Resistive vibration exercise retards bone loss in weight-bearing skeletons during 60 days bed rest

Static magnetic field: A potential tool of controlling stem cells fates for stem cell therapy in osteoporosis

Osteoporosis is a kind of bone diseases characterized by dynamic imbalance of bone formation and bone absorption, which is prone to fracture, and seriously endangers human health. At present, there is a lack of highly effective drugs for it, and the existing measures all have some side effects. In recent years, mesenchymal stem cell therapy has brought a certain hope for osteoporosis, while shortcomings such as homing difficulty and unstable therapeutic effects limit its application widely. Therefore, it is extremely urgent to find effective and reliable means/drugs for adjuvant stem cell therapy or develop new research techniques. It has been reported that static magnetic fields(SMFs) has a certain alleviating and therapeutic effect on varieties of bone diseases, also promotes the proliferation and osteogenic differentiation of mesenchymal stem cells derived from different tissues to a certain extent. Basing on the above background, this article focuses on the key words "static/constant magnetic field, mesenchymal stem cell, osteoporosis", combined literature and relevant contents were studied to look forward that SMFs has unique advantages in the treatment of osteoporosis with mesenchymal stem cells, which can be used as an application tool to promote the progress of stem cell therapy in clinical application.

Hypoxia Pathway in Osteoporosis: Laboratory Data for Clinical Prospects

The hypoxia pathway not only regulates the organism to adapt to the special environment, such as short-term hypoxia in the plateau under normal physiological conditions, but also plays an important role in the occurrence and development of various diseases such as cancer, cardiovascular diseases, osteoporosis. Bone, as a special organ of the body, is in a relatively low oxygen environment, in which the expression of hypoxia-inducible factor (HIF)-related molecules maintains the necessary conditions for bone development. Osteoporosis disease with iron overload endangers individuals, families and society, and bone homeostasis disorder is linked to some extent with hypoxia pathway abnormality, so it is urgent to clarify the hypoxia pathway in osteoporosis to guide clinical medication efficiently. Based on this background, using the keywords "hypoxia/HIF, osteoporosis, osteoblasts, osteoclasts, osteocytes, iron/iron metabolism", a matching search was carried out through the Pubmed and Web Of Science databases, then the papers related to this review were screened, summarized and sorted. This review summarizes the relationship and regulation between the hypoxia pathway and osteoporosis (also including osteoblasts, osteoclasts, osteocytes) by arranging the references on the latest research progress, introduces briefly the application of hyperbaric oxygen therapy in osteoporosis symptoms (mechanical stimulation induces skeletal response to hypoxic signal activation), hypoxic-related drugs used in iron accumulation/osteoporosis model study, and also puts forward the prospects of future research.

Fluid shear stress-induced down-regulation of miR-146a-5p inhibits osteoblast apoptosis via targeting SMAD4

Fluid shear stress (FSS) plays an important role in osteoblast apoptosis. However, the role of miRNA in osteoblast apoptosis under FSS and possible molecular mechanisms remain unknown. Our aim of the study was to explore whether miR-146a-5p regulates osteoblast apoptosis under FSS and its molecular mechanisms. FSS could down-regulate the expression of miR-146a-5p in MC3T3-E1 cells. We confirm that up-regulation of miR-146a-5p promotes osteoblasts apoptosis and down-regulation of miR-146a-5p inhibits osteoblasts apoptosis. We further demonstrated that FSS inhibits osteoblast apoptosis by down-regulated miR-146a-5p. Dual-luciferase reporter assay validated that SMAD4 is a direct target gene of miR-146a-5p. In addition, mimic-146a-5p suppressed FSS-induced up-regulation of SMAD4 protein levels, which suggests that FSS elevated SMAD4 protein expression levels via regulation miR-146a-5p. Further investigations showed that SMAD4 could inhibit osteoblast apoptosis. We demonstrated that miR-146a-5p regulates osteoblast apoptosis via targeting SMAD4. Taken together, our present study showed that FSS-induced down-regulation miR-146a-5p inhibits osteoblast apoptosis via target SMAD4. These findings may provide novel mechanisms for FSS to inhibit osteoblast apoptosis, and also may provide a potential therapeutic target for osteoporosis.

WWP1 Deficiency Alleviates Cardiac Remodeling Induced by Simulated Microgravity

Cardiac muscle is extremely sensitive to changes in loading conditions; the microgravity during space flight can cause cardiac remodeling and function decline. At present, the mechanism of microgravity-induced cardiac remodeling remains to be revealed. WW domain-containing E3 ubiquitin protein ligase 1 (WWP1) is an important activator of pressure overload-induced cardiac remodeling by stabilizing disheveled segment polarity proteins 2 (DVL2) and activating the calcium-calmodulin-dependent protein kinase II (CaMKII)/histone deacetylase 4 (HDAC4)/myocyte-specific enhancer factor 2C (MEF2C) axis. However, the role of WWP1 in cardiac remodeling induced by microgravity is unknown. The purpose of this study was to determine whether WWP1 was also involved in the regulation of cardiac remodeling caused by microgravity. Firstly, we detected the expression of WWP1 and DVL2 in the heart from mice and monkeys after simulated microgravity using western blotting and immunohistochemistry. Secondly, WWP1 knockout (KO) and wild-type (WT) mice were subjected to tail suspension (TS) to simulate microgravity effect. We assessed the cardiac remodeling in morphology and function through a histological analysis and echocardiography. Finally, we detected the phosphorylation levels of CaMKII and HDAC4 in the hearts from WT and WWP1 KO mice after TS. The results revealed the increased expression of WWP1 and DVL2 in the hearts both from mice and monkeys after simulated microgravity. WWP1 deficiency alleviated simulated microgravity-induced cardiac atrophy and function decline. The histological analysis demonstrated WWP1 KO inhibited the decreases in the size of individual cardiomyocytes of mice after tail suspension. WWP1 KO can inhibit the activation of the DVL2/CaMKII/HDAC4 pathway in the hearts of mice induced by simulated microgravity. These results demonstrated WWP1 as a potential therapeutic target for cardiac remodeling and function decline induced by simulated microgravity.

