Proximal Tubular Transport of Mercury and Effects of Reduced Renal Mass

描述(申请人提供)：慢性肾脏疾病，影响美国大约17%的成年人(约4000万成年人)，以肾单位进行性丧失为特征。一旦肾质量显著减少，剩下的功能肾单位就会发生代偿性变化，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，但它们可能会使剩余的肾脏受到更高水平的肾脏毒物，其中之一是无机汞(Hg2+)。汞在环境中普遍存在，无机形态对肾脏有严重的有害影响。事实上，肾脏，特别是近端小管，是Hg2+积累和毒性的主要部位。近端肾小管也是代偿性肾小管肥大的主要部位。我们以前已经证明，在肾脏质量减少的模型中，Hg2+的处置发生了显著变化，并增加了Hg2+中毒的风险。然而，这些研究没有确定或检查导致观察到的Hg2+处置变化的具体机制。因此，本研究的目的是评估代偿性细胞肥大对近曲小管Hg2+摄取和分泌的特定机制的影响。这些研究将集中在基底膜的有机阴离子转运体(OAT)1和3，以及腔膜中的b0，+，OAT5系统和多药耐药相关蛋白(MRP)2和4。这些研究将检验一个假设，即代偿性细胞肥大与近端肾小管细胞Hg2+转运增加有关。为了验证这一假说，我们提出了三个特定的目标：1)检验在细胞代偿性肥大后，PT细胞对Hg2+的选择性硫醇S结合物的腔内摄取增加的假说；2)检验肥厚的PT细胞对Hg2+的基侧摄取与OAT1和OAT3对可运输种类Hg2+的摄取增加有关的假说；3)检验这样的假说，即在细胞代偿性肥大后，PT细胞的腔内Hg2+输出增加，并且含有硫醇的螯合剂通过一个或多个多药耐药相关蛋白(MRPs)促进了Hg2+的腔内输出。这些研究将利用两种肾脏质量减少的动物模型：50%肾切除(NPX)和75%NPX兔。50%的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%的NPX动物是慢性肾功能衰竭早期的模型，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质量减轻模型中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治疗正常人和暴露于有害剂量Hg2+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+.