Quantity and quality of trabecular bone in the femur are enhanced by a strongly anabolic, noninvasive mechanical intervention

Low-magnitude, high-frequency vibration promotes the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells cultured on a hydroxyapatite-coated surface: The direct role of Wnt/β-catenin signaling pathway activation

The positive effect of low-magnitude, high‑frequency (LMHF) vibration on implant osseointegration has been demonstrated; however, the underlying cellular and molecular mechanisms remain unknown. The aim of this study was to explore the effect of LMHF vibration on the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) cultured on hydroxyapatite (HA)-coated surfaces in an in vitro model as well as to elucidate the molecular mechanism responsible for the effects of LMHF vibration on osteogenesis. LMHF vibration resulted in the increased expression of fibronectin, which was measured by immunostaining and RT-qPCR. Stimulation of BMSCs by LMHF vibration resulted in the rearrangement of the actin cytoskeleton with more prominent F-actin. Moreover, the expression of β1 integrin, vinculin and paxillin was notably increased following LMHF stimulation. Scanning electron microscope observations revealed that there were higher cell numbers and more extracellular matrix attached to the HA-coated surface in the LMHF group. Alkaline phosphatase activity as well as the expression of osteogenic-specific genes, namely Runx2, osterix, collagen I and osteocalcin, were significantly elevated in the LMHF group. In addition, the protein expression of Wnt10B, β-catenin, Runx2 and osterix was increased following exposure to LMHF vibration. Taken together, the findings of this study indicate that LMHF vibration promotes the adhesion and the osteogenic differentiation of BMSCs on HA-coated surfaces in vitro, and LMHF vibration may directly induce osteogenesis by activating the Wnt/β‑catenin signaling pathway. These data suggest that LMHF vibration enhances the osseointegration of bone to a HA-coated implant, and provide a scientific foundation for improving bone-implant osseointegration through the application of LMHF vibration.

In vitro cyclic compressive loads potentiate early osteogenic events in engineered bone tissue

Application of dynamic mechanical loads on bone and bone explants has been reported to enhance osteogenesis and mineralization. To date, published studies have incorporated a range of cyclic strains on 3D scaffolds and platforms to demonstrate the effect of mechanical loading on osteogenesis. However, most of the loading parameters used in these studies do not emulate the in vivo loading conditions. In addition, the scaffolds/platforms are not representative of the native osteoinductive environment of bone tissue and hence may not be entirely accurate to study the in vivo mechanical loading. We hypothesized that biomimicry of physiological loading will potentiate accelerated osteogenesis in bone grafts. In this study, we present a compression bioreactor system that applies cyclic compression to cellular grafts in a controlled manner. Polycaprolactone-β Tricalcium Phosphate (PCL-TCP) scaffolds seeded with Mesenchymal Stem Cells (MSC) were cyclically compressed in bioreactor for a period of 4 weeks at 1 Hz and physiological strain value of 0.22% for 4 h per day. Gene expression studies revealed increased expressions of osteogenesis-related genes (Osteonectin and COL1A1) on day 7 of cyclic loading group relative to its static controls. Cyclic compression resulted in a 3.76-fold increase in the activity of Alkaline Phosphatase (ALP) on day 14 when compared to its static group (p < 0.001). In addition, calcium deposition of cyclic loading group was found to attain saturation on day 14 (1.96 fold higher than its static scaffolds). The results suggested that cyclic, physiological compression of stem cell-seeded scaffolds generated highly mineralized bone grafts. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2366-2375, 2017.

Trabecular bone structural variation throughout the human lower limb

Trabecular bone is responsive to mechanical loading, and thus may be a useful tool for interpreting past behaviour from fossil morphology. However, the ability to meaningfully interpret variation in archaeological and hominin trabecular morphology depends on the extent to which trabecular bone properties are integrated throughout the postcranium or are locally variable in response to joint specific loading. We investigate both of these factors by comparing trabecular bone throughout the lower limb between a group of highly mobile foragers and two groups of sedentary agriculturalists. Trabecular bone structure is quantified in four volumes of interest placed within the proximal and distal joints of the femur and tibia. We determine how trabecular structures correspond to inferred behavioural differences between populations and whether the patterns are consistent throughout the limb. A significant correlation was found between inferred mobility level and trabecular bone structure in all volumes of interest along the lower limb. The greater terrestrial mobility of foragers is associated with higher bone volume fraction, and thicker and fewer trabeculae (lower connectivity density). In all populations, bone volume fraction decreases while anisotropy increases proximodistally throughout the lower limb. This observation mirrors reductions in cortical bone mass resulting from proximodistal limb tapering. The reduction in strength associated with reduced bone volume fraction may be compensated for by the increased anisotropy in the distal tibia. A similar pattern of trabecular structure is found throughout the lower limb in all populations, upon which a signal of terrestrial mobility appears to be superimposed. These results support the validity of using lower limb trabecular bone microstructure to reconstruct terrestrial mobility levels from the archaeological and fossil records. The results further indicate that care should be taken to appreciate variation resulting from differences in habitual activity when inferring behaviour from the trabecular structure of hominin fossils through comparisons with modern humans.

Computational characterization of fracture healing under reduced gravity loading conditions

The literature is deficient with regard to how the localized mechanical environment of skeletal tissue is altered during reduced gravitational loading and how these alterations affect fracture healing. Thus, a finite element model of the ovine hindlimb was created to characterize the local mechanical environment responsible for the inhibited fracture healing observed under experimental simulated hypogravity conditions. Following convergence and verification studies, hydrostatic pressure and strain within a diaphyseal fracture of the metatarsus were evaluated for models under both 1 and 0.25 g loading environments and compared to results of a related in vivo study. Results of the study suggest that reductions in hydrostatic pressure and strain of the healing fracture for animals exposed to reduced gravitational loading conditions contributed to an inhibited healing process, with animals exposed to the simulated hypogravity environment subsequently initiating an intramembranous bone formation process rather than the typical endochondral ossification healing process experienced by animals healing in a 1 g gravitational environment. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1206-1215, 2016.

Exercise Regulation of Marrow Adipose Tissue

Despite association with low bone density and skeletal fractures, marrow adipose tissue (MAT) remains poorly understood. The marrow adipocyte originates from the mesenchymal stem cell (MSC) pool that also gives rise to osteoblasts, chondrocytes, and myocytes, among other cell types. To date, the presence of MAT has been attributed to preferential biasing of MSC into the adipocyte rather than osteoblast lineage, thus negatively impacting bone formation. Here, we focus on understanding the physiology of MAT in the setting of exercise, dietary interventions, and pharmacologic agents that alter fat metabolism. The beneficial effect of exercise on musculoskeletal strength is known: exercise induces bone formation, encourages growth of skeletally supportive tissues, inhibits bone resorption, and alters skeletal architecture through direct and indirect effects on a multiplicity of cells involved in skeletal adaptation. MAT is less well studied due to the lack of reproducible quantification techniques. In recent work, osmium-based 3D quantification shows a robust response of MAT to both dietary and exercise intervention in that MAT is elevated in response to high-fat diet and can be suppressed following daily exercise. Exercise-induced bone formation correlates with suppression of MAT, such that exercise effects might be due to either calorie expenditure from this depot or from mechanical biasing of MSC lineage away from fat and toward bone, or a combination thereof. Following treatment with the anti-diabetes drug rosiglitazone - a PPARγ-agonist known to increase MAT and fracture risk - mice demonstrate a fivefold higher femur MAT volume compared to the controls. In addition to preventing MAT accumulation in control mice, exercise intervention significantly lowers MAT accumulation in rosiglitazone-treated mice. Importantly, exercise induction of trabecular bone volume is unhindered by rosiglitazone. Thus, despite rosiglitazone augmentation of MAT, exercise significantly suppresses MAT volume and induces bone formation. That exercise can both suppress MAT volume and increase bone quantity, notwithstanding the skeletal harm induced by rosiglitazone, underscores exercise as a powerful regulator of bone remodeling, encouraging marrow stem cells toward the osteogenic lineage to fulfill an adaptive need for bone formation. Thus, exercise represents an effective strategy to mitigate the deleterious effects of overeating and iatrogenic etiologies on bone and fat.

