Histomorphometric assessment of the long-term effects of alendronate on bone quality and remodeling in patients with osteoporosis

Differences in bone histomorphometry between White postmenopausal women with and without atypical femoral fracture after long-term bisphosphonate therapy

Bone histomorphometric endpoints in transilial biopsies may be associated with an increased risk of atypical femoral fracture (AFF) in patients with osteoporosis who take antiresorptives, including bisphosphonates (BPs). One way to test this hypothesis is to evaluate bone histomorphometric endpoints in age-, gender-, and treatment time-matched patients who either had AFF or did not have AFF. In this study, we performed transiliac bone biopsies in 52 White postmenopausal women with (n = 20) and without (n = 32) AFFs, all of whom had been treated for osteoporosis continuously with alendronate for 4-17 yr. Despite the matched range of treatment duration (4-17 yr), AFF patients received alendronate for significantly longer time (10.7 yr) than non-AFF patients (8.0 yr) (P = .014). Bone histomorphometric endpoints reflecting microstructure and turnover were assessed in cancellous, intracortical, and endocortical envelopes from transilial biopsy specimens obtained from BP-treated patients 3-6 mo after AFF and from non-AFF patients with similar age-, gender-, and range of BP treatment duration. However, in both cancellous and intracortical envelopes, AFF patients had significantly lower wall thickness (W.Th) and higher osteoclast surface (Oc.S/BS) than non-AFF patients. In addition, AFF patients had significantly higher eroded surface (ES/BS) only in the intracortical envelope. None of the dynamic variables related to bone formation and turnover differed significantly between the groups. In conclusion, in the ilium of BP-treated patients with osteoporosis, AFF patients have lower thickness of superficial bone (lower W.Th) of the cancellous and cortical envelopes than non-AFF patients. AFF and non-AFF patients have a similar bone turnover rate in the ilium. Furthermore, in this population, as in previous work, AFF is more likely to occur in BP-treated patients with longer treatment duration.

Clinical Data for Parametrization of In Silico Bone Models Incorporating Cell-Cytokine Dynamics: A Systematic Review of Literature

In silico simulations aim to provide fast, inexpensive, and ethical alternatives to years of costly experimentation on animals and humans for studying bone remodeling, its deregulation during osteoporosis and the effect of therapeutics. Within the varied spectrum of in silico modeling techniques, bone cell population dynamics and agent-based multiphysics simulations have recently emerged as useful tools to simulate the effect of specific signaling pathways. In these models, parameters for cell and cytokine behavior are set based on experimental values found in literature; however, their use is currently limited by the lack of clinical in vivo data on cell numbers and their behavior as well as cytokine concentrations, diffusion, decay and reaction rates. Further, the settings used for these parameters vary across research groups, prohibiting effective cross-comparisons. This review summarizes and evaluates the clinical trial literature that can serve as input or validation for in silico models of bone remodeling incorporating cells and cytokine dynamics in post-menopausal women in treatment, and control scenarios. The GRADE system was used to determine the level of confidence in the reported data, and areas lacking in reported measures such as binding site occupancy, reaction rates and cell proliferation, differentiation and apoptosis rates were highlighted as targets for further research. We propose a consensus for the range of values that can be used for the cell and cytokine settings related to the RANKL-RANK-OPG, TGF-β and sclerostin pathways and a Levels of Evidence-based method to estimate parameters missing from clinical trial literature.

Alendronate prolongs the reversal-resorption phase in human cortical bone remodeling

Despite their ability to reduce fracture-risk and increase Bone Mineral Density (BMD) in osteoporotic women, bisphosphonates are reported to reduce formation of new bone. Reduced bone formation has been suggested to lead to accumulation of microfractures and contribute to rare side effects in cortical bone such as atypical femur fractures. However, most studies are limited to trabecular bone. In this study, the cortical bone remodeling in human iliac bone specimens of 65 non-treated and 24 alendronate-treated osteoporotic women was investigated using a new histomorphometric classification of intracortical pores. The study showed that only 12.4 ± 11% of the cortical pore area reflected quiescent pores/osteons in alendronate-treated patients versus 8.5 ± 5% in placebo, highlighting that new cortical remodeling events remain to be activated. The percent and size of eroded pores (events in resorption-reversal phase) remained unchanged, but their contribution to total pore area was 1.4-fold higher in alendronate versus placebo treated patients (66 ± 22% vs 48 ± 22%, p < 0.001). On the other hand, the mixed eroded-formative pores (events with mixed resorption-reversal-formation phases) was 2-fold lower in alendronate versus placebo treated patients (19 ± 14% vs 39 ± 23% of total pore area, p < 0.001), and formative pores (event in formation phase) was 2.2-fold lower in alendronate versus placebo treated patients (2.1 ± 2.4% vs 4.6 ± 3.6%, p < 0.01), and their contribution to total pore area was 2.4-fold lower (1.3 ± 2.1% vs 3.1 ± 4.4%, p < 0.05). Importantly, these differences between alendronate and placebo treated patients were significant in patients after 3 years of treatment, not after 2 years of treatment. Collectively, the results support that cortical remodeling events activated during alendronate treatment has a prolonged reversal-resorption phase with a delayed transition to formation, becoming increasingly evident after 3-years of treatment. A potential contributor to atypical femur fractures associated with long-term bisphosphonate treatment.

Romosozumab and antiresorptive treatment: the importance of treatment sequence

To evaluate whether treatment sequence affects romosozumab response, this analysis reviewed studies where romosozumab was administered before or following an antiresorptive (alendronate or denosumab). Initial treatment with romosozumab followed by an antiresorptive resulted in larger increases in bone mineral density of both hip and spine compared with the reverse sequence.

INTRODUCTION

Teriparatide followed by an antiresorptive increases bone mineral density (BMD) more than using an antiresorptive first. To evaluate whether treatment sequence affects romosozumab response, we reviewed randomized clinical trials where romosozumab was administered before (ARCH, FRAME) or following (STRUCTURE, Phase 2 extension) an antiresorptive (alendronate or denosumab, respectively).

METHODS

We evaluated BMD percentage change for total hip (TH) and lumbar spine (LS) and response rates (BMD gains ≥ 3% and ≥ 6%) at years 1 and 2 (except STRUCTURE with only 1-year data available).

RESULTS

With 1-year romosozumab initial therapy in ARCH and FRAME, TH BMD increased 6.2% and 6.0%, and LS BMD increased 13.7% and 13.1%, respectively. When romosozumab was administered for 1 year after alendronate (STRUCTURE) or denosumab (Phase 2 extension), TH BMD increased 2.9% and 0.9%, respectively, and LS BMD increased 9.8% and 5.3%, respectively. Over 2 years, TH and LS BMD increased 7.1% and 15.2% with romosozumab/alendronate, 8.5% and 16.6% with romosozumab/denosumab, and 3.8% and 11.5% with denosumab/romosozumab, respectively. A greater proportion of patients achieved BMD gains ≥ 6% when romosozumab was used first, particularly for TH, versus the reverse sequence (69% after romosozumab/denosumab; 15% after denosumab/romosozumab).

CONCLUSION

In this study, larger mean BMD increases and greater BMD responder rates were achieved when romosozumab was used before, versus after, an antiresorptive agent. Since BMD on treatment is a strong surrogate for bone strength and fracture risk, this analysis supports the thesis that initial treatment with romosozumab followed by an antiresorptive will result in greater efficacy versus the reverse sequence.

Added effect of 1% topical alendronate in intra-bony and inter-radicular defects as part of step II periodontal therapy: a systematic review with meta-analysis and trial sequential analysis

Background

This systematic review and meta-analysis aimed to investigate the role of alendronate combined with step 2 of periodontal therapy in reducing probing pocket depth, improving clinical attachment level, and reducing bone defect depth in intra-bony and inter-radicular defects.

Methods

RCTs with more than 6 months follow-up were included in this study. Risk of bias assessment was performed using the Cochrane collaboration tool. In addition, meta-analysis and trial sequential analysis were used to aggregate the available evidence.

