Space research to explore novel biochemical insights on Earth

Travel to space has overcome unprecedent technological challenges and this has resulted in transfer of these technological results on Earth to better our lives. Health technology, medical devices, and research advancements in human biology are the first beneficiaries of this transfer. The real breakthrough came with the International Space Station, which endorsed multidisciplinary international scientific collaborations and boosted the research on pathophysiological adaptation of astronauts to life on space. These studies evidenced that life in space appeared to have exposed the astronauts to an accelerated aging-related pathophysiological dysregulation across multiple systems. In this review we emphasize the interaction between several biomarkers and their alteration in concentrations/expression/function by space stress factors. These altered interactions, suggest that different biochemical and hormonal factors, and cell signals, contribute to a complex network of pathophysiological mechanisms, orchestrating the homeostatic dysregulation of various organs/metabolic pathways. The main effects of space travel on altering cell organelles biology, ultrastructure, and cross-talk, have been observed in cell aging as well as in the disruption of metabolic pathways, which are also the causal factor of rare inherited metabolic disorders, one of the major pediatric health issue. The pathophysiologic breakthrough from space research could allow the development of precision health both on Earth and Space by promoting the validation of improved biomarker-based risk scores and the exploration of new pathophysiologic hypotheses and therapeutic targets. Nonstandard abbreviations: International Space Station (ISS), Artificial Intelligence (AI), European Space Agency (ESA), National Aeronautics and Space Agency (NASA), Low Earth Orbit (LEO), high sensitive troponin (hs-cTn), high sensitive troponin I (hs-cTn I), high sensitive troponin T, Brain Natriuretic Peptide (BNP), N terminal Brain Natriuretic Peptide (NT-BNP), cardiovascular disease (CVD), parathyroid hormone (PTH), urinary hydroxyproline (uHP), urinary C- and N-terminal telopeptides (uCTX and uNTX), pyridinoline (PYD), deoxypyridinoline (DPD), half-time (HF), serum Bone Alkaline Phosphatase (sBSAP), serum Alkaline Phosphatase (sAP), Carboxy-terminal Propeptide of Type 1 Procollagen (P1CP), serum Osteocalcin (sOC)), advanced glycation end products (AGEs), glycated hemoglobin A1c (HbA1c), Insulin-like growth factor 1 (IGF1), Growth Hormone (GH), amino acid (AA), β-hydroxy-β methyl butyrate (HMB), maple syrup urine disease (MSUD), non-communicable diseases (NCDs).

Receptor-Mediated and Receptor-Independent Actions of Melatonin in Vertebrates

Melatonin (N-acetyl-5-methoxytryptamine) is an indolamine that is synthesized from tryptophan in the pineal glands of vertebrates through four enzymatic reactions. Melatonin is a quite unique bioactive substance, characterized by a combination of both receptor-mediated and receptor-independent actions, which promote the diverse effects of melatonin. One of the main functions of melatonin, via its membrane receptors, is to regulate the circadian or seasonal rhythm. In mammals, light information, which controls melatonin synthesis, is received in the eye, and transmitted to the pineal gland, via the suprachiasmatic nucleus, where the central clock is located. Alternatively, in many vertebrates other than mammals, the pineal gland cells, which are involved in melatonin synthesis and secretion and in the circadian clock, directly receive light. Recently, it has been reported that melatonin possesses several metabolic functions, which involve bone and glucose, in addition to regulating the circadian rhythm. Melatonin improves bone strength by inhibiting osteoclast activity. It is also known to maintain brain activity during sleep by increasing glucose uptake at night, in an insulin-independent manner. Moreover, as a non-receptor-mediated action, melatonin has antioxidant properties. Melatonin has been proven to be a potent free radical scavenger and a broad-spectrum antioxidant, even protecting organisms against radiation from space. Melatonin is a ubiquitously distributed molecule and is found in bacteria, unicellular organisms, fungi, and plants. It is hypothesized that melatonin initially functioned as an antioxidant, then, in vertebrates, it combined this role with the ability to regulate rhythm and metabolism, via its receptors.

Adjuvant pharmacological strategies for the musculoskeletal system during long-term space missions

Despite 2 h of daily exercise training, muscle wasting and bone loss are still present after 6-month missions to the international space station. Some crew members lose bone much faster than others. In preparation for missions to the Moon and Mars, space agencies are therefore reviewing their countermeasure portfolios. Here, we discuss the potential of current pharmacological strategies. Bone loss in space is fuelled by bone resorption. Alendronate, an oral bisphosphonate, reduced bone losses in experimental bed rest and space. However, gastrointestinal side effects precluded its further utilization in space. Zoledronate (a potent bisphosphonate), denosumab (RANKL antagonist) and romosozumab (sclerostin antagonist) are all administered via injection. They effectively suppress bone resorption and are routinely prescribed against osteoporosis. Their serious adverse effects, namely, osteonecrosis of the jaw and atypical femur fractures occur very rarely when the usage is limited to 1 or 2 years. Hence, utilization of one of these compounds may outweigh the bone risks of space travelling, in particular in those with high bone resorption rates. Muscle wasting in space is likely due to hampered muscle protein synthesis. Even though this might theoretically be countered by the synthesis-boosting effects of anabolic steroids, the practical grounds for such recommendation are currently weak. Moreover, they reveal their full potential only when combined with an anabolic exercise stimulus, for example, via strength training. It therefore seems that a combination of exercise and pharmacological countermeasures should be considered for musculoskeletal health on the way to the Moon and Mars and back.

Time-resolved molecular measurements reveal changes in astronauts during spaceflight

From the early days of spaceflight to current missions, astronauts continue to be exposed to multiple hazards that affect human health, including low gravity, high radiation, isolation during long-duration missions, a closed environment and distance from Earth. Their effects can lead to adverse physiological changes and necessitate countermeasure development and/or longitudinal monitoring. A time-resolved analysis of biological signals can detect and better characterize potential adverse events during spaceflight, ideally preventing them and maintaining astronauts' wellness. Here we provide a time-resolved assessment of the impact of spaceflight on multiple astronauts (n = 27) by studying multiple biochemical and immune measurements before, during, and after long-duration orbital spaceflight. We reveal space-associated changes of astronauts' physiology on both the individual level and across astronauts, including associations with bone resorption and kidney function, as well as immune-system dysregulation.

Long-term human spaceflight and inflammaging: Does it promote aging?

Spaceflight and its associated stressors, such as microgravity, radiation exposure, confinement, circadian derailment and disruptive workloads represent an unprecedented type of exposome that is entirely novel from an evolutionary stand point. Within this perspective, we aimed to review the effects of prolonged spaceflight on immune-neuroendocrine systems, brain and brain-gut axis, cardiovascular system and musculoskeletal apparatus, highlighting in particular the similarities with an accelerated aging process. In particular, spaceflight-induced muscle atrophy/sarcopenia and bone loss, vascular and metabolic changes, hyper and hypo reaction of innate and adaptive immune system appear to be modifications shared with the aging process. Most of these modifications are mediated by molecular events that include oxidative and mitochondrial stress, autophagy, DNA damage repair and telomere length alteration, among others, which directly or indirectly converge on the activation of an inflammatory response. According to the inflammaging theory of aging, such an inflammatory response could be a driver of an acceleration of the normal, physiological rate of aging and it is likely that all the systemic modifications in turn lead to an increase of inflammaging in a sort of vicious cycle. The most updated countermeasures to fight these modifications will be also discussed in the light of their possible application not only for astronauts' benefit, but also for older adults on the ground.

