Recombinant human BMP-2 (rhBMP-2) containing implants have been shown to be as effective as autogenous bone grafts. There exist different expression systems to manufacture rhBMP-2, the two most common being the mammalian (Chinese hamster ovary (CHO)) and bacterial (E. coli). Further, to be effective, rhBMP-2 must be combined with a carrier. Medtronic’s InFuse® bioimplant combines CHO BMP-2 with an absorbable collagen sponge (ACS), while CowellMedi’s BMP bioimplant combines E. coli BMP-2 with biphasic calcium phosphate (CaP) granules. The aim of this study was to compare the potency of the 2 sources of BMP in vitro and the bone inducing activity of implants to determine the effect of BMP source (CHO vs. E. coli) and carrier (CaP vs. ACS) on their performance.
InFuse® was purchased from Medtronic, and Cowell BMP was obtained from CowellMedi. The potency of CHO and E. coli BMP-2 was compared in vitro by adding different concentrations of BMP-2 to C2C12 cells whose alkaline phosphatase (ALP) activity increases with increasing BMP potency. Implants were prepared by combining different amounts of CHO BMP and E. coli BMP with ACS, and with CaP carriers. The activity of various implants was evaluated in vivo by placing them in the thigh muscle of male CD-1 mice (n = 6 per bioimplant). After 28 days the amount of bone induced was measured using microCT, with the results corrected for the presence of the carrier, and the tissue formed was evaluated histologically. Statistical analysis was performed using 1 and 2 way ANOVA.
The C2C12 assay clearly showed that the CHO BMP was significantly more potent than the E. coli BMP (P <0.05) over a range of concentrations. In vivo, on the CaP carrier, CHO BMP produced more bone than the E. coli BMP (P <0.05). For both the CHO and the E. coli BMP, the CaP carrier had a significant effect on the density but not the quantity of bone produced versus the ACS carrier (P<0.01). It was also noted that the CaP carrier alone induced small amounts of bone.
The source of the BMP (CHO vs. E. coli) affected the in vitro potency of the rhBMP- 2. At equivalent doses, using the same carrier, CHO BMP-2 bioimplants were significantly better inducers of bone than were their E. coli derived counterparts. The carrier for the BMP also had an effect on the density of the bone. We conclude that CHO BMP-2 on CaP granules was the best combination for the induction of bone.
Funding was provided by Oral & Maxillofacial Surgery