Background
Cadmium has been thought to disturb the bone metabolism directly. The mechanism for the bone lesion is controversial, however. To examine the mechanism of cadmium on bone metabolism, we compared its effects on osteoblasts and osteoclasts in vitro. In addition, we evaluated the possibility of RANKL and OPG as mediators for bone resorption.
Materials and Methods: We used C57 mouse calvarial osteoblastic cells and MC3T3-E1, as osteoblasts and TRAP-positive multinucleated cells formed by a bone marrow culture system as osteoclasts. RT-PCR was performed for the expression of RANKL and OPG mRNA in osteoblastic cells.
Results
Cadmium decreased thymidine uptake and ALP activity in osteoblastic cells. Cadmium at 10-8 M and 10-7 M increased the total number of TRAP-positive multinucleated cells and TRAP activity. However, cadmium at 10-6 M and 10-5 M inhibited the osteoclastic cell formation from mouse bone marrow. Cadmium at 10-8 M increased the expression of RANKL mRNA, however, the expression of OPG mRNA was not changed significantly.
Conclusion
These results indicate that cadmium inhibits proliferation and ALP activity in osteoblastic cells and increases osteoclastic cell formation at lower concentration. As mediators for osteoclastic activation, the role of RANKL and OPG is not clear.
