Simple and effective osteoinductive gene therapy by local injection of a bone morphogenetic protein-2-expressing recombinant adenoviral vector and FK506 mixture in rats

Local FK506 delivery induces osteogenesis in rat bone defect and rabbit spine fusion models

Bone grafting procedures are commonly used for the repair, regeneration, and fusion of bones in a wide range of orthopaedic surgeries, including large bone defects and spine fusion procedures. Autografts are the clinical gold standard, though recombinant human bone morphogenetic proteins (rhBMPs) are often used, particularly in difficult clinical situations. However, treatment with rhBMPs can have off-target effects and increase surgical costs, adding to patients' already high economic and mental burden. Recent studies have identified that FDA-approved immunosuppressant drug, FK506 (Tacrolimus), can also activate the BMP pathway by binding to its inhibitors. This study tested the hypothesis that FK506, as a standalone treatment, could induce osteogenic differentiation of human mesenchymal stromal cells (hMSCs), as well as functional bone formation in a rat segmental bone defect model and rabbit spinal fusion model. FK506 enhanced osteogenic differentiation and mineralization of hMSCs in vitro. Standalone treatment with FK506 delivered on a collagen sponge produced consistent bone bridging of a critically sized rat femoral defect with functional mechanical properties comparable to naïve bone. In a rabbit single level posterolateral spine fusion model, treatment with FK506 delivered on a collagen sponge successfully fused the L5-L6 vertebrae at rates comparable to rhBMP-2 treatment. These data demonstrate the ability of FK506 to induce bone formation in human cells and two challenging in vivo models, and indicate FK506 can be utilized to treat a variety of spine disorders.

Local FK506 delivery induces osteogenesis in in vivo rat bone defect and rabbit spine fusion models

Bone grafting procedures are commonly used for the repair, regeneration, and fusion of bones in in a wide range of orthopaedic surgeries, including large bone defects and spine fusion procedures. Autografts are the clinical gold standard, though recombinant human bone morphogenetic proteins (rhBMPs) are often used, particularly in difficult clinical situations. However, treatment with rhBMPs can have off-target effects and significantly increase surgical costs, adding to patients' already high economic and mental burden. Recent studies have identified that FDA-approved immunosuppressant drug, FK506 (Tacrolimus), can also activate the BMP pathway by binding to its inhibitors. This study tested the hypothesis that FK506, as a standalone treatment, could induce osteogenic differentiation of human mesenchymal stromal cells (hMSCs), as well as functional bone formation in a rat segmental bone defect model and rabbit spinal fusion model. FK506 potentiated the effect of low dose BMP-2 to enhance osteogenic differentiation and mineralization of hMSCs in vitro. Standalone treatment with FK506 delivered on a collagen sponge, produced consistent bone bridging of a rat critically-sized femoral defect with functional mechanical properties comparable to naïve bone. In a rabbit single level posterolateral spine fusion model, treatment with FK506 delivered on a collagen sponge successfully fused the L5-L6 vertebrae at rates comparable to rhBMP-2 treatment. These data demonstrate the ability of FK506 to induce bone formation in human cells and two challenging in vivo models, and indicate FK506 can be utilized either as a standalone treatment or in conjunction with rhBMP to treat a variety of spine disorders.

bmp-2 Gene-Transferred Skeletal Muscles with Needle-Type Electrodes as Efficient and Reliable Biomaterials for Bone Regeneration

BACKGROUND

Bone morphogenetic protein-2 (bmp-2) has a high potential to induce bone tissue formation in skeletal muscles. We developed a bone induction system in skeletal muscles using the bmp-2 gene through in vivo electroporation. Natural bone tissues with skeletal muscles can be considered potential candidates for biomaterials. However, our previous system using plate-type electrodes did not achieve a 100% success rate in inducing bone tissues in skeletal muscles. In this study, we aimed to enhance the efficiency of bone tissue formation in skeletal muscles by using a non-viral bmp-2 gene expression plasmid vector (pCAGGS-bmp-2) and needle-type electrodes.

METHODS

We injected the bmp-2 gene with pCAGGS-bmp-2 into the skeletal muscles of rats' legs and immediately placed needle-type electrodes there. Skeletal tissues were then observed on the 21st day after gene transfer using soft X-ray and histological analyses.

