Bone morphogenetic protein-2 enhances osteoclast formation mediated by interleukin-1alpha through upregulation of osteoclast differentiation factor and cyclooxygenase-2

Multiple roles of ALK3 in osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by progressive cartilage degradation, synovial membrane inflammation, osteophyte formation, and subchondral bone sclerosis. Pathological changes in cartilage and subchondral bone are the main processes in OA. In recent decades, many studies have demonstrated that activin-like kinase 3 (ALK3), a bone morphogenetic protein receptor, is essential for cartilage formation, osteogenesis, and postnatal skeletal development. Although the role of bone morphogenetic protein (BMP) signalling in articular cartilage and bone has been extensively studied, many new discoveries have been made in recent years around ALK3 targets in articular cartilage, subchondral bone, and the interaction between the two, broadening the original knowledge of the relationship between ALK3 and OA. In this review, we focus on the roles of ALK3 in OA, including cartilage and subchondral bone and related cells. It may be helpful to seek more efficient drugs or treatments for OA based on ALK3 signalling in future.

Chi3L1 is a therapeutic target in bone metabolism and a potential clinical marker in patients with osteoporosis

BMP2 is clinically used as an ectopic bone inducer and plays a significant role in bone development, formation, and diseases. Chitinase 3-like 1 protein (Chi3L1) is found in the skeletal system. However, Chi3L1-mediated bone metabolism and aging-related bone erosion via BMP2 signaling have not yet been demonstrated. Herein, Chi3L1 increased BMP2-induced osteoblast differentiation in mesenchymal precursor cells and human primary osteoblasts. Chi3L1^KO(-/-) showed abnormal bone development, and primary osteoblasts isolated from Chi3L1^KO(-/-) exhibited impaired osteoblast differentiation and maturation. Chi3L1 also potentiated BMP2 signaling and RUNX2 expression in primary osteoblasts. Chi3L1 interacted with BMPRIa, which increased the surface expression of BMPRIa and promoted BMP2 signaling to induce osteoblast differentiation. Chi3L1^KO(-/-) mice showed bone formation reduced with a decrease in RUNX2 expression in calvarial defects. Chi3L1^KO(-/-) mice exhibited aging-related osteoporotic bone loss with decreases in the levels of RUNX2 and OPG, while serum PYD level and osteoclast number increased. Chi3L1 increased OPG via non-canonical BMP2 signaling in osteoblasts, which suppressed osteoclastogenesis in BMMs. Furthermore, ROC analysis showed that serum Chi3L1 level clinically decreased in osteoporosis patients. Our findings demonstrate that Chi3L1 promotes bone formation, suppresses osteoclastogenesis, and prevents aging-related osteoporosis.

The Role Of BMPs in the Regulation of Osteoclasts Resorption and Bone Remodeling: From Experimental Models to Clinical Applications

In response to mechanical forces and the aging process, bone in the adult skeleton is continuously remodeled by a process in which old and damaged bone is removed by bone-resorbing osteoclasts and subsequently is replaced by new bone by bone-forming cells, osteoblasts. During this essential process of bone remodeling, osteoclastic resorption is tightly coupled to osteoblastic bone formation. Bone-resorbing cells, multinuclear giant osteoclasts, derive from the monocyte/macrophage hematopoietic lineage and their differentiation is driven by distinct signaling molecules and transcription factors. Critical factors for this process are Macrophage Colony Stimulating Factor (M-CSF) and Receptor Activator Nuclear Factor-κB Ligand (RANKL). Besides their resorption activity, osteoclasts secrete coupling factors which promote recruitment of osteoblast precursors to the bone surface, regulating thus the whole process of bone remodeling. Bone morphogenetic proteins (BMPs), a family of multi-functional growth factors involved in numerous molecular and signaling pathways, have significant role in osteoblast-osteoclast communication and significantly impact bone remodeling. It is well known that BMPs help to maintain healthy bone by stimulating osteoblast mineralization, differentiation and survival. Recently, increasing evidence indicates that BMPs not only help in the anabolic part of bone remodeling process but also significantly influence bone catabolism. The deletion of the BMP receptor type 1A (BMPRIA) in osteoclasts increased osteoblastic bone formation, suggesting that BMPR1A signaling in osteoclasts regulates coupling to osteoblasts by reducing bone-formation activity during bone remodeling. The dual effect of BMPs on bone mineralization and resorption highlights the essential role of BMP signaling in bone homeostasis and they also appear to be involved in pathological processes in inflammatory disorders affecting bones and joints. Certain BMPs (BMP2 and -7) were approved for clinical use; however, increased bone resorption rather than formation were observed in clinical applications, suggesting the role BMPs have in osteoclast activation and subsequent osteolysis. Here, we summarize the current knowledge of BMP signaling in osteoclasts, its role in osteoclast resorption, bone remodeling, and osteoblast–osteoclast coupling. Furthermore, discussion of clinical application of recombinant BMP therapy is based on recent preclinical and clinical studies.

BMP2 immune complexes promote new bone formation by facilitating the direct contact between osteoclasts and osteoblasts

BMP2 antibody is proposed as a promising replacement for rhBMP2 in bone tissue engineering. Although studies have demonstrated its osteoinductive efficacy, the underlying osteogenic mechanism and adverse reactions of specific BMP2 antibody are not clarified yet, making it difficult to optimize the antibody for future application. By establishing BMP2 immune complexes (BMP2-ICs) ex vivo, we were able to introduce BMP2-ICs directly in vivo and found that BMP2-ICs promoted bone formation while suppressing osteoclastogenesis. However, ex vivo osteoclastogenic assays showed that BMP2-ICs promoted osteoclastogenesis by binding FcγR and activating PLCγ2 phosphorylation. Given that BMP2-ICs react with osteoblast and osteoclast lineage cells by the conjugated BMP2 domain and the Fc domain respectively, we introduced BMP2-ICs into coculture system of the two lineage cells and found that BMP2-ICs promoted osteogenesis while suppressing osteoclastogenesis by facilitating osteoblast-osteoclast contact and activating the EphrinB2-EphB4 signaling. This bidirectional function of BMP2-ICs was reproduced in the cranial bone resorption model, where osteoblast and osteoclast lineage cells co-localized. This study excluded the hidden problem of osteoclast overactivation that usually comes with rhBMP2 and clarified the first evidence of the mechanism of antibody-mediated bone regeneration, suggesting BMP2-ICs may present a promising therapy for bone diseases related with disrupted osteoclast-osteoblast interaction.

Vertical bone augmentation with simultaneous implantation using deproteinized bovine bone block functionalized with a slow delivery of BMP-2

OBJECTIVE

We hypothesized that a biomimetic calcium phosphate (CaP) coating which incorporates morphogenetic protein 2 (BMP-2) on the deproteinized bovine bone (DBB) blocks could be used to enhance the vertical alveolar ridge augmentation for the one-stage onlay surgery with simultaneous implants insertion. We aimed to test this hypothesis in vivo.

MATERIAL AND METHODS

Beagles dogs were used for the study (n = 6 specimens per group). One month after building the edentulous animal model, 4 mm vertical alveolar bone loss were surgically created and four groups of blocks (W × L × H: 7 mm × 10 mm × 4 mm) were randomly fixed onto the reduced alveolar ridge by implants: (a) DBB blocks alone (negative control group); (b) DBB blocks with superficial adsorption of 50 μg BMP-2 (ad.BMP-2 group); (c) DBB blocks coated by biomimetic CaP coating which incorporates 50 μg BMP-2 (inc.BMP-2 group); and (d) autologous bone blocks (positive control group). After 3 months of healing, samples were harvested for micro-CT and histomorphometric analyses.

RESULTS

In histomorphometry, the inc.BMP-2 group showed a significantly thicker (coronal-apically) and wider (buccal-lingually) augmented bone area, better bone-to-implant contact than the negative control group. In both the micro-CT and histomorphometry, the inc.BMP-2 group showed more mineralized tissue than the negative control group and the inc.BMP-2 group also showed significantly more newly formed bone and residual grafts than the negative control group in the upper half of the blocks. In micro-CT, the inc.BMP-2 group showed significantly more bone-to-graft contact percentage than the ad.BMP-2 group. In both micro-CT and histomorphometry, the inc.BMP-2 group showed significantly more percentage of mineralized tissue than the ad.BMP-2 group. No significant differences were found between the inc.BMP-2 group and the positive control group either in micro-CT or in histomorphometry.

