Distraction osteogenesis enhanced by osteoblastlike cells and collagen gel

Investigating the Role of Amino Acids in Short Peptides for Hydroxyapatite Binding and Osteogenic Differentiation of Mesenchymal Stem Cells to Aid Bone Regeneration

Bone defects show a slow rate of osteoconduction and imperfect reconstruction, and the current treatment strategies to treat bone defects suffer from limitations like immunogenicity, lack of cell adhesion, and the absence of osteogenic activity. In this context, bioactive supramolecular peptides and peptide gels offer unique opportunities to develop biomaterials that can play a dominant role in the biomineralization of bone tissues and promote bone formation. In this article, we have demonstrated the potential of six tetrapeptides for specific binding to hydroxyapatite (HAp), a major inorganic component of the bone, and their effect on the growth and osteogenic differentiation of mesenchymal stem cells (MSCs). We adopted a simplistic approach of rationally designing amphiphilic peptides by incorporating amino acids, Ser, pSer, Pro, Hyp, Asp, and Glu, which are present in either collagenous or noncollagenous proteins and render properties like antioxidant, calcification, and mineralization. A total of six tetrapeptides, Trp-Trp-His-Ser (WWHS), Trp-Trp-His-pSer (WWHJ), Trp-Trp-His-Pro (WWHP), Trp-Trp-His-Hyp (WWHO), Trp-Trp-His-Asp (WWHD), and Trp-Trp-His-Glu (WWHE), were synthesized. Four peptides were found to self-assemble into nanofibrillar gels resembling the extracellular matrix (ECM), and the remaining two peptides (WWHJ, WWHP) self-assembled into nanorods. The peptides showed excellent cell adhesion, encapsulation, proliferation, and migration and induced the differentiation of mesenchymal stem cells (MSCs), as evident from the enhanced mineralization, resulting from the upregulation of osteogenic markers, RUNX 2, COL I, OPN, and OCN, alkaline phosphatase (ALP) production, and calcium deposition. The peptides also induced the downregulation of inflammatory markers, TNF-α and iNOS, and the upregulation of the anti-inflammatory marker, IL-10, resulting in M2 macrophage polarization. RANKL and TRAP genes were downregulated in a coculture system of MC3T3-E1 and RAW 264.7 cells, implying that peptides promote osteogenesis and inhibit osteoclastogenesis. The peptide-based biomaterials developed in this work can enhance bone regeneration capacity and show strong potential as scaffolds for bone tissue engineering.

Scaffolds from Self-Assembling Tetrapeptides Support 3D Spreading, Osteogenic Differentiation, and Angiogenesis of Mesenchymal Stem Cells

The apparent rise of bone disorders demands advanced treatment protocols involving tissue engineering. Here, we describe self-assembling tetrapeptide scaffolds for the growth and osteogenic differentiation of human mesenchymal stem cells (hMSCs). The rationally designed peptides are synthetic amphiphilic self-assembling peptides composed of four amino acids that are nontoxic. These tetrapeptides can quickly solidify to nanofibrous hydrogels that resemble the extracellular matrix and provide a three-dimensional (3D) environment for cells with suitable mechanical properties. Furthermore, we can easily tune the stiffness of these peptide hydrogels by just increasing the peptide concentration, thus providing a wide range of peptide hydrogels with different stiffnesses for 3D cell culture applications. Since successful bone regeneration requires both osteogenesis and vascularization, our scaffold was found to be able to promote angiogenesis of human umbilical vein endothelial cells (HUVECs) in vitro. The results presented suggest that ultrashort peptide hydrogels are promising candidates for applications in bone tissue engineering.

Mesenchymal stem cells as adjuvant therapy for limb lengthening in achondroplasia

Staged leg lengthening allows achondroplastic dwarfs to reach nearly normal height, but it takes long periods of external fixation and it can be burdened by delayed unions. Between 2009 and 2013, eight achondroplastic dwarfs showed delayed unions in the callus formation during femoral lengthening stages in our institute. We performed in-situ injections of bone marrow-derived stem cell concentrates. Patients underwent monthly clinical and radiographic assessment for determination of the healing rate. All eight patients showed an improvement in the regenerated bone, with an average healing index of 23.1 days/cm (range: 18.7-23.8 days/cm). The complete recovery of the delayed consolidation took on an average of 5.2 months (range: 2-10 months). The use of cellular therapy in these patients could represent an innovative application.

Investigation of effects of low level laser therapy in distraction osteogenesis

PURPOSE

The purpose of the study was to investigate the histopathological effects of low level laser therapy (LLLT) application in distraction osteogenesis (DO).

MATERIALS AND METHODS

Twenty adult female New Zealand white rabbits were included in the study. Under general anesthesia unilateral mandibular corpus osteotomy was performed. Custom made external distractors were placed to right mandibles of rabbits. After five days of latency period, distractors were activated once a day for 5 days with 1mm/day frequency. Animals in the study group were exposed to LLLT from six different points transcutanously after each distractor activation. Control group was not exposed to laser irradiation. Animals were sacrificed after 15 and 30 days of consolidation periods and mandibles were processed for histopathological investigation under light microscope. Bone healing was analyzed with a semi-quantitative 4 point scale.

RESULTS

Osteoblastic activity and vascularization were found higher in the study group than control group after 15 days consolidation. Chondroblastic activity of the control group was significantly higher than the study group in both 15 and 30 days of consolidation groups. Osteoblastic activity and trabecular bone formation were found significantly higher in the study group than the control group after 15 days consolidation.

CONCLUSIONS

The use of LLLT in activation period of distraction osteogenesis stimulates bone repair in the early stages of distraction osteogenesis by inducing intramembranous healing and less cartilage tissue formation in the bone callus.