RESULTS

The use of needle-type electrodes resulted in a 100% success rate in inducing bone tissues in skeletal muscles. In contrast, the plate-type electrodes only exhibited a 33% success rate. Thus, needle-type electrodes can be more efficient and reliable for transferring the bmp-2 gene to skeletal muscles, making them potential biomaterials for repairing bone defects.

Delivery of Growth Factors to Enhance Bone Repair

The management of critical-sized bone defects caused by nonunion, trauma, infection, malignancy, pseudoarthrosis, and osteolysis poses complex reconstruction challenges for orthopedic surgeons. Current treatment modalities, including autograft, allograft, and distraction osteogenesis, are insufficient for the diverse range of pathology encountered in clinical practice, with significant complications associated with each. Therefore, there is significant interest in the development of delivery vehicles for growth factors to aid in bone repair in these settings. This article reviews innovative strategies for the management of critical-sized bone loss, including novel scaffolds designed for controlled release of rhBMP, bioengineered extracellular vesicles for delivery of intracellular signaling molecules, and advances in regional gene therapy for sustained signaling strategies. Improvement in the delivery of growth factors to areas of significant bone loss has the potential to revolutionize current treatment for this complex clinical challenge.

FK506 Induces Ligand-Independent Activation of the Bone Morphogenetic Protein Pathway and Osteogenesis

Osteoinductive bone morphogenetic proteins (BMPs), including BMP-2, have a unique capability of mediating bone formation both in orthotopic and ectopic locations. Immunosuppresive macrolides have been shown to potentiate BMP-2 activity through FKBP12, but these have yet to translate to effective osteoinductive therapies. Herein, we show the osteogenic activity of FK506 as a stand-alone agent in direct comparison to BMP-2 both in vitro and in vivo. FK506 was capable of producing stand-alone alkaline phosphatase induction in C2C12 cells comparable to that seen with rhBMP-2. FK506 treatment activated the BMP receptor, as shown by increased pSmad1/5 levels, and produced significantly higher mRNA levels of the early response genes in BMP and TGF-β pathways. Additionally, the FK506 induction of alkaline phosphatase was shown to be resistant to Noggin treatment. In vivo osteogenic activity of FK506 was tested by local delivery on a collagen sponge in an ectopic subcutaneous implantation model in the rat. Dose responses of FK506 showed increasing levels of ectopic mineralization comparable to the mineral volume produced by BMP-2 delivery. These findings suggest that the use of FK506 can enhance osteoblastic differentiation in vitro and can induce mineralization when delivered locally in vivo.

Determination of cell fate in skeletal muscle following BMP gene transfer by in vivo electroporation

We previously developed a novel method for gene transfer, which combined a non-viral gene expression vector with transcutaneous in vivo electroporation. We applied this method to transfer the bone morphogenetic protein (BMP) gene and induce ectopic bone formation in rat skeletal muscles. At present, it remains unclear which types of cells can differentiate into osteogenic cells after BMP gene transfer by in vivo electroporation. Two types of stem cells in skeletal muscle can differentiate into osteogenic cells: muscle-derived stem cells, and bone marrow-derived stem cells in the blood. In the present study, we transferred the BMP gene into rat skeletal muscles. We then stained tissues for several muscle-derived stem cell markers (e.g., Pax7, M-cadherin), muscle regeneration-related markers (e.g., Myod1, myogenin), and an inflammatory cell marker (CD68) to follow cell differentiation over time. Our results indicate that, in the absence of BMP, the cell population undergoes muscle regeneration, whereas in its presence, it can differentiate into osteogenic cells. Commitment towards either muscle regeneration or induction of ectopic bone formation appears to occur five to seven days after BMP gene transfer.

