Induction of bone formation using a recombinant adenoviral vector carrying the human BMP-2 gene in a rabbit spinal fusion model

Gene Therapy and Spinal Fusion: Systematic Review and Meta-Analysis of the Available Data

OBJECTIVE

To analyze the extant literature describing the application of gene therapy to spinal fusion.

METHODS

A systematic review of the English-language literature was performed. The search query was designed to include all published studies examining gene therapy approaches to promote spinal fusion. Approaches were classified as ex vivo (delivery of genetically modified cells) or in vivo (delivery of growth factors via vectors). The primary endpoint was fusion rate. Random effects meta-analyses were performed to calculate the overall odds ratio (OR) of fusion using a gene therapy approach and overall fusion rate. Subgroup analyses of fusion rate were also performed for each gene therapy approach.

RESULTS

Of 1179 results, 35 articles met criteria for inclusion (all preclinical), of which 26 utilized ex vivo approaches and 9 utilized in vivo approaches. Twenty-seven articles (431 animals) were included in the meta-analysis. Gene therapy use was associated with significantly higher fusion rates (OR 77; 95% confidence interval {CI}: [31, 192]; P < 0.001); ex vivo strategies had a greater effect (OR 136) relative to in vivo strategies (OR 18) (P = 0.017). The overall fusion rate using a gene therapy approach was 80% (95% CI: [62%, 93%]; P < 0.001); overall fusion rates were significantly higher in subjects treated with ex vivo compared to in vivo strategies (90% vs. 42%; P = 0.011). For both ex vivo and in vivo approaches, the effect of gene therapy on fusion was independent of animal model.

CONCLUSIONS

Gene therapy may augment spinal fusion; however, future investigation in clinical populations is necessary.

The Potential Use of Mesenchymal Stem Cells and Their Derived Exosomes for Orthopedic Diseases Treatment

Musculoskeletal disorders (MSDs) are conditions that can affect muscles, bones, and joints. These disorders are very painful and severely limit patients' mobility and are more common in the elderly. MSCs are multipotent stem cells isolated from embryonic (such as the umbilical cord) and mature sources (such as adipose tissue and bone marrow). These cells can differentiate into various cells such as osteoblasts, adipocytes, chondrocytes, NP-like cells, Etc. Due to MSC characteristics such as immunomodulatory properties, ability to migrate to the site of injury, recruitment of cells involved in repair, production of growth factors, and large amount production of extracellular vesicles, these cells have been used in many regenerative-related medicine studies. Also, MSCs produce different types of EVs, such as exosomes, to the extracellular environment. Exosomes reflect MSCs' characteristics and do not have cell therapy-associated problems because they are cell-free. These vesicles carry proteins, nucleic acids, and lipids to the host cell and change their function. This review focuses on MSCs and MSCs exosomes' role in repairing dense connective tissues such as tendons, cartilage, invertebrate disc, bone fracture, and osteoporosis treatment.

Bone Microvasculature: Stimulus for Tissue Function and Regeneration

Bone is a highly vascularized organ, providing structural support to the body, and its development, regeneration, and remodeling depend on the microvascular homeostasis. Loss or impairment of vascular function can develop diseases, such as large bone defects, avascular necrosis, osteoporosis, osteoarthritis, and osteopetrosis. In this review, we summarize how vasculature controls bone development and homeostasis in normal and disease cases. A better understanding of this process will facilitate the development of novel disease treatments that promote bone regeneration and remodeling. Specifically, approaches based on tissue engineering components, such as stem cells and growth factors, have demonstrated the capacity to induce bone microvasculature regeneration and mineralization. This knowledge will have relevant clinical implications for the treatment of bone disorders by developing novel pharmaceutical approaches and bone grafts. Finally, the tissue engineering approaches incorporating vascular components may widely be applied to treat other organ diseases by enhancing their regeneration capacity. Impact statement Bone vasculature is imperative in the process of bone development, regeneration, and remodeling. Alterations or disruption of the bone vasculature leads to loss of bone homeostasis and the development of bone diseases. In this study, we review the role of vasculature on bone diseases and how vascular tissue engineering strategies, with a detailed emphasis on the role of stem cells and growth factors, will contribute to bone therapeutics.

New Strategies in Enhancing Spinal Fusion

The biologic steps involved in creating a bony fusion between adjacent segments of the spine are a complex and highly coordinated series of events. There have been significant advancements in bone grafts and bone graft substitutes in order to augment spinal fusion. While autologous bone grafting remains the gold standard, allograft bone grafting, synthetic bone graft substitutes, and bone graft enhancers are appropriate in certain clinical situations. This article provides an overview of the basic biology of spinal fusion and strategies for enhancing fusion through innovations in bone graft material.

Application of Cytokines of the Bone Morphogenetic Protein (BMP) Family in Spinal Fusion - Effects on the Bone, Intervertebral Disc and Mesenchymal Stromal Cells

Low back pain is a prevalent socio-economic burden and is often associated with damaged or degenerated intervertebral discs (IVDs). When conservative therapy fails, removal of the IVD (discectomy), followed by intersomatic spinal fusion, is currently the standard practice in clinics. The remaining space is filled with an intersomatic device (cage) and with bone substitutes to achieve disc height compensation and bone fusion. As a complication, in up to 30% of cases, spinal non-fusions result in a painful pseudoarthrosis. Bone morphogenetic proteins (BMPs) have been clinically applied with varied outcomes. Several members of the BMP family, such as BMP2, BMP4, BMP6, BMP7, and BMP9, are known to induce osteogenesis. Questions remain on why hyper-physiological doses of BMPs do not show beneficial effects in certain patients. In this respect, BMP antagonists secreted by mesenchymal cells, which might interfere with or block the action of BMPs, have drawn research attention as possible targets for the enhancement of spinal fusion or the prevention of non-unions. Examples of these antagonists are noggin, gremlin1 and 2, chordin, follistatin, BMP3, and twisted gastrulation. In this review, we discuss current evidence of the osteogenic effects of several members of the BMP family on osteoblasts, IVD cells, and mesenchymal stromal cells. We consider in vitro and in vivo studies performed in human, mouse, rat, and rabbit related to BMP and BMP antagonists in the last two decades. We give insights into the effects that BMP have on the ossification of the spine. Furthermore, the benefits, pitfalls, and possible safety concerns using these cytokines for the improvement of spinal fusion are discussed.

Exogenous noggin binds the BMP-2 receptor and induces alkaline phosphatase activity in osteoblasts

Osteogenesis is an important process in bone remodeling and is under strict cellular signaling governed by growth factors and antagonists. Bone morphogenetic protein 2 (BMP-2) is an important osteogenic factor involved in the transcription of key osteogenic genes such as alkaline phosphatase (ALP). While, antagonists such as noggin effectively restrict osteoblast differentiation through binding to BMP-2. In this study, we sought to understand the effect of exogenous noggin in osteoblasts and its role in BMP-2 activation of osteogenesis. Enzymatic activity of ALP was monitored to ascertain the effect of the noggin. Fluorescently labelled noggin was used to determine the binding of noggin to the BMP-2 receptor. The results demonstrated that noggin significantly increases the activity of ALP at concentrations of 50 to 400 ng/mL. While, it inhibited the activity of exogenous BMP-2. Furthermore, fluorescently labelled noggin showed strong binding to osteoblasts which were perturbed when cells were preincubated with BMP-2 suggesting that noggin shares a common receptor with BMP-2. These results suggest that exogenous noggin facilitates osteogenic differentiation and provide a novel mechanism for its interplay with BMP-2.