Effect of low-frequency mechanical vibration on orthodontic tooth movement

INTRODUCTION

Our objective was to investigate the effect of low-frequency mechanical vibration (LFMV) on the rate of tooth movement, bone volume fraction, tissue density, and the integrity of the periodontal ligament. Our null hypothesis was that there would be no difference in the amount of tooth movement between different values of LFMV.

METHODS

Sixty-four male CD1 mice, 12 weeks old, were used for orthodontic tooth movement. The mice were randomly divided into 2 groups: control groups (baseline; no spring + 5 Hz; no spring + 10 Hz; and no spring + 20 Hz) and experimental groups (spring + no vibration; spring + 5 Hz; spring + 10 Hz; and spring + 20 Hz). In the experimental groups, the first molars were moved mesially for 2 weeks using nickel-titanium coil springs delivering 10 g of force. In the control and experimental groups, LFMV was applied at 5, 10, or 20 Hz. Microfocus x-ray computed tomography analysis was used for tooth movement measurements, bone volume fraction, and tissue density. Additionally, immunostaining for sclerostin, tartrate-resistant acid phosphatase (TRAP) staining, and picrosirius red staining were used on the histologic sections. Simple descriptive statistics were used to summarize the data. Kruskal-Wallis tests were used to compare the outcomes across treatment groups.

RESULTS

LFMV did not increase the rate of orthodontic tooth movement. Microfocus x-ray computed tomography analysis showed increases in bone volume fractions and tissue densities with applications of LFMV. Sclerostin expression was decreased with 10 and 20 Hz vibrations in both the control and experimental groups. Additionally, the picrosirius staining showed that LFMV helped in maintaining the thickness and integrity of collagen fibers in the periodontal ligament.

CONCLUSIONS

There was no significant increase in tooth movement by applying LFMV when compared with the control groups (spring + no vibration).

Biomechanical Screening of Cell Therapies for Vocal Fold Scar

Candidate cell sources for vocal fold scar treatment include mesenchymal stromal cells from bone marrow (BM-MSC) and adipose tissue (AT-MSC). Mechanosensitivity of MSC can alter highly relevant aspects of their behavior, yet virtually nothing is known about how MSC might respond to the dynamic mechanical environment of the larynx. Our objective was to evaluate MSC as a potential cell source for vocal fold tissue engineering in a mechanically relevant context. A vibratory strain bioreactor and cDNA microarray were used to evaluate the similarity of AT-MSC and BM-MSC to the native cell source, vocal fold fibroblasts (VFF). Posterior probabilities for each of the microarray transcripts fitting into specific expression patterns were calculated, and the data were analyzed for Gene Ontology (GO) enrichment. Significant wound healing and cell differentiation GO terms are reported. In addition, proliferation and apoptosis were evaluated with immunohistochemistry. Results revealed that VFF shared more GO terms related to epithelial development, extracellular matrix (ECM) remodeling, growth factor activity, and immune response with BM-MSC than with AT-MSC. Similarity in glycosaminoglycan and proteoglycan activity dominated the ECM analysis. Analysis of GO terms relating to MSC differentiation toward osteogenic, adipogenic, and chondrogenic lineages revealed that BM-MSC expressed fewer osteogenesis GO terms in the vibrated and scaffold-only conditions compared to polystyrene. We did not evaluate if vibrated BM-MSC recover osteogenic expression markers when returned to polystyrene culture. Immunostaining for Ki67 and cleaved caspase 3 did not vary with cell type or mechanical condition. We conclude that VFF may have a more similar wound healing capacity to BM-MSC than to AT-MSC in response to short-term vibratory strain. Furthermore, BM-MSC appear to lose osteogenic potential in the vibrated and scaffold-only conditions compared to polystyrene, potentially attenuating the risk of osteogenesis for in vivo applications.

Influence of different intensities of vibration on proliferation and differentiation of human periodontal ligament stem cells

INTRODUCTION

To understand the effects of low-magnitude, high-frequency (LMHF) mechanical vibration at different intensities on human periodontal ligament stem cell (hPDLSC) proliferation and osteogenic differentiation.

MATERIAL AND METHODS

The effect of vibration on hPDLSC proliferation, osteogenic differentiation, tenogenic differentiation and cytoskeleton was assessed at the cellular, genetic and protein level.

RESULTS

The PDLSC proliferation was decreased after different magnitudes of mechanical vibration; however, there were no obvious senescent cells in the experimental and the static control group. Expression of osteogenesis markers was increased. The expression of alkaline phosphatase (ALP) and osteocalcin (OCN) mRNA was up-regulated at 0.1 g, 0.3 g, 0.6 g and 0.9 g magnitude, with the peak at 0.3 g. The type I collagen (Col-I) level was increased after vibration exposure at 0.1 g, 0.3 g, and 0.6 g, peaking at 0.3 g. The expression levels of both mRNA and protein of Runx2 and osterix (OSX) significantly increased at a magnitude of 0.1 g to 0.9 g, reached a peak at 0.3 g and then decreased slowly. The scleraxis, tenogenic markers, and mRNA expression decreased at 0.05 g, 0.1 g, and 0.3 g, and significantly increased at 0.6 g and 0.9 g. Compared with the static group, the F-actin stress fibers of hPDLSCs became thicker and clearer following vibration.

CONCLUSIONS

The LMHF mechanical vibration promotes PDLSC osteogenic differentiation and implies the existence of a magnitude-dependent effect of vibration on determining PDLSC commitment to the osteoblast lineage. Changes in the cytoskeleton of hPDLSCs after vibration may be one of the mechanisms of the biological effects.

Physiological mechanisms and therapeutic potential of bone mechanosensing

Skeletal loading is an important physiological regulator of bone mass. Theoretically, mechanical forces or administration of drugs that activate bone mechanosensors would be a novel treatment for osteoporotic disorders, particularly age-related osteoporosis and other bone loss caused by skeletal unloading. Uncertainty regarding the identity of the molecular targets that sense and transduce mechanical forces in bone, however, has limited the therapeutic exploitation of mechanosesning pathways to control bone mass. Recently, two evolutionally conserved mechanosensing pathways have been shown to function as "physical environment" sensors in cells of the osteoblasts lineage. Indeed, polycystin-1 (Pkd1, or PC1) and polycystin-2 (Pkd2, or PC2' or TRPP2), which form a flow sensing receptor channel complex, and TAZ (transcriptional coactivator with PDZ-binding motif, or WWTR1), which responds to the extracellular matrix microenvironment act in concert to reciprocally regulate osteoblastogenesis and adipogenesis through co-activating Runx2 and a co-repressing PPARγ activities. Interactions of polycystins and TAZ with other putative mechanosensing mechanism, such as primary cilia, integrins and hemichannels, may create multifaceted mechanosensing networks in bone. Moreover, modulation of polycystins and TAZ interactions identify novel molecular targets to develop small molecules that mimic the effects of mechanical loading on bone.

Physical exercise and osteoporosis: effects of different types of exercises on bone and physical function of postmenopausal women

Physical exercise is an important stimulus for osteoporosis prevention and treatment. However, it is not clear yet which modality would be better to stimulate bone metabolism and enhance physical function of postmenopausal women. This review paper aims to summarize and update present knowledge on the effects of different kinds of aquatic and ground physical exercises on bone metabolism and physical function of postmenopausal women. Moderate to intense exercises, performed in a high speed during short intervals of time, in water or on the ground, can be part of a program to prevent and treat postmenopausal osteoporosis. Mechanical vibration has proven to be beneficial for bone microarchitecture, improving bone density and bone strength, as well as increasing physical function. Although impact exercises are recognized as beneficial for the stimulation of bone tissue, other variables such as muscle strength, type of muscle contraction, duration and intensity of exercises are also determinants to induce changes in bone metabolism of postmenopausal women. Not only osteoanabolic exercises should be recommended; activities aimed to develop muscle strength and body balance and improve the proprioception should be encouraged to prevent falls and fractures.

