High doses of bone morphogenetic protein 2 induce structurally abnormal bone and inflammation in vivo

Polyelectrolyte Complex Carrier Enhances Therapeutic Efficiency and Safety Profile of Bone Morphogenetic Protein-2 in Porcine Lumbar Interbody Fusion Model

STUDY DESIGN

Porcine lumbar interbody fusion model.

OBJECTIVE

This study evaluates the effect of polyelectrolyte complex (PEC) carrier in enhancing the therapeutic efficiency and safety profile of bone morphogenetic protein-2 (BMP-2) in a large animal model.

SUMMARY OF BACKGROUND DATA

Extremely large amounts of BMP-2 are administered to achieve consistent spinal fusion, which has led to complications. Heparin-modified PEC carrying reduced BMP-2 doses of 0.5 μg was demonstrated to achieve consistent spinal fusion with reduction of complications in rodent model. The purpose of this study was to evaluate whether PEC could improve the therapeutic efficiency of BMP-2 in porcine model.

METHODS

Three-segment (L3-L6) anterior lumbar interbody fusions with instrumentation were performed on 6 pigs using 3 different doses of BMP-2, namely, (1) 50 μg, (2) 150 μg, and (3) 300 μg. The BMP-2 was delivered using heparin-modified alginate microbeads loaded into biodegradable cage. Fusion performance was evaluated after 3 months.

RESULTS

Manual palpation and micro-computed tomography showed consistent fusion in all experimental groups. Heterotopic bone formation beyond the cage implant area was more evident in group 2 and group 3 than in group 1. Similarly, superior bone microstructure was observed in the new bone with the lowered BMP-2 dose. Biomechanical evaluation revealed enhanced stiffness of the operated segments compared with nonoperated segments (P < 0.05). Mechanical stability was maintained despite dose reduction of BMP-2. Although the mineral apposition rate was higher in group 3, unsatisfactory bony microstructure with decreased trabecular number was observed in group 3 compared with group 1.

CONCLUSION

PEC carrying low doses of BMP-2 achieved consistent interbody fusion. We observed dose-related reduction in heterotopic ossification without compromising the stability of the fused segments. PEC carrier reduces the efficacious doses of BMP-2. This could enhance the safety profile of BMP-2 and reduce dose- and carrier-related complications.

LEVEL OF EVIDENCE

N/A.

NELL-1 in the treatment of osteoporotic bone loss

NELL-1 is a secreted, osteoinductive protein whose expression rheostatically controls skeletal ossification. Overexpression of NELL-1 results in craniosynostosis in humans and mice, whereas lack of Nell-1 expression is associated with skeletal undermineralization. Here we show that Nell-1-haploinsufficient mice have normal skeletal development but undergo age-related osteoporosis, characterized by a reduction in osteoblast:osteoclast (OB:OC) ratio and increased bone fragility. Recombinant NELL-1 binds to integrin β1 and consequently induces Wnt/β-catenin signalling, associated with increased OB differentiation and inhibition of OC-directed bone resorption. Systemic delivery of NELL-1 to mice with gonadectomy-induced osteoporosis results in improved bone mineral density. When extended to a large animal model, local delivery of NELL-1 to osteoporotic sheep spine leads to significant increase in bone formation. Altogether, these findings suggest that NELL-1 deficiency plays a role in osteoporosis and demonstrate the potential utility of NELL-1 as a combination anabolic/antiosteoclastic therapeutic for bone loss.

High-dose recombinant human bone morphogenetic protein-2 impacts histological and biomechanical properties of a cervical spine fusion segment: results from a sheep model

The 'off-label' use of high-dose recombinant human bone morphogenetic protein-2 (rhBMP-2) in lumbar and cervical fusion leads to heterotopic bone formation and vertebral osteolysis. These radiographically assessed side-effects in patients were frequently associated with an over-dosage of BMP-2. However, little is so far known about the histological, functional or biomechanical tissue consequences of over-dosage of rhBMP-2 in these specific clinical situations. We hypothesized that a high dose of rhBMP-2 in cervical spinal fusion could induce substantial alterations in bone, leading to mechanical impairment. An anterior cervical spinal fusion (C3-C4 ACDF) model in 16 sheep (aged > 2.5 years; n = 8/group) was used to quantify the consequences of a high rhBMP-2 dose (6 mg rhBMP-2) on fusion tissue compared to the 'gold standard' of autologous, cancellous bone graft. The fusion site was assessed by radiography after 0, 8 and 12 weeks. Biomechanical non-destructive testing and (immuno)histological and histomorphometrical analyses were performed 12 weeks postoperatively. Although high-dose rhBMP-2 treatment led to an advanced radiological fusion result compared to autograft treatment, heterotopic bone formation and vertebral bone resorption were induced simultaneously. Histological evaluation unveiled highly active bone-forming processes ventral to the fusion segment after 12 weeks, while radiolucent areas showed still a partial loss of regular trabecular structure, with rare signs of remodelling and restoration. Despite qualitative alteration of the trabecular bone structure within the fusion site, the massive anterior heterotopic bone formation led to a substantial increase in mechanical stiffness compared to the autograft group. Copyright © 2015 John Wiley & Sons, Ltd.

In silico Mechano-Chemical Model of Bone Healing for the Regeneration of Critical Defects: The Effect of BMP-2

The healing of bone defects is a challenge for both tissue engineering and modern orthopaedics. This problem has been addressed through the study of scaffold constructs combined with mechanoregulatory theories, disregarding the influence of chemical factors and their respective delivery devices. Of the chemical factors involved in the bone healing process, bone morphogenetic protein-2 (BMP-2) has been identified as one of the most powerful osteoinductive proteins. The aim of this work is to develop and validate a mechano-chemical regulatory model to study the effect of BMP-2 on the healing of large bone defects in silico. We first collected a range of quantitative experimental data from the literature concerning the effects of BMP-2 on cellular activity, specifically proliferation, migration, differentiation, maturation and extracellular matrix production. These data were then used to define a model governed by mechano-chemical stimuli to simulate the healing of large bone defects under the following conditions: natural healing, an empty hydrogel implanted in the defect and a hydrogel soaked with BMP-2 implanted in the defect. For the latter condition, successful defect healing was predicted, in agreement with previous in vivo experiments. Further in vivo comparisons showed the potential of the model, which accurately predicted bone tissue formation during healing, bone tissue distribution across the defect and the quantity of bone inside the defect. The proposed mechano-chemical model also estimated the effect of BMP-2 on cells and the evolution of healing in large bone defects. This novel in silico tool provides valuable insight for bone tissue regeneration strategies.

Novel Protamine-Based Polyelectrolyte Carrier Enhances Low-Dose rhBMP-2 in Posterolateral Spinal Fusion

STUDY DESIGN

A rodent posterolateral spinal fusion model.

OBJECTIVE

This study evaluated a protamine-based polyelectrolyte complex (PEC) developed to use heparin in enhancing the biological activity of low-dose recombinant human bone morphogenetic protein-2 (rhBMP-2) in spinal fusion.

SUMMARY OF BACKGROUND DATA

rhBMP-2 is commonly regarded as the most potent bone-inducing molecule. However, poor pharmacokinetics and short in vivo half-life means that large amounts of the bioactive growth factor are required for consistent clinical outcomes. This has been associated with a number of adverse tissue reactions including seroma and heterotopic ossification. Glycosaminoglycans including heparin are known to stabilize rhBMP-2 bioactivity. Previous studies with poly-L-lysine (PLL) and heparin-based PEC carriers amplified the therapeutic efficacy of low-dose BMP-2. However, questions remained on the eventual clinical applicability of relatively cytotoxic PLL. In the present study, a protamine-based PEC carrier was designed to further enhance the safety and efficacy of BMP-2 by delivering lower dose within the therapeutic window.

