A novel hybrid compound LLP2A-alendronate accelerates open fracture healing in a rabbit model

PURPOSE: LLP2A-alendronate (LLP2A-Ale) is a novel bone-seeking compound that recruits mesenchymal stem cells to the bone surface and stimulates bone formation. The purpose of this study was to investigate the efficacy of LLP2A-Ale in the treatment of rabbit open fracture. METHODS: Thirty New Zealand White rabbits underwent radius mid-diaphyseal osteotomy and were randomly divided into control and treatment groups with fifteen rabbits in each group. The treatment group received only one injection of LLP2A-Ale (dosage 125 μg/kg), whereas the control group received one injection of PBS. X-ray images were taken to observe the course of fracture healing at 2, 4 and 6 weeks after treatment. Rabbits were sacrificed at 4 and 6 weeks post treatment. Calluses were then harvested and were subjected to histology, immunohistochemistry, molecular biology techniques and biomechanical test. RESULTS: X-ray images showed that the LLP2A-Ale group exhibited abundant callus formation, stronger bony callus remodeling and earlier marrow cavity recanalization compared to the control group in a time-dependent manner. Histomorphological analysis revealed an advance in woven formation at 4 weeks and lamellar bone formation at 6 weeks in the LLP2A-Ale group. Moreover, gene and protein levels suggested that LLP2A-Ale promoted osteogenesis and angiogenesis probably via upregulating the expression of osteogenesis factors (including bone morphogenetic protein 2 and Runt-related transcription factor 2) and angiogenesis factors (vascular endothelial growth factor). Besides, the radius callus biomechanical properties were significantly enhanced in the LLP2A-Ale group compared with the control group at 6 weeks. CONCLUSION: LLP2A-Ale can significantly promote open fracture healing in the rabbit model, probably through enhancing osteogenesis and angiogenesis.