Pilot Study: Short Term Impact of Radiation Therapy on Bone Mineral Density and Bone Metabolism

Despite the risk of complications, high dose radiation therapy is increasingly utilized in the management of selected bone malignancies. In this study, we investigate the impact of moderate to high dose radiation (over 50 Gy) on bone metabolism and structure. Between 2015 and 2018, patients with a primary malignant bone tumor of the sacrum that were either treated with high dose definitive radiation only or a combination of moderate to high dose radiation and surgery were prospectively enrolled at a single institution. Quantitative CTs were performed before and after radiation to determine changes in volumetric bone mineral density (BMD) of the irradiated and non-irradiated spine. Bone histomorphometry was performed on biopsies of the irradiated sacrum and the non-irradiated iliac crest of surgical patients using a quadruple tetracycline labeling protocol. In total, 9 patients were enrolled. Two patients received radiation only (median dose 78.3 Gy) and 7 patients received a combination of preoperative radiation (median dose 50.4 Gy), followed by surgery. Volumetric BMD of the non-irradiated lumbar spine did not change significantly after radiation, while the BMD of the irradiated sacrum did (pre-radiation median: 108.0 mg/cm3 (IQR 91.8-167.1); post-radiation median: 75.3 mg/cm3 (IQR 57.1-110.2); p = 0.010). The cancellous bone of the non-irradiated iliac crest had a stable bone formation rate, while the irradiated sacrum showed a significant decrease in bone formation rate [pre-radiation median: 0.005 mm3/mm2/year (IQR 0.003-0.009), post-radiation median: 0.001 mm3/mm2/year (IQR 0.001-0.001); p = 0.043]. Similar effects were seen in the cancellous and endocortical envelopes. This pilot study shows a decrease of volumetric BMD and bone formation rate after high-dose radiation therapy. Further studies with larger cohorts and other endpoints are needed to get more insight into the effect of radiation on bone. Level of evidence: IV.

Proceedings of the 2022 Santa Fe Bone Symposium: Current Concepts in the Care of Patients with Osteoporosis and Metabolic Bone Diseases

The 22^nd Annual Santa Fe Bone Symposium (SFBS) was a hybrid meeting held August 5-6, 2022, with in-person and virtual attendees. Altogether, over 400 individuals registered, a majority of whom attended in-person, representing many states in the USA plus 7 other countries. The SFBS included 10 plenary presentations, 2 faculty panel discussions, satellite symposia, Bone Health & Osteoporosis Foundation Fracture Liaison Service Boot Camp, and a Project ECHO workshop, with lively interactive discussions for all events. Topics of interest included fracture prevention at different stages of life; how to treat and when to change therapy; skeletal health in cancer patients; advanced imaging to assess bone strength; the state of healthcare in the USA; osteosarcopenia; vitamin D update; perioperative bone health care; new guidelines for managing primary hyperparathyroidism; new concepts on bone modeling and remodeling; and an overview on the care of rare bone diseases, including hypophosphatasia, X-linked hypophosphatemia, tumor induced osteomalacia, osteogenesis imperfecta, fibrodysplasia ossificans progressiva, and osteopetrosis. The SFBS was preceded by the Santa Fe Fellows Workshop on Osteoporosis and Metabolic Bone Diseases, a collaboration of the Endocrine Fellows Foundation and the Osteoporosis Foundation of New Mexico. From the Workshop, 4 participating fellows were selected to give oral presentations at the bone symposium. These proceedings represent the clinical highlights of 2022 SFBS presentations and the discussions that followed, all with the aim of optimizing skeletal health and minimizing the consequences of fragile bones.

Treatment of postmenopausal osteoporosis patients with teriparatide for 24 months reverts forming bone quality indices to premenopausal healthy control values

Postmenopausal osteoporosis (PMOP) therapies are frequently evaluated by bone mineral density (BMD) gains against patients receiving placebo (calcium and vitamin D supplementation, a mild bone turnover-suppressing intervention), which is not equivalent to either healthy or treatment-naive PMOP. The aim of the present observational study was to assess the effects of TPTD treatment in PMOP (20 μg, once daily) at 6 (TPTD 6m; n = 28, age 65 ± 7.3 years), and 24 (TPTD 24m; n = 32, age 67.4 ± 6.15 years) months on bone quality indices at actively forming trabecular surfaces (with fluorescent double labels). Data from the TPTD-treated PMOP patients were compared with those in healthy adult premenopausal women (HC; n = 62, age 40.5 ± 10.6 years), and PMOP receiving placebo (PMOP-PLC; n = 94, age 70.6 ± 4.5 years). Iliac crest biopsies were analyzed by Raman microspectroscopy at three distinct tissue ages: mid-distance between the second label and the bone surface, mid-distance between the two labels, and 1 μm behind the first label. Mineral to matrix ratio (MM), mineral maturity/crystallinity (MMC), tissue water (TW), glycosaminoglycan (GAGs), and pyridinoline (Pyd) content were determined. Outcomes were compared by ANCOVA with subject age and tissue age as covariates, and health status as a fixed factor, followed by Sidak's post-hoc testing (significance assigned to p < 0.05). Both TPTD groups increased MM compared to PMOP-PLC. While TPTD 6m had values similar to HC, TPTD 24m had higher values compared to either HC or TPTD 6m. Both TPTD groups had lower MMC values compared to PMOP-PLC and similar to HC. TPTD 6m patients had higher TW content compared to HC, while TPTD 24m had values similar to HC and lower than either PMOP-PLC or TPTD 6m. Both TPTD groups had lower GAG content compared to HC group, while TPTD 6m had higher values compared to PMOP-PLC. Finally, TPTD 6m patients had higher Pyd content compared to HC and lower compared to PMOP-PLC, while TPTD 24m had lower values compared to PMOP-PLC and TPTD 6m, and similar to HC group. The results of the present study indicate that effects of TPTD on forming trabecular bone quality indices depend on treatment duration. At the recommended length of 24 m, TPTD restores bone mineral and organic matrix quality indices (MMC, TW, Pyd content) to premenopausal healthy (HC) levels.

Bone Mineral and Organic Properties in Postmenopausal Women Treated With Denosumab for Up to 10 years

In postmenopausal women with osteoporosis, denosumab (DMAb) therapy through 10 years resulted in significantly higher degree of mineralization of bone, with a subsequent increase from years 2-3 to year 5 and no further difference between years 5 and 10. Our aim was to assess the variables reflecting the quality of bone mineral and organic matrix (Fourier transform infrared microspectroscopy), and the microhardness of bone (Vickers microindentation). Cross-sectional assessments were performed in blinded fashion on iliac bone biopsies from osteoporotic women (72 from FREEDOM trial, 49 from FREEDOM Extension trial), separately in cortical and cancellous compartments. After 2-3 years of DMAb, mineral/matrix ratio and microhardness of cortical bone were significantly higher compared with placebo, whereas mineral maturity, mineral crystallinity, mineral carbonation, and collagen maturity were not different in both bone compartments. Through 5 years of DMAb, mineral carbonation was significantly lower and mineral/matrix ratio, mineral maturity, and crystallinity were significantly higher versus 2-3 years and were not different between 5 and 10 years, with the exception of mineral maturity in cancellous bone. These data support a transition of mineral to more mature crystals (within physiological range) and the completeness of secondary mineralization within 5 years of DMAb treatment. Microhardness in cortical and cancellous compartments was significantly lower at 5 years of DMAb versus 2-3 years and was not different from years 5 to 10. The lower microhardness at years 5 and 10 is likely the result of maturation of the organic matrix in a persistently low state of bone remodeling over 5 and 10 years. © 2022 American Society for Bone and Mineral Research (ASBMR).

Effects of teriparatide and loading modality on modeling-based and remodeling-based bone formation in the human femoral neck

PURPOSE

We have previously shown that a brief course of teriparatide (TPTD) stimulates bone formation in the cancellous and endocortical envelopes of the human femoral neck, and the regions of tension and compression respond differently. The purpose of the present study was to determine how much of the new bone was formed by modeling-based formation (MBF) or remodeling-based formation (RBF).

METHODS

We performed a double-blind trial of TPTD vs. placebo (PBO) in patients about to undergo a total hip replacement (THR) for osteoarthritis. Participants were randomized to receive daily TPTD 20 μg or PBO for an average of 6.1 weeks (range 4.1-11.8 weeks) prior to THR. After an average of 3 weeks of study drug, double tetracycline labels were administered per standard protocol. During the THR an intact sample of the mid-femoral neck (FN) was procured; this was fixed, embedded, and sectioned transversely. Histomorphometric analysis was performed in the cancellous, endocortical, and periosteal envelopes. Additionally, separate analyses were performed in the tensile and compressive regions of the endocortical and periosteal envelopes. Sites of new bone formation were identified by the presence of tetracycline labels and designated as MBF if the underlying cement line was smooth and as RBF if it was scalloped. New bone formation on smooth cement lines adjacent to scalloped reversal lines was designated as overflow RBF (oRBF). The referent for all indices was bone surface (BS).

RESULTS

In the cancellous and endocortical envelopes, the proportion of mineralizing surface engaged in RBF and oRBF was higher in the TPTD-treated than the PBO-treated subjects. There was also a trend toward higher MBF in TPTD vs. PBO in both envelopes. In linear mixed-effects models, TPTD was predicted to increase formation differently on the tensile and compressive surfaces depending on patient-specific anatomy, including body weight, FN angle, offset, and cortical width and porosity. Eroded surface was not different between groups in either envelope and no significant differences were observed in any parameter in the periosteal envelope.

CONCLUSION

We conclude that the predominant early effect of TPTD in the human femoral neck is to stimulate RBF and oRBF with a trend toward an increase in MBF in the endocortical and cancellous envelopes.

In premenopausal women with idiopathic osteoporosis, lower bone formation rate is associated with higher body fat and higher IGF-1

We examined serum IGF-1 in premenopausal IOP, finding relationships that were opposite to those expected: higher IGF-1 was associated with lower bone formation and higher body fat, and lower BMD response to teriparatide. These paradoxical relationships between serum IGF-1, bone, and fat may contribute to the mechanism of idiopathic osteoporosis in premenopausal women.

