Application of BMP-2 and its gene delivery vehicles in dentistry

The restoration of bone defects resulting from tooth loss, periodontal disease, severe trauma, tumour resection and congenital malformations is a crucial task in dentistry and maxillofacial surgery. Growth factor- and gene-activated bone graft substitutes can be used instead of traditional materials to solve these problems. New materials will overcome the low efficacy and difficulties associated with the use of traditional bone substitutes in complex situations. One of the most well-studied active components for bone graft substitutes is bone morphogenetic protein-2 (BMP-2), which has strong osteoinductive properties. The aim of this review was to examine the use of BMP-2 protein and gene therapy for bone regeneration in the oral and maxillofacial region and to discuss its future use.

Gene expression, micro-CT and histomorphometrical analysis of sinus floor augmentation with biphasic calcium phosphate and deproteinized bovine bone mineral: A randomized controlled clinical trial

AIMS

The aim of this randomized controlled clinical trial was to compare the gene expression, micro-CT, histomorphometrical analysis between biphasic calcium phosphate (BCP) of 70/30 ratio and deproteinized bovine bone mineral (DBBM) in sinus augmentation.

MATERIALS AND METHODS

Twenty-four patients in need for sinus floor augmentation through lateral approach were randomized into BCP 70/30 ratio or DBBM. After at least 6 months of healing, a total of 24 bone specimens were collected from the entire height of the augmented bone at the area of implant placement and underwent micro-CT, histomorphometric and gene expression analysis. The 12 bone specimens of BCP 70/30 ratio were equally allocated to micro-CT and histologic analysis (test group, n = 6) and gene expression analysis (test group, n = 6). Similarly, the 12 bone specimens of DBBM were also allocated to micro-CT and histologic analysis (control group, n = 6) and gene expression analysis (control group, n = 6). The newly formed bone, remaining graft materials and relative change in gene expression of four target genes were assessed.

RESULTS

The micro-CT results showed no statistically significant difference in the ratio of bone volume to total volume (BV/TV ratio) for the two groups (BCP 41.51% vs. DBBM 40.97%) and the same was true for residual graft material to total volume (GV/TV ratio, BCP 9.97% vs. DBBM 14.41%). Similarly, no significant difference was shown in the histological analysis in terms of bone formation, (BCP 31.43% vs. DBBM was 30.09%) and residual graft area (DBBM 40.76% vs. BCP 45.06%). With regards to gene expression, the level of ALP was lower in both groups of bone grafted specimens compared with the native bone. On the contrary, the level of OSX, IL-1B and TRAP was higher in augmented bone of both groups compared with the native bone. However, the relative difference in all gene expressions between BCP and DBBM group was not significant.

CONCLUSIONS

The BCP, HA/β-TCP ratio of 70/30 presented similar histological and micro-CT outcomes in terms of new bone formation and residual graft particles with DBBM. The gene expression analysis revealed different gene expression patterns between augmented and native bone, but showed no significant difference between the two biomaterials.

Effect of enriched bone-marrow aspirates on the dimensional stability of cortico-cancellous iliac bone grafts in alveolar ridge augmentation

Background

The objective of the current study was to assess the clinical and radiological outcomes following autologous grafting from the iliac crest treated with autologous stem cells in-situ to reduce the postoperative bone graft resorption rate.

Materials and methods

The study group consisted of patients who underwent vertical augmentation of the jaws via bone grafts harvested from the iliac crest enriched with bone-marrow aspirate concentrates (stem cell group). The first control group (control) included 40 patients underwent a vertical augmentation with autologous bone grafts from the iliac crest. In the second control group, 40 patients received identical surgical procedure, whereas the autologous bone graft was covered with a thin layer of deproteinized bovine bone matrix and a collagen membrane (DBBM group). Clinical complications, implant survival, radiological assessment of the stability of the vertical height and histological evaluation at the recipient site have been followed up for 24 months postoperatively.

Results

No differences in terms of implant survival were observed in the groups. In the stem cell group, the resorption after 4–6 months was 1.2 ± 1.3 mm and significantly lower than the resorption of the control group with 1.9 ± 1.6 mm (P = 0.029) (DBBM group: 1.4 ± 1.2 mm). After 12 months, the resorption of the stem cell group was 2.1 ± 1.6 mm and significantly lower compared to the control group (4.2 ± 3.0 mm, P = 0.001) and DBBM group (resorption 2.7 ± 0.9 mm, P = 0.012). The resorption rate in the second year was lower compared to the first year and was measured as 2.7 ± 1.7 mm in the stem cell group (1-year bone loss in the time period of 12–24 months of 0.6 mm compared to 2.1 mm in the first 12 months). The resorption was significantly lower compared to the control group (4.7 ± 2.9 mm; P = 0.003, DBBM group: 3.1 ± 0.5 mm, P = 0.075).

