Comparative Biophysical Studies of Sartan Class Drug Molecules Losartan and Candesartan (CV-11974) with Membrane Bilayers

The interactions of the antihypertensive AT1 antagonists candesartan and losartan with membrane bilayers were studied through the application of DSC, Raman, and solid state 31P NMR spectroscopies. 1H and 13C NMR resonances of candesartan were assigned on the basis of 1D and 2D NMR spectroscopy. A 31P CP NMR broadline fitting methodology in combination with ab initio computations was implemented and, in conjunction with DSC and Raman results, provided valuable information regarding the perturbation, localization, orientation, and dynamic properties of the drugs in membrane models. In particular, results indicate that losartan anchors in the mesophase region of the lipid bilayers with the tetrazole group oriented toward the polar headgroup, whereas candesartan has less definite localization spanning from water interface toward the mesophase and upper segment of the hydrophobic region. Both sartan molecules decrease the mobilization of the phospholipids alkyl chains. Losartan exerts stronger interactions compared with candesartan, as depicted by the more prominent thermal, structural, and dipolar 1H–31P changes that are caused in the lipid bilayers. At higher concentrations, candesartan strengthens the polar interactions and induces increased order at the bilayer surface. At the highest concentration used (20 mol %), only losartan induces formation of microdomains attributed to the flexibility of its alkyl chain. These results in correlation to reported data with other AT1 antagonists strengthen the hypothesis that this class of molecules may approach the active site of the receptor by insertion in the lipid core, followed by lateral diffusion toward the binding site. Further, the similarities and differences of these drugs in their interactions with lipid bilayers establish, at least in part, their pharmacological properties.

本研究采用差示扫描量热法（DSC）、拉曼光谱（Raman）及固态31P核磁共振波谱法，针对降压AT1受体拮抗剂（AT1 antagonist）坎地沙坦（candesartan）与氯沙坦（losartan）和膜双层的相互作用展开探究。通过一维（1D）与二维（2D）核磁共振波谱法，完成了坎地沙坦的1H及13C核磁共振共振峰归属。本研究采用31P交叉极化（CP）核磁共振宽线拟合方法结合从头算（ab initio）计算，并将其与DSC及拉曼光谱结果联用，为阐明药物在膜模型中的扰动、定位、取向及动态特性提供了关键信息。
具体而言，研究结果显示：氯沙坦锚定在脂质双层的中间相区域，其四唑基团朝向极性头部基团；而坎地沙坦的定位相对模糊，其分布范围覆盖水界面至中间相及疏水区域上段。两类沙坦类（sartan）分子均可降低磷脂烷基链的流动性。相较于坎地沙坦，氯沙坦与脂质双层的相互作用更强，这一点可通过脂质双层中更显著的热学、结构及1H–31P偶极变化得到佐证。当浓度升高时，坎地沙坦会增强极性相互作用，并提升双层表面的有序性。在所用最高浓度（20 mol%）下，仅氯沙坦可诱导脂质微区形成，该现象与其烷基链的柔性密切相关。
结合已有其他AT1受体拮抗剂的相关研究数据，上述结果进一步支持以下假说：该类分子可通过插入脂质核心，再经侧向扩散抵达受体结合位点，从而接近受体活性区域。此外，这两种药物与脂质双层相互作用的异同点，可在一定程度上阐释其药理学特性的共性与差异。