Characterization of human bone cells derived from the maxillary alveolar ridge

Comparison of Intraoral Bone Regeneration with Iliac and Alveolar BMSCs

This study compared the osteogenic potential of bone marrow mesenchymal stem cells (BMSCs) of iliac and alveolar origins (I-BMSCs and Al-BMSCs, respectively), which were transplanted in combination with β tricalcium phosphate (β-TCP) in peri-implant bone defects to investigate the osseointegration between dental implants and tissue-engineered bone in dogs. Specifically, I-BMSCs and Al-BMSCs were cultured, characterized, and seeded on β-TCP and subjected to immunoblotting analyses and alkaline phosphatase activity assays. Subsequently, these cell-seeded scaffolds were implanted into defects that were freshly generated in the mandibular premolar areas of 4 dogs. The defects were covered with β-TCP + Al-BMSCs ( n = 6), β-TCP + I-BMSCs ( n = 6), or β-TCP ( n = 6) or served as the blank control ( n = 6). After healing for 12 wk, the formation and mineralization of new bones were assessed through micro-computed tomographic, histologic, and histomorphometric analyses, and bone-to-implant contacts were measured in the specimens. It was evident that in this large animal model, I-BMSCs and Al-BMSCs manifested similarly strong osteogenic potential, as significantly more new bone was formed in the Al-BMSC and I-BMSC groups than otherwise ( P < 0.01). Therefore, Al-BMSCs are emerging as an efficient alternative for autologous mesenchymal stem cells in regenerative dental and maxillofacial therapies. I-BMSCs, if not restricted in their bioavailability, can also be of great utility in bone tissue-engineering applications.

3D printed tissue engineered model for bone invasion of oral cancer

Recent advances in three-dimensional printing technology have led to a rapid expansion of its applications in tissue engineering. The present study was designed to develop and characterize an in vitro multi-layered human alveolar bone, based on a 3D printed scaffold, combined with tissue engineered oral mucosal model. The objective was to incorporate oral squamous cell carcinoma (OSCC) cell line spheroids to the 3D model at different anatomical levels to represent different stages of oral cancer. Histological evaluation of the 3D tissue model revealed a tri-layered structure consisting of distinct epithelial, connective tissue, and bone layers; replicating normal oral tissue architecture. The mucosal part showed a well-differentiated stratified oral squamous epithelium similar to that of the native tissue counterpart, as demonstrated by immunohistochemistry for cytokeratin 13 and 14. Histological assessment of the cancerous models demonstrated OSCC spheroids at three depths including supra-epithelial level, sub-epithelial level, and deep in the connective tissue-bone interface. The 3D tissue engineered composite model closely simulated the native oral hard and soft tissues and has the potential to be used as a valuable in vitro model for the investigation of bone invasion of oral cancer and for the evaluation of novel diagnostic or therapeutic approaches to manage OSCC in the future.

Characterization of Multilayered Tissue-Engineered Human Alveolar Bone and Gingival Mucosa

Advances in tissue engineering have permitted assembly of multilayered composite tissue constructs for potential applications in the treatment of combined hard and soft tissue defects and as an alternative in vitro test model to animal experimental systems. The aim of this study was to develop and characterize a novel three-dimensional combined human alveolar bone and gingival mucosal model based on primary cells isolated from the oral tissues. Bone component of the model was engineered by seeding primary human alveolar osteoblasts into a hydroxyapatite/tricalcium phosphate scaffold and culturing in a spinner bioreactor. The engineered bone was then laminated, using an adhesive tissue sealant, with tissue-engineered gingival mucosa consisting of air/liquid interface-cultured normal human gingival keratinocytes on oral fibroblast-populated collagen gel scaffold. Histological characterization revealed a structure consisting of established epithelial, connective tissue and bone layers closely comparable to normal oral tissue architecture. The mucosal component demonstrated a mature epithelium undergoing terminal differentiation similar to that characteristic of native buccal mucosa, as confirmed using cytokeratin 13 and cytokeratin 14 immunohistochemistry. Ultrastructural analysis confirmed the presence of desmosomes and hemidesmosomes in the epithelial layer, a continuous basement membrane, and newly synthesized collagen in the connective tissue layer. Quantitative polymerase chain reaction (qPCR) assessment of osteogenesis-related gene expression showed a higher expression of genes encoded collagen I (COL1) and osteonectin (ON) compared with osteocalcin (OC), osteopontin (OP), and alkaline phosphatase (ALP). Enzyme-linked immunosorbent assay quantification of COL1, ON, and OC confirmed a pattern of secretion, which paralleled the model's gene expression profile. We demonstrate in this study that, replicating the anatomical setting between oral mucosa and the underlying alveolar bone is feasible and the developed model showed characteristics similar to those of normal tissue counterparts. This trilayered model therefore offers great scope as an advanced and anatomically representative tissue-engineered alternative to animal models.