Conclusions

Autologous bone-marrow aspirate concentrate could enhance the dimensional stability of the bone grafts and improve the clinical standard of complex reconstruction of the alveolar ridge. Even though the intraoperative cell enrichment requires an additional equipment and technical specification, it represents an alternative method for in-situ regeneration by osteogenic induction with a contribution of a manageable cost factor.

Enhancement of osteoporotic bone regeneration by strontium-substituted 45S5 bioglass via time-dependent modulation of autophagy and the Akt/mTOR signaling pathway

Osteoporosis (OP) is a major systemic bone disease leading to an imbalance in bone homeostasis which remains a challenge in the current treatment of bone defects. Our previous studies on strontium (Sr) doping apparently stimulated osteogenesis of bioceramics, which suggested a promising strategy for the treatment of bone defects. However, the potential effects and the underlying mechanisms of Sr-doping on osteoporotic bone defects still remain unclear. Autophagy is a conventional self-degradation process of cells involved in bone homeostasis and regeneration under physiological and pathological conditions. Therefore, it is essential to design appropriate biomaterials and investigate the associated osteogenic mechanisms via autophagy. Based on this hypothesis, Sr-doped 45S5 bioglass (Sr/45S5) was fabricated, and ovariectomy bone marrow-derived mesenchymal stem cells (OVX-BMSCs) were applied as the in vitro cell culture model. First, the optimal Sr-doping concentration of 10 mol% was screened by cell proliferation, ALP staining, alizarin red S staining and the real-time PCR assay. Then, the results of western blot (WB) analysis showed that Sr-induced osteogenic differentiation of OVX-BMSCs was associated with time-dependent modulation of autophagy and related to the AKT/mTOR signaling pathway. Meanwhile, the autophagy in Sr-induced osteogenic differentiation of OVX-BMSCs was detected by WB, immunofluorescence staining and transmission electron microscopy. Furthermore, the effect of osteogenic differentiation of OVX-BMSCs has been significantly inhibited by the administration of autophagy inhibitors and the AKT/mTOR pathway inhibitors, respectively, in the early and late periods of osteogenic differentiation. Finally, the results of the model of femoral condyle defects in OVX-rats indicated that Sr10/45S5 granules remarkably enhanced bone regeneration which provided the evidences in vivo. Our research indicates that Sr-doping provides a promising strategy to promote osteogenic differentiation of OVX-BMSCs and bone regeneration in osteoporotic bone defects via early improvement of autophagy and late activation of the Akt/mTOR signaling pathway.

In vivo evaluation of deer antler trabecular bone as a reconstruction material for bone defects

Availability of graft materials to fill up osseous defects has always been a concern in orthopaedic surgeries. Deer antler material is a primary bone structure that is easy to collect and could serve as a xenograft. This study examines the behaviour of red deer antler trabecular cylinders in critical size distal femoral epiphyseal defects in 11 rabbits, and evaluates the effect of the decellularization protocols. Two preparation regimes (A and B) were used, with and without lipids and proteins. Radiographs were taken immediately after surgery and after euthanasia 12 weeks post-implantation. Histological evaluation was performed on non-decalcified 10-μm sections with a van Gieson picro-fuchsin staining protocol. A region of interest was defined for each histological section, evaluating the inflammatory reaction, the fibrosis process, and the osteogenesis. Each histological section was microradiographed to evaluate bone contact, presence of synostosis, remodelling and ossification processes. All antler cylinders were successfully implanted. Final radiographic analysis demonstrated osteointegration of most implants at various stages. Light to moderate inflammation around the grafts was noted with only one case showing full encapsulation. A variable degree of intimacy between implant and host bone was evidenced, with bone remodelling and osteogenesis of various intensity being present in all implanted sites. No differences were found between group A and B. Removal of lipids and proteins in the grafts surprisingly did not seem to matter. Decellularization and sterilization protocols may be advocated. Although it presents several limitations, this study shows some promising results regarding antler trabecular bone osteointegration.

