Effects of odanacatib on the radius and tibia of postmenopausal women: improvements in bone geometry, microarchitecture, and estimated bone strength

Efficacy and safety of odanacatib in the treatment of postmenopausal women with osteoporosis: a meta-analysis

BACKGROUND

Osteoporosis, a systemic skeletal disease, seriously affects the quality of life in postmenopausal women. As one type of cathepsin K (CatK) inhibitor, odanacatib (ODN) is a fresh medication for osteoporosis. Considering the potential of ODN, we further examined the effect and safety of ODN for postmenopausal osteoporosis (PMOP) with a meta-analysis.

METHODS

PubMed, EMBASE, Cochrane Library, and Web of Science were searched for eligible studies from inception to December 29th, 2023. After that, we conducted a comprehensive meta-analysis following PRISMA guidelines. Risk of bias was meticulously investigated with the Cochrane Collaboration's tool. Efficacy was assessed with bone mineral density (BMD) at different sites (lumbar spine, trochanter, radius, femoral neck) and biomarkers of bone turnover (P1NP, uNTx/Cr, s-CTx, BSAP). Safety was evaluated by analyzing total, serious, other, and skin adverse events (AEs).

RESULTS

Four random clinical trials (RCTs) were involved in our research. All trials were rated as having high quality and met the eligibility criteria. In the current research, ODN was found to elevate BMD at lumbar spine, femoral neck, total hip, trochanter and forearm, while it decreased the levels of serum C-telopeptides of type I collagen (s-CTx) as well as urinary N-telopeptide/creatinine ratio (uNTx/Cr). No significant differences were observed in AEs between the ODN group and the control group.

CONCLUSIONS

ODN is a promising alternative for the treatment of PMOP on account of its excellent efficacy and credible safety. Unclear links between ODN and cardiovascular AEs require further research to clarify.

Am I big boned? Bone length scaled reference data for HRpQCT measures of the radial and tibial diaphysis in White adults

Cross-sectional size of a long bone shaft influences its mechanical properties. We recently used high-resolution peripheral quantitative computed tomography (HRpQCT) to create reference data for size measures of the radial and tibial diaphyses. However, data did not take into account the impact of bone length. Human bone exhibits relatively isometric allometry whereby cross-sectional area increases proportionally with bone length. The consequence is that taller than average individuals will generally have larger z-scores for bone size outcomes when length is not considered. The goal of the current work was to develop a means of determining whether an individual's cross-sectional bone size is suitable for their bone length. HRpQCT scans performed at 30 % of bone length proximal from the distal end of the radius and tibia were acquired from 1034 White females (age = 18.0 to 85.3 y) and 392 White males (age = 18.4 to 83.6 y). Positive relationships were confirmed between bone length and cross-sectional areas and estimated mechanical properties. Scaling factors were calculated and used to scale HRpQCT outcomes to bone length. Centile curves were generated for both raw and bone length scaled HRpQCT data using the LMS approach. Excel-based calculators are provided to facilitate calculation of z-scores for both raw and bone length scaled HRpQCT outcomes. The raw z-scores indicate the magnitude that an individual's HRpQCT outcomes differ relative to expected sex- and age-specific values, with the scaled z-scores also considering bone length. The latter enables it to be determined whether an individual or population of interest has normal sized bones for their length, which may have implications for injury risk. In addition to providing a means of expressing HRpQCT bone size outcomes relative to bone length, the current study also provides centile curves for outcomes previously without reference data, including tissue mineral density and moments of inertia.

Automated, calibration-free quantification of cortical bone porosity and geometry in postmenopausal osteoporosis from ultrashort echo time MRI and deep learning

BACKGROUND

Assessment of cortical bone porosity and geometry by imaging in vivo can provide useful information about bone quality that is independent of bone mineral density (BMD). Ultrashort echo time (UTE) MRI techniques of measuring cortical bone porosity and geometry have been extensively validated in preclinical studies and have recently been shown to detect impaired bone quality in vivo in patients with osteoporosis. However, these techniques rely on laborious image segmentation, which is clinically impractical. Additionally, UTE MRI porosity techniques typically require long scan times or external calibration samples and elaborate physics processing, which limit their translatability. To this end, the UTE MRI-derived Suppression Ratio has been proposed as a simple-to-calculate, reference-free biomarker of porosity which can be acquired in clinically feasible acquisition times.

PURPOSE

To explore whether a deep learning method can automate cortical bone segmentation and the corresponding analysis of cortical bone imaging biomarkers, and to investigate the Suppression Ratio as a fast, simple, and reference-free biomarker of cortical bone porosity.

METHODS

In this retrospective study, a deep learning 2D U-Net was trained to segment the tibial cortex from 48 individual image sets comprised of 46 slices each, corresponding to 2208 training slices. Network performance was validated through an external test dataset comprised of 28 scans from 3 groups: (1) 10 healthy, young participants, (2) 9 postmenopausal, non-osteoporotic women, and (3) 9 postmenopausal, osteoporotic women. The accuracy of automated porosity and geometry quantifications were assessed with the coefficient of determination and the intraclass correlation coefficient (ICC). Furthermore, automated MRI biomarkers were compared between groups and to dual energy X-ray absorptiometry (DXA)- and peripheral quantitative CT (pQCT)-derived BMD. Additionally, the Suppression Ratio was compared to UTE porosity techniques based on calibration samples.

RESULTS

The deep learning model provided accurate labeling (Dice score 0.93, intersection-over-union 0.88) and similar results to manual segmentation in quantifying cortical porosity (R2 ≥ 0.97, ICC ≥ 0.98) and geometry (R2 ≥ 0.82, ICC ≥ 0.75) parameters in vivo. Furthermore, the Suppression Ratio was validated compared to established porosity protocols (R2 ≥ 0.78). Automated parameters detected age- and osteoporosis-related impairments in cortical bone porosity (P ≤ .002) and geometry (P values ranging from <0.001 to 0.08). Finally, automated porosity markers showed strong, inverse Pearson's correlations with BMD measured by pQCT (|R| ≥ 0.88) and DXA (|R| ≥ 0.76) in postmenopausal women, confirming that lower mineral density corresponds to greater porosity.

CONCLUSION

This study demonstrated feasibility of a simple, automated, and ionizing-radiation-free protocol for quantifying cortical bone porosity and geometry in vivo from UTE MRI and deep learning.

Meta-analysis of Diabetes Mellitus-Associated Differences in Bone Structure Assessed by High-Resolution Peripheral Quantitative Computed Tomography

PURPOSE OF REVIEW

Diabetes mellitus is defined by elevated blood glucose levels caused by changes in glucose metabolism and, according to its pathogenesis, is classified into type 1 (T1DM) and type 2 (T2DM) diabetes mellitus. Diabetes mellitus is associated with multiple degenerative processes, including structural alterations of the bone and increased fracture risk. High-resolution peripheral computed tomography (HR-pQCT) is a clinically applicable, volumetric imaging technique that unveils bone microarchitecture in vivo. Numerous studies have used HR-pQCT to assess volumetric bone mineral density and microarchitecture in patients with diabetes, including characteristics of trabecular (e.g. number, thickness and separation) and cortical bone (e.g. thickness and porosity). However, study results are heterogeneous given different imaging regions and diverse patient cohorts.

RECENT FINDINGS

This meta-analysis assessed T1DM- and T2DM-associated characteristics of bone microarchitecture measured in human populations in vivo reported in PubMed- and Embase-listed publications from inception (2005) to November 2021. The final dataset contained twelve studies with 516 participants with T2DM and 3067 controls and four studies with 227 participants with T1DM and 405 controls. While T1DM was associated with adverse trabecular characteristics, T2DM was primarily associated with adverse cortical characteristics. These adverse effects were more severe at the radius than the load-bearing tibia, indicating increased mechanical loading may compensate for deleterious bone microarchitecture changes and supporting mechanoregulation of bone fragility in diabetes mellitus. Our meta-analysis revealed distinct predilection sites of bone structure aberrations in T1DM and T2DM, which provide a foundation for the development of animal models of skeletal fragility in diabetes and may explain the uncertainty of predicting bone fragility in diabetic patients using current clinical algorithms.

Denosumab increases spine bone density in women with anorexia nervosa: a randomized clinical trial

Objective

Anorexia nervosa is complicated by high bone resorption, low bone mineral density (BMD), and increased fracture risk. We investigated whether off-label antiresorptive therapy with denosumab increases BMD in women with anorexia nervosa.

Design

Twelve-month, randomized, double-blind, placebo-controlled study.

Methods

Thirty ambulatory women with anorexia nervosa and areal BMD (aBMD) T-score <-1.0 at ≥1 sites were randomized to 12 months of denosumab (60 mg subcutaneously q6 months)(n = 20) or placebo (n = 10). Primary end point was postero-anterior (PA) lumbar spine aBMD by dual-energy x-ray absorptiometry. Secondary end points included femoral neck aBMD, tibia and radius volumetric BMD and bone microarchitecture by high-resolution peripheral quantitative CT, tibia and radius failure load by finite element analysis (FEA), and markers of bone turnover.

