impairment in the absorption, metabolism, excretion, and deterioration of some pharmaceuticals. Data obtained from the National Aeronautics and Space Administration through the Freedom of Information Act shows that Irwin returned from his 12-day Apollo 15 mission in 1971 and was administered a bicycle stress test. With just three minutes of exercise, his BP was >275/125 mm Hg (heart rate of only 130 beats per minute). There was no acute renal insult. Irwin’s apparent spontaneous remission is suggested to be related to the increase of a protective vasodilator, and his atrial natriuretic peptide (ANP) reduced with SF because of reduced plasma volume. With invariable malabsorption and loss of bone/muscle storage sites, there are significant (P < 0.0001) reductions of magnesium (Mg) required for ANP synthesis and release. Reductions of Mg and ANP can trigger pronounced angiotensin (200%), endothelin, and catecholamine elevations (clearly shown in recent years) and vicious cycles between the latter and Mg deficits. There is proteinuria, elevated creatinine, and reduced renal concentrating ability with the potential for progressive inflammatory and oxidative stress-induced renal disease and hypertension with vicious cycles. After SF, animals show myocardial endothelial injuries and increased vascular resistance of extremities in humans. Even without dust, hypertension might eventually develop from renovascular hypertension during very long missions. Without sufficient endothelial protection from pharmaceuticals, a comprehensive gene research program should begin now.

Plasma and Blood Volume in Space

Body fluid regulation is affected by gravity. The primary mechanisms of the etiology of hypovolemia found in simulation studies on earth and after space flight are different. The increased diuresis after increase of central blood volume postulated by Henry Gauer could not be found. Based on recent findings, new hypotheses about fluid volume regulation during space flight have emerged. The reduced blood volume in space is the result of 1) a negative balance of decreased fluid intake and smaller reduction of urine output; 2) fast fluid shifts from the intravascular to interstitial space as the result of lower transmural pressure after reduced compression of all tissue by gravitational forces especially of the thorax cage; and 3) fluid shifts from intravascular to muscle interstitial space because of less muscle tone required to maintain body posture. Additionally, loss of erythrocytes reduces blood volume. The attenuated diuresis during space flight can be explained by increased retention after stress-mediated sympathetic activation during initial phase of space flight, stimulation caused by reduced red cell mass, and activation after fast blood volume contraction. Additionally, the relation between plasma osmolarity and vasopressin release might be disturbed in microgravity.

Emergency medicine in space

Recent events, including the development of space tourism and commercial spaceflight, have increased the need for specialists in space medicine. With increased duration of missions and distance from Earth, medical and surgical events will become inevitable. Ground-based medical support will no longer be adequate when return to Earth is not an option. Pending the inclusion of sub-specialists, clinical skills and medical expertise will be required that go beyond those of current physician-astronauts, yet are well within the scope of Emergency Medicine. Emergency physicians have the necessary broad knowledge base as well as proficiency in basic surgical skills and management of the critically ill and injured. Space medicine shares many attributes with extreme conditions and environments that many emergency physicians already specialize in. This article is an introduction to space medicine, and a review of current issues in the emergent management of medical and surgical disease during spaceflight.

Renal function in space: the link between osteoporosis, hypercalciuria, and aquaporins

This article reviews bone adaptation to microgravity, during manned space missions, in humans undergoing Head Down Tilt (HDT) and in Hind-Limb-Suspended Rats. Under microgravity conditions, bone loss occurs in association with hypercalciuria, which in turn modulates Aquaporin 2 (AQP2) excretion in urine, thus avoiding stone forming in space. This report discloses the need to prevent bone loss in order to prepare for long stays at lunar bases or voyages to Mars.

