Effect of Concurrent Use of Whole-Body Vibration and Parathyroid Hormone on Bone Structure and Material Properties of Ovariectomized Mice

Discretizing low-intensity whole-body vibration into bouts with short rest intervals promotes bone defect repair in osteoporotic mice

Continuous administration of low-intensity whole-body vibration (WBV) gradually diminishes bone mechanosensitivity over time, leading to a weakening of its osteogenic effect. We investigated whether discretizing WBV into bouts with short rest intervals was effective in enhancing osteoporotic bone repair. Ten-week-old female mice were ovariectomized and underwent drill-hole defect surgery (Day 0) on the right tibial diaphysis at 11 weeks of age. The mice underwent one of three regimens starting from Day 1 for 5 days/week: continuous WBV at 45 Hz and 0.3 g for 7.5 min/day (cWBV); 3-s bouts of WBV at 45 Hz, 0.3 g followed by 9-s rest intervals, repeated for 30 min/day (repeated bouts of whole-body vibration with short rest intervals [rWBV]); or a sham treatment. Both the cWBV and rWBV groups received a total of 20,250 vibration cycles per day. On either Day 7 or 14 posteuthanasia (n = 6/group/timepoint), the bone and angiogenic vasculature in the defect were computed tomography imaged using synchrotron light. By Day 14, the bone repair was most advanced in the rWBV group, showing a higher bone volume fraction and a more uniform mineral distribution compared with the sham group. The cWBV group exhibited an intermediate level of bone repair between the sham and rWBV groups. The rWBV group had a decrease in large-sized angiogenic vessels, while the cWBV group showed an increase in such vessels. In conclusion, osteoporotic bone repair was enhanced by WBV bouts with short rest intervals, which may potentially be attributed to the improved mechanosensitivity of osteogenic cells and alterations in angiogenic vasculature.

Low-intensity pulsed ultrasound and parathyroid hormone improve muscle atrophy in estrogen deficiency mice

Due to aging and long-term estrogen deficiency, postmenopausal women suffer muscle atrophy (MA), which is characterized by decreased muscle mass and muscle quality. Low-intensity pulsed ultrasound (LIPUS) is an acoustic wave inducing biological effects mainly by the mechanical stimulation and used as a non-invasive physical therapy for muscle repair. Parathyroid hormone (PTH) is an 84-amino-acid polypeptide, and its bioactive fragment [PTH (1-34)] has potential application in the treatment of MA. We speculate that the combination of physical therapy (i.e., the LIPUS) and regulatory hormone (i.e., the PTH) would be more effective in the treatment of MA. The objective of this study was to evaluate the individual and combined effects of LIPUS and PTH therapy on MA in estrogen deficiency mice. Seventy 8-week-old female C57BL/6J mice were used in this study and the MA model was induced by an intraperitoneal injection of 4-vinylcyclohexene diepoxide (VCD) for 20 consecutive days. The VCD-induced MA mice were randomly divided into MA, LIPUS, PTH and LIPUS + PTH (Combined) groups (n = 10/group). In the LIPUS group, the mice were treated by LIPUS in bilateral quadriceps muscles for 20 min, five times a week for 6 weeks. In the PTH group, the mice received subcutaneous injection of PTH (1-34) (80 ug/kg/d) five times a week, for 6 weeks. In the Combined group, the PTH was administrated 30 min before each LIPUS session. Hematoxylin-eosin (H&E) staining, serum biochemical analysis and quantitative real-time polymerase chain reaction (qRT-PCR) were applied to evaluate the therapeutic effects of related treatments. The results showed that the MA mice had a disordered estrus cycle, significantly decreased muscle mass and myofibers cross-sectional area (CSA). After treatments, LIPUS, PTH and Combined groups had a significantly increased CSA, compared with the MA mice without treatment. In addition, Combined group had a significantly increased mRNA expression of Pax7, MyoD and MyoG, compared with LIPUS and PTH monotherapy groups. Our findings indicated that the combination of LIPUS and PTH treatment improves muscle regeneration ability, which might have potential for treating MA in postmenopausal women.

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.

Mechanical Vibration Associated With Intermittent PTH Improves Bone Microarchitecture in Ovariectomized Rats

INTRODUCTION

Intermittent 1-34 parathyroid hormone (iPTH) administration, a bone-forming treatment, is widely used as a therapy for severe osteoporosis. It can only be used for a maximum of 24 mo and must be followed by an antiresorptive drug to retain the new formed tissue. Mechanical load, in the form of low-intensity and high-frequency vibration, has received considerable attention due to its ability to prevent bone loss.

