Hu Wei, Pan Donghui, Wang Yalin, Bao Weiqi, Zuo Chuantao, Guan Yihui, Hua Fengchun, Yang Min, Zhao Jun
PET Center, Huashan Hospital, Fudan University, Shanghai, China.
Department of Nuclear Medicine, Affiliated Wuxi People's Hospital, Nanjing Medical University, Wuxi, China.
Front Neurosci. 2020 Sep 29;14:810. doi: 10.3389/fnins.2020.00810. eCollection 2020.
In the pathogenesis of Alzheimer's disease (AD), microglia play an increasingly important role. Molecular imaging of neuroinflammatory targeting microglia activation and the high expression of 18-kDa translocator protein (TSPO) has become a hot topic of research in recent years. Dynamic monitoring neuroinflammation is crucial for discovering the best time point of anti-inflammatory therapy. Motivated by this, Positron emission tomography (PET) imaging in an APP/PS1 mouse model of AD, using F-labeled DPA-714 to monitor microglia activation and neuroinflammation, were performed in this paper. We prepared [F]DPA714 and tested the biological characteristics of the molecular probe in normal mice. To obtain a higher radiochemical yield, we improved the [F]-fluorination conditions in the precursor dosage, reaction temperature, and synthesis time. We performed [F]DPA714 PET scanning on APP/PS1 mice at 6-7, 9-10, 12-13, and 15-16 months of age, respectively. The same experiments were conducted in Wild-type (Wt) mice as a control. Referring to the [F]DPA714 concentrated situation in the brain, we performed blocking experiments with PK11195 (1 mg/kg) in 12-13-months-old APP/PS1 mice to confirm the specificity of [F]DPA714 for TSPO in the APP/PS1 mice. Reconstructed brain PET images, fused with the Magnetic Resonance Imaging (MRI) template atlas, and the volumes of interests (VOIs) of the hippocampus and cortex were determined. The distribution of [F]DPA714 in the brain tissues of 15-16-months-old APP/PS1 and Wt mice were studied by immunofluorescence staining. Through the reaction of F, with 2 mg precursor dissolved in 300 ul acetonitrile at 105°C for 10 min, we obtained the optimal radiochemical yield of 42.3 ± 5.1% (non-decay correction). Quantitative analysis of brain PET images showed that the [F]DPA714 uptake in the cortex and hippocampus of 12-13-months-old APP/PS1 mice was higher than that of the control mice of the same age (cortex/muscle: 2.77 ± 0.13 vs. 1.93 ± 0.32, = 0.0014; hippocampus/muscle: 3.33 ± 0.10 vs. 2.10 ± 0.35, = 0.0008). The same significant difference was found between 15- and 16-months-old APP/PS1 mice (cortex/muscle: 2.64 ± 0.14 vs. 1.86 ± 0.52, p=0.0159; hippocampus/muscle: 2.89 ± 0.53 vs. 1.77 ± 0.48, = 0.0050). Immunofluorescence staining showed that the activation of microglia and the level of TSPO expression in the cortex and hippocampus of APP/PS1 mice were significantly higher than Wt mice. [F]DPA714, a molecular probe for targeting TSPO, showed great potential in monitoring microglia activation and neuroinflammation, which can be helpful in discovering the best time point for anti-inflammatory therapy in AD.
在阿尔茨海默病（AD）的发病机制中，小胶质细胞发挥着越来越重要的作用。针对小胶质细胞活化和18 kDa转位蛋白（TSPO）高表达的神经炎症分子成像已成为近年来研究的热点。动态监测神经炎症对于发现抗炎治疗的最佳时间点至关重要。受此启发，本文在AD的APP/PS1小鼠模型中进行了正电子发射断层扫描（PET）成像，使用F标记的DPA-714监测小胶质细胞活化和神经炎症。我们制备了[F]DPA714并在正常小鼠中测试了该分子探针的生物学特性。为了获得更高的放射化学产率，我们在前体剂量、反应温度和合成时间方面改进了[F]氟化条件。我们分别在6-7、9-10、12-13和15-16月龄的APP/PS1小鼠上进行了[F]DPA714 PET扫描。在野生型（Wt）小鼠中进行了相同的实验作为对照。参照[F]DPA714在脑中的聚集情况，我们在12-13月龄的APP/PS1小鼠中用PK11195（1 mg/kg）进行阻断实验，以确认[F]DPA714在APP/PS1小鼠中对TSPO的特异性。重建脑PET图像，与磁共振成像（MRI）模板图谱融合，并确定海马体和皮质的感兴趣区（VOI）。通过免疫荧光染色研究了15-16月龄APP/PS1和Wt小鼠脑组织中[F]DPA714的分布。通过在105°C下将2 mg前体溶解于300 μl乙腈中反应10分钟，我们获得了42.3±5.1%的最佳放射化学产率（未衰变校正）。脑PET图像的定量分析表明，12-13月龄APP/PS1小鼠皮质和海马体中[F]DPA714的摄取高于同年龄对照小鼠（皮质/肌肉：2.77±0.13 vs. 1.93±0.32，p = 0.0014；海马体/肌肉：3.33±0.10 vs. 2.10±0.35，p = 0.0008）。在15-16月龄APP/PS1小鼠之间也发现了同样显著的差异（皮质/肌肉：2.64±0.14 vs. 1.86±0.52，p = 0.0159；海马体/肌肉：2.89±0.53 vs. 1.77±0.48，p = 0.0050）。免疫荧光染色显示，APP/PS1小鼠皮质和海马体中小胶质细胞的活化和TSPO表达水平显著高于Wt小鼠。[F]DPA714作为一种靶向TSPO的分子探针，在监测小胶质细胞活化和神经炎症方面显示出巨大潜力，这有助于发现AD抗炎治疗的最佳时间点。
