Effect of low-magnitude, high-frequency vibration on osteocytes in the regulation of osteoclasts

Simulation study on parameter dependence of dynamic osteocyte response under low-magnitude high-frequency vibration

The dynamic response mechanism of osteocytes to whole-body low-amplitude high-frequency vibration (LMHFV) is investigated using numerical simulation. In this study, a finite element model of a single bone lacuna-osteocyte incorporating the cytoskeleton was established. The vibration parameter dependence characteristics (acceleration amplitude (a), frequency (f)) of the dynamic osteocyte response under LMHFV were simulated. The results demonstrate that the alternating positive and negative liquid pressure acted on the osteocyte under LMHFV protocols (0.01 g-0.05 g, 30 Hz) (g=gravitational acceleration, 1 g = 9.8 m/s2) and the fluid shear stress increase with the acceleration amplitude. Additionally, the absolute values of positive and negative liquid pressure are relatively higher in the parameters range (0.026 g-0.038 g, 30 Hz). The von Mises stress extreme value of the microtubules presents a non-linear variation with increasing vibration parameters. Moreover, cytoskeletons can generate higher stress under vibration protocols (0.02 g-0.03 g, 30-45 Hz), thus facilitating the transmission of mechanical signals while satisfying the mechanical strength conditions compared to other reasonable vibration parameter range (0.01 g-0.05 g, 30-45 Hz). In summary, LMHFV with appropriate parameters can improve the mechanical microenvironment of osteocytes and enhance cell bioactivity to some extent.

Low-magnitude high-frequency vibration reduces prostate cancer growth and extravasation in vitro

Prostate cancer (PCa) continues to rank among the most common malignancies in Europe and North America with significant mortality rates despite advancements in detection and treatment. Physical activity is often recommended to PCa patients due to its benefits in preventing disease recurrence and managing treatment-related side effects. However, physical activity may be challenging for elderly or bedridden patients. As such, vibration therapy has been proposed as a safe, effective, and easy to perform alternative treatment that may confer similar effects as physical exercise. Specifically, low-magnitude high frequency (LMHF) vibration has been shown to decrease breast cancer extravasation into the bone and reduce other types of cancer proliferation by impacting cell viability. Here, we investigated the effects of daily application of LMHF vibration (0.3 ​g, 60 ​Hz, 1 ​hour/day for 3 days) on prostate cancer growth and bone metastasis in vitro. Our findings suggest that LMHF vibration significantly reduces colony formation through a decrease in cell growth and proliferation. Moreover, using a 3D cell culture model, LMHF vibration significantly reduces PC3 spheroid size. Additionally, LMHF vibration reduces PCa cell extravasation into the bone microenvironment through the stimulation of osteocytes and subsequent osteocyte-endothelial cell cross talk. These findings highlight the potential of LMHF vibration for managing PCa growth and metastasis.

Enhancing anti-tumor potential: low-intensity vibration suppresses osteosarcoma progression and augments MSCs' tumor-suppressive abilities

Rationale: Osteosarcoma (OS), a common malignant bone tumor, calls for the investigation of novel treatment strategies. Low-intensity vibration (LIV) presents itself as a promising option, given its potential to enhance bone health and decrease cancer susceptibility. This research delves into the effects of LIV on OS cells and mesenchymal stem cells (MSCs), with a primary focus on generating induced tumor-suppressing cells (iTSCs) and tumor-suppressive conditioned medium (CM). Methods: To ascertain the influence of vibration frequency, we employed numerical simulations and conducted experiments to determine the most effective LIV conditions. Subsequently, we generated iTSCs and CM through LIV exposure and assessed the impact of CM on OS cells. We also explored the underlying mechanisms of the tumor-suppressive effects of LIV-treated MSC CM, with a specific focus on vinculin (VCL). We employed cytokine array, RNA sequencing, and Western blot techniques to investigate alterations in cytokine profiles, transcriptomes, and tumor suppressor proteins. Results: Numerical simulations validated LIV frequencies within the 10-100 Hz range. LIV induced notable morphological changes in OS cells and MSCs, confirming its dual role in inhibiting OS cell progression and promoting MSC conversion into iTSCs. Upregulated VCL expression enhanced MSC responsiveness to LIV, significantly bolstering CM's efficacy. Notably, we identified tumor suppressor proteins in LIV-treated CM, including procollagen C endopeptidase enhancer (PCOLCE), histone H4 (H4), peptidylprolyl isomerase B (PPIB), and aldolase A (ALDOA). Consistently, cytokine levels decreased significantly in LIV-treated mouse femurs, and oncogenic transcript levels were downregulated in LIV-treated OS cells. Moreover, our study demonstrated that combining LIV-treated MSC CM with chemotherapy drugs yielded additive anti-tumor effects. Conclusions: LIV effectively impeded the progression of OS cells and facilitated the transformation of MSCs into iTSCs. Notably, iTSC-derived CM demonstrated robust anti-tumor properties and the augmentation of MSC responsiveness to LIV via VCL. Furthermore, the enrichment of tumor suppressor proteins within LIV-treated MSC CM and the reduction of cytokines within LIV-treated isolated bone underscore the pivotal tumor-suppressive role of LIV within the bone tumor microenvironment.

Fracture healing research: Recent insights

Bone has the rare capability of scarless regeneration that enables the complete restoration of the injured bone area. In recent decades, promising new technologies have emerged from basic, translational and clinical research for fracture treatment; however, 5-10 % of all bone fractures still fail to heal successfully or heal in a delayed manner. Several comorbidities and risk factors have been identified which impair bone healing and might lead to delayed bone union or non-union. Therefore, a considerable amount of research has been conducted to elucidate molecular mechanisms of successful and delayed fracture healing to gain further insights into this complex process. One focus of recent research is to investigate the complex interactions of different cell types and the action of progenitor cells during the healing process. Of particular interest is also the identification of patient-specific comorbidities and how these affect fracture healing. In this review, we discuss the recent knowledge about progenitor cells for long bone repair and the influence of comorbidities such as diabetes, postmenopausal osteoporosis, and chronic stress on the healing process. The topic selection for this review was made based on the presented studies at the 2022 annual meeting of the European Calcified Tissue Society (ECTS) in Helsinki.

Computational simulation of applying mechanical vibration to mesenchymal stem cell for mechanical modulation toward bone tissue engineering

Evaluation of cell response to mechanical stimuli at in vitro conditions is known as one of the important issues for modulating cell behavior. Mechanical stimuli, including mechanical vibration and oscillatory fluid flow, act as important biophysical signals for the mechanical modulation of stem cells. In the present study, mesenchymal stem cell (MSC) consists of cytoplasm, nucleus, actin, and microtubule. Also, integrin and primary cilium were considered as mechanoreceptors. In this study, the combined effect of vibration and oscillatory fluid flow on the cell and its components were investigated using numerical modeling. The results of the FEM and FSI model showed that the cell response (stress and strain values) at the frequency of 30 H z mechanical vibration has the highest value. The achieved results on shear stress caused by the fluid flow on the cell showed that the cell experiences shear stress in the range of 0 . 1 - 10 Pa . Mechanoreceptors that bind separately to the cell surface, can be highly stimulated by hydrodynamic pressure and, therefore, can play a role in the mechanical modulation of MSCs at in vitro conditions. The results of this research can be effective in future studies to optimize the conditions of mechanical stimuli applied to the cell culture medium and to determine the mechanisms involved in mechanotransduction.

Early protection against bone stress injuries by mobilization of endogenous targeted bone remodeling

Bone stress injuries are common overuse injuries, especially in soldiers, athletes, and performers. In contrast to various post-injury treatments, early protection against bone stress injuries can provide greater benefit. This study explored the early protection strategies against bone stress injuries by mobilization of endogenous targeted bone remodeling. The effects of various pharmaceutical/biophysical approaches, individual or combinational, were investigated by giving intervention before fatigue loading. We optimized the dosage and administration parameters and found that early intervention with pulsed electromagnetic field and parathyroid hormone (i.e., PEMF+PTH) resulted in the most pronounced protective effects among all the approaches against the bone stress injuries. In addition, the mechanisms by which the strategy mobilizes targeted bone remodeling and enhances the self-repair capacity of bone were systematically investigated. This study proposes strategies to reduce the incidence of bone stress injuries in high-risk populations (e.g., soldiers and athletes), particularly for those before sudden increased physical training.

