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

为了进一步了解镉（Cd）致骨损伤的机制，我们通过定量测定DNA合成、碱性磷酸酶（ALP）活性和胶原合成来研究镉对骨细胞（MC3T3-E1）分化的影响。细胞培养3 d后，在含10%胎牛血清的培养基中加入金属离子，在5% CO_2空气中37℃条件下培养7 d。虽然10^<-8>M的Cd对细胞ALP活性没有显著影响，但10^<-7>M和10^<-6>M的Cd使细胞ALP活性分别下降了对照值的25%和30%。10^<-5>M Cd显著降低ALP活性。10^<-5>M Cd对DNA含量和羟脯氨酸含量也有降低作用，10^<-6>M Cd对这两个参数没有影响。由于有报道称锌（Zn）对Cd的毒性有保护作用，我们也研究了锌与Cd共存对MC3T3-E1的影响。有趣的是，10^<-5>M Cd的形态变化得到10^<-4>M Zn的改善。在培养基中添加10^<-4>M Zn后，ALP活性、蛋白质含量和羟脯氨酸含量也恢复了10^<-5>M Cd所降低的水平。本研究提示，在成骨细胞中合成并结合于细胞膜上的ALP分子可能是Cd的主要作用靶点。长期暴露于低浓度Cd下，ALP失活可能会影响骨内成骨细胞的功能。

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.