Effect of sustained PDGF nonviral gene delivery on repair of tooth-supporting bone defects. Gene Ther. 2017;24:31-39. [PMID: 27824330 PMCID: PMC5269540 DOI: 10.1038/gt.2016.73]

Gene-Activated Materials in Regenerative Dentistry: Narrative Review of Technology and Study Results

Treatment of a wide variety of defects in the oral and maxillofacial regions requires the use of innovative approaches to achieve best outcomes. One of the promising directions is the use of gene-activated materials (GAMs) that represent a combination of tissue engineering and gene therapy. This approach implies that biocompatible materials will be enriched with gene-carrying vectors and implanted into the defect site resulting in transfection of the recipient's cells and secretion of encoded therapeutic protein in situ. GAMs may be presented in various designs depending on the type of material, encoded protein, vector, and way of connecting the vector and the material. Thus, it is possible to choose the most suitable GAM design for the treatment of a particular pathology. The use of plasmids for delivery of therapeutic genes is of particular interest. In the present review, we aimed to delineate the principle of work and various designs of plasmid-based GAMs and to highlight results of experimental and clinical studies devoted to the treatment of periodontitis, jaw bone defects, teeth avulsion, and other pathologies in the oral and maxillofacial regions.

Gene Therapy for Regenerative Medicine

The development of biological methods over the past decade has stimulated great interest in the possibility to regenerate human tissues. Advances in stem cell research, gene therapy, and tissue engineering have accelerated the technology in tissue and organ regeneration. However, despite significant progress in this area, there are still several technical issues that must be addressed, especially in the clinical use of gene therapy. The aims of gene therapy include utilising cells to produce a suitable protein, silencing over-producing proteins, and genetically modifying and repairing cell functions that may affect disease conditions. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, non-viral gene transfection agents are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Gene therapy based on viral vectors may induce pathogenicity and immunogenicity. Therefore, significant efforts are being invested in non-viral vectors to enhance their efficiency to a level comparable to the viral vector. Non-viral technologies consist of plasmid-based expression systems containing a gene encoding, a therapeutic protein, and synthetic gene delivery systems. One possible approach to enhance non-viral vector ability or to be an alternative to viral vectors would be to use tissue engineering technology for regenerative medicine therapy. This review provides a critical view of gene therapy with a major focus on the development of regenerative medicine technologies to control the in vivo location and function of administered genes.

Comparison ofin-situversusex-situdelivery of polyethylenimine-BMP-2 polyplexes for rat calvarial defect repair via intraoperative bioprinting

Gene therapeutic applications combined with bio- and nano-materials have been used to address current shortcomings in bone tissue engineering due to their feasibility, safety and potential capability for clinical translation. Delivery of non-viral vectors can be altered using gene-activated matrices to improve their efficacy to repair bone defects.Ex-situandin-situdelivery strategies are the most used methods for bone therapy, which have never been directly compared for their potency to repair critical-sized bone defects. In this regard, we first time explore the delivery of polyethylenimine (PEI) complexed plasmid DNA encoding bone morphogenetic protein-2 (PEI-pBMP-2) using the two delivery strategies,ex-situandin-situdelivery. To realize these gene delivery strategies, we employed intraoperative bioprinting (IOB), enabling us to 3D bioprint bone tissue constructs directly into defect sites in a surgical setting. Here, we demonstrated IOB of an osteogenic bioink loaded with PEI-pBMP-2 for thein-situdelivery approach, and PEI-pBMP-2 transfected rat bone marrow mesenchymal stem cells laden bioink for theex-situdelivery approach as alternative delivery strategies. We found thatin-situdelivery of PEI-pBMP-2 significantly improved bone tissue formation compared toex-situdelivery. Despite debates amongst individual advantages and disadvantages ofex-situandin-situdelivery strategies, our results ruled in favor of thein-situdelivery strategy, which could be desirable to use for future clinical applications.

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.

