Alterations in canine vertebral bone turnover, microdamage accumulation, and biomechanical properties following 1-year treatment with clinical treatment doses of risedronate or alendronate

Trabecular bone scores in children with osteogenesis imperfecta respond differently to bisphosphonate treatment depending on disease severity

Introduction

Osteogenesis imperfecta (OI) is a congenital skeletal disorder characterized by bone fragility. Bisphosphonates (BISs) have become the mainstream treatment in children with OI. However, an optimal treatment protocol has not yet been established, while BIS treatment tends to be administered to normalize bone mineral density (BMD). Bone quality is an important component of bone strength. The trabecular bone score (TBS) is a quantitative measure of the microstructure that affects bone quality. This study investigated the TBS during BIS treatment in children with OI.

Materials and methods

Twenty-nine children with OI were enrolled and classified into two groups: mild (type 1) and moderate to severe (types 3 and 4). Dual-energy x-ray absorptiometry images were retrospectively analyzed for TBS calculation. The relationship between the areal BMD (aBMD), its Z-score, height-adjusted BMD (BMDHAZ) Z-score, TBS, and TBS Z-score with the treatment duration was assessed for each group.

Results

In the mild group, the aBMD, its Z-score, and BMDHAZ Z-score showed a significant positive correlation with treatment duration (r = 0.68, 0.68, 0.72, respectively, p < 0.01). The TBS Z-score tended to increase with treatment duration, albeit without reaching significance. In the moderate to severe group, the TBS Z-score showed a significant positive correlation with treatment duration (r = 0.48, p < 0.01), in contrast to the aBMD Z-score, which did not increase. Finally, the BMDHAZ Z-score only showed a weak positive correlation with treatment duration (r = 0.37, p < 0.01).

Conclusion

Because BIS affect the BMD and TBS differently based on the severity of OI, treatment goals may need to be stratified by disease severity.

Pharmacologic or genetic interference with atrogene signaling protects against glucocorticoid-induced musculoskeletal and cardiac disease

Despite their beneficial actions as immunosuppressants, glucocorticoids (GC) have devastating effects on the musculoskeletal and cardiac systems, as long-term treated patients exhibit high incidence of falls, bone fractures, and cardiovascular events. Herein, we show that GC upregulate simultaneously in bone, skeletal muscle, and the heart the expression of E3 ubiquitin ligases (atrogenes), known to stimulate the proteasomal degradation of proteins. Activation of vitamin D receptor (VDR) signaling with the VDR ligands calcitriol or eldecalcitol prevented GC-induced atrogene upregulation in vivo and ex vivo in bone/muscle organ cultures and preserved tissue structure/mass and function of the 3 tissues in vivo. Direct pharmacologic inhibition of the proteasome with carfilzomib also conferred musculoskeletal protection. Genetic loss of the atrogene MuRF1-mediated protein ubiquitination in ΔRING mice afforded temporary or sustained protection from GC excess in bone or skeletal and heart muscle. We concluded that the atrogene pathway downstream of MuRF1 underlies GC action in bone, muscle, and the heart, and it can be pharmacologically or genetically targeted to confer protection against the damaging actions of GC simultaneously in the 3 tissues.

Clodronate disodium does not produce measurable effects on bone metabolism in an exercising, juvenile, large animal model

Bisphosphonates are commonly used to treat and prevent bone loss, but their effects in active, juvenile populations are unknown. This study examined the effects of intramuscular clodronate disodium (CLO) on bone turnover, serum bone biomarkers (SBB), bone mineral density (BMD), bone microstructure, biomechanical testing (BT), and cartilage glycosaminoglycan content (GAG) over 165 days. Forty juvenile sheep (253 ± 6 days of age) were divided into four groups: Control (saline), T0 (0.6 mg/kg CLO on day 0), T84 (0.6 mg/kg CLO on day 84), and T0+84 (0.6 mg/kg CLO on days 0 and 84). Sheep were exercised 4 days/week and underwent physical and lameness examinations every 14 days. Blood samples were collected for SBB every 28 days. Microstructure and BMD were calculated from tuber coxae (TC) biopsies (days 84 and 165) and bone healing was assessed by examining the prior biopsy site. BT and GAG were evaluated postmortem. Data, except lameness data, were analyzed using a mixed-effects model; lameness data were analyzed as ordinal data using a cumulative logistic model. CLO did not have any measurable effects on the skeleton of sheep. SBB showed changes over time (p ≤ 0.03), with increases in bone formation and decreases in some bone resorption markers. TC biopsies showed increasing bone volume fraction, trabecular spacing and thickness, and reduced trabecular number on day 165 versus day 84 (p ≤ 0.04). These changes may be attributed to exercise or growth. The absence of a treatment effect may be explained by the lower CLO dose used in large animals compared to humans. Further research is needed to examine whether low doses of bisphosphonates may be used in active juvenile populations for analgesia without evidence of bone changes.

Intracortical remodelling increases in highly loaded bone after exercise cessation

Resorption within cortices of long bones removes excess mass and damaged tissue and increases during periods of reduced mechanical loading. Returning to high-intensity exercise may place bones at risk of failure due to increased porosity caused by bone resorption. We used point-projection X-ray microscopy images of bone slices from highly loaded (metacarpal, tibia) and minimally loaded (rib) bones from 12 racehorses, 6 that died during a period of high-intensity exercise and 6 that had a period of intense exercise followed by at least 35 days of rest prior to death, and measured intracortical canal cross-sectional area (Ca.Ar) and number (N.Ca) to infer remodelling activity across sites and exercise groups. Large canals that are the consequence of bone resorption (Ca.Ar >0.04 mm2 ) were 1.4× to 18.7× greater in number and area in the third metacarpal bone from rested than exercised animals (p = 0.005-0.008), but were similar in number and area in ribs from rested and exercised animals (p = 0.575-0.688). An intermediate relationship was present in the tibia, and when large canals and smaller canals that result from partial bony infilling (Ca.Ar >0.002 mm2 ) were considered together. The mechanostat may override targeted remodelling during periods of high mechanical load by enhancing bone formation, reducing resorption and suppressing turnover. Both systems may work synergistically in rest periods to remove excess and damaged tissue.

Importance of Whole-Body Scintigraphy or Positron Emission Tomography for Early Detection of Femoral Lesions in Breast Cancer Patients Treated with Bisphosphonates

Background

We hypothesized that most of the atypical femoral fractures (AFFs) associated with bisphosphonate treatment for breast cancer (BC) could be found before the fracture event in another radiological examination already performed by breast surgeons, rather than on simple radiographs (SRs).

Methods

We thoroughly inspected the clinical charts of BC patients treated at our institute between 2008 and 2017. In total, 228 patients were categorized into three groups based on SRs: complete AFF on at least one side (group 1); incomplete fracture on at least one side, but not any complete fracture (group 2); and no suspicious lesion (group X) on either femur. Then, we inspected whole-body scintigraphy (WBS) and positron emission tomography (PET)-computed tomography (CT) images in all groups. For group X, patients with radiological clues from at least one femur were categorized, ultimately, into final group 3 and the rest made up the normal group.

Results

About 35% of the patients showed AFFs (complete or incomplete) or suspicious lesions as AFFs, associated with the side effect of Bisphosphonate. In group 1, bilateral lesions (complete or incomplete fractures) were more frequently seen on SRs than unilateral lesions (p = 0.008). The initially identified findings in WBS and PET-CT for the respective complete and incomplete fractures on SRs of groups 1 and 2 were seen at a mean of 7 months previously. SRs did not reveal the lesions in group 3 until 5 months after the initial identification of the lesions in WBS and PET-CT.

Conclusions

Even before incomplete AFFs were detectable on SRs, they could be found at check-ups using WBS and PET-CT that had been previously examined by breast surgeons and radiologists for metastasis surveillance. Awareness of the lesions creates an opportunity for prophylactic surgery before complete fractures occur.

The AGE-RAGE Axis and the Pathophysiology of Multimorbidity in COPD

Chronic obstructive pulmonary disease (COPD) is a disease of the airways and lungs due to an enhanced inflammatory response, commonly caused by cigarette smoking. Patients with COPD are often multimorbid, as they commonly suffer from multiple chronic (inflammatory) conditions. This intensifies the burden of individual diseases, negatively affects quality of life, and complicates disease management. COPD and comorbidities share genetic and lifestyle-related risk factors and pathobiological mechanisms, including chronic inflammation and oxidative stress. The receptor for advanced glycation end products (RAGE) is an important driver of chronic inflammation. Advanced glycation end products (AGEs) are RAGE ligands that accumulate due to aging, inflammation, oxidative stress, and carbohydrate metabolism. AGEs cause further inflammation and oxidative stress through RAGE, but also through RAGE-independent mechanisms. This review describes the complexity of RAGE signaling and the causes of AGE accumulation, followed by a comprehensive overview of alterations reported on AGEs and RAGE in COPD and in important co-morbidities. Furthermore, it describes the mechanisms by which AGEs and RAGE contribute to the pathophysiology of individual disease conditions and how they execute crosstalk between organ systems. A section on therapeutic strategies that target AGEs and RAGE and could alleviate patients from multimorbid conditions using single therapeutics concludes this review.

