α-Tocopheryl Succinate Inhibits Osteoclast Formation by Suppressing Receptor Activator of Nuclear Factor-kappaB Ligand (RANKL) Expression and Bone Resorption

OBJECTIVE: Osteoclasts are bone-resorbing multinucleated cells derived from the monocyte/macrophage lineage during normal and pathological bone turnover. Recently, several studies revealed that alpha-tocopheryl succinate (αTP-suc) have demonstrated potent anti-cancer activities in vitro and in vivo. However, the effects of αTP-suc on osteoclast formation and bone resorption remain unknown. Thus, in this study, we examined the effects of αTP-suc on osteoclast differentiation and bone resorbing activity in inflammatory bone loss model. METHODS: Osteoclast differentiation assay was performed by cocultures of mouse bone marrow cells and calvarial osteoblasts in culture media including interleukin-1 (IL-1). Osteoclasts were stained for tartrate-resistant acid phosphatase (TRAP). The level of receptor activator of nuclear factor-kappaB ligand (RANKL) mRNA was determined by reverse transcriptase-polymerase chain reaction (RT-PCR). ICR mice were administered an intraperitoneal injections of αTP-suc or dimethyl sulfoxide (DMSO) 1 day before the implantation of a freeze-dried collagen sponge loaded with phosphate-buffered saline (PBS) or IL-1 over the calvariae and every other day for 7 days. The whole calvariae were obtained and analyzed by micro-computed tomography (CT) scanning, and stained for TRAP. RESULTS: αTP-suc inhibits osteoclast formation in cocultures stimulated by IL-1 and decreased the level of expression of RANKL mRNA in osteoblasts. In addition, administered intraperitoneal injections of αTP-suc prevented IL-1-mediated osteoclast formation and bone loss in vivo. CONCLUSION: Our findings suggest that αTP-suc may have therapeutic value for treating and preventing bone-resorptive diseases, such as osteoporosis.