Influence of Dimethyl Sulfoxide on the Low-Temperature Behavior of Cholesterol-Loaded Palmitoyl-oleyl-phosphatidylcholine Membranes

Abstract

The properties of lipid membranes at low temperature are important for a number of biomedical and biotechnological applications, and the success of these applications depends on understanding the effects of temperature changes on intermolecular lipid-lipid and lipid-water interactions. Here, we use Fourier transform infrared spectroscopy to study lipid suspensions in water/dimethyl sulfoxide (DMSO) solutions in the -60 to 30 °C range. DMSO is a cryopreservative agent of cellular systems, and its action is largely related to its interaction with the lipid membrane, especially in the low-temperature regime. In the present work, we analyze the effects of solvent composition on the structural and thermotropic properties of cholesterol (chol)-loaded liposomes of palmitoyl-oleylphosphatidylcholine (POPC) because POPC/chol liposomes are suitable models of the plasmatic membrane. To this extent, we compare the properties of lipid vesicles suspended in water and water/DMSO solution at 0.10 DMSO mole fraction and we observe that the gel phase of the membrane has an increased thermal stability on DMSO addition. We estimate that the amount of unfrozen water at T = -60 °C is much reduced by the presence of DMSO, both in the gel- and the liquid-ordered phase of the membrane. Interestingly, we also evidence a reduced hydration of the lipid heads in the presence of DMSO when the vesicles are dispersed in a liquid solution, whereas the addition of DMSO does not alter the hydration state of phosphate and carbonyl groups in the frozen state of the membrane.

Effect of DMSO on the Mechanical and Structural Properties of Model and Biological Membranes

“…In the presence of DMSO, this melting transition is widened and upshifted to 33°C, increasing the temperature stability of the gel phase in the phase-separated membrane ( Table 1 ). A similar effect on the thermotropic behavior of single lipid systems (phosphatidylcholines) has been observed before ( 21 , 43 , 44 , 45 ).

Figure 2 Heating curves showing the temperature dependences of the ν s (CH 2 ) band peak position for the binary (POPC/ESM 1:1) and ternary (POPC/ESM/Chol 1:1:3) MLVs in water (W) and water/DMSO (W/DMSO) solution (10 mol%).

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“…In the presence of DMSO, this melting transition is widened and upshifted to 33 C, increasing the temperature stability of the gel phase in the phase-separated membrane (Table 1). A similar effect on the thermotropic behavior of single lipid systems (phosphatidylcholines) has been observed before (21,(43)(44)(45).…”

“…The temperature trends based on the ν s (CH 2 ) mode ( Fig. 2 ) allow evaluation of the parameter , which behaves very similarly to the thermal expansion coefficient ( 37 , 45 ). The results for both binary and ternary systems are shown in Fig.…”

The Effect of an Intramembrane Light-Actuator on the Dynamics of Phospholipids in Model Membranes and Intact Cells

“…Specifically, the effect of DMSO on model membranes has been studied extensively in the last two decades, owing to its large use as cryoprotectant in cellular systems and vehicle solvent for a number of drugs. 44,[46][47][48][49][50][51] It has been observed that if employed at concentrations < 10 mol.%, which is in line with our concentration of 0.3 mol.%, DMSO tends to dehydrate the membrane by disrupting the dynamic hydrogen-bond water near the lipid membrane surface. 50 This causes a drastic decrease in the range of the steric hydration repulsion, leading to a reduction of the solvated volume of the phospholipid head groups.…”

“…Specifically, the effect of DMSO on model membranes has been studied extensively in the last two decades, owing to its large use as a cryoprotectant in cellular systems and a vehicle solvent for a number of drugs. ,− It has been observed that if employed at concentrations <10 mol %, which is in line with our concentration of 0.3 mol %, DMSO tends to dehydrate the membrane by disrupting the dynamic hydrogen-bond water near the lipid membrane surface . This causes a drastic decrease in the range of the steric hydration repulsion, leading to a reduction of the solvated volume of the phospholipid head groups. , Our QENS data seem to capture a rigidification of the bilayer both at the time/length space of internal motions, as we can observe a general increase of the characteristic times and, interestingly, more complex dynamical scenario than the other two samples in which both fluid and rigid dynamical regimes likely coexist (i.e., a sub-gel state).…”