An Efficient and Reproducible Protocol for Distraction Osteogenesis in a Rat Model Leading to a Functional Regenerated Femur

This protocol describes the use of a newly developed external fixator for distraction osteogenesis in a rat femoral model. Distraction osteogenesis (DO) is a surgical technique leading to bone regeneration after an osteotomy. The osteotomized extremities are moved away from each other by gradual distraction to reach the desired elongation. This procedure is widely used in humans for lower and upper limb lengthening, treatment after a bone nonunion, or the regeneration of a bone defect following surgery for bone tumor excision, as well as in maxillofacial reconstruction. Only a few studies clearly demonstrate the efficiency of their protocol in obtaining a functional regenerated bone, i.e., bone that will support physiological weight-bearing without fracture after removal of the external fixator. Moreover, protocols for DO vary and reproducibility is limited by lack of information, making comparison between studies difficult. The aim of this study was to develop a reproducible protocol comprising an appropriate external fixator design for rat limb lengthening, with a detailed surgical technique that permits physiological weight-bearing by the animal after removal of the external fixator.

Stem cell therapy for enhancement of bone consolidation in distraction osteogenesis: A contemporary review of experimental studies

Objectives

Distraction osteogenesis (DO) mobilises bone regenerative potential and avoids the complications of other treatments such as bone graft. The major disadvantage of DO is the length of time required for bone consolidation. Mesenchymal stem cells (MSCs) have been used to promote bone formation with some good results.

Methods

We hereby review the published literature on the use of MSCs in promoting bone consolidation during DO.

Results

Studies differed in animal type (mice, rabbit, dog, sheep), bone type (femur, tibia, skull), DO protocols and cell transplantation methods.

Conclusion

The majority of studies reported that the transplantation of MSCs enhanced bone consolidation or formation in DO. Many questions relating to animal model, DO protocol and cell transplantation regime remain to be further investigated. Clinical trials are needed to test and confirm these findings from animal studies.

Cite this article: Y. Yang, S. Lin, B. Wang, W. Gu, G. Li. Stem cell therapy for enhancement of bone consolidation in distraction osteogenesis: A contemporary review of experimental studies. Bone Joint Res 2017;6:385–390. DOI: 10.1302/2046-3758.66.BJR-2017-0023.

Injectable scaffolds: Preparation and application in dental and craniofacial regeneration

Injectable scaffolds are appealing for tissue regeneration because they offer many advantages over pre-formed scaffolds. This article provides a comprehensive review of the injectable scaffolds currently being investigated for dental and craniofacial tissue regeneration. First, we provide an overview of injectable scaffolding materials, including natural, synthetic, and composite biomaterials. Next, we discuss a variety of characteristic parameters and gelation mechanisms of the injectable scaffolds. The advanced injectable scaffolding systems developed in recent years are then illustrated. Furthermore, we summarize the applications of the injectable scaffolds for the regeneration of dental and craniofacial tissues that include pulp, dentin, periodontal ligament, temporomandibular joint, and alveolar bone. Finally, our perspectives on the injectable scaffolds for dental and craniofacial tissue regeneration are offered as signposts for the future advancement of this field.

Lansoprazole Upregulates Polyubiquitination of the TNF Receptor-Associated Factor 6 and Facilitates Runx2-mediated Osteoblastogenesis

The transcription factor, runt-related transcription factor 2 (Runx2), plays a pivotal role in the differentiation of the mesenchymal stem cells to the osteochondroblast lineages. We found by the drug repositioning strategy that a proton pump inhibitor, lansoprazole, enhances nuclear accumulation of Runx2 and induces osteoblastogenesis of human mesenchymal stromal cells. Systemic administration of lansoprazole to a rat femoral fracture model increased osteoblastogenesis. Dissection of signaling pathways revealed that lansoprazole activates a noncanonical bone morphogenic protein (BMP)-transforming growth factor-beta (TGF-β) activated kinase-1 (TAK1)-p38 mitogen-activated protein kinase (MAPK) pathway. We found by in cellulo ubiquitination studies that lansoprazole enhances polyubiquitination of the TNF receptor-associated factor 6 (TRAF6) and by in vitro ubiquitination studies that the enhanced polyubiquitination of TRAF6 is attributed to the blocking of a deubiquitination enzyme, cylindromatosis (CYLD). Structural modeling and site-directed mutagenesis of CYLD demonstrated that lansoprazole tightly fits in a pocket of CYLD where the C-terminal tail of ubiquitin lies. Lansoprazole is a potential therapeutic agent for enhancing osteoblastic differentiation.

Uncultured autogenous adipose-derived regenerative cells promote bone formation during distraction osteogenesis in rats

BACKGROUND

Adipose-derived stem cells have recently shown differentiation potential in multiple mesenchymal lineages in vitro and in vivo. These cells can be easily isolated in large amounts from autologous adipose tissue and used without culturing or differentiation induction, which may make them relatively easy to use for clinical purposes; however, their use has not been tested in a distraction osteogenesis model.

QUESTION/PURPOSES

The question of this animal study in a rodent model of distraction osteogenesis was whether uncultured adipose-derived regenerative cells (ADRCs), which can easily be isolated in large amounts from autologous adipose tissue and contain several types of stem and regenerative cells, promote bone formation in distraction osteogenesis. We evaluated this using several tools: (1) radiographic analysis of bone density; (2) histological analysis of the callus that formed; (3) biomechanical testing; (4) DiI labeling (a method of membrane staining for postimplant celltracing); and (5) real-time polymerase chain reaction.

METHODS

Sixty rats were randomly assigned to three groups. Physiological saline (control group), Type I collagen gel (collagen group), or a mixture of ADRC and Type I collagen gel (ADRC group) was injected into the distracted callus immediately after distraction termination. To a rat femur an external fixator was applied at a rate of 0.8 mm/day for 8 days.

RESULTS

The bone density of the distracted callus in the ADRC group increased by 46% (p = 0.003, Cohen's d = 10.2, 95% confidence interval [CI] ± 0.180) compared with the control group at 6 weeks after injection. The fracture strength in the ADRC group increased by 66% (p = 0.006, Cohen's d = 1.32, 95% CI ± 0.180) compared with the control group at 6 weeks after injection. Real-time reverse transcription-polymerase chain reaction of the distracted callus from the ADRC group had higher levels of bone morphogenetic protein-2 (7.4 times higher), vascular endothelial growth factor A (6.8 times higher), and stromal cell-derived factor-1 (4.3 times higher). Cell labeling in the newly formed bone showed the ADRCs differentiated into osseous tissue at 3 weeks after injection.