Physiological consequences of space flight, including abnormal bone metabolism, space radiation injury, and circadian clock dysregulation: Implications of melatonin use and regulation as a countermeasure

Exposure to the space environment induces a number of pathophysiological outcomes in astronauts, including bone demineralization, sleep disorders, circadian clock dysregulation, cardiovascular and metabolic dysfunction, and reduced immune system function. A recent report describing experiments aboard the Space Shuttle mission, STS-132, showed that the level of melatonin, a hormone that provides the biochemical signal of darkness, was decreased during microgravity in an in vitro culture model. Additionally, abnormal lighting conditions in outer space, such as low light intensity in orbital spacecraft and the altered 24-h light-dark cycles, may result in the dysregulation of melatonin rhythms and the misalignment of the circadian clock from sleep and work schedules in astronauts. Studies on Earth have demonstrated that melatonin regulates various physiological functions including bone metabolism. These data suggest that the abnormal regulation of melatonin in outer space may contribute to pathophysiological conditions of astronauts. In addition, experiments with high-linear energy transfer radiation, a ground-based model of space radiation, showed that melatonin may serve as a protectant against space radiation. Gene expression profiling using an in vitro culture model exposed to space flight during the STS-132 mission, showed that space radiation alters the expression of DNA repair and oxidative stress response genes, indicating that melatonin counteracts the expression of these genes responsive to space radiation to promote cell survival. These findings implicate the use of exogenous melatonin and the regulation of endogenous melatonin as countermeasures for the physiological consequences of space flight.

Microgravity-Related Changes in Bone Density and Treatment Options: A Systematic Review

Space travelers are exposed to microgravity (µg), which induces enhanced bone loss compared to the age-related bone loss on Earth. Microgravity promotes an increased bone turnover, and this obstructs space exploration. This bone loss can be slowed down by exercise on treadmills or resistive apparatus. The objective of this systematic review is to provide a current overview of the state of the art of the field of bone loss in space and possible treatment options thereof. A total of 482 unique studies were searched through PubMed and Scopus, and 37 studies met the eligibility criteria. The studies showed that, despite increased bone formation during µg, the increase in bone resorption was greater. Different types of exercise and pharmacological treatments with bisphosphonates, RANKL antibody (receptor activator of nuclear factor κβ ligand antibody), proteasome inhibitor, pan-caspase inhibitor, and interleukin-6 monoclonal antibody decrease bone resorption and promote bone formation. Additionally, recombinant irisin, cell-free fat extract, cyclic mechanical stretch-treated bone mesenchymal stem cell-derived exosomes, and strontium-containing hydroxyapatite nanoparticles also show some positive effects on bone loss.

The effects of microgravity on bone structure and function

Humans are spending an increasing amount of time in space, where exposure to conditions of microgravity causes 1–2% bone loss per month in astronauts. Through data collected from astronauts, as well as animal and cellular experiments conducted in space, it is evident that microgravity induces skeletal deconditioning in weight-bearing bones. This review identifies contentions in current literature describing the effect of microgravity on non-weight-bearing bones, different bone compartments, as well as the skeletal recovery process in human and animal spaceflight data. Experiments in space are not readily available, and experimental designs are often limited due to logistical and technical reasons. This review introduces a plethora of on-ground research that elucidate the intricate process of bone loss, utilising technology that simulates microgravity. Observations from these studies are largely congruent to data obtained from spaceflight experiments, while offering more insights behind the molecular mechanisms leading to microgravity-induced bone loss. These insights are discussed herein, as well as how that knowledge has contributed to studies of current therapeutic agents. This review also points out discrepancies in existing data, highlighting knowledge gaps in our current understanding. Further dissection of the exact mechanisms of microgravity-induced bone loss will enable the development of more effective preventative and therapeutic measures to protect against bone loss, both in space and possibly on ground.

Understanding the Complexities and Changes of the Astronaut Microbiome for Successful Long-Duration Space Missions

During space missions, astronauts are faced with a variety of challenges that are unique to spaceflight and that have been known to cause physiological changes in humans over a period of time. Several of these changes occur at the microbiome level, a complex ensemble of microbial communities residing in various anatomic sites of the human body, with a pivotal role in regulating the health and behavior of the host. The microbiome is essential for day-to-day physiological activities, and alterations in microbiome composition and function have been linked to various human diseases. For these reasons, understanding the impact of spaceflight and space conditions on the microbiome of astronauts is important to assess significant health risks that can emerge during long-term missions and to develop countermeasures. Here, we review various conditions that are caused by long-term space exploration and discuss the role of the microbiome in promoting or ameliorating these conditions, as well as space-related factors that impact microbiome composition. The topics explored pertain to microgravity, radiation, immunity, bone health, cognitive function, gender differences and pharmacomicrobiomics. Connections are made between the trifecta of spaceflight, the host and the microbiome, and the significance of these interactions for successful long-term space missions.

Dissociation of Bone Resorption and Formation in Spaceflight and Simulated Microgravity: Potential Role of Myokines and Osteokines?

The dissociation of bone formation and resorption is an important physiological process during spaceflight. It also occurs during local skeletal unloading or immobilization, such as in people with neuromuscular disorders or those who are on bed rest. Under these conditions, the physiological systems of the human body are perturbed down to the cellular level. Through the absence of mechanical stimuli, the musculoskeletal system and, predominantly, the postural skeletal muscles are largely affected. Despite in-flight exercise countermeasures, muscle wasting and bone loss occur, which are associated with spaceflight duration. Nevertheless, countermeasures can be effective, especially by preventing muscle wasting to rescue both postural and dynamic as well as muscle performance. Thus far, it is largely unknown how changes in bone microarchitecture evolve over the long term in the absence of a gravity vector and whether bone loss incurred in space or following the return to the Earth fully recovers or partly persists. In this review, we highlight the different mechanisms and factors that regulate the humoral crosstalk between the muscle and the bone. Further we focus on the interplay between currently known myokines and osteokines and their mutual regulation.

Simulated Microgravity Remodels Extracellular Matrix of Osteocommitted Mesenchymal Stromal Cells

The extracellular matrix (ECM) is the principal structure of bone tissue. Long-term spaceflights lead to osteopenia, which may be a result of the changes in composition as well as remodeling of the ECM by osteogenic cells. To elucidate the cellular effects of microgravity, human mesenchymal stromal cells (MSCs) and their osteocommitted progeny were exposed to simulated microgravity (SMG) for 10 days using random positioning machine (RPM). After RPM exposure, an imbalance of MSC collagen/non-collagen ratio at the expense of a decreased level of collagenous proteins was detected. At the same time, the secretion of proteases (cathepsin A, cathepsin D, MMP3) was increased. No significant effects of SMG on the expression of stromal markers and cell adhesion molecules on the MSC surface were noted. Upregulation of COL11A1, CTNND1, TIMP3, and TNC and downregulation of HAS1, ITGA3, ITGB1, LAMA3, MMP1, and MMP11 were detected in RPM exposed MSCs. ECM-associated transcriptomic changes were more pronounced in osteocommitted progeny. Thus, 10 days of SMG provokes a decrease in the collagenous components of ECM, probably due to the decrease in collagen synthesis and activation of proteases. The presented data demonstrate that ECM-associated molecules of both native and osteocommitted MSCs may be involved in bone matrix reorganization during spaceflight.

