A research facility for habitation questions to be built at the German Aerospace Center in Cologne: future challenges of Space medicine.

For long term habitation in space and for living on Moon and Mars, many questions still need to be resolved. Such habitation questions include prevention of and rehabilitation from negative effects of weightlessness that are, in many instances, comparable to problems of aging people on Earth as well as of patients during and recovery from long term stays in bed. Therefore the DLR Institute of Aerospace Medicine has designed a concept for a research facility that will make it possible to join space research directly with terrestrial applications. From a strategic point of view, one major emphasis of :envihab is to form a closely interrelated network of scientists and the industry and the public. The project has been in the planning phase for several years. After an international architectural contest, the winning concept was selected in 2007 by a Jury with ESA participation.

Regulation of body fluid and salt homeostasis--from observations in space to new concepts on Earth.

The present manuscript summarizes recent discoveries that were made by studying salt and fluid homeostasis in weightlessness. These data indicate that 1. atrial natriuretic peptide appears not to play an important role in natriuresis in physiology, 2. the distribution of body fluids appears to be tightly coupled with hunger and thirst regulation, 3. intrathoracic pressure may be an important co-regulator of body fluid homeostasis, 4. a so far unknown low-affinity, high capacity osmotically inactive sodium storage mechanism appears to be present in humans that is acting through sodium/hydrogen exchange on glycosaminoglycans and might explain the pathophysiology, e.g., of salt sensitive hypertension. The surprising and unexpected data underline that weightlessness is an excellent tool to investigate the physiology of our human body: If we knew it, we should be able to predict changes that occur when gravity is absent. But, as data from space demonstrate, we do not.

Life science research in space brings health on Earth.

NASA: Leading scientists and physicians review groundbreaking research that is leading the way to better health care for astronauts and new treatments for medical problems on Earth. This research includes the development and testing of a new Ventricular Assist Device for patients with heart failure awaiting heart transplantation; advancements in telemedicine that bring medical care to remote areas on Earth and aid in the diagnosis and treatment of illness during space flight; advanced technologies, such as a miniature mass spectrometer, cardiac ultrasound equipment, bone imaging, non-invasive High-Intensity Focused Ultrasound, non-invasive techniques for blood and tissue chemistry measurements; and advances in the treatment of spinal cord injuries.^ieng

HUMEX, a study on the survivability and adaptation of humans to long-duration exploratory missions, part I: lunar missions.

The European Space Agency has recently initiated a study of the human responses, limits and needs with regard to the stress environments of interplanetary and planetary missions. Emphasis has been laid on human health and performance care as well as advanced life support developments including bioregenerative life support systems and environmental monitoring. The overall study goals were as follows: (i) to define reference scenarios for a European participation in human exploration and to estimate their influence on the life sciences and life support requirements; (ii) for selected mission scenarios, to critically assess the limiting factors for human health, wellbeing, and performance and to recommend relevant countermeasures; (iii) for selected mission scenarios, to critically assess the potential of advanced life support developments and to propose a European strategy including terrestrial applications; (iv) to critically assess the feasibility of existing facilities and technologies on ground and in space as testbeds in preparation for human exploratory missions and to develop a test plan for ground and space campaigns; (v) to develop a roadmap for a future European strategy towards human exploratory missions, including preparatory activities and terrestrial applications and benefits. This paper covers the part of the HUMEX study dealing with lunar missions. A lunar base at the south pole where long-time sunlight and potential water ice deposits could be assumed was selected as the Moon reference scenario. The impact on human health, performance and well being has been investigated from the view point of the effects of microgravity (during space travel), reduced gravity (on the Moon) and abrupt gravity changes (during launch and landing), of the effects of cosmic radiation including solar particle events, of psychological issues as well as general health care. Countermeasures as well as necessary research using ground-based test beds and/or the International Space Station have been defined. Likewise advanced life support systems with a high degree of autonomy and regenerative capacity and synergy effects were considered where bioregenerative life support systems and biodiagnostic systems become essential. Finally, a European strategy leading to a potential European participation in future human exploratory missions has been recommended.

