The bone-regenerative properties of Emdogain adsorbed onto poly(D,L-lactic-coglycolic acid)/calcium phosphate composites in an ectopic and an orthotopic rat model.

BACKGROUND AND OBJECTIVE: The aim of this study was to evaluate the bone-regenerative properties of Emdogain in osseous and nonosseous sites. MATERIAL AND METHODS: For the orthotopic study, unloaded poly(D,L-lactic-coglycolic acid)/calcium phosphate implants, and poly(D,L-lactic-coglycolic acid)/calcium phosphate implants loaded with different concentrations (0.25, 0.50 or 0.80 mg per implant) of enamel matrix derivative (EMD), were inserted into cranial defects of 24 rats. The implantation time was 4 wk. For the ectopic study, 32 implants were placed subcutaneously. The same study period and groups as in the orthotopic study were used. Methods of evaluation consisted of descriptive histology, histomorphometry and an in vitro EMD-release study. RESULTS: In the orthotopic study, new bone formation was most abundant in unloaded implants followed by 0.50-mg EMD composites. Histomorphometric measurements showed 54 +/- 15.0% bone ingrowth for unloaded implants, 19 +/- 22.5% bone ingrowth for 0.25-mg EMD composites, 40 +/- 23.6% bone ingrowth for 0.50-mg EMD composites and 26 +/- 17.6% bone ingrowth for 0.80-mg EMD composites. Light microscopic analysis of the subcutaneous sections from the ectopic study revealed no bone formation in any group after 4 wk. The in vitro release study showed 60% cumulative EMD release after 4 wk. CONCLUSION: Emdogain is not osteoinductive and is not able to enhance bone healing in combination with an osteoconductive material, such as poly(D,L-lactic-coglycolic acid)/calcium phosphate cement.

Influence of RGD-loaded titanium implants on bone formation in vivo.

Little is known about the ability of peptide-coated surfaces to influence cell responses in vivo. Many studies have demonstrated that peptide-modified surfaces influence cell responses in vitro. Integrins, which bind specifically short peptide sequences, are responsible for these cell responses. In this way, information can be transmitted to the nucleus through several cytoplasmic signaling pathways. The peptide sequence Arg-Gly-Asp (RGD peptide) plays an important role in osteoblast adhesion. The present study was designed to investigate new bone formation in a porous titanium (Ti) fiber mesh implant, which was coated with cyclic RGD peptide. The RGD-Ti implants were inserted into the cranium of a rabbit and were compared with porous titanium fiber mesh disks without RGD sequence (Ti) and with an open control defect. Histologic and histomorphometric examinations were performed 2, 4, and 8 weeks postoperatively. A significant increase in bone formation, or bone ingrowth, was seen in the RGD-Ti group compared with the Ti group after 4 and 8 weeks. All control defects stayed open in all three periods. It was concluded that the use of cyclic RGD peptide in combination with titanium fiber mesh has a positive effect on bone formation in vivo in a rabbit animal model.

Osteoblast differentiation of bone marrow stromal cells cultured on silica gel and sol-gel-derived titania.

Primary cultures of osteogenic precursor cells derived from rat bone marrow stroma were performed on commercially available pure titanium discs (Ti c.p.) and surface modified Ti c.p.using a sol-gel technique (Ti sol). In separate repeated experimental runs, cell behavior and in vitro mineralization were compared with cultures on silica gel bioactive glass discs (S53P4). All substrates were incubated in simulated body fluid prior to the experiment. Overall, variable effects between experimental runs were seen. Apparently, this was due to the heterogeneous nature of the used cell population. Therefore, only careful conclusions can be made. Initial cell adhesion and growth rates between 3 and 5 days of culture--analyzed by cell numbers--were in general comparable for the two titanium substrates, while initial growth up to day 3 is suggested to be higher in Ti c.p. compared to Ti sol. Although initial cell adhesion on the S53P4 glass discs was lower than the titanium substrates, cell growth rates appeared to be higher on the silica gel compared to the two titanium substrates. Further, there were some indications that the early and late osteoblast differentiation markers, alkaline phosphatase and osteocalcin, monitored up to day 24, were elevated in Ti c.p cultures compared to Ti sol cultures. There were no differences observed in in vitro mineralization between the titanium groups. S53P4 seemed to display a substantially higher differentiating capacity for both osteogenic cell markers as well as in vitro mineralization compared to the two titanium substrates.

Bone formation in CaP-coated and noncoated titanium fiber mesh.