CONCLUSIONS

The DBB blocks with coating-delivered BMP-2 significantly enhanced the efficacy of vertical alveolar bone augmentation, compared with the unloaded blocks and blocks with adsorbed BMP-2, in the one-stage onlay surgery with simultaneous implant insertion.

Bone morphogenetic proteins: Their role in regulating osteoclast differentiation

The ability to create recombinant bone morphogenetic proteins (BMPs) in recent years has led to their rise as a common clinical adjuvant. Their application varies, from spinal fixation to repairing palatal clefts, to coating implants for osseointegration. In recent years questions have been raised as to the efficacy of BMPs in several of these procedures. These questions are due to the unwanted side effect of BMPs on other cell types, such as osteoclasts which can resorb bone at the graft/implant site. However, most BMP research focuses on the anabolic osteoinductive effects of BMPs on osteoblasts rather than its counterpart- stimulation of the osteoclasts, which are cells responsible for resorbing bone. In this review, we discuss the data available from multiple in-vitro and in-vivo BMP-related knockout models to elucidate the different functions BMPs have on osteoclast differentiation and activity.

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BMPs can act directly on osteoclasts to regulate differentiation and activity.

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Osteoclasts express multiple BMP signaling components.

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BMPs signal through both SMAD independent and dependent mechanisms in osteoclasts.

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SMAD dependent BMP signaling regulates osteoclast-osteoblast coupling factors.

FLT-1 gene polymorphisms and protein expression profile in rheumatoid arthritis

OBJECTIVES

Inflammation and angiogenesis are a significant element of pathogenesis in rheumatoid arthritis (RA). The FLT-1- triggering factor for production of proinflammatory cytokines-might contributes to inflammation in patients with RA. Association of the FLT-1 polymorphisms with different "angiogenic diseases" suggests that it may be a novel genetic risk factor also for RA. The aim of the study was to identify FLT-1 genetic variants and their possible association with sFLT-1 levels, susceptibility to and severity of RA.

METHODS

The FLT-1 gene polymorphisms were genotyped for 471 RA patients and 684 healthy individuals. Correlation analysis was performed with clinical parameters, cardiovascular disease (CVD) and anti-citrullinated peptide/protein antibody (ACPA) presence. The sFLT-1 serum levels were evaluated.

RESULTS

The FLT-1 gene polymorphisms showed no significant differences in the proportion of cases and controls. Furthermore, the FLT-1 rs2296188 T/C polymorphism was associated with ACPA-positive RA. Overall, rs9943922 T/C and rs2296283 G/A are in almost completed linkage disequilibrium (LD) with D' = 0.97 and r2 = 0.83. The FLT-1 rs7324510 A allele has shown association with VAS score (p = 0.035), DAS-28 score (p = 0.013) and ExRA presence (p = 0.027). Moreover, other clinical parameters were also higher in RA patients with this allele. In addition, FLT-1 genetic variants conferred higher sFLT-1 levels in RA patients compared to controls.

CONCLUSION

FLT-1 rs7324510 C/A variant may be a new genetic risk factor for severity of RA. Examined factor highly predispose to more severe disease activity as well as higher sFLT-1 levels in RA.

Complications Associated With Bone Morphogenetic Protein in the Lumbar Spine

Complications associated with the use of recombinant human bone morphogenetic protein in the lumbar spine include retrograde ejaculation, ectopic bone formation, vertebral osteolysis and subsidence, postoperative radiculitis, and hematoma and seroma. These complications are controversial and remain widely debated. This article discusses the reported complications and possible implications for the practicing spine surgeon. Understanding the complications associated with the use of recombinant human bone morphogenetic protein and the associated controversies allows for informed decision making by both the patient and the surgeon. [Orthopedics. 2017; 40(2):e229-e237.].

Nano-Hydroxyapatite Bone Substitute Functionalized with Bone Active Molecules for Enhanced Cranial Bone Regeneration

The aim of this study was to synthesize and characterize a nano-hydroxyapatite (nHAP) and calcium sulfate bone substitute (NC) for cranioplasty. The NC was functionalized with low concentrations of bone morphogenetic protein-2 (BMP-2) and zoledronic acid (ZA) and characterized both in vitro and in vivo. In vitro studies included MTT, ALP assays, and fluorescent staining of Saos-2 (human osteoblasts) and MC3T3-E1 (murine preosteoblasts) cells cultured on NC. An in vivo study divided 20 male Wistar rats into four groups: control (defect only), NC, NC + ZA, and NC + ZA + rhBMP-2. The materials were implanted in an 8.5 mm critical size defect in the calvarium for 12 weeks. Micro-CT quantitative analysis was carried out in vivo at 8 weeks and ex vivo after 12 weeks. Mineralization was highest in the NC + ZA + rhBMP-2 group (13.0 ± 2.8 mm³) compared to the NC + ZA group (9.0 ± 3.2 mm³), NC group (6.4 ± 1.9 mm³), and control group (3.4 ± 1.0 mm³) after 12 weeks. Histological and spectroscopic analysis of the defect site provided a qualitative confirmation of neo-bone, which was in agreement with the micro-CT results. In conclusion, NC can be used as a carrier for bioactive molecules, and functionalization with rhBMP-2 and ZA in low doses enhances bone regeneration.

Transient Local Bone Remodeling Effects of rhBMP-2 in an Ovine Interbody Spine Fusion Model

BACKGROUND

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a powerful osteoinductive morphogen capable of stimulating the migration of mesenchymal stem cells (MSCs) to the site of implantation and inducing the proliferation and differentiation of these MSCs into osteoblasts. Vertebral end-plate and vertebral body resorption has been reported after interbody fusion with high doses of rhBMP-2. In this study, we investigated the effects of 2 rhBMP-2 doses on peri-implant bone resorption and bone remodeling at 7 time points in an end-plate-sparing ovine interbody fusion model.

METHODS

Twenty-one female sheep underwent an end-plate-sparing discectomy followed by interbody fusion at L2-L3 and L4-L5 using a custom polyetheretherketone (PEEK) interbody fusion device. The PEEK interbody device was filled with 1 of 2 different doses of rhBMP-2 on an absorbable collagen sponge (ACS): 0.13 mg (1×) or 0.90 mg (7×). Bone remodeling and interbody fusion were assessed via high-resolution radiography and histological analyses at 1, 2, 3, 4, 8, 12, and 20 weeks postoperatively.

RESULTS

Peri-implant bone resorption peaked between 3 and 8 weeks in both the 1× and the 7× rhBMP-2/ACS-dose group. Osteoclastic activity and corresponding peri-implant bone resorption was dose-dependent, with moderate-to-marked resorption at the 7×-dose level and less resorption at the 1×-dose level. Both dose (p < 0.0007) and time (p < 0.0025) affected bone resorption significantly. Transient bone-resorption areas were fully healed by 12 weeks. Osseous bridging was seen at all but 1 spinal level at 12 and at 20 weeks.

CONCLUSIONS

In the ovine end-plate-sparing interbody fusion model, rhBMP-2 dose-dependent osteoclastic resorption is a transient phenomenon that peaks at 4 weeks postoperatively.

CLINICAL RELEVANCE

Using the U.S. Food and Drug Administration (FDA)-approved rhBMP-2 concentration and matching the volume of rhBMP-2/ACS with the volume of desired bone formation within the interbody construct may limit the occurrence of transient bone resorption.

BMP-7 and Bone Regeneration: Evaluation of Dose-Response in a Rodent Segmental Defect Model

OBJECTIVES

To develop and validate a translatable and reproducible rodent critical-sized defect (CSD) model and to determine the optimal dose of recombinant human bone morphogenetic protein (BMP)-7 required to consistently heal the CSD in the new model.

METHODS

Rats with 6-mm CSDs stabilized with a commercial radiolucent plate and screws with angular stability were randomly assigned to 4 treatment groups with varied doses of recombinant human BMP-7 (25, 50, 75, and 100 μg) on absorbable collagen sponge and a single control group (absorbable collagen sponge alone). Bone formation was evaluated by radiographs, micro-computed tomography, histology, and biomechanics.

RESULTS

All the rats treated with 100 μg of BMP-7 with CSDs were united by 4 weeks and all 75- and 50-μg-group rats united by 6 weeks. None of the animals in the 25-μg BMP-7 group or the control group were healed at the time of killing. Bone volume, bone mineral density, the ratio of bone volume to total volume, stiffness, and ultimate load to failure were maximal in the 50-μg group. Total callus volume progressively increased with increasing BMP dose. Histologic analysis demonstrated increased callus width with increasing BMP-7 doses above 50 μg, but the bone seemed structurally abnormal.

