Molecular simulation study of phospholipid bilayers and insights of the interactions with disaccharides

Molecular simulation on the interaction between trehalose and asymmetric lipid bilayer mimicking the membrane of human red blood cells

Trehalose is widely acknowledged for its ability to stabilize plasma membranes during dehydration. However, the exact mechanism by which trehalose interacts with lipid bilayers remains presently unclear. In this study, we conducted atomistic molecular dynamic simulations on asymmetric model bilayers that mimic the membrane of human red blood cells at various trehalose and water contents. We considered three different hydration levels mimicking the full hydration to desiccation scenarios. Results indicate that the asymmetric distribution of lipids did not significantly influence the computed structural characteristics at full and low hydration. At dehydration, however, the order parameter obtained from the symmetric bilayer is significantly higher compared to those obtained from asymmetric ones. Analysis of hydrogen bonds revealed that the protective ability of trehalose is well described by the water replacement hypothesis at full and low hydration, while at dehydration other interaction mechanisms associated with trehalose exclusion from the bilayer may involve. In addition, we found that trehalose exclusion is not attributed to sugar saturation but rather to the reduction in hydration levels. It can be concluded that the protective effect of trehalose is not only related to the hydration level of the bilayer, but also closely tied to the asymmetric distribution of lipids within each leaflet.

Morphological evaluation of adult domestic cat testicular biopsy after vitrification

Testicular biopsies (9 mm3) from domestic cats (n = 10) submitted to orchiectomy were submitted to equilibrium vitrification in the presence of ethylene glycol (EG) alone or combined with dimethylsulfoxide (DMSO) as intracellular cryoprotectants, and sucrose or trehalose as extracellular cryoprotectants. The samples were vitrified with 40% EG or 20% EG + 20% DMSO, plus 0.1 M or 0.5 M of sucrose or trehalose. The study was divided into Step 1 and Step 2. In Step 1, intratubular cells (spermatogonia, spermatids, spermatocytes, and Sertoli cells) were quantified and classified as intact or degenerated (pyknotic and/or vacuolated cells). Cryodamage of seminiferous cords was determined by spermatogonia and Sertoli cell scoring of nuclei alterations, tubular basement membrane detachment, epithelium shrinkage, and tubular measures (total area, epithelium area, larger and smaller diameter, and height of the epithelium). In Step 2, Hoechst 33342 stain and propidium iodide (PI) fluorescent stain were used to assess the cell viability of the four best experimental groups in Step 1. The effect of treatments on all analyses was accessed using analysis of variance (ANOVA), and Fisher's post hoc test at P < 0.05 significance was considered. In Step 1, the mean percentage of spermatogonia and Sertoli cells morphological integrity did not show a difference when using both sugars at different concentrations, but their morphology was more affected when DMSO was used. EG use associated with 0.1 M of sucrose or trehalose positively affected spermatocyte and spermatid morphology, respectively. The larger diameter and epithelium height of seminiferous tubules were increased using DMSO plus 0.5 M sucrose and DMSO plus 0.1 M trehalose. The changes in spermatogonial/Sertoli nucleoli visualization were best scored in the EG groups, while the nuclei condensation was lower with sucrose. The basement membrane was satisfactorily preserved with 0.1 M sucrose. In Step 2, the percentage of cell viability was higher when EG plus 0.1 M sucrose was used. Therefore, DMSO's negative effect on the vitrification of testicular biopsies of adult domestic cats was evident. The EG plus 0.1 M of sucrose or trehalose associations are the most suitable CPAs to preserve the testicular histology structure of adult domestic cats in vitrification.

Interfacial Glucose to Regulate Hydrated Lipid Bilayer Properties: Influence of Concentrations

A series of atomistic molecular dynamics (MD) simulations were carried out with a hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayer with the variation of glucose concentrations from 0 to 30 wt % in the presence of 0.3 M NaCl. The study suggested that although the thickness of the lipid bilayer dropped significantly with the increase in glucose concentration, it expanded laterally at high glucose levels due to the intercalation of glucose between the headgroups of adjacent lipids. We adopted the surface assessment via the grid evaluation method to compute the deviation of the bilayer's key structural features for the different amounts of glucose present. This suggested that the accumulation of glucose molecules near the headgroups influences the local lipid bilayer undulation and crimping of the lipid tails. We find that the area compressibility modulus increases with the glucose level, causing enhanced bilayer rigidity arising from the slow lateral diffusion of lipids. The restricted lipid motion at high glucose concentrations controls the sustainability of the curved bilayer surface. Calculations revealed that certain orientations of CO → of interfacial glucose with the PN → of lipid headgroups are preferred, which helps the glucose to form direct hydrogen bonds (HBs) with the lipid headgroups. Such lipid-glucose (LG) HBs relax slowly at low glucose concentrations and exhibit a higher lifetime, whereas fast structural relaxation of LG HBs with a shorter lifetime was noticed at a higher glucose level. In contrast, lipid-water (LW) HBs exhibited a higher lifetime at a higher glucose level, which gradually decreased with the glucose level lowering. The study interprets that the glucose concentration-driven LW and LG interactions are mutually inclusive. Our detailed analysis will exemplify small saccharide concentration-driven membrane stabilizing efficiency, which is, in general, helpful for drug delivery study.

