OSTEOINDUCTION CAPABILITY OF RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN-2 IN INTRAMUSCULAR AND SUBCUTANEOUS SITES - AN EXPERIMENTAL-STUDY

The osteoinduction capability of recombinant human bone morphogenetic protein-2 (rhBMP-2) in the muscle and in the subcutaneous tissue in Wi star rats (n = 20) was evaluated, using atelopeptide type-I collagen a s a carrier. The alkaline phosphatase (ALP) activity and calcium (Ca) content were quantitatively analyzed 1,3,7 and 21 days after the impla ntation of 5 mu g of rhBMP-2. At 3 days, the ALP activity began to inc rease gradually. The Ca content showed a slow increase until 7 days an d was markedly elevated at 21 days. There was no significant differenc e observed between the intramuscular and subcutaneous sites until 3 da ys. However, at 7 days, both the ALP activity and Ca content were sign ificantly higher intramuscularly than subcutaneously, Use, at 21 days they were higher in the muscle than in the subcutaneous tissue. These results suggest that the difference in osteoinduction could be related to the partial pressure of oxygen or the blood supply in the intramus cular and subcutaneous sites, and that immature mesenchymal cells in t he muscle could more easily differentiate into osteoblasts, leading to osteoinduction, This study clearly demonstrated that even a small amo unt (5 mu g) of rhBMP-2 induces nem bone in the subcutaneous tissue, w hich has a lesser blood flow than the muscle.