Results

Baseline mean (±s.d.) age (29 ± 8 (denosumab) vs 29 ± 7 years (placebo)), BMI (19.0 ± 1.7 vs 18.0 ± 2.0 kg/m2), and aBMD (PA spine Z-score -1.6±1.1 vs -1.7±1.4) were similar between groups. PA lumbar spine aBMD increased in the denosumab vs placebo group over 12 months (P = 0.009). The mean (95% CI) increase in PA lumbar spine aBMD was 5.5 (3.8-7.2)% in the denosumab group and 2.2 (-0.3-4.7)% in the placebo group. The change in femoral neck aBMD was similar between groups. Radial trabecular number increased, radial trabecular separation decreased, and tibial cortical porosity decreased in the denosumab vs placebo group (P ≤ 0.006). Serum C-terminal telopeptide of type I collagen and procollagen type I N-terminal propeptide decreased in the denosumab vs placebo group (P < 0.0001). Denosumab was well tolerated.

Conclusions

Twelve months of antiresorptive therapy with denosumab reduced bone turnover and increased spine aBMD, the skeletal site most severely affected in women with anorexia nervosa.

Cathepsin K+ Non-Osteoclast Cells in the Skeletal System: Function, Models, Identity, and Therapeutic Implications

Cathepsin K (Ctsk) is a cysteine protease of the papain superfamily initially identified in differentiated osteoclasts; it plays a critical role in degrading the bone matrix. However, subsequent in vivo and in vitro studies based on animal models elucidate novel subpopulations of Ctsk-expressing cells, which display markers and properties of mesenchymal stem/progenitor cells. This review introduces the function, identity, and role of Ctsk⁺ cells and their therapeutic implications in related preclinical osseous disorder models. It also summarizes the available in vivo models for studying Ctsk⁺ cells and their progeny. Further investigations of detailed properties and mechanisms of Ctsk⁺ cells in transgenic models are required to guide potential therapeutic targets in multiple diseases in the future.

3D Image Registration Marginally Improves the Precision of HR-pQCT Measurements Compared to Cross-Sectional-Area Registration in Adults With Osteogenesis Imperfecta

Repositioning error in longitudinal high-resolution peripheral-quantitative computed tomography (HR-pQCT) imaging can lead to different bone volumes being assessed over time. To identify the same bone volumes at each time point, image registration is used. While cross-sectional area image registration corrects axial misalignment, 3D registration additionally corrects rotations. Other registration methods involving matched angle analysis (MA) or boundary transformations (3D-TB) can be used to limit interpolation error in 3D-registering micro-finite-element data. We investigated the effect of different image registration methods on short-term in vivo precision in adults with osteogenesis imperfecta, a collagen-related genetic disorder resulting in low bone mass, impaired quality, and increased fragility. The radii and tibiae of 29 participants were imaged twice on the same day with full repositioning. We compared the precision error of different image registration methods for density, microstructural, and micro-finite-element outcomes with data stratified based on anatomical site, motion status, and scanner generation. Regardless of the stratification, we found that image registration improved precision for total and trabecular bone mineral densities, trabecular and cortical bone mineral contents, area measurements, trabecular bone volume fraction, separation, and heterogeneity, as well as cortical thickness and perimeter. 3D registration marginally outperformed cross-sectional area registration for some outcomes, such as trabecular bone volume fraction and separation. Similarly, precision of micro-finite-element outcomes was improved after image registration, with 3D-TB and MA methods providing greatest improvements. Our regression model confirmed the beneficial effect of image registration on HR-pQCT precision errors, whereas motion had a detrimental effect on precision even after image registration. Collectively, our results indicate that 3D registration is recommended for longitudinal HR-pQCT imaging in adults with osteogenesis imperfecta. Since our precision errors are similar to those of healthy adults, these results can likely be extended to other populations, although future studies are needed to confirm this. © 2022 American Society for Bone and Mineral Research (ASBMR).

RANKL-Induced Increase in Cathepsin K Levels Restricts Cortical Expansion in a Periostin-Dependent Fashion: A Potential New Mechanism of Bone Fragility

Receptor activator of nuclear factor-κΒ ligand (RANKL) is necessary and sufficient to promote osteoclastogenesis and a key pathogenic factor in osteoporosis. Failure of periosteal apposition to compensate for bone loss due to endosteal resorption further contributes to bone fragility. Whether these two processes are biologically related, however, remains unknown. Using high-resolution peripheral quantitative computed tomography (HR-pQCT), we first examined cortical bone parameters at distal radius and tibia in postmenopausal women (PMW) as well as in cadaveric human adult humeri. Increases in medullary area were negatively correlated with cortical bone volume but positively with total bone volume, and this relationship was stronger in the dominant arm, suggesting a mechanically driven process. To investigate the role of RANKL in this dual process, we used mice overexpressing huRANKL (huRANKLTg⁺ ). Trabecular and cortical bone volume (Ct.BV) are reduced in these mice, whereas cortical total volume (Ct.TV) is increased. In these bones, Sost mRNA levels are downregulated and periostin (Postn) mRNA levels upregulated, hence providing a positive message for periosteal bone formation. In turn, genetic deletion of Postn in huRANKLTg⁺  mice prevented the increase in Ct.TV and aggravated bone fragility. In contrast, cathepsin K (Ctsk) ablation improved Ct.TV in both huRANKLTg⁺  and wild-type (WT) mice and stimulated periosteal bone formation, while augmenting Postn protein levels. Therefore, bone strength in huRANKLTg⁺ /Ctsk^-/- mice was restored to WT levels. These findings suggest that high levels of RANKL not only induce endosteal bone loss but may somewhat restrict periosteal bone formation by triggering periostin degradation through cathepsin K, hence providing a biological mechanism for the observed limited increase in cortical area in postmenopausal women. © 2021 American Society for Bone and Mineral Research (ASBMR).

The clinical application of high-resolution peripheral computed tomography (HR-pQCT) in adults: state of the art and future directions

High-resolution peripheral computed tomography (HR-pQCT) was developed to image bone microarchitecture in vivo at peripheral skeletal sites. Since the introduction of HR-pQCT in 2005, clinical research to gain insight into pathophysiology of skeletal fragility and to improve prediction of fractures has grown. Meanwhile, the second-generation HR-pQCT device has been introduced, allowing novel applications such as hand joint imaging, assessment of subchondral bone and cartilage thickness in the knee, and distal radius fracture healing. This article provides an overview of the current clinical applications and guidance on interpretation of results, as well as future directions. Specifically, we provide an overview of (1) the differences and reference data for HR-pQCT variables by age, sex, and race/ethnicity; (2) fracture risk prediction using HR-pQCT; (3) the ability to monitor response of anti-osteoporosis therapy with HR-pQCT; (4) the use of HR-pQCT in patients with metabolic bone disorders and diseases leading to secondary osteoporosis; and (5) novel applications of HR-pQCT imaging. Finally, we summarize the status of the application of HR-pQCT in clinical practice and discuss future directions. From the clinical perspective, there are both challenges and opportunities for more widespread use of HR-pQCT. Assessment of bone microarchitecture by HR-pQCT improves fracture prediction in mostly normal or osteopenic elderly subjects beyond DXA of the hip, but the added value is marginal. The prospects of HR-pQCT in clinical practice need further study with respect to medication effects, metabolic bone disorders, rare bone diseases, and other applications such as hand joint imaging and fracture healing. The mostly unexplored potential may be the differentiation of patients with only moderately low BMD but severe microstructural deterioration, which would have important implications for the decision on therapeutical interventions.

Multisite longitudinal calibration of HR-pQCT scanners and precision in osteogenesis imperfecta

BACKGROUND

For high-resolution peripheral quantitative computed tomography (HR-pQCT) to be used in longitudinal multi-center studies to assess disease and treatment effects, data must be aggregated across multiple timepoints and scanners. This requires an understanding of the factors contributing to scanner precision, and multi-scanner cross-calibration procedures, especially for clinical populations with severe phenotypes, like osteogenesis imperfecta (OI).

METHODS

To address this, we first evaluated single- and multi-center short- and long-term precision errors of standard HR-pQCT parameters. Two imaging phantoms were circulated among 13 sites (7 XtremeCT and 6 XtremeCT2) and scanned in triplicate at 3 timepoints/site. Additionally, duplicate in vivo radial and tibial scans were acquired in 29 individuals with OI. Secondly, we investigated subject- and scanner-related factors that contribute to precision errors using regression analysis. Thirdly, we proposed a reference site selection criterion for multisite cross-calibration and demonstrated the external validity of phantom-based calibrations.

RESULTS

Our results show excellent short-term single-site precision in both phantoms (CV % < 0.5%) and in density, microarchitecture and finite element parameters of OI participants (CV % = 0.75 to 1.2%). In vivo reproducibility significantly improved with (i) cross sectional area image registration versus no registration and (ii) scans with no motion artifacts. While reproducibility was similar across OI subtypes and anatomical sites, XtremeCT2 scanners achieved ~2.5% better precision than XtremeCT for trabecular parameters. Finally, we demonstrate that multisite longitudinal precision errors resulting from inconsistencies between scanners can be partially corrected through scanner cross-calibration.