Effect of Low Temperature on Content of Primary Metabolites in Two Wheat Genotypes Differing in Cold Tolerance

The study of cold-tolerance mechanisms of wheat as a leading cereal crop is very relevant to science. Primary metabolites play an important role in the formation of increased cold tolerance. The aim of this research is to define changes in the content of primary metabolites (soluble proteins and sugars), growth, and photosynthetic apparatus of freezing-tolerant and cold-sustainable wheat (Triticum aestivum L.) genotypes under optimal conditions and after prolonged (7 days) exposure to low temperature (4 °C). In order to gain a deeper comprehension of the mechanisms behind wheat genotypes' adaptation to cold, we determined the expression levels of photosynthetic genes (RbcS, RbcL) and genes encoding cold-regulated proteins (Wcor726, CBF14). The results indicated different cold-adaptation strategies of freezing-tolerant and cold-sustainable wheat genotypes, with soluble proteins and sugars playing a significant role in this process. In plants of freezing-tolerant genotypes, the strategy of adaptation to low temperature was aimed at increasing the content of soluble proteins and modification of carbohydrate metabolism. The accumulation of sugars was not observed in wheat of cold-sustainable genotypes during chilling, but a high content of soluble proteins was maintained both under optimal conditions and after cold exposure. The adaptation strategies of wheat genotypes differing in cold tolerance were related to the expression of photosynthetic genes and genes encoding cold-regulated proteins. The data improve our knowledge of physiological and biochemical mechanisms of wheat cold adaptation.

Inhalable dry powders of microRNA-laden extracellular vesicles prepared by thin-film freeze-drying

Extracellular vesicles (EVs) are endogenous vesicles that comprise a variety of submicron vesicular structures. Among these, exosomes have been widely investigated as delivery systems for small and large molecules. Herein, the thin-film freeze-drying technology was utilized to engineer aerosolizable dry powders of miR-335-laden induced EVs (iEV-335) generated in B cells for potential delivery into the lung to treat primary lung cancer and/or pulmonary metastases. The size distribution, structure, and morphology of iEV-335 were preserved after they were subjected to thin-film freeze-drying with the proper excipients. Importantly, iEV-335, in liquid or reconstituted from thin-film freeze-dried powders, were equally effective in downregulating SOX4 gene expression in LM2 human triple-negative mammary cancer cells. The iEV-335 dry powder compositions showed mass median aerodynamic diameters (MMAD) of around 1.2 µm with > 60 % of the emitted doses had an MMAD of ≤ 3 µm, indicating that the powders can potentially achieve efficient deposition within the alveolar region following oral inhalation, which is desirable for treatment of primary lung cancer and pulmonary metastases. Overall, it is concluded that it is feasible to apply thin-film freeze-drying to prepare aerosolizable dry powders of iEVs for pulmonary delivery.

Phase behaviour and structural properties of SOPC model lipid system in a sucrose solution

Lipid membranes are an important component of the biological cell. The profound understanding of their structure and functionality, as well as, the influence of various biologically relevant admixtures on their main characteristics is of great importance for research and development in medicine and pharmacology. The effect of sugars on the behaviour of the membrane cell enjoys an ever-increasing interest as they are biologically significant substances. We have studied the influence of the disaccharide sucrose on the physicochemical properties of SOPC (1-stearoyl-2-oleoyl-sn- glycero-3-phosphocholine) lipid system aiming to gain better understanding of the mechanisms of the interaction between both substances. For that purpose, we have used differential scanning calorimetry and Fourier-transform infrared spectroscopy. Our results show that adding sugar up to 300 mM concentration substantially alters the thermodynamic and structural properties of SOPC. The DSC thermograms at heating reveal a general lowering of the SOPC transition temperature Tm from gel to liquid crystalline phase (main phase transition, ordered-disordered phase transition) in the presence of sugar. The corresponding peaks are smeared and harder to trace. In agreement with this, a gradual decrease of the enthalpy values up to 300 mM was measured. The IR spectroscopy study provided spectral evidence for two states of hydration of the phosphate groups in the sugar-SOPC model systems suggesting a mechanism of interaction where only part of the phospholipid headgroups are hydrogen bonded to the sugar molecules. The obtained results are in good agreement with various earlier data including results about the bending elasticity moduli, as well as, some theoretical simulations on the sugar-lipid interactions. The current results also reinforce the potential of sucrose to be used as a cell protector against drought at, both, high and low temperatures.

Impact of Biogenic and Chemogenic Selenium Nanoparticles on Model Eukaryotic Lipid Membranes

Microbial nanotechnology is an expanding research area devoted to producing biogenic metal and metalloid nanomaterials (NMs) using microorganisms. Often, biogenic NMs are explored as antimicrobial, anticancer, or antioxidant agents. Yet, most studies focus on their applications rather than the underlying mechanism of action or toxicity. Here, we evaluate the toxicity of our well-characterized biogenic selenium nanoparticles (bSeNPs) produced by the Stenotrophomonas maltophilia strain SeITE02 against the model yeast Saccharomyces cerevisiae comparing it with chemogenic SeNPs (cSeNPs). Knowing from previous studies that the biogenic extract contained bSeNPs in an organic material (OM) and supported here by Fourier transform infrared spectroscopy, we removed and incubated it with cSeNPs (cSeNPs_OM) to assess its influence on the toxicity of these formulations. Specifically, we focused on the first stages of the eukaryotic cell exposure to these samples─i.e., their interaction with the cell lipid membrane, which was mimicked by preparing vesicles from yeast polar lipid extract or phosphatidylcholine lipids. Fluidity changes derived from biogenic and chemogenic samples revealed that the bSeNP extract mediated the overall rigidification of lipid vesicles, while cSeNPs showed negligible effects. The OM and cSeNPs_OM induced similar modifications to the bSeNP extract, reiterating the need to consider the OM influence on the physical-chemical and biological properties of bSeNP extracts.