Trabecular bone microcrack accumulation in patients treated with bisphosphonates for durations up to 16 years

This study quantified the length, number, and density of microcracks in bone from patients treated with bisphosphonates as a function of duration. Anterior iliac crest bone samples from 51 osteoporotic Caucasian females continuously treated with oral bisphosphonates for 1-16 years were obtained by bone biopsy. Samples were histologically processed and analyzed for bone area, microcrack number, and microcrack length. The analyses used statistical modeling and considered patient age, bone mineral density, bone volume/total volume, trabecular thickness, and bone turnover as potential covariates. Microcrack density (number of microcracks/total examined bone area) was linearly related (p = 0.018) to bisphosphonate treatment duration. None of the analyzed covariates contributed significantly to the observed relationship between microcrack density and bisphosphonate treatment duration. Observed increases in microcrack density with increasing bisphosphonate treatment duration is important because increasing levels of microcracks may not only affect bone remodeling but also reduce elastic modulus and are suspected to adversely affect other mechanical properties that may influence fracture risk. The present findings add to our prior results showing changes in bone material properties and modulus with bisphosphonate treatment duration and thereby provide a more comprehensive assessment of the relationship between bisphosphonate treatment duration and bone quality. Statement of Clinical Significance: The present findings provide information guiding clinical use of oral bisphosphonates for post-menopausal osteoporosis therapy.

Twelve Months of Denosumab and/or Alendronate Is Associated With Improved Bone Fatigue Life, Microarchitecture, and Density in Ovariectomized Cynomolgus Monkeys

Prolonged use of antiresorptives such as the bisphosphonate alendronate (ALN) and the RANKL inhibitor denosumab (DMAb) are associated with rare cases of atypical femoral fracture (AFF). The etiology of AFF is unclear, but it has been hypothesized that potent osteoclast inhibitors may reduce bone fatigue resistance. The purpose of this study was to quantify the relationship between antiresorptive treatment and fatigue life (cycles to failure) in bone from ovariectomized cynomolgus monkeys. We analyzed humeral bone from 30 animals across five treatment groups. Animals were treated for 12 months with subcutaneous (sc) vehicle (VEH), sc DMAb (25 mg/kg/month), or intravenous (iv) ALN (50 μg/kg/month). Another group received 6 months VEH followed by 6 months DMAb (VEH-DMAb), and the final group received 6 months ALN followed by 6 months DMAb (ALN-DMAb). A total of 240 cortical beam samples were cyclically tested in four-point bending at 80, 100, 120, or 140 MPa peak stress. High-resolution imaging and density measurements were performed to evaluate bone microstructure and composition. Samples from the ALN (p = 0.014), ALN-DMAb (p = 0.008), and DMAb (p < 0.001) groups illustrated higher fatigue-life measurements than VEH. For example, at 140 MPa the VEH group demonstrated a median ± interquartile range (IQR) fatigue life of 1987 ± 10593 cycles, while animals in the ALN, ALN-DMAb, and DMAb groups survived 9850 ± 13648 (+395% versus VEH), 10493 ± 16796 (+428%), and 14495 ± 49299 (+629%) cycles, respectively. All antiresorptive treatment groups demonstrated lower porosity, smaller pore size, greater pore spacing, and lower number of canals versus VEH (p < 0.001). Antiresorptive treatment was also associated with greater apparent density, dry density, and ash density (p ≤ 0.03). We did not detect detrimental changes following antiresorptive treatments that would explain their association with AFF. In contrast, 12 months of treatment may have a protective effect against fatigue fractures. © 2022 American Society for Bone and Mineral Research (ASBMR).

Radiological Reversibility of Incomplete Atypical Femoral Fracture with Cessation of Bisphosphonate: Including an Early Stage of Incomplete Fracture

BACKGROUND

We found some important early findings in simple radiographs under the bisphosphonate (BP) treatment through a retrospective study. Here, we report the degree of reversibility of the early findings before overt fracture and analyze the factors affecting the differences through a retrospective case-control study.

METHODS

We retrospectively inspected the clinical charts of patients diagnosed with atypical femoral fracture (AFF) at our institute between March 2006 and September 2018. Among the 209 screened patients, 102 patients were ultimately divided into 3 categories: Category 1 was described as endosteal diffuse flaring (EDF, early IAFF); category 2 was typical IAFF, with a tiny/partial crack that was limited to less than half of the thickness of the cortex; and category 3 was IAFF with a crack through the entire cortex. Demographics, clinical factors, and three categories of incomplete atypical femoral fracture (IAFF) were analyzed to determine whether their radiological condition "improved" or "progressed" after cessation of BP via univariate and multivariate analyses.

RESULTS

Thirty-three, 53, and 16 were classified as categories 1, 2, and 3, respectively. Groups 1 and 2 consisted of 79 patients whose IAFF on the side of interest improved and 23 patients whose IAFF progressed, respectively. The uni/multivariate analyses of the groups demonstrated that the total period of BP (odds ratio [OR] = 1.49) and period of cessation of BP (OR = 0.24) were significant variables. In addition, prophylactic treatment for a contralateral IAFF was a strong factor for progression of the incomplete lesion on the side of interest (OR = 25.99). The rate of progression was significantly higher in patients with a mean treatment period of 43 months or longer, and in those with a mean cessation period shorter than 1.2 months.

CONCLUSION

Early-stage IAFF was found to be a unique finding in simple radiographs before the typical features of AFF. This EDF (category 1) was definitively reversible to normal bone when administration of BP was stopped. In addition, a long period of BP treatment and recent cessation of BP adversely affected IAFF with respect to spontaneous healing.

LEVEL OF EVIDENCE

Level III, a retrospective case-control study.

Medication Related Osteonecrosis of the Jaw: 2021 Position Statement of the Korean Society for Bone and Mineral Research and the Korean Association of Oral and Maxillofacial Surgeons

Antiresorptives are the most widely prescribed drugs for the treatment of osteoporosis. They are also used in malignant bone metastases, multiple myeloma, and Paget's disease, and provide therapeutic efficacy on those diseases. However, it was reported that the occurrence of osteonecrosis of the jaw (ONJ) could be related to antiresorptive exposures, and there have been many cases regarding this issue. Therefore, a clearer definition and treatment guidelines were needed for this disease. The American Society for Bone and Mineral Research and the Amnerican Association of Oral and Maxillofacial Surgeons reported statements on bisphosphonate-related ONJ (BRONJ), and a revised version was recently presented. In the revised edition, the diagnosis BRONJ was changed to medication-related ONJ (MRONJ), which reflects consideration of the fact that ONJ also occurs for denosumab, a bone resorption inhibitor of the receptor activator of the nuclear factor-κB ligand antibody family, and bevacizumab, an anti-angiogenesis inhibitor. The Korean Society for Bone and Mineral Research and the Korean Association of Oral and Maxillofacial Surgeons had collectively formed a task force for the preparation of an official statement on MRONJ based on a previous position paper in 2015. The task force reviewed current knowledge and coordinated dental and medical opinions to propose the guideline customized for the local Korean situation.

Biomechanical mechanisms of atypical femoral fracture

Antiresorptives such as bisphosphonates (BP) and denosumab are commonly used osteoporosis treatments that are effective in preventing osteoporotic fractures by suppressing bone turnover. Although these treatments reduce fracture risk, their long-term use has been associated with atypical femoral fracture (AFF), a rare potential side effect. Despite its rare occurrence, AFF has had a disproportionately significant adverse impact on society due to its severe outcomes such as loss of function and delayed healing. These severe outcomes have led to the decrease in the use and prescription of osteoporosis treatment drugs due to patient anxiety and clinician reluctance. This creates the risk for increasing osteoporotic fracture rates in the population. The existing information on the pathogenesis of AFF primarily relies on retrospective observational studies. However, these studies do not explain the underlying mechanisms that contribute to AFF, and therefore the mechanistic origins of AFF are still poorly understood. The purpose of this review is to outline the current state of knowledge of the mechanical mechanisms of AFF. The review focuses on three major potential mechanical mechanisms of AFF based on the current literature which are (1) macroscale femoral geometry which influences the stress/strain distribution in the femur under loading; (2) bone matrix composition, potentially altered by long-term remodeling suppression by BPs, which directly influences the material properties of bone and its mechanical behavior; and (3) microstructure, potentially altered by long-term remodeling suppression by BPs, which impacts fracture resistance through interaction with crack propagation. In addition, this review presents the critical knowledge gaps in understanding AFF and also discusses approaches to closing the knowledge gap in understanding the underlying mechanisms of AFF.

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.

Risk factors for atypical forearm fractures associated with bisphosphonate usage

BACKGROUND

The purpose of this study was to find the diagnostic factors for atypical forearm fractures additional to atypical femur fractures, via a retrospective case-control study. Thus, our authors performed a complete enumeration survey for patients under the treatment of bisphosphonate (BP).