Ultrasonic Backscatter Measurements of Human Cortical and Trabecular Bone Densities in a Head-Down Bed-Rest Study

This study aims to investigate the feasibility of quantitative ultrasonic backscatter in evaluating human cortical and trabecular bone densities in vivo based on a head-down-tilt bed rest study, with 36 participants tested through 90 d of bed rest and 180 d of recovery. Backscatter measurements were performed using an ultrasonic backscatter bone diagnostic instrument. Backscatter parameters were calculated with a dynamic signal-of-interest method, which was proposed to ensure the same ultrasonic interrogated volume in cortical and trabecular bones. The backscatter parameters exhibited significant correlations with site-matched bone densities provided by high-resolution peripheral quantitative computed tomography (0.33 < |R| < 0.72, p < 0.05). Some bone densities and backscatter parameters exhibited significant changes after the 90-d bed rest. The proposed method can be used to characterize bone densities, and the portable ultrasonic backscatter bone diagnostic device might be used to non-invasively reveal mean bone loss (across a group of people) after long-term bed rest and microgravity conditions of spaceflight missions.

Efficacy of low-magnitude high-frequency vibration (LMHFV) on musculoskeletal health of participants on wheelchair: a study protocol for a single-blinded randomised controlled study

BACKGROUND

Osteoporosis is an age-related disease with progressive loss of bone, leading to fragile bone. It is one of the major health issues in older adults and causes medical, social and economic impacts globally. Patients with osteoporosis have high risk of osteoporotic fractures. Low-magnitude high-frequency vibration (LMHFV) is a non-invasive biophysical intervention providing whole-body mechanical stimulation. Previous studies showed that LMHFV is beneficial to muscle strength, postural control, balancing ability, new bone formation, spinal bone mineral density (BMD) and blood circulation. During the LMHFV treatment, older adults need to stand upright on the platform for 20 min/day. However, some physically weak elderlies with poor musculoskeletal ability cannot stand for a long period. Therefore, the design of vibration platform is modified for the disabled patients to treat at sitting position and the efficacy of LMHFV on this group of elderlies will be verified. It is hypothesised that new design of LMHFV is beneficial to wheelchair users in terms of vertebral BMD, muscle health and musculoskeletal functions.

METHODS

This study is a single-blinded randomised controlled trial to investigate the effect of LMHFV on vertebral BMD, muscle health, balancing ability and functional ability in wheelchair users (mainly on wheelchair for outdoor activities). Healthy elderlies aged 65 years or above with walking difficulties and using wheelchair are eligible. Exclusion criteria are those: (1) who cannot stand and walk independently, (2) who have vibration treatment before, (3) with malignancy, (4) with acute fractures or severe osteoarthritis, (5) with cardiovascular concern such as with pacemaker in situ, (6) with chronic inflammatory conditions known to affect muscle metabolism such as rheumatoid arthritis and (7) with high frequency of physical activities, such as participants who participated in regular exercise five times a week or more. Recruited participants will be randomised to either LMHFV or control group. Participant assigned to LMHFV group will receive LMHFV (35 Hz, 0.3g (g=gravitational acceleration), 20 min/day, at least three times/week) for 6 months. The primary outcome is BMD at the lumbar spine to be assessed by dual-energy X-ray absorptiometry that is clinically recommended for the diagnosis of osteoporosis. All primary and secondary outcome assessments for all groups will be performed in the investigators' institute at baseline and 6 months post treatment.

DISCUSSION

This study aims to investigate the effects of LMHFV on wheelchair users. The findings of this study will help to confirm the efficacy of LMHFV on vertebral BMD, muscle health, balancing ability and functional outcomes in wheelchair using elderlies. LMHFV therapy is an intervention strategy that is easy to implement at the community healthcare level or individually at home that has previously been proven to reduce fall risk and muscle strength at the lower limb. The ultimate goal is to improve their bone and muscle quality of wheelchair users, as well as enhancing their quality of life.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov (NCT04180267).

Quantitative ultrasound imaging monitoring progressive disuse osteopenia and mechanical stimulation mitigation in calcaneus region through a 90-day bed rest human study

Background

Osteoporosis parallels aging and functional mechanical unloading (e.g., space flight and bed rest), jeopardizing mineral density, microstructure, and integrity of bone and leading to an increased risk of fracture. A way to combat this deterioration is to harness the sensitivity of bone to mechanical signals.

Objective

This study evaluates the longitudinal effect of a dynamic mechanical loading through the heel on human bone in vivo during 90-day bed rest, monitored by quantitative ultrasound (QUS) imaging and dual-energy X-ray absorptiometry (DXA) in localized regions of interests, i.e., calcaneus.

Methods

A total of 29 bed rest individuals were evaluated (11 control and 18 treatment) with a brief (10-minute) daily low-intensity (0.3g), high-frequency (30Hz) dynamic mechanical stimulation countermeasure through vibrational inhibition bone erosion (VIBE). Both QUS and DXA detected longitudinal bone density and quality changes.