PDGF is a potent initiator of bone formation in a tissue engineered model of pathological ossification

Heterotopic ossification (HO) is a debilitating condition defined by the rapid formation of bone in soft tissues. What makes HO fascinating is first the rate at which bone is deposited, and second the fact that this bone is structurally and compositionally similar to that of a healthy adult. If the mechanisms governing HO are understood, they have the potential to be exploited for the development of potent osteoinductive therapies. With this aim, a tissue‐engineered skeletal muscle was used model to better understand the role of inflammation on this debilitating phenomenon. It was shown that myoblasts could be divided into two distinct populations: myogenic cells and undifferentiated ‘reserve’ cells. Gene expression analysis of myogenic and osteoregulatory markers confirmed that ‘reserve’ cells were primed for osteogenic differentiation but had a reduced capacity for myogenesis. Osteogenic differentiation was significantly enhanced in the presence of platelet‐derived growth factor (PDGF)‐BB and bone morphogenetic protein 2 (BMP2), and correlated with conversion to a Sca‐1⁺/CD73⁺ phenotype. Alizarin red staining showed that PDGF‐BB promoted significantly more mineral deposition than BMP2. Finally, it was shown that PDGF‐induced mineralization was blocked in the presence of the pro‐inflammatory cytokines tumour necrosis factor‐α and interleukin 1. In conclusion, the present study identified that PDGF‐BB is a potent osteoinductive factor in a model of tissue‐engineered skeletal muscle, and that the osteogenic capacity of this protein was modulated in the presence of pro‐inflammatory cytokines. These findings reveal a possible mechanism by which HO develops following trauma. Importantly, these findings have implications for the induction and control of bone formation for regenerative medicine. © 2016 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd.

Realizing the potential of gene-based molecular therapies in bone repair

A better understanding of osteogenesis at genetic and biochemical levels is yielding new molecular entities that can modulate bone regeneration and potentially act as novel therapies in a clinical setting. These new entities are motivating alternative approaches for bone repair by utilizing DNA-derived expression systems, as well as RNA-based regulatory molecules controlling the fate of cells involved in osteogenesis. These sophisticated mediators of osteogenesis, however, pose unique delivery challenges that are not obvious in deployment of conventional therapeutic agents. Viral and nonviral delivery systems are actively pursued in preclinical animal models to realize the potential of the gene-based medicines. This article will summarize promising bone-inducing molecular agents on the horizon as well as provide a critical review of delivery systems employed for their administration. Special attention was paid to synthetic (nonviral) delivery systems because they are more likely to be adopted for clinical testing because of safety considerations. We present a comparative analysis of dose-response relationships, as well as pharmacokinetic and pharmacodynamic features of various approaches, with the purpose of clearly defining the current frontier in the field. We conclude with the authors' perspective on the future of gene-based therapy of bone defects, articulating promising research avenues to advance the field of clinical bone repair.

Gelatin coating to stabilize the transfection ability of nucleic acid polyplexes

Amphiphilic polymers are effective in complexing and delivering therapeutic nucleic acids, such as plasmid DNA (pDNA) and short interfering RNA (siRNA). However, long-term stability of the complexes is not desirable, as it may have an impact on the transfection efficiency in vivo. To develop a method to preserve complex stability we first showed that pDNA complexes formed with the amphiphilic polymer linoleic acid-substituted polyethylenimine (PEI-LA) and incubated at 37°C lost ~90% of their transfection efficiency after only 24h of complex formation. Polyethyleneglycol modification of complexes to control the increase in complex size and incubation in scaffolds used for implantation did not preserve the transfection ability of the complexes. Among a variety of approaches explored, gelatin coating of complexes was found to be the best at maintaining the original transfection efficiency. Mechanistic studies suggested that improved complex uptake, not size stability, was responsible for retention of the transfection efficiency. Similarly to the results with pDNA, gelatin coating also prevented the decreases in uptake and silencing efficiency of siRNA complexes observed following incubation at 37°C. Gelatin-stabilized complexes were, furthermore, effective in vivo and led to subcutaneous transgene expression with a low pDNA dose that was otherwise ineffective. We conclude that a simple gelatin coating approach offers an efficient means to preserve the transfection efficiency of polyplexes.

Effects of immunosuppressants, FK506 and cyclosporin A, on the osteogenic differentiation of rat mesenchymal stem cells

Purpose

The purpose of this study was to investigate the effects of the immunosuppressants FK506 and cyclosporin A (CsA) on the osteogenic differentiation of rat mesenchymal stem cells (MSCs).

Methods

The effect of FK506 and CsA on rat MSCs was assessed in vitro. The MTT assay was used to determine the deleterious effect of immunosuppressants on stem cell proliferation at 1, 3, and 7 days. Alkaline phosphatase (ALP) activity was analyzed on days 3, 7, and 14. Alizarin red S staining was done on day 21 to check mineralization nodule formation. Real-time polymerase chain reaction (RT-PCR) was also performed to detect the expressions of bone tissue-specific genes on days 1 and 7.

