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At least 1,225 records · Page 68Linked to original sources
PubMed2003

Creating conditions similar to those that occur during exposure of cells to microgravity induces apoptosis in human lymphocytes by 5-lipoxygenase-mediated mitochondrial uncoupling and cytochrome c release.

Creating conditions similar to those that occur during exposure of cells to microgravity induced a sixfold increase of apoptotic bodies and DNA fragments in human lymphocytes, paralleled by an early (within 2 h) fourfold increase in 5-lipoxygenase (5-LOX) activity and a fivefold decrease in mitochondrial membrane potential and increase in cytochrome c release (within 4 and 8 h, respectively). Similar membrane potential and cytochrome c release were observed in isolated mitochondria treated with physiological amounts of 5-LOX and were enhanced by creating conditions similar to those that occur during exposure of cells to microgravity. 5-LOX inhibitors, 5,8,11,14-eicosatetraynoic acid and caffeic acid, completely prevented apoptosis, whereas the phospholipase A(2) inhibitor methyl-arachidonoyl fluorophosphonate and the 5-LOX activating protein inhibitor MK886 reduced it to 65-70%. The intracellular calcium chelator EGTA-acetoxymethylester reduced 5-LOX activity and apoptosis to 30-40% of controls, whereas the p38 mitogen-activated protein kinase inhibitor SB203580 was ineffective. The caspase-3 and caspase-9 inhibitors Z-Asp(OCH(3))-Glu(OCH(3))-Val-Asp(OCH(3))-fluoromethylketone (FMK) and Z-Leu-Glu(OCH(3))-His-Asp(OCH(3))-FMK reduced apoptotic bodies to 25-30% of the control cells. Finally, creating conditions similar to those that occur during exposure of cells to microgravity did not induce apoptosis in human lymphoma U937 cells, which did not express an active 5-LOX.

Adult↗
PubMed2004

Effect of magnetic field on the crystalline structure of magnetostrictive TbFe2 alloy solidified unidirectionally in microgravity.

We performed unidirectional solidification experiments on TbFe(2) alloy in a static magnetic field in microgravity of 10(-4) g for 10 sec obtained by a 490 m free fall of the Japan microgravity center (JAMIC). When the magnetic field strength was increased from zero to 4.5 x 10(-2) T during unidirectional solidification in microgravity, a [1 1 1] crystallographic alignment dominated, and the maximum magnetostriction constant increased from 1,000 ppm to 4,000 ppm. For unidirectional solidification in normal gravity, the maximum magnetostriction constant remained at 2,000 ppm with increasing magnetic field. The columnar structure grows and orients along the magnetic field. TbFe(2) crystals grow in microgravity predominantly in the same direction as the magnetic field.

Alloys↗
PubMed2004

Design and preparation of a particle dynamics space flight experiment, SHIVA.

This paper describes the flight experiment, supporting ground science, and the design rationale for a project on spaceflight holography investigation in a virtual apparatus (SHIVA). SHIVA is a fundamental study of particle dynamics in fluids in microgravity. Gravitation effects and steady Stokes drag often dominate the equations of motion of a particle in a fluid and consequently microgravity provides an ideal environment in which to study the other forces, such as the pressure and viscous drag and especially the Basset history force. We have developed diagnostic recording methods using holography to save all of the particle field optical characteristics, essentially allowing the experiment to be transferred from space back to Earth in what we call the "virtual apparatus" for microgravity experiments on Earth. We can quantify precisely the three-dimensional motion of sets of particles, allowing us to test and apply new analytic solutions developed by members of the team. In addition to employing microgravity to augment the fundamental study of these forces, the resulting data will allow us to quantify and understand the ISS environment with great accuracy. This paper shows how we used both experiment and theory to identify and resolve critical issues and to produce an optimal experimental design that exploits microgravity for the study. We examined the response of particles of specific gravity from 0.1 to 20, with radii from 0.2 to 2 mm, to fluid oscillation at frequencies up to 80 Hz with amplitudes up to 200 microns. To observe some of the interesting effects predicted by the new solutions requires the precise location of the position of a particle in three dimensions. To this end we have developed digital holography algorithms that enable particle position location to a small fraction of a pixel in a CCD array. The spaceflight system will record holograms both on film and electronically. The electronic holograms can be downlinked providing real-time data, essentially acting like a remote window into the ISS experimental chamber. Ground experiments have provided input to a flight system design that can meet the requirements for a successful experiment on ISS. Moreover the ground experiments have provided a definitive, quantitative observation of the Basset history force over a wide range of conditions. Results of the ground experiments, the flight experiment design, preliminary flight hardware design, and data analysis procedures are reported.

