Bone morphogenetic proteins: indications and uses

In vivo endocultivation of CAD/CAM hybrid scaffolds in the omentum majus in miniature pigs

PURPOSE

Correction of bony mandibular defects is a challenge in oral and maxillofacial surgery due to aesthetic and functional requirements. This study investigated the potential of a novel hybrid scaffold for bone regeneration and degradation assessment of the ceramic within the omentum majus over 6 months and the extent to which rhBMP-2 as a growth factor, alone or combined with a hydrogel, affects regeneration.

MATERIALS AND METHODS

In this animal study, 10 Göttingen minipigs each had one scaffold implanted in the greater omentum. Five animals had scaffolds loaded with a collagen hydrogel and rhBMP-2, and the other five animals (control group) had scaffolds loaded with rhBMP-2 only. Fluorochrome injections and computed tomography (CT) were performed regularly. After 6 months, the animals were euthanized, and samples were collected for microCT and histological evaluations.

RESULTS

Fluorescent and light microscopic and a CT morphological density evaluation showed continuous bone growth until week 16 in both groups. Regarding the ratio of bone attachment to the Zr02 support struts, the rhBMP-2 loaded collagen hydrogel group showed with 63% a significantly higher attachment (p > 0.001) than the rhBMP-2 control group (49%).

CONCLUSION

In this study, bone growth was induced in all omentum majus specimens until post-operative week 16. Furthermore, hydrogel and rhBMP-2 together resulted in better bone-scaffold integration than rhBMP-2 alone. Further studies should investigate whether implantation of the scaffolds in the jaw after an appropriate period of bone regeneration leads to a stable situation and the desired results.

Off-label: The results of adjunctive bone morphogenetic protein for challenging femur fractures; a review of two cases

Background

Although bone morphogenetic proteins (BMPs) are used as an adjunct to promote healing, they may have unintended effects such as heterotopic ossification (HO). The literature is limited regarding the effect of using off-label BMPs for femur fractures.

Case presentation

We report two outcomes after off-label use of BMPs for the treatment of femur fractures and propose a possible explanation for the difference.

Conclusions

BMPs are critical osteoinductive factors in injured bone and muscle that facilitate bony healing. However, it may be important to recognize the potentially negative effects of adding BMP to bone graft material in certain cases to stimulate bone repair. We hope this case series helps surgeons consider the risks and benefits of using BMP for femur fractures, and therefore to decide with caution when BMP is indicated.

Nonoperative and Operative Soft-Tissue and Cartilage Regeneration and Orthopaedic Biologics of the Foot and Ankle: An Orthoregeneration Network Foundation Review

Orthoregeneration is defined as a solution for orthopaedic conditions that harnesses the benefits of biology to improve healing, reduce pain, improve function, and optimally, provide an environment for tissue regeneration. Options include drugs, surgical intervention, scaffolds, biologics as a product of cells, and physical and electromagnetic stimuli. The goal of regenerative medicine is to enhance the healing of tissue after musculoskeletal injuries as both isolated treatment and adjunct to surgical management, using novel therapies to improve recovery and outcomes. Various orthopaedic biologics (orthobiologics) have been investigated for the treatment of pathology involving the foot and ankle (including acute traumatic injuries and fractures, tumor, infection, osteochondral lesions, arthritis, and tendinopathy) and procedures, including osteotomy or fusion. Promising and established treatment modalities include 1) bone-based therapies (such as cancellous or cortical autograft from the iliac crest, proximal tibia, and/or calcaneus, fresh-frozen or freeze-dried cortical or cancellous allograft, including demineralized bone matrix putty or powder combined with growth factors, and synthetic bone graft substitutes, such as calcium sulfate, calcium phosphate, tricalcium phosphate, bioactive glasses (often in combination with bone marrow aspirate), and polymers; proteins such as bone morphogenic proteins; and platelet-derived growth factors; 2) cartilage-based therapies such as debridement, bone marrow stimulation (such as microfracture or drilling), scaffold-based techniques (such as autologous chondrocyte implantation [ACI] and matrix-induced ACI, autologous matrix-induced chondrogenesis, matrix-associated stem cell transplantation, particulated juvenile cartilage allograft transplantation, and minced local cartilage cells mixed with fibrin and platelet rich plasma [PRP]); and 3) blood, cell-based, and injectable therapies such as PRP, platelet-poor plasma biomatrix loaded with mesenchymal stromal cells, concentrated bone marrow aspirate, hyaluronic acid, and stem or stromal cell therapy, including mesenchymal stem cell allografts, and adipose tissue-derived stem cells, and micronized adipose tissue injections. LEVEL OF EVIDENCE: Level V, expert opinion.