Results

Seven studies met the inclusion criteria and were included in the systematic review. Topical application of alendronate during second step of periodontal therapy significantly improved PD and CAL.

Conclusion

Local application of alendronate may confer a beneficial effect when applied during step II of periodontal therapy even if long term studies are needed to confirm these results.

Clinical relevance

Considering the emerging role of host-inflammatory response in treatment of periodontitis and the antiresorptive and osteostimulative properties of bisphosphonates, several studies are focusing on the role of alendronate as an addition to non-surgical periodontal therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02044-1.

Interest of Bone Histomorphometry in Bone Pathophysiology Investigation: Foundation, Present, and Future

Despite the development of non-invasive methods, bone histomorphometry remains the only method to analyze bone at the tissue and cell levels. Quantitative analysis of transiliac bone sections requires strict methodologic conditions but since its foundation more 60 years ago, this methodology has progressed. Our purpose was to review the evolution of bone histomorphometry over the years and its contribution to the knowledge of bone tissue metabolism under normal and pathological conditions and the understanding of the action mechanisms of therapeutic drugs in humans. The two main applications of bone histomorphometry are the diagnosis of bone diseases and research. It is warranted for the diagnosis of mineralization defects as in osteomalacia, of other causes of osteoporosis as bone mastocytosis, or the classification of renal osteodystrophy. Bone biopsies are required in clinical trials to evaluate the safety and mechanism of action of new therapeutic agents and were applied to anti-osteoporotic agents such as bisphosphonates and denosumab, an anti-RANKL, which induces a marked reduction of the bone turnover with a consequent elongation of the mineralization period. In contrast, an increased bone turnover with an extension of the formation site is observed with teriparatide. Romosozumab, an anti-sclerostin, has a dual effect with an early increased formation and reduced resorption. Bone histomorphometric studies allow us to understand the mechanism of coupling between formation and resorption and to evaluate the respective role of bone modeling and remodeling. The adaptation of new image analysis techniques will help bone biopsy analysis in the future.

Bone Quality and Fractures in Women With Osteoporosis Treated With Bisphosphonates for 1 to 14 Years

Oral bisphosphonates are the primary medication for osteoporosis, but concerns exist regarding potential bone-quality changes or low-energy fractures. This cross-sectional study used artificial intelligence methods to analyze relationships among bisphosphonate treatment duration, a wide variety of bone-quality parameters, and low-energy fractures. Fourier transform infrared spectroscopy and histomorphometry quantified bone-quality parameters in 67 osteoporotic women treated with oral bisphosphonates for 1 to 14 years. Artificial intelligence methods established two models relating bisphosphonate treatment duration to bone-quality changes and to low-energy clinical fractures. The model relating bisphosphonate treatment duration to bone quality demonstrated optimal performance when treatment durations of 1 to 8 years were separated from treatment durations of 9 to 14 years. This may be due to a change in relationship of bone-quality parameters with treatment duration. This model also showed that the effects of bisphosphonate treatment duration were most highly correlated with changes in means and standard deviations of infrared spectroscopically derived mineral and matrix parameters and histomorphometric bone turnover parameters. A second model related treatment duration to bone fracture in all 22 patients who fractured while on treatment with bisphosphonates for more than 8 years. This second model showed that bisphosphonate treatment duration, not hip bone mineral density (BMD), was the most strongly correlated parameter to these low-energy bone fractures. Application of artificial intelligence enabled analysis of large quantities of structural, cellular, mineral, and matrix bone-quality parameters to determine relationships with long-term oral bisphosphonate treatment and fracture. Infrared spectroscopy provides clinically relevant bone-quality information of which bone mineral purity is among the most relevant. Nine or more years of bisphosphonate treatment was associated with abnormal bone mineral purity, matrix abnormalities, and low-energy fractures. These data justify limiting bisphosphonate treatment duration to 8 years. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Persistent bone resorption lacunae on necrotic bone distinguish bisphosphonate-related osteonecrosis of jaw from denosumab-related osteonecrosis

BACKGROUND

Bisphosphonate and denosumab are widely used for the treatment of osteoporosis and bone metastasis of cancer to prevent excessive bone resorption. Osteonecrosis of the jaw is a serious adverse effect of bisphosphonate or denosumab referred to as bisphosphonate-related osteonecrosis of the jaw (BRONJ) or denosumab-related osteonecrosis of the jaw (DRONJ), respectively. Since bisphosphonate and denosumab inhibit bone resorption by different mechanism, we evaluated whether these drug types result in different histopathological characteristics related to bone resorption.

MATERIALS AND METHODS

We histopathologically investigated 10 cases of BRONJ, DRONJ, and suppurative osteomyelitis. Paraffin sections prepared from decalcified dissected jaw bones were used for histopathological observation, second harmonic generation imaging, and bone histomorphometry. The samples were also observed by a scanning electron microscope.

RESULTS

Numerous bone resorption lacunae were observed on the necrotic bone surface in almost all cases of BRONJ; however, such resorption lacunae were limited in DRONJ and suppurative osteomyelitis. Prominent bone resorption lacunae were also confirmed by second harmonic generation imaging and scanning electron microscopy in BRONJ, but not in DRONJ or suppurative osteomyelitis. As determined by bone histomorphometry, the number of bone resorption lacunae and the length of the erosion surface of resorption lacunae were significantly higher in BRONJ group than in the DRONJ and suppurative osteomyelitis groups. These parameters were correlated between the necrotic bones and the vital bones in BRONJ.

CONCLUSIONS

Persistent bone resorption lacunae on the necrotic bone surface are unique to BRONJ, providing a basis for distinguishing BRONJ from DRONJ and OM in histopathological diagnosis.

Bisphosphonates impair the onset of bone formation at remodeling sites

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

Raman spectroscopy investigation shows that mineral maturity is greater in CD-1 than in C57BL/6 mice distal femurs after sexual maturity

Purpose/Aim of the study mice are the most often used pre-clinical lab models for studying the pathologies of bone mineralization. However, recent evidence suggests that two of the most often used mice strains (C57BL/6J and CD-1) might show differences in the bone mineralization process. This study sought to investigate the main compositional properties of bone tissue between nonpathological C57BL/6J and CD-1 murine knee joints. Materials and Methods : to this end, medial and lateral condylar subchondral bones and the adjacent diaphyseal cortical bone of 13 murine femurs (n = 7 C57BL/6J and n = 6 CD-1 at eight weeks old, just after sexual maturation) were analyzed with ex vivo Raman spectroscopy. Results : regardless of the bone tissue analyzed, our results showed that CD-1 laboratory mice present a more mature mineral phase than C57BL/6J laboratory mice, but present no difference in maturity of the collagen phase. For both strains, the subchondral bone of the medial condylar and cortical bone from the diaphysis have similar compositional properties, and CD-1 presents less variation than C57BL/6J. Furthermore, we depict a novel parametric relationship between the crystallinity and carbonate-to-amide-I ratio that might help in deciphering the mineral maturation process that occurs during bone's mineralization. Conclusions : Our results suggest that the timing of bone maturation might be different between non-pathological C57BL/6J and CD-1 murine knee femurs.

Zoledronate

Zoledronate is the most potent and most long-acting bisphosphonate in clinical use, and is administered as an intravenous infusion. Its major uses are in osteoporosis, Paget's disease, and in myeloma and cancers to reduce adverse skeletal related events (SREs). In benign disease, it is a first- or second-line treatment for osteoporosis, achieving anti-fracture efficacy comparable to that of the RANKL blocker, denosumab, over 3 years, and it reduces fracture risk in osteopenic older women. It is the preferred treatment for Paget's disease, achieving higher rates of remissions which are much more prolonged than with any other agent. Some trials have suggested that it reduces mortality, cardiovascular disease and cancer, but these findings are not consistent across all studies. It is nephrotoxic, so should not be given to those with significant renal impairment, and, like other potent anti-resorptive agents, can cause hypocalcemia in patients with severe vitamin D deficiency, which should be corrected before administration. Its most common adverse effect is the acute phase response, seen in 30-40% of patients after their first dose, and much less commonly subsequently. Clinical trials in osteoporosis have not demonstrated increases in osteonecrosis of the jaw or in atypical femoral fractures. Observational databases are currently inadequate to determine whether these problems are increased in zoledronate users. Now available as a generic, zoledronate is a cost-effective agent for fracture prevention and for management of Paget's disease, but wider provision of infusion facilities is important to increase patient access. There is a need to further explore its potential for reducing cancer, cardiovascular disease and mortality, since these effects could be substantially more important than its skeletal actions.

