Optic disc edema and chorioretinal folds develop during strict 6° head-down tilt bed rest with or without artificial gravity

Spaceflight associated neuro-ocular syndrome (SANS) is hypothesized to develop as a consequence of the chronic headward fluid shift that occurs in sustained weightlessness. We exposed healthy subjects (n = 24) to strict 6° head-down tilt bed rest (HDTBR), an analog of weightlessness that generates a sustained headward fluid shift, and we monitored for ocular changes similar to findings that develop in SANS. Two-thirds of the subjects received a daily 30-min exposure to artificial gravity (AG, 1 g at center of mass, ~0.3 g at eye level) during HDTBR by either continuous (cAG, n = 8) or intermittent (iAG, n = 8) short-arm centrifugation to investigate whether this intervention would attenuate headward fluid shift-induced ocular changes. Optical coherence tomography images were acquired to quantify changes in peripapillary total retinal thickness (TRT), retinal nerve fiber layer thickness, and choroidal thickness, and to detect chorioretinal folds. Intraocular pressure (IOP), optical biometry, and standard automated perimetry data were collected. TRT increased by 35.9 µm (95% CI, 19.9-51.9 µm, p < 0.0001), 36.5 µm (95% CI, 4.7-68.2 µm, p = 0.01), and 27.6 µm (95% CI, 8.8-46.3 µm, p = 0.0005) at HDTBR day 58 in the control, cAG, and iAG groups, respectively. Chorioretinal folds developed in six subjects across the groups, despite small increases in IOP. Visual function outcomes did not change. These findings validate strict HDTBR without elevated ambient CO2 as a model for investigating SANS and suggest that a fluid shift reversal of longer duration and/or greater magnitude at the eye may be required to prevent or mitigate SANS.

May the Force Be with You (Or Not): The Immune System under Microgravity

All terrestrial organisms have evolved and adapted to thrive under Earth's gravitational force. Due to the increase of crewed space flights in recent years, it is vital to understand how the lack of gravitational forces affects organisms. It is known that astronauts who have been exposed to microgravity suffer from an array of pathological conditions including an impaired immune system, which is one of the most negatively affected by microgravity. However, at the cellular level a gap in knowledge exists, limiting our ability to understand immune impairment in space. This review highlights the most significant work done over the past 10 years detailing the effects of microgravity on cellular aspects of the immune system.

Dragon's Blood Regulates Rac1-WAVE2-Arp2/3 Signaling Pathway to Protect Rat Intestinal Epithelial Barrier Dysfunction Induced by Simulated Microgravity

Dragon’s Blood is a red resin from Dracaena cochinchinensis (Lour.) S.C. Chen (Yunnan, China). As a traditional Chinese medicinal herb, it has shown protective effects on intestinal disorders. Microgravity could alter intestinal homeostasis. However, the potential herbal drugs for preventing intestine epithelial barrier (IEB) dysfunction under microgravity are not available. This study aimed to investigate the effects of Dragon’s Blood (DB) on microgravity-induced IEB injury and explore its underlying mechanism. A rat tail-suspension model was used to simulate microgravity (SMG). Histomorphology, ultrastructure, permeability, and expression of junction proteins in jejunum, ileum, and colon of SMG rats were determined. Proteomic analysis was used to identify differentially expressed proteins (DEPs) in rat ileum mucosa altered by DB. The potential mechanism of DB to protect IEB dysfunction was validated by western blotting. The effects of several components in DB were evaluated in SMG-treated Caco-2 cells. DB protected against IEB disruption by repairing microvilli and crypts, inhibiting inflammatory factors, lowering the permeability and upregulating the expression of tight and adherens junction proteins in the ileum of SMG rats. Proteomic analysis showed that DB regulated 1080 DEPs in rat ileum mucosa. DEPs were significantly annotated in cell–cell adhesion, focal adhesion, and cytoskeleton regulation. DB increased the expression of Rac1-WAVE2-Arp2/3 pathway proteins and F-actin to G-actin ratio, which promoted the formation of focal adhesions. Loureirin C in DB showed a protective effect on epithelial barrier injury in SMG-treated Caco-2 cells. DB could protect against IEB dysfunction induced by SMG, and its mechanism is associated with the formation of focal adhesions mediated by the Rac1-WAVE2-Arp2/3 pathway, which benefits intestinal epithelial cell migration and barrier repair.

Simultaneous exposure to chronic irradiation and simulated microgravity differentially alters immune cell phenotype in mouse thymus and spleen

Deep-space missions may alter immune cell phenotype in the primary (e.g., thymus) and secondary (e.g., spleen) lymphoid organs contributing to the progression of a variety of diseases. In deep space missions, astronauts will be exposed to chronic low doses of HZE radiation while being in microgravity. Ground-based models of long-term uninterrupted exposures to HZE radiation are not yet available. To obtain insight in the effects of concurrent exposure to microgravity and chronic irradiation (CIR), mice received a cumulative dose of chronic 0.5 Gy gamma rays over one month ± simulated microgravity (SMG). To obtain insight in a dose rate effect, additional mice were exposed to single acute irradiation (AIR) at 0.5 Gy gamma rays. We measured proportions of immune cells relative to total number of live cells in the thymus and spleen, stress level markers in plasma, and change in body weight, food consumption, and water intake. CIR affected thymic CD3+/CD335+ natural killer T (NK-T) cells, CD25+ regulatory T (Treg) cells, CD27+/CD335- natural killer (NK1) cells and CD11c+/CD11b- dendritic cells (DCs) differently in mice subjected to SMG than in mice with normal loading. No such effects of CIR on SMG as compared to normal loading were observed in cell types from the spleen. Differences between CIR and AIR groups (both under normal loading) were found in thymic Treg and DCs. Food consumption, water intake, and body weight were less after coexposure than singular or no exposure. Compared to sham, all treatment groups exhibited elevated plasma levels of the stress marker catecholamines. These data suggest that microgravity and chronic irradiation may interact with each other to alter immune cell phenotypes in an organ-specific manner and appropriate strategies are required to reduce the health risk of crewmembers.

Simulated microgravity accelerates aging in Saccharomyces cerevisiae

The human body experiences physiological changes under microgravity environment that phenocopy aging on Earth. These changes include early onset osteoporosis, skeletal muscle atrophy, cardiac dysfunction, and immunosenescence, and such adaptations to the space environment may pose some risk to crewed missions to Mars. To investigate the effect of microgravity on aging, many model organisms have been used such as the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and mice. Herein we report that the budding yeast Saccharomyces cerevisiae show decreased replicative lifespan (RLS) under simulated microgravity in a clinostat. The reduction of yeast lifespan is not a result of decreased tolerance to heat shock or oxidative stress and could be overcome either by deletion of FOB1 or calorie restriction, two known interventions that extend yeast RLS. Deletion of the sirtuin gene SIR2 worsens the simulated microgravity effect on RLS, and together with the fob1Δ mutant phenotype, it suggests that simulated microgravity augments the formation of extrachromosomal rDNA circles, which accumulate in yeast during aging. We also show that the chronological lifespan in minimal medium was not changed when cells were grown in the clinostat. Our data suggest that the reduction in longevity due to simulated microgravity is conserved in yeast, worms, and flies, and these findings may have potential implications for future crewed missions in space, as well as the use of microgravity as a model for human aging.

Short-term effects of simulated microgravity on morphology and gene expression in human breast cancer cells

INTRODUCTION

Microgravity has been shown to impose various effects on breast cancer cells. We exposed human breast cancer cells to simulated microgravity and studied morphology and alterations in gene expression.

MATERIALS AND METHODS

Human breast cancer cells were exposed to simulated microgravity in a random positioning machine (RPM) for 24 h. Morphology was observed under light microscopy, and gene alteration was studied by qPCR.

RESULTS

After 24 h, formation of three-dimensional structures (spheroids) occurred. BRCA1 expression was significantly increased (1.9×, p < 0.05) in the adherent cells under simulated microgravity compared to the control. Expression of KRAS was significantly decreased (0.6×, p < 0.05) in the adherent cells compared to the control. VCAM1 was significantly upregulated (6.6×, 2.0×, p < 0.05 each) in the adherent cells under simulated microgravity and in the spheroids. VIM expression was significantly downregulated (0.45×, 0.44×, p < 0.05 each) in the adherent cells under simulated microgravity and in the spheroids. There was no significant alteration in the expression of MAPK1, MMP13, PTEN, and TP53.

