Gene therapy for bone engineering

Advances in implants and bone graft types for lumbar spinal fusion surgery

The increasing prevalence of spinal disorders worldwide necessitates advanced treatments, particularly interbody fusion for severe cases that are unresponsive to non-surgical interventions. This procedure, especially 360° lumbar interbody fusion, employs an interbody cage, pedicle screw-and-rod instrumentation, and autologous bone graft (ABG) to enhance spinal stability and promote fusion. Despite significant advancements, a persistent 10% incidence of non-union continues to result in compromised patient outcomes and escalated healthcare costs. Innovations in lumbar stabilisation seek to mimic the properties of natural bone, with evolving implant materials like titanium (Ti) and polyetheretherketone (PEEK) and their composites offering new prospects. Additionally, biomimetic cages featuring precisely engineered porosities and interconnectivity have gained traction, as they enhance osteogenic differentiation, support osteogenesis, and alleviate stress-shielding. However, the limitations of ABG, such as harvesting morbidities and limited fusion capacity, have spurred the exploration of sophisticated solutions involving advanced bone graft substitutes. Currently, demineralised bone matrix and ceramics are in clinical use, forming the basis for future investigations into novel bone graft substitutes. Bioglass, a promising newcomer, is under investigation despite its observed rapid absorption and the potential for foreign body reactions in preclinical studies. Its clinical applicability remains under scrutiny, with ongoing research addressing challenges related to burst release and appropriate dosing. Conversely, the well-documented favourable osteogenic potential of growth factors remains encouraging, with current efforts focused on modulating their release dynamics to minimise complications. In this evidence-based narrative review, we provide a comprehensive overview of the evolving landscape of non-degradable spinal implants and bone graft substitutes, emphasising their applications in lumbar spinal fusion surgery. We highlight the necessity for continued research to improve clinical outcomes and enhance patient well-being.

A Genetically Engineered "Reinforced Concrete" Scaffold Regulates the N2 Neutrophil Innate Immune Cascade to Repair Bone Defects

The innate immune response is crucial to inflammation, but how neutrophils and macrophages act in bone repair and tissue engineering treatment strategies await clarification. In this study, it is found that N2 neutrophils release stronger "eat me" signals to induce macrophage phagocytosis and polarize into the M2 anti-inflammatory phenotype. Guided by this biological mechanism, a mesoporous bioactive glass scaffold (MBG) is filled with hyaluronic acid methacryloyl (HAMA) hydrogel loaded with Transforming growth factor-β1 (TGFβ1) adenovirus (Ad@H), constructing a genetically engineered composite scaffold (Ad@H/M). The scaffold not only has good hydrophilicity and biocompatibility, but also provides mechanical stress support for bone repair. Adenovirus infection quickly induces N2 neutrophils, upregulating NF-κB and MAPK signaling pathways through Toll-like receptor 4 (TLR4) to promote the inflammatory response and macrophage phagocytosis. Macrophages perform phagocytosis and polarize towards the M2 phenotype, mediating the inflammatory response by inhibiting the PI3K-AKT-NF-κB pathway, maintaining homeostasis of the osteogenic microenvironment. The role of the Ad@H/M scaffold in regulating early inflammation and promoting long-term bone regeneration is further validated in vivo. In brief, this study focuses on the cascade of reactions between neutrophils and macrophage subtypes, and reports a composite scaffold that coordinates the innate immune response to promote bone repair.

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.

Cellular uptake of modified mRNA occurs via caveolae-mediated endocytosis, yielding high protein expression in slow-dividing cells

Nucleic acids have clear clinical potential for gene therapy. Plasmid DNA (pDNA) was the first nucleic acid to be pursued as a therapeutic molecule. Recently, mRNA came into play as it offers improved safety and affordability. In this study, we investigated the uptake mechanisms and efficiencies of genetic material by cells. We focused on three main variables (1) the nucleic acid (pDNA, or chemically modified mRNA), (2) the delivery vector (Lipofectamine 3000 or 3DFect), and (3) human primary cells (mesenchymal stem cells, dermal fibroblasts, and osteoblasts). In addition, transfections were studied in a 3D environment using electrospun scaffolds. Cellular internalization and intracellular trafficking were assessed by using enhancers or inhibitors of endocytosis and endosomal escape. The polymeric vector TransIT-X2 was included for comparison purposes. While lipoplexes utilized several entry routes, uptake via caveolae served as the main route for gene delivery. pDNA yielded higher expression levels in fast-dividing fibroblasts, whereas, in slow-dividing osteoblasts, cmRNA was responsible for high protein production. In the case of mesenchymal stem cells, which presented an intermediate doubling time, the combination vector/nucleic acid seemed more relevant than the nucleic acid per se. In all cases, protein expression was higher when the cells were seeded on 3D scaffolds.

Exploring microRNAs in craniofacial regenerative medicine

microRNAs (miRs) have been reported over the decades as important regulators in bone development and bone regeneration. They play important roles in maintaining the stem cell signature as well as regulating stem cell fate decisions. Thus, delivering miRs and miR inhibitors to the defect site is a potential treatment towards craniofacial bone defects. However, there are challenges in translation of basic research to clinics, including the efficiency, specificity, and efficacy of miR manipulation methods and the safety of miR delivery systems. In this review, we will compare miR oligonucleotides, mimics and antagomirs as therapeutic reagents to treat disease and regenerate tissues. Newer technology will be discussed as well as the efficiency and efficacy of using these technologies to express or inhibit miRs in treating and repairing oral tissues. Delivery of these molecules using extracellular vesicles and nanoparticles can achieve different results and depending on their composition will elicit specific effects. We will highlight the specificity, toxicity, stability, and effectiveness of several miR systems in regenerative medicine.

Engineered cells along with smart scaffolds: critical factors for improving tissue engineering approaches

In this review, gene delivery and its applications are discussed in tissue engineering (TE); also, new techniques such as the CRISPR-Cas9 system, synthetics biology and molecular dynamics simulation to improve the efficiency of the scaffolds have been studied. CRISPR-Cas9 is expected to make significant advances in TE in the future. The fundamentals of synthetic biology have developed powerful and flexible methods for programming cells via artificial genetic circuits. The combination of regenerative medicine and artificial biology allows the engineering of cells and organisms for use in TE, biomaterials, bioprocessing and scaffold development. The dynamics of protein adsorption at the scaffold surface at the atomic level can provide valuable guidelines for the future design of TE scaffolds /implants.

Tutorial: design and execution of CRISPR in vivo screens

Here we provide a detailed tutorial on CRISPR in vivo screening. Using the mouse as the model organism, we introduce a range of CRISPR tools and applications, delineate general considerations for 'transplantation-based' or 'direct in vivo' screening design, and provide details on technical execution, sequencing readouts, computational analyses and data interpretation. In vivo screens face unique pitfalls and limitations, such as delivery issues or library bottlenecking, which must be counteracted to avoid screening failure or flawed conclusions. A broad variety of in vivo phenotypes can be interrogated such as organ development, hematopoietic lineage decision and evolutionary licensing in oncogenesis. We describe experimental strategies to address various biological questions and provide an outlook on emerging CRISPR applications, such as genetic interaction screening. These technological advances create potent new opportunities to dissect the molecular underpinnings of complex organismal phenotypes.

