[MINERAL BONE DENSITY AND BODY COMPOSITION IN PARTICIPANTS IN EXPERIMENT MARS-500].

Investigations of the bone system and body composition in Mars-500 test-subjects (prior to and on completion of the experiment) involved dual-energy X-ray absorptiometry (DXA) using the HOLOGIC Delphy densitometer and the protocol performed to examine cosmonauts. Bone density of lumber vertebrae and femoral proximal epiphysis, and body composition were measured. Reliable changes in vertebral density found in 3 test-subjects displayed different trends from +2.6 to -2.4%. At the same time, the experiment decreased significantly mineral density of the femoral proximal epiphysis, including the neck, in all test-subjects. Four test-subjects had cranial mineralization increased by 5-9%, same as in some cosmonauts after space flight. All tests-subjects incurred adipose loss from 2 to 7 kg; one test-subject lost 20 kg, i.e. his adipose mass became three times less. Changes in lean mass (1-3 kg) typically were negative; as for changes in lean mass of extremities, they could be linked with adherence to one or another type of physical activity. Therefore, extended exposure to confinement may affect mineralization of some parts of the skeleton. Unlike real space missions and long-term bedrest studies conducted at the Institute of Biomedical Problems in the past, Mars-500 did not cause clinically significant mineral losses (osteoporosis, osteopenia), probably because of the absence of effects of microgravity.

[Changes in bone structure according to the results of investigations on biosatellites of the "BION" series].

Noninvasive technologies of bone investigations measure largely the main skeletal sites and are not quite suitable to have a look at the bone internal organization in situ. However, there are data obtained noninvasively in experiments on board the space biosatellites. The review is dedicated to analysis and comparison of the evidence for the bone organic and mineral matrix restructuring due to microgravity. These changes have presumably evolved in the course of the system reaction of bone tissue and the whole skeleton.

[Interrelation of dynamics of blood lipids and bone mineral density in humans during 370-day bed rest].

Comparison of bone mineral density and fatty-acid blood content in 9 human subjects exposed to 370-d bed rest revealed correlation of the loss in femoral neck density with parameters of lipid exchange. On day-46 of BR, the absolute lipids content in erythrocyte membranes and blood serum decreased considerably (1.5-2 times) when compared with baseline data. At the end of the experiment, lipids content in serum, on the contrary, surpassed baseline values 2-3 times: however, it remained lowered in erythrocyte membranes of the control group till day-280 of BR. Arachidonic acid correlated with prostaglandins PGE2 and PGF2alpha involved in regulation of osteoclasts and osteoblasts activities. Correlation of decreases in femoral neck density and unsaturated fatty acids in blood serum and erythrocyte membranes varied with the human subjects.

[Characteristics of local human skeleton reactions to microgravity and drug treatment of osteoporosis in clinic].

Analysis of the results of long-term investigations of bones in cosmonauts flown on the orbital station MIR and International space station (n = 80) was performed. Theoretically predicted (evolutionary predefined) change in mass of different skeleton bones was found to correlate (r = 0.904) with position relatively the Earth's gravity vector. Vector dependence of bone loss ensues from local specificity of expression of bone metabolism genes which reflects mechanic prehistory of skeleton structures in the evolution of Homo erectus. Genetic polymorphism is accountable for high individual variability of bone loss attested by the dependence of bone loss rate on polymorphism of certain bone metabolism markers. Parameters of one and the other orbital vehicle did not modulate individual-specific stability of the bone loss ratio in different segments of the skeleton. This fact is considered as a phenotype fingerprint of local metabolism in the form of a locus-unique spatial structure of distribution of noncollagenous proteins responsible for position regulation of endosteal metabolism. Drug treatment of osteoporosis (n = 107) evidences that recovery rate depends on bone location; the most likely reason is different effectiveness of local osteotrophic intervention into areas of bustling resorption.

[Comparative analysis of cosmonauts skeleton changes after space flights on orbital station Mir and international space station and possibilities of prognosis for interplanetary missions].