The myosin and RhoGAP MYO9B influences osteocyte dendrite growth and responses to mechanical stimuli

Introduction: Myosin IXB (MYO9B) is an unconventional myosin with RhoGAP activity and thus is a regulator of actin cytoskeletal organization. MYO9B was previously shown to be necessary for skeletal growth and health and to play a role in actin-based functions of both osteoblasts and osteoclasts. However, its role in responses to mechanical stimulation of bone cells has not yet been described. Therefore, experiments were undertaken to determine the role of MYO9B in bone cell responses to mechanical stress both in vitro and in vivo. Methods: MYO9B expression was knocked down in osteoblast and osteocyte cell lines using RNA interference and the resulting cells were subjected to mechanical stresses including cyclic tensile strain, fluid shear stress, and plating on different substrates (no substrate vs. monomeric or polymerized collagen type I). Osteocytic cells were also subjected to MYO9B regulation through Slit-Robo signaling. Further, wild-type or Myo9b -/- mice were subjected to a regimen of whole-body vibration (WBV) and changes in bone quality were assessed by micro-CT. Results: Unlike control cells, MYO9B-deficient osteoblastic cells subjected to uniaxial cyclic tensile strain were unable to orient their actin stress fibers perpendicular to the strain. Osteocytic cells in which MYO9B was knocked down exhibited elongated dendrites but were unable to respond normally to treatments that increase dendrite length such as fluid shear stress and Slit-Robo signaling. Osteocytic responses to mechanical stimuli were also found to be dependent on the polymerization state of collagen type I substrates. Wild-type mice responded to WBV with increased bone tissue mineral density values while Myo9b -/- mice responded with bone loss. Discussion: These results demonstrate that MYO9B plays a key role in mechanical stress-induced responses of bone cells in vitro and in vivo.

Microfluidic Co-culture Platforms for Studying Osteocyte Regulation of Other Cell Types under Dynamic Mechanical Stimulation

PURPOSE OF REVIEW

Osteocytes are the most abundant cell type in bone. These unique cells act primarily as mechanosensors and play crucial roles in the functional adaptation of bone tissue. This review aims to summarize the recent microfluidic studies on mechanically stimulated osteocytes in regulating other cell types.

RECENT FINDINGS

Microfluidics is a powerful technology that has been widely employed in recent years. With the advantages of microfluidic platforms, researchers can mimic multicellular environments and integrate dynamic systems to study osteocyte regulation under mechanical stimulation. Microfluidic platforms have been developed to investigate mechanically stimulated osteocytes in the direct regulation of multiple cell types, including osteoclasts, osteoblasts, and cancer cells, and in the indirect regulation of cancer cells via endothelial cells. Overall, these microfluidic studies foster the development of treatment approaches targeting osteocytes under mechanical stimulation.

Effects of Whole-Body Vibration on Breast Cancer Bone Metastasis and Vascularization in Mice

We evaluated whether whole-body vibration (WBV) prevented bone loss induced by breast cancer (BC) metastasis and the involvement of bone marrow vasculature. One day after orthotopic transplantation of mammary 4T1 tumor cells, 8-week-old BALB/c mice were subjected to 0.3 g/90 Hz vertical vibration for 20 min/day for 5 days/week (BC-WBV) or sham-handled (BC-Sham) over 3 weeks. Age-matched intact mice (Intact) were also sham-handled. Both tibiae were harvested from BC-WBV (n = 7), BC-Sham (n = 9), and Intact (n = 5) mice for bone structure imaging by synchrotron radiation-based computed tomography (SRCT) and hematoxylin and eosin staining, whereas right tibiae were harvested from other BC-WBV and BC-Sham (n = 6 each) mice for vascular imaging by SRCT. Tumor cells were similarly widespread in the marrow in BC-WBV and BC-Sham mice. In BC-Sham mice, cortical bone volume, trabecular volume fraction, trabecular thickness, trabecular number density, and bone mineral density were smaller, and marrow volume and trabecular separation were larger than in Intact mice. However, although trabecular thickness was smaller in BC-WBV than Intact mice, the others did not differ between the two groups. Serum osteocalcin tended to be higher in BC-WBV than BC-Sham mice. Compared with BC-Sham mice, BC-WBV mice had a smaller vessel diameter, a trend of a larger vessel number density, and smaller vessel diameter heterogeneity. In conclusion, WBV mitigates bone loss in BC bone metastasis, which may be partly due to increased bone anabolism. The alteration of marrow vasculature appears to be favorable for anti-tumor drug delivery. Further studies are needed to clarify the multiple actions of WBV on bone, tumor, and marrow vasculature and how they contribute to bone protection in BC metastasis.

Vibration accelerates orthodontic tooth movement by inducing osteoclastogenesis via transforming growth factor-β signalling in osteocytes

Background

We previously found the conditions of supplementary vibration that accelerated tooth movement and induced bone resorption in an experimental rat tooth movement model. However, the molecular biological mechanisms underlying supplementary vibration-induced orthodontic tooth movement are not fully understood. Transforming growth factor (TGF)-β upregulates osteoclastogenesis via induction of the receptor activator of nuclear factor kappa B ligand expression, thus TGF-β is considered an essential cytokine to induce bone resorption.

Objectives

The aim of this study is to examine the role of TGF-β during the acceleration of orthodontic tooth movement by supplementary vibration.

Materials and methods

In experimental tooth movement, 15 g of orthodontic force was loaded onto the maxillary right first molar for 28 days. Supplementary vibration (3 g, 70 Hz) was applied to the maxillary first molar for 3 min on days 0, 7, 14, and 21. TGF-β receptor inhibitor SB431542 was injected into the submucosal palatal and buccal areas of the maxillary first molars once every other day. The co-culture of RAW264.7 cells and MLO-Y4 cells was used as an in vitro osteoclastogenesis model.

Results

SB431542 suppressed the acceleration of tooth movement and the increase in the number of osteoclasts by supplementary vibration in our experimental rat tooth movement model. Immunohistochemical analysis showed supplementary vibration increased the number of TGF-β1-positive osteocytes in the alveolar bone on the compression side during the experimental tooth movement. Moreover, vibration-upregulated TGF-β1 in MLO-Y4 cells induced osteoclastogenesis.

Conclusions

Orthodontic tooth movement was accelerated by supplementary vibration through the promotion of the production of TGF-β1 in osteocytes and subsequent osteoclastogenesis.

Yoda1 Enhanced Low-Magnitude High-Frequency Vibration on Osteocytes in Regulation of MDA-MB-231 Breast Cancer Cell Migration

Low-magnitude (≤1 g) high-frequency (≥30 Hz) (LMHF) vibration has been shown to enhance bone mineral density. However, its regulation in breast cancer bone metastasis remains controversial for breast cancer patients and elder populations. Yoda1, an activator of the mechanosensitive Piezo1 channel, could potentially intensify the effect of LMHF vibration by enhancing the mechanoresponse of osteocytes, the major mechanosensory bone cells with high expression of Piezo1. In this study, we treated osteocytes with mono- (Yoda1 only or vibration only) or combined treatment (Yoda1 and LMHF vibration) and examined the further regulation of osteoclasts and breast cancer cells through the conditioned medium. Moreover, we studied the effects of combined treatment on breast cancer cells in regulation of osteocytes. Combined treatment on osteocytes showed beneficial effects, including increasing the nuclear translocation of Yes-associated protein (YAP) in osteocytes (488.0%, p < 0.0001), suppressing osteoclastogenesis (34.3%, p = 0.004), and further reducing migration of MDA-MB-231 (15.1%, p = 0.02) but not Py8119 breast cancer cells (4.2%, p = 0.66). Finally, MDA-MB-231 breast cancer cells subjected to the combined treatment decreased the percentage of apoptotic osteocytes (34.5%, p = 0.04) but did not affect the intracellular calcium influx. This study showed the potential of stimulating Piezo1 in enhancing the mechanoresponse of osteocytes to LMHF vibration and further suppressing breast cancer migration via osteoclasts.

The Effects of Low-frequency Vibration on Aligner Treatment Duration: A Clinical Trial

OBJECTIVES

The aim of this study was to investigate the effectiveness of an orthodontic tooth movement acceleration device (AcceleDent, OrthoAccel Technologies, Houston, Texas) when used during an aligner treatment.

MATERIALS AND METHODS

Adult patients who began an aligner treatment (Lineo, Micerium Lab, Avegno, Italy) were allocated to two treatment groups. The first one (Group A), with a 7-day aligner change regimen, used the AcceleDent device for 20 min per day, whereas the second one (Group B) changed the aligners every 14 days and did not use any device. The registered outcomes were the possibility of completing the treatment, the number of aligners needed and treatment duration in the two groups. Moreover, we assessed patients' perception of pain during the first week of treatment.

RESULTS

Twenty-four patients were allocated to Group A or B depending on the acceptance of AcceleDent use. Patients which used AcceleDent (Group A) completed the treatment using each aligner for fewer days than those belonging to Group B (9.0 ± 1.0 and 15.4 ± 1.2 days, respectively) (P < 0.001). As a secondary outcome, a significant difference was found in pain perception during the first week of treatment between the two groups (P < 0.05).

CONCLUSIONS

This controlled clinical trial shows that is possible to apply a 7-day change regimen together with AcceleDent use and successfully complete an aligner treatment with a significant saving of time when compared to a standard 14-days change regimen. Finally, the use of this device allowed reduction in pain perception during the orthodontic treatment.

