PET imaging to assess blood-brain barrier function in alzheimers disease

阿尔茨海默病的一个主要特征是S病(AD)在大脑中积累了含有β-淀粉样蛋白的老年斑。有几条证据表明，大脑对Abeta的清除减少是Abeta积累的基础。表达于血脑屏障(BBB)内皮细胞的三磷酸腺苷结合盒(ABC)转运体可能在脑内分泌Abeta进入血液中起重要作用。多项研究表明，与年龄匹配的对照组相比，AD患者血脑屏障上的P-糖蛋白(ABCB1)功能可能受损。我们自己在缺乏多药耐药蛋白1(ABCC1；APPtg x ABCC1-/-)的淀粉样前体蛋白(APP)转基因小鼠(APPtg)中获得的数据表明，ABCC1在介导Abeta从大脑中清除方面可能发挥着比ABCB1更重要的作用，这反映在APPtg x ABCC1-/-小鼠大脑中的Abeta水平比表达ABCC1的对照小鼠高14倍。此外，与未经治疗的对照组动物相比，APPtg小鼠长期使用噻嗪治疗，与未经治疗的对照组动物相比，Abeta负荷显著降低。然而，到目前为止，尚不清楚在AD的进展过程中，血脑屏障的ABCC1功能是否真的发生了变化，以及噻嗪治疗是否确实增加了血脑屏障中ABCC1的功能。为了回答这些重要的问题，我们将使用正电子发射断层扫描(PET)和新开发的放射性示踪剂[18F]BFEP，在体内直接测量AD模型小鼠血脑屏障中ABCC1的功能活性。此外，将用[11C]匹兹堡化合物B([11C]PIB)评估小鼠大脑中的Aβ负荷，以建立APPtg小鼠局部ABCC1功能和Aβ负荷之间的相关性。采用这种实验方法，我们将研究AD小鼠脑内ABCC1功能下降的时间过程，并研究噻嗪对ABCC1功能的影响。体内PET实验将与病理标记物ABCC1和Abeta的全面免疫组织化学(IHC)分析以及Western印迹分析相补充。我们假设AD小鼠的ABCC1功能降低，并且局部脑Abeta负荷与ABCC1功能之间存在负相关关系。药物诱导血脑屏障ABCC1活性可能代表着未来AD治疗的一种有趣的策略，脑ABCC1功能的PET成像可能在此类新疗法的开发以及AD的早期诊断中是非常有用的成像生物标志物。

A major hallmark of Alzheimer¿s disease (AD) is the accumulation of senile plaques containing beta-amyloid in the brain. Several lines of evidence suggest that reduced Abeta clearance from the brain underlies Abeta accumulation. Adenosine triphosphate (ATP)-binding cassette (ABC) transporters that are expressed in endothelial cells of the blood-brain barrier (BBB) may play an important role in excreting Abeta from brain into the blood. A number of studies suggest that P-glycoprotein (ABCB1) function at the BBB may be impaired in AD patients as compared with age-matched control subjects. Our own data obtained in amyloid precursor protein (APP) transgenic mice (APPtg) that lack the multidrug resistance protein 1 (ABCC1; APPtg x ABCC1-/-) suggest that ABCC1 may play a more important role than ABCB1 in mediating Abeta clearance from the brain as reflected by up to 14-fold increased Abeta levels in brains of APPtg x ABCC1-/- mice as compared with control mice expressing ABCC1. Moreover, chronic treatment of APPtg mice with thiethylperazine, an antiemetic drug which activates ABCC1 transport activity in vitro, resulted in significant reductions in Abeta load as compared with untreated control animals. However, so far it is not known if ABCC1 function at the BBB is indeed altered during the progression of AD and if treatment with thiethylperazine indeed increases the function of ABCC1 at the BBB. To answer these important questions we will directly measure the functional activity of ABCC1 in vivo at the BBB of AD mouse models using positron emission tomography (PET) and the newly developed radiotracer [18F]BFEP. In addition, Abeta load in mouse brains will be assessed with [11C] Pittsburgh compound B ([11C] PIB) to establish a correlation between regional ABCC1 function and Abeta load in brains of APPtg mice. Using this experimental approach we will investigate the time course of ABCC1 function decline in AD mouse brain and study the effect of thiethylperazine treatment on ABCC1 function. In vivo PET experiments will be complemented with comprehensive immunohistochemistry (IHC) analyses of pathological markers, ABCC1 and Abeta as well as Western blot analysis. We hypothesize that ABCC1 function is decreased in AD mice and that there is an inverse relationship between regional brain Abeta load and ABCC1 function. Pharmacological induction of ABCC1 activity at the BBB may represent an interesting future therapeutic strategy in AD and PET imaging of cerebral ABCC1 function may be a very useful imaging biomarker in the development of such new therapeutics as well as in early diagnosis of AD.