Chondroitin Sulfate Glycosaminoglycan Scaffolds for Cell and Recombinant Protein-Based Bone Regeneration

Bone morphogenetic protein 2 (BMP‐2)‐loaded collagen sponges remain the clinical standard for treatment of large bone defects when there is insufficient autograft, despite associated complications. Recent efforts to negate comorbidities have included biomaterials and gene therapy approaches to extend the duration of BMP‐2 release and activity. In this study, we compared the collagen sponge clinical standard to chondroitin sulfate glycosaminoglycan (CS‐GAG) scaffolds as a delivery vehicle for recombinant human BMP‐2 (rhBMP‐2) and rhBMP‐2 expression via human BMP‐2 gene inserted into mesenchymal stem cells (BMP‐2 MSC). We demonstrated extended release of rhBMP‐2 from CS‐GAG scaffolds compared to their collagen sponge counterparts, and further extended release from CS‐GAG gels seeded with BMP‐2 MSC. When used to treat a challenging critically sized femoral defect model in rats, both rhBMP‐2 and BMP‐2 MSC in CS‐GAG induced comparable bone formation to the rhBMP‐2 in collagen sponge, as measured by bone volume, strength, and stiffness. We conclude that CS‐GAG scaffolds are a promising delivery vehicle for controlling the release of rhBMP‐2 and to mediate the repair of critically sized segmental bone defects. stem cells translational medicine2019;8:575–585

Eminent Sources of Adult Mesenchymal Stem Cells and Their Therapeutic Imminence

In the recent times, stem cell biology has garnered the attention of the scientific fraternity and the general public alike due to the immense therapeutic potential that it holds in the field of regenerative medicine. A breakthrough in this direction came with the isolation of stem cells from human embryo and their differentiation into cell types of all three germ layers. However, the isolation of mesenchymal stem cells from adult tissues proved to be advantageous over embryonic stem cells due to the ethical and immunological naivety. Mesenchymal Stem Cells (MSCs) isolated from the bone marrow were found to differentiate into multiple cell lineages with the help of appropriate differentiation factors. Furthermore, other sources of stem cells including adipose tissue, dental pulp, and breast milk have been identified. Newer sources of stem cells have been emerging recently and their clinical applications are also being studied. In this review, we examine the eminent sources of Mesenchymal Stem Cells (MSCs), their immunophenotypes, and therapeutic imminence.

A Comparative Study of the Bone Regenerative Effect of Chemically Modified RNA Encoding BMP-2 or BMP-9

Employing cost-effective biomaterials to deliver chemically modified ribonucleic acid (cmRNA) in a controlled manner addresses the high cost, safety concerns, and lower transfection efficiency that exist with protein and gene therapeutic approaches. By eliminating the need for nuclear entry, cmRNA therapeutics can potentially overcome the lower transfection efficiencies associated with non-viral gene delivery systems. Here, we investigated the osteogenic potential of cmRNA-encoding BMP-9, in comparison to cmRNA-encoding BMP-2. Polyethylenimine (PEI) was used as a vector to increase in vitro transfection efficacy. Complexes of PEI-cmRNA (encoding BMP-2 or BMP-9) were fabricated at an amine (N) to phosphate (P) ratio of 10 and characterized for transfection efficacy in vitro using human bone marrow stromal cells (BMSCs). The osteogenic potential of BMSCs treated with these complexes was determined by evaluating the expression of bone-specific genes as well as through the detection of bone matrix deposition. It was found that alkaline phosphatase (ALP) expression 3 days post transfection in the group treated with BMP-9-cmRNA was significantly higher than that in the group that received BMP-2-cmRNA treatment. Alizarin red staining and atomic absorption spectroscopy demonstrated enhanced osteogenic differentiation as evidenced by increased bone matrix production by the BMSCs treated with BMP-9-cmRNA when compared to cells treated with BMP-2-cmRNA. In vivo studies showed increased bone formation in calvarial defects treated with the BMP-9-cmRNA and BMP-2-cmRNA collagen scaffolds when compared to empty defects. The connectivity density of the regenerated bone was higher (2-fold-higher) in the group that received BMP-9-cmRNA compared to BMP-2-cmRNA. Together, these findings suggest that cmRNA-activated matrix encoding osteogenic molecules can provide a powerful strategy for bone regeneration with significant clinical translational potential.

Osseous differentiation of human fat tissue grafts: From tissue engineering to tissue differentiation

Conventional bone tissue engineering approaches require isolation and in vitro propagation of autologous cells, followed by seeding on a variety of scaffolds. Those protracted procedures impede the clinical applications. Here we report the transdifferentiation of human fat tissue fragments retrieved from subcutaneous fat into tissue with bone characteristics in vitro without prior cell isolation and propagation. 3D collagen-I cultures of human fat tissue were cultivated either in growth medium or in osteogenic medium (OM) with or without addition of Bone Morphogenetic Proteins (BMPs) BMP-2, BMP-7 or BMP-9. Ca²⁺ depositions were observed after two weeks of osteogenic induction which visibly increased when either type of BMP was added. mRNA levels of alkaline phosphatase (ALP) and osteocalcin (OCN) increased when cultured in OM alone but addition of BMP-2, BMP-7 or BMP-9 caused significantly higher expression levels of ALP and OCN. Immunofluorescent staining for OCN, osteopontin and sclerostin supported the observed real-time-PCR data. BMP-9 was the most effective osteogenic inducer in this system. Our findings reveal that tissue regeneration can be remarkably simplified by omitting prior cell isolation and propagation, therefore removing significant obstacles on the way to clinical applications of much needed regeneration treatments.

Biological Approaches to Bone Regeneration by Gene Therapy

Safe, effective approaches for bone regeneration are needed to reverse bone loss caused by trauma, disease, and tumor resection. Unfortunately, the science of bone regeneration is still in its infancy, with all current or emerging therapies having serious limitations. Unlike current regenerative therapies that use single regenerative factors, the natural processes of bone formation and repair require the coordinated expression of many molecules, including growth factors, bone morphogenetic proteins, and specific transcription factors. As will be developed in this article, future advances in bone regeneration will likely incorporate therapies that mimic critical aspects of these natural biological processes, using the tools of gene therapy and tissue engineering. This review will summarize current knowledge related to normal bone development and fracture repair, and will describe how gene therapy, in combination with tissue engineering, may mimic critical aspects of these natural processes. Current gene therapy approaches for bone regeneration will then be summarized, including recent work where combinatorial gene therapy was used to express groups of molecules that synergistically interacted to stimulate bone regeneration. Last, proposed future directions for this field will be discussed, where regulated gene expression systems will be combined with cells seeded in precise three-dimensional configurations on synthetic scaffolds to control both temporal and spatial distribution of regenerative factors. It is the premise of this article that such approaches will eventually allow us to achieve the ultimate goal of bone tissue engineering: to reconstruct entire bones with associated joints, ligaments, or sutures. Abbreviations used: BMP, bone morphogenetic protein; FGF, fibroblast growth factor; AER, apical ectodermal ridge; ZPA, zone of polarizing activity; PZ, progress zone; SHH, sonic hedgehog; OSX, osterix transcription factor; FGFR, fibroblast growth factor receptor; PMN, polymorphonuclear neutrophil; PDGF, platelet-derived growth factor; IGF, insulin-like growth factor; TGF-β, tumor-derived growth factor β; CAR, coxsackievirus and adenovirus receptor; MLV, murine leukemia virus; HIV, human immunodeficiency virus; AAV, adeno-associated virus; CAT, computer-aided tomography; CMV, cytomegalovirus; GAM, gene-activated matrix; MSC, marrow stromal cell; MDSC, muscle-derived stem cell; VEGF, vascular endothelial growth factor.