INTRODUCTION

Premenopausal women with idiopathic osteoporosis (IOP) have marked deficits in bone microarchitecture but variable bone remodeling. We previously reported that those with low tissue-level bone formation rate (BFR) are less responsive to teriparatide and have higher serum IGF-1, a hormone anabolic for osteoblasts and other tissues. The IGF-1 data were unexpected because IGF-1 is low in other forms of low turnover osteoporosis-leading us to hypothesize that IGF-1 relationships are paradoxical in IOP. This study aimed to determine whether IOP women with low BFR have higher IGF-1 and paradoxical IGF-1 relationships in skeletal and non-skeletal tissues, and whether IGF-1 and the related measures predict teriparatide response.

METHODS

This research is an ancillary study to a 24 month clinical trial of teriparatide for IOP. Baseline assessments were related to trial outcomes: BMD, bone remodeling.

SUBJECTS

 Premenopausal women with IOP(n = 34); bone remodeling status was defined by baseline cancellous BFR/BS on bone biopsy.

MEASURES

 Serum IGF-1 parameters, compartmental adiposity (DXA, CT, MRI), serum hormones, and cardiovascular-risk-markers related to fat distribution.

RESULTS

As seen in other populations, lower BFR was associated with higher body fat and poorer teriparatide response. However, in contrast to observations in other populations, low BFR, higher body fat, and poorer teriparatide response were all related to higher IGF-1: IGF-1 Z-score was inversely related to BFR at all bone surfaces (r =  - 0.39 to - 0.46; p < 0.05), directly related to central fat (p = 0.05) and leptin (p = 0.03). IGF-1 inversely related to 24 month hip BMD %change (r =  - 0.46; p = 0.01).

CONCLUSIONS

Paradoxical IGF-1 relationships suggest that abnormal or atypical regulation of bone and fat may contribute to osteoporosis mechanisms in premenopausal IOP.

Whole exome sequencing reveals potentially pathogenic variants in a small subset of premenopausal women with idiopathic osteoporosis

Osteoporosis in premenopausal women with intact gonadal function and no known secondary cause of bone loss is termed idiopathic osteoporosis (IOP). Women with IOP diagnosed in adulthood have profound bone structural deficits and often report adult and childhood fractures, and family history of osteoporosis. Some have very low bone formation rates (BFR/BS) suggesting osteoblast dysfunction. These features led us to investigate potential genetic etiologies of bone fragility. In 75 IOP women (aged 20-49) with low trauma fractures and/or very low BMD who had undergone transiliac bone biopsies, we performed Whole Exome Sequencing (WES) using our variant analysis pipeline to select candidate rare and novel variants likely to affect known disease genes. We ran rare-variant burden analyses on all genes individually and on phenotypically-relevant gene sets. For particular genes implicated in osteoporosis, we also assessed the frequency of all (including common) variants in subjects versus 6540 non-comorbid female controls. The variant analysis pipeline identified 4 women with 4 heterozygous variants in LRP5 and PLS3 that were considered to contribute to osteoporosis. All 4 women had adult fractures, and 3 women also had multiple fractures, childhood fractures and a family history of osteoporosis. Two women presented during pregnancy/lactation. In an additional 4 subjects, 4 different relevant Variants of Uncertain Significance (VUS) were detected in the genes FKBP10, SLC34A3, and HGD. Of the subjects with VUS, 2 had multiple adult fractures, childhood fractures, and presented during pregnancy/lactation, and 2 had nephrolithiasis. BFR/BS varied among the 8 subjects with identified variants; BFR/BS was quite low in those with variants that are likely to have adverse effects on bone formation. The analysis pipeline did not discover candidate variants in COL1A1, COL1A2, WNT, or ALPL. Although we found several novel and rare variants in LRP5, cases did not have an increased burden of common LRP5 variants compared to controls. Cohort-wide collapsing analysis did not reveal any novel disease genes with genome-wide significance for qualifying variants between controls and our 75 cases. In summary, WES revealed likely pathogenic variants or relevant VUS in 8 (11%) of 75 women with IOP. Notably, the genetic variants identified were consistent with the affected women's diagnostic evaluations that revealed histological evidence of low BFR/BS or biochemical evidence of increased bone resorption and urinary calcium excretion. These results, and the fact that the majority of the women had no identifiable genetic etiology, also suggest that the pathogenesis of and mechanisms leading to osteoporosis in this cohort are heterogeneous. Future research is necessary to identify both new genetic and non-genetic etiologies of early-onset osteoporosis.

Incidence of Hip and Subtrochanteric/Femoral Shaft Fractures in Postmenopausal Women With Osteoporosis in the Phase 3 Long-Term Odanacatib Fracture Trial

We prospectively assessed, with predefined criteria, the location and rates of all femur fractures (hip, subtrochanteric/femoral shaft [ST/FS], including atypical [AFF] and distal fractures) in women at increased fracture risk during treatment with the cathepsin K inhibitor, odanacatib (ODN), or placebo over 5 years in the Long-Term ODN Fracture Trial (LOFT and LOFT Extension [NCT00529373, EudraCT 2007-002693-66]). ODN was an investigational antiresorptive agent previously in development as an osteoporosis treatment that, unlike bisphosphonates, reduces bone formation only transiently. Women aged ≥65 years with a bone mineral density (BMD) T-score ≤-2.5 at the total hip (TH) or femoral neck (FN) or with a radiographic vertebral fracture and T-scores ≤-1.5 at the TH or FN were randomized (1:1) to receive ODN 50 mg/week or placebo. All patients received vitamin D₃ (5600 IU/week) and calcium (total 1200 mg/d); the analysis included 16,071 women. Rates of all adjudicated low-energy femoral fractures were 0.38 versus 0.58/100 patient-years for ODN and placebo, respectively (hazard ratio [HR] = 0.65; 95% confidence interval [CI] 0.51-0.82; nominal p < .001), and for low-energy hip fractures were 0.29 versus 0.56/100 patient-years, respectively (HR = 0.52; 95% CI 0.40-0.67; p < .001). The cumulative incidence of combined hip and ST/FS or hip fractures alone in the ODN group was consistently lower than in the placebo group (1.93% versus 3.11% for combined fractures and 1.53% versus 3.03% for hip fractures at 5 years, respectively). However, low-energy ST/FS fractures were more frequent in ODN-treated women than in placebo-treated women (24 versus 6, respectively). Among these, 12 fractures were adjudicated as AFF in 10 patients treated with ODN (0.03/100 patient-years) compared with none in the 6 placebo-treated women (estimated difference 0.03; 95% CI 0.02-0.06). These results provide insight into possible pathogeneses of AFF, suggesting that the current criteria for diagnosing these fractures may need to be reconsidered. © 2021 American Society for Bone and Mineral Research (ASBMR)..

Ten-Year Simulation of the Effects of Denosumab on Bone Remodeling in Human Biopsies

Postmenopausal osteoporosis is a disease manifesting in degradation of bone mass and microarchitecture, leading to weakening and increased risk of fracture. Clinical trials are an essential tool for evaluating new treatments and may provide further mechanistic understanding of their effects in vivo. However, the histomorphometry from clinical trials is limited to 2D images and reflects single time points. Biochemical markers of bone turnover give global insight into a drug's action, but not the local dynamics of the bone remodeling process and the cells involved. Additionally, comparative trials necessitate separate treatment groups, meaning only aggregated measures can be compared. In this study, in silico modeling based on histomorphometry and pharmacokinetic data was used to assess the effects of treatment versus control on μCT scans of the same biopsy samples over time, matching the changes in bone volume fraction observed in biopsies from denosumab and placebo groups through year 10 of the FREEDOM Extension trial. In the simulation, treatment decreased osteoclast number, which led to a modest increase in trabecular thickness and osteocyte stress shielding. Long-term bone turnover suppression led to increased RANKL production, followed by a small increase in osteoclast number at the end of the 6-month-dosing interval, especially at the end of the Extension study. Lack of treatment led to a significant loss of bone mass and structure. The study's results show how in silico models can generate predictions of denosumab cellular action over a 10-year period, matching static and dynamic morphometric measures assessed in clinical biopsies. The use of in silico models with clinical trial data can be a method to gain further insight into fundamental bone biology and how treatments can perturb this. With rigorous validation, such models could be used for informing the design of clinical trials, such that the number of participants could be reduced to a minimum to show efficacy. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Anabolic Agents for Postmenopausal Osteoporosis: How Do You Choose?

PURPOSE OF REVIEW

There are now three anabolic agents available for the treatment of postmenopausal women at high risk for fracture. The purpose of this review is to supply a rationale to aid in determining which agent should be used in which clinical settings.

RECENT FINDINGS

Studies over the last decade have shown that anabolic agents produce faster and larger effects against fracture than antiresorptive agents. Furthermore, trials evaluating anabolic antiresorptive treatment sequences have shown that anabolic first treatment strategies produce the greatest benefits to bone density, particularly in the hip region. However, there are no head-to-head evaluations of the three anabolic therapies with fracture outcomes or bone density, and these studies are not likely to occur. How to decide which agent to use at which time in a woman's life is unknown. We review the most significant clinical trials of anabolic agents which have assessed fracture, areal or volumetric bone density, microarchitecture, and/or bone strength, as well as information gleaned from histomorphometry studies to provide a rationale for consideration of one agent vs another in various clinical settings. There is no definitive answer to this question; all three agents increase bone strength and reduce fracture risk rapidly. Since the postmenopausal lifespan could be as long as 40-50 years, it is likely that very high-risk women will utilize different anabolic agents at different points in their lives.

