Response of induced bone defects in horses to collagen matrix containing the human parathyroid hormone gene

Bioactive Materials for Bone Regeneration: Biomolecules and Delivery Systems

Novel tissue regeneration strategies are constantly being developed worldwide. Research on bone regeneration is noteworthy, as many promising new approaches have been documented with novel strategies currently under investigation. Innovative biomaterials that allow the coordinated and well-controlled repair of bone fractures and bone loss are being designed to reduce the need for autologous or allogeneic bone grafts eventually. The current engineering technologies permit the construction of synthetic, complex, biomimetic biomaterials with properties nearly as good as those of natural bone with good biocompatibility. To ensure that all these requirements meet, bioactive molecules are coupled to structural scaffolding constituents to form a final product with the desired physical, chemical, and biological properties. Bioactive molecules that have been used to promote bone regeneration include protein growth factors, peptides, amino acids, hormones, lipids, and flavonoids. Various strategies have been adapted to investigate the coupling of bioactive molecules with scaffolding materials to sustain activity and allow controlled release. The current manuscript is a thorough survey of the strategies that have been exploited for the delivery of biomolecules for bone regeneration purposes, from choosing the bioactive molecule to selecting the optimal strategy to synthesize the scaffold and assessing the advantages and disadvantages of various delivery strategies.

Systematic Review of the Preclinical Technology Readiness of Orthopedic Gene Therapy and Outlook for Clinical Translation

Bone defects and improper healing of fractures are an increasing public health burden, and there is an unmet clinical need in their successful repair. Gene therapy has been proposed as a possible approach to improve or augment bone healing with the potential to provide true functional regeneration. While large numbers of studies have been performed in vitro or in vivo in small animal models that support the use of gene therapy for bone repair, these systems do not recapitulate several key features of a critical or complex fracture environment. Larger animal models are therefore a key step on the path to clinical translation of the technology. Herein, the current state of orthopedic gene therapy research in preclinical large animal models was investigated based on performed large animal studies. A summary and an outlook regarding current clinical studies in this sector are provided. It was found that the results found in the current research literature were generally positive but highly methodologically inconsistent, rendering a comparison difficult. Additionally, factors vital for translation have not been thoroughly addressed in these model systems, and the risk of bias was high in all reviewed publications. These limitations directly impact clinical translation of gene therapeutic approaches due to lack of comparability, inability to demonstrate non-inferiority or equivalence compared with current clinical standards, and lack of safety data. This review therefore aims to provide a current overview of ongoing preclinical and clinical work, potential bottlenecks in preclinical studies and for translation, and recommendations to overcome these to enable future deployment of this promising technology to the clinical setting.

Gene-activated matrix harboring a miR20a-expressing plasmid promotes rat cranial bone augmentation

Gene-activated matrix (GAM) has a potential usefulness in bone engineering as an alternate strategy for the lasting release of osteogenic proteins but efficient methods to generate non-viral GAM remain to be established. In this study, we investigated whether an atelocollagen-based GAM containing naked-plasmid (p) DNAs encoding microRNA (miR) 20a, which may promote osteogenesis in vivo via multiple pathways associated with the osteogenic differentiation of mesenchymal stem/progenitor cells (MSCs), facilitates rat cranial bone augmentation. First, we confirmed the osteoblastic differentiation functions of generated pDNA encoding miR20a (pmiR20a) in vitro, and its transfection regulated the expression of several of target genes, such as Bambi1 and PPARγ, in rat bone marrow MSCs and induced the increased expression of BMP4. Then, when GAMs fabricated by mixing 100 μl of 2% bovine atelocollagen, 20 mg β-TCP granules and 0.5 mg (3.3 μg/μl) AcGFP plasmid-vectors encoding miR20a were transplanted to rat cranial bone surface, the promoted vertical bone augmentation was clearly recognized up to 8 weeks after transplantation, as were upregulation of VEGFs and BMP4 expressions at the early stages of transplantation. Thus, GAM-based miR delivery may provide an alternative non-viral approach by improving transgene efficacy via a small sequence that can regulate the multiple pathways.