AIM

To investigate the ability of whole body mechanical vibration (MV) to potentiate the anabolic effects of iPTH and to inhibit bone resorption following discontinuation of iPTH treatment in estrogen-deficient rats.

METHODOLOGY

Fifty-four 6-month-old female Wistar rats were ovariectomized (OVX) or sham-operated. After 5 mo, they were divided into 7 groups: Sham - non-OVX; Control - OVX, vehicle for 60 d; MV - OVX, submitted to MV for 60 d; PTH60d - OVX, injected with iPTH for 60 d; PTH+MV - OVX, injected with iPTH combined with MV for 60 d; PTH30d - OVX, injected with iPTH for 30 d, and untreated for 30 d; PTH30d/MV30d - OVX, injected with iPTH for 30 d, followed by MV for 30 d. Bone mineral density (BMD) and body composition (lean mass and fat) were evaluated at OVX (T0), the beginning (T1), and at the end (T2) of treatments by dual X-ray absorptiometry (DXA). Femurs were processed for histomorphometry (bone volume - BV/TV and cortical thickness - Ct.Th) and tibias for biomechanical test.

RESULTS

Body composition and BMD were similar among the groups at T0. In T2, MV presented higher fat than other groups (except PTH60d) and PTH30d/MV30d showed greater lean mass than Control. At T1, Sham presented the highest BMD, but between T1 vs T2 there was an increase in all iPTH-treated groups. At T2, BMD was higher in PTH60d and PTH+MV than in the Control and MV groups. The highest BV/TV was observed in the PTH+MV group, followed by PTH60d. Cortical thickness was increased in PTH60d and PTH+MV compared to Sham. Vibration applied post-iPTH (PTH30d/MV30d) improved the force at failure in tibias when compared to Sham and Control groups.

CONCLUSION

MV potentiated iPTH anabolic effects in cancellous bone; however, MV was unable to maintain bone mass after stopping iPTH in ovariectomized rats.

Vibrational spectroscopic techniques to assess bone quality

Although musculoskeletal diseases such as osteoporosis are diagnosed and treatment outcome is evaluated based mainly on routine clinical outcomes of bone mineral density (BMD) by DXA and biochemical markers, it is recognized that these two indicators, as valuable as they have proven to be in the everyday clinical practice, do not fully account for manifested bone strength. Thus, the term bone quality was introduced, to complement considerations based on bone turnover rates and BMD. Bone quality is an "umbrella" term that incorporates the structural and material/compositional characteristics of bone tissue. Vibrational spectroscopic techniques such as Fourier transform infrared microspectroscopy (FTIRM) and imaging (FTIRI), and Raman spectroscopy, are suitable analytical tools for the determination of bone quality as they provide simultaneous, quantitative, and qualitative information on all main bone tissue components (mineral, organic matrix, tissue water), in a spatially resolved manner. Moreover, the results of such analyses may be readily combined with the outcomes of other techniques such as histology/histomorphometry, small angle X-ray scattering, quantitative backscattered electron imaging, and nanoindentation.

Effect of low-intensity whole-body vibration on bone defect repair and associated vascularization in mice

Low-intensity whole-body vibration (LIWBV) may stimulate bone healing, but the involvement of vascular ingrowth, which is essential for bone regeneration, has not been well examined. We thus investigated the LIWBV effect on vascularization during early-stage bone healing. Mice aged 13 weeks were subjected to cortical drilling on tibial bone. Two days after surgery (day 0), mice were exposed daily to sine-wave LIWBV at 30 Hz and 0.1 g peak-to-peak acceleration for 20 min/day (Vib) or were sham-treated (sham). Following vascular casting with a zirconium-based contrast agent on days 6, 9, or 12 and sacrifice, vascular and bone images were obtained by K-edge subtraction micro-CT using synchrotron lights. Bone regeneration advanced more in the Vib group from days 9 to 12. The vascular volume fraction decreased from days 6 to 9 in both groups; however, from days 9 to 12, it was increased in shams, while it stabilized in the Vib group. The vascular volume fraction tended to be or was smaller in the Vib group on days 6 and 12. The vessel number density was higher on day 9 but lower on day 12 in the Vib group. These results suggest that the LIWBV-promoted bone repair is associated with the modulation of vascularization, but additional studies are needed to determine the causality of this association.