Longitudinal evaluation of a novel BChE PET tracer as an early in vivo biomarker in the brain of a mouse model for Alzheimer disease.
Longitudinal evaluation of a novel BChE PET tracer as an early in vivo biomarker in the brain of a mouse model for Alzheimer disease.
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作者：
Rejc L;Gómez-Vallejo V;Joya A;Moreno O;Egimendia A;Castellnou P;Ríos-Anglada X;Cossío U;Baz Z;Passannante R;Tobalina-Larrea I;Ramos-Cabrer P;Giralt A;Sastre M;Capetillo-Zarate E;Košak U;Knez D;Gobec S;Marder M;Martin A;Llop J
目的：丁酰胆碱酯酶(BChE)活性在阿尔茨海默病(AD)患者和AD动物模型中的活性增加，使该酶成为潜在的疾病生物标志物。然而，关于BChE作为AD生物标志物的能力的信息是相互矛盾的，这也是由于对BChE活性丰度的纵向研究很少。在这里，我们报告了使用有效的BChE选择性抑制剂[11C]4和正电子发射断层扫描(PET)结合计算机断层扫描(CT)对对照组和5xFAD(AD模型)动物大脑中BChE丰度的11C标记、体内稳定性、生物分布和纵向研究。我们将结果与体内淀粉样β蛋白(Aβ)沉积相关联，通过[18F]氟倍他滨-正电子发射体层摄影进行纵向评估。方法：通过11C甲基化对[11C]4进行放射性标记。对雌性野生型(WT)小鼠的血液和脑标本进行了代谢研究。使用动态PET-CT成像技术对雌性WT小鼠进行了生物分布研究。在7个月龄的雌性WT和5xFAD小鼠身上，体外和体内的PET成像阻断研究证明了特异性结合。对4、6、8、10和12月龄的雌性5xFAD小鼠进行了BChE的纵向PET成像，并与年龄匹配的对照组动物进行了比较。此外，使用[18F]氟倍他滨在2、5、7和11个月大的小鼠中评估了β斑块的分布。通过4、8、12个月的BChE和12个月的Aβ的体外染色对结果进行了验证。结果：合成的[11C]4具有足够的放化产率和摩尔活度，可用于正电子发射计算机断层显像。新陈代谢和生物分布研究证实，[11C]4在体内具有足够的稳定性，能够穿过血脑屏障(BBB)，并能迅速从脑中洗脱。阻断研究证实了结合的特异性。纵向正电子发射计算机断层扫描研究显示，与WT仔鼠相比，老年AD鼠大脑皮层、海马体、纹状体、丘脑、小脑和脑干中的BChE水平增加。[18F]弗洛贝塔本-正电子发射计算机断层扫描显示AD动物大脑皮层和海马区A-β斑块聚集的趋势与4-8月龄BCHE动物相似。与体外染色的结果相反，在体内观察到的BChE丰度在10和12个月龄比8月龄低。结论：BChE抑制剂[11C]4跨过血脑屏障，在WT小鼠体内被迅速洗出。AD和WT小鼠之间的比较显示，在疾病发展的早期，随着时间的推移，放射性示踪剂在AD影响的大脑区域积累。这一结果与Aβ的蓄积有很好的一致性，表明BChE是一种有希望的早期AD生物标志物。
Purpose: The increase in butyrylcholinesterase (BChE) activity in the brain of Alzheimer disease (AD) patients and animal models of AD position this enzyme as a potential biomarker of the disease. However, the information on the ability of BChE to serve as AD biomarker is contradicting, also due to scarce longitudinal studies of BChE activity abundance. Here, we report 11C-labeling, in vivo stability, biodistribution, and longitudinal study on BChE abundance in the brains of control and 5xFAD (AD model) animals, using a potent BChE selective inhibitor, [11C]4, and positron emission tomography (PET) in combination with computerised tomography (CT). We correlate the results with in vivo amyloid beta (Aβ) deposition, longitudinally assessed by [18F]florbetaben-PET imaging. Methods: [11C]4 was radiolabelled through 11C-methylation. Metabolism studies were performed on blood and brain samples of female wild type (WT) mice. Biodistribution studies were performed in female WT mice using dynamic PET-CT imaging. Specific binding was demonstrated by ex vivo and in vivo PET imaging blocking studies in female WT and 5xFAD mice at the age of 7 months. Longitudinal PET imaging of BChE was conducted in female 5xFAD mice at 4, 6, 8, 10 and 12 months of age and compared to age-matched control animals. Additionally, Aβ plaque distribution was assessed in the same mice using [18F]florbetaben at the ages of 2, 5, 7 and 11 months. The results were validated by ex vivo staining of BChE at 4, 8, and 12 months and Aβ at 12 months on brain samples. Results: [11C]4 was produced in sufficient radiochemical yield and molar activity for the use in PET imaging. Metabolism and biodistribution studies confirmed sufficient stability in vivo, the ability of [11C]4 to cross the blood brain barrier (BBB) and rapid washout from the brain. Blocking studies confirmed specificity of the binding. Longitudinal PET studies showed increased levels of BChE in the cerebral cortex, hippocampus, striatum, thalamus, cerebellum and brain stem in aged AD mice compared to WT littermates. [18F]Florbetaben-PET imaging showed similar trend of Aβ plaques accumulation in the cerebral cortex and the hippocampus of AD animals as the one observed for BChE at ages 4 to 8 months. Contrarily to the results obtained by ex vivo staining, lower abundance of BChE was observed in vivo at 10 and 12 months than at 8 months of age. Conclusions: The BChE inhibitor [11C]4 crosses the BBB and is quickly washed out of the brain of WT mice. Comparison between AD and WT mice shows accumulation of the radiotracer in the AD-affected areas of the brain over time during the early disease progression. The results correspond well with Aβ accumulation, suggesting that BChE is a promising early biomarker for incipient AD.