125I-labeled OP-1 is locally retained in a rabbit lumbar fusion model

Bone morphogenetic proteins and tissue engineering: future directions

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

Formulations and delivery vehicles for bone morphogenetic proteins: latest advances and future directions

Growth factors are essential components of the diamond concept model. The bone morphogenetic proteins (BMPs) are the most potent and promising growth factors and their clinical efficacy is well demonstrated for specific indications. Application of BMPs involves a carrier material to enhance local residual time and pharmacokinetics. On the other hand carrier materials, collagen at this point, also limit the use of BMPs, for example in minimally invasive application methods. In this overview, the pharmacokinetics of BMPs, and various carrier materials (collagen, synthetic polymers, calcium phosphates, hyaluronic acid, CMC, and sodium acetate) are discussed. No other carrier material than collagen has been proven effective in clinical studies. Other formulations are needed to improve the residual time and handling.

Posterolateral Spinal Fusion in Rabbits Using a RP-based PLGA/ TCP/Col/BMSCs-OB Biomimetic Grafting Material

Three-dimensional highly porous poly(DL-lactic-co-glycolic acid)/ tricalcium phosphate (PLGA/TCP) scaffolds were fabricated using a rapid prototyping technique (RP). The 3D rhombic lamellar PLGA/TCP carriers (20 mm × 20 mm × 3 mm) subsequently were coated with collagen type I (Col) to produce PLGA/TCP/Col composites. Both the RP-based PLGA/TCP scaffolds and the PLGA/TCP/Col composites were observed by scanning electron microscopy. Forty New Zealand white rabbits were equally randomized into 2 groups (group A and group B) and bilaterally underwent posterolateral intertransverse process arthrodesis at the L4—L5 level using the following graft materials: In group A, PLGA/TCP/Col/BMSCs-OB composites (on the right side, group A1, n = 20) and autogenous iliac bone grafts (on the left side, group A2, n = 20) were used; In group B, PLGA/TCP scaffolds plus fresh autogenous bone marrow (on the right side, group B1, n = 20) and PLGA/TCP scaffolds alone (on the left side, group B2, n = 20) were utilized. In group A1, rabbit bone marrow stromal cells (BMSCs) were isolated and cultured under the osteogenic conditions (BMSCs-OB). Structural PLGA/TCP/Col composites then were efficiently loaded with BMSCs-OB and cultured 5 days to make PLGA/TCP/ Col/BMSCs-OB biomaterials. Rabbits were sacrificed after 12-week follow-up and the spinal fusion were evaluated by a general observation, a manual palpation test, histological analyses and radiography. As a result, RP established PLGA/TCP scaffolds with appropriate biomaterial properties including satisfactory microstructure, inter-connectivity and porosity. Modifications to the structural highly porous PLGA/TCP scaffolds with Col (PLGA/TCP/Col) essentially increased the affinity of the carriers to seeding cells. In group A1, radiological evaluation revealed strong ability of new bone formation and bony fusion in the implanted sites and histological analyses showed highly cellular bone marrow between the newly formed trabecular bone was present in the fusion mass. In group A2, there was a reduced amount of newly formed bone. In group B1, only a few bony fusions were obtained. In group B2, PLGA/TCP scaffolds were biocompatible and biodegradable; whereas, no newly formed bone or bony fusion was found. Twelve weeks after surgery, spinal fusion rates in groups of A1, A2, B1, and B2 were 70.0%(14/20), 45.0%(9/20), 15.8%(3/19), and 0%(0/19), respectively. The rates of fusion were significantly higher in groups of A1 and A2 compared with groups of B1 and B2 (p<0.01), and there was no significant difference of fusion rate between group A1 and group A2 (p>0.05). Therefore, RP-based 3D PLGA/TCP/Col/BMSCs-OB biomaterial holds promise as a bone grafting substitute for spinal fusion. Our attempts may provide a novel method for biofabrication of the bionic construct.

Immunogenicity of bone morphogenetic proteins

Object

The object of this paper is to review the immunogenicity of bone morphogenetic proteins (BMPs) and to compare the results of the immunogenicity characterization and clinical consequences between recombinant human (rh)BMP-2 and recombinant human osteogenic protein-1 (rhOP-1/BMP-7).

Methods

The immunogenicity of therapeutic proteins and its clinical effects were reviewed. The characteristics of BMPs were also described in terms of immunogenicity. The methods and results of antibody detection in various clinical trials of rhBMP-2 and rhOP-1 were compared, including the most recent studies using a systematic characterization strategy with both a binding assay and bioassay.

Results

Similar to all recombinant human proteins, rhBMPs induce immune responses in a select subgroup of patients. Adverse effects from this response in these patients, however, have not been reported with antibody formation to either rhBMP-2 or rhOP-1. Overall, the incidence of antibody formation was slightly higher in rhOP-1 trials than in rhBMP-2 trials.

Conclusions

Although they occur in a subgroup of patients, the immune responses against rhBMPs have no correlation with any clinical outcome or safety parameter. Clinicians, however, must be aware of the potential complications caused by the immunogenicity of BMPs until more studies clearly elucidate their safety.