Periodontal Tissue as a Biomaterial for Hard-Tissue Regeneration following bmp-2 Gene Transfer

The application of periodontal tissue in regenerative medicine has gained increasing interest since it has a high potential to induce hard-tissue regeneration, and is easy to handle and graft to other areas of the oral cavity or tissues. Additionally, bone morphogenetic protein-2 (BMP-2) has a high potential to induce the differentiation of mesenchymal stem cells into osteogenic cells. We previously developed a system for a gene transfer to the periodontal tissues in animal models. In this study, we aimed to reveal the potential and efficiency of periodontal tissue as a biomaterial for hard-tissue regeneration following a bmp-2 gene transfer. A non-viral expression vector carrying bmp-2 was injected into the palate of the periodontal tissues of Wistar rats, followed by electroporation. The periodontal tissues were analyzed through bone morphometric analyses, including mineral apposition rate (MAR) determination and collagen micro-arrangement, which is a bone quality parameter, before and after a gene transfer. The MAR was significantly higher 3-6 d after the gene transfer than that before the gene transfer. Collagen orientation was normally maintained even after the bmp-2 gene transfer, suggesting that the bmp-2 gene transfer has no adverse effects on bone quality. Our results suggest that periodontal tissue electroporated with bmp-2 could be a novel biomaterial candidate for hard-tissue regeneration therapy.

Fabricating a novel HLC-hBMP2 fusion protein for the treatment of bone defects

Treating serious bone trauma with an osteo-inductive agent such as bone morphogenetic proteins (BMPs) has been considered as an optimized option when delivered via a collagen sponge (CS). Previous works have shown that the BMP concentration and release rate from approved CS carriers is difficult to control with precision. Here we presented the fabrication of a recombinant fusion protein from recombinant human-like collagen (HLC) and human BMP-2 (hBMP2). The fusion protein preserved the characteristic of HLC allowing the recombinant protein to be expressed in Yeast (such as Pichia pastoris GS115) and purified rapidly and easily with mass production after methanol induction. It also kept the stable properties of HLC and hBMP2 in the body fluid environment with good biocompatibility and no cytotoxicity. Moreover, the recombinant fusion protein fabricated a vertical through-hole structure with improved mechanical properties, and thus facilitated migration of bone marrow mesenchymal stem cells (MSCs) into the fusion materials. Furthermore, the fusion protein degraded and released hBMP-2 in vivo allowing osteoinductive activity and the enhancement of utilization rate and the precise control of the hBMP2 release. This fusion protein when applied to cranial defects in rats was osteoinductively active and improved bone repairing enhancing the repairing rate 3.5- fold and 4.2- fold when compared to the HLC alone and the control, respectively. There were no visible inflammatory reactions, infections or extrusions around the implantation sites observed. Our data strongly suggests that this novel recombinant fusion protein could be more beneficial in the treatment of bone defects than the simple superposition of the hBMP2/collagen sponge.

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.

Exfoliated Human Deciduous Tooth Stem Cells Incorporating Carbonate Apatite Scaffold Enhance BMP-2, BMP-7 and Attenuate MMP-8 Expression During Initial Alveolar Bone Remodeling in Wistar Rats (Rattus norvegicus)

Background

Post-tooth extraction socket preservation is necessary due to alveolar bone resorptive patterns through regenerative dentistry approaches that involve the use of stem cells, scaffold and growth factor. Stem cells derived from human exfoliated deciduous teeth (SHED) are known to potentially possess the osteogenic ability. Meanwhile, carbonate apatite scaffold (CAS) can act as a biocompatible scaffold capable of supporting mesenchymal stem cells (MSCs) to proliferate and differentiate optimally. The aim of this study is to investigate the expression of bone morphogenic protein-2 and 7 (BMP2, BMP7) and Matrix Metalloproteinase-8 (MMP-8) after the transplantation of SHED-incorporated CAS during in vivo bone remodeling.

Material and Methods

A total of 14 healthy, male, Wistar rats, whose mandible anterior teeth were extracted by means of sterile needle holder clamps, constituted the subjects of this study of alveolar bone defects. Two research groups were created: a control group (CAS) as group I and an experimental group (CAS + SHED) as group II. SHED with a density of 10⁶ cells were incorporated into CAS before being transplanted into the experimental group. After 7 days, all the animals were sacrificed and their mandible anterior region extracted. The BMP2, BMP7 and MMP-8 expression were subsequently analyzed by means of immunostaining. An unpaired t-test was conducted to analyze the treatment and control group (p<0.01) data.

Results

The expression of BMP-2 and BMP-7 was higher in group II compared to group I. Meanwhile, the level of MMP-8 was lower in group II than group I. There was greater significant increased expression of BMP-2 and BMP-7 expression in Group II compared to Group I. There was significant decreased expression of MMP-8 between group II than group I (p<0.01).

