Induction of bone repair in rat calvarial defects using a combination of hydroxyapatite with phosphatidylserine liposomes.

Phosphatidylserine (PS)-normally present on the inner leaflet of the plasma membrane-translocates to the outer leaflet at an early stage of apoptosis. PS-containing liposomes (PSLs) can mimic the effect of apoptotic cells in inducing the secretion of prostaglandin E from phagocytes and inhibiting the maturation of dendritic cells and osteoclast precursors. The present study attempted to evaluate the effect of calcium phosphate (in the form of hydroxyapatite [HAP]) in the presence or absence of PSLs for repair of rat calvarial bone defects. The defects, each 5 mm in diameter, were created in the calvaria parietal bone of 8-week-old Wistar rats and subjected to one of the following treatments: no augmentation (Sham), HAP alone, or a mixture of HAP and PSL (HAP+PSL). Micro-computed tomography data showed that the HAP+PSL complexes promoted greater bone regeneration in comparison with either the Sham procedure or HAP alone at 4 and 8 weeks after implantation. The regeneration of calvarial bone defects induced by PSLs was mediated partly through upregulation of the osteogenic marker Alkaline Phosphatase, Type I collagen, osteocalcin, Runx2, and Osterix mRNAs. These data are the first to show that PSLs can influence bone regeneration by regulating osteoblast differentiation.