Effect of sustained gene delivery of platelet-derived growth factor or its antagonist (PDGF-1308) on tissue-engineered cementum

The long non-coding RNA, miRNA and mRNA landscapes of cementoblasts during cementogenesis

OBJECTIVE

Stimulation of cementogenesis is essential to cementum regeneration and root restoration. Long non-coding RNAs (lncRNAs) participate in the regulatory networks of periodontal regeneration processes. We identified and analysed differentially expressed lncRNAs, miRNAs and mRNAs associated with cementogenic differentiation of cementoblasts.

MATERIALS AND METHODS

OCCM-30 immortalized mouse cementoblast cells were induced in cementogenic medium for 7 and 14 days. Total RNA was extracted and subjected to RNA sequencing to screen for differentially expressed lncRNAs, miRNAs and mRNAs. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was performed to determine the expression levels of RNAs. Gene Ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were used to clarify the potential functions of differentially expressed genes in biological processes and pathways. lncRNA-miRNA-mRNA networks were constructed based on correlation and algorithmic analyses.

RESULTS

In all, 461 lncRNAs, 89 miRNAs and 2157 mRNAs showed differential expression in OCCM-30 cells after cementoblast differentiation. At day 7, upregulation of 248 lncRNAs, 30 miRNAs and 905 mRNAs was observed, along with downregulation of 127 lncRNAs, 34 miRNAs and 960 mRNAs. At day 14, 197 lncRNAs, 13 miRNAs and 847 mRNAs were upregulated, while 74 lncRNAs, 12 miRNAs and 760 mRNAs were downregulated. The results of qRT-PCR showed that four candidate lncRNAs, H19, Gdap10, Foxo6os and Ipw, were significantly upregulated after 7 and 14 days of cementogenic induction. The lncRNA-miRNA-mRNA network illustrated a possible competitive endogenous RNA regulatory mechanism. GO analysis showed that consistently differentially expressed mRNAs were involved in blood vessel morphogenesis, cell-substrate adhesion, cell adhesion, ossification and extracellular matrix organization. KEGG analysis indicated that extracellular matrix-receptor interaction, focal adhesion, and the PI3K-Akt, Rap1, mitogen-activated protein kinase, and Ras signalling pathways varied significantly during cementogenesis.

CONCLUSION

The expressions of lncRNA, miRNA and mRNA were significantly altered in cementoblasts after cementogenesis. This study highlighted the effect of lncRNAs in the process of cementogenesis and revealed their potential for the discovery of novel biomarkers and therapeutic targets for cementum regeneration.

Hard Dental Tissues Regeneration-Approaches and Challenges

With the development of the modern concept of tissue engineering approach and the discovery of the potential of stem cells in dentistry, the regeneration of hard dental tissues has become a reality and a priority of modern dentistry. The present review reports the recent advances on stem-cell based regeneration strategies for hard dental tissues and analyze the feasibility of stem cells and of growth factors in scaffolds-based or scaffold-free approaches in inducing the regeneration of either the whole tooth or only of its component structures.

The role of insulin-like growth factors in modulating the activity of dental mesenchymal stem cells

Regenerative treatment protocols are an exciting prospect in the management of oral pathology, as they allow for tissues to be restored to their original form and function, as compared to the reparative healing mechanisms which currently govern the outcomes of the majority of dental treatment. Stem cell therapy presents with a great deal of untapped potential in this pursuit of tissue regeneration, and, in particular, mesenchymal stem cells (MSCs) derived from dental tissues are of specific relevance with regards to their applications in engineering craniofacial tissues. A number of mediatory factors are involved in modulating the actions of dental MSCs, and, of these, insulin like growth factors (IGFs) are known to have potent effects in governing the behavior of these cells. The IGF family comprises a number of primary ligands, receptors, and binding proteins which are known to modulate the key properties of dental MSCs, such as their proliferation rates, differentiation potential, and mineralisation. The aims of this review are three-fold: (i) to present an overview of dental MSCs and the role of growth factors in modulating their characteristics, (ii) to discuss in greater detail the specific role of IGFs and the benefits they may convey for tissue engineering, and (iii) to provide a summary of potential for in vivo clinical translation of the current in vitro body of evidence.

Biomaterial-Based Approaches for Regeneration of Periodontal Ligament and Cementum Using 3D Platforms

Currently, various tissue engineering strategies have been developed for multiple tissue regeneration and integrative structure formations as well as single tissue formation in musculoskeletal complexes. In particular, the regeneration of periodontal tissues or tooth-supportive structures is still challenging to spatiotemporally compartmentalize PCL (poly-ε-caprolactone)-cementum constructs with micron-scaled interfaces, integrative tissue (or cementum) formations with optimal dimensions along the tooth-root surfaces, and specific orientations of engineered periodontal ligaments (PDLs). Here, we discuss current advanced approaches to spatiotemporally control PDL orientations with specific angulations and to regenerate cementum layers on the tooth-root surfaces with Sharpey's fiber anchorages for state-of-the-art periodontal tissue engineering.