Undercarboxylated osteocalcin inhibits the early differentiation of osteoclast mediated by Gprc6a

Osteocalcin (OCN) was the most abundant noncollagen protein and considered as an endocrine factor. However, the functions of Undercarboxylated osteocalcin (ucOCN) on osteoclast and bone resorption are not well understood. In the present study, preosteoclast RAW264.7 cells and bone marrow mononuclear cells (BMMs) were treated with ucOCN purified from prokaryotic bacteria. Our results showed that ucOCN attenuated the proliferation of RAW264.7 cells with a concentration dependant manner by MTS assay. Scrape wounding assay revealed the decreased motility of RAW264.7 cells after ucOCN treatment. RT-qPCR results manifested the inhibitory effects of ucOCN on the expression of osteoclastic marker genes in RAW264.7 cells during inducing differentiation of RANKL. It was also observed that ucOCN inhibited the formation of multinucleated cells from RAW264.7 cells and BMMs detected by TRAP staining. The number and area of bone resorb pits were also decreased after treatment with ucOCN during their osteoclast induction by toluidine blue staining. The formation and integrity of the osteoclast actin ring were impaired by ucOCN by immunofluorescent staining. Time dependant treatment of ucOCN during osteoclastic induction demonstrated the inhibitory effects mainly occurred at the early stage of osteoclastogenesis. Signaling analysis of luciferase activity of the CRE or SRE reporter and ERK1/2 phosphorylation showed the selective inhibitor or siRNA of Gprc6a (a presumptive ucOCN receptor) could attenuate the promotion of ucOCN on CRE-luciferase activity. Taken together, we provided the first evidence that ucOCN had negative effects on the early differentiation and bone resorption of osteoclasts via Gprc6a.

Population analysis of space travelers

Although many space missions have been completed in the last 60 years, space exploration is still technologically and medically challenging. While large-scale medical studies are impossible in space travelers, meta-analysis allows combining data from small crews that participated in space missions over several decades. Our primary objective was to examine space-travelers' sociodemographic characteristics and spaceflight activities, and their changes with time from the first spaceflight. Our secondary objective was to evaluate the publication practices to assess data availability for health-related meta-analytic studies. Based on state-funded space agencies used as primary sources, and third-party websites used as secondary sources, 565 humans (501 males/64 females) have currently completed spaceflight. The average age of space-travelers increased from 34±4 in the 1960s to 45±4 in the 2010s. While the duration of space missions has increased consistently, the number of missions per year varied in correlation with technological events. Using papers identified in the systematic review of bone health in astronauts, we examined the changes in reporting practices with time. The reported sample size varied from 1 to 58 people, in total providing data for 148 individuals. Data confidentiality significantly improved with time; however, the corresponding decrease in the availability of individual parameters did not allow stratification even by age, sex, and mission duration. Thus, space travelers represent a diverse population suitable for comparative studies, however, it is important to develop reporting practices that ensure consistent, transparent, and ethical presentation of outcomes to support meta-analyses that are critical for understanding the scope of spaceflight-induced health issues.

Nutritional interventions during bed rest and spaceflight: prevention of muscle mass and strength loss, bone resorption, glucose intolerance, and cardiovascular problems

Bed rest is necessary for many medical conditions but also used as a ground-based model for space flight (along with head-down tilt to simulate fluid shifts in microgravity). The purpose of this review is to examine nutritional interventions during bed rest and spaceflight for prevention of muscle and strength loss, glucose intolerance, bone resorption, and cardiovascular problems. Increased dietary protein intake and supplementation with amino acids, β-hydroxy-β-methylbutyrate, or cofactors with antioxidant properties are effective for ameliorating bed rest-induced loss of muscle mass and strength. Previous literature involving bed rest with dietary protein/amino acid supplementation had mixed findings, likely due to differences in dosage. Although high protein intake in some studies prevents bed rest-induced muscle loss, it also increases bone resorption. High calcium intake and vitamin D supplementation are not beneficial for preventing bone degradation during bed rest or spaceflight. Very few studies investigated countermeasures to prevent glucose intolerance and cardiovascular risks during bed rest/spaceflight. Low-glycemic index diets might be beneficial for the prevention of bed rest-induced glucose intolerance and cardiovascular problems. The present evidence warrants additional studies on the exact threshold of protein/amino acid intake to prevent the loss of muscle mass and strength during bed rest/spaceflight specifically to maintain the beneficial effects of proteins on muscle mass and function without increasing bone resorption. Furthermore, it is suggested to study the effects of vitamin K supplementation on bone health during bed rest/spaceflight and determine the role of long-term low-glycemic index diets on glucose regulation and cardiovascular health during extended bed rest.

A systematic review and meta-analysis of bone loss in space travelers

Bone loss in space travelers is a major challenge for long-duration space exploration. To quantify microgravity-induced bone loss in humans, we performed a meta-analysis of studies systematically identified from searching Medline, Embase, Web of Science, BIOSIS, NASA Technical reports, and HathiTrust, with the last update in November 2019. From 25 articles selected to minimize the overlap between reported populations, we extracted post-flight bone density values for 148 individuals, and in-flight and post-flight biochemical bone marker values for 124 individuals. A percentage difference in bone density relative to pre-flight was positive in the skull, +2.2% [95% confidence interval: +1.1, +3.3]; neutral in the thorax/upper limbs, −0.7% [−1.3, −0.2]; and negative in the lumbar spine/pelvis, −6.2 [−6.7, −5.6], and lower limbs, −5.4% [−6.0, −4.9]. In the lower limb region, the rate of bone loss was −0.8% [−1.1, −0.5] per month. Bone resorption markers increased hyperbolically with a time to half-max of 11 days [9, 13] and plateaued at 113% [108, 117] above pre-flight levels. Bone formation markers remained unchanged during the first 30 days and increased thereafter at 7% [5, 10] per month. Upon landing, resorption markers decreased to pre-flight levels at an exponential rate that was faster after longer flights, while formation markers increased linearly at 84% [39, 129] per month for 3–5 months post-flight. Microgravity-induced bone changes depend on the skeletal-site position relative to the gravitational vector. Post-flight recovery depends on spaceflight duration and is limited to a short post-flight period during which bone formation exceeds resorption.

Melatonin is a potential drug for the prevention of bone loss during space flight

Astronauts experience osteoporosis-like loss of bone mass because of microgravity conditions during space flight. To prevent bone loss, they need a riskless and antiresorptive drug. Melatonin is reported to suppress osteoclast function. However, no studies have examined the effects of melatonin on bone metabolism under microgravity conditions. We used goldfish scales as a bone model of coexisting osteoclasts and osteoblasts and demonstrated that mRNA expression level of acetylserotonin O-methyltransferase, an enzyme essential for melatonin synthesis, decreased significantly under microgravity. During space flight, microgravity stimulated osteoclastic activity and significantly increased gene expression for osteoclast differentiation and activation. Melatonin treatment significantly stimulated Calcitonin (an osteoclast-inhibiting hormone) mRNA expression and decreased the mRNA expression of receptor activator of nuclear factor κB ligand (a promoter of osteoclastogenesis), which coincided with suppressed gene expression levels for osteoclast functions. This is the first study to report the inhibitory effect of melatonin on osteoclastic activation by microgravity. We also observed a novel action pathway of melatonin on osteoclasts via an increase in CALCITONIN secretion. Melatonin could be the source of a potential novel drug to prevent bone loss during space flight.

