Effect of osteoprotegerin in combination with interleukin-6 on inhibition of osteoclast differentiation

Objective: To observe the effect of recombinant interleukin-6 (IL-6) and osteoprotegerin (OPG) on inhibiting bone absorption induced by receptor activator for nuclear factor-kappa B ligand (RANKL) in murine osteoclast precursor cells (OCPs) model. Methods: RAW 264.7 cells were solely treated with 50 ng/ml RANKL for 1 day, and then they were divided into three groups: RANKL (control group), RANKL+IL-6 (IL-6 group) and RANKL+IL-6+OPG(combination group). These cells were harvested and investigated by means of HE staining under light microscope after consecutive 9 days. Furthermore, staining tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells were detected by inverted phase contrast microscope. The absorption pits of bone slices were observed under scanning electron microscope. Results: The number of mature osteoclast cells in control group was more than that in IL-6 alone or IL-6 combined with OPG group (P<0.05). Interestingly, this experiment has also demonstrated that there was a large number of TRAP-positive multinucleated osteoclasts (more than 3 nuclei) and several bone absorption formation in the control group, whereas the outcome was completely different in both IL-6 group and IL-6+OPG group (P<0.05). Conclusion: IL-6 can suppress the differentiation of mature osteoclasts as directly adding it into the RAW 264.7 cells induced by 50 ng/ml RANKL, and further the effect of osteolysis is remarkably reduced. When treatment with IL-6 combined with OPG, a more effective strategy for the treatment of osteoporosis is reached.