CONCLUSIONS

Simulated microgravity induces spheroid formation in human breast cancer cells within 24 h and alters gene expression toward modified adhesion properties, enhanced cell repair, and phenotype preservation. Further insights into the underlying mechanisms could open up the way toward new therapies.

Mitochondrial Unfolded Protein Response to Microgravity Stress in Nematode Caenorhabditis elegans

Caenorhabditis elegans is useful for assessing biological effects of spaceflight and simulated microgravity. The molecular response of organisms to simulated microgravity is still largely unclear. Mitochondrial unfolded protein response (mt UPR) mediates a protective response against toxicity from environmental exposure in nematodes. Using HSP-6 and HSP-60 as markers of mt UPR, we observed a significant activation of mt UPR in simulated microgravity exposed nematodes. The increase in HSP-6 and HSP-60 expression mediated a protective response against toxicity of simulated microgravity. In simulated microgravity treated nematodes, mitochondria-localized ATP-binding cassette protein HAF-1 and homeodomain-containing transcriptional factor DVE-1 regulated the mt UPR activation. In the intestine, a signaling cascade of HAF-1/DVE-1-HSP-6/60 was required for control of toxicity of simulated microgravity. Therefore, our data suggested the important role of mt UPR activation against the toxicity of simulated microgravity in organisms.

Increased Chromosome Aberrations in Cells Exposed Simultaneously to Simulated Microgravity and Radiation

Space radiation and microgravity (μG) are two major environmental stressors for humans in space travel. One of the fundamental questions in space biology research is whether the combined effects of μG and exposure to cosmic radiation are interactive. While studies addressing this question have been carried out for half a century in space or using simulated μG on the ground, the reported results are ambiguous. For the assessment and management of human health risks in future Moon and Mars missions, it is necessary to obtain more basic data on the molecular and cellular responses to the combined effects of radiation and µG. Recently we incorporated a μG⁻irradiation system consisting of a 3D clinostat synchronized to a carbon-ion or X-ray irradiation system. Our new experimental setup allows us to avoid stopping clinostat rotation during irradiation, which was required in all other previous experiments. Using this system, human fibroblasts were exposed to X-rays or carbon ions under the simulated μG condition, and chromosomes were collected with the premature chromosome condensation method in the first mitosis. Chromosome aberrations (CA) were quantified by the 3-color fluorescent in situ hybridization (FISH) method. Cells exposed to irradiation under the simulated μG condition showed a higher frequency of both simple and complex types of CA compared to cells irradiated under the static condition by either X-rays or carbon ions.

Bone Loss Induced by Simulated Microgravity, Ionizing Radiation and/or Ultradian Rhythms in the Hindlimbs of Rats

OBJECTIVE

To better understand the pathological causes of bone loss in a space environment, including microgravity, ionizing radiation, and ultradian rhythms.

METHODS

Sprague Dawley (SD) rats were randomly divided into a baseline group, a control group, a hindlimb suspension group, a radiation group, a ultradian rhythms group and a combined-three-factor group. After four weeks of hindlimb suspension followed by X-ray exposure and/or ultradian rhythms, biomechanical properties, bone mineral density, histological analysis, microstructure parameters, and bone turnover markers were detected to evaluate bone loss in hindlimbs of rats.

RESULTS

Simulated microgravity or combined-three factors treatment led to a significant decrease in the biomechanical properties of bones, reduction in bone mineral density, and deterioration of trabecular parameters. Ionizing radiation exposure also showed adverse impact while ultradian rhythms had no significant effect on these outcomes. Decrease in the concentration of the turnover markers bone alkaline phosphatase (bALP), osteocalcin (OCN), and tartrate-resistant acid phosphatase-5b (TRAP-5b) in serum was in line with the changes in trabecular parameters.

CONCLUSION

Simulated microgravity is the main contributor of bone loss. Radiation also results in deleterious effects but ultradian rhythms has no significant effect. Combined-three factors treatment do not exacerbate bone loss when compared to simulated microgravity treatment alone.

Brain plasticity and sensorimotor deterioration as a function of 70 days head down tilt bed rest

Background

Adverse effects of spaceflight on sensorimotor function have been linked to altered somatosensory and vestibular inputs in the microgravity environment. Whether these spaceflight sequelae have a central nervous system component is unknown. However, experimental studies have shown spaceflight-induced brain structural changes in rodents’ sensorimotor brain regions. Understanding the neural correlates of spaceflight-related motor performance changes is important to ultimately develop tailored countermeasures that ensure mission success and astronauts’ health.

Method

Head down-tilt bed rest (HDBR) can serve as a microgravity analog because it mimics body unloading and headward fluid shifts of microgravity. We conducted a 70-day 6° HDBR study with 18 right-handed males to investigate how microgravity affects focal gray matter (GM) brain volume. MRI data were collected at 7 time points before, during and post-HDBR. Standing balance and functional mobility were measured pre and post-HDBR. The same metrics were obtained at 4 time points over ~90 days from 12 control subjects, serving as reference data.

Results

HDBR resulted in widespread increases GM in posterior parietal regions and decreases in frontal areas; recovery was not yet complete by 12 days post-HDBR. Additionally, HDBR led to balance and locomotor performance declines. Increases in a cluster comprising the precuneus, precentral and postcentral gyrus GM correlated with less deterioration or even improvement in standing balance. This association did not survive Bonferroni correction and should therefore be interpreted with caution. No brain or behavior changes were observed in control subjects.

Conclusions

Our results parallel the sensorimotor deficits that astronauts experience post-flight. The widespread GM changes could reflect fluid redistribution. Additionally, the association between focal GM increase and balance changes suggests that HDBR also may result in neuroplastic adaptation. Future studies are warranted to determine causality and underlying mechanisms.

Effect of Simulated Microgravity on Human Brain Gray Matter and White Matter--Evidence from MRI

BACKGROUND

There is limited and inconclusive evidence that space environment, especially microgravity condition, may affect microstructure of human brain. This experiment hypothesized that there would be modifications in gray matter (GM) and white matter (WM) of the brain due to microgravity.

METHOD

Eighteen male volunteers were recruited and fourteen volunteers underwent -6° head-down bed rest (HDBR) for 30 days simulated microgravity. High-resolution brain anatomical imaging data and diffusion tensor imaging images were collected on a 3T MR system before and after HDBR. We applied voxel-based morphometry and tract-based spatial statistics analysis to investigate the structural changes in GM and WM of brain.

RESULTS

We observed significant decreases of GM volume in the bilateral frontal lobes, temporal poles, parahippocampal gyrus, insula and right hippocampus, and increases of GM volume in the vermis, bilateral paracentral lobule, right precuneus gyrus, left precentral gyrus and left postcentral gyrus after HDBR. Fractional anisotropy (FA) changes were also observed in multiple WM tracts.

CONCLUSION

These regions showing GM changes are closely associated with the functional domains of performance, locomotion, learning, memory and coordination. Regional WM alterations may be related to brain function decline and adaption. Our findings provide the neuroanatomical evidence of brain dysfunction or plasticity in microgravity condition and a deeper insight into the cerebral mechanisms in microgravity condition.

The combined effects of X-ray radiation and hindlimb suspension on bone loss

Outer space is a complex environment with various phenomena that negatively affect bone metabolism, including microgravity and highly energized ionizing radiation. In the present study, we used four groups of male Wistar rats treated with or without four-week hindlimb suspension after 4 Gy of X-rays to test whether there is a combined effect for hindlimb suspension and X-ray radiation. We tested trabecular parameters and some cytokines of the bone as leading indicators of bone metabolism. The results showed that hindlimb suspension and X-ray radiation could cause a significant increase in bone loss. Hindlimb suspension caused a 56.6% bone loss (P = 0.036), while X-ray radiation caused a 30.7% (P = 0.041) bone loss when compared with the control group. The combined factors of hindlimb suspension and X-rays exerted a combined effect on bone mass, with a reduction of 64.8% (P = 0.003).

