Modulation of drug transport at the renal proximal tubule by uremic solutes – implications in chronic kidney disease

摘要 慢性肾脏疾病（CKD）患者中肾清除药物的剂量调整目前基于 血清肌酐浓度，肾小球滤过（GFR）的生物标志物。尽管减少了剂量， 反应在CKD患者中仍然非常普遍。通常，观察到的药物暴露变化并不遵循 基于肌酐清除率（CLcr）下降的预测，例如阿昔洛韦（PEN）和替诺福韦 （十）。我们认为，CKD患者药物剂量不理想的主要原因是未能估计 CLcr能准确反映CKD患者肾小管分泌功能的下降， 主要通过肾小管分泌清除（与滤过相比），由于抑制作用， 尿毒症溶质的积累。 肾小管的分泌需要在基底外侧膜和外排转运的协调摄取转运 在近端小管上皮的顶膜处。体外研究表明， 尿毒症溶质，如马尿酸（HA）、硫酸吲哚酚（IS）、硫酸对甲酚（pCS）和N-氧化三甲胺 （TMAO），抑制摄取OAT转运蛋白。我们的初步数据表明，这些内源性化合物也 影响顶端外排转运蛋白。我们假设：1）近端的摄取和外排转运蛋白 在CKD中，肾小管被尿毒症溶质（HA、IS、pCS、TMAO）抑制，2） 内源性尿毒症溶质构成了肾间质和肾功能之间复杂的非线性关系的主要原因。 药物清除和CLcr，并导致潜在肾毒素的细胞内积累。 将使用PEN和TEN作为代表性的肾小管药物转运底物来研究这些假设 CKD患者肾脏药物清除率下降幅度大于CLcr估计值。Oseltamivir 羧酸盐（OST）将用作比较对照，其肾清除率遵循CLcr预测。 为了表征尿毒症溶质改变肾小管转运蛋白功能的机制， 增强肾小管毒性，我们将使用现有的转染细胞技术加上创新的三- 三维，微生理，原代细胞培养模型，将允许，首次，动态测量 和实时监测模型底物阿昔洛韦的细胞内积累， 替诺福韦和奥司他韦羧酸盐。一项同期临床研究将在健康受试者中评价相同的药物 以及患有3期或4期慢性肾病的患者。 成功完成这一创新的研究计划将提供深入了解的机制， 调节疾病环境中的肾小管清除功能，这将导致我们的基础范式改变， 基于滤过、肾小管分泌和 尿毒症生物标志物。

ABSTRACT Dose adjustment of renally cleared drugs in patients with chronic kidney diseases (CKD) is currently based on serum creatinine concentration, a biomarker of glomerular filtration (GFR). Despite dose reduction, adverse drug reactions remain extremely prevalent in CKD patients. Often, observed changes in drug exposure do not follow predictions based on the decline in creatinine clearance (CLcr), as exemplified by penciclovir (PEN) and tenofovir (TEN). We assert that the primary cause of suboptimal drug dosing in patients with CKD is the failure of estimated CLcr to accurately reflect the functional decline of renal tubule secretory function in CKD patients, and that drugs cleared primaily by tubular secretion (vs filtration), are subject to further compromise in clearance due to inhibition of secretion by accumulating uremic solutes. Renal tubular secretion requires coordinated uptake transport at the basolateral membrane and efflux transport at the apical membrane of the proximal tubular epithelium. In vitro studies have established that accumulating uremic solutes such as hippuric acid (HA), indoxyl sulfate (IS), p-cresol sulfate (pCS), and trimethylamine N-oxide (TMAO), inhibit uptake OAT transporters. Our preliminary data suggests that these endogenous compounds also impact apical efflux transporters. We hypothesize that 1) both uptake and efflux transport proteins in the proximal tubule are inhibited by uremic solutes (HA, IS, pCS, TMAO) in CKD, and 2) inhibition of transporters by endogenous uremic solutes constitutes the principal cause of the complex nonlinear relationship between renal drug clearance and CLcr, and leads to intracellular accumulation of potential nephrotoxins. These hypotheses will be investigated using PEN and TEN as representative tubular drug transport substrates exhibiting a greater decline of renal drug clearance in CKD than that predicted by estimated CLcr. Oseltamivir carboxylate (OST) will serve as a comparative control, whose renal clearance does follow prediction by CLcr. In order to characterize the mechanisms by which uremic solutes alter tubular transporter protein function and potentiate tubular toxicity, we will use existing transfected cell technology coupled with an innovative three- dimensional, microphysiological, primary cell culture model that will allow, for the first time, dynamic measurement of transepithelial flux and real-time monitoring intracellular accumulation of model substrates penciclovir, tenofovir, and oseltamivir carboxylate. A concurrent clinical study will evaluate the same drugs in healthy subjects and patients with stage 3 or 4 chronic kidney disease. Successful completion of this innovative research program will provide in-depth insight into mechanisms that regulate tubular clearance function in the disease milieu which will lead to fundamental paradigm change in our clinical approach to managing drug dosing in CKD based upon a combination of filtration, tubular secretion, and uremic biomarkers.