Institute of Medicinal Chemistry, Hoshi University, Ebara 2-4-41, Shinagawa-ku, Tokyo 142-8501, Japan.
Int J Pharm. 2012 May 10;427(2):372-8. doi: 10.1016/j.ijpharm.2012.02.018. Epub 2012 Feb 18.
For the optimization of plasmid DNA (pDNA)-cationic lipid complexes and lipoplex delivery, proper indexes of the physicochemical properties of lipoplexes are required. In general, the characteristics of lipoplexes are defined by particle size and zeta-potential at various mixing ratios of cationic liposomes and pDNA. In this study, we characterized the hydration level of surfactant-modified and PEGylated cationic cholesterol-based (OH-Chol) liposomes and their lipoplexes by monitoring both the fluorescent probe laurdan and the dielectric relaxation time. Fluorescence measurement using laurdan detected hydration of the headgroup of lipids in surfactant-modified liposomes and PEGylated DOTAP-liposomes, but hardly any fluorescence was detected in PEGylated OH-Chol-liposomes because the PEG layers may extend and cover the fluorescent maker. On the other hand, the measurement of dielectric relaxation time of water molecules revealed total hydration, including hydration of the PEG layer and the headgroup of cationic lipids. Furthermore, we found an inverse correlation between hydration level and cellular uptake of PEGylated lipoplexes (R=0.946). This finding indicated that the dielectric relaxation time of water molecules provides an important indicator of hydration of liposome and lipoplexes along with the fluorescence intensity of laurdan.
为了优化质粒 DNA（pDNA）-阳离子脂质体复合物和脂质体的递送，需要适当的脂质体物理化学性质指标。通常，脂质体的特征由阳离子脂质体和 pDNA 的不同混合比例下的粒径和 Zeta 电位来定义。在这项研究中，我们通过监测荧光探针 Laurdan 和介电弛豫时间来表征经表面活性剂修饰和聚乙二醇化的阳离子胆固醇基（OH-Chol）脂质体及其脂质体的水合水平。使用 Laurdan 进行荧光测量可检测到表面活性剂修饰脂质体和聚乙二醇化 DOTAP-脂质体中脂质头部基团的水合作用，但在聚乙二醇化 OH-Chol-脂质体中几乎检测不到荧光，因为聚乙二醇层可能延伸并覆盖荧光标记物。另一方面，水分子的介电弛豫时间测量揭示了总水合作用，包括聚乙二醇层和阳离子脂质头部基团的水合作用。此外，我们发现水合水平与聚乙二醇化脂质体的细胞摄取呈负相关（R=0.946）。这一发现表明，水分子的介电弛豫时间与 Laurdan 的荧光强度一起，为脂质体和脂质体的水合作用提供了一个重要的指标。