Circular RNA atlas in osteoclast differentiation with and without alendronate treatment

BACKGROUND

Alendronate (AL) is the most widely used bisphosphonate in the treatment of osteoporosis (OP). However, the role of circular RNAs (circRNAs) in the treatment of OP with AL remains unclear.

METHODS

In this study, we showed that osteoclast (OC) precursors (OPCSs) could be induced into OCs with macrophage colony-stimulating factor (MCSF) and receptor activator of nuclear factor-κB ligand (RANKL) treatment. Subsequently, the OCs were treated with AL. OC differentiation-related biomarkers including RANK, tartrate-resistant acid phosphatase (TRAP), and cathepsin K (CTSK) were analyzed with TRAP staining, quantitative real-time (qPCR), and western blotting. Differentially expressed circRNAs (DECs) were identified among the OPCS, OC, and OC + AL groups. In addition, the expression levels of 10 DECs related to OC differentiation were verified by qPCR.

RESULTS

TRAP staining showed that MCSF and RANKL treatment effectively induced OPCSs to differentiate into OCs. In addition, qPCR and western blot analysis revealed that the three biomarkers of OC (RANK, TRAP, and CTSK) were expressed significantly more in the OC group than those in the OPCS group. In contrast, the mRNA and protein expression levels of these three biomarkers decreased significantly in OCs treated with AL compared with those non-treated OCs. GO analysis of the DECs in the OPCS group vs. the OC group revealed that their functions were mainly related to cell, cell part, binding, and single-organism terms. KEGG analysis of the top 20 DECs in a comparison between the OPCS and OC groups showed that genes involved in mitogen-activated protein kinase signaling were the most common. Results of functional analyses of DECs in an OC vs. OC + AL comparison were similar to those in the OPCS vs. OC comparison. Finally, qPCR showed that, in the OC + AL vs. OC group comparison, the expression levels of seven and three DECs significantly decreased and increased, respectively.

CONCLUSIONS

Having successfully induced OPCSs to differentiate into OCs, we showed that AL suppresses the differentiation of OPCS into OC and that 10 DECs were involved in the regulation of this process. This indicates that these DECs might be important to the treatment of OP.

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.

The effect of bisphosphosphonates on bone turnover and bone balance in postmenopausal women with osteoporosis: The T-score bone marker approach in the TRIO study

Postmenopausal osteoporosis is characterised by increased bone turnover and an imbalance between bone resorption and formation. Bisphosphonate treatment reduces bone turnover but their effect on bone balance is yet to be fully investigated. Using the T-score approach our aims were to: i) investigate the effects of oral nitrogen-containing bisphosphonates on bone balance and turnover in postmenopausal women with osteoporosis and ii) determine the relationship of the change in bone balance and turnover with the change in BMD at the lumbar spine and total hip. Women were recruited, mean age 67 years, and randomised to receive: ibandronate (n = 55, 150 mg/month), alendronate (n = 54, 70 mg/week) or risedronate (n = 56, 35 mg/week). They also received calcium and vitamin D daily. A fasting serum sample was collected at baseline and weeks 1, 2, 4, 12, 13, 48 and 96. The control group were 226 healthy premenopausal women receiving no treatments. PINP and CTX were measured using the iSYSIDS analyser and BMD (in g/cm2) of the lumbar spine and total hip were measured by DXA (Hologic Inc). PINP and CTX values were log10-transformed and normalised. T-scores were calculated using the mean and standard deviation from the premenopausal group. Bone turnover and bone balance were calculated from the T-scores. Mean levels (95% CI) of balance and turnover are shown in the table. The change in turnover at weeks 4, 12 and 48 was inversely correlated with the change in lumbar spine and total hip BMD at weeks 48 and 96, (p < .01 to p < .001). The change in balance at week 4 positively correlated with the change in total hip BMD at weeks 48, (p < .01). Bisphosphonates resulted in an initial positive balance and a reduction in turnover. Some of these changes were associated with increases in BMD. Bone turnover is a better predictor of BMD than bone balance.

Osteoporosis Therapeutics 2020

Numerous safe and efficient drug therapies are currently available to decrease risk of low trauma fractures in patients with osteoporosis including postmenopausal, male, and secondary osteoporosis. In this chapter, we give first an overview of the most important outcomes regarding fracture risk reduction, change in bone mineral density (BMD by DXA) and/or bone markers of the phase III clinical studies of well-established therapies (such as Bisphosphonates, Denosumab or Teriparatide) and also novel therapies (such as Romosozumab or Abaloparatide) and highlight their mechanisms of action at bone tissue/material level. The latter understanding is not only essential for the choice of drug, duration and discontinuation of treatment but also for the interpretation of the clinical outcomes (in particular of eventual changes in BMD) after drug administration. In the second part of this chapter, we focus on the management of different forms of osteoporosis and give a review of the respective current guidelines for treatment. Adverse effects of treatment such as atypical femoral fractures, osteonecrosis of the jaw or influence of fracture healing are considered also in this context.

Comparison of bone biomechanical properties after bone marrow mesenchymal stem cell or alendronate treatment in an osteoporotic animal model

The aim of this study was to explore the effects of bone marrow mesenchymal stem cells (BMMSCs) and alendronate sodium (ALN) intervention on osteoporosis (OP). Sixty-eight 6-month-old healthy female Sprague Dawley (SD) rats were used to generate an OP model by removal of the ovaries. After 12 weeks, rats were treated with BMMSCs (BMMSC group) or ALN (ALN group) for 5 weeks. Serum type I collagen C terminal peptide (CTX_1), procollagen type I N-terminal propeptide (PINP), and bone alkaline phosphatase (BALP) were tested along with the femur bone density and other properties, including bone mineral density (BMD), BALP, percent trabecular area (BV/TV), trabecular thickness (Tb.Th), trabecular number (TbN), maximum load, maximum stress, maximum strain, and elastic modulus. BMD, BALP, BV/TV, Tb.Th, TbN, maximum load, maximum stress, maximum strain, and elastic modulus values were higher in the BMMSC group versus the ALN group relative to the control group (p < 0.05); CTX_1, PINP, trabecular separation (Tb.Sp), and osteoclast number (OC.N) were lowest in the BMMSC group versus the ALN group relative to the control group (p < 0.05). Both BMMSCs and ALN could improve the metabolic function and bone quality in osteoporotic mice while restoring the strength and toughness of bones. The intervention effects of BMMSCs are better than ALN in this model.

Update on Menopausal Hormone Therapy for Fracture Prevention

PURPOSE OF REVIEW

The goal of the review is to assess the appropriateness of menopausal hormone therapy (MHT) for the primary prevention of bone loss in women at elevated risk in the early years after menopause.

RECENT FINDINGS

Estrogen alone or combined with progestin to protect the uterus from cancer significantly reduces the risk of osteoporosis-related fractures. MHT increases type 1 collagen production and osteoblast survival and maintains the equilibrium between bone resorption and bone formation by modulating osteoblast/osteocyte and T cell regulation of osteoclasts. Estrogens have positive effects on muscle and cartilage. Estrogen, but not antiresorptive therapies, can attenuate the inflammatory bone-microenvironment associated with estrogen deficiency. However, already on second year of administration, MHT is associated with excess breast cancer risk, increasing steadily with duration of use. MHT should be considered in women with premature estrogen deficiency and increased risk of bone loss and osteoporotic fractures. However, MHT use for the prevention of bone loss is hindered by increase in breast cancer risk even in women younger than 60 years old or who are within 10 years of menopause onset.

