Liposomes are the most used drug delivery vehicle and their therapeutic function is closely linked to their lipid composition. Since most liposome characterization is done using bulk techniques, providing only ensemble averages, the lipid composition of all liposomes within the same formulation are typically assumed to be identical. Here we image individual liposomes using confocal microscopy to quantify that liposomal drug delivery formulations, including multiple component mixtures mimicking Doxil, display more than 10-fold variation in their relative lipid composition. Since liposome function is tightly regulated by the physicochemical properties bestowed by the lipid composition, such significant variations could render only a fraction of liposomes therapeutically active. Additionally, we quantified how this degree of compositional inhomogeneity was modulated by liposome preparation method, the saturation state of the membrane lipid, and whether anti-fouling polyethylene glycol (PEG) conjugated lipids were added to the initial lipid mix or inserted after liposome formation. We believe the insights into the factors governing the degree of inhomogeneity offers the possibility for producing more uniform liposomal drug delivery systems, potentially increasing their therapeutic efficacy.

脂质体是最常用的药物递送载体，其治疗功能与其脂质组成密切相关。由于大多数脂质体的表征是使用本体技术完成的，仅提供整体平均值，因此通常假定同一制剂中所有脂质体的脂质组成相同。在这里，我们使用共聚焦显微镜对单个脂质体进行成像，以量化脂质体药物传递制剂（包括模仿Doxil的多组分混合物）在其相对脂质组成中显示超过10倍的变化。由于脂质体的功能受到脂质组合物赋予的理化特性的严格调节，因此这种显着的变化可能仅使一部分脂质体具有治疗活性。另外，我们定量了如何通过脂质体制备方法调节这种成分不均匀度，膜脂质的饱和状态，以及是否将防垢聚乙二醇（PEG）共轭脂质添加到初始脂质混合物中或在脂质体形成后插入。我们认为，对控制不均匀程度的因素的见识为生产更均匀的脂质体药物递送系统提供了可能性，从而有可能提高其治疗功效。