Recombinant human bone morphogenetic protein-2 potentiates the in vivo osteogenic ability of marrow/hydroxyapatite composites

Moderate-Affinity Affibodies Modulate the Delivery and Bioactivity of Bone Morphogenetic Protein-2

Uncontrolled bone morphogenetic protein-2 (BMP-2) release can lead to off-target bone growth and other adverse events. To tackle this challenge, yeast surface display is used to identify unique BMP-2-specific protein binders known as affibodies that bind to BMP-2 with different affinities. Biolayer interferometry reveals an equilibrium dissociation constant of 10.7 nm for the interaction between BMP-2 and high-affinity affibody and 34.8 nm for the interaction between BMP-2 and the low-affinity affibody. The low-affinity affibody-BMP-2 interaction also exhibits an off-rate constant that is an order of magnitude higher. Computational modeling of affibody-BMP-2 binding predicts that the high- and low-affinity affibodies bind to two distinct sites on BMP-2 that function as different cell-receptor binding sites. BMP-2 binding to affibodies reduces expression of the osteogenic marker alkaline phosphatase (ALP) in C2C12 myoblasts. Affibody-conjugated polyethylene glycol-maleimide hydrogels increase uptake of BMP-2 compared to affibody-free hydrogels, and high-affinity hydrogels exhibit lower BMP-2 release into serum compared to low-affinity hydrogels and affibody-free hydrogels over four weeks. Loading BMP-2 into affibody-conjugated hydrogels prolongs ALP activity of C2C12 myoblasts compared to soluble BMP-2. This work demonstrates that affibodies with different affinities can modulate BMP-2 delivery and activity, creating a promising approach for controlling BMP-2 delivery in clinical applications.

Hydroxyapatite microbeads containing BMP-2 and quercetin fabricated via electrostatic spraying to encourage bone regeneration

BACKGROUND

Hydroxyapatite (HAp) possesses osteoconductive properties, and its granular form can serve as an effective drug delivery vehicle for bone regeneration. Quercetin (Qct), a plant-derived bioflavonoid, is known to promote bone regeneration; however, its comparative and synergistic effects with the commonly used bone morphogenetic protein-2 (BMP-2) have not been investigated.

METHODS

We examined the characteristics of newly formed HAp microbeads using an electrostatic spraying method and analyzed the in vitro release pattern and osteogenic potential of ceramic granules containing Qct, BMP-2, and both. In addition, HAp microbeads were transplanted into a rat critical-sized calvarial defect and the osteogenic capacity was assessed in vivo.

RESULTS

The manufactured beads had a microscale size of less than 200 μm, a narrow size distribution, and a rough surface. The alkaline phosphatase (ALP) activity of osteoblast-like cells cultured with the BMP-2-and-Qct-loaded HAp was significantly higher than that of either Qct- or BMP-2-loaded HAp groups. The mRNA levels of osteogenic marker genes such as ALP and runt-related transcription factor 2 were found to be upregulated in the HAp/BMP-2/Qct group compared to the other groups. In micro-computed tomographic analysis, the amount of newly formed bone and bone surface area within the defect was significantly higher in the HAp/BMP-2/Qct group, followed by the HAp/BMP-2 and HAp/Qct groups, which is consistent with the histomorphometrical results.

CONCLUSIONS

These results imply that electrostatic spraying can be an efficient strategy to produce homogenous ceramic granules and that the BMP-2-and-Qct-loaded HAp microbeads can serve as effective implants for bone defect healing.

Nanospacial effect of citric acid-coordinated hydroxyapatite nanoparticle films on protein adsorption and cell adhesion states

Hydroxyapatite (HA) and citric acid (Cit)-coordinated HA (Cit/HA) nanoparticle films with different nanospaces were used to examine the nanospacial effect on the protein adsorption behavior and initial osteoblast-like cell adhesion ability through the premise of the stability and ionic dissociation characteristics of the films in biological solution. In particular, the Cit/HA nanoparticle film with a nanospace of 4.2 nm could realize massive and stereoscopic adsorption of proteins due to its larger specific surface area and smaller nanospace as compared with the case of the HA nanoparticle film. It was also found that the α-helix and (β-sheet + β-turn) component ratios of the adsorbed fetal bovine serum proteins on the Cit/HA nanoparticle films increased as compared with the case of the HA nanoparticle film through the secondary structure analysis of the adsorbed proteins, which contributed to the good initial cell culture properties on the film surfaces. Therefore, we successfully realized the control of protein adsorption states using different nanospacial HA and Cit/HA nanoparticle films to achieve excellent initial cell culture properties, which would provide new insights into the creation of novel cell culture substrate surfaces in the regenerative medicine fields.

Clinical and radiographic outcomes of dental implant after maxillary sinus floor augmentation with rhBMP-2/hydroxyapatite compared to deproteinized bovine bone

Objectives

This study aimed to evaluate the clinical and radiographic outcomes of early implant placement and functional loading in maxillary sinus floor augmentation (MSFA) using recombinant human bone morphogenetic protein 2/hydroxyapatite (rhBMP-2/HA) and to compare these outcomes with those of the conventional protocol in MSFA using deproteinized bovine bone (DBB).

Materials and methods

The rhBMP-2/HA and DBB groups consisted of 14 and 13 patients who underwent MSFA with BMP and DBB, respectively. After placement of 22 implants and 21 implants in the rhBMP-2/HA and DBB groups, respectively, abutment connections were performed 3 months after implant placement for the rhBMP-2/HA group and 6 months after implant placement for the DBB group. Changes in grafted sinus height (GSH), marginal bone loss (MBL), and implant stability were evaluated up to one year after functional loading.

Results

Survival rates for the rhBMP-2/HA and DBB groups after one year of functional loading were 90.9% and 90.5%, respectively. Both groups exhibited no significant time-course changes in GSH until one year of functional loading (rhBMP-2/HA, p = 0.124; DBB, p = 0.075). Although significant MBL occurred after one year of functional loading for both groups (rhBMP-2/HA, p < 0.001; DBB, p < 0.001), there were no significant differences in time-course changes in MBL between the two groups (p = 0.450). The mean implant stability quotient values in the rhBMP-2/HA and DBB groups were 75.3 and 75.4 after one year of functional loading, respectively, and there were no significant differences between the two groups (p = 0.557).

Conclusions

MSFA using rhBMP-2/HA allowed implant rehabilitation with early implant placement and functional loading and led to a comparable survival rate and implant stability after 1 year of functional loading with acceptable MBL and stable maintenance of GSH compared to the MSFA using DBB with 6 months of healing after implant placement.

Effect of Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2) with Hydroxyapatite Carrier in Induced Membrane Technique: A Retrospective Propensity Score-Matched Study

OBJECTIVES

To determine the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) with hydroxyapatite (HA) carrier augmentation in managing critical-sized bone defect (CSBD) with induced membrane technique (IMT).

DESIGN

Retrospective comparative study.

SETTING

Academic level I trauma center.

PATIENTS/PARTICIPANTS

The study included 14 patients who underwent rhBMP-2 with HA carrier (rhBMP-2/HA) augmentation in IMT for managing CSBD (BMP group). Moreover, 14 patients who underwent IMT without rhBMP-2 augmentation were matched by propensity score analysis (non-BMP group).

INTERVENTION

IMT with or without rhBMP-2/HA augmentation.

MAIN OUTCOME MEASUREMENT

Changes in quality and quantity measurements of grafted bone to regenerated bone using serial computed tomography.

RESULTS

In the BMP and non-BMP groups, the changes in densities from grafted bone to regenerated bone were +379.63 Hounsfield unit and +248.55 Hounsfield unit (P = 0.034), changes in dense bone percentage were +37.52% and +23.31% (P = 0.027), corticalization rates under the plate were 79.70% and 39.30% (P = 0.007), changes in volume were -20.77% and -23.35% (P = 0.812), union rates were 85.71% and 78.57% (P = 0.622), numbers of patients requiring additional procedures were 4 and 3 (P = 0.663), and time to union were 316.3 and 585.45 days (P = 0.040), respectively.

