Signs of irreversible architectural changes occur early in the development of experimental osteoporosis as assessed by in vivo micro-CT

Peak trabecular bone microstructure predicts rate of estrogen-deficiency-induced bone loss in rats

Postmenopausal osteoporosis affects a large number of women worldwide. Reduced estrogen levels during menopause lead to accelerated bone remodeling, resulting in low bone mass and increased fracture risk. Both peak bone mass and the rate of bone loss are important predictors of postmenopausal osteoporosis risk. However, whether peak bone mass and/or bone microstructure directly influence the rate of bone loss following menopause remains unclear. Our study aimed to establish the relationship between peak bone mass/microstructure and the rate of bone loss in response to estrogen deficiency following ovariectomy (OVX) surgery in rats of homogeneous background by tracking the skeletal changes using in vivo micro-computed tomography (μCT) and three-dimensional (3D) image registrations. Linear regression analyses demonstrated that the peak bone microstructure, but not peak bone mass, was highly predictive of the rate of OVX-induced bone loss. In particular, the baseline trabecular thickness was found to have the highest correlation with the degree of OVX-induced bone loss and trabecular stiffness reduction. Given the same bone mass, the rats with thicker baseline trabeculae had a lower rate of trabecular microstructure and stiffness deterioration after OVX. Moreover, further evaluation to track the changes within each individual trabecula via our novel individual trabecular dynamics (ITD) analysis suggested that a trabecular network with thicker trabeculae is less likely to disconnect or perforate in response to estrogen deficiency, resulting a lower degree of bone loss. Taken together, these findings indicate that the rate of estrogen-deficiency-induced bone loss could be predicted by peak bone microstructure, most notably the trabecular thickness. Given the same bone mass, a trabecular bone phenotype with thin trabeculae may be a risk factor toward accelerated postmenopausal bone loss.

High incidence of fractures after R-CHOP-like chemotherapy for aggressive B-cell non-Hodgkin lymphomas

Purpose

Patients with non-Hodgkin lymphoma (NHL) have a median age of 67, with 70% surviving over 5 years. Chemotherapy for aggressive NHL includes cyclophosphamide, anthracycline, and high doses of corticosteroids, which can impair bone health. By reviewing clinical characteristics and standard-of-care CT scans, we evaluate the prevalence and incidence of fractures and the clinical correlates of fractures in patients treated for aggressive B-cell NHL.

Methods

We retrospectively reviewed patients seen at the University of California San Francisco lymphoma clinic from January 1, 2016, to March 31, 2017 who had (1) aggressive B-cell NHL, (2) received first-line therapy with R-CHOP-like regimens, and had (3) CT scans pre- and post-treatment available for review. Associations between clinical variables and vertebral, rib, and pelvic fracture outcomes were assessed, and multivariate logistic regression models were used to identify predictors of prevalent and incident fractures.

Results

We identified 162 patients who met the inclusion criteria. Median age at diagnosis was 60 years. Of the 162 patients, 38 patients (28%) had prevalent fractures prior to receiving chemotherapy. Within 1 year after treatment, 16 patients (10%) developed new fractures. Having a prevalent fracture strongly predicted developing a new fracture after treatment, with incident fractures occurring in 12 of 38 patients with prevalent fractures versus 4 of 124 without prevalent fractures (odds ratio 10.45, p<0.0005).

Conclusion

Our results suggest that patients with aggressive B-cell NHL who receive R-CHOP-like therapy should be screened for fractures prior to treatment and those with existing fractures should be considered for therapy to decrease risk of new fractures.

Evaluation of hematology, general serum biochemistry, bone turnover markers and bone marrow cytology in a glucocorticoid treated ovariectomized sheep model for osteoporosis research

Osteoporosis is a metabolic disorder characterized by a loss of bone mass and structure and increasing the risk of fragility fractures, mostly among postmenopausal women. Sheep is a recognized large animal model for osteoporosis research. An experimental group of ewes (3-4 years old) was subjected to ovariectomy (OVX) and weekly glucocorticoid (GC) application for 24 weeks and compared with a sham control group. Blood and bone marrow parameters were analyzed before and 24 weeks after OVX and GC administration. Osteopenia was confirmed through micro-computed tomography and histomorphometric analysis of L4 vertebra in the study end. A statistically significant increase was observed in mean corpuscular volume, mean cell hemoglobin and monocytes and a decrease in red blood count and eosinophils (p<0.05). Alkaline phosphatase (ALP), gamma-glutamyl transpeptidase, magnesium and α1-globulin increased, and creatinine, albumin, sodium and estradiol decreased (p<0.05). A slight decrease of bone formation markers (bone ALP and osteocalcin) and an increase of bone resorption markers (C-terminal telopeptides of collagen type 1 and tartrate-resistant acid phosphatase) were observed, but without statistical significance. This study aims to contribute to better knowledge of sheep as a model for osteoporosis research and the consequences that a performed induction protocol may impose on organic metabolism.

Comparisons of Efficacy between Autograft and Allograft on Defect Repair In Vivo in Normal and Osteoporotic Rats

Introduction. In the field of orthopaedic surgery, the use of osteogenic material in larger defects is essential. Autograft and allograft are both known methods, and autograft is believed to be the best choice. But autograft is associated with additional invasive procedures which can prove difficult in fragile patients and can cause local side effect after bone harvest. For feasible purposes, the use of allograft is hereby rising and comparing efficacies, and the differences between autograft and allograft are essential for the clinical outcome for the patients.

A bioceramic scaffold composed of strontium-doped three-dimensional hydroxyapatite whiskers for enhanced bone regeneration in osteoporotic defects

Reconstruction of osteoporotic bone defects is a clinical problem that continues to inspire the design of new materials. Methods: In this work, bioceramics composed of strontium (Sr)-doped hydroxyapatite (HA) whiskers or pure HA whiskers were successfully fabricated by hydrothermal treatment and respectively named SrWCP and WCP. Both bioceramics had similar three-dimensional (3D) porous structures and mechanical strengths, but the SrWCP bioceramic was capable of releasing Sr under physiological conditions. In an osteoporotic rat metaphyseal femoral bone defect model, both bioceramic scaffolds were implanted, and another group that received WCP plus strontium ranelate drug administration (Sr-Ran+WCP) was studied for comparison. Results: At week 1 post-implantation, osteogenesis coupled blood vessels were found to be more common in the SrWCP and Sr-Ran+WCP groups, with substantial vascular-like structures. After 12 weeks of implantation, comparable to the Sr-Ran+WCP group, the SrWCP group showed induction of more new bone formation within the defect as well as at the implant-bone gap region than that of the WCP group. Both the SrWCP and Sr-Ran+WCP groups yielded a beneficial effect on the surrounding trabecular bone microstructure to resist osteoporosis-induced progressive bone loss. While an abnormally high blood Sr ion concentration was found in the Sr-Ran+WCP group, SrWCP showed little adverse effect. Conclusion: Our results collectively suggest that the SrWCP bioceramic can be a safe bone substitute for the treatment of osteoporotic bone defects, as it promotes local bone regeneration and implant osseointegration to a level that strontium ranelate can achieve.

Ketogenic diet compromises vertebral microstructure and biomechanical characteristics in mice

Ketogenic diet (KD) compromised the microstructure of cancellous bone and the mechanical property in the appendicular bone of mice, while the effects of KD on the axial bone have not been reported. This study aimed to compare the changes in the microstructure and mechanical properties of the forth lumbar (L4) vertebra in KD and ovariectomized (OVX) mice. Forty eight-week-old female C57BL/6J mice were assigned into four groups: SD (standard diet) + Sham, SD + OVX, KD + Sham, and KD + OVX groups. L4 vertebra was scanned by micro-CT to examine the microstructure of cancellous bone, after which simulative compression tests were performed using finite element (FE) analysis. Vertebral compressive test and histological staining of the L4 and L5 vertebrae were performed to observe the biomechanical and histomorphologic changes. The KD + Sham and SD + OVX exhibited a remarkable declination in the parameters of cancellous bone compared with the SD + Sham group, while KD + OVX demonstrated the most serious bone loss in the four groups. The stiffness was significantly higher in the SD + Sham group than the other three groups, but no difference was found between the remaining groups. The trabecular parameters were significantly correlated with the stiffness. Meanwhile, the OVX + Sham and KD + OVX groups showed a significant decrease in the failure load of compressive test, while there was no difference between the KD + Sham and SD + Sham groups. These findings suggest that KD may compromise the vertebral microstructure and compressive stiffness to a similar level as OVX did, indicating adverse effects of KD on the axial bone of the mice.

