Differential response of bone cells isolated by sequential digestion to dichloromethylenebisphonate in culture

Dichloromethylenebisphosphonate (Cl2-MBP), a compound structurally related to inorganic pyrophosphate but resistant to hydrolysis of endogenous phosphatase to yield inorganic phosphate, inhibits bone resorption and soft tissue mineralization in vivo. Previously, we have shown that bone cells isolated from rat calvaria respond profoundly to the exposure of Cl2MBP. To determine whether the cellular effects evoked by Cl2MBP are confined to a particular bone cell type, calvaria from 1 day postnatal rats were subjected to a sequential time-dependent enzyme digestion, yielding five bone cell populations marked by differences in PTH response, alkaline phosphatase activity and collagen, as well as hyaluronic acid synthesis. Culturing these bone cell populations with Cl2MBP revealed that previously observed results found with mixed bone cells (inhibition of cell proliferation, diminution of hyaluronic acid synthesis, and increase in alkaline phosphatase) were limited to cell populations which, according to the isolation scheme, stem from the outer tissue layer(s) of the calvaria. Collagen synthesis, however, was found to be equally increased regardless of cell type. These present results indicate that the action of Cl2MBP on bone may be cell specific.