Laurence Vico

Effects of long-term microgravity exposure on cancellous and cortical weight-bearing bones of cosmonauts.

BACKGROUND Microgravity has been thought to induce osteoporosis because of reduced weight-bearing. However, up to now, few data have been available about its precise nature and timecourse. METHODS We measured bone mineral density (BMD) at the distal radius and tibia in 15 cosmonauts of the Russian MIR space station who sojourned in space either 1 (n=two), 2 (two), or 6 months (11). After recovery periods of similar duration to the space missions, BMD was measured for the 2-month and 6-month crews. FINDINGS Neither cancellous nor cortical bone of the radius was significantly changed at any of the timepoints. On the contrary, in the weight-bearing tibial site, cancellous BMD loss was already present after the first month and deteriorated with mission duration. In tibial cortices, bone loss was noted after a 2-month flight. In the 6-month group, cortical bone loss was less pronounced than that for cancellous bone. In some individuals, tibial deterioration was great. Actual BMD did not depend on preceding cumulative periods spent in space. During recovery, tibial bone loss persisted, suggesting that the time needed to recover is longer than the mission duration. INTERPRETATION In space, despite physical training, bone loss is an adaptive process that can become pathological after recovery on Earth. Striking interindividual variations in bone responses seem to suggest a need for adequate crew preselection. Targeted treatment or prevention strategies would be useful, not only for space purposes, but also for the increasing number of osteoporotic patients on Earth.

3D micro-computed tomography of trabecular and cortical bone architecture with application to a rat model of immobilisation osteoporosis.

Bone mass and microarchitecture are the main determinants of bone strength. Three-dimensional micro-computed tomogrpahy has the potential to examine complete bones of small laboratory animals with very high resolution in a non-invasive way. In the presented work, the proximal part of the tibiae of hindlimb unloaded and control rats were measured with 3D MicroCT, and the secondary spongiosa of the scanned region was evaluated using direct evaluation techniques that do not require model assumptions. For determination of the complete bone status, the cortex of the tibiae was evaluated and characterised by its thickness. It is shown that with the proposed anatomically conforming volume of interest (VOI), up to an eight-fold volume increase can be evaluated compared to cubic or spherical VOIs. A pronounced trabecular bone loss of −50% is seen after 23 days of tail suspension. With the new evaluation techniques, it is shown that most of this bone loss is caused by the thinning of trabeculae, and to a lesser extent by a decrease in their number. What changes most radically is the structure type: the remaining bone is more rod-like than the control groups bone. Cortical bone decreases less than trabecular bone, with only −18% after 23 days.

High-Resolution pQCT Analysis at the Distal Radius and Tibia Discriminates Patients With Recent Wrist and Femoral Neck Fractures

We depict a fragility bone state in two primitive osteoporosis populations using 3D high‐resolution peripheral in vivo QCT (HR‐pQCT). Postmenopausal women (C, controls, n = 54; WF, wrist, n = 50; HF, hip, n = 62 recent fractured patients) were analyzed for lumbar and hip DXA areal BMD (aBMD), cancellous and cortical volumetric BMD (vBMD), and microstructural and geometric parameters on tibia and radius by HR‐pQCT. Principal component analysis (PCA) allowed extracting factors that best represent bone variables. Comparison between groups was made by analysis of covariance (ANCOVA). Two factors (>80% of the entire variability) are extracted by PCA: at the radius, the first is a combination of trabecular parameters and the second of cortical parameters. At the tibia, we found the reverse. Femoral neck aBMD is decreased in WF (8.6%) and in HF (18%) groups (no lumbar difference). WF showed a ∼20% reduction in radius trabecular vBMD and number. Radius cortical vBMD and thickness decrease by 6% and 14%, respectively. At the tibia, only the cortical compartment is affected, with ∼20% reduction in bone area, thickness, and section modulus and 6% reduction in vBMD. HF showed same radius trabecular alterations than WF, but radius cortical parameters are more severely affected than WF with reduced bone area (25%), thickness (28.5%), and vBMD (11%). At the tibia, trabecular vBMD and number decrease by 26% and 17.5%, respectively. Tibia cortical bone area, thickness, and section modulus showed a >30% decrease, whereas vBMD reduction reached 13%. Geometry parameters at the tibia displayed the greatest differences between healthy and fractured patients and between wrist and hip fractures.