Gene Delivery Therapeutics in the Treatment of Periodontitis and Peri-Implantitis: A State of the Art Review

BACKGROUND

Periodontal disease is a chronic inflammatory condition that affects supporting tissues around teeth, resulting in periodontal tissue breakdown. If left untreated, periodontal disease could have serious consequences; this condition is in fact considered as the primary cause of tooth loss. Being highly prevalent among adults, periodontal disease treatment is receiving increased attention from researchers and clinicians. When this condition occurs around dental implants, the disease is termed peri-implantitis. Periodontal regeneration aims at restoring the destroyed attachment apparatus, in order to improve tooth stability and thus reduce disease progression and subsequent periodontal tissue breakdown. Although many biomaterials have been developed to promote periodontal regeneration, they still have their own set of disadvantages. As a result, regenerative medicine has been employed in the periodontal field, not only to overcome the drawbacks of the conventional biomaterials but also to ensure more predictable regenerative outcomes with minimal complications. Regenerative medicine is considered a part of the research field called tissue engineering/regenerative medicine (TE/RM), a translational field combining cell therapy, biomaterial, biomedical engineering and genetics all with the aim to replace and restore tissues or organs to their normal function using in vitro models for in vivo regeneration. In a tissue, cells are responding to different micro-environmental cues and signaling molecules, these biological factors influence cell differentiation, migration and cell responses. A central part of TE/RM therapy is introducing drugs, genetic materials or proteins to induce specific cellular responses in the cells at the site of tissue repair in order to enhance and improve tissue regeneration. In this review, we present the state of art of gene therapy in the applications of periodontal tissue and peri-implant regeneration.

PURPOSE

We aim herein to review the currently available methods for gene therapy, which include the utilization of viral/non-viral vectors and how they might serve as therapeutic potentials in regenerative medicine for periodontal and peri-implant tissues.

Biomaterials, Current Strategies, and Novel Nano-Technological Approaches for Periodontal Regeneration

Periodontal diseases involve injuries to the supporting structures of the tooth and, if left untreated, can lead to the loss of the tooth. Regenerative periodontal therapies aim, ideally, at healing all the damaged periodontal tissues and represent a significant clinical and societal challenge for the current ageing population. This review provides a picture of the currently-used biomaterials for periodontal regeneration, including natural and synthetic polymers, bioceramics (e.g., calcium phosphates and bioactive glasses), and composites. Bioactive materials aim at promoting the regeneration of new healthy tissue. Polymers are often used as barrier materials in guided tissue regeneration strategies and are suitable both to exclude epithelial down-growth and to allow periodontal ligament and alveolar bone cells to repopulate the defect. The problems related to the barrier postoperative collapse can be solved by using a combination of polymeric membranes and grafting materials. Advantages and drawbacks associated with the incorporation of growth factors and nanomaterials in periodontal scaffolds are also discussed, along with the development of multifunctional and multilayer implants. Tissue-engineering strategies based on functionally-graded scaffolds are expected to play an ever-increasing role in the management of periodontal defects.

Effect of sustained PDGF nonviral gene delivery on repair of tooth-supporting bone defects

Recombinant human platelet-derived growth factor-BB (rhPDGF-BB) promotes soft tissue and bone healing, and is Food and Drug Administration-approved for treatment of diabetic ulcers and periodontal defects. The short half-life of topical rhPDGF-BB protein application necessitates bolus, high-dose delivery. Gene therapy enables sustained local growth factor production. A novel gene activated matrix delivering polyplexes of polyethylenimine (PEI)-plasmid DNA encoding PDGF was evaluated for promotion of periodontal wound repair in vivo. PEI-pPDGF-B polyplexes were tested in human periodontal ligament fibroblasts and human gingival fibroblasts for cell viability and transfection efficiency. Collagen scaffolds containing PEI-pPDGF-B polyplexes at two doses, rhPDGF-BB, PEI vector or collagen alone were randomly delivered to experimentally induced tooth-supporting periodontal defects in a rodent model. Mandibulae were collected at 21 days for histologic observation and histomorphometry. PEI-pPDGF-B polyplexes were biocompatible to cells tested and enzyme-linked immunosorbent assay confirmed the functionality of transfection. Significantly greater osteogenesis was observed for collagen alone and rhPDGF-BB versus the PEI-containing groups. Defects treated with sustained PDGF gene delivery demonstrated delayed healing coupled with sustained inflammatory cell infiltrates lateral to the osseous defects. Continuous PDGF-BB production by nonviral gene therapy could have delayed bone healing. This nonviral gene delivery system in this model appeared to prolong inflammatory response, slowing alveolar bone regeneration in vivo.