CONCLUSIONS

RhBMP-2/HA augmentation increases the density of regenerated bone, enhances corticalization under the plate, and shortens the time to union while managing CSBD with IMT.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

A novel BMP-2-loaded hydroxyapatite/beta-tricalcium phosphate microsphere/hydrogel composite for bone regeneration

Although bone morphogenetic protein (BMP) has potent osteoinductivity, the potential adverse events attributed to its burst release prevent its widespread clinical application. Therefore, there is a strong need for BMP delivery systems that maximize osteoinductivity while preventing adverse effects. We evaluated the bone-regenerating potential of NOVOSIS putty (NP), a novel composite combining hydroxyapatite, beta-tricalcium phosphate microsphere/poloxamer 407-based hydrogel, and recombinant human (rh) BMP-2. In vitro assessment of release kinetics by enzyme-linked immunosorbent assay demonstrated sustained release of rhBMP-2 from NP and burst release from collagen sponge (CS), and in vivo assessment of release kinetics by longitudinal tracking of fluorescently labeled rhBMP-2 showed a longer biological half-life of rhBMP-2 with NP than with CS. Furthermore, osteogenic gene expression in MC3T3-E1 cells was significantly higher after co-culture with NP than after co-culture with CS, suggesting that the sustained release of rhBMP-2 from NP effectively contributed to the differentiation of osteoblasts. In a rat spinal fusion model, the volume and quality of newly formed bone was higher in the NP group than in the CS group. Use of NP results in efficient bone regeneration through sustained release of rhBMP-2 and improves the quality of BMP-induced bone.

Programmed BMP-2 release from biphasic calcium phosphates for optimal bone regeneration

This study aimed to fabricate a multi-layered biphasic calcium phosphate (BCP) platform for programmed bone morphogenetic protein-2 (BMP-2) release, which means to block the initial burst release and promote releasing during the differentiation phase of osteogenic cells. And it is to confirm in vivo whether this platform has osteogenic inductivity even when extremely low doses of BMP-2 are loaded compared to the conventional soaking method. Our strategy consisted of preparing a multilayer coating on BCP to minimize the contact between BMP-2 and BCP and allow the loading of BMP-2. The multilayer, which is surface-modified on BCP, is composed of an organosilicate and a natural polymer-based layer-by-layer (LbL) film. We applied (3-Aminopropyl)triethoxysilane (APTES) as an organosilicate was used for amine-functionalized BCP and (collagen/heparin)₅ film was used to delay and sustain BMP-2 release. The coated multilayer not only reduced the initial burst release by more than 50% but also loaded more BMP-2. For in vivo experiment, histomorphometric analysis, it was observed that the BCP platform loaded with extremely low concentration BMP-2 (0.01 mg/ml) induced a significantly larger amount of new bones at 8 weeks compared to the conventional soaking method in the rabbit calvarium onlay graft model.

Scaffold-based osteogenic dual delivery system with melatonin and BMP-2 releasing PLGA microparticles

The growing safety problems about the use of bone morphogenetic protein 2 (BMP-2) is one of the recent issues that was improved by using low doses of BMP-2 with the support of other osteoinductive agents and/or using appropriate carriers. The aim of the present study is to investigate the effect of scaffold-based dual release system including melatonin (MEL) and BMP-2 loaded polylactic-co-glycolic acid (PLGA) microparticles on the osteogenic activity of pre-osteoblastic MC3T3-E1 cells. MEL and BMP-2 loaded microparticles were prepared by double emulsion solvent evaporation method in the average diameters of ~2 µm and ~11 µm, respectively and loaded into chitosan/hydroxyapatite (HAp) scaffolds. In vitro MC3T3-E1 culture studies were carried out comparatively with blank scaffolds, single (BMP-2 or MEL) releasing groups and dual (BMP-2 and MEL) releasing group. Microscopic observations and hematoxylin/eosin staining showed enhanced number of cells and dense ECM in dual release group. The expressions of differentiation markers, Runt-related transcription factor 2 (RUNX2) and alkaline phosphatase (ALP) and also mineralization were higher in dual release group than that of the other groups. Our findings showed that BMP-2 at low doses (~20 ng per scaffold) was sufficient in terms of osteogenic activity with controlled release systems where it was used in combination with MEL (~10 µg per scaffold).

Effect of bone morphogenetic protein-2/hydroxyapatite on ankle fusion with bone defect in a rabbit model: a pilot study

Background

Revision ankle-fusion surgery after a failure of total ankle arthroplasty has a problem with bone-defect management by implant removal. For the reconstruction of bone defects, autogenous bone often causes minor and major complications. Recombinant human-bone morphogenetic protein-2 (rhBMP-2) plays essential roles in bone regeneration strategies, and hydroxyapatite (HA) is beneficial as the rhBMP-2 carrier. In this study, we evaluate whether rhBMP-2/HA can replace autogenous bone in a rabbit ankle-fusion model with distal tibia bone defect.

Methods

The bone defect was created in the distal tibia. The ankle fusion was performed by a cannulated screw from lateral malleolus and various treatments on bone defect. Thirty male white New Zealand rabbits were divided into three groups of 10 animals on each group dependent on treatment methods as control group (no treatment into defect), auto-bone group (autogenous bone treatment), and rhBMP-2/HA group (40 μL of 1 μg/mL rhBMP-2/100 μL HA). Bone formation on defect and the union of the ankle joint were evaluated by X-ray, micro-CT, and histological analysis at 8 weeks and 12 weeks, postoperatively.

Results

Radiographic assessment found the control and auto-bone groups still had the bone defect present, but rhBMP-2/HA group showed complete replacement of the defect with newly formed bone at 12 weeks. Micro-CT showed significantly higher new bone formation within the defect in the rhBMP-2/HA group than in the auto-bone and control groups at 8 weeks (p > 0.05 and p < 0.01, respectively) and 12 weeks (p < 0.05, p < 0.001, respectively). Fusion rate (%) analysis of micro-CT showed a higher percentage of union in the rhBMP-2/HA group than in the auto bone and control groups at 8 weeks (p > 0.05, p < 0.001, respectively) and 12 weeks (p < 0.001 and p < 0.001, respectively). The histological showed the highest osteointegration between distal tibia and talus in the rhBMP-2/HA group at 12 weeks.

Conclusions

This study indicated that rhBMP-2/HA showed much better bone fusion than did the autogenous bone graft and was effective in promoting fusion rate and improving the quality of the ankle joint fusion.

An in vivo Comparison Study Between Strontium Nanoparticles and rhBMP2

The osteoinductive property of strontium was repeatedly proven in the last decades. Compelling in vitro data demonstrated that strontium hydroxyapatite nanoparticles exert a dual action, by promoting osteoblasts-driven matrix secretion and inhibiting osteoclasts-driven matrix resorption. Recombinant human bone morphogenetic protein 2 (rhBMP2) is a powerful osteoinductive biologic, used for the treatment of vertebral fractures and critically-sized bone defects. Although effective, the use of rhBMP2 has limitations due its recombinant morphogen nature. In this study, we examined the comparison between two osteoinductive agents: rhBMP2 and the innovative strontium-substituted hydroxyapatite nanoparticles. To test their effectiveness, we independently loaded Gelfoam sponges with the two osteoinductive agents and used the sponges as agent-carriers. Gelfoam are FDA-approved biodegradable medical devices used as delivery system for musculoskeletal defects. Their porous structure and spongy morphology make them attractive in orthopedic field. The abiotic characterization of the loaded sponges, involving ion release pattern and structure investigation, was followed by in vivo implantation onto the periosteum of healthy mice and comparison of the effects induced by each implant was performed. Abiotic analysis demonstrated that strontium was continuously released from the sponges over 28 days with a pattern similar to rhBMP2. Histological observations and gene expression analysis showed stronger endochondral ossification elicited by strontium compared to rhBMP2. Osteoclast activity was more inhibited by strontium than by rhBMP2. These results demonstrated the use of sponges loaded with strontium nanoparticles as potential bone grafts might provide better outcomes for complex fractures. Strontium nanoparticles are a novel and effective non-biologic treatment for bone injuries and can be used as novel powerful therapeutics for bone regeneration.