Frequency-specific sensitivity of 3T3-L1 preadipocytes to low-intensity vibratory stimulus during adipogenesis

Adipocyte accumulation in the bone marrow is a severe complication leading to bone defects and reduced regenerative capacity. Application of external mechanical signals to bone marrow cellular niche is a non-invasive and non-pharmaceutical methodology to improve osteogenesis and suppress adipogenesis. However, in the literature, the specific parameters related to the nature of low-intensity vibratory (LIV) signals appear to be arbitrarily selected for amplitude, bouts, and applied frequency. In this study, we performed a LIV frequency sweep ranging from 30 to 120 Hz with increments of 15 Hz applied onto preadipocytes during adipogenesis for 10 d. We addressed the effect of LIV with different frequencies on single-cell density, adipogenic gene expression, lipid morphology, and triglycerides content. Results showed that LIV signals with 75-Hz frequency had the most significant suppressive effect during adipogenesis. Our results support the premise that mechanical-based interventions for suppressing adipogenesis may benefit from optimizing input parameters.

A Bioreactor for 3D In Vitro Modeling of the Mechanical Stimulation of Osteocytes

The bone is a mechanosensitive organ that is also a common metastatic site for prostate cancer. However, the mechanism by which the tumor interacts with the bone microenvironment to further promote disease progression remains to be fully understood. This is largely due to a lack of physiological yet user-friendly models that limit our ability to perform in-depth mechanistic studies. Here, we report a tunable bioreactor which facilitates the 3D culture of the osteocyte cell line, MLO-Y4, in a hydroxyapatite/tricalcium phosphate (HA/TCP) scaffold under constant fluidic shear stress and tunable hydrostatic pressure within physiological parameters. Increasing hydrostatic pressure was sufficient to induce a change in the expression of several bone remodeling genes such as Dmp1, Rankl, and Runx2. Furthermore, increased hydrostatic pressure induced the osteocytes to promote the differentiation of the murine macrophage cell line RAW264.7 toward osteoclast-like cells. These results demonstrate that the bioreactor recapitulates the mechanotransduction response of osteocytes to pressure including the measurement of their functional ability in a 3D environment. In conclusion, the bioreactor would be useful for exploring the mechanisms of osteocytes in bone health and disease.

Circulating microRNA responses to acute whole-body vibration and resistance exercise in postmenopausal women

Evaluating alterations in circulating microRNA (c-miRNA) expression may provide deeper insight into the role of exercise in the attenuation of the negative effects of aging on musculoskeletal health. Currently, there are sparse data on c-miRNA responses to acute exercise in postmenopausal women. The purpose of this study was to characterize the effects of acute bouts of resistance exercise and whole-body vibration on expression of selected c-miRNAs in postmenopausal women aged 65-76 years (n=10). We also examined relationships between c-miRNAs and muscle strength and bone characteristics. This randomized crossover design study compared c-miRNA responses to a bout of resistance exercise (RE) (3 sets 10 reps 70% 1 repetition maximum (1RM), 5 exercises) and a bout of whole-body vibration (WBV) (5 sets 1 min bouts 20Hz 3.38mm peak to peak displacement, Vibraflex vibration platform). DXA was used to measure body composition and areal bone mineral density (aBMD) of the total body, AP lumbar spine, and dual proximal femur. pQCT was used to measure tibia bone characteristics (4%, 38%, 66% sites). Blood samples were collected before exercise (Pre), immediately-post (IP), 60 minutes post (60P), 24 hours (24H), and 48 hours (48H) after exercise to measure serum miR-21-5p, -23a-3p, -133a-3p, -148a-3p (qPCR) and TRAP5b (ELISA). There was a significant modality × time interaction for c-miR-21-5p expression (p=0.019), which decreased from 60P to 24H after WBV only. TRAP5b serum concentrations significantly increased IP then decreased below Pre at 24H for both WBV and RE (p<0.01). Absolute changes in TRAP5b were negatively correlated with c-miR-21-5p fold changes (r= -0.642 to -0.724, p<0.05) for both exercise modalities. There were significant negative correlations between baseline c-miRNAs and bone status variables (r= -0.639 to -0.877, p<0.05). Our findings suggest that whole-body vibration is a sufficient mechanical stimulus for altering c-miR-21-5p expression, whereas a high intensity resistance exercise protocol did not elicit any c-miRNA responses in postmenopausal women. Increases in the bone resorption marker, TRAP5b, were associated with greater downregulation of c-miR-21-5p expression.

Effect of External Mechanical Stimuli on Human Bone: a narrative review

Bone is a living composite material that has the capacity to adapt and respond to both internal and external stimuli. This capacity allows bone to adapt its structure to habitual loads and repair microdamage. Although human bone evolved to adapt to normal physiologic loading (for example from gravitational and muscle forces), these same biological pathways can potentially be activated through other types of external stimuli such as pulsed electromagnetic fields, mechanical vibration, and others. This review summarizes what is currently known about how human bone adapts to various types of external stimuli. We highlight how studies on sports-specific athletes and other exercise interventions have clarified the role of mechanical loading on bone structure. We also discuss clinical scenarios, such as spinal cord injury, where mechanical loading is drastically reduced, leading to rapid bone loss and permanent alterations to bone structure. Finally, we highlight areas of emerging research and unmet clinical need.

The role of micro-vibration parameters in inflammatory responses of macrophages cultured on biphasic calcium phosphate ceramics and the resultant influence on osteogenic differentiation of mesenchymal stem cells

Although in vitro studies have shown that biomaterials and mechanical stimuli can mediate inflammatory responses or regulate osteogenesis of MSCs, the underlying behaviour of the inflammatory response of macrophages on biomaterials mediated by mechanical stimuli, which regulates osteogenesis, is relatively unknown. Thus, it is imperative to explore the role of bionic mechanical stimulation in the biomaterial-mediated inflammatory response of macrophages. In this study, we used osteoinductive biphasic calcium phosphate (BCP) ceramics as the model biomaterial and chose micro-vibration stimulation (MVs) with three variable parameters (frequency, magnitude, and time). Based on orthogonal experiments, nine combinations of MVs parameters were generated, and their effects on the BCP-mediated macrophage inflammatory response were investigated. MVs significantly affected the gene expression and cytokine secretion of macrophages grown on BCP ceramics and further influenced the behaviour of bone marrow mesenchymal stem cells (BMMSCs) in a paracrine manner. Moreover, frequency seemed to be the most dominant factor (compared with magnitude and time) in regulating the inflammatory response of macrophages. The optimal combination of MVs parameters (frequency 10 Hz, magnitude 0.45 g, and time 60 min) could induce a healing-associated M2 phenotype, as evidenced by the downregulated pro-inflammatory gene (Il-1β, and Tnf-α) expression, the upregulated anti-inflammatory gene (Il10) expression, and the inhibited pro-inflammatory cytokine (Il-1β and Tnf-α) secretion of macrophages grown on BCP ceramics, and its conditioned medium (CM) could further promote osteogenic differentiation of BMMSCs. These findings provide valuable insights into the mechanical stimulus-mediated macrophage inflammatory response and osteogenesis in the presence of osteoinductive BCP ceramics and allow accurate evaluation of the biological performance of biomaterials in vitro, in order to optimize bone substitute materials to achieve the desired clinical performance.

The Osteogenic Differentiation of Human Dental Pulp Stem Cells through G0/G1 Arrest and the p-ERK/Runx-2 Pathway by Sonic Vibration

Mechanical/physical stimulations modulate tissue metabolism, and this process involves multiple cellular mechanisms, including the secretion of growth factors and the activation of mechano-physically sensitive kinases. Cells and tissue can be modulated through specific vibration-induced changes in cell activity, which depend on the vibration frequency and occur via differential gene expression. However, there are few reports about the effects of medium-magnitude (1.12 g) sonic vibration on the osteogenic differentiation of human dental pulp stem cells (HDPSCs). In this study, we investigated whether medium-magnitude (1.12 g) sonic vibration with a frequency of 30, 45, or 100 Hz could affect the osteogenic differentiation of HDPSCs. Their cell morphology changed to a cuboidal shape at 45 Hz and 100 Hz, but the cells in the other groups were elongated. FACS analysis showed decreased CD 73, CD 90, and CD 105 expression at 45 Hz and 100 Hz. Additionally, the proportions of cells in the G0/G1 phase in the control, 30 Hz, 45 Hz, and 100 Hz groups after vibration were 60.7%, 65.9%, 68.3%, and 66.7%, respectively. The mRNA levels of osteogenic-specific markers, including osteonectin, osteocalcin, BMP-2, ALP, and Runx-2, increased at 45 and 100 Hz, and the ALP and calcium content was elevated in the vibration groups compared with those in the control. Additionally, the western blotting results showed that p-ERK, BSP, osteoprotegerin, and osteonectin proteins were upregulated at 45 Hz compared with the other groups. The vibration groups showed higher ALP and calcium content than the control. Vibration, especially at 100 Hz, increased the number of calcified nodes relative to the control group, as evidenced by von Kossa staining. Immunohistochemical staining demonstrated that type I and III collagen, osteonectin, and osteopontin were upregulated at 45 Hz and 100 Hz. These results suggest that medium magnitude vibration at 45 Hz induces the G0/G1 arrest of HDPSCs through the p-ERK/Runx-2 pathway and can serve as a potent stimulator of differentiation and extracellular matrix production.