METHODS

A polyelectrolyte shell was deposited on the surface of alginate microbead templates using the polycation (protamine)/polyanion (heparin) layer-by-layer polyelectrolyte self-assembly protocol. rhBMP-2 was loaded onto the outermost layer via heparin affinity binding. Loading and release of rhBMP-2 were evaluated in vitro. The bone-inductive ability of 20-fold reduction of rhBMP-2 with the different carrier vehicle was evaluated using a posterolateral spinal fusion model in rats.

RESULTS

In vitro uptake and release analysis, protamine-based PEC showed higher uptake and significantly enhanced control release than PLL-based PEC (P < 0.05). In vivo implantation with protamine-based and PLL-based PEC showed better fusion performances than absorbable collagen sponge-delivered same dose of rhBMP-2, and negative control group through manual palpation, micro-computed tomography, and histological analyses.

CONCLUSION

Solid posterolateral spinal fusion was achieved with 20-fold reduction of rhBMP-2 when delivered using protamine-based PEC carrier in the rat posterolateral spinal fusion model.

LEVEL OF EVIDENCE

N/A.

Effects of Immobilized BMP-2 and Nanofiber Morphology on In Vitro Osteogenic Differentiation of hMSCs and In Vivo Collagen Assembly of Regenerated Bone

Engineering bone tissue is particularly challenging because of the distinctive structural features of bone within a complex biochemical environment. In the present study, we fabricated poly(L-lactic acid) (PLLA) electrospun nanofibers with random and aligned morphology immobilized with bone morphogenic protein-2 (BMP-2) and investigated how these signals modulate (1) in vitro osteogenic differentiation of human mesenchymal stem cells (hMSCs) and (2) in vivo bone growth rate, mechanical properties, and collagen assembly of newly formed bone. The orientation of adherent cells followed the underlying nanofiber morphology; however, nanofiber alignment did not show any difference in alkaline phosphate activity or in calcium mineralization of hMSCs after 14 days of in vitro culture in osteogenic differentiation media. In vivo bone regeneration was significantly higher in the nanofiber implanted groups (approximately 65-79%) as compared to the defect-only group (11.8 ± 0.2%), while no significant difference in bone regeneration was observed between random and aligned groups. However, nanoindentation studies of regenerated bone revealed Young's modulus and contact hardness with anisotropic feature for aligned group as compared to random group. More importantly, structural analysis of collagen at de novo bone showed the ability of nanofiber morphology to guide collagen deposition. SEM and TEM images revealed regular, highly ordered collagen assemblies on aligned nanofibers as compared to random fibers, which showed irregular, randomly organized collagen deposition. Taken together, we conclude that nanofibers in the presence of osteoinductive signals are a potent tool for bone regeneration, and nanofiber alignment can be used for engineering bone tissues with structurally assembled collagen fibers with defined direction.

Mosaic tetrasomy 20p associated with osteoporosis and recurrent fractures

Tetrasomy 20p is a very rare chromosome abnormality, with only two single cases previously reported in the literature, both fetuses with multiple congenital anomalies, osteopenia, and fractures. We report on the first case of mosaic tetrasomy 20p in a 13-year-old male. Amniocentesis karyotype showed mosaicism (73% of cells) for a supernumerary marker chromosome, an isodicentric chromosome 20p. At birth, cord blood karyotype was normal in all cells but uroepithelial cells showed the marker chromosome in 30% of cells analyzed. Chromosomal single nucleotide polymorphism (SNP) microarray using buccal cells confirmed the previous result with mosaicism estimated at 59% of cells. His course has been complicated by profound osteoporosis with recurrent nontraumatic fractures and vertebral compression leading to significant disability. This report describes the phenotype and evaluation of mosaic pure tetrasomy 20p syndrome and compares to nonmosaic tetrasomy 20p and trisomy 20p syndromes, both of which have been previously reported in association with osteopenia and fractures. The pathophysiology of osteoporosis in tetrasomy 20p is unknown. We hypothesize that overexpression of bone morphogenetic protein 2 may be the underlying mechanism of osteoporosis and recurrent fractures.

A high concentration of recombinant human bone morphogenetic protein-2 induces low-efficacy bone regeneration in sinus augmentation: a histomorphometric analysis in rabbits

OBJECTIVES

The aim of the study was to elucidate the efficacy of bone regeneration at the early stage of healing in rabbit sinuses grafted with a biphasic calcium phosphate (BCP) carrier soaked in a high concentration of recombinant human bone morphogenetic protein-2 (rhBMP-2).

MATERIALS AND METHODS

Both maxillary sinuses of eight male rabbits were used. The sinus on one side (assigned randomly) was grafted with BCP loaded with rhBMP-2 (1.5 mg/ml; test group) using a soaking method, while the other was grafted with saline-soaked BCP (control group). After a 2-week healing period, the sinuses were analyzed by micro-computed tomography and histomorphometry.

RESULTS

The total augmented area and soft tissue space were significantly larger in the test group than in the control group, whereas the opposite was true for the area of residual material and newly formed bone. Most of the new bone in the test group was localized to the Schneiderian membrane (SM), while very little bone formation was observed in the window and center regions of the sinus. New bone was distributed evenly in the control group sinuses.

CONCLUSION

Within the limitations of this study, it appeared that application of a high concentration of rhBMP-2 soaked onto a BCP carrier inhibited bone regeneration from the pristine bone and increased soft tissue swelling and inflammatory response at the early healing stage of sinus augmentation, although osteoinductive potential was found along the SM.

Comparison of a novel oxysterol molecule and rhBMP2 fusion rates in a rabbit posterolateral lumbar spine model

BACKGROUND CONTEXT

The nonunion rate after lumbar spinal fusion is as high as 25%. Recombinant human bone morphogenetic protein 2 (rhBMP2) has been used as a biological adjunct to promote bony fusion. However, recently there have been concerns about BMP2. Oxysterol 133 (Oxy133) has been shown to promote excellent fusion rates in rodent lumbar spine models and offers a potential alternative to rhBMP2.

PURPOSE

The purpose of this study was to compare the fusion rate of rhBMP2 and Oxy133 in a randomized controlled trial using a posterolateral lumbar rabbit spinal fusion model.

STUDY DESIGN

This was a randomized control animal study.

METHODS

Twenty-four male adult white New Zealand rabbits (3-3.5 kg) underwent bilateral posterolateral lumbar spinal fusion at L4-L5. Rabbits were divided into four groups: control (A), 30-μg rhBMP2 (B), 20-mg Oxy133 (C), and 60-mg Oxy133 (D). At 4 weeks, fusion was evaluated by fluoroscopy, and at 8 weeks, the rabbits were sacrificed and fusion was evaluated radiographically, by manual palpation, and with microcomputed tomography.

RESULTS

Fusion rates by radiographic analysis at 8 weeks were Group A, 40.0%; Group B, 91.7%; Group C, 91.7%; and Group D, 100%. Evaluation of fusion masses by manual palpation of excised spines after sacrifice showed the following fusion rates: Group A, 0%; Group B, 83.3%; Group C, 83.3%; and Group D, 90%. Microcomputed tomography scanning confirmed these findings.

CONCLUSIONS

These findings in a rabbit model demonstrate that both 20- and 60-mg Oxy133 doses promote fusion that is equivalent to fusion induced by 30-μg rhBMP2 and significantly greater than the control group. The present findings confirm that Oxy133 is a promising candidate for therapeutic development as an alternative to rhBMP2 to promote spinal fusion.