Effects of whole body vibration on the skeleton and other organ systems in man and animal models : What we know and what we need to know

Previous investigations reported enhanced osseous parameters subsequent to administration of whole body vibration (WBV). While the efficacy of WBV continues to be explored, scientific inquiries should consider several key factors. Bone remodeling patterns differ according to age and hormonal status. Therefore, WBV protocols should be designed specifically for the subject population investigated. Further, administration of WBV to individuals at greatest risk for osteoporosis may elicit secondary physiological benefits (e.g., improved balance and mobility). Secondly, there is a paucity of data in the literature regarding the physiological modulation of WBV on other organ systems and tissues. Vibration-induced modulation of systemic hormones may provide a mechanism by which skeletal tissue is enhanced. Lastly, the most appropriate frequencies, durations, and amplitudes of vibration necessary for a beneficial response are unknown, and the type of vibratory signal (e.g., sinusoidal) is often not reported. This review summarizes the physiological responses of several organ systems in an attempt to link the global influence of WBV. Further, we report findings focused on subject populations that may benefit most from such a therapy (i.e., the elderly, postmenopausal women, etc.) in hopes of eliciting multidisciplinary scientific inquiries into this potentially therapeutic aid which presumably has global ramifications.

Bone sialoprotein plays a functional role in bone formation and osteoclastogenesis.

Bone sialoprotein (BSP) and osteopontin (OPN) are both highly expressed in bone, but their functional specificities are unknown. OPN knockout (−/−) mice do not lose bone in a model of hindlimb disuse (tail suspension), showing the importance of OPN in bone remodeling. We report that BSP−/− mice are viable and breed normally, but their weight and size are lower than wild-type (WT) mice. Bone is undermineralized in fetuses and young adults, but not in older (≥12 mo) BSP−/− mice. At 4 mo, BSP−/− mice display thinner cortical bones than WT, but greater trabecular bone volume with very low bone formation rate, which indicates reduced resorption, as confirmed by lower osteoclast surfaces. Although the frequency of total colonies and committed osteoblast colonies is the same, fewer mineralized colonies expressing decreased levels of osteoblast markers form in BSP−/− versus WT bone marrow stromal cultures. BSP−/− hematopoietic progenitors form fewer osteoclasts, but their resorptive activity on dentin is normal. Tail-suspended BSP−/− mice lose bone in hindlimbs, as expected. In conclusion, BSP deficiency impairs bone growth and mineralization, concomitant with dramatically reduced bone formation. It does not, however, prevent the bone loss resulting from loss of mechanical stimulation, a phenotype that is clearly different from OPN−/− mice.

Noninvasive in vivo monitoring of bone architecture alterations in hindlimb-unloaded female rats using novel three-dimensional microcomputed tomography.

We tested a novel microcomputed tomograph designed to longitudinally and noninvasively monitor bone alterations in hindlimb‐unloaded female rats at a resolution of 26 μm over a period of 3 weeks. This prototype has a potential to detect three‐dimensional trabecular microarchitectural changes induced by growth and unloading.

Bone embedding in pure methyl methacrylate at low temperature preserves enzyme activities

Pure Methyl Methacrylate (MMA), a widely used embedding medium for undecalcified bone studies, was polymerized at low temperature (4 degrees C). MMA was prepared by a new purification procedure yielding a absolutely anhydrous and catalysed resin. The redox system benzoyle peroxide/NN-Dimethylanilin was used as the catalyzer-initiator system providing free radicals for the MMA chemical polymerization. Since the reaction is inhibited at -20 degrees C, complete infiltration of blocks is achieved within 3 d. Polymerization took place at +4 degrees C. The method provides undecalcified bone sections suitable for histomorphometric analysis of osteoid tissue, tetracycline bone labeling and Tartrate Resistant Acid Phosphatase. Enzyme histochemistry was shown to be possible in pure MMA embedded bones, when this low temperature embedding was used.

Effects of gravitational changes on the bone system in vitro and in vivo.