Results

Ultrasound velocity (UV) decreased in the control group and increased in the group treated with low-intensity loading. The UV increased by 1.9% and 1.6% at 60- and 90-day bed rest (p=0.01) in VIBE over control groups. A trend was found in broadband ultrasound attenuation (BUA), with a VIBE benefit of 1.8% at day 60 and 0.5% at day 90 in comparison with control (p=0.5). Bone mineral density (BMD) assessed by DXA decreased -4.50% for control individuals and -2.18% for VIBE individuals, showing a moderate effect of the mechanical intervention (p=0.19). Significant correlations between QUS and DXA were observed, with a combined BUA and UV vs. BMD: r²=0.70.

Conclusion

These results indicated that low-intensity, high-frequency loading has the potential to mitigate regional bone loss induced by long-term bed rest and that QUS imaging may be able to assess the subtle changes in bone alteration.

Translational potential of this article

Quantitative ultrasound has shown the efficacy of noninvasively assessing bone mass and structural properties in cadaver and isolated trabecular bone samples. While its ability in measuring in vivo bone quality and density is still unclear, a scanning confocal ultrasound imaging is developed and can perform an instant assessment for the subtle changes of such bone loss. This ultrasound imaging modality can potentially be used in the clinical assessment of bone mass. Moreover, physical stimulation has shown the ability to prevent bone loss induced by functional disuse and estrogen deficiency in animal models. However, its treatment capability is unclear. This study has shown that low-magnitude mechanical signals, introduced using low-intensity vibration (LIV), can mitigate regional bone loss caused by functional disuse. Thus localized mechanical treatment, and the quantitative ultrasound imaging have shown translational potential to noninvasively attenuate bone loss, and assess bone mass in the clinic, e.g., in an extreme condition such as long-term space mission, and long-term bedrest such as in case of spinal cord injury.

The LunHab project: Muscle and bone alterations in male participants following a 10 day lunar habitat simulation

NEW FINDINGS

What is the central question of this study? It is well established that muscle and bone atrophy in conditions of inactivity or unloading, but there is little information regarding the effect of a hypoxic environment on the time course of these deconditioning physiological systems. What is the main finding and its importance? The main finding is that a horizontal 10 day bed rest in normoxia results in typical muscle atrophy, which is not aggravated by hypoxia. Changes in bone mineral content or in metabolism were not detected after either normoxic or hypoxic bed rest.

ABSTRACT

Musculoskeletal atrophy constitutes a typical adaptation to inactivity and unloading of weightbearing bones. The reduced-gravity environment in future Moon and Mars habitats is likely to be hypobaric hypoxic, and there is an urgent need to understand the effect of hypoxia on the process of inactivity-induced musculoskeletal atrophy. This was the principal aim of the present study. Eleven males participated in three 10 day interventions: (i) hypoxic ambulatory confinement; (ii) hypoxic bed rest; and (iii) normoxic bed rest. Before and after the interventions, the muscle strength (isometric maximal voluntary contraction), mass (lean mass, by dual-energy X-ray absorptiometry), cross-sectional area and total bone mineral content (determined with peripheral quantitative computed tomography) of the participants were measured. Blood and urine samples were collected before and on the 1st, 4th and 10th day of the intervention and analysed for biomarkers of bone resorption and formation. There was a significant reduction in thigh and lower leg muscle mass and volume after both normoxic and hypoxic bed rests. Muscle strength loss was proportionately greater than the loss in muscle mass for both thigh and lower leg. There was no indication of bone loss. Furthermore, the biomarkers of resorption and formation were not affected by any of the interventions. There was no significant effect of hypoxia on the musculoskeletal variables. Short-term normoxic (10 day) bed rest resulted in muscular deconditioning, but not in the loss of bone mineral content or changes in bone metabolism. Hypoxia did not modify these results.

A comparison of exercise interventions from bed rest studies for the prevention of musculoskeletal loss

Musculoskeletal loss in actual or simulated microgravity occurs at a high rate. Bed rest studies are a reliable ground-based spaceflight analogue that allow for direct comparison of intervention and control participants. The aim of this review was to investigate the impact of exercise compared to no intervention on bone mineral density (BMD) and muscle cross-sectional area (muscle CSA) in bed rest studies relative to other terrestrial models. Eligible bed rest studies with healthy participants had an intervention arm with an exercise countermeasure and a control arm. A search strategy was implemented for MEDLINE. After screening, eight studies were identified for inclusion. Interventions included resistive exercise (RE), resistive vibration exercise (RVE), flywheel resistive exercise, treadmill exercise with lower body negative pressure (LBNP) and a zero-gravity locomotion simulator (ZLS). Lower limb skeletal sites had the most significant BMD losses, particularly at the hip which reduced in density by 4.59% (p < 0.05) and the tibial epiphysis by 6% (p < 0.05). Exercise attenuated bone loss at the hip and distal tibia compared to controls (p < 0.05). Muscle CSA changes indicated that the calf and quadriceps were most affected by bed rest. Exercise interventions significantly attenuated loss of muscle mass. ZLS, LBNP treadmill and RE significantly attenuated bone and muscle loss at the hip compared to baseline and controls. Despite exercise intervention, high rates of bone loss were still observed. Future studies should consider adding bisphosphonates and pharmacological/nutrition-based interventions for consideration of longer-duration missions. These findings correlate to terrestrial bed rest settings, for example, stroke or spinal-injury patients.

