The local administration of TNF-α and RANKL antagonist peptide promotes BMP-2-induced bone formation

Abstract

Abstract Objectives Because high doses of bone morphogenetic proteins (BMPs) are required to achieve a certain level of bone regeneration in primates, thereby causing side effects such as inflammation, combination therapies using BMPs along with agents that can reduce the required amount of BMPs have been developed. Recently, we found that subcutaneous injections of W9 peptide (W9), which has been established as a tumor necrosis factor (TNF)-α and receptor activator of nuclear factor-κB ligand (RANKL) antagonist, promoted BMP-induced ectopic bone formation. Since TNF-α is known to reduce bone formation, we investigated the stimulatory mechanism of W9 on bone formation by using TNF-α-deficient, TNF type 1 receptor (TNFR1)-deficient, and wild-type (WT) mice. Methods Collagen discs containing either BMP-2 (1μg) alone or BMP-2 (1μg) with W9 (0.56mg) (BMP-2+W9) were implanted into the back muscles of 5-week-old male mice. The animals were sacrificed on day 12 after implantation. Radiographic and histomorphometric analyses were performed on the dissected ectopic bones. Results A significant increase in ectopic bone was observed in the BMP-2+W9 group compared to the BMP-2 group in WT mice. Bone histomorphometric technique revealed a significant increase of osteoblast surface and mineralized bone indices in the BMP-2+W9 group compared to the BMP-2 group in WT mice. Interestingly, W9 also increased the bone mineral content of ectopic bone induced by BMP-2 in both TNF-α deficient and TNFR1-deficient mice, to the same extent as in WT mice. Conclusion Our data suggest that W9 promotes bone formation by a mechanism other than antagonism of TNF-α action.