Vertebral Implantation of NELL-1 Enhances Bone Formation in an Osteoporotic Sheep Model

BACKGROUND

Vertebral compression fractures related to osteoporosis greatly afflict the aging population. One of the most commonly used therapy today is balloon kyphoplasty. However, this treatment is far from ideal and is associated with significant side effects. NELL-1, an osteoinductive factor that possesses both pro-osteogenic and anti-osteoclastic properties, is a promising candidate for an alternative to current treatment modalities. This study utilizes the pro-osteogenic properties of recombinant human NELL-1 (rhNELL-1) in lumbar spine vertebral defect model in osteoporotic sheep.

METHODS

Osteoporosis was induced through ovariectomy, dietary depletion of calcium and vitamin D, and steroid administration. After osteoporotic induction, lumbar vertebral body defect creation was performed. Sheep were randomly implanted with the control vehicle, comprised of hyaluronic acid (HA) with hydroxyapatite-coated β-tricalcium phosphate (β-TCP), or the treatment material of rhNELL-1 protein lyophilized onto β-TCP mixed with HA. Analysis of lumbar spine defect healing was performed by radiographic, histologic, and computer-simulated biomechanical testing.

RESULTS

rhNELL-1 treatment significantly increased lumbar spine bone formation, as determined by bone mineral density, % bone volume, and mean cortical width as assessed by micro-computed tomography. Histological analysis revealed a significant increase in bone area and osteoblast number and decrease in osteoclast number around the implant site. Computer-simulated biomechanical analysis of trabecular bone demonstrated that rhNELL-1-treatment resulted in a significantly more stress-resistant composition.

CONCLUSION

Our findings suggest rhNELL-1-based vertebral implantation successfully improved cortical and cancellous bone regeneration in the lumbar spine of osteoporotic sheep. rhNELL-1-based bone graft substitutes represent a potential new local therapy.

Evaluation of bone morphogenic proteins in periodontal practice

Forty years ago Marshal R. Urist discovered a substance in bone matrix that had inductive properties for the development of bone and cartilage, until date, at least 20 bone morphogenetic proteins (BMPs) have been identified, some of which have been shown in vitro to stimulate the process of stem cell differentiation into osteoblasts in human and animal models. The purpose of this paper is to give a brief overview of BMPs and to review critically the clinical data currently available on the use of BMPs in various periodontal applications. The literature on BMPs was reviewed. A comprehensive search was designed. The articles were independently screened for eligibility. Articles with authentic controls and proper randomization and pertaining specifically to their role in periodontal applications were included. The available literature was analyzed and compiled. The analysis indicates BMPs to be a promising, as well as an effective novel approach to reconstruct and engineer the periodontal apparatus. Here, we represent several articles, as well as recent texts that make up a special and an in-depth review on the subject. On the basis of the data provided in the studies that were reviewed BMPs provide revolutionary therapies in periodontal practice.

Stem cells, growth factors and scaffolds in craniofacial regenerative medicine

Current reconstructive approaches to large craniofacial skeletal defects are often complicated and challenging. Critical-sized defects are unable to heal via natural regenerative processes and require surgical intervention, traditionally involving autologous bone (mainly in the form of nonvascularized grafts) or alloplasts. Autologous bone grafts remain the gold standard of care in spite of the associated risk of donor site morbidity. Tissue engineering approaches represent a promising alternative that would serve to facilitate bone regeneration even in large craniofacial skeletal defects. This strategy has been tested in a myriad of iterations by utilizing a variety of osteoconductive scaffold materials, osteoblastic stem cells, as well as osteoinductive growth factors and small molecules. One of the major challenges facing tissue engineers is creating a scaffold fulfilling the properties necessary for controlled bone regeneration. These properties include osteoconduction, osetoinduction, biocompatibility, biodegradability, vascularization, and progenitor cell retention. This review will provide an overview of how optimization of the aforementioned scaffold parameters facilitates bone regenerative capabilities as well as a discussion of common osteoconductive scaffold materials.

LIPUS promotes spinal fusion coupling proliferation of type H microvessels in bone

Low-intensity pulsed ultrasound (LIPUS) has been found to accelerate spinal fusion. Type H microvessels are found in close relation with bone development. We analyzed the role of type H vessels in rat spinal fusion model intervened by LIPUS. It was found LIPUS could significantly accelerate bone fusion rate and enlarge bone callus. Osteoblasts were specifically located on the bone meshwork of the allograft, and were surrounded by type H microvessels. LIPUS could significantly increase the quantity of osteoblasts during spine fusion, which process was coupled with elevated angiogenesis of type H microvessels. Our results suggest that LIPUS may be a noninvasive adjuvant treatment modality in spinal fusion for clinical use. The treatment is recommended for usage for at least one month.

Use of bone morphogenetic proteins in mesenchymal stem cell stimulation of cartilage and bone repair

The extracellular matrix-associated bone morphogenetic proteins (BMPs) govern a plethora of biological processes. The BMPs are members of the transforming growth factor-β protein superfamily, and they actively participate to kidney development, digit and limb formation, angiogenesis, tissue fibrosis and tumor development. Since their discovery, they have attracted attention for their fascinating perspectives in the regenerative medicine and tissue engineering fields. BMPs have been employed in many preclinical and clinical studies exploring their chondrogenic or osteoinductive potential in several animal model defects and in human diseases. During years of research in particular two BMPs, BMP2 and BMP7 have gained the podium for their use in the treatment of various cartilage and bone defects. In particular they have been recently approved for employment in non-union fractures as adjunct therapies. On the other hand, thanks to their potentialities in biomedical applications, there is a growing interest in studying the biology of mesenchymal stem cell (MSC), the rules underneath their differentiation abilities, and to test their true abilities in tissue engineering. In fact, the specific differentiation of MSCs into targeted cell-type lineages for transplantation is a primary goal of the regenerative medicine. This review provides an overview on the current knowledge of BMP roles and signaling in MSC biology and differentiation capacities. In particular the article focuses on the potential clinical use of BMPs and MSCs concomitantly, in cartilage and bone tissue repair.

Effective delivery of bone morphogenetic protein 2 gene using chitosan–polyethylenimine nanoparticle to promote bone formation

Treating bone defects is still a challenge in clinical practice.

Reduction of Adipose Tissue Formation by the Controlled Release of BMP-2 Using a Hydroxyapatite-Coated Collagen Carrier System for Sinus-Augmentation/Extraction-Socket Grafting

The effects of hydroxyapatite (HA)-coating onto collagen carriers for application of recombinant human bone morphogenetic protein 2 (rhBMP-2) on cell differentiation in vitro, and on in vivo healing patterns after sinus-augmentation and alveolar socket-grafting were evaluated. In vitro induction of osteogenic/adipogenic differentiation was compared between the culture media with rhBMP-2 solution and with the released rhBMP-2 from the control collagen and from the HA-coated collagen. Demineralized bovine bone and collagen/HA-coated collagen were grafted with/without rhBMP-2 in sinus-augmentation and tooth-extraction-socket models. Adipogenic induction by rhBMP-2 released from HA-coated collagen was significantly reduced compared to collagen. In the sinus-augmentation model, sites that received rhBMP-2 exhibited large amounts of vascular tissue formation at two weeks and increased adipose tissue formation at eight weeks; this could be significantly reduced by using HA-coated collagen as a carrier for rhBMP-2. In extraction-socket grafting, dimensional reduction of alveolar ridge was significantly decreased at sites received rhBMP-2 compared to control sites, but adipose tissue was increased within the regenerated socket area. In conclusion, HA-coated collagen carrier for Escherichia coli-derived rhBMP-2 (ErhBMP-2) may reduce in vitro induction of adipogenic differentiation and in vivo adipose bone marrow tissue formation in bone tissue engineering by ErhBMP-2.

