Effect of metal ions on calcifying growth plate cartilage chondrocytes

The effects of the trace metals zinc (Zn), manganese (Mn), and cadmium (Cd) on the metabolism of growth plate chondrocytes was examined using a mineralizing culture system. Supplementation of serum-free primary cultures of growth plate chondrocytes with 10-100 mu m Zn resulted in an increase in cell protein and greatly increased alkaline phosphatase (AP) activity; however, above 25 mu m Zn mineralization of the cultures was reduced. The effects of Zn on cellular protein and AP activity were enhanced by the addition of the albumin to the culture media. Removal of Zn from basal culture media resulted in recoverable reductions in cellular protein and AP activities. Cadmium was acutely toxic to chondrocyte cell cultures at concentrations above 5 mu m. Even at very low concentrations (0.25 mu m) Cd caused significant reductions in DNA, cellular protein, and matrix protein synthesis. In contrast, Cd had negligible effects on AP activity or culture mineralization. Manganese treatment (50 mu m) resulted in reduced levels of proteoglycan, cell protein, DNA synthesis, and collagen synthesis, although AP specific activity did not change. At 10 mu m, Mn significantly reduced mineralization but had only minor influence on other culture parameters. Both Zn (200 mu m) and Cd (0.1 mu m), but not Mn, induced the synthesis of metallothionein. The physiological and biochemical effects of specific metal ions is largely dependent on their physicochemical properties, especially their ligand affinities. Knowledge of these properties allows predictions to be made regarding whether the organic or the mineral phase are most likely to be affected in a mineralized tissue.