Biophysical insight into the interaction between  iron-based particles and liposomes

Iron is essential to most living organisms. Moreover, iron-based magnetic nanoparticles (Fe₃O₄ NPs) are synthetized and applied for their potential use in various biomedical fields due to their unique properties [1].  However, iron has been also found to accumulate and form larger aggregates in various organs, especially in the brain, which may be related to various, especially neuro-degenerative diseases [2]. Liposomes have gained an interest for their potential use as drug carriers [3] as well as biomimetic membrane models [4]. The interaction between Fe₃O₄ NPs and liposomes has not yet been investigated in sufficient details. We focused on the study of the interaction of two types of Fe₃O₄ NPs 1) less stable; zeta potential approx. -4 mV and 2) more stable; zeta potential approx. -38 mV. Three types of liposomes including a) positively charged 1,2-dioleoyl-3-trimethylammonium-propane chloride (DOTAP), b) negatively charged 1,2-dioleoylphosphatidylglycerol sodium salt (DOPG) and c) neutral phosphatidylcholine (PC) lipids were used. To note, DOTAP is used for nucleic acid/protein delivery [5], while PC and DOPG represent the main constituents of negatively charged biomembranes. Liposomes were prepared by hydration method in phosphate buffer solution followed by the extrusion through 100 nm filters. Samples were analyzed by means of size and zeta potential measurements using dynamic light scattering (DLS) and laser Doppler velocimetry methods using Zetasizer Nano ZS, respectively and visualized by the scanning electron microscopy (SEM). The hydrodynamic diameter and polydispersity index (PDI) obtained by DLS was approximately 150 nm (PDI 0,1) for pure liposomes, 2-3 µm (PDI 0,25) for less stable and 115 nm (PDI 0,15) for more stable Fe₃O₄ NPs. The strongest interaction, especially in the case of more stable and negatively charged Fe₃O₄ NPs was observed upon their incubation with DOTAP liposomes. This interaction was accompanied by the increase of hydrodynamic diameter of liposomes up to approx. 5 µm (PDI 0,7). The highest applied concentration of Fe₃O₄ NPs (100 µg/ml) moved the positive zeta potential value of DOTAP from 53 mV towards negative value -13 mV, which was followed by the formation of clusters as observed by the SEM. Altogether, the electrostatic nature of interaction between positively charged liposomes and negatively charged Fe₃O₄ NPs occurred. The formation of complexes with DOTAP liposomes can potentially improve the loading efficiency of Fe₃O₄ NPs into the cells. The further investigations are needed for the elucidation of their potential toxicity effects.