The LunHab project: Muscle and bone alterations in male participants following a 10 day lunar habitat simulation

NEW FINDINGS

What is the central question of this study? It is well established that muscle and bone atrophy in conditions of inactivity or unloading, but there is little information regarding the effect of a hypoxic environment on the time course of these deconditioning physiological systems. What is the main finding and its importance? The main finding is that a horizontal 10 day bed rest in normoxia results in typical muscle atrophy, which is not aggravated by hypoxia. Changes in bone mineral content or in metabolism were not detected after either normoxic or hypoxic bed rest.

ABSTRACT

Musculoskeletal atrophy constitutes a typical adaptation to inactivity and unloading of weightbearing bones. The reduced-gravity environment in future Moon and Mars habitats is likely to be hypobaric hypoxic, and there is an urgent need to understand the effect of hypoxia on the process of inactivity-induced musculoskeletal atrophy. This was the principal aim of the present study. Eleven males participated in three 10 day interventions: (i) hypoxic ambulatory confinement; (ii) hypoxic bed rest; and (iii) normoxic bed rest. Before and after the interventions, the muscle strength (isometric maximal voluntary contraction), mass (lean mass, by dual-energy X-ray absorptiometry), cross-sectional area and total bone mineral content (determined with peripheral quantitative computed tomography) of the participants were measured. Blood and urine samples were collected before and on the 1st, 4th and 10th day of the intervention and analysed for biomarkers of bone resorption and formation. There was a significant reduction in thigh and lower leg muscle mass and volume after both normoxic and hypoxic bed rests. Muscle strength loss was proportionately greater than the loss in muscle mass for both thigh and lower leg. There was no indication of bone loss. Furthermore, the biomarkers of resorption and formation were not affected by any of the interventions. There was no significant effect of hypoxia on the musculoskeletal variables. Short-term normoxic (10 day) bed rest resulted in muscular deconditioning, but not in the loss of bone mineral content or changes in bone metabolism. Hypoxia did not modify these results.

Sarcopenic obesity in older adults: aetiology, epidemiology and treatment strategies

The prevalence of obesity in combination with sarcopenia (the age-related loss of muscle mass and strength or physical function) is increasing in adults aged 65 years and older. A major subset of adults over the age of 65 is now classified as having sarcopenic obesity, a high-risk geriatric syndrome predominantly observed in an ageing population that is at risk of synergistic complications from both sarcopenia and obesity. This Review discusses pathways and mechanisms leading to muscle impairment in older adults with obesity. We explore sex-specific hormonal changes, inflammatory pathways and myocellular mechanisms leading to the development of sarcopenic obesity. We discuss the evolution, controversies and challenges in defining sarcopenic obesity and present current body composition modalities used to assess this condition. Epidemiological surveys form the basis of defining its prevalence and consequences beyond comorbidity and mortality. Current treatment strategies, and the evidence supporting them, are outlined, with a focus on calorie restriction, protein supplementation and aerobic and resistance exercises. We also describe weight loss-induced complications in patients with sarcopenic obesity that are relevant to clinical management. Finally, we review novel and potential future therapies including testosterone, selective androgen receptor modulators, myostatin inhibitors, ghrelin analogues, vitamin K and mesenchymal stem cell therapy.

Cortical and Trabecular Bone Microstructure Did Not Recover at Weight-Bearing Skeletal Sites and Progressively Deteriorated at Non-Weight-Bearing Sites During the Year Following International Space Station Missions

Risk for premature osteoporosis is a major health concern in astronauts and cosmonauts; the reversibility of the bone lost at the weight-bearing bone sites is not established, although it is suspected to take longer than the mission length. The bone three-dimensional structure and strength that could be uniquely affected by weightlessness is currently unknown. Our objective is to evaluate bone mass, microarchitecture, and strength of weight-bearing and non-weight-bearing bone in 13 cosmonauts before and for 12 months after a 4-month to 6-month sojourn in the International Space Station (ISS). Standard and advanced evaluations of trabecular and cortical parameters were performed using high-resolution peripheral quantitative computed tomography. In particular, cortical analyses involved determination of the largest common volume of each successive individual scan to improve the precision of cortical porosity and density measurements. Bone resorption and formation serum markers, and markers reflecting osteocyte activity or periosteal metabolism (sclerostin, periostin) were evaluated. At the tibia, in addition to decreased bone mineral densities at cortical and trabecular compartments, a 4% decrease in cortical thickness and a 15% increase in cortical porosity were observed at landing. Cortical size and density subsequently recovered and serum periostin changes were associated with cortical recovery during the year after landing. However, tibial cortical porosity or trabecular bone failed to recover, resulting in compromised strength. The radius, preserved at landing, unexpectedly developed postflight fragility, from 3 months post-landing onward, particularly in its cortical structure. Remodeling markers, uncoupled in favor of bone resorption at landing, returned to preflight values within 6 months, then declined farther to lower than preflight values. Our findings highlight the need for specific protective measures not only during, but also after spaceflight, because of continuing uncertainties regarding skeletal recovery long after landing. © 2017 American Society for Bone and Mineral Research.

One-month spaceflight compromises the bone microstructure, tissue-level mechanical properties, osteocyte survival and lacunae volume in mature mice skeletons

The weightless environment during spaceflight induces site-specific bone loss. The 30-day Bion-M1 mission offered a unique opportunity to characterize the skeletal changes after spaceflight and an 8-day recovery period in mature male C57/BL6 mice. In the femur metaphysis, spaceflight decreased the trabecular bone volume (−64% vs. Habitat Control), dramatically increased the bone resorption (+140% vs. Habitat Control) and induced marrow adiposity invasion. At the diaphysis, cortical thinning associated with periosteal resorption was observed. In the Flight animal group, the osteocyte lacunae displayed a reduced volume and a more spherical shape (synchrotron radiation analyses), and empty lacunae were highly increased (+344% vs. Habitat Control). Tissue-level mechanical cortical properties (i.e., hardness and modulus) were locally decreased by spaceflight, whereas the mineral characteristics and collagen maturity were unaffected. In the vertebrae, spaceflight decreased the overall bone volume and altered the modulus in the periphery of the trabecular struts. Despite normalized osteoclastic activity and an increased osteoblast number, bone recovery was not observed 8 days after landing. In conclusion, spaceflight induces osteocyte death, which may trigger bone resorption and result in bone mass and microstructural deterioration. Moreover, osteocyte cell death, lacunae mineralization and fatty marrow, which are hallmarks of ageing, may impede tissue maintenance and repair.

Bone Health and Osteoporosis: The Role of Vitamin K and Potential Antagonism by Anticoagulants

BACKGROUND

Vitamin K's effects extend beyond blood clotting to include a role in bone metabolism and potential protection against osteoporosis. Vitamin K is required for the gamma-carboxylation of osteocalcin. Likewise, this gamma-carboxylation also occurs in the liver for several coagulation proteins. This mechanism is interrupted by coumarin-based anticoagulants in both the liver and bone.

METHODS

A thorough review of the literature on vitamin K, osteocalcin and their role in bone metabolism and osteoporosis, as well as the potential bone effects of anticoagulant therapy was conducted.