METHODS

We identified 53 patients that met the following inclusion criteria between March 2009 and February 2019: a BP therapy history or ongoing administration of at least 1 year, presence of simple radiographs of bilateral femurs and forearms, and availability of complete medical records and radiological data. The patients were divided into two groups: those with any lesion of atypical fractures of ulna or radius, regardless of the displacement of at least one side extremity in simple radiographs (group 1, 20 patients); and those without any lesions of pathognomonic finding or fractures in either forearm in simple radiographs (group 2, 33 patients).

RESULTS

Univariate analyses of basic demographic characteristic such as age, smoking, comorbidity of diabetes mellitus or any connective tissue disease needing steroid treatment, and BMD showed no significant differences between the groups (P > 0.05). The co-morbidity of malignant cancer inevitably needing BP usage was not different between the two groups. Multivariate analyses of the several variables that differed significantly between the two groups in univariate analyses demonstrated that total period and single prescribing physician/surgeon were significantly associated with forearm fractures. A cut-off value of 65 months for the total period predicted the presence atypical forearm fractures.

CONCLUSIONS

Atypical forearm fractures are probably more common than reported in the literature to date, and all forearm lesions were accompanied by preceding atypical femur fractures. The period of BP administration had the main effect on the occurrence of atypical forearm fractures, particularly if more than 65 months. Also, the prescription by multiple physician was predicting factor for forearms lesion additionally to AFFs, however, more evidence-based study is needed to understand the effects of cancer-related BP usage on the forearm.

LEVEL OF EVIDENCE

Level III, retrospective case-control study.

A Bisphosphonate With a Low Hydroxyapatite Binding Affinity Prevents Bone Loss in Mice After Ovariectomy and Reverses Rapidly With Treatment Cessation

Bisphosphonates (BPs) are a mainstay of osteoporosis treatment; however, concerns about bone health based on oversuppression of remodeling remain. Long‐term bone remodeling suppression adversely affects bone material properties with microdamage accumulation and reduced fracture toughness in animals and increases in matrix mineralization and atypical femur fractures in patients. Although a “drug holiday” from BPs to restore remodeling and improve bone quality seems reasonable, clinical BPs have long functional half‐lives because of their high hydroxyapatite (HAP) binding affinities. This places a practical limit on the reversibility and effectiveness of a drug holiday. BPs with low HAP affinity and strong osteoclast inhibition potentially offer an alternative approach; their antiresorptive effect should reverse rapidly when dosing is discontinued. This study tested this concept using NE‐58025, a BP with low HAP affinity and moderate osteoclast inhibition potential. Young adult female C57Bl/6 mice were ovariectomized (OVX) and treated with NE‐58025, risedronate, or PBS vehicle for 3 months to test effectiveness in preventing long‐term bone loss. Bone microarchitecture, histomorphometry, and whole‐bone mechanical properties were assessed. To test reversibility, OVX mice were similarly treated for 3 months, treatment was stopped, and bone was assessed up to 3 months post‐treatment. NE‐58025 and RIS inhibited long‐term OVX‐induced bone loss, but NE‐58025 antiresorptive effects were more pronounced. Withdrawing NE‐58025 treatment led to the rapid onset of trabecular resorption with a 200% increase in osteoclast surface and bone loss within 1 month. Cessation of risedronate treatment did not lead to increases in resorption indices or bone loss. These results show that NE‐58025 prevents OVX‐induced bone loss, and its effects reverse quickly following cessation treatment in vivo. Low‐HAP affinity BPs may have use as reversible, antiresorptive agents with a rapid on/off profile, which may be useful for maintaining bone health with long‐term BP treatment. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

On the effect of antiresorptive drugs on the bone remodeling of the mandible after dental implantation: a mathematical model

Bone remodeling identifies the process of permanent bone change with new bone formation and old bone resorption. Understanding this process is essential in many applications, such as optimizing the treatment of diseases like osteoporosis, maintaining bone density in long-term periods of disuse, or assessing the long-term evolution of the bone surrounding prostheses after implantation. A particular case of study is the bone remodeling process after dental implantation. Despite the overall success of this type of implants, the increasing life expectancy in developed countries has boosted the demand for dental implants in patients with osteoporosis. Although several studies demonstrate a high success rate of dental implants in osteoporotic patients, it is also known that the healing time and the failure rate increase, necessitating the adoption of pharmacological measures to improve bone quality in those patients. However, the general efficacy of these antiresorptive drugs for osteoporotic patients is still controversial, requiring more experimental and clinical studies. In this work, we investigate the effect of different doses of several drugs, used nowadays in osteoporotic patients, on the evolution of bone density after dental implantation. With this aim, we use a pharmacokinetic-pharmacodynamic (PK/PD) mathematical model that includes the effect of antiresorptive drugs on the RANK/RANK-L/OPG pathway, as well as the mechano-chemical coupling with external mechanical loads. This mechano-PK/PD model is then used to analyze the evolution of bone in normal and osteoporotic mandibles after dental implantation with different drug dosages. We show that using antiresorptive agents such as bisphosphonates or denosumab increases bone density and the associated mechanical properties, but at the same time, it also increases bone brittleness. We conclude that, despite the many limitations of these very complex models, the one presented here is capable of predicting qualitatively the evolution of some of the main biological and chemical variables associated with the process of bone remodeling in patients receiving drugs for osteoporosis, so it could be used to optimize dental implant design and coating for osteoporotic patients, as well as the drug dosage protocol for patient-specific treatments.

Fifty years of bisphosphonates: What are their mechanical effects on bone?

After fifty years of experience with several generations of bisphosphonates (BPs), and 25 years after these drugs were approved for use in humans, their mechanical effects on bone are still not fully understood. Certainly, these drugs have transformed the treatment of osteoporosis in both men and women. There is no question that they do prevent fractures related to low bone mass, and there is widespread agreement that they increase strength and stiffness of the vertebrae. There is less consensus, however, about their effects on cortical bone, or on bone tissue properties in either trabecular or cortical bone, or their effects with longer periods of treatment. The consensus of most studies, both those based on ovariectomized and intact animal models and on testing of human bone, is that long-term treatment and/or high doses with certain BPs make the bone tissue more brittle and less tough. This translates into reduced energy to fracture and potentially a shorter bone fatigue life. Many studies have been done, but Interpretation of the results of these studies is complicated by variations in which BP is used, the animal model used, dose, duration, and methods of testing. Duration effects and effects on impact properties of bone are gaps that should be filled with additional testing.

ATRAID regulates the action of nitrogen-containing bisphosphonates on bone

Nitrogen-containing bisphosphonates (N-BPs), such as alendronate, are the most widely prescribed medications for diseases involving bone, with nearly 200 million prescriptions written annually. Recently, widespread use of N-BPs has been challenged due to the risk of rare but traumatic side effects such as atypical femoral fracture (AFF) and osteonecrosis of the jaw (ONJ). N-BPs bind to and inhibit farnesyl diphosphate synthase, resulting in defects in protein prenylation. Yet, it remains poorly understood what other cellular factors might allow N-BPs to exert their pharmacological effects. Here, we performed genome-wide studies in cells and patients to identify the poorly characterized gene, ATRAID Loss of ATRAID function results in selective resistance to N-BP-mediated loss of cell viability and the prevention of alendronate-mediated inhibition of prenylation. ATRAID is required for alendronate inhibition of osteoclast function, and ATRAID-deficient mice have impaired therapeutic responses to alendronate in both postmenopausal and senile (old age) osteoporosis models. Last, we performed exome sequencing on patients taking N-BPs that suffered ONJ or an AFF. ATRAID is one of three genes that contain rare nonsynonymous coding variants in patients with ONJ or an AFF that is also differentially expressed in poor outcome groups of patients treated with N-BPs. We functionally validated this patient variation in ATRAID as conferring cellular hypersensitivity to N-BPs. Our work adds key insight into the mechanistic action of N-BPs and the processes that might underlie differential responsiveness to N-BPs in people.