Subchondral bone deterioration in femoral heads in patients with osteoarthritis secondary to hip dysplasia: A case-control study

Objectives

Residual hip dysplasia is the most common underlying condition leading to secondary osteoarthritis (OA) of the hip. Subchondral bone alterations in OA secondary to hip dysplasia (HD-OA) are poorly investigated. The aim of the present study was to analyse the microarchitecture, bone remodelling and pathological alterations of subchondral bone in femoral heads from patients with HD-OA.

Methods

Subchondral bone specimens were extracted from both weight-bearing and non–weight-bearing regions of femoral heads from 20 patients with HD-OA and 20 patients with osteoporotic femoral neck fracture, during hip replacement surgery. Micro-CT and histological examination were performed to assess the microarchitecture and histopathological changes.

Results

The weight-bearing subchondral bone showed significantly more sclerotic microarchitecture and higher bone remodelling level in HD-OA as compared with osteoporosis. In the non–weight-bearing region, the two diseases shared similar microarchitectural characteristics, but higher bone remodelling level was detected in HD-OA. Distinct regional differences were observed in HD-OA, whereas the two regions exhibited similar characteristics in osteoporosis. In addition, HD-OA displayed more serious pathological alterations, including subchondral bone cyst, metaplastic cartilaginous tissue, bone marrow oedema and fibrous tissue, especially in the weight-bearing region.

Conclusions

Osteoarthritic deteriorations of subchondral bone induced by hip dysplasia spread throughout the whole joint, but exhibit region-dependent variations, with the weight-bearing region more seriously affected. Biomechanical stress might exert a pivotal impact on subchondral bone homeostasis in hip dysplasia.

The translational potential of this article

The histomorphometric findings in the project indicate an early intervention for the development of hip dysplasia in clinic.

Pamidronate Administration During Pregnancy and Lactation Induces Temporal Preservation of Maternal Bone Mass in a Mouse Model of Osteogenesis Imperfecta

During pregnancy and lactation, the maternal skeleton undergoes significant bone loss through increased resorption to provide the necessary calcium supply to the developing fetus and suckling neonate. This period of skeletal vulnerability has not been clearly associated with increased maternal fracture risk, but these physiological conditions can exacerbate an underlying metabolic bone condition like osteogenesis imperfecta. Although bisphosphonates (BPs) are commonly used in postmenopausal women, there are cases where premenopausal women taking BPs become pregnant. Given BPs' long half-life, there is a need to establish how BPs affect the maternal skeleton during periods of demanding metabolic bone changes that are critical for the skeletal development of their offspring. In the present study, pamidronate- (PAM-) amplified pregnancy-induced bone mass gains and lactation-induced bone loss were prevented. This preservation of bone mass was less robust when PAM was administered at late stages of lactation compared with early pregnancy and first day of lactation. Pregnancy-induced osteocyte osteolysis was also observed and was unaffected with PAM treatment. No negative skeletal effects were observed in offspring from PAM-treated dams despite lactation-induced bone loss prevention. These findings provide important insight into (1) a treatment window for when PAM is most effective in preserving maternal bone mass, and (2) the maternal changes in bone metabolism that maintain calcium homeostasis crucial for fetal and neonatal bone development. © 2019 American Society for Bone and Mineral Research.

Bone-Forming and Antiresorptive Effects of Romosozumab in Postmenopausal Women With Osteoporosis: Bone Histomorphometry and Microcomputed Tomography Analysis After 2 and 12 Months of Treatment

Sclerostin, a protein produced by osteocytes, inhibits bone formation. Administration of sclerostin antibody results in increased bone formation in multiple animal models. Romosozumab, a humanized sclerostin antibody, has a dual effect on bone, transiently increasing serum biochemical markers of bone formation and decreasing serum markers of bone resorption, leading to increased BMD and reduction in fracture risk in humans. We aimed to evaluate the effects of romosozumab on bone tissue. In a subset of 107 postmenopausal women with osteoporosis in the multicenter, international, randomized, double-blind, placebo-controlled Fracture Study in Postmenopausal Women with Osteoporosis (FRAME), transiliac bone biopsies were performed either after 2 (n = 34) or 12 (n = 73) months of treatment with 210 mg once monthly of romosozumab or placebo to evaluate histomorphometry and microcomputed tomography-based microarchitectural endpoints. After 2 months, compared with either baseline values assessed after a quadruple fluorochrome labeling or placebo, significant increases (P < 0.05 to P < 0.001) in dynamic parameters of formation (median MS/BS: romosozumab 1.51% and 5.64%; placebo 1.60% and 2.31% at baseline and month 2, respectively) were associated with a significant decrease compared with placebo in parameters of resorption in cancellous (median ES/BS: placebo 3.4%, romosozumab 1.8%; P = 0.022) and endocortical (median ES/BS: placebo 6.3%, romosozumab 1.6%; P = 0.003) bone. At 12 months, cancellous bone formation was significantly lower (P < 0.05 to P < 0.001) in romosozumab versus placebo and the lower values for resorption endpoints seen at month 2 persisted (P < 0.001), signaling a decrease in bone turnover (P = 0.006). No significant change was observed in periosteal and endocortical bone. This resulted in an increase in bone mass and trabecular thickness with improved trabecular connectivity, without significant modification of cortical porosity at month 12. In conclusion, romosozumab produced an early and transient increase in bone formation, but a persistent decrease in bone resorption. Antiresorptive action eventually resulted in decreased bone turnover. This effect resulted in significant increases in bone mass and improved microarchitecture. © 2019 American Society for Bone and Mineral Research.

Reduction of Cortical Bone Turnover and Erosion Depth After 2 and 3 Years of Denosumab: Iliac Bone Histomorphometry in the FREEDOM Trial

Denosumab, a RANKL inhibitor, reduced the risk of vertebral, hip, and nonvertebral fractures in the Fracture REduction Evaluation of Denosumab in Osteoporosis every 6 Months (FREEDOM) trial of postmenopausal women with osteoporosis compared with placebo. Previous bone histomorphometric analysis in FREEDOM showed decreased bone resorption and turnover in cancellous bone after 2 and 3 years. The purpose of the present study was to evaluate the effects of denosumab compared with placebo in the cortical compartment from transiliac bone biopsies obtained during FREEDOM. A total of 112 specimens were evaluable for cortical histomorphometry, including 67 obtained at month 24 (37 placebo, 30 denosumab) and 45 at month 36 (25 placebo, 20 denosumab). Eroded surface, osteoclast surface, erosion depth, and wall thickness were measured on the endocortical surface. Cortical thickness and cortical porosity were also measured. Dynamic parameters of bone formation were assessed for endocortical, periosteal, and intracortical envelopes. Endocortical osteoclast surface, eroded surface, and mean and maximum erosion depth were significantly lower in the denosumab group versus placebo at months 24 and 36 (p < 0.0001 to p = 0.04). Endocortical wall thickness and intracortical measures (cortical porosity and cortical thickness) were not different between the two groups. Dynamic parameters were low with tetracycline labels in cortical bone observed in 13 (43%) and 10 (50%) of denosumab biopsies at months 24 and 36, respectively, reflecting a marked decrease in bone turnover. In conclusion, our data reveal the mechanism of action of denosumab on cortical bone: inhibition of osteoclastic resorption and reduced activation of new remodeling sites. In addition, reduced endocortical erosion depth with no change of wall thickness may contribute to increased bone strength by reducing the bone loss and fragility associated with deep resorption cavities and may likely contribute to the greater BMD gain with denosumab than with other antiresorptive agents. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Severe hypocalcemia following denosumab treatment in a patient with secondary osteoporosis associated with primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) has been known as a cause of secondary osteoporosis, which often requires medication. Herein, we give the first report of a case of a 38-year-old man with fatigue and paralysis in both upper limbs who had been treated with denosumab for secondary osteoporosis associated with PSC. Since bisphosphonate (alendronate) was ineffective in our patient, the treatment was changed from alendronate to denosumab. Despite replacements with calcium and active vitamin D (alfacalcidol; 1-hydroxycholecalciferol), he developed severe hypocalcemia (albumin-adjusted serum calcium: 5.2 mg/dL) 2 weeks after the second administration of denosumab, which required immediate correction. After that, the corrected serum calcium levels were controlled within the normal range with 0.75 μg of eldecalcitol (1α,25-dihydroxy-2β-(3-hydroxypropyloxy)vitamin D3) and increased doses of calcium (1,500 mg daily) and phosphate (900 mg daily) without denosumab. Even though denosumab treatment had been terminated, the T score of the lumbar spine improved from -4.4 to -2.6 by 1 year after the second administration, possibly due to the amelioration of osteomalacia through the treatment with eldecalcitol and the higher doses of calcium and phosphate. This report indicates that denosumab can cause severe hypocalcemia in patients with osteoporosis associated with chronic diseases of the hepatobiliary system including PSC, in turn suggesting that the possibility of vitamin D deficiency or osteomalacia should be considered before administering treatments and that serum calcium levels should be closely monitored to detect life-threatening hypocalcemia in patients who have high risk factors for hypocalcemia.

