Proximal Tubular Transport of Mercury and Effects of Reduced Renal Mass

描述（由申请人提供）：慢性肾脏疾病影响美国约17%的成年人群（约40，000，000名成年人），其特征为肾单位的进行性丢失。一旦发生肾质量的显著损失，剩余的功能性肾单位经历代偿性变化，其包括肾血流量增加和肾小管细胞肥大。虽然这些变化对生存至关重要，但它们可能使剩余的肾单位受到更高水平的肾毒性物质的影响，其中之一是无机汞（Hg 2+）。汞在环境中普遍存在，无机形式对肾脏有严重的有害影响。事实上，肾脏，特别是近曲小管，是汞2+积累和毒性的主要部位。近端小管也是代偿性肾小管肥大的主要部位。我们以前已经表明，在模型中减少肾脏质量，有一个显着的变化，在处置的Hg 2+和增加的风险中毒的Hg 2+。然而，这些研究并没有确定或检查具体的机制，负责观察到的汞2+处置的变化。因此，拟议的研究的目的是评估代偿性细胞肥大对近端小管中Hg 2+的摄取和分泌所涉及的特定机制的影响。这些研究将集中在基底外侧膜中的有机阴离子转运蛋白（OAT）1和3，以及腔膜中的系统b 0，+，OAT 5和多药耐药相关蛋白（MRP）2和4。这些研究将检验代偿性细胞肥大与近端肾小管细胞中Hg 2+转运增加相关的假设。为了验证这一假设，我们提出了三个具体的目标：1）验证在代偿性细胞肥大后PT细胞对Hg 2+的选择性巯基S-缀合物的管腔摄取增加的假设; 2）验证肥大PT细胞对Hg 2+的基底外侧摄取与OAT 1和OAT 3对可转运的Hg 2+的摄取增加有关的假设; 3）验证以下假设：在代偿性细胞肥大后，PT细胞的Hg 2+腔输出增加，并且通过一种或多种多药耐药相关蛋白（MRP）由含巯基的螯合剂促进。这些研究将使用离体灌注近端小管的两种肾脏质量减少的动物模型：50%肾切除（NPX）和75% NPX家兔。50%NPX动物是肾脏质量减少的模型，其中代偿性变化维持正常的液体和电解质平衡。75%NPX动物是慢性肾衰竭早期阶段的模型，其中液体和电解质平衡改变。这些研究具有重要意义，因为它们将提供与肾脏质量减少模型中Hg 2+转运相关的新机制数据。此外，一些拟议的研究将利用已知的Hg 2+螯合剂，这些研究的数据将具有重要的临床意义，因为它们可能提供有关使用DMPS治疗正常人和暴露于有害剂量Hg 2+的肾质量减少的人的治疗效果的额外信息。

DESCRIPTION (provided by applicant): Chronic kidney disease, which affects approximately 17% of the adult population (about 40,000,000 adults) in the United States, is characterized by a progressive loss of nephrons. Once a significant loss of renal mass occurs, the remaining functioning nephrons undergo compensatory changes, which include increases in renal blood flow and hypertrophy of renal tubular cells. While these changes are vital for survival, they may subject the remaining nephrons to greater levels of nephrotoxicants, one of which is inorganic mercury (Hg2+). Mercury is prevalent in the environment and inorganic forms have serious detrimental effects in the kidney. In fact, the kidney, specifically the proximal tubule, is the primary site of Hg2+ accumulation and toxicity. Proximal tubules are also primary sites of compensatory tubular hypertrophy. We have shown previously that, in models of reduced renal mass, there is a significant change in the disposition of Hg2+ and an increased risk of intoxication by Hg2+. These studies, however, did not identify or examine specific mechanisms responsible for the observed alterations in Hg2+ disposition. Therefore, the purpose of the proposed studies is to assess the effect of compensatory cellular hypertrophy on specific mechanisms involved in the uptake and secretion of Hg2+ in proximal tubules. These studies will focus on the organic anion transporters (OAT) 1 and 3 in the basolateral membrane, and system b0,+, OAT5, and the multidrug resistance-associated proteins (MRP) 2 and 4 in the luminal membrane. These studies will test the hypothesis that compensatory cellular hypertrophy is associated with increased transport of Hg2+ in proximal tubular cells. To test this hypothesis, we propose three specific aims: 1) To test the hypothesis that luminal uptake of select thiol S-conjugates of Hg2+ into PT cells is increased following compensatory cellular hypertrophy; 2) To test the hypothesis that basolateral uptake of Hg2+ by hypertrophied PT cells is related to an increase in the uptake of transportable species of Hg2+ by OAT1 and OAT3; 3) To test the hypothesis that the luminal export of Hg2+ from PT cells increases following compensatory cellular hypertrophy and is promoted by thiol-containing chelators via one or more multidrug resistance-associated proteins (MRPs). These studies will utilize isolated perfused proximal tubules two animal models of reduced renal mass: 50% nephrectomized (NPX) and 75% NPX rabbits. 50% NPX animals are models of reduced renal mass where compensatory changes maintain normal fluid and electrolyte balance. 75% NPX animals are models of early stages of chronic renal failure wherein fluid and electrolyte balance is altered. These studies are significant in that they will provide new mechanistic data related to the transport of Hg2+ in models of reduced renal mass. Moreover, some of the proposed studies will utilize known chelator of Hg2+, data from these studies will be significant clinically in that they may provide additional information regarding the therapeutic efficacy of using DMPS to treat both normal humans and humans with reduced renal mass that have been exposed to deleterious doses of Hg2+.