Emerging regenerative approaches for periodontal reconstruction: a systematic review from the AAP Regeneration Workshop

More than 30 years have passed since the first successful application of regenerative therapy for treatment of periodontal diseases. Despite being feasible, periodontal regeneration still faces numerous challenges, and complete restoration of structure and function of the diseased periodontium is often considered an unpredictable task. This review highlights developing basic science and technologies for potential application to achieve reconstruction of the periodontium. A comprehensive search of the electronic bibliographic database PubMed was conducted to identify different emerging therapeutic approaches reported to influence either biologic pathways and/or tissues involved in periodontal regeneration. Each citation was assessed based on its abstract, and the full text of potentially eligible reports was retrieved. Based on the review of the full papers, their suitability for inclusion in this report was determined. In principle, only reports from scientifically well-designed studies that presented preclinical in vivo (animal studies) or clinical (human studies) evidence for successful periodontal regeneration were included. Hence, in vitro studies, namely those conducted in laboratories without any live animals, were excluded. In case of especially recent and relevant reviews with a narrow focus on specific regenerative approaches, they were identified as such, and thereby the option of referring to them to summarize the status of a specific approach, in addition to or instead of listing each separately, was preserved. Admittedly, the presence of subjectivity in the selection of studies to include in this overview cannot be excluded. However, it is believed that the contemporary approaches described in this review collectively represent the current efforts that have reported preclinical or clinical methods to successfully enhance regeneration of the periodontium. Today's challenges facing periodontal regenerative therapy continue to stimulate important research and clinical development, which, in turn, shapes the current concept of periodontal tissue engineering. Emerging technologies--such as stem cell therapy, bone anabolic agents, genetic approaches, and nanomaterials--also offer unique opportunities to enhance the predictability of current regenerative surgical approaches and inspire development of novel treatment strategies.

Periodontal regeneration with stem cells-seeded collagen-hydroxyapatite scaffold

Re-establishing compromised periodontium to its original structure, properties and function is demanding, but also challenging, for successful orthodontic treatment. In this study, the periodontal regeneration capability of collagen-hydroxyapatite scaffolds, seeded with bone marrow stem cells, was investigated in a canine labial alveolar bone defect model. Bone marrow stem cells were isolated, expanded and characterized. Porous collagen-hydroxyapatite scaffold and cross-linked collagen-hydroxyapatite scaffold were prepared. Attachment, migration, proliferation and morphology of bone marrow stem cells, co-cultured with porous collagen-hydroxyapatite or cross-linked collagen-hydroxyapatite, were evaluated in vitro. The periodontal regeneration capability of collagen-hydroxyapatite scaffold with or without bone marrow stem cells was tested in six beagle dogs, with each dog carrying one sham-operated site as healthy control, and three labial alveolar bone defects untreated to allow natural healing, treated with bone marrow stem cells - collagen-hydroxyapatite scaffold implant or collagen-hydroxyapatite scaffold implant, respectively. Animals were euthanized at 3 and 6 months (3 animals per group) after implantation and the resected maxillary and mandibular segments were examined using micro-computed tomography scan, H&E staining, Masson's staining and histometric evaluation. Bone marrow stem cells were successfully isolated and demonstrated self-renewal and multi-potency in vitro. The porous collagen-hydroxyapatite and cross-linked collagen-hydroxyapatite had average pore sizes of 415 ± 20 µm and 203 ± 18 µm and porosity of 69 ± 0.5% and 50 ± 0.2%, respectively. The attachment, proliferation and migration of bone marrow stem cells were satisfactory on both porous collagen-hydroxyapatite and cross-linked collagen-hydroxyapatite scaffolds. Implantation of bone marrow stem cells - collagen-hydroxyapatite or collagen-hydroxyapatite scaffold in beagle dogs with experimental periodontal defects resulted in significantly enhanced periodontal regeneration characterized by formation of new bone, periodontal ligament and cementum, compared with the untreated defects, as evidenced by histological and micro-computed tomography examinations. The prepared collagen-hydroxyapatite scaffolds possess favorable bio-compatibility. The bone marrow stem cells - collagen-hydroxyapatite and collagen-hydroxyapatite scaffold - induced periodontal regeneration, with no aberrant events complicating the regenerative process. Further research is necessary to improve the bone marrow stem cells behavior in collagen-hydroxyapatite scaffolds after implantation.

Combined delivery of PDGF-BB and BMP-6 for enhanced osteoblastic differentiation

Natural microenvironment during bone tissue regeneration involves integration of multiple biological growth factors which regulate mitogenic activities and differentiation to induce bone repair. Among them platelet derived growth factor (PDGF-BB) and bone morphogenic protein-6 (BMP-6) are known to play a prominent role. The aim of this study was to investigate the benefits of combined delivery of PDGF-BB and BMP-6 on proliferation and osteoblastic differentiation of MC3T3-E1 preosteoblastic cells. PDGF-BB and BMP-6 were loaded in gelatin and poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid) particles, respectively. The carrier particles were then loaded into 3D chitosan matrix fabricated by freeze drying. The fast release of PDGF-BB during 7 days was accompanied by slower and prolonged release of BMP-6. The premising release of mitogenic factor PDGF-BB resulted in an increased MC3T3-E1 cell population seeded on chitosan scaffolds. Osteogenic markers of RunX2, Col 1, OPN were higher on chitosan scaffolds loaded with growth factors either individually or in combination. However, OCN expression and bone mineral formation were prominent on chitosan scaffolds incorporating PDGF-BB and BMP-6 as a combination.