Acceleration↗
PubMed2006

Heat and gas exchanges between plants and atmosphere under microgravity conditions.

Fundamental studies were conducted to develop a facility having an adequate air circulation system for growing healthy plants over a long term under microgravity conditions in space. To clarify the effects of gravity on heat and gas exchanges between plant leaves and the ambient air, surface temperatures and net photosynthetic rates of barley leaves were evaluated at gravity levels of 0.01, 1.0, and 2.0 g for 20 sec each during parabolic airplane flights. Thermal images were captured using infrared thermography at an air temperature of 22 degrees C, a relative humidity of 18%, and an irradiance of 260 W/m2. The net photosynthetic rates were determined by means of a chamber method with an infrared gas analyzer at an air temperature of 20 degrees C, a relative humidity of 50%, and photosynthetic photon fluxes (PPFDs) of 250 and 500 micromol/m2/sec. Mean leaf temperatures increased by 1.9 degrees C with decreasing gravity levels from 1.0 to 0.01 g and decreased by 0.6 degrees C with increasing gravity levels from 1.0 to 2.0 g. The increase in leaf temperatures was greater at the regions closer to the leaf tip and at most 2.5 degrees C over 20 sec as gravity decreased from 1.0 to 0.01 g. The net photosynthetic rate decreased by 20% with decreasing gravity levels from 1.0 to 0.01 g and increased by 10% with increasing gravity levels from 1.0 to 2.0 g at a PPFD of 500 micromol/m2/sec. The heat and gas exchanges between leaves and the ambient air were suppressed more at the lower gravity levels. The retardation would be caused by heat and gas transfers with less heat convection. Restricted free air convection under microgravity conditions in space would limit plant growth by retarding heat and gas exchanges between leaves and the ambient air.

Acceleration↗
PubMed2006

Upside-down protein crystallization: designing microbatch experiments for microgravity.

The benefits of protein crystal growth in microgravity are well documented. The crystallization vessels currently employed for microgravity crystallization are far from optimal with regards to cost, sample volume, size, and ease of use. The use of microbatch experiments is a favorable alternative in each respect: 96 experiments of 0.5-2 microL volumes can be performed in a single microtiter tray measuring 5 x 8 cm and costing 1 pound sterling each. To date, the use of microbatch has not been pursued on account of concerns of oil leakage. To address this issue, a novel approach to microbatch crystallization experiments is described, where the microbatch plates are inverted throughout the duration of the experiment. The findings intimate the application of the microbatch method to space flight and the potential to drastically increase the output of microgravity crystallization research .

Animals↗
PubMed2000

Fuel homeostasis during physical inactivity induced by bed rest.