Pilot investigation of the molecular discrimination of human osteoblasts from different bone entities

In oral and maxillofacial surgery, autologous grafts from the iliac crest remain the 'gold standard' for alveolar ridge reconstruction, whereas intraoral bone grafts are considered in smaller defects. To date, a comparison of the osteogenic potential of osteoblasts with regard to their tissue origin is missing. Primary osteoblasts have proven useful for the investigation of the tissue-specific osteogenic properties. The present study compares primary human alveolar (aHOBs) and iliac osteoblasts (iHOBs) derived from three female patients undergoing routine intraoral bone grafting. Proliferation potential of the osteoblasts was evaluated using real-time impedance monitoring. Relative gene expression of bone specific biomarkers was analyzed and quantified using quantitative polymerase chain reactions (qPCR). Immunohistochemistry and phase contrast microscopy were performed, as well as alkaline phosphatase assay and alizarin red staining to visualize morphology and mineralization capacity. A twofold faster proliferation rate of aHOBs compared with iHOBs (130 h vs. 80 h) was observed. Alkaline phosphatase activity and alizarin red staining in both HOBs indicated similar mineralization capacity. Gene expression of seven genes (BMP1, CSF-1, TGFBR1, ICAM1, VCAM1, SPP1 and DLX5) was significantly higher in iHOB than in aHOB samples. These data suggest a higher osteogenic potential of osteoblasts derived from the iliac crest compared with primary osteoblasts from the alveolar bone and may lead to a better understanding of the molecular impact of bone cells from different bone entities on bone regeneration in alveolar ridge reconstructions.

In vivo bone formation by human alveolar-bone-derived mesenchymal stem cells obtained during implant osteotomy using biphasic calcium phosphate ceramics or Bio-Oss as carriers

OBJECTIVES

The aim of this study was to evaluate HA coated with different ratios of TCP as a carrier for hABMSCs obtained during implant osteotomy in comparison to slowly-resorbing biomaterial, Bio-Oss, as a negative control, using in vitro and in vivo experiments.

MATERIALS AND METHODS

Human ABMSCs (hABMSCs) harvested during implant osteotomy were transplanted using HA/TCP or Bio-Oss as carriers in a murine ectopic transplantation model (n = 12). Pore size and cell affinity were evaluated in vitro. The area of newly formed bone was analyzed histometrically, the number of osteocytes was counted, and immunohistochemical staining was conducted against several markers of osteogenesis, including alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX-2), osteocalcin (OCN), and osteopontin (OPN). Osteoclast formation was evaluated by tartrate-resistant acid phosphatase staining.

RESULTS

The carrier materials had comparable pore sizes. The cell affinity assay resulted in a high proportion of cell adhesion (>90%) in all experimental groups. Substantial new bone and osteocyte formation was observed on both HA/TCP carriers, whereas it was minimal with Bio-Oss. Positive immunostaining for ALP, RUNX-2, OCN, and OPN was observed with HA/TCP, but only limited expression of osteogenic markers with Bio-Oss. Conversely, there was a minimal osteoclast presence with Bio-Oss, but a significant presence of osteoclasts with both HA/TCP carriers.

