Trabecular bone microarchitecture after alendronate treatment of osteoporotic women

Effect of bisphosphonate on bone microstructure, mechanical strength in osteoporotic rats by ovariectomy

BACKGROUND

Bisphosphonate (BP) can treat osteoporosis and prevent osteoporotic fractures in clinical. However, the effect of BP on microstructure and mechanical properties of cortical and trabecular bone has been taken little attention, separately.

METHODS

In this study, BP was used to intervene in ovariectomized female SD rats. The femoral micro-CT images were used to measure the structural parameters and reconstruct the 3D models in volume of interest. The structural parameters of cortical and trabecular bone were measured, and the mechanical properties were predicted using micro-finite element analysis.

RESULTS

There was almost no significant difference in the morphological structure parameters and mechanical properties of cortical bone between normal, ovariectomized (sham-OVX) and BP intervention groups. However, BP could significantly improve bone volume fraction (BV/TV) and trabecular separation (Tb.SP) in inter-femoral condyles (IT) (sham-OVX vs. BP, p < 0.001), and had no significant effect on BV/TV in medial and lateral femoral condyles (MT, LT). Similarly, BPs could significantly affect the effective modulus in IT (sham-OVX vs. BP, p < 0.001), and had no significant difference in MT and LT. In addition, the structural parameters and effective modulus showed a good linear correlation.

CONCLUSION

In a short time, the effects of BP intervention and osteoporosis on cortical bone were not obvious. The effects of BP on trabecular bone in non-main weight-bearing area (IT) were valuable, while for osteoporosis, the main weight-bearing area (MT, LT) may improve the structural quality and mechanical strength of trabecular bone through exercise compensation.

Denosumab treatment is associated with decreased cortical porosity and increased bone density and strength at the proximal humerus of ovariectomized cynomolgus monkeys

Upper extremity fractures, including those at the humerus, are common among women with postmenopausal osteoporosis. Denosumab was shown to reduce humeral fractures in this population; however, no clinical or preclinical studies have quantified the effects of denosumab on humerus bone mineral density or bone microarchitecture changes. This study used micro-computed tomography (μCT) and computed tomography (CT), alongside image-based finite element (FE) models derived from both modalities, to quantify the effects of denosomab (DMAb) and alendronate (ALN) on humeral bone from acutely ovariectomized (OVX) cynomolgus monkeys. Animals were treated with 12 monthly injections of s.c. vehicle (VEH; n = 10), s.c. denosumab (DMAb; 25 mg/kg, n = 9), or i.v. alendronate (ALN; 50 μg/kg, n = 10). Two more groups received 6 months of VEH followed by 6 months of DMAb (VEH-DMAb; n = 7) or 6 months of ALN followed by 6 months of DMAb (ALN-DMAb; n = 9). After treatment, humeri were harvested and μCT was used to quantify tissue mineral density, trabecular morphology, and cortical porosity at the humeral head. Clinical CT imaging was also used to quantify trabecular and cortical bone mineral density (BMD) at the ultra-proximal, proximal, 1/5 proximal and midshaft of the bone. Finally, μCT-based FE models in compression, and CT-based FE models in compression, torsion, and bending, were developed to estimate differences in strength. Compared to VEH, groups that received DMAb at any time demonstrated lower cortical porosity and/or higher tissue mineral density via μCT; no effects on trabecular morphology were observed. FE estimated strength based on μCT was higher after 12-months DMAb (p = 0.020) and ALN-DMAb (p = 0.024) vs. VEH; respectively, FE predicted mean (SD) strength was 4649.88 (710.58) N, and 4621.10 (1050.16) N vs. 3309.4 (876.09) N. All antiresorptive treatments were associated with higher cortical BMD via CT at the 1/5 proximal and midshaft of the humerus; however, no differences in CT-based FE predicted strength were observed. Overall, these results help to explain the observed reductions in humeral fracture rate following DMAb treatment in women with postmenopausal osteoporosis.

Effects of anti-resorptive treatment on the material properties of individual canine trabeculae in cyclic tensile tests

Osteoporosis is defined as a decrease of bone mass and strength, as well as an increase in fracture risk. It is conventionally treated with antiresorptive drugs, such as bisphosphonates (BPs) and selective estrogen receptor modulators (SERMs). Although both drug types successfully decrease the risk of bone fractures, their effect on bone mass and strength is different. For instance, BP treatment causes an increase of bone mass, stiffness and strength of whole bones, whereas SERM treatment causes only small (4%) increases of bone mass, but increased bone toughness. Such improved mechanical behavior of whole bones can be potentially related to the bone mass, bone structure or material changes. While bone mass and architecture have already been investigated previously, little is known about the mechanical behavior at the tissue/material level, especially of trabecular bone. As such, the goal of the work presented here was to fill this gap by performing cyclic tensile tests in a wet, close to physiologic environment of individual trabeculae retrieved from the vertebrae of beagle dogs treated with alendronate (a BP), raloxifene (a SERM) or without treatments. Identification of material properties was performed with a previously developed rheological model and of mechanical properties via fitting of envelope curves. Additionally, tissue mineral density (TMD) and microdamage formation were analyzed. Alendronate treatment resulted in a higher trabecular tissue stiffness and strength, associated with higher levels of TMD. In contrast, raloxifene treatment caused a higher trabecular toughness, pre-dominantly in the post-yield region. Microdamage formation during testing was not affected by either anti-resorptive treatment regimens. These findings highlight that the improved mechanical behavior of whole bones after anti-resorptive treatment is at least partly caused by improved material properties, with different mechanisms for alendronate and raloxifene. This study further shows the power of performing a mechanical characterization of trabecular bone at the level of individual trabeculae for better understanding of clinically relevant mechanical behavior of bone.

Bisphosphonates impair the onset of bone formation at remodeling sites

Bisphosphonates are widely used anti-osteoporotic drugs targeting osteoclasts. They strongly inhibit bone resorption, but also strongly reduce bone formation. This reduced formation is commonly ascribed to the mechanism maintaining the resorption/formation balance during remodeling. The present study provides evidence for an additional mechanism where bisphosphonates actually impair the onset of bone formation after resorption. The evidence is based on morphometric parameters recently developed to assess the activities reversing resorption to formation. Herein, we compare these parameters in cancellous bone of alendronate- and placebo-treated postmenopausal osteoporotic patients. Alendronate increases the prevalence of eroded surfaces characterized by reversal cells/osteoprogenitors at low cell density and remote from active bone surfaces. This indicates deficient cell expansion on eroded surfaces - an event that is indispensable to start formation. Furthermore, alendronate decreases the coverage of these eroded surfaces by remodeling compartment canopies, a putative source of reversal cells/osteoprogenitors. Finally, alendronate strongly decreases the activation frequency of bone formation, and decreases more the formative compared to the eroded surfaces. All these parameters correlate with each other. These observations lead to a model where bisphosphonates hamper the osteoprogenitor recruitment required to initiate bone formation. This effect results in a larger eroded surface, thereby explaining the well-known paradox that bisphosphonates strongly inhibit bone resorption without strongly decreasing eroded surfaces. The possible mechanism for hampered osteoprogenitor recruitment is discussed: bisphosphonates may decrease the release of osteogenic factors by the osteoclasts, and/or bisphosphonates released by osteoclasts may act directly on neighboring osteoprogenitor cells as reported in preclinical studies.

High resolution imaging in bone tissue research-review

This review article focuses on imaging of bone tissue to understand skeletal health with regards to bone quality. Skeletal fragility fractures are due to bone diseases such as osteoporosis which result in low bone mass and bone mineral density (BMD) leading to high risk of fragility fractures. Recent advances in imaging and analysis technologies have highly benefitted the field of biological sciences. In particular, their application in skeletal health has been of significant importance in understanding bone mechanical behavior (structure and properties) at the tissue level. While synchrotron based microCT technique has remained the gold standard for non-destructive evaluation of structure in material and biological sciences, several lab based microCT systems have been developed to provide high resolution imaging of specimens with greater access, and ease of use in laboratory settings. Lab based microCT scanners are widely used in the bone field as a standard tool to evaluate three-dimensional (3D) morphologies of bone structure at image resolutions appropriate for bone samples from small animals to bone biopsy specimens from humans. Both synchrotron and standard lab based microCT systems provide high resolution imaging ex vivo for a small sized specimen. A few X-ray based systems are also commercially available for in vivo scanning at relatively low image resolutions. Synchrotron-based CT microscopy is being used for various ultra-high-resolution image analyses using complex 3D software. However, the synchrotron-based CT technology is in high demand, allows only limited numbers of specimens, expensive, requires complex additional instrumentation, and is not easily available to researchers as it requires access to a synchrotron source which is always limited. Therefore, desktop laboratory scanners (microXCT, Zeiss/Xradia, Scanco, SkyScan. etc.), mimicking the synchrotron based CT technology or image resolution, have been developed to solve the accessibility issues. These lab based scanners have helped both material science, and the bone field to investigate bone tissue morphologies at submicron mage resolutions. Considerable progress has been made in both in vivo and ex vivo imaging towards providing high resolution images of bone tissue. Both clinical and research imaging technologies will continue to improve and help understand osteoporosis and other related skeletal issues in order to develop targeted treatments for bone fragility. This review summarizes the high resolution imaging work in bone research.