Technologies for Vitrification Based Cryopreservation

Cryopreservation is a unique and practical method to facilitate extended access to biological materials. Because of this, cryopreservation of cells, tissues, and organs is essential to modern medical science, including cancer cell therapy, tissue engineering, transplantation, reproductive technologies, and bio-banking. Among diverse cryopreservation methods, significant focus has been placed on vitrification due to low cost and reduced protocol time. However, several factors, including the intracellular ice formation that is suppressed in the conventional cryopreservation method, restrict the achievement of this method. To enhance the viability and functionality of biological samples after storage, a large number of cryoprotocols and cryodevices have been developed and studied. Recently, new technologies have been investigated by considering the physical and thermodynamic aspects of cryopreservation in heat and mass transfer. In this review, we first present an overview of the physiochemical aspects of freezing in cryopreservation. Secondly, we present and catalog classical and novel approaches that seek to capitalize on these physicochemical effects. We conclude with the perspective that interdisciplinary studies provide pieces of the cryopreservation puzzle to achieve sustainability in the biospecimen supply chain.

Interaction of guanidinium and ammonium cations with phosphatidylcholine and phosphatidylserine lipid bilayers - Calorimetric, spectroscopic and molecular dynamics simulations study

The ability of arginine-rich peptides to cross the lipid bilayer and enter cytoplasm, unlike their lysine-based analogues, is intensively studied in the context of cell-penetrating peptides. Although the experiments have not yet reconstructed their internalization mechanism, the computational studies have shown that the type or charge of lipid polar groups is one of the crucial factors in their translocation. In order to gain more detailed insight into the interaction of guanidinium (Gdm⁺) and ammonium (NH₄⁺) cations, as important building blocks in arginine and lysine amino acids, with lipid bilayers, we conducted the experimental and computational study that tackles this phenomenon. The adsorption of Gdm⁺ and NH₄⁺ on lipid bilayers prepared from a zwitterionic (DPPC) and an anionic (DPPS) lipid was examined by thermoanalytic and spectroscopic techniques. Using temperature-dependent UV-Vis spectroscopy and DSC calorimetry we determined the impact of Gdm⁺ and NH₄⁺ on the thermotropic properties of lipid bilayers. FTIR data, along with molecular dynamics simulations, unraveled the molecular-level details on the nature of their interactions, showing the proton transfer between NH₄⁺ and DPPS, but not between Gdm⁺ and DPPS. The findings originated from this work imply that Gdm⁺ and NH₄⁺ form qualitatively different interactions with lipids of different charge which is reflected in the physico-chemical interactions that arginine-and lysine-based peptides establish at a complex and chemically heterogeneous environment such as the biological membrane.

Specific protection mechanism of oligosaccharides on liposomes during freeze-drying

Liposomes have been received much attention during the past decades as bioactive compounds carriers in food field. However, the application of liposomes is extremely limited by the structural instability during processing such as freeze-drying. In addition, the protection mechanism of lyoprotectant for liposomes during freeze-drying remains controversial. In this study, lactose, fructooligosaccharide, inulin and sucrose were used as lyoprotectants for liposomes and the physicochemical properties, structural stability and freeze-drying protection mechanism were explored. The addition of oligosaccharides could significantly suppress the changes in size and zeta potential, and the amorphous state of liposomes was negligible changed from XRD. The T_g of the four oligosaccharides, especially for sucrose (69.50 °C) and lactose (95.67 °C), revealed the freeze-dried liposomes had formed vitrification matrix, which could prevent liposomes from fusion via increasing the viscosity and reducing membrane mobility. The decrease in T_m of sucrose (147.67 °C) and lactose (181.67 °C), and the changes in functional group of phospholipid and hygroscopic capacity of lyophilized liposomes indicated oligosaccharides replaced water molecules to interact with phospholipids by hydrogen bonds. It can be concluded that the protection mechanism of sucrose and lactose as lyoprotectant was attributed to the combination of vitrification theory and water replacement hypothesis, while the water replacement hypothesis was dominated by fructooligosaccharide and inulin.

Beneficial effects of trehalose and gentiobiose on human sperm cryopreservation

The protection of human sperm during cryopreservation is of great importance to infertility. Recent studies have shown that this area is still a long way from its ultimate aim of maintaining the maximum viability of sperm in cryopreservation. The present study used trehalose and gentiobiose to prepare the human sperm freezing medium during the freezing-thawing. The freezing medium of sperm was prepared with these sugars, and the sperm were then cryopreserved. The viable cells, sperm motility parameters, sperm morphology, membrane integrity, apoptosis, acrosome integrity, DNA fragmentation, mitochondrial membrane potential, reactive oxygen radicals, and malondialdehyde concentration was evaluated using standard protocols. A higher percentage of the total and progressive motility, rate of viable sperm, cell membrane integrity, DNA and acrosome integrity, and mitochondrial membrane potential were observed in the two frozen treatment groups compared to the frozen control. The cells had less abnormal morphology due to treatment with the new freezing medium than the frozen control. The higher malondialdehyde and DNA fragmentation were significantly observed in the two frozen treatment groups than in the frozen control. According to the results of this study, the use of trehalose and gentiobiose in the sperm freezing medium is a suitable strategy for sperm freezing to improve its motion and cellular parameters.

Mechanisms of Interaction of Small Hydroxylated Cryosolvents with Dehydrated Model Cell Membranes: Stabilization vs Destruction

The mechanism by which cryosolvents such as alcohols modify and penetrate cell membranes as a function of their concentration and hydration state remains poorly understood. We conducted molecular dynamics simulations of 1,2-dioleoyl-sn-glycero-3-phosphocholine bilayers in the presence of aqueous solutions of four common penetrating hydroxylated cryosolvents (methanol, ethylene glycol, propylene glycol, and glycerol) at varying concentration ranges and across three different hydration states. All cryosolvents were found to preferentially replace water at the bilayer interface, and a reduction in hydration state correlates with a higher proportion of cryosolvent at the interface for relative concentrations. Minor differences in chemical structure had a profound effect on cryosolvent-membrane interactions, as the lone methyl groups of methanol and propylene glycol enhanced their membrane localization and penetration, but with increasing concentrations acted to destabilize the membrane structure in a process heightened at higher hydration states. By contrast, ethylene glycol and glycerol promoted and retained membrane structural integrity by forming hydrogen-bonded lipid bridges via distally located hydroxyl groups. Glycerol exhibited the highest capacity to cross-link lipids at relative concentrations, as well as promoted a bilayer structure consistent with a fully hydrated bilayer in the absence of cryosolvent for all hydration states investigated.