Future Drug Targets in Periodontal Personalised Medicine—A Narrative Review

Periodontal disease is an infection-driven inflammatory disease characterized by the destruction of tooth-supporting tissues. The establishment of chronic inflammation will result in progressive destruction of bone and soft tissue changes. Severe periodontitis can lead to tooth loss. The disease has complex pathogenesis with an interplay between genetic, environmental, and host factors and pathogens. Effective management consists of plaque control and non-surgical interventions, along with adjuvant strategies to control inflammation and disrupt the pathogenic subgingival biofilms. Recent studies have examined novel approaches for managing periodontal diseases such as modulating microbial signaling mechanisms, tissue engineering, and molecular targeting of host inflammatory substances. Mounting evidence suggests the need to integrate omics-based approaches with traditional therapy to address the disease. This article discusses the various evolving and future drug targets, including proteomics, gene therapeutics, vaccines, and nanotechnology in personalized periodontal medicine for the effective management of periodontal diseases.

Immunomodulation in the Treatment of Periodontitis: Progress and Perspectives

Periodontitis is one of the most common dental diseases. Compared with healthy periodontal tissues, the immune microenvironment plays the key role in periodontitis by allowing the invasion of pathogens. It is possible that modulating the immune microenvironment can supplement traditional treatments and may even promote periodontal regeneration by using stem cells, bacteria, etc. New anti-inflammatory therapies can enhance the generation of a viable local immune microenvironment and promote cell homing and tissue formation, thereby achieving higher levels of immune regulation and tissue repair. We screened recent studies to summarize the advances of the immunomodulatory treatments for periodontitis in the aspects of drug therapy, microbial therapy, stem cell therapy, gene therapy and other therapies. In addition, we included the changes of immune cells and cytokines in the immune microenvironment of periodontitis in the section of drug therapy so as to make it clearer how the treatments took effects accordingly. In the future, more research needs to be done to improve immunotherapy methods and understand the risks and long-term efficacy of these methods in periodontitis.

Regenerative benefits of using growth factors in treatment of periodontal defects: A systematic review and meta-analysis with Trial Sequential Analysis on preclinical studies

The ultimate goal in periodontal treatments is to achieve a functional and anatomical regeneration of the lost tissues. Numerous studies have in some way illustrated the beneficial effects of biologic modifiers in this process, yet they are subject to a rather large degree of diversity in their results. Thanks to the promising outcomes of bioengineering techniques in the field of periodontal regeneration, this systematic review aims to evaluate the effect of various biologic modifiers used in periodontal defects of animal models. Electronic databases (Medline, Scopus, Embase, Web of Science, and Google Scholar) were searched (March 2010-December 2020) for every study that used biomolecules for regeneration of periodontal osseous defects in animal models. Regenerated bone height or area, new cementum, new connective tissues, new regenerated periodontal ligament and the dimensions of epithelial attachment (either in mm/mm² or percentage) were the investigated outcomes. The risk of bias of the included studies was assessed using the SYRCLE tool. In closing, there was a meta-analysis carried out on the outcomes of interest. Trial Sequential Analysis was also carried out to figure out the power of meta-analytic outcomes. From 1995 studies which were found in the initial search, 34 studies were included in this review, and 20 of them were selected for the meta-analysis. The eligible studies were categorized according to the morphology of the experimental periodontal defects as one-, two-, and three-wall intrabony defects; furcation defects, and recession-type defects. The most studied biomolecules were rhFGF-2, rhGDF-5, platelet-derived growth factor, bone morphogenetic protein-2, and enamel matrix derivative (EMD). Based on the meta-analysis findings, combined application of biomolecules with regenerative treatments could improve new bone and cementum formation near 1 mm when compared to the control groups in one, two and three-wall intrabony defect models (p < 0.001). In furcation grade II defect, the addition of biomolecules was observed to enhance bone area gain and cementum height regeneration up to almost 2 mm (p < 0.001). Trial Sequential Analysis results confirmed the significant effect in the aforementioned meta-analyses. In cases of the buccal recession model, the application of rhFGF-2 and rhGDF-5 decreased the dimension of epithelial attachments besides regenerative advantages on bone and cementum formation, but EMD deposition exerted no inhibitory effect on epithelial down-growth. Application of biologic modifiers especially FGF-2 and GDF-5, could positively improve the regeneration of periodontal tissues, particularly cementum and bone in animal models. Trial Sequential Analysis confirmed the results but the power of the evidences was high just in some subgroup meta-analyses, like bone and cementum regeneration in furcation grade II model and cementum regeneration in one-wall intrabony defects. The outcomes of this study can potentially endow clinicians with guidelines for the appropriate application of growth factors in periodontal regenerative therapies.