A summary of investigations results of human bone tissue changes in space flight on the orbital station (OS) Mir and international space station (ISS) using dual energy X-ray absorptiometry (DXA) is given. Results comparative analysis revealed an absence of significant differences in bone mass (BM) changes on the both OS. Theoretically expected BM loss was observed in bone trabecular structure of skeleton low part after space flight lasting 5-7 month. The BM losses are qualified in some cases as quicly developed but reversible osteopenia and generally interpreted as evidence of bone functional adaptation to the alterating mechanical loading. It was demonstrated the high individual variability BM loss amplitudes. Simultaneously was observed the individual pattern of BM loss distribution across different segments of skeleton after repetitive flights independently upon type of OS. In according with the above mentioned individual peculiarities it was impossible to establish the dependence of BM changes upon duration of space missions. Therefore we have not sufficiently data for calculation of probability to achive the critical demineralization level by the augmentation the space mission duration till 1.5-2 years. It is more less possibility of the bone quality changes prognosis, which in the aggregate with BM losses determines the bone fracture risk. It become clearly that DXA technology is unsuffitiently for this purpose. It is considered the main direction which may optimized the elaboration of the interplanetary project meaning the perfectly safe of skeleton mechanical function.

[Analysis of polymorphism of bone metabolism genes and evaluation of the risk of osteopenia in cosmonauts].

Densitometry of cosmonauts following long-duration missions shows reduction of bone mineral density (BMD). On the average, post-flight BMD remains within the normal range and the broad variability of individual BMD values sometimes is qualified as local osteopenia. Individual reactions are typed by similarity of amount and rate of BMD loss. At present, analysis of functionally significant polymorphism of bone metabolism genes is the most effective instrument for diagnostics of susceptibility to osteopenia and osteoporosis. The investigation was aimed to analyze polymorphism of genes of vitamin-D and (VDR) and calcitonin (CALCR) receptors, and of collagen-1 alpha-1-chain (Col1a-1) in candidate cosmonauts and cosmonauts returned from 5 to 7-mo. missions. According to the results of analysis, in the majority of cosmonauts rapid BMD loss correlated with TT genotype by VDR gene but not with genotypes Tt and tt and associated with carriage of incomplete s-allele in the Col1a1 gene. Yet, in several instances high BMD loss rates were personified with carriers of VDR gene alleles (homo- and heterozygote states--tt and Tt) and heterozygote by Col1a1 gene (Ss).

[Human bone system in microgravity: review of research data, hypotheses and predictability of musculoskeletal system state in extended (exploration) missions].

The results of long-standing investigations of the human bone system in the piloted Mir and International space station missions were reviewed. The noninvasive DXA technology was used to determine bone mass (BM) and body composition. Predictable BM losses in the lower body tubular bones during 5 to 7-mo. space missions are characteristic of rapid but recoverable osteopenia and viewed as functional adaptation to altering mechanic loading of the skeleton. These changes feature high individual variability. Interestingly, the extent of BM changes in different segments of the skeleton displays stability in individual crew members irrespective of space station design. No strong dependence of BM changes on flight duration has been established and, therefore, calculation of the probability of critical bone demineralization after 1.5 to 2 years in space flight is impractical. Still less is the possibility to predict impairment of the bone structure which, together with BM losses, preconditions the risk of fracture. The data presented witness DXA inadequacy for such prediction. Main areas of researches toward optimization of the exploration mission design and planning in the context of the skeleton mechanic function maintenance are considered.

Recovery of spaceflight-induced bone loss: bone mineral density after long-duration missions as fitted with an exponential function.

The loss of bone mineral in NASA astronauts during spaceflight has been investigated throughout the more than 40 years of space travel. Consequently, it is a medical requirement at NASA Johnson Space Center (JSC) that changes in bone mass be monitored in crew members by measuring bone mineral density (BMD), with dual-energy X-ray absorptiometry (DXA) before and after flight, of astronauts who serve on long-duration missions (4-6 months). We evaluated this repository of medical data to track whether there is recovery of bone mineral that was lost during spaceflight. Our analysis was supplemented by BMD data from cosmonauts (by convention, a space traveler formally employed by the Russia Aviation and Space Agency or by the previous Soviet Union) who had also flown on long-duration missions. Data from a total of 45 individual crew members - a small number of whom flew on more than one mission - were used in this analysis. Changes in BMD (between 56 different sets of pre- and postflight measurements) were plotted as a function of time (days after landing). Plotted BMD changes were fitted to an exponential mathematical function that estimated: (i) BMD change on landing day (day 0) and (ii) the number of days after landing when 50% of the lost bone would be recovered ("50% recovery time") in the lumbar spine, trochanter, pelvis, femoral neck and calcaneus. In sum, averaged losses of bone mineral after long-duration spaceflight ranged between 2% and 9% across all sites with our recovery model predicting a 50% restoration of bone loss for all sites to be within 9 months.

