Local injection of a single dose of simvastatin augments osteoporotic bone mass in ovariectomized rats

The aim of this study was to evaluate the effects and explore the mechanism of a local injection of a single dose of simvastatin as a strategy to strengthen target bone. Simvastatin was injected into the femurs (5 or 10 mg) or caudal vertebrae (1 or 2 mg) of ovariectomized rats, with an equal volume of vehicle injected as a control. Bone mineral density (BMD), bone microstructure and strength were evaluated at 1 and 5 months post-injection for the femurs and at 12 days post-injection for the vertebrae. Bone mass, adipocyte numbers and Runx2 expression were also examined using histology and immunohistochemistry. Compared with controls, simvastatin significantly increased BMD, bone volume fraction (BV/TV), improved bone microstructural parameters and bone strength in the femurs at both time points (all P < 0.01). Simvastatin-treated femurs contained fewer adipocytes and a higher Runx2 expression. For the caudal vertebrae, simvastatin significantly improved BV/TV, bone microstructures, and bone strength (all P < 0.01) as compared with controls. In conclusion, local injection of a single dose of simvastatin induces early onset and long-lasting bone augmentation in osteoporotic bone, significantly improving BMD, and bone microstructure and biomechanical strength. Simvastatin induces Runx2 expression, which may function to induce osteogenesis and inhibit adipogenesis as an underlying mechanism to augment bone mass.