The vesicle-to-micelle transformation of phospholipid–cholate mixed aggregates: A state of the art analysis including membrane curvature effects

Abstract

We revisited the vesicle-to-micelle transformation in phosphatidylcholine-cholate mixtures paying special attention to the lipid bilayer curvature effects. For this purpose, we prepared unilamellar vesicles with different starting sizes (2r(v)=45-120nm). We then studied mixtures of the unilamellar vesicles (1-8mmol kg(-1)) and sodium cholate (0-11.75mmolkg(-1)) by static and dynamic light scattering. The transformation generally comprises at least two, largely parallel phenomena; one increases and the other decreases the average mixed aggregate size. In our view, cholate first induces bilayer fluctuations that lead to vesicle asphericity, and then to lipid bilayer poration followed by sealing/reformation (or fusion). The cholate-containing mixed bilayers, whether in vesicular or open form, project thread-like protrusions with surfactant enriched ends even before complete bilayer solubilisation. Increasing cholate concentration promotes detachment of such protrusions (i.e. mixed micelles formation), in parallel to further softening/destabilising of mixed amphipat bilayers over a broad range of concentrations. Vesicles ultimately fragment into mixed thread-like micelles. Higher cholate relative concentrations yield shorter thread-like mixed micelles. Most noteworthy, the cholate-induced bilayer fluctuations, the propensity for large aggregate formation, the transformation kinetics, and the cholate concentration ensuring complete lipid solubilisation all depend on the starting mean vesicle size. The smallest tested vesicles (2r(v)=45nm), with the highest bilayer curvature, require ~30% less cholate for complete solubilisation than the largest tested vesicles (2r(v)=120nm).

Recent advances in non-ionic surfactant vesicles (niosomes): self-assembly, fabrication, characterization, drug delivery applications and limitations

“…The addition of surfactant molecules to vesicular dispersions of phospholipids leads to breakdown or solubilization of the liposomes and formation of a mixed micellar systems (Elsayed & Cevc, 2011). Such vesicle-to-micelle transition of phosphatidylcholine liposomes has been achieved by the addition of non-ionic surfactants of the polyoxyethylene cetyl ether class (Kim & Kim, 1991).…”

Enhanced photodynamic leishmanicidal activity of hydrophobic zinc phthalocyanine within archaeolipids containing liposomes

“…Bilayer deformability depends on the mixing/demixing of edge activators (EAs; hydrophilic detergents, such as sodium cholate, deoxycholate, or Tween 80) as a response to mechanical deformation stress. 42,43 However, the lateral mobility of foreign molecules dissolved within polyisoprenoid lipids rich in sugar, such as TPA bilayers, is low. In a previous work, we observed that the addition of EAs to pure TPA bilayers does not lead to highly deformable liposomes, due to the impaired lateral mobility (mixing/demixing) of EAs in TPAs.…”

Computer Simulation of the Solubilization of Liposomes by Bile Salts

“…The simulation results support the mechanistic conclusions drawn from the experimental data of light-scattering experiments. 8 The time-resolved light-scattering data show that an increase in the vesicle size during the formation of the mixed lipid/bile salt micelles can be observed. The validity of the unfolding of the vesicle membrane in the last stage was confirmed by the images obtained from transmission electron microscopy using cryotechnique.…”