Division of Drug Delivery Technology, Leiden University, Leiden, The Netherlands.
Eur J Pharm Biopharm. 2012 Jun;81(2):294-302. doi: 10.1016/j.ejpb.2012.03.013. Epub 2012 Apr 2.
Cationic liposomes are known as potent adjuvants for subunit vaccines. The purpose of this work was to study whether the content and the physicochemical properties of the positively charged compound affect the adjuvanticity of cationic liposomes. Cationic liposomes containing a cationic compound (DDA, DPTAP, DC-Chol, or eDPPC) and a neutral phospholipid (DPPC) were prepared by the film hydration-extrusion method and loaded with influenza hemagglutinin (HA) by adsorption. The liposomes were characterized (hydrodynamic diameter, zeta potential, membrane fluidity, HA loading) and their adjuvanticity was tested in mice. The formulations were administered twice subcutaneously and mouse sera were analyzed for HA-specific antibodies by ELISA and for HA-neutralizing antibodies by hemagglutination inhibition (HI) assay. First, the influence of cationic lipid concentration in the DC-Chol/DPPC liposomes (10 vs. 50 mol%) was investigated. The DC-Chol/DPPC (50:50) liposomes showed a higher zeta potential and HA loading, resulting in stronger immunogenicity of the HA/DC-Chol/DPPC (50:50) liposomes compared to the corresponding (10:90) liposomes. Next, we used liposomes composed of 50 mol% cationic lipids to investigate the influence of the nature of the cationic compound on the adjuvant effect. Liposomes made of the four cationic compounds showed similar hydrodynamic diameters (between 100 and 170 nm), zeta potentials (between +40 and +50 mV), HA loading (between 55% and 76%) and melting temperatures (between 40 and 55 °C), except for the DC-Chol liposomes, which did not show any phase transition. HA adjuvanted with the DC-Chol/DPPC (50:50) liposomes elicited significantly higher total IgG1 and IgG2a titers compared to the other liposomal HA formulations and non-adjuvanted HA. A similar trend was observed for the HI titers. These results show that the adjuvanticity of cationic liposomes depends on both the content and the physicochemical properties of the charged compound.
阳离子脂质体是一种有效的亚单位疫苗佐剂。本研究旨在探讨带正电荷的化合物的含量和理化性质是否会影响阳离子脂质体的佐剂活性。采用薄膜水化-挤出法制备了含有阳离子化合物（DDA、DPTAP、DC-Chol 或 eDPPC）和中性磷脂（DPPC）的阳离子脂质体，并通过吸附法负载流感血凝素（HA）。对脂质体进行了表征（水动力直径、zeta 电位、膜流动性、HA 载量），并在小鼠中检测了其佐剂活性。制剂两次皮下给药，通过 ELISA 分析小鼠血清中 HA 特异性抗体，通过血凝抑制（HI）试验分析 HA 中和抗体。首先，研究了 DC-Chol/DPPC 脂质体中阳离子脂质浓度（10 与 50mol%）的影响。DC-Chol/DPPC（50:50）脂质体具有更高的 zeta 电位和 HA 载量，导致 HA/DC-Chol/DPPC（50:50）脂质体的免疫原性强于相应的（10:90）脂质体。接下来，我们使用由 50mol%阳离子脂质组成的脂质体来研究阳离子化合物的性质对佐剂效果的影响。由四种阳离子化合物制成的脂质体具有相似的水动力直径（100-170nm）、zeta 电位（+40-+50mV）、HA 载量（55%-76%）和相变温度（40-55°C），除了 DC-Chol 脂质体，其没有显示任何相变。用 DC-Chol/DPPC（50:50）脂质体佐剂的 HA 引起的总 IgG1 和 IgG2a 滴度明显高于其他脂质体 HA 制剂和非佐剂 HA。HI 滴度也呈现出类似的趋势。这些结果表明，阳离子脂质体的佐剂活性取决于带电荷化合物的含量和理化性质。
