The effects of calcium phosphates on BMP activity

In this experiment, five different soluble calcium phosphates ceramics were synthesized: HAP, β-TCP, α-TCP, OCP (octacalcium phosphate) and DCPD (dicalcium phosphate dehydrate). The effects of the ceramics on BMP activity were investigated in vitro and in vitro.Five mg of BMP was prepared along with 5 or 25 mg of ceramics. These were then combined to form complexes. These complexes were implanted epifascially in the femoral region, and their osteoinductive activities were examined at 4 weeks after implantation by means of roentogenographic and histologic observations. The amount of bone induced by the complexes was determined by a computer-supported image analysis system. For in vitro studies, a culture system which differentiated neonatal muscle into cartilage in response to BMP contained in Bone Matrix Gelatin (BMG (+)) was adopted. Calcium phosphate was applied onto the BMG, and a fetal rat muscle was placed on top, and the system was cultured. On Day 14 of culture, incorporation of [35S]-sulfate into glycosaminoglycans (GAG) was measured. Furthermore, to study the solubility of the ceramics in the culture medium, the ceramics were soaked in the same medium for 3 days, and the amounts of Ca and P and the change in pH were measured.HAP, β-TCP and α-TCP did not affect BMP activity when 5 mg and 25 mg ceramics/BMP complexes were implanted in the mice. OCP and DCPD did not affect BMP activity when 5 mg ceramics/BMP complexes were implanted, but inhibited BMP activity when 25 mg ceramics/BMP complexes were implanted. Only DCPD inhibited BMP activity while other ceramics did not in vitro. HAP, β-TCP and α-TCP produced no change in the Ca and P concentrations of the medium, but DCPD increased the concentrations of Ca and P and OCP decreased the concentrations of Ca and P. All the ceramics behaved similarly to the control in regard to the pH of the medium.It was concluded that HAP, β-TCP and α-TCP, which did not affect Ca and P concentrations in the medium, did not influence BMP activity. DCPD, which showed high solubility, inhibited BMP activity. Further investigations are necessary to determine the effect of apparent volume of OCP on BMP activity, and the effect of the phase transformation of OCP on solubility.