Lipid-Based Nano-Sized Cargos as a Promising Strategy in Bone Complications: A Review

Bone metastasis has been considered the fatal phase of cancers, which remains incurable and to be a challenge due to the non-availability of the ideal treatment strategy. Unlike bone cancer, bone metastasis involves the spreading of the tumor cells to the bones from different origins. Bone metastasis generally originates from breast and prostate cancers. The possibility of bone metastasis is highly attributable to its physiological milieu susceptible to tumor growth. The treatment of bone-related diseases has multiple complications, including bone breakage, reduced quality of life, spinal cord or nerve compression, and pain. However, anticancer active agents have failed to maintain desired therapeutic concentrations at the target site; hence, uptake of the drug takes place at a non-target site responsible for the toxicity at the cellular level. Interestingly, lipid-based drug delivery systems have become the center of interest for researchers, thanks to their biocompatible and bio-mimetic nature. These systems possess a great potential to improve precise bone targeting without affecting healthy tissues. The lipid nano-sized systems are not only limited to delivering active agents but also genes/peptide sequences/siRNA, bisphosphonates, etc. Additionally, lipid coating of inorganic nanomaterials such as calcium phosphate is an effective approach against uncontrollable rapid precipitation resulting in reduced colloidal stability and dispersity. This review summarizes the numerous aspects, including development, design, possible applications, challenges, and future perspective of lipid nano-transporters, namely liposomes, exosomes, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), and lipid nanoparticulate gels to treat bone metastasis and induce bone regeneration. Additionally, the economic suitability of these systems has been discussed and different alternatives have been discussed. All in all, through this review we will try to understand how far nanomedicine is from clinical and industrial applications in bone metastasis.

Gene therapy for bone healing: lessons learned and new approaches

Although gene therapy has its conceptual origins in the treatment of Mendelian disorders, it has potential applications in regenerative medicine, including bone healing. Research into the use of gene therapy for bone healing began in the 1990s. Prior to this period, the highly osteogenic proteins bone morphogenetic protein (BMP)-2 and -7 were cloned, produced in their recombinant forms and approved for clinical use. Despite their promising osteogenic properties, the clinical usefulness of recombinant BMPs is hindered by delivery problems that necessitate their application in vastly supraphysiological amounts. This generates adverse side effects, some of them severe, and raises costs; moreover, the clinical efficacy of the recombinant proteins is modest. Gene delivery offers a potential strategy for overcoming these limitations. Our research has focused on delivering a cDNA encoding human BMP-2, because the recombinant protein is Food and Drug Administration approved and there is a large body of data on its effects in people with broken bones. However, there is also a sizeable literature describing experimental results obtained with other transgenes that may directly or indirectly promote bone formation. Data from experiments in small animal models confirm that intralesional delivery of BMP-2 cDNA is able to heal defects efficiently and safely while generating transient, local BMP-2 concentrations 2-3 log orders less than those needed by recombinant BMP-2. The next challenge is to translate this information into a clinically expedient technology for bone healing. Our present research focuses on the use of genetically modified, allografted cells and chemically modified messenger RNA.

Mineralized polyplexes for gene delivery: Improvement of transfection efficiency as a consequence of calcium incubation and not mineralization

Gene therapy is an emerging field in which nucleic acids are used to control protein expression. The necessity of delivering nucleic acids to specific cell types and intracellular sites demands the use of highly specialized gene carriers. As a carrier modification technique, mineralization has been successfully used to modify viral and non-viral carriers, providing new properties that ultimately aim to increase the transfection efficiency. However, for the specific case of polyplexes used in gene therapy, recent literature shows that interaction with calcium, a fundamental step of mineralization, might be effective to increase transfection efficiency, leaving an ambiguity about of the role of mineralization for this type of gene carriers. To answer this question and to reveal the properties responsible for increasing transfection efficiency, we mineralized poly(aspartic acid) coated polyplexes at various CaCl₂ and Na₃PO₄ concentrations, and evaluated the resultant carriers for physicochemical and morphological characteristics, as well as transfection and delivery efficiency with MC3T3-E1 mouse osteoblastic cells. We found that both mineralization and calcium incubation positively affected the transfection efficiency and uptake of polyplexes in MC3T3-E1 cells. However, this effect originated from the properties achieved by polyplexes after the calcium incubation step that are maintained after mineralization, including particle size increase, improved pDNA binding, and adjustment of zeta potential. Considering that mineralization can be a longer process than calcium incubation, we find that calcium incubation might be sufficient and preferred if improved transfection efficiency in vitro is the only effect desired.

Rat Calvarial Bone Regeneration by 3D-Printed β-Tricalcium Phosphate Incorporating MicroRNA-200c

Advanced fabrication methods for bone grafts designed to match defect sites that combine biodegradable, osteoconductive materials with potent, osteoinductive biologics would significantly impact the clinical treatment of large bone defects. In this study, we engineered synthetic bone grafts using a hybrid approach that combined three-dimensional (3D-)printed biodegradable, osteoconductive β-tricalcium phosphate (β-TCP) with osteoinductive microRNA(miR)-200c. 3D-printed β-TCP scaffolds were fabricated utilizing a suspension-enclosing projection-stereolithography (SEPS) process to produce constructs with reproducible microarchitectures that enhanced the osteoconductive properties of β-TCP. Collagen coating on 3D-printed β-TCP scaffolds slowed the release of plasmid DNA encoding miR-200c compared to noncoated constructs. 3D-printed β-TCP scaffolds coated with miR-200c-incorporated collagen increased the transfection efficiency of miR-200c of both rat and human BMSCs and additionally increased osteogenic differentiation of hBMSCs in vitro. Furthermore, miR-200c-incorporated scaffolds significantly enhanced bone regeneration in critical-sized rat calvarial defects. These results strongly indicate that bone grafts combining SEPS 3D-printed osteoconductive biomaterial-based scaffolds with osteoinductive miR-200c can be used as superior bone substitutes for the clinical treatment of large bone defects.

Orthopaedic Gene Therapy: Twenty-Five Years On

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Orthopaedics pioneered the expansion of gene therapy beyond its traditional scope of diseases that are caused by rare single-gene defects. Orthopaedic applications of gene therapy are most developed in the areas of arthritis and regenerative medicine, but several additional possibilities exist.

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Invossa, an ex vivo gene therapeutic for osteoarthritis, was approved in South Korea in 2017, but its approval was retracted in 2019 and remains under appeal; a Phase-III clinical trial of Invossa has restarted in the U.S.

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There are several additional clinical trials for osteoarthritis and rheumatoid arthritis that could lead to approved gene therapeutics for arthritis.

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Bone-healing and cartilage repair are additional areas that are attracting considerable research; intervertebral disc degeneration and the healing of ligaments, tendons, and menisci are other applications of interest. Orthopaedic tumors, genetic diseases, and aseptic loosening are additional potential targets.