The Effect of Quercetin on the Osteogenesic Differentiation and Angiogenic Factor Expression of Bone Marrow-Derived Mesenchymal Stem Cells

Bone marrow-derived mesenchymal stem cells (BMSCs) are widely used in regenerative medicine in light of their ability to differentiate along the chondrogenic and osteogenic lineages. As a type of traditional Chinese medicine, quercetin has been preliminarily reported to promote osteogenic differentiation in osteoblasts. In the present study, the effects of quercetin on the proliferation, viability, cellular morphology, osteogenic differentiation and angiogenic factor secretion of rat BMSCs (rBMSCs) were examined by MTT assay, fluorescence activated cell sorter (FACS) analysis, real-time quantitative PCR (RT-PCR) analysis, alkaline phosphatase (ALP) activity and calcium deposition assays, and Enzyme-linked immunosorbent assay (ELISA). Moreover, whether mitogen-activated protein kinase (MAPK) signaling pathways were involved in these processes was also explored. The results showed that quercetin significantly enhanced the cell proliferation, osteogenic differentiation and angiogenic factor secretion of rBMSCs in a dose-dependent manner, with a concentration of 2 μM achieving the greatest stimulatory effect. Moreover, the activation of the extracellular signal-regulated protein kinases (ERK) and p38 pathways was observed in quercetin-treated rBMSCs. Furthermore, these induction effects could be repressed by either the ERK inhibitor PD98059 or the p38 inhibitor SB202190, respectively. These data indicated that quercetin could promote the proliferation, osteogenic differentiation and angiogenic factor secretion of rBMSCs in vitro, partially through the ERK and p38 signaling pathways.

Efficiently engineered cell sheet using a complex of polyethylenimine-alginate nanocomposites plus bone morphogenetic protein 2 gene to promote new bone formation

Regeneration of large bone defects is a common clinical problem. Recently, stem cell sheet has been an emerging strategy in bone tissue engineering. To enhance the osteogenic potential of stem cell sheet, we fabricated bone morphogenetic protein 2 (BMP-2) gene-engineered cell sheet using a complex of polyethylenimine-alginate (PEI-al) nanocomposites plus human BMP-2 complementary(c)DNA plasmid, and studied its osteogenesis in vitro and in vivo. PEI-al nanocomposites carrying BMP-2 gene could efficiently transfect bone marrow mesenchymal stem cells. The cell sheet was made by culturing the cells in medium containing vitamin C for 10 days. Assays on the cell culture showed that the genetically engineered cells released the BMP-2 for at least 14 days. The expression of osteogenesis-related gene was increased, which demonstrated that released BMP-2 could effectively induce the cell sheet osteogenic differentiation in vitro. To further test the osteogenic potential of the cell sheet in vivo, enhanced green fluorescent protein or BMP-2-producing cell sheets were treated on the cranial bone defects. The results indicated that the BMP-2-producing cell sheet group was more efficient than other groups in promoting bone formation in the defect area. Our results suggested that PEI-al nanocomposites efficiently deliver the BMP-2 gene to bone marrow mesenchymal stem cells and that BMP-2 gene-engineered cell sheet is an effective way for promoting bone regeneration.

Stem cells in preclinical spine studies

BACKGROUND CONTEXT

The recent identification and characterization of mesenchymal stem cells have introduced a shift in the research focus for future technologies in spinal surgery to achieve spinal fusion and treat degenerative disc disease. Current and past techniques use allograft to replace diseased tissue or rely on host responses to recruit necessary cellular progenitors. Adult stem cells display long-term proliferation, efficient self-renewal, and multipotent differentiation.

PURPOSE

This review will focus on two important applications of stem cells in spinal surgery: spine fusion and the management of degenerative disc disease.

STUDY DESIGN

Review of the literature.

METHODS

Relevant preclinical literature regarding stem cell sources, growth factors, scaffolds, and animal models for both osteogenesis and chondrogenesis will be reviewed, with an emphasis on those studies that focus on spine applications of these technologies.

RESULTS

In both osteogenesis and chondrogenesis, adult stem cells derived from bone marrow or adipose show promise in preclinical studies. Various growth factors and scaffolds have also been shown to enhance the properties and eventual clinical potential of these cells. Although its utility in clinical applications has yet to be proven, gene therapy has also been shown to hold promise in preclinical studies.

CONCLUSIONS

The future of spine surgery is constantly evolving, and the recent advancements in stem cell-based technologies for both spine fusion and the treatment of degenerative disc disease is promising and indicative that stem cells will undoubtedly play a major role clinically. It is likely that these stem cells, growth factors, and scaffolds will play a critical role in the future for replacing diseased tissue in disease processes such as degenerative disc disease and in enhancing host tissue to achieve more reliable spine fusion.

Spinal fusion in the next generation: gene and cell therapy approaches

Bone fusion represents a challenge in the orthopedics practice, being especially indicated for spine disorders. Spinal fusion can be defined as the bony union between two vertebral bodies obtained through the surgical introduction of an osteoconductive, osteoinductive, and osteogenic compound. Autogenous bone graft provides all these three qualities and is considered the gold standard. However, a high morbidity is associated with the harvest procedure. Intensive research efforts have been spent during the last decades to develop new approaches and technologies for successful spine fusion. In recent years, cell and gene therapies have attracted great interest from the scientific community. The improved knowledge of both mesenchymal stem cell biology and osteogenic molecules allowed their use in regenerative medicine, representing attractive approaches to achieve bone regeneration also in spinal surgery applications. In this review we aim to describe the developing gene- and cell-based bone regenerative approaches as promising future trends in spine fusion.

Synergistic effect of bone morphogenetic proteins 2 and 7 by ex vivo gene therapy in a rat spinal fusion model

BACKGROUND

Previous studies have suggested that the co-expression of two different bone morphogenetic protein (BMP) genes can result in the production of heterodimeric BMPs that may be more potent than homodimers. In this study, combined BMP-2 and BMP-7 gene transfer was performed ex vivo to compare the resulting new bone formation with that of single-BMP gene transfer in a rat spinal fusion model.

METHODS

Forty-four athymic rats underwent posterolateral fusion at L4-L5 and were implanted with a collagen sponge containing human adipose-derived stem cells. Group A received untreated cells, and the remaining groups received cells transfected with various genes in a lentivirus vector. The transferred genes were GFP (green fluorescent protein) in Group B, BMP-2 in Group C, BMP-7 in Group D, and both BMP-2 and BMP-7 in Group E. In vitro production of BMP-2 and BMP-7 was quantified by means of an enzyme-linked immunosorbent assay (ELISA) specific to BMP-2 or BMP-7. Osseous fusion was quantified with use of radiography and microcomputed tomography.