CONCLUSIONS

The injection of ADRCs promoted bone formation in the distracted callus and this mechanism involves both osteogenic differentiation and secretion of humoral factors such as bone morphogenetic protein-2 or vascular endothelial growth factor A that promotes osteogenesis or angiogenesis.

CLINICAL RELEVANCE

The availability of an easily accessible cell source may greatly facilitate the development of new cell-based therapies for regenerative medicine applications in the distraction osteogenesis.

Bone marrow aspirate concentrate and platelet-rich plasma enhanced bone healing in distraction osteogenesis of the tibia

BACKGROUND

During lower limb lengthening, poor bone regeneration is a devastating complication. Several local or systemic applications have been used to promote osteogenesis, and biologic stimulations are gaining attention, but their utility has not been proven in this setting.

QUESTIONS/PURPOSES

In patients undergoing bilateral tibial lengthening, we compared those receiving an osteotomy site injection of autologous bone marrow aspirate concentrate (BMAC) plus platelet-rich plasma (PRP) with those not receiving such an injection in terms of external fixator index (time in external fixation divided by amount of lengthening), full weightbearing index (time until a patient was permitted to do full weightbearing divided by amount of lengthening), four cortical healing indexes (time until each cortical union divided by amount of lengthening), and callus shape and type.

METHODS

Twenty-two patients (44 tibias) undergoing bilateral tibial lengthening enrolled in this randomized trial. Two patients were excluded, one due to insufficient radiographic evaluation and one who was lost to followup, leaving 20 patients (40 segments) for inclusion. Ten patients (20 segments) received BMAC combined with PRP injection (treatment group) and 10 patients (20 segments) received no injection (control group). All patients underwent stature lengthening for familial short stature with the lengthening over nail technique. Autologous BMAC combined with PRP was injected at the tibial osteotomy site at the end of the index surgery. Mean distraction rates were similar between groups (0.75 mm/day in the treatment group versus 0.72 mm/day in the control group; p = 0.24). Full weightbearing was permitted when we observed radiographic evidence of healing at two cortices; this assessment was made by the surgeon who was blinded to the treatment each patient received. Minimum followup was 24 months (mean, 28 months; range, 24-34 months).

RESULTS

There was no difference in mean external fixator index between groups. However, mean cortical healing indexes (anterior/posterior/medial/lateral) were 1.14/0.81/0.96/0.88 months/cm in the treatment group and 1.47/1.26/1.42/1.22 months/cm in the control group (all p < 0.001), showing faster healing in the treatment group at each cortex. Full weightbearing was permitted earlier in the treatment group than in the control group (index: 0.99 months/cm and 1.38 months/cm, respectively, p < 0.001). Callus shape and type were not different between groups.

CONCLUSIONS

Autologous BMAC combined with PRP injection at the osteotomy site helped improve bone healing in distraction osteogenesis of the tibia, although the effect size was small.

LEVEL OF EVIDENCE

Level I, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.

Stem cell-conditioned medium accelerates distraction osteogenesis through multiple regenerative mechanisms

Distraction osteogenesis (DO) successfully induces large-scale skeletal tissue regeneration, but it involves an undesirably long treatment period. A high-speed DO mouse model (H-DO) with a distraction speed twice that of a control DO model failed to generate new bone callus in the distraction gap. Here we demonstrate that the local administration of serum-free conditioned medium from human mesenchymal stem cells (MSC-CM) accelerated callus formation in the mouse H-DO model. Secretomic analysis identified factors contained in MSC-CM that recruit murine bone marrow stromal cells (mBMSCs) and endothelial cells/endothelial progenitor cells (EC/EPCs), inhibit inflammation and apoptosis, and promote osteoblast differentiation, angiogenesis, and cell proliferation. Functional assays identified MCP-1/-3 and IL-3/-6 as essential factors in recruiting mBMSCs and EC/EPCs. IL-3/-6 also enhanced the osteogenic differentiation of mBMSCs. MSC-CM that had been depleted of MCP-1/-3 failed to recruit mBMSCs, and consequently failed to promote callus formation. Taken together, our data suggest that MSCs produce a broad repertoire of trophic factors with tissue-regenerative activities that accelerate healing in the DO process.

Biodistribution of locally or systemically transplantedosteoblast-like cells

Objectives

In order to ensure safety of the cell-based therapy for bone regeneration, we examined in vivo biodistribution of locally or systemically transplanted osteoblast-like cells generated from bone marrow (BM) derived mononuclear cells.

Methods

BM cells obtained from a total of 13 Sprague-Dawley (SD) green fluorescent protein transgenic (GFP-Tg) rats were culture-expanded in an osteogenic differentiation medium for three weeks. Osteoblast-like cells were then locally transplanted with collagen scaffolds to the rat model of segmental bone defect. Donor cells were also intravenously infused to the normal Sprague-Dawley (SD) rats for systemic biodistribution. The flow cytometric and histological analyses were performed for cellular tracking after transplantation.

Results

Locally transplanted donor cells remained within the vicinity of the transplantation site without migrating to other organs. Systemically administered large amounts of osteoblast-like cells were cleared from various organ tissues within three days of transplantation and did not show any adverse effects in the transplanted rats.

Conclusions

We demonstrated a precise assessment of donor cell biodistribution that further augments prospective utility of regenerative cell therapy.

Experimental assessment of a novel intramedullary nail for callus distraction by the segmental bone transport method

BACKGROUND

Segmental bone transport (SBT) is a revolutionary method for treating extensive bone defects, and it is in wide clinical use. Although external fixation is generally used to perform SBT, it is associated with problems such as complications due to pin placement and limitations of the amount and rate of lengthening. As a way to overcome these problems we developed a novel intramedullary (IM) nail for SBT that minimizes damage to the surrounding tissue and improves the amount and rate of bone lengthening. The purpose of this study was to perform SBT in the femur of beagle dogs using the novel IM nail that we devised, and to evaluate the morphology and quality of the regenerated bone and circulation status in the surrounding tissue. We also considered the possibilities and limitations of the IM in regard to clinical application.

