Porcine enamel matrix derivative enhances trabecular bone regeneration during wound healing of injured rat femur

Enamel matrix derivative does not affect osteoclast formation or bone resorption in cultures of mouse bone marrow macrophages or human monocytes

OBJECTIVE

Enamel matrix derivative (EMD) is widely used under the brand name Emdogain^® to promote periodontal regeneration in surgical treatment of periodontitis and peri-implantitis. The molecular mechanisms are unclear, but it has been proposed that EMD has stimulatory effects on the root cementum and periodontal ligament cells. Since dental implants lack these structures, we hypothesized that EMD-induced bone gain involve interactions with osteoclast precursor cells, with consequent inhibitory effect on osteoclast formation and/or activity. The aim was to evaluate this hypothesis.

MATERIAL AND METHODS

Primary mouse bone marrow macrophages (BMMs) and human peripheral blood monocytes were cultured in the presence of receptor activator nuclear factor-κB ligand (RANKL) to stimulate osteoclast formation. A purified Emdogain^® fraction was added to the cell cultures and the effect on number and size of newly formed osteoclasts were evaluated. In cultures on natural bone slices, bioanalytical methods were used to assay osteoclast number and bone resorption.

RESULTS

EMD had a negative effect on osteoclastogenesis in mouse cultures on plastic surface, whereas addition of EMD to osteoclast precursor cells on bone substrate did not affect osteoclast formation or bone resorption.

CONCLUSIONS

The results on natural bone matrix contradict a direct effect of EMD on osteoclast precursor cells.

Amelogenin-Derived Peptides in Bone Regeneration: A Systematic Review

Amelogenins are enamel matrix proteins currently used to treat bone defects in periodontal surgery. Recent studies have highlighted the relevance of amelogenin-derived peptides, named LRAP, TRAP, SP, and C11, in bone tissue engineering. Interestingly, these peptides seem to maintain or even improve the biological activity of the full-length protein, which has received attention in the field of bone regeneration. In this article, the authors combined a systematic and a narrative review. The former is focused on the existing scientific evidence on LRAP, TRAP, SP, and C11's ability to induce the production of mineralized extracellular matrix, while the latter is concentrated on the structure and function of amelogenin and amelogenin-derived peptides. Overall, the collected data suggest that LRAP and SP are able to induce stromal stem cell differentiation towards osteoblastic phenotypes; specifically, SP seems to be more reliable in bone regenerative approaches due to its osteoinduction and the absence of immunogenicity. However, even if some evidence is convincing, the limited number of studies and the scarcity of in vivo studies force us to wait for further investigations before drawing a solid final statement on the real potential of amelogenin-derived peptides in bone tissue engineering.

Effect of Enamel Matrix Derivatives on Osteoclast Formation from PBMC of Periodontitis Patients and Healthy Individuals after Interaction with Activated Endothelial Cells

Background and objectives: Enamel matrix derivative (EMD) is produced from developing porcine tooth buds and represents a complex of low-molecular-weight hydrophobic enamel proteins. EMD is widely applied in periodontal regeneration. Osteoclasts are multinuclear cells, which are responsible for bone resorption. The precursors of osteoclasts, hematopoietic cells, undergo in vivo the process of transendothelial migration before differentiation. EMD is known to affect the process of osteoclastogenesis, but its effect on human osteoclasts precursors after the interaction with activated endothelium was never studied. Materials and Methods: Human umbilical vein endothelial cells (HUVECs)s were seeded in transwell inserts with a pore size of 8 µm and pre-activated by TNF-α and IL-1β for 18 h. Peripheral blood mononuclear cells (PBMCs), freshly isolated from 16 periodontitis patients and 16 healthy individuals, were added to pre-activated HUVECs. Adherent, non-adherent and transmigrated cells were collected and differentiated to osteoclasts by the standard protocol in the presence or absence of EMD. The number of osteoclasts was determined by tartrate-resistant acid phosphatase staining. Results: PBMCs isolated from periodontitis patients have formed a significantly higher osteoclast number compared to PBMCs isolated from healthy individuals (p < 0.05). EMD induced concentration-dependent inhibition of osteoclast formation from PBMCs. This was true for the different PBMC fractions isolated from both healthy individuals and periodontitis patients. Conclusions: Our data show that EMD inhibits the formation and activity of osteoclasts differentiated from the progenitor cells after the interaction with activated endothelium. This might be associated with bone resorption inhibition and supporting bone regeneration in the frame of periodontal therapy.

Enamel matrix derivative in liquid form as adjunct to natural bovine bone grafting at buccal bone dehiscence defects at implant sites: An experimental study in beagle dogs

OBJECTIVES

To evaluate the effect of enamel matrix derivative in liquid form (EMD-liquid) as adjunct to grafting with natural bovine bone (NBB), on new bone formation and osseointegration in buccal dehiscence defects at dental implants.

MATERIAL AND METHODS

In six beagles, 3 months after extraction of the mandibular premolars and first molars. Three titanium implants (3.3 Ø × 8.0 mm) were inserted, and dehiscence-type defects (mesiodistal width 3 mm × 5 mm depth) were created on their buccal aspect. The defects were randomly assigned to one of the following three treatment groups: Group 1: NBB, Group 2: NBB/EMD-L, Group 3: Control. All sites were covered with a collagen membrane. Histomorphometric measurements were performed after 3 months of healing.

RESULTS

New bone area, bone-to-implant contact (BIC), and first BIC (fBIC) in the NBB and NBB/EMD-L groups were significantly greater than in the control group (p < .05). Further, f-BIC was at a significantly more coronal position in the NBB + EMD-liquid group (0.4 ± 0.1 mm) compared with the NBB group (1.2 ± 0.2 mm).