Early Effects of Abaloparatide on Bone Formation and Resorption Indices in Postmenopausal Women With Osteoporosis

Anabolic osteoporosis drugs improve bone mineral density by increasing bone formation. The objective of this study was to evaluate the early effects of abaloparatide on indices of bone formation and to assess the effect of abaloparatide on modeling-based formation (MBF), remodeling-based formation (RBF), and overflow MBF (oMBF) in transiliac bone biopsies. In this open-label, single-arm study, 23 postmenopausal women with osteoporosis were treated with 80 μg abaloparatide daily. Subjects received double fluorochrome labels before treatment and before biopsy collection at 3 months. Change in dynamic histomorphometry indices in four bone envelopes were assessed. Median mineralizing surface per unit of bone surface (MS/BS) increased to 24.7%, 48.7%, 21.4%, and 16.3% of total surface after 3 months of abaloparatide treatment, representing 5.5-, 5.2-, 2.8-, and 12.9-fold changes, on cancellous, endocortical, intracortical, and periosteal surfaces (p < .001 versus baseline for all). Mineral apposition rate (MAR) was significantly increased only on intracortical surfaces. Bone formation rate (BFR/BS) was significantly increased on all four bone envelopes. Significant increases versus baseline were observed in MBF on cancellous, endocortical, and periosteal surfaces, for oMBF on cancellous and endocortical surfaces, and for RBF on cancellous, endocortical, and intracortical surfaces. Overall, modeling-based formation (MBF + oMBF) accounted for 37% and 23% of the increase in bone-forming surface on the endocortical and cancellous surfaces, respectively. Changes from baseline in serum biomarkers of bone turnover at either month 1 or month 3 were generally good surrogates for changes in histomorphometric endpoints. In conclusion, treatment with abaloparatide for 3 months stimulated bone formation on cancellous, endocortical, intracortical, and periosteal envelopes in transiliac bone biopsies obtained from postmenopausal women with osteoporosis. These increases reflected stimulation of both remodeling- and modeling-based bone formation, further elucidating the mechanisms by which abaloparatide improves bone mass and lowers fracture risk. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Mineral and organic matrix composition at bone forming surfaces in postmenopausal women with osteoporosis treated with either teriparatide or zoledronic acid

The ability of bone to resist fracture is dependent on the composite nature of its mineral and organic matrix content. Teriparatide (TPTD) and zoledronic acid (ZOL) are approved anabolic and antiresorptive therapies, respectively, to reduce fracture risk in women with postmenopausal osteoporosis. In the SHOTZ study, postmenopausal women with osteoporosis were treated with TPTD (20 μg daily, subcutaneous) or ZOL (5 mg/year, intravenous infusion) for 24 months. Iliac crest biopsies were obtained at 6 months and again at 24 months from approximately one third of the original study cohort. To investigate the early effects of these two drugs on the quality of newly formed bone, we used vibrational spectroscopic techniques to analyze tetracycline-labelled transiliac biopsies obtained from participants at the 6-month time point. Raman spectra were acquired at forming trabecular and intra-cortical surfaces (identified by fluorescent double labels), to determine mineral, organic matrix, glycosaminoglycan, and tissue water content, as well as mineral maturity/crystallinity at three specific tissue ages (1-5, 15, and ≥25 days). Fourier transformed infrared microspectroscopy was used to determine pyridinoline/divalent collagen cross-link ratios. At 6 months, treatment with TPTD versus ZOL resulted in lower mineral and higher organic matrix content, increased tissue water content, and lower mineral/matrix, mineral maturity/crystallinity, glycosaminoglycan content, and pyridinoline/divalent enzymatic collagen cross-link ratio. Our results suggest that TPTD and ZOL have differential effects on material properties of newly formed bone at individual remodeling sites, highlighting their different mechanisms of action.

Effect of Teriparatide on Bone Remodeling and Density in Premenopausal Idiopathic Osteoporosis: A Phase II Trial

CONTEXT

Premenopausal women with idiopathic osteoporosis (IOP) have abnormal skeletal microarchitecture and variable tissue-level bone formation rate (BFR).

OBJECTIVES

Compare 6 months (M) of teriparatide versus placebo on areal bone mineral density (aBMD) by dual-energy x-ray absorptiometry (DXA), bone turnover markers (BTMs) and BFR at 3M by quadruple-labeled transiliac biopsy. Characterize 12M and 24M effects of teriparatide on aBMD and whether BTMs and BFR predict response.

DESIGN

6M phase 2 randomized controlled trial (RCT) followed by open extension.

SETTING

Tertiary referral centers.

PATIENTS

Premenopausal women with IOP.

INTERVENTIONS

A total of 41 women were randomized to either teriparatide 20 mcg (n = 28) or placebo (n = 13). After 6M, those on placebo switched to teriparatide for 24M; those on teriparatide continued for 18M.

MAIN OUTCOME MEASURES

6M RCT: Between-group differences in lumbar spine (LS) aBMD (percent change from baseline), 3M BFR, and hypercalcemia. Open-label extension: Within-group change in LS aBMD over 12M and 24M. Secondary outcomes included aBMD change at other sites and relationship between BTMs, BFR, and changes in aBMD.

FINDINGS

Over 6M, LS aBMD increased by 5.5% (95% CI: 3.83, 7.19) in teriparatide and 1.5% (95% CI: -0.73, 3.83) in placebo (P = 0.007). There were increases in 3M BTMs, and BFR (cancellous and endocortical BFR: between-groups P = 0.004). Over 24M, teriparatide increased LS aBMD by 13.2% (95% CI: 10.3, 16.2), total hip by 5.2% (95% CI: 3.7, 6.7) and femoral neck by 5.0% (95% CI: 3.2, 6.7; all P ≤ 0.001). Serum N-terminal propeptides of procollagen type 1 (P1NP) and 3M endocortical BFR were moderately associated with LS aBMD response. Teriparatide was well-tolerated.

CONCLUSIONS

Teriparatide increased BFR and formation markers and was associated with marked aBMD improvements in most premenopausal women (82%) with IOP.

Modeling-Based Bone Formation in the Human Femoral Neck in Subjects Treated With Denosumab

Denosumab is associated with continued gains in hip and spine BMD with up to 10 years of treatment in postmenopausal women with osteoporosis. Despite potent inhibition of bone remodeling, findings in nonhuman primates suggest modeling-based bone formation (MBBF) may persist during denosumab treatment. This study assessed whether MBBF in the femoral neck (FN) is preserved in the context of inhibited remodeling in subjects receiving denosumab. This open-label study enrolled postmenopausal women with osteoporosis who had received two or more doses of denosumab (60 mg subcutaneously every 6 months [Q6M]) per standard of care and were planning elective total hip replacement (THR) owing to osteoarthritis of the hip. Transverse sections of the FN were obtained after THR and analyzed histomorphometrically. MBBF, based on fluorochrome labeling and presence of smooth cement lines, was evaluated in cancellous, endocortical, and periosteal envelopes of the FN. Histomorphometric parameters were used to assess MBBF and remodeling-based bone formation (RBBF) in denosumab-treated subjects (n = 4; mean age = 73.5 years; range, 70 to 78 years) and historical female controls (n = 11; mean age = 67.8 years; range, 62 to 80 years) obtained from the placebo group of a prior study and not treated with denosumab. All analyses were descriptive. All subjects in both groups exhibited MBBF in the periosteal envelope; in cancellous and endocortical envelopes, all denosumab-treated subjects and 81.8% of controls showed evidence of MBBF. Compared with controls, denosumab-treated subjects showed 9.4-fold and 2.0-fold higher mean values of MBBF in cancellous and endocortical envelopes, respectively, whereas RBBF mean values were 5.0-fold and 5.3-fold lower. In the periosteal envelope, MBBF and RBBF rates were similar between subjects and controls. These results demonstrate the occurrence of MBBF in the human FN and suggest that denosumab preserves MBBF while inhibiting remodeling, which may contribute to the observed continued gains in BMD over time after remodeling is maximally inhibited. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Loading modality and age influence teriparatide-induced bone formation in the human femoral neck

Teriparatide (TPTD) reduces risk of both vertebral and nonvertebral fracture, but increases bone mineral density (BMD) much more at the spine than the hip. TPTD and mechanical loading may have a synergistic anabolic effect on BMD, which may help explain these site-specific differences. Under normal daily activity, the femoral neck (FN) is under bending, placing one side under tension and the other under compression. We sought to further understand the relationship between mechanical loading and TPTD at the hip by investigating the effect of tensile versus compressive loading on TPTD stimulated bone formation indices in the human FN. Thirty-eight patients receiving total hip replacements for osteoarthritis were randomized to receive placebo (PBO) or TPTD for a mean treatment duration of 6 weeks prior to surgery, and double tetracycline labeling was administered to allow assessment of bone formation. The FN was harvested during surgery and analyzed for dynamic bone formation indices in the compressive and tensile regions of the endocortical and periosteal envelopes. Regression models relating outcome measures to patient characteristics including sex, age, body weight, and FN geometry were also analyzed. Overall, bone formation was higher with TPTD versus placebo on the endocortical surface, but not the periosteal surface. The level of bone formation in both TPTD and placebo groups was greater on the tensile endocortical surface and the compressive periosteal surface. There was a trend toward decreased endocortical eroded surface with TPTD in the compressive but not the tensile region. Patient age and sex explained the greatest variability in endocortical bone formation, and patient body mass and sex explained the greatest variability in periosteal bone formation. Our data represent the first dynamic comparison of teriparatide treatment under two loading modalities in human FN samples. Future work could determine whether specific hip loading intervention could amplify the benefits of teriparatide on the hip in clinical settings.

No evidence for alteration in early secondary mineralization by either alendronate, teriparatide or combination of both in transiliac bone biopsy samples from postmenopausal osteoporotic patients

The influence of treatment with alendronate (ALN), teriparatide (TPTD) or concurrent treatment with both on the human bone matrix mineralization has not yet been fully elucidated. For this purpose we analyzed quadruple fluorochrome labelled transiliac bone biopsy samples (n = 66) from postmenopausal osteoporotic women with prior and ongoing ALN (ALN-Rx arm) or without ALN (Rx-Naïve arm) after 7 months treatment with cyclic or daily TPTD or without TPTD using quantitative backscattered electron imaging and confocal scanning laser microscopy. Additionally to the bone mineralization density distribution (BMDD) of entire cancellous and cortical compartments, we measured the mineralization kinetics, i.e. the calcium concentration between the younger (Ca_DL2) and older double labels (Ca_DL1), and in interstitial bone (Ca_int) in a subset of the biopsy cohort.

