Anabolic effects of human biosynthetic parathyroid hormone fragment (1-34), LY333334, on remodeling and mechanical properties of cortical bone in rabbits

Glucocorticoids disrupt longitudinal advance of cortical bone basic multicellular units in the rabbit distal tibia

Glucocorticoids (GCs) are the leading cause of secondary osteoporosis. The emerging perspective, derived primarily from 2D histological study of trabecular bone, is that GC-induced bone loss arises through the uncoupling of bone formation and resorption at the level of the basic multicellular unit (BMU), which carries out bone remodeling. Here we explore the impact of GCs on cortical bone remodeling in the rabbit model. Based upon the rapid reduction of bone formation and initial elevation of resorption caused by GCs, we hypothesized that the rate of advance (longitudinal erosion rate; LER) of cortical BMUs would be increased. To test this hypothesis we divided 20 female New Zealand White rabbits into four experimental groups: ovariohysterectomy (OVH), glucocorticoid (GC), OVH + GC and SHAM controls (n = 5 animals each). Ten weeks post-surgery (OVH or sham), and two weeks after the initiation of dosing (daily subcutaneous injections of 1.5 mg/kg of methylprednisolone sodium succinate in the GC-treated groups and 1 ml of saline for the others), the right tibiae were scanned in vivo using Synchrotron Radiation (SR) in-line phase contrast micro-CT at the Canadian Light Source. After an additional 2 weeks of dosing, the rabbits were euthanized and ex vivo images were collected using desktop micro-CT. The datasets were co-registered in 3D and LER was calculated as the distance traversed by BMU cutting-cones in the 14-day interval between scans. Counter to our hypothesis, LER was greatly reduced in GC-treated rabbits. Mean LER was lower in GC (4.27 μm/d; p < 0.001) and OVH + GC (4.19 μm/d; p < 0.001), while similar in OVH (40.13 μm/d; p = 0.990), compared to SHAM (40.44 μm/d). This approximately 90 % reduction in LER with GCs was also associated with an overall disruption of BMU progression, with radial expansion of the remodeling space occurring in all directions. This unexpected outcome suggests that GCs do not simply uncouple formation and resorption within cortical BMUs and highlights the value of the time-lapsed 4D approach employed.

Immunohistochemical and Morphometric Assessment on the Biological Function and Vascular Endothelial Cells in the Initial Process of Cortical Porosity in Mice With PTH Administration

To clarify the cellular mechanism of cortical porosity induced by intermittent parathyroid hormone (PTH) administration, we examined the femoral cortical bone of mice that received 40 µg/kg/day (four times a day) human PTH (hPTH) (1-34). The PTH-driven cortical porosity initiated from the metaphyseal region and chronologically expanded toward the diaphysis. Alkaline phosphatase (ALP)-positive osteoblasts in the control mice covered the cortical surface, and endomucin-positive blood vessels were distant from these osteoblasts. In PTH-administered mice, endomucin-reactive blood vessels with TRAP-positive penetrated the ALP-positive osteoblast layer, invading the cortical bone. Statistically, the distance between endomucin-positive blood vessels and the cortical bone surface abated after PTH administration. Transmission electron microscopic observation demonstrated that vascular endothelial cells often pass through the flattened osteoblast layer and accompanied osteoclasts in the deep region of the cortical bone. The cell layers covering mature osteoblasts thickened with PTH administration and exhibited ALP, α-smooth muscle actin (αSMA), vascular cell adhesion molecule-1 (VCAM1), and receptor activator of NF-κB ligand (RANKL). Within these cell layers, osteoclasts were found near endomucin-reactive blood vessels. In PTH-administered femora, osteocytes secreted Dkk1, a Wnt inhibitor that affects angiogenesis, and blood vessels exhibited plasmalemma vesicle-associated protein, an angiogenic molecule. In summary, endomucin-positive blood vessels, when accompanied by osteoclasts in the ALP/αSMA/VCAM1/RANKL-reactive osteoblastic cell layers, invade the cortical bone, potentially due to the action of osteocyte-derived molecules such as DKK1.

Evaluation of cortical bone remodeling in canines treated with daily and weekly administrations of teriparatide by establishing AI-driven morphometric analyses and GIS-based spatial mapping

Larger animal models with a well-developed Haversian system, as observed in humans, are ideal to analyze cortical bone remodeling in pharmacological studies of anti-osteoporosis drugs, although they have some limitations in controlling individual variability in size, weight, age, and number. This study aimed to morphometrically analyze cortical bone remodeling focusing on Haversian canals in dogs using four regimens of TPTD with daily and weekly administrations at lower and higher weekly doses (4.9 μg/kg/week and 19.8 μg/kg/week, respectively) for 9 months. A micro-computed tomography-based analysis showed no significant differences among regimen groups. By establishing artificial intelligence (AI)-driven morphometric analyses and geographical information system (GIS)-based spatial mapping of Haversian canals that does not require confocal microscopy but is possible with more commonly used wide field microscopes, we successfully observed significant morphometric distinctions among regimens applied even in dogs. Our analytical results suggested that the daily higher regimen specifically increased the number of eroded pores creating spaces between existing canals, thus stimulating cortical bone remodeling.

Daily administration of parathyroid hormone slows the progression of basic multicellular units in the cortical bone of the rabbit distal tibia

Basic Multicellular Units (BMUs) conduct bone remodeling, a critical process of tissue turnover which, if imbalanced, can lead to disease, including osteoporosis. Parathyroid hormone (PTH 1-34; Teriparatide) is an osteoanabolic treatment for osteoporosis; however, it elevates the rate of intra-cortical remodeling (activation frequency) leading, at least transiently, to increased porosity. The purpose of this study was to test the hypothesis that PTH not only increases the rate at which cortical BMUs are initiated but also increases their progression (Longitudinal Erosion Rate; LER). Two groups (n = 7 each) of six-month old female New Zealand white rabbits were both administered 30 μg/kg of PTH once daily for a period of two weeks to induce remodeling. Their distal right tibiae were then imaged in vivo by in-line phase contrast micro-CT at the Canadian Light Source synchrotron. Over the following two weeks the first group (PTH) received continued daily PTH while the second withdrawal group (PTHW) was administrated 0.9 % saline. At four weeks all animals were euthanized, their distal tibiae were imaged by conventional micro-CT ex vivo and histomorphometry was performed. Matching micro-CT datasets (in vivo and ex vivo) were co-registered in 3D and LER was measured from 612 BMUs. Counter to our hypothesis, mean LER was lower (p < 0.001) in the PTH group (30.19 ± 3.01 μm/day) versus the PTHW group (37.20 ± 2.77 μm/day). Despite the difference in LER, osteonal mineral apposition rate (On.MAR) did not differ between groups indicating the anabolic effect of PTH was sustained after withdrawal. The slowing of BMU progression by PTH warrants further investigation; slowed resorption combined with elevated bone formation rate, may play an important role in how PTH enhances coupling between resorption and formation within the BMU. Finally, the prolonged anabolic response following withdrawal may have utility in terms of optimizing clinical dosing regimens.

The effect of intermittent parathyroid hormone on bone lengthening: current evidence to inform future effective interventions

PURPOSE

Recent studies have demonstrated the positive effects of parathyroid hormone (PTH) on bone healing, and findings support the use of PTH to accelerate bone healing following distraction osteogenesis. The goal of this review was to compile and discuss the mechanisms potentially underlying the effects of PTH on newly formed bone following a bone-lengthening procedure incorporating all relevant evidence in both animal and clinical studies.

METHODS

This review summarized all evidence from in vivo to clinical studies regarding the effects of PTH administration on a bone-lengthening model. In addition, a comprehensive evaluation of what is currently known regarding the potential mechanisms underlying the potential benefits of PTH in bone lengthening was presented. Some controversial findings regarding the optimal dosage and timing of administration of PTH in this model were also discussed.

RESULTS

The findings demonstrated that the potential mechanisms associated with the action of PTH on the acceleration of bone regeneration after distraction osteogenesis are involvement in mesenchymal cell proliferation and differentiation, endochondral bone formation, membranous bone formation, and callus remodeling.

CONCLUSIONS

In the last 20 years, a number of animal and clinical studies have indicated that there is a prospective role for PTH treatment in human bone lengthening as an anabolic agent that accelerates the mineralization and strength of the regenerated bone. Therefore, PTH treatment can be viewed as a potential treatment to increase the amount of new calcified bone and the mechanical strength of the bone in order to shorten the consolidation stage after bone lengthening.