Regenerative Approach to Bilateral Rostral Mandibular Reconstruction in a Case Series of Dogs

Extensive rostral mandibulectomy in dogs typically results in instability of the mandibles that may lead to malocclusion, difficulty in prehension, mastication, and pain of the temporomandibular joint. Large rostral mandibular defects are challenging to reconstruct due to the complex geometry of this region. In order to restore mandibular continuity and stability following extensive rostral mandibulectomy, we developed a surgical technique using a combination of intraoral and extraoral approaches, a locking titanium plate, and a compression resistant matrix (CRM) infused with rhBMP-2. Furthermore, surgical planning that consisted of computed tomographic (CT) scanning and 3D model printing was utilized. We describe a regenerative surgical technique for immediate or delayed reconstruction of critical-size rostral mandibular defects in five dogs. Three dogs had healed with intact gingival covering over the mandibular defect and had immediate return to normal function and occlusion. Two dogs had the complication of focal plate exposure and dehiscence, which was corrected with mucosal flaps and suturing; these dogs have since healed with intact gingival covering over the mandibular defect. Mineralized tissue formation was palpated clinically within 2 weeks and solid bone formation within 3 months. CT findings at 6 months postoperatively demonstrated that the newly regenerated mandibular bone had increased in mineral volume with evidence of integration between the native bone, new bone, and CRM compared to the immediate postoperative CT. We conclude that rostral mandibular reconstruction using a regenerative approach provides an excellent solution for restoring mandibular continuity and preventing mandibular instability in dogs.

BMP-2-transduced human bone marrow stem cells enhance neo-bone formation in a rat critical-sized femur defect

Synthetic graft materials are considered as possible substitutes for cancellous bone, but lack osteogenic and osteoinductive properties. In this study, we investigated how composite scaffolds of βTCP containing osteogenic human bone marrow mesenchymal stem cells (hBMSCs) and osteoinductive bone morphogenetic protein-2 (BMP-2) influenced the process of fracture healing. hBMSCs were loaded into βTCP scaffolds 24 h before implantation in a rat critical-sized bone defect. hBMSCs were either stimulated with rhBMP-2 or transduced with BMP-2 by gene transfer. The effect of both protein stimulation and gene transfer was compared for osteogenic outcome. X-rays were conducted at weeks 0, 1, 3, 6, 9 and 12 post-operatively. In addition, bone-labelling fluorochromes were applied at 0, 3, 6 and 9 weeks. Histological analysis was performed for the amount of callus tissue and cartilage formation. At 6 weeks, the critical-sized defect in 33% of the rats treated with the Ad-BMP-2-transduced hBMSCs/βTCP scaffolds was radiographically bridged. In contrast, in only 10% of the rats treated with rhBMP2/hBMSCs, 12 weeks post-treatment, the bone defect was closed in all treated rats of the Ad-BMP-2 group except for one. Histology showed significantly higher amounts of callus formation in both Ad-BMP-2- and rhBMP-2-treated rats. The amount of neocartilage was less pronounced in both BMP-2-related groups. In summary, scaffolds with BMP-2-transduced hBMSCs performed better than those with the rhBMP2/hBMSCs protein. These results suggest that combinations of osteoconductive biomaterials with genetically modified MSCs capable of secreting osteoinductive proteins may represent a promising alternative for bone regeneration. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of dual treatment with SDF-1 and BMP-2 on ectopic and orthotopic bone formation

Purposes

The potent stem cell homing factor stromal cell-derived factor-1 (SDF-1) actively recruits mesenchymal stem cells from circulation and from local bone marrow. It is well established that bone morphogenetic protein-2 (BMP-2) induces ectopic and orthotopic bone formation. However, the exact synergistic effects of BMP-2 and SDF-1 in ectopic and orthotopic bone regeneration models have not been fully investigated. The purpose of this study was to evaluate the potential effects of simultaneous SDF-1 and BMP-2 treatment on bone formation.

Materials and Methods

Various doses of SDF-1 were loaded onto collagen sponges with or without BMP-2.These sponges were implanted into subcutaneous pockets and critical-size calvarial defects in C57BL/6 mice. The specimens were harvested 4 weeks post-surgery and the degree of bone formation in specimens was evaluated by histomorphometric and radiographic density analyses. Osteogenic potential and migration capacity of mesenchymal cells and capillary tube formation of endothelial cells following dual treatment with SDF-1 and BMP-2 were evaluated with in vitro assays.

Results

SDF-1-only-treated implants did not yield significant in vivo bone formation and SDF-1 treatment did not enhance BMP-2-induced ectopic and orthotopic bone regeneration. In vitro experiments showed that concomitant use of BMP-2 and SDF-1 had no additive effect on osteoblastic differentiation, cell migration or angiogenesis compared to BMP-2 or SDF-1 treatment alone.

Conclusions

These findings imply that sequence-controlled application of SDF-1 and BMP-2 must be further investigated for the enhancement of robust osteogenesis in bone defects.

Sequential delivery of BMP-2 and BMP-7 for bone regeneration using a heparinized collagen membrane

To investigate the effect of the sequential delivery of bone morphogenetic proteins BMP-2 and BMP-7 on bone regeneration in rat calvarial defects (40 Sprague-Dawley rats, 8mm defect size), all animals were treated with a hydroxyapatite (HA)/tricalcium phosphate (TCP) bone graft covered with a collagen membrane. The experimental groups were as follows: (1) control group: unmodified collagen (no treatment); (2) BMP-2 group: 5 μg of BMP-2; (3) hep-BMP-7 group: 5 μg BMP-7 chemically bound to heparinized collagen; and (4) BMP-2/hep-BMP-7 group: 2.5 μg BMP-7 bound to heparinized collagen and subsequently treated with 2.5 μg BMP-2. Defect healing was examined at 2 and 8 weeks after surgery. The BMP-2 group showed the largest new bone area at week 2 (29.3 ± 7.3%; P = 0.009); new bone areas in the hep-BMP-7 and BMP-2/hep-BMP-7 groups were similar (11.8 ± 3.4% and 12.9 ± 5.71%, respectively; P = 0.917). After 8 weeks, the BMP-2/hep-BMP-7 group showed the largest new bone area (43.3 ± 6.2%), followed by the BMP-2 and hep-BMP-7 groups (P = 0.013). Accordingly, in comparison with single deliveries of BMP-2 and BMP-7, sequential delivery of BMP-2 and BMP-7 using a heparinized collagen membrane significantly induced new bone formation with a smaller quantity of BMP-2 in rat calvarial defects.

Templated repair of long bone defects in rats with bioactive spiral-wrapped electrospun amphiphilic polymer/hydroxyapatite scaffolds

Effective repair of critical-size long bone defects presents a significant clinical challenge. Electrospun scaffolds can be exploited to deliver protein therapeutics and progenitor cells, but their standalone application for long bone repair has not been explored. We have previously shown that electrospun composites of amphiphilic poly(d,l-lactic acid)-co-poly(ethylene glycol)-co-poly(d,l-lactic acid) (PELA) and hydroxyapatite (HA) guide the osteogenic differentiation of bone marrow stromal cells (MSCs), making these scaffolds uniquely suited for evaluating cell-based bone regeneration approaches. Here we examine whether the in vitro bioactivity of these electrospun scaffolds can be exploited for long bone defect repair, either through the participation of exogenous MSCs or through the activation of endogenous cells by a low dose of recombinant human bone morphogenetic protein-2 (rhBMP-2). In critical-size rat femoral segmental defects, spiral-wrapped electrospun HA-PELA with preseeded MSCs resulted in laminated endochondral ossification templated by the scaffold across the longitudinal span of the defect. Using GFP labeling, we confirmed that the exogenous MSCs adhered to HA-PELA survived at least 7 days postimplantation, suggesting direct participation of these exogenous cells in templated bone formation. When loaded with 500 ng of rhBMP-2, HA-PELA spirals led to more robust but less clearly templated bone formation than MSC-bearing scaffolds. Both treatment groups resulted in new bone bridging over the majority of the defect by 12 weeks. This study is the first demonstration of a standalone bioactive electrospun scaffold for templated bone formation in critical-size long bone defects.