Study protocol, implementation, and verification of a short versatile upright exercise regime during 5 days of bed rest

OBJECTIVES

This work provides a reference for future papers originating from this study by providing basic results on body mass, urine volume, and hemodynamic changes to 5 days of bed rest (BR) and by describing acute cardio-respiratory/mechanographic responses to a short versatile upright exercise battery.

METHODS

Ten male subjects (mean ± SEM age: 29.4 ± 1.5 years; height: 178.8 ± 1.5 cm; body mass: 77.7 ± 1.5 kg) performed, in random order, 5 days of 6° head-down tilt (HDT) BR with no exercise (CON), or BR with daily 25 minutes of quiet upright standing (STA) or upright locomotion replacement training (LRT).

RESULTS

Plasma volume, exercise capacity and orthostatic tolerance decreased similarly between interventions following 5 days of BR. Upright heart rate during LRT and STA increased throughout BR; from 137 ± 4 bpm to 146 ± 4 bpm for LRT (P<0.01); and from 90 ± 3 bpm to 102 ± 6 bpm (P<0.001) for STA.

CONCLUSION

the overall similarity in the response to BR, and increase in upright heart rate during the LRT sessions suggest early and advancing cardiovascular deconditioning during 5 days of BR bed rest, which was not prevented by the versatile exercise regime.

Bone metabolism and nutritional status during 30-day head-down-tilt bed rest

Bed rest studies provide an important tool for modeling physiological changes that occur during spaceflight. Markers of bone metabolism and nutritional status were evaluated in 12 subjects (8 men, 4 women; ages 25-49 yr) who participated in a 30-day -6° head-down-tilt diet-controlled bed rest study. Blood and urine samples were collected twice before, once a week during, and twice after bed rest. Data were analyzed using a mixed-effects linear regression with a priori contrasts comparing all days to the second week of the pre-bed rest acclimation period. During bed rest, all urinary markers of bone resorption increased ~20% (P < 0.001), and serum parathyroid hormone decreased ~25% (P < 0.001). Unlike longer (>60 days) bed rest studies, neither markers of oxidative damage nor iron status indexes changed over the 30 days of bed rest. Urinary oxalate excretion decreased ~20% during bed rest (P < 0.001) and correlated inversely with urinary calcium (R = -0.18, P < 0.02). These data provide a broad overview of the biochemistry associated with short-duration bed rest studies and provide an impetus for using shorter studies to save time and costs wherever possible. For some effects related to bone biochemistry, short-duration bed rest will fulfill the scientific requirements to simulate spaceflight, but other effects (antioxidants/oxidative damage, iron status) do not manifest until subjects are in bed longer, in which case longer studies or other analogs may be needed. Regardless, maximizing research funding and opportunities will be critical to enable the next steps in space exploration.

Cytochemical and electron probe X-ray microanalysis studies on the distribution change of intracellular calcium in columella cells of soybean roots under simulated microgravity

The columella cells of soybean roots grown under gravity and simulated microgravity induced by a clinostat were examined using potassium pyroantimonate (PA) and quantitative X-ray microanalysis of cryosections to determine the role of Ca in the regulation of the gravitropic response. Amyloplasts in the columella cells were localized exclusively at the bottom under gravity, but diffusely distributed in the cytoplasmic matrix under simulated microgravity, thus supporting the statolith theory. In the columella cells, PA precipitates containing Ca were diffusely distributed in the cytoplasmic matrix under gravity. Under simulated microgravity, however, they decreased in number and size in the cytoplasmic matrix, whereas increased only in number in the vacuole, indicating that Ca moved from the cytoplasmic matrix into the vacuole. The vacuole of columella cells contained mostly electron-dense granular structures localized along the inner surface of tonoplasts, which closely resembled the tannin vacuole reported in Mimosa pulvinar motor cells. Under simulated microgravity, their configuration changed dramatically from a granular shape to a flat plate. The quantitative X-ray microanalysis of cryosections showed that the vacuolar electron-dense structures contained a large amount of Ca. Under simulated microgravity, the concentration of Ca increased conspicuously in these vacuolar electron-dense structures, concomitantly with a marked decrease of K in the vacuoles and an increase of K in the cell walls. These results suggest that the release of Ca(2+) from, and uptake by, the vacuolar electron-dense structures is closely related to the signal transmission in the gravitropic response and that Ca movement occurs opposite to that of K.

[Expression of cytoskeleton genes in culture of human mesenchymal stromal cells in different periods of simulating the effects of microgravity]

Simulation of microgravity for cultivated multipotent mesenchymal stromal cells (MSCs) from human marrow changes transiently expression of genes associated with actin cytoskeleton; the effect fades away partially in 120 hrs. following microgravity and completely after 24-hr cell readaptation to static conditions. These changes in expression of some cytoskeleton genes seem to predetermine their reaction to simulated microgravity, and therefore inhibition of MSCs differentiation potential.

[Metabolic effects of physical countermeasures against deficient weight-bearing in an experiment with 7-day immersion]

Metabolic effects of physical countermeasures against deficient weight-loading were studied in three groups of 21-30 y.o. volunteers for 7-d dry immersion. Blood serum was investigated for 38 biochemical parameters that characterize myocardium, skeletal musculature, hepatobiliary system, kidney, pancreas, GI tract, prostate, and protein-nucleic, carbohydrate, electrolyte and mineral metabolism. Seven-day DI w/o countermeasures (n = 5) increased concentration of conjugated bilirubin, suppressed activities of muscular (creatine phosphokinase MM) and myocardial enzymes (CPK MB, OBDH), and caused an upward trend in cholesterol, its atherogenic LDP fraction and triglycerides. Mechanic sole stimulation (n = 6) intensified, within the physiological norm, erythrocyte hematolysis raising total bilirubin and potassium. Despite the stimulation, activity of muscle and myocardial enzymes made a decrease. Blood creatinine decreased to a less extent than in the immersed group w/o stimulation, however, lipid parameters did not rise. High-frequency stimulation of the lower leg and hip muscles in the course of immersion (n = 5) was noted to heighten the activity of muscle enzymes and potassium level in blood beyond the physiological norm. Change in creatinine did not reach a statistical significance and lipid metabolism parameters were not different from baseline values. Application of these physical methods of counteracting deficiency of weight bearing did not interfere with redistribution of body liquids due to immersion. Values of the parameters under study were mostly within the normal limits throughout the experimental exposure suggesting absence of pathological developments during DI or in consequence of physical stimulation. Therefore, the reactions were obviously of normal adaptive character.

[Congenital human immunity during 5-day dry immersion]

The system of congenital immunity was studied in 12 essentially healthy males 18 to 26 years of age subjected to 5-day dry immersion without use of countermeasures. Peripheral blood was analyzed for monocytes, granulocytes and lymphocytes expressing the TLR2+, TLR4+, TLR6+, CD11b+, CD14+, CD16+, CD18+, CD24+, CD36+, CD54+, CD56+ and CD206+ receptors. Expression of early activation marker CD69 on lymphocytes-natural killers was studied in unstimulated and interleukin-2 activated mononuclear cell cultures. The negative shifts in the congenital immunity system in some volunteers at the end of immersion and during recovery can be considered as warnings about depletion of the system reserve and increase of the risk of infectious diseases such as caused by normal microflora which typically does not provoke pathological reactions of the host.

Comparative study on measured variables and sensitivity to bone microstructural changes induced by weightlessness between in vivo and ex vivo micro-CT scans

Depending on the experimental design, micro-CT can be used to examine bones either in vivo or ex vivo (excised fresh or formalin-fixed). In this study we investigated if differences exist in the variables measured by micro-CT between in vivo and ex vivo scans and which kind of scan is more sensitive to the changes of bone microstructure induced by simulated weightlessness. Rat tail suspension was used to simulate the weightless condition. The same bone from either normal or tail-suspended rats was scanned by micro-CT both in vivo and ex vivo (fresh and fixed by formalin). Then, bone mineral density (BMD) and microstructural characteristics were analyzed. The results showed that no significant differences existed in the microstructural parameters of trabecular bone among in vivo, fresh, and formalin-fixed bone scans from both femurs and tibias, although BMD exhibited differences. On the other hand, most parameters of the tail-suspended rats measured by micro-CT deteriorated compared with controls. Ex vivo scanning appeared to be more sensitive to bone microstructural changes induced by tail suspension than in vivo scanning. In general, the results indicate that values obtained in vivo and ex vivo (fresh and fixed) are comparable, thus allowing for meaningful comparison of experimental results from different studies irrespective of the type of scans. In addition, this study suggests that it is better to use ex vivo scanning when evaluating bone microstructure under weightlessness. However, researchers can select any type of scan depending upon the objective and the demands of the experiment.