Enhanced bone formation by strontium modified calcium sulfate hemihydrate in ovariectomized rat critical-size calvarial defects

The development of a new generation of biomaterials with high osteogenic ability for treatment of osteoporotic fractures is being intensively investigated. The objective of this paper was to investigate new bone formation in an ovariectomized rat (OVX rat) calvarial model of critical size bone defects filled with Sr-containing α-calcium sulfate hemihydrate (SrCSH) cement compared to an α-calcium sulfate hemihydrate (α-CSH) cement and empty defect. X-ray diffraction analysis verified the partial substitution of Sr²⁺ for Ca²⁺ did not change the phase composition of α-CSH. Scanning electron microscopy showed that Sr-substituted α-CSH significantly increased the surface roughness. The effects of Sr substitution on the biological properties of SrCSH cement were evaluated by adhesion, proliferation, alkaline phosphatase (ALP) activity of osteoblast-like cells MC3T3-E1. The results showed that SrCSHs enhanced MC3T3-E1 cell proliferation, differentiation, and ALP activity. Furthermore, SrCSH cement was used to repair critical-sized OVX rat calvarial defects. The in vivo results revealed that SrCSH had good osteogenic capability and stimulated new blood vessel formation in a critical sized OVX calvarial defect within 12 weeks, suggesting that SrCSH cement has more potential for application in bone tissue regeneration.

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

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

A rabbit maxillary sinus model with simultaneous customized-implant placement: Comparative microscopic analysis for the evaluation of surface-treated implants

We describe the use of a rabbit maxillary sinus model, characterized by thin osseous tissue and low bone density, for the evaluation of surface-treated implants by histologically and histomorphometrically comparing the osseointegration patterns depending on the surface treatment methods. Twenty rabbits were randomly assigned to two groups of 10 animals, one receiving 5 × 3 mm customized implants (machined, MA or sandblasted and acid etched, SLA) placed in sinus and the other receiving implants placed in a tibia. Histological observation of the implant placed in sinus shows relatively more active new bone formation, characterized by trabecular bone pattern underneath the cortical bone in sinus as compared with that in tibia. Histomorphometric analysis in the rabbits receiving implants in a tibia, the NBIC (%) associated with the SLA surface implant was greater than that associated with the MA implant at 2 weeks (55.63 ± 8.65% vs. 47.87 ± 10.01%; P > 0.05) and at 4 weeks (61.76 ± 9.49% vs. 42.69 ± 10.97%; P < 0.05). Among rabbits receiving implants in a sinus, the NBIC (%) associated with the SLA surface implant was significantly greater than that associated with the MA surface implant both at 2 weeks (37.25 ± 7.27% vs. 20.98 ± 6.42%; P < 0.05) and at 4 weeks (48.82 ± 6.77% vs. 31.51 ± 9.14%; P < 0.05). As a result, we suggest that the maxillary sinus model is an appropriate animal model for assessing surface-treated implants and may be utilized for the evaluation of surface-treated implants in poor bone quality environment. Microsc. Res. Tech. 78:697-706, 2015.

Enhanced osteoporotic bone regeneration by strontium-substituted calcium silicate bioactive ceramics

The regeneration capacity of the osteoporotic bones is generally lower than that of the normal bones. Current methods of bone defect treatment for osteoporosis are not always satisfactory. Recent studies have shown that the silicate based biomaterials can stimulate osteogenesis and angiogenesis due to the silicon (Si) ions released from the materials, and enhance bone regeneration in vivo. Other studies showed that strontium (Sr) plays a distinct role on inhibiting bone resorption. Based on the hypothesis that the combination of Si and Sr may have synergetic effects on osteoporotic bone regeneration, the porous Sr-substituted calcium silicate (SrCS) ceramic scaffolds combining the functions of Sr and Si elements were developed with the goals to promote osteoporotic bone defect repair. The effects of the ionic extract from SrCS on osteogenic differentiation of bone marrow mesenchymal stem cells derived from ovariectomized rats (rBMSCs-OVX), angiogenic differentiation of human umbilical vein endothelial cells (HUVECs) were investigated. The in vitro results showed that Sr and Si ions released from SrCS enhanced cell viability, alkaline phosphatase (ALP) activity, and mRNA expression levels of osteoblast-related genes of rBMSCs-OVX and expression of vascular endothelial growth factor (VEGF) without addition of extra osteogenic and angiogenic reagents. The activation in extracellular signal-related kinases (ERK) and p38 signaling pathways were observed in rBMSCs-OVX cultured in the extract of SrCS, and these effects could be blocked by ERK inhibitor PD98059, and P38 inhibitor SB203580, respectively. Furthermore, the ionic extract of SrCS stimulated HUVECs proliferation, differentiation and angiogenesis process. The in vivo experiments revealed that SrCS dramatically stimulated bone regeneration and angiogenesis in a critical sized OVX calvarial defect model, and the enhanced bone regeneration might be attributed to the modulation of osteogenic differentiation of endogenous mesenchymal stem cells (MSCs) and the inhibition of osteoclastogenesis, accompanying with the promotion of the angiogenic activity of endothelial cells (ECs).