Critical issues in connection with human missions to Mars: protection of and from the Martian environment.

Human missions to Mars are planned to happen within this century. Activities associated therewith will interact with the environment of Mars in two reciprocal ways: (i) the mission needs to be protected from the natural environmental elements that can be harmful to human health, the equipment or to their operations; (ii) the specific natural environment of Mars should be protected so that it retains its value for scientific and other purposes. The following environmental elements need to be considered in order to protect humans and the equipment on the planetary surface: (i) cosmic ionizing radiation, (ii) solar particle events; (iii) solar ultraviolet radiation; (iv) reduced gravity; (v) thin atmosphere; (vi) extremes in temperatures and their fluctuations; and (vii) surface dust. In order to protect the planetary environment, the requirements for planetary protection as adopted by COSPAR for lander missions need to be revised in view of human presence on the planet. Landers carrying equipment for exobiological investigations require special consideration to reduce contamination by terrestrial microorganisms and organic matter to the greatest feasible extent. Records of human activities on the planet's surface should be maintained in sufficient detail that future scientific experimenters can determine whether environmental modifications have resulted from explorations.

Hypoxia modulates rapid effects of aldosterone on oxidative metabolism in human calf muscle.

Non-genomic effects of aldosterone on oxidative metabolism of skeletal muscle have been shown, recently. To further characterize these rapid effects on the increase of phosphocreatine (PCr) in the recovery period after isometric exercise, a randomized cross-over placebo-controlled study was conducted on 9 healthy volunteers. Hypoxia was chosen to test the dependence of the effect on oxygen supply and thus its relation to oxidative vs non-oxidative metabolism. Parameters related to the energy metabolism of calf muscles were measured by 31P magnetic resonance spectroscopy during four repetitive contractions in four different tests (hypoxia [FiO2=0.13] vs normoxia [FiO2=0.21], +/- 0.5 mg aldosterone). The area-under-curves of post-exercise PCr levels after the 4th contraction were significantly increased by aldosterone vs placebo during normoxia (875.5 +/- 5.1 vs 857.2 +/- 8.3%-min; p=0.02). In addition, aldosterone induced an undershoot of inorganic phosphate (Pi) in the recovery after isometric exercise (77.5 +/- 5.4 vs 88.9 +/- 5.1 mmol/l x min; p=0.05). Hypoxia blocked effects of aldosterone on PCr overshoot and Pi undershoot. Concentrations of ATP, ADP, phosphomonoesters, and intracellular pH were not affected by those interventions. In conclusion, these data demonstrate rapid actions of aldosterone on post-excercise PCr and Pi levels in human calf muscle, which are blocked by hypoxia. We hypothesize that aldosterone rapidly interferes with oxidative metabolism probably by direct modulation of ATP-turnover, which is induced by an oxygen-dependent imbalance of the ATP-synthesis and utilization rate.

Critical issues in connection with human planetary missions: protection of and from the environment.

Activities associated with human missions to the Moon or to Mars will interact with the environment in two reciprocal ways: (i) the mission needs to be protected from the natural environmental elements that can be harmful to human health, the equipment or to their operations: (ii) the specific natural environment of the Moon or Mars should be protected so that it retains its value for scientific and other purposes. The following environmental elements need to be considered in order to protect humans and the equipment on the planetary surface: (i) cosmic ionizing radiation, (ii) solar particle events; (iii) solar ultraviolet radiation; (iv) reduced gravity; (v) thin atmosphere; (vi) extremes in temperatures and their fluctuations; (vii) surface dust; (viii) impacts by meteorites and micrometeorites. In order to protect the planetary environment. the requirements for planetary protection as adopted by COSPAR for lander missions need to be revised in view of human presence on the planet. Landers carrying equipment for exobiological investigations require special consideration to reduce contamination by terrestrial microorganisms and organic matter to the Greatest feasible extent. Records of human activities on the planet's surface should be maintained in sufficient detail that future scientific experimenters can determine whether environmental modifications have resulted from explorations. Grant numbers: 14056/99/NL/PA.