The consequences of physical inactivity on fuel homeostasis were evaluated during 7 days of head-down bed rest (HDBR), a model mimicking weightlessness. Eight men (32.4 +/- 1.9 yr; body mass index, 23.9 +/- 0.7 kg/m2) and eight women (27.9 +/- 0.9 yr; body mass index, 20.9 +/- 0.6 kg/m2) underwent an oral glucose tolerance test (OGTT; 1 g/kg) before and after HDBR. The glucose load was labeled with 13C and associated with D-[6,6-2H2] glucose infusion, indirect calorimetry, breath tests, and plasma measurements to determine the glucose turnover and biodisponibility, substrate oxidation, and endocrine responses. Body composition was assessed using H2(18)O dilution. In addition, hormones were measured in daily blood and 24-h urine samples. No change in body composition was noted. Daily fasting insulin increased during HDBR (men, 34%; women, 26%), as did the insulin to glucose ratio (men, 30%; women, 25%). The normetanephrine level dropped (men, 30%; women, 16%), but metanephrine was unchanged. During OGTTs, the insulin response was increased after HDBR (men, 47%; women, 67%), whereas plasma glucose levels were similar. Nonesterified fatty acids and beta-hydroxybutyrate levels were lower. Endogenous glucose production dropped (28%), and exogenous glucose oxidation increased (28%) only in men. Resting energy expenditure was unchanged, but nonproteic respiratory quotient increased (men, 10%; women, 14%). Basal levels of lipid oxidation dropped in both sexes (approximately 90%), but those of carbohydrate oxidation increased in men (40%); as did lipogenesis in women (570%). In response to OGTTs, lipid oxidation was 80% reduced in both sexes after HDBR, but carbohydrate oxidation increased (25%) in men. Lipogenesis occurred in men (304%) and women (74%), but the latter had higher absolute levels. Therefore, 7 days of HDBR resulted in 1) reduced sympathetic activity, 2) insulin resistance suggested at the muscle level in men and at both the muscle and liver levels in women, 3) no changes in glucose biodisponibility, suggesting no alterations in the gastrointestinal function, and 4) a shift toward carbohydrate oxidation in men and a net lipogenesis in women. Such results suggest gender differences in response to sedentary life style and warrant further analysis.

3-Hydroxybutyric Acid↗
PubMedDate not supplied

Clinorotation differentially inhibits T-lymphocyte transcription factor activation.

T lymphocytes cultured under the low-shear stress environment of modeled microgravity demonstrate an inhibition of activation in response to T-cell receptor (TCR)-mediated signaling. Modeled microgravity culture-induced inhibition mimics the inhibition observed during spaceflight. This work investigates the molecular signaling events of interleukin 2 transcription activation in modeled microgravity as generated with clinorotation. Under normal conditions, NFAT (nuclear factor of activated T cells) is dephosphorylated and activated with sustained calcium (Ca++) influx and calcineurin activity, whereas AP-1 is activated by protein kinase C (PKC) and Ras-mediated pathways. Purified human T lymphocytes are shown to exhibit differential inhibition of transcription factor activation in modeled microgravity. Activation of AP-1 is blocked with clinorotation, whereas NFAT dephosphorylation occurs. This work supports the theory that modeled microgravity differentially blocks the activation of distinct signaling mechanism.

Calcineurin↗
PubMed2001

Suppression of antigen-specific lymphocyte activation in modeled microgravity.

Various parameters of immune suppression are observed in lymphocytes from astronauts during and after a space flight. It is difficult to ascribe this suppression to microgravity effects on immune cells in crew specimens, due to the complex physiological response to space flight and the resultant effect on in vitro immune performance. Use of isolated immune cells in true and modeled microgravity in immune performance tests, suggests a direct effect of microgravity on in vitro cellular function. Specifically, polyclonal activation of T-cells is severely suppressed in true and modeled microgravity. These recent findings suggest a potential suppression of oligoclonal antigen-specific lymphocyte activation in microgravity. We utilized rotating wall vessel (RWV) bioreactors as an analog of microgravity for cell cultures to analyze three models of antigen-specific activation. A mixed-lymphocyte reaction, as a model for a primary immune response, a tetanus toxoid response and a Borrelia burgdorferi response, as models of a secondary immune response, were all suppressed in the RWV bioreactor. Our findings confirm that the suppression of activation observed with polyclonal models also encompasses oligoclonal antigen-specific activation.

Animals↗
PubMed2001

Modeled microgravity inhibits apoptosis in peripheral blood lymphocytes.

Microgravity interferes with numerous lymphocyte functions (expression of cell surface molecules, locomotion, polyclonal and antigen-specific activation, and the protein kinase C activity in signal transduction). The latter suggests that gravity may also affect programmed cell death (PCD) in lymphocyte populations. To test this hypothesis, we investigated spontaneous, activation- and radiation-induced PCD in peripheral blood mononuclear cells exposed to modeled microgravity (MMG) using a rotating cell culture system. The results showed significant inhibition of radiation- and activation-induced apoptosis in MMG and provide insights into the potential mechanisms of this phenomenon.