We found the BMDD from the patients with prior and ongoing ALN generally shifted to higher calcium concentrations compared to those without ALN (average degree of mineralization in cancellous bone Cn.CaMean + 3.1%, p<0.001). The typical BMDD changes expected by cyclic or daily TPTD treatment due to the increased bone turnover/formation, e.g. an increase in low mineralized bone area were not observed. Additionally, we found no influence of treatment with ALN or TPTD or combination thereof on Ca_DL2, Ca_DL1, or Ca_int. Pooling the information from all groups, Ca_DL1 was +5.9% (p<0.001) higher compared to Ca_DL2, corresponding to a mineralization rate of 0.18 wt% Ca per week during the early secondary mineralization process.

Our data suggest that the patients in the ALN-Rx arm had more highly mineralized bone matrix than those without ALN due to their lower bone turnover. The reason for the unexpected BMDD findings in the TPTD treated remain unknown and cannot be attributed to altered mineralization kinetics as no differences in the time course of early secondary mineralization were observed between the treatment groups.

•

Quadruple fluorescence labeling provided analysis of early secondary bone mineralization rate in osteoporotic patients.

•

Alendronate, teriparatide or combination of both had no influence on early secondary bone mineralization in patients.

•

The early secondary mineralization rate (increase in mineral content with time) was found to be 0.18 wt% Ca per week.

•

Patients in the ALN-Rx arm had higher average bone matrix mineralization than the patients in the Rx-naïve arm.

Women With Pregnancy and Lactation-Associated Osteoporosis (PLO) Have Low Bone Remodeling Rates at the Tissue Level

Pregnancy and lactation-associated osteoporosis (PLO) is a rare, severe, early form of osteoporosis in which young women present with fractures, usually multiple vertebral fractures, during late pregnancy or lactation. In studies of idiopathic osteoporosis (IOP) in premenopausal women, we enrolled 78 women with low-trauma fractures and 40 healthy controls, all with normal menses and no secondary cause of bone loss. In 15 of the affected women, the PLO subgroup, fractures had occurred during late pregnancy or lactation. We hypothesized that clinical, bone structural, and metabolic characteristics would differ between women with PLO and those with (non-PLO) IOP and controls. All were evaluated > 12 months postpartum, when structural and remodeling characteristics would be expected to reflect baseline premenopausal status rather than transient postpartum changes. As previously reported, affected subjects (PLO and IOP) had BMD and microarchitectural deficiencies compared to controls. Women with PLO did not differ from those with IOP in terms of age, BMI, body fat, menarcheal age, parity, or age at first pregnancy. However, women with PLO had a more severe clinical presentation than those with IOP: more fractures (5.5 ± 3.3 versus 2.6 ± 2.1; p = 0.005); more vertebral fractures (80% versus 17%; p < 0.001); and higher prevalence of multiple fractures. BMD deficits were more profound and cortical width tended to be lower in PLO. PLO subjects also had significantly lower tissue-level mineral apposition rate and bone formation rates (0.005 ± 0.005 versus 0.011 ± 0.010 mm² /mm/year; p = 0.006), as well as lower serum P1NP (33 ± 12 versus 44 ± 18 µg/L; p = 0.02) and CTX (257 ± 102 versus 355 ± 193 pg/mL; p = 0.01) than IOP. The finding that women with PLO have a low bone remodeling state assessed more than a year postpartum increases our understanding of the pathogenic mechanism of PLO. We conclude that women with PLO may have underlying osteoblast functional deficits which could affect their therapeutic response to osteoanabolic medications. © 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.

Administration of teriparatide for four years cyclically compared to two years daily in treatment Naïve and alendronate treated women

PURPOSE

We evaluated if equivalent doses of TPTD given cyclically over 4-years could increase BMD >2-years of daily TPTD in 2 cohorts of women; previously untreated (Rx-Naïve) and women previously treated with ALN (ALN-Rx).

METHODS

In Rx-Naïve, women were randomized to daily TPTD for 24 months (Daily; n = 23) or cyclic TPTD for 48 months (3 months on, 3 months off; Cyclic; n = 25). In ALN-Rx, women were randomized to continued ALN plus daily TPTD for 24 months, followed by ALN alone for 24 months (Daily; n = 21) or TPTD for 48 months (3 months on, 3 months off) while ALN was continued (Cyclic; n = 20). BMD (DXA) was measured at spine (LS), total hip (TH) and femoral neck (FN). The primary analysis compared 4 years of cyclic therapy to 2 years of daily therapy in RX-naïve and ALN-RX cohorts.

RESULTS

In Rx-Naïve, BMD changes at 24 months after Daily TPTD vs. 48 months after Cyclic TPTD were: LS 8.6% vs. 6.9%; TH 2.5% vs. 2.6%, and FN 1.6% vs. 2.2%. None of the BMD changes differed significantly between groups but all changes were significant over time within each group (p < 0.01 except for FN where p = 0.17 Daily; p = 0.09 Cyclic). In ALN-Rx, BMD changes at 24 months after Daily TPTD vs. 48 months after Cyclic TPTD were: LS 7.5% vs. 7.2%; TH 3.8% vs. 4.1%, and FN 3.2% vs. 2.5%. There were no differences between groups but all changes were significant within each group (p < 0.01).

CONCLUSION

The same cumulative dose of TPTD given cyclically for 4-years, does not increase BMD more than standard daily TPTD over 2-years in either Rx-Naïve or ALN-Rx women.

TRIAL REGISTRATION

NCT00668941.

The Effects of Long-term Administration of rhPTH(1-84) in Hypoparathyroidism by Bone Histomorphometry

Hypoparathyroidism is a rare disorder that is associated with abnormal bone properties. Recombinant human parathyroid hormone (1-84) [rhPTH(1-84)] in short-term studies has beneficial skeletal effects. Although rhPTH(1-84) will likely be used indefinitely, long-term effects on skeletal microstructure are unknown. We therefore studied histomorphometric changes with transiliac crest bone biopsies before and after 8.3 ± 1 years of rhPTH(1-84) in 13 hypoparathyroid subjects compared with 45 controls. Before institution of rhPTH(1-84), skeletal remodeling indices were markedly suppressed. With long-term treatment, indices of bone remodeling increased. Mineralizing surface increased by 26-fold (0.3 ± 1 to 7.9 ± 7%, p = 0.003), bone formation rate increased by 15-fold (0.003 ± 0.01 to 0.047 ± 0.05 μm² /μm/day, p = 0.007), osteoid width doubled (1.9 ± 1 to 4.3 ± 1 lamellae, p = 0.017), and osteoid surface tripled (3.3 ± 3 to 10.8 ± 6%, p = 0.011). Bone resorption as measured by eroded surface increased (4.6 ± 2 to 7.5 ± 3%, p = 0.021). Structural changes demonstrated intratrabecular tunneling, with increases in cancellous bone volume (19.6 ± 5 to 29.1 ± 11%, p = 0.017) and trabecular number (1.8 ± 1 to 2.5 ± 1 #/mm, p = 0.025). Cortical porosity tended to increase (6.3 ± 5 to 9.5 ± 3%, p = 0.07). Mineralizing surface, osteoid surface, and eroded surface surpassed control levels, as did cancellous bone volume, trabecular number, and cortical porosity. These data, the first to reflect such long exposure of any PTH for any disease, illustrate that PTH establishes and maintains a new skeletal state for at least 8 years in hypoparathyroidism. © 2018 American Society for Bone and Mineral Research.

Effects of Long-Term Denosumab on Bone Histomorphometry and Mineralization in Women With Postmenopausal Osteoporosis

CONTEXT

Denosumab is a potent antiresorptive agent that reduces fractures in postmenopausal women with osteoporosis.

OBJECTIVE

Determine effects of up to 10 years of denosumab on bone histology, remodeling, and matrix mineralization characteristics.

DESIGN AND SETTING

International, multicenter, randomized, double-blind trial [Fracture Reduction Evaluation of Denosumab in Osteoporosis Every 6 Months (FREEDOM)] with a long-term open-label extension.

PATIENTS

Postmenopausal women with osteoporosis (92 women in FREEDOM, 46 in extension) who provided iliac bone biopsies, including 11 who provided biopsies at multiple time points.

INTERVENTIONS

FREEDOM subjects were randomized 1:1 to subcutaneous denosumab 60 mg or placebo every 6 months for 3 years. Long-term extension subjects continued receiving denosumab, open-label, for 7 additional years.

OUTCOMES

Bone histology, histomorphometry, matrix mineralization.

RESULTS

Ten-year denosumab biopsies showed normal histology. Bone histomorphometry indicated normal bone structure and reduced bone remodeling after 10 years of denosumab, similar to levels after 2 and/or 3 and 5 years of denosumab. The degree of mineralization of bone was increased and mineralization heterogeneity was reduced in the denosumab years 2/3 group vs placebo. Changes in these mineralization variables progressed from years 2/3 to year 5 of denosumab, but not thereafter.

CONCLUSIONS

Denosumab for 2/3, 5, and 10 years was associated with normal histology, low bone remodeling rate, increased matrix mineralization, and lower mineralization heterogeneity compared with placebo. These variables were unchanged from year 5 to year 10. These data, in combination with the maintenance of low fracture rates for up to 10 years as previously reported with denosumab therapy, suggest that strong, prolonged remodeling inhibition does not impair bone strength.

