Concentration-dependent effect of DMSO on lipid vesicle structure under physiological conditions

Dimethyl Sulfoxide (DMSO) is widely used for drug delivery and in biology as a cryoprotectant because of its ability to dissolve drugs and biomolecules and due to its membrane permeating properties. Despite its extensive use, it is still unclear how this solvent affects the membrane structure and whether its effect is strongly dependent on membrane lipid composition. We employed vesicles of different complexity, from the simplest membrane model (DOPC) up to more complex ones (polar lipid extract of yeast and E. coli ) in physiological conditions and under osmotic stress. A wide range of DMSO content was studied, from 0 % to ≥ 40 %, using dynamic light scattering, small-angle neutron and X-ray scattering techniques. Our results show that vesicles in PBS maintain their integrity and structure up to 20 % DMSO, but only at higher DMSO concentrations ( ≥ 40 %) a drastic alteration of vesicle structure will occur. The main effect of DMSO appears to be a reduction in inter-membrane distances, linked to dehydration, and therefore an increase in stacking of membranes. We also demonstrated that DMSO’s effects on lipid vesicles generated in PBS are dependent on lipid composition, with more complex multi-component membranes, such as lipid polar extracts, demonstrating a higher resilience towards dehydration. Our findings highlight the importance of defining a DMSO threshold concentration that would allow stable and defined vesicle formation for any given lipid composition. • A threshold DMSO concentration for utilisation of lipid vesicles as drug delivery systems is proposed. • Low concentrations of DMSO, up to 20 %, do not have a measurable effect on vesicle structure. • The main effect of DMSO on vesicles is a reduction in inter-membrane distance, which leads to an increase of stacking. • DMSO’s effects on lipid vesicles are both concentration- and lipid-composition-dependent.