Teriparatide Followed by Denosumab in Premenopausal Idiopathic Osteoporosis: Bone Microstructure and Strength by HR-pQCT

Premenopausal women with idiopathic osteoporosis (PreMenIOP) have marked deficits in skeletal microstructure. We have reported that sequential treatment with teriparatide and denosumab improves central skeletal bone mineral density (BMD) by dual-energy X-ray absorptiometry and central QCT in PreMenIOP. We conducted preplanned analyses of high-resolution peripheral quantitative computed tomography (HR-pQCT) scans from teriparatide and denosumab extension studies to measure effects on volumetric BMD (vBMD), microarchitecture, and estimated strength at the distal radius and tibia. Of 41 women enrolled in the parent teriparatide study (20 mcg daily), 34 enrolled in the HR-pQCT study. HR-pQCT participants initially received teriparatide (N = 24) or placebo (N = 10) for 6 months; all then received teriparatide for 24 months. After teriparatide, 26 enrolled in the phase 2B denosumab extension (60 mg q6M) for 24 months. Primary outcomes were percentage change in vBMD, microstructure, and stiffness after teriparatide and after denosumab. Changes after sequential teriparatide and denosumab were secondary outcomes. After teriparatide, significant improvements were seen in tibial trabecular number (3.3%, p = 0.01), cortical area and thickness (both 2.7%, p < 0.001), and radial trabecular microarchitecture (number: 6.8%, thickness: 2.2%, separation: -5.1%, all p < 0.02). Despite increases in cortical porosity and decreases in cortical density, whole-bone stiffness and failure load increased at both sites. After denosumab, increases in total (3.5%, p < 0.001 and 3.3%, p = 0.02) and cortical vBMD (1.7% and 3.2%; both p < 0.01), and failure load (1.1% and 3.6%; both p < 0.05) were seen at tibia and radius, respectively. Trabecular density (3.5%, p < 0.001) and number (2.4%, p = 0.03) increased at the tibia, while thickness (3.0%, p = 0.02) increased at the radius. After 48 months of sequential treatment, significant increases in total vBMD (tibia: p < 0.001; radius: p = 0.01), trabecular microstructure (p < 0.05), cortical thickness (tibia: p < 0.001; radius: p = 0.02), and whole bone strength (p < 0.02) were seen at both sites. Significant increases in total vBMD and bone strength parameters after sequential treatment with teriparatide followed by denosumab support the use of this regimen in PreMenIOP. © 2022 American Society for Bone and Mineral Research (ASBMR).

Direct Assessment of Rabbit Cortical Bone Basic Multicellular Unit Longitudinal Erosion Rate: A 4D Synchrotron-Based Approach

Cortical bone remodeling is carried out by basic multicellular units (BMUs), which couple resorption to formation. Although fluorochrome labeling has facilitated study of BMU formative parameters since the 1960s, some resorptive parameters, including the longitudinal erosion rate (LER), have remained beyond reach of direct measurement. Indeed, our only insights into this spatiotemporal parameter of BMU behavior come from classical studies that indirectly inferred LER. Here, we demonstrate a 4D in vivo method to directly measure LER through in-line phase contrast synchrotron imaging. The tibias of rabbits (n = 15) dosed daily with parathyroid hormone were first imaged in vivo (synchrotron micro-CT; day 15) and then ex vivo 14 days later (conventional micro-CT; day 29). Mean LER assessed by landmarking the co-registered scans was 23.69 ± 1.73 μm/d. This novel approach holds great promise for the direct study of the spatiotemporal coordination of bone remodeling, its role in diseases such as osteoporosis, as well as related treatments. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Expansion of the osteocytic lacunar-canalicular system involved in pharmacological action of PTH revealed by AI-driven fluorescence morphometry in female rabbits

Osteoporosis is an age-related disorder that is characterized by reduced bone mass. Its prevention and treatment are important healthcare issues for maintaining social activity in aged societies. Although bone fractures mostly occur at sites of weakened cortical bone, pathophysiological and pharmacological evaluations of bone mass have tended to be predominantly assessed in trabecular bone. To statistically characterize cortical bone remodeling, we originally established multimode fluorescence imaging and artificial intelligence (AI)-driven morphometric analyses in six-month-old female rabbits with well-defined cortical remodeling, similar to that in humans. We evaluated three distinct administration frequencies of teriparatide [TPTD; human parathyroid hormone, hPTH (1–34)]: once (1/w), twice (2/w), and seven times (7/w) a week, with the same total dose (140 μg/kg/week). Our analyses revealed significant expansions of the osteocytic lacunar-canalicular system and Haversian canals accompanied by the development of cortical porosity and endosteal naïve bone formation induced by a frequent administration regimen (7/w) of TPTD; however, once-weekly (1/w) and twice-weekly (2/w) administration of TPTD showed little effect. These findings demonstrate a clear contrast between the effects of frequent and infrequent administration of TPTD on cortical bone metabolism and suggest that osteocytic bone remodeling is involved in the pharmacological action of PTH.

Analysis of mechanotransduction dynamics during combined mechanical stimulation and modulation of the extracellular-regulated kinase cascade uncovers hidden information within the signalling noise

Osteoporosis is a bone disease characterized by brittle bone and increased fracture incidence. With ageing societies worldwide, the disease presents a high burden on health systems. Furthermore, there are limited treatments for osteoporosis with just two anabolic pharmacological agents approved by the US Food and Drug Administration. Healthy bones are believed to be maintained via an intricate relationship between dual biochemical and mechanical (bio-mechanical) stimulations. It is widely considered that osteoporosis emerges as a result of disturbances to said relationship. The mechanotransduction process is key to this balance, and disruption of its dynamics in bone cells plays a role in osteoporosis development. Nonetheless, the exact details and mechanisms that drive and secure the health of bones are still elusive at the cellular and molecular scales. This study examined the dual modulation of mechanical stimulation and mechanotransduction activation dynamics in an osteoblast (OB). The aim was to find patterns of mechanotransduction dynamics demonstrating a significant change that can be mapped to alterations in the OB responses, specifically at the level of gene expression and osteogenic markers such as alkaline phosphatase. This was achieved using a three-dimensional hybrid multiscale computational model simulating mechanotransduction in the OB and its interaction with the extracellular matrix, combined with a numerical analytical technique. The model and the analysis method predict that within the noise of mechanotransduction, owing to modulation of the bio-mechanical stimulus and consequent gene expression, there are unique events that provide signatures for a shift in the system's dynamics. Furthermore, the study uncovered molecular interactions that can be potential drug targets.

Effect of PTH and corticotomy on implant movement under mechanical force

Background

Osseointegrated implants are considered as clinically non-movable. Parathyroid hormone (PTH) is known to play a significant role in the regulation of bone remodeling and in intermittent, low doses, result in osteoanabolic effects. This study aimed to investigate the effects of PTH and corticotomy, both under traction force, on osseointegrated implants.

Methods

Four implants—two in each hemimandible—were placed in each of the three study mongrels. Each mongrels were designated as control, normal dose PTH (PTH-1), and high dose PTH (PTH-2) groups, with each groups further subdivided into non-surgery implant and surgery implant. After osseointegration, mechanical force with NiTi closed coil springs (500 g) was applied around each implants. Corticotomy was performed around one of four implants in each mongrels. Parathyroid hormone was administered locally on a weekly basis for 20 weeks. Clinical movement of the implants were evaluated with the superimposed 3D- scanned data, bone- microarchitectural and histologic examinations.

Results

Superimposition analysis showed continuous movement of the non-surgery implant of PTH-1 group. Movement was further justified with lowest bone implant contact (adjusted BIC; 44.77%) in histomorphometric analysis. Upregulation of bone remodeling around the implant was observed in the normal dose PTH group. In the surgery implants, the remarkably higher adjusted BIC compared to the non-surgery implants indicated increased bone formation around the implant surface.

Conclusion

The results indicate that the catabolic and anabolic balance of osseointegrated implants in terms of bone remodeling can be shifted via various interventions including pharmacological, surgical and mechanical force.

Clinical relevance

Upregulated bone remodeling by PTH and corticotomy under continuous mechanical force showed the possible implications for the movement of osseointegrated dental implant.

Cortical Bone Porosity in Rabbit Models of Osteoporosis

Cortical bone porosity is intimately linked with remodeling, is of growing clinical interest, and is increasingly accessible by imaging. Thus, the potential of animal models of osteoporosis (OP) to provide a platform for studying how porosity develops and responds to interventions is tremendous. To date, rabbit models of OP have largely focused on trabecular microarchitecture or bone density; some such as ovariectomy (OVX) have uncertain efficacy and cortical porosity has not been extensively reported. Our primary objective was to characterize tibial cortical porosity in rabbit-based models of OP, including OVX, glucocorticoids (GC), and OVX + GC relative to controls (SHAM). We sought to: (i) test the hypothesis that intracortical remodeling is elevated in these models; (ii) contrast cortical remodeling and porosity in these models with that induced by parathyroid hormone (1-34; PTH); and (iii) contrast trabecular morphology in the proximal tibia across all groups. Evidence that an increase in cortical porosity occurred in all groups was observed, although this was the least robust for GC. Histomorphometric measures supported the hypothesis that remodeling rate was elevated in all groups and also revealed evidence of uncoupling of bone resorption and formation in the GC and OVX + GC groups. For trabecular bone, a pattern of loss was observed for OVX, GC, and OVX + GC groups, whereas the opposite was observed for PTH. Change in trabecular number best explained these patterns. Taken together, the findings indicated rabbit models provide a viable and varied platform for the study of OP and associated changes in cortical remodeling and porosity. Intriguingly, the evidence revealed differing effects on the cortical and trabecular envelopes for the PTH model. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR)..

