Developing MRI contrast agents to detect progression in renal disease as a consequence of acidema

有机酸代谢障碍是一类先天性代谢障碍，其破坏氨基酸代谢， 导致在血液、尿液和其它生物材料中可检测到有机酸的异常积累。而 这些疾病个别罕见，但总体上对儿童健康有重大影响。慢性肾脏 疾病（CKD）是几种有机酸中毒的主要特征，患者需要常规监测 肾功能来管理治疗。甲基丙二酸血症（MMA）是一种有机酸血症， 由甲基丙二酰辅酶A β（Mut）突变引起的频率为1/50，000至1/100，000， 可预测的慢性肾病进展。事实上，CKD在MMA患者中的中位发病年龄为6.5岁， 肾功能不全的风险很高。不幸的是，目前监测肾脏健康的方法 包括血肌酐和血尿素氮的测定对MMA患者不可靠。一个 另一种策略是施用MRI造影剂以获得关于肾脏的功能信息。这 该提案涉及给予耐受性良好的有机化合物，通过 化学交换饱和转移（CEST）。这种机制的一个吸引人的特点是， 生成反映试剂周围环境的pH图，可能特别有用 肾脏是控制人体酸碱平衡的器官。我们将设计CEST pH传感器 它可以通过pH和灌注的变化监测CKD的进展，并将提供可靠的 肾脏整体健康状况的指标。目的一是合成一组咪唑-4，5-二甲酰胺类化合物 探头提供pH敏感的MRI对比度。质子交换率和产生的CEST对比度将是 作为缓冲溶液中pH的函数定量，以确定这些在体外的性能。我们还将 优化我们的pH和灌注成像方案，并使用C57 BL/6对照品表征药代动力学 小鼠在目标2中，我们将评估目标1中最好的试剂检测肾损害程度的敏感性。 在MMA的C57 BL/6 Mut-/-;TgINS-Alb-Mut小鼠模型中检测疾病，并使用 ISUCA。C57 BL/6 Mut-/-;TgINS-Alb-Mut小鼠表现出慢性肾小管间质性肾炎， 肾小球滤过率（GFR），其通过将小鼠置于高蛋白质（HP）饮食2个月来启动。 在目标3中，我们将在六组小鼠中测试我们最好的传感器，其中三组用柠檬酸钠处理 通过饮食补充和三个与辅酶Q10+维生素E补充到他们的饮食。的 各组还将包括诱导肾损伤的高蛋白攻击的三个不同时间。我们 我希望我们的新试剂和成像方案可以提供CKD的早期检测，而不需要 侵入性肾活检在标准监测方法不具备的情况下，这一点尤其重要。 比如MMA。

Organic acidemias are a class of inborn metabolic disorders which disrupt amino acid metabolism and lead to abnormal accumulation of organic acids detectable in blood, urine and other biomaterials. While individually rare, collectively these disorders have a significant impact on children’s health. Chronic Kidney Disease (CKD) is a cardinal feature of several organic acidemias, and patients require routine monitoring of kidney function to manage their treatment. Methylmalonic Acidemia (MMA) is an organic acidemia with a frequency of 1/50,000 to 1/100,000 caused by mutations in methylmalonyl-CoA mutase (Mut) with a predictable evolution to CKD. In fact, CKD is developed at a median onset age of 6.5 y in MMA patients who are at high risk of developing renal insufficiency. Unfortunately, current methods for monitoring renal health which include measuring blood creatinine and blood nitrogen urea are not reliable for MMA patients. An alternative strategy is to administer MRI contrast agents to acquire functional information on the kidneys. This proposal involves administering well tolerated, organic compounds which create MRI contrast through Chemical Exchange Saturation Transfer (CEST). An attractive feature of this mechanism is that it enables production of pH maps which reflect the environment surrounding the agents and might be particularly useful for the kidneys, organs which control the acid-base balance of the body. We will design CEST pH sensors which can monitor progression towards CKD through changes in pH and perfusion, and will provide a reliable indicator of the overall health of the kidneys. In Aim 1, we will synthesize a set of imidazole-4,5-dicarboxyamide probes to provide pH sensitive MRI contrast. The proton exchange rates and resulting CEST contrast will be quantified as a function of pH in buffered solutions to determine the performance of these in vitro. We will also optimize our pH and perfusion imaging protocol and characterize the pharmacokinetics using C57BL/6 control mice. In Aim 2, we will evaluate the sensitivity of our best agents from Aim 1 for detecting the extent of renal disease in the C57BL/6 Mut-/-;TgINS-Alb-Mut mouse model of MMA and validate the pH measurements using ISUCA. C57BL/6 Mut-/-;TgINS-Alb-Mut mice manifest chronic tubulointerstitial nephritis and a decreased glomerular filtration rate (GFR) which is initiated by placing the mice on a high protein (HP) diet for 2 months. In Aim 3, we will test our best sensor on six groups of mice with three groups treated with sodium citrate through diet supplementation and three more with CoQ10 + Vitamin E supplemented into their diets. The groups will also include three different timings for the high protein challenge which induces kidney injury. We expect our new agents and imaging protocols could provide an earlier detection of CKD without need of invasive kidney biopsy. This is particularly critical in conditions where standard monitoring methods are not feasible, such as MMA.