Antipostmenopausal effects of Stauntonia hexaphylla and Vaccinium bracteatum fruit combination in estrogen-deficient rats

Background

Climacterium is a series of physical and mental symptoms occurring in women and men due to decreased levels of sex hormones. Women lose the ability to become pregnant due to decreased ovarian estrogen production; the initial symptom being hot flushes. In addition, urogenital atrophy, sexual dysfunction, mood changes, and osteoporosis occur. Extracts of Stauntonia hexaphylla (SH) and Vaccinium bracteatum (VB) fruits, with a wide range of biological activities, are widely used in traditional herbal medicine.

Objective

The purpose of this study was to investigate the mitigation of menopausal symptoms, such as hot flushes and postmenopausal osteoporosis after combinatorial treatment with SH and VB (SHVB) of ovariectomized (OVX) rats.

Design

We measured the bone regenerative effect of SHVB on receptor activator of nuclear factor-κB (NF-κB) ligand-induced osteoclast differentiation in vitro and on ovariectomy-induced osteoporosis in vivo. We investigated the effect of SHVB in a rat model of menopausal hot flushes, in which the tail skin temperature increases following ovariectomy-induced rapid decline in estrogen levels.

Results

SHVB inhibited osteoclast formation and tartrate-resistant acid phosphatase activity in primary mouse bone marrow-derived cells. In an estrogen deficiency-induced rat model, measurement of serum bone turnover factors showed that treatment with SHVB lowered the increased bone turnover. Additionally, SHVB decreased OVX-induced bone loss of the total femur. SHVB inhibited osteoclast differentiation, prevented bone mass reduction, and improved trabecular bone structure and biochemical markers in OVX-induced osteoporosis. In addition, administration of SHVB significantly ameliorated the changes in skin temperature in OVX rats.

Conclusion

SHVB improved the symptoms of menopause. These results provide the foundation for developing SHVB as a natural substance to replace hormones in the future.

Adjuvant drug-assisted bone healing: Part III - Further strategies for local and systemic modulation

In this third in a series of reviews on adjuvant drug-assisted bone healing, further approaches aiming at influencing the healing process are discussed. Local and systemic modulation of bone metabolism is pursued with use of a number of drugs with completely different indications, which are characterized by a pleiotropic spectrum of action. These include drugs used to treat lipid disorders (HMG-CoA reductase inhibitors), hypertension (ACE inhibitors), osteoporosis (bisphosphonates), cancer (proteasome inhibitors) and others. Potential applications to enhance bone healing are discussed.

Femoral head trabecular micro-architecture in patients with osteoporotic hip fractures: Impact of bisphosphonate treatment

INTRODUCTION

Bisphosphonates are effective in preventing osteoporotic fractures. However, their limited efficacy of bisphosphonates has been suggested as a result of these drugs, which prevent the resorption of bone without improving bone connectivity. The trabecular microarchitecture in patients with osteoporotic hip fractures was evaluated according to their history of bisphosphonate treatment (BT).

METHODS

One hundred thirty-three patients with hip fractures admitted and treated between November 2014 and September 2016. The patients were divided into two groups based on whether they had received treatment with bisphosphonates for >3years or not [non-bisphosphonate-treated patients (NT)]. One-to-one propensity score matching generated 15 matched pairs of patients. Microstructural parameters of femoral head were measured by using micro-computed tomography (μCT). Mechanical compression test (Young's modulus, yield strength, and maximum compressive force) was performed following μCT.

RESULTS

Trabecular bone pattern factor (1.15±0.7mm^-1 versus 1.61±0.5mm^-1, p=0.037) and specific bone surface (14.1±0.8mm^-1 versus 15.4±1.9mm^-1, p=0.050) were significantly lower in the BT group than in the NT group. Furthermore, Young's modulus was significantly higher in the BT group than in the NT group (72.14±30.75MPa versus 47.89±29.89MPa, p=0.037). In both groups, trabecular bone pattern was the most closely correlated microstructural parameter to bone strength. Microstructural analysis demonstrated that bone connectivity was better preserved in the BT group than in the NT group.

CONCLUSIONS

Bisphosphonate treatment preserves bone mass and bone quality. The factors influencing osteoporotic hip fractures in patients treated with bisphosphonates warrant further research.

Changes in cortical microarchitecture are independent of areal bone mineral density in patients with fragility fractures

Dual-energy X-ray absorptiometry (DXA) and high-resolution peripheral quantitative computed tomography (HR-pQCT) are commonly used to assess the areal bone mineral density (aBMD) and peripheral microstructure, respectively. While DXA is the standard to diagnose osteoporosis, HR-pQCT provides information about the cortical and trabecular architecture. Many fragility fractures occur in patients who do not meet the osteoporosis criterion (i.e., T-score≤-2.5). We hypothesize that patients with T-score above -2.5 and fragility fracture may have abnormal bone microarchitecture. Therefore, in this retrospective clinical study, HR-pQCT data obtained from patients with fragility fractures and T-scores≥-2.5 (n=71) were compared to corresponding data from patients with fragility fractures and T-scores≤-3.5 (n=56). Types of secondary osteoporosis were excluded from the study. To verify the dependency of alterations in bone microarchitecture and T-score, the association between HR-pQCT values and aBMD as reflected by the T-score at both proximal femora, was assessed. At the distal tibia, cortical thickness was lower (p<0.001), cortical porosity was similar (p=0.61), trabecular number was higher (p<0.001), and bone volume fraction (BV/TV) was higher (p<0.001) in patients with T-scores≥-2.5 than in patients with T-scores≤-3.5. Trabecular number and BV/TV correlated with T-score (r=0.68, p<0.001; r=0.61, p<0.001), whereas the cortical values did not. Our results thus demonstrate the importance of bone structure, as assessed by HR-pQCT, in addition to the standard DXA T-score in the diagnosis of osteoporosis.

Effects of Parathyroid Hormone Administration on Bone Strength in Hypoparathyroidism

The microstructural skeletal phenotype of hypoparathyroidism (HypoPT), a disorder of inadequate parathyroid hormone secretion, is altered trabecular microarchitecture with increased trabecular bone volume and thickness. Using 2-D histomorphometric analysis, we previously found that 2 years of PTH(1-84) in HypoPT is associated with reduced trabecular thickness (Tb.Th) and an increase in trabecular number (Tb.N). We have now utilized direct 3-D microstructural analysis to determine the extent to which these changes may be related to bone strength. Iliac crest bone biopsies from HypoPT subjects (n = 58) were analyzed by microcomputed tomography (μCT) and by microfinite element (μFE) analysis. Biopsies were performed at baseline and at 1 or 2 years of recombinant human PTH(1-84) [rhPTH(1-84)]. In a subset of subjects (n = 13) at 3 months, we demonstrated a reduction in trabecular separation (Tb.Sp, 0.64 ± 0.1 to 0.56 ± 0.1 mm; p = 0.005) and in the variance of trabecular separation (Tb.SD, 0.19 ± 0.1 to 0.17 ± 0.1 mm; p = 0.01), along with an increase in bone volume/total volume (BV/TV, 26.76 ± 10.1 to 32.83 ± 13.5%; p = 0.02), bone surface/total volume (BS/TV, 3.85 ± 0.7 to 4.49 ± 1.0 mm(2) /mm(3) ; p = 0.005), Tb.N (1.84 ± 0.5 versus 2.36 ± 1.3 mm(-1) ; p = 0.02) and Young's modulus (649.38 ± 460.7 to 1044.81 ± 1090.5 N/mm(2) ; p = 0.049). After 1 year of rhPTH(1-84), Force increased (144.08 ± 102.4 to 241.13 ± 189.1 N; p = 0.04) and Young's modulus tended to increase (662.15 ± 478.2 to 1050.80 ± 824.1 N/m(2) ; p = 0.06). The 1-year change in cancellous mineralizing surface (MS/BS) predicted 1-year changes in μCT variables. The biopsies obtained after 2 years of rhPTH(1-84) showed no change from baseline. These data suggest that administration of rhPTH(1-84) in HypoPT is associated with transient changes in key parameters associated with bone strength. The results indicate that rhPTH(1-84) improves skeletal quality in HypoPT early in treatment. © 2016 American Society for Bone and Mineral Research.