Differential expression of functional guanylyl cyclases in melanocytes: absence of nitric-oxide-sensitive isoform in metastatic cells.

Nitric oxide (NO) is a reactive endogenous molecule with multiple functions and its cellular signaling activity is mainly mediated by activation of the soluble isoform of guanylyl cyclase, a heterodimeric (alpha/beta) hemeprotein. The expression of the NO-sensitive soluble isoform of guanylyl cyclase was studied in various cultured melanocytic cells by measuring the accumulation of guanosine 3',5'-cyclic monophosphate in the presence and absence of NO donors. Here we report that 3-morpholino-sydnonimine, a donor of NO redox species, and (Z)-1-[2- (2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate, a direct NO donor, induced a 20-fold increase in intracellular guanosine 3',5'-cyclic monophosphate in nonmetastatic melanoma cells and normal melanocytes in culture that could be related to cellular melanin content in a concentration-dependent manner. The increased intracellular guanosine 3',5'-cyclic monophosphate was due to stimulation of the activity of soluble guanylyl cyclase as such increase was completely abolished by using a specific inhibitor of soluble guanylyl cyclase. The involvement of functional soluble guanylyl cyclase was further confirmed by the presence of alpha1 and beta1 subunits in these cells at both mRNA and protein levels. In contrast, none of the NO donors induced guanosine 3',5'-cyclic monophosphate production in metastatic melanoma cells, which could be attributed to the absence of the beta1 subunit that is essential for catalytic activity of the soluble isoform of guanylyl cyclase. Metastatic melanoma cells produced higher levels of intracellular guanosine 3',5'-cyclic monophosphate in response to natriuretic peptides than other cell types, however, due to upregulation of membrane-bound guanylyl cyclase activities, but they are less pigmented or unpigmented. The present finding suggests that NO signaling in association with melanogenesis is dependent on the soluble isoform of guanylyl cyclase, whereas absence of soluble guanylyl cyclase but the presence of membrane-bound guanylyl cyclase correlates with the metastatic behavior of melanoma cells.

NO-independent regulatory site on soluble guanylate cyclase.

Nitric oxide (NO) is a widespread, potent, biological mediator that has many physiological and pathophysiological roles. Research in the field of NO appears to have followed a straightforward path, and the findings have been progressive: NO and cyclic GMP are involved in vasodilatation; glycerol trinitrate relaxes vascular smooth muscles by bioconversion to NO; mammalian cells synthesize NO; and last, NO mediates vasodilatation by stimulating the soluble guanylate cyclase (sGC), a heterodimeric (alpha/beta) haem protein that converts GTP to cGMP2-4. Here we report the discovery of a regulatory site on sGC. Using photoaffinity labelling, we have identified the cysteine 238 and cysteine 243 region in the alpha1-subunit of sGC as the target for a new type of sGC stimulator. Moreover, we present a pyrazolopyridine, BAY 41-2272, that potently stimulates sGC through this site by a mechanism that is independent of NO. This results in antiplatelet activity, a strong decrease in blood pressure and an increase in survival in a low-NO rat model of hypertension, and as such may offer an approach for treating cardiovascular diseases.

NO-independent regulatory site of direct sGC stimulators like YC-1 and BAY 41-2272.