CONCLUSIONS

Epidemiological studies and clinical trials consistently indicate that vitamin K has a positive effect on bone mineral density and decreases fracture risk. Typical dietary intakes of vitamin K are below the levels associated with better BMD and reduced fracture risk; thus issues of increasing dietary intakes, supplementation, and/or fortification arise. To effectively address these issues, large-scale, intervention trials of vitamin K are needed. The effects of coumarin-based anticoagulants on bone health are more ambiguous, with retrospective studies suggesting that long-term therapy adversely affects vertebral BMD and fracture risk. Anticoagulants that do not affect vitamin K metabolism are now available and make clinical trials feasible to answer the question of whether coumarins adversely affect bone. The research suggests that at a minimum, clinicians should carefully assess anticoagulated patients for osteoporosis risk, monitor BMD, and refer them to dietitians for dietary and supplement advice on bone health. Further research is needed to make more efficacious decisions about vitamin K intake, anticoagulant therapy, and bone health.

Effects of microgravity simulation on zebrafish transcriptomes and bone physiology-exposure starting at 5 days post fertilization

Physiological modifications in near weightlessness, as experienced by astronauts during space flight, have been the subject of numerous studies. Various animal models have been used on space missions or in microgravity simulation on ground to understand the effects of gravity on living animals. Here, we used the zebrafish larvae as a model to study the effect of microgravity simulation on bone formation and whole genome gene expression. To simulate microgravity (sim-μg), we used two-dimensional (2D) clinorotation starting at 5 days post fertilization to assess skeletal formation after 5 days of treatment. To assess early, regulatory effects on gene expression, a single day clinorotation was performed. Clinorotation for 5 days caused a significant decrease of bone formation, as shown by staining for cartilage and bone structures. This effect was not due to stress, as assessed by measuring cortisol levels in treated larvae. Gene expression results indicate that 1-day simulated microgravity affected musculoskeletal, cardiovascular, and nuclear receptor systems. With free-swimming model organisms such as zebrafish larvae, the 2D clinorotation setup appears to be a very appropriate approach to sim-μg. We provide evidence for alterations in bone formation and other important biological functions; in addition several affected genes and pathways involved in bone, muscle or cardiovascular development are identified.

Microgravity Stress: Bone and Connective Tissue

The major alterations in bone and the dense connective tissues in humans and animals exposed to microgravity illustrate the dependency of these tissues' function on normal gravitational loading. Whether these alterations depend solely on the reduced mechanical loading of zero g or are compounded by fluid shifts, altered tissue blood flow, radiation exposure, and altered nutritional status is not yet well defined. Changes in the dense connective tissues and intervertebral disks are generally smaller in magnitude but occur more rapidly than those in mineralized bone with transitions to 0 g and during recovery once back to the loading provided by 1 g conditions. However, joint injuries are projected to occur much more often than the more catastrophic bone fracture during exploration class missions, so protecting the integrity of both tissues is important. This review focuses on the research performed over the last 20 years in humans and animals exposed to actual spaceflight, as well as on knowledge gained from pertinent ground-based models such as bed rest in humans and hindlimb unloading in rodents. Significant progress has been made in our understanding of the mechanisms for alterations in bone and connective tissues with exposure to microgravity, but intriguing questions remain to be solved, particularly with reference to biomedical risks associated with prolonged exploration missions.

Effects of 60-day head-down bed rest on osteocalcin, glycolipid metabolism and their association with or without resistance training

INTRODUCTION

Bone loss and subclinical diabeteslike are developed during long-term spaceflight. Recently, it was demonstrated that bone was able to regulate energy metabolism and testosterone synthesis via osteocalcin. The aim of this study was to determine whether serum osteocalcin level is associated with glycolipid metabolism or testosterone under the influence of microgravity with or without resistive vibration exercise (RVE).

METHODS

A total of 14 healthy adult male volunteers (25-40 years) were randomly assigned to two groups (n = 7 each): control (CON) group and RVE group. Radioimmunoassay kits and ELISA kits were used for measurement of serum indices.

RESULTS

During 60-day bed rest, serum osteocalcin of both groups increased at day 4 during bed rest. Serum OPG started decreasing and reached its lowest value at day 30 during bed rest. In control group, serum insulin increased at day 4 during bed rest. IGF-I did not change significantly during the entire period of bed rest. The serum glucose decline 10% and 14% in CON and RVE groups at day 4 during bed rest. Relatively, the same results as glucose were found in serum HDL and LDL for both groups. Leptin rose and became highest at day 60 during bed rest in both groups. The level of serum testosterone was declined in control group at day 4 during bed rest. Cortisol kept stable in both group during bed rest. By spearman correlation analysis, serum osteocalcin was significantly associated with serum insulin (P < 0·05), LDL (P < 0·01) and Leptin (P < 0·01).

CONCLUSION

Our findings suggested that the mutual regulation may exist between skeletal and energy metabolism under simulated microgravity.

Pulsed electromagnetic fields partially preserve bone mass, microarchitecture, and strength by promoting bone formation in hindlimb-suspended rats

A large body of evidence indicates that pulsed electromagnetic fields (PEMF), as a safe and noninvasive method, could promote in vivo and in vitro osteogenesis. Thus far, the effects and underlying mechanisms of PEMF on disuse osteopenia and/or osteoporosis remain poorly understood. Herein, the efficiency of PEMF on osteoporotic bone microarchitecture, bone strength, and bone metabolism, together with its associated signaling pathway mechanism, was systematically investigated in hindlimb-unloaded (HU) rats. Thirty young mature (3-month-old), male Sprague-Dawley rats were equally assigned to control, HU, and HU + PEMF groups. The HU + PEMF group was subjected to daily 2-hour PEMF exposure at 15 Hz, 2.4 mT. After 4 weeks, micro-computed tomography (µCT) results showed that PEMF ameliorated the deterioration of trabecular and cortical bone microarchitecture. Three-point bending test showed that PEMF mitigated HU-induced reduction in femoral mechanical properties, including maximum load, stiffness, and elastic modulus. Moreover, PEMF increased serum bone formation markers, including osteocalcin (OC) and N-terminal propeptide of type 1 procollagen (P1NP); nevertheless, PEMF exerted minor inhibitory effects on bone resorption markers, including C-terminal crosslinked telopeptides of type I collagen (CTX-I) and tartrate-resistant acid phosphatase 5b (TRAcP5b). Bone histomorphometric analysis demonstrated that PEMF increased mineral apposition rate, bone formation rate, and osteoblast numbers in cancellous bone, but PEMF caused no obvious changes on osteoclast numbers. Real-time PCR showed that PEMF promoted tibial gene expressions of Wnt1, LRP5, β-catenin, OPG, and OC, but did not alter RANKL, RANK, or Sost mRNA levels. Moreover, the inhibitory effects of PEMF on disuse-induced osteopenia were further confirmed in 8-month-old mature adult HU rats. Together, these results demonstrate that PEMF alleviated disuse-induced bone loss by promoting skeletal anabolic activities, and imply that PEMF might become a potential biophysical treatment modality for disuse osteoporosis.

Effects of Vitamin D and Calcium Supplementation on Micro-architectural and Densitometric Changes of Rat Femur in a Microgravity Simulator Model

Background:

Revealing data on the role of vitamin D and calcium supplementation in bone health has led some to suggest that vitamin D and calcium treatment could also play a role in protecting bone against microgravity-induced mineral loss.

Objectives:

The aim of the present study was to investigate the effects of vitamin D and calcium administration on microscopic and densitometric changes of rat femur in a Microgravity Simulator Model.