Trabecular bone microarchitecture and characteristics in different regions of the glenoid

Success of shoulder surgery depends on implant fixation to the glenoid trabecular bone. The purpose of this study was to evaluate the anatomic characteristics of the normal glenoid trabecular bone microarchitecture to help assist in implant design and provide data for finite element analyses. Eight cadavers without evidence of osteoarthritis were used. Glenoids were scanned with micro-computed tomography and then divided into lateral and medial, then superior, inferior, anterior, and posterior quadrants (8 total segments). Each segment was analyzed for total mineral density, bone volume fraction, structure model index, and trabecular thickness (Tb.Th), number (Tb.N), and separation. Bone volume fraction was significantly higher (P<.05) in the posterolateral (20.8%±4.5%) and posteromedial (18.6%±2.5%) regions. Both Tb.N and Tb.Th were also highest in the posterolateral (Tb.N, 1.74±0.374 mm; Tb.Th, 0.148±0.017 mm) and posteromedial (Tb.N, 1.49±0.401 mm; Tb.Th, 0.165±0.016 mm) regions. Trabecular separation was greatest in the superomedial segment (1.00±0.181 mm) and lowest in the posterolateral region (0.663±0.121 mm). For structural model index, both the posterolateral (0.314) and posteromedial (0.312) regions had lower values than the other regions. The posterior segment of the normal glenoid in both the lateral and medial regions has the highest density, which is attributed to the increased trabecular number and thickness with decreased separation. This increased density may be attributed to the posterior directed loading of the glenohumeral joint. The trabecular microarchitecture in the glenoid is plate-like, as indicated by the low structural model index.

Ergonomic task reduction prevents bone osteopenia in a rat model of upper extremity overuse

We evaluated the effectiveness of ergonomic workload reduction of switching rats from a high repetition high force (HRHF) lever pulling task to a reduced force and reach rate task for preventing task-induced osteopenic changes in distal forelimb bones. Distal radius and ulna trabecular structure was examined in young adult rats performing one of three handle-pulling tasks for 12 wk: (1) HRHF, (2) low repetition low force (LRLF); or (3) HRHF for 4 wk and than LRLF thereafter (HRHF-to-LRLF). Results were compared to age-matched controls rats. Distal forelimb bones of 12-wk HRHF rats showed increased trabecular resorption and decreased volume, as control rats. HRHF-to-LRLF rats had similar trabecular bone quality as control rats; and decreased bone resorption (decreased trabecular bone volume and serum CTX1), increased bone formation (increased mineral apposition, bone formation rate, and serum osteocalcin), and decreased osteoclasts and inflammatory cytokines, than HRHF rats. Thus, an ergonomic intervention of HRHF-to-LRLF prevented loss of trabecular bone volume occurring with prolonged performance of a repetitive upper extremity task. These findings support the idea of reduced workload as an effective approach to management of work-related musculoskeletal disorders, and begin to define reach rate and load level boundaries for such interventions.

Effects of early and late treatments of low-intensity, high-frequency mechanical vibration on bone parameters in rats

Low-intensity, high-frequency mechanical vibration (LHMV) has shown to increase bone formation. However, studies comparing the effectiveness of early- and late-treatments of LHMV to counteract bone loss have not been documented. This study was designed to compare the effects of early- and late-treatments of LHMV (at 30 Hz/0.6 g, 20 min per day/five days per week, for 12 weeks) on bone parameters in ovariectomized (Ovx) rats. Thirty days after ovariectomy, 40 adult rats were randomly divided into four groups: GI (early control group); GII treated with LHMV 3 weeks after Ovx (early treatment); GIII (late control group) and GIV treated with LHMV twelve weeks after Ovx (late treatment). Bone mineral density (BMD) was analyzed before Ovx and after treatments. Then, animals were killed, and the femurs were collected and their length and diaphysis diameter were measured; the distal femurs were taken and processed for histomorphometry and polarized light microscopy for collagen fibers analysis or subjected to immunohistochemistry of cleaved caspase-3 in osteocytes. Statistical analysis was done by ANOVA followed by the Bonferroni post hoc test (p < 0.05). BMD was similar among the groups before Ovx, but after treatments, it was significantly higher in GII and GIV compared with their control groups (p < 0.05). Femur length and cortical bone thickness were similar among the groups, but the diaphysis diameter of GII was higher compared with GI. Trabecular bone area was higher in the vibrated groups, but it was greater in GII (p < 0.05). Also, the vibrated groups showed the higher content collagen fibers and lower presence apoptotic osteocytes (positive caspase-3 immunoreactivity) when compared with the other groups (p < 0.05). These results suggest that both early- and late-treatments with LHMV counteract bone loss, being the early treatment more effective than the late treatment.

Vibration therapy: clinical applications in bone

PURPOSE OF REVIEW

The musculoskeletal system is largely regulated through dynamic physical activity and is compromised by cessation of physical loading. There is a need to recreate the anabolic effects of loading on the musculoskeletal system, especially in frail individuals who cannot exercise. Vibration therapy is designed to be a nonpharmacological analogue of physical activity, with an intention to promote bone and muscle strength.

RECENT FINDINGS

Animal and human studies suggest that high-frequency, low-magnitude vibration therapy improves bone strength by increasing bone formation and decreasing bone resorption. There is also evidence that vibration therapy is useful in treating sarcopenia, which confounds skeletal fragility and fall risk in aging. Enhancement of skeletal and muscle strength involves regulating the differentiation of mesenchymal stem cells to build these tissues; mesenchymal stem cell lineage allocation is positively promoted by vibration signals.

SUMMARY

Vibration therapy may be useful as a primary treatment as well as an adjunct to both physical and pharmacological treatments, but future studies must pay close attention to compliance and dosing patterns, and importantly, the vibration signal, be it low-intensity vibration (<1g) appropriate for treatment of frail individuals or high-intensity vibration (>1g) marketed as a training exercise.

Mechanical stimulation of bone marrow in situ induces bone formation in trabecular explants

Low magnitude high frequency (LMHF) loading has been shown to have an anabolic effect on trabecular bone in vivo. However, the precise mechanical signal imposed on the bone marrow cells by LMHF loading, which induces a cellular response, remains unclear. This study investigates the influence of LMHF loading, applied using a custom designed bioreactor, on bone adaptation in an explanted trabecular bone model, which isolated the bone and marrow. Bone adaptation was investigated by performing micro CT scans pre and post experimental LMHF loading, using image registration techniques. Computational fluids dynamic models were generated using the pre-experiment scans to characterise the mechanical stimuli imposed by the loading regime prior to adaptation. Results here demonstrate a significant increase in bone formation in the LMHF loaded group compared to static controls and media flow groups. The calculated shear stress in the marrow was between 0.575 and 0.7 Pa, which is within the range of stimuli known to induce osteogenesis by bone marrow mesenchymal stem cells in vitro. Interestingly, a correlation was found between the bone formation balance (bone formation/resorption), trabecular number, trabecular spacing, mineral resorption rate, bone resorption rate and mean shear stresses. The results of this study suggest that the magnitude of the shear stresses generated due to LMHF loading in the explanted bone cores has a contributory role in the formation of trabecular bone and improvement in bone architecture parameters.