Regeneration of different types of tissues depends on the interplay of stem cells-laden constructs and microenvironments in vivo

The ability of repair and regeneration of tissues or organs has been significantly improved by using biomaterials-based constructs. Our previous studies found the regeneration of both articular cartilage and subchondral bone by implantation of a poly(lactide-co-glycolide) (PLGA)/fibrin gel/bone marrow stem cells (BMSCs)/(lipofectamine/pDNA-transforming growth factor (TGF)-β1) construct in vivo, without the step of pre-induced differentiation of the laden stem cells in vitro. To substantiate the ability to regenerate multi-types of tissues by the same constructs, in this study the constructs were implanted into three types of tissues or tissue defects in vivo, including subcutaneous fascia layer, and ear cartilage and eyelid tarsal plate defects. The ear cartilage and eyelid tarsal plate defects were fully regenerated 8 w post-implantation, showing a similar morphology to the corresponding native tissues. In the neo ear cartilage, abundant chondrocytes with obvious lacunas and cartilage-specific extracellular matrices (ECMs) were found. Neo eyelid tarsal plate with mature meibomian gland acinar units was regenerated. Furthermore, expressions of the ECMs-specific genes and proteins, as well as the cell behavior modulatory factors, Sry related HMG box 9 (Sox9) and TGF-β1 were significantly up-regulated in the regenerated ear cartilages and eyelid tarsal plate than those in the subcutaneously implanted constructs, which were filled with fibrocytes, inflammatory cells, obvious vascularization and slight ECMs deposition. These results confirm firmly the ability to regenerate multi-types of tissues by a stem cells-laden construct via adapting to the microenvironments of corresponding tissues.

Formulation, Delivery and Stability of Bone Morphogenetic Proteins for Effective Bone Regeneration

Bone morphogenetic proteins (BMPs) are responsible for bone formation during embryogenesis and bone regeneration and remodeling. The osteoinductive action of BMPs, especially BMP-2 and BMP-7, has led to their use in a range of insurmountable treatments where intervention is required for effective bone regeneration. Introduction of BMP products to the market, however, was not without reports of multiple complications and side effects. Aiming for optimization of the therapeutic efficacy and safety, efforts have been focused on improving the delivery of BMPs to lower the administered dose, localize the protein, and prolong its retention time at the site of action. A major challenge with these efforts is that the protein stability should be maintained. With this review we attempt to shed light on how the stability of BMPs can be affected in the formulation and delivery processes. We first provide a short overview of the current standing of the complications experienced with BMP products. We then discuss the different delivery parameters studied in association with BMPs, and their influence on the efficacy and safety of BMP treatments. In particular, the literature addressing the stability of BMPs and their possible interactions with components of the delivery system as well as their sensitivity to conditions of the formulation process is reviewed. In summary, recent developments in the fields of bioengineering and biopharmaceuticals suggest that a good understanding of the relationship between the formulation/delivery conditions and the stability of growth factors such as BMPs is a prerequisite for a safe and effective treatment.

Synergistic effects of overexpression of BMP‑2 and TGF‑β3 on osteogenic differentiation of bone marrow mesenchymal stem cells

Bone morphogenetic protein 2 (BMP-2) and transforming growth factor β (TGF-β) isoforms are important in advancing bone regeneration. The aim of the present study was to investigate the positive and reciprocal effect of TGF-β3, one of the three TGF-β isoforms, on BMP-2 in promoting osteogenic differentiation. Exogenous BMP-2 and TGF-β3 genes were separately, and in combination, overexpressed in rabbit bone marrow-derived mesenchymal stem cells (rBMSCs). Expression levels of BMP-2 and TGF-β3 were evaluated using reverse-transcription-polymerase chain reaction (RT-PCR) and Western blotting assays. Furthermore, the osteogenic differentiation capacities of BMSCs were assessed by measuring Alizarin Red S staining, an alkaline phosphatase activity assay, and quantification of the osteogenic-specific genes, Runt-related transcription factor 2 (Runx2) and Osterix (Osx). Using lentiviral-mediated transfection, robust co-transfection efficiency of >90% was achieved. RT-PCR and immunoblotting results indicated a marked elevated expression of BMP-2 and TGF-β3 in rBMSCs undergoing co-transfection, compared with transfection with BMP-2 or TGF-β3 alone, indicating that BMP-2 and TGF-β3 are synergistically expressed in rBMSCs. Furthermore, enhanced osteogenic differentiation was observed in rBMSCs co-transfected with BMP-2/TGF-β3. The present study successfully delivered BMP-2 together with TGF-β3 into rBMSCs with high efficiency for the first time. Furthermore, TGF-β3 overexpression was demonstrated to enhance the osteogenic efficacy of BMP-2 in rBMSCs, and vice versa. This provides a potential clinical therapeutic approach for regenerating the function of osseous tissue, and may present a promising strategy for bone defect healing.

A Review of the Clinical Side Effects of Bone Morphogenetic Protein-2

Bone morphogenetic protein-2 (BMP-2) is currently the only Food and Drug Administration (FDA)-approved osteoinductive growth factor used as a bone graft substitute. However, with increasing clinical use of BMP-2, a growing and well-documented side effect profile has emerged. This includes postoperative inflammation and associated adverse effects, ectopic bone formation, osteoclast-mediated bone resorption, and inappropriate adipogenesis. Several large-scale studies have confirmed the relative frequency of adverse events associated with the clinical use of BMP-2, including life-threatening cervical spine swelling. In fact, the FDA has issued a warning of the potential life-threatening complications of BMP-2. This review summarizes the known adverse effects of BMP-2, including controversial areas such as tumorigenesis. Next, select animal models that replicate BMP-2's adverse clinical effects are discussed. Finally, potential molecules to mitigate the adverse effects of BMP-2 are reviewed. In summary, BMP-2 is a potent osteoinductive cytokine that has indeed revolutionized the bone graft substitute market; however, it simultaneously has accrued a worrisome side effect profile. Better understanding of these adverse effects among both translational scientists and clinicians will help determine the most appropriate and safe use of BMP-2 in the clinical setting.

Mesenchymal stem cells expressing baculovirus-engineered BMP-2 and VEGF enhance posterolateral spine fusion in a rabbit model

BACKGROUND CONTEXT

Mesenchymal stem cell (MSC)-based cell therapy and gene transfer have converged and show great potential for accelerating bone healing. Gene therapy can provide more sustained expression of osteogenic factors such as bone morphogenetic protein-2 (BMP-2). We previously demonstrated that low-dose BMP-2 enhanced spinal posterolateral fusion by MSCs in a rabbit model. Herein, we genetically modified rabbit MSCs with a recombinant baculovirus encoding BMP-2 (Bac-CB) and vascular endothelial growth factor (Bac-VEGF) seeded into porous scaffolds to enhance spinal fusion.

PURPOSE

This study evaluates the success rate of the MSC-based cell therapy and gene transfer approach for single-level posterolateral spine fusion. We hypothesize that combining three-dimensional tricalcium phosphate (TCP) scaffolds and genetically modified allogeneic MSCs with baculovirus-mediated growth factor expression would increase the success rate of spinal fusion.

STUDY DESIGN

The study design was based on an animal model (approved by the Institutional Animal Care and Use Committee) using 18 adult male New Zealand rabbits.

METHODS

This study included 18 male New Zealand rabbits, weighing 3.5 to 4 kg. Allogeneic bone marrow-derived MSCs were isolated and genetically modified with Bac-CB and Bac-CV seeded onto TCP scaffolds (MSC/Bac/TCP). The animals were divided into three groups according to the material implanted into the bilateral L4-L5 intertransverse space: TCP scaffold (n=6), MSC/TCP (n=6), and MSC/Bac/TCP (n=6). After 12 weeks, the rabbits were euthanized for radiographic examination, manual palpation, and histologic study.

