Interleukin-11 acts synergistically with bone morphogenetic protein-2 to accelerate bone formation in a rat ectopic model.

We previously demonstrated that recombinant human interleukin-11 (rHuIL-11) induced osteoblast differentiation of C3H10T1/2 progenitor cells and also acted synergistically with recombinant human bone morphogenetic protein-2 (rHuBMP-2) in performing the same function. In this study, we investigated the effect of rHuIL-11 and rHuBMP-2 on bone formation in a rat ectopic model. When placed in rats, implants consisting of polymer-coated gelatin sponges containing various concentrations of rHuBMP-2 showed a dose-dependent increase in calcium content. This was confirmed by radiographic analysis of the implants. Although implants containing rHuIL-11 alone did not accumulate calcium, implants containing a combination of rHuBMP-2 and rHuIL-11 had significantly higher calcium levels than those containing rHuBMP-2 alone. This increase was rHuIL-11 dose dependent. The synergistic effect of 20 micrograms rHuIL-11 and 6 micrograms rHuBMP-2 on bone formation was estimated to be 1 week in advance of that of 6 micrograms rHuBMP-2 alone. Histologic examination revealed that the combination of rHuIL-11 and rHuBMP-2 caused spindle cells to accumulate around implants and induced cell infiltration into implants. Bone formation occurred faster in implants with the combination of rHuIL-11 and rHuBMP-2 compared with rHuBMP-2 alone. These results suggest that rHuIL-11 acts synergistically with rHuBMP-2 to more rapidly stimulate bone formation compared with rHuBMP-2 alone. This novel combined therapy may be of great clinical benefit in bone healing.