CONCLUSIONS

Natural bovine bone grafting enhances bone regeneration and osseointegration at implants with buccal bone dehiscences compared with no grafting, and adjunct use of EMD-liquid appears to further enhance bone formation and osseointegration.

Effect of Amelogenin Coating of a Nano-Modified Titanium Surface on Bioactivity

The interactions between implants and host tissues depend on several factors. In particular, a growing body of evidence has demonstrated that the surface texture of an implant influences the response of the surrounding cells. The purpose of this study is to develop new implant materials aiming at the regeneration of periodontal tissues as well as hard tissues by coating nano-modified titanium with amelogenin, which is one of the main proteins contained in Emdogain®. We confirmed by quartz crystal microbalance evaluation that amelogenin is easy to adsorb onto the nano-modified titanium surface as a coating. Scanning electron microscopy, scanning probe microscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy analyses confirmed that amelogenin coated the nano-modified titanium surface following alkali-treatment. In vitro evaluation using rat bone marrow and periodontal ligament cells revealed that the initial adhesion of both cell types and the induction of hard tissue differentiation such as cementum were improved by amelogenin coating. Additionally, the formation of new bone in implanted surrounding tissues was observed in in vivo evaluation using rat femurs. Together, these results suggest that this material may serve as a new implant material with the potential to play a major role in the advancement of clinical dentistry.

* Extracellular Matrices for Bone Regeneration: A Literature Review

The gold standard material for bone regeneration is still autologous bone, a mesenchymal tissue that consists mainly of extracellular matrix (ECM) (90% v/v) and little cellular content (10% v/v). However, the fact that decellularized allogenic bone grafts often present a clinical performance comparable to autologous bone grafts demonstrates the crucial role of ECM in bone regeneration. For long, the mechanism by which bone allografts function was not clear, but recent research has unveiled many unique characteristics of ECM that seem to play a key role in tissue regeneration. This is further confirmed by the fact that synthetic biomaterials with composition and properties resembling bone ECM present excellent bone regeneration properties. In this context, ECM molecules such as glycosaminoglycans (GAGs) and self-assembly peptides (SAPs) can improve the performance of bone regeneration biomaterials. Moreover, decellularized ECM derived either from native tissues such as bone, cartilage, skin, and tooth germs or from cells such as osteoblasts, chondrocytes, and stem cells has shown promising results in bone regeneration applications. Understanding the role of ECM in bone regeneration is crucial for the development of the next generation of biomaterials for bone tissue engineering. In this sense, this review addresses the state-of-the-art on this subject matter.

Are Cementoblasts a Subpopulation of Osteoblasts or a Unique Phenotype?

Experimental studies have shown a great potential for periodontal regeneration. The limitations of periodontal regeneration largely depend on the regenerative potential at the root surface. Cellular intrinsic fiber cementum (CIFC), so-called bone-like tissue, may form instead of the desired acellular extrinsic fiber cementum (AEFC), and the interfacial tissue bonding may be weak. The periodontal ligament harbors progenitor cells that can differentiate into periodontal ligament fibroblasts, osteoblasts, and cementoblasts, but their precise location is unknown. It is also not known whether osteoblasts and cementoblasts arise from a common precursor cell line, or whether distinct precursor cell lines exist. Thus, there is limited knowledge about how cell diversity evolves in the space between the developing root and the alveolar bone. This review supports the hypothesis that AEFC is a unique tissue, while CIFC and bone share some similarities. Morphologically, functionally, and biochemically, however, CIFC is distinctly different from any bone type. There are several lines of evidence to propose that cementoblasts that produce both AEFC and CIFC are unique phenotypes that are unrelated to osteoblasts. Cementum attachment protein appears to be cementum-specific, and the expression of two proteoglycans, fibromodulin and lumican, appears to be stronger in CIFC than in bone. A theory is presented that may help explain how cell diversity evolves in the periodontal ligament. It proposes that Hertwig’s epithelial root sheath and cells derived from it play an essential role in the development and maintenance of the periodontium. The role of enamel matrix proteins in cementoblast and osteoblast differentiation and their potential use for tissue engineering are discussed.

Osteogain improves osteoblast adhesion, proliferation and differentiation on a bovine-derived natural bone mineral

BACKGROUND

The use of enamel matrix derivative (EMD) has been shown to facilitate periodontal regeneration by histologically resulting in formation of cementum, periodontal ligament and bone. Recently, a new liquid carrier system for EMD has been introduced with better physicochemical properties specifically designed for bone graft mixing (Osteogain). The aim of this study was to investigate the combination of Osteogain with a bovine-derived natural bone mineral (NBM) on osteoblast migration, adhesion, proliferation and differentiation.

MATERIALS AND METHODS

Undifferentiated mouse ST2 stromal bone marrow cells were seeded onto 1)NBM particles alone or 2)NBM + Osteogain. Samples were compared for cell migration at 8 h, cell adhesion at 4 h, cell proliferation at 1, 3 and 5 days and real-time PCR at 3 and 14 days for genes encoding runt-related transcription factor 2 (Runx2), collagen1alpha2 (COL1a2), alkaline phosphatase (ALP) and osteocalcin (OCN). Furthermore, alizarin red staining was utilized to investigate the mineralization at 14 days.

RESULTS

Osteogain significantly upregulated cell adhesion over twofold onto NBM particles and promoted cell proliferation at 3 and 5 days after seeding. Furthermore, the combination of NBM with Osteogain significantly upregulated genes encoding Runx2, ALP, COL1a2 and OCN (from 1.5- to 3-fold) and increased alizarin red staining over 3 fold at 14 days when compared to NBM particles alone.