CONCLUSIONS

This study is the first to assess long-term reproducibility and cross-calibration in a study using first and second generation HR-pQCT scanners. The results presented in this context provide timely guidelines for future use of this powerful clinical imaging modality in multi-center longitudinal clinical trials.

Impact of whole-body vibration exercise on physical performance and bone turnover in patients with monoclonal gammopathy of undetermined significance

OBJECTIVE

Monoclonal Gammopathy of Undetermined Significance (MGUS) is a risk factor for reduced physical performance, osteoporosis, and fractures due to compromised musculoskeletal metabolism. In this condition it is unknown whether whole-body vibration (WBV) exercise favorably alters physical performance and bone metabolism.

METHODS

To evaluate the effect of three-months WBV exercise (30 min; 2x/week) including an optional three-month extension on physical performance, bone metabolism and bone mineral density. Endpoints included functional assessments, bone turnover markers and bone mineral density assessed by peripheral quantitative computed tomography of the tibia.

RESULTS

Fifteen MGUS patients (median age 62.0, nine female) completed the first three months of which ten completed the three-month extension. Measures of physical functioning including chair rise test, timed up and go and 6-minute walk test improved (p = 0.007; p = 0.009; p = 0.005) after three and six months of WBV exercise. Total tibial bone mineral density remained unaltered (p > 0.05). WBV exercise tended to increase levels of sclerostin (p = 0.093) with a transient increase in osteoclast resorption markers (N-terminal telopeptide of collagen type 1, tartrate resistant acid phosphatase 5b) after three months while Dickkopf-1 (p = 0.093), procollagen I N-terminal propeptide (p = 0.074) and total alkaline phosphatase (p = 0.016) appeared to decline. No exercise-related adverse events were reported.

CONCLUSION

WBV exercise in MGUS patients improves indicators of physical performance. Observed trends in bone turnover markers and changes in distal tibial bone mineral density may indicate a regulatory effect of WBV exercise on bone metabolism and warrants further evaluation by large scale studies.

Guidelines for the assessment of bone density and microarchitecture in vivo using high-resolution peripheral quantitative computed tomography

INTRODUCTION

The application of high-resolution peripheral quantitative computed tomography (HR-pQCT) to assess bone microarchitecture has grown rapidly since its introduction in 2005. As the use of HR-pQCT for clinical research continues to grow, there is an urgent need to form a consensus on imaging and analysis methodologies so that studies can be appropriately compared. In addition, with the recent introduction of the second-generation HrpQCT, which differs from the first-generation HR-pQCT in scan region, resolution, and morphological measurement techniques, there is a need for guidelines on appropriate reporting of results and considerations as the field adopts newer systems.

METHODS

A joint working group between the International Osteoporosis Foundation, American Society of Bone and Mineral Research, and European Calcified Tissue Society convened in person and by teleconference over several years to produce the guidelines and recommendations presented in this document.

RESULTS

An overview and discussion is provided for (1) standardized protocol for imaging distal radius and tibia sites using HR-pQCT, with the importance of quality control and operator training discussed; (2) standardized terminology and recommendations on reporting results; (3) factors influencing accuracy and precision error, with considerations for longitudinal and multi-center study designs; and finally (4) comparison between scanner generations and other high-resolution CT systems.

CONCLUSION

This article addresses the need for standardization of HR-pQCT imaging techniques and terminology, provides guidance on interpretation and reporting of results, and discusses unresolved issues in the field.

Decoding rejuvenating effects of mechanical loading on skeletal aging using in vivo μCT imaging and deep learning

Throughout the process of aging, dynamic changes of bone material, micro- and macro-architecture result in a loss of strength and therefore in an increased likelihood of fragility fractures. To date, precise contributions of age-related changes in bone (re)modeling and (de)mineralization dynamics to this fragility increase are not completely understood. Here, we present an image-based deep learning approach to quantitatively describe the effects of short-term aging and adaptive response to cyclic loading applied to proximal mouse tibiae and fibulae. Our approach allowed us to perform an end-to-end age prediction based on μCT imaging to determine the dynamic biological process of aging during a two week period, therefore permitting short-term bone aging analysis with 95% accuracy in predicting time points. In a second application, our deep learning analysis reveals that two weeks of in vivo mechanical loading are associated with an underlying rejuvenating effect of 5 days. Additionally, by quantitatively analyzing the learning process, we could, for the first time, identify the localization of the age-relevant encoded information and demonstrate 89% load-induced similarity of these locations in the loaded tibia with younger control bones. These data therefore suggest that our method enables identifying a general prognostic phenotype of a certain skeletal age as well as a temporal and localized loading-treatment effect on this apparent skeletal age for the studied mouse tibia and fibula. Future translational applications of this method may provide an improved decision-support method for osteoporosis treatment at relatively low cost. STATEMENT OF SIGNIFICANCE: Bone is a highly complex and dynamic structure that undergoes changes during the course of aging as well as in response to external stimuli, such as loading. Automatic assessment of "age" and "state" of the bone may lead to early prognosis of deceases such as osteoporosis and enables evaluating the effects of certain treatments. Here, we present an artificial intelligence-based method capable of automatically predicting the skeletal age from μCT images with 95% accuracy. Additionally, we utilize it to demonstrate the rejuvenation effects of in-vivo loading treatment on bones. We further, for the first time, break down aging-related local changes in bone by quantitatively analyzing "what the age assessment model has learned" and use this information to investigate the structural details of rejuvenation process.

HR-pQCT Measures of Bone Microarchitecture Predict Fracture: Systematic Review and Meta-Analysis

High-resolution peripheral quantitative computed tomography (HR-pQCT) is a noninvasive imaging modality for assessing volumetric bone mineral density (vBMD) and microarchitecture of cancellous and cortical bone. The objective was to (1) assess fracture-associated differences in HR-pQCT bone parameters; and (2) to determine if HR-pQCT is sufficiently precise to reliably detect these differences in individuals. We systematically identified 40 studies that used HR-pQCT (39/40 used XtremeCT scanners) to assess 1291 to 3253 and 3389 to 10,687 individuals with and without fractures, respectively, ranging in age from 10.9 to 84.7 years with no comorbid conditions. Parameters describing radial and tibial bone density, microarchitecture, and strength were extracted and percentage differences between fracture and control subjects were estimated using a random effects meta-analysis. An additional meta-analysis of short-term in vivo reproducibility of bone parameters assessed by XtremeCT was conducted to determine whether fracture-associated differences exceeded the least significant change (LSC) required to discern measured differences from precision error. Radial and tibial HR-pQCT parameters, including failure load, were significantly altered in fracture subjects, with differences ranging from -2.6% (95% confidence interval [CI] -3.4 to -1.9) in radial cortical vBMD to -12.6% (95% CI -15.0 to -10.3) in radial trabecular vBMD. Fracture-associated differences reported by prospective studies were consistent with those from retrospective studies, indicating that HR-pQCT can predict incident fracture. Assessment of study quality, heterogeneity, and publication biases verified the validity of these findings. Finally, we demonstrated that fracture-associated deficits in total and trabecular vBMD and certain tibial cortical parameters can be reliably discerned from HR-pQCT-related precision error and can be used to detect fracture-associated differences in individual patients. Although differences in other HR-pQCT measures, including failure load, were significantly associated with fracture, improved reproducibility is needed to ensure reliable individual cross-sectional screening and longitudinal monitoring. In conclusion, our study supports the use of HR-pQCT in clinical fracture prediction. © 2019 American Society for Bone and Mineral Research.

Odanacatib for the treatment of postmenopausal osteoporosis: results of the LOFT multicentre, randomised, double-blind, placebo-controlled trial and LOFT Extension study

BACKGROUND

Odanacatib, a cathepsin K inhibitor, reduces bone resorption while maintaining bone formation. Previous work has shown that odanacatib increases bone mineral density in postmenopausal women with low bone mass. We aimed to investigate the efficacy and safety of odanacatib to reduce fracture risk in postmenopausal women with osteoporosis.

METHODS

The Long-term Odanacatib Fracture Trial (LOFT) was a multicentre, randomised, double-blind, placebo-controlled, event-driven study at 388 outpatient clinics in 40 countries. Eligible participants were women aged at least 65 years who were postmenopausal for 5 years or more, with a femoral neck or total hip bone mineral density T-score between -2·5 and -4·0 if no previous radiographic vertebral fracture, or between -1·5 and -4·0 with a previous vertebral fracture. Women with a previous hip fracture, more than one vertebral fracture, or a T-score of less than -4·0 at the total hip or femoral neck were not eligible unless they were unable or unwilling to use approved osteoporosis treatment. Participants were randomly assigned (1:1) to either oral odanacatib (50 mg once per week) or matching placebo. Randomisation was done using an interactive voice recognition system after stratification for previous radiographic vertebral fracture, and treatment was masked to study participants, investigators and their staff, and sponsor personnel. If the study completed before 5 years of double-blind treatment, consenting participants could enrol in a double-blind extension study (LOFT Extension), continuing their original treatment assignment for up to 5 years from randomisation. Primary endpoints were incidence of vertebral fractures as assessed using radiographs collected at baseline, 6 and 12 months, yearly, and at final study visit in participants for whom evaluable radiograph images were available at baseline and at least one other timepoint, and hip and non-vertebral fractures adjudicated as being a result of osteoporosis as assessed by clinical history and radiograph. Safety was assessed in participants who received at least one dose of study drug. The adjudicated cardiovascular safety endpoints were a composite of cardiovascular death, myocardial infarction, or stroke, and new-onset atrial fibrillation or flutter. Individual cardiovascular endpoints and death were also assessed. LOFT and LOFT Extension are registered with ClinicalTrials.gov (number NCT00529373) and the European Clinical Trials Database (EudraCT number 2007-002693-66).