RESULTS

Bilateral fusion areas in each animal were evaluated independently. The radiographic fusion rates at 12 sites were 0 of 12 in the TCP scaffold group, 4 of 12 in the MSC/TCP group, and 10 of 12 in the MSC/Bac/TCP group. By manual palpation, there were zero solid fusions in the TCP scaffold group, two solid fusions in the MSC/TCP group, and five solid fusions in the MSC/Bac/TCP group. Fusion rates were significantly greater in the MSC/Bac/TCP group.

CONCLUSIONS

The results indicate the potential of using baculovirus as a vector for gene/cell therapy approaches to improve bone healing and support the feasibility of using allogeneic MSCs for inducing bone formation and intertransverse process fusion.

Bone Regeneration Using Bone Morphogenetic Proteins and Various Biomaterial Carriers

Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily of proteins and are very promising and intensively studied for in the enhancement of bone healing. More than 20 types of BMPs have been identified but only a subset of BMPs can induce de novo bone formation. Many research groups have shown that BMPs can induce differentiation of mesenchymal stem cells and stem cells into osteogenic cells which are capable of producing bone. This review introduces BMPs and discusses current advances in preclinical and clinical application of utilizing various biomaterial carriers for local delivery of BMPs to enhance bone regeneration.

Lumbar interbody fusion with porous biphasic calcium phosphate enhanced by recombinant bone morphogenetic protein-2/silk fibroin sustained-released microsphere: an experimental study on sheep model

Biphasic calcium phosphate (BCP) has been investigated extensively as a bone substitute nowadays. However, the bone formation capacity of BCP is limited owing to lack of osteoinduction. Silk fibroin (SF) has a structure similar to type I collagen, and could be developed to a microsphere for the sustained-release of rhBMP-2. In our previous report, bioactivity of BCP could be enhanced by rhBMP-2/SF microsphere (containing 0.5 µg rhBMP-2) in vitro. However, the bone regeneration performance of the composite in vivo was not investigated. Thus, the purpose of this study was to evaluate the efficacy of BCP/rhBMP-2/SF in a sheep lumbar fusion model. A BCP and rhBMP-2/SF microsphere was developed, and then was integrated into a BCP/rhBMP-2/SF composite. BCP, BCP/rhBMP-2 and BCP/rhBMP-2/SF were implanted randomly into the disc spaces of 30 sheep at the levels of L1/2, L3/4 and L5/6. After sacrificed, the fusion segments were evaluated by manual palpation, CT scan, biomechanical testing and histology at 3 and 6 months, respectively. The composite demonstrated a burst-release of rhBMP-2 (39.1 ± 2.8 %) on the initial 4 days and a sustained-release (accumulative 81.3 ± 4.9 %) for more than 28 days. The fusion rates, semi-quantitative CT scores, fusion stiffness in bending in all directions and histologic scores of BCP/rhBMP-2/SF were significantly greater than BCP and BCP/rhBMP-2 at each time point, respectively (P < 0.05). These findings indicate that the SF microspheres containing a very low dose of rhBMP-2 improve fusion in sheep using BCP constructs.

A review paper on biomimetic calcium phosphate coatings

Biomimetic calcium phosphate coatings have been developed for bone regeneration and repair because of their biocompatibility, osteoconductivity, and easy preparation. They can be rendered osteoinductive by incorporating an osteogenic agent, such as bone morphogenetic protein 2 (BMP-2), into the crystalline lattice work in physiological situations. The biomimetic calcium phosphate coating enables a controlled, slow and local release of BMP-2 when it undergoes cell mediated coating degradation induced by multinuclear cells, such as osteoclasts and foreign body giant cells, which mimics a physiologically similar release mode, to achieve sustained ectopic or orthotopic bone formation. Therefore, biomimetic calcium phosphate coatings are considered to be a promising delivery vehicle for osteogenic agents. In this review, we present an overview of biomimetic calcium phosphate coatings including their preparation techniques, physico-chemical properties, potential as drug carrier, and their pre-clinical application both in ectopic and orthotopic animal models. We briefly review some features of hydroxyapatite coatings and their clinical applications to gain insight into the clinical applications of biomimetic calcium phosphate coatings in the near future.

Bone regenerative efficacy of biphasic calcium phosphate collagen composite as a carrier of rhBMP-2

OBJECTIVES

This study compared the bone regenerative effects of a recombinant human bone morphogenetic protein 2 (rhBMP-2)-loaded collagen-based biphasic calcium phosphate composite (BCPC) and rhBMP-2-loaded biphasic calcium phosphate (BCP).

MATERIAL AND METHODS

The in vitro release profiles of rhBMP-2-loaded BCP and BCPC were measured. The animal surgery was performed on ten rabbits. Four 8-mm-diameter circular calvarial defects were made and filled with BCP, BCPC, rhBMP-2-loaded BCP (BMP + BCP) and rhBMP-2-loaded BCPC (BMP + BCPC). The animals were euthanized either 2 or 8 weeks after surgery.

RESULTS

The initial burst release of rhBMP-2 was greater for BCP than for BCPC, and both presented a slow release pattern thereafter. In rabbit calvarial defects, the space maintaining capability and graft resorption of all experimental groups did not show statistical differences at 2 and 8 weeks. New bone formation in the rhBMP-2-loaded groups was greater than in the non-loaded groups at both weeks, but the amount of new bone was comparable between both rhBMP-2-loaded groups at both weeks. There was a distinct histologic difference between the BMP + BCP and BMP + BCPC groups at 2 weeks; the new bone formation occurred more in the intergranular spaces and the BCP-to-bone contact was greater in the BMP + BCPC group, but these differences were no longer discernible at 8 weeks.

CONCLUSIONS

BCP- and BCPC-loaded rhBMP-2 significantly improved bone regeneration and BCPC led to a dense network of new bone and bone particles during the early healing period. BCPC can therefore be considered as a promising candidate for carrying rhBMP-2.

Bone regeneration at dental implant sites with suspended stem cells

During the maintenance of bone marrow-derived mesenchymal stem cells (BMMSCs), suspended cells are discarded normally. We noted the osteogenic potential of these cells to be like that of anchorage-dependent BMMSCs. Therefore, we characterized suspended BMMSCs from rabbit bone marrow by bioengineering and applied the suspended BMMSCs to double-canaled dental implants inserted into rabbits. After primary isolation of BMMSCs, we collected the suspended cells during primary culture on the third day. The cells were transferred and maintained on an extracellular-matrix-coated culture plate. The cells were characterized and compared with BMMSCs by colony-forming-unit fibroblast (CFU-f) and cell proliferation assay, fluorescence-activated cell sorter (FACS), in vitro multipotency, and reverse transcription polymerase chain reaction (RT-PCR). We also analyzed the osteogenic potential of cells mixed with hydroxyapatite/tricalcium phosphate (HA/TCP) and transplanted into immunocompromised mice. We compared the viability and proliferation of the suspended BMMSCs and BMMSCs on the titanium implant surface and observed cell morphology. Then, the cells mixed with HA/TCP were applied to the double-canaled implants during installation into rabbit tibia. Four weeks later, we analyzed bone formation inside the canal by histomorphometry. The suspended cells showed higher CFU-f on the extracellular matrix (ECM)-coated culture plate and similar results of proliferation capacity compared with BMMSCs. The cells also showed osteogenic, adipogenic, and chondrogenic ability. The suspended cells showed levels of attachment survival and proliferation on the surfaces of titanium implant discs to be higher than or similar to those of BMMSCs. The suspended cells as well as BMMSCs showed stronger bone formation ability in both upper and lower canals of the implants compared with controls on double-canaled implants inserted into rabbit tibia. In this study, we showed that suspended cells after primary BMMSC isolation have bone regeneration capacity like that of BMMSCs, not only in vitro but also in vivo. ECM was valuable for propagation of MSCs for cell-based bone regeneration. Therefore, the suspended cells could also be useful tools for bone regeneration after implant surgery.

