Sclerostin monoclonal antibody enhanced bone fracture healing in an open osteotomy model in rats

Sclerostin is a negative regulator of bone formation. Sclerostin monoclonal antibody (Scl‐Ab) treatment promoted bone healing in various animal models. To further evaluate the healing efficiency of Scl‐Ab in osteotomy healing, we investigated the time course effects of systemic administration of Scl‐Ab on fracture repair in rat femoral osteotomy model. A total of 120 six‐month‐old male SD rats were subjected to transverse osteotomy at the right femur mid‐shaft. Rats were treated with vehicle or Scl‐Ab treatment for 3, 6, or 9 weeks. Fracture healing was evaluated by radiography, micro‐CT, micro‐CT based angiography, 4‐point bending mechanical test and histological assessment. Scl‐Ab treatment resulted in significantly higher total mineralized callus volume fraction, BMD and enhanced neovascularization. Histologically, Scl‐Ab treatment resulted in a significant reduction in fracture callus cartilage at week 6 and increase in bone volume at week 9, associated with a greater proportion of newly formed bone area at week 6 and 9 by fluorescence microscopy. Mechanical testing showed significantly higher ultimate load in Scl‐Ab treatment group at week 6 and 9. This study has demonstrated that Scl‐Ab treatment enhanced bone healing in a rat femoral osteotomy model, as reflected in increased bone formation, bone mass and bone strength. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:997–1005, 2014.     

Sclerostin antibody treatment improves bone mass,bone strength,and bone defect regeneration in rats with type 2 diabetes mellitus

Type 2 diabetes mellitus results in increased risk of fracture and delayed fracture healing. ZDF fa/fa rats are an established model of type 2 diabetes mellitus with low bone mass and delayed bone healing. We tested whether a sclerostin‐neutralizing antibody (Scl‐AbVI) would reverse the skeletal deficits of diabetic ZDF rats. Femoral defects of 3 mm were created in 11‐week‐old diabetic ZDF fa/fa and nondiabetic ZDF +/+ rats and stabilized by an internal plate. Saline or 25 mg/kg Scl‐AbVI was administered subcutaneously (s.c.) twice weekly for 12 weeks (n = 9–10/group). Bone mass and strength were assessed using pQCT, micro–computed tomography (µCT), and biomechanical testing. Bone histomorphometry was used to assess bone formation, and the filling of the bone defect was analyzed by µCT. Diabetic rats displayed lower spinal and femoral bone mass compared to nondiabetic rats, and Scl‐AbVI treatment significantly enhanced bone mass of the femur and the spine of diabetic rats (p < 0.0001). Scl‐AbVI also reversed the deficit in bone strength in the diabetic rats, with 65% and 89% increases in maximum load at the femoral shaft and neck, respectively (p < 0.0001). The lower bone mass in diabetic rats was associated with a 65% decrease in vertebral bone formation rate, which Scl‐AbVI increased by sixfold, consistent with a pronounced anabolic effect. Nondiabetic rats filled 57% of the femoral defect, whereas diabetic rats filled only 21% (p < 0.05). Scl‐AbVI treatment increased defect regeneration by 47% and 74%, respectively (p < 0.05). Sclerostin antibody treatment reverses the adverse effects of type 2 diabetes mellitus on bone mass and strength, and improves bone defect regeneration in rats. © 2013 American Society for Bone and Mineral Research.     

Sclerostin antibody stimulates bone regeneration after experimental periodontitis