Membrane lipid and osmolyte readjustment in the alkaliphilic micromycete Sodiomyces tronii under cold, heat and osmotic shocks

Previously, we showed for the first time that alkaliphilic fungi, in contrast to alkalitolerant fungi, accumulated trehalose under extremely alkaline conditions, and we have proposed its key role in alkaliphilia. We propose that high levels of trehalose in the mycelium of alkaliphiles may promote adaptation not only to alkaline conditions, but also to other stressors. Therefore, we studied changes in the composition of osmolytes, and storage and membrane lipids under the action of cold (CS), heat (HS) and osmotic (OS) shocks in the obligate alkaliphilic micromycete Sodiomyces tronii. During adaptation to CS, an increase in the degree of unsaturation of phospholipids was observed while the composition of osmolytes, membrane and storage lipids remained the same. Under HS conditions, a twofold increase in the level of trehalose and an increase in the proportion of phosphatidylethanolamines were observed against the background of a decrease in the proportion of phosphatidic acids. OS was accompanied by a decrease in the amount of membrane lipids, while their ratio remained unchanged, and an increase in the level of polyols (arabitol and mannitol) in the fungal mycelium, which suggests their role for adaptation to OS. Thus, the observed consistency of the composition of membrane lipids suggests that trehalose can participate in adaptation not only to extremely alkaline conditions, but also to other stressors - HS, CS and OS. Taken together, the data obtained indicate the adaptability of the fungus to the action of various stressors, which can point to polyextremotolerance.

β-Hairpin Miniprotein Stabilization in Trehalose Glass Is Facilitated by an Emergent Compact Non-Native State

From stem cell freeze-drying to organ storage, considerable recent efforts have been directed toward the development of new preservation technologies. A prominent protein stabilizing strategy involves vitrification in glassy matrices, most notably those formed of sugars such as the biologically relevant preservative trehalose. Here, we compare the folding thermodynamics of a model miniprotein in solution and in the glassy state of the sugars trehalose and glucose. Using synchrotron radiation circular dichroism (SRCD), we find that the same native structure persists in solution and glass. However, upon transition to the glass, a completely different, conformationally restricted unfolded state replaces the disordered denatured state found in solution, potentially inhibiting misfolding. Concomitantly, a large exothermic contribution is observed in glass, exposing the stabilizing effect of interactions with the sugar matrix on the native state. Our results shed light on the mechanism of protein stabilization in sugar glass and should aid in future preservation technologies.

Effects of Trehalose on Lipid Membranes under Rapid Cooling using All-Atom and Coarse-Grained Molecular Simulations

We investigate the effect of the cryopreservative α-α-trehalose on a model 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid membrane undergoing cooling from 350 to 250 K using all-atom (AA) and coarse-grained (CG) molecular dynamics simulation. In the AA simulations, we find that the addition of trehalose alters the L_α (liquid crystalline) to P_β (ripple) phase transition, suppressing the major domain of the P_β phase and increasing the degree of leaflet interdigitation (the minor domain) which yields a thinner membrane with a higher area per lipid. Calculation of dihedral angle distributions for the lipid tails shows a greater fraction of gauche angles in the P_β phase as trehalose concentration is increased, indicating that trehalose increases lipid disorder in the membrane. In contrast, the CG simulations transition directly from the L_α to the L_β (gel) phase upon cooling without exhibiting the P_β phase (likely due to increased lipid mobility in the CG system). Even so, the CG simulations show that the addition of trehalose clearly suppresses the L_α to L_β phase transition, demonstrating that trehalose increases lipid disorder at low temperatures for the CG system, similar to the AA. Analysis using a two-state binding model provides net affinity coefficients between trehalose and the membrane as well as trehalose partition coefficients between the membrane interface and the bulk solution for both the AA and CG systems.

Characterization techniques: The stepping stone to liposome lyophilized product development

The primary drying is the longest step of the freeze-drying process and becomes one of the focuses for lyophilization cycle development inevitably, which is often approaching through a "trial and error" course and requires a labor-intensive and time-consuming endeavor. Nevertheless, drawing support from characterization techniques to understand the physic-chemical properties changing of the sample during lyophilization and their correlation with process conditions comprehensively, the freeze-drying development and optimization will get more from less. To get the optimal lyophilization cycle in the least time, the instrumental methods assisting primary drying design are summarized. The techniques used for estimating the collapse temperature of products are reviewed at first, aiming to provide a reference on the primary drying temperature setting to guarantee product quality. The instrumental methods for primary drying end prediction are also discussed to get optimal freeze-drying protocol with higher productivity. This review highlights the practicality of the above techniques through expounding basic principles, typical measurement conditions, merits and drawbacks, interpretation of results and practical applications, etc. At last, the techniques used for residual moisture detection of lyophilized products and size determination after liposome rehydration are briefly introduced.

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

Dimethyl sulfoxide (DMSO) is widely used in a number of biological and biotechnological applications, mainly because of its effects on the cell plasma membrane, but the molecular origins of this action are yet to be fully clarified. In this work, we used two- and three-component synthetic membranes (liposomes) and the plasma membrane of human erythrocytes to investigate the effect of DMSO when added to the membrane-solvating environment. Fourier transform infrared spectroscopy and thermal fluctuation spectroscopy revealed significant differences in the response of the two types of liposome systems to DMSO in terms of the bilayer thermotropic behavior, available free volume of the bilayer, its excess surface area, and bending elasticity. DMSO also alters the mechanical properties of the erythrocyte membrane in a concentration-dependent manner and is capable of increasing membrane permeability to ATP at even relatively low concentrations (3% v/v and above). Taken in its entirety, these results show that DMSO is likely to have a differential effect on heterogeneous biological membranes, depending on their local composition and structure, and could affect membrane-hosted biological functions.