Current and future trends in periodontal tissue engineering and bone regeneration

Periodontal tissue engineering involves a multi-disciplinary approach towards the regeneration of periodontal ligament, cementum and alveolar bone surrounding teeth, whereas bone regeneration specifically applies to ridge reconstruction in preparation for future implant placement, sinus floor augmentation and regeneration of peri-implant osseous defects. Successful periodontal regeneration is based on verifiable cementogenesis on the root surface, oblique insertion of periodontal ligament fibers and formation of new and vital supporting bone. Ultimately, regenerated periodontal and peri-implant support must be able to interface with surrounding host tissues in an integrated manner, withstand biomechanical forces resulting from mastication, and restore normal function and structure. Current regenerative approaches utilized in everyday clinical practice are mainly guided tissue/bone regeneration-based. Although these approaches have shown positive outcomes for small and medium-sized defects, predictability of clinical outcomes is heavily dependent on the defect morphology and clinical case selection. In many cases, it is still challenging to achieve predictable regenerative outcomes utilizing current approaches. Periodontal tissue engineering and bone regeneration (PTEBR) aims to improve the state of patient care by promoting reconstitution of damaged and lost tissues through the use of growth factors and signaling molecules, scaffolds, cells and gene therapy. The present narrative review discusses key advancements in PTEBR including current and future trends in preclinical and clinical research, as well as the potential for clinical translatability.

Metabolomics strategy reveals the osteogenic mechanism of yak (Bos grunniens) bone collagen peptides on ovariectomy-induced osteoporosis in rats

Our previous work demonstrated that yak bone collagen peptides (YBP) possessed excellent osteogenic activity in vitro. However, associations between YBP and osteoporosis were less established, and the positive effect and underlying mechanism of YBP in the treatment of osteoporotic rats in vivo remained unclear. Herein, ovariectomized rats were intragastrically administered with YBP or 17β-estradiol for 12 weeks. Bone turnover markers, bone biomechanical parameters and bone microarchitecture were investigated to identify the specific changes of potential antagonistic effects of YBP on ovariectomized rats. Then, serum samples were analyzed by UPLC/Q-TOF-MS to identify metabolites. The results showed that YBP treatment remarkably altered the content of serum bone turnover markers and prevented the ovariectomy-induced deterioration of bone mechanical and microarchitecture characteristics. A total of forty-one biomarkers for which levels changed markedly upon treatment have been identified based on non-targeted metabolomics. Among them, twenty-one metabolites displayed a downward expression level, while twenty metabolites showed an upward expression level in the YBP group and finally were selected as potential biomarkers. The levels of these biomarkers displayed significant alterations and a tendency to be restored to normal values in YBP treated osteoporotic rats. A systematic network analysis of their corresponding pathways delineated that the protective or recovery effect of YBP on osteoporosis occurred primarily by regulating the amino acid metabolism and lipid metabolism (especially unsaturated fatty acid). Collectively, these findings highlight that such peptides hold promise in further advancement as a natural alternative for functional and health-promoting foods, which could be potentially used in mediated treatment of osteoporosis.

Effects of platelet-derived growth factor-BB on cellular morphology and cellular viability of stem cell spheroids composed of bone-marrow-derived stem cells

Platelet-derived growth factor-BB (PDGF-BB) is a potent mitogenic, angiogenic and chemoattractant, and is one of the most abundant growth factors in platelet-derived products. The goal of the present study was to examine the effects of PDGF-BB on cellular morphology and cellular viability using 3D stem cell cultures. On day 1, spheroids formed well in silicon-elastomer-based concave microwells. The addition of 10 or 100 ng/ml PDGF-BB did not affect the morphology of the cell spheroids. During longer periods of incubation, the cell spheroids maintained their shape without noticeable alterations. The majority of cells in the spheroids exhibited green fluorescence when analyzed using a live/dead assay, indicative of live cells. On day 1, the Cell Counting Kit-8 (CCK-8) assay values for PDGF-BB at 0, 10 and 100 ng/ml were 0.241±0.003, 0.227±0.001 and 0.241±0.004, respectively; on day 3, the CCK-8 assay values for PDGF-BB were 0.233±0.005, 0.278±0.001 and 0.194±0.003, respectively; and on day 7, they were 0.248±0.014, 0.293±0.031 and 0.346±0.034, respectively. The 100 ng/ml group showed significantly higher values compared with the control group on day 7. Together, the results of the present study showed that the addition of 10 and 100 ng/ml PDGF-BB increased cellular viability, suggesting that PDGF-BB may be usable in cell therapy.