CONCLUSION

Pre-coating Osteogain onto NBM bone grafting particles significantly increased cell adhesion, proliferation and differentiation of osteoblasts in vitro. Future animal studies are now necessary to further investigate the regenerative potential of Osteogain in combination with a bone grafting material prior to clinical use for bone regeneration.

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.

Effects of enamel matrix proteins in combination with a bovine-derived natural bone mineral for the repair of bone defects

OBJECTIVES

Previously, the use of enamel matrix derivative (EMD) in combination with a natural bone mineral (NBM) was able to stimulate periodontal ligament cell and osteoblast proliferation and differentiation. Despite widespread use of EMD for periodontal applications, the effects of EMD on bone regeneration are not well understood. The aim of the present study was to test the ability of EMD on bone regeneration in a rat femur defect model in combination with NBM.

MATERIALS AND METHODS

Twenty-seven rats were treated with either NBM or NBM + EMD and assigned to histological analysis at 2, 4, and 8 weeks. Defect morphology and mineralized bone were assessed by μCT. For descriptive histology, hematoxylin and eosin staining and Safranin O staining were performed.

RESULTS

Significantly more newly formed trabecular bone was observed at 4 weeks around the NBM particles precoated with EMD when compared with NBM particles alone. The drilled control group, in contrast, achieved minimal bone regeneration at all three time points (P < 0.05).

CONCLUSIONS

The present results may suggest that EMD has the ability to enhance the speed of new bone formation when combined with NBM particles in rat osseous defects.

CLINICAL RELEVANCE

These findings may provide additional clinical support for the combination of EMD with bone graft for the repair of osseous and periodontal intrabony defects.

Evaluation of BMP-2 gene-activated muscle grafts for cranial defect repair

Large, osseous, segmental defects heal poorly. Muscle has a propensity to form bone when exposed to an osteogenic stimulus such as that provided by transfer and expression of cDNA encoding bone morphogenetic protein-2 (BMP-2). The present study evaluated the ability of genetically modified, autologous muscle to heal large cranial defects in rats. Autologous grafts (8 mm × 2 mm) were punched from the biceps femoris muscle and transduced intraoperatively with recombinant adenovirus vector containing human BMP-2 or green fluorescent protein cDNA. While the muscle biopsies were incubating with the vector, a central parietal 8 mm defect was surgically created in the calvarium of the same animal. The gene-activated muscle graft was then implanted into the cranial defect. After 8 weeks, crania were examined radiographically, histologically, and by micro-computed tomography and dual energy X-ray absorptiometry. Although none of the defects were completely healed in this time, muscle grafts expressing BMP-2 deposited more than twice as much new bone as controls. Histology confirmed the anatomical integrity of the newly formed bone, which was comparable in thickness and mineral density to the original cranial bone. This study confirms the in vivo osteogenic properties of genetically modified muscle and suggests novel strategies for healing bone.

The effect of an enamel matrix derivative (Emdogain) combined with bone ceramic on bone formation in mandibular defects: a histomorphometric and immunohistochemical study in the canine

Background. The purpose of this study was to evaluate the combination of an enamel matrix derivative (EMD) and an osteoconductive bone ceramic (BC) in improving bone regeneration. Materials and Methods. Four cylindrical cavities (6 × 6 mm) were prepared bilaterally in the mandible in three dogs. The defects were randomly assigned to four different treatments—filled with EMD/BC and covered with a nonresorbable membrane, filled with EMD/BC without membrane, membrane coverage only, or control (left untreated)—and healed for 2, 4, or 6 weeks. Harvested specimens were prepared for histologic, histomorphometric, and immunohistochemical analyses. Results. Sites treated with EMD/BC with or without membrane showed more total bone formation and lamellar bone formation than membrane-only and control defects. There were no statistically significant differences in total bone formation between EMD/BC with or without membrane. Conclusion. EMD with BC might improve bone formation in osseous defects more than membrane coverage alone; the use of a membrane had no significant additive effect on total bone formation.

One-step purification of recombinant human amelogenin and use of amelogenin as a fusion partner

Amelogenin is an extracellular protein first identified as a matrix component important for formation of dental enamel during tooth development. Lately, amelogenin has also been found to have positive effects on clinical important areas, such as treatment of periodontal defects, wound healing, and bone regeneration. Here we present a simple method for purification of recombinant human amelogenin expressed in Escherichia coli, based on the solubility properties of amelogenin. The method combines cell lysis with recovery/purification of the protein and generates a >95% pure amelogenin in one step using intact harvested cells as starting material. By using amelogenin as a fusion partner we could further demonstrate that the same method also be can explored to purify other target proteins/peptides in an effective manner. For instance, a fusion between the clinically used protein PTH (parathyroid hormone) and amelogenin was successfully expressed and purified, and the amelogenin part could be removed from PTH by using a site-specific protease.

Premature osteoblast clustering by enamel matrix proteins induces osteoblast differentiation through up-regulation of connexin 43 and N-cadherin