RESULTS

ELISA demonstrated that Group E, which was treated with both BMP-2 and BMP-7, produced less than one-fourth as much BMP as the groups treated with a single transfected BMP (Groups C and D). Radiographs showed that all of the spines in Groups C, D, and E appeared to be fused by eight weeks; the spines in Groups A and B showed minimal evidence of new bone formation. Measurements confirmed that the mean bone formation area was significantly greater in Groups C, D, and E compared with Groups A and B (p &lt; 0.001). In addition, the bone formation area was significantly greater in Group E compared with Groups C and D (p &lt; 0.001).

CONCLUSIONS

Combined BMP-2 and BMP-7 ex vivo gene transfer was found to be significantly more effective for inducing new bone formation compared with ex vivo gene transfer of an individual BMP in a rat spinal fusion model.

CLINICAL RELEVANCE

Combined BMP-2 and BMP-7 therapy may lead to efficient bone regeneration.

Using poly(lactic-co-glycolic acid) microspheres to encapsulate plasmid of bone morphogenetic protein 2/polyethylenimine nanoparticles to promote bone formation in vitro and in vivo

Repair of large bone defects is a major challenge, requiring sustained stimulation to continually promote bone formation locally. Bone morphogenetic protein 2 (BMP-2) plays an important role in bone development. In an attempt to overcome this difficulty of bone repair, we created a delivery system to slowly release human BMP-2 cDNA plasmid locally, efficiently transfecting local target cells and secreting functional human BMP-2 protein. For transfection, we used polyethylenimine (PEI) to create pBMP-2/PEI nanoparticles, and to ensure slow release we used poly(lactic-co-glycolic acid) (PLGA) to create microsphere encapsulated pBMP-2/PEI nanoparticles, PLGA@pBMP-2/PEI. We demonstrated that pBMP-2/PEI nanoparticles could slowly release from the PLGA@pBMP-2/PEI microspheres for a long period of time. The 3–15 μm diameter of the PLGA@pBMP-2/PEI further supported this slow release ability of the PLGA@pBMP-2/PEI. In vitro transfection assays demonstrated that pBMP-2/PEI released from PLGA@pBMP-2/PEI could efficiently transfect MC3T3-E1 cells, causing MC3T3-E1 cells to secrete human BMP-2 protein, increase calcium deposition and gene expressions of alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), SP7 and I type collagen (COLL I), and finally induce MC3T3-E1 cell differentiation. Importantly, in vivo data from micro-computed tomography (micro-CT) and histological staining demonstrated that the human BMP-2 released from PLGA@pBMP-2/PEI had a long-term effect locally and efficiently promoted bone formation in the bone defect area compared to control animals. All our data suggest that our PLGA-nanoparticle delivery system efficiently and functionally delivers the human BMP-2 cDNA and has potential clinical application in the future after further modification.

BMP signaling in mesenchymal stem cell differentiation and bone formation

Bone morphogenetic proteins (BMPs) are members of the TGF-β superfamily and have diverse functions during development and organogenesis. BMPs play a major role in skeletal development and bone formation, and disruptions in BMP signaling cause a variety of skeletal and extraskeletal anomalies. Several knockout models have provided insight into the mechanisms responsible for these phenotypes. Proper bone formation requires the differentiation of osteoblasts from mesenchymal stem cell (MSC) precursors, a process mediated in part by BMP signaling. Multiple BMPs, including BMP2, BMP6, BMP7 and BMP9, promote osteoblastic differentiation of MSCs both in vitro and in vivo. BMP9 is one of the most osteogenic BMPs yet is a poorly characterized member of the BMP family. Several studies demonstrate that the mechanisms controlling BMP9-mediated osteogenesis differ from other osteogenic BMPs, but little is known about these specific mechanisms. Several pathways critical to BMP9-mediated osteogenesis are also important in the differentiation of other cell lineages, including adipocytes and chondrocytes. BMP9 has also demonstrated translational promise in spinal fusion and bone fracture repair. This review will summarize our current knowledge of BMP-mediated osteogenesis, with a focus on BMP9, by presenting recently completed work which may help us to further elucidate these pathways.

Human perivascular stem cells show enhanced osteogenesis and vasculogenesis with Nel-like molecule I protein

An ideal mesenchymal stem cell (MSC) source for bone tissue engineering has yet to be identified. Such an MSC population would be easily harvested in abundance, with minimal morbidity and with high purity. Our laboratories have identified perivascular stem cells (PSCs) as a candidate cell source. PSCs are readily isolatable through fluorescent-activated cell sorting from adipose tissue and have been previously shown to be indistinguishable from MSCs in the phenotype and differentiation potential. PSCs consist of two distinct cell populations: (1) pericytes (CD146+, CD34-, and CD45-), which surround capillaries and microvessels, and (2) adventitial cells (CD146-, CD34+, and CD45-), found within the tunica adventitia of large arteries and veins. We previously demonstrated the osteogenic potential of pericytes by examining pericytes derived from the human fetal pancreas, and illustrated their in vivo trophic and angiogenic effects. In the present study, we used an intramuscular ectopic bone model to develop the translational potential of our original findings using PSCs (as a combination of pericytes and adventitial cells) from human white adipose tissue. We evaluated human PSC (hPSC)-mediated bone formation and vascularization in vivo. We also examined the effects of hPSCs when combined with the novel craniosynostosis-associated protein, Nel-like molecule I (NELL-1). Implants consisting of the demineralized bone matrix putty combined with NELL-1 (3 μg/μL), hPSC (2.5×10(5) cells), or hPSC+NELL-1, were inserted in the bicep femoris of SCID mice. Bone growth was evaluated using microcomputed tomography, histology, and immunohistochemistry over 4 weeks. Results demonstrated the osteogenic potential of hPSCs and the additive effect of hPSC+NELL-1 on bone formation and vasculogenesis. Comparable osteogenesis was observed with NELL-1 as compared to the more commonly used bone morphogenetic protein-2. Next, hPSCs induced greater implant vascularization than the unsorted stromal vascular fraction from patient-matched samples. Finally, we observed an additive effect on implant vascularization with hPSC+NELL-1 by histomorphometry and immunohistochemistry, accompanied by in vitro elaboration of vasculogenic growth factors. These findings hold significant implications for the cell/protein combination therapy hPSC+NELL-1 in the development of strategies for vascularized bone regeneration.

Canine oral mucosal fibroblasts differentiate into osteoblastic cells in response to BMP-2

Several lines of evidence show that transplantation of osteoblastic cells or genetically engineered nonosteogenic cells expressing osteoblast-related genes into bone defects effectively promotes bone regeneration. To extend this possibility, we investigated whether oral mucosal fibroblasts are capable of differentiating into osteoblastic cells by conducting in vitro and in vivo experiments. We investigated the effects of bone morphogenetic protein-2 (BMP-2) on osteoblast differentiation of cultured fibroblasts isolated from canine buccal mucosa. We also transplanted green fluorescence protein (GFP)-expressing fibroblasts with gelatin/BMP-2 complexes into the subfascial regions of athymic mice, and investigated the localization of GFP-positive cells in the ectopically formed bones. The cultured canine buccal mucosal fibroblasts differentiated into osteoblastic cells by increasing their alkaline phosphatase (ALP) activity and Osteocalcin, Runx2, and Osterix mRNA expression levels in response to BMP-2. Transplantation experiments of GFP-expressing oral mucosal fibroblasts with gelatin/BMP-2 complexes revealed that 17.1% of the GFP-positive fibroblasts differentiated into ALP-positive cells, and these cells accounted for 6.2% of total ALP-positive cells in the ectopically formed bone. This study suggests that oral mucosal fibroblasts can differentiate into osteogenic cells in response to BMP-2. Thus, these cells are potential candidates for cell-mediated bone regeneration therapy in dentistry.