Reproducibility and Radiation Effect of High-Resolution In Vivo Micro Computed Tomography Imaging of the Mouse Lumbar Vertebra and Long Bone

A moderate radiation dose, in vivo µCT scanning protocol was developed and validated for long-term monitoring of multiple skeletal sites (femur, tibia, vertebra) in mice. A customized, 3D printed mouse holder was designed and utilized to minimize error associated with animal repositioning, resulting in good to excellent reproducibility in most cortical and trabecular bone microarchitecture and density parameters except for connectivity density. Repeated in vivo µCT scans of mice were performed at the right distal femur and the 4th lumbar vertebra every 3 weeks until euthanized at 9 weeks after the baseline scan. Comparing to the non-radiated counterparts, no radiation effect was found on trabecular bone volume fraction, osteoblast and osteoblast number/surface, or bone formation rate at any skeletal site. However, trabecular number, thickness, and separation, and structure model index were sensitive to ionizing radiation associated with the µCT scans, resulting in subtle but significant changes over multiple scans. Although the extent of radiation damage on most trabecular bone microarchitecture measures are comparable or far less than the age-related changes during the monitoring period, additional considerations need to be taken to minimize the confounding radiation factors when designing experiments using in vivo µCT imaging for long-term monitoring of mouse bone.

Cathepsin K inhibition preserves compressive load in lumbar vertebrae of osteoporotic monkeys

Anti-resorptive drugs treat bone loss by blocking osteoclast activity through a variety of mechanisms of action. Once significant bone loss has occurred, the ability to restore biomechanical function may differ based on the drug chosen. To assess this question, bisphosphonate (alendronate, ALN) and cathepsin K inhibitor (MK-0674, CatKi) were employed in treatment mode to compare the relative changes to cancellous bone microstructure and mechanical properties in ovariectomized (OVX) cynomolgus monkeys. Lumbar vertebrae (LV) bone mineral density (BMD) values taken two years post-surgery prior to drug treatment show a 10-15% decrease (p < 0.05) for all OVX animals. OVX animals were then treated with vehicle (VEH), ALN (0.03 mg/kg weekly), or CatKi MK-0674 (0.6 or 2.5 mg/kg daily, CatKi-L and H respectively) for two years and compared to a control Sham surgery group. Ex-vivo microcomputed tomography (μCT) of LV2 and compression testing of LV4-6 were used to measure cancellous bone microstructure and changes in bone mechanics, respectively. After two years of treatment, ALN-treated animals showed no significant difference in μCT or biomechanical parameters when compared to Veh. However, treatment with CatKi-H resulted in a 30% increase in yield and peak loads, and apparent peak and yield stress as compared to Veh (p < 0.05) and gave average mechanical values greater than the Sham sample. Treatment with CatKi-L exhibited a similar trend of increase to CatKi-H (p < 0.08). Intriguingly, these changes were realized despite no significant differences in mean values of trabecular bone morphologic parameters. Together these data suggest matrix-level changes in bone composition that are unique to the CatK inhibition mechanism, resulting in the preservation of bone compressive load with treatment.

Can repeated in vivo micro-CT irradiation during adolescence alter bone microstructure, histomorphometry and longitudinal growth in a rodent model?

In vivo micro-computed tomography (micro-CT) can monitor longitudinal changes in bone mass and microstructure in small rodents but imposing high doses of radiation can damage the bone tissue. However, the effect of weekly micro-CT scanning during the adolescence on bone growth and architecture is still unknown. The right proximal tibia of male Sprague-Dawley rats randomized into three dose groups of 0.83, 1.65 and 2.47 Gy (n = 11/group) were CT scanned at weekly intervals from 4th to 12th week of age. The left tibia was used as a control and scanned only at the last time point. Bone marrow cells were investigated, bone growth rates and histomorphometric analyses were performed, and bone structural parameters were determined for both left and right tibiae. Radiation doses of 1.65 and 2.47 Gy affected bone marrow cells, heights of the proliferative and hypertrophic zones, and bone growth rates in the irradiated tibiae. For the 1.65 Gy group, irradiated tibiae resulted in lower BMD, Tb.Th, Tb.N and a higher Tb.Sp compared with the control tibiae. A decrease in BMD, BV/TV, Tb.Th, Tb.N and an increase in Tb.Sp were observed between the irradiated and control tibiae for the 2.47 Gy group. For cortical bone parameters, no effects were noticed for 1.65 and 0.83 Gy groups, but a lower Ct.Th was observed for 2.47 Gy group. Tibial bone development was adversely impacted and trabecular bone, together with bone marrow cells, were negatively affected by the 1.65 and 2.47 Gy radiation doses. Cortical bone microstructure was affected for 2.47 Gy group. However, bone development and morphometry were not affected for 0.83 Gy group. These findings can be used as a proof of concept for using the reasonable high-quality image acquisition under 0.83 Gy radiation doses during the adolescent period of rats without interfering with the bone development process.

Genetic profiling of decreased bone mineral density in an independent sample of Caucasian women

Genetic risk of low bone mineral density in women remains unclear. This study found that a large percentage of Caucasian women have a high genetic risk of osteoporosis, and genetic risk scores are significantly associated with BMD variation in a bone healthy sample of Caucasian women.

INTRODUCTION

We aimed to examine the distribution of risk alleles in an independent sample and to determine if such genetic components are associated with bone mineral density (BMD) variation in the sample.

METHODS

Existing genotype data of 1205 women in the cross-sectional Genomic Wide Scans for Female Osteoporosis Gene Study (GWSFO) were analyzed. Multi-loci genetic risk scores (GRSs) based on 62 BMD-associated single nucleotide polymorphisms (SNPs) were calculated. Regression analysis was employed to assess the association between GRSs and BMD. To examine the effect of SNPs clustered within key pathways associated with the development of osteoporosis, subtype weighted GRS specific to WNT signaling (6 SNPs), RANK-RANKL-OPG (3 SNPs), and mesenchymal stem differentiation (3 SNPs) were generated for analysis.

RESULTS

The unweighted GRS ranged from 48 to 80. One third of the women carried 66% risk alleles. After adjusting for age, height, and body weight, each unit increase of weighted GRS was associated with a decrease in BMD of 0.097 at femur (p < 0.0001) and 0.110 (p < 0.0001) at lumbar spine. The weighted GRS accounted for only 3.17-4.52% of BMD variance. The WNT signaling pathway GRS (6 SNPs) and the RANK-RANKL-OPG signaling pathway GRS (3 SNPs) both were significantly associated with decreased BMD at femur neck (p = 0.0004 and p = 0.0063, respectively) and lumbar spine (p < 0.0001 and p = 0.0001, respectively), while the mesenchymal stem cell differentiation pathway (3 SNPs) GRSs were associated only with the lumbar spine BMD (p = 0.045).

CONCLUSIONS

A substantially large percentage of healthy Caucasian women have a high genetic risk of osteoporosis. Weighted GRS was significantly associated with decreased BMD. The contribution of subtype GRS to the BMD variation differs by specific biological pathway and skeletal regions.

Can the contralateral limb be used as a control during the growing period in a rodent model?

The contralateral limb is often used as a control in various clinical, forensic and anthropological studies. However, no studies have been performed to determine if the contra-lateral limb is a suitable control during the bone development period. The aim of this study was to determine the bilateral symmetry of growing rat tibiae in terms of geometric shape, mechanical strength and bone morphological parameters with developmental stages. Left and right tibias of 18 male Sprague-Dawley rats at 4, 8 and 12 weeks of age were scanned with micro-CT for bone-morphometric evaluation and for 3D deviation analysis to quantify the geometric shape variations between left and right tibiae. Overall tibial lengths and curvatures were also measured, and bone mechanical strength was investigated using three-point bending tests. Deviation distributions between bilateral tibiae remained below 0.5 mm for more than 80% of the geometry for all groups. Tibial lengths, longitudinal tibial curvatures, bone-morphometric parameters and mechanical strengths changed significantly during the growing period but kept a strong degree of symmetry between bilateral tibiae. These results suggest that bilateral tibiae can be considered symmetrical in nature and that contralateral limb can be used as a control during the growing period in different experimental scenarios.

Influence of estrogen on individual exercise motivation and bone protection in ovariectomized rats

Bone protection and metabolism are directly linked to estrogen levels, but exercise is also considered to have bone protective effects. Reduced estrogen levels lead to a variety of disorders, for example, bone loss and reduced movement drive. The objective of this study was to investigate the effects of estrogen on individual voluntary exercise motivation and bone protection. We investigated sham operated, ovariectomized, and ovariectomized with estrogen supplemented Wistar rats (20 weeks old) either with or without access to exercise wheels. We selected an experimental approach where we could monitor the individual exercise of group-housed rats with ad libitum access to a running wheel with the help of a subcutaneous chip. In vivo and ex vivo microcomputed tomography analyses of the tibia were performed at two-week intervals from week 0 to week 6. Furthermore, tibial trabecular structure was evaluated based on histomorphometric analyses. We observed a significant bone protective effect of E2. For exercise performance, a substantially high intra-group variability was observed, especially in the E2 group. We presume that dominant behavior occurs within the group-housed rats resulting in a hierarchical access to the running wheel and a high variability of distance run. Exercise did not prevent ovariectomy-induced bone loss. However, lack of estrogen within the ovariectomized rats led to a drastically reduced activity prevented by estrogen supplementation. Our findings are important for future studies working with group-housed rats and exercise. The reason for the high intra-group variability in exercise needs to be investigated in future studies.

