Low-magnitude High-frequency Vibration Research Articles

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.

Low‐magnitude high‐frequency vibration (LMHFV) enhances bone remodeling in osteoporotic rat femoral fracture healing

Low-magnitude high-frequency vibration (LMHFV) (35 Hz, 0.3 g) accelerates fracture healing by enhancing callus formation and mineralization for both normal and osteoporotic rats in our previous studies.1,2 We hypothesized that LMHFV enhances fracture healing through bone remodeling. Ibandronate was used to suppress LMHFV-stimulated bone remodeling and changes in remodeling were investigated to verify our hypothesis. Closed femoral fractures were created in 80 osteoporotic female Sprague-Dawley rats. The rats were randomly assigned into control (CG), LMHFV (VG) (20 min/day, 5 days/week), ibandronate (BG) (7 µg/kg/week), or LMHFV + ibandronate (VBG) for a treatment duration of 2, 4, 6, or 8 weeks. Blood was taken and the femora were harvested for histological and radiological analyses. VG had the fastest drop in callus area (CA) and width (CW), and bone volume to tissue volume ratio (BV/TV); whereas, a plateaued trend in BG and VBG was observed. The fastest callus reduction, highest mineral apposition rate at week 6, and increased serum concentration of osteocalcin and TRAP5b in VG suggested enhanced remodeling. LMHFV partially reversed the inhibition of bone remodeling by ibandronate suggested LMHFV had an opposite effect on bone remodeling to ibandronate. In conclusion, LMHFV accelerated fracture healing by enhancing bone remodeling and the administration of ibandronate can impair this enhancement. LMHFV has great potential in improving fracture outcome clinically.

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

Osteocytes are well evidenced to be the major mechanosensor in bone, responsible for sending signals to the effector cells (osteoblasts and osteoclasts) that carry out bone formation and resorption. Consistent with this hypothesis, it has been shown that osteocytes release various soluble factors (e.g. transforming growth factor-β, nitric oxide, and prostaglandins) that influence osteoblastic and osteoclastic activities when subjected to a variety of mechanical stimuli, including fluid flow, hydrostatic pressure, and mechanical stretching. Recently, low-magnitude, high-frequency (LMHF) vibration (e.g., acceleration less than < 1 × g, where g = 9.81 m/s 2, at 20–90 Hz) has gained much interest as studies have shown that such mechanical stimulation can positively influence skeletal homeostasis in animals and humans. Although the anabolic and anti-resorptive potential of LMHF vibration is becoming apparent, the signaling pathways that mediate bone adaptation to LMHF vibration are unknown. We hypothesize that osteocytes are the mechanosensor responsible for detecting the vibration stimulation and producing soluble factors that modulate the activity of effector cells. Hence, we applied low-magnitude (0.3 × g) vibrations to osteocyte-like MLO-Y4 cells at various frequencies (30, 60, 90 Hz) for 1 h. We found that osteocytes were sensitive to this vibration stimulus at the transcriptional level: COX-2 maximally increased by 344% at 90 Hz, while RANKL decreased most significantly (−55%, p < 0.01) at 60 Hz. Conditioned medium collected from the vibrated MLO-Y4 cells attenuated the formation of large osteoclasts (≥ 10 nuclei) by 36% ( p < 0.05) and the amount of osteoclastic resorption by 20% ( p = 0.07). The amount of soluble RANKL (sRANKL) in the conditioned medium was found to be 53% lower in the vibrated group ( p < 0.01), while PGE 2 release was also significantly decreased (−61%, p < 0.01). We conclude that osteocytes are able to sense LMHF vibration and respond by producing soluble factors that inhibit osteoclast formation.

Beneficial effects of low-magnitude high-frequency vibration on fracture healing in rats

Objective To investigated the effects of whole-body low-magnitude high-frequency vibration (LMHFV), a form of biophysical intervention, on fracture healing. Methods Closed femoral shaft fracture with intramedullary fixation was established in 55 SD rats. Effects of LMHFV treatment on fracture healing were assessed through comparison with the sham control. Assessments included two- and three-dimensional quantification of mineralized callus formation using plain radiography and micro-CT.Mechanical outcomes were checked with four-point-bending tests. Results Radiography as well as micro-CT showed significantly larger amount of mineralized callus in the treatment group, together with a significantly faster remodeling process of the callus into mature bone. The mechanical strength of the healed fracture was significantly greater after 4 weeks of treatment compared with the control. Conclusions LMHFV enhances healing of the closed femoral shaft fracture in rats. Its potential clinical advantages shall be confirmed in the subsequent clinical trials. Key words: Low-magnitude high-frequency vibration; Fracture healing; Callus; Mechanical testing

Low-magnitude high-frequency vibration treatment augments fracture healing in ovariectomy-induced osteoporotic bone

Fracture healing is impaired in osteoporotic bone. Low-magnitude high-frequency vibration (LMHFV) has recently been proven to be osteogenic in osteoporotic intact bone. Our previous study found that LMHFV significantly enhanced fracture healing in adult rats. This study was designed to explore whether LMHFV was able to promote fracture healing in osteoporotic bone by enhancing callus formation, remodeling, and mineralization and to compare with age-matched nonosteoporotic ones. Nine-month-old ovariectomy (OVX)-induced osteoporotic rats were randomized into control (OVX-C) or vibration group (OVX-V); age-matched sham-operated rats were assigned into control (Sham-C) or vibration group (Sham-V). LMHFV (35 Hz, 0.3 g) was given 20 min/day and 5days/week to the treatment groups, while sham treatment was given to the control groups. Weekly radiographs and endpoint micro-CT, histomorphometry, and mechanical properties were evaluated at 2, 4, and 8 weeks post-treatment. Results confirmed that the fracture healing in OVX-C was significantly inferior to that in Sham-C. LMHFV was shown to be effective in promoting the fracture healing in OVX group in all measured parameters, particularly in the early phases of healing, with the outcomes comparable to that of age-matched normal fracture healing. Callus formation, mineralization and remodeling were enhanced by 25–30%, with a 70% increase in energy to failure than OVX-C. However, Sham-V was found to have lesser fracture healing enhancement, with significant increase in callus area only on week 2 and 3 than Sham-C, suggesting non-OVX aged bones were less sensitive to mechanical loading. The findings of this study provide a good basis to suggest that proceeding to clinical trials is the next step to evaluate the efficacy of LMHFV on osteoporotic fracture healing.