Khopade Ajay J, Shenoy Dinesh B, Khopade Surekha A, Jain Narendra K
Langmuir. 2004 Aug 31;20(18):7368-73. doi: 10.1021/la049682k.
The effect of 4th generation poly(amidoamine) dendrimer (4G PAMAM) present in an anionic phospholipid composition, consisting of hydrogenated soyphosphatidylcholine (HSPC), cholesterol (CH), dicetyl phosphate (DCP), and poly(ethylene glycol) (Mw approximately 2000) derivatized phosphatidylethanolamine (PEG2000-PE), on the hydration and liquid crystalline structure formation was investigated. The optical and polarized light microscopies of the liposomal dispersion obtained from the hydrated lipid composition show two types of birefringent structures (mesophases): plastic, wormlike microstructures and conventional, over-elongated lamellae. Differential scanning calorimetry (DSC) shows an increase in the liquid crystalline phase transition (Tg) of the lipid composition from 60 to 94 degrees C with increasing 4G PAMAM concentrations from 0 to 0.011 mM, respectively. The Tg values of the two microstructures were 68 and 84 degrees C, respectively, indicating that the plastic microstructures were 4G PAMAM/DCP-complexes-rich (alpha mesophases) and the conventional and elongated lamellae were dendrimer-doped HSPC/CH-rich microstructures (beta mesophases). Optical microscopy shows that the alpha mesophases convert into various other types of vesicular structures such as giant unilamellar vesicles and biliquid foams, upon heating above the phase transition temperature of the lipid composition (approximately 60-65 degrees C). The microstructure transformation is a result of an osmotic influx of water and the detergent action of PEG2000-PE present in the lipid composition. The transmission electron microscopy (TEM) images of the liposomal dispersion show particles embedding circular transparent domains that exactly correlate to the theoretical 4G PAMAM/DCP complex sizes, thus, providing evidence of 4G PAMAM interspersed within the two mesophases. Small-angle X-ray scattering (SAXS) measurements indicate that the alpha mesophases are a dendrimer-interlinked, symmetrically undulated lamellar phase and the beta mesophases are dendrimer-doped, occasionally kinked lamellae. An increase in dendrimer concentration in the lipid composition was found to decrease interlamellar spacing. On the basis of optical microscopy, DSC, TEM, and SAXS data, a model of dendrimer-doped mesophase structure and lamellae fusion is proposed. This investigation provides new self-assembled materials for drug/gene delivery and supplements the understanding of mechanisms involved in various biological processes such as membrane fusion, transmembrane permeation, and endocytosis.
研究了存在于由氢化大豆磷脂酰胆碱（HSPC）、胆固醇（CH）、磷酸二鲸蜡酯（DCP）和聚乙二醇（分子量约2000）衍生化磷脂酰乙醇胺（PEG2000-PE）组成的阴离子磷脂组合物中的第四代聚（酰胺胺）树枝状大分子（4G PAMAM）对水合作用和液晶结构形成的影响。从水合脂质组合物获得的脂质体分散体的光学显微镜和偏光显微镜显示出两种双折射结构（中间相）：可塑性的、蠕虫状微结构和常规的、过度伸长的片层。差示扫描量热法（DSC）表明，随着4G PAMAM浓度分别从0增加到0.011 mM，脂质组合物的液晶相转变温度（Tg）从60℃升高到94℃。两种微结构的Tg值分别为68℃和84℃，这表明可塑性微结构富含4G PAMAM/DCP复合物（α中间相），而常规的和伸长的片层是富含树枝状大分子掺杂的HSPC/CH的微结构（β中间相）。光学显微镜显示，在加热到脂质组合物的相变温度（约60-65℃）以上时，α中间相转变为各种其他类型的囊泡结构，如巨大单层囊泡和双液泡沫。微结构转变是脂质组合物中存在的水的渗透流入和PEG2000-PE的去污剂作用的结果。脂质体分散体的透射电子显微镜（TEM）图像显示颗粒嵌入圆形透明区域，这些区域与理论上的4G PAMAM/DCP复合物尺寸精确相关，因此，提供了4G PAMAM散布在两个中间相中的证据。小角X射线散射（SAXS）测量表明，α中间相是树枝状大分子相互连接的、对称起伏的片层相，β中间相是树枝状大分子掺杂的、偶尔扭结的片层。发现脂质组合物中树枝状大分子浓度的增加会减小层间距。基于光学显微镜、DSC、TEM和SAXS数据，提出了树枝状大分子掺杂中间相结构和片层融合的模型。这项研究为药物/基因递送提供了新的自组装材料，并补充了对诸如膜融合、跨膜渗透和内吞作用等各种生物过程中所涉及机制的理解。