The challenges of promoting osteogenesis in segmental bone defects and osteoporosis

Conventional clinical management of complex bone healing scenarios continues to result in 5-10% of fractures forming non-unions. Additionally, the aging population and prevalence of osteoporosis-related fractures necessitate the further exploration of novel ways to augment osteogenesis in this special population. This review focuses on the current clinical modalities available, and the ongoing clinical and pre-clinical research to promote osteogenesis in segmental bone defects, delayed unions, and osteoporosis. In summary, animal models of fracture repair are often small animals as historically significant large animal models, like the dog, continue to gain favor as companion animals. Small rodents have well-documented limitations in comparing to fracture repair in humans, and few similarities exist. Study design, number of studies, and availability of funding continue to limit large animal studies. Osteoinduction with rhBMP-2 results in robust bone formation, although long-term quality is scrutinized due to poor bone mineral quality. PTH 1-34 is the only FDA approved osteo-anabolic treatment to prevent osteoporotic fractures. Limited to 2 years of clinical use, PTH 1-34 has further been plagued by dose-related ambiguities and inconsistent results when applied to pathologic fractures in systematic human clinical studies. There is limited animal data of PTH 1-34 applied locally to bone defects. Gene therapy continues to gain popularity among researchers to augment bone healing. Non-integrating viral vectors and targeted apoptosis of genetically modified therapeutic cells is an ongoing area of research. Finally, progenitor cell therapies and the content variation of patient-side treatments (e.g., PRP and BMAC) are being studied. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1559-1572, 2018.

Gene-Activated Matrix Comprised of Atelocollagen and Plasmid DNA Encoding BMP4 or Runx2 Promotes Rat Cranial Bone Augmentation

To date, therapeutic method for in vivo gene delivery has not been established on bone engineering though its potential usefulness has been suggested. For clinical applications, an effective condition should be developed to transfer the genes in vivo without any transfection reagents or virus vectors. In this study, to facilitate the clinical setting of this strategy, particularly aimed at atrophic bone repair, we simply investigated whether manufactured gene-activated matrix (GAM) with atelocollagen containing a certain amount of plasmid (p) DNA encoding osteogenic proteins could augment the cranial bone in rat. GAMs were manufactured by mixing 0.02, 0.1, or 1 mg of AcGFP plasmid vectors harboring cDNA of BMP4 (pBMP4) or Runx2 (pRunx2) with 2% bovine atelocollagen and β-tricalcium phosphate granules. Before manufacturing GAMs, to determine the biological activity of generated pDNAs, we confirmed GFP expression and increased level of alkaline phosphatase activities in MC3T3-E1 cells transfected with pBMP4 or pRunx2 during culture. Then, GAMs were lyophilized and transplanted to onlay placement on the cranium. At 2 weeks of transplantation, GFP-expressing cells could be detectable in only GAMs containing 1 mg of AcGFP plasmid vectors. Then, at 4 weeks, significant bone formation was recognized in GAMs containing 1 mg of pDNAs encoding BMP4 or Runx2 but not in 0.02 or 0.1 mg of GAMs. These newly formed bone tissues surrounded by osteocalcin-stained area were augmented markedly until 8 weeks after transplantation. In contrast, minimal bone formation was observed in GAMs without harboring cDNA of osteogenic proteins. Meanwhile, when GAMs were transplanted to the cranial bone defect, bone formation was detectable in specimens containing 1 mg of pBMP4 or pRunx2 at 8 weeks as well. Thus, atelocollagen-based GAM reliably could form the engineered bone even for the vertical augmentation when containing a certain amount of plasmid vectors encoding osteogenic proteins. This study supports facilitating the clinical application of GAM for bone engineering.

Critical size defect regeneration by rhPTH-collagen membrane as a new tissue engineering tool

Recombinant Human Parathyroid Hormone (rhPTH 1-34) administration is an effective treatment to improve bone mass in osteoporosis. The aim of this study was to develop a Tissue Engeenering Tool for bone regeneration. We evaluated the efficacy of a freeze dried rhPTH membrane in calvarial critical size defect (CSD). Forty-four Wistar female rats (body weight 150 ± 50 g) with CSD (5 mm) were divided into four groups: group 1: rhPTH membrane (rhPTHm); group 2: atelocollagen membrane (Cm); group 3: rhPTH and atelocollagen I (CrhPTHm); group 4: without any treatment (CG). All samples were evaluated on the 1st, 3rd, and 6th weeks (weeks) post-surgery by soft X-ray, histological and histometric studies. Soft X-ray results showed a radiolucent image with many irregular radiopaque areas. Histologically, rhPTHm was replaced by reticular bone (7%) since 3rd week, and lamellar bone ossicles (30%) at 6th week. Cm showed bone formation like composite bone type on week 1st, 3rd, and 6th (2%, 44%, and 41%, respectively). With CrhPTHm, bone formation was observed in all periods (2.4%, 48%, and 53%), showing statistical difference with CG in the 3rd and 6th wks (p = 0.03 and 0.01). Our results demonstrated the effectiveness of a new biomaterial called CrhPTHm because its ability to regenerate calvarial CSD. Moreover, the membrane represents a new local intermittent delivery system allowing rhPTH slow release.