Surgical Approaches Based on Biological Objectives: GTR versus GBR Techniques

Guided tissue regenerative (GTR) therapies are performed to regenerate the previously lost tooth supporting structure, thus maintaining the aesthetics and masticatory function of the available dentition. Alveolar ridge augmentation procedures (GBR) intend to regain the alveolar bone lost following tooth extraction and/or periodontal disease. Several biomaterials and surgical approaches have been proposed. In this paper we report biomaterials and surgical techniques used for periodontal and bone regenerative procedures. Particular attention will be adopted to highlight the biological basis for the different therapeutic approaches.

Recombinant human bone morphogenetic protein-2 stimulates the osteogenic potential of the Schneiderian membrane: a histometric analysis in rabbits

This study evaluated the osteoinductive effect of the recombinant human bone morphogenetic protein-2 (rhBMP-2)-coated biphasic calcium phosphate (BCP) carrier system on the grafted sinus area, including surrounding tissues and the Schneiderian membrane. A total of 18 male rabbits were used in this study; two for in vitro and 16 for in vivo experiments. Schneiderian membranes taken from two animals were cultured with or without rhBMP-2, and quantitative reverse transcriptase-polymerase chain reaction analysis was performed. Both maxillary sinuses in each of the 16 animals were used to compare the in vivo effects of rhBMP-2-coated BCP (experimental group) and BCP alone (control group). In each animal, rhBMP-2-coated BCP was grafted into one of the maxillary sinuses, and the same amount of BCP alone was grafted into the contralateral site in random order. Radiologic and histometric analyses were performed at 2 and 8 weeks after surgery. After 2 days of culturing with or without rhBMP-2, a significant increase in the expression of early osteoblasts (RUNX2, type I collagen, alkaline phosphatase, and osteopontin) could be observed. Different histologic healing patterns were observed in experimental and control sites: newly formed bone lining the reflected sinus membrane without bone formation was observed at the central areas of experimental sites (window=0.06%; center=0%; membrane=20.86% of new bone), whereas evenly distributed new bone formation was observed at the control sites (window=7.27%; center=7.41%; membrane=15.58% of new bone).The augmented volume was well maintained at both the experimental and control sites during the experimental period, but at 2 weeks, the augmented volume was greater at the experimental sites than at the control sites (232.62 and 195.29 mm(3), respectively; p<0.001). These results suggest that good space maintenance in sinus augmentation is achieved with BCP, while the osteoinductive potential of the sinus membrane is activated at the early stage of healing with rhBMP-2.

Curculigoside promotes osteogenic differentiation of bone marrow stromal cells from ovariectomized rats

OBJECTIVES

Curculigoside, a natural compound isolated from the medicinal plant Curculigo orchioides has been reported to prevent bone loss in ovariectomized rats. However, the underlying molecular mechanisms are largely unknown. This study investigated the effects of curculigoside on proliferation and osteogenic differentiation of bone marrow stromal cells (BMSCs).

METHODS

The toxicity, proliferation and osteogenic differentiation of BMSCs cultured with various concentrations (0 as control, 10, 100 and 500 µm) of curculigoside were measured by viability assay, MTT analysis, alkaline phosphatase (ALP) activity assay, alizarin red staining and mineralization assay, real-time PCR analysis on osteogenic genes including ALP, type I collagen (Col I), osteocalcin (OCN) and osteoprotegerin (OPG), runt-related transcription factor 2 (Runx2), as well as OPG enzyme-linked immunosorbent assay.

KEY FINDINGS

No significant cytotoxicity was observed for BMSCs after supplementation with curculigoside. The proliferation of BMSCs was enhanced after administration of curculigoside, especially 100 µm curculigoside. Moreover, the osteogenic gene expression was significantly enhanced with 100 µm curculigoside treatment. Importantly, curculigoside significantly increased OPG secretion.

CONCLUSIONS

The data indicate that curculigoside could promote BMSC proliferation and induce osteogenic differentiation of BMSCs. The most profound response was observed with 100 µm curculigoside. These findings may be valuable for understanding the mechanism of the effect of curculigoside on bone, especially in relation to osteoporosis.

The rabbit as experimental model for research in implant dentistry and related tissue regeneration

The use of rabbits for experimental research has a long historical tradition. The aim of this review consists in outlining the use of the rabbit for research in implant dentistry and related tissue regeneration. Rabbits appear as a first-hand choice for fundamental implant design studies because of their size, easy handling, short life span, and economical aspects in purchasing and sustaining. In the following, the various anatomical sites in the rabbit will be summarized to provide an overview of current possibilities and limitations of this model for bone research in oral implantology.

