In vivo testing of a genetically active nano-calcium phosphate paste forbone substitution
Final Report Abstract
Objective: The aim of this study was to create a new injectable DNA-functionalized calcium phosphate paste as new bone graft substitute. We took advantage of the well-known biocompatibility of calcium phosphate as bone graft substitute. Calcium phosphate nanoparticles were loaded with DNA encoding for BMP-7 and VEGF-A for local transfection at the implantation site. Materials and methods: 24 New Zealand white rabbits were randomly divided into two groups. The first group was treated with BMP-7- and VEGF-A-encoding DNA loaded onto calcium phosphate nanoparticles. The control group was treated with the same kind of calcium phosphate nanoparticles, but without DNA. A bone defect was created at the proximal medial tibia and filled with the corresponding injectable calcium phosphate paste. The healing process was documented by fluoroscopy. To evaluate the potential as bone graft, the proximal tibia was harvested 2, 4 and 12 weeks after the operation. Histomorphological analysis was focused on the evaluation of the dynamic bone parameters using the Osteomeasure system. Results: The animals treated with DNA-loaded calcium phosphate nanoparticles showed a statistically significantly rise of bone volume per tissue volume (BV/TV) after 4 weeks in comparison to the control group. Additionally, a statistically significant rise of the trabecular number (Tb.N) and the number of osteoblasts per tissue area (N.Ob/T.Ar) in the area of interest (AOI) was observed. These results were confirmed by radiological and histological analyses. The DNA-functionalized bone paste led to a significantly faster healing of the critical size bone defect in the rabbit model. After 12 weeks, all defects had healed equally in both groups. No difference in the quality of the new bone was found. Conclusion: The injectable DNA-loaded calcium phosphate paste led to a faster and more sustained bone healing and induced a good and accelerated bone formation. The graft was not only incorporated into the bone, but new bone was also formed on its surface. The calcium phosphate paste without DNA also generated a regular healing of the critical size bone defect but slower than the DNA-loaded paste. The functionalization of calcium phosphate with BMP-7 and VEGF-A significantly improved the potential of calcium phosphate as bone graft substitute.
