In this study the authors tested the osteoinductive potential of recombinant human bone morphogenetic protein–2 (rhBMP-2) when combined with each of three commercially available contrast media (Conray, Omniscan, and Optiray).
Initial in vitro and cadaver tests verified the feasibility of using contrast media to visualize absorbable collagen sponge implants containing rhBMP-2 on fluoroscopic radiographic images. For the feasibility studies, lyophilized rhBMP-2 was prepared for injection by reconstitution with contrast media instead of sterile water. For the in vivo study, samples of an rhBMP-2 stock solution were diluted to 0.1 mg/ml by using three contrast media. In each sample, the final solution consisted of 97% contrast medium by volume. Recombinant human bone morphogenetic protein–2 diluted with sterile water for injection was used as a positive control. The rhBMP-2 solutions were applied to 0.5-cm3 collagen sponges and implanted subcutaneously on the thoracic cavity of athymic rats. At 4 weeks, the rats were killed, and the implants were removed. The explants were graded for degree of bone formation by using manual palpation and radiographic and histological assessments.
By all methods of evaluation used, rhBMP-2 diluted with Omniscan was equivalent to rhBMP-2 diluted with sterile water in inducing bone formation. Both Conray and Optiray were shown to inhibit the osteoinductive potential of rhBMP-2.