Osteoporosis Treatments Affect Bone Matrix Maturation in a Rat Model of Induced Cortical Remodeling

To test how osteoporosis drugs affect bone matrix maturation during cortical bone remodeling, 72 pregnant rats were switched from a 0.4% to a 0.01% calcium diet at parturition for a 23‐day lactation period. At weaning, eight dams were sacrificed to establish baseline values, while the remaining dams were returned to 0.4% calcium and treated with vehicle (saline), sodium fluoride (NaF), zoledronic acid (ZA), or sclerostin antibody (Scl‐Ab) for either 7 or 28 days (eight animals per group per time point). Femora were examined by μCT, dynamic histomorphometry, Fourier transform infrared imaging, and three‐point bending of notched specimens. Cortical porosity decreased in all groups from baseline to day 28. Intracortical mineralizing surface (MS/BS) and mineral apposition rate (MAR), as well as the mineral‐to‐matrix ratio were unaffected by treatment, but intracortical crystallinity was increased in the ZA group at day 10 compared with vehicle. Cortical area increased in all groups over 28 days mainly because of an addition of bone at the endocortical surface. Endocortical MS/BS did not vary among the groups, but endocortical MAR was suppressed in the NaF group at day 2 and elevated in the Scl‐Ab group at day 4 compared with vehicle. Endocortical mineral‐to‐matrix ratio was increased at days 5 and 10 following NaF treatment and endocortical crystallinity was increased at day 5 following ZA treatment compared with vehicle. Fracture toughness did not differ among the groups. Thus, the treatments affected matrix maturation more strongly at the endocortical then intracortical envelope. In this model of induced remodeling, the bone formation phase is synchronized at multiple sites, facilitating study of the effects of drugs or other bone‐targeting agents on matrix maturation independent of their effects on the initiation of remodeling. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

6'-Methoxy Raloxifene-analog enhances mouse bone properties with reduced estrogen receptor binding

Raloxifene (RAL) is an FDA-approved drug used to treat osteoporosis in postmenopausal women. RAL suppresses bone loss primarily through its role as a selective estrogen receptor modulator (SERM). This hormonal estrogen therapy promotes unintended side effects, such as hot flashes and increased thrombosis risk, and prevents the drug from being used in some patient populations at-risk for fracture, including children with bone disorders. It has recently been demonstrated that RAL can have significant positive effects on overall bone mechanical properties by binding to collagen and increasing bone tissue hydration in a cell-independent manner. A Raloxifene-Analog (RAL-A) was synthesized by replacing the 6-hydroxyl substituent with 6-methoxy in effort to reduce the compound's binding affinity for estrogen receptors (ER) while maintaining its collagen-binding ability. It was hypothesized that RAL-A would improve the mechanical integrity of bone in a manner similar to RAL, but with reduced estrogen receptor binding. Molecular assessment showed that while RAL-A did reduce ER binding, downstream ER signaling was not completely abolished. In-vitro, RAL-A performed similarly to RAL and had an identical concentration threshold on osteocyte cell proliferation, differentiation, and function. To assess treatment effect in-vivo, wildtype (WT) and heterozygous (OIM+/−) female mice from the Osteogenesis Imperfecta (OI) murine model were treated with either RAL or RAL-A from 8 weeks to 16 weeks of age. There was an untreated control group for each genotype as well. Bone microarchitecture was assessed using microCT, and mechanical behavior was assessed using 3-point bending. Results indicate that both compounds produced analogous gains in tibial trabecular and cortical microarchitecture. While WT mechanical properties were not drastically altered with either treatment, OIM+/− mechanical properties were significantly enhanced, most notably, in post-yield properties including bone toughness. This proof-of-concept study shows promising results and warrants the exploration of additional analog iterations to further reduce ER binding and improve fracture resistance.

In Vivo Bone Effects of a Novel Bisphosphonate-EP4a Conjugate Drug (C3) for Reversing Osteoporotic Bone Loss in an Ovariectomized Rat Model

Pathological bone loss is a regular feature of postmenopausal osteoporosis, and the microstructural changes along with the bone loss make the individual prone to getting hip, spine, and wrist fractures. We have developed a new conjugate drug named C3, which has a synthetic, stable EP4 agonist (EP4a) covalently linked to an inactive alendronate (ALN) that binds to bone and allows physiological remodeling. After losing bone for 12 weeks, seven groups of rats were treated for 8 weeks via tail‐vein injection. The groups were: C3 conjugate at low and high doses, vehicle‐treated ovariectomy (OVX) and sham, C1 (a similar conjugate, but with active ALN at high dose), inactive ALN alone, and a mixture of unconjugated ALN and EP4a to evaluate the conjugation effects. Bone turnover was determined by dynamic and static histomorphometry; μCT was employed to determine bone microarchitecture; and bone mechanical properties were evaluated via biomechanical testing. Treatment with C3 significantly increased trabecular bone volume and vertebral BMD versus OVX controls. There was also significant improvement in the vertebral load‐bearing abilities and stimulation of bone formation in femurs after C3 treatment. This preclinical research revealed that C3 resulted in significant anabolic effects on trabecular bone, and EP4a and ALN conjugation components are vital to conjugate anabolic efficacy. A combined therapy using an EP4 selective agonist anabolic agent linked to an inactive ALN is presented here that produces significant anabolic effects, allows bone remodeling, and has the potential for treating postmenopausal osteoporosis or other diseases where bone strengthening would be beneficial. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Voluntary Chronic Heavy Alcohol Consumption in Male Rhesus Macaques Suppresses Cancellous Bone Formation and Increases Bone Marrow Adiposity

BACKGROUND

Chronic heavy alcohol consumption is an established risk factor for bone fracture, but comorbidities associated with alcohol intake may contribute to increased fracture rates in alcohol abusers. To address the specific effects of alcohol on bone, we used a nonhuman primate model and evaluated voluntary alcohol consumption on: (i) global markers of bone turnover in blood and (ii) cancellous bone mass, density, microarchitecture, turnover, and microdamage in lumbar vertebra.

METHODS

Following a 4-month induction period, 6-year-old male rhesus macaques (Macaca mulatta, n = 13) voluntarily self-administered water or ethanol (EtOH; 4% w/v) for 22 h/d, 7 d/wk, for a total of 12 months. Control animals (n = 9) consumed an isocaloric maltose-dextrin solution. Tetracycline hydrochloride was administered orally 17 and 3 days prior to sacrifice to label mineralizing bone surfaces. Global skeletal response to EtOH was evaluated by measuring plasma osteocalcin and carboxyterminal collagen cross-links (CTX). Local response was evaluated in lumbar vertebra using dual-energy X-ray absorptiometry, microcomputed tomography, static and dynamic histomorphometry, and histological assessment of microdamage.

RESULTS

Monkeys in the EtOH group consumed an average of 2.8 ± 0.2 (mean ± SE) g/kg/d of EtOH (30 ± 2% of total calories), resulting in an average blood EtOH concentration of 88.3 ± 8.8 mg/dl 7 hours after the session onset. Plasma CTX and osteocalcin tended to be lower in EtOH-consuming monkeys compared to controls. Significant differences in bone mineral density in lumbar vertebrae 1 to 4 were not detected with treatment. However, cancellous bone volume fraction (in cores biopsied from the central region of the third vertebral body) was lower in EtOH-consuming monkeys compared to controls. Furthermore, EtOH-consuming monkeys had lower osteoblast perimeter and mineralizing perimeter, no significant difference in osteoclast perimeter, and higher bone marrow adiposity than controls. No significant differences between groups were detected in microcrack density (2^nd lumbar vertebra).

CONCLUSIONS

Voluntary chronic heavy EtOH consumption reduces cancellous bone formation in lumbar vertebra by decreasing osteoblast-lined bone perimeter, a response associated with an increase in bone marrow adiposity.

The Role of Lower-Limb Geometry in the Pathophysiology of Atypical Femoral Fracture

PURPOSEOF REVIEW

The etiology of atypical femoral fracture (AFF) is likely multifactorial. In this review, we examined the recent literature investigating the role of lower-limb geometry in the pathophysiology of AFF.

RECENT FINDINGS

Increased femoral bowing was associated with prevalent AFF and a greater likelihood of a diaphyseal versus a subtrochanteric AFF location. Femoral neck geometry or hip alignment may also be related to AFF, but findings remain equivocal. Differences in femoral geometry may, in part, be responsible for the high rate of AFF in Asian compared with Caucasian populations. Finally, simulation studies suggest that lower-limb geometry influences AFF risk via its effects on mechanical strain of the lateral femoral cortex. Femoral geometry, and bowing in particular, is related to prevalent AFF, but more prospective investigation is needed to determine whether measurements of geometry can be used for clinical risk stratification.

Glucocorticoid-Induced Bone Fragility Is Prevented in Female Mice by Blocking Pyk2/Anoikis Signaling

Excess of glucocorticoids (GCs) is a leading cause of bone fragility, and therapeutic targets are sorely needed. We report that genetic deletion or pharmacological inhibition of proline-rich tyrosine kinase 2 (Pyk2) prevents GC-induced bone loss by overriding GC effects of detachment-induced bone cell apoptosis (anoikis). In wild-type or vehicle-treated mice, GCs either prevented osteoclast apoptosis or promoted osteoblast/osteocyte apoptosis. In contrast, mice lacking Pyk2 [knockout (KO)] or treated with Pyk2 kinase inhibitor PF-431396 (PF) were protected. KO or PF-treated mice were also protected from GC-induced bone resorption, microarchitecture deterioration, and weakening of biomechanical properties. In KO and PF-treated mice, GC increased osteoclasts in bone and circulating tartrate-resistant acid phosphatase form 5b, an index of osteoclast number. However, bone surfaces covered by osteoclasts and circulating C-terminal telopeptides of type I collagen, an index of osteoclast function, were not increased. The mismatch between osteoclast number vs function induced by Pyk2 deficiency/inhibition was due to osteoclast detachment and anoikis. Further, GC prolongation of osteoclast lifespan was absent in KO and PF-treated osteoclasts, demonstrating Pyk2 as an intrinsic osteoclast-survival regulator. Circumventing Pyk2 activation preserves skeletal integrity by preventing GC effects on bone cell survival (proapoptotic for osteoblasts/osteocytes, antiapoptotic for osteoclasts) and GC-induced bone resorption. Thus, Pyk2/anoikis signaling as a therapeutic target for GC-induced osteoporosis.