Gene delivery to bone

Gene delivery to bone is useful both as an experimental tool and as a potential therapeutic strategy. Among its advantages over protein delivery are the potential for directed, sustained and regulated expression of authentically processed, nascent proteins. Although no clinical trials have been initiated, there is a substantial pre-clinical literature documenting the successful transfer of genes to bone, and their intraosseous expression. Recombinant vectors derived from adenovirus, retrovirus and lentivirus, as well as non-viral vectors, have been used for this purpose. Both ex vivo and in vivo strategies, including gene-activated matrices, have been explored. Ex vivo delivery has often employed mesenchymal stem cells (MSCs), partly because of their ability to differentiate into osteoblasts. MSCs also have the potential to home to bone after systemic administration, which could serve as a useful way to deliver transgenes in a disseminated fashion for the treatment of diseases affecting the whole skeleton, such as osteoporosis or osteogenesis imperfecta. Local delivery of osteogenic transgenes, particularly those encoding bone morphogenetic proteins, has shown great promise in a number of applications where it is necessary to regenerate bone. These include healing large segmental defects in long bones and the cranium, as well as spinal fusion and treating avascular necrosis.

Stem cell-based therapies for bone repair

This article provides an overview of the cellular and molecular events involved in bone repair and the current approaches to using stem cells as an adjunct to this process. The article emphasizes the key role of osteoprogenitor cells in the formation of bone and where the clinical applications of current research may lend themselves to large animal orthopaedics. The processes involved in osteogenic differentiation are presented and strategies for bone formation, including induction by osteogenic factors, bioscaffolds, and gene therapy, are reviewed.

Cell-mediated and direct gene therapy for bone regeneration

INTRODUCTION

Bone regeneration is required for the treatment of fracture non/delayed-unions and bone defects. However, most current treatment modalities have limited efficacy, and newer therapeutic strategies, such as gene therapy, have substantial benefit for bone repair and regeneration.

AREAS COVERED

This review discusses experimental and clinical applications of cell-mediated and direct gene therapy for bone regeneration. The review covers literature on this subject from 2000 to February 2012.

EXPERT OPINION

Direct gene therapy using various viral and non-viral vectors of cell-mediated genes has been demonstrated to induce bone regeneration, although use of such vectors has shown some risk in human application. Osteoinductive capability of a number of progenitor cells isolated from bone marrow, fat, muscle and skin tissues, has been demonstrated by genetic modification with osteogenic genes. Cell-mediated gene therapy using such osteogenic gene-expressing progenitor cells has shown promising results in promoting bone regeneration in extensive animal work in recent years.

Inflammation and immune response of intra-articular serotype 2 adeno-associated virus or adenovirus vectors in a large animal model

Intra-articular gene therapy has potential for the treatment of osteoarthritis and rheumatoid arthritis. To quantify in vitro relative gene transduction, equine chondrocytes and synovial cells were treated with adenovirus vectors (Ad), serotype 2 adeno-associated virus vectors (rAAV2), or self-complementary (sc) AAV2 vectors carrying green fluorescent protein (GFP). Using 6 horses, bilateral metacarpophalangeal joints were injected with Ad, rAAV2, or scAAV2 vectors carrying GFP genes to assess the in vivo joint inflammation and neutralizing antibody (NAb) titer in serum and joint fluid. In vitro, the greater transduction efficiency and sustained gene expression were achieved by scAAV2 compared to rAAV2 in equine chondrocytes and synovial cells. In vivo, AAV2 demonstrated less joint inflammation than Ad, but similar NAb titer. The scAAV2 vectors can induce superior gene transduction than rAAV2 in articular cells, and both rAAV2 and scAAV2 vectors were showed to be safer for intra-articular use than Ad vectors.

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.

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.

Use of a parathyroid hormone peptide (PTH(1-34))-enriched fibrin hydrogel for the treatment of a subchondral cystic lesion in the proximal interphalangeal joint of a warmblood filly

To describe the treatment of a subchondral bone cyst in the proximal phalanx with parathyroid hormone peptide-enriched fibrin hydrogel in a warmblood filly. The cyst was localized with computer-assisted orthopaedic surgery, then curetted and finally filled with parathyroid hormone fragment peptide 1-34 (PTH(1-34)) covalently attached to a fibrin hydrogel. The cyst healed quickly without any complications. This result supports the hypothesis that PTH(1-34) delivered locally in a fibrin hydrogel may improve the postoperative prognosis of surgical management of subchondral bone cysts in horses. Subchondral bone cysts are fairly common in horses. Especially in older horses, the prognosis is poor, even after surgical curettage. Therefore, different management protocols have been investigated in conjunction with surgical curettage to improve prognosis. Locally delivered PTH(1-34) seems to be a new method in the treatment of subchondral bone cysts.