In recent years, enamel matrix derivative (EMD) has garnered much interest in the dental field for its apparent bioactivity that stimulates regeneration of periodontal tissues including periodontal ligament, cementum and alveolar bone. Despite its widespread use, the underlying cellular mechanisms remain unclear and an understanding of its biological interactions could identify new strategies for tissue engineering. Previous in vitro research has demonstrated that EMD promotes premature osteoblast clustering at early time points. The aim of the present study was to evaluate the influence of cell clustering on vital osteoblast cell-cell communication and adhesion molecules, connexin 43 (cx43) and N-cadherin (N-cad) as assessed by immunofluorescence imaging, real-time PCR and Western blot analysis. In addition, differentiation markers of osteoblasts were quantified using alkaline phosphatase, osteocalcin and von Kossa staining. EMD significantly increased the expression of connexin 43 and N-cadherin at early time points ranging from 2 to 5 days. Protein expression was localized to cell membranes when compared to control groups. Alkaline phosphatase activity was also significantly increased on EMD-coated samples at 3, 5 and 7 days post seeding. Interestingly, higher activity was localized to cell cluster regions. There was a 3 fold increase in osteocalcin and bone sialoprotein mRNA levels for osteoblasts cultured on EMD-coated culture dishes. Moreover, EMD significantly increased extracellular mineral deposition in cell clusters as assessed through von Kossa staining at 5, 7, 10 and 14 days post seeding. We conclude that EMD up-regulates the expression of vital osteoblast cell-cell communication and adhesion molecules, which enhances the differentiation and mineralization activity of osteoblasts. These findings provide further support for the clinical evidence that EMD increases the speed and quality of new bone formation in vivo.

Effects of enamel matrix derivative and transforming growth factor-β1 on human osteoblastic cells

BACKGROUND

Extracellular matrix proteins are key factors that influence the regenerative capacity of tissues. The objective of the present study was to evaluate the effects of enamel matrix derivative (EMD), TGF-β1, and the combination of both factors (EMD+TGF-β1) on human osteoblastic cell cultures.

METHODS

Cells were obtained from alveolar bone of three adult patients using enzymatic digestion. Effects of EMD, TGF-β1, or a combination of both were analyzed on cell proliferation, bone sialoprotein (BSP), osteopontin (OPN) and alkaline phosphatase (ALP) immunodetection, total protein synthesis, ALP activity and bone-like nodule formation.

RESULTS

All treatments significantly increased cell proliferation compared to the control group at 24 h and 4 days. At day 7, EMD group showed higher cell proliferation compared to TGF-β1, EMD + TGF-β1 and the control group. OPN was detected in the majority of the cells for all groups, whereas fluorescence intensities for ALP labeling were greater in the control than in treated groups; BSP was not detected in all groups. All treatments decreased ALP levels at 7 and 14 days and bone-like nodule formation at 21 days compared to the control group.

CONCLUSIONS

The exposure of human osteoblastic cells to EMD, TGF-β1 and the combination of factors in vitro supports the development of a less differentiated phenotype, with enhanced proliferative activity and total cell number, and reduced ALP activity levels and matrix mineralization.

Efficacy of the enamel matrix derivative to induce cementogenesis in vital and endodontically treated teeth with osseous dehiscence defects

This experiment assessed the efficacy of the enamel matrix derivative (EMD) to regenerate cementum in vital and endodontically treated teeth with osseous dehiscence defects. Five adult female beagle dogs were used. Thirty maxillary teeth (bilateral maxillary canines and second and fourth premolars) were randomly divided into two experimental groups (groups A and B, containing 12 teeth each) and one control group (group C). Endodontic treatment was only performed on teeth in group A compared with teeth in groups B and C. Buccal osseous dehiscence defects were surgically created in teeth from all groups. Teeth in the experimental group were treated with the EMD, whereas the controls were not. After 5 months, the animals were sacrificed and block sections of the teeth in experimental and control groups were processed for histological analysis. Newly regenerated cementum was observed in all teeth in groups A and B. No cementum regeneration was observed in group C. There was a significant difference in cementum generation between the experimental and control groups (P < 0.001). EMD therapy induces cementogenesis in vital and endodontically treated teeth with osseous dehiscence defects.

Effect of coating Straumann Bone Ceramic with Emdogain on mesenchymal stromal cell hard tissue formation

Periodontal tissue engineering requires a suitable biocompatible scaffold, cells with regenerative capacity, and instructional molecules. In this study, we investigated the capacity of Straumann Bone Ceramic coated with Straumann Emdogain, a clinical preparation of enamel matrix protein (EMP), to aid in hard tissue formation by post-natal mesenchymal stromal cells (MSCs) including bone marrow stromal cells (BMSCs) and periodontal ligament fibroblasts (PDLFs). MSCs were isolated and ex vivo-expanded from human bone marrow and periodontal ligament and, in culture, allowed to attach to Bone Ceramic in the presence or absence of Emdogain. Gene expression of bone-related proteins was investigated by real time RT-PCR for 72 h, and ectopic bone formation was assessed histologically in subcutaneous implants of Bone Ceramic containing MSCs with or without Emdogain in NOD/SCID mice. Alkaline phosphatase activity was also assessed in vitro, in the presence or absence of Emdogain. Collagen-I mRNA was up-regulated in both MSC populations over the 72-h time course with Emdogain. Expression of BMP-2 and the osteogenic transcription factor Cbfa-1 showed early stimulation in both MSC types after 24 h. In contrast, expression of BMP-4 was consistently down-regulated in both MSC types with Emdogain. Up-regulation of osteopontin and periostin mRNA was restricted to BMSCs, while higher levels of bone sialoprotein-II were observed in PDLFs with Emdogain. Furthermore, alkaline phosphatase activity levels were reduced in both BMSCs and PDLFs in the presence of Emdogain. Very little evidence was found for ectopic bone formation following subcutaneous implantation of MSCs with Emdogain-coated or -uncoated Bone Ceramic in NOD/SCID mice. The early up-regulation of several important bone-related genes suggests that Emdogain may have a significant stimulatory effect in the commitment of mesenchymal cells to osteogenic differentiation in vitro. While Emdogain inhibited AP activity and appeared not to induce ectopic bone formation, longer-term studies are required to determine whether it promotes the final stages of osteoblast formation and mineralization at gene and protein levels. While used in clinical applications, whether Emdogain and other commercial preparations of EMPs truly possess the capacity to induce the regeneration of bone or other components of the periodontium remains to be established.