Simple sugars shape giant vesicles into multispheres with many membrane necks

Simple sugars such as glucose and sucrose are ubiquitous in all organisms. One remarkable property of these small solutes is their ability to protect biomembranes against dehydration damage. This property, which reflects the underlying sugar-lipid interactions, has been intensely studied for lipid bilayers interacting with a single sugar at low hydration. Here, we use giant vesicles to investigate fully hydrated lipid membranes in contact with two sugars, glucose and sucrose. The vesicles were osmotically balanced, with the same total sugar concentration in the interior and exterior aqueous solutions. However, the two solutions differed in their composition: the interior solution contained only sucrose whereas the exterior one contained primarily glucose. This sugar asymmetry generated a striking variety of multispherical or "multi-balloon" vesicle shapes. Each multisphere involved only a single membrane that formed several spherical segments, which were connected by narrow, hourglass-shaped membrane necks. These morphologies revealed that the sugar-lipid interactions generated a significant spontaneous curvature with a magnitude of about 1 μm^-1. Such a spontaneous curvature can be generated both by depletion and by adsorption layers of the sugar molecules arising from effectively repulsive and attractive sugar-lipid interactions. All multispherical shapes are stable over a wide range of parameters, with a substantial overlap between the different stability regimes, reflecting the rugged free energy landscape in shape space. One challenge for future studies is to identify pathways within this landscape that allow us to open and close the membrane necks of these shapes in a controlled and reliable manner. We will then be able to apply these multispheres as metamorphic chambers for chemical reactions and nanoparticle growth.

Does Sucrose Change Its Mechanism of Stabilization of Lipid Bilayers during Desiccation? Influences of Hydration and Concentration

Sugar-membrane interactions are believed to be responsible for cell preservation during desiccation and freezing, but the molecular mechanism by which they achieve this is still not well understood. The associated decrease of the main phase transition temperature of phospholipid bilayers is explained by two opposing views on the matter: the direct sugar-phospholipid interaction at the bilayer interface (water replacement hypothesis) and an entropy-driven phase transition with sugar molecules concentrating away from the lipid interface (hydration forces explanation). Both mechanisms are supported by experiments but molecular dynamics (MD) simulations have overwhelmingly shown the occurrence of direct sugar-phospholipid interactions. We have performed MD simulations of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers at different water and sucrose contents. The behavior of sucrose was found to depend on both the sucrose and water contents: at high sucrose concentration and at low hydration, it is best described by the hydration forces explanation model, whereas at low sucrose concentration, it is consistent with the water replacement hypothesis model. These simulations reveal that at low concentration, sucrose molecules preferentially interact directly with the membrane interface while at high concentration, they preferentially accumulate in the intermembrane solution. The transition between the two modes of interaction is revealed for the first time as being governed by the saturation of the lipid bilayer interface with sucrose molecules, and this occurs more rapidly as the level of hydration decreases.

Molecular crowding effects on the distribution of amphiphiles in biological media

Biological systems are the result of the interactions established among their many distinct molecules and molecular assemblies. The high concentration of small molecules dissolved in the aqueous media alter the water properties with important consequences in the interactions established. In this work, the effects of high concentrations of the disaccharide trehalose on the solubility of a homologous series of fluorescent amphiphiles (NBD-Cn, n=4-16) and on their interaction with a lipid bilayer and a serum protein are quantitatively characterized. Both kinetic and equilibrium aspects are reported for a better understanding of the effects observed. The aqueous solubility of the most hydrophobic amphiphiles (n ≥ 8) is strongly increased by 1 M trehalose, while no signifcant effect is observed for the most polar amphiphile (n = 4). This results from a decrease in the magnitude of the hydrophobic effect at molecular crowding conditions. A small decrease is observed on the equilibrium association with serum albumin. This is most significant for amphiphiles with longer alkyl chains, in agreement with their increased solubility in the aqueous media containing trehalose. The effects on the association of the amphiphiles with lipid bilayers are influenced by both equilibrium and kinetic aspects. On the one hand, the decreased magnitude of the hydrophobic effect leads to a decrease in the affinity of the amphiphiles towards the membrane. However, this tendency may be overbalanced by the effects on the kinetics of the interaction (insertion/desorption) due to the increase in the viscosity of the aqueous media. It is shown that the distribution of amphiphilic drugs in the crowded biological media is significantly different from that predicted from studies in dilute solutions and that the effects are dependent on the solute's hydrophobicity.

DPPC Bilayers in Solutions of High Sucrose Content

The properties of lipid bilayers in sucrose solutions have been intensely scrutinized over recent decades because of the importance of sugars in the field of biopreservation. However, a consensus has not yet been formed on the mechanisms of sugar-lipid interaction. Here, we present a study on the effect of sucrose on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayers that combines calorimetry, spectral fluorimetry, and optical microscopy. Intriguingly, our results show a significant decrease in the transition enthalpy but only a minor shift in the transition temperature. Our observations can be quantitatively accounted for by a thermodynamic model that assumes partial delayed melting induced by sucrose adsorption at the membrane interface.

