Japan Agency for Medical Research and Development, 1-7-1 Otemachi, Chiyoda-ku, Tokyo 100-0004, Japan.
Division of Drugs, National Institute of Health Sciences , 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan.
Langmuir. 2016 Jun 21;32(24):6074-82. doi: 10.1021/acs.langmuir.6b00741. Epub 2016 Jun 9.
Mechanical rigidity of the liposome membrane is often defined by the membrane bending modulus and is one of the determinants of liposome stability, but the quantitative experimental data are still limited to a few kinds of liposomes. Here, we used atomic force microscopy to investigate the membrane bending moduli of liposomes by immobilizing them on bovine serum albumin-coated glass in aqueous medium. The following lipids were used for liposome preparation: egg yolk phosphatidylcholine, dioleoylphosphatidylcholine, hydrogenated soybean phosphatidylcholine, dipalmitoylphosphatidylcholine, 1,2-dioleoyl-3-trimethylammonium-propane, cholesterol, and N-(carbonylmethoxypoly(ethylene glycol) 2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine. By using liposomes of various compositions, we showed that the thermodynamic phase state of the membrane rather than the electric potential or liposome surface modification with poly(ethylene glycol) is the predominant determinant of the bending modulus, which decreased in the following order: solid ordered > liquid ordered > liquid disordered. By using the generalized polarization value of the Laurdan fluorescent probe, we investigated membrane rigidity in terms of membrane fluidity. Atomic force microscopic analysis was superior to the Laurdan method, especially in evaluating the membrane rigidity of liposomes containing hydrogenated soybean phosphatidylcholine and cholesterol. Positively charged liposomes with a large bending modulus were taken up by cells more efficiently than those with a small bending modulus. These findings offer a quantitative method of analyzing the membrane rigidity of nanosized liposomes with different lipid compositions and will contribute to the control of liposome stability and cellular uptake efficiency of liposomal formulations intended for clinical use.
脂质体膜的力学刚性通常由膜弯曲弹性模量定义，是脂质体稳定性的决定因素之一，但定量实验数据仍然局限于少数几种脂质体。在这里，我们通过将脂质体固定在牛血清白蛋白涂覆的玻璃上，在水介质中使用原子力显微镜来研究脂质体的膜弯曲弹性模量。用于制备脂质体的脂质如下：卵黄卵磷脂、二油酰基磷脂酰胆碱、氢化大豆卵磷脂、二棕榈酰基磷脂酰胆碱、1,2-二油酰基-3-三甲铵丙烷、胆固醇和 N-(羰基甲氧基聚乙二醇 2000)-1,2-二硬脂酰-sn-甘油-3-磷酸乙醇胺。通过使用各种组成的脂质体，我们表明膜的热力学相状态而不是膜电势或聚乙二醇修饰的脂质体是弯曲弹性模量的主要决定因素，其按以下顺序降低：固体有序>液体有序>液体无序。通过使用 Laurdan 荧光探针的广义极化值，我们根据膜流动性研究了膜刚性。原子力显微镜分析优于 Laurdan 方法，特别是在评估含有氢化大豆卵磷脂和胆固醇的脂质体的膜刚性方面。具有大弯曲弹性模量的带正电荷的脂质体比具有小弯曲弹性模量的脂质体更有效地被细胞摄取。这些发现提供了一种分析具有不同脂质组成的纳米脂质体膜刚性的定量方法，并将有助于控制脂质体稳定性和用于临床用途的脂质体制剂的细胞摄取效率。