Osteogenic potential of human bone marrow-derived mesenchymal stromal cells cultured in autologous serum: a preliminary study

PURPOSE

As part of the authors' research on potential osteogenesis by filling bone defects with human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) in patients with cleft lip and palate, they examined the cytoproliferative potential and cytobiological activity of hBM-MSCs in vitro and their osteogenic potential in vivo without performing osteoinduction.

MATERIALS AND METHODS

The hBM-MSCs were collected from iliac cancellous bone and then used in primary culture, followed by 2 subcultures using an autologous serum (AS)-containing medium and a fetal bovine serum (FBS)-containing medium. Cytoproliferative potential and cytobiological activity as expressed by bone markers (alkaline phosphatase and osteocalcin) in hBM-MSCs cultured in the AS-containing medium (AS-cultured hBM-MSCs) and the FBS-containing medium (FBS-cultured hBM-MSCs) were examined in vitro, and the osteogenic potential of AS- and FBS-cultured hBM-MSCs was examined in mice.

RESULTS

On day 6 of the second subculture, the number of hBM-MSCs per milliliter of specimen from 8 pediatric patients was significantly larger (P < .05) in FBS-cultured compared with AS-cultured hBM-MSCs. The alkaline phosphatase activity of hBM-MSCs was significantly greater (P < .05) when cultured in the AS-containing medium compared with the FBS-containing medium. The in vivo study showed the formation of an osteoid-like matrix rather than definite bone tissue.

CONCLUSIONS

1) FBS is appropriate for the cytoproliferation of hBM-MSCs; 2) the AS-containing medium is likely to have a good possibility of inducing the differentiation of hBM-MSCs; and 3) AS-cultured hBM-MSCs contain a group of cells that spontaneously differentiate into an osteoid-like matrix without performing osteoinduction.

Studies of bone morphogenetic protein-based surgical repair

Over the past several decades, recombinant human bone morphogenetic proteins (rhBMPs) have been the most extensively studied and widely used osteoinductive agents for clinical bone repair. Since rhBMP-2 and rhBMP-7 were cleared by the U.S. Food and Drug Administration for certain clinical uses, millions of patients worldwide have been treated with rhBMPs for various musculoskeletal disorders. Current clinical applications include treatment of long bone fracture non-unions, spinal surgeries, and oral maxillofacial surgeries. Considering the growing number of recent publications related to clincal research of rhBMPs, there exists enormous promise for these proteins to be used in bone regenerative medicine. The authors take this opportunity to review the rhBMP literature paying specific attention to the current applications of rhBMPs in bone repair and spine surgery. The prospective future of rhBMPs delivered in combination with tissue engineered scaffolds is also reviewed.

Induction of bone formation in biphasic calcium phosphate scaffolds by bone morphogenetic protein-2 and primary osteoblasts

Bone tissue engineering strategies mainly depend on porous scaffold materials. In this study, novel biphasic calcium phosphate (BCP) matrices were generated by 3D-printing. High porosity was achieved by starch consolidation. This study aimed to characterise the porous BCP-scaffold properties and interactions of osteogenic cells and growth factors under in vivo conditions. Five differently treated constructs were implanted subcutaneously in syngeneic rats: plain BCP constructs (group A), constructs pre-treated with BMP-2 (group B; 1.6 µg BMP-2 per scaffold), seeded with primary osteoblasts (OB) (group C), seeded with OB and BMP-2 (group D) and constructs seeded with OB and pre-cultivated in a flow bioreactor for 6 weeks (group E). After 2, 4 and 6 weeks, specimens were explanted and subjected to histological and molecular biological analyses. Explanted scaffolds were invaded by fibrovascular tissue without significant foreign body reactions. Morphometric analysis demonstrated significantly increased bone formation in samples from group D (OB + BMP-2) compared to all other groups. Samples from groups B-E displayed significant mRNA expression of bone-specific genes after 6 weeks. Pre-cultivation in the flow bioreactor (group E) induced bone formation comparable with group B. In this study, differences in bone distribution between samples with BMP-2 or osteoblasts could be observed. In conclusion, combination of osteoblasts and BMP-2 synergistically enhanced bone formation in novel ceramic scaffolds. These results provide the basis for further experiments in orthotopic defect models with a focus on future applications in orthopaedic and reconstructive surgery.

Volumetric bone regenerative efficacy of biphasic calcium phosphate-collagen composite block loaded with rhBMP-2 in vertical bone augmentation model of a rabbit calvarium

Block-type biphasic calcium phosphate (BCP) carriers are more effective at delivering recombinant human bone morphogenetic protein-2 (rhBMP-2) in various clinical situations than are particle-type carriers, due to their potential for highly successful three-dimensional bone regeneration. The aim of this study was to confirm the bone-regenerative capabilities of three-dimensional BCP blocks with a low hydroxyapatite/β-tricalcium phosphate ratio (20/80) combined with collagen (10% wt) as an rhBMP-2 delivery system in a craniofacial vertical bone augmentation model. BCP blocks and BCP-collagen blocks (with average macropore sizes of 296 and 390 μm, respectively) with or without rhBMP-2 were fixed with osteosynthesis screws to the calvarial surface of rabbits. After 8 weeks, histologic and histomorphometric analyses were performed to evaluate the resulting new bone area, augmented area, bone density, and degree of integration. The area of new bone was significantly greater in specimens containing rhBMP-2 than in the control group (p < 0.05). Moreover, the area fractions of newly formed bone within the augmented area and a degree of integration between the regenerative bone and the calvarium were both significantly greater in the BCP-collagen/rhBMP-2 group than in the BCP/rhBMP-2 group (p < 0.05), whereas the two carrier systems exhibited similar rhBMP-2 release profiles, with sustained and linear release. The BCP and BCP/rhBMP-2 blocks exhibited excellent structural integrity, with large fragments of residual ceramic. In conclusion, the BCP-collagen composite block exhibited enhanced osteoinductive potential and could be a good candidate as a carrier of rhBMP-2 due to its characteristics of favorable volumetric stability, ease of handling, and excellent remodeling properties.

Osteogenic differentiation of human mesenchymal stem cells using RGD-modified BMP-2 coated microspheres

Micro-structured scaffolds formed with poly(lactic- co -glycolic acid) (PLGA) microspheres were composed of adhesion molecules and growth factors. PLGA microspheres, constructed with Arg-Gly-Asp (RGD) peptide and bone morphogenic protein 2 (BMP-2) were created as a stem cell delivery vehicle. In this study, a high potential for cell adhesion and differentiation of human mesenchymal stem cells (hMSCs) was achieved by constructing the scaffolds with different compositions of coating materials. Specific gene and protein detection by RT-PCR and western blot analysis of the embedded hMSCs revealed that a combination of RGD peptide and BMP-2 induced differentiation of bone cells. Histology and immunohistochemistry results confirmed that bone cell-differentiated transplanted hMSCs were present in the micro-structured scaffolds. The results of this study demonstrate that the regulation of stem cell differentiation by adhesion molecules and growth factors has the potential to enable formation of therapeutic vehicles for the delivery of stem cells that are easily fabricated, less expensive, and more easily controlled than currently available delivery systems. The micro-structure typed PLGA microspheres used in this study possessed unique properties of ideal scaffolds. The embedded hMSCs easily adhered onto the PLGA microspheres mediated by RGD peptide, proliferated well onto the scaffolds, and differentiated to perform the distinct functions of bone tissues.

Delivery of recombinant bone morphogenetic proteins for bone regeneration and repair. Part B: Delivery systems for BMPs in orthopaedic and craniofacial tissue engineering

Localized and release-controlled delivery systems for the sustained expression of the biologic potency of rhBMPs are essential. A substantial number of biomaterials have been investigated thus far. Most fail after implantation or administration mainly due to either being too soft, difficult to control and/or stabilize mechanically. In the second part of this review, we review a representative selection of rhBMP-2 and rhBMP-7 carrier materials and delivery systems ranging from simple nano/microparticles to complex 3-D scaffolds in sites of orthopaedic and craniofacial bone regeneration and repair.

