Properties of ternary phospholipid/dimethyl sulfoxide/water systems at low temperatures

Effect of DMSO Addition on the Hexagonal Phase of the System Triton X/Water

This research studied the role of DMSO in a binary system of Triton X and water in the hexagonal mesophase. One effect of DMSO addition, determined using polarized optical microscopy and small-angle X-ray scattering measurements, is to promote a decrease in the hexagonal to isotropic phase transition temperature, TH-ISO, decreasing the range of temperatures of the hexagonal phase until the hexagonal phase completely disappears when DMSO is added up to 5.0 mol %. The periodicity and the lattice parameter of the hexagonal arrangement, calculated as a function of DMSO concentration, slight increased due to the insertion of DMSO molecules in the water region, causing a greater distance between the cylindrical micelles, while the radius of the apolar domains kept constant at 22 (1) Å.

Freeze-Induced Phase Transition and Local Pressure in a Phospholipid/Water System: Novel Insights Were Obtained from a Time/Temperature Resolved Synchrotron X-ray Diffraction Study

Water-to-ice transformation results in a 10% increase in volume, which can have a significant impact on biopharmaceuticals during freeze-thaw cycles due to the mechanical stresses imparted by the growing ice crystals. Whether these stresses would contribute to the destabilization of biopharmaceuticals depends on both the magnitude of the stress and sensitivity of a particular system to pressure and sheer stresses. To address the gap of the "magnitude" question, a phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), is evaluated as a probe to detect and quantify the freeze-induced pressure. DPPC can form several phases under elevated pressure, and therefore, the detection of a high-pressure DPPC phase during freezing would be indicative of a freeze-induced pressure increase. In this study, the phase behavior of DPPC/water suspensions, which also contain the ice nucleation agent silver iodide, is monitored by synchrotron small/wide-angle X-ray scattering during the freeze-thaw transition. Cooling the suspensions leads to heterogeneous ice nucleation at approximately -7 °C, followed by a phase transition of DPPC between -11 and -40 °C. In this temperature range, the initial gel phase of DPPC, Lβ', gradually converts to a second phase, tentatively identified as a high-pressure Gel III phase. The Lβ'-to-Gel III phase transition continues during an isothermal hold at -40 °C; a second (homogeneous) ice nucleation event of water confined in the interlamellar space is detected by differential scanning calorimetry (DSC) at the same temperature. The extent of the phase transition depends on the DPPC concentration, with a lower DPPC concentration (and therefore a higher ice fraction), resulting in a higher degree of Lβ'-to-Gel III conversion. By comparing the data from this study with the literature data on the pressure/temperature Lβ'/Gel III phase boundary and the lamellar lattice constant of the Lβ' phase, the freeze-induced pressure is estimated to be approximately 0.2-2.6 kbar. The study introduces DPPC as a probe to detect a pressure increase during freezing, therefore addressing the gap between a theoretical possibility of protein destabilization by freeze-induced pressure and the current lack of methods to detect freeze-induced pressure. In addition, the observation of a freeze-induced phase transition in a phospholipid can improve the mechanistic understanding of factors that could disrupt the structure of lipid-based biopharmaceuticals, such as liposomes and mRNA vaccines, during freezing and thawing.

Revealing the interactions of water with cryoprotectant and protein by near-infrared spectroscopy

Taking formamide (FA) as a model compound of protein, the water structure in the ternary mixtures of dimethyl sulfoxide (DMSO)-water-FA was studied by near-infrared (NIR) spectroscopy. The interaction of DMSO and water, and the effect of FA on the interaction, were analyzed with the help of chemometric methods. Continuous wavelet transform (CWT) was used to enhance the resolution of the spectra. A peak at 6437 cm^-1 depicting the interaction of DMSO and water through hydrogen bonding (SO…HO) was observed in the transformed spectra. When FA exists in the mixture, the intensity of the peak decreases with the increase of formamide content, showing that FA may replace the water to form the hydrogen bond of SO and HN. In addition, temperature-dependent NIR spectroscopy was used to analyze the effect of the three components on the spectral variation with temperature. Analyzing the spectral data by alternating trilinear decomposition (ATLD) and multiple linear regression, two varying spectral features were obtained that are related to water and DMSO, but no spectral feature was found that significantly varies with the content of FA. The result implies that DMSO is still the key component to prevent the water from icing, although FA may reduce slightly the anti-freezing effect.

