BMP-2 modulates expression of other growth factors in a rat fracture healing model

The healing capacity and osteogenesis pattern of demineralized dentin matrix (DDM)-fibrin glue (FG) compound

Demineralized dentin matrix (DDM) is an osteoconductive and osteoinductive material that has been successfully used in sinus floor augmentation and alveolar ridge augmentation in clinical applications. It releases bone morphogenetic proteins (BMPs) and other growth factors, making DDM a suitable grafting material. However, the granular particle of DDM makes it difficult to anchor into the bone defect area. The aim of this study was to investigate the biological effects and osteoinductivity of the combination of DDM and Fibrin Glue (FG) at an optimal ratio on bone healing from a critical bone defect in an animal model. The mouse osteoblastic cell line (MC3T3-E1) was co-cultured with various ratios of DDM and FG to examine their effects on osteoblast proliferation and differentiation, as indicated by alkaline phosphatase (ALP) activity, osteocalcin (OC) production and mineralized nodules formation. The optimal ratio was then chosen for further study with a rabbit calvarial defective model, in which they were implanted with DDM or DDM-FG1 (1 g: 0.1 ml) and DDM-FG2 (1 g: 0.5 ml) compounds, or left blank for 2, 4, 8 and 12 weeks to investigate soft tissue and new bone regeneration. Micro-CT and histology analysis were used to evaluate the total grafting properties according to the different healing periods. The result from in vitro studies demonstrated that the ratio of 1:0.1 induced more ALP activity and mineralized nodules, while the ratio of 1: 0.5 (DDM-FG combined) induced more osteocalcin (OC) at specific time points. In the animal model, the 3D new bone volume in all DDM-FG treatment groups was significantly greater than that in the blank group at 2, 4, 8 and 12 weeks. Furthermore, the new bone volume was greater in DDM-FG2 when compared to the other groups during the early weeks of the healing period. In histological analysis, clusters of osteoblasts were formed adjacent to the DDM particles, and newly formed bone was observed in all groups, suggesting an osteoinductive property of DDM. Moreover, the greater new collagen synthesis observed at 4 weeks suggested that early bone healing was induced in the DDM-FG2 group. This study demonstrated that at an optimal ratio, the DDM-FG compound enhances osteogenic activities and bone regeneration.

Temporal Pattern of micro-CT Angiography Vascular Parameters and VEGF mRNA Expression in Fracture Healing: a Radiograph and Molecular Comparison

Angiogenesis plays an important role in fracture healing with vascular endothelial growth factor (VEGF) as the main protein involved. Micro-computed tomography (CT) angiography may be used to analyze this revascularization with several parameters such as number of branches, total volume, and diameter. This systematic review is aimed to assess available studies on the temporal pattern of vascular imaging on micro-CT angiographs, especially in terms of the number of branches, total volume, and diameter as well as the temporal pattern of VEGF mRNA expression as the molecular comparison during bone fracture healing. This review was conducted according to the PRISMA guidelines. Electronic database searches were performed using PubMed, ProQuest, ScienceDirect, EBSCOhost, Taylor & Francis Online, and hand searching. The search strategy and keywords were adjusted to each database using the Boolean operators and other available limit functions to identify most relevant articles based on our inclusion and exclusion criteria. Screening and filtration were done in several stages by removing the duplicates and analyzing each title, abstract, and full-text in all included entries. Data extraction was done for syntheses to summarize the temporal pattern of each parameter. A total of 28 articles were eligible and met all criteria, 11 articles were synthesized in its angiograph's analysis, 16 articles were synthesized in its VEGF mRNA expression analysis, and 1 article had both parameters analyzed. The overall temporal pattern of both three micro-CT angiographic parameters and VEGF mRNA expression was in line qualitatively. The number of branches, total volume, and diameter of the blood vessels in micro-CT angiography showed an exponential rise at week 2 and decline at week 3 of fracture healing, with the VEGF mRNA expression concurrently showing a consistent pattern in the phase.

Poly(POG)n loaded with recombinant human bone morphogenetic protein-2 accelerates new bone formation in a critical-sized bone defect mouse model

Background

Delivery of bone morphogenetic protein-2 (BMP-2) via animal-derived absorbable collagen materials is used for the treatment of large bone defects. However, the administration of bovine proteins to humans is associated with the risk of zoonotic complications. We therefore examined the effect of combining BMP-2 with collagen-like peptides, poly(POG)n, in a critical-sized bone defect mouse model.

Methods

A 2-mm critical-sized bone defect was created in the femur of 9-week-old male C57/BL6J mice. Mice were randomly allocated into one of four treatment groups (n = 6 each): control (no treatment), poly(POG)n only, 0.2 μg, or 2.0 μg BMP-2 with poly(POG)n. New bone formation was monitored using soft X-ray radiographs, and bone formation at the bone defect site was examined using micro-computed tomography and histological examination at 4 weeks after surgery.

Results

Administration of 2.0 μg of BMP-2 with poly(POG)n promoted new bone formation and resulted in greater bone volume and bone mineral content than that observed in the control group and successfully achieved consolidation. In contrast, bone formation in all other groups was scarce.

Conclusions

Our findings suggest the potential of BMP-2 with poly(POG)n as a material, free from animal-derived collagen, for the treatment of large bone defects.