Effect of supplemental vibration on orthodontic treatment with aligners: A randomized trial

INTRODUCTION

Supplemental vibration has been reported to accelerate orthodontic tooth movement and reduce discomfort. Our purpose was to investigate the effects of AcceleDent on Invisalign treatment. This randomized clinical trial was carried out in 2 orthodontic private practices with a 1:1 allocation ratio.

METHODS

Adult patients who were beginning their orthodontic treatment were randomly allocated to either an active (A) or a sham (B) AcceleDent Aura device (OrthoAccel Technologies, Inc. Houston, TX). All patients were placed on a 1-week aligner change regimen, and fit was evaluated every 3 weeks. The outcomes were the ability to complete the initial set of aligners and the incisor irregularity measurements for those who completed their regimen of aligners. In addition, aligner compliance, pain levels, and oral health-related quality of life data were gathered from questionnaires. The subjects, investigators, and assessors were all blinded to the treatment arms.

RESULTS

Twenty-seven subjects were randomized into 2 groups (A and B), 1 subject discontinued treatment, and 13 subjects were analyzed in each group. The Fisher exact test showed no significant difference in completion rates between the 2 groups (group A, 77%; group B, 85%; P = 1). Independent-sample t tests showed no significant difference between the final irregularity index or change in irregularity index between the 2 groups. Compliance was similar in both groups. The Wilcoxon rank sum test showed minimal differences in pain levels. Quality of life responses were similar in both groups. No serious harm was observed.

CONCLUSIONS

We found no evidence that the AcceleDent Aura device impacts the ability to complete a series of aligners with a 1-week change regimen or the final alignment achieved in adult patients. It also had no significant effect on the reduction of orthodontic pain or oral health-related quality of life parameters when used with Invisalign.

Myocardial CKIP-1 Overexpression Protects from Simulated Microgravity-Induced Cardiac Remodeling

Human cardiovascular system has adapted to Earth's gravity of 1G. The microgravity during space flight can induce cardiac remodeling and decline of cardiac function. At present, the mechanism of cardiac remodeling induced by microgravity remains to be disclosed. Casein kinase-2 interacting protein-1 (CKIP-1) is an important inhibitor of pressure-overload induced cardiac remodeling by decreasing the phosphorylation level of HDAC4. However, the role of CKIP-1 in the cardiac remodeling induced by microgravity is unknown. The purpose of this study was to determine whether CKIP-1 was also involved in the regulation of cardiac remodeling induced by microgravity. We first detected the expression of CKIP-1 in the heart from mice and monkey after simulated microgravity using Q-PCR and western blotting. Then, myocardial specific CKIP-1 transgenic (TG) and wild type mice were hindlimb-suspended (HU) to simulate microgravity effect. We estimated the cardiac remodeling in morphology and function by histological analysis and echocardiography. Finally, we detected the phosphorylation of AMPK, ERK1/2, and HDAC4 in the heart from wild type and CKIP-1 transgenic mice after HU. The results revealed the reduced expression of CKIP-1 in the heart both from mice and monkey after simulated microgravity. Myocardial CKIP-1 overexpression protected from simulated microgravity-induced decline of cardiac function and loss of left ventricular mass. Histological analysis demonstrated CKIP-1 TG inhibited the decreases in the size of individual cardiomyocytes of mice after hindlimb unloading. CKIP-1 TG can inhibit the activation of HDAC4 and ERK1/2 and the inactivation of AMPK in heart of mice induced by simulated microgravity. These results demonstrated CKIP-1 was a suppressor of cardiac remodeling induced by simulated microgravity.

Mechanosensitive miRNAs and Bone Formation

Mechanical stimuli are required for the maintenance of skeletal integrity and bone mass. An increasing amount of evidence indicates that multiple regulators (e.g., hormone, cytoskeleton proteins and signaling pathways) are involved in the mechanical stimuli modulating the activities of osteogenic cells and the process of bone formation. Significantly, recent studies have showed that several microRNAs (miRNAs) were sensitive to various mechanical stimuli and played a crucial role in osteogenic differentiation and bone formation. However, the functional roles and further mechanisms of mechanosensitive miRNAs in bone formation are not yet completely understood. This review highlights the roles of mechanosensitive miRNAs in osteogenic differentiation and bone formation and underlines their potential therapeutic application for bone loss induced by the altering of mechanical stimuli.

Effect of supplemental vibrational force on orthodontically induced inflammatory root resorption: A multicenter randomized clinical trial

INTRODUCTION

A multicenter parallel 3-arm randomized clinical trial was carried out in 1 university and 2 district hospitals in the United Kingdom to investigate the effect of supplemental vibrational force on orthodontically induced inflammatory root resorption (OIIRR) during the alignment phase of fixed appliance therapy.

METHODS

Eighty-one subjects less than 20 years old with mandibular incisor irregularity undergoing extraction-based fixed-appliance treatment were randomly allocated to supplementary (20 minutes a day) use of an intraoral vibrational device (AcceleDent; OrthoAccel Technologies, Houston, Tex) (n = 29), an identical nonfunctional (sham) device (n = 25), or fixed appliances only (n = 27). OIIRR was measured blindly from long-cone periapical radiographs of the maxillary right central incisor taken at the start of treatment and the end of alignment when a 0.019 × 0.025-in stainless steel archwire was placed (mean follow-up, 201.6 days; 95% confidence interval [CI], 188.6-214.6 days). Data were analyzed blindly on a per-protocol basis because losses to follow-up were minimal, with descriptive statistics, 1-way analysis of variance, and univariable and multivariable regression modeling.