BACKGROUND: The most important receptor for nitric oxide is the soluble guanylate cyclase (sGC), a heme containing heterodimer. Recently, a pyrazolopyridine derivative BAY 41-2272, structurally related to YC-1, was identified stimulating soluble guanylate cyclase in an NO-independent manner, which results in vasodilatation and antiplatelet activity. The study described here addresses the identification of the NO-independent site on soluble guanylate cyclase. RESULTS: We developed a photoaffinity label (3H-meta-PAL) for the direct and NO-independent soluble guanylate cyclase (sGC) stimulator BAY 41-2272 by introducing an azido-group into the tritium labeled compound. The synthesized photoaffinitylabel directly stimulates the purified sGC and shows in combination with NO a synergistic effect on sGC activity. Irradiation with UV light of 3H-meta-PAL together with the highly purified sGC leads to a covalent binding to the alpha1-subunit of the enzyme. This binding is blocked by unlabeled meta-PAL, YC-1 and BAY 41-2272. For further identification of the NO-independent regulatory site the 3H-meta-PAL labeled sGC was fragmented by CNBr digest. The 3H-meta-PAL binds to a CNBr fragment, consisting of the amino acids 236-290 of the alpha1-subunit. Determination of radioactivity of the single PTH-cycles from the sequencing of this CNBr fragment detected the cysteines 238 and 243 as binding residues of the 3H-meta-PAL. CONCLUSIONS: Our data demonstrate that the region surrounding the cysteines 238 and 243 in the alpha1-subunit of the sGC could play an important role in regulation of sGC activity and could be the target of this new type of sGC stimulators.

The space mission MIR'97: operational aspects.

BACKGROUND: A German astronaut visited the MIR space station between 10 February and 2 March 1997. Together with his Russian colleagues, he conducted a series of scientific investigations before, during and after his stay aboard the MIR station. Research performed during this flight was part of a global space life sciences programme and focused on metabolic homeostasis, fluid balance, calcium homeostasis and cardiovascular regulatory mechanisms. The main goal of the scientific experiments was to use this mission as a milestone to establish international networks of scientific collaboration using space research as a tool for focused research in respective fields. Thus, in most cases the results obtained from the astronaut complemented a series of results obtained on ground and from other flights. In other cases, they extended previous results and opened new fields for future research. PARTICIPANTS: Human space flight with astronauts serving as operators and at the same time as test subjects is very complex. Many people, including mission control, a science management team, medical operations, ethics committees and a medical board, participated to harmonize the different requirements, thus making a maximal scientific outcome possible. CONCLUSION: In summary, this space mission may be seen as a model for focused long-term multidisciplinary international research, and demonstrates that space medicine is no longer adventure but science.

Water and sodium balances and their relation to body mass changes in microgravity.

BACKGROUND: Since the very beginning of space physiology research, the deficit in body mass that is often observed after landing has always been interpreted as an indication of the absolute fluid loss early during space missions. However, in contrast to central hypervolemic conditions on Earth, the acute shift of blood volume from the legs to the upper part of the body in astronauts entering microgravity (microG) has neither stimulated diuresis and natriuresis nor resulted in negative water-and sodium-balances. DESIGN: We therefore examined the kinetics of body mass changes in astronauts (n = 3) during their several weeks aboard the space station MIR. A continuous diet monitoring was performed during the first mission (EuroMIR94, 30 days). The second mission (MIR97, 19 days) comprised a 15-day metabolic ward period (including predefined constant energy and sodium intake). Water and sodium balances were calculated and the kinetic of changes in basal concentrations of fluid-balance-related hormones during flight were determined. CONCLUSION: The data suggest firstly that loss of body mass during space flight is rather a consequence of hypocaloric nutrition. Secondly, microG provokes a sodium retaining hormonal status and may lead to sodium storage without an accompanying fluid retention.

High dietary sodium chloride consumption may not induce body fluid retention in humans.

A commonly accepted hypothesis is that a chronically high-sodium diet expands extracellular volume and finally reaches a steady state where sodium intake and output are balanced whereas extracellular volume is expanded. However, in a recent study where the main purpose was to investigate the role of natriuretic peptides under day-to-day sodium intake conditions (Heer M, Drummer C, Baisch F, and Gerzer R. Pflügers Arch 425: 390-394, 1993), our laboratory observed increases in plasma volume without any rise in extracellular volume. To scrutinize these results that were observed as a side effect, we performed a controlled, randomized study including 32 healthy male test subjects in a metabolic ward. The NaCl intake ranged from a low level of 50 meq NaCl/day to 200, 400, and 550 meq/day, respectively. Plasma volume dose dependently increased (P < 0.01), being elevated by 315 +/- 37 ml in the 550-meq-NaCl-intake group. However, in contrast to the increased plasma volume, comparable to study I, total body water did not increase. In parallel, body mass also did not increase. Mean corpuscular volume of erythrocytes, as an index for intracellular volume, was also unchanged. We conclude from the results of these two independently conducted studies that under the chosen study conditions, in contrast to present opinions, high sodium intake does not induce total body water storage but induces a relative fluid shift from the interstitial into the intravascular space.