Three-dimensional imaging and molecular analysis of the effects of photobiomodulation and mechanical vibration on orthodontic retention treatment in rats : Effects of photobiomodulation and mechanical vibration on orthodontic retention treatment

PURPOSE

We aimed to evaluate and compare effects of photobiomodulation (PBM) and low-magnitude high-frequency mechanical vibration (HFMV) on orthodontic retention.

METHODS

Sixty-four female Wistar albino rats were divided into 9 groups (2 negative and positive controls each, 3 PBM and 2 HFMV groups) and studied for 25 days. In the experimental groups, closed nickel-titanium closed coil springs with a 50 cN force were placed for 10 days between the maxillary incisor and molar. PBM and HFMV were applied daily over long- (15 days) and short-term (7 days) retention periods. The PBM groups received PBM with a single wavelength (650 nm) or higher wavelengths (532, 650, 940 nm) for 9 min per day. HFMV groups received HFMV of 10, 20, and 30 Hz for 10 min per day. Right and left maxilla were assessed using micro-computed tomography imaging and real-time polymerase chain reaction. The amount of tooth movement during the retention period, expression levels of cyclooxygenase‑2 (COX-2), osteoprotegerin (OPG), and receptor activator of nuclear factor-kappa B ligand (RANKL) mRNA gene expression levels, OPG/RANKL ratios, alveolar bone trabecular thickness (Tb.Th), trabecular number (Tb.N), and structure model index were analyzed. Kruskal-Wallis and Mann-Whitney U tests were used for multiple comparisons of the nonparametric distributed data and binary comparisons, respectively.

RESULTS

When using the long-term retention protocol, PBM and HFMV treatment increased Tb.N (p < 0.05) and decreased COX‑2 mRNA gene expression levels (p < 0.05) and Tb.Th (p < 0.05) compared to controls. For short-term retention, PBM and HFMV decreased the amount of relapse tooth movement compared to controls. In addition, Tb.Th (p < 0.05) and the mRNA gene expression levels of COX‑2 and RANKL (p < 0.05) were decreased.

CONCLUSION

PBM and HFMV might be able to support retention after orthodontic tooth movement by reducing bone resorption and increasing bone quality.

Possible Mechanisms for the Effects of Sound Vibration on Human Health

This paper presents a narrative review of research literature to “map the landscape” of the mechanisms of the effect of sound vibration on humans including the physiological, neurological, and biochemical. It begins by narrowing music to sound and sound to vibration. The focus is on low frequency sound (up to 250 Hz) including infrasound (1–16 Hz). Types of application are described and include whole body vibration, vibroacoustics, and focal applications of vibration. Literature on mechanisms of response to vibration is categorized into hemodynamic, neurological, and musculoskeletal. Basic mechanisms of hemodynamic effects including stimulation of endothelial cells and vibropercussion; of neurological effects including protein kinases activation, nerve stimulation with a specific look at vibratory analgesia, and oscillatory coherence; of musculoskeletal effects including muscle stretch reflex, bone cell progenitor fate, vibration effects on bone ossification and resorption, and anabolic effects on spine and intervertebral discs. In every category research on clinical applications are described. The conclusion points to the complexity of the field of vibrational medicine and calls for specific comparative research on type of vibration delivery, amount of body or surface being stimulated, effect of specific frequencies and intensities to specific mechanisms, and to greater interdisciplinary cooperation and focus.

The role of osteocytes-specific molecular mechanism in regulation of mechanotransduction - A systematic review

Background

Osteocytes, composing over 90% of bone cells, are well known for their mechanosensing abilities. Aged osteocytes with impaired morphology and function are less efficient in mechanotransduction which will disrupt bone turnover leading to osteoporosis. The aim of this systematic review is to delineate the mechanotransduction mechanism at different stages in order to explore potential target for therapeutic drugs.

Methods

A systematic literature search was performed in PubMed and Web of Science. Original animal, cell and clinical studies with available English full-text were included. Information was extracted from the included studies for review.

Results

The 26 studies included in this review provided evidence that mechanical loading are sensed by osteocytes via various sensing proteins and transduced to different signaling molecules which later initiate various biochemical responses. Studies have shown that osteocyte plasma membrane and cytoskeletons are emerging key players in initiating mechanotransduction. Bone regulating genes expressions are altered in response to load sensed by osteocytes, but the genes involved different signaling pathways and the spatiotemporal expression pattern had made mechanotransduction mechanism complicated. Most of the included studies described the important role of osteocytes in pathways that regulate mechanosensing and bone remodeling.

Conclusions

This systematic review provides an up-to-date insight to different steps of mechanotransduction. A better understanding of the mechanotransduction mechanism is beneficial in search of new potential treatment for osteoporotic patients. By delineating the unique morphology of osteocytes and their interconnected signaling network new targets can be discovered for drug development.

Translational potential of this article

This systematic review provides an up-to-date sequential overview and highlights the different osteocyte-related pathways and signaling molecules during mechanotransduction. This allows a better understanding of mechanotransduction for future development of new therapeutic interventions to treat patients with impaired mechanosensitivity.

Does Low-Magnitude High-Frequency Vibration (LMHFV) Worth for Clinical Trial on Dental Implant? A Systematic Review and Meta-Analysis on Animal Studies

Being as a non-pharmacological medical intervention, low-magnitude high-frequency vibration (LMHFV) has shown a positive effect on bone induction and remodeling for various muscle diseases in animal studies, among which dental implants osteointegration were reported to be improved as well. However, whether LMHFV can be clinically used in dental implant is still unknown. In this study, efficacy, parameters and side effects of LMHFV were analyzed via data before 15th July 2020, collecting from MEDLINE/PubMed, Embase, Ovid and Cochrane Library databases. In the screened 1,742 abstracts and 45 articles, 15 animal studies involving 972 implants were included. SYRCLE's tool was performed to assess the possible risk of bias for each study. The GRADE approach was applied to evaluate the quality of evidence. Random effects meta-analysis detected statistically significant in total BIC (P < 0.0001) and BV/TV (P = 0.001) upon loading LMHFV on implants. To conclude, LMHFV played an active role on BIC and BV/TV data according to the GRADE analysis results (medium and low quality of evidence). This might illustrate LMHFV to be a worthy way in improving osseointegration clinically, especially for osteoporosis.

Systematic Review Registration:https://www.crd.york.ac.uk/PROSPERO, identifier: NCT02612389

Effect of Low-Intensity Vibration on Bone Strength, Microstructure, and Adiposity in Pre-Osteoporotic Postmenopausal Women: A Randomized Placebo-Controlled Trial

There has been evidence that cyclical mechanical stimulation may be osteogenic, thus providing opportunities for nonpharmacological treatment of degenerative bone disease. Here, we applied this technology to a cohort of postmenopausal women with varying bone mineral density (BMD) T-scores at the total hip (-0.524 ± 0.843) and spine (-0.795 ± 1.03) to examine the response to intervention after 1 year of daily treatment with 10 minutes of vibration therapy in a randomized double-blinded trial. The device operates either in an active mode (30 Hz and 0.3 g) or placebo. Primary endpoints were changes in bone stiffness at the distal tibia and marrow adiposity of the vertebrae, based on 3 Tesla high-resolution MRI and spectroscopic imaging, respectively. Secondary outcome variables included distal tibial trabecular microstructural parameters and vertebral deformity determined by MRI, volumetric and areal bone densities derived using peripheral quantitative computed tomography (pQCT) of the tibia, and dual-energy X-ray absorptiometry (DXA)-based BMD of the hip and spine. Device adherence was 83% in the active group (n = 42) and 86% in the placebo group (n = 38) and did not differ between groups (p = .7). The mean 12-month changes in tibial stiffness in the treatment group and placebo group were +1.31 ± 6.05% and -2.55 ± 3.90%, respectively (group difference 3.86%, p = .0096). In the active group, marrow fat fraction significantly decreased after 12 months of intervention (p = .0003), whereas no significant change was observed in the placebo group (p = .7; group difference -1.59%, p = .029). Mean differences of the changes in trabecular bone volume fraction (p = .048) and erosion index (p = .044) were also significant, as was pQCT-derived trabecular volumetric BMD (vBMD; p = .016) at the tibia. The data are commensurate with the hypothesis that vibration therapy is protective against loss in mechanical strength and, further, that the intervention minimizes the shift from the osteoblastic to the adipocytic lineage of mesenchymal stem cells. © 2020 American Society for Bone and Mineral Research (ASBMR).