The effect of enamel matrix derivative (Emdogain) on bone formation: a systematic review

This systematic review focused on the question, if and to what extent enamel matrix derivative (Emdogain) [EMD]) promotes the regeneration of bone. The influence of combinations with other biomaterials was additionally evaluated. Twenty histomorphometric studies were included in this systematic review. Main results of the reviewed articles were (i) guide tissue regeneration (GTR) of infrabony defects seems to result in a higher degree of bone regeneration compared to treatment with EMD; (ii) combined therapy (GTR + EMD) of infrabony defects might not lead to better results than GTR therapy alone; (iii) there seems to be no additional benefit of combined therapy (GTR + EMD) in furcation defects over GTR therapy alone; (iv) EMD seems to lead to more bone regeneration of infrabony defects compared to open flap debridement; (v) however, EMD application might result in more bone formation when applied in supporting defects compared to nonsupporting defects; and (vi) EMD does not seem to promote external jaw/parietal bone formation in the titanium capsule model. The results of one study that suggest that EMD increases the initial growth of trabecular bone around endosseous implants by new bone induction need to be confirmed by additional research.

Cell-free and cell-based approaches for bone regeneration

The clinical augmentation of bone currently involves the use of autogenous or allogeneic bone grafts and synthetic materials, all of which are associated with limitations. Research on the safe enhancement of bone formation concerns the potential value of scaffolds, stem cells, gene therapy, and chemical and mechanical signals. Optimal scaffolds are engineered to provide mechanical stability while supporting osteogenesis, osteoconduction and/or osteoinduction. Scaffold materials include natural or synthetic polymers, ceramics, and composites. The resorption, mechanical strength and efficacy of these materials can be manipulated through structural and chemical design parameters. Cell-seeded scaffolds contain stem cells or progenitor cells, such as culture-expanded marrow stromal cells and multipotent skeletal progenitor cells sourced from other tissues. Despite extensive evidence from proof-of-principle studies, bone tissue engineering has not translated to clinical practice. Much of the research involves in vitro and animal models that do not replicate potential clinical applications. Problem areas include cell sources and numbers, over-reliance on existing scaffold materials, optimum delivery of factors, control of transgene expression, vascularization, integration with host bone, and the capacity to form bone and marrow structures in vivo. Current thinking re-emphasizes the potential of biomimetic materials to stimulate, enhance, or control bone's innate regenerative capacity at the implantation site.

Enamel matrix proteins; old molecules for new applications

Emdogain (enamel matrix derivative, EMD) is well recognized in periodontology, where it is used as a local adjunct to periodontal surgery to stimulate regeneration of periodontal tissues lost to periodontal disease. The biological effect of EMD is through stimulation of local growth factor secretion and cytokine expression in the treated tissues, inducing a regenerative process that mimics odontogenesis. The major (>95%) component of EMD is Amelogenins (Amel). No other active components have so far been isolated from EMD, and several studies have shown that purified amelogenins can induce the same effect as the complete EMD. Amelogenins comprise a family of highly conserved extracellular matrix proteins derived from one gene. Amelogenin structure and function is evolutionary well conserved, suggesting a profound role in biomineralization and hard tissue formation. A special feature of amelogenins is that under physiological conditions the proteins self-assembles into nanospheres that constitute an extracellular matrix. In the body, this matrix is slowly digested by specific extracellular proteolytic enzymes (matrix metalloproteinase) in a controlled process, releasing bioactive peptides to the surrounding tissues for weeks after application. Based on clinical and experimental observations in periodontology indicating that amelogenins can have a significant positive influence on wound healing, bone formation and root resorption, several new applications for amelogenins have been suggested. New experiments now confirm that amelogenins have potential for being used also in the fields of endodontics, bone regeneration, implantology, traumatology, and wound care.

In vitro biologic response of human bone marrow stromal cells to enamel matrix derivative

BACKGROUND

In vitro investigations suggest that enamel matrix derivative (EMD) may affect the biologic response of periodontal-related cells, including osteoblasts and their precursors, the bone marrow stromal cells (BMSCs), which could play a crucial role in the regenerative process. In this study, we investigated the effects of EMD on human BMSCs.

METHODS

Primary cultures of BMSCs were obtained from bone marrow samples of healthy donors. Cell proliferation and osteogenic marker expression in response to serial dilutions of EMD (12.5, 25, and 50 microg/ml) were assessed. Cell growth was measured by 3H-thymidine incorporation and type I collagen synthesis by immunoblotting. Alkaline phosphatase (AP)-specific activity in the early phase (7 days), in vitro mineralization by von Kossa staining and calcium quantification, and osteocalcin levels at prolonged times (3 weeks) also were evaluated.

RESULTS

EMD stimulated BMSC growth in a dose-dependent manner. When EMD 50 microg/ml was followed over time, the highest proliferative effect was evident at 24 hours (3.4-fold of the control). Type I collagen level was significantly lower than the control after a 7-day incubation with EMD 50 microg/ml. AP activity was reduced in a dose-dependent manner down to 55% of the control. Also, the extracellular matrix mineralization decreased in EMD-treated cells with respect to the control, whereas only a slight, not significant, decrease in osteocalcin levels was found.

CONCLUSIONS

EMD significantly increased BMSC growth and simultaneously decreased their osteogenic differentiation. The clinical efficacy of EMD in regenerating periodontal tissues can be attributed, in part, to the biologic effects exerted on the bone marrow stromal component of resident cells.