Young's modulus and hardness of human trabecular bone with bisphosphonate treatment durations up to 20 years

Bone modulus from patients with osteoporosis treated with bisphosphonates for 1 to 20 years was analyzed. Modulus increases during the first 6 years of treatment and remains unchanged thereafter.

INTRODUCTION

Bisphosphonates are widely used for treating osteoporosis, but the relationship between treatment duration and bone quality is unclear. Since material properties partially determine bone quality, the present study quantified the relationship between human bone modulus and hardness with bisphosphonate treatment duration.

METHODS

Iliac crest bone samples from a consecutive case series of 86 osteoporotic Caucasian women continuously treated with oral bisphosphonates for 1.1-20 years were histologically evaluated to assess bone turnover and then tested using nanoindentation. Young's modulus and hardness were measured and related to bisphosphonate treatment duration by statistical modeling.

RESULTS

All bone samples had low bone turnover. Statistical models showed that with increasing bisphosphonate treatment duration, modulus and hardness increased, peaked, and plateaued. These models used quadratic terms to model modulus increases from 1 to 6 years of bisphosphonate treatment and linear terms to model modulus plateaus from 6 to 20 years of treatment. The treatment duration at which the quadratic-linear transition (join point) occurred also depended upon trabecular location. Hardness increased and peaked at 12.4 years of treatment; it remained constant for the next 7.6 years of treatment and was insensitive to trabecular location.

CONCLUSIONS

Bone modulus increases with bisphosphonate treatment durations up to 6 years, no additional modulus increases occurred after 6 years of treatment. Although hardness increased, peaked at 12.4 years and remained constant for the next 7.6 years of BP treatment, the clinical relevance of hardness remains unclear.

Updates in CKD-Associated Osteoporosis

PURPOSE OF REVIEW

Chronic kidney disease (CKD) is associated with bone loss and fractures. The purpose of this review is to provide clinicians with an overview of the underlying pathogenesis of CKD-associated osteoporosis, and a summary of the current diagnostic and therapeutic approaches to this disease.

RECENT FINDINGS

In 2017, the Kidney Disease Improving Global Outcomes Committee on Bone Quality updated their guidelines to include screening for osteoporosis and fracture risk by dual energy X-ray absorptiometry in patients with CKD. Once a diagnosis of osteoporosis and/or fracture risk is established, it is not clear how nephrologists should manage their patients. Patients with CKD should be screened for CKD-associated osteoporosis and considered for strategies that prevent bone loss and fractures. Assessment of bone turnover via imaging, biochemical testing, or bone biopsy can help guide the choice of therapy. Randomized controlled trials are needed to assess safety and efficacy of treatments to prevent bone loss and fractures.

LRRK1 regulation of actin assembly in osteoclasts involves serine 5 phosphorylation of L-plastin

Mice with disruption of Lrrk1 and patients with nonfunctional mutant Lrrk1 exhibit severe osteopetrosis phenotypes because of osteoclast cytoskeletal dysfunction. To understand how Lrrk1 regulates osteoclast function by modulating cytoskeleton rearrangement, we examined the proteins that are differentially phosphorylated in wild‐type mice and Lrrk1‐deficient osteoclasts by metal affinity purification coupled liquid chromatography/mass spectrometry (LC/MS) analyses. One of the candidates that we identified by LC/MS is L‐plastin, an actin bundling protein. We found that phosphorylation of L‐plastin at serine (Ser) residues 5 was present in wild‐type osteoclasts but not in Lrrk1‐deficient cells. Western blot analyses with antibodies specific for Ser5 phosphorylated L‐plastin confirmed the reduced L‐plastin Ser5 phosphorylation in Lrrk1 knockout (KO) osteoclasts. micro computed tomography (Micro‐CT) analyses revealed that the trabecular bone volume of the distal femur was increased by 27% in the 16 to 21‐week‐old L‐plastin KO females as compared with the wild‐type control mice. The ratio of bone volume to tissue volume and connectivity density were increased by 44% and 47% (both P < 0.05), respectively, in L‐plastin KO mice. Our data suggest that targeted disruption of L‐plastin increases trabecular bone volume, and phosphorylation of Ser5 in L‐plastin in the Lrrk1 signaling pathway may in part contribute to actin assembly in mature osteoclasts.

Osteoclast-secreted SLIT3 coordinates bone resorption and formation

Coupling is the process that links bone resorption to bone formation in a temporally and spatially coordinated manner within the remodeling cycle. Several lines of evidence point to the critical roles of osteoclast-derived coupling factors in the regulation of osteoblast performance. Here, we used a fractionated secretomic approach and identified the axon-guidance molecule SLIT3 as a clastokine that stimulated osteoblast migration and proliferation by activating β-catenin. SLIT3 also inhibited bone resorption by suppressing osteoclast differentiation in an autocrine manner. Mice deficient in Slit3 or its receptor, Robo1, exhibited osteopenic phenotypes due to a decrease in bone formation and increase in bone resorption. Mice lacking Slit3 specifically in osteoclasts had low bone mass, whereas mice with either neuron-specific Slit3 deletion or osteoblast-specific Slit3 deletion had normal bone mass, thereby indicating the importance of SLIT3 as a local determinant of bone metabolism. In postmenopausal women, higher circulating SLIT3 levels were associated with increased bone mass. Notably, injection of a truncated recombinant SLIT3 markedly rescued bone loss after an ovariectomy. Thus, these results indicate that SLIT3 plays an osteoprotective role by synchronously stimulating bone formation and inhibiting bone resorption, making it a potential therapeutic target for metabolic bone diseases.