Longitudinal Effects of Teriparatide or Zoledronic Acid on Bone Modeling- and Remodeling-Based Formation in the SHOTZ Study

Previously, we reported on bone histomorphometry, biochemical markers, and bone mineral density distribution after 6 and 24 months of treatment with teriparatide (TPTD) or zoledronic acid (ZOL) in the SHOTZ study. The study included a 12-month primary study period, with treatment (TPTD 20 μg/d by subcutaneous injection or ZOL 5 mg/yr by intravenous infusion) randomized and double-blind until the month 6 biopsy (TPTD, n = 28; ZOL, n = 30 evaluable), then open-label, with an optional 12-month extension receiving the original treatment. A second biopsy (TPTD, n = 10; ZOL, n = 9) was collected from the contralateral side at month 24. Here we present data on remodeling-based bone formation (RBF), modeling-based bone formation (MBF), and overflow modeling-based bone formation (oMBF, modeling overflow adjacent to RBF sites) in the cancellous, endocortical, and periosteal envelopes. RBF was significantly greater after TPTD versus ZOL in all envelopes at 6 and 24 months, except the periosteal envelope at 24 months. MBF was significantly greater with TPTD in all envelopes at 6 months but not at 24 months. oMBF was significantly greater at 6 months in the cancellous and endocortical envelopes with TPTD, with no significant differences at 24 months. At 6 months, total bone formation surface was also significantly greater in each envelope with TPTD treatment (all p < 0.001). For within-group comparisons from 6 to 24 months, no statistically significant changes were observed in RBF, MBF, or oMBF in any envelope for either the TPTD or ZOL treatment groups. Overall, TPTD treatment was associated with greater bone formation than ZOL. Taken together the data support the view that ZOL is a traditional antiremodeling agent, wheareas TPTD is a proremodeling anabolic agent that increases bone formation, especially that associated with bone remodeling, including related overflow modeling, with substantial modeling-based bone formation early in the course of treatment. © 2017 American Society for Bone and Mineral Research.

Remodeling- and Modeling-Based Bone Formation With Teriparatide Versus Denosumab: A Longitudinal Analysis From Baseline to 3 Months in the AVA Study

There has been renewed interest of late in the role of modeling-based formation (MBF) during osteoporosis therapy. Here we describe early effects of an established anabolic (teriparatide) versus antiresorptive (denosumab) agent on remodeling-based formation (RBF), MBF, and overflow MBF (oMBF) in human transiliac bone biopsies. Postmenopausal women with osteoporosis received subcutaneous teriparatide (n = 33, 20 μg/d) or denosumab (n = 36, 60 mg once/6 months), open-label for 6 months at 7 US and Canadian sites. Subjects received double fluorochrome labeling at baseline and before biopsy at 3 months. Sites of bone formation were designated as MBF if the underlying cement line was smooth, RBF if scalloped, and oMBF if formed over smooth cement lines adjacent to scalloped reversal lines. At baseline, mean RBF/bone surface (BS), MBF/BS, and oMBF/BS were similar between the teriparatide and denosumab groups in each bone envelope assessed (cancellous, endocortical, periosteal). All types of formation significantly increased from baseline in the cancellous and endocortical envelopes (differences p < 0.001) with teriparatide (range of changes 2.9- to 21.9-fold), as did MBF in the periosteum (p < 0.001). In contrast, all types of formation were decreased or not significantly changed with denosumab, except MBF/BS in the cancellous envelope, which increased 2.5-fold (difference p = 0.048). These data highlight mechanistic differences between these agents: all 3 types of bone formation increased significantly with teriparatide, whereas formation was predominantly decreased or not significantly changed with denosumab, except for a slight increase in MBF/BS in the cancellous envelope. © 2017 American Society for Bone and Mineral Research.

New insights on diabetes and bone metabolism

Diabetes mellitus is a common chronic metabolic disease worldwide whose prevalence has increased during the last decades. Besides its more commonly recognized complications, such as macrovascular disease, retinopathy, nephropathy and neuropathy, diabetes related bone disease has gained growing attention. Diabetic patients are more prone to fracture than the general population as well as to low turnover bone disease in the chronic kidney disease setting. In this review, we discuss the relationship between diabetes and bone as well as the pathogenesis of bone fragility in T2D.

10 years of denosumab treatment in postmenopausal women with osteoporosis: results from the phase 3 randomised FREEDOM trial and open-label extension

BACKGROUND

Long-term safety and efficacy of osteoporosis treatment are important because of the chronic nature of the disease. We aimed to assess the long-term safety and efficacy of denosumab, which is widely used for the treatment of postmenopausal women with osteoporosis.

METHODS

In the multicentre, randomised, double-blind, placebo-controlled, phase 3 FREEDOM trial, postmenopausal women aged 60-90 years with osteoporosis were enrolled in 214 centres in North America, Europe, Latin America, and Australasia and were randomly assigned (1:1) to receive 60 mg subcutaneous denosumab or placebo every 6 months for 3 years. All participants who completed the FREEDOM trial without discontinuing treatment or missing more than one dose of investigational product were eligible to enrol in the open-label, 7-year extension, in which all participants received denosumab. The data represent up to 10 years of denosumab exposure for women who received 3 years of denosumab in FREEDOM and continued in the extension (long-term group), and up to 7 years for women who received 3 years of placebo and transitioned to denosumab in the extension (crossover group). The primary outcome was safety monitoring, comprising assessments of adverse event incidence and serious adverse event incidence, changes in safety laboratory analytes (ie, serum chemistry and haematology), and participant incidence of denosumab antibody formation. Secondary outcomes included new vertebral, hip, and non-vertebral fractures as well as bone mineral density (BMD) at the lumbar spine, total hip, femoral neck, and one-third radius. Analyses were done according to the randomised FREEDOM treatment assignments. All participants who received at least one dose of investigational product in FREEDOM or the extension were included in the combined safety analyses. All participants who enrolled in the extension with observed data were included in the efficacy analyses. The FREEDOM trial (NCT00089791) and its extension (NCT00523341) are both registered with ClinicalTrials.gov.

FINDINGS

Between Aug 3, 2004, and June 1, 2005, 7808 women were enrolled in the FREEDOM study. 5928 (76%) women were eligible for enrolment in the extension, and of these, 4550 (77%) were enrolled (2343 long-term, 2207 crossover) between Aug 7, 2007, and June 20, 2008. 2626 women (1343 long-term; 1283 crossover) completed the extension. The yearly exposure-adjusted participant incidence of adverse events for all individuals receiving denosumab decreased from 165·3 to 95·9 per 100 participant-years over the course of 10 years. Serious adverse event rates were generally stable over time, varying between 11·5 and 14·4 per 100 participant-years. One atypical femoral fracture occurred in each group during the extension. Seven cases of osteonecrosis of the jaw were reported in the long-term group and six cases in the crossover group. The yearly incidence of new vertebral fractures (ranging from 0·90% to 1·86%) and non-vertebral fractures (ranging from 0·84% to 2·55%) remained low during the extension, similar to rates observed in the denosumab group during the first three years of the FREEDOM study, and lower than rates projected for a virtual long-term placebo cohort. In the long-term group, BMD increased from FREEDOM baseline by 21·7% at the lumbar spine, 9·2% at total hip, 9·0% at femoral neck, and 2·7% at the one-third radius. In the crossover group, BMD increased from extension baseline by 16·5% at the lumbar spine, 7·4% at total hip, 7·1% at femoral neck, and 2·3% at one-third radius.

INTERPRETATION

Denosumab treatment for up to 10 years was associated with low rates of adverse events, low fracture incidence compared with that observed during the original trial, and continued increases in BMD without plateau.

FUNDING

Amgen.

IGF-1 Receptor Expression on Circulating Osteoblast Progenitor Cells Predicts Tissue-Based Bone Formation Rate and Response to Teriparatide in Premenopausal Women With Idiopathic Osteoporosis

We have previously reported that premenopausal women with idiopathic osteoporosis (IOP) have profound microarchitectural deficiencies and heterogeneous bone remodeling. Those with the lowest bone formation rate have higher baseline serum insulin-like growth factor-1 (IGF-1) levels and less robust response to teriparatide. Because IGF-1 stimulates bone formation and is critical for teriparatide action on osteoblasts, these findings suggest a state of IGF-1 resistance in some IOP women. To further investigate the hypothesis that osteoblast and IGF-1-related mechanisms mediate differential responsiveness to teriparatide in IOP, we studied circulating osteoblast progenitor (COP) cells and their IGF-1 receptor (IGF-1R) expression. In premenopausal women with IOP, peripheral blood mononuclear cells (PBMCs) were obtained at baseline (n = 25) and over 24 months of teriparatide treatment (n = 11). Flow cytometry was used to identify and quantify COPs (non-hematopoetic lineage cells expressing osteocalcin and RUNX2) and to quantify IGF-1R expression levels. At baseline, both the percent of PBMCs that were COPs (%COP) and COP cell-surface IGF-1R expression correlated directly with several histomorphometric indices of bone formation in tetracycline-labeled transiliac biopsies. In treated subjects, both %COP and IGF-1R expression increased promptly after teriparatide, returning toward baseline by 18 months. Although neither baseline %COP nor increase in %COP after 3 months predicted the bone mineral density (BMD) response to teriparatide, the percent increase in IGF-1R expression on COPs at 3 months correlated directly with the BMD response to teriparatide. Additionally, lower IGF-1R expression after teriparatide was associated with higher body fat, suggesting links between teriparatide resistance, body composition, and the GH/IGF-1 axis. In conclusion, these assays may be useful to characterize bone remodeling noninvasively and may serve to predict early response to teriparatide and possibly other bone formation-stimulating medications. These new tools may also have utility in the mechanistic investigation of teriparatide resistance in premenopausal IOP and perhaps in other populations. © 2017 American Society for Bone and Mineral Research.

Parathyroid Hormone Directs Bone Marrow Mesenchymal Cell Fate

Intermittent PTH administration builds bone mass and prevents fractures, but its mechanism of action is unclear. We genetically deleted the PTH/PTHrP receptor (PTH1R) in mesenchymal stem cells using Prx1Cre and found low bone formation, increased bone resorption, and high bone marrow adipose tissue (BMAT). Bone marrow adipocytes traced to Prx1 and expressed classic adipogenic markers and high receptor activator of nuclear factor kappa B ligand (Rankl) expression. RANKL levels were also elevated in bone marrow supernatant and serum, but undetectable in other adipose depots. By cell sorting, Pref1⁺RANKL⁺ marrow progenitors were twice as great in mutant versus control marrow. Intermittent PTH administration to control mice reduced BMAT significantly. A similar finding was noted in male osteoporotic patients. Thus, marrow adipocytes exhibit osteogenic and adipogenic characteristics, are uniquely responsive to PTH, and secrete RANKL. These studies reveal an important mechanism for PTH's therapeutic action through its ability to direct mesenchymal cell fate.