Effect of coadministration of vancomycin and BMP-2 on cocultured Staphylococcus aureus and W-20-17 mouse bone marrow stromal cells in vitro

In this study, we aimed to establish an in vitro bacterium/bone cell coculture model system and to use this model for dose dependence studies of dual administration of antibiotics and growth factors in vitro. We examined the effect of single or dual administration of the antibiotic vancomycin (VAN) at 0 to 16 μg/ml and bone morphogenetic protein-2 (BMP-2) at 0 or 100 ng/ml on both methicillin-sensitive Staphylococcus aureus and mouse bone marrow stromal cells (W-20-17) under both mono- and coculture conditions. Cell metabolic activity, Live/Dead staining, double-stranded DNA (dsDNA) amounts, and alkaline phosphatase activity were measured to assess cell viability, proliferation, and differentiation. An interleukin-6 (IL-6) enzyme-linked immunosorbent assay (ELISA) kit was used to test the bone cell inflammation response in the presence of bacteria. Our results suggest that, when delivered together in coculture, VAN and BMP-2 maintain their primary functions as an antibiotic and a growth factor, respectively. Most interestingly, this dual-delivery type of approach has shown itself to be effective at lower concentrations of VAN than those required for an approach relying strictly on the antibiotic. It may be that BMP-2 enhances cell proliferation and differentiation before the cells become infected. In coculture, a dosage of VAN higher than that used for treatment in monoculture may be necessary to effectively inhibit growth of Staphylococcus aureus. This could mean that the coculture environment may be limiting the efficacy of VAN, possibly by way of bacterial invasion of the bone cells. This report of a coculture study demonstrates a potential beneficial effect of the coadministration of antibiotics and growth factors compared to treatment with antibiotic alone.

Administration of growth factors for bone regeneration

Growth factors (GFs) such as BMPs, FGFs, VEGFs and IGFs have significant impacts on osteoblast behavior, and thus have been widely utilized for bone tissue regeneration. Recently, securing biological stability for a sustainable and controllable release to the target tissue has been a challenge to practical applications. This challenge has been addressed to some degree with the development of appropriate carrier materials and delivery systems. This review highlights the importance and roles of those GFs, as well as their proper administration for targeting bone regeneration. Additionally, the in vitro and in vivo performance of those GFs with or without the use of carrier systems in the repair and regeneration of bone tissue is systematically addressed. Moreover, some recent advances in the utility of the GFs, such as using fusion technology, are also reviewed.

Mesenchymal stem cells as a potent cell source for bone regeneration

While small bone defects heal spontaneously, large bone defects need surgical intervention for bone transplantation. Autologous bone grafts are the best and safest strategy for bone repair. An alternative method is to use allogenic bone graft. Both methods have limitations, particularly when bone defects are of a critical size. In these cases, bone constructs created by tissue engineering technologies are of utmost importance. Cells are one main component in the manufacture of bone construct. A few cell types, including embryonic stem cells (ESCs), adult osteoblast, and adult stem cells, can be used for this purpose. Mesenchymal stem cells (MSCs), as adult stem cells, possess characteristics that make them good candidate for bone repair. This paper discusses different aspects of MSCs that render them an appropriate cell type for clinical use to promote bone regeneration.

BMP-2 gene-fibronectin-apatite composite layer enhances bone formation

Background

Safe and efficient gene transfer systems are needed for tissue engineering. We have developed an apatite composite layer including the bone morphogenetic protein-2 (BMP-2) gene and fibronectin (FB), and we evaluated its ability to induce bone formation.

Methods

An apatite composite layer was evaluated to determine the efficiency of gene transfer to cells cultured on it. Cells were cultured on a composite layer including the BMP-2 gene and FB, and BMP-2 gene expression, BMP-2 protein concentrations, alkaline phosphatase (ALP) activity, and osteocalcin (OC) concentrations were measured. A bone defect on the cranium of rats was treated with hydroxyapatite (HAP)-coated ceramic buttons with the apatite composite layer including the BMP-2 gene and FB (HAP-BMP-FB). The tissue concentration of BMP-2, bone formation, and the expression levels of the BMP-2, ALP, and OC genes were all quantified.

Results

The apatite composite layer provided more efficient gene transfer for the cultured cells than an apatite composite layer without FB. The BMP-2 concentration was approximately 100~600 pg/mL in the cell-culture medium. Culturing the cells on the apatite composite layer for 27 days increased ALP activity and OC concentrations. In animal experiments, the tissue concentrations of BMP-2 were over 100 pg/mg in the HAP-BMP-FB group and approximately 50 pg/mg in the control groups. Eight weeks later, bone formation was more enhanced in the HAP-BMP-FB group than in the control groups. In the tissues surrounding the HAP button, the gene expression levels of ALP and OC increased.

Conclusion

The BMP-2 gene-FB-apatite composite layer might be useful for bone engineering.

Nell-1 protein promotes bone formation in a sheep spinal fusion model

Bone morphogenetic proteins (BMPs) are widely used as bone graft substitutes in spinal fusion, but are associated with numerous adverse effects. The growth factor Nel-like molecule-1 (Nell-1) is mechanistically distinct from BMPs and can minimize complications associated with BMP therapies. This study evaluates the efficacy of Nell-1 combined with demineralized bone matrix (DBM) as a novel bone graft material for interbody spine fusion using sheep, a phylogenetically advanced animal with biomechanical similarities to human spine. Nell-1+sheep DBM or Nell-1+heat-inactivated DBM (inDBM) (to determine the osteogenic effect of residual growth factors in DBM) were implanted in surgical sites as follows: (1) DBM only (control) (n=8); (2) DBM+0.3 mg/mL Nell-1 (n=8); (3) DBM+0.6 mg/mL Nell-1 (n=8); (4) inDBM only (control) (n=4); (5) inDBM+0.3 mg/mL Nell-1 (n=4); (6) inDBM+0.6 mg/mL Nell-1 (n=4). Fusion was assessed by computed tomography, microcomputed tomography, and histology. One hundred percent fusion was achieved by 3 months in the DBM+0.6 mg/mL Nell-1 group and by 4 months in the inDBM+0.6 mg/mL Nell-1 group; bone volume and mineral density were increased by 58% and 47%, respectively. These fusion rates are comparable to published reports on BMP-2 or autograft bone efficacy in sheep. Nell-1 is an independently potent osteogenic molecule that is efficacious and easily applied when combined with DBM.

Mesenchymal stem cells at the intersection of cell and gene therapy

IMPORTANCE OF THE FIELD

Mesenchymal stem cells have the ability to differentiate into osteoblasts, chondrocytes and adipocytes. Along with differentiation, MSCs can modulate inflammation, home to damaged tissues and secrete bioactive molecules. These properties can be enhanced through genetic-modification that would combine the best of both cell and gene therapy fields to treat monogenic and multigenic diseases.

AREAS COVERED IN THIS REVIEW

Findings demonstrating the immunomodulation, homing and paracrine activities of MSCs followed by a summary of the current research utilizing MSCs as a vector for gene therapy, focusing on skeletal disorders, but also cardiovascular disease, ischemic damage and cancer.

WHAT THE READER WILL GAIN

MSCs are a possible therapy for many diseases, especially those related to the musculoskeletal system, as a standalone treatment, or in combination with factors that enhance the abilities of these cells to migrate, survive or promote healing through anti-inflammatory and immunomodulatory effects, differentiation, angiogenesis or delivery of cytolytic or anabolic agents.