Assessment of the efficacy of teriparatide treatment for osteoporosis on lumbar fusion surgery outcomes: a systematic review and meta-analysis

Treatment of osteoporosis with medications like teriparatide, a parathyroid hormone, is known to improve bone density and reduce the risk of osteoporotic vertebral fractures. Anecdotal and limited surgical series have described the utility of this treatment for osteoporotic patients prior to spinal fusion surgery, but there is variability in adoption of this strategy as well as consensus regarding optimal treatment duration before and after surgery. In this study, the clinical results of the use of teriparatide for this application are reviewed and critically examined. We conducted a systematic review of electronic databases using different MeSH terms from 1980 to 2020. Pooled and subgroup analyses were performed using fixed and random effect models based upon the heterogeneity (I²). The results were reported as either mean difference (MD) or odds ratio (OR) with 95% confidence interval (CI). A total of 771 patients from 12 studies were identified. Three hundred seventy-seven patients (90.8% females) were treated with teriparatide. Lumbar spinal fusion rates were significantly higher among patients who received teriparatide compared to the non-teriparatide group (OR 2.15, 95%CI 1.56-2.97, p < 0.00001). Subgroup analysis revealed that patients receiving teriparatide demonstrated 2.12-fold and 2.23-fold higher likelihood of fusion compared to those in the bisphosphonate (OR 2.12, 95%CI 1.45-3.11, p = 0.0001) and placebo (OR 2.23, 95%CI 1.22-4.08, p = 0.009) cohorts, respectively. The treatment effect of teriparatide was associated with significantly reduced subsequent vertebral fractures (OR 0.16, 95%CI 0.06-0.41, p = 0.0002), sagittal malalignment (MD - 3.85, 95%CI: -6.49 to - 1.21, p = 0.004), limb visual analogue score (VAS) (MD - 0.36, 95%CI - 0.64 to - 0.09, p = 0.008), and spinal VAS (MD - 0.24, 95%CI - 0.44 to - 0.04, p = 0.02) compared to the non-teriparatide group. Patients using teriparatide had 30% less likelihood of screw loosening at last follow-up compared to the non-teriparatide group; however, this was not statistically significant (OR 0.70, 95%CI 0.43-1.14, p = 0.15). There did not exist any statistically significant difference between the two comparative groups in terms of pseudoarthrosis (OR 0.54, 95%CI 0.24-1.21, p = 0.13), cage subsidence (OR 1.30, 95%CI 0.38-4.52, p = 0.68), and bone mineral density (MD 0.04, 95%CI - 0.19-0.29, p = 0.74) at last follow-up examination. This meta-analysis corroborates the effectiveness of teriparatide resulting in higher fusion rates. Further study is required to determine the optimal duration of treatment and timing of surgery.

New Targets and Emergent Therapies for Osteoporosis

The 11 existing FDA-approved osteoporosis drug treatments include hormone replacement therapy, 2 SERMs (raloxifene and bazedoxifene), 5 inhibitors of bone-resorbing osteoclasts (4 bisphosphonates and anti-RANKL denosumab), 2 parathyroid hormone analogues (teriparatide and abaloparatide), and 1 WNT signaling enhancer (romosozumab). These therapies are effective and provide multiple options for patients and physicians. As the genomic revolution continues, potential novel targets for future drug development are identified. This review takes a wide perspective to describe potentially rewarding topics to explore, including knowledge of genes and pathways involved in bone cell metabolism, the utility of animal models, targeting drugs to bone, and ongoing advances in drug design and delivery.

Effect of teriparatide on early sinus graft healing in the ovariectomized rabbit

OBJECTIVES

The purpose of this study was to determine the effect of administering intermittent parathyroid hormone 1-34 [teriparatide, (PTH)] on the maxillary sinus lift and bone grafting in osteoporotic rabbits induced by ovariectomy and glucocorticoid.

MATERIALS AND METHODS

Ovariectomies were performed on 20 female New Zealand white rabbits that were randomly divided into two groups: (a) the PTH group (n = 10), in which 10 μg kg^-1  day^-1 PTH was injected subcutaneously 5 days a week for 5 weeks (from 1 week before until 4 weeks after sinus surgery), and (b) the saline group (n = 10), in which saline substituted PTH at the same dose, mode of administration, and duration. Bone grafting with bovine bone mineral was augmented into 13 sinuses, and bone grafts and implants were simultaneously performed in seven sinuses, in both groups. Animals were sacrificed at 4 weeks after surgery. To determine whether PTH was an effective treatment for osteoporosis, we measured the bone mineral density (BMD) of the right femur using micro-computed tomography and performed radiographic and histometric analyses of the maxillary sinus surgery site. The Mann-Whitney test was used for statistical analysis.

RESULTS

It was found that BMD increased in the femur, whereas none of the radiographic and histometric parameters differed significantly between the groups in the sinus, while there were large interindividual variations within groups.

CONCLUSIONS

These findings suggest that intermittent PTH does not promote new bone formation in the augmented maxillary sinus of ovariectomized rabbits.

Abaloparatide exhibits greater osteoanabolic response and higher cAMP stimulation and β-arrestin recruitment than teriparatide

Teriparatide and abaloparatide are parathyroid hormone receptor 1 (PTHR1) analogs with unexplained differential efficacy for the treatment of osteoporosis. Therefore, we compared the effects of abaloparatide and teriparatide on bone structure, turnover, and levels of receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin (OPG). Wild-type (WT) female mice were injected daily with vehicle or 20-80 µg/kg/day of teriparatide or abaloparatide for 30 days. Femurs and spines were examined by microcomputed tomography scanning and serum levels of bone turnover markers, RANKL, and OPG, were measured by ELISA. Both analogs similarly increased the distal femoral fractional trabecular bone volume, connectivity, and number, and reduced the structure model index (SMI) at 20-80 µg/kg/day doses. However, only abaloparatide exhibited a significant increase (13%) in trabecular thickness at 20 µg/kg/day dose. Femoral cortical evaluation showed that abaloparatide caused a greater dose-dependent increase in cortical thickness than teriparatide. Both teriparatide and abaloparatide increased lumbar 5 vertebral trabecular connectivity but had no or modest effect on other indices. Biochemical analysis demonstrated that abaloparatide promoted greater elevation of procollagen type 1 intact N-terminal propeptide, a bone formation marker, and tartrate-resistant acid phosphatase 5b levels, a bone resorption marker, and lowered the RANKL/OPG ratio. Furthermore, PTHR1 signaling was compared in cells treated with 0-100 nmol/L analog. Interestingly, abaloparatide had a markedly lower EC50 for cAMP formation (2.3-fold) and β-arrestin recruitment (1.6-fold) than teriparatide. Therefore, abaloparatide-improved efficacy can be attributed to enhanced bone formation and cortical structure, reduced RANKL/OPG ratio, and amplified Gs-cAMP and β-arrestin signaling.

Abaloparatide effect on forearm bone mineral density and wrist fracture risk in postmenopausal women with osteoporosis

PURPOSE

Wrist fractures are common, contribute significantly to morbidity in women with postmenopausal osteoporosis, and occur predominantly at the ultradistal radius, a site rich in trabecular bone. This exploratory analysis of the phase 3 ACTIVE study evaluated effects of abaloparatide versus placebo and teriparatide on forearm bone mineral density (BMD) and risk of wrist fracture.

METHODS

Forearm BMD was measured by dual energy X-ray absorptiometry in a subset of 982 women from ACTIVE, evenly distributed across the three treatment groups. Wrist fractures were ascertained in the total cohort (N = 2463).

RESULTS

After 18 months, ultradistal radius BMD changes from baseline were 2.25 percentage points greater for abaloparatide compared with placebo (95% confidence interval (CI) 1.38, 3.12, p < 0.001) and 1.54 percentage points greater for abaloparatide compared with teriparatide (95% CI 0.64, 2.45, p < 0.001). At 18 months, 1/3 radius BMD losses (versus baseline) were similar for abaloparatide compared with placebo (-0.42; 95% CI -1.03, 0.20; p = 0.19) but losses with teriparatide exceeded those of placebo (-1.66%; 95% CI -2.27, -1.06; p < 0.001). The decline with abaloparatide was less than that seen with teriparatide (group difference 1.22%; 95% CI 0.57, 1.87; p < 0.001). The radius BMD findings, at both ultradistal and 1/3 sites, are consistent with the numerically lower incidence of wrist fractures observed in women treated with abaloparatide compared with teriparatide (HR = 0.43; 95% CI 0.18, 1.03; p = 0.052) and placebo (HR = 0.49, 95% CI 0.20, 1.19, p = 0.11).

CONCLUSIONS

Compared with teriparatide, abaloparatide increased BMD at the ultradistal radius (primarily trabecular bone) and decreased BMD to a lesser extent at the 1/3 radius (primarily cortical bone), likely contributing to the numerically lower wrist fracture incidence observed with abaloparatide.

A novel hybrid compound LLP2A-alendronate accelerates open fracture healing in a rabbit model

Purpose

LLP2A-alendronate (LLP2A-Ale) is a novel bone-seeking compound that recruits mesenchymal stem cells to the bone surface and stimulates bone formation. The purpose of this study was to investigate the efficacy of LLP2A-Ale in the treatment of rabbit open fracture.

Methods

Thirty New Zealand White rabbits underwent radius mid-diaphyseal osteotomy and were randomly divided into control and treatment groups with fifteen rabbits in each group. The treatment group received only one injection of LLP2A-Ale (dosage 125 μg/kg), whereas the control group received one injection of PBS. X-ray images were taken to observe the course of fracture healing at 2, 4 and 6 weeks after treatment. Rabbits were sacrificed at 4 and 6 weeks post treatment. Calluses were then harvested and were subjected to histology, immunohistochemistry, molecular biology techniques and biomechanical test.

Results

X-ray images showed that the LLP2A-Ale group exhibited abundant callus formation, stronger bony callus remodeling and earlier marrow cavity recanalization compared to the control group in a time-dependent manner. Histomorphological analysis revealed an advance in woven formation at 4 weeks and lamellar bone formation at 6 weeks in the LLP2A-Ale group. Moreover, gene and protein levels suggested that LLP2A-Ale promoted osteogenesis and angiogenesis probably via upregulating the expression of osteogenesis factors (including bone morphogenetic protein 2 and Runt-related transcription factor 2) and angiogenesis factors (vascular endothelial growth factor). Besides, the radius callus biomechanical properties were significantly enhanced in the LLP2A-Ale group compared with the control group at 6 weeks.

Conclusion

LLP2A-Ale can significantly promote open fracture healing in the rabbit model, probably through enhancing osteogenesis and angiogenesis.

