Comparative effect of cadmium on osteoblastic cells and osteoclastic cells

Cadmium(Cd) has been thought to disturb the bone metabolism directly. The mechanism for the bone lesion is unknown, however. To examine the effects of cadmium on bone metabolism, we compared its effects on osteoblasts and osteoclasts in vitro. We used an established cell line, MC3T3-E₁, as osteoblasts and tartrate resistant acid phosphatase (TRACP)-positive multi-nucleated cells (MNC) formed by a bone marrow culture system as osteoclasts. Alkaline phosphatase (ALP) activity was decreased by 10^–7 M Cd and DNA content and hydroxyproline content of osteoblastic cells were decreased by 10^–5 M Cd. Cadmium at 10^–7 M inhibited the osteoclastic cell formation from mouse bone marrow in the presence of 10^–8 M 1,25(OH)₂ vitamin D₃. A 100-fold higher concentration of zinc(Zn) simultaneously added to the cadmium-containing medium prevented the toxicity of cadmium to osteoclastic cells as observed in the culture of osteoblastic cells. These results indicate that both bone formation and bone resorption are inhibited by cadmium. The responses of osteoclasts and osteoblasts to cadmium in this culture system were the same and the responses of cadmium-damaged osteoblasts and osteoclasts to zinc were also similar. These results suggest that another mechanism by which cadmium could cause bone damage should be considered in addition to the specific induction of osteoclastic cells by Cd.