METHODS

This experiment was conducted on six beagle dogs. The novel IM nail we devised was inserted into the marrow cavity of the femur, and a 30-mm bone defect was created. After a 7-day postoperative waiting period, a bone segment was transported by 1.0 mm per day in two 0.5-mm increments. Because the nail broke in two dogs, they received only partial elongation by 15 mm over a 15-day period, with a 15-mm defect remaining, whereas full elongation by 30 mm in 30 days was performed in the other four dogs. The elongation was followed by a 30-day bone hardening period.

RESULTS

The macroscopic and histological results demonstrated that high-quality, new bone had replaced the 30-mm bone defect created in the femur of all six dogs. The density and number of blood vessels that had penetrated the elongated segment of bone from the surrounding muscles was greater than in the corresponding segment of the contralateral femur, which served as a control. The results imply that the traction stimulus induced vigorous angiogenesis in the surrounding tissue.

CONCLUSION

We concluded that this method has tremendous potential for clinical application, and will overcome the limitations of conventional external fixators.

Transplantation of human dental pulp stem cells: enhance bone consolidation in mandibular distraction osteogenesis

PURPOSE

The main aim of the present study was to evaluate the capacity of stem cells from human exfoliated deciduous teeth (SHED) to enhance mandibular distraction osteogenesis (DO) in rabbits.

MATERIALS AND METHODS

A randomized controlled trial was conducted. Eighteen skeletally immature New Zealand white rabbits were divided into 2 groups, with 9 in the control group and 9 in the SHED group. The SHED were isolated, expanded, and characterized. Six million cells were transplanted into the distracted area during the osteotomy period. After a 4-day latency period, a total of 6 mm was distracted for 6 days. The newly formed bone was analyzed radiologically, histologically, and histomorphometrically at 2, 4, and 6 weeks postoperatively. Nonparametric analysis of variance (Kruskal-Wallis test) was used for data analysis, and P < .05 was considered statistically significant.

RESULTS

The cell lineage was positive for the 2 mesenchymal stem cell markers tested (CD105 and CD166). More mature bone in the SHED transplanted group was observed radiographically and histologically. Histomorphologically, the percentage of newly formed bone after 2, 4, and 6 weeks was 18.41% and 41.53%, 31.68% and 59.78%, and 52.34% and 65.24% in the control and SHED groups, respectively. The difference between the groups was statistically significant (P = .012). The bone union and stage of bone maturity scores were significantly different between the control and SHED groups (P = .006 and P = .011, respectively).

CONCLUSIONS

Our findings suggest that SHED can serve as an additional cell resource for DO enhancement in rabbits and might be a promising model for the reconstruction of large mandibular defects in human oral maxillofacial surgery.

Scaffold-based delivery of autologous mesenchymal stem cells for mandibular distraction osteogenesis: preliminary studies in a porcine model

Purpose

Bone regeneration through distraction osteogenesis (DO) is promising but remarkably slow. To accelerate it, autologous mesenchymal stem cells have been directly injected to the distraction site in a few recent studies. Compared to direct injection, a scaffold-based method can provide earlier cell delivery with potentially better controlled cell distribution and retention. This pilot project investigated a scaffold-based cell-delivery approach in a porcine mandibular DO model.

Materials and Methods

Eleven adolescent domestic pigs were used for two major sets of studies. The in-vitro set established methodologies to: aspirate bone marrow from the tibia; isolate, characterize and expand bone marrow-derived mesenchymal stem cells (BM-MSCs); enhance BM-MSC osteogenic differentiation using FGF-2; and confirm cell integration with a gelatin-based Gelfoam scaffold. The in-vivo set transplanted autologous stem cells into the mandibular distraction sites using Gelfoam scaffolds; completed a standard DO-course and assessed bone regeneration by macroscopic, radiographic and histological methods. Repeated-measure ANOVAs and t-tests were used for statistical analyses.

Results

From aspirated bone marrow, multi-potent, heterogeneous BM-MSCs purified from hematopoietic stem cell contamination were obtained. FGF-2 significantly enhanced pig BM-MSC osteogenic differentiation and proliferation, with 5 ng/ml determined as the optimal dosage. Pig BM-MSCs integrated readily with Gelfoam and maintained viability and proliferative ability. After integration with Gelfoam scaffolds, 2.4–5.8×10⁷ autologous BM-MSCs (undifferentiated or differentiated) were transplanted to each experimental DO site. Among 8 evaluable DO sites included in the final analyses, the experimental DO sites demonstrated less interfragmentary mobility, more advanced gap obliteration, higher mineral content and faster mineral apposition than the control sites, and all transplanted scaffolds were completely degraded.

Conclusion

It is technically feasible and biologically sound to deliver autologous BM-MSCs to the distraction site immediately after osteotomy using a Gelfoam scaffold to enhance mandibular DO.

Mesenchymal stem cells: new aspect in cell-based regenerative therapy

MSCs are multipotent progenitors which reside in bone marrow. They support hematopoietic stem cells homing, self renewal and differentiation in bone marrow. They can also differentiate into osteoblasts, adipocytes, chondrocytes, myocyates and many other tissues. In vivo, when trauma happens, MSCs operate cell renewal and migrate to the damaged tissues to regenerate that injury. In vitro, MSCs are able to proliferate and differentiate to a variety of cell lineages. This makes them a very hopeful tool for cell-based regenerative therapy for large bone defects, maxillofacial skeletal reconstruction, cardiovascular and spinal cord injury and so many other defects. The most important characteristic that make MSCs an excellent tool for cell replacement is their ability to escape from immune rejection. For therapeutic purposes they usually isolated from human bone marrow or fat and they should proliferate in order to reach an adequate number for implantation. Conventionally DMEM medium supplemented with 10% FBS is used for their expansion, but currently autologous platelet rich products are replaced FBS. Platelet granules contain so many growth factors that can support MSCs proliferation.