Scaffold-Mediated Gene Delivery for Osteochondral Repair

Osteochondral defects involve both the articular cartilage and the underlying subchondral bone. If left untreated, they may lead to osteoarthritis. Advanced biomaterial-guided delivery of gene vectors has recently emerged as an attractive therapeutic concept for osteochondral repair. The goal of this review is to provide an overview of the variety of biomaterials employed as nonviral or viral gene carriers for osteochondral repair approaches both in vitro and in vivo, including hydrogels, solid scaffolds, and hybrid materials. The data show that a site-specific delivery of therapeutic gene vectors in the context of acellular or cellular strategies allows for a spatial and temporal control of osteochondral neotissue composition in vitro. In vivo, implantation of acellular hydrogels loaded with nonviral or viral vectors has been reported to significantly improve osteochondral repair in translational defect models. These advances support the concept of scaffold-mediated gene delivery for osteochondral repair.

Mass acquisition of human periodontal ligament stem cells

The periodontal ligament (PDL) is an essential fibrous tissue for tooth retention in the alveolar bone socket. PDL tissue further functions to cushion occlusal force, maintain alveolar bone height, allow orthodontic tooth movement, and connect tooth roots with bone. Severe periodontitis, deep caries, and trauma cause irreversible damage to this tissue, eventually leading to tooth loss through the destruction of tooth retention. Many patients suffer from these diseases worldwide, and its prevalence increases with age. To address this issue, regenerative medicine for damaged PDL tissue as well as the surrounding tissues has been extensively investigated regarding the potential and effectiveness of stem cells, scaffolds, and cytokines as well as their combined applications. In particular, PDL stem cells (PDLSCs) have been well studied. In this review, I discuss comprehensive studies on PDLSCs performed in vivo and contemporary reports focusing on the acquisition of large numbers of PDLSCs for therapeutic applications because of the very small number of PDLSCs available in vivo.

Yak (Bos grunniens) bones collagen-derived peptides stimulate osteoblastic proliferation and differentiation via the activation of Wnt/β-catenin signaling pathway

BACKGROUND

As the world's population is transitioning gradually to an ageing stage, the incidence of osteoporosis is increasing annually. Yak bone is one of the major components of Tibetan medicine and it has mainly been associated with an improvement in bone health, for example against osteoporosis. However, the functional bioactive ingredients and the underlying mechanisms are still unclear.

RESULTS

Sequential purification of yak-bone hydrolysates was achieved by ultrafiltration, size exclusion chromatography, and semi-preparative reverse-phase high-performance liquid chromatography. After this, 35 novel peptides were identified by mass spectrometry analysis, of which peptide GPAGPPGPIGNV (GP-12) displayed the highest osteoblast proliferation-promoting activity, with an increase of 42.7% in cell growth. An in vitro stability study demonstrated that GP-12 was digested into smaller peptides (GP-9, GV-9, AV-10 and GP-11) after simulated gastrointestinal digestion and absorption (Caco-2 cell monolayers) experiments. However, some of them still can be absorbed intact through the (Caco-2 cell monolayers by a paracellular route (Papp: 5.36 ± 0.34 cm s^-1 ). Flow cytometry results indicated that GP-12 enhanced osteoblastic proliferation by inducing the alteration of the cell-cycle progression both from the G0/G1 to the S phase and from the S to the G2/M phase. Quantitative real-time polymerase chain reaction (PCR) and western blot results revealed that GP-12 induced osteoblastic proliferation and differentiation in a dose-response manner through the activation of a Wnt/β-catenin signaling pathway.

CONCLUSION

These findings highlighted that such peptides hold the promise of discovering candidates for functional and health-promoting foods, which could be potentially used for the treatment of osteoporosis. © 2020 Society of Chemical Industry.