Age-dependent variations of cancellous bone in response to ovariectomy in C57BL/6J mice

The ovariectomized (OVX) mouse model has been widely accepted to be suitable for the study of postmenopausal osteoporosis. However, whether C57BL/6J mice, a commonly used genetic background mouse strain, is an appropriate model for postmenopausal osteoporosis remains controversial. The present study investigated the effect of the OVX model on alterations in bone density and microarchitecture in C57BL/6J female mice of different ages. C57BL/6J mice were divided into 8-, 12- and 16-week-old groups (OVX₈, OVX₁₂ and OVX₁₆) from the beginning of OVX. At 8 weeks post-surgery, the mice were anesthetized and micro-computed tomography was used to analyze the bone density and microarchitecture. The results revealed that OVX-induced loss of cancellous bone was greatest in OVX₈, moderate in OVX₁₂, and only a weak bone loss was observed in the OVX₁₆ group when compared with the SHAM₁₆ control group. In addition, the effect of genetic backgrounds in response to the OVX model were examined. Several other strains of mice, including inbred (BALB/c) and outbred (ICR and Kunming), were used in the present study, all of which were subjected to OVX at 8 weeks of age. The present findings revealed that the highest rate of bone loss was detected in C57BL/6J female mice. In addition, treatment with estrogen (17β-estradiol, 30 µg/kg five times per week) led to a significant increase in bone density in C57BL/6J mice compared with the other strains of mice. Therefore, these results may provide novel insights into the age- and strain-associated effect of OVX on regulating turnover of bone in female mice. The present findings also suggest 8-week-old C57BL/6J mice as an animal model for postmenopausal osteoporosis and preclinical testing of potential therapies for this disease.

Proper Positioning and Restraint of a Rat Hind Limb for Focused High Resolution Imaging of Bone Micro-architecture Using In Vivo Micro-computed Tomography

The use of in vivo micro-computed tomography (µCT) is a powerful tool which involves the non-destructive imaging of internal structures at high resolutions in live animal models. This allows for repeated imaging of the same rodent over time. This feature not only reduces the total number of rodents required in an experimental design and thereby reduces the inter-subject variation that can arise, but also allows researchers to assess longitudinal or life-long responses to an intervention. To acquire high quality images that can be processed and analyzed to more accurately quantify outcomes of bone micro-architecture, users of in vivo µCT scanners must properly anesthetize the rat, and position and restrain the hind limb. To do this, it is imperative that the rat be anesthetized to a level of complete relaxation, and that pedal reflexes are lost. These guidelines may be modified for each individual rat, as the rate of isoflurane metabolism can vary depending on strain and body size. Proper technique for in vivo µCT image acquisition enables accurate and consistent measurement of bone micro-architecture within and across studies.

Ketogenic Diet Compromises Both Cancellous and Cortical Bone Mass in Mice

To clarify osteoporotic effects of ketogenic diet (KD) on cancellous and cortical bone compared with ovariectomy (OVX) in mice. Forty female C57BL/6J 8-week-old mice were randomly divided into SD+Sham, SD+OVX, KD+Sham, and KD+OVX groups, and fed for 12 weeks. The distal femur of trabecular bone and the middle femur of cortical bone were evaluated with Micro-CT scanning. The maximum bending force and stiffness of the tibia were calculated using a three-point bending test. Osteoblast and osteoclast expression of femur were identified using tartrate-resistant acid phosphatase (TRAP), collagen type I (CoLI), and osteocalcin (OCN) staining. A 2-factor analysis of variance was used to evaluate effects of KD and OVX on radiological, biomechanical, and histological parameters. KD resulted in not only remarkable cancellous bone decline comparable to OVX, but also unique cortical bone reduction. The maximum bending force and stiffness decreased in the KD+Sham and KD+OVX groups but did not change in the SD+OVX group. The KD+OVX led to significantly higher expression in TRAP and noticeably lower expression in CoLI when compared with other groups. Both KD+Sham and SD+OVX prominently increased expression in TRAP, but decreased expression in CoLI. There was no significant difference in OCN among the four groups. The present results suggest that KD compromises both the cancellous and cortical bone architecture of long bones while OVX only in cancellous bone architecture. A combination of KD and OVX may lead to more bone loss.

Automated Quantitative Bone Analysis in In Vivo X-ray Micro-Computed Tomography

Measurement and analysis of bone morphometry in 3D micro-computed tomography volumes using automated image processing and analysis improve the accuracy, consistency, reproducibility, and speed of preclinical osteological research studies. Automating segmentation and separation of individual bones in 3D micro-computed tomography volumes of murine models presents significant challenges considering partial volume effects and joints with thin spacing, i.e., 50 to [Formula: see text]. In this paper, novel hybrid splitting filters are presented to overcome the challenge of automated bone separation. This is achieved by enhancing joint contrast using rotationally invariant second-derivative operators. These filters generate split components that seed marker-controlled watershed segmentation. In addition, these filters can be used to separate metaphysis and epiphysis in long bones, e.g., femur, and remove the metaphyseal growth plate from the detected bone mask in morphometric measurements. Moreover, for slice-by-slice stereological measurements of long bones, particularly curved bones, such as tibia, the accuracy of the analysis can be improved if the planar measurements are guided to follow the longitudinal direction of the bone. In this paper, an approach is presented for characterizing the bone medial axis using morphological thinning and centerline operations. Building upon the medial axis, a novel framework is presented to automatically guide stereological measurements of long bones and enhance measurement accuracy and consistency. These image processing and analysis approaches are combined in an automated streamlined software workflow and applied to a range of in vivo micro-computed tomography studies for validation.

Comparison of ex vivo and in vivo micro-computed tomography of rat tibia at different scanning settings

The parameters of a micro-computed tomography (μCT) scan, including whether a bone is imaged in vivo or ex vivo, determine the quality of the resulting image. In turn, this impacts the accuracy of the trabecular and cortical outcomes. The absolute impact of μCT scanning at different voxel sizes and whether the sample is imaged in vivo or ex vivo on the morphological outcomes of the proximal tibia in the rat is unknown. The right proximal tibia of 6-month-old Sham-control and ovariectomized (OVX) rats (n = 8/group) was scanned using μCT (SkyScan 1176, Bruker, Kontich, Belgium) using three sets of parameters (9 μm ex vivo, 18 μm ex vivo, 18 μm in vivo) to compare the trabecular and cortical outcomes. Regardless of scan protocols, differences between Sham and OVX groups were observed as expected. At a voxel size of 18 μm, scanning in vivo or ex vivo had no effect on any of the outcomes measured. However, compared to a 9 μm voxel size scan, imaging at 18 μm resulted in significant underestimation of the connectivity density (p < 0.05) of the trabecular bone and a significant overestimation (p < 0.05) of the trabecular indices (trabecular thickness, degree of anisotropy) and of the cortical indices (cortical bone area, cortical area fraction, cortical thickness) in both Sham and OVX rats. These results suggest the benefit to scanning the proximal tibia of rats at a voxel size as low as 9 μm, although considerations must be made for the increased acquisition time, anesthesia, animal welfare, and radiation exposure associated with lower voxel size in vivo scanning. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1690-1698, 2017.

Longitudinal Use of Micro-computed Tomography Does Not Alter Microarchitecture of the Proximal Tibia in Sham or Ovariectomized Sprague-Dawley Rats

In vivo micro-computed tomography (μCT) provides the ability to measure longitudinal changes to tibia microarchitecture, but the effect of this radiation is not well understood. The right proximal tibia of Sprague-Dawley rats (n = 12/group) randomized to Sham-control (Sham) or ovariectomy (OVX) surgery at 12 weeks of age was scanned using μCT at 13, 17, 21, and 25 weeks of age, at a resolution of 18 μm and a radiation dose of 603 mGy. The left proximal tibia was scanned only at 25 weeks of age to serve as an internal non-irradiated control. Repeated irradiation did not affect tibia microarchitecture in Sham or OVX groups, although there was an increase in cortical eccentricity (P < 0.05). All trabecular outcomes and cortical BMD were different (P < 0.05) between groups after only 1 week post-surgery and differences persisted to study endpoint. Characteristic changes to trabecular bone were observed in OVX rats over time. Interactions of time and hormone status were found for cortical BMD (P < 0.001), Ps. Pm., and Ec. Pm. (P < 0.05). Repeated irradiation of the tibia at 13, 17, 21, and 25 weeks does not cause adverse effects to microarchitecture, regardless of hormone status. This radiation dose can be applied over a typical 3-month study period to comprehensively understand how an intervention alters tibia microarchitecture without confounding effects of radiation.

