A study on the mechanism of bone lesion by cadmium Effect of cadmium on the bone formation in cultured MC3T3-E1

为进一步了解镉（Cd）致骨损伤的机制，研究了Cd对骨细胞分化的影响（MC 3 T3-E1）细胞培养3d后，检测细胞DNA合成、碱性磷酸酶（ALP）活性和胶原合成，将金属离子加入到含10%胎牛血清的培养基中，然后将细胞在37 ℃、5%CO_2的空气中培养7天。10 μ <-8>M的Cd对细胞ALP活性无明显影响，但10 μ <-7>M和10 μ <-6>M的Cd使ALP活性分别降低对照值的25%和30%。10 μ <-5>M Cd显著降低ALP活性。DNA含量和羟脯氨酸含量在10 μ <-5>M的Cd胁迫下也有所下降，但低于10 μ <-6>M的Cd对这两个指标没有影响。有趣的是，10 μ <-5>M的镉的形态变化被10 μ <-4>M的锌改善。在培养液中加入10 μ M Zn，可恢复10 μ M Cd对成骨细胞ALP活性、蛋白质含量和羟脯氨酸含量的影响<-5><-4>，提示成骨细胞合成的ALP分子可能是Cd作用的主要靶点。低浓度镉长期暴露使碱性磷酸酶失活，可能影响骨成骨细胞的功能。

To obtain further information on the mechanism of bone damage caused by cadmium(Cd), the effect of Cd on the differentiation of bone cells (MC3T3-E1) were examined by quantitating DNA synthesis, alkaline phosphatase(ALP) activity and collagen synthesis.After cells were cultured for 3 days, metal ions were added to the medium containing 10% fetal bovine serum and cells were subsequently cultured for 7 days at 37ﾟC in 5% CO_2 in air. Although 10^<-8>M of Cd have no significant influence on ALP activity of the cells, 10^<-7>M and 10^<-6>M of Cd decreased ALP activity by 25% and 30% of control value. 10^<-5>M Cd remarkably decreased ALP activity. DNA content and hydroxyproline content were also decreased by exposure to 10^<-5>M of Cd, less than 10^<-6>M Cd didn't affect both the parameters.Since there are some reports that zine(Zn) has a protective effect against the toxicity of Cd, we also examined the effect of Zn coexisting with Cd on MC3T3-E1. Interestingly, morphological changes by 10^<-5>M of Cd were improved by 10^<-4>M of Zn. ALP activity, protein content, and hydroxyproline content decreased by exposure to 10^<-5>M of Cd were also recovered by the addition of 10^<-4>M Zn to the culture medium.The present study suggests that ALP molecule, sythesized in osteoblastic cells and bound to cell membrane, may be the primary target of Cd. The inactivated ALP by exposure to low concentration of Cd for a long period may affect the function of osteoblastic cells in bone.