Locally injection of cell sheet fragments enhances new bone formation in mandibular distraction osteogenesis: a rabbit model

Effective methods to shorten the treatment period of distraction osteogenesis (DO) are needed. To investigate whether injections of osteogenic bone marrow stromal cell (BMSC) sheet fragments could be used to facilitate new bone formation during DO, 30 rabbits underwent bilateral mandibular osteotomy and their mandibles were lengthened at a rate of 0.75 mm/12 h for 6 days after a 5-day latency period. There were three treatment groups (n = 10 for each group): Serum-free medium, dissociated BMSCs, and BMSC sheet fragments. A local injection was conducted with a needle directly into the distracted areas immediately after distraction. Rabbits were sacrificed for examination at 3 and 6 weeks after injection. Gross examination, radiographic evaluation, and micro-CT scanning indicated a significant increase in bony union in the BMSC sheet fragment group, compared with the medium group and the dissociated cell group. The histomorphometric analysis showed more intensive bone formation in the sheet fragment group than the other two groups at each time point. Additionally, the peak load was significantly higher in the fragment group than those in the others. The results show that injection of BMSC sheet fragments promotes bone formation in DO and indicate a promising approach to shorten the treatment period of osteodistraction.

Cell culture-based tissue engineering as an alternative to bone grafts in implant dentistry: a literature review

Several biomaterials and techniques for bone grafting have been described in the literature for atresic bone tissue replacement caused by edentulism, surgical resectioning, and traumas. A new technique involves tissue engineering, a promising option to replace bone tissue and solve problems associated with morbidity of autogenous grafting. This literature review aims to describe tissue-engineering techniques using ex vivo cell culture as an alternative to repair bone maxillary atresias and discuss the concepts and potentials of bone regeneration through cell culture techniques as an option for restorative maxillofacial surgery.

Osteogenesis by gradually expanding the interface between bone surface and periosteum enhanced by bone marrow stem cell administration in rabbits

OBJECTIVE

We investigated whether administration of mesenchymal stem cells (MSCs) promotes bone formation at the gap created by periosteal distraction.

STUDY DESIGN

A mesh plate was placed subperiosteally in rabbit parietal bones. Following elevation of the mesh plate, rabbit MSCs were administered into the gap. Controls received phosphate-buffered saline (PBS). The volume, height, bone mineral density (BMD), and bone mineral content (BMC) of newly formed bone were examined using microcomputed tomography. Histological analysis was performed by hematoxylin and eosin staining and immunohistochemistry for type I collagen and osteocalcin.

RESULTS

The experimental group showed significantly increased volume, height, BMD, and BMC in newly formed bone tissues at the gaps compared with the control group (P < .05). The newly formed bone tissues showed both type I collagen and osteocalcin expression in the MSC-administration group.

CONCLUSION

Mesenchymal stem cell administration may be useful to induce osteogenesis at sites of periosteal distraction.

The effect of the platelet concentration in platelet-rich plasma gel on the regeneration of bone

The aim of our study was to investigate the effect of platelet-rich plasma on the proliferation and differentiation of rat bone-marrow cells and to determine an optimal platelet concentration in plasma for osseous tissue engineering. Rat bone-marrow cells embedded in different concentrations of platelet-rich plasma gel were cultured for six days. Their potential for proliferation and osteogenic differentiation was analysed. Using a rat limb-lengthening model, the cultured rat bone-marrow cells with platelet-rich plasma of variable concentrations were transplanted into the distraction gap and the quality of the regenerate bone was evaluated radiologically. Cellular proliferation was enhanced in all the platelet-rich plasma groups in a dose-dependent manner. Although no significant differences in the production and mRNA expression of alkaline phosphatase were detected among these groups, mature bone regenerates were more prevalent in the group with the highest concentration of platelets. Our results indicate that a high platelet concentration in the platelet-rich plasma in combination with osteoblastic cells could accelerate the formation of new bone during limb-lengthening procedures.

Promoted new bone formation in maxillary distraction osteogenesis using a tissue-engineered osteogenic material

Bilateral maxillary distraction was performed at a higher rate in rabbits to determine whether locally applied tissue-engineered osteogenic material (TEOM) enhances bone regeneration. The material was an injectable gel composed of autologous mesenchymal stem cells, which were cultured then induced to be osteogenic in character, and platelet-rich plasma (PRP). After a 5-day latency period, distraction devices were activated at a rate of 2.0 mm once daily for 4 days. Twelve rabbits were divided into 2 groups. At the end of distraction, the experimental group of rabbits received an injection of TEOM into the distracted tissue on one side, whereas, saline solution was injected into the distracted tissue on the contralateral side as the internal control. An additional control group received an injection of PRP or saline solution into the distracted tissue in the same way as the experimental group. The distraction regenerates were assessed by radiological and histomorphometric analyses. The radiodensity of the distraction gap injected with TEOM was significantly higher than that injected with PRP or saline solution at 2, 3, and 4 weeks postdistraction. The histomorphometric analysis also showed that both new bone zone and bony content in the distraction gap injected with TEOM were significantly increased when compared with PRP or saline solution. Our results demonstrated that the distraction gap injected with TEOM showed significant new bone formation. Therefore, injections of TEOM may be able to compensate for insufficient distraction gaps.

Distraction osteogenesis of the lower extremity in patients with achondroplasia/hypochondroplasia treated with transplantation of culture-expanded bone marrow cells and platelet-rich plasma

BACKGROUND

Longer treatment period in distraction osteogenesis (DO) of the lower extremity leads to more frequent complications. We have developed a new technique of transplantation of culture-expanded bone marrow cells (BMCs) and platelet-rich plasma (PRP) during DO to accelerate new bone formation. To assess the efficacy of this cell therapy, retrospective comparative study was conducted between the bones treated with BMC and PRP and the bones treated without BMC and PRP during DO in patients with achondroplasia (ACH) and hypochondroplasia (HCH).