CONCLUSIONS

Both types of scaffolds, BCP and Bio-Oss, showed high stem cell-carrying potential, but the in vivo healing patterns of their complexes with hABMSC could be affected by the microenvironment on the surfaces of the scaffolds.

Effect of cyclic mechanical stimulation on the expression of osteogenesis genes in human intraoral mesenchymal stromal and progenitor cells

We evaluated the effects of mechanical stimulation on the osteogenic differentiation of human intraoral mesenchymal stem and progenitor cells (MSPCs) using the Flexcell FX5K Tension System that mediated cyclic tensile stretch on the cells. MSPCs were isolated from human mandibular retromolar bones and characterized using flow cytometry. The positive expression of CD73, CD90, and CD105 and negativity for CD14, CD19, CD34, CD45, and HLA-DR confirmed the MSPC phenotype. Mean MSPC doubling time was 30.4 ± 2.1 hrs. The percentage of lactate dehydrogenase (LDH) release showed no significant difference between the mechanically stimulated groups and the unstimulated controls. Reverse transcription quantitative real-time PCR revealed that 10% continuous cyclic strain (0.5 Hz) for 7 and 14 days induced a significant increase in the mRNA expression of the osteogenesis-specific markers type-I collagen (Col1A1), osteonectin (SPARC), bone morphogenetic protein 2 (BMP2), osteopontin (SPP1), and osteocalcin (BGLAP) in osteogenic differentiated MSPCs. Furthermore, mechanically stimulated groups produced significantly higher amounts of calcium deposited into the cultures and alkaline phosphatase (ALP). These results will contribute to a better understanding of strain-induced bone remodelling and will form the basis for the correct choice of applied force in oral and maxillofacial surgery.

Primary human alveolar bone cells isolated from tissue samples acquired at periodontal surgeries exhibit sustained proliferation and retain osteogenic phenotype during in vitro expansion

OBJECTIVES

Bone tissue regeneration requires a source of viable, proliferative cells with osteogenic differentiation capacity. Periodontal surgeries represent an opportunity to procure small amounts of autologous tissues for primary cell isolation. Our objective was to assess the potential of human alveolar bone as a source of autologous osteogenic cells for tissue engineering and biomaterials and drug testing studies.

MATERIALS AND METHODS

Alveolar bone tissue was obtained from 37 patients undergoing routine periodontal surgery. Tissue harvesting and cell isolation procedures were optimized to isolate viable cells. Primary cells were subcultured and characterized with respect to their growth characteristics, gene expression of osteogenic markers, alkaline phosphatase activity and matrix mineralization, under osteogenic stimulation.

RESULTS

Alveolar bone cells were successfully isolated from 28 of the 30 samples harvested with bone forceps, and from 2 of the 5 samples obtained by bone drilling. The yield of cells in primary cultures was variable between the individual samples, but was not related to the site of tissue harvesting and the patient age. In 80% of samples (n = 5), the primary cells proliferated steadily for eight subsequent passages, reaching cumulative numbers over 10(10) cells. Analyses confirmed stable gene expression of alkaline phosphatase, osteopontin and osteocalcin in early and late cell passages. In osteogenic medium, the cells from late passages increased alkaline phosphatase activity and accumulated mineralized matrix, indicating a mature osteoblastic phenotype.

CONCLUSIONS

Primary alveolar bone cells exhibited robust proliferation and retained osteogenic phenotype during in vitro expansion, suggesting that they can be used as an autologous cell source for bone regenerative therapies and various in vitro studies.