CONCLUSIONS

There was a 100% union rate in the 50-, 75-, and 100-μg BMP-7-treated groups. None of the control or 25-μg-dose rats united. The biomechanical data demonstrated that 50 μg of BMP-7 produced the highest mechanical strength in the bone regenerate. These data also suggest that administration of BMP-7 above 50 μg does not improve bone regeneration and actually seems to produce lower quality bone with diminished biomechanical properties.

Bone Healing in Ovariectomized-rabbit Calvarial Defect with Tricalcium Phosphate Coated with Recombinant Human Bone Morphogenetic Protein-2 Genetically Engineered in Escherichia coli

Purpose:

This study compares the bone formation ability of tricalcium phosphate (TCP) with and without recombinant human bone morphogenetic protein-2 (rhBMP-2) and assesses TCP as a carrier of rhBMP-2.

Methods:

Bilateral round defects (diameter: 8.0 mm) were formed in the cranium of eight New Zealand white rabbits. The defects were grafted with TCP only (control group) or with rhBMP-2-coated TCP (experimental group). The animals were sacrificed at 1st week, 2nd week, 4th week, and 8th week postoperatively; two rabbits sacrificed each time. The skulls were harvested and subjected to radiographic and histological examination.

Results:

Radiologic evaluation showed faster bone remodeling in the experimental group than in the control group. Histologic evaluation (H&E, Masson’s trichrome stain) showed rapid bone formation, remodeling and calcification in the 1st and 2nd week in the experimental group. Immunohistochemical evaluation showed higher expression rate of osteoprotegerin, receptor activator of nuclear factor κB ligand, and receptor activator of nuclear factor κB in the experimental group at the 1st and 2nd week than in the control group.

Conclusion:

rhBMP-2 coated TCP resulted in rapid bone formation, remodeling, and calcification due to rhBMP-2’s osteogenic effect. TCP performed properly as a carrier for rhBMP-2. Thus, the use of an rhBMP-2 coating on TCP had a synergic effect on bone healing and, especially, bone remodeling and maturation.

Immunohistochemical localization of key arachidonic acid metabolism enzymes during fracture healing in mice

This study investigated the localization of critical enzymes involved in arachidonic acid metabolism during the initial and regenerative phases of mouse femur fracture healing. Previous studies found that loss of cyclooxygenase-2 activity impairs fracture healing while loss of 5-lipoxygenase activity accelerates healing. These diametric results show that arachidonic acid metabolism has an essential function during fracture healing. To better understand the function of arachidonic acid metabolism during fracture healing, expression of cyclooxygenase-1 (COX-1), cyclooxygenase -2 (COX-2), 5-lipoxygenase (5-LO), and leukotriene A4 hydrolase (LTA4H) was localized by immunohistochemistry in time-staged fracture callus specimens. All four enzymes were detected in leukocytes present in the bone marrow and attending inflammatory response that accompanied the fracture. In the tissues surrounding the fracture site, the proportion of leukocytes expressing COX-1, COX-2, or LTA4H decreased while those expressing 5-LO remained high at 4 and 7 days after fracture. This may indicate an inflammation resolution function for 5-LO during fracture healing. Only COX-1 was consistently detected in fracture callus osteoblasts during the later stages of healing (day 14 after fracture). In contrast, callus chondrocytes expressed all four enzymes, though 5-LO appeared to be preferentially expressed in newly differentiated chondrocytes. Most interestingly, osteoclasts consistently and strongly expressed COX-2. In addition to bone surfaces and the growth plate, COX-2 expressing osteoclasts were localized at the chondro-osseous junction of the fracture callus. These observations suggest that arachidonic acid mediated signaling from callus chondrocytes or from callus osteoclasts at the chondro-osseous junction regulate fracture healing.

The clinical use of bone morphogenetic proteins revisited: a novel biocompatible carrier device OSTEOGROW for bone healing

PURPOSE

The purpose of this study was to revise the clinical use of commercial BMP2 (Infuse) and BMP7 (Osigraft) based bone devices and explore the mechanism of action and efficacy of low BMP6 doses in a novel whole blood biocompatible device OSTEOGROW.

METHODS

Complications from the clinical use of BMP2 and BMP7 have been systemically reviewed in light of their role in bone remodeling. BMP6 function has been assessed in Bmp6-/- mice by μCT and skeletal histology, and has also been examined in mesenchymal stem cells (MSC), hematopoietic stem cells (HSC) and osteoclasts. Safety and efficacy of OSTEOGROW have been assessed in rats and rabbits.

RESULTS

Clinical use issues of BMP2 and BMP7 have been ascribed to the limited understanding of their role in bone remodeling at the time of device development for clinical trials. BMP2 and BMP7 in bone devices significantly promote bone resorption leading to osteolysis at the endosteal surfaces, while in parallel stimulating exuberant bone formation in surrounding tissues. Unbound BMP2 and BMP7 in bone devices precipitate on the bovine collagen and cause inflammation and swelling. OSTEOGROW required small amounts of BMP6, applied in a biocompatible blood coagulum carrier, for stimulating differentiation of MSCs and accelerated healing of critical size bone defects in animals, without bone resorption and inflammation. BMP6 decreased the number of osteoclasts derived from HSC, while BMP2 and BMP7 increased their number.

CONCLUSIONS

Current issues and challenges with commercial bone devices may be resolved by using novel BMP6 biocompatible device OSTEOGROW, which will be clinically tested in metaphyseal bone fractures, compartments where BMP2 and BMP7 have not been effective.

Surface-modified functionalized polycaprolactone scaffolds for bone repair: in vitro and in vivo experiments

A porcine calvaria defect study was carried out to investigate the bone repair potential of three-dimensional (3D)-printed poly-ε-caprolactone (PCL) scaffolds embedded with nanoporous PCL. A microscopic grid network was created by rapid prototyping making a 3D-fused deposition model (FDM-PCL). Afterward, the FDM-PCL scaffolds were infused with a mixture of PCL, water, and 1,4-dioxane and underwent a thermal-induced phase separation (TIPS) followed by lyophilization. The TIPS process lead to a nanoporous structure shielded by the printed microstructure (NSP-PCL). Sixteen Landrace pigs were divided into two groups with 8 and 12 weeks follow-up, respectively. A total of six nonpenetrating holes were drilled in the calvaria of each animal. The size of the cylindrical defects was h 10 mm and Ø 10 mm. The defects were distributed randomly using following groups: (a) NSP-PCL scaffold, (b) FDM-PCL scaffold, (c) autograft, (d) empty defect, (a1) NSP-PCL scaffold + autologous mononuclear cells, and (a2) NSP-PCL scaffold + bone morphogenetic protein 2. Bone volume to total volume was analyzed using microcomputed tomography (µCT) and histomorphometry. The µCT and histological data showed significantly less bone formation in the NSP-PCL scaffolds in all three variations after both 8 and 12 weeks compared to all other groups. The positive autograft control had significantly higher new bone formation compared to all other groups except the FDM-PCL when analyzed using histomorphometry. The NSP-PCL scaffolds were heavily infiltrated with foreign body giant cells suggesting an inflammatory response and perhaps active resorption of the scaffold material. The unmodified FDM-PCL scaffold showed good osteoconductivity and osseointegration after both 8 and 12 weeks.

Microstructured titanium regulates interleukin production by osteoblasts, an effect modulated by exogenous BMP-2

Microtextured implant surfaces increase osteoblast differentiation in vitro and enhance bone-to-implant contact in vivo and clinically. These implants may be used in combination with recombinant human bone morphogenetic protein 2 (rhBMP-2) to enhance peri-implant bone formation. However, the effect of surface modifications alone or in combination with rhBMP-2 on the osteoblast-produced inflammatory microenvironment is unknown. MG63 cells were cultured on tissue culture polystyrene or titanium substrates: smooth pretreated (PT, Ra=0.2μm), sandblasted/acid-etched (SLA, Ra=3.2μm) or hydrophilic-SLA (modSLA). Expression and protein production of pro-inflammatory interleukins (IL1b, IL6, IL8, IL17) and anti-inflammatory interleukins (IL10) were measured in cells with or without rhBMP-2. To determine which BMP signaling pathways were involved, cultures were incubated with BMP pathway inhibitors to blockSmad (dorsomorphin), TAB/TAK1 ((5Z)-7-oxozeaenol) or PKA (H-8) signaling. Culture on rough SLA and modSLA surfaces decreased pro-inflammatory interleukins and increased anti-inflammatory IL10. This effect was negated in cells treated with rhBMP-2, which caused an increase in pro-inflammatory interleukins and a decrease in anti-inflammatory interleukins through TAB/TAK signaling. The results suggest that surface microtexture modulates the inflammatory process during osseointegration, an effect that may enhance healing. However, rhBMP-2 in combination with microtextured titanium implants can influence the effect of cells on these surfaces, and may adversely affect cells involved in osseointegration.

