Evaluation of the Effects of Hydrophilic Probes on Membrane Permeability and Stability

The investigation of certain features of liposomes such as their lipid bilayer permeability or their propen-sity to fuse, quite often relies on the entrapment in the internal aqueous compartment of hydrophilicmolecules whose optical properties change when they are released into the bulk. However, thoughdefined as probes, these molecules bear functional groups that can interact with the liposome compo-nents thus having the potential of affecting the properties of the aggregate. To the best of our knowledge,this issue is scarcely hashed in the literature, despite its importance for an appropriate use of hydrophilicprobes in liposome characterization.The influence of calcein, rhodamine B and phenol red, three hydrophilic dyes generally employedin liposome characterization, on the features of some cationic liposomes was investigated by dynamiclaser light scattering, fluorescence and absorption measurements. The presence of the hydrophilic dyein the internal aqueous compartment of liposomes strongly affects liposome stability, dimension andpermeability depending on the molecular structure of probe and lipid components.