Formulation and quality control of cationic liposomes

Cationic liposomes are traditionally used for delivering macromolecules such as nucleic acids to mammalian and plant cells. This paper describes a novel simple and relatively inexpensive method for preparation of cationic liposomes using an ethanol injection/pressure extrusion method. The study also evaluated the utility of a colorimetric method for quantification of cationic liposomes. Binding of erythrosine dye to cationic liposomes resulted in a shift of the absorption maximum of the dye from 528nm to 549nm in a buffer at pH 4.25, allowing quantification of these vesicles. Colour development was completed in 5 to 10 minutes at room temperature, with only 10% decrease in absorbance observed in the following 2 hours. Divergent values were noted in the presence of interfering agents such as detergents and salts. The erythrosine method is sensitive down to 0.20 µg/mL of cationic lipid and is linear to 3.13 µg/mL. The erythrosine dye method for quantitation of cationic liposomes is valuable for the field of liposome technology. In addition, a relatively simple method for separation of nucleic acids complexed to cationic liposomes from unbound molecules is presented. This method utilises a Ficoll-based gradient centrifugation method. Laboratory-formulated liposomes were just as efficient in binding nucleic acids as commercially available types.