Weekly teriparatide treatment increases vertebral body strength by improving cortical shell architecture in ovariectomized cynomolgus monkeys

Weekly teriparatide treatment is reported to reduce the incidence of osteoporotic vertebral fractures. However, the effect of weekly teriparatide on cortical bone has not been clarified. This study aimed to examine the effects of weekly teriparatide treatment on bone mass, intracortical structure, and remodeling of the lumbar vertebral cortical shell and its relation to mechanical properties in ovariectomized cynomolgus monkeys. Female monkeys, aged 9 to 15 years, were divided into four groups: (1) SHAM group, (2) ovariectomized group (OVX group), (3) OVX with 1.2 μg/kg once-weekly teriparatide group (LOW group), (4) OVX with 6.0 μg/kg once-weekly teriparatide group (HIGH group). After 18 months, all animals were double-labeled with calcein, and lumbar vertebrae were analyzed with histomorphometry and compressive mechanical tests. Following ovariectomy, we found reductions in the anterior cortical shell area of the vertebrae and reductions in nearly all of the tested vertebral mechanical properties. Weekly teriparatide significantly preserved the anterior cortical shell area and the energy absorption capacity of the lumbar vertebrae in a dose-dependent manner. Multiple regression analyses indicated that improved mechanical properties were more associated with the increased anterior cortical shell area rather than the cancellous bone volume. The intracortical structure of the Haversian canals was also preserved following teriparatide treatment after ovariectomy. These findings suggest the importance of the cortical shell as a therapeutic target in the treatment of osteoporosis. Weekly teriparatide treatment increases the compressive mechanical strength of the lumbar vertebrae by thickening the anterior cortical shell.

Bisphosphonate and Teriparatide Use in Thoracolumbar Spinal Fusion: A Systematic Review and Meta-analysis of Comparative Studies

STUDY DESIGN

Systematic review and meta-analysis.

OBJECTIVE

To compare the efficacy of the use of either bisphosphonates or teriparatide on radiographic and functional outcomes of patients that had thoracolumbar spinal fusion.

SUMMARY OF BACKGROUND DATA

Controversy exists as to whether bisphosphonates interfere with successful spinal arthrodesis. An alternative osteoporosis medication is teriparatide, a synthetic parathyroid hormone that has an anabolic effect on osteoblast function. To date, there is limited comparative data on the influence of bisphosphonates or teriparatide on spinal fusion.

METHODS

A systematic search of medical reference databases was conducted for comparative studies on bisphosphonate or teriparatide use after thoracolumbar spinal fusion. Meta-analysis was performed using the random-effects model for heterogeneity. Radiographic outcomes assessed include fusion rates, risk of screw loosening, cage subsidence, and vertebral fracture.

RESULTS

No statistically significant differences were noted between bisphosphonates and control groups regarding fusion rate and risk of screw loosening (fusion: odds ratio [OR] = 2.2, 95% confidence interval [CI]: 0.87-5.56, P = 0.09; loosening: OR = 0.45, 95% CI: 0.14-1.48, P = 0.19). Teriparatide use was associated with higher fusion rates than bisphosphonates (OR = 2.3, 95% CI: 1.55-3.42, P < 0.0001). However, no statistically significant difference was noted between teriparatide and bisphosphonates regarding risk of screw loosening (OR = 0.37, 95% CI: 0.12-1.18, P = 0.09). Lastly, bisphosphonate use was associated with decreased odds of cage subsidence and vertebral fractures compared to controls (subsidence: OR = 0.29, 95% CI 0.11-0.75, P = 0.01; fracture: OR = 0.18, 95% CI 0.07-0.48, P = 0.0007).

CONCLUSION

Bisphosphonates do not appear to impair successful spinal fusion compared to controls although teriparatide use is associated with higher fusion rates than bisphosphonates. In addition, bisphosphonate use is associated with decreased odds of cage subsidence and vertebral fractures compared to controls that had spinal fusion.

LEVEL OF EVIDENCE

3.

The challenges of promoting osteogenesis in segmental bone defects and osteoporosis

Conventional clinical management of complex bone healing scenarios continues to result in 5-10% of fractures forming non-unions. Additionally, the aging population and prevalence of osteoporosis-related fractures necessitate the further exploration of novel ways to augment osteogenesis in this special population. This review focuses on the current clinical modalities available, and the ongoing clinical and pre-clinical research to promote osteogenesis in segmental bone defects, delayed unions, and osteoporosis. In summary, animal models of fracture repair are often small animals as historically significant large animal models, like the dog, continue to gain favor as companion animals. Small rodents have well-documented limitations in comparing to fracture repair in humans, and few similarities exist. Study design, number of studies, and availability of funding continue to limit large animal studies. Osteoinduction with rhBMP-2 results in robust bone formation, although long-term quality is scrutinized due to poor bone mineral quality. PTH 1-34 is the only FDA approved osteo-anabolic treatment to prevent osteoporotic fractures. Limited to 2 years of clinical use, PTH 1-34 has further been plagued by dose-related ambiguities and inconsistent results when applied to pathologic fractures in systematic human clinical studies. There is limited animal data of PTH 1-34 applied locally to bone defects. Gene therapy continues to gain popularity among researchers to augment bone healing. Non-integrating viral vectors and targeted apoptosis of genetically modified therapeutic cells is an ongoing area of research. Finally, progenitor cell therapies and the content variation of patient-side treatments (e.g., PRP and BMAC) are being studied. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1559-1572, 2018.

Effects of phosphorus supplementation in high-grain diets on blood, chemical and physical parameters of bones of feedlot Nellore bulls

The study was conducted to evaluate the effects of phosphorus supplementation (PS) on blood, chemical and physical parameters from bones of feedlot Nellore bulls. Forty-two animals were distributed in a completely randomised design consisting of three treatments and 14 replicates. The treatments consisted of no supplementary phosphorus (P; T1; 2.4 g P/kg DM), a commercial mineral supplement formulated according to recommendations from the main Brazilian industries of mineral supplements for feedlot beef cattle (T2; 4.2 g P/kg DM) and dicalcium phosphate (T3; 5.0 g P/kg DM) in high-grain diets. The animals submitted or not to PS had similar calcium (Ca) and P values, Ca : P ratio, specific gravity, cortical thickness and bone mineral density in the 12th rib. However, a decrease in magnesium (Mg) concentration was observed in the 12th rib in T1 and T3 treatments throughout the study (P < 0.05). The animals in T1 had lower cortical thickness of the metacarpus (P < 0.05), without compromising its resistance and stiffness (P > 0.05). To evaluate the P status in the animals, we performed the needle test, which allowed an assessment of differences in bone strength on the basis of the resistance to needle penetration on the transverse process (TP) of the lumbar vertebrae. Throughout the trial period, no animals were positive for the needle test conducted in the transverse processes of the lumbar vertebrae. The PS significantly changed parathyroid hormone and alkaline phosphatase concentrations (P < 0.05) and the animals in T1 had lower concentrations of these hormones. However, there was no effect of PS on the concentration of Ca and P in the serum of animals (P > 0.05). The inclusion of a mineral mix supplement in T2 resulted in higher Mg concentrations in the serum of animals (P > 0.05). P supplementation for Nellore bulls, fed high proportions of concentrate during the feedlot period, resulted in no benefits in neither chemical nor physical properties of their bones and the level in the control diet appeared adequate in these circumstances.

Effects of continual intermittent administration of parathyroid hormone on implant stability in the presence of osteoporosis: an in vivo study using resonance frequency analysis in a rabbit model

OBJECTIVE

This study aimed to evaluate the effects of continual intermittent administration of parathyroid hormone (PTH) on implant stability in the presence of osteoporosis, using rabbit models.

MATERIAL AND METHODS

Fifteen female New Zealand white rabbits underwent ovariectomy and were administered glucocorticoids to induce osteoporosis, following which they were divided into three groups. The first group received intermittent subcutaneous PTH for 4 weeks until implant placement (PTH1), while the second and third groups received PTH (PTH2) and saline (control), respectively, for 4 weeks before and after implant placement. After intermittent administration of PTH or saline, titanium implants were inserted into the left femoral epiphyses of all animals, and the implant stability quotient (ISQ) was measured immediately after placement to assess the primary stability and at 2 and 4 weeks after implant placement to assess osseointegration. At 4 weeks after implant placement, histological and histomorphometric evaluations were conducted and the bone area around the implant socket was measured as a ratio of the total bone area to the total tissue area.

RESULTS

Regarding primary stability, the ISQ values for the PTH1 and PTH2 groups were significantly higher than those for the control group (p<0.05). Concerning osseointegration, the ISQ values at 2 and 4 weeks were significantly higher for the PTH2 group than for the PTH1 and control (p<0.05) groups. Histological assessments showed a thicker and more trabecular bone around the implant sockets in the PTH2 specimens than in the PTH1 and control specimens. The bone area around the implant socket was significantly greater in the PTH2 group than in the PTH1 and control groups (p<0.05).

CONCLUSIONS

Our results suggest that continual intermittent PTH administration before and after dental implant placement is effective for the achievement of favorable stability and osseointegration in the presence of osteoporosis.