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If successful, these endeavors will expand the scope of gene therapy from providing expensive medicines for a few patients to providing affordable medicines for many.

Apoptosis repressor with caspase recruitment domain (ARC) promotes bone regeneration of bone marrow-derived mesenchymal stem cells by activating Fgf-2/PI3K/Akt signaling

Objectives

This study aims to investigate whether apoptosis repressor with caspase recruitment domain (ARC) could promote survival and enhance osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs).

Materials and methods

The lentivirus transfection method was used to establish ARC-overexpressing BMSCs. The CCK-8 method was used to detect cell proliferation. The BD Pharmingen™ APC Annexin V Apoptosis Detection kit was used to detect cell apoptosis. The osteogenic capacity was investigated by OCN immunofluorescence staining, ALP analysis, ARS assays, and RT-PCR analysis. Cells were seeded into calcium phosphate cement (CPC) scaffolds and then inserted subcutaneously into nude mice and the defect area of the rat calvarium. Histological analysis was conducted to evaluate the in vivo cell apoptosis and new bone formation of the ARC-overexpressing BMSCs. RNA-seq was used to detect the possible mechanism of the effect of ARC on BMSCs.

Results

ARC promoted BMSC proliferation and inhibited cell apoptosis. ARC enhanced BMSC osteogenic differentiation in vitro. An in vivo study revealed that ARC can inhibit BMSC apoptosis and increase new bone formation. ARC regulates BMSCs mainly by activating the Fgf-2/PI3K/Akt pathway.

Conclusions

The present study suggests that ARC is a powerful agent for promoting bone regeneration of BMSCs and provides a promising method for bone tissue engineering.

Transcript-Activated Coatings on Titanium Mediate Cellular Osteogenesis for Enhanced Osteointegration

Osteointegration is one of the most important factors for implant success. Several biomolecules have been used as part of drug delivery systems to improve implant integration into the surrounding bone tissue. Chemically modified mRNA (cmRNA) is a new form of therapeutic that has been used to induce bone healing. Combined with biomaterials, cmRNA can be used to develop transcript-activated matrices for local protein production with osteoinductive potential. In this study, we aimed to utilize this technology to create bone morphogenetic protein 2 (BMP2) transcript-activated coatings for titanium (Ti) implants. Therefore, different coating methodologies as well as cmRNA incorporation strategies were evaluated. Three different biocompatible biomaterials were used for the coating of Ti, namely, poly-d,l-lactic acid (PDLLA), fibrin, and fibrinogen. cmRNA-coated Ti disks were assayed for transfection efficiency, cmRNA release, cell viability and proliferation, and osteogenic activity in vitro. We found that cmRNA release was significantly delayed in Ti surfaces previously coated with biomaterials. Consequently, the transfection efficiency was greatly improved. PDLLA coating improved the transfection efficiency in a concentration-dependent manner. Lower PDLLA concentration used for the coating of Ti resulted in higher transfection efficiency. Fibrin and fibrinogen coatings showed even higher transfection efficiencies compared to all PDLLA concentrations. In those disks, not only the expression was up to 24-fold higher but also the peak of maximal expression was delayed from 24 h to 5 days, and the duration of expression was also extended until 7 days post-transfection. For fibrin, higher transfection efficiencies were obtained in the coatings with the lowest thrombin amounts. Accordingly, fibrinogen coatings gave the best results in terms of cmRNA transfection. All biomaterial-coated Ti surfaces showed improved cell viability and proliferation, though this was more noticeable in the fibrinogen-coated disks. The latter was also the only coating to support significant amounts of BMP2 produced by C2C12 cells in vitro. Osteogenesis was confirmed using BMP2 cmRNA fibrinogen-coated Ti disks, and it was dependent of the cmRNA amount present. Alkaline phosphatase (ALP) activity of C2C12 increased when using fibrinogen coatings containing 250 ng of cmRNA or more. Similarly, mineralization was also observed that increased with increasing cmRNA concentration. Overall, our results support fibrinogen as an optimal material to deliver cmRNA from titanium-coated surfaces.

Osteogenic differentiation cues of the bone morphogenetic protein-9 (BMP-9) and its recent advances in bone tissue regeneration

Bone regeneration using bioactive molecules and biocompatible materials is growing steadily with the advent of the new findings in cellular signaling. Bone Morphogenetic Protein (BMP)-9 is a considerably recent discovery from the BMP family that delivers numerous benefits in osteogenesis. The Smad cellular signaling pathway triggered by BMPs is often inhibited by Noggin. However, BMP-9 is resistant to Noggin, thus, facilitating a more robust cellular differentiation of osteoprogenitor cells into preosteoblasts and osteoblasts. This review encompasses a general understanding of the Smad signaling pathway activated by the BMP-9 ligand molecule with its specific receptors. The robust osteogenic cellular differentiation cue provided by BMP-9 has been reviewed from a bone regeneration perspective with several in vitro as well as in vivo studies reporting promising results for future research. The effect of the biomaterial, chosen in such studies as the scaffold or carrier matrix, on the activity of BMP-9 and subsequent bone regeneration has been highlighted in this review. The non-viral delivery technique for BMP-9 induced bone regeneration is a safer alternative to its viral counterpart. The recent advances in non-viral BMP-9 delivery have also highlighted the efficacy of the protein molecule at a low dosage. This opens a new horizon as a more efficient and safer alternative to BMP-2, which was prevalent among clinical trials; however, BMP-2 applications have reported its downsides during bone defect healing such as cystic bone formation.

Non-viral Gene Delivery Methods for Bone and Joints

Viral carrier transport efficiency of gene delivery is high, depending on the type of vector. However, viral delivery poses significant safety concerns such as inefficient/unpredictable reprogramming outcomes, genomic integration, as well as unwarranted immune responses and toxicity. Thus, non-viral gene delivery methods are more feasible for translation as these allow safer delivery of genes and can modulate gene expression transiently both in vivo, ex vivo, and in vitro. Based on current studies, the efficiency of these technologies appears to be more limited, but they are appealing for clinical translation. This review presents a summary of recent advancements in orthopedics, where primarily bone and joints from the musculoskeletal apparatus were targeted. In connective tissues, which are known to have a poor healing capacity, and have a relatively low cell-density, i.e., articular cartilage, bone, and the intervertebral disk (IVD) several approaches have recently been undertaken. We provide a brief overview of the existing technologies, using nano-spheres/engineered vesicles, lipofection, and in vivo electroporation. Here, delivery for microRNA (miRNA), and silencing RNA (siRNA) and DNA plasmids will be discussed. Recent studies will be summarized that aimed to improve regeneration of these tissues, involving the delivery of bone morphogenic proteins (BMPs), such as BMP2 for improvement of bone healing. For articular cartilage/osteochondral junction, non-viral methods concentrate on targeted delivery to chondrocytes or MSCs for tissue engineering-based approaches. For the IVD, growth factors such as GDF5 or GDF6 or developmental transcription factors such as Brachyury or FOXF1 seem to be of high clinical interest. However, the most efficient method of gene transfer is still elusive, as several preclinical studies have reported many different non-viral methods and clinical translation of these techniques still needs to be validated. Here we discuss the non-viral methods applied for bone and joint and propose methods that can be promising in clinical use.