Regenerative potential of cultured gingival fibroblasts in treatment of periodontal intrabony defects (randomized clinical and biochemical trial)

BACKGROUND

Defective cellular elements constitute an important challenge to achieve predictable periodontal regeneration. In an attempt to improve the cellularity of periodontal defects, gingival fibroblasts were implanted without their associated extracellular elements in periodontal defects to expose them to periodontal tissue mediators. In order to investigate the regenerative potential of gingival fibroblasts translocated into periodontal defects, the present study was designed to clinically and biochemically investigate the use of gingival fibroblasts (GF) and their associated mesenchymal stem cells (GMSC) in the treatment of intrabony periodontal defects.

METHODS

A total of 20 subjects were randomly divided into two groups (n = 20). Group I: ten patients were included with ten intrabony periodontal defects that received β-calcium triphosphate (β-TCP) followed by collagen membrane defect coverage, while group II: (10 patients) ten periodontal defects received cultured gingival fibroblasts (GF) on the β-TCP scaffold and covered by a collagen membrane. The clinical evaluation was carried out at the beginning and at 6 months. Gingival crevicular fluid (GCF) samples were collected directly from the test sites for the quantitative measurement of PDGF-BB and BMP-2 using the ELISA kit at 1, 7, 14, and 21 days after surgery.

RESULTS

Group II reported a significantly greater reduction in vertical pocket depth (VPD) and CAL gain compared with group I after 6 months. Radiographic bone gain was statistically higher in group II compared with group I. A significantly higher concentration of PDGF-BB was observed in group II on days 1, 3, and 7 compared with group I.

CONCLUSIONS

Translocation of gingival fibroblasts from gingival tissue to periodontal defects could be a promising option that increases cellular elements with regeneration potential. The concept of total isolation of gingival fibroblasts using occlusive membranes must be re-evaluated.

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.

At the Intersection of Biomaterials and Gene Therapy: Progress in Non-viral Delivery of Nucleic Acids

Biomaterials play a critical role in technologies intended to deliver therapeutic agents in clinical settings. Recent explosion of our understanding of how cells utilize nucleic acids has garnered excitement to develop a range of older (e.g., antisense oligonucleotides, plasmid DNA and transposons) and emerging (e.g., short interfering RNA, messenger RNA and non-coding RNAs) nucleic acid agents for therapy of a wide range of diseases. This review will summarize biomaterials-centered advances to undertake effective utilization of nucleic acids for therapeutic purposes. We first review various types of nucleic acids and their unique abilities to deliver a range of clinical outcomes. Using recent advances in T-cell based therapy as a case in point, we summarize various possibilities for utilizing biomaterials to make an impact in this exciting therapeutic intervention technology, with the belief that this modality will serve as a therapeutic paradigm for other types of cellular therapies in the near future. We subsequently focus on contributions of biomaterials in emerging nucleic acid technologies, specifically focusing on the design of intelligent nanoparticles, deployment of mRNA as an alternative to plasmid DNA, long-acting (integrating) expression systems, and in vitro/in vivo expansion of engineered T-cells. We articulate the role of biomaterials in these emerging nucleic acid technologies in order to enhance the clinical impact of nucleic acids in the near future.

Preparation, identification and molecular docking study of novel osteoblast proliferation-promoting peptides from yak (Bos grunniens) bones

The aim of this study was to isolate and identify osteogenic bioactive peptides from yak bones collagen, while simultaneously investigating their underlying mechanisms for promoting osteoblast proliferation. Response surface methodology (RSM) was employed to investigate the effect of hydrolysis variables on the production of peptides with osteoblast proliferation-promoting activity (OPPA). The concentration of soluble peptides reached 0.5169 mg mL-1, which was well matched with the value (0.5189 mg mL-1) predicted by the model, with the following optimized conditions: hydrolysis time, 3.6 h; pH, 6.12; hydrolysis temperature, 54 °C; E/S (enzyme to substrate) of 5637 U g-1. Hydrolysates were then separated using an ultrafiltration membrane system, and the peptides (<3 kDa) possessed excellent OPPA with a dose-response relationship. A total of 59 novel peptides were identified by HPLC-MS/MS with Mascot analysis. GPSGPAGKDGRIGQPG (GP-16) and GDRGETGPAGPAGPIGPV (GD-18) were selected for docking to investigate the underlying mechanisms of interaction. The molecular docking study revealed that osteoblast proliferation stimulation activity of GP-16 and GD-18 was mainly attributed to the formation of very strong hydrogen bonds with the epidermal growth factor receptor (EGFR). These results indicate that such peptides are promising in the discovery of potential candidates for the future industrial production of functional peptides, which could be used in the mediated treatment of osteoporosis.