Influence of the TGF-β Superfamily on Osteoclasts/Osteoblasts Balance in Physiological and Pathological Bone Conditions

The balance between bone forming cells (osteoblasts/osteocytes) and bone resorbing cells (osteoclasts) plays a crucial role in tissue homeostasis and bone repair. Several hormones, cytokines, and growth factors-in particular the members of the TGF-β superfamily such as the bone morphogenetic proteins-not only regulate the proliferation, differentiation, and functioning of these cells, but also coordinate the communication between them to ensure an appropriate response. Therefore, this review focuses on TGF-β superfamily and its influence on bone formation and repair, through the regulation of osteoclastogenesis, osteogenic differentiation of stem cells, and osteoblasts/osteoclasts balance. After introducing the main types of bone cells, their differentiation and cooperation during bone remodeling and fracture healing processes are discussed. Then, the TGF-β superfamily, its signaling via canonical and non-canonical pathways, as well as its regulation by Wnt/Notch or microRNAs are described and discussed. Its important role in bone homeostasis, repair, or disease is also highlighted. Finally, the clinical therapeutic uses of members of the TGF-β superfamily and their associated complications are debated.

Photo-crosslinked alginate nano-hydroxyapatite paste for bone tissue engineering

In this study, methacrylation of alginate was carried out by reacting sodium alginate with methacrylic anhydride in the presence of sodium hydroxide. Separately synthesized nano-hydroxyapatite (nano-HAp) powder was surface functionalized using mercaptopropionic acid and ethylene glycol methacrylate phosphate (EGMP) in the presence of azobisisobutyronitrile benzene as a free radical initiator in a nitrogen atmosphere. Methacrylated alginate solution was mixed with the required amount of surface-functionalized HAp nanoparticles in the presence of 0.05% Irgacure 2959 as a photoinitiator and was placed at the centre of a 8 kW UV light source (265 nm) to prepare photo-crosslinked bone paste. X-ray diffraction analysis indicated that surface functionalization did not alter phase purity of HAp nanopowder in the prepared paste. The graft polymerization of EGMP on the surface of HAp was confirmed by the presence of the 1732 cm^-1 band, which belongs to C=-O stretching of EGMP, in addition to the characteristic peaks of nano-HAp and alginate in the composite paste. The storage and loss moduli of all the prepared pastes increased non-linearly with time up to 100 s, demonstrating their pseudo plastic behaviour. The rate of release of bone morphogenetic protein 2 (BMP-2) was significantly faster in the first few days, and the release curve gradually levelled off prior to slowing down up to 22 d. Mesenchymal stem cell adhesion studies revealed that cells could attach to the paste material and stretch over the surface of the material after 14 d of incubation. MTT assay showed that prepared paste materials were conducive to attachment and proliferation of mesenchymal stem cells. Immunocytochemical analysis revealed that the addition of surface-functionalized nano-HAp and BMP-2 to alginate hydrogel enhanced the osteogenic potential of the prepared paste. The results indicate that the newly developed photo-crosslinked paste may be physically and biologically suitable for application as a bone filler.

Bone formation promoted by bone morphogenetic protein-2 plasmid-loaded porous silica nanoparticles with the involvement of autophagy

Gene therapy is one of the most common and effective ways for the regeneration of defective bone tissue, but even highly efficient gene delivery vectors are insufficient. In this study, bone morphogenetic protein-2 plasmid (pBMP-2) was encapsulated by polyethylenimine-modified porous silica nanoparticles (PPSNs), which were synthesized via an ethyl ether emulsion method. Owing to the high specific surface area and high absorption characteristics, low cytotoxicy PPSNs can efficiently load and protect pBMP-2. The resulting PPSN/pBMP-2 can transfect MC3T3-E1 cells effectively to promote osteogenic differentiation and increase calcium deposition in vitro. Interestingly, the mass of calcium deposition nodules decreased dur to the presence of an autophagy inhibitor, demonstrating that PPSNs stimulated the autophagy pathway. Because of their excellent biocompatibility, high transfection efficiency, and ability to stimulate autophagy, the as-prepared PPSN/pBMP-2 could efficiently transfect local cells in a defect area in vivo. Micro-computed tomography and histological images demonstrated that PPSN/pBMP-2 could efficiently promote new bone formation in a 5 mm sized rat calvarial defect model. Taken together, our newly synthesized PPSNs could efficiently carry pBMP-2 and deliver it to the target cells as well as stimulating the autophagy pathway, resulting in significant osteogenic differentiation and bone regeneration.

Bone morphogenetic proteins: a powerful osteoinductive compound with non-negligible side effects and limitations

Healing and regeneration of large bone defects leading to non-unions is a great concern in orthopedic surgery. Since auto- and allografts have limitations, bone tissue engineering and regenerative medicine (TERM) has attempted to solve this issue. In TERM, healing promotive factors are necessary to regulate the several important events during healing. An ideal treatment strategy should provide osteoconduction, osteoinduction, osteogenesis, and osteointegration of the graft or biomaterials within the healing bone. Since many materials have osteoconductive properties, only a few biomaterials have osteoinductive properties which are important for osteogenesis and osteointegration. Bone morphogenetic proteins (BMPs) are potent inductors of the osteogenic and angiogenic activities during bone repair. The BMPs can regulate the production and activity of some growth factors which are necessary for the osteogenesis. Since the introduction of BMP, it has added a valuable tool to the surgeon's possibilities and is most commonly used in bone defects. Despite significant evidences suggesting their potential benefit on bone healing, there are some evidences showing their side effects such as ectopic bone formation, osteolysis and problems related to cost effectiveness. Bone tissue engineering may create a local environment, using the delivery systems, which enables BMPs to carry out their activities and to lower cost and complication rate associated with BMPs. This review represented the most important concepts and evidences regarding the role of BMPs on bone healing and regeneration from basic to clinical application. The major advantages and disadvantages of such biologic compounds together with the BMPs substitutes are also discussed.