Background: Currently, drugs for local bone formation are very limited in clinic. Simvastatin is one of most potential translational drugs by repositioning for its significant osteogenic effect and its history as a safe lipid-lowering medicine. In this study, we prepared the pre-clinical simvastatin microcrystals which could be potentially translated and industrialized.
Methods: Simvastatin microcrystals were made by wet media milling method. Characterization of microcrystal particles were evaluated by laser particle size analyzer and high-performance liquid chromatography (HPLC). Furthermore, we verified the osteogenic effect in rat ovariectomy(OVX)-induced osteoporosis model and femur defect model. For osteoporosis model, we delivered simvastatin microcrystals to tibia with poloxamer hydrogel by intraosseous injection. Bone mineral density (BMD) and ultimate force were assessed after treatment. For femur defect model, simvastatin microcrystal was incorporated in clinically used calcium phosphate cements (CPCs) as an implant. Histology and μCT were used for evaluation of the healing.
Results: The D 10 , D 50, and D 90 showed size of the most particles ranged from 0.226-3.425 μm. The mean particle size of the microcrystals is determined as 1.365 μm which demonstrated a successful preparation. For osteoporosis model, BMD and the ultimate force of the treated tibia were significantly improved in osteoporosis rat after injection of 0.5 mg and 1 mg simvastatin microcrystals compared with OVX or 0 mg groups. There were no differences observed in BMD and ultimate force between 0.5 mg, 1 mg simvastatin microcrystals group and bone morphogenetic protein (BMP) 5 ug group. For femur defect model, quantitative analysis of bone regeneration by μCT showed bone volume/tissue volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N) were significantly increased in simvastatin microcrystals 50ug (SIM-C 50 ug), SIM-C 100 ug and BMP 5 ug group compared with CPC vehicle group. Trabecular separation (Tb.Sp), and cement volume/tissue volume (CV/TV) were decreased in SIM-C 50 ug, SIM-C 100 ug and BMP 5 ug groups compared with CPC vehicle group. Semiquantitative scale for histology assessment further demonstrated a higher bone regeneration score in drug loaded groups compared with CPC group.
Conclusions: Our study shows that simvastatin microcrystals were successfully prepared by wet media milling method and the microcrystals can promote bone formation by local delivery by poloxamer hydrogel or CPC, which is of great translational potential.