METHODS

Fifty-six bones in 20 patients (ACH, 16; HCH, 4) that were lengthened in our hospital were divided into 2 groups. Twenty-four bones (femora, 12; tibiae, 12) in 11 patients (boys, 7; girls, 4) were treated with BMC and PRP transplantation (BMC-PRP group), whereas 32 bones (femora, 14; tibiae, 18) in 9 patients (boys, 3; girls, 6) did not undergo additional cell therapy (control group). The parameters, including the age at operation, the increase in length, and the healing index, were compared between the 2 groups. The clinical outcome was also compared between the femoral and tibial lengthenings.

RESULTS

Bone marrow cells (average number, +/- SD, 3.2 +/- 1.37 x 10 cells) and PRP (average platelet concentration +/- SD, 2.36 +/- 0.57 x 10 cells/muL) were transplanted. Although there were no significant differences in the age at operation and the length gained between the 2 groups, the average healing index of the BMC-PRP group (27.1 +/- 6.89 d/cm) was significantly lower than that of the control group (36.2 +/- 10.4 d/cm) (P = 0.0005). The femoral lengthening showed significantly faster healing than did the tibial lengthening in the BMC-PRP group (P = 0.0092).

CONCLUSIONS

Transplantation of BMC and PRP shortened the treatment period by accelerating new bone regeneration during DO of the lower extremity in patients with ACH and HCH, especially in the femoral lengthening.

Effect of thrombin peptide 508 (TP508) on bone healing during distraction osteogenesis in rabbit tibia

Thrombin-related peptide 508 (TP508) accelerates bone regeneration during distraction osteogenesis (DO). We have examined the effect of TP508 on bone regeneration during DO by immunolocalization of Runx2 protein, a marker of osteoblast differentiation, and of osteopontin (OPN) and bone sialoprotein (BSP), two late markers of the osteoblast lineage. Distraction was performed in tibiae of rabbits over a period of 6 days. TP508 (30 or 300 μg) or vehicle was injected into the distraction gap at the beginning and end of the distraction period. Two weeks after active distraction, tissue samples were harvested and processed for immunohistochemical analysis. We also tested the in vitro effect of TP508 on Runx2 mRNA expression in osteoblast-like (MC3T3-E1) cells by polymerase chain reaction analysis. Runx2 and OPN protein were observed in preosteoblasts, osteoblasts, osteocytes of newly formed bone, blood vessel cells and many fibroblast-like cells of the soft connective tissue. Immunostaining for BSP was more restricted to osteoblasts and osteocytes. Significantly more Runx2- and OPN-expressing cells were seen in the group treated with 300 μg TP508 than in the control group injected with saline or with 30 μg TP508. However, TP508 failed to increase Runx2 mRNA levels significantly in MC3T3-E1 cells after 2–3 days of exposure. Our data suggest that TP508 enhances bone regeneration during DO by increasing the proportion of cells of the osteoblastic lineage. Clinically, TP508 may shorten the healing time during DO; this might be of benefit when bone regeneration is slow.

The effect of recombinant human bone morphogenetic protein-2 on the osteogenic potential of rat mesenchymal stem cells after several passages

BACKGROUND

Since the osteogenic potential of bone marrow derived mesenchymal stem cells (BMSCs) becomes reduced with passage, establishment of culture condition that permit the rapid expansion of BMSCs while retaining their potential for differentiation is needed for clinical application. Bone morphogenetic proteins stimulate osteogenic differentiation in mesenchymal progenitor cells as well as increase stem cell numbers. Thus, we analyzed the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the osteogenic potential of rat BMSCs over several passages.

MATERIAL AND METHODS

Osteogenic differentiation in vitro was evaluated in terms of the alkaline phosphatase (ALP) activity and the osteocalcin (OC) concentration in the supernatants, and the expression of ALP and OC mRNA in the cultured cells. For in-vivo osteogenesis, BMSCs cultured with and without rhBMP-2 through all passages were implanted into athymic mice.

RESULTS

The levels of osteogenic markers were significantly higher in the cells of the BMP(+) group than in the cells of the BMP(-) group, although they decreased with passage irrespective of whether or not rhBMP-2 was added. Similar to the in-vitro experiments, there was a greater degree of bone and cartilage tissue formation in the BMP(+) group over all passages.

INTERPRETATION

From our results, osteogenic potential can be maintained even in BMSCs that have been passaged several times in the presence of rhBMP-2. These cells are capable of inducing and participating in bone formation and can be used for clinical applications.

Transplantation of osteoblast-like cells to the distracted callus in the rabbit mandible

BACKGROUND

The purpose of this study was to investigate whether injections of marrow-derived mesenchymal progenitor cells could be used to facilitate new bone formation during distraction osteogenesis.

METHODS

Fifteen New Zealand rabbits underwent bilateral osteotomy. After a 1-week latency period, bone distraction was activated at a rate of 2.0 mm/day for 5 days. The marrow-derived mesenchymal progenitor cells derived from the ilium marrow were cultured to a population of 10 in 0.5 ml and then unilaterally transplanted to the gap of distracted callus immediately after distraction had been terminated. Rabbits were killed at 2, 4, and 6 weeks after completion of bone lengthening. The distracted areas were harvested and evaluated by histologic, histomorphometric, radiographic, and scanning electron microscopic analysis. Bone mineral density in the lengthened callus was evaluated using dual-energy x-ray absorptiometry.

RESULTS

Radiographic evaluation indicated a significant increase in bony union of the distraction regenerate in the experimental side compared with the control side. Corresponding to the radiographic findings, the histologic examination showed an earlier and more intensive bone formation in the experimental side after 2, 4, and 6 weeks compared with the control side. Larger chondroid islands were found evident in distracted bone of the control side than in the experimental side.

CONCLUSIONS

The results show that transplantation of osteoblast-like cells promotes maturity of the distracted callus, as observed on the second and fourth weeks after lengthening. The method appears promising as a means of shortening the consolidation period of osteodistraction and decreasing complications during bone lengthening.