Apoptosis↗
PubMed1997

Inhibition of bone resorption by pamidronate cannot restore normal gain in cortical bone mass and strength in tail-suspended rapidly growing rats.

To clarify how the changes in bone formation and resorption affect bone volume and strength after mechanical unloading, the effect of inhibition of bone resorption by a potent bisphosphonate, pamidronate, on bone mineral density (BMD), histology, and strength of hind limb bones was examined using tail-suspended growing rats. Tail suspension for 14 days reduced the gain in the BMD of the femur at both the metaphysis rich in trabecular bone and the diaphysis rich in cortical bone. Treatment with pamidronate increased the total BMD as well as that of the metaphysis of the femur but had almost no effect on the BMD of the diaphysis in both control and tail-suspended rats. Histological examinations revealed that 14-day tail suspension caused a loss of secondary cancellous bone with a reduction in the trabecular number and thickness in comparison with control rats. In the femoral diaphysis, the diameter and cortical bone thickness increased to a lesser degree in tail-suspended rats when compared with rats without tail suspension, and a marked reduction in bone formation and the layers of alkaline phosphatase-positive cells was observed at the periosteal side. Pamidronate treatment increased secondary cancellous bone but could not restore normal growth-induced periosteal bone apposition and bone strength. Because the material strength of the femoral diaphysis at the tissue level was not affected by pamidronate treatment, the inability of pamidronate to prevent the reduction in physical strength of the femoral diaphysis does not appear to be due to a change in the quality of newly formed bone. These results demonstrate that tail suspension reduces the growth-induced periosteal modelling drift and that the antiresorptive agent pamidronate is unable to restore normal periosteal bone apposition.

Amino Acids↗
PubMed1997

Regional responsiveness of the tibia to intermittent administration of parathyroid hormone as affected by skeletal unloading.

To determine whether the acute inhibition of bone formation and deficit in bone mineral induced by skeletal unloading can be prevented, we studied the effects of intermittent parathyroid hormone (PTH) administration (8 micrograms/100 g/day) on growing rats submitted to 8 days of skeletal unloading. Loss of weight bearing decreased periosteal bone formation by 34 and 51% at the tibiofibular junction and tibial midshaft, respectively, and reduced the normal gain in tibial mass by 35%. Treatment with PTH of normally loaded and unloaded animals increased mRNA for osteocalcin (+58 and +148%, respectively), cancellous bone volume in the proximal tibia (+41 and +42%, respectively), and bone formation at the tibiofibular junction (+27 and +27%, respectively). Formation was also stimulated at the midshaft in unloaded (+47%, p < 0.05), but not loaded animals (-3%, NS). Although cancellous bone volume was preserved in PTH-treated, unloaded animals, PTH did not restore periosteal bone formation to normal nor prevent the deficit in overall tibial mass induced by unloading. We conclude that the effects of PTH on bone formation are region specific and load dependent. PTH can prevent the decrease in cancellous bone volume and reduce the decrement in cortical bone formation induced by loss of weight bearing.

Animals↗
PubMed2002

Regional alterations of type I collagen in rat tibia induced by skeletal unloading.

Skeletal unloading induces loss of mineral density in weight-bearing bones that leads to inferior bone mechanical strength. This appears to be caused by a failure of bone formation; however, its mechanisms still are not well understood. The objective of this study was to characterize collagen, the predominant matrix protein in bone, in various regions of tibia of rats that were subjected to skeletal unloading by 4 weeks tail suspension. Sixteen male Sprague-Dawley rats (4 months old) were divided into tail suspension and ambulatory controls (eight rats each). After the tail suspension, tibias from each animal were collected and divided into five regions and collagen was analyzed. The collagen cross-linking and the extent of lysine (Lys) hydroxylation in unloaded bones were significantly altered in proximal epiphysis, diaphysis, and, in particular, proximal metaphysis but not in distal regions. The pool of immature/nonmineralized collagen measured by its extractability with a chaotropic solvent was significantly increased in proximal metaphysis. These results suggest that skeletal unloading induced an accumulation of post-translationally altered nonmineralized collagen and that these changes are bone region specific. These alterations might be caused by impaired osteoblastic function/differentiation resulting in a mineralization defect.