The reconstruction of large osseous defects due to periodontitis is a challenge in regenerative therapy. Sclerostin, secreted by osteocytes, is a key physiological inhibitor of osteogenesis. Pharmacologic inhibition of sclerostin using sclerostin‐neutralizing monoclonal antibody (Scl‐Ab) thus increases bone formation, bone mass and bone strength in models of osteopenia and fracture repair. This study assessed the therapeutic potential of Scl‐Ab to stimulate alveolar bone regeneration following experimental periodontitis (EP). Ligature‐induced EP was induced in rats to generate localized alveolar bone defects. Following 4 weeks of disease induction, Scl‐Ab (+EP) or vehicle (+/? EP) were systemically delivered, twice weekly for up to 6 wks to determine the ability of Scl‐Ab to regenerate bone around tooth‐supporting osseous defects. 3 and 6 wks after the initiation of Scl‐Ab or vehicle treatment, femur and maxillary jawbones were harvested for histology, histomorphometry, and micro‐computed tomography (micro‐CT) of linear alveolar bone loss (ABL) and volumetric measures of bone support, including bone volume fraction (BVF) and tissue mineral density (TMD). Serum was analyzed to examine bone turnover markers during disease and regenerative therapy. Vehicle + EP animals exhibited maxillary bone loss (BVF, TMD and ABL) at ligature removal and thereafter. 6 weeks of Scl‐Ab significantly improved maxillary bone healing, as measured by BVF, TMD and ABL, when compared to vehicle + EP. After 6 weeks of treatment, BVF and TMD values in the Scl‐Ab + EP group were similar to those of healthy controls. Serum analysis demonstrated higher levels of bone formation markers osteocalcin and PINP in Scl‐Ab treatment groups. Scl‐Ab restored alveolar bone mass following experimental periodontitis. These findings warrant further exploration of Scl‐Ab therapy in this and other oral bone defect disease scenarios. © 2013 American Society for Bone and Mineral Research.     

Tissue‐Level Mechanisms Responsible for the Increase in Bone Formation and Bone Volume by Sclerostin Antibody

Bone formation can be remodeling‐based (RBF) or modeling‐based (MBF), the former coupled to bone resorption and the latter occurring directly on quiescent surfaces. Unlike osteoanabolic therapies such as parathyroid hormone (PTH) 1‐34 that increase bone remodeling and thus both formation and resorption, sclerostin antibody (Scl‐Ab) increases bone formation while decreasing bone resorption. With this unique profile, we tested our hypothesis that Scl‐Ab primarily elicited MBF by examining bones from Scl‐Ab–treated ovariectomized (OVX) rats and male cynomolgus monkeys (cynos). Histomorphometry was performed to quantify and characterize bone surfaces in OVX rats administered vehicle or Scl‐Ab (25 mg/kg) subcutaneously (sc) twice/week for 5 weeks and in adolescent cynos administered vehicle or Scl‐Ab (30 mg/kg) sc every 2 weeks for 10 weeks. Fluorochrome‐labeled surfaces in L₂ vertebra and femur endocortex (cynos only) were considered to be MBF or RBF based on characteristics of their associated cement lines. In OVX rats, Scl‐Ab increased MBF by eightfold (from 7% to 63% of bone surface, compared to vehicle). In cynos, Scl‐Ab markedly increased MBF on trabecular (from 0.6% to 34%) and endocortical surfaces (from 7% to 77%) relative to vehicle. Scl‐Ab did not significantly affect RBF in rats or cynos despite decreased resorption surface in both species. In cynos, Scl‐Ab resulted in a greater proportion of RBF and MBF containing sequential labels from week 2, indicating an increase in the lifespan of the formative site. This extended formation period was associated with robust increases in the percent of new bone volume formed. These results demonstrate that Scl‐Ab increased bone volume by increasing MBF and prolonged the formation period at both modeling and remodeling sites while reducing bone resorption. Through these unique effects on bone formation and resorption, Scl‐Ab may prove to be an effective therapeutic to rapidly increase bone mass in diseases such as osteoporosis. © 2014 American Society for Bone and Mineral Research.     

Sclerostin antibody enhances bone formation in a rat model of distraction osteogenesis

