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（约4000万成年人），其特征是肾单位的进行性损失。一旦肾团块发生显著损失，剩余的功能性肾单位发生代偿性变化，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物的影响，其中一种是无机汞（Hg2+）。汞在环境中普遍存在，无机形式的汞对肾脏有严重的有害影响。事实上，肾脏，特别是近端肾小管，是Hg2+积聚和毒性的主要部位。近端小管也是代偿性小管肥大的主要部位。我们之前已经表明，在肾块减少的模型中，Hg2+的处置有显著变化，Hg2+中毒的风险增加。然而，这些研究没有确定或检查导致观察到的Hg2+处置改变的特定机制。因此，本研究的目的是评估代偿性细胞肥大对近端小管摄取和分泌Hg2+的特定机制的影响。这些研究将重点关注基底外侧膜中的有机阴离子转运蛋白（OAT） 1和3，以及管腔膜中的系统b0、+、OAT5和多药耐药相关蛋白（MRP） 2和4。这些研究将验证代偿性细胞肥大与近端小管细胞中Hg2+转运增加有关的假设。为了验证这一假设，我们提出了三个具体目标：1)验证代偿性细胞肥大后，PT细胞对Hg2+的选择硫醇s缀合物的腔内摄取增加的假设；2)验证肥大PT细胞基底外侧摄取Hg2+与OAT1和OAT3摄取可转运物质Hg2+增加有关的假设；3)验证PT细胞在代偿性细胞肥大后Hg2+的腔内输出增加，并由含硫醇螯合剂通过一种或多种多药耐药相关蛋白（MRPs）促进。这些研究将利用分离的近端灌注小管两种肾肿块减少的动物模型：50%的肾切除（NPX）和75%的NPX兔。50%的NPX动物是肾块减少的模型，代偿性改变维持正常的液体和电解质平衡。75%的NPX动物是早期慢性肾衰竭的模型，其中液体和电解质平衡被改变。这些研究具有重要意义，因为它们将提供与肾肿块减少模型中Hg2+转运相关的新的机制数据。此外，一些拟议的研究将利用已知的Hg2+螯合剂，这些研究的数据将具有重要的临床意义，因为它们可能提供关于使用DMPS治疗暴露于有害剂量Hg2+的正常人和肾块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+.