Effect of etidronate on COX-2 expression and PGE2 production in macrophage-like RAW 264.7 cells stimulated by titanium particles

Background. The most common failure of total joint replacement is aseptic loosening in association with osteolysis. Previous reports have shown that prostaglandin E-2 (PGE(2)) secreted from macrophages that phagocytosed wear debris induced periprosthetic osteolysis. Many clinical studies have reported that bisphosphonate therapy reduced periprosthetic bone loss and loosening of the implants after total joint replacements. Bisphosphonates are synthetic compounds with the ability to decrease bone resorption. In addition, some bisphosphonates have been reported to have anti-inflammatory effects by reducing the secretion of pro-inflammatory cytokines. However, the mechanism of bisphosphonates that reduces periprosthetic bone resorption remains unclear. The purpose of this study was to investigate one of the mechanisms by which etidronate (EHDP) inhibits periprosthetic bone resorption. Methods. Macrophage-like RAW 264.7 cells were treated with EHDP at concentrations of 0.001, 0.01, 0.1, 1, 10, and 100 mu M together with the titanium particles at a concentration of 1 mg/ml. After a 24-h culture period, total mRNA was isolated and reverse transcription-polymerase chain reaction (RT-PCR) was done to examine the expression of cyclooxygenase-2 (COX-2). The supernatants were also collected and production of PGE(2), interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) were quantified using an enzyme-linked immunosorbent assay (ELISA). Results. Analyses showed that COX-2 expression and PGE(2) production were suppressed by EHDP in a dose-dependent manner. By 100 mu M of EHDP, PGE(2) production of the cells was suppressed approximately to the level of the nonstimulated cells. Production of IL-1 beta, IL-6, and TNF-alpha in the supernatant was also suppressed by EHDP. Conclusions. The blockage effect of pro-inflammatory cytokines is a possible etidronate mechanism that reduces bone resorption around implants.