Yokoyama Shoko, Inagaki Akiko, Imura Tomohiro, Ohkubo Takahiro, Tsubaki Nobuyuki, Sakai Hideki, Abe Masahiko
School of Pharmaceutical Sciences, Kyushu University of Health and Welfare, 1714-1 Yoshino-cho, Nobeoka-city, Miyazaki 882-8508, Japan.
Colloids Surf B Biointerfaces. 2005 Sep;44(4):204-10. doi: 10.1016/j.colsurfb.2005.01.005.
Cationic liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and dipalmityldimethylammmonium bromide (DPAB) were prepared by the Bangham method and the effect of DPAB on the membrane properties was examined in terms of liposomal shape, particle size, trapping efficiency, surface potential and dispersibility. The dispersibility of the mixed DPPC/DPAB liposomes (the mole fraction of DPAB (XDPAB)>==0.05) was excellent and the dispersibility was maintained for 6 months, since the zeta-potential of the mixed liposomes was approximately +40 mV. The trapping efficiency of the mixed DPPC/DPAB liposomes (XDPAB=0.05) was 10 times greater than that of the DPPC liposomes, and the value was largest among the mixed liposomes (XDPAB=0-1.0). Freeze-fracture electron micrographs indicated that the shape of the mixed DPPC/DPAB liposomes (XDPAB=0.05) was that of large unilamellar vesicles (LUVs) with a diameter of approximately 2 microm, while the shape of the DPPC liposomes was that of multilamellar vesicles (MLVs). The mixed liposomes had, therefore, a high trapping efficiency. Furthermore, the shape of the mixed DPPC/DPAB liposomes (XDPAB=0.75) was also that of LUVs with a diameter of approximately 2 microm and these had a high trapping efficiency. Whereas, the particle size (500 nm) of the mixed DPPC/DPAB liposomes (XDPAB=0.25) was smaller than that of the former and had the minimum trapping efficiency. The phase transition temperature of the liposomal bilayer membranes indicated a maximum value at 0.25-0.30 mole fractions of DPAB. These facts were considered to be due to the fact that DPPC and DPAB, whose molar ratio was 7.5:2.5, were tightly packed in the liposomal bilayer membranes and that the curvature of the liposomal particle was resultantly large. Nevertheless, LUVs having a high trapping efficiency were easily obtained by mixing a small amount of DPAB with the DPPC.
采用Bangham法制备了由二棕榈酰磷脂酰胆碱（DPPC）和二棕榈基二甲基溴化铵（DPAB）组成的阳离子脂质体，并从脂质体形状、粒径、包封率、表面电位和分散性等方面研究了DPAB对膜性质的影响。混合的DPPC/DPAB脂质体（DPAB的摩尔分数（XDPAB）>=0.05）的分散性极佳，且由于混合脂质体的ζ电位约为+40 mV，该分散性可维持6个月。混合的DPPC/DPAB脂质体（XDPAB=0.05）的包封率比DPPC脂质体高10倍，且在混合脂质体（XDPAB=0 - 1.0）中该值最大。冷冻蚀刻电子显微镜照片表明，混合的DPPC/DPAB脂质体（XDPAB=0.05）的形状为直径约2微米的大单层囊泡（LUVs），而DPPC脂质体的形状为多层囊泡（MLVs）。因此，混合脂质体具有较高的包封率。此外，混合的DPPC/DPAB脂质体（XDPAB=0.75）的形状也是直径约2微米的LUVs，且这些脂质体具有较高的包封率。然而，混合的DPPC/DPAB脂质体（XDPAB=0.25）的粒径（500纳米）比前者小，且包封率最低。脂质体双层膜的相变温度在DPAB的摩尔分数为0.25 - 0.30时显示出最大值。这些事实被认为是由于摩尔比为7.5:2.5的DPPC和DPAB在脂质体双层膜中紧密堆积，导致脂质体颗粒的曲率较大。尽管如此，通过将少量DPAB与DPPC混合，很容易获得具有高包封率的LUVs。
