Bone conditioned medium enhances cell aggregation, cell proliferation and alkaline phosphatase activity in serum-deprived medium

The effect of medium conditioned by whole bone was examined on the activity of a heterogeneous population of rat calvarial cells grown under serum-deprived conditions. Conditioned medium (CM) had pronounced effects on the appearance of cultures within 24–48 hours of addition. This was characterized by the breakdown of the cell monolayer, rounding of cells and formation of alkaline phosphatase-positive aggregates. Cellular alkaline phosphatase activity was increased compared to controls while acid phosphatase levels were reduced. These aggregates grown in the presence of 10 mM β-glycerophosphate did not show evidence of mineralization. These results show that soluble factors derived from calvarial bone are responsible for cell aggregation, cell proliferation and increase in alkaline phosphatase activity.