Tonner L E, Katz D I, Heiman A S
Environmental Toxicology Program, College of Pharmacy and Pharmaceutical Sciences, Florida A and M University, Tallahassee 32307, USA.
Toxicology. 1997 Jan 15;116(1-3):109-22. doi: 10.1016/s0300-483x(96)03529-9.
Lead exerts significant toxic effects on the nervous system, the hematopoietic system and the kidney. Specific cellular sites of action of this environmental pollutant have not been elucidated in the central nervous system. The present investigations were conducted to test the hypothesis that lead exposure perturbs glucocorticoid-mediated events in central nervous system hormonal target tissues. Utilizing the C6 glioma cell culture model in these studies, glucocorticoid receptor binding to its cytosolic receptor was investigated. Receptor binding studies yielded a Kd= 10.5 +/- 0.5 nM and a Bmax = 486 +/- 27 fmol/mg protein in untreated cells versus a Kd = 23.1 +/- 2.6 nM and Bmax = 472 +/- 35 fmol/mg protein in cells exposed to 10 microM lead acetate for 24 h. Presence of lead in these glial cells may decrease affinity of the glucocorticoid for its receptor without affecting receptor number. Treatment with 10 microM lead acetate for 48 h, resulted in a significant reduction in glucocorticoid-regulated glycerol phosphate dehydrogenase (GPDH) specific activity. These effects were not due to cell cytotoxicity assessed as cell number growth curves, [3H]thymidine incorporation or trypan blue exclusion. In protein kinase C (PKC) activity assays, treatment of cells with sodium or lead acetate and dexamethasone indicated that both lead and dexamethasone affect the distribution of PKC. In lead-treated cells cytosolic PKC activity was reduced 48% when compared to sodium acetate treated controls. Taken together, these results suggest that acute exposure of C6 cells to lead may inhibit processes involved in glucocorticoid-mediated signal transduction events within central nervous system hormonal target cells. Lead may perturb initial glucocorticoid binding events possibly by affecting PKC-mediated phosphorylations in the glucocorticoid signal transduction system.
铅对神经系统、造血系统和肾脏具有显著的毒性作用。这种环境污染物在中枢神经系统中的具体细胞作用位点尚未阐明。本研究旨在验证铅暴露会扰乱中枢神经系统激素靶组织中糖皮质激素介导的事件这一假说。在这些研究中，利用C6胶质瘤细胞培养模型，研究了糖皮质激素与其胞质受体的结合情况。受体结合研究结果显示，未处理细胞的解离常数（Kd）= 10.5 ± 0.5 nM，最大结合容量（Bmax）= 486 ± 27 fmol/mg蛋白质；而在暴露于10 μM醋酸铅24小时的细胞中，Kd = 23.1 ± 2.6 nM，Bmax = 472 ± 35 fmol/mg蛋白质。这些神经胶质细胞中铅的存在可能会降低糖皮质激素与其受体的亲和力，而不影响受体数量。用10 μM醋酸铅处理48小时，导致糖皮质激素调节的甘油磷酸脱氢酶（GPDH）比活性显著降低。这些影响并非由细胞毒性引起，细胞毒性通过细胞数量生长曲线、[3H]胸腺嘧啶核苷掺入或台盼蓝排斥试验进行评估。在蛋白激酶C（PKC）活性测定中，用醋酸钠或醋酸铅以及地塞米松处理细胞表明，铅和地塞米松都会影响PKC的分布。与醋酸钠处理的对照组相比，铅处理细胞的胞质PKC活性降低了48%。综上所述，这些结果表明，C6细胞急性暴露于铅可能会抑制中枢神经系统激素靶细胞内糖皮质激素介导的信号转导事件。铅可能通过影响糖皮质激素信号转导系统中PKC介导的磷酸化作用，扰乱糖皮质激素的初始结合事件。
