Griffiths Peter C, Khayat Zeena, Tse Stephanie, Heenan Richard K, King Stephen M, Duncan Ruth
School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K.
Biomacromolecules. 2007 Mar;8(3):1004-12. doi: 10.1021/bm060930w. Epub 2007 Feb 24.
Polymers are appealing as pH-responsive elements of multicomponent systems designed to promote cytosolic delivery of macromolecular drugs (including proteins and genes), but so far the delivery efficiency achieved has been relatively modest. Therefore, the aim of this study was to apply several physicochemical techniques that are well established in the colloid field (surface tension measurements, small-angle neutron scattering (SANS), and electron paramagnetic resonance (EPR)) to probe the mechanism of endosomolytic polymer-surface interaction over the pH range 7.4 to 5.5 using the poly(amidoamine) (PAA) ISA23 x HCl and a series of "model" micelle surfaces. These micellar models were chosen to represent increasing complexity from simple, single surfactant sodium dodecylsulfate (SDS) micelles, surfactant mixtures containing bulky malono-bis-N-methylglucamide headgroups, or highly extended ethylene oxide headgroups. Spherical micelles composed of 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (lyso-PC) were also used. Changes in the onset of micellization, micelle surface fluidity, and in selected cases, the overall micelle shape and size were all quantified as a function of pH in the presence and absence of ISA23 x HCl. This amphoteric PAA is negatively charged at pH 7.4 and becomes gradually more protonated on exposure to lower pH values representative of the endosomal-lysosomal pathway. As expected, the strength of polymer interaction with anionic micelles increased with a decrease in pH, while for cationic micelles the opposite was observed. Addition of bulky, nonionic surfactant headgroups led to weaker interactions. The observations from surface tension and SANS studies showed a complex pattern of interaction with both an electrostatic and hydrophobic component. Using EPR it was confirmed that ISA23 x HCl perturbed the micelle palisade layer leading to a decrease in fluidity of the interface with a lower degree of headgroup hydration, and a significant change in micelle morphology. Surprisingly, there was no interaction between ISA23 x HCl and globular micelles formed from lyso-PC (a more biologically relevant model), and this suggests that the PAA structure could be better optimized to promote rapid interaction with endosomal membranes at the physiologically relevant pH 6.5.
聚合物作为多组分系统的pH响应元件，在促进大分子药物（包括蛋白质和基因）的胞质递送方面颇具吸引力，但迄今为止所实现的递送效率相对较低。因此，本研究的目的是应用胶体领域中一些成熟的物理化学技术（表面张力测量、小角中子散射（SANS）和电子顺磁共振（EPR）），使用聚（酰胺胺）（PAA）ISA23·HCl和一系列“模型”胶束表面，探究在pH范围7.4至5.5内聚合物与表面相互作用的内体溶解机制。选择这些胶束模型来代表从简单的单一表面活性剂十二烷基硫酸钠（SDS）胶束、含有庞大丙二酸双-N-甲基葡糖酰胺头基的表面活性剂混合物或高度伸展的环氧乙烷头基的表面活性剂混合物逐渐增加的复杂性。还使用了由1-棕榈酰-2-羟基-sn-甘油-3-磷酸胆碱（溶血磷脂酰胆碱，lyso-PC）组成的球形胶束。在有和没有ISA23·HCl的情况下，胶束化起始、胶束表面流动性的变化，以及在某些情况下胶束的整体形状和大小都作为pH的函数进行了量化。这种两性PAA在pH 7.4时带负电荷，在暴露于代表内体-溶酶体途径的较低pH值时逐渐质子化程度增加。正如预期的那样，聚合物与阴离子胶束的相互作用强度随着pH的降低而增加，而对于阳离子胶束则观察到相反的情况。添加庞大的非离子表面活性剂头基导致相互作用较弱。表面张力和SANS研究的观察结果显示出与静电和疏水成分的复杂相互作用模式。使用EPR证实，ISA23·HCl扰乱了胶束栅栏层，导致界面流动性降低，头基水合程度降低，并且胶束形态发生显著变化。令人惊讶的是，ISA23·HCl与由lyso-PC形成的球状胶束（一种更具生物学相关性的模型）之间没有相互作用，这表明PAA结构可以更好地优化，以促进在生理相关pH 6.5下与内体膜的快速相互作用。