Thermodynamics and kinetics of joint action of antiviral agent tilorone and DMSO on model lipid membranes

Individual and joint action of two water-soluble drugs, DMSO and tilorone, on model l-α-dipalmitoylphosphatidylcholine (DPPC) membranes were studied in equilibrium and kinetic regimes by differential scanning calorimetry (DSC). For equilibrium experiments, the drugs were introduced during preparation of the model membrane. In kinetic studies, one of the drugs was added to the DPPC membrane already containing the other drug, and the effects of drug-membrane interactions were monitored in real-time regime. It was found that tilorone and DMSO had opposite effects on the membrane melting temperature, which were non-additive under joint introduction of these drugs. Analysis of kinetics of DSC profiles under drugs introduction allowed us to discriminate two processes in drug-membrane interactions with different characteristic times, i.e., drug sorption onto the membrane (minutes) and drug diffusion through stacks of lipid bilayers (hours). It was established that 0.1 mol% DMSO effectively enhanced membrane penetration for tilorone with the rate of tilorone diffusion being dependent upon the scheme of drugs administration. A model was proposed describing how sorption of a dopant onto lipid membrane could affect the membrane permeability for other dopants. Conditions were determined for enhancement of membrane permeability, as it was observed for DPPC/DMSO/tilorone system.

Low-dose action of tryptanthrin and its derivatives against developing embryos of the sea urchin Strongylocentrotus intermedius

Nine tryptanthrin derivatives, including tryptanthrin itself, were synthesized using different methods, including oxidation of the corresponding isatins to obtain 1-4, the reaction of tryptanthrin 1 with hydrazine and its derivatives to obtain 5-7, and aldol condensation of 1 with acetone and methylethylketone to obtain 8 and 9. The action of 1-9 in doses corresponding to the IC₅₀ against developing embryos of the sea urchin Strongylocentrotus intermedius and in the sperm test allowed us to estimate to potency of all the compounds and to determine which were cytotoxic. In addition, these studies showed that compounds 3, 4, 8, and 9 had a stimulatory effect at lower doses. In particular, the tryptanthrin derivatives stimulated the larval stages of development in surviving embryos at concentrations lower than the IC₅₀.

Modulation of dipalmitoylphosphatidylcholine monolayers by dimethyl sulfoxide

The action of the penetration-enhancing agent, dimethyl sulfoxide (DMSO), on phospholipid monolayers was investigated at the air-water interface using a combination of experimental techniques and molecular dynamics simulations. Brewster angle microscopy revealed that DPPC monolayers remained laterally homogeneous at subphase concentrations up to a mole fraction of 0.1 DMSO. Neutron reflectometry of the monolayers in combination with isotopic substitution enabled the determination of solvent profiles as a function of distance perpendicular to the interface for the different DMSO subphase concentrations. These experimental results were compared to those obtained from molecular dynamic (MD) simulations of the corresponding monolayer systems. There was excellent agreement found between the MD-derived reflectivity curves and the measured data for all of the H/D contrast variations investigated. The MD provide a detailed description of the distribution of water and DMSO molecules around the phosphatidylcholine headgroup, and how this distribution changes with increasing DMSO concentrations. Significantly, the measurements and simulations that are reported here support the hypothesis that DMSO acts by dehydrating the phosphatidylcholine headgroup, and as such provide the first direct evidence that it does so primarily by displacing water molecules bound to the choline group.

Calcium-activated membrane interaction of the islet amyloid polypeptide: implications in the pathogenesis of type II diabetes mellitus

The role played by Ca(2+) ions in the interaction of the human islet amyloid polypeptide (hIAPP) with model membranes has been investigated by differential scanning calorimetry (DSC) and circular dichroism (CD) experiments. In particular, the interaction of hIAPP and its rat isoform (rIAPP) with zwitterionic dipalmitoyl-phosphatidylcholine (DPPC), negatively charged dipalmitoyl-phosphatidylserine (DPPS) vesicles and with a 3:1 mixtures of them, has been studied in the presence of Ca(2+) ions. The experiments have evidenced that amorphous, soluble hIAPP assemblies interact with the hydrophobic core of DPPC bilayers. Conversely, the presence of Ca(2+) ions is necessary to activate a preferential interaction of hIAPP with the hydrophobic core of DPPS membranes. These findings support the hypothesis that an impaired cellular homeostasis of Ca(2+) ions may promote the insertion of hIAPP into the hydrophobic core of carrier vesicles which is thought to contribute to an eventual intracellular accumulation of beta-sheet rich hIAPP aggregates.