Multilayer nanoscale functionalization to treat disorders and enhance regeneration of bone tissue

The coatings application onto medical devices has experienced a continuous growth in the last few years. Medical device coating market is expected to grow at a CAGR of 5.16% to reach USD 10 million by 2023 due to the increasing geriatric population and the growing demand for continuous innovation. Layer-by-Layer (LbL) assembly represents a versatile method to modify the surface properties, in order to control cell interaction and thus enhance biological functions. Furthermore, LbL is environmentally friendly, able to coat all types of surfaces with the creation of homogenous film and to include and control the release of biomolecules/drugs. This feature review provides a critical overview on recent progresses in functionalizing materials by LbL assembly for bone regeneration and disorder treatment. An overview of emerging and visionary opportunities on LbL technologies and further combination with other existing methods used in biomedical field, is also discussed to evidence the new challenges and potential developments in bone regenerative medicine.

Tissue engineering in periodontology: Biological mediators for periodontal regeneration

Teeth and the periodontal tissues represent a highly specialized functional system. When periodontal disease occurs, the periodontal complex, composed by alveolar bone, root cementum, periodontal ligament, and gingiva, can be lost. Periodontal regenerative medicine aims at recovering damaged periodontal tissues and their functions by different means, including the interaction of bioactive molecules, cells, and scaffolds. The application of growth factors, in particular, into periodontal defects has shown encouraging effects, driving the wound healing toward the full, multi-tissue periodontal regeneration, in a precise temporal and spatial order. The aim of the present comprehensive review is to update the state of the art concerning tissue engineering in periodontology, focusing on biological mediators and gene therapy.

The role of sclerostin and dickkopf-1 in oral tissues - A review from the perspective of the dental disciplines

Wnt signaling is of high relevance in the development, homeostasis, and regeneration of oral tissues. Therefore, Wnt signaling is considered to be a potential target for therapeutic strategies. The action of Wnt is tightly controlled by the inhibitors sclerostin (SOST) and Dickkopf (DKK)-1. Given the impact of SOST and DKK-1 in hard tissue formation, related diseases and healing, it is of high relevance to understand their role in oral tissues. The clinical relevance of this knowledge is further underlined by systemic and local approaches which are currently in development for treating a variety of diseases such as osteoporosis and inflammatory hard tissue resorption. In this narrative review, we summarize the current knowledge and understanding on the Wnt signaling inhibitors SOST and DKK-1, and their role in physiology, pathology, and regeneration in oral tissues. We present this role from the perspective of the different specialties in dentistry, including endodontics, orthodontics, periodontics, and oral surgery.

Recent Advances and Future of Gene Therapy for Bone Regeneration

PURPOSE OF REVIEW

The purpose of this review is to discuss the recent advances in gene therapy as a treatment for bone regeneration. While most fractures heal spontaneously, patients who present with fracture nonunion suffer from prolonged pain, disability, and often require additional operations to regain musculoskeletal function.

RECENT FINDINGS

In the last few years, BMP gene delivery by means of electroporation and sonoporation resulted in repair of nonunion bone defects in mice, rats, and minipigs. Ex vivo transfection of porcine mesenchymal stem cells (MSCs) resulted in bone regeneration following implantation in vertebral defects of minipigs. Sustained release of VEGF gene from a collagen-hydroxyapatite scaffold to the mandible of a human patient was shown to be safe and osteoinductive. In conclusion, gene therapy methods for bone regeneration are systematically becoming more efficient and show proof-of-concept in clinically relevant animal models. Yet, on the pathway to clinical use, more investigation is needed to determine the safety aspects of the various techniques in terms of biodistribution, toxicity, and tumorigenicity.

