Evidence of Lipoplex Dissociation in Liquid Formulations

Aggregation is typically cited as the root cause of lipoplex transfection efficacy loss in liquid formulations. Typically, this conclusion is based on observed increases in lipoplex hydrodynamic size. A more detailed physical characterization of the lipoplex transfection efficacy diminution has previously never been conducted. As a result, most research has focused on either methods of forming more stable lipoplex formulations or preservation methods such as lyophilization. These studies typically consider the use of stabilizing additives, such as polymer and sugar molecules, to enhance the efficacy of lipoplex dispersions. This report details a recent multiangle laser light scattering study of the temporal evolution of lipoplex geometric size (i.e., radius of gyration) and molar mass in liquid-based formulations over several months. The results indicate that for the lipoplex systems considered, the primary factor underlying the long-term loss of lipoplex transfection efficiency is actually lipoplex dissociation caused by a decrease in the observed molar mass of some lipoplex formulations. The increasing geometric sizes observed are actually the result of lipoplex dissociation combined with an increase in volume. That is, the lipoplexes lose mass and expand in volume, leading to a less dense lipoplex structure over time. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91: 1225–1232, 2002