Conclusion

SHED-incorporated CAS can enhance BMP-2 and BMP-7 expression while attenuating MMP-8 expression during in vivo alveolar bone remodeling.

Exploring Poly(Ethylene Glycol)-Poly(Trimethylene Carbonate) Nanoparticles as Carriers of Hydrophobic Drugs to Modulate Osteoblastic Activity

Current treatment options for bone-related disorders rely on a systemic administration of therapeutic agents that possess low solubility and intracellular bioavailability, as well as a high pharmacokinetic variability, which in turn lead to major off-target side effects. Hence, there is an unmet need of developing drug delivery systems that can improve the clinical efficacy of such therapeutic agents. Nanoparticle delivery systems might serve as promising carriers of hydrophobic molecules. Here, we propose 2 nanoparticle-based delivery systems based on monomethoxy poly(ethylene glycol)-poly(trimethyl carbonate) (mPEG-PTMC) and poly(lactide-co-glycolide) for the intracellular controlled release of a small hydrophobic drug (dexamethasone) to osteoblast cells in vitro. mPEG-PTMC self-assembles into stable nanoparticles in the absence of surfactant and shows a greater entrapment capacity of dexamethasone, while assuring bioactivity in MC3T3-E1 and bone marrow stromal cells cultured under apoptotic and osteogenic conditions, respectively. The mPEG-PTMC nanoparticles represent a potential vector for the intracellular delivery of hydrophobic drugs in the framework of bone-related diseases.

The role of biologic in foot and ankle trauma-a review of the literature

PURPOSE OF REVIEW

The use of biologics in orthopedics is becoming increasingly popular as an adjuvant in healing musculoskeletal injuries. Though many biologics involved in the management of foot and ankle injuries are used based on physician preference, reports of improved outcomes when combined with standard operative treatment has led to further clinical interest especially in foot and ankle trauma.

RECENT FINDINGS

The most recent studies have shown benefits for biologic use in patients predisposed to poor bone and soft tissue healing. Biologics have shown benefit in treating soft tissue injuries such as Achilles ruptures as well as the complications of trauma such as non-unions and osteoarthritis. Biologics have shown some benefit in improving functional and pain scores, as well as reducing time to heal in foot and ankle traumatic injuries, with particular success shown with patients that have risk factors for poor healing. As the use of biologics continues to increase, there is a need for high-level studies to confirm early findings of lower level reports.

Current Orthobiologics for Elective Arthrodesis and Nonunions of the Foot and Ankle

A fusion rate of 100% would be ideal. Despite adhering to sound surgical principles, complete compliance, and no adverse comorbidities, that 100% fusion rate goal is elusive. Orthobiologics are a special class of materials developed to enhance the fusion rates in foot and ankle arthrodesis sites. Whether orthobiologics are used for the first fusion or reserved for a nonunion is debatable, especially when considering cost.

Magnesium modification up-regulates the bioactivity of bone morphogenetic protein-2 upon calcium phosphate cement via enhanced BMP receptor recognition and Smad signaling pathway

Efficient presentation of growth factors is one of the great challenges in tissue engineering. In living systems, bioactive factors exist in soluble as well as in matrix-bound forms, both of which play an integral role in regulating cell behaviors. Herein, effect of magnesium on osteogenic bioactivity of recombinant human bone morphogenetic protein-2 (rhBMP-2) was investigated systematically with a series of Mg modified calcium phosphate cements (xMCPCs, x means the content of magnesium phosphate cement wt%) as matrix model. The results indicated that the MCPC, especially 5MCPC, could promote the rhBMP-2-induced in vitro osteogenic differentiation via Smad signaling of C2C12 cells. Further studies demonstrated that all MCPC substrates exhibited similar rhBMP-2 release rate and preserved comparable conformation and biological activity of the released rhBMP-2. Also, the ionic extracts of MCPC made little difference to the bioactivity of rhBMP-2, either in soluble or in matrix-bound forms. However, with the quartz crystal microbalance (QCM), we observed a noticeable enhancement of rhBMP-2 mass-uptake on 5MCPC as well as a better recognition of the bound rhBMP-2 to BMPR IA and BMPR II. In vivo results demonstrated a better bone regeneration capacity of 5MCPC/rhBMP-2. From the above, our results demonstrated that it was the Mg anchored on the underlying substrates that tailored the way of rhBMP-2 bound on MCPC, and thus facilitated the recognition of BMPRs to stimulate osteogenic differentiation. The study will guide the development of Mg-doped bioactive bone implants for tissue regeneration.

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.