Human mesenchymal progenitor cells derived from alveolar bone and human bone marrow stromal cells: a comparative study

The aim of the present study was to evaluate the potential of intraoral harvested alveolar bone as an alternative source of multipotent mesenchymal stromal cells for future applications in oral and maxillofacial tissue engineering. Explant cultures were established from 20 alveolar bone samples harvested from the oblique line immediately before wisdom tooth removal. Morphology and proliferation characteristics of the in vitro expanded cells, referred to as human alveolar bone-derived cells (hABDCs), were studied using phase-contrast microscopy. Immunocytochemical analysis of their surface marker expression was conducted using monoclonal antibodies defining mesenchymal stromal cells. To evaluate their multilineage differentiation potential, hABDCs were induced to differentiate along the osteogenic, adipogenic, and chondrogenic lineage and compared to bone marrow mesenchymal stromal cells (hBMSCs) on mRNA and protein levels applying RT-PCR and cytochemical staining methods. hABDCs showed typical morphological characteristics comparable to those of hBMSCs such as being mononuclear, fibroblast-like, spindle-shaped, and plastic adherent. Immunophenotypically, cells were positive for CD105, CD90, and CD73 while negative for CD45, CD34, CD14, CD79α, and HLA-DR surface molecules, indicating an antigen expression pattern considered typical for multipotent mesenchymal stromal cells. As evidenced by RT-PCR and cytochemistry, hABDCs showed multilineage differentiation and similar chondrogenic and osteogenic differentiation potentials when compared to hBMSCs. Our findings demonstrate that human alveolar bone contains mesenchymal progenitor cells that can be isolated and expanded in vitro and are capable of trilineage differentiation, providing a reservoir of multipotent mesenchymal cells from an easily accessible tissue source.

Effects of directly autotransplanted tibial bone marrow aspirates on bone regeneration and osseointegration of dental implants

OBJECTIVES

Aim of the pilot trial was to evaluate applicability and effects of directly autotransplanted tibial bone marrow (BM) aspirates on the incorporation of porous bovine bone mineral in a sinus lift model and on the osseointegration of dental implants.

MATERIAL AND METHODS

Six edentulous patients with bilaterally severely resorbed maxillae requiring sinus augmentation and implant treatment were included. During surgery, tibial BM was harvested and added to bone substitute material (Bio-Oss(®) ) at the randomly selected test site. At control sites, augmentation was performed with Bio-Oss(®) alone. The cellular content of each BM aspirate was checked for multipotency and surface antigen expression as quality control. Histomorphometric analysis of biopsies from the augmented sites after 3 and 6 months (during implantation) was used to evaluate effects on bone regeneration. Osseointegration of implants was evaluated with Periotest(®) and radiographic means.

RESULTS

Multipotent cellular content in tibial BM aspirates was comparable to that in punctures from the iliac crest. No significant difference in amount of new bone formation and the integration of bone substitute particles was detected histomorphometrically. Periotest(®) values and radiographs showed successful osseointegration of inserted implants at all sites.

CONCLUSION

Directly autotransplanted tibial BM aspirates did not show beneficial regenerative effects in the small study population (N = 6) of the present pilot trial. However, the proximal tibia proved to be a potential donor site for small quantities of BM. Future trials should clarify whether concentration of tibial BM aspirates could effect higher regenerative potency.

Tri-lineage potential of intraoral tissue-derived mesenchymal stromal cells

The purpose of this study was to analyse the potential of intraoral tissues as a source of mesenchymal stromal and progenitor cells (MSPCs) for usage in future cell-based therapy models. Cells were isolated from four different tissues harvested during oral surgery intervention: (1) bone explants from the posterior maxilla, (2) bone explants from the oblique line, (3) from the mandibular periosteum, and (4) from the dental pulp. Donor sites and tissues were evaluated in terms of their accessibility, donor-site morbidity and average time period until appearance of MSPC colonies. Cell characterization was performed by flow cytometry and evaluation of in vitro osteogenic, adipogenic and chondrogenic differentiation potential. Adherent cell colonies were isolated from tissues from all sites after 4-8 days. The cells showed characteristics of MSPCs, so they were expanded up to clinical scales and demonstrated multipotency. The lowest donor-site morbidity was observed in the posterior maxilla harvests, while the highest donor-site morbidity was associated with harvests from mandibular sites. All sites seem to be potential sources of mesenchymal stromal and progenitor cells for tissue engineering approaches. Therefore, harvest morbidity and patient acceptance should affect the choice of the appropriate site.