RESULTS

Nine patients were excluded from the analysis; they were evenly distributed across the groups. Mean overall OIIRR measured among the 72 patients was 1.08 mm (95% CI, 0.89-1.27 mm). Multivariable regression indicated no significant difference in OIIRR for the AcceleDent (difference, 0.22 mm; 95% CI, -0.14-0.72; P = 0.184) and AcceleDent sham groups (difference, 0.29 mm; 95% CI, -0.15-0.99; P = 0.147) compared with the fixed-appliance-only group, after accounting for patient sex, age, malocclusion, extraction pattern, alignment time, maximum pain experienced, history of dentoalveolar trauma, and initial root length of the maxillary right central incisor. No other side-effects were recorded apart from pain and OIIRR.

CONCLUSIONS

The use of supplemental vibrational force during the alignment phase of fixed appliance orthodontic treatment does not affect OIIRR associated with the maxillary central incisor.

REGISTRATION

ClinicalTrials.gov (NCT02314975).

PROTOCOL

The protocol was not published before trial commencement.

FUNDING

Functional and sham AcceleDent units were donated by the manufacturer; there was no contribution to the conduct or the writing of this study.

Circulating microRNAs Correlated with Bone Loss Induced by 45 Days of Bed Rest

The purpose of this study was to find the circulating microRNAs (miRNAs) co-related with bone loss induced by bed rest, and testify whether the selected miRNAs could reflect the bone mineral status of human after bed-rest. We analyzed plasma miRNA levels of 16 subjects after 45 days of −6° head-down tilt bed rest, which is a reliable model for the simulation of microgravity. We characterize the circulating miRNA profile in individuals after bed rest and identify circulating miRNAs which can best reflect the level of bone loss induced by bed rest. Expression profiling of circulating miRNA revealed significant downregulation of 37 miRNAs and upregulation of 2 miRNAs, while only 11 of the downregulated miRNAs were further validated in a larger volunteer cohort using qPCR. We found that 10 of these 11 miRNAs (miR-103, 130a, 1234, 1290, 151-5p, 151-3p, 199a-3p, 20a, 363, and 451a) had ROC curve that distinguished the status after bed rest. Importantly, significant positive correlations were identified between bone loss parameters and several miRNAs, eventually miR-1234 showed clinical significance in detecting the bone loss of individuals after 45 days of bed rest.

The mechanisms underlying the beneficial effects of exercise on bone remodeling: Roles of bone-derived cytokines and microRNAs

Bone remodeling is highly dynamic and complex in response to mechanical loading, such as exercise. In this review, we concluded that a number of individual factors are disturbing the clinical effects of exercise on bone remodeling. We updated the progress made on the differentiation of osteoblasts and osteoclasts in response to mechanical loading, hoping to provide a theoretical basis to improve bone metabolism with exercise. Increasing evidences indicate that bone is not only a structural scaffold but also an endocrine organ, which secretes osteocalcin and FGF23. Both of them have been known as a circulating hormone to promote insulin sensitivity and reduce body fat mass. The effects of exercise on these bone-derived cytokines provide a better understanding of how exercise-induced "osteokine" affects the whole-body homeostasis. Additionally, we discussed recent studies highlighting the post-transcriptional regulation of microRNAs in bone remodeling. We focus on the involvement of the microRNAs in osteoblastogenesis and osteoclastogenesis, and suggest that microRNAs may be critical for exercise-induced bone remodeling.

Early and Sustained Changes in Bone Metabolism After Severe Burn Injury

CONTEXT

Severe burn injury causes a massive stress response, consecutively heightened serum levels of acute phase proteins, cortisol, and catecholamines with accompanying disturbance in calcium metabolism.

OBJECTIVE

Evaluation of early and prolonged changes of serum bone turnover markers (BTMs) and regulators of bone metabolism.

DESIGN

Longitudinal observational design.

SETTING

University clinic.

PATIENTS

A total of 32 male patients with a median age of 40.5 years and a median burned total body surface area of 40% (83% patients with full thickness burn injury).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Comparison of changes of BTM/regulators of bone metabolism in the early (d 2–7) and prolonged (d 7–56) phases after trauma.

RESULTS

All investigated BTM/regulators significantly changed. During the early phase, pronounced increases were observed for serum type 1 collagen cross-linked C-telopeptide, intact N-terminal propeptide of type I procollagen, sclerostin, Dickkopf-1, bone-specific alkaline phosphatase, fibroblast growth factor 23, and intact parathyroid hormone levels, whereas 25-hydroxyvitamin D, albumin, serum, and ionized calcium levels decreased. Changes of osteoprotegerin, osteocalcin, and phosphate were less pronounced but remained significant. In the prolonged phase, changes of intact N-terminal propeptide of type I procollagen were most pronounced, followed by elevated sclerostin, osteocalcin, bone-specific alkaline phosphatase, and lesser changes for albumin levels. Calcium and ionized calcium levels tardily increased and remained within the limit of normal. In contrast, levels of intact parathyroid hormone, fibroblast growth factor 23, C-reactive protein, and to a lesser extent serum type 1 collagen cross-linked C-telopeptide and phosphate levels declined significantly during this phase of investigation.

CONCLUSIONS

Ongoing changes of BTM and regulators of bone metabolism suggest alterations in bone metabolism with a likely adverse influence on bone quality and structure in male patients with severe burn injuries.

