Significant inhibition of bone formation in dogs was observed in areas of intense skeletal uptake of alizarin red S. Electron microscopy revealed that the organic matrix in these areas was severely disturbed. The areas which contained no recognizable collagen had the least mineral.
In vitro alizarin red S reacted strongly with hydroxyapatite and reconstituted guinea-pig-skin collagen. The collagen reaction is divalent cation dependent.
The evidence suggests that alizarin red S interferes with collagen synthesis or aggregation in vivo. The inhibition could also be related to a disturbance of the nucleation of hydroxyapatite and to retardation of crystal growth. Other possible mechanisms are also considered.