Grupo de Química Coloidal y Supramolecular, Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
Biomacromolecules. 2010 Dec 13;11(12):3332-40. doi: 10.1021/bm1008124. Epub 2010 Nov 8.
Lipoplexes constituted by calf-thymus DNA (CT-DNA) and mixed cationic liposomes consisting of varying proportions of the cationic lipid 3β-[N-(N',N'-dimethylaminoethane)-carbamoyl]cholesterol hydrochloride (DC-Chol) and the zwitterionic lipid, 1,2-dioleoyl-sn-glycero-3-phosphoetanolamine (DOPE) have been analyzed by means of electrophoretic mobility, SAXS, and fluorescence anisotropy experiments, as well as by theoretically calculated phase diagrams. Both experimental and theoretical studies have been run at several liposome and lipoplex compositions, defined in terms of cationic lipid molar fraction, α, and either the mass or charge ratios of the lipoplex, respectively. The experimental electrochemical results indicate that DC-Chol/DOPE liposomes, with a mean hydrodynamic diameter of around (120 ± 10) nm, compact and condense DNA fragments at their cationic surfaces by means of a strong entropically driven electrostatic interaction. Furthermore, the positive charges of cationic liposomes are compensated by the negative charges of DNA phosphate groups at the isoneutrality L/D ratio, (L/D)(ϕ), which decreases with the cationic lipid content of the mixed liposome, for a given DNA concentration. This inversion of sign process has been also studied by means of the phase diagrams calculated with the theoretical model, which confirms all the experimental results. SAXS diffractograms, run at several lipoplex compositions, reveal that, irrespectively of the lipoplex charge ratio, DC-Chol/DOPE-DNA lipoplexes show a lamellar structure, L(α), when the cationic lipid content on the mixed liposomes α ≥ 0.4, while for a lower content (α = 0.2) the lipoplexes show an inverted hexagonal structure, H(II), usually related with improved cell transfection efficiency. A similar conclusion is reached from fluorescence anisotropy results, which indicate that the fluidity on liposome and lipoplexes membrane, also related with better transfection results, increases as long as the cationic lipid content decreases.
由小牛胸腺 DNA（CT-DNA）构成的脂质体和由阳离子脂质 3β-[N-（N'，N'-二甲氨基乙酰胺）-氨基甲酰基]氯化胆固醇（DC-Chol）和两性离子脂质 1,2-二油酰基-sn-甘油-3-磷酸乙醇胺（DOPE）组成的混合阳离子脂质体构成的脂质体已通过电泳迁移率、小角 X 射线散射（SAXS）和荧光各向异性实验以及理论计算相图进行了分析。实验和理论研究都在几个脂质体和脂质体组成的条件下进行，这些条件是通过阳离子脂质摩尔分数α以及脂质体的质量或电荷比来定义的。实验电化学结果表明，平均水动力学直径约为（120±10）nm 的 DC-Chol/DOPE 脂质体通过强熵驱动的静电相互作用在其阳离子表面上紧凑和浓缩 DNA 片段。此外，在等电中性 L/D 比（L/D）（ϕ）下，阳离子脂质体的正电荷由 DNA 磷酸基团的负电荷补偿，该比随着混合脂质体中阳离子脂质的含量降低而降低，对于给定的 DNA 浓度。这种符号反转过程也通过理论模型计算的相图进行了研究，该相图证实了所有的实验结果。在几个脂质体组成下运行的 SAXS 衍射图表明，无论脂质体的电荷比如何，当混合脂质体上的阳离子脂质含量α≥0.4 时，DC-Chol/DOPE-DNA 脂质体显示层状结构 L（α），而对于较低的含量（α=0.2）脂质体显示出通常与提高细胞转染效率相关的反六方结构 H（II）。荧光各向异性结果也得出了类似的结论，该结果表明，只要阳离子脂质含量降低，脂质体和脂质体膜的流动性也与更好的转染结果相关，就会增加。