Spaceflight data obtained on bone cells, rodents, and humans are beginning to shed light on the importance of gravitational loading on the skeletal system. The space environment is a relevant model to explore the bone cell response to minimal strains. However, whether there is a direct effect of gravity on the cell rather than changes related to lack of convection forces in cell cultures performed in microgravity is unknown. In vitro studies carried out using osteoblastic cell cultures in space show changes in cell shape, suggesting that cell attachment structures as well as cytoskeleton reorganization might be involved. Valuable information is expected from in vitro models of an increase or decrease in mechanical stress in order to identify the different pathways of mechanoreception and mechanotransduction in the osteoblastic lineage. Results obtained from both humans and rodents after spaceflights indicated that bone mass changes are site specific rather than evenly distributed throughout the skeleton, thus emphasizing the need to perform measurements at different bone sites: weight- and non-weight-bearing bones, and cancellous and cortical envelopes. Bone mass measurements and biochemical parameters of bone remodeling are currently under evaluation in cosmonauts. Histomorphometric studies of bones from rats after space missions of various periods provided the time course of the cancellous bone cellular events: transient increase in resorption and sustained decrease in bone formation. The underlying bone loss occurred first in weight-bearing bones and later in less weight-bearing bones. During the postflight period, time required to recover the lost bone was greater than the mission length. Thus, the postflight period deserves more attention than it is currently receiving. On earth, the rat tail-suspension model is currently used to mimic spaceflight-induced bone loss. Data from the model confirmed the impairment of osteoblastic activity and showed an alteration in osteoblast recruitment with skeletal unloading. However, this model needs to be further validated.

Rotating-wall vessels, promising bioreactors for osteoblastic cell culture: comparison with other 3D conditions

Osteoblastic cells cultured on microcarriers in bioreactors are a potentially useful tool to reproduce the in vivo three-dimensional (3D) bone network. The aim is to compare different types of 3D and two-dimensional (2D) osteoblastic culture. ROS17/2.8 cells are cultured in a bioreactor (rotating-wall vessel) or in two kinds of control (3D petri dish, 3D Percoll) and on two types of microcarrier (Cytodex 3 and Biosilon). Growth and morphology are determined by cell count and SEM, and differentiation is determined by dosage of alkaline phosphatase (ALP) activity and northern blots (ALP and osteocalcin (OC)). SEM shows that Biosilon microcarriers are the best substrate. Proliferation in the RWV and 3D petri dish is still in the exponential phase, whereas growth in the 2D culture reaches a plateau after eight days of culture. ALP activity and the ALP and OC mRNA levels are similar at day 8 for both the RWV and 3D petri dish. However, at day 10, cells are more differentiated in the RWV. The study shows that osteoblasts are both proliferate and differentiate in 3D structures. A BrDU immunocytochemical approach shows that only the cells in the periphery of the aggregates proliferate. Therefore the bioreactor may be a suitable tissue culture model for investigation of growth and differentiation processes in tissue engineering.

Tail Suspension Induces Bone Loss in Skeletally Mature Mice in the C57BL/6J Strain but Not in the C3H/HeJ Strain

We assessed the effects of tail‐suspension in two skeletal genetic backgrounds, the high C3H/HeJ (C3H) and low C57BL/6J (B6) bone masses inbred mice (male, 4‐months old). Cancellous bone mass and structural parameters were evaluated in distal femoral metaphysis by three dimensional microcomputed tomography. Bone cellular activities were evaluated by histomorphometry and measurements of alkaline phosphatase activity (ALP) and osteocalcin in blood and deoxypyridinoline (D‐pyr) in urine. In C3H mice, 2‐ and 3‐week unloading experiments were performed. After an early and transient decrease in body weight, a 2‐week suspension period resulted in stimulation of both bone formation rate by 45% and active osteoclastic surfaces by 19%. D‐pyr did not change, but ALP and osteocalcin levels increased by 18% and 72%, respectively, in 2‐week suspended mice, and osteocalcin remained elevated by 30% in the 3‐week suspended mice. Such cellular modifications allowed the C3H mice to maintain their initial bone mass and trabecular structural parameters even after a 3‐week suspension period. In B6 mice, 1‐ and 2‐week unloading experiments were performed. Tail suspension resulted in decreased body weight during the first days followed by an incomplete recovery during the second week of unloading. The resorption activity was unaffected by any suspension time period, whereas a decrease of 42.5% in bone formation rate and of 21.5% in ALP were seen by the end of the first week of suspension, both values being restored after a 2‐week suspension period. At this latter time, trabeculae were thinner, leading to a 24.5% cancellous bone loss. Trabecular number and connectivity, rod‐plate index, and degree of anisotropy were not modified. We concluded that C3H mice constituted a unique model in which genetic background overwhelmed the usual effects of reduced biomechanical usage in bone, whereas B6 mice, compared with the standardized rat model, offered an alternative model of bone loss in a mature skeleton.