The effect of EmdogainR on the growth and differentiation of rat bone marrow cells

BACKGROUND AND OBJECTIVE

The major extracellular matrix (ECM) proteins in developing enamel can induce and maintain the formation and mineralization of other skeletal hard tissue, such as bone. Therefore, dental matrix proteins are ideal therapeutic agents when direct formation of functional bone is required for a successful clinical outcome. Emdogain (EMD) consists of enamel matrix proteins which are known to stimulate bone formation. However, only a few studies in the literature have reported the effect of EMD on osteoblast-like cells in vitro.

MATERIAL AND METHODS

In this study, rat bone marrow cells, obtained from the femora of Wistar rats, were precultured for 7 d in osteogenic medium. Then, the cells were harvested and seeded in 24-well plates at a concentration of 20,000 cells/well. The wells were either precoated with 100 microg/ml EMD, or left uncoated. The seeded cells were cultured in osteogenic medium for 32 d and analysed for cell attachment (by using the Live and Dead assay), cell growth (by determining DNA content) and cell differentiation (by measuring alkaline phosphatase activity and calcium content, and by using scanning electron microscopy and the reverse transcription-polymerase chain reaction).

RESULTS

The results showed that at the 4-h time point of the experiment, more cells were attached to EMD-negative wells, but this effect was no longer apparent at 24 h. DNA analysis revealed that both groups showed a similar linear trend of cell growth. No differences in alkaline phosphatase activity or calcium content were observed, and no differences in gene expression (osteocalcin, alkaline phosphatase and collagen type I) were found between the groups.

CONCLUSION

Based on our results, we conclude that EMD had no significant effect on the cell growth and differentiation of rat bone marrow cells.

Histidine tag fusion increases expression levels of active recombinant amelogenin in Escherichia coli

Amelogenin is a dental enamel matrix protein involved in formation of dental enamel. In this study, we have expressed two different recombinant murine amelogenins in Escherichia coli: the untagged rM179, and the histidine tagged rp(H)M180, identical to rM179 except that it carries the additional N-terminal sequence MRGSHHHHHHGS. The effects of the histidine tag on expression levels, and on growth properties of the amelogenin expressing cells were studied. Purification of a crude protein extract containing rp(H)M180 was also carried out using IMAC and reverse-phase HPLC. The results of this study showed clearly that both growth properties and amelogenin expression levels were improved for E. coli cells expressing the histidine tagged amelogenin rp(H)M180, compared to cells expressing the untagged amelogenin rM179. The positive effect of the histidine tag on amelogenin expression is proposed to be due to the hydrophilic nature of the histidine tag, generating a more hydrophilic amelogenin, which is more compatible with the host cell. Human osteoblasts treated with the purified rp(H)M180 showed increased levels of secreted osteocalcin, compared to untreated cells. This response was similar to cells treated with enamel matrix derivate, mainly composed by amelogenin, suggesting that the recombinant protein is biologically active. Thus, the histidine tag favors expression and purification of biologically active recombinant amelogenin.

An Amelogenin Minigene to Study Alternative Splicing

Diversity in gene expression is commonly observed as a result of alternative splicing of RNA transcripts. This is true in the case of amelogenin, one of the enamel matrix proteins. Our hypothesis is that additional amelogenin mRNA transcripts are generated in vivo, but these transcripts have yet to be observed because of the limitations of currently used detection methodologies. For this study our objective was to create an amelogenin minigene to study amelogenin RNA splicing events in cell lines of diverse character. Mouse genomic DNA was used as a PCR template to amplify the amelogenin DNA sequence spanning exons 2-7. The resulting PCR-generated DNA was subcloned in an expression vector. This resulting amelogenin minigene was shown to be functionally active by transfection into multiple cell lines. We have successfully cloned an amelogenin minigene, and as a result we describe and discuss novel amelogenin alternatively spliced transcripts.

Apatite/amelogenin coating on titanium promotes osteogenic gene expression

Osteoblast differentiation and extracellular matrix production are pivotal processes for implant osseointegration or bone tissue engineering. We hypothesized that a biomimetic coating on titanium surfaces, consisting of apatite and amelogenin, would promote such processes. Human Embryonic Palatal Mesenchymal pre-osteoblasts were used as a model for the evaluation of cell adhesion and spreading patterns, as well as mRNA expression of certain osteoblastic gene products. Real-time PCR showed significant (p < 0.05) increase in expression of type I collagen, alkaline phosphatase, and osteocalcin from cells grown on titanium with an apatite/amelogenin composite, as compared with that from cells grown on a pure titanium or apatite coating only. Osteocalcin expression was specifically stimulated by amelogenin added to the culture media. Enhanced attachment and cell spreading were also observed. The biomimetic coating promoting cell adhesion and osteoblast differentiation may have great potential for future dental and biomedical applications.

Profiling of differentially expressed genes in wound margin biopsies of horses using suppression subtractive hybridization

Disturbed gene expression may disrupt the normal process of repair and lead to pathological situations resulting in excessive scarring. To prevent and treat impaired healing, it is necessary to first define baseline gene expression during normal repair. The objective of this study was to compare gene expression in normal intact skin (IS) and wound margin (WM) biopsies using suppression subtractive hybridization (SSH) to identify genes differentially expressed during wound repair in horses. Tissue samples included both normal IS and biopsies from 7-day-old wounds. IS cDNAs were subtracted from WM cDNAs to establish a subtracted (WM-IS) cDNA library; 226 nonredundant cDNAs were identified. Detection of genes previously shown to be expressed 7 days after trauma, including the pro-α2-chain of type 1 pro-collagen (COL1A2), annexin A2, the pro-α3-chain of type 6 pro-collagen, β-actin, fibroblast growth factor 7, laminin receptor 1, matrix metalloproteinase 1 (MMP1), secreted protein acidic cystein rich, and tissue inhibitor of metalloproteinase 2, supported the validity of the experimental design. A RT-PCR assay confirmed an increase or induction of the cDNAs of specific genes (COL1A2, MMP1, dermatan sulfate proteoglycan 2, cluster differentiation 68, cluster differentiation 163, and disintegrin and metalloproteinase domain 9) within wound biopsies. Among these, COL1A2 and MMP1 had previously been documented in horses; 68.8% of the cDNAs had not previously been attributed a role during wound repair, of which spermidine/spermine- N-acetyltransferase, serin proteinase inhibitor B10, and sorting nexin 9 were highly expressed and whose known functions in other processes made them potential candidates in regulating the proliferative response to wounding. In conclusion, we identified novel genes that are differentially expressed in equine wound biopsies and that may modulate repair. Future experiments must correlate changes in mRNA levels for precise molecules with spatiotemporal protein expression within tissues.