FINDINGS

Between Sept 14, 2007, and Nov 17, 2009, we randomly assigned 16 071 evaluable patients to treatment: 8043 to odanacatib and 8028 to placebo. After a median follow-up of 36·5 months (IQR 34·43-40·15) 4297 women assigned to odanacatib and 3960 assigned to placebo enrolled in LOFT Extension (total median follow-up 47·6 months, IQR 35·45-60·06). In LOFT, cumulative incidence of primary outcomes for odanacatib versus placebo were: radiographic vertebral fractures 3·7% (251/6770) versus 7·8% (542/6910), hazard ratio (HR) 0·46, 95% CI 0·40-0·53; hip fractures 0·8% (65/8043) versus 1·6% (125/8028), 0·53, 0·39-0·71; non-vertebral fractures 5·1% (412/8043) versus 6·7% (541/8028), 0·77, 0·68-0·87; all p<0·0001. Combined results from LOFT plus LOFT Extension for cumulative incidence of primary outcomes for odanacatib versus placebo were: radiographic vertebral fractures 4·9% (341/6909) versus 9·6% (675/7011), HR 0·48, 95% CI 0·42-0·55; hip fractures 1·1% (86/8043) versus 2·0% (162/8028), 0·52, 0·40-0·67; non-vertebral fractures 6·4% (512/8043) versus 8·4% (675/8028), 0·74, 0·66-0·83; all p<0·0001. In LOFT, the composite cardiovascular endpoint of cardiovascular death, myocardial infarction, or stroke occurred in 273 (3·4%) of 8043 patients in the odanacatib group versus 245 (3·1%) of 8028 in the placebo group (HR 1·12, 95% CI 0·95-1·34; p=0·18). New-onset atrial fibrillation or flutter occurred in 112 (1·4%) of 8043 patients in the odanacatib group versus 96 (1·2%) of 8028 in the placebo group (HR 1·18, 0·90-1·55; p=0·24). Odanacatib was associated with an increased risk of stroke (1·7% [136/8043] vs 1·3% [104/8028], HR 1·32, 1·02-1·70; p=0·034), but not myocardial infarction (0·7% [60/8043] vs 0·9% [74/8028], HR 0·82, 0·58-1·15; p=0·26). The HR for all-cause mortality was 1·13 (5·0% [401/8043] vs 4·4% [356/8028], 0·98-1·30; p=0·10). When data from LOFT Extension were included, the composite of cardiovascular death, myocardial infarction, or stroke occurred in significantly more patients in the odanacatib group than in the placebo group (401 [5·0%] of 8043 vs 343 [4·3%] of 8028, HR 1·17, 1·02-1·36; p=0·029, as did stroke (2·3% [187/8043] vs 1·7% [137/8028], HR 1·37, 1·10-1·71; p=0·0051).

INTERPRETATION

Odanacatib reduced the risk of fracture, but was associated with an increased risk of cardiovascular events, specifically stroke, in postmenopausal women with osteoporosis. Based on the overall balance between benefit and risk, the study's sponsor decided that they would no longer pursue development of odanacatib for treatment of osteoporosis.

FUNDING

Merck Sharp & Dohme Corp, a subsidiary of Merck & Co, Inc, Kenilworth, NJ, USA.

Thorough QTc Evaluation and the Safety of Supratherapeutic Doses of Odanacatib in Healthy Subjects

Assessing risk for QTc interval prolongation in a thorough QTc study is a standard recommendation when evaluating new chemical entities. As part of the clinical development program for odanacatib, an oral selective inhibitor of cathepsin K previously in development for the treatment of osteoporosis, 2 clinical studies in healthy subjects assessed pharmacokinetics and overall safety (including potential for delayed ventricular repolarization) of a supratherapeutic dose. In study 1, subjects received a supratherapeutic dose regimen of odanacatib (300 mg on day 1, then daily multiple doses of 25 mg to day 21) or placebo. In study 2 (days 1-4), subjects received the odanacatib supratherapeutic dose regimen or moxifloxacin (positive control, single 400-mg dose on day 4; matching placebo for odanacatib/moxifloxacin) or placebo. All doses were administered with a high-fat meal. In study 1 (N = 12), the supratherapeutic dosing regimen achieved exposure ∼3.5-fold of the proposed therapeutic dose (50 mg once weekly) and was sufficiently well tolerated to permit assessment in the thorough QTc study (study 2). In study 2 (N = 116), the primary objective was placebo-corrected change from baseline in QTcF interval (Fridericia's correction), assessed by replicate electrocardiograms (12-lead Holter recordings; days -1 through 7). Supratherapeutic odanacatib dosing was not associated with increased risk of prolonged QT interval, unlike moxifloxacin (confirming assay sensitivity). Pooled safety data across both studies suggested that the safety profile of odanacatib at high exposures was similar to placebo, with a small clustering of oral cavity adverse events. Odanacatib was not associated with increased risk of prolonged QT interval.

Suppression of cathepsin K biomarker in synovial fluid as a free-drug-driven process

Cathepsin K (CatK) inhibitors exhibited chondroprotective and pain-reducing effects in animal models, however, improvements were relatively modest at dose levels achieving maximal suppression of CatK biomarkers in urine. In this report, a previously characterized CatK inhibitor (MK-1256) is utilized to explore the potential of reduced target engagement and/or suboptimal exposure (free drug) as limiting factors to the pharmacological potential of CatK inhibitors in the knee joint. Following oral administration of MK-1256 at a dose level achieving maximal inhibition of urinary biomarker (helical peptide) in dogs, full suppression of the biomarker in synovial fluid was observed. Subsequent tissue distribution studies conducted in dogs and rabbits revealed that MK-1256 levels in synovial fluid and cartilage were consistent with the free-drug hypothesis. Reasonable projection (within twofold) of drug levels in these tissues can be made based on plasma drug concentration with adjustments for binding factors. These results indicate that the previously observed efficacies in the animal models were not limited by compound distribution or target engagement in the knee tissues.

The effect of ovariectomy and 2 antiresorptive therapeutic agents on bone response in rats: A 3-dimensional imaging analysis

OBJECTIVE

The aim of this study was to evaluate bone mineral density (BMD) and microarchitecture in femurs and maxillary bones of ovariectomized (OVX) rats treated or not treated with alendronate (ALD) or odanacatib (ODN).

STUDY DESIGN

Twenty rats were divided into groups: SHAM, OVX, OVX/ALD, and OVX/ODN. After 12 weeks, the femurs and maxillae were removed and subjected to 3-dimensional analysis by micro-computed tomography. Results were analyzed with 1-way analysis of variance and Tukey's post hoc test (α = 0.05).

RESULTS

OVX decreased maxillary and femoral BMD and altered femoral microarchitecture (P < .05). The drugs increased BMD of both types of bones, but only ALD maintained the phenotype similar to the SHAM group. The action of ALD was limited to the femoral trabecular separation (Tb.Sp). OVX and the drugs had no effect on the microarchitecture of the maxilla (P > .05).

CONCLUSIONS

ALD and ODN therapy increased BMD in both bones after ovariectomy. ALD was more successful than ODN in preserving the morphology of bone similar to the SHAM group. ALD maintained the phenotype for Tb.Sp in the femur, but ODN did not. In the maxillae, neither ovariectomy nor the 2 antiresorptive drugs had significant effects on microarchitecture.

Appendicular and whole body lean mass outcomes are associated with finite element analysis-derived bone strength at the distal radius and tibia in adults aged 40years and older

PURPOSE

The purpose of this cross-sectional study was to determine how appendicular lean mass index (ALMI), and whole body lean (LMI) and fat mass indices (FMI) associate with estimated bone strength outcomes at the distal radius and tibia in adults aged 40 years and older.

METHODS

Dual energy X-ray absorptiometry (DXA) scans were performed to determine body composition, including whole body lean and fat mass, and appendicular lean mass. ALMI (appendicular lean mass/height²), LMI (lean tissue mass/height²) and FMI (fat mass/height²) were calculated. High-resolution peripheral quantitative computed tomography (HRpQCT) scans were performed to assess bone structural properties at the distal radius and tibia. Using finite element analysis, failure load (N), stiffness (N/mm), ultimate stress (MPa), and cortical-to-trabecular load ratio were estimated from HRpQCT scans. The associations between body composition (ALMI, LMI, FMI) and estimated bone strength were examined using bivariate and multivariable linear regression analyses adjusting for age, sex, and other confounding variables.