Intrinsic mechanical behavior of femoral cortical bone in young, osteoporotic and bisphosphonate-treated individuals in low- and high energy fracture conditions

Bisphosphonates are a common treatment to reduce osteoporotic fractures. This treatment induces osseous structural and compositional changes accompanied by positive effects on osteoblasts and osteocytes. Here, we test the hypothesis that restored osseous cell behavior, which resembles characteristics of younger, healthy cortical bone, leads to improved bone quality. Microarchitecture and mechanical properties of young, treatment-naïve osteoporosis, and bisphosphonate-treated cases were investigated in femoral cortices. Tissue strength was measured using three-point bending. Collagen fibril-level deformation was assessed in non-traumatic and traumatic fracture states using synchrotron small-angle x-ray scattering (SAXS) at low and high strain rates. The lower modulus, strength and fibril deformation measured at low strain rates reflects susceptibility for osteoporotic low-energy fragility fractures. Independent of age, disease and treatment status, SAXS revealed reduced fibril plasticity at high strain rates, characteristic of traumatic fracture. The significantly reduced mechanical integrity in osteoporosis may originate from porosity and alterations to the intra/extrafibrillar structure, while the fibril deformation under treatment indicates improved nano-scale characteristics. In conclusion, losses in strength and fibril deformation at low strain rates correlate with the occurrence of fragility fractures in osteoporosis, while improvements in structural and mechanical properties following bisphosphonate treatment may foster resistance to fracture during physiological strain rates.

The Protective Effects of Alisol A 24-Acetate from Alisma canaliculatum on Ovariectomy Induced Bone Loss in Vivo

Alisma canaliculatum is a herb commonly used in traditional Korean medicine, and has been shown in scientific studies to have antitumor, diuretic hepatoprotective, and antibacterial effects. Recently, the anti-osteoclastogenesis of alisol A 24-acetate from Alisma canaliculatum was investigated in vitro. However, the influence of alisol A 24-acetate on osteoporosis in animals has not been investigated. The present study was undertaken to investigate the anti-osteoporotic effect of alisol A 24-acetate on bone mass in ovariectomized (OVX) mice and to identify the mechanism responsible for its effects. OVX mice were treated daily with 0.5 or 2 μg/g of alisol A 24-acetate for a period of six weeks. It was found that these administrations significantly suppressed osteoporosis in OVX mice and improved bone morphometric parameters. The serum estradiol, bone alkaline phosphatase levels, regulatory T/Th17 cell numbers were significantly increased by alisol A 24-acetate as compared with untreated OVX mice. In addition, TRAP activity was inhibited by alisol A 24-acetate in OVX mice. These results suggest alisol A 24-acetate effectively prevents bone loss in OVX mice, and that it can be considered a potential therapeutic for the treatment of postmenopausal osteoporosis.

Osteoclast Deficiency Contributes to Temporomandibular Joint Ankylosed Bone Mass Formation

Ankylosed bone mass in temporomandibular joint ankylosis (TMJA) is an important factor affecting mouth-opening limitation. However, the mechanism underlying the occurrence of ankylosed bone mass remains unknown. Research has shown that osteoblasts and osteoclasts maintain balance in bone remodeling. Thus, we hypothesized that aberrant osteoclastogenesis and osteogenesis may be involved in the occurrence of ankylosed bone mass in TMJA. In this study, we characterized the osteogenesis of bone marrow stem cells and the osteoclastogenesis of myelomonocyte in clinical specimens of TMJA and normal controls. Results showed that, compared with control bone marrow stem cells, TMJA bone marrow stem cells had lower proliferative and osteogenic capacities. The number of osteoclasts in the ankylosed bone mass group dramatically decreased, and myelomonocyte osteoclastogenic potential was impaired. The RANKL/OPG ratio of the ankylosed bone mass group was lower than that of the control group. Thus, our study suggests that osteoclast deficiency may be an important factor affecting bone mass ankylosis.

The incidence of and risk factors for developing atypical femoral fractures in Japan

The long-term treatment with anti-resorptive drugs for osteoporotic patients is suggested to be associated with an increase in atypical femoral fractures (AFFs). However, their incidence, patient characteristics, and risk factors have not been fully elucidated especially in Asian countries. This retrospective observational cohort study found fourteen AFFs in ten patients (four bilateral fractures) among 2,238 hip and femoral shaft fractures treated in our associated hospitals between 2005 and 2010; this incidence (0.63%) was similar to Caucasians. Of the ten patients with AFFs, nine (90%) and six (60%) were using bisphosphonates (BPs) and glucocorticoids (GCs), respectively, compared to 14.3 and 8.6% for patients with typical femoral fractures who were using these agents. As comorbid conditions, five patients had collagen disease (CD) and two had diabetes. A fracture location-, age- and gender-matched (1:3) case-control study revealed that administration of BPs, GCs, and suffering from collagen disease (CD) were significant risk factors for developing AFFs [odds ratios 36.0 (95% confidence intervals 3.8-342.2), 13.0 (2.3-74.1) and 9.0 (1.6-50.3), respectively]. Interestingly, all of the patients with atypical subtrochanteric femoral fractures, defined as those within 5 cm of the lesser trochanter, were taking GCs due to CD, and the age of these patients (average of 54.8 years) was significantly younger than those with atypical diaphyseal femoral fractures (average of 77.2 years, p < 0.05). In conclusion, the incidence of AFFs in the Japanese population was similar to that of Caucasians, and taking BPs and GCs and suffering from CD were risk factors for developing AFFs.

Multi-level characterization of human femoral cortices and their underlying osteocyte network reveal trends in quality of young, aged, osteoporotic and antiresorptive-treated bone

Characterization of bone's hierarchical structure in aging, disease and treatment conditions is imperative to understand the architectural and compositional modifications to the material and its mechanical integrity. Here, cortical bone sections from 30 female proximal femurs - a frequent fracture site - were rigorously assessed to characterize the osteocyte lacunar network, osteon density and patterns of bone matrix mineralization by backscatter-electron imaging and Fourier-transform infrared spectroscopy in relation to mechanical properties obtained by reference-point indentation. We show that young, healthy bone revealed the highest resistance to mechanical loading (indentation) along with higher mineralization and preserved osteocyte-lacunar characteristics. In contrast, aging and osteoporosis significantly alter bone material properties, where impairment of the osteocyte-lacunar network was evident through accumulation of hypermineralized osteocyte lacunae with aging and even more in osteoporosis, highlighting increased osteocyte apoptosis and reduced mechanical competence. But antiresorptive treatment led to fewer mineralized lacunae and fewer but larger osteons signifying rejuvenated bone. In summary, multiple structural and compositional changes to the bone material were identified leading to decay or maintenance of bone quality in disease, health and treatment conditions. Clearly, antiresorptive treatment reflected favorable effects on the multifunctional osteocytic cells that are a prerequisite for bone's structural, metabolic and mechanosensory integrity.

Bisphosphonates and bone quality

Bisphosphonates (BPs) are bone-avid compounds used as first-line medications for the prevention and treatment of osteoporosis. They are also used in other skeletal pathologies such as Paget's and metastatic bone disease. They effectively reduce osteoclast viability and also activity in the resorptive phase of bone remodelling and help preserve bone micro-architecture, both major determinants of bone strength and ultimately of the susceptibility to fractures. The chemically distinctive structure of each BP used in the clinic determines their unique affinity, distribution/penetration throughout the bone and their individual effects on bone geometry, micro-architecture and composition or what we call 'bone quality'. BPs have no clinically significant anabolic effects. This review will touch upon some of the components of bone quality that could be affected by the administration of BPs.

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.

Strontium ranelate: in search for the mechanism of action

Strontium ranelate is a medicine with evidenced effects on the risk of fractures. The heterogeneity of strontium distribution in bone, quality of bone mineral crystals in young bone packets on bone surfaces formed during strontium ranelate administration, and activation of the calcium sensing receptor may, at least partially, explain the beneficial effects of SrR on reducing the risk of fractures. In this review, the concept of the dual action of strontium ranelate is also discussed. However, sufficient evidence for the bone anabolic effect of SrR does not exist in humans. The knowledge of the mechanism of action of SrR is important not only for the explanation of the effects of SrR upon the skeleton, but also for the safety of treatment for other tissues.