Neutralizing monoclonal sclerostin antibodies are effective in promoting bone formation at a systemic level and in orthopedic scenarios including closed fracture repair. In this study we examined the effects of sclerostin antibody (Scl‐Ab) treatment on regenerate volume, density, and strength in a rat model of distraction osteogenesis. Surgical osteotomy was performed on 179 Sprague Dawley rats. After 1 week, rats underwent distraction for 2 weeks, followed by 6 weeks for consolidation. Two treatment groups received biweekly subcutaneous Scl‐AbIII (a rodent form of Scl‐Ab; 25 mg/kg), either from the start of distraction onward or restricted to the consolidation phase. These groups were compared to controls receiving saline. Measurement modalities included longitudinal DXA, ex vivo QCT, and microCT, tissue histology, and biomechanical four‐point bending tests. Bone volume was increased in both Scl‐Ab treatments regimens by the end of consolidation (+26–38%, p < 0.05), as assessed by microCT. This was associated with increased mineral apposition. Importantly, Scl‐Ab led to increased strength in united bones, and this reached statistical significance in animals receiving Scl‐Ab during consolidation only (+177%, p < 0.01, maximum load to failure). These data demonstrate that Scl‐Ab treatment increases bone formation, leading to regenerates with higher bone volume and improved strength. Our data also suggest that the optimal effects of Scl‐Ab treatment are achieved in the latter stages of distraction osteogenesis. These findings support further investigation into the potential clinical application of sclerostin antibody to augment bone distraction, such as limb lengthening, particularly in the prevention of refracture. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1106–1113, 2018.

     

Sclerostin antibody improves skeletal parameters in a Brtl/+ mouse model of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a genetic bone dysplasia characterized by osteopenia and easy susceptibility to fracture. Symptoms are most prominent during childhood. Although antiresorptive bisphosphonates have been widely used to treat pediatric OI, controlled trials show improved vertebral parameters but equivocal effects on long‐bone fracture rates. New treatments for OI are needed to increase bone mass throughout the skeleton. Sclerostin antibody (Scl‐Ab) therapy is potently anabolic in the skeleton by stimulating osteoblasts via the canonical wnt signaling pathway, and may be beneficial for treating OI. In this study, Scl‐Ab therapy was investigated in mice heterozygous for a typical OI‐causing Gly→Cys substitution in col1a1. Two weeks of Scl‐Ab successfully stimulated osteoblast bone formation in a knock‐in model for moderately severe OI (Brtl/+) and in WT mice, leading to improved bone mass and reduced long‐bone fragility. Image‐guided nanoindentation revealed no alteration in local tissue mineralization dynamics with Scl‐Ab. These results contrast with previous findings of antiresorptive efficacy in OI both in mechanism and potency of effects on fragility. In conclusion, short‐term Scl‐Ab was successfully anabolic in osteoblasts harboring a typical OI‐causing collagen mutation and represents a potential new therapy to improve bone mass and reduce fractures in pediatric OI. © 2013 American Society for Bone and Mineral Research     

Evaluation of the effects of systemic treatment with a sclerostin neutralizing antibody on bone repair in a rat femoral defect model

Systemic administration of a sclerostin neutralizing antibody (Scl‐Ab) has been shown to enhance fracture callus density and strength in several animal models. In order to further evaluate the potential of Scl‐Ab to improve healing in a bone defect model, we evaluated Scl‐Ab in a 3 mm femoral defect in young male outbred rats. Scl‐Ab was given either continuously for 6 or 12 weeks after surgery or with 2 weeks of delay for 10 weeks. Bone formation was assessed by radiographs, µ‐CT, and histology. Complete bony union was achieved in only a few defects after 12 weeks of healing (Scl‐Ab treated 5/30, vehicle treated 1/15). µ‐CT evaluation demonstrated a significant increase in the BV/TV in the defect in the delayed treatment group (65%, p < 0.05), but a non‐significant increase in the continuous group (35%, p = 0.11) compared to control. However, both regimens induced an anabolic response in the bone proximal and distal to the defect and in the un‐operated femurs. We demonstrate that treatment with Scl‐Ab can enhance bone repair in a bone defect and in the surrounding host bone, but lacks the osteoinductive activity to heal it. This agent seems to be most effective in bone repair scenarios where there is cortical integrity. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:197–203, 2014.     

