Optimization of the Electroformation of Giant Unilamellar Vesicles (GUVs) with Unsaturated Phospholipids.

Giant unilamellar vesicles (GUV) are widely used cell membrane models. GUVs have a cell-like diameter and contain the same phospholipids that constitute cell membranes. The most frequently used protocol to obtain these vesicles is termed electroformation, since key steps of this protocol consist in the application of an electric field to a phospholipid deposit. The potential oxidation of unsaturated phospholipids due to the application of an electric field has not yet been considered even though the presence of oxidized lipids in the membrane of GUVs could impact their permeability and their mechanical properties. Thanks to mass spectrometry analyses, we demonstrated that the electroformation technique can cause the oxidation of polyunsaturated phospholipids constituting the vesicles. Then, using flow cytometry, we showed that the amplitude and the duration of the electric field impact the number and the size of the vesicles. According to our results, the oxidation level of the phospholipids increases with their level of unsaturation as well as with the amplitude and the duration of the electric field. However, when the level of lipid oxidation exceeds 25 %, the diameter of the vesicles is decreased and when the level of lipid oxidation reaches 40 %, the vesicles burst or reorganize and their rate of production is reduced. In conclusion, the classical electroformation method should always be optimized, as a function of the phospholipid used, especially for producing giant liposomes of polyunsaturated phospholipids to be used as a cell membrane model.