High-resolution peripheral quantitative computed tomography and finite element analysis of bone strength at the distal radius in ovariectomized adult rhesus monkey demonstrate efficacy of odanacatib and differentiation from alendronate

Translational evaluation of disease progression and treatment response is critical to the development of therapies for osteoporosis. In this study, longitudinal in-vivo monitoring of odanacatib (ODN) treatment efficacy was compared to alendronate (ALN) in ovariectomized (OVX) non-human primates (NHPs) using high-resolution peripheral computed tomography (HR-pQCT). Treatment effects were evaluated using several determinants of bone strength, density and quality, including volumetric bone mineral density (vBMD), three-dimensional structure, finite element analysis (FEA) estimated peak force and biomechanical properties at the ultradistal (UD) radius at baseline, 3, 6, 9, 12, and 18 months of dosing in three treatment groups: vehicle (VEH), low ODN (2 mg/kg/day, L-ODN), and ALN (30 μg/kg/week). Biomechanical axial compression tests were performed at the end of the study. Bone strength estimates using FEA were validated by ex-vivo mechanical compression testing experiments. After 18months of dosing, L-ODN demonstrated significant increases from baseline in integral vBMD (13.5%), cortical thickness (24.4%), total bone volume fraction BV/TV (13.5%), FEA-estimated peak force (26.6%) and peak stress (17.1%), respectively. Increases from baseline for L-ODN at 18 months were significantly higher than that for ALN in DXA-based aBMD (7.6%), cortical thickness (22.9%), integral vBMD (12.2%), total BV/TV (10.1%), FEA peak force (17.7%) and FEA peak stress (11.5%), respectively. These results demonstrate a superior efficacy of ODN treatment compared to ALN at the UD radii in ovariectomized NHPs.

Bone mineralization is elevated and less heterogeneous in adults with type 2 diabetes and osteoarthritis compared to controls with osteoarthritis alone

PURPOSE

The purpose of this study was to determine whether trabecular bone mineralization differed in adults with type 2 diabetes compared to adults without type 2 diabetes.

METHODS

Proximal femur specimens were obtained following a total hip replacement procedure from men and women ≥65 years of age with and without type 2 diabetes. A scanning electron microscope was used for quantitative backscattered electron imaging (qBEI) analysis of trabecular bone samples from the femoral neck. Gray scale images (pixel size=5.6 μm(2)) were uploaded to ImageJ software and gray level (GL) values were converted to calcium concentrations (weight [wt] % calcium [Ca]) using data obtained with energy dispersive X-ray spectrometry. The following bone mineralization density distribution (BMDD) outcomes were collected: the weighted mean bone calcium concentration (CaMEAN), the most frequently occurring bone calcium concentration (CaPEAK) and mineralization heterogeneity (CaWIDTH). Differences between groups were assessed using the Student's t-test for normally distributed data and Mann-Whitney U-test for non-normally distributed data. An alpha value of <0.05 was considered significant.

RESULTS

Thirty-five Caucasian participants were recruited (mean [standard deviation, SD] age, 75.5 [6.5]years): 14 adults with type 2 diabetes (years since type 2 diabetes diagnosis, 13.5 [7.4]years) and 21 adults without type 2 diabetes. In the adults with type 2 diabetes, bone CaMEAN was 4.9% greater (20.36 [0.98]wt.% Ca versus 19.40 [1.07]wt.% Ca, p=0.015) and CaWIDTH was 9.4% lower (median [interquartile range] 3.55 [2.99-4.12]wt.% Ca versus 3.95 [0.71]wt.% Ca, p<0.001) compared to controls. There was no between-group difference in CaPEAK (21.12 [0.97]wt.% Ca for type 2 diabetes versus 20.44 [1.30]wt.% Ca for controls, p=0.121).

CONCLUSION

The combination of elevated mean calcium concentration in bone and lower mineralization heterogeneity in adults with type 2 diabetes may have deleterious effects on the biomechanical properties of bone. These microscopic alterations in bone mineralization, which may be mediated by suppressed bone remodeling, further elucidate higher fracture risk in adults with type 2 diabetes.

[Microarchitecture assessment of human trabecular bone: description of methods]

Trabecular bone microarchitecture changes in relation to mechanical stress, effects of age, osteoporosis and anti-osteoporotic drugs. In vivo, these anomalies can be evaluated using textural parameters on high resolution radiographs and images of DXA. It is possible to extract morphological and topological parameters: apparent on MRI images and 3D with a dedicated device called High resolution peripheral quantitative computed tomography (HR-pQCT) with a resolution close to the size of the trabeculae. In vitro, it is possible to obtain on bone samples a 2D analysis by histomorphometry and a 3D analysis from 10 µm images obtained by synchrotron radiation or conventional micro-CT.

Mechanical torque measurement for in vivo quantification of bone strength in the proximal femur

INTRODUCTION

Bone strength determines fracture risk and fixation strength of osteosynthesis implants. In vivo, bone strength is currently measured indirectly by quantifying bone mineral density (BMD) which is however only one determinant of the bone's biomechanical competence besides the bone's macro- and micro-architecture and tissue related parameters. We have developed a measurement principle (DensiProbe™ Hip) for direct, mechanical quantification of bone strength within the proximal femur upon hip fracture fixation. Previous cadaver tests indicated a close correlation between DensiProbe™ Hip measurements, 3D micro-CT analysis and biomechanical indicators of bone strength. The goal of this study was to correlate DensiProbe™ Hip measurements with areal bone mineral density (BMD).

METHODS

Forty-three hip fracture patients were included in this study. Intraoperatively, DensiProbe™ Hip was inserted to the subsequent hip screw tip position within the femoral head. Peak torque to breakaway of local cancellous bone was registered. Thirty-seven patients underwent areal BMD measurements of the contralateral proximal femur. Failure of fixation was assessed radio graphically 6 and 12 weeks postoperatively.

RESULTS

Peak torque and femoral neck BMD showed significant correlations (R=0.60, P=0.0001). In regression analysis, areal BMD explained 46% of femoral neck BMD variance in a quadratic relationship. Throughout the 12-week follow-up period, no failure of fixation was observed.

CONCLUSIONS

DensiProbe™ Hip may capture variations of bone strength beyond areal BMD which are currently difficult to measure in vivo. A multicenter study will clarify if peak torque predicts fixation failure.

Targeted approaches in the treatment of osteoporosis: differential mechanism of action of denosumab and clinical utility

Denosumab is a breakthrough biological drug approved by the Food and Drug Administration and European Medicines Agency for the treatment of osteoporosis in 2010. It is a fully human monoclonal antireceptor activator of nuclear factor kappa-B ligand antibody, which inhibits the activity of osteoclasts, resulting in an antiresorptive effect with a significant increase in bone mineral density. The FREEDOM (Fracture Reduction Evaluation of Denosumab in Osteoporosis every 6 Months) trial, comparing denosumab with no treatment in 7868 women with postmenopausal osteoporosis, showed an important reduction of fracture risk at hip, vertebral, and nonvertebral sites in the treated group, while no statistically significant difference in the incidence of adverse events was detected between denosumab and placebo groups. The specific action of denosumab directed against a key regulator of osteoclasts makes it a valuable tool in preventing the occurrence of skeletal events caused by bone destruction in patients with advanced malignancies. The drug was approved for postmenopausal osteoporosis in women at increased risk of fracture and for the treatment of bone loss associated with androgen deprivation therapy in men with prostate cancer.

Adverse reactions and drug-drug interactions in the management of women with postmenopausal osteoporosis

The pharmacological management of disease should involve consideration of the balance between the beneficial effects of treatment on outcome and the probability of adverse effects. The aim of this review is to explore the risk of adverse drug reactions and drug-drug interactions with treatments for postmenopausal osteoporosis. We reviewed evidence for adverse reactions from regulatory documents, randomized controlled trials, pharmacovigilance surveys, and case series. Bisphosphonates are associated with gastrointestinal effects, musculoskeletal pain, and acute-phase reactions, as well as, very rarely, atrial fibrillation, atypical fracture, delayed fracture healing, osteonecrosis of the jaw, hypersensitivity reactions, and renal impairment. Cutaneous effects and osteonecrosis of the jaw are of concern for denosumab (both very rare), though there are no pharmacovigilance data for this agent yet. The selective estrogen receptor modulators are associated with hot flushes, leg cramps, and, very rarely, venous thromboembolism and stroke. Strontium ranelate has been linked to hypersensitivity reactions and venous thromboembolism (both very rare) and teriparatide with headache, nausea, dizziness, and limb pain. The solidity of the evidence base depends on the frequency of the reaction, and causality is not always easy to establish for the very rare adverse reactions. Drug-drug interactions are rare. Osteoporosis treatments are generally safe and well tolerated, though they are associated with a few very rare serious adverse reactions. While these are a cause for concern, the risk should be weighed against the benefits of treatment itself, i.e., the prevention of osteoporotic fracture.