Influence of Different Combinations of Permeable and Nonpermeable Cryoprotectants on the Freezing Capacity of Equine Sperm

This study was aimed to evaluate the effect of permeable cryoprotectants in combination with trehalose or sucrose on the freezing capacity of stallion sperm. For this purpose, the ejaculates (n = 24) were collected from four healthy mature Turkmen stallions. The ejaculates were pooled and diluted with one of the extenders containing a combination of 5% of permeating (dimethylacetamide [DMA]; dimethylformamide [DMF] or glycerol) and 50 mM of nonpermeating cryoprotectant agents (CPAs) (sucrose or trehalose) to a final concentration of 200 × 10⁶ spermatozoa/mL. The extended samples were cryopreserved and thawed using a standard protocol. The samples were evaluated for motion kinetics, morphological abnormalities, plasma membrane functionality (PMF), viability, and lipid peroxidation. The results showed that the sperm cryopreserved in extender containing DMA produced higher (P ≤ .05) total motility, straightness, straight line velocity, curvilinear velocity, and lower (P ≤ .05) lipid peroxidation (malondialdehyde [MDA] concentration) compared with DMF and glycerol groups. Overall, both DMA and DMF have shown higher (P ≤ .05) sperm motion kinetics, viability, PMF, and lower (P ≤ .05) morphological abnormalities and MDA concentration compared with the glycerol. However, except morphological abnormalities, all of the other parameters did not differ between trehalose and sucrose. Likewise, there was no interaction between permeating and nonpermeating CPAs (P ≥ .05) except in terms of sperm abnormalities (P ≤ .05). In conclusion, the use of DMA or DMF as alternative CPAs of glycerol could be more effective for successful cryopreservation of stallion sperm. The nonsignificant interaction between permeating and nonpermeating CPAs for most of the post-thaw sperm parameters negates possible synergism among these compounds.

Exploring Dynamics and Structure of Biomolecules, Cryoprotectants, and Water Using Molecular Dynamics Simulations: Implications for Biostabilization and Biopreservation

Successful stabilization and preservation of biological materials often utilize low temperatures and dehydration to arrest molecular motion. Cryoprotectants are routinely employed to help the biological entities survive the physicochemical and mechanical stresses induced by cold or dryness. Molecular interactions between biomolecules, cryoprotectants, and water fundamentally determine the outcomes of preservation. The optimization of assays using the empirical approach is often limited in structural and temporal resolution, whereas classical molecular dynamics simulations can provide a cost-effective glimpse into the atomic-level structure and interaction of individual molecules that dictate macroscopic behavior. Computational research on biomolecules, cryoprotectants, and water has provided invaluable insights into the development of new cryoprotectants and the optimization of preservation methods. We describe the rapidly evolving state of the art of molecular simulations of these complex systems, summarize the molecular-scale protective and stabilizing mechanisms, and discuss the challenges that motivate continued innovation in this field.

Molecular Dynamics Simulation for Mechanism Elucidation of Food Processing and Safety: State of the Art

Molecular dynamics (MD) simulation is a useful technique to study the interaction between molecules and how they are affected by various processes and processing conditions. This review summarizes the application of MD simulations in food processing and safety, with an emphasis on the effects that emerging nonthermal technologies (for example, high hydrostatic pressure, pulsed electric field) have on the molecular and structural characteristics of foods and biomaterials. The advances and potential projection of MD simulations in the science and engineering aspects of food materials are discussed and focused on research work conducted to study the effects of emerging technologies on food components. It is expected by showing key case studies that it will stir novel developments as a valuable tool to study the effects of emerging food technologies on biomaterials. This review is useful to food researchers and the food industry, as well as researchers and practitioners working on flavor and nutraceutical encapsulations, dietary carbohydrate product developments, modified starches, protein engineering, and other novel food applications.

Effect of polyols on the DMPC lipid monolayers and bilayers

In this study, the effect of polyols, erythritol, xylitol, mannitol, on a model membrane systems composed of DMPC was investigated using differential scanning calorimetry and Fourier transform infrared spectroscopy. Generally, it is considered that polyols possess strong hydrophilic properties, and either does not interact with the hydrophobic environment at all, or these interactions are very weak. To better understand the mutual interactions between polyols and the lipid system, the Langmuir technique was used to examine the molecular organization of monolayers and to calculate their thickness in the presence of polyols at the subphase. The detailed description of the interactions between polyols and DMPC molecules was complemented by the analysis of the morphology of monolayers with the application of Brewster angle microscopy. From ATR FTIR, the significant spectral shift is observed only for the PO₂^- stretching band, which correlates strongly with the polyol chain-length. The longer the polyol chain, the weaker the observed interactions with lipid molecules. The most important findings, obtained from thickness measurements, reveal that short-chain polyols may prevent the formation of bilayers by the DMPC molecules under high surface pressure. The changes in the organization of DMPC monolayers on the surface, as visualized by Brewster angle microscopy, showed that the domains observed for phospholipid film spread on pure water differ substantially from those containing polyols in the subphase.

Recrystallization and Water Absorption Properties of Vitrified Trehalose Near Room Temperature

PURPOSE

To provide the physicochemical properties of vitrified trehalose for predicting its recrystallization.

METHODS

Thin films of vitrified trehalose solutions were prepared at room temperature and exposed to various humid and temperature atmospheres. The in-situ amount of retained water in the vacuum-dried trehalose thin film during exposure was determined using its FTIR spectrum by quantifying the extremely infinitesimal amount of retained water in the trehalose solution. Recrystallization of the sample was also assessed by the FTIR spectrum of trehalose dihydrate.

RESULTS

The effective water absorption coefficient, h _meff , exponentially increased to the water activity of the trehalose sample, A _w , at 25°C and 40°C at which the increasing rates are comparable. The surface energy of trehalose dihydrate, γ, was found to be lower than the value calculated from the reported equation, neglecting the effects of the activity of the solute and solvent water.

