Thorén Per E G, Söderman Olle, Engström Sven, von Corswant Christian
Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
Langmuir. 2007 Jun 19;23(13):6956-65. doi: 10.1021/la063700b. Epub 2007 May 22.
PEG-12-acyloxystearates constitute a novel class of pharmaceutical solubilizers and are synthesized from polyethylene glycol and 12-hydroxystearic acid, which has been esterified with a second acyl chain. The hemolytic activity of these surfactants decreases drastically with increasing pendant acyloxy chain length, and surfactants with an acyloxy chain of 14 carbon atoms or more are essentially nonhemolytic. In this paper, the interactions of PEG-12-acyloxystearates (acyloxy chain lengths ranging from 8 to 16 carbon atoms) with phosphatidylcholine vesicles, used as a model system for erythrocyte membranes, were studied in search of an explanation for the large variations in hemolytic activity. Surfactant-induced alterations of membrane permeability were investigated by studying the leakage of vesicle-entrapped calcein. It was found that all of the surfactants within the series interact with the vesicle membranes and cause slow leakage at elevated surfactant concentrations, but with large variations in leakage kinetics. The initial leakage rate decreases rapidly with increasing pendant acyloxy chain length. After prolonged incubation, on the other hand, the leakage is not a simple function of acyloxy chain length. The effect of the surfactants on membrane integrity was also investigated by turbidity measurements and cryo-transmission electron microscopy. At a surfactant/lipid molar ratio of 0.4, the vesicle membranes are saturated with surfactant. When the surfactant/lipid molar ratio is further increased, the vesicle membranes are progressively solubilized into mixed micelles. The rate of this process decreases strongly with increasing acyloxy chain length. When comparing the results of the different experiments, it can be concluded that there is no membrane permeabilization below saturation of the vesicle membranes. The large variations in the kinetics suggest that several steps are involved in the mechanism of leakage induced by PEG-12-acyloxystearates and that their relative rates vary with acyloxy chain length. The slow kinetics may in part be explained by the low critical micelle concentrations (CMCs) exhibited by the surfactants. The CMCs were found to be in the range of 0.003-0.025 microM.
聚乙二醇-12-酰氧基硬脂酸酯是一类新型的药物增溶剂，由聚乙二醇和12-羟基硬脂酸合成，其中12-羟基硬脂酸已与第二条酰基链酯化。随着侧链酰氧基链长度的增加，这些表面活性剂的溶血活性急剧下降，酰氧基链含14个或更多碳原子的表面活性剂基本无溶血作用。本文研究了聚乙二醇-12-酰氧基硬脂酸酯（酰氧基链长度为8至16个碳原子）与用作红细胞膜模型系统的磷脂酰胆碱囊泡之间的相互作用，以寻求对溶血活性巨大差异的解释。通过研究囊泡包裹的钙黄绿素的泄漏情况，考察了表面活性剂引起的膜通透性变化。结果发现，该系列中的所有表面活性剂均与囊泡膜相互作用，并在表面活性剂浓度升高时导致缓慢泄漏，但泄漏动力学存在很大差异。初始泄漏速率随侧链酰氧基链长度的增加而迅速降低。另一方面，长时间孵育后，泄漏并非酰氧基链长度的简单函数。还通过浊度测量和低温透射电子显微镜研究了表面活性剂对膜完整性的影响。在表面活性剂/脂质摩尔比为0.4时，囊泡膜被表面活性剂饱和。当表面活性剂/脂质摩尔比进一步增加时，囊泡膜逐渐溶解形成混合胶束。该过程的速率随酰氧基链长度的增加而强烈降低。比较不同实验的结果可以得出结论，在囊泡膜饱和以下不存在膜通透性增加的情况。动力学上的巨大差异表明，聚乙二醇-12-酰氧基硬脂酸酯诱导的泄漏机制涉及多个步骤，且它们的相对速率随酰氧基链长度而变化。缓慢的动力学部分可能是由于表面活性剂表现出的低临界胶束浓度（CMC）所致。发现CMC范围为0.003 - 0.025微摩尔。