High-resolution computed tomography for clinical imaging of bone microarchitecture

BACKGROUND

The role of bone structure, one component of bone quality, has emerged as a contributor to bone strength. The application of high-resolution imaging in evaluating bone structure has evolved from an in vitro technology for small specimens to an emerging clinical research tool for in vivo studies in humans. However, many technical and practical challenges remain to translate these techniques into established clinical outcomes.

QUESTIONS/PURPOSES

We reviewed use of high-resolution CT for evaluating trabecular microarchitecture and cortical ultrastructure of bone specimens ex vivo, extension of these techniques to in vivo human imaging studies, and recent studies involving application of high-resolution CT to characterize bone structure in the context of skeletal disease.

METHODS

We performed the literature review using PubMed and Google Scholar. Keywords included CT, MDCT, micro-CT, high-resolution peripheral CT, bone microarchitecture, and bone quality.

RESULTS

Specimens can be imaged by micro-CT at a resolution starting at 1 μm, but in vivo human imaging is restricted to a voxel size of 82 μm (with actual spatial resolution of ~ 130 μm) due to technical limitations and radiation dose considerations. Presently, this mode is limited to peripheral skeletal regions, such as the wrist and tibia. In contrast, multidetector CT can assess the central skeleton but incurs a higher radiation burden on the subject and provides lower resolution (200-500 μm).

CONCLUSIONS

CT currently provides quantitative measures of bone structure and may be used for estimating bone strength mathematically. The techniques may provide clinically relevant information by enhancing our understanding of fracture risk and establishing the efficacy of antifracture for osteoporosis and other bone metabolic disorders.

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.

Physiology of the aging bone and mechanisms of action of bisphosphonates

Fragility fractures, a major public health concern, are expected to further increase due to aging of the world populations because age remains a cardinal, independent determinant of fracture risk. With aging the balance between bone formation and resorption during the remodeling process becomes negative, with increased resorption and reduced formation. Bisphosphonates (BPs) are widely prescribed anti-resorptive agents that inhibit osteoclasts attachment to bone matrix and enhance osteoclast apoptosis. BPs can be divided into nitrogen-containing (N-BPs) and non-nitrogen-containing BPs (non-N-BPs). Both classes induce apoptosis but they evoke it differently. Several studies have examined the molecular mechanisms underlying BPs' effects on osteoclasts and bone remodeling. N-BPs (alendronate, risedronate, zoledronate) inhibit the intracellular mevalonate pathway and protein isoprenylation, via the enzyme farnesyl pyrophosphate synthase. N-BPs act by competition, binding to the natural substrate-binding site of the enzyme. The less potent non-N-BPs (etidronate, clodronate), do not inhibit the mevalonate pathway and protein isoprenylation, but are metabolized intracellularly to metabolites, which are cytotoxic analogs of ATP. N-BPs represent the first choice treatment for diseases associated with excessive bone resorption, such as fragility fractures (due to postmenopausal-, male, glucocorticoid- and transplant-induced osteoporosis), Paget's disease of bone, and bone metastasis. Better understanding of BPs' effects on osteoblasts/osteocytes (e.g., preventing apoptosis) and differential distribution may further help explain anti-fracture benefit and bone quality effects. Lower affinity BPs (e.g., risedronate) may allow better access to osteocyte network. Effects of BPs on bone senescence, cancer cells apoptosis and prevention of cardiovascular calcifications may open new avenues for biogerontological research.

Impact of treatments for postmenopausal osteoporosis (bisphosphonates, parathyroid hormone, strontium ranelate, and denosumab) on bone quality: a systematic review

The objective of this systematic review was to examine the influence of treatments for postmenopausal osteoporosis (parathyroid hormone [PTH], bisphosphonates, strontium ranelate, and denosumab) on bone quality and discuss the clinical implications. Most bone-quality data for PTH is from teriparatide. Teriparatide results in a rapid increase in bone-formation markers, followed by increases in bone-resorption markers, opening an "anabolic window," a period of time when PTH is maximally anabolic. Teriparatide reverses the structural damage seen in osteoporosis and restores the structure of trabecular bone. It has a positive effect on cortical bone, and any early increases in cortical porosity appear to be offset by increases in cortical thickness and diameter. Bisphosphonates are antiresorptive agents which reduce bone turnover, improve trabecular microarchitecture, and mineralization. Concerns have been raised that the prolonged antiresorptive action of bisphosphonates may lead to failure to repair microdamage, resulting in microcracks and atypical fragility. Strontium ranelate is thought to have a mixed mode of action, increasing bone formation and decreasing bone resorption. Strontium ranelate improves cortical thickness, trabecular number, and connectivity, with no change in cortical porosity. Denosumab exerts rapid, marked, and sustained effects on bone resorption, resulting in falls in the markers of bone turnover. Evidence from bone-quality studies suggests that treatment-naive women, aged 60-65 years, with very low BMD T scores may benefit from PTH as primary therapy to improve bone substrate and build bone. Post-PTH treatment with bisphosphonates will maintain improvements in bone quality and reduce the risk of fracture.

One year of alendronate treatment lowers microstructural stresses associated with trabecular microdamage initiation

Alendronate, an anti-remodeling agent, is commonly used to treat patients suffering from osteoporosis by increasing bone mineral density. Though fracture risk is lowered, an increase in microdamage accumulation has been documented in patients receiving alendronate, leading to questions about the potentially detrimental effects of remodeling suppression on the local tissue (material) properties. In this study, trabecular bone cores from the distal femur of beagle dogs treated for one year with alendronate, at doses scaled by weight to approximate osteoporotic and Paget's disease treatment doses in humans, were subjected to uniaxial compression to induce microdamage. Tissue level von Mises stresses were computed for alendronate-treated and non-treated controls using finite element analysis and correlated to microdamage morphology. Using a modified version of the Moore and Gibson classification for damage morphology, we determined that the von Mises stress for trabeculae exhibiting severe and linear microcrack patterns was decreased by approximately 25% in samples treated with alendronate compared with non-treated controls (p<0.01), whereas there was no reduction in the von Mises stress state for diffuse microdamage formation. Furthermore, an examination of the architectural and structural characteristics of damaged trabeculae demonstrated that severely damaged trabeculae were thinner, more aligned with the loading axis, and less mineralized than undamaged trabeculae in alendronate-treated samples (p<0.01). Similar relationships with damage morphology were found only with trabecular orientation in vehicle-treated control dogs. These results indicate that changes in bone's architecture and matrix properties associated with one year of alendronate administration reduce trabecular bone's ability to resist the formation of loading-induced severe and linear microcracks, both of which dissipate less energy prior to fracture than does diffuse damage.

Comparing and contrasting the effects of strontium ranelate and other osteoporosis drugs on microarchitecture

Altered bone microstructure is a major component of osteoporosis and bone fragility. Whilst an important standard by which to diagnose and make treatment decisions for osteoporosis, the evaluation of bone mineral mass by dual-energy X-ray absorptiometry (DXA) at spine or hip is not sufficient for understanding the complex nature of bone microstructure nor to evaluate specific treatment effects on cancellous and cortical bone. Various alternatives to DXA have been developed, enabling the measurement of bone geometry and/or microarchitecture and/or bone strength including hip strength analysis, peripheral and central QCT, 3D analyses of iliac crest bone biopsies, and more recently HR-pQCT, which allows longitudinal assessment of bone microstructure at the distal radius and tibia. The efficacy of treatments for osteoporosis can be evaluated using these techniques. A true improvement of bone microstructure above baseline has not been demonstrated with anti-resorptive treatments; however, they may prevent the decay of cancellous bone and, potentially, cortical thinning. Anabolic agents such as parathyroid hormone (PTH) increase cancellous bone volume and cortical thickness; however, the improvement of cortical bone strength by PTH may be limited by an increase in cortical porosity. Strontium ranelate has been shown to improve not only the trabecular network but also cortical thickness, contributing to its anti-fracture efficacy at vertebral, non-vertebral, and hip sites.