Two doses of sclerostin antibody in cynomolgus monkeys increases bone formation,bone mineral density,and bone strength

The development of bone‐rebuilding anabolic agents for treating bone‐related conditions has been a long‐standing goal. Genetic studies in humans and mice have shown that the secreted protein sclerostin is a key negative regulator of bone formation. More recently, administration of sclerostin‐neutralizing monoclonal antibodies in rodent studies has shown that pharmacologic inhibition of sclerostin results in increased bone formation, bone mass, and bone strength. To explore the effects of sclerostin inhibition in primates, we administered a humanized sclerostin‐neutralizing monoclonal antibody (Scl‐AbIV) to gonad‐intact female cynomolgus monkeys. Two once‐monthly subcutaneous injections of Scl‐AbIV were administered at three dose levels (3, 10, and 30 mg/kg), with study termination at 2 months. Scl‐AbIV treatment had clear anabolic effects, with marked dose‐dependent increases in bone formation on trabecular, periosteal, endocortical, and intracortical surfaces. Bone densitometry showed that the increases in bone formation with Scl‐AbIV treatment resulted in significant increases in bone mineral content (BMC) and/or bone mineral density (BMD) at several skeletal sites (ie, femoral neck, radial metaphysis, and tibial metaphysis). These increases, expressed as percent changes from baseline were 11 to 29 percentage points higher than those found in the vehicle‐treated group. Additionally, significant increases in trabecular thickness and bone strength were found at the lumbar vertebrae in the highest‐dose group. Taken together, the marked bone‐building effects achieved in this short‐term monkey study suggest that sclerostin inhibition represents a promising new therapeutic approach for medical conditions where increases in bone formation might be desirable, such as in fracture healing and osteoporosis. © 2010 American Society for Bone and Mineral Research     

Effects of sclerostin antibody on healing of a non‐critical size femoral bone defect

Sclerostin is a glycoprotein secreted by osteocytes and inhibits osteoblastogenesis via inhibition of Wnt signaling. We hypothesized that sclerostin antibody (Scl‐AbIII) would accelerate the healing of a murine femoral non‐critical size bone defect model. A unilateral and unicortical 0.8 mm‐sized drill hole was made in the proximal femoral shaft of adult female nude mice. One group of mice received subcutaneous injections of Scl‐AbIII and a second group received vehicle only. Reporter MC3T3 osteoprogenitor cells were injected via the tail vein 3 days after surgery to monitor systemic trafficking of exogenous osteoprogenitors. Bioluminescence imaging (BLI), microcomputed tomography (microCT), micropositron emission tomography (microPET) and histological analysis were used to compare the bone healing responses to Scl‐AbIII treatment. Bone mineral density (BMD) significantly increased at the defect site after week 1, and was significantly higher in the treatment compared with the control group at all time points. This finding was also confirmed on histological analysis by increased deposition of new woven bone. MicroPET scanning showed a trend for greater activity in the control group at day 21 compared with the Scl‐AbIII group, indicating early bone maturation following treatment with Scl‐AbIII. Whereas the BLI signals derived from the injected osteoprogenitor cells showed no differences between vehicle and Scl‐AbIII treated groups, systemic migration of MC3T3 cells to the bone defect was clearly identified in both groups using immunohistochemistry. Systemic administration of Scl‐AbIII resulted in earlier healing and maturation of a non‐critical size bone defect. These findings underscore the potential use of Scl‐AbIII for treatment of complicated fractures, non‐unions, and other clinical scenarios. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:155–163, 2012     

Bone Matrix Quality After Sclerostin Antibody Treatment

Sclerostin antibody (Scl‐Ab) is a novel bone‐forming agent that is currently undergoing preclinical and clinical testing. Scl‐Ab treatment is known to dramatically increase bone mass, but little is known about the quality of the bone formed during treatment. In the current study, global mineralization of bone matrix in rats and nonhuman primates treated with vehicle or Scl‐Ab was assayed by backscattered scanning electron microscopy (bSEM) to quantify the bone mineral density distribution (BMDD). Additionally, fluorochrome labeling allowed tissue age–specific measurements to be made in the primate model with Fourier‐transform infrared microspectroscopy to determine the kinetics of mineralization, carbonate substitution, crystallinity, and collagen cross‐linking. Despite up to 54% increases in the bone volume after Scl‐Ab treatment, the mean global mineralization of trabecular and cortical bone was unaffected in both animal models investigated. However, there were two subtle changes in the BMDD after Scl‐Ab treatment in the primate trabecular bone, including an increase in the number of pixels with a low mineralization value (Z₅) and a decrease in the standard deviation of the distribution. Tissue age–specific measurements in the primate model showed that Scl‐Ab treatment did not affect the mineral‐to‐matrix ratio, crystallinity, or collagen cross‐linking in the endocortical, intracortical, or trabecular compartments. Scl‐Ab treatment was associated with a nonsignificant trend toward accelerated mineralization intracortically and a nearly 10% increase in carbonate substitution for tissue older than 2 weeks in the trabecular compartment (p < 0.001). These findings suggest that Scl‐Ab treatment does not negatively impact bone matrix quality. © 2014 American Society for Bone and Mineral Research.     