Amino Acids↗
PubMed2003

Effect of hyper- and microgravity on collagen post-translational controls of MC3T3-E1 osteoblasts.

UNLABELLED: We attempted to study the effects of microgravity (by clinostat) and hypergravity (using centrifugation) on collagen metabolism using murine MC3T3-E1 osteoblasts, especially focusing on collagen cross-link formation. We found that altered gravitational load affected the post-translational modification of collagen, particularly the collagen maturation pathway, through altered expression of enzymes involved in cross-link formation. INTRODUCTION: Gravitational loading plays important roles in the stimulation of differentiated osteoblast function and in the maintenance of skeletal tissues, whereas microgravity seems to result in osteopenia caused by impaired osteoblast differentiation. The aim of our study was to clarify the effects of altered gravitational environments on collagen metabolism, particularly the relationship between post-translational collagen quality and enzymes involved in cross-link formation, using murine osteoblastic MC3T3-E1 cells. MATERIALS AND METHODS: Cells were cultured under vector-averaged microgravity (1 x 10(-3) g) using a clinostat or under conventional centrifugation techniques to generate hypergravity (20 g and 40 g) for 72 h. We then examined the expression patterns of lysyl oxidase and the two lysyl hydroxylase isoforms telopeptidyl lysyl hydroxylase (TLH; procollagen-lysine, 2-oxyglutarate, 5-dioxigenase 2 [PLOD2]) and helical lysyl hydroxylase (HLH; [PLOD1]) by quantitative real time polymerase chain reaction (PCR) analysis. Quantitative analysis of reducible immature (dihydroxylysinonorleucine, hydroxylysinonorleucine, and lysinonorleucine) and nonreducible mature (pyridinoline and deoxypyridinoline) cross-links, and maturation rate analysis of immature to mature cross-links by conventional metabolic labeling using tritium lysine were also performed. RESULTS: Hypergravity upregulated both TLH mRNA expression and enzyme activity compared with stationary cultures, whereas microgravity stimulated both HLH mRNA expression and enzyme activity. These results were consistent with increased relative occupancy rates of telopeptidyl hydroxylysine-derived cross-links and helical hydroxylysine-derived forms observed under hypergravity and microgravity, respectively. Hypergravity stimulated not only lysyl oxidase mRNA expression but also increased enzyme activity and the sum of immature and mature cross-links. Furthermore, the conversion rate of immature cross-links to mature compounds was markedly increased under hypergravity but decreased under microgravity. CONCLUSION: Altered gravitational loading may affect the post-translational modification of collagen through altered expression of enzymes involved in cross-link formation. These observations may be important in elucidating the mechanisms of osteopenia during space flight.

3T3 Cells↗
PubMed2006

Effects of microgravity on cell cytoskeleton and embryogenesis.

The aim of this review is to compile, summarize and discuss the effects of microgravity on embryos, cell structure and function that have been demonstrated from data obtained during experiments performed in space or in altered gravity induced by clinostats. In cells and tissues cellular structure and genetic expression may be changed in microgravity and this has a variety of effects on embryogenesis which include death of the embryo, failure of neural tube closure, or final deformities to the overall morphology of the newborn or hatchling. Many species and protocols have been used for microgravity space experiments making it difficult to compare results. Experiments on the ways in which embryonic development and cell interactions occur in microgravity could also be performed. Experiments that have been done with cells in microgravity show changes in morphology, cytoskeleton and function. Changes in cytoskeleton have been noted and studies on microtubules in gravity have shown that they are gravity sensitive. Further study of basic chemical reactions that occur in cells should be done to shed some light on the underling processes leading to the changes that are observed in cells and embryos in microgravity.