Dose- and time-dependent effects of recombinant human bone morphogenetic protein-2 on the osteogenic and adipogenic potentials of alveolar bone-derived stromal cells

BACKGROUND AND OBJECTIVE

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a well-known growth factor that can induce robust bone formation, and recent studies have shown that rhBMP-2-induced osteogenesis is closely related to adipogenesis. The aim of the present study was to determine the dose- and time-dependent effects of rhBMP-2 on the osteogenic and adipogenic differentiation of human alveolar bone-derived stromal cells (hABCs) in vivo and in vitro.

MATERIAL AND METHODS

hABCs were isolated and cultured, and then transplanted using a carrier treated either with or without rhBMP-2 (100 μg/mL) into an ectopic subcutaneous mouse model. Comprehensive histologic and histometric analyses were performed after an 8-wk healing period. To further understand the dose-dependent (0, 10, 50, 200, 500 and 1000 ng/mL) and time-dependent (0, 3, 5, 7 and 14 d) effects of rhBMP-2 on osteogenic and adipogenic differentiation, in vitro osteogenic and adipogenic differentiation of hABCs were evaluated, and the expression of related mRNAs, including those for alkaline phosphatase, osteocalcin, bone sialoprotein, peroxisome-proliferator-activated receptor gamma-2 and lipoprotein lipase, were assessed using quantitative RT-PCR.

RESULTS

rhBMP-2 significantly promoted the osteogenic and adipogenic differentiation of hABCs in vivo, and gradually increased both the osteogenic and adipogenic potential in a dose- and time-dependent manner with minimal deviation in vitro. The expression of osteogenesis- and adipogenesis-associated mRNAs were concomitantly up-regulated by rhBMP-2.

CONCLUSION

The findings of the present study showed that rhBMP-2 significantly enhanced the adipogenic as well as the osteogenic potential of hABCs in dose- and time-dependent manner. The control of adipogenic differentiation of hABCs should be considered when regenerating the alveolar bone using rhBMP-2.

Behaviour of multipotent maxillary bone-derived cells on beta-tricalcium phosphate and highly porous bovine bone mineral

OBJECTIVES

The aim of this study was to test the applicability of multipotent maxillary cells (MMC) for cell therapy concepts and to evaluate their in vitro behaviour on two different bone substitutes.

MATERIAL AND METHODS

Cells isolated from maxillary bone from 10 donors were expanded using media containing human platelet lysate (HPL) replacing foetal bovine serum and differentiated towards both the osteogenic and the adipogenic lineage. Surface markers were determined by fluorescence-activated cell sorting analysis. Calcium deposits, alkaline phosphatase (ALP) and osteocalcin (OC) were used as biomarkers of osteogenic differentiation. Oil Red O was used to verify adipogenic differentiation. The osteogenic lineage and undifferentiated controls were further cultured on natural bone mineral of bovine origin (BioOss) and beta-tricalcium phosphate (Vitoss) scaffolds. Scaffold efficacy and cell migration were evaluated with live cell imaging.

RESULTS

Isolated cells presented characteristics of bone marrow (BM)-stromal cells and could easily be expanded to clinical scales. Cells expressed osteogenic and adipogenic markers when cultured with inductive media. There were no obvious differences in cell migration and growth behaviour between the two bone substitutes, but significantly higher OC expression was observed on BioOss scaffolds. Both osteogenically differentiated and undifferentiated cell lines expressed ALP activity on the scaffolds.

CONCLUSION

Isolated maxillary cells demonstrate multipotent in vitro characteristics comparable with those of BM-stromal cells. HPL can predictably be used for clinical-scale expansion of MMCs. Both grafting materials provide potential carrier characteristics when loaded with MMCs.

