Bone formation recovery with gold nanoparticle-induced M2 macrophage polarization in mice.

The prevention of fractures induced by inflammatory bone disease remains a clinical challenge. This is because of a lack of bone formation to fill in the bone defects, which are believed to be due in part to persistent inflammation caused by the imbalance of M1 over M2 macrophages. In this study, gold nanoparticles (AuNPs) were synthesized to shift the balance of macrophages at the site of bone damage to improve osteanagenesis in a mouse model of LPS-induced inflammatory bone erosion. Specifically, the AuNPs treatment improved bone structure and increased bone mineral density (BMD) by ~14% compared with model group. Macrophages recruited by LPS treatment were reduced by ~11% after AuNPs injection. Compared to LPS treatment only, the percentage of M2 macrophages increased threefold by AuNPs, while the proportion of M1 macrophages decreased by 59%. This promoted the regeneration of bone matrix proteins in the bone defect site, which finally leads to increased bone mass and improved bone structure in model mice. These data suggest that AuNPs could be a novel candidate therapeutic for inflammatory bone disease rather than a drug carrier.