Long-Term Changes in Adipose Tissue in the Newly Formed Bone Induced by Recombinant Human BMP-2 In Vivo

Recombinant human bone morphogenetic protein-2 (rhBMP-2) induces osteogenesis and adipogenesis in bone scaffolds. We evaluated rhBMP-2-induced long-term changes in adipose tissue in the newly formed bone in different scaffolds forms. Bovine bone particles and blocks were grafted along with rhBMP-2 in the subperiosteal space of a rat calvarial bone, and the formation of new bone and adipose tissue were evaluated at 6 and 16 weeks after the surgery. The bone mineral density (BMD) and trabecular thickness (TbTh) of the 16w particle group were significantly higher than those of the 6w particle group (p = 0.018 and 0.012, respectively). The BMD and TbTh gradually increased in the particle group from weeks 6 to 16. The average adipose tissue volume (ATV) of the 6w particle group was higher than that of the 16w particle group, although the difference was not significant (p > 0.05), and it decreased gradually. There were no significant changes in the bone volume (BV) and BMD between the 6w and 16w block groups. Histological analysis revealed favorable new bone regeneration in all groups. Adipose tissue was formed between the bone particles and at the center in the particle and block groups, respectively. The adipose tissue space decreased, and the proportion of new bone increased in the 16w particle group compared to that in the 6w group. To summarize, in the particle group, the adipose tissue decreased in a time-dependent manner, BMD and TbTh increased, and new bone formation increased from 6 to 16 weeks. These results suggest that rhBMP-2 effectively induces new bone formation in the long term in particle bone scaffolds.