Minimizing Interpolation Bias and Precision Error in In Vivo µCT-Based Measurements of Bone Structure and Dynamics

In vivo µCT imaging allows for high-resolution, longitudinal evaluation of bone properties. Based on this technology, several recent studies have developed in vivo dynamic bone histomorphometry techniques that utilize registered µCT images to identify regions of bone formation and resorption, allowing for longitudinal assessment of bone remodeling. However, this analysis requires a direct voxel-by-voxel subtraction between image pairs, necessitating rotation of the images into the same coordinate system, which introduces interpolation errors. We developed a novel image transformation scheme, matched-angle transformation (MAT), whereby the interpolation errors are minimized by equally rotating both the follow-up and baseline images instead of the standard of rotating one image while the other remains fixed. This new method greatly reduced interpolation biases caused by the standard transformation. Additionally, our study evaluated the reproducibility and precision of bone remodeling measurements made via in vivo dynamic bone histomorphometry. Although bone remodeling measurements showed moderate baseline noise, precision was adequate to measure physiologically relevant changes in bone remodeling, and measurements had relatively good reproducibility, with intra-class correlation coefficients of 0.75-0.95. This indicates that, when used in conjunction with MAT, in vivo dynamic histomorphometry provides a reliable assessment of bone remodeling.

Identification and Characterization of a Synthetic Osteogenic Peptide

Osteoporosis is the most common metabolic bone disorder and its management represents a tremendous public health encumbrance. While several classes of therapeutics have been approved to treat this disease, all are associated with significant adverse effects. An algorithm was developed and utilized to discover potential bioactive peptides, which led to the identification of an osteogenic peptide that mapped to the C-terminal region of the calcitonin receptor and has been named calcitonin receptor fragment peptide (CRFP). In vitro treatment of human mesenchymal stem cells with CRFP resulted in dose-specific effects on both proliferation and osteoblastic differentiation. Similarly, in vitro treatment of rat RCJ3.1C5.18 cells led to dose- and species-specific effects on proliferation. A rat ovariectomy (OVX) model was used to assess the potential efficacy of CRFP in treating osteoporosis. MicroCT analysis of distal femoral samples showed that OVX rats treated with CRFP were significantly protected from losses of 55 % in trabecular bone volume fraction (BVF), 42 % in connectivity density, and 18 % in trabecular thickness in comparison to vehicle-treated controls. MicroCT analyses of vertebrae revealed CRFP to significantly prevent a 25 % reduction in BVF. MicroCT evaluation of femoral and vertebral cortical bone found a significant reduction of 2 % in vertebral bone mineral density. In summary, our in vitro studies indicate that CRFP is both bioactive and osteogenic and our in vivo studies indicate that CRFP is skeletally bioactive. These promising data indicate that further in vitro and in vivo evaluation of CRFP as a new treatment for osteoporosis is warranted.

Oral delivery of zoledronic acid by non-covalent conjugation with lysine-deoxycholic acid: In vitro characterization and in vivo anti-osteoporotic efficacy in ovariectomized rats

We assessed the possibility of changing the route of administration of zoledronic acid to an oral dosage form and its therapeutic efficacy in an estrogen-deficient osteoporosis rat model. To enhance oral bioavailability, we formed an ionic complex by electrostatic conjugation of zoledronic acid with lysine-linked deoxycholic acid (Lys-DOCA, an oral absorption enhancer). After forming the complex, the characteristic crystalline features of pure zoledronic acid disappeared completely in the powder X-ray diffractogram and differential scanning calorimetry thermogram, indicating that zoledronic acid existed in an amorphous form in the complex. In vitro permeabilities of zoledronic acid/Lys-DOCA (1:1) (ZD1) and zoledronic acid/Lys-DOCA (1:2) (ZD2) complex across Caco-2 cell monolayers were 2.47- and 4.74-fold higher than that of zoledronic acid, respectively. Upon intra-jejunal administration to rats, the intestinal absorption of zoledronic acid was increased significantly and the resulting oral bioavailability of the ZD2 complex was determined to be 6.76±2.59% (0.548±0.161% for zoledronic acid). Ovariectomized (OVX) rats showed 122% increased bone mineral density versus the OVX control at 12weeks after treatment with once weekly oral administration of ZD2 complex (16μg/kg of zoledronic acid). Furthermore, rats treated with ZD2 complex orally showed significant improvement in the parameters of trabecular microarchitecture and bone strength: 149% higher bone volume fraction (BV/TV), 115% higher trabecular number (Tb.N), and 56% higher mean maximum load (Fmax) than in the OVX group. The trabecular microstructure and bone mechanical properties in the oral zoledronic acid group were not significantly changed compared with the OVX control. Thus, the oral ZD2 complex inhibited osteoporosis progression effectively by promoting osteogenesis and trabecular connectivity. The oral ZD2 complex would be expected to improve patient compliance by replacing the conventional injectable form and expand the indications, to include prophylaxis for osteoporosis and bone metastases.

Effects of P-15 Peptide Coated Hydroxyapatite on Tibial Defect Repair In Vivo in Normal and Osteoporotic Rats

This study assessed the efficacy of anorganic bone mineral coated with P-15 peptide (ABM/P-15) on tibia defect repair longitudinally in both normal and osteoporotic rats in vivo. A paired design was used. 24 Norwegian brown rats were divided into normal and osteoporotic groups. 48 cylindrical defects were created in proximal tibias bilaterally. Defects were filled with ABM/P-15 or left empty. Osteoporotic status was assessed by microarchitectural analysis. Microarchitectural properties of proximal tibial defects were evaluated at 4 time points. 21 days after surgery, tibias were harvested for histology and histomorphometry. Significantly increased bone volume fraction, surface density, and connectivity were seen in all groups at days 14 and 21 compared with day 0. Moreover, the structure type of ABM/P-15 group was changed toward typical plate-like structure. Microarchitectural properties of ABM/P-15 treated newly formed bones at 21 days were similar in normal and osteoporotic rats. Histologically, significant bone formation was seen in all groups. Interestingly, significantly increased bone formation was seen in osteoporotic rats treated with ABM/P-15 indicating optimized healing potential. Empty defects showed lower healing potential in osteoporotic bone. In conclusion, ABM/P-15 accelerated bone regeneration in osteoporotic rats but did not enhance bone regeneration in normal rats.

Quantitative morphometric patterns in cartilage and bone from the humeral heads of end-stage osteoarthritis patients

OBJECTIVE

The purpose of this work is to investigate in a quantitative manner, the gross and regional structural patterns in cartilage and bone from the humeral head of end-stage OA patients, with the goal of identifying patterns of disease. Since the prevalence of primary OA of the shoulder is increasing as the population ages and the non-traumatic degenerative changes leading to this disease are poorly understood, a site-specific morphometric analysis speaks to the structure-function remodelling relationship of the pathological anatomy.

METHODS

Humeral heads were harvested from twenty-one patients undergoing shoulder arthroplasty for end-stage primary OA. The samples were scanned with micro-computed tomography and magnetic resonance imaging (MRI), and registered to provide reconstructed 3D datasets of the cartilage, cortical and trabecular bone tissues. Gross visual examination of the datasets allowed samples to be classified as OA-like, osteoporosis (OP)-like or OA/OP-like.

RESULTS

Volumes of interest (VOI) separating the OA-like samples into five distinct regions showed positive correlations between bone and cartilage morphometric parameters; specifically in areas where more cartilage has been lost, the underlying subchondral cortical bone was more porous and thicker, while the subchondral trabecular bone was more dense, including more connections and trabeculae. These differences were site-specific, where the central humeral head saw the greatest destruction of cartilage and bone sclerosis, followed by the anterior aspects.

CONCLUSION

The ability to correlate bone and cartilage changes is valuable, as these structural cues may allow a more targeted diagnostic approach and a better classification of the disease, leading to improved therapies.