Effect of loperamide on mucosal guanylyl cyclase activity in rat jejunum following Escherichia coli heat-stable toxin-induced fluid accumulation.

Loperamide has antidiarrhoeal activities against secretagogues with different mechanisms of action. Besides its opioid-like effect on intestinal motility and secretion it might exhibit additional antisecretory properties which may not be completely elucidated yet. Direct effects of loperamide on mucosal guanylyl cyclase have never been observed. We therefore investigated the effect of loperamide on intestinal fluid transport altered by heat-stable Escherichia coli enterotoxin which acts by stimulating mucosal guanylyl cyclase. Net fluid movement was determined during a 1 hr incubation period in ligated jejunal loops of anaesthetised female Wistar rats. Transport rates of net fluid movement were calculated from the loop contents measured gravimetrically at the beginning and the end of the experiments. Addition of heat-stable Escherichia coli enterotoxin to the luminal solution resulted in a net secretion of water which was significantly reversed into net absorption by loperamide. The specific activity of the particulate guanylyl cyclase was determined in mucosal scrapings of the jejunum without and with the addition of heat-stable Escherichia coli enterotoxin and/or loperamide. Additions of loperamide of up to 10 micromol/l did not change guanylyl cyclase activity. We conclude that the effect of loperamide counteracting heat-stable Escherichia coli enterotoxin induced changes of intestinal fluid transport does not involve a direct effect on guanylyl cyclase.

The vasodilator-stimulated phosphoprotein (VASP): target of YC-1 and nitric oxide effects in human and rat platelets.

The effects of the different types of soluble guanylate cyclase (sGC) stimulators on the phosphorylation status of vasodilator-stimulated phosphoprotein (VASP) in both human and rat platelets were studied under in vitro and in vivo conditions. sGC-dependent VASP phosphorylation (at Ser(239) and Ser(157)) both by the new direct sGC stimulator YC-1 and by NO donors was examined by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS/PAGE) with different antibodies. One antibody, which recognizes VASP independent of its phosphorylation state, was used to detect the mobility shift of VASP caused by Ser(157) phosphorylation. The other antibody was specifically directed against VASP phosphorylated at Ser(239), the cGMP-dependent protein kinase (PKG) preferred phosphorylation site of VASP. In vitro YC-1 increased both VASP phosphorylation and cyclic guanosine monophosphate (cGMP) levels as did the NO donors 2-(N,N-diethylamino)-diazenolate-2-oxide (DEA/NO) and sodium nitroprusside (SNP). The combination of both types induced a synergistic effect in both VASP phosphorylation and cGMP increase. In rat platelets, similar effects could be shown in vitro. In vivo we observed a significant increase in cGMP and a distinct effect on VASP phosphorylation in rat platelets 1 h after oral administration of YC-1. These biochemical alterations are supported by a significant prolongation in rat-tail bleeding time. Direct stimulators of sGC like YC-1 are on the one hand direct potent stimulators of the cGMP/PKG/VASP pathway in platelets and on the other hand synergize with NO, the physiologic stimulator of sGC. Therefore YC-1-like substances are interesting tools for the development of new cardiovascular drugs with vasodilatory and antithrombotic properties.

Body fluid regulation in micro-gravity differs from that on Earth: an overview.