RESULTS

In 197 participants (127 women; mean±SD, age: 69.5±10.3y, body mass index: 27.95±4.95kg/m², ALMI: 7.31±1.31kg/m²), ALMI and LMI were significantly associated with failure load at the distal radius and tibia (explained 39%-48% of the variance) and remained significant after adjusting for confounding variables and multiple testing (R²=0.586-0.645, p<0.001). ALMI, LMI, and FMI did not have significant associations with ultimate stress in our multivariable models. FMI was significantly associated with cortical-to-trabecular load ratio at the distal radius and tibia (explained 6%-12% of the variance) and remained significant after adjusting for confounders and multiple testing (R²=0.208-0.243, p<0.001). FMI was no longer significantly associated with failure load after adjusting for confounders.

CONCLUSION

These findings suggest that ALMI and LMI are important determinants of estimated bone strength, particularly failure load, at the distal radius and tibia, and may contribute to preservation of bone strength in middle-to-late adulthood.

Effects of Denosumab and Teriparatide Transitions on Bone Microarchitecture and Estimated Strength: the DATA-Switch HR-pQCT study

In postmenopausal osteoporosis, switching from teriparatide to denosumab results in continued bone mineral density (BMD) gains whereas switching from denosumab to teriparatide results in BMD loss. To assess the effects of these transitions on bone microarchitecture and strength, we performed high-resolution peripheral QCT (HR-pQCT) at the distal tibia and radius in postmenopausal osteoporotic women who received 24 months of teriparatide 20 μg daily followed by 24 months of denosumab 60 mg every 6 months, 24 months of denosumab followed by 24 months of teriparatide, or 24 months of both medications followed by 24 months of denosumab. The 77 women who completed at least one post-switch visit are included in this analysis. Tibial cortical volumetric BMD (vBMD) increased between months 24 and 48 in the teriparatide-to-denosumab (net 48-month change -0.8% ± 2.4%) and combination-to-denosumab groups (net 48-month changes +2.4% ± 4.1%) but decreased in the denosumab-to-teriparatide group (net 48-month change -3.4% ± 3.2%, p < 0.001 for all between-group comparisons). Changes in total vBMD, cortical thickness, and estimated stiffness (by micro-finite element analysis [µFEA]) followed a similar pattern, as did changes at the radius. Conversely, tibial cortical porosity remained stable between months 24 and 48 in the teriparatide-to-denosumab and combination-to-denosumab groups (net 48-month changes +7.2% ± 14.8% and -3.4% ± 12.1%, respectively) but increased in the denosumab-to-teriparatide group (net 48-month change +16.2% ± 11.5%, p < 0.05 versus other groups). Trabecular vBMD changes did not differ among groups. Together, these findings demonstrate that in women treated with denosumab, switching to teriparatide is associated with a reduction in total and cortical vBMD, cortical thickness, and estimated strength, whereas switching to denosumab from teriparatide or combination therapy results in improvements in these parameters with the greatest improvements observed in women treated with combined therapy followed by denosumab. These findings strongly suggest that the use of teriparatide after denosumab should be avoided and that the use of combined teriparatide/denosumab followed by denosumab alone may be a useful treatment strategy in those with severe osteoporosis. © 2017 American Society for Bone and Mineral Research.

Contra-lateral bone loss at the distal radius in postmenopausal women after a distal radius fracture: A two-year follow-up HRpQCT study

Opposite to the fracture side, bone mineral density (BMD) measured by DXA at the contra-lateral side does not change after a distal radius fracture. However, it is unknown if also bone micro-architecture and strength at the contralateral side are unaffected. Therefore, the aim of this study was to assess BMD, micro-architecture and bone mechanical properties at the contra-lateral side during two years follow-up after a distal radius fracture using high resolution peripheral quantitative computed tomography (HRpQCT). The contra-lateral distal radius of 15 postmenopausal women (mean age 64±8years) with a distal radius fracture treated by cast immobilization was scanned by HRpQCT at baseline, 3months and 2years post-fracture. BMD and cortical and trabecular micro-architecture were measured and biomechanical parameters were estimated using micro finite element analysis (μFEA). Additionally, markers of bone resorption and formation were measured at each visit. Bone parameters and turnover markers across the three visits were analysed using a linear mixed-effect model with Bonferroni correction. Two years post-fracture, a significant decrease from baseline was found in cortical BMD (-4.2%, p<0.001), failure load (-6.1%, p=0.001), stiffness in compression (-5.7%, p=0.003) and bending (-6.4%, p=0.008), and bone formation (-47.6%, p=0.010). No significant changes from baseline were observed in total and trabecular BMD, nor in cortical or trabecular micro-architecture and neither in bone resorption. Results were similar between patients with or without adequate anti-osteoporosis drug treatment. We found a significant decline in BMD in the cortical but not the trabecular region, and a reduction in bone strength and stiffness at the contra-lateral side two years after a distal radius fracture. These changes exceeded the changes that may be expected due to aging, even in the presence of adequate anti-osteoporosis treatment.

Cathepsin K Controls Cortical Bone Formation by Degrading Periostin

Although inhibitors of bone resorption concomitantly reduce bone formation because of the coupling between osteoclasts and osteoblasts, inhibition or deletion of cathepsin k (CatK) stimulates bone formation despite decreasing resorption. The molecular mechanisms responsible for this increase in bone formation, particularly at periosteal surfaces where osteoclasts are relatively poor, remain unclear. Here we show that CatK pharmacological inhibition or deletion (Ctsk^-/- mice) potentiates mechanotransduction signals mediating cortical bone formation. We identify periostin (Postn) as a direct molecular target for degradation by CatK and show that CatK deletion increases Postn and β-catenin expression in vivo, particularly at the periosteum. In turn, Postn deletion selectively abolishes cortical, but not trabecular, bone formation in CatK-deficient mice. Taken together, these data indicate that CatK not only plays a major role in bone remodeling but also modulates modeling-based cortical bone formation by degrading periostin and thereby moderating Wnt-β-catenin signaling. These findings provide novel insights into the role of CatK on bone homeostasis and the mechanisms of increased cortical bone volume with CatK mutations and pharmacological inhibitors. © 2017 American Society for Bone and Mineral Research.

Vitamin K2 (menaquinone-7) prevents age-related deterioration of trabecular bone microarchitecture at the tibia in postmenopausal women

OBJECTIVE

Clinical studies suggest that vitamin K2 protects against bone loss and fractures; however, its effect on bone quality has never been investigated. We investigated the effect of vitamin MK-7 on undercarboxylated osteocalcin (ucOC), and bone mass and quality.

DESIGN

We conducted a randomised, placebo-controlled, double-blinded clinical trial.

METHODS

We investigated the effect of MK-7 375 µg for 12 months on bone mineral density (BMD) measured by dual X-ray absorptiometry (DXA), bone microarchitecture measured by high-resolution peripheral quantitative computed tomography (HRpQCT) and biochemical bone turnover markers in 148 postmenopausal women with osteopenia. All of them were supplemented with calcium and vitamin D.

RESULTS

ucOC decreased in the MK-7 group (-65.6 (59.1; 71.0) %) (median (CI)) compared with the placebo group (-6.4 (-13.5; 1.2) %) after 3 months (P < 0.01). HRpQCT after 12 months demonstrated that trabecular number in tibia was unchanged in the MK-7-group (-0.1 ± 1.9%) (mean ± s.d.) and decreased in the placebo group (-3.5 ± 2.2%), trabecular spacing was unchanged in the MK-7 group (+1.2 ± 8.0%) and increased in the placebo group (+4.5 ± 9.7%), and trabecular thickness was unchanged in the MK-7 group (+0.2 ± 1.7%) and increased in the placebo group (+4.0 ± 2.2%) (between-group changes for all: P < 0.05). There were no significant differences between the groups in HRpQCT-derived parameters at the radius or in BMD at any site.

CONCLUSION

The changes in bone microarchitecture in the placebo group are consistent with the age-related deterioration of trabecular structure, with a loss of trabeculae and a greater mean thickness of the remaining trabeculae. This suggests that vitamin MK-7 preserves trabecular bone structure at the tibia.

Association between bone indices assessed by DXA, HR-pQCT and QCT scans in post-menopausal women

Quantitative computed tomography (QCT), high-resolution peripheral QCT (HR-pQCT) and dual X-ray absorptiometry (DXA) scans are commonly used when assessing bone mass and structure in patients with osteoporosis. Depending on the imaging technique and measuring site, different information on bone quality is obtained. How well these techniques correlate when assessing central as well as distal skeletal sites has not been carefully assessed to date. One hundred and twenty-five post-menopausal women aged 56-82 (mean 63) years were studied using DXA scans (spine, hip, whole body and forearm), including trabecular bone score (TBS), QCT scans (spine and hip) and HR-pQCT scans (distal radius and tibia). Central site measurements of areal bone mineral density (aBMD) by DXA and volumetric BMD (vBMD) by QCT correlated significantly at the hip (r = 0.74, p < 0.01). Distal site measurements of density at the radius as assessed by DXA and HR-pQCT were also associated (r = 0.74, p < 0.01). Correlations between distal and central site measurements of the hip and of the tibia and radius showed weak to moderate correlation between vBMD by HR-pQCT and QCT (r = -0.27 to 0.54). TBS correlated with QCT at the lumbar spine (r = 0.35) and to trabecular indices of HR-pQCT at the radius and tibia (r = -0.16 to 0.31, p < 0.01). There was moderate to strong agreement between measuring techniques when assessing the same skeletal site. However, when assessing correlations between central and distal sites, the associations were only weak to moderate. Our data suggest that the various techniques measure different characteristics of the bone, and may therefore be used in addition to rather than as a replacment for imaging in clinical practice.