Enhancement of posterolateral lumbar spine fusion using low-dose rhBMP-2 and cultured marrow stromal cells

We tested the hypothesis that the dose of recombinant human bone morphogenetic protein-2 (rhBMP-2) required to induce spine fusion can be reduced by combination with mesenchymal stem cells (MSCs). Twenty-four adult rabbits underwent posterolateral intertransverse fusion at the L4-L5 level. The animals were divided into four groups based on the implant material: autologous iliac graft, Alginate-MSCs composite, Alginate-BMP-2-MSCs composite, and Alginate-BMP-2 composite. After 16 weeks, the rabbits were euthanized for radiographic examination, manual palpation, biomechanical testing, and histology. Radiographic union of 12 intertransverse fusion areas for the autogenous iliac graft, Alginate-MSCs, Alginate-BMP-2-MSCs, and Alginate-BMP-2 groups was 11, 8, 11, and 0, respectively. Moreover, manual palpation of six fusion segments in each subgroup found solid union to be 6, 1, 5, and 0, respectively. The average torques at failure of the first three groups were 2278 +/- 135, 1943 +/- 140, and 2334 +/- 187 N-mm, respectively. The failure torque did not differ significantly between the autograft and Alginate-BMP-2-MSCs groups; both groups were significantly higher than the Alginate-MSCs group. The results indicate that MSCs delivered with in vitro cellular doses of rhBMP-2 are more osteoinductive than MSCs without rhBMP-2. In combination with MSCs, a low dose (2.5 microg) of rh-BMP-2 could enhance bone formation and posterolateral spine fusion success in the rabbit model.

Wound therapy by marrow mesenchymal cell transplantation

BACKGROUND

Marrow mesenchymal cells are useful in regenerative medicine because they contain stem cells, but there have been few reports of clinical applications. The authors developed a new wound treatment technique by improving marrow mesenchymal cell culture methods and placing cultured cells in an artificial skin material. This new treatment was useful for tissue regeneration in 20 patients with skin wounds.

METHODS

Marrow mesenchymal cells from a 46-year-old man were cultured and placed in artificial dermis made of collagen sponge. This composite graft was implanted subcutaneously into the back of a nude mouse and removed 10 days later; immunohistological analysis confirmed regeneration of subcutaneous tissue using human marrow mesenchymal cells. Next, in 20 patients (nine men and 11 women; average age, 64.8 years; range, 22 to 91 years) with intractable dermatopathies, 10 to 20 ml of bone marrow fluid was aspirated from the ilium and cultured in medium containing either fetal calf or autologous serum. The resulting cultured cells were placed in artificial dermis made of collagen sponge, and this composite graft was used to treat skin wounds.

RESULTS

The wound mostly healed in 18 of the 20 patients; the remaining two patients died of causes unrelated to transplantation. In all patients, autologous marrow mesenchymal cell transplantation was shown to be therapeutically effective.

CONCLUSIONS

In skin regeneration therapy using a marrow mesenchymal cell/artificial dermis composite graft, skin regeneration is possible with bone marrow aspiration, a minimally invasive procedure. Compared with existing skin grafting techniques, the present technique is practical and much less invasive.

Bone transport using hydroxyapatite loaded with bone morphogenetic protein in rabbits

The feasibility of bone transport with bone substitute and the factors which are essential for a successful bone transport are unknown. We studied six groups of 12 Japanese white rabbits. Groups A to D received cylindrical autologous bone segments and groups E and F hydroxyapatite prostheses. The periosteum was preserved in group A so that its segments had a blood supply, cells, proteins and scaffold. Group B had no blood supply. Group C had proteins and scaffold and group D had only scaffold. Group E received hydroxyapatite loaded with recombinant human bone morphogenetic protein-2 and group F had hydroxyapatite alone.

Distraction osteogenesis occurred in groups A to C and E which had osteo-conductive transport segments loaded with osteo-inductive proteins. We conclude that scaffold and proteins are essential for successful bone transport, and that bone substitute can be used to regenerate bone.

Differential alkaline phosphatase responses of rat and human bone marrow derived mesenchymal stem cells to 45S5 bioactive glass

Bioactive glass is used as both a bone filler and as a coating on implants, and has been advocated as a potential osteogenic scaffold for tissue engineering. Rat-derived mesenchymal stem cells (MSCs) show elevated levels of alkaline phosphatase activity when grown on 45S5 bioactive glass as compared to standard tissue culture plastic. Similarly, exposure to the dissolution products of 45S5 elevates alkaline phosphatase activity and other osteogenic markers in these cells. We investigated whether human MSCs grown under the same laboratory conditions as rat MSCs would exhibit similar responses. In general, human MSCs produce markedly less alkaline phosphatase activity than rat MSCs, regardless of cell culture conditions, and do not respond to the growth factor BMP-2 in the same way as rat MSCs. In our experiments there was no difference in alkaline phosphatase activity between human MSCs grown on 45S5 bioactive glass or tissue culture plastic, in samples from five different orthopaedic patients, regardless of culture media composition. Neither was there any consistent effect of 45S5 dissolution products on human MSCs from three different donors. These results suggest that the positive effects of bioactive glass on bone growth in human patients are not mediated by accelerated differentiation of mesenchymal stem cells.

The influence of BMP-2 and its mode of delivery on the osteoconductivity of implant surfaces during the early phase of osseointegration

Osteogenic agents, such as bone morphogenetic protein-2 (BMP-2), can stimulate the degradation as well as the formation of bone. Hence, they could impair the osteoconductivity of functionalized implant surfaces. We assessed the effects of BMP-2 and its mode of delivery on the osteoconductivity of dental implants with either a naked titanium surface or a calcium-phosphate-coated one. The naked titanium surface bore adsorbed BMP-2, whilst the coated one bore incorporated, adsorbed, or incorporated and adsorbed BMP-2. The implants were inserted into the maxillae of adult miniature pigs. The volume of bone deposited within a defined "osteoconductive" (peri-implant) space, and bone coverage of the implant surface delimiting this space, were estimated morphometrically 1-3 weeks later. After 3 weeks, the volume of bone deposited within the osteoconductive space was highest for coated and uncoated implants bearing no BMP-2, followed by coated implants bearing incorporated BMP-2; it was lowest for coated implants bearing only adsorbed BMP-2. Bone-interface coverage was highest for coated implants bearing no BMP-2, followed by coated implants bearing either incorporated, or incorporated and adsorbed BMP-2; it was lowest for uncoated implants bearing adsorbed BMP-2. Hence, the osteoconductivity of implant surfaces can be significantly modulated by BMP-2 and its mode of delivery.

The effects of bone morphogenetic protein and basic fibroblast growth factor on cultured mesenchymal stem cells for spine fusion

STUDY DESIGN

Posterolateral lumbar transverse process fusion was carried out using cultured mesenchymal stem cells with or without bone morphogenetic protein (BMP) and basic fibroblast growth factor (FGF).

OBJECTIVES

To determine the ability of BMP and basic FGF to enhance the efficacy of bone marrow-derived mesenchymal stem cells in lumbar arthrodesis.

SUMMARY OF BACKGROUND DATA

Our previous study hypothesized that it would be important to differentiate into osteogenic cells and to implant a large number of cells for achieving solid spinal fusions.

METHODS

Thirty-six adult rabbits underwent single-level bilateral posterolateral intertransverse process fusions at L4-L5. Animals were divided into 5 groups, each according to the material implanted: (1) autologous bone (autograft; n = 8); (2) mesenchymal stem cells (n = 7); (3) mesenchymal stem cells with recombinant human bone morphogenetic protein (rhBMP)-2 (mesenchymal stem cell-BMP; n = 7); (4) mesenchymal stem cells with basic FGF (mesenchymal stem cell-FGF; n = 7); and (5) mesenchymal stem cells with rhBMP-2 and basic FGF (mesenchymal stem cell-BMP-FGF; n = 7). Fresh bone marrow cells from the iliac crest of each animal were cultured in a standard medium for 2 weeks. For an additional week, the mesenchymal stem cells (1 x 10(6) cells/mL) were cultured in 10(-8) M dexamethasone, type I collagen gel and porous hydroxyapatite particles with or without rhBMP-2 (2 microg/mL) and basic FGF (5 microg/mL). Animals were killed 6 weeks after surgery. Radiograph, manual palpation, and histology were used to evaluate spinal fusions.