Growth factor-delivery systems for tissue engineering: a materials perspective

The transplantation of organs, their surgical reconstruction or implantation of synthetic devices that can perform the function of organs, are the currently available methods for treating loss of tissue/organs in humans. However, the limitations associated with these techniques have led to the development of tissue engineering. One of the primary goals of tissue engineering is to provide growth factor delivery systems that can induce desired cell responses both in vitro and in vivo, in order to cause accelerated tissue regeneration. To make growth factors a more therapeutically viable alternative for the treatment of chronic degenerative diseases, a wide range of natural and synthetic materials have been employed as vehicles for their controlled delivery. The choice of material and design of the carrier device influence the mode of immobilization of growth factors on the scaffolds and their local/systemic administration. From a tissue engineer's perspective, materials could be used for designing scaffolds as well as for delivering single or multiple growth factors. Therefore, this review discusses growth factor delivery systems, with particular reference to carrier-based growth factor delivery systems with a focus on materials.

The effect of a bioactive collagen membrane releasing PDGF or GDF-5 on bone regeneration

Regenerative procedures using barrier membrane technology are presently well established in periodontal/endodontic surgery. The objective of this study was to compare the subsequent effects of the released platelet-derived growth factor (PDGF) and growth/differentiation factor 5 (GDF-5) from collagen membranes (CMs) on bone regeneration in vitro and in vivo. In vitro studies were conducted using MC3T3-E1 mouse preosteoblasts cultured with or without factors. Cell viability, cell proliferation, alkaline phosphatase (ALP) activity and bone marker gene expression were then measured. In vivo studies were conducted by placing CMs with low or high dose PDGF or GDF-5 in rat mandibular defects. At 4 weeks after surgery new bone formation was measured using μCT and histological analysis. The results of in vitro studies showed that CM/GDF-5 significantly increased ALP and cell proliferation activities without cytotoxicity in MC3T3-E1 cells when compared to CM/PDGF or CM alone. Gene expression analysis revealed that Runx2 and Osteocalcin were significantly increased in CM/GDF-5 compared to CM/PDGF or control. Quantitative and qualitative μCT and histological analysis for new bone formation revealed that although CM/PDGF significantly enhanced bone regeneration compared to CM alone or control, CM/GDF-5 significantly accelerated bone regeneration to an even greater extent than CM/PDGF. The results also showed that GDF-5 induced new bone formation in a dose-dependent manner. These results suggest that this strategy, using a CM carrying GDF-5, might lead to an improvement in the current clinical treatment of bone defects for periodontal and implant therapy.

Gene therapy in periodontics

GENES are made of DNA - the code of life. They are made up of two types of base pair from different number of hydrogen bonds AT, GC which can be turned into instruction. Everyone inherits genes from their parents and passes them on in turn to their children. Every person's genes are different, and the changes in sequence determine the inherited differences between each of us. Some changes, usually in a single gene, may cause serious diseases. Gene therapy is ‘the use of genes as medicine’. It involves the transfer of a therapeutic or working gene copy into specific cells of an individual in order to repair a faulty gene copy. Thus it may be used to replace a faulty gene, or to introduce a new gene whose function is to cure or to favorably modify the clinical course of a condition. It has a promising era in the field of periodontics. Gene therapy has been used as a mode of tissue engineering in periodontics. The tissue engineering approach reconstructs the natural target tissue by combining four elements namely: Scaffold, signaling molecules, cells and blood supply and thus can help in the reconstruction of damaged periodontium including cementum, gingival, periodontal ligament and bone.

Controlling the proliferation and differentiation stages to initiate periodontal regeneration

The success of periodontal regeneration depends on the coordination of early cell proliferation and late cell differentiation. The aim of this study was to investigate whether the proliferation or differentiation stage predominantly promotes the initiation of periodontal regeneration. Critical-sized periodontal defects were surgically created on rat maxillae and filled with poly-(D,L-lactide-co-glycolide)-poly-d,l-lactide hybrid microspheres encapsulating platelet-derived growth factor (PDGF, a promoter of mitogenesis), simvastatin (a promoter of osteogenic differentiation), or bovine serum albumin (a control). The encapsulation efficiency and in vitro release profiles of the microspheres were determined by high-performance liquid chromatography and enzyme-linked immunosorbent assay. The maxillae were harvested after 10 or 14 days and assessed by micro-computed tomography, histology, and immunohistochemistry for regeneration efficacy and cell viability. The rapid release of PDGF was observed within the first week, whereas a slow release profile was noted for simvastatin. The PDGF-treated specimens demonstrated a significantly higher bone volume fraction compared with bovine serum albumin- (p < 0.05) or simvastatin-treated (p < 0.05) specimens at day 14. Histologically, active bone formation originating from the defect borders was noted in both the PDGF- and the simvastatin-treated specimens, and functionally aligned periodontal ligament fiber insertion was only observed in the PDGF-treated specimens. The significant promotion of mitogenesis by PDGF treatment was also noted at day 14 (p < 0.05). In conclusion, increased mitogenesis or osteogenic differentiation may stimulate osteogenesis, and the upregulation of mitogenesis by PDGF appears to play a role in the initiation of periodontal regeneration.