Strontium ranelate and alendronate have differing effects on distal tibia bone microstructure in women with osteoporosis

The structural basis of the antifracture efficacy of strontium ranelate and alendronate is incompletely understood. We compared the effects of strontium ranelate and alendronate on distal tibia microstructure over 2 years using HR-pQCT. In this pre-planned, interim, intention-to-treat analysis at 12 months, 88 osteoporotic postmenopausal women (mean age 63.7 ± 7.4) were randomized to strontium ranelate 2 g/day or alendronate 70 mg/week in a double-placebo design. Primary endpoints were changes in microstructure. Secondary endpoints included lumbar and hip areal bone mineral density (aBMD), and bone turnover markers. This trial is registered with http://www.controlled-trials.com, number ISRCTN82719233. Baseline characteristics of the two groups were similar. Treatment with strontium ranelate was associated with increases in mean cortical thickness (CTh, 5.3%), cortical area (4.9%) and trabecular density (2.1%) (all P < 0.001, except cortical area P = 0.013). No significant changes were observed with alendronate. Between-group differences in favor of strontium ranelate were observed for CTh, cortical area, BV/TV and trabecular density (P = 0.045, 0.041, 0.048 and 0.035, respectively). aBMD increased to a similar extent with strontium ranelate and alendronate at the spine (5.7% versus 5.1%, respectively) and total hip (3.3% versus 2.2%, respectively). No significant changes were observed in remodeling markers with strontium ranelate, while suppression was observed with alendronate. Within the methodological constraints of HR-pQCT through its possible sensitivity to X-ray attenuation of different minerals, strontium ranelate had greater effects than alendronate on distal tibia cortical thickness and trabecular volumetric density.

Efficacy of continued alendronate for fractures in women with and without prevalent vertebral fracture: the FLEX trial

In the Fracture Intervention Trial (FIT) Long Term Extension (FLEX) Trial, 10 years of alendronate (ALN) did not significantly reduce the risk of nonvertebral fractures (NVFs) compared with 5 years of ALN. Continuing ALN reduced the risk of clinical but not morphometric vertebral fractures regardless of baseline vertebral fracture status. In previous studies, ALN efficacy for NVF prevention in women without prevalent vertebral fracture was limited to those with femoral neck (FN) T-scores of -2.5 or less. To determine whether the effect of long-term ALN on fracture differs by vertebral fracture status and femoral neck (FN) T-score, we performed a post hoc analysis using FLEX data, a randomized, double-blind, placebo-controlled trial among 1099 postmenopausal women originally randomized to ALN in the FIT with mean ALN use of 5 years. In the FLEX Trial, women were randomized to placebo (40%) or ALN 5 mg/day (30%) or ALN 10 mg/day (30%) for an additional 5 years. Among women without vertebral fracture at FLEX baseline (n = 720), continuation of ALN reduced NVF in women with FLEX baseline FN T-scores of -2.5 or less [relative risk (RR) = 0.50, 95% confidence interval (CI) 0.26-0.96] but not with T-scores of greater than -2.5 and -2 or less (RR 0.79, 95% CI 0.37-1.66) or with T-scores of greater than -2 (RR 1.41, 95% CI 0.75-2.66; p for interaction = .019). Continuing ALN for 10 years instead of stopping after 5 years reduces NVF risk in women without prevalent vertebral fracture whose FN T-scores, achieved after 5 years of ALN, are -2.5 or less but does not reduce risk of NVF in women whose T-scores are greater than -2.

Assessment of trabecular and cortical architecture and mechanical competence of bone by high-resolution peripheral computed tomography: comparison with transiliac bone biopsy

We compared microarchitecture and mechanical competence parameters measured by high-resolution peripheral quantitative computed tomography (HR-pQCT) and finite-element analysis of radius and tibia to those measured by histomorphometry, micro-CT, and finite-element analysis of transiliac bone biopsies. Correlations were weak to moderate between parameters measured on biopsies and scans.

INTRODUCTION

HR-pQCT is a new imaging technique that assesses trabecular and cortical bone microarchitecture of the radius and tibia in vivo. The purpose of this study was to determine the extent to which microarchitectural variables measured by HR-pQCT reflect those measured by the "gold standard," transiliac bone biopsy.

METHODS

HR-pQCT scans (Xtreme CT, Scanco Medical AG) and iliac crest bone biopsies were performed in 54 subjects (aged 39 +/- 10 years). Biopsies were analyzed by 2D quantitative histomorphometry and 3D microcomputed tomography (microCT). Apparent Young's modulus, an estimate of mechanical competence or strength, was determined by micro-finite-element analysis (microFE) of biopsy microCT and HR-pQCT images.

RESULTS

The strongest correlations observed were between trabecular parameters (bone volume fraction, number, separation) measured by microCT of biopsies and HR-pQCT of the radius (R 0.365-0.522; P < 0.01). Cortical width of biopsies correlated with cortical thickness by HR-pQCT, but only at the tibia (R = 0.360, P < 0.01). Apparent Young's modulus calculated by microFE of biopsies correlated with that calculated for both radius (R = 0.442; P < 0.001) and tibia (R = 0.380; P < 0.001) HR-pQCT scans.

CONCLUSIONS

The associations between peripheral (HR-pQCT) and axial (transiliac biopsy) measures of microarchitecture and estimated mechanical competence are significant but modest.

Three dimensional cancellous bone structure in hypoparathyroidism

By conventional 2-dimensional histomorphometric analysis, we have shown that cancellous bone architecture is markedly altered in hypoparathyroidism. We have now extended these observations to a 3-dimensional analysis using microcomputed tomography. Percutaneous iliac crest bone biopsies were analyzed by high-resolution microcomputed tomography from the following 25 subjects with hypoparathyroidism: 5 postmenopausal women, 13 premenopausal women and 7 men. Thirteen living premenopausal healthy controls and 12 cadaver subjects without bone disease served as matched controls. Hypoparathyroid subjects had significantly greater bone surface density (BS/TV: 5.74+/-4.7 vs. 3.73+/-1.01 mm(2)/mm(3) [mean+/-SD]; p=0.04), trabecular thickness (Tb.Th: 0.25+/-0.19 vs. 0.17+/-0.04 mm; p=0.04), trabecular number (Tb.N: 2.99+/-3.4 vs. 1.62+/-0.39 mm(-1); p=0.05) and connectivity density (Conn.D: 16.63+/-18.7 vs. 8.39+/-5.8 mm(3); p=0.04) in comparison to matched controls. When an additional 8 hypoparathyroid (total n=33) and 24 cadaver (total cadaver n=36) subjects were added to the groups for an unmatched analysis, hypoparathyroid subjects had significantly greater cancellous bone volume (BV/TV: 26.98+/-10 vs. 15.39+/-4%; p<0.001), while trabecular separation (Tb.Sp: 0.642+/-0.10 vs. 0.781+/-0.13 mm; p<0.001) and estimation of the plate-rod characteristic (SMI: -0.457+/-1.52 vs. 0.742+/-0.51; p<0.001) were significantly lower, the latter observation implying a more plate-like trabecular structure. Variables of cancellous bone structure in the hypoparathyroid subjects, as assessed by microcomputed tomography, were highly correlated with those assessed by conventional histomorphometry. We conclude that cancellous bone in hypoparathyroidism is abnormal, suggesting that parathyroid hormone is required to maintain normal trabecular structure. The effect of these structural changes on bone strength remains to be determined.

Bisphosphonates do not inhibit periosteal bone formation in estrogen deficient animals and allow enhanced bone modeling in response to mechanical loading

The suppressive effects of bisphosphonates (BPs) on bone remodeling are clear yet there is conflicting data concerning the effects of BPs on modeling (specifically formation modeling on the periosteal surface). The normal periosteal expansion that occurs during aging has significant benefits to maintaining/improving the bones' mechanical properties and thus it is important to understand whether BPs affect this bone surface. Therefore, the purpose of this study was to determine the effects of BPs on periosteal bone formation modeling induced by ovariectomy (OVX) and mechanical loading. Six-month-old Sprague-Dawley OVX rats (n=60; 12/group) were administered vehicle, risedronate, alendronate, or zoledronate at doses used clinically for treatment of post-menopausal osteoporosis. Three weeks after initiating BP treatment, all animals underwent in vivo ulnar loading of the right limb every other day for 1 week (3 total sessions). Periosteal surface mineral apposition rate, mineralizing surface, and bone formation rate were determined at the mid-diaphysis of both loaded (right) and non-loaded (left) ulnae. There was no significant effect of any of the BPs on periosteal bone formation parameters compared to VEH-treated animals in the non-loaded limb, suggesting that BP treatment does not compromise the normal periosteal expansion associated with estrogen loss. Mechanical loading significantly increased BFR in the loaded limb compared to the non-loaded limb in all BP-treated groups, with no difference in the magnitude of this effect among the various BPs. Collectively, these data show that BP treatment, at doses comparable to those used for treatment of post-menopausal osteoporosis, (1) does not alter the periosteal formation activity that occurs in the absence of estrogen and (2) allows normal stimulation of periosteal bone formation in response to the anabolic stimulation of mechanical loading.