Local delivery of small and large biomolecules in craniomaxillofacial bone

Current state of the art reconstruction of bony defects in the craniomaxillofacial (CMF) area involves transplantation of autogenous or allogenous bone grafts. However, the inherent drawbacks of this approach strongly urge clinicians and researchers to explore alternative treatment options. Currently, a wide interest exists in local delivery of biomolecules from synthetic biomaterials for CMF bone regeneration, in which small biomolecules are rapidly emerging in recent years as an interesting adjunct for upgrading the clinical treatment of CMF bone regeneration under compromised healing conditions. This review highlights recent advances in the local delivery small and large biomolecules for the clinical treatment of CMF bone defects. Further, it provides a perspective on the efficacy of biomolecule delivery in CMF bone regeneration by reviewing presently available reports of pre-clinical studies using various animal models.

Ex vivo bone morphogenetic protein-2 gene delivery using bone marrow stem cells in rabbit maxillary sinus augmentation in conjunction with implant placement

BACKGROUND

This study evaluates the potential of bone morphogenetic protein 2 (BMP-2) gene-transduced bone marrow stem cells (BMSCs) to facilitate osseous healing after rabbit maxillary sinus augmentation in conjunction with implant placement.

METHODS

Autologous BMSCs derived from New Zealand white rabbits were cultured and transduced with BMP-2 using an adenovirus vector. Transduced BMSCs (BMP-2/BMSCs) were then combined with a deproteinized bovine bone mineral (DBBM) scaffold. Twenty-seven animals were randomly allocated into three groups: 1) control, sinus grafted with DBBM alone; 2) BMSC, sinus grafted with non-transduced BMSCs and DBBM; and 3) BMP-2/BMSC, sinus grafted with BMP-2/BMSCs and DBBM. During these procedures, a mini-implant was placed in the floor of the sinus. Animals were sacrificed at 2, 4, and 8 weeks after surgery. New bone area and bone-to-implant contact (BIC) were evaluated histomorphometrically.

RESULTS

At 2 and 4 weeks, the BMP-2/BMSC group showed more new bone area and higher BIC than the other two groups. BMP-2/BMSCs were detected with confocal microscopy for up to 4 weeks, which indicates that transduced cells contributed to new bone formation. However, at 8 weeks, there was no difference in new bone area or BIC among the three groups.

CONCLUSIONS

These results suggest that BMP-2 delivery using BMSCs may result in earlier and increased bone formation in the maxillary sinus. This finding may offer more stable bone support to implants and reduce healing times. However, this study also revealed limitations in the stimulatory effect of BMP-2/BMSCs, such as diminished activity over time in later healing stages.

Ectopic study of calcium phosphate cement seeded with pBMP-2 modified canine bMSCs mediated by a non-viral PEI derivative

We have evaluated the ectopic new bone formation effects of CPC (calcium phosphate cement) seeded with pBMP-2 (plasmids containing bone morphogenetic protein-2 gene) transfected canine bMSCs (bone marrow stromal cells) mediated by a non-viral PEI (polyethylenimine) derivative (GenEscort™ II) in nude mice. Canine bMSCs were transfected with pBMP-2 or pEGFP (plasmids containing enhanced green fluorescent protein gene) mediated by GenEscort™ II in vitro, and the osteoblastic differentiation was explored by ALP (alkaline phosphatase) staining, ARS (alizarin red S) staining and RT-qPCR (real-time quantitative PCR) analysis. Ectopic bone formation effects of CPC/pBMP-2 transfected bMSCs were evaluated and compared with CPC/pEGFP transfected bMSCs or CPC/untransfected bMSCs through histological, histomorphological and immunohistochemical analysis 8 and 12 weeks post-operation in nude mice. Transfection efficiency was up ∼35% as demonstrated by EGFP (enhanced green fluorescent protein) expression. ALP and ARS staining were stronger with pBMP-2 gene transfection, and mRNA expression of BMP-2 (bone morphogenetic protein-2), Col 1 (collagen 1) and OCN (osteocalcin) in pBMP-2 group was significantly up-regulated at 6 and 9 days. Significantly higher NBV (new bone volume) was achieved in pBMP-2 group than in the control groups at 8 and 12 weeks (P<0.05). In addition, immunohistochemical analysis indicated higher OCN expression in pBMP-2 group (P<0.01). We conclude that CPC seeded with pBMP-2 transfected bMSCs mediated by GenEscort™ II could enhance ectopic new bone formation in nude mice, suggesting that GenEscort™ II mediated pBMP-2 gene transfer is an effective non-viral method and CPC is a suitable scaffold for gene enhanced bone tissue engineering.

Bone tissue engineering: current strategies and techniques--part I: Scaffolds

Bone repair and regeneration is a dynamic process that involves a complex interplay between the (1) ground substance, (2) cells, and (3) milieu. While each constituent is integral to the final product, it is often helpful to consider each component individually. Therefore, we created a two-part review to examine scaffolds and cells' roles in bone tissue engineering. In Part I, we review the myriad of materials use for in vivo bone engineering. In Part II, we discuss the variety cell types (e.g., osteocytes, osteoblasts, osteoclasts, chondrocytes, mesenchymal stem cells, and vasculogenic cells) that are seeded upon or recruited to these scaffolds. In Part III, we discuss the optimization of the microenvironment. The biochemical processes and sequence of events that guide matrix production, cellular activation, and ossification are vital to developing successful bone tissue engineering strategies and are thus succinctly reviewed herein.