Osteoclast progenitor cells present in significant amounts in mouse calvarial osteoblast isolations and osteoclastogenesis increased by BMP-2

Enzymatically released cells from neonatal mouse calvarial bones are frequently used as primary mouse osteoblasts for in vitro studies. We, here, report that although these cells lack mRNA expression of the osteoclastic genes Calcr, Acp5 and Mmp-9 at early time points after their isolation, these transcripts are gradually upregulated when the calvarial osteoblast cultures are differentiated to more mature osteoblasts in long term cultures. Similarly, Calcr, Acp5, Mmp-9, as well as Rank and Nfatc1 mRNA expressions are robustly increased when the osteoblast cultures were induced to differentiate by treatment with bone morphogenetic protein (BMP-2). The increased Calcr mRNA resulted in functionally active calcitonin receptors. Enhanced osteoblastic differentiation was associated with increased Rankl mRNA expression and decreased Opg and Cfs1 mRNA expression. Treatment of the osteoblastic cells with BMP-2 or RANKL, either on plastic dishes or bone slices, resulted in the formation of multinucleated tartrate-resistant acid phosphatase positive cells, which were able to excavate resorption pits and release CTX from the bones. In contrast, increased osteoblastic differentiation induced by BMP-2 in the mouse calvarial osteoblastic cell line MC3T3-E1 was not associated with increased mRNA expression of Calcr, Acp5, Rank, c-Fms or Oscar. Interestingly, Ctsk mRNA was increased during osteoblastic differentiation in both mouse calvarial osteoblast cultures and in MC3T3-E1 cultures. Also osteoblasts isolated from mouse long bones by outgrowth from explant cultures were contaminated with osteoclast progenitors able to differentiate into bone resorbing osteoclasts. These data indicate that mouse calvarial osteoblast cultures contain osteoclast progenitor cells, which will be differentiated along the osteoclastic lineage during osteoblastic differentiation. Moreover, the data show that BMP-2 not only stimulates osteoblastic differentiation but can also induce osteoclastogenesis through increased RANKL.

Effect of bone morphogenetic protein 2 on tendon-to-bone healing in a canine flexor tendon model

Tendon-to-bone healing is typically poor, with a high rate of repair-site rupture. Bone loss after tendon-to-bone repair may contribute to poor outcomes. Therefore, we hypothesized that the local application of the osteogenic growth factor bone morphogenetic protein 2 (BMP-2) would promote bone formation, leading to improved repair-site mechanical properties. Intrasynovial canine flexor tendons were injured in Zone 1 and repaired into bone tunnels in the distal phalanx. BMP-2 was delivered to the repair site using either a calcium phosphate matrix (CPM) or a collagen sponge (COL) carrier. Each animal also received carrier alone in an adjacent repair to serve as an internal control. Repairs were evaluated at 21 days using biomechanical, radiographic, and histologic assays. Although an increase in osteoid formation was noted histologically, no significant increases in bone mineral density occurred. When excluding functional failures (i.e., ruptured and gapped repairs), mechanical properties were not different when comparing BMP-2/CPM groups with carrier controls. A significantly higher percentage of BMP-2 treated specimens had a maximum force <20 N compared to carrier controls. While tendon-to-bone healing can be enhanced by addressing the bone loss that typically occurs after surgical repair, the delivery of BMP-2 using the concentrations and methods of the current study did not improve mechanical properties over carrier alone. The anticipated anabolic effect of BMP-2 was insufficient in the short time frame of this study to counter the post-repair loss of bone.

rhBMP-2/calcium phosphate matrix induces bone formation while limiting transient bone resorption in a nonhuman primate core defect model

BACKGROUND

Transient bone resorption limits the use of recombinant human bone morphogenetic protein-2 (rhBMP-2)/absorbable collagen sponge in metaphyseal bone. The purpose of the present study was to evaluate the efficacy of rhBMP-2/calcium phosphate matrix (CPM) to induce bone formation while limiting transient bone resorption in nonhuman primate core defects.

METHODS

Metaphyseal core defects were created in eighteen cynomolgus monkeys. rhBMP-2 retention was evaluated in the distal part of the radius. Bone formation was evaluated at eight weeks following treatment with 1.5 or 4.5-mg/mL rhBMP-2/CPM, CPM alone, or no treatment in the distal part of the radius, the proximal part of the tibia, and the proximal part of the femur; at twenty-four weeks following treatment with 1.5-mg/mL rhBMP-2/CPM or CPM alone in the proximal part of the tibia; and at one, two, and four weeks following treatment with 1.5-mg/mL rhBMP-2/CPM or no treatment in the distal part of the radius. Bone resorption was evaluated at four weeks following treatment with 1.5, 2.0, 3.0, and 4.5-mg/mL rhBMP-2/CPM or CPM alone in the distal part of the femur. Evaluations were performed with use of scintigraphy, radiographs, histological analysis, and computed tomography.

RESULTS

Seventy-eight percent, 64%, 50%, 35%, and 12% of the rhBMP-2 was retained in the distal part of the radius at one, seven, fourteen, twenty-one, and forty-nine days after surgery. rhBMP-2/CPM increased bone formation within core defects and surrounding trabeculae compared with CPM alone or no treatment at all anatomic locations at eight weeks, and bone formation was ongoing in the rhBMP-2/CPM-treated proximal tibial sites at twenty-four weeks. Bone formation began in the trabeculae surrounding the core defects at one week and was observed adjacent to the resorbing CPM within the core defects and in the surrounding trabecular bone at two and four weeks in the rhBMP-2/CPM-treated distal radial sites. Bone formation was confined to the region immediately surrounding the core defects in the untreated distal radial sites at all time points. Transient bone resorption was only observed in the distal femoral sites treated with 4.5 mg/mL of rhBMP-2/CPM at two weeks.

CONCLUSIONS

Treatment of nonhuman primate metaphyseal core defects with 1.5 to 3.0-mg/mL rhBMP-2/CPM resulted in bone formation without transient bone resorption.

CLINICAL RELEVANCE

rhBMP-2/CPM may be useful to accelerate healing of metaphyseal bone defects in humans.

Bone formation around zirconia implants combined with rhBMP-2 gel in the canine mandible

OBJECTIVE

The aim of this study was to estimate the effects of zirconia implants and recombinant human bone morphogenetic protein-2 (rhBMP-2) gel on the acceleration of local bone formation and osseointegration in the canine mandible.

MATERIALS AND METHODS

Four groups of 48 implants with identical geometry were installed in the mandibles of beagle dogs: alumina-blasted zirconia implants applied with rhBMP-2, alumina-blasted zirconia implants applied with demineralized bone matrix (DBM), alumina-blasted zirconia implants, and resorbable blast media-treated titanium (Ti) implants. For the first two groups, zirconia implants were inserted after the surgical sites were filled with rhBMP-2 or DBM gel. For the other two groups, zirconia or Ti implants were installed with no adjunctive treatment. Fluorescent bone markers were administered to monitor bone remodeling at weeks 2, 4, and 5 postimplantation. After healing periods of 3 weeks and 6 weeks, the animals were sacrificed, and fluorescent microscopy, histology, and histomorphometric analyses were performed.

RESULTS

Fluorescent microscopy showed that bone formation around the zirconia implants installed with rhBMP-2 gel was the most prominent at 2 weeks postimplantation, while the Ti implants acquired bone apposition mainly at week 5. No significant differences were found in bone area among the groups (P > 0.05). The zirconia implants showed similar bone-to-implant contact to the Ti implants. There were no significant differences in bone-to-implant contact between the zirconia implants with rhBMP-2 gel and those with DBM (P > 0.05).