Sclerostin Antibody Treatment Improves the Bone Phenotype of Crtap–/– Mice,a Model of Recessive Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is characterized by low bone mass, poor bone quality, and fractures. Standard treatment for OI patients is limited to bisphosphonates, which only incompletely correct the bone phenotype, and seem to be less effective in adults. Sclerostin‐neutralizing antibodies (Scl‐Ab) have been shown to be beneficial in animal models of osteoporosis, and dominant OI resulting from mutations in the genes encoding type I collagen. However, Scl‐Ab treatment has not been studied in models of recessive OI. Cartilage‐associated protein (CRTAP) is involved in posttranslational type I collagen modification, and its loss of function results in recessive OI. In this study, we treated 1‐week‐old and 6‐week‐old Crtap^–/– mice with Scl‐Ab for 6 weeks (25 mg/kg, s.c., twice per week), to determine the effects on the bone phenotype in models of “pediatric” and “young adult” recessive OI. Vehicle‐treated Crtap^–/– and wild‐type (WT) mice served as controls. Compared with control Crtap^–/– mice, micro–computed tomography (μCT) analyses showed significant increases in bone volume and improved trabecular microarchitecture in Scl‐Ab–treated Crtap^–/– mice in both age cohorts, in both vertebrae and femurs. Additionally, Scl‐Ab improved femoral cortical parameters in both age cohorts. Biomechanical testing showed that Scl‐Ab improved parameters of whole‐bone strength in Crtap^–/– mice, with more robust effects in the week 6 to 12 cohort, but did not affect the increased bone brittleness. Additionally, Scl‐Ab normalized the increased osteoclast numbers, stimulated bone formation rate (week 6 to 12 cohort only), but did not affect osteocyte density. Overall, our findings suggest that Scl‐Ab treatment may be beneficial in the treatment of recessive OI caused by defects in collagen posttranslational modification. © 2015 American Society for Bone and Mineral Research.     

Effects of sclerostin antibody on bone healing

Promoting bone healing after a fracture has been a frequent subject of research. Recently, sclerostin antibody(Scl-Ab) has been introduced as a new anabolic agent for the treatment of osteoporosis. Scl-Ab activates the canonical Wnt(cWnt)-β-catenin pathway, leading to an increase in bone formation and decrease in bone resorption. Because of its rich osteogenic effects, preclinically, Scl-Ab has shown positive effects on bone healing in rodent models; researchers have reported an increase in bone mass, mechanical strength, histological bone formation, total mineralized callus volume, bone mineral density, neovascularization, proliferating cell nuclear antigen score, and bone morphogenic protein expression at the fracture site after Scl-Ab administration. In addition, in a rat critical-size femoral-defect model, the Scl-Ab-treated group demonstrated a higher bone healing rate. On the other hand, two clinical reports have researched Scl-Ab in bone healing and failed to show positive effects in the femur and tibia. This review discusses why Scl-Ab appears to be effective in animal models of fracture healing and not in clinical cases.     