RESULTS

Fusion rates were 5/7 in the autograft group, 0/7 in the mesenchymal stem cell group, 2/7 in the mesenchymal stem cell-BMP group, 3/7 in the mesenchymal stem cell-FGF group, and 6/7 in the mesenchymal stem cell-BMP-FGF group. The histology in some of both mesenchymal stem cell-BMP and mesenchymal stem cell-FGF groups demonstrated that fibrous tissues and cartilages remained in grafted areas. In the mesenchymal stem cell-BMP-FGF group, each grafted fragment was connected with new bone ingrowths.

CONCLUSIONS

This study showed that bone marrow-derived mesenchymal stem cells cultured with rhBMP-2 and basic FGF act as a substitute for autograft in lumbar arthrodesis. This technique may yield a more consistent quality of fusion bone as compared to that with autograft.

Synthesis and Characterization of Biocompatible Polymer Interlayers on Titanium Implant Materials

A bifunctional copolymer series of (4-vinylbenzyl)phosphonic acid diethylester and N-acryloxysuccinimide was developed as an interlayer with the aim of immobilizing proteins on titanium surfaces. Copolymers with varying compositions were synthesized, and an alternating copolymerization of the two monomers was found. The copolymers form ultrathin films of about 2-8 nm on titanium surfaces in a simple dipping process, as estimated from the attenuation of the titanium X-ray photoelectron spectroscopy (Ti-XPS) signal. The films were characterized by infrared spectroscopy, XPS, and time-of-flight secondary ion mass spectrometry. The results indicate that the immobilization is due to phosphonate groups, and thus the phosphonate content of the copolymers is decisive for the final film thickness. These polymer films were examined for their potential protein binding capacity by using trifluoroethylamine derivatization and subsequent XPS analysis as a reactivity assay.

Influence of the porosity of hydroxyapatite ceramics on in vitro and in vivo bone formation by cultured rat bone marrow stromal cells

The in vitro and in vivo osteoblastic differentiation of rat bone marrow stromal cells (MSCs) was assessed on hydroxyapatite disks with 3 different porosities: 30%, 50%, and 70% (HA30, HA50, and HA70, respectively). MSCs obtained by 10-day culture of fresh bone marrow cells were subcultured for 2 weeks on 3 kinds of porous HA disks in the presence and absence of dexamethasone (Dex). After 2 weeks of subculture, alkaline phosphatase (ALP) activity and osteocalcin production of MSCs/HA composites with Dex were higher than those without, and increased with increasing porosity. The resultant bone tissue grafts "cultured-bone/HA constructs" were implanted subcutaneously into the backs of syngeneic rats, and harvested 1, 2, and 4 weeks after implantation. At 1 week, only cultured-bone/HA70 constructs exhibited expanded bone formation. At 2 and 4 weeks, active osteoblasts and progressive bone formation were observed morphologically in both cultured-bone/HA50 and HA70 constructs. At 4 weeks, bone tissue was observed even in cultured-bone/HA30 constructs. ALP activity and osteocalcin production also increased with increasing porosity and time after implantation. In this in vivo model, different scaffold porosity with similar crystal morphology of the apatite phase demonstrated marked differences in ability to support osteogenesis by implanted rat MSCs.

Enhanced osteoinduction by mesenchymal stem cells transfected with a fiber-mutant adenoviral BMP2 gene

BACKGROUND

Bone regeneration therapy using mesenchymal stem cells (MSCs) is beginning to come into clinical use. To overcome the difficulty of healing large bone defects, we previously reported the efficacy of using rat mesenchymal stem cells (rMSCs) carrying a modified adenoviral vector (Adv-F/RGD) with an RGD-containing peptide in the HI loop of the fiber knob domain of adenovirus type 5 (Ad5).

METHODS

Firstly, we evaluated the transduction efficiency of Adv-F/RGD into bone-marrow-derived human MSCs (hMSCs) using a beta-galactosidase chemiluminescent assay. Next, we evaluated whether the vector AxCAhBMP2-F/RGD carrying the human bone morphogenetic protein 2 (BMP2) gene could enhance the osteogenic activity of hMSCs in vitro and in vivo (in an ectopic model). In the ectopic model, transduced hMSCs, hMSCs in the presence of recombinant human BMP2 (rhBMP2) or hMSCs alone were implanted into a subcutaneous site of nude mice. We also applied this vector system to an orthotopic model (large bone defect model) using rMSCs.

RESULTS

The transduction efficiency of Adv-F/RGD into hMSCs was increased 10-fold over the vector containing the wild-type fiber (Adv-F/wt), as assessed by a beta-galactosidase chemiluminescent assay. AxCAhBMP2-F/RGD increased the osteogenic activity of hMSCs in vitro. In the ectopic model, AxCAhBMP2-F/RGD-transduced hMSCs were found to induce new bone at 1 week after transplantation, and a greater quantity of new bone was formed than in other groups. Similarly, AxCAhBMP2-F/RGD-transduced rMSCs induced a greater quantity of new bone than other groups (AxCAhBMP2-F/wt-transduced rMSCs, rMSCs in the presence of rhBMP2, rMSCs alone, or scaffolds alone) in the orthotopic model.

CONCLUSIONS

These data suggest that Adv-F/RGD is useful for introducing foreign genes into MSCs and that it will be a powerful gene therapy tool for bone regeneration and other tissue-engineering applications.

A comparative qualitative histological analysis of tissue-engineered bone using bone marrow mesenchymal stem cells, alveolar bone cells, and periosteal cells

For tissue-engineered bone formation, autogenous osteogenic cells are of paramount importance for successful bone formation. In order to investigate the donor cell-related differences in tissue-engineered bone, cultured bone marrow mesenchymal stem cells, cultured alveolar bone cells, and cultured periosteal cells were examined for their in vivo potential to form bone. These cells were isolated from dogs, expanded in vitro, mixed with autologous fibrin glue and BMP-2, and then injected into the subcutaneous space on the dorsum of nude mice. Bone formation was evaluated at 12 weeks. Histomorphometric analysis demonstrated that the subcutaneous nodules formed in nude mice contained 26.9% newly formed bone when using the bone marrow mesenchymal stem cells, 41.1% newly formed bone when using the alveolar bone cells, and 58.2% newly formed bone when using the periosteal cells. The results suggest that periosteal cells are the best choice for enhancing bone formation in tissue engineering of bone regeneration.

A comparative histologic analysis of tissue-engineered bone using platelet-rich plasma and platelet-enriched fibrin glue

OBJECTIVE

The aim of this study was to compare the effects of platelet-rich plasma (PRP) and platelet-enriched fibrin glue on bone formation in bone tissue engineering.

STUDY DESIGN

PRP was mixed with bone marrow mesenchymal stem cells and bone morphogenetic protein-2 (BMP-2), and the composites were injected into the subcutaneous space on the dorsum of nude mice. On the contralateral side of the dorsum, platelet-enriched fibrin glue/bone marrow mesenchymal stem cells/BMP-2 composites were injected. Bone formation was evaluated after 12 weeks.

RESULTS

The volumes of subcutaneous nodules formed in nude mice were 55 +/- 18 microL at the PRP/bone marrow mesenchymal stem cells/BMP-2 sites and 135 +/- 27 microL at the platelet-enriched fibrin glue/bone marrow mesenchymal stem cells/BMP-2 sites. Histomorphometric analysis demonstrated that the nodules contained 14.9 +/- 4.1% newly formed bone when using PRP and 19.8 +/- 3.6% newly formed bone when using platelet-enriched fibrin glue.