Osteogenic effect of low-intensity pulsed ultrasound and whole-body vibration on peri-implant bone. An experimental in vivo study

OBJECTIVES

The aims of this study were (i) to compare the osteogenic impact of low-intensity pulsed ultrasound (LIPUS) and low-magnitude high-frequency (LMHF) loading achieved with whole-body vibration (WBV) on peri-implant bone healing and implant osseointegration in rat tibiae, and (ii) to examine their combined effect on these processes.

MATERIAL AND METHODS

Titanium implants were inserted in the bilateral tibiae of 28 Wistar rats. Rats were randomly divided into four groups: LIPUS + WBV, LIPUS, WBV, and control. LIPUS was applied to the implant placement site for 20 min/day on 5 days/week (1.5 MHz and 30 mW/cm² ). WBV was applied for 15 min/day on 5 days/week (50 Hz and 0.5 g). In the LIPUS + WBV group, both stimuli were applied under the same stimulation conditions as in the LIPUS and WBV groups. After 4 weeks of treatment, peri-implant bone healing and implant osseointegration were assessed using removal torque (RT) tests, micro-CT analyses of relative gray (RG) value, and histomorphometrical analyses of bone-to-implant contact (BIC) and peri-implant bone formation (BV/TV).

RESULTS

The LIPUS + WBV group had significantly greater BIC than the WBV and control groups. Although there were no significant intergroup differences in RT, RG value, and BV/TV, these variables tended to be greater in the LIPUS + WBV group than the other groups.

CONCLUSIONS

The combination of LIPUS and LMHF loading may promote osteogenic activity around the implant. However, further study of the stimulation conditions of LIPUS and LMHF loading is necessary to better understand the osteogenic effects and the relationship between the two stimuli.

[Low-magnitude vibration promotes osteogenesis of osteoblasts in ovariectomized osteoporotic rats via the estrogen receptor ]

The purpose of this study was to investigate the effect of low-magnitude vibration on osteogenesis of osteoblasts in ovariectomized rats with osteoporosis via estrogen receptor α(ERα). The mRNA expression of osteogenic markers were examined with qRT-PCR, based on which the optimal vibration parameter for promoting osteogenesis was determined (45 Hz × 0.9 g, g = 9.8 m/s2). Then we loaded the optimal vibration parameter on the osteoblasts of ovariectomized rats with osteoporosis. The protein expression of osteogenic markers and ERα were detected with Western blot; the distribution of ERα was examined with immunofluorescence technique. Finally, through inhibiting the expression of ERα with estrogen receptor inhibitor ICI182780, the protein and mRNA expression of osteogenic markers were examined. First, the results showed that low-magnitude vibration could promote the expression of osteogenic markers and ERα in osteoblasts of ovariectomized rats with osteoporosis (P < 0.05), and make ERα transfer to the nucleus. On the other hand, the results also showed that after inhibiting the expression of ERα in osteoblasts of ovariectomized rats with osteoporosis, the protein and mRNA expression of osteogenic marker were decreased (P < 0.05). In our study, low-magnitude vibration played an important role in the osteogenesis of osteoblasts in ovariectomized rats with osteoporosis through increasing the expression and causing translocation of ERα. Furthermore, it provides a theoretical basis for the application of low-magnitude vibration in the prevention and treatment of postmenopausal osteoporosis.

Osteocytes promote osteoclastogenesis via autophagy-mediated RANKL secretion under mechanical compressive force

Osteocytes sense extracellular mechanical stimuli and transduce them into biochemical signals to regulate bone remodeling. The function is also evidenced in orthodontic tooth movement. But the underlying mechanisms haven't been clarified. Autophagy is an evolutionarily conserved cellular catabolic process which affects cellular secretory capabilities. We hypothesized that mechanical force activated osteocyte autophagy through TFE3-related signaling and further promoted osteocyte-mediated osteoclastogenesis. In the present study, we demonstrated that osteocyte autophagy was activated under mechanical compressive force using murine orthodontic tooth movement model since the number of LC3B-positive osteocytes increased by 3-fold in the compression side. In addition, both in vitro mechanical compression and chemical autophagy agonist increased the secretion of RANKL in osteocytes by 3-fold and 4-fold respectively, which is a crucial cytokine for osteoclastogenesis. Lastly, conditioned medium collected from compressed osteocytes promoted the development of osteoclasts. These results suggest that osteocytes could promote osteoclastogenesis via autophagy-mediated RANKL secretion under mechanical compressive force. Our research might provide evidence for exploring methods to accelerate tooth movement in clinic.

Vibration synergistically enhances IL-1β and TNF-α in compressed human periodontal ligament cells in the frequency-dependent manner

Objectives

To investigate whether mechanical vibration at 30 or 60 Hz combined with compressive force alter IL-1β and TNF-α expression in human periodontal ligament (hPDL) cells.

Methods

hPDL cells isolated from the roots of first premolar teeth extracted from four independent donors were cultured and exposed to vibration (0.3 g, 20 min per cycle, every 24 h for 3 cycles) at 30 or 60 Hz (V30 or V60), 2.0 g/cm² compressive force for 2 days (CF), or a combination of compressive force and vibration at 30 Hz or 60 Hz (V30CF or V60CF). Quantitative real-time polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assays (ELISAs) were used to determine IL-1β and TNF-α mRNA and protein, respectively.

Results

The levels of IL-1β and TNF-α did not alter in groups V30 and V60. While, they were upregulated in groups CF, V30CF and V60CF. In addition, IL-1β mRNA and TNF-α mRNA and protein were expressed at significantly higher levels in group V30CF compared to CF group. However, IL-1β protein levels between V30CF and CF groups did not reach statistical significance.

Conclusions

30 Hz vibration had the synergistic effects with compressive force on the upregulation of IL-1β mRNA and TNF-α mRNA and protein in PDL cells, while 60 Hz vibration did not have this synergistic effect.

Low magnitude high frequency vibrations expedite the osteogenesis of bone marrow stem cells on paper based 3D scaffolds

Anabolic effects of low magnitude high frequency (LMHF) vibrations on bone tissue were consistently shown in the literature in vivo, however in vitro efforts to elucidate underlying mechanisms are generally limited to 2D cell culture studies. Three dimensional cell culture platforms better mimic the natural microenvironment and biological processes usually differ in 3D compared to 2D culture. In this study, we used laboratory grade filter paper as a scaffold material for studying the effects of LHMF vibrations on osteogenesis of bone marrow mesenchymal stem cells in a 3D system. LMHF vibrations were applied 15 min/day at 0.1 g acceleration and 90 Hz frequency for 21 days to residing cells under quiescent and osteogenic conditions. mRNA expression analysis was performed for alkaline phosphatase (ALP) and osteocalcin (OCN) genes, Alizarin red S staining was performed for mineral nodule formation and infrared spectroscopy was performed for determination of extracellular matrix composition. The highest osteocalcin expression, mineral nodule formation and the phosphate bands arising from the inorganic phase was observed for the cells incubated in osteogenic induction medium with vibration. Our results showed that filter paper can be used as a model scaffold system for studying the effects of mechanical loads on cells, and LMHF vibrations induced the osteogenic differentiation of stem cells.

Effects of mechanical vibration on cell morphology, proliferation, apoptosis, and cytokine expression/secretion in osteocyte-like MLO-Y4 cells exposed to high glucose

Diabetic patients exhibit significant bone deterioration. Our recent findings demonstrate that mechanical vibration is capable of resisting diabetic bone loss, whereas the relevant mechanism remains unclear. We herein examined the effects of mechanical vibration on the activities and functions of osteocytes (the most abundant and well-recognized mechanosensitive cells in the bone) exposed to high glucose (HG). The osteocytic MLO-Y4 cells were incubated with 50 mM HG for 24 h, and then stimulated with 1 h/day mechanical vibration (0.5 g, 45 Hz) for 3 days. We found that mechanical vibration significantly increased the proliferation and viability of MLO-Y4 cells under the HG environment via the MTT, BrdU, and Cell Viability Analyzer assays. The apoptosis detection showed that HG-induced apoptosis in MLO-Y4 cells was inhibited by mechanical vibration. Moreover, increased cellular area, microfilament density, and anisotropy in HG-incubated MLO-Y4 cells were observed after mechanical vibration via the F-actin fluorescence staining. The real-time polymerase chain reaction and western blotting results demonstrated that mechanical vibration significantly upregulated the gene and protein expression of Wnt3a, β-catenin, and osteoprotegerin (OPG) and decreased the sclerostin, DKK1, and receptor activator for nuclear factor-κB ligand (RANKL) expression in osteocytes exposed to HG. The enzyme-linked immunosorbent assay assays showed that mechanical vibration promoted the secretion of prostaglandin E₂ and OPG, and inhibited the secretion of tumor necrosis factor-α and RANKL in the supernatant of HG-treated MLO-Y4 cells. Together, this study demonstrates that mechanical vibration improves osteocytic architecture and viability, and regulates cytokine expression and secretion in the HG environment, and implies the potential great contribution of the modulation of osteocytic activities in resisting diabetic osteopenia/osteoporosis by mechanical vibration.