Treatment Sequence Matters: Anabolic and Antiresorptive Therapy for Osteoporosis

The effects of anabolic medications (teriparatide [TPTD] and parathyroid hormone [PTH]) differ in patients who have received recent treatment with potent antiresorptives. This perspective reviews studies evaluating bone density (BMD) and histomorphometric effects of treatment sequences beginning with TPTD/PTH followed by potent antiresorptives and those beginning with potent antiresorptives followed by switching to or adding TPTD. Effect of treatment sequence on spine BMD outcome is minor, with modest quantitative differences. However, when individuals established on potent bisphosphonates are switched to TPTD, hip BMD declines below baseline for at least the first 12 months after the switch to TPTD. This transient hip BMD loss is more prominent when the antiresorptive is denosumab; in this setting, hip BMD remains below baseline for almost a full 24 months. In a controlled comparison of those who switched from alendronate to TPTD versus those who added TPTD to ongoing alendronate, the effect on hip BMD was improved with combination therapy. Furthermore, hip strength improved with the addition of TPTD to ongoing alendronate, whereas it was neutral after switching from alendronate to TPTD, primarily due to the effect on cortical bone. Bone biopsy studies indicate that TPTD stimulates bone formation in patients who have not been treated previously as well as in patients on prior and ongoing bisphosphonates. Histomorphometric evidence suggests that use of alendronate with TPTD blocks the TPTD-induced increase in cortical porosity. When possible, we suggest anabolic therapy first, followed by potent antiresorptive therapy. The common practice of switching to TPTD only after patients have an inadequate response to antiresorptives (intercurrent fracture or inadequate BMD effect) is not the optimal utilization of anabolic treatment. In fact, this may result in transient loss of hip BMD and strength. In this setting, continuing a potent antiresorptive while starting TPTD might improve hip outcomes. © 2017 American Society for Bone and Mineral Research.

Bone modeling and remodeling: potential as therapeutic targets for the treatment of osteoporosis

The adult skeleton is renewed by remodeling throughout life. Bone remodeling is a process where osteoclasts and osteoblasts work sequentially in the same bone remodeling unit. After the attainment of peak bone mass, bone remodeling is balanced and bone mass is stable for one or two decades until age-related bone loss begins. Age-related bone loss is caused by increases in resorptive activity and reduced bone formation. The relative importance of cortical remodeling increases with age as cancellous bone is lost and remodeling activity in both compartments increases. Bone modeling describes the process whereby bones are shaped or reshaped by the independent action of osteoblast and osteoclasts. The activities of osteoblasts and osteoclasts are not necessarily coupled anatomically or temporally. Bone modeling defines skeletal development and growth but continues throughout life. Modeling-based bone formation contributes to the periosteal expansion, just as remodeling-based resorption is responsible for the medullary expansion seen at the long bones with aging. Existing and upcoming treatments affect remodeling as well as modeling. Teriparatide stimulates bone formation, 70% of which is remodeling based and 20-30% is modeling based. The vast majority of modeling represents overflow from remodeling units rather than de novo modeling. Denosumab inhibits bone remodeling but is permissive for modeling at cortex. Odanacatib inhibits bone resorption by inhibiting cathepsin K activity, whereas modeling-based bone formation is stimulated at periosteal surfaces. Inhibition of sclerostin stimulates bone formation and histomorphometric analysis demonstrated that bone formation is predominantly modeling based. The bone-mass response to some osteoporosis treatments in humans certainly suggests that nonremodeling mechanisms contribute to this response and bone modeling may be such a mechanism. To date, this has only been demonstrated for teriparatide, however, it is clear that rediscovering a phenomenon that was first observed more half a century ago will have an important impact on our understanding of how new antifracture treatments work.

Effects of Daily or Cyclic Teriparatide on Bone Formation in the Iliac Crest in Women on No Prior Therapy and in Women on Alendronate

There is little information on the effects of combination therapy for osteoporosis at the tissue level. Using quadruple tetracycline-labeled bone biopsies, we have compared the bone formation response to teriparatide (TPTD) in treatment-naïve subjects (Rx-Naïve) and in subjects on prior and ongoing alendronate (ALN) treatment (ALN-Rx). Three bone envelopes were analyzed: cancellous, endocortical, and intracortical. TPTD was given as a standard, continuous daily injection or as a cyclic regimen (3 months on daily TPTD, 3 months off, 3 months on daily TPTD). Subjects were biopsied at 7 weeks and at 7 months to allow comparison of the bone formation response to the first and second cycles of TPTD. Baseline values for dynamic bone formation indices were lower in ALN-Rx than Rx-Naïve subjects. Both Rx-Naïve and ALN-RX subjects responded to TPTD with significant increases in bone formation indices at both time points. With cyclic TPTD treatment, the first and second cycles of TPTD stimulated bone formation rate in the cancellous and endocortical envelopes to a similar extent in ALN-Rx and Rx-Naïve subjects. However, in Rx-Naïve patients, bone formation rate (BFR/BS) was higher in patients receiving daily treatment compared with those receiving cyclic TPTD treatment in all three envelopes in the 7-month biopsies. This suggests that the cyclic approach does not provide a skeletal benefit in treatment-naive patients. In the 7-month biopsies, cortical porosity was higher in the Rx-Naïve group receiving daily TPTD than in all other groups. These data provide supporting evidence at the tissue level for previous biochemical and densitometric data suggesting that addition of either cyclic or daily TPTD to ongoing ALN treatment may be an effective approach for patients with severe osteoporosis already treated with ALN who remain at high risk of fracture. © 2016 American Society for Bone and Mineral Research.

Differential Effects of Teriparatide and Zoledronic Acid on Bone Mineralization Density Distribution at 6 and 24 Months in the SHOTZ Study

The Skeletal Histomorphometry in Patients on Teriparatide or Zoledronic Acid Therapy (SHOTZ) study assessed the progressive effects of teriparatide (TPTD) and zoledronic acid (ZOL) on bone remodeling and material properties in postmenopausal women with osteoporosis. Previously, we reported that biochemical and histomorphometric bone formation indices were significantly higher in patients receiving TPTD versus ZOL. Here we report bone mineralization density distribution (BMDD) results based on quantitative backscattered electron imaging (qBEI). The 12-month primary study was randomized and double blind until the month 6 biopsy, then open label. Patients (TPTD, n = 28; ZOL, n = 31) were then eligible to enter a 12-month open-label extension with their original treatment: TPTD 20 μg/d (subcutaneous injection) or ZOL 5 mg/yr (intravenous infusion). A second biopsy was collected from the contralateral side at month 24 (TPTD, n = 10; ZOL, n = 10). In cancellous bone, ZOL treatment was associated at 6 and 24 months with significantly higher average degree of mineralization (CaMEAN, +2.2%, p = 0.018; +3.9%, p = 0.009, respectively) and with lower percentage of low mineralized areas (CaLOW , -34.6%, p = 0.029; -33.7%, p = 0.025, respectively) and heterogeneity of mineralization CaWIDTH (-12.3%, p = 0.003; -9.9%, p = 0.012, respectively), indicating higher mineralization density and more homogeneous mineral content versus TPTD. Within the ZOL group, significant changes were found in all parameters from month 6 to 24, indicating a progressive increase in mineralization density. In sharp contrast, mineralization density did not increase over time with TPTD, reflecting ongoing deposition of new bone. Similar results were observed in cortical bone. In this study, TPTD stimulated new bone formation, producing a mineralized bone matrix that remained relatively heterogeneous with a stable mean mineral content. ZOL slowed bone turnover and prolonged secondary mineralization, producing a progressively more homogeneous and highly mineralized bone matrix. Although both TPTD and ZOL increase clinical measures of bone mineral density (BMD), this study shows that the underlying mechanisms of the BMD increases are fundamentally different. © 2016 American Society for Bone and Mineral Research.

A Longitudinal Study of Skeletal Histomorphometry at 6 and 24 Months Across Four Bone Envelopes in Postmenopausal Women With Osteoporosis Receiving Teriparatide or Zoledronic Acid in the SHOTZ Trial

Previously, we reported the effects of teriparatide (TPTD) and zoledronic acid (ZOL) on bone formation based on biochemical markers and bone histomorphometry of the cancellous envelope at month 6 in postmenopausal women with osteoporosis who participated in the 12-month primary Skeletal Histomorphometry in Subjects on Teriparatide or Zoledronic Acid Therapy (SHOTZ) study. Patients were eligible to enter a 12-month extension on their original treatment regimen: TPTD 20 μg/day (s.c. injection) or ZOL 5 mg/year (i.v. infusion). A second biopsy was performed at month 24. Here we report longitudinal changes between and within each treatment group in the cancellous, endocortical, intracortical, and periosteal bone envelopes in patients with evaluable biopsies at months 6 and 24 (paired data set: TPTD, n = 10; ZOL, n = 9). Between-group differences are also reported in the larger set of patients with evaluable biopsies at month 6 (TPTD, n = 28; ZOL, n = 30). Data from the cancellous envelope at month 6 or month 24 provided a reference to compare differences across envelopes within each treatment group. The 24-month results extend our earlier report that TPTD and ZOL possess different tissue-level mechanisms of action. Moreover, these differences persisted for at least 2 years in all four bone envelopes. Few longitudinal differences were observed within or across bone envelopes in ZOL-treated patients, suggesting that the low bone formation indices at month 6 persisted to month 24. Conversely, the magnitude of the effect of TPTD on bone formation varied across individual envelopes: median values for mineralizing surface (MS/BS) and bone formation rate (BFR/BS) at month 6 were approximately 3-fold to 5-fold higher in the endocortical and intracortical envelopes compared to the cancellous envelope. Although MS/BS and BFR/BS declined in these envelopes at month 24, median values continued to exceed, or were not significantly different from, those in the cancellous envelope. This study demonstrates for the first time that bone formation indices are higher with TPTD treatment than with ZOL in all four bone envelopes and the difference persists for at least 2 years. Moreover, the magnitude of the effect of TPTD in cortical bone remains robust at 24 months. © 2016 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research (ASBMR).