Inhibition of sclerostin by systemic treatment with sclerostin antibody enhances healing of proximal tibial defects in ovariectomized rats

Recent studies suggest a possible role for inhibitors of sclerostin such as sclerostin antibody (Scl‐Ab) as an anabolic treatment for osteoporosis. Since Scl‐Ab has also been shown to potentiate bone repair, we examined the effect of Scl‐Ab treatment in a metaphyseal defect repair model in ovariectomized (OVX) rats. Four weeks after OVX or sham surgery, 3 mm circular defects were created bilaterally in the proximal tibia of all rats. After defect surgery, Saline or 25 mg/kg Scl‐Ab was administered twice weekly for 3 weeks. Of note, healing was advanced in the 1‐week post‐defect surgery in OVX controls over Sham controls, with increases in bone volume and fluorochrome labeling observed. However, by week 2, OVX controls fell significantly behind in the repair response compared with Sham controls. Scl‐Ab treatment significantly increased bone volume in the defect in OVX rats over the 3‐week time course as examined by either microCT or histology. Significant increases in bone formation via fluorochrome labeling of the new bone were observed with Scl‐Ab treatment, while osteoclast parameters were not different. With its powerful anabolic potential, bone‐specific activity, and potential for low dosing frequency, Scl‐Ab treatment could provide enhanced bone repair, particularly in situations of compromised bone repair such as osteoporotic bone. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1541–1548, 2012     

The Sclerostin‐Independent Bone Anabolic Activity of Intermittent PTH Treatment Is Mediated by T‐Cell–Produced Wnt10b

Both blunted osteocytic production of the Wnt inhibitor sclerostin (Scl) and increased T‐cell production of the Wnt ligand Wnt10b contribute to the bone anabolic activity of intermittent parathyroid hormone (iPTH) treatment. However, the relative contribution of these mechanisms is unknown. In this study, we modeled the repressive effects of iPTH on Scl production in mice by treatment with a neutralizing anti‐Scl antibody (Scl‐Ab) to determine the contribution of T‐cell–produced Wnt10b to the Scl‐independent modalities of action of iPTH. We report that combined treatment with Scl‐Ab and iPTH was more potent than either iPTH or Scl‐Ab alone in increasing stromal cell production of OPG, osteoblastogenesis, osteoblast life span, bone turnover, bone mineral density, and trabecular bone volume and structure in mice with T cells capable of producing Wnt10b. In T‐cell–null mice and mice lacking T‐cell production of Wnt10b, combined treatment increased bone turnover significantly more than iPTH or Scl‐Ab alone. However, in these mice, combined treatment with Scl‐Ab and iPTH was equally effective as Scl‐Ab alone in increasing the osteoblastic pool, bone volume, density, and structure. These findings demonstrate that the Scl‐independent activity of iPTH on osteoblasts and bone mass is mediated by T‐cell–produced Wnt10b. The data provide a proof of concept of a more potent therapeutic effect of combined treatment with iPTH and Scl‐Ab than either alone. © 2014 American Society for Bone and Mineral Research.     

Sclerostin Inhibition Prevents Spinal Cord Injury‐Induced Cancellous Bone Loss

Spinal cord injury (SCI) results in rapid and extensive sublesional bone loss. Sclerostin, an osteocyte‐derived glycoprotein that negatively regulates intraskeletal Wnt signaling, is elevated after SCI and may represent a mechanism underlying this excessive bone loss. However, it remains unknown whether pharmacologic sclerostin inhibition ameliorates bone loss subsequent to SCI. Our primary purposes were to determine whether a sclerostin antibody (Scl‐Ab) prevents hindlimb cancellous bone loss in a rodent SCI model and to compare the effects of a Scl‐Ab to that of testosterone‐enanthate (TE), an agent that we have previously shown prevents SCI‐induced bone loss. Fifty‐five (n = 11–19/group) skeletally mature male Sprague‐Dawley rats were randomized to receive: (A) SHAM surgery (T8 laminectomy), (B) moderate‐severe (250 kilodyne) SCI, (C) 250 kilodyne SCI + TE (7.0 mg/wk, im), or (D) 250 kilodyne SCI + Scl‐Ab (25 mg/kg, twice weekly, sc) for 3 weeks. Twenty‐one days post‐injury, SCI animals exhibited reduced hindlimb cancellous bone volume at the proximal tibia (via μCT and histomorphometry) and distal femur (via μCT), characterized by reduced trabecular number and thickness. SCI also reduced trabecular connectivity and platelike trabecular structures, indicating diminished structural integrity of the remaining cancellous network, and produced deficits in cortical bone (femoral diaphysis) strength. Scl‐Ab and TE both prevented SCI‐induced cancellous bone loss, albeit via differing mechanisms. Specifically, Scl‐Ab increased osteoblast surface and bone formation, indicating direct bone anabolic effects, whereas TE reduced osteoclast surface with minimal effect on bone formation, indicating antiresorptive effects. The deleterious microarchitectural alterations in the trabecular network were also prevented in SCI + Scl‐Ab and SCI + TE animals, whereas only Scl‐Ab completely prevented the reduction in cortical bone strength. Our findings provide the first evidence indicating that sclerostin inhibition represents a viable treatment to prevent SCI‐induced cancellous and cortical bone deficits and provides preliminary rationale for future clinical trials focused on evaluating whether Scl‐Ab prevents osteoporosis in the SCI population. © 2014 American Society for Bone and Mineral Research.     

