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

描述(申请人提供)：血管紧张素原(AGT)是肾素的唯一已知底物，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，不仅肾素水平，而且AGT水平也可以决定RAS的活性，AGT水平的上调可能导致血管紧张素肽的形成增加，从而导致肾脏损伤。在糖尿病动物中观察到肾内AGT基因和/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重要作用。虽然有证据表明肾内RAS在各种疾病和病理生理状态下受到刺激，但目前还没有方法直接量化肾内RAS的激活程度。我们以前曾报道，AGT的尿排泄率为血管紧张素II注射的大鼠肾内RAS状态提供了一个特定的指标。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)直接测定尿AGT的方法。利用我们实验室开发的技术，基于下面描述的几个初步数据，这项临床翻译研究将定义和表征青少年和青年1型糖尿病(T1 DM)患者的尿AGT水平。总体假设是，尿AGT水平可作为肾内RAS状态的新生物标志物。根据这一假设，我们的目标是：1)建立青少年对照组和T1 DM患者尿AGT水平的临界值，并将其用于特定目的。2)在一项前瞻性研究中，证明T1 DM青少年的尿AGT水平高于年龄和性别匹配的对照组。3)用GoKindD法检测有肾病的T1 DM青少年尿AGT水平高于无肾病的T1 DM青少年。4)在T1 DM青少年中证明，入院时尿AGT水平较高的基线与肾功能障碍的进展和尿AGT水平的进一步升高有因果关系，而入院时尿AGT水平较低的患者的肾功能和尿AGT水平稳定。我们的酶联免疫吸附试验方法的定量方面使我们能够轻松地比较不同受试者之间的数据。如果达到拟议研究的目的，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。 公共卫生相关性：我们的总体假设是，尿血管紧张素原(AGT)水平可作为肾内肾素-血管紧张素系统(RAS)状态的一种新的生物标志物，并可能作为发生肾损伤的风险的预测因子。如果拟议研究的目标成功，可以通过测量患者的尿AGT水平来监测肾内RAS。因此，这项研究项目有可能对1型糖尿病患者的个体化管理产生重大影响，使用尿液AGT作为生物标记物来优化RAS阻滞剂的治疗，这项拟议研究的成功可能会改善美国慢性肾脏疾病和心血管疾病的健康和经济负担。

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. PUBLIC HEALTH RELEVANCE: Our overall hypothesis is that urinary angiotensinogen (AGT) levels are useful as a novel biomarker of the status of the intrarenal renin-angiotensin system (RAS) and potentially serve as a predictor of the risks for developing renal injury. If the aims of the proposed study are successful, the intrarenal RAS can be monitored by measuring urinary AGT levels in patients. Therefore, this research project has the potential to achieve significant impact for individualized patient management in patients with type 1 diabetes using urinary AGT as a biomarker to optimize treatments with RAS blockades, and the success of this proposed study can lead to improved health and economic burden of chronic kidney disease and cardiovascular disease in the US.