[Comparative analysis of structural and functional characteristics of soleus muscle in rats and Mongolian gerbils during gravitational unloading of various duration]

A comparative investigation of the dynamics of contractile properties of the whole soleus muscle and its fibers during 3- and 12-day-long hind limb suspension of Wistar rats and Mongolian gerbils (Meriones unguiculatus) has been performed. The data obtained indicate that the structural and functional changes caused by hypogravity in gerbils are slowed down compared with rats. A very intensive drop in water containment in gerbils was found, which can cause shifts in the ionic strength of the intracellular space of the muscle fiber. As a result, the photolytic activity of different enzymes may change, which can induce a less pronounced reduction in Z-disc and M-line stiffness and contractile capabilities in gerbils compared to rats.

The 2nd Berlin BedRest Study: protocol and implementation

Long-term bed-rest is used to simulate the effect of spaceflight on the human body and test different kinds of countermeasures. The 2nd Berlin BedRest Study (BBR2-2) tested the efficacy of whole-body vibration in addition to high-load resisitance exercise in preventing bone loss during bed-rest. Here we present the protocol of the study and discuss its implementation. Twenty-four male subjects underwent 60-days of six-degree head down tilt bed-rest and were randomised to an inactive control group (CTR), a high-load resistive exercise group (RE) or a high-load resistive exercise with whole-body vibration group (RVE). Subsequent to events in the course of the study (e.g. subject withdrawal), 9 subjects participated in the CTR-group, 7 in the RVE-group and 8 (7 beyond bed-rest day-30) in the RE-group. Fluid intake, urine output and axiallary temperature increased during bed-rest (p < .0001), though similarly in all groups (p > or = .17). Body weight changes differed between groups (p < .0001) with decreases in the CTR-group, marginal decreases in the RE-group and the RVE-group displaying significant decreases in body-weight beyond bed-rest day-51 only. In light of events and experiences of the current study, recommendations on various aspects of bed-rest methodology are also discussed.

[Preventive and therapeutic effect of strontium ranelate on osteoporosis in rats subjected to simulated weightlessness]

OBJECTIVE

To study the effects of strontium ranelate on osteoporosis induced by simulated weightlessness in male rats.

METHODS

Twenty-seven male SD rats were randomly divided into 3 groups, namely the normal control group (group A) and two groups of weightlessness simulated by tail suspension (groups B and C). The rats in group C were treated with strontium ranelate, and those in the other two groups were given the same dose of normal saline for 28 consecutive days.

RESULTS

The rats in group B showed significantly lower levels of alkaline phosphatase (ALP), bone mineral density (BMD) and bone mineral content (BMC) than those in group A (P<0.05), but serum calcium and phosphonium concentrations underwent no significant changes in the 3 groups (P>0.05). In the rats of group B, the trabeculae of the femur became thinner, fragile, and discontinuous with reduced quantity as compared with those in group A. The rats in group C had greater number of the trabeculae than those in group B with decreased resorption surface and more regular arrangement of the collagen fibers.

CONCLUSION

Strontium ranelate may produce beneficial effect on the bone microstructure, reduce bone loss and stimulate bone formation in male rats subjected to simulated weightlessness.

Body-weight distribution on forelimbs in rat tail-suspension model

To understand the tail-suspension model to simulate weightlessness better, this study was to investigate the relationship of the amount of body weight supported by forelimbs between the tilt angles of rat in the model. Normal rat had at least two basic postures. One was standing or walking, in which the forelimbs bear 44.6% of the body weight; the other one was resting, in which 23.9% of body weight was placed on the forelimbs. As for tail-suspended rat, body-weight distribution on forelimbs was linearly related to tilt angle. The linear relationship was y = -0.7423x + 70.849, R2 = 0.9269. The tilt angle should be approximately 35 degrees if normal standing load of 44.6% body weight was placed on the forelimbs. On the other hand, it should be approximately 63 degrees if normal resting load of 23.9% of body weight was placed on forelimbs. Furthermore, the body load on forelimbs in tail-suspension model became much larger if the period of different postures was considered. Therefore, it should be careful if forelimbs are used to be as convenient internal control in tail-suspended rats.

[Effect of a Chinese herbal prescription on femur calcium deposition in rats under simulated weightlessness: by using (41)Ca tracing-accelerator mass spectrometry analysis]

To study the effect of a Chinese herbal prescription on external calcium deposition to weight-bearing bone in simulated weightlessness rats.

METHOD

Twenty-one male Wistar rats were divided into 3 groups: control group, tail suspension group, tail suspension with Chinese medicine group which takes a Chinese herbal prescription extract (containing Radix Rehmanniae Preparata, Radix Acanthopanacis Bidentatae, Radix Astragali, Radix Angelicae Sinensis, Concha Ostreae prepared by acetic acid) by intragastric administration. After 1 week adaption, there start off 3 weeks simulated weightlessness by tail suspension. At the eleventh day of simulated weightlessness, every rat was given one equal dose of 41Ca tracer by intragastric administration. Right femurs were separated as experiment over, and the ratio of 41Ca to 40Ca (41Ca/40Ca) was measured by accelerator mass spectrometry (AMS), while total femur calcium was measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Femur 41Ca deposition amount (DA) and femur 41Ca deposition ratio (DR) were calculated.

RESULT

The results showed that compared with control group, 41Ca/40Ca decreased significantly (P < 0.001) in tail suspension group, while in tail suspension with Chinese medicine group, it significantly increased (P < 0.05). DA and DR were both decreased significantly (P < 0.001) in tail suspension group, but no significant change in tail suspension with Chinese medicine group as compared with control group. Compared with tail suspension group, DA and DR increased significantly (P < 0.001) in tail suspension with Chinese medicine group.

CONCLUSION

Simulated weightlessness by tail suspension can cause decreased deposition of external calcium to weight-bearing bone, and the Chinese herbal prescription in this trial is effective to prevent the decrease. Moreover, multiple mechanisms may contribute to weightlessness induced osteoporosis, besides calcium deposition disturbance.

Effects of microgravity and hypergravity on platelet functions

Many serious thrombotic and haemorrhagic diseases or fatalities have been documented in human being exposed to microgravity or hypergravity environments, such as crewmen in space, roller coaster riders, and aircrew subjected to high-G training. Some possible related organs have been examined to explore the mechanisms underlying these gravity change-related diseases. However, the role of platelets which are the primary players in both thrombosis and haemostasis is unknown. Here we show that platelet aggregation induced by ristocetin or collagen and platelet adhesion to von Willebrand factor (VWF) were significantly decreased after platelets were exposed to simulated microgravity. Conversely, these platelet functions were increased after platelets were exposed to hypergravity. The tail bleeding time in vivo was significantly shortened in mice exposed to high-G force, whereas, was prolonged in hindlimb unloaded mice. Furthermore, three of 23 mice died after 15 minutes of -8 Gx stress. Platelet thrombi disseminated in the heart ventricle and blood vessels in the brain, lung, and heart from the dead mice. Finally, glycoprotein (GP) Ibalpha surface expression and its association with the cytoskeleton were significantly decreased in platelets exposed to simulated microgravity, and obviously increased in hypergravity-exposed platelets. These data indicate that the platelet functions are inhibited in microgravity environments, and activated under high-G conditions, suggesting a novel mechanism for gravity change-related haemorrhagic and thrombotic diseases. This mechanism has important implications for preventing and treating gravity change-related diseases, and also suggests that special attentions should be paid to human actions under different gravity conditions.