Myoconductive and osteoinductive free-standing polysaccharide membranes

Free-standing (FS) membranes have increasing applications in the biomedical field as drug delivery systems for wound healing and tissue engineering. Here, we studied the potential of free-standing membranes made by the layer-by-layer assembly of chitosan and alginate to be used as a simple biomimetic system of the periosteum. The design of a periosteum-like membrane implies the elaboration of a thick membrane suitable for both muscle and bone formation. Our aim was to produce well-defined ∼50 μm thick polysaccharide membranes that could be easily manipulated, were mechanically resistant, and would enable both myogenesis and osteogenesis in vitro and in vivo. The membranes were chemically crosslinked to improve their mechanical properties. Crosslinking chemistry was followed via Fourier transform infrared spectroscopy and the mechanical properties of the membranes were assessed using dynamic mechanical analysis. The loading and release of the potent osteoinductive growth factor bone morphogenetic protein 2 (BMP-2) inside and outside of the FS membrane was followed by fluorescence spectroscopy in a physiological buffer over 1 month. The myogenic and osteogenic potentials of the membranes in vitro were assessed using BMP-2-responsive skeletal myoblasts. Finally, their osteoinductive properties in vivo were studied in a preliminary experiment using a mouse ectopic model. Our results showed that the more crosslinked FS membranes enabled a more efficient myoblast differentiation in myotubes. In addition, we showed that a tunable amount of BMP-2 can be loaded into and subsequently released from the membranes, depending on the crosslinking degree and the initial BMP-2 concentration in solution. Only the more crosslinked membranes were found to be osteoinductive in vivo. These polysaccharide-based membranes have strong potential as a periosteum-mimetic scaffold for bone tissue regeneration.

Effects of low dose FGF-2 and BMP-2 on healing of calvarial defects in old mice

There is an age-associated reduction in the bone healing activity of bone morphogenetic protein-2 (BMP-2) that is currently addressed by administering higher doses of BMP-2 in elderly patients. The unwanted medical complications from high dose BMP-2 motivated this investigation to determine whether the addition of a low dose of fibroblast growth factor 2 (FGF-2) could enhance the ability of a lower dose of BMP-2 to heal calvarial bone defects in old mice (18-20 months old). FGF-2 (5 ng) and BMP-2 (2 μg) were administered by a controlled release two-phase biomaterial scaffold placed into the bone defect. FGF-2 released more rapidly and completely in vitro than BMP-2 (40% vs 2%). In vivo, both BMP-2 and FGF-2+BMP-2 groups formed more new bone in calvarial defects than scaffold alone (p < 0.001) or FGF-2 only groups (p < 0.01). The overall total volume of new bone was not statistically increased by the addition of FGF-2 to BMP-2 as measured by microCT, but the pattern of bone deposition was different. In old mice, but not young, there was enhanced bony fill in the central bone defect area when the BMP-2 was supplemented with FGF-2. Histological analysis of the center of the defect revealed an increased bone volume (%BV/TV (p = 0.004)) from the addition of FGF-2. These studies suggest that combining a low dose of FGF-2 with a low dose of BMP-2 has the potential to increase bone healing in old mice relative to BMP-2 alone.

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.

Transforming growth factor beta 1 augments calvarial defect healing and promotes suture regeneration

BACKGROUND

Repair of complex cranial defects is hindered by a paucity of appropriate donor tissue. Bone morphogenetic protein 2 (BMP2) and transforming growth factor beta 1 (TGFβ1) have been shown separately to induce bone formation through physiologically distinct mechanisms and potentially improve surgical outcome for cranial defect repair by obviating the need for donor tissue. We hypothesize that a combination of BMP2 and TGFβ1 would improve calvarial defect healing by augmenting physiologic osteogenic mechanisms.

METHODS/RESULTS

Coronal suturectomies (3×15 mm) were performed in 10-day-old New Zealand White rabbits. DermaMatrix™ (3×15mm) patterned with four treatments (vehicle, 350 ng BMP2, 200 ng TGFβ1, or 350 ng BMP2+200 ng TGFβ1) was placed in suturectomy sites and rabbits were euthanized at 6 weeks of age. Two-dimensional (2D) defect healing, bone volume, and bone density were quantified by computed tomography. Regenerated bone was qualitatively assessed histologically. One-way analysis of variance revealed significant group main effects for all bone quantity measures. Analysis revealed significant differences in 2D defect healing, bone volume, and bone density between the control group and all treatment groups, but no significant differences were detected among the three growth factor treatment groups. Qualitatively, TGFβ1 treatment produced bone with morphology most similar to native bone. TGFβ1-regenerated bone contained a suture-like tissue, growing from the lateral edge of the defect margin toward the midline. Unique to the BMP2 treatment group, regenerated bone contained lacunae with chondrocytes, demonstrating the presence of endochondral ossification.

CONCLUSIONS/SIGNIFICANCE

Total healing in BMP2 and TGFβ1 treatment groups is not significantly different. The combination of BMP2+TGFβ1 did not significantly increase bone healing compared with treatment with BMP2 or TGFβ1 alone postoperatively at 4 weeks. We highlight the potential use of TGFβ1 to regenerate calvarial bone and cranial sutures. TGFβ1 therapy significantly augmented bony defect healing at an earlier time point when compared with control, regenerated bone along the native intramembranous ossification pathway, and (unlike BMP2 alone or in combination with TGFβ1) permitted normal suture reformation. We propose a novel method of craniofacial bone regeneration using low-dose, spatially controlled growth factor therapies to minimize potentially harmful effects while maximizing local bioavailability and regenerating native tissues.

Disequilibrium of BMP2 levels in the breast stem cell niche launches epithelial transformation by overamplifying BMPR1B cell response

Understanding the mechanisms of cancer initiation will help to prevent and manage the disease. At present, the role of the breast microenvironment in transformation remains unknown. As BMP2 and BMP4 are important regulators of stem cells and their niches in many tissues, we investigated their function in early phases of breast cancer. BMP2 production by tumor microenvironment appeared to be specifically upregulated in luminal tumors. Chronic exposure of immature human mammary epithelial cells to high BMP2 levels initiated transformation toward a luminal tumor-like phenotype, mediated by the receptor BMPR1B. Under physiological conditions, BMP2 controlled the maintenance and differentiation of early luminal progenitors, while BMP4 acted on stem cells/myoepithelial progenitors. Our data also suggest that microenvironment-induced overexpression of BMP2 may result from carcinogenic exposure. We reveal a role for BMP2 and the breast microenvironment in the initiation of stem cell transformation, thus providing insight into the etiology of luminal breast cancer.

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High BMP2 levels are provided by endothelial and stroma cells in luminal tumors

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Chronic exposure to high BMP2 levels initiate mammary epithelial transformation

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Luminal tumors likely arise from an amplified BMP2/BMPR1B-mediated normal response

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Radiation and bisphenols perturbed BMP2 production by the mammary niche stroma

The inhibitory effect of zoledronate on early-stage osteoinduction by recombinant human bone morphogenetic protein 2 in an osteoporosis model

This study evaluated the effect of the combined treatment of intravenous zoledronic acid (ZA, 0.08 mg/kg) and rhBMP-2 (5 µg) on osteogenesis in a calvarial defect model of ovariectomized SD rats. New bone formation was evaluated 4 or 8 weeks after calvarial defect implantation using micro-CT and histology. Micro-CT results revealed that the rhBMP-2 group showed significantly higher calvarial defect coverage ratio compared with the ZA + rhBMP-2 group at 4 weeks. In addition, bone formation indices were significantly lower in ZA + rhBMP-2 group when compared with the rhBMP-2 group after 4 weeks, which indicates a negative effect of ZA on the initial bone formation and the bone quality. At 8 weeks, the negative effect induced by ZA treatment was alleviated as time passed. Histological examination showed similar results to the micro-CT measurements. In conclusion, although ZA treatment lowered the new bone formation induced by rhBMP-2 initially, as time passed, the negative effect was decreased.