Effects of enamel matrix proteins on tissue formation along the roots of human teeth

OBJECTIVE

Enamel matrix-derived proteins (EMD) are thought to trigger the formation of acellular extrinsic fibre cementum (AEFC), while other reports indicate that EMD may have osteogenic potential. The aim of the present study was to characterize the tissues developing on the root surface following application of EMD.

METHODS

Twelve human periodontitis-affected teeth, scheduled for extraction, were treated with EMD. Two to 6 weeks later, the teeth were extracted, demineralized and processed for embedding in acrylic and epoxy resins. New tissue formation was analysed by light and transmission electron microscopy.

RESULTS

New tissue formation on the root was observed in the notch and on both scaled and unscaled root surfaces distant of the notch area in six defects. The newly formed tissues on the root were thick, collagenous, devoid of extrinsic fibres, and had an irregular surface contour. The presence of electron-dense, organic material in the collagenous matrix indicated at least partial mineralization. Embedded cells were numerous and the cells on the matrix surface were very large in size. Abundant rough endoplasmic reticulum and a prominent Golgi complex were evident. The presence of a split between the treated root surfaces and the newly formed tissue was a common observation, as was the presence of bacteria and host cells in the interfacial gap.

CONCLUSION

Following treatment with EMD, a bone-like tissue resembling cellular intrinsic fibre cementum may develop on the root surfaces, instead of AEFC. Furthermore, EMD may both induce de novo formation of a mineralized connective tissue on scaled root surfaces and stimulate matrix deposition on old native cementum. Interfacial bonding appeared to be weak after 6 weeks of healing.

Osteogenic Potential of Primed Periosteum Graft in the Rat Calvarial Model

Repair of bone defects remains a major concern in plastic and maxillofacial surgery. Based on modern concepts of tissue engineering, periosteum has gained attention as a suitable osteogenic material. We tested the hypothesis that surgically released and immediately repositioned periosteum would exhibit high osteogenic capacity upon grafting in a rat calvarial defect. Seven days after periosteum was released from the tibia and immediately repositioned, the "primed periosteum graft" (PPG; n = 15) was placed into a critical-sized defect of rat calvaria and the process of bone formation was evaluated histologically, immunohistologically, and radiographically at 7, 14, and 21 days after grafting. Findings were compared with a nonprimed periosteal graft (NPG; n = 15). Endochondral ossification was observed in both the PPG and NPG. The PPG showed higher expression of proliferative cell nuclear antigen, bone morphogenetic protein, and vascular endothelial growth factor than the NPG. Three-dimensional radiographic examination revealed significantly increased bone formation in the PPG than in the NPG (P < 0.01). These findings suggested that surgical stimulation of the periosteum enhanced the osteogenic potential of periosteal cells. This method may be suitable for the clinical repair of bone defects.

The use of enamel matrix derivative in the treatment of periodontal defects: a literature review and meta-analysis

BACKGROUND

Periodontal disease results in the loss of the attachment apparatus. In the last three decades, an increasing effort has been placed on seeking procedures and materials to promote the regeneration of this tissue. The aim of this paper is to evaluate the effect of enamel matrix derivative (EMD) during regenerative procedures. In addition, a meta-analysis is presented regarding the clinical results during regeneration with EMD, to gain evidence as to what can be accomplished following treatment of intrabony defects with EMD in terms of probing depth reduction, clinical attachment level gain, defect fill (using re-entry studies), and radiographic parameters.

METHODS

The review includes in vitro and in vivo studies as well as human case reports, clinical comparative trials, and histologic findings. In addition, a meta-analysis is presented regarding the regenerative clinical results. For this purpose, we used 28 studies-including 955 intrabony defects treated with EMD that presented baseline and final data on probing depth, clinical attachment level (CAL) gain, or bone gain-to calculate weighted mean changes in the different parameters. The selected studies were pooled from the MEDLINE database at the end of May, 2003.

RESULTS

The meta-analysis of intrabony defects treated with EMD resulted in a mean initial probing depth of 7.94 +/- 0.05 mm that was reduced to 3.63 +/- 0.04 mm (p = 0.000). The mean clinical attachment level changed from 9.4 +/- 0.06 mm to 5.82 +/- 0.07 mm (p = 0.000). These results were significantly better than the results obtained for either open-flap debridement (OFD) or guided tissue regeneration (GTR). In contrast, histologically, GTR is more predictable than EMD in terms of bone and cementum formation. No advantage was found for combining EMD and GTR. Xenograft, or EMD and xenograft, yielded inferior results compared with EMD alone, but a limited number of studies evaluated this issue. Promising results were noted for the combination of allograft materials and EMD.

CONCLUSIONS

EMD seems to be safe, was able to regenerate lost periodontal tissues in previously diseased sites based on clinical parameters, and was better than OFD or GTR. Its combination with allograft materials may be of additional benefit but still needs to be further investigated.