CONCLUSIONS

The retained water in trehalose considerably increases its affinity for water vapor, and the change in this affinity with regard to the water activity is nearly independent of temperature. The dihydrate nucleation rate of trehalose-water system is maximal when trehalose weight ratio is ~0.8 at 25°C and is slightly higher (~0.85) at 40°C.

Ion-induced modification of the sucrose network and its impact on melting of freeze-dried liposomes. DSC and molecular dynamics study

Disaccharides play an important role in survival of anhydrobiotic organisms during extreme environmental conditions. A key protection feature is their capability to form the hydrogen bond (HB) network in a similar fashion as the one made by water. Since various ions also affect the HB network in completely hydrated systems, it is of a great interest to understand how they impact preservation when incorporated in a disaccharide network. To address this, we employ a combination of experimental and modeling techniques to study behavior of multilamellar 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes freeze-dried with sucrose in presence of NaCl or NaH₂PO₄·H₂O at various concentrations (0.01-1M). Differential scanning calorimetry (DSC) was employed in order to determine the cooperative unit size (CUS), the number of lipid molecules that constitute a domain of cooperative motion in the liposome, and the melting temperature (T_m). In the absence of salt CUS was estimated to be 122±12, whereas in the presence of NaCl CUS increases more (347±34 for c=1M) than for NaH₂PO₄·H₂O (193±26 for 1M). When it comes to T_m, the situation is reversed; NaCl induces increase by about 1K, while NaH₂PO₄·H₂O by about 10K. These findings clearly demonstrate how different interaction forces-hydrogen bonding, charge pairing, and van der Waals interactions between acyl chains-affect CUS and T_m. Their interplay and contribution of particular interaction was further analyzed with molecular dynamics (MD) simulations. This analysis demonstrated that the HB network of DMPC and sucrose is partially disrupted in the presence of NaCl ions, and even to a greater extent in the case of NaH₂PO₄·H₂O ions. Notably, H₂PO₄^- ions outcompete and replace the sucrose molecules at the DMPC surface, which in turn alters the nature of the DMPC-surrounding interactions, from a weaker HB-dominated to a stronger CP-dominated interaction network.

The molecular behavior of a single β-amyloid inside a dipalmitoylphosphatidylcholine bilayer at three different temperatures: An atomistic simulation study: Aβ interaction with DPPC: Atomistic simulation

The behavior of a single Aβ40 molecule within a dipalmitoylphosphatidylcholine (DPPC) bilayer was studied by all-atom molecular dynamics simulations. The effect of membrane structure was investigated on Aβ40 behavior, secondary structure, and insertion depth. Simulations were performed at three temperatures (323, 310, and 300 K) to probe three different bilayer fluidities. Results show that at all above temperatures, the peptide contains two short helices, coil, bend, and turn structures. At 300 K, the peptide contains a region with β structure in C-terminal region. Our results also show that Aβ decreases the bilayer thickness and the order of lipids in its vicinity which leads to water insertion into the bilayer and concomitant increase in the local fluidity. The peptide remains embedded in the bilayer at all temperatures, and become inserted into the bilayer up to several residues at 323 and 310 K. At 310 and 300 K, the dominant interaction energy between Aβ and bilayer changes from electrostatic to van der Waals. It can be proposed that at higher temperatures (e.g., 323 K), Lys28 and the C-terminal region of the peptide play the role of two anchors that keep Aβ inside the top leaflet. This study demonstrates that Aβ molecule can perturb the integrity of cellular membranes. Proteins 2017; 85:1298-1310. © 2017 Wiley Periodicals, Inc.

Cryopreservation of testicular tissue or testicular cell suspensions: a pivotal step in fertility preservation

BACKGROUND

Germ cell depletion caused by chemical or physical toxicity, disease or genetic predisposition can occur at any age. Although semen cryopreservation is the first reflex for preserving male fertility, this cannot help out prepubertal boys. Yet, these boys do have spermatogonial stem cells (SSCs) that able to produce sperm at the start of puberty, which allows them to safeguard their fertility through testicular tissue (TT) cryopreservation. SSC transplantation (SSCT), TT grafting and recent advances in in vitro spermatogenesis have opened new possibilities to restore fertility in humans. However, these techniques are still at a research stage and their efficiency depends on the amount of SSCs available for fertility restoration. Therefore, maintaining the number of SSCs is a critical step in human fertility preservation. Standardizing a successful cryopreservation method for TT and testicular cell suspensions (TCSs) is most important before any clinical application of fertility restoration could be successful.

OBJECTIVE AND RATIONALE

This review gives an overview of existing cryopreservation protocols used in different animal models and humans. Cell recovery, cell viability, tissue integrity and functional assays are taken into account. Additionally, biosafety and current perspectives in male fertility preservation are discussed.

SEARCH METHODS

An extensive PubMED and MEDline database search was conducted. Relevant studies linked to the topic were identified by the search terms: cryopreservation, male fertility preservation, (immature)testicular tissue, testicular cell suspension, spermatogonial stem cell, gonadotoxicity, radiotherapy and chemotherapy.

OUTCOMES

The feasibility of fertility restoration techniques using frozen-thawed TT and TCS has been proven in animal models. Efficient protocols for cryopreserving human TT exist and are currently applied in the clinic. For TCSs, the highest post-thaw viability reported after vitrification is 55.6 ± 23.8%. Yet, functional proof of fertility restoration in the human is lacking. In addition, few to no data are available on the safety aspects inherent to offspring generation with gametes derived from frozen-thawed TT or TCSs. Moreover, clarification is needed on whether it is better to cryopreserve TT or TCS.

WIDER IMPLICATIONS

Fertility restoration techniques are very promising and expected to be implemented in the clinic in the near future. However, inter-center variability needs to be overcome and the gametes produced for reproduction purposes need to be subjected to safety studies. With the perspective of a future clinical application, there is a dire need to optimize and standardize cryopreservation and safety testing before using frozen-thawed TT of TCSs for fertility restoration.