TAKE HOME MESSAGE

Genetically-modified MSCs are a promising area of research that would be improved by focusing on the biology of MSCs that could lead to identification of the natural and engrafting MSC-niche and a consensus on how to isolate and expand MSCs for therapeutic purposes.

The role of NELL-1, a growth factor associated with craniosynostosis, in promoting bone regeneration

Efforts to enhance bone regeneration in orthopedic and dental cases have grown steadily for the past decade, in line with increasingly sophisticated regenerative medicine. To meet the unprecedented demand for novel osteospecific growth factors with fewer adverse effects compared with those of existing adjuncts such as BMPs, our group has identified a craniosynostosis-associated secreted molecule, NELL-1, which is a potent growth factor that is highly specific to the osteochondral lineage, and has demonstrated robust induction of bone in multiple in vivo models from rodents to pre-clinical large animals. NELL-1 is preferentially expressed in osteoblasts under direct transcriptional control of Runx2, and is well-regulated during skeletal development. NELL-1/Nell-1 can promote orthotopic bone regeneration via either intramembranous or endochondral ossification, both within and outside of the craniofacial complex. Unlike BMP-2, Nell-1 cannot initiate ectopic bone formation in muscle, but can induce bone marrow stromal cells (BMSCs) to form bone in a mouse muscle pouch model, exhibiting specificity that BMPs lack. In addition, synergistic osteogenic effects of Nell-1 and BMP combotherapy have been observed, and are likely due to distinct differences in their signaling pathways. NELL-1's unique role as a novel osteoinductive growth factor makes it an attractive alternative with promise for future clinical applications. [Note: NELL-1 and NELL-1 indicate the human gene and protein, respectively; Nell-1 and Nell-1 indicate the mouse gene and protein, respectively.]

Gene therapy for bone healing

Clinical problems in bone healing include large segmental defects, spinal fusions, and the nonunion and delayed union of fractures. Gene-transfer technologies have the potential to aid healing by permitting the local delivery and sustained expression of osteogenic gene products within osseous lesions. Key questions for such an approach include the choice of transgene, vector and gene-transfer strategy. Most experimental data have been obtained using cDNAs encoding osteogenic growth factors such as bone morphogenetic protein-2 (BMP-2), BMP-4 and BMP-7, in conjunction with both nonviral and viral vectors using in vivo and ex vivo delivery strategies. Proof of principle has been convincingly demonstrated in small-animal models. Relatively few studies have used large animals, but the results so far are encouraging. Once a reliable method has been developed, it will be necessary to perform detailed pharmacological and toxicological studies, as well as satisfy other demands of the regulatory bodies, before human clinical trials can be initiated. Such studies are very expensive and often protracted. Thus, progress in developing a clinically useful gene therapy for bone healing is determined not only by scientific considerations, but also by financial constraints and the ambient regulatory environment.

Ex vivo transfer of the Hoxc-8-interacting domain of Smad1 by a tropism-modified adenoviral vector results in efficient bone formation in a rabbit model of spinal fusion

STUDY DESIGN

Ex vivo gene transfer for spinal fusion.

OBJECTIVE

This study aimed to evaluate ex vivo transfer of the nuclear-localized Hoxc-8-interacting domain of Smad1 (termed Smad1C) to rabbit bone marrow stromal cells (BMSCs) by a tropism-modified human adenovirus serotype 5 (Ad5) vector as a novel therapeutic approach for spinal fusion.

SUMMARY OF BACKGROUND DATA

Novel approaches are needed to improve the success of bone union after spinal fusion. One such approach is the ex vivo transfer of a gene encoding an osteoinductive factor to BMSCs which are subsequently reimplanted into the host. We have previously shown that heterologous expression of the Hoxc-8-interacting domain of Smad1 in the nuclei of osteoblast precursor cells is able to stimulate the expression of genes related to osteoblast differentiation and induce osteogenesis in vivo. Gene delivery vehicles based on human Ad5 are well suited for gene transfer for spinal fusion because they can mediate high-level, short-term gene expression. However, Ad5-based vectors with native tropism poorly transduce BMSCs, necessitating the use of vectors with modified tropism to achieve efficient gene transfer.

METHODS

The gene encoding Smad1C was transferred to rabbit BMSCs by an Ad5 vector with native tropism or a vector retargeted to alphav integrins, which are abundantly expressed on rabbit BMSCs. Transduced BMSCs were maintained in osteoblastic differentiation medium for 30 days. Alkaline phosphatase activity was determined and cells stained for calcium deposition. As positive controls for osteogenesis, we used Ad5 vectors expressing bone morphogenetic protein 2. As negative controls, BMSCs were mock-transduced or transduced with an Ad5 vector expressing beta-galactosidase. In an immunocompetent rabbit model of spinal fusion, transduced BMSCs were coated onto absorbable gelatin sponge and implanted between decorticated transverse processes L6 and L7 of 8-week-old female New Zealand white rabbits. Animals were killed 4 weeks after implantation of the sponges, the fusion masses harvested and the area of new bone quantified using image analysis software.

RESULTS

The Smad1C-expressing tropism-modified Ad5 vector mediated a significantly higher level of alkaline phosphatase activity and calcium deposition in transduced rabbit BMSCs than all other vectors. The rabbit BMSCs transduced ex vivo with the Smad1C-expressing tropism-modified Ad5 vector mediated a greater amount of new bone formation than BMSCs transduced with any other vector.

CONCLUSIONS

Delivery of the Smad1C gene construct to BMSCs by an alphav integrin-targeted Ad5 vector shows promise for spinal fusion and other applications requiring the formation of new bone in vivo.

Reconstruction of peri-implant bone defects using impacted bone allograft and BMP-2 gene-modified bone marrow stromal cells

Impaction bone allografting represents an attractive procedure for bone defects reconstruction in joint replacement. And it was found that bone morphogenetic protein-2(BMP-2) gene therapy can enhance bone healing. The purpose of this study was to determine if combined adenovirus mediated human BMP-2(Adv-hBMP-2) gene-modified bone marrow stromal cells(BMSCs) with allograft enhanced the defects healing and improved the strength of implant fixation in 3-mm bone defect around a titanium alloy implant. Using the impaction grafting technique, the defects were reconstructed using freeze-dried allograft, freeze-dried allografts loaded with autogenous BMSCs, or freeze-dried allografts loaded with autogenous BMSCs modified with the human bone morphogenetic protein-2 (hBMP-2) gene. At 6 and 12 weeks, the Bone-implant Contact rate and strength of the interface in the group with BMP-2 gene medication were significantly higher than those of the non-cell or cell groups. BMP-2 gene medication also showed significant effects on allograft healing and replacement compared with those of two other groups, as evidenced by increased new bone formation and reduced graft remnants. The results suggest that BMP-2 gene medication can enhance allograft healing and osseointegration of the bone-implant interface.

Evaluation of Spinal Fusion Using Bone Marrow Derived Mesenchymal Stem Cells with or without Fibroblast Growth Factor-4

OBJECTIVE

In this study, the authors assessed the ability of rat bone marrow derived mesenchymal stem cells (BMDMSCs), in the presence of a growth factor, fibroblast growth factor-4 (FGF-4) and hydroxyapatite, to act as a scaffold for posterolateral spinal fusion in a rat model.