Unfocused extracorporeal shock wave therapy as potential treatment for osteoporosis

Extracorporeal shock wave therapy (ESWT) influences the differentiation of bone marrow stroma cells towards osteoprogenitors and increases the expression of several growth factors. To assess whether unfocused ESWT might serve as a treatment for osteoporosis, we examined the bone architecture dynamics of ESWT-treated and untreated rat tibiae using in vivo micro-computed tomography (CT) scanning. In addition, the effects of ESWT on fracture healing, using a bilateral fibula osteotomy, were examined. Unilateral unfocused ESWT with 2,000 pulses and an energy flux density of 0.16 mJ/mm(2) was applied to the hind leg of ovariectomized and sham-ovariectomized rats. A single treatment with unfocused ESWT resulted in a higher trabecular bone volume fraction (BV/TV) in the proximal tibia of the sham-ovariectomized animals. Three weeks after ESWT, BV/TV was 110% of baseline BV/TV in treated legs versus 101% in untreated contralateral control legs (p = 0.001) and 105% of baseline BV/TV versus 95% at 7 weeks after ESWT (p = 0.0004). In ovariectomized rats, shock wave treatment resulted in a diminished bone loss. At 7 weeks, the BV/TV of the treated legs was 50% of baseline BV/TV, whereas in untreated control legs this was 35% (p = 0.0004). ESWT did not influence acute fracture healing. This study shows that bone microarchitecture can be affected by unfocused shock waves, and indicates that unfocused ESWT might be useful for the treatment of osteopenia and osteoporosis.

Treatment with a potent cathepsin K inhibitor preserves cortical and trabecular bone mass in ovariectomized monkeys

The cysteine protease cathepsin K is involved in osteoclast-mediated bone resorption. We evaluated the effect of daily oral dosing of an inhibitor of human cathepsin K (SB-462795 [relacatib]) for 9 months on bone turnover, mass, and architecture in estrogen-deficient cynomolgus monkeys. Ovariectomized animals were treated orally with relacatib at 1, 3, or 10 mg/kg/day, or oral vehicle plus alendronate at 0.05 mg/kg by IV injection once every 2 weeks. The control groups, ovariectomized and sham-ovariectomized animals, received vehicle (all groups n = 20 animals). Samples for biomarker analysis were collected at various times, bone mass changes were evaluated at 6 and 9 months of treatment, and histomorphometric analysis was performed at 9 months. Relacatib significantly reduced urinary N-telopeptide excretion within 1 week of treatment at all dose levels, an effect that was maintained at the highest dose level. At some time points bone formation markers were elevated at the lowest dose of relacatib. Animals treated with relacatib had dose-dependent preservation of areal bone mineral density reaching statistical significance in distal femur. In femur neck there was significant preservation of total volumetric BMD (vBMD) by relacatib. By histomorphometry, relacatib reduced indices of bone resorption and formation at cancellous sites as did alendronate. In cortical bone, osteonal bone formation rate was reduced by alendronate but preserved at low and medium doses of relacatib. Thus, relacatib preserved cortical and cancellous bone mass in ovariectomized monkeys.

Osteonecrosis of the jaw and the role of bisphosphonates: a critical review

Osteonecrosis of the jaw (ONJ), a condition characterized by necrotic exposed bone in the maxillofacial region, has been reported in patients with cancer receiving bisphosphonate therapy, and rarely in patients with postmenopausal osteoporosis or Paget disease of bone receiving such therapy. In the absence of a uniform definition, the American Academy of Oral and Maxillofacial Surgeons (AAOMS), the American Society for Bone and Mineral Research (ASBMR), and other groups have established similar diagnostic criteria for bisphosphonate-related ONJ, which is more commonly reported in patients with advanced malignancies with skeletal metastases who receive higher doses, and is more rarely reported in patients with osteoporosis and Paget disease who receive lower doses. However, a critical review of the literature reveals that the etiology of ONJ remains unknown, and to date no direct causal link to bisphosphonates has been established. Despite an increased awareness of ONJ and recent improvements in preventive strategies, patients and physicians alike continue to express concern about the potential risks of bisphosphonate treatment in both oncologic and nononcologic settings. Although much remains to be learned about this condition, including its true incidence in various patient populations, its pathophysiology, and optimal clinical management, evidence to date suggests that the positive benefits of bisphosphonates in patients with malignant bone disease, osteoporosis, or Paget disease outweigh the relatively small risk of ONJ.

Oral ibandronate preserves trabecular microarchitecture: micro-computed tomography findings from the oral iBandronate Osteoporosis vertebral fracture trial in North America and Europe study

Micro-computed tomography (micro-CT) is a quantitative 3-dimensional (3D) scanning procedure used to assess trabecular architecture. In the 3-yr oral iBandronate Osteoporosis vertebral fracture trial in North America and Europe (BONE) study, it was found that oral ibandronate administered daily (2.5 mg) or intermittently (20 mg) significantly reduced vertebral fracture risk by 62% (p=0.0001) and 50% (p=0.0006), respectively, vs placebo. Two-dimensional histomorphometric analysis of BONE study biopsies indicated that newly formed bone was of normal quality. In the current analysis, micro-CT was used to assess 3D trabecular microarchitecture. Rod and plate distribution was quantified by differential analysis of the triangulated bone surface. Biopsies were obtained from 110 patients, with 84 evaluable by micro-CT. Median structural model index (SMI; a lower SMI indicates an increased ratio of plates to rods and thus, improved trabecular microarchitecture) was 1.001 with ibandronate vs 1.365 with placebo (90% confidence interval [CI] for difference in medians: -0.626, -0.033), and connectivity density was higher in ibandronate-treated patients (median: 3.904 vs 3.112/mm3, 90% CI for difference in medians: 0.159, 1.517). This indicates that trabecular microarchitecture was better preserved in patients receiving ibandronate than placebo. Taken together with previous results from BONE, these findings indicate that ibandronate treatment preserves bone strength by maintaining good quality trabecular microarchitecture in women with postmenopausal osteoporosis.

Bisphosphonates: how do they work?

Bisphosphonates (BPs) are taken up preferentially by the skeleton and decrease osteoclast-mediated bone resorption. The capacity of the skeleton to retain BPs is large, and there is no indication for saturation of binding sites with the doses used in osteoporosis. The anti-resorptive action of BPs includes their selective binding to calcium crystals and their subsequent release and uptake by the osteoclasts. There are differences in the affinities of PBs for bone as well as in their anti-resorptive potencies, and the whole molecule is responsible for their inhibitory effect on bone resorption. At the tissue level, they decrease the rate of bone resorption and turnover, increase bone mineral density, and maintain or improve structural and material properties of bone and thereby reduce the risk of fractures. Current studies address questions related primarily to the pharmacological properties of these compounds that are essential for their optimal clinical use, such as for example long-term safety and efficacy.