The osteogenic activity of calcium phosphate (CaP)-coated and noncoated porous titanium (Ti) fiber mesh loaded with cultured syngeneic osteogenic cells after prolonged in situ culturing was compared in a syngeneic rat ectopic assay model. Rat bone marrow (RBM) cells were loaded onto the CaP-coated and noncoated Ti scaffolds using either a droplet or a suspension loading method. After loading, the RBM cells were cultured for 8 days in vitro. Thereafter, implants were subcutaneously placed in 39 syngeneic rats. The rats were euthanized and the implants retrieved at 2, 4, and 8 weeks postoperatively. Further, in the 8 week group fluorochrome bone markers were injected at 2, 4, and 6 weeks. Histological analysis demonstrated that only the CaP-coated meshes supported bone formation. The amount of newly formed bone varied between single and multiple spheres to filling a significant part of the mesh porosity. In the newly formed bone, osteocytes embedded in a mineralized matrix could be observed clearly. On the other hand, in the noncoated titanium implants, abundant deposition of calcium-containing material was seen. This deposit lacked a bonelike tissue organization. Further analysis revealed that the cell-loading method did not influence the final amount of bone formation. In CaP-coated implants the accumulation sequence of the fluorochrome markers showed that bone formation started on the mesh fibers. In conclusion, our results prove that the combination of a thin CaP coating, Ti-mesh, and RBM cells can indeed generate ectopic bone formation after prolonged in vitro culturing. No effect of the loading method was observed on the final amount of bone.

Bone regenerative properties of rat, goat and human platelet-rich plasma.

To explore the reported contradictory osteogenic capacity of platelet-rich plasma (PRP), the aim of the study was to examine and compare the bone regenerative effect of: PRPs of different species (rat, goat, human); human bone graft (HB) vs. HB combined with human PRP (HB+hPRP); and HB+hPRP vs. synthetic hydroxyapatite-tricalcium phosphate bone substitute combined with hPRP (HA/TCP+hPRP). For this purpose, 72 implants, divided into 6 groups (n=6) were inserted in critical-sized defects of immunodeficient rats. After 2 and 4 weeks, descriptive and quantitative histological, and micro-CT analyses were performed on the specimens. Rat and goat PRP combined with HA/TCP did not enhance bone regeneration compared with HA/TCP. In contrast, human PRP combined with HA/TCP resulted in significantly increased bone fill compared to HA/TCP. The addition of human PRP to human bone graft increased significantly the amount of newly formed bone after 2 weeks. HB+hPRP demonstrated enhanced bone healing compared to HA/TCP+hPRP. In conclusion, rat and goat PRP had no effect on bone formation. Human PRP improved the initial osteogenic response of human bone graft. Human PRP combined with human bone graft had better osteogenic capacity than human PRP combined with synthetic bone substitute.

The behavior of osteoblast-like cells on various substrates with functional blocking of integrin-beta1 and integrin-beta3.

This study was designed to examine the influence of integrin subunit-beta1 and subunit-beta3 on the behavior of primary osteoblast-like cells, cultured on calcium phosphate (CaP)-coated and non coated titanium (Ti). Osteoblast-like cells were incubated with specific monoclonal antibodies against integrin-beta1 and integrin-beta3 to block the integrin function. Subsequently, cells were seeded on Ti discs, either non coated or provided with a 2 microm carbonated hydroxyapatite coating using Electrostatic Spray Deposition. Results showed that on CaP coatings, cellular attachment was decreased after a pre-treatment with either anti-integrin-beta1 or anti-integrin-beta3 antibodies. On Ti, cell adhesion was only slightly affected after a pre-treatment with anti-integrin-beta3 antibodies. Scanning electron microscopy showed that on both types of substrate, cellular morphology was not changed after a pre-treatment with either antibody. With quantitative PCR, it was shown for both substrates that mRNA expression of integrin-beta1 was increased after a pre-treatment with either anti-integrin-beta1 or anti-integrin-beta3 antibodies. Furthermore, after a pre-treatment with either antibody, mRNA expression of integrin-beta3 and ALP was decreased, on both types of substrate. In conclusion, osteoblast-like cells have the ability to compensate to great extent for the blocking strategy as applied here. Still, integrin-beta1 and beta3 seem to play different roles in attachment, proliferation, and differentiation of osteoblast-like cells, and responses on CaP-coated substrates differ to non coated Ti. Furthermore, the influence on ALP expression suggests involvement of both integrin subunits in signal transduction for cellular differentiation.

The effect of Emdogain 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.

The plasmid-encoded signal peptidase SipP can functionally replace the major signal peptidases SipS and SipT of Bacillus subtilis.

The gram-positive eubacterium Bacillus subtilis is the organism with the largest number of paralogous type I signal peptidases (SPases) known. These are specified both by chromosomal and plasmid-borne genes. The chromosomally encoded SPases SipS and SipT have a major function in precursor processing, and cells depleted of SipS and SipT stop growing and die. In this study, we show that the SPase SipP, specified by the B. subtilis plasmid pTA1015, can functionally replace SipS and SipT, unlike the three chromosomally encoded SPases with a minor function in protein secretion (i.e., SipU, SipV, and SipW). Unexpectedly, SipP is not specifically required for the processing and secretion of Orf1p, which is specified by a gene that is cotranscribed with sipP. These two genes form a conserved structural module of rolling-circle plasmids from B. subtilis. As previously shown for the chromosomal sipS and sipT genes, the transcription of plasmid-borne copies of sipP is temporally controlled, reaching maximal levels during the post-exponential growth phase when the cells secrete proteins at high levels. However, increased transcription of sipP starts at the end of exponential growth, about 2 h earlier than that of sipS and sipT. These data suggest that SipP fulfills a general role in the secretory precursor processing of pTA1015-containing cells.