Physiological, pharmacokinetic, and pharmacodynamic changes in space

Medications have been taken since the first Mercury flight in 1967 and, since then, have been used for several indications such as space motion sickness, sleeplessness, headache, nausea, vomiting, back pain, and congestion. As the duration of space missions get longer, it is even more likely that astronauts will encounter some of the acute illnesses that are frequently seen on Earth. Microgravity environment induces several physiological changes in the human body. These changes include cardiovascular degeneration, bone decalcification, decreased plasma volume, blood flow, lymphocyte and eosinophil levels, altered hormonal and electrolyte levels, muscle atrophy, decreased blood cell mass, increased immunoglobulin A and M levels, and a decrease in the amount of microsomal P-450 and the activity of some of its dependent enzymes. These changes may be expected to have severe implications on the pharmacokinetic and pharmacodynamic properties of drug substances.

Microgravity as a model of ageing

PURPOSE OF REVIEW

Longevity with good health and long-term survival in space are two of the many challenges that scientists face in the twenty-first century. Ageing and life in space are both associated with undesirable effects on normal physiological processes. This review will outline how the endocrine, metabolic, immune and musculoskeletal systems are affected by microgravity and ageing, drawing analogies between the observed changes in an attempt to highlight common mechanisms.

RECENT FINDINGS

Mild hypothyroidism, increased stress hormones (mainly catecholamines), decreased sex steroids, insulin resistance, impaired anabolic response to food intake, anorexia, altered mitochondrial function and systemic inflammatory response are common features of both ageing and microgravity. Both conditions lead to progressive bone and muscle atrophy, compromising mobility and the ability to perform essential daily tasks. In skeletal muscle, both ageing and space flight lead to weakness from whole muscle to single fibre level, accompanied by marked alterations in muscle architecture and in tendon mechanical properties.

SUMMARY

What makes microgravity an interesting and unique tool for gerontologists is that many space-related physiological changes resemble those observed during ageing, but are more or less quickly restored after re-entry, thus allowing the biology of ageing to be investigated both ways, not only during its development but also during recovery.

Validity of microgravity simulation models on earth

Many studies have used water immersion and head-down bed rest as experimental models to simulate responses to microgravity. However, some data collected during space missions are at variance or in contrast with observations collected from experimental models. These discrepancies could reflect incomplete knowledge of the characteristics inherent to each model. During water immersion, the hydrostatic pressure lowers the peripheral vascular capacity and causes increased thoracic blood volume and high vascular perfusion. In turn, these changes lead to high urinary flow, low vasomotor tone, and a high rate of water exchange between interstitium and plasma. In contrast, the increase in thoracic blood volume during a space mission is combined with stimulated orthosympathetic tone and lowered urine flow. During bed rest, body tissues are compressed by pressure from gravity, whereas microgravity causes a negative pressure around the body. The differences in renal function between space and experimental models appear to be explained by the physical forces affecting tissues and hemodynamics as well as by the changes secondary to these forces. These differences may help in selecting experimental models to study possible effects of microgravity.

Water and sodium balance in space

We have previously shown that fluid balances and body fluid regulation in microgravity (microG) differ from those on Earth (Drummer et al, Eur J Physiol 441:R66-R72, 2000). Arriving in microG leads to a redistribution of body fluid-composed of a shift of fluid to the upper part of the body and an exaggerated extravasation very early in-flight. The mechanisms for the increased vascular permeability are not known. Evaporation, oral hydration, and urinary fluid excretion, the major components of water balance, are generally diminished during space flight compared with conditions on Earth. Nevertheless, cumulative water balance and total body water content are stable during flight if hydration, nutritional energy supply, and protection of muscle mass are at an acceptable level. Recent water balance data disclose that the phenomenon of an absolute water loss during space flight, which has often been reported in the past, is not a consequence of the variable microG. The handling of sodium, however, is considerably affected by microG. Sodium-retaining endocrine systems, such as renin-aldosterone and catecholamines, are much more activated during microG than on Earth. Despite a comparable oral sodium supply, urinary sodium excretion is diminished and a considerable amount of sodium is retained-without accumulating in the intravascular space. An enormous storage capacity for sodium in the extravascular space and a mechanism that allows the dissociation between water and sodium handling likely contribute to the fluid balance adaptation in weightlessness.