CONCLUSION

The results indicated that the osteogenic characteristics of platelet-enriched fibrin glue are superior to PRP in bone tissue engineering.

The effect of the addition of a polyglutamate motif to RGD on peptide tethering to hydroxyapatite and the promotion of mesenchymal stem cell adhesion

Mimicking endogenous bone-binding proteins, RGD peptides have been synthesized with polyacidic amino acid domains in order to ionically tether the peptides to bone-like synthetic biomaterials, including hydroxyapatite (HA). However, a direct comparison of unmodified RGD with polyacidic-conjugated RGD has not been performed, and thus a benefit for the acidic domain has not been established. We evaluated the peptide/HA bond of RGD peptides with and without an attached polyglutamate sequence (E(7)), as well as examined mesenchymal stem cell (MSC) adhesion and morphology as they were affected by the conjugated peptide. We found that significantly more E(7)RGD was bound to HA than RGD at all coating concentrations tested, and moreover, more E(7)RGD was retained on the HA surface even after extended washing in serum-free media. Consistent with in vitro results, higher levels of E(7)RGD than RGD remained on HA that had been implanted in vivo for 24 h, indicating that the polyacidic domain improved peptide-binding efficiency. At several peptide concentrations, E(7)RGD increased cell adhesion compared to RGD surfaces, establishing a biological benefit for the E(7) modification. In addition, HA pre-coated sequentially with low-density E(7)RGD (1-10 microg/ml) and serum (FBS) stimulated cell adhesion and spreading, compared to either coating alone, suggesting that an ionic linkage allows for the potential adsorption of serum proteins to unoccupied sites, which may be important for bone formation in vivo. Collectively, these results suggest that tethering peptides to HA via a polyglutamate domain is an effective method for improving the peptide/HA bond, as well as for enhancing MSC adhesion.

Sinus floor elevation applied tissue-engineered bone. Comparative study between mesenchymal stem cells/platelet-rich plasma (PRP) and autogenous bone with PRP complexes in rabbits

In the present study, we compared bone regeneration ability in sinus floor elevation between a tissue engineering method using mesenchymal stem cells (MSCs) and platelet-rich plasma (PRP), and a promising new method using particulate cancellous bone and marrow (PCBM) and PRP. Bilateral sinus floor elevation procedures were performed in 18 adult Japanese white rabbits. MSCs/PRP or PCBM/PRP complexes were grafted to each maxillary sinus in the same rabbits. The MSCs were isolated from rabbit iliac crest marrow, and PRP was obtained from peripheral blood. PCBM were collected from the rabbit iliac crest and mixed with PRP. The animals were sacrificed at 2, 4, and 8 weeks after transplantation, and the bone formation ability of each implant was evaluated histologically and histometrically. According to the histological observations, both sites (MSCs/PRP and PCBM/PRP) showed well newly formed bone and neovascularization at 2 and 4 weeks. However, at 8 weeks, the lamellar bone was observed to be occupied by fatty marrow in large areas in both sites. There was no significant difference in bone volume or augmented height between MSCs/PRP and PCBM/PRP groups each week, but there were significant differences in bone volume and augmented height between 2 and 8 weeks in PCBM/PRP or MSCs/PRP groups and in bone volume between 4 and 8 weeks in the PCBM/PRP group (P<0.05). These results suggest that the MSCs/PRP complex may well be used for bone regeneration in sinus floor elevation, compared with the PCBM/PRP complex.

Osteogenic differentiation of mesenchymal progenitor cells in computer designed fibrin-polymer-ceramic scaffolds manufactured by fused deposition modeling

Biomimetic scaffolds offer great potentials in the development of bone analogs for tissue engineering. The studies presented in this paper focus specifically on the osteogenic potential of the novel PCL/CaP matrices and its degradation behavior. Biodegradable Polymer-ceramic Scaffolds were fabricated using the solid free form fabrication technology: Fused Deposition Modeling (FDM). The scaffold architecture was characterized by a honeycomb-like design and a complete interconnectivity of the pores. Human mesenchymal stem cells (MSCs) were seeded together with fibrin glue into PCL/CaP scaffolds and cultured in vitro for periods of up to eight weeks. Cellular adhesion, proliferation and osteogenic differentiation were assessed in these constructs using a range of histological and microscopic techniques. In additional experiments, degradation was assessed by measuring mass loss, diameter change, molecular weight change and by scanning electron micrographs. MSCs were able to adhere, migrate, and differentiate along the osteogenic lineage with in these scaffolds. The PCL/CaP scaffolds showed up to 27 fold increased degradation of compared to PCL scaffolds.

Experimental study of bone formation around a titanium rod with beta-tricalcium phosphate and prostaglandin E2 receptor agonists

beta-Tricalcium phosphate (beta-TCP) is an excellent bone-filling material that is completely absorbed by the body and replaced by autologous bone. Unfortunately, its mechanical strength is low, rendering its application at loaded regions difficult. The purpose of this study is to evaluate the histological and mechanical effects of single and combined use of beta-TCP and EP4 agonist on bone formation around a titanium rod. beta-TCP was loaded into the femoral bone marrow from the distal end of the femur, where the titanium implants were inserted, and the animals received twice-daily subcutaneous injections of EP4 agonist. Group I received the rod only and was designated the control group; group II received EP4 agonist only; group III received beta-TCP only; and group IV received both beta-TCP and EP4 agonist. Examination of decalcified specimens revealed favorable bone formation in all treatment groups compared with that in group I, with the most active bone formation seen in group IV. Mechanical evaluation revealed significant differences in maximum pull-out force compared with group I at weeks 4 and 8. There were no differences between groups II and III at either week 4 or 8, but the values seen in group IV at weeks 4 and 8 were significantly higher compared with the other groups. Combined use of beta-TCP and EP4 agonist is expected to compensate for bone defects resulting from revision total joint arthroplasty and to achieve stability at an early stage.

Injectable bone using chitosan-alginate gel/mesenchymal stem cells/BMP-2 composites

AIM

Several injectable materials have been used as osteogenic bone substitutes. However, none has gained universal acceptance. This study was performed to investigate whether or not chitosan-alginate gel/mesenchymal stem cells/bone morphogenetic protein-2 composites are potentially injectable materials for new bone formation.

MATERIAL AND METHODS

The composites were injected into the subcutaneous space on the dorsum of nude mice to investigate new bone tissue formation. The composites were examined histologically over a 12-week period.

RESULTS

The composites injected into the mouse were able to stimulate new bone formation, which was trabecular in type.

CONCLUSIONS

This study showed that chitosan-alginate gel/MSCs/BMP-2 composites could become clinically useful injectable materials to generate new bone.

Bone morphogenetic protein-2 decorated silk fibroin films induce osteogenic differentiation of human bone marrow stromal cells

Bone morphogenetic protein (BMP)-2 has a critical role in bone formation and regeneration. Therefore, the ability to immobilize this molecule in certain matrices may be crucial in bone tissue engineering. Using carbodiimide chemistry, BMP-2 was directly immobilized on silk fibroin films. Whereas human bone marrow stromal cells cultured on unmodified silk fibroin films in the presence of osteogenic stimulants exhibited little if any osteogenesis, the same cells cultured on BMP-2 decorated films in the presence of osteogenic stimulants differentiated into an osteoblastic lineage as assessed by their significantly elevated alkaline phosphatase activity, calcium deposition, and higher transcript levels of collagen type I, bone sialoprotein, osteopontin, osteocalcin, BMP-2, and cbfa1. Using cell culture inserts, it was demonstrated that differentiation was induced by the immobilized protein and not by protein released into the culture medium. Comparison with a similar amount of medium-supplemented BMP-2, where no additional protein was added with medium changes, showed that delivery of BMP-2 immobilized on the biomaterial surface was more efficient than soluble delivery. The results illustrate that BMP-2 covalently coupled on silk biomaterial matrices retains biological function in vitro based on the induction of osteogenic markers in seeded bone marrow stromal cells.