Whole Body Vibration Reduces Inflammatory Bone Loss in a Lipopolysaccharide Murine Model

Whole body vibration (WBV) stimulation has a beneficial effect on the recovery of osteoporotic bone. We aimed to investigate the immediate effect of WBV on lipopolysaccharide (LPS)-mediated inflammatory bone loss by varying the exposure timing. Balb/C mice were divided into the following groups: control, LPS (L), and LPS with vibration (LV). The L and LV groups received LPS (5 mg/kg) by 2 intraperitoneal injections on days 0 and 4. The LV group was exposed to WBV (0.4 g, 45 Hz) either during LPS treatment (LV1) or after cessation of LPS injection (LV2) and then continued WBV treatment for 10 min/d for 3 d. Evaluation based on micro-computed tomography was performed 7 d after the first injection, when the L group showed a significant decrease in bone volume (-25.8%) and bone mineral density (-33.5%) compared with the control group. The LV2 group recovered bone volume (35%) and bone mineral density (19.9%) compared with the L group, whereas the LV1 group showed no improvement. This vibratory signal showed a suppressive effect on the LPS-mediated induction of inflammatory cytokines such as IL-1β or TNF-α in human mesenchymal stem cells in vitro. These findings suggest that immediate exposure to WBV after the conclusion of LPS treatment efficiently reduces trabecular bone loss, but WBV might be less effective during the course of treatment with inflammatory factor.

The Role of Mechanical Stimulation in Recovery of Bone Loss-High versus Low Magnitude and Frequency of Force

Musculoskeletal pathologies associated with decreased bone mass, including osteoporosis and disuse-induced bone loss, affect millions of Americans annually. Microgravity-induced bone loss presents a similar concern for astronauts during space missions. Many pharmaceutical treatments have slowed osteoporosis, and recent data shows promise for countermeasures for bone loss observed in astronauts. Additionally, high magnitude and low frequency impact such as running has been recognized to increase bone and muscle mass under normal but not microgravity conditions. However, a low magnitude and high frequency (LMHF) mechanical load experienced in activities such as postural control, has also been shown to be anabolic to bone. While several clinical trials have demonstrated that LMHF mechanical loading normalizes bone loss in vivo, the target tissues and cells of the mechanical load and underlying mechanisms mediating the responses are unknown. In this review, we provide an overview of bone adaptation under a variety of loading profiles and the potential for a low magnitude loading as a way to counteract bone loss as experienced by astronauts.

Seven day insertion rest in whole body vibration improves multi-level bone quality in tail suspension rats

Objective

This study aimed to investigate the effects of low-magnitude, high-frequency vibration with rest days on bone quality at multiple levels.

Methods

Forty-nine three-month-old male Wistar rats were randomly divided into seven groups, namely, vibrational loading for X day followed by X day rest (VLXR, X = 1, 3, 5, 7), vibrational loading every day (VLNR), tail suspension (SPD), and baseline control (BCL). One week after tail suspension, rats were loaded by vibrational loading (35 Hz, 0.25 g, 15 min/day) except SPD and BCL. Fluorescence markers were used in all rats. Eight weeks later, femora were harvested to investigate macromechanical properties, and micro-computed tomography scanning and fluorescence test were used to evaluate microarchitecture and bone growth rate. Atomic force microscopy analyses and nanoindentation test were used to analyze the nanostructure and mechanical properties of bone material, respectively. Inductively coupled plasma optical emission spectroscopy was used for quantitative chemical analyses.

Results

Microarchitecture, mineral apposition rate and bone formation rate and macromechanical properties were improved in VL7R. Grain size and roughness were significantly different among all groups. No statistical difference was found for the mechanical properties of the bone material, and the chemical composition of all groups was almost similar.

Conclusions

Low-magnitude, high-frequency vibration with rest days altered bone microarchitecture and macro-biomechanical properties, and VL7R was more efficacious in improving bone loss caused by mechanical disuse, which provided theoretical basis and explored the mechanisms of vibration for improving bone quality in clinics.

Mechanical vibration inhibits osteoclast formation by reducing DC-STAMP receptor expression in osteoclast precursor cells

It is well known that physical inactivity leads to loss of muscle mass, but it also causes bone loss. Mechanistically, osteoclastogenesis and bone resorption have recently been shown to be regulated by vibration. However, the underlying mechanism behind the inhibition of osteoclast formation is yet unknown. Therefore, we investigated whether mechanical vibration of osteoclast precursor cells affects osteoclast formation by the involvement of fusion-related molecules such as dendritic cell-specific transmembrane protein (DC-STAMP) and P2X7 receptor (P2X7R). RAW264.7 (a murine osteoclastic-like cell line) cells were treated with 20ng/ml receptor activator of NF-κB ligand (RANKL). For 3 consecutive days, the cells were subjected to 1h of mechanical vibration with 20μm displacement at a frequency of 4Hz and compared to the control cells that were treated under the same condition but without the vibration. After 5days of culture, osteoclast formation was determined. Gene expression of DC-STAMP and P2X7R by RAW264.7 cells was determined after 1h of mechanical vibration, while protein production of the DC-STAMP was determined after 6h of postincubation after vibration. As a result, mechanical vibration of RAW264.7 cells inhibited the formation of osteoclasts. Vibration down-regulated DC-STAMP gene expression by 1.6-fold in the presence of RANKL and by 1.4-fold in the absence of RANKL. Additionally, DC-STAMP protein production was also down-regulated by 1.4-fold in the presence of RANKL and by 1.2-fold in the absence of RANKL in RAW264.7 cells in response to mechanical vibration. However, vibration did not affect P2X7R gene expression. Mouse anti-DC-STAMP antibody inhibited osteoclast formation in the absence of vibration. Our results suggest that mechanical vibration of osteoclast precursor cells reduces DC-STAMP expression in osteoclast precursor cells leading to the inhibition of osteoclast formation.

Prediction of trabecular bone qualitative properties using scanning quantitative ultrasound

Microgravity induced bone loss represents a critical health problem in astronauts, particularly occurred in weight-supporting skeleton, which leads to osteopenia and increase of fracture risk. Lack of suitable evaluation modality makes it difficult for monitoring skeletal status in long term space mission and increases potential risk of complication. Such disuse osteopenia and osteoporosis compromise trabecular bone density, and architectural and mechanical properties. While X-ray based imaging would not be practical in space, quantitative ultrasound may provide advantages to characterize bone density and strength through wave propagation in complex trabecular structure. This study used a scanning confocal acoustic diagnostic and navigation system (SCAN) to evaluate trabecular bone quality in 60 cubic trabecular samples harvested from adult sheep. Ultrasound image based SCAN measurements in structural and strength properties were validated by μCT and compressive mechanical testing. This result indicated a moderately strong negative correlations observed between broadband ultrasonic attenuation (BUA) and μCT-determined bone volume fraction (BV/TV, R²=0.53). Strong correlations were observed between ultrasound velocity (UV) and bone's mechanical strength and structural parameters, i.e., bulk Young's modulus (R²=0.67) and BV/TV (R²=0.85). The predictions for bone density and mechanical strength were significantly improved by using a linear combination of both BUA and UV, yielding R²=0.92 for BV/TV and R²=0.71 for bulk Young's modulus. These results imply that quantitative ultrasound can characterize trabecular structural and mechanical properties through measurements of particular ultrasound parameters, and potentially provide an excellent estimation for bone's structural integrity.

The interaction of force and repetition on musculoskeletal and neural tissue responses and sensorimotor behavior in a rat model of work-related musculoskeletal disorders

Background

We examined the relationship of musculoskeletal risk factors underlying force and repetition on tissue responses in an operant rat model of repetitive reaching and pulling, and if force x repetition interactions were present, indicative of a fatigue failure process. We examined exposure-dependent changes in biochemical, morphological and sensorimotor responses occurring with repeated performance of a handle-pulling task for 12 weeks at one of four repetition and force levels: 1) low repetition with low force, 2) high repetition with low force, 3) low repetition with high force, and 4) high repetition with high force (HRHF).

Methods

Rats underwent initial training for 4–6 weeks, and then performed one of the tasks for 12 weeks, 2 hours/day, 3 days/week. Reflexive grip strength and sensitivity to touch were assayed as functional outcomes. Flexor digitorum muscles and tendons, forelimb bones, and serum were assayed using ELISA for indicators of inflammation, tissue stress and repair, and bone turnover. Histomorphometry was used to assay macrophage infiltration of tissues, spinal cord substance P changes, and tissue adaptative or degradative changes. MicroCT was used to assay bones for changes in bone quality.

