Molecular Magnetic Resonance Imaging of Inflammation

项目摘要/摘要 非酒精性脂肪肝（NAFLD）影响着8000万至1亿美国公民。最常见的形式 这种疾病的最大特点是一种良性和非进行性的疾病，称为非酒精性脂肪肝（NAFL）。然而，~20% 的NALFD病例被归类为非酒精性脂肪性肝炎（NASH），这是一种炎性病症， 通常进展为肝纤维化、肝硬化，并最终发展为肝衰竭或肝癌。的唯一方法 区分NAFL和NASH是通过侵入性活检，这是昂贵的，造成不可忽视的严重风险， 内出血，因此不适合患者随访。活检不是一种实用的筛查工具， 结果NASH通常未被诊断，直到进展为晚期疾病。有一个生存的好处， 早期诊断和许多NASH治疗方法有望在未来几年内出现。无创 迫切需要诊断NASH或监测治疗反应的方法。有 对于晚期纤维化和肝硬化的放射学诊断有了进展，但是还没有方法来成像， 肝脏炎症总是先于疾病进展。 髓过氧化物酶（MPO）是鉴别诊断NASH的潜在影像学生物标志物。MPO分泌 通过活化的中性粒细胞作为炎症微环境的一部分， (ROS)由嗜中性粒细胞呼吸产生高度有害的ROS，如高氯酸。MPO是高度 在发炎肝脏的细胞外间隙中丰富，但在健康组织中稀少。 我们最近开发了一种小分子铁基MRI造影剂（Fe-PyC 3A）， 在ROS存在下弛豫率（MR信号产生效能）增加。这一空前庞大的 弛豫率变化是通过Fe 2+氧化成Fe 3+来实现的。Fe 2+离子是非常低效的弛豫剂， 高自旋Fe 3+是非常有效弛豫剂。使用急性脑梗死小鼠模型的初步成像实验 胰腺炎表明Fe-PyC 3A对健康组织的对比度增强很少或没有，但对健康组织的对比度增强很强。 和急性炎症组织的选择性对比增强。重要的是，对比增强的水平 与通过离体实验室定量测定的MPO活性水平显著正相关（r = 0.999）。 0.95，P < 0.0001）。 该提案的重点是优化和验证氧化还原活性铁络合物作为MPO特异性对照 用于肝脏MRI的药物。这项研究的最终目标是一种非侵入性的成像测试， 非进展性NAFL患者将受益于侵入性活检。的即时输出 拟议的工作将是一种MRI造影剂，1）对急性炎症特异，2）可以区分炎症 vs.小鼠中的非炎症性脂肪肝，和3）未表现出临床前安全性信号。

Project Abstract/ Summary Non-alcoholic fatty liver disease (NAFLD) affects between 80 to 100 million US citizens. The most common form of the disease is a benign and non-progressive condition called non-alcoholic fatty liver (NAFL). However, ~20% of NALFD cases are classified as non-alcoholic steatohepatitis (NASH), an inflammatory condition that commonly progresses to liver fibrosis, cirrhosis, and finally to liver failure or liver cancer. The only way to differentiate NAFL from NASH is via invasive biopsy which is expensive, poses a non-negligible risk of serious internal bleeding, and is thus ill-suited for patient follow-up. Biopsy is not a practical screening tool and as a result NASH typically goes undiagnosed until progression to advanced disease. There is a survival benefit to early diagnosis and a number of NASH therapeutics are anticipated within the next few years. Non-invasive methods to either diagnose NASH, or to monitor treatment response are sorely needed. There have been advances toward radiologic diagnosis of advanced fibrosis and cirrhosis but there are no methods to image the liver inflammation that invariantly precedes disease progression. Myeloperoxidase (MPO) is a potential imaging biomarker for differential diagnosis of NASH. MPO is secreted by activated neutrophils as part of the inflammatory microenvironment and converts reactive oxygen species (ROS) generated by neutrophil respiration into highly injurious ROS like perchlorous acid. MPO is highly abundant in the extracellular space of inflamed liver, but is scarce in healthy tissue. We recently developed a small molecule Fe-based MRI contrast agent (Fe-PyC3A) that undergoes a 10-fold increase in relaxivity (MR signal generating potency) in the presence of ROS. This unprecedentedly large relaxivity change is achieved by oxidation of Fe2+ to Fe3+. The Fe2+ ion is a very inefficient relaxation agent but high-spin Fe3+ is a very potent relaxation agent. Preliminary imaging experiments using a mouse model of acute pancreatitis demonstrate that Fe-PyC3A provides little-to-no contrast enhancement of healthy tissue but strong and selective contrast-enhancement of acutely inflamed tissue. Importantly, the level of contrast enhancement correlates significantly and positively with MPO activity levels determined by ex vivo laboratory quantitation (r = 0.95, P < 0.0001). This proposal focuses on optimizing and validating redox active Fe complexes as MPO-specific contrast agents for liver MRI. The ultimate goal of this research is a non-invasive imaging test to differentiate patients with non-progressive NAFL from patients will benefit from invasive biopsy. The immediate outputs of the proposed work will be an MRI contrast agent that is 1) specific to acute inflammation, 2) can differentiate inflamed vs. non-inflamed fatty liver in mice, and 3) does not exhibit pre-clinical safety signals.