THE EFFECT OF CADMIUM ON THE FORMATION AND PROPERTIES OF HYDROXYAPATITE IN-VITRO AND ITS RELATION TO CADMIUM TOXICITY IN THE SKELETAL SYSTEM

In order to understand the biological action of cadmium (Cd) in induci ng bone pathologies, the effect of Cd on the formation, structure, and properties of hydroxyapatite (HA) in vitro was investigated using thr ee biologically relevant test systems: (1) direct precipitation of HA with no precursor phase; (2) transformation of amorphous calcium phosp hate (ACP) to crystalline HA; and (3) growth of HA seed crystals. Cd-c ontaining HA was prepared by transforming ACP to HA in the presence of Cd at a pH of 10; Cd/Ca ratios of 0.05, 0.10, and 0.20 were obtained. Infrared and x-ray diffraction analyses were performed on the Cd-HA s amples, and measurements were made of Cd adsorption on HA and of the d issolution characteristics of Cd-containing HA. Cd incorporation in HA introduced little strain in the lattice but resulted in a decreasing C-axis spacing and a corresponding crystal size decrease in the C-axis direction. Cd incorporation had a nominal effect on HA dissolution. C d had an inhibitory effect on HA formation kinetics in all three test systems. Infrared spectroscopy of Cd-HA showed a complex series of sma ll changes in the spectra as a function of Cd concentration resulting from some distortion in the crystal perfection and symmetry. The inter ference of Cd with mineralization can be partially explained by its in hibitory effect on HA nucleation and growth in addition to any cellula r involvement. Furthermore, Cd probably has little effect on bone mine ral dissolution. Our results explain the Cd incorporation reported in bone.