Results

Several force x repetition interactions were observed for: muscle IL-1alpha and bone IL-1beta; serum TNFalpha, IL-1alpha, and IL-1beta; muscle HSP72, a tissue stress and repair protein; histomorphological evidence of tendon and cartilage degradation; serum biomarkers of bone degradation (CTXI) and bone formation (osteocalcin); and morphological evidence of bone adaptation versus resorption. In most cases, performance of the HRHF task induced the greatest tissue degenerative changes, while performance of moderate level tasks induced bone adaptation and a suggestion of muscle adaptation. Both high force tasks induced median nerve macrophage infiltration, spinal cord sensitization (increased substance P), grip strength declines and forepaw mechanical allodynia by task week 12.

Conclusions

Although not consistent in all tissues, we found several significant interactions between the critical musculoskeletal risk factors of force and repetition, consistent with a fatigue failure process in musculoskeletal tissues. Prolonged performance of HRHF tasks exhibited significantly increased risk for musculoskeletal disorders, while performance of moderate level tasks exhibited adaptation to task demands.

Ex vivo human trabecular bone model for biocompatibility evaluation of calcium phosphate composites modified with spray dried biodegradable microspheres

Our aim was to study the suitability of the ex-vivo human trabecular bone bioreactor ZetOS to test the biocompatibility of calcium phosphate bone cement composites modified with spray dried, drug loaded microspheres. We hypothesized, that this bone bioreactor could be a promising alternative to in vivo assessment of biocompatibility in living human bone over a defined time period. Composites consisting of tetracycline loaded poly(lactic-co-glycolic acid) microspheres and calcium phosphate bone cement, were inserted into in vitro cultured human femora head trabecular bone and incubated over 30 days at 37°C in the incubation system. Different biocompatibility parameters, such as lactate dehydrogenase activity, alkaline phosphatase release and the expression of relevant cytokines, IL-1β, IL-6, and TNF-α, were measured in the incubation medium. No significant differences in alkaline phosphatase, osteocalcin, and lactate dehydrogenase activity were measured compared to control samples. Tetracycline was released from the microspheres, delivered and incorporated into newly formed bone. In this study we demonstrated that ex vivo biocompatibility testing using human trabecular bone in a bioreactor is a potential alternative to animal experiments since bone metabolism is still maintained in a physiological environment ex vivo.

R-Spondin 1 promotes vibration-induced bone formation in mouse models of osteoporosis

Bone tissue adapts to its functional environment by optimizing its morphology for mechanical demand. Among the mechanosensitive cells that recognize and respond to forces in the skeleton are osteocytes, osteoblasts, and mesenchymal progenitor cells (MPCs). Therefore, the ability to use mechanical signals to improve bone health through exercise and devices that deliver mechanical signals is an attractive approach to age-related bone loss; however, the extracellular or circulating mediators of such signals are largely unknown. Using SDS-PAGE separation of proteins secreted by MPCs in response to low-magnitude mechanical signals and in-gel trypsin digestion followed by HPLC and mass spectroscopy, we identified secreted proteins up-regulated by vibratory stimulation. We exploited a cell senescence-associated secretory phenotype screen and reasoned that a subset of vibration-induced proteins with diminished secretion by senescent MPCs will have the capacity to promote bone formation in vivo. We identified one such vibration-induced bone-enhancing (vibe) gene as R-spondin 1, a Wnt pathway modulator, and demonstrated that it has the capacity to promote bone formation in three mouse models of age-related bone loss. By virtue of their secretory status, some vibe proteins may be candidates for pre-clinical development as anabolic agents for the treatment of osteoporosis.

KEY MESSAGE

Mesenchymal stem cells respond to low magnitude mechanical signals (vibration). R-Spondin 1 is upregulated by mechanical signals and secreted. R-Spondin 1 promotes bone formation in three mouse models of osteoporosis.

Effect of cyclical forces on the periodontal ligament and alveolar bone remodeling during orthodontic tooth movement

OBJECTIVE

To investigate the effect of externally applied cyclical (vibratory) forces on the rate of tooth movement, the structural integrity of the periodontal ligament, and alveolar bone remodeling.

METHODS

Twenty-six female Sprague-Dawley rats (7 weeks old) were divided into four groups: CTRL (unloaded), VBO (molars receiving a vibratory stimulus only), TMO (molars receiving an orthodontic spring only), and TMO+VB (molars receiving an orthodontic spring and the additional vibratory stimulus). In TMO and TMO+VB groups, the rat first molars were moved mesially for 2 weeks using Nickel-Titanium coil spring delivering 25 g of force. In VBO and TMO+VB groups, cyclical forces at 0.4 N and 30 Hz were applied occlusally twice a week for 10 minutes. Microfocus X-ray computed tomography analysis and tooth movement measurements were performed on the dissected rat maxillae. Tartrate-resistant acid phosphatase staining and collagen fiber assessment were performed on histological sections.

RESULTS

Cyclical forces significantly inhibited the amount of tooth movement. Histological analysis showed marked disorganization of the collagen fibril structure of the periodontal ligament during tooth movement. Tooth movement caused a significant increase in osteoclast parameters on the compression side of alveolar bone and a significant decrease in bone volume fraction in the molar region compared to controls.

CONCLUSIONS

Tooth movement was significantly inhibited by application of cyclical forces.

Bone augmentation for cancellous bone- development of a new animal model

BACKGROUND

Reproducible and suitable animal models are required for in vivo experiments to investigate new biodegradable and osteoinductive biomaterials for augmentation of bones at risk for osteoporotic fractures. Sheep have especially been used as a model for the human spine due to their size and similar bone metabolism. However, although sheep and human vertebral bodies have similar biomechanical characteristics, the shape of the vertebral bodies, the size of the transverse processes, and the different orientation of the facet joints of sheep are quite different from those of humans making the surgical approach complicated and unpredictable. Therefore, an adequate and safe animal model for bone augmentation was developed using a standardized femoral and tibia augmentation site in sheep.

METHODS

The cancellous bone of the distal femur and proximal tibia were chosen as injection sites with the surgical approach via the medial aspects of the femoral condyle and proximal tibia metaphysis (n = 4 injection sites). For reproducible drilling and injection in a given direction and length, a custom-made c-shaped aiming device was designed. Exact positioning of the aiming device and needle positioning within the intertrabecular space of the intact bone could be validated in a predictable and standardized fashion using fluoroscopy. After sacrifice, bone cylinders (Ø 32 mm) were harvested throughout the tibia and femur by means of a diamond-coated core drill, which was especially developed to harvest the injected bone area exactly. Thereafter, the extracted bone cylinders were processed as non-decalcified specimens for μCT analysis, histomorphometry, histology, and fluorescence evaluation.

RESULTS

The aiming device could be easily placed in 63 sheep and assured a reproducible, standardized injection area. In four sheep, cardiovascular complications occurred during surgery and pulmonary embolism was detected by computed tomography post surgery in all of these animals. The harvesting and evaluative methods assured a standardized analysis of all samples.

CONCLUSIONS

This experimental animal model provides an excellent basis for testing new biomaterials for their suitability as bone augmentation materials. Concomitantly, similar cardiovascular changes occur during vertebroplasties as in humans, thus making it a suitable animal model for studies related to vertebroplasty.

Femoral bone marrow adiposity and cortical bone cross-sectional areas in men with motor complete spinal cord injury

OBJECTIVES

To (1) quantify yellow and red bone marrow (BM) and cortical bone cross-sectional areas (CSAs) of the femur in persons with motor complete spinal cord injury (SCI) compared with healthy able-bodied control subjects and (2) determine the relationships between yellow and red BM, cortical CSAs, and thigh composition and measurements from dual-energy x-ray absorptiometry in men with complete SCI.

DESIGN

Cross-sectional.

SETTINGS

Clinical hospital and academic settings.

METHODS

Eight persons with motor complete SCI and 6 age-matched healthy control subjects underwent magnetic resonance imaging of both thighs to measure BM adiposity (BMA) and cortical CSA followed by whole-body dual-energy x-ray absorptiometry to measure bone mineral density and body composition for the SCI group.