Modifying MSC Phenotype to Facilitate Bone Healing: Biological Approaches

Healing of fractures and bone defects normally follows an orderly series of events including formation of a hematoma and an initial stage of inflammation, development of soft callus, formation of hard callus, and finally the stage of bone remodeling. In cases of severe musculoskeletal injury due to trauma, infection, irradiation and other adverse stimuli, deficient healing may lead to delayed or non-union; this results in a residual bone defect with instability, pain and loss of function. Modern methods of mechanical stabilization and autologous bone grafting are often successful in achieving fracture union and healing of bone defects; however, in some cases, this treatment is unsuccessful because of inadequate biological factors. Specifically, the systemic and local microenvironment may not be conducive to bone healing because of a loss of the progenitor cell population for bone and vascular lineage cells. Autologous bone grafting can provide the necessary scaffold, progenitor and differentiated lineage cells, and biological cues for bone reconstruction, however, autologous bone graft may be limited in quantity or quality. These unfavorable circumstances are magnified in systemic conditions with chronic inflammation, including obesity, diabetes, chronic renal disease, aging and others. Recently, strategies have been devised to both mitigate the necessity for, and complications from, open procedures for harvesting of autologous bone by using minimally invasive aspiration techniques and concentration of iliac crest bone cells, followed by local injection into the defect site. More elaborate strategies (not yet approved by the U.S. Food and Drug Administration-FDA) include isolation and expansion of subpopulations of the harvested cells, preconditioning of these cells or inserting specific genes to modulate or facilitate bone healing. We review the literature pertinent to the subject of modifying autologous harvested cells including MSCs to facilitate bone healing. Although many of these techniques and technologies are still in the preclinical stage and not yet approved for use in humans by the FDA, novel approaches to accelerate bone healing by modifying cells has great potential to mitigate the physical, economic and social burden of non-healing fractures and bone defects.

Pre-Clinical Evaluation of Biological Bone Substitute Materials for Application in Highly Loaded Skeletal Sites

The development of bone substitute materials (BSMs) intended for load-bearing bone defects is highly complicated, as biological and mechanical requirements are often contradictory. In recent years, biological BSMs have been developed which allow for a more efficient integration of the material with the surrounding osseous environment and, hence, a higher mechanical stability of the treated defect. However, while these materials are promising, they are still far from ideal. Consequently, extensive preclinical experimentation is still required. The current review provides a comprehensive overview of biomechanical considerations relevant for the design of biological BSMs. Further, the preclinical evaluation of biological BSMs intended for application in highly loaded skeletal sites is discussed. The selected animal models and implantation site should mimic the pathophysiology and biomechanical loading patterns of human bone as closely as possible. In general, sheep are among the most frequently selected animal models for the evaluation of biomaterials intended for highly loaded skeletal sites. Regarding the anatomical sites, segmental bone defects created in the limbs and spinal column are suggested as the most suitable. Furthermore, the outcome measurements used to assess biological BSMs for regeneration of defects in heavily loaded bone should be relevant and straightforward. The quantitative evaluation of bone defect healing through ex vivo biomechanical tests is a valuable addition to conventional in vivo tests, as it determines the functional efficacy of BSM-induced bone healing. Finally, we conclude that further standardization of preclinical studies is essential for reliable evaluation of biological BSMs in highly loaded skeletal sites.

Drug Delivery Systems Based on Titania Nanotubes and Active Agents for Enhanced Osseointegration of Bone Implants

TiO2 nanotubes (TNTs) are attractive nanostructures for localized drug delivery. Owing to their excellent biocompatibility and physicochemical properties, numerous functionalizations of TNTs have been attempted for their use as therapeutic agent delivery platforms. In this review, we discuss the current advances in the applications of TNT-based delivery systems with an emphasis on the various functionalizations of TNTs for enhancing osteogenesis at the bone-implant interface and for preventing implant-related infection. Innovation of therapies for enhancing osteogenesis still represents a critical challenge in regeneration of bone defects. The overall concept focuses on the use of osteoconductive materials in combination with the use of osteoinductive or osteopromotive factors. In this context, we highlight the strategies for improving the functionality of TNTs, using five classes of bioactive agents: growth factors (GFs), statins, plant derived molecules, inorganic therapeutic ions/nanoparticles (NPs) and antimicrobial compounds.

Active Immunoprophylaxis and Vaccine Augmentations Mediated by a Novel Plasmid DNA Formulation

Plasmid DNA (pDNA) gene delivery is a highly versatile technology that has the potential to address a multitude of unmet medical needs. Advances in pDNA delivery to host tissue with the employment of in vivo electroporation (EP) have led to significantly enhanced gene expression and the recent demonstration of clinical efficacy with the platform. Building upon this platform, this study reports that enzyme-mediated modification of the muscle tissue extracellular matrix structure at the site of pDNA delivery operates in a synergistic manner with EP to enhance both local and systemic gene expression further. Specifically, administration of chondroitinase ABC (Cho ABC) to the site of intramuscular delivery of pDNA led to transient disruption of chondroitin sulfate scaffolding barrier, permitting enhanced gene distribution and expression across the tissue. The employment of Cho ABC in combination with CELLECTRA^® intramuscular EP resulted in increased gene expression by 5.5-fold in mice and 17.98-fold in rabbits. The study demonstrates how this protocol can be universally applied to an active prophylaxis platform to increase the in vivo production of functional immunoglobulin G, and to DNA vaccine protocols to permit drug dose sparing. The data indicate the Cho ABC formulation to be of significant value upon combination with EP to drive enhanced gene expression levels in pDNA delivery protocols.

Calcium Phosphate Nanoparticles-Based Systems for RNAi Delivery: Applications in Bone Tissue Regeneration

Bone-related injury and disease constitute a significant global burden both socially and economically. Current treatments have many limitations and thus the development of new approaches for bone-related conditions is imperative. Gene therapy is an emerging approach for effective bone repair and regeneration, with notable interest in the use of RNA interference (RNAi) systems to regulate gene expression in the bone microenvironment. Calcium phosphate nanoparticles represent promising materials for use as non-viral vectors for gene therapy in bone tissue engineering applications due to their many favorable properties, including biocompatibility, osteoinductivity, osteoconductivity, and strong affinity for binding to nucleic acids. However, low transfection rates present a significant barrier to their clinical use. This article reviews the benefits of calcium phosphate nanoparticles for RNAi delivery and highlights the role of surface functionalization in increasing calcium phosphate nanoparticles stability, improving cellular uptake and increasing transfection efficiency. Currently, the underlying mechanistic principles relating to these systems and their interplay during in vivo bone formation is not wholly understood. Furthermore, the optimal microRNA targets for particular bone tissue regeneration applications are still unclear. Therefore, further research is required in order to achieve the optimal calcium phosphate nanoparticles-based systems for RNAi delivery for bone tissue regeneration.