Similar to the response to central hypervolemic conditions on Earth, the shift of blood volume from the legs to the upper part of the body in astronauts entering micro-gravity should, in accordance with the Henry-Gauer mechanism, mediate diuresis and natriuresis. However, fluid balance and kidney function experiments during various space missions resulted in the surprising observation that the responses qualitatively differ from those observed during simulations of hypervolemia on Earth. There is some evidence that the attenuated responses of the kidney while entering weightlessness, and also later during space flight, may be caused by augmented fluid distribution to extravascular compartments compared to conditions on Earth. A functional decoupling of the kidney may also contribute to the observation that renal responses during exposure to micro-gravity are consistently weaker than those during simulation experiments before space flight. Deficits in body mass after landing have always been interpreted as an indication of absolute fluid loss early during space missions. However, recent data suggest that body mass changes during space flight are rather the consequences of hypocaloric nutrition and can be overcome by improved nutrition schemes. Finally, sodium-retaining humoral systems are activated during space flight and may contribute to a new steady-state of metabolic balances with a pronounced increase in body sodium compared to respective conditions on Earth. A revision of the classical "micro-gravity fluid shift" scheme is required.

Medicine and mobility: challenge for the next century.

Advances in air traffic are the key factors that have enabled society during the present century to change from local orientation to globalization. At the end of the 20th century, millions can individually travel across continents into different cultures, climates, environments, and reach their destination within hours or, if it is real remote, in a few days. Advances in telecommunication and informatics technologies have furthermore allowed us to be in contact in real time wherever on, below or above earth s surface humans are. These progresses influence all aspects of human life. They also bring numerous chances, challenges and problems for medicine. Therefore, the different aspects of increased mobility should be viewed in a concerted fashion, that integrates all aspects of medicine that are influenced by the increased mobility of society. This new field of medicine, "Medicine and Mobility", will have a central role to fulfill the main task of medicine during the next century, namely to make individualized medicine possible, i.e. to bring individualized medical expertise to the patient, wherever he/she may be. This will end the present expertise-oriented medicine of the 20th Century, in which the patient has to come to the special expertise. This change of medical practice will have huge impacts not only on medicine, but on economies, cultures and be one of the driving forces for our main task of the next century, to peacefully unite our whole globe.

Generation and characterization of a stable soluble guanylate cyclase-overexpressing CHO cell line.

A stably transfected soluble guanylate cyclase (sGC, alpha1 and beta1 subunits of the rat lung enzyme)-overexpressing CHO cell line was generated for the characterization of different types of activators of the soluble guanylate cyclase. Polyclonal antibodies directed against both subunits of the rat enzyme were used to detect both subunits in the cytosol of the transfected CHO cells. We studied the effects of different nitric oxide (NO) donors like SNP and DEA/NO and, in particular, the direct, NO-independent stimulator of the soluble guanylate cyclase 3-(5'-hydroxymethyl-2'furyl)-1-benzyl indazole (YC-1), on intracellular guanosine 3',5'-cyclic monophosphate (cGMP) production. DEA/NO (0.01-3 microM), SNP (1-10 microM), and YC-1 (1-10 microM) induced a concentration-dependent intracellular cGMP increase with maximal effects of 16-fold (3 microM DEA/NO), 8-fold (10 microM SNP), and 6-fold (10 microM YC-1) stimulation compared to controls, respectively. In addition, a synergistic effect of the combination of the NO donor and YC-1 could be observed with a maximal stimulation of 64-fold by SNP (10 microM) and YC-1 (10 microM). 1H-(1,2,4)-Oxadiazolo-(4,3-a)-6-bromo-quinoxazin-1-one (ODQ, 10 microM), a potent and selective inhibitor of sGC, inhibited both the single effects of NO donors [DEA/NO (3 microM), 77%; SNP (3 microM), 83%] and YC-1 [YC-1 (3 microM), 82%], but moreover the synergistic effects between NO donors and YC-1 [DEA/NO (3 microM) + YC-1 (3 microM), 81%; SNP (3 microM) + YC-1 (3 microM),89%] on intracellular cGMP production. In summary,we have generated a simple, sensitive, and useful bioassay method to characterize all types of sGC activators on the cellular level without the need of primary cell culture, several transfections, or purifying enzyme from biological materials.