Materials and Methods:

After designing a Microgravity Simulator Model, 14 rats were placed in the cages as follows: seven rats as osteoporosis group and seven rats received oral supplement of calcium/vitamin D as the treatment group. Animals were sacrificed after eight weeks and then both femurs were removed. Bone mineral density was measured for one femur from each animal, and morphologic studies were evaluated for the contralateral femur.

Results:

Bone mineral density of the whole femur in the treatment group was significantly higher than the osteoporosis group (0.168 ± 0.005 vs. 0.153 ± 0.006, P = 0.003). Also, bone mineral content of the whole femur was significantly higher in treatment group (0.415 ± 0.016 vs. 0.372 ± 0.019, P = 0.003). However, resorption eroded surface percentage was higher in the osteoporosis group (18.86 ± 3.71% vs. 9.71 ± 1.61%, P = 0.002).

Conclusions:

According to the results of this study, vitamin D and calcium administration might have protective effects against microgravity-induced mineral loss in a Rat Microgravity Simulator Model.

Large gradient high magnetic fields affect osteoblast ultrastructure and function by disrupting collagen I or fibronectin/αβ1 integrin

The superconducting magnet generates a field and field gradient product that can levitate diamagnetic materials. In this study a specially designed superconducting magnet with a large gradient high magnetic field (LG-HMF), which can provide three apparent gravity levels (μ-g, 1-g, and 2-g), was used to simulate a space-like gravity environment. The effects of LG-HMF on the ultrastructure and function of osteoblast-like cells (MG-63 and MC3T3-E1) and the underlying mechanism were investigated by transmission electromicroscopy (TEM), MTT, and cell western (ICW) assays. Under LG-HMF significant morphologic changes in osteoblast-like cells occurred, including expansion of endoplasmic reticulum and mitochondria, an increased number of lysosomes, distorted microvilli, and aggregates of actin filaments. Compared to controls, cell viability and alkaline phosphatase (ALP) secretion were significantly increased, and collagen I (col I), fibronectin (FN), vinculin, integrin α3, αv, and β1 expression were changed under LG-HMF conditions. In conclusion, LG-HMF affects osteoblast ultrastructure, cell viability, and ALP secretion, and the changes caused by LG-HMF may be related to disrupting col I or FN/αβ1 integrin.

Prevention of disuse osteoporosis in rats by Cordyceps sinensis extract

Cordyceps sinensis has been known as a traditional medicine in China, and C. sinensis plus strontium could prevent osteoporosis in ovariectomized rats. The present study shows that daily oral administration of C. sinensis at higher doses in adult hind limb suspension rats can prevent disuse-induced bone loss and deterioration of trabecular microarchitecture.

INTRODUCTION

Cordyceps sinensis induces estradiol production and prevents osteoporosis in ovariectomized rats. This study was to examine whether C. sinensis can prevent disuse-induced osteoporosis.

METHODS

Rats were randomly divided into six groups, and five groups were treated with hind limb suspension (HLS). One HLS group received alendronate (2.0 mg/kg/day) orally, and to the three other HLS groups to each group, a different amount of C. sinensis (100, 300, and 500 mg/kg/day) was orally administered for 8 weeks before and after HLS. The remaining HLS group was set as a control without treatment. Each group consisted of 10 males and females. The body weights, biochemical parameters in serum and urine, bone mineral density (BMD), bone mineral content (BMC), mechanical testing, and bone microarchitecture were examined.

RESULTS

Treatments with higher C. sinensis dosage (300 and 500 mg/kg/day) or alendronate had a positive effect on body weights, mechanical strength, BMD, and BMC compared to the other HLS groups. C. sinensis decreased markers of bone turnover dose dependently and increased the osteocalcin levels in HLS rats. The result of micro-CT analysis from the L4 vertebra showed that C. sinensis (500 mg/kg) significantly prevented the reduction of the bone volume fraction, connectivity density, trabeculae number, and thickness as well as improved the trabeculae separation and structure model index in HLS rats.

CONCLUSIONS

The present study demonstrates that administration of C. sinensis at higher doses over an 8-week period can prevent the disuse osteoporosis in rats. It implies that C. sinensis might be an alternative therapy for prevention of disuse-induced osteoporosis also in humans.

Vitamin K status in spaceflight and ground-based models of spaceflight

Bone loss is a well-documented change during and after long-duration spaceflight. Many types of countermeasures to bone loss have been proposed, including vitamin K supplementation. The objective of this series of studies was to measure change in vitamin K status in response to microgravity under a variety of spaceflight and spaceflight analog (model) conditions, including long-duration spaceflight studies (n = 15), three bed rest studies (n = 15, 49, and 24), and a 14-day saturation dive (n = 6). In crew members who flew 2-6 months on the International Space Station, in-flight and postflight plasma phylloquinone concentrations were unchanged from the preflight mean. Consistent with this finding, urinary γ-carboxyglutamic acid (GLA), a measure of vitamin K-dependent protein turnover, did not change in response to flight. Serum undercarboxylated osteocalcin (%ucOC), a measure of vitamin K function, was generally unchanged in response to flight. Spaceflight findings were corroborated by findings of no changes in phylloquinone, urinary GLA, or %ucOC during or after bed rest in three separate bed rest studies (21-90 days in duration) or after a 14-day saturation dive. The data presented here do not support either a need for vitamin K supplementation during spaceflight or the suggestion of using vitamin K as a bone loss countermeasure in spaceflight.

Four-month treatment with GLP-2 significantly increases hip BMD: a randomized, placebo-controlled, dose-ranging study in postmenopausal women with low BMD

We have previously shown that repeated dosing of glucagon-like peptide-2 (GLP-2) at 10 p.m. in postmenopausal women for 14 days results in a dose-dependent decrease in the nocturnal bone resorption, as assessed by s-CTX. In contrast, bone formation, as assessed by serum osteocalcin, appeared to be unaffected by treatment with exogenous GLP-2, at least over 14 days. The present study extends the observation period to four months. The study was a double-blind placebo-controlled dose-ranging trial comparing three different doses of GLP-2 (0.4 mg, 1.6 mg and 3.2 mg GLP-2, administered nightly) against a saline control injection. We examined safety and tolerability, and the effects on biochemical markers of bone turnover and the effect on bone mineral density. Injection of 0.4 mg, 1.6 mg and 3.2 mg GLP-2 resulted in similar reduction in the nocturnal rise of s-CTX, at Treatment Day 120 the mean difference to placebo was approximately -150%*h at AUC(0-10H) (P<0.01). Osteocalcin levels were unaffected in the 10-hour period after injection indicating that injections of 0.4 mg, 1.6 mg and 3.2 mg GLP-2 do not exert any acute stimulatory or inhibitory effect on bone formation. Treatment with GLP-2 resulted in a significant dose-dependent increase in total hip BMD over the course of the study that for the 3.2 mg GLP-2 group reached 1.1% (P=0.007) from baseline. The overall rates of adverse events in the 4 treatment groups were similar and there were no signs of tachyphylaxis or antibodies against GLP-2. The results indicate that GLP-2 produces a substantial decrease in bone resorption without suppression of bone formation thereby changing the bone remodeling balance in favor of bone formation, particularly at the hip.

Nutritional biochemistry of spaceflight

As we approach the end of the first 50 years of human space travel, much has been learned about adaptation to microgravity and the risks associated with extended-duration space exploration. As the frequency and duration of flights grew, nutrition issues became more critical and the questions to be answered became more complex: What are the nutrient requirements for space travelers? Can nutrients be used as tools to mitigate the negative effects of space travel on humans? How does nutrition interrelate with other physiological systems (such as muscle, bone, and cardiovascular system) and their adaptation to microgravity? Much research has been done over the decades in both actual spaceflight and ground-based analogs. We review here much of what is known, and highlight areas of ongoing research and concerns for future exploration of the Moon, Mars, and beyond.

