Formation and transformation of calcium phosphates: relevance to vascular calcification.

Only one phase, carbonate apatite, is present in the mineral phase of normal calcification while different calcium phosphate phases are found in the mineral phases of pathological calcifications. In vascular calcification, the mineral phase has been described as hydroxyapatite; carbonate apatite, amorphous calcium phosphate. It has also been speculated that octacalcium phosphate may be a precursor for the apatite. This paper provides a brief review of: (1) the different calcium phosphates in normal and pathological calcifications; (2) the conditions for the formation and transformation of biologically relevant calcium phosphates in synthetic systems and a concise discussion on the relevance of results from synthetic systems to the calcium phosphate phase(s) involved in vascular calcification.