Results

Cell proliferation was promoted more in the FK506 groups than the control or CsA groups on days 3 and 7. The FK506 groups showed increased ALP activity compared to the other groups during the experimental period. The ALP activity of the CsA groups did not differ from the control group in any of the assessments. Mineralization nodule formation was most prominent in the FK506 groups at 21 days. RT-PCR results of the FK506 groups showed that several bone-related genes-osteopontin, osteonectin, and type I collagen (Col-I)-were expressed more than the control in the beginning, but the intensity of expression decreased over time. Runx2 and Dlx5 gene expression were up-regulated on day 7. The effects of 50 nM CsA on osteonectin and Col-I were similar to those of the FK506 groups, but in the 500 nM CsA group, most of the genes were less expressed compared to the control.

Conclusions

These results suggest that FK506 enhances the osteoblastic differentiation of rat MSCs. Therefore, FK506 might have a beneficial effect on bone regeneration when immunosuppressants are needed in xenogenic or allogenic stem cell transplantation to treat bone defects.

A novel library screen identifies immunosuppressors that promote osteoblast differentiation

Bone homeostasis can be compromised by an increase in osteoclast-mediated resorption and/or a decrease in osteoblast-mediated bone deposition. While many efforts have focused on treating osteoclast resorption, there has been less emphasis on identifying strategies for promoting osteoblast function. Herein, we describe a high-throughput screening assay to select for small molecules that augment bone morphogenetic protein-2 (BMP-2)-mediated osteoblast lineage commitment. After an initial screen of 5405 compounds; consisting of FDA-approved drugs, known bioactives, and compounds with novel chemical makeup, we identified 45 small molecules that promoted osteoblast commitment. Of the 45 candidates, there was a broad array of classes that included nine retinoid analogs/derivatives and four immunosuppressants, notably rapamycin and FK-506, which were chosen for further study. Treatment of osteoblast precursor cells with rapamycin or FK-506, either alone, or synergistically with BMP-2, increased levels of phospho-Smad 1/5/8 protein and transcription of Runx-2, Osx and Smad-7, consistent with a role in promoting osteoblast differentiation. Only FK-506 was able to enhance osteocalcin transcripts and Alizarin Red staining, both late markers for differentiation. When osteoblast differentiation was suppressed with exogenous TGF-β1 treatment, rapamycin (but not FK-506) was able to rescue expression of differentiation markers, indicating distinct but overlapping activity of these compounds. Collectively, these data add to an understanding of pathways engaged in osteoblastogenesis, support a role for non-redundant immunosuppressant signaling, and provide a novel approach for the discovery of potentially therapeutic compounds that affect bone remodeling.

Innovative collagen nano-hydroxyapatite scaffolds offer a highly efficient non-viral gene delivery platform for stem cell-mediated bone formation

The ability of nano-hydroxyapatite (nHA) particles developed in-house to act as non-viral delivery vectors is assessed. These nHA particles are combined with collagen to yield bioactive, biodegradable collagen nano-hydroxyapatite (coll-nHA) scaffolds. Their ability to act as gene-activated matrices for BMP2 delivery is demonstrated with successful transfection of mesenchymal stem cells (MSCs) resulting in high calcium production.

Osteoinduction by repeat plasmid injection of human bone morphogenetic protein-2

BACKGROUND

Bone morphogenetic protein-2 (BMP-2) is an osteoinductive protein and is considered useful for the treatment of skeletal disorders. Previous studies using BMP-2 in clinical applications have encountered difficulties, including the lack of an efficient, safe, inexpensive and simple delivery system. The gene transfer approach is a promising option for utilizing BMP-2. Although viral vector-mediated gene transfer is efficient, safety concerns prevent its clinical application for common diseases. On the other hand, plasmid-based gene transfer is a safe method and can be harnessed for practical applications.

METHODS

A plasmid encoding human BMP-2 (pCAGGS-BMP-2) was used and injected repeatedly (one to eight times) into the skeletal muscle of mice at a divided dose. We compared the capability of osteoinduction in the skeletal muscle of mice after gene transfer by repeat injection. BMP-2 production was assessed via immunohistochemistry, and osteoinduction was evaluated using radiography, histology and biochemical assays.