Bone regeneration by stem cell and tissue engineering in oral and maxillofacial region

Clinical imperatives for the reconstruction of jaw bone defects or resorbed alveolar ridge require new therapies or procedures instead of autologous/allogeneic bone grafts. Regenerative medicine, based on stem cell science and tissue engineering technology, is considered as an ideal alternative strategy for bone regeneration. In this paper, we review the current choices of cell source and strategies on directing the osteogenic differentiation of stem cells. The preclinical animal models for bone regeneration and the key translational points to clinical success in oral and maxillofacial region are also discussed. We propose comprehensive strategies based on stem cell and tissue engineering researches, allowing for clinical application in oral and maxillofacial region.

Maxillary sinus floor elevation using a tissue-engineered bone with calcium-magnesium phosphate cement and bone marrow stromal cells in rabbits

The objective of this study was to assess the effects of maxillary sinus floor elevation with a tissue-engineered bone constructed with bone marrow stromal cells (bMSCs) and calcium-magnesium phosphate cement (CMPC) material. The calcium (Ca), magnesium (Mg), and phosphorus (P) ions released from calcium phosphate cement (CPC), magnesium phosphate cement (MPC), and CMPC were detected by inductively coupled plasma atomic emission spectroscopy (ICP-AES), and the proliferation and osteogenic differentiation of bMSCs seeded on CPC, MPC, and CMPC or cultured in CPC, MPC, and CMPC extracts were measured by MTT analysis, alkaline phosphatase (ALP) activity assay, alizarin red mineralization assay, and real-time PCR analysis of the osteogenic genes ALP and osteocalcin (OCN). Finally, bMSCs were combined with CPC, MPC, and CMPC and used for maxillary sinus floor elevation in rabbits, while CPC, MPC, or CMPC without cells served as control groups. The new bone formation in each group was detected by histological finding and fluorochrome labeling at weeks 2 and 8 after surgical operation. It was observed that the Ca ion concentrations of the CMPC and CPC scaffolds was significantly higher than that of the MPC scaffold, while the Mg ions concentration of CMPC and MPC was significantly higher than that of CPC. The bMSCs seeded on CMPC and MPC or cultured in their extracts proliferated more quickly than the cells seeded on CPC or cultured in its extract, respectively. The osteogenic differentiation of bMSCs seeded on CMPC and CPC or cultured in the corresponding extracts was significantly enhanced compared to that of bMSCs seeded on MPC or cultured in its extract; however, there was no significant difference between CMPC and CPC. As for maxillary sinus floor elevation in vivo, CMPC could promote more new bone formation and mineralization compared to CPC and MPC, while the addition of bMSCs could further enhance its new bone formation ability significantly. Our data suggest that CMPC possesses moderate biodegradability and excellent osteoconductivity, which may be attributed to its Ca and Mg ion composition, and the tissue-engineered bone constructed of CMPC and bMSCs might be a potential alterative graft for maxillofacial bone regeneration.

The evaluation of the correlation between histomorphometric analysis and micro-computed tomography analysis in AdBMP-2 induced bone regeneration in rat calvarial defects

PURPOSE

Micro-computed tomography (micro-CT) has been widely used in the evaluation of regenerated bone tissue but the reliability of micro-CT has not yet been established. This study evaluated the correlation between histomorphometric analysis and micro-CT analysis in performing new bone formation measurement.

METHODS

Critical-size calvarial defects were created using a 8 mm trephine bur in a total of 24 Sprague-Dawley rats, and collagen gel mixed with autogenous rat bone marrow stromal cells (BMSCs) or autogenous rat BMSCs transduced by adenovirus containing bone morphogenic protein-2 (BMP-2) genes was loaded into the defect site. In the control group, collagen gel alone was loaded into the defect. After 2 and 4 weeks, the animals were euthanized and calvaria containing defects were harvested. Micro-CT analysis and histomorphometric analysis of each sample were accomplished and the statistical evaluation about the correlation between both analyses was performed.

RESULTS

New bone formation of the BMP-2 group was greater than that of the other groups at 2 and 4 weeks in both histomorphometric analysis and micro-CT analysis (P=0.026, P=0.034). Histomorphometric analysis of representative sections showed similar results to histomorphometric analysis with a mean value of 3 sections. Measurement of new bone formation was highly correlated between histomorphometric analysis and micro-CT analysis, especially at the low lower threshold level at 2 weeks (adjusted r(2)=0.907, P<0.001). New bone formation of the BMP-2 group analyzed by micro-CT tended to decline sharply with an increasing lower threshold level, and it was statistically significant (P<0.001).

