Biegon Anat, Gibbs Andrew, Alvarado Maritza, Ono Michele, Taylor Scott
Medical Department, Brookhaven National Laboratory, Upton, New York, USA.
Synapse. 2007 Aug;61(8):577-86. doi: 10.1002/syn.20400.
Glutamate is the major excitatory neurotransmitter in the brain. Glutamate activation of the N-methyl-D-aspartate (NMDA) receptor subtype is thought to mediate important physiological and pathological processes, including memory formation and excitotoxicity. The goal of the present work was to characterize and validate a candidate agent for noninvasive positron emission tomography (PET) imaging of this receptor. [(3)H]-labeled N-[3-(3)H]-methyl-3-(thiomethylphenyl)cyanamide (CNS-5161) was incubated with rat brain homogenates at increasing concentrations, temperatures, and times to establish the binding kinetics and affinity of the ligand in vitro. Nonspecific binding was measured with 100 microM MK-801. The compound was also injected i.v. in rats pretreated with saline, NMDA, MK801, or a combination, and organ and brain regional uptake was assessed at various times after injection by autoradiography or dissection. Blood and brain samples were assayed for metabolites by high-performance liquid chromatography. CNS-5161 binds brain membranes with high affinity (K(d) < 4 nM) and fast association and dissociation kinetics. Specific binding increased in the presence of glutamate and glycine. Intravenous administration in control rats resulted in a heterogeneous brain distribution with hippocampus and cortex > thalamus > striatum > cerebellum, and a cortex/cerebellum ratio of 1.4. Pretreatment with NMDA increased the hippocampus-to-cerebellum ratio to 1.6-1.9 while MK801 abolished this increase, resulting in ratios close to 1. Thus, CNS-5161 binds preferentially to the activated state of the NMDA receptor channel in vitro and in vivo. The high affinity and fast kinetics make it compatible with PET imaging of a carbon-11 labeled CNS-5161.
谷氨酸是大脑中主要的兴奋性神经递质。N-甲基-D-天冬氨酸（NMDA）受体亚型的谷氨酸激活被认为介导重要的生理和病理过程，包括记忆形成和兴奋性毒性。本研究的目的是表征和验证一种用于该受体非侵入性正电子发射断层扫描（PET）成像的候选药物。将[（3）H]标记的N-[3-（3）H]-甲基-3-（硫代甲基苯基）氰胺（CNS-5161）与大鼠脑匀浆在不断增加的浓度、温度和时间下孵育，以建立该配体在体外的结合动力学和亲和力。用100 microM MK-801测量非特异性结合。该化合物还静脉注射到用生理盐水、NMDA、MK801或其组合预处理的大鼠体内，并在注射后不同时间通过放射自显影或解剖评估器官和脑区摄取。通过高效液相色谱法分析血液和脑样本中的代谢物。CNS-5161以高亲和力（K（d）<4 nM）结合脑膜，具有快速的结合和解离动力学。在谷氨酸和甘氨酸存在下特异性结合增加。在对照大鼠中静脉给药导致脑内分布不均，海马和皮质>丘脑>纹状体>小脑，皮质/小脑比值为1.4。用NMDA预处理使海马与小脑的比值增加到1.6 - 1.9，而MK801消除了这种增加，导致比值接近1。因此，CNS-5161在体外和体内优先结合NMDA受体通道的激活状态。高亲和力和快速动力学使其与碳-11标记的CNS-5161的PET成像兼容。