Advanced reconstructive technologies for periodontal tissue repair

Reconstructive therapies to promote the regeneration of lost periodontal support have been investigated through both preclinical and clinical studies. Advanced regenerative technologies using new barrier-membrane techniques, cell-growth-stimulating proteins or gene-delivery applications have entered the clinical arena. Wound-healing approaches using growth factors to target the restoration of tooth-supporting bone, periodontal ligament and cementum are shown to significantly advance the field of periodontal-regenerative medicine. Topical delivery of growth factors, such as platelet-derived growth factor, fibroblast growth factor or bone morphogenetic proteins, to periodontal wounds has demonstrated promising results. Future directions in the delivery of growth factors or other signaling models involve the development of innovative scaffolding matrices, cell therapy and gene transfer, and these issues are discussed in this paper.

Bioengineering strategies for regeneration of craniofacial bone: a review of emerging technologies

Although advances in surgical techniques and bone grafting have significantly improved the functional and cosmetic restoration of craniofacial structures lost because of trauma or disease, there are still significant limitations in our ability to regenerate these tissues. The regeneration of oral and craniofacial tissues presents a formidable challenge that requires synthesis of basic science, clinical science, and engineering technology. Tissue engineering is an interdisciplinary field of study that addresses this challenge by applying the principles of engineering to biology and medicine toward the development of biological substitutes that restore, maintain, and improve normal function. This review will explore the impact of biomaterials design, stem cell biology and gene therapy on craniofacial tissue engineering.

Review paper: DNA delivery strategies to promote periodontal regeneration

Periodontal diseases are caused by bacteria with an inflammatory component that result in the loss of bone and soft tissue around the neck of the teeth. Recent therapies allow clinicians to regenerate some of the lost structures of the periodontium. Regeneration of these lost supporting structures is a highly orchestrated process, involving various cellular and molecular players, leading to the complete restoration of the periodontium (the tooth-supporting apparatus). The introduction of growth factors has positively influenced the clinical outcome of the existing regenerative procedures but the supra-physiological doses and the high cost associated with these growth factors can be drawbacks. Gene therapy may offer some interesting advantages to current therapies. In the field of periodontology, several studies have been conducted to explore the efficacy of delivering the DNA of key growth factors using viral vectors in both periodontal and peri-implant bone regeneration. Relatively few studies have explored the application of nonviral gene therapy in periodontal regeneration. This article is aimed at reviewing the studies conducted so far using viral and nonviral gene delivery approaches to achieve periodontal and peri-implant bone regeneration.

Toward delivery of multiple growth factors in tissue engineering

Inspired by physiological events that accompany the "wound healing cascade", the concept of developing a tissue either in vitro or in vivo has led to the integration of a wide variety of growth factors (GFs) in tissue engineering strategies in an effort to mimic the natural microenvironments of tissue formation and repair. Localised delivery of exogenous GFs is believed to be therapeutically effective for replication of cellular components involved in tissue development and the healing process, thus making them important factors for tissue regeneration. However, any treatment aiming to mimic the critical aspects of the natural biological process should not be limited to the provision of a single GF, but rather should release multiple therapeutic agents at an optimised ratio, each at a physiological dose, in a specific spatiotemporal pattern. Despite several obstacles, delivery of more than one GF at rates mimicking an in vivo situation has promising potential for the clinical management of severely diseased tissues. This article summarises the concept of and early approaches toward the delivery of dual or multiple GFs, as well as current efforts to develop sophisticated delivery platforms for this ambitious purpose, with an emphasis on the application of biomaterials-based deployment technologies that allow for controlled spatial presentation and release kinetics of key biological cues. Additionally, the use of platelet-rich plasma or gene therapy is addressed as alternative, easy, cost-effective and controllable strategies for the release of high concentrations of multiple endogenous GFs, followed by an update of the current progress and future directions of research utilising release technologies in tissue engineering and regenerative medicine.

PDGF-B gene therapy accelerates bone engineering and oral implant osseointegration

Platelet-derived growth factor-BB (PDGF-BB) stimulates repair of healing-impaired chronic wounds such as diabetic ulcers and periodontal lesions. However, limitations in predictability of tissue regeneration occur due in part to transient growth factor bioavailability in vivo. Here, we report that gene delivery of PDGF-B stimulates repair of oral implant extraction socket defects. Alveolar ridge defects were created in rats and were treated at the time of titanium implant installation with a collagen matrix containing an adenoviral (Ad) vector encoding PDGF-B (5.5×10⁸ or 5.5×10⁹ pfu/ml), Ad encoding luciferase (Ad-Luc; 5.5×10⁹ pfu/ml; control) or recombinant human PDGF-BB protein (rhPDGF-BB, 0.3 mg/ml). Bone repair and osseointegration were measured via backscattered SEM, histomorphometry, microcomputed tomography, and biomechanical assessments. Further, a panel of local and systemic safety assessments was performed. Results demonstrated bone repair was accelerated by Ad-PDGF-B and rhPDGF-BB delivery compared to Ad-Luc, with the high dose of Ad-PDGF-B more effective than the low dose. No significant dissemination of the vector construct or alteration of systemic parameters was noted. In summary, gene delivery of Ad-PDGF-B demonstrates regenerative and safety capabilities for bone tissue engineering and osseointegration in alveolar bone defects comparable to rhPDGF-BB protein delivery in vivo.