Effects of whole-body vibration exercise on bone mineral content and density in thermally injured children

BACKGROUND

Loss of bone mass, muscle mass, and strength leads to significant disability in severely burned children. We assessed the effects of exercise combined with whole-body vibration (WBV) on bone mass, lean mass (LM), and muscle strength in children recovering from burns.

METHODS

Nineteen burned children (≥30% total body surface area [TBSA] burns) were randomly assigned to a 6-week exercise regimen either alone (EX; n=10) or in combination with a 6-week WBV training regimen (EX+WBV; n=9). WBV was performed concurrent to the exercise regimen for 5days/week on a vibrating platform. Dual-energy X-ray absorptiometry quantified bone mineral content (BMC), bone mineral density (BMD), and LM; knee extension strength was assessed using isokinetic dynamometry before and after training. Alpha was set at p<0.05.

RESULTS

Both groups were similar in age, height, weight, TBSA burned, and length of hospitalization. Whole-body LM increased in the EX group (p=0.041) and trended toward an increase in the EX+WBV group (p=0.055). On the other hand, there were decreases in leg BMC for both groups (EX, p=0.011; EX+WBV, p=0.047), and in leg BMD for only the EX group (EX, p<0.001; EX+WBV, p=0.26). Truncal BMC decreased in only the EX group (EX, p=0.009; EX+WBV, p=0.61), while BMD decreased in both groups (EX, p<0.001; EX+WBV group, p<0.001). Leg strength increased over time in the EX group (p<0.001) and the EX+WBV group (p<0.001; between-group p=0.31).

CONCLUSIONS

Exercise in combination with WBV may help attenuate regional bone loss in children recovering from burns. Studies are needed to determine the optimal magnitude, frequency, and duration of the vibration protocol, with attention to minimizing any potential interference with wound healing and graft closure.

Mechanical Loading Synergistically Increases Trabecular Bone Volume and Improves Mechanical Properties in the Mouse when BMP Signaling Is Specifically Ablated in Osteoblasts

Bone homeostasis is affected by several factors, particularly mechanical loading and growth factor signaling pathways. There is overwhelming evidence to validate the importance of these signaling pathways, however, whether these signals work synergistically or independently to contribute to proper bone maintenance is poorly understood. Weight-bearing exercise increases mechanical load on the skeletal system and can improves bone quality. We previously reported that conditional knockout (cKO) of Bmpr1a, which encodes one of the type 1 receptors for Bone Morphogenetic Proteins (BMPs), in an osteoblast-specific manner increased trabecular bone mass by suppressing osteoclastogenesis. The cKO bones also showed increased cortical porosity, which is expected to impair bone mechanical properties. Here, we evaluated the impact of weight-bearing exercise on the cKO bone phenotype to understand interactions between mechanical loading and BMP signaling through BMPR1A. Male mice with disruption of Bmpr1a induced at 9 weeks of age, exercised 5 days per week on a motor-driven treadmill from 11 to 16 weeks of age. Trabecular bone volume in cKO tibia was further increased by exercise, whereas exercise did not affect the trabecular bone in the control genotype group. This finding was supported by decreased levels of osteoclasts in the cKO tibiae. The cortical porosity in the cKO bones showed a marginally significant decrease with exercise and approached normal levels. Exercise increased ductility and toughness in the cKO bones. Taken together, reduction in BMPR1A signaling may sensitize osteoblasts for mechanical loading to improve bone mechanical properties.

Elcatonin attenuates disuse osteoporosis after fracture fixation of tubular bone in rats

BACKGROUND

Elcatonin (ECT) is used to prevent and treat osteoporosis. However, little is known about its effect on the disuse osteoporosis (DOP). The aim of this study is to evaluate the effect of ECT on DOP caused by fracture fixation.

METHODS

Forty-five male Sprague-Dawley (SD) rats, aged 6 weeks, were randomly allocated into three groups: the control group without surgery and elcatonin treatment (CTR, n = 15), the surgery group without elcatonin treatment (SUR, n = 15), and the surgery group which received elcatonin subcutaneously (SUR + ECT, n = 15). Surgery was produced by cutting the midshaft of the right femur transversely, fixing with stainless intramedullary needle, and immobilizing the right leg. All the proximal tibias from the random five rats in each group were harvested and investigated by evaluating bone mineral density (BMD), X-ray images, and histological staining respectively at the 4th, 8th, and 12th weeks after surgery.

RESULTS

Both of the SUR and SUR + ECT groups obviously exhibited lower BMD values compared to the CTR group; however, the SUR + ECT group showed significantly higher BMD values (p < 0.001, p < 0.05, and p < 0.05) than the SUR group at each time point after surgery. Moreover, similar changes were observed between these groups when examining the radiographs and hematoxylin and eosin (HE) staining.

CONCLUSIONS

Elcatonin attenuates disuse osteoporosis after fractures in rats, which may provide a new avenue to prevent and treat disuse osteoporosis after surgery in clinic.

