Potential of Urinary AGT as a Novel Biomarker for Intrarenal RAS Activity in T1DM

描述（由申请人提供）：血管紧张素原（AGT）是肾素唯一已知的底物，肾素是肾素-血管紧张素系统（RAS）的限速酶。由于AGT水平接近肾素的Michaelis-Menten常数，因此，不仅肾素水平，AGT水平也可以决定RAS的活性，AGT水平上调可能导致血管紧张素肽形成增加，从而导致肾损伤。在糖尿病动物中观察到肾内AGT mRNA和/或蛋白水平升高。因此，肾内AGT在糖尿病肾病的发生发展中起着重要的作用。虽然有证据表明，在各种疾病和病理生理状态下，肾内RAS受到刺激，但目前还没有办法直接量化肾内RAS的激活程度。我们之前报道过AGT尿排泄率提供了血管紧张素ii输注大鼠肾内RAS状态的特定指标。为了便于定量测量，我们最近开发了一种使用人AGT酶联免疫吸附试验（ELISA）直接测量尿AGT的方法。使用我们实验室开发的技术，基于下面描述的几个初步数据，这项临床转化研究将定义和表征青少年和青年1型糖尿病（T1DM）患者尿AGT水平。总的假设是，尿AGT水平可以作为肾内RAS状态的一种新的生物标志物。根据这一假设，我们的具体目标是：1)建立青少年对照和T1DM患者尿AGT水平的临界值，这将在Specific Aim 4中使用。2)前瞻性研究表明，T1DM青少年的尿AGT水平高于年龄和性别匹配的对照组。3)利用GoKindD收集资料，证明有肾病的T1DM青少年尿AGT水平高于无肾病的T1DM青少年。4)在T1DM青少年中证明，进入期尿AGT水平基线高与肾功能恶化和尿AGT水平进一步升高有因果关系，而进入期尿AGT水平基线低的患者的肾功能和尿AGT水平稳定。我们ELISA方法的定量方面使我们能够轻松地比较受试者之间的数据。如果这项研究的目的得以实现，那么可以通过测量这些患者的尿AGT水平来监测激活的肾内RAS。因此，本研究项目有可能对糖尿病患者的个性化管理产生最大的影响。

DESCRIPTION (provided by applicant): Angiotensinogen (AGT) is the only known substrate for renin, which is the rate-limiting enzyme of the renin-angiotensin system (RAS). Because the levels of AGT are close to the Michaelis-Menten constant for renin, not only renin levels, but also AGT levels can dictate the activity of the RAS, and up-regulation of AGT levels may lead to increased angiotensin peptide formation and consequent renal injury. Enhanced intrarenal AGT mRNA and/or protein levels have been observed in diabetic animals. Thus, intrarenal AGT plays an important role in the development and progression of diabetic nephropathy. While there is evidence that the intrarenal RAS is stimulated in various diseases and pathophysiologic states, there are no means currently available to directly quantitate the magnitude of the activation of the intrarenal RAS. We previously reported that urinary excretion rates of AGT provide a specific index of intrarenal RAS status in angiotensin II-infused rats. To facilitate quantitative measurements, we recently developed a direct method to measure urinary AGT using human AGT enzyme-linked immunosorbent assays (ELISA). Using technology developed in our laboratory, based on several preliminary data described below, this clinical translational study will define and characterize the urinary AGT levels in juveniles and young adults with type 1 diabetes mellitus (T1DM). The overall hypothesis is that urinary AGT levels can be a novel biomarker of the intrarenal RAS status. In accord with this hypothesis, the following Specific Aims are targeted: 1) To establish a cutoff value of urinary AGT levels in juvenile control subjects and patients with T1DM, which will be used in Specific Aim 4. 2) To demonstrate that urinary AGT levels are higher in T1DM juveniles compared to that in age and gender-matched control subjects in a prospective study. 3) To demonstrate that urinary AGT levels are higher in T1DM juveniles with nephropathy compared to that in T1DM juveniles without nephropathy using GoKindD collection. 4) To demonstrate in T1DM juveniles that the high baseline of urinary AGT levels at the entry are causally linked to the progression of renal dysfunction and further increased urinary AGT levels, while renal function and urinary AGT levels are stable in patients with the low baseline of urinary AGT levels at the entry. The quantitative aspects of our ELISA approach allow us to compare data among subjects over time with ease. If the aims of the proposed study are achieved, the activated intrarenal RAS can be monitored by measuring urinary AGT levels in these patients. Therefore, this research project holds the potential to achieve the greatest impact for individualized patient management in DM.