Applicability of Low-intensity Vibrations as a Regulatory Factor on Stem and Progenitor Cell Populations

Persistent and transient mechanical loads can act as biological signals on all levels of an organism. It is therefore not surprising that most cell types can sense and respond to mechanical loads, similar to their interaction with biochemical and electrical signals. The presence or absence of mechanical forces can be an important determinant of form, function and health of many tissue types. Along with naturally occurring mechanical loads, it is possible to manipulate and apply external physical loads on tissues in biomedical sciences, either for prevention or treatment of catabolism related to many factors, including aging, paralysis, sedentary lifestyles and spaceflight. Mechanical loads consist of many components in their applied signal form such as magnitude, frequency, duration and intervals. Even though high magnitude mechanical loads with low frequencies (e.g. running or weight lifting) induce anabolism in musculoskeletal tissues, their applicability as anabolic agents is limited because of the required compliance and physical health of the target population. On the other hand, it is possible to use low magnitude and high frequency (e.g. in a vibratory form) mechanical loads for anabolism as well. Cells, including stem cells of the musculoskeletal tissue, are sensitive to high frequency, lowintensity mechanical signals. This sensitivity can be utilized not only for the targeted treatment of tissues, but also for stem cell expansion, differentiation and biomaterial interaction in tissue engineering applications. In this review, we reported recent advances in the application of low-intensity vibrations on stem and progenitor cell populations. Modulation of cellular behavior with low-intensity vibrations as an alternative or complementary factor to biochemical and scaffold induced signals may represent an increase of capabilities in studies related to tissue engineering.

Vibration activates the actin/NF-κB axis and upregulates IL-6 and IL-8 expression in human periodontal ligament cells

We previously reported that mechanical vibration-induced proinflammatory cytokines, interleukin-6 (IL-6) and IL-8, expression in human periodontal ligament (hPDL) cells, however, the underlying mechanism remained unclear. Mechanical stimuli are able to activate cellular responses by inducing the activation of several signaling pathways including cytoskeletal changes and inflammation. The actin cytoskeleton is a highly dynamic network and plays many important roles in intracellular events. Here, we aimed to investigate the involvement of a pivotal mediator of inflammatory responses, nuclear factor-κB (NF-κB), and actin polymerization in vibration-induced upregulation of IL-6 and IL-8 expression in hPDL cells. hPDL cells were pretreated with the NF-κB inhibitor BAY 11-7082 or cytochalasin D, respectively, before exposure to vibration. IL-6 and IL-8 messenger RNA (mRNA) and protein expression were quantified by quantitative polymerase chain reaction and enzyme-linked immunosorbent assays, respectively. Subcellular localization of the NF-κB p65 subunit was visualized by immunofluorescent staining. We found an increase in NF-κB nuclear translocation in vibrated cells compared with control cells. Pretreatment with BAY 11-7082 significantly inhibited vibration-induced IL-6 and IL-8 mRNA and protein expression in hPDL cells. Moreover, pretreatment with cytochalasin D inhibited NF-κB nuclear translocation and attenuated upregulation of IL-6 and IL-8 mRNA and protein in vibrated cells. Therefore, modulation of actin cytoskeletal polymerization in response to vibration may activate the NF-κB signaling pathway and subsequently upregulate IL-6 and IL-8 expression in hPDL cells.

Micro-vibrations at 30 Hz on bone cells cultivated in vitro produce soluble factors for osteoclast inhibition and osteoblast activity

OBJETIVE

It has been claimed that micro-pulse vibration can accelerate the rate of tooth movement during orthodontic treatment; however, the underlying cellular mechanism has yet to be elucidated. The purpose of this study was to understand the mechanisms underlying tooth movement acceleration by measuring alterations in a panel of intercellular signalling molecules and markers of osteoblast/osteoclast function following micro-pulse vibration for 20 min at 30 Hz.

DESIGN

Primary BALB/c mouse calvarial osteoblasts were cultivatedin vitro and subjected to micro-pulse vibration (0.25 N; 30 Hz) with the AcceleDent® Aura appliance for 20 min and assayed for IL-4, IL-13, IL-17, OPG, soluble RANKL and TGF-β protein by ELISA; for PCNA in osteoblasts and caspase 3/7 in osteoclasts by immunohistochemistry; for IL-4, IL-13, and Il-17 in osteoclasts by ELISA; and for cathepsin K by flow cytometry.

RESULTS

After micro-pulse vibration, the murine osteoblast culture supernatant showed increased IL-4, IL-13, IL-17, OPG and TGF-β levels and decreased RANKL levels; PCNA in osteoblasts and caspase 3/7 in osteoclasts were also upregulated. The osteoclast culture supernatant had increased levels of IL-4, IL-13 and IL-17, and cathepsin K was upregulated in the treatment group compared with the control group.

CONCLUSIONS

Micro-pulse vibration promotes the production of soluble factors that inhibit osteoclasts, promote apoptosis and activate osteoblasts in vitro, which could increase bone mineral density. Further studies should be conducted in order to understand the biological mechanism of how micro-vibration might influence tooth movement during orthodontic treatment.

Spontaneous cellular vibratory motions of osteocytes are regulated by ATP and spectrin network

Vibration at high frequency has been demonstrated to be anabolic for bone and embedded osteocytes. The response of osteocytes to vibration is frequency-dependent, but the mechanism remains unclear. Our previous computational study using an osteocyte finite element model has predicted a resonance effect involving in the frequency-dependent response of osteocytes to vibration. However, the cellular spontaneous vibratory motion of osteocytes has not been confirmed. In the present study, the cellular vibratory motions (CVM) of osteocytes were recorded by a custom-built digital holographic microscopy and quantitatively analyzed. The roles of ATP and spectrin network in the CVM of osteocytes were studied. Results showed the MLO-Y4 osteocytes displayed dynamic vibratory motions with an amplitude of ~80 nm, which is relied both on the ATP content and spectrin network. Spectrum analysis showed several frequency peaks in CVM of MLO-Y4 osteocytes at 30 Hz, 39 Hz, 83 Hz and 89 Hz. These peak frequencies are close to the commonly used effective frequencies in animal training and in-vitro cell experiments, and show a correlation with the computational predictions of the osteocyte finite element model. These results implicate that osteocytes are dynamic and the cellular dynamic motion is involved in the cellular mechanotransduction of vibration.

Applying vibration in early postmenopausal osteoporosis promotes osteogenic differentiation of bone marrow-derived mesenchymal stem cells and suppresses postmenopausal osteoporosis progression

We aimed to evaluate whether applying low magnitude vibration (LMV) in early postmenopausal osteoporosis (PMO) suppresses its progression, and to investigate underlying mechanisms. Rats were randomly divided into Sham (Sham-operated), Sham+V, OVX (ovariectomized), OVX+E2 (estradiol benzoate), OVX+V (LMV at 12–20 weeks postoperatively), and OVX+Vi (LMV at 1–20 weeks postoperatively) groups. LMV was applied for 20 min once daily for 5 days weekly. V rats were loaded with LMV at 12–20 weeks postoperatively. Vi rats were loaded with LMV at 1–20 weeks postoperatively. Estradiol (E2) rats were intramuscularly injected at 12–20 weeks postoperatively once daily for 3 days. The bone mineral densities (BMDs), biomechanical properties, and histomorphological parameters of tibiae were analyzed. In vitro, rat bone marrow-derived mesenchymal stem cells (rBMSCs) were subjected to LMV for 30 min daily for 5 days, or 17β-E2 with or without 1-day pretreatment of estrogen receptor (ER) inhibitor ICI 182,780 (ICI). The mRNA and protein expresion were performed. Data showed that LMV increased BMD, bone strength, and bone mass of rats, and the effects of Vi were stronger than those of E2. In vitro, LMV up-regulated the mRNA and protein expressions of Runx2, Osx, Col I, and OCN and down-regulated PPARγ, compared with E2. The effects of both LMV and E2 on rBMSCs were inhibited by ICI. Altogether, LMV in early PMO suppresses its progression, which is associated with osteogenic differentiation of rBMSCs via up-regulation of ERα and activation of the canonical Wnt pathway. LMV may therefore be superior to E2 for the suppression of PMO progression.

