Novel Osteotropic Biomaterial OG-PLG: In vitro release kinetics and efficacy

Statins (eg Simvastatin) have been shown to induce expression of the bone morphogenic protein-2 gene in osteoblasts. Previously, we have shown increased efficacy of statins for bone formation through diffusion-controlled release using PLG (poly[lactide-co-glycolide]) scaffolds. However, at high concentrations cytotoxicity was observed. Thus we have developed a novel osteotropic biomaterial by grafting simvastatin (Sim) to PLG (OG-PLG) to better control release kinetics and reduce dispersion due to the small molecular weight of statins. Objectives: To determine the kinetics of the degradation-controlled release of OG-PLG, and the efficacy of OG-PLG for bone formation in vitro. Methods: Emulsion freeze-dried scaffolds were made with PLG, PLG blended with Sim (PLG+Sim, 4 mg Sim/g PLG) and OG-PLG at two different concentrations (4 or 0.4mg Sim/g PLG). Scaffolds were immersed in Dulbecco's Modified Eagle's Media, and in vitro release measured using UV/Vis spectroscopy. Bioactivity was determined by suspending these scaffolds over cultured rat bone marrow cells in media and releasing either Sim or OG-PLG to stimulate cells for bone formation. Alkaline phosphatase (ALP) and von Kossa assays were used to assess bone formation in vitro up to 18 days. Results: Release kinetics showed PLG+Sim release significantly faster than OG-PLG. ALP analysis revealed that OG-PLG (0.4 mg Sim/g PLG) significantly increased ALP production on day seven. Von Kossa assay showed OG-PLG significantly enhanced bone mineralization by day 16 over all other groups. Conclusions: Release kinetics can be modulated by grafting statins to PLG. Control of drug release significantly affects bone formation in vitro. Slower degradation-controlled release of OG-PLG significantly enhanced in vitro bone formation over diffusion-controlled release of Sim. OG-PLG is able to stimulate bone formation with enhanced potency in vitro.

Funded by NIH/NIDCR RO3 DE14653