Ginsenoside-Rb2 displays anti-osteoporosis effects through reducing oxidative damage and bone-resorbing cytokines during osteogenesis

Reactive oxygen species (ROS) are a significant pathogenic factor of osteoporosis. Ginsenoside-Rb2 (Rb2), a 20(S)-protopanaxadiol glycoside extracted from ginseng, is a potent antioxidant that generates interest regarding the bone metabolism area. We tested the potential anti-osteoporosis effects of Rb2 and its underlying mechanism in this study. We produced an oxidative damage model induced by hydrogen peroxide (H2O2) in osteoblastic MC3T3-E1 cells to test the essential anti-osteoporosis effects of Rb2in vitro. The results indicated that treatment of 0.1 to 10μM Rb2 promoted the proliferation of MC3T3-E1 cells, improved alkaline phosphatase (ALP) expression, elevated calcium mineralization and mRNA expressions of Alp, Col1a1, osteocalcin (Ocn) and osteopontin (Opn) against oxidative damage induced by H2O2. Importantly, Rb2 reduced the expression levels of receptor activator of nuclear factor kappa-B ligand (RANKL) and IL-6 and inhibited the H2O2-induced production of ROS. The in vivo study indicated that the Rb2 administered for 12weeks partially decreased blood malondialdehyde (MDA) activity and elevated the activity of reduced glutathione (GSH) in ovariectomized (OVX) mice. Moreover, Rb2 improved the micro-architecture of trabecular bones and increased bone mineral density (BMD) of the 4th lumbar vertebrae (L4) and the distal femur. Altogether, these results demonstrated that the potential anti-osteoporosis effects of Rb2 were linked to a reduction of oxidative damage and bone-resorbing cytokines, which suggests that Rb2 might be effective in preventing and alleviating osteoporosis.

Quantitative analysis of bone and soft tissue by micro-computed tomography: applications to ex vivo and in vivo studies

Micro-computed tomography (micro-CT) is a high-resolution imaging modality that is capable of analysing bone structure with a voxel size on the order of 10 μm. With the development of in vivo micro-CT, where disease progression and treatment can be monitored in a living animal over a period of time, this modality has become a standard tool for preclinical assessment of bone architecture during disease progression and treatment. For meaningful comparison between micro-CT studies, it is essential that the same parameters for data acquisition and analysis methods be used. This protocol outlines the common procedures that are currently used for sample preparation, scanning, reconstruction and analysis in micro-CT studies. Scan and analysis methods for trabecular and cortical bone are covered for the femur, tibia, vertebra and the full neonate body of small rodents. The analysis procedures using the software provided by ScancoMedical and Bruker are discussed, and the routinely used bone architectural parameters are outlined. This protocol also provides a section dedicated to in vivo scanning and analysis, which covers the topics of anaesthesia, radiation dose and image registration. Because of the expanding research using micro-CT to study other skeletal sites, as well as soft tissues, we also provide a review of current techniques to examine the skull and mandible, adipose tissue, vasculature, tumour severity and cartilage. Lists of recommended further reading and literature references are included to provide the reader with more detail on the methods described.

CT imaging biomarker for evaluation of emodin as a potential drug on LPS-mediated osteoporosis mice

RATIONALE AND OBJECTIVES

To identify micro-computed tomography (CT) imaging biomarkers for evaluating the effects of emodin, a potential drug to treat osteoporosis, in the mouse model of lipopolysaccharide (LPS)-mediated osteoporosis.

MATERIALS AND METHODS

Forty male imprinting control region (ICR) mice with LPS-induced bone resorption were equally divided into four experimental groups: phosphate-buffered saline-treated (control), emodin-treated, LPS-treated, and LPS + emodin-treated groups. Emodin (50 mg/kg) was administered orally on alternate days for 8 days, and LPS (5 mg/kg) was injected intraperitoneally on days 1 and 4. After 8 days, the mice were sacrificed, and micro-CT images of the left proximal femurs were obtained. Three-dimensional images were analyzed by using commercial software to measure the bone volume to total volume fraction (BV/TV), trabecular number (Tb-N), trabecular thickness (Tb-Th), and trabecular separation (Tb-Sp) as CT imaging biomarkers. Histologic analyses of the femurs were performed using hematoxylin and eosin and tartrate-resistant acid phosphatase (TRAP) immunohistochemical staining.

RESULTS

The LPS + emodin-treated group demonstrated marked suppression of LPS-induced bone resorption compared to the LPS-treated group (BV/TV, 28.84% vs. 40.76%; Tb-N, 2.65 vs. 3.45 mm(-1); Tb-Sp, 300.81 vs. 212.31 μm; Tb-Th, 116.94 vs. 131.25 μm). TRAP immunohistochemical analysis showed fewer osteoclasts per field of tissue in the LPS + emodin-treated group than in the LPS-treated group (27.8 vs. 41.8). The BV/TV, Tb-N, and Tb-Sp data correlated well with the histomorphometric findings.

CONCLUSIONS

The findings reveal a novel effect of emodin on bone remodeling in the LPS-mediated osteoporotic mouse model. The ex vivo micro-CT imaging is a promising tool for assessing the therapeutic effects of potential drugs on osteoporosis.

Three-dimensional image registration improves the long-term precision of in vivo micro-computed tomographic measurements in anabolic and catabolic mouse models

Micro-computed tomography (micro-CT) is a widely used technique to track bone structural and mineral changes in small animals in vivo. Precise definition of volumes of interest (VOIs) in follow-up scans is required to accurately quantify these changes. To improve precision, VOIs can be transferred from baseline images onto follow-ups using image registration. We studied the performance of a registration procedure applied to in vivo data sets of anabolic and osteoporotic bone changes in mice. Micro-CT image data from two separate CD1 mouse data sets were studied. The first included a group treated with parathyroid hormone (PTH) and control and the second, an ovariectomy (OVX) group and control. Micro-CT was performed once per week for 4 weeks at the proximal tibia starting at treatment onset (PTH data set) or after surgery (OVX data set). A series consisting entirely of user-defined VOIs and a registered series where VOIs defined at baseline were transferred to follow-ups were created. Standard bone structural and mineral measurements were calculated. Image registration resulted in a 13-56 % reduction in precision error. Significant effects of registration to detect PTH-induced changes in BV/TV and trabecular BMD were observed. When changes were very pronounced or small, the qualitative improvement observed for the registered data set did not reach statistical significance. This study documents an increase in long-term precision of micro-CT measurements with image registration. Sensitivity to detect changes was improved but not uniform for all parameters. Future study of this technique on images with a smaller voxel size (<19 μm) may capture the effect in greater detail, in particular for trabecular thickness, where changes may be too small to be observed with the voxel size used here. Our results document the value of registration and indicate that the magnitude of improvement depends on the model and treatment chosen.

Pulsed electromagnetic fields improve bone microstructure and strength in ovariectomized rats through a Wnt/Lrp5/β-catenin signaling-associated mechanism

Growing evidence has demonstrated that pulsed electromagnetic field (PEMF), as an alternative noninvasive method, could promote remarkable in vivo and in vitro osteogenesis. However, the exact mechanism of PEMF on osteopenia/osteoporosis is still poorly understood, which further limits the extensive clinical application of PEMF. In the present study, the efficiency of PEMF on osteoporotic bone microarchitecture and bone quality together with its associated signaling pathway mechanisms was systematically investigated in ovariectomized (OVX) rats. Thirty rats were equally assigned to the Control, OVX and OVX+PEMF groups. The OVX+PEMF group was subjected to daily 8-hour PEMF exposure with 15 Hz, 2.4 mT (peak value). After 10 weeks, the OVX+PEMF group exhibited significantly improved bone mass and bone architecture, evidenced by increased BMD, Tb.N, Tb.Th and BV/TV, and suppressed Tb.Sp and SMI levels in the MicroCT analysis. Three-point bending test suggests that PEMF attenuated the biomechanical strength deterioration of the OVX rat femora, evidenced by increased maximum load and elastic modulus. RT-PCR analysis demonstrated that PEMF exposure significantly promoted the overall gene expressions of Wnt1, LRP5 and β-catenin in the canonical Wnt signaling, but did not exhibit obvious impact on either RANKL or RANK gene expressions. Together, our present findings highlight that PEMF attenuated OVX-induced deterioration of bone microarchitecture and strength in rats by promoting the activation of Wnt/LRP5/β-catenin signaling rather than by inhibiting RANKL-RANK signaling. This study enriches our basic knowledge to the osteogenetic activity of PEMF, and may lead to more efficient and scientific clinical application of PEMF in inhibiting osteopenia/osteoporosis.