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

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

Acute development of cortical porosity and endosteal naïve bone formation from the daily but not weekly short-term administration of PTH in rabbit

Teriparatide [human parathyroid hormone (1–34)], which exerts an anabolic effect on bone, is used for the treatment of osteoporosis in patients who are at a high risk for fracture. That the once-daily administration of teriparatide causes an increase in cortical porosity in animal models and clinical studies has been a matter of concern. However, it is not well documented that the frequency of administration and/or the total dose of teriparatide affect the cortical porosity. The present study developed 4 teriparatide regimens [20 μg/kg/day (D20), 40 μg/kg/day (D40), 140 μg/kg/week (W140) and 280 μg/kg/week (W280)] in the rabbit as a model animal with a well-developed Haversian system and osteons. The total weekly doses were equivalent in the low-dose groups (D20 and W140) and in the high-dose groups (D40 and W280). After the short-term (1 month) administration of TPDT, micro-CT, histomorphometry and three-dimensional second harmonic generation (3D-SHG) imaging to visualize the bone collagen demonstrated that daily regimens but not weekly regimens were associated with the significant development of cortical porosity and endosteal naïve bone formation by marrow fibrosis. We concomitantly monitored the pharmacokinetics of the plasma teriparatide levels as well as the temporal changes in markers of bone formation and resorption. The analyses in the present study suggested that the daily repeated administration of teriparatide causes more deleterious changes in the cortical microarchitecture than the less frequent administration of higher doses. The findings of the present study may have some implications for use of teriparatide in clinical treatment.

Effects of raloxifene and alendronate on non-enzymatic collagen cross-links and bone strength in ovariectomized rabbits in sequential treatments after daily human parathyroid hormone (1-34) administration

This study investigated the effects of raloxifene and alendronate to follow parathyroid hormone (PTH) on bone collagen and biomechanical properties in ovariectomized rabbits. Sequential treatments of raloxifene and alendronate after hPTH(1-34) treatment improved biomechanical properties with and without bone collagen improvement, respectively.

INTRODUCTION

The standard sequential treatment to follow human parathyroid hormone (hPTH) (1-34) therapy for osteoporosis has yet to be determined. The objective of this study was to compare the effects of raloxifene and alendronate treatments to follow daily hPTH(1-34) treatment on non-enzymatic collagen cross-links, bone mass, and bone strength in ovariectomized (OVX) rabbits.

METHODS

From 3 months after ovariectomy, seven month-old female New Zealand white rabbits were given either vehicle or hPTH(1-34) (8 μg/kg/day), once daily for 5 months. After hPTH(1-34) treatment, the hPTH(1-34)-treated animals were divided into two groups, and given raloxifene (10 mg/kg, daily) orally or alendronate (100 μg/kg, twice weekly) subcutaneously for 5 months. We evaluated bone mineral density (BMD), bone structural parameters, advanced glycation end product (AGE) content in collagen, and bone mechanical parameters including intrinsic parameters in the femur.

RESULTS

Raloxifene (hPTH/RLX) and alendronate (hPTH/ALN) to follow hPTH(1-34) increased cortical thickness, maximum load, and maximum stress and decreased endocortical surface in the diaphysis, in addition to increasing total BMD in the distal metaphysis. Decreased trabecular AGE, pentosidine, and homocysteine contents and increased toughness and breaking energy were noted with hPTH/RLX treatment only. With hPTH/ALN treatment, no effects on non-enzymatic collagen cross-link AGEs were noted although increases in stiffness and elastic modulus were observed.

CONCLUSION

These results suggest that sequential treatments with hPTH(1-34) and antiresorptive drugs (raloxifene and alendronate) have a beneficial effect on bone mass and biomechanical properties in OVX rabbits.

Influence of Teriparatide and Ibandronate on Cortical Bone in New Zealand White Rabbits: A HR-QCT Study

Teriparatide (TPTD) is known to increase the cortical thickness and porosity. The purpose of the present study was to determine whether switching from TPTD to ibandronate (IBN) would be useful for improving cortical bone parameters as assessed using high-resolution quantitative computed tomography (HR-QCT) analyses in mature rabbits. Forty-two female New Zealand white rabbits (18-22 weeks old) were randomized into six groups of 7 animals each as follows: 4-week vehicle administration group, 4-week TPTD administration group (20 μg/kg, subcutaneously [s.c.], daily), 12-week vehicle administration group, 4-week TPTD administration + 8-week vehicle administration group, 4-week TPTD administration + 8-week lower-dose IBN administration group (20 μg/kg, s.c., every 4 weeks), and 4-week TPTD administration + 8-week higher-dose IBN administration group (100 μg/kg, s.c., every 4 weeks). After the 4- or 12-week experimental period, the cortical bone of the distal femoral diaphysis was processed for HR-QCT analysis. The 4-week TPTD administration increased the pore ratio, number, and density as well as the cortical area, thickness, and bone mineral content (BMC), without significant influencing the volumetric bone mineral density (BMD). The 4-week TPTD administration + 8-week vehicle administration decreased the pore ratio, number, and density as well as the cortical area and thickness, compared with the 4-week TPTD administration, but the pore ratio, cortical area, and thickness were still higher compared with the 12-week vehicle administration. The 4-week TPTD administration + 8-week higher-dose IBN administration, but not the 4-week TPTD administration + 8-week lower-dose IBN administration, increased the cortical area, thickness, BMC, and volumetric BMD and decreased the pore ratio, but not the pore number or density, compared with the 4-week TPTD administration + 8-week vehicle administration. These results suggest that higher-dose IBN after TPTD therapy has a beneficial effect on the BMC, volumetric BMD, cortical area, thickness, and porosity in mature rabbits.

Development of an in vivo bone fatigue damage model using axial compression of the rabbit forelimb

Many nontraumatic fractures seen clinically in patients with metabolic bone disorders or on antiresorptive treatment show an increased incidence of microdamage accumulation and impaired intracortical remodeling. However, the lack of basal remodeling and Haversian bone in rodents limits their translatability in studying bone damage repair mechanisms. The work presented here demonstrates the development of the forelimb loading model in rabbits, the smallest mammal with intracortical Haversian remodeling. The forelimbs of post-mortem female New Zealand white rabbits were loaded in axial end compression to determine their basic monotonic and fatigue properties. Following time zero characterization, stress fractures were created in vivo and animals were allowed to recover for a period of two to five weeks. The rabbit forelimb when loaded in axial compression demonstrates a consistent mid-diaphyseal fracture location characterized by a local mixed compression-bending loading environment. Forelimb apparent stiffness, when fatigue loaded, demonstrates a progressive increase until macrocrack formation, at which time apparent stiffness rapidly declines until failure. Stress fractures in the rabbit ulna display robust periosteal expansion and woven bone formation two weeks following fracture. Subsequent healing at five weeks post-fracture is marked by woven bone densification, resorption and intracortical remodeling along the stress fracture line. The rabbit forelimb fatigue model is a promising new platform by which bone׳s response to damage may be studied.

PTH(1-34) effects on repairing experimentally drilled holes in rat femur: novel aspects - qualitative vs. quantitative improvement of osteogenesis

The timetable of effects on bone repair of the active fraction-parathyroid hormone, PTH(1-34), was analytically investigated from the morphometric viewpoint in 3-month-old male Sprague-Dawley rats, whose femurs were drilled at mid-diaphyseal level (transcortical holes). The animals were divided into groups with/without PTH(1-34) administration, and sacrificed at different times (10, 28, 45 days after surgery). The observations reported here need to be framed in the context of our previous investigations regarding bone histogenesis (Ferretti et al. Anat Embryol. 2002; 206: 21-29) in which we demonstrated the occurrence of two successive bone-forming processes during both skeletal organogenesis and bone repair, i.e. static and dynamic osteogenesis: the former (due to stationary osteoblasts, haphazardly grouped in cords) producing preliminary bad quality trabecular bone, the latter (due to typical polarized osteoblasts organized in ordered movable laminae) producing mechanically valid bone tissue. The primary function of static osteogenesis is to provide a rigid scaffold containing osteocytes (i.e. mechano-sensors) for osteoblast laminae acting in dynamic osteogenesis. In the present work, histomorphometric analysis revealed that, already 10 days after drilling, despite the holes being temporarily filled by the same amount of newly formed trabecular bone by static osteogenesis independently of the treatment, the extent of the surface of movable osteoblast-laminae (covering the trabecular surface) was statistically higher in animals submitted to PTH(1-34) administration than in control ones; this datum strongly suggests the effect of PTH(1-34) alone in anticipating the occurrence of dynamic osteogenesis involved in the production of good quality bone (with more ordered collagen texture) more suitable for loading. This study could be crucial in further translational clinical research in humans for defining the best therapeutic strategies to be applied in recovering severe skeletal lesions, particularly as regards the time of PTH(1-34) administration.

Miniscrew-assisted slow expansion of mature rabbit sutures

INTRODUCTION

In this study, we experimentally evaluated whether complex, mature sutures can be separated using skeletal anchorage and light, continuous forces.

METHODS

Twelve adult, 8- to 9-month-old female New Zealand white rabbits were randomly assigned to 1 control group and 2 experimental groups. Open-coil nickel-titanium springs delivered constant forces of 100 g across the sagittal suture to miniscrew implants placed bilaterally in the frontal bone. Sutural separation was measured biweekly. Separation was also measured with microcomputed tomography. Bone formation (mineral apposition) was measured with fluorescent labels. Qualitative histologic analyses of the suture tissues were performed using hematoxylin and eosin staining; osteoclasts were evaluated with tartrate resistant acid phosphatase staining.

RESULTS

All 24 miniscrew implants remained stable throughout the experiment. There was no statistically significant sutural separation in the control group. In the experimental groups, sutural separation was significant (P <0.05) at all time points after the initial records were taken. The rate of separation was linear during the first 42 days. There were moderate correlations (R = 0.59-0.89; P <0.05) between miniscrew implant separation and bone marker separation. Mineral apposition rate, which was not measureable in the control group, was significant in the experimental group. The mineral apposition rate was greater between 14 and 28 days than between 28 and 38 days, and it was greater on the ectocranial than on the endocranial surface. Based on the microcomputed tomography analysis, 3-dimensional sutural volume of the experimental group increased significantly (P = 0.02), but surface area did not (P = 0.26).

CONCLUSIONS

It is possible to separate the sagittal suture of mature rabbits. Sutural separation is limited, indicating involvement of other articulations.