Muscle and bone, two interconnected tissues

As bones are levers for skeletal muscle to exert forces, both are complementary and essential for locomotion and individual autonomy. In the past decades, the idea of a bone-muscle unit has emerged. Numerous studies have confirmed this hypothesis from in utero to aging works. Space flight, bed rest as well as osteoporosis and sarcopenia experimentations have allowed to accumulate considerable evidence. Mechanical loading is a key mechanism linking both tissues with a central promoting role of physical activity. Moreover, the skeletal muscle secretome accounts various molecules that affect bone including insulin-like growth factor-1 (IGF-1), basic fibroblast growth factor (FGF-2), interleukin-6 (IL-6), IL-15, myostatin, osteoglycin (OGN), FAM5C, Tmem119 and osteoactivin. Even though studies on the potential effects of bone on muscle metabolism are sparse, few osteokines have been identified. Prostaglandin E2 (PGE2) and Wnt3a, which are secreted by osteocytes, osteocalcin (OCN) and IGF-1, which are produced by osteoblasts and sclerostin which is secreted by both cell types, might impact skeletal muscle cells. Cartilage and adipose tissue are also likely to participate to this control loop and should not be set aside. Indeed, chondrocytes are known to secrete Dickkopf-1 (DKK-1) and Indian hedgehog (Ihh) and adipocytes produce leptin, adiponectin and IL-6, which potentially modulate bone and muscle metabolisms. The understanding of this system will enable to define new levers to prevent/treat sarcopenia and osteoporosis at the same time. These strategies might include nutritional interventions and physical exercise.

Supplemental Vibrational Force During Orthodontic Alignment

This prospective 3-arm parallel-group randomized clinical trial investigated the effect of supplemental vibrational force on rate of orthodontic tooth alignment with fixed appliances. Eighty-one subjects (40 males, 41 females; mean age, 14.1 y) undergoing first premolar extraction-based fixed appliance treatment were randomly allocated to treatment supplemented with daily use (20 min) of a removable intraoral vibrational device (AcceleDent; OrthoAccel Technologies Inc.; n = 29), an identical nonfunctional (sham) device ( n = 25), or fixed appliances only ( n = 27). Mandibular study casts were taken at baseline (treatment start: placement of 0.014-in. nickel-titanium arch wire), initial alignment (0.018-in. nickel-titanium arch wire), and final alignment (0.019 x 0.025–in. stainless steel arch wire). Overall mean irregularity index in the mandibular arch at baseline was 8.5 ± 3.8 mm (95% CI, 7.6 to 9.3) with no significant difference between groups ( P = 0.73). For the total sample, mean irregularity index at initial alignment was 2.7 ± 2.8 mm (95% CI, 2.2 to 3.4) with no significant difference between groups ( P = 0.40). Mean time from baseline to initial alignment was 59 ± 25 d (95% CI, 54.5 to 65.6); from initial to final alignment, 150 ± 62.5 d (95% CI, 136 to 165); and baseline to final alignment, 209 ± 65 d (95% CI, 195 to 224). Kaplan-Meier analysis demonstrated that patterns of alignment were not significantly different among the 3 groups ( P = 0.66). Multivariate linear regression for initial and overall alignment rates using initial irregularity index as the covariate showed no significant differences among groups. The most important influence on both initial and overall rates of alignment was initial irregularity ( P = 0.1 × 10−4). This prospective randomized clinical trial found no evidence that supplemental vibrational force can significantly increase the rate of initial tooth movement or reduce the amount of time required to achieve final alignment when used in conjunction with a preadjusted edgewise fixed appliance ( ClinicalTrials.gov NCT02314975).

Effects of 60-day head-down bed rest on osteocalcin, glycolipid metabolism and their association with or without resistance training

INTRODUCTION

Bone loss and subclinical diabeteslike are developed during long-term spaceflight. Recently, it was demonstrated that bone was able to regulate energy metabolism and testosterone synthesis via osteocalcin. The aim of this study was to determine whether serum osteocalcin level is associated with glycolipid metabolism or testosterone under the influence of microgravity with or without resistive vibration exercise (RVE).

METHODS

A total of 14 healthy adult male volunteers (25-40 years) were randomly assigned to two groups (n = 7 each): control (CON) group and RVE group. Radioimmunoassay kits and ELISA kits were used for measurement of serum indices.

RESULTS

During 60-day bed rest, serum osteocalcin of both groups increased at day 4 during bed rest. Serum OPG started decreasing and reached its lowest value at day 30 during bed rest. In control group, serum insulin increased at day 4 during bed rest. IGF-I did not change significantly during the entire period of bed rest. The serum glucose decline 10% and 14% in CON and RVE groups at day 4 during bed rest. Relatively, the same results as glucose were found in serum HDL and LDL for both groups. Leptin rose and became highest at day 60 during bed rest in both groups. The level of serum testosterone was declined in control group at day 4 during bed rest. Cortisol kept stable in both group during bed rest. By spearman correlation analysis, serum osteocalcin was significantly associated with serum insulin (P < 0·05), LDL (P < 0·01) and Leptin (P < 0·01).

CONCLUSION

Our findings suggested that the mutual regulation may exist between skeletal and energy metabolism under simulated microgravity.

Bone quality: the determinants of bone strength and fragility

Bone fragility is a major health concern, as the increased risk of bone fractures has devastating outcomes in terms of mortality, decreased autonomy, and healthcare costs. Efforts made to address this problem have considerably increased our knowledge about the mechanisms that regulate bone formation and resorption. In particular, we now have a much better understanding of the cellular events that are triggered when bones are mechanically stimulated and how these events can lead to improvements in bone mass. Despite these findings at the molecular level, most exercise intervention studies reveal either no effects or only minor benefits of exercise programs in improving bone mineral density (BMD) in osteoporotic patients. Nevertheless, and despite that BMD is the gold standard for diagnosing osteoporosis, this measure is only able to provide insights regarding the quantity of bone tissue. In this article, we review the complex structure of bone tissue and highlight the concept that its mechanical strength stems from the interaction of several different features. We revisited the available data showing that bone mineralization degree, hydroxyapatite crystal size and heterogeneity, collagen properties, osteocyte density, trabecular and cortical microarchitecture, as well as whole bone geometry, are determinants of bone strength and that each one of these properties may independently contribute to the increased or decreased risk of fracture, even without meaningful changes in aBMD. Based on these findings, we emphasize that while osteoporosis (almost) always causes bone fragility, bone fragility is not always caused just by osteoporosis, as other important variables also play a major role in this etiology. Furthermore, the results of several studies showing compelling data that physical exercise has the potential to improve bone quality and to decrease fracture risk by influencing each one of these determinants are also reviewed. These findings have meaningful clinical repercussions as they emphasize the fact that, even without leading to improvements in BMD, exercise interventions in patients with osteoporosis may be beneficial by improving other determinants of bone strength.