Local drug delivery for enhancing fracture healing in osteoporotic bone

Fragility fractures can cause significant morbidity and mortality in patients with osteoporosis and inflict a considerable medical and socioeconomic burden. Moreover, treatment of an osteoporotic fracture is challenging due to the decreased strength of the surrounding bone and suboptimal healing capacity, predisposing both to fixation failure and non-union. Whereas a systemic osteoporosis treatment acts slowly, local release of osteogenic agents in osteoporotic fracture would act rapidly to increase bone strength and quality, as well as to reduce the bone healing period and prevent development of a problematic non-union. The identification of agents with potential to stimulate bone formation and improve implant fixation strength in osteoporotic bone has raised hope for the fast augmentation of osteoporotic fractures. Stimulation of bone formation by local delivery of growth factors is an approach already in clinical use for the treatment of non-unions, and could be utilized for osteoporotic fractures as well. Small molecules have also gained ground as stable and inexpensive compounds to enhance bone formation and tackle osteoporosis. The aim of this paper is to present the state of the art on local drug delivery in osteoporotic fractures. Advantages, disadvantages and underlying molecular mechanisms of different active species for local bone healing in osteoporotic bone are discussed. This review also identifies promising new candidate molecules and innovative approaches for the local drug delivery in osteoporotic bone.

The BMP2 antagonist inhibitor L51P enhances the osteogenic potential of BMP2 by simultaneous and delayed synergism

Bone morphogenetic protein 2 (BMP2) is a potent osteoinductive cytokine that plays crucial roles in bone repair. However, large amounts of BMP2 are required to induce sufficient bone formation in humans possibly due to a feedback response of BMP antagonists. The engineered BMP2 variant L51P is deficient in BMP receptor type I activation but maintains affinity for BMP antagonists and can allow for the inactivation of BMP antagonists, and eventually enhance BMP2 action. As hypothesized, simultaneous addition of L51P enhanced the BMP2-induced osteogenesis. To test the ability of L51P to competitively inactivate BMP antagonists, cell binding affinity of BMP2 ligands was investigated in the presence or absence of L51P. Because the BMP antagonists were highly expressed 3 days after exogenous BMP2 stimulation, we collected supernatants from 3-day stimulated cell cultures and used as condition culture media (CM). The results showed a significant decrease in the cell binding of BMP2 ligands when cells were incubated with exogenous BMP2 and CM, whereas L51P addition competitively rescued the suppression of BMP2-to-cell binding induced by CM incubation. In a delayed experimental model, L51P was applied 3 days after exogenous BMP2 stimulation and we could observe a striking enhancement of the BMP2-induced SMAD-1/5/8 phosphorylation and luciferase activity of the Id1 promoter compared to the simultaneous addition of the two factors. These findings provide a deeper insight into the cellular and molecular mechanisms involved in the effect of L51P in suppressing the BMP antagonists and enhancing BMP activity. Additionally, these results demonstrate that L51P is a promising down regulator of BMP-induced negative feedback, which could have a significant impact in future applications of BMP2 in research and clinical settings.

Novel osteoinductive photo-cross-linkable chitosan-lactide-fibrinogen hydrogels enhance bone regeneration in critical size segmental bone defects

The purpose of this study was to develop and characterize a novel photo-cross-linkable chitosan-lactide-fibrinogen (CLF) hydrogel and evaluate the efficacy of bone morphogenetic protein-2 (BMP-2) containing a CLF hydrogel for osteogenesis in vitro and in vivo. We synthesized the CLF hydrogels and characterized their chemical structure, degradation rate, compressive modulus and in vitro BMP-2 release kinetics. We evaluated bioactivities of the BMP-2 containing CLF hydrogels (0, 50, 100 and 500ngml(-1)) in vitro using W-20-17 preosteoblast mouse bone marrow stromal cells and C2C12 mouse myoblast cells. The effect of BMP-2 containing CLF gels (0, 0.5, 1, 2 and 5μg) on bone formation was evaluated using rat critical size segmental bone defects for 4weeks. Fourier transform infrared spectroscopy spectra and scanning electron microscopy images showed chemical and structural changes by the addition of fibrinogen into the chitosan-lactide copolymer. The incorporation of fibrinogen molecules significantly increased the compressive modulus of the hydrogels. The in vitro BMP-2 release study showed initial burst releases from the CLF hydrogels followed by sustained releases, regardless of the concentration of the BMP-2 over 4weeks. Cells in all groups were viable in the presence of the hydrogels regardless of BMP-2 doses, indicating non-cytotoxicity of hydrogels. Alkaline phosphate activity and mineralization of cells exhibited dose dependence on BMP-2 containing CLF hydrogels. Radiography, microcomputed tomography and histology confirmed that the BMP-2 containing CLF hydrogels prompted neo-osteogenesis and accelerated healing of the defects in a dose-dependent manner. Thus the CLF hydrogel is a promising delivery system of growth factors for bone regeneration.

Engineering TGF-β superfamily ligands for clinical applications

TGF-β superfamily ligands govern normal tissue development and homeostasis, and their dysfunction is a hallmark of many diseases. These ligands are also well defined both structurally and functionally. This review focuses on TGF-β superfamily ligand engineering for therapeutic purposes, in particular for regenerative medicine and musculoskeletal disorders. We describe the key discovery that structure-guided mutation of receptor-binding epitopes, especially swapping of these epitopes between ligands, results in new ligands with unique functional properties that can be harnessed clinically. Given the promising results with prototypical engineered TGF-β superfamily ligands, and the vast number of such molecules that remain to be produced and tested, this strategy is likely to hold great promise for the development of new biologics.

Combination of BMP2 and MSCs significantly increases bone formation in the rat arterio-venous loop model

INTRODUCTION

In this study the induction of bone formation in an axially vascularized bone matrix using mesenchymal stem cells (MSCs) and application of bone morphogenetic protein 2 (BMP2) was analyzed in the arteriovenous loop (AVL) model.

MATERIALS AND METHODS

An AVL was created in the medial thigh of 42 rats and placed in a porous titanium chamber filled with a particulated porous hydroxyapatite and beta-tricalcium phosphate matrix and fibrin. In group A the fibrin was loaded with 5×10(6) DiI-stained fibrin gel-immobilized primary MSCs from syngenic Lewis rats, in group B the matrix was loaded with 60 μg/mL BMP2 and in group C both, BMP2 and MSCs were applied at implantation time point. After 6 and 12 weeks, specimens were investigated by means of histological, morphometrical, and micro-computed tomography analysis.

RESULTS

After implantation of an AVL a dense vascular network was visible in all groups. In group A, newly generated bone islands were detected in the periphery of the main vascular axis. Using BMP2 alone (group B), small islands of newly formed bone were visible evenly distributed in all parts of the constructs. In group C nearly the whole matrix was interspersed with bone formations. In all groups there was an increase of bone formation between the 6 and 12 weeks explantation time points.

CONCLUSIONS

This study demonstrates for the first time the successful generation of axially vascularized bone substitutes using MSCs and BMP2 in the AVL rat model using a one step procedure. Using the combination of BMP2 and MSCs there was a significant increase of bone formations detectable compared to the BMP2 or MSCs alone groups.