Delayed administration of recombinant human parathyroid hormone improves early biomechanical strength in a rat rotator cuff repair model

BACKGROUND

Despite advances in intraoperative techniques, rotator cuff repairs frequently do not heal. Recombinant human parathyroid hormone (rhPTH) has been shown to improve healing at the tendon-to-bone interface in an established acute rat rotator cuff repair model. We hypothesized that administration of rhPTH beginning on postoperative day 7 would result in improved early load to failure after acute rotator cuff repair in an established rat model.

METHODS

Acute rotator cuff repairs were performed in 108 male Sprague-Dawley rats. Fifty-four rats received daily injections of rhPTH beginning on postoperative day 7 until euthanasia or a maximum of 12 weeks postoperatively. The remaining 54 rats received no injections and served as the control group. Animals were euthanized at 2 and 16 weeks postoperatively and evaluated by gross inspection, biomechanical testing, and histologic analysis.

RESULTS

At 2 weeks postoperatively, rats treated with rhPTH demonstrated significantly higher load to failure than controls (10.9 vs. 5.2 N; P = .003). No difference in load to failure was found between the 2 groups at 16 weeks postoperatively, although control repairs more frequently failed at the tendon-to-bone interface (45.5% vs. 22.7%; P = .111). Blood vessel density appeared equivalent between the 2 groups at both time points, but increased intracellular and extracellular vascular endothelial growth factor expression was noted in the rhPTH-treated group at 2 weeks.

CONCLUSIONS

Delayed daily administration of rhPTH resulted in increased early load to failure and equivalent blood vessel density in an acute rotator cuff repair model.

Fibroblast Growth Factor Receptor 3 Deficiency Does Not Impair the Osteoanabolic Action of Parathyroid Hormone on Mice

Summary: PTH stimulates bone formation in Fgfr3 knockout mice through promotion of proliferation and differentiation in osteoblasts.

Introduction: Previous studies showed that endogenous fibroblast growth factor 2 (FGF-2) is required for parathyroid hormone (PTH)-stimulated bone anabolic effects, however, the exact mechanisms by which PTH stimulate bone formation and the function of FGF receptors in mediating these actions are not fully defined. FGF receptor 3 (FGFR3) has been characterized as an important regulator of bone metabolism and is confirmed to cross-talk with PTH/PTHrP signal in cartilage and bone development.

Methods: Fgfr3 knockout and wild-type mice at 2-month-old and 4-month-old were intraperitoneally injected with PTH intermittently for 4 weeks and then the skeletal responses to PTH were assessed by dual energy X-ray absorptiometry (DEXA), micro-computed tomography (μCT) and bone histomorphometry.

Results: Intermittent PTH treatment improved bone mineral density (BMD) and femoral mechanical properties in both Fgfr3^-/- and wild-type mice. Histomorphometric analysis showed that bone formation and bone resorption were increased in both genotypes following PTH treatment. PTH treatment increased trabecular bone volume (BV/TV) in WT and Fgfr3-deficient mice. The anabolic response in Fgfr3-deficient and wild-type bone is characterized by an increase of both bone formation and resorption-related genes following PTH treatment. In addition, we found that Fgfr3 null osteoblasts (compared to wild-type controls) maintained normal abilities to response to PTH-stimulated increase of proliferation, differentiation, expression of osteoblastic marker genes (Cbfa1, Osteopontin and Osteocalcin), and phosphorylation of Erk1/2.

Conclusions: Bone anabolic effects of PTH were not impaired by the absence of FGFR3, suggesting that the FGFR3 signaling may not be required for osteoanabolic effects of PTH activities.

Cathepsin K Inhibition: A New Mechanism for the Treatment of Osteoporosis

Cathepsin K (CatK), a cysteine protease, is highly expressed by osteoclasts and very efficiently degrades type I collagen, the major component of the organic bone matrix. Robust genetic and pharmacological preclinical studies consistently demonstrate that CatK inhibition increases bone mass, improves bone microarchitecture and strength. Recent advances in the understanding of the molecular and cellular mechanisms involved in bone modeling and remodeling suggest that inhibition of CatK decreases bone resorption, but increases the number of cells of osteoclast lineage. This in turn maintains the signals for bone formation, and perhaps may even increase bone formation on some cortical surfaces. Several CatK inhibitors, including relacatib, balicatib, odanacatib and ONO-5334 had entered clinical development for metabolic bone disorders with increased bone resorption, such as postmenopausal osteoporosis. However, odanacatib (ODN) is the only candidate continuing in development. ODN is a highly selective oral CatK inhibitor dosed once-weekly in humans. In a Phase 2 clinical trial, postmenopausal women treated with ODN had sustained reductions of bone resorption markers, while bone formation markers returned to normal after an initial decline within the first 2 years on treatment. In turn areal bone mineral density increased continuously at both spine and hip for up to 5 years. ODN has also been demonstrated to improve bone mass in women with postmenopausal osteoporosis previously treated with alendronate and in men with osteoporosis. ODN is currently in a worldwide Phase 3 fracture outcome trial for the treatment of postmenopausal osteoporosis with interim results supporting its anti-fracture efficacy at the spine, hip and non-vertebral sites.

Odanacatib Restores Trabecular Bone of Skeletally Mature Female Rabbits With Osteopenia but Induces Brittleness of Cortical Bone: A Comparative Study of the Investigational Drug With PTH, Estrogen, and Alendronate

Cathepsin K (CK), a lysosomal cysteine protease, is highly expressed in mature osteoclasts and degrades type 1 collagen. Odanacatib (ODN) is a selective and reversible CK inhibitor that inhibits bone loss in preclinical and clinical studies. Although an antiresorptive, ODN does not suppress bone formation, which led us to hypothesize that ODN may display restorative effect on the osteopenic bones. In a curative study, skeletally mature New Zealand rabbits were ovarectomized (OVX) and after induction of bone loss were given a steady-state exposure of ODN (9 mM/d) for 14 weeks. Sham-operated and OVX rabbits treated with alendronate (ALD), 17b-estradiol (E2), or parathyroid hormone (PTH) served as various controls. Efficacy was evaluated by assessing bone mineral density (BMD), bone microarchitecture (using micro-computed tomography), fluorescent labeling of bone, and biomechanical strength. Skeletal Ca/P ratio was measured by scanning electron microscopy (SEM) with X-ray microanalysis, crystallinity by X-ray diffraction, and bone mineral density distribution (tissue mineralization) by backscattered SEM. Between the sham and ODN-treated osteopenic groups, lumbar and femur metaphyseal BMD, Ca/P ratio, trabecular microstructure and geometric indices, vertebral compressive strength, trabecular lining cells, cortical parameters (femoral area and thickness and periosteal deposition), and serum P1NP were largely comparable. Skeletal improvements in ALD-treated or E2-treated groups fell significantly short of the sham/ODN/PTH group. However, the ODN group displayed reduced ductility and enhanced brittleness of central femur, which might have been contributed by higher crytallinity and tissue mineralization. Rabbit bone marrow stromal cells expressed CK and when treated with ODN displayed increased formation of mineralized nodules and decreased apoptosis in serum-deficient medium compared with control. In vivo, ODN did not suppress remodeling but inhibited osteoclast activity more than ALD. Taken together, we show that ODN reverses BMD, skeletal architecture, and compressive strength in osteopenic rabbits; however, it increases crystallinity and tissue mineralization, thus leading to increased cortical bone brittleness.

Src siRNA prevents corticosteroid-associated osteoporosis in a rabbit model

In an established steroid-associated osteonecrosis (SAON) rabbit model we found recently that blockage Src by siRNA could improve reconstructive repair of osteonecrosis via enhancing osteogenesis and inhibiting bone resorption. The current study investigated if blocking Src was able to prevent steroid-associated osteoporosis (SAOP) in the same SAON animal model. Rabbits were treated with pulsed lipopolysaccharide (LPS) and corticosteroid methylprednisolone (MPS). At 2, 4, and 6weeks after induction, Src siRNA, control siRNA and saline were intramedullary injected into proximal femur, respectively. Two fluorescent dyes xylenol orange and calcein green were injected before sacrificing the animals for in vivo labeling of the newly formed bone. At week 6 after induction, proximal femora of rabbits were dissected for micro-CT and histological analysis. Results showed significant bone loss in the metaphysis of femoral head in the control rabbits after SAON induction. Src siRNA treatment was able to prevent steroid-associate bone loss in trabecular bone and increase cortical bone thickness at femoral neck. Histomorphometry showed that Src siRNA increased the osteoblastic bone formation and decreased the eroded bone surfaces suggesting decreased osteoclastic bone resorption. This was the first study to report bone loss after SAON induction in rabbit model that could be prevented by knocking down Src by siRNA.

Intermittent Administration of Parathyroid Hormone [1-34] Prevents Particle-Induced Periprosthetic Osteolysis in a Rat Model

We examined whether intermittent administration of parathyroid hormone [1-34] (PTH[1-34]; 60 μg/kg/day) can prevent the negative effects of titanium (Ti) particles on implant fixation and periprosthetic osteolysis in a rat model. Eighteen adult male rats (12 weeks old, bones still growing) received intramedullary Ti implants in their bilateral femurs; 6 rats from the blank group received vehicle injections, and 12 rats from the control group and PTH treatment group received Ti particle injections at the time of operation and intra-articular injections 2 and 4 weeks postoperatively. Six of the rats that received Ti particles from the PTH group also received PTH[1-34] treatment. Six weeks postoperatively, all specimens were collected for assessment by X-ray, micro-CT, biomechanical, scanning electron microscopy (SEM), and dynamic histomorphometry. A lower BMD, BV/TV, Tb.N, maximal fixation strength, and mineral apposition rate were observed in the control group compared to the blank group, demonstrating that a periprosthetic osteolysis model had been successfully established. Administration of PTH[1-34] significantly increased the bone mineral density of the distal femur, BV/TV, Tb.N, Tb.Th, Tb.Sp, Con.D, SMI, and maximal fixation strength in the PTH group compared to that in the control group. SEM revealed higher bone-implant contact, thicker lamellar bone, and larger trabecular bone area in the PTH group than in the control group. A higher mineral apposition rate was observed in the PTH group compared to both the blank and control groups. These findings imply that intermittent administration of PTH[1-34] prevents periprosthetic osteolysis by promoting bone formation. The effects of PTH[1-34] were evaluated at a suprapharmacological dosage to the human equivalent in rats; therefore, additional studies are required to demonstrate its therapeutic potential in periprosthetic osteolysis.