Localization of Thy-1-positive cells in the perichondrium during endochondral ossification

We elucidated the localization of Thy-1-positive cells in the perichondrium of fetal rat limb bones to clarify the distribution of osteogenic cells in the process of endochondral ossification. We also examined the formation of calcified bone-like matrices by isolated perichondrial cells in vitro. At embryonic day (E) 15.5, when the cartilage primodia were formed, immunoreactivity for Thy-1 was detected in cells of the perichondrium adjacent to the zone of hypertrophic chondrocytes. At E17.5, when the bone collar formation and the vascular invasion were initiated, fibroblast-like cells at the sites of vascular invasion, as well as in the perichondrium, showed Thy-1 labeling. Double immunostaining for Thy-1 and osterix revealed that Thy-1 was not expressed in the osterix-positive osteoblasts. Electron microscopic analysis revealed that Thy-1-positive cells in the zone of hypertrophic chondrocytes came in contact with blood vessels. Perichondrial cells isolated from limb bones showed alkaline phosphatase activity and formed calcified bone-like matrices after 4 weeks in osteogenic medium. RT-PCR demonstrated that Thy-1 expression decreased as calcified nodules formed. Conversely, the expression of osteogenic marker genes Runx2, osterix, and osteocalcin increased. These results indicate that Thy-1 is a good marker for characterizing osteoprogenitor cells.

Maxillofacial-derived stem cells regenerate critical mandibular bone defect

Stem cell-based bone tissue regeneration in the maxillofacial complex is a clinical necessity. Genetic engineering of mesenchymal stem cells (MSCs) to follow specific differentiation pathways may enhance the ability of these cells to regenerate and increase their clinical relevance. MSCs isolated from maxillofacial bone marrow (BM) are good candidates for tissue regeneration at sites of damage to the maxillofacial complex. In this study, we hypothesized that MSCs isolated from the maxillofacial complex can be engineered to overexpress the bone morphogenetic protein-2 gene and induce bone tissue regeneration in vivo. To demonstrate that the cells isolated from the maxillofacial complex were indeed MSCs, we performed a flow cytometry analysis, which revealed a high expression of mesenchyme-related markers and an absence of non-mesenchyme-related markers. In vitro, the MSCs were able to differentiate into osteogenic, chondrogenic, and adipogenic lineages. Gene delivery of the osteogenic gene BMP2 via an adenoviral vector revealed high expression levels of BMP2 protein that induced osteogenic differentiation of these cells in vitro and induced bone formation in an ectopic site in vivo. In addition, implantation of genetically engineered maxillofacial BM-derived MSCs into a mandibular defect led to regeneration of tissue at the site of the defect; this was confirmed by performing micro-computed tomography analysis. Histological analysis of the mandibles revealed osteogenic differentiation of implanted cells as well as bone tissue regeneration. We conclude that maxillofacial BM-derived MSCs can be genetically engineered to induce bone tissue regeneration in the maxillofacial complex and that this finding may be clinically relevant.

Homologous activated platelets stimulate differentiation and proliferation of primary human bone cells

In bone tissue engineering approaches the expansion of bone cells is an essential part. In recent years the search for an appropriate alternative to fetal bovine serum (FBS) in the ex vivo expansion process has increased. This study demonstrates that platelet-rich clot releasate (PRCR) could be an appropriate alternative. The effects of PRCR on bone cell cultures derived from 5 different human donors were analyzed with respect to morphology, proliferation, apoptosis and gene expression. Five different PRCR concentrations were used: 1, 5, 10, 20 and 40%. The population doubling (PD) values were calculated for each concentration. Light microscopy analysis was done after 3 and 9 days. Flow cytometry was used to analyze cell cycle effects. The gene expression of alkaline phosphatase, collagen type 1, osteocalcin, bone sialoprotein and osteopontin was analyzed with RT-PCR. 10% FBS cultures were used as controls. With 10% PRCR the cell morphology resembled the control cultures; however, the PD values were significantly higher (p < 0.01). Concentrations of 20 and 40% had a clear cytotoxic effect, observed with light microscopy analysis and flow cytometry. PRCR had a potent effect on the expression of osteogenic markers and resulted in a concentration-dependent upregulation. We demonstrate that human bone cells derived from the maxillary alveolar ridge can be cultured in medium containing PRCR instead of FBS. The addition of PRCR results in higher proliferative capacity and upregulation of osteogenic markers. These results indicate that FBS could be avoided in future tissue engineering approaches using bone cells from this anatomic site.