High Bone Turnover in Mice Carrying a Pathogenic Notch2 Mutation Causing Hajdu-Cheney Syndrome

Hajdu-Cheney syndrome (HCS) is a rare autosomal-dominant disorder primarily characterized by acro-osteolysis and early-onset osteoporosis. Genetically, HCS is caused by nonsense or deletion mutations within exon 34 of the NOTCH2 gene, resulting in premature translational termination and production of C-terminally truncated NOTCH2 proteins that are predicted to activate NOTCH2-dependent signaling. To understand the role of Notch2 in bone remodeling, we developed a mouse model of HCS by introducing a pathogenic mutation (6272delT) into the murine Notch2 gene. By μCT and undecalcified histology, we observed generalized osteopenia in two independent mouse lines derived by injection of different targeted embryonic stem (ES) cell clones, yet acro-osteolysis did not occur until the age of 52 weeks. Cellular and dynamic histomorphometry revealed a high bone turnover situation in Notch2^+/HCS mice, since osteoblast and osteoclast indices were significantly increased compared with wild-type littermates. Whereas ex vivo cultures failed to uncover cell-autonomous gain-of-functions within the osteoclast or osteoblast lineage, an unbiased RNA sequencing approach identified Tnfsf11 and Il6 as Notch-signaling target genes in bone marrow cells cultured under osteogenic conditions. Because we further observed that the high-turnover pathology of Notch2^+/HCS mice was fully normalized by alendronate treatment, our results demonstrate that mutational activation of Notch2 does not directly control osteoblast activity but favors a pro-osteoclastic gene expression pattern, which in turn triggers high bone turnover. © 2017 American Society for Bone and Mineral Research.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Sequential treatment with zoledronic acid followed by teriparatide or vice versa increases bone mineral density and bone strength in ovariectomized rats

Bisphosphonates (BPs) and teriparatide (TPTD) are both effective treatments for osteoporosis, but BP treatment prior to daily TPTD treatment has been shown to impair the effect of TPTD in some clinical studies. In contrast, the loss of bone mineral density (BMD) that occurs after withdrawal of TPTD can be prevented by BP treatment. Although various studies have investigated the combination and/or sequential use of BP and TPTD, there have been no clinical studies investigating sequential treatment with zoledronic acid (ZOL) and TPTD (or vice versa). In this study, we evaluated the effects of sequential treatment with TPTD followed by ZOL, and ZOL followed by TPTD, using ovariectomized (OVX) rats. Two months after OVX, osteopenic rats were treated with ZOL, TPTD, or vehicle for a period of 4 months (first treatment period), and then the treatments were switched and administered for another 4 months (second treatment period). The group treated with ZOL followed by TPTD showed an immediate increase in BMD of the proximal tibia and greater BMD and bone strength of the lumbar vertebral body, femoral diaphysis, and proximal femur than the group treated with ZOL followed by vehicle. Serum osteocalcin, a marker of bone formation, increased rapidly after switching to TPTD from ZOL. The group treated with TPTD followed by ZOL did not lose BMD in the proximal tibia after TPTD was stopped, while the group treated with TPTD followed by vehicle did lose BMD. The BMD and bone strength of the lumbar vertebral body, femoral diaphysis, and proximal femur were greater in the group treated with TPTD followed by ZOL than in the group treated with TPTD followed by vehicle. The increase in serum osteocalcin and urinary CTX after withdrawal of TPTD was prevented by the switch from TPTD to ZOL. In conclusion, our results demonstrate that switching from ZOL to TPTD resulted in a non-attenuated anabolic response in the lumbar spine and femur of OVX rats. In addition, switching from TPTD to ZOL caused BMD to be maintained or further increased. If these results can be reproduced in a clinical setting, the sequential use of ZOL followed by TPTD or vice versa in the treatment of osteoporosis patients would contribute to increases in BMD that, hopefully, would translate into a corresponding decrease in the incidence of vertebral and non-vertebral fractures.

Treatment of postmenopausal osteoporosis: a literature-based algorithm for use in the public health care system

Bisphosphonates are considered first-line agents in the treatment of postmenopausal osteoporosis based on extensive experience of use, safety, and proven efficacy in reducing vertebral, non-vertebral and femur fractures. However, post-marketing reports based on the treatment of millions of patients/year over lengthy periods of time have revealed the occurrence of initially unexpected adverse effects, such as osteonecrosis of the jaw and atypical femoral fracture, leading to the restriction of treatment duration with bisphosphonates by global regulatory agencies. However, despite the association between these effects and bisphosphonates, this risk should be analyzed in the context of osteoporosis treatment, alongside the benefit of preventing osteoporotic fractures and their clinical consequences. Therefore, we consider it plausible to discuss the restriction to the use of bisphosphonates, possible indications for prolonged treatment and alternative therapies following the suspension of this drug class for patients with persistent high risk of fracture after initial treatment, especially considering the problems of public health funding in Brazil and the shortage of drugs provided by the government. Thus, to standardize the treatment of osteoporosis in the public health care system, we aim to develop a proposal for a scientifically-based pharmacological treatment for postmenopausal osteoporosis, establishing criteria for indication and allowing the rational use of each pharmacological agent. We discuss the duration of the initial bisphosphonate treatment, the therapeutic options for refractory patients and potential indications of other classes of drugs as first-choice treatment in the sphere of public health, in which assessing risk and cost effectiveness is a priority.

Administration frequency as well as dosage of PTH are associated with development of cortical porosity in ovariectomized rats

To investigate whether the administration frequency of parathyroid hormone (PTH) is associated with the development of cortical porosity, this study established 15 dosage regimens of teriparatide [human PTH(1–34), TPTD] with four distinct concentrations and four distinct administration frequencies of TPTD to 16-week-old ovariectomized rats. Our analyses demonstrated that the bone mineral density, mechanical properties, and bone turnover were associated with the total amount of TPTD administered. Our observations further revealed that the cortical porosity was markedly developed as a result of an increased administration frequency with a lower concentration of total TPTD administration in our setting, although the highest concentration also induced cortical porosity. Deconvolution fluorescence tiling imaging on calcein-labeled undecalcified bone sections also demonstrated the development of cortical porosity to be closely associated with the bone site where periosteal bone formation took place. This site-specific cortical porosity involved intracortical bone resorption and an increased number and proximity of osteocytic lacunae, occasionally causing fused lacunae. Taken together, these findings suggested the involvement of local distinctions in the rate of bone growth that may be related to the site-specific mechanical properties in the development of cortical porosity induced by frequent and/or high doses of TPTD.

Long-term effects of bisphosphonate therapy: perforations, microcracks and mechanical properties

Osteoporosis is characterised by trabecular bone loss resulting from increased osteoclast activation and unbalanced coupling between resorption and formation, which induces a thinning of trabeculae and trabecular perforations. Bisphosphonates are the frontline therapy for osteoporosis, which act by reducing bone remodelling, and are thought to prevent perforations and maintain microstructure. However, bisphosphonates may oversuppress remodelling resulting in accumulation of microcracks. This paper aims to investigate the effect of bisphosphonate treatment on microstructure and mechanical strength. Assessment of microdamage within the trabecular bone core was performed using synchrotron X-ray micro-CT linked to image analysis software. Bone from bisphosphonate-treated fracture patients exhibited fewer perforations but more numerous and larger microcracks than both fracture and non-fracture controls. Furthermore, bisphosphonate-treated bone demonstrated reduced tensile strength and Young's Modulus. These findings suggest that bisphosphonate therapy is effective at reducing perforations but may also cause microcrack accumulation, leading to a loss of microstructural integrity and consequently, reduced mechanical strength.

Metabolic Bone Disease in Patients Receiving Home Parenteral Nutrition: A Canadian Study and Review

BACKGROUND

Metabolic bone disease (MBD) is a significant complication in patients receiving long-term home parenteral nutrition (HPN). Pamidronate has been poorly studied in this population. We examine the prevalence and risk factors for MBD and examine changes in bone mineral density (BMD) after pamidronate administration.

METHODS

First, a chart review of patients receiving HPN for >1 year was performed, and Pearson correlations were used to assess associations between MBD (defined as t score<-1) and risk factors. Second, the effect of IV pamidronate on BMD was studied prospectively in 11 HPN patients. Results were compared using a t-test.

RESULTS

Charts were reviewed in 25 patients (15 F, 10 M): age, 56.9+/-3.1 years; body mass index (BMI), 21.2+/-0.57 kg/m2; months receiving HPN, 113.2+/-0.09; and days per week receiving HPN, 5.08+/-0.39. MBD was present in 33% of patients for the spine and hip and in 50% for the femoral neck; 24% had previous fractures. There was a significant negative correlation between the duration of HPN and BMD (r=-0.40) for all measurements. From those patients, 11 received IV pamidronate for a mean of 22.2+/-5.4 months. At baseline, their mean HPN treatment duration was 10.6+/-6.3 years. Overall, BMD results showed a trend toward improvement in the mean t score of the spine and hip postpamidronate therapy (pre, -3.1+/-0.75; post, -2.9+/-0.69; p=.07). After excluding 2 patients receiving corticosteroids, the mean t score of the spine showed significant improvement (prepamidronate -3.4+/-0.57 vs post-pamidronate -3.1+/-0.65, p=.036).