RESULTS

The BMP-2 gene was transferred into the skeletal muscle of mice by repeat injection using pCAGGS-BMP-2. Mature bone was frequently observed in mice injected repeatedly with pCAGGS-BMP-2 at a divided dose. This confirms that, if the total dose is fixed, repeat injection with pCAGGS-BMP-2 at a divided dose causes osteoinduction more frequently in the skeletal muscle of mice.

CONCLUSIONS

These results suggest the possibility of the effective clinical use of human BMP-2 gene therapy by direct DNA injection, and facilitate the clinical application of BMP-2 gene therapy.

Simple strategy for bone regeneration with a BMP-2/7 gene expression cassette vector

Bone morphogenetic protein (BMP) is one of the most promising candidates for bone regeneration therapy. Heterodimers of BMP family proteins, such as BMP-2/4 or BMP-2/7, are well known to have stronger osteoinduction activity than BMP homodimers. Here, we constructed a double gene cassette vector encoding BMP-2 and BMP-7, pCAGGS-BMP-2/7, and examined its potential for osteoinduction in vitro and in vivo. Expression of the pCAGGS-BMP-2/7 vector induced osteogenic differentiation in various cell lines with the same efficiency as BMP-2 and BMP-7 co-expressed from separate vectors. Moreover, the pCAGGS-BMP-2/7 vector strongly induced bone formation in rat skeletal muscle when introduced by in vivo electroporation, compared with BMP-2 or BMP-7 alone. Thus, our BMP-2/7 double gene cassette vector, or some variation of it, may be applicable for the future clinical induction of bone formation, because it does not require multiple vectors or complicated preparation.

Genetic engineering for skeletal regenerative medicine

The clinical challenges of skeletal regenerative medicine have motivated significant advances in cellular and tissue engineering in recent years. In particular, advances in molecular biology have provided the tools necessary for the design of gene-based strategies for skeletal tissue repair. Consequently, genetic engineering has emerged as a promising method to address the need for sustained and robust cellular differentiation and extracellular matrix production. As a result, gene therapy has been established as a conventional approach to enhance cellular activities for skeletal tissue repair. Recent literature clearly demonstrates that genetic engineering is a principal factor in constructing effective methods for tissue engineering approaches to bone, cartilage, and connective tissue regeneration. This review highlights this literature, including advances in the development of efficacious gene carriers, novel cell sources, successful delivery strategies, and optimal target genes. The current status of the field and the challenges impeding the clinical realization of these approaches are also discussed.

Efficient and rapid osteoinduction in an immune-competent host

Osteoinductive systems to induce targeted rapid bone formation hold clinical promise, but development of technologies for clinical use that must be tested in animal models is often a difficult challenge. We previously demonstrated that implantation of human cells transduced with Ad5F35BMP2 to express high levels of bone morphogenetic protein-2 (BMP2) resulted in rapid bone formation at targeted sites. Inclusion of human cells in this model precluded us from testing this system in an immune-competent animal model, thus limiting information about the efficacy of this approach. Here, for the first time we demonstrate the similarity between BMP2-induced endochondral bone formation in a system using human cells in an immune-incompetent mouse and a murine cell-based BMP2 gene therapy system in immune-competent animals. In both cases the delivery cells are rapidly cleared, within 5 days, and in neither case do they appear to contribute to any of the structures forming in the tissues. Endochondral bone formation progressed through a highly ordered series of stages that were both morphologically and temporally indistinguishable between the two models. Even longterm analysis of the heterotopic bone demonstrated similar bone volumes and the eventual remodeling to form similar structures. The results suggest that the ability of BMP2 to rapidly induce bone formation overrides contributions from either immune status or the nature of delivery cells.