Bone mechanobiology, gravity and tissue engineering: effects and insights

Bone homeostasis strongly depends on fine tuned mechanosensitive regulation signals from environmental forces into biochemical responses. Similar to the ageing process, during spaceflights an altered mechanotransduction occurs as a result of the effects of bone unloading, eventually leading to loss of functional tissue. Although spaceflights represent the best environment to investigate near-zero gravity effects, there are major limitations for setting up experimental analysis. A more feasible approach to analyse the effects of reduced mechanostimulation on the bone is represented by the 'simulated microgravity' experiments based on: (1) in vitro studies, involving cell cultures studies and the use of bioreactors with tissue engineering approaches; (2) in vivo studies, based on animal models; and (3) direct analysis on human beings, as in the case of the bed rest tests. At present, advanced tissue engineering methods allow investigators to recreate bone microenvironment in vitro for mechanobiology studies. This group and others have generated tissue 'organoids' to mimic in vitro the in vivo bone environment and to study the alteration cells can go through when subjected to unloading. Understanding the molecular mechanisms underlying the bone tissue response to mechanostimuli will help developing new strategies to prevent loss of tissue caused by altered mechanotransduction, as well as identifying new approaches for the treatment of diseases via drug testing. This review focuses on the effects of reduced gravity on bone mechanobiology by providing the up-to-date and state of the art on the available data by drawing a parallel with the suitable tissue engineering systems.

Bone loss patterns in cortical, subcortical, and trabecular compartments during simulated microgravity

Disuse studies provide a useful model for bone adaptation. A direct comparison of these studies is, however, complicated by the different settings used for bone analysis. Through pooling and reanalysis of bone data from previous disuse studies, we determined bone loss and recovery in cortical, subcortical, and trabecular compartments and evaluated whether the study design modulated skeletal adaptation. Peripheral quantitative tomographic (pQCT) images from control groups of four disuse studies with a duration of 24, 35, 56, and 90 days were reanalyzed using a robust threshold-free segmentation algorithm. The pQCT data were available from 27 young healthy men at baseline, and at specified intervals over disuse and reambulation phases. The mean maximum absolute bone loss (mean ± 95% CI) was 6.1 ± 4.5 mg/mm in cortical, 2.4 ± 1.6 mg/mm in subcortical, and 9.8 ± 9.1 mg/mm in trabecular compartments, after 90 days of bed rest. The percentage changes in all bone compartments were, however, similar. During the first few weeks after onset of reambulation, the bone loss rate was systematically greater in the cortical than in the trabecular compartment (P < 0.002), and this was observed in all studies except for the longest study. We conclude that disuse-induced bone losses follow similar patterns irrespective of study design, and the largest mean absolute bone loss occurs in the cortical compartment, but apparently only during the first 60 days. With longer study duration, trabecular loss may become more prominent.

Distribution of bone density and cortical thickness in the proximal femur and their association with hip fracture in postmenopausal women: a quantitative computed tomography study

The quantitative computed tomography (QCT) scans in an individually matched case-control study of women with hip fracture were analysed. There were widespread deficits in the femoral volumetric bone mineral density (vBMD) and cortical thickness of cases, and cortical vBMD and thickness discriminated hip fracture independently of BMD by dual-energy X-ray absorptiometry (DXA).

INTRODUCTION

Acknowledging the limitations of QCT associated with partial volume effects, we used QCT in an individually matched case-control study of women with hip fracture to better understand its structural basis.

METHODS

Fifty postmenopausal women (55-89 years) who had sustained hip fractures due to low-energy trauma underwent QCT scans of the contralateral hip within 3 months of the fracture. For each case, postmenopausal women, matched by age (±5 years), weight (±5 kg) and height (±5 cm), were recruited as controls. We quantified cortical, trabecular and integral vBMD and apparent cortical thickness (AppCtTh) in four quadrants of cross-sections along the length of the femoral head (FH), femoral neck (FN), intertrochanter and trochanter and examined their association with hip fracture.

RESULTS

Women with hip or intracapsular (IC) fracture had significantly (p < 0.05) lower vBMD and AppCtTh than the controls in the majority of cross-sections and quadrants of the proximal femur, and both cortical and trabecular compartments are involved. Cortical vBMD and AppCtTh in the FH and FN were associated with hip and IC fractures independent of hip areal BMD (aBMD). The combination of AppCtTh and trabecular or integral vBMD discriminated hip fracture, whereas the combination of FH and FN AppCtTh discriminated IC fracture significantly (p < 0.05) better than the hip aBMD.

CONCLUSION

Deficits in vBMD and AppCtTh in cases were widespread in the proximal femur, and cortical vBMD and AppCtTh discriminated hip fracture independently of aBMD by DXA.

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

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