Localized delivery of growth factors for periodontal tissue regeneration: role, strategies, and perspectives

Difficulties associated with achieving predictable periodontal regeneration, means that novel techniques need to be developed in order to regenerate the extensive soft and hard tissue destruction that results from periodontitis. Localized delivery of growth factors to the periodontium is an emerging and versatile therapeutic approach, with the potential to become a powerful tool in future regenerative periodontal therapy. Optimized delivery regimes and well-defined release kinetics appear to be logical prerequisites for safe and efficacious clinical application of growth factors and to avoid unwanted side effects and toxicity. While adequate concentrations of growth factor(s) need to be appropriately localized, delivery vehicles are also expected to possess properties such as protein protection, precision in controlled release, biocompatibility and biodegradability, self-regulated therapeutic activity, potential for multiple delivery, and good cell/tissue penetration. Here, current knowledge, recent advances, and future possibilities of growth factor delivery strategies are outlined for periodontal regeneration. First, the role of those growth factors that have been implicated in the periodontal healing/regeneration process, general requirements for their delivery, and the different material types available are described. A detailed discussion follows of current strategies for the selection of devices for localized growth factor delivery, with particular emphasis placed upon their advantages and disadvantages and future prospects for ongoing studies in reconstructing the tooth supporting apparatus.

Efficient gene transfer to periodontal ligament cells and human gingival fibroblasts by adeno-associated virus vectors

OBJECTIVES

We explored for the first time the possibility to deliver a reporter gene (Green Fluorescence Protein) to human primary periodontal ligament (PDL) cells and human gingival fibroblasts (HGF) using shuttle vectors derived from adeno-associated virus (AAV). Since AAV transduction rates on other human primary fibroblasts have been previously shown to depend on the particular cell lineage and on the employed viral serotype, we determined the most effective AAV variant for periodontal cells comparing different vector types.

METHODS

AAV serotypes 1-5 encoding GFP in single stranded (ss) and self-complementary (sc) vector genome conformations were used to infect primary HGF and PDL cells. Two days post-infection, the percentage of GFP expressing cells was determined by flow cytometry.

RESULTS

Highest transduction rates for both cell types were achieved with self-complementary vectors derived from AAV-2, resulting in GFP expression in up to 86% of PDL cells and 50% of HGF. Transgene expression could be observed by optical microscopy for 2 months after infection. Lower but detectable rates were obtained with serotypes 1, 3 and 5.

CONCLUSIONS

The efficacy demonstrated here and the safety and versatility of AAV technology indicated in previous studies clearly suggest the potential of AAV vectors as tools for gene transfer to periodontal tissues.

Matrices and scaffolds for drug delivery in dental, oral and craniofacial tissue engineering

Current treatments for diseases and trauma of dental, oral and craniofacial (DOC) structures rely on durable materials such as amalgam and synthetic materials, or autologous tissue grafts. A paradigm shift has taken place to utilize tissue engineering and drug delivery approaches towards the regeneration of these structures. Several prototypes of DOC structures have been regenerated such as temporomandibular joint (TMJ) condyle, cranial sutures, tooth structures and periodontium components. However, many challenges remain when taking in consideration the high demand for esthetics of DOC structures, the complex environment and yet minimal scar formation in the oral cavity, and the need for accommodating multiple tissue phenotypes. This review highlights recent advances in the regeneration of DOC structures, including the tooth, periodontium, TMJ, cranial sutures and implant dentistry, with specific emphasis on controlled release of signaling cues for stem cells, biomaterial matrices and scaffolds, and integrated tissue engineering approaches.

Craniofacial tissue engineering by stem cells

Craniofacial tissue engineering promises the regeneration or de novo formation of dental, oral, and craniofacial structures lost to congenital anomalies, trauma, and diseases. Virtually all craniofacial structures are derivatives of mesenchymal cells. Mesenchymal stem cells are the offspring of mesenchymal cells following asymmetrical division, and reside in various craniofacial structures in the adult. Cells with characteristics of adult stem cells have been isolated from the dental pulp, the deciduous tooth, and the periodontium. Several craniofacial structures--such as the mandibular condyle, calvarial bone, cranial suture, and subcutaneous adipose tissue--have been engineered from mesenchymal stem cells, growth factor, and/or gene therapy approaches. As a departure from the reliance of current clinical practice on durable materials such as amalgam, composites, and metallic alloys, biological therapies utilize mesenchymal stem cells, delivered or internally recruited, to generate craniofacial structures in temporary scaffolding biomaterials. Craniofacial tissue engineering is likely to be realized in the foreseeable future, and represents an opportunity that dentistry cannot afford to miss.

Growth factor delivery for oral and periodontal tissue engineering

The treatment of oral and periodontal diseases and associated anomalies accounts for a significant proportion of the healthcare burden, with the manifestations of these conditions being functionally and psychologically debilitating. Growth factors are critical to the development, maturation, maintenance and repair of craniofacial tissues, as they establish an extracellular environment that is conducive to cell and tissue growth. Tissue-engineering principles aim to exploit these properties in the development of biomimetic materials that can provide an appropriate microenvironment for tissue development. These materials have been constructed into devices that can be used as vehicles for delivery of cells, growth factors and DNA. In this review, different mechanisms of drug delivery are addressed in the context of novel approaches to reconstruct and engineer oral- and tooth-supporting structures, namely the periodontium and alveolar bone.