Applications of gene therapy and adult stem cells in bone bioengineering

Bone tissue engineering is an emerging field, that could become a main therapeutic strategy in orthopedics in coming years. While bone has regenerative abilities that enable the self repair and regeneration of fractures, there are extreme situations in which the extent of bone loss is too large for complete regeneration to occur. In order to achieve bone regeneration, osteogenic genes (mainly from the bone morphogenetic protein family) can be delivered either directly into the target tissue, or by using adult stem cells, which are later implanted into the target site. Engineered adult stem cells combined with biodegradable polymeric scaffolds can be implanted into target sites, with or without ex vivo culture period. Several important factors influence the success of bone engineering approaches including: choice of cell and scaffold, the vector used in order to deliver the osteogenic gene, and the osteogenic gene itself. Cutting-edge imaging technologies, bioinformatics-based analysis of gene expression and exogenous regulation of transgene expression are among the tools that are being used to optimize and control bone formation in vivo. In this review we have attempted to provide an overview of the main factors that should be considered when utilizing adult stem cells and gene therapy strategies to regenerate bone defects or to promote new bone formation in vivo.

In vitro and in vivo osteoblastic differentiation of BMP-2- and Runx2-engineered skeletal myoblasts

Genetic engineering with osteogenic factors is a promising approach for cell-based therapeutics and orthopedic regeneration. However, the relative efficacy of different strategies for inducing osteoblastic differentiation remains unclear and is further complicated by varied delivery vehicles, cell types, and evaluation criteria. In order to elucidate the effects of distinct gene-based strategies, we quantitatively evaluated osteoblastic differentiation and mineralization of primary skeletal myoblasts overexpressing either the BMP-2 growth factor or Runx2 transcription factor. Retroviral delivery of BMP-2 or Runx2 stimulated differentiation into an osteoblastic phenotype, as demonstrated by the induction of osteogenic gene expression, alkaline phosphatase activity, and matrix mineralization in monolayer culture and on collagen scaffolds both in vitro and in an intramuscular site in vivo. In general, BMP-2 stimulated osteoblastic markers faster and to a greater extent than Runx2, although we also identified experimental conditions under which these two factors produced similar effects. Additionally, Runx2-engineered cells did not utilize paracrine signaling via secreted osteogenic factors, in contrast to cells overexpressing BMP-2, as demonstrated by conditioned media studies and activation of Smad signaling. These results emphasize the complexity of gene therapy-based orthopedic therapeutics as an integrated relationship of differentiation state, construct maturation, and paracrine signaling of osteogenic cells. This study is significant in evaluating proposed therapeutic systems and defining a successful strategy for integrating gene medicine and orthopedic regeneration.

Inducible regulation of Runx2-stimulated osteogenesis

Ex vivo gene therapy is a promising approach to orthopedic regenerative medicine. These strategies typically focus on the constitutive overexpression of osteogenic factors to induce osteoblastic differentiation and matrix mineralization. However, the unregulated production of osteoinductive molecules has also resulted in abnormal bone formation and tumorigenesis. To address these limitations, this work describes a retroviral system to deliver the Runx2 osteoblastic transcription factor under control of the tetracycline-inducible (tet-off) promoter in primary skeletal myoblasts. Runx2 expression was tightly regulated by anhydrotetracyline (aTc) concentration in cell culture media. Osteoblastic gene expression, alkaline phosphatase activity, and matrix mineralization were also controlled by aTc in a dose-dependent manner. Additionally, osteoblastic differentiation was temporally regulated by adding and removing aTc from the culture media. Engineered cells were seeded onto collagen scaffolds and implanted intramuscularly in the hind limbs of syngeneic mice. In vivo mineralization by these constructs was regulated by supplementing the drinking water with aTc, as demonstrated by micro-computed tomography and histological analyses. Collectively, these results present a novel system for regulating osteoblastic differentiation of a clinically relevant autologous cell source. This system is significant to developing controlled and effective orthopedic gene therapy strategies and studying the regulation of osteoblastic differentiation.