Oxidized alginate hydrogels for bone morphogenetic protein-2 delivery in long bone defects

Autograft treatment of large bone defects and fracture non-unions is complicated by limited tissue availability and donor site morbidity. Polymeric biomaterials such as alginate hydrogels provide an attractive tissue engineering alternative due to their biocompatibility, injectability, and tunable degradation rates. Irradiated RGD-alginate hydrogels have been used to deliver proteins such as bone morphogenetic protein-2 (BMP-2), to promote bone regeneration and restoration of function in a critically sized rat femoral defect model. However, slow degradation of irradiated alginate hydrogels may impede integration and remodeling of the regenerated bone to its native architecture. Oxidation of alginate has been used to promote degradation of alginate matrices. The objective of this study was to evaluate the effects of alginate oxidation on BMP-2 release and bone regeneration. We hypothesized that oxidized-irradiated alginate hydrogels would elicit an accelerated release of BMP-2, but degrade faster in vivo, facilitating the formation of higher quality, more mature bone compared to irradiated alginate. Indeed, oxidation of irradiated alginate did accelerate in vitro BMP-2 release. Notably, the BMP-2 retained within both constructs was bioactive at 26days, as observed by induction of alkaline phosphatase activity and positive Alizarin Red S staining of MC3T3-E1 cells. From the in vivo study, robust bone regeneration was observed in both groups through 12weeks by radiography, micro-computed tomography analyses, and biomechanical testing. Bone mineral density was significantly greater for the oxidized-irradiated alginate group at 8weeks. Histological analyses of bone defects revealed enhanced degradation of oxidized-irradiated alginate and suggested the presence of more mature bone after 12weeks of healing.

Sustained delivery of rhBMP-2 by means of poly(lactic-co-glycolic acid) microspheres: cranial bone regeneration without heterotopic ossification or craniosynostosis

BACKGROUND

Commercially available recombinant human bone morphogenetic protein 2 (rhBMP2) has demonstrated efficacy in bone regeneration, but not without significant side effects. The authors used rhBMP2 encapsulated in poly(lactic-co-glycolic acid) (PLGA) microspheres placed in a rabbit cranial defect model to test whether low-dose, sustained delivery can effectively induce bone regeneration.

METHODS

The rhBMP2 was encapsulated in 15% PLGA using a double-emulsion, solvent extraction/evaporation technique, and its release kinetics and bioactivity were tested. Two critical-size defects (10 mm) were created in the calvaria of New Zealand white rabbits (5 to 7 months of age, male and female) and filled with a collagen scaffold containing either (1) no implant, (2) collagen scaffold only, (3) PLGA-rhBMP2 (0.1 μg per implant), or (4) free rhBMP2 (0.1 μg per implant). After 6 weeks, the rabbits were killed and defects were analyzed by micro-computed tomography, histology, and finite element analysis.

RESULTS

The rhBMP2 delivered by means of bioactive PLGA microspheres resulted in higher volumes and surface area coverage of new bone than an equal dose of free rhBMP2 by micro-computed tomography (p=0.025 and p=0.025). Finite element analysis indicated that the mechanical competence using the regional elastic modulus did not differ with rhBMP2 exposure (p=0.70). PLGA-rhBMP2 did not demonstrate heterotopic ossification, craniosynostosis, or seroma formation.

CONCLUSIONS

Sustained delivery by means of PLGA microspheres can significantly reduce the rhBMP2 dose required for de novo bone formation. Optimization of the delivery system may be a key to reducing the risk for recently reported rhBMP2-related adverse effects.

An activin A/BMP2 chimera, AB204, displays bone-healing properties superior to those of BMP2

Recombinant bone morphogenetic protein 2 (rhBMP2) has been used clinically to treat bone fractures in human patients. However, the high doses of rhBMP2 required for a therapeutic response can cause undesirable side effects. Here, we demonstrate that a novel Activin A/BMP2 (AB2) chimera, AB204, promotes osteogenesis and bone healing much more potently and effectively than rhBMP2. Remarkably, 1 month of AB204 treatment completely heals tibial and calvarial defects of critical size in mice at a concentration 10-fold lower than a dose of rhBMP2 that only partially heals the defect. We determine the structure of AB204 to 2.3 Å that reveals a distinct BMP2-like fold in which the Activin A sequence segments confer insensitivity to the BMP2 antagonist Noggin and an affinity for the Activin/BMP type II receptor ActRII that is 100-fold greater than that of BMP2. The structure also led to our identification of a single Activin A-derived amino acid residue, which, when mutated to the corresponding BMP2 residue, resulted in a significant increase in the affinity of AB204 for its type I receptor BMPRIa and a further enhancement in AB204's osteogenic potency. Together, these findings demonstrate that rationally designed AB2 chimeras can provide BMP2 substitutes with enhanced potency for treating non-union bone fractures.

A review of the current published spinal literature regarding bone morphogenetic protein-2: an insight into potential bias

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a potent biologic agent that carries both osteoinductive and osteoconductive properties. Its potential as an autologous bone graft substitute in spine surgery led to its approval by the United States Food and Drug Administration (FDA) in 2002 following a series of industry-sponsored trials. Although approved for a single level anterior lumbar interbody fusion from L4-S1 with a proprietary cage, the off-label use of rhBMP-2 rapidly escalated. Soon thereafter, reports of serious and potentially life-threatening complications associated with rhBMP-2 began emerging, which sparked concerns with regards to potential bias in the original FDA trials. Ultimately, an independent review of all published and unpublished data on the safety and effectiveness of rhBMP-2 by the Yale University Open Data Access (YODA) Project determined that while rhBMP-2 is as effective as iliac crest bone graft (ICBG) in potentiating spinal fusion, there was significant bias and conflicts of interests that resulted in an underreporting of complications in the original industry-sponsored trials.

BMP-2 encapsulated polysaccharide nanoparticle modified biphasic calcium phosphate scaffolds for bone tissue regeneration

Bone morphology protein-2 (BMP-2) encapsulated chitosan/chondrotin sulfate nanoparticles (CHI/CS NPs) are developed to enhance ectopic bone formation on biphasic calcium phosphate (BCP) scaffolds. BMP-2 contained CHI/CS NPs were prepared by a simple and mild polyelectrolyte complexation process. It does not involve harsh organic solvents and high temperature, and therefore retain growth factors activity. These NPs were immobilized on BCP scaffolds, and realize the sustained release of growth factors from the scaffolds. The bare BCP scaffolds, NP loaded scaffolds (BCP-NP), and NP loaded and polydopamine coated scaffolds (BCP-Dop-NP) were seeded with bone marrow stroma cells (BMSC) to evaluate the osteoinductivity of the scaffolds. BMSC culture results indicate that all scaffolds favor cell adhesion, proliferation, differentiation. Afterwards, the bare BCP, BCP-NP, and BCP-Dop-NP scaffolds were implanted into rabbits intramuscularly to evaluate the ectopic bone formation of scaffolds. In vivo results indicate that the BCP-NP and BCP-Dop-NP scaffolds enhance more ectopic bone formation than the bare BCP scaffolds. Both the in vitro and in vivo results demonstrate that BMP-2 encapsulated polysaccharide NPs are effective to improve the osteoinductivity of the scaffolds. In addition, BCP-NP scaffolds induce more bone formation than BCP-Dop-NP scaffolds. This is because BCP-NP scaffolds harness the intrinsic osteoinductivity BCP and BMP-2, whereas BCP-Dop-NP scaffolds have polydopamine coatings that inhibit the surfaces biological features of BCP scaffolds, and therefore weaken the bone formation ability of scaffolds.

A novel osteogenic oxysterol compound for therapeutic development to promote bone growth: activation of hedgehog signaling and osteogenesis through smoothened binding

Osteogenic factors are often used in orthopedics to promote bone growth, improve fracture healing, and induce spine fusion. Osteogenic oxysterols are naturally occurring molecules that were shown to induce osteogenic differentiation in vitro and promote spine fusion in vivo. The purpose of this study was to identify an osteogenic oxysterol more suitable for clinical development than those previously reported, and evaluate its ability to promote osteogenesis in vitro and spine fusion in rats in vivo. Among more than 100 oxysterol analogues synthesized, Oxy133 induced significant expression of osteogenic markers Runx2, osterix (OSX), alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin (OCN) in C3H10T1/2 mouse embryonic fibroblasts and in M2-10B4 mouse marrow stromal cells. Oxy133-induced activation of an 8X-Gli luciferase reporter, its direct binding to Smoothened, and the inhibition of Oxy133-induced osteogenic effects by the Hedgehog (Hh) pathway inhibitor, cyclopamine, demonstrated the role of Hh pathway in mediating osteogenic responses to Oxy133. Oxy133 did not stimulate osteogenesis via BMP or Wnt signaling. Oxy133 induced the expression of OSX, BSP, and OCN, and stimulated robust mineralization in primary human mesenchymal stem cells. In vivo, bilateral spine fusion occurred through endochondral ossification and was observed in animals treated with Oxy133 at the fusion site on X-ray after 4 weeks and confirmed with manual assessment, micro-CT (µCT), and histology after 8 weeks, with equal efficiency to recombinant human bone morphogenetic protein-2 (rhBMP-2). Unlike rhBMP-2, Oxy133 did not induce adipogenesis in the fusion mass and resulted in denser bone evidenced by greater bone volume/tissue volume (BV/TV) ratio and smaller trabecular separation. Findings here suggest that Oxy133 has significant potential as an osteogenic molecule with greater ease of synthesis and improved time to fusion compared to previously studied oxysterols. Small molecule osteogenic oxysterols may serve as the next generation of bone anabolic agents for therapeutic development.

