Ramani Karthik, Balasubramanian Sathyamangalam V
Department of Pharmaceutical Sciences, 541 Cooke Hall, University at Buffalo, State University of New York, Amherst, NY 14260-1200, USA.
Biochim Biophys Acta. 2003 Dec 3;1618(1):67-78. doi: 10.1016/j.bbamem.2003.10.009.
Cochleates are lipid-based delivery system that have found application in drug and gene delivery. They are precipitates, formed as a result of interaction between cations (e.g. Ca2+) and negatively charged phospholipids such as phosphatidylserine (PS). In the present study, we investigated the utility of fluorescent probe Laurdan (6-dodecanoyl-2-dimethylamino naphthalene) to monitor cochleate phase formation. Following addition of Ca2+ to Laurdan labeled lipid vesicles comprised of brain phosphatidylserine (BPS), a significant blue shift in the emission peak maximum of Laurdan was observed and the spectral features were distinct from those observed for the gel and liquid-crystalline (LC) phases. This is consistent with the formation of anhydrous cochleate cylinders that was further confirmed by electron microscopy studies. Due to dipolar relaxation, excitation and emission generalized polarization (GPEx and GPEm) indicate transition from a LC to a rigid and dehydrated (RD) cochleate phase. These spectral changes were utilized to monitor the influence of lipid composition, ionic strength and lamellarity on the formation of cochleate phase. The results indicated that the presence of phosphatidylcholine (PC) and bulk Na+ concentration influenced the formation of cochleate structures from small unilamellar vesicles (SUV) and multilamellar vesicles (MLV) composed of PS. The presence of PC and higher bulk Na+ concentration stabilized the PS vesicles against collapse and total loss of contents, intermediate molecular events in the formation of cochleate structures. From these studies, we conclude that Laurdan fluorescence is a sensitive and a rapid method to detect cochleate phase formation.
耳蜗形脂质体是一种基于脂质的递送系统，已在药物和基因递送中得到应用。它们是阳离子（如Ca2+）与带负电荷的磷脂（如磷脂酰丝氨酸，PS）相互作用形成的沉淀物。在本研究中，我们研究了荧光探针劳丹（6-十二烷酰基-2-二甲基氨基萘）监测耳蜗形脂质体相形成的效用。向由脑磷脂酰丝氨酸（BPS）组成的劳丹标记脂质体中加入Ca2+后，观察到劳丹发射峰最大值发生显著蓝移，其光谱特征与凝胶相和液晶（LC）相的不同。这与无水耳蜗形圆柱体的形成一致，电子显微镜研究进一步证实了这一点。由于偶极弛豫，激发和发射广义极化（GPEx和GPEm）表明从LC相转变为刚性脱水（RD）耳蜗形脂质体相。这些光谱变化被用于监测脂质组成、离子强度和片层性对耳蜗形脂质体相形成的影响。结果表明，磷脂酰胆碱（PC）的存在和大量Na+浓度影响了由PS组成的小单层囊泡（SUV）和多层囊泡（MLV）形成耳蜗形结构。PC的存在和较高的大量Na+浓度使PS囊泡稳定，防止其塌陷和内容物完全流失，这是耳蜗形结构形成过程中的中间分子事件。从这些研究中，我们得出结论，劳丹荧光是检测耳蜗形脂质体相形成的一种灵敏且快速的方法。