A novel, non-prostanoid EP2 receptor-selective prostaglandin E2 agonist stimulates local bone formation and enhances fracture healing.

CP-533,536, a newly discovered, non-prostanoid EP2 receptor-selective PGE2 agonist, stimulates local bone formation and enhances fracture healing in rat models. INTRODUCTION: There is a significant medical need for agents that can stimulate local bone formation and enhance fracture healing. We tested the effects of CP-533,536, a newly discovered, non-prostanoid EP2 receptor-selective prostaglandin E2 (PGE2) agonist, in stimulating local bone formation and enhancing fracture healing in rat models. MATERIALS AND METHODS: In the first model, a single injection of CP-533,536 at doses of 0.3, 1, or 3 mg/kg to the proximal tibial metaphysis of 6-week-old male rats was given on day 1, and the local bone anabolic effect was determined on day 7. We then tested the effects of this compound in inducing bone formation on rat periosteum of the femur. A single dose of 0.3 mg of CP-533,536 incorporated in a poly-(D,L-lactide-co-glycolide) (PLGH) matrix was injected onto the periosteum of the femur in 3-week-old male rats, and local bone formation was determined on day 14. Finally, the ability of CP-533,536 in PLGH matrix in enhancing fracture healing was tested using the rat femoral fracture model. CP-533,536 in PLGH matrix at doses of 0.05, 0.5, or 5 mg was delivered to the local fracture site on the same day of fracture, and its efficacy was evaluated on day 21. RESULTS AND CONCLUSIONS: A single injection of CP-533,536 at doses of 0.3, 1, or 3 mg/kg to the proximal tibial metaphysis dose-dependently stimulated local lamellar bone formation on trabecular, endocortical, and periosteal surfaces, and thus increased bone mineral content and bone strength at the injected site. Similarly, a single injection of 0.3 mg of CP-533,536 incorporated in PLGH matrix onto the periosteum of the femur induced significantly local bone formation. In the rat femoral fracture model, CP-533,536 in PLGH matrix at doses of 0.05, 0.5, and 5 mg dose-dependently increased callus size, density, and strength compared with PLGH matrix alone. These results show that CP-533,536 stimulates new bone formation on trabecular, endocortical, and periosteal surfaces and enhances fracture healing. These data reveal that EP2 receptor-selective agonists provide therapeutic potential for local bone augmentation, bone repair, and bone healing in humans.     

Sclerostin Antibody Preserves the Morphology and Structure of Osteocytes and Blocks the Severe Skeletal Deterioration After Motor‐Complete Spinal Cord Injury in Rats