Atypical Femur Fractures: Review of Epidemiology, Relationship to Bisphosphonates, Prevention, and Clinical Management

Bisphosphonates (BPs) are highly effective in treating osteoporosis and reducing hip, vertebral, and other fractures by as much as 50% to 70%. However, since 2006, atypical femur fractures (AFFs) emerged as potential side effects of BPs and other treatments. These fractures have unusual radiologic features and occur with little trauma. Public concern has led to a >50% decrease in BP usage. AFFs are rare: for each AFF, >1200 fractures, including 135 hip fractures, are prevented. Case definition criteria were updated by the American Society of Bone and Mineral Research in 2014. Many epidemiologic studies have been reported, and although methodologically challenging, generally support a BP-AFF association. However, the magnitude of the association between BPs and AFFs is uncertain: estimates of relative risk for AFFs among BP users vs nonusers range from 1 to 65 with a meta-analysis estimate of 1.7. Although mechanistic studies have proposed several hypotheses explaining how BPs might decrease bone strength, AFF pathogenesis remains uncertain and cannot explain the paradox of efficacy of reduction of common fractures while increasing risk for rare fractures at one site. There are several consistent risk factors, including Asian race (in North America), femoral bowing, and glucocorticoid use, whereas others remain unclear. Consensus is emerging about strategies to prevent AFFs in BP users (including drug holidays after 5 years' use in some patients). In conclusion, AFFs can be devastating, but even under the most pessimistic assumptions, the benefit/risk ratio is highly positive for BPs, particularly during 3 to 5 years of use. As understanding of AFFs increases, it is becoming increasingly possible to maximize BP benefits while minimizing AFF risk.

Atypical incomplete femoral neck fracture in patients taking long-term bisphosphonate: Case report, a report of 2 cases

RATIONALE

We present 2 cases of lateral incomplete impending fracture of the femoral neck without trauma in elderly patients taking long-term bisphosphonate (BP) treatment, and we defined it as atypical femoral neck fracture (AFNF). To the best of our knowledge, this is the first report on the follow-up results of AFNF.

PATIENT CONCERNS

Patients in both cases had been taking BP drugs for a long time with osteoporosis. The duration of BP treatment was 6 years, and there was no history of repeated stresses.

DIAGNOSES

All fractures were linear at the lateral aspect of the mid portion of the femoral neck, and the BMD of the femoral neck was -0.9, and -1.8, respectively.

INTERVENTIONS

Internal fixation was performed in both cases (73 years, 68 years) using cannulated screws.

OUTCOMES

In both patients who underwent screw fixation, the fracture line started to extend distally at 4 weeks and 2 weeks following surgery. In the 3-month follow-up image, the length of the fracture increased by 20.1 mm and 9.9 mm, respectively. There was a problem with active rehabilitation, and the possibility of revision was also found to be a burden in terms of mortality and cost in older patients.

LESSONS

In the case of AFNF, guidelines for treatment should be set in consideration of the decreased bone healing, even when the fracture pattern is simple. Arthroplasty based on a wider indication may be worth considering.

The enigma of atypical femoral fractures: A summary of current knowledge

Atypical femoral fractures (AFF) are stress or ‘insufficiency’ fractures, often complicated by the use of bisphosphonates or other bone turnover inhibitors. While these drugs are beneficial for the intact osteoporotic bone, they probably prevent a stress fracture from healing which thus progresses to a complete fracture.

Key features of atypical femoral fractures, essential for the diagnosis, are: location in the subtrochanteric region and diaphysis; lack of trauma history and comminution; and a transverse or short oblique configuration.

The relative risk of patients developing an atypical femoral fracture when taking bisphosphonates is high; however, the absolute risk of these fractures in patients on bisphosphonates is low, ranging from 3.2 to 50 cases per 100,000 person-years.

Treatment strategy in patients with AFF involves: radiograph of the contralateral side (computed tomography and magnetic resonance imaging should also be considered); dietary calcium and vitamin D supplementation should be prescribed following assessment; bisphosphonates or other potent antiresorptive agents should be discontinued; prophylactic surgical treatment of incomplete AFF with cephalomedullary nail, unless pain free; cephalomedullary nailing for surgical fixation of complete fractures; avoidance of gaps in the lateral and anterior cortex; avoidance of varus malreduction.

Cite this article: EFORT Open Rev 2018;3:494-500. DOI: 10.1302/2058-5241.3.170070.

Interaction of Microcracks and Tissue Compositional Heterogeneity in Determining Fracture Resistance of Human Cortical Bone

Recent studies demonstrated an association between atypical femoral fracture (AFF) and long-term bisphosphonate (BP) use for osteoporosis treatment. Due to BP treatment, bone undergoes alterations including increased microcrack density and reduced tissue compositional heterogeneity. However, the effect of these changes on the fracture response of bone is not well understood. As a result, the goal of the current study is to evaluate the individual and combined effects of microcracks and tissue compositional heterogeneity on fracture resistance of cortical bone using finite element modeling (FEM) of compact tension (CT) specimen tests with varying microcrack density, location, and clustering, and material heterogeneity in three different bone samples. The simulation results showed that an increase in microcrack density improved the fracture resistance irrespective of the local material property heterogeneity and microcrack distribution. A reduction in material property heterogeneity adversely affected the fracture resistance in models both with and without microcracks. When the combined changes in microcrack density and tissue material property heterogeneity representing BP treatment were evaluated, the models corresponding to BP-treated bone demonstrated reduced fracture resistance. The simulation results also showed that although microcrack location and clustering, and microstructure significantly influenced fracture resistance, the trends observed on the effect of microcrack density and tissue material property heterogeneity did not change. In summary, these results provide new information on the interaction of microcracks, tissue material property heterogeneity, and fracture resistance and may improve the understanding of the influence of mechanical changes due to prolonged BP use on the fracture behavior of cortical bone.

Material heterogeneity, microstructure, and microcracks demonstrate differential influence on crack initiation and propagation in cortical bone

The recent studies have shown that long-term bisphosphonate use may result in a number of mechanical alterations in the bone tissue including a reduction in compositional heterogeneity and an increase in microcrack density. There are limited number of experimental and computational studies in the literature that evaluated how these modifications affect crack initiation and propagation in cortical bone. Therefore, in this study, the entire crack growth process including initiation and propagation was simulated at the microscale by using the cohesive extended finite element method. Models with homogeneous and heterogeneous material properties (represented at the microscale capturing the variability in material property values and their distribution) as well as different microcrack density and microstructure were compared. The results showed that initiation fracture resistance was higher in models with homogeneous material properties compared to heterogeneous ones, whereas an opposite trend was observed in propagation fracture resistance. The increase in material heterogeneity level up to 10 different material property sets increased the propagation fracture resistance beyond which a decrease was observed while still remaining higher than the homogeneous material distribution. The simulation results also showed that the total osteonal area influenced crack propagation and the local osteonal area near the initial crack affected the crack initiation behavior. In addition, the initiation fracture resistance was higher in models representing bisphosphonate treated bone (low material heterogeneity, high microcrack density) compared to untreated bone models (high material heterogeneity, low microcrack density), whereas an opposite trend was observed at later stages of crack growth. In summary, the results demonstrated that tissue material heterogeneity, microstructure, and microcrack density influenced crack initiation and propagation differently. The findings also elucidate how possible modifications in material heterogeneity and microcrack density due to bisphosphonate treatment may influence the initiation and propagation fracture resistance of cortical bone.

GLUCOCORTICOID EXCESS IN BONE AND MUSCLE

Glucocorticoids (GC), produced and released by the adrenal glands, regulate numerous physiological processes in a wide range of tissues. Because of their profound immunosuppressive and anti-inflammatory actions, GC are extensively used for the treatment of immune and inflammatory conditions, the management of organ transplantation, and as a component of chemotherapy regimens for cancers. However, both pathologic endogenous elevation and long-term use of exogenous GC are associated with severe adverse effects. In particular, excess GC has devastating effects on the musculoskeletal system. GC increase bone resorption and decrease formation leading to bone loss, microarchitectural deterioration and fracture. GC also induce loss of muscle mass and strength leading to an increased incidence of falls. The combined effects on bone and muscle account for the increased fracture risk with GC. This review summarizes the advance in knowledge in the last two decades about the mechanisms of action of GC in bone and muscle and the attempts to interfere with the damaging actions of GC in these tissues with the goal of developing more effective therapeutic strategies.

