UCLA

Effects of Bone Morphogenetic Protein (rhBMP-2) and Platelet Derived Growth Factor (rhPDGF-BB) on Ectopic Bone Formation In Rats

By

Martin H. Mardirosian

Master of Science in Oral Biology

University of California, Los Angeles 2012

Dr. Tara Aghaloo, Principal Investigator

Dr. Sotirios Tetradis

Dr. Peter K. Moy

Dr. Flavia Pirih

Marshall Urist first described a reproducible method by which to evaluate potentially osteoinductive molecules using a rat ectopic model to induce bone growth in vivo in non-bony, intramuscular sites.

Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to induce de novo bone formation in ectopic implantations. When applied to an absorbable collagen sponge (ACS) carrier, the protein is retained at the site of implantation and induces bone formation in a non-bony site within two weeks in a subcutaneous rat ectopic model. The combination device of rhBMP-2/ACS has been approved by the FDA for use in anterior lumbar interbody fusions, acute, open tibial shaft fractures, and certain dental bone regenerative procedures.

Recombinant human platelet-derived growth factor-BB (rhPDGF-BB) is approved for use in the treatment of certain periodontal defects when used in combination with a β-tricaclium phosphate (TCP) carrier. Thus far, no studies have demonstrated osteoinductive properties of PDGF.

The purpose of this study was to compare the osteoinductivity of rhBMP-2 and rhPDGF-BB separately on both an ACS and carrier TCP when placed subcutaneously in rats.

Thirty-two male immunocompetent 5 month old Sprague-Dawley rats were used in this study. Investigational materials were implanted subcutaneously in the rat thorax, with four randomized implants being placed per rat (e.g., one per quadrant). Animals received implantations of: rhBMP-2/ACS (0.3mg/mL), rhBMP-2/TCP (0.3mg/mL), rhPDGF-BB/TCP (0.3mg/mL), rhPDGF-BB/ACS (0.3mg/mL), ACS alone, or TCP alone. No animal received both rhBMP-2 and rhPDGF-BB. After sacrificing the animals after 2 and 4 weeks, quantitative and qualitative results were assessed using MicroCT and histology.

rhBMP-2 showed considerable induction of bone growth at both 2 week and 4 week samples whether grown on TCP or ACS. MicroCT analysis revealed a significant increase in calcified tissue in rhBMP-2/ACS, rhBMP-2/TCP, and rhPDGF-BB/TCP in comparison to ACS alone control. However, only rhBMP-2/ACS at 2 and 4 weeks, not ACS alone nor rhPDGF-BB, was osteoinductive, as demonstrated by histology. H&E staining demonstrated immature woven bone at 2 weeks, which became more mature at the 4 week time point.rhPDGF-BB lacked the ability to induce bone formation, either with an ACS or TCP carrier .

This study confirmed the osteoinductive properties of rhBMP-2/ACS and rhBMP-2/TCP, but failed to demonstrate that rhPDGF-BB is osteoinductive on either an ACS or TCP carrier. Due to its ability to induce de novo bone formation, rhBMP-2 is an important treatment option for patients with significant alveolar bone defects in the jaws, and will serve as a viable alternative to autogenous bone grafting.