True Gold or Pyrite: A Review of Reference Point Indentation for Assessing Bone Mechanical Properties In Vivo

Although the gold standard for determining bones' mechanical integrity is the direct measure of mechanical properties, clinical evaluation has long relied on surrogates of mechanical properties for assessment of fracture risk. Nearly a decade ago, reference point indentation (RPI) emerged as an innovative way to potentially assess mechanical properties of bone in vivo. Beginning with the BioDent device, and then followed by the newer generation OsteoProbe, this RPI technology has been utilized in several publications. In this review we present an overview of the technology and some important details about the two devices. We also highlight select key studies, focused specifically on the in vivo application of these devices, as a way of synthesizing where the technology stands in 2015. The BioDent machine has been shown, in two clinical reports, to be able to differentiate fracture versus nonfracture patient populations and in preclinical studies to detect treatment effects that are consistent with those quantified using traditional mechanical tests. The OsteoProbe appears able to separate clinical cohorts yet there exists a lack of clarity regarding details of testing, which suggests more rigorous work needs to be undertaken with this machine. Taken together, RPI technology has shown promising results, yet much more work is needed to determine if its theoretical potential to assess mechanical properties in vivo can be realized.

A resorbable antibiotic eluting bone void filler for periprosthetic joint infection prevention

Periprosthetic joint infection (PJI) following total knee arthroplasty is a globally increasing procedural complication. These infections are difficult to treat and typically require revision surgery. Antibiotic-loaded bone cement is frequently utilized to deliver antibiotics to the site of infection; however, bone cement is a nondegrading foreign body and known to leach its antibiotic load, after an initial burst release, at subtherapeutic concentrations for months. This work characterized a resorbable, antibiotic-eluting bone void filler designed to restore bone volume and prevent PJI. Three device formulations were fabricated, consisting of different combinations of synthetic inorganic bone graft material, degradable polymer matrices, salt porogens, and antibiotic tobramycin. These formulations were examined to determine the antibiotic's elution kinetics and bactericidal potential, the device's degradation in vitro, as well as osteoconductivity and device resorption in vivo using a pilot rabbit bone implant model. Kirby-Bauer antibiotic susceptibility tests assessed bactericidal activity. Liquid chromatography with tandem mass spectrometry measured antibiotic elution kinetics, and scanning electron microscopy was used to qualitatively assess degradation. Results indicated sustained antibiotic release from all three formulations above the Staphylococcus aureus minimum inhibitory concentration for a period of 5 to 8 weeks. Extensive degradation was observed with the Group 3 formulation after 90 days in phosphate-buffered saline, with a lesser degree of degradation observed in the other two formulations. Results from the pilot rabbit study showed the Group 3 device to be biocompatible, with minimal inflammatory response and no fibrous encapsulation in bone. The device was also highly osteoconductive-exhibiting an accelerated mineral apposition rate. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1632-1642, 2016.

Changes over time in callus formation caused by intermittently administering PTH in rabbit distraction osteogenesis models

Background

Changes over time in the callus during intermittent administration of parathyroid hormone (PTH) were studied in rabbit distraction osteogenesis models.

Method

Models of distraction osteogenesis in Japanese white rabbits were created, and distraction osteogenesis (total length: 10.5 mm) was performed for 2 weeks. Simultaneously with the start of distraction, 30 rabbits received 4 weeks of subcutaneous administration of 30 μg/kg of PTH(1–34), teriparatide, (P-group: n = 15) or saline (N-group: n = 15) every other day. The tibias of five rabbits were dissected at 6, 8, and 10 weeks after surgery to perform bone mineral density (BMD), peripheral quantitative computed tomography (pQCT), and mechanical testing.

Results

The mean BMD had no significant differences over time at 6, 8, and 10 weeks after surgery between the P-group and the N-group. On pQCT, the P-group had significant increases in total bone cross-sectional area of the callus compared to the N-group at 8 and 10 weeks after surgery. On mechanical testing, the P-group’s absorption energy had not changed at 6 weeks after surgery compared to the N-group, but it had significantly increased at 8 weeks. At 10 weeks after surgery, the N-group’s absorption energy rapidly increased, and the difference between the two groups disappeared.

Conclusion

The intermittent administration of PTH(1–34), teriparatide, for 4 weeks every other day from the start of distraction had the potential to shorten the callus maturation period in the rabbit distraction osteogenesis models.

Development of an in vivo rabbit ulnar loading model

Ulnar and tibial cyclic compression in rats and mice have become the preferred animal models for investigating the effects of mechanical loading on bone modeling/remodeling. Unlike rodents, rabbits provide a larger bone volume and normally exhibit intracortical Haversian remodeling, which may be advantageous for investigating mechanobiology and pharmaceutical interventions in cortical bone. Therefore, the objective of this study was to develop and validate an in vivo rabbit ulnar loading model. Ulnar tissue strains during loading of intact forelimbs were characterized and calibrated to applied loads using strain gauge measurements and specimen-specific finite element models. Periosteal bone formation in response to varying strain levels was measured by dynamic histomorphometry at the location of maximum strain in the ulnar diaphysis. Ulnae loaded at 3000 microstrain did not exhibit periosteal bone formation greater than the contralateral controls. Ulnae loaded at 3500, 4000, and 4500 microstrain exhibited a dose-dependent increase in periosteal mineralizing surface (MS/BS) compared with contralateral controls during the second week of loading. Ulnae loaded at 4500 microstrain exhibited the most robust response with significantly increased MS/BS at multiple time points extending at least 2weeks after loading was ceased. Ulnae loaded at 5250 microstrain exhibited significant woven bone formation. Rabbits required greater strain levels to produce lamellar and woven bone on periosteal surfaces compared with rats and mice, perhaps due to lower basal levels of MS/BS. In summary, bone adaptation during rabbit ulnar loading was tightly controlled and may provide a translatable model for human bone biology in preclinical investigations of metabolic bone disease and pharmacological treatments.

PTH Signaling During Exercise Contributes to Bone Adaptation

Improving the structural integrity of bone reduces fracture risk and development of osteoporosis later in life. Exercise can increase the mechanical properties of bone, and this increase is often attributed to the dynamic loading created during exercise. However, the increase in systemic parathyroid hormone (PTH) levels during exercise gives reason to hypothesize that PTH signaling also regulates bone adaptation in response to exercise. Therefore, the first aim of this study was to establish the impact PTH signaling has on bone adaptation during exercise by inhibiting PTH signaling with PTH(7-34); the second aim was to determine whether increasing PTH levels during exercise with PTH(1-34) can augment bone adaptation. Thirty minutes after a single bout of running on a treadmill, mice exhibited a twofold increase in systemic PTH levels. Under the same exercise regimen, the influence of PTH signaling on bone adaptation during exercise was then evaluated in mice after 21 consecutive days of exercise and treatment with PTH(7-34), PTH(1-34), or vehicle. Exercise alone caused a significant increase in trabecular bone volume with adaptation to a more platelike structure, which was inhibited with PTH(7-34) during exercise. Changes in structural-level and tissue-level mechanical properties during exercise occurred in the absence of significant changes to cortical bone geometry. Inhibition of PTH signaling during exercise attenuated the changes in structural-level mechanical properties, but not tissue-level properties. Enhanced PTH signaling during exercise with PTH(1-34) increased trabecular and cortical bone volume, but had little effect on the structural-level and tissue-level mechanical properties compared to exercise alone. Our study is the first to demonstrate that bone adaptation during exercise is not only a function of dynamic loading, but also PTH release, and that PTH signaling contributes differently at the structural and tissue levels.

Comparative effects of teriparatide, denosumab, and combination therapy on peripheral compartmental bone density, microarchitecture, and estimated strength: the DATA-HRpQCT Study

Combined teriparatide and denosumab increases spine and hip bone mineral density more than either drug alone. The effect of this combination on skeletal microstructure and microarchitecture, however, is unknown. Because skeletal microstructure and microarchitecture are important components of skeletal integrity, we performed high-resolution peripheral quantitative computed tomography (HR-pQCT) assessments at the distal tibia and radius in postmenopausal osteoporotic women randomized to receive teriparatide 20 µg daily (n = 31), denosumab 60 mg every 6 months (n = 33), or both (n = 30) for 12 months. In the teriparatide group, total volumetric bone mineral density (vBMD) did not change at either anatomic site but increased in both other groups at both sites. The increase in vBMD at the tibia was greater in the combination group (3.1 ± 2.2%) than both the denosumab (2.2 ± 1.9%) and teriparatide groups (-0.3 ± 1.9%) (p < 0.02 for both comparisons). Cortical vBMD decreased by 1.6 ± 1.9% at the tibia and by 0.9 ± 2.8% at the radius in the teriparatide group, whereas it increased in both other groups at both sites. Tibia cortical vBMD increased more in the combination group (1.5 ± 1.5%) than both monotherapy groups (p < 0.04 for both comparisons). Cortical thickness did not change in the teriparatide group but increased in both other groups. The increase in cortical thickness at the tibia was greater in the combination group (5.4 ± 3.9%) than both monotherapy groups (p < 0.01 for both comparisons). In the teriparatide group, radial cortical porosity increased by 20.9 ± 37.6% and by 5.6 ± 9.9% at the tibia but did not change in the other two groups. Bone stiffness and failure load, as estimated by finite element analysis, did not change in the teriparatide group but increased in the other two groups at both sites. Together, these findings suggest that the use of denosumab and teriparatide in combination improves HR-pQCT measures of bone quality more than either drug alone and may be of significant clinical benefit in the treatment of postmenopausal osteoporosis.

