Mechanisms of diuretic resistance in heart failure

心力衰竭（HF）的症状和住院治疗主要是由充血引起的， 利尿剂是HF的基础治疗。这是有问题的，因为袢利尿剂抵抗（DR）是常见的， 持续拥堵的驱动因素以及随之而来的不良后果。我们最近证实：1） 人HF中DR的主要驱动因素是肾小管水平，而不是利尿剂输送不良。2)近侧 肾小管钠重吸收不是一个实质性的贡献者，而是3）在作用部位的反应减少， Henle环和代偿性远端肾小管钠重吸收驱动DR。4） 汉勒氏症似乎可以用传统上认为高于上限剂量的利尿剂剂量来解决。尽管 在定义DR的一般位置、罪魁祸首转运蛋白以及特定药物方面取得了进展 目标仍然不明确。存在三个化学计量相关的远端 钠（Na）转运途径。这三种途径的核心成分是氯化钠 在一些实施方案中，所述蛋白质包括协同转运蛋白（NCC）、上皮钠通道（ENaC）和氯碳酸氢盐交换剂pendrin。 重要的是，这些靶点可以用FDA批准的药物在人体中操纵; NCC可以选择性地被抑制。 被苄氟噻嗪（一种具有最小碳酸酐酶抑制作用的噻嗪）抑制，ENaC被阿米洛利抑制， 和pendrin下调NH 4Cl负载。我们还了解到，在循环中的钠重吸收， Henle是动态的，具有NKCC 2的实质性调节和可塑性。重要的是，NKCC 2剪接变体具有 已经确定，具有显着不同的离子亲和力，运输能力，和利尿剂的敏感性。 这项建议的主要目标是将上述知识转化为治疗 为实现这一目标，我们将开展3项机械性临床研究， 使用不同转运途径的药理学操作，内源性锂清除， 了解区域肾单位钠处理，和尿细胞外囊泡，以调查差异， 肾小管溶质转运蛋白水平和剪接变异体。具体而言，目标1将研究机制 这是人HF中袢利尿剂剂量反应曲线向右显著偏移的基础。这里我们将 连续滴定高选择性NKCC 2拮抗剂布美他尼至10 mg（400 mg呋塞米当量）， 稳定DR和利尿剂反应性HF患者。在目标2中，我们试图了解急性拮抗作用的影响， 阿米洛利敏感、噻嗪敏感或阿米洛利和噻嗪联合敏感转运途径 稳定型DR HF患者的利尿反应。我们将通过以下组合的管理来实现这一点： 安慰剂、阿米洛利和/或苄氟噻嗪联合布美他尼治疗稳定的DR HF患者。在 目的3：我们将确定已知下调pendrin的NH 4CL负载是否可以减少非阿米洛利/非阿米洛利。 噻嗪敏感性远端钠重吸收。通过实现这些目标，我们将获得巨大的 了解HF中DR的具体机制，从而制定靶向治疗策略。

Symptoms and hospitalizations for heart failure (HF) are primarily driven by congestion, making loop diuretics a cornerstone therapy in HF. This is problematic since loop diuretic resistance (DR) is common and a driver of persistent congestion and the poor outcomes that follow. We have recently confirmed that: 1) The dominant driver of DR in human HF is at the renal tubular level, rather than poor diuretic delivery. 2) Proximal tubular sodium reabsorption is not a substantial contributor, rather 3) reduced response at the site of action in the loop of Henle and compensatory distal tubular sodium reabsorption drive DR. 4) Resistance at the loop of Henle appears to be addressable with diuretic doses traditionally considered above the ceiling dose. Despite progress in defining the general locations for DR, the culprit transporters and thus specific druggable targets remain undefined. There is consensus on the existence of three stoichiometrically relevant distal sodium (Na) transport pathways. The central components to these three pathways are the sodium chloride cotransporter (NCC), the epithelial sodium channel (ENaC), and the chloride bicarbonate exchanger, pendrin. Importantly, these targets can be manipulated in humans with FDA approved drugs; NCC can be selectively inhibited by bendroflumethiazide (a thiazide with minimal carbonic anhydrase inhibition), ENaC by amiloride, and pendrin downregulated by NH4Cl loading. We have also learned that sodium reabsorption in the loop of Henle is dynamic with substantial regulation and plasticity of NKCC2. Importantly, NKCC2 splice variants have been identified that have dramatically different ion affinities, transport capacity, and diuretic sensitivities. The primary goal of this proposal is to translate the above knowledge into therapeutically actionable approaches to human DR. To accomplish this, we will conduct 3 mechanistically focused clinical trials using pharmacologic manipulation of different transport pathways, endogenous lithium clearance to understand regional nephron sodium handling, and urinary extracellular vesicles to investigate differences in tubular solute transporter levels and splice variants. Specifically, Aim 1 will investigate the mechanism underlying the substantial shift in the loop diuretic dose response curve to the right in human HF. Here we will serially titrate the highly selective NKCC2 antagonist bumetanide to 10mg (400mg furosemide equivalents) in stable DR and diuretic responsive HF patients. In Aim 2 we seek to understand the effect of acute antagonism of amiloride sensitive, thiazide sensitive, or combined amiloride & thiazide sensitive transport pathways on loop diuretic response in stable DR HF patients. We will accomplish this by administration of the combinations of placebo, amiloride, and/or bendroflumethiazide, in conjunction with bumetanide, to stable DR HF patients. In Aim 3 we will determine if NH4CL loading, known to downregulate pendrin, can reduce non-amiloride/non- thiazide sensitive distal sodium reabsorption. Through the completion of these aims we will gain substantial understanding of the specific mechanisms underlying DR in HF allowing targeted therapeutic strategies.