CONCLUSIONS

Both histomorphometric analysis and micro-CT analysis were valid methods for measurement of the new bone in rat calvarial defects and the ability to detect the new bone in micro-CT analysis was highly influenced by the threshold level in the BMP-2 group at early stage.

The use of injectable sonication-induced silk hydrogel for VEGF(165) and BMP-2 delivery for elevation of the maxillary sinus floor

Sonication-induced silk hydrogels were previously prepared as an injectable bone replacement biomaterial, with a need to improve osteogenic features. Vascular endothelial growth factor (VEGF(165)) and bone morphogenic protein-2 (BMP-2) are key regulators of angiogenesis and osteogenesis, respectively, during bone regeneration. Therefore, the present study aimed at evaluating in situ forming silk hydrogels as a vehicle to encapsulate dual factors for rabbit maxillary sinus floor augmentation. Sonication-induced silk hydrogels were prepared in vitro and the slow release of VEGF(165) and BMP-2 from these silk gels was evaluated by ELISA. For in vivo studies for each time point (4 and 12 weeks), 24 sinus floors elevation surgeries were made bilaterally in 12 rabbits for the following four treatment groups: silk gel (group Silk gel), silk gel/VEGF(165) (group VEGF), silk gel/BMP-2 (group BMP-2), silk gel/VEGF(165)/BMP-2 (group V + B) (n = 6 per group). Sequential florescent labeling and radiographic observations were used to record new bone formation and mineralization, along with histological and histomorphometric analysis. At week 4, VEGF(165) promoted more tissue infiltration into the gel and accelerated the degradation of the gel material. At this time point, the bone area in group V + B was significantly larger than those in the other three groups. At week 12, elevated sinus floor heights of groups BMP-2 and V + B were larger than those of the Silk gel and VEGF groups, and the V + B group had the largest new bone area among all groups. In addition, a larger blood vessel area formed in the remaining gel areas in groups VEGF and V + B. In conclusion, VEGF(165) and BMP-2 released from injectable and biodegradable silk gels promoted angiogenesis and new bone formation, with the two factors demonstrating an additive effect on bone regeneration. These results indicate that silk hydrogels can be used as an injectable vehicle to deliver multiple growth factors in a minimally invasive approach to regenerate irregular bony cavities.

Maxillary sinus floor elevation using BMP-2 and Nell-1 gene-modified bone marrow stromal cells and TCP in rabbits

This study evaluated the synergistic osteogenic effect of bone morphogenetic protein-2 (BMP-2) and Nel-like molecule-1 (Nell-1) genes in a rabbit maxillary sinus floor elevation model. Bone marrow stromal cells (bMSCs) were cultured and transduced with AdEGFP, AdNell-1, AdBMP-2, or AdNell-1 + AdBMP-2 overexpression virus. These gene-modified autologous bMSCs were then combined with a β-tricalcium phosphate (β-TCP) granule scaffold and used to elevate the maxillary sinus floor in rabbits. bMSCs cotransduced with AdNell-1 + AdBMP-2 demonstrated a synergistic effect on osteogenic differentiation as detected by real-time PCR analysis on markers of runt-related transcription factor-2, osteocalcin, collagen type 1, alkaline phosphatase activity, and calcium deposits in vitro. As for maxillary sinus floor elevation in a rabbit model in vivo, AdNell-1 + AdBMP-2 gene-transduced autologeous bMSCs/β-TCP complex had the largest bone area and most mature bone structure among the groups, as detected by HE staining and immunohistochemistry at weeks 2 and 8 after implantation. Our data suggested that the BMP-2 and Nell-1 genes possessed a synergistic effect on osteogenic differentiation of bMSCs, while bMSCs modified with the BMP-2 and Nell-1 genes could promote new bone formation and maturation in the rabbit maxillary sinus model.

