Nirogi Ramakrishna, Kandikere Vishwottam, Bhyrapuneni Gopinadh, Saralaya Ramanatha, Muddana Nageswararao, Komarneni Prashanth
Pharmacokinetics and Drug Metabolism, Discovery Research, Suven Life Sciences Ltd, Serene Chambers, Banjara Hills, Hyderabad 500034, India.
J Pharmacol Toxicol Methods. 2012 Jul;66(1):22-8. doi: 10.1016/j.vascn.2012.05.003. Epub 2012 May 16.
Reduction of cerebral cortical and hippocampal α7 neuronal nicotinic acetylcholine receptor (nAChR) density was observed in the Alzheimer's disease (AD) and other neurodegenerative diseases. Mapping the subtypes of nAChRs with selective ligand by viable, quick and consistent method in preclinical drug discovery may lead to rapid development of more effective therapeutic agents. The objective of this study was to evaluate the use of methyllycaconitine (MLA) in non-radiolabeled form for mapping α7 nAChRs in rat brain.
MLA pharmacokinetic and brain penetration properties were assessed in male Wistar rats. The tracer properties of MLA were evaluated in rat brain by dose and time dependent differential regional distribution studies. Target specificity was validated after blocking with potent α7 nAChR agonists ABBF, PNU282987 and nicotine. High performance liquid chromatography combined with triple quad mass spectral detector (LC-MS/MS) was used to measure the plasma and brain tissue concentrations of MLA.
MLA has shown rapid brain uptake followed by a 3-5 fold higher specific binding in regions containing the α7 nAChRs (hypothalamus - 1.60 ng/g), when compared to non-specific regions (striatum - 0.53 ng/g, hippocampus - 0.46 ng/g, midbrain - 0.37 ng/g, frontal cortex - 0.35 ng/g and cerebellum - 0.30 ng/g). Pretreatment with potent α7 nAChR agonists significantly blocked the MLA uptake in hypothalamus. The non-radiolabeled MLA binding to brain region was comparable with the α7 mRNA localization and receptor distribution reported for [(3)H] MLA in rat brain.
The rat pharmacokinetic, brain penetration and differential brain regional distribution features favor that MLA is suitable to use in preclinical stage for mapping α7 nAChRs. Hence, this approach can be employed as an essential tool for quicker development of novel selective ligand to map variation in the α7 receptor densities, as well as to evaluate potential new chemical entities targeting neurodegenerative diseases.
在阿尔茨海默病（AD）和其他神经退行性疾病中，观察到大脑皮质和海马体中α7神经元烟碱型乙酰胆碱受体（nAChR）密度降低。在临床前药物研发中，通过可行、快速且一致的方法用选择性配体绘制nAChRs的亚型，可能会促使更有效的治疗药物快速研发出来。本研究的目的是评估非放射性形式的甲基lycaconitine（MLA）在绘制大鼠脑中α7 nAChRs方面的用途。
在雄性Wistar大鼠中评估MLA的药代动力学和脑渗透特性。通过剂量和时间依赖性差异区域分布研究，在大鼠脑中评估MLA的示踪特性。在用强效α7 nAChR激动剂ABBF、PNU282987和尼古丁阻断后，验证靶点特异性。使用高效液相色谱结合三重四极杆质谱检测器（LC-MS/MS）测量MLA的血浆和脑组织浓度。
与非特异性区域（纹状体 - 0.53 ng/g、海马体 - 0.46 ng/g、中脑 - 0.37 ng/g、额叶皮质 - 0.35 ng/g和小脑 - 0.30 ng/g）相比，MLA显示出快速的脑摄取，随后在含有α7 nAChRs的区域（下丘脑 - 1.60 ng/g）有3至5倍更高的特异性结合。用强效α7 nAChR激动剂预处理可显著阻断下丘脑对MLA的摄取。非放射性MLA与脑区的结合与大鼠脑中[(3)H] MLA报道的α7 mRNA定位和受体分布相当。
大鼠的药代动力学、脑渗透和差异脑区分布特征表明，MLA适用于临床前阶段绘制α7 nAChRs。因此，这种方法可作为一种重要工具，用于更快地开发新型选择性配体，以绘制α7受体密度的变化，以及评估针对神经退行性疾病的潜在新化学实体。