MMP14 is a novel target of PTH signaling in osteocytes that controls resorption by regulating soluble RANKL production

Parathyroid hormone (PTH) affects the skeleton by acting on osteocytes (Ots) in bone through yet unclear mechanisms. We report that matrix metalloproteinase 14 (MMP14) expression/activity are increased in bones from mice with genetic constitutive activation (ca) of the PTH receptor 1 (PTH1R) in Ots (caPTH1R^Ot) and in bones from mice exposed to elevated PTH levels but not in mice lacking [conditional knockout (cKO)] the PTH1R in Ots (cKOPTH1R^Ot). Furthermore, PTH upregulates MMP14 in human bone cultures and in Ot-enriched bones from floxed control mice but not from cKOPTH1R^Ot mice. MMP14 activity increases soluble receptor activator of NF-κΒ ligand production, which in turn, stimulates osteoclast differentiation and resorption. Pharmacologic inhibition of MMP14 activity reduced the high bone remodeling exhibited by caPTH1R^Ot mice or induced by chronic PTH elevation and decreased bone resorption but allowed full stimulation of bone formation induced by PTH injections, thereby potentiating bone gain. Thus, MMP14 is a new member of the intricate gene network activated in Ots by PTH1R signaling that can be targeted to adjust the skeletal responses to PTH in favor of bone preservation.-Delgado-Calle, J., Hancock, B., Likine, E. F., Sato, A. Y., McAndrews, K., Sanudo, C., Bruzzaniti, A., Riancho, J. A., Tonra, J. R., Bellido, T. MMP14 is a novel target of PTH signaling in osteocytes that controls resorption by regulating soluble RANKL production.

The effect of long-term bisphosphonate therapy on trabecular bone strength and microcrack density

Objectives

Bisphosphonates (BP) are the first-line treatment for preventing fragility fractures. However, concern regarding their efficacy is growing because bisphosphonate is associated with over-suppression of remodelling and accumulation of microcracks. While dual-energy X-ray absorptiometry (DXA) scanning may show a gain in bone density, the impact of this class of drug on mechanical properties remains unclear. We therefore sought to quantify the mechanical strength of bone treated with BP (oral alendronate), and correlate data with the microarchitecture and density of microcracks in comparison with untreated controls.

Methods

Trabecular bone from hip fracture patients treated with BP (n = 10) was compared with naïve fractured (n = 14) and non-fractured controls (n = 6). Trabecular cores were synchrotron scanned and micro-CT scanned for microstructural analysis, including quantification of bone volume fraction, microarchitecture and microcracks. The specimens were then mechanically tested in compression.

Results

BP bone was 28% lower in strength than untreated hip fracture bone, and 48% lower in strength than non-fractured control bone (4.6 MPa vs 6.4 MPa vs 8.9 MPa). BP-treated bone had 24% more microcracks than naïve fractured bone and 51% more than non-fractured control (8.12/cm²vs 6.55/cm²vs 5.25/cm²). BP and naïve fracture bone exhibited similar trabecular microarchitecture, with significantly lower bone volume fraction and connectivity than non-fractured controls.

Conclusion

BP therapy had no detectable mechanical benefit in the specimens examined. Instead, its use was associated with substantially reduced bone strength. This low strength may be due to the greater accumulation of microcracks and a lack of any discernible improvement in bone volume or microarchitecture. This preliminary study suggests that the clinical impact of BP-induced microcrack accumulation may be significant.

Cite this article: A. Jin, J. Cobb, U. Hansen, R. Bhattacharya, C. Reinhard, N. Vo, R. Atwood, J. Li, A. Karunaratne, C. Wiles, R. Abel. The effect of long-term bisphosphonate therapy on trabecular bone strength and microcrack density. Bone Joint Res 2017;6:602–609. DOI: 10.1302/2046-3758.610.BJR-2016-0321.R1.

Preclinical Models for Skeletal Research: How Commonly Used Species Mimic (or Don’t) Aspects of Human Bone

Preclinical studies play an indispensable role in exploring the biological regulation of the musculoskeletal system. They are required in all drug development pipelines where both small and large animal models are needed to understand efficacy and side effects. This brief review highlights 4 aspects of human bone, longitudinal bone growth, intracortical remodeling, collagen/mineral interface, and age-related changes, and discusses how various animal models recapitulate (or don’t) these aspects of human skeletal physiology.

A Novel H2S-releasing Amino-Bisphosphonate which combines bone anti-catabolic and anabolic functions

Bisphosphonates (BPs) are the first-line treatment of bone loss resulting from various pathological conditions. Due to their high affinity to bone they have been used to develop conjugates with pro-anabolic or anti-catabolic drugs. We recently demontrated that hydrogen sulfide (H₂S), promotes osteogenesis and inhibits osteoclast differentiation. Here we developed an innovative molecule, named DM-22, obtained from the combination of alendronate (AL) and the H₂S-releasing moiety aryl-isothiocyanate. DM-22 and AL were assayed in vitro in the concentration range 1-33 μM for effects on viability and function of human osteoclasts (h-OCs) and mesenchymal stromal cells (h-MSCs) undergoing osteogenic differentiation. Amperometric measures revealed that DM-22 releases H₂S at a slow rate with a thiol-dependent mechanism. DM-22 significantly inhibited h-OCs differentiation and function, maintaining a residual h-OCs viability even at the high dose of 33 μM. Contrary to AL, in h-MSCs DM-22 did not induce cytotoxicity as revealed by LDH assay, significantly stimulated mineralization as measured by Alizarin Red staining and increased mRNA expression of Collagen I as compared to control cultures. In conclusion, DM-22 is a new BP which inhibits h-OCs function and stimulate osteogenic differentiation of h-MSCs, without cytotoxicity. DM-22 is an ideal candidate for a novel family of osteoanabolic drugs.

Effects of combination treatment with alendronate and raloxifene on skeletal properties in a beagle dog model

A growing number of studies have investigated combination treatment as an approach to treat bone disease. The goal of this study was to investigate the combination of alendronate and raloxifene with a particular focus on mechanical properties. To achieve this goal we utilized a large animal model, the beagle dog, used previously by our laboratory to study both alendronate and raloxifene monotherapies. Forty-eight skeletally mature female beagles (1–2 years old) received daily oral treatment: saline vehicle (VEH), alendronate (ALN), raloxifene (RAL) or both ALN and RAL. After 6 and 12 months of treatment, all animals underwent assessment of bone material properties using in vivo reference point indentation (RPI) and skeletal hydration using ultra-short echo magnetic resonance imaging (UTE-MRI). End point measures include imaging, histomorphometry, and mechanical properties. Bone formation rate was significantly lower in iliac crest trabecular bone of animals treated with ALN (-71%) and ALN+RAL (-81%) compared to VEH. In vivo assessment of properties by RPI yielded minimal differences between groups while UTE-MRI showed a RAL and RAL+ALN treatment regimens resulted in significantly higher bound water compared to VEH (+23 and +18%, respectively). There was no significant difference among groups for DXA- or CT-based measures lumbar vertebra, or femoral diaphysis. Ribs of RAL-treated animals were smaller and less dense compared to VEH and although mechanical properties were lower the material-level properties were equivalent to normal. In conclusion, we present a suite of data in a beagle dog model treated for one year with clinically-relevant doses of alendronate and raloxifene monotherapies or combination treatment with both agents. Despite the expected effects on bone remodeling, our study did not find the expected benefit of ALN to BMD or structural mechanical properties, and thus the viability of the combination therapy remains unclear.

Raloxifene Improves Bone Mechanical Properties in Mice Previously Treated with Zoledronate

Bisphosphonates represent the gold-standard pharmaceutical agent for reducing fracture risk. Long-term treatment with bisphosphonates can result in tissue brittleness which in rare clinical cases manifests as atypical femoral fracture. Although this has led to an increasing call for bisphosphonate cessation, few studies have investigated therapeutic options for follow-up treatment. The goal of this study was to test the hypothesis that treatment with raloxifene, a drug that has cell-independent effects on bone mechanical material properties, could reverse the compromised mechanical properties that occur following zoledronate treatment. Skeletally mature male C57Bl/6J mice were treated with vehicle (VEH), zoledronate (ZOL), or ZOL followed by raloxifene (RAL; 2 different doses). At the conclusion of 8 weeks of treatment, femora were collected and assessed with microCT and mechanical testing. Trabecular BV/TV was significantly higher in all treated animals compared to VEH with both RAL groups having significantly higher BV/TV compared to ZOL (+21%). All three drug-treated groups had significantly more cortical bone area, higher cortical thickness, and greater moment of inertia at the femoral mid-diaphysis compared to VEH with no difference among the three treated groups. All three drug-treated groups had significantly higher ultimate load compared to VEH-treated animals (+14 to 18%). Both doses of RAL resulted in significantly higher displacement values compared to ZOL-treated animals (+25 to +50%). In conclusion, the current work shows beneficial effects of raloxifene in animals previously treated with zoledronate. The higher mechanical properties of raloxifene-treated animals, combined with similar cortical bone geometry compared to animals treated with zoledronate, suggest that the raloxifene treatment is enhancing mechanical material properties of the tissue.