Osteoporosis drug effects on cortical and trabecular bone microstructure: a review of HR-pQCT analyses

With the development of new non-invasive analytical techniques and particularly the advent of high-resolution peripheral quantitative computed tomography (HRpQCT) it is possible to assess cortical and trabecular bone changes under the effects of ageing, diseases and treatments. In the present study, we reviewed the treatment-related effects on bone parameters assessed by HRpQCT imaging. We identified 12 full-length articles published in peer-reviewed journals describing treatment-induced changes assessed by HRpQCT. The design of these studies varied a lot in terms of duration and methodology: some of them were open-labelled, others were double-blind, placebo-controlled or double-blind, double-dummy, active controlled. In addition, the sample size in these studies ranged from 11 to 324 patients. Motion artifacts occurring during data acquisition were sometimes a real challenge particularly at the radius leading sometimes to exclude the analysis at the radius due to the uninterpretability of microstructural parameters. Responses to therapies were treatment-specific and divergent effects in cortical and trabecular bone with antiresorptive or anabolic agents were observed. Standardization of bone microarchitecture parameters (including porosity) and bone strength estimates by finite element analysis (FEA) are mandatory. The additional value of microarchitecture and FEA estimates changes with therapies in terms of improvement in fracture outcomes which have to be adequately assessed in clinical trials with fracture end point. Data from these reviewed studies advance our understanding of the microstructural consequences of osteoporosis and highlight potential differences in bone quality outcomes within therapies.

In vivo evaluation of bone microstructure in humans: Clinically useful?

In vivo evaluation of bone microstructure with high-resolution peripheral quantitative tomography (HRpQCT) has been used for a decade in research settings. In this review, we examine the value this technique could have in clinical practice. Bone microstructure parameters obtained with HRpQCT are associated with prevalent fracture in men and women. In postmenopausal women, some parameters also predict incident fracture, independently of areal bone mineral density. In specific population groups including patients with diabetes, chronic kidney disease, glucocorticosteroid therapy and rheumatic diseases, abnormal microstructure parameters from HRpQCT have been reported. Findings from HRpQCT studies may also explain ethnic differences in bone fragility. Treatment monitoring has been challenging in the various clinical trials with available HRpQCT data. The improvements were of small magnitude but tended to be proportional to the potency of antiresorptive agents. Microfinite element analysis was a better predictor of treatment efficacy than the microarchitectural parameters. In conclusion, HRpQCT remains a valuable research tool, but more work is needed to be able to use it in clinical practice.

Continuous treatment with odanacatib for up to 8 years in postmenopausal women with low bone mineral density: a phase 2 study

The efficacy and safety of weekly oral odanacatib (ODN) 50 mg for up to 8 years were assessed in postmenopausal women with low bone mineral density (BMD). Treatment with ODN for up to 8 years resulted in continued or maintained increases in BMD at multiple sites and was well tolerated.

INTRODUCTION

ODN is a selective inhibitor of cathepsin K. In a 2-year phase 2b study (3/10/25/50 mg ODN once weekly [QW] or placebo) and extensions (50 mg ODN QW or placebo), ODN treatment for 5 years progressively increased BMD and decreased bone resorption markers in postmenopausal women with low BMD ( ClinicalTrials.gov NCT00112437).

METHODS

In this prespecified interim analysis at year 8 of an additional 5-year extension (years 6 to 10), patients (n = 117) received open-label ODN 50 mg QW plus weekly vitamin D3 (5600 IU) and calcium supplementation as needed. Primary end points were lumbar spine BMD and safety. Patients were grouped by ODN exposure duration.

RESULTS

Mean (95 % confidence interval [CI]) lumbar spine BMD changes from baseline were 4.6 % (2.4, 6.7; 3-year continuous ODN exposure), 12.9 % (8.1, 17.7; 5 years), 12.8 % (10.0, 15.7; 6 years), and 14.8 % (11.0, 18.6; 8 years). Similar patterns of results were observed for BMD of trochanter, femoral neck, and total hip versus baseline. Geometric mean changes from baseline to year 8 for bone resorption markers were approximately -50 % (uNTx/Cr) and -45 % (sCTx), respectively (all groups); bone formation markers remained near baseline levels. No osteonecrosis of the jaw, delayed fracture union, or morphea-like skin reactions were reported.

CONCLUSIONS

Treatment with ODN for up to 8 years resulted in gains in BMD at multiple sites. Bone resorption markers remained reduced, with no significant change observed in bone formation markers. Treatment with ODN for up to 8 years was well tolerated.

From disease to treatment: from rare skeletal disorders to treatments for osteoporosis

During the past 15 years there has been an expansion of our knowledge of the cellular and molecular mechanisms regulating bone remodeling that identified new signaling pathways fundamental for bone renewal as well as previously unknown interactions between bone cells. Central for these developments have been studies of rare bone disorders. These findings, in turn, have led to new treatment paradigms for osteoporosis some of which are at late stages of clinical development. In this article, we review three rare skeletal disorders with case descriptions, pycnodysostosis and the craniotubular hyperostoses sclerosteosis and van Buchem disease that led to the development of cathepsin K and sclerostin inhibitors, respectively, for the treatment of osteoporosis.

Histomorphometry and Bone Matrix Mineralization Before and After Bisphosphonate Treatment in Boys With Duchenne Muscular Dystrophy: A Paired Transiliac Biopsy Study

Duchenne muscular dystrophy (DMD) is a genetic disorder causing progressive muscle weakness. To prolong independent ambulation, DMD patients are treated with glucocorticoids, which, in turn, can increase bone fragility. In a cohort with vertebral fractures, intravenous bisphosphonate (iv BP) therapy stabilized vertebrae and reduced back pain. To characterize the effects of glucocorticoid therapy and bisphosphonate treatment on bone tissue and material properties, paired transiliac biopsy samples (before and after on average 2.4 years of iv BP) from 9 boys with DMD were studied for histomorphometry and bone mineralization density distribution (BMDD) and compared to reference values. Before iv BP, the boys had low cancellous bone volume (BV/TV) and cortical thickness (Ct.Wi) (both on average 56% of the healthy average, p < 0.001 versus reference), and mineralizing surface (MS/BS) in the lower normal range (on average 74% of the healthy average). The average degree of mineralization of cancellous (Cn.CaMean) and cortical compartments (Ct.CaMean) was 21.48 (20.70, 21.90) wt% and 20.42 (19.32, 21.64) wt%, respectively (median [25th, 75th percentiles]), which was not different from reference. After iv BP, BV/TV and Ct.Wi were, on average, unchanged. However, at the individual patient level, BV/TV Z-scores increased in 2, remained unchanged in 4, and declined in 3 patients. Additionally, on average, MS/BS decreased (-85%, p < 0.001), Cn.CaMean (+2.7%) increased, whereas the heterogeneity of cancellous (Cn.CaWidth -19%) and cortical bone mineralization (Ct.CaWidth -8%, all p < 0.05) decreased versus baseline. The changes in bone mineralization are consistent with the antiresorptive action of iv BP. At the same time, our observations point to the need for novel therapies with less or absent bone turnover suppression, including the fact that bone turnover was low even before bisphosphonate therapy, that bone turnover declined further (as expected) with treatment, and that declines in trabecular bone volume were observed in some boys despite bisphosphonate therapy. © 2015 American Society for Bone and Mineral Research.

Effects of Two Years of Teriparatide, Denosumab, or Both on Bone Microarchitecture and Strength (DATA-HRpQCT study)

CONTEXT

In postmenopausal osteoporosis, combining denosumab and teriparatide increases hip and spine bone mineral density more than either monotherapy.

OBJECTIVE

The objective of the study was to determine the effects of 2 years of combination therapy on bone microarchitecture and estimated strength.

DESIGN

This was an open-label, randomized controlled trial.

PARTICIPANTS AND METHODS

We performed high-resolution peripheral quantitative computed tomography at the distal tibia and radius in 94 postmenopausal osteoporotic women randomized to 2 years of teriparatide 20 μg sc daily, denosumab 60 mg sc every 6 months, or both.