[On possible mechanisms of osteopenia in humans in microgravity and situations imitating its effects].

The review deals with the analysis of osteodensitometry data from the cosmonauts flown on Russian space station MIR and the International space station and suppositions about involvement of different levels of metabolism regulation in bone loss triggered by insufficient mechanic loading in microgravity attendant by redistribution of body liquids. It is surmised that the initial reactions are associated with the biomechanical factor and recruitment of local mechanisms, i.e. osteocyte osteolysis and inhibition of osteoblast histogenesis. Regulation on the level of tissues and organs is responsible for destabilization of calcium homeostasis (low calcium absorption in the intestine and readsorption in the kidney). Changes in the hierarchy of ion and volume regulation may provoke osteoclast resorption which further increases osteopenia.

[Functional plasticity of mammalian skeletal muscles under microgravity].

In the retrospective analysis of own experimental data and the literary overview of the slow-to-fast transformation of skeletal muscles (essentially postural and locomotor) in animals due to microgravity the authors scrutinize the muscle functional plasticity given heterodromous changes in the external mechanic field. Adaptation of the myofiber phenotype is ensured by polymorphism of muscle isoproteins and lability of the system providing energy for muscle contraction.

[Characteristics and patterns of the human bone reactions to microgravity].

Hypothesized processes of changes found in spacecrew bones following 5 to 7 mo. orbital missions are reviewed. Selective osteopenia of trabecular bones in the lower skeleton is attributed to a greater weight loading at 1 g. Increased mineral content in the upper skeleton (dual energy X-ray adsoptiometry--DXA) and hypermineralization of the limbic spongious bone (computer tomography) appear to be secondary and reflect the body liquids redistribution headword including to the abdomen. The additional negative gradient of the lower skeleton mass during early readaptation (about 1.5 mo, after landing) can be explained by remodeling (resorption and bone formation) as a reaction to the "load return". Personal variability is probably a fingerprint of genetic determinism of bone mass and metabolic phenotype that may sometimes lead to an increased risk of fracture. The authors raise the discussion about practicality of the genetic osteopenia prediction for space flyers.

[Reactions of the human bone system in space flight: phenomenology].

Results of multi-year bone observations in crewmembers of long-term (6 to 14 mos.) Salyut and Mir missions have been summarized. The theoretical expectation of bone losses (mineral bone density, MBD) was consistent only in the trabecular of the lower skeleton (lumbar spine, femur proximal epiphysis, pelvis). The upper skeleton bones (skull, cervical spine) demonstrated a clears-defined trend toward an increase in mineral content. There is a direct dependence of MBD losses on a skeleton bone position relative to the gravity vector and bone structure. Post-flight MBD did not, as a rule, deviate from the WHO-defined limits (T-criterion); in several instances MBD loss was qualified as local osteopenia. Shifts in MBD, same as MBD recovery rate, vary with subjects and, therefore, deny their dependence on flight duration. By and large, MBD shifts are interpreted as a functional adaptation of bone tissue to changing mechanic demands.

Effect of exercise and bisphosphonate on mineral balance and bone density during 360 day antiorthostatic hypokinesia.

As we enter a phase of space exploration that will involve long-duration flights, there is a need to use ground-based models to study the long-term effects of countermeasures to prevent the loss of bone mineral in microgravity. Mineral balances, hormone levels, and bone density were measured for 360 days in nine bed rest subjects treated with an exercise program used by cosmonauts. Four of these subjects received the bisphosphonate, ethane-1-hydroxy-1-disphosphonate, 900 mg daily, a drug known to inhibit bone resorption. Compared to a 120 day control period, the bisphosphonate combined with exercise reduced negative calcium balances by 50% for the first 120 days, 80% for the second 120 days, and 69% during the third 120 days. Exercise alone had no effect until the second 120 day period, when calcium balance improved 52%. Negative phosphorus balances were not affected by either treatment. Magnesium balances were negative during the first 120 days and returned to nearly normal during the last 240 days in both groups. The combined exercise and bisphosphonate treatment prevented increases in serum ionized calcium and decreases in plasma calcitonin during the first 120 days, as well as trends toward decreases in the mineral density of the femoral neck. These results suggest that bisphosphonates can be efficiently used together with exercise to reduce calcium loss and prevent some of the changes in mineral metabolism during long-term simulated microgravity.