Atypical femoral fractures related to bisphosphonate treatment: issues and controversies related to their surgical management

AIMS

Treatment guidelines for atypical femoral fractures associated with bisphosphonates have not been established. We conducted a systematic review of the treatment of atypical femoral fractures first, to evaluate the outcomes of surgical fixation of complete atypical fractures and secondly, to assess whether prophylactic surgery is necessary for incomplete atypical fractures.

MATERIALS AND METHODS

Case reports and series were identified from the PubMed database and were included if they described the treatment of atypical femoral fractures. In total, 77 publications met our inclusion criteria and 733 patients with 834 atypical complete or incomplete femoral fractures were identified.

RESULTS

For complete fractures, internal fixation was predominantly achieved by intramedullary nailing. The mean time to healing post-operatively was 7.3 months (2 to 31). Revision surgery for nonunion or implant failure was needed in 77 fractures (12.6%). A greater percentage of fractures treated with plate fixation (31.3%) required revision surgery than those treated with intramedullary nailing (12.9%) (p < 0.01). Non-operative treatment of incomplete fractures failed and surgery was eventually needed in nearly half of the patients (47%), whereas prophylactic surgery was successful and achieved a 97% rate of healing.

CONCLUSION

Intramedullary nailing is the first-line treatment for a complete fracture, although the risk of delayed healing and revision surgery seems to be higher than with a typical femoral fracture. Non-operative treatment does not appear to be a reliable way of treating an incomplete fracture: prophylactic intramedullary nailing should be considered if the patient is in intractable pain. Radiographs of the opposite side should be obtained routinely looking for an asymptomatic fracture. Bisphosphonates must be discontinued but ongoing metabolic management in the form of calcium and/or vitamin D supplements is advisable. Teriparatide therapy can be considered as an alternative treatment. Cite this article: Bone Joint J 2017;99-B:295-302.

Effects of suppressed bone remodeling by minodronic acid and alendronate on bone mass, microdamage accumulation, collagen crosslinks and bone mechanical properties in the lumbar vertebra of ovariectomized cynomolgus monkeys

Collagen crosslinking is an important determinant of the quality of bone material. We have previously shown that suppressed bone turnover by high doses of minodronic acid and alendronate increases compressive strength of vertebra, but also increases microdamage accumulation, in monkey bone. The aim of this study is to examine the effects of these bisphosphonates on collagen crosslinks and intrinsic material properties, in addition to microdamage accumulation, in vertebral cancellous bone in ovariectomized cynomolgus monkeys. Sixty female monkeys aged 9-17years were divided into five groups: sham and ovariectomized groups were treated daily for 17months with lactose vehicle, and the other three groups were given minodronic acid daily at 0.015 or 0.15mg/kg or alendronate daily at 0.5mg/kg orally. After sacrifice, lumbar vertebrae were subjected to histomorphometry, microdamage measurement, analysis of collagen crosslinking and compressive mechanical tests. Minodronic acid caused dose-dependent suppression of increased bone remodeling due to ovariectomy, and low-dose minodronic acid suppressed remodeling same level as alendronate. However, low-dose minodronic acid did not change microdamage accumulation, collagen maturity and the pentosidine level, whereas high-dose minodronic acid and alendronate increased these parameters. Compressive ultimate load was increased following high-dose minodronic acid and alendronate, but no treatment altered the reduction in intrinsic material properties caused by ovariectomy. These findings suggest that deterioration of bone material and formation of pentosidine and microdamage induced by minodronic acid is less than that expected based on the extent of remodeling suppression, in comparison with alendronate, but this was not reflected in any significant change of mechanical properties.

Pharmacologically Inactive Bisphosphonates as an Alternative Strategy for Targeting Osteoclasts: In Vivo Assessment of 5-Fluorodeoxyuridine-Alendronate in a Preclinical Model of Breast Cancer Bone Metastases

Bisphosphonates have effects that are antiresorptive, antitumor, and antiapoptotic to osteoblasts and osteocytes, but an effective means of eliciting these multiple activities in the treatment of bone metastases has not been identified. Antimetabolite-bisphosphonate conjugates have potential for improved performance as a class of bone-specific antineoplastic drugs. The primary objective of the study was to determine whether an antimetabolite-bisphosphonate conjugate will preserve bone formation concomitant with antiresorptive and antitumor activity. 5-FdU-ale, a highly stable conjugate between the antimetabolite 5-fluoro-2'-deoxyuridine and the bisphosphonate alendronate, was tested for its therapeutic efficacy in a mouse model of MDA-MB231 breast cancer bone metastases. In vitro testing revealed osteoclasts to be highly sensitive to 5-FdU-ale. In contrast, osteoblasts had significantly reduced sensitivity. Tumor cells were resistant in vitro but in vivo tumor burden was nevertheless significantly reduced compared with untreated mice. Sensitivity to 5-FdU-ale was not mediated through inhibition of farnesyl diphosphate synthase activity, but cell cycle arrest was observed. Although serum tartrate-resistant acid phosphatase (TRAP) levels were greatly reduced by both drugs, there was no significant decrease in the serum bone formation marker osteocalcin with 5-FdU-ale treatment. In contrast, there was more than a fivefold decrease in serum osteocalcin levels with alendronate treatment (p < 0.001). This finding is supported by time-lapse micro-computed tomography analyses, which revealed bone formation volume to be on average 1.6-fold higher with 5-FdU-ale treatment compared with alendronate (p < 0.001). We conclude that 5-FdU-ale, which is a poor prenylation inhibitor but maintains potent antiresorptive activity, does not reduce bone formation and has cytostatic antitumor efficacy. These results document that conjugation of an antimetabolite with bisphosphonates offers flexibility in creating potent bone-targeting drugs with cytostatic, bone protection properties that show limited nephrotoxicity. This unique class of drugs may offer distinct advantages in the setting of targeted adjuvant therapy and chemoprevention of bone diseases. © 2016 American Society for Bone and Mineral Research.

Bisphosphonates and atypical subtrochanteric fractures of the femur

OBJECTIVES

Bisphosphonates are widely used as first-line treatment for primary and secondary prevention of fragility fractures. Whilst they have proved effective in this role, there is growing concern over their long-term use, with much evidence linking bisphosphonate-related suppression of bone remodelling to an increased risk of atypical subtrochanteric fractures of the femur (AFFs). The objective of this article is to review this evidence, while presenting the current available strategies for the management of AFFs.

METHODS

We present an evaluation of current literature relating to the pathogenesis and treatment of AFFs in the context of bisphosphonate use.

RESULTS

Six broad themes relating to the pathogenesis and management of bisphosphonate-related AFFs are presented. The key themes in fracture pathogenesis are: bone microdamage accumulation; altered bone mineralisation and altered collagen formation. The key themes in fracture management are: medical therapy and surgical therapy. In addition, primary prevention strategies for AFFs are discussed.

CONCLUSIONS

This article presents current knowledge about the relationship between bisphosphonates and the development of AFFs, and highlights key areas for future research. In particular, studies aimed at identifying at-risk subpopulations and organising surveillance for those on long-term therapy will be crucial in both increasing our understanding of the condition, and improving population outcomes.Cite this article: N. Kharwadkar, B. Mayne, J. E. Lawrence, V. Khanduja. Bisphosphonates and atypical subtrochanteric fractures of the femur. Bone Joint Res 2017;6:144-153. DOI: 10.1302/2046-3758.63.BJR-2016-0125.R1.

A Case Report of Bisphosphonate-induced Bilateral Osteoporotic Subtrochanteric Fracture Femurii: Review of Literature

INTRODUCTION

Osteoporosis is a significant health-care problem characterized by excessive skeletal fragility, susceptibility to low-trauma fractures in men as well as women. Any abnormality of the bone that reduces the strength of the bone predisposes it to mechanical failure during normal activity or with minimum trauma. The mechanical failure manifests itself as a fracture, and this fracture must be recognized as a pathological fracture if the patient is to be treated properly. Osteoporosis is one of the leading causes of such pathological fractures and accounts for 1.5 million fractures annually. In the following case report, we present a 56-year-old postmenopausal female patient with bilateral pathological subtrochanteric fracture femurii due to intake of bisphosponates for 4 years for osteoporosis. Bilateral pathological subtrochanteric femurii fractures are extremely uncommon injuries which occur in adults who sustain injuries due to trivial trauma. A variety of management modalities has been tried to treat this complex fracture pattern. Standard fixation treatment is intramedullary nailing.

CASE REPORT

A postmenopausal female of rheumatoid arthritis aged 56 years, presented to our emergency department with a history of trivial fall at home. Following the fall, she was unable to bear weight on bilateral feet and complained of deformity. History revealed consumption of bisphosphonates (tablet alendronate 10 mg) for the last 4 years and glucocorticoids for rheumatiod arthritis. Radiographs were taken, which revealed bilateral pathological subtrochanteric fracture femurii. After obtaining necessary fitness, the patient was taken up for surgery. Closed reduction and Internal fixation with long proximal femoral nail were done. Bisphosphonate intake was stopped and teriparatide 20 µg/day subcutaneously given for 3 months. Fracture healed after 3 months and patient resumed her daily activities.