CONCLUSIONS

In our HPN population, 76% had MBD and 24% had previous fractures. The results suggest that these patients may benefit from pamidronate. More studies are needed to assess the efficacy of pamidronate.

Stiffness and strength of bone in osteoporotic patients treated with varying durations of oral bisphosphonates

Apparent modulus and failure stress of trabecular bone structure from 45 women with osteoporosis treated with bisphosphonates for varying durations were studied using finite element analyses and statistical modeling. Following adjustments for patient age and bone volume, increasing bisphosphonate treatment duration for up to 7.3 years was associated with treatment-time-dependent increases in bone apparent modulus and failure stress. Treatment durations exceeding 7.3 years were associated with time-dependent decreases in apparent modulus and failure stress from the peak values observed.

INTRODUCTION

The purpose of this study was to clarify the relationship between bisphosphonate (BP) treatment duration and human bone quality. This study quantified changes in the apparent modulus and failure stress of trabecular bone biopsied from patients with osteoporosis who were treated with BPs for widely varying durations.

METHODS

Forty-five iliac crest bone samples were obtained from women with osteoporosis who were continuously treated with oral BPs for varying periods of up to 16 years. Micro-CT imaging was used to develop three-dimensional virtual models of the trabecular bone from these samples. Apparent modulus and failure stress of these virtual models were determined using finite element analyses (FEA). Polynomial regression and cubic splines, adjusted for relevant (age and BV/TV) covariates, were used to statistically model the data and quantify the relationships between BP treatment duration and apparent modulus or failure stress.

RESULTS

Second-order polynomial models were needed to relate apparent modulus or failure stress to BP treatment duration. These models showed that these bone quality parameters (a) increased with increasing BP treatment duration up to approximately 7.3 years, (b) reached a maximum at this (~7.3 years) time, and then (c) declined with BP treatment durations exceeding ~7.3 years. A similar result was obtained by modeling with cubic splines.

CONCLUSIONS

Changes in FEA-derived apparent stiffness and failure stress are attributable to changes in trabecular bone structure, which in turn are related to the duration of BP treatment. These relationships are evident even after adjustments are made in the statistical models for changes in age and BV/TV. According to these models, increases in trabecular bone apparent stiffness and failure stress linked to BPs cease and appear to reverse after approximately 7.3 years of treatment. Conclusions regarding optimal BP therapy duration await study of additional bone quality parameters.

Zoledronic acid in vivo increases in vitro proliferation of rat mesenchymal stromal cells

Background and purpose - Bisphosphonates are widely used in the treatment of bone loss, but they might also have positive effects on osteoblastic cells and bone formation. We evaluated the effect of in vivo zoledronic acid (ZA) treatment and possible concomitant effects of ZA and fracture on the ex vivo osteogenic capacity of rat mesenchymal stromal cells (MSCs). Methods - A closed femoral fracture model was used in adult female rats and ZA was administered as a single bolus or as weekly doses up to 8 weeks. Bone marrow MSCs were isolated and cultured for in vitro analyses. Fracture healing was evaluated by radiography, micro-computed tomography (μCT), and histology. Results - Both bolus and weekly ZA increased fracture-site bone mineral content and volume. MSCs from weekly ZA-treated animals showed increased ex vivo proliferative capacity, while no substantial effect on osteoblastic differentiation was observed. Fracture itself did not have any substantial effect on cell proliferation or differentiation at 8 weeks. Serum biochemical markers showed higher levels of bone formation in animals with fracture than in intact animals, while no difference in bone resorption was observed. Interestingly, ex vivo osteoblastic differentiation of MSCs was found to correlate with in vivo serum bone markers. Interpretation - Our data show that in vivo zoledronic acid treatment can influence ex vivo proliferation of MSCs, indicating that bisphosphonates can have sustainable effects on cells of the osteoblastic lineage. Further research is needed to investigate the mechanisms.

Free Fatty Acid Receptor 4 (GPR120) Stimulates Bone Formation and Suppresses Bone Resorption in the Presence of Elevated n-3 Fatty Acid Levels

Free fatty acid receptor 4 (FFA4) has been reported to be a receptor for n-3 fatty acids (FAs). Although n-3 FAs are beneficial for bone health, a role of FFA4 in bone metabolism has been rarely investigated. We noted that FFA4 was more abundantly expressed in both mature osteoclasts and osteoblasts than their respective precursors and that it was activated by docosahexaenoic acid. FFA4 knockout (Ffar4(-/-)) and wild-type mice exhibited similar bone masses when fed a normal diet. Because fat-1 transgenic (fat-1(Tg+)) mice endogenously converting n-6 to n-3 FAs contain high n-3 FA levels, we crossed Ffar4(-/-) and fat-1(Tg+) mice over two generations to generate four genotypes of mice littermates: Ffar4(+/+);fat-1(Tg-), Ffar4(+/+);fat-1(Tg+), Ffar4(-/-);fat-1(Tg-), and Ffar4(-/-);fat-1(Tg+). Female and male littermates were included in ovariectomy- and high-fat diet-induced bone loss models, respectively. Female fat-1(Tg+) mice decreased bone loss after ovariectomy both by promoting osteoblastic bone formation and inhibiting osteoclastic bone resorption than their wild-type littermates, only when they had the Ffar4(+/+) background, but not the Ffar4(-/-) background. In a high-fat diet-fed model, male fat-1(Tg+) mice had higher bone mass resulting from stimulated bone formation and reduced bone resorption than their wild-type littermates, only when they had the Ffar4(+/+) background, but not the Ffar4(-/-) background. In vitro studies supported the role of FFA4 as n-3 FA receptor in bone metabolism. In conclusion, FFA4 is a dual-acting factor that increases osteoblastic bone formation and decreases osteoclastic bone resorption, suggesting that it may be an ideal target for modulating metabolic bone diseases.

Comparison of treatment effects of teriparatide and the bisphosphonate risedronate in an aged, osteopenic, ovariectomized rat model under various clinical conditions

Teriparatide and bisphosphonates are osteoporosis medications that increase bone mineral density (BMD) and prevent fracture, but each has a different mechanism of action. Teriparatide promotes bone formation, while bisphosphonates suppress bone resorption. In the clinical setting, however, drug selection is not always tailored to the particular clinical condition of the patient or mechanism of action of the drug. We compared the effects of teriparatide and the bisphosphonate risedronate on bone metabolism using two ovariectomized rat models to elucidate the optimal use of these two drugs in the clinical setting. We first performed dose-finding experiments to determine the equivalent effective doses of each drug (5.6 and 3.0 µg/kg for teriparatide and risedronate, respectively). We then compared the effects of these doses on bone metabolism after subcutaneous administration three times weekly for 4 months starting either the day after ovariectomy (preventive study) or 12 months after ovariectomy (therapeutic study). The increase in proximal tibial BMD under the physical conditions that increased bone turnover at 1 to 2 months after ovariectomy was greater in the risedronate group than in the teriparatide group. In contrast, the increases in lumbar vertebral BMD and bone strength under the physical conditions that significantly decreased BMD and bone strength at 12 months after ovariectomy were greater in the teriparatide group than in the risedronate group. The present study provides important information on the selection of antiosteoporotic drugs, including teriparatide and risedronate, in treatment protocols tailored to the clinical conditions of patients and drug mechanisms.