RESULTS

Total volumetric bone mineral density (vBMD) at the radius and tibia, trabecular vBMD at the radius, and cortical vBMD at the tibia all increased more in the combination group than both monotherapy groups (P < .002 for all comparisons with combination). Cortical thickness at the tibia also increased more in the combination group (8.1% ± 4.3%) than both other groups (P < .001). Cortical porosity at both the radius and tibia increased progressively over the 24-month treatment period in the teriparatide group but was stable in both other groups (P < .001 teriparatide vs both other groups). Trabecular vBMD at the tibia increased similarly in all groups, whereas radius trabecular vBMD increased more in the combination group than the other groups (P < .01 for both comparisons). Finite element analysis-estimated strength improved or was maintained by all treatments at both the radius and tibia.

CONCLUSIONS

Two years of combined teriparatide and denosumab improves bone microarchitecture and estimated strength more than the individual treatments, particularly in cortical bone. These findings suggest that this regimen may be beneficial in postmenopausal osteoporosis.

Effects of odanacatib on bone matrix mineralization in rhesus monkeys are similar to those of alendronate

Odanacatib (ODN) is a selective and reversible inhibitor of cathepsin K which is an important enzyme for the degradation of collagen I. Aim of the present work was the head-to-head comparison between the effects of ODN and alendronate (ALN) on bone mineralization density distribution (BMDD), based on quantitative backscattered electron imaging in relation to changes in histomorphometric mineralizing surface per bone surface (MS/BS) in 12–22 years old ovariectomized rhesus monkeys. Trabecular and cortical BMDD derived parameters from vertebrae and proximal tibiae were compared among vehicle (VEH, n = 8), odanacatib low dose (ODN-L, n = 8), odanacatib high dose (ODN-H, n = 8), and alendronate (ALN, n = 6) treated animals. Additionally, data from an intact, non-treated group of animals are shown (INT, n = 8). In trabecular bone from the vertebra and metaphyseal tibia, the BMDD of the ODN and ALN treatment groups was shifted toward higher mineralization densities (p < 0.001) consistent with the significant reduction of MS/BS (p < 0.05 in ODN-H and ALN) compared to VEH. Vertebral trabecular CaMean (average degree of mineralization) was significantly higher in ODN-L (+ 6.5%), ODN-H (+ 6.1%), and ALN (+ 6.7%, all p < 0.001). Tibial osteonal cortical bone revealed also significantly increased CaMean for ODN-L (+ 1.4%, p < 0.05), ODN-H (+ 2.2%, p < 0.05), and ALN (+ 3.4%, p < 0.001) versus VEH, while primary cortical bone (devoid of secondary osteons) did not show any significant differences between the study groups. The percentage of primary bone area in the tibial cross-sections (on average 45 ± 12%) was also not significantly different between the study groups (p = 0.232). No significant differences in any BMDD parameters of all studied skeletal sites between ODN and ALN treatment were found. Correlation analysis revealed that MS/BS was highly predictive for trabecular BMDD in vertebral bone. The higher MS/BS, the lower was CaMean. Our findings are consistent with the inhibition of bone resorption of ODN and ALN in trabecular and osteonal compartments.

•

In line with its anti-resorptive action ODN increased trabecular and osteonal bone mineralization in treated rhesus monkeys.

•

Both lower and higher dosages of ODN were similarly efficient with respect to bone matrix mineralization outcomes.

•

ODN treatment affected bone matrix mineralization in a similar manner compared to ALN.

•

ODN treatment did not significantly change the percentage of primary bone area in tibial cross-sections.

Alterations of bone mineral density, bone microarchitecture and strength in patients with ankylosing spondylitis: a cross-sectional study using high-resolution peripheral quantitative computerized tomography and finite element analysis

Introduction

Ankylosing spondylitis (AS) is an inflammatory disease associated with new bone formation and an increased risk of osteoporosis and fractures. The negative effects of AS on bone microarchitecture and strength are unclear. Thus, we conducted an observational study to analyze the effect of AS on bone microarchitecture and strength.

Methods

Patients with AS (n = 53) and non-AS subjects (n = 85) were recruited for the study. All subjects underwent clinical evaluation, DXA and high-resolution peripheral quantitative CT scans (HRpQCT).

Results

The AS patients were aged 44 ± 12 (mean ± standard deviation) years and had a median disease duration of 17 (interquartile range: 7–27) years. They were found to have lower cortical, trabecular and total vBMD at the distal radius and tibia than non-AS subjects on multivariable regression analysis. Cortical parameters such as cortical thickness and porosity, and bone strength parameters such bone stiffness and stress as estimated by finite element analysis (FEA) in AS patients were significantly worse than that of-non-AS subjects. Among patients with AS, male sex, mSASSS greater than zero and HLA-B27 negative status were associated with worse bone microarchitecture.

Conclusions

Patients with AS have worse bone mineral density, microarchitecture and strength when compared to non-AS subjects. More research is needed to understand the mechanisms underlying bone pathology in AS and to assess the effect of treatments such as TNF inhibitors on bone quality and fracture risk.

Emerging therapeutic concepts for muscle and bone preservation/building

Loss of muscle or bone mass occurs with ageing, immobility and in association with a variety of systemic diseases. The interaction of these two processes is most evident in the major contribution of falls to the risk of fractures in the elderly population. Exercise and nutrition are key common physiological variables that allow for preservation or formation of greater muscle or bone mass. However, although several pharmacological approaches have the potential to benefit both muscle and bone health, for example vitamin D, selective androgen receptor modulators and ghrelin mimetics, clinical trials with appropriate primary outcomes are lacking. Conventional approaches to address muscle loss are being extended to include stem cell biology and conserved molecular mechanisms of atrophy/hypertrophy. Pharmacological interventions to reduce fracture risk are exploring new mechanisms of action, in particular the uncoupling of bone resorption and formation. Emerging key issues for clinical trial design include adequate phenotyping of patients (personalised medicine), optimisation of the physiological background (multimodal approach) and the use of meaningful and robust outcomes relevant to daily clinical practice. At present, effective treatments that combine beneficial effects on both muscle and bone are lacking, although this is an important target for the future. This review therefore considers current and developing strategies to improve muscle function and bone strength in separate sections.

Novel therapies for osteoporosis

Since the identification of osteoporosis as a major health issue in aging populations and the subsequent development of the first treatment modalities for its management, considerable progress has been made in our understanding of the mechanisms controlling bone turnover and disease pathophysiology, thus enabling the pinpointing of new targets for intervention. This progress, along with advances in biotechnology, has rendered possible the development of ever more sophisticated treatments employing novel mechanisms of action. Denosumab, a monoclonal antibody against RANKL, approved for the treatment of postmenopausal and male osteoporosis, significantly and continuously increases bone mineral density (BMD) and maintains a low risk of vertebral, non-vertebral, and hip fractures for up to 8 years. Currently available combinations of estrogens with selective estrogen receptor modulators moderately increase BMD without causing the extra-skeletal adverse effects of each compound alone. The cathepsin K inhibitor odanacatib has recently been shown to decrease vertebral, non-vertebral, and hip fracture rates and is nearing approval. Romosozumab, an anti-sclerosin antibody, and abaloparatide, a PTH-related peptide analog, are at present in advanced stages of clinical evaluation, so far demonstrating efficaciousness together with a favorable safety profile. Several other agents are currently in earlier clinical and preclinical phases of development, including dickkopf-1 antagonists, activin A antagonists, β-arrestin analogs, calcilytics, and Src tyrosine kinase inhibitors.

Human trabecular bone microarchitecture can be assessed independently of density with second generation HR-pQCT

The second generation HR-pQCT scanner (XtremeCTII, Scanco Medical) can assess human bone microarchitecture of peripheral limbs with a 61 μm nominal isotropic voxel size. This is a marked improvement from the first generation HR-pQCT that had a nominal isotropic voxel size of 82 μm, which is at the limit to accurately determine the thickness of individual human trabeculae. We sought to determine the accuracy of a direct morphometric approach to measure trabecular bone microarchitecture with three-dimensional morphological techniques using second generation HR-pQCT, and to compare this with the approach currently applied by the first generation HR-pQCT scanner based on derived indices using ex vivo scans of human cadaveric radii. We also compared images acquired and resampled to mimic the first generation HR-pQCT with those obtained directly from the first generation HR-pQCT. We evaluated 20 human cadaveric radii and a micro-CT performance phantom using the first (XtremeCT, Scanco Medical) and second generation HR-pQCT scanner (XtremeCTII) and compared a patient evaluation (XCTII, 61 μm) with a high resolution ex vivo protocol (HR, 30μm). We generated 82 μm scans of the same specimens to mimic a first-generation HR-pQCT evaluation (XCTIM, 82 μm) and compared these with a first-generation patient evaluation (XCTI, 82 μm). A standard structural extraction approach was applied to both XCTII and HR evaluations for assessment of bone volume fraction (BV/TV), and a distance transform was used to assess trabecular number (Tb.N), trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp). For XCTI and XCTIM evaluations we followed the manufacturer's standard procedure and assessed bone mineral density (BMD), Tb.N with a distance transform, and then derived bone volume ratio (BV/TV(d)), trabecular thickness (Tb.Th(d)) and separation (Tb.Sp(d)). The spatial resolution (10% MTF) was 142.2 μm for XCTI, 108.9 μm for XCTIM, 95.2μm for XCTII, and 55.9 μm for HR. XCTI and XCTIM provided strongly associated measurements of BMD and microarchitectural outcomes (R(2)>0.97), however there were systematic differences in all outcomes. The Tb.N was highly associated with HR by both XCTII (R(2)=0.93, mean error=-0.12 mm(-1)) and XCTIM (R(2)=0.98, mean error=0.25 mm(-1)). Also, both XCTII (R(2)=0.99, mean error=0.20mm) and XCTIM (R(2)=0.99, mean error=-0.18 mm) had Tb.Sp that were strongly related to HR. For Tb.Th, the XCTII was more closely related to HR (R(2)=0.94, mean error=0.04 mm) than the relatively weak XCTIM (R(2)=0.16, mean error=- 0.076 mm). We found that trabecular microarchitecture assessment following the XCTII direct morphometric approach accurately represented the HR data. In particular, the measure of Tb.Th was markedly improved for XCTII compared with the derived approach of XCTIM. These data support the application of analysis techniques in HR-pQCT that are analogous to those traditionally used for micro-CT to assess trabecular microarchitecture. The decreased dependence of structural outcomes on density provides a new, important opportunity to monitor human in vivo bone microarchitecture.