Transplantation of culture expanded bone marrow cells and platelet rich plasma in distraction osteogenesis of the long bones

Longer treatment period in distraction osteogenesis (DO) leads to more frequent complications. We developed a new technique of transplantation of culture expanded bone marrow cells (BMC) and platelet rich plasma (PRP) in DO of the long bones. Retrospective comparative study was conducted between the bones treated with and without BMC and PRP in DO to assess the efficacy of this new technique of transplantation. Ninety-two bones (46 patients) that were lengthened in our hospital and followed up until removal of the pins were divided into two groups according to the cell (BMC+PRP) treatment. The BMC-PRP(+) group consisted of 32 bones (14 femora, 18 tibiae) in 17 patients (10 boys and 7 girls), while the BMC-PRP(-) group consisted of 60 bones (25 femora, 35 tibiae) in 29 patients (13 boys and 16 girls). The clinical outcome including the age at operation, amount of length gained, the healing index, the delay in consolidation, and complications were compared between the two groups. The healing between the femoral and the tibial lengthening was also assessed. The average age at operation was 15.8 years in the BMC-PRP(+) group and 15.5 years in the BMC-PRP(-) group. Although there were no significant differences in the age at operation and the length gained between the two groups, the average healing indices of the BMC-PRP(+) group in short stature and in limb length discrepancy were significantly lower than those of the BMC-PRP(-) group (P=0.0019 and P=0.0031, respectively). A delay in consolidation was seen in 45% of the BMC-PRP(-) group but never observed in the BMC-PRP(+) group (P<0.0001). The rate of complications was 23% of the BMC-PRP(-) group and only 6% of the BMC-PRP(+) group (P=0.0406). The femoral lengthening showed significantly faster healing than the tibial lengthening by the BMC and PRP transplantation (P=0.0004) In conclusion, transplantation of BMC and PRP shortened the treatment period and reduced associated complications by accelerating new bone formation in DO.

Stimulation of EP4 receptor enhanced bone consolidation during distraction osteogenesis

The objective of this study was to confirm whether an agonist of prostaglandin E receptor subtype EP4 can enhance bone consolidation in distraction osteogenesis. A rat distraction osteogenesis model was generated. A unilateral external fixator was fixed to the left femur of the rats of this model after osteotomy. Seven days later, 0.25 mm/12 h or 0.5 mm/12 h elongation was performed for 2 weeks. A systemic administration of an EP4 receptor agonist (ONO 4819 . CD, 3, 10, 30 microg/kg) or normal saline by subcutaneous injection was also performed for 2 weeks. The animals were sacrificed 10, 14, 17, 21, and 42 days after the operation. Radiographic examination, histological examination, and measurements of bone mineral density (BMD) and distraction-callus hardness were performed to qualitatively and quantitatively evaluate new bone formation. Twenty-one days after the operation, the experimental group had a higher BMD and a higher distraction-callus hardness than that of the control group. Forty-two days after the operation, BMD was similar among all of the groups. But the hardness of the experimental groups increased more than that of the control group, so the statistical differences in distraction-callus hardness became more distinct between the two groups, indicating an improved remodeling of the distraction callus. These findings are also supported by histological examination. Subcutaneous injection of an EP4 receptor agonist can promote bone formation and remodeling during distraction osteogenesis. ONO 4819 * CD might be a potential candidate for shortening the treatment time of distraction osteogenesis.

Effect of vascularity on canine distracted tibial callus consolidation

In the consolidation period of distraction osteogenesis, mineralization occurs before corticalization. We hypothesized that the increased rate of bone mineral density correlates to the density of vascularity in the callus. We unilaterally lengthened the tibia in eight adult beagles. After a waiting period of 7 days, tibiae were lengthened for 30 days. After a consolidation period of an additional 60 days, all animals were euthanized. Just before euthanasia, blood vessels were perfused with 50% w/v barium sulfate solution, and soft radiographs of the distracted callus and the control tibiae were taken. Bone mineral density of the regenerated bones was measured preoperatively by quantitative computed tomography on Days 37, 68, and 98. Increases of the percent bone mineral density (from Day 37 to Day 98 and from Day 68 to Day 98) correlated with the blood vessel volume density ratios on Day 98. Our results suggest that preservation of the higher density of blood vessels in the consolidation period could lead to the better mineralization of the distracted callus.

Transplantation of marrow-derived mesenchymal stem cells and platelet-rich plasma during distraction osteogenesis--a preliminary result of three cases

Clinical results of distraction osteogenesis with transplantation of marrow-derived mesenchymal stem cells (MSCs) and platelet-rich plasma (PRP) were reviewed in three femora and two tibiae of the two patients with achondroplasia and one patient with congenital pseudarthrosis of the tibia. MSCs derived from the iliac crest were cultured with osteogenic supplements and differentiated into osteoblast-like cells. PRP, which is known to contain several growth factors and coagulate immediately by a minute introduction of thrombin and calcium, was prepared just before transplantation. Culture-expanded osteoblast-like cells and autologous PRP were injected into the distracted callus with the thrombin-calcium mixture so that the PRP gel might develop within the injected site. Transplantation of MSCs and PRP was done at the lengthening and consolidation period in each patient. The target lengths were obtained in every leg without major complications and the average healing index was 23.0 days/cm (18.8-26.9 days/cm). Although these results are still preliminary, transplantation of osteoblast-like cells and PRP, which seemed to be a safe and minimally invasive cell therapy, could shorten the treatment period by acceleration of bone regeneration during distraction osteogenesis.