Black bear femoral geometry and cortical porosity are not adversely affected by ageing despite annual periods of disuse (hibernation)

Disuse (i.e. inactivity) causes bone loss, and a recovery period that is 2-3 times longer than the inactive period is usually required to recover lost bone. However, black bears experience annual disuse (hibernation) and remobilization periods that are approximately equal in length, yet bears maintain or increase cortical bone material properties and whole bone mechanical properties with age. In this study, we investigated the architectural properties of bear femurs to determine whether cortical structure is preserved with age in bears. We showed that cross-sectional geometric properties increase with age, but porosity and resorption cavity density do not change with age in skeletally immature male and female bears. These findings suggest that structural properties substantially contribute to increasing whole bone strength with age in bears, particularly during skeletal maturation. Porosity was not different between skeletally immature and mature bears, and showed minimal regional variations between anatomical quadrants and radial positions that were similar in pattern and magnitude between skeletally immature and mature bears. We also found gender dimorphisms in bear cortical bone properties: females have smaller, less porous bones than males. Our results provide further support for the idea that black bears possess a biological mechanism to prevent disuse osteoporosis.

From space to Earth: advances in human physiology from 20 years of bed rest studies (1986-2006)

Bed rest studies of the past 20 years are reviewed. Head-down bed rest (HDBR) has proved its usefulness as a reliable simulation model for the most physiological effects of spaceflight. As well as continuing to search for better understanding of the physiological changes induced, these studies focused mostly on identifying effective countermeasures with encouraging but limited success. HDBR is characterised by immobilization, inactivity, confinement and elimination of Gz gravitational stimuli, such as posture change and direction, which affect body sensors and responses. These induce upward fluid shift, unloading the body's upright weight, absence of work against gravity, reduced energy requirements and reduction in overall sensory stimulation. The upward fluid shift by acting on central volume receptors induces a 10-15% reduction in plasma volume which leads to a now well-documented set of cardiovascular changes including changes in cardiac performance and baroreflex sensitivity that are identical to those in space. Calcium excretion is increased from the beginning of bed rest leading to a sustained negative calcium balance. Calcium absorption is reduced. Body weight, muscle mass, muscle strength is reduced, as is the resistance of muscle to insulin. Bone density, stiffness of bones of the lower limbs and spinal cord and bone architecture are altered. Circadian rhythms may shift and are dampened. Ways to improve the process of evaluating countermeasures--exercise (aerobic, resistive, vibration), nutritional and pharmacological--are proposed. Artificial gravity requires systematic evaluation. This review points to clinical applications of BR research revealing the crucial role of gravity to health.

Disassociation of bone resorption and formation by GLP-2: a 14-day study in healthy postmenopausal women

We have previously shown that a single subcutaneous injection of glucagon-like peptide-2 (GLP-2) at 10 p.m. in postmenopausal women results in a dose-dependent decrease in the nocturnal serum and urine concentrations of fragments derived from the degradation of the C-terminal telopeptide region of collagen type I (s-CTX and u-CTX) and u-DPD, markers of bone resorption. In contrast, bone formation, as assessed by serum osteocalcin and procollagen type I N-terminal propeptide (PINP), appeared to be unaffected by treatment with exogenous GLP-2. These effects were further investigated in a 14-day study. The aim was to demonstrate that a parenteral formulation of GLP-2 is safe and well tolerated after repeated dosing in healthy postmenopausal women for 14 days. It was further investigated whether the effects on bone turnover markers were sustained throughout the study period. The study was a double-blind placebo-controlled trial with 60 postmenopausal women and 2 different doses of GLP-2 (1.6 mg and 3.2 mg GLP-2) against a saline control. The data for bone resorption revealed a similar reduction on Day 1 and Day 14, both based on time course and AUC. There were no signs of tachyphylaxis and no serious adverse reaction. Both GLP-2 doses resulted in similar and significant (p<0.001) reduction in bone resorption indicating that the maximum efficacious dose has been approached. Osteocalcin and PINP levels were unaffected at Day 1 and Day 14, suggesting a disassociation between bone resorption and bone formation during GLP-2 treatment.

Modeled microgravity stimulates osteoclastogenesis and bone resorption by increasing osteoblast RANKL/OPG ratio

Mechanical unloading causes detrimental effects on the skeleton, but the underlying mechanisms are still unclear. We investigated the effect of microgravity on osteoblast ability to regulate osteoclastogenesis. Mouse osteoblast primary cultures were grown for 24 h at unit gravity or under simulated microgravity, using the NASA-developed Rotating Wall Vessel bioreactor. Conditioned media (CM) from osteoblasts subjected to microgravity increased osteoclastogenesis and bone resorption in mouse bone marrow cultures. In these osteoblasts, the RANKL/OPG ratio was higher relative to 1g. Consistently, treatment with high concentrations of OPG-inhibited osteoclastogenesis and bone resorption in the presence of CM arising from osteoblasts cultured under microgravity. Microgravity failed to affect osteoblast differentiation and function in the time frame of the experiment, as we found no effect on alkaline phosphatase mRNA and activity, nor on Runx2, osteocalcin, osteopontin, and collagen1A2 mRNA expression. In contrast, microgravity induced a time dependent increase of ERK-1/2 phosphorylation, while phospho-p38 and phospho-JNK remained unchanged. Apoptosis, revealed by bis-benzimide staining, was similar among the various gravity conditions, while it was increased under microgravity after treatment with the MEK-1/2 inhibitor, PD98059, suggesting a protection role by ERK-1/2 against cell death. In conclusion, microgravity is capable to indirectly stimulate osteoclast formation and activity by regulating osteoblast secretion of crucial regulatory factors such as RANKL and OPG. We hypothesize that this mechanism could contribute to bone loss in individuals subjected to weightlessness and other unloading conditions.

The circadian rhythm of biochemical markers of bone resorption is normally synchronized in breast cancer patients with bone lytic metastases independently of tumor load

BACKGROUND

Bone metastases are devastating events resulting in disruption of local bone remodeling processes. Physiological bone turnover has a circadian rhythm. No data are available on the circadian pattern of bone turnover markers in patients with bone metastases.

METHODS

Twenty post-menopausal women with breast cancer (BC) at first disease relapse and at least one bone metastasis were consecutively recruited. Twenty healthy women served as controls. Patients were free from concomitant chemotherapy/endocrine therapy. Throughout a 24-h period, urine samples were collected at 4-h intervals, and blood samples were collected at 4-h intervals between 08:00 and 24:00, and at 2-h intervals between 24:00 and 08:00. Serum osteocalcin (OC), total and bone-alkaline phosphatase (tALP and bALP, respectively) and C-terminal telopeptide of type I collagen (CTX), and urinary NTX and free deoxypyridinoline (fDPD) were measured together with serum parathyroid hormone (PTH) and serum and urinary calcium and phosphorus. Temporal variations of measured analytes were assessed by ANOVA and the COSINOR model.