3D image registration is critical to ensure accurate detection of longitudinal changes in trabecular bone density, microstructure, and stiffness measurements in rat tibiae by in vivo microcomputed tomography (μCT)

In the recent decade, in vivo μCT scanners have become available to monitor temporal changes in rodent bone in response to diseases and treatments. We investigated short-term and long-term precision of in vivo μCT measurements of trabecular bone density, microstructure and stiffness of rat tibiae and tested whether they can be improved by 3D image registration. Rats in the short-term precision group underwent baseline and follow-up scans within the same day (n = 15) and those in the long-term precision group were scanned at day 0 and day 14 (n = 16) at 10.5 μm voxel size. A 3D image-registration scheme was applied to register the trabecular bone compartments of baseline and follow-up scans. Prior to image registration, short-term precision ranged between 0.85% and 2.65% in bone volume fraction (BV/TV), trabecular number, thickness, and spacing (Tb.N*, Tb.Th*, Tb.Sp*), trabecular bone mineral density and tissue mineral density (Tb.BMD, and Tb.TMD), and was particularly high in structure model index (SMI), connectivity density (Conn.D), and stiffness (4.29%-8.83%). Image registration tended to improve the short-term precision, but the only statistically significant improvement was in Tb.N*, Tb.TMD, and stiffness. On the other hand, unregistered comparisons between day-0 and day-14 scans suggested significant increases in BV/TV, Tb.N*, Tb.Th*, Conn.D, and Tb.BMD and decrease in Tb.Sp* and SMI. However, the percent change in each parameter from registered comparisons was significantly different from unregistered comparisons. Registered results suggested a significant increase in BV/TV, Tb.BMD, and stiffness over 14 days, primarily caused by increased Tb.Th* and Tb.TMD. Due to the continuous growth of rodents, the direct comparisons between the unregistered baseline and follow-up scans were driven by changes due to global bone modeling instead of local remodeling. Our results suggested that 3D image registration is critical for detecting changes due to bone remodeling activities in rodent trabecular bone by in vivo μCT imaging.

Comparison of estrogenic responses in bone and uterus depending on the parity status in Lewis rats

The reproductive transition of women through peri- to postmenopause is characterized by changes in steroid hormone levels due to the cessation of the ovarian function. Beside several complaints associated with these hormonal changes, the deterioration of the trabecular bone micro-architecture and the loss of skeletal mass can cause osteoporosis. At this life stage, women often have a reproductive history of one to several pregnancies. The ovariectomized skeletally mature rat (>10 months old) is one of the most commonly used animal models for postmenopausal osteoporosis research. Despite the fact that mammals can undergo up to several reproductive cycles (primi-/pluriparous), nulliparous animals are often used and the question whether changes in the hormonal milieu subsequently affect the skeleton and influence the outcome of intervention studies is often neglected in study designs. Therefore, the aim of the present study was to compare the estrogen responsiveness of nulliparous and pluriparous rats. For this purpose, one year old virgin or retired breeder Lewis rats were either sham operated or ovariectomized, whereas half of the ovariectomized animals received subcutaneous 17β-estradiol pellets eight weeks after surgery. After another four weeks, the effects on the uterus were determined by expression analysis of estrogen-dependently regulated steroid receptor genes and well-established marker genes. Moreover, trabecular bone parameters in the tibia were analyzed by micro-computed tomography (μCT). Parity-dependency in estrogen responsiveness was observed with respect to the achieved serum E2 levels in response to similar E2 treatment. This led to differences both on the uterus wet weight and on the expression level of uterine target genes. In addition, a reversal of the ovariectomy-induced changes of the bone architecture after 17β-estradiol substitution was only observed among the nulliparous. In conclusion, the observations of this study support parity-dependent differences in the responses to estrogenic compounds in the uterus and the bone of rats. These results indicate that the parity-status has an impact on the outcome of studies aiming at the investigation of estrogenic effects of compounds potentially used in hormone replacement and thus, this should be taken into consideration for further studies and particularly for the discussion of data obtained with the preclinical ovariectomized rat animal model.

Positive alterations of viscoelastic and geometric properties in ovariectomized rat femurs with concurrent administration of ibandronate and PTH

Besides bone mineral density (BMD), structural and nano-level viscoelastic properties of bone are also crucial determinants of bone strength. However, treatment induced viscosity changes in osteoporotic bone have seldom been characterized. In this study, the effects of anabolic, antiresorptive and concurrent treatments on ovariectomized rat bones were thoroughly analyzed using multiple bone strength parameters. A total of 52 female Sprague-Dawley rats of 3 months age were divided into 5 groups and subjected to sham (SHM group) or ovariectomy surgery (OVX, PTH, IBN and COM groups). Weekly low-dose parathyroid hormone (PTH) and/or ibandronate or its vehicle was administered subcutaneously to the respective groups starting from 4th week post-surgery. Four rats per group were euthanized every 4 weeks and their femurs were harvested. The BMD, micro-architectural parameters, cortical bone geometry and viscoelastic parameters were measured at the distal femoral metaphysis. Our results showed that PTH, ibandronate or its concurrent treatment can effectively reverse ovariectomy induced deteriorations in both trabecular and cortical bone. Different drugs had selective effects especially in preserving geometric and viscoelastic properties of the bone. The concurrent administration of PTH and ibandronate was shown to offer an added advantage in preserving mean BMD and had a positive effect on cortical bone geometry, resulting from an increased periosteal formation and a decreased endocortical resorption. Viscosity (η) was prominently restored in combined treatment group. It is in accordance with an observed denser alignment of collagen fibers and hydroxyapatite crystal matrix with fewer pores, which may play an important role in hindering fracture propagation.

Orthodontic tooth movement and root resorption in ovariectomized rats treated by systemic administration of zoledronic acid

INTRODUCTION

The effect of zoledronic acid, a potent and novel bisphosphonate, on tooth movement and orthodontically induced root resorption in osteoporotic animals systemically treated with zoledronic acid as similarly used in postmenopausal patients has not been elucidated. Therefore, this study was undertaken.

METHODS

Fifteen 10-week-old female Wistar rats were divided into 3 groups: ovariectomy, ovariectomy + zoledronic acid, and control. Only the ovariectomy and ovariectomy + zoledronic acid groups underwent ovariectomies. Two weeks after the ovariectomy, zoledronic acid was administered only to the ovariectomy + zoledronic acid group. Four weeks after the ovariectomy, 25-g nickel-titanium closed-coil springs were applied to observe tooth movement and orthodontically induced root resorption.

RESULTS

There were significant differences in the amounts of tooth movement and orthodontically induced root resorption between the ovariectomy and the control groups, and also between the ovariectomy and the ovariectomy + zoledronic acid groups. There was no statistically significant difference in tooth movement and orthodontically induced root resorption between the ovariectomy + zoledronic acid and the control groups. Zoledronic acid inhibited significantly more tooth movement and significantly reduced the severity of orthodontically induced root resorption in the ovariectomized rats. The ovariectomy + zoledronic acid group showed almost the same results as did the control group in both tooth movement and orthodontically induced root resorption.

CONCLUSIONS

Zoledronic acid inhibits excessive orthodontic tooth movement and also reduces the risk of severe orthodontically induced root resorption in ovariectomized rats.

Estimation of an early meaningful time point of bone parameter changes in application to an osteoporotic rat model with in vivo microcomputed tomography measurements

The commonly used preclinical animal model of postmenopausal osteoporosis is the mature ovariectomized rat, whereby cessation of ovarian oestrogen production consequently results in bone volume reduction. The study aim was to precisely define the time course of structural changes resulting from ovariectomy and thereby reduce the time animals have to be treated to judge the effects of osteoporosis treatment. For this purpose, we assessed architectural changes by microcomputed tomography ( μCT) during 10 weeks following ovariectomy or sham surgery at two-week intervals. Moreover, the trabecular microarchitecture of the lumbar vertebrae was assessed after necropsy. Besides this, serum biomarkers of bone turnover were determined. These data were in a new approach additionally correlated to femur mRNA expression profiles. We selected the osteoblast marker genes osteocalcin and type I collagen as well as the two osteoclast marker genes cathepsin k and tartrate-resistant acid phosphatase 5. The gene expression analysis suggested an activation of osteoblasts as well as octeoclasts. The significantly induced serum levels of osteocalcin and collagen degradation fragments also revealed this higher rate of bone turnover. Our results indicate that as soon as four weeks after ovariectomy the bone volume fraction exhibited a decline of 30% and 50% of the connectivity density. In addition, significant decreases of trabecular number and thickness as well as of the bone volume fraction were only observed in vertebrae of ovariectomized animals. Interestingly, changes of trabecular morphology were also found in the sham animals as a consequence of senescence.