Defining the roots of cementum formation

Significant progress has been seen in research aimed at regeneration of the disease-damaged periodontium. Our own strategy has been to approach periodontal tissue development (i.e. root, cementum, periodontal ligament, and bone) as a source for the identification of key regulators of cellular processes that may be applicable to periodontal tissue repair. Specifically, enamel-like molecules, bone morphogenetic proteins (BMPs), and phosphates have been investigated for their role in altering gene expression and cell functions in follicle cells, periodontal ligament cells, and cementoblasts. Amelogenin, leucine-rich amelogenin peptide, and tyrosine-rich amelogenin peptide have been found to similarly affect cementoblast gene expression and cementoblast-mediated mineralization in vitro; however, these enamel-like factors do not increase cell proliferation as has been observed in cells treated with Emdogain (Biora AB, Malmö, Sweden), an enamel matrix derivative. BMP-2 has been found to promote differentiation of follicle cells into a cementoblast/osteoblast phenotype, and BMP-3 is being investigated as a negative regulator of mineralization. The increased ratio of phosphate to pyrophosphate in the local region during root development has been found to significantly enhance the extent of cementum formation in animal models. Furthermore, phosphate has been identified as a regulator of cementoblast SIBLING (small integrin-binding ligand N-linked glycoprotein) gene expression in vitro. These investigations of candidate factors for periodontal regeneration have uncovered mechanisms regulating gene expression and cell function in cells controlling the behavior of periodontal tissues (i.e. follicle cells, periodontal cells, and cementoblasts) and offer new directions to consider for clinical repair of periodontal defects.

Gene therapeutics for periodontal regenerative medicine

There has been significant advancement in the field of periodontal tissue engineering over the past decade for the repair of tooth-supporting structures. Although encouraging results for periodontal tissue regeneration have been found in numerous clinical investigations using recombinant growth factors, limitations exist with topical protein delivery. Newer approaches seek to develop methodologies that optimize growth factor targeting to maximize the therapeutic outcome of periodontal regenerative procedures. Genetic approaches in periodontal tissue engineering show early progress in achieving delivery of growth factor genes, such as platelet-derived growth factor or bone morphogenetic protein, to periodontal lesions. Ongoing investigations in ex vivo and in vivo gene transfer to periodontia seek to examine the extent of the potential effects in stimulating periodontal tissue engineering.

Platelet-derived growth factor stimulates bone fill and rate of attachment level gain: results of a large multicenter randomized controlled trial

BACKGROUND

Growth factors are generally accepted to be essential mediators of tissue repair via well-established mechanisms of action that include stimulatory effects on angiogenesis and cellular proliferation, ingrowth, differentiation, and matrix biosynthesis. The aim of this study was to evaluate in a large-scale, prospective, blinded, and randomized controlled clinical trial the safety and effectiveness of purified recombinant human platelet-derived growth factor (rhPDGF-BB) mixed with a synthetic beta-tricalcium phosphate (beta-TCP) matrix for the treatment of advanced periodontal osseous defects at 6 months of healing.

METHODS

Eleven clinical centers enrolled 180 subjects, each requiring surgical treatment of a 4 mm or greater intrabony periodontal defect and meeting all inclusion and exclusion criteria. Subjects were randomized into one of three treatment groups: 1) beta-TCP + 0.3 mg/ml rhPDGF-BB in buffer; 2) beta-TCP + 1.0 mg/ml rhPDGF-BB in buffer; and 3) beta-TCP + buffer (active control). Safety data were assessed by the frequency and severity of adverse events. Effectiveness measurements included clinical attachment levels (CAL) and gingival recession (GR) measured clinically and linear bone growth (LBG) and percent bone fill (% BF) as assessed radiographically by an independent centralized radiology review center. The area under the curve (AUC), an assessment of the rate of healing, was also calculated for CAL measurements. The surgeons, clinical and radiographic evaluators, patients, and study sponsor were all masked with respect to treatment groups.

RESULTS

CAL gain was significantly greater at 3 months for group 1 (rhPDGF 0.3 mg/ml) compared to group 3 (beta-TCP + buffer) (3.8 versus 3.3 mm; P = 0.032), although by 6 months, this finding was not statistically significant (P = 0.11). This early acceleration of CAL gain led to group 1 exhibiting a significantly greater rate of CAL gain between baseline and 6 months than group 3 as assessed by the AUC (68.4- versus 60.1-mm weeks; P = 0.033). rhPDGF (0.3 mg/ml)-treated sites also had significantly greater linear bone gain (2.6 versus 0.9 mm, respectively; P < 0.001) and percent defect fill (57% versus 18%, respectively; P < 0.001) than the sites receiving the bone substitute with buffer at 6 months. There was less GR at 3 months in group 1 compared to group 3 (P = 0.04); at 6 months, GR for group 1 remained unchanged, whereas there was a slight gain in gingival height for group 3 resulting in comparable GR. There were no serious adverse events attributable to any of the treatments.