Effects of Parathyroid Hormone Administration on Bone Strength in Hypoparathyroidism

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

Differential Effects of Teriparatide and Denosumab on Intact PTH and Bone Formation Indices: AVA Osteoporosis Study

We compared effects of teriparatide and denosumab on PTH, bone turnover markers, and bone histomorphometry in osteoporotic postmenopausal women. The findings were inconsistent with an early indirect anabolic effect of denosumab.

Effect of Teriparatide on Bone Formation in the Human Femoral Neck

PURPOSE

Teriparatide (TPTD) improves bone mass and microstructure resulting in reduced risk of vertebral and nonvertebral fractures. However, hip bone mineral density improvements are modest and there are no data confirming that TPTD reduces hip fracture risk. To study the effects of TPTD on the proximal femur, we performed a double-blind trial of TPTD vs placebo (PBO) in patients with osteoarthritis from whom femoral neck (FN) samples were obtained at total hip replacement (THR) surgery.

METHODS

Participants were randomly assigned to receive TPTD or PBO for an average of 40 days before THR. Double tetracycline labeling was initiated 21 days prior to THR to allow histomorphometric assessment of bone formation. During the THR, an intact sample of the FN was procured, fixed, and sectioned transversely. Serum levels of bone turnover markers were measured at baseline and during the THR. Standard histomorphometric parameters were measured and calculated on four bone envelopes (cancellous, endocortical, intracortical, and periosteal). The primary outcome measure was bone formation rate/bone surface (BFR/BS).

RESULTS

Forty individuals were enrolled (25 women, mean age, 71.5 ± 8.0 y and 15 men, mean age, 68.9 ± 7.7 y). In cancellous and endocortical envelopes, BFR/BS was 100% higher in the TPTD vs PBO group (P < .05). Bone turnover markers measured at the time of THR correlated with BFR/BS.

CONCLUSIONS

TPTD stimulates bone formation rapidly in cancellous and endocortical envelopes of the FN. Our findings provide a mechanistic basis for TPTD-mediated improvement in FN bone mass and ultimately hip strength. This study is the first demonstration of the effect of any osteoporosis medication on osteoblast activity in the human proximal femur.

PTH(1-84) Administration in Hypoparathyroidism Transiently Reduces Bone Matrix Mineralization

Patients with hypoparathyroidism have low circulating parathyroid (PTH) levels and higher cancellous bone volume and trabecular thickness. Treatment with PTH(1-84) was shown to increase abnormally low bone remodeling dynamics. In this work, we studied the effect of 1-year or 2-year PTH(1-84) treatment on cancellous and cortical bone mineralization density distribution (Cn.BMDD and Ct.BMDD) based on quantitative backscattered electron imaging (qBEI) in paired transiliac bone biopsy samples. The study cohort comprised 30 adult hypoparathyroid patients (14 treated for 1 year; 16 treated for 2 years). At baseline, Cn.BMDD was shifted to higher mineralization densities in both treatment groups (average degree of mineralization Cn.CaMean +3.9% and +2.7%, p < 0.001) compared to reference BMDD. After 1-year PTH(1-84), Cn.CaMean was significantly lower than that at baseline (-6.3%, p < 0.001), whereas in the 2-year PTH(1-84) group Cn.CaMean did not differ from baseline. Significant changes of Ct.BMDD were observed in the 1-year treatment group only. The change in histomorphometric bone formation (mineralizing surface) was predictive for Cn.BMDD outcomes in the 1-year PTH(1-84) group, but not in the 2-year PTH(1-84) group. Our findings suggest higher baseline bone matrix mineralization consistent with the decreased bone turnover in hypoparathyroidism. PTH(1-84) treatment caused differential effects dependent on treatment duration that were consistent with the histomorphometric bone formation outcomes. The greater increase in bone formation during the first year of treatment was associated with a decrease in bone matrix mineralization, suggesting that PTH(1-84) exposure to the hypoparathyroid skeleton has the greatest effects on BMDD early in treatment.

Bone Density After Teriparatide Discontinuation in Premenopausal Idiopathic Osteoporosis

CONTEXT

Without antiresorptive therapy, postmenopausal women lose bone mass after teriparatide (TPTD) discontinuation; estrogen treatment prevents bone loss in this setting. It is not known whether premenopausal women with regular menses lose bone mass after teriparatide discontinuation.

OBJECTIVE

This study aimed to test the hypothesis that normally menstruating premenopausal women with idiopathic osteoporosis (IOP) will maintain teriparatide-associated bone mineral density (BMD) gains after medication cessation.

DESIGN

Twenty-one premenopausal IOP women previously enrolled in an open-label pilot study of teriparatide (20 mcg for 18-24 mo), had substantial BMD increases at the lumbar spine (LS; 10.8 ± 8.3%), total hip (TH; 6.2 ± 5.6%), and femoral neck (7.6 ± 3.4%). For this study, BMD was remeasured 2.0 ± 0.6 years after teriparatide cessation.

PARTICIPANTS

Fifteen women, who had gained 11.1 ± 7.2% at LS and 6.1 ± 6.5% at TH and were premenopausal at teriparatide completion, were followed without antiresorptive treatment.

RESULTS

Two years after completing teriparatide, BMD declined by 4.8 ± 4.3% (P = .0007) at the LS. In contrast, BMD remained stable at the femoral neck (-1.5 ± 4.2%) and TH (-1.1 ± 3.7%). Those who sustained LS bone loss >3% (-7.3 ± 2.9%; n = 10), did not differ from those with stable LS BMD (0.1 ± 1.1%; n=5) with regard to baseline body mass index, BMD at any site, or duration of followup, but were significantly older at re-evaluation (46 ± 3 vs 38 ± 7; P = .046), had larger increases in LS BMD during teriparatide treatment and higher cancellous bone remodeling on transiliac biopsy at baseline and completion of teriparatide treatment. Serum bone turnover markers did not differ at baseline or teriparatide completion, but tended to be higher at the re-evaluation timepoint in those with post-teriparatide bone loss.

CONCLUSIONS

These findings lead us to conclude that premenopausal women with IOP, particularly those over 40, may require antiresorptive treatment to prevent bone loss after teriparatide.

Subtle changes in bone mineralization density distribution in most severely affected patients with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is associated with low aBMD as measured by DXA and altered microstructure as assessed by bone histomorphometry and microcomputed tomography. Knowledge of bone matrix mineralization is lacking in COPD. Using quantitative backscatter electron imaging (qBEI), we assessed cancellous (Cn.) and cortical (Ct.) bone mineralization density distribution (BMDD) in 19 postmenopausal women (62.1 ± 7.3 years of age) with COPD. Eight had sustained fragility fractures, and 13 had received treatment with inhaled glucocorticoids. The BMDD outcomes from the patients were compared with healthy reference data and were correlated with previous clinical and histomorphometric findings. In general, the BMDD outcomes for the patients were not significantly different from the reference data. Neither the subgroups of with or without fragility fractures or of who did or did not receive inhaled glucocorticoid treatment, showed differences in BMDD. However, subgroup comparison according to severity revealed 10% decreased cancellous mineralization heterogeneity (Cn.CaWidth) for the most severely affected compared with less affected patients (p=0.042) and compared with healthy premenopausal controls (p=0.021). BMDD parameters were highly correlated with histomorphometric cancellous bone volume (BV/TV) and formation indices: mean degree of mineralization (Cn.CaMean) versus BV/TV (r=0.58, p=0.009), and Cn.CaMean and Ct.CaMean versus bone formation rate (BFR/BS) (r=-0.71, p<0.001). In particular, those with lower BV/TV (<50th percentile) had significantly lower Cn.CaMean (p=0.037) and higher Cn.CaLow (p=0.020) compared with those with higher (>50th percentile) BV/TV. The normality in most of the BMDD parameters and bone formation rates as well as the significant correlations between them suggests unaffected mineralization processes in COPD. Our findings also indicate no significant negative effect of treatment with inhaled glucocorticoids on the bone mineralization pattern. However, the observed concomitant occurrence of relatively lower bone volumes with lower bone matrix mineralization will both contribute to the reduced aBMD in some patients with COPD.

Marrow adiposity assessed on transiliac crest biopsy samples correlates with noninvasive measurement of marrow adiposity by proton magnetic resonance spectroscopy ((1)H-MRS) at the spine but not the femur

Measurement of marrow fat (MF) is important to the study of bone fragility. We measured MF on iliac biopsies and by spine/hip magnetic resonance spectroscopy in the same subjects. Noninvasively assessed spine MF and histomorphometrically assessed MF correlated well. MF quantity and relationships with bone volume differed by measurement site.

INTRODUCTION

Excess marrow fat has been implicated in the pathogenesis of osteoporosis in several populations. In the bone marrow, adipocytes and osteoblasts share a common precursor and are reciprocally regulated. In addition, adipocytes may secrete toxic fatty acids and adipokines that adversely affect osteoblasts. Measurement of marrow fat is important to the study of mechanisms of bone fragility. Marrow fat can be quantified on bone biopsy samples by histomorphometry and noninvasively by proton magnetic resonance spectroscopy ((1)H-MRS). In this study, we evaluate relationships between marrow fat assessed using both methods in the same subjects for the first time.

METHODS

Sixteen premenopausal women, nine with idiopathic osteoporosis and seven normal controls, had marrow fat measured at the iliac crest by bone biopsy and at the lumbar spine (L3) and proximal femur by (1)H-MRS.

RESULTS

At L3, fat fraction by (1)H-MRS correlated directly and significantly with marrow fat variables on iliac crest biopsies (r = 0.5-0.8). In contrast, there were no significant correlations between fat fraction at the femur and marrow fat on biopsies. Marrow fat quantity (%) was greater at the femur than at L3 and the iliac crest and correlated inversely with total hip and femoral neck BMD by DXA.

CONCLUSIONS

In summary, measurement of marrow fat in transiliac crest biopsies correlates with marrow fat at the spine but not the proximal femur by (1)H-MRS. There were site-specific differences in marrow fat quantity and in the relationships between marrow fat and bone volume.

