A mouse femoral defect model demonstrates the clinically relevant side effects of BMP-2

Abstract

AIM: Bone morphogenetic protein-2 (BMP-2) is an FDA approved, osteoinductive growth factor for bone regeneration. However, increasing awareness of the side effects of BMP-2, including inflammation, bone resorption and fat formation, require the development of animal surgical models that replicate these adverse events. MATERIAL & METHODS: We devised a mouse femoral uni-cortical defect (UCD) model to study the clinical side effects of BMP-2. UCDs (3×1×1 mm) were drilled in one femur of mice and filled with poly(D,L-lactide-co-glycolide) (PLGA) scaffolding coated with PBS or rhBMP-2 (0.3mg/ml or 0.6mg/ml). Post mortem analyses were performed at four weeks post-surgery. RESULTS: 100% successful surgery was achieved in mouse femoral UCD without surgical complication. Micro-CT analyses of the high dose rhBMP-2 group revealed bone cyst formation with ~2.5 fold increase in bone volume and more than 50% decrease in bone mineral density and trabecular number compared to PBS control. Tartrate-resistant acid phosphatase (TRAP) staining revealed a significant increase in osteoclast number, while immunostaining for fatty acid binding protein 4 (FABP4) and peroxisome proliferator-activated receptor gamma (PPAR-γ) confirmed significant increases in adipocyte formation with rhBMP-2 in a dose dependent manner. Lastly, rhBMP-2 treatment caused significant increases in inflammation, as determined by immunostaining for tumor necrosis factor-α (TNF- α) and interleukin 6 (IL6). CONCLUSION: Here, we established a mouse UCD model that faithfully replicates the clinically reported side effects of rhBMP-2. This model may facilitate future studies to improve upon current efforts in rhBMP-2 based bone repair.