[Fundamental and applied objectives of investigations in immersion]

The results of extended comparative investigations into the hypogravity effects on the human motor system in space flight and ground-based experiments evidenced that dry immersions (DI) is the most adequate model of microgravity as time of development, degree and depth of structural and functional motor disorders in DI are very close to what is observed in real microgravity. High intensity and speed of the hypogravity effects during immersion as compared with bed rest hypokinesia the only difference from which is the level of support removal provided insight into the leading (trigger) role of support removal in genesis of the microgravity-induced syndromes of muscular deconditioning and hypogravitational ataxia. Involvement and paths of support afferentation within the muscular system were experimentally studied and verified. Much less understood are processes changing the system mechanisms. These issues as well as some nontrivial approaches to elimination of the negative effects of hypogravity were the subject of the multisided immersion experiment the results of which are presented in this book of the journal.

[Impact of 3-month simulation of the microgravity effects on the neuromuscular junction structure in rat's m. soleus]

The neuromuscular junctions were investigated in m. soleus of rats subjected to a 3-month tail suspension simulating the microgravity effects. Electron microscopy analysis revealed some ultrastructural signs of atrophy, degeneration and adipose dystrophy of muscle fibers. The aggregate of these findings points to progressive atrophy in m. soleus, while ultrastructural changes in the neuromuscular synapses testify a reduced functional activity of the synapses and partial denervation of the muscle fibers which, probably, underlay the atrophic process in the muscle. Increases in the number of axon terminals found in some neuromuscular synapses as well as of synaptic vesicles in individual axon terminals are likely to reflect formation of a particularly active pool of spinal motoneurons at L5, possibly associated with the growth in the number of fast fibers resulted from transformation.

[Effects of creatine phosphokinase competitive inhibitor on system and tissue energy metabolism in rats in the norm and during unloading]

In an experiment with rats system and intracellular energy metabolism was assessed by cell reactions to chronic injection of beta-guanidine propionic acid (beta-GPA) stimulating AMP-dependent protein kinase (AMPK). Suspension was shown to inhibit the succinate dehydrogenase (SDH) activity, reduce glycogen in both types of muscle fibers, and stimulate the activity of alpha-glycerophosphate dehydrogenase (alpha-GPDH) in fast fibers. Supplementing the rat chow with beta-GPA did not modify these parameters during suspension; however, the blood urea level increased considerably in the suspended and control rats. In the controls, beta-GPA as well as suspension, stimulates growth of the aspartate aminotranspherase activity (AST) in blood. Yet, the suspension and beta-GPA injection had no additive effect. Moreover, their effects were opposite in rats subjected to suspension + beta-GPA. Glucose concentration was observed to become lowered in blood of resting rats treated with beta-GPA. This effect can be associated with a more intensive insulin-dependent glucose transport to muscles. The additional glucose, because of increased demand by fibers, underwent to oxidation and did not replenish the intracellular carbohydrate deposits These data suggest energy metabolism shifting toward activation of the processes of disintegration of substrates for energy production due to a sharp growth of energy demand.

Early structural adaptations to unloading in the human calf muscles

AIM

The present study investigated the influence of muscle architectural changes on muscle torque during 3-week unilateral lower limb suspension (ULLS).

METHODS

Plantarflexion maximal voluntary contraction (MVC), soleus (SOL), gastrocnemius medialis (GM) and lateralis (GL) muscle volume (VOL), GL fascicle length (L(f)) and pennation angle (theta), physiological cross-sectional area (PCSA), and electromyographic (EMG) activity were assessed in eight healthy men (aged 19 +/- 0 years) after days 14 and 23 of ULLS.

RESULTS

After 14 day of ULLS, MVC and SOL EMG decreased (P < 0.05) by 10% and 29%, respectively, but did not further decline between days 14 and 23. SOL, GM and GL muscle VOL decreased by 5%, 6% and 5%, respectively (P < 0.05), on day 14, and by 7% (SOL), 10% (GM) and 6% (GL) on day 23. In GL, theta and L(f) were reduced by 3% (P < 0.05) and 2% (NS), respectively, on day 14, and by 5% (P < 0.05) and 4% (P < 0.05), respectively, on day 23. Consequently, GL PCSA declined by 3% (P < 0.05) on day 14, but did not further decrease on day 23. Similarly, the 7% (P < 0.05) loss in GL force/PCSA observed on day 14 persisted until the end of the unloading period.

CONCLUSION

These findings suggest that rapid muscle architecture remodelling occurs with lower limb unloading in humans, with changes occurring within 14 days of weight bearing removal. These adaptations, mitigating the decline in muscle PCSA, might protect from a larger loss of muscle force.

Simulated microgravity inhibits the proliferation and osteogenesis of rat bone marrow mesenchymal stem cells

OBJECTIVES

Microgravity is known to affect the differentiation of bone marrow mesenchymal stem cells (BMSCs). However, a few controversial findings have recently been reported with respect to the effects of microgravity on BMSC proliferation. Thus, we investigated the effects of simulated microgravity on rat BMSC (rBMSC) proliferation and their osteogeneic potential.

MATERIALS AND METHODS

rBMSCs isolated from marrow using our established effective method, based on erythrocyte lysis, were identified by their surface markers and their proliferation characteristics under normal conditions. Then, they were cultured in a clinostat to simulate microgravity, with or without growth factors, and in osteogenic medium. Subsequently, proliferation and cell cycle parameters were assessed using methylene blue staining and flow cytometry, respectively; gene expression was determined using Western blotting and microarray analysis.

RESULTS

Simulated microgravity inhibited population growth of the rBMSCs, cells being arrested in the G(0)/G(1) phase of cell cycle. Growth factors, such as insulin-like growth factor-I, epidermal growth factor and basic fibroblastic growth factor, markedly stimulated rBMSC proliferation in normal gravity, but had only a slight effect in simulated microgravity. Akt and extracellular signal-related kinase 1/2 phosphorylation levels and the expression of core-binding factor alpha1 decreased after 3 days of clinorotation culture. Microarray and gene ontology analyses further confirmed that rBMSC proliferation and osteogenesis decreased under simulated microgravity.

CONCLUSIONS

The above data suggest that simulated microgravity inhibits population growth of rBMSCs and their differentiation towards osteoblasts. These changes may be responsible for some of the physiological changes noted during spaceflight.

Simulated microgravity inhibits the proliferation and osteogenesis of rat bone marrow mesenchymal stem cells

OBJECTIVES

Microgravity is known to affect the differentiation of bone marrow mesenchymal stem cells (BMSCs). However, a few controversial findings have recently been reported with respect to the effects of microgravity on BMSC proliferation. Thus, we investigated the effects of simulated microgravity on rat BMSC (rBMSC) proliferation and their osteogeneic potential.

MATERIALS AND METHODS

rBMSCs isolated from marrow using our established effective method, based on erythrocyte lysis, were identified by their surface markers and their proliferation characteristics under normal conditions. Then, they were cultured in a clinostat to simulate microgravity, with or without growth factors, and in osteogenic medium. Subsequently, proliferation and cell cycle parameters were assessed using methylene blue staining and flow cytometry, respectively; gene expression was determined using Western blotting and microarray analysis.

RESULTS

Simulated microgravity inhibited population growth of the rBMSCs, cells being arrested in the G(0)/G(1) phase of cell cycle. Growth factors, such as insulin-like growth factor-I, epidermal growth factor and basic fibroblastic growth factor, markedly stimulated rBMSC proliferation in normal gravity, but had only a slight effect in simulated microgravity. Akt and extracellular signal-related kinase 1/2 phosphorylation levels and the expression of core-binding factor alpha1 decreased after 3 days of clinorotation culture. Microarray and gene ontology analyses further confirmed that rBMSC proliferation and osteogenesis decreased under simulated microgravity.

CONCLUSIONS

The above data suggest that simulated microgravity inhibits population growth of rBMSCs and their differentiation towards osteoblasts. These changes may be responsible for some of the physiological changes noted during spaceflight.