Side-to-side and within-side variability of 3D bone microarchitecture by conventional micro-computed tomography of paired iliac crest biopsies

Bone microarchitecture in osteoporosis can be characterized by examining iliac bone biopsies and treatment effects assessed by comparing a baseline biopsy from one side to a posttreatment biopsy from the other side, a method that assumes limited side-to-side variability. New techniques based on micro-computed tomography (microCT) provide information on the three-dimensional (3D) microarchitecture of bone. We used microCT to measure side-to-side and within-side variability of 3D microarchitectural parameters of trabecular and cortical bone in paired iliac-crest biopsies, one from each side. A Bordier needle trephine was used to collect biopsies from 30 postmenopausal female cadavers (mean age, 73.7+/-10.7 years; range, 55-96 years). Biopsies were chemically defatted then imaged using a desktop microCT scanner (voxel size, 10.77 microm). Parameters measured in trabecular bone consisted of bone volume/tissue volume (BV/TV, %), direct trabecular thickness and trabecular spacing (Tb.Th and Tb.Sp, microm) using the sphere method, bone surface/bone volume (BS/BV, mm(-1)), trabecular number (Tb.N, mm(-1)), structure model index (SMI), trabecular pattern factor (Tb.Pf), and degree of anisotropy (DA). In cortical bone, we measured cortical thickness (Cort.Th), porosity (Cort.Porosity), and pore diameter (Po.Dm). For trabecular bone parameters, reproducibility as assessed from two microCT acquisitions ranged from 4.1% to 6.9%. To assess side-to-side variability, we matched the volumes of interest selected in the right and left iliac crests. The mean difference in absolute individual percent variation (mAbsDelta(ind)) between the two sides ranged from 10.8% to 14.8% for all trabecular parameters except Tb.Pf (74%) and SMI (84%). In cortical bone, mAbsDelta(ind) were 11.6% for Po.Dm, 15.1% for Cort.Porosity, and 27.6% for Cort.Th. To assess within-side variability, we divided the trabecular iliac crest volume into three equal parts, one adjacent to each cortex and one in the middle. Values of mAbsDelta(ind) versus the middle part were ranging from 7.6% for Tb.Sp to 26.2% for BV/TV. Thus, within-side variability was similar in magnitude to side-to-side variability. The considerable differences in robustness across trabecular parameters indicate a need for selecting the most stable parameters, most notably for longitudinal studies of small numbers of patients. Acquisition by microCT and image analysis must comply with stringent quality criteria, especially the distance from the cortices must be standardized.

Bone degeneration and recovery after early and late bisphosphonate treatment of ovariectomized wistar rats assessed by in vivo micro-computed tomography

Bisphosphonates are antiresorptive drugs commonly used to treat osteoporosis. It is not clear, however, what the influence of the time point of treatment is. Recently developed in vivo micro-computed tomographic (CT) scanners offer the possibility to study such effects on bone microstructure in rats. The aim of this study was to determine the influence of early and late zoledronic acid treatment on bone in ovariectomized rats, using in vivo micro-CT. Twenty-nine female Wistar rats were divided into the following groups: ovariectomy (OVX, n = 5), OVX and zoledronic acid (ZOL) at week 0 (n = 8), OVX and ZOL at week 8 (n = 7), and sham (n = 9). CT scans were made of the proximal tibia at weeks 0, 2, 4, 8, 12, and 16; and bone structural parameters were determined in the metaphysis. Two fluorescent labels were administered to calculate dynamic histomorphometric parameters. At week 16, all groups were significantly different from each other in bone volume fraction (BV/TV), connectivity density, and trabecular number (Tb.N), except for the early ZOL and control groups which were not significantly different for any structural parameter. After ZOL treatment at week 8, BV/TV, structure model index, Tb.N, and trabecular thickness significantly improved in the late ZOL group. The OVX and ZOL groups showed, respectively, higher and lower bone formation rates than the control group. Early ZOL treatment inhibited all bone microstructural changes seen after OVX. Late ZOL treatment significantly improved bone microstructure, although the structure did not recover to original levels. Early ZOL treatment resulted in a significantly better microstructure than late treatment. However, late treatment was still significantly better than no treatment.

Effects of intravenous zoledronic acid once yearly on bone remodeling and bone structure

In a substudy of the HORIZON pivotal fracture trial, in which yearly intravenous zoledronic acid 5 mg was found to significantly reduce risk of various fracture types in patients with postmenopausal osteoporosis, 152 patients underwent bone biopsy. Zoledronic acid reduced bone turnover by 63% and preserved bone structure and volume, with evidence of ongoing bone remodeling in 99% of biopsies obtained.

INTRODUCTION

In the HORIZON pivotal fracture trial (PFT), enrolling 7,736 women with postmenopausal osteoporosis, three annual intravenous infusions of the bisphosphonate zoledronic acid (5 mg) significantly reduced morphometric vertebral, clinical vertebral, hip, and nonvertebral fractures by 70%, 77%, 41%, and 25%, respectively. Whereas 79% of patients received zoledronic acid/placebo only (stratum I, n = 6,113), 21% received concomitant treatment with other antiresorptive drugs, excluding other bisphosphonates, PTH, and strontium (stratum II, n = 1,652).

MATERIALS AND METHODS

To determine effects on bone remodeling and bone architecture, iliac crest bone biopsies were obtained in 152 patients on active treatment or placebo at 3 yr after double tetracycline labeling. In five patients, only qualitative histology was performed, leaving 147 biopsy cores (79 on active treatment and 68 on placebo) for microCT analysis and histomorphometry.

RESULTS

Analysis of bone structure by microCT revealed higher trabecular bone volume (BV/TV) in the zoledronic acid group (median, 16.6% versus 12.8%; p = 0.020). In addition, patients treated with zoledronic acid exhibited higher trabecular numbers (p = 0.008), decreased trabecular separation (p = 0.011), and a trend toward improvement in connectivity density (p = 0.062), all indicating better preservation of trabecular structure after treatment with zoledronic acid. Qualitative analysis revealed presence of tetracycline label in 81 of 82 biopsies from patients on zoledronic acid and all 70 biopsies from placebo patients, indicative of continued bone remodeling. No bone pathology was observed. Zoledronic acid induced a 63% median (71% mean) reduction of the activation frequency (Ac.f; p < 0.0001) and reduced mineralizing surface (MS/BS; p < 0.0001) and volume referent bone formation rate (BFR/BV) versus placebo, indicating reduced bone turnover. Mineral appositional rate was higher in the zoledronic acid group (p = 0.0002), suggesting improved osteoblast function compared with placebo. Mineralization lag time was similar in the two groups, whereas osteoid volume (OV/BV; p < 0.0001) and osteoid thickness (O.Th; p = 0.0094) were lower in zoledronic acid-treated patients, indicating normal osteoid formation and mineralization of newly formed bone. Concomitant administration of other antiresorptive osteoporosis therapies (e.g., raloxifene, tamoxifen, tibolone, ipriflavone) did not significantly alter the tissue level response to zoledronic acid.

CONCLUSIONS

Annual dosing for 3 yr with zoledronic acid 5 mg intravenously resulted in a median 63% (mean, 71%) reduction of bone turnover and preservation of bone structure and mass without any signs of adynamic bone. Concomitant treatment with other osteoporosis therapies did not significantly affect the bone response to zoledronic acid.

Interindividual and intraspecimen variability of 3-D bone microarchitectural parameters in iliac crest biopsies imaged by conventional micro-computed tomography

Bone microarchitecture of the iliac bone is used to characterize the properties of bone tissue in osteoporosis, particularly in pharmacological studies. Trabecular bone is known to be heterogeneous media. For a few years, the analysis of three-dimensional (3-D) bone microarchitecture has been based on micro-computed tomography (micro-CT). To assess the interindividual variability (inter-indVar) and the intrasample variability (intra-sampVar) of iliac crest biopsies, we used a Bordier needle trephine in 35 postmenopausal female cadavers (mean age, 74.4 +/- 10.4 years). Finally, we had at our disposal 32 individual iliac crests to assess the inter-indVar and 21 oriented specimens to assess the intra-sampVar. All the samples were chemically defatted, and the images were performed with a desktop micro-CT with a voxel size of 10.77 microm. We measured trabecular bone parameters: bone volume/tissue volume (BV/TV %), trabecular thickness and spacing (Tb. Th*, Tb.Sp* microm), bone surface/bone volume (BS/BV, 1/mm), the trabecular number (Tb.N, 1/mm), structure model index (SMI), trabecular pattern factor (Tb.Pf), and degree of anisotropy (DA). We also measured cortical bone parameters: cortical thickness (Cort.Th), porosity (PoV/TV), and pore diameter (Po.Dm). For the inter-indVar, we analyzed a fixed volume of interest corresponding to 119.8 mm(3) centered on each iliac crest. To assess the intra-sampVar, we divided the whole trabecular volume into three equal height parts (external, middle, internal). BV/TV, Tb.N, and PoV/TV were negatively correlated with age and Tb.Sp* and SMI were positively correlated. The mean difference of absolute individual variations in percentage with the middle area used as a reference, comparatively to external and internal areas, ranged from 6.6% (Tb.Sp*) to 27.8% (BV/TV), except Tb.Pf, which showed large variability. There was no difference between external and internal areas, with a tendency for lower values of BV/TV, Tb.Th*, and Tb.N in the middle of the iliac crest and higher values of Tb.Sp* and BS/BV. The evaluation of bone microarchitecture of iliac crest samples on micro-CT images is reliable. The heterogeneity of bone inside the iliac crest is noticeable as leading to analyzing the largest possible quantity of bone, with standardized location, according to cortex but without any assumption of orientation.