COMPARISON OF NATIVE XENOGENEIC AND ALLOGENEIC BONE MORPHOGENETIC PROTEINS IN THE SHEEP SKULL DEFECT ASSAY MODEL

Background and aims: The purpose of this study was to determine, if th ere is any difference in the osteoinductive response between xenogenei c and allogeneic bone morphogenetic protein (BMP) in the skull defect assay model. Material and methods: The skull samples of two experiment al series were chosen for uniform radiomorphometric measurement. In th e xenogeneic BMP group (X-group), 52 mg of native moose (Alces alces) BMP (mBMP) was implanted in six 22-mm sheep midline skull defects, and in the allogeneic BMP (A-group), 8 mg of native sheep BMP (sBMP) was used in six same size parietal skull defects. The formation of new bon e was confirmed histologically and the quantity of it was measured rad iomorphometrically at 16 weeks after implantation from the standardize d radiographs using a common flatbed scanner and image processing soft ware, the mean grey scale intensity (radiopacity) multiplied by the or iginal defect area giving the new bone volume. This was divided by the milligram amount of implanted BMP to get the value for comparison of BMP activities. Results: The control defects in both groups, implanted with 13 mg of type IV collagen, showed that the defects did not heal spontaneously during the follow-up time. In the X-group, the healing p ercentage was 92.4 +/- 3.0 %, the calculated average bone volume (ABV) /mg being 12.4 +/- 0.5 units, whereas in the A-group the healing perce ntage was 62.9 +/- 8.5 % and ABV/mg 60.9 +/- 6.7. Hence the activity p er milligram proved to be more than four-fold with allogeneic compared to xenogeneic BMP. However, when the difference in spontaneous healin g of the defects in the two series was taken into consideration, only slight but not significant difference (P = 0.077) of activity could be demonstrated between xenogeneic (5.7 +/- 1.7) and allogeneic BMP (9.0 5 +/- 3.7). Conclusions: The result is in concordance with the previou s published results showing that no significant immune inhibition is s een after a single implantation of xenogeneic BMP in an orthotopic sit e.