Calcium Phosphate Nanoparticles for Therapeutic Applications in Bone Regeneration

Bone injuries and diseases constitute a burden both socially and economically, as the consequences of a lack of effective treatments affect both the patients' quality of life and the costs on the health systems. This impended need has led the research community's efforts to establish efficacious bone tissue engineering solutions. There has been a recent focus on the use of biomaterial-based nanoparticles for the delivery of therapeutic factors. Among the biomaterials being considered to date, calcium phosphates have emerged as one of the most promising materials for bone repair applications due to their osteoconductivity, osteoinductivity and their ability to be resorbed in the body. Calcium phosphate nanoparticles have received particular attention as non-viral vectors for gene therapy, as factors such as plasmid DNAs, microRNAs (miRNA) and silencing RNA (siRNAs) can be easily incorporated on their surface. Calcium phosphate nanoparticles loaded with therapeutic factors have also been delivered to the site of bone injury using scaffolds and hydrogels. This review provides an extensive overview of the current state-of-the-art relating to the design and synthesis of calcium phosphate nanoparticles as carriers for therapeutic factors, the mechanisms of therapeutic factors' loading and release, and their application in bone tissue engineering.

Dual delivery of encapsulated BM-MSCs and BMP-2 improves osteogenic differentiation and new bone formation

Stem cell-based therapies provide a promising approach for bone repair. In the present work, we developed a novel 3D vehicle system for dual-delivery of encapsulated bone marrow mesenchymal stem cells (BM-MSCs) and bone morphogenetic protein-2 (BMP-2) for treatment of large bone defects. The vehicle system consists of sodium alginate microcapsules and polylactic acid (PLLA) microspheres. BM-MSCs are encapsulated in the microcapsules, and BMP-2 proteins are encapsulated in the PLLA microspheres. This vehicle system acted as a multicore structure for sustained release of BMP-2, which enabled pulsed dosing induction of osteogenic differentiation of the co-embedded BM-MSCs. in vitro experiments showed that the loaded BMP-2 was constitutively released up to 30 days. Bioactivity of the incorporated BMP-2 in the microspheres was preserved and osteogenic differentiation of the BM-MSCs in the microcapsules was improved. In vivo, osteogenesis studies demonstrated that satisfactory degree of repair of a rat calvarial defect was achieved with the delivery of either encapsulated BM-MSCs alone or encapsulated BMP-2 alone. Transplantation of encapsulated both BM-MSCs and BMP-2 exhibited the greatest repair potential following 4- or 8-weeks treatment. In conclusion, microencapsulation of BM-MSCs and BMP-2 promoted the maturity of newly generated bone and improved new bone formation. Transplantation of BM-MSCs and BMP-2 in our novel 3-D vehicle system is a promising strategy for regenerative therapies of large bone defects.

[Stimulation of fracture healing by growth factors and cell-based technologies]

Bone has the special capability to completely regenerate after trauma and to re-establish its original geometry and biomechanical stability corresponding to the pretrauma conditions. Nevertheless, in daily clinical practice impaired fracture healing and nonunions are regular complications as a result of inadequate mechanical stability and/or insufficient biological processes around the fracture region. Since the beginning of the millennium, intensive research on the physiological processes in bone healing as well as the production and clinical administration of growth factors have enabled the possibility to improve the local biological processes during fracture healing by osteoinduction. Although the initial clinical results, particularly of bone morphogenetic proteins, in fracture healing were promising, growth factors did not become established for unrestricted use in the clinical application. Currently, additional growth factors are being investigated with respect to the potential supportive and osteoinductive characteristics for enhancement of fracture healing and possible clinical applications. Furthermore, the development of cell-based technologies is another promising approach to positively stimulate fracture healing. In addition to the gold standard of autologous bone grafting, harvesting of mesenchymal stroma cells by aspiration has gained in importance in recent years. Allogeneic bone cell transplantation procedures and in particular gene therapy are promising new strategies for the treatment of disorders of fracture healing. This review gives an overview of present and future possibilities for modulation of fracture healing by growth factors and cell-based technologies.

Advanced biomaterials for repairing and reconstruction of mandibular defects

Mandibles are the largest and strongest bone in the human face and are often severely compromised by mandibular defects, compromising the quality of life of patients. Mandibular defects may result from trauma, inflammatory disease and benign or malignant tumours. The reconstruction of mandibular defect has been a research hotspot in oral and maxillofacial surgery. Although the principles and techniques of mandibular reconstruction have made great progress in recent years, the development of biomedical materials is still facing technical bottleneck, and new materials directly affect technological breakthroughs in this field. This paper reviews the current status of research and application of various biomaterials in mandibular defects and systematically elaborates different allogeneic biomaterial-based approaches. It is expected that various biomaterials, in combination with new technologies such as digital navigation and 3D printing, could be tuned to build new types of scaffold with more precise structure and components, addressing needs of surgery and post-reconstruction. With the illustration and systematization of different solutions, aims to inspire the development of reconstruction biomaterials.

Gene activated adipose tissue fragments as advanced autologous biomaterials for bone regeneration: osteogenic differentiation within the tissue and implications for clinical translation

Cost-effective, expedited approaches for bone regeneration are urgently needed in an ageing population. Bone Morphogenetic Proteins (BMPs) stimulate osteogenesis but their efficacy is impeded by their short half-life. Delivery by genetically modified cells can overcome this problem. However, cell isolation and propagation represent significant obstacles for the translation into the clinic. Instead, complete gene activated fragments of adipose tissue hold great potential for bone repair. Here, using an in-vitro culture system, we investigated whether adenoviral transduction with human BMP-2 can promote osteogenic differentiation within adipose tissue fragments. Osteoinduction in adipose tissue fragments was evaluated by quantitative reverse transcriptase polymerase chain reaction, immunohistology and histomorphometry. BMP-2 transduced adipose tissue synthesized BMP-2 protein over 30 days peaking by day six, which significantly promoted osteogenic differentiation as indicated by increased calcium depositions, up-regulation of bone marker genes, and bone-related protein expression. Our results demonstrate that cells within adipose tissue fragments can differentiate osteogenically after BMP-2 transduction of cells on the surface of the adipose tissue. BMP-2 gene activated adipose tissue represents an advanced osteo-regenerative biomaterial that can actively contribute to osteogenesis and potentially enable the development of a novel, cost-effective, one-step surgical approach to bone repair without the need for cell isolation.

