The inhibitory effect of strontium-doped calcium polyphosphate particles on cytokines from macrophages and osteoblasts leading to aseptic loosening in vitro.

Aseptic loosening is a common cause of joint implant failure in humans. In order to enhance implant stability, we need to develop a new material that not only promotes the wear resistance of components of an artificial joint, but also possesses the pharmaceutical efficacy of protecting patients against aseptic loosening. Strontium-doped calcium polyphosphate (SCPP) has been found to have this potential ability. The goal of this study is to respectively quantify the levels of TNF-α (for macrophages), receptor activator of NF-kB ligand (RANKL) and osteoprotegerin (OPG) (for osteoblasts) when osteoblasts and macrophages are challenged with various particles (including SCPP). In this study, the osteoblasts ROS 17/2.8 and macrophages RAW 264.7 were challenged with various wear particles (8% SCPP, the molar percentage of Sr in SCPP is 8%, UHMWPE, hydroxyapatite (HA) and CPP). The secretion of TNF-α (from RAW 264.7), OPG and RANKL protein (from ROS 17/2.8) was analyzed by ELISA. The OPG and RANKL mRNA from ROS 17/2.8 was detected by RT-PCR. The data of ELISA indicated that the amount of TNF-α challenged with 8% SCPP particles was more than three-fold lower than that of all other test groups. The ratio of OPG/RANKL in the 8% SCPP group was significantly increased compared to that of all other test groups. The results of OPG and RANKL mRNA expression showed the same tendency as the ELISA results. In general, this study showed that 8% SCPP particles can inhibit the expression of TNF-α and RANKL, promote the expression of OPG so that SCPP can inhibit bone resorption and promote bone formation, and then inhibit aseptic loosening. Thus SCPP could be a promising material for the construction of artificial joints.