Local immunomodulation with CD4 and CD8 antibodies, but not cyclosporine A, improves osteogenesis induced by ADhBMP9 gene therapy

This study was designed to see if immunosuppression achieved using local application of cyclosporine A (Cs. A) or CD4 and CD8 antibodies would improve bone formation following intramuscular injections of human BMP-4 and BMP-9 adenoviral vectors (ADhBMP4 and ADhBMP9) in Sprague-Dawley rats. Cs. A was injected into the thigh muscle. After 2 days, ADhBMP4, ADhBMP9, and the antibodies were separately injected into the left and right rear legs. At this time, the number of CD4+/CD3+ cells was significantly lower and the number of CD8+/CD3+ cells higher in the Cs. A group than in the control group (P < 0.01). The total number of white blood cells 3 days following injection of CD4 and CD8 antibodies was significantly lower than that before the injection (P < 0.01). At 4 weeks after the viral and antibody injections, mean bone volumes at the ADhBMP9 treatment sites were 0.29 +/- 0.01 cm3 in the viral control group, 0.17 +/- 0.03 cm3 in the Cs. A-ADhBMPs group, and 0.59 +/- 0.07 cm3 in the antibodies-ADhBMPs group. ADhBMP4 did not induce new bone formation in any group. This study demonstrates that local immunomodulation may improve the osteogenic potential of bone morphogenetic protein gene therapy in the clinical setting.

Different Osteogenic Potentials of Recombinant Human BMP-6 Adeno-Associated Virus and Adenovirus in Two Rat Strains

The osteogenic potential of AAV5hBMP6 was compared with that of ADhBMP6 in immunodeficient and immunocompetent rats. AAV5hBMP6 (2.3 x 10(12) particles) and ADhBMP6 (5 x 10(7) PFU) elicited viral antibody production in immunocompetent rats. Among rats that received AAV5hBMP6, the earliest time points at which the bone was visible under CT scanner were 30 days in 2-month-old Sprague-Dawley (SD) rats and 60 days in 18-month-old SD rats. The mean volumes of ectopic bone 90 days after viral injection were 0.31 +/- 0.14 cm(3) in athymic nude rats, 0.64 +/- 0.12 cm(3) in 2-month-old SD rats, and 0.21 +/- 0.10 cm(3) in 18-month-old SD rats. In contrast, among rats that received ADhBMP6, the earliest time points to observe the bone formation by CT scan were 15 days in 2-month-old rats and no bone formation in 18-month-old SD rats. The mean volumes of ectopic bone were 4.17 +/- 0.05 cm(3) in athymic nude rats and 0.06 +/- 0.03 cm(3) in 2-month-old SD rats. Although both types of viruses induced an immune response in immunocompetent animals, this response played different roles in the process of bone formation induced by the BMP6 vectors.

Growth factor delivery for bone tissue repair: an update

Growth factors (GFs) are endogenous proteins capable of acting on cell-surface receptors and directing cellular activities involved in the regeneration of new bone tissue. The specific actions and long-term effects of GFs on bone-forming cells have resulted in exploration of their potential for clinical bone repair. The concerted efforts have led to the recent approval of two GFs, bone morphogenetic protein-2 and osteogenic protein-1, for clinical bone repair, and human parathryroid hormone (1-34) for augmentation of systemic bone mass. This review provides a selective summary of recent (2001-2004) attempts for GF delivery in bone tissue regeneration. First, a summary of non-human primate studies involving local regeneration and repair is provided, with special emphasis on the range of biomaterials used for GF delivery. Next, efforts to administer GFs for systemic augmentation of bone tissue are summarised. Finally, an alternative means of GF delivery, namely the delivery of genes coding for osteogenic proteins, rather than the delivery of the proteins, is summarised from rodent models. To conclude, future avenues of research considered promising to enhance the clinical application of GFs are discussed.

Mechanism of osteogenic induction by FK506 via BMP/Smad pathways

FK506 is an immunosuppressant that exerts effects by binding to FK506-binding protein 12 (FKBP12). Recently, FK506 has also been reported to promote osteogenic differentiation when administered locally or in vitro in combination with bone morphogenetic proteins (BMPs), although the underlying mechanism remains unclarified. The present study initially showed that FK506 alone at a higher concentration (1muM) induced osteogenic differentiation of mesenchymal cell lines, which was suppressed by adenoviral introduction of Smad6. FK506 rapidly activates the BMP-dependent Smads in the absence of BMPs, and the activation was blocked by Smad6. Overexpression of FKBP12, which was reported to block the ligand-independent activation of BMP type I receptor A (BMPRIA), suppressed Smad signaling induced by FK506, but not that induced by BMP2. BMPRIA and FKBP12 bound to each other, and this binding was suppressed by FK506. These data suggest that FK506 promotes osteogenic differentiation by activating BMP receptors through interacting with FKBP12.