Reproducibility and agreement of micro-CT and histomorphometry in human trabecular bone with different metabolic status

The use of micro-computed tomography (micro-CT) to study bone microstructure is continuously increasing. Thus, it is important to ensure that micro-CT can differentiate healthy and pathological bone. This study aimed to determine whether the reproducibility of bone histomorphometry and micro-CT, and agreement between the techniques, vary in bone samples with different metabolic status. Iliac crest biopsies (n = 36) were obtained from healthy subjects (n = 10) and from patients with osteoporosis (OP) (n = 15) or renal osteodystrophy (ROD) (n = 11). Micro-CT and histomorphometry analyses were repeated twice. Results were analyzed in separate groups and after pooling the data. Bone histomorphometry detected generally known differences between the diseases, whereas micro-CT did not detect differences between normal and ROD samples as effectively. Repeated measurements for BV/TV, Tb.Th, Tb.N, and Tb.Sp exhibited linear correlation coefficients (ρ) of 0.87-0.92 [coefficients of variations (CV), 8.3-27.2%] for histomorphometry and of 0.66-0.94 (CV, 4.4-23.4%) for micro-CT. There were no significant differences in reproducibility among samples from different study groups. Correlations between BV/TV (micro-CT) and mineralized bone volume (Md.V/TV, histomorphometry) were weaker than between BV/TV (micro-CT) and BV/TV (histomorphometry). When comparing the techniques, BV/TV, Tb.Th, and Tb.N displayed moderate correlations (ρ = 0.39-0.62, P < 0.05), and the agreement for BV/TV was highest in OP samples. The agreement between the techniques using clinical bone samples was moderate. Especially, micro-CT was less effective than bone histomorphometry in differentiating ROD from normal samples. The reproducibility was not affected by the health status of bone. Histomorphometry is still needed in clinical practice to study the remodeling balance in bone, and the methods are complementary.

Ibandronate does not reduce the anabolic effects of PTH in ovariectomized rat tibiae: a microarchitectural and mechanical study

Osteoporosis remains a challenging problem. Understanding the regulation on osteoclast and osteoblast by drugs has been of great interest. Both anabolic and anti-resorptive drugs yield positive results in the treatment of osteoporosis. However, whether the concurrent administration of parathyroid hormone (1-34) and ibandronate may offer an advantage over monotherapy is still unknown. This study, therefore, attempts to compare the efficacy of two therapeutical approaches and to investigate the beneficial effects in concurrent therapy in a rat model using three-point bending, pQCT and μCT analysis. A total of 60 female Sprague-Dawley rats of age 10 to 12 weeks were divided into 5 groups (SHAM, OVX+VEH, OVX+PTH, OVX+IBAN, OVX+PTH+IBAN) and subjected to ovariectomy or sham surgery accordingly. Low-dose parathyroid hormone (PTH) and/or ibandronate or its vehicle were administered subcutaneously to the respective groups starting from 4th week post-surgery at weekly intervals. Three rats from each group were euthanized every 2 weeks and their tibiae were harvested. The tibiae were subjected to metaphyseal three-point bending, pQCT and μCT analysis. Serum biomarkers for both bone formation (P1NP) and resorption (CTX) were studied. A total of 11 indices showed a significant difference between SHAM and OVX+VEH groups, suggesting the successful establishment of osteoporosis in the rat model. Compared to the previous studies which showed impedance from bisphosphonates in combination therapy with PTH, our study revealed that ibandronate does not block the anabolic effects of PTH in ovariectomized rat tibiae. Maximum load, strength-strain indices and serum bone formation markers of OVX+PTH+IBAN group are significantly higher than both monotherapy groups. With the proper ratio of anabolic and anti-resorptive drugs, the effect could be more pronounced.

Bone quality is partially recovered after the discontinuation of RANKL administration in rats by increased bone mass on existing trabeculae: an in vivo micro-CT study

Bone loss and recovery in a receptor activator for nuclear factor κ B ligand (RANKL)-administered rat model was assessed. Microarchitecture, mineralization and strength deteriorated faster than ovariectomy (OVX). Recovery was dependent on the loss of trabecular elements and connections. Early recovery suggests a natural mechanism in rats to overcome excess RANKL, and may have implications for long-term bone loss.

PURPOSE

To compare a model for experimental osteoporosis that induces bone loss by injecting RANKL into rats to an OVX rat model, and measure subsequent recovery of bone architecture, mineralization, and mechanics after stopping injections.

METHODS

Mature, healthy, female Wistar rats were divided into high-dose RANKL, low-dose RANKL, OVX, and vehicle control groups. The right proximal tibiae were micro-computed tomography (micro-CT) scanned in vivo every 2 weeks from week 0 to week 12 and every 4 weeks from week 12 to week 20. Bone architectural, mineralization, and mechanical changes were determined. Serum calcium, RANKL, anti-RANKL, and osteoprotegerin were measured at weeks 0, 6, and 20.

RESULTS

High-dose RANKL administration resulted in severe deterioration of the trabecular architecture (39% of baseline BV/TV), and modest decreases in tissue mineralization, bone mass, and stiffness. Bone loss occurred more rapidly than in the OVX and low-dose RANKL group, and recovery occurred prior to stopping RANKL injections. Full recovery of trabecular thickness, tissue mineralization, and cortical bone mass, partial recovery of trabecular bone volume (55% of baseline), structural model index, bone mass (69% of baseline), and stiffness (90% of baseline) but no improvement in connectivity density or trabecular number was observed.

CONCLUSION

RANKL administration resulted in rapid and dose-dependent bone loss. The recovery of trabecular bone volume and stiffness appeared to be dependent on the number of remaining trabecular elements and their interconnections. Uncontrolled recovery suggests that further investigation into the RANKL-injected rat as a model of bone loss is required.

Relationship between age, skeletal site, and time post-ovariectomy on bone mineral and trabecular microarchitecture in rats

The ovariectomized (OVX) rat is widely used in osteoporosis research, but no standard model exists. The individual effects of rat age, skeletal site, and time post-ovariectomy (post-OVX) on bone have been examined. However, the relationship between them is not yet fully explored. This study examined how various combinations of rat age, skeletal site, and time post-OVX affect bone mineral and microarchitecture. The rats used were 12 (n = 28), 24 (n = 28), and 44 (n = 31) weeks old. In each age group, approximately half underwent OVX and other half underwent Sham surgeries. Bone mineral (content and density) and trabecular morphology was assessed at 2, 5, 10, 15, 20, 25, and 30 weeks post-surgery. Sites examined included the proximal tibia, spine, distal femur, and proximal femur. Overall, the proximal tibia showed the earliest and greatest differences between OVX and Sham groups. The 24-week-old group showed the best osteoporotic response. The 12-week-old group showed growth effects, whilst the 44-week-old group showed aging effects. The response of certain sites to OVX was also found to depend on the rat age used. These findings may aid in explaining discrepancies reported in the literature as well as synergistic combinations that may signify advanced conditions. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:189-196, 2011.

Structural parameters of normal and osteoporotic human trabecular bone are affected differently by microCT image resolution

This study employed microCT to investigate whether image resolution affects bone structural parameters differently in healthy normal and osteoporotic trabecular bone. With increasing image voxel size, the originally detected differences between sample groups diminished. The results suggest that structural differences may not be reliably detected with clinical scanners.

INTRODUCTION

Structural parameters of bone reflect its health status, but are highly dependent on the image resolution. We hypothesized that image resolution affects bone structural parameters differently in normal and osteoporotic trabecular bone.

METHODS

Human trabecular bone samples from the iliac crest and the knee were analyzed (normal n = 11, osteoporotic n = 15) using a high-resolution microCT (14 or 18 µm voxel sizes). Images were re-sampled to voxel sizes 1-16 times larger than the original image and thresholded with global or local adaptive algorithms. Absolute and normalized values of each structural parameter were calculated, and the effect of decreasing image resolution was compared between the normal and osteoporotic samples.

RESULTS

Normal and osteoporotic samples had different (p < 0.05) absolute bone volume fractions. However, the normalized values showed that the osteoporotic samples were more prone to errors (p < 0.05) with increased voxel size. The absolute values of trabecular number, trabecular separation, degree of anisotropy, and structure model index were different between the groups at the original voxel size (p < 0.05), but at voxel sizes between 60 and 110 µm, those differences were no longer significant.

CONCLUSIONS

The results suggest that structural differences between osteoporotic and normal trabecular bone may not be reliably detected with clinical CT scanners providing image voxel sizes above 100 µm.

Detecting early bone changes using in vivo micro-CT in ovariectomized, zoledronic acid-treated, and sham-operated rats

SUMMARY

This study monitored in vivo the effect on bone microarchitecture of initiating antiresorptive treatment with zoledronic acid in rats at 2 weeks following ovariectomy, an early phase at which major degenerative bone changes have been found to occur. The treatment still facilitated the full reversal of cancellous bone loss in rat tibia, highlighting the importance of the time point of initiation of antiresorptive treatment.

INTRODUCTION

Injection of zoledronic acid in rats at time of ovariectomy has been found to fully preserve tibial bone microarchitecture over time, whereas injection at 8 weeks after ovariectomy has shown partial bone recovery. This study investigated the effect on microarchitecture of initiating antiresorptive treatment in the early phase following ovariectomy, at 2 weeks, a time point at which major degenerative changes in the bone have been found to occur.

METHODS

Female Sprague-Dawley rats were divided into ovariectomized group, ovariectomized group treated with zoledronic acid, and sham-operated group. In vivo micro-CT scanning of rat tibiae and morphometric analysis were performed at 0, 2, 4, 8, and 12 weeks after ovariectomy, with zoledronic acid treatment beginning 2 weeks after ovariectomy. Data were first analyzed with repeated measures analysis of variance (longitudinal study design) and then without repeated measures (cross-sectional study design).

