Studying The Membrane Fusion of Cationic Nanoliposomes Using a Simple Fusion Assay

Liposomes are spherical vesicles that can encapsulate and deliver drugs into the body. Moreover, the liposomal membrane resembles the cell membrane since they both have lipids as the main building blocks. Due to this property, liposomes can fuse into cell membranes with the help of fusogenic lipids and deliver their cargo straight into the cytosol of cells. However, this process is complicated to investigate in living cells, where there is a variety of proteins and lipids. In this study, we designed a simple experimental fusion assay that relies only on liposomes to study the fusion of nanoliposomes to micron-scale liposomes, where nanoliposomes acted as drug delivery vehicles, and micron-scale liposomes mimicked model cell membranes. Specifically, we investigated the influence of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), a cationic lipid, on the fusogenicity of nanoliposomes. Using this assay, we studied how the surface distribution of DOTAP on nanoliposomes contributes to membrane fusion. We utilized membrane phase separation to control the surface distribution of DOTAP on the liposomal membrane. We applied confocal scanning microscopy to monitor the process of membrane fusion over time through fluorescent signals. Images captured during this process were analyzed using ZEN imaging software and a personally developed MATLAB code. The results of these studies show that an increase in the amount of DOTAP in nanoliposomes’ lipid composition led to an increase in their ability to fuse into micron-scale liposomes. The results also reveal that concentrating DOTAP lipid into small regions on the surface of nanoliposomes enhanced the fusogenicity of the nanoliposomes.