CONCLUSIONS

The zirconia implants with alumina-blasted surfaces may achieve osseointegration in much the same manner as the well-established Ti implants. The area influenced by rhBMP-2 gel, including the alveolar crest, may cause active remodeling and early bone formation.

Bone morphogenetic protein 2 enhances mouse osteoclast differentiation via increased levels of receptor activator of NF-κB ligand expression in osteoblasts

1α,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] induces osteoclast formation via induction of receptor activator of NF-κB ligand (RANKL, also called TNF-related activation-induced cytokine: TRANCE) in osteoblasts. In cocultures of mouse bone marrow cells and osteoblasts, 1,25(OH)(2)D(3) induced osteoclast formation in a dose-dependent manner, with maximum osteoclast formation observed at concentrations greater than 10(-9) M of 1,25(OH)(2)D(3). In the presence of bone morphogenetic protein 2 (BMP-2), the maximum formation of osteoclasts was seen with lower concentrations of 1,25(OH)(2)D(3) (greater than 10(-11) M), suggesting that BMP-2 enhances osteoclast formation induced by 1,25(OH)(2)D(3). In addition, the expressions of RANKL mRNA and proteins were induced by 1,25(OH)(2)D(3) in osteoblasts, and further upregulated by BMP-2. In mouse bone marrow cell cultures without 1,25(OH)(2)D(3), BMP-2 did not enhance osteoclast differentiation induced by recombinant RANKL and macrophage colony-stimulating factor (M-CSF), indicating that BMP-2 does not target osteoclast precursors. Furthermore, BMP-2 up-regulated the expression level of vitamin D receptor (VDR) in osteoblasts. These results suggest that BMP-2 regulates mouse osteoclast differentiation via upregulation of RANKL in osteoblasts induced by 1,25(OH)(2)D(3).

Bone morphogenic protein 2 directly enhances differentiation of murine osteoclast precursors

Previous studies found that bone morphogenic proteins (BMPs) support osteoclast formation, but it is not clear whether this is a direct effect on osteoclasts or mediated indirectly through osteoblasts. We have shown that a mouse deficient for the BMP antagonist Twisted gastrulation suggested a direct positive role for BMPs on osteoclastogenesis. In this report, we further determine the significance of BMP signaling on osteoclast formation in vitro. We find that BMP2 synergizes with suboptimal levels of receptor activator of NF-kappaB ligand (RANKL) to enhance in vitro differentiation of osteoclast-like cells. The enhancement by BMP2 is not a result of changes in the rate of proliferation or survival of the bone marrow-derived cultures, but is accompanied by an increase in expression of genes involved in osteoclast differentiation and fusion. Treatment with BMP2 did not significantly alter expression of RANKL or OPG in our osteoclast cultures, suggesting that the enhancement of osteoclastogenesis is not mediated indirectly through osteoblasts or stromal cells. Consistent with this, we detected phosphorylated SMAD1,5,8 (p-SMAD) in the nuclei of mononuclear and multinucleated cells in osteoclast cultures. Levels of p-SMAD, BMP2, and BMP receptors increased during differentiation. RNAi suppression of Type II BMP receptor inhibited RANKL-stimulated formation of multinuclear TRAP-positive cells. The BMP antagonist noggin inhibited RANKL-mediated osteoclast differentiation when added prior to day 3, while addition of noggin on day 3 or later failed to inhibit their differentiation. Taken together, these data indicate that osteoclasts express BMP2 and BMP receptors, and that autocrine BMP signaling directly promotes the differentiation of osteoclasts-like cells.

BMP-7-induced ectopic bone formation and fracture healing is impaired by systemic NSAID application in C57BL/6-mice

Nonsteroidal antiinflammatory drugs (NSAIDs) are known to potentially impair the fracture healing process. The aim of the present study was to determine if the impairment of bone healing by systemic NSAID application is, at least in part, due to an interaction of NSAIDs with the bone anabolic BMP-7 pathway. Therefore, we first analyzed fracture healing in control and diclofenac-treated mice, where we not only found a significant impairment of fracture healing due to diclofenac treatment as assessed by biomechanical testing and microCT imaging, but also found high coexpression of bone morphogenetic protein-7 (BMP-7) and cyclooxygenase-2 (COX-2) within the fracture callus of both groups. To experimentally address the possible interaction between BMP-7 and COX-2, we then induced ectopic bone formation in control (n = 10) and diclofenac-treated mice (n = 10) by application of BMP-7 (recombinant human OP-1, rhOP-1) into the hamstring muscles. After 20 days of treatment, each ectopic bone nodule was analyzed by contact-radiography, microCT, histology, and histomorphometry. Diclofenac application decreased the trabecular number and bone mass in the ectopic bone nodules significantly due to reduced osteoblast number and activity. These data demonstrate that the bone anabolic effect of BMP-7 and fracture healing is impaired by diclofenac application, and suggest that the potential negative impact of NSAIDs on fracture healing is, at least in part, due to interference with BMP-7 signaling.

rhBMP-2 induces transient bone resorption followed by bone formation in a nonhuman primate core-defect model

BACKGROUND

Bone resorption preceding bone formation has been reported following the administration of recombinant human bone morphogenetic protein-2 (rhBMP-2) delivered in an absorbable collagen sponge (ACS) in metaphyseal bone. This study characterizes treatment with rhBMP-2/ACS in metaphyseal bone with use of a nonhuman primate core-defect model.

METHODS

Unilateral proximal femoral core defects were treated with 360 microg of rhBMP-2/ACS or ACS alone or were left untreated in seven, five, and five adult male cynomolgus monkeys, respectively. Distal femoral core defects in seven of the above animals were treated with 360 microg of rhBMP-2/ACS in one limb and ACS alone in the contralateral limb. Retention of rhBMP-2 in the proximal part of the femora was determined with use of tracer amounts of (125)I-rhBMP-2 imaged with a gamma camera. The distal part of the femora was evaluated with in vivo computed tomography. Computed tomography and histological evaluation were performed on harvested segments in all animals at twenty-four weeks. The histological response in the proximal and distal parts of the femora containing core defects treated with 360 microg of rhBMP-2/ACS in one limb and ACS alone in the contralateral limb was evaluated at one, two, and four weeks in three animals per time point.

RESULTS

Approximately 39.9%, 24.2%, 3.4%, and 0.5% of the rhBMP-2 was retained in the proximal part of the femora at one, seven, fourteen, and twenty-one days, respectively. The mineral density and trabecular volume fraction of the core defects treated with rhBMP-2/ACS, those treated with ACS alone, and untreated core defects in the proximal part of the femora were 81%, 54%, and 20%, respectively, and 94%, 36%, and 31%, respectively, of the corresponding region in the contralateral limbs at twenty-four weeks. The mineral density and trabecular volume fraction of the region surrounding the core defects treated with rhBMP-2/ACS, those treated with ACS alone, and untreated core defects were 112%, 105%, and 104%, respectively, and 117%, 108%, and 107%, respectively, of the corresponding region in the contralateral limbs. Treatment with rhBMP-2/ACS increased the size of the proximal and distal core defects compared with treatment with ACS alone. Histological evaluation of the rhBMP-2/ACS-treated limbs demonstrated that bone resorption was initiated at one week in association with osteoclasts and receptor activator of nuclear factor-kappaB ligand-positive stained spindle-shaped cells and peaked at two weeks. Bone formation was observed at two weeks and was ongoing at twenty-four weeks.

CONCLUSIONS

Treatment of metaphyseal core defects with rhBMP-2/ACS resulted in bone resorption followed by bone formation in nonhuman primates.

Bone morphogenetic proteins and tissue engineering: future directions

As long as bone repair and regeneration is considered as a complex clinical condition, the administration of more than one factor involved in fracture healing might be necessary. The effectiveness or not of bone morphogenetic proteins (BMPs) in association with other growth factors and with mesenchymal stem cells in bone regeneration for fracture healing and bone allograft integration is of great interest to the scientific community. In this study we point out possible future developments in BMPs, concerning research and clinical applications.