Sustained delivery of biomolecules from gelatin carriers for applications in bone regeneration

Local delivery of therapeutic biomolecules to stimulate bone regeneration has matured considerably during the past decades, but control over the release of these biomolecules still remains a major challenge. To this end, suitable carriers that allow for tunable spatial and temporal delivery of biomolecules need to be developed. Gelatin is one of the most widely used natural polymers for the controlled and sustained delivery of biomolecules because of its biodegradability, biocompatibility, biosafety and cost–effectiveness. The current study reviews the applications of gelatin as carriers in form of bulk hydrogels, microspheres, nanospheres, colloidal gels and composites for the programmed delivery of commonly used biomolecules for applications in bone regeneration with a specific focus on the relationship between carrier properties and delivery characteristics.

Effect of Intermittent Administration of Teriparatide (Parathyroid Hormone 1-34) on Bone Morphogenetic Protein-Induced Bone Formation in a Rat Model of Spinal Fusion

BACKGROUND

Although clinical bone morphogenetic protein (BMP) therapy is effective at enhancing bone formation in patients managed with spinal arthrodesis, the required doses are very high. Teriparatide (parathyroid hormone 1-34) is approved by the U.S. Food and Drug Administration to treat osteoporosis and is a potent anabolic agent. In this study, intermittent administration of parathyroid hormone 1-34 combined with transplantation of BMP was performed to elucidate the effect of parathyroid hormone 1-34 on the fusion rate and quality of newly formed bone in a rat model.

METHODS

A total of forty-eight male Sprague-Dawley rats underwent posterolateral lumbar spinal arthrodesis with one of three different treatments with recombinant human (rh) BMP-2: (1) 0 μg (control), (2) 2 μg (low dose), or (3) 50 μg (high dose). Each of the rhBMP-2 treatments was studied in combination with intermittent injections of either parathyroid hormone 1-34 (180 μg/kg/wk) or saline solution starting two weeks before the operation and continuing until six weeks after the operation. Osseous fusion was assessed with use of radiographs and a manual palpation test. Microstructural indices of the newly formed bone were evaluated with use of micro-computed tomography. The serum markers of bone metabolism were also quantified.

RESULTS

The fusion rate in the group treated with 2 μg of rhBMP-2 significantly increased (from 57% to 100%) with the administration of parathyroid hormone 1-34 (p < 0.05). The fusion rates in the other groups did not change significantly with the administration of parathyroid hormone 1-34. The bone volume density of the newly formed bone significantly increased in both the 2-μg and 50-μg rhBMP-2 treatment groups with the administration of parathyroid hormone 1-34 (p < 0.01). Micro-computed tomography scans of the newly formed bone clearly demonstrated an abundance of trabecular bone formation in the group treated with parathyroid hormone 1-34. In addition, serum levels of osteocalcin were significantly increased in the parathyroid hormone 1-34 treatment group.

CONCLUSIONS

Intermittent administration of parathyroid hormone 1-34 significantly increased fusion rates in the group treated with low-dose rhBMP-2, and it improved the quality of the newly formed bone in both the high and low-dose groups in a rat model of rhBMP-2-induced spinal fusion.

CLINICAL RELEVANCE

Our results suggest that the combined administration of rhBMP-2 and parathyroid hormone 1-34 may lead to efficient bone regeneration.

Controlled release of BMP-2 using a heparin-conjugated carrier system reduces in vivo adipose tissue formation

There is growing concern about unwanted effects associated with the clinical use of recombinant human bone morphogenetic protein-2 (rhBMP-2) at high concentrations, including cyst-like bone formation and excessive fatty marrow formation. We, therefore, evaluated the induction of mineralized/adipose tissue formation and the bone-healing pattern associated with the controlled release of E. coli-derived rhBMP-2 (ErhBMP-2) by a heparin-conjugated fibrin (HCF) system using ectopic and orthotopic in vivo models, respectively. In the ectopic transplantation model, mineralized tissue formed at the most superficial layer of the transplanted area and on the surfaces of grafted materials, and most of the interstitial space within the transplanted area was filled with excessive adipose tissue specifically at sites that received ErhBMP-2. However, sites that received ErhBMP-2 and HCF showed significantly increased mineralized tissue formation and decreased adipose tissue formation compared to the normal fibrin system with ErhBMP-2. In the orthotopic (calvarial defect) model, controlled release of ErhBMP-2 induced by HCF significantly reduced adipose tissue formation within the defect area compared to the clinically approved absorbable collagen sponge. From these results, it can be concluded that the use of a HCF system loaded with ErhBMP-2 may reduce adipose tissue formation and enhance mineralized tissue formation.

Characterization of the enhanced bone regenerative capacity of human periodontal ligament stem cells engineered to express the gene encoding bone morphogenetic protein 2

Human periodontal ligament stem cells (hPDLSCs) are considered an appropriate cell source for therapeutic strategies. The aims of this study were to investigate the sustainability of bone morphogenetic protein 2 (BMP2) secretion and the bone regenerative capacity of hPDLSCs that had been genetically modified to express the gene encoding BMP2 (BMP2). hPDLSCs isolated from healthy third molars were transduced using replication-deficient recombinant adenovirus (rAd) encoding BMP2 (hPDLSCs/rAd-BMP2), and the cellular characteristics and osteogenic potentials of hPDLSCs/rAd-BMP2 were analyzed both in vitro and in vivo. hPDLSCs/rAd-BMP2 successfully secreted BMP2, formed colonies, and expressed immunophenotypes similar to their nontransduced counterparts. As to their osteogenic potential, hPDLSCs/rAd-BMP2 formed greater mineralized nodules and exhibited significantly higher levels of expression of BMP2 and the gene encoding alkaline phosphatase, and formed more and better quality bone than other hPDLSC-containing or recombinant human BMP2-treated groups, being localized at the initial site until 8 weeks. The findings of the present study demonstrate that hPDLSCs/rAd-BMP2 effectively promote osteogenesis not only in vitro but also in vivo. The findings also suggest that hPDLSCs can efficiently carry and deliver BMP2, and that hPDLSCs/rAd-BMP2 could be used in an attractive novel therapeutic approach for the regeneration of deteriorated bony defects.