In vitro effects of enamel matrix proteins on rat bone marrow cells and gingival fibroblasts

Emdogain (EMD), a formulation of Enamel Matrix Proteins (EMP), is used clinically for periodontal regeneration, where it stimulates cementum formation and promotes gingival healing. In this study, we investigated the in vitro effects of EMD on rat bone marrow stromal cells (BMSC) and gingival fibroblasts (GF). EMD (at 25 micro g/mL) increased the osteogenic capacity of bone marrow, as evidenced by approximately three-fold increase in BMSC cell number and approximately two-fold increase in alkaline phosphatase (ALP) activity and mineralized nodule formation. The presence of EMD in the initial stages (first 48 hrs) of the culture was crucial for this effect. In contrast, EMD did not induce osteoblastic differentiation of GF (evidenced by lack of mineralization or ALP activity) but increased up to two-fold both their number and the amount of matrix produced. These in vitro data on BMSC and GF could explain the promotive effect of EMD on bone formation and connective tissue regeneration, respectively.

Effects of enamel matrix derivative on proliferation and differentiation of primary osteoblasts

OBJECTIVE

The aim of this study was to investigate the effects of enamel matrix derivative (EMD) on proliferation, protein synthesis, and mineralization in primary mouse osteoblasts.

STUDY DESIGN

Osteoblasts were obtained from mouse calvaria by enzymatic digestion and grown in monolayer together with EMD (2-100 microg/ml). Metabolic activity and cell proliferation were determined by tetrazolium salt assay (MTT) and by 5-bromo-2'-deoxyuridine (BrdU) incorporation. For differentiation studies, a 3-dimensional organoid culture system was used. Osteoblastic differentiation was estimated by alkaline phosphatase (ALP) activity and calcium content. Collagen synthesis was assessed by [(3)H]-proline incorporation. Morphologic observations were made by electron microscopy.

RESULTS

EMD treatments increased metabolic cell activity and BrdU incorporation. In the organoid cultures, ALP activity and calcium accumulation were enhanced by EMD treatment, but [(3)H]-proline incorporation was not. Morphologically, an increased deposition of mineralized nodules was found.

CONCLUSIONS

EMD treatment enhanced cellular activities of primary osteoblasts and might support the regeneration of periodontal bony defects.

Emdogain promotes osteoblast proliferation and differentiation and stimulates osteoprotegerin expression

PURPOSE

The purpose of this study was to investigate the effects of EMD on the growth and differentiation of osteoblastic cells (MC3T3-E1) and on the expression of osteoprotegerin (OPG), a key cytokine that inhibits osteoclastogenesis and osteoclast function.

STUDY DESIGN

MC3T3-E1 cells were treated with 100 microg/mL EMD in serum-free medium for 1, 2, 3, 5, and 7 days, or in 2% fetal bovine serum (FBS) for 3 weeks. Cells incubated without EMD served as negative control. At the end of each incubation period, cell numbers were counted and total cellular mRNA was extracted. Northern blot analysis and RT-PCR were performed to determine the mRNA levels of core binding factor alpha (Cbfa1), collagen alpha1 (I), bone sialoprotein (BSP), osteocalcin (OC), insulin-like growth factor I (IGF-I), and OPG. Alkaline phosphatase (ALP) activity was also determined and compared between treatment and control groups.

RESULTS

A marked increase in cell numbers was observed in EMD-treated groups from day 2 to day 7 (P < .01). mRNA expression of collagen alpha1 (I), BSP, OC, OPG, and IGF-I were up-regulated in cells treated with EMD. ALP activity was significantly increased by EMD treatment after 3-week culture under differentiating conditions (P < .05). The expression of Cbfa1 was not affected by EMD treatment from day 1 to day 5; the levels were elevated after culturing for 3 weeks in EMD-treated cells.

CONCLUSIONS

EMD promotes both proliferation and differentiation of MC3T3-E1 cells and indirectly inhibits osteoclastogenesis and osteoclast function by stimulating the expression of OPG.

The effects of enamel matrix derivative (EMD) on osteoblastic cells in culture and bone regeneration in a rat skull defect

OBJECTIVE

Enamel matrix derivative (EMD) has been clinically used to promote periodontal tissue regeneration. The purpose of the present study is to clarify EMD affects on osteoblastic cells and bone regeneration.

MATERIALS AND METHODS

Mouse osteoblastic cells (ST2 cells and KUSA/A1 cells) are used in culture experiments. After cells were treated with EMD, cell growth was evaluated with DNA measurement, 5-bromo-2'-deoxyurydine (BrdU) incorporation assay. Measurement of alkaline phosphatase (ALP) activity and mineralized-nodule (MN) formation, Northern blotting analysis and zymography are also performed. In addition, EMD was applied to a rat skull defect and the defect was radiographically and histologically evaluated 2 weeks after the application.

RESULTS

EMD did not stimulate ST2 cell growth; however, it enhanced KUSA/A1 cell proliferation. Although EMD stimulated ALP activity in both the cells, ALP activity in KUSA/A1 cells was affected to a much greater degree. Corresponding to the increase in ALP activity, MN formation in KUSA/A1 cells was enhanced by EMD. EMD stimulated osteoblastic phenotype expression of KUSA/A1 cells such as type I collagen, osteopontin, transforming growth factor beta 1 and osteocalcin. EMD treatment also stimulated matrix metalloproteinase production in KUSA/A1 cells. Although the effects of EMD on osteoblastic cells depend on cell type, the overall effect of EMD on osteoblastic cells is stimulatory rather than inhibitory. Finally, EMD application to a rat skull defect accelerated new bone formation.

CONCLUSION

These results indicate that EMD affects osteoblastic cells and has potential as a therapeutic material for bone healing.