Effect of mechanical vibration stress in cell culture on human induced pluripotent stem cells

The development of induced pluripotent stem cell (iPSC) techniques has solved various limitations in cell culture including cellular proliferation and potency. Hence, the expectations on wider applications and the quality of manufactured iPSCs are rapidly increasing. To answer such growing expectations, enhancement of technologies to improve cell-manufacturing efficiency is now a challenge for the bioengineering field. Mechanization of conventional manual operations, aimed at automation of cell manufacturing, is quickly advancing. However, as more processes are being automated in cell manufacturing, it is need to be more critical about influential parameters that may not be as important in manual operations. As a model of such parameters, we focused on the effect of mechanical vibration, which transmits through the vessel to the cultured iPSCs. We designed 7 types of vertical vibration conditions in cell culture vessels using a vibration calibrator. These conditions cover a wide range of potential situations in cell culture, such as tapping or closing an incubator door, and examined their effects by continuous passaging (P3 to P5). Detailed evaluation of cells by time-course image analysis revealed that vibrations can enhance cell growth as an early effect but can negatively affect cell adhesion and growth profile after several passages as a delayed effect. Such unexpected reductions in cell quality are potentially critical issues in maintaining consistency in cell manufacturing. Therefore, this work reveals the importance of continuous examination across several passages with detailed, temporal, quantitative measurements obtained by non-invasive image analysis to examine when and how the unknown parameters will affect the cell culture processes.

Whole body vibration at low-frequency can increase trabecular thickness and width in adult rats

OBJECTIVE

This study aimed to examine whether WBV becomes a possible modality for the primary prevention of osteoporosis by exploring WBV frequency that has positive effects on bone properties in adult rats.

METHODS

Thirty-six 24-week-old rats were divided into one control and 5 experimental groups, which underwent WBV at various frequencies (15, 30, 45, 60 or 90 Hz), with a magnitude of 0.5 g, for 15 min/day, 5 days/week, for 8 weeks. Bone size, muscle weight and bone mechanical strength were measured at the end of experimental period. Bone mass, trabecular bone microarchitecture (TBMA) and cortical bone geometry were analyzed by micro-CT. Circulating bone formation/resorption markers were determined by ELISA.

RESULTS

Body weight-corrected soleus weight in all experimental groups and body weight-corrected extensor digitorum longus muscle weight in the 15 and 30 Hz groups were significantly higher than those of the control group, respectively. Femur trabecular thickness and width were significantly higher in the 15 Hz group than in the control group. However, there was no difference in bone mechanical strength or bone formation/resorption markers among all groups.

CONCLUSION

These results suggest that WBV at low-frequencies may become a potent modality for the primary prevention of osteoporosis in adults.

Vibration enhances osteoclastogenesis by inducing RANKL expression via NF-κB signaling in osteocytes

To shorten the duration of orthodontic treatment it is important not only to reduce risks such as dental caries, periodontal disease, and root resorption, but also to decrease pain and discomfort caused by a fixed appliance. Several studies have investigated the effect of vibration applied to fixed appliances to accelerate tooth movement. Although it was reported that vibration accelerates orthodontic tooth movement by enhancing alveolar bone resorption, the underlying cellular and molecular mechanisms remain unclear. In this study, we investigated the effects of vibration on osteoclastogenesis in vitro and in vivo. Vibration applied to pre-osteoclast cell line RAW264.7 cells enhanced cell proliferation but did not affect their differentiation into osteoclasts. Osteocytes in bone are known to be mechanosensitive and to act as receptor activator of nuclear factor kappa B (NF-κB) ligand (RANKL). Therefore, in the present study, vibration was applied to cells from the osteocyte-like cell line MLO-Y4. In MLO-Y4 cells, vibration induced phosphorylation of the inhibitor of NF-κB (IκB) and caused nuclear localization of NF-κB p65. Additionally, vibration increased RANKL mRNA expression, but did not affect osteoprotegerin (OPG) mRNA expression in MLO-Y4 cells, thus resulting in an increased RANKL/OPG ratio. Consistent with these findings, vibration applied during experimental tooth movement increased NF-κB activation and RANKL expression in osteocytes on the compression side of alveolar bone in vivo, whereas vibration had no such effects on the tension side. Furthermore, in a co-culture of MLO-Y4 cells and RAW264.7 cells, vibration applied to MLO-Y4 cells enhanced osteoclastogenesis. These findings suggest that vibration could accelerate orthodontic tooth movement by enhancing osteoclastogenesis through increasing the number of pre-osteoclasts and up-regulating RANKL expression in osteocytes on the compression side of alveolar bone via NF-κB activation.

Microfluidic platform for studying osteocyte mechanoregulation of breast cancer bone metastasis

Bone metastasis is a common, yet serious, complication of breast cancer. Breast cancer cells that extravasate from blood vessels to the bone devastate bone quality by interacting with bone cells and disrupting the bone remodeling balance. Although exercise is often suggested as a cancer intervention strategy and mechanical loading during exercise is known to regulate bone remodeling, its role in preventing bone metastasis remains unknown. We developed a novel in vitro microfluidic tissue model to investigate the role of osteocytes in the mechanical regulation of breast cancer bone metastasis. Metastatic MDA-MB-231 breast cancer cells were cultured inside a 3D microfluidic lumen lined with human umbilical vein endothelial cells (HUVECs), which is adjacent to a channel seeded with osteocyte-like MLO-Y4 cells. Physiologically relevant oscillatory fluid flow (OFF) (1 Pa, 1 Hz) was applied to mechanically stimulate the osteocytes. Hydrogel-filled side channels in-between the two channels allowed real-time, bi-directional cellular signaling and cancer cell extravasation over 3 days. The applied OFF was capable of inducing intracellular calcium responses in osteocytes (82.3% cells responding with a 3.71 fold increase average magnitude). Both extravasation distance and percentage of extravasated side-channels were significantly reduced with mechanically stimulated osteocytes (32.4% and 53.5% of control, respectively) compared to static osteocytes (102.1% and 107.3% of control, respectively). This is the first microfluidic device that has successfully integrated stimulatory bone fluid flow, and demonstrated that mechanically stimulated osteocytes reduced breast cancer extravasation. Future work with this platform will determine the specific mechanisms involved in osteocyte mechanoregulation of breast cancer bone metastasis, as well as other types of cancer metastasis and diseases.

Efficacy of mechanical vibration in regulating mesenchymal stem cells gene expression

This study aimed at investigating the expression of osteoblast and chondrocyte-related genes in mesenchymal stem cells (MSCs), derived from rabbit adipose tissue, under mechanical vibration. The cells were placed securely on a vibrator's platform and subjected to 300 Hz of sinusoidal vibration, with a maximum amplitude of 10 μm, for 45 min per day, and for 14 consequent days, in the absence of biochemical reagents. The negative control group was placed in the conventional culture medium with no mechanical loading. The expression of osteoblast and chondrocyte-related genes was investigated using real-time polymerase chain reaction (real-time PCR). In addition, F-actin fiber structure and alignment with the help of actin filament fluorescence staining were evaluated, and the level of metabolic activity of MSCs was determined by the methyl thiazolyl tetrazolium assay. The real-time PCR study showed a significant increase of bone gene expression in differentiated cells, compared with MSCs (P < 0.05). On the other hand, the level of chondrocyte gene expression was not remarkable. Applying mechanical vibration enhanced F-actin fiber structure and made them aligned in a specific direction. It was also found that during the differentiation process, the metabolic activity of the cells increased (P < 0.05). The results of this work are in agreement with the well-accepted fact that the MSCs, in the absence of growth factors, are sensitive to low-amplitude, high-frequency vibration. Outcomes of this work can be applied in cell therapy and tissue engineering, when regulation of stem cells is required.

Effects of low magnitude high frequency mechanical vibration combined with compressive force on human periodontal ligament cells in vitro

Objective

Vibration can be used to accelerate tooth movement, though the exact mechanisms remain unclear. This study aimed to investigate the effects of low magnitude high frequency (LMHF) vibration combined with compressive force on periodontal ligament (PDL) cells in vitro.

Materials and methods

Human PDL cells were isolated from extracted premolar teeth of four individuals. To determine the optimal frequency for later used in combination with compressive force, three cycles of low-magnitude (0.3 g) vibrations at various frequencies (30, 60, or 90 Hz) were applied to PDL cells for 20 min every 24 h. To investigate the effects of vibration combined with compressive force, PDL cells were subjected to three cycles of optimal vibration frequency (V) or 1.5 g/cm2 compressive force for 48 h (C) or vibration combined with compressive force (VC). Cell viability was assessed using MTT assay. PGE2, soluble RANKL (sRANKL), and OPG production were quantified by ELISA. RANKL, OPG, and Runx2 expression were determined using real-time PCR.

Results

Cell viability was decreased in groups C and VC. PGE2 and RANKL, but not OPG, were increased in groups V, C, and VC, thus increasing the RANKL/OPG ratio. The highest level was observed in group VC. sRANKL was increased in groups V, C, and VC; however, no significant different between the experimental groups. Runx2 expression was reduced in groups C and VC.

Conclusions

Vibration increased PGE2, RANKL, and sRANKL, but not OPG and Runx2. Vibration had the additive effects on PGE2 and RANKL, but not sRANKL in compressed PDL cells.