The pericyte secretome: Potential impact on regeneration

Personalized and regenerative medicine is an emerging therapeutic strategy that is based on cell biology and biomedical engineering used to develop biological substitutes to maintain normal function or restore damaged tissues and organs. The secretory capacities of different cell types are now explored as such possible therapeutic regenerative agents in a variety of diseases. A secretome can comprise chemokines, cytokines, growth factors, but also extracellular matrix components, microvesicles and exosomes as well as genetic material and may differ depending on the tissue and the stimulus applied to the cell. With regard to clinical applications, the secretome of mesenchymal stem cells (MSC) is currently the most widely explored. However, other cell types such as pericytes may have similar properties as MSC and the potential therapeutic possibilities of these cells are only just beginning to emerge. In this review, we will summarize the currently available data describing the secretome of pericytes and its potential implications for tissue regeneration, whereby we especially focus on brain pericytes as potential new target cell for neuroregeneration and brain repair.

Wound healing related agents: Ongoing research and perspectives

Wound healing response plays a central part in chronic inflammation, affecting millions of people worldwide. It is a dynamic process that can lead to fibrosis, if tissue damage is irreversible and wound resolution is not attained. It is clear that there is a tight interconnection among wound healing, fibrosis and a variety of chronic disease conditions, demonstrating the heterogeneity of this pathology. Based on our further understanding of the cellular and molecular mechanisms underpinning tissue repair, new therapeutic approaches have recently been developed that target different aspects of the wound healing process and fibrosis. Nevertheless, several issues still need to be taken into consideration when designing modern wound healing drug delivery formulations. In this review, we highlight novel pharmacological agents that hold promise for targeting wound repair and fibrosis. We also focus on drug-delivery systems that may enhance current and future therapies.

Contributions of Bioactive Molecules in Stem Cell-Based Periodontal Regeneration

Periodontal disease is a widespread disease, which without proper treatment, may lead to tooth loss in adults. Because stem cells from the inflammatory microenvironment created by periodontal disease exhibit impaired regeneration potential even under favorable conditions, it is difficult to obtain satisfactory therapeutic outcomes using traditional treatments, which only focus on the control of inflammation. Therefore, a new stem cell-based therapy known as cell aggregates/cell sheets technology has emerged. This approach provides sufficient numbers of stem cells with high viability for treating the defective site and offers new hope in the field of periodontal regeneration. However, it is not sufficient for regenerating periodontal tissues by delivering cell aggregates/cell sheets to the impaired microenvironment in order to suppress the function of resident cells. In the present review, we summarize some promising bioactive molecules that act as cellular signals, which recreate a favorable microenvironment for tissue regeneration, recruit endogenous cells into the defective site and enhance the viability of exogenous cells.

Pro-angiogenic impact of SDF-1α gene-activated collagen-based scaffolds in stem cell driven angiogenesis

Ensuring an adequate angiogenic response during wound healing is a prevailing clinical challenge in biomaterials science. To address this, we aimed to develop a pro-angiogenic gene-activated scaffold (GAS) that could activate MSCs to produce paracrine factors and influence angiogenesis and wound repair. A non-viral polyethyleneimine (PEI) nanoparticles carrying a gene encoding for stromal derived factor-1 alpha (SDF-1α) was combined with a collagen-chondroitin sulfate scaffold to produce the GAS. The ability of this platform to enhance the angiogenic potential of mesenchymal stem cells (MSCs) was then assessed. We found that the MSCs on GAS exhibited early over-expression of SDF-1α mRNA with the activation of angiogenic markers VEGF and CXCR4. Exposing endothelial cells to conditioned media collected from GAS supported MSCs promoted a 20% increase in viability and 33% increase in tubule formation (p < 0.05). Furthermore, the conditioned media promoted a 50% increase in endothelial cell migration and wound closure (p < 0.005). Gene expression analysis of the endothelial cells revealed that the functional response was associated with up-regulation of angiogenic genes; VEGF, CXCR4, eNOS and SDF-1α. Overall, this study shows collagen-based scaffolds combined with SDF-1α gene therapy can provide enhanced pro-angiogenic response, suggesting a promising approach to overcome poor vasculature during wound healing.