Maxillary sinus floor elevation using a tissue-engineered bone with rhBMP-2-loaded porous calcium phosphate cement scaffold and bone marrow stromal cells in rabbits

The aim of this study was to evaluate the effects of maxillary sinus floor elevation by a tissue-engineered bone complex with recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded porous calcium phosphate cement (CPC) scaffold and bone marrow stromal cells (bMSCs) in rabbits. bMSCs were cultured and osteogenically induced. The osteoblastic differentiation of expanded bMSCs was detected by alkaline phosphatase activity, and calcium deposits in vitro. Thirty-six rabbits were randomly allocated into week 2, 4 and 8 observation groups. At each time point, 24 maxillary sinus floor elevation surgeries in 12 rabbits were performed bilaterally and randomly implanted by (1) CPC materials alone (group A, n = 6), (2) rhBMP-2/CPC composite materials alone (group B, n = 6), (3) CPC/bMSCs complex (group C, n = 6) and (4) rhBMP-2/CPC/bMSCs complex (group D, n = 6). As for maxillary sinus floor elevation, rhBMP-2-loaded CPC could promote new bone formation as compared to CPC, while addition of bMSCs could further enhance its new bone formation and maturity significantly, as detected by histological findings, and fluorochrome labeling. Our data suggested that rhBMP-2/CPC possessed excellent osteoinductive ability, while combining with bMSCs could further promote new bone formation and maturation in maxillary sinus elevation.

BMP-2 gene modified canine bMSCs promote ectopic bone formation mediated by a nonviral PEI derivative

The study was to explore the effects of BMP-2 gene modified canine bone marrow stromal cells (bMSCs) mediated by a nonviral PEI derivative (GenEscort™ II) in promoting bone formation in vitro and in vivo. Canine bMSCs were cultured and transfected with plasmids containing bone morphogenetic protein-2 gene (pBMP-2) or enhanced green fluorescent protein gene (pEGFP). Gene transfection conditions were initially optimized by varying GenEscort™ II/plasmid ratios. Osteogenic differentiation of gene modified bMSCs was investigated via alkaline phosphatase (ALP) activity analysis and real-time quantitative PCR (RT-qPCR) analysis in vitro. The bone formation ability of pBMP-2 transfected bMSCs combined with apatite-coated silk scaffolds (mSS) was explored and compared with pEGFP transfected bMSCs/mSS or untreated bMSCs/mSS at 8, 12 weeks after operation. Results showed that gene transfection efficiency reached up to 36.67 ± 4.12% as demonstrated by EGFP expression. ALP staining and activity assay were stronger with pBMP-2 gene transfection, and the mRNA expression of BMP-2, bone sialoprotein (BSP), Runt-related transcription factor 2 (Runx-2), and osteopontin (OPN) up-regulated in bMSCs 3, 6, 9 days in pBMP-2 group. Besides, the tissue-engineered bone complex with pBMP-2 modified bMSCs achieved significantly increased de novo bone formation compared with control groups (p < 0.01). We conclude that pBMP-2 transfection mediated by GenEscort™ II could enhance the osteogenic differentiation of canine bMSCs and promote the ectopic new bone formation in nude mice. GenEscort™ II mediated pBMP-2 gene transfer appears to be a safe and effective nonviral method for gene enhanced bone tissue engineering.

Cell- and gene-based therapeutic strategies for periodontal regenerative medicine

Inflammatory periodontal diseases are a leading cause of tooth loss and are linked to multiple systemic conditions, such as cardiovascular disease and stroke. Reconstruction of the support and function of affected tooth-supporting tissues represents an important therapeutic endpoint for periodontal regenerative medicine. An improved understanding of periodontal biology coupled with current advances in scaffolding matrices has introduced novel treatments that use cell and gene therapy to enhance periodontal tissue reconstruction and its biomechanical integration. Cell and gene delivery technologies have the potential to overcome limitations associated with existing periodontal therapies, and may provide a new direction in sustainable inflammation control and more predictable tissue regeneration of supporting alveolar bone, periodontal ligament, and cementum. This review provides clinicians with the current status of these early-stage and emerging cell- and gene-based therapeutics in periodontal regenerative medicine, and introduces their future application in clinical periodontal treatment. The paper concludes with prospects on the application of cell and gene tissue engineering technologies for reconstructive periodontology.

Biomimetic coatings for bone tissue engineering of critical-sized defects

The repair of critical-sized bone defects is still challenging in the fields of implantology, maxillofacial surgery and orthopaedics. Current therapies such as autografts and allografts are associated with various limitations. Cytokine-based bone tissue engineering has been attracting increasing attention. Bone-inducing agents have been locally injected to stimulate the native bone-formation activity, but without much success. The reason is that these drugs must be delivered slowly and at a low concentration to be effective. This then mimics the natural method of cytokine release. For this purpose, a suitable vehicle was developed, the so-called biomimetic coating, which can be deposited on metal implants as well as on biomaterials. Materials that are currently used to fill bony defects cannot by themselves trigger bone formation. Therefore, biological functionalization of such materials by the biomimetic method resulted in a novel biomimetic coating onto different biomaterials. Bone morphogenetic protein 2 (BMP-2)-incorporated biomimetic coating can be a solution for a large bone defect repair in the fields of dental implantology, maxillofacial surgery and orthopaedics. Here, we review the performance of the biomimetic coating both in vitro and in vivo.