Osteoinductivity of bioimplants containing rhBMP-7 (OP-1®) and rhBMP-2 (Infuse®)

Background: OP-1® (rhBMP-7) and Infuse® (rhBMP-2) bioimplants are used to promote bone repair in various indications. Little information is currently available as to which is more effective. Comparison of rhBMP-2 and rhBMP-7 in vitro suggests rhBMP-2 may be more osteoinductive. However, differences in the retention of BMP in the different bioimplants and effects of the BMPs on other stages of bone repair could alter the activity of the implant in vivo.

Objective: To compare the osteoinductive activity of OP-1® and Infuse® implants in an in vivo model.

Methods: The bioimplants were placed in a muscle pouch in the thighs of male Swiss Webster mice (n = 10 per group). The mice were sacrificed after 28 days, and the induced bone was analyzed using micro computed tomography (micro CT).

Results: Evaluation of the quantity of the induced bone indicated that the OP-1® bioimplants induced significantly larger ossicles (P<0.001) with more calcium (P=0.023) and bone (0.031) than Infuse® implants. No significant differences were observed for any of the bone quality measures between the groups.

Conclusions: Our results demonstrate that in this animal model, OP-1® is associated with a greater osteoinductive response than Infuse®. This result was contrary to the findings from in vitro studies using rhBMP-2 and rhBMP-7. One possible explanation is that the differences in delivery vehicle is responsible because of their role in controlling BMP retention at the surgical site and effects on osteogenesis. Another explanation is that the in vitro data is based on the osteogenic differentiation of mesenchymal cell lines. However, a variety of other cell types are involved osteoinduction in vivo. Thus rhBMP-7 may be more active in promoting some other essential step such as angiogenesis or cell migration into the wound site.

Funding: NORTH (Network for Oral Research Training and Health) program.