Morphological and morphometric study on the effect of simulated microgravity on rat testis

The present study was undertaken to determine the effect of simulated microgravity on the testis of the rats and to evaluate the possibility of spermatogenesis failure in space environment. Fifty-four adult male albino rats were used in this study. They were divided equally into intact control, stress control and experimental groups. The rats of the intact control group (Group Ia) were kept without intervention. The rats of both the stress control and experimental groups were subjected to inguinal canal ligation and tail-suspension. In the stress control group (Group Ib) the hindlimbs were not elevated above the floor of the housing units whereas in the experimental groups the hindlimbs were elevated for one week (Group II) and six weeks (Group III), respectively. In a third experimental group (Group IV) the rats were hindlimb-suspended for six weeks followed by another six weeks without suspension to allow recovery. Prior to sacrifice, the animals were weighed and anesthetized, and the testes were excised and weighed. Testicular specimens were processed for histological, histochemical and morphometric studies. The results of the present study revealed that only after six weeks of hindlimb-suspension, the rats showed a significant decline in testicular weight compared with the control groups. Histologically, few abnormalities were observed in some seminiferous tubules in one-week hindlimb-suspended group. Spermatogenesis was significantly reduced by six-week of hindlimb-suspension marked by atrophy of the testes and loss of all germ cells, except a few spermatogonia. Spermatogenesis was partially restored in the recovery group. In all groups the appearance of Sertoli cells remained the same. Proliferation of Leydig cells was observed in the experimental groups. It is concluded that spermatogenesis is severely inhibited by six weeks of hindlimb-suspension and that it is partially restored following six weeks of recovery. This study provides further insights regarding the serious effects of long-term exposure to microgravity on the testes of mammals, including human beings.

[Effects of Chinese Bushen Zhuanggu medicine on bone loss in female rats after simulated weightlessness]

OBJECTIVE

To study the effect of Bushen Zhuanggu, the traditional Chinese medicine for reinforcing kidney and strengthening bone, on bone loss in female rats after simulated weightlessness.

METHOD

Thirty-six female SD rats were randomly divided into 3 groups, namely normal control group (group A) and two groups of weightlessness simulated by tail suspension (groups B and C). Group C were treated with the Chinese medicine, while groups A and B were given the same dose of normal saline. The experiment lasted 28 days, and all rats were allowed to drink water freely.

RESULTS

In the rats of group B, serum bone Gla protein (BGP), alkaline phosphatase (ALP), estradiol (E(2)) and P content and femur bone mineral content (BMD) were significantly lower than those in group A (P<0.01, P<0.05), whereas serum calcium concentration was markedly higher than that in group A (P<0.01). In rats of group C, serum BGP, ALP, E2 and P content and femur BMD were significantly higher than those in group B (P<0.01, P<0.05), but serum calcium concentration was markedly lower (P<0.01).

CONCLUSION

This Chinese prescription can stimulate bone formation and reduce bone loss in female rats subjected to simulated weightlessness.

Why is orthostatic tolerance lower in women than in men? Renal and cardiovascular responses to simulated microgravity and the role of midodrine

BACKGROUND

Exposure to microgravity induces cardiovascular deconditioning, manifested by orthostatic intolerance (OI). We assessed the renal, cardioendocrine, and cardiovascular responses of women and men to simulated microgravity to examine the impact of gender on OI.

METHODS

Fifteen healthy female and 14 healthy male subjects were given a constant diet for 3 to 5 days, after which they underwent a tilt-stand test (pre-TST) and began 14 to 16 days of head-down tilt bed rest (HDTB), followed by a repeat tilt-stand test (post-TST). Female subjects began HDTB so that the post-TST was at the same time in their menstrual cycle as their pre-TST. Twenty-four-hour urine collections (daily), hormonal measurements, plethysmography, and cardiovascular system identification were performed.

RESULTS

The times to presyncope were significantly different for men and women before (p= .005) and after HDTB (p= .001), with all of the women but only 50% of the men experiencing presyncope during the pre-TST (p= .002) and all of the women but only 64% of the men experiencing presyncope during the post-TST. At baseline, the following differences between women and men were observed: women had higher serum aldosterone levels (p = .02), higher parasympathetic responsiveness (p = .01), lower sympathetic responsiveness (p = .05), and lower venous compliance (p = .05). Several parameters changed with HDTB in both men and women. In a double-blinded randomized trial, midodrine (5 mg orally) or placebo given to female subjects 1 hour before post-TST was ineffective in preventing 01.

CONCLUSION

In conclusion, the frequency of OI is higher in women than in men and is not modified by midodrine at the dose used. This increased susceptibility is likely secondary to intrinsic basal differences in the activity of volume-mediated parasympathetic and adrenergic systems and in venous tone. Thus, approaches to reduce OI in women are likely to differ from those effective in men.

Impact of simulated microgravity on cell cycle control and cytokine release by U937 cells

Previous experiments from flight- and ground-based model systems indicate unexpected alterations of human leukocytes, leading to growth retardation and depression of mitogenic activation. The response of myelomonocytic U937 cells to simulated microgravity was therefore investigated. To this purpose, U937 cells were cultured in the NASA-developed bioreactor Rotating Wall Vessel (RWV) as a device to simulate microgravity on earth. No apoptosis was detected, in part because of the up-regulation of hsp70. In agreement with results obtained in space-flown U937 cells, the cells grew more slowly in the RWV than under normal conditions and this correlated with the down-modulation of cdc25B. Marked alterations of the cytokine secretion profile and, in particular, of inflammatory chemokines, as well as a decrease of the proteasome activity, were also observed in response to microgravity.

Ambulation in simulated fractional gravity using lower body positive pressure: cardiovascular safety and gait analyses

The purpose of this study is to assess cardiovascular responses to lower body positive pressure (LBPP) and to examine the effects of LBPP unloading on gait mechanics during treadmill ambulation. We hypothesized that LBPP allows comfortable unloading of the body with minimal impact on the cardiovascular system and gait parameters. Fifteen healthy male and female subjects (22–55 yr) volunteered for the study. Nine underwent noninvasive cardiovascular studies while standing and ambulating upright in LBPP, and six completed a gait analysis protocol. During stance, heart rate decreased significantly from 83 ± 3 beats/min in ambient pressure to 73 ± 3 beats/min at 50 mmHg LBPP ( P < 0.05). During ambulation in LBPP at 3 mph (1.34 m/s), heart rate decreased significantly from 99 ± 4 beats/min in ambient pressure to 84 ± 2 beats/min at 50 mmHg LBPP ( P < 0.009). Blood pressure, brain oxygenation, blood flow velocity through the middle cerebral artery, and head skin microvascular blood flow did not change significantly with LBPP. As allowed by LBPP, ambulating at 60 and 20% body weight decreased ground reaction force ( P < 0.05), whereas knee and ankle sagittal ranges of motion remained unaffected. In conclusion, ambulating in LBPP has no adverse impact on the systemic and head cardiovascular parameters while producing significant unweighting and minimal alterations in gait kinematics. Therefore, ambulating within LBPP is potentially a new and safe rehabilitation tool for patients to reduce loads on lower body musculoskeletal structures while preserving gait mechanics.

Protein nitration increased by simulated weightlessness and decreased by melatonin and quercetin in PC12 cells

A variety of experiments suggest that space flight is associated with an increase in oxidative stress in organism. To explore the effects of oxidative stress on neuronal cells during microgravity, we used rat pheochromocytoma (PC12) cells as a neuronal cell model, cultured in a clinostat, which could simulate microgravity, to investigate the effects of reactive nitrogen species on protein nitration in PC12 cells during clinorotation. The effects of melatonin and quercetin on protein nitration in PC12 cells were also assayed to evaluate the possible protective role of melatonin or quercetin as an antioxidant. The results of immunological staining showed that after the 3 days' clinorotation the protein expressions of neuronal nitric oxide synthase and inducible nitric oxide synthesis were up-regulated. Our data also reflected that the concentrations of nitric oxide and nitrotyrosine were significantly increased after clinorotation, and they were reduced markedly in cells that were treated with 50 micromol/L melatonin or 0.5 micromol/L quercetin during simulated microgravity, when compared to those of control cells. These results suggest that clinorotation-induced weightlessness increases oxidative stress responses in PC12 cells, and melatonin or quercetin was shown to protect PC12 cells from oxidative damage during simulated weightlessness.

