Harada Ryuichi, Furumoto Shozo, Tago Tetsuro, Furukawa Katsutoshi, Ishiki Aiko, Tomita Naoki, Iwata Ren, Tashiro Manabu, Arai Hiroyuki, Yanai Kazuhiko, Kudo Yukitsuka, Okamura Nobuyuki
Division of Neuro-imaging, Institute of Development, Aging and Cancer, Tohoku University, Sendai, 980-8575, Japan.
Cyclotron and Radioisotope Center, Tohoku University, Sendai, 980-8578, Japan.
Eur J Nucl Med Mol Imaging. 2016 Nov;43(12):2211-2218. doi: 10.1007/s00259-016-3453-y. Epub 2016 Jul 19.
F-THK5351 is a novel radiotracer developed for in vivo imaging of tau pathology in the brain. For the quantitative assessment of tau deposits in the brain, it is important that the radioactive metabolite does not enter the brain and that it does not bind to tau fibrils. The purpose of the study was to identify a radiolabeled metabolite of F-THK5351 in blood samples from human subjects and to characterize its pharmacological properties.
Venous blood samples were collected from three human subjects after injection of F-THK5351 and the plasma metabolite was measured by high performance thin layer chromatography. In addition, mass spectrometry analysis and enzymatic assays were used to identify this metabolite. Mice were used to investigate the blood-brain barrier permeability of the radioactive metabolite. Furthermore, the binding ability of the metabolite to tau aggregates was evaluated using autoradiography and binding assays using human brain samples.
About 13 % of the unmetabolized radiotracer was detectable in human plasma at 60 min following the injection of F-THK5351. The isolated radiometabolite of F-THK5351 was the sulphoconjugate of THK5351. This metabolite could be produced in vitro by incubating THK5351 with liver but not brain homogenates. The metabolite did not penetrate the blood-brain barrier in mice, and exhibited little binding to tau protein aggregates in post-mortem human brain samples.
These results suggest that the sole metabolite detectable in plasma seems to be generated outside the brain and does not cross into the brain, which does not affect quantitative analysis of PET images.
F-THK5351是一种开发用于大脑中tau蛋白病变活体成像的新型放射性示踪剂。对于大脑中tau蛋白沉积的定量评估，重要的是放射性代谢物不会进入大脑且不会与tau蛋白原纤维结合。本研究的目的是在人类受试者的血样中鉴定F-THK5351的放射性标记代谢物，并表征其药理特性。
在注射F-THK5351后从三名人类受试者采集静脉血样，并通过高效薄层色谱法测量血浆代谢物。此外，使用质谱分析和酶促测定来鉴定这种代谢物。使用小鼠研究放射性代谢物的血脑屏障通透性。此外，使用放射自显影和用人脑样本进行的结合测定来评估代谢物与tau蛋白聚集体的结合能力。
注射F-THK5351后60分钟，在人血浆中可检测到约13%的未代谢放射性示踪剂。分离出的F-THK5351放射性代谢物是THK5351的硫酸共轭物。这种代谢物可以通过将THK5351与肝脏匀浆而非脑匀浆孵育在体外产生。该代谢物在小鼠中未穿透血脑屏障，并且在死后的人脑样本中与tau蛋白聚集体的结合很少。
这些结果表明，血浆中可检测到的唯一代谢物似乎是在脑外产生的，不会进入大脑，这不会影响PET图像的定量分析。