Photopolymerization of Dienoyl Lipids Creates Planar Supported Poly(lipid) Membranes with Retained Fluidity

Polymerization of substrate-supported bilayers composed of dienoylphosphatidylcholine (PC) lipids is known to greatly enhance their chemical and mechanical stability; however, the effects of polymerization on membrane fluidity have not been investigated. Here planar supported lipid bilayers (PSLBs) composed of dienoyl PCs on glass substrates were examined to assess the degree to which UV-initiated polymerization affects lateral lipid mobility. Fluorescence recovery after photobleaching (FRAP) was used to measure the diffusion coefficients (D) and mobile fractions of rhodamine-DOPE in unpolymerized and polymerized PSLBs composed of bis-sorbyl phosphatidylcholine (bis-SorbPC), mono-sorbyl-phosphatidylcholine (mono-SorbPC), bis-dienoyl-phosphatidylcholine (bis-DenPC), and mono-dienoyl phosphatidylcholine (mono-DenPC). Polymerization was performed in both the Lα and Lβ phase for each lipid. In all cases, polymerization reduced membrane fluidity; however, measurable lateral diffusion was retained which is attributed to a low degree of polymerization. The D values for sorbyl lipids were less than those of the denoyl lipids; this may be a consequence of the distal location of polymerizable group in the sorbyl lipids which may facilitate interleaflet bonding. The D values measured after polymerization were 0.1-0.8 of those measured before polymerization, a range that corresponds to fluidity intermediate between that of a Lα phase and a Lβ phase. This D range is comparable to ratios of D values reported for liquid-disordered (Ld) and liquid-ordered (Lo) lipid phases and indicates that the effect of UV polymerization on lateral diffusion in a dienoyl PSLB is similar to the transition from a Ld phase to a Lo phase. The partial retention of fluidity in UV-polymerized PSLBs, their enhanced stability, and the activity of incorporated transmembrane proteins and peptides is discussed.

Synergistic Interactions of Sugars/Polyols and Monovalent Salts with Phospholipids Depend upon Sugar/Polyol Complexity and Anion Identity

We found that interactions of dipalmitoylphosphatidylcholine (DPPC) lipid monolayers with sugars are influenced by addition of NaCl. This work is of general importance in understanding how sugar-lipid-salt interactions impact biological systems. Using Langmuir isothermal compressions, fluorescence microscopy, atomic force microscopy, and neutron reflectometry, we examined DPPC monolayers upon addition of sugars/polyols and/or monovalent salts. Sugar-lipid interactions in the presence of NaCl increased with increasing complexity of the sugar/polyol in the order glycerol ≪ glucose < trehalose. When the anion was altered in the series NaF, NaCl, and NaBr, only minor differences were observed. When comparing LiCl, NaCl, and KCl, sodium chloride had the greatest influence on glucose and trehalose interactions with DPPC. We propose that heterogeneity created by cation binding allows for sugars to bind the lipid headgroups. While cation binding increases in the order K(+) < Na(+) < Li(+), lithium ions may also compete with glucose for binding sites. Thus, both cooperative and competitive factors contribute to the overall influence of salts on sugar-lipid interactions.

Molecular dynamics simulations and NMR spectroscopy studies of trehalose-lipid bilayer systems

The disaccharide trehalose (TRH) strongly affects the physical properties of lipid bilayers. We investigate interactions between lipid membranes formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and TRH using NMR spectroscopy and molecular dynamics (MD) computer simulations. We compare dipolar couplings derived from DMPC/TRH trajectories with those determined (i) experimentally in TRH using conventional high-resolution NMR in a weakly ordered solvent (bicelles), and (ii) by solid-state NMR in multilamellar vesicles (MLV) formed by DMPC. Analysis of the experimental and MD-derived couplings in DMPC indicated that the force field used in the simulations reasonably well describes the experimental results with the exception for the glycerol fragment that exhibits significant deviations. The signs of dipolar couplings, not available from the experiments on highly ordered systems, were determined from the trajectory analysis. The crucial step in the analysis of residual dipolar couplings (RDCs) in TRH determined in a bicelle-environment was access to the conformational distributions derived from the MD trajectory. Furthermore, the conformational behavior of TRH, investigated by J-couplings, in the ordered and isotropic phases is essentially identical, indicating that the general assumptions in the analyses of RDCs are well founded.

Nonenzymatic Reactions above Phospholipid Surfaces of Biological Membranes: Reactivity of Phospholipids and Their Oxidation Derivatives

Phospholipids play multiple and essential roles in cells, as components of biological membranes. Although phospholipid bilayers provide the supporting matrix and surface for many enzymatic reactions, their inherent reactivity and possible catalytic role have not been highlighted. As other biomolecules, phospholipids are frequent targets of nonenzymatic modifications by reactive substances including oxidants and glycating agents which conduct to the formation of advanced lipoxidation end products (ALEs) and advanced glycation end products (AGEs). There are some theoretical studies about the mechanisms of reactions related to these processes on phosphatidylethanolamine surfaces, which hypothesize that cell membrane phospholipids surface environment could enhance some reactions through a catalyst effect. On the other hand, the phospholipid bilayers are susceptible to oxidative damage by oxidant agents as reactive oxygen species (ROS). Molecular dynamics simulations performed on phospholipid bilayers models, which include modified phospholipids by these reactions and subsequent reactions that conduct to formation of ALEs and AGEs, have revealed changes in the molecular interactions and biophysical properties of these bilayers as consequence of these reactions. Then, more studies are desirable which could correlate the biophysics of modified phospholipids with metabolism in processes such as aging and diseases such as diabetes, atherosclerosis, and Alzheimer's disease.