Bone morphogenetic protein 2 enhances PGE(2)-stimulated osteoclast formation in murine bone marrow cultures

Bone morphogenetic protein 2 (BMP-2) is used clinically to stimulate bone formation and accelerate fracture repair. Adding prostaglandin (PG) E(2) or PGE(2) receptor agonists to BMP-2 has been proposed to improve BMP-2 efficacy. However, this may enhance bone resorption, since PGE(2) can increase receptor activator of NF-kappaB ligand (RANKL) expression and decrease osteoprotegerin (OPG) expression in osteoblasts, and the RANKL:OPG ratio is critical for osteoclast formation. We used bone marrow (BM) cultures and BM macrophage (BMM) cultures from outbred CD1 mice to examine effects on osteoclast formation of BMP-2 and PGE(2). In BM cultures, which contain both osteoblastic and osteoclastic lineage cells, BMP-2 (100 ng/ml) alone did not increase osteoclast formation but enhanced the peak response to PGE(2) by 1.6-9.6-fold. In BMM cultures, which must be treated with RANKL because they do not contain osteoblastic cells, BMP-2 did not increase osteoclast formation, with or without PGE(2). Our results suggest that BMP-2 can increase osteoclast formation in response to PGE(2) by increasing the RANKL:OPG ratio in osteoblasts, which may have therapeutic implications for the use of BMP-2.

A comparative study on BMP-induced osteoclastogenesis and osteoblastogenesis in primary cultures of adult rat bone marrow cells

Bone remodeling is a process consisting of bone formation and resorption. The present study compared the relative osteoclastic and osteoblastic potency of bone morphogenetic proteins (BMP)-2, -4, -5, -6, and -7 in primary murine bone marrow cultures. All five BMPs stimulated, to varying degree, formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells in a time- and protein concentration-dependent manner. The TRAP staining intensity correlated positively with the number of nuclei per TRAP-positive cell and the mRNA levels of colony-stimulating factor (CSF-1), receptor activator of nuclear factor kappaB ligand (RANKL), TRAP, and cathepsin K. Under osteogenic conditions, all five BMPs stimulated AP activity and mineralized bone nodule formation in a protein concentration-dependent manner in the same primary murine bone marrow cell culture system. These findings should be useful in designing treatment strategies for bone regeneration.

Short-term osteoclastic activity induced by locally high concentrations of recombinant human bone morphogenetic protein-2 in a cancellous bone environment

STUDY DESIGN

An experimental study investigating osteoclastic activity induced by rhBMP-2 in sheep.

OBJECTIVE

To examine the effects of increasing local rhBMP-2 concentration on osteoclastic response and peri-implant bone resorption.

SUMMARY OF BACKGROUND DATA

Level I clinical studies have established the safe and effective volume and concentration of rhBMP-2 delivered on an absorbable collagen sponge. However, peri-implant bone resorption appearing as decreased mineral density has been observed radiographically in rare instances after implantation of rhBMP-2 on an absorbable collagen sponge (rhBMP-2/ACS).

METHODS

Bilateral corticocancellous defects were created in the distal femora of 30 adult sheep. Combinations of rhBMP-2/ACS implant volume (V) (1V = normal fill or 2V = overfilled) and rhBMP-2 solution concentration (x) (1x = normal concentration or 3.5x = hyperconcentrated) resulted in local rhBMP-2 concentrations of 0x, 1x, 2x, 3.5x, and 7x the estimated effective concentration for this model. Faxitron radiography, quantitative CT, histology, and quantitative histomorphometry were conducted in a blinded fashion to analyze the effect of the treatments.

RESULTS

At 1 week, the normal fill-normal concentration implants (1x) produced the least transient osteoclastic activity resulting in limited peri-implant resorption. Overfilled-hyperconcentrated implants (2x, 3.5x) demonstrated moderate resorption zones. Overfilled-hyperconcentrated implants (7x) demonstrated extensive osteoclastic activity and marked resorption. Results at 4 and 8 weeks revealed dense osteoid and bone in the voids with progressive bony healing. Control defects showed no osteoclastic activity with little to no bony healing.

CONCLUSION

Increasing the local rhBMP-2 concentration by overfilling the defect with rhBMP-2/ACS or hyperconcentrating the rhBMP-2 solution on the absorbable collagen sponge led to a concentration-dependent osteoclastic resorption of peri-implant bone. The osteoclastic effect was transient, and progressive healing took place over the 8-week survival period.

Influence of nonsteroidal anti-inflammatory drugs on osseointegration

This paper reviews contemporary literature concerning the possible influence of nonsteroidal anti-inflammatory drugs (NSAIDs) on osseointegration. In vitro studies concerning the effect of NSAIDs on growth factors and bone-generating cells are the primary source of data pertaining to this issue because relatively few in vivo studies have been conducted. It is concluded that prescribing NSAIDs during the early postoperative period is likely not without negative effect, although any negative influence appears to be temporary and does not affect the final outcome of osseointegration.

A comprehensive review of the safety profile of bone morphogenetic protein in spine surgery

WE REVIEW OUR current understanding of the development and potential clinical applications of bone morphogenetic protein (BMP) in spine surgery. We also review the evidence for adverse events associated with the use of BMP and suggest potential reasons for these events and means of complication avoidance. Bone morphogenetic protein 2 (rhBMP-2) is approved by the Food and Drug Administration for anterior lumbar interbody fusion; rhBMP-7, on the other hand, is approved for long bone defects and has received a humanitarian device exemption for revision posterolateral lumbar operations and recalcitrant long bone unions. Nevertheless, "off-label" use in various spinal procedures has been reported and is increasing in frequency. Specific guidelines for rhBMP-2 and rhBMP-7 use are lacking because of the limited availability of randomized controlled clinical trials and its diverse use in many spinal applications. Mechanisms of delivery, carrier type, graft position, surgical location, and variations in BMP concentration may differ from one surgery to the next. Adverse events linked to either rhBMP-2 or rhBMP-7 use include ectopic bone formation, bone resorption or remodeling at the graft site, hematoma, neck swelling, and painful seroma. Other potential theoretical concerns include carcinogenicity and teratogenic effects. In this review, we provide the reader with a historical perspective on BMP, current and past research to support its use in spinal procedures, and a critical analysis of the complications reported thus far.

OP-1 application in bone allograft integration: preliminary results in sheep experimental surgery

Massive bone allografts are frequently used in orthopaedic reconstructive surgery. However the failure rate at long term follow-up is around 25%.

AIM

Stimulation of allograft incorporation.

MATERIALS AND METHODS

In order to stimulate bone remodeling of an allograft we applied recombinant human osteogenic protein-1 (rh-OP-1, also know as bone morphogenetic protein-7, BMP-7) to a long bone critical size defect sheep model. In nine sheep we created a 3 cm osteoperiosteal metatarsal defect replaced with a structural allograft alone (control group, 4 animals), or an allograft added with rh-BMP-7 (BMP group, 5 animals). Radiographic, mechanical, histological and histomorphometric analysis were performed.

RESULTS

X-rays in the BMP group showed a better and faster callus formation, compared to the control group within the first 8 weeks after surgery. After 16 weeks there was a higher evidence of bone remodeling in the BMP group. Radiographic healing at junction sites was more evident in the BMP group at 4, 8 and 16 weeks. Mechanical testing on screw extraction showed no statistical differences between the two groups and histomorphometry showed no difference in terms of newly formed bone inside the allograft as well. The resorption rate of the graft was higher in the BMP group in comparison to the control group. The penetration of newly formed vessels was significantly higher in the BMP group.

CONCLUSIONS

These findings indicate that BMP-7 added to a structural bone allograft inducing early remodeling of the graft through stimulation of neo-angiogenesis and osteoclastic activity, without negative effects in mechanical strength and clinical outcome.

Modeling bone morphogenetic protein and bisphosphonate combination therapy in wild-type and Nf1 haploinsufficient mice

Recombinant bone morphogenetic proteins (BMPs) show promise in treating the orthopedic complications associated with neurofibromatosis type 1 (NF1), such as congenital pseudarthrosis of the tibia. Minimal scientific information regarding the effects of BMP in the context of NF1 is available. As abnormalities in both bone formation and resorption have been documented in Nf1-deficient mice, we hypothesized that inadequate BMP-induced bone formation could be augmented by cotreatment with the bisphosphonate zoledronic acid (ZA). First, primary osteoblasts isolated from wild type (Nf1(+/+)) and Nf1-deficient (Nf1(+/-)) mice were cultured in the presence and absence of BMP-2. While Nf1(+/-) cells exhibited less osteogenic potential than Nf1(+/+) cells, alkaline phosphatase expression and matrix mineralization for both genotypes were enhanced by BMP-2 treatment. To model this response in vivo, 20 microg BMP-2 was implanted intramuscularly into the quadriceps of mice to induce heterotopic bone. Radiographs revealed significantly less net bone formation in Nf1(+/-) mice compared to Nf1(+/+) controls. To test the effect of an antiresorptive agent, mice were cotreated twice weekly from postoperative day 3 with 0.02 mg/kg ZA or with saline. ZA treatment led to a synergistic increase in the amount of heterotopic bone in both Nf1(+/+) and Nf1(+/-) mice compared with saline controls, as measured by DEXA and histomorphometry. Thus, the anabolic deficiency noted in Nf1(+/-) mice is amenable to stimulation by BMP-2, but mineralized tissue formation remains below that of Nf1(+/+) controls. Bisphosphonate combination therapy is superior to BMP therapy alone in terms of net bone production in vivo in both wild-type and Nf1-deficient mice.