Alterations in the virulence potential of enteric pathogens and bacterial-host cell interactions under simulated microgravity conditions

Host immune mechanisms were proposed to decline under microgravity conditions during spaceflights, which might result in severe infections in astronauts. Therefore, it was important to investigate the effects of microgravity on infecting organisms and their interaction with host cells. Data showed that simulated microgravity (SMG) conditions markedly increased production of the enterotoxigenic Escherichia coli (ETEC) heat-labile enterotoxin, which induced fluid secretory responses in a mouse model. SMG also enhanced production of tumor necrosis factor-alpha in murine macrophages infected with enteropathogenic E. coli (EPEC). In a similar fashion, simulated microgravity conditions augmented the invasive potential of Salmonella enterica serovar typhimurium and enhanced production of tumor necrosis-factor alpha in S. typhimurium-infected epithelial cells. Furthermore, coculturing of macrophages and S. typhimurium in a simulated microgravity environment resulted in activation of stress-associated mitogen-activated protein kinase kinase 4. Using the antiorthostatic tail suspension mouse model, which simulates some aspects of microgravity, oral inoculation of S. typhimurium markedly reduced the 50% lethal dose compared to mice infected under normal gravitational conditions. Microarray analysis revealed simulated microgravity-induced alterations in the expression of 22 genes in S. typhimurium, and protein expression profiles were altered in both EPEC and S. typhimurium, based on two-dimensional gel electrophoresis. These studies indicated alterations in the virulence potential of bacteria and in host responses to these pathogens under simulated microgravity conditions, which may represent an important environmental signal. Such studies are essential for better understanding bacterial-host cell interactions, particularly in the context of spaceflights and space habitations of long duration.

Simulated weightlessness changes the cytoskeleton and extracellular matrix proteins in papillary thyroid carcinoma cells

Studies of astronauts, experimental animals, and cells have shown that, after spaceflights, the function of the thyroid is altered by low-gravity conditions. The objective of this study was to investigate the cytoskeleton and extracellular matrix (ECM) protein synthesis of papillary thyroid cancer cells grown under zero g. We investigated alterations of ONCO-DG 1 cells exposed to simulated microgravity on a three-dimensional random-positioning machine (clinostat) for 30 min, 24 h, 48 h, 72 h, and 120 h (n=6, each group). ONCO-DG 1 cells grown under microgravity exhibited early alterations of the cytoskeleton and formed multicellular spheroids. The cytoskeleton was disintegrated, and nuclei showed morphological signs of apoptosis after 30 min. At this time, vimentin was increased. Vimentin and cytokeratin were highly disorganized, and microtubules (alpha-tubulin) did not display their typical radial array. After 48 h, the cytoskeletal changes were nearly reversed. The formation of multicellular spheroids continued. In parallel, the accumulation of ECM components, such as collagen types I and III, fibronectin, chondroitin sulfate, osteopontin, and CD44, increased. The levels of both transforming growth factor beta-1 (TGF-beta(1)) and TGF-beta receptor type II proteins were elevated from 24 h until 120 h clinorotation. Gene expression of TGF-beta(1) was clearly enhanced during culture under zero g. The amount of E-cadherin was enhanced time-dependently. We suggest that simulated weightlessness rapidly affects the cytoskeleton of papillary thyroid carcinoma cells and increases the amount of ECM proteins in a time-dependent manner.

Oxygen Uptake Kinetics Following 20 Days of Unilateral Lower Limb Suspension

The purpose of the present study was to examine the effect of unilateral lower limb suspension (ULLS) deconditioning on oxygen uptake kinetics. Eight healthy males underwent ULLS for 20 days and performed a series of 6-min square-wave transitions from rest to 60-W single-leg cycling exercises just before and after ULLS. To characterize the kinetics of the oxygen uptake response, a single exponential model was applied to the data until the end of the fast component omitted the first 15 s of the on-transit using a nonlinear least-squares fitting procedure. The following results were found: (i) the time constant of oxygen uptake was unchanged before and after ULLS; (ii) although there was no significant difference in the baseline and the asymptotic amplitude of the fast component, the asymptote, i.e., the absolute asymptotic amplitude of the fast component (the sum of the baseline and the asymptotic amplitude), and the end exercise oxygen uptake were decreased after ULLS; (iii) the contribution of the slow component to the total response of oxygen uptake was unchanged at pre- and post-ULLS. In conclusion, the asymptote in the fast component and the end exercise oxygen uptake were decreased after 20-d ULLS, though the response speed and the amplitude of the slow component of oxygen uptake were not changed. It is suggested that deconditioning as a result of limb disuse affects oxygen uptake response.

[Muscle atrophy in microgravity and during its simulation]

Summarized are the results of comparative analysis of morphological changes in rat's skeletal muscles after microgravity and its simulation. On completion of space flight, hindlimb muscles of rats exhibited atrophy developed in space microgravity in consequence of the lack of weight-bearing loads and changes solely in the slow anti-g muscles due to the hemodynamic disorders appearing after space flight. Immobilization combined with clinostatting cannot be a veridical laboratory model of microgravity, as horizontally positioned animals still possess weight and, besides, experience severe chronic stress of immobilization. Tail suspension with the head-end permanently down and the hind limbs out of use appeared the most demonstrative model of the space microgravity effects. With this model, the hindlimb muscles underwent changes identical to what had been observed in space flown animals. Data of the simulation studies suggest stabilization of muscle atrophy at a certain level and an earlier and stronger reaction to the hindlimb unloading in young rats as compared to old animals. Skeletal muscles in females and males responded to suspension similarly in spite of difference in the hormonal status.

[Regulative effects of Chinese herb-compound on blood rheology and circulatory system of rabbits under simulated weightlessness]

OBJECTIVE

To investigate effects of Chinese herb-compound on blood rheology and circulatory system of rabbits under simulated weightlessness in order to provide bases for protecting against the influence of simulated weightlessness on cardiovascular function.

METHOD

Rabbits were exposed to head-down tilt (HDT -20 degrees) for 9 d to simulate weightlessness. The effect of Chinese herb-compound on indices related to blood rheology, blood-fat and orthostatic tolerance in these rabbits were examined.

RESULT

After head-down tilt, hematocrit value and red blood cells deformability decreased significantly; cholesterol and low density lipoprotein increased markedly; plasma fibrinogen content and triglyceride showed increasing trend. Administration of the Chinese herb-compound didn't improve the blood rheology indices, but showed a trend to decrease triglyceride and to inhibit the increase of cholesterol. In the head-up tilt (HUT) plus lower body negative pressure (LBNP) experiment, orthostatic tolerance time of the rabbits in the control group decreased, and myocardial ischemic changes in ECG, such as dropped ST segment, inverse T wave, and arrhythmia were observed. While in the Chinese herb-compound group, the heart rate of the rabbits kept smooth, ischemic changes in ECG were not clear, and orthostatic tolerance time increased.

CONCLUSION

The Chinese herb-compound shows an effect of preventing orthostatic tolerance from decreasing, and improves blood-fat metabolism. It regulates different human systems on the whole, and increases ability of adaptation to ill environment.

Exercise within lower body negative pressure partially counteracts lumbar spine deconditioning associated with 28-day bed rest

Astronauts experience spine deconditioning during exposure to microgravity due to the lack of axial loads on the spine. Treadmill exercise in a lower body negative pressure (LBNP) chamber provides axial loads on the lumbar spine. We hypothesize that daily supine LBNP exercise helps counteract lumbar spine deconditioning during 28 days of microgravity simulated by bed rest. Twelve sets of healthy, identical twins underwent 6° head-down-tilt bed rest for 28 days. One subject from each set of twins was randomly assigned to the exercise (Ex) group, whereas their sibling served as a nonexercise control (Con). The Ex group exercised in supine posture within a LBNP chamber for 45 min/day, 6 days/wk. All subjects underwent magnetic resonance imaging of their lumbar spine before and at the end of bed rest. Lumbar spinal length increased 3.7 ± 0.5 mm in the Con group over 28-day bed rest, whereas, in the Ex group, lumbar spinal length increased significantly less (2.3 ± 0.4 mm, P = 0.01). All lumbar intervertebral disk heights (L5–S1, L4–5, L3–4, L2–3, and L1–2) in the Con group increased significantly over the 28-day bed rest ( P < 0.05). In the Ex group, there were no significant increases in L5–S1and L4–5disk heights. Lumbar lordosis decreased significantly by 3.3 ± 1.2° during bed rest in the Con group ( P = 0.02), but it did not decrease significantly in the Ex group. Our results suggest that supine LBNP treadmill exercise partially counteracts lumbar spine lengthening and deconditioning associated with simulated microgravity.

