Bone induction in subcutaneous tissue in rats by a newly developed DNA-coated atelocollagen and bone morphogenetic protein

The Use of Tooth Particles as a Biomaterial in Post-Extraction Sockets. Experimental Study in Dogs

Objectives: The objective of this study was to evaluate new bone formation derived from freshly crushed extracted teeth, grafted immediately in post-extraction sites in an animal model, compared with sites without graft filling, evaluated at 30 and 90 days. Material and Methods: The bilateral premolars P2, P3, P4 and the first mandibular molar were extracted atraumatically from six Beagle dogs. The clean, dry teeth were ground immediately using the Smart Dentin Grinder. The tooth particles obtained were subsequently sieved through a special sorting filter into two compartments; the upper container isolating particles over 1200 μm, the lower container isolated particles over 300 μm. The crushed teeth were grafted into the post-extraction sockets at P3, P4 and M1 (test group) (larger and smaller post-extraction alveoli), while P2 sites were left unfilled and acted as a control group. Tissue healing and bone formation were evaluated by histological and histomorphometric analysis after 30 and 90 days. Results: At 30 days, test site bone formation was greater in the test group than the control group (p < 0.05); less immature bone was observed in the test group (25.71%) than the control group (55.98%). At 90 days, significant differences in bone formation were found with more in the test group than the control group. No significant differences were found in new bone formation when comparing the small and large alveoli post-extraction sites. Conclusions: Tooth particles extracted from dog’s teeth, grafted immediately after extractions can be considered a suitable biomaterial for socket preservation.

Pharmacokinetics and bone formation by BMP-2 entrapped in polyethylenimine-coated albumin nanoparticles

The osteoinductive growth factor, bone morphogenetic protein-2 (BMP-2), is capable of inducing de novo bone formation after implantation. A nanoparticulate (NP) system was developed for BMP-2 delivery based on NPs fabricated from bovine serum albumin (BSA) and stabilized by polyethylenimine (PEI) coating. In this study, the pharmacokinetics and osteoinductivity of BMP-2 delivered with different BSA NP formulations were determined by subcutaneous implantation in rats. A 7-day pharmacokinetics study showed that PEI coating on NPs effectively reduced the initial burst release of BMP-2 and prolonged the BMP-2 retention at implantation site. However, the uncoated BMP-2 NPs (BMP-2 loading of 1.44% w/w) were able to induce a robust ectopic bone formation, while no bone formation was found by the BMP-2 NPs coated with PEI. The toxicity of the PEI used for NP coating was determined to be the reason for lack of osteoinduction. Increasing BMP-2 loading (up to 5.76% w/w) was then employed to formulate NPs with lower PEI content; the higher BMP-2 loading was found to better promote induction of de novo bone. Our findings indicated that PEI coating on BSA NPs was effective for controlling BMP-2 release from NPs, but the toxicity of cationic PEI was a concern for the osteoinductive activity, which should be alleviated by further optimization of NP formulations.

DNA–collagen complex as a carrier for Ag+ delivery

The possibility of DNA-collagen complex as a drug carrier was investigated. The interaction between DNA and silver ions was proved by CD spectra. The release property of the complex of DNA-Ag+ was measured through turbidity of PBS solution to indicate that silver ions could coordinate with base pairs of DNA, and be released slowly from the complex of DNA-Ag+. Collagen film, collagen-Ag+ film, DNA-collagen film and DNA-collagen-Ag+ film were prepared, and studied through SEM. Particles were found present in DNA-collagen-Ag+ film by SEM. These show that silver ions may be enclosed inside these particles, which led to the slow release of Ag+ to the environments. Two bacteria, Escherichia coli and Staphylococcus aureus, were used to study the antibiotic properties of the complex films. The growth of E. coli and S. aureus could be inhibited by these films. It indicates that DNA-collagen may be a good drug carrier for the drug-controlled release.

Bone Repair Analysis in a Novel Biodegradable Hydroxyapatite/Collagen Composite Implanted in Bone

The purpose of this study was to evaluate a biodegradable hydroxyapatite/collagen composite and to examine the use of the calcium ion contained for bone formation and growth. Surgical holes were prepared in the femora and tibiae of beagle dogs, and were filled with the hydroxyapatite/collagen composite labeled with alizarin red. After 4 weeks, calcein was administered to the experimental dogs. After 1 additional week, the femora and tibiae were removed surgically and fixed in formalin. Light microscopy and confocal laser scanning microscopy were used to examine the surgical holes with their implanted materials and the surrounding bone. There were only a few inflammatory cells adjacent to the hydroxyapatite/collagen composite. The newly formed bone in the cortical bone was stained with calcein, which binds to serum calcium, and new bone near the hydroxyapatite/collagen composite in the holes was stained positive for alizarin red, which binds to the calcium in the hydroxyapatite/collagen composite. In addition, osteoblasts near the hydroxyapatite/collagen composite as well as newly formed bone adjacent to the osteoblasts showed alizarin red staining, but the new bone at a distance from the hydroxyapatite/collagen implant reacted only to calcein staining. These results, using the tissue labeling method with calcein and alizarin red, suggested that the calcium bound to the alizarin red released from the hydroxyapatite/collagen composite materials might have been translocated to sites of new bone formation. The present experiment showed that the novel hydroxyapatite/collagen composite is a useful implant material for bone augmentation and that the calcium in the newly formed bone might have been released from the implant.

MyoD enhances BMP7-induced osteogenic differentiation of myogenic cell cultures

The muscle-specific, basic helix-loop-helix transcription factor MyoD can induce cells from other mesenchymal lineages to express a skeletal muscle phenotype. Interestingly, MyoD is initially upregulated in myogenic cells incubated with bone morphogenetic proteins (BMPs), a treatment that induces osteogenic differentiation, suggesting that MyoD has a role in BMP-induced osteogenesis of myogenic cells. This possibility is supported by our observations that muscle satellite cells derived from adult MyoD(-/-) mice show severely impaired osteogenic induction by BMP-7 (osteogenic protein 1; OP-1) as indicated by the decreased gene expression of the bone markers alkaline phosphatase, osteocalcin, Runx2/Cbfa1, and Osterix. Ectopic expression of MyoD increased alkaline phosphatase activity and Osterix mRNA expression in response to BMP treatment. Similarly, ectopic expression of MyoD in the pluripotent mesenchymal cell line C3H10T1/2 increased alkaline phosphatase activity induced by BMP-7. Transcription assays showed that transfection with a MyoD-expression vector, but not other myogenic basic helix-loop-helix transcription factors (Myf5, myogenin) increased Runx2/Cbfa1 transactivation of a reporter gene construct containing either six OSE sequences in tandem or a single OSE site. This effect was enhanced by BMP treatment. These studies, therefore, demonstrate that the muscle transcription factor MyoD is required for efficient BMP-induced osteogenesis of myogenic cells and indicate that MyoD might exert its effects through co-operative interactions with Runx2/Cbfa1.