Interaction of bone morphogenetic proteins with cells of the osteoclast lineage: review of the existing evidence

The present review evaluates the existing scientific proofs of this supplementary role of the BMPs and summarises its clinical implications. Bone regeneration is a process consisting of bone formation and bone resorption, two different but closely coupling pathways, which in most circumstances proceed simultaneously. Plenty of evidence has also characterised the bone morphogenetic proteins (BMPs) as inducing factors of bone formation. However, there is also evidence that these multifunctioning proteins affect bone resorption and the osteoclast homeostasis utilising various pathways. The present review evaluates the existing scientific evidence of this supplementary role of the BMPs, and summarises its clinical implications.

The effect of age on prostaglandin-synthesizing enzymes in the development of gingivitis

BACKGROUND AND OBJECTIVE

The aim of this study was to identify the expression of cyclooxygenase-1, cyclooxygenase-2, cyclooxygenase-3, and microsomal prostaglandin E synthase-1 in young and elderly subjects.

MATERIAL AND METHODS

Periodontally healthy subjects were divided into young (18-30 years, n = 7) and elderly (46-77 years, n = 7). A gingival biopsy was taken at baseline. After experimental gingivitis, clinical examination was repeated and a second biopsy was taken. The expression of cyclooxygenase-1, cyclooxygenase-2, cyclooxygenase-3, and microsomal prostaglandin E synthase-1 was analyzed by means of immunohistochemistry.

RESULTS

In both healthy age groups, cyclooxygenase-1 and microsomal prostaglandin E synthase-1 were expressed in epithelial cells, endothelial cells and fibroblast-like connective tissue cells. Cyclooxygenase-1 was found in Langerhans' cells of the epithelium. Cyclooxygenase-2 expression was observed in cells exhibiting the morphology of epithelial mitosis cells, and the expression of cyclooxygenase-2 in periodontally healthy elderly subjects was significantly lower (p < or = 0.05). Following experimental gingivitis, cyclooxygenase-1 and microsomal prostaglandin E synthase-1 expression did not change. However, the expression of cyclooxygenase-2 was significantly increased in both age groups (p < or = 0.05). Cyclooxygenase-3 was not detected in any group investigated.

CONCLUSION

Cyclooxygenase-1 and microsomal prostaglandin E synthase-1 were expressed constitutively in gingival tissue, and expression was unaffected by age or inflammation states. In contrast, the expression of cyclooxygenase-2 was weaker in elderly subjects. In the course of experimental gingivitis, cyclooxygenase-2 was induced in both age groups.

Refining Retinoic Acid Stimulation for Osteogenic Differentiation of Murine Adipose-Derived Adult Stromal Cells

Murine adipose-derived adult stromal cells (ADAS) seeded onto appropriate scaffolds and pre-incubated with retinoic acid have been shown to generate in vivo bone rapidly. Prompt resorption ensues, however, as a result of osteoclastogenesis, likely secondary to retinoic acid carryover. In this study, we determined the effects of abbreviated retinoic acid exposure on ADAS osteogenic differentiation. Histological staining and gene expression analysis revealed that longer retinoic acid exposure resulted in better in vitro bone differentiation. However, significant osteogenesis was observed in ADAS after just 15 days of retinoic acid supplementation, suggesting that continual culture with retinoic acid is unnecessary for initiation of the osteogenic program. This was confirmed using ADAS pre-incubated in monolayer with an abbreviated 15 days of retinoic acid exposure before implantation into critical-sized calvarial defects. Similar rates of regeneration were observed between ADAS exposed to for 15 days or for a full 25-day course of retinoic acid before defect repair. Furthermore, by limiting retinoic acid exposure to ADAS in monolayer without scaffold, accelerated bone formation was observed without concomitant osteoclastic resorption. These data suggest that skeletal regeneration may be improved by modulating retinoic acid exposure before implantation, markedly accelerating the repair of bone defects using ADAS.

The influence of recombinant human BMP-2 on bone-implant osseointegration: biomechanical testing and histomorphometric analysis

The healing period for bone-implant osseointegration lasts 3-6 months or even longer. The aim of this study was to investigate whether osseointegration can be enhanced by the use of bone morphogenetic protein-2 (BMP-2). In the femurs of 8 Japanese white rabbits, 16 implants were applied with 1.0 mg recombinant human BMP-2 (rhBMP-2) as group A, and the other 16 implants without rhBMP-2 as group B. Calcein green 20 mg/kg and alizarin red 20 mg/kg were injected 4 and 8 weeks after implantation, respectively. At 12 weeks, the animals were killed. In 16 implant-bone blocks, binding strength was measured by pull-out test, and the extracted implants were observed under a scanning electronic microscope. The other blocks were analysed for percentage of marked bone adjacent to the implant surface by confocal laser scanning microscope. The pull-out strengths of group A were greater than that of group B (P<0.05). Scanning electronic microscopy (SEM) showed more calcified substances on the surface of the implants of group A than B. There was more marked bone around group A than B implants at 4 weeks (P<0.05) and 8 weeks (P<0.05). rhBMP-2 improves the quantity and quality of implant-bone osseointegration. Biomechanical testing and histomorphometric analysis are reliable methods to use in researching the implant-bone interface.

Effects of Dose of Recombinant Human BMP-2 on Bone Formation at Palatal Sites in Young and Old Rats

This study was designed to examine the effects of dose of recombinant human BMP-2 (rhBMP-2) on bone formation at palatal sites in 10-week-old (10w) and 70-week-old (70w) rats, when combined with a polylactate-polyglycolate copolymer/gelatine sponge (PGS). New bone formation was observed at six weeks after implantation. In the 10w rats, thickness of new bone (TNB) increased as the dosage increased from 0 microg to 4 microg, and decreased significantly as the dosage increased from 8 microg to 24 microg. In contrast, in the 70w rats, TNB increased as the dosage increased from 0 microg to 16 microg, and did not significantly change as the dosage increased from 16 microg to 24 microg. These results suggest that the most effective dosage of rhBMP-2 for induction of bone formation varies according to age.

Mixed metastatic lung cancer lesions in bone are inhibited by noggin overexpression and Rank:Fc administration

Lung cancer metastases to bone produce a primarily mixed osteolytic/osteoblastic lesion. The purpose of this study was to determine if blockade of both pathways would inhibit the formation these lesions in bone. Inhibition of the osteoblastic lesion with noggin and the osteolytic lesion with RANK:Fc was a successful treatment strategy to inhibit progression of mixed lung cancer lesions in bone.

INTRODUCTION

Approximately 9-30% of patients with lung cancer develop bone metastases, leading to significant morbidity and mortality. A549 is a non-small-cell lung cancer (NSCLC) line that produces a mixed metastatic lesion in bone. We sought to determine if blockade of key components in both osteolytic and osteoblastic pathways would result in a reduction of a NSCLC tumor progression in a murine model of bony metastasis.

MATERIALS AND METHODS

The study used a retroviral vector overexpressing noggin (RN), a specific inhibitor of BMP, and RANK:Fc, a chimeric protein that inhibits the RANK-RANKL interaction. A549 cells were transduced with RN before implantation in SCID mice. Cells were implanted in a subcutaneous model and tibial injection model. RANK:Fc was administered twice weekly at 15 mg/kg. There were five treatment groups: A549; A549 + RN; A549 + RANK:Fc; A549 + empty vector; and A549 + RN + RANK:Fc (n = 10/group).