Intensive exercise training suppresses testosterone during bed rest

Spaceflight and prolonged bed rest (BR) alter plasma hormone levels inconsistently. This may be due, in part, to prescription of heavy exercise as a countermeasure for ameliorating the adverse effects of disuse. The initial project was to assess exercise programs to maintain aerobic performance and leg strength during BR. The present study evaluates the effect of BR and the performance of the prescribed exercise countermeasures on plasma steroid levels. In a 30-day BR study of male subjects, the efficacy of isotonic (ITE, n = 7) or isokinetic exercise (IKE, n = 7) training was evaluated in contrast to no exercise ( n = 5). These exercise countermeasures protected aerobic performance and leg strength successfully. BR alone (no-exercise group) did not change steroidogenesis, as assessed by the plasma concentrations of cortisol, progesterone, aldosterone, and free (FT) and total testosterone (TT). In the exercise groups, both FT and TT were decreased ( P < 0.05): FT during IKE from 24 ± 1.7 to 18 ± 2.0 pg/ml and during ITE from 21 ± 1.5 to 18 ± 1 pg/ml, and TT during IKE from 748 ± 68 to 534 ± 46 ng/dl and during ITE from 565 ± 36 to 496 ± 38 ng/dl. The effect of intensive exercise countermeasures on plasma testosterone was not associated with indexes of overtraining. The reduction in plasma testosterone associated with both the IKE and ITE countermeasures during BR supports our hypothesis that intensive exercise countermeasures may, in part, contribute to changes in plasma steroid concentrations during spaceflight.

Amino acid supplementation alters bone metabolism during simulated weightlessness

High-protein and acidogenic diets induce hypercalciuria. Foods or supplements with excess sulfur-containing amino acids increase endogenous sulfuric acid production and therefore have the potential to increase calcium excretion and alter bone metabolism. In this study, effects of an amino acid/carbohydrate supplement on bone resorption were examined during bed rest. Thirteen subjects were divided at random into two groups: a control group (Con, n = 6) and an amino acid-supplemented group (AA, n = 7) who consumed an extra 49.5 g essential amino acids and 90 g carbohydrate per day for 28 days. Urine was collected for n-telopeptide (NTX), deoxypyridinoline (DPD), calcium, and pH determinations. Bone mineral content was determined and potential renal acid load was calculated. Bone-specific alkaline phosphatase was measured in serum samples collected on day 1 (immediately before bed rest) and on day 28. Potential renal acid load was higher in the AA group than in the Con group during bed rest ( P < 0.05). For all subjects, during bed rest urinary NTX and DPD concentrations were greater than pre-bed rest levels ( P < 0.05). Urinary NTX and DPD tended to be higher in the AA group ( P = 0.073 and P = 0.056, respectively). During bed rest, urinary calcium was greater than baseline levels ( P < 0.05) in the AA group but not the Con group. Total bone mineral content was lower after bed rest than before bed rest in the AA group but not the Con group ( P < 0.05). During bed rest, urinary pH decreased ( P < 0.05), and it was lower in the AA group than the Con group. These data suggest that bone resorption increased, without changes in bone formation, in the AA group.

Readaptation from simulated microgravity as a stimulus for improved orthostatic tolerance: role of the renal, cardioendocrine, and cardiovascular systems

BACKGROUND

Microgravity and simulated microgravity (SM) lead to important changes in orthostatic tolerance (OT), the autonomic nervous system (ANS), and the volume-regulating systems. After one is exposed to microgravity or SM, a period of readaptation to gravity is known to take place, but it is not certain if orthostatic function returns to baseline within the initial recovery and what mechanisms are involved. We hypothesized that after a period of recovery, OT, ANS, and volume-regulating systems would return to pre-SM levels.

METHODS

To test this hypothesis, 24 healthy men were placed on a constant diet for 3 to 5 days, after which a tilt-stand test (pre-TST) was performed. The TST was repeated after 14 to 16 days of head-down tilt bed rest (HDTB) (post-TST) and a 3-day period of recovery (rec-TST), at which times measurements of renal, cardioendocrine, and cardiovascular systems were conducted.

RESULTS

Presyncope occurred in 46% of subjects pre-TST, in 72% post-TST, and in 23% during rec-TST. OT was significantly better during the recovery period than at baseline (p = .03). There was a significant decrease in urinary sodium and potassium excretion, along with a decrease in plasma renin activity and serum and urine aldosterone compared with baseline. Serum norepinephrine and sympathetic responsiveness remained below baseline values.

CONCLUSION

In summary, OT improved compared with baseline after a period of readaptation. Retention of electrolytes (sodium, potassium) could be involved. These findings indicate that recovery after SM is not simply a gradual return to baseline values but is instead a dynamic process reflecting interaction of multiple regulatory systems.

Vascular adaptation to 4 wk of deconditioning by unilateral lower limb suspension

Physical inactivity or deconditioning is an independent risk factor for atherosclerosis and cardiovascular disease. In contrast to exercise, the vascular changes that occur as a result of deconditioning have not been characterized. We used 4 wk of unilateral lower limb suspension (ULLS) to study arterial and venous adaptations to deconditioning. In contrast to previous studies, this model is not confounded by denervation or microgravity. Seven healthy subjects participated in the study. Arterial and venous characteristics of the legs were assessed by echo Doppler ultrasound and venous occlusion plethysmography. The diameter of the common and superficial femoral artery decreased by 12% after 4 wk of ULLS. Baseline calf blood flow, as measured by plethysmography, decreased from 2.1 ± 0.2 to 1.6 ± 0.2 ml·min−1·dl tissue−1. Both arterial diameter and calf blood flow returned to baseline values after 4 wk of recovery. There was no indication of a decrease in flow-mediated dilation of the superficial femoral artery after ULLS deconditioning. This means that functional adaptations to inactivity are not simply the inverse of adaptations to exercise. The venous pressure-volume curve is shifted downward after ULLS, without any effect on compliance. In conclusion, deconditioning by 4 wk of ULLS causes significant changes in both the arterial and the venous system.

Morpho-functional alterations in testicular and nervous cells submitted to modelled microgravity

Humans, as well as other life forms, have developed on earth under the terrestrial gravitational field. Questions concerning the effect of the gravity vector changes on the animal physiology have begun to emerge only in the last decades. Physiological alterations were observed during space flights, but space-born investigations at cellular levels are still very limited. Earth-bound simulations of low gravity obtained with the 3-dimensional Random Positioning Machine are extensively utilized to explore the effects of microgravity on cell function. After only a few minutes, weightlessness affected the cytoskeleton of lymphocytes, astrocytes, neurons and testicular cells, disorganizing microtubules, intermediate filaments and microfilaments. Cell division was impaired, mitochondria were disrupted and apoptotic phenomena occurred. Expression of proteins involved in transmembrane ion and water transport were also affected. In the Leydig cells the key enzymes (3beta- and 17beta-hydroxysteroid dehydrogenases) leading to testosterone synthesis were depressed. However, after 20 h of clinorotation the cells were able to synthesize heat shock proteins that initiated protection and recovery. The cytoskeleton was again well organized, normal mitosis occurred and the percentage of apoptotic cells returned to the range of 5%, similar to the control cultures. Ion and water transmembrane proteins and steroid dehydrogenases returned to normal levels. Long-term experiments showed that low gravity induced only transient alterations in the cultured cells, which were able to adapt to the gravity vector changes and to regain normal activity. These data may explain the physiological adaptation occurring in astronauts during and after space flights.