Hand-arm vibration syndrome

Use of vibrating tools often leads to development of hand-arm vibration syndrome. It manifests with vascular symptoms, neurologic (carpal tunnel syndrome) and musculoskeletal symptoms (impaired grip strength, osteoarthritis, bone necrosis). Kienböck's disease is osteonecrosis of the lunate. A 61-year-old construction worker was referred to a rheumatologist because of suspected arthritis. On examination tenderness and swelling of the dorsal aspect of the right wrist were recorded without features of inflammation. The patient reported paresthesia in the right hand when working with a pneumatic drill. He reported no morning stiffness or Raynaud's phenomenon. He had undergone surgery because of right carpal tunnel syndrome two years earlier. Rheumatoid factor was negative, CRP 0.2 mg/l, uric acid 4.7 mg/dl. In magnetic resonance avascular necrosis of the lunate was diagnosed and scaphoid fracture. Kienböck's disease was diagnosed. Non-steroidal anti-inflammatory drugs were used. The patient did not give consent for surgery.

Electromagnetic Field Analysis of Low-Magnitude High-Frequency Vibrator with Multiple Plungers

Low-magnitude high-frequency (LMHF) of vibrational stimulation has been accepted as an effective method to enhance bone remolding. However, the electromagnetic field (EMF) generated by the vibrator could also be an influence factor in the vibrational experiments. This phenomenon underlies the bone remodeling effect caused by vibrational stimulation is disrupted to be investigated. This paper presents a design of LMHF vibrator with multiple plungers to generate vibrational stimulation with ultra low magnetic flux density to minimize the biological effect caused by the EMF. The EMF is analyzed in finite element method (FEM) using COMSOL.

Therapeutic ionizing radiation induced bone loss: a review of in vivo and in vitro findings

Radiation therapy is one of the routine treatment modalities for cancer patients. Ionizing radiation (IR) can induce bone loss, and consequently increases the risk of fractures with delayed and nonunion of the bone in the cancer patients who receive radiotherapy. The orchestrated bone remodeling can be disrupted due to the affected behaviors of bone cells, including bone mesenchymal stem cells (BMSCs), osteoblasts and osteoclasts. BMSCs and osteoblasts are relatively radioresistant compared with osteoclasts and its progenitors. Owing to different radiosensitivities of bone cells, unbalanced bone remodeling caused by IR is closely associated with the dose absorbed. For doses less than 2 Gy, osteoclastogenesis and adipogenesis by BMSCs are enhanced, while there are limited effects on osteoblasts. High doses (>10 Gy) induce disrupted architecture of bone, which is usually related to decreased osteogenic potential. In this review, studies elucidating the biological effects of IR on bone cells (BMSCs, osteoblasts and osteoclasts) are summarized. Several potential preventions and therapies are also proposed.

Role of Osteocytes in Myeloma Bone Disease: Anti-sclerostin Antibody as New Therapeutic Strategy

Osteocytes are terminally differentiated cells of the osteoblast lineage. They are involved in the regulation of bone remodeling by increasing osteoclast formation or decreasing bone formation by the secretion of the osteoblast inhibitor sclerostin. Monoclonal antibody anti-sclerostin, Romosozumab, has been developed and tested in clinical trials in patients with osteoporosis. In the last years, the role of osteocytes in the development of osteolytic bone lesions that occurs in multiple myeloma, have been underlined. Myeloma cells increase osteocyte death through the up-regulation of both apoptosis and autophagy that, in turn, triggers osteoclast formation, and activity. When compared to healthy controls, myeloma patients with bone disease have higher osteocyte cell death, but the treatment with proteasome inhibitor bortezomib has been shown to maintain osteocyte viability. In preclinical mouse models of multiple myeloma, treatment with blocking anti-sclerostin antibody increased osteoblast numbers and bone formation rate reducing osteolytic bone lesions. Moreover, the combination of anti-sclerostin antibody and the osteoclast inhibitor zoledronic acid increased bone mass and fracture resistance synergistically. However, anti-sclerostin antibody did not affect tumor burden in vivo or the efficacy of anti-myeloma drugs in vitro. Nevertheless, the combination therapy of anti-sclerostin antibody and the proteasome inhibitor carfilzomib, displayed potent anti-myeloma activity as well as positive effects on bone disease in vivo. In conclusion, all these data suggest that osteocytes are involved in myeloma bone disease and may be considered a novel target for the use of antibody-mediated anti-sclerostin therapy also in multiple myeloma patients.

The effect of low-magnitude, high-frequency vibration on poly(ethylene glycol)-microencapsulated mesenchymal stem cells

Low-magnitude, high-frequency vibration has stimulated osteogenesis in mesenchymal stem cells when these cells were cultured in certain types of three-dimensional environments. However, results of osteogenesis are conflicting with some reports showing no effect of vibration at all. A large number of vibration studies using three-dimensional scaffolds employ scaffolds derived from natural sources. Since these natural sources potentially have inherent biochemical and microarchitectural cues, we explored the effect of low-magnitude, high-frequency vibration at low, medium, and high accelerations when mesenchymal stem cells were encapsulated in poly(ethylene glycol) diacrylate microspheres. Low and medium accelerations enhanced osteogenesis in mesenchymal stem cells while high accelerations inhibited it. These studies demonstrate that the isolated effect of vibration alone induces osteogenesis.

Vibration enhances PGE2 , IL-6, and IL-8 expression in compressed hPDL cells via cyclooxygenase pathway

BACKGROUND

Although vibration combined with orthodontic force may accelerate orthodontic tooth movement, little is known about the mechanisms that regulate the associated cellular responses. The goal of this study was to investigate whether mechanical vibration combined with compressive force regulates cyclooxygenase (COX)-2/prostaglandin E2 (PGE₂ ) and interleukin (IL)-6 and IL-8 messenger RNA (mRNA) and protein expression in human periodontal ligament (hPDL) cells via the COX pathway.

METHODS

The primary cultured hPDL cells were exposed to mechanical vibration, compressive force or a combination of both mechanical vibration and compressive force at 24, 48, and 72 hours. The COX-2, IL-6, IL-8, receptor activator of nuclear factor kappa-Β ligand (RANKL), and osteoprotegrin (OPG) mRNA expressions were determined using quantitative real-time polymerase chain reaction (qPCR). The PGE₂ , IL-6, and IL-8 protein expressions were quantified by enzyme-linked immunosorbent assay (ELISA). To demonstrate whether the expression of PGE₂ , IL-6, and IL-8 was in the COX-dependent pathway, the hPDL cells were treated with indomethacin. To determine whether PGE₂ stimulated the hPDL cells to express IL-6 and IL-8, exogenous PGE₂ was added to the culture media.

RESULTS

The combination of mechanical vibration and compressive force synergistically upregulated RANKL/OPG, COX-2/PGE₂ , IL-6 and IL-8 mRNA, and protein expression. The indomethacin significantly attenuated the increases of PGE₂ , IL-6, and IL-8 expression in cells stimulated with compressive force or mechanical vibration combined with compressive force. In addition, exogenous PGE₂ increased IL-6 and IL-8 mRNA and protein expressions in hPDL cells.

CONCLUSION

Mechanical vibration may enhance alveolar bone resorption at the compression side during orthodontic tooth movement via a mechanism involving the cyclooxygenase pathway.

Iliac and mandible osteoblasts exhibit varied responses to LMHF vibration

The facial and long bones have distinct developmental origins, structures, and cellular compositions. This study aimed to compare the in vitro responses of human mandible and long bone osteoblasts to low-magnitude, high-frequency (LMHF) mechanical vibration in terms of expression of mediators of bone remodeling. Osteoblast-like cell cultures were prepared from iliac crest and mandibular bone specimens from three individuals and cultured in osteogenic induction media. Induction of mature osteoblastic phenotypes was confirmed by analysis of DNA content, alkaline phosphatase activity and gene expression every 3 days for 27 days. Based on gene expression, mature osteoblasts formed by day 15 of induction culture. After 15 days of culture in induction media, mature osteoblasts were subjected to vibration (0, 30, or 60 Hz) for 30 min every 24 h. After 48 h, RANKL, OPG, IL-1β, IL-6 and TGF-β gene, and protein expression were determined by real-time PCR analysis of total cellular mRNA and ELISAs of the cell supernatants. Both iliac and mandible osteoblasts responded to LMHF vibration: IL-1β and RANKL mRNA were downregulated and IL-6 mRNA was upregulated. However, TGF- β mRNA was unaltered and OPG mRNA was upregulated in iliac osteoblasts, whereas both TGF-β and OPG mRNA were downregulated in mandible osteoblasts. As a result, LMHF reduced the RANKL/OPG mRNA ratio in iliac osteoblasts but did not alter the RANKL/OPG mRNA ratio in mandible osteoblasts. This study suggests mature iliac osteoblasts exhibit a more potent anti-resorptive response to vibration, while this tendency was not obviously apparent in mature mandible osteoblasts.