Unloading, neural lesions, and hormonal disorders after acute motor‐complete spinal cord injury (SCI) cause one of the most severe forms of bone loss, a condition that has been refractory to available interventions tested to date. Thus, these features related to acute SCI provide a unique opportunity to study complex bone problems, potential efficacious interventions, and mechanisms of action that are associated with these dramatic pathological changes. This study was designed to explore the therapeutic potential of sclerostin antibody (Scl‐Ab) in a rat model of bone loss after motor‐complete SCI, and to investigate mechanisms underlying bone loss and Scl‐Ab action. SCI rats were administered Scl‐Ab (25 mg/kg/week) or vehicle beginning 7 days after injury then weekly for 7 weeks. SCI resulted in significant decreases in bone mineral density (–25%) and trabecular bone volume (–67%) at the distal femur; Scl‐Ab completely prevented these deteriorations of bone in SCI rats, concurrent with markedly increased bone formation. Scanning electron microscopy revealed that SCI reduced numbers of osteocytes and dendrites concomitant with a morphology change from a spindle to round shape; Scl‐Ab corrected these abnormalities in osteocytes. In ex vivo cultures of bone marrow cells, Scl‐Ab inhibited osteoclastogenesis, and promoted osteoblastogenesis accompanied by increases in mRNA levels of LRP5, osteoprotegerin (OPG), and the OPG/RANKL ratio, and a decrease in DKK1 mRNA. Our findings provide the first evidence that robust bone loss after acute motor‐complete SCI can be blocked by Scl‐Ab, at least in part, through the preservation of osteocyte morphology and structure and related bone remodeling. Our findings support the inhibition of sclerostin as a promising approach to mitigate the striking bone loss that ensues after acute motor‐complete SCI, and perhaps other conditions associated with disuse osteoporosis as a consequence of neurological disorders. © 2015 American Society for Bone and Mineral Research     

Biomechanical considerations of fracture treatment and bone quality maintenance in elderly patients and patients with osteoporosis

Osteoporosis is a major public health problem that is characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility and an increased susceptibility to fractures of the hip, spine, and wrist. Poor bone quality in patients with osteoporosis presents the surgeon with difficult treatment decisions. Bone fracture repair has more pathways with combinations of bone formation mechanisms, which depend on the type of fracture fixation to be applied to achieve the desirable immobilization. There only may be one remodeling principle and in less than ideal conditions, mechanical and biophysical stimuli may provide effective augmentation of fracture healing in elderly patients. A different stimulus may limit its association to a specific healing mechanism. However, no matter which fixation method is used, an accurate reduction is a requisite for bone healing. Failure to realign the fracture site would result in delayed union, malunion, or nonunion. Therefore, a basic understanding of the biomechanics of osteoporotic bone and its treatment is necessary for clinicians to establish appropriate clinical treatment principles to minimize complications and enhance the patient's quality of life. We describe the biomechanical considerations of osteoporosis and fracture treatment from various aspects. First, bone structure and strength characterization are discussed using a hierarchical approach, followed by an innovative knowledge-based approach for fracture reduction planning and execution, which particularly is beneficial to osteoporotic fracture. Finally, a brief review of the results of several experimental animal models under different fracture types, gap morphologic features, rigidity of fixation devices, subsequent loading conditions, and biophysical stimulation is given to elucidate adverse mechanical conditions associated with different bone immobilization techniques that can compromise normal bone fracture healing significantly.     

Sclerostin Antibody Administration Converts Bone Lining Cells Into Active Osteoblasts

Sclerostin antibody (Scl‐Ab) increases osteoblast activity, in part through increasing modeling‐based bone formation on previously quiescent surfaces. Histomorphometric studies have suggested that this might occur through conversion of bone lining cells into active osteoblasts. However, direct data demonstrating Scl‐Ab‐induced conversion of lining cells into active osteoblasts are lacking. Here, we used in vivo lineage tracing to determine if Scl‐Ab promotes the conversion of lining cells into osteoblasts on periosteal and endocortical bone surfaces in mice. Two independent, tamoxifen‐inducible lineage‐tracing strategies were used to label mature osteoblasts and their progeny using the DMP1 and osteocalcin promoters. After a prolonged “chase” period, the majority of labeled cells on bone surfaces assumed a thin, quiescent morphology. Then, mice were treated with either vehicle or Scl‐Ab (25 mg/kg) twice over the course of the subsequent week. After euthanization, marked cells were enumerated, their thickness quantified, and proliferation and apoptosis examined. Scl‐Ab led to a significant increase in the average thickness of labeled cells on periosteal and endocortical bone surfaces, consistent with osteoblast activation. Scl‐Ab did not induce proliferation of labeled cells, and Scl‐Ab did not regulate apoptosis of labeled cells. Therefore, direct reactivation of quiescent bone lining cells contributes to the acute increase in osteoblast numbers after Scl‐Ab treatment in mice. © 2016 American Society for Bone and Mineral Research.