CONCLUSION

In people taking long-term bisphoshponate therapy, symptomatic cortical stress reactions accompanied by evidence of a stress line across the cortical thickening suggest an increased risk of a complete stress fracture. The patients should be informed about the prodromal symptoms like pain and swelling, following this bisphosphonates should be stopped and teriparatide has to be started for osteoporosis.

Bone Mass Outcomes in Patients With Osteoporosis Treated With Risedronate After Alendronate Failure: a 12-Month Follow-Up Study

Oral bisphosphonates are the drugs most frequently used for the treatment of osteoporosis. Clinicians usually switch between these drugs in clinical practice based on differences in efficacy. We aim to investigate the reasons associated with switching between oral bisphosphonates and to evaluate bone mass response and the incidence of fractures 12 mo after the exchange in a cohort of patients with osteoporosis seen at a tertiary hospital. Patients with osteoporosis who switched between oral bisphosphonates between January 2007 and December 2014 were included. Bone mass measured by dual-energy X-ray absorptiometry and the incidence of fracture were evaluated. A total of 112 patients (73.1 yr old on average, 95.5% women, 98% postmenopausal) were included. All patients were taking alendronate at the time of the switch to risedronate. In 91 patients (81.3%), the following reasons for the exchange of medication were identified: bone loss (59.8%), adverse events (11.6%), and recent fragility fracture (10.7%). One year after the switch, bone densitometry revealed bone loss in 51 patients (45.5%), bone mass maintenance in 34 (30.4%), and bone mass gain in 27 (24.1%). No new vertebral fracture was detected and no nonvertebral fracture was reported in 12 mo of follow-up. Bone mass outcomes (gain, loss, or maintenance) were not associated with the reason for switching between oral bisphosphonates. Similarly, none of the parameters evaluated could predict good densitometric response (gain or maintenance) in this scenario. Our findings suggest that the use of risedronate should not be recommended in the scenario of treatment failure or adverse events following the use of alendronate.

Protection From Glucocorticoid-Induced Osteoporosis by Anti-Catabolic Signaling in the Absence of Sost/Sclerostin

Excess of glucocorticoids, either due to disease or iatrogenic, increases bone resorption and decreases bone formation and is a leading cause of osteoporosis and bone fractures worldwide. Improved therapeutic strategies are sorely needed. We investigated whether activating Wnt/β-catenin signaling protects against the skeletal actions of glucocorticoids, using female mice lacking the Wnt/β-catenin antagonist and bone formation inhibitor Sost. Glucocorticoids decreased the mass, deteriorated the microarchitecture, and reduced the structural and material strength of bone in wild-type (WT), but not in Sost^-/- mice. The high bone mass exhibited by Sost^-/- mice is due to increased bone formation with unchanged resorption. However, unexpectedly, preservation of bone mass and strength in Sost^-/- mice was due to prevention of glucocorticoid-induced bone resorption and not to restoration of bone formation. In WT mice, glucocorticoids increased the expression of Sost and the number of sclerostin-positive osteocytes, and altered the molecular signature of the Wnt/β-catenin pathway by decreasing the expression of genes associated with both anti-catabolism, including osteoprotegerin (OPG), and anabolism/survival, such as cyclin D1. In contrast in Sost^-/- mice, glucocorticoids did not decrease OPG but still reduced cyclin D1. Thus, in the context of glucocorticoid excess, activation of Wnt/β-catenin signaling by Sost/sclerostin deficiency sustains bone integrity by opposing bone catabolism despite markedly reduced bone formation and increased apoptosis. This crosstalk between glucocorticoids and Wnt/β-catenin signaling could be exploited therapeutically to halt resorption and bone loss induced by glucocorticoids and to inhibit the exaggerated bone formation in diseases of unwanted hyperactivation of Wnt/β-catenin signaling. © 2016 American Society for Bone and Mineral Research.

Bilateral distal fibula fractures in a woman on long-term bisphosphonate therapy

We report the case of a 53-year-old female, treated by bisphosphonate for 12 years, who presented atraumatic fractures of both fibulas. Her X-rays showed bilateral distal fibula fractures with radiological features similar to atypical femur fractures. The distal fibula should be considered as a potential site for stress fractures in bisphosphonate users. Bisphosphonates are the most widely used drugs in the treatment of osteoporosis. During the last decade, the occurrence of atypical fractures, mostly subtrochanteric and diaphyseal femoral fractures, has been acknowledged in patients with long-term use of bisphosphonates. We report the case of a 53-year-old female on alendronate therapy for the past 12 years who presented with a few months history of atraumatic right, and subsequently left, lateral ankle pain. Her X-rays showed bilateral distal fibula fractures with radiological features similar to atypical femur fractures. She had been treated conservatively with walking boots and her treatment with bisphosphonate had been stopped 5 months prior to the fractures. Callus was progressively seen on serial follow-up X-rays, and both fractures healed completely within a reasonable period of 1 year. Investigations did not reveal any secondary causes of osteoporosis or metabolic bone disorders. To our knowledge, this is the first reported case of bilateral distal fibula fractures in a patient on long-term bisphosphonate therapy.

In vivo effects of two novel ALN-EP4a conjugate drugs on bone in the ovariectomized rat model for reversing postmenopausal bone loss

Two alendronate-EP4 agonist (ALN-EP4a) conjugate drugs, C1 and C2, which differ in structure by a short linker molecule, were evaluated in ovariectomized (OVX) rats for their anabolic effects. We showed that C1 led to significant anabolic effects on cortical and trabecular bone while anabolic effects associated with C2 were minimal.

INTRODUCTION

EP4as were covalently linked to ALN to create ALN-EP4a conjugate anabolic bone drugs, C1 and C2, which differ in structure by a short linker molecule in C1. When administered systemically, C1 and C2 are delivered to bone through targeted binding of ALN, where local hydrolytic enzymes liberate EP4a from ALN to exert anabolic effects. Here, we compare effects of C1 to C2 in a curative in vivo study.

METHODS

Three-month-old female Sprague Dawley rats were OVX or sham operated and allowed to lose bone for 3 months. Animals were then treated via tail vein injections for 3 months and sacrificed. Treatment groups were as follows: C1L (5 mg/kg biweekly), C1H (5 mg/kg weekly), C2L (15 mg/kg monthly), C2H (15 mg/kg biweekly), OVX and sham control (phosphate-buffered saline (PBS) biweekly), and ALN/EP4a-unconjugated mixture (0.75 mg/kg each biweekly).

RESULTS

MicroCT analysis showed that C1H treatment significantly increased vertebral bone mineral density (vBMD) and trabecular bone volume versus OVX controls while C2 treatments did not. Biomechanical testing showed that C1H treatment but not C2 treatments led to significant improvement in the load bearing abilities of the vertebrae compared to OVX controls. C1 stimulated endocortical bone formation and increased load bearing in femurs, while C2 did not.

CONCLUSIONS

We showed that C1 led to significant anabolic effects on cortical and trabecular bone while anabolic effects associated with C2 were minimal. These results led us to hypothesize a mode of action by which presence of a linker is crucial in facilitating the anabolic effects of EP4a when dosed as a prodrug with ALN.

Role of microcracks in the pathogenesis of bisphosphonate-related osteonecrosis of the jaw

OBJECTIVES

The aim of this study was to investigate the potential role of microcrack accumulation in the pathogenesis of bisphosphonate-related osteonecrosis of the jaw (ONJ) through an animal model.

MATERIALS AND METHODS

Twenty-four ovariectomized rats were randomly divided into a bisphosphonate group (n = 19) and control group (n = 5) and weekly injected with zoledronic acid and normal saline, respectively. After 6 weeks, surgical intervention was performed, and the injections were continued for eight additional weeks. Then, the animals were sacrificed, and ONJ lesions were inspected for the presence of microcracks using scanning electron microscopy. Measurements included bone dimension, number of cracks, crack length, and normalized indices; crack density (Cr.Dn) and crack surface density (Cr.S.Dn) were used for group comparison.

RESULTS

Both number of cracks and crack length in the bisphosphonate group were greater than those in the control group (P < 0.05). Of the 19 rats injected with bisphosphonates, 13 rats (68.4 %) were classified into the ONJ group. Cr.Dn and Cr.S.Dn were significantly greater in the ONJ group than in the non-ONJ group, indicating accumulation of unrepaired microcracks (P < 0.05). Seventy-two percent of microcracks in the ONJ group conformed to the defined length that was considered significant according to a previous literature (30-80 μm); whereas 12 % of microcracks in the non-ONJ group were considered significant (P < 0.05).

CONCLUSION

Accumulation of unrepaired microcracks was significantly associated with the development of bisphosphonate-related ONJ. Further research is required to determine the role of microcracks in the pathogenesis of bisphosphonate-related ONJ.

CLINICAL RELEVANCE

Long-term bisphosphonates use may deteriorate the biomechanical and physiological bone integrity, contributing to the pathogenesis of bisphosphonate-related ONJ.