RESULTS

Cortical bone CSA adjusted to total subperiosteal bone CSA was 1.5-2 times lower in men with SCI compared with able-bodied control subjects across the femoral length (P =.003). Yellow BMA CSA was 2-3 times greater in men with SCI compared with able-bodied control subjects (P < .0001). Opposite relationships were found between the yellow BMA CSA and cortical bone CSAs in men with SCI (negative association) and able-bodied control subjects (positive association). Yellow BMA was negatively associated with bone mineral density and bone mineral content and with skeletal muscle CSA and fat-free mass (P <.05) in men with SCI. Finally, yellow BMA was positively related to thigh subcutaneous adipose tissue.

CONCLUSIONS

After SCI, cortical bone CSA becomes thinner and is associated with greater accumulation of yellow BMA. Yellow BMA is associated with changes in bone CSA and bone mass, as well as increased fat mass, after SCI.

The effects of physical activity on apoptosis and lubricin expression in articular cartilage in rats with glucocorticoid-induced osteoporosis

Glucocorticoids are considered the most powerful anti-inflammatory and immunomodulating drugs. However, a number of side-effects are well documented in different diseases, including articular cartilage, where increases or decreases in the synthesis of hormone-dependent extracellular matrix components are seen. The objective of this study has been to test the effects of procedures or drugs affecting bone metabolism on articular cartilage in rats with prednisolone-induced osteoporosis and to evaluate the outcomes of physical activity with treadmill and vibration platform training on articular cartilage. The animals were divided into 5 groups, and bone and cartilage evaluations were performed using whole-body scans and histomorphometric analysis. Lubricin and caspase-3 expression were evaluated by immunohistochemistry, Western blot analysis and biochemical analysis. These results confirm the beneficial effect of physical activity on the articular cartilage. The effects of drug therapy with glucocorticoids decrease the expression of lubricin and increase the expression of caspase-3 in the rats, while after physical activity the values return to normal compared to the control group. Our findings suggest that it might be possible that mechanical stimulation in the articular cartilage could induce the expression of lubricin, which is capable of inhibiting caspase-3 activity, preventing chondrocyte death. We can assume that the physiologic balance between lubricin and caspase-3 could maintain the integrity of cartilage. Therefore, in certain diseases such as osteoporosis, mechanical stimulation could be a possible therapeutic treatment. With our results we can propose the hypothesis that physical activity could also be used as a therapeutic treatment for cartilage disease such as osteoarthritis.

Effect of whole body vibration (WBV) therapy on bone density and bone quality in osteopenic girls with adolescent idiopathic scoliosis: a randomized, controlled trial

The aim of this randomized controlled trial was to determine whether whole body vibration (WBV) therapy was effective for treating osteopenia in adolescent idiopathic scoliosis (AIS) patients. Results showed that WBV was effective for improving areal bone mineral density (aBMD) at the femoral neck of the dominant side and lumbar spine BMC in AIS subjects.

INTRODUCTION

AIS is associated with osteopenia. Although WBV was shown to have skeletal anabolic effects in animal studies, its effect on AIS subjects remained unknown. The objective of this study was to determine whether WBV could improve bone mineral density (BMD) and bone quality for osteopenia in AIS subjects.

METHODS

This was a randomized, controlled trial recruiting 149 AIS girls between 15 and 25 years old and with bone mineral density (BMD) Z-scores <-1. They were randomly assigned to the Treatment or Control groups. The Treatment group (n = 61) stood on a low-magnitude high-frequency WBV platform 20 min/day, 5 days/week for 12 months. The Control group (n = 63) received observation alone. Bone measurement was done at baseline and at 12 months: (1) aBMD and BMC at femoral necks and lumbar spine using dual-energy X-ray absorptiometry (DXA) and (2) bone quality including bone morphometry, volumetric BMD (vBMD), and trabecular bone microarchitecture using high-resolution peripheral quantitative computed tomography (HR-pQCT) for nondominant distal radius and bilateral distal tibiae.

RESULTS

The Treatment group had numerically greater increases in all DXA parameters with a statistically significant difference being detected for the absolute and percentage increases in femoral neck aBMD at the dominant leg (0.015 (SD = 0.031)g/cm(2), 2.15 (SD = 4.32)%) and the absolute increase in lumbar spine BMC (1.17 (SD = 2.05)g) in the Treatment group as compared with the Control group (0.00084 (SD = 0.026)g/cm(2), 0.13 (SD = 3.62)% and 0.47 (SD = 1.88)g, respectively). WBV had no significant effect for other bone quality parameters.

CONCLUSIONS

WBV was effective for improving aBMD at the femoral neck of the dominant side and lumbar spine BMC in AIS subjects.

Effects of immediate and delayed loading on peri-implant trabecular structures: a cone beam CT evaluation

PURPOSE

To develop a method for characterizing trabecular bone microarchitecture using cone beam computed tomography (CBCT) and to evaluate trabecular bone changes after rehabilitation using immediate versus delayed implant protocols.

MATERIALS AND METHODS

Six mongrel dogs randomly received 27 titanium implants in the maxillary incisor or mandibular premolar areas, following one of four protocols: (1) normal extraction socket healing; (2) immediate implant placement and immediate loading; (3) delayed implant placement and delayed loading; (4) delayed implant placement and immediate loading. The animals were euthanized at 8 weeks, and block biopsies were scanned using high resolution CBCT. Standard bone structural variables were assessed in coronal, middle, and apical levels.

RESULTS

Coronal and middle regions had more compact, more platelike, and thicker trabeculae. Protocols (2), (3), and (4) had significantly higher values (p < 0.001) than protocol (1) for bone surface density, bone surface volume ratio, and connectivity density, while significantly lower values (p < 0.001) were found for trabecular separation and fractal dimension. However, protocols (2), (3), and (4) did not show significantly different bone remodeling.

CONCLUSIONS

Compared with normal extraction healing, the implant protocols have an improved bone structural integration. Results do not suggest a different bone remodeling pattern when a delayed versus an immediate implant protocol is used.

Therapeutic impact of low amplitude high frequency whole body vibrations on the osteogenesis imperfecta mouse bone

Osteogenesis imperfecta (OI) is characterized by extremely brittle bone. Currently, bisphosphonate drugs allow a decrease of fracture by inhibiting bone resorption and increasing bone mass but with possible long term side effects. Whole body mechanical vibrations (WBV) treatment may offer a promising route to stimulate bone formation in OI patients as it has exhibited health benefits on both muscle and bone mass in human and animal models. The present study has investigated the effects of WBV (45Hz, 0.3g, 15minutes/days, 5days/week) in young OI (oim) and wild type female mice from 3 to 8weeks of age. Vibration therapy resulted in a significant increase in the cortical bone area and cortical thickness in the femur and tibia diaphysis of both vibrated oim and wild type mice compared to sham controls. Trabecular bone was not affected by vibration in the wild type mice; vibrated oim mice, however, exhibited significantly higher trabecular bone volume fraction in the proximal tibia. Femoral stiffness and yield load in three point bending were greater in the vibrated wild type mice than in sham controls, most likely attributed to the increase in femur cortical cross sectional area observed in the μCT morphology analyses. The vibrated oim mice showed a trend toward improved mechanical properties, but bending data had large standard deviations and there was no significant difference between vibrated and non-vibrated oim mice. No significant difference of the bone apposition was observed in the tibial metaphyseal trabecular bone for both the oim and wild type vibrated mice by histomorphometry analyses of calcein labels. At the mid diaphysis, the cortical bone apposition was not significantly influenced by the WBV treatment in both the endosteum and periosteum of the oim vibrated mice while a significant change is observed in the endosteum of the vibrated wild type mice. As only a weak impact in bone apposition between the vibrated and sham groups is observed in the histological sections, it is possible that WBV reduced bone resorption, resulting in a relative increase in cortical thickness. Whole body vibration appears as a potential effective and innocuous means for increasing bone formation and strength, which is particularly attractive for treating the growing skeleton of children suffering from brittle bone disease or low bone density pathologies without the long term disadvantages of current pharmacological therapies.

