Comparison of the effects of recombinant human bone morphogenetic protein-2 and -9 on bone formation in rat calvarial critical-size defects.

Abstract

Among bone morphogenetic protein (BMP) family members, BMP-2 and BMP-9 have demonstrated potent osteoinductive potential. However, in vivo differences in their potential for bone regeneration remain unclear. The present study aimed to compare the effects of recombinant human (rh) BMP-2 and rhBMP-9 on bone formation in rat calvarial critical-size defects (CSD). Twenty-eight Wistar rats surgically received two calvarial defects bilaterally in each parietal bone. Defects (n=56) were allocated into four groups: absorbable collagen sponge (ACS) alone, rhBMP-2 with ACS (rhBMP-2/ACS), rhBMP-9/ACS, or sham surgery (control), on the condition that the treatments of rhBMP-2/ACS and rhBMP-9/ACS, or the same treatments were not included in the same animal. Animals were sacrificed at 2 and 8weeks post-surgery. The calvarial defects were analyzed for bone volume (BV) by micro-computed tomography and for percentages of defect closure (DC/DL), newly formed bone area (NBA/TA), bone marrow area (BMA/NBA), adipose tissue area (ATA/NBA), central bone height (CBH), and marginal bone height (MBH) by histomorphometric analysis. The BV in the rhBMP-2/ACS group (5.44±3.65mm3, n=7) was greater than the other groups at 2weeks post-surgery, and the rhBMP-2/ACS and rhBMP-9/ACS groups (18.17±2.51 and 16.30±2.46mm3, n=7, respectively) demonstrated significantly greater amounts of BV compared with the control and ACS groups (6.02±2.90 and 9.30±2.75mm3, n=7, respectively) at 8weeks post-surgery. The rhBMP-2/ACS and rhBMP-9/ACS groups significantly induced new bone formation compared to the control and ACS groups at 8weeks post-surgery. However, there were no statistically significant differences found between the rhBMP-2/ACS and rhBMP-9/ACS groups in any of the histomorphometric parameters. The ATA/NBA in the rhBMP-2/ACS group (9.24±3.72%, n=7) was the highest among the treatment groups at 8weeks post-surgery. Within the limits of this study, it can be concluded that rhBMP-2/ACS induced a slight early increase in new bone formation at 2weeks and that rhBMP-9/ACS provided comparable new bone formation to rhBMP-2/ACS with less adipose tissues after a healing period of 8weeks in rat CSD. RhBMP-9/ACS treatment provided new bone formation with less adipose tissues compared with rhBMP-2/ACS.