Experimental variation of the level and the ratio of angiogenic and osteogenic signaling affects the spatiotemporal expression of bone-specific markers and organization of bone formation in ectopic sites.

Objectives: The aim of the present study was to test the hypothesis that the ratio of angiogenic and osteogenic signaling affects ectopic bone formation when delivered in different amounts.

Materials And Methods: Porous composite PDLLA/CaCO scaffolds were loaded with rhBMP2 and rhVEGF in different dosage combinations and implanted into the gluteal muscles of 120 adult male Wistar rats. Bone formation and expression of alkaline phosphatase and Runx2 were quantified by histomorphometry. Spatial distribution across the scaffolds was assessed by using a grid that discriminated between the periphery and center of the scaffolds.

Results: The evaluation showed that the combined delivery of bone morphogenetic protein BMP2 and VEGF in different dosage combinations did not enhance the overall quantity of ectopic bone formation compared to the delivery of BMP2 alone. The addition of VEGF generally upregulated Runx2 after 4 weeks, which may have retarded terminal osteogenic differentiation. However, slow combined delivery of 1.5-2.0 μg BMP2 combined with 50 ng VEGF165 over a period of 5 weeks supported a more even distribution of bone formation across the implanted scaffolds whereas higher amounts of VEGF did not elicit this effect.

Conclusions: The findings suggest that structural organization rather than the quantity of ectopic bone formation is affected by the dosage and the ratio of BMP2 and VEGF levels at the observed intervals.

Clinical Relevance: The development of carriers for dual growth factor delivery has to take into account the necessity to carefully balance the ratio of growth release.