The potential benefits and inherent risks of vibration as a non-drug therapy for the prevention and treatment of osteoporosis

The delivery of mechanical signals to the skeleton using vibration is being considered as a non-drug treatment of osteoporosis. Delivered over a range of magnitudes and frequencies, vibration has been shown to be both anabolic and anti-catabolic to the musculoskeletal tissues, yet caution must be emphasized as these mechanical signals, particularly chronic exposure to higher intensities, is a known pathogen to many physiological systems. In contrast, accumulating preclinical and clinical evidence indicates that low intensity vibration (LIV) improves bone quality through regulating the activity of cells responsible for bone remodeling, as well as biasing the differentiation fate of their mesenchymal and hematopoietic stem cell progenitors. In vitro studies provide insights into the biologic mechanisms of LIV, and indicate that cells respond to these low magnitude signals through a distinct mechanism driven not by matrix strain but acceleration. These cell, animal, and human studies may represent the foundation of a safe, non-drug means to protect and improve the musculoskeletal system of the elderly, injured, and infirmed.

TRANSMISSIBILITY OF WHOLE BODY VIBRATION STIMULI THROUGH HUMAN BODY IN DIFFERENT STANDING POSTURES

This study focuses on the transmissibility of whole body vibration stimuli through human body in different standing postures to explore the mechanism in which vibration stimuli could be better used as a regimen for bone loss. Five volunteers were guided to stay at three standing postures and imposed of frequency-adjustable vibration stimuli on the plantar surfaces side-alternately. Motion capture system was used to acquire the vibration signals at head, pelvis, knee up, knee down and ankle, from which the transmissibility of vibration stimuli can be obtained. The results showed that transmissibility of vibration stimuli was closely correlated with frequency and skeletal sites. Transmissibility of vibration stimuli in head was much smaller than any other skeletal sites. Transmissibility in the ankle was always in the vicinity of unit one in all the three postures for the vibration stimuli applied side-alternately on the plantar surfaces of both feet. There was an obvious peak around 9 to 11 Hz in the transmissibility curves for knee joint and pelvis. In the resonant peak, transmissibility of vibration stimuli in knee joint and pelvis both exceeded unit one and reached 150%. As the frequency increased after 11 Hz, transmissibility of vibration stimuli decayed rapidly as a function of frequency and dropped to 25% at 30 Hz. This study may help to gain insight into the interaction mechanism between mechanical vibration stimuli and the responses of human musculoskeletal system.

Effects of mechanical vibration on proliferation and osteogenic differentiation of human periodontal ligament stem cells

OBJECTIVE

Paradental tissues (alveolar bone, periodontal ligament (PDL), and gingiva) have the capacity to adapt to their functional environment. The principal cellular elements of the PDL play an important role in normal function, regeneration of periodontal tissue and in orthodontic treatment. Recently, several studies have shown that low-magnitude, high-frequency (LMHF) mechanical vibration can positively influence bone homeostasis; however, the mechanism and optimal conditions for LMHF mechanical vibration have not been elucidated. It has been speculated that LMHF mechanical vibration stimulations have a favourable influence on osteocytes, osteoblasts and their precursors, thereby enhancing the expression of osteoblastic genes involved in bone formation and remodelling. The objective of this study was to test the effect of LMHF mechanical vibration on proliferation and osteogenic differentiation of human PDL stem cells (PDLSCs).

METHODS

Human PDLSCs were isolated from premolar teeth and randomized into vibration (magnitude: 0.3g; frequency: 10-180 Hz; 30 min/24h) and static cultures. The effect of vibration on PDLSC proliferation, differentiation and osteogenic potential was assessed at the genetic and protein level.

RESULTS

After LMHF mechanical vibration, PDLSC proliferation was decreased; however, this was accompanied by increased markers of osteogenesis in a frequency-dependent manner. Specifically, alkaline phosphatase activity gradually increased with the frequency of vibration, to a peak at 50 Hz, and the level of osteocalcin was significantly higher than control following vibration at 40 Hz, 50 Hz, 60 Hz, 90 Hz and 120 Hz. Levels of Col-I, Runx2 and Osterix were significantly increased by LMHF mechanical vibration at frequencies of 40 Hz and 50 Hz.

CONCLUSIONS

Our data demonstrates that LMHF mechanical vibration promotes PDLSC osteogenic differentiation and implies the existence of a frequency-dependent effect of vibration on determining PDLSC commitment to the osteoblast lineage.

Subjective experiences of men with and without spinal cord injury: tolerability of the juvent and WAVE whole body vibration plates

BACKGROUND

Device tolerability is an important determinant of subject adherence and intervention effectiveness. Although popular in rehabilitation settings, the tolerability of whole-body vibration (WBV) among patients with spinal cord injury (SCI) is unknown.

OBJECTIVE

To assess feedback from SCI and non-SCI subjects on the usability of passive standing and WBV devices (Juvent [Juvent Medical, Somerset, NJ] and WAVE [WAVE Manufacturing, Windsor, Ontario, Canada]) using a priori specified knee postures, plate amplitudes, and frequencies.

DESIGN

A matched groups design with repeated measures.

SETTING

A tertiary SCI rehabilitation center.

SUBJECTS

Eight men with chronic SCI (C4-L2, American Spinal Injury Association Impairment Scale A-D) and 10 men without SCI of similar height, weight, and body mass index.

INTERVENTION

Subjects (N = 18; 8 with SCI) underwent intermittent WBV during passive standing (EasyStand 5000 [Altimate Medical, Morton, MN]) for 45 minutes using the optimized WAVE and Juvent plates. WBV parameters were sequentially altered every 2 minutes and included parameter combinations of (1) postures of 140°, 160°, and 180° knee extension (180° with Juvent only); (2) amplitudes of 0.7 mm and 1.1 mm (WAVE only); and (3) frequencies of 25 Hz, 35 Hz, and 45 Hz. Outcome assessments were completed at 4-minute intervals throughout WBV exposure.

MAIN OUTCOME MEASURES

Qualitative, semistructured interviews were used to generate neutral, positive, and negative descriptors of the subjects' overall experience and device preference.

RESULTS

SCI subjects reported a greater frequency of positive descriptors than non-SCI subjects during WBV, regardless of plate, posture, amplitude, or frequency, with the exception of 1 combination of parameters (WAVE plate at 140°, 1.1 mm, and 25 Hz). Non-SCI subjects reported the highest frequency of negative effects with the WAVE plate at 160°, 1.1 mm, 25 Hz, and 35 Hz. Non-SCI subjects preferred the Juvent, whereas SCI subjects preferred the WAVE plate.

CONCLUSIONS

SCI and non-SCI subjects reported differing frequencies of positive and negative descriptors and indicated divergent device preferences. SCI subjects preferred the WAVE plate and vibration at high frequency. Future research will determine the therapeutic potential and adverse events associated with the device and WBV parameters tolerable for persons with SCI.

High-frequency and low-magnitude whole body vibration with rest days is more effective in improving skeletal micro-morphology and biomechanical properties in ovariectomised rodents

We explored the optimal regime in preventing or treating bone loss, using ovariectomised rodents loaded by mechanical stimuli with rest days during the loading cycle. Eighty-four Sprague-Dawley rats, aged 6 months, were randomly divided into 7 groups after bilateral ovariectomy. Mechanical vibration with 1-day rest (ML1R), with 3-day rest (ML3R), with 5-day rest (ML5R), with 7-day rest (ML7R), daily loading (DL), comparing the ovariectomised group (OVX) with baseline (BCL) measurements. After a recovery of one week, all the rodents were loaded daily by whole body vibration at 35 Hz and 0.25 g for 15 minutes. Eight weeks later, a three-point bending test of the radius and micro-CT scanning of the femoral head were performed after animal sacrifice. Large improvements in biomechanical properties occurred in all the experimental groups for failure load, elastic modulus and deflection, while a significantly enhanced efficacy was detected in ML7R compared with daily loading (p<0.05). In micro-CT scanning, bone volume fraction, trabecular thickness, number and separation were improved by the regime in all experimental groups, while ML7R showed a significant improvement over daily loading (p<0.05). Early bone loss in human subjects may be improved by high-frequency and low-magnitude whole body vibration with rest days or daily stimuli. Mechanical stimulus with a 7-day rest was more effective in improving biomechanical properties and micro-morphology compared with daily loading. This may have clinical implications in relation to the prevention and treatment of hip fractures, and in postoperative management following hip arthroplasty.