Sustained Modeling-Based Bone Formation During Adulthood in Cynomolgus Monkeys May Contribute to Continuous BMD Gains With Denosumab

Denosumab (DMAb) administration to postmenopausal women with osteoporosis is associated with continued bone mineral density (BMD) increases and low fracture incidence through 8 years, despite persistently reduced bone turnover markers and limited fluorochrome labeling in iliac crest bone biopsies. BMD increases were hypothesized to result from additional accrual of bone matrix via modeling-based bone formation-a hypothesis that was tested by examining fluorochrome labeling patterns in sections from ovariectomized (OVX) cynomolgus monkeys (cynos) treated with DMAb for 16 months. Mature OVX or Sham cynos were treated monthly with vehicle for 16 months, whereas other OVX cynos received monthly 25 or 50 mg/kg DMAb. DMAb groups exhibited very low serum bone resorption and formation biomarkers and near-absent fluorochrome labeling in proximal femur cancellous bone. Despite these reductions, femoral neck dual-energy X-ray absorptiometry (DXA) BMD continued to rise in DMAb-treated cynos, from a 4.6% increase at month 6 to 9.8% above baseline at month 16. Further examination of cortical bone in the proximal femur demonstrated consistent and prominent labeling on the superior endocortex and the inferior periosteal surface, typically containing multiple superimposed labels from month 6 to 16 over smooth cement lines, consistent with continuous modeling-based bone formation. These findings were evident in all groups. Quantitative analysis at another modeling site, the ninth rib, demonstrated that DMAb did not alter the surface extent of modeling-based labels, or the cortical area bound by them, relative to OVX controls, while significantly reducing remodeling-based bone formation and eroded surface. This conservation of modeling-based formation occurred concomitantly with increased femoral neck strength and, when coupled with a reduction in remodeling-based bone loss, is likely to contribute to increases in bone mass with DMAb treatment. Thus, this study provides preclinical evidence for a potential mechanism that could contribute to the clinical observations of continued BMD increases and low fracture rates with long-term DMAb administration.

Odanacatib for the treatment of postmenopausal osteoporosis: development history and design and participant characteristics of LOFT, the Long-Term Odanacatib Fracture Trial

SUMMARY

Odanacatib is a cathepsin K inhibitor investigated for the treatment of postmenopausal osteoporosis. Phase 2 data indicate that 50 mg once weekly inhibits bone resorption and increases bone mineral density, with only a transient decrease in bone formation. We describe the background, design and participant characteristics for the phase 3 registration trial.

INTRODUCTION

Odanacatib (ODN) is a selective cathepsin K inhibitor being evaluated for the treatment of osteoporosis. In a phase 2 trial, ODN 50 mg once weekly reduced bone resorption while preserving bone formation and progressively increased BMD over 5 years. We describe the phase III Long-Term ODN Fracture Trial (LOFT), an event-driven, randomized, blinded placebo-controlled trial, with preplanned interim analyses to permit early termination if significant fracture risk reduction was demonstrated. An extension was planned, with participants remaining on their randomized treatment for up to 5 years, then transitioning to open-label ODN.

METHODS

The three primary outcomes were radiologically determined vertebral, hip, and clinical non-vertebral fractures. Secondary end points included clinical vertebral fractures, BMD, bone turnover markers, and safety and tolerability, including bone histology. Participants were women, 65 years or older, with a BMD T-score≤-2.5 at the total hip (TH) or femoral neck (FN) or with a prior radiographic vertebral fracture and a T-score≤-1.5 at the TH or FN. They were randomized to ODN or placebo tablets. All received weekly vitamin D3 (5600 international units (IU)) and daily calcium supplements as needed to ensure a daily intake of approximately 1200 mg.

RESULTS

Altogether, 16,713 participants were randomized at 387 centers. After a planned interim analysis, an independent data monitoring committee recommended that the study be stopped early due to robust efficacy and a favorable benefit/risk profile. Following the base study closeout, 8256 participants entered the study extension.

CONCLUSIONS

This report details the background and study design of this fracture end point trial and describes the baseline characteristics of its participants.

Preclinical assessment of a new magnetic resonance-based technique for determining bone quality by characterization of trabecular microarchitecture

The utility of HR-CT to study longitudinal changes in bone microarchitecture is limited by subject radiation exposure. Although MR is not subject to this limitation, it is limited both by patient movement that occurs during prolonged scanning at distal sites, and by the signal-to-noise ratio that is achievable for high-resolution images in a reasonable scan time at proximal sites. Recently, a novel MR-based technique, fine structure analysis (FSA) (Chase et al. Localised one-dimensional magnetic resonance spatial frequency spectroscopy. PCT/US2012/068284 2012, James and Chase Magnetic field gradient structure characteristic assessment using one-dimensional (1D) spatial frequency distribution analysis. 7932720 B2, 2011) has been developed which provides both high-resolution and fast scan times, but which generates at a designated set of spatial positions (voxels) a one-dimensional signal of spatial frequencies. Appendix 1 provides a brief introduction to FSA. This article describes an initial exploration of FSA for the rapid, non-invasive characterization of trabecular microarchitecture in a preclinical setting. For L4 vertebrae of sham and ovariectomized (OVX) rats, we compared FSA-generated metrics with those from CT datasets and from CT-derived histomorphometry parameters, trabecular number (Tb.N), bone volume density (BV/TV), trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp). OVX caused a reduction of the higher frequency structures that correspond to a denser trabecular lattice, while increasing the preponderance of lower frequency structures, which correspond to a more open lattice. As one example measure, the centroid of the FSA spectrum (which we refer to as fSAcB) showed strong correlation in the same region with CT-derived histomorphometry values: Tb.Sp: r -0.63, p < 0.001; Tb.N: r 0.71, p < 0.001; BV/TV: r 0.64, p < 0.001, Tb.Th: r 0.44, p < 0.05. Furthermore, we found a 17.5% reduction in fSAcB in OVX rats (p < 0.0001). In a longitudinal study, FSA showed that the age-related increase in higher frequency structures was abolished in OVX rats, being replaced with a 78-194% increase in lower frequency structures (2.4-2.8 objects/mm range), indicating a more sparse trabecular lattice (p < 0.05). The MR-based fine structure analysis enables high-resolution, radiation-free, rapid quantification of bone structures in one dimension (the specific point and direction being chosen by the clinician) of the spine.

Effects of up to 5 years of denosumab treatment on bone histology and histomorphometry: the FREEDOM study extension

Denosumab reduced bone resorption, increased bone mineral density (BMD), and decreased new vertebral, hip, and nonvertebral fracture risk in postmenopausal women with osteoporosis in the FREEDOM trial. Consistent with its mechanism of action, transiliac crest bone biopsies from subjects treated with denosumab for 1 to 3 years demonstrated reduced bone turnover that was reversible upon treatment cessation. Long-term denosumab treatment for up to 6 years in the FREEDOM extension provides sustained bone turnover reduction and continued low fracture incidence. Here, we evaluate 5 years of denosumab treatment on bone remodeling at the tissue level. Transiliac crest bone biopsies were obtained from 41 subjects (13 cross-over and 28 long-term from the FREEDOM placebo and denosumab groups, respectively) at year 2 of the FREEDOM extension, representing up to 5 years of denosumab treatment. Demographics for this subset were comparable to the overall extension cohort. The mean (SD) duration from the last denosumab dose to the first dose of tetracycline was 5.7 (0.5) months. Qualitative bone histology assessed in all biopsy samples was unremarkable, showing normally mineralized lamellar bone. Structural indices, including trabecular bone volume, number, and surface, were similar between cross-over and long-term groups. Bone resorption was decreased as reflected by eroded surface in cross-over and long-term subjects. A total of 11 of 13 (85%) cross-over subjects and 20 of 28 (71%) long-term subjects had specimens with double or single tetracycline label in trabecular and/or cortical compartments; specimens from 5 cross-over subjects and 10 long-term subjects were evaluable for dynamic trabecular bone parameters. Dynamic remodeling indices were low for both groups and consistent with reduced bone turnover with denosumab. In conclusion, denosumab treatment through 5 years resulted in normal bone quality with reduced bone turnover. These observations are consistent with its mechanism of action and associated with continued BMD increases and low fracture incidence.

Teriparatide increases strength of the peripheral skeleton in premenopausal women with idiopathic osteoporosis: a pilot HR-pQCT study

CONTEXT

In premenopausal women with idiopathic osteoporosis (IOP), treatment with teriparatide leads to substantial improvement in bone density and quality at central skeletal sites. The effects of teriparatide may differ on cortical and trabecular bone and also at the central and the peripheral skeleton.

OBJECTIVE

The objective of the study was to determine whether teriparatide was associated with improvements in compartmental volumetric bone mineral density (BMD), bone microarchitecture, and estimated bone strength of the distal radius and tibia as assessed by high-resolution peripheral quantitative computed tomography.

DESIGN, SETTING, AND PARTICIPANTS

Premenopausal women (n = 20, age 41 ± 5 y) with IOP (low trauma fractures and/or Z-scores ≤ -2.0) were scanned with high-resolution peripheral quantitative computed tomography at baseline and after 18 months of teriparatide treatment. Cortical and trabecular volumetric BMD and microarchitecture were measured by both standard and advanced techniques, including individual trabecula segmentation, and bone strength was estimated by finite element analysis.

MAIN OUTCOME MEASURES

The total volumetric BMD and homogeneous bone stiffness were measured.

RESULTS

Trabecular volumetric BMD increased significantly by 2.6% (1.8, 6.2) [median (interquartile range)] at the radius and 2.5% (1.1, 3.6) at the tibia. In addition, trabecular plate bone volume fraction increased by 9.1% (2.1, 17.1) at the radius and 7.6% (1.0, 9.7) at the tibia. Cortical thickness and volumetric density did not change; however, cortical porosity increased at the radius but not at the tibia. Despite these changes, whole-bone stiffness and failure load estimated by finite element analysis increased at both the radius and tibia.

CONCLUSIONS

In premenopausal women with IOP, 18 months of teriparatide was associated with increases in trabecular volumetric BMD, improved trabecular microarchitecture, and estimated bone strength at both the radius and tibia.