Comparative analysis of bone regeneration behavior using recombinant human BMP-2 versus plasmid DNA of BMP-2

Bone regeneration and the osteoinductive capacity of implants are challenging issues in clinical medicine. Currently, recombinant growth factors and nonviral gene transfer are the most frequently investigated methods for bone growth enhancement, although the more favorable method remains unclear. There is a lack of knowledge in literature about the in vivo comparison of these methods for bone regeneration. BMP-2, which is the most commonly used growth factor for osteogenesis, was applied at its most efficient dose as a recombinant growth factor (rhBMP-2) and as a growth-factor-encoding copolymer protected gene vector (pBMP-2) in a critical size bone defect (CSD) model to determine the most suitable method for bone regeneration. CSDs were induced bilaterally in 32 Sprague-Dawley rats. RhBMP-2 (62.5 μg) or pBMP-2 (2.5 μg) was embedded in poly(d,l-)lactide-coated titanium discs. Survival times were set at 14, 28, 56, and 112 days. After euthanasia, samples were analyzed via micro-computed tomography, polychrome sequential fluorescent labeling, and immunohistochemistry. Whereas defects in both groups were bridged with new bone after 56 days, rhBMP-2 initially induced ectopic new bone formation that was later remodeled in an unorganized hypodense manner. In contrast, pBMP-2 led to slower but steady bone regeneration with physiological tissue morphology, as confirmed by high osteoblast activity shown by osteocalcin staining. CD68 and TRAP staining verified high osteoclast activity for the rhBMP-2 group. pBMP-2 successfully induced locally controlled physiological bone regeneration, whereas rhBMP-2 triggered rapid and ectopic but insufficient bone formation. Thus, nonviral gene transfer appears to be more favorable for clinical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 163-173, 2019.

Recent advances in gene-enhanced bone tissue engineering

The loss of bone tissue represents a critical clinical condition that is frequently faced by surgeons. Substantial progress has been made in the area of bone research, providing insight into the biology of bone under physiological and pathological conditions, as well as tools for the stimulation of bone regeneration. The present review discusses recent advances in the field of gene-enhanced bone tissue engineering. Gene transfer strategies have emerged as highly effective tissue engineering approaches for supporting the repair of the musculoskeletal system. By contrast to treatment with recombinant proteins, genetically engineered cells can release growth factors at the site of injury over extended periods of time. Of particular interest are the expedited technologies that can be applied during a single surgical procedure in a cost-effective manner, allowing translation from bench to bedside. Several promising methods based on the intra-operative genetic manipulation of autologous cells or tissue fragments have been developed in preclinical studies. Moreover, gene therapy for bone regeneration has entered the clinical stage with clinical trials for the repair of alveolar bone. Current trends in gene-enhanced bone engineering are also discussed with respect to the movement of the field towards expedited, translational approaches. It is possible that gene-enhanced bone tissue engineering will become a clinical reality within the next few years.

Exploiting Advanced Hydrogel Technologies to Address Key Challenges in Regenerative Medicine

Regenerative medicine aims to tackle a panoply of challenges from repairing focal damage to articular cartilage to preventing pathological tissue remodeling after myocardial infarction. Hydrogels are water-swollen networks formed from synthetic or naturally derived polymers and are emerging as important tools to address these challenges. Recent advances in hydrogel chemistries are enabling researchers to create hydrogels that can act as 3D ex vivo tissue models, allowing them to explore fundamental questions in cell biology by replicating tissues' dynamic and nonlinear physical properties. Enabled by cutting edge techniques such as 3D bioprinting, cell-laden hydrogels are also being developed with highly controlled tissue-specific architectures, vasculature, and biological functions that together can direct tissue repair. Moreover, advanced in situ forming and acellular hydrogels are increasingly finding use as delivery vehicles for bioactive compounds and in mediating host cell response. Here, advances in the design and fabrication of hydrogels for regenerative medicine are reviewed. It is also addressed how controlled chemistries are allowing for precise engineering of spatial and time-dependent properties in hydrogels with a look to how these materials will eventually translate to clinical applications.

Polymer-coated viral vectors: hybrid nanosystems for gene therapy

The advantages and critical aspects of nanodimensional polymer-coated viral vector systems potentially applicable for gene delivery are reviewed. Various viral and nonviral vectors have been explored for gene therapy. Viral gene transfer methods, although highly efficient, are limited by their immunogenicity. Nonviral vectors have a lower transfection efficiency as a result of their inability to escape from the endosome. To overcome these drawbacks, novel nanotechnology-mediated interventions that involve the coating or modification of virus using polymers have emerged as a new paradigm in gene therapy. These alterations not only modify the tropism of the virus, but also reduce their undesirable interactions with the biological system. Also, co-encapsulation of other therapeutic agents in the polymeric coating may serve to augment the treatment efficacy. The viral particles can aid endosomal escape, as well as nuclear targeting, thereby enhancing the transfection efficiency. The integration of the desirable properties of both viral and nonviral vectors has been found beneficial for gene therapy by enhancing the transduction efficiency and minimizing the immune response. However, it is essential to ensure that these attempts should not compromise on the inherent ability of viruses to target and internalize into the cells and escape the endosomes.

Adenovirus-mediated bone morphogenetic protein-2 promotes osteogenic differentiation in human mesenchymal stem cells in vitro

Delayed and failed bone union following fracture is a common clinical complication that requires treatment in orthopedics. Cell-based therapies and tissue-engineering approaches are potential therapeutic strategies for bone repair and fracture healing. However, the effect of adenovirus expressing bone morphogenetic protein-2 (Ad-BMP-2) on the osteogenic ability of human mesenchymal stem cells (hMSCs) has remained to be fully elucidated. Therefore, in the present study, hMSCs were transduced using Ad-BMP-2 to assess the effects of its application and to determine whether Ad-BMP-2 promotes the osteogenic differentiation of hMSCs. The purity of the hMSC cultures was assessed using flow cytometric analysis. In order to assess the osteogenic activity, alkaline phosphatase activity (ALP) was measured and to estimate the osteoblastic mineralization and calcification, von Kossa staining for phosphates was performed. Cells positive for Src homology 2 domain were determined to be hMSCs and the presence of CD34 was used to distinguish hematopoietic lineages. Following treatment, the Ad-BMP-2 and control group had significantly increased ALP levels (P<0.05). Compared to the blank group and the group transfected with adenoviral vector containing LacZ, the phosphate deposition in the Ad-BMP-2 group and the positive control group treated with dexamethasone was markedly increased. The results of the present study suggested that Ad-BMP-2 promotes osteogenic differentiation in hMSCs and may have a potential application in treating delayed union and nonunion following bone fracture.

Ultrasound-responsive gene-activated matrices for osteogenic gene therapy using matrix-assisted sonoporation

Gene-activated matrix (GAM)-based therapeutics for tissue regeneration are limited by efficacy, the lack of spatiotemporal control and availability of target cells, all of which impact negatively on their translation to the clinic. Here, an advanced ultrasound-responsive GAM is described containing target cells that facilitates matrix-assisted sonoporation (MAS) to induce osteogenic differentiation. Ultrasound-responsive GAMs consisting of fibrin/collagen hybrid-matrices containing microbubbles, bone morphogenetic protein BMP2/7 coexpression plasmids together with C2C12 cells were treated with ultrasound either in vitro or following parenteral intramuscular implantation in vivo. Using direct measurement for alkaline phosphatase activity, von Kossa staining and immunohistochemical analysis for osteocalcin expression, MAS-stimulated osteogenic differentiation was confirmed in the GAMs in vitro 7 days after treatment with ultrasound. At day 30 post-treatment with ultrasound, ectopic osteogenic differentiation was confirmed in vivo using X-ray microcomputed tomography and histological analysis. Osteogenic differentiation was indicated by the presence of ectopic bone structures in all animals treated with MAS. In addition, bone volumes in this group were statistically greater than those in the control groups. This novel approach of incorporating a MAS capability into GAMs could be exploited to facilitate ex vivo gene transfer with subsequent surgical implantation or alternatively provide a minimally invasive means of stimulating in situ transgene delivery for osteoinductive gene-based therapies. Copyright © 2017 John Wiley & Sons, Ltd.