Altered distribution of mitochondria in rat soleus muscle fibers after spaceflight.

The influence of spaceflight on the distribution of succinate dehydrogenase (SDH) activity throughout the cross section of fibers in the soleus was studied in five male rats and in five rats maintained under ground-based simulated flight conditions (control). The flight (COSMOS 1887) was 12.5 days in duration, and the animals were killed approximately 2 days after return to 1 G. Fibers were classified as slow-twitch oxidative or fast-twitch oxidative-glycolytic in histochemically prepared tissue sections. The distribution of SDH activity throughout the cross section of 20-30 fibers (each type) was determined using quantitative histochemical and computer-assisted image analysis techniques. In all the fibers, the distribution of SDH activity was significantly higher in the subsarcolemmal than in intermyofibrillar region. After spaceflight the entire regional distribution of SDH activity was significantly altered in the slow-twitch oxidative fibers. The fast-twitch oxidative-glycolytic fibers of the spaceflight muscles exhibited a significantly lower SDH activity only in their subsarcolemmal region. These data suggest that when determining the influence of spaceflight on muscle fiber oxidative metabolism enzymes, it is important to consider the location of the enzyme throughout the cross section of a fiber. Furthermore the functional properties of the soleus that depend on the metabolic support of mitochondria in the subsarcolemmal region may be primarily affected by exposure to microgravity.

Muscle sarcomere lesions and thrombosis after spaceflight and suspension unloading.

Spaceflight (flight) and tail suspension-hindlimb unloading (unloaded) produced significant decreases in fiber cross-sectional areas of the adductor longus (AL), a slow-twitch antigravity muscle. However, the mean wet weight of the flight AL muscles was near normal, whereas that of the suspension unloaded AL muscles was significantly reduced. Interstitial edema within the flight AL, but not in the unloaded AL, appeared to account for this apparent disagreement. In both experimental conditions, the slow-twitch oxidative fibers atrophied more than the fast-twitch oxidative-glycolytic and fast-twitch glycolytic fibers. Immunostaining showed that slow-twitch oxidative fibers expressed fast myosin, producing hybrid fibers containing slow and fast myosin isoforms. Two-dimensional gel electrophoresis of flight AL muscles revealed increased content of fast myosin light chains and decreased amounts of slow myosin light chains and fatty acid-binding protein. In the flight AL, absolute mitochondrial content decreased, but the relatively greater breakdown of myofibrillar proteins maintained mitochondrial concentration near normal in the central intermyofibrillar regions of fibers. Subsarcolemmal mitochondria were preferentially lost and reduced below normal concentration. Elevated fiber immunostaining for ubiquitin conjugates was suggestive of ubiquitin-mediated breakdown of myofibrillar proteins. On return to weight bearing for 8-11 h, the weakened atrophic muscles exhibited eccentric contraction-like lesions (hyperextension of sarcomeres with A-band filaments pulled apart and fragmented), tearing of the supporting connective tissue, and thrombosis of the microcirculation. Segmental necrosis of muscle fibers, denervation of neuromuscular junctions, and extravasation of red blood cells were minimal. Lymphocyte antibody markers did not indicate a significant immune reaction. The flight AL exhibited threefold more eccentric-like lesions than the unloaded AL; the high reentry G forces experienced by the flight animals, but not the unloaded group, possibly accounted for this difference. Muscle atrophy appears to increase the susceptibility to form eccentric contraction-like lesions after reloading; this may reflect weakening of the myofibrils and extracellular matrix. Microcirculation was also compromised by spaceflight, such that there was increased formation of thrombi in the post-capillary venules and capillaries. This blockage led to edema by 8-11 h after resumption of weight bearing by the COSMOS 2044 rats. The present findings indicate that defective microcirculation most likely accounted for the extensive tissue necrosis and microhemorrhages observed for COSMOS 1887 rats killed 2 days after landing.

Changes of cell-vascular complex in zones of adaptive remodeling of the bone tissue under microgravity conditions.

We examined the peculiarities of the structure of the blood-vascular bed and perivascular cells in zones of osteogenesis in the epiphyses and metaphises of femoral bones of rats, flown aboard the US laboratory SLS-2 for two weeks by electron microscopy and histochemistry. In zones of bone remodeling, there was a tendency for a reduction of sinusoid capillary specific volume. Endotheliocytes preserve the typical structure. In the population of perivascular cells, we discovered differentiating osteogenic cells that contained alkaline phosphomonoesterase as well as cells that don't contain this enzyme and differentiate into fibroblasts. The fibroblasts genesis in zones of adaptive remodeling of spongy bones leads to a further development of fibrous tissue that is not subject to mineralization.