CONCLUSIONS

To our knowledge, this study is the largest prospective, randomized, triple-blinded, and controlled pivotal clinical trial reported to date assessing a putative periodontal regenerative and wound healing therapy. The study demonstrated that the use of rhPDGF-BB was safe and effective in the treatment of periodontal osseous defects. Treatment with rhPDGF-BB stimulated a significant increase in the rate of CAL gain, reduced gingival recession at 3 months post-surgery, and improved bone fill as compared to a beta-TCP bone substitute at 6 months.

Bone Sialoprotein Gene Transfer to Periodontal Ligament Cells May Not Be Sufficient to Promote Mineralization In Vitro or In Vivo

BACKGROUND

To improve regenerative therapies, it is important to understand the cells and factors modulating periodontal tissues. Our group has focused on bone sialoprotein (BSP), a mineralized tissue-selective protein considered to be involved in the initiation of cementogenesis and osteogenesis. In this study, we examined whether gene transfer of BSP into periodontal ligament (PDL) cells would result in an increased ability of PDL cells to promote mineralization in vitro and in vivo.

METHODS

PDL cells obtained from CD-1 mice were immortalized using simian virus (SV) 40 large T antigen (TAg) and designated SV-PDL cells. SV-PDL cells were infected in vitro with LacZ gene-expressing control adenovirus vector. A 1,000 plaque-forming unit (pfu) titer was selected (based on X-gal staining) and cells were infected with mouse BSP-expressing replication-deficient adenoviral vector to determine the mRNA expression and protein level of BSP. Total RNA was isolated from cells on days 2, 4, and 6. Media were obtained on days 3, 5, and 7 for protein determination. Northern blot analysis was performed for mRNA expression and Western blot analysis for protein expression. To test the effect of BSP gene transfer on the mineralization of PDL cells, in vitro (von Kossa) and in vivo (severe combined immunodeficiency [SCID] mice) experiments were performed.

RESULTS

Under normal conditions, PDL cells do not express BSP transcripts and do not promote significant mineralization. SV-PDL cells infected with a BSP viral vector expressed and secreted substantial levels of BSP as confirmed by Northern and Western blot analysis. BSP mRNA and protein levels were strong on day 2 and still apparent on day 6, although not as great. However, no mineral nodule formation was noted either in vitro or in vivo.

CONCLUSIONS

Although BSP is an important and necessary protein for mineralization, it may not be sufficient for promoting mineralization without the addition or removal of other factors. Further studies will help to clarify the specific factors required for promoting mineralization, a required step for designing predictable periodontal regenerative therapies.

Current concepts in periodontal bioengineering

Repair of tooth supporting alveolar bone defects caused by periodontal and peri-implant tissue destruction is a major goal of reconstructive therapy. Oral and craniofacial tissue engineering has been achieved with limited success by the utilization of a variety of approaches such as cell-occlusive barrier membranes, bone substitutes and autogenous block grafting techniques. Signaling molecules such as growth factors have been used to restore lost tooth support because of damage by periodontal disease or trauma. This paper will review emerging periodontal therapies in the areas of materials science, growth factor biology and cell/gene therapy. Several different polymer delivery systems that aid in the targeting of proteins, genes and cells to periodontal and peri-implant defects will be highlighted. Results from preclinical and clinical trials will be reviewed using the topical application of bone morphogenetic proteins (BMP-2 and BMP-7) and platelet-derived growth factor-BB (PDGF) for periodontal and peri-implant regeneration. The paper concludes with recent research on the use of ex vivo and in vivo gene delivery strategies via gene therapy vectors encoding growth promoting and inhibiting molecules (PDGF, BMP, noggin and others) to regenerate periodontal structures including bone, periodontal ligament and cementum.

Engineering of tooth-supporting structures by delivery of PDGF gene therapy vectors

Platelet-derived growth factor (PDGF) exerts potent effects on wound healing including the regeneration of tooth-supporting structures. Limitations of topical protein delivery to periodontal osseous defects include transient biological activity and the bioavailability of PDGF at the wound site. The objective of this investigation was to determine the feasibility of in vivo PDGF-B gene transfer to stimulate periodontal tissue regeneration in large tooth-associated alveolar bone defects in rats. Periodontal lesions (0.3 x 0.2 cm in size) were treated with a 2.6% collagen matrix alone or a matrix containing adenoviruses encoding luciferase (control), a dominant negative mutant of PDGF-A (PDGF-1308), or PDGF-B. Block biopsies were harvested at 3, 7, and 14 days post-gene delivery and descriptive histology and histomorphometric analyses were performed. The defects treated with Ad-PDGF-B demonstrated greater proliferating cell nuclear antigen positively stained cells and strong evidence of bone and cementum regeneration beyond that of Ad-luciferase and Ad-PDGF-1308 groups. Quantitative image analysis showed a nearly fourfold increase in bridging bone and sixfold increase in tooth-lining cemental repair in the Ad-PDGF-B-treated sites compared to lesions treated with Ad-luciferase or collagen matrix alone, which showed limited hard tissue neogenesis. In addition, the Xenogen In Vivo Imaging System revealed sustained and localized gene expression of the luciferase reporter at the periodontal lesions for up to 21 days after gene transfer. These results indicate that in vivo direct gene transfer of PDGF-B stimulates alveolar bone and cementum regeneration in large periodontal defects. Gene therapy utilizing PDGF-B may offer the potential for periodontal tissue engineering applications.