Improvement of osteogenesis in dental pulp pluripotent-like stem cells by oligopeptide-modified poly(β-amino ester)s

Controlling pluripotent stem cell differentiation via genetic manipulation is a promising technique in regenerative medicine. However, the lack of safe and efficient delivery vehicles limits this application. Recently, a new family of poly(β-amino ester)s (pBAEs) with oligopeptide-modified termini showing high transfection efficiency of both siRNA and DNA plasmid has been developed. In this study, oligopeptide-modified pBAEs were used to simultaneously deliver anti-OCT3/4 siRNA, anti-NANOG siRNA, and RUNX2 plasmid to cells from the dental pulp with pluripotent-like characteristics (DPPSC) in order to promote their osteogenic differentiation. Results indicate that transient inhibition of the pluripotency marker OCT3/4 and the overexpression of RUNX2 at day 7 of differentiation markedly increased and accelerated the expression of osteogenic markers. Furthermore, terminally-differentiated cells exhibited higher matrix mineralization and alkaline phosphatase activity. Finally, cell viability and genetic stability assays indicate that this co-delivery system has high chromosomal stability and minimal cytotoxicity. Therefore, we conclude that such co-delivery strategy is a safe and a quick option for the improvement of DPPSC osteogenic differentiation.

STATEMENT OF SIGNIFICANCE

Controlling pluripotent stem cell differentiation via genetic manipulation is a promising technique in regenerative medicine. However, the lack of safe and efficient delivery vehicles limits this application. In this study, we propose the use of a new family of oligopeptide-modified pBAEs developed in our group to control the differentiation of dental pulp pluripotential stem cells (DPPSC). In order to promote their osteogenic differentiation. The strategy proposed markedly increased and accelerated the expression of osteogenic markers, cell mineralization and alkaline phosphatase activity. Finally, cell viability and genetic stability assays indicated that this co-delivery system has high chromosomal stability and minimal cytotoxicity. These findings open a new interesting path in the usage of non-viral gene delivery systems for the control of pluripotential stem cell differentiation.

Functional analysis of bioactivated and antiinfective PDLLA - coated surfaces

Common scaffold surfaces such as titanium can have side effects; for example, infections, cytotoxicity, impaired osseointegration, or low regeneration rates for bone tissue. These effects lead to poor implant integration or even implant loss. Therefore, bioactive implants are promising instruments in tissue regeneration. Osteoinductive elements-such as growth factors and anti-infectives-support wound healing and bone growth and thereby enable faster osseointegration, even in elderly patients. In this study, titanium surfaces were coated with a poly-(d,l-lactide) (PDLLA) layer containing different concentrations of copolymer-protected gene vectors (COPROGs) to locally provide bone morphogenetic protein-2 (BMP-2) or activated anti-infective agents, such as chlorhexidine gluconate, triclosan, and metronidazole, to prevent peri-implantitis. The coated titanium implants were then loaded with osteoblasts, NIH 3T3 fibroblasts, and human mesenchymal stem cells in 96-well plates. When shielded by COPROGs as a protective layer and resuspended in PDLLA, BMP-2-encoding pDNA at relatively low doses (5.63 µg/implant) induced the local expression of BMP-2. A linear dose dependence, which is common for recombinant growth factors, was not found, probably due to the retention property of the PDLLA surface. PDLLA, in general, successfully retains additional elements, such as osteoconductive growth factors (BMP-2) and anti-infective agents, which was demonstrated using metronidazole, and thus prevents the systemic application of excessive doses. These bioactive implant surfaces that provide the local release of therapeutic gene vectors or anti-infective agents allow the controlled stimulation of the implant and scaffold osseointegration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1672-1683, 2017.

Absorbable collagen sponges loaded with recombinant bone morphogenetic protein 9 induces greater osteoblast differentiation when compared to bone morphogenetic protein 2

The use of growth factors for the regeneration of soft and hard tissues has been utilized extensively in dental medicine over the past decade. Recently our group found that recombinant human bone morphogenetic protein 9 (rhBMP9) was more osteopromotive than recombinant human bone morphogenetic protein 2 (rhBMP2) when combined with a deprotenized bovine bone mineral bone grafting material. The aim of the present in vitro study was to evaluate the regenerative potential of an absorbable collagen sponge(ACS) specifically designed for extraction socket healing loaded with rhBMP9 when compared to rhBMP2. The adsorption and release kinetics of rhBMP2 and rhBMP9 were first investigated by enzyme-linked immunosorbent assay quantification. Then, the cellular effects of stromal cell line (ST2) preosteoblasts were investigated utilizing four groups including rhBMP2 and rhBMP9 at both low(10 ng/ml) and high(100 ng/ml) concentrations loaded onto ACS. Cellular attachment(8 hours) and proliferation(1, 3, and 5 days) as well as osteoblast differentiation were investigated by real-time polymerase chain reaction (PCR) at 3 and 14 days, alkaline phosphatase (ALP) activity at 7 days, and alizarin red staining at 14 days. ACS fully adsorbed both rhBMP2 and rhBMP9 that were slowly released up to 10 days. Although neither rhBMP2 nor rhBMP9 had any effects on cell attachment or proliferation, pronounced effects were observed on osteoblast differentiation. ALP activity was increased seven-fold with rhBMP2-high, whereas a marked 10-fold and 20-fold increase was observed with rhBMP9-low and high loaded to ACS, respectively. Furthermore, mRNA levels of collagen1, ALP, bone sialoprotein, and osteocalcin were all significantly higher for rhBMP9 when compared to control or rhBMP2 groups. Alizarin red staining further confirmed that rhBMP9-low and high demonstrated marked increases in mineralization potential when compared to rhBMP2-high. The results demonstrate the marked effect of rhBMP9 on osteoblast differentiation when combined with ACS in comparison to rhBMP2 at doses as much as 10 times lower. Further in vivo studies are necessary to investigate whether the regenerative potential is equally as potent.

Recent tissue engineering-based advances for effective rAAV-mediated gene transfer in the musculoskeletal system

Musculoskeletal tissues are diverse and significantly different in their ability to repair upon injury. Current treatments often fail to reproduce the natural functions of the native tissue, leading to an imperfect healing. Gene therapy might improve the repair of tissues by providing a temporarily and spatially defined expression of the therapeutic gene(s) at the site of the injury. Several gene transfer vehicles have been developed to modify various human cells and tissues from musculoskeletal system among which the non-pathogenic, effective, and relatively safe recombinant adeno-associated viral (rAAV) vectors that have emerged as the preferred gene delivery system to treat human disorders. Adapting tissue engineering platforms to gene transfer approaches mediated by rAAV vectors is an attractive tool to circumvent both the limitations of the current therapeutic options to promote an effective healing of the tissue and the natural obstacles from these clinically adapted vectors to achieve an efficient and durable gene expression of the therapeutic sequences within the lesions.