RESULTS

In SCID mice who underwent subcutaneous A549 tumor cell injection, animals treated with A549 + RN had significantly smaller subcutaneous tumor size at 8 weeks. In an intratibial model of bony metastasis, animals injected with A549 cells developed a mixed lytic/blastic lesion with cortical destruction at 8 weeks. Treatment with RANK:Fc inhibited the formation of osteoclasts, led to a smaller tumor volume in bone, and inhibited the lytic component of the mixed lesion. Animals treated with A549 + RN had a decreased number of osteoblasts in bone lesions, smaller tumor volume, and inhibition of the blastic component of the mixed lesions. Combination treatment inhibited both the lytic and blastic components of the lesion.

CONCLUSIONS

The NSCLC cell line A549 forms a mixed osteolytic/osteoblastic lesion in vivo. Noggin overexpression inhibited the formation of the osteoblastic aspect of the lesion in bone and the tumor growth in vivo. Treatment with RANK:Fc limited the formation of the lytic aspect of the mixed lesion and also inhibited the rate of in vivo tumor growth. Inhibition of both pathways is necessary to effectively inhibit the progression of mixed metastatic lesions in bone.

rhBMP-2 delivered in a calcium phosphate cement accelerates bridging of critical-sized defects in rabbit radii

BACKGROUND

Treatment of segmental bone loss remains a challenge in skeletal repairs. This study was performed to evaluate the efficacy of the use of recombinant bone morphogenetic protein-2 (rhBMP-2) delivered in an injectable calcium phosphate cement (alpha bone substitute material [alpha-BSM]) to bridge critical-sized defects in the rabbit radius.

METHODS

Unilateral 20-mm mid-diaphyseal defects were created in the radii of thirty-six skeletally mature New Zealand White rabbits. The defects in twelve rabbits each were filled with 0.166 mg/mL rhBMP-2/alpha-BSM cement, 0.033 mg/mL rhBMP-2/alpha-BSM cement, or buffer/alpha-BSM cement. Six rabbits from each group were killed at four weeks, and six were killed at eight weeks. Serial radiographs were made to monitor defect-bridging and residual alpha-BSM carrier. A semiquantitative histological scoring system was used to evaluate defect-bridging. Histomorphometry was used to quantify residual alpha-BSM; trabecular bone area; trabecular bone volume fraction; and cortical length, width, and area.

RESULTS

At four weeks, there had been more rapid resorption of alpha-BSM and filling of the defects with trabecular bone in the group treated with 0.166 mg/mL rhBMP-2/alpha-BSM than in the other two groups. Histomorphometry confirmed an increased trabecular area and volume fraction in this group compared with the other two groups. In both rhBMP-2/alpha-BSM-treated groups, the majority of the trabecular bone was formed by a direct process adjacent to the resorbing alpha-BSM. At eight weeks, complete cortical bridging and regeneration of the marrow space were present in all of the defects treated with 0.166 mg/mL rhBMP-2/alpha-BSM. That group also had reduced residual alpha-BSM and trabecular area and volume, compared with the other two groups, at eight weeks as a result of a rapid remodeling process.

CONCLUSIONS

Treatment of a critical-sized defect in a rabbit radius with 0.166 mg/mL rhBMP-2/alpha-BSM injectable cement can result in bridging with cortical bone and a regenerated bone-marrow space by eight weeks. Site-specific remodeling appears to be responsible for corticalization and marrow regeneration.

CLINICAL RELEVANCE

RhBMP-2 delivered in a calcium phosphate cement may be useful to achieve bridging of critical-sized defects in patients. Its injectable properties may allow minimally invasive use. Delayed percutaneous administration would also be possible when augmentation is desired following an initial surgical procedure or when soft-tissue injuries preclude adequate initial treatment.

Concerted action of Smad and CREB-binding protein regulates bone morphogenetic protein-2-stimulated osteoblastic colony-stimulating factor-1 expression

Bone remodeling depends upon proper osteoblast and osteoclast function. Bone morphogenetic protein-2 (BMP-2) stimulates differentiation of osteoblasts from pluripotent precursors. Osteoclast formation depends on the concerted action of osteoblast-derived receptor activator of NF-kappaB ligand and colony-stimulating factor-1 (CSF-1). BMP-2 stimulates receptor activator of NF-kappaB ligand expression. However, the effect of BMP-2 on CSF-1 expression has not been studied. We investigated the role of BMP-2 in CSF-1 expression in osteogenic C2C12 cells. Incubation of C2C12 cells with BMP-2 supported osteoclastogenesis of spleen cells with a concomitant increase in expression of CSF-1 mRNA and protein. To determine the mechanism, we identified a BMP-responsive element between -627 bp and -509 bp in the CSF-1 promoter. DNase I footprint analysis revealed the presence of consensus Smad binding motif in this region. Electrophoretic mobility shift assay showed BMP-2-stimulated binding of proteins to this motif. Mutation of core sequence as well as its 5'- and 3'-flanking sequences abolished the DNA-protein interaction resulting in inhibition of CSF-1 transcription. Supershift analysis detects the presence of Smads 1, 5, and 4 and the transcriptional coactivator CREB-binding protein in the BMP-responsive element-protein complex. In addition, Smads 1 and 5 alone or in combination with Smad 4 increased CSF-1 transcription. Furthermore, CREB-binding protein markedly increased transcription of CSF-1. These data represent the first evidence that BMP-2 increases the osteoclastogenic CSF-1 expression by a transcriptional mechanism using the canonical Smad pathway and provide a mechanism for BMP-2-induced osteoclast differentiation.

Intact surface of bioactive glass S53P4 is resistant to osteoclastic activity

Bioactive glass reacts with body fluids and is gradually dissolved in tissues and in cell cultures. We investigated whether osteoclasts contribute to this process, by culturing newborn rat bone-marrow cells containing osteoclasts on polished bioactive glass plates (glass S53P4). The cultures were inspected at days 1-5 and stained for alkaline phosphatase (ALP) to demonstrate osteoblasts and for tartrate resistant acid phosphatase (TRAP) to visualize osteoclasts. Nonosteoclastic cells proliferated several-fold both on bioactive glass and on plastic, whereas osteoclasts and their precursors matured into multicellular giant cells and degenerated. Most cells on bioactive glass became ALP-positive, whereas on plastic the majority of cells remained ALP-negative. Osteoclasts survived on bioactive glass for 4-5 days, whereas on plastic they degenerated and disappeared after 3 days. Condensed nuclei indicating apoptosis were detected both in degenerating osteoclasts and osteoblasts. The surface of the bioactive glass reacted rapidly forming rounded pits, erosions, and cracks within 24 h in areas occupied by osteoblasts. Light microscopy and scanning electron micrographs demonstrated, however, a smooth surface below the cytoplasm of osteoclasts. This indicates that when applied on an intact bioactive glass surface, osteoclasts were unable to dissolve the glass material within this culture period.

The analgesic effect of low dose focal irradiation in a mouse model of bone cancer is associated with spinal changes in neuro-mediators of nociception

Despite the widespread use of radiotherapy to treat painful bone metastases, the mechanism underlying the analgesic effect of low dose ionizing radiation is unknown. Bone cancer pain is mostly associated with an inflammatory response dominated by local activation of osteoclasts and by astrogliosis in the spinal cord. We determined the effects of a 6 Gy irradiation given focally on osteolytic sarcoma cells inoculated in humeri of mice. Pain behavior was assessed using the rota-rod and the grip force test. Seven days post-irradiation (day 17 post-tumor implantation) the performance of mice markedly improved on the rotarod (non-irradiated, 67+/-16s vs irradiated, 223 +/- 22 s; P = 0.0005), and the grip force test (non-irradiated, 34 +/- 4 g vs irradiated, 55 +/- 2 g; P = 0.001). This improvement was similar to the analgesia achieved with 30 mg/kg of the cyclooxygenase (COX) inhibitor ketorolac (Rota-rod, 67 +/- 16 s vs 178 +/- 35 s; P = 0.01: grip force test, 34 +/- 4 g, vs 60 +/- 5 g; P = 0.003). Following irradiation, the tumor mass and the number of osteoclasts did not decrease while the expression of two pro-inflammatory cytokines (monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-alpha) increased. Tumor irradiation led to clear differences in the spinal cord. These include a decrease in glial activity (astrocytes and microglial cells) as well as pain mediators such as dynorphin, COX-2 and chemotactic cytokine receptor (CCR2). We conclude that the analgesic effect of low dose irradiation of bone cancer is associated with the alteration of nociceptive transmission in the central nervous system.