Mechanical regulation of signaling pathways in bone

A wide range of cell types depend on mechanically induced signals to enable appropriate physiological responses. The skeleton is particularly dependent on mechanical information to guide the resident cell population towards adaptation, maintenance and repair. Research at the organ, tissue, cell and molecular levels has improved our understanding of how the skeleton can recognize the functional environment, and how these challenges are translated into cellular information that can site-specifically alter phenotype. This review first considers those cells within the skeleton that are responsive to mechanical signals, including osteoblasts, osteoclasts, osteocytes and osteoprogenitors. This is discussed in light of a range of experimental approaches that can vary parameters such as strain, fluid shear stress, and pressure. The identity of mechanoreceptor candidates is approached, with consideration of integrins, pericellular tethers, focal adhesions, ion channels, cadherins, connexins, and the plasma membrane including caveolar and non-caveolar lipid rafts and their influence on integral signaling protein interactions. Several mechanically regulated intracellular signaling cascades are detailed including activation of kinases (Akt, MAPK, FAK), β-catenin, GTPases, and calcium signaling events. While the interaction of bone cells with their mechanical environment is complex, an understanding of mechanical regulation of bone signaling is crucial to understanding bone physiology, the etiology of diseases such as osteoporosis, and to the development of interventions to improve bone strength.

Osteocytic network is more responsive in calcium signaling than osteoblastic network under fluid flow

Osteocytes, regarded as the mechanical sensor in bone, respond to mechanical stimulation by activating biochemical pathways and mediating the cellular activities of other bone cells. Little is known about how osteocytic networks respond to physiological mechanical stimuli. In this study, we compared the mechanical sensitivity of osteocytic and osteoblastic networks under physiological-related fluid shear stress (0.5 to 4 Pa). The intracellular calcium ([Ca(2+)](i)) responses in micropatterned in vitro osteoblastic or osteocytic networks were recorded and analyzed. Osteocytes in the network showed highly repetitive spikelike [Ca(2+)](i) peaks under fluid flow stimulation, which are dramatically different from those in the osteoblastic network. The number of responsive osteocytes in the network remained at a constant high percentage (>95%) regardless of the magnitude of shear stress, whereas the number of responsive osteoblasts in the network significantly depends on the strength of fluid flow. All spatiotemporal parameters of calcium signaling demonstrated that osteocytic networks are more sensitive and dynamic than osteoblastic networks, especially under low-level mechanical stimulations. Furthermore, pathway studies were performed to identify the molecular mechanisms responsible for the differences in [Ca(2+)](i) signaling between osteoblastic and osteocytic networks. The results suggested that the T-type voltage-gated calcium channels (VGCC) expressed on osteocytes may play an essential role in the unique kinetics of [Ca(2+)](i) signaling in osteocytic networks, whereas the L-type VGCC is critical for both types of cells to release multiple [Ca(2+)](i) peaks. The extracellular calcium source and intracellular calcium store in ER-, ATP-, PGE₂-, NO-, and caffeine-related pathways are found to play similar roles in the [Ca(2+)](i) signaling for both osteoblasts and osteocytes. The findings in this study proved that osteocytic networks possess unique characteristics in sensing and processing mechanical signals.

Bone loss following spinal cord injury in a rat model

The current study was undertaken to follow the time course of bone loss in the proximal tibia of rats over several weeks following thoracic contusion spinal cord injury (SCI) of varying severity. It was hypothesized that bone loss would be more pronounced in the more severely injured animals, and that hindlimb weight bearing would help prevent bone loss. Twenty-six female Sprague-Dawley rats (200-225 g, 6-7 weeks old) received standard thoracic (T9) injuries at energies of 6.25, 12.5, 25, or 50 g-cm. The rats were scored weekly for hindlimb function during locomotion. At 0, 2 or 3, and 8 weeks, high-resolution micro-CT images of each right tibia were obtained. Mechanical indentation testing was done to measure the compressive strength of the cancellous bone structure. The 6.25 g-cm group showed near normal locomotion, the 12.5 and 25 g-cm groups showed the ability to frequently or occasionally generate weight-supported plantar steps, respectively, and the 50 g-cm group showed only movement without weight-supported plantar stepping. The 6.25, 12.5 and 25 g-cm groups remained at the same level of bone volume fraction (cancBV/TV=0.24±0.07), while the 50 g-cm group experienced severe bone loss (67%), resulting in significantly lower (p<0.05) bone volume fraction (cancBV/TV=0.11±0.05) at 8 weeks. Proximal tibia cancellous bone strength was reduced by approximately 50% in these severely injured rats. Instead of a linear proportionality between injury severity and bone loss, there appears to be a distinct functional threshold, marked by occasional weight-supported stepping, above which bone loss does not occur.

Optimal mechanical environment of the healing bone fracture/osteotomy

The aim of this paper is to review recent experimental and clinical publications on bone biology with respect to the optimal mechanical environment in the healing process of fractures and osteotomies. The basic postulates of bone fracture healing include static bone compression and immobilisation/ fixation for three weeks and intermittent dynamic loading treatment afterwards. The optimal mechanical strain should be in the range of 100-2,000 microstrain, depending on the frequency of the strain application, type of bone and location in the bone, age and hormonal status. Higher frequency of mechanical strain application or larger number of repetition cycles result in increased bone mass at the healing fracture site, but only up to a certain limit, values beyond which no additional benefit is observed. Strain application and transition period from non-load-bearing to full load-bearing can be modified by implants allowing dynamisation of compression and generating strains at the fracture healing site in a controlled manner.

In vivo mechanical loading

The skeleton fulfils its mechanical functions through structural organisation and material properties of individual bones. Both cortical and trabecular morphology and mass can be (re)modelled in response to changes in mechanical strains engendered by load-bearing. To address this, animal models that enable the application of specific loads to individual bones have been developed. These are useful in defining how loading modulates (re)modelling and allow examination of the mechanisms that coordinate these events. This chapter describes how to apply mechanical loading to murine bones through points of articulation, which allows changes in endosteal, periosteal as well as trabecular bone to be revealed by double fluorochrome labelling and computed tomography, respectively.

Effect of low-magnitude, high-frequency vibration on osteogenic differentiation of rat mesenchymal stromal cells

Whole body vibration (WBV), consisting of a low-magnitude, high-frequency (LMHF) signal, is anabolic to bone in vivo and may act through alteration of the lineage commitment of mesenchymal stromal cells (MSC). We investigated the effect of LMHF vibration on rat bone marrow-derived MSCs (rMSCs) in an in vitro system. We subjected rMSCs to repeated (six) bouts of 1-h vibration at 0.3g and 60 Hz in the presence of osteogenic (OS) induction medium. The OS differentiation of rMSCs under the loaded and non-loaded conditions was assessed by examining cell proliferation, alkaline phosphatase (ALP) activity, mRNA expression of various osteoblast-associated markers [ALP, Runx2, osterix (Osx), collagen type I alpha 1 (COL1A1), bone sialoprotein (BSP), osteopontin (OPN), and osteocalcin (OCN)], and matrix mineralization. LMHF vibration did not enhance the OS differentiation of rMSCs. Surprisingly, the mRNA level of Osx, a transcription factor necessary for osteoblast formation, was decreased, and matrix mineralization was inhibited. Our findings suggest that LMHF vibration may exert its anabolic effects in vivo via mechanosensing of a cell type different from MSCs.