The effect of proteoglycans of cartilage and over-sulphated polysaccharides on the development of calcium-hydroxy-apatite (CHA) crystal formation in vitro.

A coulometric model system is described which facilitates the quantitative study of the kinetics of transformation of amorphous calcium phosphate (ACP) into calcium-hydroxy-apatite (CHA) crystals. Proteoglycans of high molecular weight and over-sulphated polysaccharides (Arteparon, dextran sulphate) delayed CHA crystal formation. The results have enabled us to characterize the structure activity relationship of inhibitors of CHA formation, and to postulate a general structural requirement for molecules with inhibitory effect. As working mechanism, binding of calcium ions by sulphate groups of polyanions was supposed, which might reversibly impair "the critical nuclei formation", and/or further deposition of calcium ions in the CHA crystals. The clinical, therapeutical significance of the determination of the threshold concentration of different compounds is discussed.