Animals↗
PubMed2005

"Modeled microgravity" affects cell response to ionizing radiation and increases genomic damage.

The aim of this work was to assess whether "modeled microgravity" affects cell response to ionizing radiation, increasing the risk associated with radiation exposure. Lymphoblastoid TK6 cells were irradiated with various doses of gamma rays and incubated for 24 h in a modeled microgravity environment obtained by the Rotating Wall Vessel bioreactor. Cell survival, induction of apoptosis and cell cycle alteration were compared in cells irradiated and then incubated in 1g or modeled microgravity conditions. Modulation of genomic damage induced by ionizing radiation was evaluated on the basis of HPRT mutant frequency and the micronucleus assay. A significant reduction in apoptotic cells was observed in cells incubated in modeled microgravity after gamma irradiation compared with cells maintained in 1g. Moreover, in irradiated cells, fewer G2-phase cells were found in modeled microgravity than in 1g, whereas more G1-phase cells were observed in modeled microgravity than in 1g. Genomic damage induced by ionizing radiation, i.e. frequency of HPRT mutants and micronucleated cells, increased more in cultures incubated in modeled microgravity than in 1g. Our results indicate that modeled microgravity incubation after irradiation affects cell response to ionizing radiation, reducing the level of radiation-induced apoptosis. As a consequence, modeled microgravity increases the frequency of damaged cells that survive after irradiation.

Apoptosis↗
PubMed1996

Development of centrifugal phytotron to study the gravity effect on vegetable plant growth.

The present Spacetron is used to cultivate plants over a long term by controlling environment condition. The cultivation drum was rotated in perpendicular direction creating fluctuation in gravity. Centrifugal force plus 1 G ground gravity, are distributed unevenly over the cultivation drum. This fluctuation effect on plant growth was not clear. In the modified Spacetron the cultivation drum rotates horizontally whereas the plant stage rotated in the perpendicular direction. To find the basic information for design of centrifugal phytotron the two axes Spacetron Junior (clinostat) was developed to formulate the micro and hypergravity environment. It would be used to study the effect on a plant growth process of different gravity conditions. In order to produce the different values of gravity, the clinostat's axis was rotated with a stepping motor at different angular velocity. The axis rotated at 5.2 revolutions per minute (rpm) to create a centrifugal force equivalent to 0.01 G and the plant stage was rotated at 5.2 rpm. The chlorophyll value is higher in the plants under microgravity condition of 0.01 G whereas the fresh weight and dry weight are higher in the plants under control condition of 1 G earth gravity. The result of this study showed that the plant growth was affected by microgravity along with other known factors such as vibration and unknown factors.

Biomass↗
PubMed2002

Skeletal adaptations to alterations in weight-bearing activity: a comparison of models of disuse osteoporosis.

The removal of regular weight-bearing activity generates a skeletal adaptive response in both humans and animals, resulting in a loss of bone mineral. Human models of disuse osteoporosis, namely bed rest, spinal cord injury and exposure to micro-gravity demonstrate the negative calcium balance, alterations in biochemical markers of bone turnover and resultant loss of bone mineral in the lower limbs that occurs with reduced weight-bearing loading. The site-specific nature of the bone response is consistent in all models of disuse; however, the magnitude of the skeletal adaptive response may differ across models. It is important to understand the various manifestations of disuse osteoporosis, particularly when extrapolating knowledge gained from research using one model and applying it to another. In rats, hindlimb unloading and exposure to micro-gravity also result in a significant bone response. Bone mineral is lost, and changes in calcium metabolism and biochemical markers of bone turnover similar to humans are noted. Restoration of bone mineral that has been lost because of a period of reduced weight bearing may be restored upon return to normal activity; however, the recovery may not be complete and/or may take longer than the time course of the original bone loss. Fluid shear stress and altered cytokine activity may be mechanistic features of disuse osteoporosis. Current literature for the most common human and animal models of disuse osteoporosis has been reviewed, and the bone responses across models compared.

Adaptation, Physiological↗