METHODS

Using a rat posterolateral spine fusion model, the experimental study comprised 3 groups. Group 1 was composed of 6 animals that were implanted with 0.08 gram hydroxyapatite only. Group 2 was composed of 6 animals that were implanted with 0.08 gram hydroxyapatite containing 1 x 10(6)/ 60 microL rat of BMDMSCs. Group 3 was composed of 6 animals that were implanted with 0.08 gram hydroxyapatite containing 1 x 10(6)/ 60 microL of rat BMDMSCs and FGF-4 1 microG to induce the bony differentiation of the BMDMSCs. Rats were assessed using radiographs obtained at 4, 6, and 8 weeks postoperatively. After sacrifice, spines were explanted and assessed by manual palpation, high-resolution microcomputerized tomography, and histological analysis.

RESULTS

Radiographic, high-resolution microcomputerized tomographic, and manual palpation revealed spinal fusion in five rats (83%) in Group 2 at 8 weeks. However, in Group 1, three (60%) rats developed fusion at L4-L5 by radiography and two (40%) by manual palpation in radiographic examination. In addition, in Group 3, bone fusion was observed in only 50% of rats by manual palpation and radiographic examination at this time.

CONCLUSION

The present study demonstrates that 0.08 gram of hydroxyapatite with 1 x 10(6)/ 60 microL rat of BMDMSCs induced bone fusion. FGF-4, added to differentiate primitive 1 x 10(6)/ 60 microL rat of BMDMSCs did not induce fusion. Based on histologic data, FGF-4 appears to induce fibrotic change rather than differentiation to bone by 1 x 10(6)/ 60 microL rat of BMDMSCs.

Bone formation on apatite-coated titanium with incorporated BMP-2/heparin in vivo

OBJECTIVE

The objective of this study was to investigate whether the in vivo osteoinductive activity of an implant material is enhanced by covering the surface of apatite with incorporated bone morphogenetic protein 2 (BMP-2) and heparin which maintains the activity of BMP-2.

STUDY DESIGN

Titanium implants were alkaline treated, heat activated, and soaked in stimulated body fluid with or without BMP-2/heparin to coat the apatite around them. Treated implant bars were then implanted in rat tibiae. After 3 weeks, nondecalcified sections were prepared and the new bone formation around the implants was examined.

RESULTS

A greater amount of bone formed on the apatite-coated implants containing BMP-2/heparin than on apatite-coated implants containing BMP, with >or=3 microg/mL heparin. Apatite-coated titanium implants with BMP-2/heparin had significantly enhanced new endosteal bone formation, with increases vertically (134%) and horizontally (124%).

CONCLUSIONS

Bone formation was stimulated around the apatite-covered titanium coated with BMP-2/heparin, which may be useful in improving implant therapy.

Preparation of injectable 3D-formed beta-tricalcium phosphate bead/alginate composite for bone tissue engineering

A novel, injectable bone tissue engineering material was developed that consisted of beta-tricalcium phosphate (beta-TCP) beads as the solid phase and alginate as the gel phase. To prepare the instantaneously formed composite scaffold, an aqueous calcium chloride solution was dried on the surface of beta-TCP beads and crosslinked with an alginic acid sodium solution, thereby forming stable beta-TCP beads and alginate gel which were injectable via a syringe. This biodegradable composite was a three-dimensional (3D) material that could be used as an injectable scaffold for bone tissue engineering. In particular, the composite with 2.0 wt% alginate concentration exhibited a compressive strength of 69 kPa in dry conditions, which was significantly higher than that exhibited by 1.0 wt%. Furthermore, mesenchymal stem cells (MSC) were 3D-cultured within the composite and then investigated for osteogenic markers. MSC-loaded composite was subjected to scanning electron microscope (SEM) examination and implanted subcutaneously for in vivo experiment. Results showed that the scaffold provided support for osteogenic differentiation. In light of the encouraging results obtained, this novel injectable composite material may be useful for bone tissue engineering.

Mesenchymal stem cell and gene therapies for spinal fusion

THE IDEAL GRAFT material to promote spinal fusion should possess osteoconductive, osteoinductive, and osteogenic properties. Although autogenous bone graft has all three qualities and is the standard for comparison, research has focused on finding alternatives that have similar efficacy but not the morbidities associated with graft donor sites. Efforts have focused on various osteoconductive scaffolds and introduction of osteoinductive proteins, including bone morphogenetic protein. Recently, interest in using osteoprogenitor cells, or osteogenesis, for spinal fusion has increased. Bone marrow aspiration allows the introduction of mesenchymal stem cells and ultimately osteoblasts to promote fusion. Preclinical studies suggest that the addition of osteoprogenitor cells to various osteoconductive materials results in a fusion rate similar to that of autograft. There is growing recognition that local gene therapy has the benefit of delivering therapeutic genes that encode novel osteoinductive proteins. Gene delivery offers an alternative to local implantation of recombinant protein, which typically requires high doses of the protein to result in a sufficient osteoinductive response. The findings of animal studies demonstrate that gene therapy results in sustained and regulated production of desired osteoinductive proteins and is efficacious in promoting spinal fusion; however, before treatment in humans can be undertaken, obstacles such as the safety profile, host immune response, transfection rates with insufficient transgene expression, and imprecise control of the timing of transgene expression must be overcome. In this review, the authors summarize the latest research efforts under way to promote spinal fusion with osteoprogenitor cells and gene therapy and discuss the clinical implications of these treatments.

Orthopedic gene therapy in 2008

Orthopedic disorders, although rarely fatal, are the leading cause of morbidity and impose a huge socioeconomic burden. Their prevalence will increase dramatically as populations age and gain weight. Many orthopedic conditions are difficult to treat by conventional means; however, they are good candidates for gene therapy. Clinical trials have already been initiated for arthritis and the aseptic loosening of prosthetic joints, and the development of bone-healing applications is at an advanced, preclinical stage. Other potential uses include the treatment of Mendelian diseases and orthopedic tumors, as well as the repair and regeneration of cartilage, ligaments, and tendons. Many of these goals should be achievable with existing technologies. The main barriers to clinical application are funding and regulatory issues, which in turn reflect major safety concerns and the opinion, in some quarters, that gene therapy should not be applied to nonlethal, nongenetic diseases. For some indications, advances in nongenetic treatments have also diminished enthusiasm. Nevertheless, the preclinical and early clinical data are impressive and provide considerable optimism that gene therapy will provide straightforward, effective solutions to the clinical management of several common debilitating disorders that are otherwise difficult and expensive to treat.

Osteogenic differentiation of mesenchymal stem cells using PAMAM dendrimers as gene delivery vectors

This paper reports the use of different generations of polyamidoamine (PAMAM) dendrimers for the in vitro transfection of mesenchymal stem cells (MSCs). A systematic study was carried out on the transfection efficiency achieved by the PAMAM dendrimers using a beta-galactosidase reporter gene system. Transfection results were shown to be dependent upon the generation of dendrimers, the amine to phosphate group ratio and the cell passage number. In all cases, the transfection efficiency was very low. Nevertheless, it was hypothesized that a low transfection level could be sufficient to promote the in vitro differentiation of MSCs towards the osteoblastic lineage. To address this possibility, dendrimers carrying the human bone morphogenetic protein-2 (hBMP-2) gene-containing plasmid were used. All quantitative (alkaline phosphatase activity, osteocalcin secretion and calcium deposition) and qualitative (von Kossa staining) osteogenic markers were significantly stronger in transfected cells when compared to non-transfected ones. This study not only clearly demonstrates that a low transfection level can be sufficient for inducing in vitro differentiation of MSCs to the osteoblast phenotype but also highlights the importance of focusing research on the development of gene delivery vectors in the concrete application.