CADMIUM, ZINC, METALLOTHIONEIN AND KIDNEY TOXICITY

镉暴露是人类毒理学中的一个重要问题。一个 主要毒性部位是肾脏，镉会导致中度肾损伤 失败，包括无法再吸收葡萄糖、磷酸盐等营养物质， 钙、氨基酸。在小鼠肾皮质细胞中，类似于 近曲小管细胞，镉浓度，不影响细胞 活力、ATP 水平或 (Na , K )-ATP 酶的活性，抑制 (Na ) 依赖性葡萄糖和磷酸盐协同转运。镉离子显然 直接作用于转运蛋白生物化学，而不是通过破坏 节能机制。事实上，镉离子会下调 (Na )-葡萄糖 (SGLT1) 和 (Na )-磷酸盐协同转运蛋白 mRNA。也曾被 发现金属硫蛋白（MT）是镉离子结合的主要位点， 不能逆转镉离子对 SGLT1 的抑制，尽管它是一种 蛋白质结合镉离子的有效清除剂。了解机制 (Na )-营养依赖性共转运蛋白的下调参与 镉离子肾毒性及其与金属硫蛋白诱导的关系 和作为有效金属结合剂的活性，以下具体目标将 待研究：1)明确镉离子对SGLT1 hnRNA和mRNA的影响。 2） 确定对照和 SGLT1 mRNA 降解的速率常数 镉处理的细胞。 3）测量镉离子对SGLT1蛋白的影响 降解和合成。 4）建立镉之间的关系 SGLT1 活性的离子依赖性抑制和 SGLT1 mRNA 的减少。 5） 研究SGLT1 mRNA下调的机制 SGLT1 启动子驱动的荧光素酶表达的浓度抑制。 6） 开发一个可用于评估体内重要性的体内模型 体外机制研究。 7）开展镉离子影响的研究 平行目标1-6的(Na)-磷酸盐共运输。 8) 建立 镉离子和锌离子诱导MT mRNA合成的机制。 9） 检查 SGLT1 mRNA 浓度下调的机制 化学视角。 10) 探究MT之间的金属离子交换竞争 以及与镉离子相互作用的其他关键分子。

Cadmium exposure is an important problem in human toxicology. A major site of toxicity is the kidney where cadmium causes moderate renal failure including an inability to resorb nutrients such as glucose, phosphate, calcium, and amino acids. In mouse kidney cortical cells, which resemble proximal tubule cells, concentrations of cadmium, which do not affect cell viability, ATP levels, or the activity of the (Na+, K+)-ATPase, inhibit (Na+)-dependent glucose and phosphate co-transport. The cadmium ion apparently acts directly on transporter biochemistry not indirectly through disruption of energy conservation mechanisms. Indeed, cadmium ion down regulates (Na+)-glucose (SGLT1) and (Na+)-phosphate co-transporter mRNA. It has also been found that metallothionein (MT), the principal site of binding of cadmium ion, does not reverse inhibition of SGLT1 by cadmium ion even though it is an effective scavenger for protein-bound cadmium ion. To understand the mechanisms of down regulation of (Na+)-nutrient dependent co transporters involved in cadmium ion nephrotoxicity and their relationship to metallothionein induction and activity as a potent metal binding agent, the following specific aims will be pursued: 1) Define the effects of cadmium ion on SGLT1 hnRNA and mRNA. 2) Determine the rate constants for degradation of SGLT1 mRNA from control and cadmium treated cells. 3) Measure the impact of cadmium ion on SGLT1 protein degradation and synthesis. 4) Establish the relationship between cadmium ion-dependent inhibition of SGLT1 activity and reduction in SGLT1 mRNA. 5) Investigate the mechanism of down-regulation of SGLT1 mRNA concentration-inhibition of SGLT1 promoter-driven luciferase expression. 6) Develop an in vivo model that can be used to assess the significance of the in vitro mechanistic studies. 7) Carry out studies on the effects of cadmium ion on (Na+)-phosphate co transport that parallel aims 1-6. 8) Establish the mechanism of induction of MT mRNA synthesis by cadmium ion and zinc ion. 9) Examine the mechanism of down-regulation of SGLT1 mRNA concentration from a chemical perspective. 10) Probe the metal ion exchange competition between MT and other key molecules interacting with cadmium ion.