Intermittently administered parathyroid hormone [1-34] promotes tendon-bone healing in a rat model

The objective of this study was to investigate whether intermittent administration of parathyroid hormone [1–34] (PTH[1–34]) promotes tendon-bone healing after anterior cruciate ligament (ACL) reconstruction in vivo. A rat model of ACL reconstruction with autograft was established at the left hind leg. Every day, injections of 60 μg PTH[1–34]/kg subcutaneously were given to the PTH group rats (n = 10) for four weeks, and the controls (n = 10) received saline. The tendon-bone healing process was evaluated by micro-CT, biomechanical test, histological and immunohistochemical analyses. The effects of PTH[1–34] on serum chemistry, bone microarchitecture and expression of the PTH receptor (PTH1R) and osteocalcin were determined. Administration of PTH[1–34] significantly increased serum levels of calcium, alkaline phosphatase (AP), osteocalcin and tartrate-resistant acid phosphatase (TRAP). The expression of PTH1R on both osteocytes and chondrocyte-like cells at the tendon-bone interface was increased in the PTH group. PTH[1–34] also enhanced the thickness and microarchitecture of trabecular bone according to the micro-CT analysis. The results imply that systematically intermittent administration of PTH[1–34] promotes tendon-bone healing at an early stage via up-regulated PTH1R. This method may enable a new strategy for the promotion of tendon-bone healing after ACL reconstruction.

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.

PTH [1-34]-induced alterations of the subchondral bone provoke early osteoarthritis

OBJECTIVE

To test the hypothesis that changes in the subchondral bone induced by parathyroid hormone (PTH [1-34]) reciprocally affect the integrity of the articular cartilage within a naïve osteochondral unit in vivo.

DESIGN

Daily subcutaneous injections of 10 μg PTH [1-34]/kg were given to adult rabbits for 6 weeks, controls received saline. Blood samples were continuously collected to monitor renal function. The subchondral bone plate and subarticular spongiosa of the femoral heads were separately assessed by micro-computed tomography. Articular cartilage was evaluated by macroscopic and histological osteoarthritis scoring, polarized light microscopy, and immunohistochemical determination of type-I, type-II, type-X collagen contents, PTH [1-34] receptor and caspase-3 expression. Absolute and relative extents of hyaline and calcified articular cartilage layers were measured histomorphometrically. The correlation between PTH-induced changes in subchondral bone and articular cartilage was determined.

RESULTS

PTH [1-34] enhanced volume, mineral density, and trabecular thickness within the subarticular spongiosa, and increased thickness of the calcified cartilage layer (all P < 0.05). Moreover, PTH [1-34] led to cartilage surface irregularities and reduced matrix staining (both P < 0.03). These early osteoarthritic changes correlated with and were ascribed to the increased thickness of the calcified cartilage layer (P = 0.026) and enhanced mineral density of the subarticular spongiosa (P = 0.001).

CONCLUSIONS

Modifications of the subarticular spongiosa by PTH [1-34] cause broadening of the calcified cartilage layer, resulting in osteoarthritic cartilage degeneration. These findings identify a mechanism by which PTH-induced alterations of the normal subchondral bone microarchitecture may provoke early osteoarthritis.

Effects of teriparatide on cortical histomorphometric variables in postmenopausal women with or without prior alendronate treatment

Cortical bone, the dominant component of the human skeleton by volume, plays a key role in protecting bones from fracture. We analyzed the cortical bone effects of teriparatide treatment in postmenopausal women with osteoporosis who had previously received long-term alendronate (ALN) therapy or were treatment naïve (TN). Tetracycline-labeled paired iliac crest biopsies obtained from 29 ALN-pretreated and 16 TN women were evaluated for dynamic histomorphometric parameters of bone formation at the periosteal, endocortical and intracortical bone compartments, before and after 24months of teriparatide treatment. At baseline, the frequency of specimens without any endocortical and periosteal tetracycline labeling, and the percentage of quiescent osteons, was higher in the ALN than the TN group. Endocortical and periosteal mineralizing surface (MS/BS%), periosteal bone formation rate (BFR/BS), mineral apposition rate (MAR) and the number of intracortical forming osteons were significantly lower in the ALN-pretreated patients than in the TN group. Following teriparatide treatment, the frequency of endocortical and periosteal unlabeled biopsies decreased; in the ALN-pretreated group the percentage of quiescent osteons decreased and, in contrast, forming and resorbing osteons were increased. Teriparatide treatment resulted in significant increases of MAR in the endocortical, and MS/BS% in the periosteal compartment in the ALN-pretreated group. Most indices of bone formation remained lower in the ALN-pretreated group compared with the TN group at study end. Endocortical wall width was increased in both ALN-pretreated and TN groups. Cortical porosity and cortical thickness were significantly increased in the ALN-pretreated group after teriparatide treatment. Our results suggest that 24months of teriparatide treatment increases cortical bone formation and cortical turnover in patients who were either TN or had previous ALN therapy.

Postmenopausal women treated with combination parathyroid hormone (1-84) and ibandronate demonstrate different microstructural changes at the radius vs. tibia: the PTH and Ibandronate Combination Study (PICS)

SUMMARY

In postmenopausal women receiving combination parathyroid hormone (PTH) (1-84) therapy and ibandronate, we evaluated bone microarchitecture and biomechanics using high-resolution peripheral quantitative computed tomography (HR-pQCT). Cortical and trabecular changes were different at the nonweight-bearing radius vs. the weight-bearing tibia, with more favorable overall changes at the tibia.

INTRODUCTION

PTH therapy and bisphosphonates decrease fracture risk in postmenopausal osteoporosis, but their effects on bone microstructure and strength have not been fully characterized, particularly during combination therapy. PTH increases trabecular bone mineral density (BMD) substantially but may decrease cortical BMD, possibly by stimulating intracortical remodeling. We evaluated bone microarchitecture and biomechanics with HR-pQCT at the radius (a nonweight-bearing site) and tibia (weight bearing) in women receiving combination PTH(1-84) and ibandronate.

METHODS

Postmenopausal women with low bone mass (n = 43) were treated with 6 months of PTH(1-84) (100 μg/day), either as one 6- or two 3-month courses, in combination with ibandronate (150 mg/month) over 2 years. HR-pQCT was performed before and after therapy.

RESULTS

Because changes in HR-pQCT parameters did not differ between treatment arms, groups were pooled into one cohort for analysis. Trabecular BMD increased at both radius and tibia (p < 0.01 for each). Cortical thickness and BMD decreased at the radius (p < 0.01), consistent with changes in dual-energy X-ray absorptiometry, while these parameters did not change at the tibia (p ≤ 0.02 for difference between radius and tibia). In contrast, cortical porosity increased at the tibia (p < 0.01) but not radius. Stiffness and failure load decreased at the radius (p < 0.0001) but did not change at the tibia.

CONCLUSIONS

Cortical and trabecular changes in response to the PTH/ibandronate treatment combinations utilized in this study were different at the nonweight-bearing radius vs. the weight-bearing tibia, with more favorable overall changes at the tibia. Our findings support the possibility that weight bearing may optimize the effects of osteoporosis therapy.

Parathyroid hormone [1-34] improves articular cartilage surface architecture and integration and subchondral bone reconstitution in osteochondral defects in vivo

OBJECTIVE

The 1-34 amino acid segment of the parathyroid hormone (PTH [1-34]) mediates anabolic effects in chondrocytes and osteocytes. The aim of this study was to investigate whether systemic application of PTH [1-34] improves the repair of non-osteoarthritic, focal osteochondral defects in vivo.

DESIGN

Standardized cylindrical osteochondral defects were bilaterally created in the femoral trochlea of rabbits (n = 8). Daily subcutaneous injections of 10 μg PTH [1-34]/kg were given to the treatment group (n = 4) for 6 weeks, controls (n = 4) received saline. Articular cartilage repair was evaluated by macroscopic, biochemical, histological and immunohistochemical analyses. Reconstitution of the subchondral bone was assessed by micro-computed tomography. Effects of PTH [1-34] on synovial membrane, apoptosis, and expression of the PTH receptor (PTH1R) were determined.

RESULTS

Systemic PTH [1-34] increased PTH1R expression on both, chondrocytes and osteocytes within the repair tissue. PTH [1-34] ameliorated the macro- and microscopic aspect of the cartilaginous repair tissue. It also enhanced the thickness of the subchondral bone plate and the microarchitecture of the subarticular spongiosa within the defects. No significant correlations were established between these coexistent processes. Apoptotic levels, synovial membrane, biochemical composition of the repair tissue, and type-I/II collagen immunoreactivity remained unaffected.

CONCLUSIONS

PTH [1-34] emerges as a promising agent in the treatment of focal osteochondral defects as its systemic administration simultaneously stimulates articular cartilage and subchondral bone repair. Importantly, both time-dependent mechanisms of repair did not correlate significantly at this early time point and need to be followed over prolonged observation periods.