Muller D, Houpert P, Cambar J, Hengé-Napoli M-H
IRSN, Laboratoire de Radiotoxicologie Experimentale, BP-166, 26702 Pierrelatte cedex, France.
Toxicol Appl Pharmacol. 2006 Jul 15;214(2):166-77. doi: 10.1016/j.taap.2005.12.016. Epub 2006 Feb 14.
Although uranium is a well-characterized nephrotoxic agent, very little is known at the cellular and molecular level about the mechanisms underlying the uptake and toxicity of this element in proximal tubule cells. The aim of this study was thus to characterize the species of uranium that are responsible for its cytotoxicity and define the mechanism which is involved in the uptake of the cytotoxic fraction of uranium using two cell lines derived from kidney proximal (LLC-PK(1)) and distal (MDCK) tubule as in vitro models. Treatment of LLC-PK(1) cells with colchicine, cytochalasin D, concanavalin A and PMA increased the sodium-dependent phosphate co-transport and the cytotoxicity of uranium. On the contrary, replacement of the extra-cellular sodium with N-methyl-D-glucamine highly reduced the transport of phosphate and the cytotoxic effect of uranium. Uranium cytotoxicity was also dependent upon the extra-cellular concentration of phosphate and decreased in a concentration-dependent manner by 0.1-10 mM phosphonoformic acid, a competitive inhibitor of phosphate uptake. Consistent with these observations, over-expression of the rat proximal tubule sodium-dependent phosphate co-transporter NaPi-IIa in stably transfected MDCK cells significantly increased the cytotoxicity of uranium, and computer modeling of uranium speciation showed that uranium cytotoxicity was directly dependent on the presence of the phosphate complexes of uranyl UO(2)(PO(4))(-) and UO(2)(HPO(4))(aq). Taken together, these data suggest that the cytotoxic fraction of uranium is a phosphate complex of uranyl whose uptake is mediated by a sodium-dependent phosphate co-transporter system.
尽管铀是一种特征明确的肾毒性物质，但在细胞和分子水平上，对于该元素在近端小管细胞中的摄取及毒性机制却知之甚少。因此，本研究的目的是利用源自肾近端（LLC-PK(1)）和远端（MDCK）小管的两种细胞系作为体外模型，来表征导致铀细胞毒性的铀种类，并确定参与铀细胞毒性部分摄取的机制。用秋水仙碱、细胞松弛素D、伴刀豆球蛋白A和佛波酯处理LLC-PK(1)细胞，可增加钠依赖性磷酸盐共转运及铀的细胞毒性。相反，用N-甲基-D-葡糖胺替代细胞外钠可显著降低磷酸盐转运及铀的细胞毒性作用。铀的细胞毒性还取决于细胞外磷酸盐浓度，并且0.1 - 10 mM的膦甲酸（一种磷酸盐摄取的竞争性抑制剂）可使其细胞毒性以浓度依赖性方式降低。与这些观察结果一致，在稳定转染的MDCK细胞中过表达大鼠近端小管钠依赖性磷酸盐共转运体NaPi-IIa可显著增加铀的细胞毒性，并且铀形态的计算机模拟表明，铀的细胞毒性直接取决于铀酰磷酸盐络合物UO(2)(PO(4))(-)和UO(2)(HPO(4))(aq)的存在。综上所述，这些数据表明，铀的细胞毒性部分是铀酰的磷酸盐络合物，其摄取由钠依赖性磷酸盐共转运体系统介导。