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

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

Osteoclast TGF-β Receptor Signaling Induces Wnt1 Secretion and Couples Bone Resorption to Bone Formation

Osteoblast-mediated bone formation is coupled to osteoclast-mediated bone resorption. These processes become uncoupled with age, leading to increased risk for debilitating fractures. Therefore, understanding how osteoblasts are recruited to sites of resorption is vital to treating age-related bone loss. Osteoclasts release and activate TGF-β from the bone matrix. Here we show that osteoclast-specific inhibition of TGF-β receptor signaling in mice results in osteopenia due to reduced osteoblast numbers with no significant impact on osteoclast numbers or activity. TGF-β induced osteoclast expression of Wnt1, a protein crucial to normal bone formation, and this response was blocked by impaired TGF-β receptor signaling. Osteoclasts in aged murine bones had lower TGF-β signaling and Wnt1 expression in vivo. Ex vivo stimulation of osteoclasts derived from young or old mouse bone marrow macrophages showed no difference in TGF-β-induced Wnt1 expression. However, young osteoclasts expressed reduced Wnt1 when cultured on aged mouse bone chips compared to young mouse bone chips, consistent with decreased skeletal TGF-β availability with age. Therefore, osteoclast responses to TGF-β are essential for coupling bone resorption to bone formation, and modulating this pathway may provide opportunities to treat age-related bone loss.

Comparative Effects of Ibandronate and Paclitaxel on Immunocompetent Bone Metastasis Model

PURPOSE

Bone metastasis invariably increases morbidity and mortality. This study compares the effects of ibandronate and paclitaxel on bone structure and its mechanical properties and biochemical turnover in resorption markers using an immunocompetent Walker 256-Sprague-Dawley model, which was subjected to tumor-induced osteolysis.

MATERIALS AND METHODS

Seventy rats were divided equally into 4 groups: 1) sham group (SHAM), 2) tumor group (CANC), 3) ibandronate treated group (IBAN), and 4) paclitaxel treated group (PAC). Morphological indices [bone volume fraction (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp)] and mechanical properties (failure load, stiffness) were evaluated after thirty days of treatment period. Bone resorption rate was analysed using serum deoxypyridinoline (Dpd) concentrations.

RESULTS

Morphological indices showed that ibandronate (anti-resorptive drug) had a better effect in treating tumor-induced architectural changes in bone than paclitaxel (chemotherapeutic drug). The deterioration in bone architecture was reflected in the biomechanical properties of bone as studied with decreased failure load (F(x)) and stiffness (S) of the bone on the 30th day postsurgery. Dpd concentrations were significantly lower in the IBAN group, indicating successful inhibition of bone resorption and destruction.

CONCLUSION

Ibandronate was found to be as effective as higher doses of paclitaxel in maintaining stiffness of bone. Paclitaxel treatment did not appear to inhibit osteoclast resorption, which is contrary to earlier in-vitro literature. Emphasis should be placed on the use of immunocompetent models for examining drug efficacy since it adequately reflects bone metastasis in clinical scenarios.

Early Effects of Single and Low-Frequency Repeated Administration of Teriparatide, hPTH(1-34), on Bone Formation and Resorption in Ovariectomized Rats

Intermittent repeated administration of teriparatide (TPTD) has potent anabolic effects on bones in vivo. However, TPTD has both anabolic and catabolic effects on osteoblasts in vitro, and the mechanisms underlying its promotion of bone formation are unclear. This study aimed to elucidate the time-dependent changes in bone formation and resorption by examining changes in bone turnover markers and bone tissue over time after TPTD administration with low frequency in ovariectomized rats. The amount of serum osteocalcin, a bone formation marker, was transiently reduced after single TPTD administration, but increased thereafter, remaining increased for several days. In contrast, the amount of excreted urinary C-telopeptide, a bone resorption marker, increased transiently after single TPTD administration, and subsequently returned to control levels on the day after administration. Tissue histomorphometric analyses conducted 8 h after administration showed no changes in bone formation or bone resorption parameters. However, at 48 h, the bone formation parameters OS/BS and Ob.S/BS were increased, while the bone resorption parameter ES/BS was decreased. After repeated TPTD administration for 4 weeks, OS/BS, Ob.S/BS, and MS/BS increased, while Oc.S/BS decreased. Serum osteocalcin at 4 weeks after repeated administration was significantly correlated with OS/BS and Ob.S/BS. These present findings indicate that TPTD has dual, time-dependent effects on bone resorption and bone formation. Immediately after single administration, there was transient promotion of bone resorption and suppression of bone formation. However, sustained stimulation of bone formation occurred thereafter. Furthermore, these data suggest that this sustained bone formation led to anabolic effects with repeated TPTD administration.

Teriparatide for the rapid resolution of delayed healing of atypical fractures associated with long-term bisphosphonate use

Bisphosphonates (BPs) are the most widely used drugs to treat osteoporosis. However, recent reports associated to long-term BPs use with atypical low-impact fractures and prodromal pain. It is estimated that 26% of the cases of atypical fractures associated with the long-term use of BPs show delayed healing or nonunion. Teriparatide [PTH1-34] (TPTD) is an anabolic drug shown to be effective in stimulating bone formation. The aim was to describe the course of a right diaphyseal femoral fracture sustained by a patient on long-term BPs treatment. A 57-year-old postmenopausal Caucasian female presented with delayed healing of a right femoral diaphyseal fracture 10 months after the fracture, despite having received orthopedic treatment. The fracture was preceded by progressive, severe, and bilateral thigh pain. Her medical history included osteopenia that was treated with alendronate over 7 years. On presentation at our clinic, the patient ambulated with the aid of a walking cane. The diagnosis was an atypical right femoral fracture associated with long-term alendronate use. The levels of the following parameters were measured: mineral metabolism laboratory: intact parathormone, 40 ng/mL (reference values (rv): 10-65 ng/mL); 25-hydroxyvitamin D, 40 ng/mL (rv: >30 ng/mL); serum Crosslaps, 318 ng/mL (rv: 80-590 ng/mL); and bone-specific alkaline phosphatase, 76UI/L (rv: 31-95UI/L)]. Magnetic resonance imaging of the left femur was performed, which revealed a diaphyseal stress fracture. She was prescribed 20 μg/day of subcutaneous (s.c.) TPTD (PTH1-34, Forteo; Eli Lilly Co., Indianapolis, IN, United States). A computed tomography scan performed 3 months later showed that the fracture had healed; the patient was able to resume her usual activities. Twenty micrograms per day of s.c. TPD accelerated the healing of the atypical fracture associated with long-term alendronate therapy, allowing a fast recovery of ambulation and quality of life.

Parathyroid Hormone Plus Alendronate in Osteoporosis: A Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Parathyroid hormone (PTH) increases both bone formation (BMD) and bone resorption, whereas alendronate reduces bone resorption. It is possible that the combination therapy will enhance their effects on BMD. Therefore, we conducted this meta-analysis to evaluate the efficacy of the combination therapy in osteoporosis.

METHODS

A comprehensive literature search of Pubmed, Embase, and Web of Science was conducted to identify relative studies. The outcomes included the mean percent increases in BMD of lumbar spine, femoral neck, total hip, and distal radius. A fixed-effects model or random-effects was used to pool the estimates according to the heterogeneity.

RESULTS

Six RCTs with a total number of 833 patients were included in this meta-analysis. The pooled estimates showed that, the combination therapy resulted in a higher mean percent change of increased BMD in distal radius (WMD = 2.45, 95%CI: 1.58, 3.31; 0.000), but not in lumbar spine (WMD = -0.83, 95%CI: -3.48, 1.81; p = .538), femoral neck (WMD = -0.99, 95%CI: -2.04, 0.07; p = .068), and total hip (WMD = -0.06, 95%CI: -0.93, 0.81; p = .892). Subgroup analysis revealed that among the patients in the combination therapy group, greater increases in the spine BMD were observed when the PTH was administered with a dosage of 20 μg (WMD = 2.33, 95%CI: 1.24, 3.43; p = .000), or the treatment duration lasted more than 12 months (WMD = 2.23, 95%CI: 1.00, 3.47; p = .000), or the combination therapy was used in osteoporosis women (WMD = 1.58, 95%CI: 0.63, 2.53; p = .001).

CONCLUSION

Our findings indicated that combination therapy in the treatment of osteoporosis, reduced the ability of PTH therapy to increase the BMD at the lumbar spine, femoral neck, and total hip.