RESULTS

The ovariectomized group demonstrated dramatic bone loss, first detected at week 2. Conversely, at week 4, the zoledronic acid-treated group returned microstructural parameters to baseline values. Remarkable increases in bone parameters were found after 6 weeks of treatment and maintained similar to sham group until the end. The longitudinal study design provided earlier detection of bone changes compared to the cross-sectional study design.

CONCLUSIONS

Treatment with zoledronic acid as late as 2 weeks after ovariectomy still facilitates the full reversal of cancellous bone loss in the rat tibia.

Guidelines for assessment of bone microstructure in rodents using micro-computed tomography

Use of high-resolution micro-computed tomography (microCT) imaging to assess trabecular and cortical bone morphology has grown immensely. There are several commercially available microCT systems, each with different approaches to image acquisition, evaluation, and reporting of outcomes. This lack of consistency makes it difficult to interpret reported results and to compare findings across different studies. This article addresses this critical need for standardized terminology and consistent reporting of parameters related to image acquisition and analysis, and key outcome assessments, particularly with respect to ex vivo analysis of rodent specimens. Thus the guidelines herein provide recommendations regarding (1) standardized terminology and units, (2) information to be included in describing the methods for a given experiment, and (3) a minimal set of outcome variables that should be reported. Whereas the specific research objective will determine the experimental design, these guidelines are intended to ensure accurate and consistent reporting of microCT-derived bone morphometry and density measurements. In particular, the methods section for papers that present microCT-based outcomes must include details of the following scan aspects: (1) image acquisition, including the scanning medium, X-ray tube potential, and voxel size, as well as clear descriptions of the size and location of the volume of interest and the method used to delineate trabecular and cortical bone regions, and (2) image processing, including the algorithms used for image filtration and the approach used for image segmentation. Morphometric analyses should be based on 3D algorithms that do not rely on assumptions about the underlying structure whenever possible. When reporting microCT results, the minimal set of variables that should be used to describe trabecular bone morphometry includes bone volume fraction and trabecular number, thickness, and separation. The minimal set of variables that should be used to describe cortical bone morphometry includes total cross-sectional area, cortical bone area, cortical bone area fraction, and cortical thickness. Other variables also may be appropriate depending on the research question and technical quality of the scan. Standard nomenclature, outlined in this article, should be followed for reporting of results.

Reproducibility of bone micro-architecture measurements in rodents by in vivo micro-computed tomography is maximized with three-dimensional image registration

In vivo micro-computed tomography (microCT) is a new method to monitor longitudinal changes of bone micro-architecture. Common animal models of bone diseases are mice and rats, and it is important to know the reproducibility of the bone measurements in order to correctly interpret results. When performing baseline and follow-up acquisitions, variation in the scan region will influence the parameters, and it has yet to be investigated if three-dimensional (3D) registration can improve the reproducibility. Two typical breeds of mice and one typical breed of rats were scanned four times each using microCT and standard bone morphological and density measurements were calculated. Image registration was used to find the overlapping regions between the scans within each series of animal data and only overlapping regions were analyzed for the bone parameters. Reproducibility was determined for each animal both pre- and post-registration. For the rats, results included a bone volume ratio (BV/TV) precision error of 5.46%, cortical thickness (Ct.Th) error of 1.97%, and tissue mineral density (TMD) of 2.00%. For the BL6 mice, precision errors were 3.00% (BV/TV), 0.95% (Ct.Th), and 0.94% (TMD), and for the C3H mice 2.68% (BV/TV), 1.52% (Ct.Th), and 1.72% (TMD). After image registration there was a significant improvement in reproducibility in most parameters for the rats. In general, metric parameters such as bone volume ratio had better reproducibility than the non-metric parameters connectivity density and structure model index. With 3D registration, reproducibility improved the results obtained by the experienced operators in this study. Registration may serve to equalize reproducibility of operators with different skill levels and across laboratories. It also improves efficiency by reducing the amount of hand-contouring required. This reproducibility data will be important for the interpretation of current and future longitudinal microCT studies.

Can porous tantalum be used to achieve ankle and subtalar arthrodesis?: a pilot study

A structural graft often is needed to fill gaps during reconstructive procedures of the ankle and hindfoot. Autograft, the current gold standard, is limited in availability and configuration and is associated with donor-site morbidity in as much as 48%, whereas the alternative allograft carries risks of disease transmission and collapse. Trabecular metal (tantalum), with a healing rate similar to that of autograft, high stability, and no donor-site morbidity, has been used in surgery of the hip, knee, and spine. However, its use has not been documented in foot and ankle surgery. We retrospectively reviewed nine patients with complex foot and ankle arthrodeses using a tantalum spacer. Minimum followup was 1.9 years (average, 2 years; range, 1.9-2.4 years). Bone ingrowth into the tantalum was analyzed with micro-CT in three of the nine patients. All arthrodeses were fused clinically and radiographically at the 1- and 2 year followups and no complications occurred. The American Orthopaedic Foot and Ankle Society score increased from 32 to 74. The micro-CT showed bony trabeculae growing onto the tantalum. Our data suggest tantalum may be used as a structural graft option for ankle and subtalar arthrodesis. All nine of our patients achieved fusion and had no complications. Using tantalum obviated the need for harvesting of the iliac spine.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Constrained tibial vibration does not produce an anabolic bone response in adult mice

Osteoporosis is characterized by low bone mass and increased fracture risk. High frequency, low-amplitude whole-body vibration (WBV) has been proposed as a treatment for osteoporosis because it can stimulate new bone formation and prevent trabecular bone loss. We developed constrained tibial vibration (CTV) as a method for controlled vibrational loading of the lower leg of a mouse. We first subjected mice to five weeks of daily CTV loading (0.5 G maximum acceleration) with loading parameters chosen to independently investigate the effects of strain magnitude, loading frequency, and cyclic acceleration on the adaptive response to vibration. We hypothesized that mice subjected to the highest magnitude of dynamic strain would have the largest bone formation response. We observed a slight, local benefit of CTV loading on trabecular bone, as BV/TV was 5.2% higher in the loaded vs. non-loaded tibia of mice loaded with the highest bone strain magnitude. However, despite these positive differences, we observed significantly lower measures of trabecular structure in both loaded and non-loaded tibias from CTV loaded mice compared to Sham and Baseline Control animals, indicating a negative systemic effect of CTV on trabecular bone. Based on this evidence, we conducted a follow-up study wherein mice were subjected to CTV or sham loading, and tibias were scanned at the beginning and end of the study period using in vivo microCT. Consistent with the findings of the first study, trabecular BV/TV in both tibias of CTV loaded and Sham mice was, on average, 36% and 31% lower on day 36 than day 0, respectively, compared to 20% lower in Age-Matched Controls over the same time period. Contrary to the first study, there were no differences between loaded and non-loaded tibias in CTV loaded mice, providing no evidence for a local benefit of CTV. In summary, 5 weeks of daily CTV loading of mice was, at best, weakly anabolic for trabecular bone in the proximal tibia, while daily handling and exposure to anesthesia was associated with significant loss of trabecular and cortical bone. We conclude that direct vibrational loading of bone in anesthetized, adult mice is not anabolic.

Effects of Egb 761 on bone mineral density, bone microstructure, and osteoblast function: Possible roles of quercetin and kaempferol

The effects of standardized and concentrated extract of Ginkgo biloba, Egb 761, were studied on estrogen deficiency-induced bone loss in ovariectomized (OVx) rats rendered osteopenic. Upon osteopenia development, Egb 761 was administered at a dose of 100mgkg(?1)day(?1) by oral gavage to OVx rats whereas control group received vehicle. Following 5 weeks of treatment, the OVx+Egb 761 group (n=12) of rats exhibited significantly higher whole body BMD and lower bone turnover markers (serum alkaline phosphatase and osteocalcin) than OVx rats that were given vehicle (n=12). BMD levels in excised bones were also found to be higher in both trabecular (most robustly in lumbar vertebrae) and cortical bones of OVx+Egb 761 compared with OVx+vehicle group. Egb 761 did not exhibit estrogen agonistic activity at the uterine level. Microcomputed tomography demonstrated that OVx+Egb 761 group had better bone microarchitectural parameters compared with OVx+vehicle group. Moreover, OVx+Egb 761 group had higher femoral mRNA levels of osterix, type I collagen and osteocalcin compared with OVx+vehicle group. Determination of levels of three flavonoids of Egb 761, that are known to have bone conserving property, in serum and bone marrow suggests that kaempferol and quercetin, and not rutin, likely mediate the beneficial actions observed with Egb 761 treatment. These results show for the first time that oral administration of Egb 761 restores bone mass in aged OVx rats.