Interaction of antidepressant drugs with lipid bilayers studied by high-resolution carbon-13(13C-) and high-power deuterium nuclear magnetic resonance (2H-NMR) spectroscopy: The manner of binding as deduced from the differential line-broadening of 13C-NMR signals.
作者:RYOKO TABETA、SUDHA MAHAJAN、MITSUAKI MAEDA、HAZIME SAITO
DOI:10.1248/cpb.33.1793
日期:——
The manner of binding of imipramine (IMIP) and amitriptyline (AM) as well as chlorpromazine (CPZ) to single-or multi-bilayers of egg phosphatidylcholine (PC) was analyzed by carbon-13 (13C-) and deuterium nuclear magnetic resonance (2H-NMR) methods. For this purpose, we first tried to assign or re-assign the aromatic 13C chemical shifts by the selective proton-decoupling method. We observed that the 13C-NMR signals from a specific portion of the aromatic moiety of IMIP and AM are differently broadened as a result of binding to single bilayers of egg PC. In contrast, the signals of all carbons adjacent to protons in the aromatic moiety of CPZ were completely suppressed in the presence of egg PC. The observation of such differential linebroadening for IMIP and AM was interpreted in terms of the presence of anisotropic diffusion at the tricyclic moiety incorporated into the bilayers. However, drugs tightly bound to lipids such as CPZ cannot afford signals showing such differential line-broadening because of the slowed molecular motion in the bilayers. The extent of binding to lipids as viewed from the characteristic change of the 13C-NMR signals is in parallel with that determined from binding experiments by centrifugation and equilibrium dialysis. The reason why the 13C-NMR signals of IMIP and AM are visible even in the presence of lipid bilayers is considered to be the larger proportion of these drugs involved in fast exchange between lipids and the aqueous phase, on the basis of the observation of a major central peak in the 2H-NMR spectra of [2, 4, 6, 8-2H4] IMIP in the presence of multibilayers of egg PC. Nevertheless, there appears to be some portion of IMIP which penetrates deeply into the hydrophobic portion of egg PC and has a slow exchange rate compared with the inverse of the quadrupole splitting (16kHz).
对依米帕明(IMIP)、阿米替林(AM)及氯丙嗪(CPZ)与鸡蛋磷脂酰胆碱(PC)单层或多层膜的结合方式进行了碳-13(13C)和氘核磁共振(2H-NMR)方法的分析。为此,我们首先试图通过选择性质子去耦合方法来分配或重新分配芳香族13C化学位移。我们观察到,IMIP和AM的芳香部分特定区域的13C-NMR信号因与鸡蛋PC单层的结合而表现出不同的展宽。相比之下,CPZ芳香部分中与质子相邻的所有碳的信号在鸡蛋PC的存在下完全被抑制。这种对IMIP和AM的差异性展宽现象被解释为三环结构在双层膜中存在各向异性扩散的结果。然而,紧密结合于脂质的药物,如CPZ,由于分子运动在双层膜中的减缓,无法显示出这种差异性展宽信号。从13C-NMR信号的特征变化来看,与通过离心和平衡透析的结合实验结果相符,药物与脂质的结合程度也一致。考虑到在存在鸡蛋PC多层膜时观察到[2, 4, 6, 8-2H4] IMIP的2H-NMR光谱中主要中央峰,IMIP和AM的13C-NMR信号即使在脂质双层存在下仍然可见的原因被认为是这些药物在脂质与水相之间快速交换的比例较大。然而,似乎存在一部分IMIP深度渗透到鸡蛋PC的疏水部分,其交换速率相比四极分裂的倒数(16kHz)较慢。