Methods to analyze bone regenerative response to different rhBMP-2 doses in rabbit craniofacial defects

Multiple assessment methods are available to evaluate the performance of engineered scaffolds in accepted bone healing animal models. Evaluation and comparison of these methods can aid in the planning of future animal studies, as well as, inform clinical assessments as the engineered scaffolds translate into clinical studies and applications. To evaluate multiple bone assessment techniques, bone regrowth potential of tyrosine-derived polycarbonate (TyrPC) scaffolds loaded with various dosages of recombinant human bone morphogenetic protein-2 (rhBMP-2) (0, 10, 25, and 50 μg) was assessed after 16 weeks in vivo in a rabbit calvarial model. Traditional X-ray radiography and micro-computed tomography (micro-CT) analyses were used to quantify the volume and density of regenerated bone. Histomorphometric analysis was performed as the traditional gold standard of evaluation. While these techniques are fairly standard in bone tissue engineering, we also investigated 64-slice CT, a tool more commonly used clinically, for comparison and to guide translational efforts. The 64-slice CT scans were carried out at 4 and 16 weeks to monitor temporal bone healing patterns. Study results indicated a clear dose-dependent response of increasing regenerated bone volume with rhBMP-2 loaded on the TyrPC scaffolds after 16 weeks of implantation. Significantly more bone formation was observed at the highest dose of rhBMP-2 (50 μg), which is 25-50% of the previously recommended dose (100-200 μg) for this defect. A significant difference was observed between the lowest and highest doses using radiographs (p<0.001), micro-CT (p=0.002), and CT (p<0.001) and a high correlation was found between techniques (R(2) values between 0.446 and 0.911). It was found that the number of animals required per group to detect significant dose effects ranged between 6 and 8 for the imaging methods while histomorphometric analysis would require 25 animals per group to detect similar differences (desired power=0.9, α=0.05). Radiographic analysis provided quantifiable % defect coverage and radio-opacity, micro-CT provided spatial volumetric and bone density measures, histomorphometry provided biological confirmation, and 64-slice CT allowed for establishing of clinically relevant translational guidelines. These methodologies allow for a standardized and comprehensive description of bone regeneration and provide guidelines for the planning of future preclinical and clinical studies.

Evaluation of rhBMP-2 and bone marrow derived stromal cell mediated bone regeneration using transgenic fluorescent protein reporter mice

The aim of the study is use of transgenic fluorescent protein reporter mouse models to understand the cellular processes in recombinant human bone morphogenetic protein-2 (rhBMP-2) mediated bone formation. Bilateral parietal calvarial bone defects in Col3.6Topaz transgenic fluorescent osteoblast reporter mouse were used to understand the bone formation in the presence and absence of rhBMP2 and/or Col3.6Cyan bone marrow derived stromal cells (BMSCs), using collagen-hydroxyapatite matrix (Healos) as a biomaterial. The bone regeneration was not confined to the site of BMP-2 implantation and significant bone formation was observed in the neighboring defect site. Osteogenic cellular activity with overlying alizarin complexone staining was observed in both the defects indicating host cell induced mineralization. However, implantation of BMSCs along with rhBMP-2 demonstrated a donor cell derived bone formation. The presence of rhBMP-2 did not support host cell recruitment in the presence of donor cells. This study demonstrates the potential of multiple fluorescent reporters to understand the cellular processes involved in the bone regeneration process using biomaterials, growth factors, and/or stem cells.

Complications with the use of bone morphogenetic protein 2 (BMP-2) in spine surgery

BACKGROUND CONTEXT

Recombinant human bone morphogenetic protein 2 (rhBMP-2) is a very potent osteogenic growth factor that has been used successfully in various spine fusions, obviating the need for autologous iliac crest bone graft harvest and therefore avoiding the associated morbidities.

PURPOSE

In the past few years, a tremendous increase in rhBMP-2 usage was noted, and concerns regarding costs, benefits, and safety issues were raised by many. The goal of this work was to provide a comprehensive review of the adverse events and complications associated with use of rhBMP-2.

STUDY DESIGN

Literature review.

METHODS

This is a review of the current literature on the reported adverse events, complications, and concerns associated with rhBMP-2 use.

RESULTS

This article discusses the wide spectrum of adverse outcomes related to rhBMP-2 use in the lumbar and the cervical spine; retrograde ejaculation, antibodies formation, postoperative radiculitis, postoperative nerve root injury, ectopic bone formation, vertebral osteolysis/edema, dysphagia and neck swelling, hematoma formation, interbody graft lucency, and wound healing complications are reviewed. Cost-related concerns, dosage considerations, carrier types, and theoretical carcinogenesis concerns were also presented.

CONCLUSIONS

Despite the excellent spinal fusion rates promoted by this powerful molecule, the increasingly reported adverse outcomes associated with bone morphogenetic protein usage have created real concerns. This article will provide the reader with a good understanding of the reported complications associated with rhBMP-2 use and ultimately help recognize its safety spectrum and limits for better clinical application.

Local strategies to prevent and treat osteoporosis

Despite advances in systemic osteoporosis therapeutic outcomes, management of fragility fractures and implant fixation in osteoporotic bone remain difficult clinical challenges. Low initial bone density and a prolonged healing response can lead to fracture nonunion and aseptic implant loosening. Local treatment strategies could be used to prevent fracture, accelerate healing, and increase implant fixation by locally stimulating anabolic pathways or inhibiting catabolic pathways. Local strategies under investigation include direct drug release from injectable materials or implant surface coatings. Common locally delivered drugs include bisphosphonates, parathyroid hormone, and bone morphogenetic proteins, yet additional compounds targeting novel pathways in bone biology are also being actively explored. Mechanical stimulation via low intensity pulsed ultrasound, alone or in combination with drug therapy, may also prove effective to promote local bone healing and implant fixation within osteoporotic bone.

Sequestration of rhBMP-2 into self-assembled polyelectrolyte complexes promotes anatomic localization of new bone in a porcine model of spinal reconstructive surgery

Efficient and therapeutically safe delivery of recombinant human bone morphogenetic protein 2 (rhBMP-2) continues to be a central issue in bone tissue engineering. Recent evidence indicates that layer-by-layer self-assembly of polyelectrolyte complexes (PECs) can be used to recreate synthetic matrix environments that would act as tuneable reservoirs for delicate biomolecules and cells. Although preliminary in vitro as well as small-animal in vivo studies support this premise, translation into clinically relevant bone defect volumes in larger animal models remains unreported. Here we explored the use of native heparin-based PEC, deposited on a hydrated alginate gel template, to load bioactive rhBMP-2 and to facilitate lumbar interbody spinal fusion in pigs. We observed that triple PEC deposits with the highest protein sequestration efficiency and immobilization capacity promoted higher volume of new bone formation when compared with single PEC with low sequestration efficiency and immobilization capacity. This also resulted in a significantly enhanced biomechanical stability of the fused spinal segment when compared with PEC carriers with relatively low protein sequestration and immobilization capacities (p<0.05). Most importantly, PEC carriers showed a more orderly pattern of new bone deposition and superior containment of bone tissue within implant site when compared to collagen sponge carriers. We conclude that this growth factor sequestration platform is effective in the healing of clinically relevant bone defect volume and could overcome some of the safety concerns and limitations currently associated with rhBMP-2 therapy such as excessive heterotopic ossification.

Ridge preservation using demineralized bone matrix gel with recombinant human bone morphogenetic protein-2 after tooth extraction: a randomized controlled clinical trial

PURPOSE

The aim of the present randomized controlled trial was to determine the safety and efficacy of injectable demineralized bone matrix (DBM) gel combined with recombinant human bone morphogenetic protein-2 (rhBMP-2) on alveolar ridge preservation after tooth extraction.

MATERIALS AND METHODS

A total of 69 patients were randomly assigned to either a test group (n = 35) or a control group (n = 34). In the test group, DBM, together with rhBMP-2 (0.05 mg/mL; rhBMP-2/DBM) was transplanted into the extraction sockets. The control group received DBM alone. The safety of rhBMP-2/DBM was evaluated by oral examination, serum chemistry, and hematologic examination. The radiographic changes in alveolar bone height and width were measured using computed tomography scans performed immediately after transplant and again 3 months thereafter.

RESULTS

Healing was uneventful in all subjects, with no anticipated adverse events and no clinically significant changes in the serum chemistry and hematologic findings. No meaningful immune response was found among the study groups. No significant difference was found in the radiographic changes of alveolar bone height and width (P > .05).

CONCLUSIONS

This new injectable biomaterial can be used easily and safely in clinical applications.