RESULTS

At 08:00, patients had higher levels of bone resorption indices (NTX, CTX and fDPD) than controls (p<0.0001). tALP and bALP, but not OC, were higher in patients than controls (p<0.001). PTH, serum and urinary calcium and urinary phosphorus did not differ between groups; serum phosphorus was higher in controls (p<0.0001). A circadian rhythm was evident for CTX and fDPD values in both patients and controls. A circadian rhythm in NTX, OC, phosphorus and PTH was apparent in controls only. However, it was detected also in patients when percent changes from MESOR were considered. Serum phosphorus showed a circadian rhythm, while no rhythm was detected for tALP, bALP, serum and urinary calcium. The rhythmicities in cancer patients were normally synchronized, and rhythmic parameters were independent of tumor load in the skeleton, age and menopausal status.

CONCLUSIONS

This is the first study to yield information on the maintenance of the temporal program of bone turnover in bone metastatic cancer patients. Whether administration of bisphosphonates in the nighttime leads to a different outcome with respect to the current administration in the morning is a matter of future research.

Immobilization induces a very rapid increase in osteoclast activity

We studied in a randomized, strictly controlled cross-over design, the effects of 6 days 6 degrees head-down tilt bed rest (HDT) in eight male healthy subjects in our metabolic ward. The study consisted of two periods (phases) of 11 days each in order to allow for the test subjects being their own controls. Both study phases were identical with respect to environmental conditions, study protocol and diet. Two days before arriving in the metabolic ward the subjects started with a diet. The diet was continued in the metabolic ward. The metabolic ward period (1l days) was divided into three parts: 4 ambulatory days, 6 days either HDT or control and 1 recovery day. Continuous urine collection started on the first day in the metabolic ward to analyze calcium excretion and bone resorption markers. On the 2nd ambulatory day in the metabolic ward and on the 5th day in HDT or control blood was drawn to analyze serum calcium, parathyroid hormone, and bone formation markers. Urinary calcium excretion was, as early as the first day in immobilization, increased (p<0.01). CTX- and NTX-excretion stayed unchanged in the first 24 h in HDT compared to the control. But already on the 2nd day of immobilization, both bone resorption markers significantly increased. We conclude from these results--pronounced rise of bone resorption markers--that already 24 h of immobilization induce a significant rise in osteoclast activity in healthy subjects. Thus, it appears possible to use short-term bed rest studies as a first step for the development of countermeasures to immobilization.

Physiological, pharmacokinetic, and pharmacodynamic changes in space

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

The nutritional status of astronauts is altered after long-term space flight aboard the International Space Station

Defining optimal nutrient requirements is critical for ensuring crew health during long-duration space exploration missions. Data pertaining to such nutrient requirements are extremely limited. The primary goal of this study was to better understand nutritional changes that occur during long-duration space flight. We examined body composition, bone metabolism, hematology, general blood chemistry, and blood levels of selected vitamins and minerals in 11 astronauts before and after long-duration (128-195 d) space flight aboard the International Space Station. Dietary intake and limited biochemical measures were assessed during flight. Crew members consumed a mean of 80% of their recommended energy intake, and on landing day their body weight was less (P = 0.051) than before flight. Hematocrit, serum iron, ferritin saturation, and transferrin were decreased and serum ferritin was increased after flight (P < 0.05). The finding that other acute-phase proteins were unchanged after flight suggests that the changes in iron metabolism are not likely to be solely a result of an inflammatory response. Urinary 8-hydroxy-2'-deoxyguanosine concentration was greater and RBC superoxide dismutase was less after flight (P < 0.05), indicating increased oxidative damage. Despite vitamin D supplement use during flight, serum 25-hydroxycholecalciferol was decreased after flight (P < 0.01). Bone resorption was increased after flight, as indicated by several markers. Bone formation, assessed by several markers, did not consistently rise 1 d after landing. These data provide evidence that bone loss, compromised vitamin D status, and oxidative damage are among critical nutritional concerns for long-duration space travelers.

Bone markers, calcium metabolism, and calcium kinetics during extended-duration space flight on the mir space station

Bone loss is a current limitation for long-term space exploration. Bone markers, calcitropic hormones, and calcium kinetics of crew members on space missions of 4-6 months were evaluated. Spaceflight-induced bone loss was associated with increased bone resorption and decreased calcium absorption.

INTRODUCTION

Bone loss is a significant concern for the health of astronauts on long-duration missions. Defining the time course and mechanism of these changes will aid in developing means to counteract these losses during space flight and will have relevance for other clinical situations that impair weight-bearing activity.

MATERIALS AND METHODS

We report here results from two studies conducted during the Shuttle-Mir Science Program. Study 1 was an evaluation of bone and calcium biochemical markers of 13 subjects before and after long-duration (4-6 months) space missions. In study 2, stable calcium isotopes were used to evaluate calcium metabolism in six subjects before, during, and after flight. Relationships between measures of bone turnover, biochemical markers, and calcium kinetics were examined.

RESULTS

Pre- and postflight study results confirmed that, after landing, bone resorption was increased, as indicated by increases in urinary calcium (p < 0.05) and collagen cross-links (N-telopeptide, pyridinoline, and deoxypyridinoline were all increased >55% above preflight levels, p < 0.001). Parathyroid hormone and vitamin D metabolites were unchanged at landing. Biochemical markers of bone formation were unchanged at landing, but 2-3 weeks later, both bone-specific alkaline phosphatase and osteocalcin were significantly (p < 0.01) increased above preflight levels. In studies conducted during flight, bone resorption markers were also significantly higher than before flight. The calcium kinetic data also validated that bone resorption was increased during flight compared with preflight values (668 +/- 130 versus 427 +/- 153 mg/day; p < 0.001) and clearly documented that true intestinal calcium absorption was significantly lower during flight compared with preflight values (233 +/- 87 versus 460 +/- 47 mg/day; p < 0.01). Weightlessness had a detrimental effect on the balance in bone turnover such that the daily difference in calcium retention during flight compared with preflight values approached 300 mg/day (-234 +/- 102 versus 63 +/- 75 mg/day; p < 0.01).

CONCLUSIONS

These bone marker and calcium kinetic studies indicated that the bone loss that occurs during space flight is a consequence of increased bone resorption and decreased intestinal calcium absorption.

Interventions to prevent bone loss in astronauts during space flight

This paper reviews the interventions to stabilize calcium balance and bone metabolism and prevent bone loss in astronauts during space flight. Weightlessness during space flight results in calcium, vitamin D, and vitamin K deficiency, increases urinary calcium excretion, decreases intestinal calcium absorption, and increases serum calcium level, with decreased levels of serum parathyroid hormone and calcitriol. Bone resorption is increased, whereas bone formation is decreased. The loss of bone mineral density (BMD) in the spine, femoral neck and trochanter, and pelvis is 1.0-1.6% per month. High calcium intake and vitamin D supplementation during space flight does not affect bone metabolism, but prevents an elevation of serum calcium level through increased calcitriol level, while vitamin K counteracts the reduction in bone formation. However, there are no data to show the efficacy of pharmaceutical agents for prevention of development of osteoporosis in astronauts during flight, although the preventative effect of bisphosphonates, testosterone, and vitamin K2 on cancellous bone loss in the tibia or BMD loss in the hindlimb was reported in tail-suspended mature rats. It still remains uncertain whether these agents can prevent cortical bone loss caused by weightlessness in tail-suspended rats. Therefore, in addition to calcium, vitamin D, and vitamin K supplementation, agents that have both potent anti-resorptive and anabolic effects on cancellous and cortical bone may be needed to stabilize calcium balance and bone metabolism and prevent bone loss in astronauts during space flight.