Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555, Japan.
Mol Imaging Biol. 2014 Jun;16(3):395-402. doi: 10.1007/s11307-013-0695-y. Epub 2013 Oct 24.
Rho is a small molecular weight GTP-binding protein and works as a molecular shuttling switch between an active (GTP-bound) and inactive (GDP-bound) state. Rho is known to be involved in cell motility, cell adhesion, and cytokinesis through actin cytoskeleton reorganization. The GTP-bound form of Rho interacts with its specific downstream target, triggering intracellular signaling cascades. Rho effectors such as Rho-kinases have been isolated on the basis of their selective binding to the GTP-bound form of Rho. Rho-kinase is thought to have an important role in the pathogenesis of a variety of neurological diseases because activation of the Rho/Rho-kinase pathway has been observed in various central nervous system disorders. Previous histochemical studies have shown multiple molecular mechanisms for the regulation of Rho-kinase. Neuroimaging of Rho/Rho-kinase has rarely been studied because of a lack of appropriate radiotracers. Recently, N-[(11)C]methyl-hydroxyfasudil, a new radiotracer for positron emission tomography (PET), has been introduced to measure Rho-kinase activity. In this study, the regional distribution and kinetics of N-[(11)C]methyl-hydroxyfasudil were investigated in the brains of mice.
A 90-min dynamic scan was performed following intravenous infusion of N-[(11)C]methyl-hydroxyfasudil.
The uptake of N-[(11)C]methyl-hydroxyfasudil reached a maximum within 5 min and gradually decreased in all organs. The standard uptake values (SUVs) in the brain, liver, and kidney on average between 30 to 60 min were 0.17 ± 0.03, 0.76 ± 0.18, and 0.62 ± 0.18 and from 60 to 90 min were 0.15 ± 0.01, 0.69 ± 0.33, and 0.64 ± 0.17, respectively. N-[(11)C]Methyl-hydroxyfasudil showed a widespread distribution throughout the brain, with low levels of radioactivity. Radioactivity concentration in plasma at 90 min after injection of N-[(11)C]methyl-hydroxyfasudil resulted in SUVs in the control and fasudil pretreatment of 0.0013 and 0.0023 ± 0.0008, respectively. Compared to normal control mice, about twofold higher radioactivity concentration was observed in fasudil-pretreated mice. In a cold brain injury mouse model, accumulation of N-[(11)C]methyl-hydroxyfasudil was slightly higher at the injury site than that at the control site, and the difference was statistically significant in the "24 h after injury" group (P < 0.05).
These results suggest that following brain injury, N-[(11)C]methyl-hydroxyfasudil binds to the active form of Rho-kinase. PET imaging using N-[(11)C]methyl-hydroxyfasudil could provide new insights into the pathophysiology of a variety of neurological disorders including stroke, inflammatory diseases, demyelinating diseases, Alzheimer's disease, and neuropathic pain.
Rho 是一种小分子 GTP 结合蛋白，作为一种分子穿梭开关，在活性（GTP 结合）和非活性（GDP 结合）状态之间转换。已知 Rho 参与细胞运动、细胞黏附和细胞分裂，通过肌动蛋白细胞骨架的重排。Rho 的 GTP 结合形式与特定的下游靶标相互作用，触发细胞内信号级联。Rho 效应物，如 Rho 激酶，已根据其与 Rho 的 GTP 结合形式的选择性结合而被分离出来。Rho 激酶被认为在多种神经疾病的发病机制中具有重要作用，因为在各种中枢神经系统疾病中观察到 Rho/Rho 激酶途径的激活。以前的组织化学研究表明了 Rho 激酶调节的多种分子机制。由于缺乏合适的示踪剂，对 Rho/Rho 激酶的神经影像学研究很少。最近，N-[(11)C]甲基-羟基法舒地尔作为正电子发射断层扫描（PET）的新示踪剂被引入，以测量 Rho 激酶的活性。在这项研究中，研究了 N-[(11)C]甲基-羟基法舒地尔在小鼠大脑中的区域分布和动力学。
在静脉输注 N-[(11)C]甲基-羟基法舒地尔后进行 90 分钟的动态扫描。
N-[(11)C]甲基-羟基法舒地尔的摄取在 5 分钟内达到最大值，并在所有器官中逐渐减少。脑、肝和肾的标准摄取值（SUV）在 30 到 60 分钟之间平均为 0.17±0.03、0.76±0.18 和 0.62±0.18，在 60 到 90 分钟之间分别为 0.15±0.01、0.69±0.33 和 0.64±0.17。N-[(11)C]甲基-羟基法舒地尔在整个大脑中分布广泛，放射性水平较低。注射 N-[(11)C]甲基-羟基法舒地尔 90 分钟后，血浆中的放射性浓度导致对照和法舒地尔预处理的 SUV 值分别为 0.0013 和 0.0023±0.0008。与正常对照组小鼠相比，法舒地尔预处理组的放射性浓度约高两倍。在冷脑损伤小鼠模型中，损伤部位 N-[(11)C]甲基-羟基法舒地尔的积累略高于对照部位，在“损伤后 24 小时”组差异有统计学意义（P<0.05）。
这些结果表明，脑损伤后，N-[(11)C]甲基-羟基法舒地尔与 Rho-激酶的活性形式结合。使用 N-[(11)C]甲基-羟基法舒地尔的 PET 成像可以为包括中风、炎症性疾病、脱髓鞘疾病、阿尔茨海默病和神经性疼痛在内的多种神经疾病的病理生理学提供新的见解。