Odanacatib for the treatment of osteoporosis

INTRODUCTION

Osteoporosis and fragility fractures are important public health concerns. Cathepsin K inhibitors, including odanacatib , are a novel class of medications for osteoporosis whose mechanism of action is to directly inhibit bone resorption without killing osteoclasts, thereby permitting the complex coupling between bone resorption and formation to continue.

AREAS COVERED

The physiological basis for the mechanism of action of cathepsin K inhibitors is covered in addition to a review of the preclinical, Phase I, Phase II and preliminary Phase III trial data of odanacatib.

EXPERT OPINION

Evidence suggests that odanacatib has similar efficacy to bisphosphonates at increasing bone mineral density and decreasing risk of fragility fractures. Although odanacatib may preferentially inhibit bone resorption more than formation, the clinical significance of this difference in mechanism of action is not yet known. A careful analysis of the Phase III trial data is needed with specific attention to adverse events.

Modulating Bone Resorption and Bone Formation in Opposite Directions in the Treatment of Postmenopausal Osteoporosis

Bone remodeling, the fundamental process for bone renewal, is targeted by treatments of osteoporosis to correct the imbalance between bone resorption and bone formation and reduce the risk of fractures and associated clinical consequences. Currently available therapeutics affect bone resorption and bone formation in the same direction and either decrease (inhibitors of bone resorption) or increase (parathyroid hormone [PTH] peptides) bone remodeling. Studies of patients with rare bone diseases and genetically modified animal models demonstrated that bone resorption and bone formation may not necessarily be coupled, leading to identification of molecular targets in bone cells for the development of novel agents for the treatment of osteoporosis. Application of such agents to the treatment of women with low bone mass confirmed that bone resorption and bone formation can be modulated in different directions and so far two new classes of therapeutics for osteoporosis have been defined with distinct mechanisms of action. Such treatments, if combined with a favorable safety profile, will offer new therapeutic options and will improve the management of patients with osteoporosis.

Odanacatib: a review of its potential in the management of osteoporosis in postmenopausal women

Odanacatib is a cathepsin K inhibitor developed for the treatment of postmenopausal osteoporosis. It is a bone resorption inhibitor, but which preserves bone formation to some extent. It can be administered once a week, in tablets also containing vitamin D. In a large clinical development program, it has been shown that odanacatib reduces bone resorption, with a reduction of about 60-70% in biochemical markers of resorption, while bone formation decreases to a lesser magnitude. Odanacatib continuously increases bone mineral density (BMD) at the hip and lumbar spine over 5 years. Once it is stopped, a complete resolution of effect is observed, with declining BMD and increased bone turnover. Bone microarchitecture and bone strength have also been improved in clinical trials using quantitative computed tomography (QCT) at the lumbar spine and hip, and high resolution peripheral QCT at the distal radius and tibia. In a phase III trial involving 16,713 postmenopausal women ⩾65 years of age with low BMD, the risk of fragility fracture was significantly reduced at the spine, hip and other nonvertebral sites compared with the placebo group. Odanacatib has been generally well tolerated, with no observation of osteonecrosis of the jaw so far, but with exceptional observations of subtrochanteric atypical fracture and morphea-like lesions. Odanacatib appears a useful new option in the treatment of postmenopausal osteoporosis.

[Cathepsin K antagonists: preclinical and clinical data]

Cathepsin K, a cysteine protease, is an essential enzyme in degradation of collagen type I. Since cathepsin K is relatively specific to osteoclasts, it represents a promising candidate for drug development. In the past decades, efforts have been made in developing highly potent, selective and orally applicable cathepsin K inhibitors. In contrast to balicatib and relacatib, whose drug development programmes were stopped due to cutaneous side-effects related to limited drug specificity, the more specific cathepsin K inhibitors odanacatib (ODN) and ONO-5334 have entered clinical trials. Odanacatib progressively increases bone mineral density (BMD) and decreases bone resorption markers in postmenopausal women with low BMD. Its clinical efficacy and safety was confirmed by several clinical studies but indicates that odanacatib is characterized by a resolution-of-effect with increases in bone resorption and rapid decreases in BMD following treatment discontinuation. A phase III fracture prevention study in postmenopausal women with osteoporosis is currently in the final phase.

Odanacatib treatment affects trabecular and cortical bone in the femur of postmenopausal women: results of a two-year placebo-controlled trial

Odanacatib, a selective cathepsin K inhibitor, increases areal bone mineral density (aBMD) at the spine and hip of postmenopausal women. To gain additional insight into the effects on trabecular and cortical bone, we analyzed quantitative computed tomography (QCT) data of postmenopausal women treated with odanacatib using Medical Image Analysis Framework (MIAF; Institute of Medical Physics, University of Erlangen, Erlangen, Germany). This international, randomized, double-blind, placebo-controlled, 2-year, phase 3 trial enrolled 214 postmenopausal women (mean age 64 years) with low aBMD. Subjects were randomized to odanacatib 50 mg weekly (ODN) or placebo (PBO); all participants received calcium and vitamin D. Hip QCT scans at 24 months were available for 158 women (ODN: n = 78 women; PBO: n = 80 women). There were consistent and significant differential treatment effects (ODN-PBO) for total hip integral (5.4%), trabecular volumetric BMD (vBMD) (12.2%), and cortical vBMD (2.5%) at 24 months. There was no significant differential treatment effect on integral bone volume. Results for bone mineral content (BMC) closely matched those for vBMD for integral and trabecular compartments. However, with small but mostly significant differential increases in cortical volume (1.0% to 1.3%) and thickness (1.4% to 1.9%), the percentage cortical BMC increases were numerically larger than those of vBMD. With a total hip BMC differential treatment effect (ODN-PBO) of nearly 1000 mg, the proportions of BMC attributed to cortical gain were 45%, 44%, 52%, and 40% for the total, neck, trochanter, and intertrochanter subregions, respectively. In postmenopausal women treated for 2 years, odanacatib improved integral, trabecular, and cortical vBMD and BMC at all femur regions relative to placebo when assessed by MIAF. Cortical volume and thickness increased significantly in all regions except the femoral neck. The increase in cortical volume and BMC paralleled the increase in cortical vBMD, demonstrating a consistent effect of ODN on cortical bone. Approximately one-half of the absolute BMC gain occurred in cortical bone.

Novel approaches to the treatment of osteoporosis

Despite the availability of efficacious treatments for fracture reduction in patients with osteoporosis, there are still unmet needs requiring a broader range of therapeutics. In particular, agents that are capable of replacing already lost bone and that also drastically reduce the risk of non-vertebral fractures are needed. Studies of rare bone diseases in humans and animal genetics have identified targets in bone cells for the development of therapies for osteoporosis with novel mechanisms of action. Here, we review these new developments, with emphasis on inhibitors of cathepsin K in osteoclasts and sclerostin in osteocytes, which are currently studied in phase 3 clinical trials.

Future directions for new medical entities in osteoporosis

Odanacatib, a selective cathepsin K inhibitor, decreases bone resorption, whereas osteoclast number increases and bone formation is maintained, perhaps even increased on some cortical surfaces. In a phase 2 clinical trial, post-menopausal women receiving odanacatib presented a sustained reduction of bone resorption markers, whereas procollagen type 1 N-terminal propeptide returned to normal. In turn areal bone mineral density increased continuously at both spine and hip for up to 5 years. Blosozumab and romosozumab are sclerostin neutralizing antibodies that exert potent anabolic effects on both trabecular and cortical compartments. A phase 2 clinical trial has reported areal bone mineral density gains at spine and hip that were greater with romosozumab compared with placebo, but also with teriparatide. It also showed that antagonizing sclerostin results in a transient stimulation of bone formation but progressive inhibition of bone resorption. Other new medical entities that are promising for the treatment of osteoporosis include abaloparatide, a parathyroid hormone-related analogue with improved bone formation-resorption ratio.