Microgravity and musculoskeletal system of mammals.

This review surveys data in the literature and our own findings concerning the effects of weightlessness on bones and muscles of white rats flown on Cosmos biosatellites and Spacelab-3. It has been shown that the magnitude and sign of functional changes in muscles depend on their biomechanical profile. Structural and metabolic foundations of functional adaptation and its dynamics have been identified: in 5-7 day flights muscle contractility changes are mainly associated with a diminished activity of excitation-contraction coupling, in longer-term flights they are produced by changes in myosin populations specific for myofibers of different functional profile. At early flight stages (up to 1 week) osteoporosis and bone demineralization are very mild; therefore decrease in bone mechanical strength may be caused by changes in physico-chemical parameters of the collagen-crystal system. In flights of up to 3 weeks noticeable osteoporosis develops which is primarily produced by osteogenesis inhibition and which is responsible for a marked decrease of bone strength. These changes may result from uncoupling of bone resorption and remodelling processes. This uncoupling is characterized as incomplete osteogenesis and may be caused by changes in the collagen composition of the organic bone matrix. The above-mentioned adaptive changes in muscle functions of specific skeletal compartments may play a role in different responses of various bones to weightlessness.

Ultrastructural changes in osteocytes in microgravity conditions.

We examined the histology and morphometry of biosamples (biopsies) of the iliac crest of monkeys, flown 14 days aboard the "Bion-11", using electron microscopy. We found, that some young osteocytes take part in the activation of collagen protein biosynthesis in the adaptive remodeling process of the bone tissue to microgravity conditions. Osteocyte lacunae filled with collagen fibrils; this correlates with fibrotic osteoblast reorganization in such zones. The osteolytic activity in mature osteocytes is intensified. As a result of osteocyte destruction, the quantity of empty osteocytic lacunae in the bone tissue increases.

[Quantitative histological study of the bone mass and cellular activity after 120-days decubitus. Trial of preventive protocols]. / Etude histologique quantitative de la masse et des activités cellulaires osseuses après un décubitus de 120 jours. Essai de protocoles préventifs.

Bone biopsies of iliac crests, performed at the beginning and the end of a decubitus period of 120 days, were studied in 20 healthy volunteers men. The purpose of this experiment is to simulate the bony alterations of astronauts. The bony mass of all bed-ridden patients remained constant. In strictly immobilized patients, the rate of bony mineralization is decreased and the osteoclastic resorption activity is stimulated. In bed-ridden patients subjected to preventive physical exercises, the bony formation and resorption are increased. When prevention is administered with the use of a diphosphonate, the osteoid and osteoclastic parameters are decreased. When both types of prevention are administered, the osteoid parameters and the resorption activity are decreased but less markedly than in patients treated with diphosphonate alone.

Histology and histochemistry of intervertebral discs of rats participated in spaceflight.

The qualitative and quantitative histological and histochemical changes in the structure and macromolecular composition of lumbar intervertebral discs of rat during a 12.5-day space flight (Cosmos 1887 biosatellite) were determined using light and polarization microscopy. Semiquantitative histochemical, topo-optical reactions were measured and evaluated by retardation values of birefringence. (a) Lateral expansion and accumulation of the notochordal cells in the nucleus pulposus was observed in contrast with the vivarium control, where the chondroid cells dominated. (b) The cartilage and plate showed a swelling, which consisted mainly of hypertrophied cells sometimes with mild extracellular mineralization. (c) In the external zone of annulus fibrosus and cartilage end plate a mild decrease of orientation of collagen fibers was found. (d) A significant increase of orientation of hyase sensible glycosaminoglycans in the internal zone of annulus fibrosus and nucleus pulposus was observed. (e) In the external and internal zones of annulus fibrosus an increase of orientation of glycoproteids was revealed. The alterations of macromolecular components of intervertebral discs, cartilage end plates, and the osteoporotic changes of the lumbar vertebral bodies producing the looser structure of vertebral column after 12.5 day space flight suggest the necessity of the common evaluation of these structures, and may explain the heavy spinal pains of astronauts.