Gene Therapy for Bone Defects in Oral and Maxillofacial Surgery: A Systematic Review and Meta-Analysis of Animal Studies

Craniofacial bone defects are challenging problems for maxillofacial surgeons over the years. With the development of cell and molecular biology, gene therapy is a breaking new technology with the aim of regenerating tissues by acting as a delivery system for therapeutic genes in the craniofacial region rather than treating genetic disorders. A systematic review was conducted summarizing the articles reporting gene therapy in maxillofacial surgery to answer the question: Was gene therapy successfully applied to regenerate bone in the maxillofacial region? Electronic searching of online databases was performed in addition to hand searching of the references of included articles. No language or time restrictions were enforced. Meta-analysis was done to assess significant bone formation after delivery of gene material in the surgically induced maxillofacial defects. The search identified 2081 articles, of which 57 were included with 1726 animals. Bone morphogenetic proteins were commonly used proteins for gene therapy. Viral vectors were the universally used vectors. Sprague-Dawley rats were the frequently used animal model in experimental studies. The quality of the articles ranged from excellent to average. Meta-analysis results performed on 21 articles showed that defects favored bone formation by gene therapy. Funnel plot showed symmetry with the absence of publication bias. Gene therapy is on the top list of innovative strategies that developed in the last 10 years with the hope of developing a simple chair-side protocol in the near future, combining improvement of gene delivery as well as knowledge of the molecular basis of oral and maxillofacial structures.

Hyaluronic Acid Gel-Based Scaffolds as Potential Carrier for Growth Factors: An In Vitro Bioassay on Its Osteogenic Potential

Hyaluronic acid (HA) has been utilized for a variety of regenerative medical procedures due to its widespread presence in connective tissue and perceived biocompatibility. The aim of the present study was to investigate HA in combination with recombinant human bone morphogenetic protein 9 (rhBMP9), one of the most osteogenic growth factors of the BMP family. HA was first combined with rhBMP9 and assessed for the adsorption and release of rhBMP9 over 10 days by ELISA. Thereafter, ST2 pre-osteoblasts were investigated by comparing (1) control tissue culture plastic, (2) HA alone, and (3) HA with rhBMP9 (100 ng/mL). Cellular proliferation was investigated by a MTS assay at one, three and five days and osteoblast differentiation was investigated by alkaline phosphatase (ALP) activity at seven days, alizarin red staining at 14 days and real-time PCR for osteoblast differentiation markers. The results demonstrated that rhBMP9 adsorbed within HA scaffolds and was released over a 10-day period in a controlled manner. While HA and rhBMP9 had little effect on cell proliferation, a marked and pronounced effect was observed for cell differentiation. rhBMP9 significantly induced ALP activity, mRNA levels of collagen1α2, and ALP and osteocalcin (OCN) at three or 14 days. HA also demonstrated some ability to induce osteoblast differentiation by increasing mRNA levels of OCN and increasing alizarin red staining at 14 days. In conclusion, the results from the present study demonstrate that (1) HA may serve as a potential carrier for various growth factors, and (2) rhBMP9 is a potent and promising inducer of osteoblast differentiation. Future animal studies are now necessary to investigate this combination approach in vivo.

Biomaterials to Facilitate Delivery of RNA Agents in Bone Regeneration and Repair

Bone healing after traumatic injuries or pathological diseases remains an important worldwide problem. In search of safer and more effective approaches to bone regeneration and repair, RNA-based therapeutic agents, specifically microRNAs (miRNAs) and short interfering RNA (siRNA), are beginning to be actively explored. In this review, we summarize current attempts to employ miRNAs and siRNAs in preclinical models of bone repair. We provide a summary of current limitations when attempting to utilize bioactive nucleic acids for therapeutic purposes and position the unique aspects of RNA reagents for clinical bone repair. Delivery strategies for RNA reagents are emphasized and nonviral carriers (biomaterial-based) employed to deliver such reagents are reviewed. Critical features of biomaterial carriers and various delivery technologies centered around nanoparticulate systems are highlighted. We conclude with the authors' perspectives on the future of the field, outlining main critical issues important to address as RNA reagents are explored for clinical applications.

Osteogenic potential of rhBMP9 combined with a bovine-derived natural bone mineral scaffold compared to rhBMP2

OBJECTIVES

Combination therapies of growth factors and scaffolds for bone tissue engineering are becoming routine for clinical use. BMP9 has previously been characterized as one of the most osteogenic inducers among the BMP superfamily; however, up until recently, BMP9 has only been available through adenovirus transfection experiments (gene therapy). While recombinant human (rh)BMP2 is regarded as the gold standard for bone regeneration with recombinant growth factors, recently the successful development of rhBMP9 brings intriguing new possibilities for future clinical use. The purpose of this pioneering study was to investigate the effects of rhBMP9 in comparison with rhBMP2 on an in vitro cell behavior of bone-forming osteoblasts when combined with a bone grafting material.

MATERIAL AND METHODS

Undifferentiated mouse ST2 stromal bone marrow cells were seeded onto bovine-derived natural bone mineral (NBM) particles treated with (i) control, (ii) rhBMP2 (10 ng/ml), (iii) rhBMP2 (100 ng/ml), (iv) rhBMP9 (10 ng/ml) and (v) rhBMP9 (100 ng/ml). The effects of rhBMPs were compared for cell adhesion at 8 h, cell proliferation at 1, 3 and 5 days and osteoblast differentiation as assessed by real-time PCR at 3 and 14 days for genes encoding Runx2, collagen1alpha2 (COL1a2), alkaline phosphatase (ALP) and osteocalcin (OCN). Furthermore, ALP staining and alizarin red staining were used to investigate localization of osteoblast differentiation marker and mineralization on NBM.

RESULTS

Although neither rhBMP2 nor rhBMP9 influenced cell attachment to NBM particles, both were able to stimulate cell proliferation at 3 days. Furthermore, all concentrations of rhBMPs were able to significantly induce mRNA levels of Runx2, COL1a2 and OCN at 3 days. Interestingly, only rhBMP9 was able to significantly upregulate mRNA levels of ALP up to eightfold, and ALP staining up to 25-fold, when compared to rhBMP2. In addition, only rhBMP9 (100 ng/ml) significantly increased alizarin red staining when compared to control and rhBMP2 (10 ng/ml) samples.

CONCLUSION

These results demonstrate that both rhBMP2 and rhBMP9 have osteopromotive properties on osteoblast differentiation. It was found that rhBMP9 additionally stimulated the osteopromotive potential of osteoblasts when compared to rhBMP2 by demonstrating higher levels of ALP expression and alizarin red staining. Further animal studies comparing both recombinant proteins are necessary to further characterize the osteoinductive potential of BMP9.