Matrix metalloproteinases (MMPs) safeguard osteoblasts from apoptosis during transdifferentiation into osteocytes: MT1-MMP maintains osteocyte viability

Osteoblasts undergo apoptosis or differentiate into either osteocytes or bone-lining cells after termination of bone matrix synthesis. In this study, we investigated the role of matrix metalloproteinases (MMPs) in differentiation of osteoblasts, bone formation, transdifferentiation into osteocytes, and osteocyte apoptosis. This was accomplished by using calvarial sections from the MT1-MMP-deficient mouse and by culture of the mouse osteoblast cell line MC3T3-E1 and primary mouse calvarial osteoblasts. We found that a synthetic matrix metalloprotease inhibitor, GM6001, strongly inhibited bone formation in vitro of both primary osteoblasts and MC3T3 cells by approximately 75%. To further investigate at which level of osteoblast differentiation MMP inhibition was attenuating osteoblast function, we found that neither preosteoblast nor mature osteoblast activity was affected. In contrast, cell survival of osteoblasts forced to transdifferentiate into osteocytes in 3D type I collagen gels were inhibited by more than 50% when exposed to 10 microM GM6001 and to Tissue Inhibitor of Metalloproteinase-2 (TIMP-2), a natural MT1-MMP inhibitor. This shows the importance of MMPs in safeguarding osteoblasts from apoptosis when transdifferentiating into osteocytes. By examination of osteoblasts and osteocytes embedded in calvarial bone in the MT1-MMP deficient mice, we found that MT1-MMP deficient mice had 10-fold higher levels of apoptotic osteocytes than wild-type controls. We have previously shown that MT1-MMP activates latent Transforming Growth Factorbeta (TGF-beta). These findings strongly suggest that MT1-MMP-activated TGF-beta maintains osteoblast survival during transdifferentiation into osteocytes, and maintains mature osteocyte viability. Thus, the interrelationship of MMPs and TGF-beta may play an important role in bone formation and maintenance.

Effects of osteogenic protein-1 on distraction osteogenesis in rabbits

In this study we tested the effect of locally applied osteogenic protein 1 (OP-1) on distraction osteogenesis in rabbits. Seven days after tibial osteotomy, distraction was started at a rate of 0.25 mm per 12 h for 3 weeks. At the end of the distraction period, OP-1 was injected at the site of osteotomy. Four different dosages were tested (0, 80, 800, or 2000 microg; eight rabbits per dose group). Rabbits were sacrificed 3 weeks later, and histologic, densitometric, and biomechanical parameters were assessed. No significant differences were found between groups for any parameter. To explain why this approach was only modestly successful, the expression of BMP receptor protein in the newly formed tissue was analyzed by immunohistochemistry. Strong expression of BMP receptor IA, IB, and II was found during the early distraction phase, but not during later stages of the process. Thus, it appears that the lack of receptor protein in the target tissue impairs the effect of OP-1 given at the end of the distraction period. Possibly, OP-1 could be more useful when applied early in the distraction phase.

Chondrogenesis enhanced by overexpression of sox9 gene in mouse bone marrow-derived mesenchymal stem cells

We investigated chondrogenesis of cell-mediated sox9 gene therapy as a new treatment regimen for cartilage regeneration. pIRES2-EGFP vector containing a full-length mouse sox9 cDNA was transfected into bone marrow-derived mesenchymal stem cells (MSCs) by lipofection and chondrogenic differentiation of these cells was evaluated. In vitro high density micromass culture of these sox9 transfected MSCs demonstrated that a matrix-rich micromass aggregate with EGFP expressing MSCs was positively stained by Alcian blue and type II collagen. Next, sox9 transfected MSCs were loaded into the diffusion chamber and transplanted into athymic mice to analyze in vivo chondrogenesis. A massive tissue formation in about 2mm diameter was visible in the chamber after 4 weeks transplantation. Histological examinations demonstrated that both Alcian blue and type II collagen were positively stained in the extracellular matrix of the mass while type X collagen was not stained. These results indicated that cell-mediated sox9 gene therapy could be a novel strategy for hyaline cartilage damage.

Matrix metalloproteinase-dependent activation of latent transforming growth factor-beta controls the conversion of osteoblasts into osteocytes by blocking osteoblast apoptosis

Upon termination of bone matrix synthesis, osteoblasts either undergo apoptosis or differentiate into osteocytes or bone lining cells. In this study, we investigated the role of matrix metalloproteinases (MMPs) and growth factors in the differentiation of osteoblasts into osteocytes and in osteoblast apoptosis. The mouse osteoblast cell line MC3T3-E1 and primary mouse calvarial osteoblasts were either grown on two-dimensional (2-D) collagen-coated surfaces, where they morphologically resemble flattened, cuboidal bone lining cells, or embedded in three-dimensional (3-D) collagen gels, where they resemble dendritic osteocytes constituting a network of cells. When MC3T3-E1 osteoblasts were grown in a 3-D matrix in the presence of an MMP inhibitor (GM6001), the cell number was dose-dependently reduced by approximately 50%, whereas no effect was observed on a 2-D substratum. In contrast, the murine mature osteocyte cell line, MLO-Y4, was unaffected by GM6001 under all culture conditions. According to TUNEL assay, the osteoblast apoptosis was increased 2.5-fold by 10 microm GM6001. To investigate the mechanism by which MMPs mediate the survival of osteoblasts, we examined the effect of GM6001 on MC3T3-E1 osteoblasts in the presence of extracellular matrix components and growth factors, including tenascin, fibronectin, laminin, collagenase-cleaved collagen, gelatin, parathyroid hormone, basic fibroblast growth factor, vascular epidermal growth factor, insulin-like growth factor, interleukin-1, and latent and active transforming growth factor-beta (TGF-beta). Only active TGF-beta, but not latent TGF-beta or other agents tested, restored cell number and apoptosis to control levels. Furthermore, we found that the membrane type MMP, MT1-MMP, which is produced by osteoblasts, could activate latent TGF-beta and that antibodies neutralizing endogenous TGF-beta led to a similar decrease in cell number as GM6001. Whereas inhibitors of other protease families did not induce osteoblast apoptosis, an inhibitor of the p44/42 mitogen-activated protein kinase showed the same but non-synergetic effect as GM6001. These findings suggest that MMP-activated TGF-beta maintains osteoblast survival during trans-differentiation into osteocytes by a p44/42-dependent pathway.